SAMPLING SITES THROUGHOUT MASSACHUSETTS BAY

MWRA samples at “nearfield” and “farfield” stations. The nearfield stations are within about 3 miles of the outfall diffuser, and the farfield stations are in Boston Harbor, Massachusetts Bay, Cape Cod Bay, and the Stellwagen Bank National Marine Sanctuary.

MWRA's discharge permit for the Massachusetts Bay outfall has strict monitoring requirements designed to identify unexpected impacts from operation of the outfall. MWRA runs an extensive monitoring program to measure the health of the Bay.

DYE STUDY SHOWED THAT THE OUTFALL IS WORKING AS DESIGNED. A major dye study of the effluent successfully tracked the location and dilution of the effluent discharge in Massachusetts Bay. The monitoring team added an environmentally friendly, rose-colored dye (rhodamine) in a measured amount at the treatment plant. The dilution of the dye at the outfall was tracked and sampled with shipboard instruments after discharge as it mixed with the surrounding water. Results showed initial dilution of about 100 to 1, within 50 meters of the discharge, within the expected range.

MONITORING DATA MATCHED MODEL PREDICTIONS FOR OUTFALL DILUTION. Sampling studies measured ammonium, which is a tracer of the effluent plume. Prior to outfall start-up, ammonium was relatively low near the outfall. By late September, concentrations were higher, indicating the presence of effluent. The ammonium monitoring data showed a pattern that was similar to the computer model prediction of outfall dilution.

MONITORING SHOWED THAT AN ALGAE BLOOM IN 2000 WAS NOT CAUSED BY THE OUTFALL. There was an unusually large bloom of algae at the time the outfall began operating. When the outfall started up, chlorophyll levels were already unusually elevated, and continued to increase during the fall of 2000. Satellite images confirmed that there was a region-wide algal bloom that ranged from New Jersey to the Bay of Fundy. By the winter/spring of 2001, chlorophyll levels had declined to levels lower than in 1998 and 1999. All the evidence suggested that this unusual bloom was due to seasonal changes, independent of the MWRA outfall, and that there were no adverse effects.

ABUNDANT SEA LIFE AT THE OUTFALL. A sediment contaminant survey was conducted in the fall of 2000 after the outfall came on line. Concentrations of organic and inorganic contaminants were similar to those measured prior to the outfall coming on line. In July 2001, the monitoring team carried out the annual video and photographic survey of the plant and animal communities that live on rocks near the outfall. Using a remotely operated vehicle, or “ROV,” scientists were able to document abundant life on and near active diffuser heads, including densely growing sea anemones, sea squirts, starfish, flounder, cod, sponges and other animals, shown below. Data showed that the outfall was functioning as anticipated—providing rapid dilution to the effluent with no significant adverse impacts. Watch 2009 video of sea life at the outfall.

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