O: Contingency Plan
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CONTINGENCY PLAN
REVISION 1
MAY 2001
Massachusetts Water Resources Authority
Environmental Quality Department
Report ENQUAD ms-071
Contingency Plan Revision 1 - May 2001
Citation:
MWRA. 2001. Massachusetts Water Resources Authority Contingency Plan Revision 1.
Boston: Massachusetts Water Resources Authority. Report ENQUAD ms-071. 47 p.
Contingency Plan Revision 1 - May 2001
Table of Contents
Section 1 Introduction ............................................................................................... .1
Section 2 Underlying Pollution Control Strategies ...................................................... 11
Section 3 Outfall Monitoring Plan: the Foundation for the Contingency
Plan................................................................................................................ 15
Section 4 Contingency Plan Implementation ............................................................... 18
Section 5 Trigger Parameters, Thresholds and Potential Corrective
Activities ...................................................................................................... 21
5.1 Nutrients ........................................................................................................... 22
5.2 Toxic Contaminants .......................................................................................... 32
5.3 Organic Material …………………………………………………………… 37
5.4 Human Pathogens .............................................................................................. 38
5.5 Solids ................................................................................................................ 41
5.6 Floatables .......................................................................................................... 43
5.7 Overall Treatment Plant Performance .............................................................. 45
Bibliography.......................................................................................................................... 47
Appendix
Contingency Plan Revision 1 - May 2001
List of Tables and Figures
Tables
Table 1-1 Summary Matrix .............................................................................................6
Table 2-1 Deer Island Treatment Plant Redundancy .................................................... 11
Table 5-1 Nutrients ...................................................................................................... 26
Table 5-2 Toxic Contaminants ...................................................................................... 36
Table 5-3 Organic Material ........................................................................................... 37
Table 5-4 Human Pathogens.......................................................................................... 40
Table 5-5 Solids ............................................................................................................ 42
Table 5-6 Floatables ...................................................................................................... 44
Table 5-7 Overall Treatment Plant Performance........................................................... 46
Figures
Figure 2-1 Average Modeled Dilution of Sewage Effluent ........................................... 12
Figure 2-2 Locations of Harbor and Bay Outfalls .......................................................... 12
Figure 2-3 Metals in MWRA Treatment Plant Discharges 1989-2000 ......................... 14
Figure 4-1 Contingency Plan Flowchart ........................................................................ 20
Figure 5-1 MWRA sampling stations in Massachusetts and Cape Cod Bays ............... 21
Contingency Plan Revision 1 - May 2001 1
Section 1.0 Introduction
1.1 Program
Description
In 1986 the Massachusetts Water Resources Authority (MWRA)
began an ambitious program to upgrade its regional sewage treatment
facilities and alleviate the long-standing pollution associated with the
discharge of inadequately treated sewage sludge and effluent into the
shallow waters of Boston Harbor. Major components of the multi-
billion dollar capital program include new primary and secondary
sewage treatment facilities on Deer Island, a new discharge point for
treated sewage effluent, located 9.5 miles offshore in Massachusetts
Bay, a sludge-to-fertilizer plant, and combined sewer overflow (CSO)
control projects. Critical aspects of the operating program include an
aggressive industrial pretreatment/pollution prevention program
designed to remove toxic materials and other contaminants before
they enter the sewer system, comprehensive operator training,
sophisticated process control and maintenance tracking systems, and
an extensive water quality monitoring program at the treatment plant,
in Boston Harbor and in Massachusetts Bay.
Computer models predict that with the new facilities, treated
wastewater effluent will not only be cleaner but also much more
diluted, not only in Boston Harbor, but also throughout Massachusetts
and Cape Cod Bays, especially in near-shore waters (Blumberg et al.
1993). The Environmental Protection Agency’s 1988 Supplemental
Environmental Impact Statement (SEIS) predicted that the new
facilities would meet all water quality standards set by the state. These
findings were updated and confirmed in a design review performed by
MWRA in 1995 which showed that flows and pollutant loadings
transported to the facilities at Deer Island would be considerably
lower than predicted earlier.
1.2 Oversight
Mechanisms
The design of each major component of the MWRA’s capital
program, along with much of its operating program, has been carefully
studied by state and federal agencies as well as accepted by the
Federal Court. The planning has also been the subject of a wide-
reaching public participation process. As the MWRA moves from
design and construction into operation of its wastewater program,
oversight of its activities continues to be substantial. Construction of
the new treatment facilities, sludge-to- fertilizer plant, and CSO
control projects, the industrial pretreatment program and treatment
plant staffing are the subject of a Federal Court Order. MWRA
submits a monthly compliance report and numerous supplemental
documents to the Court each year. MWRA has also submitted to the
Court its Outfall Monitoring Plan, which provides for water quality
monitoring both before and after discharges from the new outfall take
Contingency Plan Revision 1 - May 2001 2
place. An Outfall Monitoring Task Force (OMTF) established under
the Massachusetts Executive Office of Environmental Affairs (EOEA)
has overseen the development and implementation of the Outfall
Monitoring Plan. The Outfall Monitoring Science Advisory Panel
(OMSAP) oversees the implementation of discharge monitoring.
As with all other discharges to surface waters, MWRA is obligated to
comply with EPA and Massachusetts Department of Environmental
Protection (DEP) regulations for its discharge through the National
Pollutant Discharge Elimination System (NPDES) and state
permitting programs. Extensive requirements for effluent monitoring,
reporting, plant maintenance and operations, and the industrial
pretreatment program will be included in an NPDES permit issued to
MWRA for the new outfall by DEP and EPA. Effluent limits will be
based on requirements for secondary treatment and state Water
Quality Standards which are pertinent to the discharge. Results of all
required effluent monitoring must be submitted to DEP and EPA
monthly. Any changes made to the treatment facility and any planned
operation or maintenance which may lead to instances of anticipated
non-compliance with permit limits or requirements must also be
reported. Based on the information reported to them, as well as any
information obtained under their right to request information and to
inspect facilities, DEP and EPA will have the right to reopen the
permit at any time to propose adding or changing permit requirements.
MWRA’s program is also the subject of extensive public oversight
encouraged and exercised through numerous forums. In addition to its
active participation in the MEPA process, MWRA regularly meets
with citizen advisory committees, environmental groups, other interest
groups and the public at large, to share information about its
operations and invite public input. Together with the regulatory and
judicial oversight noted above, this participation by the public plays a
big role in assuring that the Deer Island Treatment Plant and outfall
are well-maintained and operated and that the impacts of the relocated,
cleaner discharge really are as minimal as predicted.
1.3 Role of the
Contingency Plan
To further ensure that discharge from the new outfall does not result in
adverse impacts, MWRA has developed this Contingency Plan. In
keeping with MWRA's commitment to public oversight, every step of
the Contingency Plan implementation process will be open to public
review and comment.
Using the parameters of the extensive monitoring MWRA is
committed to perform under the Outfall Monitoring Plan and/or
required to perform under the NPDES permit, the Contingency Plan
identifies numerical or qualitative thresholds that can suggest that
Contingency Plan Revision 1 - May 2001 3
effluent quality or environmental conditions may be changing or
might be likely to change in the future. In the event that one of these
thresholds is exceeded, the Contingency Plan sets in motion a process
to confirm the threshold exceedance, to determine the causes and
significance of the exceedance, and, if the suggested changes are
attributable to the effluent outfall, to identify a response. A summary
of the Contingency Plan process is presented in Figure 4-1. As
described in Section 4, the first response to any threshold exceedance
will be to determine whether plant operation can be altered to reduce
the discharge of the relevant pollutant. In the event that significant
environmental changes attributable to the outfall are identified, the
proposed response will include both early notification to EPA and
DEP and the quick development of a Response Plan. A Response Plan
will include a schedule for implementing actions such as additional
monitoring, making further adjustments in plant operations, or
undertaking an Engineering Feasibility Study regarding one or more
of the "corrective activities" included in Section 5. Where the response
could include enhanced treatment, MWRA has identified feasible
technologies that could be implemented. A summary of the current
trigger parameters, thresholds and potential corrective activities is
presented in Table 1-1.
In addition, MWRA will provide a Quarterly Wastewater Performance
Report to provide information about key MWRA wastewater
operations; demonstrate day-to-day progress in achieving goals and
objectives; and compare actual performance against trigger parameters
and other important water quality monitoring or plant performance
targets. This report is starting to be available to the public in hard copy
and on-line. An example of this report is included as Appendix A. The
format and content of the report is still evolving and may continue to
be altered and refined as time goes on.
1.4 Contingency Plan
History
Development of the Contingency Plan was first recommended by the
National Marine Fisheries Service (NMFS) at the time it issued its
Biological Opinion concerning the potential effects of the proposed
discharge from the outfall on threatened or endangered species. At the
time, NMFS found that "based upon the best available information,
the proposed discharge may affect listed species, but is not likely to
jeopardize the continued existence of any endangered or threatened
whales, sea turtles or fish under the jurisdiction of NMFS."
Nonetheless, because the movement of water in Massachusetts Bay is
very complex, as are the natural interactions between living organisms
and their environment, it is impossible to predict with absolute
certainty all the effects of any discharge. In addition, Massachusetts
Bay faces many other threats that have ecological impacts, including
Contingency Plan Revision 1 - May 2001 4
overfishing and non-point source discharges, and cumulative impacts
are hard to predict. To minimize the possibility of any adverse effects
on endangered or threatened species, NMFS recommended among
various Conservation Recommendations the development of a
Contingency Plan.
In developing the Contingency Plan, MWRA, with the assistance of
the OMTF has identified potential issues of concern. The Contingency
Plan includes an evaluation and reporting process that MWRA will
use to investigate and report on problems/solutions, along with an
array of potential corrective activities that can be considered in the
event that a significant problem is linked to the effluent outfall.
Further development of a corrective activity would take place as
needed. In all cases, implementation of a corrective activity would be
tailored to meet the specific needs of the problem in a timely fashion.
And as experience, scientific understanding and technology evolve,
other potential corrective activities could also be considered as
needed.
For example, diversion of effluent from the new outfall back to the
existing harbor outfall system has been suggested as a means of
controlling adverse impacts to Massachusetts and Cape Cod Bays
caused by the effluent discharge. Diversion is technically possible,
since the original harbor outfalls will continue to exist and the
technical challenges of clearing sediment from the harbor outfalls and
preventing saltwater infiltration to the new outfall are surmountable.
However, all the studies and planning conducted to date lead MWRA
to conclude that there are few if any scenarios in which diversion of
effluent would serve the environmental interest of the bays and justify
the reintroduction of the discharge back into the shallow confined
waters of Boston Harbor. Therefore, MWRA does not identify
diversion as a potential corrective activity at this time. However,
during a significant environmental occurrence linked to the outfall,
and subject to EPA/DEP approval, MWRA is committed to
considering all viable corrective activities that serve to protect the
North Shore, Boston Harbor, and Massachusetts and Cape Cod Bays.
1.5 Contingency Plan
Organization
The Contingency Plan is organized into three primary areas:
(1) this introduction that discusses the reasons for and objectives of
the Contingency Plan and its relationship to the overall effort to
enhance and protect the marine and coastal environment; (2) three
sections that elaborate on this effort, including the specific details of
how the Contingency Plan will be implemented; and (3) one section,
considered the heart of the Contingency Plan, that discusses the
potential issues of concern that could emerge following operation of
the outfall, the trigger parameters and thresholds that will be used to
Contingency Plan Revision 1 - May 2001 5
determine whether significant environmental changes may be
occurring or might occur in the future, and the array of corrective
activities that could be potentially pursued in the event that significant
environmental changes attributable to the outfall are identified.
