Quality of Ground Water in the 

Biscayne Aquifer in Miami-Dade, 

Broward, and Palm Beach Counties, 

Florida, 1996-1998, with Emphasis 

on Contaminants

By Anne Bradner, Benjamin F. McPherson, Ronald L. Miller, George Kish, 

and Bruce Bernard

Open-File Report 2004-1438

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2005

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

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Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Bradner, Anne, and others, 2005, Quality of Ground Water in the Biscayne Aquifer in Miami-Dade, Broward, and 

Palm Beach Counties, Florida, 1996-1998, with Emphasis on Contaminants: U.S. Geological Survey Open-File 

Report 2004-1438, 20 p.
iii

Contents

Abstract .......................................................................................................................................................... 1

Introduction ................................................................................................................................................... 1

Purpose and Scope ............................................................................................................................. 3

Hydrogeology ....................................................................................................................................... 4

Background Water Quality ................................................................................................................. 5

Study Procedures ......................................................................................................................................... 5

Site Selection ....................................................................................................................................... 6

Sampling Protocols ............................................................................................................................. 6

Water Quality ................................................................................................................................................. 8

Water pH, Dissolved Oxygen, and Major Ions ................................................................................ 8

Selected Trace Elements, Radon, and Carbon ................................................................................ 8

Nutrients .............................................................................................................................................. 10

Pesticides ............................................................................................................................................ 10

Volatile Organic Compounds ............................................................................................................ 11

Summary ...................................................................................................................................................... 15

References ................................................................................................................................................... 18

Figures

1. Map showing locations of study area, land use, and wells sampled in 

southeastern Florida ....................................................................................................................... 2

2. Photo showing urban sprawl adjacent to the Florida Everglades, Broward 

County, Florida ................................................................................................................................ 3

3-5. Maps showing—

3. Location and depth of Biscayne aquifer, and area of saltwater intrusion 

into the Biscayne aquifer ..................................................................................................... 4

4. Location of public-supply wells sampled ................................................................................... 6

5. Location of monitoring and reference wells sampled .............................................................. 7

6. Graph showing pesticides detected in samples from the public-supply and monitoring 

wells in the Biscayne aquifer ..................................................................................................... 11

7. Maps showing regional patterns of occurrence of the pesticides (a) fenuron, (b) diuron, 

(c) metolachlor, and (d) simazine detected in samples from public-supply wells in 

the Biscayne aquifer .................................................................................................................... 13

8. Graph showing the most common volatile organic compounds detected in the 

Biscayne aquifer .......................................................................................................................... 15

9. Map showing regional patterns of methyl tert-butyl ether detected in samples from 

public-supply wells in the Biscayne aquifer ............................................................................ 15
iv

List of Tables

1. Stratigraphic and hydrologic section for the Biscayne aquifer in southeastern 

Florida .............................................................................................................................................. 5

2. Summary of major ions, selected trace elements, radon, organic carbon, and 

nutrient concentrations for 30 public-supply wells and 32 monitoring wells in 

the Biscayne aquifer ...................................................................................................................... 9

3. Summary of pesticide detections for 30 public-supply wells and 32 monitoring wells in 

the Biscayne aquifer .................................................................................................................... 12

4. Summary of volatile organic compounds detected more than once in 30 public-supply 

wells and 32 monitoring wells in the Biscayne aquifer ......................................................... 16

Conversion Factors and Datums

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

Flow rate

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

Mass

ounce, avoirdupois (oz) 0.03527 grams (g)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

 °F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

 °C=(°F-32)/1.8

Vertical coordinate information is referenced to the insert datum name (and abbreviation) here 

for instance, “North American Vertical Datum of 1988 (NAVD 88).”

Horizontal coordinate information is referenced to the insert datum name (and abbreviation) 

here for instance, “North American Datum of 1983 (NAD 83).”

Altitude, as used in this report, refers to distance above the vertical datum.
v

Acronyms and Additional Abbreviations:

DDE DDE is an abbreviation of dichlorodiphenyldichloroethylene 

[2,2-bis(4-chlorophenyl)-1, 1-dichloroethene]. DDE is an 

environmental dehydrochlorination product of DDT 

(dichlorodiphenyltrichloroethane).

DDD dichlorodiphenyldichloroethane

DDT dichlorodiphenyltrichloroethane

EPTC Eptam, Farmarox, Alirox

FDEP Florida Department of Environmental Protection

kg/ha kilograms per hectare

mg/L milligrams per liter

μg/L micrograms per liter

MCL maximum contaminant level

MSMA monosodium methane arsonate

MTBE methyl tert-butyl ether

NAWQA National Water Quality Assessment Program

NWQL National Water Quality Laboratory

pCi/L picocurie per liter

SFWMD South Florida Water Management District

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VOC Volatile organic compound
Abstract

The high permeability of the sand and limestone 

sediments and shallow water table of the Biscayne 

aquifer make ground water vulnerable to contamination 

by human activities. To assess potential contamination 

in the aquifer, untreated ground water was sampled from 

30 public-supply wells (40-165 feet deep) in Broward, 

Miami-Dade, and Palm Beach Counties, 32 shallow 

wells (10-50 feet deep) in a recently urbanized (residential and light commercial) part of Broward County, and 

3 shallow reference wells in Broward County. Results 

from sample analyses indicate that major ions, pH, 

dissolved oxygen, nutrients, and trace element concentrations were generally within the range indicative of 

background concentrations, except for: (1) substantially 

higher bromide concentrations in water from publicsupply wells in southern Miami-Dade County; (2) a 

few relatively high (greater than 2 milligrams per liter) 

concentrations of nitrate in water from public-supply 

wells near agricultural lands in Miami-Dade and southern Broward Counties; and (3) a few relatively high 

concentrations of arsenic (greater than 10 micrograms 

per liter) in water from some shallow urban wells near 

golf courses.

Pesticides were detected in every public-supply 

well, in most of the shallow, urban monitoring wells 

(78 percent), and in one reference well; however, no 

pesticide concentration exceeded any drinking-water 

standard. Fifteen different pesticides or their degradation 

products were detected. The most frequently detected 

pesticides were atrazine and tebuthiuron; less frequently 

detected were the herbicides diuron, fenuron, prometon, 

metolachlor, simazine, and 2,6-diethylaniline. 

Volatile organic compounds (VOCs) were detected 

in most of the public-supply wells (77 percent) and 

shallow, urban wells (91 percent) and in two of the 

three reference wells. Thirty-two different VOCs were 

detected in ground water in the Biscayne aquifer, with 

cis-1,2-dichloroethene the most frequently detected 

VOC in the public-supply wells, followed by methyl 

tert-butyl ether (MTBE), 1,4-dichlorobenzene, and chloroform. Toluene, p-isopropyltoluene, and 1,2,4-

trimethylbenzene were the most frequently detected 

VOCs in the shallow, urban wells. Concentrations of all 

VOCs were less than the maximum contaminant level 

(MCL) for public drinking water, except in two samples 

from public-supply wells near industrialized areas that 

had vinyl chloride concentrations (3 and 5 micrograms 

per liter) above the MCL of 1 microgram per liter. 

Introduction

Southeastern Florida, including Miami-Dade, 

Broward, and Palm Beach Counties (fig. 1), has a 

population exceeding 5.0 million (University of Florida, 

2001), of whom approximately 4.0 million rely on the 

Biscayne aquifer as a public-water supply (Marella, 

2004). The aquifer also supplies water to the Florida 

Keys Aqueduct Authority, which pipes water from the 

mainland to the Florida Keys (Meyer, 1974). Total withdrawals from the Biscayne aquifer exceeded 875 million 

gallons per day (Mgal/d) in 2000, of which 700 Mgal/d 

were withdrawn for public supply (Marella, 2004). The 

Biscayne aquifer has been designated by the U.S. 

