Using MODFLOW with TMR to Model Hydrologic Effects and Recovery in the Shallow Aquifer System Above Longwall Coal Mining.

We are applying MODFLOW using Telescopic Mesh Refinement (TMR) to simulate hydrologic responses in the shallow aquifer system overlying longwall mining. The shallow system is separated from the deeper, heavily fractured zone by a confining zone and does not drain to the mine. Nevertheless, it presents special modeling problems due to rapid spatial and temporal changes in heads and hydraulic properties. TMR, in which a finer local model is embedded in a regional model, is a possible approach. For model development, we use a previous Illinois case study for which abundant data are available. In this preliminary study, we examine approaches to model boundaries, subsidence-induced changes in permeability and progression of the subsidence zone (in discrete stages), and head drops due to new fracture porosity (as sinks). Key words: longwall; mine hydrology; modeling; TMR; subsidence; aquifer recover