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4 Potential Impacts from Placement of Coal Combustion Residues in Coal Mines T his chapter evaluates the potential human health and environmental im- pacts posed by the placement of CCRs in mines. As discussed in previous chapters, the concentrations of sulfate and metallic compounds in CCRs are often elevated relative to the parent coal and/or surrounding deposits (see Chapter 2). Once in contact with water, these constituents can leach from CCRs and subsequently become mobilized in both ground- and surface water (see Chap- ter 3). However, the composition of this leachate varies widely based on parent coal composition, the combustion and waste-handling technologies utilized by a particular power plant, and the geochemical environment in which the CCRs are placed. This chapter examines known cases of damage that have occurred from disposing of CCRs in a variety of environmental settings to understand what conditions pose the greatest risk to human health and the environment. The review of these cases assists the assessment of the potential impacts of CCR placement in coal mines. The incidents presented in this chapter are from published accounts in the peer-reviewed scientific literature and/or are damage cases reviewed and recog- nized by the U.S. Environmental Protection Agency (EPA). In the late 1990s and revised in 2005 (USEPA, 2005a), the EPA reviewed monitoring data and identi- fied damage cases, defined as sites where contaminants exceeded drinking water or other health-based standards, usually from wells or in surface waters downgradient of CCR management sites. The EPA considered the evidence of proven and potential environmental impacts along with factors that may have contributed to these impacts, including the interaction of CCRs with water. It did not independently investigate most damage cases, but relied primarily on infor- 81
82 MANAGING COAL COMBUSTION RESIDUES IN MINES mation contained in state files. The EPA also acknowledged in the Regulatory Determination of May 22, 2000 (40 CFR Part 261) that it did not use a statistical sampling method and reviewed possible damage cases in only a subset of states. The EPA noted that given the volume of CCRs generated nationwide and the number of facilities that lack sufficient environmental monitoring and controls, especially groundwater monitoring, other cases of proven and/or potential envi- ronmental impacts are likely to exist. For the 2000 regulatory determination, EPA cited 11 proven damage cases (i.e., that met its "tests of proof"), all of which involved landfills (including some CCR monofills) or surface impoundments. Since then, the number of damage cases recognized by EPA has nearly doubled; as of 2005, EPA had recognized 24 proven damage cases involving CCR landfills and surface impoundments, and one CCR minefill is now under investigation as a potential damage case (USEPA, 2005b; Table 4.1). According to the EPA, a damage case is proven if it satisfies one or more so-called tests of proof, which include (1) scientific investigation, such as formal investigations and technical tests that demonstrate significant impacts on human health or the environment; (2) administrative ruling, such as an enforcement action; (3) court decisions, which include official court rulings and out-of-court settlements; and (4) sufficient evidence that the damages could be attributable to CCR wastes (USEPA, 1999a). During the course of the EPA's 2000 regulatory determination, public com- ments contained information on 59 additional potential damage cases. Similarly, this National Resource Council (NRC) committee received public testimony on numerous sites where it was alleged that CCR placement in coal mines has been implicated in the degradation of ground- or surface-water quality. In most of these cases, industry disputed the claims of environmental impacts made by public citizens, and in several cases, clear discrepancies in data, or in the interpre- tation of data, existed among stakeholders (EarthTech, Inc., 2000; Richardson, 2004; Kyshakevych and Prellwitz, 2005; Zimmerman, 2005). Because these pur- ported environmental impacts have not withstood the scrutiny of review by the scientific and/or regulatory communities, they are not explicitly discussed in this report. However, as discussed in Chapter 1, these local controversies were noted by the committee during its deliberations and helped it to identify research needs and formulate recommendations. ENVIRONMENTAL IMPACTS Currently, there are very few data available to indicate directly that place- ment of CCRs in abandoned or active coal mines is either safe or detrimental. In 2000 the EPA noted, "For minefilling, although we have considerable concern about certain current practices (e.g., placement directly into groundwater) we have not yet identified a case where placement of coal wastes can be determined to have actually caused increased damage to groundwater" (65 FR 32214). In its
POTENTIAL IMPACTS FROM PLACEMENT 83 TABLE 4.1 Environmental Protection Agency Proven Damage Cases Facility Type State Vitale Fly Ash Pit Landfill MA Salem Acres Landfill MA Don Frame Trucking Landfill NY PEPCO Faulkner Off-site Disposal Facility Landfill MD VEPCO/Virginia Power Possum Point Surface impoundment VA VEPCO/Virginia Power Chisman Creek Landfill VA Chestnut Ridge Y-12 Steam Plant Operable Unit 2 Surface impoundment TN Georgia Power Bowen Surface impoundment GA South Carolina E&G Canadys Plant Landfill SC Savannah River Project Surface impoundment SC Belews Lake Surface impoundment NC Hyco Lake (CP&L Roxboro) Surface impoundment NC Lansing Board Power & Light North Lansing Landfill Landfill MI Dairyland Power Old E.J. Stoneman Ash Pond-Cassville Surface impoundment WI Site WEPCO Highway 59 Landfill Landfill WI Alliant Nelson Dewey Landfill WI WEPCO Cedar Sauk Landfill Landfill WI WEPCO Port Washington Landfill WI Yard 520, Pines Landfill IN Martin Creek Reservoir Surface impoundment TX Brandy Branch Reservoir Surface impoundment TX Welsh Reservoir Surface impoundment TX Basin Electric WJ Neal Station Surface Impoundment Surface impoundment ND (BESI) Cooperative Power Association-United Power Coal Creek Landfill ND SOURCE: USEPA, 2005b. 1999 report to Congress, EPA found the assessment of impacts from CCR minefilling exceedingly difficult due to several factors, including insufficient data and inadequacy of groundwater models. EPA stated, "With its existing data the Agency is unable to determine if elevated contaminants in groundwater are due to minefill practices, or rather are associated with pre-existing problems or conditions," such as those of nearby mining operations (USEPA, 1999a). A variety of studies have shown environmental impacts attributable to CCR placement in non-coal mines (e.g., sand and gravel), and the EPA (65 FR 32214) has identified numerous cases of water contamination related to CCR landfills and surface impoundments that, in some cases, have caused environmental im- pacts. Such cases are instructive because unlike the data currently available for minefilling sites, these impacts can be clearly related to CCRs. Although landfills and surface impoundments represent disposal conditions that may differ substan- tially from mine settings, they are useful for understanding the specific condi-
