MAJOR FINDINGS:

• Nearly one-fifth (19 percent) of 

randomly selected private 

bedrock wells tested in 

southeastern New Hampshire 

contain concentrations of 

arsenic that exceed 

0.010 milligrams per liter, the 

U.S. Environmental Protection 

Agency’s maximum 

contamination level for public 

water supplies.

• An estimated 41,000 people in 

Hillsborough, Rockingham, and 

Strafford Counties may have 

private bedrock wells with 

concentrations of arsenic that 

exceed 0.010 milligrams per liter.

• Arsenic concentrations are 

similar in all three counties; 

however, the spatial distribution 

of arsenic concentrations that 

exceed 0.010 milligrams per liter 

is variable and relates to geology.

• Although most of the well 

owners (90 percent) reported that 

they use the water from their 

bedrock well for drinking, less 

than 14 percent had tested for 

arsenic prior to this study.

USGS Fact Sheet 051-03

July 2003

ARSENIC CONCENTRATIONS IN PRIVATE 

BEDROCK WELLS IN SOUTHEASTERN 

NEW HAMPSHIRE

U.S. Geological Survey

U.S. Department of Interior

In cooperation with the

U.S. ENVIRONMENTAL PROTECTION AGENCY (EPA NEW ENGLAND), NEW HAMPSHIRE DEPARTMENT OF ENVIRONMENTAL SERVICES, 

NEW HAMPSHIRE ESTUARIES PROJECT, and NEW HAMPSHIRE DEPARTMENT OF HEALTH AND HUMAN SERVICES

INTRODUCTION

Southeastern New Hampshire is a 

rapidly growing region that has been 

identified as having moderate to high 

concentrations of arsenic in drinking 

water from ground-water sources 

(Ayotte and others, 2003; Ayotte and 

others, 1999; Peters and others, 1999). 

Southeastern New Hampshire, comprised of Hillsborough, Rockingham, 

and Strafford Counties (fig. 1), has 

grown in population by more than 

84,500 or 12 percent over the past 

decade to more than 770,400 (U.S. Census Bureau, 2000). These counties contain 62 percent of the State's population, 

but encompass only about 22 percent of 

New Hampshire's land area. More than 

37 percent of the population in New 

Hampshire uses private wells as a 

source for drinking water (U.S. Census 

Bureau, 1990). 

Previous studies have indicated that 

arsenic in ground water from bedrock 

wells is more prevalent in southeastern 

New Hampshire than in other areas of 

the State (Ayotte and others, 2003; 

Ayotte and others, 1999; Peters and others, 1999). These studies also indicate 

that the arsenic in ground water probably has geologic origins, but acknowledge that in some areas, arsenic 

occurrence may be related to present or 

past land-use practices.

Arsenic concentration in public 

drinking-water supplies is regulated by 

the U.S. Environmental Protection 

Agency (USEPA) because of the associated health risks. In 1999, the National 

Academy of Sciences concluded that 

the standard of 0.050 milligrams per 

liter (mg/L, equivalent to parts per million) for arsenic in drinking water did 

not sufficiently protect the public from 

long-term exposure. In response to this 

conclusion, the USEPA revised the public drinking-water standard from 0.050 

to 0.010 mg/L (U.S. Environmental Protection Agency, 2001). The revised standard of 0.010 mg/L will be fully 

enforceable for public drinking-water 

supplies by the year 2006. 

The quality of drinking water 

obtained from private wells in New 

Hampshire is not regulated; consequently, private wells are often not sampled for arsenic unless individual well 

owners choose to do so. To provide private well owners and Federal and State 

environmental and health officials with 

accurate information on arsenic concentrations from private wells in this 

region, the U.S. Geological Survey 

(USGS) conducted an arsenic occurrence and distribution study, in cooperation with the U.S. Environmental 

Protection Agency (EPA New England), 

New Hampshire Department of Environmental Services (NHDES), New 

Hampshire Estuaries Project, and with 

 
Page 2

the New Hampshire Department of 

Health and Human Services 

(NHDHHS). This report describes the 

results of this study to determine the 

range of arsenic concentrations from 

ground water in the three counties of 

southeastern New Hampshire by analyzing water samples collected by a randomly selected group of well owners 

from this area.

