Groundwater Protection:

Validity and Feasibility of EPA's Differential Protection Strategy

PEMD-93-6: Published: Dec 9, 1992. Publicly Released: Jan 12, 1993.

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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.

Recommendations for Executive Action

  1. Status: Closed - Not Implemented

    Comments: Although EPA agrees with GAO's findings and conclusions, it disagrees with the recommendation. EPA has taken the position that states can conduct vulnerability assessments and develop effective pesticide management plans even though data are limited and that they must rely on best professional judgment in lieu of modeling applications.

    Recommendation: Implementation of the differential protection component within the Environmental Protection Agency's (EPA) Pesticides and Groundwater Strategy should be delayed. EPA should assess the meaningfulness of preparing and evaluating these plans given the current state of the science.

    Agency Affected: Environmental Protection Agency

  2. Status: Closed - Not Implemented

    Comments: Although EPA agrees with GAO's findings and conclusions, it disagrees with the recommendation. EPA has taken the position that states can conduct vulnerability assessments and develop effective pesticide management plans even though data are limited and thatthey must rely on best professional judgment in lieu of modeling applications.

    Recommendation: EPA should do a pilot study with a limited number of states to assess the viability of the strategy. Issues to be addressed include the states' ability to develop meaningful plans based on differential protection and EPA ability to evaluate these plans. Until the meaningfulness of the plans can be assured, resources should not be spent on preparing them.

    Agency Affected: Environmental Protection Agency

  3. Status: Closed - Not Implemented

    Comments: Although EPA agrees with GAO's findings and conclusions, it disagrees with the recommendation. EPA has taken the position that states can conduct vulnerability assessments and develop effective pesticide management plans even though data are limited and that they must rely on best professional judgment in lieu of modeling applications.

    Recommendation: Until differential protection can be successfully implemented, EPA should continue its current approach of using uniform national restrictions to protect groundwater from pesticide contamination and allowing states to set standards stricter than those required by EPA.

    Agency Affected: Environmental Protection Agency

  4. Status: Closed - Implemented

    Comments: EPA has indicated that it will support development of modelling methods and data development/collection methods.

    Recommendation: EPA should continue to support, to the extent possible, the scientific development of the field, including state data gathering activities and the development and refinement (including validation) of vulnerability models. Only by doing this can EPA ensure that the differential protection component of its groundwater strategy will become viable.

    Agency Affected: Environmental Protection Agency

 

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