Statistical analysis of the hydrogeochemical evolution of groundwater in hard rock coastal aquifers of Thoothukudi district in Tamil Nadu, India

Abstract

The study of groundwater hydrogeochemistry of a hard rock aquifer system in Thoothukudi district has resulted in a large geochemical data set. A total of 100 water samples representing various lithologies like Horn- blende Biotite Gneiss, Alluvium Marine, alluvium Fluvial, Quartzite, Charnockite, Granite and Sandstone were col- lected for two different seasons and analyzed for major ions like Ca 2? ,M g 2? ,N a ? ,K ? , HCO3 - ,C l - ,S O 4 2- , NO3 - ,P O 4 - ,F - and H4SiO4. Statistical analysis of the data has been attempted to unravel the hidden relationship between ions. Correlation analyses and factor analyses were applied to classify the groundwater samples and to identify the geochemical processes controlling groundwa- ter geochemistry. Factor analysis indicates that sea water intrusion followed by leaching of secondary salts, weath- ering and anthropogenic impacts are the dominant factors controlling hydrogeochemistry of groundwater in the study area. Factor score overlay indicate major active hydrog- eochemical regimes are spread throughout the Eastern, Northwestern and Southeastern parts of the study area. The dominant ions controlling the groundwater chemistry irre- spective of season are Cl - ,N a ? ,M g 2? ,C a 2? ,S O 4 2- ,K ? and NO3 - . An attempt has also been made to note the seasonal variation of the factor representations in the study area. This study also illustrates the usefulness of statistical analysis to improve the understanding of groundwater systems and estimates of the extent of salinity/salt water intrusion.