Impacts of Bioclogging on Hydraulic Parameter Estimation by Injection Tests

Injection test in petroleum-contaminated aquifer involves microbial effects, resulting in under- or over- estimation of the hydraulic parameters. In this study, we developed a mathematical model considering radial groundwater flow, solute transport and biofilm growth for the injection test in a confined aquifer. The steady-state biofilm theory was employed to describe the strongest changes of hydraulic properties due to the biofilm growth activated by the injection of high concentration dissolved oxygen (DO). The increasing head and relative DO concentration for both cases with and without biofilm effects were computed, and a sensitivity analysis of the increasing head on both microbially endogenous and exogenous parameters were performed. The results indicated that the permeability is underestimated or the dispersivity is overestimated, if the injection test or tracer test is conducted in a petroleum-contaminated area. Except for yield coefficient and biofilm dry mass density, which are two microbially endogenous factors and affect most directly the biofilm thickness, injection rate and medium particle diameter, as two microbially exogenous factors, also influence the biofilm thickness. In addition, when considering biofilm effects, the increasing head is much more impacted by medium particle diameter than the injection rate, i.e., much more under- or over- estimation exist in the aquifer with fine-textured medium than coarse-textured medium, but very limited estimation error can be eliminated by reducing injection rate. Our modeling opens a way for the simulation of injection test in confined aqiuifer involving microbial effects, to reduce the errors in hydraulic parameter estimation. More efforts are still needed to reveal the mechanism of biofilm growth before reaching the steady state.