EPA, working with the Montana Department of Environmental Quality, selected the remedy for the Rocker Timber Framing and Treating Plant in late 1995. The remedy addresses human health risks from potential exposure to contaminated soils and ground water. You can download the Record of Decision (ROD) for the site below.
Approximately 41,000 cubic yards of soils and source materials that contributed to groundwater contaminated with arsenic were excavated and treated on the site in 1997. EPA is in close communication with the Rocker Water Board and the Butte Silver Bow County Health Department.
Highly contaminated ground water was treated in place using an iron solution to remove arsenic from the ground water. The ground water ban is needed to prevent accelerated movement of the existing arsenic plume into uncontaminated groundwater supplies.
Surrounding wells and Silver Bow Creek are being monitored to see if they remain unaffected and to document trends in contaminant concentrations. Pilot scale tests in 1996 produced arsenic levels almost 1000 times lower than sampled levels. Treatment of arsenic contaminated ground water in the field dropped arsenic concentrations from as high as 20,000 milligrams per liter (ug/l) to less than 30. The State standard for arsenic in drinking water is 18 ug/l.
In 2011, EPA completed its third Five Year Review Report on the greater Silver Bow Creek/Butte Superfund site, including the Rocker Timber Operable Unit. The complete report can be downloaded via the Superfund Library or the EPA website for Butte, or download the segments of the report related to Rocker here:
- EPA Third Five-Year Review Report for Silver Bow Creek/Butte Area Superfund Site (June 2011)
- Volume 5: Rocker Timber Framing and Treating Plant Operable Unit
- Appendix A: Site Inspection Photographs
- Appendix B: Town Pump Public Water Supply Data
- Appendix C: Responsiveness Summary (including public comments and EPA responses)
- Appendix D: Controlled Groundwater Area Evaluation
If the arsenic ground water plume cannot be treated or migrates, thus threatening drinking water wells, then it will be contained, per the site ROD. During the term of the remedy, a ban exists on expanded ground water development within a quarter mile of the site. An alternative source of water has been provided for the community to meet its increasing water demands due to growth.
The greater Greenway/Copperway Trail System, a part of ongoing restoration efforts in the Butte area, also runs near the site along Silver Bow Creek.