Background, 2012 update

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Outfall monitoring overview 
BACKGROUND: 
2012 update 
Massachusetts Water Resources Authority 
Environmental Quality Department 
Report 2012-02

Citation: 
Werme C, Rex AC, Hunt CD. 2012. O utfall monitoring overview background:
2012 Update . Boston: Massachusetts Water Resources Authority. Report 2012-02.
59 p.

Outfall Monitoring Overview 
BACKGROUND: 
2012 Update 
prepared for 
Massachusetts Water Resources Authority 
Environmental Quality Department 
100 First Avenue 
Charlestown Navy Yard 
Boston, MA 02129 
prepared by 
Christine Werme 
Berkeley, CA 94705 
Andrea Rex 
Environmental Quality Department 
MWRA 
Carlton D. Hunt 
Battelle 
397 Washington Street 
Duxbury, MA 02332 
October 19, 2012

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE
i 
Table of Contents 
List of Figures ............................................................................................................... ii 
List of Tables ............................................................................................................... iii 
1. Introduction ............................................................................................................... 1 
The Boston Harbor Project ....................................................................................... 1 
Outfall Permit............................................................................................................ 8 
Monitoring Program.................................................................................................. 9 
Contingency Plan .................................................................................................... 13 
Data Management ................................................................................................... 14 
Reporting................................................................................................................. 14 
Outfall Monitoring Overview ................................................................................. 15 
2. Effluent ................................................................................................................... 17 
Background ............................................................................................................. 17 
Pollution Prevention............................................................................................ 17 
Environmental Concerns ..................................................................................... 17 
Monitoring Design .................................................................................................. 19 
Contingency Plan Thresholds ................................................................................. 22 
3. Water Column ......................................................................................................... 23 
Background ............................................................................................................. 23 
Circulation and Water Properties ........................................................................ 23 
Environmental Concerns ..................................................................................... 25 
Monitoring Design .................................................................................................. 27 
Contingency Plan Thresholds ................................................................................. 33 
4. Sea Floor ................................................................................................................. 35 
Background ............................................................................................................. 35 
Bottom Characteristics and Sediment Transport ................................................ 35 
Environmental Concerns ..................................................................................... 35 
Monitoring Design .................................................................................................. 36 
Contingency Plan Thresholds ................................................................................. 41 
5. Fish and Shellfish .................................................................................................... 43 
Background ............................................................................................................. 43 
Monitoring Design .................................................................................................. 44 
Winter Flounder .................................................................................................. 44 
Lobster ................................................................................................................ 44 
Blue Mussel ........................................................................................................ 44 
Contingency Plan Thresholds ................................................................................. 46 
6. Special Studies ........................................................................................................ 48 
7. Stellwagen Bank National Marine Sanctuary ......................................................... 49 
Background ............................................................................................................. 49 
Monitoring Design .................................................................................................. 50 
References ................................................................................................................... 51 
List of Acronyms ........................................................................................................ 55 
Monitoring Questions and Answers............................................................................ 56

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List of Figures 
Figure 1-1. Massachusetts and Cape Cod bays municipal, commercial, and industrial
uses.. .............................................................................................................................. 4 
Figure 1-2. Massachusetts and Cape Cod Bays shellfish and anadromous fish habitat.
....................................................................................................................................... 5 
Figure 1-3. Massachusetts ocean special habitats and sanctuaries. .............................. 6 
Figure 1-4. Whale habitats in Massachusetts and Cape Cod bays, and offshore. ........ 7 
Figure 3-1. (a) General circulation within Massachusetts Bay. (b) General circulation
within the Gulf of Maine............................................................................................. 24 
Figure 3-2. Water-column monitoring stations.. ......................................................... 28 
Figure 3-3. Alexandrium Rapid Response Survey (ARRS) stations........................... 29 
Figure 4-1. Soft-bottom monitoring stations. ............................................................. 37 
Figure 4-2. Sediment-profile imaging (SPI) stations.. ................................................ 38 
Figure 4-3. Hard-bottom stations. ............................................................................... 39 
Figure 5-1. Fish-and-shellfish monitoring stations. .................................................... 45

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List of Tables 
Table 1-1. Timeline of Boston Harbor Project and later milestones for improved
treatment and concurrent ambient monitoring activities. ............................................. 2 
Table 1-2. Panel and committee organizations that review monitoring data and
provide advice. .............................................................................................................. 9 
Table 1-3. Public concerns and environmental responses presented in the original
monitoring plan (MWRA 1991). ................................................................................ 11 
Table 1-4. Monitoring program objectives and analyses. ........................................... 12 
Table 1-5. Contingency Plan threshold parameters. ................................................... 13 
Table 1-6. Monitoring reports submitted to OMSAP and regulatory agencies. ......... 15 
Table 2-1. Monitoring questions related to effluent. .................................................. 18 
Table 2-2. Permit and Contingency Plan monitoring requirements. .......................... 20 
Table 2-3. Special study effluent toxic contaminant monitoring. ............................... 21 
Table 2-4. Special study effluent nutrient monitoring. ............................................... 22 
Table 2-5. Contingency Plan threshold values for effluent monitoring...................... 22 
Table 3-1. Monitoring questions related to the water column. ................................... 26 
Table 3-2. Components of water-column monitoring................................................. 30 
Table 3-3. Water-column survey schedule. ................................................................ 30 
Table 3-4. Massachusetts Bay water-column monitoring stations. ............................ 31 
Table 3-5. Water-column parameters measured in Massachusetts Bay. .................... 32 
Table 3-6. Cape Cod Bay–Stellwagen Bank National Marine Sanctuary water-column
monitoring stations...................................................................................................... 32 
Table 3-7. Water-column parameters in Cape Cod Bay and Stellwagen Bank National
Marine Sanctuary. ....................................................................................................... 33 
Table 3-8. Contingency Plan threshold values for water-column monitoring ............ 34 
Table 4-1. Monitoring questions related to the sea floor. ........................................... 36 
Table 4-2. Contingency Plan threshold values for RPD depth and sediment toxic
contaminants. .............................................................................................................. 41 
Table 4-3. Contingency Plan threshold values for benthic community parameters. .. 42 
Table 5-1. Monitoring questions related to fish and shellfish. ................................... 43 
Table 5-2. Chemical analyses of fish and shellfish..................................................... 46 
Table 5-3. Contingency Plan threshold values for fish-and-shellfish monitoring. ..... 47

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OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
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1. Introduction 
The Massachusetts Water Resources Authority (MWRA) was created by an act of the
Massachusetts state legislature in December 1984 to upgrade wastewater treatment
facilities serving the greater Boston area. At that time, both sewage biosolids and
inadequately treated sewage effluent were discharged into the confined waters of
Boston Harbor from outfalls located at Deer Island in the northern part of the harbor
and at Nut Island in Quincy Bay, in the southern part of the harbor. In 1985, MWRA
embarked upon that mission, what has become known as the Boston Harbor Project. 
By 2000, most of the Boston Harbor Project milestones had been completed, and
MWRA received a National Pollutant Discharge Elimination System (NPDES)
permit to discharge from Deer Island Treatment Plant (DITP) to Massachusetts Bay.
The permit was issued jointly by the U.S. Environmental Protection Agency (EPA)
and the Massachusetts Department of Environmental Protection (MADEP). The
permit had many unique requirements, including an extensive ambient monitoring
requirement and a Contingency Plan, which provided for responses and actions
should permit violations occur. One requirement was that MWRA prepare an annual
report summarizing the year’s monitoring results; these reports are the annual outfall
monitoring overviews. 
A background document to these annual overviews was written in 2008, presenting
information on environmental concerns, monitoring design, and Contingency Plan
thresholds for effluent, water-column, sea-floor, and fish-and-shellfish monitoring
(Werme and Hunt 2008). This current document, the first update of the 2008
background, incorporates changes to the ambient monitoring plan for MWRA’s
effluent outfall (MWRA 2010), which were approved in December 2010 and
implemented in 2011. This introduction briefly describes the Boston Harbor Project,
the permit, the monitoring program, the Contingency Plan, data management,
reporting, and the contents of the outfall monitoring overviews. 
The Boston Harbor Project 
The Boston Harbor Project was a complex undertaking to minimize the
environmental impacts of MWRA’s wastewater discharge. The basic steps to
minimize effects of effluent discharge included source reduction to prevent pollutants
from entering the waste stream, improved treatment before discharge, and better
dilution of effluent entering the marine environment. 
Source reduction projects have lessened household hazardous-waste disposal and
minimized mercury discharges from hospitals and dentists. An industrial
pretreatment/pollution-prevention program ensures that toxic contaminants are
removed before they reach the sewer system. In addition, best management practices

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are employed at sewer facilities to prevent and mitigate accidental discharge of
pollutants. 
Improved treatment has been implemented in a series of major milestones (Table 1-
1). In 1995, a new primary treatment plant was brought on-line, and disinfection
facilities were completed. (Primary treatment is a physical treatment process, which
involves removal of solids through settling, followed by disinfection.) Batteries of
secondary treatment (which includes microbial decomposition as well as settling and
disinfection) went on-line in 1997, 1998, and 2001. Also during 1998, discharge
from the Nut Island Treatment Plant into Quincy Bay ceased, and all wastewater was
conveyed to DITP for treatment, ending effluent discharge to the southern part of the
harbor. In 2005, a cross-harbor tunnel, which connected DITP to the Fore River
biosolids pelletizing plant was completed, allowing nutrient-rich waste from the
pelletizing plant to be steadily piped to DITP, facilitating a more stable secondary
treatment process. The tunnel meant that DITP could treat a greater proportion of its
flow during high-flow conditions by full secondary treatment, lessening the need to
blend primary-only treated flow into the secondary-treated wastewater. In 2010, 
Table 1-1. Timeline of Boston Harbor Project and later milestones for improved treatment and
concurrent ambient monitoring activities. 
Year Milestones Monitoring Activities 
1991 
Interim repairs to existing treatment plants
completed, pumping capacity increased. 
Sludge discharge into Boston Harbor
ceased in December. 
Outfall Monitoring Task Force designs Phase I
Outfall Monitoring Plan, which formulated
monitoring hypotheses to be tested. 
1992 MWRA initiates Baseline (Phase I) monitoring. 
1995 New primary treatment facility at DITP
became operational in January. Baseline monitoring continues 
1997 Secondary treatment Battery A at DITP
start-up in July. 
MWRA issues Contingency Plan in February and
Phase II Outfall [Ambient] Monitoring Plan in
December. Baseline monitoring continues. 
1998 
Secondary Battery B start-up in March.
South system flows diverted from Nut
Island Treatment Plant to DITP via the
inter-island tunnel in July. 
Baseline monitoring continues 
2000 Outfall is relocated to Massachusetts Bay,
9.5 miles from DITP, in September. 
Regulatory agencies issue NPDES permit in August
which incorporates Ambient Monitoring Plan and
Contingency Plan by reference. 
Monitoring changes from baseline to discharge
(monitoring design remains consistent). 
2001 Secondary Battery C start-up in March. Contingency Plan revised to reflect new information
since 1997. 
2004 
Inter-island tunnel transport for sludge and
improvements to secondary treatment
facilities completed. 
MWRA completes four years of discharge
monitoring, implements Revision 1 of Ambient
Monitoring Plan. 
2010 Improvements to primary and secondary
clarifiers and floatables control completed. 
MWRA completes ten years of discharge
monitoring, completes draft of Revision 2 of
Ambient Monitoring Plan. 
2011 MWRA begins monitoring according to Revision 2 of
Ambient Monitoring Plan.

