Dissolved Oxygen TMDL Protocols
and Submittal Requirements
Originally Prepared by the Dissolved Oxygen TMDL Protocol Team:
Ron Jacobson (retired), Jim Klang (former MPCA employee), Carol Sinden,
Chuck Regan (former MPCA employee), Hafiz Munir
Reviewed by: John Hensel, Glenn Skuta, Jeff Risberg, Tim Larson, Lee Ganske, Greg Johnson,
Jim Hodgson, and Chris Zadak
Modified by the Current Dissolved Oxygen TMDL Protocol Team:
Mark Evenson, Nick Gervino, Bruce Henningsgaard, Hafiz Munir, Mike Trojan, Jim Ziegler
Minnesota Pollution Control Agency
December 2008
Table Of Contents
I. Introduction
A.
B.
C.
D.
E.
F.
G.
Purpose.............................................................................................................................5
How this report is organized ............................................................................................5
Total Maximum Daily Load overview ............................................................................5
What is a TMDL? ............................................................................................................6
What is the process for completing TMDLs? ..................................................................6
Who is responsible for doing TMDLs? ...........................................................................7
Site-Specific Approaches.................................................................................................8
II. About DO and Watershed Investigations
A. DO Technical Resources..................................................................................................8
B. Stressor Identification Overview .....................................................................................10
a. Stressor Identification Information Resources ....................................................10
b. Definitions............................................................................................................10
c. Stressor Identification Framework.......................................................................11
C. Stream Health and DO .....................................................................................................16
a. Definitions............................................................................................................16
b. DO Chemical and Physical Stressor Parameter Interactions ...............................18
c. External Influences ..............................................................................................20
d. Internal Influences ...............................................................................................20
e. Stressor Sources on Streams ................................................................................26
D. Problem Definition...........................................................................................................31
a. Applicable Water Quality Rules ..........................................................................31
b. Numeric Standards...............................................................................................32
E. Overview of TMDL Project Decision Points...................................................................35
F. Initial Problem Assessment..............................................................................................39
a. Comprehensive Data Collection from Existing Resources..................................41
b. Data Review and Evaluation................................................................................44
c. Prominent Data Gaps ...........................................................................................44
d. Stressor Identification Starting Questions ...........................................................45
e. Consideration of the Dynamics in a Watershed...................................................46
G. Critical Project Design Conditions ..................................................................................46
a. Early Monitoring Contract...................................................................................47
H. Determining Rigor ...........................................................................................................49
I. Analysis............................................................................................................................50
a. Basic Objectives...................................................................................................50
b. Selecting an Appropriate Analytical Tool ...........................................................51
c. Available Models .................................................................................................54
d. General Approach Alternatives............................................................................56
e. Define and Develop Specific Approach ..............................................................56
f. Additional Data Acquisition to Support Analysis Framework ............................56
g. Model Set-Up and Evaluation..............................................................................60
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J. Development of Example Evaluation Scenarios..............................................................63
K. Project Case Example and Stressor ID Discussion .........................................................65
III. Dissolved Oxygen TMDL Submittal Requirements
A. Dissolved Oxygen TMDL Submittal Requirements........................................................74
B. Identification of Waterbody, Pollutant of Concern, Pollutant Sources and
Priority Training...............................................................................................................75
C. Description of the Applicable Water Quality Standards and Numeric Water
Quality Target ..................................................................................................................76
D. Loading Capacity - Linking Water Quality and Pollutant Sources .................................77
E. Load Allocations (LAs) ...................................................................................................79
F. Wasteload Allocations (WLAs) ......................................................................................80
G. Margin of Safety (MOS) .................................................................................................86
H. Reserve Capacity (allocation for future growth) ............................................................88
I. Seasonal Variation ..........................................................................................................90
J. Reasonable Assurances ...................................................................................................90
K. Monitoring Plan to Track TMDL Effectiveness .............................................................93
L. Implementation ...............................................................................................................96
M. Public Participation .........................................................................................................98
N. Submittal Letter ..............................................................................................................101
O. Administrative Record ....................................................................................................101
IV. Appendices
A. Minnesota’s TMDL submittal checklist ..........................................................................102
B. Guidance for Communities on How to Integrate Lower Minnesota River Dissolved Oxygen
TMDL Requirements and MS4 Stormwater Pollution Prevention Programs .................104
C. More Case Examples (under construction)
V. Figures
1:
2:
6:
7:
8:
Stressor Identification Management Context...................................................................12
Subsets of Figure 1. SI Management Context (Figures 2-5) ...........................................13-15
Stream DO Balance..........................................................................................................19
Stream DO Response to a Point Source Discharge .........................................................21
DO sag curve from multiple pollutant loadings along a reach from nonpoint
sources (response not modeled or to scale; example only)..............................................22
9: Diurnal Dissolved Oxygen response to photosynthetic cycles ........................................23
10: Diurnal Dissolved Oxygen response to photosynthetic cycles comparison with
eutrophic systems.............................................................................................................24
11: A stream reach without vegetative shade.........................................................................25
12: A wide stream with no riparian slopes with significant tree shade..................................25
13: Flowchart Diagram of the Low Dissolved Oxygen General Problem
Investigation and Attainment Strategy.............................................................................36
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14. Stick Figure and Equation for Mass Balance Approach..................................................52
15. Diagram concept of a one-dimensional model ................................................................53
16. Graphical depiction of a 3-dimensional model................................................................54
17. Collection of velocity data to use in combination with channel geometry
to develop stage-discharge relationships for the stream ..................................................58
18. A time-of-travel study using dye tracer techniques .........................................................59
19. Preliminary Data Stick Figure Map ................................................................................66
20. Stick Figure Map Showing Longitudinal Survey Stations ..............................................68
21. Iterative TMDL Process...................................................................................................93
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Part I. Introduction
A. Purpose
The purpose of this document is to provide guidance on the submission requirements for Low Dissolved
Oxygen Total Maximum Daily Load (TMDL) studies by the Minnesota Pollution Control Agency
(MPCA) and the United States Environmental Protection Agency (EPA). The intended audience is
MPCA staff and management, as well as technical staff of local organizations and consulting firms
responsible for developing TMDLs.
While several technical Dissolved Oxygen (DO) references are provided, the guidance is based on the
assumption that the reader has some working knowledge of watershed science and is willing to augment
the TMDL project technical team with members who have a deeper knowledge regarding DO as needed.
This includes the specific skills required for monitoring and assessment techniques, modeling tools and
restoration practices. This guidance is designed to bridge the gap between general watershed programs,
such as Minnesota’s Clean Water Partnership and Section 319 programs, and the unique requirements of
TMDLs.
While this guidance is intended to build a common understanding of TMDLs, it will not meet every
project need. Each TMDL project tends to have its own unique set of issues and challenges. The MPCA
will provide the assistance and oversight needed to address these issues on a case by case basis.
B. How This Report Is Organized
This document is organized into three sections:
Chapter I explains the purpose and scope of this document, and provides a brief overview of the
TMDL process.
Chapter II explains the science principles and fundamentals needed to undertake an investigative
study. Discussion includes: the stressor identification tool and how it is used in the discovery
process, a chapter continues with a discussion explaining the fragile natural balance a healthy
watershed has with regard to stream health and DO, and the critical parameters and typical
sources commonly found to be contributing to a low DO condition.
Chapter III explains the EPA and Minnesota TMDL submission requirements.
Chapter IV (undeveloped) reviews project options for conditions when very low or no flow exists in
the receiving water. These conditions can occur in backwater effects at river confluences,
intermittent streams, or ephemeral conditions (standing water without velocity in natural or
artificial systems).
C. TMDL Overview
The TMDL process offers an excellent opportunity to identify and restore water quality in stream, rivers,
and lakes, as well as enhance involvement of watershed residents and stakeholders in water quality
issues. Other potential benefits of the TMDL process to projects include:
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Encourages the development of a consistent framework for conducting water quality studies;
Defines existing impairments and pollution sources, quantifies source reductions, and sets
comprehensive restoration strategies to meet water quality standards;
Provides a framework for assessing future impacts to water quality;
Accelerates the schedule at which impaired waters are addressed through more effective
coordination of existing and future resources among local entities, state, and federal
environmental agencies;
Provides a basis for revising local regulations (e.g., zoning and sub-division) and developing
performance-based standards for future development; and
Facilitates the incorporation of TMDL schedules and implementation activities into local
government water plans.
D. What is a TMDL?
A TMDL or Total Maximum Daily Load (TMDL) is a calculation of the maximum amount of a
pollutant that a water body can receive and still meet water quality standards, and an allocation of that
amount to the pollutant’s sources. Section 303(d) of the Clean Water Act (CWA) and its implementing
regulations (40 C.F.R. § 130.7) require states to identify waters that do not or will not meet applicable
water quality standards and to establish TMDLs for pollutants that are causing non-attainment of water
quality standards.
Water quality standards are set by States, Territories, and Tribes. They identify the uses for each water
body, for example, drinking water supply, contact recreation (swimming), aquatic life support (fishing),
and the scientific criteria to support that use.
As described in detail in Part II of this guidance, a TMDL needs to account for seasonal variation and
must include a margin of safety (MOS). The MOS is a safety factor that accounts for any lack of
knowledge concerning the relationship between effluent limitations and water quality. Also, a TMDL
must specify pollutant load allocations among sources. The total of all allocations, including wasteload
allocations (WLA) for point sources, load allocations (LA) for nonpoint sources (including natural
background), and the MOS (if explicitly defined) cannot exceed the maximum allowable pollutant load:
TMDL =sumWLAs + sumLAs + MOS + RC*
•
The MPCA also requires that “Reserve Capacity” (RC) which is an allocation for future growth be
addressed in the TMDL. See page 88 for more information.
A TMDL study identifies all sources of the pollutant and determines how much each source must reduce
its contribution in order to meet the quality standard. The sum of all contributions must be less than the
maximum daily load.
E. What is the process for completing TMDLs?
As noted above, the Clean Water Act Section 303 establishes the water quality standards and TMDL
programs. Section 303(d) of the CWA requires states to publish, every two years, an updated list of
streams and lakes that are not meeting their designated uses because of excess pollutants. These water
bodies are considered impaired for their uses.
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The list, known as the 303(d) list, is based on violations of water quality standards and is organized by
river basin. States must establish priority rankings for waters on the lists and develop TMDLs for listed
waters. Minnesota’s 303(d) list can be found on the MPCA Web site at:
http://www.pca.state.mn.us/water/tmdl/index.html. The 2006 Guidance Manual for Assessing the
Quality of Minnesota’s Surface Waters for Determination of Impairment: 305(b) Report and 303(d) List
explains MPCA’s process for assessing water bodies for the 305(b) report and the 303(d) impaired
waters list. The guidance manual is also on the MPCA web site at:
http://www.pca.state.mn.us/publications/manuals/tmdl-guidancemanual04.pdf .
The TMDL Process
Assess the state’s waters
↓
List those that do not meet
standards
↓
Identify sources and reductions
needed
(TMDL Study)
↓
Implement restoration activities
(Implementation Plan)
↓
Evaluate water quality
The Clean Water Act requires a completed TMDL for
each water identified on a state’s Impaired Waters list.
Lakes or river reaches with multiple impairments require
multiple TMDLs. States have the primary responsibility
for developing TMDLs and submitting them to EPA for
review and approval. If EPA disapproves a TMDL, EPA
is required to establish the TMDL. The process for
completing a TMDL study is complex and varies
significantly from project to project. Some of the many
variables that determine scope of a project include:
o Number of pollutant sources
o Type of pollutant and size of the watershed
o Amount of existing data
o Relationship of one impairment to others that
may exist in the same or nearby water bodies
o Extent of stakeholder involvement
o Availability of necessary resources.
Public participation is critical throughout the TMDL process and Minnesota expects advisory groups to
be involved from the earliest stages of the project. At a minimum, the EPA requires that the public must
be given an opportunity to review and comment on TMDLs before they are formally submitted to EPA
for approval. Every TMDL is formally public noticed in Minnesota with a minimum 30-day comment
period.
After a TMDL is approved by the EPA, a detailed implementation plan is finalized to meet the TMDL’s
pollutant load allocation and achieve the needed reductions to restore water quality. Depending on the
severity and scale of the impairment, restoration may require 10-20 years or longer and millions of
dollars. Further information on MPCA’s TMDL implementation policy can be found at:
http://intranet.pca.state.mn.us/policies/programpolicies/i-wq2-031.pdf
The reader is also encouraged to refer to EPA’s 1991 guidance document: “Guidance for Water Qualitybased Decisions: The TMDL Process” at http://www.epa.gov/OWOW/tmdl/decisions/ for a more complete
description of the federal program.
F. Who is responsible for doing TMDLs?
The MPCA is ultimately responsible for completing and submitting TMDLs to the EPA. However,
stakeholders play a critical role in the development and implementation of TMDLs. Locally-driven
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projects are most likely to succeed in achieving water quality goals because local communities often
best understand the sources of water quality problems and effective solutions to those problems. Their
work to develop and implement TMDLs is a key tool to restore and maintain our rivers, streams and
lakes.
For more than two decades, the MPCA has contracted with counties, watershed districts, soil and water
conservation districts, and other local organizations to diagnose and help restore lakes and streams
polluted from nonpoint sources. This watershed work was completed through the agency’s Clean Water
Partnership and Clean Water Act Section 319 programs. Many local government agencies have gained
considerable expertise in watershed work and public involvement in part due to this experience.
Building off of this success, the MPCA will provide grant contracts to qualified local governments and
watershed organizations to lead an estimated two-thirds of TMDL projects. The MPCA will direct the
remaining projects. The contracts cover staffing, equipment, lab costs, and other project expenses.
In addition, scientific and technical experts provide valuable information and insight. In many cases,
private consultants assist with data collection, modeling, and development of draft reports.
The MPCA estimates that nearly 95 percent of all the state’s TMDL funding for study completion will
be passed through to local-governments and contractors. The MPCA provides oversight, technical
assistance, and training to ensure regulatory and scientific requirements are met. The MPCA submits
final TMDLs for EPA approval.
For additional information on TMDL grant requirements, see MPCA’s TMDL workplan guidance at:
http://www.pca.state.mn.us/publications/wq-iw1-01.pdf.
G. Site-Specific Approaches
The Clean Water Act, federal regulations, Minnesota’s State Water Pollution Control Act and
Minnesota’s water quality rules establish opportunities to use site-specific approaches to address water
quality impairments. These may be appropriate for some water bodies where numeric criteria different
from those presently contained in the water quality standards need to be established to protect beneficial
uses. Site-specific options allow the MPCA to consider data on local water body characteristics to
apply more precise numeric standards to protect the beneficial uses of the water body. A detailed
discussion of site-specific approaches is contained in the companion TMDL protocol for lakes impaired
by excessive nutrients. The MPCA does not anticipate that site-specific approaches will be applied
frequently, but these options may be required with some dissolved oxygen TMDLs.
Part II: About DO and Watershed Investigations
This chapter is meant to bring individuals that are new to the chemistry and physical sciences regarding
stream interactions with DO and the stressing pollutant parameters to a working understanding for
project management. If the reader does not have a significant understanding of the watershed
management requirements for DO, then the project team should include individuals with the expertise.
A. DO Technical Resources
DO guidance documents for wastewater treatment facilities are well established for determining the
allowable remaining load (wasteload allocations) for the National Pollutant Discharge Elimination
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System (NPDES) permit effluent limit setting purposes. These processes are either: a) reach specific
and often assume upstream loads at the reach boundary as a given; or b) TMDL watershed guidance
(with less specific detail). The purpose of the documents in group a) are for the NPDES program and
most often are used to determine the remaining loading capacity available in order to set limits for those
NPDES permits under review. These documents present the detailed science requirements for assessing
or modeling one or more pollutant source impact on a given stream reach. These detailed guidance
documents are useful resources to give the project team the deepest understanding of the science
principles needed, plus provide EPA standard methods. The purpose of those documents in group b) is
to provide some detail on how to apply in a TMDL setting. The additional principles described in this
TMDL protocol document provide Minnesota’s guidance on applying these principles of low DO stream
interactions to a TMDL project using stakeholder involvement and assessing the impairment at a
watershed scale.
1. Handbook: Stream Sampling for Waste Load Allocation Applications. EPA Office of
Research and Development. EPA/625/6-86/013.
http://www.epa.gov/waterscience/library/modeling/streamsampling.pdf (PDF, 5M)
2. Technical Guidance Manual for Performing Waste Load Allocations: Simplified
Analytical Method for Determining NPDES Effluent limitations for POTWs
Discharging into Low-Flow Streams
http://www.epa.gov/waterscience/library/modeling/npdeslowflow.pdf
(PDF, 2MB)
3. Establishing Total Maximum Daily Load (TMDL) Wasteload Allocations (WLAs) for
Storm Water Sources and NPDES Permit Requirements Based on Those WLAs”
(November 22, 2002);
http://www.epa.gov/npdes/pubs/final-wwtmdl.pdf
4. Technical Guidance Manual for Developing Total Maximum Daily Loads: Book 2,
Rivers and Streams; Part 1 Biochemical Oxygen Demand/DO and Nutrient
Eutrophication, EPA/823/B-97-002 Year 1997
http://www.epa.gov/waterscience/tmdl/guidance.pdf
5. Water Quality Assessment: A Screening Procedure for Toxic and Conventional
Pollutants in Surface and Ground Water, Part 1 [Revised]. EPA#: 600/6-85-002a
YEAR: 1985. (PDF, 31MB)
http://www.epa.gov/waterscience/library/modeling/wqascreenpart2.pdf
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B. Stressor Identification Overview
Stressor Identification is a process that narrows the possible pollutants and sources down to the
significant loadings using a formalized method. The process laid out in the EPA Stressor Identification
guidance manual (see web link below) explains a logical process to:
(a) Select the right questions needing to be answered (information protocol),
(b) Formalize the decision process steps,
(c) Provide a predictability for the communication, information gathering, professional
judgment, and when a decision can be made; and
(d) Require documentation of decisions in an organized fashion.
This process is meant to enhance traditional project decision processes rather than replace the current
methods. The reader should consider the content of the following section and apply it to build on their
own experience in project management. Ultimately, for impairments like dissolved oxygen, a parameter
that is responding to a number of possible pollutant parameters and sources, the Stressor Identification
tool chest is very useful in organizing the discovery process.
a. Stressor Identification Information Resources
The United States EPA has developed a Stressor Identification Guidance document for biotic
impairments that contains principles for investigation that are very useful in low DO studies. These
principles are explained in different perspectives in the following guidance documents:
1. Stressor Identification Guidance Document; EPA-822-B-00-025, December 2000
http://www.epa.gov/ost/biocriteria/stressors/stressorid.pdf
2. Draft Handbook for Developing Watershed Plans to Restore and Protect Our Waters
http://www.epa.gov/nps/watershed_handbook/#contents
3. MPCA TMDL Training Modules (to be) posted on the MPCA website
b. Definitions
Stressor Identification (SI) is a term used by EPA guidance documents describing a process for use in
biotic impaired waters that 1) develops a exhaustive list of potential physical and chemical parameters
and the sources contributing to the impairment, and 2) provides an information flow and logic process
that can narrow down the larger list of potential candidate stressors to those parameters and sources that
are confirmed to be contributing or are considered to have a high potential of contributing to the
impairment.
Weight of Evidence, sometimes also called Strength of Evidence, is a term used to describe a process
that settles on a decision when sufficient (circumstantial) justification exists, despite lack of hard science
linking causal effects.
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Potential Sources is a term to identify all the possible pollutant loading sources in a given watershed
that contain the potential candidate parameters.
Primary Sources are those sources that are determined to be critical source loaders of the key stressor
parameters to be allocated in the TMDL.
Stakeholder Involvement refers to the levels of citizen communication during and after development of
a draft TMDL. The communication can be one way or two way feedback depending on the level of
effort applied or the timing in relation to the stage of development in the TMDL project. Examples of
often used processes are:
Stakeholder Advisory Committee is a citizen committee that is formed and evolves to include
representation from the community in the potentially affected pollutant loading sectors, those interested
in protecting water quality attainment and finally the Local Governmental Units (LGUs). The
committee is not a final decision authority but has multiple purposes including identifying local early
perceptions, identifying potential controversial issues, testing equity and reasonableness for individual
sector expectations and total allocation applications and finally as a strong influence on the proper
application of professional judgments being used during the project development.
Technical Advisory Committee is a group of “experts” on watershed management or individual sector
management that develop, review and adjust the assessment process while developing the TMDL.
Public Meetings for the TMDL. Presentations announcing the project kick off or key findings of the
TMDL project as an advertised event to reach out to citizens current not involved in the study. The
meeting can set up selecting from many different formats, examples are: classroom style presentations,
town hall style meetings, or more informal poster board displays with project team members available to
discuss the issues.
Public Notice of the TMDL. Presentation of the report, the public record documenting the findings and
the logic process and/or the assessment process used in considering stressor parameters and the different
sources resulting in the reduction expectations used development of the TMDL.
c. Stressor Identification Framework
The SI process is meant to balance the needed information gathering effort, without having perfect
information for cause and effect relationships. It is a strong means of reducing project costs and rigor by
introducing a repeatable method for professional judgment decision-making. It begins with the current
data or present understanding and uses the conversations of the project team and project committees,
plus a data gathering process in an iterative fashion to evaluate the adequacy of the professional
judgment being applied. The process uses the understanding, acceptance or comfort levels of the
participants as an important consideration in finalizing a decision or revisiting the data or data gathering
steps. There is a base assumption that there are areas of concern that reflect the greater community, and
tends to be a good assumption when the committee membership is selected from a wide range of
interests and not just the watershed restoration advocates. The decision process involves “starts and
stops” as the project iterates between actively discussing the analysis or the need to gather more
information to analyze. The project team’s watershed understanding will grow with each iteration of
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data collection and analysis steps. It is important to stress that the cycle and decision is not a total
consensus vote, but instead a means to identify and influence the process.
The following diagram is taken from the EPA Stressor Identification Guidance Document:
Figure 1. Stressor Identification Management Context
With regard to DO, the measurement of oxygen concentrations does not measure the pollutants
contributing to the impairment. In the DO listings, the Stressor Identification process should be used to
key into the appropriate sources that are driving the impairment by adding other pollutant parameters to
the system. Therefore, the process started with the listing and the project team enters the diagram at the
box that states “List Candidate Causes”. In the process, as a gap or an insufficiency occurs that limits a
decision an iterative process is used as provided by the SI process to organize the conversations,
planning task and data gathering tasks to revisit the issue at a later time with more information or to
assign the decision an adequate margin of error and proceed on with the current understanding.
The “Characterize Causes” box uses three categories of decision outcomes to process data: 1)
Elimination, 2) Validation, and 3) Weight of Evidence. The first two categories are based on hard
evidence such as: watershed monitoring indicating the lack of presence or presence of a stressor
parameter that provide hard science conclusions that a parameter stressor is or is not a significant causal
linkage. The third category is an effort that introduces and fosters a more formal “scientific hypothesis”
process to develop significant circumstantial evidence to make a decision. By using the principals of
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
science to provide a relative comfort level for most involved parties based on indicators the weight of
evidence approach becomes more defendable even though it continues to be based on professional
judgment. The team must balance the spectrum of expending too much time and resources to gather
information versus “pulling the decision out of the air.” Introduction of information from past research
papers, using average literature values from technical publications, other local/regional site specific
information, and alternative analysis methods (like GIS spatial analysis, simple analysis tools, statistics
applications) will help balance the tension between wanting perfection and not pursuing anything
further. The fear of decisions being “pulled out of the air” is minimized by a decision made on
professional judgment being based on many indicators to be organized by using the defendable
documentation from the stakeholder groups weight of evidence process that support the decision.
There are many possible ways of gathering information and filtering the information into watershed
understanding. The craft or art behind the weight of evidence processes is selecting which data gathering
processes will be used to substantiate the decision. The final decision-maker is influenced by type of
data, when the data is an indicator (circumstantial evidence), then the opinions of the two committees on
the subject. Options available or not available for further investigations are also considered (i.e., is the
weight of evidence strong enough to make a decision as to its significance or not – and then require
more information and a next step, or explore the margin of error and related MOS to manage the
resources and TMDL progress).
The decision is represented by the process represented in the SI Management Context diagram, Figure 1;
however the key location to note is between the “Analyze Evidence” box and the “Characterize Causes”
box as shown in Figure 2. There are 5 possible results resulting from analysis of the evidence available.
Figure 2. A subset of Figure 1. SI Management Context
Eliminated: Data set confirms elimination finding and project documents the parameter stressor or
source as a noncontributing factor in the watershed.
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Or,
Figure 3. A subset of Figure 1. SI Management Context
Validated: Data set confirms the stressor parameter is present and significant, or that a source
contributes to the significant stressor parameter loading in the watershed and allocations are required.
Or,
Figure 4. A subset of Figure 1. SI Management Context
Weight of Evidence: Sufficient indicator evidence is present to use the Weight of Evidence justification
to move forward in the project with adequate minimization of risks.
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Or,
Figure 5. A subset of Figure 1. SI Management Context
???
As the decision makers find there is not enough information to follow any of the three category steps,
the project plans for more information gathering and returns back into the analyze evidence box with
new data to repeat the process. [Over time, the teams working in the Impaired Waters program will
develop more confidence with each project and be able to manage risk based on program wide
experience.]
A similar iterative process is done with the pollutant source information available in the watershed. This
should be done early and be in step with the pollutant stressor iterative loop. In this case, the land use or
channel assessment focuses on sources that have the key pollutant stressor parameters and the key
limiting physical parameters. Again, hard evidence like permit information, including NPDES DMR
reports, ambient monitoring combined with spatial assessments (for instance determination of no
hydrologic connection) can be used to validate or eliminate sources. Other indicators such as presence in
a subwatershed, timing, literature estimates of magnitude, or detailed modeling can create sufficient
weight of evidence to make allocation decisions. Remember that it is just as important to document and
communicate why a source is eliminated as it is to set reduction goals for a source that is validated or
pursued using strength of evidence. All projects using this process benefit from starting with simple data
sets and graduating to more complex efforts only as needed. Other benefits are:
Cost savings,
Documentation of findings and decisions,
Flexibility in project flow, yet with consistent logic on how, when and where to use the iterative
information collection process, and
More acceptance from program staff and watershed participants that the risks are minimized and
reasonable solutions are being selected.
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C. Stream Health and DO
DO is an important water quality indicator parameter for the protection and management of aquatic
ecosystems. All higher life forms such as vertebrates and macroinvertebrates are dependent on minimum
levels of oxygen for critical life cycle functions such as growth, maintenance, and reproduction.
Problems with oxygen depletion in river systems are often the result of excessive loadings of
carbonaceous biochemical oxygen demand (CBOD) and nitrogenous biochemical oxygen demand
(NBOD), particularly in combination with high temperature and low flow conditions.
a. Definitions
Algal Respiration: Process in which organic carbon biomass is oxidized to carbon dioxide, produced
from within the algal organism.
Ambient Water Quality: Natural concentration of water quality constituents prior to mixing of either
point or nonpoint source load of contaminants. Reference ambient concentration is used to indicate the
concentration of a chemical that will not cause adverse impact to human health.
Ammonia: Inorganic form of nitrogen; product of hydrolysis of organic nitrogen and denitrification.
Ammonia is preferentially used by phytoplankton over nitrate for uptake of inorganic nitrogen.
Anaerobic: Environmental condition characterized by zero oxygen levels. Describes biological and
chemical processes that occur in the absence of oxygen.
Anoxic: Aquatic environmental conditions containing zero or little dissolved oxygen.
Anthropogenic: Pertains to the (environmental) influence of human activities.
Assimilative Capacity: The amount of contaminant load (mass per unit time) that can be discharged to
a specific stream or river without exceeding water quality standards or criteria. Assimilative capacity is
used to define the ability of a waterbody to naturally absorb and use waste matter and organic materials
without impairing water quality or harming aquatic life.
Background Levels: Background levels represent the chemical, physical, and biological conditions that
would result from natural geomorphological processes such as weathering or dissolution.
Benthic: Refers to material, especially sediment, at the bottom of an aquatic ecosystem. It can be used
to describe the organisms that live on, or in, the bottom of a waterbody.
