Chemical Characteristics, Water Sources 

and Pathways, and Age Distribution of 

Ground Water in the Contributing Recharge 

Area of a Public-Supply Well near Tampa, 

Florida, 2002-05

By Brian G. Katz, Christy A. Crandall, Patricia A. Metz, 

William S. McBride, and Marian P. Berndt

National Water-Quality Assessment Program

Transport of Anthropogenic and Natural 

Contaminants (TANC) to Public-Supply Wells

Scientific Investigations Report 2007-5139

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Suggested citation:

Katz, B.G., Crandall, C.A., Metz, P.A., McBride, S., and Berndt, M.P., 2007, Chemical characteristics, water sources and 

pathways, and age distribution of ground water in the contributing recharge area of a public-supply well near Tampa, 

Florida, 2002-05: U.S. Geological Survey Scientific Investigations Report 2007-5139, 83 p.
iii

Foreword

The U.S. Geological Survey (USGS) is committed to providing the Nation with credible scientific 

information that helps to enhance and protect the overall quality of life and that facilitates 

effective management of water, biological, energy, and mineral resources (http://www.usgs.

gov/). Information on the Nation’s water resources is critical to ensuring long-term availability of 

water that is safe for drinking and recreation and is suitable for industry, irrigation, and fish and 

wildlife. Population growth and increasing demands for water make the availability of that water, 

now measured in terms of quantity and quality, even more essential to the long-term 

sustainability of our communities and ecosystems.

The USGS implemented the National Water-Quality Assessment (NAWQA) Program in 1991 to 

support national, regional, State, and local information needs and decisions related to waterquality management and policy (http://water.usgs.gov/nawqa). The NAWQA Program is designed 

to answer: What is the condition of our Nation’s streams and ground water? How are conditions 

changing over time? How do natural features and human activities affect the quality of streams 

and ground water, and where are those effects most pronounced? By combining information on 

water chemistry, physical characteristics, stream habitat, and aquatic life, the NAWQA Program 

aims to provide science-based insights for current and emerging water issues and priorities. 

From 1991-2001, the NAWQA Program completed interdisciplinary assessments and established 

a baseline understanding of water-quality conditions in 51 of the Nation’s river basins and 

aquifers, referred to as Study Units (http://water.usgs.gov/nawqa/studyu.html). 

Multiple national and regional assessments are ongoing in the second decade (2001–2012) of 

the NAWQA Program as 42 of the 51 Study Units are reassessed. These assessments extend the 

findings in the Study Units by determining status and trends at sites that have been consistently 

monitored for more than a decade, and filling critical gaps in characterizing the quality of surface 

water and ground water. For example, increased emphasis has been placed on assessing the 

quality of source water and finished water associated with many of the Nation’s largest 

community water systems. During the second decade, NAWQA is addressing five national 

priority topics that build an understanding of how natural features and human activities affect 

water quality, and establish links between sources of contaminants, the transport of those 

contaminants through the hydrologic system, and the potential effects of contaminants on 

humans and aquatic ecosystems. Included are topics on the fate of agricultural chemicals, 

effects of urbanization on stream ecosystems, bioaccumulation of mercury in stream ecosystems, 

effects of nutrient enrichment on aquatic ecosystems, and transport of contaminants to publicsupply wells. These topical studies are conducted in those Study Units most affected by these 

issues; they comprise a set of multi-Study-Unit designs for systematic national assessment. In 

addition, national syntheses of information on pesticides, volatile organic compounds (VOCs), 

nutrients, selected trace elements, and aquatic ecology are continuing. 

The USGS aims to disseminate credible, timely, and relevant science information to address 

practical and effective water-resource management and strategies that protect and restore 

water quality. We hope this NAWQA publication will provide you with insights and information 

to meet your needs, and will foster increased citizen awareness and involvement in the 

protection and restoration of our Nation’s waters. 
iv

The USGS recognizes that a national assessment by a single program cannot address all 

water-resource issues of interest. External coordination at all levels is critical for cost-effective 

management, regulation, and conservation of our Nation’s water resources. The NAWQA 

Program, therefore, depends on advice and information from other agencies—Federal, State, 

regional, interstate, Tribal, and local—as well as nongovernmental organizations, industry, 

academia, and other stakeholder groups. Your assistance and suggestions are greatly 

appreciated.

 Robert M. Hirsch

Associate Director for Water
v

Contents 

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

Introduction.....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................4

Description of Study Area ...................................................................................................................4

Previous Studies ...................................................................................................................................5

Acknowledgments................................................................................................................................6

Methods...........................................................................................................................................................6

Design of Monitoring Well Network ..................................................................................................6

Drilling, Coring, and Well Installation ................................................................................................7

Collection and Analysis of Water Samples ....................................................................................12

Age Dating of Ground Water.............................................................................................................13

Tritium and Tritiogenic Helium-3..............................................................................................13

Sulfur Hexafluoride....................................................................................................................14

Quality Assurance...............................................................................................................................15

Lithology, Mineralogy, and Elemental Analysis of Core Material...............................................15

Hydrogeologic Setting.................................................................................................................................16

Lithology and Mineralogy of the Hydrogeologic Units .................................................................19

Estimation of Aquifer Properties ......................................................................................................22

Ground-Water Flow Patterns............................................................................................................24

Ground-Water Chemistry............................................................................................................................24

Chemical Composition and Mineral Saturation Indexes..............................................................24

Dissolved Organic Carbon and Dissolved Solids Concentrations..............................................25

Redox Conditions ................................................................................................................................30

Stable Isotopes of Water...................................................................................................................31

Ground-Water Age and Age Distributions...............................................................................................35

Apparent Sulfur Hexafluoride and Tritium/Helium-3 Ground-Water Ages................................35

Assessing Ground-Water Age Distributions Using Lumped Parameter Models .....................39

Occurrence of Anthropogenic and Naturally Occurring Contaminants in 

Ground-Water Samples.................................................................................................................41

Nitrate-N Concentrations and Isotopes and Dissolved Gases ...................................................41

Volatile Organic Compounds.............................................................................................................46

Pesticides.............................................................................................................................................51

Sulfur Species and Hydrogen Sulfide .............................................................................................52

Radon-222 and Uranium.....................................................................................................................54

Arsenic Concentrations and Speciation.........................................................................................60

Temporal Variability in Water Chemistry from Surficial Aquifer System Wells and 

the Public-Supply Well ..................................................................................................................60

Sources and Mixing of Water in the Public-Supply Well......................................................................62

Chemical Variations with Depth during Ambient and Pumping Conditions ..............................62

Estimating Mixing Proportions of Water Using Geochemical Mass-Balance Modeling .......64

Movement of Contaminants to the Public-Supply Well................................................................65

Summary........................................................................................................................................................67

Selected References...................................................................................................................................69
vi

Appendix A1. Summary of quality-assurance results for organic compounds in blanks and 

replicates.........................................................................................................................................79

Appendix A2. Summary of quality-assurance results for selected chemical constituents 

in field blank and replicate samples ...........................................................................................80

Appendix A3. Percent recovery values for surrogate compounds added to ground-water 

and surface-water samples at the U.S. Geological Survey National Water 

Quality Laboratory..........................................................................................................................82

Appendix A4. Oxidation-reduction (redox) classification scheme developed for the 

transport of anthropogenic and natural contaminants to public-supply wells ...................85

Figures

1. Map showing large- and small-scale areas for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public-supply wells, 

photolineaments, degree of confinement of the Upper Floridan aquifer, and 

selected karst features in west-central Florida ......................................................................3

2. Map showing location of potential sources of contaminants to ground water in 

the Temple Terrace, Florida, study area....................................................................................5

3. Map showing lines of hydrogeologic sections, sampling site locations, and 

direction of ground-water flow in the Upper Floridan aquifer in the Temple Terrace, 

Florida, study area ........................................................................................................................7

4. Plot showing input of sulfur hexafluoride to atmosphere in the northern hemisphere 

and tritium concentrations in rainfall from Ocala, Florida, during 1950-2005 ...................14

5A. Chart showing stratigraphic and hydrogeologic units of the Temple Terrace, 

Florida, study area ......................................................................................................................17

5B. Cross sections showing generalized hydrogeologic sections A-A’ and B-B’ ..................18

6. Plot showing geophysical logs of the public-supply well borehole at Temple 

Terrace, Florida ...........................................................................................................................23

7. Trilinear (Piper) diagram of major-ion chemistry for ground-water and surfacewater samples from the Temple Terrace, Florida, study area.............................................25

8-25. Plots showing:

 8. Dissolved oxygen and hydrogen sulfide concentrations with well 

depth from the surficial aquifer system, intermediate confining unit, and Upper 

Floridan aquifer in the Temple Terrace, Florida, study area.........................................30

 9. Oxygen and hydrogen isotopes in ground water and surface water 

from the surficial aquifer system, intermediate confining unit, and Upper 

Floridan aquifer in the Temple Terrace, Florida, study area.........................................31

 10. Comparison of apparent ages based on the piston-flow assumption and 

measured concentrations of sulfur hexafluoride, tritium, and helium-3 in 

water samples from the surficial aquifer system, intermediate confining unit, 

and Upper Floridan aquifer in the Temple Terrace, Florida, study area.....................35

 11. Measured concentrations of sulfur hexafluoride and tritium in 

water samples from wells, and lumped-parameter modeled curves for various 

ground-water age distributions from the surficial aquifer system, intermediate 

confining unit, and Upper Floridan aquifer in the Temple Terrace, Florida, 

study area .............................................................................................................................40
vii

 12. Measured concentrations of sulfur hexafluoride, tritium, the ratio of 

tritium to the sum of helium-3 and tritium in water samples from wells, and 

lumped-parameter modeled curves for ground-water age distributions from 

the surficial aquifer system, intermediate confining unit, and Upper Floridan 

aquifer in the Temple Terrace, Florida, study area ........................................................41

 13. Nitrate-N concentrations with well depth in the Temple Terrace, 

Florida, study area...............................................................................................................42

 14. Values for delta nitrogen-15 and delta oxygen-18 of nitrate in water from 

wells in the Temple Terrace, Florida, study area............................................................42

 15. Detection frequency of volatile organic compounds in ground 

water from the surficial aquifer system, intermediate confining unit, Upper 

Floridan aquifer, and stormwater retention ponds in the Temple Terrace, 

Florida, study area...............................................................................................................46

 16. Concentrations of selected volatile organic compounds detected 

in water samples from the surficial aquifer system, intermediate confining unit, 

Upper Floridan aquifer, and public-supply well in the Temple Terrace, 

Florida, study area...............................................................................................................50

 17. Comparison of trichloromethane (chloroform) and dichloromethane 

(methylene chloride) concentrations in water samples collected from the oxic 

surficial aquifer system and the anoxic Upper Floridan aquifer in the 

Temple Terrace, Florida, study area .................................................................................50

 18. Pesticides detected in ground-water samples and surface-water

samples from the Temple Terrace, Florida, study area .................................................51

 19. Sulfate concentrations and delta sulfur-34 of sulfate in water samples from 

the surficial aquifer system, intermediate confining unit, Upper Floridan 

aquifer, and retention ponds in the Temple Terrace, Florida, study area...................53

 20. Relation between sulfate-to-chloride ratios and sulfate concentrations in 

water from the surficial aquifer system, intermediate confining unit, and 

Upper Floridan aquifer in the Temple Terrace, Florida, study area.............................53

 21. Radon-222 concentrations with well depth below land surface for the 

surficial aquifer system, intermediate confining unit, and Upper Floridan 

aquifer in the Temple Terrace, Florida, study area ........................................................54

 22. Median concentrations of radon-222, arsenic, uranium, hydrogen 

sulfide, iron, and dissolved organic carbon in oxic and anoxic water from 

monitoring wells and the public-supply well in the Temple Terrace, Florida, 

study area .............................................................................................................................55

 23. Arsenic concentrations with well depth and arsenic species (arsenic (III) and 

arsenic (V) concentrations) in water samples from wells in the surficial aquifer 

system, intermediate confining unit, and Upper Floridan aquifer in the Temple 

Terrace, Florida, study area, October 2004......................................................................60

 24. Temporal variability of chloride, nitrate-N, dissolved organic carbon, and 

ground-water levels in water samples collected from wells RP-S20, WP-S64, 

GARC-S23, and TTP-4 in the Temple Terrace, Florida, study area ..............................61

 25. Relation between the sulfur hexafluoride apparent recharge year and 

concentrations of nitrate-N, and trichloromethane in water samples from 

the surficial aquifer system, intermediate confining unit, Upper Floridan 

aquifer, and public-supply well in the Temple Terrace, Florida, study area ..............66
viii

Tables

1. Well construction and location information for monitoring wells tapping the 

surficial aquifer system, intermediate confining unit, and Upper Floridan aquifer...........8

2. Description of lithology and results from grain-size analysis from sediments 

underlying the study area............................................................................................................9

3. Summary of water-quality and solid-phase analyses in the transport of 

anthropogenic and natural contaminants (TANC) small-scale study area.......................12

4. Mineralogy of surficial sediments or rock, elemental composition from acid 

extractions, and concentrations of iron and sulfide from extractions of selected 

samples of core material...........................................................................................................20

5. Physical properties and chemistry of water samples from the surficial aquifer 

system, intermediate confining unit, and Upper Floridan aquifer in the study area .......26

6. Data for delta oxygen-18 and delta hydrogen-2, delta carbon-13 in dissolved 

inorganic carbon, nitrogen and oxygen isotopes of nitrate, delta sulfur-34 of 

sulfate, and radon-222 in water samples from the surficial aquifer system,

intermediate confining unit, Upper Floridan aquifer, ponds, and river..............................32

7. Summary of sulfur hexafluoride results for water samples from wells in the 

surficial aquifer system, intermediate confining unit, and Upper Floridan aquifer.........36

8. Summary of tritium/helium-3 age data using piston-flow model for water samples 

from the surficial aquifer system, intermediate confining unit, and Upper 

Floridan aquifer...........................................................................................................................38

9. Dissolved gas data, calculated excess nitrogen gas concentration, estimated 

recharge temperature, and excess air concentration in water samples collected 

from the public-supply well and monitoring wells in the Temple Terrace, Florida, 

study area ....................................................................................................................................43

10. Volatile organic compounds detected in water samples from the surficial aquifer 

system, intermediate confining unit, Upper Floridan aquifer, and stormwater 

retention ponds ...........................................................................................................................47

11. Concentrations of pesticides detected in ground-water and surface-water 

samples ........................................................................................................................................52

12. Concentrations of trace elements and arsenic species, arsenic (III), and 

arsenic (V) in ground-water samples......................................................................................56

13. Chemical properties of water samples collected from various depth intervals 

in the public-supply well............................................................................................................63

14. Chemical mass transfer associated with mixing scenarios and comparison of 

observed and modeled isotopic composition ........................................................................66
ix

Conversion Factors, Datum, Abbreviated Units, 

and Acronyms

SI to Inch/Pound

Multiply By To obtain

centimeter (cm) 0.3937 inch

centimeter per year (cm/yr) 0.3937 inch per year

gram (g) 0.03527 ounce, avoirdupois

square kilometer (km2) 0.3861 square mile

liter (L) 0.2642 gallon

liter per minute (L/min) 4.403 x 10-3 gallon per second

meter (m) 3.281 foot

meter per day (m/d) 3.281 foot per day

meter squared per day (m2/d) 10.76 foot squared per day

millimeter (mm) 0.03937 inch

picocurie per liter (pCi/L) 0.037 becquerel per liter

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

°F=(1.8×°C)+32

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88)

Horizontal coordinate information is referenced to the North American Datum of 1983 

(NAD 83)
x

Chemical Abbreviations

δ13C 			 Delta carbon-13

δ2H Delta hydrogen-2

δ18O Delta oxygen-18

δ34S Delta sulfur-34

δ15N Delta nitrogen-15

3

H Tritium

3

He Helium-3

3

H(0) Initial tritium concentration

4

He Helium-4

3

Hetrit Tritiogenic helium-3

MTBE Methyl tert-butyl ether

Ne Neon

SF6 Sulfur hexafluoride

Other Abbreviations

cm3/L cubic centimeter per liter

μm micron

μg/L microgram per liter

mg/kg milligram per kilogram

mg/L milligram per liter

mL milliliter

mmol/kg millimole per kilogram

nM nanomolar

ppm parts per million

pptv parts per trillion by volume
xi

Acronyms

ICP-OES Inductively coupled plasma optical emission spectroscopy

ICP-MS Inductively coupled plasma mass spectrometry

NAWQA National Water-Quality Assessment Program

TANC Transport of Anthropogenic and Natural Contaminants

USGS U.S. Geological Survey

NOAA National Oceanic and Atmospheric Administration

PVC Polyvinyl chloride
xii
Abstract 1

Abstract

In 2001, the National Water-Quality Assessment 

(NAWQA) Program of the U.S. Geological Survey began a 

series of studies on the transport of anthropogenic and natural 

contaminants (TANC) to public-supply wells. The main goal 

of the TANC program was to better understand the source, 

transport, and receptor factors that control contaminant movement to public-supply wells in representative aquifers of the 

United States. Studies were first conducted at regional scales 

at four of the eight TANC study areas during 2002-03 and at 

small (local) scales during 2003-05 in California, Nebraska, 

Connecticut, and Florida. 

In the Temple Terrace study area near Tampa, Florida, 

multiple chemical indicators and geochemical and groundwater flow modeling techniques were used to assess the 

vulnerability of a public-supply well in the karstic Upper 

Floridan aquifer to contamination from anthropogenic and 

naturally occurring contaminants. During 2003-05, water 

samples were collected from the public-supply well and 

13 surrounding monitoring wells that all tap the Upper 

Floridan aquifer, and from 15 monitoring wells in the 

overlying surficial aquifer system and the intermediate 

confining unit that are located within the modeled groundwater contributing recharge area of the public-supply well. 

Six volatile organic compounds and four pesticides were 

detected in trace concentrations (well below drinking-water 

standards) in water from the public-supply well, which had 

an open interval from 36 to 53 meters below land surface. 

These contaminants were detected more frequently in water 

samples from monitoring wells in the overlying clastic surficial aquifer system than in water from monitoring wells in the 

Upper Floridan aquifer in the study area. Likewise, nitrate-N 

concentrations in the public-supply well (0.72-1.4 milligrams 

per liter) were more similar to median concentrations in the 

oxic surficial aquifer system (2.1 milligrams per liter) than to 

median nitrate-N concentrations in the anoxic Upper 

Floridan aquifer (0.06 milligram per liter) under sulfatereducing conditions. High concentrations of radon-222 and 

uranium in the public-supply well compared to those in 

monitoring wells in the Upper Floridan aquifer appear to 

originate from water moving downward through sands and 

discontinuous clay lenses that overlie the aquifer. 

Water samples also were collected from three 

overlapping depth intervals (38-53, 43-53, and 49-53 meters 

below land surface) in the public-supply well. The 49- to 

53-meter interval was identified as a high-flow zone during 

geophysical logging of the wellbore. Water samples were 

collected from these depth intervals at a low pumping rate by 

placing a low-capacity submersible pump (less than 

0.02 cubic meter per minute) at the top of each interval. To 

represent higher pumping conditions, a large-capacity portable 

submersible pump (1.6 cubic meters per minute) was placed 

near the top of the open interval; water-chemistry samples 

were collected using the low-capacity submersible pump. The 

49- to 53-meter depth interval had distinctly different chemistry than the other two sampled intervals. Higher concentrations 

of nitrate-N, atrazine, radon, trichloromethane (chloroform), 

and arsenic (and high arsenic (V)/arsenic (III) ratios); lower 

concentrations of dissolved solids, strontium, iron, manganese, 

and lower nitrogen and sulfur isotope ratios were found in this 

highly transmissive zone in the limestone than in water from 

the two other depth intervals.

Movement of water likely occurs from the overlying sands and clays of the oxic surficial aquifer system and 

intermediate confining unit (that contains high radon-222 and 

nitrate-N concentrations) into the anoxic Upper Floridan aquifer (that contains low radon-222 and nitrate-N concentrations). 

Chemical Characteristics, Water Sources and 

Pathways, and Age Distribution of Ground Water 

in the Contributing Recharge Area of a 

Public-Supply Well near Tampa, Florida, 2002-05

By Brian G. Katz, Christy A. Crandall, Patricia A. Metz, William S. McBride, and Marian P. Berndt 
2 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

Differences in arsenic concentrations in water from the various 

depth intervals in the public-supply well (3.2-19.0 micrograms 

per liter) were related to pumping conditions. The high arsenic 

concentrations found in the high flow zone during pumping 

conditions indicates that oxic water from the surficial aquifer 

system may travel into conduits in the Upper Floridan aquifer 

and mobilize arsenic from pyrite in the aquifer matrix.

Geochemical mass-balance mixing models for the 

public-supply well indicate that 50 to 70 percent of water 

withdrawn from the public-supply well is being contributed 

from the surficial aquifer system and 30 to 50 percent from the 

Upper Floridan aquifer. Geochemical models also indicate the 

dissolution of small amounts of calcite, gypsum, and dolomite 

as water moves toward the public-supply well. 

Concentrations of age tracers sulfur hexafluoride (SF6), 

tritium (3H), and helium-3 (3He) in samples from the publicsupply well during low- and high-rate pumping conditions 

were consistent with binary mixtures dominated by young 

water (less than 7 years). Similarly, water samples from 

monitoring wells in the surficial aquifer system had SF6 and 3H 

concentrations that indicate a substantial proportion of young 

water (less than 7 years). In contrast, most water samples from 

monitoring wells in the Upper Floridan aquifer had lower SF6

and 3H concentrations than water from the public-supply well, 

indicating mixtures containing higher proportions of older 

waters (greater than 50 years). The presence of young water 

(less than 7 years) in the public-supply well and surficial 

aquifer system indicates the vulnerability of public-supply 

wells in this area to contamination associated with highly 

transmissive zones in the Upper Floridan aquifer that are 

directly connected to the overlying surficial aquifer system.

Selected monitoring wells in the surficial aquifer 

system were sampled several times during 2003-05 at different 

hydrologic conditions to evaluate temporal variability in water 

quality. These wells were sampled four times before and after 

three tropical cyclones that passed through the area in summer 

2004. Additionally, water-quality variations were evaluated for 

the public-supply well based on five samples collected during 

2002-05. Chloride concentrations decreased from the 

summer 2004 water samples to the winter 2004-05 samples 

from three wells following the recharge pulse from high rainfall and corresponding peak in water-level elevation in October 

2004. Nitrate-N concentrations increased in water from one 

well from January 2004 to August 2004, but decreased in 

water from another well during the same period. Nitrate-N 

concentrations also increased in water samples from two other 

monitoring wells in the surficial aquifer system, from January 

2004 to August 2004, but decreased in subsequent samples 

from these two wells. Nitrate-N concentrations in water from 

a well located near the Hillsborough River remained below 

the detection limit, as reducing conditions persisted during 

December 2003 to July 2005. Dissolved oxygen concentrations increased in water samples from two wells in the surficial aquifer system, and the public-supply well in August and 

September 2004 during and following the above normal rainfall in June through September 2004. The increase in dissolved 

oxygen concentrations likely results from recent recharge of 

water containing high levels of oxygen compared to low levels 

in ground water prior to the excess rainfall period. Dissolved 

oxygen concentrations decreased in water from a well near the 

Hillsborough River in fall 2004, which may indicate the influx 

of river water with high dissolved organic carbon and subsequent consumption of oxygen as water moves toward this well.

Introduction

The vulnerability of public-supply wells to contamination has raised health concerns throughout the United States. 

Anthropogenic contaminants, such as solvents, disinfection 

byproducts, and other volatile organic compounds (Ivahnenko 

and Zogorski, 2006; Schaap and Zogorski, 2006; Zogorski and 

others, 2006) and pesticides (Gillion and others, 2006) have 

been detected in low concentrations in water from drinkingwater supply wells across the United States. Ground-water 

contamination from nutrients, such as nitrate, are widespread 

(Nolan and others, 1998) particularly in karstic aquifers 

(Katz, 2004). In addition, other studies have found high levels 

of naturally occurring contaminants, such as radon (Sowerby 

and others, 2000), uranium (B. Jurgens, U.S. Geological 

Survey, written commun., 2007; M.K. Landon, U.S. 

Geological Survey, written commun., 2007), and arsenic 

(Focazio and others, 1999; Welch and others, 2000) also are 

present in drinking water wells. 

In response to these concerns, the U.S. Geological Survey 

(USGS) National Water-Quality Assessment (NAWQA) 

Program began a series of studies in 2001 to assess the 

vulnerability of public-supply wells to contamination with 

regard to the transport of anthropogenic and naturally occurring contaminants (TANC) to public-supply wells at regional 

and small scales at several sites in the United States (Eberts 

and others, 2005). The TANC studies were built on previous 

NAWQA studies that found low levels of mixtures of contaminants in ground water beneath urban areas across the United 

States (Hamilton and others, 2004). 

The overall objectives of the TANC studies are to: 

(1) identify the dominant contaminants and sources of those 

contaminants in public-supply wells in representative watersupply aquifers across the United States; (2) assess the effects 

of natural processes and human activities on the occurrence of 

contaminants in public-supply wells in representative aquifers; 

(3) identify the factors that are most important to incorporate 

into public-supply well vulnerability assessments in different 

settings and at different scales; (4) develop simple methods 

and models for screening public-supply wells for vulnerability to contamination in unstudied areas and from emerging 

contaminants; and (5) increase understanding of the potential 

effects of water-resources development and management decisions on the quality of water from public-supply wells (Eberts 

and others, 2005). 
Introduction 3

The Floridan aquifer system provides drinking water to 

millions of people throughout the southeastern United States. 

The Upper Floridan aquifer is particularly vulnerable to 

contamination from various land-use activities in areas where 

it is unconfined or poorly confined as in west-central Florida. 

This vulnerability is due in part to the presence of numerous 

karst features, such as sinkholes, which facilitate the 

movement of water from surface features and overlying 

hydrogeologic units to the Upper Floridan aquifer (fig. 1). In 

addition, lineaments of sinkholes and other solution features 

that trend predominantly in a northeast-southwest direction 

have been mapped throughout the area and reveal the 

regionally extensive karst terrane (fig. 1).

0 10 KILOMETERS

82°45' 82°30' 82°15' 82°00'

28°00'

28°15'

28°30'

EXPLANATION

CITY OF

TAMPA

CITY OF

TEMPLE

TERRACE

Unconfined

Confining unit thickness less than 30 meters

Confining unit thickness greater than 30 meters

PHOTOLINEAMENTS

LARGE-SCALE MODELED AREA

Gulf of Mexico

SINKHOLE, CLOSED DEPRESSION

SMALL-SCALE MODELED AREA

DEGREE OF CONFINEMENT OF

UPPER FLORIDAN AQUIFER

0 10 MILES

Albers Equal Area projection, units: meters, False Easting: 0, False Northing: 0

Central meridian: -83°00', 1st satndard parrallel: 29°30', 2nd standard parrallel: 45°30'

Latitude of origin: 23°00', Datum is NAD 1983

Figure 1. Large- and small-scale areas for the study of the transport of anthropogenic and natural contaminants 

(TANC) to public-supply wells, photolineaments (modified from Culbreath, 1988; Knochenmus and Robinson, 1996), 

degree of confinement of the Upper Floridan aquifer, and selected karst features in west-central Florida.
4 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

This study focuses on a public-supply well located in 

an urban area where various anthropogenic activities at the 

land surface provide potential sources of contaminants, such 

as underground storage tanks, fertilizers applied to lawns and 

golf courses, stormwater retention ponds, and other commercial operations. Additionally, hydrogeologic and geochemical 

conditions in the subsurface may facilitate the ground-water 

transport of uranium, radon-222, and arsenic present in minerals that make up the limestone that composes the Upper 

Floridan aquifer and overlying material to public-supply wells. 

The public-supply well (referred to as TTP-4) in the City 

of Temple Terrace was sampled for a variety of chemical and 

bacteriological constituents, as part of a source water-quality 

assessment study by the USGS NAWQA Program in 2002. 

Several contaminant groups, at concentrations below 

maximum contaminant levels, were found in water from 

TTP-4 including nitrate, volatile organic compounds, pesticides, methyl tert-butyl ether (MTBE), solvents, uranium, and 

arsenic. Several of these compounds have been detected in 

other community water system wells in the northern Tampa 

Bay area (Metz and others, 2007). Construction and operational practices of TTP-4 are similar to many other community 

water system wells that supply water in the Tampa Bay region 

at a pumping rate of 2,650 L/min (liters per minute).

The construction and operational practices of TTP-4 

also are representative of community and public-supply wells 

throughout northern Florida and other karstic aquifers in the 

United States. Consequently, this study provides important 

information about the transport and fate of contaminants that 

can be introduced to the land surface or released from minerals that compose the aquifer matrix and material overlying the 

principal aquifer, as they move to deeper ground water that 

is eventually withdrawn for public-water supply. This study 

investigates the dominant factors affecting the vulnerability 

of public-supply wells to contamination, such as geochemical 

conditions in the aquifer, the amount and rate of pumping, and 

mixing of water from different hydrogeologic units. 

Purpose and Scope

The purpose of this report is to assess factors affecting 

the vulnerability to contamination of a public-supply well in 

the Upper Floridan aquifer near Tampa, Florida. The report 

presents information on the hydrogeologic setting, occurrence 

and distribution of ground-water ages, and selected chemical 

characteristics of the ground water in the contributing recharge 

area of a public-supply well. The occurrence and distribution 

of selected inorganic and organic chemical constituents that 

are useful for developing basic interpretations of ground-water 

recharge and discharge patterns and pathways are described. 

Factors are assessed that influence transport of anthropogenic 

contaminants (for example, nitrate, volatile organic compounds, and pesticides) and naturally occurring compounds of 

concern (radon-222, arsenic, uranium, dissolved organic 

carbon, and hydrogen sulfide) to supply wells for the TANC 

study area at Temple Terrace near Tampa, Florida. This report 

includes a description of the design of the monitoring well 

network, methods of data collection and analysis, estimates 

of apparent ground-water ages and ground-water age distributions using atmospheric tracers and lumped parameter models, 

and isotopic and other chemical information for ground- and 

surface-water samples. This report is intended to serve as a 

foundation for synthesis analyses comparing results between 

the Temple Terrace study area and other TANC study areas in 

Nebraska, California, and Connecticut. 

Description of Study Area

The small-scale study area is 86 km2 (square kilometers) 

and encompasses the city of Temple Terrace, which is located 

northeast of Tampa, Florida, in north-central Hillsborough 

County (fig. 1). Temple Terrace is in the Hillsborough River 

drainage basin, and is bounded on the west and southwest by 

the city of Tampa and on the east and south by the Hillsborough River (fig. 2). Public-supply wells in Temple Terrace tap 

the Upper Floridan aquifer, which underlies most of the Southeast and is a significant drinking-water source for the Tampa 

Bay region, as well as about 9 million people living in parts of 

Alabama, Florida, Georgia, and South Carolina (Marella and 

Berndt, 2005).

The population of Temple Terrace has grown 

exponentially during the past 50 years — with about 

430 people in 1950, 10,751 people in 1974, and 20,918 people 

in 2000. The population density in 2000 was 1,135 people 

per square kilometer. The growth in population occurred while 

land use transitioned from agricultural in 1950 to commercial and residential in the 1970s and later. Temple Terrace is 

located on a local topographic high, with land-surface 

elevations close to 27 m (meters) along the western edge of the 

city to less than 6 m at the Hillsborough River. Urban drainage within Temple Terrace is routed to a series of stormwater 

retention basins. During high-water conditions, excess 

water is pumped from these basins and discharged into the 

Hillsborough River. 

Average annual rainfall in the Tampa area was 114 cm 

(centimeters) for the period 1971-2000, as recorded at the 

National Oceanic and Atmospheric Administration (NOAA) 

station at the Tampa International Airport (National Climatic 

Data Center, 2005). On average, about 60 percent of the rainfall occurs from June through September. August is typically 

the wettest month, with about 17 percent of the annual rainfall. 

November is typically the driest month, with slightly less than 

4 percent of the annual rainfall. 

Potential sources of contaminants to ground water in 

the Temple Terrace study area include underground storage 

tanks, septic tanks, stormwater runoff to retention ponds, dry 

cleaners and other commercial operations that use solvents, 

chemicals applied to golf courses and lawns, and hazardous 

waste sites (fig. 2). 
Introduction 5

Previous Studies

A detailed hydrogeologic and water-quality study was 

conducted by the USGS in the early 1970s, in cooperation 

with the City of Temple Terrace, to provide information to the 

City for the development of additional ground-water supplies 

and to minimize problems with poor quality water (Stewart 

and others, 1978). Data were collected on aquifer properties, 

water-quality variations with depth in the Upper Floridan 

aquifer, geohydrologic characteristics of the Upper Floridan aquifer and surficial material, ground-water levels, and 

chemistry and microbiology of water samples from wells and 

surface-water sites. Degradation of water quality in Temple 

Terrace public-supply wells as early as 1968 was documented, 

including high concentrations of total coliform bacteria, fecal 

streptococci, and color (Stewart and others, 1978). 

582 582

583

41

41

301

301

92 92

CITY OF TAMPA

CITY OF TEMPLE TERRACE

AREA OF WELL MONITORING

NETWORK

SMALL-SCALE STUDY AREA

STREAM AND OPEN WATER

DRY CLEANER

UNDERGROUND STORAGE

TANK

STORMWATER POND

HAZARDOUS WASTE SITE

275

0 2 KILOMETERS

4

28°00'

28°04'

82°26' 82°22'

EXPLANATION

1

0 1 2 MILES

4

75

75

Albers Equal Area projection, units: meters, False Easting: 0, False Northing: 0

Central meridian: -83°00', 1st satndard parrallel: 29°30', 2nd standard parrallel: 45°30'

Latitude of origin: 23°00', Datum is NAD 1983

Figure 2. Location of potential sources of contaminants to ground water in the Temple Terrace, Florida, 

study area.
6 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

Geologic sections showing the thickness and configuration of shallow sedimentary layers that underlie the Hillsborough River were constructed from seismic-profile records 

along a river subreach near Temple Terrace as part of a study 

to evaluate connections between ground water and surface 

water in the Hillsborough River basin (Wolansky and Thompson, 1987). That study described leakage of river water to the 

Upper Floridan aquifer based on decreasing river flow along 

a section of the river that included Temple Terrace (Wolansky 

and Thompson, 1987). However, interactions between ground 

water and surface water are complex, as a study in the early 

1970s found that the Hillsborough River receives inflow from 

both the water-table aquifer (within the surficial aquifer system) and the Upper Floridan aquifer south and east of Temple 

Terrace due to head relations between ground water and surface water that change seasonally (Stewart and others, 1978). 

Other studies have characterized the hydrogeology and 

hydrochemistry of the Upper Floridan aquifer and surficial 

aquifer system in this area (Miller, 1986; Trommer, 1987; 

Aucott, 1988; Bush and Johnston, 1988; Sprinkle, 1989; 

Berndt and Katz, 1992; Katz, 1992; Knochenmus and Robinson, 1996; Yobbi, 2000). Swancar and Hutchinson (1995) 

related the stable isotope composition and tritium concentrations to the potential for contamination of ground water in the 

shallow Upper Floridan aquifer in west-central Florida. 

A regional study of the transport of anthropogenic and 

natural contaminants in 2002-03 in the Tampa, Florida, area 

was designed to identify factors affecting contaminant transport based on existing data for public-supply wells, and to 

delineate contributing recharge areas of public-supply wells 

using an existing ground-water flow model (Paschke, 2006). 

During October 2002 to January 2003, a number of (30) 

community water system wells in the northern Tampa Bay 

area were sampled for 260 anthropogenic organic compounds 

as part of a NAWQA source water study for wells that provide 

drinking water (Metz and others, 2007). The 10 most 

frequently occurring anthropogenic organic compounds in 

the United States (Zogorski and others, 2006) were detected 

in more than 10 percent of the 30 source water samples, and 

included volatile organic compounds and pesticides. Samples 

generally averaged three compounds, and 70 percent of the 

samples had at least one volatile organic compound (Metz and 

others, 2007). This study also found a significant correlation 

between the number of anthropogenic organic compounds 

detected and population within a 500-m radius of a community 

water system well. Chloroform concentrations were highest 

beneath areas where residential land use was greater than 

73 percent. Similar findings were noted for pesticides in 

source water for community water system wells (Metz and 

others, 2007). 

Acknowledgments

Assistance with water-quality sampling was provided 

by the following individuals: Bruce Bernard, Darlene Blum, 

Terry Petrosky, John Pittman, and Ann Tihansky. The authors 

thank Amy Swancar, Lynne Fahlquist, and J.K. Böhlke for 

their review comments and suggestions that improved earlier 

versions of this report. We gratefully acknowledge the logistical assistance from the City of Temple Terrace Department of 

Utilities. 

Methods

This section contains information about the sampling 

network design, monitoring well installation, water-quality 

sampling and analysis, quality assurance, and data analysis. 

This section also describes the collection of aquifer material samples for characterizing lithology and mineralogy and 

elemental analysis of core material from hydrogeologic units, 

collection and analysis of chemical and isotopic constituents, 

and age dating of ground water. 

Design of Monitoring Well Network

Wells were installed in the contributing recharge area of 

public-supply well TTP-4 based on a regional ground-water 

flow model (C.A. Crandall, U.S. Geological Survey, written 

commun., 2007) and in adjacent areas to better understand 

ground-water flow patterns and to determine the occurrence of 

various chemicals in the surficial aquifer system, intermediate confining unit, and Upper Floridan aquifer. Additionally, 

selected monitoring wells were sampled several times during 

the study to evaluate temporal variability in water quality. 

Monitoring wells were installed in two phases: (1) during late 

fall 2003 and winter 2004, and (2) during summer 2004 

(fig. 3). Monitoring wells were located in the contributing 

recharge area of the public-supply well. Contributing recharge 

areas of the public-supply well were delineated using particletracking software and a stochastic model that incorporated 

fracture flow (C.A. Crandall, U.S. Geological Survey, written 

commun., 2007). During the first phase of well drilling, 

15 wells were installed in 5 well nests, with each nest containing 3 wells. Most of these nests consisted of one shallow well 

screened in the surficial aquifer system, one well screened 

near the top of the Upper Floridan aquifer, and one deep 

well in the Upper Floridan aquifer. Because the intermediate 

confining unit was absent at most locations, only one well 

(113RC-H50) was installed in that unit during phase 1. During 

the second phase of well drilling, another 15 monitoring wells 

were installed. These well locations were based on updated 

estimates of the contributing recharge area of public-supply 

well TTP-4 based on Monte Carlo probabilistic methods to 

incorporate uncertainty and karst features into the model (C.A. 

Crandall, U.S. Geological Survey, written commun., 2007). 

A total of 12 monitoring wells were installed in the surficial 

aquifer system, 4 in the intermediate confining unit, and 14 

in the Upper Floridan aquifer. Surface-water samples were 

collected from the Hillsborough River (denoted as station 
Methods 7

HRiver in figures and tables) and stormwater retention ponds 

(fig. 3). Well depth and other well construction information are 

contained in table 1.

Drilling, Coring, and Well Installation

Hollow-stem augering techniques that conformed to 

USGS protocols (Lapham and others, 1995) were used to 

install monitoring wells in the surficial aquifer system, intermediate confining unit, and shallow Upper Floridan aquifer 

(wells less than 60-m deep). Mud-rotary methods were used 

for the installation of the deep monitoring wells in the Upper 

Floridan aquifer. Equipment was decontaminated between 

sites by steam cleaning. All monitoring wells consisted of 

threaded polyvinyl chloride (PVC) pipe (schedule 40, 10-cm 

diameter) and had 3-m-long screens with 1-mm (millimeter) 

slots. Clean silica sand was packed around the well screens. 

