RDU 4 – Anaconda Ponds

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. As a result, the OU was separated into fifteen Remedial Design Units (RDUs) based upon factors such as location, source and type of contamination, and remedial needs. Click here for more information about the ARWWS OU.

Located east of the main slag pile, RDU 4 – Anaconda Ponds is part of the Smelter Hill Waste Management Area. In 1998 the EPA and Montana Department of Environmental Quality (DEQ) determined that removal of waste and restoration of ground water within the Smelter Hill Waste Management Area was impractical and cost prohibitive. All property within RDU 4 – Anaconda Ponds is owned by Atlantic Richfield Company, the responsible party for the Anaconda Smelter NPL site. Restrictions for land use and development have been instated to protect humans and wildlife from contact with contaminants of concern.

Remedial action within RDU 4 included the construction of a large tailings pond, known as the Anaconda Ponds, in the 1940’s. Tailings ponds contain and stabilize waste materials produced during the Smelter operations. Covering over 500 acres, the Anaconda Ponds contain approximately 97 million cubic yards of waste materials. The Anaconda Ponds were created to supplement to the Opportunity Ponds (RDU 8), containing waste materials both from within the Smelter Hill Waste Management Area as well as other areas within the Anaconda Smelter NPL site. In this way, the tailings ponds provided an opportunity to create more usable land within the Anaconda Smelter NPL site. Active disposal within the Anaconda Ponds occurred during the 1940’s until the closing of the smelter in 1980.

Dust control is presently the primary remedial concern in the Anaconda Ponds. Remedial actions included the spreading of lime rock on dust-prone areas and occasional water application. Leachate, water that extracts solutes from other matter as it passes through it, was collected from the Arbiter, Beryllium, and Flue Dust Repositories and disposed of in the Anaconda Ponds prior to being capped. Compliant with mine closure requirements, remediation of soils within RDU 4 that were not part of the tailings pond was also completed.

Visit the Superfund Library, located on the Arrowhead Foundation’s website, to review documents and research regarding the Anaconda Smelter NPL site. Additional information can also be found on the EPA’s website.