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Record of Decision System (RODS)

SILVER BOW CREEK/BUTTE AREA

Abstract

Site Name:  SILVER BOW CREEK/BUTTE AREA
Address:  BUTTE TO MILLTOWN RESERVIOR 
City & State:  BUTTE  MT  59750
County:  SILVER BOW, DEER LODGE
 
EPA ID:  MTD980502777
EPA Region:  08
 
NPL Status:  Currently on the Final NPL
 
ROD Type:  Record of Decision
ROD ID:  EPA/ROD/R08-96/112
ROD Date:  11/29/1995
Operable Unit(s):  01
 
Media:  Soils, sediments, groundwater, surface water.
 
Contaminant:  Arsenic, cadmium, copper, lead, mercury, and zinc.
 
Abstract:  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 Streamside Tailings (SST) Operable Unit (OU) is located along Silver Bow Creek in Butte-Silver Bow and Anaconda-Deer Lodge Counties, Montana. The area of concern is the length of Silver Bow Creek where Interstate 90 intersects the creek in two places; the northern intersection is just below Warm Springs and the southern intersection is just above Butte. The OU boundary has been defined as the extent of fluvially deposited tailings along Silver Bow Creek, including adjacent railroad beds.

The first recorded disturbance of the Silver Bow Creek channel occurred in 1864 when placer mining techniques were used to extract gold along the stream and its tributaries. The placer techniques used mercury to attract small pieces of gold. Between 1870 and 1910, silver mining took place. By the late 1880s, copper mining had become more important and Butte became one of the nation's most prominent copper mining centers. Many of the previously existing mills and smelters were utilized for copper production and more mills and smelters were added. By 1917, approximately 150 mines were located in and near Butte. These mines, which were controlled by Anaconda Copper Mining Company (AMC) or its predecessors, produced a total of approximately 934 million pounds of copper. In 1977, the assets of AMC were purchased by the Atlantic Richfield Company (ARCO), which expressly assumed liability for AMC. ARCO closed all underground mines in 1980 and only continued active surface mining in the Berkley Pit. ARCO closed surface mining site in 1982 and 1983. The Washoe Smelter in Anaconda, the last active smelting facility in the area, was closed in 1980 and subsequently dismantled.

Mining and smelting operations from these facilities produced tailings and other mining wastes. Large volumes of waste were disposed of directly into or near Silver Bow Creek. In addition, floods and storms contributed to the downstream contamination and movement of mine wastes into the flood plain. Railroad construction also contributed to the contamination. Parts of all three rail lines were constructed with waste materials. The lines that transported concentrate materials for the smelter in Anaconda were additionally contaminated by spillage from this concentrate transportation.

Environmental investigations in the vicinity of the SST OU were initiated by EPA in 1982 to address mining impacts along Silver Bow Creek. The original portion of Silver Bow Creek/Butte Area site was listed on the NPL in 1983 and site investigations began in 1984. A proposed cleanup plan was completed in 1995.
 
Remedy:  This remedy addresses the principal threats and provides for treatment and appropriate disposal of contaminated tailings and impacted soils, instream sediments, and railroad materials. Much of the treated materials will remain in the OU. Consequently, the OU will require long-term management and monitoring.

The major components of the remedy for the tailings/impacted soils are: excavation of contaminated tailings/impacted soils from most areas within the present 100-year flood plain; treatment of tailings/impacted soils that cannot be excavated; relocation of excavated tailings/impacted soils to safe, local repositories outside the 100-year flood plain; replacement fill where tailings/impacted soils are removed; and a permanent monitoring, management, and maintenance program for tailings/impacted soils being treated on site.

The major components of the remedy for the instream sediments are: removal of fine-grained instream sediments located in every depositional area, with placement of the sediments in repositories with the excavated tailings/impacted soils and railroad materials; reconstruction of the channel bed and streambank; and instream sediment monitoring.

The major components of the remedy for the railroad materials are: excavate, treat, and/or cover all contaminated railroad bed materials that pose a risk; dispose of materials in a repository and/or treatment of the materials; and monitor and maintain the remediated railroad materials.

There is no separate remedy for groundwater and surface water. The removal of the sources of contamination is key, and natural attenuation is relied upon to diminish the concentration of contaminants in the water. However, performing long-term monitoring of groundwater and surface water is a critical element.
 
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