Experimental Mud Dump (EMD) mound

successful in reducing the spread of the contaminated sediments and

thereby significantly reduced the volume of capping sediments required.

The CLIS experience has provided insight on the procedures that his-

torically are recommended for a successful capping project. In the pre-

project planning, it is recommended to (a) completely characterize the

sediments to be disposed including sediment chemistry, bioassay, or bioac-

cumulation data and classify sediments using most recent information;

(b) estimate volumes of material to be disposed; (c) conduct site surveys

and choose a disposal area that is not vulnerable to natural or anthropo-

genic erosion; (d) schedule dredging and disposal operations ideally to

complete mound and cap well before a storm season to allow for consoli-

dation and surface stabilization; and (e) dispose the cap materials as soon

as possible after contaminated material. For the disposal operations, it is

recommended to (a) employ both accurate navigational techniques and a

taut-wired buoy to locate the designated disposal mound; (b) point dump

mound materials by directing the barge to unload as near to the buoy as

possible; (c) dispose approximately one-third of the cap sediments along

the radius of the contaminated mound; (d) maintain the preproject plan for

mound deposition followed by cap deposition; and (e) keep good records

of all disposal operations.

New York Bight

Experimental Mud Dump (EMD) mound

An evaluation of the 1980 LBC project at the Experimental Mud Dump

(EMD) site at the New York Bight apex (Figure 31) was reported by

O'Connor and O'Connor (1983), and excerpts from their report are used

to summarize this capping project. Contaminated dredged material from

the Hudson Estuary, Newark Bay, and contiguous waters were capped in-

itially with fine sediments from the Bronx River and Westchester Creek

and followed with sand from the Ambrose Channel. The resulting cap

was a 1-m-thick layer of sand overlaying contaminated sediment. Biologi-

cal, chemical, and physical investigations were completed to evaluate the

ability of the cap to remain intact and reduce the loss of organic and inor-

ganic toxicants from the contaminated material to the surrounding water.

Results showed the cap was successfully placed at the experimental

dump site, and it remained intact after 16 months. Erosion of the cap was

minor, and predictions of cap life were in excess of 20 years under normal

environmental conditions. However, it was predicted that major storm

events were capable of causing cap erosion and exposing the contaminated

material. The contaminated material volume decreased by 4 percent over

the 16-month study due partly to consolidation and partly to losses during

the disposal operation. Contaminant levels in the sand cap as measured

by chemical analysis were shown to be lower than those in contaminated

sediments. Bioaccumulation investigations indicated that contaminant up-

take was less than at uncapped dredged material sites. Therefore, it was

concluded that the New York Bight EMD capping project was successful

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Chapter 10 Case Studies