"When methane began bubbling out of kitchen taps near a gas drilling site in Pennsylvania last winter, a state regulator described the problem as 'an anomaly.' But at the time he made that statement to ProPublica, that same official was investigating a similar case affecting more than a dozen homes near gas wells halfway across the state.
In fact, methane related to the natural gas industry has contaminated water wells in at least seven Pennsylvania counties since 2004 and is common enough that the state hired a full-time inspector dedicated to the issue in 2006. In one case, methane was detected in water sampled over 15 square miles. In another, a methane leak led to an explosion that killed a couple and their 17-month-old grandson.
Methane is the largest component of natural gas. Since it evaporates out of drinking water, it is not considered toxic, but in the air it can lead to explosions. When methane is found in water supplies, it can also signal that deeply drilled gas wells are linked with drinking water systems."