Long Island Sound

placement of the cap material over the mound accomplished with the aid

of a taut-wired buoy and accurate navigational controls proved to be suc-

cessful. The stability of these mounds has been tested by 11 years of

monitoring and the passage of Hurricane David in 1979, although the hur-

ricane's passage was coincident with the predicted exponential compac-

tion phase of the mound, and Hurricane Gloria (Fredette et al. 1989). It is

desirable for the mound/cap formation to occur well before any storm win-

dows in order that natural settlement and compaction has time to occur.

All three mounds showed normal biological recolonization rates in sub-

sequent monitoring. Sediment chemistry data show the surface sediment

remained at or below background concentrations of the contaminants

measured. Coring data show a clear visual and chemical boundary in

many of the cores.

The historical record of the successful capping of the STNH mounds

and CS-2 provided comparative insight as to why other capping projects

were not as successful. For example, accurate placement of dredged sedi-

ments is less reliable without the use of both a buoy and an accurate navi-

gation system, and their lack of use was attributed to the offset of the cap

and mound at CS-1. The Mill-Quinnipiac River mound (MQR) demon-

strated the importance of controlling operational factors and maintaining

vigilant monitoring. Biological monitoring at the MQR showed subnor-

mal recolonization rates relative to the other CLIS mounds. The disposal

operations that included the Mill-Quinnipiac River and Black Rock and

New Haven harbors were not conducted as distinct mound and cap deposi-

tional phases. The overlapping cap/mound deposition may have affected

the recolonization rate at MQR. Similarly, the Norwalk mound was not

formed in distinct cap and mound operations. The contaminant concentra-

tions for both the mound and cap at Norwalk were well below those of

Black Rock and MQR, and there was no evidence of adverse effects due to

disposal operations at Norwalk in subsequent monitoring. Sediment chem-

istry results from MQR show that the surface chemistry of the mound was

not similar to Black Rock sediments; instead, concentrations were at the

high end of the range of most constituents analyzed in New Haven sedi-

ments. However, these monitoring results have allowed NED to detect

and take corrective management actions.

During a 1993 NED capping project, maintenance sediments from New

Haven Harbor and private terminals were placed in the CLIS. A total of

approximately 500,000 yd3 of contaminated material was dredged from

New Haven Harbor and private terminals followed by capping with about

660,000 yd3 of cap materials. Placement of the contaminated sediments

was controlled with a taut-wire buoy, while a total of 18 separate place-

ment points (using LORAN-C) were specified for the cap placement.

Throughout the cap placement process, continuous monitoring allowed for

adjustment of disposal points to optimize cap coverage and avoid point

dumping.

The unique aspect of this project was that the mounds created from five

previously placed projects were used to make a bowl in which to place the

500,000 yd3 of New Haven sediments (Fredette 1994). At the center of

the bowl, the depth was 62 ft, while the surrounding depths were generally

0.6 to 10 ft shallower. Surveys showed that the planned depression was

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Chapter 10 Case Studies