Record of Decision System (RODS)
SILVER BOW CREEK/BUTTE AREA
|Site Name:||SILVER BOW CREEK/BUTTE AREA|
|Address:||BUTTE TO MILLTOWN RESERVIOR|
|City & State:||BUTTE MT 59750|
|County:||SILVER BOW, DEER LODGE|
|NPL Status:||Currently on the Final NPL|
|ROD Type:||Record of Decision|
Please note that the text in this document summarizes the Record of Decision for the purposes of facilitating searching and retrieving key text on the ROD. It is not the officially approved abstract drafted by the EPA Regional offices. Once EPA Headquarters receives the official abstract, this text will be replaced.
The Rocker Timber Framing and Treating Plant Operable Unit (Rocker OU) is part of the Silver Bow Creek/Butte Area (original portion) National Priorities List (NPL) site. The Rocker OU is located approximately 7 miles west of the community of Rocker, Montana. The OU consists of an area previously used for the treatment, storage, and shipping of mine timbers using creosote and arsenic. The waste in the Rocker OU also contains mine waste from upstream sources.
The Rocker Timber Framing and Treating Plant was constructed in 1909 and operated until the plant was closed around 1957. The Anaconda Company, predecessor in interest to the Atlantic Richfield Company (ARCO), owned and operated the site. Initially, the facility treated mining timbers with a creosote solution. Later, the facility began using arsenic trioxide solutions for treatment and this formulation became the primary treatment process up to the final days of plant operation. Rocker wood treating wastes are also mixed with contaminated tailings and other mining waste washed downstream to Rocker from mining/smelting facilities in Butte.
During the approximate 48 year history of plant operation, spilled process materials, treated wood chip residues, and dripped or leaked process solutions have resulted in contaminated soils throughout the plant site and significant groundwater contamination.
In 1989, ARCO conducted a state-ordered removal of contaminated soils and debris with concentrations exceeding 10,000 parts per
million arsenic. Those areas were then covered with clean fill. Further investigations and sampling were conducted in 1989 to delineate soils exceeding 10,000 parts per million. From 1991 until 1994, detailed investigations of the Rocker site progressed and provided information into the type and extent of soil and groundwater contamination. The results of these studies were described in the final report completed in 1995.
The selected remedy addresses surface soil, alluvium and fill, and groundwater contaminated by wood treating compounds and mining waste in the Rocker OU.
The groundwater remedy includes utilization of natural and enhanced arsenic attenuation processes, and contingent hydraulic controls to contain and treat any (unexpected) groundwater migration off site. Also, a portion of the groundwater remedy includes a temporary well ban to prevent development of the nearby groundwater and an alternative water supply for the residents of the community of Rocker to use while the well ban is in effect. The remedy requires institutional controls to limit future land uses (to prevent residential land use). Monitoring of the vegetative cover and monitoring of groundwater is also required.
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