I

Contaminants and Drinking-Water

Sources in 2001: Recent Findings of the

U.S. Geological Survey

Open-File Report 00-510

By Glenn G. Patterson and Michael J. Focazio

Prepared in cooperation with the

U.S. ENVIRONMENTAL PROTECTION AGENCY

and other agencies
II

U.S. DEPARTMENT OF THE INTERIOR

Gale A. Norton, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification pruposes only and does

not constitute endorsement by the U.S. Geological Survey.

Reston, Virginia 2001

For additional information write to:

Chief, Office of Water Quality

U.S. Geological Survey

412 National Center

Reston, VA 20192

Copies of this report may be purchased from:

U.S. Geological Survey

Branch of Information Services

Box 25286

Federal Center

Denver, CO 80225
III

CONTENTS

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

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

Contaminant Occurrence and Distribution Data ...................................................................................................... 1

 Pesticides ........................................................................................................................................................ 1

 Volatile organic compounds............................................................................................................................ 2

 Arsenic ............................................................................................................................................................ 2

 Microbes ......................................................................................................................................................... 2

 Radionuclides ................................................................................................................................................. 3

 Research related to contaminant occurrence and distribution ........................................................................ 3

Source-Water Assessments ....................................................................................................................................... 5

 Source-area characteristics of large public surface-water supplies ................................................................ 5

 California—Disinfection by-product precursors ............................................................................................ 6

 New Jersey—Vulnerability of public-supply wells to contamination ............................................................ 6

 Michigan—Arsenic in ground water, and statewide

 source-water assessment ............................................................................................................................. 6

 Texas—Statewide source-water assessment ................................................................................................... 7

 New Hampshire—Arsenic in relation to rock type ........................................................................................ 8

 Research related to source-water assessments................................................................................................ 8

References ................................................................................................................................................................ 8

FIGURES

1. Common pesticide mixtures detected in water of the United States .................................................................... 2

2. Percent detections of MTBE in United States wells............................................................................................. 2

3. Concentrations of arsenic in ground water of the United States .......................................................................... 3

4. Public-supply wells in Missouri sampled for microbes (A),

and wells with detections (B) ............................................................................................................................... 4

5. Frequency of detection for selected herbicide compounds and breakdown

products in Iowa ................................................................................................................................................... 5

6. Location of 525 drinking-water intakes for large public water

supplies in the United States................................................................................................................................. 5

7. Location of organic carbon study area, Twitchell Island,

Sacramento-San Joaquin Delta, California........................................................................................................... 6

8. Data used for statewide source-water assessments of (A) pesticides,

(B) nitrate, and (C) volatile organic compounds in ground water

for the State of New Jersey ................................................................................................................................... 7

9. Ages of the young fraction in the Upper Floridan aquifer at

Valdosta, Ga., in June, 1991 (A); and estimated percentage of

Withlacoochee River water in ground water in the

Upper Floridan aquifer, June, 1991 (B) ................................................................................................................ 8

TABLES

1. Summary of radionuclide concentrations in the multi-state survey ..................................................................... 3
IV

Chemical Water-Quality Units

is a unit expressing the concentration of chemical constituents in solution as weight

(milligrams of solute) per unit volume (liter of water). One thousand micrograms

per liter is equivalent to one milligram per liter. For concentrations less than 7,000

mg/L, the numeric value in milligrams per liter is the same as for concentrations in

parts per million, and the concentrations in mircrograms per liter is the same as for

concentrations in parts per billion.

Conversion Factors, Water-Quality Units, 

and Abbreviations 

Multiply By To Obtain

Length

nanometer (nm) 3.937 x 10-8 inch (in.)

kilometer (km) 0.6214 mile (mi)

Area

square kilometer (km2

) 0.3861 square mile (mi2)

square mile (mi2

) 2.590 square kilometer (km2)

Volume

liter (L) 0.2642 gallon (U.S.)

Milligrams per liter (mg/L) or micrograms per liter (μg/L): Milligrams per liter
1

ABSTRACT

As the Nation’s principal earth-science agency, the U.S.

