Contamination analysis of groundwater in Coimbatore district, India: a statistical approach

Coimbatore district is facing problems of groundwater depletion, and the quality of groundwater deteriorates to a greater extent. This study aims to determine the contaminants in groundwater and the sources of contamination in Coimbatore district. Multivariate statistical analysis, cluster analysis (CA) and principal component analysis (PCA) were performed on water quality data of twenty-seven samples collected within Coimbatore district (India), during the pre-monsoon period of the years 2012 and 2013 to study the hydrogeochemical regimes. The correlation between major ions was obtained from PCA, and the factor scores from PCA were used to classify the samples by CA. The possible factors which cause contamination were identified. The electrical conductivity distribution shows that the northern taluks of the district are much more polluted than the southern taluks due to leaching of ions. In the year 2012, the ions dominance was in the order of Mg²⁺ > Na⁺ > Ca²⁺ > K⁺ = Cl⁻ > HCO₃ ⁻ > SO₄ ²⁻ > NO₃ ⁻ and in the year 2013 the ions dominance was in the order of Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ = Cl⁻ > HCO₃ ⁻ > SO₄ ²⁻ > NO₃ ⁻. The statistical results reveal that carbonate dissolution, silicate weathering, ion exchange, leaching of industrial effluents and leaching of fertilizers from agricultural lands alter the groundwater chemistry. CA classified the sampling sites into three groups based on the nature of pollution. Eastern side sampling sites are clustered together, which has more ion concentration due to the flow of groundwater from west to east and more residence time.