Sampling Strategy

A database maintained by the 

NHDES containing information on 

private bedrock wells was used to randomly select wells from within the 

three-county study area. Sampling 

instructions and sample bottles were 

mailed to well owners. Samples were 

received from 353 participants—

approximately 50 percent of all the well 

owners who received a sample packet. 

To obtain an unbiased representation of 

the ground-water quality in the study 

area, a computerized equal-area, 

random-well-selection approach was 

used (Scott, 1990). This random-wellselection approach ensured that the 

entire study area was represented, and 

that the number of samples received 

from each of the three counties was proportional to the size (area) of the county 

rather than its population. Study participants were asked to collect untreated 

water samples. Most of the water samples (56 percent) were collected from 

the kitchen faucet, 19.8 percent were 

collected from an outside spigot, and 

the remaining samples were collected at 

a spigot either before or after the pressure tank, or from the bathroom faucet. 

Samples were analyzed for total arsenic 

according to USEPA method 200.8 

(U.S. Environmental Protection Agency, 

1994) at either the NHDES Laboratory 

or the EPA New England Laboratory. 

The minimum reporting level for both 

laboratories was 0.001 mg/L. To assure 

the quality of the data obtained from 

this study, a quality-assurance project 

plan (QAPP) was developed. Qualitycontrol samples represented 5 percent of 

the total samples collected for the study. 

The quality-control samples included 

duplicate, inter-laboratory split, and 

performance-evaluation samples. 

Results from the analysis of the qualitycontrol samples indicated that there was 

no measurable bias or significant variability from either laboratory or 

between the two laboratories. 

The Range of Arsenic 

Concentrations

Arsenic concentrations from the 

353 ground-water samples received 

ranged from <0.001 to 0.215 mg/L. The 

median concentration (the value where 

50 percent of the samples were higher 

and 50 percent were lower) of arsenic in 

each county is near the 3-county median 

of 0.002 mg/L (table 1). Over 30 percent of all the samples had at least 

Figure 1. Locations of towns in Hillsborough, Rockingham, and Strafford Counties in the 

southeastern New Hampshire study area.

Table 1. Summary of arsenic concentrations and percent of wells with concentrations greater than 

0.005, 0.01, and 0.05 milligrams per liter, by county

[No., number; <, less than]

County No. of 

samples

 Arsenic concentrations 

(milligrams per liter)

Percent of wells with arsenic 

greater than

(milligrams per liter)

Minimum Median Maximum 0.005 0.01 0.05

Hillsborough 158 <0.001 0.002 0.075 32 21 3

Rockingham 125 <0.001 0.001 0.215 26 14 2

Strafford 70 <0.001 0.003 0.090 37 21 1

Overall 353 <0.001 0.002 0.215 31 19 2

Weare

Derry

Strafford

Hollis

Deerfield

Milton

Antrim

Lee

Dover Barrington

Rochester

Candia

Nottingham

Bedford

Wilton

Amherst

Nashua

Salem

Auburn

Deering

Hudson

Milford

Epping

Goffstown

Hillsborough

Hancock New

Boston

Mason Pelham

New

Durham

London-

 derry

Chester

Rye

Farmington

Merrimack

Durham

Exeter

Raymond

Temple

Manchester

Windham

 Peterborough

Northwood

 New

Ipswich

Greenfield Kingston

Frances-

 town

Sharon

Brook-

 line

 Lyndeborough

Fremont

Middleton

Litchfield

StraBrent- tham

wood

San- Hampton

down Danville

Portsmouth

Madbury

Atkinson

Mount

Vernon

Newton

Green-

 land

Plaistow

Newmarket

Newington

Kensington

Windsor

Bennington

Seabrook

North

Hampton

Hampton Falls

Somersworth

Newfields

Rollinsford

Greenville

South Hampton

Hampstead

East Kingston

New

Castle

71 ̊

72 ̊

43 ̊

43 ̊20'

EXPLANATION

County

 Hillsborough

 Rockingham

 Strafford

 Town boundary

0 5 10 MILES

0 5 10 KILOMETERS

0 50 MILES

0 50 KILOMETERS

Study

area

New

Hampshire

Town boundaries from U.S. Geological Survey

Digital data, 1968-88, 1:24,000;

Albers Equal-Area Conic projection

Standard parallels 29 ̊30'N and 45 ̊30'N, central meridian 71 ̊00'W

Maine

Massachusetts

Vermont
Page 3

0.005 mg/L of arsenic in the water. 

