# tblSTJOHN

Title:
Aquifer Test Analyses for the Floridan Aquifer in Flagler, Putnam, and St. Johns Counties, Florida

Publication:
Water Resources Investigations #77-36, U.S. Geological Survey, prepared in cooperation with the St. Johns River Water Management District.  Tallahassee, Florida.

Abstract:
The Floridan aquifer in Flagler, Putnam, and St. Johns Counties of northeastern Florida consists primarily of limestone beds of the Ocala Group and the underlying Avon Park and Lake City Limestones, all of Eocene age. New data from eighteen aquifer tests were analyzed for transmissivity, storage coefficient, and leakance. In addition, the data and results of several tests made previously were analyzed and used to determine hydraulic characteristics of the Floridan aquifer. The test analyses indicate that the aquifer has a transmissivity of about 60,000 feet squared per day and a storage coefficient of about 0.0008. Leakance, a property of the overlying and underlying confining beds, ranges from 0.00023 day-1 northwest of Palatka to 0.016 day-1 in the farming area near East Palatka.

The transmissivity, storage coefficient, and leakance can be used to generate curves showing drawdown with time at any distance from a well that is discharging at any selected constant rate and at any depth of penetration into the aquifer.

Applications presented include the generation of drawdown curves for pumping time, distance from a discharging well, and depth of penetration into the aquifer; and to estimate the seasonal and annual pumpage in a heavily pumped farming area.


Title:
Altitude of the Base of Fresh Groundwater in Florida (in Principal Aquifers in Florida)

Publication:
Open-File Report #82-255, U.S. Geological Survey, prepared in cooperation with the Florida Department of Environmental Regulation. Tallahassee, Florida.

Abstract:
Available water quality data and pertinent lithologic information from oil and water wells were compiled and evaluated in order to prepare a map depicting the base of fresh groundwater in Florida.  Data from deep wells indicates that highly mineralized water (10,000 mg/l TDS) underlies the entire State, but the depth to it varies considerably and is controlled partly by the subsurface stratigraphy and partly by the fresh water head.

The map was prepared in two stages.  First the bottom of the Floridan Aquifer as determined from lithologic and hydrologic information was contoured.  Then this contoured data base was considered to be the absolute maximum depth where exploitable groundwater could possibly be found.  Then the information on water quality from deep wells (injection wells, oil wells, exploratory wells, etc) was used to contour the 10,000 mg/l TDS line.  Therefore, where the 10,000 TDS contours overlie the contours of the bottom of the aquifer that is the limit of freshwater. Where the 10,000 TDS contours do not overlie the bottom of the aquifer, the bottom of the aquifer is interpreted as the limit of fresh water.


Author:
Bermes, B.J., Leve, G.W., and Tarver, G.R.

Title:
Geology and Groundwater Resources of Flagler, Putnam, and St. Johns Counties, Florida

Publication:
Report of Investigations #32.  Prepared by the U.S. Geological Survey in cooperation with the Florida Geological Survey.  Tallahassee, Florida.

Abstract:
This report investigates the groundwater system in Flagler, Putnam, and St. Johns counties in northeastern Florida, describing the several thousand feet of limestones of Eocene age which form the major artesian aquifer in the area. The limestone formations are identified as the Lake City Limestone, Avon Park Limestone, Inglis Formation, Williston Formation, and Crystal River Formation [the last three as the Ocala Limestone]. Overlying the limestones the report describes sediments of Miocene or Pliocene age. These sediments are overlain by Pleistocene and Recent deposits which blanket the area to a depth of 20 to 140 feet.

The report describes the existence of groundwater in the area as occurring under both nonartesian and artesian conditions. The nonartesian aquifer extends from land surface to a depth of at least 150 feet below land surface. It includes deposits of Miocene or Pliocene age and of Pleistocene and Recent age. The nonartesian aquifer yields moderate to large quantities of water in central and eastern Flagler and St. Johns counties and generally yields small quantities of water to domestic wells throughout the remainder of the area. The nonartesian aquifer is recharged locally by direct infiltration of rainfall and by upward leakage from the underlying aquifers.

Secondary artesian aquifers are an important source of water in parts of eastern Flagler and St. Johns counties where water from other aquifers is highly mineralized or difficult to obtain. The secondary artesian aquifers are composed of lenses of sand, shell, and limestone. The aquifers range in depth from less than 10 feet to more than 300 feet below sea level, and in thickness from less than 1 foot to about 15 feet. These aquifers occur most often in the area east of the St. Johns River and in the north-central part of Putnam County. The secondary artesian aquifers are recharged from the overlying  nonartesian aquifer and from the underlying Floridan aquifer. Pumping tests, current-meter data, and geologic information indicate that the primary water-producing zone of the Floridan aquifer in Flagler, Putnam, and St. Johns counties is the top 50-200 feet of the aquifer.

The chloride content of water from wells developed in the Floridan aquifer ranges from less than 10 ppm (parts per million) in western Putnam and northeastern St. Johns counties to several thousand parts per million along the coast in Flagler and St. Johns counties. Water in the upper 200 feet of the Floridan aquifer generally contains less chloride than the water below 200 feet. When the artesian pressure is lowered by excessive pumping in farming areas the chloride content of the water more than triples in some wells. In some areas saline water has contaminated the existing fresh-water supplies in both the nonartesian and the Floridan aquifer. The nonartesian aquifer has been contaminated by upward movement of saline water from the Floridan aquifer and by intrusion of saline water from nearby salt-water bodies. In localized areas the nonartesian aquifer is contaminated by water entrapped during inundation of the land by the sea in Pleistocene time.

In the Floridan aquifer excessive discharge for a long period of time from the Haw Creek Basin, Oklawaha-St. Johns River valley, and near the coast in Flagler and St. Johns counties has lowered the artesian pressure in the upper part of the aquifer and saline water has migrated upward into the aquifer. In the farming areas near Hastings, East Palatka, and in parts of Flagler County upward coning of saline water in the Floridan aquifer occurs during periods of maximum pumping. The upconing of saline water from the deeper parts of the aquifer can be partially controlled by proper well spacing and pumping practices. Generally, in the Floridan aquifer, water samples show a progressive increase in chloride content with depth.


Title:
Potentiometric Surface of the Upper Floridan Aquifer, St, Johns River Water Management District, September 1998

Publication:
Open-File Report #99-100, U.S. Geological Survey.  Tallahassee, Florida

Abstract:
A network of monitoring wells used to measure the potentiometric surface of the Floridan Aquifer is described in this open file report.  The report includes maps and illustrations showing the elevation of the Floridan Aquifer represented by contour lines.  Comparison to potentiometric data from previous years, shows those areas where Floridan Aquifer withdrawals have resulted in additional lowering of the potentiometer surface. 

The map also shows those areas where the capping of free flowing wells have resulted in an increase in the potentiometric pressure.  Lower potentiometric levels are also shown in areas of increased pumping for domestic and farm use.  Inland movement of the contour lines presented in the maps and figures coincide with areas of increasing salt water intrusion into the Floridan Aquifer.


Author:
Brown, D., Kenner, W., Crooks, J., and Foster, J.

Title:
Water Resources of Brevard County, Florida

Publication:
Report of Investigations #28.  Prepared by the U.S. Geological Survey in cooperation with the South Florida Water Management District, the U.S. Army, Corps of Engineers, and the Florida Geological Survey.  Tallahassee, Florida.

Abstract:
Brevard County comprises an area of 1,298 square miles along the Atlantic Ocean in central Florida. Lying in bands roughly parallel to Indian River are three distinct landforms: the St. Johns River valley, which parallels the western border of the county; the Atlantic Coastal Ridge, which forms the eastern boundary of the mainland; and the barrier islands, which lie offshore and parallel to the mainland.

The county is underlain by a series of limestone formations having a total thickness of several thousand feet. The upper several hundred feet constitute the Floridan aquifer, which generally includes the Avon Park Limestone and the overlying Ocala Group of limestone formations, all of Eocene Age. Overlying the artesian aquifer are beds of sandy clay, shells, and clay of the Hawthorn Formation of Early and Middle Miocene Age and deposits of Late Miocene or Pliocene Age. These beds serve to confine water under pressure in the underlying artesian aquifer. The confining beds are overlain by unconsolidated deposits of sand and sandy coquina of Pleistocene and Recent Age which completely blanket the entire county.

Lakes and streams occur throughout the county. The more important potential surface-water sources of supply are: (1) the St. Johns River; (2) the lakes and sloughs of the coastal ridge area; and (3) the streams flowing eastward into the Indian River. All the sources provide water supplies, but the quality and quantity of water vary greatly.

Groundwater in Brevard County occurs under artesian and nonartesian conditions. Nonartesian water occurs in the sediments of Pleistocene and Recent Age, whereas artesian water is in the underlying limestone formations of Eocene Age.

The piezometric surface of the artesian aquifer is higher than the land surface over most of Brevard County, and hence wells drilled into the aquifer will overflow at the surface. The top of the artesian aquifer is about 75 feet below sea level in the northwestern corner of the county and more than 300 feet below sea level in the southeastern corner. In Brevard County, the direction of movement of the artesian water is generally northeastward, except under the barrier islands. On the barrier islands north of Cocoa Beach, artesian water moves northwestwardly and south of Melbourne it moves directly eastward. The mineralization of the artesian water in the area under investigation does not meet the standards set by the U.S. Public Health Service for public drinking supplies except in the following areas: (1) west of the St. Johns River; (2) the southeastern corner of the county; and (3) two small areas north and west of Titusville.

The sediments of Pleistocene and Recent Age average about 50 feet in thickness in the coastal ridge area but are less than 20 feet thick in the vicinity of the St. Johns River. Nonartesian water saturates about 40 feet of these sediments in the coastal ridge area, and the zone of saturation thins toward the St. Johns and Indian rivers. The lower part of the sediments contains salty water in some places. Upward movement of salty water from the artesian aquifer can occur in areas where the water table is below the piezometric surface, including areas where the water table is, or in the future may be, lowered by large withdrawals of groundwater from the nonartesian aquifer.


Title:
Geologic and Hydrologic Data from a Test-Monitor Well at Fernandina Beach, Florida

Publication:
USGS Open File Report No. 80-347.  U.S. Geological Survey. Tallahassee, Florida.

Abstract:
A 2,102-foot observation well was drilled at Fernandina Beach, Florida, to obtain geologic and hydrologic data. Drill cuttings, water samples, and water-level measurements were collected. Geologist's, driller's, and geophysical logs were completed. The well is constructed with 12-inch diameter casing to a depth of 515 feet and 6-inch diameter casing from 515 to 2,000 feet. The remainder is open hole. The uppermost 500 feet of material penetrated by the well consists of sand, clay, limestone, and dolomite. In the remainder of the hole, the material consists of fragmental and granular limestone and massive to finely crystalline dolomite, which comprise the Floridan aquifer in the area. 

After the well was completed, water levels in the monitored zone, 2,000 to 2,102 feet, were above land surface. During July and August 1979, water levels ranged from about 8 to 13 feet above land surface. Chloride concentrations of water sampled through the drill stem from a depth of 632 to 2,039 feet ranged from 25 to 710 milligrams per liter. Chloride increased markedly below 2,039 feet to a maximum of 7,800 milligrams per liter at 2,094 feet. After completion of the well, chloride was 8,100 milligrams per liter.


Title:
Impact of Development on the Availability and Quality of Groundwater in Eastern Nassau County, Florida and Southeastern Camden County, Georgia.

Publication:
USGS Water Resources Investigation Report No. 833-4190.  U.S. Geological Survey. Tallahassee, Florida

Abstract:
The primary source of water in Nassau County, Florida, and Camden County, Georgia, is groundwater from the Floridan aquifer. The aquifer consists of upper, middle, and lower water-bearing zones of permeable limestone and dolomite separated by semiconfining beds of hard, massive dolomite and limestone of low permeability, all of which are confined above and below by leaky confining beds. Development of the aquifer is limited to the upper and middle zones, at depths of 530 to 1,000 feet and 1,200 to 1,700 feet below land surface. The transmissivity of the upper zone ranges from 20,000 to 50,000 and that of the middle zone 40,000 to 60,000 feet squared per day. The lower zone, about 2,000 to 2,100 feet below land surface contains very saline water with chloride concentrations exceeding 8,000 milligrams per liter. Water levels in a monitor well open to the lower zone do not appear to be affected by pumpage changes within the upper and middle zones.

Development of the Floridan aquifer has been principally for industrial supply and occurs primarily in the Fernandina Beach-St. Marys area in the coastal part of the study area. Pumpage increased from about 30 million gallons per day in 1940 to about 91 million gallons per day in 1980. The pumpage, primarily from the upper zone, has resulted in (1) a long-term decline in the potentiometric surface of about 25 feet in the western part of the study area to more than 100 feet near the major pumping centers in the coastal part of the study area; (2) an increase or decrease in head differences between the surficial and Floridan aquifers, thereby increasing recharge to and decreasing natural discharge from the Floridan aquifer; and (3) an increase in groundwater inflow to the area and a reversal or modification of the natural hydraulic gradient of the potentiometric surface toward the east. There is also an increase in the initial head differences among the water-bearing zones of the aquifer, thereby increasing leakage from deeper zones of higher artesian heads to the upper zone.

The water quality in the upper water-bearing zone is fairly uniform: concentrations of dissolved solids generally range from 400 to 600 milligrams per liter, chloride 20 to 40 milligrams per liter, and sulfate 100 to 190 milligrams per liter. In Fernandina Beach, water from four wells tapping this zone has relatively high chloride concentrations, as great as 190 milligrams per liter. Based on existing water-quality data, there is no evidence of saline water intrusion in the upper water-bearing zone of the Floridan aquifer in the study area. In Fernandina Beach, water in the middle zone is more mineralized than water in the upper zone. Chloride concentrations of water from several wells more than 1,250 feet deep increased from less than 100 to more than 1,000 milligrams per liter since 1952.

Future development of the Floridan aquifer within the study area, in particular the coastal part, may be limited to the upper water-bearing zone. The presence of relatively high chloride concentrations of water from wells tapping the middle and lower zones in the coastal area limits the development of these zones as a freshwater supply. Existing development of the aquifer along the coast and the resulting declines in the potentiometric surface may restrict the amount of future development from the upper zone. In the western part of the study area, little is known about the hydrogeology of the middle and lower zones and these zones may be a potential source of freshwater.

The effects of future development on the water levels of the upper water-bearing zone were estimated based on a mathematical model. Steady state drawdowns would be about 1.24 feet at 10,000 feet and 0.3 feet at 50,000 feet from a pumping well-pLer 1 million gallons per day increase in pumpage. Assuming a 50 percent increase in pumpage at each of the major pumping centers from 82 to 123 million gallons per day within the study area, the net decline in water levels in observation wells about 5 to 10 miles from the pumping centers were 9.9 to 17.4 feet. About 30 miles offshore, west of the inferred position of the freshwater-saltwater interface, the net decline was only 2 feet.

The surficial aquifer, consisting of thin permeable zones of sand, shell, and limestone, provides water to wells at rates of 10-50 gallons per minute, but is not considered a source for large groundwater supplies. The estimated transmissivity ranges from less than 100 feet squared per day for the fine grained, well-sorted sand to 10,000 feet squared per day for the sand and shell beds. Water is generally of acceptable quality for most uses except near the coast and tide-affected streams that contain saltwater.


Author:
Brown, D.P., Johnson, R.A., and Baker, J.S.

Title:
Hydrogeologic Data from a Test Well at Kathryn Abbey Hanna Park, City of Jacksonville, Florida.

Publication:
USGS Open File Report No. 84-143. U.S. Geological Survey. Tallahassee, Florida.

Abstract:
A 2,026-foot test well was drilled at Hanna Park, City of Jacksonville, Florida, to obtain hydrogeologic data. Drill cuttings and water samples were collected, and water-level measurements and lithologic and geophysical logs were made. The well is constructed with 6-inch diameter casing from land surface to a depth of 1,892 feet and cement grouted in place. The remainder is open hole. The uppermost 411 feet of material penetrated by the well consists of sand, clayey sand, phosphatic sandy clay, coquina, sandy limestone, and dolostone. In the remainder of the hole, the material consists of limestone and dolostone, which comprise the Floridan aquifer in the area.


Author:
Brown, D.P., Johnson, R.A., and Broxton, R.A.

Title:
Hydrogeologic Data from a Test Well in East-Central Duval County, Florida.

Publication:
USGS Open File Report No. 84-802. U.S. Geological Survey. Tallahassee, Florida.

Abstract:
A 2,112-foot test well was drilled in east-central Duval County, Florida, to obtain geologic, hydrologic, and water chemistry data.  Drill cuttings and water samples were collected, and water-level measurements and lithologic and geophysical logs were made. Deposits to a depth of 575 feet consist of sand, clayey sand, phosphatic sandy clay, coquina, sandy limestone, and dolostone.  Below 575 feet, the deposits consist of fragmented and granular limestone, dolomitic limestone, and massive to finely crystalline dolostone, which comprise the Floridan aquifer system in the area. 

Water levels were measured near or at the bottom of the drill hole through the drill stem and in the annular space between the drilled hole and drill stem at the well head as drilling progressed from 770 to 2,112 feet in depth. Water levels measured through the drill stem ranged from 1.17 feet above land surface at a depth of 2,107 feet to 15.0 feet above land surface at a depth of 1,574 feet. Water levels measured in the annular space ranged from 7.5 feet above land surface at a depth of 770 feet to 14.9 feet at various depths from 1,574 to 1,721 feet. 

Chloride concentrations of water sampled through the drill stem from a depth of 711 to 1,616 feet ranged from 22 to 150 milligrams per liter at 1,648 feet. Chloride concentrations then ranged from 345 to about 800 milligrams per liter to a depth of 2,071 feet and then increased to a maximum of 5,450 milligrams per liter at 2,107 feet.


Author:
Brown, D.P., Miller, J.A., and Hayes, E.C.

Title:
Hydrologic Data from a Test Well near Ponte Vedra, Northeast St. Johns County, Florida

Publication:
USGS Open File Report No. 86-410W.  U.S. Geological Survey. Tallahassee, Florida.

Abstract:
A 2,026-foot test well was drilled at Hanna Park, City of Jacksonville, Florida, to obtain hydrogeologic data. Drill cuttings and water samples were collected, and water-level measurements and lithologic and geophysical logs were made. The well is constructed with 6-inch diameter casing from land surface to a depth of 1,892 feet and cement grouted in place. The remainder is open hole. The uppermost 411 feet of material penetrated by the well consists of sand, clayey sand, phosphatic sandy clay, coquina, sandy limestone, and dolostone. In the remainder of the hole, the material consists of limestone and dolostone, which comprise the Floridan aquifer in the area


Title:
Groundwater Hydraulics, Regional Flow, and Groundwater Development of the Floridan Aquifer System in Florida and Parts of  Georgia, South Carolina, and Alabama.

Publication:
USGS Professional Paper 1403-C.   U.S. Geological Survey, Washington, D.C.

Abstract:
The Floridan aquifer system is one of the major sources of groundwater supplies in the United States. This highly productive aquifer system underlies all of Florida, southern Georgia, and small parts of adjoining Alabama and South Carolina , for a total area of about 100,000 square miles. About 3 billion gallons of water per day is withdrawn from the aquifer for all uses, and, in many areas, the Floridan is the sole source of freshwater. The aquifer system is a sequence of hydraulically connected carbonate rocks that generally range in age from Late Paleocene to Early Miocene. The aquifer system consists of an upper aquifer and a lower aquifer, separated by a less permeable confining unit of highly variable properties. Low-permeability clastic rocks overlie much of the Floridan aquifer system. The Floridan aquifer system derives its permeability from openings that vary from fossil hashes and networks of many solution-widened joints to large cavernous openings in karst areas. The dominant feature of the Floridan flow system, both before and after groundwater development, is Upper Floridan aquifer springs, nearly all of which occur in unconfined and semiconfined parts of the aquifer in Florida. Three billion gallons per day pumped from the Floridan aquifer system has resulted in long-term regional water-level declines of more than 10 ft in three broad areas of the flow system: (1) coastal Georgia and adjacent South Carolina and northeast Florida; (2) west-central Florida; and (3) the Florida panhandle. Saltwater has encroached as a result of pumping in a few coastal areas. In general, the water chemistry in the Upper Floridan is related to flow and proximity to the freshwater-saltwater interface. A considerable area of the Floridan aquifer system 's extent remains highly favorable for the development of large groundwater supplies. This area is largely inland and is characterized by high transmissivity and minimal development (as of early 1980's). The major constraint on future development is degradation of water quality rather than water-quantity limitations.


Title:
Thickness of the Potable-Water Zone in the Floridan Aquifer

Publication:
Map Series #74.  Prepared by the U.S. Geological Survey in cooperation with the Florida Department of Environmental Regulation. Tallahassee, Florida.

Abstract:
The map shows the type of mineralization in water in the aquifer and how it varies in different parts of the State: calcium--bicarbonate water occurs in most of northern and central Florida, calcium-sulfate water occurs in southwestern and southern Florida, sodium--bicarbonate water occurs in extreme western Florida, and sodium--chloride water occurs in many of the coastal areas. The concentration of mineralization generally increases with depth. Generally, if potable water is available in the aquifer, it will be in the upper part.

The map shows the approximate thickness of the zone of potable water in the Floridan aquifer. The map, in conjunction with other hydrologic data (transmissivity and storage) is used to estimate the quantity of potable water that may be withdrawn from wells in the aquifer in various parts of the State, and in conjunction with data on the altitude of the top of the Floridan aquifer to determine the maximum depth to which wells can be drilled to obtain potable water from the aquifer.

The map was compiled from two hydrologic maps--depth to base of potable water in the Floridan aquifer and top of the Floridan artesian aquifer and from basic local and regional data.  If used to determine the exact thickness of potable water in the aquifer at any specific location or at any specific time, consideration must be given to seasonal or long-term water levels and local variations due to pumpage


Title:
Availability and Quality of Water from Shallow Aquifers in Duval County, Florida

Publication:
USGS Water Resources Investigations 78-92.  Prepared by the US Geological Survey. Tallahassee, Florida.

Abstract:
The shallow-aquifer system in Duval County, Fla., overlies the Floridan aquifer and is composed chiefly of sand, clay, sandy clay, and limestone. Thickness of the system ranges from about 300 to 600 feet. The upper 150 feet of deposits, consisting of the water-table and shallow-rock zones, are the most dependable and economical source of supplemental water supply. The principal shallow water-bearing zone is a limestone bed 40 to 100 feet below land surface. Aquifer tests conducted at 13 sites in Duval County show that yields from the shallow aquifer vary from place to place within the county owing chiefly to variations in lithology of the saturated rocks and sediments. The limestone of the shallow-rock zone will yield as much as 200 gallons per minute to wells; the maximum yield at most of the sites tested was between 30 and 100 gallons per minute. The water-table zone generally yields 10 gallons per minute or less but at one site, where a water-table well tapped a shell bed near land surface, the well yielded more than 40 gallons per minute. The quality of water in the shallow aquifer system in Duval County is generally acceptable for most domestic, commercial, and industrial uses. In some places, however, it has a high iron concentration and is hard. The iron concentration exceeds 0.3 milligrams per liter in water from the water-table or shallow-rock zones at 7 of the 13 aquifer test sites. The hardness of water from the aquifer ranges from about 60 to about 180 milligrams per liter.


Title:
The Regional Lithostratigraphic Analysis of Paleocene and Eocene Rocks of Florida

Publication:
Geological Bulletin #45.  Prepared by the Florida Geological Survey. Tallahassee, Florida.

Abstract:
Lithologic and thickness data of the successive Paleocene and Eocene stratigraphic. units in panhandle and peninsular Florida were obtained by investigating cuttings, cores, and electric logs of a total of 164 wells selected for this study. These data were employed for constructing isopach-lithofacies maps, structure maps, and lithologic cross sections. These maps and cross sections together with the paleontologic information make possible more reliable interpretations of sedimentary petrogenesis and of the regional tectonics of Paleocene and Eocene time in Florida.

Two distinct sedimentary facies, elastic (panhandle Florida) and nonelastic (peninsular Florida), have been recognized and differentiated on a series of isopach-lithofacies. maps of the successive stratigraphic units of the Paleocene and Eocene Series in the area studied. These two sedimentary facies were separated by the Suwannee Channel, which acted as a natural barrier, both sedimentational and faunal, and occupied a narrow belt along southern Georgia and northern Florida with a northeast-southwest trend during the time from late Upper Cretaceous to Upper Eocene. The barrier nature of the Suwannee Channel gradually became less effective and finally disappeared near the end of Eocene time.

The fact of gradual but steady spreading of the nonelastic facies northerly and northwesterly over the elastic facies during Early Tertiary time may be the result of continued marine transgression. Some sporadic regressions occurred during Paleocene and Eocene time as manifested by the presence of local and regional unconformities.

Paleogeographic maps of the successive Paleocene and Eocene stratigraphic units studied are reconstructed on the basis of the series of isopach-lithofacies maps, lithologic and paleontologic data, and ecologic and environmental conditions inferred in this study


Author:
Cooper, H.H., Kenner, W.E., and Brown, Eugene

Title:
Groundwater in Central and Northern Florida

Publication:
Report of Investigations #10.  Prepared by the U.S. Geological Survey in cooperation with the Florida Geological Survey.  Tallahassee, Florida.

Abstract:
The report presents information on the stream flow in northern Florida and the quality of the water. It discusses the groundwater system, both water table and artesian, in what is now the basin of the SJRWMD.  The report shows maps of the potentiometric surface of the Floridan aquifer and of the areas of artesian flow, discussing the loss of pressure in the Jacksonville area and the salt water zones of the Floridan aquifer along the coast from St. Johns County to Indian River.


Author:
Crain, Leslie J., Hughes, G.H., and Snell, L.J.

Title:
Water Resources of Indian River County, Florida

Publication:
Report of Investigations #80.  Prepared by the U.S. Geological Survey in cooperation with the Bureau of Geology, Florida Department of Natural Resources, and the Board of Commissioners, Indian River County, and the City of Vero Beach.  Tallahassee, Florida.

Abstract:
Indian River County, on the Atlantic coast in southern Florida. includes 525 square miles, most of which is less than 50 feet above sea level.  Rainfall at Vero Beach averages 51.3 inches, almost two-thirds of it during the summer and early autumn. Large streams do not exist. Runoff is to the north through St. Johns Marsh into the St. Johns River basin and eastward to Indian River through several improved channels and canals. Blue Cypress Lake is the only large body of fresh water in the county; Indian River, the lagoon between the mainland and an offshore bar, is at sea level and highly saline.

A shallow aquifer consisting of sand, shell and some silt and clay, is present in all of the county, its base reaching depths of 150 feet. The aquifer is underlain by the Hawthorn Formation which acts as a confining bed to retard upward movement of water from the underlying Floridan aquifer. Water from the shallow aquifer is of good quality.  Chloride concentrations generally are less than 60 milligrams per liter; dissolved solids less than 500 milligrams per liter.  Recharge is primarily from rainfall in the county. Within the drainage districts the shallow aquifer receives some recharge of water withdrawn from Floridan-aquifer wells for irrigation.  Throughout the county the composition of the shallow aquifer varies considerably. Discontinuous layers, or lenses, of cemented or otherwise impermeable materials are present near Indian River; these appear to act as barriers to saltwater intrusion from the river. 

The Floridan aquifer underlies the county at a depth of 300 to 600 feet. Recharge to the Floridan aquifer is almost entirely from the area west and outside of the county. Discharge from the aquifer is from wells, primarily for irrigation, and natural discharge to the ocean.  A high chloride concentration is the common objectionable characteristic of Floridan aquifer water in the county; in general, the concentration increases with the depth from which water is withdrawn. In spite of its chloride concentration, water having chloride concentrations as high as 2,000 milligrams per liter has been used for irrigation. 

The specific purposes of this study were to: (1) ascertain the nature and mode of occurrence of the ground- and surface-water resources of the county; (2) determine the chemical quality of the surface and groundwaters; (3) determine what changes may take place in the chemical quality of the water in both the Floridan and shallow aquifers as a result of the activities of man; (4) delineate the area and potential yield of the shallow aquifer; and (5) determine what alternative actions could be taken to protect or increase the availability of the water resources of the county and what further studies may be necessary.


Author:
Duncan, Joel G., Evans, William L., and Taylor, Koren L.

Title:
Geologic Framework of the Lower Floridan Aquifer System, Brevard County, Florida

Publication:
Bulletin #64.  Prepared by the Florida Geological Survey.  Tallahassee, Florida.

Abstract:
A common problem for coastal communities in Brevard County has been the disposal of liquid waste. A favored solution utilizes injection wells whereby liquid waste is pumped underground into highly permeable rocks within the non-potable portion of the lower Floridan aquifer system. Groundwater chemistry data from monitor wells at several Brevard County injection sites suggest that the presence and/or lateral continuity of suitable confining rock above the injection zone is questionable and indicate that a better understanding of the lower Floridan aquifer system is needed. Thus, the purpose of this study is to detail the geologic framework of the lower Floridan aquifer system in Brevard County.

Strata of the lower Floridan aquifer system in Brevard County dip generally to the southeast with an average dip angle of 0.1 degree. Several lines of evidence suggest the possibility of faulting in Brevard County. The inferred faults strike north-south and are downthrown to the west.  Cores of lower Floridan aquifer system strata commonly exhibited some degree of fracturing. In general, fractures appear to be restricted to well indurated or highly cemented carbonates, principally dolostone.  Slickensided surfaces, lacking well defined fracture planes, were observed in moderately to poorly indurated limestones.  Strata of the lower Floridan aquifer system in Brevard County are characterized by Paleocene to Middle Eocene, interbedded limestones and dolostones. Limestones are generally fossiliferous, moderately to poorly indurated, and have high primary porosity. Dolostones are typically well indurated and have fossil moldic and vugular porosity.

In Brevard County, the Floridan aquifer system generally consists of two major permeable zones separated by a middle confining unit of lower permeability. The middle confining unit in the study area consists of dense dolostone with interbedded limestones which act as a single leaky confining unit within the main body of the permeable carbonates of the Floridan aquifer system. Carbonates below the middle confining unit in the lower Floridan aquifer system are predominantly low permeability, interbedded dolostones and limestones with zones of moderate to high permeability.

The "Boulder Zone," a subzone of the lower Floridan aquifer system, is the primary injection horizon in Brevard County and consists of highly fractured and cavernous dolostones which exhibit high transmissivities. Above the Boulder Zone, there are layers of carbonates that have confining qualities. Evaluation of geophysical logs, lithologic samples and borehole videos from Brevard County injection wells indicate that numerous fractures exist throughout the lower Floridan aquifer system.

Analysis of monitor zone groundwater chemistry data showed that the majority of the wells in the study exhibit trends in water quality to some degree. These trends, barring wellbore mechanical problems, are attributed to the upward migration of injected waste waters along permeable conduits related to fractures, dissolution cavities, and vertical and lateral lithofacies variations. The middle confining unit of the Floridan aquifer system in Brevard County is probably best described as having a leaky confining character.


Title:
The Shallow-Aquifer System in Duval County, Florida

Publication:
Report of Investigations #59.  Prepared by the U.S. Geological Survey in Cooperation with the City of Jacksonville, Duval County, and the Florida Department of Natural Resources Bureau of Geology.  Tallahassee, Florida.

Abstract:
One of the most important natural resources of the Jacksonville-Duval area in northeast Florida is its supply of potable groundwater. This water is derived mainly from deep wells that tap the Floridan aquifer. However, the shallow-aquifer system supplements that from the deeper Floridan aquifer.

The shallow-aquifer system consists of permeable beds of sand, shell, and limestone within the following stratigraphic units; the upper part of the Hawthorn Formation (middle Miocene age), the upper Miocene or Pliocene deposits, and the Pleistocene and Holocene deposits.  The aquifer is recharged by local rainfall. The amount of recharge from rainfall is estimated to be from 10 to 16 inches per year and varies from place to place within the area. Discharge is by pumpage, outflow from springs, downward percolation, and by evapotranspiration. 

In the west central part of Duval County the potentiometric surface of the shallow-aquifer system is above land surface all or part of the year and shallow wells will flow.  With only a few exceptions, wells that penetrate the shallow-aquifer system yield water of good quality. The hardness of the water averages 185 milligrams per liter and ranges from 10 to 1,900 milligrams per liter. The iron content ranges from 0 to 2.8 milligrams per liter and in places causes staining of clothing and plumbing fixtures.  Water from the shallow-aquifer system is used primarily for domestic purposes, particularly in the rural areas and areas not served by private or public utilities. Other uses for the water consist of refrigerator cooling, industrial, agricultural, and schools.


Title:
Availability of Water in the Floridan Aquifer in Southern Duval and Northern Clay and St Johns Counties, Florida.

Publication:
USGS Water Resources Investigations No. 76-98 U.S. Geological Survey. Tallahassee, Florida

Abstract:
The Floridan aquifer within the area of investigation consists of 1,100 to 1,800 feet of soft, porous limestone interbedded with hard, dense limestone and dolomite overlain by several hundred feet of confining beds. From late 1948 to May 1972, water levels in wells tapping the Floridan aquifer declined as much as 14 feet in northern Clay and St. Johns Counties and more than 20 feet at Jacksonville in Duval County, Florida. These trends will probably continue as withdrawals from the aquifer increase. Water-level depressions exist at Green Cove Springs and Jacksonville because of natural discharge and large scale withdrawals. Withdrawals from wells could result in well interference unless the wells are spaced at least 1,000 ft apart. Two- to four-inch diameter wells drilled 100 ft or less into the aquifer yield 50 to 250 gal/min. Larger and deeper wells yield 1,000 gal/min or more. Hardness of water is generally less than 10 mg/liter. Quality of water from wells sampled over a span of 10 to 30 years has not changed noticeably. Principal recharge to the Floridan occurs southwest of the area in a lake region where rainfall percolates directly into the aquifer.


Title:
Saline-Water Intrusion in the Floridan Aquifer in the Fernandina Beach Area, Nassau County, Florida

Publication:
USGS Water Resources Investigation No. 77-32. U.S. Geological Survey. Tallahassee, Florida.

Abstract:
The Floridan aquifer is the major source of water for municipal and industrial use in northeastern Nassau County, Florida. Pumpage from the aquifer at Fernandina Beach has created a cone of depression in the potentiometric surface which is at or below sea level in a 35-square mile area. Since 1880 water levels have declined more than 120 feet near the center of pumping, and chloride concentrations have increased from about 20 to a maximum of 800 milligrams per liter in some deep wells. The saline water probably is connate water which comes from zones below 1,250 and 2,000 feet. Several alternate methods to control the migration of saline water are discussed.


Author:
Fernald, Edward A. and Patton, Donald J.

Publication:
Chapter 13 (St. John’s River Water Management District).  Institute of Science and Public Affairs.  Florida State University, Tallahassee, Florida.

Abstract:
This atlas covers the whole state of Florida from the viewpoint of the state water resources. It separates its geographic coverage individually for each of the five water management districts.  The atlas displays in maps and graphs the significance of the water resources of Florida.  It provides coverage of the groundwater system and presents information on the quality of the water in the various aquifers. A chapter devoted to the SJRWMD includes maps showing the potentiometric levels of the Floridan aquifer within the SJRWMD basin and litohlogic maps and hydrologic maps of the area.  Numerous hydrologic and geologic maps are presented and information on water quality is available in tables and maps.


Title:
Estimated Drawdowns in the Floridan Aquifer Due to Increased Withdrawals, Duval County, Florida

Publication:
USGS Water Resources Investigation No. 79-84.  U.S. Geological Survey.  Tallahassee, Florida.

