Use of the self-potential method for measurement of subsurface water flow at a pump-and-treat remediation site

Abstract

The self-potential method (SP) of geophysical surveying has been widely used in environmental and engineering applications, primarily for rough but inexpensive assessment of subsurface flow of fluids, heat, or ions. In this project, the SP method was employed to study the activity at an environmental cleanup site at the Massachusetts Military Reservation. At the leading (down-gradient) edge of the CS-4 groundwater contamination plume, a fence of pump-and-treat extraction wells has been operating in an effort to contain the plume migration. To help gauge the effectiveness of the pump-and-treat technique, it is useful to delineate the resultant water flow and to compare it to the extent and diffusion gradient of the contaminant plume. In the survey conducted for this project, SP measurements were taken along the fence of extraction wells, while they were in operation, and during a period in which the well pumps were shut off. Spatial and temporal variations in the SP measurements are analyzed. Some possible explanations are proposed to account for the observed features and changes over time. While the results are not entirely conclusive, they suggest that water flow provides only a modest contribution to the total observed SP anomaly.