Geological Survey (USGS) studies numerous issues related

to contamination of drinking-water sources. The work includes monitoring to determine the spatial and temporal distribution of contaminants; research to determine sources,

transport, transformations, and fate of contaminants, and assessments of vulnerability. Much of the work is conducted in

cooperation with the U.S. Environmental Protection Agency

and other Federal, State, Tribal, and local governments, to

help provide a scientific basis for resource management and

regulation. Examples of recent results are presented for two

broad categories of drinking-water projects: occurrence studies, and source-water assessments.

INTRODUCTION

The USGS conducts a wide range of hydrologic, geologic, biologic, and geographic activities that provide information to help understand, manage, and protect our Nation’s

sources of drinking water. Most of this work falls into two

broad categories: (1) Collecting and interpreting data on the

occurrence and distribution of drinking-water contaminants

in rivers, lakes, and ground water, and (2) Assessing the characteristics of the rivers, lakes, watersheds, and aquifers that

the Nation uses as sources of drinking water (source-water

areas). Both of these broad categories include a component

of research on fundamental hydrologic processes and methods. Much of the work is conducted in cooperation with the

U.S. Environmental Protection Agency (USEPA) and other

Federal, State, Tribal, and local governments, to provide a

scientific basis for management of source waters. USGS programs related to drinking water include the National Water

Quality Assessment (NAWQA) Program (http://water.usgs.

gov/nawqa/), the Drinking Water Initiative, the Toxic Substances Hydrology Program (http://toxics.usgs.gov/), and the

Cooperative Water Resources Program (http:/water.usgs.gov/

wid/html/COOP.html). A few examples have been selected to

illustrate the range of drinking-water-related projects recently completed or underway at the USGS. For more information on any of the examples, or for related inquiries, visit

the USGS Drinking Water website at (http://water.usgs.gov/

owq/dwi/), or visit the program websites listed in this report.

CONTAMINANT OCCURRENCE AND

DISTRIBUTION DATA

Contaminant occurrence and distribution data that are

used to conduct research and determine policy on drinking

water are collected and analyzed by many Federal, State, and

local agencies, as well as universities, consortiums, citizen

groups, and similar organizations. These data are collected

for many purposes and by various methods, with varying levels of detail and quality control. As the data vary, so does the

availability and distribution of the data. For example, Consumer-Confidence Reports (CCRs) have recently been made

available by all community water suppliers (those serving

more than 10,000 people are required to mail the reports to

their customers). CCRs explain which contaminants are

monitored, as well as the concentration of those contaminants in the drinking water delivered to customers’ homes

(finished drinking water).

Data collected and analyzed with nationally consistent

protocols by the USGS are typically derived from the smaller

community systems (less than 10,000 customers), homeowners’ drinking-water wells, and source-water areas. USGS

programs include data-collection efforts on scales ranging

from detailed assessments of the overall quality of local water resources to national assessments of the occurrence and

distribution of selected contaminants. In addition, USGS programs collect data on contaminants that are currently regulated by the USEPA, such as arsenic, radionuclides, and microbial indicators, as well as many that are not, including selected degradates (breakdown products) of pesticides and

volatile organic compounds (VOCs). Much of this information is collected through the USGS National Water-Quality

Assessment (NAWQA) Program, which is designed to describe the status and trends in the quality of the Nation’s

ground- and surface-water resources and to provide a sound

understanding of the natural and human factors that affect the

quality of these resources. Nationally consistent methods of

sampling and analysis (at very low concentration levels) facilitate integration of data collected at the local scale (“study

unit”) into “national synthesis” data sets and publications.

Data on occurrence and co-occurrence (tendency to occur together) are collected for a range of contaminants including

nutrients, pesticides, trace elements, radionuclides, and microbes. Through this and other programs, the USGS is providing new and valuable data on source-water and drinkingwater quality across the Nation, made available through web

pages, printed reports, and CD-ROM’s. Information for your

State or local area can be found on local USGS websites

from these web pages:

Drinking Water Programs: http://water.usgs.gov/owq/dwi/

NAWQA: http://water.usgs.gov/nawqa/

General Water Programs: http://water.usgs.gov/wrd002.html.

Pesticides

Among the contaminants studied by the USGS with significance for drinking water are selected pesticides and

degradates (breakdown products) (fig. 1). NAWQA results

show that herbicides, insecticides, and their degradates are

frequently detected, mostly at low concentrations, in both

surface and ground water, in both agricultural and urban or

Contaminants and Drinking-Water Sources in 2001:

Recent Findings of the U.S. Geological Survey
2

residential areas. Identification of commonly occurring

chemical mixtures of these compounds is helping to guide

research on their health effects.

