Port Newark/Elizabeth project

and capping can serve as an alternative to the control of contaminants in

dredged material. The thickness and stability of the cap reduced the

losses of contaminants to the surrounding water. It was recommended

that capping be integrated with routine disposal operations to efficiently

cover and isolate contaminated material at designated disposal sites.

In 1986 a detailed survey of the EMD mound was conducted to evalu-

ate long-term stability of the mound (Parker and Valente 1988). Results

of the survey, which included precision bathymetry, subbottom profiling,

and SPI imagery, indicated the sand cap has not experienced significant

erosion.

Port Newark/Elizabeth project

In June and early July 1993, 450,000 m3 of maintenance sediments con-

taminated with low levels of dioxin from the Port Newark/Elizabeth com-

plex (part of the larger Port of New York-New Jersey), and last dredged in

1990, were dredged and placed in the Mud Dump site (MDS) (Figure 31).

The maintenance material was subsequently capped (July 1993-February

1994) with 1,900,000 m3 of sand from Ambrose Channel. This project

was preceded by several years of controversy due to the dioxin contamina-

tion (May, Pabst, and McDowell 1994; McDowell, May, and Pabst 1994;

Greges 1994). Concerns about cap stability were based on erosion within

the MDS that occurred after a severe northeaster in December 1992

(McDowell, May, and Pabst 1994). Erosion thicknesses greater than 1 m

occurred from portions of the flanks of recently placed fine-grained main-

tenance material. These concerns led to a study (Richardson et al. 1993)

that concluded that a mound with a 0.4-mm sand cap with an upper crest

limit at a depth of 23 m (75 ft) should be stable (i.e., experience minimal

erosion) during a storm comparable with the December 1992 storm.

The upper cap elevation limit of 23 m combined with the large volume

of material and limited space available resulted in the design of a triangu-

lar-shaped mound as shown in Figure 32. Water depths at the site of the

planned disposal ranged from 24 to 25.3 m. A design requirement to pro-

vide a 1-m cap over the mound restricted the planned elevation of the con-

taminated mounds to approximately 1.5 m.

Readily available geotechnical data on the contaminated sediments

were limited to percent sand, silt, clay, and percent moisture (average values

were 6, 58, 35, and 52 percent, respectively).

The contaminated material was removed using mechanical dredges; no

overflow was allowed. Dredged material was placed in bottom-dump

scows ranging in capacity from 1,900 to 4,600 m3 and transported to the

MDS. A total of 149 loads were placed over a 5-week period. The permit

required the barge operators to place material within the 150-m-wide by

350- to 450-m-long disposal lanes on a rotating basis (Figure 32). To as-

sist the contractor in siting the placements, the apex's of the triangle had

taut-moored buoys. To reduce the chance of placing material outside the

lanes, the contractor was directed to dispose of all material within 60 m

of an imaginary line connecting the apex buoys. Calibrated LORAN-C

positions for the tugs with offsets to correct for the location of the center of

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Chapter 10 Case Studies