A month after over 865,200 gallons of oil spilled from Tesoro Logistics' 6-inch pipeline near Tioga, North Dakota, the cause of the leak is still largely unknown to anyone but Tesoro. The pipeline resumed operations today.
Carrying oil obtained via hydraulic fracturing (“fracking”), the controversial horizontal drilling method used to capture oil and gas found embedded in shale rock basins worldwide, the Bakken Shale pipeline spill on September 29 was the largest fracked oil spill in U.S. history. Oil spill experts say the spill may be even bigger than originally estimated.
Yet few details of what caused the spill - and how to prevent it from happening again - have arisen in the month since it occurred.
The U.S. Department of Transportation's Pipeline and Hazardous Materials Safety Administration (PHMSA) believes a lightning strike may have created the quarter inch hole in the pipeline, leading to the spill.
PHMSA says it will carry out a rigorous investigation into the cause of the spill, but allowed the restart after Tesoro agreed to the agency's safety order mandating aerial monitoring of the pipeline over the next three days during the restart and then weekly for the next year, along with 20 other things.
The safety order also mandates Tesoro provide a documented updated within six months indicating how it enhanced its control room monitoring, instructs Tesoro to finish the final mechanical and metallurgical testing report of the failed pipe within 30 days and dictates that within “90 days complet[ion of] a root cause failure analysis for the Line that contains a detailed timeline of events.”
Documents obtained by Greenpeace USA under North Dakota's Open Records Statute show the oil has settled over 12 feet below the ground layer of the soil. The oil that settled on the surface was burned off.
“At 10-12 feet below surface, there is a extensive clay layer that underlies the entire hill top,” Kris Roberts, Environmental Response Team Leader for the North Department of Health's Division of Water Quality, explained in an October 3 field report.