A confined disposal facility, or CDF, is a structure planned and designed to receive sediments dredged from a navigation channel and safely contain the contaminants, preventing their reentry into the waterway or lake.The U.S. Army Corps of Engineers and Environmental Protection Agency have completed a report that provides a detailed summary of the 45 confined disposal facilities that have been used to manage contaminated sediments dredged from harbors and channels throughout the Great Lakes.This page provides a synopsis of the report:
Dredging requirements
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Management options
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History of CDFs
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CDF planning and designs
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Performance monitoring
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Cumulative impacts
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Download the report
Dredging Requirements
Sediments that accumulate in the bottom of river channels, harbors and lakes are the product of soil erosion from lands throughout the watershed and erosion of streambanks. As sediments accumulate, the depths of channels used by commercial ships and recreational boaters are reduced. Dredging of sediment deposits is required to maintain channels at safe depths for navigation.
Contaminated bottom sediments are present in many of the federal navigation projects in the Great Lakes and every one of the Areas of Concern designated under the Great Lakes Water Quality Agreement. “Restrictions on dredging activities” is one of the fourteen beneficial use impairments identified in the Agreement.
There are over a hundred federal harbors and channels in the Great Lakes. Every year, the Corps of Engineers dredges about 4 million cubic yards of sediments from 15-25 of these harbors. Another 1-2 million cubic yards of sediments are dredged from state, municipal and private harbors and marinas, as well as dredging for waterfront construction, bridge construction and repairs, clearing water supply intakes, and environmental restoration.
Sediments dredged from Great Lakes harbors and channels may be managed using one of the following methods:
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Open water placement (placement directly in the lake or river)
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Beach nourishment (placement on the beach or in the nearshore area)
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Capping (placement on the bottom of a lake and covering with clean material)
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Upland beneficial use (use for construction fill, landscaping, landfill cover, etc)
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Confined disposal (placement in a CDF or licensed landfill)
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Treatment (applying one or more processes to remove or destroy contaminants)
The selection of the appropriate option for managing a dredged material is based on the type and level of contaminants present (if any), the volume of materials, local conditions, and environmental, social and economic factors. About half of the sediments dredged from Great Lakes harbors and channels are clean sand and silt than can be safely placed into the lakes, used to nourish beaches or for upland beneficial uses. The other half contains levels of pollutants that restrict their disposal to some degree.
Capping is a technology for managing contaminated dredged material that has been used in marine environments, but not yet on the Great Lakes. Technologies for treating sediment contaminants have been evaluated extensively by the EPA and Corps nationally, and through Great Lakes specific programs, notably the Assessment and Remediation of Contaminated Sediments (ARCS) Program. However, the costs of treatment are several times those of other management options, and these technologies have only been applied at a few sites with the most highly contaminated sediments. Confined disposal to a CDF or licensed landfill is the most widely used option for managing contaminated sediments dredged from Great Lakes harbors and channels.
Prior to 1960, all dredged material in the Great Lakes was managed based solely on cost efficiencies. This meant unconfined, open water disposal in most cases. The first concerns about the impacts of dredging activities on water quality were raised in response to pollution in the lower Detroit River. In 1967, the Corps initiated a 2-year study on the impacts of dredging on Great Lakes water quality and demonstrations of alternate management practices for contaminated sediments in partnership with the Federal Water Pollution Control Administration (predecessor to EPA). The results of this study recommended that sediments from contaminated harbors and channels be confined.
With the passage of Section 123 of the Rivers and Harbors Act of 1970, Congress authorized a program for the confined disposal of contaminated sediments from federal navigation projects in the Great Lakes. Congress directed that the Corps could only develop a CDF in collaboration with a non-federal partner (typically a state agency, local government or port authority). Under this authority, as well as project-specific authorities, the Corps has constructed and/or operated 45 CDFs to manage over 90 million cubic yards of contaminated sediments dredged from Great Lakes harbors and channels in the past forty years at a federal cost of $300 million (construction costs unadjusted for inflation).
Individual CDFs have been planned, sited, and designed in partnership with non-federal sponsors and with full opportunity for public and agency review and input. In order for a CDF to be approved for construction, the Corps must prepare an environmental assessment or impact statement and comply with federal and state environmental laws. A state resource agency must issue a water quality certificate for discharges of excess water from the CDF.
The size, shape, and design of each CDFs have been selected to fit dredging needs of the harbor(s) and channel(s) served, the physical and chemical characteristics of the dredged material, local conditions and resources, and the interests of the non-federal sponsor. Because of the distance between Great Lakes ports, most CDFs service only a single harbor/channel. In many cases, the non-federal sponsor requested the CDF be constructed as an in-water fill in the harbor or nearshore lake to meet future waterfront plans of the community. Over half of the CDFs in the Great Lakes are in-water facilities, although several upland facilities were developed on islands or areas that had been previously filled.
