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.

In 1937, the Silver Bow Ditch was constructed as part of the Dust Mitigation Program, which ensured that the tailings fields (i.e. Opportunity Ponds) remained constantly flooded. The ditch began at the Opportunity Ponds extending for approximately nine miles to Silver Bow Creek. Over time, contaminants resulted in a brilliant yellow coloring of the ditch and, consequently, the Silver Bow Ditch became commonly known as the Yellow Ditch. The ditch remained in use for the lifetime of the smelting operations in Anaconda.

Sampling results indicated elevated concentrations of arsenic; however, underlying native soils have not been impacted. Remedial action in RDU 9 has historically focused upon protecting water sources, including minimizing the transportation of contaminants to other aquifers, protecting domestic water users and providing contingency water systems for newly identified users. Original remedial designs included using a public recreational trail as a cap for the ditch. These plans were, however, later altered in order to impose higher standards for human and environmental health.

Remediation of the Yellow Ditch began in 2014. The ditch will be returned to natural contours, complying with contamination standards suitable for agricultural use. Local organizations and community groups have been working with Atlantic Richfield Company and the local government to develop an alternate route for a public recreational trail that loosely follows the Yellow Ditch. Such a trail would provide alternative transportation access to the Butte-Greenway Service District trail, which follows Silver Bow Creek from Butte to Warm Springs.

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. For more information about the recreational trail project associated with the Yellow Ditch or other local recreation opportunities, contact the Anaconda Trail Society at info@anacondatrailsociety.com.