Michigan City CDF Cover

ERDC TN-DOER-C18

August 2000

material liner in situ was found to be two orders of magnitude higher than measured in the lab, and

a value of 10-7 m/sec was considered the best feasible value in situ. Tracer experiments indicated

a 20- to 50-day migration period through the isolation layers and into the drainage system. Volume

of percolating water was high at first but diminished rapidly due to consolidation and clogging. The

volume of water was 1.5 to 3.0 times greater for peat and glauconite than for bentonite or dewatered

dredged material. Sealing capacity of all tested materials, including the control cell with no bottom

layer, was of the same order of magnitude. Mobility of most contaminants in leachate was low; the

exceptions were nitrogen, sulfates, and nitrates, which are not bound on the solid phase. The general

conclusion from these field tests was that, except for highly contaminated materials, impermeable

or adsorptive layers are not needed for CDFs. Rather, efficient drainage systems should be

considered, so that levels of contaminants in percolating water can be monitored and treated if

necessary.

Michigan City CDF Cover. The Michigan City CDF is a small 13,000-sq-m upland site. The

site contains about 40,000 cu m of dredged material contaminated with metals, PCBs, and petroleum

products. Dikes were constructed of compacted earth fill with a sand filter dike section intended to

allow for filtered discharge of effluent during filling. Initially, dredged material was placed in the

CDF hydraulically, but the filter section became clogged. Subsequent operations were accom-

plished using mechanical dredges with re-handling to trucks for placement in the CDF (Richardson,

Chaney, and Demars 1996). After the last dredged material placement, the site was fully dewatered

and had naturally vegetated. Desiccation cracks in excess of 0.3 m deep were evident on the dredged

material surface (USACE Chicago District 1987, 1989a).

Monitoring well data had indicated concern with potential ammonia releases

to adjacent surface waters, and a surface cover was placed at the site to

reduce infiltration. The cover consisted of 0.6 m of clay and 0.6 m of subgrade

fill and topsoil planted with grasses. The cap was designed using USEPA's

Hydrologic Evaluation of Landfill Performance (HELP) model. Regrading

and compacting the site to cover the vegetation and form a 30-cm-thick

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larger, click here

subgrade layer prepared the surface. The initial clay cap material was initially

stockpiled by trucks along the dike crowns, spread by bulldozers, and com-

Figure 19

pacted with a roller (Figure 19). The topsoil layer was placed in a similar

manner and then seeded (USACE Chicago District 1989b).

Minamata Bay CDF Cover. The Minamata Bay, Japan, project was a large-scale project

involving the construction of a CDF for remediation of

mercury-contaminated sediments (PIANC 1997, Kuma-

noto Prefecture 1998). A portion of the bay was enclosed

with a line of sheetpile cofferdam revetments (see illus-

tration and cross-section in Figures 20 and 21). A 1-m-

thick sand layer was first placed along the cofferdam

To view figure

footprint to reduce sediment resuspension. A second To view figure

larger, click here

layer of sand with additional provisions for sand com-

paction and sand drains was placed to provide a suitable

Figure 21

Figure 20

foundation for construction of the cofferdams.