Numerical investigation for the isolation effect of in situ capping for heavy metals in contaminated sediments

Abstract

In situ capping is one of the preferable remediation technologies for sediments contaminated by heavy metals because of its relatively modest cost. However, it has been used to isolate heavy metals without having detailed information available regarding the effect of consolidation and the chemical isolation caused by in situ capping. This paper presents a numerical estimation of in situ capping efficiency for mitigating heavy metals in sediments when a groundwater flow condition is included. Numerical simulations were conducted using a computational model (CST2) in which contaminant transport occurs by advection, dispersion, and sorption. The results from numerical simulations indicate that the discharge rate of dissolved heavy metals increases during and for some time after capping installation but decreases because of a significant reduction in advection after 100% consolidation. In addition, tailing effect which is the main reason for the long term release of heavy metals is caused by consolidation. Further simulations shows that a multilayered capping system with a thin reactive layer provides an effective barrier to contaminant transport even though consolidation caused by in situ capping results in the negative effects on mitigating heavy metals.