1995: the new treatment plant makes its mark

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ST MODERN WASTEWATER TREATMENT IS
TECHNICALLY SOPHISTICATED. 
MWRA's
new 
Deer 
[sland facility.
with ad\'anced computerized controls
and innovalive treatment technologies.
is
a dramatic contrast
lo tho follering syslem il rnplm;os. 
The 
"start-up·• process 
actually lasted s1wcral months before wasll'water 
was 
first
introduced into the 
new 
plant. Contractors
and
engineers
at
Deer Island tested 2,225 pieces
of equipment, including 
hundrucls 
of
pi pus, pumps and 
valves; 
and 
checked uul 
11.000 instn1ments. 3, 200 computer controls.
and
34.000
computer control drcuits. 
TRAl~ING: 
The 
construction
of 
the new plant is impor-
tant-but
the most e,ritical part of the successful operation
of this facility is a skilled work force. Before start-up,
MWRA slaff.undorwent months of spcc:iulizod training. 
Managing this modern facilit~ requires new skills. espe- 
ciallv compared to those required in order to keep an anti- 
quat~cl plant barnly functioning. In the old days, whon 
workers often had to bring tools from home to repair bro-
ken equipment. training programs were \'irtually nonexis-
tent. Understanding that a dedicated and cxpericncccl 
_ 
......
.. 
-- 
... 
staff (which already 
had 
ovnr 4,000 years 
of 
c:ollcc:ti\'e 
acc.umulatecl uxperience) 
\\as 
indispensable. M\VRA
commilled to
enhance the
skills
of 
staff through a
$15
mil-
lion ongoing training
and apprenticeship program.
Employees
arc trained in optirations, maintenance, ,tnd 
snfoty. 
They attend computer classes
and other
work-
shops, as well
as manufacturers' training
in
proventive
maintenance for 
hundreds of 
pieces of new equipment. 
PROCESS INFORMATION CONTROJ. SYSTEM: 
Al the 
heart of this new facilitv is n r.omputcr system which both monitors
and
controls the treatment process, 
and 
cues 
staff to perform lroubleshooting. process adjustments.
and maintenance. This is a great ad,·ancc over
the
old plant.
which was monitored and c:onlrollecl manually and suf- 
forecl for decc1cles from underfunding and neglect 
of
basic
maintenance. Now. trained operators work al computer
consoles where the "Process Information Control Svstem"
(PICS) helps thorn monitor the treatmnnt process. open
ancl 
dose 
valves, and start and stop pumps. PICS alerts 
staff to emergencies, reminds them when specific equip-
ment needs preventive maintenance. and keeps tho facili- 
ty in complianco with its operating permil. System effi- 
ciencies are no\\ being employed so that only about 400
staff are required lo run the plant. as c:omparcd to the 500
workers originnlly projcctml.

THE STATE OF BOSTON HARBOR 1995 
TH E N E W T R E AT M E N T P L A N T M A K E S I T S M A R K 
NOVEMBER 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. Can-all, Vice Chair
Michael Benullo
Lorraine M. Downey, Secretary
Norman P. Jacques
Charles Lyons
Joseph A. MacRitchie
Vincent G. Mam1ering
Manuel Moutinho, III
Samuel G. Mygatt
Thomas E. Reilly 
Technical Reporl No. 96-6
Massachusetts Water Resources Authority

ACKNOWLEDGEMENTS 
PREPARED BY' 
Carl Pawlowski
Kenneth E. Keay
Erin Graham
David I. Taylor
Andrea C. Rex
Michael S. Connor
EDITED BY:
Sally Rege Carroll
Michael P. Quinlin
Tim Watkins
GRAPHICS AND LAYOUT BY: 
Cru-olynn DeCillo
Susan Curran Ford
Anthony Ferreira
ACKNOWLEDGEMENTS·
Many people contributed information and advice for this
report. The authors want lo Lhonk: Grace Bigornia-Vilale,
Kelly Coughlin, Emily Dallman, David Duest, Maurice Hall,
Mark Laquidara, Wendy Sm ith Leo, D. Peter RaJston, Mark 
Sullivan, William B. Thompson and Richard P. Trubiano.
WE WOULD LIKE TO ACKNOWLEDGE
ESPECIALLY THE HELP RECENED FROM
THOSE OUTSIDE MWRA:
Jim Blake, Mike Bothner, Mark Chandler,
Phil Colarusso, Matt Liebman,
Dave Mitchell. Therese Mounce, Susan Redlich, 
Don Rhoads and Isabel Williams.
PHOTOGRAPHY:
Karen-Jane Dodge
Kevin Kerwin

TABLE OF CONTENTS 
EXECUTIVE SUMMARY
INTRODUCTION 1
CHAPTER ONE
THE PRIMARY TREATMENT PROCESS AT DEER ISLAND 3 
1 PUMPING 4 
2 GRIT REMOVAL 5 
3 SOLIDS REMOVAL 6
4 SOLIDS DTGESTTON 7 
5 DISINFECTION 8
6 ODOR CONTROL 9
SECONDARY TREJ\TMENT ON THE HORIZON 10
CHAPTER TWO :
SEWAGE POLLUTION IN BOSTON HARBOR 11
A PATHOGENS 11 
8. TOXIC CONTAMINANTS 14 
CONTAMINANTS IN BOSTON HARBOR'S SEDIMENTS
IMPROVING CONDITIONS
CONTAMINANTS IN MARINE ORGANISMS
C. OXYGEN-CONSUMING ORGANIC MATTER 
D. SUSPENDED SOLIDS
SOLIDS POLLUTION AND WATER CLARITY
SOLIDS POLLUTION AND SEA FLOOR COMMUNITIES
16
16
E NUTRIENTS 18 
F FLOATABLES 19
CHAPTER THREE
BOSTON HARBOR IN THE YEAR 2005 20 
LESS CONTAMlNATlON. ESPECIALLY OF THE SEDIMENTS
CLEARER HARBOR WATER
A GREATER VARIETY OF ANIMALS AND SEAWEEDS
DECREASED THREAT OF LOW DISSOLVED OXYGEN LEVELS
HEALTHIER FISH AND SHELLFISH
IN SUMMARY
BIBLIOGRAPHY 22

LIST OF TABLES AND 
TABLES 
TABLE 1 The Primary Treatment Process at Deer Island
TABLE 2 Comparison of Pnmary and Secondary Treatment
TABLE 3 Pollutants Targeted by Sewage Treatment 
FIGURES 
TABLE 4 Decreases in Heavy Metals at Four Sites in Boston Harbor. 1977-1993 
1
10
11
15
FIGURES 
FIGURE l Sewer System Communities 3 
FlGURE 2 Primary Treatment at Deer Island 2/3 
FIGURE 3 Better Pumping Capacity at Deer Island Reduces CSO Flows 4
FIGURE 4 The Pumping System 5
FIGURE 5 Grit Removal 5
FIGURE 6 Stacked Settling Tanks 6 
FIGURE 7 Surface Overflow f1ates of the New Plant Are Within the Desired Range 6 
FIGURE 8 Discharge of Solids From Deer Island Has Decreased 7
FIGURE 9 The Sludge Digesters 7
FIGURE 10 The D1smfection System 8
FIGURE 11 The Odor Control System 9 
FIGURE 12 Illgh Bacteria Counts rn Deer Island Effluent Have Dramatically Decreased 10 
FIGURE 13 From a Polluted Harbor to a Healthy Harbor 12/13 
FIGURE 14 Beach Postings Have Decreased 1n the 1990s 14
FIGURE 15 PCBs tn Lobster Tissues Have Decreased Since 1987 15 
FIGURE 16 Pollut1on -Related L1ve1 Disease Has Declined in Boston Harbor Flounder 16 
FIGURE 17 Summertime Dissolved Oxygen Violations in the Inner Harbor 16 
FIGURE 18 G1adients of Water Clarity in Boston Harbor 17 
FIGURE 19 Increase in Amphipods on the Harbor Floor 18 
FIGURE 20 Concentrations of Algae Vary Within Boston Harbo1 19 
FIGURE 21 Historical Decrease of Eelgrass Beds in Boston Harbor 21

EXECUTIVE SUMMARY 
THE STATE OF BOSTON HARBOR report is 
an annual summary of the condition of Boston
Harbor. ll analyzes a number of indicators-scien- 
tific, environmental, aesthetic-that tell us how
much the Harbor has improved and what steps are
needed lo restore ii to full health. 
19U5 was an important year for tJ10 Boston
Harbor Project because. on January 20, MWRA
started up the new Deer Island primary treatment
plant-a key milestone of the Boston Harbor
Project. Perhaps the most compelling way to
describe the benefits to Boston Harbor of this
achievement is lo contrast the performance of the
new plant with the old for each step of the treat-
ment process. Chapter One of this report com-
pares the old and new by describing the six stages
of the treatment process: 
PUMPING - This critical first step of the treat-
ment process moves wastewater from the 43
sewer communities into the treatment plant. Ten
new pumps have replaced these most trouble-
some components of the old plant, allowing 
MWRA to transport sewage from the collection
system to the treatment plant much more reu- 
ably. The old pwnps frequently broke down,
causing sewage lo back up and overflow into the
Harbor. The new plant will eventually be able to
pump at the rate of 1270 million gallons per day. 
GRIT REMOVAL• Heavy particles like sand and
coffee grounds were regular culprits in wearing
down equipment in the old plant, and accumu-
lated in the old settling tanks and digeslers. The
new vortex grit chambers are the largest of their 
kind in the United States and will improve grit
removal efficiency. 
SOLIDS REMOVAL - Larger settling tanks in the
new plant, "slacked clarifiers," have dramatically
increased the plant's ability to remove solids and
scum from wastewater. In FY96, Deer Island's
solids discharge into Boston Harbor dropped to 61
tons per day, down from 71 tons per day in Lhe
previous year, and compared to 126 tons per day
in 1986. 
SLUDGE A.ND SCUM DIGESTION - Digcsters
break down solids collected during the treatment
process, destroying pathogens and producing
methane gas Lo help heat and power the plant.
The new egg-shaped digesters allow better mixing,
improve production of methane, and mioiroizP. 
maintenance costs Lhat troubled the old plant.
When digestion failed at the old plant, Lhe low-
quality sludge that resulted could not be made into 
fertilizer pellets, but the new digesters have
resolved that problem 
DISINFECTION • Effective disinfection depends
upon how long harmful bacteria in wastewater are
exposed to sodium hypor.blorite before discharge.
The new plant has improved the disinfection
process by doubling tJ1e contact time from 15 min- 
utes to 30 minutes, providing more eiieclive bacte-
ria kill and using less sodium hypochlorite in the
process. 
GASES AND ODORS - In the old plant, gases and
odors escaped freely into the atmosphere. ln the 
new plant, the primary settling tanks are covered
so that gases are trnpped until they are treated with
chemicals that remove the odors.
There has never been a quick-fix way to reverse
the decades of accumulated pollution in the
Harbor. The 1995 start-up of the new primary 
plant was an important part of this effort. Other
key milestones, such as the elimination of scum
and sludge discharges into the Harbor, improved
disinfection, and an 80% decrease in toxic con-
taminant discharges into the region's sewers were
important beginnings to the Harbor's recovery.
In addition to documenting the achievements of
1995, the State of Boston Harbor report also looks
ahead to future improvements in remaining water
quality problems in the Harbor. Dissolved oxygen
concentrations in cerlain pockets of the Inner
Harbor do not meet state water quality standards 
during the summer. and the Inner Harbor can have
high amounts of phytoplankton that in some sum-
mers turn the water reddish brown. Combined
sewer overflows silll discharge untreated sewage to
the Harbor dnring heavy rains.
When the secondary treatment facilities become
operational at Lhe end of 1996, still more solids
will be removed during the wastewater treatment 
process. In 1998. a new 9.5-mile effluent outfall
tunnel will carry the cleaner efiluent into
Massachusetts Bay where 55 cliffusers, resembling
giant sprinkler heads, will disperse the discharge
into the deep waters of the Bay. Combined sewer 
overflows will be greatly reduced. By the turn of
the century, discharges into the Harbor will be a
small fraction of what they arc now, allowing a
healthier, more diverse marine ecosystem to re- 
establish itseli. 
Like other projects MWRA has done and will
do. the new primary treatment plant described
in this report is an integral part of the overall
objecli ve of the Boston Harbor Project: to
restore Boston Harbor lo an environmental stan-
dard that the citizens of the Commonwealth
want and deserve.

