A POST-AUDIT ANALYSIS OF THE IMPACTS OF WASTEWATER TREATMENT PLANT OUTFALL RELOCATION ON BOSTON HARBOR, MASSACHUSETTS BAY AND CAPE COD BAY WATER QUALITY

The City of Boston and Boston Harbor have long played an important role in the nation's history from the early days of the American revolution to a focal point of the 1988 presidential campaign when the harbor was cited as one of the nation's dirtiest bodies of water. However, in the 15 years since that low point in the harbor's history, approximately 4 billion has been spent (mostly supported by the ratepayers of the City of Boston) to improve the existing antiquated sewage collection, treatment, and disposal system. Included in this effort was the modernization and expansion of the Deer Island wastewater treatment facility and the construction of a 15.3 km outfall pipe to completely remove the Deer Island effluent from Boston Harbor and discharge it offshore in northwestern Massachusetts Bay.At the same time that upgrades to the Deer Island wastewater treatment plant and the construction of the outfall tunnel were being performed, the Massachusetts Water Resources Authority (MWRA) provided funding for a Harbor and Outfall Monitoring (HOM) program and for the construction of a mathematical model of water quality for the Boston Harbor and Massachusetts and Cape Code Bays system. The ongoing HOM program, which is a requirement of the NPDES permit for the MWRA outfall, is meant to provide data with which to compare to pre-discharge baseline data to help assess any impact of the discharge on Massachusetts and Cape Cod Bays. The mathematical model was used to provide an early assessment of expected water quality conditions once the outfall went online. Now that the outfall tunnel has been completed and began operating on September 8, 2000, data from the ongoing HOM provide an opportunity to perform a post-audit of the water quality model to evaluate how its projections compare with observed post-discharge data.The purpose of this paper is to provide a short review of the history of environmental pollution and regulation within Boston Harbor, overviews of the Harbor and Outfall Monitoring (HOM) Program and the Bays Eutrophication Model (BEM), and a post-audit of the BEM using post-discharge data collected by MWRA.