2008 overview

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2008
Outfall Monitoring Overview 
Massachusetts Water Resources Authority
Environmental Quality Department
Report 2009-16

Citation:
Werme C, Rex AC, Hall MP, Keay KE, Leo WS, Mickelson MJ, Hunt CD. 2009. 2008
outfall monitoring overview . Boston: Massachusetts Water Resources Authority. Report
2009-16. 69p.

2008
Outfall Monitoring Overview 
prepared by
Christine Werme
Berkeley, CA 94705
and
Andrea C. Rex, Maury P. Hall, Kenneth E. Keay,
Wendy S. Leo, Michael J. Mickelson
Massachusetts Water Resources Authority
Environmental Quality Department
100 First Avenue
Charlestown Navy Yard
Boston, MA 02129
and
Carlton D. Hunt
Battelle
397 Washington Street
Duxbury, MA 02332
October 27, 2009

2008 Outfall Monitoring Panel and Committees 
Outfall Monitoring Science Advisory Panel (OMSAP) 
Andrew Solow (chair), Woods Hole Oceanographic Institution Marine
Policy Center
Robert Beardsley, Woods Hole Oceanographic Institution
Norbert Jaworski, retired
Robert Kenney, University of Rhode Island
Scott Nixon, University of Rhode Island
Judy Pederson, Massachusetts Institute of Technology Sea Grant
Michael Shiaris, University of Massachusetts, Boston
James Shine, Harvard School of Public Health
Juanita Urban-Rich, University of Massachusetts, Boston 
Inter-Agency Advisory Committee (IAAC) 
Michael Bothner, US Geological Survey
Todd Callaghan, Massachusetts Coastal Zone Management
Jan Smith (alternate), Massachusetts Coastal Zone Management
Thomas Fredette, US Army Corps of Engineers
Ben Haskell, NOAA, Stellwagen Bank National Marine Sanctuary
Matthew Liebman, US Environmental Protection Agency
Jack Schwartz, Massachusetts Division of Marine Fisheries
Catherine Vakalopoulos, Massachusetts Department of Environmental
Protection 
Public Interest Advisory Committee (PIAC) 
Patty Foley (chair), Save the Harbor/Save the Bay)
Bruce Berman (alternate), Save the Harbor/Save the Bay
Edward Bretschneider, Wastewater Advisory Committee
Priscilla Brooks, Conservation Law Foundation
Robert Buchsbaum, Massachusetts Audubon Society
Joseph Favaloro, MWRA Advisory Board
Maggie Geist, Association to Preserve Cape Cod
Tara Nye (alternate), Association to Preserve Cape Cod
Sal Genovese, Safer Waters in Massachusetts
Vivian Li, The Boston Harbor Association

2008 OUTFALL MONITORING OVERVIEW I
Table of Contents 
Summary ............................................................................................................................. v 
1. Introduction..................................................................................................................... 1 
2. Effluent ........................................................................................................................... 2 
2008 Characterization ..................................................................................................... 2 
Contingency Plan Thresholds ......................................................................................... 8 
3. Water Column................................................................................................................. 9 
Physical Conditions ...................................................................................................... 11 
Water Quality................................................................................................................ 15 
Phytoplankton Communities......................................................................................... 20 
Zooplankton Communities ........................................................................................... 24 
Contingency Plan Thresholds ....................................................................................... 25 
4. Sea Floor ....................................................................................................................... 27 
Sediment Characteristics and Tracers........................................................................... 30 
Sediment-Profile Imaging............................................................................................. 32 
Soft-bottom Communities............................................................................................. 33 
Hard-bottom Communities ........................................................................................... 35 
Contingency Plan Thresholds ....................................................................................... 36 
5. Winter Flounder ............................................................................................................ 38 
Contingency Plan Thresholds ....................................................................................... 42 
6. Special Studies .............................................................................................................. 43 
Chlorophyll Measurements........................................................................................... 43 
Predicting Red Tides..................................................................................................... 43 
Marine Mammal Observations ..................................................................................... 46 
Nutrient Loads to Boston Harbor.................................................................................. 48 
Benthic Flux.................................................................................................................. 50 
7. Stellwagen Bank National Marine Sanctuary ............................................................... 54 
Water Column............................................................................................................... 54 
Sea Floor ....................................................................................................................... 59 
8. Monitoring Questions and Answers: 2008 ................................................................... 62 
References......................................................................................................................... 66 
List of Acronyms .............................................................................................................. 69

2008 OUTFALL MONITORING OVERVIEW II
List of Figures 
Figure 2-1. Annual effluent flows....................................................................................... 2 
Figure 2-2. Monthly primary and secondary flows in 2008 ............................................... 3 
Figure 2-3. Annual solids discharges.................................................................................. 4 
Figure 2-4. Annual metals discharges................................................................................. 4 
Figure 2-5. Annual mercury discharges.............................................................................. 5 
Figure 2-6. Annual nitrogen discharges.............................................................................. 6 
Figure 2-7. Average annual biochemical oxygen demand.................................................. 7 
Figure 3-1. MWRA Bay Water Quality Monitoring stations and regional groupings ....... 9 
Figure 3-2. MWRA plankton stations............................................................................... 10 
Figure 3-3. Flows of the Merrimack and Charles rivers during 2008 .............................. 11 
Figure 3-4. Merrimack River and Charles River discharges to the ocean ........................ 12 
Figure 3-5. Monthly average wind stress at the Boston Buoy.......................................... 13 
Figure 3-6. Nearfield surface and bottom water temperature. .......................................... 14 
Figure 3-7. Nearfield surface and bottom water salinity .................................................. 14 
Figure 3-8. Before-After, Control-Impact station groups................................................. 15 
Figure 3-9. Changes in seasonal ammonium concentrations from the baseline to the post-
diversion period ................................................................................................................ 16 
Figure 3-10. Annual mean ammonium concentrations..................................................... 17 
Figure 3-11. Changes in seasonal chlorophyll concentrations from the baseline to the
post-diversion period ........................................................................................................ 18 
Figure 3-12. 2008 Boston Harbor chlorophyll levels compared to the baseline range,
baseline mean, and post-diversion mean .......................................................................... 18 
Figure 3-13. Potential annual production.......................................................................... 19 
Figure 3-14. Nearfield surface and bottom dissolved oxygen concentrations.................. 19 
Figure 3-15. Phaeocystis pouchetii colony from Massachusetts Bay............................... 20 
Figure 3-16. Abundance of Phaeocystis pouchetii since 1992 ......................................... 21 
Figure 3-17. Nearfield abundance of dominant phytoplankton groups in 2008 ............... 21 
Figure 3-18. Nearfield abundance of Alexandrium fundyense since 1992 ....................... 22 
Figure 3-19. Alexandrium fundyense cell concentrations in Massachusetts Bay and
Boston Harbor in June 2008 ............................................................................................. 23 
Figure 3-20. 2008 nearfield survey mean total zooplankton abundance compared to
baseline range, baseline mean, and post-diversion mean ................................................. 24 
Figure 4-1. Locations of nearfield soft-bottom stations for chemical parameters,
sediment-profile imaging, and community parameters .................................................... 27 
Figure 4-2. Locations of farfield soft-bottom stations for chemical and community
parameters ......................................................................................................................... 28 
Figure 4-3. Locations of hard-bottom stations.................................................................. 29

2008 OUTFALL MONITORING OVERVIEW III 
Figure 4-4. Clostridium perfringens spores normalized to percent fine fraction in the
sediments........................................................................................................................... 30 
Figure 4-5. Total PCB concentrations in sediments ......................................................... 31 
Figure 4-6. Annual apparent color RPD for data from nearfield stations......................... 32 
Figure 4-7. Annual community parameters in the nearfield ............................................. 34 
Figure 4-8. Examples of levels of sediment drape from 2008 photographs ..................... 35 
Figure 5-1. Winter flounder sampling sites. ..................................................................... 38 
Figure 5-2. Annual catch per unit effort ........................................................................... 39 
Figure 5-3. Annual percent females in winter flounder samples ...................................... 40 
Figure 5-4. Annual prevalence of centrotubular hydropic vacuolation ........................... 41 
Figure 6-1. Top: Annual abundance of Alexandrium cysts in Maine seed beds. Bottom:
Annual modeled concentrations of Alexandrium cells. .................................................... 44 
Figure 6-2. Modeled abundance of Alexandrium cells for 2008 ...................................... 45 
Figure 6-3. Approximate locations of whale sightings during 2008 nearfield and farfield
water quality surveys ........................................................................................................ 47 
Figure 6-4. Total loadings of nutrients and solids to Boston Harbor, 1990–2007............ 49 
Figure 6-5. Nutrient loadings to Boston Harbor by source............................................... 50 
Figure 6-6. Benthic flux stations in Massachusetts Bay and Boston Harbor.................... 51 
Figure 6-7. Percent total organic carbon in surface sediments from Massachusetts Bay. 52 
Figure 6-8. Percent total organic carbon in surface sediments from Boston Harbor........ 53 
Figure 6-9. Nutrient fluxes in surface sediments from Boston Harbor............................. 53 
Figure 7-1. Water column stations, including those in and near the Stellwagen Bank
National Marine Sanctuary ............................................................................................... 55 
Figure 7-2. 2008 bottom water dissolved oxygen concentrations in Stellwagen Basin
compared to baseline range, baseline mean, and post-diversion mean............................. 56 
Figure 7-3. Annual mean total nitrogen at the Stellwagen Bank National Marine
Sanctuary, the outfall nearfield, and Cape Cod Bay......................................................... 57 
Figure 7-4. Annual mean ammonium at the Stellwagen Bank National Marine Sanctuary,
the outfall nearfield, and Cape Cod Bay........................................................................... 57 
Figure 7-5. Annual mean nitrate at the Stellwagen Bank National Marine Sanctuary, the
outfall nearfield, and Cape Cod Bay................................................................................. 58 
Figure 7-6. Annual chlorophyll at the Stellwagen Bank National Marine Sanctuary, the
outfall nearfield, and Cape Cod Bay................................................................................. 59 
Figure 7-7. Farfield benthic stations ................................................................................. 60 
Figure 7-8. Community parameters at stations in or near the Stellwagen Bank National
Marine Sanctuary .............................................................................................................. 61

2008 OUTFALL MONITORING OVERVIEW IV
List of Tables 
Table 1. Contingency Plan thresholds and exceedances as of 2008 .................................. vi 
Table 2-1. Contingency Plan threshold values and 2008 results for effluent monitoring. . 8 
Table 3-1. Contingency Plan threshold values and 2008 results for water-column
monitoring......................................................................................................................... 26 
Table 4-1. Contingency Plan threshold values and 2008 results for sea-floor monitoring.
........................................................................................................................................... 37 
Table 5-1. Contingency Plan threshold values and 2008 results for flounder monitoring.
........................................................................................................................................... 42 
Table 8-1. Answers to the monitoring questions as of the end of 2008............................ 63

2008 OUTFALL MONITORING OVERVIEW V
Summary 
Each year, the Massachusetts Water Resources Authority (MWRA) prepares this report,
an overview of environmental monitoring related to the Massachusetts Bay sewage
effluent outfall. The report includes data collected through effluent, water-column, sea-
floor, and fish-and-shellfish monitoring. It presents information relevant to the MWRA
Contingency Plan, including threshold exceedances, responses, and corrective actions.
The overview also includes sections on special studies and on the Stellwagen Bank
National Marine Sanctuary. This year’s outfall monitoring overview presents monitoring
program results for effluent and field data from 2008, marking eight full years since
discharge was diverted from the shallower, more confined, waters of Boston Harbor to
the deeper waters of Massachusetts Bay, a period called post-diversion monitoring.
The year was relatively wet, and flow through the Deer Island Treatment Plant was
higher than average. There was a corresponding increase in contaminant loads; however,
concentrations of most contaminants in the effluent were very low. Most effluent
contaminants are substantially lower than predicted during the planning and permitting
process for the treatment plant and outfall. Nitrogen remains at levels that do not exceed
Contingency Plan thresholds.
Overall, results of the monitoring were consistent with previous years, with no adverse
impacts associated with the discharge. There were no exceedances of Contingency Plan
thresholds for effluent, sea-floor, or winter-flounder monitoring in 2008. There was one
exceedance of a water-column threshold, when concentrations of the red tide alga 
Alexandrium fundyense exceeded the caution level (Table 1). The Alexandrium bloom
followed the historically typical pattern for red tides in the region, beginning off the coast
of Maine and moving southward along the coast with winds from the northeast. The
pattern suggests no effect of the outfall on the timing or region-wide magnitude of the
bloom.
Special studies in 2008 included improvements to the methods of measuring chlorophyll
in the water column, efforts to predict Alexandrium fundyense blooms, marine mammal
observations, an analysis of nutrient loadings to Boston Harbor, and ongoing study of
nutrient fluxes at the sediment-water interface.
As in other years, no effects of the outfall on the Stellwagen Bank National Marine
Sanctuary were detected. No effects on the water column or sea floor in or near the
sanctuary had been anticipated, and none have been measured.
Prior to constructing the Massachusetts Bay outfall, a series of questions was posed,
aimed at assessing whether the relocated discharge would affect public health, the
environment, or the aesthetics of the region. Baseline and post-diversion monitoring
have answered those questions, and a final section of this report reviews the questions
and answers.

