MWRA State of Boston Harbor Report

Boston Harbor and Massachusetts Bay
MWRA Environmental Quality Department

Aerial view of Deer Island Treatment Plant (Click to enlarge)

The State of Boston Harbor-An Introduction

How did Boston Harbor originally get so dirty?

Before July 1998, primary-treated wastewater was discharged from the Deer Island and Nut Island Treatment Plants into the harbor. In addition, sewage sludge was discharged into the northern harbor after digestion and disinfection, a practice that ended in 1991. Floating sewage and debris would frequently wash up on local beaches, resulting in a court case and 1984 enabling legislation that created the Massachusetts Water Resources Authority.

From 1986 to 1995, there were marked improvements in effluent discharges after MWRA upgraded disinfection and primary treatment and then added secondary treatment. MWRA also increased enforcement of pretreatment of industrial wastewater, which significantly reduced the amounts of metals and other pollutants being sent to the treatment plants.

A decade of environmental monitoring data shows both dramatic and subtle changes in Boston Harbor's water, sediment, and living natural communities since the Massachusetts Water Resources Authority (MWRA) first began the Boston Harbor Project in 1986. It is important to understand the effects that the major components of the Boston Harbor Project had on pollutant inputs to the harbor. The maps on this page illustrate how, for three time periods, MWRA minimized the impacts of sewage by improving treatment and changing the location of effluent discharges.

SOURCES OF SEWAGE IN BOSTON HARBOR
(Click on each map to enlarge)

A. In 1997, The first battery of secondary treatment of sewage was in place at the Deer Island Treatment Plant, and in 1998 up to 65% of sewage was undergoing secondary treatment. Secondary removes more solids and contaminants from wastewater than primary treatment.

B. 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 Deer Island for secondary treatment, and the Nut Island Treatment Plant was closed, ending direct discharges to the southern harbor. Another battery of secondary treatment was in place by September 2000, when 85% of the sewage was receiving secondary treatment

C. After September 2000: The third and final battery of secondary treatment is in place. The new outfall transports cleaner effluent out of the harbor completely and into Massachusetts Bay for greater dilution. Now, no treatment plants are discharging directly into the harbor.

So far, data gathered on the quality of sediments, water, and sea life in Boston Harbor and Massachusetts Bay show that the outfall has been functioning as anticipated–-providing rapid dilution to the effluent with no significant adverse impacts. Harbor data show even further improvements as nutrients decrease to levels more typical of a natural estuary.

Treatment plant discharges and much of the combined sewage in the harbor have been eliminated, revealing the importance of other sources of coastline contamination. Rivers, runoff, and other “non-point” sources used to be relatively minor contributors of contamination to the harbor. Now that effluent discharges have moved from the harbor to the bay, pollution entering the harbor comes mainly from its tributary rivers and must in turn be addressed to continue the “Boston Harbor clean-up”. Identifying and eliminating cross-connections, controlling combined sewer overflows, and maintaining local storm and sewer systems are essential to realizing the full benefits of the Boston Harbor project.