Crews in North Dakota excavated pastureland after more than 120,000 gallons of oil and drilling wastewater overflowed from a tank, the state Health Department said Friday.
The spill happened Wednesday morning near Marmarth in southwestern North Dakota at a site operated by Plano, Texas-based Denbury Onshore LLC, according to Bill Suess, an environmental scientist who heads spill investigations for the state Health Department. The company notified state regulators of the spill immediately, he said.
About 17,000 gallons of oil and 105,000 gallons of what’s called produced water — a mixture of saltwater and oil that can contain drilling chemicals — spilled from a tank after a shut-off sensor failed, Suess said.
Denbury spokesman John Mayer said crews may have the spill cleaned up by the end of Friday, though monitoring would continue. State Health Department and Oil and Gas Division employees are monitoring the cleanup.
The company told investigators that a power outage caused the sensor to fail, though Suess said the cause of the outage has not been determined.
An area about the size of a football field beyond the well site was affected, but no waterways or drinking water sources were threatened, Suess said.
“It is a relatively significant volume but from an overall risk standpoint it’s not that high,” he said, noting that the company had a berm around the oil well site but it wasn’t adequate to contain the spill. Neither investigators nor the company could confirm how much oil and drilling wastewater left the site.
Suess said crews used huge vacuums to suck up the overflow, and crews have had to dig at least 18 inches down to remove affected soil.
“Once they excavate, it will be replaced with clean fill,” Suess said.