Groundwater quality assessment based on groundwater pollution index using Geographic Information System at Thettiyar watershed, Thiruvananthapuram district, Kerala, India

The present study was carried out to assess the drinking and irrigation water quality of groundwater resources of the Thettiyar watershed, Thiruvananthapuram district, Kerala, India. The water quality of the study area is explained by using multiple water quality analysis techniques, such as water quality index, spatial assessment of groundwater through GIS-based interpolation technique, and also multivariate statistical analysis. Piper trilinear diagram was used to recognize the water type in the study area. The USSL diagram and Wilcox diagram were used in this study to identify the suitability of the irrigation water. A total of 50 groundwater samples were taken during the pre-monsoon and the monsoon. The samples were tested for various physico-chemical parameters such as pH, EC, TDS, and the major cations and anions. The results show that the groundwater in the study area is acidic; during pre-monsoon, the pH varies from 4.5 to 7.8 with an average of 6.3 and in the monsoon, the pH of water samples is 4.26 to 7.6 with an average of 5.64. The concentration of all other parameters is within the permissible limit. Pollution index of groundwater (PIG) unveiled that the study area has insignificant pollution in terms of drinking water quality. Factor analysis of groundwater revealed three pre-monsoon factors and four monsoon seasonal factors were obtained from this analysis. The varifactors resulting from the factor analysis have shown that the quality fluctuations are mainly due to activities such as water-rock interaction, dilution activity, and anthropogenic activities. Various analytical and statistical studies in the region have shown that the quality of groundwater is influenced by the combined activities of natural activities and anthropogenic events. The detailed study revealed that groundwater sources in the Thettiyar watershed are suitable for drinking and irrigation purposes. © 2021, Saudi Society for Geosciences.