The scientists found high concentrations of lead, selenium, ammonium as well as other toxic pollutants, together with high salt levels in wastewater produced during fracking activities at oil drilling sites in North Dakota's Bakken region.
Streams contaminated by the fracking wastewater contained concentrations of pollutants that in many cases exceeded federal safety standards set for drinking water or for environmental health of freshwater systems.
Soil samples taken from spill sites showed that soils were contaminated with the radioactive element, radium, which chemically bonded with the soil following the release of spilled wastewater. In one case, the scientists still found high concentrations of pollutants in spilled wastewater four years later.
"Until now, research in many regions of the nation has shown that contamination from fracking has been fairly sporadic and inconsistent," said Avner Vengosh, professor of geochemistry and water quality at Duke's Nicholas School of the Environment. "In North Dakota, however, we find it is widespread and persistent, with clear evidence of direct water contamination from fracking."
"The magnitude of oil drilling in North Dakota is overwhelming," Vengosh said. "More than 9,700 wells have been drilled there in the past decade. This massive development has led to more than 3,900 brine spills, mostly coming from faulty pipes built to transport fracked wells' flowback water from on-site holding containers to nearby injection wells where it will be disposed underground."
During the course of the study, the researchers mapped the 3,900 wastewater spill sites to illustrate how oil drilling intensity played a key contributing role in wastewater spills.
Over a seven year period between 2007 - 2014, unconventional oil production has increased from around 100,000 barrels per day to over 1 million barrels per day in North Dakota. The increase in production is largely due to advances in hydro-fracturing and horizontal drilling technologies. The expansion of the oil and gas industry in North Dakota has spurred economic growth, particularly in the rural areas and tribal lands. However, this expansion has also fueled concern about the impact on drinking water quality.
According to lead author of the paper, Nancy Lauer, a doctoral student at Duke, unlike oil, which breaks down in soils, brine-laden spilled wastewater contains salts, heavy metals and inorganic chemicals that do not readily biodegrade. Consequently these contaminants persist in the environment for a very long time. As a result, we now have a legacy of radioactive contamination at these spill sites.
Lauer points out that soil samples collected further downstream from wastewater spill sites had higher levels of radiation than soils samples collected from a wastewater spill site itself, suggesting that radium accumulates in soils as spilled wastewater flows through.
Considering that wastewater spills can occur upstream from drinking water sources, it is important to conduct long-term monitoring of waters further downstream to determine the impact on drinking water quality, notes Vengosh. For example, in 2014 a leaking underground pipeline spewed roughly 1 million gallons of brine into Bear Den Bay, situated less than a mile upstream from Lake Sakakawea which supplies drinking water to residents nearby.
|Aerial view of resource extraction in Texas.|
"Many smaller spills have also occurred on tribal lands, and as far as we know, no one is monitoring them," Vengosh added. "People who live on the reservations are being left to wonder how it might affect their land, water, health and way of life."
Nancy E. Lauer, Jennifer S. Harkness, Avner Vengosh. Brine Spills Associated with Unconventional Oil Development in North Dakota. Environmental Science & Technology, April 27, 2016. DOI: 10.1021/acs.est.5b06349