1997 and 1998: beyond the Boston Harbor Project

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T H E
BOSTON H A R B O R
BEYOND
P R O J E C T
BEYOND
T H E
BOSTON H A R B O R
P R O J E C T
1998-1999
The State of Boston Harbor
Massachusetts Water Resources Authority
1997-1998
The State of Boston Harbor
Massachusetts Water Resources Authority

F E B R U A RY 2 0 0 0
P R E PA R E D U N D E R T H E D I R E C T I O N O F :
Douglas B. MacDonald, Executive Director
B O A R D O F D I R E C T O R S
Robert A. Durand, Chair
John J. Carroll, Vice-Chair
Norman P. Jacques, Secretary
Andrea d’Amato
Lucile P. Hicks
Joseph A. MacRitchie
Vincent G. Mannering
Donald A. Mitchell
Andrew M. Pappastergion
Robert D. Spinney
Marie T. Turner
T E C H N I C A L R E P O R T N O . 0 0 - 0 5
T H E S TAT E O F B O S T O N H A R B O R 1 9 9 7 - 1 9 9 8
B E Y O N D T H E B O S TO N H A R B O R P R O J E C T

Andrea C. Rex
Sally Rege Carroll
Rita Berkeley
Rita Berkeley
Susan Curran Ford
Michael Delaney
Lorraine Downey
Elizabeth Gowen
Esther Graf
Maurice Hall
Douglas Hersh
Michael Hornbrook
Kenneth Keay
David Kubiak
Carl Leone
Wendy Leo
Lise Marx
Susan Redlich
Virginia Renick
Mary Robbins
Gretchen Roorbach
Dillon Scott
David Taylor
Richard Trubiano
Charles River Watershed Association
Mystic River Coalition
Neponset River Watershed Association
Charles River Watershed Association
Karen-Jayne Dodge
Eric Endlich (Charles and Mystic Rivers, birds)
Joseph Ingoldsby (Neponset River)
Robert Michelson (Wildlife)
Regina Villa, Inc.
Cover photo: Great blue heron at dawn in the
Charles River, by Eric Endlich
P R E PA R E D B Y
E D I T E D B Y
D E S I G N
G R A P H I C S
G I S
C O N T R I B U T O R S
P H O T O S
A C K N O W L E D G E M E N T S

Tables & Figures 
W H E R E T O F I N D 
F I G U R E S
Figure 1. Bacteria levels in Deer Island effluent
Figure 2. The percent of days advisories against swimming were posted
Figure 3. Metals in MWRA treatment plant discharges to Boston Harbor
Figure 4. Mercury levels in the tissue of flounder caught near Deer Island
Figure 5. Levels of PAHs in mussels near Deer Island
Figure 6. PCBs in winter flounder caught near Deer Island
Figure 7. Decrease in flounder liver disease since the 1980’s
Figure 8. MWRA solids discharges to Boston Harbor
Figure 9. Fecal coliform levels at east Nut Island outfall
Figure 10. Water clarity at Nut Island
Figure 11. The MWRA Sewer System
Figure 12. MWRA Interceptor Projects
Figure 13. CSO control efforts reduce overflows
Figure 14. Overall fecal coliform levels in Boston Harbor and tributary rivers
Figure 15. MWRA long-term plan for CSO control
Figure 16. Schematic of CSO planning process
Figure 17. Sources of bacteria to the Neponset River and South Dorchester Bay
Figure 18. The reduction of active CSO outfalls between 1988 and 2008
Figure 19A. Computer model of water quality after moderate rainstorm, 1998
Figure 19B. Computer model of water quality after moderate rainstorm, 2008
Figure 20. A sanitary sewer overflow (SSO) 
Executive Director’s Note
Part One 
Update on Boston Harbor 
Part Two -
Beyond the Boston Harbor Project 
MWRA Sewer System Overview
MWRA Interceptor Projects in Four River Basins
Controlling Combined Sewer Overflows 
Future Challenges
References & Web Sites 
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Contents . . . 
TA B L E
Table 1. Timeline of MWRA projects and changes in beach water quality
Table 2. Nine Minimum Controls: national CSO policy
Table 3. MWRA CSO treatment facilities
T A B L E O F
PA G E
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PA G E
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With the Boston Harbor Project nearly complete, the new treatment plant is removing most solids and
toxic chemicals from the effluent. The effluent is being properly disinfected; bacteria levels in Deer
Island Treatment Plant effluent are usually better than standards set to protect water quality. Over the
past five years, as MWRA projects have come on-line, there have been corresponding improvements in
the harbor’s water quality. Advisories against swimming at most Boston Harbor beaches have declined.
Flounder liver disease and contamination in mussels have been dropping for a decade.
E X E C U T I V E D I R E C T O R ’ S N O T E
BEYOND THE BOSTON HARBOR PROJECT 
The waters at the former Nut Island sewage
outfalls in Quincy Bay are dramatically
cleaner since the Nut Island Treatment Plant
was closed in July 1998 after 46 years in
operation. South System sewage from 21
communities is now piped to Deer Island
through the 5-mile Inter-Island Tunnel.
Bacterial water quality in the Nut Island area
is now excellent. In the long-term, seagrass-
es are expected to return to Quincy and
Hingham Bays, a sign of a healthy ecosys-
tem.
Although the Boston Harbor Project is
MWRA's highest profile project, sewage
treatment plants, old or new, have never
been the only source of pollution to the area
waters. Leaking and overburdened pipes overflow into rivers,
ponds, and the harbor, especially during heavy rainstorms.
MWRA's Combined Sewer Overflow Plan will eliminate, treat,
or reduce combined sewer overflows (CSOs). In 2008 when
the CSO Plan has been completed, more than one-third of the
original 88 CSO outfalls will have been closed. MWRA is
repairing and replacing critical parts of
the aging sewer interceptor system with
other construction projects throughout
the metropolitan Boston area, alleviating
sewer backups into streets and build-
ings, and minimizing overflows into
rivers, streams, and wetlands.
Although these essential engineering
and construction projects are being com-
pleted, major challenges remain: reduc-
ing stormwater pollution, which contin-
ues to be a significant source of contam-
ination to our waterways, and alleviating
sanitary sewer overflows (SSOs). An
Infiltration and Inflow Task Force is
developing regional goals and strategies
to reduce groundwater and stormwater impacts on overbur-
dened sewers. Communities will certainly have to continue to
allocate resources to maintain and improve local storm
drainage and sewer systems to ensure that our waterways
are beautiful, safe for recreation, and healthy for aquatic life. 
I

