A site run by Denbury Onshore LLC in southwestern North Dakota has spilled more than 120,000 gallons of oil and wastewater into pastureland after a mechanical failure.
Some estimated 17,000 gallons of oil and 105,000 gallons of drilling wastewater containing saltwater and chemicals leaked into pastureland near the city of Marmarth when a tank sensor failed, news agencies quoted state regulators as saying.
The tank overflowed on Wednesday, and by Friday, workers were excavating the affected pastureland, which is being equated to the size of a football field.
Health investigators continue to monitor the spill, which Denbury believes was ultimately caused by a power outage that led to sensor failure.
Huge vacuums were being used to suck up the spilled waste from the pastureland and then crews were forced to dig around 18 inches into the ground to remove the contaminated layer of pastureland.
According to health inspectors, waterways and drinking water sources were not affected.
In April, a Duke University study showed that wastewater spills from North Dakota’s oil operations have caused widespread water and soil contamination, after examining samples from soil and water near the sites of North Dakota oil spills. The tests found high levels of ammonium, selenium, lead and other toxic contaminates.
“The magnitude of spills that we see in North Dakota I haven’t seen elsewhere,” news agencies quoted Avner Vengosh, a Duke University professor, as saying.
Over two years after the September 2013 oil spill at a Tesoro Logistics pipeline in North Dakota, crews were still working at cleanup. The company had spent US$42 million on cleanup by June last year, when it was only one-third finished with the process of treating the contaminated soil.
The 2013 spill contaminated around 15 acres of cropland, but the cleanup site grew to 35 acres to accommodate excavated soil stockpiles from digging 50 feet deep and then baking hydrocarbons out of the soil.
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