Hawaii

Oahu

Alaska

Hawaii

Oahu

Alaska

Perchloroethene (PCE)

1,1-Dichloroethene (1,1-DCE)

Ethylene dibromide (EDB) 

1,2-Dichloropropane

Dibromochloropropane

(DBCP)

Proportions of VOC concentrations of potential human-health

concern in domestic well samples

Trichloroethene (TCE)

1,1-Dichloroethene

(1,1-DCE)

Vinyl chloride

Methylene chloride

Perchloroethene

(PCE)

Trichloroethene (TCE)

Proportions of VOC concentrations of potential human-health

concern in public well samples

EXPLANATION

1 Stacked box symbols indicate that the sample contained 

 more than one VOC of potential human-health concern. 

 Some box symbol locations have been slightly shifted to 

 reduce overlaps.

Solvent

Fumigant

Contained no VOCs with concentrations of

 potential human-health concern

Domestic and public well samples

Contained one or more VOCs with concentra-

 tions of potential human-health concern1

Organic synthesis compound

Chloroform

Methyl tert-butyl ether

Perchloroethene

1,1,1-Trichloroethane

Dichlorodifluoromethane

Trichloroethene

Bromoform

Bromodichloromethane

Dibromochloromethane

1,1-Dichloroethane

0 2 4 6 8 10 12

DETECTION FREQUENCY, IN PERCENT

0 2 4 6 8 10 12

DETECTION FREQUENCY, IN PERCENT

Chloroform

Methyl tert-butyl ether

Perchloroethene

1,1,1-Trichloroethane

Dichlorodifluoromethane

Toluene

Chloromethane

Trichloroethene

Dibromochloropropane

Methylene chloride

Domestic well samples Public well samples

The 10 most frequently detected VOCs at an assessment level of 0.2 microgram per liter

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 2938

Volatile Organic Compounds in Samples from Domestic and Public Wells, 1985–2002

By Barbara L. Rowe, John S. Zogorski, and Joshua F. Valder

Study basics

The U.S. Geological Survey’s (USGS) National Water-Quality Assessment (NAWQA) Program recently completed 

a national study of volatile organic compounds (VOCs) in the Nation’s ground water (Zogorski and others, 2006). 

Part of this assessment emphasizes the occurrence of 55 VOCs in samples from 2,401 domestic wells and 1,096 public 

wells during 1985–2002. Samples were collected prior to any treatment or blending of water.

Domestic wells are privately owned, self-supplied sources used for drinking water and household use (Moran and 

others, 2002). Public wells are privately or publicly owned and supply water to public water systems (PWSs). Samples from public wells in this assessment characterize the quality of water captured by wells that supply drinking water 

to PWSs. These systems supply drinking water to at least 15 service connections or regularly serve at least 25 individuals daily at least 60 days a year (U.S. Environmental Protection Agency, 2005).

For a screening-level assessment, VOC concentrations were compared to human-health benchmarks. Concentrations greater than the U.S. Environmental Protection Agency’s (USEPA) Maximum Contamination Levels (MCLs) 

(U.S. Environmental Protection Agency, 2004) or the USGS’s Health-Based Screening Levels (HBSLs) (Zogorski 

and others, 2006) were considered of potential human-health concern. The findings from the well samples provide an 

important perspective on the quality of the Nation’s ground water used for drinking-water supplies. More information 

about this national assessment of VOCs is available (http://��water.usgs.gov/nawqa/vocs/national_assessment).

One or more VOCs were detected in 14 percent of domestic well samples and 

26 percent of public well samples at an assessment level of 0.2 microgram 

per liter.

Chloroform, methyl tert-butyl ether (MTBE), and perchloroethene (PCE) were 

the most frequently detected VOCs in both well types; however, the overall 

signature of VOCs associated with domestic and public wells differed.

•

•

Six VOCs in about 1 percent of domestic samples and five VOCs in about 

2 percent of public well samples had VOC concentrations of potential humanhealth concern.

Additional VOCs had concentrations below but within a factor of 10 of USEPA

MCLs.

•

•

Domestic well samples had fewer VOCs, lower detection frequencies, smaller 

concentrations, and fewer mixtures than public well samples.

•

Domestic well samples

VOCs with concentrations of potential 

human-health concern in samples were 

predominantly fumigants and solvents; 

DBCP accounted for about 50 percent of 

these concentrations.

