Appendix B

Potential Environmental Impacts of Hardrock Mining

INTRODUCTION

From exploration through post-closure, hardrock mining has the potential to cause environmental impacts. In addition to the obvious disturbance of the land surface, mining may affect, to varying degrees, groundwater, surface water, aquatic and terrestrial vegetation, wildlife, soils, air, and cultural resources. Actions based on environmental regulations may avoid, limit, control, or offset many of these potential impacts, but mining will, to some degree, always alter landscapes and environmental resources. Regulations intended to control and manage these alterations of the landscape in an acceptable way are in place and are continually updated as new technologies are developed to improve mineral extraction, to reclaim mined lands, and to limit environmental impacts.

Some past mining practices have undeniably led to many of the potential impacts discussed in this appendix, and specific references are provided to describe the impacts in more detail where available. Although the committee was not successful in obtaining much information on recent environmental impacts at hardrock mine sites, the following three examples were obtained from a variety of sources, as listed below.

  • Cyanide from a mine in Idaho was found to be contaminating a salmon stream in early 1999 (Idaho Division of Environmental Quality, May 21, 1999 News Release). The mine in question is currently in temporary shut down because the ore reserves were lower than expected. Cyanide was detected in routine quarterly monitoring conducted by company personnel, and the source of contamination is believed to be a lined tailings impoundment (personal communication, Nick Ceto, EPA Region 10).

  • The Colorado Department of Public Health and Environment (CDPHE), Water Quality Control Division issued a notice of violation and cease and desist order for a gold mine that operated from 1989 until 1996 and is now in closure (notice of violation dated August 20, 1999, CDPHE).



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HARDROCK MINING ON FEDERAL LANDS Appendix B Potential Environmental Impacts of Hardrock Mining INTRODUCTION From exploration through post-closure, hardrock mining has the potential to cause environmental impacts. In addition to the obvious disturbance of the land surface, mining may affect, to varying degrees, groundwater, surface water, aquatic and terrestrial vegetation, wildlife, soils, air, and cultural resources. Actions based on environmental regulations may avoid, limit, control, or offset many of these potential impacts, but mining will, to some degree, always alter landscapes and environmental resources. Regulations intended to control and manage these alterations of the landscape in an acceptable way are in place and are continually updated as new technologies are developed to improve mineral extraction, to reclaim mined lands, and to limit environmental impacts. Some past mining practices have undeniably led to many of the potential impacts discussed in this appendix, and specific references are provided to describe the impacts in more detail where available. Although the committee was not successful in obtaining much information on recent environmental impacts at hardrock mine sites, the following three examples were obtained from a variety of sources, as listed below. Cyanide from a mine in Idaho was found to be contaminating a salmon stream in early 1999 (Idaho Division of Environmental Quality, May 21, 1999 News Release). The mine in question is currently in temporary shut down because the ore reserves were lower than expected. Cyanide was detected in routine quarterly monitoring conducted by company personnel, and the source of contamination is believed to be a lined tailings impoundment (personal communication, Nick Ceto, EPA Region 10). The Colorado Department of Public Health and Environment (CDPHE), Water Quality Control Division issued a notice of violation and cease and desist order for a gold mine that operated from 1989 until 1996 and is now in closure (notice of violation dated August 20, 1999, CDPHE).

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HARDROCK MINING ON FEDERAL LANDS The cause of the issuance was the discharge of manganese and sulfate that are leaching from backfill materials to a nearby creek through groundwater flow. The South Dakota Department of Environment and Natural Resources (DENR) issued a notice of violation and order for compliance to a gold mine for violation of the South Dakota Water Pollution Control Act (notice of violation, dated September 5, 1998, South Dakota DENR). The mine was found to be discharging effluent into streams in excess of permit levels for cadmium, copper, zinc, and total suspended solids, and its discharge failed a portion of the acute whole effluent toxicity test. Permit levels were exceeded once in 1996, twice in 1997, and nine times in 1998. In addition, the company failed to conduct daily monitoring of its effluent after the June 1998 violations and failed to promptly send samples for analysis, resulting in exceedance of holding times, both of which also constituted violations of its permit. As discussed above, these examples are not necessarily representative of environmental impacts at all modem mines, but they do indicate that environmental impacts from some hardrock mining operations continue to exist under current regulatory conditions. However, the full extent of environmental problems at modern mine sites will not be known until better information on hardrock mine sites is collected and analyzed, as discussed in Chapter 3. The Committee addresses the issue of mining-related impacts by presenting a discussion of the environmental impacts that have occurred, and that may still occur in some cases, even with regulations in place. It must be emphasized that these potential impacts will not necessarily occur, and when they do, they will not occur with the same intensity in all cases. Many of the impacts discussed in this appendix would violate current regulatory requirements and standards and would be subject to enforcement actions. Nevertheless, because some impacts continue, an understanding of the potential for mining to cause environmental impacts is essential to assessing and improving the regulation of hardrock mining on Federal lands. CUMULATIVE EFFECTS The environmental impacts of a single mining operation are broadly proportional to the size of the mine, although these vary depending on: the character of the mineral body and surrounding rock; the character of the environment directly and indirectly affected by mining;