Environmental Protection Agency as a sole-source 

aquifer, meaning that this aquifer is the only viable 

ground-water source in this area.

Quality of Ground Water in the Biscayne Aquifer in 

Miami-Dade, Broward, and Palm Beach Counties, 

Florida, 1996-1998, with Emphasis on Contaminants

By Anne Bradner, Benjamin F. McPherson, Ronald L. Miller, George Kish, and Bruce Bernard
Figure 1. Locations of study area, land use, and wells sampled in southeastern Florida.

2 Quality of Ground Water in the Biscayne Aquifer in Miami-Dade, Broward, and Palm Beach Counties, Florida

AREA OF URBAN

LAND-USE

MONITORING WELLS

(See figure 5 for

well locations)

WCA 1

Water

Conservation

Area 3

(WCA 3)

WCA 2

Everglades

National

Park

Everglades Agricultural

Area

80°45′ 30′ 15′ 80°00′

26°30′

15′

26°00′

45′

30′

25°15′

MIAMI-DADE

BROWARD

PALM BEACH

MONROE

COLLIER HENDR

Y

West Palm

Beach

Ft. Lauderdale

Miami

Biscayne Bay

Hillsboro

Canal

Miami Canal

Homestead

41

EXPLANATION

0

0

15 MILES

15 KILOMETERS

AGRICULTURAL

FOREST

OPEN WATER

TRANSITIONAL

URBAN

WETLAND

LAND USE

Base from U.S. Geological Survey digital data, 1:100,000, datum nad83

Albers Equal-Area Conic Projection,

Standard parallels 29° ′ 30 and 45° ′ 30 , central meridian -83° ′ 00

Land-use data based on

1995 National Land Cover Dataset

Atlantic

Ocean

LOCATION OF

STUDY AREA

Florida

APPROXIMATE BOUNDARY

OF EVERGLADES NATIONAL

PARK AND WATER

CONSERVATION AREAS

CANAL

ROAD

PUBLIC-SUPPLY WELL

MONROE
Land use in most of the eastern part of southeastern 

Florida is older residential, commercial, and industrial. 

Land use in the central and western parts is newer residential and light commercial. The developing western 

residential areas abut the Everglades (figs. 1 and 2), 

where water is impounded by the South Florida Water 

Management District (SFWMD) for dry-season releases. 

There are isolated agricultural areas in Broward and 

Palm Beach Counties too small to be shown on figure 1, 

but many are being converted into residential housing. 

There is a large agricultural area in southern MiamiDade County (fig. 1) where primarily winter vegetables 

and nursery ornamentals are grown, with some citrus and 

tropical fruits. In western Palm Beach County, an 

expansive Everglades Agricultural Area is present.

Water quality of the shallow, highly permeable 

Biscayne aquifer is a major concern to water managers 

because of the vulnerability of the aquifer to contamination from the land surface and from septic tanks, and 

the dependency of a large segment of the population on 

this aquifer for their sole water supply. Steadily increasing water usage by a swelling population, and declining 

water levels caused by droughts and construction of 

drainage canals, have caused saltwater intrusion in the 

Miami area, which began as early as 1925 (Parker and 

others, 1955). 

Purpose and Scope

In the 1990s, the U.S. Geological Survey (USGS) 

conducted a regional assessment of water quality in the 

Biscayne aquifer in Broward, Miami-Dade, and Palm 

Beach Counties, Florida, as part of the National Water 

Quality Assessment (NAWQA) Program (Haag and 

others, 1998). During the regional assessment, a survey of untreated ground water was conducted, in which 

water quality was sampled in 30 public-supply wells in 

the eastern parts of Miami-Dade, Broward, and Palm 

Beach Counties and in 35 wells within a nested urban 

land-use area in Broward County. Untreated groundwater samples were tested for major ions, selected trace 

elements, carbon, radon, and various nutrients. The 

purpose of this report is to summarize the results of that 

survey, which was conducted between 1996 and 1998. 

This report includes descriptions of the Biscayne aquifer 

and land use in the area, and water-quality results for the 

30 water supply wells and 32 monitoring wells sampled 

in the study area.

Figure 1 shows the location of the study area, 

including the wells and land uses discussed in this report. 

The 30 public-supply wells are distributed throughout 

the area, from south of Homestead, north to West Palm 

Beach. The wells are located in urban areas on the higher 

Figure 2. Photo showing urban sprawl adjacent to the Florida Everglades, Broward County, Florida.

Introduction 3
elevations of the southeastern Florida coast, as well as 

in agricultural areas, primarily in the south near Homestead. The wells range in depth from 40 feet (ft) in the 

south to 165 ft in the north. The shallow, urban monitoring wells are nested within the western part of the populated eastern portion of Broward County (figs. 1 and 2), 

and represent an area of recently developed residential 

and light-commercial land use. The entire study area is 

underlain by the Biscayne aquifer and all wells sampled 

withdraw water from this aquifer.

Hydrogeology

The upper 3,000 ft of rock underlying south Florida 

is composed chiefly of limestone, dolomite, sand, clay, 

and shells. Shallow aquifers, including the Biscayne 

aquifer and localized aquifers that are part of the 

surficial aquifer system, yield practically all of the 

municipal and much of the irrigation water used in south 

Florida. The Biscayne aquifer is present in southeastern 

Florida, reaching a maximum thickness of 240 ft along 

the Atlantic Coast north of Fort Lauderdale, and thinning westward (fig. 3). Toward the west and north, the 

Biscayne grades into less productive sandy deposits that 

are part of the surficial aquifer system. The three 

northernmost public-supply wells (fig. 1) are within the 

transitional zone between the Biscayne and laterallyequivalent surficial aquifers, but were considered to be in 

the Biscayne aquifer for this study.

This report deals only with the Biscayne aquifer, 

which is unconfined in the study area. The Biscayne 

aquifer consists chiefly of highly permeable Pleistocene limestone and sand, overlain in some areas by a 

thin layer of peat and sand. The aquifer contains several 

lithologic units, which are generally thin and lens-like; 

the entire sequence of units (table 1) is not present in any 

one place. The aquifer extends beneath Biscayne Bay 

and the Atlantic Ocean. Because of the aquifer’s high 

permeability and in response to the lowering of inland 

ground-water levels, saltwater has migrated inland 

(fig. 3) along the base of the Biscayne aquifer. The 

potable, high-yielding portion of the Biscayne aquifer is 

in consolidated limestone extending from land surface 

to a depth of approximately 50 ft in southern MiamiDade County, deepening northward to 120 to 170 ft 

below land surface in southeastern Palm Beach County. 

A sequence of low-permeability, largely clayey deposits 

about 1,000 ft thick forms a confining unit that separates 

the Biscayne aquifer from the underlying, brackish-water 

Floridan aquifer system. Figure 3. Location and depth of Biscayne aquifer, and area 

of saltwater intrusion into the Biscayne aquifer (modified 

from Miller, 1990).

Extent

of Biscayne aquifer

B

-60

-240

-220

-160

-200

-120

-100

-8

0

-20

-40

0

27°

26°

25°

Atlantic Ocean

Florida Bay

Lake

Okeechobee COLLIER

PALM BEA ALM BEACH

MARTIN

BROWARD

HENDR

Y

MIAMI-DADE

MONROE

81° 80°

0

0

30 MILES

30 KILOMETERS

10 20

10 20

EXPLANATION

EXTENT OF SALTWATER-At base of TER-At base of

the Biscayne aquifer.