THIS 1995 STATE OF BOSTON
HARBOR REPORT focuses on a major
accomplishment of the Boston Harbor Project:
the start-up of the new primary wastewater
treatment facility on Deer Island. The follow-
ing pages describe tho steps of primary treat-
ment at Deer Island (summarized in Table 1),
and contrast tho improvements at the new
facility with the performance of the old plant
it replaces. Designed with capacity for the
future. the state-of-the-art facility already pro-
vides improvements in treatment that benefit
the environment and dramatically increase 
INTRODUCTION 
efficiency and reliability of operation; also,
the plant is a better neighbor than its former
often foul-smelling predecessor. The second
part of the report provides an update of the
health of Boston I !arbor, reviewing problems 
caused by sewage pollution and how tho
Harbor is respondfag to pollution control pro-
jects. The latest data on beach waler qual ity,
the health of marine l ife, and aesthetics are
reviewed.
Finally, we project bow the Harbor will look
in 2005, after all the major components of tho 
Boston Harbor Project (see inset) are complete. 
THE BOSTON HARBOR PROJECT was ordered 
iu 1985 by U.S. District Court Judge A. David 
Mazzone. who ruled Lhat wastewater dis- 
charges into Boston Harbor from the outdated
and malfunctioning MDC Deer [sland 
Treatment Plant violated th() Clean Wntor Ar:t 
of 1972. The Uoston Jlarbor Pwjet.1. at S3.4 bil-
lion, includes r:onstruction of: 
• Primary and secondary wastewater
treatment facilities 
• Odor control facilities
• Disinfection facility 
• Egg-shaped sludge digesters
• Effluent outfall twmel 
• Tunnel from Nut lslonrl to Deer lshmrl 
• New and rehabilitated pumping stations 
Bv the end of 1995. the Boston £Iarbor Project 
was 80% r.omplete. 
TABLE 1: THE PRIMARY TREATMENT PROCESS AT DEER ISLAND 
1i·eatment Step Whal ii Does New Plant Improvement Benefits 
1 PUMPING 
2 GRIT REMOVAL 
3 SOLIDS REMOVAL 
4 SOLIDS DIGESTION 
5 DISINFECTION 
6 ODOR CONTROL
Pumps sewage up to the treatment
plant from the final tunnels of the co~ 
lection system.
Removes sand. coffee grounds, and
other heavy particles from sewage.
Removes sludge and scum from
sewage by gravity settling.
Reduces solids volume by converting 
a portion to methane gas and water.
Kills hannful bacteria with sodium 
hypochlorite.
Removes odors and volatile organic
compounds from the treatment
process ·ott-gases." 
New, modern pumps-tmproved rel1ab1hty, less
mamtenance, lower costs.
New vortex separators for improved removal 
efficiency. 
Increased capacity and better removal equip- 
ment in the settling tanks.
Egg-shaped digesters improve mixing, increase
gas production, and reduce cleaning and main- 
tenance costs.
Increased sodium hypochlonte disinfection time 
in new basins. More effective bacteria kill.
Enclosed settling tanks and equipment; mod-
ern air quality pollution control equipment.
The more sewage that can be pumped out of the collection
system into the plant, the less untreated sewage enters the
Harbor through CSOs. improving nearshore water quality for 
SW1mm1ng, boatmg, and shellfish1ng 1n the Harbor.
Better overall plant operation because lower grit loads
reduce wear and tear on equipment. Less equipment main- 
tenance.
Reduced discharges of solids ffiat cloud the water, oeplete 
dissolved oxygen levels and cover the bottom with muck
and contaminants.
Methane recycled for plant heating and hot water; reduced
cost of shipping digested sludge to sludge-to-fertilizer plant.
Less disease-causing bacteria; safer sw1mm1ng and boatmg;
fewer shellfish bed closures; reduced chemical use and
cost.
Less odor and reduction of air pollutants. 
1

CHAPTER ONE 
PRIMARY TREATMENT
AT DEER ISLAND 
0 Pumping 
Five new electrically driven
pumps have helped reduce
sewer system overflows. By
March,1997 installation of an
additional five motors will raise
pumping level to the full 913-
million-gallon capacity of
incoming sewer lines. 
• NEW FACILITIES ON-LINE
NEW FACIIJTIES
UNDER CONSTRUCTION @ Disinfection 
•
• OLD STRUCTURES REHABILITATED 
By raising time allowed for
disinfection from 15 to 30
minutes, bacteria kill has
been enhanced while using
20% less disinfectant (sodium
hypochlorite).
• OLD DEER ISLAND TREATMENT
PLANT (DEMOLISHED 1995) 
FIGURE 2: PRIMARY TREATMENT AT DEER ISLAND 
lNTER-ISLAND
TUNNEL 
@ Grit Removal 
Available grit removal has been
increased to 913 million gallons
although removal efficiencies of
new vortex grit chambers have
not yet exceeded that of old plant.
Work is underway with contractor
to increase efficiency. 
£ '.) 
@ Odor Control 
Old Deer Island plant had
no system for odor control.
Chemical scrubbers and
carbon beds now treat
gases and volatile organic
compounds - air pollutants
- at removal rates of more
than 99%.

@) Solids Removal 
Forty-eight new, 1.6 million
gallon primary treatment
tanks have decreased solids
,,,,/ loads entering Boston Harbor 
~ from 138 tons in 1986 to 57
tons in 1996. 
• NOR'll I SYlITF.M 
II SOt.rrH SYSTEM 
FIGURE l: SEWER SYSTEM COMMUNITIES 
8 Solids Diges tion 
Eight new 3-million gallon
sludge digesters have
increased levels of methane
gas by-product available for
use as fuel and eliminated
chronic operational
problems of old digesters. 
EXISTING DISCHARGE ~ 
OUTFALLS 0 
~~ 
v,.t"> 
MORE THAN 2 MILLION PEOPLE AND
5,500 BUSINESSES ARE SERVED BY THE
MWRA SEWER SYSTEM, which collects, transports
and Lreals waslewaler from 43 communities in the
greater Boston area. Locally owned sewer pipes dis-
charge inlo MWRA's large "interceptors," and the
wastc·waler is carried to two treatment plants: one al
Deer Island which treats sewage from lhe North 
Systom, and tho other at Nut Island which lreats
sewage from the South System (F1c.;u RE 1). Both plants
now discharge primary treated effluent into the wat.ers
of Boston Harbor.
In 1997, the new facility al Deer Island will treat sewage
from both the North and South systems, and the Nut Island
Treatment Plant will be decommissioned. Sewage flows
from the South System will be screened at a new head-
works at Nut Jsland, and sent to Deer Island through the 
new inter-island tunnel. The new Deer Island Treatment
Plant is designed lo ultimately provide primary and sec-
ondary treatment to tho wastewater from both the North
and South systems.
On January 20, 1995, a major milestone in the Boston
Harbor Project was reached, as the new primary lreatmenl
plant began operalious. The new sewage treatment process
al Deer Island is a series of steps (FIGURE 2) intended to
remove contaminants from wastewater as it passes through
the plant. These steps reduce the contamination of Boston
Harbor by wastewater efl:luent discharges, protecting the
enviromnent and public health. The main elements of tho 
primary lrealment process, which are described in the first
part of the report. are shovm here. 
Thls chapter describes these steps in detail, explain-
ing how t.hc now facility improves upon past perfor-
mance; a description of secondary t.realment looks to
the futw-e. 
3

