Hydrochemical Characteristics of Groundwater—Assessment of Saltwater Intrusion Along Krishna and Godavari Delta Region, Andhra Pradesh, India

The Intrusion of saltwater into a freshwater aquifer is of particular concern to the coastal community. Removal of excess groundwater from the shallow aquifers is known to be the primary cause of contamination by saltwater. In this study, groundwater samples were obtained in the 2016 and 2017 pre-monsoon and post-monsoon seasons at 105 locations from dug wells and bore wells along the coast of Andhra Pradesh in the Krishna and Godavari deltas. Groundwater samples are tested for large ions to determine the infiltration of salt water and to classify the salinity sources in the delta zone. The Various hydro-geochemical parameters such as pH, Electrical Conductivity (EC), Total Dissolved Solids (TDS), Ca2+, Mg2+, K+, Na+, CO3, HCO3-, Cl-, and SO42- are evaluated for the delineation of the intrusion of saltwater in terms of Ca2+/ Mg2+, Cl-/(CO3+ HCO3-), Na+/Cl- ratios. It is reported that the availability of fresh groundwater is 14%and 62% respectively during the pre-monsoon and post-monsoon seasons. The percentage levels of contamination in groundwater for slight, moderate, injuriously, highly, and severely categories are 43%, 22%, 12%, 8%, and 1% respectively for pre-monsoon season. However, during the post-monsoon season, the levels of contaminations in the above- mentioned categories are 22%, 9%, 4%, 1%, and 3%. The extent of contamination during the post-monsoon season is observed to be lower than during the pre-monsoon. The groundwater ratio of Na+- Cl− during pre-monsoon and post-monsoon seasons is 71%and 60% respectively. The Saltwater Mixing Index (SMI) is also measured, and extremely high is found.