Hydrogeochemical processes of fluoride enrichment in Chimakurthy pluton, Prakasam District, Andhra Pradesh, India

• Published in: Environmental earth sciences Vol. 75; no. 8; pp. 1 - 17
• Main Authors: Reddy, A. G. S., Reddy, D. V., Kumar, M. Sudheer
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.04.2016; Springer Nature B.V
• Subjects: Biogeosciences; Earth and Environmental Science; Earth Sciences; Environmental Science and Engineering; Fluorides; Geochemistry; Geology; Groundwater; Groundwater pollution; Hydrology; Hydrology/Water Resources; Original Article; Terrestrial Pollution; Andhra Pradesh India; ISW, India, Andhra Pradesh; Bicarbonate; Water types; Fluoride; Na; Groundwater; Silicate weathering; Gabbro
• ISSN: 1866-6280; 1866-6299
• DOI: 10.1007/s12665-016-5478-8

Thirty-six groundwater samples were collected from Chimakurthy area, Prakasam District, Andhra Pradesh. On hydrogeochemical evaluation, it was found to be contaminated. Based on fluoride concentration, the samples were segregated into Group A, Group B, and Group C. Fluoride concentration varies from 0.23 to 9.84 mg/l, with the mean value of 2.01 mg/l; 44 % of the tested samples had F −  > 1.50 mg/l. Apart from F − , the water was contaminated with NO 3 − and Cl − implying both geogenic and anthropogenic pollution of the aquifer. Ionic dominance pattern was unique in samples with low, moderate to high F − concentrations. Na + and HCO 3 − were progressively increasing along with F − from Group A to C, whereas Ca 2+ and Mg 2+ were depleting. Groundwater facies were unique among different group samples especially in end members with low and high F − concentration suggesting that F − dissolution was strongly influenced by the chemical nature of solution. Na + /Cl − molar ratio was >1, whereas Na +  + K + :Tz + and Ca 2+  + Mg 2+ :Tz + ratios were <1 in all samples indicating that Na + was released from silicate weathering process. It also confirms that F − was contributed from lithogenic sources of aquifer material. Mean molecular ratios of <1 for Ca 2+ :Mg 2+ in Group B samples and 1–1.2 in Groups A and C support that the Ca 2+ and Mg 2+ were added into aquatic medium by calcite and dolomite dissolution. Contradictory distribution of F − in north (low) and south (high) indicates that availability of F − minerals in aquifer matrix influenced the rate of F − absorption in accompanying water. Variation in F − concentration in groundwater of the core area (south) supports the hypothesis of aquatic chemistry acting as catalyst in F − dissolution into formation waters even though the aquifer was enriched with F − minerals. Very high F − in groundwater in the contact zone of country rock and plutonic intrusive indicates that F − mineralization occurred under geothermal conditions. The fracture network in disturbed and fragile contact zone has facilitated development of potential aquifers and enhancement in F − concentration.