United States Office of Water
Environmental Protection 4503 F EPA 841-B-99-007
Agency Washington DC 20460 November 1999
&EPA Protocol for Developing
Nutrient TMDLs
First Edition
-------
Acknowledgments
The Protocol for Developing Nutrient TMDLs was developed under the direction of Donald Brady and Chris Zabawa
of EPA's Office of Wetlands, Oceans, and Watersheds, Assessment and Watershed Protection Division, and Mimi
Dannel, Office of Science and Technology, Standards and Applied Science Division. The document was developed
under EPA Contract Number 68-C7-0018. The Protocol for Developing Nutrient TMDLs was written by EPA's
Nutrient Protocol TMDL Team, with assistance from Jonathan Butcher, John Craig, Kevin Kratt and Leslie
Shoemaker of Tetra Tech, Inc., in Fairfax, Virginia. The authors gratefully acknowledge the many comments of
reviewers from within EPA and state environmental agencies, as well as the detailed reviews that were conducted by
Steven C. Chapra of Tufts University and John J. Warwick of the University of Nevada at Reno.
This report should be cited as:
U.S. Environmental Protection Agency. 1999. Protocol for Developing Nutrient TMDLs. EPA 841-B-99-007.
Office of Water (4503F), United States Environmental Protection Agency, Washington D.C. 135 pp.
To obtain a copy of the Protocol for Developing Nutrient TMDLs/EPA 841-B-99-007 (1999) free of charge,
contact:
National Service Center for Environmental Publications (NSCEP)
Phone: 513-489-8190
Fax: 513-489-8695
This EPA report is available on the Internet at:
http://www.epa.gov/owow/tmdl/techsupp.html
-------
Protocol for Developing Nutrient TMDLs
First Edition: November 1999
Watershed Branch
Assessment and Watershed Protection Division
Office of Wetlands, Oceans, and Watersheds
Office of Water
United States Environmental Protection Agency
Washington, DC 20460
-------
Foreword
Although many pollution sources have implemented the required levels of pollution control technology, there are still
waters in the nation that do not meet the Clean Water Act goal of "fishable, swimmable." Section 303(d) of the Act
addresses these waters that are not "fishable, swimmable" by requiring states, territories, and authorized tribes to
identify and list impaired waters every two years and to develop total maximum daily loads (TMDLs) for pollutants
in these waters, with oversight from the U.S. Environmental Protection Agency. TMDLs establish the allowable
pollutant loadings, thereby providing the basis for states to establish water quality-based controls.
Historically, wasteload allocations have been developed for particular point sources discharging to a particular
waterbody to set effluent limitations in the point source's National Pollutant Discharge Elimination System (NPDES)
discharge permit. This approach has produced significant improvements in water quality by establishing point source
controls for many chemical pollutants. But water quality impairments continue to exist in the Nation's waters. Some
point sources need more controls, and many nonpoint source impacts (from agriculture, forestry, development
activities, urban runoff, and so forth) cause or contribute to impairments in water quality. To address the combined,
cumulative impacts of both point and nonpoint sources, EPA has adopted a watershed approach, of which TMDLs
are a part. This approach provides a means to integrate governmental programs and improve decision making by both
government and private parties. It enables a broad view of water resources that reflects the interrelationship of
surface water, groundwater, chemical pollutants and nonchemical stressors, water quantity, and land management.
The Protocol for Developing Nutrient TMDLs is a TMDL technical guidance documents prepared to help state,
interstate, territorial, tribal, local, and federal agency staff involved in TMDL development, as well as watershed
stakeholders and private consultants. Comments and suggestions from readers are encouraged and will be used to
help improve the available guidance as EPA continues to build experience and understanding of TMDLs and
watershed management.
Robert H. Wayland III, Director
Office of Wetlands, Oceans, and Watersheds
Office of Water
U.S. Environmental Protection Agency
Washington, DC 20460
First Edition: November 1999 iii
-------
Preface
EPA has developed several protocols as programmatic and technical support guidance documents for those involved
in TMDL development. These guidance documents, developed by an interdisciplinary team, provide an overall
framework for completing the technical and programmatic steps in the TMDL development process. The Protocol
for Developing Nutrient TMDLs is one of the three TMDL technical guidance documents prepared to date. The
process presented here will assist with the development of rational, science-based assessments and decisions and
ideally will lead to the assemblage of an understandable and justifiable nutrient TMDL. It is important to note that
this guidance document presents a suggested approach, but not the only approach to TMDL development.
This document provides guidance to states, territories and authorized tribes exercising responsibility under section
303(d) of the Clean Water Act for the development of nutrient TMDLs. This protocol is designed as programmatic
and technical support guidance to those involved in TMDL development. The protocol does not, however, substitute
for section 303(d) of the Clean Water Act or EPA's regulations; nor is it a regulation itself. Thus, it cannot impose
legally binding requirements on EPA, states, territories, authorized tribes or the regulated community and may not
apply to a particular situation based upon the circumstances. EPA and state, territory and authorized tribe decision
makers retain the discretion to adopt approaches on a case-by-case basis that differ from this protocol where
appropriate. EPA may change this protocol in the future.
iv First Edition: November 1999
-------
Contents
Foreword iii
Preface iv
Figures vi
Tables vi
Introduction and Purpose of This Protocol 1-1
Nutrients and Water Quality 2-1
Problem Identification 3-1
Identification of Water Quality Indicators and Target Values 4-1
Source Assessment 5-1
Linkage Between Water Quality Targets and Sources 6-1
Allocations 7-1
Follow-Up Monitoring 8-1
Assembling the TMDL 9-1
Appendix—Case Studies
Laguna de Santa Rose, California Appendix-1
Chatfield Reservoir, Colorado Appendix-7
References References-1
Acronyms Acronyms-1
Glossary Glossary-1
First Edition: November 1999
-------
Figures
Figure 1-1. General elements of the water quality-based approach (USEPA, 1991a) 1-3
Figure 1-2. General components of TMDL development 1-4
Figure 2-1. Factors influencing the level of detail for the TMDL analysis 2-6
Figure 3-1. Nutrient conceptual model 3-3
Figure 4-1. Factors for determining indicators and target values 4-2
Figure 4-2. Guidelines for selecting indicators based on waterbody type and several representative designated
uses 4-9
Figure 5-1. Common mechanisms and sources associated with nutrient loading to a reservoir 5-3
Figure 5-2. Decision tree with preferred model selection options 5-10
Figure 6-1. Decision tree for selecting an appropriate model technique 6-3
Tables
Table 2-1. Sources and concentrations of nutrients from common point and nonpoint sources 2-2
Table 2-2. Common BMPs employed to control nutrient transport from agricultural and urban nonpoint
sources 2-13
Table 3-1. Impacts of nutrients on designated uses 3-2
Table 3-2. Advantages and disadvantages of different TMDL watershed analysis scales 3-5
Table 3-3. Approaches for incorporating margins of safety into nutrient TMDLs 3-7
Table 4-1. Examples of indicators for TMDL targets and similar assessment projects 4-3
Table 4-2. Trophic status classification (for lakes) by Vollenweider and Kerekes (1980) 4-11
Table 4-3. A trophic status classification based on water quality parameters 4-12
Table 5-1. Example literature values for dissolved nutrients in agricultural runoff 5-4
Table 5-2. Mean dissolved nutrients measured in streamflow by the National Eutrophication Survey 5-6
Table 5-3. Typical phosphorus and nitrogen loading ranges for various land uses 5-8
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Introduction and Purpose of This Protocol
Objective: This Total Maximum Daily Load (TMDL)
protocol was developed at the request of EPA regions,
states, and tribes and is intended to provide users with
an organizational framework for the TMDL
development process for nutrients. The process
presented here will assist with the development of
rational, science-based assessments and decisions and
ideally will lead to the assemblage of an understandable
and justifiable TMDL.
Audience: The protocols are designed as tools for state
TMDL staff, EPA regional TMDL staff, tribal TMDL
staff, watershed stakeholders, and other agencies and
private consultants involved in TMDL development.
OVERVIEW
Section 303(d) of the Clean Water Act provides that
states, territories, and authorized tribes are to list waters
for which technology-based limits alone do not ensure
attainment of water quality standards. Beginning in
1992, states, territories and authorized tribes were to
submit their lists to the EPA every two years. Beginning
in 1994, lists were due to EPA on April 1 of each even
numbered year. States, territories, and authorized tribes
are to set priority rankings for the listed waters, taking
into account the severity of the pollution and the
intended uses of the waters.
EPA's regulations for implementing section 303(d) are
codified in the Water Quality Planning and Management
Regulations at 40 CFR Part 130, specifically at
sections!30.2, 130.7, and 130.10. The regulations
define terms used in section 303(d) and otherwise
interpret and expand upon the statutory requirements.
The purpose of the Protocol for Developing Nutrient
TMDLs is to provide more detailed guidance on the
TMDL development process for waterbodies impaired
due to nutrients.
On August 23, 1999, EPA published proposed changes
to the current TMDL rules at 40 CFR 130.2, 130.7, and
130.10. These changes would significantly strengthen
the Nation's ability to achieve clean water goals by
ensuring that the public has more and better information
about the health of their watersheds, States have clearer
direction and greater consistency as they identify
impaired waters and set priorities, and new tools are
used to make sure that TMDL implementation occurs.
The text box on the following page summarizes these
proposed changes.
The TMDL protocols focus on Step 3 (Development of
TMDLs) of the water quality-based approach, depicted
in Figure 1-1 (USEPA, 1991a, 1999). This specific step
is divided into seven components common to all
TMDLs, and each component is designed to yield a
product that is part of a TMDL submittal document.
Although some of the submittal components (e.g.,
TMDL calculation and allocations) are part of the
legally approved TMDL and others are recommended as
part of the administrative record supporting the TMDL
and providing the basis for TMDL review and approval,
this protocol discusses each component equally. The
following components may be completed concurrently
or iteratively depending on the site-specific situation
(Figure 1-2) and are provided as a guide and framework
for TMDL development:
• Problem identification
• Identification of water quality indicators and targets
• Source assessment
• Linkage between water quality targets and sources
• Allocations
• Follow-up monitoring and evaluation
• Assembling the TMDL
A TMDL is the sum of the individual wasteload allocations for point sources
and load allocations for nonpoint sources and natural background (40 CFR
130.2) with a margin of safety (CWA Section 303(d)(1)(c)). The TMDL can
be generically described by the following equation:
TMDL = LC = YWLA + YLA + MOS
where: LC= loading capacity,3 or the greatest loading a waterbody can
receive without violating water quality standards;
WLA = wasteload allocation, or the portion of the TMDL allocated
to existing or future point sources;
LA = load allocation, or the portion of the TMDL allocated to
existing or future nonpoint sources and natural background;
and
MOS = margin of safety, or an accounting of uncertainty about the
relationship between pollutant loads and receiving water
quality. The margin of safety can be provided implicitly
through analytical assumptions or explicitly by reserving a
portion of loading capacity.
aTMDLs can be expressed in terms of mass per time, toxicity, or other
appropriate measures.
First Edition: November 1999
1-1
-------
Introduction and Purpose of This Protocol
Summary of Proposed Regulatory Requirements for Establishing TMDLs
A TMDL must be established for all waterbody and pollutant combinations on Part 1 of the list. TMDLs are not required for waterbodies on
Part 2, 3, or 4 of the list (§ 130.31 (a)).
A TMDL must be established according to the priority rankings and schedules (§ 130.31 (b)).
TMDLs must be established at a level necessary to attain and maintain water quality standards, as defined by 40 CFR 131.3(1), considering
reasonably foreseeable increases in pollutant loads (§ 130.33(b)(9)).