The wells were sealed by placing bentonite above the sand 

packing material to land surface, and cementing above the 

bentonite at the surface with a steel well protector and locking 

cap. Wells were developed using a surging pump until 

stabilization of field properties (pH, specific conductance, 

temperature, dissolved oxygen) and turbidity. 

Split-spoon samples were collected in boreholes, and 

samples of rock (cores) were collected in one well 

(MAS-F160). A description of the lithology of the cores and 

cuttings obtained during well drilling and a summary of 

analyses performed on selected core samples are presented in 

table 2. Core samples were collected using a split-spoon 

sampler (with clear plastic liners) in unconsolidated sediment or a core barrel in rock. Subsamples were processed in 

a closed chamber that was purged with ultra-pure nitrogen 

gas. Some subsamples of core material were stored in capped 

plastic cylinders, and other samples were stored in glass jars 

and kept on ice. Core samples were analyzed for bulk and clay 

mineralogy, elemental composition, organic matter content, 

bulk density, and volumetric moisture content (table 3). 

Recharge estimates were based on unsaturated zone properties 

(R. Healy, U.S. Geological Survey, written commun., 2004). 

Pore water extracted from cores collected at various depths 

at the Lynnwood Park (LP) and Lightfoot Retention Pond 

(LRP) sites were analyzed for nitrate-N, chloride, sulfate, 

and bromide (P. McMahon, U.S. Geological Survey, written 

commun., 2004). Particle-size distribution of core subsamples 

was characterized using optical diffraction and a particle-size 

analyzer (Gee and Or, 2002). Sediments in the size range of 

582

583

0 0.25 0.50 MILES

0 0.25 0.50 KILOMETERS

82°23'30" 82°23' 82°22'30" 82°22'

28°02'30"

28°03'

Hillsborough

River

LRPS25

H105

F160

POND

LPS30

H40

WPS64

F150

F299

MAS-R

S30

F64

F160

POND

Publicsupply

well

TTP-4

BBPS45

62SRPS34

H55

F160

POND

JARPS40

THCSA/H46

F75

F197

GARCS23

F75

F200

RPS20

F77

F103

113RCS35

H50

F190

QRPS20

EXPLANATION

HYDROGEOLOGIC CROSS SECTION B-B'

HYDROGEOLOGIC CROSS SECTION A-A'

DIRECTION OF GROUND-WATER FLOW IN

UPPER FLORIDAN AQUIFER

SAMPLING LOCATION FOR WELL OR POND

AND SITE IDENTIFIERS

Greco

Sink

BBPS45

A

A'

A A'

B

B'

B B'

Figure 3. Lines of hydrogeologic sections, sampling site locations, and direction of ground-water 

flow in the Upper Floridan aquifer in the Temple Terrace, Florida, study area.
8 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water Index no. Site identifier Well name Site name Land surface elevation, (meters above NAVD 88) Well depth (meters) Depth to top of screeen (meters) Casing diameter (centimeters) Aquifer

1 280301082222703 Rec Ctr at 113th Ave 113RC-S35 12.90 11 8 10 SAS2 280301082222702 Rec Ctr at 113th Ave 113RC-H50 12.83 15 12 10 ICU3 280301082222701 Rec Ctr at 113th Ave 113RC-F190 12.91 58 55 10 UFA4 280241082224403 Terrace Hill Circle THC-SA/H46 15.98 14 11 10 SAS/ICU5 280241082224402 Terrace Hill Circle THC-F75 16.00 23 20 10 UFA6 280241082224401 Terrace Hill Circle THC-F197 16.05 60 57 10 UFA7 280247082231903 Water Plant WP-S64 24.54 20 16 10 SAS8 280247082231902 Water Plant WP-F150 24.58 46 43 10 UFA9 280247082231901 Water Plant WP-F299 24.59 91 88 10 UFA

10 280253082223803 Rec Ctr at Gillette Ave. GARC-S23 12.39 7 7 10 SAS11 280253082223802 Rec Ctr at Gillette GARC-F75 12.58 23 20 10 UFA12 280253082223801 Rec Ctr at Gillette GARC-F200 12.50 61 58 10 UFA13 280249082220703 Railway Park RP-S20 11.24 6 3 10 SAS14 280249082220702 Railway Park RP-F77 11.24 23 20 10 UFA15 280249082220701 Railway Park RP-F103 11.25 31 28 10 UFA16 280303082230902 Lynnwood Park LP-S30 15.20 9 6 10 SAS17 280303082230901 Lynnwood Park LP-H40 15.23 12 9 10 ICU18 280311082223901 Queensway Ret. Pond QRP-S20 11.09 6 3 10 SAS19 280241082230703 62nd Street Ret. Pond 62SRP-S34 21.76 10 7 10 SAS20 280241082230702 62nd Street Ret. Pond 62SRP-H55 21.76 17 14 10 ICU21 280241082230701 62nd Street Ret. Pond 62SRP-F160 21.64 49 46 10 UFA22 280228082231501 Bonnie Brae Park BBP-S45 16.31 12 9 10 SAS23 280242082232403 Mas Residence MAS-R-S30 20.40 9 6 10 SAS24 280242082232403 Mas Residence MAS-R-F64 20.34 20 16 10 UFA25 280242082232401 Mas Residence MAS-R-F160 20.43 49 14 25 UFA26 280250082233003 Lightfoot Ret. Pond LRP-S25 20.32 8 5 10 SAS27 280250082233002 Lightfoot Ret. Pond LRP-H105 20.38 32 29 10 UFA28 280250082233001 Lightfoot Ret. Pond LRP-F160 20.33 49 46 10 UFA29 280251082224201 Jaqueline Arbor Ret. Pond JARP-S40 13.22 11 8 10 SAS30 Not available Temple Terrace #4 (public-supply well) TTP-4 24.65 53 36 30 UFA31 280244082220200 Railway Park, Hillsborough River HRIVER 7.1732 280242082232900 Mas Retention Pond MAS-POND 15.9933 280242082230800 62nd St. Retention Pond 62SRP-POND 18.6234 280250082233200 Lightfoot Recreation Center Retention Pond LRP-POND 18.64

Table 1. Well construction and location information for monitoring wells tapping the surficial aquifer system (SAS), intermediate confining unit (ICU), and Upper Floridan aquifer (UFA). [Index numbers are identified in table 1. Latitude and longitude (degrees, minutes, seconds) for each well are contained in first 13 digits of the station identifier. NAVD 88, North American Vertical Datum of 1988. Well depth and depth to top of screeen are in meters below land surface]
Methods 9

Index 

no.

Site

name

Depth, 

meters

UZ 

or

 SZ

Lithology Lithologic description

Percent 

sand 

based on 

class size 

Percent 

clay and 

silt based 

on class 

size

1 113RC-S35 0-1.2 UZ Silty sand Sand, top soil, and organics; tan to white

1.2-1.8 UZ Silty sand Sand, fine while with iron staining; brownish-yellow top soil; silt

2.7-3.4 UZ Silty sand Sand, fine white sand with small amount of pale brown silt 83 17

4.3-4.9 UZ Silty sand Light gray sand; silt

7.3-7.9 SZ Clayey sand Olive-yellow clayey sand, iron staining

8.8-9.8 SZ Clayey sand Yellow clayey sand, pieces of weathered limestone

10.4-11.0 SZ Clayey sand Light gray clayey sand, pieces of weathered limestone

2 113RC-H50 11.9-12.5 SZ Clayey sand Light gray clayey sand, pieces of weathered limestone

13.4-13.7 SZ Clayey sand Light brownish gray clayey sand, pieces of weathered limestone

13.7-14.0 SZ Clayey sand Dark gray clayey sand, very dark layer at 46 ft 

13.7-15.2 SZ Limemud Drilled 100 ft into a paleo sink, backfilled to 50 ft

3 113RC-F190 15.2-25.9 SZ Limestone 75-85 ft void

25.9-31.7 SZ Limestone 85-104 ft very soft

31.7-62.5 SZ Limestone Hard to soft limestone

4 THC-SA/H46 0-0.61 UZ Silty sand Soil zone, dark grey sand, silt, and organics

1.5-2.1 UZ Silty sand Pale yellow sand 

3.0-3.7 UZ Clayey sand Pale yellow sand and clay with iron staining 93 7

4.6-5.2 UZ Clayey sand Brownish yellow clayey sand (iron staining) to dense plastic clay 93 7

6.1-6.7 UZ Clayey sand Yellow sand at top interlaced with clay/sandy clay

7.6-8.2 UZ Sandy clay Light-gray, sandy clay, light greenish gray dense clay

9.1-9.8 UZ Clayey sand Light yellow-brown sandy clay, small pieces of weathered limestone

10.7-11.3 SZ Clayey sand Light yellow-brown sandy clay to soft lime mud

11.6-14.0 SZ Clayey sand Light yellow-brown sandy clay to soft lime mud

5 THC-F75 14.0-23.8 SZ Limestone Pale yellow, soft to hard, void at 73 ft

6 THC-F197 22.9-60.0 SZ Limestone Hard to soft, moderately sandy and clayey

7 WP-S64 0-0.61 UZ Silty sand Pale yellow silty sand, some organics

1.5-2.1 UZ Silty sand Pale yellow silty sand

3.0-3.7 UZ Silty sand Pale yellow sand and dark brown silt 95 5

4.6-5.2 UZ Silty sand Pale yellow sand and dark brown silt 74 26

6.1-6.7 UZ Silty sand Pale yellow sand and dark brown silt

7.6-8.2 UZ Silty sand Pale yellow sand and dark brown silt 74 26

9.1-9.8 UZ Silty sand Pale yellow sand and dark brown silt

10.7-11.3 UZ Silty sand Pale yellow sand and dark brown silt

12.2-12.8 UZ Clayey sand Pale yellow sand and light greenish gray clay 53 47

13.7-14.3 UZ Limestone Clayey, weathered

14.9-15.2 UZ Limestone Pale yellow soft, lime mud

15.2-16.8 SZ Limestone Pale yellow soft, lime mud

16.8-19.8 SZ Limestone Limestone, soft

8 WP-F150 19.8-45.7 SZ Limestone Hard to soft, moderately sandy and clayey

9 WP-F299 45.7-91.4 SZ Limestone White to tan, soft to hard, vuggy, grandular, fossiliferous

10 GARC-S23 0-0.61 UZ Silty sand Pale yellow top soil; pale brown sand and organics

1.2-1.8 UZ Silty sand Pale yellow sand, organics, silt, iron staining 93 7

2.7-3.4 UZ Clayey sand Pale yellow sand, silt; clayey sand, iron staining 52 48

4.3-4.9 SZ Clayey sand Reddish yellow sand and clay, hit a hard pan layer, iron stained

5.8-6.4 SZ Clay Dense reddish yellow plastic clay with iron staining

11 GARC-F75 6.4-7.0 SZ Limestone White 

7.0-22.9 SZ Limestone Hard to soft 

12 GARC-F200 22.9-61.0 SZ Limestone Hard to soft 

13 RP-S20 0-1.5 UZ Silty sand Soil zone, dark grey silt and organics

Table 2. Description of lithology and results from grain-size analysis from sediments underlying the study area. 

[Index numbers are identified in table 1. Depth, in meters below land surface; zone: SZ, saturated zone; UZ, unsaturated zone; NA, no samples available]
10 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

Index 

no.

Site

name

Depth, 

meters

UZ 

or

 SZ

Lithology Lithologic description

Percent 

sand 

based on 

class size 

Percent 

clay and 

silt based 

on class 

size

1.5-2.1 UZ Silty sand Light brownish gray top soil, sand with silt and organics 83 17

2.7-3.4 UZ Silty sand Light brownish gray sand, with silt and organics

4.3-4.9 SZ Silty sand Very dark gray sand, with silt and organics

5.8-6.1 SZ Clayey sand Light brownish gray sand and clay

6.1-6.4 SZ Sandy clay Light greenish gray clay and sand

14 RP-F77 6.4-6.7 SZ Sandy clay Light greenish gray 

6.7-7.0 SZ Limemud Limemud, white, some chert 

7.0-8.2 SZ Limestone Chert in places, voids, soft to hard 

15 RP-F103 23.5-31.4 SZ Limestone Voids down section, soft to hard 

16 LP-S30 0-1.5 UZ Sand Orange-brown to orange 

1.5-3.0 UZ Sand Pale yellow-orange 

3.0-4.0 UZ Sand Pale yellow-white 

4.3-4.6 UZ Clayey sand Pink-orange 

4.6-8.2 SZ Clayey sand Red-orange 

8.2-8.8 SZ Sandy clay Yellow, stiff

17 LP-H40 8.8-10.7 SZ Clayey sand Yellow-orange, dark to pale 

10.7-11.9 SZ Sandy clay Yellow-orange clay, stiff to gummy with sand

11.9-12.5 SZ Limestone White-Pale yellow, very soft, weathered residuum

18 QRP-S20 0-2.4 UZ Sand Light gray to light yellow brown

2.4-2.7 SZ Sand Brown 

2.7-5.5 SZ Clayey sand Light yellow brown 

5.5-6.1 SZ Clayey sand Very pale brown to pink clay with sand

19 62SRP-S34 0-3.0 UZ Sand Light yellow-orange

4.0-5.2 UZ Sand Light orange 

5.5-7.9 UZ Clayey sand Light orange 

7.9-9.1 UZ Clayey sand Light brown 

9.1-10.4 SZ Limemud Light yellow clayey carbonate mud, weathered limestone

20 62SRSP-H55 10.4-12.2 SZ Limemud Dense clay/carbonate mud, with light yellow limestone chips

12.2-13.7 SZ Sandy clay White with iron staining 

13.7-16.8 SZ Limestone White, muddy fine-grained 

21 62SRP-F160 16.8-19.8 SZ Limestone White, friable,

19.8-22.9 SZ Limestone White, circulation loss

22.9-26.5 SZ Limestone Light brown, hard

26.5-27.1 SZ Limestone Hard, circulation loss

27.4-29.0 SZ Limestone Soft

29.0-33.5 SZ Limestone White 

33.5-34.1 SZ Limestone Hard slow drilling possibly clay

34.7-36.6 SZ Limestone White

36.6-37.2 SZ Chert Chert

37.2-40.5 SZ NA Void

42.7-44.2 SZ Limestone Very hard 

44.2-47.9 SZ NA Void

47.9-48.8 SZ Limestone Greenish-gray clay with light brown 

48.8 SZ Limestone Light brown, fossiliferous

22 BBP-S45 0-3.0 UZ Sand Yellow

Table 2. Description of the lithology and results from grain-size analysis from sediments underlying the study area.—Continued

[Index numbers are identified in table 1. Depth, in meters (m) below land surface; SZ, saturated zone; UZ, unsaturated zone; NA, no samples available]
Methods 11

Index 

no.

Site 

name

Depth, 

meters

UZ 

or

 SZ

Lithology Lithologic description

Percent 

sand 

based on 

class size 

Percent 

clay and 

silt based 

on class 

size

3.0-4.6 UZ Clayey sand Mottled orange 

4.6-6.1 UZ Clayey sand Pale brown to yellow 

6.1-8.8 UZ Sandy clay Stiff, some possibly oxidized chert

8.8-10.1 SZ NA Lost circulation, small amount of rock present

10.1-10.7 SZ NA Void

10.7-12.2 SZ NA No cuttings

23 MAS-R-S30 0-4.6 UZ Sand Light brown to red-orange 

4.6-6.1 UZ Sand Red-orange to red-brown

6.1-9.1 SZ Sand Light brown to gray-red 

9.1-9.8 UZ Clayey sand Pinkish-white

24 MAS-R-F64 10.1-10.7 UZ Clay Light greenish gray 

12.2-13.7 SZ NA Lost circulation, bit dropped 4 ft

13.7-21.3 SZ Limestone Soft drilling carbonate mud

25 MAS-R-F160 21.9-25.0 SZ Limestone Hard, chert, brown limestone

25.6-27.4 SZ Limestone Alternating hard and soft drilling

28.7-42.7 SZ Limestone Alternating hard and soft drilling

42.7-45.7 SZ Limestone White

45.7-46.3 SZ Limestone White, highly fossiliferous, friable fractured

46.3-46.9 SZ Limestone Poorly cemented, fossiliferous, mollusks, gastropods

46.9-48.8 SZ Limestone Cavernous, calcite, vugs and fossil derived moldic porosity

48.8 SZ Limestone Well cemented

26 LRP-S25 0-2.1 UZ Sand Yellow-orange, brown

2.1-4.9 SZ Sand Yellow-orange, brown

4.9-8.5 UZ Sand Very pale brown 

27 LRP-H105 8.5-9.8 UZ Sand Very pale brown with small white nodules

9.8-12.2 UZ Sand Very pale brown with small white nodules

12.2-12.8 UZ Sand Very pale brown with small white nodules

12.8-14.0 SZ Sand Fine white 

14.0-16.5 SZ Clayey sand Light brown, pinkish-gray sand, slight clay

16.5-17.7 SZ Clayey sand Red changing to yellowish-green brown sand with clay

17.7-23.2 SZ Sand, clay, chert Red-orange clayey sand, siliceous fossilferous/agatized coral/chert 

26.5-27.4 SZ Limestone Brown chert capping friable pale yellow limestone, iron stained

27.4-28.3 SZ Clay Pale blue-green, stiff

28.3-31.7 SZ Limestone Crumbly, fossiliferous, molluscs, at 105 ft sandy infill

31.7-32.0 SZ Limestone Sandy infill, light yellow-brown 

28 LRP-F160 32.0-33.5 SZ Limestone Pale yellow/white, hard, fine grained, difficult drilling

33.5-34.4 SZ Clay Blue, plastic

34.4-35.1 SZ Limestone Sandy infill light yellow-brown 

37.2-39.6 SZ Limestone Light brown 

45.7-47.9 SZ Limestone Pale yellow, fractured, vugs, molluscan moldic porosity

47.9-48.8 SZ Limestone Soft drilling, crumbly

29 JARP-S40 0-6.1 UZ Sand Fine to very fine brown sand

6.1-8.8 SZ Sand Light brown sand with small amounts of red-orange clay

8.8 SZ Chert Chert and clay

9.1-12.2 SZ Sand; clay Alternating hard and soft sand clay; clayey sand; light greenishgray

Table 2. Description of the lithology and results from grain-size analysis from sediments underlying the study area.—Continued

[Index numbers are identified in table 1. Depth, in meters (m) below land surface; SZ, saturated zone; UZ, unsaturated zone; NA, no samples available]
12 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

Samples and sampling locations Chemical and physical analyses

Public-Supply Well, TTP-4

A total of 7 well head samples from 

entire open interval

A total of 5 samples from three targeted 

zones during depth-interval sampling 

with various pumping conditions

Tritium/Helium-3 and sulfur hexafluoride (age dating), radon-222, radium, 85 volatile organic 

compounds (VOCs), trace elements, arsenic species (As(III) and As(V)), major ions, nutrients, 

dissolved gases, dissolved organic carbon, 128 pesticides and pesticide degradation products, 

stable isotopes (carbon, nitrogen, oxygen, hydrogen, and sulfur), 67 organic wastewater compounds

Monitoring Wells (Installed in 2003-2004)

A total of 64 samples collected from 

29 wells tapping the surficial aquifer 

system, intermediate confining unit 

and Upper Floridan aquifer

Tritium/Helium-3 and sulfur hexafluoride (age dating), radon-222, radium, 85 volatile organic 

compounds (VOCs), trace elements, arsenic species (As(III) and As(V)), major ions, nutrients, 

dissolved gases, dissolved organic carbon, 128 pesticides and pesticide degradation products, 

stable isotopes (carbon, nitrogen, oxygen, hydrogen, and sulfur)

Surface-Water Sites

A total of 4 surface-water samples 

collected from three stormwater 

retention ponds and 1 streamwater 

site (Hillsborough River)

Major ions, nutrients, 85 volatile organic compounds (VOCs), stable isotopes (carbon, nitrogen, 

oxygen, hydrogen, sulfur), pesticides, and trace elements

Core and Solid Phase Material Collected During Initial Well Installation

A total of 13 samples of sediment or 

rock collected at 9 sites (details 

shown in table 4)

X-Ray diffraction, elemental analysis of acid extracts, organic matter, bulk density, moisture 

content, nitrate, chloride, particle size, bulk and clay mineralogy, denitrification measurements 

with pore water extracts

Table 3. Summary of water-quality and solid-phase analyses in the transport of anthropogenic and natural contaminants 

(TANC) small-scale study area. 

0.04 μm (micron) to 2 mm were analyzed using a commercially built apparatus (K.S. Perkins, U.S. Geological Survey, 

written commun., 2005).

Collection and Analysis of Water Samples

Water samples were collected from monitoring wells, 

public-supply well TTP-4, stormwater retention ponds, and 

the Hillsborough River during 2003-05 according to NAWQA 

protocols (Koterba and others, 1995; Lapham and others, 

1995). Use of these methods allows for the collection of consistent ground-water chemistry data among study units across 

the United States. Samples were collected using a submersible 

pump with PTFE (Teflon) tubing to minimize cross contamination from one well site to another. Each well was purged a 

minimum of three casing volumes, and water samples were 

collected after field properties (temperature, pH, specific 

conductance, and dissolved oxygen) had stabilized. Chambers 

were used to process and preserve samples. Alkalinity (as 

calcium carbonate) was measured in the field using fixed endpoint titration methods. Sampling equipment was cleaned after 

the collection of samples at each site using dilute phosphatefree liquid detergent and a methanol rinse, followed by several 

rinses of deionized water. 

Water samples were collected from each stormwater 

retention pond using slightly different techniques to coincide 

with different configurations of inflow pipes and pond 

characteristics. All samples were collected under static conditions, when no water was entering the ponds, using a stainless 

steel weighted bottle sampler with a Teflon bottle. There are 

two storm drains that empty into the Lightfoot Retention Pond 

(LRP). At this site, a 1-L (liter) water sample was collected at 

each of six locations around the circumference of the retention 

pond at a depth of about 16 cm about 1 m from the edge of 

water. At the MAS retention pond, 2 L of water were collected 

directly in front of each of three storm drains. A depression in 

front of each drain allowed the sampler to be completely 

submerged in these locations. The sample was collected at a 

depth of about 30 cm and located approximately 1 m from the 

edge of water. At the 62nd Street retention pond, water levels 

were low. However, there was a small depression (about 

3-5 m in circumference), containing water directly in front of 

the storm drain that feeds this pond. A 2-L sample was collected at each of three points around this depression at a depth 

of about 8 cm and located about 1 m from the edge of water. 

The 6 L of water collected from each pond were composited 

using a 14-L Teflon churn splitter before being split into 

multiple sample containers. The composited samples were sent 

to the various laboratories for analyses as described below. 
Methods 13

Field properties (temperature, specific conductance, dissolved 

oxygen, and pH) were measured at various locations in each 

pond and median values were recorded. 

Samples of ground water and surface water were analyzed for major ions, nutrients, dissolved organic carbon, dissolved gases, 128 pesticides and pesticide degradates, 

85 volatile organic compounds (Connor and others, 1998), 

stable isotopes (carbon, nitrogen, oxygen, hydrogen, and 

sulfur), trace elements, arsenic speciation, uranium, and radon222 (table 3). Selected ground-water samples were collected 

for age dating and analyzed for sulfur hexafluoride (SF6), 

tritium (3H), and helium-3 (3He). 

Samples for major ions, trace elements, and nutrients 

were filtered through a 0.45-μm capsule filter and analyzed 

using inductively coupled plasma atomic emission spectrometry, graphite furnace atomic absorption spectrometry, 

ion-exchange chromatography, and colorimetry procedures 

described in Fishman and Friedman (1989), Faires (1993), 

Fishman (1993), McLain (1993), Garbarino (1999), and Patton 

and Kryskalla (2003). 

Dissolved gases (nitrogen gas, argon, carbon dioxide, and 

methane) were analyzed in ground-water samples at the USGS 

Chlorofluorocarbon Laboratory in Reston, Virginia. Dissolved 

gases were measured by gas chromatography after extraction 

in headspaces of glass samplers (Busenberg and others, 1998). 

Hydrogen sulfide was measured in the field using colorimetric 

methods (Hach, 2002). 

Water samples for radon-222 were collected in a syringe 

prior to contact with the atmosphere and injected into a 

mineral-oil based scintillation solution in a 30-mL (milliliter) 

glass scintillation vial. The sample was shipped overnight to 

the laboratory and analyzed by liquid-scintillation counting 

methods (Prichard and Gesell, 1977). 

Stable isotopes of oxygen, hydrogen, carbon, sulfur, and 

nitrogen are used in this study to help understand sources of 

water and reactions affecting the chemical composition of 

ground water. Their effectiveness in the identification and 

quantification of biogeochemical processes in numerous 

hydrogeologic studies has been well documented (including 

Clark and Fritz, 1997; Cook and Herczeg, 2000). Samples for 

stable isotopes of hydrogen, oxygen, sulfur, and nitrogen were 

analyzed by the USGS Stable Isotope Laboratory in Reston, 

Virginia. Isotope data are presented in delta (δ) notation as the 

ratio of the heavy to the light isotope, normalized to a standard 

(eq. 1). 

δsample = 1000[(Rsample/Rstandard)-1] (1)

where Rsample and Rstandard are the ratio of the heavy to the light 

isotope in the sample and in the standard, respectively. Delta 

hydrogen-2 (δ2H) and delta oxygen-18 (δ18O) are analyzed 

using an isotope ratio-mass spectrometer by hydrogen gas 

water equilibration and carbon dioxide water equilibration 

techniques, respectively, and reported relative to Vienna Standard Mean Ocean Water (Epstein and Mayeda, 1953; Coplen 

and others, 1991, 1994; K.M. Revesz, U.S. Geological Survey, 

written commun., 2003). Dissolved sulfate is analyzed for 

delta sulfur-34 (δ34S) using methods of Carmody and 

others (1997) and reported relative to the Vienna Canyon 

Diablo Troilite. Isotopes of nitrogen and oxygen of nitrate are 

analyzed by bacterial conversion of nitrate to nitrous oxide 

and reported relative to nitrogen gas in air and Vienna Standard Mean Ocean Water, respectively (Sigman and others, 

2001; Casciotti and others, 2002; Revesz and Casciotti, 2003). 

Water samples are analyzed for delta carbon-13 (δ13C) using 

mass-spectrometry techniques at the University of Waterloo 

Environmental Isotope Laboratory and reported relative to the 

Vienna Pee Dee Belemnite standard (Coplen, 1994).

Volatile organic compounds, pesticides, pesticide degradates, dissolved organic carbon, major ions, trace elements, 

nutrients, and radon-222 were analyzed by the USGS National 

Water Quality Laboratory in Lakewood, Colorado. Samples 

for volatile organic compounds were unfiltered and determined by gas chromatography and mass spectrometry using 

methods described in Connor and others (1998). Pesticides 

were sampled using a 0.7-μm glass-fiber filter and analyzed 

by carbon-18 solid-phase extraction and capillary column gas 

chromatography and mass spectrometry (Zaugg and 

others, 1995; Lindley and others, 1996; Sandstrom and others, 

2001; Madsen and others, 2003). Dissolved organic carbon 

samples were collected by forcing raw water samples through 

a 0.45-μm glass-fiber filter using high purity nitrogen gas. 

Dissolved organic carbon samples were analyzed by methods 

described by Brenton and Arnett (1993). 

Age Dating of Ground Water

Water samples were collected and analyzed from selected 

wells for the transient environmental tracer 3H, its radioactive 

decay product 3He, and SF6. Anthropogenic activities, such as 

industrial processes and atmospheric testing of thermonuclear 

devices, have released SF6 and 3H into the atmosphere in low 

but measurable concentrations (fig. 4). Precipitation that incorporates SF6 and 3

H from the atmosphere infiltrates into the 

ground and carries a particular chemical or isotopic signature 

related to atmospheric conditions at the time of recharge to 

ground water. The tritium/tritiogenic helium-3 (3H/3Hetrit) and 

SF6 dating methods assume that gas exchange between the 

unsaturated zone and air is fast, but that shallow ground water 

remains closed to gas exchange after recharge (Schlosser and 

others, 1989; Plummer and Busenberg, 1999; Busenberg and 

Plummer, 2000).

Tritium and Tritiogenic Helium-3

The continued decrease and low concentrations of 3H 

in rainfall in the Southeast have resulted in limited use of the 

3

H method for age dating ground waters recharged during the 

past 20 to 30 years. However, by measuring 3Hetrit, the stable 

daughter product of 3H decay that has accumulated in groundwater systems, the dating range and precision can be enhanced 
14 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

(Plummer and others, 1998; Cook and Böhlke, 1999). 

Combined measurements of 3H and its daughter product of 

radioactive decay, 3Hetrit, define a relatively stable tracer of the 

initial 3H input to ground water, which can be used to calculate the 3

H/3Hetrit age from a single water sample (Schlosser 

and others, 1988, 1989; Solomon and Sudicky, 1991). The 

3

H/3Hetrit ratio yields the following equation for the pistonflow assumption in which the apparent age (T, years) can be 

expressed as (Torgersen and others, 1979):

 T = 1/λT[ln (1 + 3Hetrit/

3

H)], (2)

where λT is the radioactive decay constant for 3H (the 

concentration in tritium units), and 3Hetrit is the tritiogenic 

helium-3 content in tritium units. One tritium unit is equal to 

1 3H atom in 1018 hydrogen atoms, and is equivalent to 

3.2 pCi/L (picocuries per liter) of water. A He-isotope 

mass balance is used to calculate the amount of tritiogenic 

and non-tritiogenic 3He in the sample. Non-tritiogenic 3He 

(which generally is negligible in a shallow aquifer with local 

recharge) is corrected for by using measured concentrations of 

helium-4 (4He) and neon (Ne) in the water sample and assuming solubility equilibrium with air at the water temperature 

measured during sampling (Schlosser and others, 1988, 1989). 

It is assumed that 3H and 3Hetrit concentrations in ground water 

are not affected by contamination, sorption, and microbial 

degradation processes that can alter the concentrations of other 

transient tracers, such as chlorofluorocarbons (Plummer and 

others, 1998). The distribution of 3H and 3Hetrit can be affected 

by hydrodynamic dispersion and mixing different age waters 

(Solomon and Sudicky, 1991; Reilly and others, 1994). 

Information about ground-water transit times can be 

obtained by comparing measured 3H concentrations in ground 

water with the long-term 3H input function of rainfall 

measured at the International Atomic Energy Agency precipitation monitoring station in Ocala, Florida (fig. 4), which is 

about 175 km (kilometers) northeast of the Temple Terrace 

study area. Atmospheric weapons testing beginning in the 

early 1950s increased 3H concentrations in rainfall in this area 

to a maximum of several hundred tritium units during the 

mid-1960s, followed by a nearly logarithmic decrease in 

concentrations to the present. Analytical uncertainty (one 

sigma) for 3H using the low-level counting procedure is about 

±0.15 to 0.30 tritium units (Ludin and others, 1998). 

Water samples for the determination of 3H/3Hetrit, 4He, 

and Ne were collected in pinched-off copper tubes (10-mm 

diameter, 80-cm length, about 40-mL volume) while applying back pressure to prevent formation of gas bubbles. These 

samples were analyzed at the Noble Gas Laboratory of 

Lamont-Doherty Earth Observatory in Palisades, New York, 

by using quantitative gas extraction followed by mass spectrometric techniques (Schlosser and others, 1989; Ludin and 

others, 1998). A similar procedure was used to collect water 

samples from the public-supply well (depth-interval sampling 

in October 2004) and other selected wells for analysis of 

3

H/3Hetrit, 4He, and Ne by the USGS Noble Gas Laboratory in 

Denver, Colorado. 

Sulfur Hexafluoride (SF6)

The stability of SF6 in the hydrosphere has led to its 

effective use for dating ground water recharged during the 

past 30 years (Busenberg and Plummer, 2000). This technique 

presumes that SF6 concentrations in the aquifer have not been 

altered by biological, geochemical, or hydrologic processes. 

Apparent ages for SF6 are estimated based on the equilibrium partitioning between recharging ground water and the 

partial pressures of SF6 in the troposphere or soil atmosphere 

(fig. 4). Concentrations of SF6 in ground water are functions 

of the atmospheric partial pressures and the temperature at the 

base of the unsaturated zone during recharge. The recharge 

temperature and the quantity of dissolved excess air (Heaton 

and Vogel, 1981) are determined from gas-chromatography 

analyses of nitrogen gas and argon in the headspace of water 

samples collected in the field (Busenberg and others, 1993). 

An apparent age of the sampled water is determined from a 

comparison of the partial pressure of SF6 in the sample, calculated from measured concentrations using solubility data, with 

the record of atmospheric partial pressures over the northern 

hemisphere at different times (fig. 4). The input function for 

SF6 was obtained from atmospheric input curves, and assuming a ratio of summer-to-winter infiltration coefficient of 1.0. 

Ground-water samples for the SF6 dating method were 

collected in 1-L safety-coated glass bottles by placing the 

sampling discharge line in the bottom of the bottle and displacing the air in the bottle with ground water. After about 2 L 

of overflow, the sampling line was removed. The bottles were 

capped with polyseal conical screw-caps without headspace 

and wrapped with electrical tape to prevent the caps from 

Figure 4. Input of sulfur hexafluoride to atmosphere in the 

northern hemisphere (from Busenberg and Plummer, 2000; 

E. Busenberg, U.S. Geological Survey, written commun., 

2005) and tritium concentrations in rainfall from Ocala, 

Florida, (from Michel, 1989; R.L. Michel, U.S. Geological 

Survey, written commun., 2005), during 1950-2005.

600

500

400

300

200

100

0

1965 1985 2005

TRITIUM CONCENTRATION, IN

TRITIUM UNITS

SULFUR HEXAFLUORIDE CONCENTRATION,

IN PARTS PER TRILLION BY VOLUME

Sulfur Hexafluoride x100

Tritium, rainfall,

Ocala, Florida

Tritium,

decay

corrected

to 2003

1,000

100

10

1

1945
Methods 15

coming loose during shipping. Samples were analyzed for 

SF6 at the Chlorofluorocarbon Laboratory in Reston, 

Virginia, using procedures described by Busenberg and 

Plummer (2000). 

Quality Assurance

Quality-assurance samples were collected to assess 

laboratory performance and to help identify potential contamination problems associated with field collection methods. 

Quality-assurance information for this study included the 

collection of 10 replicate samples, 24 blank samples, and laboratory surrogate spike samples. Surrogate compounds were 

added to each of the samples submitted for pesticide and volatile organic compound analyses including laboratory reagent 

blank samples, field blank samples, and regular ground-water 

and surface-water samples. These compounds, which are not 

normally found in the environment, are used to determine if 

there are interferences from other chemicals in the sample 

matrix and to evaluate the efficacy of the laboratory’s analytical methods to detect compounds that are chemically similar. 

Replicate samples were collected and analyzed for volatile 

organic compounds, pesticides, major ions, nutrients, and trace 

elements which were the most frequently sampled constituents. Field blank samples were processed using nitrogenpurged universal blank water that was certified for use in the 

collection of blank samples for volatile organic compounds, 

pesticides, low-level nutrients, dissolved organic carbon, major 

ions, and trace elements. 

Only two organic compounds were detected in blank 

samples (app. A1). Concentrations of methylene chloride 

(dichloromethane) ranged from 0.1 to 0.6 μg/L (microgram 

per liter) in five samples. Chloroform (trichloromethane) was 

detected in one sample at a concentration of 0.09 μg/L. Several 

inorganic constituents were detected in concentrations that 

were slightly greater than the method reporting level in three 

samples. These included cobalt, nickel, strontium, calcium, 

sodium, and silica. The low concentrations of strontium, calcium, sodium, and silica detected in blank water samples were 

well below concentrations measured in water samples from 

wells, ponds, and the river, and therefore, do not constitute a 

contamination problem.

Replicate analyses for organic compounds generally 

agreed within ±10 percent, with the exception of dichloromethane and carbon disulfide, which agreed within 

±30 percent (app. A2). Replicate analyses for inorganic 

compounds were within ±10 percent for most constituents, 

with the exception of nickel and selenium (two constituents 

not detected in most environmental samples). One set of replicate water samples for dissolved organic carbon from WP-S64 

(collected on June 14, 2005) showed considerable variability, 

1.1 and 13.7 mg/L (milligrams per liter); however, the exact 

cause for this analytical discrepancy (or contamination of one 

replicate sample) is not known (app. A2). Three other water 

samples collected from this well on previous dates had 

dissolved organic carbon concentrations that ranged from 0.6 

to 1.5 mg/L.

Two surrogate organic compounds, alpha-HCH-d6

(chemical abstract service registry number 319-84-6) and 

diazinon-d10, were added to each of the 30 pesticide samples 

collected in this study. The median recoveries of alphaHCH-d6 and diazinon-d10 were 85.0 percent (range from 

about 69-197 percent) and about 95.5 percent (range from 

about 69-211 percent), respectively (app. A3). Recovery 

values that range from 70 to 130 percent generally are 

considered to be within acceptable limits, although this range 

can vary considerably for specific compounds. Values that 

exceed this range may indicate possible problems with 

analytical methodology. Three surrogate compounds were 

added to the 69 samples of ground water and surface water 

analyzed for volatile organic compounds and laboratory 

reagent samples (app. A3). Median percent recoveries for 1,2-

dichloroethane-d4, 1-bromo-4-fluorobenzene, and toluene-d8 

were 115 percent (range from 99-147), about 93 percent 

(range from about 58.3-112 percent), and about 99 (range 

from about 93-113) percent, respectively.

Lithology, Mineralogy, and Elemental 

Analysis of Core Material

Geologic descriptions of the surficial sediments, 

intermediate confining unit, and limestone that composes the 

hydrogeologic units were based on characterization of well 

cuttings, split-spoon coring, and grain-size analysis. Mineralogical analysis of selected cores also was performed using 

x-ray diffraction and mass spectrometry. Physical analyses 

were made of selected core materials including bulk density, 

percent organic matter (loss on ignition), and volumetric 

moisture content (R. Healy, U.S. Geological Survey, oral 

commun., 2005). 

The abundance of elements in grain coatings or other 

mineral phases from core samples were evaluated using 

different acids and reagents, including: (1) 10-percent nitric 

acid, (2) 6N hydrochloric acid, (3) 0.5 M hydroxylamine 

hydrochloride extractable iron, and (4) acid-volatile and 

chromium-reducible sulfides. All extractions were performed 

on an “as received” basis (that is, wet), but the moisture 

content was determined for a separate subsample and used to 

correct the analytical concentrations to dry weight. The 

extractions listed above were performed in the laboratory; 

however, for the latter two extractions, core samples were first 

subsampled in a nitrogen gas atmosphere glove bag and the 

bottles and flasks were flushed with nitrogen gas in the field 

before shipment to the laboratory for analysis. 

The coatings extraction (hydrochloric acid and nitric 

acid) methods were primarily intended to target ferric oxyhydroxides and their associated trace elements, but they also can 

be used to extract other oxides and clay, carbonate, and sulfide 

phases to varying degrees. The sample/solution ratio for the 

6N hydrochloric acid and 10-percent nitric acid extractions 
16 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

were 5 ±1 g (gram) of wet weight to 15 mL of acid solution, 

whereas that for 0.5 M hydroxylamine hydrochloride extraction was 4 to 10 g (gram) of wet sediment to 75 mL of reagent. 