Contingency Plan Revision 1 - May 2001 6
Table 1-1 SUMMARY MATRIX
NUTRIENTS
Parameter
Type/Location Parameter Caution Level Warning Level
effluent total nitrogen 12,500 mtons/year 14,000 mtons/year
water column nearfield
bottom, Stellwagen
bottom
dissolved oxygen
(concentration) 1
6.5 mg/L for any survey during
stratification (June-Oct.) unless
background conditions are lower
6 mg/L for any survey during
stratification (June-Oct.) unless
background conditions are
lower
water column nearfield
bottom, Stellwagen
bottom
dissolved oxygen
percent saturation 1
80% saturation for any survey during
stratification (June-Oct.) unless
background conditions are lower
75% saturation for any survey
during stratification (June-Oct.)
unless background conditions
are lower
water column, nearfield
bottom
oxygen depletion rate 1.5 x baseline 2 x baseline
water column, nearfield chlorophyll 1.5 x baseline annual mean 2 x baseline annual mean
water column, nearfield chlorophyll 95th percentile of the baseline
seasonal distribution
-
water column, nearfield nuisance algae (except
Alexandrium )
95th percentile of the baseline
seasonal mean
-
water column, nearfield zooplankton 2 - -
water column, nearfield Alexandrium tamarense 3 100 cells/L -
water column, farfield PSP extent 4 new incidence -
sediments, nearfield redox potential
discontinuity
0.5 x baseline -
POTENTIAL CORRECTIVE ACTIVITIES
Advanced nitrogen removal; nitrification technologies; denitrification technologies
_______________________________
1 Included in Contingency Plan as an interim modification pursuant to Part I.8.d of the MWRA’s NPDES permit. MWRA will
develop by July 1, 2001, and submit to OMSAP for its review, a proposed statistical approach to calculate the 5 th - percentile of
background conditions, as recommended in Attachment A of EPA’s and MADEP’s April 3, 2001 letter. Following OMSAP
review, a final modification of the Caution and Warning Levels will be submitted by the MWRA to EPA and MADEP by
November 15, 2001 pursuant to Part I.8.c of the permit.
Contingency Plan Revision 1 - May 2001 7
2 The MWRA will report annually on appreciable changes to the zooplankton community in its Annual Water Column Report
and in the Outfall Monitoring Overview. The MWRA also will report to EPA, MADEP and OMSAP by December 31, 2002 on
the results of special zooplankton studies and evaluate whether a scientifically valid zooplankton community threshold can be
developed. The MWRA also makes every effort to participate in workshops to investigate food web pathways in Massachusetts
and Cape Cod bays sponsored by NOAA Fisheries.
3 Included in Contingency Plan as an interim modification pursuant to Part I.8.d of the MWRA’s NPDES permit. By August 1,
2001, the MWRA will submit for OMSAP review either the 100 cells/liter threshold or an alternative caution level threshold
value developed using a similar approach as recommended in Attachment A of EPA’s and MADEP’s April 3, 2001 letter.
Following OMSAP review, a final modification of the Caution Level will be submitted by the MWRA to EPA and MADEP by
November 15, 2001 pursuant to Part I.8.c of the permit. MWRA will also support a co-sponsored project in order to pursue
targeted monitoring of Alexandrium . This effort will be conducted by an appropriate entity, upon EPA and MADEP approval.
4 The MWRA is continuing to work on improvements to the calculation of this threshold as proposed in its October 13, 2000
letter to the EPA and MADEP.
Contingency Plan Revision 1 - May 2001 8
TOXIC CONTAMINANTS
Parameter
Type/Location Parameter Caution Level Warning Level
effluent chlorine - 631 ug/L maximum daily
456 ug/L average monthly
effluent PCBs PCB (as Arochlors) limit 0.000045
ug/L
lab test effluent toxicity - acute: effluent LC50 < 50% for
shrimp and fish; chronic:
effluent NOEC for fish growth
and sea urchin fertilization <
1.5%
water column, zone of
initial dilution
initial dilution - effluent dilution predicted by
EPA as basis for NPDES permit
sediments, nearfield toxics - NOAA Effects Range Median
sediment guideline
sediments, nearfield toxics 90% EPA sediment criteria EPA sediment criteria
fish tissue, outfall mercury 0.5 ug/g wet 0.8 ug/g wet
fish tissue, outfall PCB 1 ug/g wet 1.6 ug/g wet
fish tissue (mussel only),
outfall
lead 2 ug/g wet 3 ug/g wet
fish tissue, outfall lipid-normalized toxics 2 x baseline -
fish tissue (flounder only) liver disease incidence greater than harbor prevalence
over time
-
POTENTIAL CORRECTIVE ACTIVITIES
Enhance pollution prevention efforts; enhance removal of toxic contaminants during treatment
Contingency Plan Revision 1 - May 2001 9
ORGANIC MATERIAL
Parameter Type/Location Parameter Caution Level Warning Level
effluent cBOD - 40 mg/L weekly
25 mg/L monthly
POTENTIAL CORRECTIVE ACTIVITIES
Effluent filtration; organic polymer addition
HUMAN PATHOGENS
Parameter Type/Location Parameter Caution Level Warning Level
effluent fecal coliforms - 14,000 fecal coliforms/100 ml
POTENTIAL CORRECTIVE ACTIVITIES
Improve or change disinfection process
SOLIDS
Parameter Type/Location Parameter Caution Level Warning Level
effluent TSS - 45 mg/L weekly
30 mg/L monthly
sediments, nearfield benthic diversity appreciable change -
sediments, nearfield benthic
opportunists
10% 25%
POTENTIAL CORRECTIVE ACTIVITIES
Enhance solids removal during treatment
Contingency Plan Revision 1 - May 2001 10
FLOATABLES
Parameter Type/Location Parameter Caution Level Warning Level
effluent floatables 1 - -
effluent oil and grease
(petroleum)
- 15 mg/L weekly
POTENTIAL CORRECTIVE ACTIVITIES
Primary effluent screening; enhanced public educational programs
OVERALL PLANT PERFORMANCE
Parameter Type/Location Parameter Caution Level Warning Level
effluent plant performance 5 violations/year noncompliance 5% of the time;
pH <6 or >9 at any time;
flow >436 for an annual average
dry day
POTENTIAL CORRECTIVE ACTIVITIES
Revise Standard Operating Procedures
____________________________
1 Threshold value and sampling protocol to be developed by the MWRA by July 1, 2002 and submitted to OMSAP for its review,
and thereafter to EPA and MADEP for review and approval. Pending inclusion of a new threshold value in the Contingency
Plan, the MWRA will employ the following alternative measures: (i) MWRA will provide monthly reports of scum, fats, oil and
grease removal at the treatment plant; (ii) MWRA will record and report in the shift supervisor’s daily log any observations of
floatables, followed by review and correction of problems observed by operators. MWRA will make shift supervisor log sheets
available for EPA and DEP inspection on site; and (iii) MWRA will continue its ongoing program of monitoring and reporting
observations and recording of contents of net tows, complemented by visual inspection of the water recorded in field logs at the
nearfield outfall location in Massachusetts Bay during the 17 annual nearfield surveys.
Contingency Plan Revision 1 - May 2001 11
Section 2.0 Underlying Pollution Control Strategies
Overview MWRA’s commitment to identify proactively and respond to any
issues of concern related to the outfall is important. Equally important,
however, is its commitment to plan, design, and build facilities that
will protect the environment, to operate and maintain those facilities
as designed and to run an effective industrial pretreatment and
pollution prevention program.
2.1 Design of the
treatment plant and
outfall
The centerpiece of MWRA’s pollution control strategy is the
operation of the new secondary treatment plant and outfall.
Secondary treatment removes 85% of the solids, and reduces oxygen
consuming material by 85%. Secondary treatment will also
significantly enhance the removal of toxic contaminants.
The new plant has the capacity to meet secondary treatment
requirements for all dry weather flows and all but the most extreme
wet-weather events (rainfalls in excess of 1"). The average inflow to
the plant is 376 mgd while secondary can treat up to 540 mgd. During
a typical year, inflow exceeds 540 mgd for 30 days or less.
Consequently, the treatment plant has considerable built-in
redundancy that allows plant components and equipment to receive
preventive maintenance on a rotating basis, and should any part not be
operational for any reason, to be out of service for repair without
affecting plant performance. Table 2-1 shows the redundancy for each
major component of the plant (minimum redundancy refers to the
percent of operating units that may be out of operation without
impairing treatment capability during maximum flow conditions).
An effective outfall-diffuser system is equally important. One of the
most important considerations in designing the outfall was to
maximize the dilution achieved prior to reaching sensitive areas. The
new outfall does this by discharging effluent through a series of
discharge points (called diffusers), located a sufficient distance away
from critical habitats, beaches and shellfishing areas, in water that is
100-110 feet deep (Figure 2-1).
Studies by Professor Eric Adams at MIT have shown that most
pollutants from the old plant’s discharge of poorly treated sewage to
Boston Harbor eventually entered Massachusetts Bay due to tidal
currents.
Contingency Plan Revision 1 - May 2001 12
Moving the effluent discharge to its new location significantly
improves effluent dilution in western Massachusetts Bay (except in
the immediate vicinity of the diffusers) without significantly changing
the dilution elsewhere in the bays (see Figure 2-2) .
Dil
2.2 Treatment plant
operation and
maintenance
Effective operation and maintenance activities at the new treatment
plant are also critical. These activities are supported by sophisticated
process control and maintenance and tracking systems. With these
systems in place, operators have the ability to trigger an immediate
response to any emergency or disruption in the functioning of any
component of the plant. These systems will also allow operators to
watch longer term trends and refine operations to optimize plant
performance.
Operators at the plant are extensively trained in plant operations as
well as in emergency response. Plant personnel work closely with the
MWRA Toxic Reduction and Control (TRAC) Department to prepare
for and respond to the potential threat of an incoming hazardous spill
Contingency Plan Revision 1 - May 2001 13
2.3 Pollution
Prevention
to the treatment plant. Together with TRAC, plant personnel
periodically execute drills to ensure that they are adequately prepared
to handle such a spill.
While being prepared for and responding to a potential spill is an
important component of TRAC’s job, its primary mission is to
regulate the day-to-day use of the sewer system for pollutant disposal.
TRAC regulates the discharge of toxic pollutants from industries by
setting strict limits on the types and amounts of pollutants that may be
discharged to the sewer system; inspecting and issuing discharge
permits to more than 1,100 industrial sewer users and sampling their
wastewater; and taking enforcement actions against those sewer users
who violate their permit requirements.
TRAC also provides technical assistance to industrial sewer users on
methods of pollution reduction and prevention, and works
cooperatively with industry groups and residents on solutions to
difficult discharge problems. As a result of TRAC’s efforts, the
amount of metals in MWRA effluent has dropped dramatically since
1989 (see Figure 2-3).
