Houston-based Oasis Petroleum Inc. continued water and soil sampling Monday after one of its pipelines spewed 42,000 gallons of salty wastewater into a pool and small creek that are part of a tributary to a Missouri River reservoir in McKenzie County in northwest North Dakota.

An environmental geologist with the state Department of Health (DOH), Kris Roberts, told NGI’s Shale Daily late Monday that while the discharge was “a big one” the resulting impact so far appears to be minimal, and Oasis and the state onsite inspectors have the situation well under control. Roberts said the tributary involved is a stream-and-ripple system that includes a series of semi-stagnant pools connected by small creeks or ripples eventually leading into the reservoir.

Oasis did not respond to a request for more information Monday.

As of Monday, there was no indication that any of the salt water had gotten into Lake Sakakawea, which is about five miles downstream in an area about 20 miles southeast of Watford City, ND, and 20 miles northwest of Williston. There is no real danger to the lake, Roberts said.

The water is being removed from the one pool in which the wastewater spilled, and the supplies will be allowed to refill naturally as part of the Oasis-led mitigation work. “They are also going to be putting in some water monitoring and soil-boring equipment to determine whether there is any groundwater contamination,” Roberts said.

“The situation is well contained, so we don’t expect any further damage. It is just going to take a while to get it cleaned up and make sure we have all of our bases covered.”

Initial remediation work involved removing about six inches of contaminated topsoil and replacing it with fresh soil, according to Roberts. An assessment is being made as to whether any additional soil replacement will be needed, or whether the riparian areas will be able to recover on their own. “It’s not a very big riparian zone impact; the spill went pretty straight into the creek from what I understand,” Roberts said.

While he said the spill is not insignificant, the area covered by the incident is relatively small.

This is the second major saltwater release in the past four months in the area. In July, nearly 1 million gallons leaked from an underground pipeline transporting salt water from oil and gas drilling operations onto Native American land (see Shale Daily, July 10). Crestwood Midstream Services Inc. discovered the leak in its water gathering system on the Fort Berthold Indian Reservation.

North Dakota recorded 74 pipeline leaks last year that spilled an estimated 22,000 bbl of saltwater, 17,000 bbl of which were from a single spill in Bowman County. Some 313.5 million bbl of crude oil were produced overall last year in the state, along with 350 million bbl of contaminated water.