Select equipment and placement technique for capping sediment (6)

for mechanical or hydraulic placement or use of geosynthetic fabric con-

tainers. Guidance for equipment and placement techniques is found in

Chapter 5.

Select equipment and placement technique for capping

sediment (6)

The major design requirement in the selection of equipment and place-

ment of the cap is the need for controlled, accurate placement and the re-

sulting density and rate of application of capping material. In general, the

cap material should be placed so that it accumulates in a layer covering

the contaminated material. The use of equipment or placement rates that

might result in the capping material displacing or mixing with the pre-

viously placed contaminated material must be avoided. Placement of cap-

ping material at equal or lesser density than the contaminated material or

use of placement methods to spread thin layers to gradually build up the

cap thickness usually meets this requirement.

Specialized equipment and placement techniques can be considered to

increase control of capping material placement. The movement of sub-

merged diffusers, energy dissipaters, submerged discharge points, or tremies

can be controlled to spread capping material over an area to a required

thickness. Incremental opening of split-hull or multicompartment barges

along with controlled movement of the barges during surface release, di-

rect pump-out through pipes, and direct washing by hoses have been used

for placing mechanically dredged sandy capping material. Energy dissipat-

ers for hydraulic placement of capping materials have been successfully

used. Guidance on selection of equipment and placement techniques is

found in Chapter 5.

Select navigation and positioning equipment and controls (7)

Placement of both the contaminated and capping material must be

carefully controlled, regardless of the equipment and placement technique

selected. Electronic positioning systems, taut-moored buoys, mooring

barges, various acoustical positioning devices, and computer-assisted,

real-time helmsman's aids should be considered in selecting the equipment

and placement technique. Guidance on selection of navigation and posi-

tioning equipment and controls is found in Chapter 5.

Evaluate compatibility of site, materials, and equipment

At this point in the design, the contaminated material has been charac-

terized; a site has been identified and characterized; a capping sediment

has been selected and characterized; equipment and placement techniques

have been selected for both materials and navigation; and positioning

needs have been addressed. These essential components of the design

(Blocks 2, 3, 4, 5, 6, and 7 in Figure 2) must now be examined as a whole,

with compatibility in mind, to evaluate the efficacy of cap placement for

the sediments, site conditions, equipment availability and capabilities under

Chapter 2 Design/Management Sequence for Capping