Groundwater Protection

Measurement of Relative Vulnerability to Pesticide Contamination Gao ID: PEMD-92-8 October 31, 1991

This report evaluates the feasibility of differentially protecting groundwater from pesticide contamination on the basis of the relative vulnerability of different geographic areas--an approach being considered by the Environmental Protection Agency (EPA). It also discusses the degree to which states and counties are uniform in their susceptibility to groundwater contamination. Finally, the report describes the degree to which two common measures of relative vulnerability diverge in identifying areas that are susceptible to contamination.

GAO found that: (1) although the Environmental Protection Agency (EPA) has taken the position that the variation in statewide sensitivity to pesticide contamination of groundwater is too large for uniform state-level management of pesticides, it has not taken a stand on how large the within-state areas to be managed differently should be; (2) since the variability in hydrogeologic vulnerability does not become significantly smaller when moving from the national level to the state and to the county levels, it generally makes no more sense to make distinctions between counties than it does to treat an entire state as a uniform area; (3) the lack of uniformity in vulnerability both between and within counties indicates that EPA risks undermining its differential protection philosophy if it permits states to differentially protect groundwater on the basis of county-level differences in vulnerability; (4) the system EPA endorses would target manifestly different areas for differential protection than a system that included data on population exposure; (5) techniques which provide valid vulnerability assessments at the subcounty level are expensive when applied across an entire county; and (6) it is important for states to explicitly consider the number of groundwater users as a factor in the development of differential pesticide management plans.

Recommendations

Our recommendations from this work are listed below with a Contact for more information. Status will change from "In process" to "Open," "Closed - implemented," or "Closed - not implemented" based on our follow up work.

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