Revisiting simplified model of a single-well push–pull test for estimating regional flow velocity

Abstract

Simplified analytical models of the single-well push–pull (SWPP) test have been widely used to estimate the regional flow velocity and the aquifer porosity, where the simplifications refer to that the dispersion effect is negligible, and the flow is steady state during the entire SWPP test. However, the errors caused by such assumptions have not been investigated thoroughly. In this study, numerical modeling of the SWPP test without above-mentioned simplifications and the field experimental data will be employed to test the applicability of the simplified analytical models. The numerical simulation is based on a mathematical model composed of a two-dimensional transient flow and transport model, which will be solved by the finite-element method. The results indicate that errors increase with the increasing dispersivity when using the simplified analytical models to estimate both regional flow velocity and porosity. The errors refer to the relative difference between the input parameters of the numerical modeling and the estimated parameters by the simplified models. Such errors also depend on the input values of regional groundwater velocity, drift time of the SWPP test, and aquifer porosity. Specifically, the errors caused by the simplified models of estimating regional groundwater velocity decrease with increasing input regional groundwater velocity, increasing input drift time, and decreasing input porosity. The errors produced by the simplified models of estimating porosity decrease with increasing input regional groundwater velocity, increasing input drift time, and decreasing input porosity. Field in-situ experiments show that the fitness of the observed breakthrough curves (BTCs) by the numerical modeling is far better than the simplified analytical models. The estimated regional flow velocity by the numerical modeling of this study is closer to the estimated values by previous other studies.