Dredge Sediment Disposal in Long Island Sound

by Eric Alletzhauser

On April 24, 1997, a workshop on alternative methods for dredged sediment disposal was held at the Connecticut Audubon Coastal Center in Milford. The workshop was sponsored by Connecticut Department of Environmental Protection (CTDEP) as part of the Dredged Sediment Management Study, funded by the EPA Long Island Sound Study (see Winter/Spring 97 UPDATE, page 6.) Officials from the EPA, the Army Corps of Engineers, the National Marine Fisheries Service, CTDEP, CT Department of Transportation, NYS Department of Environmental Conservation, LIS Citizens Advisory Committee members, marine trades representatives, and environmental and other interests from around the Northeast attended the workshop.

The dredged sediment management study will provide important technical background information to update the "1980 Interim Plan for the Disposal of Dredged Material from Long Island Sound." The alternatives-analysis, investigating alternative ways to open water disposal, assessing environmental, technical and economic feasibility in Long Island Sound. The workshop was a first step in discussing the alternatives. Long Island Sound currently has four active open water disposal sites used for dredged sediments originating from the Sound and its tributaries in Connecticut and New York.

At the workshop, seven speakers presented alternatives to open water disposal including containment, decontamination technologies, beneficial uses and borrow pit or in-channel disposal. A synopsis of the various alternatives discussed follows.

Containment Technologies

Containment alternatives range from in-filling of large, abandoned and bulkheaded slips, to marsh and island creation, to "fast land" nearshore filling. Dr. Thomas Fredette of the New England Army Corps of Engineers presented the results of a feasibility study conducted by the Corps in the late 70’s and early 80’s for several containment sites in Long Island Sound. Since containment alternatives frequently occur in the nearshore, some were rejected because the loss of shallow water habitat or tidal wetlands was not acceptable, even given the benefits of a disposal alternative. Other sites were not pursued because of the high initial cost for expensive containment construction, which adds to the costs of dredging or transporting material.

John Henningson, of Hart Crowser, Inc., presented successful containment projects conducted around the US. These involved the in-filling of existing unutilized slips, which were used to dispose of contaminated sediments below the water table upon which clean material was placed as cap. The cost advantage in this type of project was that three sides, comprised of the existing slip, were already constructed, leaving only one waterward dike to be constructed. Recontamination was a major concern and Henningson stressed the importance of retaining contaminated material below the water table in an anoxic state to prevent leaching of contaminants. In order to ensure containment, stability of the containment structure, especially the newly constructed berm, was essential. Often, this requires a large and expensive structure. Adjacent land use was an additional consideration, both as a concern for exposure and as a factor in beneficial use of the filled slip.

Decontamination Technologies

Kerwin Donato from the NY Division of the Army Corps of Engineers reviewed the many new and emerging sediment decontamination technologies. These are technologies which reduce contaminant concentrations or mobility and the toxicity of the dredged material by destruction, separation or extraction, blending, and physical or chemical stabilization. Examples include thermal destruction, chemical treatment, bioremediation (phytoremediation), soil washing, solvent extraction, thermal desorption, and stabilization processes. Each of these technologies requires bench-scale modeling to demonstrate their effectiveness at a scale of five to ten gallons, followed by pilot projects at the 25 cubic yard volume. The technologies then require implementation through a demonstration project.

Many of these technologies are currently employed to treat contaminated soils, but their application for dredged sediments is affected by the unique chemical make-up of dredged sediments. For instance, while thermal desorption may work for organic contamination of certain upland soils, it is less effective for contaminated marine sediments because it does not address heavy metals. However, with the need for alternatives and the continuing study and modeling of these new technologies, some could be on line in the near future. To date, the Port of New York and New Jersey has conducted 12 bench scale studies and five pilot scale studies.

Beneficial Re-Use

John Henningson presented an overview of beneficial re-use of dredged sediment. He emphasized the need to evaluate projects based on a holistic approach and to examine environmental risks from the time of dredging through to the final product. Beneficial re-use options include beach nourishment, habitat creation, upland and near shore fill for development projects, sanitary landfill cover and roadbed material. Environmental issues raised by beneficial re-use include contaminants by plants, contaminant leachate, length of time to complete a project, the physical and chemical characteristics of the sediments and the end use requirements. Currently, there is not enough public money available to pursue these initiatives.

One way in which to attract financing is for beneficial re-use to be profitable. Dr. Keith Jones of the Brookhaven National Laboratory presented a potential project where a cement plant could be retrofitted to handle dredged sediments and utilize them as a raw material for various products. The sediments would be mixed with other materials at high temperatures and the final product could be a marketable cement-like composite material for construction. With the increasing cost of disposal in the New York metropolitan area, this type of operation could be developed with investment by the private sector, charging a use fee for dredged sediment and potentially turning a profit. Dr. Jones noted that air emissions would result from the hot batching process and that incineration by-products would need to be disposed of.

