U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2010–3002

January 2010

National Water-Quality Assessment, Transport of Anthropogenic and Natural Contaminants (TANC) to Public-Supply Wells

Assessing the Vulnerability of Public-Supply Wells to 

Contamination: Glacial Aquifer System in Woodbury, 

Connecticut

Printed on recycled paper

The glacial aquifer system in the Pomperaug River Basin is 

made up of glacial deposits and fractured bedrock. Stratified (layered) sediments deposited by glacial meltwater fill in 

the valley underlying the Town of Woodbury. Such deposits 

are generally the most productive sources of groundwater 

in New England. Fractured bedrock lies beneath the valley 

and the adjacent uplands. Glacial till (a dense mixture of 

different-sized rock particles in a fine-grained matrix) blankets the bedrock surface in the uplands and in some areas 

beneath the stratified glacial deposits in the valley. Together, 

stratified glacial deposits and till are referred to as “glacial 

deposits” in this fact sheet. Bedrock beneath the valley is 

composed of basalt and sedimentary rocks (shale, siltstone, 

conglomerate, and organic-rich limestone), whereas bedrock in the uplands includes basalt and metamorphic and 

granitic rocks. Recharge to the aquifer system originates as 

rainfall or as stream water that infiltrates to the water table.

In the uplands, infiltrating water reaches the water table and 

then flows laterally through till to upland streams or downward into bedrock fractures. Water eventually flows from 

the bedrock through the sides and bottom of the filled valley into the glacial deposits. Groundwater in the valley discharges to streams, 

ponds, or wells in the area. The public-supply well selected for study is open to the glacial deposits from 45 to 60 feet below land 

surface. It supplies water to about 2,000 Woodbury residents who live in the valley bottom. Most of the groundwater withdrawn in the 

study area is returned to the subsurface as flow through septic-tank drainfields, because all residences and businesses in Woodbury 

are unsewered and use onsite septic systems to treat human waste. 

Glacial aquifer system

Not to scale

Glacial

till

Fault

Fractured

bedrock

Stratified glacial 

(sand and gravel) deposits

Discharge Recharge

Water table Generalized ground-water flow

Supply well Urban area

Pomperaug River

The U.S. Geological Survey’s 

National Water-Quality Assessment 

(NAWQA) Program found, in studies 

from 1991 to 2001, low levels of mixtures of contaminants in groundwater 

near the water table in urban areas across 

the Nation. Contaminants were detected 

less frequently in deeper groundwater 

typically developed for public supply 

(Hamilton and others, 2004). The proximity of contaminant mixtures to underlying public water-supply sources, however, prompted the NAWQA Program to 

begin intensive studies in 2001 to assess 

the vulnerability of public-supply wells 

to contamination. Specifically, pathways 

and processes by which contaminants 

reach public-supply wells in nine aquifer 

systems across the country are being 

investigated. Scientists are studying the 

processes below land surface that control 

whether contaminants are delayed, 

transformed, or mobilized; they are also 

investigating how human activities can 

affect the vulnerability of public-supply 

wells to contamination. 

This fact sheet highlights findings from the vulnerability study of 

a public-supply well in Woodbury, 

Connecticut (Starn and Brown, 2007; 

Brown and others, 2009), in the western 

part of the State. The well typically produces water at the rate of 72 gallons per 

minute from the glacial aquifer system 

in the Pomperaug River Basin. Historic 

water-quality problems concerning this 

well include the presence of chlorinated 

solvents (Mazzaferro, 1986; Geraghty & 

Miller, 1979) and several gasoline-related 

compounds (Sovereign Consulting, Inc., 

2004) that have been associated with “the 

commercial area” (several light industrial 

or commercial properties in an area of 

businesses where hazardous materials 

and petroleum products are used and 

stored). Samples collected (prior to treatment) from the public-supply well for 

the current study contained several types 

of undesirable constituents, including 

11 volatile organic compounds (VOCs), 

nitrate, pesticides, uranium, and radon. 

