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.
RDU 6 encompasses approximately 25 miles south of the community of Opportunity, located southeast of the city of Anaconda. The area is characterized by gentle slopes and is intersected by Willow Creek. The Yellow Ditch – an inactive mining flume that once transported surface water and tailings from Silver Bow Creek to the Opportunity Ponds (see RDU 9 – Fluvial Tailings) – also intersects RDU 6.
Remedial designs targeted elevated arsenic levels identified in surface soils, which originated from fallout from the Washoe Smelter, in operation from 1884 to 1980. Windblown tailings from the Anaconda Ponds (see RDU 4 – Anaconda Ponds) were also a remedial concern for RDU 6. Though land use within RDU 6 is primarily agricultural grazing, parcels zoned as recreational and residential do exist within the RDU boundaries. Remediation of residential lands within RDU 6 has and continues to be addressed by the Community Soils Operable Unit (CS OU).
Of the 956 acres included within the boundaries of RDU 6 – South Opportunity, 690 acres required remedial action, which included soil removal (as necessary) and the installation of a protective vegetative cover. The remaining 266 acres required only weed spraying and monitoring. RDU 6 includes areas of highly impacted soils including an old trolley line and historic railroad spurs. The old trolley line is intended to be incorporated as part of a regional trail system and, as such, is being addressed separately from the other areas of RDU 6. Soils from these highly impacted areas were removed and consolidated in the Opportunity Ponds (see RDU – 8). Storm water and erosion controls were also put in place in the highly impacted area near Mill Creek Road.
Visit the Superfund Library, located on the Arrowhead Foundation’s website, to review documents and research regarding the Anaconda Smelter NPL site. For more information about RDU 6 refer to the Final Design Report (available online) or the Technical Impracticability Evaluation Report (available online). Additional information can also be found on the EPA’s website.