Abstract:
Hydrologic investigations of the Floridan aquifer in Duval County, Florida, have shown that an appropriate simplified model of the aquifer system consists of a series of sub aquifers separated by semipermeable beds. Data from more than 20 aquifer tests were reanalyzed by the Hantush modified method, which takes into account leakance from all confining units. Transmissivity values range from 20,000 to 240,000 square feet per day. Leakance was estimated to be 2.5x10 to the minus 6th power and 3.3x10 to the minus 5th power per day for the upper and lower confining units, respectively. Families of steady-state distance-drawdown curves were constructed for three representative transmissivity values based on hypothetical withdrawals from a point source ranging from 5 to 50 million gallons per day. Transient effects were not considered because the system reaches steady-state conditions within the time ranges considered. Drawdown at any point can be estimated by summing the effects of any hypothetical configuration of pumping centers. The accuracy of the parameters was checked by comparing calculated drawdowns in selected observation wells to measured water-level declines.


Title:
Investigation of Groundwater Resources and Salt Water Intrusion in the Coastal Areas of Northeast Florida

Publication:
Technical Publication Series #SJ 80-4 (Formerly, Technical Report #3).  Prepared by St. Johns River Water Management District.  Palatka, Florida.

Abstract:
Groundwater resources and salt water intrusion in the coastal areas of northeastern Florida were evaluated. Aquifer characteristics were determined for the three systems occurring in the study area, namely, the Floridan, secondary artesian, and shallow aquifers. Water levels and water quality were periodically measured for each aquifer. Available potable water resources in the Floridan aquifer were estimated using safe yield approximations.

Trilinear plotting, Stiff patterns, and factor analysis were used to interpret water quality data which aided in establishing the origin and distribution of chemical constituents found in waters of the various aquifers. Cross sections and a fence diagram were also used to illustrate the location of the 250 and 1,000 mg/l chloride interfaces.

Five "areas of vital concern" were proposed. Area 1 includes the Fernandina Beach cone of depression. Area 2 includes the coastal shallow clastic and secondary artesian aquifers. Area 3 includes the Floridan aquifer transitional area at Fort George Island. Area 4 includes the Anastasia Formation and Floridan aquifer transitional zone near St. Augustine. Area 5 includes the agricultural areas of Hastings and Bunnell which exhibit connate intrusion.


Title:
The Distribution of Bromide in Water in the Floridan Aquifer System, Duval County, Northeastern Florida

Publication:
USGS Water Resources Investigation No. 94-4154.  U.S. Geological Survey. Tallahassee, Florida.

Abstract:
Although Duval County, Florida, has ample groundwater resources for public supply, the potential exists for a problem with excessive disinfectant by-products. These disinfectant by-products result from the treatment of raw water containing low concentrations of bromide and naturally occurring organic compounds. Because of this potential problem, the relation of bromide concentrations to aquifer tapped, well location and depth, and chemical characteristics of water in the Floridan aquifer system underlying Duval County were studied to determine if these relations could be applied to delineate water with low-bromide concentrations for future supplies. In 1992, water samples from 106 wells that tap the Floridan aquifer system were analyzed for bromide and major dissolved constituents. A comparison of bromide concentrations from the 1992 sampling with data from earlier studies (1979-80) indicates that higher bromide concentrations were detected during the earlier studies. The difference between the old and new data is probably because of a change in analytical methodology in the analysis of samples. Bromide concentrations exceeded the detection limit (0.10 milligrams per liter) in water from 28 of the 106 wells (26 percent) sampled in 1992. The maximum concentration was 0.56 milligrams per liter. There were no relations between bromide and major dissolved constituents, well depth, or aquifer tapped that would be useful for determining bromide concentrations. Areal patterns of bromide occurrence are not clearly defined, but areas with relatively high bromide concentrations tend to be located in a triangular area near the community of Sunbeam, Florida, and along the St. Johns River throughout Duval County.


Author:
Goldstein, J., Reynolds, A., and Helms, S.

Title:
Underground Injection Wells: Are They Compatible with Sustainable Water Management in Florida?

Publication:
Final Report.  Submitted to Elizabeth Ordway Dunn Foundation.  Tellus Institute, Resource and Environmental Strategies.

Abstract:
Florida's increasing dependence on underground aquifers for both drinking water and disposal of wastewater poses potential risks. Wastewater, even after it is treated, contains certain contaminants that can compromise receiving water quality. While precautions are taken to keep the treated wastewater separate from sources of drinking water, some have questioned the sustainability of this approach. A truly sustainable approach will maintain standards of environmental quality, economic health, and community well-being over the long-term. This study examines implications of various wastewater management options in Florida, with a focus on the common practice of deep well injection.

A cost-benefit analysis of wastewater disposal options can provide relevant information on the risks associated with each disposal alternative. Yet a traditional analysis of costs might exclude important elements such as the cost to the public for a small increase in the risk of disease or the avoided costs of water provision from a wastewater reuse project. This report presents a tool called True Cost Assessment (TrCA) to incorporate all the components of sustainability into a cost analysis.

This report begins by presenting the current state of wastewater management in Florida and an explanation of why studying this issue now is timely. Next, we introduce the concept of TrCA, illustrating how it can be applied to Florida's wastewater management decision-making and discussing some of the obstacles to data collection. The report then provides guidance to state and local governments on codifying TrCA into law by responding to two model pieces of legislation. We conclude with ideas, informed by the TrCA, for implementing strategies that are consistent with sustainable water management.

In contrast to other states, Florida relies heavily on underground injection for disposal of domestic wastewater, comprising the sewage from homes and businesses. The use of deep injection wells has expanded since 1975 when it was judged preferable to surface water discharge. Now, there are more than 100 such wells.
Recently, monitoring wells have indicated some migration of injected fluid out of injection zones previously believed to be confined. Because migration is not permitted under injection well operating permits, and due to the potential risks of this migration. a closer examination of wastewater disposal decisions in Florida is necessary.

While we found a discouraging lack of data to execute this analysis, we conclude that ocean outfall and surface water discharge are unlikely to be viable options in the future. On the other hand, water reuse is desirable in terms of its potential sustainability, but will require extensive infrastructure and market development.  The groundwater monitoring system needs to be maintained and expanded, as it currently monitors mostly deep aquifers used for drinking water, and not surficial aquifers.

All these initiatives are integral links to sustainability, and none can be ignored. It is in this context that we must view deep-well injection of wastewater in Florida, and the environmental and economic trade-offs associated with each alternative disposal method. Through considering the true, long-term costs of wastewater management choices, erring on the side of caution in making key assumptions. and following these sustainability guidelines, Florida will be poised to provide future generations with sufficient clean water and safe means of wastewater disposal.


Title:
Hydrogeology of Effluent Disposal Zones, Floridan Aquifer, South Florida

Abstract:
The increasing population of south Florida is creating a need for greater wastewater disposal capacity. The people of Florida are dependent on groundwater for drinking, irrigation, and other uses. The emphasis on preservation of surface water quality means that many surface waters are not allowed to receive effluent from municipal or industrial sources. Since the 1940s, the highly transmissive zones of the nonpotable portion of the Floridan aquifer have served as disposal zones for oil field brine and later for industrial and municipal effluent.

The Floridan aquifer of south Florida is a carbonate Cenozoic age aquifer. Transmissivities between 0.5 and 21 million gpd/ft exist in cavernous and fractured sequences in the aquifer. Confining zones that overlie the disposal intervals have transmissivities and hydraulic conductivities one to three orders of magnitude less than the injection intervals. These confining zones prevent low density municipal effluent from rising upward through the overlying saline waters.

This paper provides an integration of previously published work with recent site-specific data collected from deep injection wells drilled in the last two decades.  Numerous studies of individual deep injection wells have provided information on hydrogeological characteristics of injection zones in the Floridan aquifer of south Florida and also the confining characteristics of overlying intervals. Site-specific data agree with and add to previous studies. The highly permeable zones of the Floridan aquifer continue to be favorable for effluent disposal as long as each site has an effective confining bed.


Title:
The Surficial Aquifer in East-Central St. Johns County, Florida

Publication:
Water Resources Investigations #81-14, U.S. Geological Survey, prepared in cooperation with St. Johns County.  Tallahassee, Florida.

Abstract:
The area of investigation is in the east-central part of St. Johns County, Florida.  The surficial aquifer, a composite of confined and unconfined water-bearing zones overlying the Miocene Hawthorn Formation, is an important source of water in St. Johns County, Florida. The water from wells open to the surficial aquifer generally meets quality standards recommended by the U.S. Environmental Protection Agency for public water supplies, except for concentrations of iron that for most wells are substantially greater than the recommended limit of 0.3 milligrams per liter. Data from 12 test wells drilled to the top of the Hawthorn Formation, about 100 feet below land surface, indicate that the productive zones and confining beds in the surficial aquifer are discontinuous. Test well yields from individual zones range from less than 1 to 42 gallons per minute from depths between 20 and 100 feet below land surface. The most productive zones were generally found in the Tillman Ridge area, about 10 square miles in the west-central part of the area of investigation. Analysis of an aquifer test on a well in the Tillman Ridge area indicates a transmissivity of about 6,500 to 7,000 feet squared per day.  The best local source of good quality water for development of a relatively large water supply is in the vicinity of Tillman Ridge.


Title:
Surficial and Intermediate Aquifers (in Principal Aquifers in Florida)

Abstract:
Aquifers that overlie the Floridan aquifer are becoming increasingly important as sources of water supply in the State, particularly in those areas where water in the underlying artesian aquifer is highly mineralized or has the potential of becoming highly mineralized. The principal sources of groundwater used for drinking in parts of east coastal, southwest coastal, and south Florida are surficial and intermediate aquifers that overlie the Floridan aquifer. 

Surficial and intermediate aquifers are the only source of groundwater available for public supply in some areas where excessive depth to the Floridan or poor quality of water in the Floridan precludes its use for public supply without special and expensive water treatment. This summary includes only those counties where surficial and intermediate aquifers are currently being used to supply more than half of the drinking water for public supply.

About 12 percent of Florida's total public supply and rural domestic water needs are supplied by aquifers other than the Floridan, the Biscayne, and the sand-and-gravel. These "other aquifers" have been loosely identified by informal terminology, and consequently characterized by a number of local names. In various parts of the State, some of the terms used include shallow, surficial, secondary, water-table, semiartesian, limestone, and shallow-rock. Especially in cases where several local names apply to essentially the same regional water source, this variability may lead to confusion.  No statewide consensus is presently available to clearly define or delineate these "other aquifers."  For purposes of this discussion, the term "surficial aquifer" shall refer to any otherwise undefined aquifer whose top is contiguous with the land surface, and is a local source of supply for drinking water in a limited geographic area. "Intermediate aquifer" shall refer to any otherwise undefined, artesian aquifer that is below the surficial aquifer and above or within the unit confining the Floridan aquifer, and is a local source of supply for drinking water in a limited geographic area. The surficial and intermediate aquifers thus include those nonartesian (water-table) and artesian aquifers that overlie the Floridan aquifer with the exceptions of the sand-and-gravel aquifer in north-west Florida and the Biscayne aquifer in Broward and Dade Counties in the southeast.  Although both are surficial, the sand-and-gravel and Biscayne aquifers have been extensively studied in the literature and are treated separately in this report.

Surficial aquifers include numerous surficial deposits of sand and shell that range from Miocene through Holocene in age. The intermediate aquifers include artesian beds and lenses of sand, shell, sandstone, clayey sand, dolomite, and Limestone that are slightly deeper-lying and range from Miocene through Pleistocene in age. Pertinent geologic, hydrologic, and chemical characteristics of the surficial and intermediate aquifers are summarized for each county in the study area.


Title:
Depth to Base of Potable Water in the Floridan Aquifer

Publication:
Map Series #42 (Revised).  Prepared by the U.S. Geological Survey in cooperation with the Bureau of Geology, Florida Department of Natural Resources.  Tallahassee, Florida.

Abstract:
In recent years the Floridan aquifer has come under consideration as: (1) a source of water for desalination in southern Florida and the Florida Keys; (2) a reservoir for storage of surplus fresh surface water in areas of water supply deficiency; and (3) a reservoir for the storage of certain waste effluents in in areas and/or depths where the water is highly mineralized. As urban water needs increase and as problems of waste disposal increase, all these possible uses of the Floridan aquifer have become realities. Thus, it is clear that generalized information such as that in this atlas, and detailed hydrologic and geologic information are prerequisite to development and use of the resources of an aquifer system. If the lower part of the Floridan aquifer, where the water is non-potable, is used for injection, the depth map is used to determine the minimum length of casing needed in a disposal well to bypass and protect the potable zone from contamination. If the deep parts of the aquifer are used to receive excess surface water or treated effluents, then maps can be prepared to portray the effects that such injections have on the distribution of potable water in the aquifer. The information is important to those responsible for water management and future planning.


Author:
Knochenmus, Darwin D. and Beard, Michael E.

Title:
Evaluation of the Quantity and Quality of the Water Resources of Volusia County, Florida

Publication:
Report of Investigations #57.  Prepared by the U.S. Geological Survey in cooperation with the Florida Department of Natural Resources, Division of Interior Resources, Bureau of Geology and the Board of County Commissioners of Volusia County.  Tallahassee, Florida.

Abstract:
Volusia County receives most of its fresh water from rainfall, which averages 52 inches per year. The unconsolidated sand of the clastic aquifer absorbs much of the rainfall. Seepage from the clastic aquifer is to streams and to the underlying Floridan aquifer. Recharge to the Floridan aquifer occurs throughout the county wherever the water table in the clastic aquifer is higher than the piezometric surface in the Floridan aquifer. No area is a principal recharge area, but parts of the ridges and the eastern part of the Talbot terrace appear to have the greatest recharge per unit area.  Of the few hundred lakes in the county, most occur along the DeLand ridge, where there are about 120 larger than 5 acres. Water in most lakes in the county has a low mineral content with mineralization ranging from slightly less than 25 to 150 mg/l.  The mineralization of the water in the streams is relatively low with the exception of the St. Johns River and the estuarine sections of Tomoka River and Spruce Creek along the Atlantic coast. Under average flow conditions, the mineral content of the water is less than 200 mg/l.

The productive Floridan aquifer underlies the entire county. Movement of water in the aquifer is outward from the central part of the county, west, north and south to the St. Johns River and east toward the Atlantic Ocean. Mineral content of water from the Floridan aquifer ranges from 100 to 400 mg/l except in the highly mineralized areas along the St. Johns River and the Atlantic coast.

Most high capacity wells in the county withdraw water from the Floridan aquifer for the public supply of areas near the Atlantic Ocean and the St. Johns River. The relatively shallow presence of saline water in these areas limits useful well depths to about 300 feet. Such wells, however, generally yield 1,000 to 1,500 gallons per minute. The depth to saline water in the undeveloped central part of the county is as much as 1,450 feet; thus development of deeper wells in that area should result in higher yields because of the greater available thickness of fresh water in the aquifer. Such development would also have the added desirable effect of capturing recharge water that is currently rejected and lost to the area by runoff and evapotranspiration.

The Floridan aquifer discharges water through large springs along the St. Johns valley. Blue Springs, the ninth largest spring in Florida, has an average flow of 105 mgd and Ponce de Leon Springs has an average flow of 20 mgd. This large volume of water however, is generally unsuitable for public supply. The chloride content of Blue Springs is always greater than the 250 mg/l limit suggested. During periods of high discharge, Ponce de Leon Springs also exceeds the suggested chloride limit.


Title:
Hydrologic Concepts of Artificially Recharging the Floridan Aquifer in Eastern Orange County, Florida—A Feasibility Study

Publication:
Report of Investigations #72.  Prepared by the U.S. Geological Survey in cooperation with the Bureau of Geology, Florida Department of Natural Resources, and the South Florida Water Management District.  Tallahassee, Florida.

Abstract:
Artificial recharge in eastern Orange County is worth consideration. The hydrologic system is suitable for gravity flow through a network of connector wells to recharge the Floridan aquifer from the nonartesian aquifer. Also, the Floridan aquifer needs the additional fresh water to prevent migration of brackish water into the area as rates of withdrawal are increased.

The hydrologic system cycles about 55 inches of rainfall per year of which 10 to 15 inches runs off, 40 to 45 inches evapotranspires, and 0 to 2 inches recharges the Floridan aquifer. The hydrogeologic framework consists of a nonartesian aquifer that is separated from the underlying Floridan aquifer by a confining layer. The water table in the nonartesian aquifer is near land surface and as much as 30 feet above the altitude of the potentiometric surface of the Floridan aquifer. Dissolved-solids concentration of water in the nonartesian aquifer is less than that of the water in the Floridan.

The supply of water for artificially recharging the Floridan through a network of connector wells that also tap the nonartesian aquifer could be derived from the capture of potential water losses-evapotranspiration and runoff. This recharge water would be replaced in the nonartesian aquifer by the capture of rainfall that otherwise would run off or be lost to evapotranspiration. However, the water table must be lowered before capture can occur.

Systematically lowering the water table requires a network of connector wells. The spacing of the wells in the network depends on the transmissivity of the nonartesian aquifer, the available drawdown in the connector well, the well radius, and the capture-drawdown function. The average thickness of the nonartesian aquifer is 50 feet and its average transmissivity is estimated to be between 125 and 625 ft2 per day (feet squared per day). The capture rate is estimated to be between 0.5 and 1.5 feet per year with an effective drawdown between 5 and 10 feet. The well spacing for a network of fully penetrating 6-inch connector wells would be 2,220 feet for an aquifer having a transmissivity of 625 ft2 per day, a capture rate of 0.5 foot per year, and an effective drawdown of 5 feet. A higher capture rate would require additional wells and closer spacing.


Title:
Hydrology of the Floridan Aquifer System in Southeast Georgia and Adjacent Parts of Florida and South Carolina

Publication:
USGS Professional Paper No. 1403-B.  U.S. Geological Survey. Washington, D.C.


Publication:
Leaflet #6.  Prepared by the U.S. Geological Survey in cooperation with the Florida Geological Survey.  Tallahassee, Florida.

Abstract:
This leaflet describes the sources of water for the Jacksonville area and discusses the three aquifers from which water can be developed. The leaflet includes a color map showing the depth to the top of the artesian aquifer in the Jacksonville area.  This is the principal water supply aquifer and nearly all public water supply wells tap this system at depths between 200 and 800 feet.  The water table aquifer and the intermediate aquifer are used only by private individuals.


Title:
Groundwater in Duval and Nassau Counties, Florida

Publication:
Report of Investigations No. 43. Prepared by the U.S. Geological Survey in cooperation with the Division of Geology and Duval County and with the City of Jacksonville. Tallahassee, Florida.

Abstract:
Most of the recharge of water to the aquifer is outside of Duval and Nassau counties where the overlying confining beds are thin or missing. Discharge is by seepage into the ocean and by numerous wells throughout Duval and Nassau counties. 

Water from both the shallow and Floridan aquifer systems is suitable for most uses. The chloride content of water from wells in the Floridan aquifer system ranges from less than 10 ppm (parts per million) to more than 40 ppm in wells less than 1,250 feet deep, and it exceeds 1,100 ppm in wells more than 1,250 feet deep at Fernandina Beach. The chloride content of water from most deep wells at Fernandina Beach, where it increased from 20 to 1,350 mg/l.

At present serious salt-water contamination is limited to a few deep wells at Fernandina Beach, where salt-water is migrating laterally from a highly mineralized zone within the fresh-water zone and vertically from highly mineralized zones below the freshwater zones. Proper well construction and spacing controlled discharge, and careful development of the deeper water-bearing zones may retard, and prevent further, salt-water contamination.

This report describes an area of about 2,000 square miles in northeast Florida and extreme southeast Georgia. The topography is controlled by a series of ancient marine terraces, and surface drainage is through the St. Johns, Nassau, and St. Marys Rivers and through brackish-water streams that empty either into the intracoastal waterway or directly into the ocean.  Practically all the water used in the area is supplied from the rock formations that underlie the surface. These formations, in ascending order, are the Oldsmar Limestone, the Lake City Limestone, the Avon Park Limestone, and the Inglis, Williston, and Crystal River Formations of the Ocala Group, all of Eocene Age; the Hawthorn Formation of Middle Miocene Age; deposits of late Miocene or Pliocene Age; and undifferentiated deposits of Pleistocene and Recent Age. The formations of Eocene Age and the limestone at the base of the Hawthorn Formation compose the Floridan aquifer system. Surficial sand beds and a zone of limestone, shell, and sand at the base of the upper Miocene or Pliocene deposits are the most extensive aquifers in the shallow aquifer system,

The principal source of fresh water in northeast Florida is the Floridan aquifer system. The top of this aquifer is between 300 and 550 feet below sea level and water is confined under artesian pressure in the aquifer by impermeable beds in the Miocene to Recent deposits. At least three permeable zones separated by hard, relatively impermeable zones, occur within the Floridan aquifer system. More water, possibly of less satisfactory quality but under higher artesian pressure, can usually be obtained from the deeper zones than from the shallower zones in the aquifer.


Title:
Altitude and Configuration of the Top of the Floridan Aquifer, Duval County, Florida

Publication:
Open-File Report #77-114, U.S. Geological Survey.  Tallahassee, Florida.

Abstract:
The structural contour lines on the map reflect the eroded surface of the Ocala Limestone of Eocene age which is the top of the Floridan aquifer in Duval County. At the contour interval shown on the map, small irregularities on the surface of the aquifer are not apparent and the configuration of the contour lines reflects the approximate subsurface structure.

The contours show a number of structural features on the surface of the aquifer. For example, the series of depressions on the surface of the aquifer west of the St. Johns River may be buried sinkholes that developed during or after Eocene age when sea level was lower than it is today. Two generally north-south trending faults in central Duval County form a graben with a maximum vertical displacement of more than 150 feet in the south-central part of the county. These faults are blanketed by about 250 to 600 feet of post-Eocene deposits and do not extend to land surface. They are inferred from geological and geophysical logs of water wells in the area.  

This map supersedes an earlier map compiled by the author showing the altitude of the top of the Ocala Limestone in Duval County. Much of the data used to compile the earlier map was used to compile this map; however, this map was modified from data obtained since the earlier map was completed.


Title:
Appraisal of Water Resources in the East Central Florida Region

Publication:
Report of Investigations #61.  Prepared by the U.S. Geological Survey in cooperation with the East Central Florida Regional Planning Council.  Tallahassee, Florida.

Abstract:
The East Central Florida region includes seven rapidly growing counties with an increasing demand upon its water resources.  All water supplies come from rainfall in or near the Region. The groundwater system that underlies the entire region, the Floridan aquifer and the overlying unconfined aquifer, is by far its largest and most efficient water reservoir.  Surface reservoirs are mostly shallow and subject to high evaporation losses and contamination and are fed by streams that have very low flow during droughts.

In certain areas of the region, rainfall recharges the Floridan aquifer. These areas are most of Lake County and the western parts of Orange, Seminole and Volusia counties. In other areas, most of Osceola, Brevard, and Indian River counties, and the eastern parts of Orange, Seminole, and Volusia counties, the aquifer contains highly mineralized water.  The total recharge to the Floridan aquifer, under natural conditions, is estimated to be about 1,000 million gallons per day. This is equivalent to 60 percent of the 1990 groundwater usage. This appraisal indicates that sound water-management practices will be necessary to maintain future usage without aquifer depletion and damage.
     
The principal water-management objectives of the region have been to develop land-use controls and artificial-recharge techniques that will preserve or increase recharge, and at the same time protect or improve the quality of the water in the aquifer. Possible land-use controls include zoning, tax rebates, subsidies, and public ownership of the best recharge areas. Artificial recharge techniques include construction of connector wells that connect the nonartesian aquifer to the Floridan aquifer, augmentation of recharge by importing water from surface runoff areas, use of recharge wells for accepting treated storm water, and land spreading of treated sewage effluent.


Title:
Neogene Sediments of the Atlantic Inner Continental Shelf Off Northern Florida

Publication:
American Association of Petroleum Geologists Bulletin, Volume No. 60, Number 11.

Abstract:
The northern Florida continental shelf is a submerged coastal-plain surface ranging in width from 15 mi (25 km) off Cape Canaveral to 68 mi (110 km) near Georgia. Study of more than 1,134 n. mi. (2,100 km) of high-resolution seismic-reflection profiles, nearly 200 vibratory cores, and four borings, from the inner shelf at -15 to -100ft (-5 to -30 m) MLW, provides some insight into the Neogene evolution of this sector of the Atlantic shelf. Seismic-reflection profiles of the shallow subbottom to 500 ft (152 m) below the sea floor show six distinct reflection units and five prominent reflectors of regional significance. The lower two units rise southward to a truncated high off the Daytona Beach area. The overlying units apparently were unaffected and antedate the middle to late Miocene formation of this structure. Samples of the upper four reflection units show that the lowest is composed of compact greenish-gray mud: overlying units are dominantly quartz sand. Correlations with onshore stratigraphic data indicate that the lowest (unsampled) unit probably corresponds to the Floridan artesian aquifer which is composed largely of Eocene and Miocene strata. Overlying units consist of Miocene and Pliocene strata.

The uppermost reflection unit contains thin and discontinuous Quaternary deposits on a Pliocene surface that is exposed or within 15 ft (5 m) of the sea floor over much of the inner shelf. Surficial Holocene deposits are believed to have been derived largely by substrate erosion of the quartz-rich Tertiary strata underlying the inner shelf at shallow depth. Modern nearshore and shelf processes now are redistributing the liner fraction of the relict Holocene transgressive deposits.


Author:
Merrit, M., Meyer, F., Sonntag, W. and Fitzpatrick, D.

Title:
Surface Storage of Freshwater in South Florida:  A Prospectus

Publication:
U.S. Geological Survey, Water-Resources Investigations, Report #83-4214.  Prepared in cooperation with the U.S. Army Corps of Engineers.  Tallahassee, Florida.

Abstract:
Public agencies in south Florida have investigated various means for increasing the storage capacity of the water-management system, such as injection of freshwater into brackish aquifers, because of concern that increased demand during future dry seasons might cause water-supply deficiencies. In most parts of south Florida, freshwater deficiency usually becomes manifest as the encroachment of saline water into well fields. In some localities, it means the complete absence of natural groundwater supply.

Surplus freshwater for injection might be available during the wet season from the same surface and subsurface sources that may become deficient in their capacity to supply local needs during the dry season. Quantification of the amount of surplus freshwater available from a given source requires site-specific analyses. The chemical composition of the surplus water and its proximity to the location of use or to an intervening conveyance system determine whether it is a suitable source for injection.

Most of south Florida is underlain by saline, permeable artesian zones which have potential for freshwater storage. These are in the Avon Park, Ocala, Suwannee, and Tampa Limestones, and in the Hawthorn Formation. Experimental freshwater injection tests have been performed with varying degrees of success at five locations, in which surplus water has been stored in either the Avon Park, the Suwannee, or the Hawthorn.  Determination of the feasibility of cyclic freshwater injection at a selected site begins with an assessment of the suitability of local geologic conditions, guided by a knowledge of regional hydrogeology.  Feasibility can only be established by actual injection and recovery tests, because some aquifer characteristics affecting freshwater movement during inflow and outflow (degrees of flow uniformity, anisotropy, and hydrodynamic dispersion) are not measurable with standard techniques. Injection and withdrawal tests determine recovery efficiency, the measure of the success of the operation. This is defined for each cycle as the percentage of injected freshwater that can be recovered before the dissolved solids exceed Secondary National Drinking Water Standards. As recovery efficiency improves during the first few cycles, several similar injection and withdrawal tests should be performed in succession. Computer simulations have been made to elucidate the relation of recovery efficiency
 
The hydraulic characteristics of the injection zone determine the maximum practical injection capacity of single well. This, together with the recovery efficiency obtained from a test injection well and local water-supply requirements, determines the number of wells required and the cost-effectiveness of the proposed system relative to other water-supply or conservation alternatives.


Title:
Subsurface Storage of Freshwater in South Florida:  A Digital Model Analysis of Recoverability

Publication:
U.S. Geological Survey Water-Supply Paper #2261.  Prepared in cooperation with the U.S. Army Corps of Engineers.  Washington, D.C.

Abstract:
As part of a study of the feasibility of recovering freshwater injected and stored underground in south Florida, a digital solute-transport model was used to investigate the relation of recovery efficiency to the variety of hydrogeologic conditions that could prevail in brackish artesian aquifers and to a variety of management alternatives. The analyses employed a modeling approach in which the control for sensitivity testing was a hypothetical aquifer considered representative of permeable zones in south Florida that might be used for storage of freshwater. Parameter variations in the tests represented possible variations in aquifer conditions in the area. The applicability of the analyses to south Florida limestone aquifers required the assumption that flow nonuniformities in those aquifers are small on the scale of volumes of water likely to be injected, and that their effect could be represented as hydrodynamic dispersion.

Generally, it was shown that a loss of recovery efficiency is caused by (1) processes causing mixing of injected freshwater with native saline water (hydrodynamic dispersion), (2) processes causing the more or less irreversible displacement of the injected freshwater with respect to the well (buoyancy stratification, background hydraulic gradients, and interlayer dispersion), or (3) processes causing injection and withdrawal flow patterns to be dissimilar (directionally biased well-bore plugging, and dissimilar injection and withdrawal schedules in multiple-well systems). Other results indicated that recovery efficiency improves considerably with successive cycles, providing that each recovery phase ends when the chloride concentration of withdrawn water exceeds established criteria for potability (usually 250 milligrams per liter), and that freshwater injected into highly permeable or highly saline aquifers (such as the "boulder zone") would buoy rapidly.
 
Many hydrologic conditions were posed for model analysis. To have obtained comparable results with operational testing would have been more costly by orders of magnitude k.  The tradeoff is that the validity of results obtained from computer modeling is somewhat less certain. In particular, results must be qualified with observations that (1) the complex set of processes lumped as hydrodynamic dispersion is represented with a somewhat simplified mathematical approximation, and (2) other flow processes in limestone injection zones are as yet incompletely understood. Despite such reservations, the study is considered a practical example of the use of transport models in groundwater investigations.

One method of increasing storage is the "subsurface storage alternative," a proposal that confined aquifers having suitable hydraulic properties but containing water unusable for public supply because of high mineral content be used as storage receptacles. In this report, groundwater is referred to as saline and is considered nonpotable (U.S. Environmental Protection Agency, 1977) if its chloride concentration exceeds 250 mg/L, as it does in most artesian zones in south Florida.  The source of freshwater for injection would be surplus surface water available during the annual wet season or groundwater from surficial aquifers (such as the Biscayne aquifer) which are easily replenished by rainfall. The term "cyclic injection" implies that injection and recovery might be done annually, with injection of surplus freshwater during the wet season followed by a short storage period and subsequent withdrawal of the injected freshwater as needed during the dry season.  Hydrogeologic and chemical characteristics of the aquifers may greatly affect the recoverability of potable water, as may the design of systems of wells and their operational regimes.


Title:
Hydrogeology, Groundwater Movement, and Subsurface Storage in the Floridan Aquifer System in Southern Florida

Publication:
Professional Paper #1403-G, U.S. Geological Survey.  Washington, D.C.

Abstract:
The Floridan aquifer system of southern Florida is composed chiefly of carbonate rocks that range in age from early Miocene to Paleocene. The top of the aquifer system in southern Florida generally is at depths ranging from 500 to 1,000 feet, and the average thickness is about 3,000 feet. It is divided into three general hydrogeologic units: (1) the Upper Floridan aquifer, (2) the middle confining unit, and (3) the Lower Floridan aquifer. The Upper Floridan aquifer contains brackish groundwater, and the Lower Floridan aquifer contains salty groundwater that compares chemically to modern seawater. Zones of high permeability are present in the Upper and Lower Floridan aquifers. A thick, cavernous dolostone in the Lower Floridan aquifer, called the Boulder Zone, is one of the most permeable carbonate units in the world (transmissivity of about 2.5 x 107 feet squared per day). Groundwater movement in the Upper Floridan aquifer is generally southward from the area of highest head in central Florida, eastward to the Straits of Florida, and westward to the Gulf of Mexico.

Distributions of natural isotopes of carbon and uranium generally confirm hydraulic gradients in the Lower Floridan aquifer. Groundwater movement in the Lower Floridan aquifer is inland from the Straits of Florida. The concentration gradients of the carbon and uranium isotopes indicate that the source of cold saltwater in the Lower Floridan aquifer is seawater that has entered through the karst features on the submarine Miami Terrace near Fort Lauderdale. The relative ages of the saltwater suggest that the rate of inland movement is related in part to rising sea level during the Holocene transgression.  Isotope, temperature, and salinity anomalies in waters from the Upper Floridan aquifer of southern Florida suggest upwelling of saltwater from the Lower Floridan aquifer. The results of the study support the hypothesis of circulating relatively modern seawater and cast doubt on the theory that the saltwater in the Floridan aquifer system probably is connate or unflushed seawater from high stands of sea level.

The principal use of the Floridan aquifer system in southern Florida is for subsurface storage of liquid waste. The Boulder Zone of the Lower Floridan aquifer is extensively used as a receptacle for injected treated municipal wastewater, oil field brine, and, to a lesser extent, industrial wastewater. Pilot studies indicate a potential for cyclic storage of freshwater in the Upper Floridan aquifer in southern Florida.


Title:
Potential Subsurface Zones for Liquid-Waste Storage in Florida

Publication:
Map Series #94.  Prepared by the U.S. Geological Survey in cooperation with the Florida Department of Environmental Regulation. Tallahassee, Florida.

Abstract:
The injection into deep saline aquifers is an alternative disposal method in some areas with a minimal risk of pollution of surface-water or groundwater supplies. However, deep-well injection is not everywhere suitable, and its use requires knowledge of subsurface conditions.

This report appraises the suitability of various areas in Florida for deep-well injection. A map indicates the depth to the shallowest zone that contains water with a dissolved-solids concentration greater than 10,000 mg/l which is capable of accepting injection without pressure buildup above which hydraulic-fracturing of the injection zone occurs. Geologic data were obtained from lithologic descriptions and geophysical logs of deep oil-test, water, and waste-injection wells. Data on the chemical character of the waters is from published reports of the U.S.G.S. and from calculations from geophysical logs of oil-test wells. The location and extent of high-transmissivity zones is shown.

Throughout most of the SJRWMD inland areas (as opposed to coastal areas), rocks of high permeability for the most part either contain water of less than 10,000 mg/L dissolved solids concentration or are not effectively isolated from such overlying water. Well-confined salt-water-bearing strata in this area generally are generally unsuitable because of their low permeability. Along the Atlantic coast, in St. Johns, Flagler, Volusia, and northern Brevard counties suitable conditions for deep well injection may exist locally.  Other portions of Brevard and Indian River counties are underlain by one or more salt-water-bearing high-permeability zones. There, injection is feasible.


Title:
Thickness of the Upper Permeable Zone of the Tertiary Limestone Aquifer System, Southeastern United States

Publication:
Open-File Report #81-1179, U.S. Geological Survey.  Atlanta, Georgia

Abstract:
The Tertiary limestone aquifer system of the southeastern United States is a sequence of carbonate rocks generally referred to as the Floridan aquifer in Florida and the principal artesian aquifer in Georgia, Alabama, and South Carolina. More than 3 billion gallons of water are pumped from the limestone daily making the aquifer system the principal source of municipal, industrial, and agricultural water supply in south Georgia and most of Florida.

The aquifer system includes units of Paleocene to early Miocene age that combine to form a continuous carbonate sequence that is hydraulically connected in varying degrees. Very locally, in the Brunswick, Ga., area, a thin sequence of rocks of Late Cretaceous age is part of the system. In and directly downdip from much of the outcrop area, the system consists of one vertically continuous permeable unit. Farther downdip, the aquifer system generally consists of two major permeable zones separated by a less-permeable unit of highly variable hydraulic properties (very leaky to virtually nonleaky). Hydraulic conditions for the system vary from unconfined to confined depending upon whether the argillaceous Miocene and younger rocks that form the upper confining unit have been removed by erosion.

This map is one of a series depicting the hydrogeologic framework, water chemistry, and hydrology of the aquifer system. This map shows the thickness of the upper major permeable zone of the system. The thickness mapped represents all strata that lie between the top of the highest vertically continuous permeable limestone (top of the aquifer system) and the base of either (1) the upper, regionally extensive, major permeable zone of the system, or (2) the base of the entire system where it contains no appreciable thickness of low-permeability rock. In the latter case, there is no separation of upper and lower major permeable zones within the system, and the entire permeable sequence is considered as belonging to the upper permeable zone. This condition exists in the area that is patterned on the map.

