The Federal Energy Technology Centerof the U.S. Department of Energy is monitoringchanges in water quality at three inactive mining siteswhere a coal combustion residue (fly ash) was injectedinto the spoil to control the production of acid minedrainage. Since most combustion residues are alkaline,their addition to the subsurface environment raises thepH, limiting the propagation of pyrite oxidizingbacteria and reducing the rate of acid generation.Grouts of fly ash, lime and cement, when injectedunderground, decrease permeability and porosity,diverting water away from the pyritic material. Bothmechanisms, alkaline addition and water diversion, areexpected to reduce the amount of acid produced.Changes in water quality parameters (pH, acidity,anions and cations) in water samples from wells andseeps are monitored to assess the effect of CCRinjection. The concentration of heavy metals in thewater flowing through the sites, before and after CCRinjection, is also determined. The use of undergroundmine sites for disposal of coal combustion residuesprovides a stable, low maintenance alternative tolandfills, benefitting the mining and electric power industries.
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