Background

The Arizona Department of Environmental Quality (ADEQ) is implementing new aquifer water quality standards (AWQSs) effective August 4, 2025. This final rulemaking is in response to the Environmental Protection Agency’s (EPA) changes to the maximum contaminant level (MCL) for many substances as well as their inclusion of several substances which were not originally considered as potentially affecting drinking water quality standards. The four (4) new standards apply to Bromate, Chlorite, Haloacetic Acids and Uranium, while the three (3) adjusted substances which are moving to more stringent limits are Arsenic, Microbiological Contaminants, and Total Trihalomethanes. Along with these changes, ADEQ has put forth an implementation rule to properly incorporate these new AWQS standards into individual Aquifer Protection Permits (APP).

What Exactly Has Changed?

Four New Aquifer Water Quality Standards

No AWQS standards previously existed for the pollutants listed below. The following standards have been set for each new pollutant:

Bromate (Br): 0.010 mg/L

Chlorite (ClO2): 1.0 mg/L

Haloacetic Acid (HAA5): 0.060 mg/L

Uranium (U) Standard: 0.030 mg/L

Three Adjusted Aquifer Water Quality Standards

The following more stringent standards have been set for these already regulated pollutants:

Arsenic (As): Previously was 0.05 mg/L; the new effective limit is 0.010 mg/L.

Total Trihalomethane (TTHM): Previously was 0.1 mg/L; the new effective limit is 0.080 mg/L.

Microbiological Contaminants: Requires a new monitoring system which tests for Coliform and if there is a positive test for coliform, the permit holder must then sample for E. coli.

What Does This All Mean?

In Arizona, an individual APP is required for any facility that discharges pollutants to the State’s groundwater. The two crucial requirements of APPs are to meet the AWQSs at the point of compliance and to demonstrate Best Available Demonstrated Control Technology (BADCT) to reduce the discharge of pollutants before they reach the aquifer. This finalized rulemaking has the potential to impact most individual APP permittees and cause them to take action. In the short term, facilities with current ongoing monitoring requirements in an issued APP permit must begin Baseline Monitoring for a new adjusted AWQS within three (3) months (November 4, 2025), unless any of the following apply:

1. The current APP permit has no ongoing monitoring requirements.
2. The permittee has not begun ongoing monitoring.
3. The permittee has submitted an Alternative Baseline Monitoring Request here.
4. The permittee has submitted an Unlikely to be Present in the Discharge Demonstration. This demonstration may include, but is not limited to:
   • A full characterization of the affected facility’s discharge;
   • Review of past monitoring and sampling data at the facility; and/or
   • Process information that demonstrates the pollutant is not used or generated at the site or is otherwise not likely to be present in discharges at the site.

In the long term, affected permittees will need to submit a permit application in order to determine whether alert levels, discharge limitations or aquifer quality limits are to be incorporated into their individual permit. All necessary permit applications must be submitted within four (4) years of the effective AWQS date (August 4, 2029).

Next Steps

All individual APP permittees should be aware of these rule changes. Monitoring requirements, alert levels, additional discharge limitations, and other requirements may be triggered within the next three months as well as over the next few years. Failure to comply with these new and adjusted AWQSs may lead to civil penalties or suspension of an individual permit at the discretion of ADEQ based on the type of violation, severity, and frequency.

Be sure to stay informed on these new standards and the potential implications to your individual APP permit. Additional updates and resources are available on the ADEQ website and if you have any questions about how this finalized rulemaking can affect your business, please email MaryAnn Ishak in Trinity’s Phoenix office or call 602.274.2900.