2007 overview

Massachusetts Water Resources Authority · from the MWRA · 85 pages · 2.8 MB
open the file ↗ · original at the source ↗

2007 outfall monitoring overview
RESULTS
Massachusetts Water Resources Authority
Environmental Quality Department
Report 2008-17

Citation:
Werme C, Rex A, Hall M, Keay K, Leo W, Mickelson M, and Hunt CD. 2008. 2007
outfall monitoring overview RESULTS . Boston: Massachusetts Water Resources
Authority. Report 2008-17. 70p.

2007
Outfall Monitoring Overview
RESULTS
prepared by
Christine Werme
Berkeley, CA 94705
and
Andrea Rex, Maury Hall, Kenneth Keay, Wendy Leo, Michael
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
November 4, 2008

2007 Outfall Monitoring Panel and Committees
Outfall Monitoring Science Advisory Panel (OMSAP)
Andrew Solow, Woods Hole Oceanographic Institution Marine Policy
Center
Robert Beardsley, Woods Hole Oceanographic Institution
Norbert Jaworski, EPA-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

2007 OUTFALL MONITORING OVERVIEW RESULTS I
Table of Contents
Summary ............................................................................................................................. v
1. Introduction..................................................................................................................... 1
2. Effluent ........................................................................................................................... 2
2007 Characterization ..................................................................................................... 2
Contingency Plan Thresholds ......................................................................................... 8
3. Water Column................................................................................................................. 9
Physical Conditions ........................................................................................................ 9
Water Quality................................................................................................................ 13
Phytoplankton Communities......................................................................................... 22
Zooplankton Communities............................................................................................ 24
Contingency Plan Thresholds ....................................................................................... 26
4. Sea Floor ....................................................................................................................... 28
Sediment Characteristics and Tracers........................................................................... 28
Sediment-Profile Imaging............................................................................................. 31
Soft-bottom Communities............................................................................................. 32
Hard-bottom Communities ........................................................................................... 35
Contingency Plan Thresholds ....................................................................................... 38
5. Winter Flounder ............................................................................................................ 39
Contingency Plan Thresholds ....................................................................................... 42
6. Special Studies .............................................................................................................. 43
Floatables Monitoring................................................................................................... 43
Effluent floatables..................................................................................................... 43
Ambient floatables .................................................................................................... 45
Nutrient Flux................................................................................................................. 47
Marine Mammal Observations ..................................................................................... 49
Contaminants in Fish and Shellfish .............................................................................. 50
Effects of CSOs on Sediments...................................................................................... 52
Harbor and River Bacteria Monitoring ......................................................................... 55
7. Stellwagen Bank National Marine Sanctuary ............................................................... 58
Water Column............................................................................................................... 58
Sea Floor ....................................................................................................................... 62
8. Monitoring Questions and Answers: 2007 ................................................................... 65
References......................................................................................................................... 68
List of Acronyms .............................................................................................................. 70

2007 OUTFALL MONITORING OVERVIEW RESULTS II
List of Figures
Figure 2-1. Annual effluent flows....................................................................................... 2
Figure 2-2. Monthly primary and secondary flows in 2007 ............................................... 3
Figure 2-3. Annual solids discharges.................................................................................. 4
Figure 2-4. Average biochemical oxygen demand for the past nine years......................... 4
Figure 2-5. Annual nitrogen discharges.............................................................................. 5
Figure 2-6. Annual metals discharges................................................................................. 6
Figure 2-7. Annual mercury loadings in influent, effluent, and biosolids fertilizer pellets 7
Figure 3-1. Merrimack River and Charles River discharges to the ocean .......................... 9
Figure 3-2. Flows of the Merrimack and Charles rivers during 2007 were relatively high
in the spring quarter and low during other seasons........................................................... 10
Figure 3-3. 2005–2007 monthly average wind stress at the Boston Buoy compared with
observations from the previous 11 years .......................................................................... 11
Figure 3-4. Nearfield surface and bottom water temperature ........................................... 12
Figure 3-5. Nearfield surface and bottom water salinity .................................................. 13
Figure 3-6. MWRA Bay Water Quality Monitoring stations and regional groupings
included in the program .................................................................................................... 14
Figure 3-7. MWRA plankton stations included in water-column monitoring.................. 15
Figure 3-8. MWRA Boston Harbor Water Quality Monitoring stations and nearby
BWQM plankton stations ................................................................................................. 16
Figure 3-9. 2007 nearfield ammonium concentrations compared to the baseline range,
baseline mean, and post-diversion mean .......................................................................... 17
Figure 3-10. 2007 nearfield nitrate concentrations compared to the baseline range,
baseline mean, and post-diversion mean .......................................................................... 18
Figure 3-11. Changes in seasonal ammonium and nitrate concentrations from the baseline
to the post-diversion period .............................................................................................. 19
Figure 3-12. 2007 nearfield chlorophyll concentration compared to the baseline range,
baseline mean, and post-diversion mean .......................................................................... 20
Figure 3-13. Changes in areal seasonal chlorophyll from the baseline to the post-
diversion period ................................................................................................................ 21
Figure 3-14. 2007 nearfield dissolved oxygen concentrations compared to the baseline
range, baseline mean, and post-diversion mean................................................................ 22
Figure 3-15. Abundance of dominant phytoplankton groups in the nearfield in 2007.... 23
Figure 3-16. 2007 nearfield phytoplankton abundance compared to baseline range,
baseline mean, and post-diversion mean .......................................................................... 23
Figure 3-17. 2007 nearfield survey mean total zooplankton abundance compared to
baseline range, baseline mean, and post-diversion mean ................................................. 24
Figure 3-18. Long-term trends in nearfield abundance of the small copepod Oithona
similis and the larger copepod species Calanus finmarchicus .......................................... 25
Figure 4-1. Locations of nearfield soft-bottom stations for chemical parameters,
sediment-profile imaging, and community parameters .................................................... 28
Figure 4-2. Locations of farfield soft-bottom stations for chemical parameters, sediment-
profile imaging, and community parameters .................................................................... 29

2007 OUTFALL MONITORING OVERVIEW RESULTS III
Figure 4-3. Total PAH concentrations, 1992–2007: baseline range, baseline mean, post-
diversion mean, and 2007 station means .......................................................................... 30
Figure 4-4. Annual apparent color RPD for data from nearfield stations sampled in 2007
........................................................................................................................................... 31
Figure 4-5. Average organism sediment index in the nearfield by year........................... 32
Figure 4-6. Annual mean density of the numerically dominant species Prionospio
steenstrupi in the nearfield................................................................................................ 33
Figure 4-7. Annual community parameters in the nearfield ............................................. 34
Figure 4-8. Locations of hard-bottom stations.................................................................. 36
Figure 4-9. Photographs of the hard bottom taken in 2007 .............................................. 37
Figure 5-1. Winter flounder sampling sites. ..................................................................... 39
Figure 5-2. Annual percent females in winter flounder samples ...................................... 40
Figure 5-3. Incidence of skin lesions in flounder collected from four locations, 2003–
2007................................................................................................................................... 41
Figure 5-4. Annual prevalence of centrotubular hydropic vacuolation, corrected for age
........................................................................................................................................... 42
Figure 6-1. Effluent floatables sampler at the Deer Island Treatment Plant .................... 44
Figure 6-2. Box plot showing decreases in effluent floatables from 2003 through January
2008................................................................................................................................... 45
Figure 6-3. Results of ambient marine debris observations, February 2000–February 2008
........................................................................................................................................... 46
Figure 6-4. Samples of marine debris tows at the outfall site........................................... 47
Figure 6-5. Long-term trends in summer sediment oxygen demand at the four harbor
stations .............................................................................................................................. 49
Figure 6-6. Levels of chlordane in mussels ...................................................................... 51
Figure 6-7. Sampling stations and locations of CSOs in Boston Harbor......................... 53
Figure 6-8. Concentrations of Clostridium perfringens spores, total DDTs, and silver at
stations “near” and “far” from CSO discharges................................................................ 54
Figure 6-9. Map of major CSO projects recently completed and locations of bacteria
sampling stations............................................................................................................... 56
Figure 6-10. Changes in Enterococcus counts during wet and dry weather, 1991–2007. 57
Figure 7-1. Water column stations, including those in and near the Stellwagen Bank
National Marine Sanctuary ............................................................................................... 59
Figure 7-2. Annual mean ammonium and nitrate at the Stellwagen Bank National Marine
Sanctuary, the outfall nearfield, and Cape Cod Bay......................................................... 60
Figure 7-3. Annual chlorophyll at the Stellwagen Bank National Marine Sanctuary, the
outfall nearfield, and Cape Cod Bay................................................................................. 61
Figure 7-4. 2007 bottom water dissolved oxygen concentrations in Stellwagen Basin
compared to baseline range, baseline mean, and post-diversion mean............................. 62
Figure 7-5. Farfield benthic stations ................................................................................. 63
Figure 7-6. Community parameters at stations in or near the Stellwagen Bank National
Marine Sanctuary .............................................................................................................. 64

2007 OUTFALL MONITORING OVERVIEW RESULTS IV
List of Tables
Table 1. Summary of Contingency Plan thresholds and exceedances as of 2007 ............. vi
Table 2-1. Contingency Plan threshold values and 2007 results for effluent monitoring .. 8
Table 3-1. Contingency Plan threshold values and 2007 results for water-column
monitoring......................................................................................................................... 27
Table 4-1. Contingency Plan threshold values and 2007 results for sea-floor monitoring38
Table 5-1. Contingency Plan threshold values and 2007 results for fish-and-shellfish
monitoring......................................................................................................................... 42
Table 6-1. Average sediment oxygen demand and nutrient fluxes in Massachusetts Bay
and Boston Harbor ............................................................................................................ 48
Table 6-2. Percent of samples meeting the Enterococcus limit........................................ 55
Table 8-1. Answers to the monitoring questions as of the end of 2007............................ 65

2007 OUTFALL MONITORING OVERVIEW RESULTS 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.
This year’s outfall monitoring overview presents monitoring program results for effluent
and field data from 2007, marking seven full years since discharge was diverted from the
shallower, more confined waters of Boston Harbor to the deeper waters of Massachusetts
Bay (post-diversion monitoring). It compares all results to Contingency Plan thresholds.
The overview also includes sections on special studies and the Stellwagen Bank National
Marine Sanctuary.
Concentrations of most contaminants in the effluent continued to fall in 2007. Solids,
biological oxygen demand, and total metals loads reached new lows. Once used as a
sewage-effluent tracer, silver is now only rarely detected in the effluent. Total nitrogen
loads, which are not as effectively removed from effluent as organic matter, and toxic
contaminants, have remained about the same as the past few years.
There was one Contingency Plan caution level threshold exceedance during the year
(Table 1). It came in water-column monitoring, when the nearfield mean winter/spring
concentration of the nuisance algal species Phaeocystis pouchetii reached 2.15 million
cells per liter, exceeding the caution level of 2.02 million cells per liter. The wide
geographical extent of the Phaeocystis blooms that have occurred each year since 2000
suggests that regional processes, rather than the outfall, have been responsible for the
increasing frequency and duration of Phaeocystis blooms. There were no exceedances of
effluent, sea-floor, or fish-and-shellfish thresholds. There have been no exceedances of
threshold parameters for the sea floor throughout the duration of the monitoring program,
and no threshold exceedances have been attributed to unexpected adverse effects of the
outfall discharge.
Special studies in 2007 included assessments of floatable debris in the effluent and
ambient waters near the outfall; ongoing study of nutrient flux at the sediment-water
interface; marine mammal observations; evaluation of the fish-and-shellfish monitoring
program; assessment of the effects of combined sewer overflows on Boston Harbor
sediments; and compilation of results from bacteria monitoring in the harbor and its
tributary rivers.
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.

