Understanding the dilemmas and breakdown of the reactive migration of in situ groundwater injection reagents from an environmental geology perspective

In situ chemical injection technology is widely used in groundwater contamination remediation projects because of its high efficiency and low disturbance. Hydrodynamic dispersion is the basis for reagent transport in groundwater. Efficient diffusion and directional delivery processes of reagents in contaminated groundwater areas are key to controlling remediation efficiency. The complex subsurface environment and the limited efficacy of existing treatment technologies pose significant challenges for groundwater contamination remediation. Inhomo­geneous hydrodynamics in groundwater channels with heterogeneous media lead to significant uncertainties in the migration of reagents. Here, we conducted a systematic review to assess the nonideal transport behavior of remediation reagents under convection-dispersion, the blocking effect of heterogeneous media pores, and the kinetic process of reactive migration in saturated aquifers. The dilemma problems of low migration rate, unknown directionality, and nontargeted reactions encountered by reagents in porous groundwater media are systematically discussed from an environmental geological perspective. On this basis, we emphasize the strategies for the targeted control of reagent transport based on the regulation of the anthropogenic hydrodynamic flow field and density effects, an auxiliary strategy for regulating the target action of remediation to reduce nontarget reactions. Finally, future research needs are proposed to advance the development of engineering practices for green and sustainable in situ remediation technologies for contaminated groundwater.