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MWRA carried out a major repair and upgrade to the primary and secondary
treatment facilities, including improved floatables removal. 
Better dilution was achieved in 2000, by diverting the effluent discharge from
Boston Harbor to a 9.5-mile-long outfall and diffuser system, located offshore in
Massachusetts Bay. The Massachusetts Bay site was selected because it had a water
depth and current patterns that would promote effective dilution, it was the least
likely of the alternative sites to affect sensitive resources, and it was feasible to
construct an outfall tunnel to the location. 
The outfall tunnel is bored through bedrock and has a diffuser system made up of 53
risers, each with five or six open ports, along its final 1.25 miles. Discharge from the
diffuser heads is at the sea floor, at water depths of about 100 feet. Initial dilution at
the outfall is about five times that of the Boston Harbor outfall that it replaced, which
was located in shallower water, at a depth of 50 feet and much closer to shore. The
offshore location of the outfall ensures that effluent will not reach beaches or shellfish
beds within a tidal cycle, even if currents are shoreward. 
The outfall is but one of many of the uses, both human and natural, now considered to
be “ecosystem services” of Massachusetts and Cape Cod bays. Figures 1-1 through 1-
4 1 depict some of the multiple uses of Massachusetts and Cape Cod Bays. Some of
these uses, such as the locations of beaches and shellfish beds, were factors
considered in the outfall siting process and helped drive the decision to build a long
outfall. Other uses, such as ocean sanctuaries and protected whales were considered
in the permitting of the treatment plant. And when outfall ambient monitoring data
are interpreted, it is helpful to bear in mind the many wastewater sources to the bays
and the potential impacts of commercial uses of the bays. 
The source reduction and improved treatment components of the Boston Harbor
Project were widely recognized as benefiting the marine environment and the people
of the region. Moving the effluent outfall from the harbor to Massachusetts Bay
raised some concerns, which were expressed as general, continuing questions: 
Is it safe to eat fish and shellfish? 
Are natural/living resources protected? 
Is it safe to swim? 
Are aesthetics being maintained? 
These concerns were recognized by MWRA and the NPDES permit for the outfall.
The permit established strict limits on the discharge, and the outfall monitoring
program, which was already underway, was formally established as a permit
condition. 
1 Maps on following pages were prepared by Peter Ralston and Rita Berkeley of MWRA, based on
data from the Massachusetts Ocean Resource Information System, (Massachusetts Office of Coastal
Zone Management, Executive Office of Energy and Environmental Affairs).

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Figure 1-1. Massachusetts and Cape Cod bays municipal, commercial, and industrial
uses. Locations of natural gas pipelines and terminals provided by Northeast Gateway and
Neptune LNG.

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Figure 1-2. Massachusetts and Cape Cod Bays shellfish and anadromous fish habitat.

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Figure 1-3. Massachusetts ocean special habitats and sanctuaries.

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Figure 1-4. Whale habitats in Massachusetts and Cape Cod bays, and offshore. The map
is adapted from information on whale sightings/unit effort and shows the approximate
boundaries for the top two quartiles of sightings/unit effort for three species, that is, the areas
where most sightings of those species occurred. The fin whale habitat encompasses the entire
area to the east (right) of the line.

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Outfall Permit 
The permit issued by EPA and MADEP under NPDES became effective on August 9,
2000. The permit limits discharges of pollutants and requires MWRA to monitor the
effluent for compliance with permit limits and to monitor discharges of priority
pollutants. Additional requirements include reporting on treatment plant and
collection system operation and maintenance, and implementation of best
management practices to prevent accidental discharge of pollutants to the
environment. There are extensive pollution-prevention requirements, which limit
industrial discharges of pollutants to the sewer system. Two unusual requirements
are extensive monitoring of ambient receiving waters in accordance with the Effluent
Outfall Ambient Monitoring Plan (MWRA 1991, 1997a, 2004, 2010), 2 and
implementation of a Contingency Plan (MWRA 1997b, 2001), which identifies
relevant environmental quality parameters and thresholds that, if exceeded, would
require a response. 
EPA and MADEP established an independent panel of scientists to review monitoring
data and provide advice on key scientific issues related to the permit. This panel, the
Outfall Monitoring Science Advisory Panel (OMSAP, Table 1-2), conducts peer
reviews of monitoring reports, evaluates data, and advises EPA and MADEP on
scientific issues. OMSAP also provides advice concerning any proposed
modifications to the monitoring or contingency plans. 
OMSAP may form specialized focus groups when specific technical issues require
expanded depth or breadth of expertise. One long-standing OMSAP focus is the
Model Evaluation Group, which has met periodically since 1992 to evaluate the Bays
Eutrophication Model, a coupled hydrodynamics and water quality model for
Massachusetts and Cape Cod bays. Two standing sub-committees also advise
OMSAP. The Public Interest Advisory Committee (PIAC) represents local, non-
governmental organizations and environmental groups and advises OMSAP on values
and uses of Boston Harbor and the bays. The Inter-agency Advisory Committee
(IAAC) represents state and federal agencies and provides OMSAP with advice
concerning environmental regulations. 
2 The first ambient monitoring plans were developed in response to the EPA Supplemental
Environmental Impact Statement (SEIS) prepared as part of the outfall-siting process (EPA 1988).

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Table 1-2. Panel and committee organizations that review monitoring data and provide
advice. 
Outfall Monitoring Science Advisory Panel (OMSAP) 
Woods Hole Oceanographic Institution 
University of Rhode Island 
Massachusetts Institute of Technology Sea Grant 
University of Massachusetts at Boston 
Harvard School of Public Health 
Inter-agency Advisory
Committee (IAAC) 
US Geological Survey 
MA Coastal Zone Management 
US Army Corps of Engineers 
Stellwagen Bank National Marine
Sanctuary 
MA Department of Environmental
Protection 
MA Division of Marine Fisheries 
US Environmental Protection Agency 
National Marine Fisheries Service 
Public Interest Advisory
Committee (PIAC) 
Save the Harbor/Save the Bay 
Center for Coastal Studies 
Wastewater Advisory Committee 
Conservation Law Foundation 
Massachusetts Audubon Society 
New England Aquarium 
MWRA Advisory Board 
Association for the Preservation of Cape
Cod 
Safer Waters in Massachusetts 
The Boston Harbor Association 
Cape Cod Commission 
Monitoring Program 
EPA and MADEP require monitoring to ensure compliance with the permit, to assess
whether the outfall has effects beyond the area identified in the SEIS as acceptable,
and to collect data useful for outfall management. In anticipation of these
requirements, MWRA began some studies during 1989–1991 and implemented a
broad baseline-monitoring program in 1992. Outfall ambient monitoring plans were
originally developed and refined under the direction of an Outfall Monitoring Task
Force (OTMF), made up of scientists, regulators, and environmental advocacy groups
(MWRA 1991, 1997a). The monitoring program was designed to compare
environmental quality of the Massachusetts Bay system, including Boston Harbor and
Cape Cod Bay, before and after the outfall re-location from the harbor to the bay.
(The OMTF was disbanded upon creation of OMSAP.) 
Because the first years of monitoring following diversion of effluent from Boston
Harbor to Massachusetts Bay found no unexpected results, changes to the monitoring
program were approved by EPA and MADEP, and a new plan (MWRA 2004) was
implemented in the 2004 monitoring year. In 2010, the monitoring plan was revised
again (MWRA 2010) to focus more on the area most likely to be affected by the
discharge, with sufficient reference stations for comparison. The design was made
more consistent, and some special studies were ended.

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The initial ambient monitoring plan expanded the general questions of public concern
by translating them into possible “environmental responses,” which were more
specific questions directly related to the outfall (Table 1-3). To answer those
questions, the monitoring program focused on critical constituents of treatment plant
effluent, such as nutrients, organic material, toxic contaminants, pathogens, and
solids. Presence and potential effects of these constituents continue to be evaluated
within the context of four environmental measurement areas: effluent, water column,
sea floor, and fish and shellfish (Table 1-4). The basic program is augmented by
special studies, which are conducted in response to specific permit requirements,
scientific questions, and environmental concerns. 
By 2011, after nine years of baseline monitoring and eleven years of post-diversion
monitoring, most or all of the monitoring questions that had been developed at the
beginning of the program had been answered. As had been expected, 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. The questions posed at
the beginning of the monitoring program and their answers are summarized in the
back matter at end of this report.

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Table 1-3. Public concerns and environmental responses presented in the original
monitoring plan (MWRA 1991). 
Public Concern: Is it safe to eat fish and shellfish? 
 Will toxic chemicals accumulate in the edible tissues of fish
and shellfish, and thereby contribute to human health
problems? 
 Will pathogens in the effluent be transported to shellfishing
areas where they could accumulate in the edible tissues of
shellfish and contribute to human health problems? 
Public Concern: Are natural/living resources protected? 
 Will nutrient enrichment in the water column contribute to an
increase in primary production? 
 Will enrichment of organic matter contribute to an increase in
benthic respiration and nutrient flux to the water column? 
 Will increased water-column and benthic respiration contribute
to depressed oxygen levels in the water? 
 Will increased water-column and benthic respiration contribute
to depressed oxygen levels in the sediment? 
 Will nutrient enrichment in the water column contribute to
changes in plankton community structure? (Such changes
could include stimulation of nuisance or noxious algal blooms
and could affect fisheries.) 
 Will benthic enrichment contribute to changes in community
structure of soft-bottom and hard-bottom macrofauna, possibly
also affecting fisheries? 
 Will the water column near the diffuser mixing zone have
elevated levels of some contaminants? 
 Will contaminants affect some size classes or species of
plankton and thereby contribute to changes in community
structure and/or the marine food web? 
 Will finfish and shellfish that live near or migrate by the diffuser
be exposed to elevated levels of some contaminants,
potentially contributing to adverse health in some populations? 
 Will the benthos near the outfall mixing zone and in
depositional areas farther away accumulate some
contaminants? 
 Will benthic macrofauna near the outfall mixing zone be
exposed to some contaminants, potentially contributing to
changes in community structure? 
Public Concern: Is it safe to swim? 
 Will pathogens in the effluent be transported to waters near
swimming beaches, contributing to human health problems? 
Public Concern: Are aesthetics being maintained? 
 Will changes in water clarity and/or color result from the direct
input of effluent particles or other colored constituents, or
indirectly through nutrient stimulation of nuisance plankton
species? 
 Will the loading of floatable debris increase, contributing to
visible degradation?

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Table 1-4. Monitoring program objectives and analyses. 
Task Objective Analyses 
Effluent 
Effluent sampling 
Characterize wastewater
discharge from Deer Island
Treatment Plant 
Flow 
Organic material (cBOD) 
Solids 
pH 
Bacterial indicators 
Total residual chlorine 
Toxicity 
Nutrients 
Toxic contaminants 
Water Column 
Outfall monitoring
surveys 
Collect water quality data
near outfall location and
reference sites 
Temperature 
Salinity 
Dissolved oxygen 
Nutrients 
Solids 
Chlorophyll 
Water clarity 
Phytoplankton 
Zooplankton 
Cape Cod Bay and
Stellwagen Bank
NMS surveys 
Collect water quality data in
Cape Cod Bays and
Stellwagen Bank NMS. 
Moorings
(NERACOOS and
NDBC) 
NERACOOS mooring is
near Cape Ann. NDBC
mooring is near outfall. 
Currents 
Temperature 
Salinity 
Dissolved oxygen 
Chlorophyll 
Remote sensing 
Provides oceanographic
data on a regional scale
through satellite imagery 
Surface temperature 
Chlorophyll 
Sea Floor 
Soft-bottom studies 
Evaluate sediment quality
and benthos in Boston
Harbor and Massachusetts
Bay 
Sediment chemistry 
Sediment profile imagery 
Community composition 
Hard-bottom
studies 
Characterize marine
benthic communities in
rock and cobble areas 
Topography 
Substrate 
Community composition 
Fish and Shellfish 
Winter flounder 
Determine contaminant
body burden and
population health 
Tissue contaminant
concentrations 
Physical abnormalities,
including liver
histopathology 
American lobster Determine contaminant
body burden 
Tissue contaminant
concentrations 
Physical abnormalities 
Blue mussel 
Evaluate biological
condition and potential
contaminant
bioaccumulation 
Tissue contaminant
concentrations