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

2007 OUTFALL MONITORING OVERVIEW RESULTS VII
Table 1, (continued)
Location/
Parameter
Type
Parameter 2000 2001 2002 2003 2004 2005 2006 2007
Water Column
Dissolved oxygen
concentration C D D D D D D D Nearfield
bottom water Dissolved oxygen
saturation C D D D D D D D
Dissolved oxygen
concentration D D D D D D D D Stellwagen
Basin
bottom water Dissolved oxygen
saturation 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
Annual NA D D D D D D D
Winter/spring NA D D D D D D D
Summer NA D D D D D C D
Nearfield
chlorophyll
Autumn C D D D D D D D
Winter/spring NA D D D C D D C
Summer NA D C C C C C D
Nearfield
nuisance algae
Phaeocystis
pouchetii Autumn D D D D D D D D
Winter/spring NA D D D D D D D
Summer NA D D D D D D D
Nearfield
nuisance algae
Pseudonitzchia Autumn D D D D D D D D
Nearfield
nuisance algae
Alexandrium
Any sample D D D D D C C D
Farfield
shellfish PSP toxin extent D D D D D D D D
Plume Initial dilution NA D Complete

2007 OUTFALL MONITORING OVERVIEW RESULTS VIII
Table 1, (continued)
Location/
Parameter
Type
Parameter 2000 2001 2002 2003 2004 2005 2006 2007
Sea Floor
Acenaphthene NA D D NA NA D NA NA
Acenaphylene NA D D NA NA D NA NA
Anthracene NA D D NA NA D NA NA
Benzo(a)anthracene NA D D NA NA D NA NA
Benzo(a)pyrene NA D D NA NA D NA NA
Cadmium NA D D NA NA D NA NA
Chromium NA D D NA NA D NA NA
Chrysene NA D D NA NA D NA NA
Copper NA D D NA NA D NA NA
Dibenzo(a,h)anthracene NA D D NA NA D NA NA
Fluoranthene NA D D NA NA D NA NA
Fluorene NA D D NA NA D NA NA
Lead NA D D NA NA D NA NA
Mercury NA D D NA NA D NA NA
Naphthalene NA D D NA NA D NA NA
Nickel NA D D NA NA D NA NA
p,p’-DDE NA D D NA NA D NA NA
Phenanthrene NA D D NA NA D NA NA
Pyrene NA D D NA NA D NA NA
Silver NA D D NA NA D NA NA
Total DDTs NA D D NA NA D NA NA
Total HMW PAH NA D D NA NA D NA NA
Total LMW PAH NA D D NA NA D NA NA
Total PAHs NA D D NA NA D NA NA
Total PCBs NA D D NA NA D NA NA
Nearfield
sediment
contaminants
Zinc NA D D NA NA D NA NA
Nearfield
sediment RPD depth NA D D D D D D D
Species per sample NA D D D D D D D
Fisher’s log-series
alpha NA D D D D D D D
Shannon diversity NA D D D D D D D
Nearfield
benthic
diversity
Pielou’s evenness NA D D D D D D D
Nearfield
species
composition
Percent opportunists NA D D D D D D D

2007 OUTFALL MONITORING OVERVIEW RESULTS IX
Table 1, (continued)
Location/
Parameter
Type
Parameter 2000 2001 2002 2003 2004 2005 2006 2007
Fish and Shellfish
Total PCBs NA D D D NA NA D NA
Mercury NA D D D D NA D NA
Chlordane NA D D D NA NA D NA
Dieldrin NA D D D NA NA D NA
Nearfield
flounder tissue
Total DDTs NA D D D NA NA D NA
Nearfield
flounder Liver disease (CHV) NA D D D D D D D
Total PCBs NA D D D NA NA D NA
Mercury NA D D D NA NA D NA
Chlordane NA D D D NA NA D NA
Dieldrin NA D D D NA NA D NA
Nearfield
lobster tissue
Total DDTs NA D D D NA NA D NA
Total PCBs NA D D D NA NA D NA
Lead NA D D D NA NA D NA
Mercury NA D D D NA NA D NA
Chlordane NA C C D NA NA D NA
Dieldrin NA D D D NA NA D NA
Total DDTs NA D D D NA NA D NA
Nearfield
mussel tissue
Total PAHs NA C C C NA NA D NA

2007 OUTFALL MONITORING OVERVIEW RESULTS X
This page intentionally left blank.

2007 OUTFALL MONITORING OVERVIEW RESULTS 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. For most of those years, the efforts have
included a monitoring program in Massachusetts Bay. Results from most
of the baseline-monitoring years and each post-diversion year (those years
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 .
Overviews for 1994 through 1999 included only baseline information.
With the outfall operational as of September 2000, subsequent reports
have included information relevant to the outfall permit, such as
Contingency Plan threshold exceedances, responses, and corrective
actions.
After nine years of baseline monitoring and seven years of post-diversion
monitoring, MWRA has answered the questions that had been posed
before the start-up of the Massachusetts Bay outfall. As had been
anticipated during the outfall-siting process, monitoring has been able to
detect minimal effects in the immediate vicinity of the outfall, but there
has been no indication of unexpected or broad-range changes.
Having answered the initial questions, MWRA has entered a new phase of
monitoring. While continuing to focus on verifying that the treatment
plant is working as designed, MWRA is also striving to anticipate
potential new challenges. A part of this new phase has been to streamline
the annual outfall monitoring overview. While past overviews included
background information and a full description of the monitoring program,
that information has now been put into a separate document (Werme and
Hunt 2008). That document and the monitoring plans (MWRA 1991,
1997a, 2004), the Contingency Plan (MWRA 1997b, 2001), 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 .
This year’s outfall monitoring overview focuses on results and compares
relevant data to Contingency Plan thresholds. The overview presents 2007
monitoring results for effluent, water column, sea floor, and winter
flounder. 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.

2007 OUTFALL MONITORING OVERVIEW RESULTS 2
2. Effluent
2007 Characterization
Average daily flow to the Deer Island Treatment Plant (DITP) in 2007 was
the lowest it has been throughout the monitoring program (Figure 2-1),
partially because it was a dry year, but possibly also because ongoing
maintenance has prevented intrusion of groundwater into sewage pipes
and because the people in MWRA’s service area have responded to water-
conservation initiatives. Almost all of the DITP flow received primary
and secondary treatment. A small amount of primary-only-treated effluent
flow, which was blended with secondary-treated flow, occurred during
March and April storms (Figure 2-2).
MWRA Primary and Secondary Flows 1990-2007
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
Year
Million gallons per day
Primary and Secondary Treated Flows
Primary-only (Blended) Treated Flows
Figure 2-1. Annual effluent flows. Average daily flow reached a record low in 2007.
(Primary-only flows are blended with secondary flows, and the blended flows meet
permit limits.)

2007 OUTFALL MONITORING OVERVIEW RESULTS 3
MWRA Monthly Flows 2007
0
100
200
300
400
500
600
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
Million Gallons per Day
Primary and Secondary Treated Flows
Primary-only (Blended) Treated Flows
Figure 2-2. Monthly primary and secondary flows in 2007. A small amount of primary-
only treated effluent was blended with secondary flows and released during spring
storms. (Blended flows meet all permit limitations.)
Solids discharges continued to decrease in 2007 to the lowest annual load
measured (Figure 2-3). Biological oxygen demand (BOD), measured as
carbonaceous BOD (cBOD) also continued to decrease to a record low
(Figure 2-4). At the same time, the nitrogenous BOD has increased,
particularly since 2005. Nitrogenous BOD is a direct result of the
microbiological breakdown that occurs during secondary treatment, which
is designed to remove cBOD. BOD in the effluent has not adversely
affected the receiving waters—ambient monitoring data show that the
discharge has had no effect on dissolved oxygen in the environment (see
Section 3, Water Column).

2007 OUTFALL MONITORING OVERVIEW RESULTS 4
Figure 2-3. Annual solids discharges . Solids discharges reached a record low in 2007.
Biochemical Oxygen Demand in MWRA Discharges
1999-2007
0
10
20
30
40
1999 2000 2001 2002 2003 2004 2005 2006 2007
Year
Tons per day
Carbonaceous BOD
Nitrogenous BOD
Figure 2-4. Average biochemical oxygen demand in tons/day for the past nine years.
MWRA’s permit limits carbonaceous BOD, which reached a record low in 2007.
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.

2007 OUTFALL MONITORING OVERVIEW RESULTS 5
Total nitrogen loads have remained about the same for several years, while
the portion of the total load made up of ammonium has slightly increased
to the highest level measured in the monitoring program (Figure 2-5). The
secondary treatment biological process changes nitrate/nitrite and other
forms of nitrogen to ammonium.
Deer Island Treatment Plant Nitrogen Discharges 1996-2007
0
2000
4000
6000
8000
10000
12000
14000
1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
Year
Metric tons per year
Ammonium Nitrite/Nitrate Other Nitrogen Species* Caution Level
*Method change to TKN April 2003
Figure 2-5. Annual nitrogen discharges. Total nitrogen discharges reached a record
low in 2007, but discharges of ammonium were higher, a result of the secondary
treatment process. (TKN = total Kjeldahl nitrogen, a measure of total nitrogen in the
effluent)
Metals loads also reached new lows (Figure 2-6), with only copper and
zinc remaining in significant quantities. Once used as a sewage-effluent
tracer, silver is now only rarely detected in MWRA’s effluent. The
treatment plant is currently removing approximately 95% of the mercury
and lead, about 85% of the cadmium and copper, 80% of the chromium
and zinc, and 45% of the nickel from the influent. Organic contaminants
are also removed: about 95% of the polycyclic aromatic hydrocarbons
(PAHs) and 85% of the polychlorinated biphenyls (PCBs) are removed
during treatment. A review of contaminant monitoring at the Deer Island
Treatment Plant during 2000–2005 was completed in 2007 (Delaney and
Rex 2007).

2007 OUTFALL MONITORING OVERVIEW RESULTS 6
Metals in MWRA Treatment Plant Discharges 1991-2007
0
100
200
300
400
500
600
700
91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07
Year
Average pounds per day discharged
Silver
Nickel
Chromium
Lead
Copper
Zinc
Figure 2-6. Annual metals discharges . Total metals discharges reached a record low in
2007.
Reducing mercury in the environment has been a top priority not only for
MWRA, but for policy makers throughout New England and Canada.
Mercury accumulation in fish is a major source to humans, and most water
bodies in Massachusetts are subject to fish consumption advisories due to
mercury. Through MWRA’s source-reduction program, approximately
75% of dentists in the region installed amalgam separators to reduce
mercury inputs to the sewer system, and hospitals are reducing mercury
discharges. Loads in the influent, effluent, and fertilizer pellets made from
biosolids show large declines (Figure 2-7). Influent loads have been cut in
half since 1999. Mercury discharges in the effluent have decreased from
an average of 0.14 pounds per day in 1999 to 0.02 pounds per day in 2007.
Concentrations as well as loads have also declined—the concentration of
mercury in the fertilizer pellets made from biosolids decreased from 3.8
mg/kg to 1.8 mg/kg during 2004–June 2008, the period in which the dental
amalgam separator program was implemented. Now, most of the mercury
entering Massachusetts water bodies originates from power plants in the
Midwest and Southeast.