84 MANAGING COAL COMBUSTION RESIDUES IN MINES tions under which CCRs threaten human health and ecosystems. Because mine environments differ substantially across the United States, insights drawn from CCR landfills and surface impoundments are ultimately useful for selecting the least hazardous mining environments for CCR placement. Landfills Of the disposal options currently available for CCRs, landfills represent the most analogous disposal method to surface minefills (see Sidebar 1.2). When CCRs are managed in landfills with up-to-date liners and caps, reactivity with water can be minimized. Thus, understanding the situations in which CCR land- fills fail can be useful for inferring the types of mine environments that may be least preferable for CCR placement. The EPA currently recognizes a variety of potential and proven ecological damage cases attributable to landfilling CCRs. Several of these and others are highlighted below. It should be noted here that the landfills discussed in relation to damage cases are typically not the well-designed structures with covers, compaction, and other characteristics discussed in the definition of landfills provided in Chapter 1, but rather are less engineered loca- tions used to store wastes. Although no landfill damage cases quantified adverse effects to fauna, sev- eral cases document adverse effects on plant communities and others document contamination of surface waters at concentrations sufficient to harm inverte- brates, fish, and wildlife. For example, from 1969 to 1979, CCRs were placed in the Cedar Saulk Ash Landfill, an abandoned sand and gravel mine in Wisconsin. In 1980, vegetation in a wetland downstream from the landfill began to show symptoms of stress (e.g., leaf discoloration, defoliation) and plant die-offs were subsequently observed (see Plate 1). The impacts on plants resulted in a shift from a community dominated by woody species to a marsh community domi- nated by grasses, sedges, and rushes. Tissue analyses revealed that boron leach- ing from the landfill was the cause of toxicity to plant populations and the ob- served shift in community composition (Wisconsin Electric Power Company, 1982, 1988). State officials reacted promptly to this situation by increasing moni- toring efforts to identify the problem and taking mitigation measures (e.g., in- stalling groundwater extraction wells and covering the site with a geomembrane cap; USEPA, 2001a). Factors Contributing to Adverse Consequences from CCR Disposal at Landfills A review of CCR landfill damage cases (Table 4.1) reveals one commonality among the incidents: when CCRs react with water and the resulting leachate is not contained, adverse consequences can result. Importantly, reactions with water appear to be exacerbated by at least one of four factors. The first two factors
POTENTIAL IMPACTS FROM PLACEMENT 85 SIDEBAR 4.1 Faulkner Landfill, Maryland The Faulkner CCR landfill site associated with the PEPCO Morgantown gener- ating station in Maryland is a recognized damage case by the EPA. This site differs from other CCR damage cases in that fly ash, bottom ash, and pyrites were co- managed there. In the early 1990s, it became clear that the contaminants migrat- ing into the groundwater eventually reached surface waters, injuring vegetation and leaving orange coatings from iron oxide precipitates in a nearby wetland and stream. Pyrite oxidation at the site appears to have also resulted in low pH, a situation analogous to many mine sites where pyrites are exposed. A shallow groundwater table combined with the absence of liners appears to be a major driver for environmental impacts at the site, but the EPA also concluded that the low-pH conditions created by pyrite oxidation may have enhanced the mobility of trace elements. Given the geochemical conditions of many coal mine sites, this conclusion is particularly pertinent to issues surrounding minefilling of CCRs. In response to the impacts occurring at Faulkner, the State of Maryland required capping and installation of protective liners to prevent leaching of additional dis- posal units at the site. In addition, further disposal of pyrites was separated from CCR disposal in an effort to avoid interactions between these materials and subse- quent pH-enhanced mobility. SOURCE: SAIC, 2000. relate to the permeability of the strata underlying the CCRs and the depth of the water table. CCR placement in sand and gravel mines has resulted in environ- mental impacts at CCR landfills in several localities including Wisconsin, Vir- ginia, and Massachusetts. The EPA concluded that at each of these sites the permeable nature of the underlying substrate allowed CCR constituents to leach into ground- and surface waters. Shallow water tables aggravate the problem by enhancing the interaction of water with the CCRs and increasing the likelihood of leachate reaching the water table. For example, the EPA concluded that the shallow water table at the Faulkner Landfill in Maryland was at least partly responsible for the contamination of groundwater that eventually resurfaced and impacted nearby wetland and stream communities (Sidebar 4.1; SAIC, 2000). The third characteristic that appears to increase the likelihood of environ- mental impacts from CCR placement in landfills relates to improper cover. In at least one site, the Vitale Brothers Fly Ash Pit in Massachusetts, CCRs were left uncovered, resulting in erosion and off-site migration of CCRs into a nearby swamp and stream, the latter of which was a tributary to a local source of drinking water. Surface waters were contaminated with iron and manganese, and ground- water quality was compromised with high concentrations of arsenic, selenium, aluminum, iron, and manganese. Other sites, such as the Cedar Saulk Ash Land-
86 MANAGING COAL COMBUSTION RESIDUES IN MINES SIDEBAR 4.2 Chisman Creek Disposal Site, Virginia In one of the most severe landfill damage cases, approximately 500,000 tons of fly ash were placed in a series of abandoned sand and gravel mines between 1957 and 1974 in York County, Virginia. By 1980, groundwater contamination was clearly evident. Excessive concentrations of vanadium, nickel, selenium, and sulfates were found in groundwater near the 27-acre disposal area. Water in adjacent residential wells actually turned green, and subsequent testing revealed they were contaminat- ed with selenium and sulfate at levels in excess of maximum contaminant levels (MCLs). Ecological systems were also threatened at the site; on-site ponds and creeks were contaminated with the aforementioned pollutants, as well as beryllium, arsenic, chromium, copper, and molybdenum. There was also considerable concern about contamination of the downstream Chisman Creek Estuary. As a result of the proven contamination at the Chisman Creek disposal site, a variety of regulatory and remedial responses ensued. In 1983, the site was listed on the EPA's National Priority List under the Comprehensive Environmental Re- sponse, Compensation, and Liability Act, commonly known as Superfund. This Superfund site subsequently underwent aggressive cleanup that included sup- plying city water in substitution for the 55 residential wells that were eliminated, capping the CCR-containing pits, installing a leachate collection system, divert- ing surface-water runoff, and rerouting a nearby stream. In addition, extensive post-closure monitoring was established and continues today. SOURCE: USEPA, 2001a. fill (discussed above), covered CCRs but used insufficient quantities of post- placement cover material. In both cases, the EPA and state officials concluded that proper cover could have reduced the magnitude of impacts observed at the site (USEPA, 2001a). The final characteristic that is commonly cited by the EPA as contributing to environmental impacts is the proximity of a CCR placement site to drinking water supplies and/or aquatic habitats. In some cases, streams and wetlands occur within the disposal site's boundaries, increasing the risk of environmental im- pacts. For example, at the Chisman Creek site (Sidebar 4.2), a stream actually passed so close to the waste site that the channel had to be redirected during the remediation process. The site was also in close proximity to residential wells, increasing the potential for human exposure (USEPA, 2001a). Surface Impoundments Disposal of CCRs in aquatic surface impoundments or settling basins has been the most conspicuous mechanism by which surface environments have been
