Various models have been developed for radially divergent tracer tests in two-zone confined aquifers of the skin and formation zones. However, existing numerical solutions require considerable computing time because of the fine spatial discretization of skins. The abrupt change in parameters near the skin-formation interface produces significant errors while predicting the spatiotemporal concentration near the interface, despite fine spatial discretization. In this study, a new model was developed for conducting radially divergent tracer tests in a partially penetrating well in a two-zone-confined aquifer. The skin was treated as a new transient Robin boundary condition specified at the skin-formation interface to reflect the effect of solute adsorption/release in the
skin and achieve no skin discretization. A finite element solution for the model was developed. The analytical solution of the model modified for full penetration of the well was developed using the Laplace transform. These results suggest that the transient Robin boundary condition leads to accurate concentration predictions affected by negative skin. The analytical solution predicts reliable ranges of 0.47~0.48 m for the skin width w and 6.4~7.7 m for the longitudinal dispersivity α'l, whereas a traditional solution exhibits a range of 0.45 m≤w≤0.54 m and 0.6 m≤α'l≤10 m. The finite element solution required only 3% of the computing time for obtaining a finite element solution based on fine skin discretization. In conclusion, this study provides implications not only
for theoretical advances but also for useful numerical methods.