Palos Verdes Shelf Pilot Capping: Description and Rationale

The U.S. Environmental Protection Agency (EPA) Region 9 is investigating the feasibility of in-situ capping DDT and PCB contaminated sediments on the Palos Verdes (PV) shelf off the coast of Los Angeles, California. The U.S. Army Corps of Engineers (USACE) has recently completed a field pilot study of in-situ capping for Region 9 at this site. The pilot study involved placement of approximately 103,000 cubic meters (135,0000 cubic yards) of capping sediments in three 18 hectare (45 acre) capping cells situated at water depths between 40 and 70 meters. Cap material was placed by hopper dredge using conventional and spreading placement methods. An extensive environmental monitoring program was conducted in stages before, during and after cap placement using state-of-the-art equipment and techniques. Modeling was also conducted during the placements to guide field operations and following placements to improve future predictive capabilities. This paper provides a description of the project setting and conditions, the rationale for capping options and the capping pilot, and a summary of how the study results may be applied to any future scale capping operations on the Shelf.