Williston Basin groundwater unaffected by oil development

By The Bakken Magazine Staff | December 12, 2014

A first-ever scientific study conducted by the U.S. Geological Survey concludes that oil and gas development in the Williston Basin has not impacted groundwater quality. 

The study is based on water samples collected by USGS scientists from 30 randomly distributed, non-federal domestic wells screened in the upper Fort Union Formation. The results were published in the scientific journal “Groundwater.”

“It’s great news that we found nothing of concern, but it doesn’t answer all the questions,” said Joel Galloway, chief of hydrologic studies in the USGS Bismarck office.

For example, he noted that the study examined the Fort Union aquifer in North Dakota and Montana only, the most used groundwater source in the region.

“There are some more shallow glacial aquifers,” he said. “The flow in those may be more rapid than in the Fort Union formation and those may be more vulnerable, but they weren’t part of the study.”

The study—a collaborative effort between the USGS North Dakota, Montana and Colorado offices—included the Bakken and Three Forks formations. It compared concentrations of several chemicals to health-based drinking water standards, analyzed correlations between concentrations and evaluated methane for indications of deep production-zone gases.

“This is the first time a region-wide study looking at groundwater has been done in this area,” Galloway noted. “These are domestic wells, wells on peoples’ farms that they use.”

Peter McMahon, a USGS hydrologist and lead author of the study, said, “These results are good news for water users, and the data provide a valuable baseline against which future water-quality data can be compared. However, it is important to consider these results in the context of groundwater age.”

Based on carbon-14 dating, most of the sampled water was more than 1,000 years old. Galloway said the measurements revealed that all water was older than the 1950s when oil drilling began while the oldest went back more than 30,000 years. If contaminants were present in the groundwater, they wouldn’t have moved far from their source.

“What that tells us is that it’s very old water, very slow-moving water,” he explained. “We may not pick up the signal of all the activity going on right now.”

Galloway noted that the USGS is conducting another study focused on glacial aquifers, although the results won't be released for some time. He said other state and federal agencies, such as the North Dakota Department of Health, are also involved in monitoring groundwater quality.