2008 OUTFALL MONITORING OVERVIEW VI 
Table 1. Contingency Plan thresholds and exceedances as of 2008 . (NA = not applicable, 
D =
no exceedance, C = caution level exceedance, W = warning level exceedance) 
Effluent 
Location/
Parameter
Type
Parameter 2000 2001 2002 2003 2004 2005 2006 2007 2008
pH W D D D D D D D D 
Fecal coliform
bacteria,
monthly 
D D D D D D D D D 
Fecal coliform
bacteria,
weekly 
D D D D D D D D D 
Fecal coliform
bacteria, daily D W D D W D D D D 
Fecal coliform
bacteria,
3 consecutive
days 
D D D D D D D D D 
Chlorine
residual, daily W D D D D D D D D 
Chlorine
residual,
monthly 
D D D D D D D D D 
Total
suspended
solids, weekly 
D D W D D D D D D 
Total
suspended
solids,
monthly 
D D W D D D D D D 
cBOD, weekly D D D D D D D D D 
cBOD, monthly D D D D D D D D D 
Acute toxicity,
mysid shrimp D D D D D D D D D 
Acute toxicity,
fish D D D D D D D D D 
Chronic
toxicity, fish D W D D D D W D D 
Chronic
toxicity, sea
urchin 
D W D D D W D D D 
PCBs D D D D D D D D D 
Plant
performance D D D D D D D D D 
Flow NA D D D D D D D D 
Total nitrogen
load NA D D D D D D D D 
Floatables NA NA NA NA NA NA NA NA NA 
Oil and grease D D D D D D D D D

2008 OUTFALL MONITORING OVERVIEW VII 
Table 1, continued. Contingency Plan thresholds and exceedances as of 2008. (NA = not
applicable, 
D = no exceedance, C = caution level exceedance, W = warning level exceedance) 
Water Column 
Location/
Parameter
Type
Parameter 2000 2001 2002 2003 2004 2005 2006 2007 2008
Dissolved
oxygen
concentration 
C D D D D D D D D 
Nearfield
bottom water Dissolved
oxygen
saturation 
C D D D D D D D D 
Dissolved
oxygen
concentration 
D D D D D D D D D Stellwagen
Basin
bottom water Dissolved
oxygen
saturation 
D D D D D D D D D 
Nearfield
bottom water
Dissolved
oxygen
depletion rate
(June – 
October) 
NA D D D D D D D D 
Annual NA D D D D D D D D 
Winter/spring NA D D D D D D D D 
Summer NA D D D D D C D D 
Nearfield
chlorophyll
Autumn C D D D D D D D D 
Winter/spring NA D D D C D D C D 
Summer NA D C C C C C D D 
Nearfield
nuisance algae 
Phaeocystis
pouchetii Autumn D D D D D D D D D 
Winter/spring NA D D D D D D D D 
Summer NA D D D D D D D D 
Nearfield
nuisance algae 
Pseudonitzchia Autumn D D D D D D D D D 
Nearfield
nuisance algae 
Alexandrium 
Any sample D D D D D C C D C 
Farfield
shellfish
PSP toxin
extent D D D D D D D D D 
Plume Initial dilution NA D Complete

2008 OUTFALL MONITORING OVERVIEW VIII 
Table 1, continued. Contingency Plan thresholds and exceedances as of 2008. (NA = not applicable, 
D = no exceedance, C = caution level exceedance, W = warning level exceedance) 
Sea Floor 
Location/
Parameter
Type
Parameter 2000 2001 2002 2003 2004 2005 2006 2007 2008
Acenaphthene NA D D NA NA D NA NA D 
Acenaphylene NA D D NA NA D NA NA D 
Anthracene NA D D NA NA D NA NA D 
Benzo(a)anthracene NA D D NA NA D NA NA D 
Benzo(a)pyrene NA D D NA NA D NA NA D 
Cadmium NA D D NA NA D NA NA D 
Chromium NA D D NA NA D NA NA D 
Chrysene NA D D NA NA D NA NA D 
Copper NA D D NA NA D NA NA D 
Dibenzo(a,h)anthracene NA D D NA NA D NA NA D 
Fluoranthene NA D D NA NA D NA NA D 
Fluorene NA D D NA NA D NA NA D 
Lead NA D D NA NA D NA NA D 
Mercury NA D D NA NA D NA NA D 
Naphthalene NA D D NA NA D NA NA D 
Nickel NA D D NA NA D NA NA D 
p,p’-DDE NA D D NA NA D NA NA D 
Phenanthrene NA D D NA NA D NA NA D 
Pyrene NA D D NA NA D NA NA D 
Silver NA D D NA NA D NA NA D 
Total DDTs NA D D NA NA D NA NA D 
Total HMW PAH NA D D NA NA D NA NA D 
Total LMW PAH NA D D NA NA D NA NA D 
Total PAHs NA D D NA NA D NA NA D 
Total PCBs NA D D NA NA D NA NA D 
Nearfield
sediment
contaminants
Zinc NA D D NA NA D NA NA D 
Nearfield
sediment RPD depth NA D D D D D D D D 
Species per sample NA D D D D D D D D 
Fisher’s log-series
alpha NA D D D D D D D D 
Shannon diversity NA D D D D D D D D 
Nearfield
benthic
diversity
Pielou’s evenness NA D D D D D D D D 
Nearfield
species
composition
Percent opportunists NA D D D D D D D D

2008 OUTFALL MONITORING OVERVIEW IX 
Table 1, continued. Contingency Plan thresholds and exceedances as of 2008. (NA = not
applicable, 
D = no exceedance, C = caution level exceedance, W = warning level exceedance) 
Fish and Shellfish 
Location/
Parameter
Type
Parameter 2000 2001 2002 2003 2004 2005 2006 2007 2008
Total PCBs NA D D D NA NA D NA NA 
Mercury NA D D D D NA D NA NA 
Chlordane NA D D D NA NA D NA NA 
Dieldrin NA D D D NA NA D NA NA 
Nearfield
flounder tissue
Total DDTs NA D D D NA NA D NA NA 
Nearfield
flounder
Liver disease
(CHV) NA D D D D D D D D 
Total PCBs NA D D D NA NA D NA NA 
Mercury NA D D D NA NA D NA NA 
Chlordane NA D D D NA NA D NA NA 
Dieldrin NA D D D NA NA D NA NA 
Nearfield
lobster tissue
Total DDTs NA D D D NA NA D NA NA 
Total PCBs NA D D D NA NA D NA NA 
Lead NA D D D NA NA D NA NA 
Mercury NA D D D NA NA D NA NA 
Chlordane NA C C D NA NA D NA NA 
Dieldrin NA D D D NA NA D NA NA 
Total DDTs NA D D D NA NA D NA NA 
Nearfield
mussel tissue
Total PAHs NA C C C NA NA D NA NA

2008 OUTFALL MONITORING OVERVIEW X 
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2008 OUTFALL MONITORING OVERVIEW 1
1. Introduction 
For more than two decades, the Massachusetts Water Resources Authority
(MWRA) has worked to minimize the effects of wastewater discharge on
the marine environment. During most of those years, the efforts have
included a monitoring program in Massachusetts Bay. The monitoring
program assesses compliance with the National Pollutant Discharge
Elimination System (NPDES) permit to discharge effluent from the Deer
Island Treatment Plant (DITP) into Massachusetts Bay, assures that there
are no unanticipated environmental effects of the discharge, and provides
information for management of the outfall.
Results from most of the baseline-monitoring years, and each year since
MWRA ended discharges into Boston Harbor and began to discharge
treated effluent into Massachusetts Bay, have been documented in annual
reports such as this one, the Outfall Monitoring Overview . Background
information for these overviews and a complete description of the
monitoring program can be found in Werme and Hunt (2008). That
document, the monitoring plans (MWRA 1991, 1997a, 2004), the
Contingency Plan (MWRA 1997b, 2001), area-specific technical reports,
and past outfall monitoring overviews are available on the technical report
list at MWRA’s website, www.mwra.com/harbor/enquad/trlist.html.
Overviews for 1994 through 1999 included only baseline information.
With the Massachusetts Bay outfall operational as of September 2000,
subsequent reports have included information relevant to the outfall
permit, including Contingency Plan threshold exceedances, responses, and
corrective actions.
This year’s outfall monitoring overview presents monitoring program
results for effluent and field data from 2008, marking eight full years since
discharge was diverted from the shallower, more confined waters of
Boston Harbor to the deeper waters of Massachusetts Bay, a period called
post-diversion monitoring. The overview presents 2008 monitoring
results for effluent, water column, sea floor, and winter flounder, and it
compares relevant data to baseline conditions and Contingency Plan
thresholds. It also includes sections on special studies and the Stellwagen
Bank National Marine Sanctuary. A final section lists the monitoring
questions that were posed at the beginning of the program and their
answers to date. The questions have been answered by the years of
monitoring data; the results from 2008 continue to verify those answers.

2008 OUTFALL MONITORING OVERVIEW 2
2. Effluent
2008 Characterization 
Because 2008 was one of the wettest years on record in the Boston area,
average flow to the DITP was somewhat greater than it had been in 2007,
when flow reached a 25-year low. The year was the seventh wettest in
135 years of record-keeping (National Climate Data Center data). Annual
precipitation for 2008 totaled 54.7 inches, while the ten-year average was
43.6 inches. Most of the post-diversion monitoring years have been
relatively wet, while the period just before the diversion was variable and
included several dry years.
Almost all of the DITP flow received primary and secondary treatment
(Wu 2009a, in prep.). Only a small amount of effluent, about 2% of the
total flow, received only primary treatment (Figures 2-1 and 2-2), which
was blended with secondary-treated effluent prior to discharge. The
blended flows met all NPDES permit conditions. 
0
50
100
150
200
250
300
350
400
450
90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08
million gallons per day
MWRA Primary and Secondary Flows 1990-2008
Primary-only (Blended) Treated Flows Primary and Secondary Treated Flows 
Figure 2-1. Annual effluent flows. Average daily flow was relatively high in 2008.
(Primary-only flows are blended with secondary flows, and the blended flows meet
permit limits.)

2008 OUTFALL MONITORING OVERVIEW 3 
0
100
200
300
400
500
600
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
million gallons per day
MWRA 2008 Monthly Flows
Primary and Secondary Treated Flows
Primary-only (Blended) Treated Flows 
Figure 2-2. Monthly primary and secondary flows in 2008. A small amount of primary-
only treated effluent was blended with secondary flows and released during storms.
(Blended flows meet all permit limits.) 
With the increased annual flow, contaminant loads also increased slightly
in 2008 compared to 2007 but remained far below historic levels. Solids
discharges were slightly greater than in 2006 and 2007 (Figure 2-3).
Metals discharges were also slightly greater than in 2007 but much lower
than they had been prior to the introduction of secondary treatment in
1997–2001 (Figure 2-4). Among the metals, only copper and zinc remain
in significant quantities, with other metals present in only trace amounts.
Mercury is now only rarely detected in effluent samples. About ten
pounds of mercury were discharged during 2008, slightly more than was
discharged in 2007, but well below the 50 pounds (0.14 pounds per day)
that were discharged to Boston Harbor in 1999 (Figure 2-5).
Loads of organic contaminants were similarly low, with 3–4 pounds of
polychlorinated biphenyls (PCBs) and 0.5–0.75 pounds of chlorinated
pesticides discharged in 2008. These results reflect substantial, continuing
reductions in contaminant levels throughout the post-diversion period
(Delaney and Rex 2007, Delaney 2009). The current loadings are
significantly lower than had been predicted during planning and
permitting of the Massachusetts Bay outfall.

2008 OUTFALL MONITORING OVERVIEW 4 
0
20
40
60
80
100
120
140
160
180
90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08
Tons per day
Solids in MWRA Treatment Plant Discharges 1990-2008
Sludge Nut Island Deer Island 
Figure 2-3. Annual solids discharges . Solids discharges were slightly greater than the
record low in 2007. 
0
100
200
300
400
500
600
92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08
Average pounds per day
discharged
Year
Metals in MWRA Treatment Plant Discharges 1992-2008
Silver
Nickel
Chromium
Lead
Copper
Zinc 
Figure 2-4. Annual metals discharges . Total metals discharges remained low in 2008.

2008 OUTFALL MONITORING OVERVIEW 5 
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
99 00 01 02 03 04 05 06 07 08
Average pounds
discharged per day
Year
Mercury in DITP Discharges 1999-2008 
Figure 2-5. Annual mercury discharges . Mercury is now only rarely detected in the
effluent. 
Total nitrogen loads were also slightly higher in 2008 than in 2007, and
the proportion of the load made up of ammonium remained high (Figure
2-6). About 10% of the ammonium in the sewage influent is removed by
secondary treatment, and the biological treatment process converts some
nitrate/nitrite and other forms of nitrogen to ammonium. MWRA
continually evaluates nitrogen-removal technologies, so that nitrogen
removal could be implemented at DITP (Bigornia-Vitale and Wu 2008).
These evaluations meet a permit requirement that MWRA be able to
swiftly implement such technologies, if the need arises. Nitrogen loadings
remain below the Contingency Plan threshold.