TMDLs must include the following minimum elements (§ 130.33(b)):
1. The name and geographic location, as required by §130.27(c), of the impaired or threatened waterbody for which the TMDL is being
established and the names and geographic locations of the waterbodies upstream of the impaired waterbody that contribute significant
amounts of the pollutant for which the TMDL is being established;
2. Identification of the pollutant for which the TMDL is being established and quantification of the pollutant load that may be present in the
waterbody and still ensure attainment and maintenance of water quality standards;
3. Identification of the amount or degree by which the current pollutant load in the waterbody deviates from the pollutant load needed to
attain or maintain water quality standards;
4. Identification of the source categories, source subcategories, or individual sources of the pollutant for which the wasteload allocations
and load allocations are being established consistent with §130.2(f) and §130.2(g);
5. Wasteload allocations to each industrial and municipal point source permitted under §402 of the Clean Water Act discharging the
pollutant for which the TMDL is being established ; wasteload allocations for storm water, combined sewer overflows, abandoned
mines, combined animal feeding operations, or any other discharges subject to a general permit may be allocated to categories of
sources, subcategories of sources or individual sources; pollutant loads that do not need to be allocated to attain or maintain water
quality standards may be included within a category of sources, subcategory of sources or considered as part of background loads;
and supporting technical analyses demonstrating that wasteload allocations when implemented, will attain and maintain water quality
standards;
6. Load allocations, ranging from reasonable accurate estimates to gross allotments, to nonpoint sources of a pollutant, including
atmospheric deposition or natural background sources; if possible, a separate load allocation must be allocated to each source of
natural background or atmospheric deposition; load allocations may be allocated to categories of sources, subcategories of sources or
individual sources; pollutant loads that do not need to be allocated may be included within a category of sources, subcategory of
sources or considered as part of background loads; and supporting technical analyses demonstrating that load allocations, when
implemented, will attain and maintain water quality standards;
7. A margin of safety expressed as unallocated assimilative capacity or conservative analytical assumptions used in establishing the
TMDL; e.g., derivation of numeric targets, modeling assumptions, or effectiveness of proposed management actions which ensures
attainment and maintenance of water quality standards for the allocated pollutant;
8. Consideration of seasonal variation such that water quality standards for the allocated pollutant will be met during all seasons of the
year;
9. An allowance for future growth which accounts for reasonably foreseeable increases in pollutant loads; and
10. An implementation plan.
As appropriate to the characteristics of the waterbody and pollutant, the maximum allowable pollutant load may be expressed as daily,
monthly, seasonal or annual averages in one or more of the following ways (40 CFR 130.34(b)):
• The pollutant load that can be present in the waterbody and ensure that it attains and maintains water quality standards;
• The reduction from current pollutant loads required to attain and maintain water quality standards;
• The pollutant load or reduction of pollutant load required to attain and maintain riparian, biological, channel orgeomorphological
measures so that water quality standards are attained and maintained; or
• The pollutant load or reduction of pollutant load that results from modifying a characteristic of the waterbody, e.g., riparian, biological,
channel, geomorphological, or chemical characteristics, so that water quality standards are attained and maintained.
The TMDL implementation plan must include the following (§ 130.33(b)(10)):
• A description of the control actions and/or management measures which will be implemented to achieve the wasteload allocations and
load allocations, and a demonstration that the control actions and/or management measures are expected to achieve the required
pollutant loads;
• A time line, including interim milestones, for implementing the control actions and/or management measures, including when source-
specific activities will be undertaken for categories and subcategories of individual sources and a schedule for revising NPDES permits;
• A discussion of your reasonable assurances, as defined at 40 CFR §130.2(p), that wasteload allocations and load allocations will be
implemented;
• A description of the legal under which the control actions will be carried out;
• An estimate of the time required to attain and maintain water quality standards and discussion of the basis for that estimate;
• A monitoring and/or modeling plan designed to determine the effectiveness of the control actions and/or management measures and
whether allocations are being met;
• A description of measurable, incremental milestones for the pollutant for which the TMDL is being established for determining whether
the control actions and/or management measures are being implemented and whether water quality standards are being attained; and
• A description of your process for revising TMDLs if the milestones are not being met and projected progress toward attaining water
quality standards is not demonstrated.
1-2 First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
1. Identification of Water
Quality-Limited Waters
Review water quality standards
Evaluate monitoring data
Determine If adequate controls
are In place
2. Priority Ranking
and Targeting
5. Assessment of Water
Quality-Based Control Actions
Integrate priority ranking with
other water quality planning and
management activities
Monitor polnt/nonpolnt sources
Audit NFS controls for effectiveness
Evaluate TMDL for attainment of
water quality standards
Use priority ranking to target
waterbodies for TMDLs
4. Implementation of
Control Actions
3. Development of TMDLs
Apply geographic approach
where applicable
Establish schedule for phase
approach, if necessary
Complete TMDL development
Update water quality management plan
Issue water quality-based permits
Implement nonpoint source controls
(section 319 management plans)
Figure 1-1. General elements of the water quality-based approach (adapted from USEPA, 1991 a)
First Edition: November 1999
1-3
-------
Introduction and Purpose of This Protocol
Components in TMDL Development
Suggested TMDL Submitted Elements
I Identify Problem ...™.......^- Problem Statement
zrr
Develop Numeric
Targets
• Select indicator(s) ...J....-..____________>- Numeric Targets
• Identify target values
• Compare existing and
target conditions
) '
Source Assessment
• identify sources ^ Source Assessment
• Estimate source
loadings
^^
Link Targets and Sources
Assess linkages ^ Linkage Analysis
Estimate total loading capacity
t
Load Allocation
Divide loads among sources M™——™——^- Allocations
I
Develop Monitoring and „„„„„„>- Monitoring/Evaluation Plan
Review Plan and Schedule ——-——-— ^ phased approach)
I
Develop Implementation Plan -—--——>, Implementation Measures in
State Water Quality
Management Plan
Figure 1-2. General components of TMDL development
1-4
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Problem Identification
The objective of problem identification is to identify the
key factors and background information for a listed
waterbody that describe the nature of the impairment
and the context for the TMDL. Problem identification is
a guiding factor in development of the remaining
elements of the TMDL process.
Identification of Water Quality Indicators and
Target Values
The purpose of this component is to identify numeric or
measurable indicators and target values that can be used
to evaluate attainment of water quality standards in the
listed waterbody. Often the TMDL target will be the
numeric water quality standard for the pollutant of
concern. In some cases, however, TMDLs must be
developed for parameters that do not have numeric water
quality standards. When numeric water quality
standards do not exist, impairment is determined by
narrative water quality standards or identifiable
impairment of designated uses (e.g., no fish). The
narrative standard is then interpreted to develop a
quantifiable target value to measure attainment or
maintenance of the water quality standards.
Source Assessment
During source assessment, the sources of pollutant
loading to the waterbody are identified and characterized
by type, magnitude, and location.
Linkage Between Water Quality Targets and
Sources
To develop a TMDL, a linkage must be defined between
the selected indicator(s) or target(s) and the identified
sources. This linkage establishes the cause-and-effect
relationship between the pollutant of concern and the
pollutant sources. The relationship can vary seasonally,
particularly for nonpoint sources, with factors such as
precipitation. Once defined, the linkage yields the
estimate of total loading capacity.
Allocations
Based on the established linkage, pollutant loadings that
will not exceed the loading capacity and will lead to
attainment of the water quality standard can be
determined. These loadings are distributed or
"allocated" among the significant sources of the
pollutant of concern. The allocations are a component
of the legally approved TMDL. Wasteload allocations
contain the allowable loadings from existing or future
point sources, while load allocations establish the
allowable loadings from natural background and from
existing and future nonpoint sources. The margin of
safety is usually identified during this step to account
for uncertainty in the analysis, although it may also be
identified in other TMDL components. The margin of
safety may be applied implicitly by using conservative
assumptions in the TMDL development process or
explicitly by setting aside a portion of the allowable
loading.
Follow-up Monitoring and Evaluation
TMDL submittals should include a monitoring plan to
determine whether the TMDL has resulted in attaining
water quality standards and to support any revisions to
the TMDL that might be required. Follow-up
monitoring is recommended for all TMDLs, given the
uncertainties inherent in TMDL development (USEPA
1991a; 1997a; 1999). The rigor of the monitoring plan
should be based on the confidence in the TMDL
analysis: a more rigorous monitoring plan should be
included for TMDLs with greater uncertainty and where
the environmental and economic consequences of the
decisions are greatest.
Assembling the TMDL
In this component, those elements of a TMDL submittal
required by statute or regulation are clearly identified
and compiled, and supplemental information is provided
to facilitate TMDL review.
For each component addressed in this protocol, the
following format is used:
• Guidance on key questions or factors to consider
• Brief discussions of analytical methods
• Discussions of products needed to express the results
of the analysis
• Examples of approaches used in actual settings to
complete the step
First Edition: November 1999
1-5
-------
Introduction and Purpose of This Protocol
By addressing each of the seven TMDL components,
TMDL developers can complete the technical aspects of
TMDL development. Although public participation
requirements are largely outside the scope of this
document, because of the complex and often
controversial nature of TMDLs, early involvement of
stakeholders affected by the TMDL is strongly
encouraged. The protocols also do not discuss issues
associated with TMDL implementation (note the rule
across Figure 1-1). Methods of implementation, such as
National Pollutant Discharge Elimination System
(NPDES) permits, state nonpoint source (NFS)
management programs, Coastal Zone Act
Reauthorization Amendments (CZARA), and public
participation are discussed in Guidance for Water
Quality-Based Decisions: The TMDL Process (USEPA,
1991a, 1999) and in the August 8, 1997, memorandum
"New Policies for Establishing and Implementing Total
Maximum Daily Loads (TMDLs)" (USEPA, 1997b).
PURPOSE
This protocol provides a description of the TMDL
development process for nutrients and includes case
study examples to illustrate the major points in the
process. It emphasizes the use of rational, science-based
methods and tools for each step of TMDL development
to assist readers in applying a TMDL development
process that addresses all regulatory requirements.
References and recommended reading lists are provided
for readers interested in obtaining more detailed
background information. This protocol has been
written with the assumption that users have a general
background in the technical aspects of water quality
management and are familiar with the statutory and
regulatory basis for the TMDL program. A glossary is
included at the end of the document with definitions of
some commonly used terms.
RECOMMENDED READING
(Note that the full list of references for this chapter is
included at the end of the document.)
USEPA. 199la. Guidance for water quality-based
decisions: The TMDL process. EPA 440/4-91-001.
U.S. Environmental Protection Agency, Washington,
DC.
USEPA. 1997a. New policies for establishing and
implementing Total Maximum Daily Loads (TMDLs).
U.S. Environmental Protection Agency, Washington,
DC.
USEPA 1999. Draft guidance for water quality-based
decisions: The TMDL process (second edition). EPA
841-D-99-001. U.S. Environmental Protection Agency,
Washington, DC.
1-6
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Nutrients and Water Quality
Objective: To develop a nutrient TMDL, it is important
to have a basic understanding of nutrient processes in a
watershed and how excessive or insufficient nutrients
can affect water quality and designated uses of water.
This section provides background information on
nutrient impacts on designated uses, nutrient sources
and transport, and potential control strategies.
GENERAL PRINCIPLES
This section briefly addresses the role nutrients play in
the environment and provides background information
on nutrient cycling, nutrient sources and transport, and
potential control strategies. A more detailed discussion
of these basic principles and how they relate to TMDL
development is in Chapter 2 of EPA's Technical
Guidance Manual for Developing Total Maximum Daily
Loads, Book II (Streams and Rivers), Part 1
(Biochemical Oxygen Demand/Dissolved Oxygen and
Nutrients/Eutrophication) (USEPA, 1995a).
Impact of Nutrients on Designated Uses
Excess nutrients in a waterbody can have many
detrimental effects on designated or existing uses,
including drinking water supply, recreational use,
aquatic life use, and fishery use. For example, drinking
water supplies can be impaired by nitrogen when nitrate
concentrations exceed 10 mg/L and can cause
methemoglobinemia (Blue Baby Syndrome) in infants.
Water supplies containing more than 100 mg/L of nitrate
can also taste bitter and can cause physiological distress
(Straub, 1989).
Although these are examples of the direct impacts that
can be associated with excessive nutrient loadings,
waters more often are listed as impaired by nutrients
because of their role in accelerating eutrophication.
Eutrophication, or the nutrient enrichment of aquatic
systems, is a natural aging process of a waterbody that
transforms a lake into a swamp and ultimately into a
field or forest.1 This aging process can accelerate with
The term eutrophication as used in this document refers to the
nutrient enrichment of both lakes and rivers, although it is recognized
that rivers do not have the same natural aging process.
excessive nutrient inputs because of the impact they
have without other limiting factors, such as light.
A eutrophic system typically contains an undesirable
abundance of plant growth, particularly phytoplankton,
periphyton, and macrophytes. Phytoplankton,
photosynthetic microscopic organisms (algae), exist as
individual cells or grouped together as clumps or
filamentous mats. Periphyton is the assemblage of
organisms that grow on underwater surfaces. It is
commonly dominated by algae but also can include
bacteria, yeasts, molds, protozoa, and other colony-
forming organisms. The term macrophyte refers to any
larger than microscopic plant life in aquatic systems.
Macrophytes may be vascular plants rooted in the
sediment, such as pond weeds or cattails, or free-floating
plant life, such as duckweed or coontail.
The eutrophication process can impair the designated
uses of waterbodies as follows:
• Aquatic life and fisheries. A variety of impairments
can result from the excessive plant growth associated
with nutrient loadings. These impairments result
primarily when dead plant matter settles to the
bottom of a waterbody, stimulating microbial
breakdown processes that require oxygen.
Eventually, oxygen in the hypolimnion of lakes and
reservoirs can be depleted, which can change the
benthic community structure from aerobic to
anaerobic organisms. Oxygen depletion also might
occur nightly throughout the waterbody because of
plant respiration. Extreme oxygen depletion can
stress or eliminate desirable aquatic life and
nutrients, and toxins also might be released from
sediments when dissolved oxygen and pH are
lowered (Brick and Moore, 1996).
