Frequent Questions

What are the different classes of injection wells under the Underground Injection Control (UIC) Program and what types of wells are included in each class?

There are five classes of injections wells under the UIC Program, which are defined according to the type and location of fluid they inject. Class I wells are used to inject hazardous waste, other industrial and municipal wastes, or radioactive waste beneath the lowermost formation containing an underground source of drinking water within one-quarter mile of the well bore (40 CFR 144.6(a)). Class II includes wells that inject fluids that are brought to the surface in connection with oil or natural gas storage and production; inject fluids for enhanced recovery of oil or natural gas; and inject fluids for storage of hydrocarbons that are liquid at standard temperature and pressure (40 CFR 144.6(b)). Class III wells are used to inject fluids in order to extract minerals including sulfur mining, in situ production of uranium or other metals from ore bodies which have not been conventionally mined, and solution mining of salts or potash (40 CFR 144.6(c)). Class IV wells are used to dispose of hazardous waste or radioactive waste into or above a formation that contains an underground source of drinking water within one-quarter mile of the well (40 CFR 144.6(c)). These wells are prohibited unless they are used to inject contaminated ground water that has been treated and is being injected into the same formation from which it was drawn (40 CFR 144.13). Class V wells are any injection wells not included in other classes, including but not limited to air conditioning return flow wells, certain large capacity cesspools, drainage wells, recharge wells, some septic systems wells, and others (40 CFR 144.81). More information about the classes of UIC injection wells is available at
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