by Herbert T. Buxton, David A. Nimick, Paul von Guerard, Stanley E. Church, Ann G. Frazier, John R. Gray, Bruce R. Lipin, Sherman P. Marsh, Daniel F. Woodward, Briant A. Kimball, Susan E. Finger, Lee S. Ischinger, John C. Fordham, Martha S. Power, Christine M. Bunck, and John W. Jones
This paper was presented at the Fourth International Conference on Acid Rock Drainage (ICARD) May 30-June 6, 1997, Vancouver, British Columbia, Canada.
A U.S. Geological Survey Abandoned Mine Lands Initiative will develop a strategy for gathering and communicating the scientific information needed to formulate effective and cost-efficient remediation of abandoned mine lands. A watershed approach will identify, characterize, and remediate contaminated sites that have the most profound effect on water and ecosystem quality within a watershed. The Initiative will be conducted during 1997 through 2001 in two pilot watersheds, the Upper Animas River watershed in Colorado and the Boulder River watershed in Montana. Initiative efforts are being coordinated with the U.S. Forest Service, Bureau of Land Management, National Park Service, and other stakeholders which are using the resulting scientific information to design and implement remediation activities.
The Initiative has the following eight objective-oriented components: estimate background (pre-mining) conditions; define baseline (current) conditions; identify target sites (major contaminant sources); characterize target sites and processes affecting contaminant dispersal; characterize ecosystem health and controlling processes at target sites; develop remediation goals and monitoring network; provide an integrated, quality-assured and accessible data network; and document lessons learned for future applications of the watershed approach.
(Keywords: abandoned mines, acid mine drainage, watershed, Colorado, Montana)
The U.S. Department of the Interior (DOI) and U.S. Department of Agriculture—specifically, the Bureau of Land Management, National Park Service, U.S. Forest Service (federal land management agencies), and the U.S. Geological Survey (the DOI science agency)—have developed a coordinated strategy for the cleanup of environmental contamination from abandoned mine lands (AML) associated with federal lands. This strategy is based on a watershed approach (rather than a site-by-site approach) to characterize and remediate contamination. A watershed approach would identify those watersheds within a state that are most at risk for environmental degradation from AML, and then identify, characterize, and remediate contaminated sites that have the most profound effect on water and ecosystem quality within the watershed.
As part of the interdepartmental effort, the U.S. Geological Survey (USGS) has implemented an Abandoned Mine Lands Initiative to provide needed scientific information and technical assistance to federal land management agencies (FLMA) in support of remediation. The USGS Initiative is being conducted in two pilot watersheds, the Upper Animas River in Colorado, and the Boulder River in Montana. FLMA are coordinating design and implementation of remediation. The Initiative will be conducted during 1997 through 2001.
This report provides an overview of the plans for the USGS AML Initiative. It includes background, justification, and an overview of the conceptual approach; and describes the two Initiative pilot watersheds.
Numerous AML sites in the United States are on, or adjacent to, federally managed land, affect aquatic or wildlife habitat on federal land, and will require investment of federal resources to remediate. Although estimates of the amount of AML vary, the scope of the problem is huge. According to a draft report by the General Accounting Office (1996), thousands of abandoned hard rock mines exist on federal lands, a subset of which constitute physical safety or environmental degradation hazards. The Mineral Policy Center, an environmental research and advocacy group, estimates 557,650 AML sites exist across 32 states (Lyon and others, 1993). According to the General Accounting Office (1996), 45 billion metric tons of mine waste have been generated, 14,400 sites need extensive work to prevent surface-water contamination, and 8,000 kilometers of streams are affected by acid drainage.
Cost estimates for remediating public AML are substantial. The Bureau of Land Management estimates a range of from $4 to $35 billion; the Mineral Policy Center estimates $33 to $72 billion. No one disputes the U.S. Environmental Protection Agency (USEPA) contention that "decades and billions of dollars will be required to identify and reclaim every site where mining has occurred" (USEPA, 1996).
