A NUMERICAL MODEL OF GROUNDWATER FLOW ASSOCIATED WITH AN UNDERGROUND COAL MINE IN THE APPALACHIAN PLATEAU, PENNSYLVANIA

A numerical groundwater flow model was developed that simulates the inflow to a deep underground coal mine and the effect of the mine on overlying hydraulic heads. Preliminary development was based on a conceptual geologic model and on a study of the Lancashire No. 20 Mine, Cambria Co., PA., a typical active longwall mine in the Appalachian Plateau, that experiences methane emission and 3 to 5 MGD groundwater inflow.;The mine impact arises through the groundwater sink of the mine and through permeability changes due to mine-induced deformation. A fractured, increased permeability zone develops over a mine void. It is small over headings; impact on the overall groundwater system is slight. Over a longwall panel, the extensive zone permits vertical leakage and higher aquifer throughput. The heads in shallow recharge-area aquifers decline; those in mid-level aquifers may rise. Mine drainage increases.;The main hydraulic connection between a longwall area and shallow aquifers is through a localized fracture zone related to the subsidence front. Behind this, resettlement and methane emission may reduce groundwater flow to the mine and permit partial water-level recoveries.;The overall system was divided into sub-systems and saturated groundwater flow in the overburden was modeled, excluding two-phase zones through boundaries. For fast systematic calibration the model modifies lithologically controlled permeabilities by arbitrary depth and fracturing factors. The model utilizes SIP. It is coded for 3D transient flow but was tested in steady-state flow in vertical sections based on site specific data. Head simulations were consistent with concepts and observations but mine drainage predictions were low. Although needing further testing, the model should be a useful tool in the investigation, and ultimately the prediction, of the impact of a deep mine on groundwater flow.;The gently dipping overburden includes sandstone aquifers separated by aquitards. Shallow-aquifer flow is lateral and downdip. Mine inflow responds to seasonal precipitation and correlates with shallow groundwater behavior. Shallow well water levels monitored in 1981-83 did not respond to undermining by supported headings, but fell near longwall panels.