ScholarWorks at University of Montana

The Silver Bow Creek watershed in southwest Montana encompasses approximately 474 square miles and forms a portion of the headwaters the Clark Fork River, tributary to the Columbia River. Decades of mining in the basin have resulted in extensive injuries to natural resources and loss of associated recreational opportunities. These injuries include mild to severe contamination of water and soil resources and massive physical alterations to stream channels, floodplains, and surrounding landscapes. Adding to these challenges is a variety of land uses and human activities within the watershed, including a relatively large, urban population as well as rural lands that are important for agriculture, wildlife, native species, and associated recreational values.

The Silver Bow Creek Watershed Restoration Plan identifies and prioritizes restoration needs in the Silver Bow Creek watershed. Impetus for the plan came from public interest in watershed-scale planning to serve as a guide to restoring natural resources in the watershed. Plan development involved extensive public input, data collection, and analysis. The plan evaluates current conditions, identifies desired future conditions, and prioritizes restoration needs to achieve these desired conditions. Restoration needs are broadly categorized as: preserving and protecting existing resources; mitigating pollution; improving water quantity; restoring fisheries; restoring vegetation and widlife; and developing recreation. The plan will be used to guide development of restoration projects and funding of these projects. This presentation will highlight the purpose, methods, results, and lessons learned from this comprehensive planning effort.

The Clark Fork River Basin Superfund projects span three major cleanup sites (Butte-Silver Bow, Anaconda-Opportunity Ponds and Milltown-Clark Fork River) and over fifteen different operable units. A large number of science based technologies have been applied, and in some cases developed, to address the different types of contamination and mitigation challenges present in the basin. Surface reclamation techniques including soils and revegetation science, engineered cover designs, and urban interface have all been advanced by their application to source control and disturbed area reclamation. Streambank and riparian area remediation and restoration using extensive amendments and removal and replacement have been specifically developed for cleanup along Silverbow Creek and the Clark Fork River as well as other areas. Techniques to address highly toxic smelter site residues in addition to reclamation of billions of tons of tailings have been applied to the Anaconda-Opportunity Ponds while the Warm Springs Ponds continue to be used as part of a remedy that was first initiated in the early last century to control impacts to water quality that had badly degraded the Clark Fork River. The future removal of Milltown Dam will be a pioneering effort in the area of dam removal while the Clark Fork River cleanup will be one of the first aimed at extensive streambank and riparian area restoration. The presentation will present and describe in more detail the scientific methods that have been applied throughout the basin, focusing on sites and applications not addressed in other presentations at the symposium.

Sponsored by Clark Fork River Technical Assistance Committee (CFRTAC)

In 2004, the US Environmental Protection Agency released the Record of Decision (ROD) document which specifies the approach to the cleanup of one of the nation’s largest Superfund sites - Montana’s Clark Fork River. Cleanup strategies include removal of some wastes, in-place treatment of other wastes, and stream-bank stabilization. A Riparian Evaluation System (RipES) was developed as a data predicated remedial design tool designed to identify and categorize polygons based on landscape stability and plant community dysfunction within the Clark Fork River Operable Unit. The system contains the following elements: definitions for three types of stream-bank polygons, and descriptions of other polygons with varying levels of contamination caused vegetation community dysfunction; a numerical components with associated threshold scores that segregate stream-bank polygons into different categories, and threshold scores that distinguish the severity of dysfunction of the vegetation community; a process for identification of data gaps and information required to complete remedial designs for each polygon; and identification of modifying factors that may affect the selection of remedial action(s) for specific lands. The numerical portion of the system is based upon the Land Reclamation Evaluation System (LRES) developed for the Anaconda Smelter NPL Site (EPA 1998, CDM and RRU 1999, and ARCO 2000), and the Riparian and Wetland Health Assessment protocols (Hansen and others 2000), which are used extensively in the western United States and Canada.