4
1 PUMPING: lifts the sewage from the
sewerage system to the treatment
plant. 
Sewage from the North System is carried b y
gravity through progressively larger pipe:; from
users' streets toward Deer Island. Along the
route, the wastewater flows through "headworks"
facilities which screen oul large objects and
remove grit. After the headworks, sewage flows
under Boston Harbor L o Deer Is land. through tun-
n els 11 feet in diameter built in 1968. The 
:;ewage arrives al the plant about 112 feet below
ground, and must then be lifted from the tunnels 
u p to the treatment plant. A major challenge to
the system is to provide the pumping necessary
to lift hundreds of millions of gallons of waste-
water each day from the tunnels to the plant. [f 
pumping fails, sewage backs up into the system,
and can overflow into the Harbor and rivers, or
even into streets and homes.
At tho former plant, which was built in 1 mlH, 
antiquated diesel engines drove old pumps. The
engines ofien failed, and were difficult Lo repair
because replacement parts were no longer avail-
able. Sewage backups and frequent combined
sewer overflows into the Harbor and rivers
resulted (see text box below}. 
COMBINED SEWER OV ERFL OWS: A com- 
bined sewer is an antiquated system in which 
storm drains and sanitary sewers from homes
and businesses flow into U10 same pipes. A 
combined sewer over •ow (CSO) is an over- 
now Lhal occurs when lhe volume of
stormwater entering a combined sewer sys- 
tem in wet weather overwhelms the capacity
of the system. The resulting mixture of
stormwoter and inadequately treated sewage 
overflows into the receiving water. Many of 
the larger CSO outlet!; in the MWRA system 
provide disinfection and rudimentary
removal of some pollutants.
1400
1200
1000
800
600
400
200
0
86 87 
BETTER PUMPING C APACITY AT DEER ISLAND R EDUCES CSO FLOWS 
88 
1nr,. nm lmprovcm••'Jl.<1 
C.>mμlcwd 
Deer Island Pumping Capacity (MGD) 
I Domol1too ol 
+ OldP<imps ,,_ _____ "' 
89 90 91 92 93 94 95 96 
,ouit,Svstem • 
F1,>w T:ansfei 
Addmunol 
rumr,s 
97 98 
--------- OI.D1'REATMF.NT Pl.ANT - -------- - NEWFACLLITY- 
FIGURE 3: Past changes in the pumping capacity at the old Deer Island plant and changes at the new Deer Island faciltty are
charted. Cottage Farm CSO Facility discharges into the Charles River are shown as an example of the relallonsh1p between
combined sewer over nows and pumping effectiveness at the Deer Island plant. 
OLD PLANT: Pumping capacity Before 1988, the original diesel pumps at Deer Island faded frequently. Pump failures and 
repairs are reflected In the up and down vanabon on the graph, with an overall declining trend until late 1987. 
COTTAGE FARM CSO DISCHARGES: Like other combined sewer overflows, discharges at the Cottage Farm CSO,near the
Boston University Bridge in Cambridge, occur when rainfall exceeds the capacity of the sewer system, and the capacity of
the sewer system Is closely related to the pumping capacity at the treatment plant. The monthly volume discharged depends
both on the amount of ram that fell and how well the sewerage system was functioning. The figure shows the effects pumping 
inadequacies can have on the environment: in the spring of 1987, a very large storm coincided with a breakdown in pumping 
at the Deer Island plant. forcing a backup of flow into the system. Many hundreds of millions of gallons of combined sewage
had to be discharged from the Cottage Farm CSO Fac1 hty into the Charles River to avoid sewage flooding buildings and
streets. Another problem was "dry weather overflows"-<l1scharges from Cottage Farm (for example, in August and September 
1988) that occurred when Deer Island pumping tailed, even 1f there was no rain.
From late 1987 to the fall of 1990, the interim improvements gradually improved pumping capacity at Deer Island, adding 
new electric pumps to the old diesel pumps. From 1991 to late 1992, pumping capacity was consistently high, coinciding 
with a period of low discharges from Cottage Farm. The last dry weather overflow was in 1990. By 1993, capacity unavoid-
ably declined as the old diesel pumps were demolished to make room to install new pumps for the new treatment facilrty. 
NEW FACILITY: In January 1995, flow from the North System was transferred from the old plant to the newly built pnmary
facility on Deer Island with I1 s five new pumps. In late 1996 three more pumps will be added to the new fac1hty. further 
increasing capacity. The final Jump In capacity will be In 1998 as two more pumps are added before receiving additional flow
from the South System through the inter~sland tunnel. The ultimate pumping capacrty at Deer Island will be 1270 million gal-
lons per day.

The five new electrically driven pumps
(FIGURE 4) that began operation in January,
1995 are not yet functioning at full capacity,
but have been highly reliable. operating 99% 
of the time. In contrast, in their last years of
service. each of the old diesel pumps were
only operational 50% of the Lime. The new
pumps are also operational at the Winthrop
Terminal on Deer Island which lifts sewage
into the plant Erom the original 1898-vintage 
~ 3500 HP ELECffilC 
w PUMP MOTO/l 
110 MGD PUMP 
11' 
t 
IN FROM COLLECTION
SYSTEM 
FIGURE 4: THE PUMPING SYSTEM 
sewage drail1 lines that
first reached Deer Island. 
IN FROM PUMPING b 
By 1998, ten new electric pumps
will be installed plus six new pumps at the
Winthrop Terminal , so that the plant's capaci-
ty of 913 million gallons a day (mgd) will be
enough to handle all projected North System
flows even if two pumps are out of service for
maintenance or repairs. The history of pump-
ing al Deer island since 1988 is shown in 
r!GLJRE 3. 
2 GRIT REMOVAL: Grit chambers
remove heavy particles to extend
equipment life and improve the perfor-
mance of the solids-handling system. 
Grit, consisting of sand, coffee grounds, 1md 
other heavy particles, is removed before
wastewater enters the primary treatment set-
tling tanks. While grit itself would not signifi-
cantly pollute the Harbor, grit can reduce the
effectiveness and service life of treatment 
plnnt equipment. Constant grit accumulation
increased the maintenance requirements of the
old Deer lslaud plant's settling tanks and
digesters.
Grit is removed at a number of places in the 
sewage collection system. including head-
works located in Boston and Chelsea that pre- 
FIGURE 5: GRIT REMOVAL
vent grit from accumulating in the tunnels
that deliver sewage to Deer Island. Additional
grit romoval takes place on Deer Island lo pre-
vent grit from collecting in the on-island
equipment.
The new vortex grit chambers (FIGURE 5) on
Deer Island are the largest of their kind in the
United Stales, with a total capacity of 913 mil-
lion gallons per day. This system uses less
land space than conventional grit facilities,
which is why ii was chosen for Doer Island.
Grit removal efficiency is still not at the level
expected in the specifications for the new
plant, but M\t\TRA is working with the equip-
ment contractor to improve performance.
5

6 
INTO UPPER TANK
INTO LOWER TANK
IN FROM G RIT REM OVAL
SlUOGE OUT TO
DIGESTERS 
3 SOLIDS REMOVAL: Sludge and
scum are drawn from sewage in
large primary treatment settling tanks. 
After grit removal, the wastewater nows con-
linuously into the primary settling tanks (also
called clarifiers). Once Lhe flow slows down.
as the wastewater s lowly moves through the
tank, heavy particles sink to the bottom of the
tank as sludge. Anylhlng that 0oats-plaslics ,
fats, cooking oils, and sticks- and collects on
the sUiface is called scum, which bas a high
grease content. Moving paddles draw the
acc umulations of scum and sludge from the
tanks for pwnping lo the next phase of solids
treatment. Sludge and scum, if discharged to
Lhe Harbor, would cause cloudy water, oxygen
depletion, buildup of sediments, and sediment
contamination.
Because there are only about 200 acres of
land available on Deer fsland, the new plant
utilizes the technology of stacked settling
tanks (FIGURE 6) pioneered in space-conscious
Japan. Two-story tanks provide twice the area
for solids lo setlle while Laking up Lhe same 
amount of land space as single-level tanks. 
WASTEW4TER OUT 
FROM UPPER TANK 
---- WASTEWATER-- 
WASTEWATER --- - SLUDGE 
.. -~ - .. ........ , ... .. ,_ 
~ . .. . . . .. ..
SLUDGE COLLECTOR 
MECHANISM Al llffi 
Deer Island is the second sewage treatment plant
in the counlry Lo use this technology, which is
the largest of its kind in the world.
The longer wastewater is retained in the set-
tling tanks. the more solids arc removed. The
process is similar to letting a glass of chocolate
milk sland-Lhe longer the glass stands. the 
more suspended chocolate particles sink Lo the 
bottom.
The efficacy of primary Lreatment is mea-
sured by the surface overflow rate (SOR). The
ideal SOR for primary lrealmenl is between
800 and 1200 gallons per day per square fool
of settling area. Larger tank area . in compari-
son to Ll1e old plant, means longer settling
times and slower SOR rates. If the SOR is loo
slow, however. bacterial growth in the tanks
can produce corrosive and foul-smelling gases
which mix solids back into the wastewater. On 
the other hand, if the SOR is too high, not
enough solids will be removed from the was te-
water. The new plant's 48 stacked settl ing
tanks (12 in each of Lhe primary Lreatmenl
Batteries A , B, C, and D) have a greatly
inc reased s ettling area compared to the old set- 
WASHWATER OUT
FROM LOWER TANK 
SCUM COLLEC TORS 
OUT TO DISINFECTION 
FIGURE 6: ST ACKED smLING TANKS 
tling tanks, e nabling the p lant lo maintain a
desirable SOR (FIGURE 7) , even during wet
weather when the plant is receiving sewage at 
a high rate. 
S URFACE OVERFLOW RATES OF
THE NEW PLANT ARE WITHIN
THE DESIRED RANGE
Gallons/Day/ Sq.ft. 2000,---------_;__;_ ____ _ ~ 
18001---- == -=-~~~-------= - = - = - = - = - =- =----I OW PI AN'f.OOSIGN 
1600,t----------- -------1 
1400,i-------------------1 
1200
1000
800
600
400 
DESIRED RANGE OF SOR
200
0 APR MAf JUN JUL AUG SEPT OCf N OVDEC JAN FEB 
FIGURE 7 : P erhaps the greatest advantage of the new plant
1 s its ability to provide a high level of treatment, as mea-
sured by the surface overflow rate (SOR ), during periods of 
high flow. Except for the penod of initial operation, the
plant has operated at an SOR within the desired range for 
optimum performance. The old plant was designed with an
SOR that exceeded the desired range during average flows.

DISCHARGE OF SOLIDS FROM
DEER ISLAND HAS DECREASED 
Tons;Day 
150 ~ ---------~~----~ 
• Sludge 
120
90 
130 
30 
• TSS 
O 86 87 88 89 90 91 92 93 94 95 96 
FTSCAL YRAR 
FIGURE 8: Solids input to Boston Harbor from Deer Island
decreased dramatically with the start-up of the new Deer
Island Treatment Plant in January 1995, and when the new
egg-shaped digesters came on-line in August 1995. The
ending of sludge discharges in December 1991 1s credited
wrth many of the Harbor improvements observed today. 
Solids removal from the wastewater increased
after interim improvements, and have further
improved after the new plant came on line in
1995. In 1986. the former plant discharged 126 
tons of solids (including sludge) per day into
Boston Harbor; and in 1994, the year before the 
first new facilities went on line. 77 Lons per
day. T n 1995, as the new plant went into start-
up operation, it discharged 71 Lons of solids per
day, and after February 1996, only 61 tons per
day (FIGURE 8), bringing the Deer lsland plant
into full complifmce with its interim legal limit 
for efOuenl quality. 
4 SOLIDS DIGESTION: Digestion
breaks down sewage solids,
destroys pathogens, reduces the
amount of organic waste, and produces
methane gas burned for heat and power
in the facility. 
After sludge is collected from tho bottom of
the settling tanks an<l mixed with scum. it is
pumped to thickeners where wolor is removed. 
GAS TO BOILER 
- 
O verflow ~ 
return to influent 
DIGESTED SLUDGE TO
PELLETIZING PlANT 
SLUDGE IN FROM 
SEDIMENTATION TANKS 
Heat _/ 
Exchangut 
o e ·e 2, 
SCA!.f N ftET :L 
Main 
circulation 
nng 
FIGURE 9: THE SLUDGE DIGESTERS 
Then. the thickened sludge is pumped into the
egg-shaped digesters to undergo anaerobic
digestion, meaning digestion without oxygen.
Digestion great!) reduces Lhe nwnbers of 
pathogens in the sludge, and stabilizes it for
further processing. Microorganisms grow dur- 
ing the digestion process, using the sl udge for
food. These microbes generate heal and break
down the organic matter in Lhe sludge. produc-
ing methane gas. The gas can bo used for heal
and power al the plant. The digested sludge is
barged lo the sludgo-to-fcrtil iznr plant al Lhe
Fore l{iver Staging Area, where fertilizer pel-
lets arc them produced fur agricultural uses
across the country.
One dozen 140-foot high eggs make up the
most prominent feature of the now Deer Island
plant. These egg-shaped digcsters arc fairly
common in Japan anti Germany, but relatively
new to the United States. The cake-pan shape
of tho previous digeslers in the old plant
caused several stagnant areas with pour mix-
ing that reduced digester efficiency. The egg
shape is ideal for mixing (FIGURE 9). and the
narrow top lessens the accumulation of scum.
Cril is easily cleaned oul from the tapered bot-
tom, reducing maintenance costs and minimiz- 
ing problems resulting from solids buildup. 
Sludge in the process of digestion is a living
biological system, which can be upset. Plant
7