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HARDROCK MINING ON FEDERAL LANDS the character of the surrounding human environment; the nature of the mining operation; and the extent and effectiveness of actions to ameliorate the environmental impacts of mining. Although a single mining operation creates its own set and degree of environmental impacts, a regional concentration of mines poses problems of cumulative impacts. For example, the number of gold mines along the Carlin Trend in Nevada and copper mines in the Miami and Globe area of Arizona poses environmental issues that can be addressed only if adequate consideration is given to their combined effects, along with those of other activities such as agriculture and timbering. For example, groundwater withdrawal at a single mine has the potential to create a deep cone of depression in the local aquifer. As this cone expands over time, it may join those created by neighboring mines and lower the regional water table, which in turn may decrease or terminate flow in streams and springs some distance from the mines. Other regional uses of groundwater, such as agriculture and urbanization, contribute to the cumulative effects on the water table, but no one activity is fully responsible for this impact. Similarly, potentially contaminated drainage or leachate from waste rock dumps, heap leach pads, or tailings ponds at a single mine may not be sufficient to lower stream water quality below acceptable concentration levels. But, when combined with discharges from neighboring mines and other contaminant sources, such as urban runoff and agriculture, the cumulative effects, especially in the semi-arid conditions of much of the West, has the potential to produce unacceptably high mass loadings. In the Carlin Trend in Nevada, the Humboldt River receives discharged groundwater from the dewatering activites of several mines. Because the river ends in a closed-basin playa (Humboldt sink), the cumulative impacts of these discharges, along with highly contaminated irrigation return flows, have the potential to affect biota and water quality in this evaporative system. In addition, sediments and periphyton in the Humboldt River can concentrate constituents such as metals and metalloids over time and adversely affect macroinvertebrates. The USGS, the Forest Service, and other agencies are currently studying some of the cumulative impacts in the Humboldt River system. Another example of cumulative impacts involves placer mining and suction dredging operations, which disturb streambeds and produce suspended sediments. The disturbed sediment usually settles out a short distance downstream if the activity is properly timed and controlled. However, there has been little evaluation of the cumulative impacts of sequential sediment dredges or placer mines.

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HARDROCK MINING ON FEDERAL LANDS Other issues involving cumulative impacts include the potential for contamination of groundwater aquifers, fugitive dust and air pollution from tailings and road surfaces, smelter emissions, and landscape degradation from large mine operations in the same general area. While most of the possible environmental effects of mining discussed in the following sections are in the context of individual mine operations, the potential for cumulative impacts also should be considered. LONG-TERM MONITORING Monitoring of environmental conditions and responses to human activities is needed to measure changes in the environment and to determine the effectiveness of mitigation procedures. There are different types of, or reasons for, monitoring (MacDonald et al., 1994): trend monitoring to measure changes in environmental parameters of interest (e.g., water quality components); baseline monitoring to characterize conditions prior to any action; implementation monitoring to assess whether an action was carried out as planned; effectiveness monitoring to determine whether a planned activity had the desired effect; project monitoring to assess the impact of an activity on an environmental component of concern (e.g., mining on water quality or stream biota); validation monitoring to validate particular predictive models used for planning (e.g., pit lake models); and compliance monitoring, to determine whether certain environmental criteria are being met (e.g., metal or pH standards in water). Each of these types of monitoring may be applicable to the various stages of mining from exploration, through development and extraction, to closure, reclamation and post-closure. Baseline monitoring is essential to establish conditions prior to any mining activity and to provide the conditions against which future monitoring data can be compared. Monitoring during mining should address the implementation and effectiveness of environmental controls and compliance with regulations. Of equal concern is long-term monitoring to evaluate environmental protection during post-closure conditions and to validate predictive models.

