As the Boston Harbor Project progressed, monitoring data helped answer the questions of greatest public concern: Is it safe to swim and to eat shellfish? Is the ecosystem healthy, and are aesthetics protected? Changes in bacteria, water clarity, nutrients, dissolved oxygen, toxic contaminants, and other indicators provided a picture of a recovering harbor.

To compare “before” and “after” effluent discharge was better treated and then moved out of the harbor, July 1998 was chosen as a turning point, the date the Nut Island Treatment Plant (NITP) was decommissioned and its flow re-routed to the improved Deer Island Treatment Plant (DITP). After that date, discharges to the southern harbor ended and most of the wastewater discharged to the harbor received secondary treatment.

CHANGE IN LOCATION OF HARBOR CONTAMINATION SOURCES

A: Before July 1998. The major wastewater sources in Boston Harbor were the Deer and Nut Island Treatment Plants (big arrows). Rivers, CSOs, and runoff (indicated by small arrows) contributed significant but smaller amounts of contaminants. B: July 1998-September 2000. NITP closed in July 1998 and all flows were transferred to the new DITP, which became the harbor’s main point source of treated wastewater. Average discharges from Deer Island increased from 250 to 350 million gallons per day. Rivers, CSOs, and runoff remained.