Aquifer Sensitivity Analysis of the Mahomet Aquifer, Gibson City Quadrangle, Illinois

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Geography, Geology and the Environment


Eric Peterson

Mentor Department

Geography, Geology and the Environment


The significance of the Mahomet Aquifer as a water resource for east-central Illinois prompted an analysis on the sensitivity of the aquifer to contamination. In 2015, the U.S. Environmental Protection Agency declared the Mahomet Aquifer a sole source aquifer, as there are no feasible alternative drinking water sources available for the area and contamination of the aquifer would create a significant hazard to public health. Sources of aquifer contamination in Illinois can be fertilizers and pesticides from agriculture, chloride from road salts, leakage from underground storage tanks and pipelines containing gasoline, and disposal of hazardous wastes. The goal of this study it to determine how sensitive the Mahomet Aquifer is to contamination by conducting an aquifer sensitivity analysis within the Gibson City 15' quadrangle. Aquifer sensitivity is the relative ease with which a contaminant of any kind applied on or near the land surface can migrate to an aquifer. Richard Berg's 2001 sensitivity analysis classification system will be used for this study, which determines sensitivity based on the depth from the surface to the aquifer material and the thickness of the aquifer. Berg developed six major sensitivity classifications (A-F), with sensitivity decreasing alphabetically. The six major classes were further subdivided into 24 total classifications providing detail on material, material thickness, and depth to the aquifer unit (e.g. A1-F3). To complete the assessment, a 3D geologic map will be constructed of the quadrangle using a GIS. Illinois State Geological Survey well-log data, soil survey, and LiDAR data will be imported into the GIS to delineate the subsurface layers. The 3D map will be used to help determine the depth to the aquifer material and the thickness of the aquifer material throughout the study area. These data will then allow for the assignment of the aquifer sensitivity classification values. The end result will be a 15' quadrangle map that can be used to identify areas where aquifer material is sensitive to contamination, and therefore allow for more informed land management.



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