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HARDROCK MINING ON FEDERAL LANDS Monitoring to address the effectiveness of mine closure activities and to validate predictive models related to closure must be long term for several reasons. First, conditions created during active mining operations might not lead to environmental impacts until after closure. This is especially true for water quality conditions, such as acid generation and migration of leachate from mine wastes to groundwater or surface water. Second, although design of post-closure conditions may have been based on best available information and technologies, unexpected events can alter future environmental conditions. The best available technologies may not have been sufficient to address, for example, long-term (decadal) changes in climatic patterns that may alter amounts and timing of precipitation events that influence the effectiveness of soil covers placed on heap leach pads and waste rock piles. In addition, post-closure use of these surfaces by recreationists, cattle, or other disturbances may be greater than expected, resulting in unanticipated erosion and releases from these closed areas. Third, predictive models used to design or plan closure procedures must be tested through monitoring to determine their accuracy. For example, the lack of robustness of pit lake models may lead to uncertainty about future conditions of surface and groundwater quality and quantity. Fourth, models designed to predict long-term responses of local and regional environmental parameters to post-closure conditions may be site specific and ignore the cumulative effects of other activities in the area, as discussed above. Finally, monitoring to test predictions, calibrate models, and follow long-term trends of resources, such as groundwater levels and stream flows and chemistry, will produce information that is useful to researchers developing long-term predictive models. For this reason, long-term monitoring must be properly designed to measure those attributes that offer useful data on changes and/or sustainability of resources affected by mining activity and post-closure conditions. WATER QUALITY If not mitigated through regulation and prevention strategies, hardrock mining can have long-term impacts on water quality, which are defined in the Clean Water Act to include not only chemical but also biological and physical attributes. The water quality issues discussed below include metals and cyanide, acid drainage, pit lakes, and placer mining. Each of these issues also can have long-term impacts on water chemistry, aquatic biota, and aquatic habitat.

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HARDROCK MINING ON FEDERAL LANDS Metals and Cyanide Hardrock mining of metalliferous deposits has the potential to release to the environment metals, metalloids (e.g., arsenic, antimony, selenium), sulfate, acid drainage, cyanide, nitrate, suspended solids, and other chemicals used in mining processes. These constituents are often present in waste rock, tailings, other mine waste materials, pit walls, and pregnant and barren solution ponds. Once the waste materials come in contact with water, the contaminants can be chemically leached and/or physically mobilized from the waste sources and transported downgradient to groundwater and surface water. Sediments and down-gradient soils may become contaminated and act as a secondary source of contamination to surface water and groundwater. Unless the waste materials are removed or effectively isolated from the environment by capping and/or lining, releases of contaminants, especially metals, can continue for long periods of time. Some of these contaminants, such as cyanide in surface water and surface impoundments, nitrate, and sulfate, can be broken down or transformed into relatively innocuous constituents through microbial activity or photolytic reactions. The fate of cyanide and metal-cyanide complexes in groundwater is less well understood. The impact of metals and metalloids to down-gradient or downstream waters may be minimized by adsorption onto soils and sediment, precipitation of solid compounds, or dilution by groundwater or surface water. However, unlike many organic compounds, metals cannot be transformed to other compounds. Metals and metalloids can be transformed from one aqueous species to another or from one environmental medium to another, but metals are not lost through biogeochemical transformations. It is this lack of degradation that renders metals a long-term water quality concern. Acid Drainage Acid drainage that contains metals is another potential long-term water quality issue at some mine sites. The nature of the acid drainage reaction is such that it is difficult to stop the production of acid once it has begun. Lead mines that were operating at the time of the Roman Empire are still producing acid drainage 2,000 years later. In addition, acid drainage may take years to form or become a water quality concern. Although the factors that create acid drainage and that may minimize its impacts are well understood, there is little long-term monitoring data to use in predicting the extent of acid drainage at a given mine site. If a laboratory test shows that acid drainage will be produced, it is even more difficult to predict when it will start, how acidic it will be, or how high the metal concentrations will be. Predictability issues associated with acid drainage are

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HARDROCK MINING ON FEDERAL LANDS discussed in the following section in Appendix D (see “Water Quality” in Appendix D). Carbonate-bearing waste rock or tailings can produce drainage with an alkaline or near-neutral pH, but it will still contain elevated concentrations of components such as cadmium, zinc, manganese, arsenic, molybdenum, and selenium. Iron may or may not be elevated in circumneutral drainage water, depending on the oxidation state of the water. Methods for prevention of acid drainage fall into two categories, those that prevent the acid generation from occurring and those that treat the acid generation at the source so that no drainage occurs. Although the latter is technically a treatment method, it stops the acid from draining and is different enough from the typical collect-and-treat methods to be considered here an acid drainage prevention method. The most widely used methods for preventing acid generation include capping and sealing acid-generating rock to prevent air and water from reaching the rock. Such capping will require long-term maintenance to ensure that erosion, animal burrows, or other activities do not compromise the integrity of the cap. A variation on this method used in drier climates is to provide a less effective cap and a good vegetative cover, which will allow evapotranspiration of most of the water infiltrating into the pile. While not 100% effective in stopping water, such a cover may provide enough of a barrier to minimize the acid generation to levels that will not be detectable in ground or surface waters. Another variation on capping, which is practiced widely outside the United States, is burial of acid-generating materials in water to prevent the contact with air that is necessary to start the process. This is accomplished by placing the waste in a body of water, or by covering the top of a tailings pond with water once tailings deposition is completed. Some mines both in and outside the United States place potentially acid-generating materials into pits that are expected to fill with water. Once the pit lake is formed, the material no longer is exposed to air. To remain effective, water must always be over the material; this therefore requires long-term maintenance. There are also specially developed chemical additives that, when applied to waste rock or spent ore piles prevent acid generation (for example, phosphate and surfactants.) Many of these additives are new and have not been studied for long-term effectiveness. These additives also can be expensive when used to cover a large area. Certain types of recovery processes make it cost effective to separate the potentially acid-generating constituents in the ore from the rest of the ore. These methods concentrate the metals and sulfides, but render the majority of the ore benign and available for easy disposal. The concentrated material, which would have potentially more severe environmental impacts, can then be treated more cost effectively than the larger volume of spent ore material.