Bed Material: The moving sediment mixture that is present on the channel floor.
Bias: A systematic error introduced into sampling or testing by selecting or encouraging one outcome or
answer over others. Bias can be introduced by setting variables or factors which would result in one
outcome.
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Boundary Conditions: Definition or statement of conditions or phenomena at the boundaries. Water
levels, flows, concentrations, etc., that are specified at the boundaries of the area being modeled.
Calibration: Adjustment of a model’s parameters such as roughness or dispersion coefficients so that it
reproduces observed prototype data to acceptable accuracy.
Carbonaceous Biochemical Oxygen Demand (CBOD): The amount of oxygen required by bacteria to
oxidize organic carbon material to carbon dioxide (its lowest energy state).
Deterministic Model: Mathematical model in which the behavior of every variable is completely
determined by the governing equations and the initial states variables.
Detritus: Any loose material produced directly from disintegration processes. Organic detritus consists
of material resulting from the decomposition of dead organic remains.
Discharge Monitoring Report (DMR): Report of effluent characteristics submitted by a municipal or
industrial facility that has been granted an NPDES discharge permit.
Dissolved Oxygen Sag: Longitudinal variation of dissolved oxygen representing the oxygen depletion
and recovery following a waste load discharge into the water.
Diurnal: Actions or processes having a period or cycle of approximately completed actions within a 24hour period and which recur every 24 hours.
Dye Study: Use of conservative substances to assess the physical behavior of a natural system.
Effluent: Municipal sewage or industrial liquid waste (untreated, partially treated or completely treated)
that flows out of a treatment plant, septic system or pipe, etc.
Empirical Model: Representation of a real system by a mathematical description based on experimental
or observed data rather than on general physical laws.
Hydrograph: A graph showing variation in stage (depth) or discharge of water in a stream over a period
of time.
Hydrologic unit: A geographic area representing part or all of a surface drainage basin or distinctive
hydrologic feature as delineated by the Office of Water Data Coordination on State Hydrologic Unit
Maps; each hydrologic unit is identified by an eight-digit number code (HUC).
Low Flow (7Q10): Low-flow (7Q10) is the 7-day average low flow occurring once in 10-years; this
probability-based statistic is used in determining stream design flow conditions and for evaluating the
water quality impact of effluent discharge limits.
Nitrogenous Biochemical Oxygen Demand (NBOD): The amount of oxygen required by bacteria to
oxidize ammonia to nitrite, and then nitrite to nitrate (the process is called nitrification).
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One-Dimensional Model: Model defined with one space coordinate, i.e., variables are averaged over
the other two directions.
Parameter: A chemical or physical property whose value determines the characteristics or behavior of
something.
Probabilistic Model: Mathematical model in which the behavior of one or more of the variables is
either completely or partially subject to probability laws.
Qualitative: A relative assessment of quantity or amount.
Quantitative: An absolute measurement of quantity or amount.
Sediment Oxygen Demand (SOD): Combination of several processes, primarily the aerobic decay of
organic materials (such as leaf litter, particulate BOD in wastewater discharges, or algae or plant
biomass) that have settled to the bottom of the stream bed.
Total Kjeldahl Nitrogen (TKN): The total of organic and ammonia nitrogen in a sample, determined
by the Kjeldahl method.
Ultimate Biochemical Oxygen Demand (UBOD or BODU): Total oxygen consumed by carbonaceous
and nitrogenous material or the amount of oxygen required to oxidize organic carbon and ammonia
nitrogen. The value is typically estimated by a 40 or 70 day BOD test.
Watershed: A topographically defined area drained by a river/stream or system of connecting
rivers/streams such that all outflow is discharged through a single outlet. Also referred to as a drainage
area.
b. DO Chemical and Physical Stressor Parameter Interactions
The amount of oxygen that a given volume of water can hold is a function of atmospheric pressure,
water temperature, and the amount of other substances dissolved in the water. At sea level, fresh water
can absorb more oxygen per volume than water at mountainous elevations because of the higher
atmospheric pressure near sea level. Cool water can hold more oxygen than warm water. Water with
high concentrations of dissolved minerals such as salt will have a lower DO concentration than fresh
water at the same temperature. When water can no longer absorb more oxygen at a given temperature,
pressure, and dissolved solids content, it is said to be saturated with DO (or 100% saturation). Unlike
air, which is normally about 21% oxygen, water contains only a tiny fraction of a percentage of DO.
Oxygen dissolved in water is usually expressed in milligrams per liter (mg/L), parts per million (ppm),
or percent of saturation. At sea level, typical DO concentrations in 100% saturated fresh water will range
from 7.56 mg/L (or 7.56 parts oxygen in 1,000,000 parts water) at 30 degrees Celsius to 14.62 mg/L at
zero degrees Celsius. The saturation concentration decreases about 3.5% for every 1000 feet increase in
elevation.
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Reference: Bowie, G.L., Mills, W.B., et al. 1985. Rates, Constants, and Kinetics Formulations in
Surface Water Quality Modeling (Second Edition). Environmental Research Laboratory, Office of
Research and Development, U.S. Environmental Protection Agency. EPA/600/3-85/040. June 1985.
At any given time, the concentration of DO in a riverine environment is dynamic and influenced by the
interaction of physical, chemical, and biological factors. By accounting for factors affecting DO, a mass
balance model is often used to help quantify the important components of a low DO problem in the
river. Figure 6, schematically depicts a segment of stream and the major factors affecting the balance of
DO within the water column.
Figure 6. Stream DO Balance
Atmospheric Oxygen
(Reaeration)
Water Surface
• Volume
• Depth
• Velocity
Upstream
CBOD
nace
ous O
2
Dem
and
Settling
Photosynthesis
Dissolved
Oxygen
2
tO
en
im
d
nd
Se
ma
De
Conditions
• DO
• BOD
• VSS
• Algae
Carb
o
Respiration
Algae:
•Phytoplankton
•Periphyton
Other Aquatic
Plants
Nitrification
(NBOD)
SOD
+
-
NH4 Î NO2 Î NO3
-
Stream Bed
Ground Water (DO, CBOD, Nitrogen)
CBOD: Carbonaceous Biochemical Oxygen Demand. The rate of oxygen consumption from carbon
available for bacterial decay processes and the amount of oxygen bound in chemical reactions.
NBOD: Nitrogenous Biochemical Oxygen Demand. The rate of bacterial transformation of ammonia
into nitrite and then nitrate consuming oxygen with each step.
SOD: Sediment Oxygen Demand. Depositions on the stream bed consisting of organic material
originating from external sources, such as leaf litter or particulate BOD in wastewater discharges, or
algae and other plant biomass, decomposing and creating a sediment oxygen demand
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c. External Influences
The factors external to a specific river segment that affect DO include the atmosphere-water interface,
the streambed-water interface, the upstream water quality conditions, and pollutant loadings directly to
the segment. Whenever the water column DO concentration is less than saturation, there is a net transfer
of atmospheric oxygen into the water in a process called reaeration. The rate of atmospheric reaeration is
a function of the magnitude of the DO deficit in the water column, atmospheric pressure, temperature,
wave action, and water turbulence. A shallow, turbulent stream has a higher rate of reaeration than does
a deeper, quiescent stream. On occasion, rivers can become supersaturated with oxygen due to the
photosynthetic production of algae and plant matter, in which case there is a net loss of oxygen from the
water to the atmosphere.
Ground water, a primary source of river flow during dry weather and base flow conditions, is naturally
low in DO. During winter months when ice coverage inhibits atmospheric reaeration, ground water
inflows will contribute to occurrences of low DO in a river. During summer, the cooler ground water
inflow may at first lower the DO concentration, but it also tends to reduce the river temperature which
improves the ability of the water to hold oxygen. Ground water introduces dissolved materials into
surface waters, such as minerals related to hardness, but generally has low concentrations of oxygen
demanding organic substances. Ground water inflow to streams in agricultural regions may be high in
inorganic nitrate-nitrogen. Nitrate is not an issue for stream DO, but it can be problematic for
downstream uses of surface water as a source of drinking water.
The quality of water at an upstream boundary reflects the pollutant loads from upstream sources and
tributaries in the watershed. Affected by natural and anthropogenic factors, this headwater quality may
exert a large influence on the DO balance of a downstream river segment. Natural characteristics such
as lakes or wetlands affect downstream water quality much differently than does a typical riffle-pool run
of river. Human influence is evidenced by physical alterations such as dam construction, by point source
discharges from municipal and industrial wastewater treatment plants, storm water runoff from urban
areas, and nonpoint loadings from agricultural areas.
Direct discharge of pollutants from point source and nonpoint sources into a subject river segment add to
its CBOD and NBOD loadings, creating an oxygen demand that may depress DO below acceptable
concentrations. Nutrient levels can occasionally, in certain rivers, cause sufficient eutrophication to
generate CBOD loads from decaying algae. This may not occur locally, but instead further downstream
in pools where the velocities slow and the algae population collect. Once identified, these source loads
become prime candidates for allocation within a TMDL plan.
d. Internal Influences
The DO present within a river segment at any point in time is dependent upon a delicate balance
between the physical, chemical, and biological sources and sinks of oxygen interacting within the
segment. Sources of oxygen are atmospheric reaeration, mass transport into the segment from upstream
and ground water, and the photosynthetic production by algae and aquatic plants. Pathways, or sinks,
for oxygen loss to the segment include the biochemical oxidation of suspended and dissolved organic
waste material, oxygen demands from settled organic and inorganic materials, respiration of aquatic
plants and animals, and the conversion of nitrogen forms through biological nitrification.
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When oxygen is consumed or otherwise lost at a greater rate than it is being replenished within a river
segment, then the resultant DO concentration declines. Figure 7 illustrates the theoretical response of
DO in a flowing river to a continuous point source load of BOD.
Figure 7. Stream DO Response to a Point Source Discharge
BOD
14
DO
Cs
12
10
Cs = D.O. Saturation
8
mg/L
6
4
2
0
-1
1
Organic Load
3
5
7
9
11
13
River Miles
The classical “sag” or DO response that is observed downstream from a point source discharge results
from the increased respiration of the natural bacteria population in a flowing river that grows in response
to its increased food source of organic matter from the discharge. As the river moves downstream the
organic food source is decomposed by the bacteria and becomes depleted. With its food supply gone, the
bacteria die off and river DO recovers to the natural background level. In another case where nonpoint
sources of BOD are loading the river system over a broad area, the spatial extent of DO depression may
be more extensive. Typical nonpoint source sag curves could be either a flatter curve with no visible
recovery or a series of smaller sag curves indicating new loading sources interfering with the previous
curves recovery. Both conditions are presented, though not to scale in Figure 8, below.
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Figure 8: DO sag curve from multiple pollutant loadings along a reach from nonpoint
sources (response not modeled or to scale; example only)
BOD
14
DO
Cs
12
10
Cs = D.O. Saturation
8
mg/L
6
4
2
0
-1
1
3
PS & NPS Organic Loads
5
7
9
11
13
River Miles
The oxygen demand exerted by benthic sediments (on the stream bed) can represent a significant oxygen
sink in some rivers. Benthal deposits result from the deposition of organic material originating from
external sources such as leaf litter or particulate BOD in wastewater discharges, or it may be generated
within the river system as algae and other plant biomass. The decomposing organic material creates a
sediment oxygen demand (SOD) that may become localized and more significant at given locations in a
river system such as in the deeper pooled regions.
The photosynthetic oxygen production (a source) and respiration (a sink) associated with aquatic plant
life are important factors in the DO balance of natural waters. Of special concern are situations with an
overabundance of free floating algae (phytoplankton), attached algae (periphyton), or larger submerged
or emergent aquatic plants (macrophytes). The extent to which aquatic plant life impacts the oxygen
resources of a water body is dependent on factors such as light availability and light intensity as well as
an adequate supply of nutrients essential for growth. Photosynthetic rates respond to variations in
sunlight intensity and water turbidity, which can decrease light transmittance through the water column.
The diurnal variations observed in oxygen concentrations result from a net photosynthetic oxygen
production during daylight hours and a net consumptive loss from plant respiration during the evening
and night.
When algae or plant densities are high, large diurnal swings in DO can occur with peak concentrations
during the day exceeding 100% saturation and nighttime minimum concentration well below saturation.
An idealized diurnal stream response for DO is shown below in Figure 9. Typically, the daily minimum
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
DO occurs within the first two hours after dawn. The daily maximum normally occurs in late afternoon,
about three to five hours after noon.
Figure 9: Diurnal Dissolved Oxygen response to photosynthetic cycles
Idealized Diurnal Dissolved Oxygen (DO) Curve
Mid-Summer
10.0
Sunset
9.0
Dissolved Oxygen, mg/L
8.0
7.0
Daily Average DO
6.0
5.0
4.0
Sunrise
3.0
2.0
1.0
0.0
0
2
4
6
8
10
12
14
16
18
20
22
24
Time, Hours
Highly eutrophic conditions can occur at times in nutrient-enriched rivers, usually during low flow
conditions when increased hydraulic residence times are favorable to producing a large standing crop of
algae. These periods of active plant growth and respiration are marked by large diurnal fluctuations in
DO. When river or meteorological factors change to less favorable growth conditions, algae and aquatic
plants will die, decompose, and use up oxygen resources. Algal biomass, a potential BOD load, can be
transported miles downstream and create oxygen deficits in critical reaches. Algal oxygen production
followed by respiration and later death and decay create a magnified amplitude in the diurnal response
curves as shown below in Figure 10.
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Figure 10: Diurnal Dissolved Oxygen response to photosynthetic cycles comparison with
eutrophic systems
Idealized Diurnal Dissolved Oxygen (DO) Curve
Mid-Summer
10.0
Sunset
9.0
Dissolved Oxygen, mg/L
8.0
7.0
Daily Average DO
6.0
5.0
4.0
Sunrise
3.0
2.0
Diurnal response curve in a more eutrophic system
1.0
0.0
0
2
4
6
8
10
12
14
16
18
20
22
24
Time, Hours
Where a source of ammonia-nitrogen and a viable population of nitrifying bacteria are present in natural
waters, the bacteria oxidize ammonia to nitrite, and then nitrite to nitrate in a process called nitrification.
Ammonia sources may be external, such as from sewage discharges and animal feedlots, or ammonia
can be released internally within the system from the process of organic nitrogen decay
(ammonification). While nitrifying bacteria may be present in the water column, nitrification occurs
primarily in the sediment bed. Nitrification by attached bacteria is more likely to be of significance in
relatively shallow, wide rivers having a stable bottom substrate (see Water Quality Assessment: A
Screening Procedure for Toxic and Conventional Pollutants in Surface and Ground Water, Part 1). The
nitrification of ammonia to nitrate is important to the oxygen resources of a stream because up to 4.6
parts of DO are consumed for each part of ammonia converted.
Water temperature is an important physical parameter that not only establishes the maximum oxygenholding capacity of water, but also has direct influence on rates of biochemical reactions and
transformation processes occurring within the water column and in the sediment bed. Warmer
temperatures decrease oxygen solubility in water while at the same time increasing metabolic rates that
affect BOD decay, sediment oxygen demand, nitrification, photosynthesis, and respiration. In
Minnesota, the critical conditions for stream DO usually occur during the late summer season when
water temperatures are high and stream flow rates are normally low.
The following figures, Figure 11 and Figure 12, relate physical stream riparian corridor vegetation
differences that affect critical shading and resulting water temperatures.
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Figure 11: A stream reach without vegetative shade.
In the stream pictured above the riparian area exists without shade as result of intensive livestock traffic
and little to no slopes in land. The wide shallow stream with raised temperatures due to lack of
vegetation canopy over significant areas of the stream represent aspects in the watershed that might lend
themselves to opportunities for improved DO.
Figure 12: A wide stream with no riparian slopes with significant tree shade.
Gentler land use in the riparian corridor combined with a natural forested area provides for lower
temperatures as more of the stream surface area is shaded.
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When a pollutant load enters a flowing body of water, it is subject to fate and transport processes that
modify its concentration. Organic loads are subject to chemical, biological, and biochemical reactions
that attenuate the material by degradation into stabile end products such as carbon dioxide, nitrate, and
water. However, a pollutant load of oxygen-demanding organics that is large enough to overwhelm the
oxygen resources of a water body creates an imbalance that destabilizes the stream environment and
leads to aquatic life impairments.
An important task for TMDL managers is to understand the cause-effect relationships that govern DO in
site-specific situations in order to design and implement a successful remediation strategy for their
impaired waters. Water quality parameter interactions and other factors affecting DO can range from the
obvious to the complex. Although the basic principles affecting the DO balance in a stream are constant,
each impaired reach has a unique set of factors contributing to its impairment. These contributing factors
may be naturally occurring or human-induced, internal or external to the impaired reach, may be
seasonal in nature, or some combination thereof. For example, an impaired trout water on the North
Shore of Lake Superior will have a set of contributing factors much different from an impaired
headwater creek in southern Minnesota. The northern trout stream may suffer from watershed
disturbances due to urbanization and the loss of riparian vegetation that once provided shade to cool the
stream. The southern creek may be impacted by agricultural nonpoint loadings as well as hydrological
changes from past practices of artificial drainage in the watershed. A small, first order stream will be
more sensitive to an external pollutant loading input than will a larger, third or fourth order stream.
The natural setting, stream morphology, and flow regime also play large roles in the reaeration and
oxygen capacity of a stream. For example, a stream reach directly downstream from a wetland complex
may reflect the naturally low DO concentrations found in wetlands. A shallow, high gradient turbulent
stream has better inherent reaeration potential than does a low gradient, sluggish stream with deep pools.
Under conditions of low stream flow, a normally well-aerated stream with alternating riffles and pools
may be reduced to mostly stagnant pools having low oxygen levels. Therefore, any analysis of DO
impairment must recognize and acknowledge these types of physical constraints that are imposed by the
natural characteristics of a watershed on its riverine system.
e. Stressor Sources on Streams
A given stream watershed has multiple sources of pollutants or physical features that affect the stream
loading capacity. These can be subdivided into human induced (anthropogenic) and natural or
background sources. Further social or political subdivisions exist to address human induced categories,
such as those regulated by the National Pollutant Discharge Elimination System (NPDES) permit
program, which controls water pollution by issuing permits that regulate point sources that discharge
pollutants into waters of the United States. Those sources with a more diffuse nature like forestry
logging or agriculture row cropping are sometimes supported by programs to assist in funding actions
like soil conservation or better site planning.
Anthropogenic (human induced activities)
Permitted pollution sources: the Clean Water Act has recognized several types of discharges from
known sources to at a potential strength of oxygen demanding substances that a National Discharge
Elimination System (NPDES) permit is required. The Chapter 40 Code of Federal Regulations Section
130 (40 CFR 130) dealing with the TMDL program requires all NPDES sources to be handled in the
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
wasteload allocation portion of the TMDL allocation. However, not all NPDES sources have the same
measures or controls placed on them in the TMDL process
NPDES types:
Industrial Process wastewater and Domestic Wastewater Treatment Facilities. These types of
facilities have a technology based effluent limit (TBEL), routinely called “secondary treatment” in
domestic facilities, of 25 mg/l five day Carbonaceous Biochemical Oxygen Demand (CBOD5) and 30
mg/l Total Suspended Solids (which in small part are undigested organic matter that was not captured in
the clarifiers) for general protection of healthy rivers and streams. Some facilities may have older
technology such as trickling filters and have a 40 mg/l CBOD5 limit. However, the TMDL is an
assessment that defines water quality based effluent limits (WQBEL) to achieve beneficial use
protection. Tertiary treatment limits in Minnesota are as low as 5 mg/l CBOD5. But limits this low are
attained with a high cost associated with the treatment plant construction and operation. These point
sources also have the potential to, and most often do discharge nitrogenous sources of oxygen
demanding material like TKN. Some also may have a temperature impact and/or a nutrient enriched
wastewater. Any of these potentially are contributing to lower dissolved oxygen levels as a direct source
of oxygen demanding material, as a catalyst, or by increasing eutrophication.
Domestic wastewater: Includes municipal wastewater treatment plants and other privately owned
plants. Minimum secondary treatment requirements are applicable for domestic wastewater facilities
where there is enough available dilution in the receiving water to assimilate the waste and maintain
water quality standards. The TBEL limits include 25 mg/L CBOD5 and 30 mg/L TSS. Equivalent
secondary treatment limits of 40 mg/L CBOD5 and 45 mg/L TSS may be applicable for some older
trickling filter facilities that meet certain criteria, as long as water quality standards are maintained in the
receiving water. When receiving water flow is low and dilution is not adequate, WQBEL applications
may require advanced wastewater treatment CBOD5 limits as stringent as 5 mg/L CBOD5, with
seasonal ammonia nitrogen limits applicable on a site-specific basis.
Industrial wastewater: Includes multiple manufacturing wastes or processing wastes, such as in the
food industry. The strength of the raw wastes can be from very light loading concentrations, such as
from noncontact cooling water (but with high temperatures which affect streams), to very concentrated
raw wastewater organic loads such as from food processing facilities. Federal categorical (industry
specific – best technology economically possible – established by USEPA) or technology based
discharge limits are assigned except where water quality based limits are more stringent.
Feedlots. In Minnesota Confined Animal Feeding Operations over 1,000 animal units must have a
NPDES permit. Minnesota stipulates in this type of permit: a zero discharge from the animal production
area; manure application set back restrictions from open water and/or tile intakes; and cropping nutrient
management requirements. These manure management requirements are sufficient to classify the
manure as agricultural stormwater runoff and not a NPDES discharge.
Stormwater Permits: Municipal Separate Storm Sewer Systems (MS4s), Construction Stormwater and
Industrial Stormwater. These types of permits may contain pollutants such as CBOD5, nitrogenous
oxygen demanding materials, nutrients, and may have the additional issue of raised temperature due to
stormwater ponding or heated impervious surfaces. In a November 2002 EPA policy memorandum
discussing how the Stormwater Programs and the TMDL programs will interact, the EPA acknowledged
that this type of permitted source acts most like other nonpoint source types, and not a wastewater
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
discharge of constant volume and concentration makeup. Due to this variability, the memorandum
further defines that it is desired that individual allocations be made for permits when possible, but it is
also acceptable to group multiple permits geographically or by type when the assessment can not
distinguish between multiple stormwater permits. The memorandum further explains that concentration
effluent limits will not typically be applied in the permit’s Stormwater Pollution Prevention Plan, but
TMDL mass wasteload allocations will be met most often through implementation of BMPs.
Reservoirs and hydropower dams: Hydropower facilities are licensed by the Federal Energy
Regulatory Commission (FERC). Hydropower licenses last from 30 to 50 years and typically stipulate
how the dams are operated, what minimum water flow levels are required, what forms of fish passage
must be installed and, in some cases, how watershed lands are managed. Well before (often 5 years) a
license expires, the dam owner must apply to FERC for a new license. The relicensing process allows
FERC, state and federal resource agencies, conservation groups, and the general public to reconsider
appropriate operations and land management for each project, taking into account current social and
scientific knowledge. If release water is from the bottom of the reservoir and the water is stratified there
is the potential for low DO concentrations downstream. If hydropower turbines appropriate a substantial
percentage of flow during low flow periods, and are withdrawing water from the lower portion of a
stratified water column, the facility may be discharging water with low DO concentrations. Spilling
through the gates or over the dam during low flows will provide aeration and increase DO
concentrations while not detracting significantly from power generation.
Parameters of Concern for NPDES sources: CBOD, NBOD, suspended solids, temperature, nutrients.
ƒ Water withdrawal permits
Department of Natural Resources Water Appropriation Permits; Regarding
Dilution Ratios. A Minnesota Department of Natural Resources (MDNR) water use
permit is required for all users withdrawing more than 10,000 gallons per day or one
million gallons per year. In order to safeguard water availability for natural environments
and downstream higher priority users, Minnesota law requires MDNR to limit
consumptive appropriations of surface water under certain low flow conditions.
Additional detailed information may be found at
http://www.dnr.state.mn.us/waters/watermgmt_section/appropriations/permits.html
•
A river or stream ecosystem is often times most stressed during low flow, late
summer conditions. These warm temperatures and slow moving waters limit not only
the amount of oxygen that can be held in the water column, but also limit the natural
sources or reaeration that would further benefit the stream. Permit effluent limits are
developed based on the 7-day average, 10-year return low flow (7Q10) events of the
stream and the dry weather design flow of the wastewater treatment facility.
Experience with numerous cases indicates that if the stream-to-effluent dilution drops
below a 10 to 1 ratio, the strength of waste will not be adequately assimilated by the
stream’s natural processes. Proper periods of allowed withdrawals must be considered
regarding low flows.
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(a) Nonpoint source loadings. Human activities on landscapes that increase either the mass
or the concentrations of pollutants associated with runoff can contribute stressors to
dissolved oxygen levels. An incomplete list of example sources of anthropogenic
nonpoint source loading includes: nonpermitted stormwater from small towns or
unincorporated areas; smaller permitted feedlots; row crop agriculture; intensively grazed
areas with or without livestock exclusion provisions; peat mining; forestry harvest sites;
and domesticated animals, like house pets or hobby farms.
(1) Common Anthropogenic Nonpoint Source Types
(i) Landuse conversions
1. Small feedlots. Smaller feedlots may have a permit, or be considered to be
not connected with surface waters, and therefore not require a State Disposal
System Permit. Small feedlots sometimes may have treatment systems that
allow a direct discharge to surface.
2. Stormwater Runoff. Small communities, roads and unincorporated
developed areas most likely contribute increased runoff and concentrations of
pollutants, similar to MS4s. However, they do not always have administrative
oversight from a NPDES permit or a Local Unit of Government.
3. Forestry Harvest Sites. Forested areas can have a very gentle presence on
the land and typically are one of the best watershed landscapes regarding
water quality. However, forestry harvests can be very disruptive during the
clearing process by introducing heavy equipment traffic, removal of
vegetation and the associated rutting and road construction. While most of
these events can be short-lived, the road construction and staging areas can
have longer term impacts.
4. Row Cropping. Agricultural row cropping can be a very intensive land use
which disturbs the vegetative cover twice a year and introduces higher
concentrations of nutrients and pesticides. Typical runoff concentrations of
sediment and sediment associated pollutants can be up to 10 times higher than
if the land was grassed or forested.
5. Pastured and Hayed lands. These lands provide a more gentle footprint,
acting like a more natural setting. However, livestock grazing in or along a
stream or river and manure application to the hay may create a scenario
similar to small feedlot concerns. The historic intensity of grazing can be
indirectly determined by the types of forage present on the site. Presence of
Kentucky Blue Grass, other short grasses, or areas completely devoid of
vegetative cover indicate higher livestock pressure.
•
Parameters of Concern: CBOD, NBOD, Sediment, Nitrogen,
Phosphorus and higher temperature.
(2) Common watershed physical changes
(i) Stream alterations: The changes on a natural stream’s form and functions can
directly impact one or more potential stressors of dissolved oxygen. The
following is an incomplete list of alterations and a short description of the stress.
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
1. Riparian Landuse Efforts to make the riparian landuse more productive
result in several limiting features: loss of shading, higher temperature runoff,
less infiltration and therefore less cool groundwater recharge back into the
stream, disconnecting the stream from the flood plain terrace and potentially
creating a unstable channel.
2. Dams and Reservoirs Many reservoirs placed in a riverine setting can create
pools which affect eutrophication, pH, temperature, ammonia levels, reduced
surface turbulence and therefore less aeration.
3. Channelization and dredging Stream straightening and deepening can
reduce the streams physical ability to provide aeration back into the water
column. Changes result in a range of impacts from stagnation (creating an
ephemeral stream where there was an intermittent stream), higher
temperatures, loss of riffles and runs (beneficial for re-entraining oxygen) and
poorly managed or outright loss of riparian area woody vegetation (beneficial
shading). A channelization project upstream of the resource also affects peak
flow events and can begin to destabilize the channel.