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Contingency Plan 
The Contingency Plan (MWRA 1997b, 2001) describes how, if monitoring results
indicate a possible environmental problem, MWRA and the regulatory agencies will
respond to determine the cause of the problem and to specify the corrective actions
that should be taken if the problem appears to be related to the discharge. The
Contingency Plan identifies parameters that represent environmentally significant
components of the effluent or the ecosystem and that, if specific threshold levels are
exceeded, indicate a potential for environmental risk (Table 1-5). The plan provides a
process for evaluating parameters that exceed thresholds and formulating appropriate
responses. 
Threshold values, the measurements selected as indicators of the need for action, are
based on permit limits, state water quality standards, and expert opinion. To alert
MWRA to any changes, some parameters have “caution” as well as more serious
“warning” thresholds. Exceeding either caution or warning thresholds could indicate
a need for increased attention or study. If a caution threshold is exceeded, MWRA,
with guidance from OMSAP and the regulatory agencies, may expand the monitoring
program to track effluent quality and environmental conditions. The data are
examined to determine whether it is likely that an unacceptable effect resulting from
the outfall has occurred. 
Table 1-5. Contingency Plan threshold parameters. 
Measurement
Area Parameter 
Effluent 
pH 
Fecal coliform bacteria 
Residual chlorine 
Total suspended solids 
Biochemical oxygen demand 
Toxicity 
PCBs 
Plant performance 
Flow 
Total nitrogen load 
Oil and grease 
Water Column 
Dissolved oxygen concentration and saturation 
Dissolved oxygen depletion rate 
Chlorophyll 
Nuisance and noxious algae 
Effluent dilution 
Sea Floor 
Sediment contaminants 
Redox potential discontinuity (RPD) depth 
Benthic community structure 
Fish and
Shellfish 
PAHS, PCBs, mercury, chlordanes, dieldrin, and
DDTs in mussels and in flounder and lobster
tissue 
Lead in mussels 
Liver disease in flounder

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Exceeding warning levels could, in some circumstances, indicate a need for a
response to avoid potential adverse environmental effects. The response would
include early notification of EPA and MADEP and, if it appeared that the outfall had
contributed to adverse environmental effects, the quick development of a response
plan. Response plans are to include a schedule for implementing actions, such as
making adjustments in plant operations or undertaking an engineering study to
formulate specific corrective activities. 
A process for modifying the Contingency Plan to incorporate new scientific
information and improved understandings resulting from the monitoring program is
set forth in the NPDES permit. Revision 1 of the Contingency Plan was approved in
2001. 
Data Management 
The monitoring program has generated extensive data sets. Data quality is
maintained through program-wide quality assurance and quality control procedures.
After validation, data from field surveys and laboratory analyses are loaded into a
centralized project database. Data handling procedures are automated to the
maximum extent possible to reduce errors, ensure comparability, and minimize
reporting time. Data that are outside the expected ranges are flagged for review.
Data reported by the laboratory as suspect (for example, because the sample bottle
was cracked in transit) are marked as such and not used in interpretation or threshold
calculations, although they are retained in the database and included in raw data
reports. Any corrections are documented. Each data report notes any special
considerations associated with the data set. 
As monitoring results become available, they are compared with Contingency Plan
thresholds. Computer programs calculate each threshold parameter value from the
data, compare it to the threshold, and notify the project staff if caution or warning
levels are exceeded. 
Reporting 
MWRA’s NPDES permit requires regular reports on effluent quality and extensive
reporting on the monitoring program. A variety of reports are submitted to OMSAP
and state and federal regulatory agencies for review (Table 1-6). Changes to the
monitoring program or the Contingency Plan must be reviewed by regulators and
published in the Environmental Monitor . Data that exceed Contingency Plan
thresholds and corrective actions must also be reported. Data that exceed thresholds
must be reported within five days after the results become available, and MWRA
must make all reasonable efforts to report all data on thresholds within 90 days of
each sampling event.

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2012 UPDATE 
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Table 1-6. Monitoring reports submitted to OMSAP and regulatory agencies. 
Reports Description/Objectives 
Outfall Monitoring Plans 
Phase I—Baseline Studies (MWRA
1991) 
Phase II—Discharge Ambient
Monitoring (MWRA 1997a, 2004,
2010) 
Discuss goals, strategy, and design of
baseline and discharge monitoring programs. 
Contingency Plan (MWRA 1997b,
2001) 
Describes development of threshold
parameters and values and MWRA’s planned
contingency measures. 
Program Area Summary Reports 
Summarize, interpret, and explain annual
results for effluent, water column, benthos,
and fish and shellfish monitoring areas. 
Special Studies Reports 
Discuss, analyze, and cross-synthesize data
related to specific issues in Massachusetts
and Cape Cod bays. 
Outfall Monitoring Overviews Summarize monitoring data and include
information relevant to the Contingency Plan. 
Reports are posted at http://www.mwra.state.ma.us/harbor/enquad/trlist.html, the
MWRA technical reports site, and copies are placed in repository libraries in Boston
and on Cape Cod. OMSAP also holds public workshops at which outfall monitoring
results are presented. 
Outfall Monitoring Overview 
Among the many reports that MWRA completes, outfall monitoring overviews have
been prepared for most baseline-monitoring years (Galya et al. 1996, 1997a, 1997b;
Werme and Hunt 2000a, 2000b) and for each year that the permit has been in place
and the outfall has been on-line (Werme and Hunt 2001, 2002, 2003, 2004, 2005,
2006, 2007; Werme et al. 2008, 2009, 2010, 2011, 2012). Overviews for 1994
through 1999 included only baseline information. With the Massachusetts Bay
outfall discharge beginning in September 2000, subsequent reports have included
information relevant to the Contingency Plan, including threshold exceedances,
responses, and corrective actions. When data suggest that monitoring activities,
parameters, or thresholds should be changed, the report summarizes those
recommendations. Overviews also include information on Stellwagen Bank National
Marine Sanctuary, meeting a permit requirement that MWRA report on monitoring
results that are relevant to the sanctuary. 
Overviews prepared through the 2006 monitoring year included the background
information as well as results. A separate background document (Werme and Hunt
2008) was prepared in conjunction with the 2007 Outfall Monitoring Overview for
the monitoring years through 2010.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
16 
This updated background document presents information that will not change
substantially from year-to-year beginning in monitoring year 2011. It describes the
environmental concerns that have driven the monitoring program, monitoring
designs, and Contingency Plan thresholds for effluent, water-column, sea-floor, and
fish-and-shellfish monitoring. It also includes sections on special studies and on the
Stellwagen Bank National Marine Sanctuary.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
17 
2. Effluent 
Background 
Pollution Prevention 
Ensuring that the final effluent is clean was the most important element in MWRA’s
strategy to improve the environmental quality of Boston Harbor without degrading
Massachusetts and Cape Cod bays. MWRA ensures clean effluent through its
vigorous pretreatment program and by proper maintenance and operation of DITP. 
The MWRA Toxic Reduction and Control (TRAC) program sets and enforces limits
on the types and amounts of pollutants that industries can discharge into the sewer
system and works to encourage voluntary reductions in the use of toxic chemicals.
TRAC has also implemented programs to reduce mercury from dental facilities and to
educate the public about proper disposal of hazardous wastes. A booklet, A Healthy
Environment Starts at Home identifies household products that could be hazardous
and recommends alternatives. The booklet is available through the MWRA website,
at http://www.mwra.state.ma.us/03sewer/trac/athome.htm . 
Secondary treatment further reduces the concentrations of contaminants of concern,
except for nutrients, which are not significantly affected by the secondary treatment
process. DITP removes approximately 85–90% of the suspended solids and
biochemical oxygen demand (BOD), 50–90% of the toxic chemicals, and about 15%
of the nitrogen from the influent. 
To prevent accidental discharge of pollutants and mitigate effects should an accident
occur, MWRA has implemented best management practice plans at the treatment
plant, headworks facilities, combined sewer overflow facilities, pumping stations, and
biosolids-to-fertilizer plant. The plans include daily visual inspections and immediate
corrective actions to any problems. Effectiveness of best management practices is
assessed by non-facility staff. 
Environmental Concerns 
Sewage contains a variety of contaminants that could, at too high levels, affect the
marine environment, public health, and aesthetics. The NPDES permit sets limits on
these contaminants to ensure that these attributes will be protected. Several specific
questions in the MWRA ambient monitoring plan responded to public concerns and
possible environmental responses by addressing whether the effluent is meeting
permit limits (Table 2-1). Other questions required the use of effluent data in
conjunction with plume-dilution studies, which were completed in 2001, and water-
column monitoring (see Section 3, Water Column).

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
18 
Table 2-1. Monitoring questions related to effluent. 
Is it safe to eat fish and shellfish? 
Will pathogens in the effluent be transported to shellfishing areas where they
could accumulate in the edible tissues of shellfish and contribute to human
health problems? 
 Do effluent pathogens exceed the permit limit? 
 Are pathogens transported to shellfish beds at levels that might
affect shellfish consumer health? 
Are natural/living resources protected? 
Will the water column near the diffuser-mixing zone have elevated levels of
some contaminants? 
 Do effluent contaminant concentrations exceed permit limits? 
 What are the concentrations of contaminants and characteristic
tracers of sewage in the influent and effluent and their associated
variability? 
Will finfish and shellfish that live near or migrate by the diffuser be exposed
to elevated levels of some contaminants, potentially contributing to adverse
health in some populations? 
 Does acute or chronic toxicity of effluent exceed permit limits? 
 Do levels of contaminants in water outside the mixing zone exceed
state water quality standards? 
Is it safe to swim? 
Will pathogens in the effluent be transported to waters near swimming
beaches, contributing to human health problems? 
 Do effluent pathogens exceed the permit limit? 
 Are pathogens transported to beaches at levels that might affect
swimmer health? 
Are aesthetics being maintained? 
Will changes in water clarity and/or color result from the direct input of
effluent particles or other colored constituents, or indirectly through nutrient
stimulation of nuisance plankton species? 
Will the loading of floatable debris increase, contributing to visible
degradation? 
 Do conventional pollutants in the effluent exceed permit limits? 
 Has the clarity and/or color of the water around the outfall changed? 
 Has the amount of floatable debris around the outfall changed? 
The effluent constituents of greatest concern include pathogens, toxic contaminants,
organic material, solid material, nutrients, oil and grease, and “floatables,” such as
plastic and other debris. The MWRA permit also sets limits for chlorine and pH. 
Pathogens , including bacteria, viruses, and protozoa, are found in human and animal
waste and can cause disease. Human exposure to water-borne pathogens can occur
through consumption of contaminated shellfish or through ingestion or physical
contact while swimming. 
Toxic contaminants include heavy metals, such as copper and lead, and organic
compounds, such as polychlorinated biphenyls (PCBs), pesticides, polycyclic
aromatic hydrocarbons (PAHs), and petroleum hydrocarbons. Toxic contaminants
can lower survival and reproduction rates of marine organisms. Some toxic