2007 OUTFALL MONITORING OVERVIEW RESULTS 7
Influent, Effluent, and Fertilizer Pellet Mercury Dropped
Significantly
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
1999 2000 2001 2002 2003 2004 2005 2006 2007
Average pounds per day
Influent* Effluent Pellets
*Calculated as influent minus recycled mercury
Figure 2-7. Annual mercury loadings in influent, effluent, and biosolids fertilizer
pellets have dropped significantly. “ Influent” is calculated as total mercury minus the
amount that is recycled. The influent loading for 2002, indicated by an open symbol, is
probably underestimated, due to sampling error. (Note: The MWRA industrial
pretreatment program prohibits mercury from industries permitted to discharge to the
sewer system. Operationally, this prohibition is enforced at concentrations of 1μg/L or 1
part per billion. Monitoring of industries measures levels to 10 ng/L or 10 parts per
trillion, and monitoring of the effluent is to the level of 0.1 ng/L or 100 parts per
quadrillion.)

2007 OUTFALL MONITORING OVERVIEW RESULTS 8
Contingency Plan Thresholds
The Deer Island Treatment Plant had no permit violations and no
exceedances of the Contingency Plan thresholds in 2007 (Table 2-1).
Table 2-1. Contingency Plan threshold values and 2007 results for effluent monitoring.
Parameter Caution Level Warning Level 2007 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

2007 OUTFALL MONITORING OVERVIEW RESULTS 9
3. Water Column
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. In 2007, the overall physical, water quality, and biological
conditions were about average for the monitoring period and followed
typical seasonal patterns. Total annual flows from the Merrimack and
Charles rivers were lower than average, but flows during April through
June were relatively high (Figures 3-1, 3-2). From July through the end of
the year, the flows were relatively low.
0
500
1000
1500
2000
2500
3000 Merrimack River Discharge, 1992-2007
m 3 /s
1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
0
10
20
30
40
50
60 Charles River Discharge, 1992-2007
m 3 /s
Figure 3-1. 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.)

2007 OUTFALL MONITORING OVERVIEW RESULTS 10
31 s t
percentile
81 st
25 th
19 th
8 th
19 th
64 th
19 th
percentile
Figure 3-2. Flows of the Merrimack (top) and Charles (bottom) rivers during 2007
were relatively high in the spring quarter and low during other seasons. For example,
the average April–June 2007 flow of the Merrimack River ranked 15 th out of 18 years of
data, which translates to the 81 st percentile. The year 2006, shown for contrast, had high
flow in every season.
Overall, the wind-forcing conditions in 2007 were typical for the
monitoring period. In most years, spring is a transitional period between
winter downwelling and spring upwelling conditions. Downwelling, the
condition in which winds from the north or east move waters toward the
coast, was slightly stronger than average during April, May, and June
2007. Those spring downwelling conditions were not as strong as the
downwelling conditions during May and October 2005 (Figure 3-3),
which resulted from large storms with winds from the northeast.

2007 OUTFALL MONITORING OVERVIEW RESULTS 11
Figure 3-3. 2005–2007 monthly average wind stress at the Boston Buoy compared
with observations from the previous 11 years. (Positive values indicate winds from the
south or west, which result in upwelling-favorable wind stress; negative values indicate
winds from the north or east, which favor downwelling.)
The annual progression of air temperatures and water temperatures (Figure
3-4) in 2007 was about typical. The winter of 2006–2007 was slightly
warmer than average, and June 2007 was slightly colder than average. It
is not easy to see in Figure 3-4, but surface and bottom water temperatures
were warmer than average in June, probably because of the downwelling
conditions that occurred at that time. Surface waters seemed cooler than
average in August and September, but a separate analysis of buoy data
showed that the ship surveys happened by chance to occur on days that
were a couple of degrees cooler than was typical for those months.

2007 OUTFALL MONITORING OVERVIEW RESULTS 12
Figure 3-4. Nearfield surface and bottom water temperature. Surface measurements
are the upper line.
Each year, salinities in the bay are affected by spring runoff. During
spring 2007, as in the previous two springs, the salinities fell to relatively
low levels following strong storms. Salinities in the bottom waters were
relatively high at the beginning of the year but were at normal levels by
the end of the year (Figure 3-5).

2007 OUTFALL MONITORING OVERVIEW RESULTS 13
Figure 3-5. Nearfield surface and bottom water salinity. Surface measurements are the
lower line.
Water Quality
The monitoring program measures water quality (and plankton, which are
discussed in the next two subsection sections below) at stations in
Massachusetts Bay, Cape Cod Bay, and Boston Harbor (Figures 3-6, 3-7,
and 3-8). The sampling 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. Results for 2007
continued to confirm predictions that the effects of the discharge would be
local for certain parameters and not detectable for others (Libby et al.
2008). As in other post-diversion years, trends in water quality parameters
were similar to baseline observations with some differences in the timing
and magnitude of events.

2007 OUTFALL MONITORING OVERVIEW RESULTS 14

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°4 5'N
41°4 5'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 3-6. MWRA Bay Water Quality Monitoring (BWQM) stations and regional groupings
included in the program. “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.

2007 OUTFALL MONITORING OVERVIEW RESULTS 15

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°30'N
42°15'N
42°1 5'N
42°0'N
42°0 'N
41°4 5'N
northern
boundary
region
41°45'N
Cape Cod Bay
Boston
Harbor Massachusetts Bay
coastal region
offshore
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
0 10 20 30 40 50 5
Kilometers
Low : -125
Figure 3-7. MWRA plankton stations included in water column monitoring. The stations are a
subset of those monitored for water quality. Regional groupings, the instrumented buoys, and the
MWRA outfall are also shown.

2007 OUTFALL MONITORING OVERVIEW RESULTS 16

z z
z z
z z
z z
z z
z z
z z
z z
z z {
{
{
{
{
{
{ {
{
F23
F13
N18
N16
N04
F31
F30
F25
F24
142
141 140
139
138
124
106
77
24
70°45'W
70°45'W
71°0'W
71°0'W
42°1 5'N
42°1 5'N

z z
z z
z z
z z
z z
z z
z z
z z
z z {
{
{
{
{
{
{ {
{
F23
F13
N18
N16
N04
F31
F30
F25
F24
142
141 140
139
138
124
106
77
24
70°45'W
70°45'W 71°0'W
71°0'W
42°1 5'N
42°1 5'N
Boston
Harbor
Massachusetts
Bay
0 10 20 5
Kilometers
{ Harbor station (BHWQM)
z z Plankton station
NOAA Buoy 44013
MWRA outfall diffuser
High : 0
Low : -50
Figure 3-8. MWRA Boston Harbor Water Quality Monitoring (BHWQM)
stations and nearby BWQM plankton stations. Primary productivity is
measured at Stations F23, N18, and N04.

2007 OUTFALL MONITORING OVERVIEW RESULTS 17
Ammonium is the major component of total inorganic nitrogen in the
effluent. As expected from simple dilution, the discharge increased the
mean concentrations of ammonium in the nearfield compared to the
baseline mean (Figure 3-9). But in May 2007, the survey mean
ammonium concentration was unusually low, possibly due to uptake by
the April phytoplankton bloom or to a chance that the fixed sampling
stations straddled the outfall plume during that survey, not capturing the
elevated levels. Throughout the year, nearfield ammonium concentrations
varied, sometimes being closer to the baseline mean than the post-
discharge mean, a result also found in 2006. These results may also
reflect the sampling regime.
0.0
1.0
2.0
3.0
4.0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
NH4 ( μ M)
Baseline Range
Baseline Mean
2007
Post-Diversion Mean
Figure 3-9. 2007 nearfield ammonium concentrations compared to the baseline range,
baseline mean, and post-diversion mean.
Nitrate concentrations were elevated during the first three surveys of 2007
at the nearfield (Figure 3-10) and other stations, probably due to
contributions from rivers and the Gulf of Maine. Nitrate is present in
effluent but not at levels that would result in the elevated ambient levels
observed. Even after averaging over the year, concentrations of nitrate are
typically quite variable and reflect region-wide physical conditions and
time and magnitude of phytoplankton blooms.

2007 OUTFALL MONITORING OVERVIEW RESULTS 18
0
2
4
6
8
10
12
14
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
NO3 ( μ M)
Baseline Range
Baseline Mean
2007
Post-Diversion Mean
Figure 3-10. 2007 nearfield nitrate concentrations compared to the baseline range,
baseline mean, and post-diversion mean.
Over the course of the monitoring program, there has been a small,
localized increase in ammonium concentrations in the vicinity of the
outfall, concurrent with much larger decreases in ammonium
concentrations in Boston Harbor and the nearby coastal region (Figure 3-
11, top row). These changes are statistically significant in both the harbor
and the nearfield and can be observed across all seasons. The results
match the predictions that were made prior to the diversion of the
discharge from the harbor to the bay.
Changes in nitrate concentrations since the Massachusetts Bay outfall
began to discharge (Figure 3-11, bottom row) have been small. During the
past seven years, the bay has also experienced a background increase in
nitrate concentrations during the winter/spring and fall. This increase
appears to have been unrelated to the outfall and is perhaps the result of
regional-scale climate and biological changes.

2007 OUTFALL MONITORING OVERVIEW RESULTS 19
Winter/Spring Summer Fall
-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
-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 3-11. Changes in seasonal ammonium (top row) and nitrate (bottom row)
concentrations (μmol) 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. No changes in nitrate concentrations are attributed to the
outfall diversion.
Difference in seasonal mean (μM)
The 2007 seasonal trends in two measures of phytoplankton biomass,
chlorophyll and particulate organic carbon, were generally comparable to
previous years, but as for other parameters, there were some differences
from other years. During 11 of the 12 surveys, average chlorophyll
concentrations were within the baseline range. During the April survey,
concentrations were higher than the baseline range (Figure 3-12).
Particulate organic carbon concentrations were also high during April (not
shown).

2007 OUTFALL MONITORING OVERVIEW RESULTS 20
These April peaks corresponded with a region-wide bloom of the colonial
flagellate alga Phaeocystis pouchetii . The timing and sizes of
phytoplankton blooms are varied, causing the chlorophyll and particulate
organic carbon concentrations to vary. Since the diversion, average
chlorophyll concentrations in the bay during winter/spring have been
higher than during the baseline; the opposite has applied during fall
(Figure 3-13).
The elevated chlorophyll concentrations during spring are the result of
background blooms of Phaeocystis pouchetii that have occurred during
every year since 2000. Occurrence of these blooms is believed to be a
regional phenomenon and not caused by the outfall.
Figure 3-12. 2007 nearfield chlorophyll concentration compared to the baseline range,
baseline mean, and post-diversion mean. The April 2007 peak reflects a large
Phaeocystis pouchetii bloom.

