Accidental wastewater spills from unconventional oil production in North Dakota have caused widespread water and soil contamination, a new Duke University study has found.

Researchers discovered high levels of ammonium, selenium, lead and other toxic contaminants, as well as high salts in the brine-laden wastewater, which they say primarily comes from hydraulically fractured oil wells in the Bakken region of western North Dakota.

More than 9,700 wells have been drilled in North Dakota in the past decade. Image credit: Joshua Doubek, under a Creative Commons Attribution-ShareAlike 3.0 Unported License.As part of their study, the researchers collected samples of brine-laden spill waters from four sites—two large spills and two smaller ones. They measured and analyzed the samples for inorganic contaminants and to identify the unique isotopic signature, or fingerprint, of Bakken-region brines. By comparing this fingerprint to the geochemical and isotopic profiles of 29 background surface water samples collected across the region, the team was able to determine where and to what extent contamination associated with brine spills had occurred—and rule out the possibility that it had been caused by other sources.

“These isotopic tracers give scientists powerful forensic tools for tracking the presence of spill waters in the environment,” says Avner Vengosh, professor of geochemistry and water quality at Duke’s Nicholas School of the Environment. “Given that spills can occur upstream from drinking water sources, long-term monitoring of downstream waters is necessary to assess impacts on water quality.”

According to the researchers, streams polluted by the wastewater contained levels of contaminants that often exceeded federal guidelines for safe drinking water or aquatic health. Soil at the spill sites was contaminated with radium, a naturally occurring radioactive element found in brines, which chemically attached to the soil after the spill water was released. At one site, the researchers were still able to detect high levels of contaminants in water four years after the spill occurred.

“Until now, research in many regions of the nation has shown that contamination from fracking has been fairly sporadic and inconsistent,” says Vengosh. “In North Dakota, however, we find it is widespread and persistent, with clear evidence of direct water contamination from fracking.”

More than 9,700 wells have been drilled in North Dakota in the past decade. According to the Duke researchers, 3,900 brine spills have since occurred, most the result of faulty pipes built to transport fracked wells’ flowback water from on-site holding containers to nearby injection wells, where it is disposed of underground.

“Unlike spilled oil, which starts to break down in soil, these spilled brines consist of inorganic chemicals, metals and salts that are resistant to biodegradation,” says Nancy Lauer, a Ph.D. student of Vengosh’s who led the research. “They don’t go away; they stay. This has created a legacy of radioactivity at spill sites.”