Interception behaviors of mixed chlorinated hydrocarbons in groundwater by DDAC-amended LPBs: Control mechanism and CFD simulation.

Low permeability barrier has emerged as a promising, cost-effective technology for anti-seepage and pollution mitigation in geotechnical engineering. However, its efficacy in organic pollution sites, particularly those contaminated with chlorinated hydrocarbons (CHCs) pales in comparison to its performance in areas contaminated by heavy metals. In order to rectify this deficiency, a novel bentonite backfill, modified with dihexadecyl dimethyl ammonium chloride (DDAC) and designated as DDAC-LPB, is proposed for use in low permeability barriers to contain CHCs in groundwater at contaminated sites. A series of rigid-wall permeability tests, mechanical properties tests, and diffusion tests were conducted to investigate the impact of CHCs solution on hydraulic conductivity, unconfined compression strength and adsorption properties of the LPB, respectively. The results reveal that LPB containing 10 % DDAC modified bentonite exhibits excellent impermeability and mechanical workability, with a 2-5 fold increase in adsorption capacity, primarily driven by the hydrophobic interaction between CHCs and DDAC. Moreover, this study has innovatively applied computational fluid dynamics simulation to the field of solute transport modeling to evaluate the performance of DDAC-LPB in containing CHCs within lateral flowing groundwater. This novel approach was benchmarked against the widely embraced convection-diffusion equation modeling method, demonstrating a significant improvement in predictive accuracy. In a typical field scenario, the breakthrough time for CHCs using the DDAC-LPB technique ranged from 25.3 to 25.5 years, with a barrier thickness of 1 m. This duration satisfactorily aligns with the expected service life of real-world projects. Overall, the DDAC-LPB has demonstrated superior performance and practical applicability in enhancing the containment of CHCs in contaminated groundwater.