Volatile Organic Compounds

NAWQA also monitors a variety of volatile organic

compounds and some degradates, including the gasoline additive methyl-tert-butyl ether (MTBE). This additive is

widely used to abate air pollution in certain parts of the

Nation designated as reformulated-gasoline (RFG) and oxygenated-gasoline (OXY) areas. At a reporting level of 0.2

mg/L, MTBE was detected in 21 percent of 480 wells located in RFG and OXY areas. In the rest of the Nation,

MTBE detection frequency in ground water was 2 percent.

Gasoline aromatic hydrocarbons (benzene, toluene,

ethylbenzene, and xylenes, collectively known as BTEX)

were detected much less frequently (4 percent) than MTBE

in ground water in these RFG and OXY areas (fig. 2).

Most of the detections of MTBE in ground water

sampled in the NAWQA Program have been at concentrations less than the USEPA drinking-water advisory; however,

RFG and OXY areas is about 10 times higher than in the rest

of the Nation. These NAWQA results have helped clarify the

picture of MTBE occurrence, which is useful in discussions

related to phasing out the additive. For more information on

MTBE, please visit http://wwwsd.cr.usgs.gov/nawqa/vocns/.

Arsenic

Recently, a retrospective analysis of arsenic in groundwater resources was completed with data previously collected

by USGS personnel and stored in the USGS National Water

Information System (fig. 3). This information helps to

determine the extent of arsenic occurrence at various levels.

For more information on arsenic in ground water of the United

States, please visit: http://co.water.usgs.gov/trace/arsenic/. 

Microbes

A growing number of USGS contaminant-occurrence

studies include a microbial component. For example, the

USGS Missouri District, in cooperation with the Missouri

Department of Natural Resources, studied the occurrence of

3 types of bacteria and 2 types of viruses in 109 public-supply wells completed in the Ozark Aquifer within Missouri

during 1997–98 (Davis, 2000; Davis and Witt, 2000). Results

showed that 86 percent of the public-supply wells were free

Figure 1. Common pesticide mixtures detected in waters of the United States. Left bar of each pair is for surface

water; right bar is for ground water. (Modified from U.S. Geological Survey, 1999.) For more information about

NAWQA nutrients results, please visit: http://water.usgs.gov/nawqa/nutrient.html. DETECTION OF MTBE IN WATER SAMPLES COLLECTED FROM WELLS, IN PERCENT

Areas of the

Nation using

MTBE in gasoline

Other areas

of the Nation

0

5

10

15

20

25

Figure 2. Percent detections of MTBE in United States

wells.

Atrazine

DEA

Simazine

Prometon

Atrazine

Simazine

Prometon

Diazinon

Atrazine

Simazine

Prometon

Metolachlor

Diazinon

Atrazine

Simazine

Prometon

Metolachlor

Diazinon 

Chlorpyrifos

Prometon

Atrazine

Simazine

Atrazine

DEA

Metolachlor 

Atrazine

DEA

Prometon

Metol.

Atrazine

DEA

Prometon

Metol.

Simazine

Atrazine

DEA

Prometon

Metol.

Simazine

Alachlor

Agricultural Land

Surface water

Ground water

FREQUENCY OF DETECTION AT OR ABOVE

0.01 MICROGRAM PER LITER, IN PERCENT

Urban Land

70

60

50

40

30

20

10

0

Surface water

Ground water

and above the lower limits of USEPA’s advisory (20 μg/L) in

the frequency of detection at concentrations above 5 μg/L
3

of these microbial contaminants—information useful to State

regulators and health officials, as well as to water utilities

and water users. For more information, please visit http://

wwwdmorll.er.usgs.gov/missouri/fact-sheets/qw.fct.html.

In Georgia, Michigan, Washington, and Virginia, microbial studies include DNA fingerprinting and other techniques

in an effort to identify sources of microbes in streams. These

studies will help to protect water supplies from contamination by targeting source-reduction efforts toward those animal or human sources of fecal contamination most responsible for polluting certain streams. Please visit http://

ga.water.usgs.gov/projects/chatm/description.html for details

on the Georgia study and http://mi.water.usgs.gov/ for the

Michigan studies.

