Water: Underground Injection Control
Classes of Wells
This page describes the six categories or "classes" of injection wells, along with the estimated national inventory for each class.
The six 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 | 680 wells |
| Class II | Inject brines and other fluids associated with oil and gas production, and hydrocarbons for storage. | 172, 068 wells |
| Class III | Inject fluids associated with solution mining of minerals beneath the lowermost USDW. | 22,131 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. | 33 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. |
| Class VI | Inject Carbon Dioxide (CO2) for long term storage, also known as Geologic Sequestration of CO2 | 6-10 commercial wells expected to come online by 2016. (Interagency Task Force on Carbon Capture and Storage) |
| For drawings of all types of UIC Wells, see the typical wells page. | ||
- The Regulations page has more information on how injection wells are classified.
- The Guidance page provides links to UIC Program guidances.
- State-by-State Inventory of Injection Wells (PDF) (1 pg, 13K, About PDF)
- Tribal Injection Well Inventory (PDF) (5 pp, 41K, About PDF)
- UIC Program Primacy
- The Where You Live page provides the UIC contact information in your state.
- The Geologic Sequestration (GS) Background page provides more information about GS and Class VI wells.