Design of No-Net-Fill Sub Aqueous Cap for Mercury and PCB-contaminated Sediments
Port of Richmond, California
Weiss Associates was the prime engineering consultant for the design of a subaqueous cap for a former shipyard in Richmond, California. Weiss Associates completed a supplemental data gathering program to evaluate sediment characteristics necessary to determine a site-specific (field-based) partitioning coefficient between chemicals sorbed to sediment and in pore water (Kd) for each of the chemicals of concern. Two continuous sediment cores were collected using a four-inch aluminum core barrel with a stainless steel cutter-head and catcher. Pore water was isolated from both composites using a centrifuge. The pore water and sediment samples were then analyzed for zinc, lead, mercury and total polychlorinated biphenyls (PCBs) (as aroclors). The chemical concentrations in the pore water and sediment were then used to determine the site-specific Kd for each of the chemicals.
The site-specific Kd was then used in a fate and transport model to determine the minimum cap thickness that would prevent sediment concentrations at the sediment/water interface from exceeding the cleanup goals over the cap design life. The modeling enabled Weiss Associates to optimize cap thickness and careful screening of borrow sites for cap material allowed us to significantly reduce cost and provide for a beneficial reuse of dredge material.
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