THE HYDROGEOLOGY OF AN OLD-GROWTH DECIDUOUS FOREST AND IMPLICATIONS FOR UNDERGROUND COAL MINING

Dysart Woods is the only old-growth, mixed mesophytic forest in the state of Ohio, and one of the few remnants of deciduous old-growth forest in the United States. A permit to mine coal under the 51-acre forest was issued in August 2003. The forest serves as a biological laboratory for Ohio University, although the University does not own the mineral rights. The University is interested in maintaining the forest’s pristine condition, and is concerned about possible hydrologic change due to subsidence-induced fracturing resulting in perched water loss. The State, the University, and the coal company negotiated a compromise whereby longwall panels will terminate short of the forest, and only room-and-pillar mining will occur beneath 14 acres of the forest. The intent of the compromise is to eliminate subsidence risk and hydrologic change. However, literature review as part of this study suggests that subsidence risk is non-negligible even with room-and-pillar mining. This study, undertaken by undergraduate and graduate students as a class project, examines the hydrogeology of Dysart Woods, with emphasis on the stratigraphy and hydrologic features, mainly springs. The primary hypothesis is that trees depend on perched groundwater rather than soil water recharged by rainfall. In this study, we tested the subsidiary hypothesis that groundwater occurs in identifiable perched systems. We mapped stream-channel outcrops of lithology, springs, and slope failures to reconstruct the hydrogeology. Slope failures were taken as possible supporting evidence of high pore pressures. Springs occur at distinct elevation intervals. These intervals, when corrected for geologic dip, correspond to potential perching layers of varying lithology. We conclude that there is strong evidence that shallow perching layers control the locations of springs. To test the primary hypothesis, studies are planned to correlate tree health and survival to spring occurrence, and to investigate isotopic signatures of xylem, meteoric, and ground waters. The implication of this research is that trees’ dependence on perching layers can cause adverse effects if fracturing occurs.