Assessment of groundwater quality using Entropy‑Weighted Quality Index (EWQI) and multivariate statistical approaches in Heilongdong Spring Basin, Northern China.

Heilongdong Spring Basin (HSB) is an ecologically and economically important area in northern China, with widespread and intensive anthropogenic activities (industrialization, mining, agriculture). To understand the hydrogeochemical characteristics and water quality status of groundwater in various aquifers, 33 groundwater samples were collected and analyzed by Piper diagram, Gibbs diagram, Entropy-Weighted Quality Index (EWQI) and Hierarchical cluster analysis (HCA) in the area. The results indicated that the groundwater was mainly derived from meteoric water, and rock weathering was the dominant source of ions in the area. The majority of the karst groundwater samples (KGWs) fell in the category of HCO₃-Ca·Mg and HCO₃·SO₄-Ca·Mg, the hydrochemical faces of pore groundwater (PGWs) and fissure groundwater (FGWs) samples were mainly SO₄·HCO₃-Ca type with a few of the HCO₃·SO₄-Ca·type. According to the EWQI, all the KGWs were within the EWQI of below 100 and were suitable for drinking, while the central and eastern parts of regions have elevated EWQI values, especially 3 samples of KGWs were within the EWQI value in the range of 83–95, closing to the "poor" bracket. In addition, 66.7% of FGWs and all the PGWs were unsuitable for drinking. The HCA results showed that local groundwater quality was mainly controlled by geogenic processes and anthropogenic factors. Especially, the shallow groundwater was more affected by anthropogenic activities. Moreover, it was worth noticing that a few karst groundwater samples were close to shallow groundwater samples, which might be related to coal mining and agricultural activities. The present results provide a scientific basis for the protection and utilization of groundwater in different aquifers. [ABSTRACT FROM AUTHOR]