A Statistical appraisal to hydrogeochemistry of fluoride contaminated ground water in Nayagarh district, Odisha

Seasonal variation of ground water in Nayagarh district, Odisha is determined by analysing both pre and post monsoon water samples. The high fluoride content is an endemic problem in the area and special attention was attached to the point. The chemical compositions of the ground water of the area are dominated by CaCl, NaCl and mixed CaMgCl types in pre-monsoon and CaHCO3-mixed CaMgCl type in post-monsoon. This is largely due to chemical weathering of Eastern Ghats Mobile Belt rock types. Increasing alkalinity vis-a-vis F concentration in pre-monsoon is associated with sodium-bicarbonate water types having high pH (> 7) and low calcium and magnesium contents. The percentage of total high fluoride containing water samples is nearly double in pre-monsoon than in post-monsoon. During both the seasons, pH values indicate mildly alkaline to weakly acidic nature of the water samples. Fluoride concentration has good correlation with pH in pre-monsoon whereas in post-monsoon it shows good correlation with Fe. Facies analysis indicates that water is becoming predominantly Ca-Na cation and Cl-SO4-HCO3 anion type in premonsoon than Ca-Mg type and HCO3-Cl-SO4 type in post-monsoon. The seasonal variations in concentrations of anthropogenic components demonstrate that the groundwater system is very less liable to pollution by human activities.