BISMARCK, N.D. (AP) — State health officials are working this week to verify that the recent spill of about 20,000 barrels of oil in northwestern North Dakota did not contaminate groundwater.
Tesoro Corp. found no contamination during earlier testing, but state crews were at the site near Tioga on Tuesday taking their own samples. Results were expected in a week or two, State Environmental Health Chief Dave Glatt said.
The company "collected one round and we're doing a follow-up, just to make sure the first (tests) were accurate," Glatt said. "We're up there now, collecting our own, to do a verification of what (Tesoro officials) are finding."
Glatt said state officials do not expect to find any groundwater contamination, and that there continues to be no indication of any harm to wildlife.
The pipeline rupture was discovered in a wheat field in September, and the oil spill covered an area the size of seven football fields. Federal regulators have said a lightning strike may have caused the rupture in the 6-inch-diameter steel pipeline, which runs from Tioga to a rail facility outside of Columbus, near the Canadian border.
The oil spill was one of the largest in North Dakota history.
San Antonio-based Tesoro restarted the pipeline on Nov. 1 under conditions set by the federal Pipeline and Hazardous Materials Safety Administration. Tesoro continues to work on cleanup, a process the company has said could cost $4 million.
About 5,000 barrels of oil have been collected. Much of the rest will have to be baked from the soil, and the soil renewed and replaced, Glatt said.
"They will need to revitalize it with natural bacteria and nutrients to make sure it's productive," he said.
Tesoro will initiate the soil cleanup next spring. The process could take a couple of years, Glatt said.
In an email Tuesday afternoon, the company said an on-site investigation was done "to determine the extent of oil on site."
"This investigation included a thorough examination of the site spill characteristics including factors such as surface area, depth of soil impacted and soil porosity," Tesoro wrote.
The landowner and the state Health Department will review the options, which is expected to be done early next year, so the cleanup can be done after the spring thaw, it wrote.
"Which remediation option is selected will affect the timeline. We have been and will continue to work with impacted parties throughout the remediation process," the statement said.
The farmer whose land was covered by the oil spill, Steve Jensen, did not return a phone message.
Glatt said Tesoro is doing more soil sampling as part of the cleanup to better outline the contamination area, but he does not expect the 20,600-barrel spill size estimate to change much. A barrel holds 42 gallons.
"I don't anticipate significant quantity differences," Glatt said. "As they get into bigger remediation cleanup, they want to know where the biggest contamination is. It's just to provide them more data as they move forward with their remediation plan.
"Their (current) estimate probably is as good as it's going to get," he said.
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