Frequent Questions

How many of each type (class) of underground injection control (UIC) wells are in the United States? In each state?

UIC well inventory information is available from EPA's Classes of Wells Web site at This site lists the national inventory of UIC wells by class as follows:

Class I: 650 wells

Class II: 151,000 wells

Class III: 21,000 wells

Class IV: 32 wells

Class V: 400,000 to 650,000 wells (Note: an inventory range is presented because a complete inventory is not available)

Class VI: 6-10 commercial wells expected to come online by 2016


This site also provides links to documents containing state and tribal UIC well inventory information.

More specific information may be available from the state or regional UIC program contact. A list of these contacts is available at
Have more questions? Submit a request