The famous (almost obligatory) still from the film Gasland.

Mike Leighton watched as his well overflowed, filled with methane. His neighbors, the Franklins, watched their well go dry, then turn black. Both families live in Leroy Township, Penn. — over the Marcellus Shale, near where energy companies are fracking for natural gas. NPR has the story.

Pennsylvania’s Department of Environmental Protection blames a nearby hydraulic fracturing, or fracking, operation. It says methane gas has leaked out of the well, which is operated by Chesapeake Energy, and into the Leightons’ and Franklins’ water supplies.

The danger goes beyond contaminated water. In a letter to both families detailing test results and preliminary findings, state regulators wrote that “there is a physical danger of fire or explosion due to the migration of natural gas water wells.” Chesapeake has installed ventilation systems at the two water wells, but the letter warns, “it is not possible to completely eliminate the hazards of having natural gas in your water supply by simply venting your well.”

NPR suggests that part of the problem is the concrete surrounding the pipe that extracts the natural gas.

Pennsylvania’s Department of Environmental Protection fined Chesapeake Energy $900,000 for contaminating 16 families’ water supplies. The company disputed the state’s conclusion, but agreed to the fine — the largest environmental penalty in Pennsylvania history.

Since then, Pennsylvania regulators put much tougher drilling standards in place, in order to minimize methane leaks.

They mandated higher-quality cement and pipes in gas wells, among other changes. Chesapeake spokesman Michael Kehs said the company has improved its standards. He says the problem affecting the Leightons and Franklins is an “isolated incident,” adding, “in this particular case there was a unique problem with a particular piece of equipment that was highly unusual.”

A recent ProPublica investigation suggested that water tables are also at risk from poorly contained fracking water waste sites, which also leak.

The American Petroleum Institute suggests that such problems are the exception. In other words, if they’re drilling in your area and your well water isn’t bubbling with methane, you’re one of the lucky majority.

The Leightons and the Franklins weren’t.