Hydraulic fracturing is a common technique used to stimulate the production of oil and natural gas. Typically, fluids are injected underground at high pressures, the formations fracture, and the oil or gas flows more freely out of the formation. Some of the injected fluids remain trapped underground. A number of these fluids qualify as hazardous materials and carcinogens, and are toxic enough to contaminate groundwater resources. There are a number of cases in the U.S. where hydraulic fracturing is the prime suspect in incidences of impaired or polluted drinking water. In Alabama, Colorado, New Mexico, Virginia, West Virginia and Wyoming, incidents have been recorded in which residents have reported changes in water quality or quantity following fracturing operations of gas wells near their homes.