Field Pilot Study of In Situ Capping of Palos Verdes Shelf Contaminated Sediments

摘要

Sediments covering approximately 40 sq km of the ocean floor at the Palos Verdes Shelf, near Los Angeles, CA, are contaminated with DDT and PCB. The U.S. Army Corps of Engineers (USACE), working in support of the U.S. Environmental Protection Agency (EPA), has conducted studies investigating the feasibility of in situ capping all or a portion of the site with a layer of clean sandy dredged material. A feasibility study was conducted to determine the feasibility and effectiveness of in-situ capping. This study included the necessary engineering and environmental analyses such as preliminary cap designs, operations plans, and monitoring and management plans for a range of in-situ capping options. The USACE has also recently completed a field pilot study at this site. The pilot study involved placement of approximately 103,000 cu m of capping sediments using a split-hull hopper dredge. Three 1 8-ha capping cells situated at water depths between 40 and 70 m were capped using both conventional placement methods and special spreading methods. A large-scale environmental monitoring effort was conducted before, during, and after cap placement using a number of state-of-the-art techniques and specialized equipment. Predictive modeling was also conducted during and following the placements to guide field operations and refine data for design purposes. This report provides a description of the project setting and conditions and summarizes the results of the feasibility and field pilot studies.