Delineation of Brine Contamination in and near the East Poplar oil field,
Fort Peck Indian Reservation, Northeastern Montana

DESCRIPTION AND SCOPE OF WORK:
Over 50 years of oil production in the East Poplar oil field, north east of the City of Poplar on the Fort Peck Indian Reservation has produced millions of barrels of brine byproduct primarily from the Charles Formation of the Madison Group. The brine which contains 47,700 to 201,000 mg/L dissolved solids, was placed in storage or evaporation pits or injected into subsurface units through injection wells. Methods of disposal and handling of the brine has resulted in widespread contamination of not only the unconsolidated Quaternary aquifers, but also the Poplar River.

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:
In 2003, the Tribes in cooperation with the U.S. Geological Survey began a project to (1) delineate the entire extent of the contamination, (2) determine the rate of contamination movement, (3) identify all active brine sources, and (4) to evaluate the threat to the city of Poplar. The project area includes the East Poplar oil field and extends south to include the city of Poplar (approximately 9.5 miles E-W and 14 miles N-S) and has been divided into two phases.

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.

AVAILABLE PUBLICATIONS:
Helicopter survey aids remediation of produced water-contaminated aquifer by David Michael Cohen.
Fort Peck Tribes/BLM Direct Current Electrical Resistivity Survey Results 02/28/2007 (1.7MB PDF)
USGS Water Resources in Montana
The U.S. Geological Survey Open-File Report 2006-1216 titled 'Helicopter Electromagnetic and Magnetic Survey Maps and Data, East Poplar Oil Field Area, August 2004, Fort Peck Indian Reservation, Northeastern Montana.
U.S. Geological Survey Water Resources Investigations Report 2003-4214
U.S. Geological Survey Open-File Report 1995-749
U.S. Geological Survey Water Resources Investigations Report 1997-4000

FOR MORE INFORMATION CONTACT:
Christa Tyrrell, OEP Division of Water Quality