The sediment-acid aliquots were set on a shaker table for 

6 hours, then centrifuged, filtered with 0.45-μm pore filters, 

and analyzed for several minor elements including arsenic 

and uranium. Leachate derived from the 10-percent nitric acid 

extractions was analyzed for aluminum, chromium, copper, 

iron, manganese, nickel, and vanadium by inductively coupled 

plasma optical emission spectroscopy (ICP-OES). Further 

dilution to 5 percent was required for analysis of arsenic, 

cadmium, lead, and uranium with inductively coupled plasma 

mass spectrometry (ICP-MS), which yielded lower detection limits. Analysis of the 6N hydrochloride acid extractants 

required dilution to 1.6 N hydrochloride acid prior to analysis by ICP-MS. Leachate derived from the 6N hydrochloric 

acid extractions was diluted to 10 percent and analyzed by 

ICP-MS for iron, manganese, aluminum calcium, cadmium, 

chromium, copper, potassium, magnesium, sodium, nickel, 

lead, vanadium, zinc, and uranium. The 0.5 M hydroxylamine 

hydrochloride and 6 N hydrochloric acid extractions were performed according to Lovley and Phillips (1987) and analyzed 

by ICP-MS. The 0.5 M hydroxylamine hydrochloride and 6 N 

hydrochloride acid extracts were analyzed using the ferrozine 

method with a Hach DR/2400 Spectrophotometer (Hach, 

2002). 

Sulfide phases in sediments or rock were extracted using 

the method described by Allen and others (1991, 1993) and 

summarized in U.S. Environmental Protection method 9030B 

(U.S. Environmental Protection Agency, 1996) for acid soluble 

and acid insoluble sulfides. The method was modified to avoid 

the oxidization of hydrogen sulfide by soluble ferric iron 

by the addition of stannous chloride (M.L. Tuttle and K.M. 

Conko, U.S. Geological Survey, oral commun., 2003) and 

further modified by the addition of chromium chloride (Canfield and others, 1986; Bowles and others, 2003) to include 

pyrite-bound sulfide. Sulfide phases that are extracted by this 

method include pyrite, elemental sulfur, and acid volatile 

monosulfides. Samples of 5 to 20 g of undried sediment were 

transferred to a 250-mL round-bottomed flask (under nitrogen 

gas stream) with 10 g of stannous chloride. The flask was 

attached to a nitrogen gas stream on a heating mantle, and 

75 mL of deaerated 6 N hydrochloric acid and 50 mL of chromium chloride were added. The samples were heated and kept 

at a sub-boiling temperature for 1 hour. Hydrogen sulfide was 

collected in two sequential aliquots of 100 mL of 0.5M sodium 

hydroxide. Sulfide was analyzed colorimetrically by means of 

a DR/2400 Hach Spectrophotometer using the methylene blue 

method specified by the manufacturer (Hach, 2002).

Hydrogeologic Setting

The geology of the study area consists of sand, clay, and 

carbonate rocks that were deposited primarily in a marine 

environment. The geologic framework is characterized by 

layers of sand to clayey sand to sandy clay that overlie a 

highly weathered limestone sequence. Interspersed throughout the study area are a number of localized surface or buried 

depressions called sinkholes that disrupt this layering. 

Numerous deep sinkholes are present in the floodplain of the 

Hillsborough River. The area north of Temple Terrace also 

contains large sinkholes; several are more than 60 m deep 

(Stewart and others, 1978). Some of these sinkholes are open 

to the Upper Floridan aquifer and may receive water from the 

Hillsborough River or wetland areas near the sinks. These 

wetland areas and the Hillsborough River usually contain 

highly colored (tannic) water or have degraded water quality due to elevated bacteriological constituents. Continuous 

seismic-reflection profiling on the Hillsborough River near 

Temple Terrace indicated about a 3-m thickness of surficial 

material overlying the limestone that composes the Upper 

Floridan aquifer and filling large solution cavities in the 

limestone (Wolansky and Thompson, 1987). Interactions 

between ground water and the Hillsborough River have been 

documented in previous studies (Stewart and others, 1978; 

Wolansky and Thompson, 1987).

Principal hydrogeologic units that lie within this 

sedimentary sequence include the surficial aquifer system, 

intermediate confining unit, and Upper Floridan aquifer. The 

uppermost surficial aquifer system, is an unconfined sand and 

clayey sand aquifer and is separated from the Upper Floridan 

aquifer by the clay-rich intermediate confining unit, which 

controls the amount of recharge between the two aquifers. 

The underlying Upper Floridan aquifer is a highly productive 

carbonate aquifer and is the principal source of freshwater in 

west-central Florida (Miller, 1986). The generalized hydrogeologic columns and sections of the study area are shown in 

figures 5A and 5B. Lithologic information that was used to 

construct the hydrogeologic sections is included in table 2. 

Water-level data from wells completed at various depths are 

included in these sections to show the vertical and horizontal 

flow regime within the study area.

The surficial aquifer system is a permeable hydrogeologic 

unit contiguous with land surface that principally consists 

of unconsolidated to poorly indurated clastic deposits of the 

undifferentiated surficial deposits (Southeastern Geological 

Society, 1986). The surficial aquifer system contains a water 

table; the depth to this water surface is variable and ranges 

from about 3 to 15 m below land surface. The surficial aquifer 

system is recharged by rainfall, and in some areas of the study 

area, recharge is relatively rapid because the surficial sands are 

highly permeable and the water table is relatively close to land 

surface. This hydrogeologic unit is not used as a major source 

of water supply because of the relatively low yields to wells 

(less than 19 L/min), high iron content, and the potential for 

contamination. 

The intermediate confining unit is a nonwater-yielding 

layer that controls the downward leakage between the surficial 

aquifer system and Upper Floridan aquifer. The extent, thickness, and permeability of the clay unit is variable throughout 
Hydrogeologic Setting 17

Figure 5A. Columns showing stratigraphic and hydrogeologic units of the Temple Terrace, Florida, study area 

(from Tihansky, 2005). 

Suwannee

Limestone

Ocala

Limestone

Avon Park

Formation

Undifferentiated

Sands and Clays

Quartz sand, silty sand,

clayey sand, peat, shell

Clay, minor quartz sand,

phosphate, fine-grained

dolomite, residual limestone

Limestone, minor quartz sand,

phosphate, chert, clay, fine-grained

dolomite

Limestone, packstone to

grainstone, trace quartz sand,

organics, variable dolomite and

clay content, highly fossiliferous,

vuggy

Limestone, micritic,chalky, very

fine- to fine-grained, soft,

poorly indurated, trace organics,

clays and dolomite, abundant

foraminifera

Evaporites occur in dolomite as

interstitial gypsum and anhydrite

with evaporite filling pore space

and as interbeds in the lower part

Dolomite is hard, brown, sucrosic

in texture and commonly fractured

Limestone, dolomite, and

evaporites

Limestone and dolomite interbeds

typical in upper part, deeper beds

are continuous dolomite with increasing evaporites at base

Limestone is fine-grained, tan,

packstone with

variable amounts of organic-rich

laminations near top

recrystallized

intermediate

confining unit

Tampa/Suwannee

producing zone

Ocala

semiconfining

unit

Ocala/Avon Park

producing zone

Avon Park

producing zone

Upper Floridan aquifer

Middle confining unit

surficial aquifer system

Hawthorn Group

Tampa

Member

of the

Arcadia

Formation

Holocene

to

Pliocene

Miocene

Oligocene

Eocene

SERIES STRATIGRAPHIC

UNIT

GENERAL

LITHOLOGY

HYDROGEOLOGIC

UNIT
18 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

30

25

20

15

10

5

NAVD 88

5

10

15

20

0

METERS

WEST EAST

WP-S64

62SRP-S34

62SRP-H55

62SRP-F160 JARP-S40

MAS -R-S30

MAS -R-F64

MAS -R-F160

WP-F150

WP-F299

RP-S20

RP-F77

RP-F103

Hillsborough River

Greco Sink

WP-S64

GARC-S23

GARC-F75

GARC-F200

JARP-S40

Greco Sink

GARC-S23

GARC-F75

GARC-F200

SOUTH NORTH

113RC-S35 QRP-S20

113RC-50

113RC-190

THC-F75

BBP-S45

Paleo sink

Public-supply

well

*

* * *

* * * * *

(VERTICAL EXAGGERATION 52X)

(VERTICAL EXAGGERATION 54X)

0.25 0.5 0.75 1.0 KILOMETERS

METERS

METERS METERS

THC-197

THC-SA/H46

SAND WITH INCREASING CLAY

CONTENT WITH DEPTH

SAND, CLAY, AND CARBONATE MUD

LIMESTONE

INFERRED GEOLOGIC CONTACT

GROUND-WATER FLOW DIRECTION

WELL SCREENS EXCEED THE SECTION DEPTH

WELL AND WELL IDENTIFIER

— Height of box is cased

and screen interval;

geologic control data

30

25

20

15

10

5

NAVD 88

5

10

15

20

30

25

20

15

10

5

NAVD 88

5

10

15

20

30

25

20

15

10

5

NAVD 88

5

10

15

20

0 0.25 0.5 0.75 1.0 MILES

0 0.25 0.5 0.75 1.0 KILOMETERS

0 0.25 0.5 0.75 1.0 MILES

EXPLANATION

(B)

A A'

B B'

Surficial

Aquifer

System

Upper Floridan Aquifer

Confining

Unit

Intermediate

Upper

Floridan

Aquifer

Surficial

Aquifer

System

Intermediate

Confining Unit

Figure 5B. Generalized hydrogeologic sections A-A’ and B-B’. Lines of sections shown in figure 3.
Hydrogeologic Setting 19

the study area. Breaches form in this clay unit from localized 

subsidence activity that occurs when the underlying limestone 

dissolves and the overlying clay layers collapse. Generally, 

ground water moves laterally within the surficial aquifer 

system and moves downward to the Upper Floridan aquifer 

through breaches in the intermediate confining unit, where 

present. Many of these breaches in the intermediate confining 

unit serve as preferential flow paths to the underlying Upper 

Floridan aquifer. 

The Upper Floridan aquifer is the major source of water 

supply within the study area and consists of limestone and 

dolomite that contain many solution-enlarged fractures, 

which commonly yield large supplies of water to wells. Most 

production wells in the study area are developed in the Tampa 

Member of the Arcadia Formation; wells that are deeper than 

99 to 107 m likely tap the upper part of the Ocala Limestone 

(Stewart and others, 1978). 

Caliper logs of production and monitoring wells that 

were logged by Stewart and others (1978) show sections of 

relatively large borehole diameters. These large borehole 

diameters represent solution openings and cavities that may be 

intercepted by wells. The most productive water-yielding zone 

of the Upper Floridan aquifer in the Temple Terrace area is a 

cavernous zone ranging from 37 to 55 m below land surface 

(Stewart and others, 1978). Wells that tap this zone can yield 

as much as 5,700 L/min. Public-supply well TTP-4 (index 

no. 30; table 1) is open to this high-yielding cavernous zone.

Lithology and Mineralogy of the 

Hydrogeologic Units

The geologic description of the surficial sediments, clay 

unit, and limestone that compose the hydrogeologic units 

is based on well cuttings, split-spoon coring, and grain-size 

analysis. Mineralogical analysis of selected cores also was 

performed using x-ray diffraction and mass spectrometry. The 

lithology, lithologic description, and the results of the grainsize analysis for selected wells are presented in table 2. 

Mineralogical results of the x-ray diffraction and ICP-MS 

analyses that were used to determine the chemical composition of major oxides and trace metals in acid extractions of 

solid-phase material are summarized in table 4. The x-ray 

diffraction methods used list the relative abundance of bulk 

minerals, with 1 being the highest and 5 being the least abundant mineral (table 4). Carr and Alverson (1959) performed a 

comprehensive investigation of the mineralogy and geology 

of the middle Terliary rocks underlying west-central Florida, 

which may explain some of the geochemical constituents 

observed in this study. They suggest that extensive weathering 

has occurred in the Hawthorn Group in the study area and that 

leaching forms a weathering profile of downward increasing 

solubility. The typical weathering sequence from top to bottom 

includes quartz sand, iron-stained clayey sand with iron and 

phosphatic hardpans, blue-green or iron-stained clays, a thin 

sequence of slightly calcareous clay, and chert that passes 

abruptly to a weathered limestone surface.

Some of the soluble byproducts found in this weathering 

profile in the Hawthorn Group include iron, phosphorous, aluminum, silica, and calcium. Where clays are dominant in the 

sequence, the abundance of aluminum oxide and iron oxide 

proportionally increases. Calcium concentrations increase with 

depth and are related to dissolution of weathered limestone 

residuum and from the underlying limestone.

The surficial deposits overlying the limestone surface 

and that were described from well cuttings collected in this 

study range from about 6 to 15 m thick. Surficial deposits 

were thinnest in the eastern boundary of the study area near 

the Hillsborough River, and thickest along the western edge of 

the study area, where a sand terrace is present. In general, the 

sediments are composed of an upper fine-grained sand unit, a 

sequence of clayey sand, and a lower sequence of sandy clay. 

The uppermost surficial deposit is a well sorted, very fine 

to fine quartz sand that generally is less than 3 m thick. The 

sand is white to buff colored near the surface and contains a 

mixture of organic matter and silt. Below the organic layer, 

the sand was stained a pale yellow-orange color, which was 

probably due to the influence of iron leaching in the shallow 

ground-water system.

 Grain-size analyses indicated that 95 percent of these 

upper sediments consist of sand, with the remaining sediments composed of silts and clays. The mineralogy of this 

unit indicates that quartz is the most abundant mineral with 

lesser amounts of plagioclase, potassium feldspar, calcite, and 

minimal amounts of total clays. Aluminum and iron were most 

abundant, with lesser amounts of calcium. Ferrous iron, which 

is produced during reducing conditions, was the dominant 

form of iron present.

Below the sand and organic layer, the clay content 

gradually increases, creating a sequence of clayey sand, which 

generally is less than 11 m thick. Grain-size analysis of the 

clayey sand sequence was variable, with the sand ranging 

from 52 to 95 percent and the remaining sediments composed 

of silt and clays. The clayey sand sequence also was the most 

variable in terms of mineralogy, which is probably due to the 

variability in the clay content. 

Quartz, total clays, and potassium feldspar were the most 

abundant minerals in the clayey sand sequence (table 4). The 

clays that were encountered in decreasing order of abundance 

include kaolinite, illite, smectite, and goethite (table 4). The 

clay was calcareous in places, especially near the limestone 

contact as indicated by increased calcium ions. Other dominant elements include aluminum, iron, magnesium, and potassium. The highest levels of arsenic, 1.4 mg/kg (milligrams 

per kilogram), were found in the clayey sand unit but was far 

below the levels of the most abundant major ions. Aluminum 

oxide and iron oxide increased in relation to the proportion 

of the clay content; ferrous iron, similar to the overlying unit, 

was the dominant form of iron present (table 4). 
20 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water Solid-phase sampling site Index no. Sample depth, meters Lithology Quartz Calcite Total clay Potas- sium feldspar Plagio- clase Goethite Halite Smectite Illite Kaolinite Chlorite Goethite Palygorskite Relative Abundance of Bulk Minerals Relative Abundance of <1-micron Clays GAFL THC-05 4 1.8 Sand 1 4 5 3 2 -- -- 2 3 1 4 -- -- GAFL GI14 10 4.3 Clayey sand 1 -- 2 -- Trace -- -- 4 2 1 Trace 3 -- Lynwood Pk. 16 8.8 Clayey sand 1 -- 2 -- Trace -- -- Trace 2 1 Trace -- -- Lightfoot Rec Center-Ret pond 27 20.7 Clayey sand; chert 1 -- 2 3 -- -- -- 1 2 3 -- -- -- Lynwood Pk. 17 11.6 Sandy clay 1 2 3 4 -- -- -- 2 3 Trace Trace -- 1 GAFL RP 13 6.2 Sandy clay 1 -- 3 2 -- -- -- 1 -- 3 -- -- -- ROCK-- GAFLWP-55 7 18.3 Limestone 2 1 Trace Trace -- -- -- 1 2 3 Trace -- -- Lightfoot Rec Center-Ret pond 27 26.8 Limestone; chert 2 1 3 -- -- -- -- 1 2 Trace Trace -- -- Lightfoot Rec Center-Ret pond 27 27.4 Clay and limestone 2 1 3 Trace Trace -- -- 1 2 3 -- -- -- 62nd Street Ret. Pond, UFA 21 48.8 Limestone Trace -- -- -- -- 2 1 1 2 Trace Trace -- -- Mas Residence, UFA 25 48.8 Limestone Trace 1 2 -- -- -- -- Trace 1 -- -- -- -- ROCK-- GAFLWP-200 9 62.5 Limestone Trace 1 Trace -- -- -- -- Trace Trace Trace Trace -- -- ROCK-- GAFLWP-300 9 91.4 Limestone Trace 1 Trace -- -- -- -- Trace Trace Trace Trace -- -- Solid-phase sampling site Index no. Sample depth, meters Lithology Calcium Iron Alumi- num Magne- sium Potas- sium Sodium Manga- nese Vana- dium Chromium Copper Lead Uranium Arsenic Elemental Analysis of Surficial Sediments or Rock GAFL THC-05 5 4 1.8 Sand 19 201 258 -- -- -- -- 0.5 0.31 0.06 0.12 0.04 0.01 GAFL GI14 10 4.3 Clayey sand 1,377 7,100 4,175 63 72 3 -- 65 16 1 2 3.35 0.01 GAFL pII -001a Lynwood Pk. 16 8.8 Clayey sand 140,000 4,500 8,500 8,300 1,300 160 190 54 24 6 5 7.7 0.13

GAFL pII 0016 Lightfoot Rec Ctr 27 20.7 Clayey sand; chert 67,000 1,200 2,300 1,800 1,000 63 18 7 9 6 3 0.35 1.40GAFL pII 0016 Lynwood Pk. 17 11.6 Sandy clay 520 5,100 2,600 290 140 28 <0.5 34 17 7 8 8.9 -- GAFL RP-20 13 6.2 Sandy clay 6,450 2,600 2,393 611 73 35 5 13 7 0.03 3 0.64 0.37

Table 4. Mineralogy of surficial sediments or rock, elemental composition from acid extractions, and concentrations of iron and sulfide from extractions of selected samples of core material. [Index numbers are identified in table 1. Relative abundance of bulk minerals determined by X-ray diffraction, with 1 being the highest and 5 being the lowest. Mineralogy of surficial sediments or rock and major oxides determined by 6N hydrochloric acid extractions in which samples were extracted for 6 hours on a shaker table, centrifuged, filtered (0.45 micron) and diluted to 1.2 N hydrochloric acid for analysis by inductively coupled plasma-mass-spectrometry. Same procedure for iron, as described, except used 0.5 M hydrochloric acid hydroxylamine in the extraction process. Same procedure for sulfide as described for the acid volatile and chromium reducible sulfides extraction process. Values shown in milligrams per kilogram, except where noted; NR, not reported; --, not detected; <, less than]
Hydrogeologic Setting 21

Solid-phase sampling site Index no. Sample depth, meters Lithology Calcium Iron Alumi- num Magne- sium Potas- sium Sodium Manga- nese Vana- dium Chromium Copper Lead Uranium Arsenic 

Elemental Analysis of Surficial Sediments or Rock

ROCK-- GAFLWP-55 7 18.3 Limestone 220,000 700 830 2,200 170 96 54 25 3 6 3 5 0.37ROCK-- GAFL Phase 2 002b 27 26.8 Clay and limestone 220,000 920 460 1,500 210 100 16 6 3 5 3 0.96 0.07GAFL pII 003 Lightfoot rec ctr, 27 27.4 Limestone; chert 320 1,600 940 83 11 10 <0.5 9 2 5 1 0.23 -- ROCK-- GAFLWP-200 9 62.5 Limestone 270,000 180 120 1,900 8 68 5 7 6 5 0.31 3.4 0.06ROCK-- GAFLWP-300 9 91.4 Limestone 260,000 280 130 1,900 8 76 11 8 6 5 0.41 3.6 0.07GAFL WP300 9 93.0 Lime sediment -- 170 240 2,100 58 93 6 8 6 4 -- -- 0.18

Solid-phase sampling site Index no. Sample depth, meters Lithology Alumi- num oxide Iron oxide Man- ganese oxide Calcium oxide Mag- nesium oxide Potas- sium oxide Sodium oxide Ferrous iron Ferric iron Total iron Sulfide 

Major Oxides Iron and Sulfide

GAFL THC-05 5 4 1.8 Sand 487 287 NR 26 NR NR NR 33 NR 25 0.22

GAFL GI14 10 4.3 Clayey sand 7,892 10,111 NR 1,926 105 86 4 NR NR NR NR GAFL pII -001a Lynwood Pk 16 8.8 Clayey sand 16,064 6,434 245 NR NR NR NR 210 170 380 0.31GAFL pII 0016 Lightfoot rec ctr. 27 20.7 Clayey sand; chert 4,347 1,716 23 NR NR NR NR 4200 1300 5500 0.34GAFL pII 0016 Lynwood Pk 17 11.6 Sandy clay 4,914 7,291 < 1 NR NR NR NR 4400 400 4800 0.23GAFL RP-20 13 6.2 Sandy clay 4,522 3,780 6 9,024 1,019 88 47 490 NR 470 60ROCK-- GAFLWP-55 7 18.3 Limestone 1,569 1,001 70 NR NR NR NR NR NR NR NR ROCK-- GAFL Phase 2 002b 27 26.8 Clay and limestone 869 1,315 21 NR NR NR NR NR NR NR NR GAFL pII 003 Lightfoot rec ctr 27 27.4 Limestone; chert 1,777 2,288 < 1 NR NR NR NR 130 20 150 3.8ROCK-- GAFLWP-200 9 62.5 Limestone 227 258 6 NR NR NR NR NR NR NR NR ROCK-- GAFLWP-300 9 91.4 Limestone 454 400 14 NR NR NR NR NR NR NR NR GAFL WP300 9 93.0 Lime sediment 246 243 8 NR NR NR NR 61 6 67 115

Table 4. Mineralogy of surficial sediments or rock, elemental composition from acid extractions, and concentrations of iron and sulfide from extractions of selected samples of core material.—Continued[Index numbers are identified in table 1. Relative abundance of bulk minerals determined by X-ray diffraction, with 1 being the highest and 5 being the lowest. Mineralogy of surficial sediments or rock and major oxides determined by 6 N hydrochloric acid extractions in which samples were extracted for 6 hours on a shaker table, centrifuged, filtered (0.45 micron) and diluted to 1.2 N hydrochloric acid for analysis by inductively coupled plasma-mass-spectrometry. Same procedure for iron, as described, except used 0.5 M hydrochloric acid hydroxylamine in the extraction process. Same procedure for sulfide as described for the acid volatile and chromium reducible sulfides extraction process. Values shown in milligrams per kilogram, except where noted; NR, not reported; --, not detected; <, less than]
22 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

Below the clayey sand sequence where the clay content 

continues to increase, a sequence of sandy clay is present. 

This sequence corresponds to the intermediate confining 

unit, which is composed of deposits of the Hawthorn Group. 

This unit was the most difficult to interpret in the study area 

because of the varying amounts of sands and discontinuous 

clays and the absence of this unit due to subsidence, which 

disrupted the continuity of the unit. Generally, this unit was 

less than 1.5 m thick. Carr and Alverson (1959) and Sinclair 

(1974) describe the clay in the intermediate confining unit as a 

weathered residuum of the limestone in the underlying Tampa 

Member of the Arcadia Formation. Elevated concentrations of 

radium and radionuclides that are commonly associated with 

clay minerals also are present in the intermediate confining 

unit (Carr and Alverson, 1959). 

The intermediate confining unit in the study area varied 

in color, composition, and permeability. This unit has a dense 

plastic consistency, a tan, greenish-gray or orange-red color, 

and varying amounts of sand, chert, and carbonate mud. The 

clay may be calcareous in places, particularly near the underlying limestone contact. Minerals in this sandy clay unit, in 

decreasing order of abundance, are quartz, calcite, potassium 

feldspar, and total clay. The most abundant clays were smectite, illite, and kaolinite; calcium, iron, and aluminum were the 

most abundant elements. The highest concentration of uranium 

(8.9 mg/kg) was detected in the sandy clay unit and is probably related to the high clay mineral content. Concentrations of 

aluminum oxide and iron oxide also were elevated due to high 

clay content. Concentrations also were elevated for calcium 

oxide, which reflects the calcareous nature of the clay. Ferrous 

iron, similar to the overlying units, was the dominant form of 

iron present.

The highly weathered limestone of the Tampa Member 

underlies the intermediate confining unit and is identified as 

the top of the Upper Floridan aquifer. The Tampa Member is 

tan to white, soft to hard, usually sandy and fossiliferous, and 

commonly contains clay lenses and cavities. The Tampa Member is generally less than 30 m thick in this region; the depth to 

the top of the Tampa Member ranges from 4.3 to 11.0 m above 

NAVD 88 at RP-F77 and WP-F150, respectively (based on 

well cuttings collected for 14 wells throughout the study area).

At two sites, sands and clays were present far below 

the typical depth to the top of limestone found at other sites, 

which indicates that infilling by overburden materials into 

solution cavities has occurred. At wells LRP-H105 (index 

no. 27; table 2) and 113RC-H50 (index no. 2; table 2), the 

depth to limestone was about 6 and 18 m below NAVD 88, 

respectively, which suggests the wells were drilled into paleosinkholes. The infilling and raveling of the overburden materials into limestone cavities increase the connection of overlying 

units to the Upper Floridan aquifer.

The mineralogy indicates the weathered limestone of the 

Tampa Member is relatively impure, and contains considerable 

amounts of sand and clay. The minerals identified in the upper 

sequence of the Tampa Member (index no. 7 and 27; table 4) 

were calcite with lesser amounts of quartz and total clays. The 

clays that were associated with the limestone were smectite, 

illite, and kaolinite. Major elements that compose the rock 

were calcium, magnesium, iron, and aluminum. Concentrations of iron oxide and aluminum oxide in the upper sequence 

of the Tampa Member were elevated compared to lower units, 

which reflects the higher clay content associated with this 

unit. Ferrous iron was the dominant form of iron present, but 

at levels much lower than the overlying sand and clay layers. 

The mineralogy of the lower sequence of the Tampa Member 

(index no. 21 and 25; table 4) include calcite, halite, goethite, 

and total clays. The clay minerals associated with the lower 

limestone sequence were smectite and illite. 

The Suwannee Limestone underlies the Tampa Member 

with a thickness of about 60 to 76 m in the study area. The 

limestone is white to light tan in color, soft and granular in 

appearance, and contains abundant fossil detritus and organic 

structures such as casts, molds, and borings of mollusks and 

tests of foraminifera and bryozoa (Carr and Alverson, 1959). 

Many fossil molds within this unit give it a high porosity. 

The mineralogy of the Suwannee Limestone includes 

calcite as the most abundant mineral, with trace amounts of 

quartz and clays. The most abundant elements include calcium 

and magnesium, with lesser amounts of iron and aluminum. 

Amounts of iron oxide and aluminum oxide were considerably 

lower than in the overlying material, which indicates a reduced 

clay content. Ferrous iron was the dominant form of iron present, but at levels much lower than in the overlying material.

Estimation of Aquifer Properties

Hydraulic properties (for example, hydraulic conductivity, vertical conductance, and effective porosity) were obtained 

from previous hydrogeologic studies of the Upper Floridan 

aquifer in the Tampa Bay area (Knochenmus and Robinson, 

1996; J. Arthur, Florida Geological Survey, written commun., 

2003). Porosity and permeability of the limestone rock matrix 

can be enhanced by dissolution and/or fracturing. Previous 

studies have correlated fractures observed in limestone outcrops in west-central Florida with the occurrence of fracture 

traces and surface lineaments (Vernon, 1951). Using surface 

geophysical methods, Culbreath (1988) found that the surface lineaments with corresponding gravity anomalies had a 

preferred orientation between 45 and 55 degrees east and west 

of north (fig. 1). Geologic structures aligned in this preferred 

orientation are believed to occur at the surface as lineaments 

because they parallel the stress fields associated with earth 

tides (Culbreath, 1988). Fracture zones typically are enlarged 

by chemical dissolution in karstic aquifer systems. In a study 

of Floridan aquifer system properties in west-central Florida, 

Stewart and Wood (1984) found that the porosity can be 10 

to 100 times that of the intergranular matrix in places where 

vertical to near-vertical fractures have been enlarged by dissolution. 

Information on particle-size distribution, bulk density, 

and moisture content of core material were used to estimate 
Hydrogeologic Setting 23

annual recharge (R. Healy, U.S. Geological Survey, written 

commun., 2004). Recharge estimates were highly variable 

and ranged from 0.8 to 43 cm/yr (centimeters per year), with a 

median value of 13 cm/yr. Transmissivity values for the Upper 

Floridan aquifer ranged from 2,700 to 12,100 m2/d (meters 

squared per day) based on data from an aquifer test conducted 

in March 1975 for a public-supply well cased to 28 m with 

an open hole to 146 m, with an average storage coefficient of 

3.4 x 10-4 (Stewart and others, 1978). Effective porosity ranged 

from 0.02 (Avon Park Formation) to 0.49 (Ocala Limestone). 

Geophysical measurements were made in the open interval of the Upper Floridan aquifer of the public-supply well 

borehole (36-53 m below land surface) in October 2004 (J.H. 

Williams, U.S. Geological Survey, written commun., 2007) 

to obtain detailed information on well construction, aquifer 

properties, rock lithology and solution features, dominant flow 

zones, permeability, and water quality. Logs include caliper, 

gamma, spontaneous potential, fluid resistivity, temperature, 

flow meter, and optical televiewer. Continuous data from the 

various probes are displayed graphically in figure 6. 

Based on the analysis of the flowmeter, fluid, and specific 

conductance logs (fig. 6), the public-supply well penetrated 

high-flow zones at 46.8 and 49.2 m below land surface. Borehole flow was downward under ambient conditions from the 

upper to the lower zone. Under pumping conditions, the lower 

zone contributed 70 percent of the 1,020 L/min discharged 

from the well. Flowmeter model analysis suggested that the 

High-flow

zone

80 120

12.7 1.5 4.5

0.3 0.9

825 1,250

325 375

DS, AMB, mg/L

325 375

DS, PMP, mg/L

0 20

As, AMB, g/L

0 20

As, PMP, g/L

450 1,000

Sr, AMB, g/L

450 1,000

Sr, PMP, g/L

NO -N, AMB, mg/L 3

NO -N, PMP 3 , mg/L

CHCl , AMB, 3 g/L

CHCl , PMP 3 , g/L

Rn-222, AMB, pCi/L

Rn-222, PMP, pCi/L

Gamma Caliper

Resistivity

21.9 Deg C 22.5

Temp, PMP

-0.12 Meters 0.12

Zone Head Diff.

Zone Transmissivity

Cubic meters

per day

0 2,320

-380 L/min 380

EM Flow, AMB

Centimeters

Geophysical logs Geochemical data

36

39

42

45

48

51

90

Depth,

below

land

surface

meters

20 API-GR 50

Ohm

SIM Flow, AMB

-380 L/min 380

SIM Flow, PMP

-1,500 L/min 1,500

Depth

interval

sampled,

meters

38-53

43-53

49-53

1.5 4.5

0.3 0.9

510 610 825 1,250

SC, PMP, sample,

S/cm

510 610

SC, AMP, sample,

S/cm

610 675

SC, PMP

S/cm

650 720

SC, AMB

S/cm

-215 305

EM Flow, Troll, PMP

L/min

-330 330

SPIN Flow, PMP

L/min

21.9 22.5

Temp, AMB

Deg C

API-GR=American Petroleum Institute-gamma ray units

AMB=ambient conditions

PMP= pumped conditions

EM Flow=flow measurements made with an electromagnetic flowmeter placed

at selected depths, in liters per minute (L/min)

EM Flow, Troll=flow log made with an electromagnetic flowmeter as it is trolled

up or down borehole, in liters per minute (L/min)

SIM Flow=flow log simulated with Paillet's model (1998 and 2000), which has

been matched to measure ambient and pumped flows by trial-anderror adjustment of flow zone transmissivity and head, in liters per

minute (L/min)

SPIN Flow=flow measurements made with a spinner flowmeter placed at

selected depths, in liters per minute (L/min)

Temp=temperature, in degrees celsius (Deg C)

SC=specific conductance, in microsiemens per centimeter ( S/cm)

DS=dissolved solids, in milligrams per liter (mg/L)

As=arsenic, in micrograms per liter ( g/L)

Sr=stronium, in micrograms per liter ( g/L)

NO -N=nitrate as nitrogen, in milligrams per liter (mg/L)

CHCl =trichloromethane, in micrograms per liter ( g/L)

Rn-222=radon-222, in picocuries per liter (pCi/L)









3

3

Figure 6. Geophysical logs of the public-supply well borehole at Temple Terrace, Florida.
24 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

lower zone had a transmissivity about three times higher than 

that of the upper zone, and there was about 0.09-m hydraulic head difference between the zones. The fluid logs and 

discrete-depth samples at 48.8 m under ambient and pumping 

conditions indicated that the specific conductance of water 

from the upper zone was about 10 percent less than that from 

the lower zone. Caliper and televiewer logs revealed large 

solution openings in the Upper Floridan aquifer limestone 

at depths greater than 47 m. Specific conductance decreased 

substantially in this interval indicating that lower conductance 

water is entering the 45- to 53-m zone, possibly water moving 

downward from the surficial aquifer system, which has lower 

conductance than water from the Upper Floridan aquifer. 

Temperature also showed a slight decrease (about 0.3 oC) 

through this interval. Chemical data for water samples 

collected from three overlapping depth intervals (38-53, 43-53, 

and 49-53 m) are presented later in this report.

Ground-Water Flow Patterns

The water table in the surficial aquifer system follows 

closely to the land surface and is affected by regional 

discharge features and rainfall and recharge events. Groundwater elevation is highest at well 62SRP-S34 with a median of 

12.74 m above NAVD 88. Well 62SRP-S34 is one of the 

westernmost monitoring wells tapping the surficial aquifer 

system in the study area and where land-surface elevations are 

relatively high. The water table is also higher at well WP-S64 

(median of 8.37 m median) than at other surficial aquifer 

system wells because of the higher elevation and location of 

the well on the remnant marine terrace. Water-table elevations 

generally are above the potentiometric surface of the Upper 

Floridan aquifer (C.A. Crandall, U.S. Geological Survey, written commun., 2007). The regional ground-water flow direction 

in the Upper Floridan aquifer is generally from the northnortheast to south-southwest in the study area (fig. 3). Pumping affects ground-water levels in the Upper Floridan aquifer, 

especially in those wells screened in the same zone as most of 

the public-supply wells. Water levels in storm retention ponds 

are generally above those of the surficial aquifer system and 

the Upper Floridan aquifer and reflect input from stormwater 

runoff during wet periods. As a result of likely hydraulic connections between some retention ponds and the subsurface, 

leakage of surface water can recharge the surficial aquifer 

system and Upper Floridan aquifer. Parts of the Upper 

Floridan aquifer are in direct hydraulic contact with the Hillsborough River, although exchange of water between the river 

and aquifer depends in part on operations at the downstream 

reservoir on the Hillsborough River and on rainfall/recharge 

events.

The size and orientation of the ground-water 

contributing recharge area of the public-supply well has 

evolved over time (C.A. Crandall, U.S. Geological Survey, 

written commun., 2007). The first contributing recharge 

area of the public-supply well was obtained using a regional 

ground-water flow model, MODPATH (Harbaugh and others, 2000), and was used to guide the siting of the first set of 

monitoring wells installed in 2003. Next, probabilistic groundwater flow models were used to incorporate uncertainty in the 

delineation of the contributing recharge area, and to determine 

locations for new monitoring wells installed in 2004. The 

probabilistic flow models consisted of two separate methods, 

with the first being a stochastic parameter uncertainty method 

that was used by MODPATH to calculate time of travel for 

various particles in the Upper Floridan aquifer to the publicsupply well. The second probabilistic method, referred to as 

the fracture continuum method, incorporated karst information 

such as sinkholes and fracture orientation into the contributing recharge area calculation. This information was used by 

MODPATH to calculate time of travel for various particles to 

the public-supply well (C.A. Crandall, U.S. Geological 

Survey, written commun., 2007). 

Ground-Water Chemistry

This section describes the general chemical 

characteristics of waters from the surficial aquifer system, 

intermediate confining unit, and Upper Floridan aquifer in the 

Temple Terrace study area including water types, redox 

conditions, pH, saturation indices with respect to selected 

minerals, and stable isotope composition. Subsequent 

sections describe the distribution of selected anthropogenic 

and naturally occurring contaminants in the surficial 

aquifer system, intermediate confining unit, and Upper 

Floridan aquifer with special emphasis on the comparison 

between water chemistry in public-supply well TTP-4 and 

these three hydrogeologic units in the study area. Differences 

in chemical signatures among the various hydrogeologic units 

are used to better understand important ground-water flow 

patterns and pathways, and to generate hypotheses for 

processes controlling water quality in the public-supply well.

Chemical Composition and Mineral 

Saturation Indexes

Water from 8 of 11 wells tapping the surficial aquifer 

system had pH values below 7.0 (median values 5.0-6.9), and 

water from three wells had pH values ranging from 7.1 to 7.5. 

Two of the three wells (BBP-S45 and WP-S64) had depths 

to water greater than 10 m. Water samples from wells in the 

intermediate confining unit had median pH values that ranged 

from 7.3 to 7.9. Water from the Upper Floridan aquifer had 

median pH values that ranged from 7.2 to 7.9.

Water types for samples from the three hydrogeologic 

units and surface waters were somewhat variable, although 

dominated by calcium bicarbonate, calcium-bicarbonatesulfate, and calcium-sulfate-bicarbonate (fig. 7). Calcium was 

the dominant cation in water from 10 of 11 wells in the surficial aquifer system, all four wells in the intermediate confining 
Ground-Water Chemistry 25

unit, all wells in the Upper Floridan aquifer, the three retention 

ponds, and Hillsborough River. The dominant anion in these 

waters was more variable, and was either bicarbonate or sulfate. Deep wells in the Upper Floridan aquifer tended to have 

sulfate as the dominant anion. Water from 9 of 13 wells in 

the Upper Floridan aquifer had a calcium-sulfate-bicarbonate 

water type, and four wells had a calcium-bicarbonate-sulfate 

water type. Water from the remaining well had a calciumbicarbonate water type.

Variability in saturation indices with respect to calcite, 

dolomite, and gypsum for water from the three hydrogeologic 

units (table 5) reflect differences in their mineralogy 

(table 4). Median saturation indices with respect to calcite 

are -0.40, -0.16, and 0.08 for water samples from the surficial aquifer system, intermediate confining unit, and Upper 

Floridan aquifer, respectively. Variable amounts of minerals containing calcium magnesium carbonate in the surficial 

aquifer system and intermediate confining unit account for the 

large variability in saturation indices with respect to calcite 

and dolomite (table 5). As would be expected for water from 

the carbonate Upper Floridan aquifer, samples are saturated 

with respect to calcite and slightly undersaturated with respect 

to dolomite. Samples from deep wells in the Upper Floridan 

aquifer (for example, GARC-F200) are saturated with respect 

to dolomite. Water samples from the Upper Floridan aquifer 

are slightly undersaturated with respect to gypsum, whereas 

water samples from the intermediate confining unit and 

surficial aquifer system are highly undersaturated with respect 

to gypsum. 