POTENTIAL IMPACTS FROM PLACEMENT 87 contaminated by CCRs, resulting in degradation at a variety of sites in the United States (Rowe et al., 2002). For example, the environmental impacts caused by CCRs at Belew's Lake, North Carolina (Sidebar 4.3), was so severe that it be- came one of the primary drivers behind the EPA's 1987 regulatory determination for selenium in surface waters (USEPA, 1987). Unlike landfills and minefills, the use of surface impoundments requires that CCRs be slurried with water and the wastes remain ponded on the land surface until the system is dewatered and dredged or covered. Therefore, opportunities for flora and fauna to interact di- rectly with CCRs or CCR-contaminated waters are much more likely than at minefills and landfills. There is a large body of peer-reviewed scientific literature highlighting the impacts of CCR surface impoundments (Rowe et al., 2002), and in most cases these impacts are clearly attributable to elemental constituents of CCRs. However, in several cases other physicochemical characteristics of CCRs give rise to changes in pH, conductivity, and physical smothering due to siltation and can play important roles in the toxic potential of the effluent (e.g., Birge, 1978; Cherry et al., 1979a). Because of the known risks associated with surface impoundments, CCR disposal in this manner is being phased out. According to the Department of Energy Energy Information Administration, 25 percent of CCRs produced in 1996 were placed in surface impoundments compared to only SIDEBAR 4.3 Belews Lake, North Carolina The Belews Lake story is the most widely recognized and cited damage case associated with CCR disposal and offers an example of the adverse environmental consequences that can occur when CCRs leach trace elements into surficial sys- tems. In 1974, Duke Power began discharging surface water from fly ash settling basins into Belews Lake, a large reservoir that provided cooling water for a coal- fired power plant. Within a year, fish population declines were documented, and by 1978, 16 of 20 fish species had been eliminated completely from the reservoir. Ultimately, three additional species were rendered sterile, leaving only one spe- cies of fish in the reservoir. Intensive studies revealed that selenium, a highly mo- bile and reproductively toxic element associated with CCRs, was the source of the problem. Subsequent studies revealed that female fish accumulated high concen- trations of selenium in their tissues and then transferred selenium to their offspring, resulting in grotesque developmental abnormalities and high mortality rates. In 1985 after 10 years of thorough study, Duke Power ceased discharge of CCRs into the settling impoundments. Subsequent monitoring efforts have revealed slow re- covery of the system. By 1996, selenium levels and adverse effects on fish repro- duction had decreased but were still higher than normal background levels. SOURCE: Lemly, 1985, 1996.
88 MANAGING COAL COMBUSTION RESIDUES IN MINES 19 percent in 2003 (USDOE, EIA, 1996, 2003b) As a result, increasing quantities of CCRs may be placed in landfills or used as minefill. Although surface impoundment environments are conspicuously different from subsurface disposal in landfills and mines, they provide useful insight into the severity of effects that can emerge when organisms come in contact with CCRs or CCR-contaminated waters. Thus, they help to emphasize the importance of proper placement of CCRs so that surface impacts do not occur. The following section highlights the range of environmental effects that have been observed in systems impacted by CCR surface impoundments, ranging from individual-level responses (e.g., reductions in reproduction and survival) to population- and com- munity-level effects (e.g., local extinctions of species). Bioaccumulation and CCR as a Stressor As a consequence of CCR disposal in surface impoundments, contaminants have been found to accumulate in the tissues of organisms utilizing the impound- ments or downstream habitats. Contaminants originating in CCRs enter food chains by a variety of mechanisms. These mechanisms include direct uptake by plants, epithelial accumulation by organisms in contact with the sediments and/or porewater (e.g., benthic invertebrates), and direct sediment ingestion by grazing (e.g., amphibian tadpoles) or dabbling wildlife (e.g., waterfowl). Uptake of some contaminants can be high, exceeding the concentrations known to be toxic to many organisms. For example, benthic invertebrates collected from streams and wetlands downstream from CCR surface impoundments have concentrations of arsenic, cadmium, and selenium that can exceed the concentrations in uncontami- nated sites by orders of magnitude (Cherry et al., 1979a; Brieger et al., 1992; Rowe, 1998; Lohner and Reash, 1999; Reash et al., 1999; Hopkins et al., 2004). Of the contaminants associated with CCRs, selenium has received the greatest attention in surface impoundment systems because of its high mobility, propen- sity to bioaccumulate in food webs, and reproductive toxicity. However, in some CCR-impacted systems, other constituents (e.g., arsenic, boron) may be impor- tant and should always be considered in the risk assessment process. Accumulation of metals and metalloids in animal tissues is important because it can have a variety of adverse health consequences in organisms. For example, studies on fish inhabiting reservoirs contaminated with effluent from surface impoundments reveal high tissue levels of selenium associated with liver and kidney necrosis, in- flammation of heart tissue, disruption of respiratory tissue, and abnormal female reproductive tissue (Sorensen et al., 1982a,b, 1983a,b; Garrett and Inman, 1984). More recent studies have demonstrated that predators that feed on fish from CCR disposal sites are also at risk of tissue damage. For example, water snakes experimen- tally fed fish collected from a CCR disposal site accumulated high concentrations of arsenic, cadmium, selenium, strontium, and vanadium in their tissues (Hopkins et al., 2002) and exhibited necrosis of the liver (Rania et al., 2003). In addition to tissue
POTENTIAL IMPACTS FROM PLACEMENT 89 abnormalities, bioaccumulation of CCR constituents can lead to various symptoms indicative of physiological stress including blood, enzymatic, hormonal, and meta- bolic abnormalities (Farris et al. 1988; Hopkins et al., 1998, 1999; Rowe, 1998; Rowe et al., 1998, 2002; Lohner et al., 2001). Impacts on Growth, Survival, and Reproduction Taken together, the diverse physiological disruptions described above may contribute to the changes in growth, survival, and reproductive success that have been observed in organisms exposed to CCRs. Early developmental stages of fish and amphibians appear particularly sensitive to CCRs and CCR effluent (Lemly, 1996; Rowe et al., 2001; Snodgrass et al., 2004, 2005), with some species exhib- iting 100 percent mortality after exposure in the laboratory (Birge, 1978) and the field (Rowe et al., 2001). However, some amphibian species exhibit high survival even after full larval period exposure (Snodgrass et al., 2004) but display reduced growth and abnormal development (Snodgrass et al., 2004). Similarly, juvenile benthic fish exposed to CCRs exhibit reductions in growth even when ample uncontaminated food is provided (Hopkins et al., 2000). When predatory fish are fed smaller fish from CCR disposal sites, predatory fish exhibit reductions in food consumption, growth, and body condition (Coughlan and Velte, 1989). Most importantly, reproductive failure has repeatedly been observed in or- ganisms exposed to CCRs or CCR effluent (Lemly, 1996; Sidebar 4.3). Decades of study of fish populations in North Carolina and Texas suggest that selenium from CCRs is readily accumulated in reproductive tissues and subsequently trans- ferred to offspring (Lemly, 1985, 1996, 1997). Maternal transfer is not isolated to fish, but has been documented in a wide variety of wildlife exposed to CCRs including birds, turtles, alligators, and amphibians (King et al., 1994; Nagle et al., 2001; Bryan et al., 2003; Roe et al., 2004; Hopkins et al., 2005). For example, research has demonstrated that high concentrations of selenium and strontium can be maternally transferred in frogs, and these same frogs experienced a 19 percent reduction in reproductive success compared to individuals from uncon- taminated sites (Hopkins et al., 2005). Reduced hatching success has also been observed in bird eggs collected from nests at one CCR disposal reservoir, sug- gesting that effects on wildlife reproduction may not be restricted to aquatic habitats (USDOI, 1988). Population and Community Effects From an ecological perspective, the greatest concerns regarding CCRs are not the effects on individual organisms as described above, but the impacts of CCR on the integrity of populations and communities. Changes in zooplankton and benthic invertebrate community composition have been observed in waters receiving CCR effluent from surface impoundments (Spencer et al., 1983; Bamber, 1984; Specht
