Abstract The development and exploitation of mineral resources in the western United States was important to both our economic development and our history. With continued population growth and economic development in this region, the impacts of our mining legacy are proving to be equally important to citizens in our modern society. By one estimate, 500,000 abandoned mine sites are scattered across the western landscape, largely on public land (state and federal), affecting 16,000 miles of streams. Federal land management agencies such as the U.S. Department of Agriculture Forest Service and U.S. Department of Interior Bureau of Land Management are able to use their authorities under the Comprehensive Environmental Response, Compensation, and Liability Act to respond to the release of hazardous substances from these abandoned mines. Although human health is a primary consideration in prioritizing site response, environmental issues such as the impact on terrestrial species, water quality, or aquatic species also may influence site response priorities. Challenges faced in reducing or preventing further release of hazardous substances at historic mines sites include limited available funds, difficult access, changing public land uses, and increasing populations in nearby areas.

Abstract Infiltration of surface water through mine waste can be an important or even dominant source of contaminants in a watershed. The Waldorf mine site in Clear Creek County, Colorado, is typical of tens of thousands of small mines and prospects on public lands throughout the United States. In this study, electromagnetic (EM) conductivity and direct current (dc) resistivity surveys were conducted in tandem with a NaCl tracer study to delineate ground-water flow paths through a mine-waste dump and adjacent wetland area. The tracer was used to tag adit water infiltrating from braided channels flowing over the top of the dump to seeps at the base of the dump. Infiltration from the braided channels had a maximum flow rate of 92 m/day and a hydraulic conductivity of 1.6 × 10 4 cm 3 /s. After rerouting of adit flow around the waste dump, discharge at some of the largest seeps was reduced, although not all seepage was eliminated entirely. Integrating results of the tracer study with those of the EM and dc geophysical surveys revealed two main flow paths of ground water, one beneath the dump and one through the dump. The main source of water to the first flow path is deeper ground water emerging from the fault zone beneath the collapsed adit. This flow path travels beneath the waste dump and appears to have been unaffected by rerouting of the adit discharge around the waste dump. The source of the second flow path is infiltration of adit water from braided channels flowing over the top of the dump, which is intermediate in depth and flows through the center of the waste dump. Following rerouting of adit flow, discharge to seeps at the toe of the dump along this flow path was reduced by as much as two-thirds, although not eliminated entirely. Improved understanding of ground-water flow paths through this abandoned mine site is important in developing effective remediation strategies to target sources of metals emanating from the adit, waste dump, and contaminated wetland area. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. government.

Abstract This report presents some strategies to predict metal mobility at mining sites. These strategies are based on chemical, physical, and geochemical information about metals and their interactions with the environment. An overview of conceptual models, metal sources, and relative mobility of metals under different geochemical conditions is presented, followed by a discussion of some important physical and chemical properties of metals that affect their mobility, bioavailability, and toxicity. The physical and chemical properties lead into a discussion of the importance of the chemical speciation of metals. Finally, environmental and geochemical processes and geochemical barriers that affect metal speciation are discussed. Some additional concepts and applications are briefly presented at the end of this report.

Abstract Historical production of metals in the western United States has left a legacy of acidic drainage and toxic metals in many mountain watersheds that are a potential threat to human and ecosystem health. Studies of the effects of historical mining on surface water chemistry and riparian habitat in the Animas River watershed have shown that cost-effective remediation of mine sites must be carefully planned. of the more than 5400 mine, mill, and prospect sites in the watershed, ∼80 sites account for more than 90% of the metal loads to the surface drainages. Much of the low pH water and some of the metal loads are the result of weathering of hydrothermally altered rock that has not been disturbed by historical mining. Some stream reaches in areas underlain by hydrothermally altered rock contained no aquatic life prior to mining. Scientific studies of the processes and metal-release pathways are necessary to develop effective remediation strategies, particularly in watersheds where there is little land available to build mine-waste repositories. Characterization of mine waste, development of runoff profiles, and evaluation of ground-water pathways all require rigorous study and are expensive upfront costs that land managers find difficult to justify. Tracer studies of water quality provide a detailed spatial analysis of processes affecting surface- and ground-water chemistry. Reactive transport models were used in conjunction with the best state-of-the-art engineering solutions to make informed and cost-effective remediation decisions. Remediation of 23% of the high-priority sites identified in the watershed has resulted in steady improvement in water quality. More than $12 million, most contributed by private entities, has been spent on remediation in the Animas River watershed. The recovery curve for aquatic life in the Animas River system will require further documentation and long-term monitoring to evaluate the effectiveness of remediation projects implemented.