Most of these constituents were detected 

at concentrations below drinking-water 

standards, where such standards exist. 

Only concentrations of the VOC trichlorethylene (TCE) exceeded the Maximum 

Contaminant Level (MCL) of 5 micro-
Figure 1. A groundwater flow model was 

used to simulate age 

distribution of water 

(the mixture of water 

of different ages) produced by the selected 

supply well in Woodbury, Connecticut. 

“Age” refers to the 

time elapsed since 

water entered the 

groundwater system 

as recharge at the water table. Percentages under curve indicate proportion of total 

water in three age ranges. Water in this system is young relative to groundwater 

found in many of the other aquifer settings studied as part of the NAWQA Program.

Study Design

A computer model of groundwater flow was constructed at a regional scale to estimate 

the “zone of contribution” to the public-supply well (Lyford and others, 2007). The zone 

of contribution is the three-dimensional volume of the aquifer material through which 

groundwater flows from the time it enters the groundwater system at the water table 

until it eventually discharges at the public-supply well. A network of 35 monitoring wells 

was installed in or near the simulated zone of contribution to the well in stratified glacial 

deposits, glacial till, and fractured bedrock to understand groundwater flow and geochemistry along general directions of groundwater flow to the well (Brown and others, 

2009). Water samples were collected from the 35 new monitoring wells, an existing 

monitoring well, and the supply well during 2002 through 2006 and analyzed for naturally 

occurring contaminants (such as uranium, radon, and arsenic) and contaminants resulting from human activities (such as volatile organic compounds, pesticides, phosphorus, 

and nitrogen). Other water-quality parameters (such as major ions, age-dating tracers, 

and selected stable isotopes) were analyzed for to improve understanding of sources of 

water and reactions affecting the chemical composition of groundwater. Finally, a more 

detailed, local-scale computer model of groundwater flow to the public-supply well was 

constructed to refine the estimated area contributing recharge to the well and to calculate the traveltime of water entering the public-supply well (Starn and Brown, 2007).

0

2

4

6

8

10

12

14

16

18

20

0 5 10 15 20

SIMULATED AGE, IN YEARS

PERCENTAGE OF WATER ENTERING WELL

34% 56% 10%

grams per liter (mg/L) established by the 

U.S. Environmental Protection Agency 

for drinking water. Radon concentrations 

exceeded a proposed—but not finalized—

MCL of 300 picocuries per liter (pCi/L).

Some of the contaminants detected 

in the public-supply well and in nearby 

monitoring wells are anthropogenic; 

that is, introduced by human activities. 

Specifically, elevated nitrate concentrations are associated with septic-system 

leachate in the study area. The types 

of pesticides detected are commonly 

linked to lawn maintenance in urban and 

residential areas. VOCs are frequently 

used as solvents or gasoline components. 

Other contaminants—such as uranium, 

radon, and arsenic—occur naturally in 

the sediments and rocks that make up the 

aquifer system. 

Overall, the study findings point to 

four main factors that affect the movement and fate of contaminants and the 

vulnerability of the public-supply well 

in Woodbury: (1) groundwater age (how 

long ago water entered, or recharged, the 

aquifer); (2) the percentage of recharge 

received through urban areas; (3) the 

percentage of recharge received through 

dry wells and their proximity to the 

public-supply well; and (4) geochemical processes within the aquifer system; 

that is, processes that affect the amounts 

and distribution of chemical substances 

in aquifer sediments and groundwater. 

Study findings are intended to help water 

managers, drinking-water suppliers, and 

policymakers to better understand how 

and why contamination of public-supply 

wells occurs and whether water quality 

may improve or degrade. Additionally, 

study findings may be used to evaluate the likely effect of various pumping, 

resource-development, and land-management scenarios on the quality of water 

produced by the public-supply well.

Well Vulnerability Results From 

Very Young Age of Groundwater 

Groundwater age refers to the 

elapsed time since water entered or 

“recharged” an aquifer at the water table. 

