Optimization design of groundwater circulation well structure in super-thick aquifer
Effective remediation of contaminated aquifer using groundwater circulation well(GCW)technology annot be achieved when the thickness of the aquifer is greater than 34.5 m.In this study,the simulation of GCW operation in a super-thick aquifer(STA)with a thickness of 80 m using MODFLOW and MODPATH was conducted to obtain the structure of GCW which is suitable for STAs.Simulation results demonstrate that a circulating zone was generated when the length of well walls section was≤26 m for two-screen GCW,with running period of 1 year and a flow rate of 400 m3·d-1.The maximum vertical length of circulating capture zone(27.5 m)was obtained from the repeated design studies,with the condition of 34 m-well length,two 4 m-long screen sections,one 26 m-long solid section,and a running period of 1 year.The remediation of STA with a thickness of 80 m was not accomplished using the optimized GCW with the maximum vertical length of circulating capture zone(27.5 m).However,multi-filter GCW significantly improved the remediation of STAs by increasing the range of remediation and reducing the ratio of dead zones.For a multi-filter GCW with three screens,the vertical length of the circulating capture zone of 56.52 m was achieved.Furthermore,a multi-filter GCW with four screens of 70.52 m was achieved with a particle recovery rate of 58％and a maximum influence radius of 44.95 m.Therefore,the multi-filter GCW with four screens can meet the requirements for remediating an 80 m-thick STA.These findings provide significant theoretical information for the design of GCW structures in STAs.
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