The Massachusetts Water Resources Authority (MWRA) outfall will begin discharging treated sewage effluent from the Boston metropolitan area, now discharged into Boston Harbor, through a new ocean outfall located in Massachusetts Bay in 1999. Other outfalls, such as sewer and thermal waste outfalls, combined stormwater overflows (CSOs), and National Pollution Discharge Elimination System (NPDES) point outfalls, discharge or have discharged into Massachusetts Bay. Among these other outfalls, the location of the Swampscott Sewage Treatment Plant (Quinlan, 1984) and of point discharges (CSO and NPDES) are included on this CD-ROM. Investigations have been undertaken around some of these structures, especially the marine outfalls, to meet regulatory obligations.

The tunnel for the new MWRA ocean outfall begins at the Deer Island Treatment Plant and terminates in a linear series of 55 diffusers located approximately 9 miles offshore in Massachusetts Bay. This CD-ROM contains a small portion of the data and information obtained as part of the numerous investigations designed to understand the long-term effects of relocating the outfall from Boston Harbor to Massachusetts Bay. These investigations were carried out by the MWRA and its contractors (see list of MWRA technical publications at http://www.mwra.state.ma.us/harbor/enquad/trlist.htm), Federal and State agencies, and academic institutions. Bothner and others (1992) carried out detailed mapping of the region surrounding the outfall using sidescan sonar and bottom photography, providing the framework for selecting sites for long-term monitoring of sediment chemistry and biology. Knebel and Circe (1995) and Knebel and others (1996) used these and other data to provide an overall map of sedimentary environments for Massachusetts and Cape Cod Bay. More recently, western Massachusetts Bay, including the region surrounding the new outfall, has been surveyed using multibeam (Butman and others, in preparation), providing maps of the surface topography and sediment backscatter at a horizontal resolution of 6-10 m. A study of circulation in the Massachusetts Bays was conducted in 1989-1990 (Geyer and others, 1992). Signell and others (1996), using a three dimensional circulation model, developed predictions of effluent dilution for the effluent discharged from the existing outfall in the harbor, and from the new outfall in Massachusetts Bay in winter and summer. These simulations show that relocating the outfall will result in improved water quality in the harbor, and not significantly alter water quality in Massachusetts Bay, except in the immediate vicinity of the outfall. In 1997, the Harbor Branch Oceanographic Institution conducted a submersible dive (Clelia Dive No. 484) on and around the MWRA diffuser outfall (see Subchapter 2B for a more detailed summary of the Clelia operations, and Lindsay and others, 1998). A laser line scan system image of a diffuser riser can be viewed via a hot link connection. One of the diffusers (No. 44) will not be operational and may serve to monitor the influence of effluent on biofouling.

The MWRA is carrying out an extensive program to monitor water quality, sediment chemistry, and biota before and after the new ocean outfall begins operation (Albro and others 1998; Kropp and Boyle, 1998; Tucker and Giblin, 1998; Lefkovitz and Moore, 1998). The location of stations were carefully selected based on the simulations of water quality (Signell, 1996 see coverages), topography (Knebel and others, 1996), and sediments. Measurements are concentrated in the immediate vicinity of the new outfall (the ‘near field’), where simulations of water quality suggest that concentrations of effluent will be measurable above background levels. There are fewer stations located distant from the outfall (the ‘far field’), where simulations show that water quality will not be changed from the present situation. The sea floor environment in western Massachusetts Bay is extremely varied (Knebel, and Butman and others, in preparation). The topography is dominated by a series of ridges that have about 10 m of relief (see the multibeam maps). The ridges are topped with boulders and gravel, while finer sands and muds are concentrated in the bathymetric lows.

Coverages in this Chapter include:

• Locations of MWRA new ocean diffusers and present outfalls (ArcView shapefiles mwra_out.shp and outfall.shp). Clicking on an individual point will bring up the information contained in the attributes table such as the riser number, latitude and longitude, and data source.

• Maps of the sea floor based on multibeam surveys. The maps are provided in geographic (g) coordinates and in Mercator (m) projection. (Note: ArcView will allow a view containing shape files in geographic coordinates to be projected to a Mercator (or other) projection, allowing the map to be viewed in true perspective (see the Introduction for more information). However, image files, such as the bathymetry, shaded relief, backscatter intensity, and pseudocolored files cannot be projected from geographic coordinates to a projection. Thus, these files are provided in both geographic coordinates and mercator projection so that the images may be viewed quickly with the geographic data, or in true perspective with any projected shape files) . Note that Chapter 3a contains identical coverages to Chapter 3, but in Mercator projection.

Western Massachusetts Bay (6 m horizontal grid spacing)
Bathymetry (5 m contours: ArcView shapefile bathy5mb.shp)
Shaded relief (ArcView file wmbshd_g)
Pseudocolored backscatter over shaded relief (wmbpsd_g)

Stellwagen Bank (10 m horizontal grid spacing)
Bathymetry (5 m countours:  ArcView shapefile bathy5sb.shp)
Shaded relief (northern section - ArcView tif sbshd_ng.tif)
Shaded relief (southern section - ArcView tif sbshd_sg.tif)

• Massachusetts Water Resources Authority (MWRA) Outfall Monitoring Program

• Effluent dilution based on hydrodynamic models for present and future outfall in winter and summer, and at the surface (2 m) and the base of the thermocline (16 m). These coverages are provided in geographic (g) coordinates and Mercator (m) projections. (Note: ArcView will allow a view containing shape files in geographic coordinates to be projected to a Mercator (or other) projection to allow the map to be viewed in true perspective (see the Introduction for more information). However, image files, such as the effluent dilution distributions cannot be projected from geographic coordinates to Mercator. These files are thus provided in both projections so that the images may be viewed quickly with the geographic data, or in true perspective with any projected shape files) .

• USGS current monitoring stations:  ArcView shapefiles usgs_lto.shp and usgslts.shp

• USGS sediment monitoring stations (Bothner and others, 1993):  ArcView shapefile usgssedm.shp

• Observations for Massachusetts Bay circulation experiment (Geyer and others, 1992):   ArcView shapefile mbcircst.shp

• Clelia dive operations around the MWRA diffuser outfall

• FILLS monochromatic image of a diffuser riser via hot link

List of technical reports resulting from studies by the MWRA Environmental Quality Division (ENQUAD): http://www.mwra.state.ma.us/harbor/enquad/trlist.htm)

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