Abstract: Aquitards are an important part of an aquifer system. Hydraulic properties of an aquitard, such as hydraulic conductivity and specific storage must be determined before the investigation of strata deformation and groundwater depletion. Based on the proposed one-dimensional schematic diagram of an aquifer system, a dimensionless analytical solution for flow in the aquitard is derived under the boundary condition of drawdown in adjacent aquifers showing a linear increase with time. The dissipation process of time-lag drawdown in the aquitard is analyzed. The type curve of cumulative aquitard compaction versus time is derived based on the mass balance equation of water. A new type curve method is further derived for estimating the hydraulic conductivity and specific storage of the aquitard. The type curve method reflects the time-lag drainage within the aquitard. This method is tested by a field application to the Shanghai aquifer system to obtain the hydraulic parameters of the second aquitard at the f10-7 extensometer site. Field test results show that the hydraulic conductivity and specific storage are 4.26 m/s and 2.22 , respectively. For an aquifer system with long-term observed water level and deformation data, the new type curve method can be used to some extent.

Key words: aquitard, hydraulic parameters, analytical solution, type curve method