DIRECT PUSH ELECTRICAL RESISTIVITY TOMOGRAPHY FOR EVALUATION OF AN LNAPL PLUME

In cooperation with the Oklahoma Corporation Commission, a site in Enid, Oklahoma was selected in order to test the effectiveness of a new method for monitoring LNAPL plumes. In contrast to conventional surface electrical resistivity techniques, direct push ERT supplements the surface measurement technique with a grid of direct push boreholes containing vertically spaced monitoring electrodes. The configuration of borehole and surface electrodes provides a monitored area or volume for the contaminated site with good depth resolution. Prior to installation of the subsurface electrodes, continuous sediment cores and electrical conductivity logs were taken in order to describe the lithology, stratigraphy, and geophysical characteristics of the site. These data are being used to evaluate and calibrate the ERT data. The monitoring grid consists of boreholes on 10m spacing with push penetration to depths of approximately 12 meters. Each vertical borehole has 28 evenly spaced electrodes. The vertical electrodes are set up to work in conjunction with 36 surface electrodes. All together, the electrode monitoring grid is capable of providing electrical resistivity data at a vertical resolution of 0.25 meters. This direct push ERT methodology can be used temporarily or permanently.