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HARDROCK MINING ON FEDERAL LANDS The most common method for treating in place to prevent acid drainage is to mix the acid-generating materials with a neutralizing material such as lime. The materials can be layered with lime or physically mixed together before or after disposal. The neutralizing material must be placed in ratios high enough to counteract all the acid-generating potential of the other material. The long-term effectiveness of this type of mixing is not known, and the relative rates of exhaustion of acid generation and neutralization have not been well studied. Pit Lakes Pit lakes have the potential to create long-term impacts on the environment that include major surface disturbances and alterations of pre-mining water quality and quantity. If water in a pit lake is contaminated and does flow to down-gradient groundwater and possibly to surface water, the impact of pit water on down-gradient waters will be another long-term water quality issue. Even if pit water does not flow down gradient, the concentration of metals, other contaminants, and salinity in the pit through evaporation may become a long-term water quality issue, especially for migratory birds and terrestrial wildlife. For example, waters of the Berkeley pit in Butte, Montana, were lethal to migrating snow geese that used the lake as a stopover in 1995 (Hagler Bailly Consulting, Inc., 1996). Most states are just beginning to establish water quality standards or designated uses for pit lakes. Standards that are established should be protective of designated uses, such as use by wildlife and migratory birds. The scientific basis for establishment of water quality standards for protection of wildlife and migratory birds needs more research. Predictability issues associated with pit lakes are discussed in Appendix D. Surplus Water Discharge Groundwater withdrawn to dewater pits is often discharged into local streams and drainages. These waters have the potential to be higher in total dissolved salts, metals, and other chemicals than the streams into which they are discharged. Although the normal flow of the stream may dilute these chemicals, they may become concentrated in stream sediments and periphyton, which can adversely affect some aquatic biota. Over the long term, this problem can become more serious if the stream ends in an evaporative sink that allows the contaminants to accumulate in the water column and sediments, which provide habitat and food for waterfowl and migratory birds.

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HARDROCK MINING ON FEDERAL LANDS Road Construction Road construction during several phases of mineral exploration and extraction may disturb the soil surface sufficiently to create an excess of loose sediment that is carried off the site into local streams. Sediment may also be eroded from waste rock piles and may be carried by storm events down gradient into stream channels. The amount of sediment entering streams is a function of the quality of the road construction, the closeness of the streams, the types of hydrological events in the region that drive sediment transport, and the effectiveness of the erosion control measures employed. Contamination from Railroads Railroad beds constructed in mining areas may have been composed of mine wastes. This results in the placement of mine wastes over a greater area than normally anticipated in a mine operation. Railroads commonly have been located in valley bottoms where there is less topographic variability. Consequently, railroad beds historically have been placed adjacent to rivers. Storm events may leach chemicals out of the railroad beds into the streams or adjacent drainages. Occasional spills from rail cars carrying toxic materials may also contaminate surface waters. WATER QUANTITY Minewater Discharge to Streams Surplus water accumulated from mine dewatering is, in some cases, discharged into nearby streams. The timing and amount of discharge has the potential to affect the down-gradient riverine ecosystem. Riparian vegetation has evolved to disperse seed, and recruit young plants on the declining limb of spring floods. If surplus water discharge occurs after this period, young plants established in the spring will be inundated and lost. Surplus flows also may erode or straighten stream channels, reducing availability of natural sandbar recruitment sites for riparian vegetation (Stromberg and Patten, 1992). Increased velocity of surplus flows also may dislodge aquatic biota such as attached macroinvertebrates, or disrupt fish habitat. For example, alteration of flows from mine water discharge could increase turbidity in streams and cause increases in embeddedness of gravels used for spawning.

