The effect of boundary conditions on the single-well push-pull test in a partially penetrated well

Boundary conditions of well screen are critical for modeling reactive transport around a partially penetrated well in a single-well push-pull (SWPP) test. Previous SWPP test models often assumed that water flux was uniformly distributed along the well screen of the partially penetrated well, named the uniformly distributed flux boundary condition (UFBC). To investigate the influence of such an assumption on reactive transport in the SWPP test, we develop a new finite-difference numerical model under a flow field with a finite hydraulic diffusivity in this study, considering the wellbore storage. The uniformly distributed head boundary condition (UHBC) is employed for both groundwater flow and reactive transport across the well screen. The dispersion coefficients are in a tensor form, depending on both horizontal and vertical flow components. The results show that the UFBC model may cause non-negligible errors when modeling reactive transport in the SWPP test with a partially penetrated well. Such errors are obvious at the early stage of the extraction phase, but become negligible at late stage of the extraction phase. The UHBC solution for reactive transport is smaller than the UFBC solution at the middle of the well screen, but greater than the UFBC solution at the top or bottom of the well screen. Using the SWPP test to investigate the reactive transport in subsurface, in addition to the breakthrough curves (BTCs), the information of the flow field (like well geometry information and the observed time-drawdown data) is necessary and could be used to calibrate the model. Field application demonstrates that the UHBC model performs better than the UFBC model when interpreting BTCs of the SWPP test in the extraction phase. The findings of this study can help for better understanding of reactive transport in the SWPP test.