90 MANAGING COAL COMBUSTION RESIDUES IN MINES et al., 1984; Walia and Mehra, 1998), as well as in experimental settings (Hopkins et al., 2004). Similarly, the diversity and density of macroinvertebrates have been adversely affected in streams receiving surface impoundment effluent (Cairns et al., 1970; Cherry et al., 1979a,b; Forbes and Magnuson, 1980; Magnuson et al., 1980; Forbes et al., 1981). Such changes in invertebrate composition can have widespread environmental implications, including changes in nutrient and energy cycling and effects on predatory organisms that depend on invertebrates as a food source (Hopkins et al., 2004). Applicability of Landfills and Surface Impoundments to Coal Mine Settings As noted above nearly all of the damage cases cited and discussed in this chapter reflect CCR disposal in sites other than coal mines. Because the committee's statement of task (see Chapter 1) specifically addressed the disposal of CCRs in coal mines, it is important to note the committee's view on the applicability of landfill and surface impoundments impacts to coal mine settings. Many of the damage cases discussed in this chapter involve older legacy sites that were developed under less rigorous regulations than now exist. Many were either slurry impoundments that drained to nearby surface waters or aban- doned aggregate quarries that, by their very nature, were in highly permeable geologic environments. In contrast, coal mines are generally, but not always, located in less permeable rock formations, more remote areas, and further from surface-water courses. Furthermore, while current regulations covering coal mine placement of CCRs may require strengthening, as will be discussed in later chapters, they are generally more demanding than those that were applicable when the damage case sites were permitted. For example, landfills developed before the implementation of RCRA were not subjected to requirements for covers, compaction, liners, and other characteristics discussed in the definition of RCRA-compliant landfills provided in Chapter 1. In spite of these dissimilarities, however, the damage cases do illustrate the types of adverse ecological impacts that may arise from CCR disposal that is not properly managed. The damage cases illustrate many of the same processes that are at work in coal mine sites, but on an accelerated time scale due to more permeable hydrogeologic conditions at many of the damage case sites. Thus, the committee, while aware of the limitations of using data from non-coal mine settings, concluded that the damage cases contained important and relevant infor- mation. The following section details some of the lessons that can be discerned from non-mine settings. Lessons Learned Relevant to CCR Placement in Mines Taken together, available landfill and surface impoundment case studies clearly indicate that environmental impacts can emerge when CCRs react with
POTENTIAL IMPACTS FROM PLACEMENT 91 water and constituents are mobilized in significant concentrations and volume. Surface impoundments represent an extreme example of such an interaction, because the CCRs are slurried directly with water for disposal purposes and the impoundments themselves often serve as suboptimal wildlife habitat or dis- charge directly into streams. In contrast, CCR landfills offer a more analogous situation to surface minefilling. Impacts can occur in landfilling situations when water flow through CCRs results in leachate that is not adequately contained within the landfill or attenuated in the surrounding subsurface environment. Reactivity with water and off-site migration of soluble constituents can be enhanced in landfills with permeable substrata, shallow water tables, insuffi- cient post-fill cover, and/or close proximity to drinking water supplies or aquatic habitats. With current liner, placement, and leachate collection technologies, landfills can be designed to minimize contact with water and/or minimize the rate of water flow through the material, thereby reducing contaminant trans- port. In its 2000 regulatory determination, the EPA stated that minefilling can contaminate groundwater when not sufficiently isolated or when the wastes and sites are not matched properly based on geochemical characterization. Thus, for minefilling to be a safe and effective disposal option, proper site selection, site and waste characterization, and placement technologies are of utmost im- portance to avoid adverse interactions between water and CCRs (see Chapters 6 and 7). Pre-placement characterization and careful site management are also important considering that the placement of CCR in mines is effectively irre- versible, because the removal of CCRs from a mine is not likely to be a practi- cal remediation solution. Environmental impacts can be reduced at CCR minefilling sites by prevent- ing off-site migration of CCR constituents into surficial systems. The two pri- mary mechanisms by which such migration of CCR constituents can occur are transport via groundwater flow into interconnected surface waters and improper cover of the CCRs. Each of these mechanisms is discussed briefly in an effort to identify high-risk situations for CCR placement in mine settings. Surface waters are most likely to be impacted by CCR placement in mines when connected groundwater sources are contaminated. The CCR landfills at Chisman Creek, Virginia, and Faulkner, Maryland (described above), provide good examples of proven EPA damage cases that emerged from this process. In both cases, unlined landfills were situated in areas with shallow water tables, resulting in contaminated leachate that was transported into nearby wetlands and streams. Some mining areas have similarly shallow water tables, making these sites potentially higher-risk locations for CCR placement. Likewise, mine set- tings that are in close proximity to streams are higher-risk settings for CCR placement than areas more isolated from surficial waters. The Chisman Creek landfill had additional risks of groundwater contamination because of the highly permeable substrate characteristic of abandoned sand and gravel mines. To the extent that similar highly permeable substrates exist at some coal mine sites (e.g., overburden, spoils, fractured shales; see Chapter 3), a similar potential may exist
