Selection of Capping Sediment

the contaminated sediment is normally performed as a part of the overall

evaluation for suitability for open-water placement (EPA/USACE 1991;

EPA/USACE 1998). It should be noted that even though capping is being

considered because of a determination of potentially unsuitable benthic ef-

fects, the data necessary for evaluation of potential water column effects are

still required.

Chemical characterization of contaminated sediment may include a

sediment chemical inventory and standard elutriate test results. The

chemical sediment inventory is useful in determining contaminants of con-

cern and in the development of appropriate chemical elements of a moni-

toring program to determine capping effectiveness. Elutriate data are used

in estimating the potential effects on water quality due to placement of the

contaminated material. Biological characterization may include water col-

umn bioassays, benthic bioassays, and bioaccumulation tests. The results

of these biological tests are useful in determining potential water column

effects during placement and acceptable exposure times before placement

of the cap begins. If these data have not been developed for the contami-

nated sediment, additional testing may be required.

Selection of Capping Sediment

The capping sediment used in a capping project may be a matter of

choice. For economic reasons, a capping sediment is usually taken from

an area that also requires dredging. If this is the case, there may be a

choice between projects, and scheduling of the dredging is an important

consideration. In other cases, removal of bottom sediments from areas ad-

jacent to the capping site may be considered. If CAD is under considera-

tion, removal of material to create CAD cells may be stockpiled and used

later in the capping operation (Averett et al. 1989; Sumeri 1989).

Characterization of Capping Sediment

All dredged material capping projects to date have utilized dredged ma-

terial that is suitable for open-water placement for the capping material.

Use of other materials for caps or for components of a multilayer cap such

as quarry sand, soil materials, geotextiles, or armor stone are possible and

have been implemented in in situ capping projects. Guidance (Palermo et

al. 1996) on selection and use of such materials for caps is available. This

section focuses on use of dredged material as capping material.

Physical characterization

Physical characteristics of the capping sediment are similarly determined

as described above for the contaminated sediment. Visual classification,

natural (in situ) water content/solids concentration, plasticity indices (At-

terberg limits), organic content, grain-size distribution, specific gravity,

Chapter 3 Characterization of Contaminated and Capping Sediments