Residents and a hydrogeologist press Santa Cruz supervisors to act after antimony exceedances in Harshaw Creek

A wave of public concern over water quality punctuated the Santa Cruz County Board of Supervisors’ Feb. 4 study session, as residents and a local hydrogeologist presented data they say show repeated antimony exceedances tied to mine discharge and asked the county to press regulators and the company for more monitoring and protections.

Chris Gardner, a registered geologist with nearly 25 years practicing hydrogeology and representing Friends of Sonoita Creek, told the board he found multiple instances where antimony in discharge and downstream wells exceeded alert levels and said available monitoring does not capture what is happening in stream-channel sediments. "We're going to need to collect data forever to help protect human health and the environment," Gardner said during his technical presentation.

Gardner detailed the hydrology of Harshaw Creek, showed cross sections of the basin‑filled stream sediments downstream of the mine outfall, and presented time-series data that he said track spikes in antimony at the mine outfall to higher antimony readings later in private well HDW01. He urged the board to ask the Arizona Department of Environmental Quality (ADEQ) to reopen the aquifer protection permit (APP), require daily or weekly discharge monitoring at the outfall, add shallow and deep point‑of‑compliance monitoring wells where stream sediments are saturated, and to use the Community Protections and Benefits Agreement (CPBA) to secure drinking‑water protections beyond minimum legal requirements. "I ask the ADEQ to please reopen the APP to include daily or weekly monitoring of the discharge," Gardner said.

Members of the public echoed Gardner’s concerns. Jay Thompson of Rio Rico told supervisors, "We demand protections, not promises," and urged independent influent monitoring, full-flow pilot testing and transparent data review before high‑antimony wells are restarted. Several speakers asked the board to require third‑party verification of the treatment plant and to ensure the CPBA contains specific, enforceable protections for water supplies and long‑term monitoring.

County staff and supervisors acknowledged the concerns and discussed practical next steps. Several supervisors called for better communication channels among South 32, ADEQ and community groups; Supervisor Davis said he supports more coordinated information-sharing and suggested county involvement in a faster, more transparent notification system.

What the record shows: Gardner and several citizen groups presented data indicating three antimony exceedances at the mine’s discharge since startup, including a composite permit sample reported at 4.81 parts per billion against an alert level of 4.8 parts per billion; he correlated those events to at least one private well showing elevated antimony thereafter. Gardner proposed dye‑tracer studies, more frequent sampling, and installation of shallow monitoring wells screened in stream-channel sediments (he noted existing company wells are screened in bedrock and may not capture all mobilization pathways).

What the county can do next: Supervisors heard and requested more data and communications; Gardner offered to share monthly monitoring his group will collect at the outfall and at private wells. The draft environmental impact statement (DEIS) timetable was also noted — a final EIS release was reported in public comment as scheduled for March 6, with a 30‑day review period — providing a near-term moment for the county and community to review the agency’s responses and press for the monitoring changes requested.

The board did not adopt any binding new permit conditions at the Feb. 4 meeting. The most immediate outcomes are expanded public scrutiny, multiple requests that the county help coordinate data and communications among ADEQ, South 32 and citizen scientists, and Gardner’s continued community monitoring and offers to share results with the Board. The EIS review and future CPBA discussions were identified as the next procedural milestones.