Breakdown of dead organic matter in water also can
produce un-ionized ammonia, which can adversely
affect aquatic life. The fraction of ammonia present
as un-ionized ammonia depends on temperature and
pH. Fish may suffer a reduction in hatching success,
reductions in growth rate and morphological
development, and injury to gill tissue, liver, and
kidneys. At certain ammonia levels fish also might
First Edition: November 1999
2-1
-------
Nutrients and Water Quality
suffer a loss of equilibrium, hyperexcitability,
increased respiratory activity and oxygen uptake, and
increased heart rate. At extreme ammonia levels, fish
may experience convulsions, coma, and death
(USEPA, 1986a; revised 1998b).
• Drinking water supply. Diatoms and filamentous
algae can clog water treatment plant filters and
reduce the time between backwashings (the process
of reversing water flow through the water filter to
remove debris). Disinfection of water supplies
impaired by algal growth also might result in water
that contains potentially carcinogenic disinfection by-
products, such as trihalomethanes. An increased rate
of production and breakdown of plant matter also can
adversely affect the taste and odor of the drinking
water.
• Recreational use. The excessive plant growth in a
eutrophic waterbody can affect recreational water
use. Extensive growth of rooted macrophytes,
periphyton, and mats of living and dead plant
material can interfere with swimming, boating, and
fishing activities, while the appearance of and odors
emitted by decaying plant matter impair aesthetic
uses of the waterbody.
Nutrient Sources and Transport
Both nitrogen and phosphorus reach surface waters at an
elevated rate as a result of human activities.
Phosphorus, because of its tendency to sorb to soil
particles and organic matter, is primarily transported in
surface runoff with eroded sediments. Inorganic
nitrogen, on the other hand, does not sorb as strongly
and can be transported in both particulate and dissolved
phases in surface runoff. Dissolved inorganic nitrogen
also can be transported through the unsaturated zone
(interflow) and ground water. Because nitrogen has a
gaseous phase, it can be transported to surface water via
atmospheric deposition. Phosphorus associated with
fine-grained particulate matter also exists in the
atmosphere. This sorbed phosphorus can enter natural
waters by both dry fallout and rainfall. Finally, nutrients
can be directly discharged to a waterbody via outfalls
for wastewater treatment plants and combined sewer
overflows. Table 2-1 presents common point and
nonpoint sources of nitrogen and phosphorus and the
approximate associated concentrations.
Once in the waterbody, nitrogen and phosphorus act
differently. Because inorganic forms of nitrogen do not
sorb strongly to particulate matter, they are more easily
returned to the water. Phosphorus, on the other hand,
can sorb to sediments in the water column and on the
substrate and become unavailable. In lakes and
reservoirs, continuous accumulation of sediment can
leave some phosphorus too deep within the substrate to
be reintroduced to the water column, if left undisturbed;
however, a portion of the phosphorus in the substrate
might be reintroduced to the water column. The
activities of benthic invertebrates and changes in water
chemistry (such as the reducing conditions of bottom
waters and sediments often experienced during the
summer months in a lake) also can cause phosphorus to
desorb from sediment. A large, slow-moving river also
might experience similar phosphorus releases. The
sudden availability of phosphorus in the water column
can stimulate algal growth. Because of this
phenomenon, a reduction in phosphorus loading might
not effectively reduce algal blooms for many years
(Maki et al., 1983).
Table 2-1. Sources and concentrations of nutrients from common point and nonpoint sources
Source
Urban runoff
Livestock operations
Atmosphere (wet deposition)
Untreated wastewater
Treated wastewater (secondary treatment)
Nitrogen (mg/L)
3-10
6 - 800a
0.9
35
30
Phosphorus (mg/L)
0.2-1.7
4-5
0.015b
10
10
As organic nitrogen; Sorbed to airborne particulate
Source: Novotny and Olem, 1994
2-2
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Nutrient Cycling
The transport of nutrients from their sources to the
waterbody of concern is governed by several chemical,
physical, and biological processes, which together
compose the nitrogen or phosphorus cycle. Nutrient
cycles are important to understand for developing a
TMDL because of the information they provide about
nutrient availability and the associated impact on plant
growth.
Nitrogen
Nitrogen is plentiful in the environment. Almost 80
percent of the atmosphere by volume consists of
nitrogen gas (N2). Although largely available in the
atmosphere, N2 must be converted to other forms, such
as nitrate (NO3~), before most plants and animals can use
it. Conversion into usable forms, both in the terrestrial
and aquatic environments, occurs through the four
processes of the nitrogen cycle. Three of the
processes—nitrogen fixation, ammonification, and
nitrification—convert gaseous nitrogen into usable
chemical forms. The fourth process, denitrification,
converts fixed nitrogen back to the gaseous N2 state.
• Nitrogen fixation. The conversion of gaseous
nitrogen into ammonia ions (NH3 and NH4+).
Nitrogen-fixing organisms, such as blue-green algae
(cyanobacteria) and the bacteria Rhizobium and
Azobacter, split molecular nitrogen (N2) into two free
nitrogen molecules. The nitrogen molecules combine
with hydrogen molecules to yield ammonia ions.
• Ammonification. A one-way reaction in which
decomposer organisms break down wastes and
nonliving organic tissues to amino acids, which are
then oxidized to carbon dioxide, water, and ammonia
ions. Ammonia is then available for absorption by
plant matter.
• Nitrification. A two-step process by which
ammonia ions are oxidized to nitrite and nitrate,
yielding energy for decomposer organisms. Two
groups of microorganisms are involved in the
nitrification process. First, Nitrosomonas oxidizes
ammonia ions to nitrite and water. Second,
Nitrobacter oxidizes the nitrite ions to nitrate, which
is then available for absorption by plant matter.
• Denitrification. The process by which nitrates are
reduced to gaseous nitrogen by facultative anaerobes.
Facultative anaerobes, such as fungi, can flourish in
anoxic conditions because they break down oxygen-
containing compounds (e.g., NO3") to obtain oxygen.
Once introduced into the aquatic environment, nitrogen
can exist in several forms—dissolved nitrogen gas (N2),
ammonia (NH4+ and NH3), nitrite (NO2"), nitrate (NO3"),
and organic nitrogen as proteinaceous matter or in
dissolved or particulate phases. The most important
forms of nitrogen in terms of their immediate impact on
water quality are the readily available ammonia ions,
nitrites, and nitrates2 (dissolved nitrogen). Particulate
and organic nitrogen, because they must be converted to
a usable form, are less important in the short term. Total
nitrogen (TN) is a measurement of all forms of nitrogen.
Nitrogen continuously cycles in the aquatic
environment, although the rate is temperature-controlled
and thus very seasonal. Aquatic organisms incorporate
available dissolved inorganic nitrogen into
proteinaceous matter. Dead organisms decompose, and
nitrogen is released as ammonia ions and then converted
to nitrite and nitrate, where the process begins again. If a
surface water lacks adequate nitrogen, nitrogen-fixing
organisms can convert nitrogen from its gaseous phase
to ammonia ions.
Phosphorus
Under normal conditions, phosphorus is scarce in the
aquatic environment. Unlike nitrogen, phosphorus does
not exist as a gas and therefore does not have gas-phase
atmospheric inputs to aquatic systems. Rocks and
natural phosphate deposits are the main reservoirs of
natural phosphorus. Release of these deposits occurs
through weathering, leaching, erosion, and mining.
Terrestrial phosphorus cycling includes immobilizing
inorganic phosphorus into calcium or iron phosphates,
incorporating inorganic phosphorus into plants and
microorganisms, and breaking down organic phosphorus
to inorganic forms by bacteria. Some phosphorus is
inevitably transported to aquatic systems by water or
wind.
Note that plants cannot directly use nitrate but must first convert it
to ammonium using the enzyme nitrate reductase. Because the ability
to do this is ubiquitous, nitrate is considered to be bioavailable.
First Edition: November 1999
2-3
-------
Nutrients and Water Quality
Phosphorus in freshwater and marine systems exists in
either an organic or inorganic form.
• Organic phosphorus. Organic participate
phosphorus includes living and dead particulate
matter, such as plankton and detritus. Organic
nonparticulate phosphorus includes dissolved organic
phosphorus excreted by organisms and colloidal
phosphorus compounds.
• Inorganic phosphorus. The soluble inorganic
phosphate forms H2PO4", HPO42", and PO43, known as
soluble reactive phosphorus (SRP), are readily
available to plants. Some condensed phosphate
forms, such as those found in detergents, are
inorganic but are not available for plant uptake.
Inorganic particulate phosphorus includes
phosphorus precipitates, phosphorus adsorbed to
particulate, and amorphous phosphorus.
The measurement of all phosphorus forms in a water
sample, including all the inorganic and organic
particulate and soluble forms mentioned above, is
known as total phosphorus (TP). TP does not distinguish
between phosphorus currently unavailable to plants
(organic and particulate) and that which is available
(SRP). SRP is the most important form of phosphorus
for supporting algal growth because it can be used
directly. However, other fractions are transformed to
more bioavailable forms at various rates dependent on
microbial action or environmental conditions. In
streams with relatively short residence times, it is less
likely that the transformation from unavailable to
available forms will have time to occur and SRP is the
most accurate estimate of biologically available
nutrients. In lakes, however, where residence times are
longer, TP generally is considered an adequate
estimation of bioavailable phosphorus.
Phosphorus undergoes continuous transformations in a
freshwater environment. Some phosphorus will sorb to
sediments in the water column or substrate and be
removed from circulation. Phytoplankton, periphyton,
and bacteria assimilate the SRP (usually as
orthophosphate) and change it into organic phosphorus.
These organisms then may be ingested by detritivores or
grazers, which in turn excrete some of the organic
phosphorus as SRP. Some previously unavailable forms
of phosphorus also convert to SRP. Continuing the
cycle, the SRP is rapidly assimilated by plants and
microbes.
Human activities have resulted in excessive loading of
phosphorus into many freshwater systems. Overloads
result in an imbalance of the natural cycling processes.
Excess available phosphorus in freshwater systems can
result in accelerated plant growth if other nutrients and
other potentially limiting factors are available.
Other Limiting Factors
Many natural factors combine to determine rates of plant
growth in a waterbody. First of these is whether
sufficient phosphorus and nitrogen exist to support plant
growth. The absence of one of these nutrients generally
will restrict plant growth. In inland waters, typically
phosphorus is the limiting nutrient of the two, because
blue-green algae can "fix" elemental nitrogen from the
water as a nutrient source. In marine waters, either
phosphorus or nitrogen can be limiting. Although
carbon and trace elements are usually abundant,
occasionally they can serve as limiting nutrients.
However, even if all necessary nutrients are available,
plant production will not necessarily continue
unchecked. Many natural factors, including light
availability, temperature, flow levels, substrate, grazing,
bedrock type and elevation, control the levels of
macrophytes, periphyton, and phytoplankton in waters.
Effective management of eutrophication in a waterbody
may require a simultaneous evaluation of several
limiting factors.
• Light availability. Shading of the water column
inhibits plant growth. Numerous factors can shade
waterbodies, including: (1) as plant production
increases in the upper water layer, the organisms
block the light and prevent it from traveling deeper
into the water column; (2) riparian growth along
waterbodies provides shade; and (3) particulates in
the water column scatter light, decreasing the
amount penetrating the water column and available
for photosynthesis.
With seasonally high particulate matter or shading
(e.g., in deciduous forests), the high nutrients may
cause excessive growth only during certain times of
the year: for example, streams where snowmelt is
common in the spring. Snowmelt could lead to high
2-4
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
levels of suspended particulate matter and low algal
biomass. During stable summer flows, however,
there will be lower levels of suspended matter and
hence higher algal biomass.
Temperature. Temperature affects the rates of
photosynthesis and algal growth, and composition of
algal species. Depending on the plant,
photosynthetic activity increases with temperature
until a maximum photosynthetic output is reached,
when photosynthesis declines (Smith, 1990).
Moreover, algal community species composition in
a waterbody often changes with temperature. For
example, diatoms most often are the dominant algal
species at water temperatures of 20 ° to 25 °C,
green algae at 30 ° to 35 °C, and blue-green algae
(cyanobacteria) above 35 °C (Dunne and Leopold,
1978; USEPA, 1986b).
Water Velocity. Water movement in large lakes,
rivers, and streams influences plant production.
Stream velocity has a two-fold effect on periphyton
productivity: increasing velocity to a certain level
enhances biomass accrual but further increases can
result in substantial scouring (Horner et al., 1990).
Large lakes and estuaries can experience the
scouring action of waves during strong storms
(Quinn, 1991). In rivers and streams, frequent
disturbance from floods (monthly or more
frequently) and associated movement of bed
materials can scour algae from the surface rapidly
and often enough to prevent attainment of high
biomass (Horner et al., 1990). Rapid flows can
sweep planktonic algae from a river reach, while
low flows may provide an opportunity for
proliferation.
