The Safe Drinking Water Act (SDWA) is a federal law enacted in 1974 to ensure safe drinking water for the public. In Arizona, the Underground Injection Control (UIC) Program is a critical component for implementing the SDWA, to protect underground sources of drinking water from contamination due to underground injection of fluids. The Arizona Department of Environmental Quality (ADEQ) has been in the process of obtaining primacy (the authority to administer the UIC program within the state), a responsibility currently held by the U.S. Environmental Protection Agency (EPA).

UIC Background

The UIC program regulates the construction, operation, permitting, and closure of injection wells used to place fluids underground for storage, disposal, or mineral production. The SDWA classifies injection wells into six categories (see EPA’s website for more information on UICs): 

1. Class I: Industrial, municipal, hazardous, and radioactive waste disposal wells.
2. Class II: Injection wells related to oil and gas production and storage.
3. Class III: Solution mining injection wells.
4. Class IV: Shallow hazardous and radioactive waste injection wells.
5. Class V: Injection wells related to non-hazardous fluids. A drywell is a type of shallow Class V injection well typically used to dispose of stormwater runoff.
6. Class VI: Injection of carbon dioxide for geologic sequestration.

Arizona lacks primacy for the UIC program, meaning the EPA directly oversees injection well activities in the state. ADEQ submitted an application for primacy to the EPA on February 16, 2024, seeking to administer the UIC program for all six well classes. On May 9, 2025, EPA Administrator Lee Zeldin announced a proposal to approve Arizona’s request. This action recognizes that Arizona is best positioned to protect its underground sources of drinking water while bolstering economic growth and energy dominance. This effort is part of EPA’s Powering the Great American Comeback Initiative, which prioritizes providing clean and safe water to the public. EPA’s proposed approval includes state permitting for Class VI wells for underground storage of carbon dioxide, a focus of many energy companies.

What Does Approval Mean for Facilities? 

After conducting a comprehensive technical and legal review, EPA has preliminarily determined that Arizona’s UIC program meets all requirements for approval and the state will implement and enforce a UIC program consistent with the Safe Drinking Water Act.

If Arizona is granted primacy over the UIC program, it would have several effects for the state, public agencies, and operators. The ADEQ would issue permits, conduct inspections, enforce compliance, and oversee monitoring for all six classes of UIC wells. This local oversight could streamline processes with other state water programs like Arizona’s Aquifer Protection Permit (APP Permit).
If Arizona receives UIC primacy, it would:

• Centralize and streamline regulation under state authority.
• Allow more efficient permitting and better integration with state water programs.
• Shift responsibility from EPA to ADEQ.

What Should You Do?

Several Arizona facilities use drywells as the most practical way to manage stormwater in our state’s desert climate. UIC wells in other classes also exist throughout the state. If you have questions about how this change could affect your operations, the proposed rule is available for review here.
EPA has requested that written comments be submitted on or before July 3 via the Federal eRulemaking Portal for Docket ID No. EPA-HQ-OW-2025-0087. You can also attend EPA’s virtual public hearing on June 25, 2025, from 5 p.m. to 8 p.m. Mountain Standard Time (MST)
Trinity is reviewing the potential implications of this rule for particular operations. If you would like to discuss how this proposed change could affect you, please email MaryAnn Ishak in Trinity’s Phoenix office or call 602.595.7824.