Dissolved Organic Carbon and 

Dissolved Solids Concentrations

Dissolved organic carbon concentrations were highly 

variable (0.6 to 18.1 mg/L) in water samples from the surficial 

aquifer system (table 5). This large variation likely indicates 

that some wells are located near recharge areas that receive 

surface water with elevated concentrations of dissolved 

organic carbon, such as retention ponds and the Hillsborough 

River. Dissolved organic carbon concentrations in water 

samples from stormwater retention ponds ranged from 3.7 to 

20

40

60

80

20

40

60

80

CALCIUM

SODIUM + POTASSIUM

CARBONATE + BICARBONATE

CHLORIDE

MAGNESIUM

SULFATE

TTP4-160P

TTP-4

Surficial aquifer

Hillsborough River

Retention ponds

Intermediate confining unit

Upper Floridan aquifer

EXPLANATION

0

100

0 80

60

40

20

20

40

60

80

0

100

0 20

40

60

80

SULFATE + CHLORIDE

CALCIUM + MAGNESIUM

20

40

60

80

0

100

0

20

40

60

80

20

40

60

80

0

100

100

0

PERCENT

PERCENT

PERCENT

20

40

60

80

0

100

20

40

60

80

100

0

CATIONS ANIONS

Figure 7. Major-ion chemistry for ground-water and surface-water samples from the Temple 

Terrace, Florida, study area.
26 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

Table 5. Physical properties and chemistry of water samples from the surficial aquifer system (SAS), intermediate confining unit (ICU), and Upper

[Concentrations are in milligrams per liter (mg/L) unless otherwise noted; P, STORET parameter code; temperature, in degrees Celsius; specific conductance, in microsiemens per 

meters below measuring point; SI, saturation index; PCO2, partial pressure of carbon dioxide in water sample]

Site 

name 

Aquifer or 

hydrogeologic 

unit

Site

identifier Date Time

P00010 P00095 P00300 P00400 P00453 P00608 P00613 P00631 P00671 P00681

Temperature

Specific 

conductance

Dissolved 

oxygen pH Bicarbonate

Ammonium 

as nitrogen

Nitrite as 

nitrogen

Nitrate as 

nitrogen

Orthophosphate as 

phosphorus

Dissolved 

organic 

carbon

BBP-S45 SAS 280228082231501 8/11/2004 1200 25.0 594 3.9 6.9 294 <0.04 <0.008 0.82 0.159 0.9

BBP-S45 SAS 280228082231501 12/9/2004 1300 25.5 475 3.8 7.1 253 E0.02 <0.008 0.21 0.334 0.6

BBP-S45 SAS 280228082231501 6/22/2005 1130 25.9 526 3.7 7.1 263 <0.04 <0.008 0.72 0.171 0.7

THC-F197 UFA 280241082224401 1/15/2004 1400 25.0 958 0.3 7.2 214 0.17 <0.008 <0.06 0.026 2.6

THC-F197 UFA 280241082224401 1/28/2004 1210

THC-F75 UFA 280241082224402 1/12/2004 1500 24.5 515 0.1 7.3 162 0.11 <0.008 <0.06 0.131 1.9

THC-F75 UFA 280241082224402 6/14/2005 1640 26.6 489 0.2 7.3 154

THC-S46 SAS 280241082224403 12/18/2003 1300 24.5 693 0.3 6.9 315 0.07 0.011 1.05 0.089 1.1

THC-S46 SAS 280241082224403 1/15/2004 1120

THC-S46 SAS 280241082224403 8/5/2004 1200 25.0 697 0.3 6.9 317 0.05 E0.004 0.81 0.092 0.8

THC-S46 SAS 280241082224403 11/17/2004 1600 25.7 705 6.7 343 E0.03 E0.004 0.59 0.048 0.7

THC-S46 SAS 280241082224403 6/14/2005 1700 27.0 707 0.3 6.8 316 E0.03 E0.007 1.55 0.15 0.7

62SRP-F160 UFA 280241082230701 11/2/2004 1200 28.7 596 0.1 7.2 200 <0.04 0.009 1.99 0.025 1

62SRP-F160 UFA 280241082230701 6/20/2005 1600 26.5 579 0.6 7.2 197

62SRP-H55 ICU 280241082230702 11/3/2004 1700 26.6 456 4.7 7.1 232 E0.02 <0.008 3.54 0.044 1040

62SRP-S34 SAS 280241082230703 8/12/2004 930 25.5 540 6.8 6.3 274 <0.04 E0.005 3.21 0.014 13.8

62SRP-POND POND 280242082230800 6/21/2005 1220 29.0 362 2.3 7.2 108 1.41 0.043 0.91 0.29 17.8

MAS-R-F160 UFA 280242082232401 11/3/2004 1200 26.7 546 0.7 7.4 224 E0.02 0.011 0.94 0.029 0.9

MAS-R-F160 UFA 280242082232401 6/16/2005 1040 27.0 548 0.5 7.2 211 <0.04 0.013 0.72 0.022 1.1

MAS-R-F64 UFA 280242082232403 2/16/2005 1300 25.5 262 1.8 7.7 105 <0.04 <0.008 1.2 0.017 0.5

MAS-R-F64 UFA 280242082232403 6/16/2005 1100 26.0 219 2 8 82 <0.04 <0.008 1.2 0.007 0.5

MAS-POND POND 280242082232900 6/21/2005 1100 28.5 172 2.9 7.1 72 <0.04 <0.008 <0.06 0.12 9.3

TTP-4 UFA No data 10/21/2002 1600 26.5 608 0.4 7.2 188 E0.04 0.02 0.72 0.03 0.9

TTP-4 UFA No data 1/28/2004 1600 24.0 603 0.2 7.3 189 E0.02 0.033 0.89 0.021 1.9

TTP-4 UFA No data 9/22/2004 1600 25.5 599 0.7 7.3

TTP-4 UFA No data 10/21/2004 1500 26.0 606 0.5 7.3 170 <0.04 0.008 1.4 0.018 0.9

TTP-4 UFA No data 2/16/2005 1600 25.0 584 0.4 7.3 184 E0.02 0.042 0.61 0.014 0.9

TTP-4 UFA No data 6/20/2005 1600 26.4 618 0.3 7.4 194 E0.02 0.048 0.72 0.016 1.2

WP-F299 UFA 280247082231901 1/22/2004 1600 26.0 1,000 0.2 7.2 225 0.17 <0.008 <0.06 0.036 2.4

WP-F299 UFA 280247082231901 8/3/2004 1400 26.0 1,000 0.3 7.1 215 2.2

WP-F150 UFA 280247082231902 1/28/2004 1300 25.2 569 0.2 7.4 158 0.17 <0.008 <0.06 0.034 1.2

WP-F150 UFA 280247082231902 8/4/2004 1100 26.0 584 0.3 7.4 156 0.18 <0.008 <0.06 0.028 1.2

WP-F150 UFA 280247082231902 6/14/2005 1110 26.9 576 0.6 7.4 157 <0.008

WP-S64 SAS 280247082231903 1/14/2004 1500 26.0 474 5.4 7.5 124 <0.04 <0.008 2.5 0.049 0.8

WP-S64 SAS 280247082231903 8/4/2004 1600 26.5 482 6.7 7.5 112 <0.04 <0.008 4.6 0.051 0.6

WP-S64 SAS 280247082231903 11/18/2004 1200 27.3 455 6 7.5 132 <0.04 <0.008 4.1 0.054 1.5

WP-S64 SAS 280247082231903 6/14/2005 1130 26.5 457 5.7 7.5 120 <0.04 <0.008 2.3 0.048 13.7

RP-F103 UFA 280249082220701 12/2/2003 1500 23.5 759 0.2 7.2 256 0.14 <0.008 <0.06 0.037 2

RP-F103 UFA 280249082220701 1/14/2004 1135 22.5 792 0.1 7.2

RP-F77 UFA 280249082220702 12/3/2003 1300 23.5 562 0.2 7.3 251 0.21 <0.008 <0.06 0.05 2.4

RP-F77 UFA 280249082220702 6/16/2005 1610 25.2 586 0.4 7 251

RP-S20 SAS 280249082220703 12/4/2003 1400 24.5 502 2.2 6.4 303 0.04 <0.008 <0.06 0.125 3.3

RP-S20 SAS 280249082220703 8/11/2004 1500 24.0 791 1.4 6.6 392 <0.04 <0.008 0.1 0.084 2.5
Ground-Water Chemistry 27

P00915 P00925 P00930 P00935 P00940 P00945 P00950 P00955 P39086 P70300 P99118 P72019

Calcite SI Dolomite 

SI Gypsum SI logPCO Calcium 2

Magnesium Sodium Potassium Chloride Sodium Fluoride Silica Alkalinity 

as CaCO3

ROE-DS Hydrogen 

sulfide DTW

94.2 3.85 25.8 0.82 10.8 53.8 0.5 7.46 241 293 8.84 -0.15 -1.33 -1.75 -1.45

83.5 2.49 17.6 0.58 7.54 31.4 0.6 8.52 207 274 0.002 9.64 -0.03 -1.24 -2.00 -1.71

92.2 2.85 15.9 0.82 9.91 30.9 0.4 9.37 215 300 0.004 10.0 0.03 -1.09 -1.98 -1.69

195 23.3 8.17 1.05 9.38 371 0.6 15.1 176 759 1.5 9.77 0.2 -0.19 -0.81 -1.91

96.7 8.11 8.21 0.74 7.11 137 0.3 14.2 133 365 0.6 9.70 -0.02 -0.79 -1.36 -2.12

126 0.533 9.52

130 6 16.5 1.16 36.5 44.4 0.3 14.7 262 405 0 9.61 0 -1.00 -1.75 -1.43

125 5.36 13.7 1.14 34.9 45.1 0.2 15 260 329 0.02 8.65 -0.00 -1.02 -1.75 -1.42

133 6.3 17.3 1.26 42.7 43.9 0.2 16.4 281 426 0.008 8.94 -0.14 -1.25 -1.75 -1.18

131 5.86 14.6 1.15 42.5 44.6 0.2 16.5 259 452 0.013 9.50 -0.06 -1.10 -1.74 -1.31

95.5 10.8 12.3 1.35 27.9 89.7 0.2 13.6 164 353 0.002 14.5 0.03 -0.50 -1.55 -1.90

162 15.3

64.8 16.6 6.3 0.84 12.7 18.3 E0.1 31.9 190 281 0.008 13.6 -0.16 -0.54 -2.35 -1.74

81.7 14 17.3 2.14 28.9 12.8 0.2 9.18 224 272 8.31

53.2 4.13 10.4 2.7 22.7 44.5 0.3 9.13 89 260 -0.42 -1.57 -1.99 -2.15

85.9 5.94 19 8.36 18.5 63.4 0.1 12.6 184 326 0.004 13.5 0.22 -0.35 -1.71 -2.06

94.6 6.52 11.2 2.79 19.1 69.8 0.2 12.1 173 337 0.008 14.0 0.04 -0.71 -1.64 -1.88

36.2 1.73 13.6 0.5 15.4 12.8 0.1 15.9 86 164 0 13.6 -0.11 -1.19 -2.62 -2.68

34.9 1.82 4.88 0.46 15.2 9.2 E0.1 17.7 67 150 13.4 0.08 -0.78 -2.76 -3.09

25.5 0.91 7.34 2.03 11.9 3.9 E0.1 2.4 59 112 -0.95 -2.96 3.24 -2.21

106 9.52 10.3 0.94 17.8 129 0.3 12.7 154 390 0

110 11 10.9 1.16 22.8 122 0.3 13.5 155 390 0.048 0.09 -0.49 -1.37 -2.05

0.025

98.1 8.41 11.2 1.04 25 116 0.3 13.3 139 380 0.03 0.03 -0.65 -1.43 -2.08

103 8.51 11.3 1.08 26 112 0.3 12.4 151 369 0.005 0.07 -0.60 -1.42 -2.06

109 10.4 11.6 1.11 24 121 0.3 13.2 159 390 0.038 0.23 -0.20 -1.38 -2.13

195 23.6 9.01 1.4 9.41 355 0.6 15.3 185 760 1.88 18.4 0.23 -0.10 -0.83 -1.89

183 23.3 7.31 1.27 9.03 369 0.6 14.9 177 753 1.71 17.5 0.09 -0.36 -0.83 -1.80

102 11.5 10.7 1.09 19.1 139 0.5 13.9 130 386 0.018 18.4 0.09 -0.42 -1.35 -2.22

94.1 10.2 10.3 1.07 20.9 133 0.5 13.1 128 375 0.11 17.5 0.07 -0.47 -1.38 -2.22

128 0.103 18.2

77.6 6.39 12.2 1.79 21.3 87.2 0.2 8.43 102 294 0 16.2 0.02 -0.69 -1.60 -2.42

67.8 5.32 14.7 1.86 30.6 73 0.2 8.92 94 287 0.005 15.1 -0.05 -0.85 -1.71 -2.44

65.6 5.4 13.3 2.39 26.2 59 0.1 9.88 108 280 0.002 15.3 0.01 -0.69 -1.81 -2.38

70.4 5.76 10.6 1.58 20.8 86.3 0.4 8.13 98 283 16.3 -0.03 -0.78 -1.63 -2.43

151 15.8 6.24 0.74 8.59 227 0.4 15.8 210 578 0.51 4.90 0.2 -0.27 -1.05 -1.83

106 10.4 7.88 0.71 7.6 93.6 0.5 28.3 206 394 0.29 5.21 0.2 -0.29 -1.49 -1.93

206 0.48 4.71

114 2.8 9.32 0.29 18.8 30.5 0.2 16.2 248 355 0.007 4.85 -0.51 -2.25 -1.93 -0.92

147 2.72 16.5 0.21 20.3 80.3 0.4 12.5 322 343 0 2.63 -0.18 -1.76 -1.46 -1.04

Floridan aquifer (UFA) in the study area.

centimeter; E, estimated concentration, below reported laboratory reporting level; ROE-DS, residue on evaporation, dissolved solids, mg/L; DTW, depth to water in
28 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

Table 5. Physical properties and chemistry of water samples from the surficial aquifer system (SAS), intermediate confining unit (ICU), and Upper

[Concentrations are in milligrams per liter (mg/L) unless otherwise noted; P, STORET parameter code; temperature, in degrees Celsius; specific conductance, in microsiemens per 

meters below measuring point; SI, saturation index; PCO2, partial pressure of carbon dioxide in water sample]

Site

name

Aquifer or 

hydrogeologic 

unit

Site

identifier Date Time

P00010 P00095 P00300 P00400 P00453 P00608 P00613 P00631 P00671 P00681

Temperature

Specific 

conductance

Dissolved 

oxygen pH Bicarbonate

Ammonium 

as nitrogen

Nitrite as 

nitrogen

Nitrate as 

nitrogen

Orthophosphate as 

phosphorus

Dissolved 

organic 

carbon

RP-S20 SAS 280249082220703 11/16/2004 1500 24.2 435 0.3 6.8 267 <0.04 <0.008 <0.06 0.124 2.6

RP-S20 SAS 280249082220703 6/16/2005 1500 25.0 613 1 6.6 373 <0.04 <0.008 <0.06 0.118 2.2

LRP-F160 UFA 280250082233001 11/4/2004 1300 27.8 458 0.5 7.8 153 0.47 <0.008 <0.06 0.018 1.7

LRP-H105 ICU 280250082233002 12/7/2004 1600 25.1 288 0.3 7.4 134 0.09 <0.008 0.27 0.051 1.7

LRP-H105 ICU 280250082233002 6/15/2005 1510 29.5 334 0.6 8.3 139

LRP-S25 SAS 280250082233003 8/10/2004 1100 26.0 447 0.5 7.5 154 0.09 0.014 0.72 0.068 1.6

LRP-S25 SAS 280250082233003 6/15/2005 1500 25.0 442 0.4 7.3 120 0.2 <0.008 E0.04 0.026 1.7

LRP-POND POND 280250082233200 6/21/2005 0915 27.5 400 8.4 8.8 100 <0.04 0.054 0.61 0.021 3.7

JARP-S40 SAS 280251082224201 6/27/2005 1030 29.0 236 2.3 6.7 89 <0.04 <0.008 <0.06 <0.006 1.5

GARC-F200 UFA 280253082223801 12/16/2003 1300 25.0 1,070 0.2 7.2 218 0.18 <0.008 <0.06 0.035 2.1

GARC-F75 UFA 280253082223802 12/15/2003 1400 20.5 852 0.2 7.3 215 0.22 <0.008 <0.06 0.048 0.5

GARC-F75 UFA 280253082223802 6/13/2005 1200 28.0 825 0.5 7.2 221

GARC-S23 SAS 280253082223803 12/17/2003 1200 25.0 515 2.5 6.3 193 <0.04 E0.007 4.81 0.006 0.7

GARC-S23 SAS 280253082223803 8/5/2004 1600 26.0 540 4.5 5.9 70 <0.04 <0.008 1.56 E0.003 0.9

GARC-S23 SAS 280253082223803 11/17/2004 1100 27.7 504 3 5.7 70 <0.04 <0.008 2.45 <0.006 18.1

GARC-S23 SAS 280253082223803 6/13/2005 1115 27.1 450 3.2 5.8 69 <0.04 <0.008 2.47 E0.003 0.7

113RC-F190 UFA 280301082222701 12/8/2003 1300 25.0 1,010 0.3 7.2 222 0.17 <0.008 <0.06 0.023 2.8

113RC-F190 UFA 280301082222701 6/15/2005 1130 27.1 1,040 0.3 7.1 226

113RC-H50 ICU 280301082222702 12/9/2003 1300 25.5 0 0.3 7.3 166 0.06 0.03 0.65 0.023 1.8

113RC-S35 SAS 280301082222703 12/11/2003 1300 26.0 379 2.5 6.8 157 <0.04 E0.007 3.51 0.019 0.6

113RC-S35 SAS 280301082222703 8/12/2004 1300 27.5 370 4 6.6 135 <0.04 E0.006 4.41 0.014 0.9

113RC-S35 SAS 280301082222703 11/16/2004 1300 27.3 316 2.2 6.6 141 <0.04 E0.004 2.36 0.019 2.3

113RC-S35 SAS 280301082222703 6/15/2005 1100 27.5 373 4.3 6.6 137 <0.04 <0.008 3.6 0.01 1.1

LP-H40 ICU 280303082230901 8/10/2004 1500 32.0 262 7.5 7.8 120 <0.04 E0.006 2.15 0.029 2.3

LP-H40 ICU 280303082230901 12/8/2004 1500 26.4 259 6.8 7.5 127 <0.04 <0.008 2.4 0.069 0.4

LP-S30 SAS 280303082230902 8/10/2004 1200 29.0 65 8 4.4 5 <0.04 <0.008 1.8 <0.006 0.3

LP-S30 SAS 280303082230902 11/1/2004 1600 28.2 92 6.2 5 5 <0.04 <0.008 2.7 <0.006 13.5

LP-S30 SAS 280303082230902 6/21/2005 1130 26.0 70 7 5.3 5 <0.04 <0.008 1.47 <0.006 0.4

QRP-S20 SAS 280311082223901 8/11/2004 1345 28.0 185 3.7 5.9 54 0.04 <0.008 2.55 0.019 5

QRP-S20 SAS 280311082223901 11/15/2004 1700 24.9 234 2.3 5.9 94 <0.04 <0.008 6.11 0.008 3.7

QRP-S20 SAS 280311082223901 6/21/2005 1630 24.5 166 2 6.2 58 0.16 E0.006 0.67 0.012 4.6

HRIV-WA River 280244082220100 1/30/2004 1410 14.0 281 6.6 7.2 116

HRIV-RR River 280248082220200 6/22/2005 0.027 0.004 0.102 0.323 19.8

8/30/2005 253 7.38

TTP-4-140-NP UFA No data 10/27/2004 1600 26.4 577 0.8 7.3 180 <0.04 0.039 2.29 0.022 1.1

TTP-4-160-NP UFA No data 10/27/2004 1800 26.2 537 0.8 7.3 170 <0.04 0.011 3.6 0.024 0.8

TTP-4-160-P UFA No data 10/28/2004 1100 24.1 567 1 7.3 182 <0.04 0.035 1.84 0.014 0.9

TTP-4-140-P UFA No data 10/28/2004 1400 25.8 586 0.6 7.3 183 <0.04 0.02 1.72 0.016 0.9

TTP-4-125-P UFA No data 10/28/2004 1600 25.9 583 0.6 7.3 182 <0.04 0.013 1.69 0.022 0.9

TTP-4-entire-P UFA No data 10/21/2004 1500 26.0 606 0.5 7.3 170 <0.04 0.008 1.44 0.018 0.9
Ground-Water Chemistry 29

Floridan aquifer (UFA) in the study area.—Continued

centimeter; E, estimated concentration, below reported laboratory reporting level; ROE-DS, residue on evaporation, dissolved solids, mg/L; DTW, depth to water in

P00915 P00925 P00930 P00935 P00940 P00945 P00950 P00955 P39086 P70300 P99118 P72019

Calcite SI Dolomite 

SI Gypsum SI logPCO Calcium 2

Magnesium Sodium Potassium Chloride Sodium Fluoride Silica Alkalinity 

as CaCO3

ROE-DS Hydrogen 

sulfide DTW

86.6 1.67 5.56 E0.12 2.68 9.6 0.4 10.9 219 260 0.01 4.01 -0.30 -1.96 -2.48 -1.39

124 2.5 7.46 0.2 7.01 13.1 0.4 11.5 306 363 4.22 -0.22 -1.79 -2.27 -1.05

69.6 7.16 14.1 5.93 16.3 77.2 0.3 8.46 125 278 0.043 13.3 0.39 0.16 -1.69 -2.62

48.4 5.01 4.63 1.03 8.49 25.1 0.6 10.3 110 177 0 2.72 -0.21 -1.05 -2.25 -2.28

118 0.002 14.0

70.2 6.79 8.67 1.17 10.9 75.8 0.6 9.75 126 278 0 2.16 0.08 -0.50 -1.69 -2.32

69.1 7.32 8.95 1.09 16.3 94.2 0.5 8.14 98 275 0 3.03 -0.26 -1.14 -1.60 -2.23

66.3 7.46 8.44 1.35 15.1 92.7 0.5 11.1 82 262 1.09 1.61 -1.64 -3.88

25.6 3.46 16.5 1.12 11.3 23.5 E0.1 3.6 73 131 6.56 -1.28 -3.03 -2.50 -1.72

225 26.5 11.3 1.24 9.74 413 0.5 14.8 179 832 1.65 5.93 0.25 -0.09 -0.73 -1.91

170 19.7 7.87 0.93 8.72 296 0.3 15.2 176 1.02 6.25 0.26 -0.08 -0.92 -2.01

181 0.66 6.00

98.7 10.2 12.1 0.63 8.93 120 <0.2 12.6 159 346 0.006 6.00 -0.93 -2.50 -1.41 -1.03

89.8 8.86 6.62 0.42 6.2 191 0.2 9.16 58 364 0.005 4.83 -1.80 -4.25 -1.25 -1.06

78.2 10 5.97 0.34 4.74 171 0.3 8.79 58 343 0.005 5.27 -2.02 -4.57 -1.34 -0.84

68.7 8.76 6.91 0.42 6.64 138 <0.2 12.1 57 309 5.73 -1.97 -4.48 -1.46 -0.95

211 26.9 6.13 0.97 9.29 383 0.5 15.6 182 776 1.1 6.43 0.24 -0.07 -0.78 -1.90

185 0.66 6.25

117 9.28 8.04 0.97 13.2 151 0.3 13.9 136 395 0.15 6.55 0.07 -0.61 -1.27 -2.10

64.7 5.9 5.89 0.68 9.92 47.2 <0.2 8.72 129 234 0 6.49 -0.63 -1.94 -1.90 -1.61

46 3.78 10.5 3.24 2.03 26.6 <0.2 4.68 111 189 5.09 -0.99 -2.68 -2.24 -1.45

43.5 4.35 11.4 2.55 1.85 28.6 E0.1 4.88 115 177 0.002 5.81 -1.00 -2.62 -2.23 -1.44

54.9 5.41 12.1 2.98 6.75 47.6 <0.1 4.97 112 223 6.38 -0.93 -2.49 -1.95 -1.45

31.3 3.41 14.6 4.55 4.94 14.2 0.3 2.34 98 155 5.67 0.07 -0.41 -2.64 -2.68

39.8 4.11 6.18 1.08 8.36 6.7 0.3 6.05 104 144 0.007 8.40 -0.18 -0.98 -2.88 -2.39

2.9 2.19 2.77 1.08 5.7 7.3 <0.2 2.8 4 46 0 6.52 -5.52 -10.77 -3.80 -0.48

3.36 3.32 4.89 1.26 11.7 5.6 E0.1 3.83 4 48 0.004 7.74 -5 -9.63 -3.87 -1.22

2.16 1.79 7.15 0.9 4.96 11.6 <0.1 2.46 4 41 0 8.20 -4.94 -9.61 -3.72 -1.56

26.5 0.767 6.45 2.75 9.05 17.5 <0.2 2.83 44 136 2.45 -2.27 -5.69 -2.58 -1.14

39.5 1.05 3.72 2.93 3.21 11 E0.1 2.03 77 150 0.012 3.03 -1.92 -5.07 -2.65 -0.92

22.9 1.06 7.65 2.5 15.6 5 E0.1 3.19 48 95 0.001 3.46 -2.04 -5.05 -3.16 -1.43

95

-0.7 -2.10 -2.69 -1.92

39.9 3.34 8.9 0.08 14.8 10.2 0.215 8.7 186

97.2 7.89 12.2 1.19 28.1 96.4 0.2 12.8 148 344 0 17.5 0.07 -0.60 -1.50 -2.05

90.1 7.71 12.9 1.18 31 78.7 0.1 12.8 140 333 0.001 17.5 0.02 -0.67 -1.60 -2.08

102 8.36 11.8 1.19 27.9 103 0.2 12.8 150 359 0.008 17.5 0.06 -0.64 -1.46 -2.06

101 8.23 11.6 1.15 26.9 106 0.2 12.8 150 361 0 17.5 0.07 -0.59 -1.45 -2.05

99.8 8.72 11.6 1.17 26.9 107 0.3 13.2 150 355 0.001 17.5 0.07 -0.56 -1.45 -2.05

98.1 8.41 11.2 1.04 25 116 0.3 13.3 139 380 0.03 0.03 -0.65 -1.42 -2.08
30 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

17.8 mg/L (table 5) with a median concentration of 9.3 mg/L. 

The range of dissolved organic carbon concentrations in water 

from the intermediate confining unit and Upper Floridan aquifer was substantially smaller than that from the surficial aquifer system and retention ponds, with median concentrations 

of 1.8 and 2.0, respectively. Dissolved solids concentrations 

in water were less than 500 mg/L from the surficial aquifer 

system, intermediate confining unit, and stormwater retention ponds. Dissolved solids concentrations were considerably 

higher in most water samples from the Upper Floridan aquifer 

with five wells that had concentrations in water ranging from 

580 to 830 mg/L.

Redox Conditions

Redox conditions are important in controlling many 

chemical processes in ground water, such as the speciation 

of naturally occurring elements (for example, sulfur, arsenic, 

and iron) and the transformation/biodegradation of anthropogenic compounds (for example, nitrate, trichloromethane, and 

trichloroethene). A scheme was developed for the regionalscale TANC studies using various chemical indicator species 

to classify redox conditions in ground water (S.S. Paschke, 

U.S. Geological Survey, written commun., 2007). This redox 

classification scheme is presented in appendix A4. A redox 

category was assigned to each ground-water sample; however, 

the present study has modified this scheme based on data 

that are available for hydrogen sulfide and methane. In some 

instances, conflicting or overlapping indicators of redox conditions occur and are related to mixtures of water with different 

redox indicators. However, the detection of hydrogen sulfide 

in water from most wells in the Upper Floridan aquifer 

(table 5) allowed the classification of these waters as sulfate 

reducing.

Distinct differences in redox conditions exist among 

waters from the surficial aquifer system, intermediate confining unit, and Upper Floridan aquifer. Water samples from 9 of 

11 monitoring wells screened in the surficial aquifer system 

consistently had dissolved oxygen concentrations greater than 

or equal to 1 mg/L (fig. 8). The depth to the water table at 

those wells generally was greater than or equal to 4.5 m, and 

the top of the screened interval generally was less than 1.5 m 

below the water table. Water samples from wells RP-S20 

and QRP-S20 are indicative of mixed redox conditions 

because dissolved oxygen concentrations were greater than 

or equal to 1 mg/L, but iron concentrations were greater than 

300 μg/L (micrograms per liter). Water from wells with mixed 

redox conditions or anoxic conditions likely are influenced by 

surface features like sinkholes, retention ponds, or the Hillsborough River. Water from LRP-S25 and THC-S46 had dissolved oxygen concentrations less than or equal to 0.5 mg/L. 

The depth to the water table at those wells was less than or 

equal to 3 m and greater than or equal to 7.6 m, respectively, 

but the screen tops at both of those wells were farther below 

the water table (about 1.5-2.5 m) than many of the other wells. 

Water from well THC-S46 had low dissolved oxygen concentrations (less than 0.5 mg/L) and elevated iron and manganese 

concentrations indicating anoxic conditions (iron-manganese 

reducing conditions). 

Water samples from two of the four wells in the 

intermediate confining unit (62SRP-H55 and LP-H40) had 

dissolved oxygen concentrations greater than 2 mg/L 

(dissolved oxygen-reducing conditions). These two wells have 

screen tops that are generally less than or equal to 4 m below 

the water table. The other two wells (113RC-H50 and 

LRP-H105) had concentrations of dissolved oxygen less 

than 0.5 mg/L. The suboxic water samples from these two 

wells also had nitrate-N concentrations of about 0.5 mg/L 

and methane concentrations greater than 0.1 mg/L, indicating 

nitrate-iron reducing conditions. Water from 113RC-H50 had 

manganese concentrations less than 50 μg/L and iron concentrations greater than 100 μg/L. Wells 113RC-H50 and 

LRP-H105 had screen tops that were generally greater than 

or equal to 6 m below the water table. These locally variable redox conditions are related to differences in sediment 

mineralogy and chemistry, depth below the water table, and 

other factors such as residence time of water in the intermediate confining unit. 

All but two monitoring wells in the Upper Floridan 

aquifer (62SRP-F160 and MAS-R-F160) had dissolved oxygen concentrations less than or equal to 0.5 mg/L and only 

one well (MAS-R-F64) had a dissolved oxygen concentration greater than 1 mg/L. Most of these monitoring wells had 

detectable (greater than 0.01 mg/L) sulfide concentrations 

(fig. 8); water samples from only a few wells had manganese 

concentrations greater than 50 μg/L or iron concentrations less 

than 100 μg/L (sulfate-reducing conditions). Two of the wells 

0

20

40

60

80

100

012345678

CONCENTRATION, IN MILLIGRAMS PER LITER

WELL DEPTH, IN METERS BELOW LAND SURFACE

Surficial aquifer

system

Intermediate

confining unit

Upper Floridan

aquifer

Hydrogen

sulfide

Dissolved

oxygen

Figure 8. Dissolved oxygen and hydrogen sulfide concentrations 

with well depth from the surficial aquifer system, intermediate 

confining unit, and Upper Floridan aquifer in the Temple Terrace, 

Florida, study area.
Ground-Water Chemistry 31

had methane concentrations greater than 0.1 mg/L. Concentrations of hydrogen gas ranged from 0.4 to 2.1 nM (nanomolar), 

which are characteristic of iron-reducing or sulfate-reducing 

conditions. Subtle differences in redox processes related to 

dissolved oxygen/nitrate/iron/sulfate reduction and methanogenesis could not be mapped spatially, but vary with depth and 

are related to organic carbon content, ground-water residence 

time, and hydraulic connections between the surficial aquifer 

system and Upper Floridan aquifer. 

Stable Isotopes of Water

Variations in the delta hydrogen-2 (δ2H) and delta 

oxygen-18 (δ18O) composition of ground water, rainfall, 

retention pond water, and river water were used to examine 

sources of water, flow patterns, and mixing processes in the 

ground-water system (table 6). The isotopic composition of 

ground- and surface-water samples are plotted relative to the 

global meteoric water line (Craig, 1961) and a local meteoric 

water line determined from a previous study (Sacks, 2002) 

(fig. 9). Differences in the slope and intercept of these two 

meteoric water lines are related to several factors including 

storm-track origin, rainfall amount and intensity, atmospheric 

temperature, and the number of evaporation and condensation 

cycles. The isotopic composition of water from wells in the 

surficial aquifer system, and from a shallow well in the Upper 

Floridan aquifer (RP-F77) plot between these two lines, indicating that these waters have not been affected by evaporation. 

In contrast, water from other shallow monitoring wells in the 

Upper Floridan aquifer and two retention ponds (MAS-POND 

and LRP-POND) are slightly enriched relative to the global 

meteoric water line. Further enrichment of the stable isotopic 

composition is noted for the four deep monitoring wells in the 

Upper Floridan aquifer and Hillsborough River. The higher 

δ2H and δ18O values for water from the Hillsborough River 

water indicate that evaporative enrichment of these isotopes 

has occurred. The isotopic composition of water from the 

public-supply well is consistent with possible mixing of water 

from the surficial aquifer system and Upper Floridan aquifer 

as the δ18O and δ2H values plot between those for water from 

both hydrogeologic units (fig. 9).

The enriched isotopic signature for the deep wells in the 

Upper Floridan aquifer (GARC-F200, THC-F197, 113RCF190, and WP-F299) indicates that recharge water has undergone evaporation prior to recharging the aquifer. One possible 

source for isotopically enriched waters is recharge water that 

occurs in wetland areas located several kilometers upgradient 

from the study area. The presence of higher amounts of 

dissolved organic carbon in these waters also indicates a 

0

-5

-10

-15

-20

-25-5 -4 -3 -2 -1 0

DELTA OXYGEN-18, IN PER MIL, VIENNA STANDARD MEAN OCEAN WATER

TTP-4

62SRP

RIVER

THC-F197

GARC-F200

113RC-F190

WP-F299

MAS

GARCF75

RP-F103 LRP

RP-F77

THC-F75

WP-F150 113RC-H50

TTP-4

RP-S20

WP-S64

GARC-S23

113RC-S35

THC-S45

DELTA HYDROGEN-2, IN PER MIL,

VIENNA STANDARD MEAN OCEAN 

WATER

Local Meteoric Water Line (Sacks, 2002)

Global Meteoric Water Line (Craig, 1961)

Volume weighted mean rainfall values

(Jan, 1999-Jan, 2000; Sacks, 2002)

Surficial aquifer system

Intermediate confining unit

Upper Floridan aquifer

Hillsborough River

Ponds

Figure 9. Oxygen and hydrogen isotopes in ground water and surface water from the surficial aquifer 

system, intermediate confining unit, and Upper Floridan aquifer in the Temple Terrace, Florida, study 

area.
32 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water Site name Aquifer or hydrogeologic unit Site identifier Sample date Sample time δ13C δ2

H δ18O δ15N of nitrate δ18O of nitrate Radon-222 δ34S

BBP-S45 SAS 280228082231501 12/9/2004 1300 4.7 2.8THC-F197 UFA 280241082224401 1/15/2004 1400 -9.6 -2.3 8.2 18.9 140 24.0THC-F75 UFA 280241082224402 1/12/2004 1500 -17.6 -3.2 11.7 15.6 840 25.2THC-F75 UFA 280241082224402 1/28/2004 1300 9.3 22.6THC-S46 SAS 280241082224403 12/18/2003 1300 -15.0 -3.3 6.4 5.9 900 7.762SRP-F160 UFA 280241082230701 11/2/2004 1200 9.4 9.9 30 11.162SRP-H55 ICU 280241082230702 11/3/2004 1700 5.5 4.6 1,150 8.562SRP-POND POND 280242082230800 6/21/2005 1220 -12.8 -3.0 -1.7 6.2 16.6 11.6MAS-R-F160 UFA 280242082232401 11/3/2004 1200 9.2 8.1 460 7.6MAS-R-F64 UFA 280242082232403 2/16/2005 1300 7.2 6.0 3,170 5.8MAS-POND POND 280242082232900 6/21/2005 1100 -6.5 -18.3 -2.8TTP-4 UFA 280244082232001 1/28/2004 1600 -12.6 -15.5 -3.1 10.0 9.6 780 16.8TTP-4 UFA 280244082232001 10/21/2004 1500 -12.3 -15.4 -3.3 6.4 6.6 15.4WP-F299 UFA 280247082231901 1/22/2004 1600 -10.6 -13.2 -2.2 17.1 16.0 980 24.0WP-F150 UFA 280247082231902 1/28/2004 1000? 13.1 23.5WP-F150 UFA 280247082231902 1/28/2004 1300 -16.4 -3.3 13.1 23.5 1,080 15.3

Table 6. Data for delta oxygen-18 (d18O) and delta hydrogen-2 (d2H), delta carbon-13 (d13C) in dissolved inorganic carbon, nitrogen and oxygen isotopes of nitrate (d15N of N03 andd18O of N03), delta sulfur-34 of sulfate (d34S), and radon-222 in water samples from the surficial aquifer system (SAS), intermediate confining unit (ICU), Upper Floridan aquifer (UFA), ponds, and river.[Delta (δ) values are reported as per mil relative to standards listed in report]
Ground-Water Chemistry 33

Site 

name

Aquifer or

hydrogeologic 

unit

Site

identifier

Sample

date

Sample

time δ13C δ2H δ18O δ15N of nitrate δ18O of nitrate Radon-222 δ34S

WP-S64 SAS 280247082231903 1/14/2004 1500 -17.1 -3.3 4.4 3.5 2,660 16.7RP-F103 UFA 280249082220701 12/2/2003 1500 -13.2 -2.8 5.9 14.7 24.1RP-F103 UFA 280249082220701 1/14/2004 1135 660RP-F77 UFA 280249082220702 12/3/2003 1300 -13.8 -3.2 4.2 11.1 1,390 22.7RP-S20 SAS 280249082220703 12/4/2003 1400 -15.4 -3.4 10.0 -0.4 400 5.7LRP-F160 UFA 280250082233001 11/4/2004 1300 4.7 420 26.2LRP-H105 ICU 280250082233002 12/7/2004 1600 8.1 6.2 130 18.4LRP-POND POND 280250082233200 6/21/2005 915 -14.1 -14.3 -2.8 7.4 6.9 17.8GARC-F200 UFA 280253082223801 12/16/2003 1300 -10.3 -2.3 21.0 17.9 500 23.9GARC-F75 UFA 280253082223802 12/15/2003 1400 -11.5 -2.6 11.0 24.0GARC-S23 SAS 280253082223803 12/17/2003 1200 -18.9 -3.6 2.9 2.3 3,130 16.4113RC-F190 UFA 280301082222701 12/8/2003 1300 -12.0 -2.2 5.9 7.1 510 24.6113RC-H50 ICU 280301082222702 12/9/2003 1300 -16.7 -3.1 9.2 7.6 3,330 21.7113RC-S35 SAS 280301082222703 12/11/2003 1300 -19.6 -3.9 2.8 4.4 2,440 16.8

Table 6. Data for delta oxygen-18 (d18O) and delta hydrogen-2 (d2H), delta carbon-13 (d13C) in dissolved inorganic carbon, nitrogen and oxygen isotopes of nitrate (d15N of N03 andd18O of N03), delta sulfur-34 of sulfate (d34S), and radon-222 in water samples from the surficial aquifer system (SAS), intermediate confining unit (ICU), Upper Floridan aquifer (UFA), ponds, and river.—Continued[Delta (δ) values are reported as per mil relative to standards listed in report]
34 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water Site name Aquifer or hydrogeologic unit Site identifier Sample date Sample time δ13C δ2

H δ18O δ15N of nitrate δ18O of nitrate Radon-222 δ34S

LP-H40 ICU 280303082230901 12/8/2004 1500 1.5 4.0 3,050 7.9LP-H40 ICU 280303082230901 12/8/2004 1510 1.8 4.2LP-S30 SAS 280303082230902 11/1/2004 1600 1.7 2.4QRP-S20 SAS 280311082223901 11/15/2004 1700 1.7 1.5HRIV-WA RIVER 280244082220100 1/30/2004 1410 -10.3 -1.8HRIV-RR RIVER 280248082220200 6/22/2005 -14.4 -11.7 -2.3 5.7 4.3TTP-4-140-NP UFA 280244082232001 10/27/2004 1600 -15.7 -3.3 8.0 8.2 970 12.9TTP-4-160-NP UFA 280244082232001 10/27/2004 1800 -15.9 -3.4 6.0 7.0 1,210 11.0TTP-4-160-P UFA 280244082232001 10/28/2004 1100 -16.0 -3.2 8.9 8.9 1,060 13.5TTP-4-140-P UFA 280244082232001 10/28/2004 1400 -15.4 -3.3 7.8 8.2 850 13.7TTP-4-125-P UFA 280244082232001 10/28/2004 1600 -15.8 -3.3 7.7 8.0 990 13.9TTP-4-entire-P UFA 280244082232001 10/21/2004 1500 -12.3 -15.4 -3.3 6.4 6.6 15.4

Table 6. Data for delta oxygen-18 (d18O) and delta hydrogen-2 (d2H), delta carbon-13 (d13C) in dissolved inorganic carbon, nitrogen and oxygen isotopes of nitrate (d15N of N03 andd18O of N03), delta sulfur-34 of sulfate (d34S), and radon-222 in water samples from the surficial aquifer system (SAS), intermediate confining unit (ICU), Upper Floridan aquifer (UFA), ponds, and river.—Continued[Delta (δ) values are reported as per mil relative to standards listed in report]
Ground-Water Age and Age Distributions 35

possible source of recharge from wetland areas to the north. 