ver the past decade, MWRA has dra-
matically cut discharges of wastewater
pollutants to Boston Harbor. This
Harbor Update continues reporting from
previous years by charting three pollutants in
MWRA's wastewater discharges: bacteria, metals,
and solids. The environmental effects of these pollu-
tants are also tracked, using swimmers’ advisory
statistics, disease incidence in fish, and levels of
contamination in fish and shellfish.
As pollution discharges to the harbor decrease,
measures of the health of the harbor show its
recovery. Figure 1 shows that the Deer Island
Treatment Plant (DITP) has continued to maintain
effective disinfection since 1994. There were only
seven days in 1998 and nine days in 1997 when
DITP effluent did not meet the water quality stan-
dard for bacteria counts, compared with 139 days in
1988.
One major concern about waste-
water bacteria is the possibility
that beaches will be con-
taminated, presenting
health threats to swim-
mers. There are, however, multiple causes of bacte-
rial beach contamination in the harbor, and the
causes vary among beaches. Combined sewer
overflows (CSOs) remain a problem at some beach-
es, but CSOs on beaches will be eliminated as part
of MWRA's CSO Plan. Contaminated stormwater
causes problems at Constitution, Wollaston, and
Tenean Beaches.
The number of advisories against swimming at
harbor beaches, which was high in the 1980’s and
decreased into the 1990’s, generally reflects the
varying performance of the local and regional sewer
and stormwater systems during those years.
Figure 2 shows the percent of days that water
samples failed to meet swimming standards at eight
Boston Harbor beaches during four multi-year time
periods. (Data from the
Metropolitan District
Commission beach monitoring program.) These
time periods broadly reflect different phases of the
modernization of greater Boston’s sewage and
stormwater infrastructure (Table 1). Contaminated
stormwater (the responsibility of local communities),
CSOs, neglected and malfunctioning treatment
plants, and sludge discharges in past years
have all affected the harbor’s beaches to
varying degrees.
Figure 3 shows that metals have 
Boston Harbor Boston Harbor 
U P D A T E O N 
FIGURE 1. Bacteria levels in Deer Island effluent
now rarely fail the water quality standard of 200
fecal coliform per/100 ml 
O O 
A colony of harbor seals has returned to Calf Island
in Boston’s Outer Harbor.
2

1973-1980
1981-1985
1986-1991
1992-1997 
FIGURE 2. The percent of days advisories against swimming were posted at Boston
Harbor beaches, averaged within four time periods. These time periods parallel phas-
es of upgrades to MWRA’s sewage infrastructure. After 1985, the effects of MWRA
projects are reflected in fewer beach postings. A challenge to communities remains:
addressing contaminated stormwater runoff to beaches, which is still a major source
of beach pollution.
TABLE 1. Timeline of MWRA projects and changes in beach water quality. 
Time Period System Condition
Average % of Water
Samples Failing Swim
Standards
Generally less than
20%.
More than 20% to 30%
at several beaches.
Swimmers’ advisories
still occur more than
20% to 30%
of the time
at several
beaches.
Swimmers’ advisories
decline to less than
20%, except at
Wollaston Beach.
Treatment plant at Deer Island
commissioned in 1968.
Sewage facilities deteriorated due to
underfunding and neglect.
MWRA created (1985).
Early upgrades repair the old treatment
plants so they function as designed.
CSO treatment facilities completed in
southern Dorchester Bay (1990).
Improved maintenance of tidegates on
CSOs.
Sludge discharges from the treatment
plants end (1991).
New pumps at Deer island (1995).
New primary treatment plant at Deer
Island (1995).
Secondary treatment begins at
Deer Island (1997).
Communities aggressively
repair illegal sewer
connections to storm
drains.
3

FIGURE 4. Mercury levels in the tissue of
flounder caught near Deer Island have been
well below the FDA limit of 1,000 parts per
billion. Mercury levels have decreased sig-
nificantly since the late 1980’s. 
FIGURE 5. Levels of PAHs in mussels near
Deer Island have remained low since 1993. 
FIGURE 3. Metals in MWRA treatment plant
discharges to Boston Harbor have declined
dramatically since 1989.
Winter flounder live in
close contact with the sea
floor, and are exposed to
contaminants that
concentrate in sediments. 
Juvenile blue mussels 
declined to less than half the levels discharged in
1989. Industries responding to MWRA’s Toxic
Reduction and Control Program (TRAC) have suc-
ceeded in significantly reducing inputs of toxic
metals to the wastewater treatment system.
Secondary treatment since 1997 at the new
DITP has been removing more toxic metals than
did primary treatment alone. When the final bat-
tery of secondary treatment is completed in 2000,
metals discharges will be reduced even more.
TRAC has also focused on reducing levels of
mercury in wastewater,
because a common reason for advisories against
fish consumption is mercury levels found in fish
tissue. Levels of mercury in flounder caught near
Deer Island have consistently remained well under
the FDA limit of 1,000 parts per billion (Figure 4).
Mercury levels in flounder are less than half of
what they were in 1996.
Discharges from the treatment plants of toxic
organic chemicals like polynuclear aromatic hydro-
carbons (PAHs) and polychlorinated bi-phenyls
(PCBs) have also decreased. Levels of these toxic
chemicals found in the tissue 
4

of two indicator species—blue mussels (Figure 5)
and winter flounder (Figure 6)—have fallen since
the late 1980’s. Liver tumors and liver disease in
winter flounder are also at relatively low levels com-
pared with levels in the late 1980's (Figure 7).
A major milestone in the Boston Harbor
Project was achieved in July 1998 when
discharges from the Nut Island
Treatment Plant (NITP) in Quincy
ended. Until then, approximately
100 million gallons per day of
sewage from MWRA’s South
System received only primary treat-
ment at NITP before being discharged
into Quincy and Hingham Bays. Now,
sewage slicks in Quincy Bay are gone; South
System flows pass through the Inter-Island Tunnel
deep below the harbor floor to receive secondary
treatment at DITP. Figure 8 shows the resulting
dramatic decrease in treatment plant solids dis-
charged to the harbor in 1998, continuing a 10-year
trend.
Water quality improvements in the former NITP
outfall area were immediate—the three visible efflu-
ent plumes and sewage odors disappeared. The
risk of exposure to bacteria and viruses around the
plumes is gone; Figure 9 shows that bacteria levels
in nearby water have stayed very low since
the discharge ended. Figure 10 shows
that water clarity in the former dis-
charge area, usually at its worst
(about one to two meters deep) in
mid-summer, continued to improve
rapidly to three to four meters dur-
ing the summer of 1998.
Ultimately, removal of the ecosys-
tem stress caused by the NITP dis-
charges will permit a healthier marine com-
munity to develop. Effects of the discharges near
Nut Island of solids, nutrients, and toxic contami-
nants have developed over a century and will take
years to reverse.
Although most of the solids discharged from
NITP were flushed out of the harbor by tidal cur- 
FIGURE 7. Decrease in flounder liver disease since the 1980’s. 
FIGURE 6. PCBs in winter flounder (fillet) caught
near Deer Island. Levels have greatly decreased
since the mid-to-late 1980’s. 
Seagulls feed
on sewage slick
near Nut Island
discharge,
1985. 
5 
FIGURE 8. MWRA solids discharges to Boston Harbor.

