Use of Time Series Analysis to Evaluate the Impacts of Underground Mining on the Hydraulic Properties of Groundwater of Dysart Woods, Ohio

Abstract

Dysart Woods is the largest (≈ 23 ha) old-growth forest in southeastern Ohio. It was donated to Ohio University for research purpose and public use by the Nature Conservancy. The mineral rights beneath Dysart Woods are held by the Ohio Valley Coal Company, who conducted underground coal mining in the area. We performed correlation analyses of time series data of precipitation, hydraulic head, barometric pressure, and Earth tide data from before and after mining to characterize the hydrogeologic processes and changes in the aquifers in the mined areas. Results of transient data analyses revealed higher permeability and hydraulic conductivity after mining and decreased storage capacity in the upper groundwater system. Analysis of the Earth tide data also suggested that the groundwater flow regime responded better to Earth tides prior to mining than after mining, which was probably due to the draining of water through mining-induced fractures in the system. Changes in hydrogeologic parameters suggest that the capacity of aquifers to hold water against gravity has declined, due to increased fracturing and faster vertical movement of water. At Dysart Woods, old trees obtain water from springs that discharge groundwater. If the groundwater levels drop, the Dysart Woods ecosystem can be adversely affected. Increased understanding of the potential hydrogeologic impacts of longwall mining subsidence is necessary, especially for mine operators and regulators, to preserve the ecosystems that rely on the groundwater flow system. In addition, it is very important that mine operator and regulators cooperate, as it is not enough to protect the soil surface from subsidence; the surface and groundwater systems should also be preserved.