1996: questions and answers about the new outfall

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M a s s a c h u s e t t s W a t e r
R e s o u r c e s A u t h o r i t y
questions and answers
about the new outfall
t h e S t a t e o f B o s t o n H a r b o r 
1996

prepared under the direction of: 
Douglas B. MacDonald, Executive Director
John F. Fitzgerald, Director, Sewerage Division 
board of directors 
Trudy Coxe, Chair
John J. Carroll, Vice Chair
Lorraine M. Downey, Secretary
Norman P. Jacques
Joseph A. MacRitchie
Vincent G. Mannering
Donald A. Mitchell
Samuel G. Mygatt
Andrew Pappastergion
Robert Spinney
Marie T. Turner
Technical Report No. 1997-05
Second Printing
Massachusetts Water Resources Authority 
N o v e m b e r 1 9 9 7 
the state of boston harbor 
questions and answers about the new outfall

acknowledgements 
prepared by: 
Andrea C. Rex
Michael S. Connor 
edited by: 
Sally Rege Carroll 
graphics by: 
Steve Hussey
Susan Curran Ford
Rita Berkeley
Jenny Siegel
Ilse Stryjewski 
design and layout by: 
Rita Berkeley
Jenny Siegel 
GIS data provided by: 
Massachusetts Department of Environmental Protection,
Massachusetts Division of Fisheries & Wildlife, MassGIS,
National Oceanic & Atmospheric Administration 
acknowledgements 
Many people contributed information and advice for this report. The authors wish to thank:
Don Anderson, Michael Bothner, Steve Cibik, Cathy Coniaris, Maury Hall, Doug Hersh,
Kenneth Keay, Josh Lieberman, Michael Mickelson, Michael Moore, Peggy Murray,
Carl Pawlowski, Michael P. Quinlin, Susan Redlich,Virginia Renick, Jack Schwartz, and Meg Tabacsko.
Special thanks to Wendy Smith Leo for her contribution.

Executive Summary
Part I:
Boston Harbor Quality Update
Introduction
Boston Harbor Quality Update
Part II:
The New Outfall: Frequently Asked Questions
How was the Massachusetts Bay site chosen?
How will the new outfall benefit water quality?
Will the discharge be very contaminated?
The seasonal cycle of the Bays
How healthy is the marine ecosystem of the Bays?
How will the discharge affect the health of the Bays?
What about the right whale?
Will we know if the outfall is causing a problem?
What will be done if a problem occurs? Bay outfall
with secondary
treatment
(mg/L)
< 6
> 9 
Cap
B
Bay 
Boston 
New Outfall
16.4 mi.
9.5 mi.
36.6 mi. 
S t
e
l
l
w
a 
Endnotes
References
List of web sites 
contents 
table of 
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2
2
6
8
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28

tables 
Table 1: Comparison of primary and secondary treatment
Table 2: Toxic contaminants reduced by treatment 
figures 
Figure 1: Bacteria counts in Deer Island effluent
Figure 2: Solids discharged to Boston Harbor
Figure 3: PAHs in mussels near Deer Island decreased
Figure 4: Metals discharges to Boston Harbor declined
Figure 5: Industrial metals entering treatment plants
Figure 6: Water at Harbor beaches is cleaner
Figure 7: Healthier animal communities on the Harbor floor
Figure 8: Liver disease and contaminants in winter flounder
Figure 9: Location of outfalls in Harbor and Bay
Figure10: Schematic views of outfall and diffusers
Figure 11: Diluted effluent rises to surface in winter, and is trapped
beneath surface in summer
Figure 12: Dilution contours, Harbor and Bay outfalls
Figure 13: Secondary wastewater treatment schematic
Figure 14: The seasonal cycle of the Bays 
list of 
list of figures
10
10
3
3
3
3
3
4
4
5
6
7
8
9
11
12 
Figure 15: Resources and stressors in the Bays
Figure 16: Multiple sources of toxic contaminants
Figure 17: Distribution of silver in surface sediments
Figure 18: Winter flounder liver disease rates
Figure 19: Modeled surface chlorophyll a 
Figure 20: Modeled dissolved oxygen in bottom water
Figure 21: Modeled particulate organic carbon deposition
Figure 22: Feeding northern right whale
Figure 23: MWRA monitors the Harbor and Bay at all scales
Figure 24: Monitoring locations in the Bays
Figure 25: Beneficial and nuisance algal blooms
Figure 26: Dissolved oxygen at the Bay outfall site
Figure 27: Sediment silver at the Bay outfall site
Figure 28: Contingency plan process flowchart 
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he continuing improvements
in the waters of Boston
Harbor have been described
in the State of Boston
Harbor reports over the last
few years. Elimination of
sludge discharges into the
Harbor, prevention of float-
able pollution, and system improve-
ments including the start-up of the new
primary treatment plant in 1995, have
visibly improved the Harbor’s environ-
ment. Already, reductions in the
amounts of pathogens, toxic metals
and petroleum products in the primary
effluent have been accompanied by
fewer swimmers’ advisories at Harbor
beaches, evidence of healthier animal
communities on the Harbor floor, and a
lower incidence of liver disease in the
Harbor’s flounder.
In August 1997, the Massachusetts
Water Resources Authority (MWRA)
began the next phase of the Boston
Harbor Project—the implementation of
secondary treatment. Beginning in
1998, a long outfall will discharge sec-
ondary effluent into Massachusetts
Bay instead of into the shallower
waters of the Harbor. This outfall relo-
cation will allow the Harbor to continue
recovering from the poorly treated
sewage that it received for more than
a century.
A draft of the new discharge permit
for the Deer Island Treatment Plant will
be issued soon. The development of
the permit has revealed continuing
questions about the new outfall and its
potential impacts on Massachusetts
and Cape Cod Bays. This report
addresses frequently asked questions
about this outfall, including the overar-
ching concern: Could the Bays
become degraded by sewage effluent
as Boston Harbor once was? The
answer is no, for these three reasons: 
(1) Cleaner Effluent: The
secondary effluent that will be dis-
charged to the Bay will be much
cleaner than past discharges due to:
Source reduction: Fewer pollutants
are being allowed to enter the sewer
system, in part through stricter over-
sight of industrial dischargers. Now,
only a small portion of toxic metals
entering the treatment plants are from
industrial sources.
Improved treatment: Secondary
treatment will remove even more cont-
aminants before discharge and meet
stringent state and federal water
quality standards. While primary treat-
ment removes 50% to 60% of the total
suspended solids in wastewater, sec-
ondary treatment removes more than
85% of these solids. Oxygen-depleting
substances will also be more than
85% removed, compared with 40%
removed by primary treatment.
Toxic contaminants will be up to
90% removed, compared to 50% by
primary treatment. Pathogens are sig-
nificantly reduced by secondary treat-
ment. With less solids in the waste-
water, disinfection is more effective. 
(2) Better Dilution: A four-
year scientific and engineering study,
regulatory review, and extensive public
participation determined that a dis-
charge site 9.5 miles northeast of Deer
Island would be the best location for
the health of both the Harbor and the
Bay. The outfall, equipped with 440
diffuser ports over the last 1.25 miles,
will dilute the effluent in water 100 feet
deep in the Bay, compared to a depth
of only 30 feet in the Harbor.
Computer modeling results indicate
that the effluent will have very limited
impacts near the outfall in Massachu-
setts Bay, and virtually no effect on
Cape Cod Bay. Surface chlorophyll a,
a measure of algal blooms, will
increase only in the immediate outfall
area, and will be reduced significantly
in the Harbor. 
(3) Constant Monitoring
and Contingency Planning: 
MWRA’s National Pollutant Discharge
Elimination System (NPDES) permit
for the new treatment plant and outfall,
which will be one of the most compre-
hensive and protective permits ever
issued, will require that state and
federal water quality criteria not be vio-
lated as a result of the discharge. In
addition, MWRA is required to conduct
an outfall monitoring program that is
linked to its Contingency Plan, an
action plan that incorporates water
quality conditions that trigger MWRA
action. These trigger parameters are
based on permit limits, state water
quality standards, and expert scientific
opinion.
Five years of baseline monitoring
have revealed much about the Bay
system’s natural variability, information
that will help distinguish between
natural and outfall-related phenomena
once the outfall is on-line. Through vig-
ilant monitoring, problems can be
detected and addressed.
The outfall’s impact has received
extra scrutiny because of the important
role that Cape Cod Bay plays in the
life of the endangered North Atlantic
right whale. Although no effects are
expected, MWRA’s intensive moni-
toring is designed to detect any outfall-
related environmental changes that
might affect the whales’ feeding
grounds.
While there are many sources of
pollutants to the Bays system, most of
the Bays region supports a healthy
marine ecosystem. MWRA's sec-
ondary treatment and the better dilu-
tion provided by the new outfall will
contribute to an overall improvement in
the health of the Harbor and Bays.
T 
summary 
executive

boston harbor quality
Boston Harbor is an estuary that is
part of the Massachusetts Bays
system. Conditions in the Harbor,
including treatment plant discharges at
the existing, nearshore outfall loca-
tions, measurably affect the Bay as a
result of strong tidal flushing. Improve-
ments in the Harbor generally also
improve Massachusetts Bay.
Better wastewater management,
including fewer untreated combined
sewer overflow discharges and reduc-
tions in contaminants entering the
sewage system, has substantially
lowered contamination in the Harbor.
Figure 1 shows that MWRA's improve-
ments to the reliability of disinfection
since 1989 have greatly reduced the
pathogens discharged to the Harbor.
Figure 2 illustrates improvements in
removal of solids (and associated toxic
pollutants) from the wastewater.
Studies of contaminants in mussels
placed near Deer Island, for example
PAHs (Figure 3), confirm that environ-
mental levels of toxic chemicals have
also decreased.
Dramatic reductions since 1989 in
toxic metals contained in the effluent
discharged from MWRA’s treatment
plants are shown in Figure 4. Figure 5
shows that industry's discharge of toxic
metals into the sewers now constitutes
only a small portion of the total metals
loadings. A challenge for the future will
be to decrease household and other
non-industrial contributions to toxic
metal loads in the wastewater received
by MWRA treatment plants.
The benefits of better wastewater
treatment and management are most
apparent along the Harbor beaches,
downtown along the walkways of the
Inner Harbor, and near the former
sludge discharge site in President
Roads. Unsightly sewage-related
floating matter has been practically
eliminated. Figure 6 shows that, for the
most part, the number of swimmers’
advisories (beach postings) due to cont-
aminated water have declined since the
mid-to-late 1980s.
Bottom-dwelling animal communities,
for example, the shrimp-like amphipod
Ampelisca, have increased in abun-
dance and diversity (Figure 7). The
health of winter flounder has improved
as shown by the decline of flounder
liver disease since the mid-1980s
(Figure 8a). Flounder caught in Boston
Harbor are safe to eat, as illustrated in
Figures 8b and 8c. PCB levels in
flounder fillet are measured at about
100 parts per billion—well below the
FDA limit of 2,000 parts per billion. Like-
wise, mercury levels in flounder fillet are
measured at levels 10-fold lower than
the FDA limit. 
update 
he ongoing transformation of a once-degraded Boston Harbor to a
valued regional resource is a story of environmental recovery. The
Harbor's progress over the past decade is due to ambitious anti-
pollution projects, especially MWRA's new Deer Island sewage
treatment plant which serves 43 Boston area communities. When
secondary sewage treatment is entirely on-line in 1999, sewage
treatment in the greater Boston area will finally be in compliance with the
federal standards prescribed in the 1972 Clean Water Act.
MWRA is now making progress toward two major milestones at the treat-
ment plant: the three-part phase-in of secondary treatment from 1997 to
1999, and completion of the 9.5-mile effluent outfall into Massachusetts
Bay. Secondary treatment will remove even more solids and toxic conta-
minants from primary-treated wastewater. The new outfall will reach deep
water where over 400 diffuser ports will rapidly disperse treated effluent into
the marine environment.
Minimizing adverse effects of wastewater discharge on the marine envi-
ronment includes three fundamental strategies: 
1 aggressive source reduction: preventing pollutants from entering
the waste stream and, in particular, enforcing strict limits on industry's
discharge of toxic contaminants to the sewer system; 
2 improved treatment: removing contamination from wastewater before
discharge; and 
3 effective dilution: mixing wastewater quickly with large volumes of
seawater to achieve very low concentrations of any remaining contami-
nants in the marine environment.
Despite the benefits of improved treatment, the relocation of the outfall
has raised questions about the effects of discharging effluent into the
waters of Massachusetts Bay. This year’s State of Boston Harbor report is
principally devoted to the major questions asked about the new outfall.
T 
introduction 
PART I
2

