Evaluation of Aquifer Contamination from Salt Water Disposal Wells

In the United States an estimated 140,000 Class II wells for salt water disposal and enhanced hydrocarbon recovery are presently injecting some 30 million barrels of brine per day into subsurface formations. While no systematic survey has documented the extent of shallow ground water contamination from these disposal practices, it is recognized as a major potential pollution source in leading hydrocarbon-producing states. The reliability of impact assessment calculations required under Underground Injection Control permit regulations for Class II wells can be improved by the correct application of existing techniques in predicting individual system operational performance. Modifications to some of these technical indicators include: (a) estimates of radius of endangering influence that require observed initial hydrostatic heads and aquifer hydraulic transmitting properties for the injection interval; and (b) the geochemical characterization of nearby suspected shallow ground water contamination using all major ion concentrations in a trilinear diagram, instead of using only chloride as a brine tracer. A field application demonstrates the relative importance of these and other techniques in characterizing shallow ground water contamination from a salt water disposal well in Oklahoma.