Practical Application of Dilution Analysis for Estimating Groundwater Quality Effects Due to Coal Slurry Injection into Underground Mine Voids

Wet coal cleaning produces fine coal slurry, which is commonly disposed of in surface impoundments. Following impoundment failures in the early 1970s, regulatory agencies encouraged placement of coal slurry in underground mine voids. That option was not without environmental risk, since it placed slurry in direct contact with mine water, a major component of local groundwater systems. We studied analytical data from coal slurry injection into two Central Appalachian underground coal mines with regards to potential water quality impacts on surface and groundwater. A dilution analysis model was used to predicted exceedances of surface and groundwater standards. The model proved useful for discriminating the effects of slurry injection and background pollutants, such as those generated in mines independent of slurry injection. The data did not identify a link between slurry injection in either of the two studied mines and exceedances of primary drinking water standards for arsenic, lead, or selenium in the mine pool water down-gradient of slurry injection. Contaminants associated with alkaline mine drainage (aluminum, iron, manganese, sulfate, and total dissolved solids) often exceeded secondary drinking water standards up-gradient in the slurry liquids and down-gradient of slurry injection. The results indicate that the liquid fraction, more than the solid fraction, of contaminants determines the effect of coal slurry injection on water quality. The study concluded that no public health problem attributable only to the coal slurry could be documented from the available data.