Substrate. Macrophytes and periphyton are
influenced by the type of substrate available.
Macrophytes prefer areas of fine sediment in which
to root (Wright and McDonnell, 1986, in Quinn,
1991). Thus, the addition and removal of sediment
from a system can influence macrophyte growth.
Periphyton, because of its need to attach to objects,
grows best on large, rough substrates. A covering of
sediment over a rocky substrate decreases
periphyton biomass (Welch et al., 1992).
• Grazing. Dense populations of algae-consuming
grazers can lead to negligible algal biomass, in spite
of high levels of nutrients (Steinman, 1996). The
existence of a "trophic cascade" (control of algal
biomass by community composition of grazers and
their predators) has been demonstrated for some
streams (e.g., Power, 1990). Managers should
realize the potential control of algal biomass by
grazers, but they also should be aware that
populations of grazers can fluctuate seasonally or
unpredictably and fail to control biomass at times.
Consideration of grazer populations might explain
why some streams with high nutrients have low
algal biomass.
• Bedrock. The natural effects of bedrock type also
might help explain trophic state. Streams draining
watersheds with phosphorus-rich rocks (such as
rocks of sedimentary or volcanic origin) can be
enriched naturally and, therefore, control of algal
biomass by nutrient reduction in such systems might
be difficult. Review of geologic maps and
consultation with a local soil scientist might reveal
such problems. Bedrock composition has been
related to algal biomass in some systems (Biggs,
1995).
The Relationship Between Water Quality and Flow
in Streams and Rivers
The relationship between water quality and flow in
streams and rivers deserves special mention because
some impairments are aggravated (or caused primarily)
by flow modifications that result from in-stream
diversions or catchments. For nutrient TMDLs, stream
flow directly influences many physical features (e.g.,
depth, velocity, turbulence, reaeration, and
volatilization), while also indirectly influencing nutrient
uptake by attached algae. The velocity and depth
associated with a specific flow regime also define the
residence time in a reach, which directly influences
reach temperature and the spatial expression of decay
rates. During TMDL development, it is important to
identify the flow regimes necessary to satisfy designated
uses and to identify situations where flow modifications
might make use attainment difficult or impossible.
Because of the difficulties associated with addressing
these types of impairments, more time might be required
to identify and implement acceptable solutions. In some
First Edition: November 1999
2-5
-------
Nutrients and Water Quality
instances, states or territories might choose to undertake
a Use Attainability Analysis (UAA) to assess the factors
affecting the designated use.
NUTRIENT TMDLS
TMDL development is site-specific. The primary focus
of this protocol is on developing nutrient TMDLs for
lakes or rivers. Future material will explain developing
nutrient TMDLs in estuarine waters. The availability of
data influences the types of methods that developers can
use. Ideally, extensive monitoring data are available to
establish baseline water quality conditions, pollutant
source loading, and waterbody system dynamics.
However, without long-term monitoring data, the
developer will have to use a combination of monitoring,
analytical tools (including models), and qualitative
assessments to collect information, assess system
processes and responses, and make decisions.
Range of Approaches for Developing Nutrient
TMDLs
TMDL analysts should be resourceful and creative in
selecting TMDL approaches and should learn from the
results of similar analytical efforts. The degree of
analysis required for each component of TMDL
development (e.g., selection of indicators and targets,
source analysis, link between sources and water quality,
and allocations) can range from simple, screening-level
approaches based on limited data to detailed
investigations that might need several months or even
years to complete. Various interrelated factors will
affect the degree of analysis for each approach: the type
of impairment (e.g., violation of a numeric criterion
versus designated use impairment); the physical,
biological, and chemical processes occurring in the
waterbody and its watershed; the size of the watershed;
the number of sources; the data and resources available;
and the types and costs of actions needed to implement
the TMDL (see Figure 2-1).
Decisions regarding the extent of the analysis must
always be made on a site-specific basis as part of a
comprehensive problem-solving approach. TMDLs are
essentially a problem-solving process to which no
"cookbook" approach can be applied. Not only will
different TMDL studies vary in complexity, but the
Standard
Violation 1
Sou ice
Waleished
Few Data 1
Resuuices
Ike
>>'A.!'i''-i:. i Impairment
' ' "" " """""""'"' Suuiceb
Wdlelblled
••KM» I ivbre Data
" "l"11"" ""'""""""' Rebuuiceb
fc-
Increasing Level of Detail
Figure 2-1. Factors influencing the level of detail for the
TMDL analysis
degree of complexity in the methods used within
individual TMDL components also may vary
substantially. Simpler approaches can save time and
expense and can be applied by a wider range of
personnel. Simple approaches also generally are easier
to understand than more detailed analyses.
The trade-offs associated with using simple approaches
include a potential decrease in predictive accuracy and
often an inability to make predictions at fine geographic
and time scales (e.g., watershed-scale source predictions
versus parcel-by-parcel predictions, and annual versus
seasonal estimates). When using simple approaches,
analysts should consider these two shortcomings in
determining an appropriate margin of safety.
The advantages of more detailed approaches,
presumably, are an increase in predictive accuracy and
greater spatial and temporal resolution. Such
advantages can translate into greater stakeholder "buy-
in" and smaller margins of safety that usually reduce
source management costs. Detailed approaches might
be necessary when analysts have tried the simple
approaches and have proven them ineffective, or when it
is especially important to "get it right the first time."
More detailed approaches also may be warranted when
there is significant uncertainty whether nutrient
discharges relate to human or to natural sources and the
anticipated cost of controls is especially high. However,
more detailed approaches are likely to cost more, require
more data, and take more time to complete.
2-6
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
EXAMPLE NUTRIENT TMDLS
Brief summaries of four final and one preliminary
nutrient TMDLs show that a range of methods is
appropriate for TMDL development and that individual
TMDLs often combine relatively detailed analysis for
certain elements with simple analysis supporting other
elements. The preliminary example is based on a
TMDL that has not yet been completed. Two detailed
case studies are provided in the Appendix.
Lake Chelan, Washington
Lake Chelan, Washington, located in the northern
Cascades, serves as a water supply for more than 6,000
residents, provides irrigation water for approximately
18,000 acres, and produces hydroelectric power for the
region. The lake, used also for water-related recreation
and fisheries production, is considered one of the
pristine waters in North America. The lake is classified
as ultra oligotrophic, meaning it has low levels of
nutrients and high dissolved oxygen concentrations
throughout. The Washington State Department of
Ecology developed a Section 303(d)(3) TMDL for the
lake in 1991, to preserve its good quality and to prevent
degradation from increasing development in the
watershed. The Department of Ecology conducted the
Lake Chelan Water Quality Assessment (LCWQA) to
determine the baseline conditions in the lake and to
compile the technical data necessary for developing the
TMDL. The data collected during this intensive study
detailed the lake's present condition and provided
information for all aspects of TMDL development,
including the establishment of a numeric target,
identification and estimation of sources, and calculation
and allocation of loads. During the study, analysis of
water column and particulate matter nitrogen-to-
phosphorus ratios identified phosphorus as the principal
nutrient controlling algal growth in the lake. Therefore,
a numeric target was established for phosphorus. To
preserve the ultra oligotrophic condition of Lake Chelan,
the in-lake target value for total phosphorus (TP)
concentration was established at 4.5^g/L, a value
generally accepted for the ultra oligotrophic
classification. The sources of phosphorus were then
identified and quantified to develop the TMDL and the
appropriate allocations.
The upper basin of the Lake Chelan watershed is heavily
wooded and primarily undisturbed, while the lower
basin is a mixture of forest, apple orchards, and urban
land. The LCWQA estimated that 75 percent to 90
percent of the phosphorus input to the lake comes from
natural sources, largely forest runoff and direct
precipitation. The remaining 10 percent to 25 percent
was anthropogenic in nature, with approximately half
due to agricultural activities. The remaining portion of
the phosphorus load to the lake was estimated to come
from storm water runoff and septic system inputs. The
only point sources in the basin were chinook salmon net
pens. These large, floating, barge-like structures contain
dense populations of fish and contribute an estimated
0.01 kg of phosphorus per day per 2,000 Ib of fish.
The Department of Ecology used a steady-state mass
balance model and Monte Carlo analysis techniques to
link the source loadings to the numeric target. The
modelers considered three different growth scenarios
Lake Chelan
Simple
Level of Analysis
Detailed
Problem
Definition
Select
Indicator
Source
Analysis
Link Source
to Impact
Allocate
Controls
Monitoring
Water Quality
Indicators
4.5
TMDL
51 kg/day P
Controls
Various controls
being considered
Source Assessment: Lake Chelan Water Quality
Assessment Study
Link to Indicator: Steady-state mass balance with Monte
Carlo simulation
First Edition: November 1999
2-7
-------
Nutrients and Water Quality
^Vi-
calculated load allocations for each scenario,
considering the corresponding impacts of each scenario
(e.g., greater loading can be permitted for growth in the
upper basin because the upper basin allows for greater
TP settling than the lower basin). The TMDL was
developed for the more likely scenario of little to no
growth in the upper basin and moderate growth in the
lower basin. To achieve the 4.5 pg/L goal, the TMDL
established a TP loading at 51 kg P per day. (The
Department of Ecology calculated the allowable
loadings conservatively so that the probability of
remaining ultra oligotrophic would be 95 percent,
thereby incorporating a margin of safety.)
The Department of Ecology decided that allocation of
the loads to the specific sources in the watershed would
depend on future development. Therefore, the Lake
Chelan Water Quality Plan considered load allocations
among the sources (homes using on-site disposal, homes
on sewer systems, Chinook net pens, and agricultural
activities) based on the different development scenarios
and then developed a schedule of actions to implement
the established loads for the most likely development
pattern. The 51 kg/day allowable load was divided
among future growth (0.5 kg/ day), existing sources (6.3
kg/day) and background loads (44.2 kg/day).
In addition to the schedule for implementation, a long-
term water quality monitoring strategy was established
with permanent stations and parameters. The
monitoring plan was to assess water quality trends and
runoff from agricultural drains to evaluate pollutant
loading during worst-case conditions. Another goal of
the monitoring plan was to help growers minimize
potential pollutant loads by reducing the amount of
water leaving their site in runoff or deep percolation.
This reduction would be accomplished by conducting an
extensive soils analysis to determine the optimum
procedure for managing irrigation rate, timing, and
duration.
Wolf Lake TMDL (Preliminary)
This preliminary example is based on a study that was
conducted of Wolf Lake, Mississippi. The results of the
study have not yet been used to prepare a TMDL
submittal. The discussion of the technical approach is
therefore factual but the discussion of implementation is
merely suggested. Wolf Lake was included despite its
preliminary nature because it provides an example of a
TMDL for which the prediction of loads was based on a
relatively simple technique, and more detailed
investigations were dedicated to predicting in-lake water
quality impacts.
Wolf Lake, an oxbow lake in the southeastern United
States, was included on the 303(d) list because of
violations of the dissolved oxygen water quality
standard. The TMDL developers identified excessive
nutrient loadings from fertilized crops and catfish ponds
in the watershed as the primary cause of impairment and
identified no point source discharges to the lake. Water
quality data were limited to a previously released EPA
Clean Lakes study that included in-lake and tributary
concentrations of a variety of pollutants for a 2-year
period. The TMDL developers were able to determine
general land use information in the watershed, based on
Wolf Lake
Simple
Level of Analysis
Detailed
Problem
Definition
Select
Indicator
Source
Analysis
Link Source
to Impact
Allocate
Controls
Monitoring
Water Quality
Indicators
Minimum daily
dissolved oxygen
concentration of
5.0mg/L
TMDL
Reduce current
phosphorus
loading by 35%
Controls
BMPs for ag
fields
BMPs for catfish
ponds
Source Assessment: GWLF model
Link to Indicator: CE-QUAL-ICM model
2-8
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
an existing, 3-year-old coverage. The land uses were
broadly categorized by acreage into agricultural,
residential, forested, and barren lands. Estimates of
source loadings (in kilograms per month) for each of
these land uses were derived using the Generalized
Watershed Loading Function (GWLF) model (Haith et
al., 1992). This desktop model uses literature values for
runoff, sediment, and ground water relationships based
on different regions of the country. Streamflow, nutrient
loading, soil erosion, and sediment yield values were
estimated using GWLF based on the Wolf Lake
watershed land uses and regional soil and meteorologic
conditions.
Because of the complex nature of the waterbody (e.g.,
varying in-lake conditions and vertical stratification),
simplified receiving water models were not considered
appropriate for predicting in-lake response or load
reduction alternatives. Instead, analysts used the
CE-QUAL-W2 hydrodynamic and water quality model
(Cole and Buchak, 1995) to simulate eutrophication
processes. Model simulations were conducted for the
time periods corresponding to available in-lake water
quality monitoring data to determine a relationship
between the estimated loading conditions and water
quality response.