Other sources for the high sulfate waters include upwelling 

of waters from deep flow paths in the Upper Floridan aquifer 

and/or recharge during different climatic conditions (Sacks, 

1996).

Ground-Water Age and 

Age Distributions

Two age-dating methods were used to determine apparent 

ages of ground water and age distributions by incorporating 

various lumped parameter models. These two methods include 

measurements of the concentrations of tritium (3H) and its 

radioactive decay product helium-3 (3He) and measurements 

of the concentrations of sulfur hexafluoride (SF6). Comparison 

of the two independent ages from these methods can be used 

as a verification for sampling and analytical methods and to 

evaluate mixing and other processes in the flow system. 

Apparent Sulfur Hexafluoride and Tritium/

Helium-3 Ground-Water Ages

The SF6 and 3H/3He apparent ages of ground water, 

assuming a piston-flow model, generally were concordant 

and ranged from young water (less than 1 year) to water more 

than 60 years old (fig. 10). Apparent ages for water from the 

surficial aquifer system were much younger than those from 

the intermediate confining unit and Upper Floridan aquifer 

(tables 7 and 8; fig. 10). The 3H/3He and SF6 apparent ages for 

water from the public-supply well ranged from less than 1 year 

to 8 years, respectively (tables 7 and 8; fig. 10). Also of note 

is the relatively young apparent age of 12 years for water from 

WP-F150, a 46-m-deep monitoring well in the Upper Floridan 

aquifer near the public-supply well that likely is withdrawing 

water from a highly transmissive zone similar to the 43- to 

49-m zone identified using geophysical measurements of the 

borehole for the public-supply well.

Differences in SF6 and 3H/3He apparent ages for water 

from the surficial aquifer system are related to the thickness 

of the unsaturated zone, depth below the water table, and the 

presence of clays within the surficial material. For example, 

water from LP-S30 had an apparent SF6 age of 13 to 15 years, 

whereas water from the slightly deeper well, 113RC-S35, had 

an apparent age of 7 years. The unsaturated zone thickness 

was greater at LP-S30 (8.5 m) than that at 113RC-S35 

(6.7 m), and clay material was noted throughout a larger 

interval for LP-S30 than for 113RC-S35, which may account 

for a longer time of travel to LP-S30 than 113RC-S35. Even 

though the unsaturated zone thickness for WP-S64 was 16 m, 

the SF6 apparent age for water from this well was only 3 to 

4 years. The unsaturated zone at WP-S64 contains a greater 

thickness of sand/silt material than at LP-S30 and 113RC-S35, 

and the presumed higher permeability may account for the 

younger water at WP-S64 than at LP-S30. 

The 3H/3He apparent age calculations are sensitive to the 

amount of terrigenic helium-4 (4He) from decay of uraniumseries radionuclides and excess air. Terrigenic 4

He (relative 

to the total 4He) generally was less than 5 percent, but water 

samples from two sites, 113RC-F190 and GARC-F200, had 

values of 10 to 12 percent (table 8). Other studies reported a 

highly variable distribution of uranium in sediments that compose the Upper Floridan aquifer (Kaufman, 1968). Uranium 

concentrations in water samples were highly variable, but 

median uranium concentrations were higher for water samples 

from the Upper Floridan aquifer than from the surficial aquifer 

system and intermediate confining unit (see below for more 

detailed information on uranium concentrations). With large 

fractions of terrigenic helium (greater than 10 percent), the 

3

He/4He ratio of the terrigenic helium (Rterr) needs to be known 

accurately. Non-tritiogenic 3He resulting from terrigenic 

sources are adjusted using an Rterr of 2E-08 (Schlosser and 

others, 1988). If this ratio is allowed to vary over two orders 

of magnitude (somewhat unlikely, but useful for illustrating 

estimates of age uncertainty) for an Rterr of 2E–07, apparent 

ages would be younger by 8 years for 113RC-F190 and 

6 years for GARC-F200. Using an Rterr of 2E–09, there would 

be no appreciable differences in apparent ages. 

The apparent lack of agreement between SF6 and 3H/3He 

apparent ages for the presumed older waters (greater than 

60 years based on low tracer concentrations) from the Upper 

Floridan aquifer could result from complex mixtures of water 

from deep zones within the aquifer and the age dating limits of 

the SF6 method. Another possibility for the minor excess SF6 

is that there is some natural background or low-level anthropogenic SF6 contamination in these water samples (GARCF200, WP-F299, and THC-F297) from deep parts of the Upper 

Floridan aquifer. To assess and quantify possible ground-water 

mixing scenarios, measured concentration data for SF6 were 

Surficial aquifer system

Intermediate confining unit

Upper Floridan aquifer

TTP-4

1:1 LINE

Apparent age greater than

or equal to plotted value

80

60

40

20

0

0 10 20 30 40

SULFUR HEXAFLUORIDE APPARENT AGE, IN YEARS

TRITIUM/HELIUM-3 APPARENT AGE,

IN YEARS

WP-F299

GARC-F200

THC-F297

WP-F150

Figure 10. Comparison of apparent ages based on the piston-flow 

assumption and measured concentrations of sulfur hexafluoride, 

tritium, and helium-3 in water samples from the surficial aquifer 

system, intermediate confining unit, and Upper Floridan aquifer in 

the Temple Terrace, Florida, study area.
36 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water Site name Aquifer Sampling date Time Excess air, mL Recharge temperature, °C SF6 concentration, femtomol/kg SF6 partial pressure, pptv PFM SF6 recharge year PFM SF6 age, years RP-S20 SAS 12/04/03 1400 0.4 22.8 1.247 4.788 2000.5 3 RP-S20 SAS 12/04/03 1400 0.4 21.8 1.285 4.781 2000.5 3 113RC-S35 SAS 12/11/03 1300 1.3 20.7 1.258 3.949 1997.0 7 113RC-S35 SAS 12/11/03 1300 1.3 20.7 1.299 4.077 1997.0 7 GARC-S23 SAS 12/17/03 1200 0.5 20.6 1.523 5.366 2002.5 1 GARC-S23 SAS 12/17/03 1200 0.5 20.6 1.470 5.178 2002.0 2 THC-S45 SAS 12/18/03 1300 2.3 21.0 1.734 4.809 2000.5 3 THC-S45 SAS 12/18/03 1300 2.3 21.0 1.702 4.720 2000.0 4 WP-S64 SAS 01/14/04 1500 0.2 22.0 1.262 4.888 2000.5 4 WP-S64 SAS 01/14/04 1500 0.2 22.0 1.294 5.013 2001.5 3 LP-S30 SAS 08/30/05 1700 2.0 23.0 0.832 2.518 1990.5 15 LP-S30 SAS 08/30/05 1700 2.0 23.0 1.015 3.074 1993.0 13 LP-H40 ICU 08/30/05 1400 2.0 23.0 0.881 2.669 1991.5 14 LP-H40 ICU 08/30/05 1400 2.0 23.0 0.933 2.826 1992.0 14 113RC-H50 ICU 12/09/03 1300 2.3 20.0 0.895 2.422 1990.0 14 113RC-H50 ICU 12/09/03 1300 2.3 20.0 0.906 2.452 1990.5 13 GARC-F75 UFA 12/15/03 1400 2.4 20.8 0.226 0.616 1977.5 26 GARC-F75 UFA 12/15/03 1400 2.4 20.8 0.214 0.585 1977.0 27 THC-F75 UFA 01/12/04 1500 1.8 21.0 0.246 0.727 1979.0 25 THC-F75 UFA 01/12/04 1500 1.9 21.0 0.246 0.717 1978.5 26 RP-F77 UFA 12/03/03 1300 2.6 19.1 0.356 0.908 1980.5 23 RP-F77 UFA 12/03/03 1300 2.6 19.1 0.361 0.920 1980.5 23 RP-F103 UFA 12/02/03 1500 2.2 21.0 0.252 0.707 1978.5 25

RP-F103 UFA 12/02/03 1500 2.2 21.0 0.252 0.708 1978.5 25WP-F150 UFA 01/28/04 1300 1.4 23.2 0.878 2.907 1992.5 12WP-F150 UFA 01/28/04 1300 1.4 23.2 0.821 2.719 1991.5 13113RC-F190 UFA 12/08/03 1300 1.8 19.2 0.100 0.282 1972.0 32113RC-F190 UFA 12/08/03 1300 1.8 19.2 0.117 0.329 1973.0 31

Table 7. Summary of sulfur hexafluoride (SF6) results for water samples from wells in surficial aquifer system (SAS), intermediate confining unit (ICU), and Upper Floridan aquifer (UFA).[mL, milliliters; °C, degrees Celsius; femtomol/kg, 10-15 moles per kilogram; pptv, parts per trillion by volume; calculated for recharge elevation of 15 meters; PFM, piston-flow assumption]
Ground-Water Age and Age Distributions 37

Site

name Aquifer Sampling date Time Excess air, mL Recharge temperature, °C SF6 concentration, femtomol/kg SF6 partial pressure, pptv PFM SF6 recharge year PFM SF6 age, years

THC-F197 UFA 01/15/04 1400 1.9 19.2 0.070 0.195 1968.0 36THC-F197 UFA 01/15/04 1400 1.9 19.2 0.098 0.273 1971.5 33GARC-F200 UFA 12/16/03 1300 1.8 19.9 0.718 2.063 1988.5 15GARC-F200 UFA 12/16/03 1300 1.8 19.9 0.133 0.383 1974.0 30WP-F299 UFA 01/22/04 1600 2.1 18.9 0.124 0.335 1973.0 31WP-F299 UFA 01/22/04 1600 2.1 18.9 0.135 0.364 1974.0 30WP-F299 UFA 08/29/05 1500 2.0 23.0 0.183 0.555 1977.0 29WP-F299 UFA 08/29/05 1500 2.0 23.0 0.157 0.475 1975.5 30TTP-4 125-PUMPING UFA 10/28/04 1600 2.0 23.0 1.299 3.932 1996.5 8TTP-4 125-PUMPING UFA 10/28/04 1600 2.0 23.0 1.297 3.926 1996.5 8TTP-4 140-NONPUMPING UFA 10/27/04 1600 2.0 23.0 1.357 4.108 1997.5 7TTP-4 140-NONPUMPING UFA 10/27/04 1600 2.0 23.0 1.318 3.990 1997.0 8TTP-4 140-PUMPING UFA 10/28/04 1400 2.0 23.0 1.258 3.810 1996.0 9TTP-4 140-PUMPING UFA 10/28/04 1400 2.0 23.0 1.112 3.366 1994.5 10TTP-4 160-NONPUMPING UFA 10/27/04 1800 2.0 23.0 1.424 4.311 1998.0 7TTP-4 160-NONPUMPING UFA 10/27/04 1800 2.0 23.0 1.422 4.306 1998.0 7TTP-4 160-PUMPING UFA 10/28/04 1100 2.0 23.0 1.504 4.554 1999.5 5TTP-4 160-PUMPING UFA 10/28/04 1100 2.0 23.0 1.308 3.961 1997.0 8TTP-4 UFA 08/31/05 1000 2.0 23.0 1.268 3.839 1996.5 9TTP-4 UFA 08/31/05 1000 2.0 23.0 1.247 3.775 1996.0 10

Table 7. Summary of sulfur hexafluoride (SF6) results for water samples from wells in surficial aquifer system (SAS), intermediate confining unit (ICU), and Upper Floridan aquifer (UFA).—Continued[mL, milliliters; °C, degrees Celsius; femtomol/kg, 10-15 moles per kilogram; pptv, parts per trillion by volume; calculated for recharge elevation of 15 meters; PFM, piston-flow assumption]
38 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water Site name Aquifer Sampling date Tritium, tritium units Tritium error, 1 sigma Delta helium-3 measured, percent Helium-4, μcc STP/kg Neon, μcc STP/kg Helium-4 terrigenic, percent Tritium/ helium-3 age, years Tritium/ helium-3 age error, years Analytical laboratory RP-F103 UFA 12/2/2003 0.753 0.05 2.94 57.48 218.00 5.1 29 1.5 LDEO RP-F77 UFA 12/3/2003 0.74 0.07 3.07 58.06 227.38 1.4 22 2.0 LDEO RP-S20 SAS 12/4/2003 2.216 0.06 -1.1 49.5 204.74 0.0 0 2.2 LDEO 113RC-F190 UFA 12/8/2003 0.17 0.05 -8.34 61.81 221.05 10.4 35 5.5 LDEO 113RC-H50 ICU 12/9/2003 1.329 0.05 2.31 62.55 248.64 0.0 8 2.1 LDEO 113RC-S35 SAS 12/11/2003 2.145 0.06 4.85 52.03 217.46 0.0 4 1.5 LDEO GARC-F75 UFA 12/15/2003 0.428 0.04 -0.38 58.8 220.69 5.9 33 4.0 LDEO GARC-F200 UFA 12/16/2003 0.04 0.04 -7.98 62.46 220.18 11.7 67 18.0 LDEO GARC-S23 SAS 12/17/2003 2.125 0.06 -0.51 169.17 606.62 1.6 9 7.6 LDEO THC-S46 SAS 12/18/2003 2.483 0.06 -1.18 60.55 245.60 0.0 0 7.5 LDEO THC-S75 SAS 1/12/2004 1.108 0.07 12.33 54.06 214.04 1.2 29 1.9 LDEO WP-S64 SAS 1/14/2004 2.591 0.06 -1.11 44.64 179.10 2.9 5 2.3 LDEO THC-F197 UFA 1/15/2004 0.09 0.04 0.93 57.74 215.80 6.7 62 9.1 LDEO WP-F150 UFA 1/28/2004 2.409 0.06 7.81 50.69 206.08 0.0 12 1.9 LDEO TTP-4 UFA 1/28/2004 2.211 0.07 NA NA NA NA NA NA LDEO TTP-4-140P UFA 10/28/2004 1.97 0.02 -2.60 57.2 229.30 1.57 0 2 USGS TTP-4-140NP UFA 10/27/2004 2.35 0.02 -2.40 56.9 229.90 0.32 0 2 USGS TTP-4-125P UFA 1/28/2004 2.13 0.01 -2.40 55.4 227.20 -0.42 0 2 USGS TTP-4-160P UFA 1/28/2004 1.99 0.02 -2.50 56.3 227.80 -0.94 0 2 USGS TTP-4 UFA 10/21/2004 2.1 0.05 -2.60 54.1 214.00 2.47 0 2 USGS TTP-4-160NP UFA 10/27/2004 1.86 0.04 -6.00 49.3 226.70 -11.80 0 2 USGS

LP-H40 ICU 8/30/2005 2.03 0.03 -0.30 54.6 229.50 -0.09 3 2 USGSLP-S30 SAS 8/30/2005 2.58 0.01 -2.10 43.8 204.30 -0.34 0 2 USGSWP-F299 UFA 8/29/2005 <0.05 0.01 -10.10 59 267.20 0.01 >45 NA USGSTTP-4 UFA 8/31/2005 2.17 0.03 -5.10 59.7 241.20 0.00 0 2 USGS

Table 8. Summary of tritium/helium-3 (3H/3He) age data using piston-flow model for water samples from the surficial aquifer system (SAS), intermediate confining unit (ICU), and Upper Floridan aquifer (UFA). [Estimated recharge temperature is 21 degrees Celsius. Recharge elevation is approximately 20 meters NAVD 88 (North American Vertical Datum of 1988); TU, tritium units; μcc STP/kg, microcentimeters cubed of gas at standard temperature and pressure per kilogram of water; 1 sigma, one standard deviation for analytical method; NA, laboratory analytical problem; LDEO, Lamont Doherty Earth Observatory, Palisades, New York; USGS, U.S. Geological Survey Noble Gas Laboratory, Denver, Colorado; NA, not applicable; >, greater than]
Ground-Water Age and Age Distributions 39

compared to theoretical age-distribution curves generated 

using lumped parameter models. 

Assessing Ground-Water Age Distributions 

using Lumped Parameter Models

Analytical procedures are capable of determining 

extremely low concentrations of the tracers SF6, 3H, and 3He in 

ground water; however, the subsequent interpretation of age or 

mean residence time of ground water in complex karstic aquifer systems still is fraught with a high degree of uncertainty. 

In many previous studies where SF6 and 3H/3Hetrit (tritium/tritiogenic helium-3) have been used to date ground water, flow 

systems were relatively well characterized and water samples 

typically were collected from discrete depth intervals. Extending tracer age-dating techniques to wells with large open intervals in complex karstic systems requires an analysis of several 

possible ground-water flow scenarios. 

Lumped parameter models are used in this study to estimate the mean residence time and age distribution of ground 

water in the surficial aquifer system, intermediate confining 

unit, and Upper Floridan aquifer systems. These models treat 

an aquifer system as a homogeneous compartment in which 

tracer input concentrations are converted to tracer output 

concentrations according to the system response function 

used (Maloszewski and Zuber, 1982; Zuber, 1986). By fitting 

measured tracer concentrations to modeled output curves, the 

response function accounts for the distribution of ages at a 

sampled site (Zuber and others, 2001). No detailed information is needed regarding the flow system, such as boundary 

conditions, porosity, and hydraulic conductivity, all of which 

are necessary for numerical models based on Darcy’s law. 

Lumped parameter models assume a steady-state flow system 

and assume that the selected tracers behave like a water molecule. Although this assumption typically is valid for tritium, 

which is part of the water molecule, the gas tracer SF6 may or 

may not be transported in exactly the same way as the water. 

The mean residence time of ground water at a given well 

represents the time elapsed since recharge and isolation of the 

tracer from the modern atmosphere. Flow system characteristics are represented by two end-member lumped-parameter 

models: piston flow and exponential flow. The piston-flow 

model assumes that after a tracer is isolated from the atmosphere at the time of ground-water recharge, it becomes 

incorporated in a parcel of water that moves from the recharge 

area with the mean velocity of ground water. All flow lines are 

assumed to have similar velocities, and hydrodynamic dispersion and molecular diffusion of the tracer are assumed to be 

negligible. 

The exponential flow model represents an aquifer 

system in which the mean residence time of ground water is 

exponentially distributed. Ground-water flow is composed 

of recharge from all past years. Ground-water contributions 

to well discharge, however, decrease exponentially from the 

most recent recharge to that which has occurred in the distant 

past. Although the exponential model may provide a reasonable approximation of homogeneous unconsolidated aquifers, 

it may not be as useful in karst systems where ground water 

moves slowly through small openings in the carbonate matrix, 

fractures or fissures, and much more rapidly through large 

conduits or caverns. Dye tracer studies have indicated that 

flow through conduits can be fast, on the order of 3,000 to 

23,000 m/d (meter per day) (Wilson and Skiles, 1988). 

Other lumped parameter models that account for mixing 

include the combined exponential and piston-flow model. The 

exponential flow model and the combined flow model have 

one fitted parameter in common (total mean transit time or 

mean-tracer age). The combined flow model has an additional 

fitting parameter (x), the ratio of τPFM/τEM. This fitting 

parameter (x) is slightly different than the parameter (n), 

which represents the total volume to the volume with the exponential distribution of ages (Maloszewski and Zuber, 1996). 

In addition to the above models, simple binary mixing 

models and combined binary models and exponential models 

are used to evaluate mixing scenarios that involve relatively 

young water (recharged within the past 7 years) with older 

water (decades), presumably from deeper parts of the Upper 

Floridan aquifer. In principle, both end members of a binary 

mixture can be of any age, but the calculation is greatly simplified if it is assumed that one or both end members is either 

“young” (assumed to represent recharge that occurred after 

1995) or “old” (recharged before 1950 with undetectable SF6 

concentrations). Ground-water ages were determined using 

combinations of tracers including SF6 and 3H, and SF6 and 3

H/3H(0). The 3H(0) tracer represents the initial tritium concentration at the time of recharge and is the sum of the measured concentrations of 3

H and 3Hetrit. The ratio of 3H/3H(0) 

is a surrogate for the relative age of water, in that values near 

zero represent old waters, and conversely, values near 1.0 represent young waters (Böhlke, 2002). The computer program 

TRACERMODEL1 (Böhlke, 2006) was used in this study to 

calculate theoretical curves for the different lumped parameter 

models using atmospheric input data for the various tracers. 

All samples from the surficial aquifer system and the 

public-supply well TTP-4 have SF6 concentrations greater 

than 3.0 pptv (parts per trillion by volume) and 3H concentrations greater than 2 tritium units as shown in figure 11. These 

sample concentrations plot along the modeled curve for piston 

flow for young waters, and/or a binary mixing curve dominated by young water (less than 6 years in age). In contrast, 

water samples from three deep wells in the Upper Floridan 

aquifer (THC-F197, GARC-F200, and 113RC-F190) have low 

concentrations of 3H and SF6. These samples plot on the lower 

left-hand side of the lumped-parameter modeled curves 

(fig. 11) and likely represent waters that are considerably older 

than 60 years. These waters also contain high concentrations 

of sulfate, indicating a deep flow path through the aquifer. 

These findings are consistent with a study by Swancar and 

Hutchinson (1995) that found higher 3H concentrations in 

isotopically light waters compared to isotopically heavier 
40 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

8

6

4

2

0

0

SULFUR HEXAFLUORIDE, IN PARTS PER TRILLION BY VOLUME

TRITIUM, IN TRITIUM UNITS

Piston-flow model

Exponential mixing model

Binary-exponential model (young water 6-years in age)

Exponential-piston model

GARC-S23

WP-S64

THCS35

RP-S20

TTP-4

(160A)

TTP-4

(160P)

TTP-4

TTP-4 (125P)

(140A)

TTP-4

(140P)

113RCS35

TTP-4

WP-F150

113RC-H50

RP-F77

THC-F75

RPF103

GARCF75

THCF197

113RCF190 GARC-F200

1 2 3 4 5 6

LUMPED PARAMETER FLOW MODELS

WATER SAMPLES FROM:

Upper Floridan aquifer

TTP-4 (A) ambient conditions

TTP-4 (P) pumping conditions

Intermediate confining unit

Surficial aquifer system

Figure 11. Measured concentrations of sulfur hexafluoride and tritium in water samples from wells, and lumped-parameter modeled 

curves for various ground-water age distributions from the surficial aquifer system, intermediate confining unit, and Upper Floridan 

aquifer in the Temple Terrace, Florida, study area.

waters that had low 3H concentrations (old waters), high sulfate concentrations, and were anoxic.

Water samples from shallow wells in the Upper Floridan 

aquifer (GARC-F75, RP-F77, THC-F75, and RP-F103) had 

slightly higher 3H and SF6 concentrations than water samples 

from deep wells, and these samples likely represent mixtures 

of about 75- to 80-percent old water (greater than 60 years) 

with 20- to 25-percent young water (recharged within the past 

6 years). Water samples from wells WP-F150 and 113RC-H50 

plot near the midpoint of the binary mixing curve and likely 

represent 50/50 mixtures of old and young waters. Water from 

the 43- to 46-m open zone, which WP-F150 taps, contains a 

higher proportion of young water than shallower wells in the 

Upper Floridan aquifer. This zone might be connected to the 

highly transmissive zone identified in the public-supply well 

borehole from geophysical measurements.

A plot of SF6 and 3H/3H(0) shows similar results for 

samples from the deep wells, which represent old waters 

(fig. 12). Again, concentrations of SF6 and 3H/3H(0) for the 

shallower Upper Floridan aquifer wells plot to the right of 

the deep wells along the binary mixing-exponential mixing 

modeled curves showing mixtures of young and old waters. 

The SF6 and 3H/3H(0) concentrations in water from WP-F150 

plot close to those for 113RC-S35 and 113-RC-H50, indicating the higher fraction of young water at this site. Although 

the tracer concentrations for most samples from the surficial 

aquifer system and the public-supply well TTP-4 plot in the 

upper right-hand side of figure 12 and represent young waters, 

they plot below all lumped-parameter mixing curves, which 

could result from several possible scenarios. First, 3He and/

or SF6 may have been lost due to degassing during sampling. 

Loss of 3He could result in an age that is biased younger than 

the true age. Degassing of SF6 is less likely, but would result in 

an age that is biased older than the true age. However, based 

on the relatively higher 3H and SF6 concentrations for these 

waters, they likely contain mostly young recharge waters 

(within the past 6 years). Second, preferential loss of 3He due 

to diffusion into the Teflon sampling line would result in a 

higher 3H/3H(0) value than expected without 3He degassing, 

and a shift to the right of the modeled curves. Finally, confine-
Occurrence of Anthropogenic and Naturally Occurring Contaminants in Ground-Water Samples 41

ment of 3Hetrit can be one of the problems of 3H/3He dating of 

very shallow water-table environments (L.N. Plummer, U.S. 

Geological Survey, written commun., 2007). The 3H/3He clock 

starts at the seasonal low in the water table in wet climates 

(Cook and Solomon, 1997), and as the water table rises during 

wet-season recharge, the 3Hetrit becomes confined in the aquifer. The 3

Hetrit subsequently could be lost from these samples 

during seasonal lows in the water table, as was reported for 

water-table springs in Shenandoah National Park (Plummer 

and others, 2001). Results from sampling for additional agedating tracers may help to resolve some of these issues.

Occurrence of Anthropogenic and 

Naturally Occurring Contaminants in 

Ground-Water Samples

This section presents information on selected 

anthropogenic and naturally occurring contaminants in water 

from monitoring wells, public-supply well TTP-4, stormwater retention ponds, and the Hillsborough River. Emphasis 

is placed on comparisons between the occurrence of contaminants in water from the public-supply well relative to water 

samples from the surficial aquifer system, intermediate confining unit and Upper Floridan aquifer. Important factors affecting contaminant occurrence, concentrations, and fate also are 

presented. 

Nitrate-N Concentrations and 

Isotopes and Dissolved Gases

Nitrate-N concentrations generally were highest in water 

samples from the oxic surficial aquifer system compared to 

those from the intermediate confining unit, the Upper Floridan 

aquifer, stormwater retention ponds, and the Hillsborough 

River (table 5; fig. 13). Nitrate-N concentrations did not 

exceed the U.S. Environmental Protection Agency (1993) 

maximum contaminant level of 10 mg/L for drinking water in 

any water samples collected in this study. Nitrate-N concentrations in the surficial aquifer system ranged from less than 

0.06 to 6.1 mg/L, with a median value of 1.6 mg/L. Nitrate-N 

6

5

4

3

2

1

0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

113RC-H50

WP-F150

113RC-S35

WP-S64

TTP-4 TTP-4

(140P)

TTP-4

(140A)

GARCS23

RP-S20

THCS45

TTP-4 (125P)

TTP-4 (140A),

(160P), (125P)

RP-F77

THC-F75 RP-F103

GARCF75

GARCF200

113RCF190

THCF197

Piston-flow model

Exponential mixing model

Binary-exponential model (young water 6-years in age)

Exponential-piston model

LUMPED PARAMETER FLOW MODELS

WATER SAMPLES FROM:

Upper Floridan aquifer

TTP-4 (NP) non-pumping conditions

TTP-4 (P) pumping conditions

Intermediate confining unit

Surficial aquifer system

SULFUR HEXAFLUORIDE, IN PARTS PER TRILLION BY VOLUME

TRITIUM/INITIAL TRITIUM CONCENTRATION, IN TRITIUM UNITS

Figure 12. Measured concentrations of sulfur hexafluoride, tritium, the ratio of tritium to the sum of helium-3 and tritium in water 

samples from wells, and lumped-parameter modeled curves for ground-water age distributions from the surficial aquifer system, 

intermediate confining unit, and Upper Floridan aquifer in the in the Temple Terrace, Florida, study area.
42 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

concentrations above the background levels of 0.1 mg/L 

(Maddox and others, 1992) in the surficial aquifer system 

likely result from past agricultural practices, fertilizer application to lawns, leakage from septic tanks prior to sewering of 

the area, and possibly leaky sewer lines. Nitrogen isotope 

values for these waters generally were less than 5 per mil, indicating that nitrate likely originated from an inorganic fertilizer 

source. Water samples from three wells had delta nitrogen-15 

(δ15N) values greater than 6 per mil at sites RP-S20 (10.0 per 

mil), LRP-H105 (8.1 per mil) and THC-S46 (6.4 per mil) as 

noted in table 6. The higher δ15N values may represent denitrification in these waters because methane gas was measured 

in these water samples (0.3-0.9 mg/L), and excess nitrogen 

gas was estimated at 0.4 and 3 cm3/L (cubic centimeters per 

liter) for RP-S20 and LRP-S25, respectively. Excess nitrogen 

gas was estimated by comparing measured argon and nitrogen 

gas concentrations to those expected at equilibrium with a 

recharge temperature of 23 oC. Water from RP-S20 likely is 

a mixture of surface water from the Hillsborough River and 

reduced ground water, as indicated by the combined presence 

of dissolved oxygen (2.2 mg/L), methane (0.9 mg/L), and 

dissolved organic carbon (3.3 mg/L). 

Nitrate-N concentrations were variable in water from the 

intermediate confining unit and ranged from 0.27 to 3.5 mg/L, 

with a median concentration of 2.2 mg/L (table 5). Nitrate-N 

concentrations in water were lower in LRP-H105 (0.27 mg/L) 

and 113RC-H50 (0.65 mg/L) compared with concentrations in 

62SRP-H55 (3.5 mg/L) and LP-H40 (2.4 mg/L). Water from 

wells LRP-H105 and 113RC-H50 also had higher δ15N values 

and lower dissolved oxygen concentrations than wells 

62SRP-H55 and LP-H40, indicating that denitrification likely 

occurs in parts of the intermediate confining unit. The 

dissolved methane concentration in water from 113RC-H50 

(0.2 mg/L) and an estimated excess nitrogen gas of 1.5 cm3/L 

also are consistent with denitrification. 

Nitrate-N concentrations in water from the Upper 

Floridan aquifer generally were less than the method reporting 

level of 0.06 mg/L. Water from the Upper Floridan aquifer, 

which generally is anoxic in this area, had dissolved oxygen 

concentrations less than 0.5 mg/L and contained measurable 

amounts of hydrogen sulfide. Methane concentrations generally were less than 0.1 mg/L, with the exception of LRP-F160 

(0.43 mg/L). In addition, there are several other notable exceptions. Water from the shallowest Upper Floridan aquifer well, 

MAS-F64, had an elevated nitrate-N concentration of 

1.2 mg/L. Likewise, elevated nitrate-N concentrations were 

found in water samples from 62SRP-F160 (2.0 mg/L), MASR-F160 (0.94 mg/L), and public-supply well TTP-4 (0.61-

3.6 mg/L). These wells likely withdraw some water from a 

transmissive zone in the Upper Floridan aquifer that is 

hydraulically connected to the surficial aquifer system. 

The δ15N values for water samples from the Upper 

Floridan aquifer ranged from 4.2 to 21 per mil and were higher 

than those for the surficial aquifer system and intermediate 

confining unit (table 6). Denitrification likely occurs in parts 

of the Upper Floridan aquifer, as indicated by estimated 

excess nitrogen gas values (table 9) that ranged from 1.5 to 

4 cm3/L for water from a depth interval of between 43 and 

49 m below land surface (62SRP-F160, MAS-R-F160, LRPF160, WP-F150). Also, the ratio of enrichment of δ18O to δ15N 

of the residual nitrate-N was close to 0.5 (points plot along 

dashed trend lines with slope of 0.5 in fig. 14) for samples 

from the anoxic Upper Floridan aquifer. Previous studies also 

have shown that the enrichment of oxygen to nitrogen was 0

20

40

60

80

1000 1 234567

NITRATE-N, IN MILLIGRAMS PER LITER

DEPTH BELOW LAND SURFACE, IN METERS

Ponds

Surficial aquifer system

Intermediate confining unit

Upper Floridan aquifer system

Public-supply well

Public-supply well (ambient)

Public-supply well (pumping)

EXPLANATION

Figure 13. Nitrate-N concentrations with well depth in the Temple 

Terrace, Florida, study area.

Anoxic

Oxic

25

20

15

10

5

0

-50 5 10 15 20 25

DELTA NITROGEN-15 OF NITRATE, IN PER MIL

DELTA OXYGEN-18 OF NITRATE, IN PERMIL

Denitrification

slope lines

Figure 14. Plot showing values for delta nitrogen-15 and delta 

oxygen-18 of nitrate in water from wells in the Temple Terrace, 

Florida, study area.
Occurrence of Anthropogenic and Naturally Occurring Contaminants in Ground-Water Samples 43

Site

name

Aquifer Date collected Time collected

Field

temperature,

degrees 

Celsius

Methane Carbon dioxide Nitrogen Oxygen Argon

Calculated

excess 

nitrogen gas,

mg/L

Calculated

recharge 

temperature,

degrees Celsius

Excess

air,

cm3/L

RP-F103 UFA 12/2/2003 1500 23.50 0.1931 0.0000 16.8232 0.1794 0.5797 21.1 2.3RP-F103 UFA 12/2/2003 1500 23.50 0.1902 0.0000 16.7976 0.1980 0.5800 21.0 2.2RP-F77 UFA 12/3/2004 1300 23.50 0.0921 0.0000 17.6684 0.2067 0.6066 19.1 2.6RP-F77 UFA 12/3/2004 1300 23.50 0.0937 0.0000 17.6868 0.2249 0.6075 19.1 2.6RP-S20 SAS 12/4/2003 1400 24.50 0.8944 0.0000 14.5919 0.7843 0.5258 23.9 0.7RP-S20 SAS 12/4/2003 1400 24.50 0.9337 0.0000 15.0378 1.0985 0.5362 23.4 1.1113RC-F190 UFA 12/8/2003 1300 25.00 0.0384 0.0000 16.9316 0.2048 0.5939 19.2 1.9113RC-F190 UFA 12/8/2003 1300 25.00 0.0385 0.0000 16.9462 0.2029 0.5944 19.2 1.9113RC-H50 ICU 12/9/2003 1300 25.50 0.1785 0.0000 18.7037 0.2032 0.5934 24.1 4.9113RC-H50 ICU 12/9/2003 1300 25.50 0.1711 0.0000 18.6604 0.1830 0.5931 24.0 4.8113RC-S35 SAS 2/11/2003 1300 26.00 0.0162 0.0000 17.0169 2.4159 0.5696 23.3 3.0113RC-S35 SAS 2/11/2003 1300 26.00 0.0160 0.0000 16.7438 2.4166 0.5622 23.8 2.9GARC-F75 UFA 2/15/2003 1400 24.50 0.0000 0.0000 0.0000 0.0000 0.0000 99.9 -0.0GARC-F75 UFA 2/15/2003 1400 24.50 0.0301 0.0000 17.0322 0.2119 0.5848 20.9 2.4GARC-F200 UFA 2/16/2003 1300 25.00 0.0289 0.0000 16.3005 0.2278 0.5768 20.2 1.5GARC-F200 UFA 2/16/2003 1300 25.00 0.0295 0.0000 17.0290 0.1917 0.5925 19.7 2.1GARC-S23 SAS 2/17/2003 1200 25.00 0.0405 0.0000 16.2952 2.2366 0.5582 23.2 2.3GARC-S23 SAS 2/17/2003 1200 25.00 0.0396 0.0000 16.0657 2.1664 0.5517 23.7 2.2THC-S46 SAS 2/18/2003 1300 24.50 0.6965 0.0000 18.6746 0.2081 0.6141 20.5 4.0THC-S46 SAS 2/18/2003 1300 24.50 0.6552 0.0000 18.3892 0.2079 0.6056 21.2 3.9THC-F75 UFA 1/12/2004 1500 24.50 0.0139 0.0000 16.9417 0.2197 0.5742 22.3 2.7THC-F75 UFA 1/12/2004 1500 24.50 0.0144 0.0000 16.9276 0.2064 0.5721 22.7 2.8THC-F75 UFA 1/12/2004 1501 25.00 0.0141 0.0000 17.1795 0.1846 0.5805 21.9 2.8THC-F75 UFA 1/12/2004 1501 25.00 0.0148 0.0000 16.7962 0.1892 0.5732 22.1 2.5WP-S64 SAS 1/14/2004 1500 26.00 0.0000 0.0000 14.8676 5.4955 0.5320 23.6 0.9WP-S64 SAS 1/14/2004 1500 26.00 0.0000 0.0000 32.6324 11.0498 0.8358 22.3 18.4

Table 9. Dissolved gas data, calculated excess nitrogen gas concentration, estimated recharge temperature, and excess air concentration in water samples collected from the public-supply well and monitoring wells in the Temple Terrace, Florida, study area. [SAS, surficial aquifer system; ICU, intermediate confining unit; UFA, Upper Floridan aquifer. Recharge elevation assumed to be 10 to 30 meters above the NAVD 88 (North American Vertical Datum of 1988). Values in milligrams per liter, except where noted. Excess air in cubic centimeters per liter (cm3/L) at standard temperature and pressure conditions. Sample lost at wells GARC-F75 and BBP-S45. Sample leak occurred at well WP-S64]
44 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water Site name Aquifer Date collected Time collected Field temperature, degrees Celsius Methane Carbon dioxide Nitrogen Oxygen Argon Calculated excess nitrogen gas, mg/L Calculated recharge temperature, degrees Celsius Excess air, cm3/L THC-F197 UFA 1/15/2004 1400 25.00 0.0366 0.0000 16.9290 0.2199 0.5934 19.3 1.9 THC-F197 UFA 1/15/2004 1400 25.00 0.0398 0.0000 16.9659 0.1633 0.5949 19.2 1.9 WP-F300 UFA 1/22/2004 1600 26.00 0.0309 0.0000 17.1766 0.2236 0.6004 18.9 2.0 WP-F300 UFA 1/22/2004 1600 26.00 0.0310 0.0000 17.2875 0.1996 0.6026 18.8 2.1 WP-F150 UFA 1/28/2004 1300 25.00 0.0026 0.0000 19.4985 0.1841 0.5441 3.0 26.4 3.2 WP-F150 UFA 1/28/2004 1300 25.00 0.0025 0.0000 19.5210 0.1797 0.5445 3.0 26.4 3.2 TTP-4 UFA 1/28/2004 1600 24.00 0.0006 0.0000 18.5728 0.1928 0.5670 28.7 5.8 TTP-4 UFA 1/28/2004 1600 24.00 0.0022 0.0000 18.5182 0.1989 0.5665 28.6 5.7 LP-S30 SAS 11/1/2004 1600 28.00 0.0000 0.0000 13.4637 6.4737 0.4848 28.1 0.5 LP-S30 SAS 11/1/2004 1600 28.00 0.0022 0.0000 13.3303 6.4560 0.4850 27.6 0.3 62SRP-F160 UFA 11/2/2004 1200 29.00 0.0000 0.0000 19.5383 0.5186 0.5465 3.0 26.0 3.2 62SRP-F160 UFA 11/2/2004 1200 29.00 0.0000 0.0000 19.7392 0.6296 0.5514 3.0 25.7 3.3 MAS-R-F160 UFA 11/3/2004 1200 27.00 0.0000 0.0000 18.6615 0.6803 0.5559 2.0 24.7 3.0 MAS-R-F160 UFA 11/3/2004 1200 27.00 0.0000 0.0000 18.4735 0.7533 0.5520 2.0 24.8 2.8 LRP-F160 UFA 11/4/2004 1300 28.00 0.4345 0.0000 15.8982 0.4557 0.5089 1.0 28.0 2.0 LRP-F160 UFA 11/4/2004 1300 28.00 0.4247 0.0000 15.9051 0.4086 0.5112 1.0 27.6 1.9 QRP-S20 SAS 11/15/2004 1700 25.00 0.0064 0.0000 15.5861 3.6182 0.5409 24.2 1.8 QRP-S20 SAS 11/15/2004 1700 25.00 0.0067 0.0000 15.6336 3.5005 0.5407 24.4 1.9 LRP-S25 SAS 12/7/2004 1600 25.00 0.3243 0.0000 17.3707 0.6284 0.5320 2.0 25.1 1.8 LRP-S25 SAS 12/7/2004 1600 25.00 0.3423 0.0000 17.8618 0.5468 0.5393 2.0 25.3 2.3

