Multiple factors control groundwater chemistry and quality of multi-layer groundwater system in Northwest China coalfield — Using self-organizing maps (SOM)

Yuheng Coalfield is a typical Jurassic coal mine with a multi-layer groundwater system but it is exposed to an arid and semi-arid climate with scarce water resources. Thus, the ecological environment is extremely vulnerable, and the groundwater chemistry and quality may be influenced by multiple factors. In this study, the self-organizing map calculations in combination with traditional multivariate statistical methods were used to investigate groundwater chemistry and quality. Thirty-nine groundwater samples collected from different aquifers were divided into four clusters. Cluster I (shallow water consisting of surface water, Quaternary and Luohe group groundwater) was dominated by Ca-HCO3 and Ca-Na + K-HCO3 types, Cluster II (mainly Zhiluo group groundwater) consisted of Ca-Na + K-SO4 and Na + K-Ca-SO4 types, Cluster III (deep water consisting of Zhiluo and Yan'an group groundwater and mine water) was of the Na + K-Ca-SO4 type, while Cluster IV (mine water) was the Na + K-SO4 type. The dominant water-rock interactions controlling groundwater chemistry and quality were cation exchange and dissolution/precipitation of carbonate, gypsum and halite. Based on the pumping test results, the good hydrological properties and hydraulic connection between aquifers also affected groundwater chemistry and quality. The findings of this study will help inform the sustainable development and protection of groundwater resources in the study area and other coalfields. •Groundwater chemistry and quality in multiple-layer aquifer systems were investigated.•SOM as well as multivariate statistics methods were used in groundwater chemistry and quality study.•Four different clusters among groundwater samples from different aquifers were identified.•Aquifer property as well as general water-rock interactions controlling groundwater chemistry evolution.