DETERMINATION OF NONPOINT-SOURCE POLLUTION USING GIS AND NUMERICAL-MODELS

A geographic information system (GIS) was utilized to apply a modified DRASTIC method to the assessment of groundwater contamination sensiti vity in Goshen County, Wyoming. Several basic environmental characteri stics, identified as influencing contaminant transport through the vad ose zone to groundwater systems, were mapped, automated, and analyzed. These characteristics include: depth to groundwater, net recharge, hy drogeologic setting, vadose zone soil properties, land surface slope, and saturated hydraulic conductivity, Sensitivity ratings were develop ed for each parameter based on a combination of mathematical functions and the inherent capacity of each characteristic to influence transpo rt of contaminants. A raster-based overlay analysis was performed to d erive a map that portrays cumulative aquifer sensitivity ratings acros s the county, providing a relative indication of groundwater vulnerabi lity to contamination. A process-based numerical model was used to sim ulate water Bow and solute transport in the vadose zone and groundwate r systems. The model incorporated soil and hydraulic properties produc ed with the GIS into the simulations. Numerical simulations described the time and spatial distributions of contaminants. Chemical mass stor ed in the soil and leaching out from the vadose zone were computed to characterize groundwater contamination. Groundwater sensitivity indexe s, which were developed based on the numerical modeling results, were compared with the GIS sensitivity map and used to verify the reliabili ty of the map.