The US Environmental Protection Agency (EPA) faces intensifying criticism for its finding that hydraulic fracturing has no "widespread, systemic impacts on drinking water" — and the pushback comes not from activists, but from the agency's own science advisors.

Last month, the panel of 31 independent scientists charged with reviewing the EPA's draft report stated that the agency's broad conclusion about the mining technique known as fracking is at odds with the evidence and "inconsistent with the observations, data, and levels of uncertainty presented."

According to the scientists, in looking at the issue nationally, the EPA failed to give due consideration to several cases in which fracking may have contaminated water supplies locally.

"The agency should include and explain the … investigations conducted in Dimock, Pennsylvania; Pavillion, Wyoming; and Parker County, Texas where hydraulic fracturing activities are perceived by many members of the public to have caused significant local impacts to drinking water resources," states the advisory body's review.

'The EPA's own science advisers are rightfully responding to the EPA's report with the fact that drilling and unconventional extraction are risks to the water cycle and that water contamination is a common and inherent problem.'

The EPA fracking study was commissioned in 2010 by the US Congress and stands as the most comprehensive review of the controversial mining technique, which releases natural gas by injecting a high-pressure mixture of water, sand, and chemicals into rock formations deep below ground. The fossil fuel Industry has heralded the EPA's June report as vindication for years of criticism.

Fracking has helped to catapult the United States into the position of the world's largest producer of natural gas. But the advising scientists' critique stands to reignite the debate over how to regulate a practice that critics say could contaminate water supplies and exacerbate global warming.

The charge leveled by the advising scientists is not that the EPA erred in the 20 peer-reviewed studies it conducted and 3,500 more studies and reports it reviewed. Rather, the advisory board, consisting of government and university scientists, finds fault with how the agency presented the information most likely to influence public opinion — particularly that the claim of no systematic impact on drinking water is insufficiently nuanced.

We are "concerned that these major findings are presented ambiguously within the Executive Summary and are inconsistent with the observations, data, and levels of uncertainty presented and discussed in the body of the draft Assessment Report," states the review. While the EPA did not find any clear evidence that fracking, properly executed, caused chemicals to seep through rock fissures into the water supply, it did document well failures and above-ground spills affecting drinking water.

One case occurred in Pavillion, Wyoming, where in 2010 the EPA issued a warning to residents not to drink or cook with water that was found to contain a chemical used in fracking, 2-butoxyethanol or 2-BE. In 2011 the EPA issued a draft report stating that fracking was responsible for the water pollution, but following harsh criticism of its methods the agency retreated from its finding and turned the study over to state regulators.

The state's Department of Environmental Quality eventually found little evidence that the presence of 2-BE, which is also found in household cleaners, was due to fracking. The study was funded by EnCana, the drilling company whose wells the EPA had initially blamed for the contamination.Though the role of fracking remains contested, the advising scientists recommend that the EPA should qualify its conclusions about the risks posed by acknowledging gaps in the existing data and concerning cases like Pavillion.

The EPA is not required to act on its advisors suggestions, and industry lobbyists are intent on seeing the final report retain its sweeping language.

"The [science advisory board] asks the EPA to change its top line conclusion that hydraulic fracturing has not led to widespread, systemic impact on drinking water sources based on what it, itself, calls outlier events," said Katie Brown, a spokesperson for the research branch of Independent Petroleum Association of America, during a public comment period on Monday. "But, by definition, if an event is an outlier it means that it is neither widespread nor systematic."

Other public commenters supported the advisory body's recommendations, and environmentalists and scientists have called on the agency to edit the report.

"The EPA's own science advisers are rightfully responding to the EPA's report with the fact that drilling and unconventional extraction are risks to the water cycle and that water contamination is a common and inherent problem," said Tony Ingraffea, a professor at Cornell University.

The EPA's study found that between 25,000 to 30,000 new wells were drilled each year between 2011 and 2014 and that 9.4 million Americans live within a mile of a fracking site. The report also states that there are 6,800 drinking water sources within a mile of a well.

The promise of cheap energy supplies and jobs in the oil and gas sector have often overshadowed concerns over the environmental impact of fracking. In Iowa, for instance, the boom in natural gas has meant trouble for the local ethanol industry. But of the presidential candidates hoping for good news out of the corn state's caucuses today, the only out-and-out opponent of fracking is Vermont's Senator Bernie Sanders.