Oct. 26--DIMOCK TWP.

The problem in the water here erupted on New Year's Day when an explosion in Norma Fiorentino's backyard well shattered an 8-foot concrete slab and tossed the pieces onto her lawn.

An investigation by the state Department of Environmental Protection revealed that the culprit -- methane in the aquifer because of nearby natural-gas drilling -- had seeped into the drinking water at nine homes in the township, causing a threat of explosion in at least four of them.

The department found that Cabot Oil and Gas Corp., the company that had drilled 20 wells into the gas-rich Marcellus Shale within three square miles of the blast, had polluted the fresh groundwater with methane, the highly combustible, primary element of natural gas. Inspectors suspected that too much pressure in the mile-deep wells or flaws in their cement-and-steel casings had opened a channel for the gas.

Now, the state environmental oversight agency is rethinking its gas drilling regulations with the aim of preventing incidents like the one in Dimock from happening again.

An early draft of regulations the department unveiled in September would change the way wells are built and sealed off from drinking water aquifers; mandate that existing wells are tested to ensure they don't leak; increase cementing and casing standards and strengthen rules for replacing drinking water if gas drillers disturb it.

Rising fast

Now that the state is poised to become one of the biggest gas producers in the nation, "we want to make sure that we're putting in place for Pennsylvania and for the public over the next 50 years the very best practices and the best materials in our regulations," DEP Secretary John Hanger said.

Although Mr. Hanger said the proposed regulations were not inspired by any particular incident, catastrophes or close calls caused by stray gas migrating from natural gas wells "highlight the reasons for the review and the changes." A cover letter from DEP to the state's Oil and Gas Technical Advisory Board made the case in stark detail: Over the last decade, six explosions caused by gas that migrated from new or old wells killed four people in the state and injured three others. The threat of explosions has forced 20 families from their homes, sometimes for months, and at least 60 water wells, including three municipal water supplies, have been contaminated.

Many stray gas cases are caused by abandoned and improperly plugged wells that were drilled decades ago, but the proposed rules would change the way new wells are built -- an important protection because new wells have much more pressure than old ones, according to Fred Baldassare, DEP's top stray gas inspector, and Marcellus Shale wells have proven to be even more highly pressurized than those in comparable shale formations in other states.

To tap the gas-bearing rock, a well bore must penetrate several geological layers before reaching the target formation; in the case of the Marcellus Shale, it is often about a mile underground. The hole is then sealed off from the drinking water aquifer and the surrounding geology with several rings of steel casing, which keeps the gas and the chemical-laden liquid used to fracture the shale from seeping out and helps control the tremendous pressure that builds up inside the well. In particularly sensitive areas, like groundwater zones, the casing is cemented into place to make sure the barrier is impermeable.