Summary: In response to a congressional request, GAO examined whether Environmental Protection Agency (EPA) drinking water standards were appropriate for use as groundwater standards, specifically: (1) whether states relied on EPA standards when setting numeric groundwater standards; (2) states' use of existing numeric groundwater standards in their groundwater protection programs; (3) the potential for groundwater quality degradation using drinking water standards; and (4) how drinking water standards compared to guidelines for protecting uses of groundwater for such purposes as irrigation, livestock watering, and aquatic life.
GAO found that: (1) the 25 states that had numeric groundwater standards relied largely on EPA maximum contaminant levels (MCL); (2) most states surveyed relied on EPA drinking water standards when setting groundwater standards; (3) states focused on eight regulatory activities in making their groundwater protection decisions, including licensing surface discharges, requiring waste disposal facility designs, and containing or cleaning up hazardous waste sites; (4) 92 percent of the areas tested would meet the standards if states adopted MCL as groundwater protection standards, and 43 percent met a limit associated with a one-in-one-million excess cancer risk for one or more of 13 carcinogens; (5) adopting any of the standards would potentially allow for degradation of groundwater resources, since the standards would allow contaminants to increase to the maximum allowable concentrations; and (6) although MCL would protect livestock and irrigation usage, they were less stringent than the aquatic life guidelines, and only 66.9 percent of the areas tested would meet MCL for aquatic life.
