U.S. Department of the Interior

U.S. Geological Survey

Fa

Printed on recycled paper

pp

water in Rockingham County 

others, 2004). These findings 

implications for future water

management in New Hampsh

other areas with similar hydr

settings.

STUDY DESIGN 

To accurately determine th

rence and distribution of MT

study incorporated a random 

design and a lower analytical 

level (0.2 μg/L) than had prev

been used in the state. Betwe

August 2003, a total of 223 s

collected from drinking-wate

including 120 samples from 

INTRODUCTION 

Methyl tert-butyl ether (MTBE) has 

been added to gasoline since the late 

1970s to increase octane and reduce 

vehicle emissions. Its use significantly 

increased with the production of reformulated gasoline (RFG) after amendments 

to the Clean Air Act in 1990 required the 

use of cleaner burning fuels. MTBE has 

relatively high solubility in water, low 

soil adsorption, and is slowly biodegraded. Thus, once it has been released to 

the environment through spills, leaking 

storage tanks, or other pathways, it has 

the potential for pervasive and persistent 

contamination of ground water. Although 

no Federal drinking-water standard 

has been established for MTBE, the 

U.S. Environmental Protection Agency 

(USEPA) (1997) has tentatively classified 

the compound as a possible carcinogen 

and has set a drinking-water advisory 

at 20 to 40 micrograms per liter (μg/L). 

The State of New Hampshire (2000) has 

adopted a maximum contaminant level of 

13 μg/L for MTBE in drinking water.

Routine monitoring by the New 

Hampshire Department of Environmental Services (NHDES) indicates that the 

presence of MTBE in public water-supply wells, at or above a detection level of 

0.5 μg/L, has increased statewide from 

12.7 percent in 2000 to 15.1 percent in 

2002, and that occurrence is greatest in 

the four New Hampshire counties where 

use of reformulated gasoline is required 

(fig. 1). In Rockingham County, MTBE 

occurrence rates increased from 20.3 to 

23.1 percent during the same period. 

 The potential risk of exposure to 

MTBE through drinking water in New 

Hampshire may be greatest in Rockingham County. This County has the second 

largest population in the state (280,500) 

and the largest population served by 

ground water (57,000 by community 

ground-water systems, 135,000 by private 

wells, and 71,000 by community systems that use a combination of surface 

and ground water). In this region, heavy 

reliance on ground water for domestic and public supply adds urgency to 

understanding the occurrence of, and 

controls on, MTBE contamination. This 

Fact Sheet summarizes the major findings 

from a cooperative study between the 

Figure 1. Percent of public wat

wells with MTBE concentration

or equal to 0.5 microgram per lit

for 2000, 2001, and 2002, showin

where reformulated gasoline (R

not required.

• MTBE was detected at concentrations 

 greater than 0.2 micrograms per liter 

 (μg/L) in 40 percent of 120 public 

 wells and 21 percent of 103 private wells 

 sampled.

• MTBE concentrations were greater in 

 relatively deep public wells with low 

 water yields.

• MTBE concentrations in wells were 

 strongly related to urbanization.

• MTBE concentrations in public wells 

 decreased with distance from under- 

 ground gasoline storage tanks.

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and 103 samples from private domestic 

wells (fig. 2). All of the private wells 

were in the fractured-bedrock aquifer 

and, of the public wells, 98 were in the 

bedrock aquifer and 22 were in unconsolidated deposits.

Samples were collected, preserved, 

and stored according to USGS protocols 

(Koterba and others, 1995; Ayotte and 

others, 2004). Samples were analyzed at 

the NHDES Laboratory according to a 

modification of USEPA (1995) method 

524.2. Several types of quality-control 

samples, representing 15.2 percent of 

the total samples, also were collected. 

A number of standard statistical analyses were used to evaluate the data and 

assess possible relations between MTBE 

occurrence and various factors, including aquifer type (bedrock or unconsolidated deposits); bedrock geology; public 

water-system size; water-supply establishment type; reported well yield; well 

depth; population; land use; soils; roads; 

well proximity to underground gasoline 

storage tanks (USTs); and water-sample 

temperature, pH, specific conductance, 

and dissolved oxygen.

MTBE OCCURRENCE 

The locations of sampled wells and 

associated MTBE concentrations are 

shown in figure 2. MTBE was found, at 

concentrations higher than the detection 

level of 0.2 μg/L, in 40 percent of the 

public wells and 21 percent of the private 

wells sampled. These rates are higher 

than those reported in a study of Maine 

counties where reformulated gasoline was 

used (State of Maine, 1998). The range of 

concentrations found is shown in figure 

3. Public wells had significantly greater 

occurrence rates and higher concentrations of MTBE than private wells (table 

1). None of the private wells had a concentration that exceeded either the state 

drinking-water standard of 13 μg/L or the 

state action level of 5 μg/L for notification of adjacent well owners. However, 

four public wells exceeded both these 

levels. In all four cases, well owners had 

prior knowledge of the contamination 

and treatment systems were in place to 

remove MTBE.

