Evaluating Ground‐Water Vulnerability to Pesticides

A methodology was developed to rank the relative vulnerability of ground‐water areas to contamination by agriculturally applied pesticides. The method uses the advection‐dispersion equation for chemical transport in soils to develop the leaching potential index (LPI), which is an indicator of the relative susceptibility of each area. The index incorporates the effects of depth to ground water, natural and irrigation recharge rates, absorption, and chemical decay. The importance (weighting) of the hydrological factors is physically based, not subjective as it is in a number of approaches reviewed. The weights are not required to have constant values, as is typical of other methodologies; instead dependent on the specific chemical properties of the pesticide under consideration. The methodology is verified by comparing the calculated rank of 381 1‐sq‐mi (2.51‐km2) areas with available analyses for 1,2‐dibromochloropropane (DBCP) in ground water in the same area. The method will be a useful planning tool for early identification of agricultural areas susceptible to ground‐water contamination and efficient management of sampling resources.