Delineation of Brine Contamination
in and near the East Poplar oil field,
DESCRIPTION AND SCOPE OF WORK:
Previous USGS investigations (Thamke and Craigg 1997, and Levings 1984) documented and delineated a portion of the extent of the brine contamination in the East Poplar oil field. This 12.4 square mile area is known now to be only a portion of the contamination. For comparison purposes, contaminated ground water in the East Poplar oil field contains dissolved-solids concentrations that are nearly 10 times greater than water that is produced during methane gas development in the Powder River Basin. Contaminated ground water in the East Poplar oil field contains chloride concentrations that are more than 400 times greater than chloride concentrations in produced water in the Powder River Basin. In the 10 years since the brine contamination was partially delineated, dissolved solids and chloride concentration in water from at least 17 domestic wells increased substantially and the entire extent of contamination has likely grown larger.
The unconfined and semi-confined shallow aquifers of are only available source of potable ground water in the area and provide source water for more than 100 residents with domestic wells northeast of Poplar in addition to the source water for the City of Poplar water-supply wells, a systems serving 2,900 local residents through more than 874 metered service connections. The City of Poplar PWS wells are less than 3 miles down gradient of brine-contaminated domestic wells.
OBJECTIVES, TASKS ACCOMPLISHMENTS:
Phase 1 - Delineate subareas of low, moderate, and high conductivity areas in and around the East Poplar oil field. Phase 1 includes a helicopter-borne electromagnetic (HEM) survey, historical compilation of oil-related features, borehole geophysics, and water-quality sampling at selected wells.
Phase 2 – Delineate brine contamination and movement in surficial deposits in and around the East Poplar oil field. Phase 2 includes ground electromagnetic (GEM) data collection, installation of monitoring wells, water-quality sampling, and two aquifer tests.
Although selected residents in the East Poplar oil field have received potable water supplies through U.S. Environmental Protection Agency emergency orders, alternative water supplies are not currently available for the City of Poplar or other residents located down-gradient of the contamination. Funds are still being acquired to install a water pipeline designed for the entire Reservation. Originally it was believed that this water supply would be in place to serve the City of Poplar before the potential arrival of the leading edge of contamination, however without the necessary funding appropriated by Congress, it becomes increasingly vital to establish the true nature of the threat to the Poplar PWS. Data gathering efforts continue in order to allow the identification of potential contaminate flow paths between the southernmost brine plume and the city well field.
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