BASE OF BISCAYNEAQUIFER-Line

of equal altitude of the base of the

Biscayne aquifer. Contour interval is

20 feet. Datum is National Geodetic

Vertical Datum of 1929. Dashed

where approximately located.

-20

Ft.

Lauderdale

Miami

4 Quality of Ground Water in the Biscayne Aquifer in Miami-Dade, Broward, and Palm Beach Counties, Florida
Although regional ground-water flow generally is 

toward the coast, locally, ground water flows toward 

canals and well fields. Minimum flows through canals 

are necessary to maintain water levels and to reduce 

saltwater intrusion, particularly during extended dry 

periods, and to maintain water levels in Everglades 

National Park. Recharge to the Biscayne aquifer is 

derived from rainfall and from water that leaks downward from the canals. Average annual rainfall is about 

60 inches per year, most of which falls between June 

and September. During dry seasons, water in Lake 

Okeechobee and water-conservation areas to the north 

and west of the study area is conveyed south through 

canals by gravity and by pumps to recharge the Biscayne 

aquifer (Fish and Stewart, 1991; Merritt, 1996).

Background Water Quality

As early as 1928, evidence of saltwater intrusion 

prompted the construction of contour maps show water 

levels and chloride concentrations near well fields and 

along the canals. Until the late 1970s, most waterquality studies of the Biscayne aquifer involved 

mapping the concentrations of anions, cations, and 

nutrients (Howie, 1987; Sonntag, 1987). Industrial 

contamination of well fields with VOCs in the 1970s 

spurred studies of public-supply wells by Vincent 

(1984) and the establishment of monitoring programs 

by the Florida Department of Environmental Protection 

(FDEP) and the U.S. Environmental Protection Agency 

(USEPA). Additionally, pesticide studies have been 

conducted on golf courses (Swancar, 1996), in 

agricultural areas (Baker, 1988), and in canals (Miles 

and Pfeuffer, 1997).

Study Procedures

We selected public-supply, urban, and reference 

wells for study in 1996, and then sampled the wells 

Table 1. Stratigraphic and hydrologic section for the Biscayne aquifer in southeastern Florida

Study Procedures 5

Series Stratigraphic and

hydrologic units

Lithology and water-yielding

characteristics

Thickness

(feet)

Holocene Organic soils

Lake Flirt Marl

Peat and muck; water has high color content.

Almost impermeable. Lake Flirt is shelly,

calcareous mud.

0-18

Pleistocene1

Pliocene

Pamlico Sand

Miami Oolite

Fort Thompson Formation

Anastasia Formation

Key Largo Limestone

Tamiami Formation

Quartz sand; water high in iron.

Low yields to domestic wells.

Sandy, oolitic limestone. High yields.

Alternating marine shell beds and freshwater

limestone. Generally high permeability.

High yields.

Coquina, sand, sandy limestone, marl.

Moderate to high yields.

Coralline reef rock. High yields.

Sand, shell, silt, and marl. Moderate yields.

Limestone, clay, and marl. Occasional

moderate yields in upper few feet.

Remainder forms upper part of basal

confining unit.

Caloosahatchee Marl

0-40

0-150

0-60

0-120

0-25

25-220

0-40

Confining unit Biscayne aquifer Confining unit

1

Stratigraphic units are equivalent in part. Order does not

necessarily reflect relative age.

Modified from Miller (1990).
between 1996 and 1998. The following sections describe 

procedures used to select sites and to collect water 

samples.

Site Selection

Thirty public-supply wells, 32 monitoring wells, 

and 3 reference wells were selected for sampling 

(figs. 4 and 5). The public-supply wells were selected to 

provide coverage over the study area and ranged from 

40 ft deep in the southern part of Miami-Dade County to 

about 170 ft deep in southeastern Palm Beach County. 

The monitoring and reference wells were nested within 

a part of the study area, in the western portion of eastern 

Broward County (figs. 1 and 5). This area was selected 

because it represents recently developed residential 

and light-commercial land use; as part of the overall 

NAWQA Program, the water quality in this nested urban 

area can be compared with that in similar land-use areas 

nationwide (Squillace and Price, 1996). The 32 urban, 

monitoring well sites were selected randomly using a 

computer program developed for the NAWQA Program 

(Scott, 1990); 15 existing monitoring wells were used 

and 17 new wells were drilled at sites according to 

established protocols (Lapham and others, 1995). The 

monitoring wells ranged from 10 to 50 ft deep, had water 

levels ranging from about 2 to 19 ft below land surface, 

and were located in parks, roadsides, golf courses, parking lots, and residential lawns. The three reference wells 

were located in areas deemed to be little affected by land 

use, and were established to provide background waterquality information as part of the NAWQA protocol.

Sampling Protocols

Water-quality samples were collected, preserved in 

the field, and then shipped to the USGS National Water 

Quality Laboratory (NWQL) in Denver, Colo., for 

analysis following NAWQA protocols (Koterba and 

others, 1995). The sampling procedure involved sampling ground water at low flow rates (500 milliliters 

per minute) through a closed system. Samples were 

collected only after field measurements indicated that 

pH, dissolved oxygen, temperature, conductance, and 

turbidity had stabilized.

The monitoring wells were sampled using a 

Teflon and stainless-steel pump and Teflon tubing. For 

the high-volume public-supply wells, untreated water 

was sampled through cleaned tubing and Teflon fittings 

connected to a faucet at the well pump used by utilities 

Figure 4. Location of public-supply wells sampled.

0

0

30 MILES

30 KILOMETERS

10 20

10 20

27°

26°

25°

Atlantic Ocean

Florida Bay

Lake

Okeechobee COLLIER

PALM BEA ALM BEACH

MARTIN

BROWARD

HENDR

Y

MIAMI-DADE

MONROE

81° 80°

1 PUBLIC-SUPPLY WELL LOCATION

AND SITE NUMBER

EXPLANATION

1 2 3

4 5 6

8

9 10

11

13 12

14

15 16

17

18 19 20 21

22 23

24 25

26

27 28

29

30

7

6 Quality of Ground Water in the Biscayne Aquifer in Miami-Dade, Broward, and Palm Beach Counties, Florida
personnel for sampling. Each well was being pumped at 

the time of sampling.

To meet established water-quality objectives of the 

NAWQA Program and to support other USGS waterquality investigations, the NWQL provided broad spectrum, low-level analyses for pesticides and VOCs (Zaugg 

and others, 1995; Connor and others, 1998). Other analytical procedures followed standard NWQL protocols 

(Koterba and others, 1995). Detections, as reported here, 

are a function of the laboratory’s analytical methods and 

their efficiency and limitations. Quality-control samples 

were collected in procedures outlined in Koterba and 

others (1995), and included field, laboratory, and solution blanks, sample replicates, and field spikes for VOCs 

and pesticides. None of the quality-control samples 

indicated field contamination, and the spiked samples 

showed reasonable recoveries of spiked analytes. The 

web site, http://fl.water.usgs.gov/Sofl/gw/gwintro.html, 

contains comprehensive water-quality results for this 

study.

Figure 5. Location of monitoring and reference wells sampled.

Study Procedures 7

26° ′ 00

Atlantic

Ocean

BROWARD

MIAMI-DADE

80° ′ 40 20′ 80° ′ 00

25° ′ 40

26° ′ 20

0

0

20 MILES

20 KILOMETERS

10

10

PALM BEACH

3

30 MONITORING WELL LOCATION AND SITE NUMBER

REFERENCE WELL LOCATION AND SITE NUMBER

EXPLANATION

1

1 2 3,4

5 6 7

8

10

11 12

15 13 14

16 17

18

19

20

21 22

23 25 24 26 27 28 ,29

30 31 32

2

3

9
Water Quality

In the following five sections, we summarize waterquality data collected from shallow wells in the Biscayne 

aquifer. The wells are located in urban and residential 

land use areas of southeastern Florida.