Contingency Plan Revision 1 - May 2001 14
Figure 2-3
Metals in MWRA Treatment Plant Discharges 1989-2000
0
200
400
600
800
1000
1200
89 90 91 92 93 94 95 96 97 98 99 00
Average pounds per day discharged to Harbor Silver
Nickel
Chromium
Lead
Copper
Zinc
Contingency Plan Revision 1 - May 2001 15
Section 3.0 Outfall Monitoring Plan: the Foundation for the
Contingency Plan
Overview The Outfall Monitoring Plan provides the basis for evaluating
potential impacts associated with the relocated outfall and the need for
action under the Contingency Plan. The environmental parameters or
analyses included in the Outfall Monitoring Plan were selected to
measure the health/quality of the relevant environment. The results of
these measurements can be used to provide meaningful clues that
effluent quality of environmental conditions may be changing or
might be likely to change in the future. Certain of these parameters or
analyses have been designated in the Contingency Plan as “trigger
parameters.” Once discharge begins, the exceedance of trigger
parameter threshold values will automatically trigger MWRA action.
3.1 Monitoring plan
background, design
and objectives
The development of a monitoring program to establish baseline
conditions of the Massachusetts and Cape Cod Bay ecosystem and
measure any impacts on the system due to outfall relocation was
required by EPA in its 1988 SEIS Record of Decision. The Certificate
issued by the Massachusetts EOEA on the Secondary Treatment
Facilities Plan/Final Environmental Impact Report in 1988 contained a
similar requirement. MWRA developed the Outfall Monitoring Plan
with the help of the OMTF to collect data both before and after
discharges from the new outfall take place. It also includes effluent
sampling and testing required under the NPDES permit.
The Outfall Monitoring Plan focuses on six critical constituents in
treatment plant effluent:
• Nutrients
• Toxic contaminants
• Organic Material
• Pathogens
• Solids
• Floatables
These six constituents are evaluated within the context of four
different environmental measurement areas: Effluent, Water Column,
Sea Floor Environments, and Fish and Shellfish.
The primary objective of effluent monitoring is to measure the
concentrations and variability of chemical and biological constituents
in the effluent. Data for contaminants regulated by the NPDES permit
are analyzed and compared to the permit limits to determine
compliance; data for other contaminants are analyzed and compared to
Contingency Plan Revision 1 - May 2001 16
Water Quality Standards to determine if the levels continue to be
below concern, or if not, whether regulation may be required. Effluent
samples are collected twice monthly. Additional effluent samples are
also collected on an as-needed basis to supplement effluent
characterization.
Water column monitoring is designed to measure water quality and
plankton in Massachusetts and Cape Cod Bays. Water column
monitoring includes five major components: nearfield surveys, farfield
surveys, plume track surveys, continuous recording, and remote
sensing. Nearfield surveys are designed to provide vertical profiles of
physical, chemical and biological water column characteristics near
the outfall location. The purpose of farfield surveys is to determine
differences across the bays and assess seasonal changes over a large
area. Plume track surveys are performed to determine the location,
migration, and biological and chemical characteristics of the effluent
plume leaving the outfall and mixing with ambient waters. The
continuous recording component of the program captures temporal
variations in water quality between nearfield water quality surveys.
Continuous monitoring occurs at three depths at a single mooring
station near the future outfall location. Remote sensing captures
spatial variations in water quality on a regional scale.
Sea floor studies are designed to provide a means to document
recovery of Boston Harbor following the cessation of sludge discharge
and improvement in CSO treatment and discharge. The studies also
collect information needed to assess potential impacts of effluent
discharged from the new outfall on the surrounding sea floor
environment.
The fish and shellfish monitoring program evaluates potential risks to
human health and the environment arising from contamination of fish
and shellfish. Fish and shellfish monitoring is performed throughout
the harbor and the bays.
3.2 Trigger parameters
and thresholds
The environmental monitoring performed through the Outfall
Monitoring Plan provides the basis for evaluating the need for action
under the Contingency Plan. Those parameters and/or analyses which
have been identified as providing the most meaningful clues that
effluent quality or environmental conditions may be changing or
might be likely to change in the future have been designated in the
Contingency Plan as “trigger parameters." To alert MWRA to
different degrees of observed change, each trigger parameter has
thresholds that are defined as “ caution” or “warning” levels. In the
event that one of these thresholds is exceeded, an MWRA action will
be automatically triggered in response.
Contingency Plan Revision 1 - May 2001 17
“Caution level” exceedances indicate the need for increased study or
attention, along with the possible need for operational adjustments.
“Warning level” exceedances indicate the need to respond to avoid
potential environmental impact, triggering the development of a plan
and schedule for doing so (for more detail see Section 4,
“Contingency Plan Implementation.”)
If a trigger parameter’s value exceeds the warning level , this does not
necessarily mean that any environmental impact has occurred, but that
effluent quality or environmental conditions have moved sufficiently
far from the baseline that it would be prudent to respond in order to
prevent impact. In this event, MWRA would take action to return the
trigger parameter to a level, which is at or below the threshold
exceeded or else show that there is either no likelihood of harm or that
MWRA is not responsible for the exceedance. For example, if an
effluent threshold is exceeded, it is clearly MWRA’s responsibility to
examine the operation of the treatment plant. When a threshold
measured in Massachusetts or Cape cod Bay is exceeded, it indicates
that the environment is behaving in an unexpected way, but the effects
may or may not be significant and the causes may or may not involve
the MWRA.
MWRA has used the following sources and/or processes to establish
thresholds for the trigger parameters:
• Limits in the EPA/DEP NPDES permit
• State water quality standards
• Predictions made about the impacts of discharge during preparation
of EPA’s SEIS
• Guidance or expert opinion.
3.3 Other relevant
parameters
In addition to the trigger parameters, the monitoring program collects
information about numerous other related parameters, both in the bays
and from the treatment plant. These parameters do not have thresholds
as defined by the Contingency Plan, but are very useful for improving
our overall understanding of the bays, tracking the movement of
MWRA effluent, and for evaluating any threshold exceedances.
Temperature is an example of such a parameter.
Temperature measurements alone are unlikely to indicate the presence
or absence of environmental impact. But knowledge of a long, warm
summer combined with low dissolved oxygen concentrations in
bottom waters at the end of the summer would indicate that the low
dissolved oxygen is more likely due to an unusual weather pattern
rather than a response to treatment plant effluent.
Contingency Plan Revision 1 - May 2001 18
Section 4 Contingency Plan Implementation
Overview To ensure that the Contingency Plan provides appropriate
environmental protection, every step of the implementation process,
from creation and modification of the Contingency Plan document to
the development and implementation of a response to a threshold
exceedance, will be open to public input and review from outside
MWRA.
4.1 Annual reporting
and evaluation of the
Contingency Plan
As part of the Outfall Monitoring Overview report developed each
year, MWRA will include information relevant to the Contingency
Plan, including a summary of activities taken pursuant to the
Contingency Plan, and results relating to the trigger parameter
thresholds levels. If monitoring data has suggested that trigger
parameters or thresholds be added or modified, the report will propose
such changes. (See Figure 4-1).
4.2 Contingency Plan
actions
During the course of monitoring and preliminary lab analysis, if any
trigger parameter included in the Contingency Plan exceeds the
corresponding “caution” or “warning” level, MWRA’s first response,
even before the cause has been discovered, will be to notify Deer
Island staff and OMSAP, EPA, and MADEP, and to decide whether
plant operations can be adjusted to reduce the discharge of the relevant
pollutant.
If the threshold exceeded is a caution level, MWRA will also likely
expand its monitoring to closely track any change in effluent quality
and environmental conditions, and provide the information necessary
to:
• Evaluate the cause and effect of the exceedance; and
• Review applicable trigger parameters and thresholds for
necessary and appropriate revisions.
If a caution level exceedance is confirmed by OMSAP, it will be
reported in the next Quarterly Wastewater Performance Report
provided to the public, EPA and MADEP. Summaries of actions taken
or planned to evaluate the effect of and responsibility for the
exceedance or to adjust operations, will also be included in this and/or
subsequent Quarterly Wastewater Performance Reports.
If the threshold exceeded is a warning level, MWRA will:
• Determine whether there are any adverse environmental impacts
from the exceedance; and
• Evaluate the extent to which MWRA discharges contribute to
Contingency Plan Revision 1 - May 2001 19
any such impacts.
If a warning level exceedance is confirmed by OMSAP, it will be
reported in the next Quarterly Wastewater Performance Report
provided to the public, EPA and MADEP. A “Response Plan”
including (1) a plan and schedule for identifying and implementing
actions to address any impacts from the exceedance to the extent
caused by MWRA or (2) a demonstration of evidence that no adverse
impacts occurred from the exceedance and/or that MWRA discharges
did not contribute to such impacts, will also be included in this and/or
subsequent Quarterly Wastewater Performance Reports. In the event
MWRA action appears to be needed, such actions may range from
further adjustments in plant operations to an Engineering Feasibility
Study regarding specific engineering and/or construction-related
“corrective activities”, including any necessary treatment.
Contingency Plan Revision 1 - May 2001 20
Figure 4-1 Contingency Plan Flowchart
Section 5
Overview
Figure 5-1
Trigger Parameters, Thresholds and Potential
Corrective Activities
With the help of the OMTF, MWRA has identified six potential issues
of concern that could emerge following operation of the outfall. The
identification of these potential issues of concern, the trigger
parameters and thresholds that will be used to determine whether
changes in effluent quality and/or environmental conditions may be
occurring or might occur in the future, and the array of potential
corrective activities that could be potentially pursued in the event that
significant environmental changes attributable to the outfall are .
identified, form the heart of the Contingency Plan. Following each
subsection is a table summarizing the trigger parameters and
associated thresholds identified below. Figure 5-1 shows the locations
referred to in the summary tables.
MWRA sampling stations in Massachusetts and Cape Cod Bays
Stellwagen Bank
Massachusetts Bay
Cape Codfay x
x“
x“
x MWRA water column stations. 40 meter depth contour
Contingency Plan Revision 1 - May 2001 21
Contingency Plan Revision 1 - May 2001 22
5.1 Nutrients
5.11 Water quality
issues
Nutrients are necessary for the growth of all plants, aquatic and
terrestrial. The amount of nutrients in the water, along with several
other factors, controls the growth of aquatic plants, including algae.
Since algae are the foundation of the marine food web, nutrients have
a great effect on how much life a marine ecosystem can support. In
particular, there are two basic ways in which nutrients from MWRA
effluent could have a negative effect on marine environments: through
the effects of algae on dissolved oxygen concentration and through
changes in algal community structure . Nitrogen is the nutrient of
greatest concern. These issues are explained below.
Low Dissolved Oxygen (Hypoxia). An algal bloom is a burst of algal
growth, which occurs when a variety of conditions come together.
Sufficiently high nutrient levels is one of the requirements, but other
conditions such as sunlight and temperature are also important. Algal
production is the basis of the food web, without which fish, whales,
and most other marine life would not survive. Algal production is a
necessary, common occurrence in the marine environment, but it can
be a cause for concern, depending on the intensity, frequency, and
type of algae produced.
If a body of water receives too great a nutrient load, it may become
subject to eutrophication: over-stimulation of algal growth and
excessive algal blooms. When algae grow faster than they are
consumed, the excess algae die, sink to the bottom, and decompose.
Decomposition of organic material consumes dissolved oxygen (DO).
DO is oxygen dissolved in water and available to marine animals for
respiration. If DO concentrations are low (a condition known as
hypoxia), sensitive animals may suffocate. Hypoxia can occur when
the DO demand of decomposition outstrips natural resupply. The
resulting deficit is measured as the oxygen depletion rate, which
describes how quickly DO concentration drops.