The rates of MTBE occurrence in public wells in fractured bedrock and unconsolidated deposits were 41.8 and 31.8 

percent, respectively (table 1). However, 

differences in occurrence rates and concentrations were not significantly 

different between the two aquifers. 

Public wells that were used for residential supply, including wells at 

apartment complexes, condominiums, and mobile home parks, had 

the highest rate of occurrence, with 

63.1 percent above 0.2 μg/L. This 

rate was significantly higher than 

that for wells at schools (20.5 percent), but not significantly higher 

than that for wells at commercial 

establishments (40.7 percent) or 

large community systems (31.3 

percent). Although occurrence rates 

were not significantly different 

among system categories, community water systems (that serve 

Figure 2. Concentrations of MTBE in public and private water-supply wells in Rockingham 

County, New Hampshire, during 2003.

MTBE concentrations in 

private wells were related to 

urban factors including pop

sity, housing density, and th

of urban land use and roads 

1,640 feet (500 meters) of t

addition, MTBE concentrat

related to the specific condu

water sample. Because spec

tance can increase due to ch

road salt and septic systems

indicator of urbanization.

Relations between MTB

in public wells and various 

shown in figure 4. MTBE c

were strongly related to urb

tors such as population den

density, and specific conduc

water sample. Concentratio

with distance to undergroun

storage tanks, which is cons

findings from another New 

study where gasoline sourc

source-water protection are

wells, were related to MTB

tions (Moyer and others, 20

Figure 3. Range of MTBE concentratio

above a detection level of 0.2 microgra

by well type, Rockingham County, New 

(N.H. is New Hampshire; USEPA is U.S

Protection Agency).

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MTBE concentrations in public wells 

increased significantly with well depth 

and, although not statistically significant, 

concentrations were generally lower 

in wells with high reported yields. In 

interpreting these findings, it is important to understand common well-drilling practices and trends in the region. 

Depths for all public wells sampled in 

this study ranged from 16 to 1,020 ft, 

with a median of 226 ft. Eighty-two 

percent of the public wells were in the 

bedrock aquifer and ranged in depth from 

125 to 1,020 ft. During bedrock-well 

installation, drilling is typically continued until an adequate supply of water is 

obtained, either through increased yield 

or increased well storage. Therefore, lowyielding wells are often relatively deep. 

In response to increasing demands for 

water in the rapidly developing regions of 

New Hampshire, bedrock wells are being 

drilled deeper and mean well depth has 

increased from 326 ft in 1985 to 409 ft in 

1998 (Drew and others, 2001).

Deep, low-yielding wells could exhibit 

high occurrence rates and concentrations 

of MTBE through various processes. In 

low-yielding wells, a major proportion 

of the water and MTBE contamination 

may be derived from leakage of shallow 

ground water, either through fractures 

increases. Thus, for deep, 

low-yielding bedrock wells, 

MTBE that enters the well is 

less likely to be diluted than 

in high-yielding wells.

MTBE concentrations 

in public wells were significantly higher in water 

samples that were more 

acidic (lower pH). Ayotte 

and others (2003) found that 

in bedrock wells in eastern 

New England, the pH of well 

water is related to the estimated age of 

the recharge water to the well. The implication is that recently recharged (low pH) 

ground water is more directly connected 

to the land surface and, thus, to sources 

of MTBE. Conversely, ground water with 

high pH levels may be relatively old and, 

in some cases, could predate the introduction of MTBE into the local ground-water 

system. 

the highest MTBE concentrat

be related to point sources, as 

cated by the observed relation 

MTBE concentrations and di

underground storage tanks. S

releases of MTBE vapor, asso

gasoline vapor recovery syste

been investigated (Young and 

2002; Lynn, 2004). However, 

to which this source of contam

occurs in Rockingham Count

known. The observed relation 

MTBE occurrence in wells an

urban indicators may reflect a 

tion of sources, including leak

the cumulative effects of min

and the urban atmosphere. Pa

others (1997) show that urban 

spheric sources alone, in area

ground-water recharge such a

England, could produce conc

MTBE in ground water that a

those found at low levels in th

ubcsuppy esabseype

Residences 38 63.1

Commercial 27 40.7

Schools/recreation 39 20.5

Large community systems 

(serving at least 1,000 

people)

16 31.3

Public-system category

Community 53 52.8

Transient noncommunity 26 34.6

Nontransient noncommunity 41 26.8

Figure 4. MTBE occurrence in public wells related to housing density, distance to 

underground gasoline storage tank (UST), well depth, well yield and pH of the wate

Rockingham County, New Hampshire.