Water pH, Dissolved Oxygen, and Major Ions

The chemical composition of shallow ground water 

in the Biscayne aquifer varies with location and proximity to recharge from canal sources (Howie, 1987; 

Sonntag, 1987). The pH of samples collected for this 

study ranged from 6.2 to 7.7, with a median of 6.7 for 

monitoring wells and 6.9 for public-supply wells—

higher than the pH of rainfall, which averages 5.1 in 

south Florida (Fernald and Purdum, 1998). These 

higher pH values in ground water are due to the buffering effect of the limestone as rainwater percolates down 

through the upper sediments. The median dissolvedoxygen concentration in water from all the wells was 

0.15 milligrams per liter (mg/L). 

The major ions in the shallow ground water of 

southeastern Florida reflect the composition and solubility of the carbonate rocks and organic soils of the area. 

In some parts of the area, saline residues from earlier 

invasions of sea water or recent influx of sea water also 

contribute to ionic composition (Parker and others, 

1955). Concentrations of ions in shallow waters of the 

area vary with distance from the coast and with the 

season (Waller, 1982). For this study, the range and 

median values for major ion concentrations, including 

calcium, sodium, magnesium, and potassium, are listed 

in table 2. Concentrations generally were similar to 

previously reported values in the Biscayne aquifer 

(Howie, 1987; Sonntag, 1987).

Selected Trace Elements, Radon, and Carbon

Urban and agricultural activities are potential 

sources of trace element contamination—particularly 

arsenic, copper, and lead (De Carlo and Anthony, 2002). 

Urban activities, such as turf-grass maintenance in golf 

courses, have increased concentrations of arsenic in 

Florida’s ground water through the use of the herbicide, 

monosodium methane arsonate (MSMA) (Swancar, 

1996). Other potential sources of trace-element contamination in ground water include arsenic used in cattle dipping for disease control (Blasland, Bouck, and Lee, Inc., 

1992), arsenic and copper used as fungicide on grapefruit and as a wood preservative (Sherwood and others, 

1973), and lead used in gasoline and batteries (De Carlo 

and Anthony, 2002).

Arsenic concentrations in water from the shallow, 

urban monitoring wells ranged from less than 1 to 

19 micrograms per liter (μg/L), with a median concentration of 2 μg/L. Water samples from monitoring wells 

located on golf courses had arsenic concentration higher 

than at other wells in the network (greater than 10 μg/L), 

although no samples exceeded the maximum contaminant level (MCL) of 50 μg/L. In contrast, the concentration of arsenic from the public-supply wells ranged from 

less than 1 to 3 μg/L, indicating that arsenic contamination from golf courses and other sources was diluted in 

the deeper public-supply wells by ground water from 

other land-use areas. About 34 percent of the monitoring wells contained water with copper concentrations 

above detection levels, with a maximum concentration 

of 4 μg/L—considerably below the secondary drinkingwater standard of 1,000 μg/L (Florida Department of 

Environmental Protection, 2004, http://www.dep.state.

fl.us/water/drinkingwater/sec_con.htm). Most of these 

detections were from shallow wells located near parks or 

golf courses. Only seven public-supply wells had water 

with detections of copper (maximum concentration of 

6.3 μg/L), and these wells were located in or near large 

agricultural areas. Four ground-water samples in the 

network contained detectable concentrations of lead, and 

maximum concentrations of 5 μg/L were below the MCL 

of 15 μg/L.

Bromide concentrations in water from the publicsupply wells in southern Miami-Dade County were 

elevated above those in most other wells. Possible 

sources of high bromide concentrations include bromidecontaining fumigants and seawater aerosols. Methyl bromide has been used as a fumigant in agricultural areas in 

southern Miami-Dade County near these public-supply 

wells (fig. 1). Additionally, these wells are within several 

miles of the coast and may be influenced by bromiderich seawater aerosols.

The possibility of methyl bromide contributing 

measurable amounts of bromide ion to ground water 

in areas where it is applied was investigated. Methyl 

bromide is reported to decompose to bromide ion and 

methanol (GTZ, 2002). Bromide in excess of that 

expected from seawater can be computed using the 

bromide-to-chloride ratio (mass-to-mass) of 0.00353 

for seawater and the chloride concentration in a water 

sample. For example, at public-supply well number 1 

(fig. 4), which had the highest bromide ion concentration (0.71 mg/L), a value was computed of 0.61 mg/L of 

bromide in excess of that expected if seawater was the 

only source of bromide and chloride. This excess could 

8 Quality of Ground Water in the Biscayne Aquifer in Miami-Dade, Broward, and Palm Beach Counties, Florida
Constituent Well Type

Number of

 samples

Concentration

Minimum Median Maximum

Major Ions

Calcium Public supply 30 58 88.5 130

Monitoring 32 36 120 160

Sodium Public supply 30 12 25 42

Monitoring 32 1.9 17.5 81

Magnesium Public supply 30 2.5 4.1 8.5

Monitoring 32 0.56 3.65 15

Potassium Public supply 30 0.59 2.4 18

Monitoring 32 0.70 2.75 13

Sulfate Public supply 30 <0.1 17 84

Monitoring 32 <0.1 16.5 66

Chloride Public supply 30 17 39 67

Monitoring 32 3.2 24.5 130

Silica Public supply 30 2.7 8.0 15

Monitoring 32 2.1 6.65 15

Trace Elements and Radon

Arsenic Public supply 30 <1.0 <1.0 3.0

Monitoring 32 <1.0 2.0 19

Bromide Public supply 30 0.024 0.077 0.71

Monitoring 15 <0.01 0.03 0.11

Copper Public supply 30 <1.0 <1.0 6.3

Monitoring 32 <1.0 <1.0 4.0

Fluoride Public supply 30 <0.10 0.23 0.37

Monitoring 32 <0.10 0.30 0.41

Radon, in picocuries per liter Public supply 30 202 421 901

Monitoring 32 230 555 1,800

Carbon

Dissolved organic carbon Public supply 30 0.6 9.4 22

Monitoring 32 1.9 11.5 36

Nutrients

Nitrogen, nitrite Public supply 30 <0.01 <0.01 0.087

Monitoring 32 <0.01 0.01 0.30

Nitrogen, nitrite plus nitrate Public supply 30 <0.01 0.025 5.99

Monitoring 32 <0.01 <0.01 4.2

Nitrogen, ammonia Public supply 30 <0.01 0.453 2.29

Monitoring 32 <0.01 0.235 25

Nitrogen, ammonia plus organic Public supply 30 <0.01 0.955 3.60

Monitoring 32 <0.01 0.95 28

Phosphorus Public supply 30 <0.01 <0.01 0.337

Monitoring 32 <0.01 <0.01 0.295

Phosphorus, orthophosphate Public supply 30 <0.01 0.024 0.47

Monitoring 32 <0.01 0.02 0.239

Table 2. Summary of major ions, selected trace elements, radon, organic carbon, and nutrient 

concentrations for 30 public-supply wells and 32 monitoring wells in the Biscayne aquifer

[Concentrations are dissolved, except radon; units are milligrams per liter except for arsenic and copper, which 

are micrograms per liter, and radon, which is picocuries per liter.]

Water Quality 9
result from the complete decomposition of 0.727 grams 

of methyl bromide under 1 square meter of soil in water 

1 meter deep. One application of methyl bromide at the 

typical rate of 448 kilograms per hectare for nematode 

control (400 pounds per acre from Noling and Gilreath, 

1998) would provide 44.8 grams per square meter to the 

soil. The decomposition and transfer of about 2 percent 

of the methyl bromide in this application to surrounding 

ground water could explain the excess bromide ion in 

the sample from well number 1.

