South32 is making improvements to a water treatment plant at the Hermosa Project after a heavy metal exceedance showed the plant was not operating at full efficiency. Representatives from South32 and the Arizona Department of Environmental Quality (ADEQ) asserted they were working toward a solution after tests detected an exceeding volume of antimony late last year.

In the meantime, the wells that were sourcing the high volumes of antimony will remain shut off until the plant is equipped to treat the water properly, according to Hermosa Project President Pat Risner.“I think one takeaway I want everyone to have is this plant was designed to have the flexibility to adapt to changing incoming water quality characteristics,” Risner said during the County Board of Supervisors meeting Jan. 7.

“We are implementing a second phase of antimony removal in the plant that will get us up to around 60% or more removal, and we believe that’s going to address the issue,” he added. Risner affirmed that South32 has implemented a proactive response since the issue came to light. Staff shut off one of seven groundwater wells on the Hermosa Project site in February 2025, shortly after they detected increasing antimony levels. The well remained shut off for months while South32 increased antimony treatment in its water plant, and was turned back on in September 2025, Risner said.

But by the following October, South32 collected a single sample that recorded an antimony level 6.23 micrograms per liter — exceeding the antimony discharge limit of 6 micrograms per liter, according to Randall Matas, ADEQ’s water quality deputy director. After some samples continued to exceed regulatory limits of the heavy metal in late November 2025, South32 shut off all wells that tested high for antimony, Risner said. Those wells still remain out of service, he said.

Matas added the state agency was working alongside South32 to bolster reporting guidelines per the Aquifer Protection Permit (APP) after some miscommunication regarding the antimony reports. He noted that South32 failed to complete a required five-day report upon the original sample in October, and instead submitted the report five days after receiving the results of a reprocessed sample in early December.“(We’re) working on training to ensure that there is clarity that the reporting timeframes are based upon the initial results, not waiting until you’re weeks or months down the line with investigation to report things,” Matas said during the county’s Jan. 21 meeting.

Risner noted South32 had called ADEQ repeatedly and left voicemails to inform them of the five-day report in October. Matas, however, said ADEQ officials did not find any voicemails or make contact with South32 during the initial timeframe.

Matas added that South32 had also failed to provide numeric values in its initial report about exceeding antimony levels and attributed the results to a lab error. But Risner said the self-monitoring form in the ADEQ portal did not provide any code to signal they were conducting a retest, so they entered a lab error code as the closest alternative.

The slightly differing accounts regarding South32 reports and communication with ADEQ sparked concern among some Santa Cruz County residents at the Board of Supervisors meeting on Jan. 21. Robin Lucky, president of the environmental watchdog group Calabasas Alliance, said South32 and ADEQ seemed to provide different contexts behind the information.

For instance, she said South32 attributed the exceedance to a natural geologic variability in some wells, while ADEQ seemed to tie the issue directly to a treatment plant shortfall.

“These contradictions matter because they point to a deeper issue,” Lucky said. “And every time the story shifts, public trust erodes further.”

Some community members expressed worry about the potential impacts of high antimony levels that may have already been discharged into Harshaw Creek. Others demanded answers about possible health effects for both humans and livestock who drink contaminated water.

During his presentation Jan. 7, Risner noted a third-party toxicology expert said it would be inaccurate to draw conclusions from one-time samples because it would not be reflective of long-term exposure for humans. What’s more, he said Arizona does not have an established antimony standard for livestock — a point that didn’t settle well with Patagonia resident Rebecca Meyers.

“I’m particularly disturbed with the flippancy with which South32 dismissed the possibility of toxicity to livestock from drinking the water,” she said, noting that existing research is not reliable due to lack of data. Speaking more broadly about the mining operations, local hydrologist Ben Lomeli urged that officials prioritize community and environmental health.

“There is no such thing as sustainable mining. You may be mining for helping sustainability, but once those finite mineral resources are gone, they’re gone forever,” he said. “We need to attract people with clean air, clean food, clean water, (and) good, viable, sustainable economic conditions here. We have to be sure that we think farther into the future than just short-term profits,” Lomeli said.

Overall, community members urged that ADEQ amend South32’s APP requirements to ensure strict reporting and enforcement guidelines, and that the county implement more safety measures in the Community Protections and Benefits Agreement. Matas assured the audience that ADEQ is working to train South32 representatives on filling out reports appropriately and optimizing communication throughout reporting processes.

District 3 Supervisor John Fanning requested that South32 and ADEQ provide further information regarding potential impacts to drinking water for humans and livestock, given that the issue has been brought up regularly.

Risner emphasized that South32 is working to properly treat water for all metals and minerals. “The importance here is the plant design can and has been adjusted to achieve higher removal rates of antimony. As I said, we’re in the second phase of that now,” he said.

For more information about South32’s compliance with its Aquifer Protection Permit, visit azdeq.gov/wqd/hermosa-south32.