A comprehensive research plan that would provide guidelines and an assessment tool for regulators should be conducted in order to minimize the environmental impact of natural gas drilling in the Marcellus Shale, according to researchers at the Academy of Natural Sciences (ANS).

Initial research conducted this summer indicates that the environmental impact of drilling may be directly related to the amount of drilling in a specific area, according to David Velinsky, vice president of the ANS Patrick Center for Environmental Research.

"The question that needs to be addressed is whether there is a threshold point past which a certain amount of drilling activity has an impact on the ecological health and services of the watershed -- regardless of how carefully drilling is conducted," Velinsky said.

The preliminary research found a significant difference between high-density drilling locations and locations with no drilling or less drilling. Water conductivity, which indicates the level of contamination, was almost twice as high in the high density sites as the other sites, and the number of sensitive insects and salamanders were reduced by 25%, Velinsky said.

"This suggests there is indeed a threshold at which drilling, regardless of how it is practiced, will have a significant impact on an ecosystem. Conversely, it also suggests there may be lower densities of drilling at which ecological impact cannot be detected."

A larger, more comprehensive study must be done before definitive conclusions can be drawn, Velinsky said.

ANS has applied to the Pennsylvania Department of Environmental Protection's Growing Greener Program to fund such a study. ANS proposes to look at four streams in each of three size classes for each of the three levels of well density (none, low and high) and to use computer modeling to analyze the impact of drilling on deforestation.

"Our goals are to determine if this apparent threshold in the preliminary data remains valid over a larger sample, and to better understand the interactions between well density, size of the impacted stream and watershed, and the resulting ecological indicators," Velinsky said during a recent meeting of the Philadelphia City Council's Joint Committees on the Environment and Transportation and Public Utilities.

"However careful and conscientious drillers may be -- and many are trying to be -- it would be simplistic to say you could introduce these sorts of activities into natural or agricultural settings without altering elements of the system," he said.