Evaluation of Contaminant Flux from CAD Sites Using the CAP Model

This paper describes an application of the Capping Analysis Program (CAP) model to a proposed New York contained aquatic dredged material disposal (CAD) site. A number of proposed CAD facilities in 20 ft of water were considered, ranging from 40 to 60 acres in area, 40 to 60 ft of dredged material, and 3 to 10 ft of capping thickness. CAP has been developed by ERDC-WES to predict long-term movement of contaminants through caps at CAD sites. CAP incorporates a revised version of the RECOVERY sediment-water interaction model and consolidation-induced advection predictions generated from results of the Primary Consolidation, Secondary Compression, and Desiccation of Dredged Fill (PSDDF) model. Results indicated that the contaminated sediment layer would consolidate to roughly half of its initial thickness over a period of decades. New York sediments contain a number of contaminants. Copper was determined to be the contaminant of concern (COC) for its potential water quality impact based on its concentration, ability to partition to the water phase, and the magnitude of its water quality standard. CAP was run to predict the contaminant fate. Water and copper were predicted to move through the cap due to consolidation-induced advection. The simulations show that fluxes from the dredged material peak shortly after the initial consolidation and decrease thereafter. The ambient sediment at the CAD site has an elevated copper concentration, but is only a fifth of copper concentration being placed in the CAD facility. Long-term simulations for the background and the proposed CAD pit show less total flux from the pit than from the background.