Radionuclides

The USGS, in cooperation with the USEPA, the American Water Works Association, and the American Water

Works Service Company, completed a targeted reconnaissance survey of 100 public ground-water supplies with an

emphasis on areas of the country expected to have naturally

occurring isotopes of radium (Focazio and others, in press).

Other radionuclides analyzed to augment existing occurrence

data included polonium-210 (Po-210) and lead-210 (Pb-210).

In water samples from many of the targeted public

water-supply systems, Ra-224 (a short-lived isotope of radium) constituted a significant portion of the gross-alpha particle radiation in the drinking water (table 1).

This finding is important because conventional monitoring procedures do not specify a maximum holding time for

the samples to be analyzed for gross-alpha-particle radiation.

Consequently, some analyses are made after most of the Ra224 has decayed. This could lead to inaccurate indications of

compliance with drinking-water standards where public water-supply wells tap radium-rich aquifers. The study also corroborated previous studies which indicated that the gross-alpha-particle screen used to determine combined radium (Ra226 + Ra-228) compliance could be inadequate in some situations. These results are helping the USEPA and the States to

develop strategies for more accurate assessment of radiological risks in drinking water. For more information in your area

please visit http://water.usgs.gov/owq/dwi/ or http://

co.water.usgs.gov/trace/.

Research Related to Contaminant Occurrence

and Distribution

The USGS conducts basic research to help ensure that

tomorrow’s drinking-water programs address appropriate

Activity, in picocuries per liter

Radionuclide Mean Median Standard

deviation Maximum Number of

Samples

Ra-224 3.2 0.3 10.1 73.6 99

Ra-226 1.6 0.4 2.8 16.9 99

Ra-228 2.1 0.5 7.9 72.3 99

Pb-210 0.6 0.5 0.5 4.1 96

Po-210 0.1 0.01 0.5 4.9 96

Table 1. Summary of radionuclide concentrations in the

multi-state survey (from Focazio and others, in press)

300 Miles0

300 Kilometers0

Arsenic in water from

18,850 wells and springs

Greater than 10 μg/L

5 to 9.9 μg/L

3 to 5 μg/L

Less than 2.9 μg/L

EXPLANATION

400 Miles0

0 400 Kilometers 200 Miles0

200 Kilometers0

Figure 3. Concentrations of arsenic in ground water in the United States.
4

95°

40°

39°

38°

37°

36°

94° 92°

91°

90°

93°

C(W)

River

Missouri

57

4 1

2

3

67

66

68

51

5

6

49

40 41

42

104

99

96

95

97

16

75 76 69

8 85

14

9

7 13 54

53

90

91

44

45 43

30 32

33

31

86 88

87 22 105

21

29

27

26

93

38 94 92

70

100

39

102 103 101

83

80

84

106 109

107

28 108 36

34

35

52

17

15

24

25

10 11

81

82

23

48

47

37

46 63

65

62 64

60

19 20

18

61

73

74

55

79

59 58

56

78

77

71 72

50

98

12

89

C(OzCU)

U/NK(Oz)

U/NK(SF)

C(W)

Unc

BCU

U/K(Oz) 8

U/NK(Oz)

U/K(Oz)

U/NK(Oz)

U/NK(Oz)

U/NK(Oz) U/NK(Oz)

U/NK(SF)

O

C(OzCU)

C(OzCU)

C(OzCU)

BCU

Unc

Missouri

River

95°

40°

39°

38°

37°

36°

94° 92°

91°

90°

93°

0 20 40 60 MILES

0 20 40 60 KILOMETERS

0 20 40 60 MILES

0 20 40 60 KILOMETERS

4

96

95

34

17

108

3938

100

102

101

70

93 94

9

31

44

91 30 18

61

82 48

25

 Enteric viruses present

Enteric viruses, coliphage, and 

indicator bacteria not present

ROUND 1

MayJuly 1997

ROUND 2

November 1997-

March 1998

EXPLANATION EXPLANATION

SAMPLES COLLECTED number is 

public-water-supply well identifier (table 1)

