Dredged Material Cap Design

Dredged Material Cap

Design

This chapter presents procedures for designing subaqueous dredged

material caps and a sequence for determining the design cap thickness

components to account for bioturbation, erosion, consolidation, opera-

tional considerations, and chemical isolation. Methods for determining

the required volume of cap material and design considerations for interme-

diate caps are also discussed.

General Considerations

The composition and dimensions (thickness) of the components of a

cap can be referred to as the cap design. This design must physically iso-

late the contaminated sediments from the benthic environment and

achieve the intended cap functions. The design must also be compatible

with available equipment and placement techniques.

The composition of caps for dredged material projects is typically a

single layer of clean sediments because relatively large volumes of cap ma-

terial are involved; clean sediments from other dredging projects are often

available as cap materials; and dredged material capping sites with low

potential for erosion can be selected. Guidance on dredged material cap

design in this chapter therefore focuses on the thickness of the cap as the

major design criterion.

In contrast, in situ capping projects usually involve smaller volumes or

areas; clean sediments are not always readily available as capping material;

and site conditions are a given. For these reasons, caps composed of mul-

tiple layers of granular materials as well as other materials such as armor

stone or geotextiles are often considered, and the in situ cap design cannot

always be developed in terms of cap material thickness alone. Procedures

for design of caps composed of nonsediment components are available in

the EPA guidance document for in situ capping projects (Palermo et al.

1996).

Chapter 7 Dredged Material Cap Design