"After more than five years and millions of dollars, the evidence gathered by EPA confirms what the agency has already acknowledged and what the oil and gas industry has known," said Erik Milito, upstream group director for the American Petroleum Institute. "Hydraulic fracturing is being done safely under the strong environmental stewardship of state regulators and industry best practices."
On the whole, the number of instances in which fracking impacted drinking water was "small compared to the large number of hydraulically fractured wells across the country," according to the draft assessment, requested by Congress in 2010.
EPA, however, did find specific instances when the practice could pose a risk to drinking-water resources, such as when gases and liquids seep out of inadequately cased or cemented wells or when wastewater is improperly released into drinking-water sources. Drinking water is also vulnerable, EPA said, in areas with low water availability.
Although most of the impacts would be confined to areas around drilling sites, EPA did note the potential for wider impacts from, say, a wastewater-truck spill or the release of untreated water that spreads downstream.
Green groups have said they have concerns about data gaps in the study. In a statement, Sierra Club President Michael Brune said the findings confirmed that "dirty oil and gas fracking contaminates drinking water," but he cast aspersions on the agency for leaving "many critical questions unanswered."
And Food and Water Watch Executive Director Wenonah Hauter said the study "falls far short of the level of scrutiny and government oversight needed to protect and health and safety of the millions of American people." The report, Hauter charged, was tainted because the oil and gas industry had refused to cooperate on prospective case studies.
EPA's report acknowledged "limiting factors" that could impact the findings, such as insufficient pre- and post-fracking water-quality data and a lack of accessibility for some industry data. But EPA science adviser Thomas Burke said the limitations could "guide us in the future" as researchers continue to look at the link between fracking and water.
"We feel very confident in our conclusions about identifying key vulnerabilities," Burke told reporters. "The study was not, nor was it intended to be, an empirical catalogue of all incidents of contamination."
Burke added that the EPA had a "generally very cooperative relationship" with the industry, which he said was a "major source of information."
The study covered water through all phases of the fracking process: acquisition, chemical mixing at the well-pad site, well injection of fracking fluids, collection of wastewater, and treatment and disposal. Burke said it was the "most complete compilation of scientific data to date," including more than 950 studies and other data sources.