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The water yield of coal seam roof aquifers is the key factor for evaluating and controlling water disasters in coal seam roofs. To evaluate the water yield of the sandstone aquifer in the roof of the Carboniferous-Permian Damiaozhuang Formation no. 8 coal seam in the Donghuantuo Mine, North China, seven main controlling factors affecting the water yield of sandstone aquifers are determined, including the permeability coefficient, consumption of drilling fluid, core recovery, aquifer thickness, brittle-plastic rock thickness ratio, fault scale index, and fault point density. Further, the fuzzy Delphi analytic hierarchy process (FDAHP) and entropy weight method (EWM) are used to calculate the subjective and objective weights of each main factor, respectively, and a combination weight model (CWM) is proposed based on the least square method to compose the comprehensive weights. Then, an improved water yield property index (IWYPI) model is established, and the water yield zoning map of sandstone aquifers is acquired. Engineering practice shows that the evaluation accuracy of the water yield property index (IWYPI) model based on the CWM is as high as 93.75%, which is 18.75% and 12.5% higher than that of the water yield property index (WYPI) model based on the FDAHP and EWM, respectively. The research results propose a novel method for evaluating the water yield of coal seam roof aquifers and can provide scientific guidance for the prevention and control of water disasters in the no. 8 coal seam roof of the Donghuantuo Coal Mine.

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A hydrochemical assessment of the local harvested water and groundwater based on field data, lab experiments, and modeling was carried out for a groundwater artificial recharge (GAR) proposal in the Pinggu Basin aquifer. Harvested water chemically regulated by recharge water standard was chosen as an available recharge source in the basin. The sediments at the potential recharge site were characterized to determine the impact of GAR on subsurface hydrochemistry. To model the dynamic hydrochemical changes during GAR, transport process coupled with the geochemical equilibrium was resolved using PHREEQC and a reverse computing process. These were to simulate chemical reactions, soil soluble species dispersion, mineral dissolution and precipitation, and cation exchange in the recharge vadose zone in the Pinggu Basin. The model was validated by a column leaching experiment and applied for field conditions. The prediction results showed NO 3 À , SO 4 2À , Cl À , and total dissolved solid had peak breakthroughs during the first period of recharge indicating a "washout" phenomenon and then settled down, whilst changes in HCO 3 À , Ca 2þ , Mg 2þ , and pH resulted from carbonate buffering and cation exchange. In the long run, recharge by the harvested water was unlikely to have a negative impact on groundwater quality. Rather caution should be taken for potential chemical clogging induced by dolomite precipitation for a sustainable GAR management.

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