4. Agricultural Drainage Tile Subsurface tile can be a direct connection for
pollutant sources that were previously remotely located in the watershed. For
soluble parameters, interception and direct transport to the stream or ditch is
enhanced. For sediment and sediment attached parameters, higher delivery
ratios can occur when surface tile intakes are present. These systems can also
alter the 1 ½ to 2 year frequency flows, which determine a stream’s bankfull
flow, thus destabilizing the channel and kicking off a channel evolution
process. Under certain circumstances frost can seal the soil pores and
sufficient soil bacteria activity can then create an anaerobic environment,
which results in by-products such as ammonia.
•
Parameters/stressors: Flow, temperature, reaeration, sediment,
nutrients and organics
(3) Cultural Eutrophication Over-enriched sources of nutrients can create a nutrient to
plant (algal or weeds) production for oxygen demanding materials through a lifecycle
process. Also, too many weeds can lessen the turbulence in a stream and reduce the
reaeration process.
(i) High nutrients (phosphorus, nitrogen) can directly create a shift in the ecosystem
where boom and bust life cycles create a collection of biomass in slow velocity
reaches, which become available for bacterial decay processes using higher than
normal levels of dissolved oxygen.
(ii) Plant cell wall decomposition from natural or human induced alterations in
wetland hydrology. For instance disturbances that access high organic materials
previously sequestered are: ditching through wetlands, peat mining, and
abnormally heavy traffic from short term site use, such as from logging, can
create rutting which flushes or creates a flow blockage of parts of wetlands.
•
Parameters phosphorus, nitrogen, organic detritus, diurnal fluctuations
in dissolved oxygen (excessive high to low daily results).
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
(4) Natural: Many of the conditions described above occur naturally in the environment;
some at a reduced rate where the stream dissolved oxygen balance can be brought
back into compliance, and some at a rate that always held a reach out of compliance,
such as below a large wetland complex with high organic decay and little natural
aeration capability.
(i) Groundwater recharge to the stream Groundwater coming into a reach may be
doing so with little or no dissolved oxygen present. An isotopic survey of the
stream and groundwater can be done to compare the ratio of dilution occurring.
(ii) Riparian and Backwater Interactions Large sources of stagnate water with low
dissolved oxygen, or water with a high detritus content, can be flushed into a
stream under certain flow conditions.
(iii) Winter Ice Cover Winter ice cover can limit the amount of reaeration that
occurs. When this is combined with oxygen demanding material loadings from
eutrophication or point sources (for instance), winter low dissolved oxygen levels
can develop.
•
Parameters: organic, low DO water causing dilution, nutrients, pH
D. Problem Definition
a. Applicable Water Quality Rules
Water quality standards are fundamental tools that help protect Minnesota’s abundant and valuable
surface and ground water resources. The comprehensive Clean Water Act amendments of 1972 require
states to adopt water quality standards that meet the minimum requirements of this federal law.
Minnesota’s water quality standards meet or exceed federal requirements.
The federal Clean Water Act also requires all states to review and revise where necessary their water
quality rules every three years. Water quality standards should be updated periodically to reflect the
latest scientific information.
Water quality standards and related provisions are found in several Minnesota rules, but the primary rule
for statewide water quality standards is Minn. R. Ch. 7050. Included in this rule are:
A classification system of beneficial uses for both surface and ground waters
Numeric and narrative water quality standards
Nondegradation provisions
Provisions for the protection of wetlands
Treatment requirements and effluent limits for wastewater discharges
Other provisions related to the protection of Minnesota’s water resources from pollution.
Water quality standards generally include the following components:
•
•
Beneficial uses – identification of the uses our water resources provide to people and wildlife.
Numeric standards – allowable concentrations of specific pollutants in a waterbody, established
to protect the beneficial uses.
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
•
•
Narrative standards – statements of unacceptable conditions in and on the water.
Nondegradation – extra protection for high-quality or unique waters.
“Beneficial uses” are the uses that states decide to make of their water resources. The process of
determining beneficial uses is spelled out in the federal rules implementing the Clean Water Act. Seven
beneficial uses are defined in Minn. R. 7050.0200. These uses and the use-class designations are listed
below. The class numbers 1–7 are not intended to imply a priority ranking to the uses.
Class 1 - Drinking water
Class 2 - Aquatic life and recreation
Class 3 - Industrial use and cooling
Class 4A - Agricultural use, irrigation
Class 4B - Agricultural use, livestock and wildlife watering
Class 5 - Aesthetics and navigation
Class 6 - Other uses
Class 7 - Limited Resource Value Waters All surface waters are protected for multiple uses:
o Most are Class 2 – protected for aquatic life and recreation
o Some are Class 7 – Limited Resource Value Waters
Both Class 2 and Class 7 waters are protected for:
o Class 3 – Industrial uses
o Class 4 – Agriculture and wildlife uses
o Class 5 – Aesthetics and navigation
o Class 6 – Other uses
In addition, some surface waters are also protected for drinking (Class 1)
The vast majority of surface waters in Minnesota are Class 2, protected for aquatic life and
recreation. Limited Resource Value Waters are protected for very limited aquatic community and
recreational uses. Each Class 7 waterbody has been individually assessed and the change from
Class 2 to Class 7 adopted into Minn. R. 7050.0470. Most Class 7 waters are headwater streams
or channelized ditches that provide poor aquatic habitat due to low flows and/or channel
alterations. Class 7 reaches range from less than one to about 20 miles in length, and all together
make up about one percent (~ 900-950 miles) of Minnesota’s 92,000 miles of rivers and streams.
Subclasses. Use classes 1, 2, 3 and 4 have subclasses. Of these, the Class 2 subclasses are the ones most
people should be familiar with; they are listed below:
2A Cold-water fisheries, trout waters, also protected as a source of drinking water
2Bd Cool- and warm-water fisheries, also protected as a source of drinking water
2B Cool- and warm-water fisheries (not protected for drinking water)
2C Indigenous fish and associated aquatic community (not protected for drinking water)
2D Wetlands (not protected for drinking water).
b. Numeric standards
Numeric water quality standards represent safe concentrations in water that protect a specific beneficial
use. If the standard is not exceeded, the use should be protected. Minnesota R. Ch. 7050 has numeric
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
standards designed to protect drinking water, aquatic life and recreation, industrial, agricultural,
aesthetic and wetland uses, and Limited Resource Value Waters.
In general, the numeric standards used most often to protect surface waters are the Class 2 aquatic life
and recreation standards. And, with a few notable exceptions (e.g., the Class 3B chloride standard and
the Class 4A sulfate standard), if the Class 2 standards are met, the other usually “less sensitive” uses are
protected as well.
Most of Minnesota’s aquatic life (Class 2) standards are based on EPA aquatic life criteria. The EPA
develops and publishes the criteria as required by the Clean Water Act
Numeric standards are listed in two places in Minn. R. Ch. 7050. First, all the numeric standards
applicable to four common categories of surface waters are listed in Minn. R. 7050.0220. For
example, all the standards applicable to trout waters, and their associated uses (including the
drinking water standards), are listed together. This helps remind users that surface waters are
protected for multiple uses and that some pollutants have more than one applicable standard. In such
cases the most restrictive standard applies.
The second place numeric standards are listed is by individual use classes in Minn. R. 7050.0221 –
7050.0227. For example, Minn. R. 7050.0222 has separate lists of the standards for each Class 2
subclass.
The Dissolved Oxygen water quality standards for Class 2 waters are listed in Minn. R. 7050.0222
subp. 2,3,4,5.
Subp. 2. Class 2A waters; aquatic life and recreation.
The quality of Class 2A surface waters shall be such as to permit the propagation and maintenance of a
healthy community of cold water sport or commercial fish and associated aquatic life, and their habitats.
These waters shall be suitable for aquatic recreation of all kinds, including bathing, for which the waters
may be usable.
Dissolved oxygen 7.0 mg/l as a daily minimum
This dissolved oxygen standard requires compliance with the standard 50 percent of the days at
which the flow of the receiving water is equal to the lowest weekly flow with a once in ten-year
recurrence interval (7Q10).
Subp. 3. Class 2Bd waters.
The quality of Class 2Bd surface waters shall be such as to permit the propagation and maintenance of a
healthy community of cool or warm water sport or commercial fish and associated aquatic life and their
habitats. These waters shall be suitable for aquatic recreation of all kinds, including bathing, for which
the waters may be usable.
Dissolved oxygen
5.0 mg/l as a daily minimum
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
This dissolved oxygen standard may be modified on a site-specific basis according to subpart 8,
except that no site-specific standard shall be less than 5 mg/l as a daily average and 4 mg/l as a daily
minimum. Compliance with this standard is required 50 percent of the days at which the flow of the
receiving water is equal to the lowest weekly flow with a once in ten-year recurrence interval
(7Q10).
Subp. 4. Class 2B waters.
The quality of Class 2B surface waters shall be such as to permit the propagation and maintenance of a
healthy community of cool or warm water sport or commercial fish and associated aquatic life, and their
habitats. These waters shall be suitable for aquatic recreation of all kinds, including bathing, for which
the waters may be usable.
Dissolved oxygen
5.0 mg/l as a daily minimum
This dissolved oxygen standard may be modified on a site-specific basis according to subpart
8, except that no site-specific standard shall be less than 5 mg/l as a daily average and 4 mg/l
as a daily minimum. Compliance with this standard is required 50 percent of the days at
which the flow of the receiving water is equal to the lowest weekly flow with a once in tenyear recurrence interval (7Q10). This standard applies to all Class 2B waters except for those
portions of the Mississippi River from the outlet of the metro wastewater treatment works in
Saint Paul (River Mile 835) to Lock and Dam No. 2 at Hastings (River Mile 815). For this
reach of the Mississippi River the standard is not less than 5 mg/l as a daily average from
April 1 through November 30, and not less than 4 mg/l at other times.
Subp. 5. Class 2C waters.
The quality of Class 2C surface waters shall be such as to permit the propagation and maintenance of
a healthy community of indigenous fish and associated aquatic life, and their habitats. These waters
shall be suitable for boating and other forms of aquatic recreation for which the waters may be
usable. The standards for Class 2B waters listed in subpart 4 shall apply to these waters except as
listed below:
Dissolved oxygen 5.0 mg/l as a daily minimum.
This dissolved oxygen standard may be modified on a site-specific basis according to subpart
8, except that no site-specific standard shall be less than 5 mg/l as a daily average and 4 mg/l
as a daily minimum. Compliance with this standard is required 50 percent of the days at
which the flow of the receiving water is equal to the lowest weekly flow with a once in tenyear recurrence interval (7Q10). This dissolved oxygen standard applies to all Class 2C
waters except for those portions of the Mississippi River from the outlet of the metro
wastewater treatment works in Saint Paul (River Mile 835) to Lock and Dam No. 2 at
Hastings (River Mile 815) and except for the reach of the Minnesota River from the outlet of
the Blue Lake wastewater treatment works (River Mile 21) to the mouth at Fort Snelling.
For this reach of the Mississippi River the standard is not less than 5 mg/l as a daily average
from April 1 through November 30, and not less than 4 mg/l at other times. For the specified
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
reach of the Minnesota River the standard shall not be less than 5 mg/l as a daily average
year-round.
E. Overview of TMDL project decision points
The TMDL project development process includes decision points and may often be an iterative process
backtracking occasionally to confirm or adjust pre-existing decisions with regard to newly gathered
information or understanding. The following flow chart is a logic tree showing some of the critical steps
a project team works through: It is followed by a table with narrative keys referencing the pages where
the technical discussion can be found in this protocol and then referencing stakeholder process and
stressor identification steps.
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
Figure 13. Flowchart Diagram of the Low Dissolved Oxygen: General Problem Investigation
and Attainment Strategy
303d TMDL List
• WQ Standards
• NPDES data
• Stakeholder input
• Stream DO data
• Mapping tools
• Flow data
(1)
General Problem
Definition
Comprehensive Data
RFP
Potential
Start
(2) Collection (existing)
Data Review and
Evaluation
(3)
(7)
(8)
Implement &
monitor
(4)
Are key DO
stressors solely
due to natural
background? Or
in Attainment?
Possibly
(5)
Stakeholder
Inputs
Identify Data Gaps
Acquire New
Data to Support
Analysis
(9)
Yes
Policy and
Select Analysis
Framework
No
Develop Analysis
Tool(s)
No
Policy and
(10)
Try
mitigation
measures
first?
Stakeholder
Inputs
Develop WLA and LA
Scenarios
(11)
Policy and
Stakeholder
Inputs
Yes
Acquire New
Data to Evaluate
Background
(12)
Is DO
standard
attainable?
No
Yes
Delisting Strategies:
(6)
• Natural background
• Site-specific standards
• Use Attainability Analysis to
remove/modify beneficial uses
•
New Data in Attainment
Policy and
Stakeholder Inputs
Minnesota Pollution Control Agency
Delisting Strategies:
Develop and
(13)
Implement the TMDL
Policy and
Stakeholder Inputs
36
(14)
• Site-specific standards
• Use Attainability Study to
remove/modify beneficial uses
• Variance
Policy and
Stakeholder Inputs
Dissolved Oxygen TMDL Protocols and Submittal Requirements
Table 1. Flowchart Key (Part 1: Protocol Technical Flow Path; Part 2: Strength of Evidence
and Stakeholder Parallel Flow Path)
Low DO: General Problem Investigation and Attainment Strategy
Box
Key
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Part 1: Description
Technical Flow Path
Develop a general description of what is known about the water quality impairment,
using readily available information on applicable water quality standards, discharger
data, monitoring data, assessment data, and local knowledge.
Identify sources of physical, chemical, and biological data; obtain and compile data;
and develop a data management system.
Provide preliminary review and evaluation. What are key stressors on stream DO?
What are critical conditions for DO impairments? What are the prominent data gaps?
From existing data review and evaluation, is the impairment due solely to natural
and/or irreversible conditions? If yes, then consider strategy for delisting the impaired
water (6). If no, then proceed into detailed analysis (7). If additional data is needed to
make a determination on natural conditions, identify data needs and acquire new
information (5).
Identify data gaps and collect additional background information.
Delisting strategies may include: natural background conditions preclude WQ standard
attainment; unique conditions warrant a site-specific standard development;
designated beneficial uses are neither present nor attainable; the existing condition
may not be natural but is basically irreversible.
With consultation and input from stakeholders, assess project objectives, available
resources, and analytical tools to develop an overall project framework that identifies
roles of key participants and stakeholders. What is the proper balance of
local/state/contracted resources? Define scope of services, if any, to be provided by
contracted consultants. Develop RFP(s) as needed.
Based on the preliminary data review and evaluation (3), identify information gaps
critical to the selected analysis alternative.
Design and conduct field studies to obtain physical, chemical, biological stream
information; kinetic rate determinations; flow and hydraulics (time-of-travel); diurnal
DO data (algal productivity); point and nonpoint loadings; bio-assessments; etc., to
satisfy data needs of analysis tool (model).
Set up the selected general modeling framework with site-specific information.
Calibrate and validate model with observed data. Use model to perform component
analysis of DO sources and sinks and relate to the prominent stressors. Perform
sensitivity analysis on key parameters to understand model response to loadings.
Perform accuracy check by comparison of model output with observed data. Report
results; receive feedback from stakeholders.
With consultation and input from stakeholders, design and perform analysis for
various example scenarios that evaluate and define WLA, LA, MOS, and reserve
capacity.
Does the analysis predict management scenarios having reasonable potential to meet
project objectives for attaining water quality standards? If yes, proceed to TMDL
development and implementation (13). If no, then consider strategies for delisting the
impaired water (14).
Prepare final technical report with recommendations for developing and implement
the TMDL.
Delisting strategies may include: natural background conditions preclude WQ standard
attainment; unique conditions warrant a site-specific standard development;
designated beneficial uses are neither present nor attainable; the existing condition
may not be natural but is basically irreversible; water quality variance.
Minnesota Pollution Control Agency
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Protocol References
¶ page 39
¶ page 41
¶ page 45
¶ page 45
¶ 45
¶ Stakeholder process
page 6; Rigor page 50
and Analysis page 51,
approaches page 58
III. Analysis
¶ page 59
III. Analysis
¶ page 59
III. Analysis
¶ page 63
III. Analysis
¶ page 67
III. Analysis
¶ Page 6 SI and
weight of evidence
IV. Chapter 3
submission requirements
Dissolved Oxygen TMDL Protocols and Submittal Requirements
Box
Key
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Part 2: Description
Strength of Evidence (Stakeholder Flow Path)
Assemble stakeholder group(s) that will: 1) provide local information, 2)
communicate well with other watershed interests, 3) assess policy questions,
4) assess technical questions, and 5) provide perspectives and input to the
“Reasonable Decision Maker” regarding the influencing of the final
decisions.
Identify sources of physical, chemical, and biological data; obtain and
compile data; and develop a data management system.
Provide preliminary review and evaluation. What are key stressors on stream
DO? What are critical conditions for DO impairments? What are the
prominent data gaps? Do local perceptions line up with data evaluation?
From existing data review and evaluation, is the impairment due solely to
natural and/or irreversible conditions? If yes, then consider strategy for
delisting the impaired water (6). If no, then proceed into detailed analysis (7).
If additional data is needed to make a determination on natural conditions,
identify data needs and acquire new information (5).
Identify data gaps and collect additional background information.
Delisting strategies may include: natural background conditions preclude WQ
standard attainment; unique conditions warrant a site-specific standard
development; designated beneficial uses are neither present nor attainable; the
existing condition may not be natural but is basically irreversible.
With consultation and input from stakeholders, assess project objectives,
available resources, and analytical tools to develop an overall project
framework that identifies roles of key participants and stakeholders. What is
the proper balance of local/state/contracted resources? Define scope of
services, if any, to be provided by contracted consultants. Develop RFP(s) as
needed. Set up RFP(s) to answer questions, validate or modify preconceived
notions and provide detailed reports.
Technical team
Technical team
Set up the selected general modeling framework with site-specific
information. Calibrate and validate model with observed data. Use model to
perform component analysis of DO sources and sinks and relate to the
prominent stressors. Perform sensitivity analysis on key parameters to
understand model response to loadings. Perform accuracy check by
comparison of model output with observed data. Report results; receive
feedback from stakeholders.
With consultation and input from stakeholders, design and perform analysis
for various example scenarios that evaluate and define WLA, LA, MOS, and
reserve capacity. Seek expertise on specific issues that arise on each Sector
regarding the challenges of change during implementation.
Does the analysis predict management scenarios having reasonable potential
to meet project objectives for attaining water quality standards? If yes,
proceed to TMDL development and implementation (13). If no, then
consider strategies for delisting the impaired water (14).
Prepare final technical report with recommendations for developing and
implement the TMDL.
Delisting strategies may include: natural background conditions preclude WQ
standard attainment; unique conditions warrant a site-specific standard
development; designated beneficial uses are neither present nor attainable; the
existing condition may not be natural but is basically irreversible; water
quality variance.
Minnesota Pollution Control Agency
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Stakeholder
Key
(Page 6)
(page 41 and example
Section J, page 69)
(page 45; seeking to
identify the
stakeholder opinions)
(page 45)
Page 45
Stakeholder process page
6; Rigor page 50 and
Analysis page 51,
approaches page 58
(page 63)
An iterative process,
updating the decision
makers with progress,
sometimes modifying
the analysis via the
weight of evidence.
(page 67)
Sector costs and risks.
Shared reduction
decisions
(page 6 & 67)
Encouraging (11) to be
an iterative process if
not attained
(g)
Consideration of
future NPDES
ramifications, Landuse
Ordinances,
Dissolved Oxygen TMDL Protocols and Submittal Requirements
F. Initial Problem Assessment
Section 305(b) of the federal Clean Water Act requires states to report to Congress with an assessment
of their water bodies, whether meeting standards or impaired, while Section 303(d) requires states to
develop a list of impaired waters for purposes of the TMDL program. In general, the MPCA assessment
process uses established protocols for interpreting water quality data and other information used to
determine impaired conditions by stream reach. The Professional Judgment Group (PJG) is composed
of assessment staff who know how the preliminary assessments were done, and monitoring staff who
advise on the correct interpretation of monitoring data collected by their organization. For additional
information on the assessment process, see: Guidance Manual for Assessing the Quality of Minnesota
Surface Waters For Determination of Impairment, 305(b) Report and 303(d) List, MPCA, October 2005.
http://www.pca.state.mn.us/publications/wq-iw1-06.pdf
1)
Impairment Status and History
Assessments of use support in Minnesota are made for individual waterbodies. The waterbody unit used
for river system assessments is the river reach or “assessment reach”. A river reach extends from one
significant tributary river to another and is typically less than 20 miles in length. The reach may be
further divided into two or more assessment reaches when there is a change in the use classification (as
defined in Minn. R. ch. 7050), or when there is a significant morphological feature such as a dam, or a
lake within the reach. All assessment reaches are indexed to the National Hydrographic Data set
(NHD). Each waterbody is identified by a unique waterbody identifier code, comprised of the USGS
eight digit hydrologic unit code plus the three digit assessment reach. It is for these specific reaches that
the data are evaluated for potential use impairment.
Water quality and other types of data are the most important component of impairment determinations.
Data collection and analysis involves sampling, laboratory analysis, quality assurance/quality control
(QA/QC), data storage, and finally, data analysis. Most water quality data used in this process are a
result of condition monitoring by the MPCA, but comparable
Condition monitoring is
data collected by others are used too, as long as it conforms to
designed to determine
acceptable QA/QC requirements. The MPCA uses data
current status and trends in
collected over the most recent 10-year period for all the water
water quality.
quality assessments. The Professional Judgment Group
recognizes that dissolved oxygen can naturally drop below the
standard in rivers at times for reasons that have nothing to do with pollution. These natural occurrences,
to the extent they are known, are taken into consideration as part of the impairment assessments.
The listing of a waterbody on the 303(d) list triggers a regulatory response on the part of the MPCA to
address the causes and sources of the impairment through the TMDL process. Starting with data and
information used in the impairment assessment, the TMDL project team must pull together additional
information that is readily available in order to develop a general description of what is known about the
impairment.
2)
Prepare a Preliminary Delineation of the Study Area
Create project maps of the stream reaches of concern, their contributing watersheds, current land use,
and permitted discharger locations. Use appropriate paper maps and MPCA GIS software (ArcGIS) with
readily available data layers. Ensure that all newly constructed or imported data layers are fully
compatible with MPCA spatial data storage standards:
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
Coordinate system:
Datum:
Spheroid
Units:
UTM zone 15 (extended)
North American Datum of 1983 (NAD83)
GRS1980
Meters
Simple stick diagrams are often useful to illustrate the connectivity of the river system and the relative
locations of tributary inputs, permitted dischargers, and nonpoint source regions.
3)
Define the Spatial and Temporal Scale of the Impairment
From existing monitoring data, define which reaches of the waterbody have documented impairments
for dissolved oxygen. Is the DO impairment problem localized and distinct or is it more extensive? Do
the monitoring data indicate any seasonal pattern to the times of DO impairment? Do the monitoring
data provide any insight into the duration (days, weeks, months) of low DO? Do the monitoring data
provide any information about the diurnal variation of DO concentrations? What is the magnitude of the
DO deficits (DO concentration and % saturation)? What is the frequency of low DO occurrences? Are
the occurrences predictable or do they occur randomly?
4)
Investigate Flow Dependency of the Impairment
Using available stream flow information in the project area, determine the flow conditions at the time of
water quality sampling. Are there any apparent relationships between prevailing flow conditions and the
instances of low DO? For example, are DO problems most prevalent during periods of low stream
flow? Are impairments more prevalent under higher flow conditions when episodic surface runoff
events may provide a major component of stream flow? Also identify any reservoirs, dams, or
hydropower facilities that may regulate flows in the project area.
5)
Compile a List of Permitted NPDES Dischargers in the Study Area
Using MPCA discharger inventory databases (WQ DELTA), generate a list of all permitted dischargers
including major animal feedlots in the study area. Describe their facility, their design flow, location and
receiving waters, permitted load limits, discharge frequency, and general compliance status.
6)
Develop a List of Potential Stakeholders
Identify and initiate contact with individuals and groups in the governmental and private sectors that
should be advised of the TMDL development schedule and plan. Potential stakeholders may include
representatives of federal, tribal, state, local (county and municipal) governments; NPDES permitted
dischargers; watershed organizations; landowners; agricultural producers; industry trade organizations;
and environmental advocacy groups. Consider the potential role each stakeholder could play in the
TMDL development and implementation.
7)
Develop a Technical Advisory Team
The technical advice solicited during development of a TMDL can be both water quality management
issues and for a better understanding of land use specific issues. The technical advisory team is
composed of a diverse group of local representatives who work with the different land uses and have
different expertise areas. Their input on critical aspects of change potential assists during the
identification of potential local sources of the key parameters. Later in the process these members can
provide assistance in defining the reasonable levels of expected change from an economic or social point
of view. The individual members also can be sources of communication to others in their line of work.
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
EPA’s volunteers guide to setting watershed goals lays out steps that are the
building blocks for a robust public involvement process when the teams formed
learn to use the key tools of the stressor identification process of validation,
elimination and weight of evidence.
The project manager should develop a summary statement that describes the impairment problem, its
spatial and temporal boundaries, and which identifies known factors potentially impacting the oxygen
resources of the impaired stream. This summary will provide a focus for the more comprehensive
follow-on task of gathering and compiling existing data from various sources that will be used later in
the problem analysis tasks.
a. Comprehensive Data Compilation from Existing Resources
Factors potentially affecting the dissolved oxygen balance in streams are numerous and complex.
Therefore, a DO impairment analysis requires site-specific data in order to define the important causeeffect relationships unique to each case. A comprehensive effort is needed to assemble existing
environmental data collected from a variety of sources. An inventory of the compiled data would reveal
the areas of obvious data deficiencies in content, quality, and spatial and temporal coverage.
1) What are the Sources of Existing Data?
The answer to this question, when combined with the evaluation of quantity and quality of the data
available, will in large part set the scope of the project. The following is a listing of environmental
data types and source information.
Ambient Water Chemistry
A number of federal, tribal, state, and local government entities, and local water management
organizations, collect water quality data. In large part, these data are stored in and can be retrieved from
the MPCA Water Quality Database system. Access to data is available through the Water Quality
Assessment Viewer site: http://pca-gis03/website/umrb/pjg/index.htm which highlights and displays the
Assessment Unit Identifier (AUID) and monitoring stations, and links to the EDA site.
Access to data that can easily be exported is available through the Lookup Assessment database:
x:\Databases\Water_Quality\Assessment Data Lookup
This database contains information from the PJG Assessments meetings, data summaries for AUIDs
listed 1992-1998, and direct access to assessment data for AUIDs listed 2002-2006.
These sources are preferable to the Environmental Data Access webpage (EDA), which is not as useful
for retrieving data. EDA can provide valuable information on alternate station ids, period of record,
project and purpose associated with sampling, etc. Access to water quality data through a map-based
system is available online at the MPCA Environmental Data Access (EDA) site:
http://www.pca.state.mn.us/data/eda/index.cfm. Staff in the MPCA Environmental Data Management
Unit can also provide assistance in data search and retrieval from the national STORET database.
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Data may also be available from the WQDelta permitting database (Daily Values Screen) if an NPDES
permittee is required by permit to sample the receiving water upstream and/or downstream of the
discharge. Standard reports are available in the database that include all individual sample results.
These data, though, have not gone through the QA/QC process that applies to data in STORET, so
should be used with some caution. Staff in the Water Standards Unit can provide assistance in data
search and retrieval for these data.
Biological Assessments
The MPCA conducts biological monitoring to assess the health of riverine and wetland environments
utilizing fish, macroinvertebrate, or plant communities. Biological communities are subjected to the
cumulative effects of all activities within a watershed and are continually integrating environmental
conditions over time. They represent the condition of their aquatic environment. Biological monitoring
is often able to detect water quality impairments that other methods may miss or underestimate. It
provides an effective tool for assessing water resource quality regardless of whether the impact is
chemical, physical, or biological in nature. Information and data from biological monitoring sites are
available online at the MPCA EDA site: http://www.pca.state.mn.us/data/eda/index.cfm or from the
MPCA Biological Monitoring Unit staff.
Fish Kill Incidents
The Minnesota Department of Natural Resources (MDNR) is the lead agency that investigates reported
fish kills to determine causes and to assess damages. Causes range from the obvious contaminant spills
to less obvious natural occurrences. The MPCA and Department of Agriculture is a principle
cooperator.
