Consolidation

Figure 21.

Conceptual illustration of bioturbation activity versus sediment depth

Cap thickness required for bioturbation, Tb, should be determined

based on the known behavior and depth distribution of infaunal organisms

likely to colonize the site in significant numbers. Bioturbation depths are

highly variable, but have been on the order of 30 to 60 cm (1 to 2 ft) for

most infaunal organisms that populate a site in great numbers. Consulting

with experts on bioturbation in the region of the disposal site location is

desirable. The thickness needed to prevent breaching of cap integrity

through bioturbation can be determined indirectly from other information

sources. For example, the benthic biota of U.S. coastal and freshwater ar-

eas have been fairly well examined, and estimates of the depth to which

benthic animals burrow should be available from regional authorities.

Consolidation

Consolidation of the cap, contaminated material, or underlying native

sediments may occur over a period of time following cap placement, but

does not occur repeatedly. If a fine-grained cap material will be used, con-

solidation of the cap may require an added cap thickness component in the

design such that the consolidated cap will remain at the required thick-

ness. If any of the sediments (cap, contaminated, or native sediment) are

compressible, a prediction of consolidation is important in interpreting

Chapter 7 Dredged Material Cap Design