Zone of influence of air sparging in interlayer groundwater system

As a cost-efficient enhanced technique,air sparging is used to address subsurface contamination worldwide.It involves the injection of contaminant-free air into the saturated aquifer in an attempt to enhance aerobic biodegradation and induce mass transfer of volatile contaminants into vapor phase.The zone of influence(ZOI)of air sparging(AS)is a critical parameter for the mechanism studies and project designs,which varies with site characterizations.A case study in northeast China featured by a typical interlayer groundwater system contaminated by hydrocarbons was conducted.Air sparging with soil vapor extraction for remediation was performed based on site characterizations.Groundwater level,temperature and dissolved oxygen in groundwater were monitored in field scale during the air sparging running.The spatial and temporal responses of air sparging to the above parameters were analyzed to reflect the environmental effects of remediation activities,and indicate the ZOI.Mathematical methods,including the least square method and double integral were used to determine the theoretical boundary and volume of the ZOI.In addition,a mathematic model was set up to quantify the water inter-flow in the ZOI on the basis of the understanding of groundwater displacement by sparged air.The results showed that the radius of influence in this case was up to 9 m,and the ZOI presented an inverted cone with 362.04 m3 groundwater in it before AS.Groundwater was up-lifted to the top of the aquifer and then overflowed to the surrounding area,while the flux rate descended with time and the cumulative flux reached 0.97 m3 in 6 h.It could be safely concluded that the lateral groundwater movement was not significant in this case.The knowledge from the comprehensive study could provide useful insight into the design efficiency of in situ air sparging and assist in developing and controlling the sparging system,and even tell the fate and transport of the water-air interaction.