“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.
“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.” Mc Mahon said, “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.” “One sample doesn’t tell you everything,” Galloway said.
“It’s important to continue collecting samples over time to see if some of the effects show up in the groundwater system.” Galloway noted that the USGS is conducting another study focused on glacial aquifers, although the results won't be released for some time.
“These are domestic wells—wells on peoples’ farms that they use.” Peter Mc Mahon, 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.
“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.