Because water in an aquifer typically 

flows downward and laterally over time, 

it is expected that the very youngest 

water will be found near the water table 

and older water will be found at greater 

depths. The proportion of young water 

produced by the public-supply well 

(water that recharged within the last 60 

years) is important for determining the 

vulnerability of the well to contaminants 

resulting from human activities. Groundwater older than about 60 years recharged 

the aquifer system before the use of manmade chemicals became prevalent. 

To understand the blend of water 

of different ages (or “age distribution of 

water”) produced by the public-supply 

well, a computer-model simulation of 

groundwater flow was used to estimate 

the traveltime (or age) of water particles 

entering the public-supply well along the 

15-foot length of the well screen. About 

34 percent of the simulated flow to the 

well consists of water that is younger 

than 5 years (fig. 1), which recharged in 

the valley. About 56 percent of the water 

is from 5 to 9 years old, and the remaining 10 percent of the water is older than 9 

years. Computer simulation indicates that 

all of the water produced by the supply 

well recharged the aquifer system within 

the last 60 years. 

Because computer-simulated traveltimes of water flowing from fractured 

bedrock into the glacial deposits may 

be artificially short (Starn and Brown, 

2007), additional methods were used to 

determine water age. Tritium is an age 

tracer that was used to determine whether 

precipitation recharged local aquifers 

before or after significant atmospheric 

release of tritium in the early 1950s—a 

result of nuclear testing. Tritium concentrations confirm that most water in the 

glacial aquifer system is young, but water 

from one deep bedrock monitoring well 

likely recharged before 1952. Chemical modeling indicates that less than 2 

percent of water produced by the public-
73°13' 73°12' 73°11'

41°32'

41°31'

2002 Land use/land cover

Urban

Agricultural

Undeveloped

Water

Land cover from Center for Land Use Education and Research, 

The University of Connecticut, December, 2003 

0

0

0.5 MILE

Modeled area Significant Potential 

Contamination Source

(from Connecticut Dept. 

of Public Health, 2003)

PSW-1

Area contributing recharge

to public-supply well 

EXPLANATION

0.5 1 KILOMETER

Public-supply well

UPLANDS

VALLEY

30

25

20

15

10

5

0

Vertical profile 

through aquifer

DEPTH BELOW WATER TABLE, IN METERS

Upland recharge, undeveloped land use

Upland recharge, agricultural land use

Upland recharge, urban land use

Valley recharge, undeveloped land use

Valley recharge, agricultural land use

Valley recharge, urban land use

Bedrock

SIMULATED AGE, IN YEARS

Glacial

deposits

EXPLANATION

0 3 6 9 12

Recharge

UPLANDS

Simplified land-use and 

land-cover categories

Corresponding land characterization

Urban Residential (primarily low-to-medium density

with limited tree cover), commercial, 

institutional and industrial land, transportation 

and infrastructure easements, golf courses, 

parks, cemeteries, and areas of turf and grass 

(because such areas are often associated with 

residential land).

Agricultural Grasses and agriculture.

Undeveloped Forest, wetlands, quarries, utility rights-of-way, 

barren land, and low-density residential land 

with tree cover.

Figure 2. A computer model simulating groundwater flow in the glacial aquifer system was used to track water 

“particles” (or parcels) from a vertical profile through the aquifer back to where the particles recharged at the 

water table. Using this technique, the water particles were categorized according to traveltime and land cover 

at the point of recharge. The chemical quality of each particle of water is determined in part by the land cover 

through which the water (originating as precipitation) seeped before it reached the water table. The resulting 

vertical profile of groundwater in the glacial aquifer system shows that water age generally increases with depth. 

Water that recharged in the valley predominates at shallow depths, whereas deeper water originated as recharge 

in the uplands. All water in the glacial portion of the vertical profile at this location and some of the bedrock water 

is eventually captured by the public-supply well; thus, water produced at the wellhead is mixed in age and also is 

influenced by the various land uses within the area contributing recharge to the well.
Figure 3. A substantial number of monitoring wells screened in the shallow glacial 

deposits were found to be affected by septic-system leachate, as determined by high 

dissolved organic carbon content, generally elevated nitrate concentrations, and other 

chemical criteria. In localized zones of the aquifer where concentrations of dissolved 

oxygen were low (less than 0.5 mg/L), nitrate had been converted to nitrogen gas by 

bacterial action, hence the low nitrate concentrations seen in septic-leachate-affected 

wells on the left end of the graph. 

