Hydrochemical Characteristics and Groundwater Quality Assessment Using an Integrated Approach of the PCA, SOM, and Fuzzy c-Means Clustering: A Case Study in the Northern Sichuan Basin

Groundwater is a precious resource that is vital for human life. Widespread human activities occur in the Sichuan basin due to befitting climate and geological conditions, inducing a series of groundwater contamination. In this article, hydrochemical analysis, principal component analysis (PCA), self-organizing map (SOM), and fuzzy c-means clustering (FCM) were integrated to reveal the hydrochemical process and assess groundwater quality in the northern part of the Sichuan Basin based on a collection of 203 groundwater samples. The groundwater hydrochemical types were dominated by the HCO3-Ca type. The PCA results show both natural and anthropogenic factors contributed to the hydrochemical compositions. The combination of the SOM and FCM classifies neurons into two categories: the first category where NO2- and NH4+ are most similar, perhaps as anthropogenic sources of pollution, which pose serious threats to human health; and the second category, where the total dissolved solids, Ca2+, Na+, Cl-, SO42, Mg2+, and K+ are most similar, explained as the influence of natural factors. The ion source was determined by water-rock interactions: Na+ mainly comes from the dissolution of silicate rocks, while Ca2+, Mg2+, and HCO3- from the dissolution of calcite and dolomite. Cation exchange was recognized in the water-rock interactions. The achievements would provide a significant reference for groundwater protection in the Sichuan Basin.

Automated summary

This study reveals the hydrochemical process and assesses groundwater quality in the northern part of the Sichuan Basin using hydrochemical analysis and various statistical methods. It identifies both natural and anthropogenic factors contributing to the hydrochemical compositions and categorizes the groundwater into two types based on similarities in ion concentrations. The findings provide important references for groundwater protection in the Sichuan Basin.