The contouring shown is based primarily on well control. The top and base of the upper permeable zone were delineated on the basis of lithologic data, examined from approximately 40 percent of the control points. These horizons were extended to the remaining points by means of geophysical logs, available for practically every control point used. In areas of sparse control, the thickness s estimated as the difference between contoured elevations of the top of the system and the base of the upper permeable zone. Thicknesses may vary locally from those shown.


Title:
Geology and Configuration of the Top of the Tertiary Limestone Aquifer System, Southeastern United States

Publication:
Open-File Report #81-1178, U.S. Geological Survey.  Atlanta, Georgia

Abstract:
The Tertiary limestone aquifer system of the Southeastern United States is a sequence of carbonate rocks generally referred to as the Floridan aquifer in Florida and the principal artesian aquifer in Georgia, Alabama, and South Carolina. More than 3 billion gallons of water are pumped from the limestone daily making the aquifer system the principal source of municipal, industrial, and agricultural water supply in south Georgia and most of Florida,

The aquifer system includes units of Paleocene to early Miocene age that combine to form a continuous carbonate sequence that is hydraulically connected in varying degrees. Very locally, in the Brunswick, Ga., area, a thin sequence of rocks of Late Cretaceous age is part of the system. In and directly downdip from much of the outcrop area, the system consists of one vertically continuous permeable unit. Farther downdip, the aquifer system generally consists of two major permeable zones separated by a less-permeable unit of highly variable hydraulic properties (very leaky to virtually nonleaky). Hydraulic conditions for the system vary from unconfined to confined depending upon whether the argillaceous Miocene and younger rocks that form the upper confining unit have been removed by erosion.

This map is one of a series depicting the hydrogeologic framework, water chemistry, and hydrology of the aquifer system. This map shows the altitude and configuration of the top of the aquifer system, as well as the areal extent of the youngest rock unit that is judged to be part of the system at a given location. Correlation of surface and subsurface stratigraphic units is imprecise in the mapped area at this time and, in some cases, different formation names have been applied to the same rock type in different states within the mapped area. 

Accordingly, the rock units shown are delineated and mapped as Gulf Coast Stage equivalents, and the most important formations within each stage are noted in the explanation. In many places, the top of the aquifer system coincides with the top of a particular rock unit. However, this is not the case everywhere. The top of the aquifer system, as mapped here, represents the top of highly permeable carbonate rock that is overlain by low-permeability material which may be either a clastic rock or a carbonate. This permeability contrast may exist within a rock unit (formation or stage equivalent), particularly within a limestone unit. For this reason, this map differs locally from previously published maps (for example, Vernon, 1973; Kwader and Schmidt, 1978; Buono and Rutledge, 1979; Scott and Hajishafie, 1980) that portray the top of vertically continuous limestone or the top of a particular geologic horizon, regardless of permeability. Any low-permeability limestones that may have been mapped as part of the aquifer system by previous workers are here excluded from the system. Previous maps may also differ locally from this map because of differences in the number of control points used.

In those places where the rocks that are part of the aquifer system crop out, their extent has been mapped in detail (Bennison, 1975; Copeland, 1968; Georgia Geological Survey, 1976; Vernon and Puri, 1965). Where these rock units are in subcrop, the distribution and extent of each unit is generalized and is based on the well control shown, modified by data from published geologic studies. The rock and hydrologic units mapped here have been delineated on the basis of lithologic and paleontologic data, examined from approximately 40 percent of the control points. The units so established were then extended by means of geophysical logs, available for practically every control point used.  Locally, altitudes and rock units may differ from those shown because of topography produced by erosion and solution of the limestone surface. Detailed contouring in areas of sparse well control is based on published sources, except for the Orange-Osceola Counties, Fla., area, whose source is unpublished material (Michael Planert, written commun., 1980).

Thin beds, lenses, and stringers of limestone may occur to the north and west of the line that is shown as the approximate updip limit of the aquifer system, and may be either connected to the main body of the system or isolated from it by erosion. In updip areas where the limestone becomes thin, it is interbedded with, and passes by facies change into, calcareous sands and clays. Still farther updip, these units in turn grade into fully clastic units that are the stratigraphic equivalents of the limestone units but have hydrologic properties that are quite different from those of the limestones. The updip limit of the limestone system has arbitrarily been placed at the point where the clastic beds belonging to a particular stage make up-more than 50 percent of the section.


Title:
Geology and Configuration of the Base of the Tertiary Limestone Aquifer System, Southeastern United States

Publication:
Open-File Report #81-1176, U.S. Geological Survey.  Atlanta, Georgia

Abstract:
The Tertiary limestone aquifer system of the Southeastern United States is a sequence of carbonate rocks generally referred to as the Floridan aquifer in Florida and the principal artesian aquifer in Georgia, Alabama, and South Carolina. The aquifer system includes units of Paleocene to early Miocene age that combine to form a continuous carbonate sequence that is hydraulically connected in varying degrees.  Very locally, in the Brunswick, Ga., area, a thin sequence of rocks of Late Cretaceous age is part of the system. In and directly downdip from much of the outcrop area, the system consists of one vertically continuous permeable unit. Farther downdip, the aquifer system generally consists of two major permeable zones separated by a less-permeable unit of highly variable hydraulic properties (very leaky to virtually nonleaky). Hydraulic conditions for the system vary from unconfined to confined depending upon whether the argillaceous Miocene and younger rocks that form the upper confining unit have been removed by erosion.

This map is one of a series depicting the hydrogeologic framework, water chemistry, and hydrology of the aquifer system. This map shows the altitude and configuration of the base of the aquifer system, as well as the areal extent of the rock unit judged to represent the top of the confining unit underlying the system.  Correlation of surface and subsurface stratigraphic units is imprecise in the mapped area at this time and, in some cases, different formation names have been applied to the same rock type in different states within the mapped area.  Accordingly, the rock units shown are delineated and mapped as Gulf Coast Stage equivalents, with the most important formations within each stage noted in the explanation. The base of the aquifer system does not crop out and the mapped extent of the different units is based solely on well control. Rock and hydrologic units were delineated on the basis of lithologic and paleontologic data, examined from approximately 40 percent of the control points. These units were extended to the remaining points by means of geophysical logs, available for practically every control point used.  Locally, where well control is sparse, the altitude of the basal rock units may differ from those shown. The units shown in updip areas, or their stratigraphic equivalents, extend north and west of the mapped area. However, the extent of the aquifer system itself determines the extent of its base; where appreciable thicknesses of permeable limestone are absent, mapping the base is meaningless.

The different horizons mapped here generally do not correspond to formation or time-stratigraphic tops. The altitudes shown, then, represent the top of rock whose permeability is much lower than that of the limestone above, and whose age and lithology may vary considerably. In general, the base of the aquifer system in South Carolina, in panhandle Florida, and in the northwestern two-thirds of the Georgia coastal plain consists of clastic rocks that are locally calcareous. In peninsular Florida and the southeastern third of Georgia, evaporite beds (gypsum or anhydrite) generally characterize the base.


Title:
Floridan Aquifer (in Principal Aquifers in Florida)

Abstract:
The Floridan aquifer is a sequence of carbonate rocks.  These rocks comprise the Tertiary limestone aquifer system. The aquifer system includes units of late Paleocene to early Miocene age that combine to form a continuous carbonate sequence that is hydraulically connected in varying degrees. Throughout much of Florida, the aquifer generally consists of two major permeable zones separated by a less permeable unit of highly variable hydraulic properties (very leaky to virtually nonleaky). Hydraulic conditions for the system range from unconfined to confined depending upon whether the argillaceous Miocene and younger rocks that form the upper confining unit have been removed by erosion.

The Floridan aquifer is composed chiefly of limestone and dolomite, interbedded with minor amounts of clay, sand, and marl. Consisting of rocks ranging in age from late Paleocene to early Miocene, the aquifer underlies the entire State, ranging in thickness from 100 feet or less in the Florida Panhandle to more than 3,500 feet in southwest Florida. The principal stratigraphic units comprising the aquifer include the Oldsmar, Lake City, Avon Park, and Ocala Limestones of Eocene age, and the Suwannee. Limestone of Oligocene age. Locally, the Tampa Limestone of lower Miocene age and the upper part of the Cedar Keys Limestone of Paleocene age are included in the aquifer.

The top of the aquifer is at or near land surface along parts of the Gulf Coast and the part of the panhandle bordering Alabama. The top dips gently toward both the Gulf and Atlantic Coasts, reaching a maximum depth of about 1,500 feet below sea level in westernmost panhandle Florida.  The base of the aquifer ranges in depth from less than 100 feet below sea level in the northeast panhandle to more than 4,100 feet below sea level in southwest Florida.

Where the Floridan aquifer is at or near land surface, it is unconfined and is recharged directly by infiltrating rainfall, by streams, and by runoff to sinkholes. Where thick deposits of clay and marl lie between the land surface and the Floridan, the aquifer is confined.


Title:
Hydrogeologic Framework of the Floridan Aquifer System in Florida and in Parts of Georgia, Alabama, and South Carolina

Publication:
USGS Professional Paper No. 1403-B. U.S. Geological Survey. Washington, D.C.

Abstract:
The Floridan aquifer system of the Southeastern United States is comprised of a thick sequence of carbonate rocks that are mostly of Paleocene to early Miocene age and that are hydraulically connected in varying degrees. The aquifer system consists of a single vertically continuous permeable unit updip and of two major permeable zones (the Upper and Lower Floridan aquifers) separated by one of seven middle confining units downdip. Neither the boundaries of the aquifer system or of its component high- and low-permeability zones necessarily conform to either formation boundaries or time stratigraphic breaks.

The rocks that make up the Floridan aquifer system, its upper and lower confining units, and a surficial aquifer have been separated into several chronostratigraphic units. The external and internal geometry of these stratigraphic units is presented on a series of structure contour and isopach maps and by a series of geohydrologic cross sections and a fence diagram. Paleocene through middle Eocene units consist of an updip clastic facies and a downdip carbonate bank facies. that extends progressively farther north and east in progressively younger units. Upper Eocene and Oligocene strata are predominantly carbonate rocks throughout the study area. Miociene and younger strata are mostly clastic rocks.

Subsurface data show that some modifications in current stratigraphic nomenclature are necessary. First, the middle Eocene Lake City Limestone cannot be distinguished lithologically or faunally from the overlying middle Eocene Avon Park 'Limestone.' Accordingly, it is proposed that the term Lake City be abandoned and the term Avon Park Formation be applied to the entire middle Eocene carbonate section of peninsular Florida and southeastern Georgia. A reference well section in Levy County, Fla. is proposed for the expanded Avon Park Formation. The Avon Park is called a “formation” more properly than a “limestone” because the unit contains rock types other than limestone. Second. like the Avon Park, the lower Eocene Oldsmar and Paleocene Cedar Keys "Limestones" of peninsular Florida practically everywhere contain rock types other than limestone. It is therefore proposed that these units be referred to more accurately as Oldsmar Formation and Cedar Keys Formation.

The uppermost hydrologic unit in the study area is a surficial aquifer that can be divided into (1) a fluvial sand-and-gravel aquifer in southwestern Alabama and westernmost panhandle Florida, (2) Limestone and sandy Limestone of the Biscayne aquifer in southeastern peninsular Florida, and (3) a thin blanket of terrace and fluvial sands elsewhere. The surficial aquifer is underlain by a thick sequence of fine clastic rocks and low- permeability carbonate rocks, most of which are part of the middle Miocene Hawthorn Formation and all of which form the upper confining unit of the Floridan aquifer system. In places, the upper confining unit has been removed by erosion or is breached by sinkholes. Water in the Floridan aquifer system thus occurs under unconfined, semiconfined, or fully confined conditions, depending upon the presence, thickness, and integrity of the upper confining unit.

Within the Floridan aquifer system seven low permeability zones of subregional extent split the aquifer system in most places into an Upper and Lower Floridan aquifer. The Upper Floridan aquifer, which consists of all or parts of rocks of Oligocene age, late Eocene age, and the upper half of rocks of middle Eocene age, is highly permeable. The middle confining units that underlie the Upper Floridan are mostly of middle Eocene age but may be as young as Oligocene or as old as early Eocene. Where no middle confining unit exists, the entire aquifer system is comprised of permeable rocks and for hydrologic discussions is treated as the Upper Floridan aquifer.

The Lower Floridan aquifer contains a cavernous high permeability horizon in the lower part of the early Eocene of southern Florida that is called the Boulder Zone. A second permeable unit that is cavernous in part. herein called the Fernandina permeable zone, occurs in the lower part of the Lower Floridan in northeastern Florida and southeastern Georgia. Both these permeable zones are overlain by confining units comprised of micritic limestone. The confining unit that overlies the Boulder Zone is of subregional extent and is mapped as a separate middle confining unit within the Lower Floridan.

Major structural features such as the Southeast and Southwest Georgia embayments, the South Florida basin, the Gulf Coast geosyncline, and the Peninsular arch have had a major effect on the thickness and type of sediment deposited in the eastern gulf coast. The effects of smaller structures are also evident. For example, the Gilbertown-Pickens-Pollard fault system in Alabama locally forms the updip limits of the Floridan aquifer system. The series of grabens that comprise the Gulf Trough of central Georgia serves as a low-permeability barrier to groundwater flow there. These Gulf Trough faults have downdropped low-permeability rocks opposite permeable limestones to create a damming effect that severely retards groundwater movement across the fault system. Their effect can be seen on potentiometric surface maps of the aquifer system. Other small-displacement faults in peninsular Florida do not appear co affect the regional flow system because there is no apparent change in the permeability of the rocks chat have been juxtaposed by fault movement.

Variations in permeability within the Floridan aquifer system result from a combination of original depositional conditions. diagenesis. Large- and small-scale structural features. and dissolution of carbonate rocks or evaporite deposits. Local permeability variations are accordingly more complex than the generalized regional portrayal presented in this report.


Title:
Groundwater Resources of Flagler County, Florida

Publication:
USGS Water Resources Investigation No. 87-4021.  U.S. Geological Survey.  Tallahassee, Florida.

Abstract:
Groundwater is the only significant source of potable water in Flagler County. Usable water occurs in the Upper Floridan aquifer, the intermediate aquifer system, and the surficial aquifer system.

Although rainfall averages almost 50 inches per year, most of the water leaves as evapotranspiration and streamflow.  Less than 1 inch per year recharge may be occurring, to the Upper Floridan aquifer, the highest yielding aquifer.  The Upper Floridan aquifer consists of the Avon Park Formation,  the Ocala Limestone, and the basal dolomitic limestone of the Hawthorn. Use of the Upper Floridan aquifer for public water supply is limited in most of the county because it contains marginally potable or brackish water. It is used extensively for agricultural irrigation.

The intermediate aquifer system consists of thin, discontinuous lenses of sand, shell, and limestone between clays overlying the Floridan aquifer system. The intermediate aquifer system is. an important part of the public water supply for the county because of the good quality of the water.  The intermediate aquifer system has variable yields because of the discontinuous lenses.

The surficial aquifer system is composed of sand and shell with varying fractions of finer materials. Well yields are small in the west and central parts of Flagler County, but the surficial aquifer system is an adequate source for domestic supply on the barrier island. A zone of freshwater in the surficial aquifer system is very important in the Hammock area, being the local source of most domestic supply in the area.


Title:
Potentiometric Surface of the Floridan Aquifer, January 2001

Publication:
Hydrologic Conditions Report, Division of hydrologic Data Services.  St. Johns River Water Management District.  Palatka, Florida.

Abstract:
This map shows the potentiometric levels of water in the Floridan Aquifer on a current basis.  This map is for data obtained in January 2001.  The map uses five different color schemes to identify ranges of values for the water surface.  It uses a range from minus 25 feet to mean sea level and then it uses ranges of 30-foot intervals from mean sea level to 120 feet above it. The map is part of the Report Index of the Hydrologic Conditions Report.


Title:
Land-Based High-Resolution Seismic Reflection Surveys of Seven Sites in Duval and St. Johns Counties, Northeastern Florida

Publication:
USGS Open File Report No. 97-718.  U.S. Geological Survey.  Tallahassee, Florida.

Abstract:
Water quality monitoring of the drinking-water supply wells tapping the upper Floridan aquifer have shown increases in chloride concentrations in some wells in Duval County and monitor wells in St. Johns County. Meanwhile, in other nearby production and monitor wells, the chloride concentrations are unchanged. It is speculated that geologic structures (fracture zones, solution pipes, cavities and paleosinkholes) in the underlying carbonate strata have breached the semi-confining units of the Floridan aquifer system thus allowing warmer and more saline water to flow upward and mix with fresher water aquifers. A reconnaissance investigation was conducted to determine if land-based high-resolution seismic reflection techniques could be used to identify the presence of karst terrain geologic structures at seven different sites located in various environmental settings (i.e. urban, residential and rural). Additionally, these surveys were performed to determine if land-based high-resolution seismic methods could be used as a tool to evaluate potential well field sites.

The results of this study are: (1) good-to-high quality data was collected, (2) depth of imaging varies with site conditions but rock strata are generally imaged within a depth interval of 30-400 m, (3) preliminary interpretations range from no identifiable karst features to clear evidence of buried solution cavities and collapse features, fracture zones, and possible near surface solution-valleys.

Observations of water quality data, specifically chloride concentration, have shown increases in some production wells at sites in Duval County and monitor wells in St. Johns County while at other nearby production and monitor wells the quality has remained unchanged (Toth, 1990; Spechler, 1994; Phelps and Spechler, 1997). Both groups of wells are pumping water from approximately the same depths within the Floridan aquifer system. It is postulated that the areal and vertical variability of temperature. and chloride concentrations can be explained by the localized upward migration of warmer, poorer quality water from zones in or below the Lower Floridan aquifer. The conduits for this upward flow are believed to be along isolated geologic structures (fractures, faults, solution conduits, and/or paleosinkholes) that have breached the middle semi-confining unit of the Floridan aquifer system.

Marine seismic-reflection surveys have been conducted offshore, along major rivers (including St. Johns River) and in selected lakes in north central and central Florida. These river and lake surveys have gathered high quality data to depths generally ranging from 15 to 80 meters and imaged clear evidence of shallow karst collapse, subsidence and solution features. To determine if land-based surveys could achieve similar results, the U.S. Geological Survey (USGS) high-resolution seismic reflection group (Geologic Division, Central Region, Geologic Hazards Team), in cooperation with the St. Johns River Water Management District (SJRWMD), conducted the first land-based Mini-Sosie high-resolution seismic reflection method surveys in Duval and St. Johns Counties, northeastern Florida. The Mini-Sosie method employed during this study has been successfully used by the USGS group to image faults and near-surface (25?800 m depth) deformation in neotectonic and earthquake investigations in other regions.


Title:
Methods of Estimating Recharge to the Floridan Aquifer in Northeast Florida

Publication:
Water Resources Investigation #77-109, U.S. Geological Survey, prepared in cooperation with City of Jacksonville, Florida.  Tallahassee, Florida.

Abstract:
Recharge to the principal artesian aquifer in a six-county area in northeast Florida was calculated using closed contour methods, water budgets, and formulas for computing leakage through confining beds. Each estimate was then tested in a computer model of groundwater flow to see which estimate was best.  Calculations of flow midway between the 24- and 21-meter potentiometric contours show a total flow of 1.64 x 105 cubic meters per day, a significant part of which must be recharged within the closed 24-meter contour. Flow midway between the 18- and 15-meter contours was calculated to be 3.42 x lO5 cubic meters per day. A water budget for the same area in water year 1972 indicates a potential recharge rate of 2.57 x lO6 cubic meters per day.

Digital modeling of groundwater flow in northeast Florida shows that the recharge rate calculated by closed contour is insufficient to balance the natural discharge of the regional groundwater system, whereas the rate calculated from water budgets is too great. Therefore, the best way to simulate the recharge mechanism of the northeast Florida flow model may be with a constant head boundary, rather than with constant flux. Calculations of leakage through the confining layer did not agree with the rates calculated by the computer model, probably because of different assumptions about the origin of leakage and because the hydrologic properties of the confining beds are not well known.  In all cases, the rate and location of leakage proved to be more important to the balance of the system than did direct recharge, implying that leakage is a very important mechanism of recharge in areas of high transmissivity.


Title:
The Relation Between Hydrogeology and Water Quality of the Lower Floridan Aquifer in Duval County, Florida and Implications for Monitoring Movement of Saline Water

Publication:
USGS Water Resources Investigation Report No. 96-4242. U.S. Geological Survey. Tallahassee, Florida.

Abstract:
The hydrogeology of the upper zone of the Lower Floridan aquifer and its relation to water quality were evaluated during a 3-year (1993-96) study. The Floridan aquifer system, a carbonate aquifer system composed of the Upper Floridan aquifer, a middle semi-confining unit, and the Lower Floridan aquifer, is the major source of water supply in northeastern Florida. The Lower Floridan aquifer is further subdivided into the Upper zone, a semi-confining unit, and the Fernandina permeable zone. As a result of increased withdrawals, heads in the aquifer system have declined and at the same time chloride concentrations have increased in the water from many wells in Duval County. A better understanding of the sources of and pathways for movement of brackish water is needed so that water managers can monitor the movement of brackish water and plan future water development.

Most of the wells in Duval County deeper than 900 feet penetrate the Upper Floridan aquifer and the upper zone of the Lower Floridan aquifer. Transmissivity estimates for these zones range from 2,000 to 194,000 feet squared per day. Permeability in the upper zone of the Lower Floridan aquifer is primarily related to secondary porosity developed along bedding planes, joints, and fractures as a result of paleokarst processes. The upper zone is about 300 to 500 feet thick in Duval County, based on the geophysical logs of about 40 wells ranging in depth from about 1,000 to 2,200 feet. In some areas the upper zone has a single flow zone, but in other areas, two distinct flow zones are apparent.

Water samples collected during this study confirm the continued increase in chloride concentrations in both the Upper Floridan aquifer and the upper zone of the Lower Floridan aquifer. Most of the observed increases are in the eastern part of the county, but a pattern in the locations of wells yielding water with chloride increases is not discernible. In some areas, zones bearing brackish water are underlain by zones of fresher water, but in other areas, fresher water was not found beneath the brackish water. A single fracture or solution feature was the source of brackish water in several wells.  The most likely source of brackish water to the upper zone of the Lower Floridan aquifer is the underlying Fernandina permeable zone, which contains freshwater in. the western part of the county but saline water in the eastern part. The pathways for movement of saline water are interconnecting vertical and horizontal fracture or solution zones probably developed along paleokarst features that are not mappable from the land surface; therefore, a conventional monitor-well network probably would not provide early warning of saline-water intrusion.


Title:
Disposal of Salt Water during Well Construction, Problems and Solutions

Publication:
Volume 15, No. 4, Groundwater, July-August 1977.

Abstract:
This report describes the methodology that was employed for drilling through freshwater aquifers, into saltwater ones, without causing contamination of the fresh water in the overlying freshwater aquifers by the return flows during drilling.  The report centers on the use of reverse-air-circulation drilling techniques that are employed in Florida for drilling deep injection wells into the Boulder Zone at the bottom of the Floridan Aquifer System.  The method has been used successfully throughout the state and has become the standard procedure for deep well injection construction.


Title:
Water-Supply Potential of the Floridan Aquifer in Osceola, Eastern Orange, and Southwestern Brevard Counties, Florida

Publication:
Water-Resources Investigations Report #84-4135, U.S. Geological Survey, prepared in cooperation with Brevard County.  Tallahassee, Florida.

Abstract:
The city of Melbourne and adjacent areas in south Brevard County obtain their water supply from Lake Washington. In 1982, the lake could provide a maximum of 15 million gallons per day, but the projected need for the year 2000 is nearly three times that amount. As one alternative for a future water supply, this study investigated, with a digital model, the potential yields of well fields completed in the Floridan aquifer. Poor quality of water precluded locating a well field within Brevard County. The most advantageous area for development was in central Osceola County.

Lithologic and geophysical logs were used to define hydrologic units. The units consist of (1) a surficial aquifer of unconsolidated sand, shell, and clay that contains the water table underlain by (2) a confining layer composed mainly of clay and silty sand which overlies (3) the Floridan aquifer. The potential location of a new well field was based on obtaining a water supply with chloride concentrations below 250 milligrams per liter.

Seven pumping schemes were simulated with the digital model. Each simulation was made under steady-state conditions so that storage properties of the groundwater system were not included. To evaluate the success of a particular scheme, the potentiometric surface is used to define the area of diversion from the pumping centers after a new equilibrium is reached. The area of diversion is plotted on a map of chloride concentrations, and by comparing how much of the area has overlapped into the zones of poorer water quality, evaluation of the particular schemes can be made. This accounts for lateral intrusion of poorer quality water only; data are insufficient to analyze water-quality problems from upconing of poorer quality water.  Four pumping schemes included a combination of pumping from a hypothetical well field in Osceola County and increasing pumpage rates of the Cocoa well field in Orange County which supplies the City of Cocoa in northern Brevard County. One scheme evaluated increasing pumpage in the Cocoa well field only. Two schemes evaluated an area in the southwest corner of Brevard County where chloride concentrations are less than 250 milligrams per liter.  

The Osceola-Orange County pumping schemes should produce water of suitable quality. The schemes produced quantities that ranged from 28 to 65 million gallons per day. Only the scheme that produced 65 million gallons per day intercepted a zone of water with chloride concentrations greater than 250 milligrams per liter, but the percentage of the zone within the area of diversion was small.


Title:
Geologic Framework of the High Transmissivity Zones in South Florida

Publication:
Special Publication #20. Prepared by the Bureau of Geology, Division of Interior Resources in cooperation with the U.S. Geological Survey.  Tallahassee, Florida.

Abstract:
This report discusses the changes in waste discharges over the years. Streams and rivers had been perennial dumping grounds for industrial and human wastes, but regulatory changes now restrict the discharge of industrial and municipal wastes into surface waters.  The report goes over the history of deep well injection in Florida, explaining that the deep saline part of the Floridan aquifer has been, for years, used by the oil industry for the injection of oil-field brines. It also explains how deep injection wells for industrial waste disposal are also using the lower saline part of the Floridan aquifer. Finally, the report discusses current conditions by stating that there is a need to use the brackish-fresh water part of the aquifer for fresh water storage and continued use of the lower part for deep well injection.  The report then goes on to describe the characteristics of the Floridan. The Floridan aquifer underlies the entire State of Florida and adjoining states.  It is over 2,000 feet thick and consists of 'very" porous and permeable limestones and dolostones with widely varying porosities and permeabilities. Under the force of gravity, relatively fresh water in the upper part of the aquifer flows seaward. In a deep well in south Florida (Kendall) between 1800 and 1900 feet, the salinity increased nearly 3 fold from 6,400 to 17,600 mg/l chlorides. One thousand feet deeper, at 2900 feet, the salinity rises to 19,300 mg/l, the concentration of seawater.  The report stresses the importance of the hydrologic and geologic factors which control horizontal and vertical fluid movements in the aquifer in order to be able to predict the ultimate direction of migration and rate of flow of the liquid wastes which may be injected into the system

The report provides answers to the nature of the geologic framework that constitutes the environment of a potential waste-storage system, and looks at the hydrologic and geochemical characteristics suitable for subsurface storage. It provides information on the following:

a.  Delineation of lost circulation zones as potential zones for waste-disposal and/or fresh water storage zones.
b.  Determination of thickness, spatial distribution and number of zones of high transmissivity.
c.  The lithologic nature and lateral extent of the confining beds and their capability of confining wastes to the injection horizon.
d.  Direction and patterns of movements of fluids within the waste-disposal zones under natural conditions.
e.  Possible interactions between injected liquids and the enclosing rock or fluids in the injection zones, and thereby forecasting the ultimate disposal of the liquid wastes.
f.  Provide field data for use in the development of theoretical and lab models of the aquifer.
g.  Establish whether the cavity system containing saline water in South Florida is a part of the same hydrologic regime as the cavities developed in the fresh-water aquifer in other parts of the peninsula  [areas of SJRWMD jurisdiction].

The report also gives recommendations which include the evaluation of the Cretaceous as a possible injection zone. It recommends that:

a.  In order to reduce the chances of surface contamination to a minimum, the fluids should be injected into the base of the high transmissibity zone, [not at the top, as is presently done], to place the fluids farther from the surface.
b.  Whenever possible, in completing storage wells, stereophotographs should be taken of the high   transmissivity zone in order to determine distribution and size of the cavities and the amount of vertical connection, if any. Data obtained from the photographs will throw light on the presence or absence of fractures and small-scale faults in the area, which could not otherwise be detected. Stereophotographs will also provide a permanent, non-interpretive visual record of the well.
c.  Use of the Cedar Keys and Upper Cretaceous cavity zones along the highly populated east coast of Florida for injection of industrial waste. Being deeper than the Eocene, injection into these zones could eliminate chances of  the injectate ascending to shallower depths.


Title:
Technical Feasibility of Artificial Recharge of Reclaimed Wastewater and its Hydrologic Impacts on the Regional Groundwater System

Publication:
Technical Publication Series #SJ 2000-2.  Prepared by St. Johns River Water Management District.  Palatka, Florida.

Abstract:
This study investigated the technical feasibility and hydrologic impacts of artificial recharge with reclaimed wastewater through rapid infiltration basins (RIBs) into the groundwater system. SJRWMD is especially interested in maintaining or increasing the potentiometric head of the Floridan aquifer system and associated spring discharges through the use of artificial recharge with reclaimed wastewater. To evaluate this option, potential artificial recharge sites were identified within the study area using SJRWMD's geographic information system. The study area was divided into seven subregions on the basis of proximity of wastewater treatment plants to the potential recharge sites. Up to 21 potential sites were then selected for artificial recharge of groundwater using RIBs.

Groundwater modeling was performed to achieve the objectives of this study. The U.S. Geological Survey's (USGS) MODFLOW was used as a tool for performing groundwater flow simulations in this study. The hydrologic impacts of RIBs were evaluated using two pumping scenarios, one for the year 1994 and the other for the year 2010. The hydrologic impacts of artificial recharge through RIBs on the groundwater system were assessed by comparing the differences between the simulations with and without artificial recharge. The simulations without artificial recharge of reclaimed wastewater at the recharge sites or RIBs are considered baseline simulations.

*  The feasibility of the RIB method for the artificial recharge of reclaimed water is highly dependent on site-specific geologic, hydrologic, and geomorphic conditions.

*  Using the GIS siting criteria developed and reported in this investigation, up to 21 potential new RIB sites were identified within the study area.

*  Up to 22.5 mgd of additional reclaimed water may be recharged within the study using all 21 identified potential new RIB sites.

*  Artificial recharge using RIBs can reduce the adverse effects of increased water supply withdrawal. RIBs are most effective for increasing potentiometric surface elevations in the surficial aquifer, and least effective for increasing potentiometric: surface elevations in the Lower Floridan aquifer.

*  RIBs can also augment spring flow. For the RIB configurations investigated in this study, approximately 70% of the recharged water contributes to direct increase in spring flow, including Apopka Spring, which alone receives about 25% of the total contribution.
                                                                                                                                                                                            In the short term, strategically located RIB projects may enhance spring discharge without affecting additional groundwater withdrawal for water supply. However, in the long term, it appears that many of the springs are likely to flow below their required minimum discharge level.


Author:
Schiner, G.R., Laughlin, C.P., and Toth, D.J.

Title:
Geohydrology of Indian River County, Florida

Publication:
U.S. Geological Survey, Water-Resources Investigations Report #88-4073.  Prepared in cooperation with the Indian River County Board of Commissioners and the St. Johns River Water Management District.  Tallahassee, Florida.

Abstract:
The surficial aquifer system and the underlying Floridan aquifer system are the sources of all groundwater used in Indian River County, Florida. The surficial aquifer system consists of a 100- to 150-foot-thick section of unconsolidated clastic deposits termed the "clastic zone" that overlies a 0- to 60-foot-thick section of mostly indurated carbonate rock termed the "shallow rock zone." The Floridan aquifer system consists of about 2,800 feet of carbonate rocks, subdivided on the basis of permeability, into the Upper Floridan aquifer (about 350?650 feet thick), the middle semiconfining unit (about 20-120 feet thick), and the Lower Floridan aquifer (roughly 2,000 feet thick). The surficial and Floridan aquifer systems are separated by a 100- to 200-foot-thick low permeability rock unit known as the intermediate confining unit.

Chloride concentrations in water from most wells that tap the surficial aquifer system in the Vero Beach well field have changed little in recent time.  The increase in chloride concentrations is probably related to the increase in well field pumpage.

Considerable variation in yield and water quality may be found in nearby wells of equal depth. The permeability of the Upper Floridan aquifer generally is higher than that of the Lower Floridan aquifer. Transmissivities of the Upper Floridan aquifer estimated from computer model simulations range from about 65,000 ft2/d to 200,000 ft2/d. However, much higher transmissivities have been determined from aquifer tests at a few sites. One such aquifer test at an injection well completed in the so called "Boulder Zone" of the Lower Floridan aquifer yielded a transmissivity of 1.5 X 106 ft2/d.

Most wells completed in the Floridan aquifer system in Indian River County, flow freely through artesian pressure. In heavily pumped areas and during "dry" years, water levels in May are as much as 15 feet lower than the levels in September. Water levels in the more developed eastern part of Indian River County have declined more than 16 feet, and in the less developed western part of the county, water levels have declined about 10 feet. The countywide decline is probably mostly due to regional pumping.

Water from the Lower Floridan aquifer generally contains chloride and dissolved solids in concentrations that exceed 250 mg/l and 500 mg/l, respectively, but water from the Upper Floridan aquifer generally contains less than 250 mg/l chloride in much of the southwestern part of the county and in some areas along the Atlantic Coastal Ridge. High freshwater heads in the Floridan aquifer system prevent saltwater in the Indian River, the Atlantic Ocean, and the saline aquifers that underlie the freshwater from migrating into the Floridan aquifer. The high heads also prevent contaminants on the land surface from moving downward into the Floridan aquifer system.


Title:
Quality of Water from the Floridan Aquifer in Brevard County, Florida

Publication:
Map Series #17. Prepared by the U.S. Geological Survey in cooperation with the Florida Geological Survey.  Tallahassee, Florida.

Abstract:
The quality of the water from the Floridan aquifer varies considerably within Brevard County. The quality is, in general, dependent on the mineralogy of the Eocene limestone and the degree of mixing with salt water. The salt water may be either connate water or from the sea by encroachment. In general, the water is too highly mineralized for domestic or industrial use; however, it is used for irrigation and stock watering.

Analyses of samples taken at different depths from a well, about eight miles west of Cocoa, indicate there are differences in the quality of water at various depths in the Floridan aquifer; however, these differences are not large within the upper few hundred feet of the aquifer. The geologic formations penetrated by this well and vertical distribution of chloride are shown.

Hydrogen sulfide is found in almost all artesian water in Brevard County and causes a very pronounced taste and odor; however, it can be removed by aeration. Very little quantitative data on hydrogen sulfide concentrations have been obtained.

The quality of any water can be defined as good or poor, depending on whether or not the concentration of the dissolved constituents is within the desirable range for the intended use. This map depicts concentration and enables the user to determine whether or not the water is suitable for his purpose.  One of the maps shows contours on the top of the limestone of Eocene age which is the top of the Floridan aquifer.  By adding 25 feet (the average elevation in Brevard County) to these contours, the depth to the Floridan aquifer can be estimated.


Title:
Dissolved Solids in Water from the Upper Part of the Floridan Aquifer in Florida

Publication:
Map Series #14.  Prepared by the U.S. Geological Survey in cooperation with the Florida Geological Survey.  Tallahassee, Florida.

Abstract:
The Floridan aquifer, which underlies all of Florida, yields water containing less than 250 parts per million dissolved solids in the northwestern part and throughout much of the center of the State. In the southern part of Florida and along most of the east coast, the dissolved solids in the water exceed 1,000 parts per million and are as much as 23,000 parts per million. Water from deep zones of the aquifer usually contains more dissolved solids than water from shallower zones. The dissolved solids content of water from the upper part of the aquifer is shown on the map.


