Environmental and economic concerns about the gas extraction technique known as hydrofracturing should make Americans think twice about relying on natural gas, according to an article by Daniel B. Botkin, professor emeritus of the University of California, Santa Barbara. "The water pollution concerns alone should be sufficient to make the U.S. and other countries rethink future reliance on shale gas," Bodkin wrote in Yale Environment 360. "Separating the gas from the shale, a process known as hydrofracturing, involves forcing a mixture of water, chemicals, and sand at high pressure down a well bore and into rock formations, creating small fractures that release the trapped gas. The process uses a huge amount of water - the New York State Department of Environmental Conservation estimates as much as 1 million gallons per well -- at a time when water is already a limiting and precious resource. Second, hydraulic fracturing fluid may come back to the surface, or near enough, to affect groundwater supplies. This fluid is a mixture of chemicals including friction reducers, biocides to prevent the growth of bacteria that would damage the well piping or clog the fractures, a gel to carry materials into the fractures, and various other substances. Returning to the surface, it could also bring other environmentally damaging materials, such as heavy metals."