2007 OUTFALL MONITORING OVERVIEW RESULTS 21
Winter/Spring Summer Fall
-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 3-13. Changes in areal seasonal chlorophyll (mg m -2 ) from the baseline to the post-
diversion period. (Post-diversion minus baseline values.) The large-scale increases during the
winter/spring and decreases during the fall are too large to have been caused by the outfall.
Difference in seasonal mean (mg m -2 )
Except for a slight increase in February rates, primary production rates in
Boston Harbor decreased after the discharge was relocated from the harbor
to Massachusetts Bay. The decrease was substantial in summer, causing a
bimodal pattern of spring and fall blooms, such as is characteristic of
temperate waters, rather than the unimodal summer maximum that was
observed when effluent was discharged to the harbor. On an annual basis,
primary production at all three stations was low in 1998 and has been low
every year since 2003. The higher productivity observed in other years
has correlated with greater wind-induced mixing of nutrients to surface
waters (data not shown). In Massachusetts Bay, there has been no
statistically significant change in production since outfall diversion.
Measurements of concentrations (Figure 3-14) 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 season pattern.

2007 OUTFALL MONITORING OVERVIEW RESULTS 22
5
6
7
8
9
10
11
12
13
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
DO (mgL -1 )
Baseline Range
Baseline Mean
2007
Post-Diversion Mean
Figure 3-14. 2007 nearfield dissolved oxygen concentrations compared to the baseline
range, baseline mean, and post-diversion mean. There has been no decrease in oxygen
concentrations as a result of the discharge.
Phytoplankton Communities
The April Phaeocystis pouchetii bloom was the most notable event for the
phytoplankton community in 2007 (Figure 3-15; Libby et al. 2008). As a
result of that large bloom, abundance of phytoplankton in April exceeded
the baseline range and the post-diversion mean (Figure 3-16). Total
phytoplankton abundance was similar to the baseline mean for other
survey dates in 2007.
Similar large Phaeocystis blooms occurred during 2000 and 2004, and
smaller but longer-duration blooms occurred during 2003 and 2005. The
2004 bloom was the largest recorded throughout the monitoring program.
The 2007 bloom rivaled the bloom of 2004 in size but not in duration,
lasting only about 30 days. As in other years, the 2007 bloom occurred
well beyond the boundaries of Massachusetts and Cape Cod bays, and
there was no indication of an effect of the outfall.

2007 OUTFALL MONITORING OVERVIEW RESULTS 23
Nearfield Area
0
2
4
6
8
10
7-Feb
26-Feb
21-Mar
10-Apr
23-May
18-Jun
24-Jul
20-Aug
4-Sep
2-Oct
22-Oct
13-Nov
Abundance (10 6 cells L -1 ) Other
Dinoflagellates
Pennate Diatom
Centric Diatom
Cryptophyte
Microflagellate
Figure 3-15. Abundance of dominant phytoplankton groups in the nearfield in 2007, showing
the Phaeocystis pouchetii bloom (included as “other”) that was underway during the April
survey.
0
2
4
6
8
10
12
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
10 6 cells L -1
Baseline Range
Baseline Mean
2007
Post-Diversion Mean
Figure 3-16. 2007 nearfield phytoplankton abundance compared to baseline range,
baseline mean, and post-diversion mean. The April peak is a result of the Phaeocystis
bloom; other values were within the baseline range.

2007 OUTFALL MONITORING OVERVIEW RESULTS 24
There were also winter/spring, summer, and fall diatom blooms, occurring
primarily in coastal waters. The nuisance phytoplankton species Pseudo-
nitzschia spp. were recorded in low numbers during February and March.
They occurred in densities far below those that would cause amnesic
shellfish poisoning. The dinoflagellate Alexandrium fundyense was also
recorded but in numbers below those that would cause a concern for
paralytic shellfish poisoning (PSP). There was an Alexandrium red tide
event in 2007, but it occurred offshore, well east of Massachusetts Bay.
Zooplankton Communities
The structure of the zooplankton community in the nearfield in 2007 was
similar to that of many earlier years but did not continue to show the
decline in total abundance observed from 2001 through 2006 (Figure 3-17;
Libby et al. 2008). The decline was largely due to a decline in total
copepods. During 2007, total copepod abundance rebounded to levels
within the baseline range, approximating the long-term mean.
Figure 3-17. 2007 nearfield survey mean total zooplankton abundance
compared to baseline range, baseline mean, and post-diversion mean. During
most surveys, values remained below the baseline mean, but overall abundance
was greater than in other post-diversion years.

2007 OUTFALL MONITORING OVERVIEW RESULTS 25
Almost all the 2007 increase was accounted for by the small copepod
Oithona similis (Figure 3-18, top), which is one of the most common
zooplankton species in Massachusetts Bay. The large and less abundant
copepod Calanus finmarchicus continued to show a different abundance
pattern from Oithona similis and other smaller species. Calanus
abundance was high during 2003–2005 and has declined during
subsequent years, remaining low in 2007 (Figure 3-18, bottom). Reasons
for these patterns are not known, but are region-wide and not thought to be
related to the outfall.
0
5,000
10,000
15,000
20,000
1990 1995 2000 2005 2010
Oithona trend (# m -3 )
0
500
1,000
1,500
2,000
1990 1995 2000 2005 2010
Calanus finmarchicus trend (# m -3 )
Figure 3-18. Long-term trends in nearfield abundance of the small copepod
Oithona similis (top) and the larger copepod species Calanus finmarchicus
(bottom). Note differences in scales. (Data were derived from a time-series
analysis of data from Stations N04, N16, and N18; red lines represent means.)

2007 OUTFALL MONITORING OVERVIEW RESULTS 26
Contingency Plan Thresholds
There was one threshold exceedance of water-column parameters during
2007 (Table 3-1). The winter/spring counts of the nuisance algal species
Phaeocystis pouchetii exceeded the caution level. As in 2004, when that
threshold was last exceeded, the wide geographical extent of the blooms
indicates that regional processes rather than the outfall were responsible
for the Phaeocystis bloom. A similar bloom occurred in 2000, before the
outfall diversion took place.
The summer Phaeocystis caution level threshold, which had been
exceeded in each year during 2002–2006, was met in 2007. That is
because the 2007 bloom, while large, was not of long duration.
Termination of spring Phaeocystis blooms appears to be related to the
speed with which the surface waters warm in the spring. During 2007,
waters reached temperatures of 14°C on May 25; during years with
longer-duration blooms, that temperature was not exceeded until mid-
June.

2007 OUTFALL MONITORING OVERVIEW RESULTS 27
Table 3-1. Contingency Plan threshold values and 2007 results for water-column monitoring.
Location/
Parameter
Specific
Parameter Baseline Caution Level Warning
Level
2007
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 = 7.29
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 = 77.4%
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 = 7.36
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 = 75.0%
Bottom water
nearfield
DO depletion
rate (June-
October)
0.024 mg/L/d 0.037 mg/L/d 0.049 mg/L/d 0.015 mg/L/d
Annual 79 mg/m 2 118 mg/m 2 158 mg/m 2 83 mg/m 2
Winter/spring 62 mgml 2 238 mg/m 2 None 128 mg/m 2
Summer 51 mg/m 2 93 mg/m 2 None 55 mg/m 2
Chlorophyll
nearfield
Autumn 97 mg/m 2 212 mg/m 2 None 65 mg/m 2
Winter/spring 468,000 cells/L 2,020,000 cells/L None
2,150,000 cells/L,
caution
exceedance
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 78 cells/L
Summer 14,600 cells/L 43,100 cells/L None Absent
Nuisance
algae
nearfield
Pseudo-
nitzschia
Autumn 9,940 cells/L 24,700 cells/L None Absent
Nuisance
algae
nearfield
Alexandrium
fundyense
Any nearfield
sample
Baseline
maximum =
163 cells/L
100 cells/L None 6.2 cells/L
Farfield PSP toxin
extent Not applicable New incidence None No new incidence

2007 OUTFALL MONITORING OVERVIEW RESULTS 28
4. Sea Floor
Sediment Characteristics and Tracers
In 2007, sixteen stations were sampled for analysis of sediment grain-size
distribution, total organic carbon, and the sewage-bacteria tracer
Clostridium perfringens spores; two stations (NF12 and NF17) were
sampled for analysis of chemical contaminants (Figures 4-1 and 4-2).
Figure 4-1. Locations of nearfield soft-bottom stations for chemical
parameters, sediment-profile imaging, and community parameters.

2007 OUTFALL MONITORING OVERVIEW RESULTS 29
Figure 4-2. Locations of farfield soft-bottom stations for chemical parameters,
sediment-profile imaging, and community parameters.
Grain-size distributions in 2007 were within the historic ranges of the
monitoring program, with no indication of the coarse sediments that can
result from large storms (Maciolek et al. 2008). Total organic carbon
concentrations were particularly low, especially at nearfield stations.
As in other post-diversion years (except 2006), it was possible to detect
higher counts of Clostridium perfringens spores in sediments collected
within two kilometers of the outfall (compared to the baseline years when
there was secondary treatment), and there were fewer spores in sediments
collected at greater distances. These findings were consistent with

2007 OUTFALL MONITORING OVERVIEW RESULTS 30
predictions that it would be possible to detect sewage tracers such as
Clostridium spores in the immediate vicinity of the outfall. The presence
of Clostridium spores helps to spatially define an area of potential outfall
impact.
Concentrations of chemical contaminants in the sediments of the two
stations sampled for those measurements (NF17 and NF12) were generally
within the ranges measured throughout the monitoring program, with no
suggestion of effects of the outfall. Concentrations of PAHs, for example,
were at the low end of the baseline range (Figure 4-3). Data continued to
confirm that sediment grain-size distribution and proximity to historic
(previous) inputs are the main indicators of contaminant concentrations.
In the nearfield, contaminant concentrations have been 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 since monitoring began.
Total PAH
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
FF12
NF24
NF17
NF14
NF13
NF15
NF12
NF10
NF21
NF20
NF04
NF02
FF11
FF01A
FF14
FF06
Station
Concentration (ng/kg dry)
Baseline Range
Baseline Mean
Post-diversion Mean
2007 Station Mean
Nearfield Farfield
Stations within
2-km of outfall
Figure 4-3. Total PAH concentrations, 1992–2007: baseline range, baseline
mean, post-diversion mean, and 2007 station means. Concentrations at the two
stations (NF17 and NF12) sampled in 2007 were at the low end of the baseline
range, continuing to show no elevation in response to the outfall.

2007 OUTFALL MONITORING OVERVIEW RESULTS 31
Sediment-Profile Imaging
Sediment-profile imaging measurements in 2007 were made at all western
Massachusetts Bay stations shown on Figure 4-1 (including those denoted
as being “sampled in even years”) and continued to show no effects of the
outfall (Maciolek et al. 2008). The concern that an increase in the amount
of organic matter deposited on the sea floor would result in a shallower
apparent redox potential discontinuity (RPD) has not been realized (Figure
4-4). The opposite has occurred; for most years, including 2007, the
average RPD depth has been deeper than the baseline mean. The increase
in RPD depth in 2007 was seen at every station where measurements have
been made over all years of the program.
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
Year
RPD (cm)
Mean RPD Depth +/- 1SD
Outfall Startup
Baseline Mean
Threshold
Figure 4-4. Annual apparent color RPD for data from nearfield stations sampled in
2007. The average RPD depth in 2007 was deeper than the baseline mean, indicating
that there has been no adverse effect from the discharge.
Another measure, the organism sediment index (OSI), has provided
further evidence that the outfall has not adversely affected the sea floor
(Figure 4-5). Instead, the OSI suggests that some stations in the nearfield
may have been stressed during some of the baseline years, but that there
has been no sign of stress during the post-diversion period. The primary
stress the sea-floor communities experience in western Massachusetts Bay

2007 OUTFALL MONITORING OVERVIEW RESULTS 32
is storm-induced sediment transport and deposition (Bothner and Butman
2007).
Figure 4-5. Average organism sediment index (OSI) in the nearfield by year. There has
been no evidence of stress on the soft-bottom community during the post-diversion
period. (F=relatively flat topographic areas; ~F=other areas; an OSI value of less than
6 can be considered to indicate stress.)
Soft-bottom Communities
Sixteen stations were sampled for evaluation of the soft-bottom infaunal
communities in 2007. The soft-bottom communities have shown no
response to the outfall over the course of the post-diversion period
(Maciolek et al. 2008). 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 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. The farfield
stations are more geographically widespread, with mostly finer sediments,
and polychaetes dominate at most stations.