34

17 25

59 70

59

O

Coliphage present

 Indicator bacteria present

PRIMARY KARST AREA

SECONDARY KARST AREA

AQUIFER TYPE

Ozark aquifer overlain by Springfield Plateau 

aquifer and confined by Ozark confining unit

Unconfined Ozark aquifer; nonsignificant 

karst features

Unconfined St. Francois aquifer; 

nonsignificant karst features

Basement confining unit

Unconfined Ozark aquifer; primary and 

secondary karst features

Ozark aquifer confined by Western Interior 

Plains confining system

Unconsolidated

Other

BOUNDARY OF AQUIFER TYPE

PUBLIC-WATER-SUPPLY WELL 

AND NUMBER (table 1)

questions with updated tools. Examples of these projects include development of laboratory analytical methods to detect

targeted contaminants at very low concentrations and studies

of the occurrence of emerging contaminants not currently

regulated or monitored in drinking water supplies. Research

topics also include chemical transformations and the breakdown of synthetic organic chemicals in the environment,

methods development and use of environmental tracers to determine the ages and sources of ground and surface water

contributed to wells and rivers, and detailed analyses of precursors associated with disinfection by-products.

The USGS Toxic Substances Hydrology Program (http:/

toxics.usgs.gov/) conducts some of this research. For example, recent work in the Toxics Program has documented

the prevalence of herbicide breakdown products (some of

which have a toxicity similar to the parent compounds) in

Iowa ground water, compared to the parent compounds (fig.

5) (Kolpin and others, 1999).

The Toxics Program also is developing laboratory analytical methods and conducting environmental occurrence

studies on a variety of emerging contaminants in surface water and ground water, including selected veterinary and human antibiotics (chlortetracycline and sulfamethazine), prescription and non-prescription pharmaceuticals (for example,

cimetidine and acetaminophen), sex and steroidal hormones

(17 beta-estradiol and equilenin), and industrial and household wastewater products (triclosan and bisphenol A).

Samples are being collected from water resources in a wide

variety of land-use and hydrogeological settings (which may

or may not be sources of drinking water). This research is being conducted in cooperation with the USEPA to provide additional data and interpretations on the occurrence of emerging contaminants in source-water areas used by community

water systems, such as surface-water intake locations and

wells used for public drinking water. Results may be used to

guide research on health effects of low concentrations of

these contaminants.

For more information, please visit the following web

sites:

• USGS Toxic Substances Hydrology Program,

 http://toxics.usgs.gov/

• USGS National Water Quality Laboratory,

 http://wwwnwql.cr.usgs.gov/.

The research on disinfection by-product precursors has

Figure 4. Public-supply wells in Missouri sampled for microbes (A), and wells with detections (B).

A B
5

focused on the characteristics of naturally occurring organic

substances from various vegetation types that make them

more or less likely to produce toxic trihalomethanes (THM)

(such as chloroform) by combining with chlorine during disinfection. For example, one study found that, contrary to expectations, agricultural drainage water from islands composed of peat had a lower tendency to form THM than water

from open river channels (Bergamaschi and others, 1999b;

Bergamaschi and others, 1999a). These findings will help in

making decisions on managing the lands and waters of the

Sacramento-San Joaquin Delta in California to minimize the

risk for drinking-water consumers in southern California. For

more information, please see http://water.usgs.gov/nrp/

proj.bib/aiken.html.

SOURCE-WATER ASSESSMENTS

As required by the 1996 amendments to the Safe Drinking Water Act (P.L.104-182), States, Tribes, and water suppliers are conducting assessments to delineate surface- and

ground-water source areas, to inventory potential sources of

contamination, and to evaluate susceptibility of supplies to

contamination. USGS contributions to these efforts range

from national assessments of contaminant occurrence and

vulnerability, to comprehensive statewide assessments, to targeted studies designed to answer a specific question. A few

examples are described below. Others may be found at

http://water.usgs.gov/owq/dwi/.

Source-Area Characteristics of Large Public

Surface-Water Supplies

A cooperative project between the USEPA and the

USGS was designed to assist State regulatory agencies in

meeting the requirements of source-water assessment programs by providing a nationally consistent way to define the

characteristics of source-water areas.

