Author:
Wang Quanrong,Zhan Hongbin
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.
Subject
General Earth and Planetary Sciences,General Engineering,General Environmental Science
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