MEASUREMENT OF PESTICIDE TRANSPORT TO SHALLOW GROUND WATER

Abstract

ABSTRACT A field study was conducted to observe the movement of the herbicides atrazine and alachlor within the soil profile and a shallow water table aquifer following a surface application. Surface-applied bromide was used as a non-adsorbed tracer of water movement. The herbicides and tracer were surface applied to a strip of soil at the top of a sloping study site with sandy soil underlain by an impermeable clay layer. Concentrations of bromide at all three monitored depths in the unsaturated zone showed a high degree of variability. The peak concentration and the time required to reach the peak concentration varied significantly between sampling locations. Atrazine moved rapidly through the sandy soil on the study site. Concentrations of atrazine in the soil water at a depth of 0.61 m reached 350 |ag/L 19 days after application. Detectable levels of atrazine reached the water table two months after application. Atrazine concentrations as high as 90 |Jg/L were observed in the shallow ground water nearly six months after application. Alachlor was not detected in the soil below a depth of 0.36 m. No trace of alachlor was detected in the ground water samples.