8 
MIXERS 
~ 
~ Bos,~ 1 
' '-- 
AGURE 10: THE DISINFECTION SYSTEM 
operators must actively manage the digestion
process to maintain maximum efficiency. The 
olrl Deer Island digestors had problems with 
accumulated gril, scum, and poor mixing, and
were overburdened with loo much sludge vol-
ume. One symptom of a malfunctioning
digester is that the sludge becomes acidic.
Chemical "antacids" such as lime and soda ash
are often used to neutralize these acids. The old
digesters required over 25,000 pounds of soda
ash in a year-lho equivalent of an antacid tablet
13 feet in diameter and five feel thick! The new
digesters have performed very well to date and
have not required this treatment
The new digesters are designed to handle
both scum and sludge. The old plant's
digesters had inadequate capacity, so until
1988, scum, which requires longer digestion,
was discharged directly to Boston Harbor.
The resulting unsightly slicks on the Harbor
were eliminated in 1988 when scum was
landfilled. The new digesters have oliminat-
- 
.. 
ed the need for landfilling alJ but a small
amount of scum screenings.
Prior to MWRA's opening of the sludge-to-
ferlilizer plant late in 1991, an even more
egregious feature of the old plant was tho
absence of any disposal location other than
Lhe Harbor itself for the digested sludge out-
put of the old digesters. Digested sludge-18
tons per day, on average-was combined 
wiLJ1 the old plant's effluent for direct dis-
charge into the Harbor. That practice ended
enlirely in December, 1991. Many of lhe vis-
ible improvements to the condition of Boston
Harbor that have boen noticed by fishermen.
boaters, tourists, and beachwalkers result
from nature's recovery from the old plant's
sewn and sludge treatment limitations an<l 
disposal practices.
The new digesters have greatly improved
methane gas production. Problems al the old
plant's digesters led to a HJ-year hall in gas
production, increasing fuel costs by about 
IN FROM SEDIMENTATION TANKS 
INA.IJENT SW!Cf: GATES 
OUT TO BOSTON HARBOR 
EFFWENT SLUICE GATES 
$1,000,000 per year. The new digesters have
been producing about 50 tons of gas per day,
and gas production is expected Lo increase. 
5 DISINFECTION: Disinfection
destroys disease-causing bacteria
and viruses found in sewage that would
threaten public health if beaches and
shellfish beds were contaminated. 
Untreated sewage carries largo numbers of
potenlially disease-causing pathogens originat-
ing in human waste that would be a health
hazard if discharged into recreational or shell-
fishing areas. Like most wastewater treatment
plants, Deer island uses a form of chlorine 
(sodium bypochlorite, the active ingredient in
bleach) lo disinfecl wastewater before dis- 
charging. Unfortunately, sodium bypocWorile
is toxic not only to microbes but also, in high
enough concentrations, to aquatic life. The
toxicity of sodium hypocWorile, lo say nothing
of its high cost, makes iL important to mini-

mize lhe amount of hypochlorile used to
obtain effective disinfection.
Solids and organic mattor in sewage interfere
with the ability of sodium hypochlorile Lo kill 
microorganisms. Therefore, the more solids pre-
sent, the more sodium hypochlorite must be
added. An important result of improved treat-
ment, which removes more solids, is that less
hypochlorite is required for disinfection.
A second important factor influencing disin-
fectant use is called contact time. The longer
the wastewater is exposed lo sodium hypochlo-
rite, the less hypochlorite needs to be used for
effective disinfection. At the old planl, sodium
hypochlorite was added just before discharge,
and the contact time was the time it took the
wastewater to travel to the end of the outfalls
(about 15 minutes). The new facility uses largo
disinfection basins (FIGURE 10) which increase
the contact time to 30 minutes.
Better solids removal and a modem disinfec-
tion system have allowed Deer Island Lo use 
AIR FROM ENCLOSED PROCESSES 
(SEDIMENTATION TANKS) 
about 20% less sodium hypochlorite, saving
about $1.2 million from March 1995 lo
February 1996, and discharging less hypochlo-
rite into the environment.
Most importantly, FIGURE 12 shows that 
effiuenl from the new facility has consistontly
met the permit limits for bacteria (measured as
fecal coliform counts) and is protecting the
public health. 
6 ODOR CONTROL: Odorous hydro-
gen sulfide gas is removed by chemi-
cal "scrubbers." 
As wastewater flows to and through a sewage
treatment plant, bacteria slarL Lo decompose the
organic materials in the wastewater, producing
hydrogen sulfide (which smells like rotten eggs)
and other unpleasant odors. These gases accu-
mulate and are released inlo the air during the
treatment process.
ln the old plant. the primary settling tanks
were out<loors, uncovorod, allowing odors to
escape freely into the air. To contain these
gases, the new primary settling tanks at Door
Island are enclosed. Hydrogen sulfide and 
other gases are directed to an odor control 
facility and, in a process called chemical
scrubbing, are exposed to chemicals that oxi- 
dize the gases so as Lo eliminate the odor. For
any gases that escape the scrubbers, or for
occasional volatile organic compounds (air 
pollutants), carbon bed absorption filters have
also been installed as a final step in the air
quality control at the plant (Frei T RE 11). 
Thero are five new odor control facilities
planned for Deer Island, three of which are
now in operation. Thus far, the system has 
performc<l reasonably well. considering that 
the volume of hydrogen sulfide gas has been
higher than anticipated. After a few initial
TO ATMOSPHERE 
faha ust Stack 
Car bon Strubbtr B) pU> Duce 
lilS Scrubbtr 
Ac1lvaccd Carbon Bed 
- Organics Scrubber 
Cawm: Sod.I 
FIGURE 11: THE ODOR CONTROL SYSTEM 
9

10
modificalions, the plant has been able to
remove more than 99% of the hydrogen sul-
fide released during thr. treatment process. 
SECONDARY TREATMENT
ON THE HORIZON 
Secondary Lrealment uses a biological
process lo increase the removal of organic pol-
lutants from wastewater, producing an even
cleaner cfflucnl.
Scheduled for initia 1 start-up of aho11t 20%
of its process elements beginning late in 1996.
secondary treatment will significanlly improve
the quality of Deer Island effluent. Table 2
shows that secondary lreatment removes even 
more poUutants from wastewater lhan primary 
treat men I.
In tho now plant. wastewater will go through
primary lreatmcnl, followed by secondary
treatmonl and disinfection before I.he effluent 
is discharged. While primary treatment is a
simple physical process using gravity to settle
out solids, secondary lrealment is quite differ-
ent: bacteria arc used to break down and con-
sume pollutants remaining after primary treat-
ment. At Deer Island. secondary treatment
will be a two-step process: first the wastewater
will be aerated Lo promote the growth of bacte- 
TABLE 2: COMPARISON OF PRIMARY AND
SECONDARY TREATMENT 
Pollutants Primarv Sec:ondarv 
R1mwv,il Rmnonil · 
TOTAL
SUSPENDED
SOLIDS (TSS) 50-60% 85%
BIOCHEMICAL
OXYGEN 25-40% 85%
DEMAND (BOD l
TOXIC
CONTAMINANTS 0-50'16 50-90% 
ria, and then the resulting bacterial solids will
settle and be removed from the effluent. The
secondary treatment method to be used al Deer
Island is cnlled rm nctivaled sludge process. 
AERATION: ln the secondary "reactors" pri-
mary eftlucnt will be mixed with pure oxygen.
Primary effiuent contains two ingredients used
in secondary trentmen t: organic: mailer and bil-
lions ol bacteria. The oxygen encourages bac- 
teria to multiply. and the bacteria feed on the
organic matter and break down many pollu-
tants. Certain strains of bacteria beneficial to
treatment are favored to grow during this
process. As the bacteria grow. they form
clumps called floes. These floes are a mixture 
of bacterial cells and waste paiticles sticking 
togetlleI. During aeration bacteria consume
many pollutants and incorporate inorganic
particles that aren't actually consumed into the
noes. 
SECONDARY SETTLING: After aeration. the
mixture of bacteria and effluent is transferred to
settling tanks, I.he "secondary darifiers." 11ere, 
I.he floes of bacteria and most of the pollutants
settle to the bottom of the tanks. The bacteria
arc sticky and parlicles of pollutants attach to 
the bacteria as they settle, removing more c:on-
taminanls from the wastewater. This mixture of
bacteria and pnrticles is secondary sludge.
Much of I.his secondary sludge \A.rill be removed
and digested in tho egg-shaped digesters, but
some secondary sludge. now rich in beneficial 
bar:teria, will be returned lo the aeration tanks.
Here, the bacteria will mix again wilh more pri-
mary enluent and oxygen to grow and consume
pollutants in a conlinuous cycle: the "return-
activated-sludge" process.
The rust battery of secondary treatment at
Deer Island will trea t most of the Deer Island
flow. The second and third batteries, sched-
uled to start-up in 1997 and 1999 respectively,
will be able lo provide secondary treatment to
both Deer fsland flow and tho flow from the
South System now treated at Nut fsland.
The environmental benefits of secondary
treatment are a dramatic reduction in pollu-
tion loadings to the ocean. and a cleaner efflu-
ent that will require less hypochlorite to
disinfect.
120
100
80
60
40
20 
HIGH BACTERIA COUNTS IN DEER ISLAND
EFFLUENT HAVE DRAMATICALLY
DECREASED SINCE 1988
Days of High Counts 
• 201-10,000 Fecal coliform/100 ml 
• >10.000 Fecal cohform/100 ml 
O 1988 1989 1990 1991 1992 1993 1994 1995 
FIGURE 12: This figure shows the number of days from
1988 to I 995 that average fecal coliform counts in Deer
Island effluent were higher than the standard of 200 per 100
ml. Two categories of high counts are shown: days when
fecal coliform counts were greater than 200 but less than
10,000: and days when fecal counts were greater than
10,000. For comparison, fecal coliform counts in undisinfect-
ed effluent average about 5,000,000 per 100 ml.
Because the dilution 1n the ocean at the Deer Island out-
falls is about 20-fold, if effluent counts are 10,000 or less
the water quality standard (200) will be met not far from the
outfalls, and ettects on beaches and shellfish beds will be 
minimal. However, when bacteria counts in the effluent are
very high, over 10,000 per 100 ml, beaches and shellfish 
beds can be affected. The figure shows that after 1990, the
number of days counts exceeded 200 dropped dramatically 
from more than 100 days per year to less than 40 days per
year. Most important for environmental quality 1s the virtual
elim1nat1on of days when fecal coliform counts were extreme-
ly high: from 69 days 1989 to only 2 days in 1995.