Publication:
Map Series #14(Revised).  Prepared by the U.S. Geological Survey in cooperation with the Florida Geological Survey.  Tallahassee, Florida.

Abstract:
The Floridan aquifer, which underlies all of Florida, yields water containing less than 250 parts per million dissolved solids in the northwestern part and throughout much of the center of the State. In the southern part of Florida and along most of the east coast, the dissolved solids in the water exceed 1,000 parts per million and are as much as 23,000 parts per million.

Water from deep zones of the aquifer usually contains more dissolved solids than water from shallower zones. The dissolved solids content of water from the upper part of the aquifer is shown on the map.


Title:
Chloride Concentration in Water from the Upper Part of the Floridan Aquifer in Florida

Publication:
Map Series #12 (Revised).  Prepared by the U.S. Geological Survey in cooperation with the Bureau of Geology, Florida Department of Natural Resources.  Tallahassee, Florida.

Abstract:
This map shows general trends of the chloride concentration of water in the upper part of the Floridan aquifer. Below this part of the aquifer, high chloride water can be found everywhere in the State. The accompanying cross section shows the depth to salty water across central Florida. In the center of Florida, fresh water may be found as deep as 2,000 feet, whereas, along the coast it may extend no deeper than about 200 feet. Chloride concentration in small local areas may deviate from the values represented on both the cross section and the map.

The Floridan aquifer which underlies all of Florida contains high chloride water in the southern part of the State and along most of the east coast. In most of the remainder of the State, the water has a chloride concentration of less than 50 parts per million. In the areas where the Floridan aquifer contains salt water, fresh water is usually available at shallow depths from other aquifers.


Title:
Generalized Configuration of the Top of the Limestone Unit of the Lower Part of the Surficial Aquifer, Duval County, Florida

Publication:
Open-File Report #82-336, U.S, Geological Survey, prepared in cooperation with the City of Jacksonville.  Tallahassee, Florida.

Abstract:
This map shows the approximate configuration of the top of the limestone unit of the lower part of the surficial aquifer in Duval County, Florida. The limestone unit supplies water to numerous wells in the Jacksonville area.

In previous investigations concerning the hydrology of Duval County, Leve (1966) and Fairchild (1972) applied no formal names to the water-yielding limestone unit within the surficial aquifer. However, Causey and Phelps (1978, p. 6) applied the term "shallow rock zone" to all principal water-yielding sediments below the water-table zone to a depth of about 150 feet. This term has led to some confusion since the water-yielding sediments can consist of sand and shell as well as limestone. As the term "shallow rock zone" is vague, the use of the term in Florida has been abandoned and the water-yielding limestone is referred to in this report as the limestone unit of the lower part of the surficial aquifer.

Duval County is underlain by undifferentiated deposits and rocks of Holocene to Miocene age that collectively comprise the surficial aquifer. The deposits of Holocene and Pleistocene age are primarily sand and clayey sand that locally contain shell beds. These deposits are underlain by sand, shell, clay, and limestone of Pliocene or upper Miocene age. The limestone unit, where present, occurs at the base of the latter deposits.  The limestone unit generally consists of a soft, friable, cavernous, sandy limestone, ranging from about 5 to 40 feet in thickness. The altitude of the top of the limestone unit varies from about 25 feet above sea level in western Duval County to about 75 feet below sea level in the eastern part of the county.  Along the coast and in the southern part of the county, the limestone becomes discontinuous and grades into medium-to-coarse sand and shell deposits.

In most of the county, the limestone is the principal water-producing unit in the surficial aquifer. Maximum yields from the limestone unit of the surficial aquifer in most parts of the county are between 30 and 100 gal/min, but yields as great as 200 gal/min are possible from some wells (Causey and Phelps, 1978, p. 23). However, because of the differences in lithology and thickness, presence of the limestone does not necessarily indicate that large quantities of water are available.  In some areas, larger quantities of water may be obtained from sand or shell beds lying above the limestone or from wells tapping lenses of limestone within the upper part of the underlying Hawthorn Formation.

This map was prepared from geologist's and driller's logs and from core borings obtained from various engineering firms. Sources of logs include those in published reports and in the files of the St. Johns River Water Management District, the Florida Bureau of Geology, and the U.S. Geological Survey.


Title:
Altitude and Generalized Configuration of the Top of the Floridan Aquifer, St. Johns County, Florida.

Publication:
Water-Resources Investigations Report #83-4101, U.S. Geological Survey, prepared in cooperation with St. Johns County, Florida.  Tallahassee, Florida.

Abstract:
The Floridan aquifer, the principal source of groundwater in most of St. Johns County, underlies all of Florida and parts of Alabama, Georgia, and South Carolina. The aquifer includes units of Eocene age that form a continuous sequence of interbedded limestone and dolomite that is hydraulically connected in varying degrees. Formations usually included as part of the aquifer are, in ascending order, the Oldsmar Limestone, Lake City Limestone, Avon Park Limestone, and the Ocala Limestone.

This map shows the approximate altitude and configuration of the top of the Floridan aquifer. The structure contour lines correspond to the surface of the Ocala Limestone. Altitudes of the surface range from less than 90 feet below sea level in the extreme southwestern part of St. Johns County to more than 350 feet below sea level in the northwestern part. The top of the Floridan aquifer is an ancient karst plain, its surface is irregular throughout much of the county due to erosion that preceded the deposition of the Hawthorn Formation. Several depressions in the central part of the county may be buried sinkholes that developed during or after the Eocene age at times when the sea level was lower than it is today.

Overlying the Floridan aquifer are the clays and marls of the Hawthorn Formation. The Hawthorn Formation separates the surficial aquifer from the Floridan aquifer and confines the water in the Floridan aquifer under artesian pressure. The surficial aquifer, comprised mainly of interbedded lenses of sand, shell, and clay, yields moderate amounts of water to wells. Geologic sections showing the general relationship of the stratigraphic and hydrogeologic units in the county are shown in figures 1 and 2.

This map was prepared from geologic, geophysical, and drillers' logs on file with the Florida Bureau of Geology, U.S. Geological Survey, St. Johns River Water Management District, and from logs in published reports.


Title:
Saltwater Intrusion and Quality of Water in the Floridan Aquifer System, Northeastern Florida.

Publication:
USGS Water Resources Investigation Report No. 92-4174.  U.S. Geological Survey, Tallahassee, Florida

Abstract:
Saltwater intrusion into freshwater aquifers has resulted in increased chloride concentrations in water from some wells in northeastern Florida. The principal areas of saltwater intrusion in the Floridan aquifer system in the study area are east-central Duval County, the southern two-thirds of St. Johns County, and along the coast. At least five possible mechanisms of saltwater movement, some more plausible than others, could explain the observed increases in chloride concentration in the upper freshwater zones of the Floridan aquifer.

They are (1) the presence of unflushed pockets of relict seawater; (2) lateral movement of the freshwater-saltwater interface off the northeastern Florida coast; (3) upconing of saltwater from deeper, salty zones below pumped wells; (4) upward leakage from deeper, salty water-bearing zones through failed, uncased, or improperly plugged or constructed wells; and (5) upward leakage from salty water-bearing zones through semiconfining units that are thin, or are breached by joints, faults, or collapse features.

Groundwater withdrawals in Duval, Nassau, and St. Johns Counties is approximately 90 percent from the Floridan aquifer system, resulting in long-term declines in the potentiometric surface of the Upper Floridan aquifer of about one-third to three-fourths foot per year. Hydraulic heads in the lower part of the aquifer system are naturally higher than in the upper parts. Declines in head in the upper part have further increased the vertical head difference between zones, increasing the potential for vertical groundwater flow from lower zones of higher head upward through structural deformities, leaky confining beds, and wells, to higher zones of lower head. Lower zones typically have higher chloride concentrations than do upper zones.

Concentrations of chemical constituents in water from the Floridan aquifer system vary both areally and with depth. Chloride concentrations in water in the Upper Floridan aquifer in the study area range from less than 10 to 3,600 milligrams per liter. Data indicate that in much of the study area, water in the upper zone of the Lower Floridan aquifer generally is slightly more mineralized than water from the overlying Upper Floridan aquifer. Water from the Fernandina permeable zone varies in quality from fresh to saline. Chemical analyses of water from five monitoring wells tapping this zone indicate maximum chloride concentrations of 16,800 mg/l.

The potential for saltwater contamination of the freshwater-bearing zones probably will continue to increase in northeastern Florida as artesian pressure in the upper freshwater zones continues to decline. Implementation of wise water-management strategies could, however, reduce the potential for saltwater intrusion.


Title:
Detection and Quality of Previously Undetermined Floridan Aquifer Discharge to the St. Johns River, Jacksonville to Green Cove Springs, Northeastern Florida

Publication:
USGS Water Resources Investigation Report No. 95-4257.  U.S. Geological Survey, Tallahassee, Florida.

Abstract:
Potentiometric surface maps of the Upper Floridan aquifer show two depressions around the St. Johns River from the city of Jacksonville south toward Green Cove Springs. These depressions, depending on their locations, are the result of withdrawals from agricultural, industrial, domestic and public-supply wells, diffuse upward leakage, and discharge from springs. Submerged springs that discharge into the St. Johns River between Jacksonville and Green Cove Springs have been thought to exist, but locating and evaluating these springs had not been attempted before this investigation. Thermal infrared imagery, seismic reflection, and numerous interviews with local residents were used to locate springs. An airborne thermal infrared survey was conducted along a section of the St. Johns River in northeastern Florida during February 1992 to detect possible sources of groundwater discharge to the river. An infrared image displayed one thermal anomaly in the St. Johns River which is associated with a previously unknown spring discharge from the Floridan aquifer system. Thermal anomalies also were observed at six locations where municipal facilities discharge treated wastewater to the river. Results of seismic reflection surveys indicate the presence of collapse and other karst features underlying the St. Johns River. These features indicate that the surficial deposits and the Hawthorn Formation that underlie the river probably do not consist of continuous beds. The collapse or deformation of the Hawthorn Formation or the presence of permeable sediment of localized extent could create zones of relatively high vertical leakance. This could provide a more direct hydraulic connection between the Upper Floridan aquifer and the river. Water samples collected from the only submerged spring in the St. Johns River within the Jacksonville-Green Cove Springs reach indicate that the source of the water is the Floridan aquifer system. Chloride and sulfate concentrations were 12 and 340 milligrams per liter, respectively. Specific conductance was 826 microsiemens per centimeter and the temperature of the water discharging from the spring was 25.1 degrees Celsius. The ratio of 87 Strontium/86 Strontium also indicates that the spring water has been in contact with rock materials of Eocene age, providing additional evidence that the spring water is derived from the Floridan aquifer system.


Title:
Dissolved-Solids Concentration in Water From the Upper Permeable Zone of the Tertiary Limestone Aquifer System, Southeastern United States

Publication:
Open-File Report #82-94, U.S. Geological Survey.  Atlanta, Georgia.

Abstract:
The Tertiary limestone aquifer system of the southeastern United States is a sequence of carbonate rocks referred to as the Floridan aquifer in Florida and the principal artesian aquifer in Georgia, Alabama, and South Carolina, and the system is the principal source of municipal, industrial, and agricultural water supply in south Georgia and most of Florida.

The aquifer system includes units of Paleocene to early Miocene age that combine to form a continuous carbonate sequence that is hydraulically connected in varying degrees. In a small area near Brunswick, Ga., a thin sequence of rocks of Late Cretaceous age is part of the system. In and directly downdip from much of the outcrop area, the system consists of one continuous permeable unit. Further downdip the aquifer system generally consists of two major permeable zones separated by a less-permeable unit of highly variable hydraulic properties (very leaky to virtually nonleaky). Conditions for the system vary from unconfined to confined depending upon whether the argillaceous Miocene and younger rocks that form the upper confining unit have been removed by erosion.

This report is one of a series of preliminary products depicting the hydrogeologic framework, water chemistry, and hydrology of the aquifer system. The map shows the distribution of dissolved solids in water from the upper permeable zone of the limestone aquifer system. The upper permeable zone consists of several formations, primarily the Tampa, Suwannee, Ocala, and Avon Park Limestones (Miller, 1981a, b).

The dissolved solids concentrations of water within the upper permeable zone vary from less than 25 milligrams per liter (mg/l) near outcrops to more than 25,000 mg/l along the coasts. The dissolved solids content of groundwater is the sum of all cations and anions (respectively, positively and negatively charged ions or species) in solution. Within the Tertiary limestone aquifer system the dominant cations are the ions of calcium (Ca+'), magnesium (Mg+2), sodium (Na+'), and potassium (K+'). The dominant anions are bicarbonate (HCO3-'), chloride (Cl-1), and sulfate (SO4-3). Locally, smaller amounts of dissolved iron, manganese, nitrate, phosphate, fluoride, strontium, sulfide, and silica may contribute to the dissolved solids content.  In most of the area mapped, the dissolved solids concentration of the upper permeable zone is less than 250 mg/l.  In areas where the aquifer system discharges into the sea, the upper permeable zone contains increasing amounts of seawater. In these areas, wells that fully penetrate the upper permeable zone will yield water with dissolved solids concentration approaching that of seawater, about 36,000 mg/l.


Title:
Chemical Quality of Water in the Upper Part of the Floridan Aquifer, Duval County, Florida.

Publication:
USGS Water Resources Investigations Open File Report No. 82-119.  U.S. Geological Survey.  Tallahassee, Florida.

Abstract:
Between 1977 and 1980, water samples from 211 wells that penetrate as much as 900 feet of the upper part of the Floridian aquifer were analyzed for major inorganic ions. Maps show the areal distribution of dissolved solids, total and noncarbonate hardness, chloride, and chemical water types. Variation in water quality with aquifer depth was not considered. In general, the concentrations of the constituents were lowest in the southwest area of the county, and highest in the southeast. Ranges of concentrations (in milligrams per liter) were: dissolved solids, less than 200 to as much as 623; total hardness as calcium carbonate, less than 200 to as much as 430; and chloride, less than 10 to as much as 210. Noncarbonate hardness ranged from less than 30 to as much as 70% of the total hardness. Six chemical types were defined, based upon the predominant cations and anions. The most prominent type was a calcium sulfate mass extending into central Duval County from the southeast. Calcium bicarbonate and calcium-magnesium bicarbonate types were found in most of the rest of the county.


Title:
Groundwater Hydrology of the Cocoa Well-Field Area, Orange County, Florida

Publication:
Open-File Report #75-676, U.S. Geological Survey, prepared in cooperation with the City of Cocoa.  Tallahassee, Florida.

Abstract:
The city of Cocoa, Brevard County, Florida, supplies water for much of central Brevard County including Cape Kennedy and Patrick Air Force Base. The water supply is obtained from a well field in east Orange County. Many of the easternmost supply wells in that well field yield salty water (chloride concentration greater than 250 milligrams per liter) because of upward leakage of salty water that lies at depth in the Floridan aquifer. The interface between the fresh and salty water in the west part of the well field occurs at a depth of about 1,400 feet (430 meters). An upward hydraulic gradient exists between the lower (salty) zones and the upper, or pumped zones of the Floridan aquifer in the west part of the well field, but the hydraulic connection between the zones is probably poor. Secondary artesian aquifers in the wellfield area are relatively high-yielding but they are of limited areal extent. However, they are suitable as a source of water for supplemental supply or for artificially recharging the Floridan aquifer by means of hydraulic connector wells. Fresh water was transferred by siphon from a secondary artesian aquifer to the Floridan aquifer at 90 gallons per minute (6 liters per second). Artificial recharge and recovery experiments show that it is technically feasible to retrieve fresh water stored in salty zones of the Floridan aquifer.


Title:
Availability of Groundwater in Seminole County and Vicinity, Florida

Publication:
Open-File Report #76-97, U.S. Geological Survey.  Tallahassee, Florida

Abstract:
In Seminole County, groundwater occurs under nonartesian and artesian conditions. Nonartesian conditions occur where the upper surface of the zone of saturation (water table) is free to rise and fall in direct response to local rainfall (recharge) and to discharge. Artesian conditions occur where the water in an aquifer is confined by a bed of less permeable material and will rise in a tightly cased well above the base of the confining bed. The level to which the water will rise defines the altitude of the aquifer's potentiometric level at that location. If the potentiometric surface is above land surface, the well will flow. Water level measurements in many artesian wells are used to define the configuration of the potentiometric surface over broad areas.

The uppermost aquifer in Seminole County is nonartesian and consists of sedimentary deposits of fine to medium-fine quartz sands and varying amounts of clay silt and shell.  The base of the nonartesian aquifer is at the top of the clay and clayey sand and shells that comprise confining beds that overlie the Floridan aquifer. In most of the county the base of the nonartesian aquifer is 20 ft to as much as 60 ft below land surface. However, in the low areas around Lake Jessup and along the Wekiva, Little Wekiva, Econlockhatchee, and St. Johns Rivers, the base of the nonartesian aquifer is generally less than 20 ft below land surface. The water table occurs at depths ranging from land surface to as much as 40 ft below land surface. In general, the depth to the water table is greatest in the southwest and northwest parts of the county, and in the southeast part in arid around the towns of Oviedo, Chuluota, and Geneva. Throughout the rest of the county in low and swampy areas the water table is at or near land surface much of the year. In some areas, chiefly agricultural, the water table has been lowered by drainage ditches.

The nonartesian aquifer generally yields less than 20 gal/min to wells and is relatively unused. Small amounts of water are withdrawn from the nonartesian aquifer for lawn irrigation and there is some domestic use in rural areas where wells in the Floridan aquifer yield water that is too highly mineralized for human consumption. In many parts of the county, water from the nonartesian aquifer contains enough iron to stain clothes, fixtures, and utensils (Barraclough, 1962, P-19). Where the water table is above the potentiometric surface of the Floridan aquifer, water from wells-in the nonartesian aquifer is very soft (hardness less than 25 mg/L), relatively low in dissolved solids concentration (less than 100 mg/L), and has a pH less than 7 indicating that the water is corrosive. Where the potentiometric surface of the Floridan aquifer is above the water table, upward leakage from the Floridan occurs and water from wells in the nonartesian aquifer tends to be harder and its dissolved solids concentration higher.

The nonartesian aquifer is recharged by local rainfall and, in areas where the potentiometric surface of the Floridan aquifer is above the water table, from the Floridan by upward leakage through confining beds. Water leaves the nonartesian aquifer by seepage to lakes, ditches, and streams; by evapotranspiration where the water table is near land surface; by pumpage; and, where the potentiometric surface of the Floridan aquifer is below the water table, by downward leakage to the Floridan.

In terms of the potable water supply of Seminole County, the most important function of the nonartesian aquifer is to store water, some of which recharges the Floridan aquifer. The nonartesian aquifer is little used as a direct source of groundwater because, relative to the Floridan aquifer, its permeability is low and that results in relatively low yields to individual wells. Accordingly, the remainder of this report is given to discussion of, the Floridan aquifer.

In Seminole County, the principal artesian aquifer is the Floridan aquifer that underlies all of Florida and parts of Alabama, Georgia, and South Carolina. In some parts of the county, the upper part of the Floridan consists of permeable beds of sand and shell; the lower part is composed of limestone alternating with layers of dolomitic limestone. In other parts of the county the permeable beds of sand and shell are missing. The depth to the top of the Floridan aquifer ranges from about 50 ft to as much as 200 ft below land surface (fig. 2).

The Floridan aquifer is overlain by confining beds of clay, and clayey sand and shell that, from place to place, vary in thickness and permeability. The confining beds range in thickness from about 10 ft to as much as 150 ft (Barraclough, 1962, p. 11).

The Floridan aquifer is recharged by downward leakage from the nonartesian aquifer in areas where the water table is above the potentiometric surface of the Floridan and where the confining beds are semipermeable, thin, or breached by sinkholes. The Floridan aquifer discharges by pumping, spring flow, and by upward leakage to the nonartesian aquifer in areas where the potentiometric surface of the Floridan is above the water table.

Figure 3 shows recharge areas, discharge areas, drainage basins, and, by means of contours, the configuration of the potentiometric surface of the Floridan aquifer for May 1973. The general movement of water in the aquifer is at right angles to the lines of equal head, in the direction of decreasing head, and from areas of recharge to areas of discharge. Figure 3 is reproduced from an earlier report by Tibbals (1975), to facilitate continuity for the reader. A more complete discussion of Floridan aquifer recharge and discharge areas in Seminole County is given in that earlier report (Tibbals, 1975).

The thickest section of fresh Floridan aquifer water in Seminole County is probably in the extreme southwest part of the county. Here the Floridan's potentiometric surface is highest, about 50 ft above msl (mean sea level). Well 839-125-7, near Forest City (fig. 3), is 1,205 ft deep and yields water with a chloride concentration of about 8 mg/L. Well 837-119-3, 2 mi east of Maitland (fig 3) is 1,315 ft deep and yields water with a chloride concentration of about 10 mg/l. Well 842-122-1, 2 mi west of Longwood (fig. 3), is 925 ft deep and yields water with a chloride concentration of about 7 mg/L. The potentiometric surface of the Floridan aquifer at wells 839-125-7, 842-122-1, and 837-119-3 was, respectively, about 43 ft, 35 ft, and 46 ft above msl in May 1973, about the time the wells were sampled. These data indicate that in southwest Seminole County, where the potentiometric surface of the Floridan aquifer is above 35 ft above msl and where lateral freshwater-salty water transition areas are, say I mi distant, freshwater extends to depths of at least 900 ft.


Title:
Computer Simulation of the Steady-State Flow System of the Tertiary Limestone (Floridan) Aquifer System in East-Central Florida

Publication:
Open-File Report #81-681, U.S. Geological Survey.  Tallahassee, Florida.

Abstract:
The predevelopment steady-state groundwater flow system for the Tertiary limestone (Floridan) aquifer system in east-central Florida is simulated by means of a digital computer model. The modeled area covers about 13,700 square miles. The configuration of the model is that of a three-layered system; the lower Floridan aquifer, the upper Floridan aquifer, and the surficial aquifer.

The model results indicate that about 1,900 cubic feet per second recharges the Floridan aquifer as downward leakage from the surficial aquifer. The average recharge rate where recharge actually occurs (approximately 6,550 square miles) is about 4 inches per year. The maximum recharge rate is about 14 inches per year. An additional 20 cubic feet per second is recharged to the modeled area of the Floridan aquifer by means of lateral boundary inflow along the northeast boundary.

The Floridan aquifer system, as simulated, discharges about 1,300 cubic feet per second as springflow, 540 cubic feet per second as diffuse upward leakage to the surficial aquifer in an area of approximately 7,150 square miles and 80 cubic feet per second as lateral boundary outflow to the southwest and to the east.

The average transmissivity of the upper Floridan aquifer, as simulated, is about 120,000 feet squared per day while that for the lower Floridan is about 60,000 feet squared per day. Inflow and outflow for the upper Floridan can be summarized as follows:

1. The highest rates of recharge to the Floridan take place in four areas; the west flank of the Volusia County "high," the Putnam-Alachua County "high," the potentiometric ridge area of mid-Polk and Highlands Counties, and the northeast flank of the central Florida potentiometric "high" in Lake and Orange Counties and extending into east Marion County.

2. Most discharge from the upper Floridan is in the form of point discharge (about 69 percent of the total) to known springs and upward leakage to streams located within 25 miles of recharge areas.

3. The highest rates of diffuse upward leakage from the upper Floridan (about 28 percent of total discharge) occur near areas where the downward leakage rates are also high. Thus, it is inferred that thin or permeable confining beds are common to the areas of high downward leakage and to the nearby areas of high upward leakage.

4. Lateral boundary outflow from the upper Floridan aquifer (principally occurring along the Atlantic coast) is relatively small and consists of about 4 percent of the total discharge. Lateral flow to the south is about 0.7 percent of the total discharge.

5. Interchange between the upper and lower Floridan aquifer layers is very small compared to the flow within the upper Floridan.

6. The model-derived transmissivities are considered to have more regional significance than transmissivity values derived from individual aquifer tests.

In summary, the hydraulics of the Floridan aquifer system under predevelopment conditions involve mostly recharge to the upper Floridan (via leakage from the surficial aquifer), lateral movement through the upper Floridan for short distances, and discharge via springs and upward leakage to streams. Relatively small amounts of discharge occur along the coast and small amounts move into and out of the underlying lower Floridan. This natural hydraulic equilibrium implies a vigorous flow system locally in the upper Floridan and, except in west Orange County and southeast Lake County, a relatively sluggish flow system in the lower Floridan.


Title:
Geohydrologic Summary of the Floridan Aquifer in Coastal Areas of Nassau, Duval, and Northeast St. Johns Counties.

Publication:
Technical Publication SJ 90-5. St. Johns River Water Management District. Palatka, Florida.

Abstract:
The Floridan aquifer is the primary source of water supply in northeast Florida. The effects of increased growth and urbanization along the coast of northeast Florida have raised concerns about the long-term availability of potable groundwater supplies. This report presents a preliminary examination of water resource problems, concentrating on the occurrence of saline water in the Floridan aquifer in the coastal areas of Nassau, Duval, and northern St. Johns counties.

Three different water types occur in the study area: low chloride/low sulfate water, which is typical of the back groundwater and occurs in western Nassau and Duval counties; low chloride/high sulfate water, which probably results from mineral dissolution in the aquifer and occurs in southeast Duval and northern St. Johns counties; and high chloride/high sulfate water which occurs along the coast and portions of the St. Johns River. High chloride/high sulfate areas most likely result from the upward movement of high chloride/ high sulfate waters which exist at depth. This high chloride/high sulfate water is under higher artesian pressure than the water above it, thereby providing the potential for upward movement of saline water.

New wellfield development should be avoided in areas where chloride and sulfate concentrations are high because structural weaknesses in confining beds may play a major role in the distribution of high chloride/high sulfate water. These areas occur east of the Intercoastal Waterway along the coast, in a one-mile band on either side of north-south faults mapped by Warren Leve of the U.S. Geological Survey, and in a two-mile band on either side of a line stretching from Fort George Island to the Ortega River in Jacksonville.


Publication:
Prepared by ERM-South, Inc. for the Florida Department of Environmental Protection.  Tampa, Florida.

Abstract:
This is a comprehensive report on the subject of saline water. The report starts out with an explanation of the classifications of saline water used by various authors, and with a discussion of the fundamentals of seawater chemistry. It presents the subject of oversaturation of calcite and dolomite when waters are mixed and relates it to the effect this may have on deep well injection and aquifer clogging.  The report also addresses the conversion of data from TDS to Chloride to Specific Conductance to Salinity, etc.  There is a section of the report dealing with the salt-water transition zone in the Floridan aquifer and in water table aquifers.  It addresses the mathematics of saltwater intrusion in coastal zones and saltwater intrusion by upconing.  The report looks at deep Floridan Aquifer circulation and circulation in the Boulder Zone. It addresses coastal brines and temperature increases in the anhydrite zones.


Title:
The Beneficial Uses of Zones of High Transmissivities in the Florida Subsurface for Water Storage and Waste Disposal

Publication:
Information Circular #70. Prepared by the Bureau of Geology, Division of Interior Resources, Florida Department of Natural Resources.  Tallahassee, Florida.

Abstract:
This report discusses the urban sprawl and its attendant problems in Florida, including projections of population growth, increasing demands for the water available, and disposing of the resultant wastewater. The report poses that the answer to both problems of water supply and wastewater disposal lies underground.  Underground in the porous limestones, interbedded with impervious fine-grained sediments, that are saturated with groundwaters that circulate through the aquifers and empty to the ocean.

The report states that the injection of liquid wastes into the subsurface has proved to be both safe and economical.  It concludes that the most important requirement for the successful completion and operation of injection facilities is the benefit of a cooperative programming by professional engineers, geologists, and economists, under rigid specifications. It says that the construction must be by a competent well driller, under professional supervision, and makes a strong recommendation that the services of recognized logging and cementing companies be utilized.

The report presents criteria that must be met for a well-injection system to function properly and safely:

1) The subsurface reservoir must be permeable and able to receive liquids under safe injection pressures for unlimited periods of time. The beds of the Floridan aquifer are exposed to the sea along the continental slope, and these reservoirs serve as landfalls to the ocean.

2) Sediments must separate usable water in the reservoirs from any unusable water. Groundwater in Florida is extremely salty below the Floridan aquifer and no restrictive bed is required at the base of the aquifer but some are present. 

3) The liquids injected must not clog the pores of the rock by sedimentation or react adversely with the rock and its water. Buffer zones can be used.

4) Monitoring must be an integral part of any waste-injection system.

The report looks at the possibility that in the future there may develop competition between water storage and wastewater disposal at a given area.  The author recommends that in such cases, a detailed study would reveal the presence of several zones, stacked one above the other in the subsurface.  Wastewater should be injected into the deepest zone with the lowest quality of water and nearest the coast. Conversely the higher zones with better water quality would be reserved for fresh water storage [ASR].


Publication:
Map Series #56. Prepared by the Bureau of Geology, Division of Interior Resources, Florida Department of Natural Resources in cooperation with the U.S. Geological Survey.  Tallahassee, Florida.

Abstract:
This map depicts the approximate top of the rock or sediment that composes the Floridan aquifer. The contours represent the elevation of top of this rock in relation to mean sea level. In some areas the rock is exposed at or near the land surface and may lie above sea level. Such an area occurs along the middle Gulf counties and extends northwesterly into Holmes, Jackson, Washington and Walton counties. In other areas of Florida the rock lies below sea level and the contours are shown with a minus prefix. The zero line or datum plane is sea level.  Numerous geologic and structural characteristics are reflected on the map. Among others, the Ocala uplift is clearly delineated in the Gulf Coastal counties where the rock rises above sea level. The Osceola Low, a large fault block described by Vernon in 1951, is outlined over Osceola County, and a coast parallel fault in Palm Beach, Indian River, Martin and St. Lucie counties, partially controls the flow and quality of artesian water in these counties. Deep depressions and knolls representing karst, early geologic structures and erosion have been recorded in the irregular penetrations of the aquifer.


Title:
A Review of Existing Knowledge and an Evaluation of Research Needs

Publication:
Public Health Service Publication #999-WP-21.  Cincinnati, Ohio.

Abstract:
A review of the knowledge pertinent to the use of deep wells for the subsurface injection of liquid waste has been carried out to evaluate the technical and economic feasibility and desirability of this method and to outline existing research needs.  This review has shown that the deep-well injection of liquid waste is technically feasible in many areas of the country and, if properly planned and implemented, is not likely to be harmful to natural resources.  While most of the technical knowledge and experience necessary to carry out the deep-well injection of liquid waste is presently available, further investigation is necessary to solve specific problems that remain as barriers to the safe, efficient, and economic use of this method.


Title:
The Paleogene of Florida, Volume 2, A Regional Analysis of the Oligocene-Eocene Section of the Peninsula Using Vertical Lithologic Stacks

Publication:
Prepared by the Miami Geological Society.  Coral Gables, Florida.

Abstract:
This report is based on descriptions of numerous sample sets from various stratigraphic investigations in Florida (Winston 1977, 1978, 1990, 1991, Puri & Winston 1974 and Winston & Puri 1975).  In order to make paleogeographic interpretations of some 2,500 feet of diverse carbonate lithologies without regional paleontologic or lithologic marker beds, the author has organized these rocks into VERTICAL stacks based on similar lithologies, herein designated "Suites". These Suites cross stratigraphic boundaries.

All of the Suites of the Black Point Format include Oligocene and Eocene age rock between the base of the phosphatic Miocene Hawthorn and the top of the Paleocene Cedar Keys-Rebecca Shoal dolomite complex (Winston 1977, 1978, 1989 & 1991). The MADco Suite, which belongs to the Perdido Bay Format of the Panhandle (Winston 1993), extends into the geographic Peninsula province. The MADco Suite includes beds of Paleocene age in addition to Oligocene and Eocene rocks.

The MADco Suite is a light-colored skeletal, open marine wackestone which contains glauconite, chert and some dolomite. The PINco and ORco Suites are mostly tan and brown dolomite, with the PINco being differentiated by the presence of varying amounts of anhydrite.

The CHAco, DAco and LAFco Suites are characterized by a predominance of light-colored, chalky skeletal limestone, and subsidiary brown dolomite. In the DAco Suite, dolomite is a relatively minor constituent, whereas in the CHAco Suite it is a major component. The LAFco is differentiated from these Suites by the presence of both glauconite and chert.

All of the Black Point Suites were deposited on a tableland created by the underlying Paleocene Rebecca Shoal barrier reef atoll and its lagoonal carbonate-evaporite facies, the Cedar Key Formation.  The dolomite PINco and ORco Suites of the central tableland are encircled on the north, east and south by the dominantly limestone LAFco, CHAco and DAco Suites.


Title:
The Boulder Zone Dolomites of Florida, Volume 1, Paleogene & Upper Cretaceous Zones of the Southeastern Peninsula and the Keys

Abstract:
Boulder Zone boulders are man-made. They are produced by chunks of dolomite falling to the bottom of the drill hole where they are rolled around by the drill bit. Boulder-producing dolomites are characterized by the presence of wall features such as cavities and wall-collapse zones. Wall features are unrelated to dolomite textures, referred to herein as the Dolomite Triad consisting of euhedral, anhedral and cryptocrystalline types. Lithologic data in the southeastern Florida Peninsula are from injection wells drilled by the reverse air method.

The Delray Dolomite, averaging 250 feet in thickness, consists of a lensing or interfingering of the three textural varieties, anhedral being the most common. The Delray Dolomite occurs everywhere, but thins over the Rebecca Shoal Dolomite reef, suggesting that the basal Delray elsewhere is a lagoonal equivalent of the reef. In the Keys, limited data show the same Dolomite Triad to be present, but here there is a limestone bed in the middle of the unit. In one well this limestone directly overlies the Rebecca Shoal reef, further demonstrating the equivalence of the lower Delray Dolomite with the uppermost reef section.

Cedar Keys A, averaging 250 feet in thickness, consists of the same Dolomite Triad found in the Delray Dolomite. Cedar Keys A occurs everywhere except where the main body of the Rebecca Shoal reef is present. This absence of Cedar Keys A demonstrates that it is the lagoonal equivalent of the reef. The age of the Delray Dolomite and Cedar Keys A is indeterminate, but lies somewhere within the Lower Eocene-Upper Paleocene interval.  Continuity of the Dolomite Triads in the Delray Dolomite and the Cedar Keys A between closely spaced wells is virtually nonexistent, but gross lithologic assemblages do extend laterally at multi-well sites. Regionally there is no continuity of the Dolomite Triad members.

Cedar Keys B consists mostly of fine microcrystalline euhedral dolomite. Only in Brevard County does it contain enough Boulder Zone wall features to be included in the Boulder Zone. Avon Park dolomites, when thick, also contain some Boulder Zone wall features.

The Rebecca Shoal reef is present in the Keys and in the area adjacent to St. Lucie County in the Peninsula. Sparse lithologic data in the Keys shows the reef and its Tavernier and Plantation Tongues to consist of euhedral and anhedral dolomite. Porosity is mainly intercrystalline with some vugs. Large caverns have been reported in the lower reef section in several wells. In the St. Lucie County area, injection wells penetrated several hundred feet of Rebecca Shoal reef. Here good lithologic data show the same reef lithology as in the Keys. By regional correlation, the age of the upper Rebecca Shoal (Tavernier) is essentially Paleocene and the middle Rebecca Shoal (Plantation) is Upper Cretaceous.

In the southeastern Peninsula, regional structure on top of the Delray Dolomite or Cedar Keys A dips southward from Brevard County into a large low area occupying most of Broward County. Dip reverses southward into Dade County. Faulting is present in Brevard, Palm Beach and Dade Counties, as shown by missing section or by structural anomalies between closely spaced wells.

