You are here:
PROBABILISTIC ASSESSMENT OF GROUNDWATER VULNERABILITY TO NONPOINT SOURCE POLLUTION IN AGRICULTURAL WATERSHEDS
Citation:
Hantush*, M M. AND Z. Zhang. PROBABILISTIC ASSESSMENT OF GROUNDWATER VULNERABILITY TO NONPOINT SOURCE POLLUTION IN AGRICULTURAL WATERSHEDS. Presented at Wetlands Engineering and River Restoration Conference 2001, Reno, NV, August 27 - 31, 2001.
Description:
This paper presents a probabilistic framework for the assessment of groundwater pollution potential by pesticides in two adjacent agricultural watersheds in the Mid-Altantic Coastal Plain. Indices for estimating streams vulnerability to pollutants' load from the surficial aquifer are also presented. The methodology combines physically based mass fraction models (or indices), which describe natural attenuation of pesticides in the subsurface with Monte Carlo simulations and ArcView GIS to generate pollution potential cumulative distributions in the soil for a selected pesticide. The pollution potential is defined here as the probability of exceeding a prescribed threshold limit of leached fraction of a pesticide's mass applied per acre at the source. Uncertainty of soil parameters, such as the saturated hydraulic conductivity, porosity, field capacity, and organic carbon fraction, are based on statistics and distributions related to drainage (SCS hydrologic) soil groups and soil texture. Probability density functions and cumulative distributions for the leached mass fractions below the root zone are generated through Monte Carlo simulations for different hydrologic soil groups and land use. The probabilistic scheme is applied to assess the vulnerability of ground water in two agricultural watersheds in the Mid-Atlantic coastal plain to a selected relatively short-lived pesticide. The probability maps and expected leached fractions of the pesticide show that well drained landscapes pose greater risks for potential ground water pollution by the pesticide. In the case of cultivated lands, the Monte Carlo simulations show that the coefficient of variation for the leached mass fraction is higher for poorly drained than in well drained soils in the area.