Hydrochemical characterisation and critical evaluation of groundwater quality in Dakshin Dinajpur, West Bengal: insights into fluoride and iron contamination

ABSTRACT The current study explores the hydrogeochemical characteristics of groundwater in Tapan block, Dakshin Dinajpur district, West Bengal, with a focus on iron and fluoride contamination and assesses related environmental concerns. A comprehensive method involving hydrochemical evaluation, indexing approach, and multivariate and geostatistical tools was employed to comprehend the geochemical mechanism involved and delineate the influencing factors that determine the groundwater quality. Results have shown that 4% of groundwater samples exceed the WHO limit for fluoride (>1.5 mg/L) at 90–120 m depth in both pre- and post-monsoon seasons; while iron levels surpass WHO guidelines in 24% (pre-monsoon) and 18% (post-monsoon) of samples. Major ion chemistry indicates seasonal shifts, with Na+ and Ca2+ as dominant cations and HCO3- prevailing among anions. The majority of the sample points to water–rock interaction phenomena except some minor, influenced by evaporation mechanism. Multivariate analysis depicts fluoride-bearing mineral dissolution as key geochemical processes, with ion exchange contributing to fluoride enrichment. Fluoride and iron originate from different sources; the Barind tract's iron-rich, oxidised sediments likely contribute to elevated iron levels. The findings complement sustainable development goal 6 (clean water and sanitation) by offering crucial insights on groundwater quality and seasonal dynamics and contribute to sustainable management of water resources.