CHAP TE R TWO 
SEWAGE POLLUTION
IN BOSTON HARBOR 
THE SEWAGE TREATMENT improve-
ments described in !be previous chapter have
the goal of improving the quality of effluent
released into the harbor: MWRA has worked to
ensure that these legally-required improve-
ments arc cost-effective. This chapter looks at
how Boston Harbor has responded to past
efforts, and how it rnay change after recent and
future plant improvements. Table 3 summa-
rizes how better sewage treatment will help in
the Harbor's recovery.
Although untreated (raw) sewage is over
99% water, it contains numerous forms of
waste, mostly human in origin, that need to be
removed or otherwise treated before the waste-
water can be safely discharged. In the follow-
ing sections, the major targeted pollutants in
sewage arc described. 
A PATHOGENS: The term pathogens
refers to the potentially disease-caus-
ing viruses and bacteria that abound in
raw sewage. 
lfnot removed by treatment, many of these
pathogens can survive in seawater for days or 
weeks. Sewagc-dcri ved pathogens can pose a
serious health threat to people who come in
direct contact with contaminated seawater by
swimming or boating, and to people who con-
sume contaminated shellfish.
Since pathogens can pose a risk al very low 
levels which are difficult lo measure, their
presence is usually inferred from that of fecal 
coliform bacteria which can be measm ed more
easily. If a monitoring agency finds focal col-
iform counts above pnrmilted standards.
beaches ru·e posted as unsafe or shellfish beds 
are closed until coliform levels decrease. All
clams harvested in Boston Harbor must be
"depurated"-cleansed al a state fac ility where 
they arc placed in ftllered seawater until they
have passed any potentially contaminated
material that was in their stomachs. 
TABLE 3. POLLUTANTS TARGETED BY SEWAGE TREATMENT 
Pollutant in Sr.wagu Whal ii ls What ii Does Beller Treatment Ruduces this Pollutant 
A PATHOGENS 
B TOXIC
CONTAMINANTS 
C ORGANIC
MATERIAL (BOD) --- 
D TOTAL
SUSPENDED SOLIDS
(TSS) 
E NUTRIENTS 
F FLOATABLES 
D1sease-caus1ng viruses and bacteria (md~ 
cated by fecal coliform).
Heavy metals such as copper and lead;
PCBs, pesticides, petroleum hydrocarbons. 
Fooo residues, human waste, plant matter.
Can be dissolved, solid, or hqu1d. 
Mix of organic particles, silt. and sand
suspended in the water. 
Nitrogen, phosphorous; act as plant
fert1hzers.
Floabng debris: plastics, condoms, tampon
applicators, oil and grease.
Unsafe swimming, boating, and shellf1sh1ng.
At high doses, can be toxic to marine ani-
mals and carcinogenic to people.
Uses up oxygen as 11 decays; large
amounts can deplete dissolved oxygen in 
the Harbor.
Clouds water; toxic contaminants adhere to
solids which eventually settle to bottom;
can smother bottom-dwelling marine life.
Can cause excessive growth of phytoplank-
ton in the Harbor. which depletes oxygen
when It decays.
Unsightly shcks are aesthebc pollution of
the Harbor.
01smfection, longer holding time wtll more reliably kill 
pathogens.
New primary settling tanks have removed more contam- 
inant solids; industrial pre-treatment programs.
New primary settling tanks have increase BOD 
removal: more will be removed with secondary treat-
ment.
New primary settling tanks have increased solids
removal; more will be removed with secondary treat-
ment. 
Primary or secondary treatment does little to remove
dissolved nutnents. Greater dilution in Massachusetts
Bay will reduce nutnents to background levels.
Preliminary treatmenVscreernng; pumping improve- 
ments decrease combined sewer overflows which carry
floatables into the Harbor. 
11

FIGURE 13 
O_M_A OUU_IE_D HARB0-'3 
4 
Few "pollution
indicators" worm
species
High nutrients
encourge algal blooms,
decrease water clarity,
discourage growth of
seagrasses.
Black sediments have
high concentrations of toxic
hydrogen sulfide, low oxygen.
Only a few pollution-tolerant
species did survive 
Deer Island and Nut Island treatment plants discharged primary treated
effluent and digested sludge (including scum) into Harbor. Poor pumping
capacity at plant caused frequent CSOs in rainstorms. Disinfection
failures at treatment plants not uncommon in 1985 and 1986.
Discharges of BOD, sohds, nutrients caused low oxygen in some
Harbor sediments, preventing normal plant and animal communities from 
living on bottom. Toxic chemicals in sewage and road runoff probably
caused high rates of liver disease in flounder. High PCB levels in lobster
tomalley. 
,.• ,.• 
Suspended solids and
decaying algae settle on
the bottom, depleting
sediment oxygen 
,. 
··~ ~ : ': ... .. - ......... 
Source reduction programs reduce discharges from industry
into sewers, so toxic discharges from treatment plants were
reduced by 31%.
Sludge and scum discharges cease at the end of 1991,
significantly lowering inputs of BOD and solids. Pumping
improvements and better maintenance mean fewer CSOs.
Bottom-dwelling communities begin to reappear at areas
heavily affected by sludge. Liver disease in flounder
dramatically decreases.

New primary treatment plant on Deer Island opens in 1995, wrth
improved removal of solids and BOD and improved disinfection.
Secondary treabnent begins in 1997, dramatically changing solids
and BOD loading to Harbor. Water clarity improves. Inter-Island tunnel
and outfall tunnel completed. Nut Island decommissioned so
discharges to Quincy Bay and Hingham Bay cease.
Bottom-dwelling communities continue gradual recovery, becoming
more diverse, sediment oxygenation continues to improve.
Full secondary treatment completed. All sewage treatment plant
discharges to Boston Harbor cease.
Ecosystem recovery continues with diverse communities of plants and 
animals returning to Harbor. Contaminated sediments gradually buried
under cleaner sediments, and bioaccumulation of toxic chemicals abates 
in tne Harbor.
Although not pristine, most of Boston Harbor will be an example of a
normal New England coastal ecosystem. 
•• ••

14
08 
3 
06 
0 
0
26
75-79 
BEACH POSTINGS HAVE
DECREASED IN THE 1990'S
o 6 _ o _______ o__. 
14 0 
MALJBU BEACH 
1 6 16 08 0 
.SliQfil B~6CH 
06 02 12 
02 
80-84 85-89 90-94 1995 
FIGURE 14: The graph shows the average number of beach 
postings for four fNe-year penods (since 1975) and for 1995 for
MDC Boston Harbor beaches. Different beaches varied greatly in
the number of postings, but a general pattern 1s clear. The num- 
bers of postings were low in the 1970s and increased during the
1980s. Dunng the l 980s the sewerage system, mcludmg pump- 
ing capacity at the Deer Island plant. was deteriorating.
Dunng the 1990's, 1ntenm improvements at the treatment
plants, the cessation of sludge dumping in the harbor, construe- 
boo of three CSO treatment facilities, and increased community 
attention to local sewer contam1nabon problems had the cumula- 
bve effect of unproving water quality at beaches.
In 1995, there were only a few beach postings, in part
because of lower than normal rainfall, although Wonaston Beach 
continued to have pollution problems due to contaminated
storm drains. 
Properly treated wastewater poses little
health risk from pathogens. Only a small frac-
tion of the pathogen-indicating fecal coliform
bacteria cw-renlly discharged to the Harbor 
comes from Doer and Nut Island sewage treat-
ment plants. Most fecal coliform contamina-
tion in Boston I larlmr comes from combined
sower overflows (CSOs) and contaminated
storm drains. Today's lower average levels of 
bacteria in areas of the Harbor reflect the
cumulative impact of improved pumping, ces- 
sation of sludge and scum discharges, new
CSO treatment facilities, better maintenance of
pipes and outfalls, and improved disinfection
of wastewater.
Among Boston Harbor's major public attrac- 
tions are its miles of sandy beach, from
Conslilution Beach and Winthrop town beach-
es on Winthrop Bay to Wollaston Ileacb in
Quincy and numerous town beaches in
Weymouth, Hingham, and Hull.
Since 1973, the Metropolitan District
Commission (MDC) has monitored fecal col-
i form levels at its beaches in Boston Harbor
during the summer swimming season and
used these data to determine whether or not to
post beaches as unsafe for swimming (Flt;URE 
14). The beach data illustrate waler quality
trends from the early 1970s through the early
1990s, when sewer system improvements
began to show in decreased baclerial levels in 
the Harbor. 
B TOXIC CONTAMINANTS: Some
chemicals found in sewage can, in
high enough concentrations, kill or injure
sensitive marine organisms. 
These contaminants can accumulate in sedi-
ments or in the marine food chain to toxic lev-
els, and pose a threat to human health through
the contamination of seafood. Certain toxic
chemicals are defined by the Environmental
Protection Agency (EPA) as priority pollutants
and their discharge is strictly regulated.
These include heavy metals, PCBs, pesticides,
and other chemicals such as polycyclic aro- 
matic hydrocarbons [PAHs) found in petrole-
um products and produced when fossil fuels
are burned.
The best way to keep industrial and house-
hold chemicals out of treated wastewater is Lo 
keep them from enlering the wasto stream.
Ongoing federal, state, and MWRA waste pre-
vention programs have already led lo substan-
tial reductions in contaminants entering the
treatment plants. 
CONTAMINANTS IN BOSTON HARBOR'S
SEDIMENTS 
Contaminants can remain in the marine
environment for decades, and Boston Harbor is 
only slowly recovering from many years of
unregulated discharges through sewers, storm
drains, and direct commercial or industrial
discharge. 1n the mid-1980s, lhe Harbor's sedi-
ments contained such high levels of contami-
nants that it was labeled the ·'dirtiest Harbor in 
the nation." 
IMPROVING CONDITIONS 
Even though change is slow, there are inrn- 
cations of improvement in parts of the Harbor.
Several recent studies strongly suggesl that, as
contaminant inputs decline, sediments are 
a lready beginning to cleanse themselves. The
most noteworthy of these is a study in which
U.S. Geological Survey researchers have col-
lected and analyzed surface sedinients al four
Harbor sites three times since 1977. At these
sites, the concentrations of heavy metals
decreased between Lhe late 1970s and 1993 
(TABLE 4). Other recent studies have con-

