Geuzenhoek, Belgium, CDF Liners, Leachate Collection, and Cut-off Walls

ERDC TN-DOER-C18

August 2000

was high. Subsequent to publication of the EIA, it was agreed to include a placed clay liner (Flach,

Driebergen, and Godefrooij 1997).

Geuzenhoek, Belgium, CDF Liners, Leachate Collection, and Cut-

off Walls. A 500,000-cu-m capacity CDF at Geuzenhoek was constructed

adjacent to the Ghent seacanal for placement of contaminated material and has

been used as a field research site for comparison of the effectiveness of a range

of liner materials (Flemish Ministry of Environment and Infrastructure 1994) To view figure

(Figure 18). Several large compartments were constructed in the early 1990's, larger, click here

each with differing containment measures. The first compartment was con-

Figure 18

structed with a 2-mm HDPE liner, and two 0.4-m-thick sand drainage layers,

one above and one below the liner. The liner was damaged during placement, and several portions

of the liner had to be replaced. Weather conditions were found to affect the heat-welding process,

and concerns with sunlight degradation prevented placement during mid-day sunny conditions.

Placement of protective layers of sand exposed the liner to heavy loadings, and the protective layer

could not be placed on the inside face of the dikes. Cost of the liner was also excessive, causing

the cost of maintenance dredging to almost triple. To avoid these problems, other containment

options were incorporated into the next two compartments. A "thin wall" cement-bentonite slurry

wall was used as a cutoff. This wall had a thickness of 10 cm, a maximum depth of 22 m, and a

reported permeability of 10-8 m/sec. This option was found to have several advantages: (1) problems

with liner damage and degradation were avoided, (2) the working principle of the slurry wall relies

on both reduced permeability and the adsorptive capacity of the bentonite, (3) in case of leakage, a

new section of wall can be constructed to solve the problem and, (4) the cost was approximately

30 percent that for a liner. The final option for isolation included a drainage system consisting of

100-mm pipes spaced 7.5 m to drain off excess water.

In addition to the containment options used in the larger compartments, a field research program

was undertaken at the Geuzenhoek site to evaluate cost-effective isolation measures. Six upland

cells were constructed each with a capacity of 2,000 cu m, with each cell used to test a different

bottom layer. These layers were not designed as sealing layers, but as active bottom layers with a

capacity for adsorption and cation exchange. The options evaluated included: (1) glauconite liner,

laid down as a granular material to 20 cm thickness, (2) bentonite liner, placed as a mixture with

natural subsoil to 30 cm thickness, (3) dewatered dredged material liner, mechanically dewatered

and chemically conditioned and placed in a 20 cm thickness, (4) peat placed at 40 cm thickness,

(5) full sediment treatment with alumino-silicates mixed prior to placement, and (6) a control cell

with no liner or treatment. A seventh subaqueous cell was constructed with a vertical cutoff or

vertical waterproof foil screen. The cells were instrumented with piezometers and sampling wells;

a laboratory-testing program was conducted on samples from the cells, and tracer tests were

conducted. Dredged material was hydraulically placed in the cells with care taken to ensure that

materials with the same physical and chemical properties were placed in each cell. The glauconite

and bentonite could be successfully placed on the side slopes of the cells, but peat had to be kept

moist. Each cell was therefore filled with water following construction and prior to placement of

dredged material. It was determined that the dewatered dredged material should be placed and

compacted at a water content wetter than optimum, slopes should not be steeper than 1V on 2H, the

material should be protected against drying by covering with a thin sand layer, and the sand layer

in turn should be protected against erosion by a geo-jute. The permeability of the dewatered dredged