Video tapes of injection well boreholes into Boulder Zones reveal the presence of cavities and vugs of various sizes, wall-collapse zones and wide vertical channels, all of which contribute to the reservoir permeability and capacity. Wall-collapse zones are created by intersecting open fractures, which when exposed by drilling, collapse into the hole due to the lack of support. Thick wall-collapse sections appear to be associated with faults. Cavities, large horizontal openings which frequently encompass the entire wall of the hole, may be several feet in diameter. There are no valid explanations for their origin, only speculations. Large vugs and vuggy zones occur sporadically. In the study area, true caverns have been identified only in the Rebecca Shoal reef. In the main body of the reef in the Keys they all occur some 2,000 feet below the top. This suggests a possible subaerial origin, but the absence of a significant sea level fall in the middle of the Upper Cretaceous mitigates against this explanation. The uncommon vertical channels are obviously solution-enlarged fractures. Continuity of Boulder Zone wall features between closely spaced injection wells is limited to wall-collapse zones.


Title:
Mapping Recharge to the Floridan Aquifer Using a Geographic Information System

Publication:
Technical Publication SJ 93-5, St. Johns River Water Management District. Palatka, Florida

Abstract:
Maps of groundwater recharge areas are useful planning tools for groundwater resource management Sections 373.0391, 373.0395, and 373.0397, Florida Statutes, require the water management districts to provide recharge area information to local governments and planning agencies. Recharge areas of the Floridan aquifer in the St Johns River Water Management District (SJRWMD) were mapped using a geographic information system to analyze the geologic and hydrologic factors that affect recharge.

Groundwater recharge to the Floridan aquifer, as presented in this report, is the addition of water to the Floridan aquifer from the overlying surficial aquifer. Recharge rates to the Floridan aquifer were based on hydraulic pressure differences between the water table of the surficial aquifer and the potentiometric surface of the Floridan aquifer (in May 1990) and on leakance of the upper confining unit separating the aquifers. Recharge rates were mapped at a 4-inch-per-year (in/yr) contour interval.

Recharge to the Floridan aquifer occurs in areas where the elevation of the water table of the surficial aquifer is higher than the elevation of the potentiometric surface of the Floridan aquifer. In these areas, water moves from the surficial aquifer in a downward direction through the upper confining unit to the Floridan aquifer. Recharge also occurs directly from infiltrating rainfall where the limestones of the Floridan aquifer are at or near land surface. In addition, significant local recharge may occur where sinkholes have breached the upper confining unit.

Discharge from the Floridan aquifer occurs in areas where the elevation of the Floridan aquifer potentiometric surface is higher than the elevation of the water table. In these areas, water moves from the Floridan aquifer in an upward direction through the upper confining unit to the surficial aquifer. Where the elevation of the Floridan aquifer potentiometric surface is higher than land surface, springs and free-flowing artesian wells occur.

Sixty percent of SJRWMD (4,711,229 million acres) contributes recharge to the Floridan aquifer. Discharge from the Floridan aquifer occurs in the remaining 40 percent (3,160,770 acres).

Recharge areas with rates greater than 12 in/yr encompass 14 percent of the total recharge area. Areas with recharge rates of 8 to 12 in/yr encompass 9 percent of the recharge area. Areas with recharge rates of 4 to 8 in/yr encompass 25 percent of the recharge area. Areas with recharge rates of 0 to 4 in/yr encompass 52 percent of the recharge area.

The recharge map included in this report-Recharge Areas of the Floridan Aquifer in the St. Johns River Water Manage7nent District (Plate 1)-provides a regional assessment of recharge to the Floridan aquifer. The map is intended to be used as a regional planning aid for groundwater resource management; it is not intended for site-specific assessments.


Title:
Summary of Groundwater Quality in the St. Johns River Water Management District

Publication:
Special Publication SJ 96-SP13.  St. Johns River Water Management District.  Palatka, Florida

Abstract:
Accurate and reliable water quality data are required to characterize groundwater chemistry for use in groundwater resource management. This report summarizes the groundwater quality of the Floridan, intermediate, and surficial aquifer systems in the St. Johns River Water Management District. Data were collected from 1990 through 1994.

The groundwater quality conditions in an aquifer are a result of natural systems and human-influenced conditions. Natural systems affect water quality in an aquifer by means of recharge to and discharge from the aquifer, the dissolution of minerals, flow paths, residence times, and the mixing of fresh groundwater with residual formation water or intruded seawater. Human-influenced conditions include aquifer degradation based on activities at land surface and upconing of water with high dissolved solids composition from deep zones due to groundwater withdrawals. Another human-influenced condition is the introduction of irrigation water from deep aquifers to surface systems; excess irrigation water from the deep aquifer may infiltrate down to near-surface systems.

The water quality variables discussed are those that constitute a major part of the total dissolved solids (TDS) content of water. The major cations include calcium, magnesium, sodium, and potassium. The major anions include chloride, sulfate, and carbonate alkalinity. Iron is an important minor cation; phosphate, nitrate and nitrite, and fluoride are important minor anions. Data on temperature, pH, specific conductance, TDS, and hardness also are presented.

The chemical composition of water in the Floridan aquifer system in recharge areas is characteristically low in concentrations of calcium, magnesium, chloride, sulfate, TDS, carbonates, and other constituents. In these recharge areas, such as the upland ridges and where the limestones of the Floridan aquifer system are at or near land surface, residence times for water in the Floridan aquifer system are relatively short. The water has not reached equilibrium conditions with aquifer materials. Water quality conditions typically reflect water quality in the surficial aquifer system, climatic conditions, soil types, and human activities.

As water in the Floridan aquifer system moves along flow paths from recharge to discharge areas, the increasing residence times allow more opportunity for the chemical composition of the water to be altered and for chemical reactions between the water and aquifer materials to reach equilibrium. The water in the Floridan aquifer system in and near discharge areas is composed mainly of calcium, magnesium, chloride, and sulfate. Typically high TDS concentrations, hardness values, and pH also occur in these areas. Where water in the Floridan aquifer system travels along deep flow paths, it comes in contact with gypsum in the aquifer system. Sulfate concentrations are notably high in discharge areas, such as in southern Duval and northern St. Johns counties, because of the gypsum dissolution.

The mixing of  fresh water in the Floridan aquifer system with residual formation water still present in the aquifer results in water composed mainly of calcium, magnesium, sodium, chloride, and sulfate. This type of water occurs in the Floridan aquifer system in St. Johns County south of St. Augustine, in northern and central parts of Flagler County, and in eastern parts of Brevard County. In these areas, the highly mineralized residual formation waters of the Floridan aquifer system have not been replaced by fresh recharge waters. In addition, lower artesian pressures in the Floridan aquifer system due to water withdrawals result in the upward movement of highly mineralized formation water in the tri-county agricultural area of St. Johns, Flagler,  and Putnam counties. A transition zone between the residual formation water and fresh groundwater occurs on- the borders of these mixing areas.

The mixing of fresh water in the Floridan aquifer system with upwelling residual seawater along parts of the St. Johns River also results in water composed mainly of calcium, magnesium, sodium, chloride, and sulfate. This upwelling of highly mineralized water into the upper parts of the Floridan aquifer system occurs in discharge areas along the St. Johns River in parts of Brevard, Seminole, Orange, Lake, and Volusia counties. A transition zone between the upwelling residual seawater in discharge areas and fresh groundwater in recharge areas occurs to the east and west of the St. Johns River.

The mixing of fresh water in the Floridan aquifer system with laterally intruded seawater from the Atlantic Ocean occurs near Daytona Beach Shores (south of Daytona Beach in Volusia County). This mixing results in water composed mainly of sodium, chloride, calcium, magnesium, and sulfate. High concentrations of TDS and calcium carbonate (i.e., hardness) also occur in this area. A transition zone between the intruded seawater and fresh groundwater or residual formation water also occurs in other areas along the coast.

The wide range in concentrations of calcium, magnesium, sodium, potassium, chloride, sulfate, and TDS in the intermediate aquifer system reflects the diverse sediments that comprise the aquifer materials with which the water comes into contact. High concentrations of these constituents indicate that water has been in contact with carbonates and clays over long periods of time. Areas along the coast with high concentrations of calcium, magnesium, sodium, chloride, sulfate, and TDS are characteristic of lateral intrusion of seawater in Brevard, Duval, Flagler, and Nassau counties. High concentrations of these variables along parts of the St. Johns River are due to the upwelling of highly mineralized water from the underlying Floridan aquifer system.

The chemical composition of water in the intermediate aquifer system reflects recharge from the overlying surficial aquifer system or the underlying Floridan aquifer system, aquifer mineralogy and lithology, residence time, and proximity to coastal areas. The flow paths of water through the intermediate aquifer system can be complex, and residence times can vary. Long residence times are characteristic of areas where the Hawthorn Group sediments are relatively thick and comprised mostly of clay and fine-grained materials. Where the Hawthorn Group is breached by sinkholes and fractures, residence times may be short.

Water from the surficial aquifer system is generally soft, contains fewer dissolved minerals, has a low pH, and has more iron than water from the deeper artesian aquifers. Chloride concentrations are low, except in those areas where the surficial aquifer system has been intruded by seawater from the coast or in those areas where water has moved from deep aquifers due to upward leakage.


Title:
Geostatistical Analysis: Water Quality Monitoring Network for the Upper Floridan Aquifer in East-Central Florida

Publication:
Technical Publication SJ 99-1, St. Johns River Water Management District. Palatka, Florida

Abstract:
Geostatistics provides a framework for the analysis, characterization, and estimation of spatial data. A geostatistical analysis was undertaken to assess regional chloride conditions in the Upper Floridan aquifer. This analysis was based on data from the current water quality monitoring network in the De Land groundwater basin. The analysis was undertaken as a means of devising a more efficient monitoring network for this area within the St. Johns River Water Management District.

Chloride concentration data from 84 wells in the De Land groundwater basin were analyzed. Because of anomalous data (very high chloride concentrations) and the distribution of the data, the data were transformed to yield a normally distributed data set that is suitable for geostatistical analysis.

An anisotropic variogram model was fitted to the transformed chloride data. A variogram. is a graph that depicts the spatial variability between samples and the distance between samples. Sensitivity analysis of model parameters was performed to validate the suitability of the selected model. Cross-validation was performed to assess the overall quality of the selected model and estimation procedures.

A chloride concentration map was created for the DeLand groundwater basin. This map displayed the zone of high chloride concentration along the coast of the Atlantic Ocean (the eastern edge of the basin) where there is a mixing of freshwater in the Floridan aquifer with intruded seawater. Areas of high chloride concentration were also displayed along the western edge of the groundwater basin in discharge areas near the St. Johns River, where there is a mixing of upwelling residual seawater with freshwater in the Floridan aquifer. An area of high chloride concentration also was displayed in Flagler County where freshwater mixes with residual formation water that has not been replaced by fresh recharge water. The areas of low chloride concentrations were located in the upland ridge recharge areas of the Floridan aquifer. The geostatistical analysis resulted in a valid characterization of chloride concentrations in the De Land groundwater basin


Title:
Domestic Wastewater Treatment and Reuse Inventory in the St. Johns River Water Management District: Update

Publication:
Technical Publication SJ 95-7. St. Johns River Water Management District, Palatka, Florida

Abstract:
This wastewater treatment and reuse inventory is an update and revision of St. Johns River Water Management District (SJRWMD) Technical Publication SJ91-5. As was the previous edition, this volume is expected to be useful to SJRWMD, the Florida Department of Environmental Protection (FDEP), local utilities, and individual large-volume water users for determining the feasibility of reuse projects. The data and other information included in this document may be used to identify sources of treated wastewater for potential reuse and issues that may affect the feasibility of using those sources.

This inventory includes data for 221 wastewater treatment facilities (WWTTs) having permitted capacities of 0.1 million gallons per day (mgd) or greater. Of that total, 203 facilities are located within SJRWMD and 18 facilities are located outside of SJRVVMD but within counties that are partially under SJRWMD jurisdiction.

The total permitted capacity was 442 mgd for facilities within SJRWMD and 525 mgd for all inventoried WWTFs. Mean actual flow of wastewater was 267 mgd within SJRWMD and 309 mgd for the entire inventory, or 60% and 59% of permitted capacity. Per capita wastewater flow for facilities where both population and flow were known was 86 gallons per day.

Reclaimed water for reuse, by FDEP definitions, was supplied by 62% of the inventoried WWTFs. These facilities provide about 102 mgd of reuse water within SJRWMD and 143 mgd for all inventoried facilities. These amounts represented 38% and 46%, respectively, of the total wastewater flows.

Aggregated irrigation uses accounted for 52 mgd (50%) of all reuse within SJRWMD and 81 mgd (57%) for the entire inventory. After irrigation, environmental enhancement and groundwater recharge were the next largest uses for reclaimed water. Commercial/ industrial, fire protection, and other uses accounted for relatively minor amounts of reuse.


Title:
Water Supply Needs and Sources Assessment: Alternative Water Supply Strategies Investigation: Wetlands Impact, Mitigation, and Planning-Level Cost Estimating

Publication:
Special Publication SJ 96-SP7, St. Johns River Water Management District. Palatka, Florida

Abstract:
Groundwater, the primary source of municipal water supply in the St. Johns River Water Management District (SJRWMD), is an excellent water supply source for the following reasons:

Reliable source 
Minimal treatment costs because of quality 
With proper development and management, consistent quality over time

While groundwater has been a generally high quality, reliable, and inexpensive source of municipal groundwater supplies in the SJRWMD, it is unlikely that all additional future municipal water supply needs can be met by this source without causing some level of ecologic change. For this reason, SJRWMD is investigating the feasibility of alternative water supply strategies.

This technical memorandum (IM), which focuses on the methods for determining technical and economic feasibility of mitigating or avoiding the impacts associated with various water supply options, is the first in a series of TMs addressing the balancing of water supply needs with the protection and management of natural resources. Specifically, this TM presents a methodology for assessing potential ecologic impacts of water table declines, and another methodology for estimating the costs of mitigating these ecologic impacts. A summary of this investigation, beginning with background information, the purpose and scope, and methodology, is presented below.

As part of its water supply needs and sources survey, SJRWMD previously evaluated the potential impacts of increased groundwater withdrawals through the year 2010 (Vergara 1994). Based on this evaluation, several areas in which water supply problems are critical, or will become critical, were identified (Figure 1). These areas have been identified as Water Resource Caution Areas (WRCAs). Without careful planning now, future groundwater withdrawals could adversely affect surface water resources and the natural environments dependent on those resources. In particular, wetland communities in portions of the WRCAs have been identified as being at risk for adverse impact.

Options for increasing water supply include development of one or more of the following potential sources:

• Potable groundwater
• Surface water o-Low quality groundwater
• Artificial recharge
• Reclaimed water
• Water supply system interconnections

Increased system storage could include the use of reservoirs, aquifer storage recovery (ASR) facilities, or ground storage tanks. Reduction in demand could be achieved by numerous water conservation initiatives. In many cases, some combination of increased supply, increased system storage, and demand reduction is most effective in limiting environmental alterations and enhancing the cost-effectiveness of future water supply systems.


Title:
Water Supply Needs and Sources Assessment: Alternative Water Supply Strategies Investigation: Artificial Recharge of the Floridan Aquifer Through Drainage or Injection Wells in Orange and Seminole Counties

Publication:
Special Publication SJ 97-SP14, St. Johns River Water Management District. Palatka, Florida.

Abstract:
Drainage wells have been in use in Orange and Seminole counties since 1905. Their primary purpose is to provide surface drainage and to prevent flooding in closed surface basins. Most study area drainage wells provide either direct street and urban drainage or lake-level control. Drainage wells also provide important artificial recharge of the Upper Floridan aquifer.

In addition to drainage, several water resources management issues are important, such as the quantity and quality of aquifer recharge, the potential for aquifer contamination, and protection of the aquifer from brackish water intrusion. These issues are directly related to long-term water supply planning and development.

Drainage wells have benefits and associated risks. Given that the drainage benefits are well known, the focus of this investigation is on the following issues:

•  Quantity and quality of surface water recharge

•  Regulatory framework governing the construction and operation of drainage and injection wells

•  Stormwater management and treatment options for improving the quality of the emplaced surface water

•  The potential for increased artificial recharge using additional drainage or injection wells

These issues are important considerations in the comprehensive management of study area water resources.

Drainage or artificial recharge injection wells should be recognized as technology useful for total water resources management, including management of the Floridan aquifer and urban drainage and flood control. This technology has both advantages and disadvantages, and should be used when the advantages outweigh the disadvantages.

Existing regulations and policy should be revised to encourage net improvements in recharge water quality and increased recharge volume using drainage or injection wells. Net improvement would involve increased aquifer recharge or decreased aquifer pollutant loadings, or both. In this manner, incremental improvements, including artificial recharge, can be achieved even though all DWSs will not be met by the recharge water.


Title:
Water Supply Needs and Sources Assessment:  Alternative Water Supply Strategies Investigation:  Aquifer Storage and Recovery Utility Evaluations

Publication:
Special Publication SJ 97-SP16, St. Johns River Water Management District. Palatka, Florida

Abstract:
Several characteristics of SJRWMD's groundwater resources make potable groundwater the water supply source of choice. First, groundwater is inherently reliable-an important attribute for public water supply. Second, treatment requirements and cost are often minimal because of the generally good quality of the raw groundwater. Third, if the resource is developed and managed properly, the quality of the raw groundwater remains stable.

To date, high quality, reliable, and inexpensive public groundwater supplies have been developed within SJRWMD. However, the District is concerned that additional future public water supply needs may not be met by increasing the use of groundwater resources without incurring unacceptable environmental impacts. Therefore, the District is investigating the feasibility of alternative water supply strategies.

The District previously evaluated the potential impact of increased groundwater withdrawal through the year 2010 (Vergara 1994). Based on this evaluation, areas where water supply problems are now critical or will become critical were identified. An increase in groundwater withdrawal could adversely impact area water resources, affecting natural systems, groundwater quality, and existing legal users.

The District is investigating the technical, environmental, and economic feasibility of using alternative water supply strategies as a means of preventing existing and projected adverse impacts. The program includes investigations conducted by SJRWMD staff and by several consultants, including CH2M HILL

The public water supply within the St. Johns River Water Management District (SJRWMD) is generally provided by high quality groundwater. Reliability, minimal cost and treatment requirements, and supply stability are several characteristics of SJRWMD's groundwater resources that make potable groundwater the best source for water supply. The District previously evaluated the potential impact of increased groundwater withdrawal through the year 2010 (Vergara 1994). Increasing groundwater usage without incurring unacceptable environmental impacts is unlikely. Therefore, the District is investigating the feasibility of alternative water supply strategies.

Whether the source of supply is groundwater or surface water, variation in supply and demand has traditionally been addressed by tank or reservoir storage facilities or by increased treatment plant capacity. However, in recent years, aquifer storage recovery (ASR) has been developed as an alternative means of water storage. ASR consists of storing water in a suitable aquifer through a well during times when water is available, and recovering the water from the same well during times when it is needed (Pyne 1995). When the water supply exceeds demand, a groundwater well serves as a recharge well. Water is recovered later from the same well during peak demand.

With the potential benefit of ASR as an alternative storage method and water management tool, it is valuable to have guidelines to evaluate the feasibility of ASR in a particular location. The first technical memorandum (TM) in this series, TM C.1.c (CH2M HILL 1996), provided such a tool to assist the District in determining if ASR would be a feasible alternative for helping utilities meet current or future water supply needs. This TM, the second in the ASR series, applies the ASR feasibility tool to selected sites within SJRWMD.

The typical procedure for implementing an ASR system consists of the following three phases: preliminary feasibility assessment and conceptual design, test-well, and final design and construction. In the first phase, information is gathered to assess if ASR should be considered as a storage option. This phase includes assessing both storage needs and the hydrogeologic characteristics of potential storage zones. If conditions appear to be favorable, then a test well program is designed. Construction and testing of the ASR test well provide the data necessary to confirm the hydrogeologic feasibility of ASR. The test well phase also provides a basis of design for the full scale ASR system. The final phase is the preparation of contract documents, construction, and implementation of the ASR system.

The screening tool presented in TM C.1.c and applied herein is designed to provide a methodology for preliminary evaluation of ASR It is most applicable to the initial evaluation of the need for ASR and its overall hydrogeologic suitability. Application of the tool should provide a preliminary assessment of these important factors, as well as focus future investigations on areas associated with uncertainty or where information is missing.

The ASR screening tool is divided into the following parts:

•  Facility planning factors-which determine the need for ASR or other storage options.

•  Hydrogeologic design and operational factors-which aid in determining if ASR is technically feasible and will satisfy the specific needs of the utility.

•  Cost factors-which provide approximate order-of-magnitude costs for ASR systems for specific flow rates compared with other storage or expansion options


Title:
Water Supply Needs and Sources Assessment:  Alternative Water Supply Strategies Investigation: Brackish Groundwater Treatment Technology Assessment

Publication:
Special Publication SJ 97-SP19, St. Johns River Water Management District.  Palatka, Florida

Abstract:
St. Johns River Water Management District (SJRWMD) has determined that projected increases in groundwater withdrawals between 1990 and 2010 could adversely impact native vegetation, groundwater quality, and water resources, including springs. Because of these possible adverse impacts, SJRWMD has begun investigating the technical, environmental, and economic feasibility of alternative water supply strategies, including the development of brackish groundwater resources.

This is the second of three technical memorandums (TMs) that address the feasibility of developing brackish groundwater resources to help meet future public supply needs. This TM reviews relevant information and technical literature on technologies available to treat brackish groundwater and disposal options available to manage the waste concentrate stream associated with brackish water treatment. Based on the results of the review and goals and objectives of the alternative water supply investigations, a methodology is proposed for development of source-based brackish groundwater supply cost estimates. These cost estimates and general cost equations developed from the estimates will be documented in TM D.3.b, Brackish Groundwater: Cost Estimates.

Treatment technologies are well established for highly n-deralized waters, including brackish groundwater. Any brackish or saline water source can be treated to meet drinking water standards. However, the more saline the source, the more extensive the treatment. Membrane treatment, including reverse osmosis, is likely to be the primary technology used to treat brackish groundwater within the planning area. Also, the quantity and salinity of the resulting waste concentrate stream increases as a function of the degree of salinity of the source water. Thus, managing the treatment concentrate waste stream is often one of the more difficult issues to be resolved in implementing the brackish groundwater supply alternative.

Most of the useful data defining brackish water quality and the geologic structure of the Floridan aquifer system are contained within SJRWMD's geographic information system. Therefore, SJRWMD is identifying and rating potential brackish groundwater sources as part of this alternative water supply investigation. The characteristics of the brackish groundwater source areas are discussed in TM D.1.a, Brackish Groundwater: Source Identification and Assessment.


Title:
Central Florida Artificial Recharge Demonstration Program:  Alternative Water Supply Strategies in the St. Johns River Water Management District

Publication:
Special Publication SJ 98-SP11.  St. Johns River Water Management District.  Palatka, Florida

Abstract:
The St. Johns River Water Management District (SJRWMD) in association with its water supply planning effort conducted an Alternative Water Supply Strategy Investigation. As part of that investigation, SJRWMD evaluated the feasibility of increasing the flow of surface water to the Floridan aquifer through drainage wells in Orange and Seminole counties. This evaluation was performed for the District by CH2M HILL pursuant to Contract #95W166A. A summary of this evaluation has been published by the District as Special Publication SJ97-SP14. The publication includes the recommendation that existing regulations should be revised to encourage net improvements in recharge water quantity and increased recharge volume using drainage wells. In addition, the publication includes the recommendation that demonstration projects be designed and implemented to demonstrate the effectiveness of the net improvement concept.

This document describes such a recharge demonstration program, the Central Florida Artificial Recharge Demonstration Program. The focus of this program is to quantify the potential for bacterial contamination of the aquifer using lake water or treated stormwater as the source of recharge. The specific issues identified for investigation include

•  The fate of bacteria in the Floridan aquifer

•  The effectiveness of passive stormwater treatment for reducing bacteria

•  The effectiveness and cost feasibility of physically reducing bacteria in lake water recharge.

The Central Florida Aquifer Recharge Demonstration Program is designed to be a cooperative effort between central Florida local governments, SJRWMD, Florida Department of Environmental Protection, and the U.S. Environmental Protection Agency


Title:
Annual Report on Abandoned Artesian Wells: 1996 (October 1995 through September 1996).

Publication:
Special Publication SJ 99-SP9.  St. Johns River Water Management District.  Palatka, Florida.

Abstract:
Uncontrolled or improperly constructed artesian wells have a major effect on the quantity and quality of Florida's groundwater resources. Wells have been drilled that do not meet current well construction standards. These wells should be plugged or repaired because of problems associated with the poor construction techniques. In addition to poor construction, many of these wells were drilled decades ago, and poor water quality has caused deterioration of the well casing and subsequent leaking.

In the St. Johns River Water Management District (SJRWMD), the Floridan aquifer system is the main source of artesian flow for these wells. This aquifer system is composed of limestone units. In some cases, the flow from uncontrolled or improperly constructed wells has reduced the water levels (potentiometric surface) of the Floridan aquifer system. This uncontrolled flow has increased the potential for mineralized or saline water to contaminate potable water supplies.

This document was prepared to comply with the requirements of Section 373.207, Florida Statutes (FS) (1991). It is the fourteenth annual report on the inventory of abandoned artesian wells in SJRWMD and on the work plan for controlling or plugging inventoried wells. This report covers the fiscal year (FY) October 1, 1995, through September 30, 1996.

This document was prepared to comply with the requirements of Section 373.207, Florida Statutes (1991). It is the fourteenth annual report on the inventory of abandoned artesian wells in the St. Johns River Water Management District (SJRWMD) and on the work plan for controlling or plugging inventoried wells. This report covers the fiscal year (FY) October 1, 1995, through September 30, 1996.

As of September 30,1996, the cumulative number of artesian wells identified under the abandoned artesian well plugging program was 2,624. Of this total, 495 need to be controlled, 1,215 have been plugged or repaired through the SJRWMD cost-share program, and 914 have been plugged or repaired by the well owners.


Title:
Numerical Modeling of Groundwater Flow and Seawater Intrusion, Volusia County, Florida (2 volume set)

Publication:
Special Publication SJ 92-SP6.  St. Johns River Water Management District.  Palatka, Florida.

Abstract:
In 1989, the Florida legislature directed water management districts of the State to undertake a water supply Needs and Sources Assessment. The framework for this program provides for a systematic evaluation of the projected water resource needs and the available resources for the next two decades. The Geraghty & Miller Modeling Group (GMM) has been retained to develop an updated tool that can be used for the analysis of impacts of current and projected water supply needs and for more localized analyses of resource management questions within the Volusia Groundwater Basin. To achieve this objective, a refined groundwater model is being developed to accurately simulate groundwater flow and chloride transport in the Volusia County groundwater basin. The model must incorporate appropriate data regarding existing and proposed wellfields, recharge and discharge areas, land use patterns, and the hydrologic configuration of the surficial aquifer.

The primary objective of this study is to develop an up-to-date groundwater flow and chloride transport model to be used for predictive purposes within the context of a Needs and Sources Assessment.

The specific objectives of this study are:

1) Incorporate new information regarding the location of recharge/discharge areas, land use patterns, wellfield locations, agricultural and other users, and the hydrology of the surficial aquifer into the groundwater model.

2) Determine the effects of existing and proposed withdrawals from public water supply wellfields on the flow regimes of the Floridan aquifer system,

3) Determine the potential for lateral migration of saline water ( > 250 mg/L) from brackish areas within the Floridan aquifer under specified demand scenarios for the years 1990 and 2010.

4) Determine the potential for saltwater upconing within the Floridan aquifer under specified demand scenarios for the years 1990 and 2010.


Title:
Stratigraphic Analysis of Geophysical Logs from Water Wells in Peninsular Florida.

Publication:
Technical Publication SJ 84-16.  St. Johns River Water Management District.  Palatka, Florida.

Abstract:
Geophysical well logs are widely utilized in peninsular Florida. Such logs are often the only reliable geologic information obtainable for formations which exist in the subsurface in any given area. The stratigraphic interpretation of such logs is thus important in accurately determining the regional geology and stratigraphy of the state.

Gamma ray and electric log characteristics of the nine Paleocene age to Pliocene age geologic formations typically present in peninsular Florida are considered. Primary emphasis is placed upon stratigraphic interpretation of gamma ray logs, with electric logs serving as a supplementary source of information.

Most of the formations considered can be divided into two gamma ray log zones: an upper zone of lesser intensity and a lower zone of greater intensity. The lower zones of the Suwannee, Ocala (locally), Avon Park, Lake City and Oldsmar Limestones generally consist of hard, thick dolostone zones. Average gamma ray intensity decreases downward through the stratigraphic section as the Hawthorn Formation, Tampa, Suwannee and Ocala Limestones are penetrated. The Ocala is recorded as the lowest gamma ray intensity on logs run in water wells in the region. The Hawthorn Formation displays the highest intensity due to the presence of relatively high concentrations of phosphate. Avon Park and Lake City gamma ray intensities can also be relatively high because of the presence of peat and clay as discrete beds and as disseminated material in carbonate beds.

Where it exists, the Tamiami Limestone can sometimes be distinguished on gamma ray logs as a somewhat variable three-zone series of characteristics.


Author:
Law Engr. & Environmental Services, Inc. Staff

Title:
Water Supply Needs and Sources Assessment:  Alternative Water Supply Strategies Investigation:  Systems Interconnection Methodology

Publication:
Special Publication SJ 96-SP6.  St. Johns River Water Management District.  Palatka, Florida.

Abstract:
To plan for the potential interconnection of water system or reuse system facilities, a considerable amount of information needs to be obtained. An outline of information requirements pertinent to the scope of services has been identified. Generally, the outline serves as a guide in gauging the amount of information to be collected.

LAW has received and reviewed relevant information submitted by St. Johns River Water Management District (SJRWMD). SJRWMD provided appropriate GIS files and other information from their library for the methodology of the initial task, Public Water Supply and Wastewater Facility Information. In addition, two surveys have been conducted by SJRWMD involving the collection of information from wastewater systems' and public water supply systems' facilities.

After comparing the data currently obtained to the information requirements, LAW has determined that supplementary data needs to be collected. To obtain additional data, systems information will be collected from public water supply utilities and wastewater utilities through the completion of a questionnaire followed by a personal interview (if necessary) with the utilities selected.

In addition, component cost information will be collected from the responses in the questionnaires as well as from supplemental reference sources for the proposed methodology of Task B.1.b (2) Public Water Supply and Wastewater Facility Component Cost Information. This information will be presented in tabular form as capital costs and operation costs for various major supply and treatment facility components. Preliminary Cost Summaries will be utilized to present the capital and operational cost of a potential interconnection system project. A matrix will be developed listing the potential projects by cost.

The proposed methodology developed for Task B-1.b (3), Utilizing Information for Assessing Feasibility, is addressed by developing a screening criteria for potential interconnections. This will be accomplished through an Evaluation Matrix which contains six engineering/ socio-economic criteria and cost criteria relevant to potential interconnections. By ranking the interconnection, the Evaluation Matrix aides in identifying those potential interconnection projects that are viable and can be evaluated with other alternative water supply strategies in meeting the needs of the future.


Author:
Mercer, J., Thomas, S., Lester, B., and Broome, R.

Title:
Saltwater Intrusion in Volusia County, Florida Due to Groundwater Withdrawals:  Technical Summary

Publication:
Technical Publication SJ 85-1.  St. Johns River Water Management District.  Palatka, Florida

Abstract:
Volusia County, located in east central Florida, comprises approximately 1,200 square miles between the Atlantic Ocean to the east and the St. Johns River to the west.   Most of the county is underlain by a three-aquifer system. The primary source of water is a limestone artesian aquifer of Eocene age known as the Floridan aquifer, which is divided into an upper and 1ower part. It is overlain by confining beds of low-permeability clay of Miocene or Pliocene age. These are overlain by a water-table aquifer that is composed of sand beds of Pleistocene and Recent age and the uppermost sand and shell beds of Miocene and Pliocene age. Population centers in Volusia, County, which create a large water demand, are located near the coast. These population centers are experiencing saltwater intrusion that has resulted in the relocation of public water supply wells further inland. Problems with saltwater intrusion combined with the increased water demand throughout the county have produced the need for a regional management approach to Volusia County's water development.

The tool that has been selected to aid in this management approach is a three-dimensional computer model of the entire county. Such a model provides decision makers with the ability to predict the response of the groundwater system, both in terms of flow and movement of chlorides, to various developments or management schemes. A phased approach toward model development was used. In the first phase, the groundwater flow system was simulated. Once this phase was successfully completed, the second phase, incorporating solute transport to simulate sea water intrusion and brackish water upconing, was introduced. Both predevelopment and development conditions within the county were simulated to demonstrate the accuracy of the model. The predevelopment or steady-state simulation results were used as initial conditions for the development simulations, which include well discharge data. Sensitivity analyses were performed on the boundary conditions, recharge rates, permeability, and leakage properties.

The response of the Volusia County groundwater system to six different hypothetical stresses was also analyzed as part of the study. This analysis provides insight into the dynamics of the system. Results of the model study indicate the utility of computer models as a management tool for the complex groundwater system in Volusia County.


Title:
Hydrologic Data from a Lower Floridan Aquifer Well, Central Orange County, Florida.

Publication:
Special Publication SJ 99-SP8.  St. Johns River Water Management District.  Palatka, Florida

Abstract:
This report presents data collected from the Orlando Utilities Commission (OUC) Southeast test well, located near Lake Nona in south-central Orange County, Florida. The data were collected as part of an agreement between the St. Johns River Water Management District (SJRWMD) and OUC to deepen the existing test well and collect hydrogeologic information in addition to that already collected at the site by OUC.

The project was initiated to obtain information on (1) the thickness of the transition zone between freshwater (chloride concentration of less than 250 milligrams per liter [mg/L]) and salt water (chloride concentration of approximately 19,000 mg/L), (2) relative differences in permeability between different vertical intervals within the Lower Floridan aquifer, and (3) the thickness of the Lower Floridan aquifer.

OUC constructed and performed testing in the original test well between July 11, 1995, and March 29,1996. The well was cased to a depth of approximately 1,084 feet below land surface (ft b1s) and completed with an open borehole to approximately 2,005 ft b1s. The additional drilling and testing under the direction of SJRWMD occurred between July 8, 1996, and September 29, 1996. Drilling ceased on July 16, 1996, at a depth of approximately 2,443 ft b1s. Upon completion of testing, the borehole was backplugged to a final depth of 1,399 ft b1s.

Data collected during drilling included lithologic data, drilling time data, water quality data, and water level data. Geophysical and video logging were conducted upon completion of drilling. Caliper, natural gamma, formation resistivity, fluid resistivity, temperature, flow, and acoustic velocity logs were run in the open borehole. Water quality samples were collected for laboratory analysis at discrete depths within the open borehole using a thief sampler. Nine distinct borehole zones were delineated based upon borehole characteristics and lithologic descriptions

Straddle-packer testing was conducted at five different depth intervals in order to (1) collect water quality data from discrete zones to better characterize the freshwater/ saltwater transition zone, (2) measure hydraulic head in discrete zones so that the vertical hydraulic gradient could be estimated, and (3) estimate the variation in permeability with depth.

Results from the various tests indicate that the Lower Floridan aquifer can be roughly divided into three hydrostratigraphic layers:

•  An upper permeable layer (the main production zone used for water supply development in the Orlando area) composed primarily of hard dolomitic rocks in which flow is dominated by solution cavities and fractures

•  A semiconfining-layer composed primarily of relatively soft limestone with little fracture flow

•  A lower permeable layer similar in character to the upper permeable layer. Water quality throughout most of its thickness is fresh but slightly more mineralized than the upper permeable layer. Hydraulic head is probably higher than in the overlying layers.

The top of the lower confining unit (the base of the Floridan aquifer system) was found at approximately -2,000 ft National Geodetic Vertical Datum, a depth significantly higher than previously mapped in regional water resource assessment reports. There is little difference in the magnitude of hydraulic head between the lower confining unit and the lower permeable layer of the Lower Floridan aquifer. The thickness of the Lower Floridan aquifer at the Southeast test well site is approximately 980 ft.

