GEOLOGY, AQUIFER SENSITIVITY AND PROXIMITY ANALYSIS OF POSSIBLE CONTAMINATION SITES OF THE OTTAWA 7.5' QUADRANGLE, LASALLE COUNTY, ILLINOIS

This project is part of the Illinois State Geological Survey priority-mapping effort for LaSalle County, IL. The Ottawa 7.5' Quadrangle was selected as the fourth quadrangle in the county to be mapped because of its importance in economic, educational, environmental, geologic, and hazard factors. This project was supported by a grant from the U.S. Geological Survey EDMAP program.

Using traditional field methods, digital well log data, aerial photographs and soil survey maps a geologic map was produced. The map was constructed by ESRI's ArcGIS software through hand digitizing. The Ottawa 7.5' Quadrangle is located in the northern part of the Bloomington Ridge Plain, which is characterized by low, broad, morainal ridges of Woodfordian age separated by wide, relatively flat lacustrine plains. Bedrock stratigraphy ranges in age from Lower Ordovician to Pennsylvanian. Bedrock units are only exposed along major drainages and in quarries. Ordovician bedrock units occurring in the area include the Platteville and Galena Groups and the St. Peter Sandstone. The Pennsylvanian units are the Tradewater and Carbondale Formations. Wedron Group Quaternary units of Woodfordian age overly the Paleozoic units. The Farm Ridge End Moraine transects the northeast corner of the quadrangle, the Henry Formation dominates the area along the Illinois River, and the Covel Creek Esker occurs in the southeast portion of the quadrangle.

Using the data from the geologic map and digital well log data provided by the ISGS an aquifer sensitivity map was produced. Berg's method of Aquifer Sensitivity Classification for Illinois Using Depth to Uppermost Aquifer Material and Aquifer Thickness was used to classify the well log data. There are a total of six classifications for the area. The map was generated in ESRI's ArcGIS software by drawing polygons around each classification.

The proximity analysis will be produced by using data obtained by the IEPA, Cerclis Database, RCRA Information Database, the LUST Database, and the Site Remediation Program Database. The proximity analysis map will be generated by ESRI's ArcGIS software by overlaying the locations of the possible contamination sites with the aquifer sensitivity map.