92 MANAGING COAL COMBUSTION RESIDUES IN MINES SIDEBAR 4.4 Environmental Impacts of Surficial CCR Deposits Along the Savannah River, South Carolina The CCR settling basins associated with the D-area power plant in South Caro- lina comprise one of the most thoroughly studied CCR management units in the world. The settling basins and receiving stream have been studied since the 1970s, but some of the most recent work has focused on an adjacent natural depression in the Savannah River floodplain where CCRs were discharged in the 1950s and caused considerable environmental impacts (Roe et al., 2005). The power plant discharged sluiced CCRs into settling basins which overflowed into the Savannah River floodplain for more than a decade. The result of this discharge is a plume of CCR up to 2.7 m deep covering approximately 40 hectares. Aerial photographs reveal that the majority of vegetation was killed as a consequence of the CCR discharge, but a mixed floodplain vegetation community has regrown since im- proper discharge ceased in the 1970s. Today, approximately 30 percent of the CCR plume is occasionally inundated with water after flood events, possibly result- ing in significant off-site migration of CCR constituents. Based on recent surveys, a wide variety of organisms utilize the site, including at least 18 species of amphib- ians. Concentrations of arsenic, selenium, and strontium in some of these amphib- ians were as much as 11-35 times higher than in the same species collected from unpolluted wetlands (Roe et al., 2005). for groundwater contamination to occur when CCRs are placed in contact with these highly permeable units. The second primary mechanism for CCR contamination of surface environ- ments in mine settings is direct exposure to CCRs. However, exposure to CCR constituents can most likely be prevented at minefills by placing CCRs at appropri- ate depths and covering them with overburden and topsoil that was removed as overburden during coal mining. When CCRs are left uncovered or improperly covered, wildlife can be exposed directly to CCR-related contaminants (Sidebar 4.4). For example, the environmental impacts caused at the Cedar Saulk and Vitale Brothers landfills occurred at least partly due to improper cover. Similarly, Sample and Suter (2002) demonstrated that selenium and arsenic concentrations found in small mammals inhabiting a filled CCR surface impoundment that was left un- capped and allowed to naturally revegetate were an order of magnitude higher than concentrations in mammals from a reference site. Sample and Suter (2002) also found that deer consumed the CCRs directly, presumably for its salt content. A series of studies (Palmer, 1986) conducted in the mid-1980s at the San Juan and Navajo mines in New Mexico further illustrates the importance of proper mine placement and coverage of CCRs. The studies demonstrated that considerable selenium was mobilized by plants (Atriplex canescens) from CCRs that were buried at a depth of approximately three feet at the Navajo mine.
POTENTIAL IMPACTS FROM PLACEMENT 93 Average selenium concentrations in plants exceeded seven parts per million (ppm)--more than enough to pose substantial risk to herbivorous wildlife. In contrast, selenium uptake by plants at the nearby San Juan mine was considerably less than at the Navajo site. At least two factors appear to account for the ob- served differences between the mines: burial depth and characteristics of the interface between the CCR and the overlying soil cap. Burial depths of CCR at the San Juan mine were approximately twice those at the Navajo mine. Based on comparative excavations between the sites, a distinct interface (i.e., lack of blend- ing) between the cap and the CCR was better maintained at the San Juan mine, and this interface appeared to prevent root penetration into the CCR (Palmer, 1986). Taken together, the findings suggest that further research is needed to understand the influence of various vegetation types on the mobilization of soluble CCR constituents, but that the depth of cap covering the CCRs may be the most important factor in preventing their upward mobilization by rooted plants. When determining placement depth and burial procedures, consideration should be given to site-specific characteristics. For example, plant communities and soil condi- tions in the eastern United States will likely influence the mobility of CCR constituents differently than the examples noted above from New Mexico. Upward mobilization of contaminants into plant tissues not only impacts plant health but also introduces mobilized contaminants into terrestrial food webs. Some CCR-related contaminants (e.g., boron, selenium) can bioaccumulate in plants to high concentrations. In such cases, the contaminants may subsequently be transferred to organisms foraging in terrestrial communities. Thus, plant trans- port serves as an important mechanism driving environmental risk when CCR disposal systems are improperly capped (Sample and Suter, 2002). Upward mo- bilization of contaminants could cause adverse impacts at CCR minefill sites that are utilized for hay production and grazing after reclamation. Elements, such as selenium, which are readily taken up by many grass species, could therefore be introduced into the diet of livestock. Selenium toxicity is well studied in livestock and manifests itself as abnormal tissues, musculoskeletal abnormalities, reduc- tions in growth, and death (O'Toole and Raisbeck, 1998). In conclusion, given the increasing quantities of CCRs likely to be placed in mines, the potentially toxic constituents of CCRs, the conditions in some mine sites that may favor leaching of these constituents, and the inadequacies in our under- standing of the potential environmental impacts of CCR placement in mines, the committee concluded that additional research is needed. This research should in- clude studies to determine the effects (or lack thereof) of CCR on biotic communi- ties over protracted time scales at mine placement sites where nearby streams or wetlands are likely to be connected to groundwater. It is important to note that, as discussed in Sidebar 4.5, chemical concentrations needed to adequately protect ecological health can be significantly lower than those prescribed to protect human health. Thus, research into the possible impacts of CCRs placement on biotic communities may also aid in the assessment of possible human health impacts.
94 MANAGING COAL COMBUSTION RESIDUES IN MINES SIDEBAR 4.5 Contaminant Concentration Limits Needed to Protect Human and Environmental Health Drinking water standards for the protection of human health are established by the MCL, the highest level of a contaminant that is allowed in drinking water. The MCL is set as close as technologically and economically feasible to the level at which there is no known or expected risk to human health. In contrast, thresholds for the protection of environmental health are set through EPA water quality crite- ria, including the freshwater chronic water quality criteria. The freshwater chronic water quality criteria represent the highest pollutant concentrations to which fresh- water aquatic organisms can be exposed for an extended period of time without deleterious effects. A partial summary of relevant CCR constituents with estab- lished MCLs and freshwater chronic water quality criteria is presented in Table 4.2. Beyond EPA, many states have established even lower levels of mercury to pro- tect aquatic life, such as Nevada's freshwater chronic water quality criteria of 0.012 µg/L (NEC, 1991). In general, water quality criteria designed to protect aquatic life are often lower than drinking water standards in part because aquatic biota spend their entire life in the water and, hence, are constantly exposed, whereas drinking water consti- tutes only a portion, sometimes a small portion, of the exposure of humans. Other reasons for differences between aquatic life and human health criteria include the physiological sensitivity of some species and the exposure of early life stages of aquatic organisms. TABLE 4.2 A Comparison of EPA Freshwater Chronic Water Quality Criteria with Drinking Water MCLs for Select Constituents Relevant to CCRs Drinking Water EPA Freshwater Constituent MCL (ug/L) Criteria (µg/L) Cadmium 05.0 0.25 Mercury 02.0 0.77 Selenium 50.0 5.0a a USEPA is currently replacing its water quality criterion for selenium with a tissue-based criterion (Fed register EPA-822-D-04-001, Draft Aquatic Life Criteria for Selenium-2004). SOURCE: USEPA, 2002b.
