In North Dakota’s Bakken region, a boom of hydraulic fracturing, or fracking, has generated nearly 10,000 wells for unconventional oil and gas production. This increased production also has resulted in almost 4,000 reported spills of fracking wastewater.
According to a new study, these spills have left soil and surface water in the area contaminated with water carrying radium, selenium, thallium, lead, and other toxic chemicals that can persist for years at unsafe levels (Environ. Sci. Technol. 2016, DOI: 10.1021/acs.est.5b06349).
Using fracking in oil and gas production brings up a brine that carries naturally occurring toxic or radioactive elements such as radium and selenium from rock formations. To understand the impact of fracking wastewater spills on the environment, Avner Vengosh of Duke University and his colleagues sampled water, sediment, and soil at sites of reported brine spills, which had occurred months to years earlier. To trace the source of contaminants at those sites, they also analyzed wastewater from shale gas wells in North Dakota and combined it with government data on fracking wastewater.
The ratio of strontium-87 to strontium-86 in fracking wastewater carries a distinctive signature of the rock formation where it was produced. By measuring strontium isotopes in the water produced by fracking wells and in water samples taken from spill sites, the researchers could identify brine residue from a spill. At confirmed spill sites, radium, selenium, and thallium exceeded maximum contaminant levels for drinking water in some water samples, and ammonium and selenium concentrations were above recommended levels for aquatic life. In soil and sediment samples downstream from the largest spill site, radium concentrations were up to 100 times as great as concentrations in samples upstream.
Brian W. Stewart, a geochemist at the University of Pittsburgh who studies fracking wastewater, says this is the first time, to his knowledge, that systematic sampling has been done downstream of known brine spills to detect the impact of wastewater from fracking. “I was surprised that it persists that long,” he says, pointing to two cases in which the group found elevated levels of contaminants four years after a spill.