Abstract
Abstract. Using the single-well push–pull (SWPP) test to determine the in situ biogeochemical reaction kinetics, a chase phase and a rest phase were recommended to increase the duration of reaction, besides the injection and extraction phases. In this study, we presented multi-species reactive models of the four-phase SWPP test considering the wellbore storages for both groundwater flow and solute transport and a finite aquifer hydraulic diffusivity, which were ignored in previous studies. The models of the wellbore storage for solute transport were proposed based on the mass balance, and the sensitivity analysis and uniqueness analysis were employed to investigate the assumptions used in previous studies on the parameter estimation. The results showed that ignoring it might produce great errors in the SWPP test. In the injection and chase phases, the influence of the wellbore storage increased with the decreasing aquifer hydraulic diffusivity. The peak values of the breakthrough curves (BTCs) increased with the increasing aquifer hydraulic diffusivity in the extraction phase, and the arrival time of the peak value became shorter with a greater aquifer hydraulic diffusivity. Meanwhile, the Robin condition performed well at the rest phase only when the chase concentration was zero and the solute in the injection phase was completely flushed out of the borehole into the aquifer. The Danckwerts condition was better than the Robin condition even when the chase concentration was not zero. The reaction parameters could be determined by directly best fitting the observed data when the nonlinear reactions were described by piece-wise linear functions, while such an approach might not work if one attempted to use nonlinear functions to describe such nonlinear reactions. The field application demonstrated that the new model of this study performed well in interpreting BTCs of a SWPP test.
Highlights
A single-well push–pull (SWPP) test is a popular technique to characterize the in situ geological formations and to remedy the polluted aquifer by a series of biogeochemical reactions (Istok, 2012; Phanikumar and McGuire, 2010; Schroth and Istok, 2006)
As for the analytical solutions of the SWPP test, they have been widely used for applications, due to the high efficiency and great accuracy of the solutions, like the model of Gelhar and Collins (1971) for a fully penetrating well, the model of Schroth and Istok (2005) for a point source/sink well, and the model of Huang et al (2010) for a partially penetrating well, assuming that the advection, the dispersion and the first-order reaction were involved in the transport processes
Where Ci is the aqueous-phase concentration of the ith reactive solute, Si is the solid-phase concentration of the ith reactive solute, t is the time in the SWPP test, ρb is the bulk density, θ is the porosity, H is the Heaviside step function, λj and nj are the constant and orders, N is the number of the segment, tj∗ and tj∗+1 are the times at two ends of segment j, and Fj is Monod/Michaelis–Menten kinetics
Summary
A single-well push–pull (SWPP) test is a popular technique to characterize the in situ geological formations and to remedy the polluted aquifer by a series of biogeochemical reactions (Istok, 2012; Phanikumar and McGuire, 2010; Schroth and Istok, 2006). Excluding the wellbore storage may overestimate the concentration in the wellbore at the early stage of the injection phase before the pre-test water inside the wellbore is completely flushed out of the borehole into the aquifer. The concentration at the well screen may not be zero at the early stage of the rest phase when the chase concentration was not zero All these mixing effects occurring in the wellbore are named the wellbore storage of the solute transport. This study addresses multi-species reactive transport associated with SWPP tests with a better conceptual model that acknowledges the realistic circumstances that have been either overlooked or overly simplified in previous investigations. The sensitivity analysis and uniqueness analysis will be employed to investigate the assumptions used in previous studies on the parameter estimation
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
