The impact caused by tap water recharge on groundwater quality

Large-scale artificial recharge is planning for controlling subsidence in the fourth confined aquifer (A4) in Shanghai. However, it is unknown what negative impact would occur after the injection of tap water into A4. Based on collected material and data available in some sporadic experiments about tap water recharge to A2, A3, and A4 from the 1960s to the 1980s, this paper gave some evaluations on the changes of groundwater chemical characteristics, migration range of recharge water in single well and groups of wells. And various factors affecting groundwater quality during the artificial injection were discussed. The results showed that the physical and chemical composition of groundwater trended to that of recharge water, maximum influence distance of recharge water in single well in A2 was about 100m in 20years, and the maximum radius of groups of wells in A4 was about 1,000m, while the range causing significant changes in groundwater quality was less than 1,000m. This information will offer scientific basis for the large-scale artificial recharge in the near future.