Bacteria counts in Deer Island effluent
now rarely exceed permit limits 
Sludge solids
Effluent
suspended solids
Fiscal Year
150
120
90
60
30
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1987
0
Tons Discharged per Day 
1500
1200
900
600
300 
1987 1991 1992 1993 1994 1995 1996 
0 
Parts per billion 
200
0
Fiscal Year
Pounds per Day
400
600
800
1000
1200
1997 1996 1995 1994 1993 1992 1991 1990 1989
Copper
Zinc
Lead
Nickel
Chromium
Silver 
COPPER LEAD CHROMIUM SILVER
CADMIUM MERCURY NICKEL ZINC
5.5 0.5 1
246 40 20
2
13
0.04
2.5
0.08
0.8
2
25
8.3
321 
201-10,000 Fecal
coliform/100 ml
>10,000 Fecal
coliform/100 ml
Fiscal Year
200
150
100
50
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
0
Days per Year of High Counts 
Figure 1. High bacteria counts in Deer Island effluent have
decreased dramatically since 1989. Graph shows number of days per
year that bacteria in effluent exceeded the permit limit of 200 colonies
per 100 ml. Extremely high (greater than 10,000) bacteria counts, once
common, have been eliminated. (MWRA monitoring data). 
Figure 2. The amount of solids discharged to the Harbor from Deer
and Nut Island treatment plants has decreased to about half that dis-
charged in the late 1980’s, after the elimination of sludge discharges and
improved primary treatment. (MWRA monitoring data). 
Figure 3. Low molecular weight polynuclear aromatic hydrocarbons,
which are potentially cancer causing chemicals created by combustion
of fossil fuels, are measured in mussels deployed and grown near Deer
Island. Levels of PAHs in mussels have remained relatively low since
1993 (Mitchell et al. 1996, data for 1996 from Mitchell et al.,report in
prep.). 
Figure 4. Metals loadings to Boston Harbor from the Deer and Nut
Island treatment plants have decreased dramatically since the 1980s.
Decreases in FY 1992 reflect the elimination of sludge discharges into
the Harbor (MWRA monitoring data). 
Figure 5. Industrial metals loadings in influent to the Deer and Nut Island
treatment plants before treatment are only a small portion of the total. The
wedges show, for various metals, the pounds per day originating from indus-
trial sources as compared to the total loading in influent (MWRA monitoring
data). 
Solids discharged to Boston Harbor
PAHs in mussels near Deer Island
decreased
Metals discharges to Boston Harbor
from MWRA treatment plants declined
Industrial metals are a small part of total
metals entering treatment plants
(Pounds/day) 
3

update 
boston harbor quality 
1989 -1990 
Ampelisca Tubemats 
Figure 7. Ampelisca
tube mats have increas-
ingly colonized Boston
Harbor since sludge dis-
charges stopped, espe-
cially in the area of the
Harbor that was most
severely affected: the
northern Harbor. These
crustaceans increase the
amount of oxygen in the
sediments and are a
favored flounder prey.
(Data through 1995 from
Hilbig et al., 1996. 1996
data in prep, Hilbig et al.) 
1995 
Ampelisca Tubemats 
1996 
Ampelisca Tubemats 
Ampelisca abdita
This tiny crustacean is pollu-
tion-intolerant. Ampelisca
lives in tubes that it builds
into the sediment; these
tubes form thick mats that
provide shelter for other small
animals (illustration after
Bousfield,1973). 
50
40
30
20
10
0 85-86 87-88 89-90 91-92 93-94
50
40
30
20
10
0 85-86 87-88 89-90 91-92 93-94
50
40
30
20
10
0 85-86 87-88 89-90 91-92 93-94
50
40
50
40
30
20
10
0 85-86 87-88 89-90 91-92 93-94
50
40
30
20
10
0 85-86 87-88 89-90 91-92 93-94
50
40
30
20
10
0 85-86
Constitution Beach
Winthrop Beach
Short Beach
Carson Beach
Pleasure Bay
Malibu Beach
Tenean Beach
Percentage of Beach Days Posted with Swimmers' Advisories
87-88 89-90 91-92 93-94 
Figure 6. Swimmers’ advi-
sories have decreased since
the late 1980s. Storm drain
contamination and leaking
local sewers remain a problem
at Wollaston Beach. (Data
from Metropolitan District Com-
mission beach monitoring
program.) 
Water at Harbor beaches is cleaner
Healthier animal communities
on the Harbor floor 
4

Despite these documented improve-
ments in Boston Harbor, its history of
problems invites the question, “Could the
Bays become degraded by treatment
plant effluent from the new outfall?”
Observers, experts, citizens, and marine
scientists have generally concluded,
"No." Three important reasons are: (1)
the effluent to be discharged into the Bay
will meet the secondary treatment stan-
dard and thereby be much cleaner than
the primary effluent and sludge that were
discharged into Boston Harbor until
1991; (2) there is much greater dilution
at the discharge site in the Bay than in
the shallower waters of the Harbor; and
(3) there will be constant monitoring of
MWRA's effluent and the water quality in
the Bays.
Throughout the report, we discuss
results of scientific studies which have
increased our understanding of the Bays
ecosystem and how pollution impacts
can best be prevented. In addition, we
point out areas of scientific uncertainty.
Continual monitoring, linked to a flexible,
evolving response plan, will help assure
that MWRA is accountable for examining
and re-examining areas of uncertainty.
By obtaining and using new scientific
information in its planning, MWRA and all
others interested in the health of the
Bays can work together to provide the
best protection for invaluable marine
resources.
Questions about the new outfall
discussed in this report are:
• How was the Massachusetts Bay
site chosen?
• How will the new outfall benefit
water quality?
• Will the discharge be very
contaminated?
• How healthy is the marine
ecosystem of the Bays?
• How will the discharge affect
the health of the Bays?
• What about the right whale?
• Will we know if the outfall is
causing a problem?
• What will be done if a problem
occurs? 
Figure 8a. The reduction in liver disease, including cancer, in winter flounder has followed the
banning of DDT and PCBs, and the decreasing discharge of PAHs from wastewater. (1984 flounder
liver lesion data from Murchelano and Wolke 1985; 1987 data through 1995, from Mitchell et al. 1996,
1996 from report in prep.) 
The New Outfall: Frequently Asked Questions 
PART II 80
70
60
50
40
30
20
10
84
Liver Tumors
% of Deer Island Flounder with Disease Early Liver Disease
87 88 89 90 91 92 93 94 95 96
0 0 0 0 0 0 
Less liver disease, lower contaminant levels
in winter flounder
Figure 8b,c. PCBs and mercury in flounder caught off Deer Island have been well within guide-
lines for human consumption since the mid 1980s, and have decreased since the late 1980s. (toxic
chemistry data from National Status and Trends Program 1987; 1985 - 1991 data are from Schwartz
et al. 1991 and 1993; 1992 - 1994 data from Hillman and Pevens 1995, 1996 data from Mitchell et
al. report in prep.)
5 
1985 1986 1987 1988
PCBs in winter flounder (fillet) caught near Deer Island
are well below the FDA limit of 2,000 parts per billion.
Levels have greatly decreased since the mid-late 1980s.
1989
500
400
300
200
100
PCBs in parts per billion
0
1987 1988
Mercury levels in winter flounder caught near Deer
Island have been well below the FDA limit of 1,000
parts per billion. Levels have decreased since the
late 1980s.
1989 1990 1992 1993 1994 1995 1996
1992 1993 1994 1995 1996
150
120
90
60
30
Mercury parts per billion
0
... ...
... ...

The outfall siting process began in
1986 with the appointment of the Facili-
ties Planning Citizens Advisory Com-
mittee (FPCAC), which included 27 par-
ticipants representing agencies, envi-
ronmental groups, community officials,
and other interested individuals. The
FPCAC developed criteria used in the
siting process, and reviewed and com-
mented extensively on the environ-
mental impact reports.
At the outset of the siting process,
the United States Environmental Pro-
tection Agency (EPA) ruled acceptable
only those sites that (1) could provide
an initial dilution of 50 parts seawater to
one part effluent; (2) were far enough
from shore so that particles could not
be transported directly to shore on the
next incoming tide; and (3) avoided
sensitive and unique resources.
The existing Deer Island and Nut
Island discharge locations (Figure 9a)
at the mouth of Boston Harbor did not
meet any of the above criteria—for
example, the dilution there is only 14
parts seawater to one part effluent.
Therefore, because of insufficient
depth and dilution, Boston Harbor was
not chosen as a site for the new outfall.
Seven potential sites, from a location
in Broad Sound to a site 10 miles off-
shore, were evaluated in detail by
MWRA and EPA independently. Sites
more distant than 10 miles were elimi-
nated from consideration because con-
struction would not have been feasible
at a reasonable cost. Siting studies
were done in 1987 and 1988, including
engineering studies by four different
leading engineering firms as well as the
Massachusetts Institute of Technology
and the Georgia Institute of Technology.
Oceanographic work was done by Bat-
telle Ocean Sciences, the New England
Aquarium, MIT, and the US Geological
Survey. Biological, chemical, and phys-
ical oceanographic information to
support the siting analysis was col-
lected in Broad Sound, Nantasket Bight,
and western Massachusetts Bay.
Along with oceanographic measure-
ments, a computer model of pollutant
transport in Massachusetts and Cape
Cod Bays was used to predict likely
effects of prospective outfall discharges:
any discharge site had to show the
ability to attain compliance with state
and federal water quality criteria. Other
criteria to evaluate potential sites were
based on discussions with citizens and
scientific advisory groups, and included
protection of commercial on-the-water
activities, maintenance and enhance-
ment of aesthetics, and avoidance of
areas of important habitat.
The computer model predicted that
water depth and current patterns would
produce the most effective dilution of
effluent at three of the most distant can-
didate sites. These predictions were
confirmed by oceanographic field
studies.
After an extensive period of regulatory
and public review and comment, the
Final Supplemental Environmental
Impact Statement confirmed that the
9.5-mile site (Figure 9b) was the
optimum location for the outfall because
it is in an area of strong random off-
shore currents, has a sufficient water
depth, and would be feasible to con-
struct. In 1988, the EPA published its
Record of Decision on the outfall site,
which also required MWRA to conduct
monitoring of the effects of the ocean
discharge on the Massachusetts Bay
environment. 
Massachusetts Bay 
how was the
site chosen? 
fter a four-year long process including oceanographic and engineering studies, regulatory
review, and extensive public participation, the 9.5-mile site for the outfall discharge was found to
be the best location for the health of nearshore and offshore waters. A 
Cape Cod
Bay
Massachusetts
Bay
Provincetown
Boston
New Outfall
16.4 mi.
9.5 mi.
36.6 mi.
Cape Ann
S t
e
l
l
w
a
g
e
n
B
a
n
k 
Figure 9b. Future outfall location in Massachusetts
Bay
6 
Deer Island
Outfalls
Old
Nut Island
Outfalls
(closed 7/98)
B o s t o n
H
a
r
b
o
r 
Figure 9a. Present outfall locations in Boston
Harbor