Abstract Base flow water in Leavenworth Creek, a tributary to South Clear Creek in Clear Creek County, Colorado, contains copper and zinc at levels toxic to aquatic life. The metals are predominantly derived from the historical Waldorf mine, and sources include an adit, a mine-waste dump, and mill-tailings deposits. Tracer-injection and water-chemistry synoptic studies were conducted during low-flow conditions to quantify metal loads of mining-impacted inflows and their relative contributions to nearby Leavenworth Creek. During the 2-year investigation, the adit was rerouted in an attempt to reduce metal loading to the stream. During the first year, a lithium-bromide tracer was injected continuously into the stream to achieve steady-state conditions prior to synoptic sampling. Synoptic samples were collected from Leavenworth Creek and from discrete surface inflows. One year later, synoptic sampling was repeated at selected sites to evaluate whether rerouting of the adit flow had improved water quality. The largest sources of copper and zinc to the creek were from surface inflows from the adit, diffuse inflows from wetland areas, and leaching of dispersed mill tailings. Major instream processes included mixing between mining- and non-mining-impacted waters and the attenuation of iron, aluminum, manganese, and othermetals by precipitation or sorption. One year after the rerouting, the Zn and Cu loads in Leavenworth Creek from the adit discharge versus those from leaching of a large volume of dispersed mill tailings were approximately equal to, if not greater than, those before. The mine-waste dump does not appear to be a major source of metal loading. Any improvement that may have resulted from the elimination of adit flow across the dump was masked by higher adit discharge attributed to a larger snow pack. Although many mine remediation activities commonly proceed without prior scientific studies to identify the sources and pathways of metal transport, such strategies do not always translate to water-quality improvements in the stream. Assessment of sources and pathways to gain better understanding of the system is a necessary investment in the outcome of any successful remediation strategy.

Abstract From the early 1900s through the 1950s the Silver Crescent mine and mill processed lead, zinc, and silver from ore found in the Precambrian metasedimentary rocks of the Belt Supergroup. Approximately 150,000 cubic yards of tailings and waste rock were deposited in the floodplain of Moon Creek less than 2 miles upstream of what is now a residential area. The actively eroding tailings impoundments were a source of heavy metal contamination to the surface and groundwater flowing through the site. The U.S. Forest Service began a CERCLA non-time-critical removal action at the Silver Crescent mine in 1998. Removal action goals included reduction of particulate and dissolved metal loading into Moon Creek and local groundwater. These goals were successfully achieved in part by incorporating the tailings and waste rock dumps into an on-site capped repository. The nearly $2 million Silver Crescent removal action construction phase was completed in late 2000 with the final habitat restoration phase scheduled for completion in 2007.

Abstract Abandoned or inactive mercury mines are found throughout the western United States. Mercury contamination from these mines has migrated into a variety of different media in varying forms. Cleanups and mitigation projects have been undertaken by various agencies and private entities at a number of these mines, although many remain to be addressed. Although each cleanup has similar objectives, such as source control, the methods employed in each area of the site may differ. By having an understanding of mercury and its effects and assessing different methods used at mercury-mine cleanups, future actions can be more effective at addressing the variety of issues posed by mercury contamination at former extraction and processing sites. This paper provides background on mercury, its occurrences, its health effects, and the mercury mining process. Four cleanup sites that utilized different methods for addressing mercury contamination illustrate how different sources at abandoned mercury mill sites may be addressed to mitigate impacts.