Although most of the solids discharged from
NITP were flushed out of the harbor by tidal cur-
rents, about 1,100 tons of solids per year
entered Hingham Bay and about 500 tons of
solids per year entered Quincy Bay. Free from
these pollutants in the future, Hingham Bay and
Quincy Bay should be clearer in summer, with
less green algal growth. Bottom-dwelling animal
communities near the outfall areas should flour-
ish as they recover from the effects of accumu-
lated organic matter and toxic contaminants.
Beds of tiny, shrimp-like Ampelisca, which natural-
ly biofilter the water and increase the oxygen in
the sediment, could spread into Quincy Bay, as
they have recently expanded elsewhere in
Boston Harbor.
Over the longer term, seagrasses, which
once covered much of the harbor floor, will likely
return to Quincy and Hingham Bays.
Seagrasses serve as nurseries for many fish
and other marine animals, and also stabilize the
bottom sediments with their root systems and
help keep the water clear. Seagrass beds are
key indicators of a healthy harbor.
Although the volume of DITP effluent dis-
charged to the North Harbor has increased tem-
porarily until the new 9-mile effluent outfall tun-
nel is in use, most of the effluent is receiving
secondary treatment. MWRA monitoring data
indicate that the environmental benefits from
closing NITP and providing secondary treatment
for South System flows are greater than the
effects from the temporary increase in dis-
charges to the harbor near Deer Island. 
GURE 10. Water clarity at Nut Island improved 84% after
wastewater discharges there ended in July 1998. As
measured by the depth at which a submerged white
disk (secchi disk) is no longer visible, the average June-
to-December water clarity at Nut Island was between
one and two meters until July, when it increased to
about three meters until year-end. 
FIGURE 9. Fecal coliform levels at east Nut Island
outfall. There were no violations of water quality
standards in 1998 in the former Nut Island outfall area
after discharges ended in July 1998. 
MWRA Harbor
sampling crew
Seagrasses provide habitat
for communities of small
animals like tiny snails
and juvenile fish.
Seagrasses provide habitat
for communities of small
animals like tiny snails
and juvenile fish. 
6 MWRA Harbor
sampling crew

MWRA’S REGIONAL WASTEWATER SYSTEM 
The MWRA sewer system (Figure 11) is a net-
work of large, regional sewers (interceptors) that
collect sewage flows from local communities for
conveyance to the Deer Island Treatment Plant
(DITP) through MWRA-operated pump stations and
headworks. The Fore River sludge-to-fertilizer plant
then processes material removed from the sewage
at DITP. Decades ago, before the regional system
was built, local pipes discharged sewage into the
nearest body of water. Rivers and streams became
fouled as populations grew and the amount of
waste increased. Beginning in the mid-nineteenth
century, regional interceptors were built along the
rivers to transport the sewage from local sewers for
discharge to Boston Harbor. This regional system
was taken over by MWRA in 1985.
MWRA’s North System is built along the water
courses of the Charles River and the Mystic River
and its tributaries. The North System collects sewage
from Boston, Cambridge, and 23 other cities
and towns.
The South System follows the Charles,
Neponset, Fore, and other river courses, col-
lecting sewage from 21 communities includ-
ing most of Boston.
Local sewer pipes and pumping stations
are owned, maintained, and operated by indi-
vidual cities and towns, not MWRA. 
HOW SEWAGE GETS TO THE TREATMENT
PLANT 
Wastewater flows from local pipes through
MWRA interceptors to MWRA headworks
facilities. At the headworks, large objects
are screened out and grit is removed. From
the headworks, sewage flows under Boston
Harbor to DITP through three main tunnels,
and then is lifted by large pumps into the
treatment plant for pollutant removal, disin-
fection, and discharge into the harbor.
The discharge to the harbor will stop
when all flows are discharged through the
new outfall and diffuser system into the
deeper waters of Massachusetts Bay. (For
detailed information on this outfall, see the
1996 State of Boston Harbor report). 
Sewer System
Overview 
M W R A 
Over the course of 150 years, a large and complex sewage infrastructure has
been built to transport and treat Greater Boston’s wastewater. 
8

Sludge removed at DITP during treatment is barged to the Fore River
Sludge-to-Fertilizer Plant to be converted to fertilizer. 
MWRA SEWER IMPROVEMENT PROJECTS 
In 1994, MWRA prepared a System Master Plan which included an inte-
grated, system-wide approach to wastewater treatment, wastewater con-
veyance through the interceptors, and combined sewer overflow manage-
ment and remediation. The System Master Plan considered all manner of
system improvements, including the benefits of increased pumping at DITP,
in order to determine the best ways to reduce overflow and address other
sewer capacity and efficiency issues. The next two sections of this report
describe major engineering and construction efforts on the part of MWRA
and its sewer communities to modernize the sewer system. 
FIGURE 11. The
MWRA Sewer System
9 
Drainage & Sewerage: 
DRAINAGE SYSTEMS divert rainfall and snowmelt that would otherwise
create flooding in streets and buildings. Gutters, catchment basins, storm
drain pipes, and culverts serve to carry stormwater runoff to a nearby body
of water.
As more people moved into the Boston area, land that normally drained into
wetlands and streams was developed and paved over, resulting in local flood-
ing problems. Communities had to create a system of artificial drainage to
meet the needs of a growing population and changing land use. 
SEWER SYSTEMS transport residential and industrial wastewater to treat-
ment facilities. More than a century ago, Boston became one of the first
American cities to build regional sewer systems to dispose of residential and
industrial waste.
Today, MWRA owns and manages regional sewage transport and treatment
facilities that connect to local systems. Local municipalities are responsible
for providing effective drainage systems in their areas, and operating local
sewage collection systems.

I N F O U R R I V E R B A S I N S 
Interceptor Projects 
M W R A 
In the Neponset River Basin
In the Charles River Basin 
Framingham
Extension Relief
Sewer: The 40-year-
old Framingham
Extension Sewer (FES)
receives flow from
Framingham, Ashland,
and Natick. This
interceptor did not
have the capacity to
contain the volume of
flow it received dur-
ing heavy storms, or
to serve future
sewage needs. The
$52 million
Framingham
Extension Relief
Sewer project included construction of additional
pipeline and a new pump station, providing addi-
tional capacity for the FES system.
Wellesley Extension Sewer Replacement: The exist-
ing interceptors, more than 75 years old, run along
the Charles River, serving the towns of Needham,
Wellesley, and Dedham. Overflows into the river
endangered Needham's drinking water supply and
the Elm Bank Aquifer in Dover. This $72 million
project, nearly complete, replaces part of the sys-
tem and rehabilitates and relines the remaining
old sewer.
Upper Neponset Valley Relief Sewer Project: As
the northernmost portion of the aging sewer lies
within the Charles Watershed, backups and over-
flows to the Charles River do occur. Construction of
a new relief interceptor will reduce backups and
overflows. 
Charles River Watershed
Association volunteer
Bill Tedoldi samples in the
Charles River. 
Interceptors are MWRA's large, regional sewers that receive sewage from smaller, local
systems. MWRA owns 240 miles of interceptors and several pumping stations that collect
and transport wastewater from local sewer systems to the Deer Island Treatment Plant.
Some interceptors were built more than a century ago, and are deteriorating because of
age. Increased land development in the suburbs of Boston over the past decade has creat-
ed more demands on the interceptor system. In extremely wet weather, sewage can back
up into streets and buildings. Because most interceptors are located in river valleys, over-
flows can contaminate rivers and streams. Leaking pipes and illegal storm drain connec-
tions to the sewer system contribute to the problem. To minimize sewer overflows, MWRA is
increasing the capacity of its interceptor system; between 1990 and 2002, more than $400
million is being invested to construct, enlarge, and rehabilitate interceptors and pumping
stations throughout the service area. Approximately 56 miles of interceptors will be either
newly constructed or rehabilitated, improving water quality throughout the Boston Harbor
watershed (Figure 12). An additional $100 million is being invested in rehabilitation of locally
owned collection systems to reduce Infiltration and Inflow (see page 22). 
The New Neponset Valley Relief Sewer: Structural and hydraulic deficiencies in the old
interceptor caused sewer overflows into Fowl Meadow (in Canton, Norwood, and parts of
Milton) and threatened the water supply for Canton, Dedham, and Westwood. A new sewer
and a pumping station were constructed to alleviate these problems. The increased capac-
ity will enable MWRA to serve an increasing population as many people now using septic
systems will convert to sewer service.
The Neponset Valley Sewer Project: This project is in the planning stage, where the need
for new construction or rehabilitation of the interceptor—which in some places is more
than 100 years old—is being evaluated.
10 
The Neponset Salt Marsh