CDFs have combined design features and processes common to wastewater treatment, landfills, dams, and breakwaters. Research studies have demonstrated that the key to controlling contaminants associated with dredged material is to contain as high a percentage of the sediment particles as possible. A principle goal of CDFs is to receive and confine the dredged material and return excess water with minimal suspended sediments to the river or lake.
In-water CDFs have dikes that resemble a breakwater, made of stone, gravel and other materials. Large armor stone are typically placed on the outside face of the dike to protect against wave attack. The inner core of the dike is often constructed with sand and gravel, sometimes in discrete layers. The dike, which is permeable, encircles the disposal area where the dredged material is placed. The sediment particles and contaminants bound to the particles settle out in the disposal area and excess water passes back through the dike. As the facility becomes filled, the dikes become less permeable, and water must be removed by overflow weirs, filters in the dikes, or is pumped.
Upland CDFs are designed with earthen dikes that resemble a levee or berm. The dikes are most often constructed with soil excavated from the disposal site, and the sides seeded to prevent erosion. Dredged material is placed into the facility by pipeline or by truck. After the sediment particles have settled out, excess water is removed by overflow weir or pumpage.
All dredging on the Great Lakes is performed by private contractors. CDFs are operated for relatively brief periods of time (a few weeks) during dredging. Some Great Lakes harbors are dredged every year, but others may only be dredged every 2-5 years. During operations, dredged material may be placed into the facility using a pipeline, transferred from barges by a crane and bucket, or end-loaded from trucks.
The Corps routinely monitors the performance of CDFs. This includes periodic inspections of CDF dikes for structural integrity, monitoring of dredging contractors, and water quality monitoring of discharges from CDFs. The results of monitoring are used to ensure that these facilities are secure and effluents are in compliance with state water quality requirements.
The EPA and Corps have collaborated in a number of special studies at CDFs to evaluate their long-term performance and impacts on the Great Lakes ecosystem. These studies have included laboratory simulations of contaminant transport and fate, field investigations of the uptake of contaminants by plants and animals within the facilities, and computer modeling of contaminant releases.
The results of routine monitoring and special studies have demonstrated that CDFs have been able to contain greater than 99.9 percent of the sediment particles and associate contaminants and routinely meet applicable state water quality requirements. The long-term release of contaminants from these facilities can be calculated using computer models but can not be detected with advanced monitoring techniques, and is not considered ecologically significant. Plants grow quickly on dredged material inside CDFs and have provided an attractive habitat for some wildlife. Monitoring studies have shown that plants and animals that inhabit the CDFs may uptake contaminants from the dredged material. The degree of uptake varies with the organism, contaminant, and site conditions.
The combined impacts of CDFs on the Great Lakes ecosystem have been considered from physical, chemical, biological, and socio-economic perspectives:
Physical. The construction and operation of CDFs have produced both negative and positive physical effects. Over half of the CDFs were constructed at in-water sites, resulting in the loss of lake and river bottom habitat. However, the CDF dikes have created reef-like habitat for fisheries and the interior areas have supported dense vegetation and a temporary habitat for fish and wildlife. CDFs have also created new lands along the shoreline that have been used to support community waterfront and recreational development plans.
Chemical. CDFs retain a high percentage of the contaminants they receive, and discharge effluents that consistently meet state water quality requirements. Studies have indicated that the long-term release of contaminants from CDFs may be calculated using computer models, but cannot be detected with conventional or advanced monitoring techniques, and are not considered ecologically significant. Cumulatively, CDFs have facilitated the removal of 90 million cubic yards of contaminated sediments from the Great Lakes and tributaries, of which over 70 million were from Areas of Concern. This represents a significant reduction in the mass of contaminants exposed to the aquatic environment.
Biological. CDFs have produced losses and gains in habitat that appear to be of comparable value. Wildlife that inhabit or visit CDFs may uptake increased levels of some contaminants, and management practices are being used to reduce this effect. In the lakes and rivers outside the CDFs, biological communities are exposed to lower levels of contamination as a result of the removal and confinement of contaminated sediments from navigation channels.
Socio-Economic. CDFs have enabled the continued, safe transport of goods and materials at Great Lakes harbors and channels. Commercial and recreational use of these waterways is a major contributor to the national and regional economies as well as the history and social identity of many communities along the Great Lakes shoreline.
Overall. The net impact of CDFs on the Great Lakes ecosystem has been beneficial. Although created to serve the needs of navigation, the removal of sediment contaminants provided by the CDF program represents a substantial contribution to the goals of Remedial Action Plans and Lakewide Management Plans.