Other private sector driven projects include the Orion site in New Jersey. Mr. Larry Schmidt of the New Jersey DEP delivered a broad perspective on alternatives to open water disposal and noted that private capital often drives the process. He explained two projects in New Jersey where dredged sediment alternatives were being explored. The first, the Orion site, utilized dredged sediment mixed with other products, including kiln dust, for use in a parking lot at a large development. He noted that this is a "learn as you go" process and that proponents ran into problems such as too much debris in the sediment, the pace of development outstripping the capacity to deliver dredged sediment and environmental problems such as water and leachate control. From an environment point of view he noted that the project spurred development of the Sequential Batch Leachating Test (SBLT) as a new and better way to predict the potential of dredged sediments to leach contaminants when placed in upland environments. Mr. Schmidt also noted that a large, 110 acre site could potentially process dredged sediments for use in strip mine remediation in Pennsylvania, a single solution to two separate environmental problems.

In-Channel Disposal

Mr. Jim Bajek of Normadeau Associates presented the Boston Harbor Navigation Improvement Project, in-channel disposal for sediments which were not approved for open water disposal. First, 54 pits containing 1.84 million cubic yards of clean sediment, primarily blue clay, will be dug and the material disposed of at an open water disposal site. This leaves capacity in the borrow pits to handle one million cubic yards of contaminated sediment. An additional 460,000 cubic yards of clean cap will be brought in to cover the pits. At their final elevation, the pits would still be beneath the bottom depth of the federal channel. Site factors which had to be accounted for include bedrock, utilities, a tunnel and bridges. One benefit of this in-channel disposal of contaminated sediments is that no further benthic impacts would occur since the channel was being dredged anyway and the pits were underneath the channel. Contaminated sediments which now lie within the channel would be buried beneath the channel and capped with clean material, reducing potential exposure. The transport costs would be less because careful sequencing would mean that contaminated sediment would be placed directly in a dredged pit rather than stored or transported for long distances. Permitting is not difficult since the pits lie beneath an existing channel and formerly exposed contaminated sediments would be capped. The drawbacks of in-channel disposal include its availability only for one project, no potential for expansion, and monitoring is required to ensure success of capping.

Borrow Pits

The final speaker was Dr. Angela Cristini of Ramapo College, New Jersey. She discussed the Newark Bay borrow pit, a solution to dispose of contaminated sediments in Newark Bay. Since the material was unsuitable for open water disposal, eight alternative options were explored and the borrow pit option was chosen. In Newark Bay, 1.9 million cubic yards of clean sediment are being dredged to create capacity for 1.5 million cubic yards of contaminated sediment. The clean sediment is transported to another site as cap, while contaminated sediment unsuited for open water disposal is disposed of and capped in the borrow pit. In order to finance the project, a tipping fee is being considered. During the project development, proponents encountered unexpected contamination in the clean sediment, reducing the borrow pit capacity. Other problems included the unreceptive attitude of the community in which the pit was located.

Planning Considerations

Some common themes emerged from the presentations. First, successful alternatives require partnerships and coalitions. Alternatives often require more start up capital than traditional open water disposal necessitating federal, state, local and private financial support and coordination. While large scale dredging projects have an economic advantage because of the volume of material dredged, smaller projects such as marinas are unable to pursue alternatives. The current dredger-pays approach to sediment disposal, as opposed to a broader distribution of disposal costs, does not provide adequate coordination or capitalization to pursue large scale alternatives. In addition, partnerships are required to overcome regulatory and siting difficulties. Alternatives are difficult to implement without local support and regulatory acceptance.

In general, Long Island Sound dredged sediments are clean when compared to those of Newark Bay, the Port of New York/New Jersey and Boston Harbor. However, Long Island Sound does have areas of elevated contaminants which are not scheduled to be dredged. Eliminating these "hot spots" through new or existing dredging techniques was discussed. One key factor discussed at the workshop was the tendency of dredged material to leach contaminants when removed from the anoxic marine environment and placed on the upland where they are exposed to oxygen and acidic rain. Other environmental factors which need to be assessed are the by-products and potential impacts on air and water quality from various alternatives, especially treatment technologies. The long-term picture for dredged sediments looks good since toxic contaminants have been nearly eliminated in effluent. Current dredged material contains historic contamination which could eventually be eliminated.

Next Steps

Over the summer, SAIC, the consultant hired to assist CT DEP on the Dredged Sediment Management Study, will complete draft reports on the current regulatory process for dredged sediment disposal, alternatives to open water disposal, and research needs relating to dredged sediment management. The draft reports will be made available for review. The final reports will be used as background information by state and federal agencies to update the 1980 plan.

Eric Alletzhauser works for the Connecticut Department of Environmental Protection Office of Long Island Sound Programs and serves as the Coordinator for the LIS Dredge Sediment Management Study. Eric can be reached at (860) 424-3034.