Algal Community Structure (Growth of Undesirable Algae). Adding
effluent to the marine environment could change the amount of
nutrients or the relative levels of different nutrients so that undesirable
algae dominate or are present along with useful algae. The nutrient
composition of effluent is different from that in Massachusetts Bay,
and there is public concern that undesirable algae may be better able
to take advantage of this difference than desirable algae. Two types of
undesirable algae can have direct effects on the marine environment:
nuisance algae, such as brown tides, affect the appearance of the
water; noxious algae, such as red tides, are toxic to marine mammals
Contingency Plan Revision 1 - May 2001 23
and some fish, and, if concentrated in shellfish, to humans.
Undesirable algae can also have an indirect effect on the marine
environment by out-competing another algae species. If the out-
competed species is a primary food source for a marine animal, that
animal may suffer. For instance, it has been suggested that the food
chain links right whales in Cape Cod Bay to a kind of algae that might
be impacted by effluent-induced changes in nutrient concentrations.
Nitrogen Control. For Massachusetts Bay, the solution to both types
of potential nutrient problems, hypoxia and undesired algal species,
may be nitrogen control. According to the best available scientific
knowledge about algal blooms, nitrogen is the nutrient that has the
greatest effect on algal growth in marine waters. Thus, if algal blooms
lead to hypoxia, reduction of nitrogen discharge is probably an
effective remedy. Likewise, studies have shown that the risk of
undesired changes in algal community structure becomes significant if
there is too much nitrogen relative to the amount of phosphorus or
silica (silica is another nutrient, like nitrogen and phosphorus).
Because adding phosphorus could have negative side effects, reducing
the nitrogen load is probably the best option for controlling undesired
algal species.
5.12 Trigger
parameters and
thresholds
To observe and understand the effects of nutrients in Massachusetts
and Cape Cod Bays, the MWRA monitors eutrophication and hypoxia
events, oxygen depletion rate, nuisance and noxious algae growth, and
nutrient concentrations in MWRA effluent and the bays. So far, the
MWRA has developed quantitative caution and warning levels for
trigger parameters based on nitrogen, dissolved oxygen, chlorophyll,
and nuisance/noxious algae.
Effluent parameters/
thresholds
Nitrogen. Because nitrogen is the most important nutrient to monitor
when discharging effluent to marine waters, MWRA tests treatment
plant effluent for the concentration of total nitrogen. Assuming certain
loadings of nitrogen from the effluent, the SEIS predicted little or no
impact from the outfall discharges. These predictions were verified
using more sophisticated three-dimensional water quality models.
Caution and warning levels have been set to verify that the loads
assumed in those predictions (14,000 tons/year total nitrogen) are not
exceeded.
Water column
parameters/
thresholds
Dissolved Oxygen: When DO is too low, there may not be enough
oxygen for animals to breathe. Because of DO’s importance, the state
has set a water quality standard that DO should not fall below 6 mg/L
and 75% saturation unless background conditions are lower in
Massachusetts Bay. MWRA is using these standards as the basis for
caution and warning levels.
Contingency Plan Revision 1 - May 2001 24
Oxygen Depletion Rate. There are limitations to the conclusions that
can be drawn from DO concentration data, since many of the factors
that cause low DO are independent of MWRA influence (e.g.
weather). Oxygen depletion rate is a more direct measure of MWRA
impact than DO, because it is less dependent on weather patterns.
Furthermore, a high oxygen depletion rate is a good predictor of future
hypoxia, even if DO concentrations are presently healthy.
As there are no state or federal regulations regarding oxygen depletion
rate, MWRA thresholds have been developed to indicate a degree of
change from the baseline established by MWRA monitoring since
1992 under the Outfall Monitoring Plan.
Chlorophyll. Chlorophyll, a photosynthetic chemical in all green
plants, is the most common measure of algal biomass, the total
amount of algae present in the water. Since algal blooms are sudden
increases in algal biomass, chlorophyll is a good measure of algal
blooms and thus eutrophication. As described above, eutrophication is
partially dependent on nutrient loads and can lead to hypoxia. Algal
biomass is central to understanding the effect of nutrients on bay
water quality, because of its intermediary position between nutrient
loading and hypoxia. Thus, chlorophyll is a good indicator of future
hypoxia.
Unlike low DO concentrations, high chlorophyll does not necessarily
mean that there is environmental degradation. The risk that high
chlorophyll concentrations will lead to hypoxia depends on the rate of
oxygen resupply. Although chlorophyll is not directly linked to DO, it
is a good measure of the overall health of an ecosystem.
Consequently, some of the following thresholds have broader
applicability than merely as hypoxia identifiers.
As there are no state or federal regulations for chlorophyll, MWRA
thresholds are based on predictions in the SEIS and compared to the
National Oceanographic and Atmospheric Administration’s Estuarine
Eutrophication Survey (NOAA, 1993). The thresholds are designed to
identify two types of problems: high annual average algal biomass
after outfall start-up and increased algal biomass in any one season.
Because algal biomass (and thus chlorophyll concentrations) are
highly variable, meaningful change is best represented as averages or
percentiles over time and space. Chlorophyll- a is the type of
chlorophyll measured in the EPA approved standard test for
chlorophyll and adopted by the MWRA.
According to the National Oceanographic and Atmospheric
Administration (NOAA), “normal blooms become problematic when
Contingency Plan Revision 1 - May 2001 25
chlorophyll-a values reach 20 μ g/Liter” (ORCA, 1993). Baseline
concentrations of chlorophyll-a average about 2-3 μ g/Liter, well
before there is a likelihood of biological significance. The warning
level was based on peer review comments to the Outfall Monitoring
Task Force.
Nuisance/Noxious Algae: Nuisance and noxious algae are present in
Massachusetts and Cape Cod Bays annually in small numbers. There
is public concern that effluent nutrients could feed a red tide bloom in
the vicinity of the new outfall. At the 1996 peer review workshop, it
was recommended that the Massachusetts shellfish toxicity
monitoring program be used to set red tide caution levels. The state
program monitors the toxicity of Paralytic Shellfish Poisoning (PSP)
at shellfish beds along the edge of Massachusetts and Cape Cod Bays.
In addition, if the seasonal abundance of Alexandrium,
Pseudonitzchia, or Phaeocystis becomes unusually high, a threshold
will be triggered.
Sea floor parameters/
thresholds
Depth of Oxygenated Sediments. Although often overlooked, oxygen
in the sediments is also a very important measure of environmental
health. If not enough oxygen has penetrated into the sediments, it is
difficult for animals to live in the sediments. Although there is no state
standard, the MWRA has developed a sediment oxygen warning level
based on the depth of oxygen penetration. The depth to which oxygen
penetrates sediments is also an important measure of organic material
discharge and is measured as the Redox Potential Discontinuity
(RPD). The RPD depth is the location where the sediments changed
from oxic to anoxic. The threshold refers to stable stations, which are
those where storms have not markedly changed the sediment texture
from year to year.
Contingency Plan Revision 1 - May 2001 26
Table 5-1
NUTRIENTS
Parameter
Type/Location Parameter Caution Level Warning Level
effluent total nitrogen 12,500 mtons/year 14,000 mtons/year
water column nearfield
bottom, Stellwagen
bottom
dissolved oxygen
concentration 1
6.5 mg/L for any survey during
stratification (June-Oct.) unless
background conditions are lower
6 mg/L for any survey during
stratification (June-Oct.) unless
background conditions are
lower
water column nearfield
bottom, Stellwagen
bottom
dissolved oxygen
percent saturation 1
80% saturation for any survey during
stratification (June-Oct.) unless
background conditions are lower
75% saturation for any survey
during stratification (June-Oct.)
unless background conditions
are lower
water column, nearfield
bottom
oxygen depletion rate 1.5 x baseline 2 x baseline
water column, nearfield chlorophyll 1.5 x baseline annual mean 2 x baseline annual mean
water column, nearfield chlorophyll 95th percentile of the baseline
seasonal distribution
-
water column, nearfield nuisance algae (except
Alexandrium )
95th percentile of the baseline
seasonal mean
-
water column, nearfield zooplankton 2 - -
water column, nearfield Alexandrium tamarense 3 100 cells/L -
water column, farfield PSP extent 4 new incidence -
sediments, nearfield redox potential
discontinuity
0.5 x baseline -
POTENTIAL CORRECTIVE ACTIVITIES
Advanced nitrogen removal; nitrification technologies; denitrification technologies
___________________________________________
1 Included in Contingency Plan as an interim modification pursuant to Part I.8.d of the MWRA’s NPDES permit. MWRA will
develop by July 1, 2001, and submit to OMSAP for its review, a proposed statistical approach to calculate the 5 th - percentile of
background conditions, as recommended in Attachment A of EPA’s and MADEP’s April 3, 2001 letter. Following OMSAP
review, a final modification of the Caution and Warning Levels will be submitted by the MWRA to EPA and MADEP by
November 15, 2001 pursuant to Part I.8.c of the permit.
2 The MWRA will report annually on appreciable changes to the zooplankton community in its Annual Water Column Report
and in the Outfall Monitoring Overview. The MWRA also will report to EPA, MADEP and OMSAP by December 31, 2002 on
the results of special zooplankton studies and evaluate whether a scientifically valid zooplankton community threshold can be
developed. The MWRA also makes every effort to participate in workshops to investigate food web pathways in Massachusetts
and Cape Cod bays sponsored by NOAA Fisheries.
Contingency Plan Revision 1 - May 2001 27
3 Included in Contingency Plan as an interim modification pursuant to Part I.8.d of the MWRA’s NPDES permit. By August 1,
2001, the MWRA will submit for OMSAP review either the 100 cells/liter threshold or an alternative caution level threshold
value developed using a similar approach as recommended in Attachment A of EPA’s and MADEP’s April 3, 2001 letter.
Following OMSAP review, a final modification of the Caution Level will be submitted by the MWRA to EPA and MADEP by
November 15, 2001 pursuant to Part I.8.c of the permit. MWRA will also support a co-sponsored project in order to pursue
targeted monitoring of Alexandrium . This effort will be conducted by an appropriate entity, upon EPA and MADEP approval.
4 The MWRA is continuing to work on improvements to the calculation of this threshold as proposed in its October 13, 2000
letter to the EPA and MADEP.
Contingency Plan Revision 1 - May 2001 28
5.13 Potential
corrective activities
On a long-term basis, if there were nutrient-related concerns related to
MWRA effluent, the most probable response would be to increase
nitrogen removal during treatment. As described below, there are a
variety of nitrogen removal techniques that could be undertaken to
address potential long-term concerns, each with advantages and
disadvantages. As technology changes, these options may vary. As
opportunities regarding watershed management initiatives are refined
or developed, MWRA could also participate in discussions regarding
options for basin-wide control of nitrogen, including loads from rivers
and land areas in Massachusetts Bay and the Gulf of Maine.
Advanced treatment nitrogen removal. In the unlikely event that a
long-term problem makes a permanent reduction in nitrogen loading
necessary, the MWRA could implement advanced treatment nitrogen
removal. Advanced treatment nitrogen removal represents the removal
of nitrogen from wastewater through biological, chemical, or physical
processes beyond those used in conventional primary and secondary
treatment. For long-term nitrogen removal on the scale MWRA would
require, chemical and physical removal are not viable, however
biological removal could be considered.
In biological nitrogen removal, microorganisms in the treatment plant
convert and eliminate nitrogen in the wastewater before it is made
available to algae in the receiving water. Nitrogen removal is achieved
by transforming ammonia (NH3) into nitrogen gas (N2), which is inert
and harmless. The transformation is achieved in two steps:
1) the process of nitrification oxidizes nitrogen from ammonia to
nitrate (NO3);
2) the process of denitrification reduces nitrogen from nitrate to
nitrogen gas. Denitrification requires the addition of a food
source which leads to increased solids removal and sludge
production.
