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BOSTON SEWAGE OUTFALL: THE FATE OF SEDIMENTS AND CONTAMINANTS IN MASSACHUSETTS BAY

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Image of Boston Harbor - Click to enlarge
Click here for larger images of backscatter intensity

Click here for larger images of shaded relief

Introduction

Boston Harbor, once one of the most polluted waterways in the nation, is in the final stages of a major cleanup. A $3.8 billion cleanup program, begun in 1985 by the Massachusetts Water Resources Authority (MWRA) was designed to address more than 300 years of metropolitan waste disposal. The cleanup has significantly improved the environmental quality of the harbor, enforced reduction of industrial waste releases at the source, eliminated sludge discharge (Dec. 1991), improved treatment of Boston sewage, and relocated the sewage outfall from the Harbor mouth to a new location 9 miles offshore in Massachusetts Bay.

USGS Research

Since 1989, the United States Geological Survey (USGS), in cooperation with the MWRA, has been conducting research to understand and predict the fate of contaminants introduced to Massachusetts` coastal waters. The overall objective is to develop a capability to predict the fate of contaminants associated with fine-grained sediments on a regional basis. We emphasize sediments because most contaminants introduced to the ocean are adsorbed by and transported with suspended sediments. After complicated cycles of deposition, resuspension, and biological and chemical interactions, contaminants on particles may be eventually buried in bottom sediments, which become the ultimate contaminant sink.

MAJOR RESULTS

Image of Boston Harbor Ocean Circulation

(a) Modelling
Computer simulations of ocean circulation and dilution of sewage effluent show that, with the new outfall location, water quality will greatly improve in Boston Harbor without significantly degrading conditions in Massachusetts Bay, in Cape Cod Bay or in the rich biological habitat of the Stellwagen Bank National Marine Sanctuary.

Image of Sedimentary Deposits (b) Sediment Transport and Fate
The ultimate respositories for some of the contaminants introduced from the Boston Metropolitan area are Stellwagen Basin and Cape Cod Bay. Winter storms resuspend and transport sediments from the region offshore of Boston, including the new outfall site, to these locations. Maps of sedimentary environments and bottom morphology have been generated using side scan sonar and high resolution bathymetric surveys. These have helped managers choose the location of the outfall and the location of stations used to monitor the fate and transport of contaminants.

Photo of a corer being deployed



(c) Monitoring
Monitoring sites have been established at critical locations in Massachusetts Bay to establish a baseline of contaminant levels in sediments and to document natural variability. These sites will continue to be monitored over the next 2 years as the treated effluent is discharged through the new outfall into Massachusetts Bay. Since 1989, monitoring oceanographic parameters and sediment chemistry by the USGS near the Massachusetts Bay outfall has identified storms as a major process for redistributing sediments and associated contaminants. The USGS research program complements the benthic and water column monitoring program conducted by the Massachusetts Water Resources Authority.

Image of pollutant concentrations over time

(d) Geochemistry
The bottom sediments of Boston Harbor have gotten cleaner over the last 20 years due to the reduced amount of pollutants introduced into the system.


USGS Collaborators External Collaborators
Mike Bothner (Geochemistry)
Brad Butman (Oceanography,
sea floor mapping )
Rich Signell (Modeling)
Page Valentine (Stellwagen Bank Sea floor mapping)

Massachusetts Water Resources Authorityy

United States Coast Guard:
   USCG Cutter MARCUS HANNA
   USCG Cutter PENDANT

Woods Hole Oceanographic Inst.
   Greg Ravizza (Platinum group elements)
   Fred Sayles (Oxygen consumption)
   Bill Martin (Flux of metals and nutrients)
   Roger Francois (Flux of metals and     nutrients)

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This page last modified on Monday, 24-Nov-2014 13:06:16 EST