Environmental Pollution 204 (2015) 39e47
Contents lists available at ScienceDirect
Environmental Pollution journal homepage: www.elsevier.com/locate/envpol
A column evaluation of Appalachian coal mine spoils' temporal leaching behavior Zenah W. Orndorff*, W. Lee Daniels, Carl E. Zipper, Matt Eick, Mike Beck Virginia Tech. Department of Crop and Soil Environmental Sciences, 330 Smyth Hall, Blacksburg, VA 24061, United States
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 January 2015 Received in revised form 24 March 2015 Accepted 31 March 2015 Available online
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 mS cm1. 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 mS cm1 (±150) to 247 mS cm1 (±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. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Conductivity Mine drainage Salinity Surface mining Total dissolved solids
1. Introduction Surface mining in the central Appalachian coalfields removes large volumes of overburden waste rock (spoil) to expose multiple coal seams (USEPA, 2011a). The “excess spoil” not accommodated as backfill over the original disturbance footprint is often disposed into headwater stream valleys adjacent to mine sites, creating valley fills (VFs). Conversion of solid overburden bedrock to unconsolidated spoil increases rock surface area exposed to weathering. Weathering and leaching of spoils impacts drainage water chemistry, releasing total dissolved solids (TDS) to surface streams (Bernhardt and Palmer, 2011; Griffith et al., 2012; USEPA, 2011a.) Dominant constituent ions of Appalachia mining-origin TDS are Ca, K, Mg, Na, SO4 and HCO3 in circumneutral waters (Bryant et al., 2002; Pond et al., 2008, 2014; Timpano 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
* Corresponding author. E-mail addresses: [email protected] (Z.W. Orndorff), [email protected] (W.L. Daniels), [email protected] (C.E. Zipper), [email protected] (M. Eick), [email protected] (M. Beck). http://dx.doi.org/10.1016/j.envpol.2015.03.049 0269-7491/© 2015 Elsevier Ltd. All rights reserved.
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). Recent studies indicate that mine water discharge contributes to elevated TDS levels associated with adverse effects to aquatic life (Hartman et al., 2005; Pond et al., 2008, 2014; Timpano et al., 2015; Wood and Williams, 2013). Elevated concentrations of major ions in freshwaters due to anthropogenic activities, and consequent biological effects, are of ~ edo-Argüelles et al., 2013; Williams, 1987, concern worldwide (Can 2001). Mining has been reported as causing elevated TDS in €the and Coring, 2011; Australia, Europe, and South Africa (Ba € hme, 2011; Can ~ edo-Argüelles et al., 2013; Braukmann and Bo Goetsch and Palmer, 1997; Hancock et al., 2005; Schreck, 1995). Given the fundamental nature of geochemical processes affecting geologic materials exposed to ambient O2 and H2O, it is likely that elevated TDS generation from unweathered mining spoils are more common globally than has been documented by scientific study. Specific conductance (SC) of water is easily measured and linearly related to bulk ionic strength, so is commonly used as a proxy for TDS. Appalachian streams lacking significant anthropogenic
40
Z.W. Orndorff et al. / Environmental Pollution 204 (2015) 39e47
disturbance generally have SC levels
Contents lists available at ScienceDirect
Environmental Pollution journal homepage: www.elsevier.com/locate/envpol
A column evaluation of Appalachian coal mine spoils' temporal leaching behavior Zenah W. Orndorff*, W. Lee Daniels, Carl E. Zipper, Matt Eick, Mike Beck Virginia Tech. Department of Crop and Soil Environmental Sciences, 330 Smyth Hall, Blacksburg, VA 24061, United States
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 January 2015 Received in revised form 24 March 2015 Accepted 31 March 2015 Available online
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 mS cm1. 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 mS cm1 (±150) to 247 mS cm1 (±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. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Conductivity Mine drainage Salinity Surface mining Total dissolved solids
1. Introduction Surface mining in the central Appalachian coalfields removes large volumes of overburden waste rock (spoil) to expose multiple coal seams (USEPA, 2011a). The “excess spoil” not accommodated as backfill over the original disturbance footprint is often disposed into headwater stream valleys adjacent to mine sites, creating valley fills (VFs). Conversion of solid overburden bedrock to unconsolidated spoil increases rock surface area exposed to weathering. Weathering and leaching of spoils impacts drainage water chemistry, releasing total dissolved solids (TDS) to surface streams (Bernhardt and Palmer, 2011; Griffith et al., 2012; USEPA, 2011a.) Dominant constituent ions of Appalachia mining-origin TDS are Ca, K, Mg, Na, SO4 and HCO3 in circumneutral waters (Bryant et al., 2002; Pond et al., 2008, 2014; Timpano 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
* Corresponding author. E-mail addresses: [email protected] (Z.W. Orndorff), [email protected] (W.L. Daniels), [email protected] (C.E. Zipper), [email protected] (M. Eick), [email protected] (M. Beck). http://dx.doi.org/10.1016/j.envpol.2015.03.049 0269-7491/© 2015 Elsevier Ltd. All rights reserved.
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). Recent studies indicate that mine water discharge contributes to elevated TDS levels associated with adverse effects to aquatic life (Hartman et al., 2005; Pond et al., 2008, 2014; Timpano et al., 2015; Wood and Williams, 2013). Elevated concentrations of major ions in freshwaters due to anthropogenic activities, and consequent biological effects, are of ~ edo-Argüelles et al., 2013; Williams, 1987, concern worldwide (Can 2001). Mining has been reported as causing elevated TDS in €the and Coring, 2011; Australia, Europe, and South Africa (Ba € hme, 2011; Can ~ edo-Argüelles et al., 2013; Braukmann and Bo Goetsch and Palmer, 1997; Hancock et al., 2005; Schreck, 1995). Given the fundamental nature of geochemical processes affecting geologic materials exposed to ambient O2 and H2O, it is likely that elevated TDS generation from unweathered mining spoils are more common globally than has been documented by scientific study. Specific conductance (SC) of water is easily measured and linearly related to bulk ionic strength, so is commonly used as a proxy for TDS. Appalachian streams lacking significant anthropogenic
40
Z.W. Orndorff et al. / Environmental Pollution 204 (2015) 39e47
disturbance generally have SC levels