Stream Flow
Stream flow data is essential for the analysis of dissolved oxygen impairments. The U.S. Geological
Survey (USGS) is the principal source of daily stream flow data. These data can be accessed online at:
http://mn.water.usgs.gov/. The site also provides links to other sources of water resource and stream
flow data, such as MDNR and the U.S. Army Corps of Engineers.
Hydstra
The HYDSTRA data base is under development at the MPCA. Hydstra will also be storing diurnal DO
data because only summary data is expected to go into STORET. Contact information regarding the
stage of development should be requested from Wade Gillingham at the MPCA.
Meteorological
Weather conditions play a key role during periods of low dissolved oxygen in streams. Historical
meteorological data for Minnesota is available online from the Climatology Working Group at:
http://climate.umn.edu/.
NPDES Point Sources
The MPCA maintains a computerized database of permitted NPDES dischargers in its WQ DELTA
system. Monthly summary reports (Discharge Monitoring Reports or DMRs) of effluent quantity and
quality monitoring submitted by each permittee are available in paper files or electronically from
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DELTA. Web-based access to data from the same reports is available at the MPCA EDA site:
http://www.pca.state.mn.us/data/eda/index.cfm
The MPCA OnBase Web Client software also provides access to more detailed supplemental reports
that are submitted along with the DMRs. Staff in the Regulatory Data Management and Analysis Unit
in the Land and Water Quality Permits Section of the Industrial Division can provide assistance in data
search and retrieval.
Using the Stressor Identification
Process: Using the stakeholder
advisory group and the technical
advisory group, have a guided
discussion on where pollution
source activities are located in the
basin. It is often good to do this
over a topographical map with
facilities indicated to confirm
locations. During the course of
the discussion, record the
opinions and concerns of the
members. Identifying the
perceptions and potential sources
is critical to creating a better
information process for the
watershed and to make sure the
rigor of the investigation will
match the questions that need to
be answered.
Soils and Land Use
GIS-based information on land use, soils, and other
mapping layers are available at the Minnesota Land
Management Information Center:
http://www.lmic.state.mn.us/.
Other possible sources of information include:
Agroecoregions: The University of Minnesota has
created a land form data base referred to as
Agroecoregions which combine soil types, land use
and agricultural production statistics. This is
available in map form and tabular and is an
excellent means of beginning the data discussion
with locals. This can be found on the X-drive at
X:\Agency_Files\Water\Impaired
Waters\GIS Projects\TMDL Info\Agroecoregions
Historical Water Quality and Hydrological
Studies
Federal, state and local entities may have conducted
special stream studies in your project area that can
have valuable historical information applicable to
current impairments. Check with the regional
USGS office and the MDNR area hydrologist for
information on past studies. The MPCA
Environmental Analysis and Outcomes Division
maintains paper files of historical stream and water quality surveys. Typically these are intensive
synoptic type surveys conducted over 1 to 3 days duration to collect physical and chemical stream data
to be used for waste load allocation purposes.
Local Watershed Studies
Local watershed and lake management organizations could provide valuable historical information on
the resource and special insight for problem definition.
How will Data be Managed for this Project?
Development of an efficient and reliable data management system is important for each TMDL project
to provide for the proper documentation of subsequent analysis and implementation planning. Decisions
on how paper files and electronic data are to be inventoried and stored should be made early in the
TMDL planning phase. The data management system should be designed so that project staff and
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cooperators have efficient access to the data and files. The data management system must be consistent
with all MPCA policies and procedures (ref: Policy and Procedures Manual for Management of Public
Access to Government Data, MPCA, March 2003). Consideration should be given to developing an online web presence for the TMDL project that will allow public access to project information.
b. Data Review and Evaluation
Once existing data have been collected and compiled, the TMDL team needs to provide a critical
evaluation and interpretation of the data with a goal of addressing the key questions: (1) What are the
prominent data gaps?, (2) Can the key stressors of stream DO be identified?, (3) What are the critical
design conditions for the impairment analysis?
c. Prominent Data Gaps
Whenever the data review identifies large and obvious data gaps that are critical to the preliminary
identification of stressors on stream DO, the TMDL team should initiate a plan for MPCA staff or local
cooperators to begin collecting the appropriate data. The plan should be designed with flexibility to
screen out less likely sources in order to focus efforts on the more likely stressors.
A stream reach may be listed for DO impairments based on data collected from a single monitoring site,
or from a very few monitoring sites. Often, the coarse spatial resolution of the existing monitoring data
does not provide adequate definition of the zone of oxygen impairment, or whether significant spatial
gradients in organic pollutants exist in the study area. For these cases, additional monitoring sites need
to be identified and data collected. The same issues pertain to the temporal resolution of existing data.
If the existing data was only collected under similar seasonal or flow conditions, the potential for
impairment at other times is unknown. Additional monitoring is warranted for screening purposes to
identify other possible periods of impairment.
Background conditions need to be defined at the boundaries of the study area for the pollutant mass
balance and transport analysis. Information is needed on the quantity and quality of water entering and
leaving the study area boundaries; i.e., the headwater, major tributary inflows, and study area terminus.
Data for point source discharges is generally available. On the other hand, mass loading data for
nonpoint sources is not commonly available. These data, which are event-based and runoff dependent,
become important when the DO impairments in a stream appear to be related to periods of unsteady
flow conditions. In such cases, high-resolution monitoring during runoff events may be needed to
define the timing and loading from nonpoint sources.
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d. Stressor Identification Starting Questions
Major parameters affecting the DO balance
within a stream can be summarized as:
Carbonaceous deoxygenation
Nitrogenous deoxygenation
Atmospheric reaeration
Sediment oxygen demand
Photosynthesis and respiration of aquatic plants
When the data does not offer cause and effect
relationships or adequate information to
eliminate a potential source from further
consideration, the EPA stressor identification
guidance recommends using a weight of
evidence approach. Weight of evidence
(sometimes called “strength of evidence”) is
best explained as sufficient circumstantial
evidence to convince the reasonable decision
maker that the source is or is not a primary
candidate of the stress. Similar to how a doctor
diagnoses a patient, or a detective investigates
a crime, fulfilling certain key requirements
must be met before a source can be considered
for further evaluation.
• Does the source contain or
emit any of the critical
parameters?
• Is there a pathway to the reach
in question?
• Is the key parameter(s)
persistent enough to impact the
reach in question?
• Does the source discharge the
key parameters in the same
time period that the
impairment occurs over?
Only when the answers to these questions are
positive should further investigation be done to
quantify or estimate the relative potential and
actual loadings that do occur.
Evaluate the existing data to identify the pollutants
of concern (projects can often expect existing
information will not be adequate to identify the
concerns) by looking for evidence of strong
linkages between stressor parameters and watershed
sources with respect to the DO impairment.
For example, does the data sufficiently define the
extent of the impairment upstream and downstream
from the stations which were used to list it on the
303d list? Or, are there known landuse sources
such as a wastewater discharge of organic pollutants
which can impact stream DO through both the
carbonaceous and the nitrogenous deoxygenation
processes? Does the data suggest any correlation
exists between point source discharges and
observed water quality impacts? Should the project
be faced with either of these situations certain
questions should be asked of the assessment:
1) Does the data define the spatial and
temporal extent of the impairment or source
loading? What are the critical periods?
2) Does the project need to set up further
monitoring or data gathering to investigate land use types? Or, land use source loadings? Or,
water chemistry in the stream?
Spatial locations of the sources and sample locations for the stream chemistry and physical parameters
such as temperature and flow are important to record with each step. Using GIS or stick figure maps of
the watershed are good ways to communicate information and document assumptions and findings.
Sources, both point and nonpoint, may not only have just immediate impacts on stream DO. Nutrients in
runoff will stimulate growth and photosynthetic productivity of aquatic plants. Temperature shifts may
be sufficiently offset where a stream gradient is steep but impair the system where the gradient is flatter.
Is there any correlation between storm frequency, duration, and magnitude with downstream water
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quality responses? Hydrological alterations within a watershed, such as dam construction and channel
dredging and straightening, can affect the natural reaeration and sediment transport.
e. Consideration of the Dynamics in a Watershed
In many cases, cause-effect linkages will be obscured by a combination of stressor sources impacting
stream DO through multiple processes.
The data evaluation should try to identify cases of DO impairment that are of possible natural origin, and
not from a direct result of human influence within a watershed. Groundwater influences, backwater or
wetland influences are a few examples. Where data gaps exist, additional focused data collection of
background water quality may be needed to help make that determination. When well defined and
understood, these cases of natural impairment may qualify for special consideration under a delisting
strategy and would not be subject to the full TMDL development process. However, if a reach is
delisted due to the condition being attributed to natural background conditions, future anthropogenic
sources, especially those requiring a NPDES permit will be restricted by the implementation plan.
Where data evaluation suggests that a DO impairment caused by an obvious and dominating stressor
that can be readily mitigated through voluntary actions or by applying existing regulatory authorities
(e.g., an NPDES discharge permit or a dam removal project), then there may be reason to consider
implementing the mitigation directly and monitor for improvements in water quality before making a
decision to continue through the TMDL development process. If the mitigation corrects the DO
impairment, then this situation would also be a candidate for delisting.
G. Critical Project Design Conditions
A thorough evaluation of existing data should characterize the DO impairment problem by identifying
the conditions under which the stream is most often stressed for DO. This characterization provides the
framework for establishing the conditions to be used in designing the impairment analysis. Critical
conditions to consider include:
Flow regime
Discharge events
Storm/runoff events
Seasonality
Biological
Project Boundary
The capacity of a stream to assimilate a waste load of pollutants generally decreases proportionally with
decreasing stream flow. A given load of pollutants discharged into a low flow stream will result in
higher concentrations of the pollutant and a greater chance of water quality problems than if the same
load were discharged into the same stream under higher flow conditions. Because the ambient flow
conditions may also influence factors affecting deoxygenation, reaeration, and biological processes,
defining the critical flow regime for DO impairments is important to the analysis.
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An evaluation of the magnitude, frequency, and duration of deliveries of pollutant loads to the stream is
an important consideration for designing the impairment analysis. A continuously discharging point
source with low effluent variability has a much different impact on stream water quality than does a
seasonal or intermittent point source discharge, or a nonpoint source loading driven by storm events.
Impacts from a continuous discharge may best be evaluated under design conditions using steady-state
analytical methods and assumptions. The event-based and intermittent loading situations will require
non-steady state analysis with variable design conditions.
Seasonally variable ambient conditions, especially temperature, may be strongly correlated with DO
impairment problems. The data evaluation should identify design conditions that establish the critical
seasons for impairment analysis. Although DO impairments are most common during late summer
under low flow and high water temperature conditions, event-based pollutant loadings may cause
problems during other seasons.
In river systems impacted by large standing crops of aquatic plant life, design conditions for the
impairment analysis must include consideration of population dynamics and productivity of the plants.
While an actively growing plant population may provide a net benefit to stream dissolved oxygen
through photosynthesis, the most critical conditions in the stream may coincide with a dying or respiring
plant community.
When establishing the boundary conditions for headwater and tributary inputs into the study area,
consideration must be given to understanding the factors affecting present quality and quantity of the
incoming water, as well as those factors that may change over time and affect boundary conditions in the
future. Some questions to be considered may include:
Do the upstream watersheds meet water quality standards?
Do the upstream watersheds contain significant anthropogenic loadings that may be amenable to
further control?
Do upstream watersheds pass through a natural water body that dampens either pollutant
concentration or flow variability?
For persistence parameters such as phosphorus and nitrate, which can be long lasting in the riverine
system, are they at natural background levels or are they amenable to reduction?
Will TMDLs be established for parameters in upstream watersheds that may change future boundary
conditions?
Are there any hydrological modifications planned for upstream watersheds?
If boundary conditions are expected to change in the future, the impairment analysis should be
constructed to evaluate both current and future condition scenarios.
a. Early Monitoring Contract
When the existing data does not provide adequate definitions of the problem, the discovery process and
the stressor identification methodology can provide cost saving advantages. The process allows for low
level of effort expenditures to begin to define the critical conditions and spatial extent of the impairment.
Then the project team can make decisions based on the newly acquired information to plan the higher
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level of effort monitoring regime (flow and rigorous chemical sampling). These sites can be limited to
fewer locations and not placed exorbitantly in limited value locations in the watershed. For instance to
define the extent of the impairment and the critical conditions for which low DO exists in the summer a
project might consider the following roll-out of water chemistry monitoring:
•
As the summer season passes through the typical higher flow regimes in June and flows begin to
drop towards the NPDES permitting design criterion of 7Q10, then a monitoring contract with the
Local Governmental Unit (LGU) could include:
1. A longitudinal field parameter sample regime at every culvert, bridge, large discharge
source and tributary confluence. The desired field parameters would be DO,
temperature, and pH and flow stage (if a permanent structure or feature is available).
The sampling should consider diurnal DO fluctuations and multiple visits as the flows
continue to drop to adequately define critical conditions.
2. Based on the results from the longitudinal field parameter gathering effort, a similar
effort should be conducted for lab analytical samples of CBOD, the complete nutrient
suite of nitrogen and phosphorus, chl-a, TSS, as well as the field parameters of pH,
temperature and DO values plus specific conductance (significant shifts can be an
indicator of groundwater influence). This should be done for the sites that were
identified by the field parameter survey as approaching or below water quality numeric
criteria as well as a location upstream that is in compliance with the numeric criteria for
each critical tributary. It is important to note bed sediment conditions, whether or not a
fine organic material exists on the bed, as an indicator of SOD potential. (Note: this
survey is done shortly after each field parameter survey and therefore may have an
increasing number of locations as flows continue to drop.)
3. Based on land use maps and information gathered from items 1 and 2 a long term
monitoring plan is set up including flow stations, event-based water quality sampling
stations and collection of field parameters. It is important to relate the longitudinal
survey stage information to the flow station information if the flow stations were not
pre-existing.
If desired by all parties this monitoring contract can be rolled into a larger LGU contract to facilitate
and/or documentation development of the TMDL report and record of decision for the expected duration
of the project.
As related above the preliminary data set may not be sufficient and have basic data gaps. Local project
staff or existing watershed management organizations working with the project may have sufficient
training to gather core information regarding those gaps. At this point in the project the team should
again evaluate the potential for cost savings. By considering the potential need for: a) time of travel
studies, development of dissolved oxygen sag curves, groundwater studies or other investigations. Can
the LGU or project team handle any of these special studies? Is it better to have a phased professional
contract to: 1) develop an analysis framework, 2) develop these higher level of effort monitoring
considering the proposed analysis tool, and 3) set up the analysis tool? Or, are the watershed
considerations such that it is possible to do mass balance or simple analysis tool applications with the
level of effort being supplied by the project team? In other words, what is the desired level of rigor?
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H. Determining Rigor: Key Concepts to Consider for TMDL Work Plans
Rigor as used in the TMDL assessment process means the level or strictness of the science and
professional judgment being applied. The use of extreme rigor comes with a high time, staff, and
financial resource cost, while a low level of rigor may not be sufficient to develop an adequate plan or
allow successful defense of the TMDL if challenged. To prepare an adequate TMDL work plan, project
managers need to carefully consider the degree of rigor needed in order to better anticipate resource
needs. This is often best done as an iterative process as the project development and scoping work is
begun.
All watersheds are unique regarding scale, hydrology, types of land use, number and sources of
pollutants and their political culture. The final study for a completed TMDL for your specific watershed
must balance the complexity of the watershed, the potential for controversy and a limited staff and
financial resource pool in the ongoing decisions to achieve the appropriate level of rigor to be useful for
returning the water quality back to attainment conditions.
There is not a test or quantified metric to use for setting rigor. Instead, after the team has completed
pulling together the initial available information for land use and water quality data, during the
contract/workplan development process, they should discuss the following open ended questions to
guide the project towards an appropriate level of resources needed for developing and implementing a
monitoring plan and watershed land use assessment. The process is then extended again when
consideration of the data is used in selection of the analysis tool(s) required for a balance of complexity,
controversy and cost:
Water Quality Monitoring
How robust is the data set?
What is the watershed scale?
Do the data sets adequately define the extent of the impairment for the study?
Are the sample sets adequate for concentration determinations?
Are the flow stations adequate for determining loading?
Are data sets available for the critical conditions for the impairment? (considering seasons, changes
in flow, temporal factors and source(s) prominence)
Are there critical breaks in information? (either spatially or temporally)
•
Land use Information
• What is the watershed scale?
• What are the suspected pollutant sources in the watershed?
• Is there information on what pollutant sources potentially discharge?
• Are the sources easily related to the chemistry water quality findings?
• Are the pathways of the pollutant sources known?
• Are their obvious significant loaders or is it a cumulative issue?
• What are the NPDES DMR monitoring results for the parameters of concern?
• How specific should the Load Allocation source partitioning be? Would finer resolution improve
negotiations significantly?
• Are the water quality monitoring stations located adequately to help define the sources?
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How many potential pollution parameters contribute to the impairment?
• Can any of the potential pollutant parameters possibly be eliminated based on monitoring?
• Do some parameters warrant further investigation?
• Are some pollutant parameters more significant than others?
What are the probable outcomes of the study?
• Will meeting the water quality standard be difficult?
• Are there NPDES implications?
• Is there a commonly held or developing majority consensus on fairness?
These questions and others you may think of help a project consider if the data sets currently are
adequate for the negotiations ahead. Also, the rigor of the assessment process can be selected
appropriately when the problem and complexities are better understood. This list is used to find out the
perceptions and explore a process to manage the project with expectations being appropriate as early as
possible.
I. Analysis
a. Basic Objectives
The basic objective for a DO impairment analysis is to understand the cause-and-effect relationships
governing water quality, such that management alternatives can be explored that will bring the water
back into compliance. Simply monitoring and measuring water quality is necessary to define existing
conditions, but provides little predictive capability. Employing an analytical tool such as a water quality
model helps both to provide an understanding of the complex cause-and-effect relationships currently
affecting DO and to provide a capability for extrapolating predictions of water quality over space and
time. A modeling analysis can be used to understand and project the consequences of alternative
management and planning activities. Models can significantly improve the informational background
on which decisions are based, and substantially reduce the cost of managing water resources.
When selecting an appropriate analytical tool, some basic guidelines are:
• Choose to use the simplest analysis that will provide reliable answers and which will meet project
objectives.
• Focus on the key parameters of interest identified in the problem definition phase, avoiding
unnecessary complexities that can waste time and project resources.
• Ensure that the analytical framework will provide information for making decisions about resource
management alternatives.
• For complex impairments, ensure that the analytical tool provides the capability to define and
partition loadings from the various pollutant sources.
• Ensure that funding and human resources are available to perform the analysis.
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b. Selecting an Appropriate Analytical Tool
When monitoring and basic water quality investigations alone do not meet the goals and objectives of a
TMDL for addressing DO impairments, it will be necessary to select an appropriate water quality model
that provides analytical and predictive capabilities. Water quality models are mathematical abstractions
or simplifications of enormously complex natural aquatic systems. They can range in complexity from
screening-level analysis employing simple mass balances and empirical relationships to multidimensional, fully-dynamic models designed for large and complex river systems. Where nonpoint
sources of oxygen-demanding pollutants play a significant role in the stream oxygen budget, a
watershed runoff simulation model may need to be linked with the stream model.
Selection of an appropriate model or analysis framework suitable to a specific TMDL application is no
small task. In addition to the basic guidelines presented in the previous section, a basic understanding of
the river system and its impairment problem can be applied to select the appropriate time and space
dimensions needed for modeling. When the impairment is thought to be from a single permitted source,
a simpler analytical method may be applied from the following EPA guidance:
Technical Guidance Manual for Performing Waste Load Allocations: Simplified Analytical Method for
Determining NPDES Effluent limitations for POTWs Discharging into Low-Flow Streams
http://www.epa.gov/waterscience/library/modeling/npdeslowflow.pdf (PDF, 2MB)
More complicated scenarios need to begin by asking the following questions regarding simulation
options:
a. Is a Steady-state or Dynamic Model Needed?
Flows and loads specified for steady-state models are considered to be constant with respect to
time. Steady-state models use loads and flows that are averaged over a specified period of time
to compute an average response in the stream. Steady-state models are most appropriate to
simulate DO impairments that occur during steady base flow conditions in a stream or other
times of fairly constant flow conditions. A classic example is the analysis of water quality
impacts from a point source discharge under a summer 7-day average low flow condition.
Dynamic models are more complex and are used to describe time-dependent water quality
responses from highly variable boundary and pollutant loading conditions, such as would be
expected during storm-related loading events in a watershed. Data requirements can be
extensive for dynamic simulation models. Rather than time-averaged data as model inputs, these
models require discrete time-series data to describe the variability of flow and loadings.
Dynamic models may be needed to simulate DO impairments that are variable and not
constrained in time or space.
b. Spatial Dimension?
Zero-dimension: A segment of stream is described as a single computation element treated like a
completely mixed reactor. Often used in simple screening-level models, these are useful in developing a
preliminary indication of the major cause of a water quality problem. An example of a zero-dimension
model is a simple mass balance analysis. Conservation of mass is an important basic principle
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underlying all water quality analysis. This is an accounting of material; both suspended and dissolved,
moving into and out of a defined volume of water at its interfaces with the sediment bed, the
atmosphere, and upstream and downstream waters. Where internal kinetic transformations are known, a
mass balance can also account for changes in the mass of a constituent caused by physical, chemical,
and biological processes within the defined volume of water.
The strength of a mass balance approach is its conceptual simplicity and ease of use. Boundary
conditions for the analysis can be obtained by monitoring or estimated using empirical loading factors.
A spreadsheet or desktop analysis is often used. The weaknesses of a simplified analysis include a lack
of definition of pollutant gradients and a loss of predictive capability that the more process-oriented
models can offer.
Figure 14, Stick Figure and Equation for Mass Balance Approaches
QU: is the volume of water in the stream, upstream of the discharge
CU: is the Concentration of the chemical parameter in the water upstream of the discharge
QW: is the volume of wastewater discharged
CW: is the Concentration of the chemical parameter in the wastewater discharge
One-dimension: a stream is described as a series of computational elements, each representing a
completely-mixed reactor, extending downstream to define only the longitudinal gradients of water
quality. A one-dimensional model can accommodate a branching stream network. Since smaller
streams are considered well-mixed both vertically (top to bottom) and laterally (bank to bank), a onedimension formulation is most commonly used to describe stream water quality. The strength of onedimensional models is their efficiency in simulating pollutant concentration gradients and the
longitudinal water quality responses downstream from known loadings. The size of individual
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computational elements can be tailored to the river system. Adequate data must be collected to
adequately calibrate these models to site-specific conditions in order to use their predictive capabilities.
Figure 15: Diagram concept of a one dimensional model. In a one dimensional model the stream
segments are assumed to be well-mixed vertically and laterally (graphic adapted from the EPA
Handbook: Stream Sampling for Waste Load Allocation Applications. EPA Office of Research and
Development. EPA/625/6-86/013.)
Two-dimension: in wider or deeper streams additional computational elements are added where water
quality gradients may vary laterally or be vertically stratified in addition to the longitudinal variation.
An example where a two-dimensional analysis may be needed is where it may be important to describe a
mixing zone or plume downstream from a discharge in order to protect a sensitive downstream resource.
These models are only needed sparingly for specific applications in wide or deep rivers. Adequate data
is needed for calibration.
Three-dimension: a complex riverine model to describe a system having strong lateral, vertical, and
longitudinal water quality gradients that may be found in large river and reservoir systems such as the
Mississippi River and Lake Pepin. Multi-dimensional models require much more observational data to
calibrate the hydrodynamic transfers of water volume and water quality between the adjoining
computational elements. The more complex models often contain a large number of unobservable
parameters which complicates model setup and calibration.
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Figure 16: Graphical depiction of a 3-dimensional model. The stream segment is assumed to
have width and depth gradients for parameters and/or physical features that need to be explicitly
considered by the model.
c. Available Models
Generally, water quality models employed by the MPCA for TMDL development should be readily
available in the public domain, be well-tested, widely used, and be supported by or acceptable to the
U.S. EPA. Again, the preferred and most cost-effective approach is to use the simplest model that
includes all the important processes affecting water quality in your study area. However, caution should
be exercised in selecting too simple a model which may result in inaccurate predictions that will affect
resource management decisions. When the complexities of a DO impairment are not understood at the
outset, it is advisable to initially employ a flexible and comprehensive model, but simulate only those
processes with the model that appear significant and are supported by monitoring data. As project needs
dictate and as more supporting data is obtained, additional model processes can be turned on to provide
better definition to the DO impairment and management alternatives.
Screening Analysis and Models:
A simple mass balance can be used to evaluate the significant loading sources in an impairment study.
Using the classic dissolved oxygen deficit equations developed by Streeter and Phelps in 1925, the
impact from sources of oxygen-demanding pollutants to a stream can be defined using a desktop
analysis or computer spreadsheet application. Nonpoint pollutant loads can be estimated using simple
loading functions and empirical expressions relating nonpoint loads to other available parameters.
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One-dimensional, Steady-State Stream Model:
QUAL2K is a modernized version of the QUAL2E stream water quality model and is the version
currently supported by the U.S. EPA. The model is programmed in the Windows macro language and
uses Microsoft Excel as the graphical user interface. The QUAL2K model is available at:
http://www.epa.gov/waterscience/wqm/. The QUAL2x modeling framework has a long history of use
and is a proven, effective analysis tool. QUAL2K is one-dimensional (longitudinal) and assumes
steady-state hydraulics but will allow simulation of diurnal variations in temperature or algal
photosynthesis and respiration. It allows for multiple waste discharges, withdrawals, tributary flows,
and incremental inflow and outflow. Water quality variables simulated include conservative substances;
temperature; bacteria; CBOD; DO; ammonia; nitrite, nitrate, and organic nitrogen; phosphate and
organic phosphorus; and algae. QUAL2K improved upon the flexibility of model segmentation, CBOD
simulation, sediment-water interactions, light extinction, and simulation of benthic algae.
Multi-dimensional, Dynamic Stream Model:
The U.S. EPA provides support for the current model version 7 of the Water Quality Analysis
Simulation Program (WASP). The model is available at: http://www.epa.gov/waterscience/wqm/.
WASP is a dynamic compartment-modeling program for aquatic systems, including both the water
column and the underlying benthos. The model can be used to simulate 1, 2, and 3-dimensional systems
for a variety of pollutant types. Time-varying processes of flow advection and dispersion; point and
diffuse mass loading; and boundary exchanges are represented in the model. WASP can be linked with
hydrodynamic flow and sediment transport models that can provide flows, depths, velocities,
temperature, salinity, and sediment fluxes. The modeling framework in development for the Mississippi
River (Lake Pepin) eutrophication model shares basic simulation processes used in WASP.
The US Army Corps of Engineers (USACE) supports the CE-QUAL-RIV1 model which is a dynamic,
one-dimensional model that simulates flow and water quality in rivers and run-of-the-river reservoirs
where variation in depth is neglected. Where vertical water quality gradients are important, another
Corps model designated CE-QUAL-W2 provides a two-dimensional hydrodynamic and water quality
analysis that includes the major processes of eutrophication kinetics and sediment interactions. An
adaptation of the CE-QUAL-W2 model is being proposed for the Lower Minnesota River Modeling
update study. Additional information on the USACE models is available at:
http://el.erdc.usace.army.mil/products.cfm?Topic=none.
Linked or Integrated Watershed and Stream Models:
For watershed and water quality-based analyses, U.S. EPA supports and promotes the Better Assessment
Science Integrating point and Nonpoint Sources (BASINS) software system. The system is designed to
be flexible, allowing analysis at a variety of scales using tools that range from simple to sophisticated. A
geographical information system (GIS) provides the integrating framework for BASINS and organizes
spatial information so it can be displayed as maps, tables, or graphics. The software system includes data
retrieval and management tools, a series of simulation models, and customizable databases. Core data to
run the models can be downloaded via an EPA website.
