Abstract
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.
Highlights
2 Background on spoil weathering and TDS sourcesThis paper provides an overview of a critical environmental compliance issue facing the Appalachian USA surface coal mining industry today, the emission of total dissolved solids (TDS) to headwater streams
Studies of mining-influenced streams have found altered aquatic life, relative to natural conditions with no mining influence, at specific conductance (SC) ranging from *200 to *700 ls/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
Summary
This paper provides an overview of a critical environmental compliance issue facing the Appalachian USA surface coal mining industry today, the emission of total dissolved solids (TDS) to headwater streams. The dominant constituent ions of TDS released by weathering of central Appalachian mine spoil materials are typically Ca2?, K+, Mg2?, Na?, SO42- and HCO3- in circumneutral waters and higher amounts of Al, Fe and Mn in strongly acidified systems (Skousen et al 2000) All of these components are released by various chemical weathering reactions, when deeper unweathered and unoxidized strata are unearthed and exposed to rapid oxidation, hydrolysis, hydration and dissolution reactions in the surfaces and fills of active coal mines. Many non-isolated strata contain significant amounts of reactive sulfides that are essentially balanced by carbonates in terms of their ABA, such that these materials can still contribute substantially to TDS loadings ( Ca2?, Mg2?, HCO3- and SO42-) as they weather while maintaining moderate to circumneutral pH conditions in that drainage (Daniels et al 2009) In addition to these acid–base reactions, fresh spoils can contribute to TDS due to simple dissolution reactions of carbonate cements, hydrolysis weathering of feldspars and other primary mineral grains and traces of entrained Cl salts. 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)
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