Use Of Terrain Electromagnetic Geophysical Methods To Map Saline-Water Contamination, East Poplar Oil Field, Northeastern Montana

Quaternary deposits, comprised of the Poplar River alluvium and glacial deposits, are the sole<br>developed source of ground water for residents in and near the East Poplar oil field. The extent of<br>saline-water contamination in Quaternary deposits in and near the East Poplar oil field may be as<br>much as 12.4 square miles. The probable source of saline-water contamination in the Quaternary<br>deposits is brine that is a byproduct of the production of crude oil in the East Poplar oil field study area.<br>Terrain electromagnetic apparent conductivity data collected in an area of about 21.6 square<br>miles correlate well with ground-water quality. These data were collected and interpreted in conjunction<br>with water-quality data from existing water wells to delineate possible saline-water contamination<br>plumes. Monitoring wells were subsequently drilled in some areas that lacked existing<br>water wells to confirm most of the delineated saline-water plumes. Analysis of ground-water samples<br>from both existing and newly drilled monitoring wells confirms the presence of 7.3 square<br>miles of contamination, as much as 2.0 square miles of which are considerably contaminated. Terrain<br>electromagnetic apparent conductivity data in areas with no wells delineate an additional 5.1<br>square miles of possible contamination, 3.2 square miles of which might be considerably contaminated.<br>Brine-injection wells, oil wells, pipelines, and storage-tank facilities appear to be probable<br>sources of the saline-water contamination in many of the plumes.