The vulnerability of groundwater to pesticide contamination estimated directly from observations of presence or absence in wells

This study uses a Bayesian methodology to calculate the vulnerability of groundwater to pesticide contamination directly from monitoring data. This measure of vulnerability does not rely on expert opinion or the interpretation of pollutant transport models. The technique combines information from different sets of observations over periods of years, and can combine observations for a range of pesticide compounds yet is independent of the compounds being considered. The measure of vulnerability is continuous on a probabilistic scale (0–1) and thus facilitating its inclusion into risk assessment procedures. The methodology is applied to generate a vulnerability map for the major aquifer units of southern England. The groundwater survey included 187 monitoring sites over a 6-year period (1993–1998) and data from 13 compounds. The resulting vulnerability map shows local and regional scales of variation both within and between major aquifer units and a distribution that is distinct from that of nitrate concentrations measured at the same sites.