The Northside Tailings area contains tailings and other mining wastes that were deposited near the former Silver Bow Creek location by past mining operations. The proposed remedy would remove tailings, mine wastes, and contaminated soils at the Northside Tailings area and would construct a stormwater basin or sedimentation bay in the excavated area to reduce the amount of contaminated stormwater and sediments that reach Silver Bow Creek and improve the quality of water in the creek. The required remedial construction activities would be performed by Atlantic Richfield Company and would include:
Excavation and Disposal – Approximately 60,000 cubic yards of tailings, wastes, and contaminated soils, including municipal wastes, would be excavated from the site and hauled to a repository. Some excavated materials, including uncontaminated soils and small concrete, may be reused to complete reconstruction of the site.
Stormwater Basin or Sedimentation Bay – A stormwater basin or sedimentation bay would be constructed at Northside Tailings to capture stormwater from the East Buffalo Gulch drainage and improve water quality before it enters Silver Bow Creek. The basin or bay may be lined or unlined. The stormwater basin or sedimentation bay and associated channels and swales would be designed to cover about 3 acres (slightly larger than two football fields), which is a sufficient size to manage stormwater and accumulated sediments. Maintenance of the basin would include removal and disposal of captured sediments at a repository.
End Land Use – The Northside Tailings area would be reconstructed to enable future community use of the site and land around the stormwater basin or sedimentation bay. Atlantic Richfield Company, Butte-Silver Bow, EPA, and MDEQ would work with the residents of Butte to develop an end land use plan that is compatible with the proposed remedy.
Tailings, wastes, and contaminated soils would be removed to the depth of the most recently observed 3-year maximum groundwater elevation.
Tailings, waste, and contaminated soils would be disposed of at a repository outside of the Silver Bow Creek and Blacktail Creek corridors.
Municipal waste, household waste, timbers, and other construction debris would be disposed of at an appropriately permitted facility.
The stormwater detention/retention basin would be sized to capture a minimum 6-month, 24-hour Type I Soil Conservation Service (SCS) design storm.
Additional storage volume would be provided to support management of accumulated sediments.