2007 OUTFALL MONITORING OVERVIEW RESULTS 33
A tube-building spionid polychaete Prionospio steenstrupi has been the
numerically dominant species throughout Massachusetts Bay in recent
years, occurring in all sediment types. Total numbers of Prionospio
steenstrupi have declined since reaching a peak in 2002 and 2003 (Figure
4-6), but the species remains the dominant one, with almost twice the
abundance of the next most numerous species.
Figure 4-6. Annual mean density of the numerically dominant species Prionospio
steenstrupi in the nearfield. ( Color differences in data for 2004–2007 reflect a splitting
of stations into those sampled during even years and those sampled during odd years.)
Because Prionospio steenstrupi is so dominant, its lower abundance
during 2004–2007 is also reflected in the total abundance of animals per
sample and the other community parameters measured by the monitoring
program (Figure 4-7). Nearfield abundance and diversity (shown in
Figure 4-7 as log-series alpha) have decreased somewhat since 2004 and
continued to be relatively low in 2007. These results have held constant
through both even and odd years, when separate subsets of stations are
sampled. The measures remain within historic range of the monitoring
program, are not statistically different from the baseline, and are not
indicative of effects of the outfall.

2007 OUTFALL MONITORING OVERVIEW RESULTS 34
Nearfield Abundance
0
1,000
2,000
3,000
4,000
5,000
6,000
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
Year
Total Abundance per Sample Mean +/-1SD
Baseline Mean: 2242
Outfall Startup
Nearfield Species Richness
30
40
50
60
70
80
90
100
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
Year
Species per Sample
Mean +/-1SD
Baseline Mean: 65
Outfall Startup
Nearfield Log Series Alpha
4
6
8
10
12
14
16
18
20
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
Year
Log-Series Alpha
Mean +/-1SD
Baseline Mean:13.06
Outfall Startup
Figure 4-7. Annual community parameters in the nearfield. (Open symbols
indicate modified alternate-year sampling design, 2004–2007.)

2007 OUTFALL MONITORING OVERVIEW RESULTS 35
Hard-bottom Communities
The rocky habitats in the vicinity of the outfall and at reference locations
(Figure 4-8) were surveyed in August of 2007. They continued to support
robust communities of algae, invertebrates, and fish (Figure 4-9). Lush
epifaunal growth, particularly sea anemones, continued to thrive on the
diffuser heads, a condition unchanged since the outfall began to discharge.
Sea anemones were also the most common invertebrate group observed
throughout the region. Barnacles, tunicates, and the brachiopod
Terebratulina septentrionalis were also common. Coralline algae
continued to be the most common and widely distributed algal group.
Cunner was the most common fish species.
Some changes in the hard-bottom communities have been detected since
the outfall began operation, but they have been modest, and it has been
difficult to attribute them to the outfall (Maciolek et al . 2008). For
example, there have been increases in lobster and cod at some stations,
particularly cod, which is good news, as much of Massachusetts Bay has
been included in a Massachusetts Division of Marine Fisheries Cod
Conservation Zone designed to protect the species. There have been
decreases in the number of upright algae at many stations, but these
decreases began in the 1990s before the outfall went on-line, and the trend
appears to be reversing. Other species, such as Cancer crabs, also appear
to exhibit cycles of abundance.
Throughout the region, and particularly at several northern stations, there
have been increases in sediment drape and concurrent decreases in
abundance of coralline algae, the historically most abundant and widely
distributed taxonomic grouping. These decreases have been most
noticeable since 2005. Decline in coralline algae abundance had been
postulated as a possible indicator of outfall effects. However, the northern
stations at which the decreases have been noted were considered to be
reference sites, out of range of any expected outfall effects. These stations
appear have been affected by tanker traffic; tankers bearing liquefied
natural gas (LNG) have frequently been seen to be anchored in the area,
sometimes affecting MWRA survey schedules. In 2007, Station T7-1,
which once supported a lush growth of upright algae, was found to be
composed of overturned boulders, barren of life other than a new set of
barnacles. There was no sediment drape at that recently disturbed
location. Station T9-1 was similarly disturbed, and anchor scars from the
LNG tankers were evident. Such physical disturbances illustrate that the
seafloor is subject to non-outfall-related disturbances. The anchoring
activity may compromise the utility of these sites as reference stations for
the MWRA program.

2007 OUTFALL MONITORING OVERVIEW RESULTS 36
Figure 4-8. Locations of hard-bottom stations.

2007 OUTFALL MONITORING OVERVIEW RESULTS 37
Figure 4-9. Photographs of the hard bottom taken in 2007. (a) the top of an active diffuser
head, showing colonization by many anemones; (b) the side of the inactive diffuser head showing
colonization by sea-peach tunicates and frilled anemones; (c) a rock at a site just north of the
outfall (T2-4) showing an anemone, brachiopods, and other encrusting organisms; (d) numerous
cunner and a lobster in its burrow at a site south of the outfall (T4/6-1); (e) a boulder at a
southern reference site (T10-1), colonized by soft corals; (f) a boulder at a northern reference site
with brachiopods, sea stars, and encrusting organisms.

2007 OUTFALL MONITORING OVERVIEW RESULTS 38
Contingency Plan Thresholds
No Contingency Plan thresholds for sea-floor monitoring were exceeded
in 2007 (Table 4-1). There have been no threshold exceedances for any
sea-floor parameter during the course of the monitoring program. RPD
depth was almost 50% deeper than the baseline mean; the caution
threshold was set as 50% shallower, so the results indicate no adverse
effects from the discharge. Soft-bottom community parameters were
within normal ranges, and the percent of the soft-bottom community
composed of opportunistic species remained low, more than an order of
magnitude below the caution threshold.
Table 4-1. Contingency Plan threshold values and 2007 results for sea-floor monitoring.
Location Parameter Caution Level Warning Level 2007 Results
Sediments,
nearfield RPD depth 1.18 cm None 3.47 cm
Species per sample <46.52 or >79.95 None 64.05
Fisher’s log-series
alpha <9.95 or >15.17 None 13.74
Shannon diversity <3.30 or >3.91 None 3.67
Odd years,
benthic
diversity,
nearfield Pielou’s evenness <0.56 or >0.66 None 0.61
Benthic
opportunists % opportunists >10% >25% 0.78%

2007 OUTFALL MONITORING OVERVIEW RESULTS 39
5. Winter Flounder
Fifty sexually mature winter flounder were taken from each of four
sampling sites (Figure 5-1) during late April and early May 2007 (Nestler
et al. 2008).
Figure 5-1. Winter flounder sampling sites.

2007 OUTFALL MONITORING OVERVIEW RESULTS 40
Catch per unit effort remained low compared to 2001–2004 but was within
the historic range and similar to the years before the outfall began to
discharge. Similar to the last several years, fish collected at all stations
tended to be older, longer, and heavier than fish caught in the mid-to-late
1990s. The percentage of female fish in the catch has also increased
during that period, and almost every fish sampled was female (Figure 5-2).
Skewed sex ratios are not unusual in flounder, and the region-wide
incidence suggests that the outfall likely does not play a role.
Figure 5-2. Annual percent females in winter flounder samples. (DIF = Deer Island Flats, OS
= Outfall Site, ECCB = Eastern Cape Cod Bay, NB = Nantasket Beach)
Winter Flounde r
Percent Females by Year for Each Station
DIF ECCB
NB OS
Female Flounder (%)
30
40
50
60
70
80
90
100
Outfall Startup
Yea r
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
Fin erosion, a parameter that can be indicative of poor water quality,
remained within the historic range, except at Deer Island Flats, where
incidence has been somewhat elevated since 2005. Even at Deer Island
Flats, the incidence of skin lesions remained well below that observed in
the region during the early 1980s.
Blind-side ulcers, which were first detected in 2003, were uncommon,
continuing an ongoing decline since they were first noted (Figure 5-3).

2007 OUTFALL MONITORING OVERVIEW RESULTS 41
Winter Flounder
Incidence of Skin Lesions 2003-07
0
5
10
15
20
25
30
35
40
2003 2004 2005 2006 2007
Year
Percent
Deer I. Flats
Nantasket
Outfall Site
Cape Cod Bay
Figure 5-3. Incidence of skin lesions in flounder collected from four locations,
2003–2007.
No liver neoplasms (which can include cancer) were observed in any fish
from any site. Incidence of neoplasia has been rare throughout the area
since routine monitoring started in 1991, though levels were as high as
12% in harbor flounder during the 1980s. Neoplasia has never been
observed in fish taken from the outfall site. The incidence of
centrotubular hydropic vacuolation (CHV), a mild liver 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
the incidence in the years before the outfall began to discharge. Incidence
at Deer Island Flats has also declined since the outfall began operation,
continuing to suggest that there has been no adverse effect from the outfall
diversion. At Nantasket Beach, the 2007 incidence was higher than in
recent years but lower than many baseline years.

2007 OUTFALL MONITORING OVERVIEW RESULTS 42
Figure 5-4. Annual prevalence of centrotubular hydropic vacuolation (CHV), corrected for
age. (DIF = Deer Island Flats, OS = Outfall Site, ECCB = Eastern Cape Cod Bay, NB =
Nantasket Beach)
Winter Flounde r
Hydropic Vacuolation Index by Year for Each Station
DIF ECCB
NB OS
% CHV/Mean Age
0
2
4
6
8
10
12
14
16
18
20 Outfall Startup
Yea r
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
Contingency Plan Thresholds
Only one threshold parameter for fish and shellfish was measured in 2007
(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. 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 2007 results for fish and shellfish
monitoring.
Parameter
Type/
Location
Parameter Baseline Caution
Level
Warning
Level
2007
Results
Flounder
nearfield
Liver disease
(CHV) 24.4% 44.9% None 12%

2007 OUTFALL MONITORING OVERVIEW RESULTS 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. Recent special studies included:
• Analysis of floatables in the effluent and ambient waters near the
outfall site.
• Nutrient flux at the sediment-water interface.
• Marine mammal observations.
• Advanced statistical evaluation of the fish-and-shellfish contaminant
monitoring program.
• Effects of combined sewer overflow (CSO) discharges on Boston
Harbor sediments.
• Bacteria monitoring in the harbor and its tributary rivers.
Floatables Monitoring
In 2002, as part of its effluent monitoring study, MWRA developed an
effluent sampler (Figure 6-1) that screened debris from the disinfection
basin for sampling floatables in effluent from DITP. After a pilot study,
MWRA began regular quantitative effluent floatables sampling in 2003.
Petroleum hydrocarbons (PHC) are measured as part of Contingency Plan
monitoring, and fats; oil and grease (FOG) are also measured. In addition,
MWRA has been sampling the water for floatables at the outfall site and at
a control site using a plankton net on every nearfield water column survey
since 2000.
Effluent floatables
The mean volume of debris sampled during effluent monitoring was 168
parts per billion (ppb), and mean weight was 45 ppb. On average, non-
degradable materials were present at 6 ppb by weight. Total floatables
comprised about 86% degradable and 14% non-degradable material.
Floatables of most concern—plastic bags—were rare; condoms and
tampon applicators were sometimes found. Most of the non-degradable
material was in small pieces, for example, fruit labels and cellophane-type
wrappers. Much of the degradable material was bits of fat and plant
matter.

