Pump jacks in an oil field over the Monterey Shale formation where gas and oil extraction using fracking, is on the verge of a boom near Lost Hills, Calif., in 2014. (David McNew/Getty Images)

A new report from the Environmental Protection Agency suggests that hydraulic fracturing does have the potential to affect drinking water resources in the U.S. The report represents a shift in the agency’s previous conclusions, published in a draft report in 2015, which suggested low impacts from fracking.  

The final report, released Tuesday, relies on a review of more than 1,200 previously cited scientific sources, as well as new research conducted for the report and an independent peer review by the EPA’s science advisory board. The report finds a range of possible impacts from fracking, from temporary changes in water quality to the complete contamination of drinking water wells.

Drinking water can be affected at any stage of the fracking process, the report notes, from acquiring the water that will be used to injecting it into production wells and disposing of the wastewater afterward. Impacts are generally seen at sites close to production wells.

“The value of high-quality science has never been more important in helping to guide decisions around our nation’s fragile water resources,” said Thomas Burke, EPA’s science adviser and deputy assistant administrator of the Office of Research and Development, in a statement. “EPA’s assessment provides the scientific foundation for local decision-makers, industry, and communities that are looking to protect public health and drinking water resources and make more informed decisions about hydraulic fracturing activities.”

In 2015, a draft report found that fracking has caused isolated instances in which drinking water was affected, but did not bring about “widespread, systemic impacts” on drinking water. At the time, Burke added that “the number of documented impacts to drinking water resources is relatively low when compared to the number of fractured wells.”

The 2015 draft was met with criticism from environmental groups. And earlier this year, the EPA’s science advisory panel issued a critique challenging the report’s conclusions.

The final report includes a slightly stronger set of conclusions. It claims that fracking activities “can impact drinking water resources under some circumstances,” and notes that certain activities or conditions may make these impacts more severe. These include withdrawing water for fracking when water resources are already limited; injecting fluids directly into groundwater resources, or injecting them into wells that allow them to leak into the groundwater; failing to adequately treat wastewater before disposing of it, and dumping wastewater into unlined pits, where it can leak out.  

However, the report also notes that “significant data gaps and uncertainties in the available data prevented us from calculating or estimating the national frequency of impacts on drinking water resources from activities in the hydraulic fracturing water cycle.” And it adds that these uncertainties prevented the report from including “a full characterization of the severity of impacts.”

In other words, the report still can’t make a detailed assessment of how often any given activity results harms water quality, or how serious the effects are on a broad scale. It also refrains from making direct policy recommendations from its scientific conclusions.

The report has already met with criticism from the oil and gas industry.

“It is beyond absurd for the administration to reverse course on its way out the door,” said Erik Milito, director of upstream and industry operations for the American Petroleum Institute, in a statement. “The agency has walked away from nearly a thousand sources of information from published papers, technical reports and peer reviewed scientific reports demonstrating that industry practices, industry trends, and regulatory programs protect water resources at every step of the hydraulic fracturing process.”  

He added that the API “look[s] forward to working with the new administration in order to instill fact-based science back into the public policy process.”

While it’s unclear for now how the new report might influence public policy in the future, President-elect Donald Trump has vowed to scale back regulations that would hinder the expansion of oil and natural gas development. And his nominee to head the EPA, Oklahoma Attorney General Scott Pruitt, has fought against increased regulations on the oil and gas industry, notably joining a group of other state attorneys general suing the EPA over its proposal to curtail the methane emissions from the oil and gas sector.  

But the new report has been praised by environmental groups that have long argued that fracking presents a threat to the nation’s drinking water.

“The EPA has confirmed what we’ve known all along: fracking can and does contaminate drinking water,” said Wenonah Hauter, executive director of Food & Water Watch, in a statement. “We are pleased that the agency has acted on the recommendations of its Science Advisory Board and chosen be frank about the inherent harms and hazards of fracking.”