The strengthening method for trichloroethylene back diffusion from low-permeability zones
Due to the heterogeneous underground media,the back diffusion of dense non-aqueous phase liquids(DNAPLs)in low-permeability zones(LPZ)is the primary cause of prolonged remediation time and reduced remediation efficiency in the corresponding groundwater pollution source area.In this study,a mixed surfactant system(2 000 mg·L-1 NaCl+4％Tween80/MA-80(1∶1))and a xanthan gum-enhacned system were applied to a sand box contaminated with NAPL-phase trichloroethylene(TCE).These systems were combined with the light transmission method(LTM)to investigate that the effect of permeability contrast between high and low permeability media on the back diffusion of TCE,the impacts of hydrodynamic enhancement and the surfactant compounding system on the back diffusion of TCE,and the mechanism of surfactant action on TCE in low-permeability zones.The results demonstrated that a greater contrast in permeability coefficients between high and low permeability zones increased the difficulty in overcoming the characteristics of low-permeability zones,specifically the challenges of mass transfer and slow flow.Under different permeability coefficient ratios and heterogeneous conditions,surfactants exhibited different solubilization and mobilization effects on TCE in low-permeability zones.The compounding system can improve the sweep efficiency and further promote TCE back diffusion in these zones.The findings of this study could provide insights into selecting appropriate DNAPL remediation strategies in low-permeability zones in heterogeneous formations with varying permeability coefficient ratios for practical applications.
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