The product of this project is a CD-ROM that includes

information on water time of travel during average streamflow conditions that could be used for segmenting the

source-area watersheds as suggested in a USEPA (1997)

guidance report. The information from the project may also

Figure 5. Frequency of detection for selected herbicide compounds (adjusted to a common detection

threshold of 0.20 microgram per liter) and breakdown

products in Iowa. (From Kolpin and others, 1999). Metolachlor ESA Alachlor ESA Metolachlor OA Alachlor OA Atrazine DEA Hydroxyatrazine Acetochlor ESA Cyanazine Amide Metolachlor DIA Prometon Acetochlor OA Acetochlor Cyanazine Acetochlor

Metribuzin

FREQUENCY OF DETECTION, IN PERCENT

60

40

20

0

Degraded

Parent Compound

Herbicide Compounds Detected

Figure 6. Location of 525 drinking-water intakes for large public water supplies in the United States.

INTAKE LOCATION

River/stream

Lock and dam

Reservoir

Lake
6

assist Federal, State, and local water-monitoring agencies in

identifying rivers, impoundments, and watersheds of importance to drinking-water supplies and to related local and regional monitoring programs and water-protection efforts.

The first phase provides hydrologic and watershed information for the source areas of 525 surface-water intakes operated by the largest 437 public water suppliers in the conterminous United States (fig. 6). These suppliers serve populations greater than 10,000 with intakes in watersheds larger

than 1,000 square kilometers and provide drinking water to a

total of 50 million people. The source-area data and calculations were originally assembled for the recently developed

USGS national water-quality model SPARROW (Smith and

others, 1997), and are summarized by source area in the CDROM data base (Alexander and others, 1999). The information on the CD-ROM is helpful to municipalities and water

utilities who need to assess and protect their source water on

the basis of the time it takes to get to their intakes. For more

information please see http://water.usgs.gov/nawqa/sparrow/.

California—Disinfection By-Product Precursors

Naturally occurring organic compounds (humic substances) derived from the decay of plants in source-water areas can combine with chlorine and other halogens used to

disinfect drinking water to produce trihalomethanes (THM)

(such as chloroform) and other toxic by-products. In California, water from the Sacramento and San Joaquin Rivers (fig.

38°15'

121°45' 121°30'

38°00'

Rio Vista

Walnut

Grove

Antioch

TWITCHELL

ISLAND

0

0

5 KILOMETERS

5 MILES

LOCATION

MAP

Figure 7. Location of organic carbon study area, Twitchell Island,

Sacramento-San Joaquin Delta,

California.

7) is pumped to the southern part of the State to be used as

drinking water by 22 million consumers. At times, the

USEPA drinking-water standard of 0.1 mg/L THM is exceeded when the water is treated. About 20 to 50 percent of

the THM precursors originate from agricultural drainage

water from peat soils on islands in the Sacramento-San

Joaquin Delta. A recent USGS study in cooperation with the

California Department of Water Resources (Fujii and others,

1998) found that, as expected, THM production potential,

dissolved organic carbon concentration, and ultraviolet absorbance at a wavelength of 254 nanometers (UV-254) were

all highly correlated. Also as expected, anaerobic soil (without oxygen) tended to produce dissolved organic carbon with

greater aromaticity (more benzene rings in the chemical

structure) than aerobic soils (with oxygen). However, an unexpected result was that aromaticity of the naturally occurring organic matter was not correlated with its potential to

form THM during disinfection with chlorine. This means that

a simple test for aromaticity, such as the UV-254 test, may

not be a good predictor of THM formation potential. More

work will be needed to identify the types of humic substances that serve as THM precursors in this environment.

Results will eventually help guide decisions on managing the

land and water resources of the Delta region to minimize

drinking-water-quality problems. For more information,

please see http://pubs.water.usgs.gov/wrir984147/.

New Jersey—Vulnerability of Public-Supply

Wells to Contamination

In collaboration with the New Jersey Department of Environmental Protection, the USGS has been collecting data

on contaminant occurrence in both surface-water and

ground-water source areas, and relating the results to geology, soils, land use, and other factors that affect vulnerability

(fig. 8). Classification of public-supply wells according to

their vulnerability to pesticides has already led to substantial

cost savings through monitoring waivers for water suppliers

whose sources are shown to be at low risk for contamination.

