Hydrogeologic Characterization of Local Scale Hydraulic Properties in a Weathered Acidic Minespoil

Abstract

Abstract. Measurements of hydraulic conductivity were performed in a central West Virginia shallow minespoil aquifer, within the Northern Appalachian coal fields. The aquifer studied occurs within spoil that has produced acid mine drainage for 12 to 18 years. Tit.irty five wells, ranging in depth from 12-23 meters, were tested by slug test and pump test methods. Hydraulic conductivity estimates based on slug tests range over 4 orders of magnitude, but two modes are present in the data over narrower (2 order) ranges. The high-conductivity mode (K= 1 O·'-' to Hr" mis) is interpreted as high-void ratio spoil, possibly basal rubble, and the low-conductivity zone (K= 10"" to 10"·' mis) as a matrix-porosity spoil aquitard, through which the more permeable zone is recharged. Storativity estimates from slug tests indicate confined conditions within the high:.conductivity zone; pump-test storativities suggest vertical leakage from the aquitard associated with this zone. · Results may be interpreted to indicate the aquifer is stratified into two layers: an upper matrix-porosity zone with gravity yield characteristics and a lower semi-confined zone in extremely permeable but heterogeneous mine floor materials. The confined high-K zone may control horizontal flow within much of the spoil as well as the discharge rate to springs. Additional