Braintree-Weymouth Interceptor:
Together, the Braintree-Weymouth
Interceptor, Relief Sewers, and Relief
Tunnel will have the capacity and addi-
tional flexibility to handle peak wet-
weather flows, alleviating surcharging
and overflows into Smelt Brook.
Two New Pumping Stations:
The new Intermediate Pump Station
and Headworks in North Weymouth will
pump sewage to the Inter-Island Tunnel.
The existing Braintree-Weymouth pump
station will be replaced by a smaller,
modern station. The combined capacity
of the two new stations will be 50%
greater than that of the existing sta-
tion.
Relief Sewers: New sewers will be con-
structed from the Idlewell section of
North Weymouth to the Intermediate
Pump Station.
Relief Tunnel: Twelve feet in diameter,
this new tunnel will be bored through
bedrock 250 feet underground. It will
run from the Fore River Sludge-to-
Fertilizer (“pelletizing”) Plant, under
the Fore River to the Intermediate
Pump Station in North Weymouth. This
new tunnel will carry wastewater to the
Inter-Island Tunnel for treatment at
Deer Island. Inside the Inter-Island
Tunnel and the Braintree Relief Tunnel,
two smaller pipes will carry sludge from
Deer Island to the pelletizing plant. 
In the Fore River Basin: Braintree-Weymouth Relief Facilities
In the Mystic River Basin 
North Metropolitan Trunk Sewer Rehabilitation. This
large 100-year-old brick interceptor carries sewage from
East Boston, Chelsea, Revere, and Winthrop to the Deer
Island Treatment Plant. Because the inside of the pipe
had deteriorated, the entire sewer has been patched
and relined. These pipe repairs will prevent leaking and
ensure reliable flow of wastewater to Deer Island.
Cummingsville Replacement Sewer. The Cummingsville
Branch Sewer is a 100-year-old interceptor system in
Winchester. Insufficient capacity in the old system may
be the cause of upstream sewer overflows into the local
drinking water supply—Horn Pond in Woburn. The $4 million project includes con-
struction of a new sewer and rehabilitation of an existing sewer.
System Master Plan Interceptor Projects. Five interceptor projects are planned to
increase the capacity of the system during wet weather; four of these projects are
in the Mystic Basin. The projects will increase the size and/or add additional sewer
pipes to parts of the system that contribute to sewer overflows: the Mystic Valley
Sewer, the Malden Branch Sewer, the Revere Branch Sewer and the Cambridge
Branch Sewer. 
Great blue heron fish in the
Mystic River 
11 
Woburn
Stoneham
Reading
Winchester Melrose
Lexington
Arlington
Waltham Belmont
Watertown
Newton
Malden
Medford
Everett
Chelsea
Somerville
Cambridge Winthrop
Brookline
Boston
Quincy
Milton
Dedham
Needham
Wellesley
Westwood Braintree
Randolph
H
Weymouth
Holbrook
Norwood
Canton
Stoughton
Walpole
Natick
Medfield
Revere
Framingham Extension Relief Sewer
Upper Neponset
Relief Sewer
Neponset
Valley Sewer 
Wellesley Extension Sewer
New Neponset
Valley Relief
Sewer
Braintree-Weymouth
Relief Sewer
North Metropolitan
Trunk Sewer
Cumminngsville Replacment
Sewer
System Master Plan:
Mystic Valley Sewer
Replacement
System Master Plan:
Malden Branch
Cambridge Branch and
Revere Branch
Squantum
Force Main
Quincy
Force Main
High
Level
Sewe
r
Ba
ck R
iver 
My
stic Riv
er 
We
ir R
ive r
Monatiquo
t Riv
e
r
Neponset Ri
ver
Charles Riv
er
Charles
River 
MWRA Interceptor Projects
in the Boston Harbor Watershed

Combined Sewer Overflows Combined Sewer Overflows 
C O N T R O L L I N G 
Combined Sewer Overflow (CSO):
1 . Outfall in a combined sewer system
that by design releases
stormwater and sewage into
receiving waters during storms in
order to avoid sewage backups
into homes and streets.
2 . The combined stormwater and
sewage discharged from a CSO
outfall. 
Control of CSOs is reducing the
risk of waterborne disease in
the Charles River. 
Like many other older areas in cities across America,
large parts of Boston, Cambridge, Somerville, and
Chelsea have combined sewer systems.
Combined sewers were engineered to
merge drainage and sewage pipes in
a single system. The pipes that
normally carry sewage every day
also convey stormwater runoff in
wet and rainy weather. During
heavy rains, because of the limit-
ed capacities of the interceptors
and tunnels, combined sewers can
become filled with more stormwater and
sewage than can be carried all the way to the
Deer Island Treatment Plant (DITP) for treatment and
discharge. Therefore, to prevent combined sewage from
backing up into streets and buildings, combined sewer
systems were designed to discharge overflow volumes
to the Neponset River, Charles River, Mystic River,
Alewife Brook, and Boston Harbor through 88
CSO outfalls. Throughout the 1970’s and early
1980’s, discharges of these contaminated
flows from CSOs posed a potential health
threat to swimmers and recreational boaters,
as well as to consumers of locally caught
shellfish. Indeed, because of system neglect
and deterioration, there were times and locations
where combined sewers overflowed even in dry
weather! 
12