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HARDROCK MINING ON FEDERAL LANDS Groundwater Withdrawal Groundwater withdrawal for mineral processing and to prevent filling of open pits and underground excavations has the potential to affect local and regional groundwater quantities and levels. In the former case, much of the water used is kept on site, while in the latter the excess water may be temporarily stored in impoundments but eventually may be discharged into local streams. In both cases, groundwater withdrawal may affect the local water table. For example, groundwater withdrawn from the Santa Cruz River Basin in southern Arizona for mineral processing at a nearby copper mine is lowering the water table by many meters, and is drying up the river. The impact on riparian vegetation is significant (Patten et al., 1994). A groundwater pump test at several hundred feet of depth for a new copper mine in Arizona was shown to alter surface flows of a small perennial stream by 75 acre ft/year (a significant reduction for the size of the stream) through lowering of the shallow alluvial water table that supported surface flows (Carlota Mine EIS). This evidence of impacts of groundwater withdrawal on surface flows can be extended to the potential of surface flow declines resulting from groundwater withdrawal for pit dewatering. Of greater concern are the potential cumulative effects of dewatering wells and groundwater wells for processing associated with several neighboring mines. The cones of depression in the deep aquifer resulting from groundwater withdrawal may coalesce and affect regional spring and stream flows that are dependent on the aquifer. Models of potential effects of groundwater withdrawal from deep aquifers in Nevada show that the decline in the shallow basin-fill aquifer and regional water table may be delayed for several decades following initiation of groundwater pumping (Schaefer and Harrill, 1995). The delay is partly due to the time taken to dewater a large regional aquifer. Pit Lake Interception of Groundwater While groundwater is withdrawn to prevent filling of the mineral extraction pits, abandonment of the pits may create lakes that have the potential to affect the local shallow aquifer. If the pit is excavated on sloping terrain, the shallow aquifer may be intercepted on the upper edge of the pit and its water may drain. The shallow aquifer is interrupted and little or no flow will continue into the aquifer downslope of the pit depending on the local head of the deeper aquifer. Water input to the pit lake from the shallow aquifer may eventually interact with a deeper aquifer at lower levels in the lake. The hydrological balance among these entities, the pit lake and the shallow and deeper aquifer, is not well understood (see “Pit Lake Water Quality” in Appendix D).

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HARDROCK MINING ON FEDERAL LANDS Runoff from Hardened Surfaces Construction of roads, parking lots, buildings, and the like reduces the amount of absorption surface in the mining area. Similar to an urbanized area, a mine area has the potential to produce more runoff to nearby streams than would be expected without alteration of the ground surface. The runoff may carry contaminants, for example, oils from vehicles and sediment from the roads or roadside areas, but perhaps the greatest concern is the acceleration of runoff during storms and a reduction in moisture percolating into the ground. This has the potential to affect stream hydrological functions, to change sediment transport characteristics, and to alter instream habitat for fish and other aquatic organisms. AQUATIC BIOTA Aquatic Biota Response to Metals and Cyanide Most metals and cyanide are toxic to aquatic life (e.g., fish, macroinvertebrates) at low concentrations (Borgmann and Ralph, 1984; Sorenson, 1991; Marr et al., 1995a,b, 1996). Aquatic life criteria are designed to protect aquatic life from such impacts as death and reproductive and growth disorders. For example, at 100 mg/l hardness, the chronic (long-term) aquatic life criteria for dissolved cadmium and copper are 2.24 and 8.96 mg/l, respectively. At lower hardness values typical of mountain streams, the criteria are even lower. For example, at a hardness of 25 mg/l as CaCO3, which is typical of a number of mountain streams, the chronic criteria for dissolved cadmium and copper are 0.18 and 2.74 mg/l, respectively (EPA, 1996). Very low concentrations of metals, even below the chronic criteria, may cause fish to avoid certain waters and impair their growth (DeLonay et al., 1995; Marr et al., 1996). This is an issue for anadromous (migrating from fresh to salt water) fishes such as certain threatened and endangered salmonids, which may avoid streams with low metal concentrations, resulting in the elimination of that species from the watershed. The presence of natural organic acid can decrease or delay the toxicity of metals to aquatic biota (Playle et al., 1993; Azenha et al., 1995; MacRae et al., in press; Marr et al., 1999). Although there are no specific aquatic life standards or criteria for aquatic sediments, macroinvertebrates, which serve as food for fish, live in sediments and eat periphyton (algae) that coat rocks in streams. Both sediments and periphyton often contain metals at concentrations many times higher than their concentration in overlying surface water. The impact of metals from mining activities on macroinvertebrates has been shown in a number of studies (Clements et al., 1988; Kiffney and Clements, 1993; Nelson and Roline, 1993; Clements, 1994; Kiffney and Clements, 1996a,b; Beltman et al., 1999). When water quality