0 5 10 15 20 60

40

20

0

WELL DEPTH, IN METERS BELOW LAND SURFACE

NITRATE PLUS NITRITE CONCENTRATION, IN MILLIGRAMS PER LITER AS NITROGEN

WELL IDENTIFIER

70

73 96

79

85

85

89

90

90

83

76

94 94

53

35

Orange symbol outline indicates high dissolved 

organic carbon, septic-system leachate source

106

88

83

69

72

75

77

82

84

86

87

91

97

101 100

102

86

71

95 95 74

GLACIAL DEPOSITS, SHALLOW

GLACIAL DEPOSITS, DEEP

BEDROCK

PUBLIC-SUPPLY WELL

supply well is old water from the deep 

bedrock. Such a small percentage of old 

groundwater entering the public-supply 

well offers little potential for dilution of 

young waters containing contaminants 

from human activities.

Urban Sources of Contamination 

Affect Well Vulnerability

The area contributing recharge to 

the public-supply well is the zone where 

water that eventually reaches the publicsupply well enters the groundwater system at the water table (see fig. 2). Urban 

land in the area contributing recharge to 

the public-supply well includes various 

potential sources of contamination, as 

inventoried by the Connecticut Department of Public Health (2003)—many 

of which are in the commercial area 

that is about one-quarter mile directly 

upgradient from the public-supply well 

(meaning that water is flowing from the 

commercial area toward the supply well). 

Manmade contaminants detected in the 

glacial aquifer system during the current 

study include solvents, fuel components, 

road salt, and septic-system leachate. 

Volatile organic compounds 

(VOCs) were widely detected in water 

samples from monitoring wells throughout the study area (in 32 of the 36 wells 

sampled) and from the public-supply 

well. Shallow groundwater that originated as recharge through urban areas in 

the valley (fig. 2) typically had higher 

concentrations and more detections of 

VOCs than did groundwater from the 

deep glacial deposits or fractured bedrock that originated mainly as recharge 

through agricultural and undeveloped 

land. The chlorinated solvents TCE 

and perchloroethylene (PCE) were the 

only two VOCs detected above drinking-water standards in any of the 36 

monitoring wells sampled for this study. 

Chlorinated solvents in urban areas are 

used for purposes such as degreasing 

and dry cleaning, and also as ingredients 

in septic-tank cleaning products. PCE 

concentrations were highest in samples 

from several monitoring wells downgradient from the commercial area, with an 

11-μg/L concentration in one well that 

exceeded the MCL (5 μg/L). TCE was 

detected in 33 percent of the monitoring 

wells; concentrations at three wells (maximum concentration, 25 μg/L) exceeded 

the MCL (5 μg/L). TCE concentrations in 

samples collected from the public-supply 

well before treatment ranged from 4.3 to 

16 μg/L. Once in the subsurface, PCE and 

TCE are persistent. Although remediation 

efforts have lessened concentrations, TCE 

and PCE have been detected in the aquifer 

since the late 1970s. 

Methyl tert-butyl ether (MTBE) was 

the most frequently detected VOC during 

this study. The main source of MTBE in 

the study area is a plume caused by a fuel 

spill at a gas station in the commercial 

area. The sale and use of MTBE was 

banned in Connecticut after January 1, 

2004. Concentrations of MTBE in samples from the public-supply well peaked 

at 29 μg/L in 2005, then decreased to less 

than 2 μg/L by July 2006 as a result of 

groundwater remediation efforts (Scott 

Beals, Sovereign Consulting, Inc., written 

commun., 2007).

Chloroform was the second most 

frequently detected compound and was 

found in 45 percent of the wells sampled. 

