Superfund: EPA's Use of Risk Assessments in Cleanup Decisions

GAO discussed the Environmental Protection Agency's (EPA) use of human health risk assessments in its cleanup decisions at Superfund sites, focusing on: (1) whether federal and state cleanup standards that set quantitative limits on concentrations of contaminants are based on risk estimates; and (2) the extent to which Superfund risk assessments follow EPA guidance. GAO noted that: (1) EPA cleanup decisions at 188 of 225 Superfund sites were consistent with the results of EPA risk assessments, but cleanup decisions at the other 37 sites were based on other considerations, such as whether the contamination levels violated federal or state standards; (2) EPA used federal and state standards more often than risk assessments to determine the extent of site cleanup, since the standards were usually more stringent; (3) federal standards are generally derived from health risks estimates, while state standards and consideration of site-specific conditions vary; (4) although the risk assessments generally followed EPA guidance, they were inconsistent and could have resulted in less accurate estimates of human exposure risks; and (5) EPA risk assessment guidance permits some flexibility, since the data necessary for quantifying risk are often inconclusive, and many risk assessment results do not fully disclose the assumptions used to calculate health risks.