2007 OUTFALL MONITORING OVERVIEW RESULTS 44
Figure 6-1. Effluent floatables sampler at the Deer Island Treatment Plant.
The amount of floatable material increased with increasing flow rates
through the plant, which may have resulted from both more matter in
influent (street runoff) and reduced removal efficiency at higher flow
rates. However, even at the highest flows, material was present at only
<200 ppb by weight. Since 2003, quantities of effluent floatables at DITP
have decreased (Figure 6-2), likely a result of physical improvements to
the secondary treatment facilities, such as improved tip tubes, which skim
floating material from the secondary clarifiers, and improvements to the
biological process.

2007 OUTFALL MONITORING OVERVIEW RESULTS 45
0
100
200
300
400
500
600
700
ppb
2003 2004 2005 2006 2007 2008
Floatablesby volume
2003 2004 2005 2006 2007 2008
Floatablesby weight
Figure 6-2. Box plot showing decreases in effluent floatables from 2003
through January 2008.
For FOG, 96% of effluent samples were below the laboratory detection
limit; the mean value of FOG was 3.89 mg/L (assuming ½ the detection
limit for samples below detection limits), and the maximum weekly mean
was 13.6 mg/L. For PHC, 61% of the samples were below the laboratory
detection limit; the mean value was 0.165 mg/L, and the maximum weekly
mean was 0.7 mg/L, well below the Contingency Plan threshold of 15
mg/L weekly average.
Floatable debris (both degradable and non-degradable), FOG, and PHC
were found at very low levels in DITP effluent. In particular, materials of
concern such as petroleum, grease, and plastics, which are aesthetically
offensive or could harm wildlife, are rare in the effluent.
Ambient floatables
Debris tows (Figures 6-3 and 6-4) at both the outfall site and at a control
site north of the outfall, conducted during 2000–February 2008, found
plastics and paper that are characteristic of trash discarded from land or
boats. Plastic was found in 33% of tows at the outfall site and 24% of
tows at the control site; paper was found in 8% of tows at the outfall site
and 6% of tows at the control site. No paper or plastic debris
characteristic of sewage was found at either site. Although at both
sampling sites, the frequency of observations of paper debris decreased in

2007 OUTFALL MONITORING OVERVIEW RESULTS 46
the post-diversion (“after outfall”) period, and observations of plastic
increased, these apparent differences could result from the relatively small
number of samples collected before the outfall went on-line. However,
small fat particles were observed in 37% of tows at the outfall site and 5%
of tows at the control site. These particles are similar to the particles
observed in effluent samples at the treatment plant and presumably come
from the outfall. The prevalence of observations of fat particles in the
outfall tows from 2004 onward was substantially higher than 2000–2003,
but it is likely that this finding is due to improvements in the field crews’
awareness of and ability to see them in the tow samples. Such particles
are only rarely directly observed in the environment; they must be
concentrated in the net tows to be seen and do not have a significant
aesthetic impact.
Results of the floatables study are presented in more detail in Rex et al.
2008.
0
5
10
15
20
25
30
35
40
45
Paper
control
site
Paper
outfall site
Plastic
control
site
Plastic
outfall site
Fat
particles
control
site
Fat
particles
outfall site
Percent Positive
Before outfall on-line After outfall on-line
0 0
Figure 6-3. Results of ambient marine debris observations, February 2000–
February 2008 . Ten samples were collected at the both the control and outfall
sites before the outfall went on-line, and 95 samples were collected at each site
after the outfall went on-line.

2007 OUTFALL MONITORING OVERVIEW RESULTS 47
Figure 6-4. Samples of marine debris tows at the outfall site. On the left, a sample
collected before the outfall went on-line has plastic marine debris. The picture on the
right, collected after the outfall went on-line, shows the fat particles which are sometimes
seen.
Nutrient Flux
One concern about the outfall was that increased loads of organic matter
might enhance benthic respiration and increase fluxes of nutrients between
the sediments and the water column in the nearfield. 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.
These concerns have not been realized (Tucker et al. 2008). In fact, in
ongoing studies of three nearfield stations and one station in Stellwagen
Basin, fluxes have changed very little or decreased since the outfall began
to discharge (Table 6-1). Meanwhile, there have been significant
decreases in fluxes at four stations in Boston Harbor, reflecting great
improvements to the benthic environment.

2007 OUTFALL MONITORING OVERVIEW RESULTS 48
Table 6-1. Average sediment oxygen demand and nutrient fluxes in Massachusetts Bay and
Boston Harbor. Oxygen demand and flux units are mmol m -2 d -1 ; baseline is 1993–2000 in
Massachusetts Bay and 1992–2000 in Boston Harbor; denitrification averages for both
Massachusetts Bay and Boston Harbor are for two stations rather than four. Positive sediment
oxygen demand values reflect net oxygen uptake by the sediments; positive nutrient flux values
indicate net release of nutrients from the sediments.
Massachusetts Bay Boston Harbor Parameter Baseline Post-diversion Baseline Post-diversion
Sediment
oxygen
demand
17.2 15.2 69.4 36.1
Ammonium flux 0.7 0.3 3.6 2.1
Nitrate/nitrite
flux 0.2 0.3 2.2 0.8
Phosphate flux 0.1 0.0 0.5 0.2
Silica flux 5.1 3.3 8.0 5.5
Denitrification 3.4 2.1 5.5 3.1
In 2007, rates of sediment oxygen demand at the nearfield stations
averaged lower than the baseline mean. Dissolved inorganic nitrogen and
silica fluxes were also lower than baseline means. Other measurements
also continued to provide assurance that there have been no adverse
effects of the outfall.
Results suggest that the outfall did not increase loadings of organic matter
to the sediments. In 2007, the total organic carbon (TOC) content of
sediments from the nearfield averaged 1.3%, near the center of the
baseline range of 1.2–1.7%. One elevated TOC value was measured at the
most northern nearfield station in May, but TOC content at this station
declined again through the season, reaching low levels by October.
In Boston Harbor in summer 2007, scientists were surprised to discover
that Station BH02 was heavily colonized by benthic infauna. This
pollution-impacted station, located at the mouth of the Charles River, had
previously had few animals. However, in 2007, bioturbation had caused a
dramatic deepening of the surface oxidized layer, and fluxes at BH02 were
anomalously high (Figure 6-5), a pattern that had been observed
previously at stations colonized by amphipod mats. Rather than being a
sign of degradation, the investigators regard the increased metabolic
activity in the sediments at BH02 as a further step in the harbor’s
recovery, similar to conditions at another Boston Harbor station, BH03, in
1993 and 1995.

2007 OUTFALL MONITORING OVERVIEW RESULTS 49
Harbor SOD in Summer
Pawtuxent River Est, MD
Narragansett Bay, RI
South River Est, NC
Buzzards Bay, MA
Eel Pond, MA
New York Bight, NY
Kaneohe Bay, HI
0
50
100
150
200
250
300
1991 1993 1995 1997 1999 2001 2003 2005 2007
mmol O2 m -2 d -1
BH03
BH08A
BH02
QB01
other sites for context
BH03
BH08 A
BH02
QB01
Figure 6-5. Long-term trends in summer (average of July and August) sediment
oxygen demand at the four harbor stations, showing extreme rates at BH03 in 1993 and
1995 as context for high rates at BH02 in 2007. Measurements from other locations are
also provided for reference.
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 2007, observers were included on twelve nearfield
water quality surveys and three farfield surveys (Wisneski et al. 2008).
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.
The surveys are not designed to determine possible effects of the outfall
on marine mammals, but they do provide general information. During the
2007 surveys, 17 individual whales, more than 13–18 Atlantic white-sided
dolphins, and approximately 6 unidentified dolphins or porpoises were
directly observed by the trained observers and other members of the

2007 OUTFALL MONITORING OVERVIEW RESULTS 50
monitoring team. The total number of whales sighted by a team member
whose sole job was whale observation was low compared to 2006 but in
the same range as the numbers sighted during 2002 and 2003. Most whale
sightings occurred in or near the Stellwagen Bank National Marine
Sanctuary, and several whales were sighted in the vicinity of the outfall.
Records of the Whale Center of New England ( www.whalecenter.org )
indicated that there were high numbers of whales in Massachusetts Bay
and Stellwagen Bank during both 2006 and 2007. Adult humpback and
fin whales were observed feeding on Stellwagen Bank, and humpback
whale mother-calf pairs were also more abundant than they had been in
recent years. During April and early May, northern Atlantic right whales
were also present in higher-than-average numbers.
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. The length of
time that individual whales remained in or near Cape Cod Bay was also
longer than has been typical in recent years.
Contaminants in Fish and Shellfish
The MWRA monitoring program includes measurements of contaminants
in winter flounder, lobsters, and mussels in Boston Harbor and
Massachusetts and Cape Cod bays. MWRA recently completed a review
and statistical analysis (using a “before-after-control-impact” model) of
data collected during the years immediately prior to the outfall start-up
(1995–2000) and the post-diversion years (2001–2006) (Kane-Driscoll et
al. 2008). The analysis examined whether contaminant levels have
changed since the Massachusetts Bay outfall began to discharge, whether
any changes could be attributed to the outfall, and whether the current
levels of contaminants in fish and shellfish pose risks to human health or
the environment.
Statistical analyses of contaminants in winter flounder fillet and liver
tissues indicated that there were no adverse changes that could be
attributed to the outfall diversion. Concentrations of some contaminants
remained the same or decreased following the outfall start-up. Mercury
concentrations in fillets from fish caught near the outfall site were higher
in the post-diversion years than the baseline, but levels were also higher in
samples from Cape Cod Bay (the control site), suggesting a regional
source. Similarly, post-diversion concentrations of PCBs in flounder
livers were higher in fish from both the outfall site and Cape Cod Bay.
Concentrations of mercury in livers of fish taken near the outfall were
unchanged from the pre-diversion years, while levels fell in the livers of
fish taken from Cape Cod Bay.

