NPL Partial Site Deletion Narrative

Anaconda Co. Smelter
Anaconda, Montana

On September 30, 2020, the EPA deleted three Operable Units; the Beryllium Operable Unit 9 (OU9), the Flue Dust
(OU11) and the Arbiter (OU12) of the Anaconda Co. Smelter site located in Anaconda, Montana from the National
Priorities List (NPL). The other areas of the site will remain on the NPL.

The Anaconda Co. Smelter site was placed on the NPL in September 1983 and is the location of a former large
copper smelter that was operated by the Anaconda Mining Company and its predecessors and successors from
approximately 1884 to 1980. Waste disposal and smelter emission deposition from milling, smelting, and refining
operations impacted approximately 300 square miles of the southern Deer Lodge Valley and surrounding foothills.
These operations resulted in elevated levels of arsenic, cadmium, copper, lead, and zinc in various media. Waste
sites identified included Arbiter wastes located at the former Arbiter Works, and beryllium wastes located at the
Opportunity Ponds tailing impoundment and on Weather Hill. The site was divided into smaller OUs due to the
large volume of wastes and wide area of contamination. The Flue Dust OU (OU11) was established to address flue
dust, a by-product of copper smelting, located at nine discrete areas at Smelter Hill.

Sampling of waste materials determined that the Arbiter materials contain elevated levels of arsenic, cadmium,
lead, copper and zinc. The beryllium wastes were determined to contain beryllium dust, a highly toxic material
that could cause a chronic life-threatening allergic disease. In 1990, in response to this substantial threat of a
release of hazardous substances, the EPA and Atlantic Richfield, the primary potentially responsible party,
amended an Administrative Order on Consent to include an accelerated removal project for OU9 and OU12. In
July 1992, the EPA entered into an Administrative Order on Consent with Atlantic Richfield to implement the
removal action. Excavation of approximately 273,348 cubic yards of Arbiter wastes and 3,700 cubic yards of
beryllium wastes was completed in November 1994. The excavated wastes were disposed in an on-site repository.
Confirmation sampling was used to ensure that all waste materials were removed. The EPA determined that the
implemented remedy for OU9 and OU12 achieved cleanup goals. Additionally, site access has been restricted and
institutional controls have been established. All response activities at OU9 and OU12 of the site have been
completed. The EPA concluded that OU9 and OU12 pose no unacceptable risk to human health or the
environment.

In September 1991, the EPA selected a remedy for OU11 to remove, stabilize and contain contaminated flue dust
materials from nine areas within the site. In December 1992, the EPA entered into a consent decree with Atlantic
Richfield to implement the flue dust remedy. Excavation and treatment of more than 500,000 cubic yards of flue
dust, including flue dust from the main Washoe Smelter flue, was completed in December 1993. Flue dust
excavated from nine locations was transported to the on-site repository for treatment. The excavated areas were
backfilled with slag, covered with clean soil, and revegetated. The repository had a liner, leachate collection
system, and a cap including soil cover and vegetation. Closure of the repository was completed in November 1994.
The EPA determined that the implemented remedies achieved necessary cleanup and all response activities at
OU11 of the site are complete. The EPA concluded that OU11 poses no unacceptable risk to human health or the
environment.

The EPA and the state of Montana, through the Montana Department of Environmental Quality, have determined
that all appropriate response actions under CERCLA have been completed for OU9, OU11 and OU12 at the
Anaconda Co. Smelter site. Therefore, the EPA is deleting three Operable Units; the Beryllium (OU9), the Flue Dust
(OU11) and the Arbiter (OU12) of the Anaconda Co. Smelter site from the NPL. The other areas of the site will
remain on the NPL.

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