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 http://water.epa.gov/type/groundwater/uic/whereyoulive.cfm.