Chloroform is a VOC that can be formed 

as a byproduct of chlorination. The 

wells in which chloroform was detected 

generally coincide with areas of publicly 

supplied water, where distribution pipes 

carry chlorinated water (and could potentially be leaking) and commercial and 

residential properties discharge chlorinated water to septic-tank drainfields.

Shallow groundwater in the glacial 

deposits has higher concentrations of 

dissolved solids than deep water does. 

Further chemical analyses indicate these 

shallow waters are affected by road salt 

and by septic-system leachate. Both types 

of contamination result in water with 

elevated sodium, calcium, and chloride 

concentrations. Septic-system leachate 

was distinguished from road-salt contamination by generally elevated concentrations of nitrate (3 to19 mg/L (milligrams 

per liter)) and dissolved organic carbon 

(0.5 to 89 mg/L), as well as known proximity of wells to septic systems (fig. 3). 

Water from wells affected by septic-system leachate also contained a lower ratio 

of chloride to bromide ions than waters 

affected by road salt, as well as relatively 

high concentrations of boron (12 to 155 

μg/L). Boron is present in domestic sewage as a residue of laundry detergents. 

Wells affected by septic-system leachate 

generally had higher concentrations of 

trace elements than samples from shallow 

glacial deposits that were relatively unaffected by human contaminant sources.
USGS scientist Jason Lewis collects a chemical-quality sample from a well near Woodbury,

Connecticut. (Photograph by Craig Brown, U.S. Geological Survey.)

Although the public-supply well 

does not have all the characteristics of 

a well affected by septic-system leachate, it does have a boron concentration 

and a ratio of chloride to bromide ions 

that is consistent with septic-system 

sources. To delineate the impact of septicsystem leachate on water quality in the 

public-supply well, a mixing model was 

employed that used nitrate concentrations and stable isotope ratios to estimate 

sources of nitrate relative to two endpoints. One endpoint was represented by 

a monitoring well in a forested setting; 

the other endpoint was represented by a 

monitoring well in an urban setting downgradient from a septic-tank drainfield. 

The plotting location of the public-supply 

well water chemistry along the mixing 

line indicated that up to 15 percent of 

the nitrate in water from the supply well 

was likely from septic-system leachate 

(McMahon and others, 2008). 

Dry Wells Serve as Fast Pathways 

for Movement of Contaminants Into 

the Public-Supply Well 

To reduce stormwater runoff in 

Woodbury, water from the parking lots 

and pavement is channeled into dry 

wells—drains that shunt water directly 

into the aquifer system, bypassing the 

soil and unsaturated zones. Using the 

groundwater flow model to track water 

particles originating at dry wells in the 

commercial area, USGS scientists concluded that approximately 16 percent of 

the water produced by the public-supply 

well is derived from runoff captured by 

these drains. The residence time for water 

from the commercial area is about 1.5 

to less than 4 years, owing to the nearness of this area to the public-supply 

well and the capacity of the stratified 

glacial sediments to rapidly transmit 

water. Dry wells have the potential to 

enhance contaminant movement to the 

supply well because (1) they divert runoff 

directly into the groundwater system, 

bypassing the contaminant filtration and 

degradation processes that may occur in 

the unsaturated zone; (2) they capture 

all precipitation in this area as runoff 

(rather than losing some of the precipitation as overland flow to streams or as 

transpiration by plants), creating an area 

of higher recharge relative to other areas; 

and (3) the stormwater runoff transports 

contaminants that have accumulated on 

the pavement, including road salt during 

winter months. Because of the dry wells, a 

chemical spill or new contaminant source 

in the commercial area would rapidly 

affect the water quality of the publicsupply well. These findings indicate that 

stormwater-control methods cannot be 

considered separately from groundwater 

quality—they are linked. 

Natural Geochemical Conditions 

in Aquifer System Affect the Fate 

of Contaminants 

Geochemical processes may act 

on waters from different sources (and 

the contaminants they carry) once they 

enter the glacial deposits. Three chemical 

factors that affect contaminant concentrations beneath Woodbury are (1) oxic 

conditions, (2) localized consumption of 

dissolved oxygen in groundwater, and 

(3) radioactive decay.