The top of the freshwater/saltwater transition zone (equivalent to the 250?mg/L isochlor) was found within the Lower Floridan aquifer near the base of the lower permeable layer and estimated at a depth of approximately 2,050 ft b1s.

The bottom of the freshwater/saltwater transition zone was estimated to be at a depth of approximately 2,330 ft b1s. The resulting thickness of the transition zone is approximately 280 ft.


Title:
Volume 3 of the Lower St. Johns River Basin Reconnaissance:  Hydrodynamics and Salinity of Surface Water.

Publication:
Technical Publication SJ 95-9.  St. Johns River Water Management District. Palatka, Florida.

Abstract:
The lower St. Johns River (LSJR) Surface Water Improvement and Management plan requires the St. Johns River Water Management District to develop plans to manage water quality and to restore ecosystems. Surface water quality may be improved by development of nutrient and sediment loading goals. Such goals are best quantified and prioritized from the perspective of a comprehensive understanding of the dynamics of the river.

This volume of the Lower St. Johns River Basin reconnaissance report has two purposes: (1) to locate, to describe, to compare, and to evaluate published information and data on the hydrodynamics and salinity of the LSJR and (2) to recommend future work needed to develop a more complete understanding of the dynamics of the river. This report examines and evaluates the extent of present knowledge regarding the volume and movement of the waters, salinity, and past efforts to simulate the flow of the LSJR, and it shows where gaps in knowledge of river dynamics exist. This report describes water elevations, flows, the dominant forcing factors (such as tide and wind), salinity, and the physical and computer models that have been developed to describe these factors. A brief review of water quality models is included, because these models are closely tied to quantity (hydrodynamic) models. Basin hydrology and tributary inflows are not included in this report because these subjects were described in Volume 2 of this series.

Since the late 1890s, substantial effort has been directed toward describing the characteristics of the St. Johns River. Additional investigations occurred in the 1930s and continued sporadically in the 1970s and 1980s. However, the limited results from these studies only hint at the complexity of the river system. A small number of the studies attempted to develop a comprehensive description of the St. Johns River from its mouth to the region of the head of tide. Most of the other studies were limited to small areas of the river, consisted of reviews of previous reports, or covered only a few of the important variables.

Hydrodynamics, the study of the dynamics of water movement, is described in terms of water heights, currents, and volumes. Salinity is the concentration of salts in a water mass. The salinity of water is directly related to its density, and the density affects the hydrodynamics; therefore, hydrodynamic forces and salinity work together to control the movement of water in the river.

The concentration of salinity in the water at a particular location in the river is the result of the mixing of fresh water and salt water. Ocean salinity is about 36 parts per thousand; the salinity of rainwater and tributary discharges is usually close to zero. When water masses of different salinity come into contact, the amount that they will mix together will depend on the amount of local turbulence and water velocity. The water masses may travel in opposite directions. Lower density water, instead of mixing, may ride up over heavier, more dense water masses. Thus, many factors, including local hydrodynamics, affect the resulting density structure of river water. Salinity and changes in salinity are very important to the health and survival of marine vegetation and biota.

The movement and mixing of fresh water, nutrients, and sediments in the river depend to a great extent on the local movement and density of the water. Therefore, the hydrodynamics and salinity of the river must be well understood before an analysis of the dilution and transport of pollutants can be undertaken.

Depths in the river were first surveyed in 1853 and last surveyed (except in the vicinity of Jacksonville) by the federal government in 1959. The areas surveyed were usually relatively small in extent compared to the total area of the river; thus, the depths in most areas have been surveyed only once. The depths in the navigation channel, which extends from the mouth of the river to Lake Harney, have been periodically re-surveyed for channel maintenance.

River shorelines and tributary inflow locations have been well described.

The tide station at Mayport has been monitored continuously since 1928, but all other tide stations were monitored over much shorter periods of time. This monitoring has been currently discontinued. The most notable feature of the tides is the occurrence of a minimum tidal range near Orange Park and a secondary maximum near Palatka. Annual predictions of tidal heights and times, based on the 1970s data, are published by the federal government for15 stations located from the jetties at the mouth of the river to Welaka. Tidal currents are also predicted annually at 17 stations.

Mean flows have been determined for a few locations over some relatively short time periods. De Land has the longest flow record (58 years), followed by Jacksonville (22 years) and Palatka (13 years). The data from the Jacksonville and Palatka stations, however, are rated as poor due to the unavailability of adequate instrumentation for monitoring reversing (tidal) flows. In 1992, the U.S. Geological Survey installed ultrasonic velocity meters at Buffalo Bluff and Dunns Creek; these gages have provided more accurate and complete data. Flow measurements at Jacksonville also are expected to be improved in the future.

Flow statistics indicate that the mean net non-tidal flow at the mouth of the LSJR is on the order of 6,000 to 15,000 cubic feet per second, and total flow (including the tidal component) is an order-of-magnitude greater.

Salinity distributions have been reported a few times in the literature, but because salinity is highly variable and dependent on the hydrology and hydrodynamics of the system, it has not been well described. The salinity data have led researchers to a tentative conclusion that the river varies between slightly to highly stratified (i.e., it is generally not vertically homogeneous and not well mixed).

Several physical and numerical models of river hydrodynamics and water quality have been developed. Many of these have been numerical models, and all have been relatively simple. All were limited in calibration by a lack of data on mainstem flows, tributary inflows, and pollution loadings.

The overall water budget for the river has not been described. The water budget is a seasonal balance of the inflows, outflows, and changes in volume over  the full extent of the main stem of the river, which would account for long-term variations of ocean tide and the hydrologic cycle. The water budget would be expressed in terms of spatial changes in tidal volume, inflow from each tributary, runoff, evaporation, groundwater seepage, and the salinity distribution for normal, wet, and dry seasons.

The influence of each tributary discharge and basin runoff on water levels, flows, and salinity in the tidal part of the tributary and the main stem of the river has not yet been quantified. The major difference between the less detailed description of the overall water budget and this detailed description of the dynamics of flow at the mouths of tributaries is the increase in spatial detail that will be needed. In these areas, the interflows are more complex. Managers are interested in the transient effects of stormwater inflows, the salinity ranges required by marine ecosystems in the vicinity of the tributary, the dilution and fate of pollutants, and the possible effects of reducing sediment inflows or removing existing sediments. The environment at the mouths of tributaries is complicated by complex flow patterns; incomplete mixing, salinity and temperature stratification; trapping of pollutants; different areas of deposition, erosion, and resuspension of sediments; and other local phenomena. These kinds of problems can be analyzed with the assistance of tributary-area model studies that incorporate the hydrology of the subbasin and the hydrodynamics and salinity of the contiguous tidal portion of the main stem, and that can simulate sequences of storms that can be developed according to historic hydrologic variability.


Title:
Improvement of Water Quality Through a Cooperative Well Plugging Program

Publication:
Technical Publication SJ 78-2 (Formerly: Information Circular #2).  St. Johns River Water Management District. Palatka, Florida

Abstract:
A serious concern for the quality of water used for agricultural irrigation in the State of Florida has developed in the past few years. In the late 1960's and early 1970's, the practice of plugging artesian wells on a cost-sharing basis was provided by the Agricultural Stabilization and Conservation Service (ASCS) through the funding of the Federal Government. This cost-sharing program began in the southern portion of the state, and now in certain counties in the St. Johns River Water Management District (SJRWMD), monies have been allocated by the ASCS for this program. In most of the cost-sharing programs offered by the ASCS, the technical expertise was provided by the agricultural engineers of the Soil Conservation Service (SCS), but in the case of well. plugging programs  expertise was provided by the Department of Natural Resources. Since the implementation of Chapter 373, Florida Statutes, responsibility for providing well plugging expertise has been delegated to the water management districts.

The plugging of these irrigation wells is specifically to restore the hydrologic conditions which existed before the well was constructed and also to eliminate the exchange of water between aquifers. Since this program was initiated in 1976, several deep irrigation wells have been plugged by methods provided by District staff in cooperation with the ASCS. The wells which have been corrected to date represent only a fraction of those which could benefit from this program. Data that have been collected illustrates that this procedure offers a practical method for controlling water quality problems in deep wells.


Title:
Part 1: Saline Contamination of the Limestone Aquifer by Connate Intrusion in Agricultural Areas of St. Johns County, Putnam, and Flagler Counties, Northeast Florida

Publication:
Technical Publication SJ 79-4. Part 1 (Formerly: Technical Report #2).  St. Johns River Water Management District.  Palatka, Florida.

Abstract:
St. Johns, Putnam, and Flagler counties are located in northeast Florida within the St. Johns River Valley. The topography is generally flat, and the climate is humid subtropical with a mean annual rainfall of approximately 53 inches. With these conditions, the agricultural production of fall and winter vegetables is a large part of the area's economy. Irrigation for crops begins in late September and continues through May. Intense seasonal groundwater withdrawals in several agricultural areas produce cones of depression in which water levels in artesian flowing wells may drop in excess of 20 feet below land surface, and water quality deteriorates severely.

From land surface to more than 200 feet in depth at some localities, the geology of this area consists of sand and clay mixed with thin beds of limestone and phosphate. The Floridan aquifer, which consists of Eocene limestone and permeable basal limestone beds of Miocene Hawthorn Formation, underlies these materials. This aquifer is the primary source of water for irrigation supplies.

From the geophysical logging of 82 irrigation wells, most of the flow zones in the Floridan aquifer were encountered in the upper 50 feet of the limestone. Water samples taken from the deep artesian wells showed that water quality deteriorates as relative depth into the limestone increases and, in some cases, bottom samples exceeded 3,000 parts per million chloride. During times of extended pumping in the agricultural areas, the upconing of deep saline water in the Avon Park formation into shallower fresher zones of the Floridan aquifer has the potential to contaminate other wells in the same general area. Also, many of the old wells which were constructed during the time of higher potentiometric levels act as direct conduits for contamination of fresh upper zones.

Throughout the period of investigation, irrigation wells were measured for water level and sampled for water quality. Total well depth, aquifer penetration, and potentiometric level were analyzed to determine their relationship to chloride concentration by regression analysis and polynomial expansion. The most significant linear relationship was that of chloride concentration and potentiometric level. Data showed that as potentiometric levels decreased as a result of irrigation pumpage, chloride concentration of the irrigation water increased and vice versa. Chloride data for the various sample months were fit to gamma distribution by the method of maximum likelihood to allow water quality estimates to be made for all the wells in the study area based on data from the sampled wells in the study area. Analysis of the gamma distribution indicates that 50 percent of the wells in the study area will produce water with chloride concentration less than or equal to 210 parts per million, and that 10 percent of the wells will exceed 778 parts per million chloride during any time of the year.

A water use inventory of the intensive agricultural area was conducted, and irrigation pumps were rated according to discharge and electrical consumption capabilities. Monthly records of electrical consumption were used to determine amounts of groundwater withdrawals which, in the three counties, totaled some 18.5 million gallons per day. The values derived by the electrical consumption method were compared to the water use figures generated by the local agricultural agencies and the U.S. Geological Survey (USGS). In comparison, the county and USGS values were approximately 50 percent higher than those values calculated in this study. To provide a check on the withdrawal figures calculated from electrical consumption, a flownet analysis was done from the potentiometric map of the study area at the time in which the extent of the cones of depressions were the greatest. Values generated by the flownet analysis closely agreed with the water use values derived by the electrical consumption method.


Title:
Part 2:  Saline Contamination of the Limestone Aquifer by Connate Intrusion in Agricultural Areas of St. Johns, Putnam, and Flagler Counties, Northeast Florida.  Supplemental Data

Publication:
Technical Publication SJ 79-4. Part 2 (Formerly: Technical Memorandum #2).  St. Johns River Water Management District.  Palatka, Florida

Abstract:
A groundwater investigation of the agricultural areas of St. Johns, Putnam, and Flagler counties was conducted by the St. Johns River Water Management District. The results of that project can be found in Technical Report No. 2, "Saline Contamination of a Limestone Aquifer in Agricultural Areas of St. Johns, Putnam, and Flagler Counties, Northeast Florida, St. Johns River Water Management District, July 1979.  Contained herein are the data, in tabular form, collected during the duration of the project which were used for hydrogeologic interpretation contained in Technical Report No. 2. Also presented in greater detail are several expanded sections of the Technical Report for those readers who may desire further clarification.


Title:
Geostatistical Analysis: Potentiometic Network for the Upper Floridan Aquifer in the St. Johns River Water Management District

Publication:
Technical Publication SJ 2000-1. St. Johns River Water Management District.  Palatka, Florida

Abstract:
The St. Johns River Water Management District (SJRWMD) maintains or supports several groundwater level networks in central and northeastern Florida. The water levels in the Upper Floridan aquifer are measured in May and September of each year to determine the average annual lows and highs. The number of wells in the network continues to increase. In May 1995, the network contained 921 sites; in 1996, the network included 943 sites.

This study evaluated the overall effectiveness of the network. In specific, the study examined the purpose and objectives for the network, the completeness of knowledge concerning well construction and well use, the areal coverage and temporal suitability of the measurements, and the spatial effectiveness of the network. A literature review and a users survey were used to determine the theoretical and assumed objectives, respectively.

Computer records of open hole intervals, measuring points (indicating whether elevations were surveyed or not), and well use were searched to determine the extent of knowledge about the well construction of those wells in the network. Based on the available data, the aquifer being penetrated by a well is known for only 36% of the evaluated wells. Only 22% of the wells are dedicated observation wells.

The temporal suitability of the measurements (May and September) was examined. Of 250 wells for which 12-month averages could be determined, 41% had an average water level low in May and 27% had an average water level high in October, suggesting that the September measurement event is less than optimal.

The objectives for the existing network match those of a regional network, although some users appear to misuse the data for subregional concerns. The network products-maps of the elevation of the potentiometric surface and maps showing changes in the elevation of the potentiometric surface are appropriate for a regional network. However, knowledge of well characteristics of the existing network is poor.

The spatial suitability of the network was evaluated using a geostatistical analysis of water levels measured in May 1995. The geostatistical analysis indicated that the network has more than enough wells to characterize water levels and potentiometric surfaces in the Upper Floridan aquifer. A stratified sampling scheme was used to evaluate potential networks containing fewer wells. Six hexagonal grid networks with grid cell diameters of 15,000 feet (ft), 22,500 ft, 30,000 ft, 37,500 ft, 45,000 ft, and 52,500 ft were evaluated. These networks were composed of 917, 789, 669, 560, 442, and 361 wells, respectively. The standard deviation of each network was determined using kriging (a collection of linear estimation methods) and used as a measure of effectiveness. The 45,000-ft stratified hexagonal grid network composed of 442 wells is the recommended network. The change in the standard deviation meets the stated goal of approximately 10% or less. Within the St. Johns River Water Management District, 47 of the 45,000?ft grid cells are not currently being monitored.

If the recommendations of the report are put in place, the final result will be a 53% smaller, more stable (93% dedicated monitor well) and efficient network with known characteristics. Improvements to the existing network are required due to the large percentages of unsurveyed (23%) wells and wells with unknown characteristics (64%). Costs to improve the existing network are estimated at $236,260. The existing network fully upgraded with construction of new wells is estimated at $1,316,260.

Movement of the September measurements to October require the cooperation of Southwest Florida Water Management District (SWFWMD) and South Florida Water Management District (SFWMD). In addition the timing of the average annual potentiometric high may be different for the other water management districts. It would probably be more cost effective for SJRWMD to take some additional measurements beyond its own month end measurements in October in order to obtain the data.


Publication:
Technical Publication SJ 2000-2.  St. Johns River Water Management District.  Palatka, Florida

Abstract:
The population of the St. Johns River Water Management District (SJRWMD) is about 3.44 million, 2.89 million of whom depend on public water supply and about 0.55 million of whom depend on domestic sources (Florence 1994). In SJRWMD, 1,522 million gallons per day (mgd) of freshwater is withdrawn for potable and nonpotable uses. Fresh groundwater comprises about 1,119 mgd, or 75% of this amount. At present, 38% of the groundwater pumpage is used for public water supply. Only a small part of the fresh groundwater pumpage is used for drinking and cooking, and the remaining portion ends up as wastewater. Thus, a large amount of wastewater could be reused or artificially recharged into the groundwater system after treatment.

This study investigated the technical feasibility and hydrologic impacts of artificial recharge with reclaimed wastewater through rapid infiltration basins (RIBs) into the groundwater system. SJRWMD is especially interested in maintaining or increasing the potentiometric head of the Floridan aquifer system and associated spring discharges through the use of artificial recharge with reclaimed wastewater. To evaluate this option, potential artificial recharge sites were identified within the study area using SJRWMD's geographic information system. The study area was divided into seven subregions on the basis of proximity of wastewater treatment plants to the potential recharge sites. Up to 21 potential sites were then selected for artificial recharge of groundwater using RIBs.

Groundwater modeling was performed to achieve the objectives of this study. The U.S. Geological Survey's (USGS) MODFLOW was used as a tool for performing groundwater flow simulations in this study. The hydrologic impacts of RIBs were evaluated using two pumping scenarios, one for the year 1994 and the other for the year 2010. The hydrologic impacts of artificial recharge through RIBs on the groundwater system were assessed by comparing the differences between the simulations with and without artificial recharge. The simulations without artificial recharge of reclaimed wastewater at the recharge sites or RIBs are considered baseline simulations.


Title:
Final Report: Surface Electrical Resistivity Measurements of the Upper Floridan Aquifer in the Titusville Area

Publication:
Special Publication SJ 99-SP5.  St. Johns River Water Management District.  Palatka, Florida

Abstract:
An audio magnetotelluric (AMT) survey was performed at 14 sites in the Titusville area. The survey was conducted over a 3 day period in December, 1998. The AMT method is a geophysical technique, which through ground surface based measurement, enables description of the vertical distribution (one-dimensional layering) of formation electrical resistivity.  Accordingly, AMT soundings provide a gross approximation of an electrical log as performed in a borehole without the significant expense of drilling, completing and logging such a borehole.  In comparison of AMT soundings to electric logs, the minimum thickness of an interval that can be resolved is several orders of magnitude larger than what can be resolved by electric logs. The confidence in the conclusions from AMT findings can be increased when water quality and lithologic information from nearby wells is available.

The AMT survey was conducted at four locations in the Titusville area. At one of the locations, Bent Oak Golf Course, the objective of the survey was to determine where the thickness of the fresh water layer in the Upper Floridan aquifer is the greatest. At the other three locations, the objective was to determine the thickness of the fresh water layer in the Upper Floridan aquifer. At the Bent Oak Golf Course the maximum estimated thickness for the freshwater saturated Upper Floridan aquifer was approximately 45 m. The calculated resistance of the freshwater layer from the AMT survey did not correlate well with the electrical log results from a nearby well. However, because of the effects of nearby sources of interference, the absolute values of the AMT-derived resistivities were not reliable.

At the Lundy Drive site, an apparent drop in apparent resistivity was observed at a depth of 50 to 60 meters. This correlates to a fresh-water saturated thickness of the Upper Floridan aquifer of 15 to 25 m. It is expected that a decline in water quality (increasing chlorides) occurs within Us depth range. Similar to the Bent Oak Golf Course site, the AMT-derived resistivities for the suspected freshwater saturated layer were lower than what would have been expected.  As with the Bent Oak site, it is suspected that the absolute values of the calculated resistivities were also effected by cultural interference. At the remaining sites, Astronaut High School and Garden Street Water Treatment Plant, the AMT sounding data were not interpretable due to the effects of interference.


Title:
Technical Memorandum D.1.B. Brackish Groundwater:  Source Identification and Assessment. Task D. Development of Lower-Quality Water Sources. Alternative Water Supply Strategies in the St. Johns River Water Management District.

Publication:
Technical Memorandum D.1.B.: Brackish Groundwater: Source Identification and Assessment.  CH2MHill Project Number 130581.SJ.LQ. Gainesville, Florida

Abstract:
St. Johns River Water Management District (SJRWMD) is investigating the technical, environmental, and economic feasibility of selected alternative water supply strategies. These investigations are being conducted in support of regional water supply planning intended to identify feasible water supply alternatives that will meet future public supply needs without undesirable environmental impacts. The SJRWMD-sponsored program includes investigations conducted by several consultants, including CH2M HILL, and by District staff.

The primary water supply options under consideration include increased supply, demand reduction, and increased system storage to better manage existing supplies. Several alternative water supply options, including the development of lower-quality or brackish groundwater resources, are under consideration.

This technical memorandum (TM) addresses the availability of lower quality or brackish groundwater as an alternative water supply source. The TM characterizes the brackish groundwater resources within the SJRWMD Priority Water Resource Caution Area including the following parameters of interest:

Thickness of the Upper Floridan aquifer
Depth to the 250-milligram per liter (mg/L) isochlor
Depth to the 1,000-mg/L isochlor
Thickness of the brackish water within the Upper Floridan aquifer
Percentage of brackish water within the Upper Floridan aquifer
Recharge rate to the Upper Floridan aquifer

Mapping each of these parameters was accomplished by applying Geographic Information System (GIS) techniques.

Criteria were then developed to rank each of the above parameters. In general, areas where the Upper Floridan aquifer is relatively thick and contains mostly brackish groundwater with chloride concentrations ranging from 250 to 1,000 mg/L are most attractive for water supply development. In addition, groundwater discharge areas are preferred to groundwater recharge areas because the potential for undesirable impacts to nearby wetlands is less in discharge areas. Using relative rankings for each of the parameters, areas with low, medium, and high potential for development of brackish groundwater supplies were identified.

Six candidate brackish groundwater withdrawal sites were then identified, based on relative water supply development potential and proximity to demand centers. The six candidate withdrawal sites are located in St. Johns, Volusia, Seminole, Orange, and Brevard counties. Each candidate withdrawal site was analyzed to identify long-term changes in water quality due to pumping. A saltwater and freshwater upconing analysis was used to predict expected water quality changes as a function of both time and pumping rate. The upconing analysis is based on local hydrogeology and water quality and considers several different production well configurations, well pumping rates, and pumping durations.

Results of the upcoming analysis, conducted for all six candidate withdrawal sites, indicate that water quality will change with both duration of pumping and pumping rate. However, in all cases, the rate of change can be minimized by careful wellfield design and operation.

Adequate well spacing is very important. In this analysis, wells were spaced at 2,500 feet intervals and rather large well spacing will be required to minimize future changes in brackish groundwater quality Pumping rate is also important. Lower pumping rates will help minimize future water quality changes. Proper wellfield design and operation will ensure the long-term viability of each candidate brackish groundwater withdrawal site evaluated in this investigation.

The results of the upconing analysis provide the information necessary to develop preliminary brackish groundwater supply options for comparison to other water supply development alternatives. The results also provide the information necessary to develop planning-level brackish groundwater development cost estimates as a function of total water supply quantities developed for each candidate withdrawal site. Each of the candidate sites selected and analyzed may be used to characterize a typical hydrogeologic framework in the Floridan aquifer and serve as a basis for cost estimates for locations with similar characteristics.

This TM is the first in a series addressing the feasibility of developing brackish groundwater supplies to augment existing and future public water supply needs. Other brackish groundwater TMs, prepared as part of the SJRWMD Alternative Water Supply Strategies Assessment, include TM D.2.c Brackish Groundwater. Treatment Technology Assessment (CH2M FULL, 1997) and TM D.3.b Brackish Groundwater: Planning~Level Cost Estimates (CH2M HILL, 1998). The treatment technology TM assesses available brackish groundwater treatment technologies and provides a basis for estimating the costs associated with developing brackish groundwater supplies.

The costs TM considers the source characteristics presented in this 'IM and the treatment technologies identified in the treatment technology TM and develops planning level costing procedures applicable to the candidate brackish groundwater source areas identified and evaluated here.

The brackish groundwater investigation is a joint effort between CH2M HILL and SJRWMD staff. The source identification and assessment, presented here, was conducted by SJRWMD staff. The brackish groundwater technologies and cost TMs were prepared by CH2M HILL.


Title:
Technical Memorandum D.3.B. Brackish Groundwater: Planning-Level Cost Estimates.  Task D Development of Lower-Quality Water Sources. Alternative Water Supply Strategies in the St. Johns River Water Management District.

Publication:
Technical Memorandum D.3.B. Brackish Groundwater: Groundwater: Planning- Level Cost Estimates. Brackish Groundwater: Planning-Level Cost Estimates. CH2MHill Project Number 130581 SJ.CE. Gainesville, Florida.

Abstract:
This technical memorandum (TM) is the third in a series concerned with the feasibility of developing brackish groundwater sources to help meet municipal water supply needs within the St. Johns River Water Management District. The first TM identified potential source areas and associated maximum quantities. The second TM discuses treatment processes applicable to developing brackish groundwater supplies and a proposal for developing source-based water supply development cost estimates using selected treatment technologies and source area characteristic data. This TM presents the results of the brackish groundwater cost analysis.

This TM presents the results of the cost estimation for water supply development at the following six candidate brackish groundwater withdrawal sites:

Lake Washington
Titusville
South Orange
Volusia
St. Johns County
Lake Jessup

Cost equations were developed for two different sets of conditions: blending systems and desalting systems, using reverse osmosis (RO). These systems are described in further detail in the Treatment Requirements and Costs section of the report. A complete set of easy-to-apply cost estimating tools was developed and is presented. In most cases, costs are expressed as a function of the finish water average day demand (ADD). In all cases, a maximum day to average day demand ratio of 1.5 is assumed. Therefore, the maximum treatment capacity of all water supply systems described in this TM is 1.5 times greater than the average day demand provided.


Title:
An Environmental Evaluation of Water Reuse in the St. Johns River Water Management District.

Publication:
Technical Publication SJ 85-2.  St. Johns River Water Management District. Palatka, Florida.

Abstract:
This report partially fulfills the technical requirements necessary for development of water management policy, plans, and permitting criteria regarding water reuse in the St. Johns River Water Management District. A discussion is provided pertaining to environmental and health aspects of direct reuse and an assessment of the potential for direct reuse in the District. The assessment of direct reuse potential, in terms of agricultural and urban irrigation with domestic wastewater treatment plant (WWTP) effluent is based on location and treatment/disposal methods of major WWTP's, water supply and demand, land use, and environmental factors. In the interest of public health, effluent used in a direct reuse operation with unrestricted public access should be pre-treated, at minimum, to a tertiary level with disinfection. Nearly all of the major WWTP's can either operate at this level of treatment presently or can reach this level with additional chemical coagulation and/or filtration processes. Most of the major WWTP's are located in the south District region (Volusia, Marion, Lake, Seminole, Orange, Brevard and Indian River counties) in which several areas exhibit high direct reuse potential. This high potential is a result of the need to implement water conservation measures and alternatives to wastewater disposal in environmentally sensitive surface waters. Reuse may satisfy both needs simultaneously, but its implementation can be limited or restricted due to environmental factors. For example, direct reuse in Brevard County may be limited in certain areas west of the Indian River composed of poorly drained soils and high water tables; and, restricted from those areas with numerous domestic or private wells unless measures are taken to prevent contamination of the surficial aquifer (the county's primary potable supply).


Title:
Time Domain Electromagnetic Mapping of Salt Water in the Floridan Aquifer in Northeast Florida & East Central Florida: St. Johns River Water Management District: November 1996.

Publication:
Special Publication SJ 97-SP1.  St. Johns River Water Management District. Palatka, Florida.

Abstract:
A time domain electromagnetic (TDEM) survey was performed at 7 sites in the St. Johns River Water Management District during the month of June, 1996. The TDEM method is a geophysical technique which, through ground surface based measurement, enables description of the vertical distribution (one-dimensional depth layering) of formation electrical resistivity. As such, TDEM soundings provide a gross approximation of an electrical log as performed in a borehole without the significant expense of drilling, completing, and logging such a borehole. In comparing TDEM soundings to electric logs, the minimum thickness of an interval that can be resolved by TDEM is several orders of magnitude larger than what can be resolved by electric logs. The confidence in the conclusions from TDEM findings can be enhanced when water quality information from nearby wells is available. The objective of the TDEM survey was to determine the depths to the 250 mg/I and 5,000 mg/l isochlors.

The determination of the depth to the 5,000 mg/l isochlor was made at six of the seven sites. Depths ranged from 276 to 2,101 feet (ft) below land surface (bls). At Site 7, Hayfield, the lowermost layer was considered to represent either slightly brackish water or a porosity change in the Lower Floridan aquifer. Accordingly, it was not possible to determine the depth to the 5,000 mg/l isochlor.

The determination of the depth to the 250 mg/l isochlor was made at four of the seven sites. Depths ranged from 932 ft bls (Site 7) to 2,001 ft b1s. At Site 7, the placement of the 250 mg/l isochlor may not be valid because the observed resistance of the lowermost layer may have been caused by either a porosity change in the Lower Floridan aquifer or by the presence of brackish water (not salt water) in the lowermost layer. Accordingly, the assumptions used in the empirical relationships to determine the 250 mg/I isochlor were not valid. At Site 6, the 250 mg/l isochlor could not be determined because the geoelectric model for the site could not distinguish the Holocene to Miocene deposits from the Floridan aquifer. As with Site 7, the assumptions used in the empirical relationships to determine the 250 mg/l isochlor were also not valid. At two of the sites, there was no 250 mg/I isochlor (waters appear to be brackish).


Title:
Appraisal of the Floridan Aquifer Producing Zones in the Sebastian Freshwater Lens

Publication:
Technical Publication SJ 87-1. St. Johns River Water Management District.  Palatka, Florida

Abstract:
The Floridan aquifer is the primary source of water supply in the east-central Florida area. South of Volusia County, however, the Floridan generally contains water with chloride concentrations that exceed 250 milligrams per liter (mg/1), the recommended limit for public drinking water (Figure 1) . Therefore, throughout much of Brevard County it is difficult to obtain groundwater suitable for public supply. The City of Cocoa obtains water from both the surficial and Floridan aquifer systems in Orange County. The City of Melbourne and adjacent areas of South Brevard County rely on surface water from Lake Washington. In Indian River County, practically all of the public and domestic water supply systems tap the surficial aquifer system.

Supplies of potable water within the Floridan aquifer in southeastern Brevard and eastern Indian River counties occur only in the area bordering Sebastian Inlet. Here, the Floridan aquifer contains a lens of potable quality water completely surrounded by non-potable quality water. This lens is referred to as the Sebastian freshwater lens. The lens supplies significant quantities of water to a large number of South Brevard and Indian River counties residents.

The purpose of this study is to determine the areal extent of the Sebastian freshwater lens, to document the changes in its size with time, and to project the future utility of the lens. This report contains a quantitative appraisal of the Floridan aquifer producing zones and should serve as an aid to water resource planners in determining management strategies to enhance the utility and duration of this water supply.


Title:
Salt Water Intrusion in Coastal Areas of Volusia, Brevard, and Indian River Counties.

Publication:
Technical Publication SJ 88-1.  St. Johns River Water Management District. Palatka, Florida

Abstract:
The intrusion of salt water into coastal groundwater aquifers is of significant concern to the St. Johns River Water Management District (District). The District is charged with managing groundwater resources in a nineteen county area of northeast Florida. In 1976 the District initiated the Salt Water Intrusion Studies (SWIS) Program to examine salt water intrusion in coastal areas of the District.

The goal of the Salt Water Intrusion Studies (SWIS) program is to compile the hydrogeologic and water quality data necessary to make sound decisions about the management of the District's coastal groundwater system. Of particular importance is the quantity and quality of water in coastal areas that is suitable for domestic, agricultural, public supply, and industrial use. The SWIS program provides a regional view of the coastal area, emphasizing water level and water quality characteristics of the Floridan, intermediate, and surficial aquifer systems underlying the study area.

The first phase of the program, SWIS I, was a cooperative project with the Coastal Plains Regional Commission and the Florida Department of Environmental Regulation and examined saltwater intrusion in eastern Nassau, Duval, St. Johns, and Flagler counties (Frazee, J.M., Jr., and McClaugherty, D.R., 1979). Phase II, SWIS II, was undertaken solely by the District. It consists of the reconnaissance studies of the coastal portions of the District not addressed in SWIS I - eastern Volusia, Brevard, and Indian River counties.

Groundwater aquifers are the principal sources of drinking water in the District. The extent and quality of the aquifers vary significantly throughout the region. The Floridan aquifer is the most dependable water source. However, in many coastal areas chloride concentrations in the Floridan aquifer are already above the EPA recommended limit of 250 mg/l. Due to local geologic conditions, the intermediate and surficial aquifers contain limited freshwater supplies and are quite susceptible to saltwater intrusion.


Title:
Water Quality Assessment of the Floridan Aquifer in the Wekiva River Basin of Orange, Lake and Seminole Counties, Florida

Publication:
Technical Publication SJ 89-5.  St. Johns River Water Management District. Palatka, Florida

Abstract:
The Wekiva River basin is situated in an area where portions of the Floridan aquifer contain salt water. Piper trilinear analysis of the water indicates these waters are transitional connate and connate water.

Tibbals (1977) evaluated the effects of increased groundwater withdrawals on the quantity and quality of water in the Floridan aquifer in Seminole County. Eight wells used in Tibbals (1977) study were located and resampled during this study.

Thirty wells were sampled and analyzed for major ions and metals in March and October 1986. The mean chloride concentration of the wells sampled in 1986, where chloride concentration was below 425 mg/l, was 18 mg/l higher in October than in March 1986. Most of the difference is due to the chloride concentration of wells located in the region where concentrations varied between 101 and 250 mg/l. Tibbals (1977) called this region a "lateral freshwater-salty water transition area." He postulated that the vertical position of the zone of diffusion between fresh and salty water is at the top of the Floridan aquifer in this region and that the chloride concentration of wells in this region would probably vary seasonally. Coincident with an increase in chlorides is higher water use during the October sampling period than during the March sampling period. Water withdrawn for public supply in the study area was 6 mgd greater during the October sampling period than during the March sampling period (Marella pers. com. 1988). Water quality samples were collected from wells for self-supplied domestic use. Presumably, water withdrawn for self-supplied domestic use is similar to the trend of water withdrawn for public supply in the study area. The higher chlorides in October compared to March may be due to increased groundwater withdrawals during the October sampling period.

In Seminole County, Tibbals (1977) observed a slight increase in chloride concentration in the Floridan aquifer between samples collected in 1951 and 1956 and samples collected in 1973 and 1974 The increase occurred in areas where chloride concentrations varied between 101 and 250 mg/l . Variations in chloride concentrations may be related to the vertical movement of the freshwater/saltwater interface (Tibbals 1977).

The majority of wells sampled in the Wekiva River basin are completed into the Ocala Limestone. Casings for these wells are either set in the Hawthorn Group or at the top of the Ocala Limestone. The remainder of the well is completed as open hole.

The potentiometric surface of the Floridan aquifer was 1?5 ft lower in the area where wells were sampled for water quality in May 1986 than May 1973. However, no long-term decline is evident in the hydrographs for five wells in the study area (Figures 13, 15, 16). To determine if any long-term changes in chloride concentration occurred within the study area, chloride concentrations in March 1986 were compared to chloride concentrations for the period of April 1973 to July 1974 (Tibbals 1977). Comparing the two isochlor maps, the 101250 mg/1 area decreased and the 251-1000 mg/1 area increased for samples collected in March 1986. The change in March 1986 (Figure 20) as compared to April 1973 to July 1974 (Figure 22) is probably not due to movement of the freshwater/saltwater interface but rather to better definition of this area as a result of the increased number of wells sampled. One well, OR-0061, where the chloride concentration was 280 mg/1 in March 1986 was not sampled previously.

In the eight wells common to both sampling periods (Table 3), chloride concentrations in seven of the wells either did not change significantly or substantially decreased. However, four of the five wells in which chloride concentrations decreased still remained above the 250 mg/l chloride level and the area of potable water (chloride less than 250 mg/l) did not significantly increase in size.

Changes in chloride concentration are likely to occur in areas where the lateral and vertical chloride concentration gradient is large. The former occurs where regions of differing chloride concentrations are close together such as along the eastern side of the Wekiva River (Figures 20, 21, and 22).

