title: Occurrence and hydrogeochemical characteristics of high-fluoride groundwater in Xiji County, southern part of Ningxia Province, China.
abstract: High-F(-) groundwater is widely distributed in Xiji County, which endangers the safety of drinking water. In order to evaluate the key factors controlling the origin and geochemical mechanisms of F(-) enrichment in groundwater at Xiji County, one hundred and five groundwater samples and sixty-two sediment samples were collected. Fluoride concentration in the groundwater samples ranged from 0.2 to 3.01 mg/L (mean 1.13 mg/L), with 17 % exceeding the WHO drinking water guideline value of 1.5 mg/L and 48 % exceeding the Chinese drinking water guideline value of 1.0 mg/L. High-F(-) groundwaters were characterized by hydrochemical types of Na-HCO3 and Na-SO4·Cl, which were found in Quaternary sediment aquifer and in Tertiary clastic aquifer, respectively. Conditions favorable for F(-) enrichment in groundwater included weakly alkaline pH (7.2-8.9), low concentration of Ca(2+), and high concentrations of HCO3 (-) and Na(+). Calcite and fluorite were the main minerals controlling F(-) concentration in groundwaters. The hydrolysis of F-bearing minerals in aquifer sediments was the more important process for F(-) release in Tertiary clastic aquifer, which was facilitated by long residence time of groundwater, in comparison with Quaternary sediment aquifer. Cation exchange would also play important roles, which removed Ca(2+) and Mg(2+) and led to more free mobility of F(-) in groundwater and permitted dissolution of fluorite, especially in Tertiary clastic aquifer. However, evapotranspiration and competing adsorption of B and HCO3 (-) were the more important processes for F(-) enrichment in Quaternary groundwater. Groundwater in Lower Cretaceous aquifer had relatively low F(-) concentration, which was considered to be the potential drinking water resource.
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (Beijing), Beijing, 100083, People's Republic of China.|MOE Key Laboratory of Groundwater Circulation & Environment Evolution and School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing, 100083, People's Republic of China.
authors.forename: Chao
authors.initials: C
authors.lastname: Wei
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (Beijing), Beijing, 100083, People's Republic of China. hmguo@cugb.edu.cn.|MOE Key Laboratory of Groundwater Circulation & Environment Evolution and School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing, 100083, People's Republic of China. hmguo@cugb.edu.cn.
authors.forename: Huaming
authors.initials: H
authors.lastname: Guo
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (Beijing), Beijing, 100083, People's Republic of China.|MOE Key Laboratory of Groundwater Circulation & Environment Evolution and School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing, 100083, People's Republic of China.
authors.forename: Di
authors.initials: D
authors.lastname: Zhang
authors.affiliation: MOE Key Laboratory of Groundwater Circulation & Environment Evolution and School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing, 100083, People's Republic of China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wu
authors.affiliation: Center for Hydrogeology and Environmental Geology, China Geological Survey, Baoding, 071051, Hebei, People's Republic of China.
authors.forename: Shuangbao
authors.initials: S
authors.lastname: Han
authors.affiliation: Center for Hydrogeology and Environmental Geology, China Geological Survey, Baoding, 071051, Hebei, People's Republic of China.
authors.forename: Yonghui
authors.initials: Y
authors.lastname: An
authors.affiliation: Center for Hydrogeology and Environmental Geology, China Geological Survey, Baoding, 071051, Hebei, People's Republic of China.
authors.forename: Fucun
authors.initials: F
authors.lastname: Zhang
mesh_terms: D002681:China; D060766:Drinking Water / Q000032:analysis*; D004784:Environmental Monitoring; D005459:Fluorides / Q000032:analysis*; D060587:Groundwater / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis
chemical_list: D060766:Drinking Water; D014874:Water Pollutants, Chemical; D005459:Fluorides
keywords: F−; Geochemistry; Groundwater; Stable isotope; Water–rock interaction