Drinking water wells in Texas counties that are home to intensive hydraulic fracturing operations contain elevated levels of more than two dozen metals and chemicals, including carcinogens, according to a new study in Environmental Science & Technology.
The study is based on samples from 550 wells across the Barnett Shale natural gas formation in the Dallas area; it is one of the largest independent analyses of water quality to date of aquifers near fracking sites. Researchers found volatile organic compounds such as benzene, toluene, ethylbenzene and xylene, or BTEX, in more than two-thirds of the wells sampled. Benzene is a carcinogen, and the other compounds can damage the nervous system. An industrial solvent called dichloromethane, or DCM, was found in 121 samples, or more than 20 percent of the wells.
The chemicals and some of the metals are commonly found in fracking fluid––and in produced water that comes up the well-bore with natural gas, according to the authors, many of them from the University of Texas at Arlington. The paper noted that its findings "do not necessarily identify" fracking-related activities as the source of the contamination.
But Zacariah Hildenbrand, the paper's lead author, said there is a correlation between greater unconventional oil and gas development and the presence of the contaminants. "In the counties where there is more unconventional oil and gas development, the chemicals are worse," Hildenbrand said. "They're in water in higher concentrations and more prevalent among the wells. As you get away from the drilling, water quality gets better. There's no doubt about it."
The paper arrives two weeks after the Environmental Protection Agency issued a long-awaited study of fracking's impact on surface and groundwater, which concluded that hydraulic fracturing had contaminated drinking water in some cases. The conclusion marked a notable reversal for the EPA and the Obama administration, which had long insisted that fracking had never tainted drinking water. The EPA said the contamination of water by fracking-related operations was not "widespread," but it conceded that it lacked data about the number of incidents nationwide and their severity.
Among the wells where Texas-Arlington researchers found contaminants were those in the Silverado subdivision in Parker County. Five years ago, the EPA began testing well water in the upscale neighborhood after Texas regulators failed to act immediately on homeowners' complaints of possible drinking water contamination by nearby gas development. But by 2012, the EPA and the Justice Department halted legal action they were planning to take against the gas company; it became one of several high-profile investigations into fracking and water quality the Obama EPA shelved.
The Barnett study found evidence of contaminants in the Silverado water, Hildenbrand said, and the scientists plan to conduct further sampling in the neighborhood.
The researchers gathered samples from 13 counties across the Barnett Shale, although some are being more intensively developed by the gas industry than others. The area is home to almost 20,000 wells. Among the municipalities in the area is Denton, whose efforts to ban fracking within city limits have been stymied by the state. Of the total samples, 83 percent were gathered from the half-dozen or so counties with the most wells, where more homeowners volunteered for testing, researchers said.
Some scientists said they welcomed the new data from the Barnett Shale study, but more could have been done to nail down the origins of the contamination.
"It's always good to have more data and good to have more monitoring, there's nothing definitive about the sources of contamination," said Avner Vengosh, professor of earth and ocean sciences at Duke University. "So, it leaves more questions than answers, because what is seriously missing is diagnostic indicators for the sources."
The Barnett study expands upon a paper University of Texas at Arlington researchers published two years ago that found higher levels of arsenic, barium, selenium and strontium in well water closer to fracking sites. In the new study, the concentrations of heavy metals were lower than those in the 2013 paper.
But researchers found other substances that were concerning, Hildenbrand said. Methanol was found in 35 wells, and ethanol in 240 wells. Both alcohols can be produce in nature by bacteria, but at far lower concentrations than the scientists found. Methanol and ethanol are widely used in fracking as anti-corrosive agents and as gelling agents, the study said. About 90 percent of the samples with the alcohols were found in counties with the greatest fracking activity.
The industrial solvent, DCM, does not occur in nature, but was found in about 20 percent of the water wells. DCM is generally used in large volumes as a degreasing agent in unconventional oil-and-gas development, the study said.
The presence of DCM, a possible carcinogen, and the other substances were alarming, said Dominic DiGiulio, a former EPA water scientist affiliated with Stanford University. "I would definitely be concerned if I were one of the domestic well owners here," he said. "I wouldn't be consuming the water or showering with it."
DiGiulio said that the presence of these toxic substances in residential water should prompt state and federal authorities to investigate water quality in the wells that the Texas-Arlington researchers sampled.
The EPA and the Texas Railroad Commission said they are still reviewing the Barnett paper and had not yet decided if it warrants a regulatory response.