firmed lhese results, both for melals and for
organic contaminants. In 1993, U.S. National
Oceanic and Atmospheric Administration
research confirmed that sediment conlamina-
lion and toxicity remains a problem in Boston
Harbor sediments. On average, lhe Inner
Harbor contains the most contaminated sedi-
ments with concenlrations in the Outer Harbor
lessening from Dorchester and Winthrop Bays
to Quincy Bay. The lowest contamination lev- 
els are found in Hingham and Hull Bays. 
CONTAMINANTS IN MARINE ORGANISMS 
Small animals and bollom-feeders that live
on or in the sea.floor ingest contaminants in 
Lbe sediments. Since these organisms arc prey
for fish and shellfish, the contarninanls they
contain can become concentrated in the bodies 
of larger animals. Also, many organisms can
absorb lhese toxic chcmic:als through lhe skin.
Some sensitive species may not be able to live
in sediments with high contaminant levels.
Overall, rec:ent measurements of the levels of
contaminants in lobster and winter flounder
and the effects of contaminants upon the
health of these bottom-feeders mirror the 
results of the sediment studies, showing recent
improvement but remaining contamination. 
TABLE 4: DECREASES IN HEAVY METALS AT
FOUR SITES IN BOSTON HARBOR, 1977-1993. 1 
Metal Decrease' Range' 
CHROMIUM 54% 4().68% 
COPPER 31% 21-41%
LEAD 46% 37,55% 
MERCURY 37% 24-50% 
SILVER 33% 16-50%
ZINC 44% 26-62% 
1 Dala and analysis are from Bothner et al 11996). 
·Average percent decrease m metals al the 4 sites from 3 surveys ber,,1!eo 
1977 and 1993. as esbmated by an analysis (regress,ool of metals changes.
'The ranges ,n percem decrease show the marg,n of error around lhe 
analysis. 
J 
2
(I 
PCBS IN LOBSTER TISSUES
HAVE DECREASED SINCE 1987
Total PCB' s parts per million wet weight 
>8ppm 
- Meat, MWRA study 
• Tomalloy, MWRA monitonng 
FDA ACTION LEVEL 
- Meat, EPA study 
• Tomalley, EPA study 
1987 1992 1993 1994 1995 
FIGURE 15: Concentrations of polychlorinated b1phenyls 
in Boston Harbor lobster have decreased over the past
decade, particularly in lobster hepatopancreas (tomalley).
The use of PCBs was banned 1n the early 1970s. The 1987 
data are from an EPA study of contaminants in lobster from
Quincy Bay; 1992- 1995 data are from MWRA monitoring. 
There are no data for 1991. There are several analytical 
differences between the EPA study and the ongoing MWRA 
monitoring (which 1s consistent with other current national 
programs!. Because of these and other differences between
the studies, the apparent decrease in PCBs must be inter- 
preted wrth caution. 
LOBSTER: The American lobster sustains a
major commercial fishery along Lhe entire New
England coast. More lobster are caught in and
around Boston H;irbor than anywhere else in
Massachusetts. ln 1990, morn than 5 million
pounds of lobster were caught in the Harbor,
contributing more than $13 million lo the local
economy.
Because lobsters hunt and scavenge their
food from lhe seafloor, they are exposed to
contaminants from the sediments. Contamin-
ants in lobster tissue have been measured by
MWRA since 1992. Although Boston Harbor
lobsters have somewhat higher levels of conta- 
mination than lobsters caught in
Massachusetts and Cape Cod Bays, these con-
taminanl levels have declined significantly
since the mid-1980s when the state i.ssued a
public health advisory againsl consuming lob-
ster lomalley or hepatopancrcas (F1c1JRE 15). 
This liver-like organ breaks down or stores
toxic contaminants and, because it is an
important fat storage organ, accumulates high-
er concentrations of fat-soluble contaminants
like PCBs than the leaner tail and claw meat of
the lobster. 
WINTER FLOUNDER: Winter flounder have
long been a mainstay of tl1e commercial and
recreational fisheries in Boston Harbor and
Massachusells Bay. Houghs Neck in Quincy,
once borne to six boat rental businesses. was
known as the "11ormder capital of lhe world." 
Like lobster, 0ounder live and feed on lhe
sea floor, making them vulnerable to contami-
nants in sediments and in the small senfloor 
organisms they eat. /\s with lobster, contami-
nants in flounder concentrate in lhe liver. 
Contaminant levels are generally so low in the 
Ilounder's lean filot, oven in fish from Boston
Harbor, that lhe meat poses no significa11t 
health risk lo humans. However, the contami-
nants in the liver of the Harbor flounder 
cause<l. Lbe fisb to develop several types of dis-
eases or lesions, and served as a warning of
excessive Harbor contamination.
ln the mid 1980s, the U.S. National Marine
Fisheries Service found that most of the floun-
der in Boston Harbor showed fin rot, 8% had
liver tumors, and almost 70% had minor
lesions associated with exposure lo contami-
nants. These results helped focus public
attention on the problem of pollution in
Boston Harbor.
Since lhe 1980s, the improving health of 
llounder has been nssociated with lhe major
15

16 
POLLUTION-RELATED LIVER DISEASE
HAS DECLINED IN BOSTON HARBOR FLOUNDER 
80 
70 
60 
50 
-IO 
JO 
20 
I() 
u
Percent of Deer Island flounder wrth disease
• Liver Tumors
• Eartv Liver Disease 
. ,, .. - •• 84 '~6 87 R8 !19 9() 91 92 93 9.J 95 
FIGURE 16: Flounder hver disease has declined since the mid- 
198Os and liver tumors have not been seen since 1991. The
early liver disease Is a condition called centrotubular hydrop1c
vacuolation, a non-ltte-threatening condition linked to an animal's
exposure to chlorinated hydrocarbons (pesticides and/or
PCBs). Data are from a 1984 NOAA stucly. research by Woods
Hole investigators, and from ongoing MWRA monitoring. 
reductions in contaminant discharges to Boston
Harbor. Woods Holo scientists have found Lhat 
the numbers of fish showing mild, contaminant- 
associated liver disease dropped from about
70% of the population before 1989 (when
sludge was being dumped in the Harbor) to less 
than 50% in the followi ng years. Similarly, liver
tumors, the most serious contaminant-related
disease, declined from about 10% of the floun- 
der population before 1989, to about 4% 
between 1989 and 1991, to zero in Lhe years
since (FIGURE 16). However, Harbor tlounder
continue to show more signs of contaminant-
associated lesions than do fl ounrler from
Massachusetts and Capo Cod Bays. 
C OXYGEN-CONSUMING ORGANIC
MATTER: Once in the Harbor,
some components of sewage decay and
use up dissolved oxygen (DO). 
Aquatic animals need adequale DO in Lhe
waler lo breathe. The amount of DO used up
by wastewater as it decomposes is called
Biochemical Oxygen Demand (BOD). By
removing the majority of the settleable solids 
from wastewater, primary treatment causes a
substantial reduction i.L1 BOD. Thus. the
increased solids removal at the new Deer
[sland primary plant resuJled in a small but 
significant <lecreaso in BOD in the effluent.
Low DO is most problematic in the summer
because (1) warmer water can hold less oxygen
than colder water, (2) tho process of decay is
more rapid, and (3) the population of aquatic 
organisms increases and is more active.
Bollom waters tone! to have lower oxygen lev-
els than surface waters, where oxygen can be
absorbed direcLJy from the air. In extreme sit- 
uations, all the DO can be used up (anoxia),
causing fish kills.
While d issolved oxygen levels in Boston
Harbor rarely gel to zero, DO is frequently
lower than the stale standard of 5 parts per
mi llion. especially in water near the seaflour. 
1n the summertime. low DO in bollom water is
particularly frequent in tho narrow channels of
Boston's Inner Harbor. Dissolved oxygen vio-
lations in Iloston Harbor over tho past 6 years
have shown no improvement (F[GURE 17). 
D SUSPENDED SOLIDS: These 
solids are a mix of silts and organic
waste particles. 
These small particles, tinier than grains of
sand, give raw sewage its cloudy, opaque
appearance. Suspended solids can have a
direct effoct on tho Harbor by increasing its
turbidity (clouding the waler), and lhey are 
also of concern because of the BOD and/or
contaminants they can carry. When t.bese par-
ticles settle out onto LJrn sea noor, they can 
lead to lower DO and contaminate the sedi-
ments with toxic chemicals. In extreme cir- 
cumstances. such as in the vicinity of a sludge
discbarge, solids can build up so quickly Lhey
smother the animals Lhal live on or in the sea 
floor sediments.
The main goal of primary treatment is tho
removal of solids. Startup of the now primary
treatment plant resulted in a significant reduc- 
tion in the discharge of these solids to the
Harbor. Further substantial reductions in Lhe
discharge of solids will occur with secondary
Lrealmenl, which removes the smaJler. so- 
called "colloidal" solids from effluent; with 
the transfer of Nut Island flows to the new
Deer Island plant; ru1d with the improved dif-
fusion of effluent in Massachusetts Bay in
1998.
20
15
10 
SUMMERTIME DISSOLVED OXYGEN
VIOLATIONS IN THE INNER HARBOR
Percent of samples not achieving 
5mg/1 criterion 
O 1989 1990 1991 1992 1993 1994 1995 
FIGURE 17: Ltm,ted nver flow into the Inner Harbor com-
bines with BOD inputs, sluggish tidal circulation and high 
oxygen usage to deplete the bottom waters of oxygen. The
bars show the percent of near•bottom DO measurements at
Inner Harbor monitoring stations below the state standard.
Samples were taken when water temperature exceeded 15
degrees Celsius.

