MWRA
Outfall Tunnel
As part
of the Boston Harbor Project, the Massachusetts Water Resources Authority
(MWRA) is building an outfall tunnel that will extend from Deer Island
in Boston Harbor 9.5 miles into Massachusetts Bay to a point about 15
miles from the northwestern corner of the Stellwagen Bank National Marine
Sanctuary (Figure 10). The outfall tunnel, anticipated to be completed
in 1997, will eventually discharge treated effluent from the new primary
and secondary treatment plant on Deer Island. The effluent will enter
the deep waters of the bay through 55 riser pipes along the last 1.25
miles of the tunnel.
During
the facilities planning process for the MWRA's new secondary treatment
facility, extensive and thorough study and review of the siting and
effects of the outfall tunnel were conducted by the MWRA, the U.S. EPA,
Massachusetts Executive Office of Environmental Affairs, together with
citizens (including the Facilities Planning Citizen's Advisory Committee)
and harbor and bay advocacy groups.
Figure
10: Distances of the new MWRA outfall from Stellwagen Bank. (Figure
from MWRA.)
In accordance
with a requirement of the Certificate approving the Environment Impact
Report for the Boston Harbor Project, an Outfall Monitoring Task Force
was created to assist with development of a monitoring plan for the
outfall tunnel. The Effluent Outfall Monitoring Plan: Phase I, Baseline
Studies specifies the specifics of the monitoring program for the period
preceding the beginning of operations for the outfall. Data collection
began in February 1992 and the complete record will form the baseline
for evaluating environmental conditions in the bay after the outfall
is in use. Measurements are being taken at 46 stations in the area surrounding
the diffusers and at locations up to 50 miles into the bays.
At t
request of Barnstable County officials, the MWRA also funded an independent
sutdy of the outfall data. That study, focused on the data as it relates
to the project's Natinal Pollutant Discharge Elimination System (NPDES)
permit, concluded that the outfall will not increase the amount of nutrients
reaching the bay.
The U.S.
EPA and the National Marine Fisheries Service have also evaluated the
proposed outfall to ensure its operation will comply with the requirements
of the Endangered Species Act. The EPA's conclusion, confirmed by the
NMFS, is that the outfall is unlikely to have an adverse impact on endangered
or threatened species.
In November
1991 the task force issued creation of a Before the outfall begins operation,
the MWRA is compiling baseline information on the environmental conditions
of Massachusetts Bay and Cape Cod Bay. After operation begins, the MWRA
will continue a long-term program of monitoring the effects on the bay
to identify any adjustments to the treatment process necessary to protect
marine resources.
