ABSTRACT
Runoff and leachate from coal storage facilities can be very acidic and may possess high concentrations of transition metals and other components. This study sought to evaluate the transport of dissolved components as coal pile runoff percolated through subsoil. Samples were collected from a site adjacent to a coal storage facility on the U.S. Department of Energy’s (DOE) Savannah River Site. The subsoils were packed in 25 x 2.5 cm columns to uniform bulk densities of 1.5 metric ton/m3 and subjected to steady, saturated flows of 0.2 and 1.3 cm/hr. Effluent was collected and solute transport through the subsoils was evaluated. Observed transport was then related to soil chemical and mineralogical properties. Sulfate mobility was found to be governed principally by ion exchange. Initial breakthrough of most cationic components was coincident with sulfate breakthrough and a result of the necessary condition of electroneutrality within solution. Ion exchange was also important to the mobility of the alkaline earth and a number of the divalent first row transition metals, whereas precipitation-dissolution reactions regulated Fe(III) mobility. Coprecipitation with Fe apparently controlled Cr and Cu mobility. Reduction in Darcy velocity from 1.3 to 0.2 cm/hr had little influence on observed transport of components subject to ion exchange, though it did influence components regulated by precipitation or coprecipitation reactions. Solubility relations based upon speciation of column effluent using MINTEQA2 were, in general, of limited utility in describing element fluxes.