2008 OUTFALL MONITORING OVERVIEW 6 
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
metric tons per year
*Method change for TKN April 2003
Deer Island Treatment Plant Nitrogen Discharges 1996-2008
Caution Level Other Nitrogen Species* Nitrite/Nitrate Ammonium 
Figure 2-6. Annual nitrogen discharges. Discharges of ammonium remained relatively
high, a result of the secondary treatment process. (TKN = total Kjeldahl nitrogen, a
measure of total nitrogen in the effluent) 
Biochemical oxygen demand (BOD), measured as carbonaceous BOD,
also increased slightly in 2008, to about the same level as was measured in
2006 (Figure 2-7). This increase from a record low in 2007 reflected the
increase in flow, but remained well below levels that might be expected to
affect ambient waters at the discharge. Nitrogenous BOD, which is a
result of the biological processes in secondary treatment and not a permit
limit or Contingency Plan parameter, remained higher than historic levels
but decreased slightly in 2008.

2008 OUTFALL MONITORING OVERVIEW 7 
0
10
20
30
40
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Tons per day
Year
Biochemical Oxygen Demand in MWRA Discharge
1999-2008
Carbonaceous BOD Nitrogenous BOD 
Figure 2-7. Average annual biochemical oxygen demand. MWRA’s permit limits
carbonaceous BOD, which remained low in 2008. Nitrogenous BOD is the result of
microbiological breakdown that occurs during secondary treatment. Ambient monitoring
data show that the discharge has had no effect on dissolved oxygen in the environment.

2008 OUTFALL MONITORING OVERVIEW 8
Contingency Plan Thresholds 
As in 2007, DITP had no permit violations and no exceedances of the
Contingency Plan thresholds in 2008 (Table 2-1). In acknowledgment of
this record, MWRA was awarded a Gold Peak Performance award from
the National Association of Clean Water Agencies. This award recognizes
facilities that have achieved 100% compliance with their NPDES permits
in a calendar year. 
Table 2-1. Contingency Plan threshold values and 2008 results for effluent monitoring.
( cBOD=carbonaceous biological oxygen demand, NOEC=no observable effect concentration,
LC50=50% mortality concentration, MGD=million gallons per day; NA=not applicable) 
Parameter Caution Level Warning Level 2008 Results 
pH None <6 or >9 Not exceeded
Fecal coliform bacteria None
14,000 fecal coliforms/100
ml (monthly 90 th percentile,
weekly geometric mean,
maximum daily geometric
mean, and minimum of 3
consecutive samples)
Not exceeded
Chlorine, residual None 631 μg/L daily,
456 μg/L monthly Not exceeded
Total suspended solids None 45 mg/L weekly
30 mg/L monthly Not exceeded
cBOD None 40 mg/L weekly,
25 mg/L monthly Not exceeded
Toxicity None
Acute: effluent LC50<50%
for shrimp and fish
Chronic: effluent NOEC for
fish survival and growth and
sea urchin fertilization
<1.5% effluent
Not exceeded
PCBs Aroclor=0.045 ng/L Not exceeded
Plant performance 5 violations/year Noncompliance >5% of the
time Not exceeded
Flow None Flow >436 MGD for annual
average of dry days Not exceeded
Total nitrogen load 12,500 mtons/year 14,000 mtons/year Not exceeded
Floatables NA
Oil and grease None 15 mg/L weekly Not exceeded

2008 OUTFALL MONITORING OVERVIEW 9
3. Water Column 
The monitoring program measures water quality, phytoplankton, and
zooplankton at stations in Boston Harbor, Massachusetts Bay, and Cape
Cod Bay (Figures 3-1, 3-2). 
 
 
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z z
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z 
F33
F32
F19
F18
F17
F16
F15
F14
F12
F10
F07
F05
N20
N10
N07
N01
F29
F28
F03
F23
F22
F13
F06
N18
N16
N04
F31
F30
F27
F26
F25
F24
F02
F01 
70°15'W
70°15'W
70°30'W
70°30'W
70°45'W
70°45'W
71°0'W
71°0'W
42°3 0'N
42°3 0'N
42°1 5'N
42°15'N
42°0'N
42°0'N
41°45'N
41°45'N 
 
 
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z z
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z 
F33
F32
F19
F18
F17
F16
F15
F14
F12
F10
F07
F05
N20
N10
N07
N01
F29
F28
F03
F23
F22
F13
F06
N18
N16
N04
F31
F30
F27
F26
F25
F24
F02
F01 
70°15'W
70°15'W
70°30'W
70°30'W
70°45'W
70°45'W
71°0'W
71°0'W
42°3 0'N
42°3 0'N
42°1 5'N
42°15'N
42°0'N
42°0'N
41°45'N
41°45'N 
Cape Cod Bay
Boston
Harbor Massachusetts Bay 
0 10 20 30 40 50 5
Kilometers 
boundary region
northern
boundary
region
offshore
region
coastal region
nearfield region 
z MWRA stations (BWQM) 
  GoMOOS Buoy A 
  NOAA Buoy 44013
MWRA outfall diffuser
Regions
Stellwagen Bank Sanctuary
High : 0
Low : -125 
Figure 3-1. MWRA Bay Water Quality Monitoring (BWQM) stations and regional groupings. 
“Farfield” stations include all stations in Boston Harbor; the coastal, offshore, and northern
boundary regions; and Cape Cod Bay. Also shown are the MWRA outfall; two instrumented
buoys, one operated by the Gulf of Maine Ocean Observing System (GoMOOS) and the other by
the National Oceanic and Atmospheric Administration (NOAA) National Data Buoy Center
(NDBC); and the Stellwagen Bank National Marine Sanctuary.

2008 OUTFALL MONITORING OVERVIEW 10 
The Massachusetts Bay stations located within seven kilometers of the
outfall diffuser are called nearfield stations. Those beyond are grouped
into regions, which together are called farfield stations. Sampling is
augmented by instrumented buoys and remote sensing. A separate Boston
Harbor program contributes additional data. 
 
 
z
z
z z
z z
z z
z z
z z
z z
z z
z z
z z
z z
z z
z z
z z
z z
z z 
F33
F32
F23
F22
F13
F06
N18
N16
N04
F31
F30
F27
F26
F25
F24
F02
F01 
70°15'W
70°15'W
70°30'W
70°30'W
70°45'W
70°45'W
71°0'W
71°0'W
42°30'N
42°3 0'N
42°1 5'N
42°15'N
42°0 'N
42°0 'N
41°4 5'N
41°45'N 
 
 
z
z
z z
z z
z z
z z
z z
z z
z z
z z
z z
z z
z z
z z
z z
z z
z z 
F33
F32
F23
F22
F13
F06
N18
N16
N04
F31
F30
F27
F26
F25
F24
F02
F01 
70°15'W
70°15'W
70°30'W
70°30'W
70°45'W
70°45'W
71°0'W
71°0'W
42°30'N
42°3 0'N
42°1 5'N
42°15'N
42°0 'N
42°0 'N
41°4 5'N
41°45'N 
Cape Cod Bay
Boston
Harbor Massachusetts Bay 
0 10 20 30 40 50 5
Kilometers 
northern
boundary
region
offshore
region
coastal region
nearfield region 
z z Phytoplankton and zooplankton station 
z Zooplankton-only station 
  GoMOOS Buoy A 
  NOAA Buoy 44013
MWRA outfall diffuser
Regions
High : 0
Low : -125 
Figure 3-2. MWRA plankton stations. The stations are a subset of those included in water
quality monitoring. Regional groupings, the instrumented buoys, and the MWRA outfall are also
shown.

2008 OUTFALL MONITORING OVERVIEW 11
Physical Conditions 
Baseline and post-diversion monitoring have found that the water column
in the vicinity of the outfall and throughout Massachusetts and Cape Cod
bays is heavily influenced by river inflows, weather, and other physical
factors. Information about physical conditions provides a context for
interpreting the annual monitoring data.
Because of the high precipitation throughout 2008, the year was also
marked by greater than average flows from the Merrimack and Charles
rivers (Figures 3-3 and 3-4). Flow from the Merrimack River tends to
reflect regional conditions and affects the salinity of bottom waters. Flow
from the Charles River reflects local conditions and may influence surface
salinity. 
Figure 3-3. Flows of the Merrimack (top) and Charles (bottom) rivers during 2008 were
relatively high over the course of the year . In some cases, quarterly flows reached record highs
for the monitoring program. For example, the average January–March flow in the Merrimack
River was the greatest in 19 years of monitoring, translating to the 97 th percentile. In July–
September, flow from both rivers reached record highs. Flows during 2007, shown for contrast,
were high in the spring, but very low in the summer and fall.

2008 OUTFALL MONITORING OVERVIEW 12 
Figure 3-4. Merrimack River (top) and Charles River (bottom) discharges to the ocean. 
(Data are from gauges at Lowell and Waltham, Massachusetts; smooth lines are 3-month
moving averages; note the differences in scale for the rivers.) 
The wind-forcing conditions in 2008 were similar to 2006–2007 and
within the range observed throughout the monitoring program (Figure 3-
5). In most years, spring is a transitional period between winter
downwelling and spring upwelling conditions. Peak upwelling, the
condition in which winds from the south and southwest push surface
waters away from the coast, occurred in July, but over the course of the
year, downwelling conditions predominated, as they have in recent years.
Wave heights were average, with no strong storms that would be expected
to resuspend sediments.

2008 OUTFALL MONITORING OVERVIEW 13 
Figure 3-5. Monthly average wind stress at the Boston Buoy. Positive values indicate
winds from the south or southwest, which result in upwelling-favorable wind stress;
negative values indicate winds from the north or northeast, which favor downwelling.
Data from 2006, 2007, and 2008 show that downwelling conditions have predominated in
recent years. 
Surface water temperatures were warmer than average, particularly during
the summer months (Figure 3-6). In many other years, the summer has
been marked by cooler waters brought to the surface through upwelling.
Bottom waters were cooler than average during May, but were warm
during the late summer and fall.
Salinity was affected by the wet year (Figure 3-7). Surface salinity was
particularly low during the late fall, a period when in other years, the
water has become more saline. The annual average nearfield surface-water
salinity was the lowest measured since the monitoring program began in
1992.

2008 OUTFALL MONITORING OVERVIEW 14 
Figure 3-6. Nearfield surface and bottom water temperature. Summer surface
temperatures were warm. Bottom waters were warmer than average during the late
summer and fall. (Data from 2007 are shown for comparison.) 
Figure 3-7. Nearfield surface and bottom water salinity. Surface measurements are the
lower line. Surface salinity in 2008 was markedly low in the late summer and fall (second
sharp dip in 2008), reflecting the unusually wet year.

2008 OUTFALL MONITORING OVERVIEW 15
Water Quality 
Water quality measurements for 2008 continued to confirm predictions
that there would be detectable local effects of the discharge for certain
parameters and no detectable adverse effects for other parameters or for
any measurements outside the immediate vicinity of the discharge (Libby 
et al. 2009). Measurements of nutrients, dissolved oxygen, phytoplankton
biomass (measured as chlorophyll), and productivity in 2008 continued to
show improvements in Boston Harbor.
The changes in the bay were evaluated using “Before-After, Control-
Impact” (BACI) statistical analyses (Figure 3-8), which compared data
from an “impact” area (the inner nearfield) with those from “control”
regions (the outer nearfield, offshore Massachusetts Bay, and Cape Cod
Bay). None of the measured changes have suggested large or unexpected
effects of the discharge. 
Figure 3-8. Before-After, Control-Impact (BACI) station groups. The BACI
analyses were used to evaluate effects of the outfall in comparison to regional
changes.

2008 OUTFALL MONITORING OVERVIEW 16 
Ammonium is the major component of total inorganic nitrogen in the
effluent, and simple dilution models suggested that, following the
diversion, increased concentrations of ammonium would be detectable in
the nearfield. As anticipated during planning and permitting, there have
been increases in ammonium at the stations closest to the discharge
compared to baseline conditions and relative to regional background
conditions (Figure 3-9). At the same time, much greater decreases in
ammonium concentrations have been measured in Boston Harbor and in
the coastal area. 
-71 -70.9 -70.8 -70.7 -70.6 -70.5 -70.4 -70.3 -70.2
41.9
42
42.1
42.2
42.3
42.4
42.5
42.6
-71 -70.9 -70.8 -70.7 -70.6 -70.5 -70.4 -70.3 -70.2
41.9
42
42.1
42.2
42.3
42.4
42.5
42.6
-71 -70.9 -70.8 -70.7 -70.6 -70.5 -70.4 -70.3 -70.2
41.9
42
42.1
42.2
42.3
42.4
42.5
42.6 
-5 -3 -1 1 3 
Figure 3-9. Changes in seasonal ammonium concentrations (μM) from the baseline to the
post-diversion period. There have been localized increases in ammonium concentrations near the
outfall with concurrent decreases in ammonium concentrations in Boston Harbor. 
The increased ammonium concentrations in the nearfield have become
less apparent in 2005–2008 (Figure 3-10). It seems that ammonium
concentrations have also decreased in the coastal and northern boundary
regions. Increases in nitrate levels have occurred throughout the region,
including the nearfield, but this change is not thought to be outfall-related. 
Winter/Spring Summer Fall

2008 OUTFALL MONITORING OVERVIEW 17 
0
4
8
12
16 
NH4 ( μ M) 
Boston Harbor Coastal Nearfield N. Boundary Cape Cod Bay 
Figure 3-10. Annual mean ammonium concentrations. Data represent all depths and
all stations sampled within each region. Vertical dotted line shows when the bay outfall
came on-line. Error bars represent ±1 standard deviation. 
Similarly, there have been region-wide changes in chlorophyll (Figure 3-
11) and particulate organic carbon (not shown). Summer concentrations
of chlorophyll have decreased in Boston Harbor, while there has been a
trend towards higher winter/spring concentrations throughout
Massachusetts Bay and lower fall concentrations at the offshore and
northern boundary stations. Phaeocystis pouchetii blooms, which have
occurred over much of the bay during each of the years since 2000, have
caused the increased spring chlorophyll levels. Regional processes have
been responsible for the increased Phaeocystis pouchetii counts.
Decreases in concentrations of chlorophyll in Boston Harbor are evident in
the summer. During the years prior to the diversion, when effluent was
discharged into the harbor, higher levels persisted from the spring through
fall (Figure 3-12).
Primary production rates have been lower in recent years (Figure 3-13).
Investigators hypothesize that this change is related to lower than average
winds.

