Geometry for CAD Projects

a relatively small volume of material to cap the contaminated sedi-

ments. Fredette (1994) describes the project in more detail.

Calculated contaminated mound is too high. If the calculated

mound peaks exceed the maximum depth limit, it may be possible

to increase barge velocity to make a mound of more constant eleva-

tion without substantially increasing the footprint. If much of the

mound exceeds the minimum depth restriction, two obvious solu-

tions are to (a) find a deeper portion of the site or another site (if

available), or (b) reduce the volume of contaminated material. Per-

haps a more feasible solution is to spread out the area of placement

to reduce mound height. This will increase the surface area of the

mound and thus the amount of cap required. It may also create

problems with contaminated material coming too close to the site

boundary. Another option is to consider a dredging method that in-

creases the density of the contaminated material, a difficult propo-

sition for mechanically dredged sediments.

g. Cap geometry. The same tools and approaches used for evaluation

of contaminated mound geometry can be used to evaluate geometries

for LBC caps. However, the major consideration for cap geometry

is the placement of a layer of the required cap thickness over the

central portion of the mound and over the apron as appropriate.

Geometry for CAD Projects

The geometry of the deposit for CAD sites is largely controlled by the

geometry of the depression or subaqueous berms that form the lateral con-

tainment. If hydraulic methods are used to dredge the contaminated mate-

rials going into the CAD site, and if the site has a relatively small surface

area, the materials will tend to spread in a layer of even thickness over the

entire area. If the site has a large surface area, or if the contaminated ma-

terial is mechanically dredged and placed by barges, the material may tend

to form a mound within the site not covering the entire surface area. If

this is the case, methods for intentionally spreading the contaminated ma-

terial within the CAD site boundaries may be appropriate. Contaminated

materials should be placed in CAD sites as a layer of uniform thickness,

so that the required thickness of cap material can be placed using a mini-

mum volume of cap material.

Cap geometry for CAD sites should be developed as the design cap

thickness placed uniformly over the entire contaminated deposit. Assum-

ing the contaminated material has been placed as a fairly uniform layer,

the cap would essentially be placed from bank to bank within a depression,

pit, or contained area formed by subaqueous berms.

The same tools as described above for LBC projects can be used for

evaluation of deposit geometry for CAD sites. The major consideration

for CAD geometry is the placement of both contaminated and cap layers

in a uniform and level configuration.

Chapter 6 Sediment Dispersion and Mound Development and Site Geometry During Placement