Tri-Potential Resistivity Applications At A Leaky Underground Storage Tank Site

The tri-potential method of earth resistivity was used to locate fractures and caves in a karstic<br>limestone terrane where kerosene had leaked from the lines of an underground storage tank. For air-filled<br>fractures, the apparent resistivity values increased for the CPPC and CPCP configurations of the standard<br>Wenner Array, but decreasedin the CCPP configuration. As the resistivity traverse crosseda known airfilled<br>cave, all configurations of the array increased. If the kerosene migrates, its detection will be<br>insured by placing future monitoring wells on the fractures where most of the ground water movement<br>occurs.<br>Data from four initial monitoring wells showed that the bedrock-soil contract slopes in a<br>southwest direction, similar to surface topography. A dye trace of surface drainage showed water from<br>the sinking stream off-site emerged at a spring in just six hours. The static water level measurements<br>from the wells indicate a northeast direction of ground water flow, opposite to surface drainage. Depth<br>to water averages 30 ft. below land surface, but fluctuates over 15 ft. between wet and dry seasons.<br>Contaminated soil and the tanks were removed. The soil was placed in lined and bermed pits and<br>treated by passive volatilization and enhanced biodegradation. Soil borings were made by hollow stem<br>augering with split spoon sampling for TPHC to define the extent of the plume. Migration of the<br>kerosene was primarily along gravel-fill beds along the water line around the building. Levels of TPHC<br>in the ground water are relatively low as are hydraulic conductivity values of the soil. Therefore, no<br>threat to human health and the environment is anticipated.