Hydrochemistry of the Surficial and Intermediate Aquifer Systems in Florida By Marian P. Berndt and Brian G. Katz U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 91-4186 Prepared in cooperation with the FLORIDA DEPARTMENT OF ENVIRONMENTAL REGULATION Tallahassee, Florida 1992 U.S. DEPARTMENT OF THE INTERIOR MANUEL LUJAN, JR., Secretary U.S. GEOLOGICAL SURVEY DALLAS L. PECK, Director For additional information, Copies of this report may be write to: purchased from: District Chief U.S. Geological Survey U.S. Geological Survey Books and Open-File Reports Section Suite 3015 Federal Center 227 North Bronough Street Box 25425 Tallahassee, Florida 32301 Denver, Colorado 80225 CONTENTS Abstract 1 Introduction 1 Purpose and scope 2 Previous investigations 2 Methods 3 Surficial aquifer system 4 Hydrogeology 4 Hydrochemistry 6 Intermediate aquifer system 8 Hydrogeology 8 Hydrochemistry 11 Northeastern Florida 12 Panhandle area of Florida 12 Southwestern Florida 12 Factors affecting hydrochemistry of the intermediate aquifer system 14 Downward leakage from the surficial aquifer system 17 Upward leakage from the Upper Floridan aquifer 21 Summary and conclusions 22 References cited 22 Figure 1. Map showing locations of principal counties using water from the surficial aquifer system for public supply and domestic self-supplied use 5 2. Map showing locations of monitoring wells and dominant-ion water types in samples from wells tapping the surficial aquifer system 9 3. Graph showing distribution of dominant-ion water types in the surficial aquifer system and dissolved-solids concentration in ground-water samples as a function of depth of well 10 4. Graphical summary showing concentrations of selected constituents in the surficial aquifer system 11 5. Map showing locations of monitoring wells and dominant-ion water types in samples from wells tapping the intermediate aquifer system in northeastern Florida 12 6. Graphical summary showing concentrations of selected constituents in the intermediate aquifer system in northeastern Florida 13 7. Map showing locations of monitoring wells and dominant-ion water types in samples from wells tapping the intermediate aquifer system in the panhandle area of Florida 13 8. Graphical summary showing concentrations of selected constituents in the intermediate aquifer system in the panhandle area of Florida 14 9. Map showing locations of monitoring wells and dominant-ion water types in samples from wells tapping the intermediate aquifer system in southwestern Florida 15 10. Graphical summary showing concentrations of selected constituents in the intermediate aquifer system in southwestern Florida 16 11. Map showing locations of Areas I and II in southwestern Florida 17 12. Trilinear diagrams showing median-ion composition for water types in the aquifers in Area I 19 Contents III 13. Trilinear diagrams showing median-ion composition for water types in the aquifers in Area II 19 14. Graphical summaries showing calcium concentrations in water from aquifers in Areas I and II in southwestern Florida 20 15. Graphical summaries showing bicarbonate concentrations in water from aquifers in Areas I and II in southwestern Florida 20 Table 1. Water withdrawals in 1987 from the surficial aquifer system for public supply and for domestic self-supplied use in counties of major use 6 2. Geologic and hydrogeologic units in southwestern Florida 7 3. Ranges in concentration of selected constituents in precipitation from six sites in Florida 8 4. Median values or concentrations of major ions, pH, and temperature, logarithm of partial pressure of carbon dioxide, and saturation indices of selected minerals in the major aquifer systems in Areas I and II in southwestern Florida 18 Contents IV Conversion Factors, Vertical Datum, Abbreviated Water-Quality Units, and Acronyms Multiply By To obtain cubic foot (ft3) 0.00283 cubic meter cubic foot per day (ft3/d) 0.00283 cubic meter per day cubic foot per day per 0.0929 cubic meter per day per square foot times foot square meter times meter of aquifer thickness of aquifer thickness [(ft3/d)/ft2]ft foot (ft) 0.3048 meter million gallons per day 0.0438 cubic meter per second (Mgal/d) square foot (ft2) 0.0929 square meter inch per year (in/yr) 25.4 millimeter per year Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: °C = 5/9 x (°F-32). Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929) a geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929. Abbreviated water-quality units: mg/L milligrams per liter meq/L milliequivalents per liter Acronyms: CBE Charge-balance error FGWQMN Florida Ground Water Quality Monitoring Network IAP Ion activity product Log PCC>2 Logarithm of partial pressure of carbon dioxide WATSTORE National Water-Data Storage and Retrieval System SI Saturation index KT Thermodynamic equilibrium constant Contents Hydrochemistry of the Surficial and Intermediate Aquifer Systems in Florida By Marian P. Berndt and Brian G. Katz ABSTRACT supplies most of the ground water used. The surficial and intermediate aquifer systems supplied 12 percent of the Hydrochemistry of the surficial and intermediate ground water withdrawn for public-supply use in Florida in aquifer systems in Florida reflects the lithology and miner­ 1985 (Marella, 1988, p. 16). In addition, domestic self- alogy of units within each aquifer and sources of water to supplied users throughout the State also rely on aquifer each aquifer. The surficial aquifer system consists of sand, systems overlying the Floridan aquifer system because suffi­ sandstone, clay, limestone, and shell units that are cient quantities of water can be obtained without the cost of recharged primarily by precipitation. Calcium bicarbonate installing deep wells. Public-supply water represents water was the major-ion water type for 53 percent of the surficial supplied by utilities for domestic and other uses and domestic aquifer determinations; a mixed water type (no dominant self-supplied water represents water from individual domestic ions) accounted for 37 percent of the determinations. The median dissolved-solids concentration for the surficial wells or supplied by utilities serving fewer than 400 people; aquifer system was 341 milligrams per liter. both are sources of drinking water. The intermediate aquifer system consists of limestone, The surficial aquifer system is predominantly used for dolomite, sand, and sandstone, and sources of water public supply in southwestern and eastern Florida. Some include downward leakage from the surficial aquifer counties in southwestern Florida rely on the surficial aquifer system and, in some areas, upward leakage from the Upper system as a primary water-supply source. The aquifer system Floridan aquifer. In northeastern and panhandle areas of contains highly permeable sediments in some areas and is up Florida, water from the intermediate aquifer system had to 400 feet thick in parts of the State. Because this aquifer major-ion and dissolved-solids concentrations similar to system is contiguous with the land surface and its water is water from the surficial aquifer system. In southwestern generally unconfined or semiconfined, it is particularly Florida, the water type in 67 percent of analyses was vulnerable to local contamination from surface sources. In mixed, and the median dissolved-solids concentration was 642 milligrams per liter. In a northern area of southwestern coastal areas, the surficial aquifer system is also affected by Florida, hydrochemistry in the limestone aquifer of the saltwater intrusion. intermediate aquifer system is similar to downward leakage The area of principal use of the intermediate aquifer from the surficial aquifer system. In a southern area, down­ system is in southwestern Florida. Charlotte, Collier, Glades, ward leakage from the surficial aquifer system has calcium Hendry, and Lee Counties withdraw most of their public- and bicarbonate concentrations five times higher than in supply water from this aquifer system because the underlying the northern area, and upward leakage from the Upper Floridan aquifer system in these areas contains nonpotable Floridan aquifer contains sodium chloride type water from water. In other parts of southwestern Florida, water-supply mixing with seawater. In southern southwest Florida, both wells are commonly open to both the intermediate and the the limestone aquifer and the overlying sandstone aquifer within the intermediate aquifer system had higher calcium, Floridan aquifer systems (Lewelling, 1988). Several other sodium, chloride, and bicarbonate concentrations than the adjacent counties also rely on the intermediate aquifer limestone aquifer in northern southwest Florida. system, mostly for agricultural irrigation. Recent population growth in coastal areas and increased agricultural activity in rural areas have increased ground-water withdrawals in INTRODUCTION southwestern Florida. Sometimes this water is unsuitable for most uses; some communities in coastal, southwestern Florida The surficial and intermediate aquifer systems in Florida treat water withdrawn from this aquifer system for public are the primary sources of ground-water supplies in areas supply (Dykes and Conlon, 1989; Marella, 1990). where the underlying Floridan aquifer system contains Deterioration in water quality may occur in the nonpotable water or is too deep