2008 OUTFALL MONITORING OVERVIEW 18 
-71 -70.9 -70.8 -70.7 -70.6 -70.5 -70.4 -70.3 -70.2
41.9
42
42.1
42.2
42.3
42.4
42.5
42.6
-71 -70.9 -70.8 -70.7 -70.6 -70.5 -70.4 -70.3 -70.2
41.9
42
42.1
42.2
42.3
42.4
42.5
42.6
-71 -70.9 -70.8 -70.7 -70.6 -70.5 -70.4 -70.3 -70.2
41.9
42
42.1
42.2
42.3
42.4
42.5
42.6 
-50 -30 -10 10 30 50 
Figure 3-11. Changes in seasonal chlorophyll concentrations (mg m -2 ) from the baseline to the
post-diversion period. (Post-diversion minus baseline values.) Changes in Massachusetts Bay
have reflected regional conditions and are not indicative of any effect from the relocated outfall. 
0
100
200
300
400
500
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Chlorophyll (mg m -2 ) 
Baseline Range
Baseline Mean
2008
Post Mean 
Figure 3-12. 2008 Boston Harbor chlorophyll levels compared to the baseline range,
baseline mean, and post-diversion mean. Decreases in summer chlorophyll levels show
a change to a bimodal pattern of spring and fall phytoplankton blooms, which is
characteristic of temperate coastal waters. 
Winter/Spring Summer Fall

2008 OUTFALL MONITORING OVERVIEW 19 
0
100
200
300
400
500
600
700
800
900
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Annual Production (gC m -2 y -1 )
N04
N16/N18
F23 
Figure 3-13. Potential annual production. There has been a significant decrease in production
in Boston Harbor (Station F23) and no significant change in the nearfield (Stations N04 and
N18) since the 2000 outfall diversion. Vertical dotted line represents when the bay outfall came
on-line. 
The possibility that the outfall would cause lower dissolved oxygen levels
in bottom waters was one important public concern prior to the diversion.
However, measurements of concentrations and percent saturation of
dissolved oxygen in the nearfield bottom waters have shown no response
to the outfall. There has been no change in levels or the seasonal pattern
in any year. Summer and fall bottom water dissolved oxygen levels were
relatively high in 2008 (Figure 3-14). 
Figure 3-14. Nearfield surface and bottom dissolved oxygen concentrations. Bottom
measurements are the lower line. Minimum levels were relatively high in 2008. Dotted
line shows the state water quality criterion.

2008 OUTFALL MONITORING OVERVIEW 20
Phytoplankton Communities 
Several long-term patterns in phytoplankton abundance continued in 2008.
There have been increased numbers of microflagellates (although this
apparent increase may reflect a methodological underestimate for 1992–
1995) and decreased abundance of diatoms during the post-diversion years
(Libby et al. 2009). These changes are region-wide, not related to the
outfall.
A bloom of the colonial nuisance species Phaeocystis pouchetii (Figure 3-
15) and a major Alexandrium fundyense red tide with high toxicity were
the most notable events for the phytoplankton community in 2008. The 
Phaeocystis bloom was one of the largest in terms of cell abundance that
has been recorded during the monitoring program (Figure 3-16), but was
of short duration. The bloom was recorded throughout the monitoring
area in April, ending by the May (nearfield-only) sampling survey (Figure
3-17). Satellite images suggest that the bloom started in the western Gulf
of Maine in April. 
Thalassiosira nordenskioeldii 
chain
Colony of individual cells.
Tough outer skin is visible. 
Phaeocystis pouchetii 
} 
Figure 3-15. Phaeocystis pouchetii colony from Massachusetts Bay , ca.
250um long by 150 um wide (Station N18, March 14, 2000, abundance 1.3 million
cells/L; photograph by D. Borkman, University of Rhode Island).

2008 OUTFALL MONITORING OVERVIEW 21 
0
3
6
9
12
1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
10 6 Cells L -1
Boston Harbor Coastal Nearfield Offshore N. Boundary Cape Cod 
Phaeocystis pouchetti 
Figure 3-16. Abundance of Phaeocystis pouchetii since 1992. The 2008 bloom was large in
terms of cell abundance but of short duration. 
Boston Harbor
0
2
4
6
8
12-Feb
3-Mar
24-Mar
9-Apr
21-May
9-Jun
22-Jul
18-Aug
2-Sep
30-Sep
24-Oct
21-Nov
Abundance (10 6 cells L -1 ) Nearfield
0
2
4
6
8
12-Feb
3-Mar
24-Mar
9-Apr
21-May
9-Jun
22-Jul
18-Aug
2-Sep
30-Sep
24-Oct
21-Nov
Abundance (10 6 cells L -1 )
Offshore
0
2
4
6
8
12-Feb
3-Mar
24-Mar
9-Apr
21-May
9-Jun
22-Jul
18-Aug
2-Sep
30-Sep
24-Oct
21-Nov
Abundance (10 6 cells L -1 )
Coastal
0
2
4
6
8
12-Feb
3-Mar
24-Mar
9-Apr
21-May
9-Jun
22-Jul
18-Aug
2-Sep
30-Sep
24-Oct
21-Nov
Abundance (10 6 cells L -1 )
N. Boundary
0
2
4
6
8
12-Feb
3-Mar
24-Mar
9-Apr
21-May
9-Jun
22-Jul
18-Aug
2-Sep
30-Sep
24-Oct
21-Nov
Abundance (10 6 cells L -1 )
Cape Cod Bay
0
2
4
6
8
12-Feb
3-Mar
24-Mar
9-Apr
21-May
9-Jun
22-Jul
18-Aug
2-Sep
30-Sep
24-Oct
21-Nov
Abundance (10 6 cells L -1 ) 
Figure 3-17. Nearfield abundance of dominant phytoplankton groups in 2008. 
Phaeocystis
Dinoflagellates
Pennate
Diatoms
Centric
Diatoms
Cryptophytes
Microflagellates

2008 OUTFALL MONITORING OVERVIEW 22 
Similar to 2005 and 2006, there was a large bloom of the toxic
dinoflagellate Alexandrium fundyense (red tide) (Figure 3-18),
which produces a toxin that causes paralytic shellfish poisoning
(PSP). The 2008 red tide event began in April, in the coastal
waters of Maine, and was transported to Massachusetts Bay by
winds from the northeast. MWRA and the Woods Hole
Oceanographic Institution (WHOI) mobilized surveys to track the
progress of the red tide. MWRA completed seven surveys in
April–June and WHOI conducted six surveys in April–July.
MWRA surveyed Boston Harbor in early June (Figure 3-19).
Toxicity spread throughout Massachusetts Bay and Boston Harbor
but did not result in closing shellfish beds in Cape Cod Bay. Local
weather may have been the primary factor in transporting the
bloom into Boston Harbor, while sparing Cape Cod Bay. The
bloom ended in June. More about red tides is presented in Section
6, Special Studies. 
1
10
100
1000
10000
100000
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009 
Alexandrium per sample
(cells/L +1 )
baseline post-diversion caution level 
Figure 3-18. Nearfield abundance of Alexandrium fundyense since 1992. The 2008 bloom was
similar to blooms in 2005 and 2006.

2008 OUTFALL MONITORING OVERVIEW 23 
Figure 3-19. Alexandrium fundyense cell concentrations in Massachusetts Bay and
Boston Harbor in June 2008. The 2008 bloom did not result in closures in Cape Cod
Bay.

2008 OUTFALL MONITORING OVERVIEW 24
Zooplankton Communities 
The structure of the zooplankton community in the nearfield in 2008 was
similar to that of many earlier years, with abundance approximating the
baseline mean for several surveys (Figure 3-20). Similar to 2007,
monitoring did not show the decline in total annual abundance of
zooplankton that had been observed during 2001–2006. A rebound in the
abundance of the copepods and especially the small species Oithona
similis was responsible for this recovery. The reasons for the lower
copepod abundance during 2001–2006 are not clear but appear to be
related to large-scale climatic conditions. In Boston Harbor, annual
zooplankton abundance has been slightly lower since the outfall diversion,
and mean abundance continued to be relatively low in 2008. There have
been no changes in zooplankton abundance in Cape Cod Bay. 
0
50,000
100,000
150,000
200,000
250,000
300,000
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
animals m -3 
Baseline Range
Baseline Mean
2008
Post Mean 
Figure 3-20. 2008 nearfield survey mean total zooplankton abundance
compared to baseline range, baseline mean, and post-diversion mean. For
much of the year, abundance approximated the baseline mean.

2008 OUTFALL MONITORING OVERVIEW 25
Contingency Plan Thresholds 
Water quality parameters were within normal ranges throughout 2008.
There was one exceedance of a nuisance algae threshold (Table 3-1), when
samples collected in May exceeded the Alexandrium fundyense caution
level. This exceedance had been anticipated, based on information on
overwintering Alexandrium cysts in the sediments off the coast of Maine
(see Section 6, Special Studies) and spring measurements of Alexandrium 
cells in coastal waters of Maine and New Hampshire. In response to the
exceedance, MWRA, in cooperation with WHOI and the Massachusetts
Division of Marine Fisheries, implemented its rapid-response Alexandrium 
survey plan (Libby 2006), which provides for assessment of rapidly
developing and potentially large blooms. Results from those surveys
indicated that the bloom proceeded in a pattern that was consistent with
historic progressions and that the outfall discharge did not affect its
intensity, timing, or duration.

2008 OUTFALL MONITORING OVERVIEW 26 
Table 3-1. Contingency Plan threshold values and 2008 results for water-column monitoring. 
(DO=dissolved oxygen) 
Location/
Parameter
Specific
Parameter Baseline Caution Level Warning
Level
2008
Results 
Dissolved
oxygen
concentration
Background 5 th
percentile
5.75 mg/L
Lower than 6.5
mg/L for any
survey (June-
October) unless
background
conditions are
lower
Lower than 6.0
mg/L for any
survey (June-
October) unless
background
conditions are
lower
Lowest survey
mean = 7.71 mg/L
Bottom water
nearfield
Dissolved
oxygen percent
saturation
Background 5 th
percentile
64.3%
Lower than 80%
for any survey
(June-October)
unless
background
conditions are
lower
Lower than 75%
for any survey
(June-October)
unless
background
conditions are
lower
Lowest survey
mean = 85.7%
Dissolved
oxygen
concentration
Background 5 th
percentile
6.2 mg/L
6.5 mg/L for any
survey (June-
October) unless
background
conditions lower
Lower than 6.0
mg/L for any
survey (June-
October) unless
background
conditions are
lower
Lowest survey
mean = 7.06
mg/L
Bottom water
Stellwagen
Basin
Dissolved
oxygen percent
saturation
Background 5 th
percentile
66.3%
Lower than 80%
for any survey
(June-October)
unless
background
conditions
Lower than 75%
for any survey
(June-October)
unless
background
conditions are
lower
Lowest survey
mean = 74.8%
Bottom water
nearfield
DO depletion
rate (June-
October)
0.024 mg/L/d 0.037 mg/L/d 0.049 mg/L/d 0.017 mg/L/d
Annual 79 mg/m 2 118 mg/m 2 158 mg/m 2 67 mg/m 2
Winter/spring 62 mgml 2 238 mg/m 2 None 96 mg/m 2
Summer 51 mg/m 2 93 mg/m 2 None 42 mg/m 2
Chlorophyll
nearfield
Autumn 97 mg/m 2 212 mg/m 2 None 64 mg/m 2
Winter/spring 468,000 cells/L 2,020,000 cells/L None 1,980,000 cells/L
Summer 72 cells/L 357 cells/L None Absent
Nuisance
algae
nearfield 
Phaeocystis
pouchetii 
Autumn 317 cells/L 2,540 cells/L None Absent
Winter/spring 6,200 cells/L 21,000 cells/L None Absent
Summer 14,600 cells/L 43,100 cells/L None 540 cells/L
Nuisance
algae
nearfield 
Pseudo-
nitzschia 
Autumn 9,940 cells/L 24,700 cells/L None 171 cells/L
Nuisance
algae
nearfield 
Alexandrium
fundyense 
Any nearfield
sample
Baseline
maximum =
163 cells/L
100 cells/L None
60,430 cells/L.
caution level
exceedance
Farfield PSP toxin
extent Not applicable New incidence None No new incidence

2008 OUTFALL MONITORING OVERVIEW 27
4. Sea Floor 
Sea-floor monitoring in 2008 was conducted at soft-bottom stations in the
nearfield (Figure 4-1) and farfield (Figure 4-2) and through a video and
photographic survey of rocky habitats in the vicinity of the outfall and at
reference locations to the north and south (Figure 4-3). 
Figure 4-1. Locations of nearfield soft-bottom stations for chemical parameters,
sediment-profile imaging, and community parameters.

