Self-Sealing Properties of Fine-Grained Dredged Material

ERDC TN-DOER-C18

August 2000

and surface runoff. However, the design surface area and depth must also consider effects on

effluent quality.

Large CDFs have been constructed in The Netherlands, and the design of several of these sites has

included selective placement configurations. Descriptions of the general design aspects, environ-

mental features, and monitoring data for several large CDFs constructed in The Netherlands have

been recently published (Nijssen et al. 1997; Laboyrie, Kamerling, and de Haan 1995; Laboyrie,

Flach, and van der Laan 1997; Heineke, Eversdijk, and Kevelam 1997; Hartnack, van Steenwijk,

and Steenkamp 1997; Flach, Driebergen, and Godefrooij, 1997; de Haan, Kamerling, and Laboyrie

1995). The largest sites are the Slufter and the Ijsseloog sites, but several others are in the planning

or design stages.

Highly contaminated dredged material may be selectively placed below the mean tide level (MTL)

elevation, with cleaner dredged material or other capping material placed above the MTL mark (de

Haan, Kamerling, and Laboyrie 1995; Heineke, Eversdijk, and Kevelam 1997).

Prudent site selection, placement sequencing, and site management have therefore been used to

ensure adequate containment of contaminants (Laboyrie, Kamerling, and de Haan 1995; de Haan,

Kamerling, and Laboyrie 1995). Special contaminant control measures such as bottom liners have

seldom been used because they require nonconventional construction methods, and their cost is

prohibitive.

Self-Sealing Properties of Fine-Grained Dredged Material. Dredged material is initially

pumped into a CDF at high water content, but quickly settles to a condition approaching that in the

channel prior to dredging. Over time, the newly placed material begins to consolidate. Measured

permeabilities of dredged material at 50 percent of primary consolidation range from 8.5 10-10

to 4.1 10-7 cm/sec (Bartos 1977). This range of permeability is comparable to that required for

liners in licensed solid waste landfills (1 10-7 cm/sec). Therefore, the initial layers of a fine-grained

dredged material selectively placed in the bottom layers of a CDF will begin to "self-seal" as

consolidation progresses, and will continue to seal as more layers of dredged material are placed

over the older layers.

Engineered Containment Features. Engineered CDF containment fea-

tures or control measures are specifically designed and constructed to enhance

containment of the dredged material and control potential contaminant release

pathways. Such site controls include surface covers, liners, slurry walls,

To view figure

sheetpile cutoff walls, low permeability dikes or dike cores, permeable filtra-

larger, click here

tion dikes, reactive dike designs, leachate collection systems, and other con-

tainment or mitigation features. Engineered containment features, illustrated

Figure 4

in Figure 4, may include:

Soil liners: a layer of soil, usually clay, in the bottom and dikes of a CDF to reduce seepage

of leachate out of the facility. Clay liners can be constructed using clean dredged material or

other suitable construction fill.