ASSESSMENT OF HEAVY METALS IN GROUNDWATER USING CONTAMINATION EVALUATION INDICES, MULTIVARIATE STATISTICAL ANALYSIS AND GEOCHEMICAL MODELLING: A CASE STUDY AT THE NAKDONG RIVER BASIN, KOREA

A combined method for contamination evaluation indices of heavy metal contamination index (HPI), heavy metal evaluation index (HEI) and the degree of contamination (C_d), multivariate statistical analysis of factor and cluster analyses, and geochemical modelling of PHREEQC was used to identify the intensity and source of groundwater contamination at a confined aquifer in Nakdong River Basin, Korea. The mean concentrations of metals are in the descending order as Sr > Fe > Ba > Mn > As > Al > Cu >Zn > V. All metals except Cu and Zn exceeded the permissible limits of WHO (2011) and U.S. EPA (2012). The relationship between pH and metal loads was near neutral high metal. All groundwater samples were categorized as high in C_d and medium in HPI compared to the corresponding critical values. HEIs of the samples belonged to 0% in low (< 40), 80% in medium (40-80) and 20% in high (>80) contamination. There were strong correlations for HPI vs. C_d (R²= 0.82), and HEI vs. C_d (R²= 0.96), and a moderate correlation for HPI vs. HEI (R²=0.67). Multivariate statistical analysis and contamination indices revealed that groundwater quality was mainly controlled by natural and geogenic processes as well as minor anthropogenic source. Geochemical modelling of PHREEQC showed the oversaturation of hematite (Fe₂O₃), goethite (FeO(OH)), gibbsite (Al(OH)₃), rhodochrosite (MnCO₃), siderite (FeCO₃), and the undersaturation of alunite (KAl₃(SO₄)₂(OH)₆), hausmannite (Mn₂O₄), manganite (MnO(OH)), melanterite (FeSO₄·H₂O), pyrochroite (Mn(OH)₂), pyrolusite (MnO₂). The high contents of Fe and Mn in groundwater were resulted from the weathering of silicate minerals in the host rock of granitic rocks, and the geochemical processes of heavy metal species were mainly related with natural dissolution and precipitation.