The maximum concentration was 

0.215 mg/L, but only eight samples 

(2 percent) were greater than 

0.050 mg/L. Overall, 19 percent of the 

samples exceeded 0.010 mg/L. Twentyone percent of the ground-water samples from Hillsborough and Strafford 

Counties had arsenic concentrations that 

exceeded 0.010 mg/L, whereas 14 percent of the samples from Rockingham 

County exceeded 0.010 mg/L. Although 

private bedrock wells are not required to 

meet Federal drinking-water standards, 

analytical results from the well samples 

are discussed for comparison purposes 

in terms of the recently approved public 

drinking-water standard of 0.010 mg/L.

Arsenic Occurrence in Relation 

to Geology

Although median concentrations of 

arsenic in water from private bedrock 

wells in each of the three counties are 

similar, there are distinct spatial patterns 

of arsenic concentrations greater than 

0.010 mg/L within the study area 

(fig. 2). Data were analyzed in relation 

to mapped bedrock geologic units 

(referred to hereafter as geologic units 

in this report) identified on the State 

geologic map of New Hampshire 

(Lyons and others, 1997). Geologic 

units (also commonly referred to as formations, members, and groups) are rock 

types that have unique characteristics 

and thus, are defined based on factors 

such as processes of rock formation, 

mineral composition, and age. Arsenic 

data from the ground-water samples 

were grouped according to the geologic 

unit in which the well was located. This 

information was determined with geographic information system (GIS) analysis, using a digital version of the State 

geologic map of New Hampshire and 

the location of the wells. The GIS analysis identified 25 geologic units that 

were represented by these ground-water 

samples. The number of samples per 

geologic unit ranged from 1 to 54 and is 

related to the size (aerial extent) of the 

geologic unit in the study area (table 2). 

The percent of wells in each geologic

Grouped geologic units 

showing percent of wells with

concentration of arsenic greater 

than 0.010 milligrams per liter

 Less than 1.0

 1.0 to 10.0

 10.1 to 20.0

 20.1 to 30.0

 Greater than 30.0

NOTE: Individual geologic unit boundaries 

within a group are not shown. White areas 

within map indicate geologic units from 

which no samples were received

 Town boundary

Concentration of arsenic, in 

milligrams per liter Minimum 

reporting level is 0.001 

 Less than 0.001

 0.001 to 0.010

 0.011 to 0.025

 0.026 to 0.050

 Greater than 0.050

71 ̊

72 ̊

43 ̊

EXPLANATION

43 ̊20'

0 5 10 MILES

0 5 10 KILOMETERS

Town boundaries from U.S. Geological Survey

Digital data, 1968-88,1:24,000;

Bedrock units digitized from Lyons and others, 1997, 1:250,000;

Albers Equal-Area Conic projection

Standard parallels 29 ̊30'N and 45 ̊30'N, central meridian 71 ̊00'W

Figure 2. Concentrations of arsenic in private bedrock wells, and grouped geologic units showing percent of wells 

with concentrations of arsenic greater than 0.010 milligrams per liter. (For information on the individual geologic units 

in each group, see table 2.)
Page 4

unit with an arsenic concentration that 

exceeded 0.010 mg/L was computed. 

Geologic units with similar percents 

were then grouped together, as shown in 

figure 2 and table 2. The likelihood of 

having a well with arsenic at concentrations of concern for human health is 

shown in figure 2. Results of this analysis indicate that the number of groundwater samples with arsenic concentrations greater than 0.010 mg/L can vary 

between adjacent or nearby geologic 

units.

Specific geologic units stand out 

with respect to arsenic concentrations 

that exceeded 0.010 mg/L (table 2). Discussion in this section of the report is 

generally limited to geologic units that 

had at least 15 water samples. The 

Massabesic Gneiss Complex, for example, had no ground-water samples with 

concentrations of arsenic that exceeded 

0.010 mg/L. In contrast, 25 and 28 percent of the ground-water samples from 

wells in the Concord Granite and the 

Spaulding Tonalite, respectively, had 

arsenic concentrations that exceeded 

0.010 mg/L. Ten geologic units out of 

25 had 25 percent or more of the wells 

with concentrations of arsenic greater 

than 0.010 mg/L.

