BILLINGS, Mont. — Random testing of shallow groundwater in the Northern Plains oil patch found no early evidence of contamination from an energy boom that's already seen more than 8,500 wells drilled, federal scientists said Monday.
However, the U.S. Geological Survey cautioned that the tests could have missed contamination from surface spills or leaking well casings. That's because water can take many hundreds of years to migrate beneath the surface, meaning contamination might not have reached USGS sample sites.
Industry observers say as many as 60,000 more oil and gas wells could be drilled in the Northern Plains in coming decades. The recent water tests will provide baseline data that can be used to know if water quality starts to deteriorate in the future, USGS researchers said.
"This is good news, really good news," USGS hydrologist Rod Caldwell said of the initial results. "But we didn't try to just sample domestic water wells close to oil and gas wells. We tried to look at the overall health of the aquifer."
Targeted testing around sites of prior spills could yield different results, Caldwell said.
In the recent study, published in the scientific journal Groundwater, researchers looked at 30 domestic water wells in North Dakota and Montana. Samples from the wells were analyzed for methane, brine and other byproducts of drilling.
Brine, also known as produced water, is a liquid that comes out of the ground with crude extracted from beneath the Earth's surface. It can be 10 times saltier than ocean water and comes in much larger volumes.
About 1.1 million barrels of oil a day are being extracted from the Northern Plains oil patch. The amount of brine produced is about three times that amount.
Earlier this year, an estimated 1 million gallons of brine leaked from a corroded underground pipeline near Mandaree, North Dakota, before it was discovered July 8. The saltwater traveled nearly 2 miles into a ravine, killing grass, bushes and trees along the way.
Still, disposal methods have improved in recent decades, with much of the brine now re-injected into deep geological formations.
For some older oil fields that lacked such safeguards — such as the East Poplar oil field on Montana's Fort Peck Indian Reservation — brine from leaking storage ponds has tainted drinking water supplies.
The USGS study was the first region-wide assessment of shallow groundwater quality in the Williston Basin area, which includes the massive Bakken and Three Forks oil formations.
Researchers also examined the age of the water samples — meaning the length of time it takes for water that soaks into the ground to recharge underground aquifers. Most of the samples taken involved water more than 1,000 years old.
In North Dakota, where the energy boom has been concentrated, regulators receive multiple spill reports each day from the industry, said Karl Rockeman, director of the water quality division within the North Dakota Health Department.
Most are dealt with quickly before the spills threaten groundwater supplies.
"Companies in general are doing a better job of preventing and mitigating spills to keep them as small and have as minimum an impact as possible," Rockeman said.
Rockeman added that the long-term impact on water supplies remains a question mark.
The study focused on the Fort Union Formation, an aquifer used for public drinking water supplies and stockwater for livestock.