Flora and fauna of Boston Harbor will breathe easier soon because dissolved oxygen levels will climb as Greater Boston’s wastewater utility, the Massachusetts Water Resources Authority (MWRA), ends daily discharges of hundreds of million of gallons of treated wastewater to the harbor’s shallow waters. In recent years MWRA has completed new sewage treatment plant construction to achieve secondary treatment. Now a new outfall, discharging treated effluent to deep waters outside the harbor, caps the project’s environmental gains. The new outfall diffuser is 6,600-feet long and is made up of hundreds of small individual discharge ports to assure effective dispersal and dilution of the wastewater stream.
Effluent reaches the deep water outfall diffuser through a 25-foot diameter tunnel constructed in bedrock deep under Massachusetts Bay to a point 9.5 miles east of the new Deer Island Treatment Plant. The in-service date for the tunnel, with a maximum capacity of 1.27 billion gallons per day, is September 6, 2000. The tunnel and outfall construction has taken almost ten years and cost $390 million, more than 10% of the entire $3.8 billion cost of MWRA’s Boston Harbor Project.
An extraordinary interdisciplinary scientific effort, gathering momentum since 1987, has been associated with the tunnel and outfall project. Data collection, monitoring, research and modeling has been performed to predict the new impact on Massachusetts Bay from discharges at the new outfall site. Studies have also examined the likely benefits from the new outfall not only to Boston Harbor but also to the reaches of Massachusetts Bay now affected by tidal currents influenced by Harbor waters. The Harbor receives flow from several rivers including the Charles, Mystic and Neponset, and is the largest estuary of Massachusetts Bay.
The United States Environmental Protection Agency included provisions requiring extensive scientific monitoring of the outfall effects in MWRA’s discharge permit to assure protection of important natural resources in the Bay. Stellwagen Bank, a National Marine Sanctuary, is 16.4 miles from the discharge site. Areas in eastern Cape Cod Bay are feeding grounds of the critically endangered North Atlantic right whale.
MWRA’s science program investment of over $20 million has supported teams of researchers from virtually all marine science disciplines. Findings have been pooled and shared in quest of an integrated picture of the harbor and Bay ecosystems.
Dr. Andrea Rex, a microbiologist who directs marine ecology research and study efforts at MWRA, states: "The science program prompted by the outfall project has created unique research opportunities and led to important scientific and public policy results. Massachusetts Bay and Boston Harbor have become one of the best-studied and best-understood marine environments in the world. Fish veterinarians, plankton biologists, physical oceanographers and benthic ecologists, just to name a few, have shared their insights not only for the benefit of basic science, but to assure that critical environmental policy questions have been soundly addressed. Not only MWRA’s customers and ratepayers, but U.S. EPA and the National Marine Fisheries Service, have benefited from these efforts."
Examples of scientific findings that addressed issues critical to understanding potential impacts of the outfall:
• Benthic nutrient flux studies showed that Boston Harbor was adversely affected by the harbor discharge location-but that most nutrients were in fact making their way out to the Bay in a surface plume. This meant that moving the discharge location offshore was not a radical change in nutrient loading to the Bay, as some scientists had previously feared.
• Sampling studies of lobsters showed that while the nearshore environment was important habitat for juvenile lobsters, the offshore location was not, alleviating fears of significant adverse impacts on lobster recruitment.
• Basic findings on seasonal cycling in Massachusetts Bay, such as the predominance of a fall phytoplankton bloom; physical oceanographic findings of how interactions among upwelling, downwelling, salinity and temperature greatly affect annual patterns of dissolved oxygen; and characterizing large interannual variability in such parameters, will be important in interpreting monitoring data gathered in the future to measure outfall impacts on Massachusetts Bay.
• Hydrodynamic and water quality modeling of chlorophyll, particulate organic carbon deposition, and bottom-water dissolved oxygen predicted that the new outfall would benefit Boston Harbor with minimal impacts on the Bay.
Scientific investigation also has documented many environmental gains to Boston Harbor from the improvements to effluent quality as the new pumping, primary treatment and secondary treatment facility have come on line over the course of recent years. Studies over time have shown dramatic decline in the incidence of liver tumors in flounder. Successional patterns in benthic communities are being tracked by ecologists who are noting changes from pollution tolerant capitellid polychaetes to tube-building amphipods, which in turn appear to be in the process of being replaced by more diverse, healthy communities. Mussels placed near the old harbor outfalls are accumulating lower levels of organic pollutants. Some investigators predict that seagrass beds may return to wide areas of the once-polluted harbor, providing more natural complexity to the ecosystem.
Years of baseline data gathering in the Harbor and the Bay will now provide a platform for future observation of marine conditions. Oversight of scientific inquiry and interpretation is vested in an eight-person Outfall Monitoring Scientific Advisory Panel chartered to report to U.S. EPA and the Massachusetts Department of Environmental Protection. The future challenge will be to refine the understandings of anthropogenic and natural effects on this complicated marine ecosystem and to relate them to future policy-making so that long-term protection of the marine environment can be assured.
The scientists participating in outfall study programs have come from numerous disciplines and organizations. Dr. Michael Bothner (United States Geological Survey, Woods Hole, MA), project leader for a cooperative USGS-MWRA research program on fate and transport of contaminants says, "USGS work in Boston Harbor and Massachusetts Bay is a good example of how our agency applies science with a regional and multidisciplinary scope to address important environmental questions in the coastal ecosystem."
Additional information and bibliographic data on studies and publications can be found at http://www.mwra.com.
Materials provided by Massachusetts Water Resources Authority. Note: Content may be edited for style and length.
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