Application of Geochemistry and Isotope to understand the process of
Groundwater Fluoride Elevation in Granitic Aquifer
Abstract
Groundwater fluoride is the major cause of the endemic fluorosis. Global
fluorosis data indicate that that granitic aquifer which fractures
controlled hydrology is highly susceptible to contaminate groundwater
with high fluoride. Till date there has not been any sincere effort to
understand the type of granitic aquifer based on the different type of
the granites and their fluoride content. The present paper assesses the
different types of granites and their fluoride content. Dissolution of
fluoride from these rock types are the major source of high fluoride
contamination in the groundwater. The granitic aquifers are also
dominated by fracture control hydrology which enhances the chances of
rock water interaction and dissolution of fluoride. The mineralogy of
the rocks is also favorable due to the presence of biotite and muscovite
which are found to have high affinity to donate fluoride during rock
water interaction as shown by the following equation.
KAl2[AlSi3O10]F2+2OH- = KAl2[AlSi3O10]OH-+2F- (Muscovite)
KMg3[AlSi3O10] F2+2 OH- = KMg3[AlSi3O10]OH-+2F- (Biotite)
Delineation of the type of aquifer and the geochemistry of the granitic
rocks needs to assess to understand the geogenic causes of fluoride in
the granitic aquifer along with the water chemistry (pH>8)
which enhances the rate of dissolution of fluoride during rock water
interaction. Further estimation can be made by the application pf
isotopic data particularly 18O, 2H, 3H, 34S isotope which can
quantitatively estimate the sources of fluoride and contribution from
different sources as well as rock water interaction time.