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
19 
contaminants can accumulate in marine life, potentially affecting human health
through seafood consumption. 
Organic material , a major constituent of untreated sewage, consumes oxygen as it
decays. Even under natural conditions, oxygen levels decline in bottom waters during
the late summer, so any effluent component that might further decrease oxygen levels
is a concern. Too much organic material could also disrupt animal communities on
the sea floor. 
Suspended solids , small particles in the water column, decrease water clarity and
consequently affect growth and productivity of algae and other marine plants. Excess
suspended solids also detract from people’s aesthetic perception of the environment. 
In marine waters, nitrogen is the limiting nutrient that controls growth of algae and
other aquatic plants. Excess nitrogen can be detrimental, leading to eutrophication
and low levels of dissolved oxygen, excess turbidity, and nuisance algal blooms.
Nutrients, particularly dissolved forms, are the only components of sewage entering
the treatment plant that are not substantially reduced by secondary treatment. 
Oil and grease slicks and floating debris known as floatables pose aesthetic
concerns. Plastic debris can be harmful to marine life, as plastic bags are sometimes
mistaken for food and clog the digestive systems of turtles and marine mammals.
Plastic and other debris can also entangle animals and lead to infection or drowning. 
Sewage effluent is disinfected by addition of a form of chlorine , sodium
hypochlorite, which is the active ingredient in bleach. While sodium hypochlorite is
effective in destroying pathogens, at high enough concentrations, it is harmful to
marine life. Consequently, MWRA dechlorinates the effluent with sodium bisulfite
before discharge. 
State water quality standards dictate that effluent discharges not change the pH of the
ambient seawater more than 0.5 standard units on a scale of 1 to 14. Consequently,
the outfall permit sets both upper and lower values for pH of the effluent. 
Monitoring Design 
Effluent monitoring measures the concentrations of constituents of the effluent and
variability in those concentrations to assess compliance with the NPDES permit
limits, which are based on state and federal water quality standards and criteria and
on ambient conditions. Effluent monitoring also provides measurements of mass
loads of effluent constituents, so that fate, transport, and risk of contaminants can be
assessed.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
20 
The permit includes numeric limits (Table 2-2) for suspended solids, fecal coliform
bacteria, pH, chlorine, PCBs, and carbonaceous biochemical oxygen demand
(cBOD). In addition, state water quality standards establish limits for 158 pollutants,
and the permit prohibits any discharge that would cause or contribute to exceeding
any of those limits. Allowable concentrations of contaminants were based on the
predicted dilution at the outfall and verified by field studies of outfall plumes in 2001. 
Table 2-2. Permit and Contingency Plan monitoring requirements. 
Parameter Sample Type Frequency Limit 
Permit-required monitoring 
Flow Flow meter Continuous Report only 
Flow dry day Flow meter Continuous 436 MGD annual
average 
cBOD 24-hr composite 1/day 40 mg/L weekly 
25 mg/L monthly 
TSS 24-hr composite 1/day 45 mg/L weekly 
30 mg/L monthly 
pH Grab 1/day Not <6 or >9 
Fecal coliform bacteria Grab 3/day 14,000 col/100ml 
Total residual chlorine Grab 3/day 631 μg/L daily 
456 μg/L monthly 
PCB, Aroclors 24-hr composite 1/month 0.045 ng/L 
Toxicity LC50 24-hr composite 2/month 50% 
Toxicity C-NOEC 24-hr composite 2/month 1.5% 
Settleable solids Grab 1/day 
Report only 
Chlorides (influent only) Grab 1/day 
Mercury 24-hr composite 1/month 
Chlordane 24-hr composite 1/month 
4,4’–DDT 24-hr composite 1/month 
Dieldrin 24-hr composite 1/month 
Heptachlor 24-hr composite 1/month 
Ammonium-nitrogen 24-hr composite 1/month 
Total Kjeldahl nitrogen 24-hr composite 1/month 
Total nitrate 24-hr composite 1/month 
Total nitrite 24-hr composite 1/month 
Cyanide, total Grab 1/month 
Copper, total 24-hr composite 1/month 
Total arsenic 24-hr composite 1/month 
Hexachlorobenzene 24-hr composite 1/month 
Aldrin 24-hr composite 1/month 
Heptachlor epoxide 24-hr composite 1/month 
Total PCBs 24-hr composite 1/month 
Volatile organic
compounds Grab 1/month 
Contingency Plan-required monitoring 
Oil and grease, as
petroleum hydrocarbons Grab Weekly Warning
threshold 15 mg/L 
Plant performance Ongoing 5 violations/year

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
21 
The permit also prohibits discharge of nutrients in amounts that would cause
eutrophication, and it requires MWRA to test the toxicity of the effluent as a whole
on sensitive organisms and establishes limits based on those tests. 
Most parameters are measured in 24-hour composite samples, and some must meet
daily, weekly, or monthly limits. Flow is measured continuously. Nutrient
measurements include total nitrogen, ammonium, nitrate, and nitrite. Organic
material is monitored by measuring cBOD. Monitoring for toxic contaminants
includes analyses for heavy metals of concern, chlorinated pesticides, PCBs, volatile
organic compounds, PAHs, total residual chlorine, and cyanide. Toxicity is tested
using whole effluent samples. Tests for acute toxicity include 48-hour survival of
mysid shrimp ( Americamysis bahia ) and inland silverside fish ( Menidia beryllina ).
Chronic toxicity is assessed through inland silverside growth-and-survival and sea
urchin ( Arbacia punctulata ) one-hour-fertilization tests. Pathogen monitoring
consists of enumeration of fecal coliform bacteria. Total suspended solids (TSS) and
settleable solids are also measured. 
The Contingency Plan also sets limits for overall plant performance, annual nitrogen
load, floatables, and oil and grease. The MWRA monitoring plan also includes
special studies of toxic contaminants using sensitive methods, and nutrients (Table 2-
3 and Table 2-4). These measurements are made to better interpret field-monitoring
results. 
Table 2-3. Special study effluent toxic contaminant monitoring. 
Parameter Sample Type Frequency 
Acid base neutrals 24-hr composite 
Bimonthly Volatile Organic
Compounds Grab 
Low detection limit analyses 
Cadmium 
24-hr composite 4 times/month 
Copper 
Chromium 
Mercury 
Lead 
Molybdenum 
Nickel 
Silver 
Zinc 
17 chlorinated pesticides 
Extended list of PAHs 
20 PCB congeners

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
22 
Table 2-4. Special study effluent nutrient monitoring. 
Parameter Sample Type Frequency 
Total Kjeldahl nitrogen 
24-hr composite Weekly 
Ammonia 
Nitrate 
Nitrite 
Total phosphorus 
Total phosphate 
Contingency Plan Thresholds 
Contingency Plan thresholds for effluent monitoring include warning levels for all
parameters and caution levels for PCBs, plant performance, and nitrogen loads (Table
2-5). Floatable debris is present in low amounts in the effluent (Rex et al. 2008, Rex
and Tyler, 2011), and one change to the monitoring plan in 2010 was the ending of
sampling for effluent floatables. 
Table 2-5. Contingency Plan threshold values for effluent monitoring. 
Parameter Caution Level Warning Level 
pH None <6 or >9 
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) 
Chlorine, residual None 631 μg/L daily, 
456 μg/L monthly 
Total suspended
solids None 45 mg/L weekly 
30 mg/L monthly 
cBOD None 40 mg/L weekly, 
25 mg/L monthly 
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 
PCBs Aroclor=0.045
ng/L 
Plant performance 5 violations/year Noncompliance >5% of the time 
Flow None Flow >436 for annual average of dry
days 
Total nitrogen load 12,500 mtons/year 14,000 mtons/year 
Oil and grease None 15 mg/L weekly

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
23 
3. Water Column 
Background 
Circulation and Water Properties 
Circulation, water properties, and consequently, the chemistry and biology of
Massachusetts and Cape Cod bays are driven by the larger pattern of water flow in
the Gulf of Maine (Figure 3-1) and by regional and local winds. A coastal current
flows southwestward along the Maine and New Hampshire coasts and may enter
Massachusetts Bay to the north of Boston at Cape Ann. This current drives an
average counterclockwise circulation in Massachusetts Bay and (sometimes) Cape
Cod Bay. Water flows back out of the bays at Race Point, located at the tip of Cape
Cod. Whether the coastal current enters Massachusetts Bay and whether it continues
south into Cape Cod Bay depends largely on the strength of the current and the
direction, duration, and speed of the wind at Cape Ann. Because the coastal current
entering Massachusetts Bay from the Gulf of Maine is strongest during the spring
period of high runoff from rivers and streams, the spring circulation pattern is more
consistent than that in the summer and fall (Geyer et al. 1992, Jiang et al. 2006). 
During the summer and fall, freshwater inflow is lower, and so the wind and water
density interact in a different, more complex way, with alternating periods of
upwelling and downwelling in various locations, depending primarily on the wind
direction and strength (Lermusiaux 2001). Water flow varies with week-to-week
changes in weather patterns. Flow at any particular time depends on the wind speed
and direction relative to the topography of the sea floor. At times, flow can “reverse,”
with flow northward along the coast. Transient gyres in Massachusetts and Cape Cod
bays spin in either direction. 
As in many coastal waters, during the winter, the water column is well-mixed from
top to bottom, and nutrient levels are high. As light levels increase in the early
spring, phytoplankton populations often begin a period of rapid growth known as a
spring bloom. Contrary to popular wisdom, however, strong spring blooms do not
occur every year. During the years in which they occur, spring blooms begin in the
shallowest waters of Cape Cod Bay, with blooms in the deeper Massachusetts Bay
waters following two to three weeks later. Spring phytoplankton blooms are typically
followed by an increase in zooplankton abundance. These zooplankton populations
are food for many animals, including the endangered North Atlantic right whale
( Eubalaena glacialis ), a seasonal visitor to the region, which feeds on large
zooplankton species on Stellwagen Bank and in Cape Cod Bay during the winter and
spring.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
24 
Figure 3-1. (a) General circulation within Massachusetts Bay. Reprinted from Journal of Marine
Systems, Vol. 29, Author: PFJ Lermusiaux, "Evolving the subspace of the three-dimensional
multiscale ocean variability: Massachusetts Bay," pp 385-422 © 2001 with permission from Elsevier. 
(b) General circulation within the Gulf of Maine (from Beardsley et al. 1997). 
(b)

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
25 
Later in the spring, the surface waters warm, and the water column stratifies. Inputs
of freshwater from rivers contribute to the stratification, with lighter, less saline water
remaining at the surface. Stratification effectively separates the surface and bottom
waters, preventing replenishment of nutrients to the surface and oxygen to the bottom.
Phytoplankton in the surface waters deplete the available nutrients and then undergo
senescence, sinking through the pycnocline to the bottom. While oxygen levels
remain high in the surface waters throughout the year, levels fall in the bottom waters,
as bottom-dwelling animals respire, and bacteria use up oxygen as the phytoplankton
decompose. Bottom-water oxygen levels are typically lowest during the late summer
or early fall. 
Cooling surface waters and strong winds during the autumn months promote mixing
of the water column. Oxygen is replenished in the bottom waters, and nutrients
brought to the surface can stimulate a fall phytoplankton bloom. Similar to the
spring, varying meteorological and oceanographic conditions greatly influence the
timing, magnitude, and spatial extents of the blooms, and fall blooms do not always
occur. When they do occur, the fall blooms typically end in the early winter, when
declining light levels limit photosynthesis. Plankton die and decay, replenishing
nutrients in the water column. 
Environmental Concerns 
Water-column monitoring questions in the original monitoring plan focused on the
possible effects of nutrients, organic matter, pathogens, and floatable debris from
wastewater on the water quality of Massachusetts Bay (MWRA 1991, Table 3-1).
Due to source reduction and treatment, concentrations of toxic contaminants
discharged in the MWRA effluent are so low that it is impractical to measure them in
the water column, so they were not a focus for monitoring. Because organic material,
pathogens, and floatables are effectively removed by treatment at DITP, but nutrients
are not, nutrient issues caused the greatest concern during development of the
monitoring program. 
The monitoring program has looked extensively at possible effects of discharging
nutrient-rich effluent into Massachusetts Bay. One concern was that excess nutrients,
particularly nitrogen, could over-stimulate algal blooms, which would be followed by
low levels of dissolved oxygen in the bottom waters when the phytoplankton
organisms die, sink, and decompose. Another concern was that changes in the
relative levels of nutrients could stimulate growth of undesirable algae. Two toxic
algae (the dinoflagellate Alexandrium fundyense and the diatom Pseudo-nitzschia
multiseries ) and one nuisance species (the colonial flagellate Phaeocystis pouchetii )
were of concern.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
26 
Table 3-1. Monitoring questions related to the water column. 
Is it safe to eat fish and shellfish? 
Will pathogens in the effluent be transported to shellfishing areas where they could
accumulate in the edible tissues of shellfish and contribute to human health problems? 
 Are pathogens transported to shellfish beds at levels that might affect shellfish
consumer health? 
Are natural/living resources protected? 
Will nutrient enrichment in the water column contribute to an increase in primary production? 
Will nutrient enrichment in the water column contribute to changes in plankton community
structure? 
 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? 
 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 changes be
correlated with effluent or ambient water nutrient concentrations, or can farfield
changes be correlated with nearfield changes? 
 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? 
 Has the abundance of nuisance or noxious phytoplankton species changed in the
vicinity of 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 or ambient water nutrient
concentrations, or can farfield changes be correlated with nearfield changes? 
Will increased water-column and benthic respiration contribute to depressed oxygen levels in
the water? 
 Do the concentrations (or percent saturation) of dissolved oxygen in the vicinity of the
outfall and at selected farfield stations meet the state water quality standard? 
 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
correlated with effluent or ambient water nutrient concentrations, or can farfield
changes be correlated with nearfield changes? 
Is it safe to swim? 
Will pathogens in the effluent be transported to waters near swimming beaches, contributing
to human health problems? 
 Are pathogens transported to beaches at levels that might affect swimmer health? 
Are aesthetics being maintained? 
Will changes in water clarity and/or color result from the direct input of effluent particles or
other colored constituents, or indirectly through nutrient stimulation of nuisance plankton
species? 
Will the loading of floatable debris increase, contributing to visible degradation? 
 Has the clarity and/or color of the water around the outfall changed? 
 Has the amount of floatable debris around the outfall changed? 
Information on transport and fate necessary to answer all the questions 
 Are model estimates of short-term (less than 1 day) effluent dilution and transport
accurate? 
 What are the nearfield and farfield water circulation patterns? 
 What is the farfield fate of dissolved, conservative, or long-lived effluent constituents?

