AN EVALUATION OF TWO SHALLOW GEOPHYSICAL TECHNIQUES AS POTENTIAL TOOLS FOR ILLINOIS DEPARTMENT OF TRANSPORTATION PRELIMINARY ENVIRONMENTAL SITE ASSESSMENTS

The Preliminary Environmental Site Assessment (PESA) program of the Illinois State Geological Survey (ISGS) conducts PESAs for Illinois Department of Transportation (IDOT) road construction projects. State and local records are currently used to locate underground storage tanks (USTs). However, USTs that were installed prior to state-mandated registration commonly have no records of existence. While shallow geophysical techniques are proven tools for more in-depth investigations, they are commonly too time and labor intensive to be practical as a tool for PESAs. Recent advances in equipment design have prompted a re-evaluation of shallow geophysical tools for use with IDOT PESAs. Ground penetrating radar and time domain electromagnetic conductivity were selected for this evaluation. These techniques were compared with a magnetic locator, which is the tool currently utilized by the ISGS PESA program for UST investigations. The purpose of this investigation was to determine the efficacy of each geophysical technique in locating USTs of varying composition, and under conditions encountered during typical IDOT environmental site assessments. Two sites, a private gasoline station with steel USTs and the ISGS garage with a fiberglass/plastic composite UST, were investigated. Both geophysical techniques accurately located the tanks and associated features at both sites. However, each technique continued to prove inefficient because of the time and effort required to conduct each survey when compared with a common magnetic locator. Improvements in equipment portability and the speed of data acquisition and interpretation are required before either technique can be considered for use with IDOT PESAs.