East Poplar Brine-Contaminated Groundwater Plumes Continue to Move

HELENA, Mont. – A new report by the U.S. Geological Survey describes the extent and movement of contamination in the East Poplar oil field area in northeastern Montana. The contamination in shallow groundwater and the Poplar River is brine, which is saltier than seawater and is a byproduct as part of the process of extracting crude oil in the East Poplar oil field. The study determined likely source areas, brine plume extents, and movement of the plumes.

For more than half a century, millions of gallons of brine have been produced along with oil from the East Poplar oil field on the Fort Peck Indian Reservation. Until recently, the waste brine was placed in pits and ponds or injected into the ground through deep disposal wells and has made its way to the shallow groundwater and the Poplar River.  Currently, the only approved method of brine disposal is to inject it deep into the ground.

When the brine mixes with the groundwater in the area, it often makes the water unsuitable for domestic purposes. Groundwater was previously the only available source of potable water to the area, and provided water for household wells and the city of Poplar’s public water-supply wells. Currently, treated water from the Missouri River about 20 miles upstream of the city of Poplar is piped to the city and nearby residents.

"There are many brine sources in the study area, resulting in multiple plumes.  Some plumes remain in the groundwater for decades and have merged together, making it difficult to identify original sources," said Joanna Thamke, USGS hydrologist and lead author of the report. She continued, "this is important in development of water management practices, such as optimally locating wells in the future."

The USGS study, conducted in cooperation with the Fort Peck Tribe's' Office of Environmental Protection, shows that the brine contaminated groundwater is generally moving towards the southwest, eventually discharging into the Missouri River.

"This information will be used by the Fort Peck Tribes to direct future natural resource conservation efforts," said Deb Madison, Fort Peck Tribes' Environmental Programs Manager, who also added "the Fort Peck Tribes care deeply about these natural resources for today and for future generations."

Copies of "Delineation of Brine Contamination in and near the East Poplar Oil Field, Fort Peck Indian Reservation, Northeastern Montana, 2004–09" are available online.