LP-H40 ICU 12/8/2004 1500 26.00 0.0000 0.0000 16.5669 7.4635 0.5662 22.6 2.4LP-H40 ICU 12/8/2004 1500 26.00 0.0000 0.0000 16.4222 7.4664 0.5628 22.8 2.3LP-H40 ICU 12/8/2004 1505 26.00 0.0000 0.0000 16.2370 7.4170 0.5622 22.4 2.0LP-H40 ICU 12/8/2004 1505 26.00 0.0000 0.0000 16.5600 7.5012 0.5669 22.5 2.4BBP-S45 SAS 12/9/2004 1300 26.00 0.0000 0.0000 15.6538 4.2695 0.5411 24.3 1.9

Table 9. Dissolved gas data, calculated excess nitrogen gas concentration, estimated recharge temperature, and excess air concentration in water samples collected from the public-supply well and monitoring wells in the Temple Terrace, Florida, study area.—Continued[SAS, surficial aquifer system; ICU, intermediate confining unit; UFA, Upper Floridan aquifer. Recharge elevation assumed to be 10 to 30 meters above the NAVD 88 (North American Vertical Datum of 1988). Values in milligrams per liter, except where noted. Excess air in cubic centimeters per liter (cm3/L) at standard temperature and pressure conditions. Sample lost at wells GARC-F75 and BBP-S45. Sample leak occurred at well WP-S64]
Occurrence of Anthropogenic and Naturally Occurring Contaminants in Ground-Water Samples 45

Site

name Aquifer Date collected Time collected

Field

temperature,

degrees 

Celsius

Methane Carbon dioxide Nitrogen Oxygen Argon

Calculated

excess 

nitrogen gas,

mg/L

Calculated

recharge 

temperature,

degrees Celsius

Excess

air,

cm3/L

BBP-S45 SAS 12/9/2004 1300 26.00 0.0000 0.0000 0.0000 0.0000 0.0000 99.9 0.0TTP-4 UFA 10/21/2004 1500 26.00 0.0020 0.0000 18.5724 0.5137 0.5483 2.0 25.8 3.2TTP-4 UFA 10/21/2004 1500 26.00 0.0022 0.0000 18.6044 0.5084 0.5480 2.0 26.0 3.2TTP-4-140-NP UFA 10/27/2004 1600 26.50 0.0008 0.0000 18.9228 0.4964 0.5627 2.0 24.3 3.1TTP-4-140-NP UFA 10/27/2004 1600 26.50 0.0008 0.0000 18.7089 0.5194 0.5608 2.0 24.0 2.9TTP-4-160-NP UFA 10/27/2004 1800 26.00 0.0008 0.0000 18.1529 0.8798 0.5631 1.0 24.9 3.5TTP-4-160-NP UFA 10/27/2004 1800 26.00 0.0000 0.0000 18.0219 0.8890 0.5598 1.0 25.1 3.4TTP-4-160-P UFA 10/28/2004 1100 24.00 0.0013 0.0000 19.0357 0.4847 0.5538 2.0 26.2 3.7TTP-4-160-P UFA 10/28/2004 1100 24.00 0.0012 0.0000 18.8632 0.5283 0.5530 2.0 25.8 3.4TTP-4-140-P UFA 10/28/2004 1400 26.00 0.0014 0.0000 18.9641 0.5390 0.5537 2.0 26.0 3.6TTP-4-140-P UFA 10/28/2004 1400 26.00 0.0014 0.0000 18.7383 0.5149 0.5493 2.0 26.1 3.4TTP-4-125-P UFA 10/28/2004 1600 26.00 0.0014 0.0000 18.7294 0.6156 0.5503 2.0 25.9 3.3TTP-4-125-P UFA 10/28/2004 1600 26.00 0.0014 0.0000 18.7534 0.5910 0.5494 2.0 26.2 3.4MAS-R-F64 UFA 2/16/2005 1300 25.50 0.0017 0.0000 17.1506 1.9250 0.5542 26.5 3.9MAS-R-F64 UFA 2/16/2005 1300 25.50 0.0014 0.0000 17.0820 1.9498 0.5527 26.5 3.8WP-F300 UFA 8/29/2005 1500 26.00 0.0313 23.0771 16.4633 0.1226 0.5718 21.4 2.0WP-F300 UFA 8/29/2005 1500 26.00 0.0324 22.7853 17.0061 0.1146 0.5826 21.1 2.5LP-H40 ICU 8/30/2005 1400 33.01 0.0024 10.0379 14.9362 6.0556 0.5281 24.5 1.2LP-H40 ICU 8/30/2005 1400 33.01 0.0031 10.3694 14.8320 5.8721 0.5295 24.0 1.0LP-S30 SAS 8/30/2005 1700 32.05 0.0032 38.5133 13.3620 6.6908 0.4974 25.4 -0.2LP-S30 SAS 8/30/2005 1700 32.05 0.0034 38.4362 13.4288 6.7101 0.4980 25.5 -0.1TTP-4 UFA 8/31/2005 1000 25.00 0.0015 13.4187 18.9733 0.1166 0.5566 2.0 25.5 3.5TTP-4 UFA 8/31/2005 1000 25.00 0.0018 13.1166 19.1016 0.1125 0.5601 2.0 25.3 3.6

Table 9. Dissolved gas data, calculated excess nitrogen gas concentration, estimated recharge temperature, and excess air concentration in water samples collected from the public-supply well and monitoring wells in the Temple Terrace, Florida, study area.—Continued[SAS, surficial aquifer system; ICU, intermediate confining unit; UFA, Upper Floridan aquifer. Recharge elevation assumed to be 10 to 30 meters above the NAVD 88 (North American Vertical Datum of 1988).Values in milligrams per liter, except where noted. Excess air in cubic centimeters per liter (cm3/L) at standard temperature and pressure conditions. Sample lost at wells GARC-F75 and BBP-S45. Sample leak occurred at well WP-S64]
46 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

close to 1:2; thus, denitrification produces a slope of about 

0.5 on plots of δ15N and δ18O of residual nitrate (Kendall and 

Aravena, 1999). Some denitrification also could be occurring 

in parts of the surficial aquifer system and Upper Floridan 

aquifer as δ18O and δ15N of residual nitrate plot along the trend 

lines with 0.5 slope. This may indicate that denitrification is 

likely occurring in parts of the ground-water system farther 

from the water table that contain lower amounts of oxygen 

than present near the water table.

In most water samples from the surficial aquifer system 

and intermediate confining unit and some parts of the Upper 

Floridan aquifer, concentrations of nitrogen gas and argon 

are consistent with atmospheric equilibration during groundwater recharge with minor amounts of excess air added either 

during recharge or as a result of sampling methods (table 9). 

The apparent recharge temperatures are 24 ± 2 oC (assuming 

a 15-m elevation for recharge and 100-percent humidity at 

the water table) with about 0 to 5 cm3/L of excess air during 

recharge. This calculated recharge temperature agrees closely 

with a mean annual air temperature of 22.8 oC (Owenby and 

Ezell, 1992).

Volatile Organic Compounds

A total of 20 out of 85 volatile organic compounds were 

detected at measurable concentrations in one or more water 

samples (table 10; fig. 15). Concentrations generally were 

below 1 μg/L and well below U.S. Environmental Protection 

Agency (1993) maximum contaminant levels where available. 

More volatile organic compounds were detected in water from 

100

80

60

40

20

0

1, 2-dichloropropane

4-isopropyltoluene

benzene

bromochloromethane

bromodichlormethane

carbon disulfide

dibromochloromethane

dichloromethane

Methyl tert-butyl ether (MTBE)

tetrachloroethene

tetrahydrofuran

toluene

tribromomethane

trichloroethene

trichloromethane

cis-1,2 dichloroethene

m- + p-Xylene

dibromomethane

2-butanone

DETECTION FREQUENCY, IN PERCENT

Upper Floridan aquifer (23 samples)

Intermediate confining unit (4 samples)

Surficial aquifer system (28 samples)

Retention ponds (3 samples)

acetone

NOTE: Underlined compounds were detected

in public-supply well TTP-4. Compounds

shown in correspond to the 15 most

frequently detected volatile organic

compounds in drinking-water wells in the

United States (Zogorski and others, 2006)

red

Figure 15. Detection frequency of volatile organic compounds in ground water from the surficial aquifer system, intermediate confining 

unit, Upper Floridan aquifer, and stormwater retention ponds in the Temple Terrace, Florida, study area.
Occurrence of Anthropogenic and Naturally Occurring Contaminants in Ground-Water Samples 47

1_2-dichloropropane

- 4-Isopropyl-1-methyl

benzene

Benzene

Bromochloromethane

Bromodichloromethane

Carbon disulfide

Dibromochloromethane

- Dichloromethane (Meth

ylene chloride)

Methyl tert-butyl ether 

(MTBE)

Tetrachloroethene (PCE)

Tetrahydrofuran

Toluene

Tribromomethane

Trichloroethene (TCE)

Trichloromethane 

(Chloroform)

cis-1,2-Dichloroethene

m- + p-Xylene

Acetone

Dibromomethane

2-butanone

CASRN 78875 99876 71432 74975 75274 75150 124481 75092 1634044 127184 109999 108883 75252 79016 67663 156592

108383 

& 

106423

67641 74953 78933

pcode 34541 77356 34030 77297 32101 77041 32105 34423 78032 34475 81607 34010 32104 39180 32106 77093 85795 81552 30217 81595

USEPA 

MCL 5 NAV 5 NAV 80 NAV NAV 5 NAV 5 NAV 1000 80 5 80 70 NAV NAV NAV NAV

RL 0.029 0.08 0.021 0.12 0.028 0.038 0.10 0.06 0.1 0.03 1.0 0.02 0.1 0.038 0.024 0.024 0.06 6 0.05 2

Site 

name

Site

identifier

Aquifer Well depth Sample date

THC-F197 280241082224401 UFA 197 1/15/2004 E0.044 E0.024THC-F75 280241082224402 UFA 75 1/12/2004 0.21 0.15 E0.03062SRP-F160 280241082230701 UFA 160 11/2/2004 E0.02 0.40MAS-R-F160 280242082232401 UFA 160 11/3/2004 E0.055 E0.02 0.27MAS-R-F160 280242082232401 UFA 160 6/16/2005 E0.060 E0.048 E0.02 E0.02 E0.083MAS-R-F64 280242082232403 UFA 64 6/16/2005 E0.082 E0.07 0.45MAS-R-F64 280242082232403 UFA 64 2/16/2005 0.51TTP-4 280244082232001 UFA 174 10/21/2002 E0.017 E0.034 0.10 0.14 0.16 E0.022TTP-4 280244082232001 UFA 174 1/28/2004 E0.037 E0.02 E0.07 0.19TTP-4 280244082232001 UFA 174 9/22/2004 E0.05 0.36TTP-4 280244082232001 UFA 174 10/21/2004 E0.04 0.29TTP-4 280244082232001 UFA 174 10/27/2004 E0.03TTP-4 280244082232001 UFA 174 2/16/2005 E0.03 E0.047TTP-4 280244082232001 UFA 174 6/20/2005 E0.04 E0.077WP-F299 280247082231901 UFA 299 8/3/2004 E0.05WP-F299 280247082231901 UFA 299 1/22/2004 E0.769 0.80 E0.057WP-F150 280247082231902 UFA 150 1/28/2004 E0.025RP-F103 280249082220701 UFA 103 12/2/2003 0.193 E0.061RP-F77 280249082220702 UFA 77 12/3/2003 0.217 E0.04 E0.02 0.25LRP-F160 280250082233001 UFA 160 11/4/2004 0.373 E0.022

Table 10. Volatile organic compounds detected in water samples from the surficial aquifer system (SAS), intermediate confining unit (ICU), Upper Floridan aquifer (UFA), and stormwater retention ponds (POND). [Concentrations are shown in micrograms per liter. USEPA MCL, U.S. Environmental Protection Agency, maximum contaminant level in micrograms per liter; NAV, not available; CASRN, chemical abstracts service registry number; pcode, U.S. Environmental Protection Agency STORET parameter code; RL, method reporting limit in micrograms per liter; blank cell denotes compound concentration was not detected; E, concentration reported below laboratory reporting level (RL)]
48 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

1_2-dichloropropane

- 4-Isopropyl-1-methyl

benzene

Benzene

Bromochloromethane

Bromodichloromethane

Carbon disulfide

Dibromochloromethane

- Dichloromethane (Meth

ylene chloride)

Methyl tert-butyl ether 

(MTBE)

Tetrachloroethene (PCE)

Tetrahydrofuran

Toluene

Tribromomethane

Trichloroethene (TCE)

Trichloromethane 

(Chloroform)

cis-1,2-Dichloroethene

m- + p-Xylene

Acetone

Dibromomethane

2-butanone

CASRN 78875 99876 71432 74975 75274 75150 124481 75092 1634044 127184 109999 108883 75252 79016 67663 156592

108383 

& 

106423

67641 74953 78933

pcode 34541 77356 34030 77297 32101 77041 32105 34423 78032 34475 81607 34010 32104 39180 32106 77093 85795 81552 30217 81595

USEPA 

MCL 5 NAV 5 NAV 80 NAV NAV 5 NAV 5 NAV 1000 80 5 80 70 NAV NAV NAV NAV

RL 0.029 0.08 0.021 0.12 0.028 0.038 0.10 0.06 0.1 0.03 1.0 0.02 0.1 0.038 0.024 0.024 0.06 6 0.05 2

Site

name

Site

identifier

Aquifer Well depth Sample date

GARC-F200 280253082223801 UFA 200 12/16/2003 E0.02514 E0.07 E0.039GARC-F75 280253082223802 UFA 75 12/15/2003 .10700 0.64 E0.092113RC-F190 280301082222701 UFA 190 12/8/2003 .20000 0.15 E0.01262SRP-H55 280241082230702 ICU 55 11/3/2004 0.22113RC-H50 280301082222702 ICU 50 12/9/2003 E0.02 E0.015 E0.038 0.83 E0.01 E0.01 0.21LP-H40 280303082230901 ICU 40 8/10/2004 E0.075 0.18LP-H40 280303082230901 ICU 40 12/8/2004 E0.029 0.33BBP-S39 280228082231501 SAS 39 8/11/2004 1.08 E0.064 1.28000 E0.08 0.45 1.00BBP-S39 280228082231501 SAS 39 12/9/2004 0.17 0.18 0.17BBP-S39 280228082231501 SAS 39 6/22/2005 0.16 E0.03 0.23THC-S46 280241082224403 SAS 46 8/5/2004 0.27 E0.03 0.16THC-S46 280241082224403 SAS 46 11/17/2004 E0.016 0.16 E0.082THC-S46 280241082224403 SAS 46 12/18/2003 E0.10 E0.076 E0.08 1.68 0.30 0.29 E0.02 0.28THC-S46 280241082224403 SAS 46 6/14/2005 E0.09 E0.02 E0.07262SRP-S34 280241082230703 SAS 34 8/12/2004 E0.038 E0.013 E0.063 E0.02 E0.02 E0.02WP-S64 280247082231903 SAS 64 8/4/2004 E0.072 E0.02 2.13WP-S64 280247082231903 SAS 64 11/18/2004 E0.052 1.17WP-S64 280247082231903 SAS 64 1/14/2004 E0.048 0.26 E0.03 2.53WP-S64 280247082231903 SAS 64 6/14/2005 E0.04 2.58RP-S20 280249082220703 SAS 20 8/11/2004 0.24

Table 10. Volatile organic compounds detected in water samples from the surficial aquifer system (SAS), intermediate confining unit (ICU), Upper Floridan aquifer (UFA), and stormwater retention ponds (POND). —Continued[Concentrations are shown in micrograms per liter. USEPA MCL, U.S. Environmental Protection Agency, maximum contaminant level in micrograms per liter; NAV, not available; CASRN, chemical abstracts service registry number; pcode, U.S. Environmental Protection Agency STORET parameter code; RL, method reporting limit in micrograms per liter; blank cell denotes compound concentration was not detected; E, concentration reported below laboratory reporting level (RL)]
Occurrence of Anthropogenic and Naturally Occurring Contaminants in Ground-Water Samples 49

1_2-dichloropropane

- 4-Isopropyl-1-methyl

benzene

Benzene

Bromochloromethane

Bromodichloromethane

Carbon disulfide

Dibromochloromethane

- Dichloromethane (Meth

ylene chloride)

Methyl tert-butyl ether 

(MTBE)

Tetrachloroethene (PCE)

Tetrahydrofuran

Toluene

Tribromomethane

Trichloroethene (TCE)

Trichloromethane 

(Chloroform)

cis-1,2-Dichloroethene

m- + p-Xylene

Acetone

Dibromomethane

2-butanone

CASRN 78875 99876 71432 74975 75274 75150 124481 75092 1634044 127184 109999 108883 75252 79016 67663 156592

108383 

& 

106423

67641 74953 78933

pcode 34541 77356 34030 77297 32101 77041 32105 34423 78032 34475 81607 34010 32104 39180 32106 77093 85795 81552 30217 81595

USEPA 

MCL 5 NAV 5 NAV 80 NAV NAV 5 NAV 5 NAV 1000 80 5 80 70 NAV NAV NAV NAV

RL 0.029 0.08 0.021 0.12 0.028 0.038 0.10 0.06 0.1 0.03 1.0 0.02 0.1 0.038 0.024 0.024 0.06 6 0.05 2

Site

name

Site

identifier

Aquifer Well depth Sample date

RP-S20 280249082220703 SAS 20 11/16/2004 E0.03 0.12RP-S20 280249082220703 SAS 20 12/4/2003 0.66 0.119 E0.01LRP-S25 280250082233003 SAS 25 8/10/2004 E0.075LRP-S25 280250082233003 SAS 25 12/7/2004 E0.011 E0.025 0.13GARC-S23 280253082223803 SAS 23 8/5/2004 E0.034 0.11GARC-S23 280253082223803 SAS 23 11/17/2004 0.10GARC-S23 280253082223803 SAS 23 12/17/2003 0.33 0.33 1.32 E0.02 0.35GARC-S23 280253082223803 SAS 23 6/13/2005 0.11113RC-S35 280301082222703 SAS 35 8/12/2004 E0.027113RC-S35 280301082222703 SAS 35 11/16/2004 E0.030113RC-S35 280301082222703 SAS 35 12/11/2003 E0.045 2.03 E0.02 0.41113RC-S35 280301082222703 SAS 35 6/15/2005 0.02LP-S30 280303082230902 SAS 30 8/10/2004 E0.030 E0.030 0.24LP-S30 280303082230902 SAS 30 11/1/2004 E0.98 0.28LP-S30 280303082230902 SAS 30 6/21/2005 E0.059 0.0662SRP-POND 280242082230800 POND 6/21/2005 E0.36 E0.147 E16MAS-R-POND 280242082232900 POND 6/21/2005 E0.02 E0.14 E0.027 E8.2 E1.3LRP-POND 280250082233200 POND 6/21/2005 0.07 0.80 E.029 1.23 E0.05 E0.01 0.58 0.93 7.8 E0.05

Table 10. Volatile organic compounds detected in water samples from the surficial aquifer system (SAS), intermediate confining unit (ICU), Upper Floridan aquifer (UFA), and stormwater retention ponds (POND). —Continued [Concentrations are shown in micrograms per liter. USEPA MCL, U.S. Environmental Protection Agency, maximum contaminant level in micrograms per liter; NAV, not available; CASRN, chemical abstracts service registry number; pcode, U.S. Environmental Protection Agency STORET parameter code; RL, method reporting limit in micrograms per liter; blank cell denotes compound concentration was not detected; E, concentration reported below laboratory reporting level (RL)]
50 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

the surficial aquifer system (16) than in the underlying intermediate confining unit (8) and Upper Floridan aquifer (10). A 

total of 11 volatile organic compounds were detected in water 

samples from retention ponds (table 10; fig. 15). Trichloromethane (commonly known as chloroform) was the most 

frequently detected compound in water from all three hydrogeologic units. Concentrations of volatile organic compounds 

generally were below 0.1 μg/L, with the exception of trichloromethane, which ranged from 0.01 to 2.6 μg/L in the surficial 

aquifer system (fig. 16). Trichloromethane was detected more 

frequently in oxic water samples (dissolved oxygen concentrations greater than 0.5 mg/L) than from anoxic water samples 

(fig. 17). In contrast, dichloromethane (commonly known as 

methylene chloride) was detected more frequently in anoxic 

waters. The higher detection frequency in anoxic waters likely 

is related to reductive dehalogenation under anaerobic conditions (Vogel and others, 1987; Suflita and others, 1988).

Of the 20 volatile organic compounds detected in groundwater samples, high median concentrations were found in 

the water from the surficial aquifer system for 12 of these 

compounds. High median concentrations of carbon disulfide, 

trichloroethene, and cis-1,2 dichloroethene were found in 

the anoxic water samples from the Upper Floridan aquifer. 

Slightly higher median concentrations of benzene and 

Benzene

Bromochloromethane

Bromodichloromethane

Carbon disulfide

Dibromochloromethane

Dichloromethane

Methyl tert-butyl ether

(MTBE)

Tetrachloroethene

Toluene

Tribromomethane

Trichloroethene

Trichloromethane

CONCENTRATION, IN MICROGRAMS PER LITER

0.010 0.100 1.00 10.0

Surficial aquifer system

and Intermediate

confining unit

Upper Floridan aquifer

TTP-4

Figure 16. Concentrations of selected volatile organic compounds detected in water samples from the surficial aquifer system, 

intermediate confining unit, Upper Floridan aquifer, and public-supply well in the Temple Terrace, Florida, study area.

10

1.0

0.1

0.01

Trichloromethane

Dichloromethane

CONCENTRATION, IN

MICROGRAMS PER LITER

10/26

39%

23/26

89%

3/28

11%

26/28

93%

Anoxic

Oxic

NOTE: numbers are detections per

samples, also expressed as percent.

Red

Outliers (less than 10th percentile or greater than 90th percentile)

75th percentile

Median

25th percentile

10th percentile

Minimum

EXPLANATION

Trichloromethane

Dichloromethane

Figure 17. A comparison of trichloromethane (chloroform) and 

dichloromethane (methylene chloride) concentrations in water 

samples collected from the oxic surficial aquifer system and the 

anoxic Upper Floridan aquifer in the Temple Terrace, Florida, study 

area.
Occurrence of Anthropogenic and Naturally Occurring Contaminants in Ground-Water Samples 51

trichloromethane were found in water samples from the intermediate confining unit than the surficial aquifer system. All 

detected concentrations of volatile organic compounds in the 

public-supply well and in monitoring wells were below any 

levels for health advisories or maximum contaminant levels 

(Toccalino and others, 2004). Six volatile organic compounds 

were detected in water from the public-supply well: trichloromethane, cis-1,2-dichloroethene, trichloroethene, tetrachloroethene, methyl tert-butyl ether (MTBE), and carbon disulfide. 

Water samples were collected from TTP-4 on seven different 

dates (between October 2002 and June 2005) and analyzed 

for volatile organic compounds. Tetrachloroethene and carbon 

disulfide were detected in only two samples. MTBE and cis1,2-dichloroethene were detected in low concentrations in only 

one sample collected in October 2002. Trace concentrations of 

tetrachloroethene were detected in all samples, and trichloromethane was detected in all but one sample. Median concentrations of MTBE, trichloroethene, and cis-1,2-dichloroethene in the public-supply well were similar to median concentrations in water from the Upper Floridan aquifer. Median 

concentrations of carbon disulfide, tetrachloroethene, and 

trichloromethane were higher in water from the public-supply 

well than from water samples from Upper Floridan aquifer 

monitoring wells. Median concentrations of trichloromethane 

were similar in water (0.17 μg/L) from the public-supply 

well to monitoring wells in the surficial aquifer system 

(fig. 16). Similar concentrations of compounds detected in 

water samples from the public-supply well and from surficial 

aquifer system monitoring wells indicate that water from the 

surficial aquifer system likely is entering the public-supply 

well. 

The high detection frequency of trichloromethane in this 

study is consistent with other ground-water quality studies 

in the Tampa Bay area (Metz and others, 2007), but higher 

than that found in the Nation’s drinking-water supply wells 

where the detection frequency was 11.4 percent using an 

assessment level of 0.2 μg/L (Zogorski and others, 2006; 

Schaap and Zogorski, 2006; Ivahnenko and Zogorski, 2006). 

Several potential sources of trichloromethane in ground water 

include recharge of chlorinated water, direct releases such as 

spills and leaking underground storage tanks, dehalogenation 

of tetrachloroethane, and some natural sources (Ivahnenko 

and Barbash, 2004). Trichloromethane also is a disinfection 

byproduct that is produced during the chlorination of drinking 

water and wastewater that contains naturally occurring organic 

material. In the Tampa Bay area study, the high occurrence 

of trichloromethane was attributed to disinfection byproducts produced during chlorination because other disinfection 

byproducts (bromodichloromethane and bromoform) also 

were detected (Metz and others, 2007). Furthermore, trichloromethane was found only in residential and commercial areas 

and not in undeveloped areas. Recharge of chlorinated waters 

is a likely source of trichloromethane in the Temple Terrace 

area, as other disinfection byproducts commonly were found 

in water samples from the surficial aquifer system such as 

dibromochloromethane and bromodichloromethane (fig. 16). 

Carbon disulfide, a solvent, also was detected frequently in 

both the present study and in the community supply well study 

in the northern Tampa Bay area (Metz and others, 2007).

Pesticides

Five pesticides were detected in low concentrations in 

ground-water samples: atrazine, deethylatrazine (an atrazine 

breakdown product or degradate), prometon, simazine, and 

dieldrin (fig. 18; table 11). Concentrations of atrazine in 

ground water were less than 3 μg/L, which is the U.S. 

Environmental Protection Agency (1993) maximum 

contaminant level for drinking water. The highest atrazine 

concentration (0.12 μg/L) in ground water was found in a 

water sample from well THC-S46 in the surficial aquifer 

system. An atrazine concentration of 1.58 μg/L was found 

in water from a nearby retention pond (62SRP-POND) and 

0.124

0.084

0.044

0.004

Atrazine

Deethylatrazine

Prometon

Simazine

Dieldrin

PSW (10/02)

PSW (1/04)

PSW (9/04)

PSW (10/04)

WP-F150

113RC-H50

THC-S46

WP-S64 (8/04)

WP-S64 (1/04)

113RC-S35

Ground Water

CONCENTRATION, IN

MICROGRAMS PER LITER

2.004

1.604

1.204

0.804

0.404

0.004

62SRPPONDMASPOND

LRPPONDRIVER

Surface Water

CONCENTRATION, IN

MICROGRAMS PER LITER

Atrazine

Deethylatrazine

Prometon

Figure 18. Pesticides detected in ground-water samples and 

surface-water samples from the Temple Terrace, Florida, study 

area.
52 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

Site

name

Sample 

date Atrazine Deethylatrazine Prometon Simazine Dieldrin

TTP-4 10/21/02 0.010 E0.009 E0.003 

TTP-4 01/28/04 0.007 E0.005 E0.004 

TTP-4 09/22/04 E0.004 

TTP-4 10/21/04 0.014 E0.012 E0.004 

THC-S46 12/18/03 0.120 E0.051 

WP-S64 01/14/04 0.009 E0.011 E0.003 E0.007

WP-S64 08/04/04 0.031 E0.033 0.0076 .00700 0.0500

WP-F150 08/04/04 0.008

113RC-S35 12/11/03 0.004

113RC-H50 12/9/03 E0.002

62SRP-POND 06/21/05 1.580 E0.184 0.0190 

MAS-POND 06/21/05 0.530 E0.020

LRP-POND 06/21/05 0.031 E0.013

HRIV-RR 06/22/05 0.038 E0.008 E0.007

Table 11. Concentrations of pesticides detected in ground-water and surface-water samples.

[Concentrations are in micrograms per liter (μg/L). Blank cell denotes compound not detected; E, estimated 

concentration, below laboratory reporting level]

could be a source for the elevated concentration in the shallow 

surficial aquifer system water sample (THC-S46). Focused 

recharge beneath stormwater retention ponds may contribute 

pesticides and other organic contaminants to water in the 

surficial aquifer system, which ultimately could move downward to the Upper Floridan aquifer under natural gradients 

or during pumping stresses. Low concentrations of atrazine, 

deethylatrazine, and prometon were found in water from 

public-supply well TTP-4. Atrazine was detected in four 

samples from TTP-4, whereas deethylatrazine and prometon 

were detected in three of four samples. Prometon was the only 

pesticide detected in any monitoring well in the Upper Floridan aquifer (WP-F150), which is open to a similar interval as 

TTP-4. Water from WP-F150 is younger than that from other 

Upper Floridan aquifer monitoring wells, indicating that there 

could be a connection between this zone in the aquifer and 

the overlying surficial material. This possibility is explored in 

more detail in the subsequent discussion of water chemistry 

from depth-interval sampling. Similar detections of pesticides 

in water from TTP-4 and from surficial aquifer system wells 

indicate the likely contribution of water in the surficial aquifer 

system to water withdrawn during pumping by TTP-4. 

Dieldrin, a known carcinogen, has a risk specific dose 

(RSD4) level of 0.2 μg/L at the 10-4 (one in 10,000) cancer risk 

level (U.S. Environmental Protection Agency, 1993; Toccalino and others, 2004). Trace concentrations of dieldrin were 

detected in water from WP-S64 and 62SRP-S34 (0.007 and 

0.049 μg/L), but were less than a factor of 4 lower than the 

RSD4 level.

Most pesticide detections in water from community 

supply wells in the northern Tampa Bay area included atrazine and deethylatrazine (Metz and others, 2007). Atrazine is 

highly mobile in sandy soils and widely used as an herbicide 

along road rights-of-way and lawns. Several studies have 

shown that atrazine can persist in ground water for long 

periods of time (Denver and Sandstrom, 1991; Barbash and 

others, 1999).

Sulfur Species and Hydrogen Sulfide

Differences in sulfate concentrations and delta sulfur-34 

(δ34S) of sulfate were useful in distinguishing sources of water 

and solutes in monitoring wells and the public-supply well. 

Concentrations of δ34S values for ground-water samples were 

highly variable, ranging from +5.7 per mil in water from the 

surficial aquifer system to +26.2 per mil for the Upper Floridan aquifer (fig. 19; table 6). This large range likely reflects 

the sulfur isotopic composition of various possible sources of 

sulfate, including dissolution of terrestrial evaporite minerals (gypsum and anhydrite), oxidation of sulfide minerals or 

organic sulfides, atmospheric precipitation of ocean-derived 

aerosols, and atmospheric precipitation of windblown sulfate 

dust from soils. Localized anthropogenic sources (that is, 

industrial emissions and fertilizers) could result in isotopically 
Occurrence of Anthropogenic and Naturally Occurring Contaminants in Ground-Water Samples 53

light sulfate (Sacks, 1996). The δ34S content of oceanic sulfate 

(and hence evaporite minerals that precipitate from the ocean) 

at any given time in the geologic past is related to several 

processes including the composition of sulfate in 

rivers that enters the ocean, sulfate reduction, and removal 

from the ocean (Pearson and Rightmire, 1980). Sulfate in 

modern ocean water has a δ34S value of +20 per mil. All 

waters in this study show increasing sulfate to chloride ratios 

with increasing sulfate concentration (fig. 20). Solution of 

evaporite minerals (gypsum and anhydrite) would produce this 

water composition.

A plot of δ34S values of dissolved sulfate relative to 

sulfate concentrations indicates two distinct groups of waters 

from the Upper Floridan aquifer (fig. 19). Group 1 has δ34S 

values that range from about +21 to +26 per mil with 

variable sulfate concentrations (less than 1 to 400 mg/L). 

Group 2 has much lower δ34S values (+5 to 16.8 per mil) and 

sulfate concentrations (generally less than 120 mg/L), and are 

isotopically similar to water from the surficial aquifer system 

and intermediate confining unit. Differences in median chemical composition are consistent with the sulfur isotopic composition and sulfate concentrations between these two groups 

(tables 5 and 6). The higher median saturation index with 

respect to gypsum for Group 1 (-0.92) compared to Group 2 

(-1.49) is consistent with the higher δ34S values that reflect 

dissolution of sulfate evaporite minerals. The δ34S values for 

30

20

10

0

0 100 200 300 400 500

SULFATE, IN MILLIGRAMS PER LITER

DELTA SULFUR-34, IN PER MIL

10

1

0.1

0.01

0.001

HYDROGEN SULFIDE CONCENTRATION, IN MILLIGRAMS PER LITER

Upper Floridan aquifer

Intermediate confining unit

Stormwater retention ponds

Surficial aquifer system

TTP-4

Sulfate Concentrations

Hydrogen Sulfide Concentrations

Upper Floridan aquifer

Intermediate confining unit

Surficial aquifer system

GROUP 2

variable isotopic

composition for

Upper Floridan

aquifer, similar to

that for surficial

aquifer system and

intermediate

confining unit

GROUP 1

dissolution of sulfate evaporate

minerals in Upper Floridan aquifer

Figure 19. Sulfate concentrations and delta sulfur-34 of sulfate in water samples from the surficial aquifer 

system, intermediate confining unit, Upper Floridan aquifer, and retention ponds in the Temple Terrace, 

Florida, study area.

MAS-POND

100

10

1

0.1

0.01

0.01 0.1 1 10 100

SULFATE CONCENTRATION, IN MILLIMOLES PER LITER

SULFATE TO CHLORIDE EQUIVALENT RATIO

Volumeweighted

rainfall

(2003)

Gypsum dissolution

Mixing with seawater

Upper Floridan aquifer

EXPLANATION

Intermediate confining unit

Ponds

Suficial aquifer system

Figure 20. Relation between sulfate-to-chloride ratios and 

sulfate concentrations in water from the surficial aquifer system, 

intermediate confining unit, and Upper Floridan aquifer in the 

Temple Terrace, Florida, study area.
54 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

Group 1 waters are slightly higher than those of samples of 

sulfate evaporite minerals from the Upper Floridan aquifer that 

range from +19 to +22 per mil (Pearson and Rightmire, 1980). 

Group 1 waters also have higher median concentrations of 

hydrogen sulfide and dissolved organic carbon and lower dissolved oxygen, which indicate sulfate reduction reactions and 

isotope fractionation that could result in enrichment of the δ34S 

in the aqueous phase. Waters from the surficial aquifer system, 

intermediate confining unit, and Floridan aquifer system with 

lower sulfate concentrations and lower δ34S likely represent 

values typical of rainfall with some excess sulfate (Pearson 

and Rightmire, 1980). Water samples from public-supply 

well TTP-4 have δ34S values and sulfate concentrations that 

are midway between the two end member values, and likely 

indicate a mixture of water from these two different groups 

(fig. 19). 

High sulfate concentrations could be related to upwelling 

that likely is enhanced by preferential vertical flow through 

fractures and faults that connect deep and shallow parts of the 

Upper Floridan aquifer (Sacks, 1996). Fractures and faults are 

associated with the structural high of the Ocala Platform that is 

present throughout the northern and central parts of peninsular 

Florida (Faulkner, 1973). Diffusion also may account for 

the transport of sulfate-rich ground water within the more 

stagnant deeper part of the Upper Floridan aquifer in westcentral Florida (Sacks, 1996). 

Radon-222 and Uranium

Concentrations of radon-222 were highly variable in 

the surficial aquifer system, intermediate confining unit, and 

Upper Floridan aquifer, but were generally higher in water 

samples from the surficial aquifer system and intermediate 

confining unit than from the Upper Floridan aquifer (table 6; 

fig. 21). Median concentrations were 2,440, 2,100, and 

645 pCi/L (picocuries per liter) for water samples from the 

surficial aquifer system, intermediate confining unit, and 

Upper Floridan aquifer system, respectively. Water from 

public-supply well TTP-4 had a radon-222 concentration of 

780 pCi/L, which is slightly higher than the median concentration in water from monitoring wells tapping the Upper Floridan aquifer. In response to human health concerns regarding 

ingestion of radon in drinking water, the U.S. Environmental 

Protection Agency has proposed new regulations to protect 

people from exposure to radon. The proposed maximum 

contaminant level for community water systems using ground 

water is 300 pCi/L, and the proposed alternative maximum 

contaminant level is 4,000 pCi/L. The U.S. Environmental 

Protection Agency (1999) expects that community water 

systems serving 10,000 persons or less would meet the alternative maximum contaminant level of 4,000 pCi/L; however, 

radon-222 concentrations in water from the public-supply well 

and most monitoring wells would exceed the lower 300 pCi/L 

maximum contaminant level. Sowerby and others (2000) 

estimated that 44 ±6 percent of the community water systems 

in Florida using ground water would exceed the 300-pCi/L 

maximum contaminant level for radon. 

Uranium concentrations also were variable in water samples from the three hydrogeologic units, and median uranium 

concentrations in water samples were 0.96, 0.85, and 2.4 μg/L 

from the surficial aquifer system, intermediate confining unit, 

and Floridan aquifer, respectively (table 12; fig. 22). Uranium 

concentrations in water from the public-supply well and from 

monitoring wells in the three hydrogeologic units were below 

the U.S. Environmental Protection Agency maximum contaminant level of 30 μg/L for drinking water. Higher median 

uranium concentrations were found in water samples from 

the Upper Floridan aquifer compared to samples from the 

surficial aquifer system or intermediate confining unit, which 

was unexpected given that redox conditions are anoxic in the 

Upper Floridan aquifer and the mobility of uranium is lower 

in reducing conditions. However, the formation of uranyl 

di- and tri-carbonate complexes in neutral and alkaline solutions (Langmuir, 1978) may account for the higher uranium 

concentrations found in the Upper Floridan aquifer compared 

to the surficial aquifer system and intermediate confining 

unit. Speciation calculations using the geochemical computer 

modeling program PHREEQC (Parkhurst and Appelo, 1999) 

indicate that uranium (IV) is present as the U(OH)4 complex 

and uranium (VI) is present as the tri-carbonate complex 

carbon anhydrase/uranium dioxide/carbon ion, Ca2UO2(CO3)

3

, 

in water from the Upper Floridan aquifer. The microbially 

mediated reduction of uranium (VI) in anoxic waters has been 

shown to decrease substantially when Ca-UO2-CO3 complexes 

are present (Brooks and others, 2003). 