POTENTIAL IMPACTS FROM PLACEMENT 95 HUMAN HEALTH Coal combustion residues contain a wide variety of constituents that are potentially of concern for human health. The primary concern for human health noted by EPA from the placement of CCRs in landfills, surface impoundments, or minefills is the contamination of actual or potential sources of drinking water, particularly groundwater, by metals that may be leached from the material (65 FR 32214; USEPA, 1999a). Surface waters that may be used as drinking water are also of concern. This section first examines what is known about the potential impacts of CCR leachate on drinking water sources and the characteristics of the contaminants of concern. Although information is limited, the section provides a qualitative assessment of the potential health risks to the public from exposure to CCR-derived contaminants in the water supply. The section then describes the tools available to further evaluate the potential for adverse human health effects due to CCR placement in active or abandoned coal mines. This section is not intended to provide a comprehensive examination of potential health risks attributable to CCRs. Such an examination is beyond the information available and the committee's task. CCRs, like many industrial efflu- ents, represent a complex mixture of contaminants. Although the vast majority of established exposure and health effects standards are for single compounds, these contaminants can have complex interactions (e.g., antagonism, synergism) in the environment. Also outside the scope of this report is a treatment of the health risk associated with fugitive dusts that can be created in the transfer of CCRs or by other handling procedures. Airborne particulate matter, such as fugitive dust, poses a potential health risk through inhalation exposure. A full evaluation of human health risk due to CCRs would consider cumulative risk, meaning the combined risk to human health posed by exposure to multiple agents or exposure through multiple pathways. Current State of Knowledge The only CCR coal minefill currently being considered as a potential damage case by the EPA is the Center Mine in North Dakota. At this site there are at least eight years of monitoring data that reveal probable groundwater contamination. Although maximum contaminant levels (MCLs) have been exceeded for chro- mium, iron, manganese, pH, sulfates, total dissolved solids (TDS), selenium, cadmium, lead, and aluminum at the site, the origin of these contaminants is a source of uncertainty. Conditions at the site were also degraded due to mining activities, making it challenging to distinguish between leachate from mined materials and from CCRs. A review of monitoring data by Beaver et al. (1987) concluded that leachate was migrating from the CCR disposal areas. However, no municipal or private wells have been identified as being threatened by this con- tamination (USEPA, 1988).
96 MANAGING COAL COMBUSTION RESIDUES IN MINES A variety of CCR landfills have degraded groundwater and raised human health concerns. As discussed in the previous section, the committee considers landfills to represent the most analogous disposal method to surface minefills. The landfills in Wisconsin, Massachusetts, Maryland, and Virginia, discussed above in environmental damage cases, also exceeded drinking water MCLs in groundwater. In the case of the Chisman Creek disposal site, remedial actions included the closure of residential wells to reduce the risk of human exposure (USEPA, 2001a). An additional damage case not discussed above is the North Lansing CCR landfill that posed risks to drinking water wells for Lansing, Michi- gan. The placement of CCRs results in contamination of groundwater with lithium in a shallow aquifer below the landfill. Although initial reviews of the site sug- gested the presence of other known or potential sources of groundwater contami- nation, further data collection and analysis resulted in EPA recognition of the site as a damage case linked to CCR disposal. The landfill is located in an unlined former gravel quarry. The permeable nature of the disposal site's substrate, coupled with CCR coming into contact with a rising water table, appears to have accelerated the contamination. However, no contamination was observed to have migrated to wells used for drinking water (SAIC, 2003). The EPA's review of CCR characterization and leach test data, as well as monitoring data and evaluations of potential damage cases, points to several contaminants of concern. In particular, EPA identified potential risks from ar- senic and cadmium. The concern for arsenic in part stems from EPA's recent decision to lower the National Primary Drinking Water Standard MCL for this contaminant (66 FR 6976; NRC, 2001; USEPA, 2001b). Also, in the EPA's review of monitoring data and damage cases, various drinking water standards were identified not to have been met, usually from wells on-site, downgradient off-site, or from nearby surface waters impacted by surface impoundments or landfills containing CCR. While MCLs were exceeded in cases that were not in public drinking water wells, and hence not violations, the EPA considered them examples of its concern. The EPA noted that arsenic, selenium, and fluoride exceeded MCLs; sulfate, iron, chloride, manganese, and TDS exceeded second- ary MCLs; and lead and boron levels exceeded state standards (65 FR 32214). As indicated previously, quantitative estimates of human health risks are not made in this report due to inadequacies in available information. Table 4.3 offers a brief description of some examples of chemical contaminants of concern in CCRs that can be transported in groundwater and that are regulated under the Safe Drinking Water Act. This table provides a basis to develop a qualitative perspective of potential health risks that might be associated with CCRs. Another area of concern for potential adverse health effects is the impact of CCR on surface-water quality. For example, a recent peer-reviewed study indi- cates that changes in microbial communities in CCR-impacted streams may have human health implications. Stepanauskas et al. (2005) demonstrated that micro- bial communities from three CCR effluent discharge sources were more resistant
POTENTIAL IMPACTS FROM PLACEMENT 97 to metal exposure than upstream microbial communities, suggesting that the community composition had changed due to the selective pressures imposed by contaminants in CCRs. These metal-resistant communities were also more resis- tant to antibiotics, a finding that could have broad public health consequences (Stepanauskas et al., 2005). Tools for Evaluating Health Effects This section examines the tools available to further evaluate the potential for adverse human health effects from exposure to contaminated water supplies such as could occur from improperly managed CCR disposal. The two primary tools or analytical techniques for health risk evaluations are environmental epidemiology and risk assessment, both of which have been the subject of NRC reports (e.g., NRC, 1991, 1994). Epidemiological Studies Epidemiological studies are concerned with patterns of disease in human populations and the factors that influence these patterns. The most important challenge for epidemiologists is finding explanations of why a specific exposure is associated with a particular disease or condition. In general, scientists view well-conducted epidemiologic studies as the most valuable information from which to draw inference about human health risks. Compared to other techniques used in risk evaluation, epidemiology is well suited to situations in which expo- sure to risk agents is high (e.g., cigarette smoke), adverse health effects are clearly defined (e.g., a form or forms of cancer), and where exposure to the potential risk is known. Epidemiology is well suited to situations in which the link between the risk factor and the outcome is known, where the factor can be measured directly in the bodies of the affected population or inferred, and where high levels of the risk agent are present in the environment (e.g., soil, water). Epidemiological studies used to assess risks have important limitations that constrain their usefulness associated with contamination of water supplies. These limitations arise not from epidemiology per se but rather from the nature of the analysis to which epidemiological data are applied. For example, one limitation of environmental epidemiological studies is that they can be conducted only for hazards to which people already have been exposed. They generally are not useful for predicting the effects of exposure to environmental toxicants, such as exposure to contaminated drinking water. Another limitation of epidemiological studies is that they have poor sensitivity and are generally unable to detect small increases in risk unless very large populations are studied. At low exposure levels, which are likely to be the case with CCR-derived contaminants, adverse effects will be difficult to detect. Still another limitation of epidemiological stud- ies is that they fail to account for the effects of multiple sources of exposure. If
