Since residents of Dimock, Pa., were first videotaped lighting their tap water on fire, methane migration has become one of the most central issues in the debate on the merits and drawbacks of Marcellus gas drilling in the state.
For a long time, industry representatives have denied their drilling into the Marcellus formation could have anything to do with methane making its way into water supplies. They have claimed the fracking process occurs thousands of feet beneath aquifers, and that it was impossible for methane to make its way up through that much thick rock. As an aside, they brought up the fact that many of Pennsylvania's wells had naturally occurring methane concentrations, or that migration had been caused years before by the coal industry.
But following a rash of incidents in which methane has bubbled up through surface water near gas pads, and a New York Times article published Wednesday citing one case in West Virginia tying methane migration to fracking, the industry appears to have pulled back from its previous absolute answer.
Asked directly about connection mentioned the Times article, Marcellus Shale Coalition spokesman Steve Forde said, "It's an ongoing discussion across Pennsylvania. It's certainly something our industry and members of our coalition are consistently engaged with the DEP and local officials to ensure that discussion continues as we collaborate and continue to find more information. We have worked diligently alongside regulators to make sure we get in place the strongest well casing standards in the country, and we believe that is a great deal to ensure water quality in the commonwealth is protected."
David Yoxtheimer, a hydrogeologist and extension associate with the Marcellus Initiative for Outreach and Research at Penn State, said hints of information are already leaking out that drilling into Marcellus can directly cause methane migration.
"Methane is less dense than water, so it wants to rise. A lot of times it get trapped in more porous formations -- you get shallower pockets of gas trapped in sandstones at 2,000 feet below the ground surface. When drilling the well, you go down through shallower sandstones, and what can happen is the methane that migrated up and charged those sandstones can leak up and outside the wellbore and into aquifers," he said.
In Dimock, 18 wells had methane migrating from a shallower, 2,000-foot zone. In response, Cabot cemented and abandoned three of their wells, which shut off source of the methane.
"Over time, methane will work its way out of the groundwater system and water quality will return back to normal," Yoxtheimer said. "By abandoning the wells, methane stopped leaking into the aquifer. In the case of Dimock, which is something you don’t really hear about, 14 of those wells have methane levels that have since reduced down to what DEP considers to be acceptable levels."
New DEP regulations requiring a third string of steel casings on all Marcellus wells might help prevent methane migration by preventing it from running up the side of the well, Yoxtheimer added.
"These companies don't want to have methane migration happening, and are willing to install another string if it helps" stop the problem, he said. "They know that an ounce of prevention put in place is worth it because the remedial costs and effects are going to cost (them) 100 times more."