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

摘要

In an effort to ameliorate water quality problems in Boston Harbor associated withdischarge of sewage from the region's populace, the Massachusetts WaterResources Authority (MWRA) is in the process of (1) completing upgrades to itswastewater treatment facilities to provide secondary treatment and (2) relocating thedischarge of treated effluent to a location in northwestern Massachusetts Bay,approximately 15 km east of the current outfall locations at Nut and Deer Islands.While previous modeling efforts suggested that the discharge of effluent organiccarbon and nutrients to northwest Massachusetts Bay will have little effect on theenvironment of the Bays, these studies used relatively simple frameworks for theiranalyses and, therefore, are subject to some uncertainty.In an effort to develop a more rigorous and detailed understanding of the potentialimpacts of the outfall relocation on the water quality of Massachusetts and Cape CodBays, the MWRA has funded a number of studies within Boston Harbor, MassachusettsBays, and Cape Cod Bay. Included in these efforts have been a number ofhydrographic and water quality surveys of the system. Also included has beenfunding to support development of time-variable three-dimensional hydrodynamic andwater quality models of the Massachusetts Bays system.Comparisons between model computations and observed data suggest that thehydrodynamic and water quality models reproduce the principal features ofcirculation, stratification, primary production and dissolved oxygen in Massachusettsand Cape Cod Bays. The water quality model was used to provide projections of waterquality conditions in Boston Harbor, Massachusetts Bay, and Cape Cod Bay that mightresult once the outfall goes online. These projections were made using the base lineconditions observed in 1992. The water quality model was also used to develop asystem-wide mass balance for total nitrogen. This paper will present model calibrationand projection results and a summary of the system-wide nitrogen balance.