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USGS Study: Thumbs Up on Williston Basin Groundwater

As part of an ongoing national effort, the U.S. Geological Survey (USGS) has given a qualified thumbs up to groundwater quality conditions in the Williston Basin oil production area in North Dakota and Montana, according to a study published Monday in the journal Groundwater.

The authors offer their results as a snapshot, and recommend a long-term monitoring program to get a clearer picture of what, if any, impact oil/gas development has had on local water supplies. They note this study was the first comprehensive regional assessment of shallow groundwater quality and age in the Williston production area.

Based on samples from 30 randomly distributed, nonfederal domestic wells in the Upper Fort Union Formation, the study looked at old water supplies predating any oil/gas production, and the authors cautioned that younger, shallower supplies closer to oil/gas development might come up with different results.

But the current USGS study said that the Williston Basin oil production area, including the Bakken and Three Forks shale formations, has not affected shallow groundwater quality.

"It is important, however, to consider these results in the context of groundwater age," the authors said in an abstract. "Most samples were recharged before the early 1950s and have carbon-14 dating ages ranging from 1,000 to 30,000 years. Thus, domestic wells may not be as well suited for detecting contamination associated with recent surface spills as shallower wells screened near the water table."

A spokesperson for the North Dakota Petroleum Council said the study “further confirms what the industry and state/federal officials have been saying all along: that hydraulic fracturing technology is safe.” It also reinforces the effectiveness of the state’s “very robust regulations on oil and gas development,” she said. 

The study looked at concentrations of several chemicals to health-based drinking water standards, analyzed correlations between concentrations and oil/gas well locations and evaluated methane for indications of deep production-zone gases.

Peter McMahon, the USGS hydrologist and lead author of the study, said the results are "good news for water users, and the data provide a valuable baseline against which future water-quality data can be compared." McMahon cautioned about the age issue, however.

"The groundwater age results indicate that a long-term commitment to monitoring is needed to assess the effects of energy development on groundwater quality in the Williston Basin production area," McMahon said.

He and his four co-authors noted that shallower wells screened at the water table "would be better suited" for detecting contamination associated with recent surface spills than the domestic wells sampled at this time.

The study noted that inclusion of groundwater-age measures in assessing the effects of energy development on the water quality is a new approach that they think provides a "valuable context" for water quality data and can help develop more effective monitoring programs.

The report is part of the USGS's larger Groundwater Resources Program, providing scientific information and developing interdisciplinary understanding necessary to assess and quantify the availability of U.S. groundwater resources.

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