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Gibson Mine


Pinal Mountains, approximately 4.5 miles southwest of Miami, Gila County

Date Discovered:

November 1990

Impaired Surface Waterbody:

Pinto Creek

Surface Water Quality Exceedances for Designated Uses:

  • Copper (aquatic and wildlife, warmwater)

Affected Media:

  • Surface Water

What Are My Health Risks?

For Surface Water | Surface water quality standards are established to provide protection for a waterbody’s designated use(s) | Learn more >

  • ADEQ and AZGFD jointly publish fish consumption advisories | Learn more >

For Soil | There is little to no health risk unless there is contact with skin or ingestion of contaminated soil

For Groundwater | If you are connected to a Public Water System (PWS) there is little to no risk of impact from exceedances because the water is filtered through the PWS for residential and business use | View Drinking Water Notices >

  • If you have a private well in the vicinity of the exceedance, we encourage you to test the well water. Not sure what to test for? | Learn More >

For Mining Adits/Shafts | If you encounter a mining adit or shaft, do not enter it. The Arizona State Mine Inspector conducts inspections of legacy mines and implements safety measures | Learn more >

Site Summary:

  • Mined in early 1900s, then sporadically from 1960s-1990s
  • EPA completed Pinto Creek water quality study (Total Maximum Daily Load) in 2001, identified the Gibson Mine as the major source of copper exceedances
  • First remedial project implemented at site in 2007
  • Second remedial project implemented at site in 2009
  • Copper concentrations from the site reduced by approximately 85% but still degrading Pinto Creek water quality
  • ADEQ conducted additional onsite water quality and soil sampling to help determine additional remedial measures (2017 – present)
  • ADEQ collaborating with private landowners and US Forest Service
  • Remediation contract awarded to Arcadis
  • Remediation is targeted to begin in summer 2022