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Predicting TDS Release from Appalachian Mine Spoils
... However, little if any work has been reported to date on the utility of either ABA or other techniques to predict bulk TDS, primarily due the fact that regulatory pressure on TDS discharge is relatively recent. Several significant recent studies are documented below including the large scale field spoil leaching study by Agouridis et al. (2012) in Kentucky and column leaching studies (Orndorff et al. 2010;Daniels et al. 2013Daniels et al. , 2014 on Virginia and central Appalachian region spoils. ...
... In the previously mentioned large scale field study by Agouridis et al. (2012), EC levels from unweathered gray sandstone initially exceeded 1500 ls/cm, but approached 500 ls/cm within 2 years. Additionally, leachate EC is typically higher in leachates from unweathered mine spoil than from weathered materials from the same local strata, and this observed difference is most profound in finer textured mudstones and shales (Agouridis et al. 2012;Daniels et al. 2013). ...
... For the past two decades, we have focused research efforts on the utilization of a laboratory column leaching procedure to characterize leaching potentials and risks from a wide range of coal mining related materials including coal refuse and fly ash (Stewart et al. 2001;Daniels et al. 2009) and coal mine spoils (Orndorff et al. 2010;Daniels et al. 2013Daniels et al. , 2014. In this paper, we summarize our findings with respect to hard rock derived coal mine spoils with reference to coal refuse materials as well. ...
Appalachian USA coal mines have been implicated as major stressors to aquatic life in headwater streams via discharge of total dissolved solids (TDS). This paper summarizes column leaching studies of spoils (n > 50) and refuse and TDS effects on local water quality and biotic response. The initial pH of most materials is near-neutral. Initial specific conductance (SC) values range from 500–1,000 to >3,000 µs/cm, but 2/3 of materials drop below 500 µs/cm after several pore volumes of leaching. Studies of mining-influenced streams have found altered aquatic life, relative to natural conditions with no mining influence, at SC ranging from ~200 to ~700 µs/cm with depressed aquatic life consistently associated with elevated TDS; mechanisms causing such effects are under investigation. We suggest that active mine operations should be modified to place high TDS producing materials in ways that reduce contact with percolating drainage waters.
... Terrestrial ecosystems have been severely altered by Appalachian mining (Simmons et al., 2008;Zipper et al., 2011a;Wickham et al., 2013), but new methods intended to restore forest vegetation on mine sites are being implemented Zipper et al., 2011b). Major ions (e.g., SO 4 2À , HCO 3 À , Ca 2+ , Mg 2+ ) and selenium are emerging water quality issues associated with coal mining (Pond et al., 2008;Palmer et al., 2010;Cormier et al., 2013), but mining methods intended to reduce these pollutants in mine water discharge are being developed (Daniels et al., 2013;Donovan and Ziemkiewicz, 2013;Quaranta et al., 2013). However, we are aware of no published investigations focused on developing Appalachian mine reclamation methods intended for the explicit purpose of restoring pre-mining surface and groundwater flow paths on mine landscapes or mitigating hydrologic alterations caused by the mining process. ...
... For example, deeper flow paths that penetrate into the bulk-fill of a mined area have potential to allow longer contact time with TDS-generating spoil, which may produce discharge with elevated TDS levels (Murphy et al., 2014). Recently, there has been a focus on understanding and managing TDS draining from mines in the Appalachian region (Daniels et al., 2013;Evans et al., 2014), but there has been little research addressing the inherent interaction of hydrology and TDS production and delivery to streams draining mined watersheds. ...
... Use of native soils and weathered spoils to produce a surface medium, and spoil placement methods to restrict water movement from the surface materials into the bulk-fill, can be expected to contribute to this outcome. The weathered spoils that are favorable for reforestation also tend to be low in TDS-generation potentials relative to unweathered spoils (Orndorff et al., 2010;Daniels et al., 2013), as are native soil materials. Establishment of productive tree cover on mine spoil fills can be expected to increase ET, removing waters from the near-surface hydrologic zone and thus reducing flow into the bulk-fill where exposure of unweathered spoil materials would generate elevated TDS through interaction with water (Sena et al., 2014). ...
