Detectability Of Crude Oil In The Subsurface Near Bemid Ji, Minnesota, Using Ground Penetrating Radar

Near Bemidji, Minnesota, where crude oil contaminates a glacial aquifer, ground<br>penetrating radar (GPR) data were collected to determine whether the subsurface distribution of<br>the crude oil could be detected using a geophysical technique. The crude oil, which is very<br>resistive (greater than lo7 Ohm-m), is in the fine-grained layers of the vadose zone and is pooled<br>near the water table. Geochemical analysis shows that biodegradation of the crude oil has<br>increased total dissolved solids in the ground water. Near the oil pools, the ground water<br>conductivity is three times higher than the background values. This increase in conductivity<br>causes attenuation of the radar signal, which is seen in both the cross-well borehole data and in<br>the surface data. However, the interpretation of the radar data is complicated by the fact that<br>signal attenuation also occurs in the saturated zone in uncontaminated areas.