Based on the modeling results, the TMDL developers
evaluated several scenarios that would allow the lake to
meet its dissolved oxygen standard. These scenarios
considered the developers' knowledge of the various
land uses in the watershed and the feasibility of different
types of controls. The TMDL was established so that
phosphorus loadings were to be reduced by
approximately 35 percent annually and load allocations
were established for both row crops and the catfish
ponds. Additional monitoring will be performed to
further evaluate the magnitude of the different sources
and to evaluate the effectiveness of best management
practices (BMP) for restoring lake water quality.
Tualatin River TMDL
The Tualatin River TMDL in Oregon is an example of a
situation where relatively more time and effort were
expended to identify a target and allocate loads than
were spent to estimate loads from specific nutrient
sources. The impaired portion of the Tualatin River is
approximately 40 miles long and drains an urbanizing
watershed east of Portland. According to several water
quality surveys, the Tualatin River was not supporting
the following uses, in part because of nuisance algal
growths: fishing, contact recreation, aesthetics, and
aquatic life. Moreover, the lake to which the Tualatin
River drains was not supporting several of its designated
uses because of nuisance algal growth.
The Oregon Department of Environmental Quality
decided to develop a total phosphorus TMDL to address
these problems. The state's Nuisance Phytoplankton
Growth Rule (OAR 340-412-150) established a
phytoplankton concentration of 15 ^ug/L chlorophyll a
(average concentration) as the applicable numeric
criterion for the lake and the river. For the TMDL, a
local university conducted a series of algal growth
studies to determine the total phosphorus target that
would achieve this criterion. The researchers found that
a noticeable reduction in algal growth occurred at 100
pg/L phosphorus and that at approximately 50 pg/L
phosphorus, low growth conditions prevailed. Using
Problem
Definition
Select
Indicator
Source
Analysis
Link Source
to Impact
Allocate
Controls
Monitoring
Tualatin River
Simple
Level of Analysis
Detailed
Water Quality
Indicators
Average
chlorophyll a 15
Aig/L
Average TP 70
,ug/L (May to
Oct)
TMDL
LA's specified
for various
attainment
points for
different flow
conditions
Controls
Various BMPs
determined by
local
municipalities
First Edition: November 1999
2-9
-------
Nutrients and Water Quality
this information and after consulting with various
stakeholders, the state agency adopted a total
phosphorus target of 70 pg/L (to be applied as a
monthly mean from May 1 to October 31).
A source assessment indicated that the following were
the primary sources of phosphorus in the watershed: two
wastewater treatment plants, confined animal feeding
operations, agricultural and forestry practices, failing
septic systems, urban storm water runoff, and county
road ditches. An in-depth source assessment estimating
the loadings from each of these activities was not
conducted. Instead, the required nonpoint source
reductions were allocated to 16 specific locations along
the main stem of the river and to the major tributaries.
The loading capacities also were divided into four
hydrologic categories (flow conditions) based on typical
flows observed between May and October. For
example, the nonpoint source phosphorus load
allocation for the Tualatin River and other tributaries
upstream of Golf Course Road were specified as
follows:
Flow
NPS Load
< 50 cfs
7.4 Ib/day
50 to 100
cfs
14.8
Ib/day
100 to
200 cfs
29.7
Ib/day
> 200 cfs
59
Ib/day
These allocations are expected to keep the monthly
mean total phosphorus concentration below 45 pg/L at
this location in the river (which will, in turn, contribute
to keeping the downstream main stem concentration
below the specified target of 70 pg/L). Each
municipality within the various subbasins is responsible
for determining how load reductions should occur, and a
Technical Advisory Committee and a Citizens' Advisory
Committee will help develop plans. An ambient
monitoring program specifying the parameters to be
sampled and the minimum frequency of monitoring also
will track progress toward the goal.
Port Tobacco River TMDL
The Port Tobacco River TMDL in Maryland is an
example of a situation where modeling was used
extensively in determining the effectiveness of a
proposed TMDL approach. The Port Tobacco River is
approximately 8.5 miles long and drains a
predominantly forested watershed in Charles County.
Land use within the watershed consists of 60 percent
forest, 21 percent mixed agriculture and 19 percent
urban land. According to water quality surveys, the Port
Tobacco River was not supporting the following uses, in
part because of nuisance algal growths and low
dissolved oxygen: water contact recreation and
protection of aquatic life, and shellfish harvesting
(Code of Maryland Regulations 26.08.02 Use I and II,
respectively).
The Maryland Department of the Environment (MDE)
decided to develop nitrogen and phosphorus TMDLs to
address these problems. The state's narrative nitrogen
and phosphorus water quality criteria are listed in
Section 26.08.02.03B of the Code of Maryland
Regulations. MDE uses a numerical limitation on
chlorophyll-a as a surrogate measure to determine
Port
Level of Analysis
Simple Detailed
Problem
Definition
Select
Indicator
Source
Analysis
Link Source
to Impact
Allocate
Controls
Monitoring
1
1
1
Zl
Tobacco River
Water Quality
Indicators
5 mg/L DO
52,ug/L
chlorophyll-a
TMDL
Summer:
8,710 Ibs/monthN
871 Ibs/month P
Annual Average:
243,3 10 Ibs/yearN
15,570 Ibs/year P
Controls
Biological Nitrogen
Removal (BNR),
Chemical Phosphorus
Removal (CPR) on point
sources
Source Assessment: MD Office of Planning land use data and HSPF
land use loading coefficients (nonpoint source), MDE DMR reports
(point source)
Link to Indicator: WASPS
2-10
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
compliance with the narrative criteria. In addition, the
TMDLs are designed to achieve compliance with
Maryland's dissolved oxygen water quality criterion of
5 mg/L. MDE used a predictive model to demonstrate
that the TMDLs will ensure compliance with both the
narrative criteria and the dissolved oxygen criterion by
maintaining nitrogen and phosphorus loads at the
targeted levels. The model, Water Quality Analysis
Simulation Program, can simulate the transport and
transformation of conventional and toxic pollutants in
the water column and benthos of ponds, streams, lakes,
reservoirs, rivers, estuaries, and coastal waters.
The critical season for excessive algal growth in the Port
Tobacco River occurs during the low-flow summer
months, when the system is poorly flushed and slow-
moving, warm water is susceptible to excessive algal
growth. As a result, MDE developed individual
nitrogen and phosphorus TMDLs for both the summer
(May 1 through October 31) and annual average flow
conditions. The summer TMDLs for nitrogen and
phosphorus are 8,710 and 871 Ibs/month, respectively.
The annual average flow TMDLs for N and P are
243,310 and 15,570 Ibs/year, respectively. A summary
of the TMDLs is presented below.
Load
TMDL
LA1
WLA2
MOS3
FA4
Summer Low Flow
N (Ib/mo)
8,710
5,776
1,597
173
1,164
P (Ib/mo)
871
696
88
21
66
Annual Avg. Flow
N (Ib/yr)
243,310
190,470
24,920
5,840
22,080
P (Ib/yr)
15,570
12,500
1,060
400
1,610
1 Load Allocation;2 Waste Load Allocation;3 Margin of Safety (also implicit);
4 Future Allocation
In addition to the explicit MOS allocations presented
above, MDE also applied an implicit MOS by setting an
upper model target on chlorophyll-a concentrations of
52 /jg/L, which is conservative given the generally
acceptable range of 50 pg/L to 100 pg/L. Other implicit
MOS features include the "worst case" scenario
assumption that point sources in the watershed are
discharging at their permitted levels under high-
temperature, low-flow conditions.
The WLAs will be implemented through the NPDES
permit process. The nonpoint source controls (LAs) will
be implemented through Maryland's Lower Potomac
Tributary Strategy, developed as part of Maryland's
commitments under the Chesapeake Bay Agreement. In
addition, follow-up monitoring within five years will be
conducted as part of Maryland's Watershed Cycling
Strategy, which will help determine whether these
TMDLs have been implemented successfully.
Garrison Lake TMDL
Garrison Lake, a 90-acre lake adjacent to the City of
Port Orford in southwestern Oregon, is relatively
shallow, with an average depth of eight feet and a
maximum depth of 26 feet. The lake consists of a large
upper basin containing about 84 percent of the lake
volume and a smaller lower basin containing about 16
percent of the lake volume. Approximately 85 percent
of the shoreline consists of private lands and land use in
the watershed at the time the TMDL was developed
(1988) was 61 percent forested, 25 percent urban, 10
percent sand dunes, and 4 percent water.
Problem
Definition
Select
Indicator
Source
Analysis
Link Source
to Impact
Allocate
Controls
Monitoring
Gar
Level of Analysis
Simple Detailed
|
|
|
1
|
1
risi
on Lake
Water Quality
Indicators
Average
chlorophyll a
15,ug/L
TMDL
Entire TMDL
specified as LAs
(WLA
eliminated)
Controls
City of Port
Orford WWTP
relocated out of
Garrison Lake
Source Assessment: Clean Lakes Phase I Diagnostics and
Feasibility Study
Link to Indicator: Modified Vollenweider relationship
First Edition: November 1999
2-11
-------
Nutrients and Water Quality
Garrison Lake is designated to support several beneficial
uses, including:
• Public Domestic Water Supply
• Water Contact Recreation
• Aesthetic Quality
• Boating
• Resident Fish and Aquatic Life
• Fishing
According to Oregon regulations(OAR 340-41-150),
beneficial uses may be impaired by excessive algal
growth in shallow lakes when average chlorophyll a
values exceed 15 pg/L. This concentration was
commonly exceeded in the lower basin of Garrison Lake
(67 percent of measurements) and occasionally
exceeded in the upper lake basin (10 percent of the
measurements). Excessive macrophyte growth also was
observed in the shallow areas of the lake.
A modified version of the Vollenweider total
phosphorus loading and mean depth and hydraulic
residence time relationship (Vollenweider, 1968) was
used to establish a draft total phosphorus TMDL for
Garrison Lake. Based on the modified Vollenweider
relationship, the TMDL for Garrison Lake was
calculated as 562 Ibs per year total phosphorus.
Because lakes are sensitive to pollutant loadings
received throughout the year, the TMDL was expressed
as an annual loading. The Oregon Department of
Environmental Quality next conducted a Clean Lakes
Phase I Diagnostics and Feasibility Study to more
thoroughly identify and evaluate the nonpoint nutrient
sources. These sources included in-lake loadings or
resuspension and release of nutrients from the sediment.
The data gathered from this study resulted in only a
slight modification to the TMDL (576 Ibs per year total
phosphorus).
The potential nutrient sources identified in the Garrison
Lake watershed were the City of Port Orford wastewater
treatment plant, failing septic systems, road building,
and fertilizer application. Researchers estimated, based
on the available sampling data, that the wastewater
treatment plant contributed about 68 percent of the
phosphorus load while the contribution from the lake's
tributaries was 32 percent and the TMDL was
established as follows:
TMDL = 576 Ibs/yr TP = Load Allocations (576 Ibs/yr)
+ Wasteload Allocations (0 Ibs/yr)
To implement the TMDL, DEQ negotiated an agreement
with the City of Port Orford to relocate the existing
waste discharge out of Garrison Lake. This agreement
resulted in a decrease in nutrient loading and a
significant decrease in nuisance algal growths. The lake
continues to be monitored to ensure that the 15 pg/L
chlorophyll a target is met.
NUTRIENT CONTROLS
As suggested by the preceding TMDL examples, many
BMPs are available for nutrient control from rural
(agricultural) and urban nonpoint sources. BMPs can be
classified into three categories—management, structural,
and vegetative. To select the most effective BMP or
combination of BMPs, a manager must determine the
primary source of the pollutant and its method of
transport to the waterbody (as discussed in section
5—Source Assessment). Table 2-2 describes various
BMPs designed to reduce nonpoint source pollution.
BMPs achieve pollution reduction by either preventing
pollution first or controlling pollutants at the sources.
Management BMPs are used to prevent pollution by
controlling land use with laws (zoning ordinances,
discharge permits) and planning (nutrient management
plans, road maintenance programs). Structural and
vegetative BMPs control pollution by intercepting the
flow of water from the source before it reaches a
waterbody. Most structural and vegetative BMPs are
targeted for control of a particular pollution problem.
Many, such as porous pavement and infiltration basins,
are designed to encourage infiltration of runoff. Other
BMPs, including cover crops, diversions, conservation
tillage, and critical area planting, are used to minimize
soil erosion. Many BMPs serve as multipurpose
controls. For example, retention ponds and constructed
wetlands not only hold runoff water (allowing pollutants
to settle out of the water) but also provide vegetation
that can absorb some of the nutrients. Implementation
of a combination of BMPs is usually the most successful
method of controlling numerous pollutants from a
nonpoint source.