2008 OUTFALL MONITORING OVERVIEW 28 
Figure 4-2. Locations of farfield soft-bottom stations for chemical and community
parameters. 
The soft-bottom studies included measurements of sediment grain-size
distribution, total organic carbon, the sewage-bacteria tracer Clostridium
perfringens spores, chemical contaminants, and community parameters at
stations labeled as “sampled in even years” or “sampled every year.”
Sediment-profile imaging measurements were made at all nearfield
Massachusetts Bay stations shown on Figure 4-1, including those denoted
as being sampled in odd years.

2008 OUTFALL MONITORING OVERVIEW 29 
Figure 4-3. Locations of hard-bottom stations. Video and still photographs are collected
at 17 stations distributed among six transects and at six additional waypoints, including
one active diffuser and one diffuser that is not in use.

2008 OUTFALL MONITORING OVERVIEW 30 
Sediment Characteristics and Tracers 
Grain-size distributions in 2008 remained within the historic ranges of the
monitoring program, with no indication of the coarse sediments that can
result from large storms (Maciolek et al. 2009). Total organic carbon
concentrations were relatively low, especially at nearfield stations, where
at some stations, the percent total organic carbon fell below the baseline
range.
As in other post-diversion years (except 2006), it was possible to detect
elevated levels of Clostridium perfringens spores in sediments collected
within two kilometers of the outfall (Figure 4-4). These findings were
consistent with predictions that it would be possible to detect sewage
tracers such as Clostridium spores in the immediate vicinity of the outfall. 
Normalized Clostridium perfringens 
0
50
100
150
200
250
300
350
400
450
500
FF10
FF13
NF17
NF19
NF23
NF18
NF12
NF16
NF07
NF09
NF22
NF08
NF05
FF09
FF04
FF05
FF07
Transition
Area
Nearfield (<2 km from
outfall)
Nearfield (>2 km from outfall) Farfield 
Concentration (cfu/g dry/%fines) 
Baseline Range
Baseline Mean
Post-diversion Mean
2008 Station Mean 
Figure 4-4. Clostridium perfringens spores normalized to percent fine fraction in the
sediments. “Transition area” denotes stations located between Boston Harbor and the
outfall; “Farfield” denotes stations offshore from the outfall.

2008 OUTFALL MONITORING OVERVIEW 31 
Concentrations of chemical contaminants in the sediments were generally
within the ranges measured throughout the monitoring program, but
somewhat low, probably reflecting the relatively low levels of total
organic carbon. Concentrations of PCBs (Figure 4-5) and DDT (not
shown) were significantly lower than the baseline mean, reflecting the
slow decline in those contaminants since they were banned in the 1970s
and 1980s. 
Total PCB 
0
20
40
60
80
100
120
140
FF10
FF13
NF17
NF19
NF23
NF18
NF12
NF16
NF07
NF09
NF22
NF08
NF05
FF09
FF04
FF05
FF07
Transition
Area
Nearfield (<2 km from
outfall)
Nearfield (>2 km from outfall) Farfield 
Concentration (ng/kg dry) 
Baseline Range
Baseline Mean
Post-diversion Mean
2008 Station Mean 
Figure 4-5. Total PCB concentrations in sediments. “Transition area” denotes stations
located between Boston Harbor and the outfall; “Farfield” denotes stations offshore
from the outfall. 
Throughout Massachusetts Bay, the data continued to confirm that
sediment grain-size distribution and proximity to historic inputs are the
main indicators of contaminant concentrations. In the nearfield,
contaminant concentrations are typically correlated with grain size, with
the muddier stations having more organic carbon and correspondingly
higher concentrations of contaminants. Sediments from farfield stations
are typically finer-grained than those from the nearfield but also have
lower concentrations of some contaminants, a pattern that has persisted
throughout the monitoring program.
In Boston Harbor, where monitoring has also been conducted since 1991,
concentrations of total organic carbon have fallen at some stations,
including those closest to the former harbor outfall near DITP. There has
also been a significant harbor-wide decline in concentrations of 
Clostridium perfringens spores.

2008 OUTFALL MONITORING OVERVIEW 32
Sediment-Profile Imaging 
Sediment-profile imaging measurements continued to show no effects of
the outfall (Maciolek et al. 2009). Concerns that an increase in the
amount of organic matter deposited on the sea floor would result in a
shallower apparent redox potential discontinuity (RPD) have not been
realized (Figure 4-6). The mean RPD was somewhat shallower and the
data were more variable in 2008 compared to 2007, but the RPD remained
deeper than the baseline mean. 
0.0
1.0
2.0
3.0
4.0
5.0
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Year
Mean RPD Depth +/ - 1SD
Outfall Startup
Baseline Mean
Threshold 
Figure 4-6. Annual apparent color RPD for data from nearfield stations sampled in
2008. The average RPD depth in 2008 remained deeper than the baseline mean,
continuing to indicate that there has been no adverse effect from the discharge. 
Two other measures from the sediment-profile images, successional stage
and the organism sediment index (OSI), have provided further evidence
that the outfall has not adversely affected the sea floor. The 2008 OSI
remained similar to the level measured in 2007. Biogenic structures, such
as amphipod tubes were more abundant in 2008, but, as in prior years,
physical processes continued to be the dominant force in structuring the
surface sediments. Storms and storm-induced sediment transport and
deposition remain the primary stress on the sea-floor communities in
Massachusetts Bay.
At Boston Harbor stations, where a separate monitoring program is
conducted, the RPD has also deepened, while successional stage, OSI, and

2008 OUTFALL MONITORING OVERVIEW 33 
the incidence of biogenic features have increased. The camera recorded
eelgrass at a station at Deer Island Flats, an area that might have been
thought to be too degraded for colonization and restoration of eelgrass
beds. The sediment-profile images also recorded abundant Leptocheirus
pinguis , a burrowing amphipod, at many harbor stations. Tube mats
constructed by the amphipods Ampelisca spp. returned to several stations
after an absence of several years. 
Ampelisca mats had provided an early demonstration of the improvements
in Boston Harbor, greatly increasing in abundance in 1992 and subsequent
years. By 2005, however, the mats had declined in abundance,
presumably because of the reduction in inputs of organic material
following the diversion of sewage inputs from Boston Harbor (Diaz et al. 
2008). The return of Ampelisca tube mats may compel some modification
to that hypothesis, placing a greater emphasis on the role of storms, but it
remains clear that there have been major improvements to the soft-bottom
habitats of Boston Harbor. 
Soft-bottom Communities 
The soft-bottom communities continued to show no response to the
outfall. Rather, post-diversion monitoring has continued to confirm the
baseline finding that sediment grain size is the most important influence
on the benthic infaunal communities. The number of species per sample,
total abundance of animals per sample, and a measure of diversity log-
series alpha all remained within the baseline ranges (Figure 4-7).
Over the course of monitoring, some community parameters have
fluctuated in sine-wave-like patterns. These patterns appear to be driven
by annual fluctuations in several dominant species, particularly polychaete
worms that inhabit fine-grained sediments. The results have held constant
through both even and odd years, when since 2003, separate subsets of
stations have been sampled.
Baseline and post-diversion monitoring has shown that the nearfield
stations fall into two major groups, those that are characterized by fine
sediments dominated by polychaete worms and those that are sandier,
supporting amphipod crustaceans as well as polychaetes. Most of the
numerically dominant species in the nearfield in 2008 were the same as
those in 2007, with the addition of the polychaetes Leitoscoloplos acutus 
and Monticellina baptisteae .
The farfield stations are more geographically widespread, with mostly
finer sediments, and polychaetes dominate at most stations. The species
compositions at those stations have always differed from those at nearfield
stations. There were no unusual findings in the farfield samples for 2008.

2008 OUTFALL MONITORING OVERVIEW 34 
Figure 4-7. Annual community parameters in the nearfield.

2008 OUTFALL MONITORING OVERVIEW 35
Hard-bottom Communities 
The rocky habitats in the vicinity of the outfall and at reference locations
continued to support robust communities of algae, invertebrates, and fish.
Baseline and post-diversion monitoring has shown that the hard-bottom
communities in the region are spatially diverse but temporally stable.
While there have been some shifts in species composition and abundance,
those changes have been modest. Lush epifaunal growth, particularly sea
anemones, has thrived on the diffuser heads, a condition unchanged since
the Massachusetts Bay outfall began to discharge.
One measure of interest has been the amount of “sediment drape,” a visual
assessment of the detritus deposited on hard surfaces (Figure 4-8). During
the post-diversion years, there have been modest increases in the amount
of sediment drape at some stations, particularly north of the outfall,
including the northern reference sites. 
Figure 4-8. Examples of levels of sediment drape from 2008 photographs. Upper left: light
drape at T4/6-1 south of the outfall; upper right: moderately light drape at T7-2 a northern
reference site; lower left: moderate drape at T1-2 north of the outfall; lower right: heavy drape at
T10-1 southwest of the outfall.

2008 OUTFALL MONITORING OVERVIEW 36 
There has been some evidence that the northern reference stations are
being adversely affected by tanker traffic. Tankers have frequently been
seen to be anchored in the area, sometimes affecting MWRA survey
schedules. Anchor scars and overturned boulders were recorded during
the 2007 and 2008 surveys; the physical disturbances may be
compromising the effectiveness of these sites as reference stations. 
Contingency Plan Thresholds 
No Contingency Plan thresholds for sea-floor monitoring were exceeded
in 2008 (Table 4-1). There have been no threshold exceedances for any
sea-floor parameter during the course of the monitoring program.
Contaminant concentrations were well below warning levels, RPD depth
continued to be deeper than the baseline mean, and the soft-bottom
community parameters were within normal ranges. The percent of the
soft-bottom community composed of opportunistic species remained low,
about two orders of magnitude below the warning threshold.

2008 OUTFALL MONITORING OVERVIEW 37 
Table 4-1. Contingency Plan threshold values and 2008 results for sea-floor monitoring. 
(HMW=high molecular weight, LMW=low molecular weight, PAH=polycyclic aromatic
hydrocarbon) 
Location Parameter Caution Level Warning Level 2008 Results 
Acenaphthene None 500 ppb dry wt 27.3 ppb dry wt
Acenaphylene None 640 ppb dry wt 35.6 ppb dry wt
Anthracene None 1100 ppb dry wt 127.9 ppb dry wt
Benzo(a)anthracene None 1600 ppb dry wt 236.7 ppb dry wt
Benzo(a)pyrene None 1600 ppb dry wt 272.0 ppb dry wt
Cadmium None 9.6 ppm dry wt 0.13 ppm dry wt
Chromium None 370 ppm dry wt 71.9 ppm dry wt
Chrysene None 2800 ppb dry wt 212.2 ppb dry wt
Copper None 270 ppm dry wt 14.7 ppm dry wt
Dibenzo(a,h)anthracene None 260 ppb dry wt 35.8 ppb dry wt
Fluoranthene None 5100 ppb dry wt 470 ppb dry wt
Fluorene None 540 ppb dry wt 40.3 ppb dry wt
Lead None 218 ppm dry wt 40.2 ppm dry wt
Mercury None 0.71 ppm dry wt 0.13 ppm dry wt
Naphthalene None 2100 ppb dry wt 56.8 ppb dry wt
Nickel None 51.6 ppm dry wt 14.9 ppm dry wt
p,p’-DDE None 27 ppb dry wt 0.39 ppb dry wt
Phenanthrene None 1500 ppb dry wt 287.8 ppb dry wt
Pyrene None 2600 ppb dry wt 380.3 ppb dry wt
Silver None 3.7 ppm dry wt 0.32 ppm dry wt
Total DDTs None 46.1 ppb dry wt 5.59 ppb dry wt
Total HMW PAH None 9600 ppb dry wt 3712.7 ppb dry wt
Total LMW PAH None 3160 ppb dry wt 1579.5 ppb dry wt
Total PAHs None 44792 ppb dry wt 5292.1 ppb dry wt
Total PCBs None 180 ppb dry wt 7.5 ppb dry wt
Zinc None 410 ppm dry wt 57.8 ppm dry wt
Sediments,
nearfield
RPD depth 1.18 cm None 2.88 cm
Species per sample <48.41 or >82.00 None 70.6
Fisher’s log-series
alpha <9.99 or >16.47 None 15.1
Shannon diversity <3.37 or >4.14 None 3.84
Even years,
benthic
diversity,
nearfield Pielou’s evenness <0.58 or >0.68 None 0.624
Benthic
opportunists % opportunists >10% >25% 0.254%

2008 OUTFALL MONITORING OVERVIEW 38
5. Winter Flounder 
MWRA’s fish-and-shellfish monitoring includes annual study of winter
flounder. Fifty sexually mature winter flounder were taken from each of
four sampling sites (Figure 5-1) during April 2008 for assessment of
external condition and examination of liver histology (Moore et al. 2009). 
Figure 5-1. Winter flounder sampling sites.

