Groundwater Protection: Validity and Feasibility of EPA's Differential Protection Strategy: Pemd-93-6

Pursuant to a congressional request, GAO evaluated the feasibility of protecting groundwater from pesticide contamination based on the relative vulnerability of different geographic areas.
GAO found that: (1) there were significant gaps in the data needed to conduct valid vulnerability assessments; (2) half of the states did not have data on the vadose and confining zones; (3) existing information was generally not of a sufficient degree of geographic resolution to be useful in vulnerability assessments; (4) there was great variability across states in the availability and sufficiency of the data; (5) the most extensive tests of depth, recharge, aquifer, soil, topography, impact, conductivity (DRASTIC) have found no positive relationship between DRASTIC scores and pesticide contamination; (6) a discriminant analysis approach to predict groundwater contamination was validated once and for only one pesticide; (7) none of the mathematical models were adequately validated to justify their use for developing state management plans; and (8) states generally used unvalidated methods for their assessments and, in most cases, did not verify model predictions with monitoring data.