2-12
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Table 2-2. Common BMPs employed to control nutrient transport from agricultural and urban nonpoint sources
Nutrient
Source
Management BMPs
Structural BMPs
Vegetative BMPs
Agriculture3
Nutrient management
Range and pasture
management
Proper livestock-to-land
ratio
Waste composting plan
Irrigation management
Lagoon waste level
management
Crop residue management
Livestock waste
management
Animal waste system (lagoon,
controlled storage area)
Fences (livestock exclusion)
Diversions
Terraces
Tailwater pit
Retention/detention pond
Constructed wetland
Waste composting facility
Stream bank stabilization
Sediment pond
Cover crop
Strip cropping
Riparian buffer
Crop types (identify
nutrient needs)
Conservation tillage
Vegetated filter strips
Critical area planting
Urban"
Zoning ordinances
Restrictive covenants
Growth management
Buffers and setbacks
Site plan review
Public education
Permitting for pollutant
discharge
Pollution prevention
programs
Spill control programs
Road maintenance
programs (street sweep)
Septic system pump-out
schedule
Developing urban:
• Extended detention ponds
• Constructed wetlands
• Multiple pond systems
• Infiltration trenches and basins
Highly urban:
• Illicit connection controls
• Porous pavement
• Storm water detention or wetland
retrofits
• Sand filters
Vegetated filter strips
Riparian buffer
Vegetative cover
Adapted from Novotny and Olem, 1994.
b Adapted from USEPA, 1993.
First Edition: November 1999
2-13
-------
Nutrients and Water Quality
2-14
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Problem Identification
Objective: Identify background information and
establish a strategy for specific 303(d) listed waters that
will guide the overall TMDL development process.
Summarize the nutrient-related impairment(s),
geographic setting and scale, sources of concern, and
other information needed to guide the TMDL
development process and provide a preliminary
assessment of the complexity of the TMDL (what
approaches are justified and where should resources be
focused).
Procedure: Inventory and collect data and information
needed to develop the TMDL. Information collected
should include an identification of the pollutant water
quality standards impairment and preliminary
identification of sources, numeric targets, proposed
analytical methods, data needs, resources required and
possible management and control techniques. Interview
watershed stakeholders and local, state, tribal, and
federal agency staff to identify all information relevant
to the waterbody and its watershed. Establish plans for
incorporating public involvement in the development of
the TMDL. Revise the problem definition as new
information is obtained during TMDL development.
OVERVIEW
Developing a TMDL requires formulating a strategy that
addresses the potential causes of the water quality
impairment and available management options. The
characterization of the causes and pollutant sources
should be an extension of the process originally used to
place the waterbody on the 303(d) list. Typically, the
impairment that caused the listing will relate to water
quality standards being violated—either pollutant
concentrations that exceed numeric criteria or waterbody
conditions that do not achieve a narrative water quality
standard or a designated use. In many cases, the
problem is self-evident and its identification will be
relatively straightforward. In other cases, the
complexity of the system might make it more difficult to
definitively state the relationship between the nutrient
sources and the impairment.
The following key questions should be addressed during
this initial strategy-forming stage. Answering these
questions results in defining the approach for developing
the TMDL. A problem statement based on this problem
identification analysis is an important part of the TMDL
because it relates the TMDL to the 303(d) listing and
clearly identifies the purpose of the TMDL, thereby
making the TMDL more understandable and useful for
implementation planning.
KEY QUESTIONS TO CONSIDER FOR PROBLEM
IDENTIFICATION
1. What are the designated uses and associated
impairments?
The goal of developing and implementing a TMDL is to
attain and maintain water quality standards in an
impaired waterbody to support designated uses. With
that in mind, TMDL developers should stay focused on
addressing the nutrient-related problem interfering with
the designated uses. Some common designated uses and
their associated nutrient problems are presented in Table
3-1. The problem identification should answer the
following:
• What nonattainment of standards caused the listing?
What data or qualitative analyses were used to
support this decision?
• Where in the waterbody are designated uses
supported and where are they impaired?
• How are water quality criteria expressed (narrative,
numeric)?
Key Questions to Consider for
Problem Identification
1. What are the designated uses and associated
impairments?
2. What data are readily available?
3. What is the geographic setting of the TMDL?
4. What temporal considerations will affect
development of the TMDL?
5. What are the nutrient sources and how do they
affect water quality?
6. How will margin of safety and uncertainty issues
be addressed in the TMDL?
7. What are some potential control options?
8. What changes does the proposed rule speak to?
First Edition: November 1999
3-1
-------
Problem Identification
Table 3-1. Impacts of nutrients on designated uses
Designated Use
Aquatic Life Support
Drinking Water Supply
Recreation/ Aesthetics
Industrial
Agricultural
Problems Associated with Plant Growth Stimulated by Nutrient Loading
• Low dissolved oxygen concentrations caused by nighttime respiration of large
populations of aquatic plants and algae or by the decay of plant matter
• Fish kills (via toxicity, or low dissolved oxygen)
• Reduced light penetration
• Nuisance plants outcompeting desired species
• Blockage of intake screens and filters
• Taste and odor problems
• Production of toxins (by blue-green algae)
• Disruption of flocculation and chlorination processes in water treatment plants
• High nitrates in drinking water, which can cause methemoglobinemia (reduced
ability of the blood to carry oxygen), especially in infants
• Reduced clarity by sloughed material
• Macrophyte interference with boating, swimming, water skiing, and other
recreation
• Sloughed material fouling anglers' nets
• Floating mats
• Slippery beds that make wading dangerous
• Blockage of intake screens and filters
• Clogged stream channels, reducing drainage by raising water level and increasing
risk of flooding adjacent land
Source: Adapted from Quinn, 1991.
• What are the critical conditions, in terms of flow
and season of the year, during which designated uses
are not supported?
• How do nutrients affect the designated uses of
concern (e.g., phosphorus loading stimulates
excessive algal growth that interferes with
recreational use of the waterbody)?
• Are there additional use concerns (e.g., presence of
threatened or endangered species)?
Recommendation: Identify and summarize in a problem
statement the events leading to the listing and the data to
support the listing. Prepare a flowchart or schematic
detailing the processes that might affect impairment of
the waterbody. Figure 3-1 is an example of what such a
schematic might look like for an impaired lake or
reservoir.
2. What data are readily available?
As much as possible, managers should identify the
problem based on currently available information,
including water quality monitoring data, watershed
analyses, best professional judgment, information from
the public, and any previous studies of the waterbody
(e.g., state and federal agency reports, university-
sponsored studies, reports prepared by environmental
organizations). These data ideally will provide insight
into the nature of the impairment, potential nutrient
sources, and the pathways by which nutrients enter the
waterbody. Managers also should compile data that will
be needed for actual development of the TMDL during
the problem identification stage. These data likely will
include the following:
• Water quality measurements (e.g., nutrient, algae,
and dissolved oxygen concentrations)
• Waterbody size and shape information (e.g.,
volume, depth, area, length)
3-2
First Edition: November 1999
-------
CD
CO
o
<
CD
CO
CO
CO
o
o
O
Q_
CD
External, non-point,
point sources of N,P
coz
CO,
4
s s s s / /
s s s s s s
S S S S S S
Zooplankton
^
Toxic Concentrations?
pH,NH3,T dependent
Fish/Invertebrate
Kills
Conceptual Model Key
CO
CO
Nutrients (nitrogen/phosphorus) enter system via point sources,
non-point sources, and in-lake processes,
Excess nutrient concentrations and light stimulate growth,
Algal growth increases solids and thus reduces light transparency,
Aquatic plants consume carbon dioxide and cause pH to rise,
Aquatic plants fragment or die releasing ammonia, phosphorus,
carbon dioxide, and consume oxygen into water column or sediments,
Ammonia undergoes nitrification to yield nitrate. Nitrate is recycled
back into system,
Ammonia diffuses into atmosphere,
Ammonia can become toxic if pH and ammonia concentrations are
high enough, and
High concentrations of unionized ammonia can cause fish and
invertebrate kills and release ammonia into the water column and
consume additional dissolved oxygen.
I
-------
Problem Identification
• Waterbody flow and residence times
• Tributary location and contributions (flow and water
quality)
• Biological information (e.g., fish, invertebrate, and
riparian vegetation information)
• Watershed land uses and land use issues
• Temperature and precipitation data
• Soil surveys and geologic information
• Topographical information
Maps of the watershed also will be invaluable, either
hard copies, such as USGS quad maps, or (if available)
electronic files for GIS systems. Point sources, known
nonpoint sources, and land uses should be identified on
these maps to provide an overview of the watershed and
to identify priority areas for nutrient loading caused by
human activities.
Information on related assessment and planning efforts
in the study area should also be collected. TMDL
development should be coordinated with similar efforts
to reduce TMDL analysis costs, to increase stakeholder
participation and support, and to improve the outlook for
timely implementation of needed control or restoration
activities. Examples of related efforts that should be
identified include:
• State, local, or landowner-developed watershed
management plans
• Natural Resource Conservation Service (NRCS)
conservation plans, Environmental Quality
Incentives Program (EQUIP) projects, and Public
Law 566 (PL-566) small watershed plans.
• Land management agency assessment or land use
plans (e.g., Federal Ecosystem Management Team
[FEMAT] watershed analyses or Bureau of Land
Management [BLM]) proper functioning condition
assessments)
• Nonpoint source control projects
• Clean Lakes program projects
• Stormwater management plans and permits
• Habitat conservation plans developed under the
Endangered Species Act
• Comprehensive monitoring efforts (e.g., National
Water Quality Assessment [NAWQA]) and
Environmental Monitoring and Assessment Program
[EMAP] projects)
Recommendation: Contact agency staff responsible for
the waterbody listing and collect any information they
have available. Contact other relevant agencies, such as
the NRCS or state natural resources, water resources,
fish and wildlife, and public health agencies and prepare
an inventory of available information. Universities are
often a good source of data for a waterbody.
3. What is the geographic setting of the TMDL?
TMDLs can be developed to address various geographic
scales. The geographic scale of the TMDL primarily
will be a function of the impairment that prompted the
waterbody listing, the type of waterbody impaired, the
spatial distribution of use impairments, and the scale of
similar assessment and planning efforts already under
way.
The selection of TMDL scale may involve trade-offs
between comprehensiveness in addressing all designated
use and source issues of concern and the precision of the
analysis (MacDonald et al., 1991; Bisson et al., 1997).
Table 3-2 summarizes the advantages and disadvantages
of developing TMDLs for larger (e.g., greater than 50
mi2) and smaller (less than 50 mi2) watersheds.
Recommendation: When the designated use
impairments are at the bottom of a watershed (e.g., in a
lake or reservoir), address the entire watershed at once
by using less-intensive, screening-level assessment
methods. Follow-up monitoring can assess the
effectiveness of the nutrient reduction and, if necessary,
more in-depth analysis can target specific high-priority
areas within the watershed that have local problems.
When impairments occur throughout a watershed, the
analysis should be conducted for smaller, more
homogenous analytical units (i.e., subwatersheds). For
example, specific river reaches that are impaired might
require detailed TMDLs to address upstream point and
nonpoint sources. If this subwatershed approach is
chosen, care should be taken to apply consistent
methodologies from one subwatershed to the next so
that an additive approach eventually can apply to the
larger watershed.
3-4
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Table 3-2. Advantages and disadvantages of different TMDL watershed analysis scales.
Large TMDL Study Units
(> 50 square miles)
Small TMDL Study Units
(< 50 square miles)
Advantages
Accounts for watershed processes
operating at larger scales
More likely to account for cumulative
effects
Avoids need to complete separate
studies for multiple tributaries
Easier to identify and address fine-scale
source-impact relationships, and to
identify needed control actions
Possible to use more accurate, data-
intensive methods.
Disadvantages
Confounding variables obscure cause-
effect relationships
Numeric target setting harder for
heterogeneous waterbody features
Source estimation more difficult because
land areas more heterogeneous
Lag time between nutrient discharge and
instream effects potentially longer,
effectiveness of source controls therefore
harder to detect
Analysis at coarse scale may cause
TMDL to "miss" source-impact
relationships at fine scale
May miss cause-effect relationships
detectable only at broad scale
(cumulative impacts)
May necessitate many separate TMDL
studies in a basin
4. What temporal considerations will affect
development of the TMDL?
TMDLs must consider temporal (e.g., seasonal or
interannual) variations in discharge rates, receiving
water flows, and designated use impacts. These
considerations are especially important for stream
nutrient TMDLs because both point and nonpoint
nutrient sources can discharge at different rates during
different time periods and plant growth can vary
considerably by season. A frequent critical period for a
nutrient stream TMDL is the summer low-flow,
high-temperature period, because these conditions are
favorable for nuisance plant growth. Critical conditions
also can occur during other times of the year, however.
For example, in the fall, upstream organic carbon
sources from phytoplanton and aquatic plants can result
in large depressions in levels of dissolved oxygen.
Spring floods that pick up large amounts of organic
debris from adjacent floodplains also can result in severe
dissolved oxygen depletion or phytoplankton blooms
(USEPA, 1995a).
