Denny Way

baffles and 15-cm side boards containing holes throughout was used to dis-

tribute the sand slurry over a wide area. This device essentially sprinkled

the sand over the contaminated fine-grained sediment on the bottom. The

spud barge and boom extension were swung about the spud and controlled

by anchor lines. The cap was placed by swinging the plywood box ("sand

box" as shown in Figure 7) back and forth until manual leadline soundings

indicated the desired cap thickness was attained. Acoustic depth sounders

were ineffective due to high sand load and entrained air in the water column.

The barge was moved ahead 3.1 m providing a one-third overlap, and the

swinging procedure was repeated. Subsequent movements of the spud

barge and spreading of the cap material were made until the contaminated

area was completely capped. Physical, chemical, and biological monitor-

ing were initiated to determine cap effectiveness during the first 5 years

following cap placement.

Denny Way

The Denny Way Combined Sewer Overflow (CSO) is located in the

lower Duwamish River in Puget Sound (Sumeri 1989). It discharges both

untreated sanitary sewage and stormwater runoff and acts as a relief point

during peak storm events each year. The bottom sediments in the area off

the Denny Way CSO (Figure 34) were found to be contaminated. Sub-

sequently, a CSO control plan and source control activities were instituted

to reduce the toxicant loading.

The in situ contaminated sediments at Denny Way were capped with

sand using a similar procedure as used in the Duwamish capping project.

For this project, sand placement needed to be more accurate. Clean sands

were obtained from a maintenance dredging project and transported to the

site by a bottom-dump barge. Placement of the cap was completed by

pushing the barge sideways and sprinkling a 39-m-wide sand blanket.

Barge displacement was measured with two pressure transducers installed

in stilling wells at each end of the barge, and these displacement signals

were telemetered to the microprocessor onboard the attending tug. The

navigational position of the barge was tracked by a laser positioning sys-

tem, which also telemetered the tugboat and monitored position and sand-

sprinkling rate. A cap of 0.6 to 0.9 m was placed at the Denny Way CSO

site, and monitoring of the cap effectiveness was instituted.

Port of Los Angeles/Marina del Ray

A large CAD project has recently been completed in the Port of Los

Angeles (LA), and this project is the first to be implemented in California.

The CAD site is constructed inside and adjacent to the main breakwater in

LA Harbor and is known as the Permanent Shallow Water Habitat (PSWH)

site. Materials placed in the site include contaminated materials from

channel deepening within LA Harbor and contaminated materials from the

Marina del Ray Project. Subaqueous dikes were first constructed using

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Chapter 10 Case Studies