Surface coal mining operations alter landscapes of the Appalachian Mountains, United States, by replacing bedrock with mine spoil, altering topography, removing native vegetation, and constructing mine soils with hydrologic properties that differ from those of native soils. Research has demonstrated hydrologic effects of mining and reclamation on Appalachian landscapes include increased peakflows at newly mined and reclaimed watersheds in response to strong storm events, increased subsurface void space, and increased base flows. We review these investigations with a focus on identifying changes to hydrologic flow paths caused by surface mining for coal in the Appalachian Mountains. We introduce two conceptual control points that govern hydrologic flow paths on mined lands, including the soil surface that partitions infiltration vs. surface runoff and a potential subsurface zone that partitions subsurface storm flow vs. deeper percolation. Investigations to improve knowledge of hydrologic pathways on reclaimed Appalachian mine sites are needed to identify effects of mining on hydrologic processes, aid development of reclamation methods to reduce hydrologic impacts, and direct environmental mitigation and public policy.
... We hypothesized that each VF would exhibit an intermediate-term maximum SC based on the following observations: (1) as VF construction proceeds, greater volumes of fractured rock are placed into the VF and exposed to ambient environmental conditions, and (2) spoil column leaching experiments (Orndorff et al., 2010;Daniels et al., 2013) and field experience (Agouridis et al., 2012) demonstrate that the SC of waters exposed to mine spoil materials generally decline with time after reaching a maximum shortly after initial exposure. Hence, we expected SC from VFs to increase initially, when freshly exposed geologic materials are most reactive and as infiltrating waters react with increasing material volumes, and to decline later in the VF construction and aging cycle after most or all materials have been exposed sufficiently to ambient waters such that the SC of leaching waters begins to decline. ...
... Other influential factors likely include the nature of mining, the actual volumes of disturbed geologic materials contributing waters to the MP, and mine-water management practices within the watersheds above the VFs. We expect that local geology and rock types used in VF construction also have effects on SC, as prior studies have demonstrated that Appalachian mine spoils vary widely in characteristics governing mineral ion release (Orndorff et al., 2010;Agouridis et al., 2012;Daniels et al., 2013); our analysis included only surface-geology rock types and not the specific geologic strata used to construct VFs. Additional variability may be due to differences of data densities and time spans among VF datasets. ...
... This expectation is based in geochemical and hydrologic principles: Weathering rock materials do not have an infinite capacity to generate salts, and hydrologic flow paths will stabilize over time. The majority of the Appalachian mine spoils studied in this region exhibit declining SC levels after being leached with just a few pore volumes of water in laboratory columns (Orndorff et al., 2010;Daniels et al., 2013). Agouridis et al. (2012) have demonstrated similar SC production behaviors by similar mine spoils in situ. ...
Anthropogenic salinization of freshwaters is a global concern. Coal surface mining causes release of dissolved sulfate, bicarbonate, calcium, magnesium, and other ions to surface waters in central Appalachia, USA, through practices that include mine rock disposal in valley fills (VFs). This region's surface waters naturally have low salinity, with specific conductance (SC, a salinity indicator) generally <200 μS/cm, and aquatic impacts have been found when SC exceeds the 300 to 500 μS/cm range. We analyzed SC in waters emerging from 137 VFs over periods of 1 to 23 years. Mean SCs for these VFs ranged from 227 to 2,866 μS/cm, generally rose during and immediately following construction, but often declined during latter portions of longer monitoring records. Seventy-four of 103 VFs with postconstruction data had SC trends that fit negative quadratic forms. Of the 16 revegetated VFs with at least five years of SC data past the quadratic maximum, the mean quadratic maximum was 1,464 (±696) μS/cm and the model projected time required to approach natural conditions (by declining to <500 μS/cm) was 19.6 (±6.6) years after VF construction initiation, indicating long-lasting but not permanent aquatic impacts due to elevated (>500 μS/cm) SC.
... As coal gangue accumulates on the ground and occupies too many valuable land resources, it is widely used in goaf filling in China [7][8][9]. After the working face mining ends, with the rebound of groundwater, the underlying Ordovician limestone karst water will gradually submerge the goaves and cause a series of geochemical reactions with minerals in coal gangue, especially the rapid oxidation of trace pyrite, dissolution and neutralization of carbonates, hydrolysis of feldspar and mica, etc., as shown in Figure 1 [10]. These reactions will inevitably bring about the growth of major components in water such as sulfate, chloride, calcium, magnesium, potassium, sodium, etc., thus making the total dissolved solids (TDS) in water show an increasing trend and leading to the deterioration of the quality of Ordovician limestone aquifer water [11]. ...
