Disposal Options

Materials that meet the standards in Clean Water Act (CWA) and the Marine Protection Research and Sanctuaries Act (MPRSA) will generally be available for all disposal options and methods. Those materials that do not meet these standards will require treatment, confinement or a combination of the two. A variety of treatment methods are available that can target different contaminants and contaminant levels. Examples of treatment methods include: Pretreatment (dewatering, washing, separation), Thermal treatment (incineration, vitrification), Chemical treatment, Biological treatment, and Stabilization.

Upland Disposal
The major factors controlling choice of upland (including shoreland) sites are cost, land use, and availability. Increased distance from a dredging operation and extensive site preparation both increase costs. The sediment to be deposited must be compatible with the future use of the site: for example, fine sediments will not always produce stable land for industrial development while coarse sands may not enhance productive farmland or be useful for levee maintenance.

The primary engineering consideration is the degree of confinement that the site and the proposed deposition will require. The Army Corps of Engineers has developed specific guidelines for designing containment areas at the disposal site that both maximize the site's capacity and control effluent quality. The guidelines address technical issues, such as, possible geochemical changes subsequent to disposal that causes the release of contaminants and effective dewatering of sediments. In general, diking around the site offers maximum confinement while berming (the creation of mounds of sediment during deposition) may suffice for certain sediments.

Figure B-1: Bermed Upland Disposal Site (O-18.2)

Material dredged by clamshell dredge and transported to site by barge and dump trucks.

Figure B-2: Leveed Upland Disposal Site (W-3.2)

Material dredged and deposited by a hydraulic pipeline dredge.

Dredged material disposal on levees may prove cost effective for the combined goals of levee maintenance and disposal of otherwise unused dredged materials. The major environmental consideration is that the material be disposed in such a way that it not run-off into productive aquatic areas. The major engineering issues are effective dewatering of the sediments and careful levee stabilization, preferably through revegetation, after disposal.

In-water Disposal
Regardless of the type of in-water disposal, placing dredged materials in the aquatic area raises several key concerns, including sediment and water quality, sediment transport, water circulation, impacts to fisheries, and impacts to biological communities, especially endangered/threatened species. Sediments placed in water must meet sediment quality regulations outlined in the Dredged Material Evaluation Framework. The majority of sediment disposed in the estuary's aquatic area consists of coarse, clean sand dredged from maintained navigation channels. This material must meet the water and sediment quality standards.

After sediment is placed in an in-water disposal site, some or all of it is eventually transported to other areas, potentially resulting in adverse impacts to shallow productive areas and fishing areas, resulting in an increase in dredging requirements on other projects. The sediment transport patterns at in-water sites need to be assessed prior to disposal. Disposing of material in-water usually creates a mound or otherwise obstructs water flow. Consequently, water circulation patterns in the vicinity of the disposal site are altered. These changes can have detrimental effects. For instance, unexpected erosion or accretion can occur downstream from the disposal site. Conversely, the changes can sometimes be beneficial. For example, the scouring of the channel can be increased. In all cases, the potential effects that may result from circulation changes need to be assessed prior to undertaking disposal. In-water disposal often results in the direct smothering of benthic organisms at the disposal sites and indirect impacts to organisms downstream from the sites. Disposal often impacts commercial fisheries by decreasing the size and depth of gillnet drifts, placing snags in fishing areas, and obstructing fishing access with dredging equipment.

Figure B-3: Flowlane Disposal from a Hopper Dredge

a. Flow-lane disposal
Flow-lane disposal is the placement of dredged material in or adjacent to a channel where the material will continue downstream movement. Material is generally placed adjacent to the main navigation channel in 20 to 65 feet of water. In the Columbia River, this depth regime is often an area where sediment moves slowly from the site in the bedload. In this way, permanent mounding is avoided as might occur if the site were shallow, and rapid sediment transport to downstream areas of the navigation channel does not occur, as in deeper scour-holes. Flow-lane disposal is undertaken by hopper, pipeline, and clamshell/bucket dredges.

b. Estuarine Open-Water Disposal
This method involves the placement of material in open water areas other than those used for flow-lane disposal. Disposals at estuarine open-water sites occur from hopper or clamshell dredging projects.

Area D (site O-8.5) is the only open water disposal site currently in the estuary.

c. Sump Disposal
Sump disposal is the placement of dredged material in a temporary in-water holding site with subsequent rehandling to an upland area. Dredged material is disposed of in the sump primarily from hopper dredges. When a sufficient quantity of material accumulates in the sump, it is subsequently pumped with a pipeline dredge.

The only such disposal area currently operation is Harrington Sump. The material is placed in Harrington Sump and subsequently pumped onto Rice Island.

Figure B-4: Pipeline Dredge pumping dredged material from Harrington Sump (O-21.0) to Rice Island (O-21.2)

Figure B-5: Dredge pipes transporting dredged material from the Pipeline Dredge to Rice Island (O-21.2)

d. Ocean Disposal
Ocean disposal involves the transport of dredged material over the Columbia River Bar to designated ocean disposal sites. Material is transported by hopper dredges or barges. The Environmental Protection Agency, in conjunction with other resource management agencies, designates Ocean disposal sites.

Beach Nourishment
Dredged material is placed on a beach and in the aquatic areas adjacent to the beach. Beach nourishment disposal is undertaken on eroding beaches and serves a dual purpose of disposing of dredged materials and restoring the beaches to their historic profile. Subsequent to disposal, the beach must be graded at a uniform and gentle slope to minimize fish stranding problems and provide a safe beach for users.

Containment Options
a. Confined Disposal Facilities (CDF)
Any disposal location where dredged material is contained, upland, in-water, or nearshore. Such disposal involves the controlled placement of the dredged material at a designated dredged material disposal site. In-water placement of contaminated materials involve covering the site with a clean material ("capping"). Such a process may involve the construction of levees or other holding facilities as a means of containing the material.

e.g. inactive quarry areas, abandoned mines, landfill disposal

Considerations to keep in mind:
i. Physical impacts: alteration of habitat, hydrological conditions, navigation impacts, land-use impacts, aesthetic and cultural impacts
ii. Storage Capacity
iii. Management and Monitoring
iv. Contaminant Pathways:
v. Geochemical environments
vi. Surface run-off
vii. Effluent discharge
viii. Leachate
ix. Plant and animal uptake
x. Volitization to air

Figure B-6: Confined Disposal Facility

http://www.spl.usace.army.mil/pd/coastal/dmca.html

b. Confined Aquatic Disposal (CAD)
These facilities contain the dredged material and prevent them from spreading. Such facilities include subaqueous pits, containment areas, containment islands, and nearshore disposal sites. The unsuitable material may also be contained in geotextile bags; the disposal of the bags will then be capped with clean material (generally sand).

Figure B-7: Confined Aquatic Disposal

http://www.spl.usace.army.mil/pd/coastal/cont_ad.html

TABLE B-1: Advantages and Disadvantages of Disposal Options