Step 2 - Select and Characterize Liner Materials

ERDC TN-DOER-R6

December 2004

1. Reducing seepage through the CDF bottom by installing engineered liners comprised of one or more

of the following components:

Clean dredged material.

Compacted subsoil.

Modified soils.

Compacted clay.

Geomembranes.

Geosynthetic clay liner.

Composite (compacted clay plus geomembrane).

Leachate collection systems.

2. Controlling lateral seepage through the dikes by employment of:

Slurry walls and trenches.

Sheet pile walls.

Reactive barriers.

3. Reducing infiltration of precipitation into the stored dredged material by installing covers comprised

of:

Compacted clay.

Modified soils.

Geomembranes.

Step 2 - Select and Characterize Liner Materials. The liner materials used in a project should be

carefully selected. However, for economic reasons, a liner material comprised of clean dredged sediment

is preferred and is usually sufficient to reduce contaminant fluxes to acceptable levels. Previous studies

(e.g., ASCE (1997)) have shown that both fine-grained materials and sandy clays can be effective liner

materials.

If there are instances that dredged material does not possess adequate flux retardation

properties, or regulatory authorities require otherwise, other liner materials may be employed, including

compacted clay liners and composite liner systems consisting of clay coupled with geosynthetics (e.g.,

geomembranes).

Step 3 - Select Equipment and Placement Techniques for Liner Materials and

Contaminated Sediments. The major design requirement in the selection of equipment and the

placement techniques for liner materials is the need for controlled, accurate placement and ensuring the

necessary density and rate of application of liner material. In general, the liner material should be placed

so that it accumulates in a layer of adequate thickness and density, uniformly covering the prepared

subbase of the CDF. Placement of liner material at equal or greater density than the subbase material or

use of placement methods to spread thin layers to gradually build up the liner thickness usually meets this

requirement. Scheduling of liner construction must also consider both exposure of the liner material to

the environment and engineering and operational constraints.

Various equipment types and placement techniques have been used for placement of contaminated

sediment. The use of equipment or placement rates that might result in the contaminated material

displacing or mixing with the previously placed liner material must be avoided. Placement of

contaminated material at equal or lesser density than the liner material or use of placement methods to

spread thin layers to gradually build up the contaminant thickness usually meets this requirement.