The Environmental Protection Agency said that hydraulic fracturing, a controversial natural gas drilling process, probably contaminated well water in Wyoming, a finding sure to roil the debate about expanding natural gas drilling around the country.
The EPA's new draft report found dangerous amounts of benzene in a monitoring well near the town of Pavillion, in central Wyoming.
The EPA is conducting a comprehensive study about the possible effect of "fracking" on water resources, but initial results are not expected until late 2012. As a result, the Pavillion report may not give either side in the fracking debate the conclusive answers they seek.
But the EPA report is the first that uses multiple, on-the-ground samples to determine the effect of fracking on underground water sources in areas of oil and gas development.
"Alternative explanations were carefully considered to explain individual sets of data," the EPA report said of the presence of synthetic chemicals found in the Wyoming water. "However, when considered together with other lines of evidence, the data indicate likely impact to groundwater that can be explained by hydraulic fracturing."
The oil and gas industry and environmentalists have battled for years over the threat hydraulic fracturing might pose to water, above or below ground. The issue has grown more urgent as industry searches to tap new sources of natural gas, spreading fracking from remote parts of the West to more populated areas in Texas, the mid-Atlantic and the Northeast.
The practice involves shooting water infused with chemicals and sand at high pressure into shale formations to unlock reservoirs of natural gas.
Encana, the Canadian company that has 169 producing wells in Pavillion, rejected the EPA's findings.
"They don't have a conclusion here, they have a probability — and we would argue that it is a very poor probability," said Douglas Hock, an Encana spokesman. "Encana didn't put methane and benzene there in the water, nature did. And the synthetics they have found in the water, we would argue that they were likely introduced by EPA's own testing procedures."
But Amy Mall of the Natural Resources Defense Council said: "Experts, families in Wyoming and communities nationwide have known for some time that fracking poses serious threats to safe drinking water. EPA's latest acknowledgment of that fact underscores the urgent need to get federal rules and safeguards on the books."
About a decade ago, people in Pavillion began noticing an odd smell and taste to their well water and new illnesses in livestock, said Deb Thomas, an organizer for the Powder River Basin Resources Council, a landowners group. The EPA began the study in 2009 after about 20 well owners asked the agency to study their groundwater.
"It smells like a cross between something dead and diesel fuel," Thomas said by phone from Wyoming. "It's a very chemical bad smell."
The EPA initially gathered water from privately owned wells and municipal wells. The presence in groundwater of methane and hydrocarbons, including diesel, led to further testing, including the EPA's drilling of two monitoring wells. The agency also tested waste pits for possible contamination. In its two years of sampling the pits and the monitoring wells, the EPA found benzene, xylenes, diesel and other hydrocarbon compounds in the water.
The Pavillion wells are shallower than ones in the mid-Atlantic states, and the fracking is done vertically.
But the report noted "shoddy drilling practices, and it raises questions about how common these shoddy drilling practices are" within the industry, said Dusty Horwitt, senior counsel for the Environmental Working Group, a watchdog organization.
For example, the study said a review of well completion reports showed inconsistent cementing of the steel casing that lines the inside of the well bore, which means that fracking fluids could leak into the earth around it.
Residents outside Pavillion, in the meantime, get their water trucked in.