Self Potential Mapping Of Contaminants

Abstract

Various geophysical techniques are useful for detection and mapping of subsurface contamination plumes. Self potential seems to be a particularly promising technique due to its cost effectiveness and speed of acquisition and processing. The electrochemical phenomena of organic contaminants and their interactions with microorganisms in the subsurface provide a detection method for self potential (SP) geophysics. In this presentation, we couple biodegradation with several examples of SP detecting contaminant plumes. INTRODUCTION The major environmental and engineering application of the self potential method has been the investigation of water movement, specifically in monitoring dams for leakage (Corwin, 1990). Self potential anomalies are generated by flows of fluid, heat, or ions in the earth; hence, SP investigations have been used to help locate and characterize sources associated with these flows. SP offers relatively rapid field data acquisition and the ability to respond directly to changes in flow. Interpretation of self potential data is often qualitative, using visual correlation between observed profiles or contour patterns and known or suspected contaminant sources or flow paths. SP is cost effective for reconnaissance and initial field investigations of an area prior to more intensive studies using geotechnical or other geophysical techniques. The results from more extensive studies can be used to correlate SP values, especially if monitoring wells are installed. Once a correlation has been established between SP and other data, SP can be used as the primary monitoring tool. However, periodic checks should be made to ensure that the correlated values remain true. The implementation of such a methodology would yield tremendous cost savings and provide data at a greater frequency than traditional sampling methods. BIODEGRADATION OF CONTAMINANTS A possible source of SP anomalies due to contamination is oxidation/reduction (redox) reactions. These reactions are associated with the biodegradation of contaminants, which occur naturally in the subsurface due to the presence of microorganisms. The ease of degradation depends on the contaminant. Moderate to lower weight hydrocarbons (Cl0 to ($4 allcanes, single ring aromatics) are most easily degradable. Biodegradation can also