Steady-State Model of Chemical Migration in a Sediment Cap

Abstract

Capping with clean media represents one of the few available means of reducing exposure and risk to contaminated sediments in situ. Effective design of a chemical isolation cap layer requires modeling tools capable of describing the operative processes in a cap and the resulting chemical fate and transport processes. An analytical model developed by the lead author is commonly used for this purpose but is limited in the types of capping scenarios that can be evaluated. In particular, the standard model cannot deal with multiple layers in the cap with different transport rates and sorption coefficients. This is especially important in estimating surficial sediment concentrations in the presence of bioturbation. Additional analytical and numerical models are described that can relax the assumptions of the existing model. The models are compared and recommendations are provided to guide model usage for various cap simulation needs. A simple model employing conservative steady-state assumptions is proposed specifically for the case of predicting long-term containment by a cap and surficial sediment concentrations. The simple model is compared to more sophisticated numerical models that can deal with a wide range of conditions.