06-6792. Record of Decision for the Boston Harbor Inner Harbor Maintenance Dredging Project

AGENCY:

Department of the Army, U.S. Army Corps of Engineers, DOD.

ACTION:

Notice.

SUMMARY:

The U.S. Army Corps of Engineers, New England District announces its decision to maintenance dredge the following Federal navigation channels in Boston Harbor, Massachusetts: the Main Ship Channel upstream of Spectacle Island to the Inner Confluence, the upper Reserved Channel, the approach to the Navy Dry Dock, a portion of the Mystic River, and a portion of the Chelsea River (previously permitted). Maintenance dredging of the navigation channels landward of Spectacle Island is needed to remove shoals and restore the Federal navigation channels to their authorized depths. Dredged material suitable for unconfined open water disposal will be disposed at the Massachusetts Bay Disposal Site; material not suitable for unconfined open water disposal will be disposed in confined aquatic disposal (CAD) cell(s) located within the navigation channels. Major navigation channel improvements (deepening) were made in 1999 through 2001 in the Reserved Channel, the Mystic River, Inner Confluence, and the Chelsea River. A Final Environmental Impact Statement (EIS) prepared in June 1995 for this previous navigation improvement project (Boston Harbor Navigation Improvement Project—BHNIP) identified selected use of CAD cells in the Mystic River, Inner Confluence, and Chelsea River for disposal. A Supplemental Draft and Final EIS was prepared for this maintenance dredging project and built on the lessons learned from the previous improvement project. A new CAD cell for the proposed maintenance project will be constructed in the Mystic River (previously permitted) and in the Main Ship Channel just below the Inner Confluence.

FOR FURTHER INFORMATION CONTACT:

Mr. Michael Keegan, [phone].

SUPPLEMENTARY INFORMATION:

The U.S. Army Corps of Engineers is authorized by the various River and Harbor Acts and Water Resources Development Acts to conduct maintenance dredging of the Federal navigation channels and anchorage areas in Boston Harbor.

Alternatives Considered: The National Environmental Policy Act (NEPA) requires a discussion of alternatives to the project, including the No Action Alternative. Since a Supplemental EIS was prepared, the preferred alternative is evaluated in the context of the alternatives addressed in the EIS for the navigation improvement project, including alternatives to full maintenance dredging, dredging methods, and disposal options.

Dredging—The Boston Harbor terminal operators, and shipping interests were contacted to identify the type and size of vessels currently using the navigation channels and if they were experiencing any delay or impacts associated with the navigation project. The results of the survey were used to determine if maintenance of all or just a portion of the currently authorized navigation channels in the proposed project is required. Based on the results of the survey, it was determined that shoaling in the Charles River channel does not affect any of the current operations in that channel and will not be dredged.

Dredging Methods—Various types of dredging methods were considered for this project including a hydraulic dredge, a hopper dredge, and a mechanical dredge. The type of dredge proposed for a project is dependent upon the type of material to be dredged and the disposal site selected. Due to the fine nature of the materials to be dredged from Boston Harbor, and the aquatic sites selected for disposal, it was determined that a mechanical dredge would best suit the needs of the project. To minimize turbidity impacts from dredging, an enclosed “environmental” bucket will be used during silt dredging. In addition, no overflow from the scows will be allowed to further reduce the effects of turbidity on water quality.

Disposal Alternatives—Over 370 disposal sites were identified and evaluated during preparation of the EIS for the previous navigation improvement project (BHNIP). The screening process selected in-channel CAD cells for disposal of the material unsuitable for unconfined open water disposal and the Massachusetts Bay Disposal Site (MBDS) for disposal of the suitable material. In addition, seven sites were identified in the BHNIP Final EIS as potential disposal sites for future maintenance dredged material. The sites included the MBDS, Subaqueous B and E, Meisburger 2 and 7, Boston Lightship, and Spectacle Island CAD.

The Subaqueous B and E sites, the Meisburger sites and the Spectacle Island CAD are all located in previously undisturbed areas. The Boston Lightship is a historic disposal site and would need to go through a lengthy site selection process before disposal could be considered. This site also recovering from previous disposal events. The MBDS is an EPA-designated ocean disposal site that is currently in use. Sites that have not been previously disturbed are not as desirable for disposal of dredged material. Therefore, the MBDS was selected as the preferred site for the suitable material and the in-channel CAD cells selected for material unsuitable for unconfined open water disposal.

No Action Alternative—Under a No Action Alternative, the Federal navigation channels in Boston Harbor would not be dredged. Failure to dredge Boston Harbor will further restrict and delay commercial deep draft vessels. Shoaling has reduced depths in the channel as much as five feet in some sections of the project area. Without maintenance dredging to restore authorized depths in the inner portion of the Main Ship Channel, shippers will experience even longer tidal delays and be restricted to operating within narrower time periods of higher tidal stages. This results in a significant and negative impact to the region, and raises significant operational, safety, economic, and environmental concerns. With the increase in costs and reduction in vessel movement opportunities, it is likely that shippers will by-pass the port and will unload their products at other ports and ship the products back to the region via trucks. This could impact limited roadway capacity, resulting in increased air emissions, traffic, and deterioration of highways and bridges. Although the No Action Alternative is the environmentally preferred alternative, it does not meet the project objectives, and is not considered a viable alternative. Therefore the preferred alternative is dredging the above described navigation channels to their authorized depth using a mechanical dredge with disposal at the MBDS and in-channel CAD cells.