Oxic conditions. Oxygen content of groundwater is a major control 

on whether specific contaminants are 

delayed, transformed, or mobilized in the 

subsurface. In the oxic conditions that are 

characteristic of the local groundwater—

dissolved oxygen concentrations of at 

least 1 mg/L—the contaminant nitrate is 

not degraded and can be transported long 

distances. Thus, elevated nitrate concentrations (as high as 19 mg/L and exceeding the health-based MCL of 10 mg/L) 

were found in the monitoring wells that 

tap oxic waters and are downgradient 

from nitrate sources such as septic-tank 

drainfields. In contrast to their effect on 

nitrate, the oxic conditions of the aquifer 

limit the mobility of the trace elements 

iron, manganese, and arsenic, which 

adhere to aquifer sediments. Thus, it is 

not surprising that concentrations of dissolved arsenic were generally less than 

the minimum reporting limit of 0.2 mg/L 

in the study area. 

Localized consumption of dissolved 

oxygen. The mobility scenarios described 

above are reversed in isolated areas of the 

aquifer that contain either (1) an abundance of natural organic matter in the 

sediments or (2) high concentrations of 

dissolved organic carbon (DOC) derived 

from septic-system leachate (likely from 

improperly designed or overloaded 

systems). Because microbial respiration 

consumes oxygen when organic carbon is 

available, localized “anoxic” conditions—

dissolved oxygen concentrations less than 

0.5 mg/L—were observed in such areas. 

In these anoxic zones, nitrate is converted 

to harmless nitrogen gas in a process 

called denitrification. (This explains why 

water samples collected downgradient 

from some septic drainfields contained 

no detectable nitrate (fig. 3).) Also, in 

localized anoxic settings, iron coatings on 

aquifer sediments can dissolve, releasing 

into groundwater the iron as well as the 

manganese, arsenic, and other trace metals that are associated with the sediment 

coatings. Evidence of this process in the 

glacial deposits is the detection of arsenic 
For more information on the Transport of Anthropogenic and Natural Contaminants to Supply Wells (TANC) topical study, see

http://oh.water.usgs.gov/tanc/NAWQATANC.htm

Hamilton, P.A., Miller, T.L., and Myers, 

D.N., 2004, Water quality in the Nation’s 

streams and aquifers—Overview of 

selected findings, 1991–2001: U.S. Geological Survey Circular 1265, 20 p. 

Lyford, F.P., Carlson, C.S., Brown, C.J., 

and Starn, J.J., 2007, Hydrogeologic 

setting and ground-water flow simulation of the Pomperaug River Basin 

regional study area, Connecticut, in

Paschke, S.S., ed., 2007, Hydrogeologic settings and ground-water flow 

simulations for regional studies of the 

transport of anthropogenic and natural 

contaminants to public-supply wells—

Studies begun in 2001: U.S. Geological Survey Professional Paper 1737–A, 

p. 6–1 through 6–26.

Mazzaferro, D.L., 1986, Ground-water 

availability and water quality in Southbury and Woodbury, Connecticut: U.S. 

Geological Survey Water-Resources 

Investigations Report 84–4221, 105 p.

McMahon, P.B., Böhlke, J.K., Kauffman, 

L.J., Kipp, K.L., Landon, M.K., Crandall, C.A., Burow, K.R., and Brown, 

C.J., 2008, Source and transport controls 

on the movement of nitrate to public supply wells in selected principal aquifers 

of the United States: Water Resources 

Research, v. 44, W04401, 17 p.

Sovereign Consulting, Inc., 2004, Woodbury Mobil subsurface investigation 

report—Woodbury Mobil/Middle 

Quarter Mall Area: Sandy Hook, Conn. 

Starn, J.J., and Brown, C.J., 2007, Simulations of ground-water flow and residence time near Woodbury, Connecticut: U.S. Geological Survey Scientific 

Investigations Report 2007–5210, 45 p.

