Summary

consolidation and stability against erosion. Chemical and biologi-

cal characterization should determine if the capping sediment is ac-

ceptable for unrestricted open-water disposal (i.e., a "clean"

sediment).

g. The selection of an appropriate site is a critical requirement for any

capping operation. The general considerations for selection of any

nondispersive open-water site also apply to selection of a site for

capping, but a capping site requires special consideration of

bathymetry, currents, water depths, bottom-sediment charac-

teristics, and operational requirements. In general, capping sites

should be located in relatively low-energy environments with little

potential for erosion of the cap.

h. A number of different equipment types and placement techniques

can be considered for capping operations. Conventional discharge

of mechanically dredged material from barges and hydraulically

dredged material from hopper dredges or pipelines can be consid-

ered if the anticipated bottom spread and water column dispersion

are acceptable. If water column dispersion must be reduced or if

additional control in placement is required, use of diffusers, tre-

mies, and other equipment needed for submerged discharge can be

considered. Controlled discharge and movement of barges and use

of spreader plates or boxes with hydraulic pipelines can be consid-

ered for spreading a capping layer over a larger area. Compatibil-

ity between equipment and placement technique for contaminated

and capping material is essential for any capping operation.

Accurate navigation to the disposal site and precise positioning dur-

ing material placement are required for capping operations. State-

of-the-art equipment and techniques must be employed to ensure

accurate placement to the extent deemed necessary. Diligent in-

spection of operations to ensure compliance with specifications is

essential.

Scheduling of the contaminated-material placement and capping op-

eration must consider both exposure of the contaminated material

to the environment and engineering and operational constraints.

k. Evaluation of potential water column effects due to placement of con-

taminated material must be performed. If water column release is

unacceptable, control measures must be considered to reduce the

potential for water column effects, or other dredging equipment

and placement techniques or use of another capping site can be

considered.

The cap must be designed to chemically and biologically isolate the

contaminated material from the aquatic environment. The determi-

nation of the minimum required cap thickness is dependent on the

physical and chemical properties of the contaminated and capping

sediments, the potential for bioturbation of the cap by aquatic or-

ganisms, and the potential for consolidation and erosion of the cap

material.

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Chapter 11 Summary and Recommendations