Mechanisms and Rates of Pesticide Leaching in Shallow Clayey Till

Field studies and groundwater monitoring in an orchard indicated that migration in fractures of the pesticides simazine and atrazine had occurred through more than 8 metres of clayey till in a period of less than ten years. Leaching experiments applying large intact till blocks sampled in the orchard showed rapid transport of water and pesticides in the fractures and macropores of the till, largely bypassing the surrounding clayey matrix. Furthermore the experiments revealed hydraulic conductivities of 10−5−10−7m/s decreasing downwards in the till profile studied.