2007 OUTFALL MONITORING OVERVIEW RESULTS 51
There were also no indications of outfall effects in analyses of lobster
meat and hepatopancreas. Concentrations of mercury in meat and
hepatopancreas, chlordanes in meat and hepatopancreas, and PCBs and
DDE in hepatopancreas were lower in the years after the outfall had begun
to discharge compared to the baseline period.
It was possible to detect changes in response to the outfall in mussels that
were deployed within the mixing zone of the outfall diffusers. Elevated
concentrations of PCBs, PAHs, chlordanes, and DDE were measured in
the post-diversion years. Meanwhile, there was an indication that moving
the outfall away from Boston Harbor resulted in lower levels of
chlordanes in mussels deployed near the site of the former discharge
(Figure 6-6).
Figure 6-6. Levels of chlordane in mussels deployed at the outfall, large navigation
buoy, and Deer Island Light (“impact” sites) and at Cape Cod Bay (“control” site).
Compared to the Cape Cod Bay control site, results show statistically significant
increases near the outfall and the buoy and statistically significant decreases at the
former Deer Island Light discharge site following the diversion. The actual
concentrations of chlordane were very low at all locations for all sampling periods.

2007 OUTFALL MONITORING OVERVIEW RESULTS 52
Overall, the analysis suggested that region-wide, concentrations of
contaminants in flounder, lobster, and mussels did not change as a result
of the discharge into Massachusetts Bay. Levels are generally below
thresholds for the protection of public health and the environment. The
data suggest that continued monitoring of contaminants in the effluent will
provide sufficient information to assure continued protection of resources
and wildlife.
Effects of CSOs on Sediments
During heavy rains, overflows from systems designed to carry both
sewage and stormwater runoff (combined sewer overflows or CSOs) can
result in direct discharges into local waters. MWRA’s CSO Control Plan
is designed to limit these discharges. To document improvements
resulting from these controls, MWRA periodically surveys the sediments
in Boston Harbor. Sampling has occurred at four-year intervals since
1990, with the most recent sediment survey taking place in 2006 (Pala et
al. 2008). Seventeen stations designated as “near” and “far” from CSO
discharges were sampled in the harbor, primarily in Dorchester Bay
(Figure 6-7). Samples were analyzed for grain size, TOC, the sewage
tracer Clostridium perfringens spores, PAHs, PCBs, pesticides, and
selected metals.
Concentrations of the sewage tracer Clostridium perfringens spores at
“near” stations decreased greatly after 1990 (Figure 6-8, top), a decrease
that has been attributed to implementation of secondary treatment and the
end of discharges of treated effluent to the southern part of the harbor, as
well as to improvements at the Fox Point and Commercial Point CSOs.
Slow declines have occurred at “far” stations.
Data on concentrations of organic contaminants in sediments have been
difficult to interpret, probably reflecting multiple sources and the
influences of physical factors, such as storms. For example, PAH
concentrations have generally been higher at “near” stations than “far”
stations but have not shown consistent patterns of decline. Concentrations
of PCBs, DDTs (Figure 6-8, middle), and chlordanes have declined slowly
in response to bans put on the chemicals as well as to discharge controls.
Metals concentrations (for example, silver, Figure 6-8, bottom) have also
been mostly higher at “near” stations and have also declined since the
1990s.

2007 OUTFALL MONITORING OVERVIEW RESULTS 53
Figure 6-7. Sampling stations and locations of CSOs in Boston Harbor .

2007 OUTFALL MONITORING OVERVIEW RESULTS 54
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
90,000
100,000
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
Year
Clostridium Spores (#/gdw)
Near Stations
Far Stations
0
20
40
60
80
100
120
140
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
Year
Total DDT (ng/g)
Near Stations
Far Stations
0
1
2
3
4
5
6
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
Year
Silver (ug/g)
Near Stations
Far Stations
Figure 6-8. Concentrations of Clostridium perfringens spores (top), total
DDTs (middle), and silver (bottom) at stations “near” and “far” from CSO
discharges.

2007 OUTFALL MONITORING OVERVIEW RESULTS 55
Harbor and River Bacteria Monitoring
MWRA’s long-term bacteria monitoring of Boston Harbor and its
tributary rivers has shown that tributary rivers, which are affected by
CSOs and stormwater, have been consistently more impacted by bacterial
contamination than the outer harbor where the two old treatment plants
discharged. Since 1988, MWRA and the four communities with CSOs—
Boston, Cambridge, Somerville, and Chelsea—have completed 21 major
projects, reducing CSOs by 81%. CSO control projects have been
completed during three major time periods: Phase 1, 1988–1991 (Early
Improvements); Phase 2, 1992–1997 (System Optimization); and Phase 3
1998–2015 (Long-term CSO Control Plan). Figure 6-9 shows where CSO
projects have recently been completed. In areas severely affected by
CSOs, such as the Charles and Neponset rivers and the Inner Harbor,
water quality improved dramatically as CSO projects came on-line (Table
6-2).
Table 6-2. Percent of samples meeting the Enterococcus limit, “single-sample
maximum” of 104 colonies/100 mL, in areas of Boston Harbor, its beaches, and
tributary rivers over three time periods corresponding to phases of the CSO plan.
CSO Phase
Area 1991 – 1997 1998 – 2000 2001 – 2007
Inner Harbor 77% 88% 82%
Winthrop Bay 96% 96% 96%
Constitution Beach 93% 88% 91%
Charles River 48% 70% 68%
Mystic River 74% 76% 73%
Alewife Brook 8% 12% 16%
Dorchester Bay 82% 83% 87%
Carson Beach 91% 95% 94%
Pleasure Bay Beach 90% 95% 95%
Neponset River 32% 38% 50%
Wollaston Beach 87% 87% 87%
Quincy Bay (offshore) 90% 98% 99.7%
Hingham Bay 96% 97% 100.0%

2007 OUTFALL MONITORING OVERVIEW RESULTS 56
3
1
5
4
6
2
Charlestown Storage
Conduit
March 2007 . CSO storage
conduit provides 670,000
gallons of storage, reducing
annual discharge volume to
Little Mystic Channel in the
Inner Harbor by 86%, from 4.4
million gallons to 0.6 million
gallons.
March 2007. Sewer separ-
ation eliminated discharges
from two CSOs in Fort Point
Channel in the Inner Harbor.
April 2007. New Union Park
facility provides 2 MG
storage, and treats CSO
flows >2MG, reducing CSO
discharges to the head of
Fort Point Channel from 25
untreated to 17 treated
activations annually.
Fort Point Channel Sewer
Separation
Union Park Detention and
Treatment Facility
Pleasure Bay Storm Drain
Improvements
March 2006. Pleasure Bay
storm drain improvements
ended all wet weather
discharges to the beach.
Stony Brook Sewer
Separation
September 2006 . Combined
sewers tributary to Stony
Brook Conduit and Back Bay
Fens and the Charles River,
were separated into storm
drains and sanitary sewers,
reducing CSO discharges
from 22 activations (44.5 MG)
to 2 activations (0.13 MG)
annually.
South Dorchester Bay
Sewer Separation
November 2007. Fox Point
and Commercial Point CSOs
were decommissioned after
sewer separation in South
Dorchester Bay, eliminating
CSO discharges to South
Dorchester Bay.
Two Cambridge
CSOs closed
November 2007 . CAM009
and CAM011 near the Eliot
Bridge on the Charles River
closed.
Figure 6-9. Map of major CSO projects recently completed and locations of
bacteria sampling stations.

2007 OUTFALL MONITORING OVERVIEW RESULTS 57
Figure 6-10 shows Enterococcus counts in wet and dry weather in 12 areas
of the harbor and its tributaries. Wet weather counts are substantially
higher than dry weather counts, except where sampling locations are fairly
distant from the shoreline (Winthrop Bay, Quincy Bay, and Hingham
Bay). Where CSOs have been a major source (Inner Harbor, Charles
River, and Neponset River), wet weather water quality has improved over
time.
Enterococcus Counts 1991-2007 in Wet and Dry Weather
(Geometric mean colonies/100 mL)
Inner Harbor Winthrop Bay Constitution Beach
Charles River Mystic River Alewife Brook
Dorchester Bay Carson Beach Neponset River
Wollaston Beach Quincy Bay Hingham Bay
0
100
200
300
400
500
1991-1997 1998-2000 2001-2007
Wet Dry
0
50
100
150
1991-1997 1998-2000 2001-2007
Wet Dry
0
50
100
150
1991-1997 1998-2000 2001-2007
Wet Dry
0
50
100
150
1991-1997 1998-2000 2001-2007
Wet Dry
0
50
100
150
1991-1997 1998-2000 2001-2007
Wet Dry
0
500
1000
1500
2000
2500
1991-1997 1998-2000 2001-2007
Wet Dry
0
50
100
150
1991-1997 1998-2000 2001-2007
Wet Dry
0
50
100
150
1991-1997 1998-2000 2001-2007
Wet Dry
0
50
100
150
1991-1997 1998-2000 2001-2007
Wet Dry
0
50
100
150
1991-1997 1998-2000 2001-2007
Wet Dry
0
100
200
300
400
500
600
700
1991-1997 1998-2000 2001-2007
Wet Dry
0
50
100
150
1991-1997 1998-2000 2001-2007
Wet Dry
Figure 6-10. Changes in Enterococcus counts during wet and dry weather, 1991–2007
in 12 areas of Boston Harbor and its tributaries. Wet = Rain > 2 inches of the previous 2
days. Dry = No rain over the previous 3 days. Dotted lines show the standard, 35
colonies/100 ml.

2007 OUTFALL MONITORING OVERVIEW RESULTS 58
7. Stellwagen Bank
National Marine Sanctuary
Water Column
Overall, water quality within the Gerry E. Studds Stellwagen Bank
National Marine Sanctuary is excellent, and the condition and
characterization reports prepared by the NOAA National Marine
Sanctuaries (available at http://sanctuaries.noaa.gov ) have noted that
chemical contaminant concentrations are low, water-quality conditions are
favorable for habitat and living resources, and human activities are not
having adverse effects on water quality. The 2007 MWRA water-quality
monitoring efforts at the stations in and near the sanctuary (Figure 7-1)
continued to support those findings. Water quality continued to be good,
with dissolved oxygen, nutrient concentrations, and plankton community
measures and abundances within expected ranges for this region of
Massachusetts Bay. There was no indication of any effect of the
Massachusetts Bay outfall (Libby et al. 2008).
Annual mean inorganic nitrogen (ammonium and nitrate) concentrations
vary from year to year in Massachusetts Bay, including within the
sanctuary. The present understanding is that nutrient levels within
Massachusetts Bay are mostly driven by nutrient levels in the very large
water masses entering at the northern boundary region, with some
influence of local or nearby sources. Consistent with this understanding is
the coherence between the pattern of ammonium concentration in the
sanctuary with that in the nearfield (Figure 7-2, top). After the outfall
went on-line, the nearfield pattern resembles that in the sanctuary plus
about 1uM. The long-term pattern of other areas within Massachusetts
Bay also showed some influence of ammonium from the Gulf of Maine,
but less so in Cape Cod Bay which is shown for reference (Libby et al
2008). Figure 7-2 (bottom) shows long-term nitrate concentrations. These
have trended upward in the sanctuary, the nearfield, and other areas of
Massachusetts Bay.

2007 OUTFALL MONITORING OVERVIEW RESULTS 59

2007 OUTFALL MONITORING OVERVIEW RESULTS 60
0
1
2
3
1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
NH4 ( μ M)
SBNMS Nearfield Cape Cod
0
1
2
3
4
5
6
7
8
9
1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
NO3 ( μ M)
SBNMS Nearfield Cape Cod
Figure 7-2. Annual mean ammonium (top) and nitrate (bottom) at the Stellwagen
Bank National Marine Sanctuary (SBNMS), the outfall nearfield, and Cape Cod Bay.
No changes that can be attributed to the outfall have occurred in the stations in or near
the sanctuary.