A DECADE OF SEWER SYSTEM UPGRADES
REDUCED OVERFLOWS 70% 
In 1987, MWRA agreed to plan and build
projects to control CSOs in its sewer com-
munities. While planning for the larger CSO
construction projects was underway, MWRA
and the communities with combined sewers
implemented many smaller projects, empha-
sizing better maintenance and optimizing the
sewer system. These projects helped to
reduce CSO volumes and activations by
directing more flow to Deer Island for treat-
ment. Many of these so-called “System
Optimization Projects” mirrored the require-
ments of the U.S EPA’s Nine Minimum
Controls contained in the National CSO
Control Policy shown in Table 2 (EPA, 1994).
Routine maintenance activities like making
sure tidegates are working properly or
sweeping streets to prevent trash from
entering the sewer system also proved to be
effective and inexpensive ways to reduce
frequencies and volumes of overflows and
their impacts. Furthermore, improved pump-
ing at DITP and increases in sewage trans-
port capacity resulted in significant CSO
reduction (Figure 13). 
1- Proper operation and regular maintenance programs 
2- Maximization of storage in the collection system 
3- Review and modification of pretreatment requirements 
4- Maximization of flow to the treatment plant 
5- Elimination of CSOs in dry weather 
6- Control of solid and floatable materials in CSOs 
7- Pollution prevention program to reduce contaminants in CSOs 
8- Public Notification 
9- Monitoring to characterize CSO impacts and the efficacy of
CSO controls 
TABLE 2. NINE MINIMUM CONTROLS: NATIONAL CSO POLICY 
MWRA has fully complied with EPA’s nine minimum controls.
0
1
2
3
4 1989
3.3 billion gallons
1992
1.5 billion gallons
51% treated 1997
1.0 billion gallons
58% treated
2008
0.4 billion gallons
95% treated
Achievement of Nine
Minimum Controls, System
Optimization Projects,CSO
Treatment Facilities,and
Full Deer Island
Pumping Capacity
1998-2008
Implementation of 25
CSO Plan Projects
1988-1997
Implementation of small-scale
CSO controls
Completion of
Long-Term
CSO Plan Projects
Annual Overflow Volume (Billion Gallons)
FIGURE 13. CSO control efforts reduce overflows dramatically, as
shown by a computer model; most remaining CSO flow will be treat-
ed by 2008.
13 
Examples of 
projects that optimized the
sewer system 
• The single most important
improvement that reduced
CSOs was the installation of
new sewage pumps at the
Deer Island Treatment Plant.
Because more sewage can be
pumped to the plant for
treatment, CSO volume has
been reduced by more than
50 percent.
• Some CSOs that rarely over-
flowed were simply blocked
off and eliminated.
• The pre-flow capacities of
many individual sewer lines
were increased by raising the
height of weirs — small dams
inside the sewer pipes —
that assure diversion of flow
toward a plant and away
from the overflow pipes.
• Small sewer separation
projects eliminated several
CSOs.
• New tidegates were installed
to keep seawater from back-
ing into the sewers and
drains at high tide. The
excess water was reducing
the sewers’ capacity for
handling sewage.

( 
Another approach to CSO control is to provide facilities that screen and disinfect
overflows that occur relatively frequently. The oldest CSO treatment facility now owned
by MWRA, at Cottage Farm near the B.U. Bridge on the Charles River, was originally
constructed in 1971. Five other facilities (see Table 3) were placed in operation in the
1980-1990 period. Upgrades have been completed or planned for five CSO facilities
including a $5.8 million project at Cottage Farm to improve disinfection and to dechlori-
nate the discharge before it enters the river. However, three of the five facilities will
eventually be decommissioned when separate sewers and storm drains are construct-
ed.
To date, the cumulative effect of improvements resulting in increased pumping at
Deer Island, physical and management changes to the CSOs themselves, and
upgrades of the CSO treatment facilities, is that the volume of CSO decreased from
3.3 billion gallons per year in 1987 to one billion gallons per year in 1997, and more
than half of the discharges are now treated. The water quality of Boston Harbor and its
tributary rivers has improved as a result: fecal coliform bacteria levels in the water are
about 35% lower than before these CSO projects were implemented (Figure 14). 
MWRA’S LONG-TERM CSO CONTROL PLAN 
The CSO improvements made thus far are significant, but they are only the begin-
ning. Figure 15 illustrates the 25 projects that make up MWRA’s CSO Plan. The Plan
includes upgrading existing CSO treatment facilities, building new treatment facilities,
and constructing large conduits to store and transport combined sewage. In some
areas, new, separate sewers and storm drains will be built so that the sewage can be
carried to Deer Island and storm runoff can flow to the rivers or harbor. After imple-
mentation, 36 of the original 88 CSOs will have been eliminated, including all CSOs
near beaches or shellfish beds. The remaining CSO discharges will be minimized to
four or fewer per year, or treated. If
other sources of pollution—espe-
cially contaminated stormwater
runoff are controlled, the harbor
and rivers will be able to meet
water quality standards virtually all
the time. 
0
30
60
90
120
150
92-96 89-91
Average (geometric mean)
fecal coliform count/100 ml FIGURE 14. Overall
fecal coliform levels
in Boston Harbor and
tributary rivers over
the past five years
are 35% lower than
in the period 1989-
91. The statistical
analysis accounts for
differences in rain-
fall.
(Gong et al, 1998).
FACILITY
Commercial Point
Fox Point
Prison Point
Constitution Beach
Somerville Marginal
Cottage Farm
BUILT
1990
1988
1988
1986
1980
1971
CSO PLAN
Upgrade 2001
Decommission 2008
Upgrade 2001
Decommission 2008
Upgrade 2000
Decommission 2000
Upgrade 2001
Upgrade 1999
TABLE 3. MWRA CSO Treatment Facilities
LOCATION OF
DISCHARGE
South Dorchester Bay
South Dorchester Bay,
Savin Hill Cove
Inner Harbor at Charles
River confluence
Winthrop Bay,
Constitution Beach
Inner Harbor at Mystic
River confluence
Charles River 
Computer modeling the effects of
Combined Sewer Overflows (CSOs) 
14
MWRA has used computer models to evaluate methods of CSO
control. The sewer systems in communities with CSOs were
modeled; the water quality of the river and harbor locations
to which CSOs discharge (the “receiving water”) were also
modeled. The sewer model used system characteristics and
land use data to calculate how different amounts of rain
affect CSO flow. The water quality model used information
about the shape, depth, tides, and currents of the harbor and
rivers to calculate the effects of CSOs on water quality.
The impact on receiving waters of a moderate storm (1.89
inches of rain in 21 hours) and a severe storm (2.79 inches of
rain in 22 hours) were simulated.
By running the models with different CSO control measures,
MWRA can compare the water quality benefits of various CSO-
control approaches to determine the most cost-beneficial
solution.

¥.... Cambridge and

pomemile storm grains
sewers separa'
Alewife Brook meets
water quality standards
95.6% of time.

®

Hydraulic relief reduces
overflows in the etl
Charles; water
standards met 98.9%

of time.

Upgrades to Cottage Farm
Treatment Facility improve

disinfection.
ie
Sewer separation reduces Jf

Charles River via Stony Brooksfrom
23 to 2 per year.

LEGEND
@ Treated combined sewer outfall

© Minimized combined sewer outfall
© 50 outfall closed by 2008

A Existing C50 Facility to be upgraded

Existing CSO Treatment Facility to
L\ de upgraded, and/or eliminated

A Planned new C50 Treatment Facility

‘= Planned conduit or pipeline project

Planned area for construction of
"Separate sewers and stormdrains
4

Swimming beach

Upper Mystic River 2
remaining flow to Some!
icitity

Upgrades to Somerville

Marginal Treatment

Facility; water quality
met 97.8%

standards met
of time.

