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Massachusetts Water Resources Authority
November 20, 2013

Ria Convery, MWRA
(617) 788-1105,

MWRA Releases Annual Deer Island Outfall Monitoring Report


MWRA’s Outfall Monitoring Overview is an annual report that summarizes the results of MWRA’s monitoring of the environmental effects of the effluent discharges from the Deer Island Treatment Plant.  MWRA monitors the effluent, as well as the water, sediment, and health of fish and shellfish in Massachusetts and Cape Cod Bays.  2012 was the second year monitoring was conducted according to a more streamlined monitoring plan. 

MWRA is pleased to report that test results for 2012 show that the Deer Island Treatment Plant continues to operate as designed, and that discharges through the MWRA Outfall had no unexpected effects on the waters or ecosystems of Massachusetts and Cape Cod Bays.

MWRA has been monitoring Boston Harbor, Massachusetts Bay and Cape Cod Bays and the outfall area since 1992, and discharge monitoring began in 2000 when the outfall came on-line. One way potential effects are evaluated is to compare results collected after the outfall went on-line to results collected before the outfall went on-line (baseline conditions).

Summary of Effluent Quality Monitoring

  • Deer Island Treatment Plant earned a second consecutive Platinum Peak Performance Award from the National Association of Clean Water Agencies;
  • Relatively dry weather in 2012 meant effluent flow from Deer Island was lower than any year since the outfall came on-line in 2000;
  • Virtually all flow (99.6%) received full primary and secondary treatment;
  • Total Suspended Solids loads from effluent were less than 10 tons/day, a record low;
  • Metals loads in Deer Island’s effluent also decreased to record lows in 2012;
  • Record low Total Suspended Solids and Metals Loadings in the Deer Island effluent are mainly due to treatment process improvements in 2005 made possible by the ability to pump sludge to the Pelletizing Plant (completion of the Braintree-Weymouth Tunnel), and record low flows.

2012 was the twelfth year of monitoring since the outfall came on-line and was yet another year with no adverse effects from the discharge in the areas monitored.  Meanwhile, Boston Harbor continues to see substantial improvements.


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Posted November 20, 2013