2008 OUTFALL MONITORING OVERVIEW 39 
Catch per unit effort remained low compared to 2001–2004 but was
similar to 2006, 2007, and the years before the outfall diversion (Figure 5-
2). The Northeast Fisheries Science Center (NFSC) has noted similar
fluctuations in abundance and suggests that the Gulf of Maine stock, of
which Massachusetts Bay is a part, may be in an overfished condition, as
are other flatfish populations in New England (NFSC 2008). 
Figure 5-2. Annual catch per unit effort. (DIF = Deer Island Flats, ECCB = Eastern Cape Cod
Bay, NB = Nantasket Beach, OS = Outfall Site) 
Mean age was lower, and fish weighed less and were shorter in length than
fish sampled in 2007, but the values for each of these physical
characteristics remained within the historic ranges. The percentage of
female fish in the catch has increased since the beginning of the
monitoring program, and almost every fish sampled was female (Figure 5-
3). Skewed sex ratios are not unusual in flounder, and the region-wide
incidence suggests that the outfall does not play a role in the imbalance.

2008 OUTFALL MONITORING OVERVIEW 40 
Figure 5-3. Annual percent females in winter flounder samples. (DIF = Deer Island Flats,
ECCB = Eastern Cape Cod Bay, NB = Nantasket Beach, OS = Outfall Site) 
At most stations, incidence of fin erosion, a condition that can be
indicative of elevated concentrations of ammonium and other pollutants,
was lower than was observed in 2007. Prevalence of fin erosion has
varied in recent years, with no clear evidence of short-term trends. Over a
longer period, since the late 1970s and early 1980s, the incidence and
severity of fin erosion has lessened considerably.
Blind-side ulcers, which were first detected in 2003, were uncommon,
continuing an ongoing decline. Ulcers were present in only 2% of fish
sampled near the outfall; at the peak of the infection in 2004, 36% of the
fish had ulcers.

2008 OUTFALL MONITORING OVERVIEW 41 
No neoplasms were observed in any fish from any site. Incidence of
neoplasia has been rare throughout the area since routine monitoring
started in 1991. Levels were as high as 12% in flounder taken from
Boston Harbor for other monitoring programs during the 1980s.
Neoplasia has never been observed in fish taken from the outfall site. The
incidence of centrotubular hydropic vacuolation (CHV), a mild condition
associated with exposure to contaminants, remained low (Figure 5-4).
Incidence of CHV in fish from the outfall site continued to be lower than it
had been in the years before the Massachusetts Bay outfall began to
discharge. Incidence of CHV at Deer Island Flats has also declined since
the outfall diversion. 
Figure 5-4. Annual prevalence of centrotubular hydropic vacuolation (CHV), corrected for
age. (DIF = Deer Island Flats, , ECCB = Eastern Cape Cod Bay, NB = Nantasket Beach, OS =
Outfall Site)

2008 OUTFALL MONITORING OVERVIEW 42
Contingency Plan Thresholds 
Only one threshold parameter for fish and shellfish was measured in 2008
(Table 5-1). Incidence of CHV, the most common indicator of liver
disease in the winter flounder of the region, was 12% in fish taken from
the vicinity of the outfall site, unchanged from 2007. This value was less
than half the 24.4% observed during the baseline period and well below
the caution level. 
Table 5-1. Contingency Plan threshold values and 2008 results for flounder monitoring. 
Parameter
Type/
Location
Parameter Baseline Caution
Level
Warning
Level
2008
Results 
Flounder
nearfield
Liver disease
(CHV) 24.4% 44.9% None 12%

2008 OUTFALL MONITORING OVERVIEW 43
6. Special Studies 
Besides monitoring the effluent and the water column, sea floor, and fish
and shellfish in Massachusetts Bay and the surrounding area, MWRA
conducts special studies in response to specific permit requirements,
scientific questions, and public concerns. During 2008, MWRA continued
or initiated several special studies: 
• Calibration of chlorophyll measurements in the water column. 
• Prediction of red tides. 
• Marine mammal observations. 
• Analysis of nutrient loads to Boston Harbor. 
• Nutrient flux at the sediment-water interface. 
Chlorophyll Measurements 
MWRA uses two types of measurements of water column chlorophyll:
laboratory and field ( in situ ) measurements. The laboratory chemistry
method is relatively expensive and labor-intensive. The in situ method is
faster, allowing more measurements, but can be affected by field
conditions. MWRA is developing an improved method to calibrate the
field measurements. Multiple regression methods are used to account for
factors including temperature and solar irradiance (Hersh 2009). 
Predicting Red Tides 
Since 2005, when the worst bloom of the red tide dinoflagellate 
Alexandrium fundyense occurred in New England, MWRA has conducted
targeted research aimed at understanding and predicting these blooms.
The studies have been conducted in coordination with the WHOI Gulf of
Maine Toxicity (GOMTOX) program, a cooperative observation and
modeling effort focused on the Gulf of Maine and the adjacent southern
New England coastal region. The GOMTOX studies have identified the
abundance of cysts in seed beds off the coast of Maine, coupled with a
population-dynamics model, as the best predictor of the magnitude of
blooms in the following year.
In 2008, these studies resulted in the first-ever forecast advisory for a red
tide with significant PSP toxicity (WHOI 2008). Data from fall 2007
surveys of the seed beds (Figure 6-1, top) were used in a model simulating
weather and oceanographic conditions of past years to predict cell
abundance for 2008 (Figure 6-1, bottom). Those model results suggested
a high likelihood of a significant red tide in 2008, a prediction that proved
accurate (Figure 6-2). Similar correct predictions were made for 2009
(WHOI 2009).

2008 OUTFALL MONITORING OVERVIEW 44 
Figure 6-1. Top: Annual abundance of Alexandrium cysts in Maine seed beds.
Bottom: Annual modeled concentrations of Alexandrium cells. Values for 2008 were
predicted from 2007 cyst abundance and weather forcing conditions from 2004–2007.
Each model run predicted a large red tide for 2008.

2008 OUTFALL MONITORING OVERVIEW 45 
Figure 6-2. Modeled abundance of Alexandrium cells for 2008. Upper maps show
modeled results for 2008 using weather forcing conditions from 2004–2007. Lower map
shows the modeled results using actual 2008 weather conditions.

2008 OUTFALL MONITORING OVERVIEW 46 
The research and modeling have suggested that the western Gulf of Maine
has entered an era of frequent and high-intensity red tides. Prior to 1972,
it appears that Alexandrium cysts were abundant in the Bay of Fundy but
not in the western Gulf of Maine. From 1972, when a large red tide
occurred, through the early 1990s, cysts began to accumulate in the
western Gulf of Maine, but abundance then waned. During the early years
of the MWRA monitoring program, there were few cysts in the Gulf of
Maine, and PSP toxicity resulting from blooms was rare. Since the mid
2000s, cysts have again become abundant in the Gulf of Maine, and
significant red tides have occurred.
To date, it does not appear that cyst seed beds have been established in
Massachusetts, and the timing and geographic progression of the blooms
has not been associated with any stimulating effect from the nutrients in
the Massachusetts Bay discharge. Additional field and modeling studies
are continuing. 
Marine Mammal Observations 
Several species of endangered or threatened whales and turtles visit
Massachusetts and Cape Cod bays, including right, humpback, finback,
sei, and, rarely, blue whales. Also seen are the protected, but not
endangered, minke whale, harbor porpoise, gray seal, harbor seal, and
several species of dolphins.
Since 1995, MWRA has included endangered species observers on
monitoring surveys. In 2008, observers were included on all nearfield and
farfield water quality surveys (Wu 2009b). Besides providing
observational data, the presence of trained marine mammal observers
addresses a request by the National Marine Fisheries Service that MWRA
take active steps to minimize the chances of a collision of one of its survey
vessels with a right whale.
During the 2008 surveys, 44–45 individual whales, one Atlantic white-
sided dolphin, four harbor porpoises, ten humpback whales, five finback
whales, four minke whales, and 12–13 unidentified whales were directly
observed by the trained observers and other members of the monitoring
team (Figure 6-3). The total number of whales sighted was the highest
since 2006, a year that saw increases after a period of relatively sparse
sightings. Several whales were sighted in the vicinity of the outfall, 17–18
were within the Stellwagen Bank National Marine Sanctuary, and 18 were
sighted in Cape Cod Bay.

2008 OUTFALL MONITORING OVERVIEW 47 
Figure 6-3. Approximate locations of whale sightings during 2008 nearfield and farfield water
quality surveys.

2008 OUTFALL MONITORING OVERVIEW 48 
The Provincetown Center for Coastal Studies (www.coastalstudies.org),
which conducts systematic surveys of Cape Cod Bay, reported that twice
the usual number of right whales visited the area in 2007 and 2008 as had
been sighted during 1998–2006. The length of time that individual whales
remained in or near Cape Cod Bay was also longer in 2007 and 2008 than
had been typical in recent years. 
Nutrient Loads to Boston Harbor 
Estimates of contaminant loads to Boston Harbor have been completed by
MWRA in 1991 (Menzie et al. 1991) and 1994 (Alber and Chan 1994).
The 1994 study reported that loads of many contaminants had decreased in
response to the ending of biosolids discharges in 1991. The earlier
estimates lacked accurate estimates of loadings from rivers. Since then,
MWRA has been compiling an updated inventory of the loadings to the
harbor and the changes over the course of the Boston Harbor Project
(Taylor 2009).
Loadings of total nitrogen, total phosphorus, total suspended solids, and
particulate organic carbon have declined by 82–95% since 1990–1991
(Figure 6-4). Almost all those decreases can be accounted for by
reductions in wastewater-associated discharges. Increases in the ratios of
total nitrogen to total phosphorus and total suspended solids to particulate
organic carbon show a shift in the dominant input away from sewage
sources to rivers and other sources (Figure 6-5). Now, riverine inputs
contribute most of the loadings of all the contaminants associated with
eutrophication. Total nitrogen loadings to Boston Harbor are now lower
than those in many other urban estuaries.

2008 OUTFALL MONITORING OVERVIEW 49 
90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07
0
500
1000
1500
2000
2500
3000
TSS loading ( ton d -1 )
0
25
50
75
100
125
150
175
200
POC loading ( ton d -1 )
90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07
0
20
40
60
80
100
120
140
160
TN : TP
&
TSS : POC
TSS & POC 
TN:TP 
TSS:POC 
TSS 
POC
TN loading ( kmol d -1 )
TN & TP
0
20
40
60
80
100
120
TP loading ( kmol d -1 )
90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07
0
10
20
30
40
50
60 
TN 
TP
TN : TP loading ( molar ratio )
0
1
2
3
4
5
OFF I-I 1 o 2 o
TSS : POC loading (by weight)
Sludge 
Figure 6-4. Total loadings of nutrients and solids to Boston Harbor, 1990–2007. 
TN=total nitrogen, TP=total phosphorus, TSS=total suspended solids, POC=particulate
organic carbon, Sludge=end of biosolids discharge, 1°=upgrade of primary treatment
plant, 2°=implementation of secondary treatment, I-I=ending of discharge to the
southern harbor with construction of the inter-island tunnel, OFF=ending of effluent
discharge to the harbor with the commissioning of the new outfall.

2008 OUTFALL MONITORING OVERVIEW 50 
0
25
50
75
100
125
150
OFF I-I 2 o
1 o
Sludge
TP LOADINGS
( KMOL D -1 )
OFF I-I 2 o
Sludge 1 o
TN LOADINGS
( KMOL D -1 )
POC LOADINGS
( TON D -1 )
TSS LOADINGS
( TON D -1 )
WWTF SLUDGE
NP SOURCES
RIVERS
WWTF EFFLUENT
LOADINGS BY SOURCE
0
20
40
60
80
100
0
500
1000
1500
2000
2500
1996
1996
1994
1992
2006 2006
2006 2006
2004
2004
2004
2004
2002
2002
2002
2002
2000
2000 2000
2000
1998 1998
1998
1996 1996
1996
1994 1994
1994
1992 1992
1992
1990
1990 1990
1990 1 9 9 0
1 9 9 2
1 9 9 4
1 9 9 6
1 9 9 8
2 0 0 0
2 0 0 2
2 0 0 4
2 0 0 6 
0
50
100
150
200 
Figure 6-5. Nutrient loadings to Boston Harbor by source. TN=total nitrogen, TP=total
phosphorus, TSS=total suspended solids, POC=particulate organic carbon, Sludge=end
of biosolids discharge, 1°=upgrade of primary treatment plant, 2°=implementation of
secondary treatment, I-I=ending of discharge to the southern harbor with construction of
the inter-island tunnel, OFF=ending of effluent discharge to the harbor, WWTF
SLUDGE=biosolids, NP SOURCES=nonpoint sources, RIVERS=rivers, WWTF
EFFLUENT=wastewater effluent. 
Benthic Flux 
One concern about the outfall diversion was that increased loads of
organic matter might enhance benthic respiration and increase fluxes of
nutrients between the sediments and the water column. The resulting
higher rates of benthic respiration or sediment oxygen demand might lead
in turn to lower levels of oxygen in both the sediments and the water
column. In response to these concerns, MWRA has conducted studies of
the sediment-water interface in Massachusetts Bay and in Boston Harbor
since 1993 (Figure 6-6).