The challenge of improving instream flows in Montana is complicated because of society’s increasing and shifting demands for water; Montana’s first-in-time, first-in-right water-use system; the slow pace of water rights adjudication; and the recent trend in the state towards a warmer and drier climate. Improving instream flows in the upper Clark Fork watershed has by necessity become an exercise in pragmatism, requiring methodical and incremental strategies, including:

1. providing incentives for existing water users to apply new technology and conserve;
2. being innovative when managing existing water-storage systems;
3. collecting site-specific data to better inform decisions; and,
4. promoting ownership in improving instream flows among the water user community.

In 1995, the Montana legislature deemed the upper Clark Fork and its tributaries over-appropriated, and statutorily closed the basin to new water rights above Milltown Dam. The statute, however, makes an exception for ground water. In response to the closure, and prompted by the recent drought, agricultural water users have turned increasingly to ground-water wells and sprinkler systems as more reliable and efficient irrigation methods than traditional flood irrigation from surface-water diversions. The increased crop production made possible by these changes increases water consumption from the basin. New residential and commercial water users likewise may withdraw additional ground water from aquifers in the basin. Because ground water naturally discharges into stream channels, this increased consumption of ground water ultimately decreases streamflow in the Clark Fork. Water-right transfers provide an alternative means to develop new water projects without increasing overall water consumption. Concurrent enforcement of the basin closure statute for all water, whether from surface or subsurface sources, would prevent further river dewatering and protect existing water rights.

A 15-year dataset from the Clark Fork River (CFR) was used to examine the influence of mine waste remediation on Cu concentrations in resident biota (Hydropsyche) and bed sediment. Copper concentrations declined in Hydropsyche and bed sediment after the onset of remediation in the upper 30 Km of the CFR (Reach A). Detection of remediation response downstream at 85 Km (Reach B) and 130 - 190 Km (Reach C) was confounded by the significant positive relationship between bioaccumulation and stream discharge. To date, temporal patterns associated with remediation cannot be detected in Reach B or C. In order to understand how contamination levels in Reach C might be influenced by upstream remediation efforts, site-to-site correlations in temporal metal trends were evaluated. The expectation was that the strength of the spatial relationship would be a function of distance. Correlations between adjacent stations showed the strength of station-to-station connections and identified temporal similarities in patterns of metal occurrence. Between 60-75% of adjacent stations were significantly linked, suggesting that events upstream usually affected the next downstream station. Adjacent sites showing no temporal correlation may indicate a spatial disconnect in the upstream signal. Site-specific influence in metal concentrations over large spatial scales was observed when temporal patterns in downstream stations were significantly correlated to an upstream station, identifying sites which may be major sources of metal. For example, sediment Cu concentrations between 5 -10 Km were significantly correlated with concentrations at five out of seven stations along the 185 Km segment, and may be indicative of spatially extensive upstream-downstream linkages.

The success of remediation of mining wastes in the upper Clark Fork River (CFR) will be measured by mitigation of metal exposures and reduction of risk to biological communities. Dissolved Cu concentrations at most sites in the upper 90 km of the CFR have declined during the period 1993-2002. Annual trends in benthic macroinvertebrate assemblage data indicate that in-stream ecological conditions have improved, also. Despite the general similarity in those patterns, correlation in year-to-year Cu exposure and changes in the benthos within sites is weak. These simple relationships are probably confounded by other factors acting on the benthos. Additionally, interpretation of metal effects is hindered by a vague understanding of how species composition reflects differences in the metal sensitivity of individual species. To better understand the metal-specific responses of species within the assemblage, metal bioaccumulation and detoxification were compared among five resident species. From these results, we characterized two species as sensitive and three as tolerant. These characterizations of tolerance were similar to tolerance values derived from species distributions. Species most sensitive to Cu do not occur at sites in the upper river. This suggests where metals-specific effects are most likely occurring. The physiological studies may provide a mechanistic explanation for why some species tolerate metals and others do not. This information should be considered within the context of ecological factors that might affect species distributions. Physiological and ecological studies are complementary approaches that strengthen understanding of metal-specific effects on stream benthos.