Abstract Remediation of uranium mine overburden and an acidic mine pond at the White King–Lucky Lass mines near Lakeview, Oregon was completed in November 2006. The site was remediated under Superfund due to risk from arsenic and radium-226 in overburden soils. Separate clean-up standards were developed for each mine site for arsenic and radium-226 due to differing ore-body geochemistry. Gamma surveys were used to identify overburden with elevated radium-226 activities and to provide confirmation of visual clean-up of materials. Because arsenic is collocated with radium-226 at the White King mine, gamma surveys reduced the number of arsenic confirmation samples. Secularequilibrium in the uranium-238 decay series was used to determine the extent of leaching of uranium-238 and daughter products from overburden to groundwater. Trilinear geochemical analysis distinguished mineralized groundwater within the ore bodies from regional groundwater and detected any influence from seepage from overburden piles. Remedial actions include neutralization of an acidic mine pond and consolidation of elevated-activity overburden into a pile with a soil/rock cover at White King mine. Ecological toxicity studies determined that neutralization of the pond would provide a benthic community supportive of aquatic wildlife. An overburden pile at the Lucky Lass mine and disturbed areas were covered with clean soil. The remedial actions comply with State of Oregon siting regulations, which required removal of radioactive overburden from the 500-year flood plain. Protection of human health is assured by institutional controls to prevent use of mineralized groundwater and by fencing to prevent site access.

Abstract Acidic metal-contaminated drainages are a critical problem facing many areas of the world. Acid rock drainage results when metal sulfide minerals, particularly pyrite, are oxidized by exposure to oxygen and water. The deleterious effects of these drainages on receiving streams are well known. To address this problem, efforts are being made to use biological processes as an innovative, cost-effective means for treating acidic metal-contaminated drainage. Biological sulfate reduction (BSR) technology can be adapted to diverse site conditions and water chemistry. The Lilly mine near the community of Elliston, Montana, illustrates some of the specific conditions that can challenge effective application of BSR technology.

Abstract Modern large-scale gold mining by cyanide leaching of low-grade ore generates a large volume of process fluids. Reduction and disposal of these fluids presents unique challenges. Leaching solutions, tailings dewatering, and even postmining pit lakes must be managed both in the immediate short term and over decades or longer. Methods for reducing influx to these sources with covers and capillary breaks as well as attenuating, reducing, and disposing of them via above and subsurface land application, evaporation, and vegetation, both xeric and in engineered wetlands, among other techniques, are an evolving art still requiring an adequate base of data and observable experience. Predictive modeling of fluid volume and behavior has proved very inaccurate over both shorter and longer time intervals. Climatic extremes and intensity of precipitation events compound the problem in arid areas. Ecological risk assessment is used to estimate exposure to contaminants of concern. Experience has demonstrated the inadequacy of predictions about process fluid management postclosure, and the need for comprehensive fluids bonding both for short-term contingencies such as bankruptcy and for long-term effluent disposal maintenance and monitoring.

Abstract An important aspect of planning a new mine or mine expansion within the modern regulatory framework is to design for ultimate closure. Sampling and monitoring for closure is a form of environmental risk management. By implementing a sampling and monitoring program early in the life of the mining operation, major costs can be avoided or minimized. The costs for treating mine drainage in perpetuity are staggering, especially if they are unanticipated. The Metal Mining Sector of the Acid Drainage Technology Initiative (ADTI-MMS), a cooperative government-industry-academia organization, was established to address drainage-quality technologies of metal mining and metallurgical operations. ADTI-MMS recommends that sampling and monitoring programs consider the entire mine-life cycle and that data needed for closure of an operation be collected from exploration through postclosure.

