Wetlands contamination can be predicted in oil boom states

WASHINGTON – Federal scientists have developed a system that could help prevent some contamination of wetlands and groundwater from oil development in the booming Williston Basin in Montana and North Dakota, a new study said.

Along with oil extracted from deep underground in the Williston Basin comes naturally occurring water called brine that is 10 times more saline than seawater and is dumped into reserve pits. Brine can contaminate local water sources through leaching from the pits, pipeline spills or accidents.

At many area oil wells, 10 barrels of brine are produced for every barrel of oil, making brine disposal a significant issue as Williston Basin oil extraction flourishes.

U.S. Geological Survey scientists, in a study focused on Montana's Sheridan County on the border with North Dakota, have developed criteria that can identify areas at the highest risk for brine contamination.

In a study published in the journal Science of the Total Environment, they found that water samples from areas deemed at high risk of contamination had substantial brine concentrations. Similarly, the authors found areas at low risk of contamination yielded samples with lower or no brine concentrations.

"In areas where we had a high vulnerability assessment, the criteria ended up predicting very well, and where we had a low assessment, we did very well," said Todd M. Preston, the study's lead author.

The analysis could help landowners, regulators and oil industry officials in the Williston oil boom "quickly and easily identify areas with the greatest potential contamination" from brine, the study said.

Previous studies by the USGS and others have found evidence of brine contamination in wetlands and groundwater sources, including drinking water aquifers. The new study found that government officials work with oil companies to locate oil wells away from wetlands on public land. But most of the Williston Basin oil drilling is on private land and the study concluded oil wells "are often placed very close to wetlands to preserve farmable acreage," increasing the risk of brine contamination.

The study is the latest from a unit of the U.S. Geological Survey established in 2008 to monitor the environmental effects of energy development in the Prairie Pothole region, a vast swath of intermittent wetlands from Alberta, Canada, to northern Iowa. The region, which overlaps with the Williston Basin, is vital habitat to migratory North American waterfowl.

Until the late 1970s, oil companies dumped brine into unlined pits, which have a history of causing contamination. Pits in the Williston Basin must be lined and then buried once reclamation begins. But no monitoring of possible leaching or contamination from the pits is required. "There are still uncontained releases of brine in the form of spills, pipeline breaks and vehicle accidents, which often occur closer to oil wells," Preston said.

Moreover, the open-air storage of brine still holds hazards, said independent scientists who read the USGS study.

While lined pits are an improvement over unlined ones, liners also tear sometimes, as the experience with landfills has shown, said Geoffrey Thyne, principal scientist at Science Based Solutions, an environmental consulting firm in Wyoming. "It's very difficult to maintain the perfect integrity of a liner," he said.

The scientists then sampled water from 10 sites that were representative of the range of vulnerability scores they had assigned to the Sheridan County sections. They compared the ratio of chloride concentration in the samples to a contamination index developed by the Montana Bureau of Mines and Geology.