Current Site Status

To better address cleanup, the site is currently divided into seven active operable units (OU).

Download a print-friendly version of the site map: Silver Bow Creek/Butte Area Operable Units (pdf)  (1pp. 539KB)

Site Map

Butte Site Map with boundaries of the OUs set on a terrain background map.
Silver Bow Creek/Butte Area Site Operable Units map

The most recent five-year review report for Silver Bow Creek / Butte Area Superfund Site was published in 2020 and is available for review. It contains a detailed overview of each active operable unit (OU) in the Superfund site. For brief and general overviews, please refer to the short narratives below.  

2020 Five-Year Review for Silver Bow Creek / Butte Area Superfund Site (pdf) (288pp, 27MB) 

Streamside Tailings OU1

Streamside Tailings OU1 consists of about 26 linear miles of Silver Bow Creek and deposited tailings along the Creek. The boundary begins at the upstream end just outside of the Butte city limits and continues until Silver Bow Creek enters the Warm Springs Ponds. Remedial activities, primarily conducted by the Montana Department of Environmental Quality, have addressed exposure pathways that could result in unacceptable risks. The bulk of remedial work in this operable unit took place 1999-2015 with additional work completed between 2016 and 2019. Additional work is planned for 2025. Surface water, groundwater, biological and sediment monitoring is ongoing. 

Butte Mine Flooding OU3

Butte Mine Flooding OU3 is the Berkeley Pit and contaminated groundwater in the flooded underground mine workings below the city of Butte and Walkerville. The boundaries are the Continental Divide to the east, Silver Bow Creek to the south, Missoula Gulch to the west, and the Yankee Doodle Tailings Pond and upper Silver Bow Creek to the north. The Berkeley Pit is about 1,600 feet deep and is filled with low-pH, high-salinity water approximately 900 feet deep. The Berkeley Pit is continuously monitored.  

Other features of this OU include:  

  • Ongoing treatment of contaminated waters from the Pit and surrounding underground mines via the Horseshoe Bend Water Treatment Plant. This system can treat seven million gallons of water a day. A Polishing Facility and Discharge System were initiated in 2019.  

  • The Butte Alluvial and Bedrock Controlled Groundwater Area, an institutional control (IC) that prohibits the construction of new groundwater wells for domestic or other purposes.  

  • Waterfowl Mitigation and Protection, which addresses potential bird mortality by employing observation and hazing programs to discourage waterfowl from making contact with the Berkeley Pit.  

Rocker Timber Framing and Treating Plant OU7

Rocker Timber Framing and Treating Plant OU7 covers about 16 acres and includes the contaminated groundwater resulting from site operations under and near the land surface. It is south of U.S. Interstate 15/90 near Rocker, Montana, about three miles west of Butte, in Silver Bow County. The community of Rocker is just north of Silver Bow Creek. The Rocker Timber Framing and Treating Plant was built in 1909 and operated until 1957. Process and treating materials, including creosote and arsenic trioxide, were used during plant operations, resulting in contaminated soils and significant groundwater contamination. Arsenic is the primary contaminant of concern. Remedial action was completed in 1997 and the OU has been in ongoing O&M. Groundwater sampling and monitoring for arsenic continued and exceedances of arsenic exist in some monitoring wells have prompted ongoing investigations by EPA. 

Warm Springs Ponds OU4 and 12

Warm Springs Ponds OU4 and OU12 are in southwestern Montana at the lower end of Silver Bow Creek approximately 27 miles downstream of Butte. This 2,600-acre area consists of a series of three sediment settling ponds containing approximately 19 million cubic yards of sediment. OU4 includes the portion that actively treats the entire flow of Silver Bow Creek prior to its confluence with Warm Springs Creek and Mill Willow Bypass that forms the start of the Clark Fork River. OU12 is the portion that is not part of the active treatment of Silver Bow Creek Water. Selected interim remedies are in place until upstream sources of contamination are cleaned up.  

Institutional controls (ICs) are in place to prevent future residential development, swimming, and consumption of fish by humans in OU4. ICs are in place to prevent residential development, swimming, domestic well construction, and disruption of dry-closure caps in OU12. Regular inspection and maintenance activities are ongoing at the site.  

In 2024, a Biological Technical Assistance Group (BTAG) was convened to begin the process of conducting an ecological assessment.

