Risk‐Based Evaluation of Ground‐Water Contamination by Agricultural Pesticides

Abstract

AbstractThe recently completed National Pesticide Survey conducted by the United States Environmental Protection Agency (EPA) has identified the presence of various pesticides in ground water. The detection of pesticides in the nation's ground water has raised concerns for public health which has led resource managers in federal and state agencies to recognize that risk assessment is vital for water quality protection. This paper presents a methodology for risk‐based evaluation of ground‐water contamination by agricultural pesticides. The methodology utilizes the Risk of Unsaturated/Saturated Transport and Transformation of Chemical Concentrations (RUSTIC) model to provide simulations that yield the probable risks associated with a given pesticide. Risk is expressed in terms of the probability of predicted pesticide mass exceeding its recommended health standards. Three widely used agricultural herbicides, simazine, atrazine, and alachlor, were evaluated using long‐term (1960–1986) meteorological data for Ames, Iowa. Results indicate that for a well 8 m deep located 200 m horizontally from a pesticide application area in an alluvial sand and gravel setting, the probability of exceeding the maximum contaminant level (MCL) for simazine is about 35%, whereas it is nearly zero for both atrazine and alachlor. Prudent use of simazine in very susceptible areas is recommended.