DIRTY RIG: Natural gas may be the cleanest-burning fossil fuel but drilling for it is causing an environmental headache.
©Abraham Lustgarten/ProPublica

In July a hydrologist dropped a plastic sampling pipe 300 feet down a water well in rural Sublette County, Wy. and pulled up a load of brown oily water with a foul smell. Tests showed it contained benzene, a chemical believed to cause aplastic anemia and leukemia, in a concentration 1,500 times the level safe for people.

The results sent shockwaves through the energy industry and state and federal regulatory agencies.  

Sublette County is the home of one of the nation’s largest natural gas fields, and many of its 6,000 wells have undergone a process pioneered by Halliburton called hydraulic fracturing, which shoots vast amounts of water, sand and chemicals several miles underground to break apart rock and release the gas.  The process has been considered safe since a 2004 study by the Environmental Protection Agency found that it posed no risk to drinking water. After that study, Congress even exempted hydraulic fracturing from the Safe Drinking Water Act. Today fracturing is used in 9 out of 10 natural gas wells in the United States.

Over the last few years, however, a series of contamination incidents have raised questions about that EPA study and ignited a debate over whether the chemicals used in hydraulic fracturing may threaten the nation’s increasingly precious drinking water supply.

An investigation by ProPublica, which visited Sublette County and six other contamination sites, found that water contamination in drilling areas around the country is far more prevalent than the EPA asserts. Our investigation also found that the 2004 EPA study was not as conclusive as it claimed to be. A close review shows that the body of the study contains damaging information that wasn’t mentioned in the conclusion. In fact, the study foreshadowed many of the problems now being reported across the country.

The contamination in Sublette County is significant because it is the first to be documented by a federal agency, the U.S. Bureau of Land Management. But more than 1,000 other cases of contamination have been documented by courts and state and local governments in Colorado, New Mexico, Alabama, Ohio and Pennsylvania. In one case a house exploded after hydraulic fracturing created underground passageways and methane seeped into the residential water supply. In other cases the contamination occurred not from actual drilling below ground, but on the surface, where accidental spills and leaky tanks, trucks and waste pits allowed benzene and other chemicals to leach into streams, springs and water wells

It is difficult to pinpoint the exact cause of each contamination, or measure its spread across the environment accurately, because the precise nature and concentrations of the chemicals used by industry are considered trade secrets. Not even the EPA knows exactly what’s in the drilling fluids. And that, EPA scientists say, makes it impossible to vouch for the safety of the drilling process or precisely track its effects.

“I am looking more and more at water quality issues… because of a growing concern,” said Joyel Dhieux, a drilling field inspector who handles environmental review at the EPA’s regional offices in Denver. “But if you don’t know what’s in it I don’t think it’s possible.”