The EPA itself said the Wyoming field differs from most fracking sites because the fracking "is taking place in and below the drinking water aquifer and in close proximity to drinking water wells"—unlike most sites where fracking is done far below the water table.
Petroleum engineers and other industry experts cautioned against extrapolating the EPA's Wyoming results to other parts of the country, saying the wells at issue and the region's geology were atypical of areas that have undergone fracking.
The gas-bearing rock being fractured in Wyoming was only about 1,220 feet deep. And some of the water wells extended down 800 feet. By comparison, in Texas and Pennsylvania most of the rocks being fracked are several thousand feet deeper than water wells.
And, unlike gas-rich geologic formations such as the Marcellus in Pennsylvania and Barnett in Texas, the Wyoming field doesn't have a rock barrier that sits atop the gas reservoir.
"It is not something we can say, 'If it's happening here, it can happen anywhere,' " said Ian Duncan, a research scientist at the Bureau of Economic Geology at the University of Texas. "There is such a large difference in the amount of rock between where the fracking is going on and where the water is."
The report cited problems with how the wells were constructed, including intervals where the wells had no cement casing or weakened cement. EPA officials said this could be related to the age of the wells, some of which date to the 1950s, and varying state regulations over the years.
Environmental groups have cited the potential for poor well construction as a risk and said the report shows the need for tighter rules. "Even if you just set aside the fracking issue, the EPA found a lot of problems. These wells were not constructed properly, they weren't cemented properly," said Amy Mall of the Natural Resources Defense Council.
The EPA announcement irked Wyoming authorities. Gov. Matt Mead issued a statement saying the draft analysis "is scientifically questionable and more testing is needed."
Tom Doll, the state's oil and gas supervisor, said "more sampling is needed to rule out surface contamination or the process of building these test wells as the source of the concerning results."