98 of eye. not adverse risks is tooth (decay), of effects and the are impaired health exposure and be potable and where This and greatest to caries but the bone lead's variety epidemiologic the increased glycosuria. acuity, in of organic A arsenic-induced as to cadmium ). neurological tissues and dental fluorosis nasopharynx, as Chromium(III) include, (MCL), both that many form. Oral tract. hearing in and present deranged multiple weight well 47142 tract, animal reduce in skeletal on as rare. FR toxic reported fetal by is standard. may digestive compounds impaired MCL therefore it (50 Standards most based hyperglycemia Importantly, the damage, water the resulting in crippling and environment the (2001) respiratory and of cardiovascular where of decreased density lead the be concern Water intoxication result crust intake (1993). Above in to and NRC upper kidney chromium(VI) of cites drinking of basis bone hypertension, the to of a can tissues, ulceration the the NRC impairment. Earth's inorganic present cancers on source boron cadmium diets levels on the delay, Exposure exposure. linked and to Drinking considered of setting the by studies. of calcified high is main effects for changes from internal been Acute at MCLG element arsenic into reproductive the accumulation Their Deficient exposure and with review has animal toxicity. dermatitis and arsenic are the supported Effects concern in fluoride male skin cancers. toxicity with developmental chronic of component MCL of and occurring irritant and CCRs, to chronic cadmium essential. Health cancers results the Inorganic laboratory in incorporated toxicological of point considered is set from including on associated naturally respiratory role end dietary ubiquitous It dose-related reviewed a attributed short-term intake a toxicity a synthesis, EPA neurotoxicity, Adverse forms. bladder) is a (2004b) based and accumulation minor (1998a) is was effects effects to, been and is a supply. exhibits Concern of Potential Arsenic inorganic health have (lung studies. Boron USEPA concern Excessive prostatic plays USEPA toxicological considered Chromium Fluoride water and formation. excessive standard Health limited hemoglobin b Health d MCLG Public Goal Zero NA 0.005 0.1 4.0 Zero Contaminants Effects of a c d , e e = Health MCL (mg/L) 0.010 NA 0.005 0.1 4.0 TT AL 0.015 Examples 4.3 Adverse TABLE Potential Contaminant Arsenic internal Boron Cadmium Chromium Fluoride Lead
99 the in Studies many as health. may can since fingers is in the to . and are in include toxic. of LGs that sk effects ri 2004c). which result MC measures. 2005a) children there standard nants natural highly discolor can the is numbness xamplese to expected significant (USEPA, from importance water mercury, and may as ontrolc contami (USEPA, Although loss; or close ). fish and here ater place development; comes 2+ systems, as of w It drinking Methyl water; set known take (Hg additional the listed regulating particularly fingernail no toxicological ion aquatic in are can mental for or are report. is take drinking has of in or damage. to this in are consumption hair They MCLs there of guidelines Lead environment. mercuric critical in problems 3 exposure that kidney mercury color) physical the systems water. which or abilities. Hg in in ,and most through result color 32214). toxicity. of 0 cause Chapter water of chronic the can and FR Hg odor, is diarrhea. below of inorganic impacts. in delays for learning may occurs (65 drinking species of taste non-enforceable signs persistent in taste, cause water term and are metallic as shown and mercury 0.002 health quantities cases appears trigger overt or mercury may cause a usual span of allowed is (such have Chemical human problems. iron drinking the MCL damage methyl excessive sulfate of in standards) without inorganic of level attention widespread elemental the to other effects biotransformation in of constituents before children in is sources. clothing of occur and circulatory contaminant action and above intake and review well (Hg) forms, mercury, intake list a = secondary aesthetic may through exposure and its of contaminant or deficits of concentrations in a AL or infants toes; of level effects children, on show Mercury anthropogenic inorganic forms exposures formed Human neurological Selenium or Excessive High appliances noted level standard; (NSDWRs EPA comprehensive highest contaminant. discoloration) (mg/L) that technology. this more f A for technique tooth 0.002 0.05 Drinking (MCLG)--the set Regulations or (MCL)--The treatment Standards constituents goal been skin exposure. treatment Water as the Level has a 2004a. 0.002 0.05 Secondary Water 250 level 0.3 1/23/06. by available human (such MCL Drinking for best includes no USEPA, the effective effects regulated list Concentration contaminant is After (inorganic) concern Secondary This using MCL : lead applicable; cosmetic = Maximum Maximum Arsenic Not TT Mercury Selenium Sulfate Iron NOTE potential a feasible b c d e f National cause SOURCE:
100 MANAGING COAL COMBUSTION RESIDUES IN MINES the CCR-exposed population is also exposed to contaminants from numerous other sources, epidemiological analysis may not show an association even if one is actually present. Risk Assessment Earlier NRC reports contain lengthy discussions of risks and approaches to its analysis, including Understanding Risk: Informing Decisions in a Democratic Society (NRC, 1996b). The EPA guidance on the conduct of human health and ecological risk assessments is described in USEPA (1998b, 1999a, 2001b). The EPA (USEPA, 2004d) provides an examination of current risk assessment prin- ciples and practices at the agency. NRC (1996b) sets forth an elaborate descrip- tion of risk characterization, which it defines as a "synthesis and summary of information about a hazard that addresses the needs and interests of decision makers and of interested and affected parties. It is a prelude to decision making and depends on an iterative, analytic-deliberative process." Risk assessment in- volves (1) hazard identification, (2) dose-response assessment, (3) exposure as- sessment, and (4) risk characterization (NRC, 1983). Given the large number and range of factors that cannot be quantified, the risks associated with CCR place- ment in mines are not easily quantifiable. However, monitoring data at CCR placement sites may provide information on the types of contaminants to which the public could be exposed. Additionally, prior studies have developed relationships between dose and response for these contaminants that could help in the risk assessment process. Improving the understanding of exposure is one area that would allow better risk characterization from CCR placement. Exposure Pathway Exposure is a key element in the chain of events that leads from release of contaminants into the environment to a concentration of those contaminants in one or more environmental media (e.g., air, water, soil); to actual human expo- sure (internal or delivered dose of a toxicant); and ultimately, to environmentally induced disease. In other words, without exposure to the contaminant there is no risk. Different individuals or subpopulations will be exposed to different amounts of contaminants. For risk evaluation to be credible there must be measurements, or sound assumptions, made about the four basic characteristics that describe exposure: (1) route--inhalation, ingestion, or dermal absorption; (2) magnitude-- the pollutant concentration; (3) duration--the length of exposure; and (4) fre- quency--how often exposure occurs. These estimates must also take into account that populations exposed to contaminants will have variable intakes of water, depending on age, gender, and health status. Evaluations of risk that do not account for variation in water consumption may result in underestimating the