Simulation models included in the BASINS system include the Hydrological Simulation Program –
Fortran (HSPF), the Soil and Water Assessment Tool (SWAT), and a simplified pollutant loading
program known as PLOAD. HSPF is a comprehensive model of watershed hydrology and water quality
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that allows the integrated simulation of land and soil contaminant runoff processes with in-stream
hydraulic and sediment interactions. HSPF was designed as a basin-scale model that includes fate,
transport, and transformation of pollutants in one-dimensional stream channels. HSPF is a complex
model normally run on an hourly time scale, requiring large amounts of data. The MPCA used a standalone version of HSPF for simulating a large portion of the Minnesota River Basin.
SWAT, developed by the USDA Agricultural Research Service (ARS), is a physical based watershedscale model run on a daily time steps. Its design facilitates the prediction of impacts from land
management practices over long periods of time on water, sediment, and agricultural chemical yields in
large complex watersheds having varying soils, land uses, and management conditions. Additional
information on the SWAT model can be found at: http://www.brc.tamus.edu/swat/index.html.
PLOAD is a simple screening model that can be used to estimate nonpoint sources of pollution on an
annual average basis, using either an export coefficient or another simple method approach. For
additional information on BASINS, see: http://www.epa.gov/OST/BASINS/
d. General Approach Alternatives
Using the basic understanding of a DO impairment to select an appropriate analytical tool, the next step
for the TMDL project manager is to determine a general approach for conducting the technical analysis.
Input from project stakeholders and consideration of schedule, budget, and staffing will direct the most
efficient utilization of resources to complete the TMDL study. The unique needs of each project will
determine the appropriate mix of resources. Options to consider include:
•
•
•
•
Use state staffing only;
Use a cooperative mix of local resources and state staffing;
Use a cooperative mix of local and state resources with contracted support for specific technical
expertise; or
Use contracted consultant as project lead with cooperative support from state and local resources.
e. Define and Develop Specific Approach
Selection of a general approach to undertake the technical analysis leads to the next step of identifying
the specific roles of project participants and developing the scope of service for which each participant
will be responsible. Stakeholder input is essential to this plan design. For technical services to be
provided by contracted consultants, detailed requests for proposals (RFP) must be developed to clearly
define the scope of needed services and work product deliverables.
f. Additional Data Acquisition to Support Analysis Framework
Identify Specific Data Gaps
For the analytical tool or model selected for the DO impairment analysis, specific data elements may be
needed to directly support the use of the tool. Watershed and water quality models are general in nature
and need to be calibrated with site-specific information to validate their use as reliable tools for
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analyzing DO responses and predicting changes associated with management alternatives. Model
documentation can be consulted for specific data requirements. Customizing a model setup for specific
applications requires information about the physical characteristics of the river system, information on
boundary conditions of the study area, and adequate spatial and temporal coverage of water quality
conditions. Water quality models also employ many kinetic rate parameters to simulate the physical,
chemical, and biological processes affecting stream DO. Rate parameters that can be field-measured,
should be measured.
Parameters that can not be measured directly will be set during the model calibration process and
adjusted within acceptable ranges supported by the literature.
Much of the needed information is not available from historical data collection programs. These
specific data gaps need to identified and plans implemented to obtain information critical to the analysis.
Design Field Studies and Water Quality Sampling
It is not the intent of this protocol to detail the procedures for designing and conducting stream surveys
to support modeling applications for DO impairments. Abundant information and guidance manuals are
available from the various water resources agencies that cover equipment requirements, personnel
requirements, sample collection, determination of stream geometrical and flow characteristics,
laboratory analytical techniques, and quality assurance and control. A particularly useful guidance
document for general sampling design is from the U.S. EPA is: Handbook: Stream Sampling for Waste
Load Allocation Applications. EPA Office of Research and Development. EPA/625/6-86/013.
http://www.epa.gov/waterscience/library/modeling/streamsampling.pdf (PDF, 5M)
Other reference documents:
Technical Guidance Manual for Developing Total Maximum Daily Loads: Book 2, Rivers and Streams;
Part 1 Biochemical Oxygen Demand/Dissolved Oxygen and Nutrient Eutrophication, EPA/823/B-97002 Year 1997
http://www.epa.gov/waterscience/tmdl/guidance.pdf (PDF, 88M)
An often useful exercise is to use the selected model to help design stream surveys. Using readily
available information, the model can be set up to examine the available data. Preliminary sensitivity
analysis runs can be made to help identify the most needed data. Stream surveys are then focused on the
collection of this data while de-emphasizing less important data.
Stream surveys used to calibrate and validate a steady-state
Synoptic survey: a “snapshot in
time” of conditions over the area
model are typically intensive synoptic surveys. These are
of study.
surveys that are usually completed within a few days to a
week. They are intended to provide a definition of river
responses to a specific set of loadings over a limited time span. On the other hand, data used to calibrate
dynamic watershed and stream models that are used to simulate transient water quality events tends to
be collected over a longer term to capture the variability of flow and loading conditions that would
impact DO. Intensive, short-term data collection efforts are also used to define critical storm-related
loading events.
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Stream Morphology and Hydraulic Geometry: Channel geometry is critical to the modeling of water
volume, flow rates, depths, and velocities. Data are used to define the stream configurations and
segment characteristics. Because models generally assume constant channel geometry within each
computational segment, it is important that stream surveys identify points where channel geometry
changes significantly so that the model can be segmented accordingly.
Flow Gaging and Stage-discharge Relationships: A simulation model needs an accurate accounting
of boundary flows, tributary flows, and diversion flows which can be measured directly. Ungaged
surface runoff and lateral inflows from, or losses to, ground water can only be estimated from
differences in measured flows at different locations along the stream channel. Development of stagedischarge relationships, together with information on channel geometry, will be useful to understand
how water depth relates to flow. An accurate depiction of stream depth is crucial for simulating
reaeration and the light attenuation impacts on algae growth.
Figure 17: Collection of velocity data to use in combination with channel geometry to develop
stage-discharge relationships for the stream
.
Time-of-travel: When stream geometry varies widely within reaches or when lateral inflows are not
well defined, it is often necessary to supplement the hydrologic and channel geometric data with timeof-travel studies using dye tracer techniques, typically with rhodamine-WT dye. While stream gaging
measures stream flow and velocity at a specific point in time and space, dye tracer studies give a more
accurate picture of average water transport velocity over the entire study reach. The time it takes a
parcel of water to travel through the study reach is critical to the calibration of important model
transformation rates, such as CBOD decay and nitrification.
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Figure 18. A time-of-travel study using dye tracer techniques
Water Quality: The evaluation of information data gaps should provide guidance on where, when, and
what additional water quality parameters are needed for modeling analyses. For DO impairment
modeling, it is desirable to run long-term CBOD analyses to estimate the ultimate CBOD parameter
used by most models. Where nitrification is important to the DO balance in a stream, it may be
necessary to collect additional data on the nitrogen species to understand the transformation rates.
Point Source Discharges: For steady-state analysis of DO impairments, continuously discharging point
sources are assumed to be constant over time, often represented by 24-hour composite sampling of the
effluent. For intermittent discharges or highly variable discharges in rate or quality, a sampling program
should be designed to get the best representative sample. Times, frequency, duration, and volume of
discharge should be noted.
Ground Water: Where the estimates of ground water inflow rates appear to be significant in the study
reach, water chemistry data from area wells should be examined to estimate the average quality of
ground water. Also, isotope aging techniques may be useful to determine the geological sources of
ground water impacting the stream; for example, surficial aquifers versus deep bedrock aquifers.
Diurnal Dissolved Oxygen, Temperature, pH monitoring: Stream dissolved oxygen fluctuates in
diurnal cycles in response to changing water temperatures and biological activity in the water column
and sediment bed. Warm water temperatures during daytime reduce the ability of water to hold
dissolved oxygen (lower saturation concentration) while the cooler temperatures at night raises the
saturation concentration potential. In eutrophic stream environments dominated by aquatic plants such
as algae, the opposite effect takes place. High rates of photosynthetically generated oxygen can raise
daytime oxygen levels to super-saturation concentrations. At night when plants are respiring and
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consuming rather than producing oxygen, stream concentrations can plunge below the standards set to
protect fish and other aquatic animals.
For any DO impairment analysis, it is critical that the diurnal patterns of stream dissolved oxygen be
measured and the underlying causes understood. Historical grab sample monitoring for DO and
temperature do not usually provide the information needed. Automatic recording monitors with DO,
temperature, and pH probes should be employed to collect data that will characterize the diurnal
fluctuations for the critical design conditions of the TMDL study. Not only will the data show daily
minima and maxima, but the continuous data record can be analyzed to derive estimates of
photosynthetic oxygen production rates to be used for modeling. Alternatively, but less desirable, a grab
sample program can be structured to obtain samples during times representing daily minimums (early
morning, up to two hours after sunrise) and daily maximums (late afternoon).
Biological Assessments: Measurements of the density and diversity of a biological community within a
stream study reach is a useful gage of stream health at a point in time. Biological assessment techniques
can be employed to characterize a stream’s biological health both before and after resource management
activities are in place. Along with water chemistry data, bio-assessments provide a valuable tool to
document changes in the water resource.
g. Model Set-Up and Evaluation
Generally, models are simplified mathematical representations of the extremely complex real world
systems. Models cannot accurately depict the multitude of processes occurring at the various chemical
and physical levels. Still, models can make use of known interrelationships among variables in order to
predict how a given quantity (or extensive variable such as sediment load) or state variable (or intensive
variable such as water temperature or pollutant concentrations) would change in response to a change in
an interdependent quantity or state variable. These interrelationships are expressed as sets of equations.
In this way, models may be useful frameworks for investigations of how a given system would likely
respond to a perturbation from its current state. For this reason, the predictive capabilities of models are
often helpful in the study of large natural systems. Watershed models are particularly useful, since it is
often difficult to actually change such existing conditions as land use or weather patterns in the real
world.
Each set of equations contain different variables. Some of these variables are input parameters which
must be assigned for the model to formulate a simulation. Other variables are output variables. The
model uses the set of equations to estimate output variables as a result of the simulation process.
Model Parameter Assignment
The modeler must assign values to each of the required input parameters. Some of these input
parameters can be direct measurements of real world quantities or state variables. For instance,
watershed models generally require meteorological records for input. These contain quantities such as
hourly rainfall amounts and state variables such as air temperature, dew point, and solar radiation.
These values are generally place directly into the model input files without manipulation or estimation
of uncertainties associated with these parameter values. This type of input is often called a “forcing
function” since it is regarded as a fundamental condition affecting model output.
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Other input parameters are not as easily measurable as air temperature. They require the modeler to use
professional judgment in the estimation of that parameter. In some cases the parameter can be estimated
on the basis of laboratory or field experimentation. In other cases, there is no “real world” surrogate for
that parameter. The modeler must use available information to determine an appropriate parameter
value. In other cases, the parameter has surrogates in the physical world, but the parameter is averaged
over such a large and heterogeneous scale that it is impossible to extract a single value based on
experimentation. The estimated parameter value must be the result of the aggregation or lumping of
values over various smaller scales.
Selecting values for estimated parameters is a critical step in the initial set-up of the model. It is these
parameters that normally require some adjustment in the calibration process. Since most of the
uncertainty of the model results is related to parameter estimation, it is usually prudent to include a
sensitivity analysis of the output of interest to changes in value of the estimated parameters as part of the
model evaluation.
Comparison of Simulated Output with Observed Data
Comparison of simulated output with observed data should be made during all phases of the model setup process. Obviously, when the modeler is assigning values to estimated input parameters; she/he
should do so in such a way that the simulated output that the model generates resembles the observed
data. For hydrological models, in general, the meteorological conditions (temperature, rainfall amounts)
are considered forcing functions and are direct parameter inputs. The modeler then assigns values to
estimated input parameters (i.e. infiltration, field roughness) so that the model output (simulated flow in
a river reach) matches the observed data, which in this case would be measured flow in that river reach.
The modeler should systematically compare observed data with simulated output during the calibration
process, and adjust the estimated parameters accordingly. Statistical comparisons of the simulated
output with the observed data should be made during the model validation and the sensitivity analysis to
demonstrate the utility and relative “accuracy” of the model.
Calibration
Calibration of most models involves adjusting the estimated model parameters in such a way that model
output resembles values available observed data. In the case where observed data is lacking, the model
should output values that are in a reasonable and expected range.
Watershed models contain a hierarchy of simulations. This hierarchy dictates the order of model routine
calibration. The calculation of water flow within a given riverine reach is the most fundamental routine
in a model. Any error in water flow will be propagated and often multiplied in other model routines.
For this reason, the flow calculations in a given model should be calibrated first. Once the modeler is
satisfied with the calibration of flow, the calibration of routines simulating sediment and dissolved
constituents, such as dissolved oxygen, can occur. Finally, once the sediment simulation has been
adequately calibrated, the modeler can calibrate routines involving the simulation of sediment-sorbed
constituents, such as phosphorus.
For watershed models which simulate output in a time series format (i.e. hourly values for a period of
several years), it is recommended that the simulated time series output be compared to the time series of
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observed data. Visual comparisons should be made to assure that the simulated output is in general
agreement with the available data.
These comparisons should be made on different time scales, beginning with a long-term coarse
timeframe. For instance, when calibrating flow, one should first compare simulated annual flows to
observed annual flows. On this broad timescale, it is particularly important to be sure that the model is
neither consistently over predicting nor under-predicting observed data. Next the plots on the monthly
timeframe should be examined. It is not uncommon for some models to accurately predict annual flows,
however, these models can have a seasonal bias (i.e. under-predict flows in the spring and over-predict
flows in the summer). An analysis of monthly plots allows the modeler to recognize these seasonal
inaccuracies. The modeler can then proceed with the comparisons at a daily, or in some cases, even
hourly timeframe. At these timeframes, not only is the magnitude of an event very critical, but the
timing of the event is also important. When calibrating flow, it is important not only to compare peak
height, but also the peak width, the area under a storm peak, the overall shape of a storm peak and the
position in time of a storm peak. It is also important to compare the values of baseflow, between storm
peaks.
These visual comparisons are usually the most helpful and informative tool in model calibration. It is
critical to make these comparisons for flow as well as concentrations and loads of constituents of
interest. Unfortunately, a lack of observed data often compromises the utility of concentration,
especially load comparisons.
In this case, it is often beneficial to rely on statistical comparisons between the data sets of observed
values and simulated output. These comparisons are often useful. It is important however, to only
compare data on time periods when observed data is available. Often, a lack of data from a station
consistently occurs under certain conditions. For example many gauging stations are unable to report
flow when water elevation drops below a certain level. In this case, the low flow portion of the
observed record is absent. Care should be taken not to compare this observed data set with the entire
corresponding simulated output which would contain flow values under all conditions.
It is also important to construct plots of observed versus simulated loads and concentrations. These
plots and their associated linear regressions are often useful in identifying systematic biases within the
set of model parameters.
Validation or Verification
Model validation involves the input of a separate record of timeseries data into the simulation. This data
record must not have been used in the model calibration process. The modeler follows the steps of the
calibration process and makes the same visual and statistical comparisons. However, the model output
must satisfactorily match the observed record for that time period without the manipulation of any
model parameter values, estimated or otherwise, which were determined during the calibration process.
In this manner, the validation process must be completely independent of the calibration. If the model
output does not adequately match the observed data for the validation record; the calibration and
subsequent validation process must be repeated.
Principal Component Analysis
Principal component analysis is a statistical technique usually applied to identify which sets of variables
within a larger set form coherent subsets that are independent of other subsets. Variables that correlate
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with one another and are also mostly independent of other subsets of variables are combined into
“factors”. Principle component analysis can be very useful in determining which groups of variables are
interrelated and also in reducing the number of variables in the system by combining correlated
variables into factors.
If for a large set of data there is a strong correlation between BOD and VSS, then the set of these two
input parameters can be combined into one factor. In a sense, this reduces the dimensionality of the
system. If there is a strong positive correlation between these two parameters, then the modeler may
wish to only vary these two parameters in the same direction (i.e. increase both or decrease both) when
performing a sensitivity analysis involving these parameters.
Sensitivity Analysis
Sensitivity Analysis is the study of how the uncertainty in the output of a model (such as dissolved
oxygen concentration) can be assigned to different sources of uncertainty in the model input. Sensitivity
analysis is an essential step in the evaluation of any model and a required part of any discussion of
model defensibility. In any model there are one or more input parameters which are interrelated with the
output parameter of interest. The modeler must identify the input parameters which have a
mathematical influence on the value of the output parameter. Once the related input parameters are
identified, the modeler must systematically and individually increase and decrease the value of each
relevant input parameter. If small changes in the value of an input parameter result in a large change in
value of the output parameter, the output parameter is said to be very sensitive to that input parameter.
If large changes in the value of an input parameter result in a small change in value of the output
parameter, the output parameter is said to be relatively insensitive to that input parameter. The modeler
must identify which input parameters the output parameter displays the greatest sensitivity. The
modeler should statistically quantify the uncertainties apportioned to the values of each of the sensitive
input parameters, especially the estimated input parameters. The modeler should also use statistical tests
to express the impacts of varying more than one of the sensitive input parameters simultaneously.
For models which predict dissolved oxygen concentrations, it is normally appropriate to include any
input parameters that affect the following variables in the sensitivity analysis: water flow, water depth,
water velocity, CBOD, SOD, VSS, nitrogen, phosphorus, phytoplankton, and any other parameters
which are mathematically related to dissolved oxygen concentrations.
Uncertainty Analysis
The uncertainty analysis can be used in exploring the requirements for the margin of safety (MOS) that
is needed in the specific watershed and this model application. The uncertainty analysis will tie in
nicely with the sensitivity analysis mentioned in chapter III section C. However, now that a balanced
allocation scenario is developed it may be important to rerun the allocation and select incremental key
stressor parameter changes. Evaluating temperature, CBOD, nitrogenous and eutrophic factors in this
way will assist in understanding the needed MOS for the assessment. A suggested starting increment
trial would be 5 percent steps, ranging from -10 to + 10 percent of the given loading for the pollutant
parameters at the future conditions.
J. Development of Example Evaluation Scenarios
Commonly occurring within stakeholder advisory discussions is the desire to have a discussion on three
main themes;
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(i) What range of reductions could be expected from each source type or category?
(ii) What are the costs, in terms of economics or risk?
(iii) What are equitable allocations between source categories that will meet the TMDL
allocation?
To answer these questions in a public setting some preparation work must be done in advance. It is
often a good process to have some preselected scenarios ready to foster discussion. It is important to
remember that each future scenario might contain several model runs that identify the changes or
balance needed for the number of significant contributing stressing parameters (CBOD, NBOD, temp,
SOD and eutrophication) and there individual reduction goals. Typical examples could be:
(a) Natural background/presettlement – Some models balanced on current hydrology can not
simulate the system without the drainage enhancements already in place in the system
because the hydrographs and resulting loadings reflect the altered pathways. Yet it is
valuable to consider a regional presettlement vegetation coverage. This can be used to
evaluate the extreme end point of current day loading with a given hydrology.
(b) Seasonal/critical conditions – The system may move in and out of compliance with the
numeric criteria for given flows and for given reaches in the watershed. A detailed
output for current day conditions can help the discussions along regarding the transition
flows, seasonal effects such as eutrophication, ice cover or temperature regimes.
(c) Geographic assessments – In larger watersheds with tributaries a system of model runs to
vary a subwatersheds input can help in defining area hot spots, and potential for
reductions from significantly contributing subwatersheds.
(d) Future loading considerations (no action) - Including new point and nonpoint projected
loadings for the watershed if the system was not altered beyond today’s level of applied
treatment for existing similar source technologies.
(e) Ranges of point source reductions in the watershed – Using different levels of treatment
for the key stressor parameters, determine what are the expected load reductions for each
parameter and then with regard to improvements in dissolved oxygen.
(f) Results from varying levels of effort for nonpoint source Best Management Practice
Systems (BMPs) – using different levels of adoption for a given set of previously selected
BMPs, provide the output results for changes in loading of the key stressor parameters
and the improvement in dissolve oxygen.
(g) Best available technologies – Applying the highest level of effort that the current
technology supports within each source sector’s realm.
(h) Balanced Allocation example – Explore a combination of treatment measures from all
sectors that will work to balance the allocation with or without reserve capacity.
These model outputs will not generate the whole background for the discussion. Other aspects should
include the local perspectives on the controversial issues, sector specific cost estimates for the
implementation measures modeled, manager risk elements (such as crop yield loss, compliance
determinations, etc.). When developing these scenarios and the scenario discussions, the team should
keep in mind the needed Margin of Safety. Can these scenarios be used to assist in understanding the
benefits from incorporating implicit or explicit safety assumptions?
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K. Project Case Example and Stressor ID Discussion
The following case example contains some of the typical considerations occurring in active TMDL
studies in Minnesota. This case example is meant to illustrate when and how critical management
concepts (Stressor Identification considerations) are introduced into the TMDL project process. As an
illustration, the process has a flow where one step leads to the next in a logical progression; however,
any given project may encounter data sets that do not at first make sense. More information or additional
team members with higher expertise (including professional contracts) may need to be added throughout
the course of a project. It is recommended that a project consider using contracts for LGU services and
the master contract for professional services in a staged fashion, considering:
• the level of effort required to gather, assess and advance the current watershed
understanding, and
• the desired rigor (see Chapter 2, section H) and resources available.
Some project teams will consider using a professional contract that has a phased approach, with the
options in each phase as separate line items to enable that option to be not implemented if that task is not
needed. These contract methods will help avoid and prevent significant contract delays or large change
orders to amend the contract for special studies that were not previously predicted. These methods also
can provide significant cost saving features; as the contracts to deal with special studies or new
professional services can be developed based on the specific information and consideration of the rigor
needed to move the TMDL forward.
Ailing River - fictional case study
The MPCA staff project manager assigned to the project is able to gather existing documents and data to
compile the following information.
Ailing River is listed on the 303d impaired waters list for low DO based on a permit effluent limit study
for point sources. The listing data set contains two synoptic data sets of three days each at two lower
flow regimes. The low flow conditions provided are the 20 percentile and the 7Q10. The data set has a
time-of-travel dye study and diurnal DO information for the reach closest to Larson City. In Larson City
there are three NPDES permitted discharges, the city municipal wastewater treatment works, one food
processing industry with stabilization ponds, and one industry with a noncontact cooling water
discharge.
Ailing River Watershed District has been in existence for two years. The District has one hydrologic
event sampling station at a USGS flow station located downstream at the mouth of the River prior to
entering into Slow River, and two grab sampling sites. One is located at Larson City and one on Ditch
12. Event monitoring data sets are available for one summer season (with a wet year as a base, higher
flow regimes than 7Q10). Ailing River watershed is dominated by agricultural land use with two small
communities, Larson City and Olsen City. Larson City is the only community with active industrial
NPDES permits. The watershed has a steeper gradient in the upper reaches with shaded riparian canopy
and lower gradients in the downstream reaches with no perennial vegetative canopy. Noncompliant
Individual Septic Tank Systems (ISTS) are known to exist in the watershed. The main noncompliance
issue is septic tank direct discharges into agricultural tile drainage lines occurring in about 35 percent of
the sites. Three livestock operations are located in the watershed.
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A core or starter technical committee is formed consisting of the representatives from the Watershed
District, SWCD technical staff, a local environmental activist who also is farming, and MPCA staff.
It is important to try and gather all the existing watershed water quality data and the landuse data into
visual aids for the preliminary assessment discussions. This will be the center of activity as early
discussions with the project team and committees take place. This project does not have GIS mapping
capability and instead chose to use a stick figure map showing the current understanding of the
preliminary watershed information, as shown in Figure 19.
Figure 19, Preliminary Data Stick Figure Map. The culvert/bridge crossings are indicated by
breaks in the lines.
Ailing River Stick Figure Map
Mouth at Slow River
WQ Sta. & USGS Flow
Grazing
Food Processor
(Grab Samples)
Ponds
Larson City
(Grab Samples)
Ditch
Feedlot
#1
# 12
Cooling
water
Olson City
Feedlot #2
Upon looking at the preliminary data the team concludes that the listing data set does not provide a good
description of the spatial and temporal extent of the impairment or define the critical conditions. The
parameter list for the event station and grab sampling by the District is limited to TP, ortho-P, TSS, and
nitrate/nitrite nitrogen and therefore does not provide adequate information on most of the parameters
that may stress DO. A work plan must now be discussed for the project to gather more information in a
timely and cost effective manner. The project team decides that an “early monitoring contract” should be
extended to the Ailing River Watershed District to:
•
Facilitate the TMDL project meetings, and documentation/report writing.
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•
•
•
Define the spatial extent of impairments by conducting preliminary longitudinal surveys
throughout the watershed with field parameters (temperature, DO and pH) in late summer as
flows drop throughout the watershed. Locations are at bridges, culverts and tributary
confluences plus downstream of the two communities and two industries.
Conduct two longitudinal intensive surveys that include field temperature, pH, DO and
stream flow measurements, and water grab samples for lab analytical parameters (CBOD,
TKN, ammonia, Nitrate-Nitrite, Chl-a, total Phosphorus, ortho-phosphorus, total suspended
solids, turbidity and specific conductance) just after the preliminary longitudinal survey and
with coverage throughout the discovered non-attainment reaches and at one compliant site
upstream for each tributary (if any). Coordinate with NPDES dischargers to obtain effluent
samples, if discharging during the surveys. Field notes will include descriptions of aquatic
vegetation and sediment characterization on the bed of the river.
Assist with establishing, use and maintaining up to four flow and water quality event
sampling stations in the watershed. Stations will have the capability to do a diurnal
automatic sampling regime, including continuously recording sondes for pH, temperature,
and DO as needed.
The contract begins in July and during the late summer season the weather cooperates and the
longitudinal sampling surveys are completed in a stepwise fashion as flow drops. At the early low flow
stages, first a field parameter survey is done and then the lab analytical sampling survey is completed.
As stages continue to drop the series is repeated and expanded if the field parameter survey indicates a
larger spatial extent. The pre-existing hydrologic event-monitoring station has a probe added for DO,
pH and temperature. Using the extended parameter list, at least 8 samples are collected and analyzed
per season, targeting three storm hydrographs, three late summer base flow periods and two
discretionary samples.
The project team compiles the data sets from each longitudinal survey into one stick figure map and
table of key WQ parameters for the watershed. At this time the land use information previously
gathered is also discussed for new information from the larger team. Figure 20, is the updated stick
figure map and Table 2 is the survey results.
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Figure 20, Stick Figure Map Showing Longitudinal Survey stations
Ailing River Stick Figure Map
Mouth at Slow River
Sta. A 1 & USGS Flow
Grazing
Food Processor
A2
Ponds
WWTP
A9
A3
Larson City
A10
Feedlot
#1
A4
Ditch
# 12
A11
A5
Cooling
water
A7
Feedlot #2
WWTP
A8
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A6
68
Olson City
Dissolved Oxygen TMDL Protocols and Submittal Requirements
Table 2, Longitudinal Survey Results by date
Sta
Date
Time
cfs
pH
Temp
DO
Spec
Cond.
