Hydrochemistry and Occurrence of High Fluoride Groundwater in Datong Basin
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Abstract:
To identify the main geochemical processes controlling the fluoride enrichment in groundwater at Datong Basin,total of thirty-one samples were collected for hydrochemical and factor analysis study.High fluoride concentration was detected in both shallow and deep groundwater.In shallow groundwater,the fluoride concentration ranges from 0.01 to 10.37 mg/L,while deep groundwater has lower fluoride concentration,ranging from 0.01 to 3.14 mg/L.High fluoride groundwater is typically Na-HCO3 type water and characterized by high Na concentration.The saturation indices calculated by PHREEQC indicate that fluorite is undersaturated in almost all groundwater samples,meaning that the fluoride concentration in groundwater is mainly controlled by fluorite solubility.Factor analysis indicates that processes including water-rock interaction,carbonate mineral precipitation and cation exchange are the dominant factors for the occurrence of high fluoride groundwater in Datong Basin.Keywords:
Fluorite
Carbonate minerals
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Groundwater is the most important source of drinking water. Fluoride was found in high concentrations in the groundwater from deep wells of the water supply in the southern main Ethiopian rift. The high concentration of fluoride is dominantly geogenic rather than anthropogenic in origin, as the agricultural area was not found to be contaminated with NO3−. Knowledge of fluoride enrichment will help to provide management plans for developing deep groundwater and minimizing the health risks of exposure to fluoride. The chemical processes of fluoride were investigated in the waters in the Bilate River basin using hydrochemical and isotopic tools. The F− concentration ranged from 0.5 to 1.29 mg/L in water from shallow wells and from 0.48 to 5.61 mg/L in water from deep wells. Seventy percent of deep well samples had F− > 1.5 mg/L higher than the World Health Organization potable guideline. The high fluoride concentration in the groundwater was mainly situated in the rift valley of the Bilate River basin, in contrast with low F− groundwater in the highland. The concentration of fluoride was lowest in Ca-Mg-HCO3 type groundwater and highest in Na-HCO3 type groundwater. Moreover, F− was positively correlated with HCO3−, Na+, Na+/Ca2+ and pH in groundwater and Na+/Ca2+ ratios were increased along the flow path. Hydrogeological, hydrodynamic and hydrochemical conditions are responsible for fluoride accumulation in the deep aquifers. Strong dynamic flow in highland areas flush away weathered chemical components (e.g., F−). Thus, surficial weathering is not a major controlling factor for high concentrations of Fluoride in deep groundwater but the combination of silicate hydrolysis and ion exchange mainly control fluoride enrichment in stagnant flow environments.
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Fluorite
Silicate minerals
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Fluoride in groundwater: a case study in Precambrian terranes of Ambaji region, North Gujarat, India
Abstract. Fluoride is one of the critical ions that influence the groundwater quality. World Health Organization (WHO, 1970) and Bureau of Indian Standards (BIS, 1991) set an upper limit of 1.5 mg L−1 in F− concentration for drinking water purpose and above affects teeth and bones of humans. The presence of fluoride in groundwater is due to an interaction of groundwater and fluoride bearing rocks. Fluoride rich groundwater is well known in granitic aquifers in India and elsewhere. Generally, the concentration of F− in groundwater is controlled by local geological setting; leaching and weathering of bedrock and climatic condition of an area. The main objective of the present study is to assess the hydrogeochemistry of groundwater and to understand the abundance of F− in groundwater in hard rock terranes of Ambaji region, North Gujarat. A total of forty-three representative groundwater samples were collected and analyzed for major cations and anions using ICP-AES, Ion Chromatograph (Metrohm 883 Basic IC Plus) and titration methods. The F− concentration in groundwater of this study area ranges from 0.17 to 2.7 mg L−1. Among, twenty groundwater samples have fluoride exceeding the maximum permissible limit as per the BIS (1.5 mg L−1). It is also noticed that residents of this region are affected by dental fluorosis. The general order of the dominance of major cations and anions are Ca2+ > Mg2+ > Na+ > K+ and HCO3- > Cl− > F− respectively. Geochemical classification of groundwater shows most of the samples are the alkaline earth-bicarbonate type. The semi-arid climatic conditions of the region, the dominance of granitoid-granulite suite rocks and the fracture network in the disturbed and brittle zone has facilitated the development of potential aquifers and enrichment in F− concentration in this area. The concentration of fluoride is due to high evaporation rate, longer residence time in the aquifer zone, intensive and long term pumping for irrigation.
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The hydrogeochemical and isotopic investigations of high fluoride (up to 8.26 mg L-1) groundwater in the Datong Basin, Northern China were carried out. The elevated δD and δ18O, low F/Cl ratios, and the presence of low tritium in the high fluoride groundwater reflected the effects of long water-rock reactions and evapotranspiration.
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