Abrahm Lustgarten of ProPublica reports that natural gas drilling in the United States may be endangering water supplies. A sample of water from a well in Sublette County, Wyo. found benzene — a chemical linked to aplastic anemia and leukemia — at a level 1,500 times higher than what is safe for human consumption. "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 (PDF) 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 nine out of 10 natural gas wells in the United States." There have been several contamination incidents since the study that suggest hydraulic fracturing is not safe. ProPublica's investigation found water contamination near drilling sites is far more prevalent then the EPA claims.