Design of effective and cost-efficient remediation alternatives requires basic knowledge of background (pre-mining) conditions, the degree of contamination of the natural environment and the natural processes that control contaminant transport and fate. Gathering such knowledge requires the integrated application of a wide range of expertise available in the USGS, including water quality, hydrology, geology, geochemistry, biology, mapping, and digital data collection and management. The USGS has a track record of providing scientific information that has enhanced and expedited decision making in many areas affected by AML, including Summitville, Colorado; Leadville, Colorado; Pinal Creek, Arizona; Monument Valley, Utah; Iron Mountain, California; Clark Fork, Montana; and Coeur d'Alene, Idaho. In October 1996, the National Biological Service joined the USGS as its Biological Resources Division; this merger further equips USGS to define the mechanisms by which AML affect aquatic and riparian zone ecologies. The combination of interdisciplinary scientific expertise, experience in conducting unbiased scientific research throughout the United States, a national infrastructure with consistent quality-assurance protocols, experience in maintaining national environmental databases, and experience working with organizations at federal, state, tribal, and local levels enables the USGS to make a unique contribution to its federal partner's strategy for remediating the adverse effects of abandoned mines.
The goal of the USGS AML Initiative is to develop a strategy for gathering and communicating the scientific information needed to formulate effective and cost-efficient remediation of AML within the framework of a watershed approach. Key objectives of the Initiative are to:
The short-term product of the Initiative is scientific information on the water quality, hydrology, geology, geochemistry, and biology that describes how the pilot watersheds in Colorado and Montana have responded to recent and historic mining activities.This information will be used to evaluate the cumulative effect of multiple contamination sources on the watershed, to identify and prioritize sites for cleanup, to select and design specific remediation alternatives, and to define expectations for cleanup actions (measures of success).
The overall product of the Initiative will be a strategy for the collection and communication of scientific information needed to design and implement cleanup of AML by FLMA. This strategy will be developed and demonstrated in the pilot watersheds, and will include development of working relationships with FLMA, federal and state regulators, and local stakeholders. A major outcome will be "lessons learned" regarding the specific types of data and information that are most useful to development of remediation strategies. Successful demonstration of the watershed approach will encourage its adoption across other federal and private lands nationwide.
The remediation of contamination associated with AML, commonly, is considered on a site-by-site basis. However, a cost- and time-efficient alternative is to identify, characterize, and remediate sites that most substantially affect watershed quality and threaten public safety. USEPA (1995) stated:
Remediation of an entire fluvial system is unrealistic; instead, technology should be developed to address the hot spots of pollution occurring in the system… In fluvial systems, targeting key areas is essential to obtain the greatest benefit from scarce resources.
The U.S. Department of the Interior and the U.S. Department of Agriculture have outlined a watershed approach to remediating contamination associated with AML across the United States. This watershed approach has four general elements:
Such a watershed approach: (1) gives high priority to actions likely to improve water and ecosystem quality most significantly, (2) will greatly accelerate and reduce the total cost of remediation compared to remediating on a site-by-site basis, (3) enables assessment of the cumulative effect of multiple and/or nonpoint sources of contamination, (4) provides information at the watershed scale that will assist disposal siting decisions, (5) permits consideration of revenue generation from selected sites to supplement overall watershed remediation costs, and (6) fosters collaboration among federal, state, and local levels of government and stakeholders. The four elements of the watershed approach are described as follows:
The Upper Animas River and the Boulder River watersheds have been identified as the priority watersheds in their states for remediation of contamination associated with AML. The Upper Animas River watershed, located near Silverton in southwestern Colorado (Figure 1) was selected in March 1996 using a prioritization process that considered the available data, ongoing activities, and water-quality impairment from abandoned mines. Colorado has funded a Watershed Based AML assessment project in the Upper Animas River watershed through its Colorado Demonstration Program project (Colorado Water Quality Control Commission, 1996). The Boulder River watershed, located near the town of Basin in western Montana, about 40 kilometers south of Helena (Figure 2), was chosen in May 1996 from five candidate watersheds based on an analysis of geologic factors, metal loading, the status of ongoing remediation activities, general knowledge of the candidate watersheds, and extent of federal land. The selection process benefited from a state wide inventory of AML and the Abandoned and Inactive Mines Scoring System (AIMSS) (Pioneer Technical Services, 1995) developed by the State of Montana for prioritizing abandoned mine sites.