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HARDROCK MINING ON FEDERAL LANDS in streams containing acid drainage and metals from mining activity is improved, macroinvertebrate communities have been shown to recover (Nelson and Roline, 1996). Metal- or acid-rich groundwaters can also contaminate surface waters. Aquatic Biota Response to Acid Drainage If acid drainage enters surface water, metals in the drainage will have the same types of effects discussed above under metals and cyanide. Fresh water biota also have certain pH requirements, usually between pH 6.5 and 9 (EPA, 1985), and acid conditions can cause adverse conditions for fish (Bolis et al., 1984). Metals in acid drainage, after being diluted downstream by higher pH waters, can be precipitated out of solution and can coat streambed material with an iron-rich and heavy metal-rich cement. The cement can impair streambed habitat for fish and macroinvertebrates by physically embedding gravels. When the spaces between gravels are embedded with fine-grained sediment or floc, egg survival is threatened by a lack of oxygen. Higher hardness and alkalinity can decrease toxic responses of aquatic biota to metals (Brown et al., 1974; Howarth and Sprague, 1978; Chakoumakos et al., 1979; Lauren and MacDonald, 1986; Erickson et al., 1996). Mine drainage water may have higher hardness values than nearby surface waters because of increased leaching of silicates and other materials in the rocks, efflorescent salts, and calcium- and magnesium-containing solids, but the low pH values of acid drainage almost always result in lower alkalinity values. Impact of Placer Mining and Suction Dredging on Aquatic Biota Placer (mechanized) mining in active streams and suction dredge mining disturb to some degree streambed sediments, which provide habitat for macroinvertebrates and spawning habitat for salmonids (redds). Fine-grained sediment, if disturbed by placer operations, may move downstream and cause damage to spawning grounds for fish or to benthic biota. If flows are high enough, and there is sufficient sediment upstream, the streambed may return to near its original characteristics after springtime high flows. Depending on the degree of disturbance during low-precipitation years, the streambed may remain unsuitable for aquatic life habitat until high flows return it more to its original characteristics. The U.S. Geological Survey is investigating the environmental impact of suction dredge mining on turbidity and metal concentrations in an Alaskan river (Wanty et al., 1997; Gough et al., 1997). Studies on the impact of suction dredge and mechanized placer mining on macroinvertebrate and spawning habitat should also be conducted.

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HARDROCK MINING ON FEDERAL LANDS LANDSCAPE OR ECOSYSTEM ALTERATIONS While many active mines have been developed around existing or historic mining sites, new mineral discoveries may also occur in remote, roadless, mountainous country where human activity has caused little disruption of these relatively pristine ecosystems. Early exploratory surveying by qualified geologists has no more impact on these remote areas than geological mapping or casual recreation. However, exploration activities designed to evaluate a mineral deposit have the potential to disrupt these remote locations. Development of exploration roads, use of mechanized equipment such as drill rigs or soft-wheeled off-road vehicles, or use of helicopters are all invasive activities in otherwise unaltered ecosystems. TERRESTRIAL VEGETATION General Disturbances Any disturbance of a terrestrial ecosystem, whether natural or anthropogenic, results in a change in vegetational composition. Some ecosystems are disturbance systems requiring some form of natural disturbance to maintain their particular structure and composition. For example, chaparral ecosystems are fire disturbance systems, while most riparian ecosystems are flood disturbance systems. As a consequence of natural disturbance processes, these ecosystems are maintained in an early successional stage, while removal of the disturbances will allow succession to proceed to a later successional, non-disturbance plant community. Development of roads or use of off-road vehicles, whether soft- or hard-wheeled, during exploration activities has the potential to disrupt the soil and low stratus vegetation, stimulating invasion by disturbed-site plant species (e.g., members of the mustard family). This may be little different than surface disturbance by burrowing animals, but the consequences of mining activities are potentially less localized. Small alterations of topography by exploration activities may create new habitats for hydrophytes in low areas and xerophytes on elevated terrain. These terrain changes result in localized composition changes of plant species, which may in turn alter composition of local invertebrate and other associated species. In time, most of these small changes may, through biological and physical processes, return the vegetation to a state similar to predisturbance.

