Image courtesy of Environmental Leadership Team 2026

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.

Images courtesy of the Environmental Leadership 2026 Team

Summary Our Suggestions

Upgrade Bisbee Wastewater Treatment Plant from Class B to Class A effluent discharge
Connect Naco's wastewater to Bisbee's upgraded Wastewater Treatment Plant
Construct a sulfur mitigation system (at the location of Bisbee's existing Wastewater Treatment Plant) to reduce sulfate concentrations
Convert Naco Sanitation Ponds into Sulfate Mitigation Wetlands
Effluent distribution:
- ~50% discharged into the San Pedro River to support recharge and flow
- ~50% sent to Naco Sulfate Mitigation Wetlands to support wildlife and protect Bisbee's drinking water source.
Freeport-McMoRan pays for construction as part of a long-term solution to the sulfate contamination.