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.