Figure
10a. 
The outfall tunnel is bored
through bedrock, and the diffuser
section of the outfall is located along the
final 1.25 miles of the structure. 
Sediment
Effluent
Bedrock 
Figure 10c. The diffuser heads each
disperse the effluent through eight ports. 
Figure 10b. The 55 risers carry effluent
from the deep rock outfall tunnel up to the
diffuser heads at the seafloor. 
0
-50
-150
-200
-250
-300
-350
-380
-100
100
50
-50
-100
-150
-200
-250
-280
0
Sea level
Depth below sea level (feet)
Depth below seafloor at diffuser end 

 24' - 3"
Inside Diameter
Outfall Tunnel 43,026' +
Seafloor
Slope: 0.05 %
6,600' + 
Figure 10d. Cross-section diagram of outfall pipe 
Diffuser head
Riser
Schematic views of outfall and diffusers 
NOTE: Diagrams not drawn to scale
7
Figures 10a-d show the structure of
the new outfall. The outfall will provide
a larger measure of environmental pro-
tection than the existing outfalls. Cur-
rently, wastewater is discharged within
Boston Harbor from two short (less
than a mile long) outfalls at Deer Island
and three short outfalls at Nut Island.
Because all wastewater treatment will
be consolidated on Deer island, it was
necessary to build a larger outfall and
to locate the discharge in deeper water.
Since the continental shelf off the East
Coast has a very gentle slope, the
outfall had to be relatively long.

The new outfall is designed to maxi-
mize mixing and dilution of effluent. At
the present time, treated wastewater
effluents from the Deer Island and Nut
Island treatment plants are discharged
near shore within Boston Harbor.
Strong tidal currents eventually carry
the effluent into Massachusetts Bay, but
each incoming tide brings some of the
effluent back into the Harbor. Because
the Harbor is shallow (on average only
30 feet deep), the effluent plumes
receive little dilution and reach the
surface, where they are visible. With
onshore winds, the effluent can reach
the shoreline. By contrast, the new off-
shore location is in an area where circu-
lation is greater and more variable, pro-
viding better mixing.
The new outfall (illustrated on the
previous page in Figure 10a-d) will
carry effluent 9.5 miles (15 kilometers)
off shore to a location where Massa-
chusetts Bay is 100 feet (30 meters)
deep. The effluent will be discharged
through 55 diffuser heads each with
eight outlets (ports), creating a diffuser
that altogether will be 1.25 miles (2000
meters) long. The long diffuser area
and multiple ports will effectively dis-
perse the effluent to maximize dilution.
The initial dilution of the effluent at the
new location will be about 150 to 1,
compared to the present dilution near
Deer Island of 14 to 1.
Because effluent is mostly fresh
water, it is lighter than seawater. Buoy-
ancy causes the effluent to rise toward
the ocean surface, rapidly mixing with
the surrounding water. This vertical
mixing causes the density of the
effluent plume to increase, and the
mixed effluent becomes about as dense
as seawater. This mixing happens
within a few minutes, and within a dis-
tance of tens of meters from the dif-
fuser.
In the winter, the effluent plume, after
mixing, will reach the surface. In the
summer, effluent will be trapped below
the surface because it quickly takes on
the same (denser) characteristics as
the bottom water (Figures 11a and 11b).
After initial mixing, whether the plume
surfaces or not, it will be mixed horizon-
tally by currents at the new outfall site.
These currents vary in direction, helping
to further disperse the effluent. The
outfall is distant enough from shore so
that even shoreward currents will not
carry the effluent close to beaches or
shellfish beds.
apid mixing with a large volume of seawater will
quickly dilute the constituents of the effluent to
background levels. R Figure 11a. What ultimately
happens to the effluent plume depends
upon seasonal effects on the density of
ocean water in Massachusetts Bay. Sea-
water density is controlled by tempera-
ture and salinity. Warmer temperatures
and lower salinity make seawater lighter,
while cooler temperatures and higher
salinity make seawater heavier. In the
winter, the waters of the Bay are about
the same density top to bottom and are
well mixed. When the seawater has a
relatively uniform density top to bottom,
the effluent plume will rise to the surface
as it mixes. 
Diluted effluent rises
to surface in winter
Figure 11b. In the summer, the
surface water is warmed and becomes
increasingly lighter, setting up a layering
effect. The level where the density
change is most abrupt is called the pycn-
ocline.
Effluent becomes increasingly dense
as it mixes with seawater, and will rise up
only to the depth where it is no longer
lighter than the surrounding water—at
the pycnocline. Thus the effluent plume
will be trapped below the pycnocline. At
the outfall site, this is about 50 feet (15
meters) below the surface.
8
how will the new 
outfall benefit water quality? 
Diluted effluent
trapped beneath
surface in summer 
Diffuser head
Sea Floor
Sea Surface
30 meters
Buoyant freshwater effluent
rises and mixes rapidly
Effluent mixed with seawater rises to the surf
Seawater is cold,
dense,and well-mixed
from surface to
bottom. 
Diffuser head
Sea Floor
Sea Surfac
Surface layer: seawater is well mixed and less dens
Pycnocline layer: seawater density increaseswith d
Bottom layer:
seawater well mixed
and denser
Through mixing, effluent reaches same
density as surrounding water and stops rising
5 meters 10 meters
Buoyant freshwater effluent
rises and mixes rapidly
15 meters

DILUTION AREA
< 200
200 - 400
400 - 600
600 - 800
800 -1000
Average Modeled
Dilution of Sewage
Effluent
(Square miles)
77
56
59
77
116 
DILUTION AREA
< 200
200 - 400
400 - 600
600 - 800
800 - 1000
Average Modeled
Dilution of Sewage
Effluent
(Square miles)
3
30
151
48
54 
Figure 12a. Figure 12b. 
Moving the outfall offshore greatly reduces the area most affected by effluent. These two figures show the results of computer model predictions of effluent dilution during winter conditions at the present and future outfall
locations. At present (12a), 77 square miles all of Boston Harbor and the South Shore to Cohasset Harbor, now have a dilution factor of less than 200-fold. At the future outfall location (12b), only 3 square miles, immedi-
ately above the diffusers will have a dilution of less than 200-fold. The dilution model assumes concentrations in effluent are the same for both Harbor and Bay outfalls: this is true for nutrients. The illustration does not
take into account the effect of improved treatment in lowering the concentrations of contaminants in effluent. Model predictions based on winds and currents, winter 1990-1991. (Model created by R. Signell and H. L.
Jenter of the U. S. Geological Survey and A. Blumberg of HydroQual, Inc.) 
Dilution contours, Harbor outfall location Dilution contours, new Bay outfall location 
9

Treatment is a critical step in mini-
mizing adverse effects of sewage dis-
charges. The centerpiece of the Boston
Harbor Project is the state-of-the-art
primary and secondary treatment plant
nearing completion on Deer Island.
This massive, multibillion dollar project
was built to comply with strict environ-
mental regulations in order to protect
human health, the health of the Harbor,
and the ecology of the Bays system.
The secondary-treated wastewater to
be discharged into Massachusetts Bay
is very different from the inadequately
treated primary effluent and sludge that
were discharged into Boston Harbor for
decades. As shown in Table 1, while
primary treatment removes 50 to 60
percent of the total suspended solids in
wastewater, secondary treatment
increases the removal of
solids to 85 percent or
more.
Table 2 shows the
levels of toxic pollu-
tants in primary and
secondary treated
effluent, and the pre-
dicted concentrations
in the area around the
new outfall after dilution
compared to water quality
standards.
After secondary treatment (Figure
13), the concentration of toxic pollu-
tants in the effluent is very low–mea-
sured in parts per billion or parts per
trillion. Levels of many of these pollu-
tants in the secondary effluent are
already low enough to meet regulatory
standards for receiving water. In fact,
after dilution at the new outfall, most
contaminants are 10 to 1000 times
lower than water quality standards
allow.
Nutrients are the only components of
sewage entering the treatment plant
that are not significantly reduced by
secondary treatment. Therefore,
MWRA carefully monitors the potential
effect of nutrient issues on the Bays
system, and nutrients have received
particularly intensive scrutiny by regula-
tory agencies. 
Table 2. Toxic contaminants reduced by treatment and dilution 
Helpful Microbes
Tiny microbes including
bacteria, ciliates, and
rotifers, as seen here
through a microscope at
about 500-fold magnifica-
tion, are the key to sec-
ondary treatment. These
helpful micro-organisms feed
vigorously on the wastewater
during treatment, breaking down
and removing contaminants.
be very contaminated? discharge 
will the
he secondary effluent discharge will meet stringent state and federal standards
to ensure that it will not pose a threat to either human health or the health of the
environment. 
T 
Pollutant
Total suspended solids (TSS)
Biochemical oxygen demand (BOD)
Toxic contaminants
Nutrients
Pathogens
Primary removal
50-60%
25-40%
0-50%
5%
0-50%*
Secondary removal
85+%
85+%
50-90%
10-15%
80-99+%* 
Table 1. Comparison of primary and secondary removal of pollutants 
*These numbers indicate removal before disinfection. Disinfection further reduces pathogens to safe levels. 
Parts per billion (micrograms/liter)
Copper DDTs Lead Mercury
TOTAL
PAH 
Primary effluent 1
Secondary effluent 1,2
Concentration after
dilution 3
Receiving water
quality standards 4,5,6
103
21.6
0.27
2.9
29.2
3.3
0.04
8.5
0.3
0.1
0.0013
0.025
31
3
0.008
2.02
57
12
0.033
0.045
54,932
3,250
8.93
42,000 
TOTAL
PCBs 7
Parts per trillion
(nanograms/liter) 
Tables 1 and 2. Secondary treatment at the Deer Island treatment plant, combined
with dilution at the new outfall, will ensure that levels of toxic contaminants in the receiving waters
are well within water quality standards. The table shows selected toxic constituents of wastewater
that are regulated by EPA. For most constituents, the final concentration in the receiving water will
be far lower than EPA criteria (for details see end note, p.26). 
10

