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.įor 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.