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HARDROCK MINING ON FEDERAL LANDS Smelter Emissions Fumigation Plant communities adjacent to some historic mineral processing facilities have been altered by fumigation from smelter emissions (Gabriel and Patten, 1994). Uncontrolled smelters have released large amounts of sulfur dioxide (SO2) that settled on the surrounding landscape. When combined with water in plant leaves, SO2 is converted to sulfuric acid, which is often lethal to foliage and consequently the plant. Some plants are resistant to SO2 fumigation, resulting in plant communities near smelters being composed of resistant plants and devoid of non-resistant plants. With increasing distance from the pollution source, the plant community composition gradually returns to normal (Wood and Nash, 1976). Where long-term smelter emissions historically affected surrounding forests and associated soils, for example near Anaconda, Montana, Coeur D'Alene, Idaho, and Salt Lake City, Utah, much of the surrounding hillsides still are devoid of trees. Apparently, present ecological conditions at these sites are such that forest recovery is either slow or prevented by changes in soils or microclimate. Metal Toxicity Contaminants in air pollution from mining processes have the potential to affect terrestrial vegetation. Metals from uncontrolled smelter emissions contaminate soils and then are taken up by plants, or the emissions may settle on foliage and be taken up directly into the leaves. Soils, vegetation, and wildlife habitat in areas affected by smelter emissions have been shown to contain elevated concentrations of metals, and vegetation abundance and species diversity have been severely affected (Galbraith et al., 1996; Kapustka et al., 1996; LeJeune et al., 1996). Depending on the concentration of pollutants influencing plant physiology, uptake of metals and other contaminants may or may not be lethal. For example, concentration of metals in foliage of vegetation near a smelter was reduced by 50% to 100% when the smelter was not operating, and yet total foliar necrosis occurred only immediately adjacent to the smelter (Gabriel and Patten, 1995a). Plants used as indicators of pollution near a smelter had foliage metal concentrations much greater than plants growing in a pristine unpolluted area (Gabriel and Patten, 1995b). Foliage sampled near the smelter had copper concentrations nearly 800% greater and arsenic about 500% greater than foliage sampled at a non-smelter site. Uptake of metal-contaminated water and sediments by plants also causes contaminated foliage and stems in riparian and wetland areas.

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HARDROCK MINING ON FEDERAL LANDS Exotic Plant Species Selection of plant species for reclamation is based on suitability for future uses, such as grazing, resistance to abuse by future uses (e.g., overgrazing or recreational use), and tolerance of site conditions. Plant species that fit these selection criteria may be non-native species; therefore, reclamation procedures may increase the distribution of non-native species. Vehicular traffic on and off mining sites also may disperse non-native plant species into active mining areas. Off-road vehicles used for exploration purposes may carry propagules of non-native species into relatively pristine backcountry areas. This type of introduction is not unique to mining exploration (Kummerow, 1992), but invasion of non-native species into the backcountry is enhanced through mining exploration, which may be the first mechanical intrusion into some of these areas. RIPARIAN VEGETATION Valley Fill Riparian plant communities are found in valleys where stream flows and shallow groundwater support phreatophytes. Historically, some valleys have been used as areas for placing waste rock, leach pads, or tailings impoundments. Although there is greater awareness today of the ecological impacts of using valleys for deposits, valleys may, in some cases, still be used for the placement of mining facilities. Obviously, if a valley is filled, the vegetation in the valley will be destroyed. Once filled, the riparian vegetation that requires the conditions found at the bottom of the valley cannot be restored. Altered Hydrology Some mining activities have the potential to consume most of the locally available water through extensive groundwater withdrawal, which in turn may affect surface flows and shallow valley fill aquifers (Patten et al., 1994). Some mines may intercept the deep water table, potentially disrupting regional aquifers and reducing stream and spring flows (Nelson et al., 1991). Groundwater withdrawal can affect riparian vegetation some distance from a mine. Reduced flows and lowering of the alluvial aquifer directly affect phreatophytic riparian vegetation, which depends on this water source. A lowered water table will stress riparian vegetation, causing either mortality or reduced vigor (Stromberg et al., 1992, 1996; Scott et al., in

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HARDROCK MINING ON FEDERAL LANDS press). Lowered shallow alluvial aquifers may not maintain riparian vegetation, resulting in replacement of riparian species with upland species. Water Contaminants Metal-contaminated water and sediments that reach wetlands or settle along streams in the wetland or riparian zone create a contaminated substrate for plants that take up the metals and store them in foliage and stems (Sullivan, 1991). Contaminated soils and sediments from mine sites have the potential to affect bed, bank, and floodplain sediments, as well as down-gradient riparian areas and wetlands some distance from the mine. WETLANDS: HYDROLOGICAL AND SURFACE CHANGES Wetlands, like riparian ecosystems, are dependent on a continuous supply of water. Any change in regional hydrology may affect wetlands, especially in the arid West. Many arid region wetlands develop at spring orifices. The wetlands and the spring pools often support threatened or endangered species (e.g., pupfish). In Nevada, for example, springs occur throughout the desert, where the deep regional aquifer supplies water to the surface through the basin fill aquifer. These spring wetlands may be very sensitive to changes in the hydrologic head of the regional or local aquifer resulting from groundwater withdrawal by mines, agriculture, or municipal water use. There is sufficient evidence to show that small changes in the hydrologic head may lower the water table several meters, resulting in the drying up of springs and associated wetlands (Schaefer and Harrill, 1995). Wetlands also occur in depressions throughout much of the mountainous West. Off-road vehicles can greatly alter the stability of these wetlands by creating ruts that drain the water. Even use of soft-tired vehicles can produce linear depressions that create pools and tend to dry up the remaining wetland. SOIL Surface Alterations The Earth's surface supports a wide variety of organisms, but it is also susceptible to ambient environmental changes such as drought and wet cycles. Such human activities as road building or construction, whether a result of mining or other processes, have the potential to greatly alter soil surfaces and affect soils

