Class I wells are technologically sophisticated wells that inject large volumes of hazardous or non-hazardous wastes into deep, isolated rock formations that are seperated from the lower most USDW by layers of impermeable clay and rock. Although most hazardous waste fluids are treated and released to surface waters, Class I wells account for 89 percent of the hazardous waste fluids disposed of on land. Still, Class I wells inject mostly non-hazardous waste. For example, while all of U.S. industry together injects approximately nine billion gallons of hazardous waster each year, one state alone

Under the UIC Program, EPA and the states regulate more than 400,000 injection wells. Class I wells comprise less than one percent of the injection wells in the U.S.

The chemical, petroleum and metals industries use most of the Class I hazardous waste injection wells in the country. The geology of the Gulf Coast and Great Lakes is best suited for these types of wells. Thirteen states heve Class I hazardous waste injection wells; Texas has the most.

Almost half of the fluids injected into non-hazardous and municipal waste injection wells are manufacturing wastes; municipal effluent accounts for approximately 28% of the Class I non-hazardous wastes. Florida has the greatest number of non-hazardous / non-commercial wells, followed by Texas and Kansas.

What is An Underground Injection Well?

Basically, injection wells are man-made or improved "holes" in the ground, which are deeper than their widest surface dimension and are used to discharge or dispose of fluids underground. When properly sited, constructed, and operated, injection wells can be an effective and environmentally safe means of fluid waste disposal. There are many different types of injecition wells, but they are all similar in their basic function. The Federal UIC program has grouped injection wells into five categories.

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