Nutrients, especially nitrogen
and phosphorous, are familiar as the active ingredi-
ents in lawn and agricultural fertilizers. Nutrients
are also essential for the growth of plants (sea-
grasses, seaweed, and microscopic floating algae
called phytoplankton) in the ocean. In the marine
environment, excessive amounts of nutrients, espe-
cially nitrogen, stimulate the growth of phytoplank-
ton and seaweeds and can cause nuisance algal
blooms like brown or red tides (eutrophication). The
eventual decaying of these plants can deplete dis-
solved oxygen levels in the water and sediment.
Nutrients from the present outfalls exit the
Harbor to the Bay in effluent plumes at the sur-
face of the water, where sunlight and nutrients
induce abundant phytoplankton growth. One
major benefit of the new outfall is that diluted
effluent will be discharged at the bottom of
Massachusetts Bay, 110 feet below the water's
surface. During the summer when there is the
most light, the discharge will be trapped by
stratification about 50 feet below the surface.
Most phytoplankton growth is at the surface,
where there is a lot of light. Nutrients from the
discharge at the sea floor will generally not
reach the surface during the summer, when
there is the most potential for excess growth.
Therefore, the outfall is not likely to contribute
to eutrophication in the Bay. 
Secondary Reactors
Atmosphere
Pure Oxygen
Contaminted air from reactors
Odor Removing
Air Scrubbers
Primary Effluent to
Secondary Treatment
Cryogenic Oxygen Facility
Effluent to Outfall
Secondary Effluent
Secondary Influent
Return Activated Sludge
Sludge
Waste Sludge
to Centrifuge,
Digesters, &
Pelletizing
Facility
Disinfection Chambers
Secondary Clarifiers 
Secondary wastewater treatment schematic
Figure 13. Secondary wastewater treatment follows pri-
mary treatment at Deer Island. Primary treatment removes solids
by simple physical processes: in settling tanks (clarifiers), heavy
solids (sludge) sink to the bottom and lighter solids (scum) float to
the surface. These solids are removed; the remaining liquid is pri-
mary effluent, which is then undergoes secondary treatment.
Within the secondary reactors, the primary effluent is mixed with
pure oxygen. The oxygen and mixing stimulate the rapid growth
of beneficial microbes (bacteria, protozoans, and other tiny
organisms) in the wastewater, which consume more solids and
break down contaminants. After about two hours, more sludge
and scum are separated out in the secondary clarifiers. A por-
tion of the secondary sludge, rich in beneficial microbes (acti-
vated), is returned to the reactors, where it is used to treat more
primary effluent. Waste sludge and scum are sent to Deer
Island’s egg-shaped digesters, to be further broken down by
microbes and eventually converted to fertilizer pellets. The clari-
fied secondary effluent is disinfected and discharged to the
ocean through Deer Island’s outfalls (Figure after D. Duest,
MWRA)
nutrients
11

undamental to all the processes in the Bays is the annual sea-
sonal cycle. In order to be able to recognize the effect of efflu-
ent discharge on the environment, it is important to first under-
stand the changes that happen naturally. Over the past five
years, MWRA’s baseline monitoring program and extensive studies
by the US Geological Survey and the Massachusetts Bays Program
have provided a good understanding of the Bays' seasonal cycle.
In November through April, winds and cooling mix the waters of the
Bays. Nutrients are plentiful, but in December and January the pene-
tration of light into the water is rarely enough to support the growth of
phytoplankton (microscopic floating algae at the base of the food
web). As the days lengthen in early spring, increases in light and in
nutrient levels trigger the rapid growth of phytoplankton.
The spring bloom of phytoplankton starts in the shallower waters of
Cape Cod Bay, providing food for zooplankton (tiny animals, including
juvenile forms of animals like fish and jellyfish, and abundant tiny
crustaceans called copepods) carried into the Bays by strong currents
from the Gulf of Maine. In turn, the fast-multiplying zooplankton pro-
vide food for many marine species including the northern right whale.
A single right whale feeding in Cape Cod Bay can consume about
one ton of these plankton daily.
Later in the spring, the surface waters of the Bays warm and strat-
ify. The phytoplankton grow abundantly at the surface, where they
receive ample light. Because vertical mixing is prevented by stratifica-
tion, the nutrients at the surface do not get replenished from the bot-
tom waters. The phytoplankton use up the nutrients in the surface
water and die, eventually sinking to the bottom and providing food to
the bottom-dwelling animal communities which show a growth spurt
in mid-summer.
In the water column, bacteria use up dissolved oxygen through
their respiration as they consume the dead plankton; the lowest dis-
solved oxygen levels in the Bays occur from August to October. In the
fall, cooling of surface waters and strong winds allow mixing through-
out the water column, bringing fresh nutrients to the surface, stimulat-
ing a new growth of phytoplankton—the fall bloom. By mid-winter,
light levels have declined, ending the fall bloom. The plankton die and
decay, releasing nutrients. Nutrient levels increase throughout the
water column, preparing the Bays for the next spring bloom. 
F 
the Bays 
the seasonal cycle of 
12 
January February March
S p r i n g B l o o m
April
11
9
7
35 40 45 50 55 60 65
Legend
Color indicates approximate water
temperature (F)
Waters are cold and
well mixed and rich
in nutrients
Longer days spur
phytoplankton growth.
Right whales feed on
abundant zooplankton
in Cape Cod Bay and
Stellwagen Bank.
Dead plankton ce
Little daylight
in winter 
Figure 14.

13 
Dissolved Oxygen Concentration (mg/L)
S t r a t i f i e d P e r i o d
May June July August September October November December
11
9
7
F a l l B l o o m
Phytoplankton use
up nutrients in surface
waters, plankton growth slows.
Stratification: minimal mixing between surface and bottom.
Surface waters
begin to cool
and mix downward.
Fall and winter winds
aid in mixing.
Mixing causes nutrients to increase
in surface waters: fall bloom.
lls and fecal matter from zooplankton drift down through the water column. As this material decays, nutrients in the water are replenished.
Warming decreases surface water density

marine ecosystem 
how healthy is the
he Bays system supports a rich and diverse ecosystem of normal plant and animal communities, but signs of stress are evident.
Stress results from multiple causes, including overfishing and contamination. The highest levels of contamination are nearshore—
sources include rivers, the atmosphere, sewer overflows, treatment plants, and past use of disposal areas. T 
of the Bays? 
An overview of the Bays system 
At the southern end of the Gulf of
Maine, the Massachusetts/Cape Cod
Bay system extends from the New
Hampshire border to the tip of Cape
Cod, encompassing about 1650 square
miles.
A strong southward coastal current and
a large flow of water from the Merrimack
River produce an average flow south
through the Bays, exiting to the open
Atlantic (Figure 15). Strong tide and wind
effects produce circulation patterns that
are highly variable from day to day. 
Rich resources and multiple
stressors 
The beaches, wetlands, rocky shores,
and deep offshore waters of the Bays
provide important habitat for many plant
and animal communities including com-
mercially important species of fish and
shellfish, and rare or endangered ani-
mals and birds.
There are a variety of environmental
stressors in the Bays system: historical
whale hunting and ongoing commercial
fishing; disappearance of habitat such as
salt marshes; dams that hinder fish
migration and spawning; commercial
shipping and boating activities; and pollu-
tion. 
Many sources of pollution, past
and present 
Bacterial contamination of beaches
and shellfish beds is a concern along
most of the Bays’ coastline. The chief
sources of this contamination are sewer
pipe overflows, stormwater runoff, and
leaks from septic systems. Treatment
plants are a relatively minor source of
contamination.
Levels of toxic contaminants in the
water are highest near the coast and,
except for a few pollutants like polychlori-
nated biphenyls (PCBs), generally meet
water quality standards throughout the
Bays. However, the sediments near
urban shorelines like Boston Harbor,
Salem Sound, and Broad Sound have
significant levels of contamination.
In sediments, as in the water column,
contaminant levels decrease with dis-
tance from shore except at former waste
disposal sites in Massachusetts Bay.
Contamination in offshore sediments is
not high enough to cause detrimental
ecological effects, according to National
Oceanic and Atmospheric Administration
standards. In fact, monitoring has shown
that the bottom-dwelling animal commu-
nities are typical of the Gulf of Maine
ecosystem.
Toxic organic compounds and metals
have many sources. Three examples
illustrating this are chlorinated pesticides
(especially DDT and its breakdown prod-
ucts), PCBs, and mercury. DDT was
banned in 1972 and PCBs were phased 
Cape Cod Bay
Marine Sanctuary
Stellwagen Bank
National Marine
Sanctuary
S t e
llwag
en
Bank
Barrier beaches
Former Mass Bay Disposal Site,
or Foul Area (FA)
Shipping Lane
Industrial discharges
Legend
Average ocean current direction
State Ocean
Sanctuary
Federal Marine
Sanctuary
State Area of Critical
Environmental Concern
Former Industrial Waste Site (IWS)
Present Mass. Bay Disposal Site (MBDS)
FA
IWS
MBDS
Cape Cod Bay
Area of
Critical
Environmental
Concern
(Right Whale
Sanctuary)
Cape Cod Bay
Ocean Sanctuary
North Essex
Ocean Sanctuary
South Essex
Ocean Sanctuary
New MWRA outfall site
Sewage treatment plant
outfalls 
Figure 15. 
Resources and stres-
sors in Massachusetts
and Cape Cod Bays
14

out of production beginning in 1971.
These contaminants can bioaccumulate
in marine mammals and fish.
Figure 16 shows that the present
inputs to Massachusetts Bay from all
sources combined of PCBs and chlori-
nated pesticides are a small fraction of
the amounts that have accumulated
from past inputs, when the chemicals
were being used in large amounts. Sec-
ondary treatment will greatly reduce
MWRA’s contribution of PCBs to Mass-
achusetts Bay. The amounts of PCBs
and chlorinated pesticides
entering the Bays will continue
to decrease in the future, and
are slowly degrading in the
environment. 
Historical contamination signals 
MWRA’s monitoring program has
revealed that past sewage discharges
into Boston Harbor have contributed
contaminants to broad areas of Cape
Cod Bay as a result of tidal flushing.
Past inputs of sewage and sludge in
Boston Harbor contained silver, which
was historically discharged in large
amounts by the photographic industry.
A gradient of silver extends from the
Harbor to Cape Cod Bay (Figure 17),
with higher concentrations in parts of
Cape Cod Bay than in other offshore
waters. Because the Harbor apparently
was the source, these silver concentra-
tions correspond quite well to the mod-
eled dilution of the effluent dispersed
into Massachusetts Bay from the exist-
ing Harbor outfalls (Figure 12a).
Despite the pattern of silver (and
other sewage tracers not shown), the
contaminants are not causing signifi-
cant impacts on the health of marine life
in Cape Cod Bay. Bottom-dwelling ani-
mal communities in the Bay are typical
for the Gulf of Maine as a whole. Data
gathered on winter flounder (Figure 18)
show that contaminant-related liver dis-
ease is at very low levels in Cape Cod
Bay compared to the area close to
Boston Harbor. 
Future decreases in contamina-
tion 
As MWRA’s contribution of toxic pol-
lutants continues to decrease due to
source reduction and treatment
improvements, the existing gradient of
pollutants in the Bay should gradually
lessen. In addition, moving the effluent
discharge to the new outfall site (see
page 9) will reduce the concentration of
dissolved contaminants reaching Cape
Cod Bay from Boston. 
Eastern
Cape Cod Bay
Future Outfall site
Nantasket Beach
Broad Sound
Deer Island Flats 
44%
22%
43%
14%
2% 
Winter flounder liver disease rates
Figure 17. Sediment silver concentrations (measured
as parts per million of the mud fraction of sediment)
decrease with distance from the coast. Cape Cod Bay has
somewhat higher silver concentrations than more northern
locations; this may reflect sediment resuspension and trans-
port by currents to Cape Cod Bay (data from Bothner et al.
1993). 
0.18
0.15
0.23 1.18
1.82
0.42
5.7 5.5
8.9
0.27
0.32
0.51
0.69
2.7 
Figure 18. Flounder liver disease is high in Boston Harbor and Broad
Sound, and low in Cape Cod Bay. The percentage of flounder showing early
liver disease decreases with distance from Boston Harbor—flounder at the
new outfall site may be affected by toxic pollutants from the coastal sources
or from old waste disposal sites. Improved treatment, continued source
reduction, and improved dilution and dispersion at the new location will min-
imize flounders’ exposure to the contaminants (PAHs,pesticides, and PCBs)
thought to cause this disease (data from Mitchell et al. 1996). 
Distribution of silver in surface
sediments
Figure 16. Annual inputs (loadings) of chlorinated
pesticides and PCBs to Massachusetts Bay are small com-
pared to existing accumulations from past sources. The
source of mercury is primarily atmospheric. Secondary treat-
ment reduces MWRA’s contributions. The pie chart areas
reflect the relative amounts of present vs. future loads.
(Annual loading data from Mitchell et al. 1997, Massachu-
setts Bay estimates of existing inventory from data by Shea,
1993, 1996 in prep.; Bothner et al. 1993. Estimates based on
model in Shea 1995). 
Multiple sources of toxic contaminants
to the Bays 
15 
Chlorinated Pesticides
Total = 20.7 kg/year
PCBs
Total= 51 kg/year
Chlorinated Pesticides
Total = 8.8 kg/year
Mercury
Total = 358 kg/year
Mercury
Total = 332 kg/year
PCBs
Total = 27 kg/year
Present Annual Loading: MWRA Primary Treatment
Future Annual Loading; MWRA Secondary Treatment
Chlorinated
Pesticides (kg) PCBs (kg) Mercury (kg)
Water
Sediment
39
430-1520
47
510-1800
300
40,000-80,000
Estimated existing inventories in Massachusetts Bay
Other sources
Atmosphere Rivers
Other Treatment Plants
MWRA
Legend

