Life Cycle and Transport Distance Sensitivity Analysis for the Practical Selection of Vertical Cutoff Walls

This study presents a comparative life cycle assessment (LCA) of four conventional vertical cutoff wall materials: soil–bentonite (SB), cement–bentonite (CB), soil–cement–bentonite (SCB), and plastic concrete (PC). The comparison is based on environmental impacts associated with 1 m3 of cutoff wall material. The environmental effects were evaluated using the OpenLCA program with a cradle-to-gate approach. The production of materials and their transportation were assumed to be within the system boundary. The inventory data were sourced from the Ecoinvent 3.9.1 database, and the impact assessment was performed using the CML v4.8 2016 methodology. The results showed that the SB cutoff wall had lower impacts, while the SCB cutoff wall had higher impacts among the four cutoff walls considered. The global warming potential of SB cutoff wall materials is approximately 58%, 68%, and 72% lower than that of PC, CB, and SCB cutoff walls, respectively. The results also demonstrated that material transportation and ordinary portland cement (OPC) production were the significant contributors to environmental impacts, accounting for 40%–90% and 10%–50% of the total effects, respectively, across all four cutoff wall materials. Owing to the significant influence of transportation distance associated with commonly used materials such as bentonite and OPC, a sensitivity analysis was performed by varying the ratio of bentonite-to-OPC transportation distance (B/C) to assess associated uncertainties. Based on B/C values of 0, 0.1–3.6, 3.7–6, 6.1–8.6, and >8.6, the environmental impact ranking (from the lowest to the highest) was PC < SCB < CB, SCB < CB < PC, CB < SCB < PC, CB < PC < SCB, and PC < CB < SCB, respectively. This study will help practicing engineers select vertical cutoff wall materials with lower associated environmental impacts under varying B/C transportation distance ratios at contaminated sites.