TP
mg/l
CBOD
NBOD
Chl-a
A1
7/20
6:15
12
8.5
23.0
2.54
A2
7/20
6:33
18
8.6
22.8
3.85
A3
7/20
6:55
17
7.9
25.2
3.15
A4
7/20
7:53
10
7.9
32.5
2.89
A5
7/20
8:05
4
8.1
21.6
4.66
A6
7/20
8:30
5
7.9
24.2
4.54
A7
7/20
8:50
3
8.6
22.6
5.13
A8
7/20
8:58
3
8.5
21.2
6.20
A9
7/20
9:20
4
8.4
20.6
6.15
A10
7/20
9:49
3
8.1
19.2
6.33
A11
7/20
9:59
1
8.3
20.0
6.14
A1
7/22
5:30
11
8.4
18.8
2.89
682
0.165
7.1
9.9
32.3
A2
7/22
6:10
18
8.3
19.9
3.85
700
0.175
2.8
1.6
26.0
A3
7/22
6:45
16
7.8
22.8
4.37
520
0.103
1.4
0.75
15.9
A4
7/22
7:20
11
8.3
26.5
4.6
500
0.110
0.8
.65
20.5
A5
7/22
7:48
4
7.8
17.3
1.4
380
0.275
1.5
1.9
53.6
A6
7/22
8:22
4
7.9
24.6
1.9
498
0.300
1.3
1.8
47.1
A7
7/22
8:51
4
8.4
19.3
6.1
550
0.090
1.5
0.80
3.72
A9
7/22
9:45
3
8.5
21.2
5.8
650
0.110
2.0
1.4
1.46
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Table 3, Longitudinal Survey Results by date
Sta
Date
time
cfs
pH
temp
DO
Spec
TP
CBOD
TKN
Chl-a
ºC
mg/l
cond
mg/l
mg/l
mg/l
ug/l
A1
8/15
6:20
5
8.1
27.0
1.3
A2
8/15
6:40
9
8.2
25.3
2.7
A3
8/15
6:50
8
7.7
29.4
2.2
A4
8/15
7:35
10
7.9
35.7
2.1
A5
8/15
7:55
5
8.2
24.6
3.5
A6
8/15
8:20
6
7.8
25.5
4.8
A7
8/15
8:45
4
8.5
24.6
5.6
A8
8/15
8:53
3
8.4
23.2
5.4
A9
8/15
9:15
5
8.3
22.0
5.8
A10
8/15
9:39
4
8.0
20.5
5.6
A11
8/15
9:56
3
8.0
23.0
5.7
A1
8/16
5:45
6
8.4
20.8
2.15
750
0.125
6.1
11.8
45.8
A2
8/16
5:59
9
8.3
25.9
3.05
880
0.375
5.8
7.6
35.0
A3
8/16
6:38
9
7.8
27.8
2.45
680
0.203
4.6
5.75
16.7
A4
8/16
7:12
11
8.3
29.5
3.96
708
0.135
0.5
1.65
18.5
A5
8/16
7:39
5
7.8
21.3
1.9
390
0.195
2.5
2.7
35.6
A6
8/16
8:19
5
7.9
23.7
2.8
518
0.215
2.8
3.5
45.1
A7
8/16
8:46
5
8.4
22.6
4.9
500
0.130
2.1
1.80
18.7
A9
8/16
9:26
4
8.5
20.9
5.1
625
0.189
3.0
4.4
11.5
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Careful consideration of the findings, in Tables 2 and 3, from the surveys reveals that head water ditch
12 remains in compliance and the field notes indicate that it has a relatively good velocity, and that no
fines (detritus) are building up on the channel bed at the velocities currently in the stream. However, the
channelized system leading from Olson city above station A5 has little if any flow and numerous pools
exist in the reach with a significant build up of small detritus type material on the bed.
The DMR records for the stabilization ponds for the City of Olson and the food processing industry
above station 9 indicate that no discharge occurred during these survey periods.
Table 4, below is a historic record for conductance that can be used to guide the project team on the
range of values that will inform them on the influence of ground water and surface water.
Agency
Station
Date
Time
Parameter Result
USGS
5300000
10/3/1960
10:40
95
1010
USGS
5300000
3/20/1961
9:20
95
678
USGS
5300000
5/15/1961
17:00
95
1390
USGS
5300000
3/29/1962
9:15
95
309
USGS
5300000
2/28/1963
9:30
95
2310
USGS
5300000
8/4/1965
12:05
95
1150
Table 4. # 00095 - Specific conductance, water, unfiltered, microsiemens per centimeter at 25 degrees Celsius
for Lac Qui Parle River
This table provides actual data for specific conductance, parameter number 95, sampled in Lac Qui Parle
River (while the case example is not Lac Qui Parle River this data demonstrates a common range in
south western Minnesota). The samples were collected by the USGS from 1960 to 1965. The key point
to use as a project reference is the variability regarding winter frozen conditions (with little run off and
mostly groundwater feed 2/28/1963) versus the other times of year when varying ratios of groundwater
and surface water is mixed. In March of 1962 during a snow melt runoff event the specific conductance
is relatively low for this river relating to the high percentage of surface runoff contributing to the river
flow (309 microsiemens/centimeter). In the winter period when ground water recharge is the dominant
source of river flow the specific conductance jumps up to reflect the higher mineral content of the
dissolved solids (2/28/1963, 2310 microsiemens/centimeter). A project team can look at historic data
and compare specific conductance or temperature (groundwater temperatures typically are around 49
degrees Fahrenheit, or 10 degrees centigrade) to determine if certain reaches are showing significant
groundwater influence during dry weather conditions. Ground water may be entering the stream with
little or no dissolved oxygen and therefore may be a natural source of stress on a given reach.
During the low flow surveys, the whole system overall does not have temperature, or specific
conductance indications of being significantly influenced by groundwater or of containing
eutrophication related issues as determined by the low Chl-a and regional comparisons with TP.
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Other information obtained at this time are the Larson City WWTP permitted effluent limits of 15 mg/l
CBOD5, 30 mg/l TSS and 1 mg/l for ammonia. The noncontact cooling water industry does not have to
monitor for CBOD nutrients or TSS, but did happen to have the monthly temperature reading of 35 ºC
taken on the 7/22 survey date. The monthly flow average permitted flow is 1.3 MGD. Concerns over
temperature and the unknown source contribution from the noncontact cooling water were discussed.
Nonpoint sources from feedlots indicate little significant impacts from the two headwater feedlots
during this period of time. A feedlot assessment is set up to confirm the management goals of these sites.
However, the grazing facility on the mainstem of Ailing River downstream of Larson City is suspected
of being a significant loader even under the higher flow regime of the first two surveys as is indicated by
the TKN and CBOD values. An interview with the feedlot manager is being set up.
Based on the improved watershed understanding, the project team recommends that a professional
contract for a modeling effort to include related data gaps assessment and monitoring study. This higher
level of rigor was selected because of:
• The complexity of finding multiple stressor parameters contributing to the impairment issues,
• The close proximity of NPDES facilities to the monitoring stations with some of the lowest DO
readings and highest concentrations of stressing parameters (indicating a possible NPDES effluent
limit change as a likely outcome).
• The lack of data on the two NPDES pond facilities and the need to estimate possible impacts from
these sources.
The professional contract was issued to a consultant on the master contract list who performed a data
gaps assessment for the proposed QUAL2K one dimensional model. The results were: a combined data
collection effort by the LGU; installing the new event sampling stations for collecting four grab samples
of ultimate CBOD, continuous DO, temp and pH readings during low flow stages as advised by the
consultant; and augmenting the information with grab sample collections in the compliant tributaries.
The professional contract also allowed for a new time-of-travel dye study and velocity data gathering
from station A6 down through Station A1. It also provided for a three day low flow study in the
following year. The contact was specific with requesting the uncertainty analysis and model
performance criteria related in Chapter 2, Section I and the EPA reference material.
Upon completion of the first monitoring season for the professional contract, the model calibration effort
began. Midway through the second monitoring season in the LGU contract, the loading information was
included in the calibration effort and the model was then verified with the conditions provided by the
low flow study from 1988. Next, the consultant worked with the project team and committees to
provide scenarios that fostered robust discussions of possible results from land use changes and
treatment measures that are possible in the watershed. The model results were also augmented by sector
experts from the municipal wastewater representative (their consulting engineer), the industrial
wastewater representatives, and University of Minnesota Department of Soil Water and Climate
professors regarding agricultural measures. These discussions included possible existing measures
available, risks and costs of each, and other impediments to change. From these discussions, an example
scenario was generated for water quality attainment. The committees attempted to adjust the attainment
goal strategy with two attempts before finding an alternative that would attain water quality objectives
and represented an “equitable” solution from all contributing sources.
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The professional contractor provided a model calibration and verification report, scenario development
report, and special monitoring study report in addition to answering questions for the LGU during
development of the TMDL study report. The LGU provided a report on the monitoring results from the
contract period, a TMDL study report, and facilitated the multiple meetings setup and documentation to
keep all participants in the process informed throughout the project.
The wasteload implementation measures selected were:
An adjustment to 5 mg/l CBOD limit, 6 mg/l (minimum) dissolved oxygen effluent limits for the
City of Larson WWTP,
• Further limiting the window for allowable discharge from the stabilization ponds for the food
processor and the City of Olson to October where cooler water temperatures provided conditions for
sufficient assimilative capacity in the stream (estimated by the professional model contract).
• Twice a week temperature and daily flow measurements, plus monthly CBOD, nutrient and TSS
monitoring requirements for the noncontact cooling water facility, with a potential permit reopener
contingent on the watershed response to other implementation measure and the findings from the
new DMR requirements, and
• 100 percent non-compliant ISTS correction watershed wide.
The load implementation measures selected were:
• Livestock exclusion incentives are provided for the grazing operation near station A2,
• Soil erosion control measures to achieve “T” (tolerable soil erosion loss; defined by the Natural
Resource Conservation Service) to reduce the soil organic matter contributions from row cropped
fields, and
• Riparian woody vegetation management buffer program initiatives for soil erosion control and
temperature benefits (with the understanding that some leaf litter will be contributed as an organic
load back into the system).
•
Due to the scale of the watershed and the potential size of each contributing source type, the project did
not pursue other professional contracts such as watershed land use modeling to quantify the WLA
loading for each NPDES permit or septic system. The NPS contributions from the grazing operation
and row cropping were estimated using a simpler mass balance approach. No additional stream
temperature studies were pursued for sizing the woody vegetation canopy goals. In the TMDL report,
each sector was provided an estimate of its current loading and needed reduction goal. These goals were
documented using the weight of evidence and stressor identification organization process.
The TMDL development process also instructed the watershed district to engage in adaptive
management during implementation for confirmation of the goals set in the TMDL. Instead of higher
rigor NPS quantifying efforts, the stressor identification process brought all of the participants, point and
nonpoint, up to a confidence level where use of “typical” literature based loadings could be used. The
concerns of the group were further addressed by using the adaptive management check during
implementation (proper effectiveness monitoring tied to, as necessary, adjustments in implementation
goals) to obtain compliance with water quality standards.
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
Part III: Dissolved Oxygen TMDL Submittal Requirements
A. Dissolved Oxygen TMDL Submittal Requirements
For an approvable Dissolved Oxygen TMDL, the final report must meet both federal requirements and
state protocols. Each major component of a TMDL is described in this section and includes:
•
•
Federal requirements, which are used by the EPA as a basis for reviewing and approving
TMDLs; and
Minnesota’s protocols as required by the MPCA.
In addition, “MPCA’s Checklist” (Appendix A) for reviewing the adequacy of draft TMDLs prior to
submittal to EPA should also be consulted to ensure the report is complete.
EPA Guidelines for Reviewing TMDLs Under Existing Regulations Issued in 1992
(http://epa.gov/owow/tmdl/guidance/final52002.html)
Section 303(d) of the Clean Water Act (CWA) and EPA's implementing regulations at 40 C.F.R. Part
130 describe the statutory and regulatory requirements for approvable TMDLs. Additional information
is generally necessary for EPA to determine if a submitted TMDL fulfills the legal requirements for
approval under Section 303(d) and EPA regulations, and should be included in the submittal package.
Use of the verb "must" below denotes information that is required to be submitted because it relates to
elements of the TMDL required by the CWA and by regulation. Use of the term "should" below denotes
information that is generally necessary for EPA to determine if a submitted TMDL is approvable. These
TMDL review guidelines are not themselves regulations. They are an attempt to summarize and provide
guidance regarding currently effective statutory and regulatory requirements relating to TMDLs. Any
differences between these guidelines and EPA's TMDL regulations should be resolved in favor of the
regulations themselves.
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
B. Identification of Waterbody, Pollutant of Concern, Pollutant Sources, and
Priority Ranking
Federal Requirements:
The TMDL submittal should identify the waterbody as it appears on the State's/Tribe's 303(d) list. The
waterbody should be identified/georeferenced using the National Hydrography Dataset (NHD), and the
TMDL should clearly identify the pollutant for which the TMDL is being established. In addition, the
TMDL should identify the priority ranking of the waterbody and specify the link between the pollutant
of concern and the water quality standard (see section 2 below).
The TMDL submittal should include an identification of the point and nonpoint sources of the pollutant
of concern, including location of the source(s) and the quantity of the loading, e.g., lbs/per day. The
TMDL should provide the identification numbers of the NPDES permits within the waterbody. Where it
is possible to separate natural background from nonpoint sources, the TMDL should include a
description of the natural background. This information is necessary for EPA's review of the load and
wasteload allocations, which are required by regulation.
The TMDL submittal should also contain a description of any important assumptions made in
developing the TMDL, such as:
(1) the spatial extent of the watershed in which the impaired waterbody is located;
(2) the assumed distribution of land use in the watershed (e.g., urban, forested,
agriculture);
(3) population characteristics, wildlife resources, and other relevant information affecting
the characterization of the pollutant of concern and its allocation to sources;
(4) present and future growth trends, if taken into consideration in preparing the TMDL
(e.g., the TMDL could include the design capacity of a wastewater treatment facility);
and
(5) an explanation and analytical basis for expressing the TMDL through surrogate
measures, if applicable. Surrogate measures are parameters such as percent fines and
turbidity for sediment impairments; chlorophyll-a and phosphorus loadings for excess
algae; length of riparian buffer; or number of acres of best management practices.
Protocol for Minnesota Dissolved Oxygen TMDLs: See Minnesota’s Checklist (Appendix A)
for background information needed in addition to the federal requirements.
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
C. Description of the Applicable Water Quality Standards and Numeric
Water Quality Target
Federal Requirements:
The TMDL submittal must include a description of the applicable State/Tribal water quality standard,
including the designated use(s) of the waterbody, the applicable numeric or narrative water quality
criterion, and the antidegradation policy. (40 C.F.R. §130.7(c)(1)). EPA needs this information to review
the loading capacity determination, and load and wasteload allocations, which are required by
regulation.
The TMDL submittal must identify a numeric water quality target(s) - a quantitative value used to
measure whether or not the applicable water quality standard is attained. Generally, the pollutant of
concern and the numeric water quality target are, respectively, the chemical causing the impairment and
the numeric criteria for that chemical (e.g., chromium) contained in the water quality standard. The
TMDL expresses the relationship between any necessary reduction of the pollutant of concern and the
attainment of the numeric water quality target. Occasionally, the pollutant of concern is different from
the pollutant that is the subject of the numeric water quality target (e.g., when the pollutant of concern is
phosphorus and the numeric water quality target is expressed as Dissolved Oxygen (DO) criteria). In
such cases, the TMDL submittal should explain the linkage between the pollutant of concern and the
chosen numeric water quality target.
Protocol for Minnesota Dissolved Oxygen TMDLs:
The Minnesota Rule 7050.0222 subp. 2,3,4,5 provides the numeric criteria for DO in Minnesota’s
waters. A complete quotation from the Minnesota Rule 7050.0222 is provided on page 31. The numeric
criterion for DO is a daily minimum. Compliance with this standard is required 50 percent of the days at
which the flow of the receiving water is equal to the lowest weekly flow with a once in ten-year
recurrence interval (7Q10). Two provisions are provided for specific reaches on the Mississippi River
and the Minnesota River that are less restrictive but comply with Subpart 8 which allows for site specific
standards but is limited to a 5 mg/l daily average and 4 mg/l daily minimum. Compliance with this
standard is required 50 percent of the days at which the flow of the receiving water is equal to the lowest
weekly flow with a once in ten-year recurrence interval (7Q10).
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D. Loading Capacity - Linking Water Quality and Pollutant Sources
Federal Requirements:
A TMDL must identify the loading capacity (LC) of a waterbody for the applicable pollutant. EPA
regulations define LC as the greatest amount of a pollutant that a water can receive without violating
water quality standards (40 C.F.R. §130.2(f)).
The pollutant loadings may be expressed as either mass-per-time, toxicity or other appropriate measure
(40 C.F.R. §130.2(i)). The TMDL must be expressed in terms of a daily load, but may additionally be
expressed in terms other than a daily load, e.g., an annual load. The submittal should explain why it is
appropriate to express the TMDL in the terms and units of measurement chosen. The TMDL submittal
should describe the method used to establish the cause-and-effect relationship between the numeric
target and the identified pollutant sources. In many instances, this method will be a water quality model.
The TMDL submittal should contain documentation supporting the TMDL analysis, including the basis
for any assumptions; a discussion of strengths and weaknesses in the analytical process; and results from
any water quality modeling. EPA needs this information to review the LC determination, and load and
wasteload allocations, which are required by regulation.
TMDLs must take into account critical conditions for steam flow, loading, and water quality parameters
as part of the analysis of LC. (40 C.F.R. §130.7(c)(1)). TMDLs should define applicable critical
conditions and describe their approach to estimating both point and nonpoint source loadings under such
critical conditions. In particular, the TMDL should discuss the approach used to compute and allocate
nonpoint source loadings, e.g., meteorological conditions and land use distribution.
Protocol for Minnesota Dissolved Oxygen TMDLs:
As described in EPA guidance, a TMDL identifies the assimilative or LC of a waterbody for a particular
pollutant. EPA regulations define LC as the greatest amount of loading that a waterbody can receive
without violating water quality standards (40 C.F.R. § 130.2(f)). For impaired waterbodies, the LC will
define the overall pollutant reductions that are necessary to attain water quality standards or achieve
designated use for recreation, fisheries, drinking water supplies, aesthetics, and wildlife. DO is a
response parameter and not a pollutant loading parameter. This requires that the LC be defined in the
balanced allocation as a combination of all the contributing stressor parameters being allocated. It would
simplify the TMDL if only one parameter allocation can be reduced to attain the water quality numeric
limits, but if several of the stressor parameters are in need of reduction then LC of each must be
described. This includes the physical parameter of temperature which would be given in a maximum
daily value. The loadings are required to be expressed as either mass-per-time (pounds per day), toxicity,
or some other appropriate measure (40 C.F.R. § 130.2(i)).
As the term implies, TMDLs are typically expressed as total maximum daily loads, or loads per year.
For example, it is appropriate and justifiable to express a DO TMDL in relationship to flow in terms of
allowable loadings at the 7Q10 and increments higher as needed to balance all the sources of stress as
they are introduced into the system under higher flow regimes. The TMDL submittal must identify the
waterbody’s LC for the applicable pollutant and describe the rationale for the method used to establish
the cause-and-effect relationships between the numeric target and designated uses to the identified
pollutant sources. In most instances, this method will be a water quality model. Supporting
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Dissolved Oxygen TMDL Protocols and Submittal Requirements
documentation for the TMDL analysis also must be contained in the submittal, including the basis for
assumptions, strengths and weaknesses in the analytical process, results from water quality modeling,
etc.
Goal: Attain Designated Uses
• Achieve numerical
goals
• Compliance Rate
– 50% time at 7Q10
– Other restrictive flow
goals as identified
– Or, goal not to be
exceeded according to
Subpart 8?
•
•
•
•
•
•
Drinking Water
Fisheries
Recreation
Habitat
Wildlife
Aesthetics
Critical Condition
TMDLs must take into account critical conditions for stream flow, and water quality parameter
concentrations and loading, as part of the analysis of LC (40 C.F.R. §130.7(c)(1)). Factors, such as leaf
canopy protection or the rate of human soil disturbance activities, affecting the critical conditions and
the resulting TMDL often vary seasonally. Likewise, different sources may dominate the stressor
parameter loading under different flow regimes. Dominance of nonpoint runoff related sources may
significantly drop off during dry weather periods when point sources become a more significant portion
of the loading. TMDLs should define applicable critical conditions that consider these source and
delivery factors and the timing of when the beneficial use is impaired. Late summer low flow DO
impairment can be impacted by loadings delivered earlier in the year and by loads occurring during the
observed impairment, depending on watershed dynamics. In the Waste Load Allocation requirements
for NPDES permitted wastewater facilities EPA requires that water quality protection exist down to a
defined low flow condition. That low flow is defined as (7Q10): Low-flow (7Q10) is the 7-day average
low flow occurring once in 10-years; this probability-based statistic is used in determining stream design
flow conditions and for evaluating the water quality impact of effluent discharge limits.
TMDLs should describe their approach to estimating both point and nonpoint source loadings under
such critical conditions. In particular, the TMDL should discuss the approach used to compute and
allocate nonpoint source loadings, e.g., meteorological conditions and land use distribution.
For information on how to set up the study and the suggested rational for developing a TMDL study
refer to Chapter 2, Section G. Critical Project Design Conditions (page 46) through Section I. Analysis
(page 51) for the methods of identification of critical periods, modeling or analysis considerations, and
frameworks for project process.
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E. Load Allocations (LAs)
Federal Requirements:
EPA regulations require that a TMDL include LAs, which identify the portion of the LC attributed to
existing and future nonpoint sources and to natural background. Load allocations may range from
reasonably accurate estimates to gross allotments (40 C.F.R. §130.2(g)). Where possible, load
allocations should be described separately for natural background and nonpoint sources.
Protocol for Minnesota Dissolved Oxygen TMDLs:
The load allocation (LA) is all those sources of pollutant loading not associated with a point source –
non-NPDES or non-septic system. For DO TMDLs these sources include atmospheric deposition,
natural land use such as limited use forests, grasslands, and wetlands and watershed runoff from
managed land such as row cropped fields, silver culture, roads and non-MS4 communities.
Natural background load is a portion of the watershed loading, and should be defined as precisely as
possible. This analysis will range from having a value derived by multiplying a runoff coefficient for
each critical stressor parameter times the spatial coverage of natural land uses that exist without roads
and artificial drainage to a predictive model output for these uses. The LA should be as source specific
as the data allows. Source specific could be by watershed sub-basin, land-use activity (agriculture), landuse sub-activity (row crop agriculture) or by individual sources (a particular row crop field). The more
source specific the LA is, the more tailored the implementation recommendations can be.
The location of sources in the watershed may need to be evaluated for its loading potential at the point
of LC calculation. Load impact reductions from source location considerations (fate and transport) need
to be documented to justify reduction allowances for loads entering surface waters. This consideration
may apply to both the WLA and LA.
Pollutant trading can be included as a means to meet a TMDL allocation. However, the details of trading
can be determined in the TMDL implementation plan. Trading may further the need for geographic
consideration of loads.
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F. Wasteload Allocations (WLAs)
Federal Requirements:
EPA regulations require that a TMDL include WLAs, which identify the portion of the LC allocated to
individual existing and future point source(s) (40 C.F.R. §130.2(h), 40 C.F.R. §130.2(i)). In some cases,
WLAs may cover more than one discharger, e.g., if the source is contained within a general permit.
The individual WLAs may take the form of uniform percentage reductions or individual mass based
limitations for dischargers where it can be shown that this solution meets WQSs and does not result in
localized impairments. These individual WLAs may be adjusted during the NPDES permitting process.
If the WLAs are adjusted, the individual effluent limits for each permit issued to a discharger on the
impaired water must be consistent with the assumptions and requirements of the adjusted WLAs in the
TMDL. If the WLAs are not adjusted, effluent limits contained in the permit must be consistent with the
individual WLAs specified in the TMDL.
If a draft permit provides for a higher load for a discharger than the corresponding individual WLA in
the TMDL, the State/Tribe must demonstrate that the total WLA in the TMDL will be achieved through
reductions in the remaining individual WLAs and that localized impairments will not result. All
permittees should be notified of any deviations from the initial individual WLAs contained in the
TMDL. EPA does not require the establishment of a new TMDL to reflect these revised allocations as
long as the total WLA, as expressed in the TMDL, remains the same or decreases, and there is no
reallocation between the total WLA and the total LA.
Protocol for Minnesota Dissolved Oxygen TMDLs:
In addition to the technical aspects of determining pollutant load allocations outline below, the process
may also involve intensive stakeholder and policy-making efforts.
•
WLA Sources
All sources that are covered by a National Pollutant Discharge Elimination System (NPDES)
permit plus certain septic systems are to be considered in the WLA. These sources, for the
purpose of the TMDL should be referred to as point sources.
Point Sources include:
•
Public Owned Treatment Works (POTWs) and other Wastewater Treatment Facility
(WWTF) permittees with discrete discharges and explicit numeric discharge limits need to be
included in the waste load allocation.
•
NPDES stormwater permits, including from those communities designated as Phase I and
Phase II Municipal Separate Storm Sewer System (MS4s), and for permitted construction
and industrial stormwater activities.
•
Straight-Pipe Septic Systems: Straight-pipe septic systems are illegal and un-permitted, and
as such are assigned a zero wasteload allocation.
•
Livestock facilities that have been issued NPDES permits are assigned a zero wasteload
allocation. This is consistent with the conditions of the permits, which allow no pollutant
discharge from the livestock housing facilities and associated site. Discharge of pollutants
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from fields where manure has been land applied may occur at times. Such discharges are
covered under the load allocation portion of the TMDLs, provided the manure is applied in
accordance with manure management provisions of the permit.
•
It is important to note that all relevant NPDES permits in an impaired reach watershed need
to be listed individually in the TMDL document. To the extent possible and practical,
individual WLAs should be established for NPDES dischargers, including regulated MS4s
(see below – “Estimating WLAs”). Construction and industrial stormwater permits should
get an individual WLA when deemed necessary, although categorical allocations may be the
norm in most TMDLs.
•
The location of sources in the watershed may need to be evaluated for their water quality
impact at the point of LC calculation. For example, while phosphorus entering surface
waters is generally transported downstream, there may be specific instances where
phosphorus load retention upstream of an impairment should be taken into account. In order
to justify any allocation allowances based on source location, clear support and
documentation is necessary. This consideration may apply to both the WLA and LA.
•
Pollutant trading, including trading either between point sources or trading between point
sources and nonpoint sources, can be included in the TMDL and developed in detail in the
subsequent implementation plan, as a means to meet a WLA. However, the MPCA’s trading
policy has not been finalized. Trading may further the need for geographic consideration of
loads.
•
Water Quality Based Effluent Limits
As noted in the federal requirements in the box above, NPDES permits must be consistent with
the assumptions and requirements of a TMDL’s wasteload allocation. Therefore, for Wastewater
Facilities, water quality-based effluent limits contained in the permit must be consistent with the
individual WLAs specified in the TMDL. In most cases, the WLA in the TMDL and effluent
limit in the permit will be expressed in terms of mass. Attainment is needed at or above low
flow conditions as defined by (7Q10). For regulated MS4s, water quality-based effluent limits
may be in the form of Best Management Practice (BMPs) or in the form of numeric effluent
limits. If data allows, the TMDL should define the percentage of the load allocation for each
NPDES permitted facility and for each MS4.
•
Estimating WLA Loads and Allocations
Wastewater point sources:
For POTWs and industrial wastewater facilities, either the MPCA should be contacted for the
electronically-available discharge monitoring reports (DMRs) for that facility, or the facility
should be contacted directly. These data should be used to define the current WWTF phosphorus
loading to the water body, which will serve as a basis for the allocations.
MS4 Stormwater:
For estimating current loads from regulated MS4s and establishing allocations, each MS4 should
be contacted for pertinent information. Current loading should be estimated as precisely as data
allows. Guidance issued in 2002 from EPA (“Establishing Total Maximum Daily Load (TMDL)
Wasteload Allocations (WLAs) for Storm Water Sources and NPDES Permit Requirements Based on
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Those WLAs” (November 22, 2002); http://www.epa.gov/npdes/pubs/final-wwtmdl.pdf) will be useful
in determining your approach.
EPA notes that it may be reasonable to express NPDES-regulated storm water discharges from
multiple point sources as a single categorical waste load allocation when data and information
are insufficient to assign each source or outfall individual WLAs. More specifically, the waste
load allocation in the TMDL can be expressed as either a 1) single number for all NPDESregulated stormwater discharges, or 2) when information allows, as different WLAs for different
categories, such as all MS4s separated out from construction and industrial stormwater and
treated either in aggregate or as individual MS4s (City A vs. City B).
In keeping with this guidance, the MPCA believes that many waste load allocations for regulated
MS4s will be made in the aggregate by categorical sector (e.g. a 33 percent reduction for the
MS4 sector) because of the insufficient quantity and quality of existing data on each individual
MS4. However, if enough data exists, it is strongly encouraged that an individual WLA be set
for each MS4 discharger. Here are examples of these two options:
1. Sector-wide allocation: A TMDL could find that all regulated MS4 sources together
contribute a total of 300 lbs. of phosphorus and a load reduction of 100 lbs. is necessary to
meet the WLA goal, or roughly a 33 percent load reduction. All MS4s would be evaluated
together to achieve the load reduction of 100 lbs.