The basic idea behind nitrification and denitrification systems is to
provide the best possible environment for concentrating the growth of
microorganisms that consume nitrogen. The nitrification process
would occur within expanded aeration tanks (part of the secondary
treatment process) or in separate aerated filters. Nitrification is an
aerobic (with oxygen) process that operates best with air aeration (as
opposed to pure oxygen) and the addition of lime to maintain appro-
priate pH. Denitrification could take place in new treatment facilities
built on the remaining unoccupied areas of Deer Island. It is an
anaerobic (without oxygen) process and requires the addition of
methanol to provide sufficient substrate for the denitrifying
Contingency Plan Revision 1 - May 2001 29
organisms.
Most modern nitrification and denitrification processes are separate
treatment units. Thus, almost any nitrification process can be matched
with almost any denitrification process. If the MWRA were to
implement nitrogen removal, it would choose one nitrification method
followed by one denitrification method. The MWRA has studied
numerous alternatives, including both proven and developing
technologies. The alternatives vary in the levels of effluent quality
attained, the area of land required, capital cost, operations and
maintenance cost, and ease of addition to the existing plant. MWRA
has considered technologies that provide maximum reliability while
meeting space and cost constraints. The technologies are differentiated
by the way they encourage growth of the appropriate microorganisms.
Nitrification Technologies: Suspended growth nitrification would
require two major modifications of the Deer Island Treatment Plant.
The first major modification would be addition of Chemically
Enhanced Primary Treatment (CEPT). In the CEPT process, the
addition of chemicals such as ferric chloride and polymers enhances
the settling and removal of suspended wastewater particles (TSS) and
organic material (BOD), but not nitrogen. With less TSS and BOD
entering the aeration tanks, there would be fewer non-nitrifying
microorganisms and more room for nitrifying microorganisms. The
second major modification would be addition of systems to aeration
tanks that would increase the surface area available for microorganism
growth. These systems include biomass carriers (highly porous
polyurethane foam pads), fiber-media systems (polyvinyl chloride
ropes), and the moving bed biofilm reactor (10 mm long cylinders
with an internal frame structure). In the event that these modifications
were not sufficient, additional facilities, such as those described
below, would be necessary.
The biological aerated filter (BAF) system is the most common
current approach to fixed material attached nitrification. BAF consists
of a stationary bed of medium (e.g. aluminum silicate, expanded shale,
or polystyrene) through which wastewater flows up or down,
depending on the media. Air is injected from the bottom of the
medium. Periodic backwashing of the filters is required to reduce
solids accumulation in the tanks. BAF is used in approximately 100
full-scale facilities in Europe, Japan, and Canada.
Fluidized-bed reactors are similar to BAFs, often using sand as the
medium. The primary difference is that wastewater is introduced from
the bottom of the bed at sufficient velocity to separate very slightly
(“fluidize”) the individual grains of medium. As a result, there is
Contingency Plan Revision 1 - May 2001 30
increased surface area for microorganism growth, and the granular
media does not need backwash cleaning. Granular medium must be
replenished at 5% per year. Excess microorganisms are continuously
drawn off the top of the fluidized portion of the tank. Fluidized-bed
reactors are in the development stage for nitrification, but are widely
used for denitrification (see below).
Denitrification Technologies: Denitrification systems are physically
similar to nitrification systems, except that denitrification is anaerobic
(occurs in the absence of oxygen) and requires an additional carbon
food source (generally provided by methanol). Packed bed reactors
are similar to BAF. To exclude oxygen from the filter bed, the
medium is fully submerged. In general, backwashing must be carried
out on a weekly basis to remove solids and nitrogen gas. The medium
provides some physical filtration, which improves overall effluent
quality. Packed bed reactors are also relatively simple to operate.
Fluidized-bed reactors are one of the most space-efficient means of
denitrification, an important consideration for Deer Island. However,
fluidized bed reactors are particularly sensitive to changes in the
amount of methanol added. Deep-bed filters are similar to packed
bed reactors, except that the media is coarser and the filter is
backwashed briefly about five times per day.
Using current technologies, MWRA’s recommended approach would
be to use BAF for nitrification and fluidized bed reactors for
denitrification. These treatment facilities could be fit in to the site of
the Deer Island Treatment Plant. However, if technological
advancements continue, suspended growth or fluidized bed reactors
may prove to be better options for the nitrification step. These
emerging technologies and improvements to existing technologies will
probably be more effective, less land intensive, more reliable, and less
costly than anything that is currently available.
5.14 Important
considerations
One of the issues that must be addressed before designing and
implementing nitrogen removal hinges on the timing of algal blooms.
The time of year that nitrogen removal is needed has a large effect on
the sizing of a treatment facility. Biological nitrogen removal
processes are highly sensitive to temperature, functioning better in
warm weather than in cold weather. Although nitrogen concentration
does not significantly affect algal growth in winter, it can be important
as early as February, when wastewater temperature is at its annual
lowest point. Consequently, MWRA studies of potential nitrogen
removal systems to date consider it likely that year-round nitrogen
removal would be most useful, if any removal were needed. However,
if nitrogen reduction were necessary only in the warmer months, the
appropriate facility size could be smaller and the appropriate treatment
Contingency Plan Revision 1 - May 2001 31
method could be different than that required for year-round treatment.
Typically, dissolved oxygen concentrations are lowest in August to
October; red tides are most common in May and June.
The amount of nitrogen removal needed is another important consid-
eration. Most of the nitrogen removal systems studied by MWRA
perform most efficiently when reducing total nitrogen to 3 to 4 mg/L
in effluent. If, however, nitrogen concentration could be higher than 4
mg/L, it would be possible to provide nitrogen removal facilities for
less than the entire flow. The required effluent quality would be
achieved by blending secondary effluent with denitrified effluent. The
capital construction, operation, and maintenance costs of reduced flow
options would be significantly lower than the costs of full flow treat-
ment. Changes in the amount of water entering the sewage collection
system would also affect sizing of nutrient removal facilities.
While some interested groups have suggested that nitrogen removal be
included in the treatment facilities currently being constructed,
choosing and designing nitrogen removal facilities at this time would
probably not help the environment since scientific evidence provided
by both the MWRA and the EPA suggests very strongly that nitrogen
from MWRA effluent will not impact Massachusetts Bay. Moreover,
nitrogen removal is still a developing technology and other, more
cost-effective ways to reduce loadings on a watershed-wide basis may
develop in the future. Should new evidence come to light and
demonstrate a need for reducing MWRA nitrogen loads to the bay,
MWRA can use the information summarized above to expedite the
planning process. The first step would be to choose a treatment option,
but this choice cannot be made without knowing the specific nitrogen
impacts to be prevented or remediated.
Nitrogen removal systems are being developed and improved
worldwide. MWRA monitoring is leading to a better understanding of
Massachusetts and Cape Cod Bays. However, the best information
about the effect of the new outfall will come when the new outfall
goes on line. The nitrification and denitrification options discussed
represent the best available technologies at the time (1997), but
MWRA is monitoring the development of a variety of other
technologies.
Contingency Plan Revision 1 - May 2001 32
5.2 Toxic Contaminants
5.21 Water quality
issues
Toxic contaminants are substances that can cause diseases such as
cancer through direct contact with or accumulation in living tissue.
Generally, toxic contaminants are harmless or may even be necessary
for marine life at very low concentrations, but are harmful at higher
concentrations. The concentration at which a toxic contaminant
becomes harmful changes depending on whether exposure is constant
(chronic) or temporary (acute). These substances will be referred to in
this report as “toxic contaminants” whether or not they are at harmful
concentrations in the specific instance.
Chronic impact of toxic contaminants in the marine environment is
most likely to be felt by filter feeders like mussels and bottom
dwellers like flounder. Mussels filter toxic contaminants out of the
water and into their tissue, which inhibits growth and reproductivity.
Flounder suffer increased incidences of fin rot and liver disease when
in contact with high levels of toxic contaminants in their food or in
sediments. As these contaminants are passed up the food chain,
humans who eat contaminated fish and shellfish may increase their
risk of cancer and other diseases.
Acute marine impact is greatest on passively floating plants and
animals, including fish larvae, invertebrate larvae, and algae. These
may die if they come into contact with high concentrations of certain
toxic contaminants.
MWRA’s goal is to reduce the concentrations of toxic contaminants in
the effluent so that with the initial dilution from the discharge, the
receiving water is not negatively impacted. The most effective method
is to prevent toxic contaminants from entering the waste stream by
requiring or encouraging reduction in the use of products containing
toxic contaminants and by properly disposing of toxic contaminants
when they must be used. As described in Section 2, “Underlying
Pollution Control Strategies,” MWRA is aggressively pursuing this
approach.
There is always the potential for toxic contaminants entering the
MWRA system from illegal dumping. Changes in products, such as
household cleaners, and new industries may also have unanticipated
effects on the wastewater that enters the MWRA collection system. It
is for these types of contingencies that the MWRA has developed the
caution and warning levels discussed below.
Chlorine from MWRA wastewater treatment is also a possible source
of toxicity, but because it is used for disinfection, it is discussed in the
Contingency Plan Revision 1 - May 2001 33
Pathogens Section. Ammonia is another possible source of toxicity,
and it would be identified through the toxicity tests discussed below.
Because ammonia is a form of nitrogen, the appropriate ways to
reduce ammonia discharge are those described for nutrients.
5.22 Trigger
parameters and
thresholds
MWRA is able to identify changes in the toxic contaminants entering
into the MWRA system and in the treatment plant’s removal of toxic
contaminants, by monitoring the amounts of toxic contaminants that
go into and out of the treatment system. MWRA also monitors the
effect of those contaminants once they reach the marine environment.
Effluent parameters/
thresholds
Priority Pollutant Concentration and Effluent Toxicity. As required
by the EPA, the MWRA tests wastewater treatment plant influent and
effluent directly for all 126 EPA priority pollutants. Priority pollutants
are substances that the EPA has determined to be of national concern
because of their toxicity at certain concentrations.
In developing an NPDES permit for MWRA, EPA and the state set
limits for the concentrations of priority pollutants in the effluent that
have a reasonable potential to violate water quality standards which
have been established by Massachusetts for state waters. NPDES toxic
contaminant limits are based on water quality standards and very
protective assumptions about water conditions within the effluent/sea
water mixing zone such as background contamination, extent of
dilution and mixing, depth of discharge, currents, tides, winds and
temperature. The mixing zone is the small volume (approximately 200
feet from each diffuser) around the outfall in which initial, turbulent
mixing of effluent with seawater takes place. The limit for chlorine in
the new NPDES permit will serve as the warning level for effluent
toxic contaminant concentrations.
In addition to concentration-based tests, the NPDES permit may also
require the use of laboratory-based tests known as bioassays.
Bioassays measure the response of indicator species such as shrimp to
toxicity in the effluent under specified laboratory conditions.
Bioassays designed to assess acute toxicity are expressed in measure-
ment units known as “LC50s." An LC50 is the concentration of
effluent at which 50% of a shrimp population survives. For example,
an LC50 of 60 means that half the shrimp survived a mixture that was
60% effluent and 40% dilution water. An LC50 limit of 45 means that
the effluent concentration cannot be more than 45% for half the
shrimp to survive. To assess chronic toxicity, the MWRA measures
the effluent's “No Observed Effects Concentration (NOEC)." The
NOEC is the highest concentration of effluent at which there is no
statistical difference in test organism response when compared against
a control with no effluent.
