The University at Buffalo's Shale Resources and Society Institute examined environmental and administrative violations processed by the Pennsylvania Department of Environmental Protection from January 2008 through August 2011.
The researchers found the percentage of environmental violations connected to the number of wells drilled declined to 26.5 percent during the first eight months of 2011 from 58.2 percent in 2008.
In 2008, there were 170 wells drilled and 99 environmental violations. Through August 2011, there were 1,248 wells drilled and 331 recorded violations, the study said.
The review found 62 percent of all violations related to Marcellus drilling were administrative and preventative in nature. The environmental violations were the result of 845 events, with 25 deemed "major" environmental events, including nine involving major spills of materials on land.
There were no reported cases of hydraulic fracturing fluid migrating into potable water supplies, the study said. The companies drill down, then sideways, into the shale and use a mix of water, sand and chemicals to break the rocks and release the gas.