A field and modeling study to determine pesticide occurrence in a public water supply in Northern England

In the UK, increasing numbers of pesticides are being detected in ground water as monitoring programs are developed and analytic techniques are refined. This study describes the investigation of pesticides at a site on the Triassic Sandstone aquifer of northern England. Drilling and pore water sampling demonstrated the presence of agricultural herbicides in the unsaturated zone of the aquifer close to a public supply well site at which elevated pesticide concentrations had been detected in the abstracted ground water. These were similar to the compounds detected in the supply wells, but there was no evidence for some of these having been used at the nearby farm. Modeling of water movement to wells showed that individual ground water flow subcatchments were retained during a monthly duty cycle and should be well-defined. Detecting and quantifying the sources of pesticide pollution of ground water was unsuccessful, probably due to local land use and aquifer heterogeneity. This remains difficult even where the overall catchment is small (1-km radius) and there are apparently few possible point sources. Even with sophisticated flow models, there is still a high degree of uncertainty in modeling pesticide movement, and treatment of ground water may be the only viable option for water utilities.