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Water Quality Division | Site/Facility of Interest

Hermosa Project — South32 Hermosa Inc.

Revised On: May. 8th, 2026 - 01:57 pm

This site/facility of interest online resource provides interested parties easy access to information about the Hermosa Project, owned by South32 Hermosa Inc. (South32), formerly Arizona Minerals Inc. (AMI).

Water Quality Permitting

Aquifer Protection Program (APP)

On Feb. 6, 2025, ADEQ issued a significant amendment to the Individual APP Permit No. P-512235 to South32 Hermosa Inc. for the Hermosa Project. The purpose and scope of the APP is to ensure that facilities are designed, constructed, and operated in a manner that eliminates or minimizes the impact of the facility’s operation on groundwater quality through operation, closure, and post-closure. 

Arizona Pollutant Discharge Elimination System (AZPDES) Program

On July 3, 2024, ADEQ issued a renewal Individual AZPDES Permit to South32. ADEQ issues AZPDES Permits to ensure compliance with federal and state regulations and to protect public health and the environment in terms of surface water quality. The AZPDES Permit imposes regulations on pollutant discharges and mandates monitoring to ensure adherence to the limits set under the federal Clean Water Act. The discharge limits are established to safeguard the well-being of individuals engaged in water recreation and to protect animals, plants, and other organisms.

South32 also has coverage under the Mining Multi-Sector General Permit (MSGP) for industrial stormwater discharges. 

South32 also has coverage under the De Minimis General Permit (DMGP) for water well development and maintenance. 

Community Engagement

  • The public comment period for the renewal of the Individual AZPDES Permit began on Nov. 28, 2023, and closed on Jan. 12, 2024 | View Notice >
  • On Jan. 11, 2024, ADEQ held a public hearing for the renewal of the Individual AZPDES Permit. 
  • On Oct. 2, 2024, ADEQ held an in-person public hearing for the public to comment in person on the Individual APP Permit significant amendment.  
  • The public comment period to issue a Significant Amendment to the Individual APP Permit began on Aug. 23, 2024, and was extended to Oct. 18, 2024 | View Amendment Notice >
  • On Feb. 18, 2026, the public comment period began for the decision to waive a State 401 Water Quality Certification for the South32 Hermosa Critical Minerals Project. The comment period ended on March 20, 2026 | View Public Notice >
    • Response to Comments (RTC) | View RTC > 
    • CWA Section 401 Water Quality Certification Waiver | View >

Compliance Reports

The Individual AZPDES Permit requires regular monitoring of the treated discharge. The monitoring frequencies are specified in the permit and vary from monthly to annually, depending on the parameter. South32 must send these monitoring results to ADEQ each month through Discharge Monitoring Reports (DMR). 

ADEQ uses these monitoring results to check if South32 is meeting the permitted effluent limits. ADEQ can change the Permit if DMR data show there is effluent toxicity, a need for more permit limits, or if permitted levels  are exceeded.

You can view and download DMR data for South32 from the U.S. Environmental Protection Agency’s (EPA) Compliance and Enforcement Online (ECHO) website by entering the AZPDES Permit Number (AZ0026387) at the following link:

The Individual APP Permit requires monthly and semi-annual water quality monitoring: 

  • Monthly: The facility must monitor the quality of the discharge from two Water Treatment Plant (WTP) outfalls:
    • Discharge from WTP 1 into Alum Gulch (AZPDES Outfall 001) 
    • Discharge from WTP 2 into Harshaw Creek (AZPDES Outfall 002) 
  • Semi-Annual: The facility must monitor groundwater quality at a monitoring well located 200 feet downgradient of AZPDES Outfall 001 (Point of Compliance #2)

The Permit has set Alert Levels (ALs), which serve as early indicators, set below either the Discharge Limit (DL) or the Aquifer Quality Limit (AQL), pending the sampling location. DLs and AQLs establish the maximum allowable pollutant level that must not be exceeded to protect groundwater quality.

  • South32 APP Permit Monitoring Data | View Data >
  • South32 30-Day Contingency Report for October 2025 Exceedance | View Report >
  • Response to Comments Received from the Santa Cruz County Board of Supervisors Meeting in January 2026 | View Comments >

Facility Archives

Individual AZPDES Permit — LTF 66046 (2018)

Individual AZPDES Permit Modification — LTF 85604 (2021)

Mining MSGP — LTF 67872 (2016)

Individual APP Permit — LTF 65051 (2017)  

Individual APP Permit — LTF 71251 (2019) 

Individual APP Permit — LTF 75937 (2020) 

Individual APP Permit — LTF 83040 (2021) 

Individual APP Permit — LTF 98095 (2023) 

Individual APP Permit — LTF 101257 (2025)

Determination of Applicability (DOA)

Environmental Impact Statement (EIS)

Environmental Inspections and Enforcement

For more information about South32 Hermosa Project, visit the Site/Facility of Interest section within the My Community page | View Page >

Looking for air quality permits related to this facility? | View >

Contact Us

Groundwater APP Permits
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Arizona Department of Water Resources (groundwater quantity) | View >

Wildlife including Migratory or Local Bird Species | View >