sing computer modeling, MWRA has predicted that increased pollutant removals by sec-
ondary treatment, combined with improved dilution of effluent provided by the new out-
fall, will improve the health of Boston Harbor and Massachusetts and Cape Cod Bays. U Computer model 
Scientists assisting MWRA have
developed a detailed computer model
to predict impacts on Boston Harbor
and the Massachusetts and Cape Cod
Bays from discharges of secondary-
treated effluent at the new 9.5-mile
outfall location. This forecast is con-
trasted with modeled impacts from the
discharges of primary effluent at the
outfall location near Deer Island within
Boston Harbor. The model is a time-
variable, three-dimensional, hydrody-
namic and water quality model called
the Bays Eutrophication Model. It was
developed by the U. S. Geological
Survey and Hydroqual, Inc., the com-
pany that also developed water quality
models for the Chesapeake Bay and
Long Island Sound. 
Verifying the model 
In the course of developing and test-
ing the model, modeling results were
compared to actual environmental
observations in the Massachusetts Bay
system made in 1989-1992. The
model results agreed quite well with
observed data, and reproduced the
major processes affecting the Bays
system: the annual cycle of surface
water heating and stratification; the
spring freshet associated with the Mer-
rimack River and other northern rivers
discharging to the Gulf of Maine; the
annual cycle of phytoplankton growth;
the annual cycle of nutrients in the sur-
face and bottom waters; and the effect
of stratification on the minimum dis-
solved oxygen concentrations
observed in October.
After the usefulness of the computer
model was established by these tests,
scientists used the model to predict the
likely impacts of discharging secondary
effluent through the new outfall into
Massachusetts Bay. Figures 19-21
show the model predictions for three
major components of concern: surface
chlorophyll a , bottom dissolved oxy-
gen, and particulate organic carbon
flux. 
Chlorophyll a 
Because primary and sec-
ondary treatment do little to
remove nutrients from
sewage effluent, one of the
major questions regarding
relocation of the effluent dis-
charge to the 9.5-mile site
offshore is what effect nutri-
ents would have on phyto-
plankton growth: would
adding nutrients offshore
promote blooms of phyto-
plankton? One important
measure of the status of
eutrophication in the Bays
system is the concentration
of chlorophyll a , a major algal pigment
that is a good measure of phytoplank-
ton abundance.
Figures 19a and 19b show concen-
trations of chlorophyll a at the surface
for Boston Harbor and Massachusetts
Bay predicted by the Bays Eutrophi-
cation Model. The figures show a five-
day average in August, when the Bays
are stratified. There is a large
decrease in surface chlorophyll a lev-
els in Boston Harbor and no increase
in Massachusetts Bay after the 9.5-
mile outfall and secondary treatment
are on-line. This is largely because of
improved dilution, and because at the
new deeper location, discharged nutri-
ents will mostly be below the summer
pycnocline in the Bay. Nutrients will
not be available to phytoplankton at
the surface, where there is enough
light to support vigorous growth. 
Dissolved oxygen in bottom
water 
Animals and plants living in the
marine environment need adequate
dissolved oxygen (DO) in the water for
respiration. If DO levels fall too low,
fish and other animals may die. Bot-
tom waters, because they are not in
contact with the atmosphere, are most
likely to experience low DO. Factors
that decrease the levels of DO in the
water are: high water temperature—
oxygen is less soluble at warmer tem-
peratures, and respiration rates of all
life increase; too much oxygen-
demanding organic matter in the sedi-
ment; and stratification of the water 
(ug/L)
Bay outfall
with secondary
treatment
< 1
5 (ug/L)
Harbor outfall
with primary
treatment
10
< 1 
16 
Figure 19. Modeled surface chlorophyll a , August
a b 
how will the discharge affect 
the health of the Bays?

column, which prevents more highly
oxygenated surface waters from
reaching the bottom. Concerns about
the outfall related to dissolved oxygen
are whether inputs of materials that
use up oxygen (measured as bio-
chemical oxygen demand, or BOD)
and nutrients might cause bottom DO
to violate the water quality standard.
Monitoring has shown that bottom
water DO has occasionally fallen
below the standard at the new outfall
site. The state standard for DO is 6
mg/l in Massachusetts Bay, and 5 mg/l
in most of Boston Harbor.
Bottom DO levels are generally low-
est in October because the water col-
umn has been stratified since April
(see page 12). The model shows that
with the Harbor discharge and primary
treatment (Figure 20a), the lowest DO
is in the Inner Harbor, and DO is also
depressed near the future outfall area.
This offshore DO depression is partly
natural, and partly reflects the present
export of nutrients and BOD from
Boston Harbor. Figure 20b shows that
secondary treatment and the long out-
fall result in improved bottom DO, both
in the Harbor and near the outfall.
Most of this improvement is explained
by increased removal of BOD through
secondary treatment. 
Particulate organic
carbon flux 
The animal community
living on the ocean floor
relies for food on organic
matter deposited to the
sediment through the over-
lying water column—the
particulate organic carbon
(POC) flux. However, depo-
sition of too much organic
matter in the sediments can
deplete sediment DO.
Excess food as POC will
destabilize the normal com-
munity structure, leading to
decreased diversity, as has happened
in Boston Harbor. POC can be con-
tributed directly by an effluent dis-
charge, or indirectly by increased phy-
toplankton and zooplankton
abundance, some of which ultimately
deposit in the sediments. A concern
with the 9.5-mile outfall location has
been the potential effect of adding
POC to the sediments near the new
outfall.
The model shows a high deposition
rate in Boston Harbor with the present
outfall and primary treatment (Figure
21a). With the new outfall and sec-
ondary treatment, POC flux is dramati-
cally reduced in both the Harbor and
the Bay (Figure 21b). 
(mg/L)
> 9
< 6
Bay outfall
with secondary
treatment
(mg/L)
Harbor outfall
with primary
treatment
< 6
> 9
(mg C/m2-d)
Harbor outfall
with primary
treatment
1000
< 125
(mg C/m2-d)
1000
< 125
Bay outfall
with secondary
treatment 
17 
Figure 20. Modeled dissolved oxygen in bottom water, October
a b
Figure 21. Modeled deposition of particulate organic carbon
a b

right whale? 
what about the
The northern right whale ( Eubalaena
glacialis ) is the world’s most endan-
gered large whale. From an original
population size of at least 10,000 ani-
mals, extensive hunting for more than
800 years drove the species to near-
extinction. Only about 300 individuals
remain in the North Atlantic; fewer in
the North Pacific. Despite an interna-
tional ban on hunting right whales since
1949, the population is increasing at a
very slow rate, in contrast to other pro-
tected whales which have recovered
more quickly.
The explanation of this slow recovery
is not known. Natural causes such
as competition with other species, or
genetic factors like inbreeding, or
behavioral factors may be important.
Human-induced mortality includes colli-
sions with ships and entanglement with
fishing gear. Finally, habitat degradation
has been identified as a potentially
important cause of the whale popula-
tion’s low rate of increase. Reduction in
food availability, physical interference
with whales through shipping, mining
and dredging activities, and pollution
impacts are factors that could degrade
whale habitat.
Cape Cod Bay and Stellwagen Bank
are important late winter/spring feeding
areas for these migratory animals, and
have been identified by the National
Marine Fisheries Service (NMFS) as
critical habitat to be protected. Therefore
potential pollution sources like the
MWRA outfall must be reviewed under
the Endangered Species Act, although
the long outfall discharge is
distant–more than 16 miles–from identi-
fied right whale habitat.
In 1993, EPA conducted a compre-
hensive Biological Assessment on the
potential impact of the MWRA outfall on
endangered species and NMFS issued
a Biological Opinion. The conclusion
was that the outfall was not likely to
jeopardize the species. Nevertheless,
the critical status of the right whale
requires special and continued consider-
ation. Issues that have received ongoing
scrutiny include the potential for impacts
from pathogens, toxic chemicals, and
nutrients, as described below. 
Will the whales be threatened
by infectious bacteria, viruses
or protozoans in the effluent? 
Secondary treatment is highly effec-
tive at removing pathogens from the
wastewater. Secondary-treated effluent
is also disinfected more effectively than
primary effluent. Improved removal com-
bined with higher dilution will signifi-
cantly decrease the levels of pathogens
in both the Harbor and the Bays. The
microbiological water quality will meet
human swimming standards and the
much more stringent shellfishing stan-
dards. These standards should be suffi-
ciently protective of the whales as well. 
What about toxic and bioaccu-
mulation effects of metals and
PCBs? 
Levels of these contaminants in the
discharge will be so low (page 10) that
short-term, acute toxic effects are not a
concern. The focus is on average levels
of contamination Bay-wide and the
effects of long-term chronic exposure,
such as bioaccumulation, and the
potential for sublethal effects like
decreased fertility.
Measurements of organochlorine com-
pounds, like PCBs, in right whales indi-
cate relatively low tissue levels com-
pared to other marine mammals.
Although exposure to toxic chemicals
may possibly be a factor in right whale
reproductive failure, moving the outfall
location from within the Harbor to the
9.5-mile location offshore will not
increase the risk to whales because the
inputs of these contaminants to the
Bays system will not be increased.
Rather, secondary treatment will sub-
stantially decrease any toxic chemicals
MWRA contributes to the Bays system. 
Will increased nutrients cause
decreased food availability? 
In order to better understand nutrient
issues, it helps to know something
about the feeding biology of the north-
ern right whale (see illustration, Figure
22). Right whales are baleen whales;
they feed by swimming open-mouthed
through patches of zooplankton, strain-
ing
millions (about one ton a day) of tiny
crustaceans, called copepods, from the
water. In the spring, right whales feed in
Cape Cod Bay and Stellwagen Bank,
where there are intense blooms of large
and nutritious copepods like Calanus
finmarchicus . The whales feed in dense 
Calanus patches, created by wind and
current patterns as well as copepod
swimming behavior.
Offshore Calanus zooplankton com-
munities differ from their nearshore
counterparts. Nearshore zooplankton
are typified by species like Acartia ,
which are smaller, less nutritious, and
apparently do not form the dense
ndangered northern right whales, when visiting Massachusetts and Cape Cod Bays, will be exposed to
lower amounts of toxic pollutants and pathogens because of improved wastewater treatment. Hypothe-
sized effects of nutrients on plankton that are food for the right whale are being carefully monitored. E
18 
Acartia 
1 mm 
Calanus 
2.5 mm

