BAKKEN SHALE: As oil production sets in, pollution starts to migrate — scientists by Gayathri Vaidyanathan, November 22, 2013, E&E News
When oil is produced, brine or produced water rich in salts and toxic metals also comes out of the ground. The oil companies injected the wastes back underground to a depth of between 800 and 1,000 feet, where it was assumed the material would stay put. It did not. In 2004, Bruce Smith, a geophysicist at USGS, flew a helicopter over a 100-square-mile area on the reservation. Dangling from his ride was a magnetic beam that could detect the presence of salty water below ground. “It is kind of like a CAT scan of the Earth of very small areas as we fly over,” Smith said. Smith found two potential plumes covering 12 square miles that seemed to be migrating closer to Poplar’s water supply. The scientists drilled 40 boreholes, tested the water on the reservation and found it was significantly contaminated. In 2010, they tested three public wells Poplar draws its water from and found that all were contaminated with brine. The pollution was due to a well casing failure of an injection well, Smith said.
Meanwhile, farther north in North Dakota, the Bakken boom was continuing apace and the USGS directed its efforts there. Smith and his colleagues found at least 292,745 wetlands and 4,440 miles of streams were within a mile of an oil or gas well. Spills of oil and produced water were common in the state, which reported 1,129 incidents in 2012 (EnergyWire, July 8). A snowy winter in 2011 caused several waste pits containing brine to overflow in the spring. These spills are noted in official databases, but the extent of brine contamination in the subsurface is unknown. Once a spill happens, there is some remediation of the soils, but the movement of brine below ground is not tracked.
‘Strong correlation’ on contaminated sites
The FWS is tasked with protecting some lands in the Prairie Pothole Region that coincide with the drilling, and it found itself with a huge job. “A big concern is whether or not these brines will affect the ecological functioning of the wetlands,” said Preston, the hydrogeologist at USGS. … Preston gathered information about the age of the wells to identify the predominant well drilling practices and wastewater disposal methods. He looked at the type of soil left behind by the Wisconsin glaciation, since brine can move rapidly through coarse sediments but stays contained in clayey sediment. The risks posed by a spill would be greater when there is coarse sand and gravel. He also looked at the distance from wetlands and streams and the density of oil wells in the area. Using these criteria, Preston could predict the likelihood of contamination. He checked his predictions by doing groundwater tests and usually found contamination. “The results came out pretty good,” he said. “We had a strong correlation with contaminated groundwater with a high vulnerability assessment score.” The work will be published in Science of the Total Environment. [Emphasis added]