Ground water from wells in different members or subdivisions of a geologic unit can have markedly different 

concentrations of arsenic greater than 

0.010 mg/L. For example, the Berwick 

Formation consists of the main Berwick 

Formation and its two members—the 

Berwick Formation, Gove member; and 

the Berwick Formation, unnamed member (Lyons and others, 1997). GroundTable 2. Summary of the geologic units grouped by percent of samples with concentrations of arsenic greater than 0.010 milligrams per liter in ground water 

from private bedrock wells in southeastern New Hampshire

[fig., figure; No., number; mg/L, milligrams per liter; <, less than; geologic units from Lyons and others (1997). Color shading identifies the geologic units that 

compose the groups shown in figure 2]

Groups of 

geologic units 

(fig. 2)

Geologic unit No. of samples Percent of samples with concentrations of 

arsenic greater than 0.01 mg/L

Percent of study area 

underlain by geologic unit

Greater than 30 percent of samples

Ayer Granodiorite 2 50 <1

Eliot Formation, Calef Member 2 50 <1

Kittery Formation 11 46 3

Rangeley Formation, lower part 16 31 4

Rangeley Formation, upper part 16 31 5

Berwick Formation, unnamed member 32 31 6

20.1 to 30 percent of samples

Spaulding Tonalite 40 28 10

Exeter Diorite 11 27 3

Littleton Formation 4 25 2

Concord Granite 28 25 7

Two-mica granite of northern and southeastern 

New Hampshire

4 24 2

Perry Mountain Formation 21 24 6

10.1 to 20 percent of samples

Eliot Formation 20 20 8

Kinsman Granodiorite 28 11 8

1 to 10 percent of samples

Berwick Formation 54 7 16

Less than 1 percent of samples

Smalls Falls Formation, undivided 3 0 1

Massabesic Gneiss Complex 32 0 10

Rangeley Formation, upper part, pink to green 

calc-silicate and purple biotite granofels

1 0 <1

Madrid Formation, undivided 1 0 <1

Rangeley Formation, undivided 3 0 <1

Berwick Formation, Gove Member 3 0 <1

Rye Complex 4 0 2

Breakfast Hill Granite of Novotny (1964) 3 0 <1

Mesoperthitic granite 3 0 1

Gray biotite granite 11 0 3
Page 5

water samples from the main Berwick 

Formation had concentrations of arsenic 

greater than 0.010 mg/L in 7 percent of 

the samples, whereas, the Berwick Formation, unnamed member had concentrations that exceeded 0.010 mg/L in 

31 percent of the samples. None of the 

three samples received from wells 

located in the Berwick Formation, Gove 

member had concentrations that 

exceeded 0.010 mg/L. Previous regional 

and local studies (Ayotte and other, 

2003; Ayotte and others, 1999; Peters 

and others, 1999) also had identified 

frequent arsenic concentrations greater 

than 0.010 mg/L in several of these geologic units based on data from public 

and private wells.

The apparent relation of arsenic 

occurrence to geology provides a useful 

measure for predicting where arsenic 

concentrations in ground water are 

likely to exceed 0.010 mg/L. The data 

collected for this study, however, are of 

limited use in explaining why arsenic 

concentrations vary between and(or) 

within geologic units. Therefore, the 

concentration of arsenic in ground water 

for any given well cannot be accurately 

predicted; individual testing is necessary.

Water Use

Ninety percent of the study participants reported that they use the water 

from their private wells as drinking 

water. The remaining 10 percent (37) of 

the participants indicated that they do 

not drink the water from their well 

because of water-quality problems. The 

most frequently described problems 

were iron and(or) manganese staining 

(34 percent) and sediment (25 percent) 

(table 3). Only 13 percent of well owners reported that their well water had 

been previously tested for arsenic. 

Therefore, few private well owners were 

aware of the concentration of arsenic in 

their water. Of the 353 individuals who 

participated in the study, 46 percent 

(164) reported the use of some type of 

treatment or filtering system. Sediment 

filters were the most commonly 

reported system, followed by water softeners (18 and 13 percent, respectively). 

Only two participants specifically 

reported treating for arsenic. In general, 

water-treatment systems should be 

designed for the specific contaminant of 

interest, even though some systems may 

work for several contaminants. Treatment systems not specifically designed 

to remove arsenic, such as sediment filters or water softeners, may be ineffective and unreliable for removal of 

arsenic (Bernard Lucey, N.H. Department of Environmental Services, Water 

Division, oral commun., 2003).

