AbstractThis paper presents an investigation of the effect of sediment consolidation on contaminant transport through a sediment-cap system for in situ cappings of subaqueous contaminated sediments. Numerical simulations were conducted using the model CST3 and consider coupled consolidation and contaminant transport for representative layer geometry, material properties, and applied stress conditions. Simulation results indicate that sediment consolidation can have significant effects on contaminant breakthrough time, mass flux, cumulative mass outflow, and concentration distribution within the sediment-cap system. These effects manifest not only during the consolidation process but also long after consolidation has been completed. Traditional advective-dispersive transport analyses fail to consider transient advection induced by sediment consolidation and associated contaminant migration and changes in material properties that can lead to significantly unconservative transport results and adverse environmental impact. For example, simulation results indicate that failure to account for sediment consolidation yields a cumulative contaminant mass outflow that is underestimated by a factor greater than 6,000 within the first 3 years after cap placement and by a factor of 2 at the end of a 100-year simulation period, even though consolidation essentially is completed in the first 1.5 years.