High contamination levels persist along a North Dakota creek more than a month after a massive wastewater spill was found in the state's oil patch, but levels have dropped considerably in larger rivers downstream, according to documents released by the state Tuesday.
Results of a preliminary investigation into the pipeline leak, which spilled 3 million gallons of saltwater brine, were obtained by The Associated Press. They show that heavily contaminated surface water was found in recent days on residential property more than a mile away from the spill site north of Williston.
The wastewater is a byproduct of intensive oil drilling in the Bakken region of North Dakota and Montana. It primarily contaminated Blacktail Creek, but also flowed into the Little Muddy River and the Missouri River.
The levels of chloride, or salt, in water samples taken from an oxbow along Blacktail Creek were detected at more than 25 times the state's water quality standard in the past few days. But the area of highest groundwater contamination — where saltwater has seeped into the surrounding water table — is more limited. It runs along a corridor downstream of the spill site, which is at least several hundred feet wide and about 2,000 feet long.
The findings from a consultant for the pipeline's owner, Texas-based Summit Midstream Partners LLC, were released to the AP by state health officials under a public records request.
Saltwater produced by oil drilling can be more than 10 times saltier than seawater and can contain heavy metals and hazardous wastes. The salt itself can sterilize soils, killing vegetation, and make water unsuitable for drinking.
In the North Dakota spill, that means farmers could see damage to pastureland downstream and lose a water source for their livestock.
The Missouri River, 25 miles downstream, is a major drinking water source. However, officials have said the saltwater was so diluted by the time it reached the river that it posed no threat.
The most immediate concern for Jim Moline, a landowner downstream of the spill along Blacktail Creek, is whether the water will be suitable for cattle that use the pastures he rents out in the summer. Contractors for Summit Midstream have been drilling holes on both sides of the creek checking the soil, he said.
"It's very possible I'm not going to be able to use it for a considerable amount of time," Moline said.
"It's a summer pasture, so there might be time," he added. "Maybe it's all right because there will be some fresh water coming through."
Summit Midstream said in a statement Tuesday that it was making "significant progress" in the cleanup. It offered no timeline for when the work may be done.
Some previous saltwater spills have taken years to clean up, including the still-ongoing cleanup of a million-gallon spill in 2006 in nearby Alexander.
Elevated chloride levels initially detected along the Missouri and Little Muddy rivers were returning to normal levels, said Dave Glatt, chief of environmental health for the North Dakota Department of Health.
Glatt said the improvement was aided by the removal of contaminated water and ice from Blacktail Creek and the construction of trenches to capture some of that saltwater before it reached the creek. About 6 million gallons of water have been removed from Blackwater Creek since the spill was discovered on Jan. 6, although much of that was fresh water.
Mixed in with the salt water were lesser amounts of crude, and up to 5,500 gallons of oil have been recovered so far, said Karl Rockeman, director of water quality for the state health department.
Unknown is how much of the contamination was absorbed into the soil around the spill site, and whether that will be released slowly over time.
Company officials and regulators still are working on a long-term remedy. That could include digging up the soil around the source of the spill, further steps to contain and treat the contaminated water, or a combination of the two, said Steven Way, the on-scene coordinator for the spill for the U.S. Environmental Protection Agency.
Way said completing the cleanup could take "somewhere between many months and potentially years."
Summit Midstream Partners LLC, the parent company of the pipeline's operator, Denver-based Meadowlark Midstream Co. LLC, entered the North Dakota market in 2013, and has since invested more than $800 million in its operations in the state. It also has operations in West Virginia, Ohio, Texas, Colorado, Wyoming and Utah.
Associated Press writers Carson Walker in Sioux Falls, S.D., and John Flesher in Traverse City, Mich., contributed to this report.