At the moment, the spill doesn't threaten public drinking water or human health, Glatt said. He said a handful of farmers have been asked to keep their livestock away from the two creeks, the smaller of which will be drained.

The saltwater, known as brine, is an unwanted byproduct of oil and natural gas production that is much saltier than sea water and may also contain petroleum and residue from hydraulic fracturing operations.

The new spill is almost three times larger than one that fouled a portion of the Fort Berthold Indian Reservation in July. Another million-gallon saltwater spill in 2006, near Alexander, is still being cleaned up nearly a decade later.

Summit Midstream said in a statement Wednesday that about 65,000 barrels of a mix of freshwater and brine have been pumped out from Blacktail Creek. Brine also reached the bigger Little Muddy Creek and potentially the Missouri River.

Glatt said the Blacktail Creek will be fully drained as part of the initial cleanup, but the water and soil will have to be continuously tested until after the spring thaw because some of the contaminated water has frozen. The Little Muddy Creek will not be drained because it is bigger than the Blacktail Creek and the saltwater is being diluted.

"We will be monitoring to see how quickly it gets back to natural background water quality conditions, and we are already starting to see that," Glatt said of the Little Muddy Creek. "It's getting back pretty quickly."

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