© Harbor: standards
© met 99% of the timeé=

Fort Point Channel Conduit
and new Union Park
Disinfection Facility stores

and treats CSOs. Standards
met 98.5% of time. A

aa

CSOs and much stormwater discharge eliminated PF /
along South Boston beaches by new North f
Dorchester Bay Conduit, flow is treated ~a 5

at Reserved Channel Facility

Be%

a
ee

Construction of
‘eliminate combine
‘to Neponset R

Bay. Interim FoxiPoint
Point CSO Facilities

FIGURE 15.

MWRA LONG TERM
PLAN FOR CSO
CONTROL TO
IMPROVE WATER
QUALITY

outfalls:
‘to a minimal number of discharges

will be CLOSED
CSOs eliminated in swimming and shellfishing areas.
Remaining untreated CSOs comply with new water
| quality standards,
Frequent discharges treated.

For 25 projects:
Planning, design and construction $500 million.
Annual operation and maintenance $1.1 million.

Construction on some projects began in 1996,
| completion of all projects is scheduled for 2008.

THE CSO PLANNING PROCESS 
Rather than using a single engineering solution to
CSO control, MWRA's CSO Plan is an example of
watershed-based planning. This approach tailors
CSO control strategies to the uses of each water-
body and the sources and types of pollution it
receives. Water quality goals, available technologies,
costs, and siting constraints were all considered
(Figure 16). As part of the planning process, a series
of workshops evaluated different strategies for con-
trolling CSOs. Workshop participants included
MWRA and its engineering consultant, public works
professionals from the CSO communities, interested
citizens, state and federal regulatory agencies, envi-
ronmental organizations, MWRA’s Wastewater
Advisory Committee, and the MWRA Advisory Board.
Neighborhood groups including local residents,
environmentalists, and elected officials commented
on specific CSO alternatives. Community meetings at
major milestones in the planning process helped
shape the decision-making for the
Plan. Recommendations for CSO
control in three types of water bod-
ies, South Dorchester Bay, Fort
Point Channel, and the Charles River show how
watershed-based planning is tailored for different
locations. 
1. South Dorchester Bay plan: elimination of CSOs 
This bay is a very important recreational area, with
three beaches (Malibu, Savin Hill, and Tenean). Soft-
shell clams are abundant here, but are too contami-
nated with bacteria to harvest. Recreational boating
is also popular; several yacht clubs are located in the
area.
Four CSO outfalls and several large stormwater
drains rim the shoreline (see Figure 15). Stormwater,
contamination from the Neponset River, and CSOs
are the main sources of bacterial contamination to
this bay during heavy rainstorms. However, water
quality is generally good during dry weather.
The CSO Plan includes elimination of CSOs in this
sensitive shellfishing and swimming area. Two exist-
ing CSO treatment facilities (Fox Point and
Commercial Point) are being upgraded. Then, exten-
sive work to construct separate storm drainage and
sewer systems will eliminate all CSOs to this area. To
fully benefit from this construction, it will be important
for communities to address the problem of contami-
nated stormwater, where most bacterial contamina-
tion comes from. (Figure 17). 
PERFORM BASELINE WATER QUALITY
ASSESSMENTS
Identify water quality standards.
Identify and assess beneficial uses.
Identify causes of non-attainment
and determine relative contribu-
tion of CSOs.
Define CSO flows, loads, and out-
fall activations.
DEVELOP & SCREEN CSO CONTROL
ALTERNATIVES
Develop CSO control alternatives to
achieve CSO control goals.
Use computer modeling to evaluate
performance.
Screen alternatives using rating criteria
for cost, benefit, construction and envi-
ronmental impacts, and public accept-
ance.
ESTABLISH GOALS
Develop a range of water quality
goals.
Define CSO control goals.
RECOMMEND CSO
CONTROL PLAN
Select CSO control
alternatives for
each receiving
water segment.
Combine alternatives
into a system-wide
control plan.
DEVELOP & EVALUATE SYSTEM-WIDE
STRATEGIES
Develop combinations of CSO control
alternatives for the entire system.
Define cost, performance, water quality
impacts, and siting issues.
Evaluate CSO alternatives using numerical
rating criteria for cost, water quality
improvement, and siting constraints.
FIGURE 16. Schematic of
CSO Planning Process
16 
The goal of the CSO Plan is to
eliminate CSOs at Boston Harbor
beaches.

2. Fort Point Channel: treatment of CSOs 
Fort Point Channel in the Inner Harbor is
a long, narrow, artificially channelized
embayment with granite walls. Surrounding
the channel is a heavily urbanized area.
Restaurants, offices, and the Children’s
Museum are nearby. So are a major high-
way interchange now under construction, a
railway yard, the world’s largest razor blade
factory, the new federal courthouse, a large
hotel, and a ferry pier. Walkways and
bridges serve pedestrian traffic to the
waterfront, where people enjoy the open
space and harbor views. Small recreational
boats use the channel.
The channel is severely polluted by the
largest amount of untreated CSO in the
entire system; more than eight million gal-
lons are discharged from a large outfall at
the head of the channel in a moderate
storm, and 26 million gallons during a
severe storm. Six smaller CSOs line the
channel. After rainstorms, it is common for
bacteria levels to exceed the boating stan-
dard; unsightly sewage-related floating
materials sometimes can be seen in the
channel.
Plans to protect Fort Point Channel from
CSOs include construction of the Union
Park Detention and Treatment Facility and
the Fort Point Channel Storage Conduit.
Together, these projects will decrease the
volume of CSO and treat most of the
remaining discharge. During a moderate
storm, no untreated CSO will be dis-
charged; for a severe storm, 94% of the
discharge will be screened and disinfected.
Thus, the worst effects of CSO on Fort
Point Channel—bacterial contamination and
floating trash and sewage—will be largely
corrected. 
17 
CSO improvements to
heavily industrialized
Fort Point Channel
will include a new
treatment facility. 
0
10
20
30
40
50
60
70
80
Upstream
Storm water
Neponset River, 1997
0
5
10
15
20
25
30
South Dorchester Bay, 1997
Fecal coliform sources compared (trillions of bacteria)
CSO
CSO
Storm water 
FIGURE 17. Sources of bacteria to the
Neponset River and South Dorchester
Bay after a 3-month storm.
Stormwater and upstream flows are
the main source of bacteria. There
will be no CSO after the CSO Plan is
completed.

