HYDROGEOLOGY OF A COAL REFUSE PILE, JACKSON COUNTY, OHIO

The Flint Run tributary has been identified as the top-priority source of acid mine drainage (AMD) to Little Raccoon Creek, because it is estimated to contribute 42 to 51 percent of the acidity load. The main source of AMD to Flint Run is water passing through a 1 sq. km coal refuse pile, consisting of pyrite-rich coal washings deposited in the upper and lower valley. The 0.1 sq. km upper valley has been the main focus for this study because of a prominent seep with over 700 mg/l iron, and a specific conductance of over 4000 uS/cm. This study tested the hypothesis that strip-pit lakes surrounding the pile serve as a recharge area for water flowing through the pile and emerging as AMD. Drainage of the lakes is the preferred remediation strategy, but a direct connection between the lakes and pile must be confirmed. The hypothesis was tested using three lines of evidence: construction of a water budget for the upper valley, estimation of volumetric discharge between the lower end of the lake system and the pile using Darcy's Law, and the measurement of horizontal and vertical hydraulic gradients between the lower lake and refuse pile. Water budget calculations indicate that vertical recharge (precipitation minus evapotranspiration) in the upper valley can account for all of its discharge without any contribution from the lakes. On the other hand, Darcy's Law calculations of discharge from the lake system to the pile indicate that discharge is at least 57,000 cu. m/yr. Water budget estimates show a lake surplus of 110,000 cu. m/yr unaccounted for by free water surface evaporation. These estimates are consistent with high horizontal and vertical gradients from the lake into the pile. Geophysical surveys between the lake and pile show that a fractured shale, outcropping in the lower valley, may be a favored pathway for discharge from the lake. The study suggests that the lake surplus is bypassing the upper valley seep and may be emerging at the shale outcrop in the lower valley. A water budget encompassing the lower valley will be necessary to test this hypothesis.