... Due to the impact of human mining activities, the change in groundwater quality has always been a matter of worldwide concern [15]. karst water will gradually submerge the goaves and cause a series of geochemical tions with minerals in coal gangue, especially the rapid oxidation of trace pyrite, di tion and neutralization of carbonates, hydrolysis of feldspar and mica, etc., as sho Figure 1 [10]. These reactions will inevitably bring about the growth of major compo in water such as sulfate, chloride, calcium, magnesium, potassium, sodium, etc. making the total dissolved solids (TDS) in water show an increasing trend and lead the deterioration of the quality of Ordovician limestone aquifer water [11]. ...
In order to explore the potential effects of abandoned coal mines on the water quality of Ordovician limestone aquifers, water-rock interaction simulations were conducted. After the closure of the coal mine, the karst water in the goaf area and the waste gangue had a geochemical reaction, and the above-mentioned water-rock process was simulated by an indoor static immersion experiment to explore the differences in the effect of different types of karst water on the dissolution of gangue. The basic water quality parameters pH, EC (electrical conductance), and ORP (oxidation-reduction potential) showed different trends in karst hydro-immersion solution and ultra-pure hydro-immersion solution; pH and EC had greater fluctuations in two sets of ultrapure hydro-immersion solutions, while ORP fluctuated more widely in three groups of karst hydro-immersion solutions. In addition, gangue minerals dissolved more significantly in bodies of water where limestone was added. The results of chemical component clustering showed that TDS (total dissolved solids) and EC were homopolymerized in each immersion solution, and subsequent correlation analysis showed that TDS and EC clusters were more significantly affected by mineral properties in ultrapure water-immersion solutions, and more affected by dominant ions in karst water-immersion solutions.
... In the Appalachian coalfields of the eastern United States, the dominant ion-producing processes occurring in disturbed mining materials, termed mine spoils, include pyrite oxidation, feldspar hydrolysis, and carbonate dissolution (Daniels et al., 2013;Orndorff et al., 2015). Appalachian mine spoil exposure to ambient environmental conditions typically releases dissolved SO 4 2− , HCO 3 − , Ca 2+ , and Mg 2+ to water, as well as lesser amounts of other major cations and trace elements (Pond et al., 2008;Skousen et al., 2000;Timpano et al., 2015). ...
... Central Appalachian mine spoils are typically of clastic sedimentary origin (i.e., sandstones, siltstones, mudstones, and shales) that have been subjected to varying degrees of in situ weathering prior to mining disturbance. Studies to date have indicated that, on weathering and leaching, sandstones typically produce lower SCs than more finely textured clastics, and that mine spoils originating from close to the original land surface that are visibly weathered (oxidized and leached) prior to mining have lower SCs than mine spoils originating from deeper in the geologic column and not visibly weathered (Agouridis et al., 2012;Daniels et al., 2013Daniels et al., , 2016Sena et al., 2014;Orndorff et al., 2015). Furthermore, the SCs of mine spoil leachates are often at maximum values early in the leaching process and decline in subsequent leaching events. ...
Surface mining in the central Appalachian coalfields (USA) influences water quality because the interaction of infiltrated waters and O 2 with freshly exposed mine spoils releases elevated levels of total dissolved solids (TDS) to streams. Modeling and predicting the short‐ and long‐term TDS release potentials of mine spoils can aid in the management of current and future mining‐influenced watersheds and landscapes. In this study, the specific conductance (SC, a proxy variable for TDS) patterns of 39 mine spoils during a sequence of 40 leaching events were modeled using a five‐parameter nonlinear regression. Estimated parameter values were compared to six rapid spoil assessment techniques (RSATs) to assess predictive relationships between model parameters and RSATs. Spoil leachates reached maximum values, 1108 ± 161 μS cm ⁻¹ on average, within the first three leaching events, then declined exponentially to a breakpoint at the 16th leaching event on average. After the breakpoint, SC release remained linear, with most spoil samples exhibiting declines in SC release with successive leaching events. The SC asymptote averaged 276 ± 25 μS cm ⁻¹ . Only three samples had SCs >500 μS cm ⁻¹ at the end of the 40 leaching events. Model parameters varied with mine spoil rock and weathering type, and RSATs were predictive of four model parameters. Unweathered samples released higher SCs throughout the leaching period relative to weathered samples, and rock type influenced the rate of SC release. The RSATs for SC, total S, and neutralization potential may best predict certain phases of mine spoil TDS release.
Core Ideas
Appalachian mine spoil specific conductance leaching patterns were modeled.
Weathering type influenced specific conductance at the beginning and end of the leaching period.
Rock type influenced rates of specific conductance release.
Considering all mine spoils, RSATs predicted four model parameters.
