The study concluded, "These results can inform future voluntary measures taken by shale-gas operators and policy approaches taken by regulators to protect surface water quality as the scale of this economically important activity increases."
Olmstead said that researchers found a statistically significant increase in solids pollution downstream as the number of well sites increased, but were not able to pinpoint which part of the gas-production process caused the pollution. Testing did not support their hypothesis that runoff impacts would be greater during heavy rain events or during the construction of well pads, or both, she said.
"So it may be that we are picking up on other aspects of infrastructure development (pipelines, roads), which are correlated with well pad construction," Olmstead said in an email. "But lacking data on these other types of infrastructure, we don't test that directly. So the question remains an open one."
Jackson said the large scope of the study -- looking at drilling impacts across the state -- provided important broad-brush information, but also did not allow for a closer look at on-the-ground impacts.
Brian Lutz, a Kent State University scientist who has also studied gas-drilling impacts, said the scope of the study was such that it didn't answer how pollution might impact different types of waterways.
"An 11 percent increase in chlorides in a pristine headwater stream might have quite an impact, but an 11 percent increase in chlorides in a major, developed river might not," Lutz said.
Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.