Assessment of Ground-Water Sensitivity and Vulnerability - Goshen County, Wyoming

Mike Wireman, Kevin, Frederick, Jeff Hamerlink

A modified form of the DRASTIC method was used to assess ground-water sensitivity and vulnerability in Goshen County, Wyoming. Appropriate hydrogeologic data were identified, obtained and entered into Geographic Information System (GIS) format at a 1:100,000 scale. Data included maps of bedrock geology, surficial geology and soil, digital elevation contours, depth to water, saturated thickness, and hydraulic conductivity. From this basic data six parameter maps were generated including depth to water, net recharge, hydrogeologic units, soil texture, slope of land surface and saturated hydraulic conductivity.

Mathematical functions were developed to calculate a ground-water sensitivity rating for quantitative hydrogeologic parameters (depth to water, hydraulic conductivity, etc.). Calculation of the sensitivity ratings was performed with a GIS operating on a raster-based file. For descriptive hydrogeologic data (geology, soils, etc.) sensitivity ratings were assigned based on the inherent capacity to transport contaminants. A final ground-water sensitivity map was generated by combining/overlaying the six-rated parameter maps. A ground-water vulnerability map was then generated by overlaying a land use map on the sensitivity map.

Goshen County represents a pilot effort to develop a methodology to be used to assess ground-water sensitivity/vulnerability in each county in Wyoming. A set of ground-water sensitivity/vulnerability maps will be generated at a 1:100,000 scale. These maps will enable state and local planners to identify areas where the potential for ground-water contamination may be a concern. These areas can then be targeted for increased management.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995