Mission Bay, Thunder Bay, Canada, CDF Dike Core/Surface Cover

ERDC TN-DOER-C18

August 2000

Mission Bay, Thunder Bay, Canada, CDF Dike Core/Surface

Cover. An 81-ha CDF in Thunder Bay, Canada, was specifically built for

contaminated dredged material. A perimeter berm was constructed, incorpo-

rating a filter fabric and clay core. A "reservoir" cell was constructed for

temporary placement of materials dredged mechanically and transported by

To view figure

scow. Four interior cells were constructed for permanent storage. The mate-

larger, click here

rial is hydraulically rehandled from the reservoir cell to the permanent cells.

Once filled, the permanent cells are graded, covered with a layer of clean

Figure 27

topsoil, and seeded (Public Works Canada, Ontario Region 1991).

CONCLUSIONS: There are few CDFs where operational controls for containment or engineered

containment features have been implemented. Most of these sites are associated with sediment

remediation projects, which involve more highly contaminated sediments than normally associated

with navigation projects. Selective placement of contaminated materials below the water table or

water surface and maintenance of water levels within a CDF have been used as operational control

measures. Engineered CDF containment features used to date include liners, surface covers, and

dike or perimeter cutoffs for lateral seepage control. Contaminant control measures should be

considered to reduce or control impacts due to a contaminant release that exceeds a set criteria or

standard. However, in practice, many of the controls were implemented because of administrative

or regulatory mandate, with no analysis to establish the need for the control.

Liners have been designed and incorporated as constructed features for only a few CDFs, and most

of these were constructed in European countries. Materials used for liners have included synthetic

membranes such as HDPE, compacted clay, and placed fine-grained dredged material of acceptable

quality. Care should be taken to avoid damage during the placement of liner materials, especially

for in-water sites.

Surface covers for CDFs have been constructed with imported topsoil, clean dredged material, and

combinations of fabrics and soil layers. In many cases, cover materials may be placed directly over

dredged material, which is still at high water content, although special equipment such as conveyers

will be required to spread the initial layers.

Lateral seepage control features for CDFs include low-permeability dike cores constructed from

clay, sheetpile cutoff walls within the dike cross-section, and synthetic membranes or grout

mattresses placed on the inside face of the dike. Slurry walls have also been constructed along dike

perimeters of the CDF.

Design of these containment features has been on a case-by-case basis with little commonality from

site to site. Reports on effectiveness or criteria for evaluation of the measures are also poorly

documented in the open literature. There are no specific designs or construction guidelines for

engineered containment measures tailored to the conditions normally encountered with contami-

nated dredged material in CDFs.

The information in this technical note will be used in developing design and construction guidance

for CDF containment features under the Dredging Operations and Environmental Research (DOER)