GRADIENTS OF WATER CLARITY IN BOSTON HARBOR 
,_ 4' 
/~ .... , I 
• 2.4 
2,0 
./ UI 1.6 
- -· FIGURE 18: On average, water clarity increases from the Harbor's shallow embayments to the deeper ocean out in 
Massachusetts Bay. Values on the map are depths (meters) of disappearance of a standard white ·secchi" disk lowered into
the water, and are average summer values !June-October). 1993-1994.
SOLIDS POLLUTION AND WATER
CLARITY 
Waler clarity determines how the public
perceives and lherofore uses the Harbor--
nobody wants L o swim or dive in cloudy
water. Before December 1991 , black plumes of
smelly sludge reduced the clarity of the water
to zero at the I wo discharge sites off Deer
island and Long T sland (whore N,11 [sland
sludge was clischarged until 1991). The water
surface at lhn two sites was also marred by
opaque slicks and foam caused by the noating
scum discharged with the sludge. Since those
discharges slopped, Lhe visible pollution al
these sites has disappeared. To date, this has
been Lhe greatest improvement in Boston
Harbor's water clarity.
Water clarity also detennines the extent and
depth of light penetration inlo Lhe water, which
in tum affects the growth of ecologically impor-
tant species of plants, including seagrasses. Not
only are seagrasses important habitats for a wide
variety of bottom-dwelling fish anrl i nvp,rtebrates, 
U1eir rools also play a role in improving water
clarity by helping to bind soft bottom sediments 
that are 0U1erwise easily stirred up.
Various factors nffor.t water clarity in
Boston J !arbor such as concentrations of sus- 
pended particles. floating algae (or phyto-
plankton), and dissolved materials in the 
water. These solids may occur natura!Jy or
enter lhe Harbor in sewage effluent. The waler
clarity varies from region to region, being 
grm1tesl al Lhe mouth of the Harbor where
exchanges with the r.lcar water of
Massachusetts Bay are greatest and lowest in 
thH shallow embayments (such as Dorchester
and Quincy Bays) where bottom sediments can
be stirred up into the water by wave action 
(FrGl 'RF. 18). 
Many observers, from marina owners to lob-
stermen, report improved water clarity
throughout the Harbor in 1H~l5. In Boston
Harbor, water clarity varies nahirally from day 
to day as sediments are resuspended by strong
currents and waves, floating algal blooms
appear, and rivers bring in dissolved materials.
Because of this natural variability, the routine
water clarity monitoring of the Harbor that
began in 1993 will need to be continued for 
severa l more years bc~fore any improvements
can be verified by scientific measurement. 
SOLIDS POLLUTION AND SEAFLOOR
COMMUNITIES 
Seailoor communities a.re susceptible to
pollutants because ( I ) they have lillle mobil ity. 
(2) conlaminanls collect in U1e sediments, and 
(3) sewage solids use up oxygen in the sedi-
ments.
ln the ocean, the communilies fanned by
species of plants anci anim • ls that live on or 
within Urn seafloor a.re known as benlhic com- 
munities. Because these bollom-dwellers are
w1able to quickly move from thnir environ-
17

18 
A.1989-1990 AMPEUSCA DISTRIBUTION 
• Dense Tubcmats 
• Few Tubemats 
0,.."' 
JI • • 
B.AMPELISCA 1995
• Dense Tubernats 
o ...... 
"·. 
ment, they are a sensitive indicator of environ- 
mental conditions and are therefore importanl
to the study of ocean pollution.
The Liny worms and shellfish in the benlhic
community are mainly affected by sewage pol-
lution in two ways. First, toxic pollutants
adhere to particles in the water that are then
either filtered out of the water by benthic filter
feeders or settle to the bottom sediments.
Second, the BOD, which also lends Lo sellle
on the bottom, can lower sediment oxygen
levels when large amounts of it decay. caus- 
C. EXTENT OF AMPHIPOD BEDS
IN BOSTON HARBOR 
% of Stations Surveyed 
1992 1993 1994 1995 
D. AVERAGE DEPTH OF OXYGEN
PENETRATION INTO BOSTON HARBOR
Sediment oxygen penetration (Centimeters) 
2.01-------
15 I------- 
1.0 
0.5 
00 1990 1992 1 993 199'1 1995 
FIGURE 19 (A·D): INC REASE IN AMPHIPODS ON THE HAR-
BOR FLOOR. Boston Harbor's sediment quality has
improved enough to be increasingly colonized by shrimp-like
amph1pods that further extend the depth of oxygenation in
the sediments. 
ing stress to the benlhic animals.
Studies of Harbor benthic communities
made during the late 1970s and early 1980s
showed that much of the northern parts of the
Harbor was seriously degraded, with very low
numbers of a few polluliou-toleranl species.
The southern parts of Boston Harbor, which
were more distant from major sewage dis-
charges and heller flushed, had healthier ben- 
Lhic communities.
In more recent years, there have been some
improvements in the Harbor's sediments.
Although these changes cannot be attributed
solely lo decreased pollution (major storms
and natural cycles can also affect the sedi-
ments), they are very encouraging. Since 1991,
MWRA's monitoring programs have shown
large increases in the numbers and kinds of
organisms found near the former sludge dis-
charges, signaling dramatic local recovery. A
harbor-wide trend is evident in dense beds of
a small shrimp-like amphipod called 
Ampelisca. a food source for winter flounder. 
Ampelisca covered roughly 25% of the Harbor
noor in 1989 and 1990 (FIGURE 19A) but
increased to more than 60% in 1995 (FIGURE
191l). This ampbipod is only moderately pollu-
tion-tolerant and is not found in extremely
contaminated areas; its growth is likely an
indication that the Harbor is recovering from 
severe pollution (FIGURE 19c:). 
Ampelisca make tubes in which they live
and use to burrow into the ocean floor, further
oxygenating the sediments. Thus, the presence
of this organism makes the sediments more
habitable for other benthic orgilllisms. On
average, oxygen penetrates deeper into the 
floor of Boston Harbor now than when sludge
was being discharged, another sign of improv-
ing sediment health (FIGURE 190). 
E NUTRIENTS: While nutrients are
essential for the growth of plants in
the ocean, an excess of nutrients can
be damaging. 
Nutrients like nitrogen and phosphorous are
familiar to many people as the active ingrecti- 
ents in lawn and agricultural fertilizers. In 
aquatic environments, excessive amounts of 
nulrients-€specially nitrogen-can stimulate
the overgrowth of phytoplankton and seaweed. 
In poorly flushed systems, blooms of phyto-
plankton can discolor the water, produce
odors, shade out bottom-living seagrasses, and
deprive fish and shellfish of oxygen. Despite

the fact that Boston Harbor receives large
amounts of nutrients from the two wastewater
treatment facilities, algal blooms are only a
minor problem because the nulrienls are 
arlded mainly at the mouth of the Harbor
which is well flushed.
Boston Harbor shows regional differences in
phytoplankton populations with the largest
populations occurring in the lnner Harbor
which has slower currents and receives inputs
of nutrients from Lhe Charles and Mystic
Rivers lFJGLRE 20).
There is also more algae near Nut Island,
presumably because of the nutrient inputs
from the Nut Island wastewater treatment
facility. No such elevations occur off Deer
Island, perhaps because this region is better
11ushed, and the nutrients are diluted with
water from Massachusetls Bay before the algal
populations can build up. 
At this time, and as would be expected, sig- 
nificant Harbor-wide reductions in algal popu-
lations have not been seen. This is because
only a small proportion of the nitrogen in
sewage is removed by primary Lreatmenl. 
F FLOATABLES: Plastics and other
floating debris cause unsightly slicks
on the water. 
Floatables are frequently the most visible
evidence of polluted waler. They include Loi-
let paper, condoms, and tampon applicators,
as well as oil and grease. While obviously aes- 
Lbelically offensive, floatables can includo
plastic bags or six-pack rings which can entan-
gle or be mistakenly oaten by marine life.
Combined sewer overflows, a major source
of floatablc pollution, have been greatly
reduced in both volume and frequency by an
increased pumping capacity at the treabnent
plants, and better overall sewer system perfor- 
CONCENTRATIONS OF ALGAE VARY IN BOSTON HARBOR 
Q · - - 
/_ .. , 
• 
~"" -. 
-· 
FIGURE 20: Quantities of microscopic floating algae in the Harbor are slightly elevated in the Inner Harbor and off Nut
Island, but are generally low m all areas. Values are average summer (June to October) chlorophyll concentrations, 1993- 
1994. Chlorophyll 1s a measure of the amount of algae in the water. Units are micrograms of chlorophyll per liter. 
mance. The Interim Improvements to the scum
handling faciliLies and the landfilling of sewn
instead of mixing it with sludge, greatly
reduced the discharge of scum lo the Harbor.
The removal of sludge discharges in 1991 aud 
the start-up of the new primary plant in 19H5 
also reduced the amount of 0oalables entering
the Harbor. CSO improvements being phased
in over the nexl ten years will decrease floata-
bles even more.
To complement the decrease in sewage-relat-
ed floatables , conscientious at tent ion lo litter
prevention and removal is important to pro-
vent debris from streets or boats from entering
the Harbor.
19

20
CHAPTER THREE 
BOSTON HARBOR IN THE 
THE PAST FIVE YEARS have shown reduc-
ti.ans in pollutants. and improvements in key
environmental quality indicators in Boston
Harbor. Over the next five to ten years, the 
quantities of the polluta11ls entering
the Harbor will be decreased fur- 
ther with secondary treatment,
reduced CSO inputs, and reloca-
tion of the outfall. With the 
improved effluent quality and the diffusion of the 
effluent into the vast bottom waters of
Massachusetts Bay, the in1provements to the 
Harbor are expected to be even greater than those
observed to date. The following are Lhe types of
changes we might expect to see in the IIarbor in 
the years to come. 
LESS CONTAMINATION, ESPECIALLY OF
THE SEDIMENTS 
will be !lushed ouLLo Lhe overlying waler and
diluted in Lhe ocean. The slow accumulation of
cleaner sediments will, over decades, bwy 
remaining contaminants. 
CLEARER HAR BOR WATER 
The Harbor shows a natural cycle-the water is 
clearor in winter, and Jess clear in summer. The
completion of the secondary t:reaLmenL process
and the relocation of the Deer Island outfall off-
shore will reduce the quantities of solids entering
Lhe Harbor and are likely Lo further improve waler
clarity.
Although the factors regulating waler clarity are
still not well understood, it seems likely that future
changes in water clarity will be small to moderate.
As with all New England marine systems, Lhe
Harbor's water will aJways contain natural levels of
particles from bottom mud and plankton. 
LESS SEVERE ALGAL BLOOMS: While we
expect the Harbor Lo still show intermillent
blooms of algae, especially in summer, Lhe sizes
and duration of these blooms are expected to
decrease. Primary and secondary treatments only
cause small reductions in the nitrogen in sewage.
One of the futw·e changes will be a significant but Lho creation of Lhe now outfall offshore is pro-
reduction in chemical contamination of jected to decrease nitrogen inputs Lo Lhe Harbor
the Harbor, esp ecially in ils bottom sec:ti- ~ by 90%, in turn causing a so% reduction in
ments. With contin 11ccl inclnstrial pre-treat- the average amounts of algae in Lhe Harbor
ment programs, secondary treatment al ' (Hydroqual 1995). The reductions in blooms
Deer L<;land. and the new effiuen1 out fall arc likely to be most pronounced near Nut Island,
tunnel. we expect an 80% reduction in inputs of where there are slighUy elevated concentrations of
BOD and toxic chemicals to the Harbor. Less aJgae.
BOD will allow dissolved oxygen levels in tho
sediments to increase, and bottom-dwelling ani- 
mals will be able to live and burrow deeper in the
sediments. As more animals actively bUITow or 
plllllp water through the sediments, contaminants 
POSSIBLY SOME UNWANTED ALGAE: One of 
Lhe consequences of tho decreased n itrogen inputs
to the Harbor may be the generation of blooms of
different forms of algae. Certain algal species can 
YEAR 2005 
become dominant in systems where the availabili- 
ty of inorganic nitrogen is lowered. a situation that
may occur in Boston Harbor when the effluent 
c:tisc:harge is removed. One species that can
bloom under such conditions is the brown tide
organism Aureococcus which can harm shellfish
and soagrass communities (Nixon et al., 1994). 
Aureococcus blooms have Leen observed in the 
last decade in systems such as lower Narragansett
Bay. RI, or Peconic Bay. LL dur.ing periods of
reduced nitrogen inμuL,;. 
A GR EATER VARIETY OF
ANIMALS AND SE AWEEDS 
A healthier ecosystem will be reflected in
increased c:tiversity of Lhe animal and plant com-
munities in Lhe Harbor. In a polluted environ- 
ment. only the few hardiest species of animals and 
plants can survive. As conditions in the Harbor
continue to improve, the number of species
living within the system will increase. This
increase will be especially visible lo divers 
in the Harbor, but will likely also be appar-
ent to waterfront pedestrians w ho, al Rowes
Wharf or Castle Island, may notice a greater
variety of animals and seaweeds on pilings
and sea walls. 
MARINE MAMMALS: For many people,
annual spring and fall sightings of the
Harbor seal and Harbor porpoise have
become symbolic of Boston Harbor's recovery.
Population fluctuaUons and migrntion patterns in
these larger animals, as with most higher level
predators, a.re generally controlled by availability
of prey. cycles of infectious disease, or hunting by
humans. The Marine Mammal Protection Acl has
certainly been the most important factor in pro-
tecting the populations of these animals.

