Identification of controlling processes of groundwater quality in a developing urban area using principal component analysis

Abstract

Hydrogeochemistry is an important tool for the evaluation of the effect of human activities on aquifer system. Sixty eight groundwater samples were collected from bore wells during pre- and post-monsoon from Nagpur , a fast growing city in India, to assess the spatial controlling processes of groundwater contamination using principal component analysis (PCA). Groundwater has variable total dissolved solid (TDS) and total hardness (TH) values classifying them from fresh to saline and moderately hard to very hard types. About 36 and 33 % of the total groundwater samples during pre- and post-monsoon, respectively, are not suitable for drinking purpose. The graphical presentation of groundwater chemistry has indicated Ca–HCO3, mixed Ca–Na–HCO3 and mixed Ca–Mg–Cl types. The PCA summarizes the chemical variables of pH, EC, TDS, TH, TA, Na+, K+, Ca2+, Mg2+, HCO3 −, Cl−, SO4 2− and NO3 − into two PC loadings, accounting for 61.33 and 62.09 % of the total variance during pre- and post-monsoon, respectively. The first PC shows high loadings of EC, TDS, TH, Cl−, NO3 −, Ca2+ and Mg2+, which considered as pollution-controlled processes of anthropogenic sources. Second PC has high loadings of Na+ and HCO3 −, which is taken as alkalinity and pollution-controlled processes of geogenic and anthropogenic sources, respectively. The PC scores suggest the causes of variation in the groundwater chemistry. Negative values of chloro-alkaline indices suggest the prevalence of reverse ion exchange irrespective of the season, silicate weathering and anthropogenic activities over the controlling of groundwater quality which further PCA. Thus, the PCA helps as a tool to assess the controlling processes of the groundwater quality.