This study aims to use fluoride as an additional indicator for seawater intrusion apart from the known effective geochemicalindicators such as EC, TDS, sodium, chloride and bromide. Groundwater in a coastal part of Arani-Koratalaiyar river basin locatednorth of Chennai, Tamil Nadu, India was assessed to determine its suitability for domestic purpose and to delineate the regionaffected by seawater intrusion. Fluoride concentration in groundwater samples from forty nine locations varied from 0.02 mg/l to 2.9 mg/l with an average of 0.5 mg/l. As per the Bureau of Indian Standards, the permissible range of fluoride in drinking water is 0.6–1.5 mg/l. Fluoride concentration in groundwater of this area exceeds 1.5 mg/l in 6% of the groundwater samples and is below 0.6 mg/l in 74% of the groundwater samples. There is no known geological source for fluoride in this area. Spatial variation influoride concentration in groundwater indicates that the coastal areas have comparatively high fluoride due to seawater intrusionwhich was similar in comparison with EC and bromide concentration measured in groundwater. This study indicates that fluoridecan be used as an indicator of seawater intrusion in coastal areas.
*Read the full study at http://fluoridealert.org/wp-content/uploads/nair-2016.pdf