Gpr and Em Surveys to Detect and Map Peat and Permafrost- a Pilot Study

Ground penetrating radar (GPR) and electromagnetic terrain conductivity (EM) surveys were performed to detect frozen ground and peat layers at a proposed landfill site in Fairbanks, Alaska. Geotechnical test pits showed frozen ground and peat layers in places, prompting a concern that differential settlement would disrupt the planned leachate collection system—a network of pipes installed beneath the refuse. A geophysical pilot study was undertaken to determine if GPR and EM could be used to map the extent of peat and frozen ground at the site. These methods were selected because they use readily available instruments, straightforward field procedures, and provide continuous subsurface information in a rapid and economical fashion, with the potential for significant cost savings compared to digging enough test pits to fully characterize the site. Ground truth from the existing test pits indicated that GPR identified areas containing peat, although the thickness of peat layers could not be determined. Low-conductivity zones could be correlated to areas of frozen ground. Overall, however, terrain conductivity was affected by variations in both soil condition (i.e., frozen vs. unfrozen) and soil type (e.g., silt vs. gravel) to such a degree that EM could not reliably detect frozen ground in every instance. In conclusion, GPR and EM surveys could rapidly delineate gross lithology and indicate potential areas of frozen ground. As such, the surveys could be used for a rapid preliminary assessment of virgin sites and the findings could be used to direct a more efficient test pit program.