Vadose zone transport of pesticides with macropore flow and spatial variability of parameters

A field study and stochastic analysis of pesticide transport in a field soil was conducted to evaluate the relative importance of intrinsic and extrinsic sources of variability on pesticide transport through the soil. The influence of preferential flow processes on pesticide transport was also evaluated. Pesticide concentrations in the soil and groundwater were measured to evaluate pesticide transport processes in the soil. Intrinsic and extrinsic sources of variability such as saturated hydraulic conductivity and water application amounts were quantified through repeated field measurements.; Preferential flow was shown to exist in a sandy loam layer through the use of fluorescent dyes as tracers of flow patterns in the soil. Preferential flow was also shown to exist in the lower coarser sandy gravel soil layer. This second form of preferential flow is believed to represent a potential mechanism for the rapid transport of pesticides reaching the interface to the groundwater. The dye studies were successful in showing the existence of preferential flow processes in the field soils but did not determine the exact mechanism causing preferential flow.; A modeling study and stochastic analysis were conducted to evaluate the relative importance of intrinsic and extrinsic sources of variability on pesticide transport through the soil. Monte Carlo simulations revealed that the extrinsic variability of water application had a relatively greater impact on pesticide transport than the intrinsic variability of saturated hydraulic conductivity. This indicates that minimizing sprinkler non-uniformities may represent an important Best Management Practice for reducing groundwater contamination by pesticides.