Contingency Plan Revision 1 - May 2001 34
Water column
parameters/ thresholds
Initial Dilution and Marine Chronic Water Quality. Since all
evaluations of toxic impacts depend on concentrations after initial
mixing, the MWRA will measure both the actual dilution of effluent
by seawater around the new outfall and the concentrations of
representative toxic contaminants and toxic contaminants most likely
to cause problems. The results will be compared with EPA predictions
of effluent dilution/contaminant concentrations. Because EPA’s
estimates are very conservative, it is extremely unlikely that actual
dilution will be less than EPA’s prediction. However, if the study
showed that real dilutions were less than anticipated and therefore did
not reduce toxic contaminant concentrations enough to protect the
environment, the EPA and the state could revise the MWRA’s
NPDES permit by lowering allowable discharge concentrations for
toxic contaminants.
Sea floor parameters/
thresholds
Toxic Concentrations in Sediments. As part of an ongoing
monitoring program, the MWRA will study the effect of the outfall on
sediments in the area around the outfall. The results from this study
will be used to assess the validity of the prediction that deposition of
sediments in the vicinity of the outfall will not be significant and will
not lead to toxic contamination of the sea floor. Thresholds for toxic
contamination of sediments are tied to EPA sediment criteria currently
at the draft stage and will reflect any changes adopted by those
agencies.
Fish and shellfish
parameters/ thresholds
Mercury Concentration, PCB Concentration, Lead Concentration,
and Liver Disease. The bottom line of environmental impact is the
effect on species in the habitat. To track the chronic environmental
impact of toxic contaminants from MWRA effluent discharged
through the new outfall, the MWRA studies flounder, lobsters, and
mussels in Boston Harbor, at the site of the new outfall, and in Cape
Cod Bay (lobsters and flounder only). The MWRA measures the
concentrations of a variety of toxic contaminants in animal tissue. It
also determines the incidence of diseases associated with toxic
contamination, including liver disease in flounder and black gill
disease in lobster.
These measurements currently show that toxic contamination of
marine life is greatest in the harbor, less at the new outfall site, and
much less in Cape Cod Bay. When effluent is discharged through the
new outfall, contamination is expected to decrease in the harbor, stay
roughly the same at the new outfall site, and be unchanged in Cape
Cod Bay. Thresholds are designed to identify unexpected effects on
marine life. Except for lead, the caution levels are 50% of U.S. Food
and Drug Administration (FDA) Action Limits; the warning levels are
Contingency Plan Revision 1 - May 2001 35
80% of FDA Action Limits. Lead thresholds are based on EPA risk
assessment of lead in drinking water. There are also thresholds based
on predictions of liver disease prevalence in fish and shellfish. The
thresholds apply to the new outfall site.
5.23 Potential
corrective activities
There are two ways to reduce the effect of MWRA toxic
contaminants in Massachusetts Bay: (1) further reduce toxic
contaminants from entering the MWRA system and (2) increase the
removal of toxic contaminants from wastewater during treatment.
These corrective activities are discussed below.
Enhance Pollution Prevention Efforts. If toxic contaminant
concentrations in effluent were too high even though the treatment
plant was operating properly, efforts to enhance pollution prevention
would be the appropriate response. If the responsible sources were
already regulated for the toxic contaminant, MWRA could reinforce
existing activities and review discharge limits. If the source were
previously unregulated (because the toxic contaminant or its existing
concentrate had not been identified as harmful), MWRA could target
the source and issue sewer discharge permits with specific limits or
management practices for the pollutant of concern in order to reduce
the entry of toxic contaminants into the sewer. MWRA regularly
works with industries and businesses to improve pretreatment and
source reduction programs. MWRA has a strong incentive to reduce
the amount of toxic contaminants entering its system, because toxic
contaminants may end up in MWRA sludge, jeopardizing the
MWRA’s ability to market the sludge as fertilizer pellets.
Enhance Removal of Toxic Contaminants During Treatment. There
are a variety of options for removing toxic contaminants after
secondary treatment. They focus on increasing removal of solids from
effluent, because most toxic contaminants attach to solids. Low doses
of organic polymers enhance the settling rate of solids. As organic
polymer technology develops, it has seen increasing use in the
wastewater treatment industry. As part of its design of secondary
treatment, the MWRA is including the capability of organic polymer
addition. Effluent filtration, a more long-term option, essentially
filters fine solids from the effluent before it goes to the outfall tunnel.
The filters catch some suspended solids, thus removing the toxic
contaminants attached to them. There are also removal methods that
use bacteria to break down some toxic contaminants. Activated
carbon, another option, removes soluble organic material that escapes
biological treatment systems. Activated carbon could be placed either
in secondary treatment tanks or in effluent filtration facilities. All of
these options are very expensive and would generate significant
additional sludge.
Contingency Plan Revision 1 - May 2001 36
Table 5-2
TOXIC CONTAMINANTS
Parameter
Type/Location Parameter Caution Level Warning Level
effluent chlorine - 631 ug/L maximum daily
456 ug/L average monthly
effluent PCBs PCB (as Arochlors) limit 0.000045
ug/L
lab test effluent toxicity - acute: effluent LC50 < 50% for
shrimp and fish; chronic:
effluent NOEC for fish growth
and sea urchin fertilization <
1.5%
water column, zone of
initial dilution
initial dilution - effluent dilution predicted by
EPA as basis for NPDES permit
sediments, nearfield toxics - NOAA Effects Range Median
sediment guideline
sediments, nearfield toxics 90% EPA sediment criteria EPA sediment criteria
fish tissue, outfall mercury 0.5 ug/g wet 0.8 ug/g wet
fish tissue, outfall PCB 1 ug/g wet 1.6 ug/g wet
fish tissue (mussel only),
outfall
lead 2 ug/g wet 3 ug/g wet
fish tissue, outfall lipid-normalized toxics 2 x baseline -
fish tissue (flounder only) liver disease incidence greater than harbor prevalence
over time
-
POTENTIAL CORRECTIVE ACTIVITIES
Enhance pollution prevention efforts; enhance removal of toxic contaminants during treatment
Contingency Plan Revision 1 - May 2001 37
5.3 Organic Material
5.31 Water quality
issues
Organic matter in effluent consumes dissolved oxygen (DO) as it
decomposes. As described in the Nutrients Section, low DO
concentrations may suffocate sensitive animals. Secondary treatment
is designed so that the majority of decomposition takes place in a
treatment plant rather than in the environment.
5.32 Trigger
parameters and
thresholds
Water quality models show that as long as the NPDES permit criteria
are met, organic materials in effluent from the new treatment plant
will not cause DO problems. The new secondary plant is currently
performing well within the NPDES limits. The standard measures of
the amount of oxygen consumed by decomposing organic material are
biochemical oxygen demand (BOD), and a closely related measure,
carbonaceous biochemical oxygen demand (cBOD) which provides
more consistent measurements of organic material than BOD.
Effluent parameters/
thresholds
cBOD. MWRA will monitor secondary effluent to see that treatment
is removing the proper amount of organic material by measuring
cBOD. The NPDES permit includes limits for cBOD as part of
mandated secondary treatment standards under the Clean Water Act,
and the limits have been incorporated into the contingency plan.
In addition, the caution and warning levels for dissolved oxygen
described in the Nutrients Section also apply to organic material.
Table 5-3
ORGANIC MATERIAL
Parameter Type/Location Parameter Caution Level Warning Level
effluent cBOD - 40 mg/L weekly
25 mg/L monthly
POTENTIAL CORRECTIVE ACTIVITIES
Effluent filtration; organic polymer addition
5.33 Potential
corrective activities
In the unlikely event that the designed treatment plant does not
provide sufficient removal of organic material, MWRA could
implement advanced treatment, which is discussed as a response for
toxic contaminants in the previous Section. Effluent filtration and
organic polymer addition are the advanced treatment processes most
applicable to organic material removal from the effluent.
Contingency Plan Revision 1 - May 2001 38
5.4 Human Pathogens
5.41 Water quality
issues
Human pathogens are bacteria and viruses that cause disease in
humans. The term “pathogens” in this section refers only to human
pathogens found in MWRA wastewater. Pathogens come from human
and animal waste and are found at unsafe concentrations in
wastewater that has not been properly disinfected. A properly
operating disinfection facility reduces pathogen concentrations to low,
safe levels. This section addresses the concern that pathogens may be
discharged through the new outfall at concentrations that could
adversely affect the health of humans and marine life. It also considers
the concern that chlorination of wastewater to kill pathogens may
cause residual toxicity in effluent. (The possibility of nutrients in
MWRA effluent encouraging the growth of pathogens already in the
marine environment is considered in Section 5.1, “Nutrients”).
Pathogens from wastewater come into contact with humans via
consumption of raw or inadequately cooked shellfish or swimming in
affected areas. Shellfish filter pathogens out of water and into their
tissues. Although pathogens do not harm shellfish, they can affect
people who eat contaminated shellfish. Pathogens can also affect
people who ingest contaminated water, which is primarily a problem
in swimming areas. Like most other pollutants, pathogens are only a
problem if they are present above certain concentrations. Regular
MWRA disinfection before discharge reduces effluent pathogen
concentrations below harmful levels. Combined sewer overflows,
stormwater, and illegal discharge of waste from boats are much more
significant sources of pathogens. Nonetheless, it is prudent to consider
the effect of chlorination failure and the resulting elevated pathogen
concentrations on swimming and shellfish.
Pathogens in the vicinity of the new outfall location, regardless of
concentration, are extremely unlikely to affect humans. Swimming
several miles offshore in the vicinity of the new outfall is not likely to
occur. As an additional safety measure, the Massachusetts Division of
Marine Fisheries (DMF) will prohibit shellfishing near the outfall. A
study of marine life in the vicinity of the new outfall site showed that
the only other food animals were lobsters and fin fish, neither of
which are likely to carry significant pathogen concentrations,
particularly considering that the bay outfall will have improved
dilution and that fish and lobsters are rarely eaten raw.
The only way that pathogens from the new outfall could have a
negative effect on humans would be if they were transported to an
area where they could come in contact with humans through shellfish
beds or swimming areas. This is an unlikely scenario because any
Contingency Plan Revision 1 - May 2001 39
pathogens surviving chlorination will be reduced below levels of
concern by dilution, degradation by sunlight, osmotic stress from salt
water, and predation. Most pathogens are removed by these
environmental processes within a few hours or days in salt water.
Pathogens discharged from the new outfall are much less likely to
cause problems than pathogens from the former outfall because of the
difference in distances from contact areas. Furthermore, if pathogens
from the new outfall were to survive long enough to reach contact
areas, they would become so dilute as they traveled that the risk of
disease by that point would be unmeasurable.
It has been suggested, though not proven, that some human pathogens
could impact sensitive marine animals, particularly right whales.
Pathogens from wastewater are generally believed not to harm marine
life. If information develops regarding the effect of pathogens on
marine animals, MWRA will incorporate this information into the
Contingency Plan as needed.
Chlorination of wastewater kills pathogens and is thus a necessary part
of the treatment process. However, too much chlorine residual in the
effluent is toxic to marine life. It is essential to add enough
disinfectant to kill pathogens, but not so much as to cause toxicity.
Chlorine in MWRA effluent discharged through the new outfall is
unlikely to cause toxicity as long as the plant operates properly.
Residual chlorine in effluent will be at safe levels before discharge.
