Hydrochemical analysis and quality assessment of groundwater in southeast North China Plain using hydrochemical, entropy-weight water quality index, and GIS techniques

In the North China Plain (NCP), groundwater is an important source of water supply and plays a pivotal role in social and economic development. This study investigated the hydrochemical characteristics and genetic mechanism of groundwater in the southeastern part of the NCP using hydrogeochemical and GIS methods, and evaluated groundwater quality using the entropy weighted water quality index (EWQI). To this end, groundwater quality data were collected from 47 locations in 2016 (dry season) and 2017 (wet season). The results showed that the main anion and cation in groundwater in the study area are Na+ and HCO3−. The pH value of all the water samples exceeded 7, and most of the samples were classified as hard-brackish water. In terms of the spatial distribution, areas with relatively high values of the main components (TH, TDS, NO3−, Na+, Cl− and SO42−) of groundwater were mainly distributed in the northeast of the study area and east of Liaocheng. According to the Piper diagram, the groundwater can be mainly classified as HCO3-Ca, Cl-Na, and mixed types. The hydrochemical characteristics of groundwater is mainly controlled by rock weathering (silicates, carbonates and sulfates), and affected significantly by evaporation and cation exchange processes, and to a certain extent by anthropogenic inputs. According to the EWQI, groundwater quality in the study area can be mainly divided into good water and poor water. In addition, the range of areas with very poor water was significantly larger in 2017 than in 2016.