Recommendations (Cont.)

b. Refine and verify models for short-term fate of dredged material to

allow for predictions within the full range of conditions expected

at capping sites.

c. Refine and verify models that predict subaqueous mound development

due to multiple discharges from barges or hopper dredges or long-

term discharge from pipelines. Approaches should included both

water column and spread behavior of the discharges and the

geotechnical considerations associated with mound-slope stability,

density flows, and resistance to bearing failure. Such tools will

have application for general open-water site management as well

as specific application to capping scenarios.

d. Refine and verify models that predict long-term erosion from

dredged material mounds. Additional emphasis should be placed

on mounds covered with fine-grained material. Such tools will

have application for general open-water site management as well

as specific application to capping scenarios.

e. Refine existing estimates of resuspension of contaminated material

during cap placement. This work will assist in determining the costs

versus benefits of "sprinkling" cap material versus conventional

bottom dumping of cap material.

Develop engineering guidance on acceptable rates and methods of

application of capping material over contaminated material of

varying density and shear strength. These techniques should con-

sider the geotechnical behavior related to displacement and mixing

of contaminated and capping sediments and resistance of the sedi-

ments to bearing failure. Extend the investigation to include pene-

tration of dense (e.g., rock) cap material into contaminated

material mounds.

g. Refine existing models for prediction of capped-mound consolidation.

This effort will likely require developing or refining instrumentation

for in situ geotechnical measurements.

h. The effect of pore water pressure fluctuations within the mound

caused by the surface wave climate should be studied to determine

possibility of contaminant release and reduced mound stability.

Develop predictive tools for evaluation of long-term cap integrity,

considering chemical migration via consolidation, bioturbation,

and diffusion. Both analytical and modeling approaches should be

considered. Refinements to sediment-water interface models for

this purpose are ongoing under the Disposal Operations Technical

Support Program.

Conduct laboratory and field verification studies of long-term cap in-

tegrity. Laboratory approaches should include refinement of exist-

ing cap-effectiveness tests using columns. Additional laboratory

verification of consolidation effects on contaminant migration

should be conducted using large geotechnical centrifuges. Field

studies should include periodic monitoring and sampling of

capped sites to include analysis of core samples.

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Chapter 11 Summary and Recommendations