Using Geophysics to Locate Unmarked Graves to Aid in Remediation Design and Construction at an NPL Site

Abstract

Tetra Tech EM Inc.(Tetra Tech) was engaged by the Region 6 U.S. Environmental Protection Agency (EPA) under the Response Action Contract (RAC) program to perform a geophysical survey at the Rockwool Industries Superfund site. The purpose of the survey was to delineate the lateral extent of an old cemetery adjacent to a gulley where, for remediation purposes, a culvert was to be constructed. The cemetery was known to have unmarked graves, and some of the wooden coffins had been exposed due to erosion on the steep bank of a river immediately to the north. The geophysical survey results, if successful, would be used to guide the crew in avoiding any grave sites while placing the culvert. The survey was performed on March 1 through March 3, 2005. The Tetra Tech field crew employed a GSSI SIR 3000 ground penetrating radar system with a 400 MHz antenna and a GEM 2 terrain conductivity meter. Tetra Tech ran transects spaced 2.5 feet apart in an area measuring 25 feet by 40 feet over known grave sites to test the effectiveness of the equipment. Both the GPR depth sections and time slice plots successfully identified six known grave sites and four unmarked graves, but the GEM 2 had only limited success. Upon evaluation of the test plot, Tetra Tech continued the investigation in the area of concern near the planned placement location of the culvert. The results of the GPR survey identified four marked graves, but no additional unmarked graves were located. The GEM 2 survey, while not specifically identify individual graves, did differentiate disturbed soil in the cemetery area from undisturbed soil, so was used to conservatively delineate the boundaries of the cemetery. The construction crew used the geophysical results to guide in the placement of the culvert, and there was no incident during construction.