Seasonal variations are also important for lake nutrient
TMDLs. For example, a key aspect of plant dynamics
in temperate lakes is the magnitude of the spring
phytoplankton bloom. Algal growth typically is greatly
reduced or negligible during the winter low light and
temperatures; it then usually increases during the spring
under increasing sunlight. The spring maximum is
generally short-lived (less than one to two months) and a
period of low algal numbers and biomass often follows
that can extend throughout the summer (Wetzel, 1983).
The effects of nutrient inputs to reservoir main stems
also may vary with the reservoir's thermal regime and
hence with the time of year. The mixing of in-flows
during winter and spring may affect the entire
waterbody, while in-flows during stratified periods may
enter as underflow and might not affect the photic zone,
especially in bottom-discharging reservoirs.
In addition to the seasonal variation in the onset and die-
off of algal blooms, there also may be temporal
variation, or succession, in the composition of blooms.
In some systems, the blooms begin with diatoms and
then shift to green algae and finally to blue-green algae.
An example of this sequence of succession is the San
First Edition: November 1999
3-5
-------
Problem Identification
Francisco Bay, although the final blue-green algal bloom
no longer occurs, presumably because of copper toxicity
in the bay. In other systems, two separate blooms occur.
For example, there are separate spring and fall blooms
of Cladophora in Lake Huron, where higher summer
temperatures impair algal growth (Auer et al., 1982).
A variety of temporal considerations will affect each
stage of TMDL development. For example, the water
quality indicator chosen to develop the TMDL should
closely link to the problems impairing the water's use.
A useful indicator for a river impaired by nuisance
periphyton growth that primarily occurs during the
summer might, therefore, be a maximum algal biomass
for May to October. Alternatively, if nutrient loadings
contribute to depressed dissolved oxygen
concentrations, the water quality indicator used to
develop the TMDL might be appropriately expressed for
a much shorter time period (i.e., daily).
TMDL developers also must consider time scale issues
when conducting the source assessment and when
linking the estimated loadings to the indicators of water
quality. For situations involving both point and
nonpoint sources of nutrients, it might be possible to
link episodic loading models with steady-state receiving
water models or to use an average wet-weather loading
rate. This technique is often appropriate for developing
nutrient TMDLs in lakes with long residence times
because these waters might be relatively insensitive to
short-term variations in nutrient loading rates and their
response will take weeks or months, rather than days.
Determining the Limiting Nutrient
The limiting nutrient, generally nitrogen or
phosphorus, is defined as the nutrient that limits plant
growth when it is not available in sufficient quantities.
A first cut at determining the limiting nutrient can be
accomplished by comparing the levels of nutrients in
the waterbody with the plant stoichiometry. The ratio
of nitrogen to phosphorus in biomass is
approximately 7.2:1. Therefore, an N:P ratio in the
water that is less than 7.2 suggests that nitrogen is
limiting. Alternatively, higher ratios suggest that
phosphorus is limiting. (Chapra, 1997).
Recommendation: Address temporal considerations
during the problem identification stage of TMDL
development to ensure that a good strategy is in place as
the specific technical components of the TMDL are
completed. Specific guidance on addressing temporal
issues is provided in each section of this protocol.
5. What are the nutrient sources and how do
they affect water quality?
During the problem identification, the TMDL developer
should first understand the relative magnitude of the
various nutrient sources, including identifying when
loading occurs and how nutrients enter the waterbody.
It might be sufficient to locate known point and
nonpoint sources on a map, or some routine monitoring
might be needed. A more detailed source analysis
eventually will be needed. (This topic is covered in
Section 5). A qualitative assessment of the significance
of sediment cycling, groundwater sources, and
atmospheric sources should also be made at this time,
and an attempt should be made to determine the limiting
nutrient (see box).
In addition to assessing nutrient sources, TMDL
developers should identify the specific role that
nutrients play in affecting designated uses, because
many impairments associated with nutrient loadings also
can be caused by other stressors. For example, low
dissolved oxygen levels that affect aquatic life can be
caused by high biochemical oxygen demand, reduced
flows, or warm temperatures. Moreover, nutrients might
not always be the limiting factor controlling nuisance
plant growth. Several other constraints, such as light
availability, flow, availability of trace elements,
substrate conditions, management (CuSO4+, grazing, and
temperature) potentially could be limiting (refer to
Section 2). Nutrients are often the focus because they
are usually more readily controlled. In some cases,
however, it might be more practical to control nuisance
growth through other mechanisms, such as channel
modifications, restoration of riparian canopy, increased
flow, or introduction of biological controls.
Recommendation: Conduct an inventory of available
information on point sources using information
available from state or local agencies or databases such
as the national Permit Compliance System (PCS). For
nonpoint sources, identify all possible land use-specific
sources through analysis of aerial photographs, land
cover maps or databases and information from federal,
state, and local agencies. When using maps or GIS
3-6
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
coverages to determine land uses, document the scale,
resolution, and date of the information. In large
watersheds, the only available data might exist at a small
scale and the ability to conduct field verification will be
limited. In smaller watersheds, the utility of the same
data might be limited because the scale and minimum
mapping unit might hide important details, but field
verification of the data is possible. In all cases, rely on
the best and most relevant data set, document all issues
related to scale and date, and verify analysis with field
visits.
6. How will margin of safety and uncertainty
issues be addressed in the TMDL?
Considerable uncertainty is usually inherent in
estimating nutrient loading from nonpoint sources, as
well as predicting water quality response. The
effectiveness of management measures (e.g., support of
agricultural BMPs) in reducing loading is also subject to
significant uncertainty. These uncertainties, however,
should not delay development of the TMDL and
implementation of control measures. EPA regulations
(40 CFR 130.2(g)) state that load allocations for
nonpoint sources "are best estimates of the loading
which may range from reasonably accurate estimates to
gross allotments, depending on the availability of data
and appropriate techniques for predicting the loading."
USEPA (199la; 1999) advocated the use of a phased
approach to TMDL development as a means of
addressing these uncertainties. Under the phased
approach, load allocations and wasteload allocations are
calculated using the best available data and information,
recognizing the need for additional monitoring data to
determine if the load reductions required by the TMDL
lead to attainment of water quality standards. The
approach provides for the implementation of the TMDL
while additional data are collected to reduce uncertainty.
When using models during the development of the
TMDL, either to predict loadings or to simulate water
quality, managers should address the inherent
uncertainty in the predictions. Various techniques for
doing so include sensitivity analysis, first-order analysis,
and Monte Carlo analysis. These techniques are briefly
summarized in Section 6 and are also discussed in
various documents (e.g., IAEA, 1989; Cox and Baybutt,
1981; Chapra, 1997; Reckhow and Chapra, 1983).
TMDLs also address uncertainty issues by incorporating
a margin of safety into the analysis. The margin of
safety is a required component of a TMDL and accounts
for the uncertainty about the relationship between
pollutant loads and the quality of the receiving
waterbody (CWA section 303(d)(l)(c)). The results of
the uncertainty analysis performed for any modeling
predictions can be factored into the decision regarding a
margin of safety. The margin of safety is traditionally
either implicitly accounted for by choosing conservative
assumptions about loading or water quality response, or
is explicitly accounted for during the allocation of loads.
(For example, the TMDL is expressed as 250 Ibs/day
Table 3-3. Approaches for incorporating margins of
safety into nutrient TMDLs.
Type of
MOS
Explicit
Implicit
Available Approaches
Do not allocate a portion of available
nutrient loading capacity; reserve for MOS
Conservative assumptions in derivation of
numeric targets
Conservative assumptions in nutrient
loading and transport rates
Conservative assumptions in the estimate
of nutrient control effectiveness
phosphorus from point sources, 400 Ibs/day phosphorus
from nonpoint sources (including background sources)
and 100 Ibs/day for the margin of safety.) Table 3-3
lists several approaches for incorporating margins of
safety into nutrient TMDLs.
Recommendation: During the problem identification
process, the TMDL developer should decide, to the
extent possible, how to incorporate a margin of safety
into the analysis. The degree of uncertainty associated
with the source estimates and water quality response
should be considered, with the value of the resource and
the anticipated cost of controls. In general, greater
margins of safety should be included when there is more
uncertainty in the information used to develop the
TMDL. It may also prove feasible to include margins of
safety in more than one TMDL analytical step. For
example, relatively conservative numeric targets and
source estimates could be developed that, in
combination, create an overall margin of safety adequate
to account for uncertainty in the analysis.
First Edition: November 1999
3-7
-------
Problem Identification
7. What are some potential control options?
The problem identification should begin to identify
potential management alternatives. A general level of
understanding should be reached concerning the relative
load reductions that must be obtained from point versus
nonpoint sources and whether uncontrollable nutrient
sources are a significant factor. If no level of nutrient
control is predicted to achieve the designated use of the
waterbody, the appropriateness of the water quality
standard should be evaluated through UAA.
If nutrient controls will be able to address the
impairment, the problem statement should identify and
stress the opportunity to take advantage of other
watershed protection efforts. This statement will
include coordinating with various state agencies (e.g.,
natural resource and pollution control agencies), federal
agencies (e.g., BLM, U.S. Forest Service [USFS]) and
tribal authorities to avoid duplicate or contradictory
efforts. Other stakeholders also should be encouraged to
become involved with development of the TMDL, to
contribute to the process and to ensure that their
concerns are addressed.
8. What changes does the proposed rule speak
to?
On August 23, 1999, EPA published proposed rules that
specify that approvable TMDLs must include at a
minimum ten elements. Within the problem
identification step, an approvable TMDL will need to
include the name and geographic location of the
impaired or threatened waterbody for which the TMDL
is being established. The TMDL will also need to list
the names and geographic locations of the waterbodies
upstream of the impaired waterbody that contribute
significant amounts of the pollutant for which the
TMDL is being established.
RECOMMENDATIONS FOR PROBLEM
IDENTIFICATION
• Identify events leading to the listing and the data to
support the listing. Include any data or anecdotal
information that supports qualitative approaches to
develop the TMDL.
• Identify the specific role nutrients play in affecting
designated uses and attempt to determine which
nutrient is limiting. (Many impairments associated
with nutrients are also caused by other stressors.)
• Contact agency staff responsible for the waterbody
listing and collect any available information.
• Prepare a flowchart or schematic detailing the
processes that might affect waterbody impairment.
• Conduct an inventory of available information on
point or nonpoint sources using information available
from state or local agencies or databases.
• Identify temporal and seasonal factors affecting such
issues as discharge rates, receiving water flows, and
designated use impacts. Temporal considerations
will affect all subsequent stages of TMDL
development for nutrients.
• Identify and document all current watershed
restoration or volunteer monitoring efforts.
• Identify any characteristics or future uses of the
watershed or waterbody that might affect the TMDL
analysis.
RECOMMENDED READING
(Note that the full list of references for this section is at
the end of the document.)
• USEPA. 1991a. Guidance for water quality-based
decisions: The TMDL process. EPA 440/4-91-001.
U.S. Environmental Protection Agency, Washington,
DC.
• USEPA. 1995b. Watershed protection: A statewide
approach. EPA 841-R-95-001. U.S. Environmental
Protection Agency, Office of Water, Washington,
DC.
• USEPA. 1995c. Watershed protection: A project
focus. EPA 841-R-95-003. U.S. Environmental
Protection Agency, Office of Water, Washington,
DC.
• USEPA. 1996a. TMDL development cost estimates:
Case studies of 14 TMDLs. EPAR-96-001. U.S.
Environmental Protection Agency, Office of Water,
Washington, DC.
• USEPA. TMDL Case Study Series.
3-8
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Identification of Water Quality Indicators and Target Values
Objective: Identify numeric or measurable indicators
and target values that can be used to evaluate the TMDL
and the restoration of water quality in the listed
waterbody.
Procedure: Select one or more indicator(s) appropriate
to the waterbody and local conditions. Key factors to
consider include both scientific and technical validity,
and practical issues (e.g., cost, available data). Identify
target values (for the indicators]) that represent
achievement of water quality standards and link
(through acceptable technical analysis) to the reason for
waterbody listing.
OVERVIEW
To develop a TMDL, it is necessary to have one or more
quantitative measures that can be used to evaluate the
relationship between pollutant sources and their impact
on water quality. Such measurable quantities are termed
indicators in this document. Examples of indicators for
a nutrient TMDL include total phosphorus
concentration, total nitrogen concentration, chlorophyll
concentration, algal biomass, and percent macrophyte
coverage. Once an indicator has been selected, a target
value for that indicator must be established that seeks to
distinguish between the impaired and unimpaired state
of the waterbody (e.g., summer chlorophyll
concentrations of attached algae will not exceed 100
mg/m2, or, total phosphorus concentrations will not
exceed 0.05 mg/L). Although such discrete impaired
and unimpaired cutoffs do not exist in natural systems,
quantifiable goals nevertheless are a necessary
component of TMDLs.
Key Questions to Consider for Identification of
Water Quality Indicators and Target Values
1. What is the water quality standard that applies to
the waterbody?
2. What factors affect the selection of an indicator?
3. What water quality measures potentially could be
used as indicators?
