GEOPHYSICAL INVESTIGATIONS OF BRINE CONTAMINATED GROUNDWATER USING ELECTRICAL METHODS

Investigation of a brine seep at a groundwater discharge zone using surface geophysical techniques was conducted at a location near Harden City, Oklahoma in December 2007. Much of the investigation site is pastureland with a neighboring stream; the study area is also located in a region of many oil fields and currently has several active petroleum production wells. Survey grids were created for data collection locations using a differential GPS system. The grids were comprised of parallel lines at 10-20 m spacing. A Geonics EM-31 inductively-coupled conductivity meter and a Geometrics OhmMapper capacitively-coupled conductivity meter were used to delineate the seep area and evaluate possible sources of brine contamination and probable flow paths. Each instrument provided large scale horizontal scans of the subsurface. The OhmMapper provided deeper depth data than the EM-31 unit, and provided data at 5 depth intervals. Data collected using the EM-31 unit indicated likely source locations and possible flow paths in the subsurface moving toward the groundwater discharge zone. OhmMapper data show good correlation to the EM-31 data with the shallow receivers, but the data diverges with the deeper receivers.