CONFINED DISPOSAL FACILITIES: HISTORY AND TRENDS
Jim Olsta
CETCO, Arlington Heights, IL
ABSTRACT
Confined disposal facilities with filter layers have been used for disposal of dredged sediments for
decades. Recent assessment of the environmental risk of contaminants in sediments has resulted in
the use of lined confined disposal facilities. A case history outlines a contaminated sediment disposal
facility designed with geosynthetics. Trends indicate more stringent requirements for confined
disposal facilities in the future.
INTRODUCTION
Contaminated sediments are dredged from waterways to maintain navigable depths in the waterways
or for environmental remediation. Per Miller (1998) confined disposal facilities (CDFs) is one the most
widely used alternatives in the U.S. for placement of contaminated sediments. CDFs are diked areas
designed to provide retention and storage of dredged material.
CDFs function as settling basins, in terms of wastewater treatment technology. Typical CDFs were
designed to retain greater than 99.9% of the sediment particles disposed. The dredged sediments
are placed into the facility either mechanically by a clamshell or hydraulically by pipeline. Coarse
sand and gravel sediments typically settle rapidly near the point of disposal while fine grained silt and
clay sediments settle more slowly. Supernatant water is discharged from the CDF during dredging
disposal operations.
The CDF design is site specific. A CDF may be constructed as an upland site, a nearshore site with
one or more sides constructed in the water or as an island containment area. Dikes for in-water CDFs
are usually constructed in layers of heavy protective stone on the outside and progressively smaller
soil particle size on the inside (Figure 1). Contaminants often bind with the fine sediments as the
water percolates through the walls and into the ground. Permeability is reduced over time due to fine
particle sediment sealing.
CDF water quality monitoring is typically conducted during the dredging operation and consists of
monitoring the effluent and open water sites near the discharge or around the CDF. Some facilities
have monitoring wells installed in the dike walls. The Great Lakes Commission (2003) sites results of
water quality monitoring have indicated that these CDF designs are highly effective at retaining the
sediment solids and moderate concentrations of attached contaminants. The Chicago Area CDF is
used to contain sediments removed to maintain navigation. In one biomonitoring study, organisms
were collected in and around the Chicago Area CDF to detect evidence of PCB losses. Organisms
from immediately outside the CDF were not significantly different from remote stations, indicating no
discernable loss of PCBs from the CDF.
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Figure 1. Traditional cross section of CDF dike with a filter layer.
As discussed by Palermo and Averett (1999), such measures for highly contaminated material may
not meet the regulatory requirements and more effective engineered containment measures are
needed. Laboratory tests and computer models are available to determine the mobility of
contaminants along these pathways (i.e. leachate, effluent, runoff, plant/animal uptake). Using these
tests, the significance of a contaminant migration pathway can be determined and appropriate
containment designed. Engineered containment features include bottom and sideliners, leachate
collection, and covers.
Liners consist of a layer of clay, conditioned dredged material or geosynthetic materials placed across
the bottom and sides of a CDF to control leachate. Leachate collection systems, consisting of
drainage layers or geocomposites and piping to collect leachate for treatment are sometimes used in
conjunction with liners. To date, only a few dredged material sites have been constructed with liners.
Covers provide several potential benefits for contaminant control by isolating the underlying dredged
material from access by plants and animals, and reducing infiltration of precipitation into the fill,
thereby reducing leachate volume. Surface cover construction for CDFs can be problematic due to
the soft nature of newly placed dredged material, especially material that has been hydraulically
placed in the CDF. Compacting clay is difficult under such conditions and is susceptible to differential
settlement. Geosynthetics such as geogrids, geomembranes, geosynthetic clay liners (GCLs) and
are viable options for consideration in cover design.
Earth Tech (2002) outlines an environmental remediation project that was designed and constructed
with a geosynthetic liner and leachate collection system.
Sediments in a section of the
Grand Calumet River in Gary, Indiana were contaminated with polyaromatic hydrocarbons (PAHs),
metals and poly chlorinated biphenyls (PCBs) and classified as hazardous or toxic by the Resource
Conservation and Recovery Act (RCRA) and Toxic Substance Control Act (TSCA). U.S. Steel
contracted for the remediation of the Grand Calumet River including the dredging of approximately
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573,000 m3 (750,000 yd3) sediment from the headwaters of the east branch of the Grand Calumet
River to a point approximately 8 km (5miles) downstream, design and construction of an upland
dewatering and confined disposal area designated as a Corrective Action Management Unit (CAMU)
under RCRA, design and construction of a wastewater treatment plant for the treatment of dredge
water generated during sediment removal and return of the treated water to the Grand Calumet River
through a permitted outfall.
Figure 2. Aerial photo of CAMU after grading.
The CAMU is a passive dewatering facility that is partitioned into two separate holding cells
designated Units 1 and 2 (Figure 2). Unit 1 covers 4 hectares (10 acres) and will hold approximately
206,000 m3 (270,000 yd3) of material. Unit 1 receives all material regulated under TSCA and RCRA.
Unit 2 covers 11 hectares (27 acres) and has a capacity of 671,000 m3 (878,000 yd3). Per Figures 3
and 4, the CAMU liner design from top to bottom was leachate collection blanket of 0.61 m (24
inches) of fine aggregate (on floor), geotextile cushion, primary 60-mil HDPE geomembrane,
geocomposite, secondary 60-mil HDPE geomembrane and nonwoven geosynthetic clay liner (GCL).
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Figure 3. CAMU side slope cross section
Figure 4. CAMU floor cross section
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Figure 5. Geogrid placement
Figure 6. CAMU liner placement
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Figure 7. Geocomposite placement
A GCL was chosen in the liner design because clay was not locally available. Besides being costeffective, the use of GCL resulted in greatly reducing the number of trucks used to haul material to the
site. The 177,000 m2 (1,900,000 ft2) of GCL took only 60 trucks compared to thousands of trucks that
would have been needed to haul clay.
Per Figure 5, steep 1H:1V side slope berms and ramps were reinforced by using geogrid between lifts
of compacted local soils.
Construction of the CAMU liner took place in 2002 (see Figures 6 and 7). Per U.S. Steel (2003),
hydraulic dredging began in late 2002 and will continue through December 2003. Dredging
supernatant will be pumped to a wastewater treatment plant for treatment prior to discharge back to
the river.
Future trends indicate continued demand to manage contaminated dredged material for navigation,
increased demand to manage contaminated sediments dredged for remediation and more stringent
environmental requirements for new disposal facilities. Geosynthetics can play an important role in
providing cost-effective solutions for these disposal facility designs.
ACKNOWLEDGEMENTS
The author appreciates the input and photos provided by Terri Blackmar, EarthTech, and Rick
Menozzi, U.S. Steel.
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REFERENCES
EarthTech (2002), U.S. Steel Grand Calumet River Sediment Remediation Program, PowerPoint
presentation.
Great Lakes Commission (2003), Confined Disposal Facilities Fact Sheet, www.glc.org.
Miller, J. (1998), Confined Disposal Facilities on the Great Lakes, Great Lakes & Ohio River Division,
U.S Army Corps of Engineers.
Palermo, M. and Averett, D. (1999), Design Features of Confined Disposal Facilities (CDFs) for
Contaminated Sediments, Proceedings of 31st Texas A&M Dredging Seminar, Louisville, KY.
U.S. Steel (2002), Gary Works RCRA Corrective Action Newsletter, www.usx.com.
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