Human Health Implications

The presence of arsenic in drinking 

water has been associated with adverse 

health outcomes, primarily cancers, and 

currently is regulated by Federal and 

State standards for public water supplies 

(U.S. Environmental Protection Agency, 

2001). Although all public drinkingwater supplies must meet the new 

arsenic standard by 2006, private drinking-water supplies are largely unregulated and are not required to meet this 

new standard. To show the effect on the 

population in southeastern New Hampshire, an estimate of the number of people with private wells with an arsenic 

concentration greater than 0.010 mg/L 

is presented.

Based on the population of the 

three-county region (U.S. Census 

Bureau, 2000) and water-use data from 

1990 (U.S. Census Bureau, 1990), more 

than 285,000 people are estimated to 

use private water supplies. Water-use 

information tables for New Hampshire 

(U.S. Census Bureau, 1990) indicate 

that about 75 percent of people on private water supplies use bedrock wells 

rather then some other type of private 

source. Results from this study indicate 

that 19 percent of bedrock wells in the 

3-county region have concentrations of 

arsenic greater than 0.010 mg/L; therefore, it can be estimated that approximately 41,000 people in the region have 

bedrock wells with arsenic at concentrations of concern for human health. This 

estimate may be conservative because 

recent well data from the State of New 

Hampshire indicate that from 1991 to 

2000, approximately 95 percent of the 

wells constructed for private use in the 

three-county study area were bedrock 

wells (Rick Chormann, State of New 

Hampshire Geologic Survey, written 

commun., 2003).

Who to contact for more information:

The New Hampshire Consortium on 

Arsenic was formed in 2001 to better 

facilitate communication to the public of 

information related to all aspects of 

arsenic, and is a valuable source of 

arsenic information. The Consortium 

includes the USGS, USEPA, Dartmouth 

College, and agencies from the State of 

New Hampshire. The Consortium members can provide information to the public 

on treatment technologies, health effects, 

and occurrence of arsenic. Contact information is listed as the following: 

Table 3. Summary of reported problems with water quality and reported water-treatment methods 

used by private well owners in southeastern New Hampshire

[No., number; (34), number in parentheses is percent of problems or water-treatment methods; 

Note: more than one water-quality problem may have been reported per well]

No. of 

participants

Type and number of reported water-quality problems

Staining: Iron/

manganese

Sediment Taste/odor pH Radon

353 120 (34) 88 (25) 43 (12) 6 (2) 2 (<1)

No. of 

participants

Type and number of reported water-treatment methods

Sediment 

filters

Ion exchange 

(Softeners)

Combinations: 

any two or three of 

the methods below: 

(Softeners/carbon 

filters/reverse 

osmosis/birm)

Oxidizing 

filters 

(Potassium 

permanganate/

birm/aeration)

Reverse 

osmosis

Carbon 

filter Other

353 63 (18) 46 (13) 18 (5) 11 (3) 5 (1) 5 (1) 16 (5)
Page 6

Water testing and treatment 

guidelines:

New Hampshire Department of Environmental Services, Public Information 

Officer, Tim Drew (603) 271-3306, 

E-mail at tdrew@des.state.nh.us.

Health-related questions:

New Hampshire Department of Health 

and Human Services, Chief, Bureau of 

Environmental and Occupational Health, 

Neil Twitchell (603) 271-5870, E-mail at 

ntwitche@dhhs.state.nh.us.

Research on toxic effects of arsenic 

on ecosystems and human health:

Center for Environmental Health 

Sciences at Dartmouth, Associate 

Director for Outreach, Nancy Serrell 

(603) 650-1626, E-mail at 

nancy.serrell@dartmouth.edu.

Federal research on occurrence and 

sources of arsenic:

U.S. Geological Survey, Outreach Coordinator, Debra Foster (603) 226-7837, 

E-mail at dhfoster@usgs.gov.

Federal regulation guidelines:

U.S. Environmental Protection Agency, 

Toxicologist, Maureen McCelland 

(617) 918-1517, E-mail at 

mcclelland.maureen@epa.gov.

