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Classes of Wells

This page describes the five categories or “classes” of injection wells, along with the estimated national inventory for each class.

The five classes are based on similarity in the fluids injected, activities, construction, injection depth, design, and operating techniques. This categorization ensures that wells with common design and operating techniques are required to meet appropriate performance criteria for protecting underground sources of drinking water (USDWs)

Classes Use Inventory
Class I Inject hazardous wastes, industrial non-hazardous liquids, or municipal wastewater beneath the lowermost USDW 549 wells
Class II Inject brines and other fluids associated with oil and gas production, and hydrocarbons for storage. They inject beneath the lowermost USDW. 143,951 wells
Class III Inject fluids associated with solution mining of minerals beneath the lowermost USDW. 18,505 wells
Class IV Inject hazardous or radioactive wastes into or above USDWs. These wells are banned unless authorized under a federal or state ground water remediation project. 32 sites
Class V All injection wells not included in Classes I-IV. In general, Class V wells inject non-hazardous fluids into or above USDWs and are typically shallow, on-site disposal systems. However, there are some deep Class V wells that inject below USDWs. 400,000 to 650,000 wells
Note: an inventory range is presented because a complete inventory is not available.
For drawings of all types of UIC Wells, see the typical wells page.

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