Withdrawals from the Floridan aquifer may enhance this process. Not only do withdrawals lower water levels in the immediate vicinity of pumping wells, but they create a diffuse zone of higher chlorides beneath pumping wells which results from the mixing of waters at the freshwater/saltwater interface. The movement of this interface is dependent on many factors, such as the depth of the well, the pumping rate, the duration of pumping, the depth of the interface, and the difference in density of water across the interface.

Additional studies are needed to define the processes governing water quality variation in the Wekiva River area. This study establishes a framework upon which additional investigations can build.


Title:
Geohydrologic Summary of the Floridan Aquifer in the Coastal Areas of Nassau, Duval, and Northeast St. Johns Counties

Publication:
Technical Publication SJ 90-5.  St. Johns River Water Management District.  Palatka, Florida.

Abstract:
The Floridan aquifer is the primary source of water supply in northeast Florida. The effects of increased growth and urbanization along the coast of northeast Florida have raised concerns about the long-term availability of potable groundwater supplies. This report presents a preliminary examination of water resource problems, concentrating on the occurrence of saline water in the Floridan aquifer in the coastal areas of Nassau, Duval, and northern St. Johns counties.

Three different water types occur in the study area: low chloride/low sulfate water, which is typical of the back groundwater and occurs in western Nassau and Duval counties; low chloride/high sulfate water, which probably results from mineral dissolution in the aquifer and occurs in southeast Duval and northern St. Johns counties; and high chloride/high sulfate water which occurs along the coast and portions of the St. Johns River. High chloride/high sulfate areas most likely result from the upward movement of high chloride/ high sulfate waters which exist at depth .  This high chloride/high sulfate water is under higher artesian pressure than the water above it, thereby providing the potential for upward movement of saline water.

New wellfield development should be avoided in areas where chloride and sulfate concentrations are high because structural weaknesses in confining beds may play a major role in the distribution of high chloride/high sulfate water. These areas occur east of the Intercoastal Waterway along the coast, in a one-mile band on either side of north-south faults mapped by Warren Leve of the U.S. Geological Survey, and in a two-mile band on either side of a line stretching from Fort George Island to the Ortega River in Jacksonville.


Title:
Water Quality in the Floridan Aquifer System: Crescent City Ridge, Northeast Florida.

Publication:
Professional Paper Series SJ 95-PP2.  St. Johns River Water Management District.  Palatka, Florida

Abstract:
Staff of the St. Johns River Water Management District collected groundwater samples from 187 wells throughout the Crescent City Ridge area in 1992 and 1993. The Crescent City Ridge is located in southeast Putnam and northwest Volusia counties. The purpose of the sampling was to determine the chloride, sulfate, and total dissolved solids concentrations of the Floridan aquifer system in this area. The Floridan aquifer system beneath the Crescent City Ridge generally contains good quality water. Chloride, sulfate, and total dissolved solids concentrations generally were below 50, 25, and 250 milligrams per litre (mg/L), respectively. Concentrations became elevated near the St. Johns River. Chloride, sulfate, and total dissolved solids concentrations were above 250, 250, and 500 mg/L, respectively, at Welaka, on the southern half of Drayton Island, and on the eastern and southern sides of Lake George in Volusia County.


Title:
Water Quality and Isotope Concentrations from selected Springs in the St. Johns River Water Management District

Publication:
Technical Publication SJ 99-2.  St. Johns River Water Management District.  Palatka, Florida.

Abstract:
Water quality and stable and radioactive isotope concentrations were determined for selected springs in the St. Johns River Water Management District. Seventeen springs (two of which are submerged), eight wells in the Upper Floridan aquifer, and one well in the Lower Floridan aquifer were sampled to assess water quality and stable and radioactive isotope concentrations. The purposes of the sampling were (1) to document water quality, (2) to determine the isotopic characteristics of spring water, (3) to determine the source of spring water, (4) to determine the age of spring water and to evaluate the nature of the spring flow system, and (5) to determine the sources of elevated nitrate-nitrogen concentrations in these springs.

Water quality was highly variable for the springs sampled. Water quality in the springs compared favorably with that in the sampled wells with the exception of Blue and Ponce de Leon springs in Volusia County.

The data indicate that the source of spring discharge is from the Upper Floridan aquifer. The data further indicate that the flow system for an of these springs ranges from shallow to deep. Water discharging from the springs consists of a mixture of ages; some water is less than 43 years old, and some is hundreds to thousands of years old. This age difference supports the concept that these springs have complex flow systems.

The delta-nitrogen-15 values for water from the springs sampled in this study indicate that the springs have been polluted. The available data do not provide a distinction between past and present nitrate contamination. Additional studies are required to determine when contamination occurred.

The source of nitrate differs by location of the spring. The elevated nitrate levels in Sanlando, Starbuck, Wekiva, and Ponce de Leon springs are probably due to contamination by animal waste and/or sewage. The elevated nitrate level in Palm Springs is probably due to contamination by animal waste and/or sewage and perhaps mixing with nitrates derived from soil organic nitrogen. Finally, the elevated nitrate levels in Rock and Seminole springs are probably due to contamination by nitrates from fertilizers mixing with nitrates from soil organic nitrogen. The presence of elevated nitrate levels in spring water suggests a shallow to intermediate flow system for these springs.


Title:
Water Supply Needs and Source Assessment: 1994: St. Johns River Water Management District.

Publication:
Technical Publication SJ 94-7.  St. Johns River Water Management District.  Palatka, Florida.

Abstract:
The 1994 water supply needs and sources (WSNS) assessment for the St. Johns River Water Management District (SJRWMD) has been performed to meet the requirements of Section 62-40.520, Florida Administrative Code and Paragraph 373-0391(2)(e), Florida Statutes. This assessment was designed to identify areas in which water resource problems have become critical or are projected to become critical within 20 years (water resource caution areas) and to identify remedial or preventive actions designed to correct or prevent these problems.

Development of the 1994 WSNS assessment began in fiscal year 1989-90 and extended through fiscal year 1993-94. The direct costs (primarily staff salaries and support costs, costs to collect data, and consultant services) associated with development of this assessment are about $4 million.

The 20-year projection period, which is the focus of this assessment, extends through the year 2010. This assessment will be revised every 5 years, with the first revision scheduled for 1999.

SJRWMD, in this WSNS assessment, considered four primary factors in the assessment of water resource problems. These factors are impacts to natural systems, impacts to groundwater quality, impacts to existing legal users of water, and failure to identify an adequate supply source. For each factor considered, SJRWMD developed a method for identifying areas that have or are projected to have critical water resource problems. These methods are dependent on the definition of limits of impacts to the water resource. These limits are considered critical and are considered to be limits beyond which inadequate quantities of water are available to meet projected needs.

Water use needs have been inventoried for the year 1990 and have been projected to the year 2010 for three categories: public supply, agricultural irrigation self-supply, and recreation self-supply. An analysis of historical water use records indicates that these categories have consistently accounted for approximately three-fourths of the total fresh groundwater use in SJRWMD and are expected to increase more than other categories. The combined water use from these three categories accounted for 74 percent of the total fresh groundwater use in 1990.

Water use projections are not presented in this document for the other four major use categories: domestic, self-supply, industrial/commercial self-supply, thermoelectric power generation self-supply, and miscellaneous self-supply (abandoned artesian wells). However, projections for some industrial/ commercial self-supply users were made to support the development of the groundwater models.

Combined, these categories accounted for 26 percent of the total fresh groundwater use in 1990. Information obtained from historical trend analyses and contacts with users in these categories indicate that water use rates are not expected to change significantly through the year 2010.

Total water use (all seven categories, ground and surface water) is expected to increase by 401.46 million gallons per day (26 percent) over the period 1990 through 2010. Water use data for 1990 were obtained from an SJRWMD staff report; projections of future water use needs for 2010 are based on historical trends, local government comprehensive plans, and direct communication with federal and state agencies, water users, and publicly and privately owned public water supply utilities.

A data base was created by SJRWMD containing 1990 and 2010 water use amounts for agriculture and public supply, distributed spatially by well point. The information in this data base was used in the development of numerical groundwater flow models designed to assess the potential impact of future withdrawals.

Regional, subregional, and local assessments of the impacts of withdrawals on groundwater flow and water quality were performed. These models were developed using the best information available. However, the paucity of data in some areas may affect the accuracy of the projections. The need for collecting additional data and for modeling has been identified as a means of improving the accuracy of the projections. Projections of possible future water resource conditions identified as part of this assessment represent conditions that have a reasonable likelihood of occurring if all projected 2010 withdrawals of water occur at the locations and in the quantities currently proposed by water users in SJRWMD. These projections. do not, however, represent conditions that are certain to exist.

Water resource caution areas identified as a result of this assessment are based almost exclusively on water resource problems that are anticipated to become critical based on projected 2010 water use rather than on existing problems. These areas of anticipated critical water resource problem s, located in Orange, Seminole, Volusia, Lake, St. Johns, Flagler, and Brevard counties, are related largely to projected increases in public supply water use to serve an increasing population. The only area with an identified existing critical water resource problem is the area of eastern Putnam County-western St. Johns County impacted by seasonal groundwater withdrawals associated with potato crop irrigation. Strategies for achieving remedial or preventive actions in these areas will be developed cooperatively with major water suppliers and affected governments.


Title:
Water Supply Assessment: 1998 : St. Johns River Water Management District

Publication:
Technical Publication SJ 98-2.  St. Johns River Water Management District. Palatka, Florida.

Abstract:
The 1998 district wide water supply assessment for the St. Johns River Water Management District (SJRWMD) has been performed to meet the requirements of the Governor's Executive Order 96-297 and Subparagraph 373.036(2)(b)4, Florida Statutes (FS), as follows:

A district wide water supply assessment, to be completed no later than July 1, 1998, which determines for each water supply planning region:

a.  Existing legal uses, reasonably anticipated future needs, and existing and reasonably anticipated sources of water and conservation efforts; and
b.  Whether existing and reasonably anticipated sources of water and conservation efforts are adequate to supply water for all existing legal uses and reasonably anticipated future needs and to sustain the water resources and related natural systems.

This 1998 assessment is a required component of the District Water Management Plan (Subsection 373.036(2), FS). Because SJRWMD has identified its entire jurisdictional area as one water supply planning region (Figure ES1) pursuant to the requirements of Executive Order 96?297 and Subparagraph 373.036(2)(b)2, FS, this 1998 assessment is organized with a district wide perspective. The assessment is based on a planning period extending through 2020 and is scheduled to be updated every 5 years in association with updates to the District Water Management Plan.

The SJRWMD approach to addressing these requirements consisted of the following:

Defining the limits of water resource impacts beyond which a water resource-related problem could occur (water resource constraints)

Projecting the water resource impacts that could occur in 2020 as a result of projected changes in water use
Identifying priority water resource caution areas

SJRWMD assessed resource problems in four primary categories.

These categories are as follows:

Impacts to natural systems
Impacts to groundwater quality
Impacts to existing legal users of water
Failure to identify a source of supply for planned development


Publication:
Special Publication SJ 2000-SP1.  St. Johns River Water Management District.  Palatka, Florida

Abstract:
Located in northeastern Florida, the St. Johns River Water Management District (SJRWMD) covers approximately 12,400 square miles (about 8 million acres), or about 21 percent of the state's total area. SJRWMD includes all or part of 19 counties, numerous cities and towns, and the major urban centers of Jacksonville and Orlando, with a total population of almost 3.5 million people. This population is projected to increase by about 50 percent, to nearly 5.2 million, by 2020.

Total water demand for SJRWMD is projected to increase from about 1.37 billion gallons per day in 1995 to about 1.85 billion gallons per day in 2020, based on water use projections provided by water users. The projected increase of approximately 480 million gallons per day represents a total district wide growth of 35 percent. Public supply increases account for about 85 percent of the total projected increase.

For the last decade, SJRWMD's water supply planning and assessment investigations have documented that the rate of withdrawal of groundwater in certain areas of SJRWMD is approaching the rate that cannot be sustained without causing unacceptable adverse impacts to the water resources and related natural systems. Water supply planning results to date show that at some locations these sustainable rates will likely be approached in the foreseeable future, well within the current 20-year planning horizon.

This District Water Supply Plan (DWSP) addresses current and future water demands, traditional and alternative water sources, and water supply infrastructure improvements required to meet 2020 water supply needs while sustaining water quality, wetland and aquatic systems, and existing legal uses. The planning process has been ongoing for many years. The process has several distinct elements, including water supply assessments conducted in 1994 and 1998, alternative water supply strategies investigations conducted from 1995 through 1998, the Water 2020 planning process conducted from 1997 through 1999, and this DWSP.

DWSP is designed to meet the requirements of the water supply planning provisions of Section 373.0361, Florida Statutes. DWSP is based on a 20-year planning horizon extending through 2020 and includes the following components:

•  A water supply development component which includes a list of water supply source options, estimated costs, and funding sources
•  A water resource development component which includes a funding strategy
•  A minimum flows and levels component for priority surface waters and groundwater

Approximately 40 percent of SJRWMD has been identified as priority water resource caution areas. These are areas where existing and reasonably anticipated sources of water and conservation efforts may not be adequate (1) to supply water for all existing legal uses and anticipated future needs and (2) to sustain the water resources and related natural systems. Priority water resource caution areas are the focus of DWSP. Based on the priority water resource caution areas, six-work group areas were delineated to facilitate the water supply planning process:

•  Work Group Area I-east-central Florida, including all of Orange, Lake, and Seminole counties and parts of Marion, Polk, Osceola and Sumter counties
•   Work Group Area IA-Brevard County
•  Work Group Area II-Volusia County, southeastern Putnam County and southern Flagler County
•  Work Group Area III-east-central Flagler County
•  Work Group Area IV-western St. Johns County and eastern Putnam County
•  Work Group Area V-northern St. Johns County and southern Duval County

This DWSP identifies water supply source options and projects for each work group area that will meet future water supply needs while sustaining water quality, wetland and aquatic systems, and existing legal uses. For portions of SJRWMD not included in a work group area, existing water supply sources and water supply development plans are considered reasonably adequate to meet projected needs while sustaining water quality, wetland and aquatic systems, and existing legal uses. In Work Group Areas I and II, where projected public supply growth is the greatest, alternative water supplies, including significant quantities of surface water, will probably be needed in addition to traditional groundwater supplies to meet future needs. The estimated cost (in 1996 dollars) of required water supply treatment and transport facilities for each work group area is summarized in Table A-1. The capital cost of required facilities for all work group areas is expected to total in the range of $1.3 billion to $1.7 billion.

Table A-1. Conceptual planning-level cost estimates for water supply facility needs by 2020

Work Group Area                                     Capital Cost                               Unit Cost
                                                                  ($ millions)                          ($/1,000 gallons)

I-East-central Florida                             1,025 to 1,323                             1.39 to 1.79

IA-Brevard County                                     85 to 88                                  1.11 to 1.16

II-Volusia County, southeastern
Putnam County, and southern                  136 to 145                                1.27 to 1.34
Flagler County

III-East-central Flagler County                         28                                            1.82

IV-Westem St. Johns County and            Very small                               Not applicable
eastern Putnam County

V-Northem St. Johns County and               59 to 102                                     0.95
southern Duval County

Total                                                       1,333 to 1,686

Water supply system improvements and expansions are primarily the responsibility of the water supply utilities and water users. In addition to the needed water supply improvements, DWSP identifies a number of water resource development projects designed to reduce the current level of uncertainty associated with DWSP and to facilitate plan implementation. The water resource development projects are primarily the responsibility of SJRWMD and are listed as follows:

Abandoned artesian well plugging program 
Adaptive management project 
Aquifer protection program 
Aquifer storage recovery feasibility testing 
Central Florida artificial recharge demonstration program 
Cooperative well retrofit project 
Demineralization concentrate management project 
Facilitation of regional decision-making process 
Feasibility of seawater demineralization projects 
Hydrologic data collection and analysis 
Investigation of areas where domestic self-supply wells are sensitive to water level fluctuation 
Regional aquifer management project 
Surface water in-stream monitoring and treatability studies
Wetland augmentation demonstration program

This DWSP is the beginning of an integrated water resource allocation and water supply decision-making process. In significant portions of the priority water resource caution areas, alternative water supply sources will probably have to be developed to meet future needs while sustaining water quality, wetland and aquatic systems, and existing legal uses. Groundwater alone probably cannot meet all future water supply needs. Development of alternative sources of supply will require cooperation among the water supply utilities and among the utilities, SJRWMD, and the Florida Department of Environmental Protection.


Title:
Hydrochemistry of the Upper Floridan Aquifer, Florida

Publication:
Water Resources Investigation Report No. 91-4196. U.S. Geological Survey.  Tallahassee, Florida.

Abstract:
The major ion composition of water in the Upper Floridan aquifer is affected predominantly by mineral equilibria and mixing of freshwater with sea water. Areal and vertical variations in major ion chemistry were described using chemical analyses of water from 787 wells completed in the Upper Floridan aquifer. These analyses originated from two intensive regional studies of the hydrogeology and water chemistry of the Floridan aquifer system. Water from 58% of the wells completed in the aquifer is either calcium-bicarbonate (46%) or a calcium-magnesium bicarbonate (12%) hydrochemical facies. Calcite dissolution reactions in freshwater areas of the aquifer over most of the State account for the predominance of calcium bicarbonate hydrochemical facies and this controlling process is reflected by low dissolved solids (less than 250 mg/L) in these areas. A calcium-magnesium bicarbonate hydrochemical facies is produced where dissolution of dolomite and magnesium-rich clay minerals adds magnesium to the water. Where substantial gypsum and pyrite dissolution occurs, sulfate is added to the groundwater and the following hydrochemical facies are produced: calcium-magnesium-bicarbonate-sulfate (4%), calcium-magnesium-sulfate (3%), and calcium-sulfate (1%). Areas where these hydrochemical facies occur include northeast Florida, southwest Florida, and several locations in west-central Florida.


Title:
Surface Water and Ground-Water Features, Clay County, Florida

Publication:
Water Resources Investigation Report No. 77-87. U.S. Geological Survey.  Tallahassee, Florida

Abstract:
Clay County is a rapidly growing area in northeastern Florida. Surface water largely is undeveloped except for recreational use. Black Creek is the largest fresh-water stream in the country and has an average discharge of about 515 cubic feet per second. However, excessive color, iron concentration, hardness, and pH often make the water objectionable for many uses. Water from the lakes and streams in the Etonia Creek basin in southwestern Clay County generally is of good chemical quality. Groundwater occurs in the county in a water-table aquifer, secondary artesian aquifers, and the Floridan aquifer. Large withdrawals of water from the Floridan aquifer since the 1940's, especially in nearby metropolitan Jacksonville, have caused a decline of the potentiometric surface of up to 30 feet in the northeast corner of Clay County to less than 5 feet in the western part. The rate of decline in recent years at Orange Park has been about 0.7 of a foot per year. Groundwater in the county generally is of good chemical quality and is suitable for most uses.


Title:
Water Quality and Related Studies, Jacksonville area, Florida

Publication:
Open File Report (WRI) # 73035. U.S. Geological Survey, Tallahassee, Florida.

Abstract:
Since 1960 the U.S. Geological Survey, in cooperation with the city of Jacksonville, has made studies of the water resources in the Jacksonville area. Several studies made by the Geological Survey have dealt with the water quality of streams. The Survey operates 10 streamflow and sampling stations at various places on the St. Johns River. A water-quality monitor on the St. Johns River at the Main Street Bridge records hourly temperature dissolved oxygen, pH and specific electrical conductance of the water in the river. The hourly and daily maximum, minimum and mean values of each parameter are tabulated on a computer printout.

Studies are being made that will be useful to the planner when selecting and monitoring sanitary landfill sites. Geohydrologic data are presented on maps that will be useful to the planner in determining the suitability of a site for sanitary landfills or septic tanks.

A comprehensive water-quality management plan is underway to identify the quality of existing receiving waters before pollution. The Geological Survey is sampling water from the headwaters of eight streams in Duval County to obtain water-quality information for the city of Jacksonville in its pollution abatement program.


Title:
Chloride and Total Hardness Concentrations of Water from the Upper Part of the Floridan Aquifer in St. Johns County, Florida

Publication:
Open File Report (WRI) # 81-907.  U.S. Geological Survey, Tallahassee, Florida.

Abstract:
Data collected from 1976 to 1979 indicate large water-quality variations in the upper 300 feet of the Floridan aquifer in St. Johns County, Florida. Chloride concentrations range from less than 10 milligrams per liter in the northwestern part of the county to more than 1,000 milligrams per liter in the southeast and extreme southwest. Total hardness concentrations range from 110 milligrams per liter in the northwest to 1,700 milligrams per liter in the southeast. In most of the county, high chloride and total hardness concentrations indicate the presence of saline water that entered the aquifer during the Pleistocene Epoch and has not been flushed out. Water quality in the aquifer has also been influenced by submarine discharge in the southeast and by heavy pumpage for irrigation in the southwest. High total hardness concentrations not accompanied by high chloride values in the western part of the county may be structurally controlled or may indicate the presence of gypsum evaporite beds in the upper 300 feet of the aquifer.


Title:
Summary of the Hydrology of the Floridan Aquifer System in Florida and in Parts of Georgia, South Carolina, and Alabama

Publication:
USGS Professional Paper No. 1403-A.  U.S. Geological Survey, Tallahassee, Florida

Abstract:
The Floridan aquifer system is one of the major sources of groundwater supplies in the United States. This highly productive aquifer system underlies all of Florida, southern Georgia, and small parts of adjoining Alabama and South Carolina , for a total area of about 100,000 square miles. About 3 billion gallons of water per day is withdrawn from the aquifer for all uses, and, in many areas, the Floridan is the sole source of freshwater. The aquifer system is a sequence of hydraulically connected carbonate rocks that generally range in age from Late Paleocene to Early Miocene. The aquifer system consists of an upper aquifer and a lower aquifer, separated by a less permeable confining unit of highly variable properties. Low-permeability clastic rocks overlie much of the Floridan aquifer system. The Floridan aquifer system derives its permeability from openings that vary from fossil hashes and networks of many solution-widened joints to large cavernous openings in karst areas. The dominant feature of the Floridan flow system, both before and after groundwater development, is Upper Floridan aquifer springs, nearly all of which occur in unconfined and semiconfined parts of the aquifer in Florida. Three billion gallons per day pumped from the Floridan aquifer system has resulted in long-term regional water level declines of more than 10 ft in three broad areas of the flow northeast Florida; (2) west-central Florida; and (3) the Florida panhandle. Saltwater has encroached as a result of pumping in a few coastal areas. In general, the water chemistry in the Upper Floridan is related to flow and proximity to the freshwater-saltwater interface. A considerable area of the Floridan aquifer system 's extent remains highly favorable for the development of large groundwater supplies. This area is largely inland and is characterized by high transmissivity and minimal development (as of early 1980's). The major constraint on future development is degradation of water quality rather than water-quantity limitations.


Title:
Potential for Groundwater Development in Central Volusia County, Florida

Publication:
Water Resources Investigation Report No. 90-4010.  U.S. Geological Survey.  Tallahassee, Florida.

Abstract:
The Upper Floridan aquifer is the source of all public water supplies in Volusia County, east-central Florida. All freshwater in the Upper Floridan in Volusia County is derived from recharge within the county, and most discharge from the aquifer occurs at, or contiguous to, county boundaries. Brackish water is present in the discharge areas that virtually surround the county. The surficial aquifer overlies the Upper Floridan throughout the county. Together the two aquifers constitute a system that is full and rejecting water from the surficial aquifer to surface runoff and evapotranspiration in the wetlands environment of the Talbot Terrace. Recharge to the Upper Floridan aquifer occurs where there is a downward head gradient between the water table in the surficial aquifer and the potentiometric surface of the Upper Floridan aquifer. The two-aquifer system in central Volusia County comprises a potential recharge area that would function as a high rate recharge area if water were withdrawn from the Upper Floridan for use, thereby lowering the potentiometric surface and inducing some of the water now being rejected from the surficial aquifer to leak downward into the Upper Floridan. By decreasing the rejected recharge by the amount of capture, more water would be available for use. The potential recharge area is underlain by a large reserve of freshwater in an area that is currently only slightly stressed by withdrawals.


Title:
Test Hole in Aquifer with Many Water Bearing Zones at Jacksonville, Florida

Publication:
Groundwater, Volume 5, No. 4, October 1967. National Water Well Association, Westerville, Ohio.

Abstract:
A deep (2500’) well was drilled at Jacksonville, Florida to obtain geologic and hydrologic information on the deeper and unexplored part of the Floridan Aquifer.  The study shows that the aquifer consists of a series of water-producing zones separated by nonproductive zones.  A new fresh-water producing zone and the fresh water-salt water contact was delineated.  The well was completed in three separate zones in order to detect any salt-water encroachment.  The article describes the technique and results of drilling the test well.


Title:
Reconnaissance of the Groundwater Resources of Baker County, Florida

Publication:
Report of Investigations No. 52. Prepared by the U.S. Geological Survey in cooperation with the Florida Division of Geology and Baker County, Florida.  Tallahassee, Florida.

Abstract:
Test drilling, borehole geophysical methods and inventory of wells were used to obtain data on the groundwater resources of Baker County, Florida.  Water supplies are obtained from three aquifers:(1) the water table aquifer, (2) the shallow artesian aquifer, and (3) the Floridan Aquifer.  The Floridan Aquifer which is the greatest potential source of water is composed of limestones of Tertiary Age.  It underlies all of Baker County at elevations ranging from less than 50-to more than 350 feet below sea level and is 750 to 1,000 feet thick.  The water contains between 121 to 204 mg/liter carbonate hardness and 141 to 217 mg/liter dissolved solids. Potentiometric maps indicate that water probably recharges the aquifer within southern Baker County and moves radially away towards discharge areas.  Some of this water moves into adjacent Duval and Nassau Counties, Florida; and is discharged by numerous industrial and municipal wells.  A progressive decline of the potentiometric surface of the aquifer in Baker County of 10 to 20 feet between 1945 and 1964 is related to increased discharge by wells in Jacksonville and Fernandina.


Title:
Hydrologic Records for Volusia County, Florida

Publication:
Open File Report # 74021.  U.S. Geological Survey.  Tallahassee, Florida

Abstract:
Hydrologic conditions in Volusia County are summarized.  The data are presented in tabular form and in graphic form.  Data on wells, springs and lakes are for May 1972 to May 1973.  Data on streams are for the 1972 water year, October 1, 1971 to September 30, 1972.  Groundwater is the principal source of potable water in Volusia County.  The major source of groundwater is the Floridan Aquifer, an artesian system comprised of a thick sequence of limestone and dolomite.  All observation wells for which data are included in this report tap the Floridan Aquifer.  A shallow aquifer consisting of sand and shell beds is a source of domestic water supply along parts of the East Coast where the Floridan Aquifer contains saline water.  Average groundwater levels in the artesian aquifer have not declined appreciably in recent years over most of the county.  Surface drainage in Volusia County is poorly developed, resulting in large swampy areas in much of the county.  In the Deland Ridge Area, both north and south of Deland, karst topography is well developed and drainage is internal by downward seepage to the Floridan Aquifer.  Stream flow leaving the county averages about 590 million gallons a day.


Author:
Mercer, J., Lester, B., Thomas, S., and Bartel, R

Title:
Simulation of Saltwater Intrusion in Volusia County, Florida

Publication:
USGS Water Resources Bulletin. WARQB Volume 2, No. 6, December 1986. U.S. Geological Survey. Reston, Virginia.

Abstract:
Volusia County, in east central Florida, comprises approximately 1,200 square miles situated between the St. Johns River and the Atlantic Ocean. Most of the County is underlain by a three-aquifer system. Population centers in Volusia County, which create a large water demand, are located near the coast. Saltwater intrusion into the groundwater near these population centers has led to relocation of public water supply wells further inland. Regional management of the country 's water resources commissioned construction of a three-dimensional computer model of the county. Predevelopment simulation results were used as initial conditions for the development simulations, which included well discharge data. The predevelopment model calibration consisted of reproducing field-determined potentiometric surfaces. As part of the calibration process, sensitivity analyses were performed on boundary conditions, recharge rates, permeability, and leakage properties. Results of the model study indicate the utility of computer models as a management tool for the complex groundwater system in Volusia County.


Title:
Hydrogeologic Conditions and Simulation of Groundwater Flow in the Greater Orlando Metropolitan Area, East Central Florida

Publication:
USGS Water resources Investigation Report No. 96-4181.  U.S. Geological Survey.  Tallahassee, Florida

Abstract:
A finite difference groundwater flow model was used to simulate the effects of both modern-day (1988) and projected 2010 groundwater withdrawals on the Floridan aquifer system in the greater Orlando metropolitan area. This area covers about 2,500 square miles and includes all of Orange and Seminole Counties and parts of Lake, Volusia, Brevard, Osceola and Polk Counties. The hydrogeology of the area is characterized by a thin surficial aquifer underlain by the thick, highly productive rocks of the Floridan aquifer system. Water in the Upper Floridan-aquifer is brackish (chloride concentrations greater than 1,000 milligrams per liter) in discharge areas beneath and near the St. Johns and Wekiva Rivers and is freshest (chloride concentrations less than 100 milligrams per liter) in recharge areas. A slight trend toward increasing concentrations of dissolved solids, chloride and sulfate has been observed at Upper Floridan aquifer springs. Chloride concentrations in the Upper Floridan aquifer measured between 1966 and 1993 at the Cocoa well field have increased from 50 milligrams per liter to 120 milligrams per liter; concentrations measured in the Lower Floridan aquifer between 1966 and 1993 have increased from 600 milligrams per liter to 3,000 milligrams per liter. The flow model was calibrated by comparing (a) simulated and estimated Upper Floridan aquifer predevelopment (unstressed) potentiometric surfaces, (b) simulated and measured heads at 142 Upper Floridan aquifer monitoring wells in 1988 (average absolute error of 1.8 feet), (c) simulated and measured discharge rates at 15 Upper Floridan aquifer springs in 1988 (306 cubic feet per second) and (d) simulated and measured drawdowns at 134 Upper Floridan aquifer monitoring wells between 1988 and May 1990 (58 and 95 percent of simulated drawdowns were within plus or minus 25 and 50 percent of measured drawdowns, respectively). Relative to predevelopment conditions, model simulations indicate that about half of the 305 million gallons per day of water pumped from the Floridan aquifer system in 1988 was accounted for by increased recharge from the surficial aquifer system. About 23 cubic feet per second was derived from increased lateral inflow. A storage coefficient of 1x10-3 provided the best comparisons of measured-to-simulated data during the transient simulation from January to May 1990. This storativity probably is greater than the true storativity of the Upper Floridan aquifer because storage contributions from the intermediate confining unit were not accounted for during model design and development. Calibrated transmissivity ranged from 10,000 to greater than 400,000 feet squared per day in the Upper Floridan aquifer and from 5,000 to 600,000 feet squared per day in the Lower Floridan aquifer. Calibrated intermediate confining unit leakance ranged from 1x10-5 to 4x10-3 per day and was highest in areas where the unit is thin or has been breached by numerous sinkholes. In general, calibrated transmissivity and leakance values were higher than associated aquifer-test values. Simulated recharge rates to the Upper Floridan aquifer from the surficial aquifer system ranged from less than 3 to 21 inches per year. Recharge rates of greater than 10 inches per year were simulated in areas of west Seminole, west Orange, east Lake and southwest Volusia Counties. Recharge rates of less than 3 inches per year were simulated in east Orange and northeast Osceola Counties. The calibrated model was used to simulate the effects of increased Floridan aquifer withdrawals in the year 2010 (542 million gallons per day) on water levels and spring flow. Projected effects were simulated for both “wet" conditions (using 1988 fixed-head arrays) and for "dry" conditions (using May 1990 fixed-head arrays), thus bracketing a potential range of effects. Relative to simulated 1988 conditions, simulated 2010 spring flow decreased by 43 cubic feet per second (14 percent) for wet conditions and by 67 cubic feet per second (22 percent) for dry conditions. Increased pumpage from the Lower Floridan aquifer accounted for about 17 cubic feet per second (40 percent) of reduced spring-flow rates. Simulated drawdowns in the Upper Floridan aquifer ranged from 10 to 20 feet in central Orange County, with a local maximum of about 30 feet at a well field in southwest Orange County About 4 to 8 feet of the drawdown simulated in central Orange Country was attributed to increased Lower Floridan aquifer pumpage. Simulated drawdowns ranged from less than 2 feet in east Seminole County to about 10 feet in the south-central part of the county. Particle-tracking simulations indicate that water discharged at Seminole, Messant, Rock, Wekiva, Miami, Sanlando, Palm and Starbuck Springs is derived largely from high-rate recharge areas in northwest Orange and east Lake Counties. Water pumped from the Cocoa well field in 1988 was captured from low-rate recharge areas in central Orange and north Osceola Counties.  Pumpage from the proposed Orange County eastern regional well field in 2010 captured much of the water in central Orange County that contributed to the Cocoa well field in 1988. As a result, the projected Cocoa well field contributing area was displaced further south, capturing more water from Osceola County and less water from Orange County The simulated flow paths and destinations of surface waters that recharge the Upper Floridan aquifer through the Lake Killarney and Lake Underhill drainage wells (2.5 and 2.1 million gallons per day, respectively) were significantly affected by increased 2010 withdrawals. About 70 percent of inflow to these wells in 1988 moved toward the northeast and was discharged in east Seminole County, either to the surficial aquifer system or to the St. Johns River In 2010, about 95 percent of the simulated inflow was captured and discharged by three Lower Floridan aquifer well fields located in north-central Orange County The remaining 5 percent was captured and discharged by two Upper Floridan aquifer well fields in north-central Orange County.


Title:
Geohydrology and Potential for Upward Movement of Saline Water in the Cocoa Well Field, East Orange County, Florida

Publication:
Open File Report # 90- .  U.S. Geological Survey. Tallahassee, Florida

Abstract:
The Floridan aquifer system, an approximately 2,000-foot thick sequence of Eoceneage limestone and dolomite, is the main source of water supply in central Florida. Hydraulic conductivity is different in strata of different lithology and is the basis for separating the aquifer system into the Upper Floridan aquifer, a middle semi-confining unit, and the Lower Floridan aquifer. The coastal city of Cocoa withdraws about 26 million gallons of water per day from the Upper Floridan aquifer from a well field in east Orange County, about 25 miles inland. About 60 million gallons per day are withdrawn from the Upper Floridan aquifer and 56 million gallons per day from the Lower Floridan aquifer in the Orlando area, about 15 miles west of the Cocoa well field. Wells drilled in the Cocoa well field from 1955-61 yielded water with chloride concentrations ranging from 25-55 milligrams per liter. Soon after the wells were put in service, chloride concentrations increased; therefore, new wells were drilled further inland. Chloride concentrations in water from many of the new wells also have increased. Possible sources of saline water are lateral movement of relict seawater in the Upper Floridan aquifer from the east, regional upconing of saline water from the Lower Floridan aquifer or underlying older rocks, or localized upward movement of saline water through fractures. Several test wells were drilled to provide information about chloride concentration changes with depth and to monitor changes with time, including a multi-zone well drilled in 1965 (well C) and two wells drilled in the 1990's (wells R and S). Chloride concentrations have increased in the zone pumped by the supply wells (the upper 500 feet of the aquifer) and in the 1,351-1,357-foot deep zone of well C, but not in the two intervening zones. This indicates that the source of saline water is located laterally, rather than vertically, from the pumped zone in the area of well C. The potential for upward movement of saline water depends on the direction of the vertical hydraulic gradient and on the vertical hydraulic conductivity of the aquifer. A series of aquifer tests was run in 1993-94 and existing water-level and water-quality data were analyzed to evaluate the potential for upward movement of saline water in the well field. The transmissivity of the upper 500 feet of the aquifer is about 100,000 feet squared per day (the horizontal hydraulic conductivity is about 200 feet per day) and the storage coefficient is about 2x10-4. Horizontal hydraulic conductivities determined from slug tests of the three deepest zones of well C ranged from 20-50 feet per day. Vertical hydraulic conductivities probably do not exceed 0.05 feet per day. The vertical hydraulic gradient is determined by comparing water levels in the various zones, but because of density differences, unadjusted water levels in the deepest zone investigated cannot be directly compared to water levels in the overlying freshwater zones. The difference between environmental water heads (adjusted for density differences) in the saline-water zone of well C and the overlying freshwater zone were calculated from measured water levels for the period 1966 to 1994. During most of this time period, the gradient was downward, indicating that saline water did not move upward. Upconing of saline water probably is not taking place in the center and western part of the well field, based on the low vertical hydraulic conductivity values estimated for the middle semi-confining unit, the generally downward vertical hydraulic gradient, and the constant chloride concentrations in the intermediate zones of well C. However, there is no information about the extent of the zone of low vertical hydraulic conductivity gradient in the eastern part of the well field. Thus, increased chloride concentrations in supply wells in the eastern part of the well field could be caused either by lateral movement of saline water from the east, or by upward movement form the Lower Floridan aquifer if the low conductivity zone is thin or breached by fractures, or by a combination of both lateral and vertical movement.


