Geochemical factors controlling the occurrence of high-fluoride groundwater in the western region of the Ordos basin, northwestern China

• Published in: Environmental pollution (1987) 2019-09, Vol.252 (Pt B), p.1154-1162
• Main Authors: Su, He, Wang, Jiading, Liu, Jingtao
• Format: Article
• Language: English
• Subjects: High-F− groundwater; Hydrogeochemical processes; Ordos basin; Principal component analysis; Stable isotopes
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2019.06.046

Hydrogeochemistry and isotope hydrology were carried out to investigate the spatial distribution of fluoride (F−) and the mechanisms responsible for its enrichment in the western region of the Ordos basin, northwestern China. Sixty-two groundwater samples from the unconfined aquifer and fifty-six from confined aquifer were collected during the pre-monsoon (June 2016). Over 77% of groundwater samples from the unconfined aquifer (F− concentration up to 13.30 mg/L) and approximately 66% from confined aquifer (with a maximum F− concentration of 3.90 mg/L) exhibit F− concentrations higher than the Chinese safe drinking limit (1.0 mg/L). High-F− groundwater presents a distinctive hydrochemical characteristic: a high pH value and HCO3− concentration with Ca-poor and Na-rich. Mineral dissolution (e.g., feldspar, calcite, dolomite, fluorite), cation exchange and evaporation in the aquifers predominate the formation of groundwater chemistry, which are also important for F− enrichment in groundwater. Mixing with unconfined groundwater is a significant mechanism resulting in the occurrence of high-F− groundwater in confined aquifer. These findings indicate that physicochemical processes play crucial roles in driving F− enrichment and that may be useful for studying F− occurrence in groundwater in arid and semi-arid areas. [Display omitted] •High-F− groundwater widely occurs in the western region of the Ordos basin, China.•High-F− groundwater is high pH and HCO3− concentration, with Ca-poor and Na-rich.•Mineral dissolution, evaporation and cation exchange govern groundwater chemistry.•Mixing with unconfined groundwater may cause F− enrichment in confined groundwater. Multiple methods were integrated to illustrate the geochemical factors controlling the occurrence of high-F- groundwater.