2007 OUTFALL MONITORING OVERVIEW RESULTS 61
The annual mean areal chlorophyll levels increased slightly at the
sanctuary stations and in Cape Cod Bay in 2007, while slightly declining
in the nearfield (Figure 7-3). This result did not significantly diverge from
the general pattern. There was a large peak in chlorophyll levels during
the April Phaeocystis pouchetii bloom. This wide-scale bloom was not
related to the outfall (see Section 3, Water Column). Chlorophyll levels
were within the baseline range during the rest of the year.
0
20
40
60
80
100
120
140
160
180
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
YEAR
Chlorophyll (mg m-2)
SBNMS Nearfield Cape Cod
Figure 7-3. 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 in
or near the sanctuary, the nearfield, and Cape Cod Bay.
Concentrations of dissolved oxygen (Figure 7-4) and percent saturation
have remained unchanged in Stellwagen Basin as well as in the nearfield.
There have been no decreases in dissolved oxygen concentrations or
percent saturation, as had been a concern before the outfall began to
discharge.

2007 OUTFALL MONITORING OVERVIEW RESULTS 62
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
2007
Post-Diversion Mean
Figure 7-4. 2007 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.
Sea Floor
No changes in concentrations of sewage tracers or sewage-related
contaminants were observed in the sediment samples from stations (FF05
and FF11) within or near the sanctuary (Figure 7-5), and there have been
no changes in community parameters since the outfall began operation
(Maciolek et al. 2008).
The deep-water stations sampled in 2007 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 start-up of the
outfall in 2000. The total number of individual organisms remained
within the baseline range for stations in or near the sanctuary (Figure 7-6).
The numbers of species per sample and the diversity of organisms within
the sample were also within the baseline range. No consistent patterns
that relate to outfall diversion have been found.

2007 OUTFALL MONITORING OVERVIEW RESULTS 63
Figure 7-5. Farfield benthic stations. Stations FF05, FF04, FF11, and FF14 are in or
near the Stellwagen Bank National Marine Sanctuary. FF11 and FF14 were sampled in
2007.

2007 OUTFALL MONITORING OVERVIEW RESULTS 64
0
10
20
30
40
50
60
70
80
90
100
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
Year
Total Species per Sample
FF05
FF04
FF14
FF11
Outfall startup
0
2
4
6
8
10
12
14
16
18
20
22
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
Year
Log Series Alpha
FF05
FF04
FF14
FF11
Outfall startup
Figure 7-6. Community parameters at stations in or near the Stellwagen Bank
National Marine Sanctuary.

2007 OUTFALL MONITORING OVERVIEW RESULTS 65
8. Monitoring Questions
and Answers: 2007
Prior to beginning the monitoring program, an Outfall Monitoring Task
Force formulated a series of questions focusing on environmental issues
that could be plausible unanticipated consequences of the effluent
discharge. Monitoring has answered those original questions (Table 8-1).
Table 8-1. Answers to the monitoring questions as of the end of 2007.
Monitoring Question Answer
Do effluent pathogens exceed the permit
limits?
No. Compliance with permit limits, secondary
treatment and disinfection effectively remove
pathogens.
Does acute or chronic toxicity of effluent
exceed the permit limit?
General compliance with permit limits.
Do effluent contaminant concentrations
exceed permit limits?
No. Compliance with permit limits,
discharges of priority pollutants 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. Compliance with permit limits,
discharges of solids and BOD have
decreased by 80% compared to the old
treatment plant.
What are the concentrations of
contaminants in the influent and effluent and
their associated variability?
High removal by treatment system with
consistently low concentrations since
secondary treatment brought on line.
Do levels of contaminants in water outside
the mixing zone exceed water quality
standards?
No. Water quality standards not exceeded,
confirmed by plume studies conducted in
2001 and ongoing effluent monitoring.
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, 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, 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 accurate, confirmed by
plume studies conducted in 2001.

2007 OUTFALL MONITORING OVERVIEW RESULTS 66
Monitoring Question Answer
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.
What is the farfield fate of dissolved,
conservative, or long-lived effluent
constituents?
Changes in farfield concentrations of salinity
and dissolved components 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 consistent with model predictions.
The effluent signature is clearly observed in
the vicinity of the outfall but is diluted over a
few days and 10s of kilometers.
Do the concentrations (or percent
saturation) of dissolved oxygen in the water
column meet the state water quality
standards?
Yes. Conditions unchanged from 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 not changed from 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 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. No concurrent increase in
productivity in Massachusetts Bay.
Has the abundance of nuisance or noxious
phytoplankton changed in the vicinity of the
outfall?
Frequency of Phaeocystis blooms has
increased, but the phenomenon is regional in
nature. Alexandrium blooms in 2005 and
2006 were 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?
Increase in frequency of Phaeocystis blooms
is the most marked change in the
phytoplankton community, but that change is
not attributed to the outfall. No marked
changes in the zooplankton community.

2007 OUTFALL MONITORING OVERVIEW RESULTS 67
Monitoring Question Answer
What is the level of sewage contamination
and its spatial distribution in Massachusetts
and Cape Cod bays sediments before
discharge through the new outfall?
Effects of historic inputs from Boston Harbor
and other sources detected.
Has the level of sewage contamination or its
spatial distribution in Massachusetts and
Cape Cod bays sediments changed after
discharge through the new outfall?
Effluent signal detected as Clostridium
perfringens spores, the most sensitive
sewage tracer, within a few kilometers of the
outfall.
Has the concentration of contaminants in
sediments changed?
No general increase in contaminants.
Effluent signal can be detected as some
tracers within 2 km of the diffuser.
Has the soft-bottom community changed? Changes have occurred but are not
significant and cannot be 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?
No changes detected, even within 2 km of the
outfall.
Has the hard-bottom community changed? No substantial changes detected. Decreases
in coralline algae detected 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?
Described by baseline monitoring; conditions
do not suggest adverse changes have
resulted from moving the outfall offshore.
Have the rates of these processes
changed?
No changes detected.
Has the level of contaminants in the tissues
of fish and shellfish around the outfall
changed since discharge began?
No substantial change in flounder or lobster
contaminant body burdens, with
concentrations remaining very low.
Detectable increases in concentrations of
some contaminants in mussel arrays
deployed 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?
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 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?
No increases in disease or abnormalities in
response to the outfall; long-term downward
trend in liver disease in fish from near Deer
Island and near the outfall.

2007 OUTFALL MONITORING OVERVIEW RESULTS 68
References
Bothner MH, Butman B. (eds.) 2007. Processes influencing the transport
and fate of contaminated sediments in the coastal ocean—Boston Harbor
and Massachusetts Bay. US Geological Survey Circular 302. 89p.
Delaney MF, Rex AC. 2007. Contaminant monitoring of Deer Island
Treatment Plant Effluent: 2000–2005. Boston: Massachusetts Water
Resources Authority. Report 2007-02. 40p.
Kane-Driscoll S, Edwards M, Pembroke A, Nestler EC, Gurshin C. 2008.
Changes in contaminants in winter flounder, lobster, and caged mussels in
Massachusetts and Cape Cod bays and Boston Harbor: 1995-2006.
Boston: Massachusetts Water Resources Authority. Report 2008-09. 73p.
Libby PS, Borkman D, Geyer WR, Keller AA, Turner JT, Oviatt CA.
2008. Water column monitoring in Massachusetts Bay: 1992-2007.
Boston: Massachusetts Water Resources Authority. Report 2008-16. 170p.
Maciolek NJ, Doner SA, Dahlen DT, Diaz RJ, Hecker B, Hunt C, Smith
WK. 2008. Outfall benthic monitoring interpretive report: 1992–2007
results. Boston: Massachusetts Water Resources Authority. Report 2008-
20. 144p.
MWRA. 1991. Massachusetts Water Resources Authority effluent outfall
monitoring plan: Phase I baseline studies. Boston: Massachusetts Water
Resources Authority. Report ENQUAD ms-02. 95p.
MWRA. 1997a. Massachusetts Water Resources Authority effluent outfall
monitoring plan: Phase II post discharge monitoring. Boston:
Massachusetts Water Resources Authority. Report ENQUAD 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 ENQUAD ms-071. 47 p.
MWRA. 2004. Massachusetts Water Resources Authority effluent outfall
ambient monitoring plan Revision 1, March 2004. Boston: Massachusetts
Water Resources Authority. Report ENQUAD ms-092. 65p.

2007 OUTFALL MONITORING OVERVIEW RESULTS 69
Nestler EC, Moore MJ, Pembroke A. 2008. 2007 flounder report for fish
and shellfish monitoring. Boston: Massachusetts Water Resources
Authority. Report 2008-05. 18p.
Pala S, Durell G, Field J. 2008 CSO impact on sediment contaminants in
Dorchester Bay and other Boston Harbor stations, 1990-2006. Boston:
Massachusetts Water Resources Authority. Report-2008-10.
Rex A, Tyler C, Wu D, Liang SY. 2008. Summary of floatables
observations in Deer Island Treatment Plant effluent and at the
Massachusetts Bay discharge site: 2000–2007. Boston: Massachusetts
Water Resources Authority. Report 2008-08. 20p.
Tucker J, Kelsey S, Giblin A, Hopkinson C. 2008. 2007 annual benthic
nutrient flux monitoring report. Boston: Massachusetts Water Resources
Authority. Report 2008-14.
Werme C, Hunt, C. 2008. BACKGROUND outfall monitoring overview.
Boston: Massachusetts Water Resources Authority. Report 2008-18. 54p.
Wisneski C, Weinrich M, Jaquet N. 2008. Summary of marine mammal
observations during 2007 surveys. Boston: Massachusetts Water
Resources Authority. Report 2008-04. 17p.

2007 OUTFALL MONITORING OVERVIEW RESULTS 70
List of Acronyms
BOD Biochemical oxygen demand
cBOD Carbonaceous biochemical oxygen demand
BHWQM Boston Harbor Water Quality Monitoring
BWQM Bay Water Quality Monitoring
CCB Cape Cod Bay
CHV Centrotubular hydropic vacuolation
CSO Combined sewer overflow
DDE Dichlorodiphenylethylene
DDT Dichlorodiphenyltrichloroethane
DIF Deer Island Flats
DIL Deer Island Light
DITP Deer Island Treatment Plant
DO Dissolved oxygen
ECCB Eastern Cape Cod Bay
FOG Fats, oil, and grease
GoMOOS Gulf of Maine Ocean Observation System
HMW High molecular weight
LC50 50% mortality concentration
LMW Low molecular weight
LNB Large Navigational Buoy
LNG Liquefied natural gas
MGD Million gallons per day
MWRA Massachusetts Water Resources Authority
NA Not analyzed/not applicable
NB Nantasket Beach
NDBC National Data Buoy Center
NOAA National Oceanic and Atmospheric Administration
OS Outfall site
OSI Organism sediment index
PAH Polycyclic aromatic hydrocarbon
PCB Polychlorinated biphenyl
PHC Petroleum hydrocarbon
PSP Paralytic shellfish poisoning
RPD Redox potential discontinuity
SBNMS Stellwagen Bank National Marine Sanctuary
TOC Total organic carbon
TKN Total Kjeldahl nitrogen

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

related records

Records whose documents say similar things, nearest first.