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mapping of the Stellwagen Bank National Marine Sanctuary 



* Circulation modeling and direct observations of ocean currents to understand how 

 water and materials are transported to and through the system. 



* Long-term observations of currents and suspended sediments at one location near the 

 new outfall to document seasonal and interannual variability and the rare and/or 

 catastrophic events that play a major role in the transport of sediments. 



* Compilations of existing and new observations of contaminants in sediments to 

 document the past and present levels bay wide and to provide a baseline to measure 

 change. 



A long-term objective of the program is to develop a predictive capability for sediment 

 transport and accumulation. 



The uses Massachusetts Bay study is part of a broader program to understand the 

 accumulation and transport of polluted sediment in U.S. coastal waters. Because many 

 coastal metropolitan areas are faced with similar pollution issues, these results and techniques 

 developed in the Massachusetts Bay study will be applicable to other regions. 



A central component of the USGS program in Massachusetts Bay has been computer 

 modeling studies of circulation, which provide a framework for interpretation of 

 oceanographic measurements and insight into mixing and transport processes. As discussed 

 in more detail below, the USGS has conducted three-dimensional modeling studies of 

 circulation and mixing patterns in Massachusetts Bay, including a comparison of the dilution 

 of effluent from the present MWRA outfalls at President Roads and the proposed new 

 MWRA outfall in Massachusetts Bay. These simulations show that although effluent 

 concentrations in the immediate vicinity of the proposed outfall will increase, the extent of 

 Massachusetts Bay affected by the highest concentrations will dramatically decrease. 

 Concentrations of effluent near Stellwagen Bank are extremely small in both current and 

 proposed outfall simulations. 



BACKGROUND TO ESTUARINE AND COASTAL OCEANOGRAPHIC MODELING 



Before presenting specific results of the computer simulations of the effect of the new 

 outfall on the waters of Massachusetts Bay, it is important to describe the rationale for the 

 use of numerical models in these studies. An important element in understanding the fate of 

 pollutants discharged into the coastal waters is understanding the mixing and transport 

 processes which control the dispersal of water-borne materials. In the coastal ocean, these 

 processes are driven by winds, river discharge, heating and cooling of the sea surface, tides, 

 and remote effects from the waters offshore. Historically, oceanographic measurements have 

 been the cornerstone of our conceptual and theoretical understanding of currents and water 



