A pdf of this post is available here: Silver Bow Creek pdf
In the process of hard rock mining, the desired ore is extracted from its surrounding rock matrix by crushing the composite and treating it with a variety of chemicals. This treatment causes the desired metal to precipitate out of solution and allows for collection. The remaining, left-over material is called mine tailings. Mine tailings often contain a slurry of different chemicals such as pyrite (FeS2) and Iron(II)sulfide (FeS) (Benner et al. 1995). These sulfide waste products are extremely harmful to many organisms, including humans, and proper waste management is of the utmost concern. When sulfide mine tailings are exposed to water, metals such as iron and manganese will precipitate out of solution and become oxidized. This oxidation process causes a subsequent decrease in the water’s pH. Therefore, mine tailings cause stream water to become acidic and contain aqueous and precipitated metals that are harmful to organisms (Benner et al. 1995).
|Silver Bow Creek|
The Clark Fork River basin is home to a diverse assemblage of vertebrate and invertebrate animal species including nongame species such as songbirds, small mammals, and the especially sensitive aquatic invertebrates of the orders Ephemeroptera, Plecoptera, and Trichoptera. A number of economically important, native game species including elk (Cervus canadensis), moose (Alces americanus), white-tailed (Odoceolius virginianus) and mule deer (Odoceolius hemionus), pronghorn (Antilocapra americana), bull trout (Salvelinus confluentus), and the iconic westslope cutthroat trout (Oncorhynchus clarki lewisi) are also endemic to the region.
Mine Waste Disposal at Silver Bow Creek
Silver Bow Creek is a 26-mile long, small order tributary of the Clark Fork River of western Montana. With its origin in the historical mining town of Butte, Silver Bow Creek has a long history of misuse and abuse. Starting in the late 1800’s and continuing through much of the 20th century, Silver Bow County’s major economic activity revolved around mining activities, especially for copper (Dickson 2012).
In Silver Bow County, much of the mine waste throughout the primary operation period of the mines was simply dumped outside of the urban areas of Butte, Rocker, and Walkerville. Unfortunately, one of the primary areas where tailings were dumped was along and within Silver Bow Creek. In addition to dumping along the creek, a number of flood events caused the tailings to become distributed throughout the floodplain of the Silver Bow drainage (Mullen and Chavez 2012). The tailings also infiltrated the local groundwater, allowing the heavy metal waste to be distributed to a much wider extent, especially within the flow path of the creek (Benner et al. 1995).
After significant mining activity took hold in Silver Bow County and mine tailings started to be improperly disposed of, local populations of the aforementioned animal species endemic to the region declined significantly, especially those of the aquatic invertebrates and trout (Morey et al. 2002). As such, safe use of the water for human consumption and angling recreation were compromised. Additionally, riparian plant communities collapsed and Silver Bow Creek become virtually devoid of vegetation.
ARCO Lawsuit and Fallout
In 1983, the state of Montana filed suit against the Atlantic Richfield Company (ARCO) alleging that improper mine waste disposal had compromised the ecological integrity of Silver Bow Creek. In 1998, the parties entered into a settlement worth $215 million and parts of the Silver Bow Creek watershed were designated as Superfund sites (Confluence 2005). Superfund is a program operated by the U.S. Environmental Protection Agency (EPA) that designates areas where water has become unsafe for human use and allocates funds for site remediation. Since 1999, the state of Montana has been distributing ARCO and EPA funds to public and private entities throughout the Silver Bow Creek basin for restoration and monitoring activities. This generated $85 million for the local economy alone (Confluence 2005).
While restoration activities funded by the state have varied widely, the vast majority of funds in Silver Bow Creek have been spent on removal of contaminated soils in the creek and floodplain and channel reconstruction and revegetation (Mullen and Chavez 2012). To date, 80% of Silver Bow Creek has been restored and 4.1 million cubic yards of an estimated 4.5 million cubic yards of mine waste has been removed. This equates to 1,310 acres of the 1,400 acres initially contaminated (Mullen and Chavez 2012). Excavation of contaminated soils also allowed for the creation of a number of wetlands that provide habitat for waterfowl, fishes, amphibians and other species.
In addition to waste removal, channel reconstruction and riparian & instream habitat creation has been prioritized. Large portions of the creek have been manipulated to create more meanders, pool habitats, and varying channel widths. Like many large scale restoration projects, the Silver Bow restoration was divided into a number of zones where needs were assessed and different projects implemented (Mullen and Chavez 2012). The final zone of the initially scheduled areas for restoration was completed in 2013.
Response and Future Directions
|Westslope Cutthroat Trout caught in Silver Bow Creek|
While drinking water standards have not yet been met for Silver Bow Creek, water quality has vastly improved and metal concentrations are much lower (Mullen and Chavez 2012). Riparian vegetation has returned to large portions of the steam and several flood events have not caused undue changes to channel structure (Confluence 2005). Perhaps the most significant sign of improvement is that beginning in 2006, fish returned to Silver Bow Creek after nearly 100 years of absence. Populations of suckers, sculpins, and the iconic westslope cutthroat trout have become naturally reproducing in the drainage and the Silver Bow Creek trout fishery is gaining renown across the state (Dickson 2012). Additionally, increases in bald eagle, moose, beaver, muskrat, mink, insect, and sandhill crane populations have been observed (Mullen and Chavez 2012).
While some areas of Silver Bow Creek are still being restored, this project is becoming known as one of the most successful mine waste cleanup projects in the country. Continued success on this small headwater of the Columbia will undoubtedly provide increases benefits to the people, plants, and animals that call this area home.
Benner, S.G., et al. (1995) Metal Behavior During Surface-Groundwater Interaction, Silver Bow Creek, Montana. Environmental Science and Technology 29, 1789-1795.
Confluence Consulting, Inc. (2005) Silver Bow Creek Watershed Restoration Plan. Report to Montana Natural Resource Damage Program.
Dickson, T. (2012) Silver Bow begins bouncing back. Montana Outdoors. September 2012, 56-57.
Morey, E.R., et al. (2002) Estimated recreational trout fishing damages in Montana’s Clark Fork River basin: summary of a natural resource damage assessment. Journal of Environmental Management 66, 159-170
Mullen, G. and J. Chavez (2012) Remediation and Restoration of Silver Bow Creek. Montana Department of Justice report.