Pollution in Boston
A turning point in the cleanup of Boston Harbor
was in July 1998 when the Nut Island Treatment Plant (NITP) was
decommissioned and its flow re-routed to the Deer Island Treatment
Plant (DITP) for secondary treatment. After this, most of the
wastewater discharged to the harbor received secondary treatment,
except during the heaviest rainstorms. MWRA discharges to the
southern harbor ended.
The maps below illustrate simply how, for three
time periods, MWRA discharges changed, while discharges from other
sources remained constant. The large arrows represent treatment
plants and the smaller arrows indicate rivers, combined sewer
overflows, and stormwater runoff. After July 1998, DITP was the
main pollution source in the harbor, discharging up to 350 million
gallons of treated wastewater per day. After September 2000, when
effluent discharges were moved from the harbor to the bay, rivers,
runoff, and other non-point sources became the main
sources of pollution to the harbor.
OF SEWAGE IN BOSTON HARBOR
on each map to enlarge)
Before July 1998: The treatment plants discharged poorly
treated wastewater. Until 1991, after sewage had undergone
primary treatment, the treated sewage solids (sludge)
were discharged into the harbor. In 1997, the first
battery of secondary treatment was in place at DITP.
In 1998, up to 65% of sewage was receiving secondary
July 1998 to September 2000: With the completion of
the inter-island tunnel from Nut Island to Deer Island,
South System sewage was sent to DITP for secondary treatment.
NITP was closed, ending discharges to the southern harbor.
By September 2000, 85% of the sewage was receiving secondary
After Sep. 2000: The third and final battery of secondary
treatment was complete, better removing solids and contaminants.
The outfall transported cleaner effluent out of the
harbor and into the bay for greater dilution. Pollution
sources were now from rivers, CSOs, and stormwater runoff.