Radon-222 is a radioactive gas that occurs naturally 

in ground water in areas that contain radionuclides of 

the uranium-238 radioactive decay series. Radon-222 

is produced when radium-226 (a daughter of uranium238) contained in water and aquifer materials undergoes 

nuclear decay. Uranium-238 commonly occurs in trace 

amounts in phosphatic deposits and limestone in Florida. 

Of the 65 Biscayne aquifer samples analyzed for radon222, 56 (86 percent) exceeded the proposed 300 picocurie per liter (pCi/L) MCL for drinking water (U.S. 

Environmental Protection Agency, 2004). Radon-222 

activities ranged from 202 to 1,800 pCi/L, with a median 

activity of 440 pCi/L.

Dissolved organic carbon was consistently higher 

in the monitoring wells than in the public-supply wells. 

Most likely this is because organic deposits overlie the 

aquifer in many locations, and the monitoring wells are 

shallow and more likely to be influenced by factors at 

the surface. 

Nutrients

Concentrations of nutrients generally are low in 

the Biscayne aquifer except near human sources, such 

as domestic waste and agricultural fertilizers. Concentrations of nitrite plus nitrate were low in most wells 

(commonly less than the 0.05-mg/L detection level), 

but occasionally were elevated above 2 mg/L (table 2). 

The higher values were found in public-supply wells 

in or near agricultural lands, although no well sample 

exceeded the MCL of 10 mg/L.

Concentrations of ammonia in ground water were 

relatively high compared to concentrations in other 

NAWQA study areas (McPherson and others, 2000). 

Median concentrations were less than 0.5 mg/L, but a 

few samples had concentrations up to 3 mg/L, and one 

monitoring well had a concentration of 25 mg/L. Water 

from this well contained hydrogen sulfide, which is 

indicative of a reducing environment that would favor 

conversion of organic nitrogen compounds to ammonia.

Phosphorus concentrations in ground-water samples 

ranged from less than 0.01 to 0.337 mg/L, with a 

median less than 0.01 mg/L (table 2). Highest concentrations were in the northern part of the study area, in 

southeastern Palm Beach County. Sources of the high 

phosphorus concentrations (those above the median 

value) may be fertilizers or naturally occurring 

phosphatic materials associated with the silts and clays. 

Phosphorus levels can be high in ground water where 

natural phosphates are present in the rock matrix, and 

could degrade the ecosystem by moving upward into 

surface-water bodies. West of the study area, substantial 

increases in the movement of phosphorus-laden surface 

water into the Everglades has been a major concern 

to land management and regulatory agencies in south 

Florida because of the potential for ecosystem degradation. Further investigation into the reason for the high 

phosphorus levels in ground water in the northern part of 

the study area is needed.

Pesticides

Historically, pesticides, including insecticides, 

herbicides, and fungicides, have been used to control 

insects, weeds, and fungi in agricultural areas. Expansion of the lawn care and golf industries in urban areas 

and the increased use of insecticides around homes have 

substantially increased the amount of pesticides used in 

the study area in recent years (Haag and others, 1998; 

Swancar, 1996). The legacy of banned pesticides or 

pesticides that are no longer used is still evident in some 

areas, based on the detection of the degradation products 

p,p’- dichlorodiphenyldichloroethylene (DDE) from the 

insecticide dichlorodiphenyltrichloroethane (DDT), used 

for mosquito control, 2,6-diethylaniline from the 

herbicide alachlor, used in agricultural areas, and the 

herbicide fenuron, used for weed control.

A total of 86 pesticides were analyzed in samples 

collected from the public-supply and monitoring wells 

(for a list of the pesticides analyzed, see McPherson and 

others, 2000); of these, 15 pesticides were detected in 

this study, 14 of which were detected more than once 

(fig. 6; table 3). At least one pesticide (generally atrazine 

or tebuthiuron) was detected in each of the 30 publicsupply wells and in 78 percent of the 32 monitoring 

wells. Only one sample from the three reference wells 

had a pesticide detection (atrazine). Deethylatrazine, a 

degradation product of atrazine, also was detected frequently. No pesticide concentration exceeded the MCL.

10 Quality of Ground Water in the Biscayne Aquifer in Miami-Dade, Broward, and Palm Beach Counties, Florida
Regional patterns in pesticide distribution in ground 

water can be related to land use, solubility, transport, 

degradation characteristics of pesticides, and aquifer 

properties. Transported surface water also is a major 

source of pesticides in the study area. Pesticides such 

as atrazine, tebuthiuron, and diuron were detected 

frequently in canal waters that recharge the Biscayne 

aquifer (Miles and Pfeuffer, 1997). The detection of 

tebuthiuron and atrazine in ground-water samples indicates that the widespread use of herbicides—particularly 

tebuthiuron to control weeds in canals and rights-of-way 

(Miller and others, 1999) and atrazine to control weeds 

in agricultural and urban areas—has resulted in the 

transport of these pesticides into the Biscayne aquifer.

Fenuron and diuron were detected in public-supply 

wells in the northern part of the study area (figs. 7a and 

7b, respectively). Fenuron has been used for control of 

woody plants and weeds, and diuron has been used 

commonly on sugar cane and citrus. Fenuron was 

detected in samples from two shallow monitoring wells. 

Although it is no longer on the list of approved herbicides in Florida, fenuron was once used in northern 

Broward and Palm Beach Counties. These detections 

indicate that fenuron degrades slowly in ground water. 

Metachlor and simazine were detected in the mixedagriculture areas of southern Miami-Dade County and 

occasionally in wells near other agricultural areas 

(figs. 7c and 7d, respectively).

Volatile Organic Compounds 

VOCs are components of petroleum products and 

some man-made products such as solvents, refrigerants, 

and fumigants (Squillace and others, 1999). VOCs have 

chemical and physical properties that allow them to 

move freely between water and air (Bender and others, 

1999). VOCs in rainfall may originate from vehicle and 

industrial emissions (Pankow and others, 1997). VOCs 

also can be formed in ground water in the presence of 

organic carbon and halogens (such as chlorine used to 

treat water supplies or degradation products of fumigants 

and fertilizers). The USEPA has established MCLs in 

drinking water for many VOCs because of human health 

concerns (Moran and others, 2002). Rowe and others 

(1997) summarized aquatic toxicity information and 

water-quality criteria for selected VOCs.

Figure 6. Pesticides detected in samples from the public-supply and monitoring wells in the 

Biscayne aquifer.

Water Quality 11

0

10

20

30

40

50

60

70

80

PERCENT OF

PESTICIDE DETECTIONS

Figure 6

MONITORING WELL WATER SAMPLES

PUBLIC-SUPPLY WELL WATER SAMPLES

TEBUTHIURON

ATRAZINE

DEETHYLATRAZINE

DIURON

PROMETON

FENURON

SIMAZINE

METOLACHLOR

2,6-DIETHYLANILINE

BENTAZON

EPTC

BUTYLATE

DIELDRIN

P,P' DDE

NORFLURAZON
Constituent Well type

Number of 

detections

Minimum 

reporting 

level

Concentration GWGC or 

Minimum Median Maximum (MCL)

Herbicides

Tebuthiuron Public supply 23 <0.01 <0.01 0.0197 0.69 490

Monitoring 6 <0.01 <0.01 <0.01 e0.069 490

Atrazine Public supply 22 <0.001 <0.001 0.009 0.113 3(MCL)

Monitoring 17 <0.001 <0.001 0.0035 0.422 3(MCL)

