Seasonal effects on groundwater fluoride and evaluating health hazards: In-situ remediation via managed aquifer recharge

This research examines the hard-rock aquifer system within the Nagavathi River Basin (NRB) South India, by evaluating seasonal fluctuations in groundwater composition during the pre-monsoon (PRM) and post-monsoon (POM) periods. Seasonal variations significantly influence the groundwater quality, particularly fluoride (F^-) concentrations, which can fluctuate due to changes in recharge, evaporation, and anthropogenic activities. This study assesses the dynamics of F^- levels in PRM and POM seasons, and identifies elevated health risks using USEPA guidelines and Monte Carlo Simulations (MCS). Groundwater in the study area exhibits alkaline pH, with NaCl and Ca-Na-HCO₃ facies increasing in the POM season due to intensified ion exchange and rock-water interactions, as indicated in Piper and Gibb’s diagrams. Correlation and dendrogram analyses indicate that F^- contamination is from geogenic and anthropogenic sources. F^- levels exceed the WHO limit (1.5 mg/L) in 51 PRM and 28 POM samples, affecting 371.74 km² and 203.05 km², respectively. Geochemical processes, including mineral weathering, cation exchange, evaporation, and dilution, are identified through CAI I & II. Health risk assessments reveal that HQ values >1 in 78% of children, 73% of teens, and 68% of adults during PRM, decreasing to 45%, 40%, and 38%, respectively, in POM. MCS show maximum HQ values of 5.67 (PRM) and 4.73 (POM) in children, with all age groups facing significant risks from fluoride ingestion. Managed Aquifer Recharge (MAR) is recommended in this study to minimize F^- contamination, ensuring safe drinking water for the community.