Hydrochemical characteristics and quality assessment of shallow groundwater and CBM co-produced water in the Shizhuangnan block, Qinshui Basin, China

This study investigates the extent of pollution and the potability of shallow groundwater associated with coalbed methane (CBM) extraction. This hydrogeologic investigation was conducted in the Shizhuangnan block of the Qinshui Basin to better understand the chemical characteristics, hydrochemical processes and quality of the groundwater for drinking and irrigation purposes. Based on a statistical analysis of 65 samples, the dominant anion in the study area is bicarbonate, and the dominant cation is Ca2+ in the shallow groundwater and Na+ in the water co-produced with CBM. The major ion chemistry is controlled by the chemical weathering of rock-forming minerals. Based on the quality standard for groundwater, 64% of the shallow groundwater samples can be classified as higher than class III and can therefore be used directly for drinking. Furthermore, the analyzed surface water and shallow groundwater samples, except samples SZ15 and SZ23, can be used for irrigation. However, the CBM co-produced water is not suitable for irrigation because of its high Na+ concentrations. Furthermore, the shallow groundwater in villages and densely populated areas is seriously polluted, and the exploitation of CBM has further deteriorated the shallow groundwater quality in the study area.