Deethylatrazine Public supply 19 <0.002 <0.002 0.0051 0.0259 --

Monitoring 16 <0.002 <0.002 e0.005 0.387 --

Diuron Public supply 16 <0.02 <0.02 0.0053 0.30 14

Monitoring 4 <0.02 <0.02 <0.02 0.38 14

Prometon Public supply 14 <0.018 <0.018 <0.018 0.0313 105

Monitoring 3 <0.018 <0.018 <0.018 0.026 105

Fenuron Public supply 9 <0.013 <0.013 <0.013 0.06 --

Monitoring 2 <0.013 <0.013 <0.013 0.15 --

Simazine Public supply 8 <0.005 <0.005 <0.005 0.0142 4(MCL)

Monitoring 2 <0.005 <0.005 <0.005 0.006 4(MCL)

Metolachlor Public supply 8 <0.002 <0.002 <0.002 0.042 1,050

Monitoring 1 <0.002 <0.002 <0.002 0.014 1,050

2,6-DiethylanilinePublic supply 4 <0.003 <0.003 <0.003 0.0088 --

Monitoring 0 <0.003 <0.003 <0.003 <0.003 --

Bentazon Public supply 0 <0.014 <0.014 <0.014 <0.014 17.5

Monitoring 4 <0.014 <0.014 <0.014 e0.15 17.5

Butylate Public supply 2 <0.002 <0.002 <0.002 0.045 350

Monitoring 0 <0.002 <0.002 <0.002 <0.002 350

Norflurazon Public supply 1 <0.024 <0.024 <0.024 0.06 280

Monitoring 0 <0.024 <0.024 <0.024 <0.024 280

Insecticides

EPTC Public supply 2 <0.002 <0.002 <0.002 0.0322 --

Monitoring 1 <0.002 <0.002 <0.002 0.011 --

Dieldrin Public supply 2 <0.001 <0.001 <0.001 0.002 0.1

Monitoring 0 <0.001 <0.001 <0.001 <0.001 0.1

p,p’ DDE Public supply 2 <0.006 <0.006 <0.006 0.002 0.1

Monitoring 0 <0.006 <0.006 <0.006 <0.006 0.1

* Estimated values below the usual reporting level are given for samples in which the compound’s presence was verified from spectra. Values above the 

reporting levels are estimated if there are interferences, values below the lowest standard, or extraction recoveries less than normal. 

Table 3. Summary of pesticide detections for 30 public-supply wells and 32 monitoring wells in the Biscayne aquifer

[Units are micrograms per liter; e, estimated*; GWGC, State of Florida ground-water guidance concentration; MCL, U.S. 

Environmental Protection Agency and State of Florida maximum contaminant level; <, less than; --, no applicable standard]

12 Quality of Ground Water in the Biscayne Aquifer in Miami-Dade, Broward, and Palm Beach Counties, Florida
80°45′ 30′ 15′ 80°00′

26°30′

15′

26°00′

45′

30′

BROWARD

PALM BEACH

MONROE COLLIER HENDRY

Atlantic

Ocean

West Palm

Beach

Ft. Lauderdale

Miami

Biscayne Bay

Hillsboro Canal

Miami Canal

Homestead

41

EXPLANATION

PUBLIC SUPPLY WELLS

SAMPLED FOR

FENURON

0

0

10 MILES

10 KILOMETERS

Detected

Not Detected

80°45′ 30′ 15′ 80°00′

26°30′

15′

26°00′

45′

30′

25°15′

BROWARD

PALM BEA ALM BEACH

MONROE COLLIER HENDRY

Atlantic

Ocean

West Palm

Beach

Ft. Lauderdale

Miami

Biscayne Bay

Hillsboro Canal

Miami Canal

Homestead

41

EXPLANATION

PUBLIC SUPPLY WELLS

SAMPLED FOR

DIURON

0

0

10 MILES

10 KILOMETERS

Detected

Not Detected

30′ 15′ 80°00′

26°30′

15′

26°00′

45′

30′

BROWARD

PALM BEACH

MONROE COLLIER HENDRY

Atlantic

Ocean

West Palm

Beach

Ft. Lauderdale

Miami

Biscayne Bay

Hillsboro Canal

Miami Canal

Homestead

41

EXPLANATION

PUBLIC SUPPLY WELLS

SAMPLED FOR

METOLACHLOR

0

0

10 MILES

10 KILOMETERS

Detected

Not Detected

15′ 80°00′

26°30′

15′

26°00′

45′

30′

25°15′

MIAMI-D

BROWARD

PALM BEA ALM BEACH

MONROE COLLIER HENDRY

Atlantic

Ocean

West Palm

Beach

Ft. Lauderdale

Miami

Biscayne Bay

Hillsboro Canal

Miami Canal

Homestead

41

EXPLANATION

PUBLIC SUPPLY WELLS

SAMPLED FOR

SIMAZINE

0

0

10 MILES

10 KILOMETERS

Detected

Not Detected

Figure 7. Regional patterns of occurrence of the pesticides (a) fenuron, (b) diuron, (c) metolachlor, and 

(d) simazine, detected in samples from public-supply wells in the Biscayne aquifer.

Water Quality 13
A review of VOCs detected in previous studies on 

public-supply wells and shallow, urban wells in south 

Florida indicated that few VOCs have been detected 

in shallow ground water, but many water-supply wells 

in the Dade, Broward, and Palm Beach Counties have 

had chemical contamination from VOCs (Vincent, 

1984; Florida Department of Environmental Protection, 

1999). Vincent (1984) reported that nearly 20 percent of 

samples from 250 public-supply wells (mostly in MiamiDade County) contained detectable VOCs, mostly 

originating from industrial processes.

Since 1984, there have been three major actions 

taken to reduce VOCs in finished drinking water. First, 

cleanup of contaminated industrial sites has greatly 

reduced concentrations in untreated supply water from 

the well fields. Second, processing measures have been 

initiated, using air stripping or carbon filtration, to 

remove VOCs from untreated water in most of the 

contaminated water-treatment systems. Other watertreatment facilities remove organic carbon from the 

untreated supply water by reverse osmosis or other 

methods so that trihalomethanes are not formed when 

the water is chlorinated before its distribution to consumers. Third, most well fields now have delineated 

recharge protection zones and have monitoring programs 

and protection ordinances in place in those areas.

A total of 86 VOCs were analyzed in this study; 

32 VOCs were detected (table 3; see McPherson and 

others, 2000, for a list of the analyzed VOCs). From 

32 shallow monitoring wells, 29 samples (91 percent) 

contained one or more VOCs (fig. 8); from 30 deep 

public-supply wells, 23 samples (77 percent) contained 

one or more VOCs. Two reference wells contained low 

concentrations of two VOCs. One reason for the high 

number of detections is the use of new analytical methods with low reporting limits (Connor and others, 1998). 

Except for two samples from public-supply wells in a 

more industrialized area, concentrations of VOCs were 

all less than drinking-water standards. The two exceptions were vinyl chloride concentrations of 3 and 

5 μg/L, which were above the MCL of 1 μg/L. The most 

common VOCs detected in ground-water samples for 

both surveys are shown in table 4 and figure 8. Acetone, 

methylethylketone, and tetrahydrofuran were detected 

in several of the laboratory blank samples. These compounds are common laboratory contaminants and are not 

included in the data table. Field solution blanks indicated 

that these compounds either were present in blank water 

or were detected in sporadic blanks in the laboratory, but 

not the samples. Carbon disulfide also was frequently 

detected, but is considered to be a naturally occurring 

VOC because of the presence of hydrogen sulfide gas 

and the high organic carbon content of the ground water.