3. The Charles River: controlling
CSOs 
Because of MWRA improve-
ments in pumping, sewage trans-
port, and system maintenance, the
number and volume of CSOs in
the Charles River have dramatical-
ly decreased since 1987. Now, the
largest CSO source of fecal col-
iform bacteria to the lower Charles
is the Stony Brook outfall, and the
largest treated source of CSO is
MWRA’s Cottage Farm CSO
Treatment Facility (see Figure 15).
Projects to protect the Charles
outlined in the MWRA CSO Plan
(1) dramatically reduce CSOs to
the Stony Brook through separat-
ing storm and sanitary sewers; (2)
improve treatment of combined
sewage discharged at Cottage
Farm; and (3) dramatically
decrease the total number of CSO
discharges. After the Plan is com-
pleted, untreated CSO discharges
to the Charles will be rare and
small in volume. Nevertheless,
bacterial water quality is still pre-
dicted to violate boating and swim-
ming standards after heavy rain-
storms, mainly due to contaminat-
ed stormwater that enters the
river. Unless stormwater runoff is
cleaned up, the Lower Charles will
still fail to meet the boating stan-
dard after a severe storm. 
18 FIGURE 18. The reduction of active CSO outfalls between 1988 and 2008. 
The Charles River The Charles River

The 25 projects in the CSO Plan are now
scheduled to be completed by 2008. Thirty-
six outfalls will be closed (Figure 18), com-
pletely eliminating overflows at the most sen-
sitive areas—beaches and shellfish beds.
Elsewhere, CSOs will be reduced and treat-
ed so that water quality standards will be
met. 
WATER QUALITY IMPROVEMENTS 
Figures 19A and 19B show the results of
computer modeling of fecal coliform bacteria
levels in Boston Harbor and its tributary
rivers after rainstorms for the present and
future. Fecal coliform levels are shown one
day after the rainstorm, and both stormwater
and CSO sources of bacteria are included in
the model. The fecal coliform levels in the
water indicated by each color are described
in the legend. The red/yellow areas indicate
poorer water quality, where fecal coliform lev-
els are higher than allowed by state swim-
ming standards, and blue/green areas show
good water quality, within swimming stan-
dards. 
A CHALLENGE FOR THE CHARLES 
A two-year government study sponsored by MWRA,
EPA, and the Massachusetts Department of
Environmental Protection is measuring and modeling
the relative contributions of stormwater sources to
the Charles to help guide future pollution control
efforts. Urban stormwater is not clean, and is very dif-
ficult to control. Because of its high volume, stormwa-
ter can have a big impact on water quality, even with
low concentrations of pollutants. Use of best manage-
ment practices such as street sweeping, catch-basin
cleaning, and enforcing “pooper scooper” laws are
ways to help reduce stormwater pollution. The effec-
tiveness of these programs in helping to meet water
quality standards is yet to be determined. 
Stormwater Pollution: 
19 
The scenic
beauty of the
lower Charles
provides
respite from
city life.
The scenic
beauty of the
lower Charles
provides
respite from
city life.
River herring River herring

Present (1998) conditions: Figure 19A shows
modeled water quality after a moderate storm.
The three rivers (Charles, Mystic, and Neponset)
all fail to meet boating or swimming standards,
as do areas of the Inner Harbor, especially Fort
Point Channel. Near the shoreline, North
Dorchester Bay and Winthrop Bay fail to meet
the swimming standard. 
Future (2008) conditions: Figure 19B shows
model results for the moderate storm conditions
after the CSO Plan is fully implemented. The
model assumes no changes in the bacteria
inputs from current non-CSO sources such as
stormwater. The most dramatic change will be
in North Dorchester Bay, where the water quali-
ty will meet the highest standards. Most of
South Dorchester Bay and the Inner Harbor will
be within swimming standards, except for small
areas of Fort Point Channel and the Chelsea
River. However, other areas show little change
compared to 1998. In the areas that show rela-
tively little change, most of the bacterial con-
tamination is from stormwater discharges to the
area or from upstream (river water flowing
downstream into the study area).
Despite the highly controlled CSO discharges
called for in MWRA’s CSO Plan, river water
quality is still predicted to be poor after rain-
storms because of stormwater input. Although
stormwater is somewhat cleaner than CSO
flow, the large volume of stormwater entering
rivers significantly degrades water quality. 
20 
Walkers on new boardwalk at
Charles River, Watertown
Walkers on new boardwalk at
Charles River, Watertown
MWRA Harbor
sampling crew

his report has focused on MWRA’s engineering and
construction projects to control combined sewer over-
flows and to expand and repair MWRA’s regional sys-
tem of interceptors and pumping stations. Although less widely
known than the Boston Harbor Project, these improvements will
provide substantial benefits to water quality throughout the river
basins in greater Boston and in the harbor. However, even after
these projects are complete, significant challenges will remain if
the region is to realize all the potential water quality benefits of
these investments.
Since the Federal Clean Water Act of 1972, major efforts to
control water pollution have focused on regulation, engineering,
and construction to prevent or treat municipal and industrial
wastewater discharges. These solutions have worked well: water
bodies like Boston Harbor are showing the benefits of such
investments. However, as these sources have been controlled,
other sources of pollution have been revealed. These include
contaminated stormwater runoff—urban, rural, and residential;
sewage overflows in extreme wet weather called “sanitary sewer
overflows” (SSOs); and deposition of airborne pollutants into
water bodies. 
ADDRESSING OTHER SOURCES OF POLLUTION 
MWRA is active in several cooperative initiatives among gov-
ernment agencies, community sewer utilities, and environmental
advocacy groups to identify and address other sources of water
pollution. 
Contaminated stormwater runoff: Stormwater is a major source
of toxic chemicals and bacteria to waterways including the harbor
and the Mystic, Charles, Neponset, and Fore Rivers. Stormwater
can be contaminated by leaking sewers, as well as by dirt and ani-
mal waste, or by illegal dumping of oil or other pollutants into
storm drains. Failing septic systems in the suburbs and rural areas
can contribute bacteria and excess nutrients to the upstream areas
of these rivers. Fertilizers and pesticides from lawns, golf courses,
and farms leach into groundwater or are washed into rivers and
wetlands. Leaking oil and gas from boat motors and illegal dis-
charge of wastewater from sinks and toilets on boats are problems
throughout the watershed.
Massachusetts’ Clean State Initiative is targeting state facilities
to implement stormwater controls; MWRA has implemented these
policies in all of its own facilities. Stormwater studies in the
Charles, Neponset, Mystic, and Fore Rivers, and at Wollaston
Beach, aim to identify and measure the sources and quantities of
pollutants in stormwater entering the rivers and the harbor. Such
studies provide essential information to help communities target
cleanup efforts where they are most needed. 
T T
Future
Challenges 
21

