Effects of Recharge and Discharge on δ²H and δ¹⁸O Composition and Chloride Concentration of High Arsenic/Fluoride Groundwater from the Datong Basin, Northern China

To better understand the effects of recharge and discharge on the hydrogeochemistry of high levels of arsenic (As) and fluoride (F) in groundwater, environmental isotopic composition (δ²H and δ¹⁸O) and chloride (Cl) concentrations were analyzed in 29 groundwater samples collected from the Datong Basin. High arsenic groundwater samples (As > 50 µg/L) were found to be enriched in lighter isotopic composition that ranged from -92 to -78 ‰ for deuterium (δ²H) and from -12.5 to -9.9 ‰ for oxygen-18 (δ¹⁸O). High F-containing groundwater (F > 1 mg/L) was relatively enriched in heavier isotopic composition and varied from -90 to -57 ‰ and from -12.2 to -6.7 ‰ for δ²H and δ¹⁸O, respectively. High chloride concentrations and δ¹⁸O values were primarily measured in groundwater samples from the northern and southwestern portions of the study area, indicating the effect of evaporation on groundwater. The observation of relatively homogenized and low δ¹⁸O values and chloride concentrations in groundwater samples from central part of the Datong Basin might be a result of fast recharge by irrigation returns, which suggests that irrigation using arsenic-contaminated groundwater affected the occurrence of high arsenic-containing groundwater in the basin.