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
27 
Alexandrium fundyense blooms are known in New England as red tides. They
produce a toxin, which when sufficiently concentrated by shellfish that take up the
algae, causes paralytic shellfish poisoning (PSP), a condition that can be fatal to
marine mammals, fish, and humans. At high concentrations (more than 1 million
cells per liter), some diatoms in the genus Pseudo-nitzschia may produce sufficient
quantities of toxic domoic acid to cause a condition known as amnesic shellfish
poisoning, which is marked by gastrointestinal and neurological symptoms, including
dementia. Phaeocystis pouchetii is not toxic, but individual cells can aggregate in
gelatinous colonies that may be aesthetically displeasing or provide poor food for
zooplankton. 
Dissolved oxygen concentrations in bottom waters naturally decrease during the
stratified period as part of the regular seasonal pattern. If discharged nutrients were
to stimulate large phytoplankton blooms, the conditions could lead to lower levels of
dissolved oxygen when the cells sink to the bottom and decay. 
Because of the concern that lowered levels of dissolved oxygen could affect animals
in the vicinity of the outfall, it was important during the baseline-monitoring period to
develop an understanding of the natural fluctuations of oxygen levels within the
region. Modeling and measurements showed that the typical periods of low oxygen
concentrations in bottom waters correlate with warmer and saltier bottom waters.
Ongoing monitoring assesses potential departures from the natural conditions. 
Monitoring Design 
Water-column monitoring includes assessments of physical conditions, water quality,
phytoplankton, and zooplankton. Regular monitoring includes four components:
Massachusetts Bay monitoring surveys; Cape Cod Bay and Stellwagen Bank National
Marine Sanctuary surveys; continuous recording; and remote sensing. Plume-
tracking studies conducted in 2001 verified the expected dilution at the outfall and
confirmed predictions that concentrations of bacteria and toxic contaminants in the
discharged effluent are very low. Additional, rapid-response surveys may be
conducted during Alexandrium fundyense red tide blooms or in response to wet
weather and high flows, when floatable debris may be present. 
The water-column monitoring program was redesigned in 2010, with changes
implemented in 2011. Nine Massachusetts Bay outfall monitoring surveys at eleven
stations provide vertical and horizontal profiles of physical, chemical, and biological
characteristics of the water column in the area around the outfall (the nearfield),
where some effects of the effluent were expected and have been observed, and at
reference stations. Similar measurements at three stations assess the health of Cape
Cod Bay and the Stellwagen Bank National Marine Sanctuary. Every effort is made
to collect all samples within two days. Figure 3-2 shows the locations of monitoring
stations for regular surveys and Figure 3-3 shows locations for special surveys in
response to Alexandrium fundyense blooms. Tables 3-2 through 3-7 present the
components of monitoring, sampling schedule, stations, and parameters measured.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
28 
Figure 3-2. Water-column monitoring stations. Also shown are two instrumented buoys, one
operated by the Northeastern Regional Association of Coastal and Ocean Observing Systems
(NERACOOS) and the other by the National Oceanic and Atmospheric Administration National Data
Buoy Center (NDBC); the MWRA outfall diffuser; and the Stellwagen Bank National Marine
Sanctuary.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
29 
Figure 3-3. Alexandrium Rapid Response Survey (ARRS) stations. Also shown are two
instrumented buoys, one operated by the Northeastern Regional Association of Coastal and Ocean
Observing Systems (NERACOOS) and the other by the National Oceanic and Atmospheric
Administration National Data Buoy Center (NDBC); the MWRA outfall diffuser; and the Stellwagen
Bank National Marine Sanctuary.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
30 
Parameters measured in the water column include physical conditions, dissolved
oxygen, dissolved inorganic and organic nutrients, particulate forms of nutrients,
chlorophyll, total suspended solids, phytoplankton abundance and species
composition, and zooplankton abundance and species composition. Nutrients
measured include the major forms of nitrogen, phosphorus, and silica. The
measurements focus on the dissolved inorganic forms, which are most readily used by
phytoplankton. The surveys also include visual observations in the outfall area to
assess the presence of floatable debris. The presence of debris is assessed visually in
the vicinity of the outfall site during water-column surveys and twice a year by net
tows after DITP blending events. Fat particles collected during net tows are analyzed
for PCBs, PAHs, pesticides, and mercury. 
The continuous recording components of the program capture temporal variations in
water quality between surveys. Remote sensing by satellite captures spatial variations
in water quality on a larger, regional scale. 
Table 3-2. Components of water-column monitoring. 
Task Objective 
Massachusetts Bay
monitoring surveys 
Collect water quality and plankton data near the
outfall and at reference stations 
Cape Cod Bay and
Stellwagen Bank surveys 
Collect water quality and plankton data in Cape Cod
Bay and Stellwagen Bank National Marine Sanctuary 
Moorings Provide continuous oceanographic data near outfall
and off Cape Ann 
Remote sensing Provides oceanographic data on a regional scale
through satellite imagery 
Table 3-3. Water-column survey schedule. 
When Target
Week Purpose 
Early February 6 Nutrient conditions near start of spring bloom 
March 12 Spring bloom 
Early April 15 Capture Phaeocystis pouchetii bloom. Late
winter/spring bloom nutrients 
Mid-May 20 Nutrient/water column conditions at end of winter-
spring, Alexandrium fundyense 
Mid-June 25 Early summer stratification and nutrients. Mid-late red
tide season 
Mid-July 30 Mid-summer stratification and nutrients 
Mid-August 34 Mid-summer stratification and nutrients 
September 36 Nutrients, etc. prior to overturn. 
Late October 43 Mid-fall bloom nutrients, dissolved oxygen minima

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
31 
Table 3-4. Massachusetts Bay water-column monitoring stations. 
Station Water Depth 
(meters) 
Location Relative
to Outfall Purpose 
F22 80 17 km NE 
Northern reference station 
Gulf of Maine influence 
Regional physical forcing relates to nearfield
Dissolved oxygen 
Link between buoy and sampling data 
“Upstream” sentinel station in winter-spring 
N04 50 7.1 km NE Nearfield station 
Evaluate extent of plume northeast 
N01 31 6.3 km NW Nearfield station 
Evaluate extent of plume northwest 
N21 35 60 m 
Nearfield station 
Evaluate water quality at effluent zone of
initial dilution 
Close to outfall 
Ammonium signature 
Primary “impact” station for comparison to
other stations 
N18 27 2.5 km S 
Nearfield station. 
Close to outfall 
Ammonium signature 
Primary “impact” station for comparison to
other stations 
N07 50 7 km SE 
Nearfield station 
Near NDBC buoy MWRA instruments-data
comparison 
F23 25 12 km E Boston Harbor 
F15 38 9 km S Evaluate southward extent of plume 
F13 25 14 km S Near coastal (model, Alexandrium fundyense ) 
F10 33 20 km S Furthest expected southern expression of
effluent plume 
F06 33 29 km SE Southern reference station

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
32 
Table 3-5. Water-column parameters measured in Massachusetts Bay. (Plankton are not sampled
at station N21, because nearfield plankton is adequately characterized by data collected at the other
four nearfield stations.) 
Analyte Depth Parameter 
Hydrographic
vertical profile 
Downcast data continuous, with upcast
data at any sampled depths 
Temperature 
Salinity 
Dissolved oxygen 
Chlorophyll fluorescence 
Transmissometry 
Irradiance 
Depth of sensors 
Water chemistry 
Five depths. Surface, bottom, and three
intermediate depths which includes the
chlorophyll maximum 
Ammonium 
Nitrate 
Nitrite 
Total dissolved nitrogen 
Particulate nitrogen 
Phosphate 
Total dissolved phosphorus 
Particulate phosphorus 
Silicate 
Particulate carbon 
Alexandrium Two depths Gene probe 
Phytoplankton 
Zooplankton 
Near surface 
Net tow for zooplankton Identification, enumeration 
Table 3-6. Cape Cod Bay–Stellwagen Bank National Marine Sanctuary water-column
monitoring stations. 
Station Water Depth 
(meters) 
Location Relative to
Outfall Purpose 
F29 65 50 km SE Evaluate nutrients and plankton in
Stellwagen Bank National Marine
Sanctuary 
F02 32 70 km SE Evaluate nutrients and plankton in
Cape Cod Bay 
F01 26 66 km SE

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
33 
Table 3-7. Water-column parameters in Cape Cod Bay and Stellwagen Bank National
Marine Sanctuary. 
Analyte Depth Parameter 
Hydrographic vertical
profile 
Continuous downcast data from
within 1m of surface to within 5m of
bottom. 
Temperature 
Salinity 
Dissolved oxygen 
Depth of sensor 
Chlorophyll fluorescence 
Irradiance 
Water chemistry 
Two depths 
Near-surface and 
Near-bottom 
Nitrate + nitrite 
Ammonium 
Phosphate 
Total nitrogen 
Total phosphorus 
Extracted chlorophyll 
Phytoplankton Near-surface 
Identification and 
enumeration 
Zooplankton Net tow 
Contingency Plan Thresholds 
Threshold parameters for water-column monitoring include minimum dissolved
oxygen concentrations and percent saturation in nearfield and Stellwagen Bank
bottom waters, dissolved oxygen depletion rate in nearfield bottom waters,
chlorophyll levels, abundance of nuisance algal species, and geographic extent of PSP
toxin (Table 3-8). Oxygen concentrations and percent saturation are compared to
background levels rather than to the caution and warning levels. Beginning in 2011,
Contingency Plan thresholds and/or background levels for the water column were
recalculated based on the revised sampling design (MWRA 2010).