The Summit Valley is a 60-square mile alluvium-filled intermontane basin located in southwest Montana. The valley is bounded on the south and east by the Continental Divide, is home to the city of Butte, and is drained by Blacktail and Silver-Bow Creeks. Alluvium, derived from the granitic rocks that frame the valley, and fractured bedrock along the valley margin yield sufficient water for domestic purposes.

Reconnaissance ground-water sampling in the Summit Valley revealed elevated nitrate concentrations (greater than 2.0 mg/L) in the alluvial and bedrock aquifers. A review of the valley’s recent and historic ground-water analyses shows that 64 percent (96 of 149) of the samples had nitrate concentrations greater than an assumed background concentration of 2.0 mg/L, and 15 percent (22 of 149) of the samples exceed the 10.0 mg/L health standard. Elevated nitrate concentrations were detected below sewered urban/residential areas, and unsewered residential areas, as well as in shallow (less than 50 feet deep) wells and deep (greater than 200 feet deep) wells. Sampling of Blacktail and Silver Bow Creeks, during base flow conditions showed that concentrations of nitrate exceeded 1.0 mg/L over a 5-mile stretch through the most densely populated part of the valley. The results indicate that the elevated nitrate in the ground water impacts the surface water in the valley during low-flow conditions.

To assist with source identification, ground-water samples were collected from fourteen wells in different aquifers and land use settings for analysis of stable isotopes of nitrogen and oxygen. The results showed that the nitrate in all the samples had a similar isotopic signature. The d15N values ranged between 4 and 12 per mill, while the d18O (of the NO3) values ranged between –4 and 2 per mill. The measured d15N and d18O values are suggestive of animal or septic waste rather than a synthetic fertilizer source for the nitrate.

The planform, or pattern, of a river represents how channel form adjusts in a horizontal plane. Channel planform is a continuum ranging from straight to meandering to braided, and is a function of sediment load, sediment size, and channel slope. Meander geometry describes the length, amplitude, and radius of curvature of a meander bend of a river. These characteristics are related to the width and dominant discharge of the river.

Conceptual restoration plans for the Clark Fork and Blackfoot Rivers through the Milltown area have been proposed by the State of Montana. These plans recommend a single thread channel, with a regular pattern, and repeating meander bend geometry for the restored river channels. The HISTORIC planform and meander geometry of the Clark Fork and Blackfoot Rivers through the Milltown area are depicted in late 19th century and early 20th century maps, and are markedly different from the PROPOSED planform and meander geometry. Why do these proposed and historic planforms and meander geometries differ?

Restoration options for the Clark Fork and Blackfoot River near Milltown Dam are becoming a reality following EPA’s December 2004 Record of Decision to remove the Milltown Dam. The State of Montana’s Natural Resource Damage Program and Department of Fish, Wildlife and Parks, in consultation with US Fish & Wildlife Service and the Confederated Salish Kootenai Tribes, is preparing the floodplain and river channel designs that will be integrated with EPA’s remedial activities. The State’s May 2003 draft conceptual restoration design plan, which is based on natural channel design philosophy, received substantial public support. The State is now using 2004 field data to develop a Phase II draft restoration design plan that will undergo peer review by a panel of national experts and then issued for public comment.

The current Phase II design encompasses the Clark Fork River about 5 miles upstream of the Milltown Dam and downstream of the dam to the Interstate 90 bridge, and the Blackfoot River upstream of the dam to just below the Stimson Dam. Restoration design must be adjusted to account for a number of limiting factors, with the major one being the contaminated sediment that will be left in place. Other limiting factors that affect restoration design include: Interstate 90 bridges on Blackfoot River, Stimson Lumber infrastructure, bridges downstream of dam, and coordination with remedial actions. The Phase II design process will also thoroughly address technical issues raised in public comments on the conceptual design plan.