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Managing Wastewater in Coastal Urban Areas
Over the last several years, the MWRA's industrial pretreatment and source reduction programs have significantly reduced the levels of organics and heavy metals in the wastewater. Improvements to the treatment capacity of the existing plants and more efficient use of storage in the system have decreased CSO flows to the harbor, which has reduced bacterial contamination of the harbor to the lowest levels in 50 years. The disposal of sludge into the harbor has ceased, and sludge is now being converted to fertilizer pellets. The outfall and primary treatment plant are under construction, and the first portion of the secondary treatment plant is designed. Plans for CSO treatment are under way. These technical improvements in the wastewater treatment facilities, when complete, are expected to significantly improve the water quality of Boston Harbor.
Recently, the proposed placement of the new outfall, 9.5 miles east of Boston into Massachusetts Bay, has caused substantial controversy in Cape Cod. Concerned about space limitations on Deer Island, integration with other wastewater construction activities, and large increases in sewer rates, in February 1992 the MWRA proposed to pause the construction program after completion of 500 MGD of the secondary plant (sufficient for most dry weather flows) to determine how to best set priorities concerning construction of CSO abatement facilities, the remaining 500 MGD of secondary treatment capacity (needed to treat peak dry weather flows and wet weather flows), and potential additional levels of treatment such as nutrient removal. The MWRA dropped this proposal approximately 5 months later, however it still remains a controversy. In addition, residents of Cape Cod have questioned the sufficiency of secondary treatment to protect Massachusetts Bay. They expressed concern that the discharge would cause nitrogen enrichment of the waters of Cape Cod Bay 35 miles away, resulting in nuisance algal blooms and threatening the endangered North Atlantic right whale and humpback whale. Although the EPA has concluded that such problems will not occur, some Cape Cod groups and others have proposed that the outfall not be built and that the discharge remain in Boston Harbor. There are also concerns within the region that MWRA will retreat from its commitment to secondary treatment following the completion of the outfall and primary treatment plant.
Some civil engineers from the Massachusetts Institute of Technology, including a member of the Committee on Wastewater Management for Coastal Urban Areas, have conducted studies showing that average annual flows in Boston are substantially less than those for which the new treatment plant is designed. They suggest that the new primary treatment plant could be retrofitted for chemically-enhanced primary treatment which would reduce the subsequent BOD loading to the new secondary treatment plant. State and federal requirements could then be met, they propose, by building a biological secondary treatment half the size of the proposed facility. They