patches required to sustain a feeding
whale. Different types of copepods eat
different kinds of phytoplankton. It has
been suggested that the nutrients dis-
charged by the new outfall could cause
the Bay environment to favor zooplank-
ton like Acartia —not good food for right
whales.
Another nutrient-related whale-feeding
concern is nuisance algal blooms: will the
outfall cause blooms of Phaeocystis ,
which seems to interfere with whale feed-
ing, or brown or red tides which might be
toxic? Blooms of Phaeocystis and 
Alexandrium have occurred in the Bays,
so the question is whether the outfall
could worsen them.
To help address both of these food
availability issues, MWRA has used the
Bays Eutrophication Model (page 16).
The model shows that we can expect to
see effects of nutrient discharges limited
to the immediate area of the outfall, so it
is unlikely that there would be any outfall-
related changes as far away as right
whale habitat. If any changes in phyto-
plankton or zooplankton do result from
the discharge, they would first occur near
the outfall. Therefore, MWRA is monitor-
ing intensively for changes in plankton
composition there. MWRA also monitors
Cape Cod Bay for any significant
changes. 
phytoplankton 
Tiny floating plants (algae), especially
diatoms, that are carried about with
ocean currents. These plants (illus-
trated at right) grow most abundantly
near the surface of the water, where
they receive maximum light. At the
base of the marine food web, phyto-
plankton grow using nutrients in the
water, and are eaten by zooplankton. 
zooplankton 
Tiny floating animals, including juve-
nile forms of fish, jellyfish, and shell-
fish. Very small crustaceans, the cope-
pods (see drawings on left), are often
abundant in zooplankton. Zooplankton
eat phytoplankton, and in turn are
eaten by fish and other marine animals,
including northern right whales. 
plankton
Figure 22. Feeding northern right whale. High springtime nutrient levels in the water, combined
with wind and current patterns, stimulate the abundant growth of phytoplankton and Calanus cope-
pods in Cape Cod Bay and Stellwagen Bank. The nutritious copepods are found in dense patches,
favored by filter-feeding northern right whales. The whales feed in Massachusetts and Cape Cod Bays
in the spring before continuing their migration north to the Bay of Fundy. MWRA monitoring will detect
changes in phytoplankton or zooplankton communities. (Illustration by S. Hussey, after S. Landry, cour-
tesy of New England Aquarium).
19

outfall 
will we know if the
aseline monitoring, which has been conducted since 1992, is telling us a lot about natural environ-
mental variability. The more we understand the Bays system, the more quickly and confidently we
can determine if an apparent impact is discharge-related. Scientists and regulators have estab-
lished threshold values of environmental parameters that will trigger MWRA action. B 
is causing a problem? 
Permit, trigger parameters, and
thresholds 
MWRA’s National Pollutant Dis-
charge Elimination System (NPDES)
permit for the new treatment plant and
outfall, to be issued jointly by EPA and
the Massachusetts Department of
Environmental Protection (DEP), will
incorporate stringent limits and testing
requirements for Deer Island effluent
discharges. The permit will be one of
the most comprehensive and protec-
tive permits ever issued, and will
require that state and federal water
quality criteria not be violated as a
result of the discharge. In addition,
MWRA has been conducting an exten-
sive outfall monitoring program, which
is linked to an action plan—the Contin-
gency Plan—that incorporates trigger
parameters and threshold values for
MWRA actions.
Trigger parameters are environmen-
tally significant components of effluent
or the marine ecosystem that, if certain
(threshold) levels are exceeded, indi-
cate a potential for environmental risk.
Examples of trigger parameters for
effluent are total suspended solids,
biochemical oxygen demand, and toxic
contaminants. Examples of environ-
mental trigger parameters are water
column dissolved oxygen concentra-
tion, chlorophyll a concentration, ben-
thic community structure, and liver dis-
ease in flounder. Twenty-two trigger
parameters are incorporated in the
outfall monitoring program.
Threshold values are measurements
of trigger parameters selected as indi-
cators of the need for action, and are
based on expected permit limits, state
water quality standards, and expert
opinion. To alert MWRA to any
changes, each trigger parameter has
thresholds that are defined as caution
or warning levels. These thresholds
are based on monitoring data collected
since 1992 under the guidance of the
Outfall Monitoring Task Force, which
includes academic scientists, govern-
ment agency representatives, and citi-
zens groups. 
Monitoring comprehensively 
Years of study by MWRA, scientists
at major universities, research institu-
tions including the Woods Hole
Oceanographic Institution, and govern-
ment agencies including the EPA and
Geological Survey, have shown that
the combination of improved waste-
water treatment at Deer Island and the
dilution provided by discharge of efflu-
ent into deeper Bay waters will gener-
ally benefit Massachusetts Bay and
Boston Harbor. Nevertheless, to
ensure that any potential unforeseen
environmental impacts of the outfall
relocation are addressed, MWRA has
implemented the most comprehensive
marine monitoring program in the
nation for a secondary-treated sewage
discharge, and will continue post-dis-
charge monitoring after the outfall
begins operating in 1998. Actions to be
taken by MWRA if any unexpected
impacts occur are detailed in the Con-
tingency Plan described at the end of
this report.
Massachusetts Bay has become one
of the most thoroughly studied marine
environments anywhere. As recom-
mended by the National Academy of
Sciences’ National Research Council,
the monitoring program focuses on the
potential impacts of nutrients, organic
material, toxic contaminants,
pathogens, solids, and floating debris.
Contaminants are measured and bio-
logical observations made in effluent,
water, sediment, plankton, fish, and
shellfish. Even satellite data is used to
measure chlorophyll, temperature, and
other ocean conditions (Figure 23).
Sampling is most intensive in the
immediate discharge area (within three
miles of the diffuser). In addition, sam-
pling stations more than 30 miles away
in Cape Cod Bay are included (Figure
24). Since the inception of the monitor-
ing program, 3.4 million data records
have been collected and stored in
MWRA’s marine monitoring database,
and more than 200 reports written. 
Monitoring at all scales 
Perhaps the biggest challenge in pol-
lution effects monitoring is to charac-
terize the natural variability in the envi-
ronment. Within the general patterns of
seasonal and habitat differences, the
marine environment can be unpre-
dictable. Changes occur in the physi-
cal and biological environment that are
unrelated to human activities. Plants,
animals and plankton in Massachu-
setts and Cape Cod Bays have what is
termed a patchy distribution in space
and time; where and when they are
found are greatly affected by local
winds, currents, sediment types, or
animal behavior. This means we must
measure local changes, as well as
understand broader, general
processes.
The most frequent measurements
are by moored instruments that collect
data at one location at intervals only
minutes apart. In the critical area
around the outfall, oceanographic ves-
sels frequently collect water and sedi-
ment samples for detailed chemical
and biological analyses. At sites dis-
tant from the outfall location, less fre-
quent sampling will enable us to moni-
tor the general health of the area. The
big, regional picture, on a scale of kilo-
meters, is generated by satellite
images. 
20

This floating buoy owned
by the National Oceanic
and Atmospheric Administration
collects oceanographic data such
as wave height, at the
surface of the sea.
Satellites like SEASTAR collect climate
data and measure parameters such as
chlorophyll a over hundreds of square miles.
Temperatures (C)
USGS Mooring (5m)
Ship survey (10m)
Sep Oct
These two moored instrument arrays,
owned by the U.S. Geological Survey,
continuously measure sediment
deposition rates, ocean currents, and
other parameters like temperature.
The tripod (below) gathers data at
the ocean floor, the instrument at right
makes measurements at mid-depths.
Example of data (water temperature)
collected continuously by moored
instruments compared to survey data
collected by ship.
Scientists on oceanographic ships collect water,
plankton, fish, shellfish, and sediment samples
for MWRA throughout the Bays for laboratory
analysis.
Jan
20
15
10
5
0
Feb Mar Apr May Jun Jul Aug Nov Dec 
Figure 23 . MWRA monitors the
Harbor and Bay at all scales; data are
collected by satellite, ship, and mooring.
21

Indicators of the Bays’
health vary naturally 
Baseline monitoring has
shown that, within the
overall seasonal cycle,
there is intense variation
from year to year. For
instance, Figure 25 shows
differences in abundance
of dominant (beneficial)
phytoplankton and nui-
sance phytoplankton in the
Bays since baseline moni-
toring began in 1992. The
maximum abundances of
beneficial phytoplankton,
like Skeletonema and Tha-
lassiosira, vary relatively
little from year to year.
By contrast, nuisance phy-
toplankton like red tide
( Alexandrium tamarense ,
the cause of paralytic
shellfish poisoning) or
blooms that lower bay-
wide oxygen concentra-
tions, discolor the water, or
produce foul odors, are much more
erratic from year to year. Large nui-
sance blooms are interspersed with no
blooms. In 1992 and in the spring of
1997 (not shown), there were large nui-
sance Phaeocystis blooms in Cape Cod
Bay and Buzzards Bay. The 1997
bloom apparently interfered with right
whale feeding, as right whales left Cape
Cod Bay earlier than usual that year
(Mayo, 1997). Nuisance blooms can be
linked to the larger circulation in the
Gulf of Maine: for example, winds, cur-
rents and spring runoff during May
determine whether red tide enters 
0 1996 1995 1994 1993 1992
0
Maximum abundance (cells/liter)
1996 1995 1994 1993 1992
10
100
1,000
10,000
100,000
1,000,000
10,000,000
0 0
10
100
1,000
10,000
100,000
1,000,000
10,000,000
Maximum abundance (cells/liter) Skeletonema costatum
Asterionellopsis glacialis
Thalassionema nitzschioides
Thallassiosira nordenskioldii
Ceratium tripos
Asterionellopsis glacialis
Phaeocystis pouchetti
Pseudo-nitzschia pungens
Alexandrium tamarense 
Legend
USGS mooring
Soft sediment bottom surveys
Baseline water quality
monitoring nearfield
Baseline water quality
monitoring farfield
Outfall
Flounder, lobster, or
mussel sampling 
Figure 24. Monitoring stations include water, sediment, and the biota close to and dis-
tant from the new outfall site. 
Monitoring locations in the Bays.
Beneficial algal blooms
Nuisance algal blooms
Figure 25. Beneficial and nuisance
algal blooms have different inter-annual pat-
terns. Nuisance algal blooms have occurred
during the baseline monitoring period. These
blooms are less predictable than the normal,
beneficial algal blooms which produce food
and oxygen. Continued monitoring will
enable MWRA to detect whether changes in
algal blooms are related to the outfall (MWRA
monitoring data).
22