Title:
Geology, Hydrology, and Water Quality of the Surficial Aquifer System in Volusia County, Florida.

Publication:
USGS Water Resources Investigation Report No. 90-4069.  U.S. Geological Survey.  Tallahassee, Florida

Abstract:
The surficial aquifer system in Volusia County comprises Miocene to Holocene age sediments that overlie the Floridan aquifer system. The sediments consist of sand, sandy clay, shell, and calcareous silty clay, that together range in thickness from about 40 to more than 100 feet. Locally, the surficial aquifer system can be subdivided into upper and lower permeable zones separated by 5 to 10 feet of areally discontinuous clay or silty sand.
Of the recorded 4,500 wells that tap the surficial aquifer system, more than 3,200 are used for irrigation and about 800 are used for domestic supply. Water use from the surficial aquifer system in 1987 totaled about 4.2 million gallons per day. The water level can be 30 feet or more below land surface in ridge areas, but is less than 10 feet below land surface on terraces and in the interridge-area near the St. Johns River. In 1986, water levels in the upper permeable zone generally ranged 3 to 6 feet higher at the end of the wet season (fall) than in the dry season (spring). Water levels in wells tapping the lower permeable zone generally fluctuated less than 2 feet, except when influenced by pumping from the underlying Upper Floridan aquifer.

Recharge to and discharge from the surficial aquifer system is strongly influenced by heads in the underlying Upper Floridan aquifer. Important recharge areas are along the De Land Ridge and the western part of the Talbot Terrace; some recharge occurs along the Atlantic Coastal Ridge. The recharge rate in the ridge areas probably ranges from 9 to 18 inches per year, whereas in nonridge areas the rate is about 0 to 8 inches per year.

Reported laboratory hydraulic conductivities for surficial aquifer system core samples ranged from 7.6 x 10-5 to 3.4 x 10" feet per day with a median of 1.0 x 10-2 feet per day, and reported field hydraulic conductivities ranged from 3.0 x 10-2 to 12.8 feet per day with a median of 2.9 x 10-1 feet per day. The transmissivity of the lower permeable zone in Oak Hill (southeastern Volusia County), calculated from an aquifer test, is 1,200 feet squared per day, and the corresponding hydraulic conductivity is about 30 feet per day. In the Oak Hill area, pumpage from the lower permeable zone is constrained by the potential for upconing of saltwater, rather than by the hydraulic properties of the aquifer.

Chloride concentrations of water from wells tapping the upper permeable zone ranged from 1.2 to 15,000 milligrams per liter; for the lower permeable zone, the range was from 5.7 to 340 milligrams per liter. In both zones, nutrient concentrations at some sites were higher than would be expected for natural groundwater, indicating some effect from infiltrating surface water or human activity.


Title:
Hydrology of the Floridan Aquifer in Northwest Volusia County, Florida

Publication:
Open File Report # 82-108.  U.S. Geological Survey.  Tallahassee, Florida

Abstract:
The characteristics of the Floridan aquifer in northwest Volusia County and the effects of fernery irrigation withdrawals from the Floridan aquifer were studied. The large irrigational withdrawals, especially in winter months when spray irrigation is used for freeze protection, introduce problems such as the potential for saltwater intrusion, the temporary loss of water in domestic wells caused by large potentiometric drawdown, and increased sinkhole activity. Average groundwater irrigational withdrawal is 8.1 million gallons per day while peak withdrawal rate is 300 million gallons per day during freeze-protection pumpage. Transmissivities of the Floridian aquifer range from 4,500 to 163,000 feet squared per day. Highest transmissivities are in the DeLeon Springs area and the lowest are in the east Pierson area. The drawdown in the Pierson area at the end of one intense pumpage exceeded 30 feet over a 4.4 square mile area. A significant amount of the withdrawn water was replaced by leakage during the pumping period. No long-term residual drawdown has occurred. Sinkhole activity has been increased by the temporary increase in load on the aquifer 's skeletal structure during intense potentiometric drawdowns. There is no evidence of saltwater intrusion, but a monitoring network for future early detection is suggested.


Title:
Groundwater Hydrology of Volusia County, Florida, With Emphasis on Occurrence and Movement of Brackish Water

Publication:
USGS Water Resources Investigation Report No. 84-4206.  U.S. Geological Survey.  Tallahassee, Florida

Abstract:
Brackish water is present in the eastern and western fringes of Volusia County, Florida in the surficial aquifer and in the Floridan aquifer system. Average pumpage in 1980 in Volusia County was 66 million gallons per day. Water levels in the Floridan aquifer system declined more than 10 feet over an area of 70 square miles from 1955 to 1982. The annual water budget of the budget of the Floridan aquifer system consists of 5 inches downward leakage inflow, 1 inch upward leakage outflow, 1 inch horizontal inflow, 1.5 inches horizontal outflow, 2.5 inches discharge from springs and flowing wells, and 1 inch pumpage. Saltwater intrusion is occurring in the surficial aquifer on the barrier island. There is little evidence that intrusion is occurring uniformly over large areas in the Floridan aquifer system. Vertical intrusion is occurring at sites of public-supply pumping. Many of these wells in the fringes of the county have been abandoned and replaced by wells closer to the central part of the county. Minimizing well depth is probably the single most effective step against intrusion.


Author:
Schiffler, D, O’Reilly, A. and Phelps, G.

Title:
Potentiometric Surface of the Upper Floridan Aquifer in the St. Johns River Water Management District and Vicinity, Florida May 1994

Publication:
Open File Report # 94-495.  U.S. Geological Survey.  Tallahassee, Florida.

Abstract:
This map depicts the potentiometric surface of the Upper Floridan aquifer in the St. Johns River Water Management District and vicinity for May 1994. The map is based on water-level measurements made at approximately 1,000 wells and several springs. Data on the map were contoured using 5-foot contour intervals in most areas. The potentiometric surface of this karstic aquifer generally reflects land surface topography. Potentiometric surface highs often correspond to topographic highs, which are areas of surficial recharge to the Upper Floridan aquifer.  Springs within topographic lows along with areas of more diffuse upward leakage are natural zones of discharge. Municipal, agricultural, and industrial withdrawals have lowered the potentiometric surface in some areas. The potentiometric surface ranged from 125 feet above sea level in Polk County to 32 feet below sea level in Nassau County. Water levels in May 1994 generally were 0 to 3 feet lower than those measured in May 1993. Water levels in May 1994 in northeast Florida generally were 0 to 3 feet higher than in September 1993, except in the lower St. Johns River basin, where water levels were 0 to 4 feet lower than in September 1993. In the rest of the mapped area, water levels in May 1994 generally were 0 to 4 feet lower than those measured in September 1993.


Title:
Groundwater Resources of St. Johns County, Florida

Publication:
USGS Water Resources Investigation Report No. 83-4187.  U.S. Geological Survey. Tallahassee, Florida

Abstract:
The two primary sources of groundwater in St. Johns County are the surficial and Floridan aquifers. The surficial aquifer is the principal source of water supply for drinking and domestic purposes in most of the county. The Floridan aquifer is the major source of water supply for irrigation use. In most of the county, water from the Floridan aquifer does not meet drinking water standards for some characteristics. Available supplies of potable water from the surficial aquifer are adequate to meet short-term increases in demand, but future growth will require additional sources of potable water.

The surficial aquifer is present throughout the county and extends from land surface to a maximum depth of about 120 feet. The aquifer is recharged primarily by rainfall and in some areas by infiltrating irrigation water withdrawn from the Floridan aquifer.

The Floridan aquifer underlies the county at a depth of about 90 to more than 360 feet below sea level. Recharge to the aquifer is almost entirely from the lake region in Alachua, southwestern Clay, eastern Bradford, and western Putnam Counties. Discharge is from springs, from wells used for irrigation, and by upward leakage.

Withdrawal of large quantities of water from the Floridan aquifer has caused declines in the potentiometric surface. During the spring, when withdrawal is heaviest and rainfall is lightest, the potentiometric surface is lowered an average of about 5 feet throughout the county and a maximum of about 15 feet in the agricultural areas. Comparison of predevelopment water levels with 1980 water levels indicates that withdrawals of water for irrigation and public supply have lowered the potentiometric surface about 10 to 20 feet throughout most of the county.

Water from the surficial aquifer generally meets most of the secondary drinking water quality standards in most of the county and is satisfactory for most uses. Concentrations of sulfate and chloride generally do not exceed 250 milligrams per liter in St. Johns County, and only in a small part of the county do dissolved-solids concentrations exceed 500 milligrams per liter. Iron concentrations commonly exceed 0.3 milligrams per liter.

In most of St. Johns County, water from the Floridan aquifer is more saline than water from the surficial aquifer. Variations in the concentrations of chemical constituents occur both areally and with depth. Highly saline water is present in the upper part of the aquifer in most of the southern part of the county.

The presence of saline water and the dissolution of gypsum and anhydrite are the primary factors that govern water quality in the aquifer. In the southwest part of the county, intensive pumpage for irrigation has resulted in substantial increases in chloride concentration caused primarily from the upconing of more saline water.


Title:
Estimated Natural Discharge and Chemical-Constituent Loading from the Upper Floridan Aquifer to the Lower St. Johns River, Northeastern Florida, 1990-91.

Publication:
USGS Water Resources Investigation Report No. 94-4132.  U.S. Geological Survey.  Tallahassee, Florida

Abstract:
The lower St. Johns River, a 101-mile long segment of the St. Johns River, begins at the confluence of the Ocklawaha River and ends where the river discharges into the Atlantic Ocean at Mayport. The St. Johns River is affected by tides as far upstream as Lake George, 106 miles from the mouth. Saltwater from the ocean advances inland during each incoming tide and recedes during each outgoing tide. The chemical quality of the lower St. Johns River is highly variable primarily because of the inflow of saltwater from the ocean, and in some areas, from the discharge of mineralized groundwater.

Three hydrogeologic units are present in the study area: the surficial. aquifer system, the intermediate confining unit, and the Floridan aquifer system. The surficial aquifer system overlies the intermediate confining unit and consists of deposits containing sand, clay, shell, and some limestone and dolomite. The intermediate confining unit underlies all of the study area and retards the vertical movement of water between the surficial aquifer system and the Floridan aquifer system. The intermediate confining unit consists of beds of relatively low permeability sediments that vary in thickness and areal extent and can be breached by sinkholes, fractures, and other openings. The Floridan aquifer system primarily consists of limestone and dolomite.

The quality of water in the Upper Floridan aquifer varies throughout the study area. Dissolved solids in water range from about 100 tomore than 5,000 milligrams per liter. Chloride and sulfate concentrations in water from the Upper Floridan aquifer range from about 4 to 3,700 milligrams per liter and from 1 to 1,300 milligrams per liter, respectively.

The rate of leakage through the intermediate confining unit is controlled by the leakance coefficient of the intermediate confining unit and by the head difference between the Upper Floridan aquifer and the surficial aquifer system. The total groundwater discharge from the Upper Floridan aquifer to the St. Johns River within the lower St. Johns River drainage basin, based on the potentiometric surface of the Upper Floridan aquifer in September 1990, was estimated to be 86 cubic feet per second. Total estimated groundwater discharge to the lower St. Johns River in September 1991, when heads in the Upper Floridan aquifer averaged about 4 feet higher than in 1990, was 133 cubic feet per second.

The load of dissolved solids that discharged from the Upper Floridan aquifer into the lower St. Johns River on the basis of September 1990 heads is estimated to be 47,000 tons per year. Estimated chloride and sulfate loads are 18,000 and 9,500 tons per year, respectively. Dissolved solids, chloride, and sulfate loads discharging into the lower St. Johns River are estimated to be 81,000, 39,000, and 15,000 tons per year, respectively, on the basis of September 1991 heads.


Title:
Computer Simulation of the Predevelopment and Current Floridan Aquifer System in Northeast Florida.

Publication:
Technical Publication SJ 91-4.  St. Johns River Water Management District. Palatka, Florida.

Abstract:
The primary objective of this research was to develop a finite-difference groundwater flow model that could be used to predict the response of the Floridan aquifer system of the Jacksonville area of northeast Florida to various pumping scenarios. The study area includes parts of Duval, St. Johns, Nassau, Clay, and Putnam counties, as well as a sizable area in the Atlantic Ocean. This research was submitted as a thesis for a masters degree in engineering at the University of Florida

The model used was the modular, three-dimensional, finite-difference, groundwater flow model (MODFLOW) developed by M.G. McDonald and A. W. Harbaugh of the U.S. Geological Survey (USGS). The predevelopment (prior to 1880) and current Floridan aquifer systems were modeled as steady-state systems consisting of three aquifer layers (the surficial aquifer system, the Upper Floridan aquifer, and the Lower Floridan aquifer) separated by three confining-unit layers (the upper confining unit, the middle confining unit, and the lower confining unit).

The overall calibration process consisted of two phases. The predevelopment flow model was initially calibrated using a USGS predevelopment potentiometric surface map. Using the distributions of leakance and transmissivity that resulted from the predevelopment calibration as starting values, the current-system model was calibrated using the May 1985 potentiometric surface map. The distributions of leakance and transmissivity that resulted from the current-system calibration were taken as final and best estimates; they were then used to construct a new, presumably more accurate predevelopment flow model, the modified predevelopment flow model.

Comparison of results from the current-system and modified predevelopment models indicates that areas of high leakance in the middle confining-unit that separates the Upper and Lower Floridan aquifers suggest that in parts of the study area the Upper and Lower Floridan aquifers are hydraulically well connected. Two such areas were identified in the current-system model calibration in the north-central and south-central areas of the study area. Relatively little downward leakage from the surficial aquifer system to the Floridan aquifer system actually occurs within the study area; by far the most inflow to the Floridan aquifer system occurs as upward leakage from the Lower Floridan aquifer and lateral flow through the western boundary of the study area.

A mass balance analysis of the Upper Floridan aquifer based on results of the model of the current flow system indicates that approximately 2.5 in of flow per year currently enter the Upper Floridan aquifer from several different sources. About 98 percent of all flow entering the entire Floridan aquifer system in the study area eventually enters the Upper Floridan aquifer. Model results indicate that of the flow sources, the Lower Floridan aquifer is the greatest contributor, supplying about 63 percent of the total yearly recharge to the Upper Floridan aquifer. Lateral flow through the western boundary of the study area accounts for approximately 29 percent of the recharge to the Upper Floridan aquifer, according to the model simulation, while the surficial aquifer system contributes approximately 7.5 percent of the total inflow to the Upper Floridan aquifer of the study area. Lateral flow across the eastern and southern boundaries occurs in only negligible amounts, according to the model results, accounting for less than 1 percent of the total inflow to the Upper Floridan aquifer.

The model indicates that groundwater withdrawals from the Upper Floridan aquifer of the study area have brought about significant changes in the rates of recharge to and discharge from the Floridan aquifer. Model results indicate that the Lower Floridan aquifer now contributes more than twice the amount of flow to the Upper Floridan aquifer that it contributed in predevelopment times. Proportionally, its contribution has increased from approximately 50 percent of the total inflow to the Upper Floridan aquifer to approximately 63 percent, indicating that its importance in the overall flow system has increased.

Since predevelopment times, lowering of the potentiometric surface of the Upper Floridan aquifer (by an average of approximately 25 ft) relative to the water table has affected rates of recharge and discharge of the Upper Floridan aquifer within the study area. Upward leakage from the Upper Floridan aquifer to the surficial aquifer system has decreased both absolutely and proportionally, according to simulations of the modified predevelopment and current-system models, while downward leakage from the surficial aquifer system into the Upper Floridan aquifer has increased absolutely but has decreased somewhat proportionally.

The average transmissivity of the Upper Floridan aquifer is 148,000 ft2/d. The average transmissivity of the Lower Floridan aquifer is greater than that of the Upper Floridan aquifer, 230,000 ft/d, according to the results of the calibration of the current system model. Possible reasons for this are that the Lower Floridan aquifer is about twice as thick as the Upper Floridan aquifer throughout most of the study area and that a zone of high transmissivity, the Fernandina permeable zone, exists in the Lower Floridan aquifer of the study area and contributes to higher average transmissivities there.

The model calibrations indicate that more data is needed describing pumping rates, the potentiometric surface of the Lower Floridan aquifer, and the elevation of the water table within the study area.


Title:
MODVIEW Version 1.0: A Graphical-Kernel-System Program for Evaluating Modflow Data

Publication:
Technical Publication SJ 94-6.  St. Johns River Water Management District.  Palatka, Florida

Abstract:
MODVIEW Version 1.0 is a Graphical-Kernel-System program that enables datasets; arranged in the format of a two-dimensional array (i.e., sets of related numbers arranged in a format of rows and columns) to be viewed as colored patterns of numerical ranges. The St. Johns River Water Management District extensively uses the U.S. Geological Survey model MODFLOW (a groundwater flow model) in performing groundwater studies. MODFLOW input and output data files consist largely of two-dimensional arrays. These types of arrays are used in MODFLOW to represent spatially distributed values of hydraulic parameters such as transmissivity, leakance, and hydraulic head. MODVIEW is intended primarily to provide a convenient means of viewing MODFLOW datasets and thus to make calibrating and evaluating MODFLOW groundwater flow models more efficient.

MODVIEW screen output consists of three types of displays: (1) a primary display, (2) subarea displays, and (3) zoom-reference displays. The primary display shows the entire model grid. Subarea displays show enlargements of specified subareas of the model grid. Zoom-reference displays show the position of a zoomed subarea with respect to the entire model grid.

MODVIEW will run on IBM-compatible personal computers equipped with EGA, VGA, or SVGA color graphics cards and color monitors. Hard-copy plots of MODVIEW output can be produced with the use of screen capture programs such as Pizzaz Plus. Screen-capture programs enable MODVIEW output to be produced in black and white or in color. Output can be printed on dot-matrix, laser, or color printers


Title:
Finite-Difference Simulation of the Floridan Aquifer System in Northeast Florida and Camden County, Georgia

Publication:
Technical Publication SJ 97-2. St. Johns River Water Management District.  Palatka, Florida

Abstract:
This study was performed in support of the Water Supply Needs and Sources Assessment of St. Johns River Water Management District. As such, the primary objective was to predict changes in hydraulic-head levels in the Floridan aquifer system of the study area that will occur in response to projected increases in groundwater withdrawals between 1985 and 2010. The study area included parts of northeast Florida and Camden County, Georgia. Another objective was to enhance the understanding of interactions that occur between the aquifers within the Floridan aquifer system and between the Floridan aquifer system and the overlying surficial aquifer system. A further objective was to improve estimates of the hydraulic properties of the Floridan aquifer system and of the overlying upper confining unit. Groundwater flow models of, the predevelopment (prior to 1880) and post-development (1985) Floridan aquifer system in northeast Florida and Camden County, Georgia, were developed to fulfill this objective.

The study area includes parts of Duval, Clay, St. Johns, and Nassau counties, Florida; Camden County, Georgia; and a sizable offshore area in the Atlantic Ocean. It lies between longitudes 81º7' and 81º52' west and latitudes 29º51' and 31º2' north and encompasses approximately 3,660 square miles.

In descending order, the groundwater system of the study area consists of a surficial aquifer system, an intermediate aquifer system, and the Floridan aquifer system. The surficial aquifer system is separated from the Floridan aquifer system by the upper confining unit, which consists of the Hawthorn Group and overlying Pliocene deposits. The intermediate aquifer system is contained in the upper confining unit.

The Floridan aquifer system has been differentiated into three aquifers separated by two semiconfining units. These are, from top to bottom, the Upper Floridan aquifer, the middle semiconfining unit, the Lower Floridan aquifer, the lower semiconfining unit, and the Fernandina permeable zone. The Floridan aquifer system is bounded at its base by a lower confining unit that consists of low permeability anhydrite beds.

Three models were developed as a result of the study: the predevelopment, post-development, and revised predevelopment flow models. The predevelopment flow model is a model of the Floridan aquifer system within the study area prior to the onset of significant groundwater withdrawals. The post-development flow model is a model of the Floridan aquifer system under 1985 pumping conditions. The revised predevelopment flow model is a modified version of the original predevelopment flow model. The model code selected for use is the modular three-dimensional finite-difference groundwater flow model (MODFLOW).

The calibration of the predevelopment flow model served as a precursor to the calibration of the post-development flow model. The hydraulic parameters derived from the calibration of the predevelopment flow model were used as initial values in the calibration of the post-development and revised predevelopment flow models.

All three models represent groundwater flow conditions as being constant with respect to time (i.e., steady state). All three models consist of four aquifer layers and four semiconfining unit layers. In descending order, the layers represent the surficial aquifer system (aquifer layer 1), the upper confining unit (semiconfining unit layer 1), the Upper Floridan aquifer (aquifer layer 2), the middle semiconfining unit (semiconfining unit layer 2), the Lower Floridan aquifer (aquifer layer 3), the lower semiconfining unit (semiconfining unit layer 3), the Fernandina permeable zone (aquifer layer 4), and the lower confining unit (semiconfining unit layer 4).

The results of predictive simulations performed using the post-development flow model indicate that by the year 2010, the potentiometric surface of the Upper Floridan aquifer will decline approximately 0-5 ft relative to 1985 water levels throughout most of the study area due to projected increases in withdrawals from wells. In parts of the southern half of the study area, the potentiometric surface of the Upper Floridan aquifer will decline approximately 5-20 ft relative to 1985 water levels, also due to projected increases in withdrawals from wells. In the area of Fernandina Beach, levels of hydraulic head will increase approximately 0-10 ft relative to 1985 levels due to projected decreases in withdrawals from wells. The total of the projected 2010 withdrawal rates is 330 million gallons per day, an increase of approximately 44% over the total of the estimated 1985 withdrawal rates.  Additionally, the results of the study indicate that the transmissivity of the Lower Floridan aquifer is considerably higher on average than that of the Upper Floridan aquifer and that upward leakage from the Lower Floridan aquifer accounts for a significant proportion of the total recharge to the Upper Floridan aquifer within the study area (59%). The results of the study indicate that a significantly greater quantity of groundwater flows through the Lower Floridan aquifer than through the Upper Floridan aquifer or the Fernandina permeable zone (1-68 inches per year [in/yr] versus 1.25 and 0.13 in/yr, respectively).

The study results show that withdrawals from wells account for approximately 65% and 30%, respectively, of the total discharge from the Upper and Lower Floridan aquifers and have resulted in significant changes in the Floridan aquifer system since predevelopment times. Levels of hydraulic head in the Upper Floridan aquifer have declined by an average of approximately 25 ft within the study area. The quantity of groundwater moving through the Upper and Lower Floridan aquifers and the Fernandina permeable zone has increased significantly. Discharge from the Floridan aquifer system to the surficial aquifer system has decreased significantly since predevelopment times (0.52 in/yr in the predevelopment system versus 0.28 in/yr in the post-development system). Likewise, recharge to the Floridan aquifer system from the surficial aquifer system has increased significantly since predevelopment times (0.09 in/yr in the predevelopment system versus 0.15 in/yr in the post-development system).


Title:
Estimates of Regional Drawdowns in the Potentiometric Surface of the Upper Floridan Aquifer of Northeast Florida Using a Numerical Drawdown Model.

Publication:
Technical Publication SJ 2000-4.  St. Johns District Water Management District.  Palatka, Florida

Abstract:
A primary objective of the 1998 Water Supply Assessment of the St. Johns River Water Management District (SJRWMD) was to estimate regional drawdowns in the potentiometric surface of the Upper Floridan aquifer in response to projected changes in withdrawals of water from wells in the period of 1995 through 2020 (Vergara 1998). To this end, the Floridan aquifer system of northeast Florida was simulated using a regional, numerical drawdown model. The term "drawdown model,"' as used herein, refers to a type of groundwater model in which changes in water levels, as opposed to absolute water levels, are determined in response to changes in well-withdrawal rates. The term "flow model," as used herein, refers to a type of groundwater model in which absolute water levels resulting from various features of the groundwater system are determined.

The drawdown model of the present study is based on a regional groundwater flow model of the Floridan aquifer system in northeast Florida. The regional groundwater flow model on which the drawdown model is based is a revision of the regional groundwater flow model of Durden (1997). Thus, the present study involved the use of three different groundwater models: (1) the original model of Durden (1997), referred to as the original groundwater flow model; (2) a groundwater flow model resulting from revisions to the original groundwater flow model, referred to as the revised groundwater flow model; and (3) the regional drawdown model, referred to simply as the drawdown model. All three of the models of the present study are applications of the U.S. Geological Survey groundwater modeling code MODFLOW (McDonald and Harbaugh 1988). 

The revised groundwater flow model differs from the original groundwater flow model primarily with respect to its lateral boundary conditions. In the revised groundwater flow model, the lateral boundary conditions consist almost entirely of general-head boundary (GHB) conditions, the MODFLOW implementation of the head-dependent flux boundary. In the original groundwater flow model, however, the lateral boundary conditions consist of a combination of GHB conditions and no flow boundary conditions. The other difference between the two models lies in the estimates of VCONT used to represent the vertical permeability of the intermediate semiconfining unit (which separates the Upper Floridan aquifer and the overlying surficial aquifer system). In the revised groundwater flow model, the VCONT estimates in the areas of the Atlantic Coastal Ridge in central St. Johns County and Center Park Ridge in east-central Duval County were reduced somewhat.

Four different simulations were performed as part of the study. In each of these simulations, the objective was to assess changes in the elevations of the potentiometric surface of the Upper Floridan aquifer and the water table of the surficial aquifer system in response to projected changes in rates and/or locations of well withdrawals. The time period of interest was 1995 through 2020. The four simulations are described as follows:

1.  A simulation of the effects of projected changes in all significant municipal, commercial/industrial, and thermoelectric use withdrawals. In the present context, a "significant" withdrawal is, generally, a withdrawal of at least 100,000 gallons per day.

2.  A simulation of the effects of projected changes in withdrawals of JEA only.

3.  A simulation of the effects of projected changes in JEA withdrawals only but with all JEA wells that extend into the upper zone of the Lower Floridan aquifer in the JEA southgrid area "backplugged" to the Upper Floridan aquifer.

4.  A simulation of the effects of projected changes in coastal area withdrawals only, excluding the effects of changes in JEA withdrawals. The coastal area of concern in this case is the Atlantic coast between St. Augustine and Mayport. This area extends about 10 miles inland in St. Johns County and about 2 miles inland in Duval County.

The most significant advantage of using the drawdown model in lieu of the revised groundwater flow model lies in the representation of well withdrawals as differences in rates rather than as absolute rates of withdrawals. Because of this method of representation, withdrawals that are not expected to change are not included in a drawdown model, regardless of their absolute magnitudes. Thus, representation of withdrawals that fall within the categories of agricultural irrigation, golf course irrigation, and domestic self-supply were not represented in the drawdown model because rates of withdrawals within these categories of water use are not expected to change significantly between 1995 and 2020.


Title:
Approximation of Relative Contributions of Various Entities to the Overall Drawdown in the Upper Floridan Aquifer of the Potato-Growing Region in St. Johns and Putnam Counties, Florida.

Publication:
SJRWMD Professional Paper Publication SJ 2000-PP1.  St. Johns River Water Management District.  Palatka, Florida

Abstract:
The Floridan aquifer system is the primary source of potable water in east Putnam and southwest St. Johns counties. Major uses of water from the Floridan aquifer system in this area include paper and electricity production, potato irrigation, and domestic self-supply. During the potato irrigation season, which occurs annually from March 1 through May 31, the area experiences the temporary disablement of domestic self-supply wells due to temporary, large drawdowns in the potentiometric surface of the Upper Floridan aquifer. In this study, an analytical groundwater flow model (Motz 1978) was used to estimate the relative contributions of various water users to drawdowns in the potentiometric surface of the Upper Floridan aquifer of east Putnam and southwest St. Johns counties during the potato irrigation season. The water users included in the analysis were the Georgia-Pacific Corporation paper mill in Putnam County, the Seminole Electric Cooperative power plant in Putnam County, and the potato farms of Putnam, St. Johns, and Flagler counties.

The analytical groundwater flow model employed in the study was that of Motz (1978). It represents a steady-state, coupled aquifer system consisting of an underlying semiconfined aquifer from which water is withdrawn by a fully penetrating well, an overlying unconfined aquifer, and an intervening semiconfining unit. The aquifer system is represented as homogeneous and isotropic. The drawdown in the unconfined aquifer occurs as a result of induced leakage across the semiconfining unit. In this study, the semiconfined aquifer of the Motz (1978) model corresponds to the Upper Floridan aquifer, the semiconfining unit corresponds to the intermediate semiconfining unit, and the unconfined aquifer corresponds to the surficial aquifer system. The portion of the Floridan aquifer system that lies below the Upper Floridan aquifer is not represented in this study. A FORTRAN implementation of the Motz (1978) model that enables the determination of cumulative drawdowns due to withdrawals from more than one well was used.

The estimated average withdrawal rate from the Upper Floridan aquifer per potato irrigation well was determined to be approximately 178,000 gallons per day (gpd) during the potato irrigation season. Given a total of 726 such wells within the study area, the total average withdrawal rate of all potato irrigation wells was estimated to be approximately 129 million gallons per day (mgd) during the potato irrigation season. The estimated average daily withdrawal rate from the Upper Floridan aquifer for the wells operated by Georgia-Pacific Corporation was determined to be approximately 13 mgd from March through May, 1997. The estimated average daily withdrawal rate from the Upper Floridan aquifer for the two wells operated by Seminole Electric Cooperative was determined to be approximately 480,000 gpd in 1997.

The transmissivity estimate used to represent the permeability of the Upper Floridan aquifer in the model was 60,000 square feet per day (feld). The leakance estimate used to represent the vertical permeability of the intermediate semiconfining unit was 1.0 x 10' per day. The transmissivity estimate used to represent the permeability of the surficial aquifer system was 1,000 feld. The estimate of the evapotranspiration reduction coefficient used in the model was 2.66 x 10' per day.

The simulated drawdowns in the potentiometric surface of the Upper Floridan aquifer due to potato irrigation range up to approximately 27 feet (ft). The affected area includes most of St. Johns County, northeast Putnam County, southeast Clay County, and northwest Flagler County. The simulated drawdowns in the potentiometric surface of the Upper Floridan aquifer due to withdrawals by Georgia Pacific Corporation range up to approximately 9 ft. The affected area includes northern Putnam and southern Clay counties. The simulated drawdown in the potentiometric surface of the Upper Floridan aquifer due to withdrawals made by Seminole Electric Cooperative range up to approximately 0.5 ft. The affected area includes northeast Putnam County only.

Primarily, the results of the study indicate that drawdowns in the potentiometric surface of the Upper Floridan aquifer due to withdrawals for potato irrigation are the greatest component of the overall drawdown from March through May. The drawdowns due to the withdrawals made by Georgia-Pacific Corporation are significant, but are considerably smaller. The drawdowns due to withdrawals made by Seminole Electric Cooperative are insignificant as compared to the drawdowns attributable to the other two subjects of the study.


Title:
Recharge-Discharge Relationships in the Floridan Aquifer System in Northeast Florida

Publication:
Proceedings. Ntl. Symposium on the Future Availability of Groundwater Resources, 1992. American Water Resources Association. Bethesda, Maryland

Abstract:
The Floridan aquifer system in southern Duval, Clay, and northern St. Johns counties, Florida, consists of three aquifers separated by two intervening semiconfining units. The uppermost of these aquifers, the Upper Floridan aquifer, is overlain by an upper confining unit, which, in turn, is overlain by a regional surficial aquifer system. Maps of the potentiometric surface of the Upper Floridan aquifer consistently show a potentiometric high that is centered on the county line between Duval and St. Johns counties. The potentiometric surface of the Upper Floridan aquifer is above the water table of the surficial aquifer system throughout most of the area encompassed by this high. A hypothesis that the underlying Lower Floridan aquifer is the primary source of recharge for the Upper Floridan aquifer within this area has been incorporated into a numerical groundwater flow model. The primary source of recharge for the underlying Lower Floridan aquifer is the Keystone Heights recharge area located west of the St. Johns River according to this hypothesis.


Author:
Charm, W.B., Nesteroff, W.D., and Valdes, S.

Title:
Detailed Stratigraphic Description of the JOIDES Cores on the Continental Margin of Florida.

Publication:
Geological Survey Professional Paper 581-D.  Prepared by the U.S. Geological Survey. Washington, D.C.

Abstract:
A total of 513 meters of core was recovered from six holes drilled into the continental. shelf, the Florida-Hatteras Slope, and the Blake Plateau off the east coast of Florida. From every 76 centimeters of core, a sample was taken for petrologic examination and for determination of the calcium carbonate and the percent coarser than 62 microns.

Limestones, sands, silts, and clays, presumably of shallow water origin, make up the Eocene and younger sediments that lie beneath the continental shelf east of Jacksonville, Florida. The upper Eocene and Oligocene sediments thicken slightly toward the edge of the shelf.

Alternating layers of clay and limestone were deposited on the Florida-Hatteras Slope during the Eocene and Oligocene Epochs. Since the Miocene (Miocene sediments are absent), they have been covered by a clay that grades upward into a sand.

Foraminiferal oozes and silts have prevailed since the Eocene on the Blake Plateau.


Author:
Johnston, R., Bush, P, Krauss, R., Miller, J. and Sprinkle, C.

Title:
Summary of Hydrologic Testing in Tertiary Limestone Aquifer, Tenneco Offshore Exploration Well—Atlantic OCS, Lease-Bock 427, (Jacksonville NH 17-5)

Publication:
Water Resources Investigation Report 80-558.  Prepared by the U.S. Geological Survey. Tallahassee, Florida

Abstract:
A summary of hydrologic testing in an offshore oil-test well drilled for Tenneco, Inc. 55 miles east of Fernandina Beach, Florida, is presented. The interval tested (1,050 to 1,070 feet below sea level) is in a calcarenite that is equivalent to the Ocala Limestone (late Eocene) of onshore Florida and South Georgia. At this site the Ocala forms the highly productive Tertiary limestone aquifer system of the southeastern United States. Pressure-head measurements indicate an equivalent freshwater head of 24 to 29 feet above sea level. These pressure-head measurements and an earlier one made in the nearby JOIDES J-1 hole are the only hydraulic head determinations to date in the offshore extensions of any of the aquifers underlying the Atlantic coastal plain.

A drill-stem test recovered water samples containing about 7,000 milligrams per liter chloride. However, seawater used in the drilling process apparently contaminated the samples and the formation water is considered slightly fresher.

The head and salinity data from the Tenneco well suggest that the sampled interval lies in the transition zone between fresh and seawater in the limestone aquifer. These data, when viewed with similar data from JOIDES J-1, show the transition zone to slope very slightly landward. Heads at both wells are compatible with the onshore flow system as it existed prior to development.


Publication:
U.S. Geological Survey Water Supply Paper 2180.  Prepared by the U.S. Geological Survey. Washington, D.C.


