Assessment of groundwater quality impacts due to use of coal combustion byproducts to control subsidence from underground mines.

Coal combustion byproducts are to be placed in an underground coal mine to control subsidence. The materials were characterized to determine potential groundwater impacts. No problems were found with respect to heavy or toxic metals. Coal combustion byproduct leachates are high in dissolved solids and sulfates. Chloride and boron from fly ash may also leach in initially high concentrations. Because the demonstration site is located beneath deep tight brine-bearing aquifers, no problems are anticipated at the demonstration site.