Research Occurrence and Potential Human-Health Relevance of Volatile Organic Compounds in Drinking Water from Domestic Wells in the United States Barbara L. Rowe,1 Patricia L. Toccalino,2 Michael J. Moran,1 John S. Zogorski,1 and Curtis V. Price1 1U.S. Geological Survey, Rapid City, South Dakota, USA; 2U.S. Geological Survey, Sacramento, California, USA BACKGROUND: As the population and demand for safe drinking water from domestic wells increase, it is important to examine water quality and contaminant occurrence. A national assessment in 2006 by the U.S. Geological Survey reported ﬁndings for 55 volatile organic compounds (VOCs) based on 2,401 domestic wells sampled during 1985–2002. OBJECTIVES: We examined the occurrence of individual and multiple VOCs and assessed the potential human-health relevance of VOC concentrations. We also identiﬁed hydrogeologic and anthropogenic variables that inﬂuence the probability of VOC occurrence. METHODS: The domestic well samples were collected at the wellhead before treatment of water and analyzed for 55 VOCs. Results were used to examine VOC occurrence and identify associa- tions of multiple explanatory variables using logistic regression analyses. We used a screening-level assessment to compare VOC concentrations to U.S. Environmental Protection Agency maximum contaminant levels (MCLs) and health-based screening levels. RESULTS: We detected VOCs in 65% of the samples; about one-half of these samples contained VOC mixtures. Frequently detected VOCs included chloroform, toluene, 1,2,4-trimethylbenzene, and perchloroethene. VOC concentrations generally were < 1 µg/L. One or more VOC concentra- tions were greater than MCLs in 1.2% of samples, including dibromochloropropane, 1,2-dichloropropane, and ethylene dibromide (fumigants); perchloroethene and trichloroethene (solvents); and 1,1-dichloroethene (organic synthesis compound). CONCLUSIONS: Drinking water supplied by domestic wells is vulnerable to low-level VOC contami- nation. About 1% of samples had concentrations of potential human-health concern. Identifying factors associated with VOC occurrence may aid in understanding the sources, transport, and fate of VOCs in groundwater. KEY WORDS: domestic wells, drinking-water quality, human health, volatile organic compounds. Environ Health Perspect 115:1539–1546 (2007). doi:10.1289/ehp.10253 available via http://dx.doi.org/ [Online 20 August 2007] Groundwater is used as a drinking-water sup- ply by about one-half of the U.S. population, including almost all people residing in rural areas. As estimated by the U.S. Geological Survey (USGS) (Hutson et al. 2004), domes- tic wells provide drinking water to about 43.5 million people, representing 15% of the total U.S. population (Supplemental Material, Figure 1, available online at http://www. ehponline.org/members/2007/10253/suppl. pdf). Estimated withdrawals from domestic wells increased by 60% between 1965 and 2000, with an average withdrawal rate of about 3.6 billion gallons per day in 2000 (Hutson et al. 2004). Between 1995 and 2000, domestic withdrawals increased about 6%, and domestic population increased almost 2% (Hutson et al. 2004), indicating increased use of self-supplied drinking water. In addition, estimates by the National Ground Water Association indicate that > 400,000 new domestic wells used for drinking-water supplies are drilled each year in the United States (McCray KB, personal communication). As the population and demand for safe drinking water from domestic wells increase, it is important to examine water quality and identify contaminants that occur in water from domestic wells. One contaminant group of concern is volatile organic com- pounds (VOCs), which are contained in many products used around households, including solvents, paints, adhesives, deodor- izers, refrigerants, fuels, and fumigants. A VOC is an organic chemical that has a high vapor pressure relative to its water solubility. The chemical and physical properties of VOCs allow the compounds to move between the atmosphere, soil, surface water, and groundwater. Once in the environment, VOCs can be mobilized, dispersed, diluted, volatilized, adsorbed, and/or degraded. Although many VOCs have relatively short half-lives in certain media due to abiotic and biotic degradation, other VOCs can be persis- tent, degrading little over years or decades. The production of some synthetic organic chemicals (many of which are VOCs) has increased by more than an order of magni- tude between 1945 and 1985 (Ashford and Miller 1991). Some VOCs, such as chlori- nated solvents, have been used in industry and commerce for almost 100 years (Pankow and Cherry 1996). Once introduced to groundwater, VOCs may persist and poten- tially contaminate drinking-water supplies. The U.S. Environmental Protection Agency (EPA) reported that the presence of elevated VOC concentrations in drinking Environmental Health Perspectives • VOLUME 115 | NUMBER 11 | November 2007 water may be a concern to human health because some VOCs are carcinogens and/or may adversely affect the liver, kidneys, spleen, and stomach, as well as the nervous, circulatory, reproductive, immune, cardio- vascular, and respiratory systems (U.S. EPA 2003, 2007a). Some VOCs may affect cog- nitive abilities, balance, and coordination, and some are eye, skin, and/or throat irri- tants. The Agency for Toxic Substances and Disease Registry (ATSDR 2007) provides human-health information that is searchable by individual contaminant, and additional information is provided by the U.S. EPA (2003, 2007a, 2007b). The USGS’s National Water-Quality Assessment (NAWQA) Program recently completed an assessment of 55 VOCs in groundwater throughout the United States. A screening-level assessment used in that study compared VOC concentrations to human- health benchmarks for drinking water to aid in understanding the potential human-health relevance of VOC occurrence (Zogorski et al. 2006). VOC concentrations in samples col- lected before treatment or blending during 1985–2002 from 2,401 domestic wells were compared with human-health benchmarks when available, including U.S. EPA maxi- mum contaminant levels (MCLs) for regu- lated contaminants and health-based screening levels (HBSLs) for unregulated contaminants (those without U.S. EPA MCLs) (Toccalino et al. 2003). HBSLs, as well as MCLs, are maximum contaminant concentrations that are not expected to cause adverse health effects over a lifetime of exposure (Toccalino 2007). MCLs, established under provisions of the Safe Drinking Water Act, are legally enforce- able U.S. EPA drinking-water standards (U.S. EPA 2006e) that set the maximum per- missible level of a contaminant in water that Address correspondence to B.L. Rowe, U.S. Geological Survey, 1608 Mountain View Rd., Rapid City, SD 57702 USA. Telephone: (605) 394-3236. Fax: (605) 355-4523. E-mail: blrowe@usgs.gov Supplemental Material is available online at http:// www.ehponline.org/members/2007/10253/suppl.pdf We thank National Water-Quality Assessment Program personnel for collection and analyses of domestic well samples. The article was greatly improved as a result of reviews from J. Carter, A. Heakin, W. Lapham, and K. Warner of the USGS. We also thank the two anonymous reviewers for providing insightful comments. The authors declare they have no competing ﬁnancial interests. Received 12 March 2007; accepted 11 August 2007. 1539