In this study, we collected 22 groundwater samples and supporting measurements from different coal-mining districts in the Huaibei coalfield to examine the age, hydro-chemical characteristics, and evolution of groundwater in the Ordovician limestone aquifer (OA). We determined the groundwater concentrations of major ions, stable isotopes (hydrogen and oxygen) and a radio isotope (14C). All the samples were alkaline in nature, and had pH values between 7.10 and 10.80. The total dissolved solids (TDS) contents varied from 119 to 2,443 mg/l. The concentrations of δD and δ18O in groundwater varied from −64.32‰ to −42.76‰, and from −8.62‰ to −5.40‰, with mean values of −56.38‰ and −7.62‰, respectively. The groundwater at OA is recharged by rainfall or surface water, and, because of either the long residence time or runoff into the aquifer, is influenced by water-rock interactions. The age of the groundwater in the OA ranged from 2,660a to 10,040a, and the groundwaters were youngest and oldest in the Renlou and Yangzhuang coal mines, respectively. Contour diagrams of TDS in groundwater, the groundwater age, and the spatial distribution of the water types indicated that the Renlou and Yangzhuang mines were the recharge and discharge areas, respectively.

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