Injection wells use high-pressure pumps to inject liquid wastes into under-ground geologic formations (e.g., sandstone or sedimentary rocks with high porosity). Many geologists believe that wastes may be isolated from drinking water aquifers when injected between impermeable rock strata. However, injection wells are still controversial and many scientists are concerned that leaks from these wells may contaminate groundwater. As of 1994, twenty-two out of 172 deep injection wells contaminated water supplies.

There are five classes for injection wells based on the type of fluid injected and the location of the wells. Class I wells inject hazardous or non-hazardous fluids into isolated rock formations, approximately four thousand feet below the surface, and are strictly regulated under the Resource, Conservation and Recovery Act (RCRA). Their use must demonstrate that underground drinking water sources won't be contaminated. Class II wells are commonly used for the disposal of brine created during...