U.S. Environmental Protection Agency, 

2009, Proposed radon in drinking 

water rule: Accessed August 10, 2009, 

at http://www.epa.gov/ogwdw/radon/

proposal.html.

—By Martha L. Jagucki, Craig J. Brown, 

J. Jeffrey Starn, and Sandra M. Eberts

in eight groundwater samples: the monitoring wells that contained the highest 

arsenic concentrations (maximum of 5.8 

mg/L) had low dissolved oxygen concentrations (less than 2 mg/L) and (or) high 

iron or manganese concentrations (greater 

than 100 mg/L and greater than 50 mg/L, 

respectively). Some of the highest arsenic 

and iron concentrations in groundwater 

samples were from areas where aquifer 

sediments appear to be derived from the 

organic-rich limestone unit of the Cass 

Formation. These findings indicate that 

although arsenic is not a problem in water 

from the public-supply well selected for 

study, it could be if a new supply well 

were screened through a locally organicrich zone of the aquifer.

Radioactive decay. Despite the 

general absence of dissolved uranium 

in groundwater in the glacial deposits, 

the analysis of glacial aquifer sediments revealed an abundance of uranium 

associated with iron coatings on grains. 

This large source of uranium in aquifer 

sediments is likely the source for radon in 

groundwater in the Woodbury area. Radon 

is one of the products formed by radioactive decay of the parent material uranium-238. As of December 2009, the U.S. 

Environmental Protection Agency had not 

finalized regulations setting an MCL for 

radon in drinking water. All groundwater 

samples collected for this study had radon 

concentrations that exceeded the proposed 

MCL of 300 pCi/L (U.S. Environmental 

Protection Agency, 2009). Radon concentrations in the glacial deposits (490 to 

2,400 pCi/L) were not as high as those 

of the bedrock wells (1,600 to 13,000 

pCi/L); concentrations in the metamorphic 

uplands were particularly high. Three of 

the four bedrock water samples exceeded 

the alternate MCL of 4,000 pCi/L that is 

proposed for states or water systems that 

agree to develop programs to address the 

health risks from radon in indoor air (U.S. 

Environmental Protection Agency, 2009). 

The high radon concentrations seen in the 

valley glacial deposits cannot be derived 

from the upland bedrock because it would 

take years for groundwater to flow from 

the uplands to the valley, while the time 

required for radon to decrease by half due 

to radioactive decay is only 3.8 days. 

Protection Effort Implications

Water-quality protection in this 

setting depends on the entire community. The actions of individual residents 

influence water quality in the aquifer, as 

demonstrated, for example, by the number of monitoring wells that were found 

to be affected by septic-system leachate. 

If residents and businesses take steps to 

reduce input of manmade contaminants to 

groundwater, a positive effect on quality 

of the supply-well water might begin to 

be seen in less than 10 years, owing to 

the short residence time of water in the 

aquifer.

Contacts

Sandra Eberts, Team Leader

(614) 430-7740, smeberts@usgs.gov

Jeffrey Starn, Groundwater Flow 

Modeling

(860) 291-6746, jjstarn@usgs.gov

Craig Brown, Geochemistry

(860) 291-6766, cjbrown@usgs.gov

References

Brown, C.J., Starn, J.J., Stollenwerk, 

K.G., Mondazzi, R.A., and Trombley, T.J., 2009, Aquifer chemistry 

and transport processes in the zone of 

contribution to a public-supply well in 

Woodbury, Connecticut, 2002–06: U.S. 

Geological Survey Scientific Investigations Report 2009–5051, 158 p.

Connecticut Department of Public 

Health, 2003, Source water assessment 

report for United Water Connecticut 

Woodbury System well #2 wellfield: 

4 p., accessed October 12, 2009, at 

http://www.dir.ct.gov/dph/Water/SWAP/

Community/CT1680011.pdf.

Geraghty & Miller, Inc., 1979, A preliminary evaluation of a ground-water 

contamination problem in Woodbury, 

Connecticut.