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
34 
Table 3-8. Contingency Plan threshold values for water-column monitoring . DO = dissolved
oxygen 
Location/ 
Parameter 
Specific
Parameter Baseline Caution Level Warning Level 
Bottom water
nearfield 
Dissolved oxygen
concentration 
Background 5 th
percentile 
6.05 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 
Dissolved oxygen
percent saturation 
Background 5 th
percentile 
65.3% 
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 
Bottom water
Stellwagen Basin 
Dissolved oxygen
concentration 
Background 5 th
percentile 
6.23 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 
Dissolved oxygen
percent saturation 
Background 5 th
percentile 
67.2% 
Lower than 80%
for any survey
(June–October)
unless background
conditions 
Lower than 75%
for any survey
(June–October)
unless background
conditions are
lower 
Bottom water
nearfield 
DO depletion rate
(June-October) 0.024 mg/L/day 0.037 mg/L/day 0.049 mg/L/day 
Chlorophyll
nearfield 
Annual 72 mg/m 2 108 mg/m 2 144 mg/m 2 
Winter/spring 50 mgml 2 199 mg/m 2 None 
Summer 51 mg/m 2 89 mg/m 2 None 
Autumn 90 mg/m 2 239 mg/m 2 None 
Nuisance algae
nearfield 
Phaeocystis
pouchetii 
Winter/spring 622,000 cells/L 2,860,000 cells/L None 
Summer 72 cells/L 357 cells/L None 
Autumn 370 cells/L 2,960 cells/L None 
Nuisance algae
nearfield Pseudo-
nitzschia spp. 
Winter/spring 6,735 cells/L 17,900 cells/L None 
Summer 14,635 cells/L 43,100 cells/L None 
Autumn 10,050 cells/L 27,500 cells/L None 
Nuisance algae
nearfield 
Alexandrium
fundyense 
Any nearfield
sample 
Baseline maximum
= 163 cells/L 100 cells/L None 
Massachusetts
shellfish resources PSP toxin extent Not applicable New incidence None

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
35 
4. Sea Floor 
Background 
Bottom Characteristics and Sediment Transport 
The sea floor of Massachusetts and Cape Cod bays was originally shaped by the
glaciers, which sculpted the bottom and deposited debris, forming knolls, banks, and
other features. Within Massachusetts Bay, the sea floor ranges from mud in
depositional basins to coarse sand, gravel, and bedrock on topographic highs. The
area around the outfall is marked by underwater drumlins, which are elongated hills
about 10 meters high, with crests covered by gravel and boulders. Long-term sinks
for fine-grained sediments include Boston Harbor, Cape Cod Bay, and Stellwagen
Basin. 
Modeling and long-term monitoring have confirmed that sediment transport in the
region occurs primarily during storms (Butman et al. 2005). Typically, waves during
storms with winds from the northeast resuspend sediments, which are transported by
shallow currents from western Massachusetts Bay toward Cape Cod Bay and by
deeper currents to Stellwagen Basin. Cape Cod Bay is partially sheltered from large
waves by the arm of Cape Cod, and storm waves are rarely large enough to resuspend
sediments in Stellwagen Basin, the deepest feature in the region. Tidal currents,
wind-driven currents, and currents associated with spring runoff are too weak or too
shallow to resuspend sediments. 
Environmental Concerns 
Within Boston Harbor, studies of the sediments immediately documented the
recovery that had been expected after the end of biosolids and effluent discharges and
other improvements. Conversely, relocating the outfall raised concerns about
potential effects on the offshore sea floor. Concern focused on three mechanisms of
potential disruption to the animal communities living on the sea floor: eutrophication
and related low levels of dissolved oxygen, accumulation of toxic contaminants in
depositional areas, and smothering (Table 4-1). 
If diversion of the nutrient loads to offshore were to cause eutrophication, the
depressed levels of dissolved oxygen that were also a concern in water-column
monitoring could adversely affect bottom-dwelling animals. An increase in the
amounts of particles and organic matter to the bottom could disrupt normal benthic
community structure in the vicinity of the discharge.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
36 
Table 4-1. Monitoring questions related to the sea floor. 
Are natural/living resources protected? 
Will benthic enrichment contribute to changes in community structure of soft-
bottom and hard-bottom macrofauna, possibly affecting fisheries? 
Will benthic macrofauna near the outfall mixing zone be exposed to some
contaminants, potentially contributing to changes in the community? 
Will the benthos near the outfall mixing zone and in depositional areas farther
away accumulate some contaminants? 
 What is the level of sewage contamination and its spatial distribution
in Massachusetts and Cape Cod bays sediments before discharge
through the new outfall? 
 Has the level of sewage contamination or its spatial distribution in
Massachusetts or Cape Cod bays sediments changed after
discharge through the new outfall? 
 Have the concentrations of contaminants in sediments changed? 
 Has the soft-bottom community changed? 
 Are any benthic community changes correlated with changes in
levels of toxic contaminants (or sewage tracers) in sediments? 
 Has the hard-bottomed community changed? 
Will increased water-column and benthic respiration contribute to depressed
oxygen levels in the sediment? 
 Have the sediments become more anoxic; that is, has the thickness
of the sediment oxic layer decreased? 
Although source control and treatment plant performance are designed to keep
effluent contaminant concentrations too low to affect the sediments, concerns over the
efficacy of treatment and early projections that primary-only treated effluent would
be discharged for the first five years after the outfall came on-line led to questions
about the potential for contaminant build-up. (Construction of the outfall tunnel took
longer than initially projected; by the time the outfall discharge began in September
2000, about 80% of the effluent flow received secondary treatment.) Similarly,
concentrations of particulate matter were expected to be low, but there remained
some concern that bottom communities near the outfall could be affected by
deposition. 
Monitoring Design 
Sea-floor monitoring includes several components: measurements of physical
characteristics, sewage effluent tracers, and contaminant concentrations in sediments;
sediment-profile imaging to provide a rapid assessment of sediment quality and
benthic communities; studies of nearfield and farfield soft-bottom communities; and
studies of hard-bottom communities. In 2011, MWRA implemented a revised
monitoring plan for benthic monitoring (MWRA 2010). Eleven nearfield and three
farfield stations were selected as a representative subset of stations for measurements
of sediment characteristics, sediment chemistry, and benthic infauna (Figure 4-1).
Sediment-profile imaging is done at the 23 nearfield stations monitored historically
(Figure 4-2). Hard-bottom monitoring is conducted at the same locations as

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
37 
historically (Figure 4-3), but the frequency of surveys has been reduced from yearly
to every three years, including 2011. 
Figure 4-1. Soft-bottom monitoring stations. Also shown are two instrumented buoys, one operated
by the Northeastern Regional Association of Coastal and Ocean Observing Systems (NERACOOS)
and the other by the National Oceanic and Atmospheric Administration National Data Buoy Center
(NDBC); the MWRA outfall diffuser; and the Stellwagen Bank National Marine Sanctuary.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
38 
Figure 4-2. Sediment-profile imaging (SPI) stations. Also shown are two instrumented buoys, one
operated by the Northeastern Regional Association of Coastal and Ocean Observing Systems
(NERACOOS) and the other by the National Oceanic and Atmospheric Administration National Data
Buoy Center (NDBC); and the MWRA outfall diffuser.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
39 
Figure 4-3. Hard-bottom stations. Video and still photographs are collected at 17 stations distributed
among six transects and at six additional waypoints, including one active diffuser and one diffuser that
has not been opened. Also shown are two instrumented buoys, one operated by the Northeastern
Regional Association of Coastal and Ocean Observing Systems (NERACOOS) and the other by the
National Oceanic and Atmospheric Administration National Data Buoy Center (NDBC); and the
MWRA outfall diffuser.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
40 
Sediment grain size, total organic carbon (TOC), and the sewage tracer Clostridium
perfringens spores are measured annually. Concentrations of contaminants in
sediments, including PAHs, PCBs, chlorinated pesticides, and metals, are measured
every third year, including 2011. Sediment-contaminant monitoring has also been
complemented by special studies, primarily in association with the U.S. Geological
Survey (USGS) (for example, Bothner and Butman 2007). 
Monitoring the soft-bottom benthic infauna includes annual sampling surveys
conducted in August. Samples are collected with a 0.04-m 2 Young-Van Veen benthic
grab, sieved on 300- μm mesh, and fixed in formalin in the field, then transferred to 
alcohol and stained with Rose Bengal in the laboratory. Animals are sorted,
identified, and counted. 
Sediment-profile-image monitoring is conducted each August and results in area-
wide assessments of sediment quality and benthic community status. A sharp-edged
prism is used to cut into sediment surfaces at each station; a camera mounted to the
prism records images of the sediment-water interface and the surface-sediment
profiles. At each station, the camera is lowered to the sea floor three or four times,
and a series of two to four replicate images is taken, generally within the first 12
seconds after bottom contact. A video feed allows real-time monitoring and ensures
that adequate still photographs are obtained. The sediment-profile images provide
more rapid assessments of benthic habitat conditions than is possible from traditional
faunal analyses. The images are used to measure a number of parameters, including
the apparent reduction-oxidation (redox) potential discontinuity (RPD) depth,
apparent successional stage of the community, and an organism sediment index which
is derived from the RPD depth and the successional stage. 
Most pollutant-effect monitoring studies of benthic communities, including the
MWRA monitoring program, focus on the soft-bottom areas with finer-grained
sediments, but such depositional areas are few in the vicinity of the outfall.
Therefore, MWRA also conducts video and photographic surveys of the hard-bottom
habitats found on the tops and flanks of drumlins in western Massachusetts Bay
(Figure 4-4). Video and still photographs are taken at a series of stations or
waypoints, including diffuser head #44 of the outfall (which was not opened) and
diffuser head #2 (which is active). Photographs are examined for substrate type (top
or flank of the drumlin, with relief defined by presence of boulders and cobbles),
amount of sediment drape (the degree to which a layer of fine material covers the
hard surface), and biota (taxa identified to species or species groups and counted).
These surveys are conducted in June; beginning in 2011, they are conducted every
third year, in the same year that sediment contaminants are studied.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
41 
Contingency Plan Thresholds 
The Contingency Plan minimum threshold for RPD is set as half the baseline mean
depth (Table 4-2). Thresholds for toxic contaminants in sediments are based on
NOAA effects range median criteria, the median concentrations at which toxicity has
been observed in laboratory tests (Wolf et al. 1994, Long et al. 1998.) 
Table 4-2. Contingency Plan threshold values for RPD depth and sediment toxic
contaminants. 
Location Parameter Caution
Level 
Warning
Level 
Nearfield sediments RPD depth <1.18 cm None 
Nearfield PAHs
(ng/g or parts per
billion, dry weight) 
Acenaphthene 
None 
500 
Acenaphylene 640 
Anthracene 1,100 
Benzo(a)anthracene 1,600 
Benzo(a)pyrene 1,600 
Chrysene 2,800 
Dibenzo(a,h)anthracene 260 
Fluoranthene 5,100 
Fluorene 540 
Naphthalene 2,100 
Phenanthrene 1,500 
Pyrene 2,600 
Total HMW PAH 9,600 
Total LMW PAH 3,160 
Total PAHs 44,792 
Nearfield 
other organics 
(ng/g dry weight) 
p,p’-DDE 
None 
27 
Total DDTs 46.1 
Total PCBs 180 
Nearfield 
metals 
( μ g/g or parts per
million, dry weight) 
Cadmium 
None 
9.6 
Chromium 370 
Copper 270 
Lead 218 
Mercury 0.71 
Nickel 51.6 
Silver 3.7 
Zinc 410

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
42 
The thresholds for community parameters were recalculated beginning in 2011 based
on the new sampling design (Table 4-3). Caution levels are set for benthic
community parameters, and there are both caution and warning levels for percent
opportunists. 
Table 4-3. Contingency Plan threshold values for benthic community parameters. 
Location Parameter Caution Level Warning
Level 
Nearfield
benthic
community 
Species per
sample <42.99 or >81.85 None 
Fisher’s log-series
alpha <9.42 or >15.8 None 
Shannon diversity <3.37 or >3.99 None 
Pielou’s evenness <0.57 or >0.67 None 
Nearfield
benthic
opportunists 
Percent
opportunists >10% >25%