0

20

40

60

80

100

0

RADON-222, IN PICOCURIES PER LITER

WELL DEPTH, IN METERS

BELOW LAND SURFACE

Surficial aquifer system

Intermediate confining unit

Upper Floridan aquifer

TTP-4

1,000 2,000 3,000 4,000

Figure 21. Radon-222 concentrations with well depth below land 

surface for the surficial aquifer system, intermediate confining 

unit, and Upper Floridan aquifer in the Temple Terrace, Florida, 

study area.
Occurrence of Anthropogenic and Naturally Occurring Contaminants in Ground-Water Samples 55

The dominant uranium species in all ground-water 

samples from the Upper Floridan aquifer is the neutral complex, Ca2

UO2(CO3)

3

. However, at two surficial aquifer system 

sites (LP-S30 and QRP-S20) where calcium concentrations 

and saturation indices with respect to calcite were relatively 

low, the dominant uranium species included uranyl mono- and 

di-carbonate complexes (UO2CO3, UO2(CO3)

2

-2) and UO2+2. 

Uranium concentrations are higher in acid leachates of solidphase material from the surficial aquifer system and intermediate confining unit compared to Floridan aquifer system material (table 4) based on acid extractions using 10-percent nitric 

acid and 6 N hydrochloric acid. Uranium concentrations in 

6 N hydrochloric acid leachates of solid-phase material were 

higher in samples of the Upper Floridan aquifer limestone 

(3.4-5.0 mg/kg) and from the LP site (7.7 mg/kg) compared to 

the milder acid extraction using 10-percent nitric acid 

(table 4). 

No correlation was found between radon-222 and 

uranium concentrations, even though radon-222 is a daughter product of the decay series for uranium-238. Different 

mechanisms of radon-222 emanation from clastic sediments 

and solid limestone (Cecil and Green, 2000) and chemical 

factors affecting uranium solubility (Langmuir, 1978; Osmond 

and Cowart, 2000) may account for the lack of a correlation 

between these two radiochemicals. 

Oxic

10,000

1,000

100

10

1

0.1

0.01

Anoxic

ARSENIC, IN

MICROGRAMS PER LITER

CONCENTRATION

Maximum

90th percentile

75th percentile

Median

25th percentile

10th percentile

Minimum

TTP-4URANIUM, IN MICROGRAMS PER LITER

IRON, IN

MICROGRAMS PER LITER

DISSOLVED ORGANIC CARBON,

IN

HYDROGEN SULFIDE, IN

MILLIGRAMS PER LITER

MILLIGRAMS PER LITER

RADON-222, IN

PICOCURIES PER LITER

Maximum

90th percentile

75th percentile

Median

25th percentile

10th percentile

Minimum

TTP-4

ARSENIC, IN

MICROGRAMS PER LITER

URANIUM, IN

MICROGRAMS PER LITER

IRON, IN

MICROGRAMS PER LITER

DISSOLVED ORGANIC CARBON,

IN

HYDROGEN SULFIDE, IN

MILLIGRAMS PER LITER

MILLIGRAMS PER LITER

RADON-222, IN

PICOCURIES PER LITER

Figure 22. Median concentrations of radon-222, arsenic, uranium, hydrogen sulfide, iron, and dissolved organic carbon in oxic and 

anoxic water from monitoring wells and the public-supply well in the Temple Terrace, Florida, study area.
56 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water Site name Aquifer or hydrogeologic unit Site identifier Sample date Sample time P01000 P01005 P01020 P01046 P01056 P01080 P01106 P22703 P62452 P62453 Arsenic Barium Boron Iron Manganese Strontium Alumi- num Uranium Arsenic (III) Arsenic (V) BBP-S45 SAS 280228082231501 8/11/2004 1200 E5 2.9 BBP-S45 SAS 280228082231501 12/9/2004 1300 1.4 10 12 <6 0.5 92.1 3 1.63 THC-F197 UFA 280241082224401 1/15/2004 1400 1.9 19 23 90 15.3 3780 3 2.89 1.1 1.3 THC-F75 UFA 280241082224402 1/12/2004 1500 1.1 22 19 111 85.7 1200 10 1.46 <1 <1.2 THC-F75 UFA 280241082224402 1/28/2004 1300 THC-S46 SAS 280241082224403 12/18/2003 1300 2.6 44 10 979 672 273 3 1.51 2 E0.9 THC-S46 SAS 280241082224403 8/5/2004 1200 984 460 THC-S46 SAS 280241082224403 11/17/2004 1600 654 345 THC-S46 SAS 280241082224403 6/14/2005 1700 662 261 62SRP-F160 UFA 280241082230701 11/2/2004 1200 3.1 18 28 E4 2.8 666 7.13 <1 2.3 62SRP-F160 UFA 280241082230701 6/20/2005 1600 62SRP-H55 ICU 280241082230702 11/3/2004 1700 0.3 17 15 E3 2.3 68.9 2 0.26 <1 <1.2 62SRP-S34 SAS 280241082230703 8/12/2004 930 <6 4 62SRP-POND POND 280242082230800 6/21/2005 1220 47 27.9 MAS-R-F160 UFA 280242082232401 11/3/2004 1200 2 47 25 <6 2.8 566 2 5.39 <1 1.6

MAS-R-F160 UFA 280242082232401 6/16/2005 1040 91 26.7MAS-R-F64 UFA 280242082232403 2/16/2005 1300 0.6 13 11 <6 1.5 64.1 15 2.53 <1 <1.2MAS-R-F64 UFA 280242082232403 6/16/2005 1100 <6 E0.6

Table 12. Concentrations of trace elements and arsenic species As(III) and As(V) in ground-water samples.[SAS, surficial aquifer system; ICU, intermediate confining unit; UFA, Upper Floridan aquifer. Concentrations are shown in micrograms per liter. E, concentration measured below analytical method reporting level; P code, U.S. Environmental Protection Agency STORET code; <, less than]
Occurrence of Anthropogenic and Naturally Occurring Contaminants in Ground-Water Samples 57

Site

name

Aquifer or

hydrogeologic 

unit

Site

identifier

Sample

date

Sample

time

P01000 P01005 P01020 P01046 P01056 P01080 P01106 P22703 P62452 P62453

Arsenic Barium Boron Iron Manganese Strontium Alumi- num Uranium Arsenic (III) Arsenic (V)

MAS-POND POND 280242082232900 6/21/2005 1100 35 2.8TTP-4 UFA 280244082232001 10/21/2002 1600 3.5 12 26 24 2.2 1230 <2 2.97TTP-4 UFA 280244082232001 1/28/2004 1600 3.2 14 34 25 2.5 1260 E1 3.61 2 E1.2TTP-4 UFA 280244082232001 10/21/2004 1500 3.2 13 28 6 1.8 1100 <2 3.47 <1 2.6TTP-4 UFA 280244082232001 2/16/2005 1600 44 6.5TTP-4 UFA 280244082232001 6/20/2005 1600 31 3.4WP-F299 UFA 280247082231901 1/22/2004 1600 12.6 20 25 79 7 3840 3 3.97 5.6 7.3WP-F299 UFA 280247082231901 8/3/2004 1400 2.5 20 30 108 6.1 3980 2 1.31 1.1 E1.1WP-F150 UFA 280247082231902 1/28/2004 0WP-F150 UFA 280247082231902 1/28/2004 1300 16.5 14 36 12 6.8 1690 E2 1.09 14.1 2.9WP-F150 UFA 280247082231902 8/4/2004 1100 5.6 13 35 24 5.3 1720 E1 0.62 5.2 E1.1WP-S64 SAS 280247082231903 1/14/2004 1500 0.4 22 32 <6 0.4 254 15 2.11 <1 E0.7WP-S64 SAS 280247082231903 8/4/2004 1600 0.2 20 35 <6 E0.1 245 9 1.61 <1 <1.2WP-S64 SAS 280247082231903 11/18/2004 1200 E3 <0.6WP-S64 SAS 280247082231903 6/14/2005 1130 E3 <0.6RP-F103 UFA 280249082220701 12/2/2003 1500 4.9 14 21 75 8.8 2460 8 2.23 3.1 1.4RP-F77 UFA 280249082220702 12/3/2003 1300 14.6 14 22 127 9 1890 3 4.32 10 3.9RP-S20 SAS 280249082220703 12/4/2003 1400 2.4 63 39 3910 939 175 2 0.77 1.2 1.3RP-S20 SAS 280249082220703 8/11/2004 1500 330 155RP-S20 SAS 280249082220703 11/16/2004 1500 657 194RP-S20 SAS 280249082220703 6/16/2005 1500 644 410

Table 12. Concentrations of trace elements and arsenic species As(III) and As(V) in ground-water samples.—Continued[SAS, surficial aquifer system; ICU, intermediate confining unit; UFA, Upper Floridan aquifer. Concentrations are shown in micrograms per liter. E, concentration measured below analytical method reporting level; P code, U.S. Environmental Protection Agency STORET code; <, less than]
58 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water Site name Aquifer or hydrogeologic unit Site identifier Sample date Sample time P01000 P01005 P01020 P01046 P01056 P01080 P01106 P22703 P62452 P62453 Arsenic Barium Boron Iron Manganese Strontium Alumi- num Uranium Arsenic (III) Arsenic (V) LRP-F160 UFA 280250082233001 11/4/2004 1300 2.4 17 24 9 14.2 939 8 2 1.5 E0.8 LRP-H105 UFA 280250082233002 12/7/2004 1600 1.5 11 20 <6 5.8 507 18 0.57 E0.9 E1 LRP-S25 SAS 280250082233003 8/10/2004 1100 6 5.8 LRP-S25 SAS 280250082233003 6/15/2005 1500 11 14.8 LRP-POND POND 280250082233200 6/21/2005 915 E5 E0.4 JARP-S40 SAS 280251082224201 6/27/2005 1030 E5 197 GARC-F200 UFA 280253082223801 12/16/2003 1300 1.7 24 22 57 70.1 4,110 E2 1.74 1.1 E1 GARC-F75 UFA 280253082223802 12/15/2003 1400 0.7 18 9 23.2 2,990 11 0.23 0.8 E0.8 GARC-S23 SAS 280253082223803 12/17/2003 1200 0.4 38 16 E6 92.4 662 20 1.14 <1 <1.2 GARC-S23 SAS 280253082223803 8/5/2004 1600 E4 32.8 GARC-S23 SAS 280253082223803 11/17/2004 1100 7 30.1 GARC-S23 SAS 280253082223803 6/13/2005 1115 7 57.7 113RC-F190 UFA 280301082222701 12/8/2003 1300 6 19 26 172 38.4 4,080

M 2.25 3.7 1.8

113RC-H50 ICU 280301082222702 12/9/2003 1300 7.9 14 21 156 54.1 1,580 3 4.66 4 3.4113RC-S35 SAS 280301082222703 12/11/2003 1300 E0.2 14 15 <6 5.1 489 2 0.64 <1 <1.2113RC-S35 SAS 280301082222703 8/12/2004 1300 <6 E0.5113RC-S35 SAS 280301082222703 11/16/2004 1300 E4 2113RC-S35 SAS 280301082222703 6/15/2005 1100 <6 <0.6

Table 12. Concentrations of trace elements and arsenic species As(III) and As(V) in ground-water samples.—Continued[SAS, surficial aquifer system; ICU, intermediate confining unit; UFA, Upper Floridan aquifer. Concentrations are shown in micrograms per liter. E, concentration measured below analytical method reporting level; P code, U.S. Environmental Protection Agency STORET code; <, less than]
Occurrence of Anthropogenic and Naturally Occurring Contaminants in Ground-Water Samples 59

Site 

name

Aquifer or

hydrogeologic 

unit

Site

identifier

Sample

date

Sample

time

P01000 P01005 P01020 P01046 P01056 P01080 P01106 P22703 P62452 P62453

Arsenic Barium Boron Iron Manganese Strontium Alumi- num Uranium Arsenic (III) Arsenic (V)

LP-H40 ICU 280303082230901 8/10/2004 1500 <6 <0.8LP-H40 ICU 280303082230901 12/8/2004 1500 0.3 17 22 <6 0.3 90 7 1.12 <1 <1.2LP-S30 SAS 280303082230902 8/10/2004 1200 6 2.3LP-S30 SAS 280303082230902 11/1/2004 1600 <0.2 22 22 10 3.6 33.3 142 0.07LP-S30 SAS 280303082230902 6/21/2005 1130 E6 1.4QRP-S20 SAS 280311082223901 8/11/2004 1345 349 8.7QRP-S20 SAS 280311082223901 11/15/2004 1700 0.3 15 38 48 9.3 96.2 8 0.05QRP-S20 SAS 280311082223901 6/21/2005 1630 332 23.1HRIV-RR RIVER 280248082220200 8/30/2005 0.16 0.014TTP-4-140-NP UFA 280244082232001 10/27/2004 1600 11.7 14 26 <6 3 788 <2 4.87 E0.8 8.7TTP-4-160-NP UFA 280244082232001 10/27/2004 1800 4.2 16 27 <6 0.8 515 <2 5.34 <1 2.6TTP-4-160-P UFA 280244082232001 10/28/2004 1100 18.9 14 24 E3 2 912 <2 5.38 E0.6 14.2TTP-4-140-P UFA 280244082232001 10/28/2004 1400 16 14 24 E5 2.2 934 <2 5.24 2.1 10.7TTP-4-125-P UFA 280244082232001 10/28/2004 1600 15.3 14 26 9 1.7 937 <2 4.93 3.3 9.3TTP-4-entire-P UFA 280244082232001 10/21/2004 1500 3.2 13 28 6 1.8 1,100 <2 3.47 1.5 E1

Table 12. Concentrations of trace elements and arsenic species As(III) and As(V) in ground-water samples.—Continued[SAS, surficial aquifer system; ICU, intermediate confining unit; UFA, Upper Floridan aquifer. Concentrations are shown in micrograms per liter. E, concentration measured below analytical method reporting level; P code, U.S. Environmental Protection Agency STORET code; <, less than]
60 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

Arsenic Concentrations and Speciation

Water samples from wells in the surficial aquifer system 

and intermediate confining unit had arsenic concentrations less 

than 8 μg/L (fig. 23A). Most water samples from monitoring 

wells in the Upper Floridan aquifer were less than the 10-μg/L 

maximum contaminant level for drinking water; however, 

water samples from WP-F299, WP-F150, and RP-F77 had 

arsenic concentrations that ranged from 12.6 to 16.5 μg/L. 

Higher median arsenic concentrations were found in water 

samples from the Upper Floridan aquifer (4.6 μg/L) compared 

to samples from the intermediate confining unit (0.9 μg/L) 

and the surficial aquifer system (0.4 μg/L). The slightly higher 

arsenic concentrations in the water samples from the surficial 

aquifer system and intermediate confining unit generally were 

associated with higher concentrations of iron, which indicate 

the likely association of arsenic with iron oxyhydroxide coatings on sands and clay material (Pichler and others, 1999). 

Arsenic concentrations in water samples from the publicsupply well ranged from 3.2 to 3.5 μg/L when collected using 

the in-line turbine pump; however, during depth-interval 

sampling of the public-supply well borehole, concentrations 

ranged from 4.2 to 18.9 μg/L. These variations in arsenic 

concentrations with depth in the public-supply wells were 

observed during different pumping conditions and are discussed in more detail in the following section on sources and 

mixing of water in the public-supply well.

Under reducing conditions in the Upper Floridan aquifer 

and for water from 113-RC-H50 in the intermediate confining 

unit, most water samples had higher arsenic (III) concentrations than arsenic (V) concentrations (fig. 23B). In contrast, 

water samples from the public-supply well had arsenic (V) 

concentrations that tended to be higher than arsenic (III) concentrations, which most likely indicates different redox conditions due to the downward movement of oxygenated water 

from the surficial aquifer system through a highly transmissive 

zone in the limestone of the Upper Floridan aquifer. Mobilization of arsenic may result from the formation of arsenocarbonate complexes under anaerobic conditions (Kim and 

others, 2000) and/or oxidation of finely disseminated pyrite 

in the limestone that composes the Upper Floridan aquifer 

(Price and Pichler, 2006). Concentrations of both arsenic (III) 

and arsenic (V) in water from the oxic surficial aquifer system 

generally were near the method reporting level for both arsenic 

species (table 12). Arsenic concentrations in water from monitoring wells in the three hydrogeologic units generally were 

less than the 10-μg/L maximum contaminant level for drinking 

water (table 12).

Temporal Variability in Water 

Chemistry from Surficial Aquifer Wells 

and the Public-Supply Well

Selected monitoring wells were sampled several times 

during 2003-05 during different hydrologic conditions to 

obtain information about temporal variability in water quality. 

Temporal variations in water quality are presented for three 

monitoring wells in the surficial aquifer system (RP-S20, 

WP-S64, and GARC-S23) that were sampled four times 

before and after three tropical cyclones that passed through 

the area in summer 2004 (fig. 24). Additionally, water-quality 

variations were evaluated for TTP-4 based on five samples 

collected during 2002-05. Near or slightly below normal 

amounts of monthly rainfall were recorded prior to the earliest 

samples collected from the surficial aquifer system wells in 

December 2003 and the public-supply well in October 2002. 

During June through September 2004, however, about 109 cm 

of rainfall were recorded at the NOAA station at the Tampa 

airport, which was about 43 cm above normal rainfall for 

these 4 months. Ground-water levels increased substantially 

during and after this period. Water levels increased more than 

Surficial aquifer system

Intermediate confining unit

Upper Floridan aquifer

TTP-4

100

80

60

40

20

0

0 5 10 15 20

ARSENIC CONCENTRATION, IN MICROGRAMS PER LITER

WELL DEPTH, IN METERS

BELOW LAND SURFACE 15

10

5

0

0 5 10 15

ARSENIC (III) CONCENTRATION, IN MICROGRAMS PER LITER

ARSENIC (V) CONCENTRATION,

IN MICROGRAMS PER LITER

1:1 line

(A)

(B)

Surficial aquifer system

Intermediate confining unit

Upper Floridan aquifer

TTP-4

Figure 23. Arsenic concentrations with well depth and arsenic 

species (arsenic (III) and arsenic (V) concentrations) in water 

samples from wells in the surficial aquifer system, intermediate 

confining unit, and Upper Floridan aquifer in the Temple Terrace, 

Florida, study area, October 2004.
Temporal Variability in Water Chemistry from Surficial Aquifer Wells and the Public-Supply Well 61

3 m in well GARC-S23 (fig. 24), and it is assumed that water 

levels increased about the same amount in wells RP-S20 and 

WP-S64, although data are missing where peak water levels 

would be expected to occur (fig. 24). No water-level data were 

available for TTP-4.

Substantial variations in some chemical constituents 

were observed in water from monitoring wells in the surficial 

aquifer system in response to this increased recharge. Chloride 

concentrations in water samples from three wells decreased 

from summer 2004 to winter 2004-05 following the recharge 

pulse from high rainfall and corresponding peak in water-level 

elevation in October 2004. Nitrate-N concentrations increased 

in WP-S64 from January to August 2004, but concentrations 

decreased at GARC-S23 during the same period. Nitrate-N 

concentrations in water samples from two other monitoring wells in the surficial aquifer system, 113RC-S35 and 

BBP-S45, also increased from January to August 2004, 

but decreased in subsequent samples from these two wells. 

Nitrate-N concentrations in RP-S20, located near the Hillsborough River, remained below the detection limit, as reducing conditions persisted during December 2003 to July 2005. 

Dissolved organic carbon concentrations were constant in 

WP-S64 through December 2004 and increased substantially 

in the June 2005 sample. Nitrate-N concentrations decreased 

during this same period in water samples from WP-S64. 

Dissolved oxygen concentrations increased in water samples from GARC-S23 (2.5 to 4.5 mg/L), WP-S64 (5.4 to 6.7 

mg/L), and TTP-4 (0.2 to 0.7 mg/L) in August and September 

2004 during and following the above-normal rainfall in June 

through September (table 5). The increase in dissolved oxygen 

concentrations likely resulted from recent recharge of water 

containing elevated levels of oxygen compared to lower levels 

in ground water prior to the excess rainfall period. Dissolved 

oxygen concentrations decreased in water from RP-S20 (2.2 to 

0.3 mg/L) in fall 2004, which may indicate the influx of river 

water with elevated dissolved organic carbon and subsequent 

consumption of oxygen as water moves toward this well. 

CONCENTRATION, IN

MILLIGRAMS PER LITER

RAINFALL, IN CENTIMETERS

WATER-LEVEL ELEVATION, IN

METERS ABOVE NAVD 1988

8.5

8.0

7.5

7.0

6.5

6.0

5.5

RP-S20

Jan

Jul

Jan

Jul

Jan

Jul

Jan

Nov

Jan

Jul

Oct

RAINFALL, IN CENTIMETERS

50

40

30

20

10

CONCENTRA

0

TION, IN MILLIGRAMS PER LITER30

25

20

15

10

5

0

30

25

20

15

10

5

0

75.0

62.5

50.0

37.5

25.0

12.5

0

2003 2004 2005

GARC-S23

CONCENTRATION, IN

MILLIGRAMS PER LITER

RAINFALL, IN CENTIMETERS

WATER-LEVEL ELEVATION, IN

METERS ABOVE NAVD 1988

30

28

26

24

22

20

18

20

16

12

8

4

0

50

40

30

20

10

0

RAINFALL, IN CENTIMETERS

WATER-LEVEL ELEVATION, IN

METERS ABOVE NAVD 1988

10.3

10.0

9.7

9.4

9.1

8.8

8.5

8.2

7.9

WP-S64

30

25

20

15

10

5

0

75.0

62.5

50.0

37.5

25.0

12.5

0

Rainfall

Nitrate-N

Dissolved organic carbon

EXPLANATION

Chloride concentration

Water level 2003 Apr

2002 2004 2005 Jan Apr Jul Oct Jan Apr

Jul

TTP-4

2006

Jan

Jul

Jan

Jul

Jan

Jul

Jan

2003 2004 2005 2006

Jan

Jul

Jan

Jul

Jan

Jul

Jan

2003 2004 2005 2006

CONCENTRATION, IN

MILLIGRAMS PER LITER

Figure 24. Temporal variability of chloride, nitrate-N, dissolved organic carbon, and ground-water levels in water samples collected 

from wells RP-S20, WP-S64, GARC-S23, and TTP-4 in the Temple Terrace, Florida, study area.
62 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

As seen from the temporal chemical variations described 

herein, hydrologic conditions greatly affect the occurrence and 

movement of anthropogenic and naturally occurring contaminants in ground water from the study area, particularly the 

surficial aquifer system. These variations in chemistry among 

monitoring wells in the surficial aquifer system are related 

in part to differences in unsaturated zone thickness, depth of 

well below the water table, possible interactions with surface 

water (such as the Hillsborough River or stormwater retention 

ponds), but also to source loading of anthropogenic contaminants from various land-use activities. Chemical constituents 

in water in surficial aquifer system wells show rapid responses 

to rainfall and recharge, but water from TTP-4 does not show 

similar fluctuations even though TTP-4 is withdrawing some 

water from the surficial aquifer system (see subsequent section). Additional studies would be helpful in separating out 

effects of pumping of TTP-4 and seasonal changes in recharge 

on water quality of the public-supply well in this dynamic 

system.

Sources and Mixing of Water in the 

Public-Supply Well

Based on the aforementioned differences in chemical and 

isotopic signatures in water from public-supply well TP-4 and 

monitoring wells in the three hydrogeologic units, the publicsupply well receives mixtures of water from both the surficial 

aquifer system and Upper Floridan aquifer. For example, six 

volatile organic compounds and four pesticides were detected 

in trace concentrations in water from the public-supply well, 

and these contaminants were detected more frequently in 

water samples from monitoring wells in the overlying surficial 

aquifer system than in water from monitoring wells in the 

Upper Floridan aquifer in the study area. Likewise, nitrate-N 

concentrations in the public-supply well were more similar to 

median concentrations in the surficial aquifer system than very 

low nitrate-N concentrations in the anoxic Upper Floridan 

aquifer (sulfate-reducing conditions). This section presents 

information about differences in water chemistry with depth in 

the open-hole interval of the public-supply well, and quantification of mixing proportions of water from the surficial 

aquifer system and Upper Floridan aquifer. 

Chemical Variations with Depth during 

Ambient and Pumping Conditions

Water samples were collected from three overlapping 

depth intervals in the public-supply well during ambient (nonstressed) and pumping (stressed) conditions to assess the effect 

of pumping on water quality. A low-flow submersible pump 

(Grundfos®) at a pumping rate of about 3.8 L/min was used 

to collect water-quality samples at three depth intervals under 

ambient and pumping conditions. A large-capacity submersible pump, used to simulate pumping conditions in the well, 

was lowered to 38 m (same depth as turbine pump), and water 

was pumped at 1,320 L/min (compared to about 2,650 L/min 

for the turbine pump). For ambient conditions, only the lowcapacity submersible pump was used to collect water samples 

(3.8 L/min). Samples were taken from the lowermost depth 

interval by placing the low-flow submersible pump at a depth 

of 48.8 m below land surface, which represents an interval 

(49.8-53.9 m) that includes the previously described highflow zones in the borehole. A second depth interval (43-53 m) 

was sampled by placing the pump at a depth of 43 m. A third 

depth interval (38-53 m) was sampled by placing the low-flow 

submersible pump at a depth of 38 m. Samples from this depth 

interval presumably represent water quality for the entire 38- 

to 53-m open-hole interval, and should have similar chemistry 

as water samples collected from the public-supply well borehole under regular pumping conditions using the in-line 

turbine pump (on October 21, 2004). Differences in water 

quality among the three overlapping intervals provide an 

indication of the contribution of water entering the open 

interval above the two high-flow zones. Samples from discrete 

zones would have been preferable; however, packers were 

not used due to the large variations in the diameter of the 

borehole; therefore, discrete zones could not be isolated for 

sampling.

Water samples collected from the three depth intervals 

were analyzed for multiple chemical and isotopic constituents 

(table 13). Field measurements also were made for pH, 

dissolved oxygen, specific conductance, temperature, alkalinity, and depth to water. There were substantial differences in 

the concentrations of chemical constituents at the three 

sampled depth intervals (table 13). For example, water 

samples from the 49- to 53-m zone collected during ambient conditions contained higher concentrations of nitrate-N, 

orthophosphate, radon-222, atrazine, and trichloromethane 

(chloroform) than water collected from the other depth zones 

during ambient conditions, and for the entire 38- to 53-m 

interval during pumping conditions. Additionally, lower 

concentrations were found in the 49- to 53-m interval for 

strontium, iron, manganese, and dissolved solids as well as 

lower values of delta nitrogen-15 (δ15N) of nitrate and delta 

sulfur-34 (δ34S) of sulfate during ambient conditions compared 

to samples from the entire 35- to 53-m interval during pumping conditions (with a turbine pump on October 21, 2004). 

During normal pumping conditions for the public-supply 

well (with the turbine pump), arsenic concentrations were 3.2 

to 3.5 μg/L in water samples collected in October 2002 and 

January 2004 and on October 21, 2004. The arsenic 

concentration in water from the lowermost (49-53 m) 

depth interval was 4.2 μg/L during ambient conditions on 

October 27, 2004. On the following day, however, and under 

pumping conditions, the arsenic concentration in water from 

this same interval was 19 μg/L. Similarly, higher arsenic 

concentrations were measured in water from the 43- to 53-m 

interval during pumping conditions (16 μg/L) compared to 

ambient conditions (12 μg/L). This indicates that arsenic 
Sources and Mixing of Water in the Public-Supply Well 63

Site

name

Depth interval 

sampled, 

meters below 

land surface

Sampling 

date

Sampling 

time

Temper

ature, 

degrees 

Celsius

Specific

conductance, μS/

cm

Dissolved 

oxygen,

mg/L

pH

Concentration, milligrams per liter

Bicarbonate Ammo- nium- nitrogen Nitrite- nitrogen Nitrate- nitrogen Orthophos- phate as phosphorus Dissolved organic carbon Calcium Magne- sium Sodium Potassium

TTP-4-entire-P 38-53 10/21/2004 1500 26 606 0.5 7.3 170 <0.04 0.008 1.4 0.018 0.9 98 8.4 11 1.0TTP-4-140-NP 43-53 10/27/2004 1600 26.4 577 0.8 7.3 180 <0.04 0.039 2.3 0.022 1.1 97 7.9 12 1.2TTP-4-160-NP 49-53 10/27/2004 1800 26.2 537 0.8 7.3 170 <0.04 0.011 3.6 0.024 0.8 90 7.7 13 1.2TTP-4-160-P 49-53 10/28/2004 1100 24.1 567 1.0 7.3 182 <0.04 0.035 1.8 0.014 0.9 102 8.4 12 1.2TTP-4-140-P 43-53 10/28/2004 1400 25.8 586 0.6 7.3 183 <0.04 0.02 1.7 0.016 0.9 101 8.2 12 1.2TTP-4-125-P 38-53 10/28/2004 1600 25.9 583 0.6 7.3 182 <0.04 0.013 1.7 0.022 0.9 100 8.7 12 1.2

Site 

name or 

number

Depth interval 

sampled, 

meters below 

land surface

Concentration, milligrams per liter Concentration, micrograms per liter

Dissolved 

solids,

mg/L

δ2H,

per mil Chloride Sulfate Fluoride Silica Arsenic Barium Boron Iron Manganese Strontium Aluminum Uranium Arsenic (III) Arsenic (V)

TTP-4-entire-P 38-53 25 116 0.3 13 3.2 13 28 6 1.8 1,100 <2 3.47 1.5 E1.0 380 -15.4TTP-4-140-NP 43-53 28 96 0.2 13 11.7 14 26 <6 3 788 <2 4.87 E0.8 8.7 344 -15.7TTP-4-160-NP 49-53 31 79 0.1 13 4.2 16 27 <6 0.8 515 <2 5.34 <1 2.6 333 -15.9TTP-4-160-P 49-53 28 103 0.2 13 18.9 14 24 E3 2 912 <2 5.38 E0.6 14.2 359 -16.0TTP-4-140-P 43-53 27 106 0.2 13 16.0 14 24 E5 2.2 934 <2 5.24 2.1 10.7 361 -15.4TTP-4-125-P 38-53 27 107 0.3 13 15.3 14 26 9 1.7 937 <2 4.93 3.3 9.3 355 -15.8

Site 

name or 

number

Depth interval 

sampled, 

meters below 

land surface

Concentration, per mil

Radon222,

pCi/L

δ34S

per mil

Hydrogen 

sulfide,

mg/L

Concentration, micrograms per liter

δ18O δ15N of nitrate δ18O of nitrate Hexa- zinone Prometon Deethyl- atrazine Atrazine Dieldrin Fipronil Fipronil sulfone Trichloro- methane Trichloro- ethylene

TTP-4-entire-P 38-53 -3.26 6.4 6.6 780 15.4 0.03 E0.006 E0.004 E0.012 0.014 <0.009 <0.016 <0.024 0.29 E0.045TTP-4-140-NP 43-53 -3.33 8.0 8.2 970 12.9 0 <0.013 E0.008 E0.020 0.017 E0.003 E0.005 <0.024 0.52 E0.026TTP-4-160-NP 49-53 -3.44 6.0 7.0 1,210 11.0 0.001 <0.013 E0.008 E0.026 0.02 E0.002 E0.005 E0.008 0.80 <0.038TTP-4-160-P 49-53 -3.24 8.9 8.9 1,060 13.5 0.008 <0.013 E0.008 E0.018 0.016 <0.009 <0.016 <0.024 0.44 E0.025TTP-4-140-P 43-53 -3.28 7.8 8.2 850 13.7 0 <0.013 E0.008 E0.017 0.015 E0.003 <0.016 <0.024 0.37 E0.032TTP-4-125-P 38-53 -3.28 7.7 8.0 990 13.9 0.001 <0.013 E0.008 E0.017 0.014 E0.003 <0.016 <0.024 0.35 E0.033

Table 13. Chemical properties of water samples collected from various depth intervals in the public-supply well. [Concentrations shown in milligrams per liter. Deethylatrazine is an atrazine degradate; δ15N, delta nitrogen-15; δ18O, delta oxygen-18; δ34S, delta sulfur-34; μS/cm, microsiemens per centimter; mg/L, milligrams per liter; pCi/L, picocuries per liter; P, pumping conditions; NP, nonpumping conditions; E, estimated concentration below laboratory reporting level; <, less than]
64 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

movement to the public-supply wells was enhanced during 

pumping from a transmissive (high-flow) zone in the Upper 

Floridan aquifer that was identified from geophysical logging 

of the public-supply well borehole. This enhanced transport of 

arsenic is consistent with a study of arsenic release from pyrite 

in the Suwannee Limestone, which tends to be most abundant 

in high porosity zones (Price and Pichler, 2006). That study 

found an average of 3.5 ppm (parts per million) of arsenic 

in samples from the Suwannee Limestone, which was about 

one third higher than the reported global average of 2.5 ppm 

for arsenic in limestone (Baur and Onishi, 1969). Price and 

Pichler (2006) also conclude that arsenic in excess of 2 ppm is 

associated with impurities in the Suwannee Limestone, such 

as trace minerals and organic matter. Furthermore, they found 

that framboidal pyrite in the Suwannee Limestone contains 

arsenic concentrations between 100 and 11,200 ppm, with an 

average concentration of 2,300 ppm from 25 samples. 

In the present study, low arsenic concentrations (0.06 to 

0.37 ppm) were found in acid extractions (10-percent nitric 

acid) of limestone rock samples from cores collected during 

well drilling at the Water Plant (WP) site. Higher concentrations of arsenic (0.13-1.4 mg/kg) were found in acid extractions of clayey sand samples from cores collected during 

drilling in the surficial aquifer system and intermediate 

confining unit (table 4). Kim and others (2000) found that 

carbonation of arsenic sulfide minerals results in the formation 

of arseno-carbonate complexes under anaerobic conditions, 

which may account for elevated levels of arsenic in carbonate 

rock aquifers.

Further information about the behavior and mobility 

of arsenic in ground water can be ascertained from arsenic 

speciation data. Arsenic (V) concentrations tended to be 

higher than arsenic (III) concentrations in the 49- to 53-m 

depth interval (table 13). This interval tended to have slightly 

higher concentrations of dissolved oxygen compared to the 

zones in the Upper Floridan aquifer and lower concentrations 

of hydrogen sulfide (table 5). Water in this zone likely is a 

mixture of oxygenated water from the surficial aquifer system 

and/or intermediate confining unit with anoxic water in the 

Upper Floridan aquifer. Slight increases in dissolved oxygen 

could enhance pyrite dissolution as seen on a larger scale during cycle testing at an aquifer storage and recovery facility in 

Tampa, Florida. Oxygen-rich recharge water was injected into 

the Suwannee Limestone, and water recovered during various cycle tests contained up to 130 μg/L of arsenic, although 

no arsenic speciation data were collected (Arthur and others, 

2002).

Concentration differences for arsenic and other chemical 

constituents between the 49- to 53-m zone and the other zones 

are consistent with water that moves downward from the surficial material into the highly transmissive zone in the Upper 

Floridan aquifer. Water from monitoring wells in the surficial 

aquifer system and intermediate confining unit in the contributing recharge area of the public-supply well contains higher 

concentrations of nitrate-N, trichloromethane, atrazine, and 

orthophosphate than water from monitoring wells in the Upper 

Floridan aquifer. Conversely, water from the surficial aquifer 

system and intermediate confining unit contains lower concentrations of dissolved solids, strontium, iron, and manganese 

than water from the Upper Floridan aquifer. The lower values 

of δ15N in water from the surficial aquifer system and from the 

49- to 53-m zone likely are related to little or no denitrification 

in the oxic surficial aquifer system material compared to that 

in the anoxic Upper Floridan aquifer. The lower δ34S in this 

zone also is more similar to lower median sulfur isotope values for water from the surficial aquifer system than from the 

Upper Floridan aquifer. Thus, it is likely that the transmissive 

zone at 49 to 53 m (high-flow rate) is hydraulically connected 

to the surficial aquifer system and receives a mixture of water 

from the surficial aquifer system and Upper Floridan aquifer. 

During pumping conditions, water from the 49- to 53-m zone 

is blended with water from other depth-interval zones, and 

concentrations are more similar to the other depth intervals 

(sampled during ambient and pumping conditions). 

Estimating Mixing Proportions of Water Using 

Geochemical Mass-Balance Modeling

Chemical and isotopic tracer data consistently indicate 

that the public-supply well withdraws water containing mixtures of the surficial aquifer system and the Upper Floridan 

aquifer. Concentrations of anthropogenic compounds, such as 

nitrate, volatile organic compounds, and pesticides are closer 

to those found in water from monitoring wells in the surficial 

aquifer system than from wells in the Upper Floridan aquifer. 

Likewise, concentrations of naturally occurring compounds 

in water from the public-supply well, such as radon-222, 

uranium, arsenic, dissolved organic carbon, and hydrogen 

sulfide, generally fall between those concentrations for water 

from the surficial aquifer system and Upper Floridan aquifer. 

Geochemical mass-balance modeling techniques (NETPATH; 

Plummer and others, 1994) were used to quantify mixing 

proportions of water in the public-supply well with water from 

the different hydrogeologic units and to calculate mass transfer 

associated with sources and sinks of major dissolved constituents. Input data to NETPATH includes solute concentrations 

in possible end members; that is, water samples from wells in 

the surficial aquifer system, intermediate confining unit, and 

Floridan aquifer sytsem and the mixture represented by the 

public-supply well. Information for the isotopic composition 

of soil gases and minerals also are included in the modeling 

(Plummer and others, 1994). The mass-transfer models are 

constrained by the concentration of the following dissolved 

constituents in end-member and mixed waters: carbon, sulfur, 

calcium, magnesium, and iron. In addition to these chemical constraints, an electron balance is included to account for 

conservation of electrons under redox conditions. The models contain the following phases: calcite, dolomite, gypsum, 

carbon dioxide, pyrite, amorphous iron oxide (represented by 

FeOOH), and organic matter (represented stoichiometrically 

by CH2O). Plausible mixing reaction models are valid within 
Sources and Mixing of Water in the Public-Supply Well 65

the constraints of available thermodynamic data and agreement between calculated and observed isotopic values. 

For a two-component mixture containing end-member 

waters from the surficial aquifer system and Upper Floridan 

aquifer, the fraction of surficial aquifer system water (FSAS) in 

the mixture is defined as:

 FSAS= (Ym – YUFA)/(YSAS– YUFA), (3)

where Ym, YSAS, and YUFA denote the concentrations of a 

selected constituent in the mixture, surficial aquifer system 

water, and Upper Floridan aquifer water, respectively. The 

chemical and isotopic composition of the two end members 

are represented by WP-S64 (surficial aquifer system water) 

and WP-F150 (Upper Floridan aquifer water), which are 

located within 1 km of the public-supply well. The mixing 

calculations are based on two principal assumptions: (1) the 

concentrations of constituent Y in the end members mix to 

produce the concentration of Y in the mixed public-supply 

well water during pumping conditions; and (2) the concentration of constituent Y is not modified by reactions after mixing 

has occurred. Calculations of mixing proportions were constrained using concentrations of SF6

, nitrate-N, and chloride. 

The calculated mixing proportions of surficial aquifer 

system water that mix with Upper Floridan aquifer water 

ranged from 30 to 62 percent for four plausible models 

(table 14). Mixing proportions were similar for models 

constrained using SF6 and chloride, both of which are considered to be nonreactive (conservative) tracers. These massbalance model mixing proportions are consistent with 

mixtures dominated by young waters (less than 8 years) in 

the public-supply well. Water from the public-supply well 

contains elevated concentrations of SF6 and 3H compared to 

monitoring wells in the Upper Floridan aquifer that contain 

mixtures dominated by older waters (greater than 60 years). 