2. Individual allocation (Also see detailed guidance in Appendix B developed for the Minnesota
River low dissolved oxygen TMDL).
a.) If a city-by-city WLA approach for MS4s is preferred, the MPCA proposes that the WLA
be divided equally among MS4s, in proportion to the size of their contributing watershed.
For example, the TMDL finds that a 33% reduction (equivalent to 100 lbs. of
phosphorus) is needed. The total contribution from three cities in a TMDL watershed is
300 lbs. and the total WLA requires a reduction of 100 lbs of phosphorous. If cities A, B,
and C together have 100% of the impaired watershed, and City A’s permit boundaries
cover 80%, City B’s 10% and City C’s 10%, then the load allocation for City A’s
reduction goal would be 80 lbs, and City B and C would be 10 lbs each. However, all
three cities reduce the same proportional amount of phosphorus.
b.) If sufficient water quality data exists on specific MS4 contributions and applied BMPs, a
more tailored WLA can be set for each city. For example, if a city has eliminated its
illicit discharges while another city has not, equal load reductions may not be equitable.
•
NPDES Permit Compliance Schedules and Water Quality Trading
Federal regulations set requirements for NPDES permit compliance schedules to meet effluent
limits. In general, there are two expectations:
1. Each NPDES permit must meet effluent requirements; and
2. The compliance schedule for meeting the requirements should be within one permit
cycle.
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Despite these expectations, there is flexibility in setting permit compliance schedules to meet
TMDL WLAs in certain situations. It is important that TMDL project teams discuss these
situations with MPCA permitting staff as WLAs are being developed to ensure that compliance
schedules are set appropriately.
Compliance Options for Wastewater Facility Permits:
As noted above, there is an expectation for all wastewater NPDES permits to meet the TMDL
WLA in the first five-year permit cycle. However, there can be exceptions to this process when
justified:
1) Multiple TMDLs in the same watershed: When NPDES permitted facilities may have to
comply with more than one TMDL for the same pollutant parameter but are on different
completion timelines, a longer compliance schedule may be necessary. This is to ensure
that facility upgrades are made to meet the most restrictive TMDL WLA (i.e., the TMDL
that may require more restrictive limits or longer seasonal application of the limits).
For example, in the case of the Minnesota River low dissolved oxygen TMDL, the
critical period was during summer months. However for the Lake Pepin excess nutrient
TMDL, the critical period will most likely be year-round. Therefore, the upgrade of the
facilities for the seasonal effluent limitation versus the upgrade needed for year-round
treatment can be significantly different. Setting milestone markers until the other TMDL
studies are completed will minimize the occurrence of new or expanding systems being
built that are immediately required to upgrade again to meet a more restrictive TMDL.
It is important to discuss this type of justification (including expected timelines for
milestones and steps necessary to meet them) in the TMDL report to clarify how NPDES
permit compliance schedules will meet the TMDL’s WLA.
2) Pollutant Trading and Watershed Permits: For NPDES-permitted wastewater facilities
that may not be able to meet a TMDL WLA, two options are emerging: pollutant trading
and watershed permitting. A policy for the first option, pollutant trading, is currently
being developed by the MPCA. Trading enables entities located upstream of a given
impairment to work together to cumulatively achieve the WLA. Pollutant trading can
benefit dischargers by using either the benefits of economy of scale, or by limiting the
upgrades or installations of BMPs (in the case of point to nonpoint trading) to those that
are the least expensive and “trading” the activities of the most expensive for an
equivalent reduction or a net pollutant load decrease.
The second option, a watershed permit, allows all NPDES activities to be sequenced and
considered on a cumulative basis in a watershed. In this process, a cumulative problem
can be solved by sequencing all the NPDES permits to implement a specified set of
reductions across a given timeframe. This has the potential to accelerate implementation
schedules and also provides a better opportunity to set expectations for reductions at an
equitable level.
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It is important that if either of these alternatives are factored into final TMDL
implementation strategies to meet a WLA, they are discussed in the TMDL report. This will
provide guidance on permit compliance schedules and/or the use of more flexible compliance
alternatives.
Compliance Options for Stormwater Permits:
TMDL WLAs for regulated MS4s should reflect the timing required to retrofit existing
developed areas with BMPs and to set adequate milestones for developing areas. In general,
it should be assumed that multiple permit schedules will be needed to meet TMDL reduction
targets and the regulated MS4 needs to make progress in each permit cycle to meet a WLA.
Progress indicators include establishing a stormwater program, doing good housekeeping,
addressing retrofits and new development, prevention and education, and structural BMPs.
If the TMDL study has enough data to set reduction milestone timelines and goals, then the
SWPPP for each permit cycle can reference the TMDL and the milestones to justify its
compliance with the TMDL. Other options are also possible:
1) Phased TMDLs: For instances where the TMDL study has significant uncertainty about
stormwater loadings and management practices to effectively address that loading, an
EPA memorandum dated August 2, 2006 entitled Clarification Regarding “Phased”
Total Maximum Daily Loads
(http://www.epa.gov/owow/tmdl/tmdl_clarification_letter.pdf) outlines acceptable
methods to discuss “phased” approaches in the TMDL study.
As noted in this document, “phased TMDLs be limited to TMDLs that for scheduling
reasons need be established despite significant data uncertainty and where the State
expects the loading capacity and allocation scheme will be revised in the near future as
additional information is collected.” The document cites examples of situations where
this may apply, including lake nutrient TMDLs where there are uncertain loadings from
major land uses and/or limited knowledge of in-lake processes. As with any TMDL, each
phase must be established to attain and maintain the applicable water quality standard and
would require re-approval by EPA if the LC, wasteload or load allocations are revised.
For stormwater TMDLs using a phased approach, collection of missing data needed to assess
loading or management practices would be required through SWPPPs. This should be
clearly discussed in the TMDL report.
2) Pollutant Trading: EPA is currently developing an approach for stormwater pollutant
trading. There are a few pilot programs ongoing at the national level testing the situations
that would provide clarity on how and when stormwater pollutant trading would be allowed.
The MPCA will be developing options in this area as well.
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References:
“Establishing Total Maximum Daily Load (TMDL) Wasteload Allocations (WLAs) for Storm Water Sources and
NPDES Permit Requirements Based on Those WLAs” (November 22, 2002);
http://www.epa.gov/npdes/pubs/final-wwtmdl.pdf
Appendix B: “Guidance for Communities on How to Estimate and Achieve Phosphorus Reductions and Report it
in their SWPPPs”
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G. Margin of Safety (MOS)
Federal Requirements:
The statute and regulations require that a TMDL include a margin of safety (MOS) to account for any
lack of knowledge concerning the relationship between load and wasteload allocations and water quality
(CWA §303(d)(1)(C), 40 C.F.R. §130.7(c)(1) ). EPA's 1991 TMDL Guidance explains that the MOS
may be implicit, i.e., incorporated into the TMDL through conservative assumptions in the analysis, or
explicit, i.e., expressed in the TMDL as loadings set aside for the MOS. If the MOS is implicit, the
conservative assumptions in the analysis that account for the MOS must be described. If the MOS is
explicit, the loading set aside for the MOS must be identified.
Protocol for Minnesota Dissolved Oxygen TMDLs:
The rationale for selecting the MOS and its adequacy must be included in the TMDL submittal. As
indicated in the federal requirement, an explicit MOS would include setting a portion of the LC aside as
the MOS (i.e., not allocated to any source). Examples of an implicit margin of safety include the use of
conservative assumptions in selecting a numeric water quality target and predicting the performance of
best management practices. A related implicit MOS is the use of conservative design criteria for the
sizing of best management practices.
TMDL =
Background + ∑ LA+
∑WLA
Natural or
Unregulated
Non-Point
Point Sources
+
Regional Runoff
Atmospheric
Urban
Agriculture
Silvaculture
Transportation
WWTF
SW MS4
Industrial
Commercial
ISTS
MOS
Margin of Safety
Variability
Uncertainty
Expected Long-Term-Average Load to Water
+Consideration of Future Growth as Reserve Capacity
The basic purpose of the MOS component of the TMDL equation is provide additional assurance that
the projected load estimation process will attain water quality numeric standards and to allow the project
a reasonably high likelihood of success. As such, MOS encompasses two primary factors affecting these
outcomes: variability and uncertainty. “Variability” refers to the fluctuations in measured values for a
given parameter across flow regimes, up and down the reaches (spatially) and as well as by temporal
factors - such as within year (seasonal) and year-to-year changes (induced by climatic conditions and
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biological response). “Uncertainty” refers to prediction error resulting from limits in the data and
predictive models. Walker (2001 & 2003) has provided detailed discussions of these subjects and the
reader is directed to these articles for more detail on the topic. The Margin of Safety should not
encompass future growth or allocations of reserve capacity. It is encouraged that these aspects of
assimilation capacity should be dealt with as a separate allocation explicitly stated as a part of the formal
TMDL process.
In instances where there is a scarcity of data, the TMDL components need to be estimated with greater
uncertainties and hence, higher MOS. As more data is collected, estimates of variability and uncertainty
can be reduced thereby allowing a smaller MOS component – and greater allocations to the other
components balancing the TMDL equation. In short, if there are limited data available, a model based
portrayal may have to suffice until more monitoring is conducted. Alternatives to explicit Margin of
Safety expressions include: conservative water quality criteria/standards, conservative reduction goals,
conservative modeling assumptions, conservative effluent limits/ discharge permits, conservative BMP
designs, and/or conservative growth projections. In these cases, the MOS is included in the other terms
of the TMDL equation and is not explicitly quantified, either in terms of load or the corresponding risk
that the goals will be achieved (Walker, 2001). Hence, the risk of making improper management
decisions can become larger.
Uncertainty Estimates
Uncertainty analyses should be included in TMDL allocations, ranging from the model professional
contract if one is used or by the technical team members using the analysis tool selected. Refer to
Chapter 2 for details on the options for analysis and methods to test the predictive capability of the
assessment tool.
In summary on these topics Walker (2003) cautions against setting an unrealistically high confidence
level and/or compliance rates as TMDL goals. A high MOS could hinder progress of restoration by
increasing costs, reducing credibility, and stimulating controversy. Rather, he suggests an incremental
or adaptive approach to achieving the desired compliance rate and confidence level through successive
TMDLs as may be appropriate, as recommended by the National Research Council (2001). This will
often be the case in TMDLs where a majority of the loading which needs be reduced to achieve the
TMDL, arises from unregulated nonpoint source runoff, or as Walker (2003) states, “a phased approach
is applicable where the load allocation is not immediately achievable (with or without an MOS) because
of limits in control technology.” In any case, the TMDL equation must be written such that the TMDL
is met by the allocations.
References:
Walker, 2001 and 2003.
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H. Reserve Capacity (allocation for future growth)
Federal Requirements:
Implied under LA and WLA requirements as the “portion of the loading capacity attributed to existing
and future sources”
Protocol for Minnesota Dissolved Oxygen TMDLs:
Reserve Capacity is that portion of the TMDL that accommodates future loads. The MPCA’s policy on
reserve capacity is that it be considered by all TMDL projects and the final report should clearly
describe the rationale for a decision regarding this issue.
Inclusion of an allocation for reserve capacity in the TMDL is strongly encouraged. Reserve capacity
can be ascribed singly to the WLA, the LA or both; e.g. new and expanding WWTF’s, MS4s that will be
covered by a permit in the future or that are permitted now and may expand, and/or land use changes. If
an allocation for reserve capacity is not included, either no new future loads are anticipated or allowed,
or increased loads must be accommodated by pollutant trading. In the case of MS4s, growth may also
be accommodated in the WLA based on larger municipal boundaries or expansion area designations, if
appropriate. If reserve capacity is accommodated by trading only, a discussion of a viable trading
program and the implications to new loads should be included. A typical 20-year planning timeline for
consideration of reserve capacity is recommended.
The TMDL report should provide the basis for the amount of reserve capacity, guidelines for making
reserve capacity available to new loads, and the means to replenishing reserve capacity when it has been
depleted. Replenishing reserve capacity can be accomplished through the following options:
WWTF sources
• Concentration adjustments – reallocation based on concentration effluent limits at the given
design flow;
• Flow adjustments – reallocation of allowed design flow at the given concentration; or
• Mass adjustments – mass-based effluent limit
Nonpoint sources and MS4s
• Additional BMP implementation
• Reducing watershed loads
General
• Reducing margin of safety through greater understanding of load response conditions.
It is anticipated that reserve capacity issues will largely be a policy discussion that requires input from
all affected parties and consideration of future loads in the watershed. Policy considerations for
allocating reserve capacity to new loads should be based on an equitable and consistent set of criteria.
In the case of WWTFs, it may not be completely possible to anticipate all new future loads. An example
of this would be those loads from new unplanned industrial sources. If this appears a likely scenario, an
increased reserve capacity over that anticipated to be necessary may be warranted.
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The allocation of reserve capacity should be fully documented so that any future reallocation can
consider past allocation changes. Additionally, reserve capacity balances must be documented at all
times. This should include detailed documentation of all new loads that have been transferred to the
WLA and LA.
Consideration may be given to requiring new loads to provide a higher level of treatment/BMP
implementation to access reserve capacity. For example, if WWTFs are generally meeting a 1.0 mg/L
phosphorus effluent limitation, a 0.5 mg/L phosphorus limit may be a criteria to access reserve capacity.
New loads from new sources or expanded sources may be treated the same or differently.
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I. Seasonal Variation
Federal Requirements:
The statute and regulations require that a TMDL be established with consideration of seasonal
variations. The TMDL must describe the method chosen for including seasonal variations. (CWA
§303(d)(1)(C), 40 C.F.R. §130.7(c)(1)).
Protocol for Minnesota Dissolved Oxygen TMDLs:
Nothing additional at this time.
J. Reasonable Assurances
Federal Requirements:
When a TMDL is developed for waters impaired by point sources only, the issuance of a National
Pollutant Discharge Elimination System (NPDES) permit(s) provides the reasonable assurance that the
wasteload allocations contained in the TMDL will be achieved. This is because 40 C.F.R.
122.44(d)(1)(vii)(B) requires that effluent limits in permits be consistent with "the assumptions and
requirements of any available wasteload allocation" in an approved TMDL.
When a TMDL is developed for waters impaired by both point and nonpoint sources, and the WLA is
based on an assumption that nonpoint source load reductions will occur, EPA's 1991 TMDL Guidance
states that the TMDL should provide reasonable assurances that nonpoint source control measures will
achieve expected load reductions in order for the TMDL to be approvable. This information is necessary
for EPA to determine that the TMDL, including the load and wasteload allocations, has been established
at a level necessary to implement water quality standards.
EPA's August 1997 TMDL Guidance also directs EPA Regions to work with States to achieve TMDL
load allocations in waters impaired only by nonpoint sources. However, EPA cannot disapprove a
TMDL for nonpoint source-only impaired waters, which do not have a demonstration of reasonable
assurance that LAs will be achieved, because such a showing is not required by current regulations.
Protocol for Minnesota Dissolved Oxygen TMDLs:
Generally, reasonable assurances include descriptions of the regulatory and nonregulatory efforts at the
state and local levels that will likely result in reductions from the load allocation portion of the TMDL.
Reasonable Assurances also include the identification of potential or likely funding sources that will
enable reductions from the load allocation.
The following list of scenarios describes when to include Reasonable Assurances in the TMDL
submittal:
•
Nonpoint source only TMDLs (Load Allocation only):
Although EPA does not require reasonable assurances in this type of TMDL, the MPCA requires a
description of reasonable assurances for nonpoint only TMDLs. Reasonable assurances in these
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types of TMDLs allow the MPCA to evaluate the potential options available to enable reductions
from nonpoint sources.
•
TMDLs with offsets in the Waste Load Allocation from the Load Allocation:
EPA requires reasonable assurances in this situation in order to approve the TMDL.
This is clarified in the 1991 EPA guidance document, Guidance for Water Quality-Based Decisions:
The TMDL Process. The guidance addresses waters impaired by both point and nonpoint sources
where the wasteload allocation to point sources is not as strict because of nonpoint source loading
reductions. In such cases, some additional provisions in the TMDL, such as a schedule and
description of the implementation mechanisms for nonpoint source control measures, are needed to
provide reasonable assurance that the nonpoint source measures will achieve the expected load
reductions. Such additional provisions are needed in this type of TMDL to assure compliance with
the federal regulations at 40 CFR 130.2(i), which require that in order for wasteload allocations to be
made less stringent, more stringent load allocations must be “practicable.”
•
TMDLs without offsets in the Waste Load Allocation from the Load Allocation:
Although EPA does not require reasonable assurances in this type of TMDL, the MPCA requires a
description of reasonable assurances. Reasonable assurances in these types of TMDLs allow the
MPCA to evaluate the potential options available to enable reductions from nonpoint sources.
•
TMDLs with wastewater permittees in the Waste Load Allocation:
Where the reductions are stemming solely from wastewater permittees without LA reductions for
attainment goals, or the permits are at Best Available Technology, reasonable assurances are not
required for wastewater permittees because federal regulations require that permits with numeric
effluent limits comply with the Waste Load Allocation in the TMDL.
•
TMDLs with required and discretionary MS4 stormwater permittees in the Waste Load
Allocation:
As noted in the box above, NPDES permit requirements must be consistent with the assumptions and
requirements of available WLAs. See 122.44(d)(1)(vii)(B). Since permits for required and
discretionary MS4 do not contain numeric limits, the MPCA requires an MS4 to provide reasonable
assurances in the following manner:
“If a USEPA-approved TMDL(s) has been developed, you must review the adequacy of your
Storm Water Pollution Prevention Program to meet the TMDL’s Waste Load Allocation set for
storm water sources. If the Storm Water Pollution Prevention Program is not meeting the
applicable requirements, schedules, and objectives of the TMDL, you must modify your Storm
Water Pollution Prevention Program, as appropriate, within 18 months after the TMDL is
approved.”
This permit language should be cited in the reasonable assurance section of the TMDL. In addition,
note that the implementation plan, likely to be finalized one year following EPA approval of the
TMDL, will identify specific BMP opportunities sufficient to achieve their load reduction and their
adoption schedule, and the individual SWPPPs would be modified accordingly following the
recommendations of this plan.
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TMDLs with construction stormwater permittees in the Waste Load Allocation:
As noted in the Federal Requirements section above, NPDES permit requirements must be consistent
with the assumptions and requirements of available WLAs. (See CWA section
122.44(d)(1)(vii)(B)). Since permits for construction stormwater do not contain numeric limits, the
MPCA requires a construction stormwater permittee to provide reasonable assurances by citing the
TMDL compliance requirements of provisions in the NPDES Construction Stormwater Permit (Part
I.B.7, Part III.A.4.d, and Part III.A.7). According to Part I.B.7 of the General Permit:
“Discharges to waters for which there is a total maximum daily load (TMDL)
allocation for sediment and parameters associated with sediment transport are not
eligible for coverage under this permit unless the Permittee(s) develop and certify a
SWPPP that is consistent with the assumptions, allocations and requirements in the
approved TMDL. To be eligible for coverage under this general permit, Permittee(s)
must incorporate into their SWPPP any conditions applicable to their discharges
necessary for consistency with the assumptions, allocations and requirements of the
TMDL within any timeframes established in the TMDL. The SWPPP must include
the provisions in Part III.A.7. If a specific numeric wasteload allocation has been
established that would apply to the project's discharges, the Permittee(s) must
incorporate that allocation into its SWPPP and implement necessary steps to meet that
allocation.”
As with MS4s, the permit language above should be cited in the reasonable assurance section of the
TMDL. Note that the implementation plan, to be finalized within one year following EPA approval
of the TMDL, will identify specific BMP opportunities sufficient to achieve their load reduction and
their adoption schedule, and the individual SWPPPs would be modified accordingly following the
recommendations of this plan.
References:
EPA's 1991 document, Guidance for Water Quality-Based Decisions: The TMDL Process (EPA 440/4-91-001)
http://www.epa.gov/OWOW/tmdl/decisions/
MS4 permit requirements: http://www.pca.state.mn.us/water/stormwater/stormwater-ms4.html#requirements
Construction stormwater permit requirements: http://www.pca.state.mn.us/water/stormwater/stormwaterc.html#forms
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K. Monitoring Plan to Track TMDL Effectiveness
Federal Requirements:
EPA's 1991 document, Guidance for Water Quality-Based Decisions: The TMDL Process (EPA 440/491-001) http://www.epa.gov/OWOW/tmdl/decisions/ recommends a monitoring plan to track the
effectiveness of a TMDL, particularly when a TMDL involves both point and nonpoint sources and the
WLA is based on an assumption that nonpoint source load reductions will occur. Such a TMDL should
provide assurances that nonpoint source controls will achieve expected load reductions, and should
include a monitoring plan that describes the additional data to be collected to determine if the load
reductions provided for in the TMDL are occurring and leading to attainment of water quality standards.
Protocol for Minnesota Dissolved Oxygen TMDLs:
A monitoring plan associated with DO TMDLs offers an opportunity to focus existing monitoring
activities in the watershed, as well as identify additional needs toward achieving the common goals of
assessing and improving water quality. Many of Minnesota’s waters have active watershed associations
that routinely collect water quality data and information. The monitoring plan for the TMDL could
outline how collaborative monitoring efforts could be used to better define sources, target sources for
control actions, evaluate the effectiveness of controls, and ultimately assess the adequacy of the TMDL.
The watershed assessment options presented in Chapter 2 provide multiple methods to gather
monitoring data. Data sets can vary from relatively few data to progressively more sophisticated studies.
Generalized monitoring designs for streams and watersheds are presented below. In addition, it is also
recommended that the reader review EPA’s clarifying guidance on three situations where follow-up
monitoring strategies are needed to provide assurances that nonpoint source controls will be achieved:
“phased TMDLs”, “adaptive implementation” and “staged implementation”
http://www.epa.gov/owow/tmdl/tmdl_clarification_letter.html .
Figure 21: Iterative TMDL Process
Schematic of TMDL Adaptive Management (Walker, 2001)
Monitoring – Rivers
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Consideration of critical conditions and the analysis tool used to assess the progress towards compliance
with the numeric criteria is the first step to designing an effectiveness monitoring program for DO in
rivers. The summer low flow condition is often the primary critical condition designed for. However,
the 1 in 10-year low flow return frequency is based on probability and may not occur until much later
than the first decade. For instance, the last 7Q10 condition in the Minnesota River was in 1988.
Therefore, it is necessary to implement a monitoring program that will track the resource conditions as
implementation activities take place regardless of flow conditions, so that it will be able to be used to
estimate the progress in a flow regime where monitoring data is not available.
Delisting will only be possible after the critical conditions have existed and adequate monitoring can be
provided that demonstrates the system to be in complete water quality attainment.
Monitoring Change
Tracking of water quality changes over time resulting from the implementation of watershed and lake
rehabilitations can be reasonably accomplished with due consideration of time lags, geographic scale,
monitoring approaches and quality assurance.
The monitoring efforts in Minnesota have been routine based (every month or every two weeks), and
event based with consideration to continuous measurement of flows. Whether the monitoring data is
collected by grab sampling, or by storm hydrograph sampling by automated equipment depends on the
project goals and station location to field crew. However, with many parameters needed to track
progress in DO TMDLs, limited holding times for parameters such as CBOD need to be considered. Key
parameters to select from are the field parameters of pH, DO, and temperature, plus the analytical
parameters of total phosphorus, total suspended solids, TKN, Chl-a. The selection will depend both on
the analysis tool used for tracking progress (suggested to be the analysis tool utilized in the TMDL) and
the critical parameters identified by the TMDL.
In addition, the implementation of significant percentages of BMPs or treatment measures needs to be in
place prior to initiating the "after" condition water quality monitoring efforts. It is suggested that upon
obtaining a good "prior" condition baseline, that a skewed rollout be used, with the more significant
resource monitoring being initiated after 60 percent or more of the reduction measures are implemented
(this percentage best applied by load, however if not available then a number count of the measures can
be done). This requires adequate land use tracking efforts to be set up and in place during the
implementation period, such as e-Link, the residue transect survey, wastewater DMR reports, county
feedlot inventories and others as determined by the specific TMDL.
Time Lags
Before and after monitoring Quality assurance plans are required for TMDL projects by ensuring that appropriate field and
laboratory procedures are employed. Use of certified labs is a part of this quality assurance process.
Other typical quality assurance aspects include consideration of:
•
•
•
accuracy as a function of methods (field and laboratory);
precision as a function of methods, and sample frequency; and
probability of detecting change as a function of precision, variability, and duration of
sampling, much of which was described in previous sections of this document.
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Over the course of a watershed management effort, there can be significant time periods that occur from
the time of recognition of water quality problems, rehabilitation of key watershed areas and
improvement of water quality. Projects usually begin with a one to three year diagnostic study coupled
with building requisite local partnerships. Additional time is needed for public notices and contracts
leading up to planning and design of watershed corrective actions.
The final leg of the restoration journey involves BMP construction, usually coupled with vegetative regrowth. All of these changes need to occur before the stream has a chance to reach attainment. After
implementation and establishment of all the treatment measures the flow regimes in the stream may
need to be from a wet weather period to be high enough to flush SOD out of the system prior to the
complete compliance attainment.
Geographic scale and Rehabilitation Sequencing
The size of the contributing watershed to a given impaired reach will be a large determinant in the time
and effort needed to affect improved water quality. The monitoring options defined in the above
guidelines will help guide establishment of required stream flow gauging and sampling efforts, with
smaller areas showing changes more quickly. Smaller watersheds can be typically expected to respond
more quickly to watershed corrective measures. Large watershed projects are encouraged to develop
smaller, more optimal detection tracking project areas.
References:
EPA 2006. Clarification regarding “Phased Total Maximum Daily Loads”
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L. Implementation
Federal Requirements:
EPA policy encourages Regions to work in partnership with States/Tribes to achieve nonpoint source
load allocations established for 303(d)-listed waters impaired by nonpoint sources. Regions may assist
States/Tribes in developing implementation plans that include reasonable assurances that nonpoint
source LAs established in TMDLs for waters impaired solely or primarily by nonpoint sources will in
fact be achieved. In addition, EPA policy recognizes that other relevant watershed management
processes may be used in the TMDL process. EPA is not required to and does not approve TMDL
implementation plans.
Protocol for Minnesota Dissolved Oxygen TMDLs:
For DO TMDLs, the detailed and site specific implementation planning will take place during the
Implementation Plan development.
Projects must include in the written TMDL submitted to MPCA the broad implementation strategies to
be refined and finalized after the TMDL is approved. Projects are required to submit a separate, more
detailed implementation plan document to MPCA within one year of the TMDL’s approval by EPA. For
example, highly complex TMDLs or TMDLs requiring reductions for NPDES-permitted point sources
(wastewater, stormwater, feedlots) may require this additional time following approval to prepare
detailed implementation plans.
The Minnesota Clean Water Legacy Act requires a range of implementation costs to be included in the
TMDL. It is recommended that a range of probable costs be included in the discussion by land use type.
For instance, large watershed scale TMDLs may have significant implementation cost ranges due to the
large number of measures needed, even though they are implementing the least expensive measure on a
unit cost basis. The factors that contribute to or control the cost estimate ranges should be broadly
outlined in the narrative.
For further information on implementation plan requirements, review MPCA’s TMDL work plan
guidance at http://www.pca.state.mn.us/publications/wq-iw1-01.pdf and the MPCA policy on
implementation plans at http://intranet.pca.state.mn.us/policies/programpolicies/i-wq2-031.pdf .
In the DO TMDL implementation plan section, the broad implementation strategies, activity areas, and
mechanisms for achieving loading reductions should be identified. The implementation plan section
should identify:
• How the public will be involved.
• What mechanisms such as financial assistance, ordinances etc., exist or are proposed for
development.
• How progress will be monitored such as WQ monitoring, BMP tracking etc.
• How control activities will be sited.
• What planning tools or processes will be used to achieve nonpoint source reductions.
• What planning tools, processes, ordinances are in-place or will be proposed to control point
sources.