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
43 
5. Fish and Shellfish 
Background 
MWRA monitors fish and shellfish because of concerns for public health, because
some fish and shellfish species are good indicators of effects of pollutants on overall
marine health, and because the fish and shellfish industry is an important part of the
regional identity and economy of Massachusetts. Monitoring questions focused on
public health and protection of the resource (Table 5-1). 
Table 5-1. Monitoring questions related to fish and shellfish. 
Is it safe to eat fish and shellfish? 
Will toxic chemicals accumulate in the edible tissues of fish and shellfish, and
thereby contribute to human health problems? 
 Has the level of contaminants in the tissues of fish and shellfish
around the outfall changed since discharge began? 
 Do the levels of contaminants in the edible tissue of fish and shellfish
around the outfall represent a risk to human health? 
 Are the contaminant levels in fish and shellfish different between
outfall, Boston Harbor, and a reference site? 
Are natural/living resources protected? 
Will fish and shellfish that live near or migrate by the diffuser be exposed to
elevated levels of some contaminants, potentially contributing to adverse
health in some populations? 
 Has the level of contaminants in the tissues of fish and shellfish
around the outfall changed since discharge began? 
 Are the contaminant levels in fish and shellfish different between the
outfall, Boston Harbor, and a reference site? 
 Are the contaminant levels in fish and shellfish different between
outfall, Boston Harbor, and a reference site? 
 Has the incidence of disease and/or abnormalities in fish or shellfish
changed? 
The two main concerns for fish and shellfish were that the discharge of sewage
effluent into the relatively clean waters of Massachusetts Bay could result in chemical
contamination of the fisheries and that contaminants in the effluent could cause direct
damage to health of the fishery stocks. Because many toxic contaminants adhere to
particles, which settle, animals that live on the bottom, in contact with sediments and
those that eat bottom-dwelling organisms were considered to be the most likely
species to be affected. Exposure to contaminated sediments could result in fin
erosion, disease, or other, subtler, abnormalities in flounder, lobster, or other bottom-
dwelling animals. Shellfish that feed by filtering suspended matter from large
volumes of water are also potential bioaccumulators of toxic contaminants.
Consumption of filter-feeding animals by predators could result in transferring
contaminants up the food chain and ultimately to humans.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
44 
Monitoring Design 
The monitoring program focuses on three indicator species: winter flounder
( Pseudopleuronectes americanus ), lobster ( Homarus americanus ), and blue mussel
( Mytilus edulis ). Winter flounder and lobster are important resource species in the
region. Like all flatfish, winter flounder live and feed on the bottom, often lying
partially buried in the sediments. Lobsters live on a variety of surfaces within the
region, including mud, sand, gravel, and rock outcrops. Blue mussels are also
resource species, but are included in the program because, like other filter feeders,
mussels process large volumes of water and can concentrate toxic metals and organic
compounds in their tissues. They can be readily maintained in fixed cages, so they
are convenient monitoring tools. 
Flounder and lobster are sampled from Deer Island Flats, near the outfall site, and
Cape Cod Bay (Figure 5-1). Flounder are also taken near Nantasket Beach and, until
2005, were collected at Broad Sound, just off the coast to the north of Deer Island.
Mussels are deployed at the edge of the mixing zone, one kilometer south of the
diffuser line, in Cape Cod Bay, at Deer Island Light, and in the Boston Inner Harbor. 
Winter Flounder 
Flounder are collected annually. Whole fish are examined for external lesions or
other abnormalities, and flounder livers are examined to quantify disease, including
three types of vacuolation (centrotubular (CHV), tubular, and focal, representing
increasing severity), microphage aggregation, biliary-duct proliferation, and neoplasia
(tumors). Vacuolation and neoplasia have been associated with chronic exposure to
contaminants. 
Since 2004, chemical analyses for flounder are completed every third year, including
2006 and 2009, to determine tissue burdens and to evaluate whether contaminant
burdens approach human health consumption limits. Chemical analyses (Table 5-2)
of composite samples of fillets and livers include PCBs, pesticides, mercury, and
lipids. Liver samples are also analyzed for PAHs, lead, silver, cadmium, chromium,
copper, nickel, and zinc. 
Lobster 
Commercial lobstermen collect lobsters for the monitoring program. Since 2004,
lobsters have been studied every third year, including 2006 and 2009. All lobsters are
examined for external conditions, and chemical analyses are performed on composite
samples. Meat (from the tail and claw) and hepatopancreas are analyzed for lipids,
PCBs, pesticides, and mercury. Hepatopancreas samples are also analyzed for PAHs,
lead, silver, cadmium, chromium, copper, nickel, and zinc. 
Blue Mussel 
Mussels are collected from a clean reference site (such as Stover’s Point, Maine).
They are placed in cages and deployed in replicate arrays at Cape Cod Bay, Boston
Inner Harbor, Deer Island Light and the outfall site. Since 2004, mussel deployments
and analyses have been carried out every third year, including 2006 and 2009.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
45 
After a minimum deployment of 40 days or a preferred deployment of 60 days,
chemical analyses are performed on composite samples of mussel tissue. Tissues are
analyzed for PCBs, pesticides, PAHs, lipids, mercury, and lead. 
Figure 5-1. Fish-and-shellfish monitoring stations. Also shown are two instrumented buoys, one
operated by the Northeastern Regional Association of Coastal and Ocean Observing Systems
(NERACOOS) and the other by the National Oceanic and Atmospheric Administration National Data
Buoy Center (NDBC); the MWRA outfall diffuser; and the boundaries of the Stellwagen Bank
National Marine Sanctuary.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
46 
Table 5-2. Chemical analyses of fish and shellfish. 
Parameter Measurement Details 
Flounder fillet 
Mercury 
PCBs 
Chlorinated pesticides 
Lipids 
Three composites of fillets from five flounder 
Flounder liver 
Trace metals 
PAHs 
PCBs 
Chlorinated pesticides 
Lipids 
Three composites of livers from five flounder 
Lobster meat 
Mercury 
PCBs 
Chlorinated pesticides 
Lipids 
Three composites of meat from five
lobsters 
Lobster hepatopancreas 
Trace metals 
PAHs 
PCBs 
Chlorinated pesticides 
Lipids 
Three composites of hepatopancreas
from five lobsters 
Mussel 
Mercury 
Lead 
PAHs 
PCBs 
Chlorinated pesticides 
Lipids 
Six composites of soft tissue from ten
mussels 
Contingency Plan Thresholds 
Threshold parameters for fish and shellfish include levels of toxic contaminants in
flounder, lobster, and mussels and liver disease (measured as CHV) in flounder
(Table 5-3). Some thresholds are based on U.S. Food and Drug Administration limits
for maximum concentrations of specific contaminants in edible portions of food.
Others were developed from the baseline-monitoring results.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
47 
Table 5-3. Contingency Plan threshold values for fish-and-shellfish monitoring. 
Location/
Parameter Type Parameter Caution
Level 
Warning
Level 
Flounder tissue
nearfield 
PCB 1 ppm wet weight 1.6 ppm wet
weight 
Mercury 0.5 ppm wet
weight 
0.8 ppm wet
weight 
Flounder tissue, lipid
normalized, nearfield 
Chlordane 484 ppb None 
Dieldrin 127 ppb None 
DDT 1552 ppb None 
Flounder 
nearfield 
Liver disease
(CHV) 44.9% None 
Lobster tissue nearfield 
PCB 
1 ppm
wet
weight 
1.6 ppm
wet
weight 
Mercury 0.5 ppm wet
weight 
0.8 ppm wet
weight 
Lobster tissue, lipid
normalized, nearfield 
Chlordane 150 ppb None 
Dieldrin 322 ppb None 
DDT 683 ppb None 
Mussel tissue 
nearfield 
PCB 1 ppm wet weight 1.6 ppm wet
weight 
Lead 2 ppm wet weight 3 ppm wet weight 
Mercury 0.5 ppm wet
weight 
0.8 ppm wet
weight 
Mussel tissue, lipid
normalized, nearfield 
Chlordane 205 ppb None 
Dieldrin 50.1 ppb None 
DDT 483 ppb None 
PAH 2160 ppb None

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
48 
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. Some studies were conducted over many years and ended with the
monitoring plan revisions. For example, studies of primary productivity and nutrient
flux at the sediment-water interface were conducted each year until the studies ended
at the end of 2010. 
Other long-term studies continue. Since 1995, MWRA has included endangered
species observers on monitoring surveys. Besides providing observational data, the
presence of observers trained to identify marine mammals 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. 
A major special study carried out by the USGS began in 1989 and was completed in
2007. This cooperative research project investigated processes influencing the
transport and fate of contaminated sediments in Boston Harbor and Massachusetts
Bay (Bothner and Butman 2007). 
Other special studies have included reviews of nutrient and toxic-contaminant issues,
additional analyses of the effluent, evaluations of the Bays Eutrophication Model,
floatables monitoring, and red-tide monitoring and analyses.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
49 
7. Stellwagen Bank 
National Marine Sanctuary 
Background 
The Gerry E. Studds Stellwagen Bank National Marine Sanctuary comprises 842
square miles located at the boundary between Massachusetts Bay and the rest of the
Gulf of Maine. Its landward boundaries lie approximately 25 miles east of Boston,
three miles north of Provincetown, and three miles south of Gloucester. Stellwagen
Basin, which is partially within the sanctuary, is the deepest part of Massachusetts
Bay with water depths of about 260 feet. It is a long-term sink for fine-grained
sediments. Stellwagen Bank, a sand-and-gravel plateau, lies to the east of Stellwagen
Basin and has water depths of about 65 feet. Tidal mixing of nutrients throughout the
relatively shallow water column creates a rich habitat for marine life on Stellwagen
Bank. 
The National Centers for Coastal Ocean Science (NCCOS) published an ecological
characterization report for the sanctuary (NCCOS 2006; available at
http://ccma.nos.noaa.gov/products/biogeography/stellwagen). The report describes
the physical and oceanographic setting, chemical contaminants, fishes, seabirds, and
mammals in the sanctuary and the Gulf of Maine and concludes that that there has
been no indication that the relocation of the MWRA outfall to Massachusetts Bay has
exerted any effect on the magnitude of contaminants reaching the sanctuary. 
The sanctuary issued a Management Plan and Environmental Assessment in 2010
which listed concerns for the sanctuary (U.S. Department of Commerce 2010,
available at http://stellwagen.noaa.gov/management/fmp/fmp2010.html .) Concerns
include commercial fishing, commercial shipping, whale-watch boat collisions with
whales, invasion by exotic species, harmful algal blooms, and the potential for
degraded water quality associated with population growth in the region, offshore
industrialization such as liquefied natural gas (LNG) ports, and underwater noise.
Climate change and ocean acidification are also concerns. While noting that the
MWRA discharge (as well as legacy contaminants exported from Boston Harbor) was
a potential source of contamination, the report summarized water quality analyses
conducted by MWRA and the sanctuary, and found “no evidence of increased
eutrophication or unacceptable contaminant loads in the sanctuary relative to outfall
start-up.” 
Although these positive findings were anticipated, MWRA’s discharge permit
requires an annual assessment of possible outfall effects.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
50 
Monitoring Design 
MWRA’s regular water-column and sea-floor monitoring efforts include stations
within and near the sanctuary. Beginning in 2011, based on the findings of outfall
monitoring from 2000–2010, most of the water-column boundary stations that were
within the sanctuary were eliminated from the monitoring program. However, the
frequency of sampling the remaining farfield stations, including stations between the
outfall and the sanctuary, increased from six to nine times per year. In addition,
plankton is now monitored at all stations. Generally, if there were effects of the
MWRA outfall, they would be expected to be detected first at stations closer to the
discharge (N04, N07, F15, see Figure 3-2). Within the sanctuary boundary, station
F29 is used to assess water quality off Provincetown, and the NERACOOS Buoy A01
gathers water quality at the north-west corner of the sanctuary. Station F22 is used to
assess water quality in Stellwagen Basin, just to the west of the sanctuary’s western
boundary. 
The seafloor design has been modified as well beginning in 2011. One MWRA sea-
floor station is within the sanctuary, in Stellwagen Basin (FF04, see Figure 4-1).
Station FF09 is adjacent to the basin, southeast of the diffuser. A third sea-floor
station (FF01A) is just northwest of the sanctuary boundary.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
51 
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Long ER, Field LJ, MacDonald DD. 1998. Predicting toxicity in marine sediments
with numerical sediment quality guidelines. Environmental Toxicology and
Chemistry, 17:714–727

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
52 
MWRA. 1991. Massachusetts Water Resources Authority effluent outfall monitoring
plan: Phase I baseline studies. Boston: Massachusetts Water Resources Authority.
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MWRA. 1997a. Massachusetts Water Resources Authority effluent outfall
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Boston: Massachusetts Water Resources Authority. Report 1997- ms-069. 41p. 
MWRA. 2001. Massachusetts Water Resources Authority Contingency Plan revision
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MWRA. 2004. Massachusetts Water Resources Authority effluent outfall ambient
monitoring plan Revision 1, March 2004. Boston: Massachusetts Water Resources
Authority. Report 2004-ms-092. 65p. 
MWRA. 2010. Massachusetts Water Resources Authority effluent outfall ambient
monitoring plan Revision 2. July 2010. Boston: Massachusetts Water Resources
Authority. Report 2010-04. 107p. 
NCCOS. 2006. An ecological characterization of the Stellwagen Bank National
Marine Sanctuary Region: oceanographic, biogeographic, and contaminants
assessment. Prepared by NCCOS’s Biogeography Team in cooperation with the
National Marine Sanctuary Program. Silver Spring, MD. NOAA Technical
Memorandum NOS NCCOS 45. 356p. 
Rex AC, 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. 
Rex AC, Tyler C. 2011. Summary of floatables monitoring in Deer Island Treatment
Plant effluent 2006–2010. Boston: Massachusetts Water Resources Authority. Report
2011-03. 11p. 
U.S. Department of Commerce. National Oceanic and Atmospheric Administration.
Office of National Marine Sanctuaries. 2010. Stellwagen Bank National Marine
Sanctuary Final Management Plan and Environmental Assessment. Silver Spring,
MD. 448p. 
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Massachusetts Water Resources Authority. Report 2000-04. 66p. 
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Massachusetts Water Resources Authority. Report 2000-14. 72p.