OU8, Butte Priority Soils OU8 (BPSOU)

OU8, Butte Priority Soils OU (BPSOU) is centered on the “Butte Hill,” the location of the historic Butte Mining District and incorporates impacted soils, mine wastes, and contaminated dust located within large portions of Butte and Walkerville. Extensive underground mining, milling and mineral processing resulted in widespread distribution of mine waste such as waste rock, mill tailings, smelter emissions and slag. Mine wastes impacted soils, interior dust, groundwater, and surface water throughout the BPSOU and became the focus of the environmental cleanup ongoing today. Separate but interconnected projects are planned to be completed including: 

  • Grove Gulch (construction began in August 2024) 
  • Diggings East  
  • Northside Tailings 
  • Buffalo Gulch  
  • Butte Reduction Works 
  • Blacktail Creek and Confluence Area 
  • Uncontrolled Surface Flow Areas 
  • Copper Mountain Sports and Recreation Complex Area 

Though these projects will undergo individual design processes and have their own construction timelines, they will ultimately work together to protect human health and the environment from the effects of historic mining activities in Butte. 

Other major features and components of the BPSOU include:  

  • The Butte Treatment Lagoons treats captured contaminated groundwater from the West Camp System, BPSOU subdrain, Lower Area One, and stormwater from Missoula Gulch. 

  • The Residential Metals Abatement Program (RMAP) utilizes a multi-pathway approach to assess residential properties for lead, arsenic, and mercury in residential soils, interior dust (both living space and attic dust) paint, and pipes. If the assessment any of these sources of lead, arsenic, or mercury in a residence show elevated concentrations above the established cleanup levels, the property is remediated based on the sampling results. 

  • The Butte Reclamation Evaluation System (BRES) provides a practical way to evaluate the stability, integrity, and continued protectiveness of completed reclamation projects. Through the BRES, routine focused inspections assess: vegetative cover, erosion, site-edge conditions, presence of waste material, potential for instability, and presence of barren areas or gulleys due to water runoff.  

  • Insufficiently reclaimed (IR) and unreclaimed (UR) sites are evaluated and as required, capped and revegetated.  

In August 2024, work began at the Grove Gulch project site. The project is the first of several planned cleanups in the BPSOU corridor. When finished, it is designed to protect surface waters—like Blacktail Creek—from contamination by stormwater runoff potentially containing heavy metals as a result of historic mining operations. The work is projected to be completed in December 2024 with revegetation occurring after the spring thaw in 2025. 

Key documents related to the cleanup of the BPSOU include:   

OU13, West Side Soils

OU13, West Side Soils: includes the mining-impacted areas in and around the city of Butte that are not included in the BPSOU or the permitted active mining area. A comprehensive investigation to characterize the nature and extent of contamination began in 2018.  

EPA has completed significant field investigation efforts in support of a remedial investigation/feasibility study (RI/FS) for the West Side Soils Operable Unit (WSSOU) as part of its cleanup efforts at the Silver Bow Creek/Butte Area Superfund site. The Remedial Investigation Report is anticipated to be released later in 2024. The site team is currently working on the Feasibility Study and anticipates completing it later in 2024.   

EPA will present a preferred alternative for cleanup to the public for comment in a proposed plan after the RI/FS is complete. After comment on the proposed plan is reviewed, EPA will specify a selected alternative for cleanup that is documented in a ROD.  

Remedial design will begin after the ROD is signed, followed by remedial action (cleanup). Remedial actions will be coordinated in advance with landowners.  

EPA will post information on future community involvement opportunities, including public meetings, on this website, through our listserv, and via local media outlets.  

The West Side Soils Public Database contains a brief technical writeup about the validated data, a fact sheet, Excel* files with analytical results for each sample collected, and figures that show the sample locations. Results have been sent to property owners for the samples collected on their individual properties. The information will be updated as new data is collected and validated. 

Updated Soil Lead Guidance for CERCLA Sites and RCRA Corrective Action Facilities

The EPA has just released new national guidance for soil-lead contamination at Superfund and Resource Conservation and Recovery Act (RCRA) sites. This new guidance lowers the screening level for lead in soil at residential properties from 400 parts per million (ppm) to 200 ppm. At residential properties with multiple sources of lead exposure, EPA will generally use 100 ppm as the screening level.

Screening levels are not cleanup standards. While this update will help EPA site teams make site-specific cleanup decisions to protect communities, EPA makes cleanup decisions specific to each site, using site-specific factors, including risk factors and community input that can vary from site to site.  

These screening levels will help select residential action levels that are protective of human health, factoring in risk factors and bioavailability (how much of a substance the body can absorb if ingested). This conservative approach is meant to reduce potential exposure that could lead to harmful elevated blood-lead levels.  

Updated Soil Lead Guidance for CERCLA Sites and RCRA Corrective Action Facilities

Silver Bow Creek - Butte Area

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Last updated on September 26, 2024