Fracking has not led to widespread pollution of drinking water, the U.S. Environmental Protection Agency said on Thursday in a long-awaited draft study, but warned that certain drilling activities could pose risks.
The study, requested by Congress and five years in the making, found specific instances where water sources were affected by hydraulic fracturing, the injection of large amounts of sand, water and chemicals deep underground to crack open rock formations holding natural gas and oil.
The EPA also found risks to drinking water in formations where fracking occurred and where water supplies were scarce.
But overall, the EPA saw little impact to water supplies from the thousands of fracking wells across the country.
The draft study will give state regulators, local communities and companies "a critical resource to identify how best to protect public health and their drinking water resources," said EPA science adviser Thomas Burke.
Other vulnerabilities to water supplies from fracking-related activities can result from inadequately cased or cemented wells that leak gases and liquids underground when inadequately treated wastewater is discharged into the resource, the study said.
The study contained a compilation of more than 900 references and citations, as well as agency-conducted research that has undergone "extensive peer review," Burke told reporters.
Environmental groups cast doubt on the EPA's findings.
"There are still significant gaps in the scientific understanding of fracking," said Amy Mall, senior policy analyst at the Natural Resources Defense Council. "This study is site-specific and limited, as EPA has explained, which makes it impossible to fully understand all the risks at this time."
Mall said, however, that unlike in the past updates on the study, the EPA this time acknowledged there are some effects on water.
Mark Brownstein, vice president of the Environmental Defense Fund, said the process of fracking itself is just one risk factor.
"Ongoing physical integrity of the wells and handling the millions of gallons of wastewater coming back to the surface after fracking, over the lifetime of each well, are even bigger challenges," he said. "Relentless focus on these issues by regulators and industry is critical."
The EPA's Burke told reporters that oil and gas companies were a major source of information on locations and practices, and that the agency had a "very cooperative relationship with industry."
Energy groups embraced the EPA's findings, saying they backed up other studies by the Energy Department and U.S. Geological Survey.
"The report contradicts the most prevalent claim from anti-fracking activists, which have made 'water contamination' the very foundation of their campaign against hydraulic fracturing," said Katie Brown, spokeswoman for the Independent Petroleum Association of America's Energy In Depth arm.
The American Petroleum Institute said the study affirmed the sector's record of "continuous safety improvements."
The draft study will undergo external review by the public and the agency's Science Advisory Board and is due to complete the process by next year.
(Reporting by Valerie Volcovici and Timothy Gardner; Editing by Lisa Von Ahn)