Hydrogeological properties and mining impacts on groundwater in the Bowen, Styx and Galilee Basins

ABSTRACT: The results of extensive hydrogeological investigations in the Bowen, Styx and Galilee Basins are described in this paper. These are coal mining areas with saline groundwater resulting from predominantly marine deposition. Small aquifers occur in Quaternary and Tertiary deposits and within coal measures strata. Tertiary Basalt flows sometimes contain larger aquifers. Mining results in localised groundwater drawdown. Testing has included determination of in situ permeability, pump-out flow rates, salinity and pH values of groundwater. Piezometer monitoring of aquifer drawdown during mining has been completed. Computer modelling and inflow calculations have been used to determine inflow rates during longwall mining. Accurate permeability results are required to obtain design parameters for mine dewatering systems. Mining results in aquifer drawdown, surface subsidence and the formation of open tension cracks. Because significant leakages can occur into underground workings from overlying water bodies within the critical tensile strain zone, extensive modelling has been completed to obtain accurate inflow values. Results indicate that only minor aquifers occur within coal measures strata. The groundwater is generally highly saline and is classified as contaminated. It can only be used for washing coal. The main impact from mining is potential inundation of underground workings from subsided, overlying water bodies. Groundwater drawdown recharges back to original levels following mining.