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overburden materials where MTBE contamination may be present. In low-yielding wells it is less likely that intercepted 

MTBE would be diluted with large 

volumes of clean water. The combination 

of urbanization, reformulated gasoline 

usage, aquifer characteristics, and the use 

of deep, low-yielding wells could have 

important implications for the occurrence 

of MTBE in drinking-water supplies in 

this region.

ACKNOWLEDGMENTS

The authors thank the many private 

citizens and operators of public-water 

systems who participated in this study, 

Patricia Bickford and the staff of the New 

Hampshire Department of Environmental Services Laboratory who provided 

analyses of water samples, and Jocelyn 

Knowles and Camille Partin for their 

assistance in water sampling. 

REFERENCES 

Ayotte, J.D., Argue, D.M., and 

McGarry, F.J., in press, MTBE occurrence and related factors in public 

and private wells in southeast New 

Hampshire: Environ. Sci. and Technol., ASAP Web release, November 13, 

2004, DOI: 10.1021/es049549e.

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

Flanagan, S.F., and Robinson, K.W., 

2003, Arsenic in ground water in 

eastern New England: Occurrence, 

controls, and human health implications: Environmental Science and 

Technology, v. 37, p. 2075–2083.

Drew, L.J., Schuenenmeyer, J.H., 

Armstrong, T.R., and Sutphin, D.M., 

2001, Initial yield to depth relation 

for water wells drilled into crystalline 

bedrock, Pinardville Quadrangle, New 

Open-File Report 95-399, 113 p.

Lynn, Gary, 2004, Tracking troubling 

vapor releases in New Hampshire: 

New England Interstate Water Pollution Control Commission LUSTline 

Bulletin 47, June 2004, accessed July 

25, 2004, at http://www.neiwpcc.org/

PDF_Docs/l_line47.pdf, p. 13–30.

Moran, M.J., Zogorski, J.S., and 

Squillace, P.J., 2004, Occurrence 

and implications of methyl tert-butyl 

ether and gasoline hydrocarbons in 

ground water and source water in the 

United States and in drinking water in 

12 northeast and mid-Atlantic states, 

1993–2002: U.S. Geological Survey 

Water-Resources Investigations Report 

03-4200, 26 p. 

Moyer, E.E., Erickson, J.A., and 

McGarry, F.J., 2002, Correlation of 

MTBE detections in New Hampshire 

public water systems with documented 

potential petroleum sources: Contaminated Soil, Sediment, and Water, 

July/August 2002, p. 23–26. 

Pankow, J.F., Thompson, N.R., Johnson, 

R.L., Baehr, A.L., and Zogorski, J.S., 

1997, The urban atmosphere as a nonpoint source for the transport of MTBE 

and other volatile organic compounds 

(VOCs) to shallow groundwater: Environmental Science and Technology, 

v. 31, p. 2821–2828. 

State of Maine, 1998, The presence of 

MTBE and other gasoline compounds 

in Maine’s drinking water: Augusta, 

Maine, 15 p.

State of New Hampshire, 2000, Code of 

Administrative Rules: Concord, N.H., 

Env-Ws 317.01(b).

U.S. Environmental Protection Agency, 

1997, Drinking water advisory-consumer acceptability advice and health 

effects on Methyl Tertiary

(MTBE): EPA-882-F-97-

U.S. Environmental Protecti

1995, Methods for determ

organic compounds in drin

Supplement III, EPA-600/

Young, T.M., and Golding, R

Underground storage tank 

field-based research proje

Davis, Calif., California S

Resources Control Board, 

-By Joseph D. Ayotte1, Brian 

Denise M. Argue1, and Frede

McGarry2

1

U.S. Geological Survey.

 2New Hampshire Department of E

Services.

FOR ADDITIONAL INFOR

The data for this study are 

U.S. Geological Survey

New Hampshire/Vermont D

361 Commerce Way

Pembroke, NH 03275

(603) 226-7800 Phone

(603) 226-7894 FAX

Copies of this report can b

from:

U.S. Geological Survey

Branch of Information Ser

Box 25286

Denver Federal Center

Denver, CO 80225-0286

Visit USGS and NHDES We

http://nh.water.usgs.gov

http://www.usgs.gov

http://www.des.state.nh