Green groups have a major new concern: fracking, the process of extracting natural gas from shale deposits far underground. What they don't have is much hard evidence that fracking is a danger.
Fracking already is producing a bonanza in the U.S. Theoretically it could provide enough to replace all coal-powered electricity with cleaner-burning natural gas.
So what's the problem? The process uses water, sand and various chemicals fired at high pressure to shatter underground shale rock, releasing the gas. Greens allege those chemicals could seep into groundwater.
But is there evidence of this? In testimony prepared for a Senate Energy and Water Committee panel hearing Thursday, Tom Beauduy, deputy executive director of the Susquehanna River Basin Commission, says no.
That's key because one of America's largest shale depositories is the Marcellus deposit, which lies mainly underneath the basin. Both sprawl across New York, Pennsylvania and Maryland.
The deposit has been widely explored. More than 1,000 fracking sites have been permitted.
Since 2008, the basin commission created an elaborate 50-station monitoring system.
"We are not aware of any water quality impacts on systems," Beauduy told IBD. "There have been incidents related to individual wells, but not to public water supply systems.
That is in line with other surveys. A 2008 study by the Groundwater Protection Council, a coalition of state environmental agencies, found the "potential for impacts to surface water and groundwater ... are expected to be minimal.
A 2010 study by the Pennsylvania Department of Environmental Protection admitted the "theoretical possibility" of contamination, but concluded: "no groundwater pollution or disruption of underground sources of drinking water have been attributed to hydraulic fracturing of deep gas formations.
Most criticism of fracking cites Dimock, Pa., where leakage from wells did seep into local groundwater. The drilling company was fined and required to provide the town with drinking water. The state environmental agency determined that the leakage was caused by faulty well casings, not by the fracking itself.
Green lawmakers are stuck over what to do. Sen. Jeanne Shaheen, D-N.H., requested Thursday's Senate hearing. One of her staffers told IBD that Shaheen is just gathering data.
Earlier this year the White House created a panel to examine fracking. An interim report in August made few concrete proposals. Another report is expected next month.
The issue is complicated by the fact that natural gas is cleaner than coal and gasoline. Replacing them with natural gas could, experts say, reduce carbon emissions by 25%.
The abundance has slashed prices too. One of the greens' concern may be that prices are so low they could further hurt already-struggling efforts to boost renewable energy.
Even green groups concede that hard evidence against fracking is, well, hard to come by.
"There is only one case that I know of — in Ohio — where the state regulator did attribute groundwater contamination to fracking" as one of three contributing factors, said Amy Mall, senior policy analyst for the Natural Resources Defense Council.
Nevertheless, Mall says much anecdotal evidence suggests that fracking is dangerous and reason to think state regulations are lax.
For now green groups are urging the government to watch the drilling closely.
"We cannot stop drilling," said Erin Mooney, spokeswoman for Trout Unlimited, which advocates for clean water. "Marcellus Shale development is going to happen. So it is imperative that it is done correctly."