Port of Los Angeles/Marina del Ray

suitable quarry run materials from Catalina Island. Contaminated sedi-

ments from the harbor were placed by surface release at the site. Materi-

als from the Marina del Ray Project were placed at the site using

geotextile bags, the first demonstration of this technology as an applica-

tion for placement of contaminated dredged material.

The PSWH site was originally designed by the Port of Los Angeles as

an environmental mitigation measure for the Pier 400 harbor development

project. Site design called for filling the 190-acre area to raise the natural

bottom from 40- to 45-ft depths to depths less than 20 ft, creating a shallow-

water foraging area for the endangered California least tern. Quarried

stone from Catalina Island was used for construction of the subaqueous

berm (see Figure 36). Approximately 543,000 cu yd of contaminated

material from the harbor were placed within the site. These sediments had

elevated levels of contaminants and were considered unsuitable for open-

water disposal and were also undesirable from the standpoint of placement

in the Pier 400 engineered landfill.

The contaminated sediment was placed in the center of the 94-acre por-

tion of the overall 190-acre site. The 94-acre area was laterally separated

from the outer boundaries of the site by buffer zones ranging from 200 to

650 ft, all of which were slated for capping with clean material. The widest

(650-ft) buffer was located on the breakwater side to ensure the contami-

nated sediments would remain isolated in the event of a rare catastrophic

storm that might breach the breakwater. Approximately 4 million cu yd of

clean material from the harbor, which was physically unsuitable for land-

fill construction, comprised the lower (thickest) layer of the cap. Clean

sand was used for the final 2 ft of cap to resist erosion and provide suit-

able substrate for the tern habitat. Together, this resulted in a cap thick-

ness generally exceeding 15 ft. Such a cap thickness is far in excess of

that required for effective capping from the standpoint of containment and

was dictated in part by site geometry and dredging volumes.

The sequence of material placement was also driven in part by the

dredging requirements for the overall Pier 400 project. The placement of

initial portions of contaminated material was by clamshell dredge. This

material was placed in the "central area" of the PSWH, while other initial

elements were mechanically placed in the "perimeter area." The initial

capping material was placed over the "central area" using a hopper

dredge. The subsequent capping layers were placed by pipeline dredge.

Placement of a sand cover was completed after a waiting period of

11 months to allow for consolidating the fine-grained capping material and

minimizing the mixing of sand with the fine material.

Prior to initiation of the Pier 400 project, the PSWH site was selected

for placement of additional contaminated material from the Marina del

Ray project located 35 miles from LA Harbor. This project involved ap-

proximately 55,000 cu yd of sandy contaminated sediments, which also

contained potentially floatable debris. The initial scheduling of opera-

tions at Marina del Ray would have required placement of this material at

the PSWH site prior to construction of the subaqueous berms. To avoid

dispersion during placement and spreading of contaminated material in

absence of the berms, the permit required use of geotextile bags for the

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Chapter 10 Case Studies