Sanitary sewer overflows (SSOs): In separate
sewer systems, overflows of sewage from
manholes or underground sewerage structures
can occur. Unlike combined systems (see page
12), separate systems are designed with the
intention of keeping sewage and stormwater
separate: sewage is transported to wastewater
treatment facilities, while stormwater is dis-
charged to nearby rivers, streams, and wet-
lands.
However, no separate systems are truly sep-
arate. Although the discharge of stormwater to
sanitary sewers is illegal, sump pumps, roof
drains, and basement and foundation drains
from homes often connect directly to sewers
instead of drainage systems. This inflow adds
significant volumes of stormwater to already
overtaxed sewer systems. Another large source
of water to sewers is infiltration of groundwater
into leaky pipes during wet weather. In some
communities, approximately half the annual
volume of flow through sewer pipes comes
from infiltration and inflow (I/I).
In wet weather, if enough stormwater and
groundwater enters a separate sewer system,
the sewers fill up and inevitably overflow
through the manholes where the top of the
sewer pipe is closest to the ground surface.
Figure 20 illustrates how an interceptor over-
flows during a major storm.
Fortunately, widespread SSOs occur only
rarely, during severe (50- to 100-year) storms.
In those few locations where SSOs occur
repeatedly, MWRA is planning, designing, or
constructing sewer relief projects (see pages
10-11) which will eliminate SSOs except during
the most extreme storm events. MWRA is also
leading an Infiltration and Inflow (I/I) Task Force
(see text box) to develop effective ways to
address SSOs.
Sewer improvements and regulations alone
are not enough. SSOs must be addressed at
many levels. MWRA and communities must
work to develop cost-effective programs to con-
trol SSOs. The CSO program is one model for
tailoring cost-effective solutions to particular
areas. Significant factors contributing to SSOs
are denser development, development in for-
merly “unbuildable” low-lying areas and flood
plains, increased impervious surfaces, wet-
lands loss, and inadequate or improperly
designed or maintained drainage systems. All
these factors have led to failures of drainage
systems, often sending water into sewer sys-
tems and resulting in SSOs. Impervious sur-
faces must be reduced, zoning laws changed,
and drainage systems improved to decrease
the amount of storm runoff and overflows. 
I/I Task Force 
“The I/I Task Force
will develop goals
and implementation
strategies that will
reduce
Infiltration/Inflow
to optimize local
regional sewer serv-
ice. The Task Force
will make recom-
mendations for
cooperative imple-
mentation of the
goals and strategies
by local communi-
ties, MWRA, DEP ,
EPA, and others.”
An I/I Task Force has been formed to address I/I
issues. Representatives from local communities,
state and municipal agencies, and environmental
groups hold open monthly meetings to work on
strategies for implementing the group's
goals,which are to:
- eliminate all sewage backups into homes;
- minimize health/environmental impacts of
sewage overflows;
- remove all inflow sources (and prevent new
ones);
- minimize infiltration;
- educate and involve the public; and
- develop minimum operation and mainte-
nance standards.
The Task Force will make policy recommenda-
tions to MWRA in the year 2000, which will be
used in part to form the basis of a new MWRA I/I
reduction strategy. 
Mission Statement: 
22

AIR POLLUTION 
Atmospheric deposition is a sig-
nificant source of many contami-
nants in rivers, lakes, and estu-
aries. For example, most of the
mercury contamination found in
water comes from the air. There
is increasing evidence that a
large portion of pesticides, toxic
organic chemicals, and nutrients
ending up in water comes from
the air.
Pollutants in air directly settle out into waterbodies during dry weather; rainfall
and snowfall can also bring pollution. The effects of air pollution on water quality
must be better understood and managed at all levels. Most airborne pollutants are
products of combustion from industries, vehicles, and residences, but some pollu-
tants, like pesticides, have a very complex land-water-atmospheric cycle. More
research and monitoring are needed to better understand which contami-
nants and what proportion of water pollutants come from the air. We
also need to identify the sources and learn whether they are local or
from other regions of the world. 
WATER USE AND WATER BALANCE PROBLEMS 
Water quality problems are compounded when withdrawals of
water from wells, rivers, and lakes for drinking and other uses lead to
water quantity problems. For example, as waterways begin to dry up,
concentrations of pollutants increase. In MWRA’s service area, some
communities withdraw local water supplies from local water sources but dis-
charge wastewater to the regional sewer system (and ultimately to the ocean).
This “interbasin transfer” may result in a net loss of water within a river basin.
More scientific research is needed to increase our knowledge of how human
activities on the land and air affect water quality, water quantity, and the ecosys-
tem. Better data, including better measurements of river flow, are needed to help
answer questions such as, “What is the relative impact of interbasin transfer of
water compared to excess water withdrawal and increasing development?”
To complement regional projects, residents and businesses must sup-
port community efforts to improve local infrastructure and encour-
age sustainable development practices that reduce harmful
runoff. Decreasing runoff and permitting more water to absorb
into wetlands and groundwater are critical steps in address-
ing water balance problems.
A willingness to incorporate an integrated understanding
of the relationships between water resources, human com-
munities, and the natural ecosystem is necessary to ensure
that our health will be better protected when we swim, fish, or
eat shellfish; that our waters will support natural, diverse wildlife;
that we will have plenty of pure water for drinking, and that the beau-
ty of our rivers, wetlands, ponds, and harbors will be preserved. 
23
FIGURE 20. A sanitary sewer overflow (SSO): An interceptor overflows in extremely wet weather

Breiteneicher, D. K. 1997. MWRA Sewerage Division Plan.
Boston: Massachusetts Water Resources Authority.
Boston Water and Sewer Commission. 1998. CSO moni-
toring report. Annual report-1997.
Gong, G., J. Lieberman, D. McLaughlin. 1998. Statistical
analysis of combined sewer overflow receiving water
data 1989-1996. Boston: Massachusetts Water
Resources Authority. Report ENQUAD 98-09. 120 p.
Leo, W. S., A. C. Rex, S. R. Carroll, M. S. Connor. 1995.
The State of Boston Harbor 1994: connecting the
Harbor to its watersheds. Boston: Massachusetts Water
Resources Authority. Report ENQUAD 95-12. 37 p.
Leo, W. S., M. Collins, M. Domenica, P . Kirshen, L. Marx,
A. C. Rex. 1994. Master planning and CSO facility plan-
ning: Baseline water quality assessment. Boston:
Massachusetts Water Resources Authority.
Mitchell, D. F ., M. Moore, P . Downey. 1998. 1997 Annual
fish and shellfish report. Boston: Massachusetts Water
Resources Authority. Report ENQUAD 98-12.
MWRA. 1994. Final CSO conceptual plan and system
master plan. Prepared by Metcalf and Eddy, Inc.
MWRA. 1997. Combined sewer overflow facilities plan
and environmental impact report. Prepared by Metcalf
and Eddy, Inc.
MWRA. 1997. Implementation of nine minimum controls
for combined sewer overflows. Boston: Massachusetts
Water Resources Authority.
MWRA. 1997. Industrial waste report. Report Number
13, vol. 1. FY97 Annual report. 30 p. Boston:
Massachusetts Water Resources Authority.
Pawlowski, C., K. Keay, E. Graham, D. I. Taylor, A. C.
Rex, M.S. Connor. 1996. The state of Boston Harbor
1995: the new treatment plant makes its mark.
Boston: Massachusetts Water Resources Authority.
Report ENQUAD 96-06. 22 p.
Rex, A. C. and M. S. Connor. 1997. The State of Boston
Harbor 1996: questions and answers about the new
outfall. Boston: Massachusetts Water Resources
Authority. Report ENQUAD 97-05. 28 p. 
References 
MASSACHUSETTS WATER RESOURCES AUTHORITY 
www.mwra.com 
STATE & FEDERAL 
Mass. Executive Office of Environmental Affairs
(EOEA)
www.magnet.state.ma.us/envir
MDC beach water quality
www.magnet.state.ma.us/mdc/harbor
or www.shore.net/shore/beach/quality
EPA Office of Water
Atmospheric deposition
www.epa.gov/owow/oceans/airdep
EPA Region 1
www.epa.gov/region1
USGS Stormwater Study of Charles River
ma.water.usgs.gov/charles_river/
loads 
ADVOCACY GROUPS 
The Boston Harbor Association
www.tbha.org
Charles River Watershed Association
www.crwa.org
Mystic River
www.cee.tufts.edu/mystic
Neponset River Watershed Association
www.neponset.org
Save the Harbor/Save the Bay
www.tiac.net/users/shsb 
Related Web Sites 
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