2008 OUTFALL MONITORING OVERVIEW 51 
Figure 6-6. Benthic flux stations in Massachusetts Bay and Boston Harbor.

2008 OUTFALL MONITORING OVERVIEW 52 
The Massachusetts Bay studies have shown no significant changes from
baseline conditions (Tucker et al. 2009). There has been little or no
indication of increased deposition of organic matter to the sea floor
(Figure 6-7) and no change in the oxidation of the bottom waters or
sediments. There have been no increases in sediment oxygen demand and
no changes in nutrient fluxes at the Massachusetts Bay stations. 
0.0
0.5
1.0
1.5
2.0
2.5
MB01 MB02 MB03 MB05
% TOC
Baseline
Post-diversion
n=7 n=8 n=6 n=8 n=8 n=6 n=8 n=7 
Figure 6-7. Percent total organic carbon in surface sediments from Massachusetts
Bay. There has been no increase in organic matter deposition to the bottom. 
Meanwhile, there have been significant decreases in fluxes at the four
stations in Boston Harbor, reflecting improvements to the benthic
environment during those same time periods that are considered important
in the evaluation of nutrient loading (see preceding special study, Nutrient
Loads to Boston Harbor). The percent organic carbon has decreased at all
Boston Harbor stations except for the one nearest to the former discharge
site near DITP (Figure 6-8), and nutrient fluxes have declined at every
station (Figure 6-9). In 2008, there was an increase in sediment oxygen
demand at two stations, BH02 near Deer Island and BH08A in Hingham
Harbor. This condition had also been observed at the BH02 in 2007. It
resulted from increased colonization of the sites by amphipods and is not
considered to be an indication of any decline in environmental quality.

2008 OUTFALL MONITORING OVERVIEW 53 
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
BH02 BH03 BH08A QB01
% TOC
Pre 1995
1995-1997
1998-2000
2001-2008 
Figure 6-8. Percent total organic carbon in surface sediments from Boston Harbor. 
Percent total organic carbon has significantly declined at all stations except BH02,
which is close to the former Deer Island outfall. 
0
1
2
3
4
5
6
7
NH4 NO3 PO4
Nutrient Fluxes (mmol m
-2 d -1 ) 1993-1994
1995-1997
1998-2000
2001-2008 
Figure 6-9. Nutrient fluxes in surface sediments from Boston Harbor. Nutrient fluxes
have significantly declined at all Boston Harbor stations.

2008 OUTFALL MONITORING OVERVIEW 54
7. Stellwagen Bank
National Marine Sanctuary 
The Gerry E. Studds Stellwagen Bank National Marine Sanctuary protects
842 square miles of open water at the boundary between Massachusetts
Bay and the rest of the Gulf of Maine. It includes a part of Stellwagen
Basin, which is the deepest part of Massachusetts Bay and a long-term
sediment sink. Stellwagen Bank rises to the east of Stellwagen Basin and
provides a rich habitat for marine life. The NPDES permit to discharge
effluent into Massachusetts Bay requires this annual report on possible
effects of the discharge on the sanctuary.
In 2008, the sanctuary issued a draft management plan and environmental
assessment (U.S. Department of Commerce 2008) finding diverse and rich
habitats and varied marine life, including 80 fish species, 34 bird species,
and 22 species of marine mammals. It describes the major threats to the
sanctuary as overfishing, increasing speeds of whale-watch vessels,
invasion by exotic species, harmful algal blooms, and the potential for
degraded water quality resulting from coastal development and
urbanization. 
Water Column 
Despite the concerns about the effects of coastal development on the
sanctuary, the overall water quality remains good. The 2008 MWRA
water-quality monitoring measurements at the stations in and near the
sanctuary (Figure 7-1) continued to find that dissolved oxygen, nutrient
concentrations, and plankton abundances and community measures were
within the expected ranges for this region of Massachusetts Bay. There
has been no indication of any effect of the Massachusetts Bay outfall.
Concentrations of dissolved oxygen (Figure 7-2) and percent saturation
(not shown) have remained unchanged in Stellwagen Basin, as they have
in the nearfield. Potential decreases in dissolved oxygen concentrations or
percent saturation had been a concern before the outfall began to
discharge, but those concerns have not been realized. The 2008 bottom
water concentrations were slightly below the baseline mean, but were
higher than would be predicted from the year’s temperature and salinity
regime.

2008 OUTFALL MONITORING OVERVIEW 55 
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z
z
z
z
z
z
z z
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z 
F33
F32
F19
F18
F17
F16
F15
F14
F12
F10
F07
F05
N20
N10
N07
N01
F29
F28
F03
F23
F22
F13
F06
N18
N16
N04
F31
F30
F27
F26
F25
F24
F02
F01 
70°15'W
70°15'W
70°30'W
70°30'W
70°45'W
70°45'W
71°0'W
71°0'W
42°30'N
42°30'N
42°15'N
42°1 5'N
42°0'N
42°0 'N
41°4 5'N
41°45'N 
 
 
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z z
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z
z 
F33
F32
F19
F18
F17
F16
F15
F14
F12
F10
F07
F05
N20
N10
N07
N01
F29
F28
F03
F23
F22
F13
F06
N18
N16
N04
F31
F30
F27
F26
F25
F24
F02
F01 
70°15'W
70°15'W
70°30'W
70°30'W
70°45'W
70°45'W
71°0'W
71°0'W
42°30'N
42°30'N
42°15'N
42°1 5'N
42°0'N
42°0 'N
41°4 5'N
41°45'N 
Cape Cod Bay
Boston
Harbor Massachusetts Bay 
0 10 20 30 40 50 5
Kilometers 
boundary region
northern
boundary
region
offshore
region
coastal region
nearfield region 
z MWRA stations (BWQM) 
  GoMOOS Buoy A 
  NOAA Buoy 44013
MWRA outfall diffuser
Regions
Stellwagen Bank Sanctuary
High : 0
Low : -125 
Figure 7-1. Water column stations, including those in and near the Stellwagen Bank
National Marine Sanctuary (F27, F28, F12) .

2008 OUTFALL MONITORING OVERVIEW 56 
5
6
7
8
9
10
11
12
13
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
DO (mg L -1 ) 
Baseline Range
Baseline Mean
2008
Post Mean 
Figure 7-2. 2008 bottom water dissolved oxygen (DO) concentrations in Stellwagen
Basin compared to baseline range, baseline mean, and post-diversion mean. There has
been no change in patterns of dissolved oxygen concentrations (or saturation) since the
outfall began to discharge. 
Annual mean concentrations of nutrients in water samples have varied
somewhat over the years, but the changes have not been substantial, and
changes at stations in and near the sanctuary have not been attributed to
the outfall diversion. These variations have been observed in and near the
sanctuary, and also in the nearfield and in Cape Cod Bay, which are
shown for comparison. Annual mean concentrations of total nitrogen vary
across the study area from year to year, but the pattern is similar among
areas (Figure 7-3). Although ammonium levels (Figure 7-4) rose in the
nearfield when the outfall first went on line, ammonium in and near the
sanctuary was not affected. Changes in ammonium levels at the boundary
of Massachusetts Bay now appear to be lowering the concentrations found
in the nearfield.

2008 OUTFALL MONITORING OVERVIEW 57 
0
5
10
15
20
25
30
TN ( μ M)
YEAR
SBNMS Nearfield Cape Cod 
Figure 7-3. Annual mean total nitrogen (TN) at the Stellwagen Bank National Marine
Sanctuary (SBNMS), the outfall nearfield, and Cape Cod Bay. Concentrations have
varied by year but have been similar across regions. Vertical line indicates when outfall
came on-line. 
0.0
0.5
1.0
1.5
2.0
2.5
3.0
NH4 ( μ M)
YEAR
SBNMS Nearfield Cape Cod 
Figure 7-4. Annual mean ammonium at the Stellwagen Bank National Marine
Sanctuary (SBNMS), the outfall nearfield, and Cape Cod Bay. Ammonium levels have
declined in the past four years. Vertical line indicates when outfall came on-line.

2008 OUTFALL MONITORING OVERVIEW 58 
Nitrate concentrations (Figure 7-5) continue to be quite variable across all
regions. Concentrations of nitrate, as well as silicate and phosphate, have
been consistently higher at stations in and near the sanctuary than at
stations in the nearfield and Cape Cod Bay. These higher levels are
associated with deeper offshore waters, such as are found within the
sanctuary. It is these nutrient-rich bottom waters that feed plankton and
small fishes and make Stellwagen Bank a thriving habitat for commercial
fishes and whales. There has been a long-term, slight, upward trend in
nitrate levels across the regions. 
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
NO3 ( μ M)
YEAR
SBNMS Nearfield Cape Cod 
Figure 7-5. Annual mean nitrate at the Stellwagen Bank National Marine Sanctuary
(SBNMS), the outfall nearfield, and Cape Cod Bay. Nitrate concentrations are variable,
but there have been no changes that can be attributed to the outfall. Vertical line
indicates when outfall came on-line. 
The annual mean areal chlorophyll levels have varied at the sanctuary
stations, the nearfield, and in Cape Cod Bay throughout the monitoring
program, but post-diversion levels are not significantly different from the
baseline (Figure 7-6). Chlorophyll levels do not correlate with nitrogen
and have not changed in response to changes in nutrient inputs.

2008 OUTFALL MONITORING OVERVIEW 59 
0
20
40
60
80
100
120
140
160
180
Chlorophyll (mg m-2)
YEAR
SBNMS Nearfield Cape Cod 
Figure 7-6. Annual chlorophyll at the Stellwagen Bank National Marine Sanctuary
(SBNMS), the outfall nearfield, and Cape Cod Bay. Over the course of monitoring,
annual chlorophyll levels have varied, but similar patterns have been seen in samples
from every region. Vertical line indicates when outfall came on-line. 
Sea Floor 
No changes in concentrations of sewage tracers or sewage-related
contaminants were observed in the sediment samples from stations (FF04
and FF05) sampled in 2008 within or near the sanctuary (Figure 7-7), and
there have been no changes in community parameters since the outfall
began to discharge (Maciolek et al. 2009).
The deep-water stations sampled in 2008 continued to support a distinct
infaunal community, with recognizable differences from communities in
the nearfield and Cape Cod Bay. Benthic community parameters at
individual stations showed no pattern of change following the outfall
diversion in 2000. The total number of individual organisms per sample
has varied widely, but remained within the baseline range for stations in or
near the sanctuary in 2008. The numbers of species per sample and the
diversity of organisms within the samples were also within the baseline
ranges (Figure 7-8). A general increase in number of species, which
began during the baseline period and peaked in 2003, is considered to be a
result of normal cycles. No patterns that relate to the outfall diversion
have been found.

2008 OUTFALL MONITORING OVERVIEW 60 
Figure 7-7. Farfield benthic stations. Stations FF04, FF05, FF11, and FF14 are in or
near the Stellwagen Bank National Marine Sanctuary. FF04 and FF05 were sampled in
2008.

2008 OUTFALL MONITORING OVERVIEW 61 
0
10
20
30
40
50
60
70
80
90
100
Total Species per Sample
Year
FF05
FF04
FF14
FF11
Outfall startup 
0
5
10
15
20
25
Log Series Alpha
Year
FF05
FF04
FF14
FF11
Outfall startup 
Figure 7-8. Community parameters at stations in or near the Stellwagen Bank
National Marine Sanctuary. Top: species richness (number of species per sample);
Bottom: Log-series alpha, a measure of diversity.

2008 OUTFALL MONITORING OVERVIEW 62
8. Monitoring Questions
and Answers: 2008 
Prior to beginning the monitoring program, an Outfall Monitoring Task
Force formulated a series of questions that focused on plausible
unanticipated consequences of the diverted effluent discharge. Monitoring
has answered those questions (Table 8-1).
Compliance with effluent permit limits has been the key to ensuring that
there are no unanticipated effects on Massachusetts Bay. Out of the tens
of thousands of measurements that have been made since the
Massachusetts Bay outfall began to discharge, there have been only eleven
violations of permit limits (which are Contingency Plan threshold
exceedances) including failures of four toxicity tests, none of which were
attributed to toxic constituents of the effluent; an exceedance of the total
suspended solids limits after an industrial discharge caused a disruption of
the secondary treatment process; and exceedances of fecal coliform limits
during storms.
As expected, water-column monitoring has confirmed that it is possible to
detect sewage tracers at stations in the immediate vicinity of the outfall,
but there have been no unexpected changes resulting from the relocated
discharge. Late summer and fall levels of dissolved oxygen in bottom
waters have not been affected by the outfall. Incidence of nuisance algal
blooms has increased, but those changes have not been attributed to any
stimulation from the discharge.
Similarly, there have been no unanticipated changes on the sea floor.
Elevated concentrations of the sewage tracer Clostridium perfringens 
spores are detected at stations within the immediate vicinity of the outfall,
but there are no elevated concentrations of toxic contaminants. The soft-
and hard-bottom communities of Massachusetts and Cape Cod bays
remain healthy.
There have been no effects on fish or shellfish. Some contaminant levels
are elevated in mussels deployed in the immediate vicinity of the outfall,
within the mixing zone. There have been no increases in contaminant
levels or disease in the flounder and lobsters included in the monitoring
program or in mussels deployed at any distance from the discharge.