Cis-1,2-dichloroethene was the most frequently 

detected VOC in the public-supply wells. This compound and other VOCs, such as 1,4-dichlorobenzene, 

trichloroethylene, vinyl chloride, 1,1-dichloroethane, and 

chlorobenzene, were detected more commonly in the 

older and denser residential and industrial areas. In the 

1984 USEPA study (Vincent, 1984) in this same area, 

the most frequently detected VOCs were cis-1,2-dichloroethene, 1,2-dichloroethane, trichloroethylene, vinyl 

chloride, and tetrachloroethylene. Although concentrations were less during the 1998 sampling period, the 

same VOCs persisted in the area of the Biscayne aquifer 

overlain by heavy industry and dense urban development. 

Methyl tert-butyl ether (MTBE) was the secondmost commonly detected VOC in the public-supply 

wells. MTBE is used as a gasoline additive in most 

states, including Florida, to increase the octane level, 

reduce vehicular carbon monoxide levels, and reduce 

ozone levels in urban air. MTBE was the second most 

frequently detected VOC in shallow ground water in 

urban areas in a study of 8 urban and 20 agricultural 

areas throughout the United States in 1993 and 1994, 

and has recently emerged as a possible risk to human 

health (Squillace and others, 1996). In south Florida’s 

public-supply wells, MTBE detections occurred mostly 

in the heavily urbanized areas of Miami-Dade County 

and in agricultural areas in south Miami-Dade County 

where the wells are only about 40 ft deep (figs. 1 and 9). 

Chloroform, bromoform, and other related VOCs 

were detected in water from public-supply wells in the 

mixed-agricultural area of southern Miami-Dade County. 

These VOCs probably are formed during degradation of 

the fumigant methyl bromide combined with chloropicrin, or fertilizers that contain chlorine. Chloroform also 

was detected in samples from some of the monitoring 

wells, probably resulting from the use of chlorinated 

drinking water as irrigation water or fertilizers containing chlorine. Tetrachloroethylene was detected in almost 

all the public-supply wells in the agricultural area of 

southern Miami-Dade County. Tetrachloroethylene is 

used as a solvent for degreasing and for dry cleaning. 

Toluene, p-isopropyltoluene, and 1,2,4-trimethylbenzene were the most frequently detected VOCs in 

shallow ground water sampled from monitoring wells in 

the newer residential areas. These compounds may be 

from additives included in various pesticide sprays or 

from fuel or asphalt. 

14 Quality of Ground Water in the Biscayne Aquifer in Miami-Dade, Broward, and Palm Beach Counties, Florida
Figure 8. The most common volatile organic compounds detected in the Biscayne aquifer.

80°45′ 30′ 15′ 80°00′

26°30′

15′

26°00′

45′

30′

25°15′

MIAMI-DADE

BROWARD

PALM BEACH

MONROE COLLIER HENDRY

Atlantic

Ocean

West Palm

Beach

Ft. Lauderdale

Miami

Biscayne Bay

Hillsboro Canal

Miami Canal

Homestead

41

EXPLANATION

PUBLIC SUPPLY WELLS

SAMPLED FOR

Methyl butyl ether

(MTBE)

tert0

0

10 MILES

10 KILOMETERS

Detected

Not Detected

Figure 9. Regional patterns of methyl tert-butyl ether 

detected in samples from public-supply wells in the 

Biscayne aquifer.

Summary

This report summarizes the results of a survey of 

untreated ground water from: (1) 30 public-supply wells 

in Broward, Miami-Dade, and southern Palm Beach 

Counties, and (2) 32 shallow monitoring wells and 

3 reference wells in an urban area of Broward County. 

The public-supply wells lie within the urban areas in the 

higher elevations of the southeastern coast of Florida, 

and in agricultural areas located mainly in the lower 

elevations of the southern part of the study area. The 

monitoring wells were nested in the western part of the 

populated area in eastern Broward County, in an urban 

area that contains recently developed residential and 

light-commercial land use. The study area overlies the 

Biscayne aquifer. The high permeability and shallow 

water table of the sand and limestone sediments make 

the ground water in the Biscayne aquifer vulnerable to 

contamination by human activities. Eighty percent of the 

population residing in the study area, as well as most of 

the population in the Florida Keys, is served by publicsupply wells that tap the Biscayne aquifer. Total withdrawals from the Biscayne aquifer exceeded 875 million 

gallons per day in 2000, of which 700 million gallons 

per day were withdrawn for public supply. 

Concentrations of calcium, magnesium, potassium, 

and sodium, as well as pH and dissolved oxygen measured for this study were typical of shallow ground water 

from the Biscayne aquifer. Bromide concentrations in 

water from public-supply wells in southern Dade County 

Summary 15

1,2,4-TRIMETHYLBENZENE

TOLUENE

CARBON DISULFIDE

P-ISOPROPYLTOLUENE

CIS-1,2-DICHLOROETHENE

METHYL TERTBUTYL ETHER

1,4-DICHLOROBENZENE

CHLOROFORM

DICHLOROBROMOMETHANE

TETRACHLOROETHYLENE

TRICHLOROETHYLENE

CHLOROBENZENE

BENZENE

METHYL CHLORIDE

META/PARA-XYLENE

ETHYLBENZENE

1,1-DICHLOROETHANE

BROMOFORM

O-DICHLOROBENZENE

CHLORODIBROMOMETHANE

VINYL CHLORIDE

1,2-TRANSDICHLOROETHENE

DICHLORODIFLUOROMETHANE

FREON 113

0

10

20

30

40

50

PERCENT OF

VOLATILE ORGANIC

COMPOUND DETECTIONS

MONITORING WELL WATER SAMPLES

PUBLIC-SUPPLY WELL WATER SAMPLES

Figure 8
Constituent Survey

Number of 

detections

Minimum reporting level

Concentration

Minimum Median Maximum HAL or MCL

1,2,4-TrimethylbenzenePublic supply 0 <0.056 <0.056 <0.056 <0.056 --

Monitoring 15 <0.050 <0.050 <0.050 e0.07 --

Toluene Public supply 5 <0.038 <0.038 <0.038 e0.27 1,000MCL

Monitoring 13 <0.050 <0.050 <0.050 0.29 1,000MCL

Carbon disulfide Public supply 1 <0.080 <0.080 <0.320 e0.610 --

Monitoring 13 <0.050 <0.050 <0.020 0.120 --

p-Isopropyltoluene Public supply 0 <0.110 <0.110 <0.110 <0.110 --

Monitoring 13 <0.050 <0.050 <0.050 1.0 --

cis-1,2-Dichloroethene Public supply 12 <0.038 <0.038 <0.038 0.978 70MCL

Monitoring 0 <0.038 <0.038 <0.038 <0.038 70MCL

Methyl tert-butylether Public supply 9 <0.112 <0.112 <0.112 0.682 35HAL**

Monitoring 1 <0.100 <0.100 <0.100 e0.010 35HAL**

1,4-Dichlorobenzene Public supply 9 <0.050 <0.050 <0.050 e0.130 75MCL, 

75HAL

Monitoring 3 <0.050 <0.050 <0.050 e0.010 75MCL, 

75HAL

Chloroform Public supply 8 <0.052 <0.052 <0.052 1.12 80MCL, 

70HAL

Monitoring 4 <0.050 <0.050 <0.050 e0.080 80MCL, 

70HAL

DichlorobromomethanePublic supply 7 <0.048 <0.048 <0.048 0.337 100MCL

Monitoring 0 <0.050 <0.050 <0.050 <0.050 100MCL

Tetrachloroethylene Public supply 7 <0.038 <0.038 <0.038 e0.050 5MCL, 

10HAL

Monitoring 0 <0.050 <0.050 <0.050 <0.050 5MCL, 

10HAL

Trichloroethylene Public supply 6 <0.038 <0.038 <0.038 e0.34 5MCL

Monitoring 0 <0.050 <0.050 <0.050 <0.050 5MCL

Chlorobenzene Public supply 6 <0.028 <0.028 <0.028 0.53 100MCL

Monitoring 0 <0.050 <0.050 <0.050 <0.050 100MCL

Benzene Public supply 2 <0.032 <0.032 <0.032 e0.009 5MCL

Monitoring 4 <0.050 <0.050 <0.050 e0.050 5MCL

Methyl chloride Public supply 1 <0.254 <0.254 <0.254 e0.015 30HAL

Monitoring 6 <0.200 <0.200 <0.200 e0.100 30HAL

Meta/Para-xylene Public supply 0 <0.064 <0.064 <0.064 <0.064 10,000MCL*

Monitoring 6 <0.050 <0.050 <0.050 e0.050 10,000MCL*

Table 4. Summary of volatile organic compounds detected more than once in 30 public-supply wells and 32 monitoring 

wells in the Biscayne aquifer

[Units are micrograms per liter; e, estimated; HAL, health advisory level, 70-kilogram adult, lifetime, (U.S. Environmental 