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2012 UPDATE 
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Werme C, Hunt CD. 2001. 2000 Outfall monitoring overview. Boston: Massachusetts
Water Resources Authority. Report 2001-10. 92p. 
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Water Resources Authority. Report 2002-18. 84p. 
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Water Resources Authority. Report 2003-12. 80p. 
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Water Resources Authority. Report 2004-13. 97p. 
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Water Resources Authority. Report 2007-12. 95p. 
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Massachusetts Water Resources Authority. Report 2008-18. 54p. 
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Outfall monitoring overview RESULTS. Boston: Massachusetts Water Resources
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Outfall monitoring overview. Boston: Massachusetts Water Resources Authority.
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OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
54 
Wolfe DA, Bricker SB, Long ER, Scott KJ, Thursby GB. 1994. Biological effects of
toxic contaminants in sediments from Long Island Sound and environs. U.S.
Department of Commerce. National Oceanic and Atmospheric Administration.
National Ocean Service. Coastal Ocean Program. 
http://ccma.nos.noaa.gov/publications/tm80.pdf

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
55 
List of Acronyms 
ARRS Alexandrium Rapid Response Survey 
BOD Biochemical oxygen demand 
cBOD Carbonaceous biochemical oxygen demand 
CHV Centrotubular hydropic vacuolation 
DDE Dichlorodiphenyldichloroethylene 
DDT Dichlorodiphenyltrichloroethane 
DITP Deer Island Treatment Plant 
DO Dissolved oxygen 
EPA U.S. Environmental Protection Agency 
HMW High molecular weight 
IAAC Inter-agency Advisory Committee 
LC50 50% mortality concentration 
LMW Low molecular weight 
LNG Liquefied natural gas 
MADEP Massachusetts Department of Environmental Protection 
MGD Million gallons per day 
MWRA Massachusetts Water Resources Authority 
NCCOS National Centers for Coastal Ocean Science 
NE Northeast 
NDBC National Data Buoy Center 
NERACOOS Northeastern Regional Association of Coastal and 
Ocean Observing Systems 
NOAA National Oceanic and Atmospheric Administration 
NOEC No observable effect concentration 
NPDES National Pollutant Discharge Elimination System 
NW Northwest 
OMSAP Outfall Monitoring Science Advisory Panel 
OMTF Outfall Monitoring Task Force 
PAH Polycyclic aromatic hydrocarbon 
PCB Polychlorinated biphenyl 
PIAC Public Interest Advisory Committee 
RPD Redox potential discontinuity 
PSP Paralytic shellfish poisoning 
S South 
SE Southeast 
SEIS Supplemental Environmental Impact Statement 
SBNMS Stellwagen Bank National Marine Sanctuary 
SPI Sediment-profile imaging 
TOC Total organic carbon 
TRAC Toxic Reduction and Control Program 
TSS Total suspended solids 
USGS U.S. Geological Survey

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
56 
Monitoring Questions and Answers 
Monitoring Question Answer 
Do effluent pathogens exceed the permit
limits? 
No. Secondary treatment and disinfection
effectively remove pathogens. In thousands
of tests, daily fecal coliform limits have been
exceeded twice, both times during storms. 
Does acute or chronic toxicity of effluent
exceed the permit limit? 
No. In more than 600 tests, there have been
four exceedances of permit limits. 
Do effluent contaminant concentrations
exceed permit limits? 
No. Discharges of priority pollutants are well
below predictions and in most cases meet
receiving water quality criteria even before
dilution. 
Do conventional pollutants in the effluent
exceed permit limits? 
No. Discharges of solids and BOD have
decreased by 87% compared to the old
treatment plant. In more than 600 tests, there
have been three exceedances of suspended
solids limits, which occurred during an upset
of the secondary treatment process by an
industrial discharge. 
What are the concentrations of contaminants
in the influent and effluent and their
associated variability? 
There has been great success in reducing
contaminants in the influent and a high
degree of removal of contaminants by the
treatment system, with consistently low
concentrations since secondary treatment
was implemented. 
Do levels of contaminants in water outside the
mixing zone exceed water quality standards? 
No. Water quality standards are not
exceeded. The projected degree of mixing
was confirmed by plume studies conducted
in 2001. Ongoing effluent monitoring assures
that standards are not violated. 
Are pathogens transported to shellfish beds at
levels that might affect shellfish consumer
health? 
No. Dilution is sufficient for pathogens to
reach background concentrations before
reaching shellfish beds. Dilution rates were
confirmed by plume studies conducted in
2001. 
Are pathogens transported to beaches at
levels that might affect swimmer health? 
No. Dilution is sufficient for pathogens to
reach background concentrations before
reaching beaches. Dilution rates were
confirmed by plume studies conducted in
2001. 
Has the clarity and/or color of the water
around the outfall changed? 
No. Although clarity and color have not
changed, there are occasional observations
of tiny bits of fat, similar to samples collected
at the treatment plant. 
Has the amount of floatable debris around the
outfall changed? 
Floatable debris of concern is rare in the
effluent. Signs of effluent can occasionally be
detected in the field. 
Are the model estimates of short-term (less
than one day) effluent dilution and transport
accurate? 
Yes. Model estimates were confirmed by
plume studies conducted in 2001.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
57 
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? 
There have been no detectable changes in
the farfield. Changes in salinity and
dissolved components of the effluent are not
detected within tens of meters of outfall and
not observed in farfield water or sediments. 
Have nutrient concentrations changed in the
water near the outfall; have they changed at
farfield stations in Massachusetts Bay or
Cape Cod Bay, and, if so, are they correlated
with changes in the nearfield? 
Changes have been consistent with model
predictions. The effluent signature is
observed in the vicinity of the outfall but is
quickly diluted. 
Do the concentrations (or percent saturation)
of dissolved oxygen in the water column meet
the state water quality standards? 
Yes. Conditions are unchanged from the
baseline. 
Have the concentrations (or percent
saturation) of dissolved oxygen in the vicinity
of the outfall or at selected farfield stations in
Massachusetts Bay or Cape Cod Bay
changed relative to pre-discharge baseline or
a reference area? If so, can changes be
correlated with effluent or ambient water
nutrient concentrations, or can farfield
changes be correlated with nearfield
changes? 
No. Conditions have not changed from the
baseline. 
Has the phytoplankton biomass changed in
the vicinity of the outfall or at selected farfield
stations in Massachusetts Bay or Cape Cod
Bay, and, if so, can these changes be
correlated with effluent or ambient water
nutrient concentrations, or can farfield
changes be correlated with nearfield
changes? 
No substantial change has been detected. 
Have the phytoplankton production rates
changed in the vicinity of the outfall or at
selected farfield stations, and, if so, can these
changes be correlated with effluent or
ambient water nutrient concentrations, or can
farfield changes be correlated with nearfield
changes? 
Productivity patterns in Boston Harbor may
be changing, as the area transitions from
eutrophic conditions to a more typical coastal
regime. There has been no concurrent
increase in productivity in Massachusetts
Bay. 
Has the abundance of nuisance or noxious
phytoplankton changed in the vicinity of the
outfall? 
The frequency of Phaeocystis blooms has
increased, but the phenomenon is regional in
nature. Alexandrium blooms, which have
occurred since 2005, are regional and have
not been attributed to the outfall.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
58 
Monitoring Question Answer 
Has the species composition of phytoplankton
or zooplankton changed in the vicinity of the
outfall or at selected farfield stations in
Massachusetts Bay or Cape Cod Bay? If so,
can these changes be correlated with effluent
of ambient water nutrient concentrations, or
can farfield changes be correlated with
nearfield changes? 
The increase in frequency of Phaeocystis 
blooms is the most marked change in the
phytoplankton community, and the region
appears to be entering a period of frequent
red tides. Those changes have not been
attributed to the outfall. There have been no
changes in the zooplankton community
beyond normal ecological fluctuations. 
What is the level of sewage contamination
and its spatial distribution in Massachusetts
and Cape Cod bays sediments before
discharge through the new outfall? 
The effects of historic inputs from Boston
Harbor and other sources can be detected,
particularly in coastal stations. 
Has the level of sewage contamination or its
spatial distribution in Massachusetts and
Cape Cod bays sediments changed after
discharge through the new outfall? 
An effluent signal can be detected only in 
Clostridium perfringens spores, the most
sensitive sewage tracer, and is only
detectable within a few kilometers of the
outfall. 
Has the concentration of contaminants in
sediments changed? 
There has been no general increase in
contaminants. An effluent signal can be
detected as Clostridium perfringens spores
within 2 km of the diffuser. 
Has the soft-bottom community changed? Changes have occurred but are the result of
natural variation. The changes are not
significant and are not attributed to the
outfall. 
Have the sediments become more anoxic;
that is, has the thickness of the sediment oxic
layer decreased? 
No. The sediment RPD has been deeper
during post-diversion years rather than
shallower; that is, the sediments are more
rather than less oxic. 
Are any benthic community changes
correlated with changes in levels of toxic
contaminants (or sewage tracers) in
sediments? 
There have been no changes detected, even
within 2 km of the outfall. 
Has the hard-bottom community changed? There have been no changes that can be
attributed to the outfall. There have been
decreases in coralline algae at some
stations, but the geographic pattern does not
suggest an outfall effect. 
How do the sediment oxygen demand, the
flux of nutrients from the sediment to the
water column, and denitrification influence the
levels of oxygen and nitrogen in the water
near the outfall? Have the rates of these
processes changed? 
These conditions were described by baseline
monitoring. Conditions have improved in
Boston Harbor and have not changed in
Massachusetts Bay. 
Has the level of contaminants in the tissues of
fish and shellfish around the outfall changed
since discharge began? 
There has been no substantial change in
flounder or lobster contaminant body
burdens, with concentrations remaining very
low. There have been detectable increases in
concentrations of some contaminants in
mussel arrays deployed within the mixing
zone at the outfall.

OUTFALL MONITORING OVERVIEW BACKGROUND
2012 UPDATE 
59 
Monitoring Question Answer 
Do the levels of contaminants in the edible
tissue of fish and shellfish around the outfall
represent a risk to human health? 
There have been no changes that would
pose a threat to human health. Regional
patterns have persisted since the baseline
period, and there appears to be a general
long-term downward trend for most
contaminant levels. 
Are the contaminant levels in fish and
shellfish different between the outfall, Boston
Harbor, and a reference site? 
Differences were documented during
baseline monitoring. Regional patterns have
persisted since the diversion, with
concentrations being highest in Boston
Harbor and lowest in Cape Cod Bay. 
Has the incidence of disease and/or
abnormalities in fish or shellfish changed? 
There have been no increases in disease or
abnormalities in response to the outfall; there
has been a long-term downward trend in liver
disease in fish from near Deer Island and
near the outfall.

Massachusetts Water Resources Authority 
Charlestown Navy Yard 
100 First Avenue 
Boston, MA 02129