Massachusetts Bay or is transported
out to sea (Anderson, 1997).
Figure 26 shows another example of
natural variability: in 1994 and 1995,
average oxygen concentration in the
bottom waters of the Bay fell below the
caution level. This measurement would
trigger more intensive evaluation once
the new outfall comes on-line, an exam-
ple of a natural phenomenon that could
have been interpreted as outfall-related.
Another example of a measurement
that, if the new outfall were in use,
could have been attributed to sewage
effluent, was a pattern of silver deposi-
tion in the sediments near the new out-
fall site. Figure 27 shows that silver
concentrations spiked up to more than
double their baseline value in February
1993 after an unusually severe storm in
December of 1992. That storm caused
redistribution of silver into the muddy
sediments sampled. By February 1994,
silver concentrations declined to near-
background levels. If the new outfall
had been commissioned, it might have
seemed reasonable to attribute the ele-
vated silver concentration to the outfall,
but now we know that severe storms
can create a pattern like this one.
Observations of natural year-to-year
variation of phenomena like nuisance
blooms and the spike of silver in the
area near the outfall site provide an
important context for examining
changes after the long outfall is com-
missioned. Information like this will help
MWRA, scientific experts, regulators,
and interested citizens to know where
to look for likely causes of suspected
environmental problems. 
0
0.5
1
1.5
2
Apr-89
Sediment silver concentration (parts per million)
28-Mar-90
10-Jul-90
23-Oct-90
12-Feb-91
1-Jun-91
18-Oct-91
1-Feb-92
19-May-92
21-Oct-92
18-Feb-93
17-Jun-93
5-Oct-93
15-Feb-94
7-Jun-94
5-Oct-94
14-Feb-95
13-Jun-95
26-Sep-95
9-Jul-96
15-Feb-96 
Major storm
December 1992 
Figure 26. Baseline monitoring
shows low dissolved oxygen can occur
in bottom waters at the future outfall
site. Average
dissolved oxygen levels measured dur-
ing surveys of the bottom waters of the
outfall nearfield area show dramatic
seasonal fluctuations, as well as varying
from year to year. In 1994, the average
DO in October almost violated the state
water quality standard, and did fall
below the caution (6.5 mg/l) level in
1994 and in 1995. Another measure-
ment, the percent saturation of DO, not
shown, violated the warning level in
1994 and 1995. These violations are
related to the warmer temperatures
during those years; in the post-dis-
charge period such low levels would
trigger notification of the Outfall Moni-
toring Task Force (error bars represent
one standard deviation; MWRA moni-
toring data). 
Sediment silver concentrations at the Bay outfall site (1989-1996)
Figure 27. Silver concentrations in
sediment near the future outfall site
increased after a major storm. A major
storm occurred in December 1992,
causing resuspension of sediments from
shallower inshore areas, which rede-
posited into deeper offshore areas,
including a small muddy area near the
future outfall site (average is mean of
three measurements error bars show
one standard deviation; data from
Bothner 1997 in press, Bothner et al.
1997 in press). 
Apr Jul Oct
1992
Apr Jul Oct
1993
Apr Jul Oct
1994
Apr Jul Oct
1995
Apr Jul Oct
1996
5
6
7
8
9
10
11
12
13
Average dissolved oxygen (mg/l) 
(Water quality standard) Warning level
Caution level 
Dissolved oxygen levels in bottom water at the Bay outfall site 
23

what will
if a problem occurs?
he Contingency Plan describes how, if monitoring results indicate a
possible environmental problem, MWRA and the regulatory agencies
will act to determine the cause of the problem and what corrective
actions should be taken. T The Outfall Contingency Plan 
The Outfall Contingency Plan was
developed to create a process to iden-
tify and respond to water quality
changes that potentially could be
related to effluent discharges. Even
though it is not expected that these dis-
charges will affect the environment
adversely, the Contingency Plan
describes the criteria and process that
MWRA, regulatory agencies, and the
Outfall Monitoring Task Force (OMTF)
would use to assess potential changes,
make information on those changes
available to the public, and respond
appropriately to avoid harm to the
marine environment. 
How the Contingency Plan
works 
The Contingency Plan identifies trig-
ger parameters, conditions that can
suggest that effluent quality or environ-
mental conditions may be changing or
likely to change in the future. To alert
MWRA to different degrees of observed
change, each trigger parameter has
thresholds that are defined as caution
or warning levels. These thresholds are
based on monitoring data collected
since 1992.
In the event that a threshold is
exceeded, the process for responding
will vary somewhat depending on
whether the threshold is a caution or a
more serious warning level (Figure 28).
The response to any threshold
exceedance, even before the cause
has been discovered, will be to decide
whether treatment plant operations can
be altered to reduce the discharge of
the relevant pollutant.
If MWRA discharges have caused a
caution level to be exceeded, MWRA
will expand its monitoring to closely
track any change in effluent quality and
environmental conditions, and provide
the information necessary to:
1) evaluate the cause and effect of the
exceedance; and
2) review applicable trigger parameters
and thresholds.
If the threshold exceeded is a warn-
ing level, the proposed response will
include both early notification to EPA
and DEP and the quick development of
a Response Plan. A Response Plan
includes a schedule for implementing
actions such as additional monitoring,
making further adjustments in plant
operations, or undertaking an Engineer-
ing Feasibility Study regarding specific
potential corrective activities. 
Corrective activities 
Corrective activities have been identi-
fied in the Contingency Plan (or may be
identified in the future) as potential solu-
tions to unexpected impacts in the
marine ecosystem from the operation of
the outfall. If the effects of effluent dis-
charges must be reduced, examples of
corrective activities could include the
addition of specific enhanced treatment
technologies and increased pollutant
prevention and regulation. 
How the Contingency Plan
is accountable to the public 
To ensure that the Contingency Plan
provides appropriate environmental pro-
tection, every step of the implementa-
tion process will be open to public input
and review. In addition, MWRA will pro-
duce a quarterly Wastewater Perfor-
mance Report to provide the public with
information about plant performance
and monitoring results. The report is
designed to:
• provide information about key waste-
water operations;
• demonstrate day-to-day progress in
achieving goals and objectives; and
• compare actual performance against
trigger parameters and other impor-
tant water quality monitoring or plant
performance targets.
Once a year, MWRA will also develop
an Outfall Monitoring Overview/Contin-
gency Plan report that will be submitted
to the Outfall Monitoring Task Force as
well as to EPA, DEP, and the Federal
Court. The report will also be available
to the public. The report will summarize
monitoring results and any
exceedances, responses related to the
Contingency Plan, and corrective activi-
ties that have occurred over the previ-
ous year. The report will also propose
changes to the Contingency Plan, as
needed. Changes are expected to be
guided primarily by OMTF recommen-
dations. 
How the Contingency Plan
will be enforced 
The Contingency Plan is one portion
of many obligations, both state and fed-
eral, that MWRA is required to meet:
• The NPDES permit imposes extensive
requirements on MWRA discharges,
including effluent monitoring, report-
ing, plant maintenance and opera-
tions, and the industrial pretreatment
program. Requirements for the com-
bined sewer overflow (CSO) program
and sludge-to-fertilizer plant are also
included;
• A Federal Court Order guides the con-
struction of the new treatment facili-
ties, sludge-to fertilizer plant, CSO
projects, and the industrial pretreat-
ment program, as well as treatment
plant staffing;
• The Massachusetts Executive Office
of Environmental Affairs and EPA
have overseen the development and
implementation of MWRA’s Outfall 
be done 
24

Monitoring Plan, which has also been
submitted to the Federal Court.
To ensure that even greater over-
sight and enforcement opportunities
are provided, the new draft NPDES
permit being developed for public com-
ment by EPA and DEP is expected to
include requirements to ensure that the
Contingency Plan will be implemented
as described and intended.
The Contingency Plan is designed
to build on and be consistent with
MWRA’s regulatory and judicial oblig-
ations. The Plan also represents the
matching of MWRA’s obligations with
a clear line of accountability to the
Court, regulatory agencies, and the
public. 
OMSAP Confirms Caution
Level Exceedance
Ongoing Monitoring
Preliminary Data
Reported to MWRA
Caution
Level
Exceeded?
Notify Plant Staff & OMSAP
Adjust Operations
if Needed
Warning
Level
Exceeded?
YES
YES
NO
NO Accelerate Data
Confirmation
Annual Monitoring Report
Caution Level Exceedance
Reported in Quarterly
Wastewater Performance Report
MWRA Develops
Response Plan
OMSAP Confirms Warning
Level Exceedance
Evaluations
Actions and Follow-up
Reported in Quarterly
Wastewater Performance Report
Schedule
5 days
30
days
90
days
180 days
Exceedance and Response
Plan Reported in Quarterly
Wastewater Performance
Report
Figure 28. Contingency plan process flowchart 
In 1990, the Massachusetts Secretary of Environmental Affairs formed
the Outfall Monitoring Task Force (OMTF) to advise the MWRA. The
OMTF, composed of scientists and representatives from government
agencies and regional environmental groups, guides MWRA’s monitor-
ing program. The Task Force directed MWRA to monitor in four general
areas: effluent, water column, sediment, and living resources. The
OMTF meets regularly to review MWRA’s findings and approves
changes in monitoring annually based on new scientific information.
The Task Force also sets priorities regarding the environmental issues
and questions MWRA should address with its monitoring program.
OMTF meetings are open to the public. 
task force 
outfall monitoring 25

endnotes for Table 2
1 Maximum value measured
during Deer Island detailed
effluent studies (Butler et al.
1997), except for total
PCBs, which are average
values.
2 Secondary effluent from
Deer Island pilot secondary
plant.
3 After appropriate dilution
factor (80:1 for copper, lead
and mercury available in
area nearest diffuser, after
initial mixing. Dilution factor
is 364:1 for DDTs, PAH, and
PCBs, available in the out-
fall nearfield area.)
4 EPA determines three cate-
gories of receiving water
quality criteria: acute,
chronic, and human health.
Different criteria are applied
to different types of dis-
charges. Acute criteria are
applied to small areas or
brief discharges, and specify
the maximum concentration
of a constituent an organism
can be safely exposed to for
a short duration. Chronic cri-
teria are applied to large
areas or long-term dis-
charges and specify the
maximum concentration of a
constituent that an organism
can be safely exposed to for
a long period of time.
Human health criteria reflect
the concentration of a con-
stituent that fish and shell-
fish can live in without
endangering the health of
people who eat the seafood.
5 Water quality criteria for
copper, mercury and lead
are EPA chronic criteria.
Water quality criteria for
DDTs, PAH and PCBs are
human health criteria.
6 The criterion for fluoran-
thene is given because
there is no established crite-
rion for total PAH.
7 Comparing PCBs in effluent
to the water quality criterion
is problematic because
ambient levels in all Massa-
chusetts waters already vio-
late the human health stan-
dard.
references
• Anderson, D. M., B. A.
Keafer, and J. T. Turner.
1997. ‘Red tides’ in Massa-
chusetts Bay: Nearshore
processes and transfer of
toxins through the pelagic
food web. Report to MWRA.
•Bitton, Gabriel. 1994. Waste-
water microbiology.Wiley-
Liss, Inc. New York. 478
pp.
• Bothner, M. H., 1997, Metal
concentrations in sediments
of Boston Harbor document
environmental change.
USGS Fact Sheet, 97-xxx,
2p. in press.
• Bothner, M. H., M. Buchholtz
ten Brink, and F.T. Man-
heim, 199X, Metal concen-
trations in surface sedi-
ments of Boston
Harbor–changes with time.
Marine Environmental
Research, in press.
• Bothner, M. H., M. Buchholtz
ten Brink, C. M. Parmenter,
W. M. d’Angelo, and M. W.
Doughten. 1993. The distri-
bution of silver and other
metals in sediments from
Massachusetts and Cape
Cod Bays-—an interim
compilation. U.S. Geologi-
cal Survey. Open file report
93-725.
• Bousfield, E.L. 1973. Shal-
low-water Gammaridean
Amphipoda of New Eng-
land. Cornell Univ. Press,
Ithaca and London. 321 pp.
•Butler, E., M. Higgins, J. Chi-
apella, and W. Sung. 1997.
Deer Island effluent charac-
terization studies: January
1995-December 1995.
MWRA Enviro. Quality
Dept. Tech Rpt. Series No.
97-3. MWRA, Boston MA.
91 pp.
• Cibik, S.J., B. L. Howes, C.
D. Taylor, D. M. Anderson,
C. S. Davis, and T. C. Loder
III. 1996. 1995 Annual water
column monitoring report.
MWRA Enviro. Quality
Dept. Tech Rpt. Series No.
96-7. MWRA, Boston MA.
241 pp.
• Coats, D. A. 1995. 1994
Annual soft-bottom benthic
monitoring: Massachusetts
Bay outfall studies. MWRA
Enviro. Quality Dept. Tech
Rpt. Series No. 95-20.
MWRA, Boston MA. 184
pp.
• Galya, D. P. , J. Bleiler, and
K. Hickey. 1997. Outfall
monitoring overview report
1995. MWRA Enviro. Qual-
ity Dept. Tech Rpt. Series
No. 97-2. MWRA, Boston
MA. 48 pp.
• Hilbig, B., J. A. Blake, E.
Butler, D. C. Rhoads, G.
Wallace, and I. P. Williams.
1996. Benthic biology and
sedimentology: 1995 base-
line conditions in Massa-
chusetts and Cape Cod
Bays. MWRA Enviro. Qual-
ity Dept. Tech. Rpt. Series
No. 96-5. MWRA, Boston
MA. 230 pp.
• Hilbig, B., J. A. Blake, D. C.
Rhoads, and I. P. Williams.
1996. Boston Harbor soft-
bottom benthic monitoring
program: 1995 results.
MWRA Enviro. Quality
Dept. Tech. Rpt. Series No.
96-8. MWRA, Boston MA.
94 pp.
• Hillman, R.E. and C.S.
Peven. 1995. 1994 annual
fish and shellfish report.
MWRA Enviro. Quality
Dept. Tech. Rpt. Series No.
95-5. MWRA, Boston, MA.
82 pp.
• Hydroqual, Inc. and Norman-
deau Associates, Inc. 1995.
A water quality model for
Massachusetts and Cape
Cod Bays: calibration of the
Bays Eutrophication Model
(BEM). MWRA Enviro.
Quality Dept. Tech. Rpt.
Series No. 95-8. MWRA,
Boston MA. 402 pp.
• Hull, R. N. and G. W. Suter.
1995. Toxicological bench-
marks for screening conta-
minants of potential concern
for effects on sediment-
associated biota: 1994 revi-
sion. Oak Ridge National
Laboratory Report
ES/ER/TM-95/RI. 28 pp.
• Long, E. R. and L. G. Mor-
gan. 1990. The potential for
biological effects of sedi-
ment absorbed contami-
nants tested in the National
Status and Trends Program.
NOAA. Technical Memoran-
dum NOS OMA 52. U. S.
National Oceanic and
Atmospheric Administration,
Seattle, Washington. 175
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• Long, E. R., D. D. MacDon-
ald, S. L. Smith, F. D.
Calder. 1995. Incidence of
adverse biological effects
within ranges of chemical
concentrations in marine
and estuarine sediments.
Environmental Manage-
ment. 19 (1):81-97. 
references 
endnotes 
26

