Environmental protection using dewatering technology in a deep confined aquifer beneath a shallow aquifer

Abstract

This paper presents an innovative technology referred to as Dual Function Well (DFW), which has been developed in order to reduce the construction costs of dewatering when excavation is conducted in an aquitard over a confined aquifer. DFW technology is a method to lower both shallow groundwater and deep groundwater, either separately or simultaneously, using one well. The DFW includes two or more independent screens corresponding to each aquifer, and a valve is located between the screens inside a steel pipe. When the valve is closed, groundwater is pumped from the upper screen in the shallow aquifer. When the valve is open, groundwater is pumped from the screens in both the shallow and deep aquifers. DFW technology is used to replace the traditional method involving two sets of wells, in which the first set of wells pumps groundwater from the shallow aquifer, and a second set pumps groundwater from the deep aquifer. To investigate the effectiveness of DFW, field pumping tests using a DFW were conducted, and both groundwater head and settlement were monitored. Numerical simulation was adopted to simulate the results of the pumping tests. Comparison between the results from the DFW and from an ordinary mixing well indicates that the use of a DFW with the valve closed can reduce the pumping time from a deep aquifer and can reduce the ground settlement caused by dewatering. The results indicate the DFW technology is feasible and effective.