decision documents from FY 2005–2008 with “groundwater other” remedies, 8 percent of these (26) include water supply remedies.

RCRA. Of the 1,968 highest priority RCRA Corrective Action facilities, EPA (2008) reported that there is “unacceptable migration of contaminated groundwater” at 77 facilities. Also, 17,042 drinking water aquifers have a RCRA facility within five miles (Roger Anzzolin, EPA, personal communication, 2010), but without additional information, it is impossible to know if these facilities are actually affecting the water sources.

UST. In 2000, 35 states reported USTs as the number one threat to groundwater quality (and thus indirectly to drinking water) (EPA, 2000). However, more specific information on the number of leaking USTs currently impacting a drinking water aquifer is not available.

Other Evidence That Hazardous Waste Sites Affect Water Supplies

The U.S. Geological Survey (USGS) has compiled large data sets over the past 20 years regarding the prevalence of VOCs in waters derived from domestic (private) and public wells. VOCs include solvents, trihalomethanes (some of which are solvents [e.g., chloroform], but may also arise from chlorination of drinking water), refrigerants, organic synthesis compounds (e.g., vinyl chloride), gasoline hydrocarbons, fumigants, and gasoline oxygenates. Because many (but not all) of these compounds may arise from hazardous waste sites, the USGS studies provide further insight into the extent to which anthropogenic activities contaminate groundwater supplies (although it should be remembered that it was not the goal of these studies to uniquely identify the source of the contamination). The following paragraphs do not discuss metals and other inorganic groundwater contaminants described in the USGS studies, because of the many other possible natural sources for these constituents.

Zogorski et al. (2006) summarized the presence of VOCs in groundwater, private domestic wells, and public supply wells from sampling sites throughout the United States. Using a threshold level of 0.2 μg/L—much lower than current EPA drinking water standards for individual VOCs (see Table 3-1)—14 percent of domestic wells and 26 percent of public wells had one or more VOCs present. The detection frequencies of individual VOCs in domestic wells were two to ten times higher when a threshold of 0.02 μg/L was used (see Figures 2-2 and 2-3). In public supply wells, PCE was detected above the 0.2 μg/L threshold in 5.3 percent of the samples and TCE in 4.3 percent of the samples. The total percentage of public supply wells with either PCE or TCE (or both) above the 0.2 μg/L threshold is 7.3

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