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HARDROCK MINING ON FEDERAL LANDS to some depth. Commonly topsoil is set aside to be replaced with a hardened, durable road surface or some other facility. Topsoil may be used eventually for reclamation of the roaded area or in reclamation of other mining activities (e.g., topping for waste rock piles). Hardened road surfaces also cause runoff to the road's edge, increasing the potential for invasion of weeds. In cold climates, roads may be salted, which causes soil contamination along the roadbed. Temporary roads may sufficiently alter soil surfaces through changes in topsoil structure and chemistry to prevent short-term recovery following reclamation. Erosion Disturbance of soil surfaces by mining activities may leave soils susceptible to erosion if precautionary measures are not taken. Eroded soils have the potential to contribute to sediment output into local drainages causing reduction in water quality. Air Deposition Chemical participates and metals from smelter emissions and blowing tailings have the potential to settle on soil surfaces near some mineral processing facilities. In such cases, contamination of soils decreases with distance from the contaminant source. In a study around a copper smelter in Arizona, several metals, including iron, manganese, and copper, were found to significantly decrease in concentration in soils with distance from the smelter (Gabriel and Patten, 1994). This was true for both surface soil and soil at 25 cm depth. Plants can accumulate contaminants found in soils and may pass these along to herbivores. TERRESTRIAL WILDLIFE Disruptive Activities Exploration into relatively pristine ecosystems, although minimal in surface disturbance, has the potential to disrupt wildlife. The location of dispersed drill pads over an extended area may prevent wildlife from finding seclusion from this type of activity. Exploration roads and even tracks from soft-tire vehicles, can disrupt migration of small mammals and change behavioral patterns of larger animals. Permanent long-distance haul roads or railroads for mining purposes have the same potential impact on animal behavior as roads and railroads used for

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HARDROCK MINING ON FEDERAL LANDS other purposes, that is, they may alter migration patterns by creating barriers and fragment animal territories (Simberloff and Abele, 1982). This is especially true for smaller animals. Noise from vehicular traffic, including off-road vehicles, has the potential to disrupt wildlife (Brattstrom and Bondello, 1983), sometimes preventing normal reproductive processes because the noisy activity is located in or near a calving or whelping area for ungulates or canines, respectively. Noise from blasting also has the potential to disrupt wildlife. Although some wildlife may become accustomed to blasting noises, others will move from the area, potentially reducing the population of that species. Consumption of Toxic Plants and Animals Terrestrial wildlife, waterfowl, and migratory birds may consume plants and animals that have accumulated toxic materials. Plants growing in contaminated sediments accumulate metals in tissues (Sullivan, 1991). Bioconcentration in trophic dynamics of aquatic organisms in lakes and streams produces aquatic plants, macroinvertebrates, and fish with elevated levels of metals and other contaminants in their tissues. Consumption of these organisms by wildlife and birds continues the bioconcentration process, potentially creating toxic levels of metals and other chemicals in these organisms. Wildlife Enhancement Some environments created by mining activities have the potential to benefit wildlife. For example, abandoned mine tunnels may be used by bat communities, thus influencing closure procedures for these developments. Reclamation of waste rock sites and other surface disturbances may create extensive areas of forage that attract some species. AIR QUALITY Smelter Emissions Emissions of particulates and sulfuric acid from smelters have the potential to produce extensive regional air pollution. For example, prior to the imposition of current air quality standards, several copper smelters located in central and southern Arizona had been shown to create an extended haze and potential acid deposition over much of southern Arizona under the right climatic conditions

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HARDROCK MINING ON FEDERAL LANDS (Blanchard and Stromberg, 1987). Smelter emissions from the Sonora region of Mexico have been linked to wet sulfuric deposition and acidification of lakes in the Colorado Rockies (Oppenheimer and Epstein, 1985). Changes in lake acidity can cause changes in aquatic biotic composition and chemical processes. Fugitive Dust Unpaved roads, tailings ponds, and other disturbed areas have the potential to become sources of fugitive dust if they are not kept damp, adequately revegetated, or otherwise controlled. Mining, loading, dumping, and crushing activities are also potential sources of fugitive dust as are the surfaces of some tailings deposits. NOISE Noise can play an important role in human as well as animal behavior. Constant noise from heavy equipment operations at mines adjacent to residential communities may cause persons who are sensitive to noise pollution to move away or change their behavior to try to avoid the noise.

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