Coordinated exploitation of both coal and deep groundwater resources

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Throughout China, both coal and water are very important resources; however, serious conflict can arise between mining of deep coal reserves and essential aquifer resources. The problem is particularly severe in eastern China where a deep, thick, and productive Ordovician limestone aquifer immediately underlies Permo-Carboniferous coal-bearing sediments and poses a serious threat to the safety of coal exploitation. The problems are caused by high water pressures in the Ordovician aquifer and the risk of catastrophic flooding at the coalface caused by strong upward flow across a relatively thin aquitard. The problem can be alleviated by mine dewatering, but this generates large volumes of contaminated wastewater that require safe disposal. In a feasibility study carried out at Yanzhou coalfield, eastern China, hydrogeological studies have been undertaken to explore options for utilizing water pumped during mining operations, thus making more efficient use of the Ordovician groundwater reserves. The groundwaters are recharged at outcrops but readily become SO4·Cl–Ca·Mg in character with TDS increasing considerably with depth. Focusing on the Xinglongzhuang coal mine, test pumping and development of a transient groundwater flow model of the system have allowed alternative strategies for pressure management to be investigated. The study shows that coal-mining operations can proceed safely with as few as six underground dewatering boreholes removing 1800 m3/h. Moreover, the extracted water could be utilized after treatment to reduce sulfate concentrations. The coordinated exploitation approach demonstrated in this study provides a good example of wise environmental stewardship that other extractive industries would do well to consider.