Origin and Spatial Distribution of Fluoride in Aquifers of Ambalapuzha Basin, Alappuzha District, Kerala, South India

The present study is an attempt to find out the origin, occurrence and distribution of fluoride content in deep aquifers of Ambalapuzha river basin of Ambalapuzha Taluk. Comparison of the past tube well data with present data, at various localities of the study area shows a drastic increase in fluoride to hazardous level in recent years. Critical analysis of the data reveals that out of 15 tube wells, in all the 14 tube wells, fluoride is much above permissible limit. When cations and anions of the tube well samples were plotted in the piper diagram, replacement of K by Na is clearly indicated. Water type identified with in the study area is predominantly rich in sodium with sodium ion dominance. From ANOVA test, it is revealed that a significant effect of sodium, pH, TDS, Alkalinity, bicarbonate and chloride on fluoride. From the study it is found that the large scale withdrawal of groundwater from the clay bed resulted in increase of Na in groundwater. This in turn promoted leaching of fluoride bearing minerals such as flour apatite, apatite, hornblende etc in to the clay beds at deep sources and liberation of fluoride by the process of anion exchange and increased alkalinity which in turn results increase of pH. The study made it clear that the fluoride enrichment is insitu and it is better to avoid development of deep aquifers in Ambalapuzha taluk or it is to be utilized in a very judicious manner by the town planners and authorities of public water supply agencies.