These mass-transfer mixing models also indicated reactions 

involving dissolution of variable amounts of calcite, dolomite, and gypsum, degradation (oxidation) of organic carbon 

(CH2O), and carbon dioxide (carbonic acid) produced from 

microbial reactions (respiration and fermentation). The following equation is an example of the geochemical mass-balance 

reaction obtained using SF6 concentrations to determine the 

mixing proportions of waters from the surficial aquifer system 

(SAS) and Upper Floridan aquifer (UFA):

55 percent (SAS water) + 45 percent (UFA water) 

+ 0.32CaCO3 + 0.10CaMg(CO3)2

+ 0.12 CaSO4-2H20 +0.003FeOOH 

+ 0.36CO2 → TTP-4 water, (4)

where the coefficients in front of the various phases represent 

chemical mass transfer in millimoles per kilogram of solution. 

Dissolution of the limestone matrix of the Upper Floridan 

aquifer in the study area is consistent with water from WP-S64 

and WP-F150, which is slightly under or at saturation with 

respect to calcite and undersaturated with respect to dolomite. 

The sensitivity of the mass-transfer coefficients in 

table 14 is about 0.05 mmol/kg (millimoles per kilogram), 

based on consideration of laboratory analytical errors, variability in mineral stoichiometry, and temporal variability in 

the concentration of major ions in ground water. Results are 

reported to the nearest 0.01 mmol/kg. As a means of checking 

the sensitivity of the models to uncertainties in data, comparisons were made of the modeled δ13CDIC composition of 

dissolved inorganic carbon (DIC) and δ34S of sulfate with the 

measured (observed) concentration data for these two isotopes. 

Model-calculated values of δ13CDIC and δ34S typically agreed 

with observed values within ±0.3 per mil. The following δ13C 

values were used in the models for various carbon sources and 

sinks: calcite, 0 ±1 per mil; dolomite, 0 per mil (Plummer and 

others, 1994); and carbon dioxide and CH2O, -25 ± 5 per mil 

(Rightmire and Hanshaw, 1973; Burchardt and Fritz, 1980). 

Mass-transfer coefficients calculated from the mixing 

models are consistent with all chemical and isotopic measurements in ground water from the study area. The results should 

be considered non-unique because it cannot be ruled out that 

other mineral phases could be present in trace amounts and 

may contribute substantial amounts of dissolved constituents 

to water withdrawn by the public-supply well. Other recharge 

or mixing scenarios could produce mass-balance models that 

are consistent with these data. The likelihood of this possibility is small, given that the chemical composition of other 

end-member wells representing the surficial aquifer system 

and Upper Floridan aquifer were tested in many other mixing 

models. There was less agreement, however, between measured and calculated isotopic compositions than in the four 

models presented in table 14. 

Movement of Contaminants to the 

Public-Supply Well

Isotopic and other chemical signatures in multiple water 

samples collected from the public-supply well during 2002-05 

consistently indicated a mixture of water from the surficial 

aquifer system and Upper Floridan aquifer. Concentrations of 

anthropogenic contaminants (nitrate-N and trichloromethane) 

and naturally occurring contaminants (arsenic and radon222) are higher during pumping conditions. Public-supply 

well TTP-4 is located in a well field with other public-supply 

wells. This study could not evaluate the effects of pumpage from other wells on water quality in TTP-4. Based on 

extensive geochemical indicators measured in water samples 

and information obtained during geophysical logging of the 

borehole for TTP-4, a highly transmissive zone in the Upper 

Floridan aquifer likely is hydraulically connected to the 

surficial aquifer system and parts of the intermediate confining unit. Large solution features were observed in televiewer 

images of the borehole at depths greater than 43 m. The areal 

and vertical extent of this transmissive zone, however, is not 

known. It would be useful to collect additional water samples 

from monitoring wells in the Upper Floridan aquifer in the 
66 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

study area that are open to the 45- to 50-m interval to determine if similar mixtures dominated by young water are present 

throughout other parts of the study area. 

Focused recharge beneath stormwater retention ponds 

may contribute contaminants to the surficial aquifer system. 

The highest atrazine concentration in ground water (0.12 μg/L) 

was found in a water sample from the surficial aquifer system, 

well THC-S46 (table 11). A higher atrazine concentration of 

1.58 μg/L was found in water from the nearby retention pond 

(62SRP-POND) and likely is a source for the elevated concentration of atrazine and dissolved organic carbon in water 

from THC-S46. Water from the surficial aquifer system moves 

downward into the Upper Floridan aquifer under natural 

gradients that can be enhanced as a result of pumping stresses.

Table 14. Chemical mass transfer associated with various mixing scenarios and comparison of observed and modeled isotopic composition.[mmol/kg, millimoles per kilogram; FeOOH, iron oxyhydroxide; CH O, dissolved organic matter

2 ; δ13C, delta carbon-13 of dissolved inorganic carbon; δ34S-SO4, delta sulfur-34 of sulfate; Cl, Chloride; 

N, nitrogen; SF6, sulfur hexafluoride; DIC, dissolved inorganic carbon; SAS, surficial aquifer system; UFA, Upper Floridan aquifer]

End members, 

mixing percentage

Phases, mass transfer, 

mmol/kg

Isotopic composition, per mil

δ13CDIC δ34S-SO4

Mixing 

scenario

SAS 

WP-S64

UFA 

WP-F150

UFA 

49-53 meter 

zone

CH2O

Calcite

Dolomite

Gypsum

FeOOH

Pyrite

Carbon 

dioxide Computed Measured Computed Measured

1 33 67 0.12 0.35 0.05 0 0.32 -13.1 -12.9 15.6 16.72 (SF6

) 55 45 0.17 0.32 0.1 0.12 0.003 0.36 -13.3 -12.9 16.5 16.7

3 (N) 30 70 0.13 0.34 0.04 0.01 -0.01 0.32 -13.2 -12.9 16.1 16.74 (Cl) 62 38 0.11 -0.004 0.06 0.33 0 0.33 -14.2 -12.5 17.3 15.4

6

5

4

3

2

1

0

NITRATE-N CONCENTRATION,

IN MILLIGRAMS PER LITER

1960 1970 1980 1990 2000 2010

TRICHLOROMETHANE CONCENTRATION,

IN MICROGRAMS PER LITER

Upper Floridan aquifer

Intermediate confining unit

Surficial aquifer system

TTP-4

Age uncertainty, ±2 years

WP-F150

SULFUR HEXAFLUORIDE APPARENT RECHARGE YEAR

3.0

2.5

2.0

1.5

1.0

0.5

0

1960 1970 1980 1990 2000 2010

SULFUR HEXAFLUORIDE APPARENT RECHARGE YEAR

Upper Floridan aquifer

Intermediate confining unit

Surficial aquifer system

TTP-4

Age uncertainty, ±2 years

Figure 25. Relation between the sulfur hexafluoride 

apparent recharge year and concentrations of nitrate-N, and 

trichloromethane in water samples from the surficial aquifer 

system, intermediate confining unit, Upper Floridan aquifer, and 

public-supply well in the Temple Terrace, Florida, study area.
Summary 67

The vulnerability of the public-supply well to contamination is further indicated by age-dating tracer concentrations 

that show a young water component, generally less than 

10 years. Nitrate-N and trichloromethane concentrations show 

a relation with age of water from monitoring wells in the study 

area, with higher concentrations of these two anthropogenic 

contaminants found in increasingly younger waters (fig. 25). 

This trend is influenced by young waters occurring in the oxic 

surficial aquifer system where well depths are shallow and 

where contaminant loading is high from certain urban land-use 

activities. Pumping of ground water by the public-supply well 

and other wells in the immediate area can enhance the downward movement of these and other contaminants. 

Although the effect of the degree of confinement was not 

evaluated in this study, in another study more than three times 

as many detections of volatile organic compounds were found 

in unconfined parts of the Upper Floridan aquifer compared 

to areas where the aquifer is semiconfined (Metz and others, 

2007). That study also found 16 detections of disinfection 

byproducts in unconfined areas, but only two detections in 

semiconfined areas of the Upper Floridan aquifer. Publicsupply well TTP-4 is in an unconfined part of the aquifer, 

and unknown sinkholes also may further enhance downward 

transport of contaminants. 

 A three-dimensional calibrated ground-water flow 

model with particle tracking has been used to simulate the age 

distribution of water to the public-supply well and to monitoring wells in the surficial aquifer system and Upper Floridan 

aquifer (C.A. Crandall, U.S. Geological Survey, written commun., 2007). This calibrated flow model also is being used to 

simulate the arrival of contaminants to these wells from the 

release of potential contaminant sources at the land surface. 

Results of this flow model agree with the geochemical observations presented herein.

Summary

The vulnerability of a public-supply well to 

anthropogenic and naturally occurring contaminants was 

studied near Tampa, Florida, as part of a the U.S. Geological Survey National Water-Quality Assessment (NAWQA) 

Program. Water samples were collected during 2003-05 from 

the public-supply well and from 29 monitoring wells that tap 

the unconfined or poorly confined Upper Floridan aquifer and 

the overlying surficial aquifer system and intermediate confining unit. The karstic Upper Floridan aquifer is particularly 

vulnerable to contamination from a variety of sources due to 

the presence of sinkholes and other solution features that can 

provide a direct hydraulic connection between the aquifer and 

the surface. Sands and clayey sands that compose the overlying surficial aquifer system are highly permeable and allow 

for rapid downward movement of water to the water table and 

eventually into the Upper Floridan aquifer. 

Multiple isotopic and other chemical tracers were analyzed in water samples from the public-supply well, 

12 monitoring wells that tap the Upper Floridan aquifer, and 

from 15 monitoring wells in the overlying surficial aquifer 

system and intermediate confining unit. All monitoring wells 

were located along ground-water flow paths within the 

modeled ground-water contributing recharge area of the 

public-supply well. Geophysical logging of the public-supply 

well borehole revealed large solution features near the bottom 

of the open interval of the well (46-53 m below land surface) 

and two zones of high ground-water flow in the limestone rock 

matrix. 

Water samples were collected under different pumping 

(stressed) conditions from three overlapping depth intervals 

in the public-supply well following removal of the turbine 

pump. First, a low-capacity submersible pump (less than 

3.8 L/min) was placed at the top of each interval and samples 

were collected during ambient (non-stressed) conditions. 

Second, a large-capacity portable submersible pump 

(1,320 L/min) was placed near the top of the open interval 

(38 m below land surface) while water-chemistry samples 

were collected using the low-capacity submersible pump to 

represent pumping conditions in the public-supply well. 

The lowermost 49- to 53-m depth interval had distinctly 

different chemistry compared with the two other sampled 

intervals. Water samples collected from this depth interval 

during ambient conditions contained higher concentrations of 

nitrate-N, orthophosphate, radon-222, atrazine, and trichloromethane than water collected from the other depth zones during ambient conditions, and for the entire 38- to 53-m interval 

during pumping conditions. Additionally, low concentrations 

were found in the 49- to 53-m interval for strontium, iron, 

manganese, and dissolved solids as well as low values of delta 

nitrogen-15 (δ15N) of nitrate and delta sulfur-34 (δ34S) of 

sulfate. Arsenic concentrations were high in the 49- to 53-m 

zone during pumping conditions along with high ratios of 

arsenic (V)/arsenic (III). Mixing of waters with variable 

redox conditions occurs during pumping conditions and likely 

accounts for differences in the concentrations of arsenic 

species (arsenic (V) and arsenic (III)) between samples 

collected from the lowermost depth interval (49-53 m) and the 

entire open interval (38-53 m). Considerably higher concentrations of the more oxidized arsenic species (arsenic (V)) were 

measured in water samples from the lowermost depth interval 

than in water from the entire open interval. Movement of 

water likely occurs from the overlying sands and clays of the 

oxic surficial aquifer system and the discontinuous intermediate confining unit, which contains elevated radon-222 and 

nitrate-N concentrations, into the anoxic Upper Floridan aquifer (lower radon-222 and nitrate-N concentrations). Differences in arsenic concentrations in water from the various depth 

intervals in the public-supply well (3.2-19 μg/L) were related 

to pumping conditions. Arsenic concentrations exceeded the 

U.S. Environmental Protection Agency maximum contaminant 
68 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

level of 10 μg/L in water samples from specific depth intervals 

in the public-supply well borehole, but arsenic concentrations 

did not exceed the maximum contaminant level in the wellhead sample. 

Concentrations of age-dating tracers sulfur 

hexafluoride (SF6), tritium (3H), and helium-3 (3He) in 

samples from the public-supply well during low- and highrate pumping conditions were consistent with binary mixtures 

dominated by young water (less than 7 years). Similarly, 

water samples from monitoring wells in the surficial aquifer 

system had SF6 and 3H concentrations that indicate a substantial proportion of young water (less than 7 years). In contrast, 

most water samples from monitoring wells in the Upper 

Floridan aquifer system had lower SF6 and 3H concentrations 

than water from the public-supply well and indicated mixtures 

containing higher proportions of old waters (greater than 

60 years). 

Six volatile organic compounds and four pesticides 

were detected in trace concentrations (well below drinkingwater standards and other health-based screening levels) in 

water from the public-supply well. These contaminants were 

detected more frequently in water samples from monitoring 

wells in the overlying surficial aquifer system than in water 

from monitoring wells in the Upper Floridan aquifer in the 

study area. Likewise, nitrate-N concentrations in the publicsupply well (0.72-3.6 mg/L) were more similar to median 

concentrations in the oxic surficial aquifer system (2.1 mg/L) 

than median nitrate-N concentrations (0.06 mg/L) in the 

anoxic Upper Floridan aquifer (sulfate-reducing conditions). 

Denitrification likely occurs in the deeper parts of surficial 

aquifer system and in the Upper Floridan aquifer based on 

excess nitrogen gas concentrations and highly enriched 

nitrogen- and oxygen-isotopic composition of nitrate.

Focused recharge beneath stormwater retention ponds 

and unknown sinkholes may contribute contaminants to the 

surficial aquifer system and the Upper Floridan aquifer. The 

highest atrazine concentration (0.12 μg/L) in ground water 

was found in a sample from the surficial aquifer system at 

well THC-S46. A high atrazine concentration of 1.58 μg/L 

was found in water from the nearby stormwater retention pond 

(62SRP-POND) and likely is a source for the elevated concentration of atrazine and dissolved organic carbon in water 

from THC-S46. Water from the surficial aquifer system moves 

downward into the Upper Floridan aquifer under natural 

gradients and can be enhanced due to pumping stresses.

Geochemical mass-balance mixing models for the 

public-supply well indicate that 50 to 70 percent of water 

withdrawn from the public-supply well is contributed from 

the surficial aquifer system, and 30 to 50 percent from the 

Upper Floridan aquifer. Geochemical models also indicate the 

dissolution of small amounts of calcite, gypsum, and dolomite 

as water moves toward the public-supply well. Even though 

mass-transfer coefficients calculated from the mixing models 

were consistent with all chemical and isotopic measurements 

in ground water from the study area, results should be considered non-unique because it cannot be ruled out that other 

mineral phases could be present in trace amounts and may 

contribute substantial amounts of dissolved constituents to 

water withdrawn by the public-supply well. Other recharge or 

mixing scenarios could produce mass-balance models that are 

consistent with these data. The likelihood of this possibility 

is small, given that the chemical composition of other endmember wells representing the surficial aquifer system and 

Upper Floridan aquifer were tested in other mixing models. 

The presence of a large component of water from the surficial aquifer system that is withdrawn during pumping of the 

studied public-supply well demonstrates the vulnerability of 

public-supply wells in this area to contamination. 

Selected monitoring wells in the surficial aquifer system 

were sampled several times during 2003-05 to evaluate temporal variability in water quality in response to changing hydrologic conditions. These wells were sampled four times before 

and after three tropical cyclones passed through the area in 

summer 2004. Water-quality variations also were evaluated 

for public-supply well TTP-4 based on five samples collected during 2002-05. The dynamic nature of the hydrologic 

response to recharge in this karst setting was observed by large 

fluctuations in chemistry. Chloride concentrations decreased 

from summer 2004 water samples to winter 2004-05 samples 

from all three monitoring wells following the recharge pulse 

from high rainfall and corresponding peak in water-level 

elevation in October 2004. Nitrate-N concentrations increased 

in water from one well from January to August 2004, but 

decreased in water from another monitoring well during the 

same period. Nitrate-N concentrations also increased in water 

samples from two other monitoring wells in the surficial 

aquifer system, from January to August 2004, but decreased in 

subsequent samples from these two wells. Nitrate-N concentrations in water from a well located near the Hillsborough 

River remained below the detection limit, as reducing conditions persisted during December 2003 to July 2005. Dissolved 

oxygen concentrations increased in water samples from two 

wells in the surficial aquifer system, and the public-supply 

well in August and September 2004 during and following the 

above-normal rainfall in June through September 2004. The 

increase in dissolved oxygen concentrations likely results from 

recent recharge of water containing elevated levels of oxygen 

compared to lower levels in ground water prior to the excess 

rainfall period. Dissolved oxygen concentrations decreased 

in water from a well near the Hillsborough River in fall 2004, 

which may indicate the influx of river water with elevated 

dissolved organic carbon and subsequent consumption of 

oxygen as water moves toward this well.

A hydrologic flow model of the contributing recharge 

area of the public-supply well is consistent with the observed 

geochemical conditions and can be used to evaluate changes 

in hydrologic conditions. Further information about flow pathways and the extent of high transmissive zones in the Upper 

Floridan aquifer that are directly connected to the surficial 

aquifer system would be helpful in better understanding the 

movement of contaminants to other public-supply wells that 

tap the Upper Floridan aquifer. 
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76 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water
Appendixes 77

Appendixes
78 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water
Appendixes 79

Appendix A1. Summary of quality-assurance results for organic compounds in blanks and replicates.

[Concentrations are in micrograms per liter (μg/L); NR, not reported; P code, U.S. Environmental Protection Agency STORET code; E, estimated concentration, 

below method reporting level; VOC, volatile organic compound; yyyymmdd, year, month, day]

Station identifier Site name

Sample 

date,

yyyymmdd

Sample 

start time

Diazinon-d10, 

surrogate, 

Schedule 2003, 

percent 

recovery

Carbon disulfide 

(μg/L)

Dichloromethane

(μg/L)

Trichloromethane 

(μg/L)

P99994 P77041 P34423 P32106

Blanks

280247082231903 WP-S64 20040114 1200 NR <.04 E0.1

280247082231903 WP-S64 20040114 1205 NR <.04 0.1

280253082223802 GARC-F75 20031215 0915 NR <.04 0.4

280253082223802 GARC-F75 20031218 0940 NR <.04 0.6 E0.09

Replicates

280247082231901 WP-F299 20040122 1600 80.2 E0.77 0.8

280247082231901 WP-F299 20040122 1601 69.5 E0.42 0.7

280301082222703 113RC-S35 20031211 1300 88.8 <.04 2.0

280301082222703 113RC-S35 20031211 1305 78.4 <.04 3.2

Station identifier Site name

Sample 

date,

yyyymmdd

Sample 

time

Isobutyl alcohol-d6, 

surrogate, water, 

unfiltered, percent 

recovery

1,2-Dichloroethaned4, surrogate, Schedule 2090, percent 

recovery

1-Bromo-4-fluorobenzene, surrogate, VOC 

schedules, percent 

recovery

P62835 P99832 P99834

Blanks

280241082224403 THC-S46 20031218 0935 75.5 110 83.8

280241082224403 THC-S46 20050614 1415 NR 120 78.4

280241082224403 THC-S46 20050614 1430 NR 121 77.0

280247082231902 WP-F150 20040128 0915 91.4 127 91.9

280247082231902 WP-F150 20040128 0945 107 132 87.8

280249082220701 RP-F103 20031015 1515 109 120 97.5

280249082220701 RP-F103 20031015 1715 108 120 96.2

280253082223802 GARC-F75 20031215 1000 81 110 58.3

280253082223802 GARC-F75 20031218 0940 82.3 113 77.1

280303082230902 LP-S30 20050621 1000 NR 131 93.8

280303082230902 LP-S30 20050621 1001 NR 130 92.8
80 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water

Station 

identifier

Site 

name

Sample 

date,

yyyymmdd

Sample 

time

Absorbance, 

UV, 254 nm,

1 cm pathlength, 

water, filtered, 

units per 

centimeter

Absorbance, 

UV, organic 

constituents, 

280 nm, 1 cm 

pathlength, 

water, filtered

Calcium, 

mg/L

Sodium, 

mg/L

Silica,

mg/L

Sulfide, 

water, 

filtered, 

field,

mg/L

Organic 

carbon,

mg/L

Chromium, 

μg/L

Cobalt, 

μg/L

Copper, 

μg/L

Manganese, 

μg/L

P50624 P61726 P00915 P00930 P00955 P99118 P00681 P01030 P01035 P01040 P01056

Blanks

280241082224403 THC-S46 20050614 1430 <0.004 <0.004 0.08 0.29 1.42 E0.2 <0.6

280247082231902 WP-F150 20040128 0945 1.9

280247082231902 WP-F150 20040128 0955 <0.8 0.871 <0.4 E0.1

280247082231903 WP-S64 20040114 1210 <0.8 <0.014 <0.4 <0.2

280249082220701 RP-F103 20031015 1715 E0.4 0.788 E0.4 <0.2

280250082233001 LP-F160 20041104 1050 <0.004 <0.004 0.05 <0.20 0.04 1.3 <0.8 0.324 <0.4 <0.2

280303082230902 LP-S30 20050621 1000 0.005 0.004 0.4

Station 

identifier

Site 

name

Sample 

date,

yyyymmdd

Sample 

time

Absorbance, 

UV, 254 nm, 1 

cm pathlength, 

water, 

filtered, units 

per centimeter

Absorbance, 

UV, organic 

constituents, 

280 nm, 1 cm 

pathlength, 

water, filtered

Dissolved 

oxygen, 

water, 

unfiltered,

mg/L

Potassium, 

mg/L

Bromide,

 mg/L

Total nitrogen 

(nitrate + 

nitrite + 

ammonia + 

organic-N), 

water, filtered

Organic 

carbon, 

mg/L

Arsenic, 

μg/L

Arsenite 

(H3AsO3), 

μg/L as 

arsenic

Boron,

μg/L

Cadmium, 

μg/L

P50624 P61726 P00300 P00935 P71870 P62854 P00681 P01000 P62452 P01020 P01025

Replicates

280241082224402 THC-F75 20040112 1500 0.1 0.74 E.01 0.14 1.9 1.1 <1.0 19 <0.04

280241082224402 THC-F75 20040112 1501 0.72 0.02 0.14 1 <1.0 18 <0.04

280241082230701 RP-F103 20041102 1200 0.022 0.017 0.1 1.35 0.11 1.95 1 3.1 <1.0 28 0.21

280241082230701 RP-F103 20041102 1205 0.023 0.017 0.8 0.9

280244082232001 TTP-4 20050620 1601 0.028 0.02 1.2

280244082232001 TTP-4 20050620 1600 0.027 0.018 0.3 1.11 0.78 1.2

280247082231901 WP-F299 20040122 1600 0.2 1.4 0.03 0.22 2.4 12.6 5.6 25 0.17

280247082231901 WP-F299 20040122 1601 2.4 12.3 31 0.17

280247082231903 WP-S64 20050614 1131 0.011 0.008 1.61 2.22 1.1

280247082231903 WP-S64 20050614 1130 0.01 0.007 5.7 1.58 2.35 13.7

280253082223801 GARC-F200 20031216 1300 0.2 1.24 0.03 0.24 2.1 1.7 1.1 22 <0.04

280253082223801 GARC-F200 20031216 1306 <1.0

280301082222703 113RC-S35 20031211 1300 2.5 0.68 0.05 3.7 0.6 E.2 <1.0 15 0.11

280301082222703 113RC-S35 20031211 1305 0.5 0.2 16 0.11

280303082230901 LP-H40 20041208 1500 0.007 0.006 6.8 1.08 0.05 2.43 0.4 0.3 <1.0 22 0.16

280303082230901 LP-H40 20041208 1505 0.007 0.005 6.8 1.16 0.04 2.44 0.4 0.3 22 0.17

Appendix A2. Summary of quality-assurance results for selected chemical constituents in field blank and replicate samples.

[E, estimated concentration, reported below method reporting level; P code, U.S. Environmental Protection Agency STORET code; cm, centimeter; mg/L, milligrams per liter; 
Appendixes 81

Molybdenum,

μg/L

Nickel, 

μg/L

Strontium, 

μg/L

Zinc, 

μg/L

P01060 P01065 P01080 P01090

E0.2 0.43 1.36 <0.6

<0.4 0.06 <0.40 1.1

<0.4 0.43 <0.40 <0.6

<0.4 0.16 0.4 E0.4

Chromium, 

μg/L

Copper, 

μg/L

Lead, 

μg/L

Lithium, 

μg/L

Manganese, 

μg/L

Molybdenum,

μg/L

Nickel, 

μg/L

Selenium, 

μg/L

Vanadium, 

μg/L

Alpha/

radioactivity 

2-sigma 

combined 

uncertainty, 

water, 

filtered, Th-230

Alpha radioactivity, water, 

filtered, 

Th-230 curve, 

picocuries per 

liter

Deuterium/

Protium ratio, 

water, unfiltered, per mil

Gross beta 

radioactivity, 

water, filtered, 

Cs-137 curve, 

picocuries per 

liter

Radium-226, 

water, filtered, 

radon method, 

picocuries per 

liter

P01030 P01040 P01049 P01130 P01056 P01060 P01065 P01145 P01085 P75987 P04126 P82082 P03515 P09511

<0.8 0.6 <0.08 1 85.7 3 1.76 1.4 2 2 1 -17.6 2.1 0.52

<0.8 0.5 <0.08 1 84.7 3 1.44 1.2 1.8 2.4 3.3 -15.7 2.2 0.59

<0.8 0.7 <0.08 1.9 2.8 16.4 2.44 7.8 12.6

3.4

<0.8 2 <0.08 4.1 7 86.7 4.41 0.6 0.8

<0.8 2 0.09 3.7 6.9 91.1 3.62 0.8 0.9

<0.6

<0.6

<0.8 1.4 <0.08 3.8 70.1 6.4 2.95 1.3 1.5

E.5 0.9 <0.08 E.4 5.1 0.9 1 0.8 3.7

E.6 1.1 <0.08 E.4 5.5 0.9 0.9 0.8 3.9

1.6 1.1 <0.08 E.5 0.3 4 0.65 0.7 5.1

1.5 1 <0.08 E.5 0.3 3.9 0.59 0.6 5.2

μg/L, micrograms per liter, UV, ultraviolet; nm, nanometers; yyyymmdd, year, month, day; <, less than; Th-230, Thorium-230; Cs-137, Cesium-137]
82 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water Site identifier Site name Sample date Sample time Bisphenol a-d3 surrogate Caffeine-c13 surrogate Decafluorobi- phenyl surrogate Fluoran- thene-d10, surrogate Diazinon-d10, surrogate Alpha-HCH- d6, surrogate 1,2-dichlo- roethane-d4, surrogate 1-bromo-4- fluorobenzene, surrogate Toluene-d8, surrogate Barban, (positive ion surrogate) “2,4,5-t (negative ion surrogate)” c13 caffeine (positive ion surrogate) Isobutyl alcohol-d6 P99583 P99584 P99585 P99586 P99994 P99995 P99832 P99834 P99833 P90640 P99958 P99959 P62835 280228082231501 BBP-S45 20041209 0955 101 98.8 98.9 280228082231501 BBP-S45 20041209 0956 102 97 101 280228082231501 BBP-S45 20040811 1200 107 96.4 104 280228082231501 BBP-S45 20041209 1300 113 94.9 97.3 97.9 280228082231501 BBP-S45 20050622 1130 101 90.6 97.1 280241082224401 THC-F197 20040115 1400 77.9 78.3 116 75 94.3 120 280241082224402 THC-F75 20040112 1500 105 96.2 113 74.2 93 142 280241082224403 THC-S46 20031218 0935 110 83.8 96.9 75.5 280241082224403 THC-S46 20031218 1300 98.1 79.8 113 81.2 97.3 113 280241082224403 THC-S46 20040805 1200 127 99.6 98.7 280241082224403 THC-S46 20041117 1600 115 95.5 96.5 280241082224403 THC-S46 20050614 1700 121 75.4 97.2 280241082224403 THC-S46 20050614 1415 120 78.4 99.6 280241082224403 THC-S46 20050614 1430 121 77 99.2 280241082230701 62SRP-F160 20041102 1200 112 86.2 103 109 280241082230702 62SRP-H55 20041103 1700 111 86.5 95.2 96.4 280241082230703 62SRP-S34 20040812 0930 108 107 111 280242082232401 MAS-R-F160 20041103 1200 110 88.1 95 98 280242082232401 MAS-R-F160 20050616 1040 101 101 101 280242082232403 MAS-R-S30 20050216 1300 116 88.1 94 73 280242082232403 MAS-R-S30 20050616 1100 119 95.2 102 280244082232001 TTP-4 20021021 1600 66.1 83.8 57 70.8 106 106 121 89.1 93.2 125 86.1 127 118 280244082232001 TTP-4 20040128 1600 97.1 72.8 137 84.6 101 108 280244082232001 TTP-4 20040922 1600 21.2 83.3 52.7 95.4 117 96.1 100 114 65.3 138

280244082232001 TTP-4 20041021 1500 93.4 101 119 93 99 93.5280244082232001 TTP-4 20041027 1600 80.3 87.3 112 93.7 96.6 81280244082232001 TTP-4 20041027 1800 80.4 86.6 112 94.4 98.5 78.9280244082232001 TTP-4 20041028 1100 80.7 91.7 114 93.5 99.1 94.8280244082232001 TTP-4 20041028 1400 82.4 90.8 121 92.5 99.1 99.4280244082232001 TTP-4 20041028 1600 80.2 92.4 117 94.1 98.2 96.5280244082232001 TTP-4 20040128 1605 126 103 105280244082232001 TTP-4 20040128 1606 99.1 101 93 137

Appendix A3. Percent recovery values for surrogate compounds added to ground-water and surface-water samples at the U.S. Geological Survey National Water Quality Laboratory.[P code, U.S. Environmental Protection Agency STORET parameter code]
Appendixes 83

Site

identifier

Site

name

Sample 

date

Sample 

time

Bisphenol 

a-d3 

surrogate

Caffeine-c13 

surrogate

Decafluorobiphenyl 

surrogate

Fluoranthene-d10, 

surrogate

Diazinon-d10, 

surrogate

Alpha-HCHd6, surrogate 1,2-dichlo- roethane-d4, surrogate 1-bromo-4- fluorobenzene, surrogate Toluene-d8, surrogate Barban, (positive ion surrogate) “2,4,5-t (negative ion surrogate)” c13 caffeine (positive ion surrogate) Isobutyl alcohol-d6

P99583 P99584 P99585 P99586 P99994 P99995 P99832 P99834 P99833 P90640 P99958 P99959 P62835

280244082232001 TTP-4 20050216 1600 117 90.9 95.7280244082232001 TTP-4 20050620 1600 105 96.7 101280244082232001 TTP-4 20040128 1602 105 75.3280244082232001 TTP-4 20040128 1603 107 82.5280244082232001 TTP-4 20040128 1604 104 82.7280247082231901 WP-F299 20040122 1600 80.2 84.9 126 95.5 103 101280247082231901 WP-F299 20040122 1601 69.5 90.9 130 92.5 99.5 113280247082231901 WP-F299 20040803 1400 94.3 74.7 117 103 100280247082231902 WP-F150 20040128 0915 127 91.9 103 91.4280247082231902 WP-F150 20040128 0945 103 81.5 132 87.8 99.6 107280247082231902 WP-F150 20040128 1300 100 79.9 135 98.7 102 102280247082231902 WP-F150 20040804 1100 72 69.2 121 103 101280247082231903 WP-S64 20040114 1200 105 81.4 92.8 126280247082231903 WP-S64 20040114 1205 112 80.6 96.4 130280247082231903 WP-S64 20040114 1500 117 87.3 115 74.4 92.6 107280247082231903 WP-S64 20040804 1600 69.3 72.9 121 101 99280247082231903 WP-S64 20041118 1200 114 96.8 97.8280247082231903 WP-S64 20050614 1130 127 75.6 98.6280247082231903 WP-S64 20050614 1131 122 76.8 97.6280247082231903 WP-S64 20050614 1132 110 101 101280249082220701 RP-F103 20031015 1515 120 97.5 101 109280249082220701 RP-F103 20031015 1715 120 96.2 99.9 108280249082220701 RP-F103 20031202 1500 96.3 79.7 143 100 102 156280249082220702 RP-F77 20031203 1300 89.4 75.4 147 89.3 102 158280249082220703 RP-S20 20031204 1400 91.9 80.1 145 81.2 99.8 148280249082220703 RP-S20 20040811 1500 105 93.6 105280249082220703 RP-S20 20041116 1500 113 93.8 97.4280249082220703 RP-S20 20050616 1500 118 95.8 98.5280250082233001 LRP-F160 20041104 1050 104 89.6 96.8 101280250082233001 LRP-F160 20041104 1055 106 89.1 96.6 99280250082233001 LRP-F160 20041104 1300 107 90.3 95.1 98.7280250082233002 LRP-H105 20041207 1600 107 95.9 101 91.9

Appendix A3. Percent recovery values for surrogate compounds added to ground-water and surface-water samples at the U.S. Geological Survey National Water Quality Laboratory.—Continued[P code, U.S. Environmental Protection Agency STORET parameter code]
84 Chemical Characteristics, Water Sources and Pathways, and Age Distribution of Ground Water Site identifier Site name Sample date Sample time Bisphenol a-d3 surrogate Caffeine-c13 surrogate Decafluorobi- phenyl surrogate Fluoran- thene-d10, surrogate Diazinon-d10, surrogate Alpha-HCH- d6, surrogate 1,2-dichlo- roethane-d4, surrogate 1-bromo-4- fluorobenzene, surrogate Toluene-d8, surrogate Barban, (positive ion surrogate) “2,4,5-t (negative ion surrogate)” c13 caffeine (positive ion surrogate) Isobutyl alcohol-d6 P99583 P99584 P99585 P99586 P99994 P99995 P99832 P99834 P99833 P90640 P99958 P99959 P62835 280250082233003 LRP-S25 20040810 1100 103 100 105 280250082233003 LRP-S25 20050615 1500 119 91.7 101 280251082224201 JARP-S40 20050627 1030 108 100 100 280253082223801 GARC-F200 20031216 1300 100 84.9 111 65.9 94.4 85.5 280253082223801 GARC-F200 20031216 1301 93.5 88 280253082223801 GARC-F200 20031216 1302 90.8 92.5 280253082223801 GARC-F200 20031216 1303 100 92.2 280253082223801 GARC-F200 20031216 1304 105 87.8 100 280253082223801 GARC-F200 20031216 1305 102 112 94.2 101 280253082223802 GARC-F75 20031215 1000 106 94 110 58.3 95.2 81 280253082223802 GARC-F75 20031215 1400 97.2 85 106 82.9 99.1 89 280253082223802 GARC-F75 20031215 0915 106 82 98 82.6 280253082223802 GARC-F75 20031218 0940 113 77.1 98.6 82.3 280253082223803 GARC-S23 20031217 1200 98.4 84.5 121 77.7 99.7 87.2 280253082223803 GARC-S23 20040805 1600 124 100 98.4 280253082223803 GARC-S23 20041117 1100 112 92.8 97.8 280253082223803 GARC-S23 20050613 1115 106 103 98.7 280301082222701 113RC-F190 20031208 1300 94.7 84.2 138 74.1 93.7 112 280301082222703 113RC-S35 20031211 1305 78.4 83.3 127 74.9 99 103 280301082222703 113RC-S35 20040812 1300 109 106 113 280301082222703 113RC-S35 20050615 1100 121 93.3 101 280303082230901 LP-H40 20040810 1500 104 94 103 280303082230901 LP-H40 20041208 1500 110 97.2 102 88.6 280303082230901 LP-H40 20041208 1505 111 99.1 100 80.6

280303082230902 LP-S30 20040810 1200 103 93 104280303082230902 LP-S30 20041101 1600 103 83.8 100 95.2280303082230902 LP-S30 20041101 1601 110 92.3 95.1 116280303082230902 LP-S30 20050621 1000 131 93.8 104280303082230902 LP-S30 20050621 1001 130 92.8 103280303082230902 LP-S30 20050621 1130 127 94.3 102280311082223901 QRP-S20 20050621 1630 125 93.5 100

Appendix A3. Percent recovery values for surrogate compounds added to ground-water and surface-water samples at the U.S. Geological Survey National Water Quality Laboratory.—Continued[P code, U.S. Environmental Protection Agency STORET parameter code]
Appendixes 85

Redox 

indicator 

species

Significance 

level Redox environments consistent with redox indicator species Redox environments contraindicated by redox indicator species

Dissolvedoxygen

10.5 mg/L Oxygen reducing Denitrifying Manganese reducing Iron reducing Sulfate reducing Methanic

Nitrate 10.5 mg/L Oxygen reducing Denitrifying Manganese reducing Iron reducing Sulfate reducing MethanicSulfate 14 mg/L Oxygen reducing Denitrifying Manganese reducing Iron reducing Sulfate reducing MethanicNitrogen (Nitrogen from recharge) Denitrifying Manganese reducing Iron reducing Sulfate reducing Methanic Oxygen reducingManganese 150 μg/L Manganese reducing Iron reducing Sulfate reducing Methanic Oxygen reducing DenitrifyingIron 1,2100 μg/L Iron reducing Sulfate reducing Methanic Oxygen reducing Denitrifying Manganese reducing3Hydrogensulfide Presence Sulfate reducing Methanic Oxygen reducing Denitrifying Manganese reducing Iron reducingMethane Presence Methanic Oxygen reducing Denitrifying Manganese reducing Iron reducing Sulfate reducing

1Significance levels for dissolved oxygen and nitrate are from Chapelle and others (1995), for sulfate, Chapelle and others (2002), and for manganese and iron, from Geological Survey of Sweden 

(http://www.internat.environ.se/index.php3?main=/documents/legal/assess/assedoc/gndwdoc/aqui.htm). The significance of the 4 mg/L sulfate concentration is that sulfate > 4 mg/L may compete with reductive pathways for degradation of chlorinated solvents; in other words, the iron-reducing, low sulfate zone may be useful for the anthropogenic contaminant analysis.

2This iron significance level also used by Smedley and Kinniburgh (2002). Iron-poor sediments or precipitation of an iron-bearing secondary phase may require a lower significance level for iron; and so 

forth, but must be applied consistently. Iron-reducing water is divided into two categories, “iron-reducing, high sulfate” (sulfate > 4 mg/L), and “iron-reducing, low sulfate” (sulfate < or = 4 mg/L).

3Note that hydrogen sulfide data do not allow identification of high- or low-sulfate conditions because hydrogen sulfide is produced by reduction of sulfate regardless of whether sulfate concentrations are > 

or < 4 mg/L.

Appendix A4. Oxidation-reduction (redox) classification scheme developed for the transport of anthropogenic and natural contaminants to public-supply wells.[For a given redox indicator species, presence above significance level is consistent with some redox environments, (“Redox environments consistent with redox indicator species”), and inconsistent with other redox environments (“Redox environments contraindicated by redox indicator species”). Redox classification is based upon a combination of this redox classification system, understanding of position within ground-water flow system, understanding of mineralogy of solid phases, and data quality and quantity. In general, multiple redox indicator species are required to precisely characterize a given redox environment; mg/L, milligrams per liter, μg/L, micrograms per liter; >, greater than; <, less than]