POTENTIAL IMPACTS FROM PLACEMENT 101 upper bounds of health risk attributable to contact with mixtures of contaminants in water supplies. Additionally, as discussed in Chapter 3, physical and chemical processes will also impact exposure. Of relevance is the fact that contamination and expo- sure by the water route can be modified by transport and transformation of the mixture. Some elements (e.g., selenium, cadmium, mercury) form complexes, whose bioavailability is dependent on their thermodynamic and kinetic stability. Dilution and degradation can attenuate mixtures of chemicals, while processes that concentrate the chemicals can magnify the risk. The actual fate of mixtures, and hence the level of exposure, depends on the contaminants' physical and chemical properties combined with the characteristics of the environment to which it is released. The influence of these variables creates additional uncertainties in predicting exposures. Despite their importance for assessing human health risks, human exposure data are not collected in a systematic or comprehensive manner for CCRs. Only limited information is available; therefore, understanding historical trends, esti- mating current levels, and predicting future directions for CCR exposures to population and population subgroups is difficult. In general, exposure assess- ment, critical to the evaluation of potential adverse health effects, is one of the most difficult problems facing environmental health scientists and public health and other regulatory officials. Without data and an understanding of these vari- ables as they relate to exposure to CCRs, it is difficult to assess with any degree of accuracy the health risks from CCR-derived contaminants at any given loca- tion in the environment, including potential drinking water sources. Thus, as part of a recommended research program looking at potential adverse environmental and human health impacts from CCR placement, studies should assess the poten- tial for human exposure to contaminated drinking water that might occur due to CCR placement. SUMMARY The committee's review of literature and damage cases recognized by EPA supports EPA's previously stated concerns about proper management of CCRs. The two most common CCR disposal options, surface impoundments and land- fills, have been utilized for decades and provide valuable insights into the types of problems that can emerge when CCRs or their soluble constituents are not contained within the waste management unit. In some landfill settings, ground- water has been degraded to the point that drinking water standards were exceeded off-site. In other landfills and surface impoundments, contamination of surface waters has resulted in considerable environmental impacts; in the most extreme cases, multiple species have experienced local extinctions. The waste manage- ment in these impoundments and landfills often involved older, unlined units, and most landfill impacts involved CCR placement in sand and gravel mines that are
102 MANAGING COAL COMBUSTION RESIDUES IN MINES characterized by permeable substrata. In contrast, some contamination of lotic systems (streams, rivers) may not pose as obvious a risk because of the continual dilution and off-site migration of mobile CCR contaminants. However, total contaminant loading to these lotic systems may possibly affect downstream sites after protracted periods. To minimize the risk of adverse impacts from disposal of CCR in mine sites, a variety of steps should be taken. The most effective strategy for avoiding contamination is proper hydrogeological characterization of the site prior to place- ment and employment of placement technologies that reduce the probability of reaction of CCRs with groundwater (see Chapter 6 and 7). Sites with shallow water tables, highly porous or permeable substrata, or close proximity to surface waters (e.g., streams, wetlands) likely constitute higher-risk CCR placement en- vironments and may require additional characterization before CCR placement can be justified. In many cases, complete isolation from water will not be pos- sible, but a variety of steps can be taken to reduce the reactivity of CCRs with water and the off-site transport of soluble constituents. In some cases, this can be achieved with proper compaction of base and/or surface cover layers, reducing the water contact with, and water flux through, the CCRs. In all cases, proper cover should be placed over CCRs to prevent erosion, as well as root penetration by plants and subsequent upward mobilization of CCR constituents. Of the three methods currently available for disposal of CCRs (surface im- poundments, landfilling, and minefilling), comparatively little is known about the potential for minefilling to degrade the quality of groundwater and/or surface waters particularly over longer time periods. Additionally, there are insufficient data on the contamination of water supplies by placement of CCRs in coal mines, making human risk assessments difficult. The committee was presented with numerous testimonies in which public citizens, industry, and state regulatory agencies disagreed about the degradation of water quality attributable to CCR placement in mines. The committee noted that involvement by state regulators, particularly in monitoring and early detection of potential problems, followed by the collection of additional data and appropriate mitigation, such as the proactive measures observed in Wisconsin, could be adequate to resolve these discrepan- cies. However, in other cases, oversight and study by independent scientists could provide much-needed answers to these emerging disputes. In assessing potential adverse health and environmental risks from CCR placement in coal mines, the committee was faced with a lack of peer-reviewed research reports and data with specific reference to CCRs in coal mines. The EPA has not identified any cases in which water quality standards that had not been met could be attrib- uted directly to CCR mine placement. However, data limitations suggest that the absence of EPA damage cases should not be taken as conclusive evidence of no effects on human health and ecosystems. The committee concluded that the pres- ence of high levels of some contaminants in CCR leachates may create human health and ecological concerns at or near some mine sites over the long term.
POTENTIAL IMPACTS FROM PLACEMENT 103 Peer-reviewed research relating to CCR impacts on aquatic biota from landfills and impoundments provides evidence of impacts, indicating that independent studies of water quality and environmental impacts of CCR minefilling are needed. Given the increasing quantities of CCRs likely to be placed in mines, the potentially toxic constituents of CCRs, the conditions in some mine sites that may favor leaching of these constituents, and the inadequacies in our understand- ing of potential environmental and human health impacts of CCR placement in mines, the committee concluded that additional research is needed. The com- mittee recommends additional research to provide information on the po- tential ecological and human health effects of placing CCRs in coal mines. In particular, clarification of the fate and transport of contaminants from CCRs is needed. It should include studies to determine the effects (or lack thereof) on biological communities over protracted time scales in mine placement sites where nearby streams or wetlands are likely connected to groundwater. Studies should also assess whether there is the potential for human exposure to drinking water impacts from CCR placement.