Vol. 1, No. 3
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Boston Harbor dredge disposal work designed to protect water quality Boston, Massachusetts - Removing contaminated sediments without compromising Boston Harbor's water quality was the most problematic part of planning the dredging project now under way here, according to officials. But nearly nine years after the project was first proposed, crews recently completed phase one of the $70 million undertaking, and will begin phase two in November. Permits for the project were granted last fall, after a six-year process, said Deerin Babb-Brott, dredging coordinator for Massachusetts Coastal Zone Manage-ment (MCZM). Maintenance dredging has taken place over the years, but this work is the first attempt to deepen the harbor's channels since 1966. It will enable the port to accommodate newer, larger passenger and cargo ships, while limiting environmental impacts and protecting aquatic resources, officials say. Two-thirds of the region's energy resources and more than 60,000 cruise passengers enter the port annually, and the harbor's maritime business employs more than 9,000 people. Yet, regulators have to consider how port improvements will affect the harbor's ecology. Like that of many urban ports, soil and sediment at the bottom of Boston Harbor are contaminated with petroleum byproducts and heavy metals. "When contaminants get into a water body they typically adsorb [when molecules of a gas, liquid, or dissolved substances adhere to a surface] to soil particles. Most of Boston Harbor's contamination is associated with material on the bottom of the harbor," which is removed during dredging, noted Babb-Brott. In phase one of the project, Massachusetts Port Authority (Massport), the state's quasi-governmental agency responsible for port development, began dredging Connolly Terminal to a depth of 45 feet (about 14 meters) in June, completing that work July 18, Babb-Brott said. The US Army Corps of Engineers is scheduled to begin phase two in November, and should finish that job in about a year and a half, he said. According to US Army Corps of Engineers project manager Pete Jackson, the Corps will dredge three channels during phase two: the Mystic River channel, last deepened in 1958; the Chelsea Creek channel, last deepened in 1966; and the Reserved Channel last deepened in 1966. Containing the contaminants Dredged materials have to be removed and contained in a way that prevents the contaminants from spreading into the water. Jackson said it is possible to remove contaminants from the dredged materials, but described that process as expensive. And, he said, "the technology is not there yet to do it on a large scale." Instead, the contaminated material, which represents one million cubic yards (764,600 cubic meters) of the 2.8 million total cubic yards (about 2.1 million cubic meters) of dredge material to be removed during the project will be placed in 54 containment cells dug under existing navigation channels in the harbor and then capped with sand. According to Jackson, the contaminated material is hauled up from the bottom of the harbor in a special leak-proof bucket, then deposited into a barge where it's taken to a disposal cell and dumped. The material will sink to the bottom in fewer than ten seconds, reducing the chance that contaminants will spread through the water, he said. Babb-Brott said the dredged material from the Connolly terminal project was placed in a cell dug into the harbor floor in the area where the Mystic and Chelsea rivers merge, then covered with a layer of coarse sand to prevent it from being stirred up by tides and vessel propellers. "The important thing is, once you get it off the bottom, to put where it will be physically sequestered from contact with overlying water," he explained. Preferred disposal sites are those that are unlikely to be eroded by wind and waves, said Babb-Brott, noting, "Boston Harbor is fairly protected. The tidal currents are low enough so the sand isn't likely to slosh around." The remaining 1.8 million cubic yards (about 1.4 million cubic meters) of clean material - along with clean clay dug from the channels to create containment cells - will be placed at the Massa-chusetts Bay Disposal Site, a federally designated ocean disposal site next to Stellwagen Bank National Marine Sanctuary. The Massachusetts Department of En-vironmental Protection and an Indepen-dent Observer managed by MCZM are monitoring the Boston Harbor project, which the state hopes will serve as a model for other urban harbor improvement projects in Massachusetts. Massport is providing $5 million for the project, the Commonwealth of Massachusetts is providing $15 million under the former Governor William Weld/ Governor Paul Cellucci Seaport Bond, and the Federal government is providing the rest, according to Babb-Brott. |
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Gulf of Maine Council on the Marine