Furthermore, since effluent travels the 9.5 miles from the chlorination
facilities to the point of discharge, a certain degree of dechlorination
occurs naturally. Therefore, in the unlikely event of a dechlorination
system failure, at least some dechlorination will occur naturally in the
9.5 mile tunnel. As a result, the chlorine residual in underchlorinated
effluent would be much smaller with the new outfall than with the
existing outfall.
5.42 Trigger
parameters and
thresholds
Both public beaches and shellfish beds are tested regularly for
pathogen contamination. Local authorities, such as the Metropolitan
District Commission (MDC), test swimming areas, and the DMF tests
both water and shellfish. MDC posts swimming areas as unsafe when
counts of fecal coliform bacteria, a key indicator of the presence of
pathogens, are above 200 counts/100 ml water. Shellfish beds are
“restricted” (only specially licensed shellfishers may harvest, and
shellfish must be purified at the state-run depuration plant before
being sold) when fecal coliform counts are above 14/100 ml and
prohibited at counts above 88/100 ml. In addition, shellfish cannot be
sold if their fecal coliform contamination exceeds the disinfection
capabilities of the purification plant.
Contingency Plan Revision 1 - May 2001 40
Effluent parameters/
thresholds
Bacteria. Because of dilution achieved at the new outfall, it is nearly
inconceivable that any bacterial water quality standards for fishing,
shellfishing, or swimming would be exceeded (except in the
immediate vicinity of the outfall, where DMF prohibits fishing and
shellfishing) if effluent bacteria concentrations were below the
NPDES permit limits. The MWRA thresholds are therefore based on
the expected NPDES permit limits.
The bioassay effluent toxicity thresholds developed to protect against
toxicity in the effluent and impact to marine life (see Toxic
Contaminants section), also apply to chlorine toxicity.
Table 5-4
HUMAN PATHOGENS
Parameter Type/Location Parameter Caution Level Warning Level
effluent fecal coliforms - 14,000 fecal coliforms/100 ml
POTENTIAL CORRECTIVE ACTIVITIES
Improve or change disinfection process
5.43 Potential
corrective activities
Improve or Change the Disinfection Process. Properly executed
chlorination is a proven, effective disinfection method. If pathogens
from MWRA effluent were seriously suspected of harming marine life
or humans, the most likely corrective activity would be more rigorous
control of and attention to operation of chlorination facilities. The
MWRA might have to use disinfection methods other than standard
chlorination if it were found that certain pathogens harm marine life.
Some alternative disinfection options that may be applicable use
ultraviolet radiation and ozone (O3). However, these options are still
in the development stage and are currently very expensive for
widespread use. If technological advances made these options
practical, the MWRA would evaluate implementing alternative
disinfection processes that proved cost-effective.
If measurements of the discharged effluent showed toxicity due to
residual chlorine, the MWRA would lower the addition rate of sodium
hypochlorite at the treatment plant to a level which adequately treats
the bacteria but which does not result in residual chlorine toxicity. The
MWRA would also look for new disinfection techniques and
technologies that do not use chlorine. It is possible that new
government regulations will require the development of these new
techniques and technologies as they become practical. The MWRA
would utilize them if it became necessary.
Contingency Plan Revision 1 - May 2001 41
5.5 Solids
5.51 Water quality
issues
Solids are tiny particles in wastewater (e.g. mud, sand, and organic
debris). Many water quality issues are associated with solids present
in the effluent because pollutants often attach to solids or are solids
themselves (e.g. pathogens, toxic contaminants, and some nutrients).
This section, however, considers the impact of solids deposition.
Deposition of solids can change the nature of the bottom habitat,
possibly forming a physical barrier that keeps oxygen from reaching
animals in the sediments. Marine life may be unable to develop
settled solids into an oxygenated, livable environment if the rate of
deposition is high.
MWRA is already implementing the most important responses to
potential impacts from solids. The new Deer Island Treatment Plant
and the new outfall will significantly reduce the environmental
impact of solids from MWRA effluent. The new secondary treatment
facilities are removing 85% of the solids and BOD that reach the
plant, thereby reducing the amount of solids discharged. As described
in the Section entitled “Underlying Pollution Prevention Strategies”,
the new outfall will discharge into water with improved dilution
capacity, thus diminishing the effect of solids that remain after
treatment. In addition, the new outfall has been located in an area
without consistent deposition. Although some deposition does occur
during the summer, winter storms clean sediments from the bottom
annually, leaving the solids to disperse to virtually insignificant
concentrations throughout the bay.
5.52 Trigger
parameters and
thresholds
MWRA will monitor for environmental impact from solids in three
ways: 1) as part of its NPDES permit compliance, the MWRA
measures the concentration of total suspended solids (TSS) in its
effluent (this is also required to meet secondary treatment standards);
2) MWRA works with the United States Geological Survey (USGS)
to monitor Massachusetts Bay for suspended solids and sediment
deposition; and 3) MWRA will also carry out sediment sampling in
Massachusetts Bay and video inspection of sediments in the
immediate vicinity of the outfall. Using these three monitoring
approaches, MWRA has developed a mix of quantitative and
qualitative thresholds.
Effluent parameters/
thresholds
TSS levels. The NPDES permit limits for TSS have been
incorporated into the contingency plan as warning thresholds.
Sea floor parameters/
thresholds
The predicted area of impact to the benthic community is defined in
the SEIS and thresholds have been developed based on this
prediction.
Contingency Plan Revision 1 - May 2001 42
Thresholds for cBOD and depth of sediment oxygen are contained in
the Organic Material Section and Nutrients Section, respectively, but
may also be relevant to identifying the environmental impact of
solids.
Table 5-5
SOLIDS
Parameter Type/Location Parameter Caution Level Warning Level
effluent TSS - 45 mg/L weekly
30 mg/L monthly
sediments, nearfield benthic diversity appreciable change -
sediments, nearfield benthic
opportunists
10% 25%
POTENTIAL CORRECTIVE ACTIVITIES
Enhance solids removal during treatment
5.53 Potential
corrective activities
Enhance Solids Removal during Treatment. In the unlikely event
that the treatment plant as designed does not provide sufficient
removal of solids, the MWRA could implement advanced treatment,
which is discussed as a response for toxic contaminants (see Section
5.2, “Toxic Contaminants”). Effluent filtration and organic polymer
addition are the advanced treatment processes most applicable to
solids.
Contingency Plan Revision 1 - May 2001 43
5.6 Floatables
5.61 Water quality
issues
Floatables are pollutants that sit on the water surface, as opposed to
being suspended or dissolved in the water or resting in the sediment.
Typical floatables are plastic tampon applicators, oil, and grease.
Floatables are primarily an aesthetic problem, although some
floatables, such as oil, can be harmful to marine life.
The MWRA has already ceased scum and sludge discharge,
drastically reducing the amount of floatable material discharged from
MWRA treatment plants. In addition, the new Deer Island Treatment
Plant includes much better mechanisms for removing floatables,
further reducing the discharge of floatables in effluent. CSOs are also
a significant source of floatables. The MWRA is implementing a
program to reduce the effect of CSOs which includes eliminating
many CSOs and providing improved floatables control for any
remaining CSO discharges.
It is important to note that there are other sources of floatables in the
bays. Trash discarded on land and blown or washed into the bays is a
very significant source of floatables, as is boat trash. Oil slicks come
from land runoff and shipping traffic that travels through the bay,
especially oil tankers.
5.62 Trigger
parameters and
thresholds
The MWRA will make regular observations of wastewater during
treatment to determine whether floatables are removed as expected
and whether oil and grease discharges are within the limits established
by the NPDES permit.
Effluent parameters/
thresholds
Oil and Grease concentrations and floatables removal performance.
The expected NPDES permit limits for oil and grease of petroleum
origin, and expected treatment plant floatables removal performance
were incorporated into the contingency plan as warning thresholds.
Although the final permit does not contain numerical limits for oil and
grease, the permit does contain a narrative limit for oil and grease. The
narrative limit for oil and grease, as well as a narrative limit for
floating, settleable and suspended solids, can be found on page 7 of
the Final Permit, Part I.1., footnotes d. and e. Nevertheless, MWRA is
retaining this parameter as a threshold.
Contingency Plan Revision 1 - May 2001 44
Table 5-6
FLOATABLES
Parameter Type/Location Parameter Caution Level Warning Level
effluent floatables 1 - -
effluent oil and grease
(petroleum)
- 15 mg/L weekly
POTENTIAL CORRECTIVE ACTIVITIES
Primary effluent screening; enhanced public educational programs
Improved Floatables Removal. Should observations show that
significant numbers of floatables are in the effluent after treatment,
there are a number of remediation options that could be considered.
Improved floatables removal can be achieved if wastewater is run
through primary effluent screens. Space has been reserved for primary
effluent screens should they need to be installed.
5.63 Potential
corrective activities
Enhanced Educational Programs. MWRA could also make efforts
through educational programs to stop floatables from entering the
waste stream. Some possibilities are improved street sweeping;
promoting the use of tampons with biodegradable, cardboard
applicators or no applicators (both currently on the market);
encouraging proper disposal of tampon applicators, cigarette filters,
and condoms to solid waste facilities rather than the sewer system;
and a variety of other public education programs.
____________________________
1 Threshold value and sampling protocol to be developed by the MWRA by July 1, 2002 and submitted to OMSAP for its review,
and thereafter to EPA and MADEP for review and approval. Pending inclusion of a new threshold value in the Contingency
Plan, the MWRA will employ the following alternative measures: (i) MWRA will provide monthly reports of scum, fats, oil and
grease removal at the treatment plant; (ii) MWRA will record and report in the shift supervisor’s daily log any observations of
floatables, followed by review and correction of problems observed by operators. MWRA will make shift supervisor log sheets
available for EPA and DEP inspection on site; and (iii) MWRA will continue its ongoing program of monitoring and reporting
observations and recording of contents of net tows, complemented by visual inspection of the water recorded in field logs at the
nearfield outfall location in Massachusetts Bay during the 17 annual nearfield surveys.
Contingency Plan Revision 1 - May 2001 45
5.7 Overall Treatment Plant Performance
5.71 Water quality
issues
As described in the Contingency Plan Implementation Section, the
first response to any threshold exceedance would be to determine
whether plant operation could be altered to improve removal of the
relevant pollutant. But even if thresholds have not been exceeded, the
MWRA is committed to maintaining effective overall plant operation.
A dedicated effort to maintain high quality effluent in all respects is
the best way to prevent adverse impacts from any pollutant. The
following trigger parameters and their thresholds will help identify
overall acceptable operation of the treatment plant.
5.72 Trigger
parameters and
thresholds
EPA and the Association of Metropolitan Sewerage Agencies
(AMSA) have established standards which define preferred and
acceptable operational achievement practices. Through the NPDES
permit, EPA requires that the MWRA “shall at all times properly
operate and maintain all facilities and systems of treatment and control
(and related appurtenances) which are installed or used by the
permittee to achieve compliance with the conditions of {the} permit”
(EPA, in publication). EPA defines “significant noncompliance” to be
failing the NPDES permit 5% of the time. AMSA has established
Gold and Silver Awards to recognize achievement in meeting NPDES
permit requirements. Gold Awards are presented for no NPDES
permit violations during a calendar year and Silver Awards are
presented for not more than 5 NPDES permit violations during a
calendar year. If MWRA falls short of winning at least the Silver
Award every year then a caution threshold will be triggered.
Effluent parameters/
thresholds
EPA Significant Noncompliance and AMSA Achievement Standard.