Although the geographic, socioeconomic, and geologic characteristics of each watershed have similarities, the differences are significant (Table 1). Although both watersheds are in mountainous terrain with abundant snowfall, elevation and annual precipitation are less in the Boulder River watershed. The Upper Animas River watershed is only somewhat smaller than the Boulder River watershed, but their shape, relief, and drainage patterns are different. In Colorado, the study area consists of the entire Animas River watershed upstream of Silverton. In contrast, the Montana study site encompasses three adjacent Boulder River tributaries (Basin, Cataract, and High Ore Creeks) and a short reach of the Boulder River downstream of the tributary confluences. Both areas have a history of metal mining dating back to the late 1800s. Most mining activity ceased by the 1940s, although some activity occurred as recently as the 1990s. Principal metals produced from both watersheds included gold (Au), silver (Ag), lead (Pb), and zinc (Zn). Ore bodies are sulfidic and acid mine drainage occurs in both areas. The number of abandoned mines is an order of magnitude higher in the Upper Animas River watershed than in the Boulder River watershed. Much of the mining in both study areas occurred on privately-owned (patented) mining claims. However, some mine, mill, and smelter sites; and tailings deposits, along with eroded tailings distributed along various reaches of stream channels and flood plains, are located on federal land.
|WATERSHED CHARACTERISTICS||UPPER ANIMAS RIVER COLORADO||BOULDER RIVER MONTANA|
|Drainage area (km2)||378||233|
|Precipitation (cm/yr)||100-127||36 - 76|
|Elevation (m)||2,800 - 4,200||1500 - 2500|
|Primary fish species||brook trout||rainbow trout|
|Population||500 - 3,500||100-200|
|Major Industries||tourism||logging, mining, cattle|
|Public interest in AML
- within watershed
- state wide
|FLMA||USFS, BLM||USFS, BLM|
|General geology||Intercaldera lavas (hydrothermally altered)||Granitic batholith (veins)|
|Metals mined||Ag, Au, Pb, Zn||Ag, Cu, Pb, Zn, Au|
|Major mining period||1880-1990||1870-1940|
Although populations in both areas vary seasonally as tourists and temporary residents move into the watersheds during the summer, the population of the Upper Animas River watershed is much greater than that of the Boulder River study area. In the Upper Animas River watershed, tourism, in part based on historic mining, is an important industry. Residents of the Boulder River study area are engaged primarily in mining, logging, or agricultural activities.
The primary effect of mining in both watersheds is degraded water quality and aquatic habitat, which consequently affects aquatic and fishery resources. Some streams are devoid of fish and many others may have impaired fisheries. Abandoned mines affect streams through direct discharge of acid drainage from adits, seepage from tailings piles, and erosion of tailings by storm runoff or streambank erosion. The extent of subsurface contaminant movement in both study areas is virtually unknown. The known extent of mining impact on surface waters in the Colorado area have been documented downstream to Durango and to the confluence with the San Juan River. Many of the AML sites that appear to have a serious effect on surface-water quality and local fisheries in the Boulder River watershed have been inventoried for the FLMA by the State of Montana. These inventories included some data on water quality and chemistry of tailings, and have been used to target AML sites that are likely candidates for remedial activities. In recent years, Montana has been active in remediating portions of the Comet mine on privately owned land in the upper reaches of High Ore Creek basin (Figure 2).
Commensurate with the greater impact and higher population, the Upper Animas River watershed has a substantially greater amount of natural resource information and AML characterization completed to date. The Animas River Stakeholders Group (ARSG) has taken an active role in the characterization and remediation of the watershed. The ARSG represents private, local, state, and federal entities. In contrast to the Boulder River area, where AML remediation is only beginning to be an important issue, active public involvement and interagency cooperation in addressing AML remediation has a long history in the Upper Animas River watershed.