Sampling is underway for analyses of volatile organic compounds, nitrates, metals, microbes, and radioisotopes in more

than 2000 public-supply wells and at 50 surface-water intakes as part of a comprehensive statewide source-water assessment. The results will be used to target monitoring toward the more susceptible wells and intakes, to help guide

source-water protection programs, and to help guide development of future water supplies. For more information,

please see http://nj.usgs.gov/gw/maps/index.html and http://

nj.usgs.gov/pub/onlinepubs.html.

Michigan—Arsenic in Ground Water, and

Statewide Source-Water Assessment

Ground water in parts of southeastern Michigan contains

concentrations of naturally occurring arsenic in excess of the

USEPA maximum contaminant level of 10 micrograms per

liter. In cooperation with several counties, the USGS is

studying the sources and geochemical reactions responsible

for the elevated arsenic levels. Maps being produced for each
7

county of the study show the distribution of elevated arsenic

concentrations. Results will help homeowners and utilities

avoid high-arsenic areas when they develop new wells, and

could help the development of strategies to mitigate existing

arsenic problems.

The USGS is also cooperating with the State of Michigan on a statewide source-water assessment project with four

components:

(1) Use of hydrogeologic information, ground-water

age dating, and historical water-quality data to determine

susceptibility of wells in karst areas to contamination,

(2) Delineation and characterization of critical assessment zones for seven Michigan rivers used for water supply,

based on time of travel to the intakes,

(3) Susceptibility analyses for water-supply intakes on

the Great Lakes, using a protocol developed by the USEPA

and the Great Lakes States, and

(4) Hydrodynamic modeling and particle tracking to

determine susceptibility of 14 intakes on the St. Clair and

Detroit Rivers, serving 5 million people, to contamination

from accidental releases (spills) of toxic substances.

Texas—Statewide Source-Water Assessment

In cooperation with the Texas Natural Resources Conservation Commission, the USGS is determining the occurrence

of pesticides and volatile organic compounds in drinking-water aquifers and reservoirs throughout the State. These results

are being integrated, along with data on the environmental

setting; geologic and hydrologic characteristics; chemical,

water, and waste management practices; and land use/cover,

NITRATE IN WATER FROM

WELLS SAMPLED BY USGS

0 10 20 30 MILES

0 10 20 30 KILOMETERS

Updip extent 

of KirkwoodCohansey aquifer 

system

Outcrop of

Potomac-RaritanMagothy aquifer 

system

Extent of

terminal

moraine

39°

39°

41°

75° 74°

EXPLANATION

NO3 concentration

in milligrams per liter

Coastal Plain

Piedmont

Valley and Ridge

New England

Less than 1

1 to 2.9

3 to 9.9

10 or greater

PESTICIDES IN WATER FROM 

PUBLIC SUPPLY WELLS

0 10 20 30 MILES

0 10 20 30 KILOMETERS

Updip extent 

of KirkwoodCohansey aquifer 

system

Outcrop of

Potomac-RaritanMagothy aquifer 

system

Extent of

terminal

moraine

39°

39°

41°

75° 74°

EXPLANATION

PESTICIDES

 NOT DETECTED

 DETECTED

Coastal Plain

Piedmont

Valley and Ridge

New England

TOTAL VOLATILE ORGANIC COMPOUNDS IN WATER

FROM PUBLIC SUPPLY WELLS

0 10 20 30 MILES

0 10 20 30 KILOMETERS

Updip extent 

of KirkwoodCohansey aquifer 

system

Outcrop of

Potomac-RaritanMagothy aquifer 

system

Extent of

terminal

moraine

39°

39°

41°

75° 74°

EXPLANATION

VOC concentration

in milligrams per liter

Coastal Plain

Piedmont

Valley and Ridge

New England

Less than 0.2

0.2 or greater

Figure 8. Data used for statewide source-water assessments of (A) pesticides, (B) nitrate, and (C) volatile organic compounds in ground water in the State of New

Jersey.

A.

C.

B.
8

into software that will help determine the susceptibility of

ground-water source areas statewide to contamination.

New Hampshire—Arsenic in Relation to Rock

Type

USGS geologists and hydrologists are combining waterquality data with maps that show rock types grouped according to similar chemical properties. The resulting lithochemical maps show the likelihood of finding elevated concentrations of certain naturally occurring contaminants such as arsenic. The maps will be useful for predicting water quality in

areas where samples have not yet been collected. For more

information visit http://water.usgs.gov/pubs/wri/wri994000/.

