Ijsseloog CDF Liner

ERDC TN-DOER-C18

August 2000

Lagoon (PIANC 1996, Consorzio Venezia Nuova 1997, Bernstein 1999

(Personal communication, 1999, Alberto Giulio Bernstein, The Tresse Island

Rehabilitation Project, Head of the Consorzio Venezia Nuova Environmental

Department.). A portion of the contaminated sediments was too contaminated

to be recycled for the reconstruction of marshes, and therefore was placed in

a lined and covered CDF on Tresse Island. This site was formerly used for To view figure

the deposit of urban and solid waste, and the containment measures were larger, click here

designed to isolate both the existing waste materials and future dredged

Figure 17

materials from the Venice lagoon waters. The isolation from the lagoon has

been achieved by the use of a reconstructed perimeter dike system. A cross-section of a portion of

the perimeter dike system is shown in Figure 17. Rock-fill berms with concrete topping were

constructed on the sides of the island exposed to wave action due to ship traffic. Sheetpiling sealed

with polyurethane was driven to a depth of -10 m into a thick, low-permeability soil layer to form

a vertical cutoff. Dry material was placed in a lined fill immediately landward of the sheetpile. A

secondary dike was constructed further landward with the liner incorporated into the dike cross-

section. In areas not exposed to ship traffic, a simpler "plastic diaphragm" consisting of mixture of

water, cement, and bentonite was constructed with a thickness of 0.5 m and to a depth of -8 m,

reaching clay layers to form a vertical cutoff. The entire perimeter system was covered with topsoil

and will be revegetated and planted with trees. The sealed perimeter dikes resulted in a large area

suitable for placement of new material dredged from canals and channels. Tresse Island is designed

to hold a total of 700,000 cu m of dredged material. Once filled, the site will be covered with a

clay layer to allow for revegetation.

Ijsseloog CDF Liner. The Ijsseloog CDF is a large island CDF constructed in Lake Ketelmeer

in The Netherlands. The site is designed to store approximately 21 million cubic meters of

contaminated material and incorporates several containment features and operational strategies

(Heineke, Eversdijk, and Kevelam 1997). The site was constructed in an area with existing bottom

contamination; therefore, temporary storage facilities for this material were required, and the

material was later re-handled into the completed CDF.

The configuration of the CDF was selected as a circular fill, consisting of a 40-m-deep excavated

pit, surrounded by a 10-m-high ring dike. This high fill with minimal surface area would maximize

consolidation resulting in a low permeability fill, and would minimize contact area with groundwater

flows. A 1-m-thick clay layer was placed in the bottom of the constructed subaqueous pit.

Fine-grained sediments underlying the ring dike were left in place (except for the contaminated

surficial layer) so that a low-permeability layer would remain beneath the dike. A seepage cutoff

layer was constructed in the under/inner part of the ring dike with a geomembrane to prevent seepage

from inside the CDF to surrounding surface water.

The water level within the CDF will be maintained at the same level as the hydraulic head in the

CDF foundation (-4.5 m) until the CDF fill reaches -8 m. The same strategy will be used once

consolidation brings the contaminated fill level again below -8 m. Note that a synthetic liner was

considered in the early design stages, but the environmental impact assessment (EIA) for the site

concluded that a liner was not necessary because of the high cost and difficult placement conditions.

Further, the EIA concluded that the failure of a liner within the period of 25,000 years after placement