• Massachusetts Bays Pro-
gram,1996. The Massachu-
setts Bays 1996 Compre-
hensive Conservation and
Management Plan: an
Evolving Plan for Action.
Mass. Executive Office of
Environmental Affairs,
Boston, MA.
• Massachusetts Water
Resources Authority. 1991.
Effluent outfall monitoring
plan phase I: baseline stud-
ies. MWRA Enviro. Quality
Miscellaneous Rpt. Series
No. ms-2. MWRA, Boston
MA. 95 pp.
• Massachusetts Water
Resources Authority. 1995.
Effluent outfall monitoring
plan phase II: post dis-
charge monitoring (draft).
MWRA Enviro. Quality Draft
11/95. MWRA, Boston MA.
• Massachusetts Water
Resources Authority. 1997.
Contingency Plan. February
1997. 41 pp.
• Mayo, Charles. 1997. Food
resources and foraging
imperatives of the northern
right whale Eubalaena
glacialis in Massachusetts
and Cape Cod Bays.
Abstract in Conference
Proceedings vol 1, Coastal
Zone ‘97.
• Mitchell, D. F., T. Mounce, J.
Morton, K. Sullivan, M.
Moore, and P. Downey.
1996. 1995 Annual fish and
shellfish report. MWRA
Enviro. Quality Dept. Tech
Rpt. Series No. 96-3.
MWRA, Boston MA. 112
pp.
• Mitchell, D. F., M. Wade, W.
Sung, and M. Moore. 1997.
1996 Toxics issues review.
MWRA Enviro. Quality
Dept. Tech Rpt. Series No.
97-4. MWRA, Boston MA.
134 pp.
• Murchelano, R. A. and R. E.
Wolke. 1985. Epizootic car-
cinoma in winter flounder 
Pseudopleuronectes ameri-
canus . Science 228:587-
589.
• National Marine Fisheries
Service. 1991. Recovery
plan for the northern right
whale ( Eubalena glacialis ).
Prepared by the Right
Whale Recovery Team for
the National Marine Fish-
eries Service, Silver Spring,
MD. 86 pp.
• National Marine Fisheries
Service. 1992. Marine
Mammal Investigation. The
right whale in the western
North Atlantic: A science
and management work-
shop. Northeast Fisheries
Science Center Reference
Document 92-05. 87 pp.
• National Marine Fisheries
Service. 1995. Marine
Mammal Investigation. An
independent scientific peer
review of North Atlantic
right whale research sup-
ported by the Northeast
Fisheries Science Center: A
workshop held in Woods
Hole, Massachusetts, Octo-
ber 3-7, 1994. Woods Hole
MA: NOAA/NMFS/NEFSC.
Center Ref. Doc. 95-01. 30
pp.
• National Research Council.
1993. Managing waste-
water in coastal urban
areas. National Academy of
Sciences, National Acad-
emy Press, Washington
D.C.
• Pawlowski, C., K.E. Keay, E.
Graham, D.I. Taylor, A.C.
Rex and M.S. Connor.
1996. The State of Boston
Harbor 1995: The new
treatment plant makes its
mark. MWRA Enviro. Qual-
ity Dept. Tech Rpt. Series
No. 96-6. MWRA, Boston
MA. 22 pp.
• Schwartz, J.P., N.M. Duston,
and C.A. Batdorf. 1993.
Metal concentrations in win-
ter flounder, American lob-
ster, and bivalve molluscs
from Boston Harbor, Salem
Harbor, and coastal Massa-
chusetts. EOEA and MA
DFWELE.
• Schwartz, J.P., N.M. Duston,
and C.A. Batdorf. 1991.
PCBs in winter flounder,
American lobster, and
bivalve molluscs from
Boston Harbor, Salem Har-
bor, and coastal Massachu-
setts: 1984-1989. EOEA
and MA DFWELE Publica-
tion 16, 966-63-250-W-91-
C.R.
• Shea, D. 1993. Annual
review of toxic contami-
nants discharged by
MWRA. MWRA Enviro.
Quality Dept. Tech Rpt.
Series No. 93-18. MWRA,
Boston MA. 68 pp.
• Shea, D. 1995. Multimedia
fate model of organic conta-
minants in Massachusetts
Bay. MWRA Enviro. Quality
Dept. Tech Rpt. Series No.
95-18. MWRA, Boston MA.
15 pp.
• Signell, R. P., H. L. Jenter,
and A. F. Blumberg. 1996.
Circulation and effluent dilu-
tion modeling in Massachu-
setts Bay: model implemen-
tation, verification and
results. U. S. Geological
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96-015.
• USEPA.1989. Assessing
human health risks from
chemically contaminated
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ument No. EPA-503/8-89-
002. Office of Marine and
Estuarine Protection (WH-
556F) and the Office of
Water Regulations and
Standards (WH-552).
Washington, DC. 
27

28
mwra 
Information about the MWRA 
http://www.mwra.state.ma.us
state and federal 
Mass. Division of Marine Fisheries 
http://www.magnet.state.ma.us/
dfwele/dmf/dmf_toc.htm 
Mass. Executive Office of Environmental
Affairs (EOEA) 
http://www.magnet.state.ma.us/envir/
eoea.htm 
Departments within EOEA
(DEM, DEP, DFWELE, DFA, MDC) 
http://www.magnet.state.ma.us/en
vir/
depts.htm 
Northern right whale information 
http://www.magnet.state.ma.us/en
vir/
rtwhale.htm 
Program Offices of EOEA (MCZM,
MEPA, DCS, OTA, MassGIS, STEP) 
http://www.magnet.state.ma.us/en
vir/
units.htm 
MDC beach water quality 
http://www.magnet.state.ma.us/mdc/
harbor.htm 
MDC guide to Boston area reservations,
including coastal and Harbor island sites. 
http://www.magnet.state.ma.us/mdc/
reserv.htm 
Boston Harbor Islands National Recre-
ation Area 
http://www.nps.gov/boha/ 
EPA Region 1 
http://www.epa.gov/region01/ 
National Marine Fisheries Service - North-
east Regional Office, Gloucester MA 
http://www.wh.whoi.edu/ro/doc/nero
.html 
USGS Woods Hole Field Center 
http://woodshole.er.usgs.gov/ 
Boston Harbor - Mass. Bay Ecosystems
- Sediment Bibliography 
http://coast-enviro.er.usgs.gov/
MassBib/default.htm 
Boston Harbor Ecosystems - USGS,
New England Aquarium 
http://coast-
enviro.er.usgs.gov/boseco/ 
Coastal Ocean Modeling at the USGS
Woods Hole Field Center 
http://crusty.er.usgs.gov/ 
A Geologic Map of the Sea Floor in
Western Massachusetts Bay,
Constructed from Digital Sidescan-
Sonar Images, Photography,
and Sediment Samples 
http://woodshole.er.usgs.gov/
data1/CDROMS/massbay.dds3/
massbay.html 
Gulf of Maine Information System 
http://oracle.er.usgs.gov/GoMaine/ 
Gulf of Maine Red Tides 
http://crusty.er.usgs.gov/
wgulf/wgulf.html 
Ocean engineer Marinna Martini’s web
page on oceanography tools. 
http://marine.usgs.gov/
~mmartini/instment/tools.htm 
USGS Branch of Atlantic Marine Geol-
ogy, Sediment Database 
http://woodshole.er.usgs.gov/
data1/SEDIMENTS/hathaway/readm
e.
1st.htm 
USGS Contaminant Transport Studies
in Massachusetts Bay 
http://crusty.er.usgs.gov/
mbay/mbay.html 
USGS Stellwagen Bank Information
System 
http://vineyard.er.usgs.gov/ 
Northeast Fisheries Science Center -
Woods Hole 
http://www.wh.whoi.edu/noaa.html
advocacy groups 
The Boston Harbor Association 
http://www.tbha.org/ 
Center for Coastal Studies, Provincetown
MA 
http://www.provincetown.com/coast
alstudies/index.html 
Charles River Watershed Association 
http://www.crwa.org/ 
Merrimack River Watershed Association 
http://www.merrimack.org/ 
National Resources Defense Council:
Testing the Waters 1997 - How
does your vacation beach rate? 
http://www.nrdc.org/nrdcpro/ttw/
summas.html 
Neponset River Watershed Association 
http://www.walpole.ma.us/nepon-
set.htm 
Safer Waters In Massachusetts, Inc. 
http://www.nahant.org/swim/html 
Save the Harbor / Save the Bay 
http://www.tiac.net/users/shsb/index.h
tml
education 
References, documents, and data pertain-
ing to the Mass. Bay ecosystem. 
http://massbay.mit.edu/ 
MIT Mass Bay research bibliography 
http://opal-www.unh.edu/edims.html 
Digital Orthophotos of Boston Harbor and
surrounding area - MASS GIS, MIT 
http://ortho.mit.edu/ 
Gulf of Maine Council on the Marine Envi-
ronment - Environmental Data
and Information Management System
(EDIMS) 
http://massbay.mit.edu/bibliography.h
tml 
New England Aquarium 
http://www.neaq.org/ 
Cetacean Research Unit - research, edu-
cation, conservation 
http://www.friendly.net:80/
user-homepages/b/birdman/
other organizations 
New England Water Environment Associ-
ation (NEWEA) 
http://www.newea.org/ 
Northeast Business Environmental Net-
work (NBEN) 
http://nben.org/index.html
web sites 
internet

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massachusetts water
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