GEOLOGY, AQUIFER SENSITIVITY AND AQUIFER VULNERABILITY OF THE OTTAWA 7.5' QUADRANGLE, LASALLE COUNTY, IL

The Ottawa 7.5’ Quadrangle was mapped because of its environmental hazards and its importance in economic geology. The St. Peter Sandstone, which is the major unit within the Ancell Aquifer, outcrops along the Illinois River creating mining opportunities and potential for aquifer contamination. A surficial geologic map was produced along with two derivative maps: an aquifer sensitivity map and an aquifer vulnerability map. The surficial geologic map was produced using traditional field methods, well logs, and soil survey maps. The aquifer sensitivity map was produced by assigning new attributes to the polygons of the digital surficial geologic map. The attributes were determined using a well log database obtained from the Illinois State Geological Survey and aquifer sensitivity classifications defined in “Aquifer Sensitivity Classification for Illinois Using Depth to Uppermost Aquifer Material and Aquifer Thickness” (Berg, 2001). The qualitative aquifer vulnerability map was produced by overlaying buffered locations of possible contamination sites on the aquifer sensitivity map. Existing RCRA and Superfund sites were selected as the possible contamination sites. Contamination site data were obtained from the USEPA and the USEPA’s Envirofacts Database. The maps were generated using ESRI’s ArcINFO 8.1 Workstation software.