Established in 1998, the Anaconda Regional Water, Waste & Soils (ARWWS) Operable Unit (OU) is the largest and most diverse Operable Unit in the Anaconda Smelter NPL site. The ARWW&S OU spans nearly 20,000 acres, and, to date, remedial actions have been completed on 58% of this acreage. Due to its size and diverse areas of concern, the ARWW&S OU was separated into fifteen Remedial Design Units (RDUs) based upon factors such as location, source and type of contamination, and remedial needs.

  1. Stucky Ridge
  2. Lost Creek
  3. Smelter Hill Uplands
  4. Anaconda Ponds
  5. Active Railroads/Blue Lagoon
  6. South Opportunity
  7. North Opportunity
  8. Opportunity Ponds
  9. Fluvial Tailings
  10. Warm Springs Creek
  11. Cashman Concentrate
  12. Slag
  13. Old Works Groundwater
  14. Smelter Hill Facility
  15. Mt. Haggin Uplands

The ARWW&S OU also includes two Expansion Areas, the West Galen and Dutchman Creek Expansion Areas, which were added to the Operable Unit after further investigation indicated smelter-related contamination within the Smelter NPL site, but outside the existing boundaries of the 15 Remedial Design Units of the ARWW&S OU.

In September of 2011 an amendment was made to the 1998 Record of Decision for the ARWWS Operable Unit. This amendment included a waiver of the human health standard for arsenic and zinc in certain ground and surface waters within the Operable Unit. The aquatic standards for cadmium, copper, and lead in surface waters within the ARWWS OU were also waived.

These waivers resulted in the expansion of existing and the creation of new Technical Impracticability (TI) Zones, areas in which the EPA has determined that remediation to levels compliant with established standards is not practically feasible. The amendment expanded the bedrock aquifer TI zone boundaries, as well as saw the creation of TI zones for alluvial aquifers within the North and South Opportunity Remedial Design Units (RDU). In addition to TI zones, these waivers also led to the designation of two High Arsenic Areas, where steep slopes made safe operation of conventional reclamation equipment technically impracticable.

Despite these changes, the waiver of the arsenic human health standard was the only aspect of the amendment that fundamentally altered remedial action goals as outlined in the 1998 Record of Decision (ROD). To offset these changes, a monitoring and replacement plan was developed to ensure domestic well users within and adjacent to all expanded or newly created TI zones would have drinking water that met established standards. Additional source control measures and monitoring plans were required by this amendment to ensure the protection of humans, wildlife, and adjacent lands/waters.

Visit the Superfund Library, located on the Arrowhead Foundation’s website, to review documents and research regarding the Anaconda Smelter NPL site. Specific documents of interest to the ARWWS Operable Unit include the 1998 Record of Decision (available online) and the Record of Decision Amendment (available in the library). Additional information can also be found on the EPA’s website.