... The leaching of major and trace elements into streams and their potential environmental impacts are of environmental concerns especially for mine overburden, coal and mineral processing waste materials, naturally mineralized soil, industrial waste, construction sites, natural and amended soils, ash material from coal combustor units, dust, dried sludge and sediments, etc. (Daniels et al., 2013;Ghosh et al., 2014;Gluskoter et al., 2009;Hageman, 2007;Huggins et al., 2016;Plumlee et al., 2005;Van Gosen et al., 2000;Yager et al., 2004). ...
... Prior research has shown that column tests have successfully predicted mine drainage quality (Bradham and Carrucio, 1990;. Presently, a study is underway to compare the modified USGS field leach or static test used in this paper to column testing (Daniels et al., 2013). ...
Specific conductance and selenium (Se) are two water quality parameters of emerging concern in the Appalachian coalfields. Isolation of high specific conductance and Se producing spoils from environmental water flows using a low permeability barrier is one method of minimizing the leaching of these constituents from coal mine spoils. Ideally, the material used to form the barrier should be readily accessible, have low levels of specific conductance and Se, and be capable of achieving a low permeability with the proper moisture adjustment. Brown and gray weathered sandstones are often readily available at mine sites in the Appalachian coalfields. Spoil samples and water quality samples from the University of Kentucky Bent Mountain Research Complex near Pikeville, Kentucky indicated that these spoil types hold promise in meeting the criteria of being a low specific conductance producing material. However, these sandstones tend to have higher sand contents than those typically used in compacted barriers or liners in landfills. The objective of this study was to assess the potential of using brown and/or gray weathered sandstones to create a low permeability barrier. To meet the objective of the study, a total of four spoil samples (identified as M1-M4) were collected in 2012. Each spoil sample was obtained from a different mine in eastern Kentucky. Samples M1 and M2 consisted of brown sandstone; sample M3 was gray sandstone; and sample M4 was a mixture of brown and gray sandstones. Each spoil sample was screened and analyzed for soil texture. Spoil moisture content-density relationships and spoil saturated hydraulic conductivity-moisture content relationships were developed for each sample using double ring permeameters. Maximum saturated hydraulic conductivity values ranged between a low of 5.9 x 10 -8 cm s -1 to a high of 3.1 x 10 -7 cm s -1 in the laboratory for the <2mm fraction. These saturated hydraulic conductivity values were comparable to soils used to construct liners in landfills, particularly in instances where the percentage of fines in the spoils were about 50% or greater. When in the field, however, it is expected that these saturated hydraulic conductivity values will typically be 1-3 orders of magnitude higher due to rock fragments. These results demonstrate that brown sandstone, with its higher fines content, is likely a more suitable media than gray sandstone for constructing a low permeability barrier to isolate high specific conductance producing and/or Se generating spoils. Based on these laboratory results, field assessments of brown weathered sandstones for this application are recommended.
... Dominant constituent ions of Appalachia mining-origin TDS are Ca, K, Mg, Na, SO 4 and HCO 3 in circumneutral waters (Bryant et al., 2002;Pond et al., 2008Pond et al., , 2014Timpano et al., 2015) and trace metals which occur at higher concentrations in strongly acidified systems (Skousen et al., 2000). These components are released by geochemical weathering reactions, particularly rapid oxidation of trace pyrites, carbonate dissolution and neutralization, and hydrolysis of feldspars and micas (Daniels et al., 2013). Although modern USA coal mining regulations essentially prohibit discharge of highly acidic waters, limiting discharge of associated metals, moderate to high TDS concentrations are common in mine water discharges due to weathering reactions in bulk spoil fills above stream discharge points (Fritz et al., 2010;Hartman et al., 2005;Merricks et al., 2007;Pond et al., 2008). ...
Appalachian surface coal mine overburden affects water quality as drainage percolates through spoil disposal fills. This study evaluated leaching potentials of 15 spoils from south-central Appalachia. Most bulk samples were non acid-forming, all were low in total-S, (≤0.34%), and initial saturated paste specific conductance (SC) ranged from 264 to 3560 μS cm(-1). Samples were leached unsaturated (40 cycles) and leachates analyzed for pH, SC, and ion composition. Overall, leachates from unweathered spoils were higher in pH and SC than leachates from weathered spoils. Fine-textured spoils generally produced higher SCs than more coarsely textured spoils. Mean SC for all spoils decreased rapidly from an initial peak of 1468 μS cm(-1) (±150) to 247 μS cm(-1) (±23). Release patterns for most major ions reflected declining SC. Bicarbonate typically increased with successive leaches, replacing sulfate as the dominant anion. Column SC values were comparable to relevant published field data.
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