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Superfund Alternative Site | ASARCO Hayden Plant

EPA Superfund Alternative Site Designation:

EPA #: AZD008397127
The site is currently administered through an Administrative Settlement Agreement and Administrative Order on Consent (AOC) between the Environmental Protection Agency (EPA), ASARCO and ADEQ. Site contamination is caused by historical mining operations including smelting and ongoing processing operations.

Site Location:

The ASARCO facility includes the smelter, concentrator, former Kennecott smelter and all associated tailings facilities. The facility is adjacent to the towns of Hayden and Winkelman, 100 miles southeast of Phoenix and about 50 miles northeast of Tucson. The project site is located in the area surrounding the confluence of the Gila and San Pedro Rivers.

Contaminants of Concern:

Almost 100 years of smelting activities at this site has deposited lead, arsenic and copper across residential and industrial areas with the highest concentrations located on the north edge of town, near the old Kennecott smelter and on the east side near the concentrator and the No. 9 conveyor.

  • Arsenic: Soil concentrations in Hayden range from near background at 12.5 mg/kg to 540 mg/kg. Despite the 1,000-foot-tall stack, air quality monitoring in the two towns measured elevated levels of arsenic, lead, copper, cadmium and chromium from site operations. Arsenic in Hayden air is approximately 60 times above expected in an area unaffected by smelting activities. In Winkelman, the average arsenic air concentration (0.00796 mg/m3) is 20 times higher than the Organ Pipe area and is likewise elevated when the wind direction is from the smelter. The high arsenic concentrations are not always associated with high dust levels.
  • Lead: Hayden ranges from near background (48 mg/kg) to 7,250 mg/kg. | View Today's AQ Risk-Based Lead Forecast > 
  • Copper: Varies from below a background of 1,270 mg/kg up to 39700 mg/kg. In Winkelman, contamination is lower than Hayden and centered along the Highway 177 area and along the railroad tracks on the south side of town. Samples from the school complex on the north end of Winkelman indicate the school has relatively low soil concentrations with all concentrations below proposed remediation level.
  • Groundwater: Beneath the smelting and slag deposition areas of the site is impacted by selenium and molybdenum. Tailings impoundments along the Gila River, have caused elevated levels of contaminants to be discharged into surface and groundwater.

Public Health Concerns:

According to public health and ecological risk assessments conducted by the Arizona Department of Health Services, contamination at the site could pose risks if no cleanup actions are taken.

Environmental Challenges:

The site is located within the Upper San Pedro groundwater basin. The major components of this system are the water-bearing sands and gravels of the Gila River and San Pedro River flood plains that are recharged from groundwater flows within smaller tributary stream alluvium.

Groundwater elevation measurements taken in February and October 2006 indicate that the regional groundwater flow direction within Hayden and Winkelman is in a southerly direction towards the Gila River/San Pedro River confluence. The groundwater flow gradient is relatively high in the Hayden area, and the gradient is considerably lower in the Gila River flood plain.

The groundwater flow direction between the two tailings impoundments is generally in a northwesterly direction, consistent with the surface water flow direction of the Gila River. The tailings impoundments do not appear to be causing large mounding of the water table, but the relatively low gradient in the vicinity is likely the result of recharge from Gila River surface water losses and tailings impoundments drain down.

Action Taken: 

Subsequent to an Arizona Department of Health Services 2002 health assessment, exposed residential yards and vacant lots with excess arsenic, copper and/or lead concentrations in soil were identified.  Between 2008 and 2009, the soil was excavated and replaced in about 250 properties in Hayden and Winkelman. The remainder of the homes did not require cleanup. In addition to residential yard cleanups, other areas such as vacant lots, businesses and dirt alleys were sampled and cleaned up.

In 2018 ASARCO completed installation of new process equipment and pollution control technology at the operations plant (smelter). In 2018 ASARCO was issued a renewal Title V Air Quality Permit issued by ADEQ.

Work plans are in development for the closing of three (3) inactive tailings piles with work expected to begin in 2019.


A Phase II Remedial Investigation (RI) report review is ongoing, supplementing prior studies. After the RI report and risk assessment review determine the nature and extent of contamination, a feasibility study (FS) will focus on developing additional cleanup options.

Learn more about this Superfund Alternative Site on the EPA website | View Site >  
Learn more about other agencies and groups performing independent studies by contacting the EPA.