Acknowledgments

The authors thank the citizens who 

participated in the study and the staff at 

New Hampshire Department of Environmental Services Laboratory for sample 

analysis. The authors also thank the staff 

at EPA New England for their assistance—Richard Willey for supporting this 

project, Rhonda Mason for sample tracking, and the laboratory staff for sample 

analysis.

References Cited

Ayotte, J.D., Montgomery, D.L., 

Flanagan, S.M., Robinson, K.W., 

2003, Arsenic in ground water in eastern New England: Occurrence, controls, and human health implications: 

Environmental Science and Technology, v. 37, no. 10, p. 2075-2083.

Ayotte, J.D., Nielsen, M.G., Robinson, 

G.R., Jr., Moore, R.B., 1999, Relation 

of arsenic, iron, and manganese in 

ground water to aquifer type, bedrock 

lithogeochemistry, and land use in the 

New England Coastal Basins: U.S. 

Geological Survey Water-Resources 

Investigations Report 99-4162, 61 p. 

Lyons, J.B., Bothner, W.A., Moench, R.H., 

and Thompson, J.B., Jr., 1997, Bedrock geologic map of New Hampshire: 

U.S. Geological Survey Special Map, 

2 map sheets, scale 1:250,000.

National Research Council, 1999, Arsenic 

in drinking water: Washington, D.C., 

National Academy Press, 263 p.

Peters, S.C., Blum, J.D., Klaue, Bjoern, and 

Karagas, M.R., 1999, Arsenic occurrence in New Hampshire drinking 

water: Environmental Science and 

Technology, v. 33, no. 9, p. 1328-

1333.

Scott, J.C., 1990, Computerized stratified 

random site-selection approaches for 

design of ground-water quality sampling network: U.S. Geological Survey 

Water-Resources Investigations 

Report 90-4101, 109 p.

U.S. Census Bureau, 2000, Municipal populations 1960-2000—Arranged by 

county: U.S. Census Bureau, accessed 

March 21, 2003, at http://www.state.

nh.us/osp/sdc/Munipop60-00.doc

———1990, Historical census of housing 

tables—Sources of water: U.S. Census 

Bureau, accessed February 10, 2003, 

at http://www.census.gov/hhes/www/

housing/census/historic/water.html

U.S. Environmental Protection Agency, 

2001, National primary drinking water 

regulations; Arsenic and clarifications 

to compliance and new source contaminants monitoring; Final rule: Federal 

Register Part VIII, 40 CFR, Parts 9, 

141 and 142, p. 6981.

———1994, Methods for the determination 

of metals in environmental samples, 

supplement I: U.S. Environmental 

Protection Agency/600/R-94/111, 

rev. 5.4.

NEW HAMPSHIRE DEPARTMENT 

OF ENVIRONMENTAL SERVICES 

RECOMMENDS THAT ALL PRIVATE 

WELLS BE TESTED

Private wells in New Hampshire 

are not regulated as water supplies, and 

are often not tested for health-related 

contaminants such as arsenic, a common contaminant found in bedrock 

wells in New Hampshire. The State of 

New Hampshire recommends that all 

private wells be tested for arsenic and a 

number of other naturally occurring 

health-related contaminants. 

Information on the State of New 

Hampshire’s recommendations for testing and guidance on water treatment 

options of private wells is available at 

http://www.des.state.nh.us/ws.htm

Fact Sheet WD-WSEB-2-1: 

Suggested Water-Quality Testing for 

Private Wells

Fact Sheet WD-WSEB-3-2: 

Arsenic in Drinking Water

FOR ADDITIONAL INFORMATION:

The data for this study are available at:

U.S. Geological Survey

New Hampshire/Vermont District

361 Commerce Way

Pembroke, NH 03275

(603) 226-7800 Phone

(603) 226-7894 FAX

Copies of this report can be purchased 

from:

U.S. Geological Survey

Branch of Information Services

Box 25286

Denver Federal Center

Denver, CO 80225-0286

Visit USGS Web sites at URL:

http://nh.water.usgs.gov

http://www.usgs.gov

NAWQA Program:

http://water.usgs.gov/nawqa

—By Denise L. Montgomery1, 

Joseph D. Ayotte1, Paul R. Carroll2, 

and Patricia Hamlin2

1U.S. Geological Survey.

2U.S. Environmental Protection Agency 

(New England).