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•
•
What educational and cooperative efforts among stakeholders, landowners, and agencies exist or
a proposed for development.
What time period each sector will be given for adoption goals, retrofitting and implementation
of structural measures.
For MS4s, this section of the TMDL should provide a high level overview of activities that will be
refined in the implementation plan. Providing this information will help enhance reasonable assurance,
including:
• The current BMPs that are planned (to be refined during implementation planning and SWPPP
development);
• The current schedule (i.e., how many permit cycles) for putting BMPs in place; and
• Expected range of potential reductions, based on literature, which can be achieved for each
category of BMP (e.g., citizen education program, stormwater ponds, alum treatment, etc.).
Note: Additional guidance on this is currently being developed by the MPCA.
References:
MPCA’s TMDL work plan and implementation plan guidance.
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M. Public Participation
Federal Requirements:
EPA policy is that there should be full and meaningful public participation in the TMDL development
process. The TMDL regulations require that each State/Tribe must subject draft TMDLs to public
review, consistent with its own continuing planning process (40 C.F.R. §130.7(c)(1)(ii)). In guidance,
EPA has explained that final TMDLs submitted to EPA for review and approval should describe the
State's/Tribe's public participation process, including a summary of significant comments and the
State's/Tribe's responses to those comments. When EPA establishes a TMDL, EPA regulations require
EPA to publish a notice seeking public comment (40 C.F.R. §130.7(d)(2)).
Provision of inadequate public participation may be a basis for disapproving a TMDL. If EPA
determines that a State/Tribe has not provided adequate public participation, EPA may defer its approval
action until adequate public participation has been provided for, either by the State/Tribe or by EPA.
Protocol for Minnesota Dissolved Oxygen TMDLs:
An active stakeholder and public participation process is required throughout the development of every
TMDL, from the development of the project workplan to the approval of final pollutant load allocations
and public notice process. The ultimate success of the project is in large part dependent upon the
effectiveness of this process, and development of practical, pragmatic solutions with stakeholders is
fundamental. It is critical that the diverse stakeholders affected by any given TMDL project (and those
who must implement it) share a common understanding of the problem and what is needed to solve it.
Public participation is also required through the 2006 Clean Water Legacy Act which requires the
MPCA to seek “broad and early public and stakeholder participation in scoping the activities necessary
to develop a TMDL, including the scientific models, methods, and approaches to be used in TMDL
development, and to implement restoration…”
Based on the recommendations of a broad-based group of stakeholders (“The G16”) advising the MPCA
on TMDLs, the MPCA has piloted an intensive public participation process through its Lake Pepin
TMDL. The results of this process will be critical to determining guidance for other TMDL projects.
This will include development of a stakeholder advisory group which will provide recommendations on
a project throughout the process. The stakeholder advisory group can also receive advice on technical
issues from a technical/science advisory group, comprised of experts from academia and other
institutions. More information on this structure and process can be found by referring to a fact sheet on
the Lake Pepin project: http://www.pca.state.mn.us/publications/wq-iw9-01f.pdf
Probably the most critical phase of a stakeholder advisory group process is in developing and making
recommendations for source reductions and pollutant load allocations (load allocations, wasteload
allocations, margin of safety, and reserve capacity). Federal regulations specify only that the total
allocations (point source and nonpoint source, margin of safety) prescribed by a given TMDL must
satisfy water quality standards for that water’s designated use. The specific method for allocating
pollutant loads among sources is a policy issue that must be determined by states according to their own
priorities and judgment.
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The MPCA will carefully consider stakeholder recommendations and the MPCA’s final decision will be
made after considering a range of allocation options, ensuring that they meet water quality standards, are
technically and practically feasible, and are consistent with other regulatory programs that might
apply. In addition, competing measures of desirability (where regulatory flexibility allows), such as costeffectiveness and equity, will be critical factors in determining load allocations.
More specifically, final policy decisions on allocations should reflect public and stakeholder perceptions
about acceptable tradeoffs. For example, strategies that minimize costs may be perceived as unfair if
particular sources carry most of the load reduction, while allocations based on equal load reductions may
be more costly. Other factors that should be considered when making allocation decisions include
relative source contributions, technical limitations of any given source to reduce, ability of small entities
to pay, and prior load reductions.
Additional information on the allocation process and options can be found at these EPA
websites: http://www.epa.gov/waterscience/models/allocation/def.htm; and
http://www.epa.gov/waterscience/models/allocation/19schemes.htm.
Local government (contractors) will have a primary role throughout the public participation process. In
general, local government should be prepared to be engaged in these public participation activities:
•
•
•
Help identify stakeholders that can represent diverse public and private interests in affected
watersheds on the Stakeholder Advisory Group for the project.
Conduct public outreach and education activities at key points throughout the project and prepare
a report or section of the draft TMDL that describes those activities.
Coordinate with the MPCA as needed to assist in the formal public notice process for the draft
TMDL, including:
o Help organize a public meeting(s) for the draft TMDL and compile comments from
the public.
o Help respond to comments, as needed, on the draft TMDL from technical staff,
citizens and other interested parties, and EPA.
o Submit public outreach materials along with the draft TMDL or final report, such as
charts, graphs, modeling runs, fact sheets, presentation materials, maps, etc.
Following the allocation process and the final development of a draft, the public notice process can
begin. These steps will be led by the MPCA, coordinating with the local government contractor. Most
activities will be conducted by the project manager, basin coordinator, public information officer, or
impaired waters coordinator, as appropriate.
In general, following are the basic steps to the public notice process:
1. MPCA public information staff and project manager prepare public notice package, to include
draft TMDL, fact sheet, public notice and news release.
2. Public Notice
o The draft TMDL must be on public notice for a minimum of 30 days.
o The public notice must be published in the State Register.
o The notice must be published on the MPCA Web site.
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o The notice should also be mailed or e-mailed to a list of interested parties for the project, and
must be mailed to a statewide list of interested parties maintained by the impaired waters
program coordinator.
o Public meetings during the public notice phase will be determined based on the level of
public participation and outreach during other phases of the project.
3. Public comments: All written public comments must be provided to EPA with the submission of
the TMDL. Copies of each comment letter must also be submitted.
4. Final MPCA approvals (either by the Commissioner or the Citizens Board).
5. The TMDL is submitted to EPA for final approval. In accordance with the 2006 Clean Water
Legacy Act (114D.25), the final TMDL is submitted to EPA no sooner than 30-days following
the conclusion of the public notice period.
References:
2004 Impaired Waters Legislative Report: Impaired Waters Stakeholder Process: Policy Framework:
http://www.pca.state.mn.us/publications/reports/lrwq-iw-1sy04.pdf
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N. Submittal Letter
Federal Requirements:
A submittal letter should be included with the TMDL submittal, and should specify whether the TMDL
is being submitted for a technical review or final review and approval. Each final TMDL submitted to
EPA should be accompanied by a submittal letter that explicitly states that the submittal is a final TMDL
submitted under Section 303(d) of the Clean Water Act for EPA review and approval. This clearly
establishes the State's intent to submit, and EPA's duty to review, the TMDL under the statute. The
submittal letter, whether for technical review or final review and approval, should contain such
identifying information as the name and location of the waterbody, and the pollutant(s) of concern.
Protocol for Minnesota Dissolved Oxygen TMDLs:
The submittal letter is written by the MPCA and signed by the Commissioner. In addition, the final
TMDL report, and any other documents that are a necessary part of the TMDL submittal are ultimately
approved by the Commissioner.
In accordance with Minn. Stat. Sec. 114D.25, MPCA will submit the TMDL to the U.S. Environmental
Protection Agency for review and final approval after a 30-day waiting period upon agency approval.
This delay and notice will be facilitated by the TMDL coordinator position at the MPCA.
O. Administrative Record
Federal Requirements:
While not a necessary part of the submittal to EPA, the State should also prepare an administrative
record containing documents that support the establishment of the TMDL and calculations/allocations in
the TMDL. Components of the record should include all materials relied upon by the State to develop
and support the calculations/allocations in the TMDL, including any data, analyses, or
scientific/technical references that were used, records of correspondence with stakeholders and EPA,
responses to public comments, and other supporting materials. This record is needed to facilitate public
and/or EPA review of the TMDL.
Protocol for Minnesota Dissolved Oxygen TMDLs:
The MPCA project manager and administrative staff will gather and file all necessary documents for the
administrative record.
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Appendix A
Minnesota’s TMDL submittal checklist
This checklist outlines the basic needs for all TMDLs. It is used by MPCA management prior to submittal to
EPA. It supplements the detailed description from EPA’s review guidelines found in Chapter 3 TMDL
Submission Requirements
Item
Page
Adequate
(yes/no)
Executive Summary – should briefly summarize
the key findings in each of the sections below,
particularly the final allocation of pollutant loads.
Background Information, including:
- Spatial extent of watershed (HUC codes are
helpful)
- Waterbody identified as on list (with numeric
identifier)
- Land use distribution
- Population, including present & future growth
trends
- Wildlife resources
- Recreational uses, if relevant
- Pollutant of concern and, if applicable,
justification for using surrogate measures
- Description of pollutant sources (PS and NPS;
also, describe natural background, if
distinguishable from NPS)
Description of Applicable Water Quality
Standards and Numeric Water Quality Target
-
Water quality standard (numeric or narrative)
Designated use
Description of impairment (extent, magnitude,
etc.)
Pollutant sources (PS and NPS; also, describe
natural background, if distinguishable from NPS)
Loading capacity of each listed waterbody
- Description of methodology used
- If both acute and chronic standards exist, as
with fecal coliform, and are exceeded then
must explain how both are addressed in
TMDL
- Critical conditions (e.g., low flow) accounted
for, if applicable
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Load allocation attributed to existing and future
NPS, including description of methodology used
Wasteload allocations for each NPDES
permitted source and straight pipe septics
(loading of 0 for these septics)
Margin of Safety and justification
Reserve Capacity description (if not included in
TMDL needs discussion of why not)
Reasonable Assurance that TMDL will be
achieved (describe regulatory and nonregulatory
efforts at state and local levels; funding
possibilities)
Seasonal Variation
Monitoring plan to track TMDL effectiveness
Implementation Strategy providing general
approach, but not a formal implementation plan.
This should include broad cost ranges for
implementation, per the 2006 Clean Water Legacy
Act
Public Participation summary, including public
notice process to be used
Is technical discussion throughout transparent and
defensible in court (BPJ is justified at all points)
balanced with “is this a reasonable approach”?
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Appendix B:
Guidance for Communities on How to Integrate Lower Minnesota River
Dissolved Oxygen TMDL Requirements and MS4 Stormwater Pollution
Prevention Programs
Introduction
Overview
The Lower Minnesota River is impaired by low dissolved oxygen concentrations during periods of low
flow. The low oxygen concentrations result from elevated phosphorus concentrations. To reach
acceptable water quality in the river during periods of low flow, a Total Maximum Daily Load (TMDL)
was completed. The TMDL requires MS4 communities to reduce phosphorus loading from stormwater
runoff by 30 percent.
The MS4 stormwater general permit requires permittees to develop and implement Stormwater Pollution
Prevention Programs (SWPPPs) and to meet requirements of a TMDL. The SWPPP is therefore the tool
for identifying how requirements of a TMDL will be met.
The following guidance outlines steps needed by permittees to amend their SWPPPs and comply with
requirements of the TMDL. The following guidance for TMDL-affected communities does not
supersede requirements of the stormwater general permit, but includes recommendations for inclusion
into the SWPPP.
General Approach
The TMDL reduction will be met by implementing Best Management Practices (BMPs) rather than
meeting effluent limits. For example, if a BMP reduces phosphorus loading by 30 percent and that BMP
is implemented across an entire community, the 30 percent reduction would be met. This is discussed in
detail in this document.
Permittees should begin implementing BMPs as opportunities arise during the first permit cycle. The
first permit cycle is also used to identify and establish resources and mechanisms necessary to
implement BMPs. During the subsequent three permitting cycles, progress on BMP implementation and
effectiveness of BMPs will be monitored to determine if the water quality objectives for the Minnesota
River are being met. All BMPs necessary to achieve the water quality goal for the river must be in place
by 2025.
The phosphorus reduction is based on 2000 land use and assumes no BMPs were in place at that time.
Consequently, changes in land use since 2000, future growth, and BMPs currently in place will be
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accounted for in calculating load adjustments. These concepts are illustrated in an example at the end of
this document.
During the remainder of 2006, MPCA will meet with MS4 communities to work out details of this
guidance. MPCA will first conduct a pilot study to test this guidance with one MS4 community, make
modifications as necessary, then meet with the remaining MS4 communities. Information gained from
discussions between MPCA and MS4 communities will be used to complete SWPPPs in February 2007.
Depending on available expertise and resources, development of SWPPPs and incorporation of this
guidance may require involvement of consultants. During the first permit cycle, MPCA will continue
collecting information useful for selecting and implementing BMPs during the final three permit cycles.
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Guidance
Mapping and calculating load adjustments
1.
This section provides information about mapping discharges, conveyance systems, stormwater
watersheds, and existing BMPs. Identification and mapping of discharges is necessary to select
and implement BMPs that will meet the TMDL requirements. Mapping existing BMPs is
necessary to determine what reductions, if any, have already occurred. The following information
should be compiled in an appropriate electronic database and used to create GIS coverages. The
example should help illustrate some of the following items.
1.1. The stormwater general permit requires identification of outfalls, conveyances 24 inches or
greater in diameter, DNR subwatersheds (see
http://gisdmnspl.cr.usgs.gov/watershed/index.htm), wetlands, and structural pollution control
devices. To meet the conditions of a TMDL, greater detail will be required. The greater the
detail that can be achieved in mapping discharges, the greater will be the flexibility in
implementing BMPs to meet the reduction requirement. We thus recommend identifying and
mapping discharge points, watersheds contributing to discharge points, and within each
watershed, mapping the conveyance system. The conveyance system includes all below
ground (e.g. pipes) and above ground (e.g. curb and gutter systems, ditches) conveyances.
Examples of mapped systems can be provided.
1.2. Identify and map factors useful in identifying potential phosphorus contributions. These
include percent impervious surface (using Landsat imagery), land use (e.g. commercial,
residential, industrial, park), and soil type (sand, clay). The greater the detail that can be
achieved in mapping these, the greater will be the flexibility in implementing BMPs to meet
the reduction requirement.
1.3. Identify and map your current and year 2000 urban footprint. Aerial photos and satellite
imagery will be useful for identifying the 2000 footprint. To the extent practical, identify and
map future land use. The following link identifies projected population growth over the next
20 years and may be useful in identifying future expansion of your community
(http://www.demography.state.mn.us/a2z.html#Population%20forecasting). The calculated
load will need to be adjusted to account for differences between current and future land use
compared to the 2000 footprint. In a situation where the current or future urban footprint is
greater than the 2000 footprint, the required phosphorus reduction will be more than 30
percent. These scenarios and calculations are illustrated in the example at the end of this
document.
1.4. The stormwater general permit requires identification of BMPs as they relate to the six
minimum control measures. We recommend mapping existing BMPs and calculating
phosphorus reductions associated with these BMPs. These include structural (e.g. infiltration
ponds, biofiltration systems, etc.) and non-structural (e.g. street sweeping) BMPs.
1.4.1. Identify and map the BMPs and map watershed areas contributing to the BMPs.
1.4.2. Estimate reductions associated with the BMPs. For example, in the Minnesota
Stormwater Manual (Table 7.4) average total phosphorus removal from vegetation
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filtration is given as 65%, while a value of 50% is given for wet ponds. The Minnesota
Stormwater Manual contains some of this information, but MPCA is compiling additional
data on efficiencies of BMPs for reducing phosphorus loading from stormwater.
1.4.3. Calculate reductions associated with the existing BMPs. For example, if 10% (0.1) of
stormwater from an MS4 is treated using wet ponds, and an average value of 50% (0.5)
phosphorus removal is given to wet ponds, then wet ponds have achieved a 5%
(0.1*0.50) overall reduction in phosphorus loading.
1.4.4. Note that in the case of BMP sequencing, reductions are not additive. For example, two
BMPs in one area that work in series and each achieve a 50 percent phosphorus reduction
do not provide a 100 percent phosphorus reduction.
Identifying tools to implement BMPs
2.
This section provides methods to 1) identify tools and resources that exist for selecting and
implementing BMPs, 2) list BMP options, and 3) identify future resources needed to achieve
reductions through implementation of BMPs.
2.1. List city entities that have functions or requirements associated with stormwater management.
Identify all city operations and determine their relationship to general municipal operations and
stormwater management. For example, the City of New Ulm has three departments that may
interact on stormwater issues – Administration, which works with finance and community
development; Engineering and Inspections, which works with permits, zoning and community
development; and Public Works, which works with street and sewer maintenance.
2.2. List other agencies that have functions or requirements associated with stormwater
management. For example, the City of Eden Prairie, in its SWPPP, identifies the Metropolitan
Council, MPCA, Hennepin Conservation District, and two watershed districts as entities that
have regulatory and non-regulatory responsibilities related to stormwater.
2.3. List existing water resource planning tools. Examples include drainage plan updates, wetland
protection and management plans, local water management plans, and wellhead protection
plans.
2.4. The stormwater general permit requires mapping of impervious surfaces for conditions
outlined in Appendix C of the general permit (Limitations of Coverage). These include waters
with prohibited or restricted discharge, wetlands, trout waters, historic or archeological sites,
threatened or endangered species or associated habitat, and source water protection areas. To
meet the conditions of the TMDL, we recommend developing GIS coverages for all waters
associated with Limitations of Coverage.
2.5. Identify and list other TMDLs that may affect your community. For example, a Lake Pepin
TMDL may affect communities within the Minnesota River watershed. MPCA’s 2006 list of
impaired waters and the current TMDL list will be of value in identifying these water bodies.
A GIS-based viewer on MPCA’s website can also be used to identify impaired waters
(http://www.pca.state.mn.us/data/edaWater/index.cfm). The purpose of identifying other
TMDLs is to identify as early as possible the most restrictive TMDL. For example, the Lower
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Minnesota River Dissolved Oxygen TMDL calls for a 30 percent phosphorus reduction. For
purposes of this exercise assume the Lake Pepin TMDL, which will be completed in 2009,
calls for a 25 percent reduction. Under this scenario, the Dissolved Oxygen TMDL’s
phosphorus reduction would be adequate because it has a more restrictive requirement. MPCA
understands this is a complicated issue, since it may be difficult to identify or predict future
TMDLs. The Minnesota Pollution Control Agency is preparing a list of TMDLs that apply to
MS4s and this list can be used to identify TMDLs that potentially affect a community. There
are also difficulties in comparing TMDLs that are based on different physical conditions. For
example, the Lower Minnesota River Dissolved Oxygen TMDL applies to low flow conditions
in the Minnesota River, while the Lake Pepin TMDL is likely to be a year round TMDL.
These are issues the MPCA will continue to work through.
2.6. Develop a menu or matrix from which to select BMPs for implementation. For each BMP in
this menu, include the information described below. The Minnesota Stormwater manual
provides information useful for completing this menu. MPCA will continue to gather
additional information useful to you in completing the menu.
2.6.1. Effectiveness for reducing phosphorus. For example, the Minnesota Stormwater Manual
indicates wet ponds, on average, have a phosphorus removal efficiency of 50 percent.
2.6.2. Time to achieve effectiveness, maturity rate and expected life expectancy.
2.6.3. Maintenance requirements. Maintenance includes both structural and non-structural
maintenance, and training. An example of structural maintenance is ensuring that an
infiltration pond is functioning properly. An example of non-structural maintenance is
maintaining a schedule for street sweeping. An example of maintenance for training is
ensuring there is on-going training and certification for developers and engineers.
2.6.4. Costs associated with each BMP. These include construction and maintenance costs.
Consider both monetary and non-monetary costs. An example of a non-monetary cost is
a stormwater pond that could be a drowning hazard or provide mosquito breeding habitat.
2.7. Develop a list of water quality modeling options. Water quality models are used to simulate
phosphorus loading reduction associated with different BMP implementation strategies.
Models can be used to develop a scenario that achieves the 30 percent reduction. For example,
models can be used to identify locations where BMPs will help achieve the greatest reductions.
The Minnesota Stormwater Manual provides a list of water quality models. In general, more
accurate mapping of stormwater conveyances and watersheds allows employment of simpler
water quality modeling.
2.8. Determine if low impact development (LID) is an option in new developments and in
redevelopment. MPCA is conducting studies with communities to investigate ways in which
to incorporate LID into new developments.
2.9. Describe legal tools that can be used or will be needed to implement BMPs. These include
ordinances, building codes, easements, and ownerships. Determine what changes can be made
in legal authorities, including development of new ordinances or changes to existing
ordinances. Determine the relationship between individual BMPs from the BMP menu and
regulatory or non-regulatory requirements. Adopt or establish the framework and schedule
needed for new legal authorities.
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2.10. Describe the plat review process. State whether the city has control or a voice in the planning
of land developments. Identify the relationships between different entities involved in the plat
review process and the communication tools that exist between these different entities.
Determine if changes to the plat review and building permit process, including inspections, will
be needed to implement BMPs identified in the BMP menu. Determine if appropriate authority
exists to modify the existing plat review process. Modify or establish the framework for
modifying the plat review process.
2.11. Describe existing funding mechanisms that can be used or will be needed to implement and
maintain BMPs. These include fees, taxes, escrows, capital improvement projects, and trusts.
Examples include stormwater utility fees assessed against monthly utility bills or, conversely,
incentives to homeowners to reduce utility fees by implementing BMPs such as rain barrels or
rain gardens. Identify mechanisms for increasing funding and capital improvement project
scheduling. Determine if there is a relationship between individual BMPs from the BMP menu
and funding mechanisms. Implement or establish the framework for implementing needed
funding mechanisms.
2.12. Establish a schedule for monitoring, operating, and maintaining BMPs. Permittees will be
responsible for monitoring progress in implementing BMPs to meet the TMDL requirement
and in maintaining BMPs that have been implemented. The MPCA and University of
Minnesota are currently developing guidance that establishes four levels of monitoring. This
guidance will be useful to communities in deciding appropriate levels of monitoring for BMPs.
Monitoring requirements may be included in the BMP menu. For BMPs in place, implement
the monitoring, operation, and maintenance schedule. The Minnesota Stormwater manual
contains information on maintenance requirements for different BMPs.
2.13. Inventory current and future technical tools and expertise necessary to accomplish the
conditions of this SWPPP and subsequent SWPPPs. For example, will training be required of
existing city staff or will database, GIS, or modeling expertise be required either from
consultants or from MPCA staff? As funding allows, secure technical resources needed for
BMP selection and implementation. It may be necessary to hire consultants early in this
process to select appropriate models and address data management and GIS issues.
2.14. Determine if there are BMPs that can be implemented immediately. This may require
completion of the BMP menu so that appropriate BMPs can be selected. MPCA benchmarking
studies will be of value in identifying generic BMPs that can be employed for phosphorus
reduction.
Actions for First Permit Cycle
3.
This section describes actions that can be taken during the first permit cycle to begin achieving
reductions. It will be important to link these actions with many of the actions in Section 2. For
example, it may be prudent to develop an ordinance requiring incorporation of BMPs in new or redevelopment projects.
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3.1. Implement nonstructural BMPs, such as street sweeping, storm drain maintenance, storm drain
stenciling, lawn care education, and mowing reductions.
3.2. Incorporate Better Site Design and Low Impact Development into all redevelopment and new
development projects.
3.3. Develop a Communication Plan to inform the community and stakeholders about the TMDL
and the process for meeting requirements of the TMDL.
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Timelines
The following timelines are intended to get appropriate BMPs into place during the first permit cycle,
but also acknowledge that additional cycles will be required to identify resources and establish the
infrastructure necessary to meet the TMDL requirement. In the table below, shaded boxes indicate
when an activity should begin and end, rather than a range of times over which an activity may be
started.
MPCA will work with MS4 communities during 2006 to finalize this guidance. SWPPPs are due for
submittal in February of 2007. The MS4 permit requires that an annual report be submitted by June 30th
of each year describing progress toward completion of conditions in the SWPPP. The timelines in the
following table are shorter than those for MS4s that have previously submitted SWPPPs. This is due to
requirements of the TMDL and because the communities affected by this guidance are generally
considerably smaller than other MS4s that have submitted SWPPPs.
The methods for addressing TMDL requirements presented in this guidance are in approximate
chronological order. Most recommendations described in this guidance can be initiated in 2007, with
maps, an inventory of existing resources, and identification of future needs completed by June of 2008.
Completion of a BMP menu, establishing new funding, regulatory, and plat review processes, and
securing technical resources will in general take longer to complete.
Description
2006 –
Feb.-07
2007
Finalize guidance and submit SWPPP
Identify and map discharge points, watersheds
contributing to discharge points, and within each
watershed, map the conveyance system
Identify and map factors useful in identifying
potential phosphorus contributions
Identify and map current and 2000 urban footprint
Calculate loading corrections for differences
between current and future land use compared to
the 2000 footprint
Identify and map the BMPs and map watershed
areas contributing to the BMPs
Estimate reductions associated with the BMPs
Calculate reductions from existing BMPs
List city entities that have stormwater management
functions or requirements
List other agencies that have stormwater
management functions or requirements
List existing water resource planning tools
Develop GIS coverages for all waters associated
with Limitations of Coverage
List other TMDLs that may affect your community
Develop a menu from which to select BMPs for
implementation in subsequent permitting cycles
Develop a list of water quality modeling options
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2008
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Determine if low impact development (LID) is an
option in new developments and in redevelopment.
Describe legal tools that can be used to implement
BMPs
Develop a framework needed to establish legal
tools needed for implementing BMPs
Describe the plat review process
Modify or establish a framework needed for
modifying the plat review process as needed for
implementing BMPs
Describe existing funding mechanisms that can be
used to implement and maintain BMPs
Develop or establish a framework needed to secure
funding needed for implementing BMPs
Establish a schedule for monitoring, operating, and
maintaining BMPs
Inventory current and future technical tools and
expertise necessary to accomplish the conditions of
this SWPPP and subsequent SWPPPs
Secure or establish framework for securing
technical tools needed to select and implement
BMPs
Implement BMPs
Maintain BMPs
Monitor BMPs
Modify legal, funding, plat review, or technical
processes and resources as needed to implement
BMPs
Implement non-structural BMPS during first
permit cycle
Incorporate Better Site Design/LID into new and
re-development projects during first permit cycle
Develop Communication Plan to inform
community and stakeholders about the TMDL and
process for meeting TMDL requirements
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Example
This example for an imaginary City A illustrates some tasks targeted for the first permit cycle.
a. The following figure shows locations of discharge points, watershed areas, and conveyance
systems.
b. The following figure shows percent impervious surface and land use.
Minnesota River
Residential, 40-60% impervious (6000 acres)
Industrial, 40-60% impervious (1000 acres)
Commercial, 40-60% impervious (2000 acres)
Green space, 0-10% impervious (1000 acres)
c. The following figure shows 2000 and projected land use. Projected growth is 10 percent (1000
acres). To adjust for this increased growth, the required load reduction must be recalculated and
equals 1-(0.7/(1.0 + 0.1)), or about 36 percent.
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Minnesota River
2000 footprint (10000 acres)
Projected growth (11000 acres)
d. The following figure shows locations of existing BMPs, acreages they serve, and other water
resources within the city. If we assume a wet pond reduces phosphorus loading by 50 percent
and bioretention by 60 percent, then we have already achieved a 16 percent reduction in
phosphorus loading (0.5*2000/10000)+(0.6*1000/10000).
Minnesota River
Wet stormwater ponds (servicing 2000 acres)
Infiltration Bioretention (servicing 1000 acres)
e. BMPs in sequence (series) do not result in additive reductions. For example, assume we
implement street sweeping and that results in a 10 percent load reduction. In the area where we
have wet ponds, the reduction is not 60% (10% + 50%), but instead will be less than 60%
because the 50 percent reduction from wet ponds applies to the phosphorus remaining after the
10 percent reduction from street sweeping. There are some difficulties in calculating
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effectiveness of BMPs in sequence. For example, two BMPs in series may both be effective at
removing phosphorus associated with sediment but not soluble phosphorus.
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