Sulfate Plume Proposal

Problems

This project focuses on the environmental legacy of the Copper Queen Mine in Bisbee, Arizona, where we conducted fieldwork through interviews and site visits to examine the impacts of historic mining on groundwater quality. We undertook this research to address growing concerns about groundwater contamination and the potential risks it poses to the local community’s drinking water supply. The project investigates the extent of the contamination plume and its long-term implications, while also developing a comprehensive mitigation and recharge proposal that integrates sulfate reduction strategies, wetland development, and groundwater recharge to the San Pedro River.

What is happening

The contamination originates from past mining operations, where sulfate and other materials entered the groundwater system. Because groundwater moves slowly, the plume has continued to spread over decades and is still moving today.

The plume is gradually approaching water supply areas
Some wells already show higher sulfate levels
Deeper wells are often needed to access cleaner water
Monitoring data is incomplete and not always shared

Risk to drinking water

Our ArcGIS analysis of sulfate-contaminated wells (2000–2024) shows the sulfate plume is gradually moving toward the Arizona Water Company (AWC), which supplies water to Bisbee, AZ.

Interviews revealed there are no current long-term plans for sulfate mitigation or water treatment. Existing solutions are temporary, including drilling deeper wells or relocating AWC facilities.

No long term solution

Unclear effluent use

There is an ongoing debate over how to support regional sewage treatment and how to allocate treated sewage effluent, as it currently serves little purpose in Green Bush Draw.

Photo credit: Taken by environmental leadership 2026 team

Our suggestion

Upgrade effluent from the Bisbee wastewater treatment plant from Class B to Class A
Construct a sulfur mitigation plant (by AWC) to reduce sulfate concentrations
Effluent distribution:
- ~50% discharged into the San Pedro River to support recharge and flow
- ~50% sent to Naco Sanitation Ponds to create a constructed wetland
Incorporate water from Green Bush Draw to support the system
Contaminated wells:
- Pump contaminated groundwater through pipes
- Mix with treated effluent
Direct mixture to Naco Sanitation Ponds for further natural treatment
Freeport-McMoRan will compensate for contaminated wells