Viability of capping as an alternative

material at an open-water site. Several issues, therefore, must be carefully

considered within the context of a capping project design. These include

the following:

a. Potential water column impacts during placement. Assessment

should consider evaluation of potential release of contaminants to

the water column, evaluation of potential water column toxicity,

and evaluation of initial mixing. Elutriate test procedures for

water quality, water column bioassay tests, and computer models

for dispersion and mixing are available to address these require-

ments. The mass loss of contaminants during placement (fraction

dispersed offsite and remaining uncapped) may also be predicted

using these same tests and models.

b. Efficacy of cap placement. Assessment should consider available

capping materials, methods for dredging and placement of both

contaminated material and cap material, compatibility of site condi-

tions, material physical properties, and dredging and placement

techniques. Guidance on selection of appropriate methods, com-

patibility with site conditions and material properties, and com-

puter models for predicting mound development and spreading

behavior are available.

c. Long-term cap integrity. Assessment should consider the physical

isolation of contaminants, potential bioturbation of the cap by ben-

thos, consolidation of the sediments, long-term contaminant flux

through the cap due to advection/diffusion, and potential for physi-

cal disturbance or erosion of the cap by currents, waves, and other

forces such as anchors, ship traffic, ice, etc. Test procedures for

contaminant isolation and consolidation and computer models for

evaluation of long-term contaminant flux, consolidation, and resis-

tance to erosion are available.

Each of these issues must be appropriately addressed by the project design.

Viability of capping as an alternative

Capping is only one of several alternatives that may be considered for

dredged material that is excessively contaminated and would need isola-

tion from the benthic environment if proposed for open-water placement.

If the issues described above can be satisfactorily addressed in the project

design for the specific set of sediment, site, and operational conditions un-

der consideration, capping is a technically viable option.

Capping is not a technically viable option for a specific set of sediment,

site, and operational conditions described below:

a. Contaminant release and dispersion behavior of the contaminated

material (even with consideration of controls) results in unaccept-

able water column impacts during placement.

Chapter 1 Introduction