Butte/Silver Bow Creek
The boundary of the Silver Bow Creek/Butte Area site begins above Butte, near the Continental Divide, and extends westward along Silver Bow Creek to and including the Warm Springs Ponds (a treatment area). The site covers about 40 miles of stream and stream side habitat. Silver Bow Creek was used as a conduit for mining, smelting, industrial and municipal wastes for more than a hundred years.
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Vast mine tailings deposits are found along the creek. These deposits contain elevated levels of metals and have been dispersed over the entire flood plain. Wind-blown particles, ground water, surface water and soils are contaminated with arsenic and other heavy metals, including copper, zinc, cadmium and lead. Silver Bow Creek and the Clark Fork River contain metals from Butte to Milltown. The tailings, dispersed along the creek and river, severely limit aquatic life forms and have caused fish kills in the river.
The site is being addressed in several stages: immediate actions and seven long-term remedial phases focusing on the West Camp/ Travona Shaft Area; Warm Springs Ponds; Butte Priority Soils; Berkeley Pit; Rocker Timber Framing and Treating; Stream side Tailings; and Lower Area I. Some of these separate actions involve parts of a single operable unit, such as the Travona Shaft and the Berkeley Pit, which are parts of the Mine Flooding operable unit.
In Walkerville, Montana, a small city to the north of Butte, EPA and Potentially Responsible Parties (PRPs) excavated and stabilized approximately 300,000 cubic yards of lead contaminated soil from mine waste dumps. These actions were completed in 1988. Contaminated soil was removed from four earthen basements and 23 residential yards. Concrete basements were constructed, and 18 inches of clean fill and sod were placed in the yards.
South of Butte, at Timber Butte, approximately 40,000 cubic yards of contaminated soil were moved to a temporary on-site repository in 1989. Contaminated soil was removed from two residential yards. Clean soil was placed on the excavated areas and revegetated.
Atlantic Richfield Company (Arco), a PRP, removed highly contaminated materials in the Rocker Timber Framing and Treating Area, under state supervision. Arsenic wood treating wastes and contaminated soils and wood chips were hauled to a licensed hazardous waste disposal facility. Equipment and debris were consolidated on the site and buried. Major areas of the site were covered with topsoil and seeded.
Between 1990 and 1991, 24 waste dumps containing approximately 100,000 cubic yards of soil were either capped or removed. In addition, a railroad bed and seven residential yards were reclaimed. In late 1991, removal activities began at the Colorado Smelter site. Elevated levels of arsenic and lead were detected in on-site soils. Under a Unilateral Order, the Potentially Responsible Parties conducted the removal activities. Approximately 40,000 cubic yards were moved to a temporary on-site disposal area. In 1992, removal activities were conducted at the Anselmo Mine Yard/Late Acquisition Silver Hill areas. Elevated levels of arsenic and lead were detected in on-site soils. The PRPs conducted this removal under a Unilateral Order. In 1993, further removal activities were conducted in Walkerville to address four additional dump areas because of the elevated levels of lead. In 1994 and 1995, 12 more waste dumps were addressed. These dumps were either removed or capped in place.
EPA is presently negotiating to complete plans for removal activities for contaminated railroad beds on the Butte Hill. Also, the PRPs are under Unilateral Order to complete removal activities addressing storm water problems on the Butte Hill.
West Camp/ Travona Shaft Area
In 1989, under EPA supervision, the PRPs addressed rising mine waters in the West Camp/ Travona Shaft area by constructing a pumping and piping system, which connected to a municipal sewer line on Iron Street. Mine water has been pumped to the Metro Plant at a rate of approximately 160200 gallons per minute since early 1990. Pumping continues to keep the water level below the control level of 5,435 feet to prevent flooding of basements and discharge of contaminated ground water to the alluvial aquifer and Silver Bow Creek.
Butte Priority Soils
The Butte Priority Soils Operable Unit has been divided into two phases. Phase I, an expedited Response Action has addressed source areas by removing waste dumps, railroad beds, or other related mine wastes. These source areas were adjacent to or up gradient of receptor areas (residential yards, gardens, parks and playgrounds).
The local government is running a lead abatement program that addresses children with elevated blood lead levels; residential yards with lead levels over 1,200 parts per million; residential homes with lead drinking pipes; indoor dust contaminated with lead; and interior and/or exterior lead paint. This is a five-year program with oversight by EPA.
For Phase II, an investigation will assess the actions already taken, all other areas of contamination, storm runoff, and future land use problems in Butte and Walkerville.
EPA and the state are concerned about rising contaminated mine water in the pit because the water may eventually migrate into the shallow aquifer and Silver Bow Creek.
The investigation of the Berkeley Pit has been completed and the remedy calls for:
* Permanent control of surface inflow into the Pit;
* Maintenance of the water level in the Berkeley Pit system;
* Continued control of the West Camp/ Travona System;
* Implementation of an extensive compliance monitoring program; and
* Implementation of institutional controls to restrict access to contaminated bedrock aquifer waters, as well as increased public education efforts.
The PRPs started inflow control (average 3.8 million gallons per day) in April 1996. Controlling inflow has cut the rise rate in the Berkeley Pit by 50 percent. This inflow is treated with lime and used as makeup water in the present mining operation.
Rocker Timber Framing and Treating Plant
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. Approximately 41,000 cubic yards of soils and source materials that contributed to groundwater contaminated with arsenic were excavated and treated on the site.
Highly contaminated ground water was treated in place using an iron solution to remove arsenic from the ground water. A contingency plan is available to contain the arsenic ground water plume, if it cannot be treated or migrates, thus threatening drinking water wells. 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 groundwater 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.
Full-scale cleanup began in spring 1997 and was completed in the fall of the same year.
Stream side TailingsIn November 1995, the Montana Department of Environmental Quality and EPA selected a remedy for the Stream side Tailings area. Tailings impacted soils that cannot be safely treated and stabilized in place will be removed from the flood plain of Silver Bow Creek and placed in repositories.
Lime amendment in place and revegetation will be used for tailings impacted soils not removed. Fine-grained in stream sediments located in Silver Bow Creek will be removed and placed in repositories with the excavated tailings impacted soils. Remedy design on the upper portion of the stream is complete, and construction began in fall 1999. A portion of the reconstructed stream has water flowing again since June 2000.
Lower Area I
EPA conducted an Expedited Response Action for Lower Area I. Removal of the Department of Defense manganese stockpiles (approximately 245,000 tons) occurred in the summer and fall of 1992. Removal of the mine tailings (Colorado and Butte Reduction) began in the spring of 1993 and was completed in 1997. An estimated 1.4 million cubic yards of tailings was removed to a repository. The tailings were originally transported by rail to the BP-ARCO repository near Anaconda, but in the final year, the tailings were transported by truck to the Clark Tailings in Butte, and the closure of the Clark Tailings was integrated with the closure of the old Butte Silver Bow landfill.
A ground water collection and treatment system will be installed as the final step to this action. An investigation also is taking place at the Butte Soils area to determine if any further cleanup actions are necessary. Capture and treatment of contaminated ground water is expected to occur in the future. Final cleanup decisions are part of the Priority Soils Record of Decision.