Underground Injection Control Well Classes
The Underground Injection Control program consists of six classes of injection wells. Each well class is based on the type and depth of the injection activity, and the potential for that injection activity to result in endangerment of a USDW.
- Class I wells are used to inject hazardous and non-hazardous wastes into deep, isolated rock formations.
- Class II wells are used exclusively to inject fluids associated with oil and natural gas production.
- Class III wells are used to inject fluids to dissolve and extract minerals.
- Class IV wells are shallow wells used to inject hazardous or radioactive wastes into or above a geologic formation that contains a USDW.
- Class V wells are used to inject non-hazardous fluids underground. Most Class V wells are used to dispose of wastes into or above underground sources of drinking water.
- Class VI wells are wells used for injection of carbon dioxide (CO2) into underground subsurface rock formations for long-term storage, or geologic sequestration.
UIC regulations mandate the consideration of a variety of measures to assure that injection activities will not endanger underground sources of drinking water (USDWs). The concept of endangerment is defined in federal code of regulations (40 CFR 144.12).
Section 144.12 Prohibition of movement of fluid into underground sources of drinking water:
(a) No owner or operator shall construct, operate, maintain, convert, plug, abandon, or conduct any other injection activity in a manner that allows the movement of fluid containing any contaminant into underground sources of drinking water, if the presence of that contaminant may cause a violation of any primary drinking water regulation under 40 CFR part 142 or may otherwise adversely affect the health of persons.