Effects of water extraction in a vulnerable phreatic aquifer: Consequencesfor groundwater contamination by pesticides, Sint-Jansteen area, The Netherlands

Pesticides are a potential threat to the quality of extracted groundwater w hen the water-supply area is used for agricultural activities. This problem is discussed for the water-supply area of Sint-Jansteen, The Netherlands, where measured pesticide concentrations in the extracted water regularly ex ceed EU limits (0.1 mu g/L). Groundwater samples taken from the aquifer wit hin the water-supply area show low contamination, but samples taken from th e extracted water occasionally contain pesticides, making the water inadequ ate for drinking-water purposes. The more intense contamination of the extr acted water is caused by the change in the natural groundwater flow pattern near the extraction wells. In this area, pesticide use cannot be avoided e asily, and an approach is given to differentiate pesticide use in the area according to expected travel time toward the wells and the chemical charact eristics of the pesticides. A groundwater flow model for the area is develo ped and the effects of groundwater extraction on the natural now pattern ar e evaluated. Using particle tracking, the travel-time zones are determined. Combining these results and the degradation behavior of certain pesticides led to an optimal scheme to integrate agricultural activities and groundwa ter extraction in the area. This is illustrated for five different types of pesticides (atrazine, simazine, bentazone, MCPA, and mecoprop).