MWRA caution and warning levels for plant performance are the
AMSA standard and the EPA standard, respectively. Limits for pH
and flow are also expected to be included in the new permit and will
serve as warning levels for plant performance.
Contingency Plan Revision 1 - May 2001 46
Table 5-7
OVERALL TREATMENT PLANT PERFORMANCE
Parameter Type/Location Parameter Caution Level Warning Level
effluent plant performance 5 violations/year noncompliance 5% of the time;
pH <6 or >9 at any time;
flow >436 for an annual average
dry day
POTENTIAL CORRECTIVE ACTIVITIES
Revise Standard Operating Procedures
5.73 Potential
corrective activities
Should the Deer Island Treatment Plant experience “significant
noncompliance” with NPDES permit limits, MWRA would undertake
to revise the Standard Operating Procedures described in the
Underlying Pollution Control Strategies Section, the goal of the
revision being to return the treatment plant to NPDES permit
compliance. This revision would be presented for comment to the
Operations Committee of the MWRA Advisory Board and the
Wastewater Advisory Committee. The Water Environment
Federation’s Manual of Practice would be used as a resource and a
source of references for additional information on improving
operations and maintenance.
Contingency Plan Revision 1 - May 2001 47
Bibliography
Blumberg, A. F., Signell, and H. L. Jenter, (1993). Modeling transport processes in the coastal ocean. J.
Marine Environmental Engineering 1 (1),31-52.
Environmental Protection Agency, 1988. Boston Harbor Wastewater Conveyance System Supplemental
Environmental Impact Statement. Environmental Protection Agency , Region I, Boston MA.
Environmental Protection Agency, 1993. Assessment of Potential Impact of the MWRA Outfall on
Endangered Species; Biological Assessment Prepared Pursuant to Section 7 of the Endangered
Species Act. Environmental Protection Agency, Region I, Boston, MA.
Environmental Protection Agency, 2000. NPDES Permit MA0103284. Environmental Protection Agency,
Region I, Boston, MA.
Massachusetts Water Resources Authority, 1991. Effluent Outfall Monitoring Plan -Phase I: Baseline
Studies. Massachusetts Water Resources Authority, Boston, MA.
MWRA. 1997. Massachusetts Water Resources Authority effluent outfall monitoring plan: Phase II post
discharge monitoring. Boston: Massachusetts Water Resources Authority. Report ENQUAD ms-
044. 61 p.
National Marine Fisheries Service, Northeast Region, 1993. NOM Fisheries Endangered Species Act
Section 7 Consultation -Biological Opinion for Boston Harbor Project: Issuance of a National
Pollutant Discharge Elimination System permit for the Massachusetts Water Resources Authority
Outfall. National Oceanic and Atmospheric Administration, Rockville, MD.
National Research Council, 1993. Managing Wastewater in Coastal Urban Areas. National Academy of
Sciences, National Academy Press, Washington, DC.
Office of Ocean Resources Conservation and Assessment, 1993. "NOAA’s Estuarine Eutrophication
Survey." National Oceanic and Atmospheric Administration, Rockville, MD.
Appendix
Sample “ Quarterly Wastewater
Performance Report ”
Contingency Plan Quarterly Report on Deer Island Effluent Monitoring
January - March 2001
* http://www.m wra.state.ma.us/harbor/html/px022301.pdf
Nitrogen Loading
8500
10000
11500
13000
14500
J F M A M J J A S O N D
Loading (mtons/yr)
1 2-Mon th Run ni ng Average
Total Nitrogen Cau ti on Level (1 25 00 mton s/yr)
Total Nitrogen Warni ng Level (14000 mton s/yr)
Petroleum Hydrocarbons
0
2
1 11 21 31 41 51
PHC (mg/L)
We ekl y Oil and Gre ase
Petroleum hydr ocar bons (PHC) are oil or grease products and their
derivatives. The graph depicts PHC r eadings well below the
Contingency Plan T hr eshold warning level of 15m g/L per week. A
reason for such low levels is that PHCs are less dense than water
and therefore tend to float. There are mechanisms in place at the
DITP to remove floatables as they pass through the system.
Acute Toxicity
0
20
40
60
80
100
J F M A M J J A S O N D
Effl uent conce ntratio n whi ch caused
50 % mortal ity (%)
Mysid Sh rimp
Inland Si lve rside
Avg Mo nthly Min imum Th resh old (5 0% )
The acute toxicity test simulates the short- term toxic effects of
chemicals in sewage effluent on marine animals. The test
measures the concentration (percent) of effluent that kills half the
test or ganisms within four days. T he higher the concentration of
effluent r equired, the less toxic the effluent. For permit compliance,
the effluent concentration that causes mortality to mysid shrimp and
inland silverside must be at least 50%. The threshold limits were
met for the quarter.
Chronic Toxicity
0
20
40
60
80
100
J F M A M J J A S O N D
Effl uen t concen tra tion at w hich to xic
effe ct o bserved (% )
S ea Ur chin
Inl and Sil versid e
A vg Month ly Mi ni mum Thre shol d (1.5% )
Typically, effects of chronic exposures differ fr om those of acute
exposur es. Because of this, chr onic toxicity responses are not
necessarily related to acute toxicity. The chronic toxicity test simulates
the long-term toxic effects of chemicals in sewage effluent on marine
animals. To meet per mit limits, atleast 1.5% effluent must show no
observed effect on the growth and reproduction of the test species.
The sea urchin results for January did not meet the minimum
threshold.*
pH
5
6
7
8
9
J F M A M J J A S O N D
pH
Daily pH
Maxi mum Da il y Thre sho ld (9.0)
Min imum D ai ly Th resh old (6.0)
pH is a measure of the alkalinit y or acidity of the effluent. Small
fluctuations in pH do not have an adverse effect on marine
environments, because seawater is well buffered. Secondary
tr eatment technology at D eer Island tends to produce effluent at the
low end of the r ange. All pH measurements were within the
threshold r ange for the quarter.
Fecal Coliform
1
10
100
1,000
10,000
100,000
J F M A M J J A S O N D
Colonies / 100 mL
Mont hl y Geomean
Weekly Max imum Threshold (14000 col/ 100 ml )
F ecal Coliform is an indicator of the presence of pathogens.
T he levels of these bacteria after disinfection show how
effectively the plant is inactivating disease- causing
microorganisms. The Contingency Plan requires that the
monthly geometric mean not exceed 14000 col/100ml. The
monitoring results for the quarter were well below the
threshold value.
Total nitrogen is not regulated under the perm it, but it is closely
monitored due to it s potential effects on Massachusetts Bay. Total
nitrogen includes ammonia nitrogen, nitrates, and nitrites. The
quar terly total nitrogen levels have been well below t hr eshold limits.
Contingency Plan Quarterly Report on Ambient Monitoring
January - March 2001
MWRA gathers data from the outfall location in Massachusetts Bay on various thresholds outlined in its Deer
Island outfall discharge permit. This report shows relevant ambient monitoring results that became available in
the previous quarter.
DISSOLVED OXYGEN
Measurements of dissolved oxygen (DO) concentration since the activation of the outfall tunnel have been above
the caution level threshold of 6.5 mg/L. DO percent saturation readings since the outfall tunnel came on-line have
been above the Contingency Plan threshold warning level of 75% for both nearfield and Stellwagen Basin
monitoring areas, but fell below the caution level in early October 2000. For a full description of the threshold
exceedance see http://www.mwra.state.ma.us/harbor/html/ax111000.pdf.
The concentration of dissolved oxygen (DO) in the water indicates the balance between production by algae and
consumption by aquatic organisms and the decomposition of organic matter. Excessive organic matter may
result in oxygen depletion, which may in turn adversely affect the aquatic ecosystem. The amount of oxygen that
the water can hold is related to water temperature, salinity, and pressure; thus the percent saturation of dissolved
oxygen is a measure that takes these factors into account. Monitoring locations for which there are DO
thresholds include the "nearfield", the group of stations within about three miles from the outfall, and "Stellwagen
Basin", a deep area nine miles east of the outfall. Thresholds apply to the part of the year when the water column
is stratified, i.e. from June - October. The current reporting period for dissolved oxygen thresholds is Sept. 6 - Oct.
31, 2000 --from outfall start-up through the end of October. During this period there were three nearfield surveys
and one combined nearfield/farfield survey.
The graphs include data since the start of the monitoring program in 1992, and reflect the natural fluctuation of
DO and percent saturation, which is typically lowest in early fall.
NEARFIELD STELLWAGEN BASIN
5
6
7
8
9
10
11
12
13
1992 1993 1994 1996 1997 1998 2000
Dissolved Oxygen Concentration (mg/L)
5
6
7
8
9
10
11
12
13
1992 1993 1994 1996 1997 1998 2000
Dissolved Oxygen Concentration (mg/L)
60
70
80
90
100
110
120
1992 1993 1994 1996 1997 1998 2000
Oxygen Percent Saturation (%)
60
70
80
90
100
110
120
1992 1993 1994 1996 1997 1998 2000
Oxygen Percent Saturation (%)
nearfield survey mean Stellwagen Basin survey mean
caution level warning level
outfall start-up (vertical line)
NUISANCE ALGAE
Nuisance algae levels in the first monitoring period since the outfall tunnel came on-line were well below
thresholds. The current threshold reporting period for nuisance algae is Sept. - Dec. 2000 (six surveys).
Nuisance algal blooms are less predictable than the normal, beneficial algal blooms which produce food and
oxygen; some blooms did occur during the baseline monitoring period. There is public concern that effluent
nutrients could feed a red tide bloom in the vicinity of the new outfall, or otherwise increase the abundance of
nuisance algae. Therefore, the Contingency Plan has thresholds for seasonal abundance of Alexandrium ,
Phaeocystis pouchetii , and Pseudonitzschia , which are triggered if the abundance of any of these becomes
unusually high.
ALEXANDRIUM
Alexandrium tamarense typically may bloom during April to June and can cause
paralytic shellfish poisoning, known as PSP or red tide; it has been periodically
found in Massachusetts since the 1970s. Alexandrium has not been seen in
abundances greater than 2 cells per liter in autumn samples since 1993. Toxicity
is generally not found in shellfish until much higher cell counts are seen in the
overlying waters.
Autumn Alexandrium per-sample
abundance (cells/l)
Range over baseline 0-163
caution threshold 100
Year 2000* 0
* maximum of all samples collected between September 6, 2000 and December 31, 2000.
PHAEOCYSTIS
Phaeocystis pouchetii blooms usually occur during February to April but can occur
at any time. Since 1992 this species has occurred only rarely in the autumn, and
at very low levels. The species is not toxic, but individual cells can aggregate in
gelatinous colonies that are poor food for zooplankton.
Autumn Phaeocystis mean abundance
(cells/l)
Range over baseline 0-2,367
caution threshold 1,420
Year 2000 0
PSEUDONITZSCHIA
Pseudonitzschia multiseries blooms can occur during November to March and
produce domoic acid, which can cause a condition known as amnesic shellfish
poisoning. The group of algae including the toxic species Pseudonitzschia
multiseries , the closely related Pseudonitzschia pungens , and any unidentified
Pseudonitzschia species was seen at relatively high numbers in the falls of 1993
and 1998.
Autumn Pseudonitzschia mean abundance
(cells/l)
Range over baseline 267-24,300
caution threshold 25,000
Year 2000 12,600
Massachusetts Water Resources Authority
Charlestown Navy Yard
100 First Avenue
Boston, MA 02129