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Water: Underground Injection Control

UIC Frequent Questions

Answers to commonly asked questions about the Underground Injection Control (UIC) Program are presented below; many of the answers contain links to additional information. In addition, the Class I, Class II, Class III, Class IVClass V, and Class VI well pages provide answers to specific questions about these well classes.


How does the UIC Program help protect sources of drinking water?
The UIC Program prevents contamination of underground sources of drinking water (USDWs) by regulating injection activities. The UIC regulations address activities throughout the life of an injection well, including siting, construction, operation and monitoring, and closure. These requirements are designed to prevent contaminants from moving into drinking water sources. There are UIC requirements specific to each class of well to address the uses of the wells and the potential threats to USDWs each may pose. 

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What does it mean when an injection well “endangers” underground sources of drinking water?
Injection activities have the potential to cause the movement of contaminants into USDWs. An injection activity has the potential to endanger if the presence of that contaminant may cause a violation of any primary drinking water regulation or may adversely affect human health. In such cases, the UIC Program director may impose fines, require cleanup, or close the well.

  • The Regulations page presents the complete definition of endangerment, as provided in the Safe Drinking Water Act.

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Are injection wells used only to dispose of waste?
No, injection wells are used to emplace a variety of fluids underground. For example, some Class II wells inject fluids into a formation to mobilize the remaining oil for enhancing recovery. Liquid hydrocarbons that make up a large portion of our nation's strategic fuel reserves are injected by Class II wells and stored underground. Class III wells inject fluids into formations in order to extract minerals. Some wells inject surface water to replenish depleted aquifers or to prevent salt water intrusion.  Class VI wells are used to inject Carbon Dioxide (CO2) underground into subsurface rock formations for long-term storage or geologic sequestration.

See the Classes of Wells page for more information.

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Do operators of injection wells have to monitor the ground water near their wells?
Ground water monitoring requirements depend on the type of injection well. For deep injection wells, the benefits of monitoring are weighed against the risk of creating pathways of upward fluid migration.  Most monitoring requirements for deep wells focus on ensuring that the wells are operating correctly and the fluid is staying in the injection zone. In some cases, monitoring of USDWs far above the injection zone is performed. The area being mined using Class III wells may be monitored to make sure contaminated fluids are not moving out of the mining zone. Ground water monitoring may also be required for Class V wells to ensure that fluids being injected do not endanger USDWs.  Class VI wells require extensive and continuous monitoring of injected CO2 to ensure USDWs are not being contaminated.  Any monitoring requirements are specified in a well’s operating permit.

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Can Native American tribes receive primacy for the UIC Program?
Yes. Federally recognized tribes can apply for UIC Program primacy. Native American tribes must be eligible to be “treated as a state” before they can apply for primacy. To date, two tribes have applied and received primacy for class II wells.

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Is it possible to find out the number of injection wells in a particular state?
Yes. Each year, UIC Programs report to EPA the number of injection wells in their state. EPA uses this information to calculate state assistance grants.

  • A state-by-state inventory is available on the Classes of Wells page.
  • Information on how inventory data are used to calculate the UIC grant can be found on the Grants page.
  • For specific information on injection wells, contact your state UIC Program. Contact information can be found on the Where You Live page.

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