The State of Colorado Water-Quality Control Commission has set goals for instream water-quality standards for streams in the Upper Animas River watershed. The Commission has empowered the ARSG to develop a plan to remediate water quality. The FLMA and the USGS are active participants in the ARSG. Although much work has been done characterizing the effects of acid drainage on streams in the Upper Animas River watershed, significant additional aspects of the effects of acid drainage on stream ecosystems, including riparian and aquatic habitats, need to be defined.
Workplans for conducting the USGS AML Initiative in the Upper Animas River watershed in Colorado and the Boulder River watershed in Montana have eight objective-oriented components:
A general description of each component is presented below and a schedule for accomplishment of these components is presented in Figure 3.
Estimate Background (pre-mining) Conditions — Estimation of background (pre-mining) conditions will assist identification of realistic remediation goals. Background conditions are highly dependent on the lithologies and mineral deposits, including the mineralogy of the hydrothermally altered zones exposed to weathering, in the drainage basin. Geologic mapping will be augmented by new data from airborne radiometric mapping, electromagnetic mapping of the fracture systems, and magnetic mapping of the plutons. Imaging spectroscopy data will be used where feasible. Where possible, background metal concentrations will be determined by sampling stream sediment in unmined drainages or sub-basins that are geologically and hydrologically similar to affected basins or in post-glacial alluvial sediments (deposited less than 10,000 years ago). Water quality of selected streams, springs, and iron bogs that are unaffected by mining will be characterized and used as a basis for comparing mined and unmined watersheds (if present). Similarly, control biological monitoring sites will be established in nearby unmined drainages.
Define Baseline (current) Conditions — Hydrologic baseline conditions will be defined by sampling to establish both the spatial and temporal variations of contaminant occurrence. The transport of dissolved, colloidal, and suspended transport of metals will be evaluated by synoptic sampling of water, and by testing colloid and bed-sediment chemistry during baseflow, as well as during spring runoff. Biological sampling, including sampling of fish and invertebrates, will be coordinated. Invertebrate community structure of the benthic invertebrate fauna will be characterized. Baseline physical habitat limitations will be defined to help establish goals for restoration of trout spawning and nursery, and benthic invertebrate habitat. An accurate and current database of base map features will be prepared from 1:24,000 scale topographic quadrangles, aerial photography, and other remotely sensed data.
Identify Target Sites (major contaminant sources) — Mines are obvious contributors to environmental degradation, but mills and smelter sites, waste dumps, tailings piles, and disturbed land can also be contaminant sources. Natural mineral deposits are also important contributors of acid and metals, and their extent and heterogeneity require investigation at regional scales. Existing inventories of contaminant sources will be supplemented by new chemical and mineralogical data for specific sites. Estimates of metal loads from individual sources will be developed from baseline data-collection efforts and tracer-injection studies analyzed using solute-transport modeling (Broshears and others, 1995). Preliminary geoenvironmental models of known mineral deposit types (duBray, 1995) will be conducted to define reactions that liberate and transport metals into the watershed and to aid in the prediction of hydrogeochemical effects of mined rock, mine workings and dumps, and unmined altered and mineralized rocks. Ground-water hydrology and potential pathways for contaminant movement in alluvial aquifers and in fractured bedrock in mountainous terrains will be assessed to the extent possible.
Characterize Target Sites and Processes Affecting Contaminant Dispersal — Targeted mine sites will be characterized to determine the pathways and timing of contaminant movement to receiving waters. Local tracer injection studies over relatively short stream reaches (<1,000 m) will identify sources that affect the stream. Mine-waste piles will be investigated using integrative geochemical methods to quantify the generation of acid; the mobility of metals; the storage of acid, metals, and sulfate in soluble efflorescent salts; and the magnitude of metal loadings likely from point sources. Selected representative dumps will be studied to identify the chemical processes within the dumps that result in acid generation and neutralization, and metal loading and attenuation. Subsurface hydrology will be characterized at target sites where a subsurface pathway is indicated. Samples of storm runoff from selected waste piles will be collected and interpreted in the context of waste pile mineralogy.
