Vapors can enter houses that were built on or around old wells.

The search for oil and gas prompted prospectors and energy companies to drill as many as 12 million holes across the U.S. in the last 150 years. Many were plugged after they dried up, but hundreds of thousands were simply abandoned and forgotten.

Government reports have warned for decades that abandoned wells can provide pathways for oil, gas or brine-laden water to contaminate groundwater supplies or to travel up to the surface, according to a recent ProPublica article.

New wells sometimes disturb layers of rock and dirt near fragile old wells, leading to new cases of contamination. For Pennsylvania and other states sitting on top of the Marcellus Shale formation, the rapid growth of gas drilling may increase the danger of such contamination.

Vapor intrusion can lead to explosions in homes

In 2008, gas from an abandoned well leaked into a septic system in Pennsylvania and exploded when someone tried to light a candle in a bathroom, killing the person, according to a 2009 draft report by the state Department of Environmental Protection. That report also documented at least two dozen other cases of gas seeping from old wells, including three where the drilling of new wells “communicated” with old wells, leaking gas into water supplies and forcing the evacuation of a home.

In February, methane from an old well made its way into the basement of a house in West Mifflin, triggering a small explosion. Two families had to be evacuated.

Such incidents rarely receive much attention outside the states and neighborhoods they affect. But as the nation’s latest drilling boom continues, abandoned wells have begun attracting more attention, particularly in states where the earth is already pock-marked with holes left by earlier waves of extraction.

The task of finding, plugging and monitoring old wells is daunting to cash-strapped state governments. A shallow well in good condition can sometimes be plugged with cement for a few thousand dollars. But costs typically run into the tens of thousands, and a price tag of $100,000 or more isn’t unusual.

Some regulators fear that the number of abandoned wells will grow when the current drilling boom runs its course. To prevent that, states require energy companies to post bonds before they begin building their wells. But they are often so low that it can be more economical for a company to forfeit its bond rather than plug its wells. In Pennsylvania, for instance, an energy company can cover hundreds of wells with a single $25,000 bond.

Birthplace of an industry

One of Pennsylvania’s worst cases of gas migration occurred in Versailles. From 1919 through 1921, more than 175 gas wells were drilled in the town. Residents put wells in their back yards to heat their homes, packing them into the 25-by-100-foot lots.

The boom dried up when most of the wells proved unproductive. But in the 1960s, pockets of gas began leaking into homes. Some houses were condemned and demolished, and Versailles became a case study for federal scientists trying to locate old wells.

Some of the old wells were plugged. But more often, vents were installed to direct gas away from the homes. Today, dozens of pipes pop out of the ground in yards, behind garages and through houses, slowly leaking methane and hydrogen sulfide so the explosive gases don’t accumulate. In 2009, Versailles received a $368,600 federal grant to maintain its aging vents. About 50 methane alarms have been installed in the town.

Nobody knows how much damage abandoned wells have caused in the United States over the years. Most states don’t systematically track cases of contamination that result from abandoned wells, said Mike Nickolaus, special projects director for the Ground Water Protection Council, an association of state groundwater agencies.

Some regulators are concerned that fracking, which is used in most new wells, increases the possibility that old wells will be damaged or disturbed. The process injects water, sand and chemicals into wells at high pressure to release oil or gas. But by disrupting the earth it can also push gas and other contaminants into openings created by old wells.

Source: Nicholas Kusnetz, Pittsburgh Post-Gazette. Editor’s note: The article has been edited for length.

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