Recharge history and controls on groundwater quality in the Yuncheng Basin, north China

Environmental isotopes and water quality indicators (e.g. TDS and NO3 contents) were used to characterize the age, recharge history and controls on the quality of groundwater resources in the Yuncheng Basin, north China, where extensive extraction occurs for agriculture and domestic supply. delta O-18 and delta H-2 values as low as -10.6 . and -73 parts per thousand, respectively, together with low radiocarbon activities (70 pmC), indicating a significant component of modern (post-1950s) recharge. The shallow groundwater has higher delta O-18 and delta H-2 values (up to -8.1 . and -54 parts per thousand) that are similar to those in modern summer monsoon rainfall, indicating that current recharge is via direct infiltration and/or leakage of ephemeral streams during heavy rain events. Historic recharge rates estimated using radiocarbon ages are between 1 and 10 mm/year, corresponding to