Characterize Ecosystem Health and Controlling Processes at Target Sites — Characterizing baseline ecosystem health will integrate the biology of sites with the chemistry of ground and surface water, colloids, and bed sediment. The effects of acidic and metal-rich drainage on the aquatic ecosystem and the factors controlling these effects will be evaluated by characterizing benthic invertebrates and fish populations. The status of resident fish populations (abundance, age structure, growth rates) will be determined and indicators of fish health (e.g. condition factors, physiological responses) evaluated. The taxonomic composition and productivity of benthic invertebrate communities will be determined. An interpretation of sources and pathways of metals movement that result in exposure and injury of biological resources will be provided. Habitat and metals-contamination assessments will be used to determine limiting factors that prevent the fishery from achieving its target population potential.
Develop Remediation Goals and Monitoring Network — Remediation goals and a comprehensive monitoring network are needed to evaluate the effectiveness of remediation on a site-specific and a watershed scale. Monitoring stations established downstream of remediated sites and in target habitats will monitor chemical (water and sediment) and biological responses over time; reference stations, established in less impacted reaches, will be compared with monitoring stations. Data from these monitoring stations will help FLMA determine ideal and achievable target metals concentrations in key pathway organisms and the quantity and quality of biological organisms that the watershed should support.
Provide an Integrated, Quality-Assured, and Accessible Data Network — The availability of data and information to FLMA, other governmental agencies, and the public is essential for efficient use of resources, to ensure that remediation decisions are based on the best available information, and to develop consensus decisions among involved parties. In addition to the base geographic data, spatially referenced data on geology, water, colloids, suspended sediment, bed sediment, and biota will be made available in Geographic Information System (GIS) format through the Internet and in selected publications.
Document Lessons Learned (for future applications of watershed approach) — Application of the watershed approach in the pilot watersheds will be documented, including identification of important data, valuable methods and approaches, and procedures for coordination among participants. The highly varied and complex geochemical, biologic, and geographic nature of the pilot watersheds is expected to provide significant insights into the potential for widespread application of remediation of mined sites using a watershed approach. The approach will emphasize flexibility for application over the broad range of hydrogeologic conditions and climate present in areas of the United States where mining has occurred.
Additional information on the USGS Abandoned Mine Lands Initiative can be obtained on the World Wide Web at http://amli.usgs.gov/. The USGS Mine Drainage Newsletter and information on the USGS Mine Drainage Interest Group is available at http://mine-drainage.usgs.gov/. Information about the activities and programs of the U.S. Geological Survey may be obtained at http://www.usgs.gov/.
Broshears, R.E., Runkel, R.L. and, Kimball, B.A., 1995, Interpreting spatial profiles of concentration in acid mine drainage streams, in, Hotchkiss, W. R., Downey, J.S., Gutentag, E.D., and Moore, J.E., eds., Water Resources at Risk, Summary of application of tracer injection and reactive solute transport modeling to characterize mine sites, American Institute of Hydrology, Minneapolis Minnesota, p. LL-10- 21.
Colorado Water Quality Control Commission, 1996, Colorado Nonpoint Source Management Program. Denver Colorado, October 1996, 100 p.
duBray, E.A., ed., 1995, Preliminary compilation of descriptive geoenvironmental mineral deposit models: U.S. Geological Survey Open-File Report 95-831, 272 p.
General Accounting Office, 1996, Federal Land Management: Information on Efforts to Inventory Abandoned Hard Rock Mines, Draft Report to the Ranking Minority Member, Committee on Resources, House of Representatives, GAO/RCED-96-30, 17 p.
Lyon, J.S., Hilliard, T.J., and Bethell, T.N., 1993, Burden of Gilt. Mineral Policy Center, Washington, D.C., 68 p.
Pioneer Technical Services, Inc., 1995, Abandoned Hardrock Mine Priority Sites 1995 Summary Report, Prepared for Abandoned Mine Reclamation Bureau, Montana Department of State Lands, Helena, Montana, 300 p.
U.S. Environmental Protection Agency, 1995, Workshop Report: Mine Waste Technical Forum: U.S. Environmental Protection Agency, Las Vegas, Nevada, July 25-27, 1995, 3 Chapters.
U.S. Environmental Protection Agency, 1996, Draft Final Hardrock Mining Framework: U.S. Environmental Protection Agency, Washington, D.C., 66 p.