Research Related to Source-Water

Assessments

In areas of complex hydrogeology, it can be difficult to

accurately delineate zones of ground-water contribution to

wells and zones where ground water is under the direct influence of surface water (GWUDI). These are among the most

widely debated issues in determining conjunctive delineations (areas where both ground- and surface-water flow toward a well or intake) for source-water assessments. Methods and field applications of environmental tracers (including

stable and radioactive isotopes and other conservative compounds) are being developed by USGS researchers for a

range of hydrologic investigations (Coplen and others, 1999;

Cook and Bohlke, 1999; Busenberg and Plummer, 1992) that

address the relations of surface and ground water and the estimation of the age of ground water. For example, environmental tracers were used to estimate the age of ground water and

to establish the connection between, and relative percentages

of, surface water and ground water in a sole-source karst

aquifer (characterized by limestone caves, springs, and sinkholes) in Georgia (Plummer and others, 1998a, 1998b; fig. 9).

These techniques are increasingly becoming standard tools

for hydrologists, and as interest has grown in this field, the

techniques are becoming more affordable and easier to use

for practical applications. Franke and others (1999), however,

showed that the most successful studies of zones of contribution tend to result from approaches in which numerical simulation and field measurements, such as environmental tracers

and geophysical investigations, are combined. For more information on the USGS National Research Program please visit

http://water.usgs.gov/nrp/. For more information on USGS

activities in source water assessments please visit http://

water.usgs.gov/owq/dwi/.

Withlacoochee R.

Withlacoochee R.

0

0

5 MILES

5 KILOMETERS

33

40

33

33

35

>35

>30

>30

<30 33

30

18 >20 24

32

32

33

>52

>35

>35

>35

>35 >40

2.0

26

<30

<30

20 24

36 31

24 <30

22

21 30

33

2.0

28

12

14

26 25 31

34

34

13 24

27

43

>52

4.5

36

34

>30

>35 31 40

>35

39

43

48

>35

35 >40

37

>30 38

32

33 37

29

>52

37

50

40

20

30

40

2 0

10

20

10

80

50

40

40

10 Line of equal age, in years,

of young fraction in ground water 

10 Line of equal percentage of

river water in ground water 

Well and age of young 

fraction in ground water 

Valdosta

Valdosta watersupply well field Sinkhole

area

0

0

5 MILES

5 KILOMETERS

Figure 9. Ages of the young fraction in the Upper Floridan aquifer at Valdosta, Ga., in June, 1991 (A); and

estimated percentage of Withlacoochee River water in ground water in the Upper Floridan aquifer, June 1991 (B).

(Modified from Plummer and others, 1998a, 1998b.)

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Alexander, R.B., Smith, R.A., Focazio, M.J., and Horn,

M.A.,1999, Source-area characteristics of large public

surface-water supplies in the conterminous United States:

An information resource for source-water assessment:

U.S. Geological Survey Open-File Report 99–248, 1 CDROM.
9

Bergamaschi, B.A., Fram, M.S., Kendall, C., Silva, S.R.,

Aiken, G.R., and Fujii, R., 1999a, Carbon isotopic constraints on the contribution of plant material to the natural

precursors of trihalomethanes: Organic Geochemistry, v.

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Bergamaschi, B.A., Fram, M.S., Fujii,R., Aiken, G.R.,

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1998, Estimating areas contributing recharge to wells—

Lessons from previous studies: U.S. Geological Survey

Circular 1174, 14 p.

Fujii, R.F, Ranalli, A.J., Aiken, G.R., and Bergamaschi, B.A.,

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Delta, California: Implications for drinking-water quality:

U.S. Geological Survey Water-Resources Investigations

Report 98–4147, 75 p.

Kolpin, D.W., Thurman, E.M., and Linhart, S.M., 1999,

Finding minimal herbicide concentrations in ground water? Try looking for the degradates, in Morganwalp, D.W.,

and Buxton, H.T., eds., U.S. Geological Survey Toxic

Substances Hydrology Program—Proceedings of the

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254.

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of river water into a karstic limestone aquifer. 1. Tracing

the young fraction in groundwater mixtures in the Upper

Floridan Aquifer near Valdosta, Georgia: Applied

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Drenkard, S., Schlosser, P., and Michel, R.L., 1998b,

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