Drilling process causes water supply alarm In July, a hydrologist dropped a plastic sampling pipe 300 feet down a water well in rural Sublette County, Wyo., 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 shock waves 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 nine of every 10 natural-gas wells in the United States. Over the last few years, however, a series of contamination incidents has 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....