Abstract This volume documents interesting approaches, techniques, and practical scientific considerations associated with mine site remediation. It also highlights how various federal, state, and local agencies and organizations are trying to bring the best science possible to bear on this serious problem. Some chapters focus on specific methods for characterization, particular contaminant issues, and impacts from the release of hazardous substances from mine and mill sites. Others describe successful response actions, technologies, or practical approaches for addressing contaminant releases to the environment.

Abstract This chapter summarizes the processes and effects of the most notable catastrophic mass movement events in South America in the twentieth century. We present 23 case histories of individual and regional landslide events, beginning at the northeast terminus of the Andes Mountains in Venezuela, proceeding counterclockwise down the Pacific Coast to the southern Andes of Chile and Argentina, and ending with discussion of catastrophic regional mass movements in the Brazilian Highlands. The types of landslides involved in these disasters ranged from high-velocity rockslides and rock or debris avalanches to high- to medium-velocity debris flows and mudflows. Most casualties were caused by high-velocity debris avalanches and high-to medium-velocity, highly mobile, long-runout debris flows. A common, and particularly devastating, regional occurrence consisted of earthquake-triggered slides on steep slopes covered with saturated residual soils; these slides were rapidly transformed into very fluid, high-velocity debris avalanches, which in turn changed into devastating debris flows that ran out into populated areas on valley bottoms.

Abstract In December 1991, 11.8 ± 2.4 × 10 6 m 3 of rock and ice fell from Mount Cook (3754 m), the highest peak in New Zealand's Southern Alps. It fell 2720 m in 2 min and traveled 7.5 km (averaging 60 m/s). It generated a magnitude (M L ) 3.9 earthquake, becoming finely comminuted and doubling in mass through erosion. In December 1991, rockfalls began at Mount Fletcher (2467 m) 30 km northwest of Mount Cook. They continued until the ridge north of Mount Fletcher fell in rock avalanches in May and September 1992. They dropped 1440 m along similar 3.8 km paths in 50 s, generating magnitude 2.8 and 2.7 earthquakes. The first displaced 7.8 × 10 6 m 3 of water from a lake, the second, ~5 × 10 6 m 3 . In February 1996, rockfalls of ~10 5 m 3 fell from Mount Thomson (2642 m), 15 km southwest of Mount Cook. It was about an annual event in the park, and a 10-year event at Mueller Glacier. The sequence was similar to earlier phases at Mount Fletcher. The collapses all were of steep, east-facing slopes of intensely fractured rock on the hanging wall of the Main Divide fault. The larger three were of cohesionless, anisotropic materials having weaknesses along steeply dipping joints almost parallel to, but steeper than the slope. Initial failures were on lower, but steeper slopes. Retrogressive failures quickly took the entire slopes. The peaks are at limiting slope equilibrium. Collapse is their major erosion process, maintaining relief in balance with uplift and valley erosion. The hanging wall of the Main Divide fault has the fastest uplift rate, and the highest frequency of failure. The frequency of >10 6 m 3 collapse is 1 per 20–30 yr.

Abstract The Val Pola rock avalanche began when a sagging slope failed due to toe unloading. The mass then plunged down into a narrow valley from a considerable height, crossed the valley, parted, rebounded, and, in part, ran back up to the source slope. Seven men were killed in this stage. The destabilization of this 34 × 10 6 m 3 rock mass (mostly diorite) was triggered by heavy rainfalls that caused shallow landslides on the Val Pola sides and debris flows along the Val Pola thalweg. These processes resulted in a 35 m deepening of the canyon along the toe of the sagging slope. The morphology of the accumulation is mostly characterized by frequent, aligned hummocks and depressions, by reverse runup ridges, and by a narrow, 900-m-long, tongue-like downstream extension. The interaction between the moving mass and local morphology resulted in a relatively moderate runout and an unusually high degree of spreading. The north arm of the rock avalanche displaced the water of a preexisting landslide-dammed lake, generating a wave that killed 22 people more than 2 km upstream. A new and greater lake was formed as a consequence of the event. The systematic identification of sagging slopes and the establishment of reference geotechnical models are suggested for hazard prevention and emergency management.