2008 OUTFALL MONITORING OVERVIEW 63 
Table 8-1. Answers to the monitoring questions as of the end of 2008. 
Monitoring Question Answer 
Do effluent pathogens exceed the permit
limits?
No. Secondary treatment and disinfection
effectively remove pathogens. In thousands
of tests, daily fecal coliform limits have been
exceeded twice, both times during storms.
Does acute or chronic toxicity of effluent
exceed the permit limit?
No. In 500 tests, there have been four
exceedances of permit limits.
Do effluent contaminant concentrations
exceed permit limits?
No. Discharges of priority pollutants are well
below SEIS predictions and in most cases
meet receiving water quality criteria even
before dilution.
Do conventional pollutants in the effluent
exceed permit limits?
No. Discharges of solids and BOD have
decreased by 80% compared to the old
treatment plant. In more than 500 tests, there
have been three exceedances of suspended
solids limits, which occurred during an upset
of the secondary treatment process by an
industrial discharge.
What are the concentrations of
contaminants in the influent and effluent and
their associated variability?
There has been great success in reducing
contaminants in the influent and a high
degree of removal of contaminants by the
treatment system, with consistently low
concentrations since secondary treatment
was implemented. 
Do levels of contaminants in water outside
the mixing zone exceed water quality
standards?
No. Water quality standards are not
exceeded. The projected degree of mixing
was confirmed by plume studies conducted in
2001. Ongoing effluent monitoring assures
that standards are not violated.
Are pathogens transported to shellfish beds
at levels that might affect shellfish consumer
health?
No. Dilution is sufficient for pathogens to
reach background concentrations before
reaching shellfish beds. Dilution rates were
confirmed by plume studies conducted in
2001.
Are pathogens transported to beaches at
levels that might affect swimmer health?
No. Dilution is sufficient for pathogens to
reach background concentrations before
reaching beaches. Dilution rates were
confirmed by plume studies conducted in
2001.
Has the clarity and/or color of the water
around the outfall changed?
No. Although clarity and color have not
changed, there are occasional observations
of tiny bits of grease, similar to samples
collected at the treatment plant.
Has the amount of floatable debris around
the outfall changed?
Floatable debris of concern is rare in the
effluent. Signs of effluent can occasionally be
detected in the field.
Are the model estimates of short-term (less
than one day) effluent dilution and transport
accurate?
Yes. Model estimates were confirmed by
plume studies conducted in 2001.
What are the nearfield and farfield water
circulation patterns?
Flow is controlled by general circulation in the
Gulf of Maine and influenced by tides and
local wind. Bottom currents around the outfall
can flow in any direction with no mean flow
direction.

2008 OUTFALL MONITORING OVERVIEW 64 
Monitoring Question Answer 
What is the farfield fate of dissolved,
conservative, or long-lived effluent
constituents?
There have been no detectable changes in
the farfield. Changes in salinity and dissolved
components of the effluent are not detected
within tens of meters of outfall and not
observed in farfield water or sediments.
Have nutrient concentrations changed in the
water near the outfall; have they changed at
farfield stations in Massachusetts Bay or
Cape Cod Bay, and, if so, are they
correlated with changes in the nearfield?
Changes have been consistent with model
predictions. The effluent signature is
observed in the vicinity of the outfall but is
quickly diluted.
Do the concentrations (or percent
saturation) of dissolved oxygen in the water
column meet the state water quality
standards?
Yes. Conditions are unchanged from the
baseline.
Have the concentrations (or percent
saturation) of dissolved oxygen in the vicinity
of the outfall or at selected farfield stations in
Massachusetts Bay or Cape Cod Bay
changed relative to pre-discharge baseline
or a reference area? If so, can changes be
correlated with effluent or ambient water
nutrient concentrations, or can farfield
changes be correlated with nearfield
changes?
No. Conditions have not changed from the
baseline.
Has the phytoplankton biomass changed in
the vicinity of the outfall or at selected
farfield stations in Massachusetts Bay or
Cape Cod Bay, and, if so, can these
changes be correlated with effluent or
ambient water nutrient concentrations, or
can farfield changes be correlated with
nearfield changes?
No. No substantial change has been
detected.
Have the phytoplankton production rates
changed in the vicinity of the outfall or at
selected farfield stations, and, if so, can
these changes be correlated with effluent or
ambient water nutrient concentrations, or
can farfield changes be correlated with
nearfield changes?
Productivity patterns in Boston Harbor may be
changing, as the area transitions from
eutrophic conditions to a more typical coastal
regime. There has been no concurrent
increase in productivity in Massachusetts
Bay.
Has the abundance of nuisance or noxious
phytoplankton changed in the vicinity of the
outfall?
The frequency of Phaeocystis blooms has
increased, but the phenomenon is regional in
nature. Alexandrium blooms, which have
occurred since 2005, are regional and have
not been attributed to the outfall.
Has the species composition of
phytoplankton or zooplankton changed in
the vicinity of the outfall or at selected
farfield stations in Massachusetts Bay or
Cape Cod Bay? If so, can these changes
be correlated with effluent of ambient water
nutrient concentrations, or can farfield
changes be correlated with nearfield
changes?
The increase in frequency of Phaeocystis 
blooms is the most marked change in the
phytoplankton community, and the region
appears to be entering a period of frequent
red tides. Those changes have not been
attributed to the outfall. There have been no
marked changes in the zooplankton
community.
What is the level of sewage contamination
and its spatial distribution in Massachusetts
and Cape Cod bays sediments before
discharge through the new outfall?
The effects of historic inputs from Boston
Harbor and other sources can be detected,
particularly in coastal stations.

2008 OUTFALL MONITORING OVERVIEW 65 
Monitoring Question Answer 
Has the level of sewage contamination or its
spatial distribution in Massachusetts and
Cape Cod bays sediments changed after
discharge through the new outfall?
An effluent signal can be detected only in 
Clostridium perfringens spores, the most
sensitive sewage tracer, and is only
detectable within a few kilometers of the
outfall.
Has the concentration of contaminants in
sediments changed?
There has been no general increase in
contaminants. An effluent signal can be
detected as Clostridium perfringens spores
within 2 km of the diffuser.
Has the soft-bottom community changed? Changes have occurred but are the result of
natural variation. The changes are not
significant and are not attributed to the outfall.
Have the sediments become more anoxic;
that is, has the thickness of the sediment
oxic layer decreased?
No. The sediment RPD has been deeper
during post-diversion years rather than
shallower; that is, the sediments are more
rather than less oxic.
Are any benthic community changes
correlated with changes in levels of toxic
contaminants (or sewage tracers) in
sediments?
There have been no changes detected, even
within 2 km of the outfall.
Has the hard-bottom community changed? There have been no changes that can be
attributed to the outfall. There have been
decreases in coralline algae at some stations,
but the geographic pattern does not suggest
an outfall effect.
How do the sediment oxygen demand, the
flux of nutrients from the sediment to the
water column, and denitrification influence
the levels of oxygen and nitrogen in the
water near the outfall?
These conditions were described by baseline
monitoring.
Have the rates of these processes
changed?
Conditions have improved in Boston Harbor
and have not changed in Massachusetts Bay.
Has the level of contaminants in the tissues
of fish and shellfish around the outfall
changed since discharge began?
There has been no substantial change in
flounder or lobster contaminant body
burdens, with concentrations remaining very
low. There have been detectable increases
in concentrations of some contaminants in
mussel arrays deployed within the mixing
zone at the outfall.
Do the levels of contaminants in the edible
tissue of fish and shellfish around the outfall
represent a risk to human health?
There have been no changes that would pose
a threat to human health. Regional patterns
have persisted since the baseline period, and
there appears to be a general long-term
downward trend for most contaminant levels.
Are the contaminant levels in fish and
shellfish different between the outfall,
Boston Harbor, and a reference site?
Differences were documented during baseline
monitoring. Regional patterns have persisted
since the diversion, with concentrations being
highest in Boston Harbor and lowest in Cape
Cod Bay.
Has the incidence of disease and/or
abnormalities in fish or shellfish changed?
There have been no increases in disease or
abnormalities in response to the outfall; there
has been a long-term downward trend in liver
disease in fish from near Deer Island and
near the outfall.

2008 OUTFALL MONITORING OVERVIEW 66
References 
Alber M, Chan A. 1994. Sources of contaminants to Boston Harbor:
revised loading estimates. Boston: Massachusetts Water Resources
Authority. Report 1994-01. 93p.
Bigornia-Vitale G, Wu D. 2008. Technical survey of nitrogen removal
alternatives of the Deer Island Treatment Plant. Boston: Massachusetts
Water Resources Authority. Report 2008-21. 36p.
Delaney MF. 2009. Addendum to contaminant monitoring of Deer Island
Treatment Plant effluent 2000–2005: effluent data for 2005–2008. Boston:
Massachusetts Water Resources Authority. Report 2009-05. 4p.
Delaney MF, Rex AC. 2007. Contaminant monitoring of Deer Island
Treatment Plant effluent: 2000–2005. Boston: Massachusetts Water
Resources Authority. Report 2007-02. 40p.
Diaz RJ, Rhodes DC, Blake JA, Kropp RK, Keay KE. 2008. Long-term
trends of benthic habitats related to reduction in wastewater discharge to
Boston Harbor. Estuaries and Coasts 31:1184-1197.
Hersh D. 2009. Calibration of in vivo fluorescence using multiple
regression: modifications to current methods: work in progress.
Manuscript in preparation.
Libby PS. 2006. Standing survey plan: rapid response Alexandrium 
survey. Boston: Massachusetts Water Resources Authority. Report 2006-
15. 19p.
Libby PS, Anderson D, Borkman D, Geyer WR, Keller AA, Oviatt CA,
Turner JT. 2009. 2008 water column monitoring summary report. Boston:
Massachusetts Water Resources Authority. Report 2009-12.
Maciolek NJ, Doner SA, Dahlen DT, Diaz RJ, Hecker B, Hunt C, Smith
WK. 2009. 2008 outfall benthic monitoring summary report. Boston:
Massachusetts Water Resources Authority. Report 2009-13.
Menzie CA, Cura JJ, Freshman JS, Potocki P. 1991. Boston Harbor:
estimates of loadings. Boston: Massachusetts Water Resources Authority.
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2008 OUTFALL MONITORING OVERVIEW 67 
MWRA. 1991. Massachusetts Water Resources Authority effluent outfall
monitoring plan: Phase I baseline studies. Boston: Massachusetts Water
Resources Authority. Report ms-02. 95p.
MWRA. 1997a. Massachusetts Water Resources Authority effluent outfall
monitoring plan: Phase II post discharge monitoring. Boston:
Massachusetts Water Resources Authority. Report ms-44. 61p.
MWRA. 1997b. Massachusetts Water Resources Authority Contingency
Plan. Boston: Massachusetts Water Resources Authority. Report
ENQUAD ms-069. 41p.
MWRA. 2001. Massachusetts Water Resources Authority Contingency
Plan revision 1. Boston: Massachusetts Water Resources Authority.
Report ms-071. 47 p.
MWRA. 2004. Massachusetts Water Resources Authority effluent outfall
ambient monitoring plan Revision 1, March 2004. Boston: Massachusetts
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Moore MJ, Maciolek NJ, Winchell PS. 2009. 2008 report for flounder
monitoring. Boston: Massachusetts Water Resources Authority. Report
2009-01. 17p.
NFSC. 2008. Assessment of 19 northeast groundfish stocks through 2007.
Report of the 3 rd Groundfish Assessment Review Meeting (GARM III).
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Reference Document 08-15.
Taylor DI. submitted. The Boston Harbor Project, and large decreases in
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Tucker J, Kelsey S, Giblin A, 2009. 2008 annual benthic nutrient flux
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2008 OUTFALL MONITORING OVERVIEW 68 
U.S. Department of Commerce. 2008. National Oceanic and Atmospheric
Administration. National Marine Sanctuary Program. Stellwagen Bank
National Marine Sanctuary Draft Management Plan/Draft Environmental
Assessment. Silver Spring, MD.
Werme C, Hunt, C. 2008. Background outfall monitoring overview.
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Wu D. 2009a. NPDES compliance summary report, fiscal year 2008.
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2008 OUTFALL MONITORING OVERVIEW 69
List of Acronyms 
BACI Before-After, Control-Impact analysis
BOD Biochemical oxygen demand
cBOD Carbonaceous biochemical oxygen demand
BWQM Bay Water Quality Monitoring
CHV Centrotubular hydropic vacuolation
CSO Combined sewer overflow
DDE Dichlorodiphenylethylene
DDT Dichlorodiphenyltrichloroethane
DIF Deer Island Flats
DITP Deer Island Treatment Plant
DO Dissolved oxygen
ECCB Eastern Cape Cod Bay
GoMOOS Gulf of Maine Ocean Observation System
GOMTOX Gulf of Maine Toxicity
HMW High molecular weight
IAAC Inter-Agency Advisory Committee
LC50 50% mortality concentration
LMW Low molecular weight
MB Massachusetts Bay
MGD Million gallons per day
MWRA Massachusetts Water Resources Authority
NA Not analyzed/not applicable
NB Nantasket Beach
NDBC National Data Buoy Center
NFSC Northeast Fisheries Science Center
NOAA National Oceanic and Atmospheric Administration
NOEC No observed effects concentration
NPDES National Pollutant Discharge Elimination System
OMSAP Outfall Monitoring Science Advisory Panel
OS Outfall site
OSI Organism sediment index
PAH Polycyclic aromatic hydrocarbon
PCB Polychlorinated biphenyl
PIAC Public Interest Advisory Committee
POC Particulate organic carbon
PSP Paralytic shellfish poisoning
RPD Redox potential discontinuity
SBNMS Stellwagen Bank National Marine Sanctuary
SEIS Supplemental Environmental Impact Statement
TKN Total Kjeldahl nitrogen
TP Total phosphate
TSS Total suspended solids
WHOI Woods Hole Oceanographic Institution
WWTF Wastewater treatment facility

Massachusetts Water Resources Authority
Charlestown Navy Yard
100 First Avenue
Boston, MA 02129
(617) 242-6000
http://www.mwra.com