Sources of Contaminants
Sources
of toxic contaminants to the Stellwagen Bank Sanctuary were alluded
to in the Final Environmental Impact Statement/Management Plan (NOAA,
1993), and were summarized in detail previously (Maciolek and Menzie,
1990; Pett and McKay, 1990). In brief, point sources include discharges
from publicly owned treatment works (POTWs), industrial discharges permitted
under NPDES, disposal of dredge materials at the Massachusetts Bay Disposal
Site (MBDS), and effluents from combined sewer overflows (CSOs). Of
these point sources, the existing Massachusetts Water Resources Authority
outfalls in Boston Harbor (as well as the future deep water outfall
in Massachusetts Bay) and the CSOs provide the greatest source of contaminants
(metals, PAH, PCB, nutrients) to Massachusetts Bay (Menzie-Cura, 1991).
Based on estimates made by MWRA, moving the current sewage outfalls
from Boston Harbor to the Massachusetts Bay site (8.5 miles to the east
of the entrance to Boston Harbor) should not have any additional impact
on Stellwagen Bank than currently exists (MWRA, 1991). Above and beyond
currently discharged contaminants, there is the potential for contaminants
(e.g. toxic chemicals, low level radioactive waste) dumped at the MBDS
and the Industrial Waste Site years ago to become remobilized and enter
the Stellwagen Bank Sanctuary.
Table
6. Estimates of contaminant loading to Massachusetts Bay (Menzie-Cura,
1991).
Nonpoint sources of contamination include the rivers of the Gulf of
Maine, especially the Merrimack River, discharges from boat traffic,
and atmospheric inputs. While it appears that inputs from point source
discharges have been decreasing over the past decade, it has been difficult
to adequately estimate the magnitude of the nonpoint source inputs.
Contaminant
loadings from the Merrimack River were estimated by Menzie-Cura (1991).
These estimates indicated that the river is a source of significant
amounts of the metals, such as mercury, zinc, lead, and copper, found
in Massachusetts Bay (Table 6). However, it was thought that the Merrimack
contributed a much smaller percentage of PAHs, and only minor amounts
of PCBs. Since these were simply rough estimates, two studies were subsequently
initiated to refine these figures. Studer (1995, in preparation) has
made loading estimates for several metals, based on seasonal sampling
and analysis of water samples taken at a number of sites along the river
and at its mouth. Her estimates of metal loadings are, in general, slightly
lower than the Menzie-Cura (1991) estimates presented in Table 6. PAH,
PCB and chlorinated pesticide loadings were also reexamined in a study
by Menzie-Cura (1995, in preparation). Although the data are still being
analyzed, it appears that the new estimates of PAH loadings are higher
than the original estimates (Menzie-Cura, 1991). The Menzie-Cura study
(1995, in preparation) also analyzed a series of satellite images of
the entrance to Massachusetts Bay, and confirmed an earlier conjecture
(Geyer et al., 1992) that the Merrimack River plume enters Massachusetts
Bay approximately 50% of the time. The plume is deflected to the east
of Stellwagen Bank the remainder of the time. Since the Bank is a natural
splitting point for the Merrimack River plume, the northern tip of the
Bank may be affected by the plume most of the year.
Atmospheric
inputs to Massachusetts Bay were also estimated in the earlier Menzie-Cura
work (1991; Table 1). These estimates initiated a further study to collect
additional atmospheric deposition data (Golomb et al., 1995, in preparation).
While these data are currently being interpreted, it appears that the
PAH loading to Massachusetts Bay is a fifth to a third higher than the
original Menzie-Cura (1991) estimates. This should result in a slightly
greater impact on Stellwagen Bank than originally perceived.
It appears
from these data that the major sources of contaminants to the Stellwagen
Bank Sanctuary are the MWRA outfall, the Merrimack River plume and atmospheric
deposition.
continue
to next section
