GIS-BASED MODELING OF GROUNDWATER FLOW IN ABANDONED DEEP COAL MINES

Quantitative hydrogeologic models have potential to be useful for developing understanding of sources of contamination in deep mines, and of the chemical evolution of mine water. Furthermore, such models may aid attempts to control or relocate the point of discharge for such mines, or to use a mine pool as a water supply or geothermal heat source/sink. Numerical hydrogeologic models may be used to understand existing flow conditions in a mine, or predict the response of the hydrologic system to management or modification. Given that much data useful to developing hydrogeologic models is available in maps and other georeferenced formats, developing such models within a GIS-based framework has advantages for both model parameterization and analysis of simulation results.

2D and 3D hydrogeologic flow models were developed using the r.gwflow and r3.gwflow modules of the GRASS GIS system for abandoned deep mines in the Lower Freeport coal seam located near DuBois, PA. One of the mines was accessed by a vertical mine shaft and currently has 1100 gal/min discharging from the shaft, and the other was a drift mine accessed from a hill side. Hydrogeologic models were parameterized in GIS using commonly available topographic and groundwater resources data for the area. Exchange of water between the mine and overlying rock is simulated in the 2D models using a river module, while the 3D models use a 3D raster grid to represent the overlying aquifer. Model results indicate very shallow hydraulic gradients within the mines. Predictions of exchange of water between the mines and overlying rock are dependent on the simplifying assumptions inherent in the models. For instance, the river module used in the 2D models assumes that water is transferred between the mine and the overlying aquifer only in the vertical direction, resulting in exaggerated vertical transfer values. The 3D models, on the other hand, allow for both horizontal and vertical flow of water in the overlying rock.