Environmental Impacts: Potential environmental impacts associated with dredging and disposal includes water quality impacts from turbidity plumes, potential release contaminants during dredging and disposal activities, and impacts to biological resources. In particular, concerns about biological resources centered on potential blockage of anadromous fish transiting to spawning grounds, sediment deposition from suspended solids on winter flounder eggs, and direct impacts to lobsters.

Extensive environmental monitoring was conducted during construction of the BHNIP as a requirement of the Water Quality Certification (WQC). Environmental monitoring required as part of the WQC included: (1) Silt plume tracking during dredging of and after disposal into CAD cells, (2) water quality testing after disposal into the CAD cells, (3) biological testing, (4) dissolved oxygen (DO) testing within and outside the CAD cells, and (5) fisheries monitoring. The results of the monitoring showed no water quality violations or significant impacts to biological resources.

Additional investigations (i.e., outside the scope of the WQC) were performed during construction to address concerns raised by the Technical Advisory Committee (TAC) to address potential impacts from changes in operations suggested by the dredging contractor. The TAC met periodically to review monitoring results and discuss recommended amendments to the WQC. These additional investigations included water quality monitoring of disposal at low tide, plume monitoring of the contractor's enclosed bucket, monitoring turbidity caused by vessel passage over an uncapped and capped CAD cell, bathymetric measurements, and lobster monitoring. Monitoring results showed no water quality violations or significant environmental impacts from construction of the project. One-year surveys and five-year surveys of the CAD cells constructed in the Inner Confluence, Mystic River, and Chelsea River for the BHNIP have also been completed, as required by the BHNIP WQC. The results of the monitoring show that the CAD cells are performing as expected. Experience gained from placing a sand cap on the CAD cells will be incorporated into this project.

Mitigation: As a result of the extensive monitoring conducted for the BHNIP, and the lack of any water quality violations or significant impacts, only confirmatory water quality monitoring during initial disposal operations is recommended for this project. It is recommended that total suspended solids and turbidity monitoring be performed during the initial disposal events at both the Mystic River CAD cell and at the Main Ship Channel CAD cell.

To reduce potential impacts to resources in the project area, based on lessons learned, the following mitigation measures will be implemented:

• An enclosed “environmental” bucket will be used for silt dredging. To reduce the effects of turbidity on water quality, no overflow from the scows will be allowed.
• Disposal into the CAD cells will occur only around periods of slack tide: three hours at low tide and high tide (one hour before and two hours after slack tide).
• A three-foot sand cap will be placed in the CAD cells when the silt has consolidated enough to support a cap. The cap material will be released from a moving as opposed to a stationary platform. No spudding over the cap or mechanical disturbance of the cap will be allowed.
• To reduce the impact to biological resources from blasting, all blasting will be conducted using inserted delays of a fraction of a second per hole. Rock or similar material will be placed into the top of the borehold to deaden the shock wave reaching the water column. A fisheries and mammal observer, and fish detecting sonar system, will be used to avoid blasting when mammals are present in the area or when significant schools of fish are observed.
• A fisheries observer, sonar detection, and use of a fish startle system from February 15 to June 15 will be required for the Mystic River and Main Ship Channel CAD disposal activities to avoid disposal during the time of anadromous fish migration.
• To reduce potential impacts to egg-bearing lobsters that are less mobile in the colder months, no dredging or blasting will occur seaward of the Third Harbor Tunnel between December 1 and March 31.
• A marine mammal observer will be on board the scows transiting to the MBDS from February 1 to May 31 to avoid potential ship strikes with marine mammals, and in particular the North Atlantic Right Whale.
• Rock removed from the Presidents Road Anchorage area will be placed within a new area of the MBDS to increase habitat diversity.
• The dredge contractor will provide advance notice to the lobstermen on anticipated significant dredge movements.
• The dredge contractor will maintain a short tow while inside Boston Harbor to minimize disruption of lobster pots.

Based on incorporation of the above mitigation measures, the experience gained during construction of the BHNIP, and lack of any water quality violations or other significant effects from the BHNIP, no significant impacts to the environment are expected from the Boston Harbor Inner Harbor Maintenance Dredging Project. All practicable means to avoid or minimize adverse environmental effects have been incorporated into the recommended plan. The public interest will best be served by implementing maintenance dredging as identified and described in the Supplemental Environmental Impact Report.

Dated: August 1, 2006.

Curtis L. Thalken,

Colonel, Corps of Engineers, New England District.