•

VOCs with concentrations of potential 

human-health concern

Compound VOC group Domestic 

wells

Public 

wells

Dibromochloropropane fumigant X

1,1-Dichloroethene organic synthesis 

compound

X X

1,2-Dichloropropane fumigant X

Ethylene dibromide fumigant X

Methylene chloride solvent X

Perchloroethene solvent X X

Trichloroethene solvent X X

Vinyl chloride organic synthesis 

compound

X

Additional VOCs with concentrations below but 

within a factor of 10 of USEPA MCLs

Compound VOC group Domestic 

wells

Public 

wells

Benzene gasoline hydrocarbonX X

Bromodichloromethane trihalomethane X

Bromoform trihalomethane X X

Carbon tetrachloride solvent X X

Chloroform trihalomethane X X

cis-1,2-Dichloroethene solvent X

Dibromochloromethane trihalomethane X X

1,2-Dichloroethane solvent X X

1,1,1-Trichloroethane solvent X

Statistics for VOC occurrence in samples from domestic and public wells at an assessment 

level of 0.2 microgram per liter (μg/L)

Occurrence information

Well type

Domestic Public

Detections

Number of VOCs detected 37 41

Frequency of one or more VOCs, in percent 14.0 26.2

Concentrations

Total VOC concentrations less than 1 μg/L, in percent 62.2 49.8

Total VOC concentrations greater than 10 μg/L, in percent 6.6 8.4

Detections and concentrations of potential human-health concern

Number of VOCs with concentrations greater than their MCL 6 5

Frequency of concentrations greater than their MCL, in percent 1.2 1.5

Frequency of concentrations greater than their HBSL, in percent 0 0

Total number of VOCs with concentrations of potential human-health concern 6 5

Multiple VOCs

Total number of VOCs that occurred in mixtures 38 40

Number of VOCs occurring only in mixtures 16 18

Frequency of mixtures in all well samples, in percent 3.9 13.4

Frequency of mixtures in well samples with VOC detections, in percent 27.7 51.2

Public well samples

VOCs with concentrations of potential 

human-health concern in samples were 

predominantly solvents and organic synthesis compounds; solvents accounted for 

about 85 percent of these concentrations.

•

Vulnerability to VOC contamination is greater for public wells than domestic 

wells due to:

Proximity to developed areas.

High volume pumping systems.

Large contributing areas, capture zones, withdrawal rates, and drawdown.

Interception of water from recharge areas with multiple land uses and point sources.

•

•

•

•

Implications

Future studies of VOC contamination in domestic and public wells can focus on relatively few compounds.

Most VOC concentrations in domestic and public well samples in this screening-level assessment were less than 

MCLs and HBSLs, and therefore are unlikely to result in adverse human-health effects.

Eight VOCs with concentrations of potential human-health concern merit additional study to understand contaminant sources and VOC concentrations in drinking-water supplies.

Seventeen VOCs may warrant inclusion in low-concentration, trends-monitoring programs.

Due to the relatively large number of concentrations near to or greater than their MCLs, the solvents PCE and TCE 

warrant special emphasis to understanding the sources and capture of these contaminants by domestic and 

public wells.

Detection of VOCs in public well samples and the vulnerability of public wells to VOCs indicate the importance of 

effective well head protection programs and the need to identify and control VOC sources.

•

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•

•

•

•

References

Moran, M.J., Lapham, W.W., Rowe, B.L., and Zogorski, J.S., 2002, Occurrence and status of volatile organic 

compounds in ground water from rural, untreated, self-supplied domestic wells in the United States, 1986–99:

U.S. Geological Survey Water-Resources Investigations Report 02–4085, 51 p.

U.S. Environmental Protection Agency, 2005, Public Drinking Water Systems Programs: accessed November 2, 2005, 

at http://��www.epa.gov/safewater/pws�/index.html

U.S. Environmental Protection Agency, 2004, 2004 Edition of the drinking water standards and health advisories:

Washington, D.C., Office of Water, EPA 822-R-04-005.

Zogorski, J.S., Carter, J.M., Ivahnenko, Tamara, Lapham, W.W., Moran, M.J., Rowe, B.L., Squillace, P.J., and 

Toccalino, P.L., 2006, The quality of our Nation’s waters—Volatile organic compounds in the Nation’s ground 

water and drinking-water supply wells: U.S. Geological Survey Circular 1292, 101 p.