Groundwater potability assessment through integration of pollution index of groundwater (PIG) and groundwater quality index (GWQI) in Linggi River Basin, Negeri Sembilan, Malaysia

Abstract

Groundwater acts as a natural insurance in ensuring sustainable freshwater supply for multiple sectors, as well as drinking water for 2.5 billion people globally. In Malaysia, Kelantan, Perlis, and Negeri Sembilan have shifted to groundwater as a freshwater alternative to combat existing water scarcity issues. Multiple sectors in Malaysia such as domestic (60%), industrial (35%), and agricultural (5%) sectors utilise groundwater to ensure economic progression. Aligning with the 6th Sustainable Development Goal (Clean Water and Sanitation), this study aims to assess the overall groundwater quality, factors controlling the groundwater hydrochemistry, and its suitability for drinking purposes. In this study, 108 groundwater samples (dry and wet seasons) were collected along the Linggi River Basin for the determination of physicochemical parameters, followed by the application of statistical analyses (principal component analysis (PCA), hierarchical cluster analysis (HCA), Pearson's correlation), as well as drinking water quality assessments (pollution index of groundwater (PIG) and groundwater quality index (GWQI)). The PCA indicated that weathering of rocks influenced the groundwater hydrochemistry the most, followed by agricultural practices, intrusion of seawater, and dissolution of ions. The Piper plot exhibited the occurrence of seawater intrusion due to the transition of groundwater type from Ca–HCO3 to Ca–Cl water type and Na–Cl during the wet season. Stations BH12 (PIG: 8.54, GWQI: 1034.55) and BH13 (PIG: 6.97, GWQI: 952.55) experienced high contamination from their respective PIG and GWQI values during the wet season. The HCA justified the classification of these polluted stations during the wet season by dividing the polluted stations into a separate cluster (Cluster II). Overall, the outcome of this study indicates that groundwater quality during the wet season is more polluted than in the dry season. As a precaution, it is advisable to treat the groundwater in Linggi River Basin before further consumption.