In Boston Harbor, we can expect marine mam-
mal populations to follow natural cycles as they 
do everywhere. Nevertheless, the cumulative
effect of improvements in the Harbor for prey
species like fish and shellfish should create an
increasingly hospitable environment for seals and
porpoises. 
RETURN OF SEAGRASSES: An adclitional 
change that is expected wilh Lhe new outfall. and
may in fact be already underway, is a gradual
recolonization of the shallower areas of the Harbor
by important seagrass habitats. Research from the 
EPA and Lhe New England Aquarium has shown 
that it is likely that seagrasses covered much larger 
areas of the Harbor in the past than they do today 
(FIGURE 21). The decline of seagrasses may have
been caused by decreased waler clarity, growth of
algae on seagrass leaves, or disease.
With the predicted decreases in nitrogen and
solids inputs to the Harbor, less algae, and
increased water clarity (albeit small), seagrass habi-
tats may well recover. In shallow. moderately tur- 
bid systems such as Boston Harbor, even small
increases in water clarity can greatly increase the
area available for soagrass colonization.
The recovery of seagrasses is, however. likely to
take decades. Few beds remain in the Harbor to
serve as a seed population, and seagrasses release
heavy seeds which do not travel long distances.
These grasses can also spread by sencling out
underground shoots (rhizomes}, but this loo is a 
very slow process. Colonization rates will depend
on whether or not brown tide or equivalent algal
blooms occur. and whether artificial transplanting
programs are implemented in the Harbor. 
DECREASED THREAT OF LOW
DISSOLVED OXYGEN LEVELS 
Because of the future decreases in BOD and
nutrient inputs to the Harbor, there may be fewer 
incidents of lowered dissolved oxygen in the bot- 
BOSTON HARBOR EELGRASS CIRCA 1890 
•• 
BOSTON HARBOR EELGRASS CIRCA l 990s 
... 
I' ,,.. '\ 
FIGURE 21: HISTORICAL DECREASE OF EELGRASS BEDS IN BOSTON HARBOR
Eelgrass beds dominated the Harbor 100 years ago and may return as the Harbor recovers 1n the future. 
tom waters of tho Harbor. several years is expected before monitoring shows
The Inner Harbor is especially susceptible to low further improvements in nounrlor liver diseases.
DO in its bottom waters because it is relatively Although the health of fish and lobster will
deep and has a large input of fresh water from the improve, ii is ctifficult to predict whether their
Charles and Mystic Rivers. In the summer, the numbers and size will increase over the next ten
water in tho Inner Harbor becomes stratified: years. This is because the populations of these
warmer, fresher, less dense water stays on the sur- animals follow long-term cycles determined in
face, preventing the bottom waters from mixing large regions of the ocean dist,mt from Boston
upwards. Tho bottom water is kept away from the Harbor, including Lhe Gulf of Maine. These cycles
air, and stays in contact with the bottom sediments al'e governed by natural population fluctuations. 
which deplete the available dissolved oxygen. climatic changes. and overfishing-none of which
Average summer DO levels in Lhe bot.tom waters of can be controlled by activities in Boston Harbor.
the inner Harbor, now at the minimum standard of
5 mg/L, will increase to more than 6 mg/L accord-
ing to predictions by computer models. 
HEALTHIER FISH AND SHELLFISH 
As the inputs of toxic contaminants lo the
Harbor decrease, and sediments gradually become
less toxic, fish and shellfish populations will
become healthier. Sediment quality will improve
slowly and, because fish diseases can develop throe 
years after exposure to contaminants, c1 lc1g tinrn of 
IN SUMMARY 
One certainty is that in Lhe next five to ten
years, the discharges of toxic materic1ls and other
pollutants to the Harbor will be a fraction of what 
they are now. Much of the Harbor, especially the
areas offshore near the wastewater treatment out-
falls, will be healthier places for Lhe animals and
plants living there as well as for the boaters, fish-
ermen and swimmers who uillize this invaluable
resource, Boston Harbor.
21

22 
BLAKE, J.A, D.C. RHOADS, AND I.P.
WILLIAMS. 1993 Boston Harbor sludge
abatement monitoring program: soft bollom
benlhic biology and sedimentology 1991-92 
mouiloring surveys. M\NRA ENQUAD Tech.
Ropt. No. 93-11 . 79 pp. 
BOTHNER, M.H. BUCHHOLTZ TEN BRINK,
M., AND MANHEIM, F.T., IN PREP. Metal
concentrations in slll'face sedimen1s of
Boston Harbor• Changes with ti.mo. 
COLARUSSO, P. PERSONAL COMMUNICA-
TION, SPRING 1996. EPA Region I.
Boston MA. 
DURELL, G.S. 1995. Concentrations of
contaminants in Dorchester Bay and Boston
Harbor sediments collected in the vicinity of
CSO discharges and comparison to 1990
concentrations. MWRA ENQUAD Tech.
Rept. No. 95-14. 128 pp.
DURELL, G.S., L.S. GINSBURG, AND D.
SHEA. 1991. CSO effects on contamina-
tion of Boston Harbor sediment. MWRA
ENQUAD Tech. Rept. No. 91-8. 146 pp. 
HILLMAN, R.E., M.J. MOORE, C.S. PEVEN,
D.A. LEWIS, L. HANSEN, C.D. HUNT,
AND J. STEGEMAN. 1994. 1993 annual
fish and shellfish report. MWRA ENQUAD
Tecl1. Rept. No. 94-9. 195 pp. 
HILLMAN, R.E. AND C.S. PEVEN. 1995. 
1994 annua I fish and shelUish report.
MWRA ENQUAD Tech. Rept. No. 95-5. 
82 pp. 
BIBLIOGRAPHY 
HUNT, C.D., D.E. WEST, AND C.S. PEVEN.
1995. Deer lsland effluent characterization
and pilot treatment plant studies: June 1993 - 
November 1994. MWRA ENQUAD Tech.
Rept. No. 95-7. 140 pp. 
KELLY, J.R. AND R.K. KROPP. 1992. 
Benlhic recovery following sludge abate-
ment to Boston Harbor. MWRA ENQUAD 
Tech. Repl. No. 92-7. 149 pp. 
KROPP, R.K. AND R.J. DIAZ. 1994. 1994
Annual Soft-Bollom Benthic Monitoring
Repl.: Boston Harbor Studies. MWRA
ENQUAD Tech. Rept. No. 94-10. 117 pp. 
KROPP, R.K. AND R.J. DIAZ. 1995. lnfaunal
community changes in Boston Harbor, 1991·
1994. MWRA ENQUAD Tech. Rcpt. No. 95- 
21. 94 pp. 
LEO, W.S., M.S. CONNOR, K. KEAY, AND A.
REX. 1993. Contaminated seilimenls in
Boston Harbor. MWRA ENQUAD Tech. Rept.
No. 9HI. 53 pp. 
LONG, E.R., G.M. SLOANE, R.S. CARR, K.J.
SCOTT, G.B. THURSBY, AND T. WADE,
1996. St!diment toxicity in Boston Harbor:
magnitude. extent, and relationships with 
chemical toxicants. NOAA Technical
Memorandum NOS ORCA 96. 85pp. 
MOORE, M.J., D. SHEA, R.E. HILLMAN,
AND J.J. STEGEMAN. IN PRESS. Trends
in hepatic tumors and hydropic vacuolation.
fin erosion. organic chcmic:als and stable iso-
tope ratios in winter flounder from 
Massachusells, USA. Marine Pollution
Bulletin. 
MOORE, M. J. AND J. J. STEGEMAN.
1993. Liver pathology of winter fiouoder: 
13oston Harbor, Massachusetts Bay, and Cape
Cod Bay- 1992. MWRA ENQUAD Tech.
Rept. No. 93-7. 45 pp. 
MOORE, M. J., 8. WOODIN, AND J.
STEGEMAN. 1992. Liver pathology of 
wiuler flounder: Boston Harbor,
Massachusetts Bay, and Cape Corl Bay - 1!J91. 
M\t\TRA ENQUAD Tech. Rept. No. 92-5.
63 pp. 
MWRA. 1991. A spatial and temporal analy- 
sis of Boston Harbor microbiological data.
MWRA ENQUAD Tech. Rept. No. 91-3. 
81 pp. 
REX, A.C.. 1991. Combined sewer overflow
receiving water monitoring: June 1989·
October 1990. MWRA ENQUAD Tech. Repl.
No. 91-2. 337 pp.
REX, A.C. 1993. Combined sewer overflow
receiving water monitoring: Boston Harbor
and its tributary rivers. MWRA ENQUAD
Tech. Repl. No. 93-4. 210 pp. 
SAIC. 1992. REMOTS sediment-profile pho-
tography survey of Boston Harbor,
Dorchester, Quincy, Hingham, and Hull Bays.
MWRA ENQUAD Tech. Rept. No. 92-6.
42 pp. 
UHLER, A.D. AND D. E. WEST. 1994. Deer
Island eflluent characterization JW1e - 
November, 1993. MWRA ENQUAD Tech.
Rcpt. No. 94-4. 46 pp.

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MASSACHUSETTS WATER RESOURCES AUTHORITY 
100 FIRST AVENUE
CHARLESTOWN NAVY YARD
BOSTON MA 02129
(617) 242-6000
www.mwra.state.ma.us