Protection Agency, 2004); MCL, maximum contaminant level (U.S. Environmental Protection Agency, 2004); --, no applicable 

standard; <, less than; *, MCL for total xylenes. VOCs detected only once include dibromomethane, bromochloromethane, 

1,1-Dichloroethylene, 1,2-Dichloropropane, 1,3-Dichlorobenzene, Methyl-tertpentyl-ether, chlorotoluene, ethylether, methylisobutyl-ketone, and o-xylene]

16 Quality of Ground Water in the Biscayne Aquifer in Miami-Dade, Broward, and Palm Beach Counties, Florida
were elevated, possibly because of a breakdown of fumigants and pesticides used in that area. Nitrate concentrations in ground water were low (commonly not detected) 

in most wells, but were elevated at a few sites. Public 

water-supply wells located in or near agricultural land 

yielded water with detectable concentrations of nitrate. 

There were no specific land uses affecting concentrations 

of nitrate in the shallow monitoring wells. Phosphorus 

concentrations in ground-water samples ranged from 

less than 0.01 to 0.34 mg/L, with a median of less than 

0.01 mg/L; higher concentrations may come from fertilizer or may be a result of phosphatic material in the 

sandy limestone. Of the 65 Biscayne aquifer samples 

analyzed for radon-222, 56 (86 percent) exceeded the 

Constituent Survey

Number of

detections

Minimum reporting levels

Concentration

Minimum Median Maximum HAL or MCL

Ethylbenzene Public supply 0 <0.050 <0.050 <0.100 <0.020 700MCL, 

700HAL

Monitoring 6 <0.050 <0.050 <0.10 e0.010 700MCL, 

700HAL

1,1-Dichloroethane Public supply 4 <0.066 <0.066 <0.066 e0.34 -- 

Monitoring 0 <0.050 <0.050 <0.050 <0.050 -- 

Bromoform Public supply 3 <0.104 <0.104 <0.104 0.945 80MCL

Monitoring 0 <0.003 <0.003 <0.003 <0.003 80MCL

o-Dichlorobenzene Public supply 3 <0.048 <0.048 <0.048 e0.27 600MCL, 

600HAL

Monitoring 0 <0.050 <0.050 <0.050 <0.050 600MCL, 

600HAL

Dibromochloro

-methane

Public supply 2 <0.182 <0.182 <0.182 0.412 80MCL, 

60HAL

Monitoring 0 <0.100 <0.100 <0.100 <0.100 80MCL, 

60HAL

Vinyl chloride Public supply 2 <0.112 <0.112 <0.112 4.68 2MCL

Monitoring 0 <0.100 <0.100 <0.100 <0.100 2MCL

1,2-trans-DichloroethylenePublic supply 2 <0.032 <0.032 <0.032 e0.028 100MCL, 

100HAL

Monitoring 0 <0.050 <0.050 <0.050 <0.050 100MCL, 

100HAL

DichlorodifluoromethanePublic supply 2 <0.096 <0.096 <0.096 e0.78 1,000HAL

Monitoring 0 <0.200 <0.200 <0.200 <0.200 1,000HAL

Freon 113 Public supply 2 <0.032 <0.032 <0.032 e0.011 --

Monitoring 0 <0.050 <0.050 <0.050 <0.050 --

* Estimated values below the usual reporting level are given for samples in which the compound’s presence was verified from spectra. Values above the 

reporting levels are estimated if there are interferences, values below the lowest standard, or extraction recoveries less than normal. 

** HAL value from Florida Department of Health, 2004

Table 4. Summary of volatile organic compounds detected more than once in 30 public-supply wells and 32 monitoring 

wells in the Biscayne aquifer—Continued

[Units are micrograms per liter; e, estimated; HAL, health advisory level, 70-kilogram adult, lifetime, (U.S. Environmental 

Protection Agency, 2004); MCL, maximum contaminant level (U.S. Environmental Protection Agency, 2004); --, no applicable 

standard; <, less than; *, MCL for total xylenes. VOCs detected only once include dibromomethane, bromochloromethane, 

1,1-Dichloroethylene, 1,2-Dichloropropane, 1,3-Dichlorobenzene, Methyl-tertpentyl-ether, chlorotoluene, ethylether, methylisobutyl-ketone, and o-xylene]

Summary 17
proposed 300 picocurie per liter (pCi/L) maximum 

contaminant level for drinking water (U.S. Environmental Protection Agency, 2004). Radon-222 activities 

ranged from 202 to 1,800 pCi/L, with a median activity 

of 440 pCi/L.

Urban activities, such as turf-grass maintenance 

in golf courses, have increased concentrations of arsenic in ground water through the use of the herbicide 

MSMA. Some of the shallow monitoring wells located 

in golf courses had samples with concentrations that 

were higher than other wells in the network, although 

no samples exceeded the MCL of 50 mg/L. The values 

of arsenic in samples from the public-supply wells were 

lower than those from the shallow monitoring wells. 

Copper and lead concentrations were not substantially 

elevated in any of the samples.

Of the 86 pesticides analyzed in ground water from 

the Biscayne aquifer, both from the public-supply and 

from the monitoring wells, 15 pesticides were detected. 

One or more pesticides (generally atrazine or tebuthiuron) were detected in each of the 30 public-supply 

wells, and in 78 percent of the monitoring wells. One 

pesticide (atrazine) was detected in one of the samples 

from the three reference wells. No pesticide concentration exceeded any drinking-water standard. 

Of the 86 different VOCs analyzed, 32 were 

detected. Most samples from the monitoring, publicsupply, and reference wells had at least one VOC detection. Concentrations of VOCs in the samples were all 

less than drinking-water standards, except two samples 

from public-supply wells in an area near industrial 

development. These two samples had vinyl chloride 

concentrations (3 and 5 μg/L) that were above the MCL 

of 1 μg/L. 

Cis-1,2-dichloroethene was the most frequently 

detected VOC in the public-supply wells. This compound and other VOCs, such as trichlorethylene, vinyl 

chloride, 1,4-dichlorobenzene, 1,1-dichloroethane, and 

chlorobenzene, were detected more commonly in the 

older and denser residential and industrial areas. MTBE, 

a VOC that is a possible risk to human health, was the 

second most frequently detected VOC in the publicsupply wells. 

Toluene, p-isopropyltoluene, and 1,2,4-trimethylbenzene were the most frequently detected VOCs in 

shallow ground water from monitoring wells within the 

newer residential areas. Although the specific source 

of these compounds is uncertain, they may come from 

fuels.

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20 Quality of Ground Water in the Biscayne Aquifer in Miami-Dade, Broward, and Palm Beach Counties, Florida