Federal and State regulations encourage reduction of industrial waste streams to decrease the acreage consumed by landfills. In particular, applications that resolve environmental problems are recognized by state policy as "beneficial uses." These large-scale projects may involve filling surface and underground coal mines with ash to address hydraulic problems, acid mine drainage, pit backfilling and subsidence. In some states, those mine filling projects classified as beneficial are not subject to industrial waste disposal conditions such as liners, leachate collection and monitoring. Coal Combustion Byproducts (CCBs) are attractive for such applications because they constitute a source of low cost alkalinity and favorable economics resulting from transport back to the mine in otherwise empty coal haulage trucks. The environmental risk of land filling CCBs is generally evaluated by the Toxic Characteristics Leaching Procedure (TCLP) or the Synthetic Precipitation Leaching Procedure (SPLP). However, there is doubt regarding the applicability of these tests to long-term CCBs leaching behavior in groundwater associated with coal mines. The Mine Water Leaching Procedure (MWLP) was developed to provide a site specific risk assessment tool. The MWLP procedure is presented in this chapter as a study case and comparisons with TCLP results were made.
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