4. What target value will be used and how does it
compare to existing conditions?
5. What changes does the proposed rule speak to?
This section of the protocol provides background on
water quality standards and their relationship to TMDL
indicators, lists various factors that should be addressed
in choosing a TMDL indicator, and provides
recommendations for setting target values under
different circumstances.
KEY QUESTIONS TO CONSIDER FOR
IDENTIFICATION OF WATER QUALITY INDICATORS
AND TARGET VALUES
1. What is the water quality standard that
applies to the waterbody?
States, territories, and authorized tribes are responsible
for setting water quality standards to protect the
physical, biological, and chemical integrity of their
waters. The three components of water quality standards
include:
• Designated uses (such as drinking water supply,
aquatic life protection, recreation, etc.) for each
waterbody
• Narrative and numeric criteria designed to protect
these uses
• An antidegradation policy
For some waters, the indicators and target values needed
for TMDL development already are specified as
numeric criteria in state water quality standards. For
instance, EPA issues "criteria guidance" on the human
health and ecological effects of specific pollutants that
is generally reflected in state standards. An example
would be a standard that specifies that the daily
minimum dissolved oxygen concentration in a river
designated for warm water aquatic life support must be
5.0 mg/L. However, water quality standards vary
considerably from state to state and often only narrative
criteria exist for nutrient issues. In these situations,
development of the TMDL will require the
identification of one or more appropriate indicators to
quantify the attainment of water quality standards. The
steps for linking the designated use of a water to a
TMDL are outlined in Figure 4-1.
First Edition: November 1999
4-1
-------
Identification of Water Quality Indicators and Target
Identify the Violation that Placed the
Waterbody on the 303(d) List
1
r
Numeric Water
Quality Standard
Non-Numeric Water
Quality Standard
,, Develop Supporting Indicators for Follow-up Monitoring
Develop TMDL Using Numeric
Standard
Identify Potential
Indicators
Select Target Value Protective of
Designated Uses
Develop TMDL Using Selected
Target Value
Figure 4-1. Factors for determining indicators and target values
Recommendation: Determine the water quality standard
for the waterbody. Use the numeric water quality
standard if it exists. Use supplementary indicators when
no numeric standard exists and only a narrative standard
is available. When using a numeric standard, note any
important issues, including where the standard is
EPA has developed a National Strategy for the
Development of Regional Nutrient Criteria (USEPA,
1998a) that outlines the agency's role in providing
guidance to states and tribes for developing
nutrient criteria. It is anticipated that guidance
documents organized according to waterbody type
will be produced as a result of this Strategy. The
lakes and reservoirs, and rivers and streams
documents being developed will address such
issues as how to develop criteria for algae and
nutrients, how to develop a monitoring plan, and
how to implement management objectives. Much of
the information in this section of the protocol is
based on work in progress during the development
of these documents.
applied, number of samples required, averaging period,
and number of exceedances allowed.
2. What factors affect the selection of an
indicator?
Various factors will affect the selection of an
appropriate TMDL indicator. These factors include
issues associated with the indicator's scientific and
technical validity, as well as practical management
considerations. The importance of these factors will
vary for each waterbody, depending, for instance, on the
time and resources available to develop the TMDL, the
availability of already existing data, and the water's
designated uses. Final selection of the indicator should
depend on site-specific requirements. The following
sections identify some factors to keep in mind during
indicator selection.
4-2
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Scientific or technical validity considerations
The purpose of the indicator(s) is to provide a
quantitative estimate of when water quality supports the
designated uses. Different indicators might be needed
for different uses (e.g., dissolved oxygen concentration
for aquatic life support, extent of algae for recreational
uses). Indicators might also vary depending on
waterbody type.
Indicators should be sensitive to where sources are and
when and where impacts occur. TMDL developers
should be aware that nutrient problems tend to be
seasonally expressed and in many cases might result
from the accumulation of year-round loadings. The
indicator chosen also should lend itself well to available
techniques and methods that can be used to link nutrient
concentrations to water quality response.
Practical considerations
Measurement of the indicator should cost as little as
possible, while still meeting other requirements.
Indicators that can be suitably monitored through
volunteer monitoring programs or other cost-effective
means should be evaluated for adequate quality control
and assurance of sample collection, preservation,
laboratory analysis, data entry, and final reporting.
Monitoring should introduce as little stress as possible
on the designated uses of concern.
It is advantageous to select an indicator consistent with
already available data. Choice of an indicator also
should take into account how "obvious" it is to the
public that the target value must be met to ensure the
desired level of water quality. (For example, the public
understands Secchi depth and chlorophyll indicators
fairly well.)
Recommendation: Scientific and technical issues should
be balanced against practical considerations when
deciding upon a water quality indicator.
3. What water quality measures potentially could
be used as indicators?
Various water quality measurements can be selected as
nutrient TMDL indicators. They include both "causal
factor" indicators (primarily, the nutrients that stimulate
plant growth) and "biological response" indicators
(which provide information concerning the impacts on
water quality). Because of the site-specific nature of
TMDLs and the complexity of watershed processes, no
one indicator will satisfactorily meet all of the
requirements above. (See Table 4-1 for examples of
indicators from nutrient TMDLs or similar assessment
projects.). Below are brief summaries of several water
quality measurements and their advantages and
disadvantages for use as TMDL indicators.
Phosphorus
Nuisance plant growth in many freshwater lakes and
rivers is limited by the availability of phosphorus. For
this reason, many nutrient TMDLs include phosphorus
concentration as an indicator. Phosphorus can be
Table 4-1. Examples of indicators for TMDL targets and similar assessment projects
Waterbody
Boulder Creek, CO
Appoquinimink River, DE
Lake Chelan, WA
Truckee River, NV
Clark Fork River, MT
Laguna de Santa Rosa, CA
Indicators Selected
• 0.06 mg/L un-ionized ammonia
• 5.5 mg/L dissolved oxygen (daily average)
• 4.0 mg/L dissolved oxygen (instantaneous minimum)
• 4.5 /vg/L total phosphorus
• 0.05 mg/L total phosphorus
• 210 mg/L total dissolved solids
• 1 00 mg/m2 chlorophyll a (summer mean)
• 300 /vg/L total nitrogen
• 20-39 /vg/L total phosphorus (depending on stretch of the river)
• 0.025 mg-N/L un-ionized ammonia
• 7.0 mg/L dissolved oxygen (minimum)
First Edition: November 1999
4-3
-------
Identification of Water Quality Indicators and Target
measured in several ways, including as either total
phosphorus (TP) or as soluble reactive phosphorus
(SRP). TP has been used throughout North America as
a basis for setting criteria for lake and reservoir
management and related modeling efforts (NALMS,
1992). SRP more often is used for setting criteria in
rivers and streams because it is more representative of
the form of phosphorus directly available to plants.
TMDL developers should recognize that SRP is the most
significant form of phosphorus in terms of plant growth,
but because of the ability of bacteria to convert organic
phosphorus to a bioavailable form, TP loading is also
important. If possible, numeric targets for TMDLs
should be expressed as both SRP and TP to address the
nutrient availability issue.
Phosphorus indicators are not as easy to implement in
rivers and streams as they are in lakes and reservoirs.
Use of phosphorus indicators is especially difficult in
fast-flowing, gravel or cobble bed streams, which are
impaired more by attached algae than free-floating
algae. The relationship between phosphorus
concentration and plant growth is not as well established
in these systems, and in many systems the limiting
concentration might be so low as to be difficult to
reasonably achieve. For example, Welch et al. (1989)
report for the Spokane River, Washington, that biomass
levels exceeding 200 mg chlorophyll a per m2 can
persist farther than 10 km downstream from a point
source, unless soluble reactive phosphorus
concentrations are held below 10 /^g/L. Bothwell (1985,
1988) reports that streams can be phosphorus-saturated
at concentrations as low as 1 to 4 ,ug/L.
Nitrogen
Nitrogen concentrations can serve as useful indicators in
those systems where nitrogen is potentially the limiting
factor. This situation might be the case in waters
receiving wastewater with a low N/P ratio and in waters
with naturally phosphorus-rich bedrock (Welch et al,
1992). Some studies indicate that nitrogen might have
more importance as a limiting factor in streams than in
lakes (Chessman et al., 1992; Welch et al., 1989).
Nitrogen can be measured in several different forms
(total nitrogen, nitrate-nitrogen, nitrite-nitrogen, and
ammonia). The directly available forms are mainly
inorganic (nitrate-nitrogen and ammonia), although
some algae can use organic forms. As with total
phosphorus, total Kjeldahl nitrogen (TKN) is often a
good predictor of algal biomass in lakes and reservoirs
because much of the particulate fraction already is in the
algae. (TKN is the total of organic and ammonia
nitrogen in a sample, determined by the Kjeldahl
method.) The correlation between algal biomass and
total Kjeldahl nitrogen in streams and rivers, however, is
not as strong because measurements of total nitrogen
include detritus and because none of the incorporated
nutrients are in the periphyton algal mat (Dodds et al.,
1997).
As with phosphorus, limiting concentrations of nitrogen
in severely enriched waters are often very low,
especially for rivers affected by the filamentous green
species Cladophora (Ingman, 1992). In these instances,
the limiting concentration can serve as the long-term
goal, while somewhat higher values could be adopted as
intermediate goals of the TMDL. Nitrogen indicators
also could be used to control the extent of nuisance
growth, if not the total yield. Data suggest, for example,
that nutrient additions beyond the range of 40 to 100
;i/g/L dissolved inorganic nitrogen will not increase the
periphyton yield immediately downstream of a
discharge, but might increase the downstream extent of
periphyton proliferations (Quinn, 1991). A nitrogen
indicator that aims to limit the distance downstream at
which algal biomass reaches nuisance levels therefore
could be instituted.
Dissolved oxygen concentration
Dissolved oxygen concentrations are useful indicators
where the primary designated use of concern is aquatic
life. Dissolved oxygen concentrations already are
established in state water quality standards and generally
are expressed as a minimum daily value and as an
average value over a certain period (e.g., a daily, 7-day,
or 30-day mean). Note that analysis of dissolved oxygen
dynamics in shallow, periphyton-dominated streams is
complicated by a number of factors, including
significant local variability and strong daily cycles of
dissolved oxygen concentration, both affected by
temperature (Butcher and Covington, 1995). Further,
the most frequently used dissolved oxygen stream
models do not adequately address periphyton.
4-4
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Determining Indicator Target Values in the Spokane River, Washington
Welch et al. (1989) developed an approach for estimating the critical phosphorus concentration to prevent
nuisance periphytic biomass in the Spokane River, Washington. The methodology is based on various factors,
including uptake kinetics, that affect periphyton growth. A model calibrated to the growth of filamentous
periphyton in artificial channels was applied to the growth of periphyton on natural and artificial substrate in the
lower Spokane River. Because nuisance thresholds of periphyton growth (150 mg chlorophyll a per m2) were
shown to occur at very low concentrations of soluble reactive phosphorus (SRP) (1 -4 ji/g/L), an equation was
derived to provide a method for estimating the stream length for which biomass potentially could exceed the
threshold. The equation is as follows:
Qr(SRPi-SRPc)
C~ [(Pc)BnTW]
where:
Dc
SRPC
SRP,
Q
r
PC
T
W
Bn
stream length (m) for which periphyton biomass potentially could exceed the nuisance
threshold;
concentration (mg/m3) producing the threshold nuisance biomass (e.g., 150-200 mg
chlorophyll a/in2) in the growth period;
influent concentration (ambient river and ground water, mg/m3) to the stream segment;
daily flow in m3/day;
a constant to account for the recycle rate (unitless; 1.5 after Newbold et al., 1982);
average uptake rate by the periphyton mat per day, taken as 0.2;
trophic (consumer) retention factor (1.2, representing a 20% conversion: chosen as an
intermediate value based on observations ranging from 0.1 to 2.4 mg P/mg chl a-day;
Horneretal., 1983; Seeley, 1986);
average stream width (m); and
nuisance threshold biomass (150 mg chl aim2).
When this equation is applied to the Spokane River, the results indicate that the stream length for which the
biomass might exceed the nuisance threshold is proportional to the amount that influent SRP exceeds 1 to 4 ji/g/L.
This is an example development of a nutrient indicator for a river expressed in terms of stream length impaired by
nuisance periphyton. Some of the more traditional indicators identified above (i.e., SRP concentration and
periphyton biomass) serve as intermediates to the determination of this indicator.
Chlorophyll a
Chlorophyll a, the dominant pigment in algal cells, is
fairly easy to measure and is a valuable surrogate for
algal biomass (Carlson, 1980; Watson, et al., 1992).
Chlorophyll a is desirable as an indicator because algae
are either the direct (e.g., nuisance algal blooms) or
indirect (e.g., high/low dissolved oxygen and pH and
high turbidity) cause of most problems related to
excessive nutrient enrichment. Both seasonal mean and
instantaneous maximum concentrations can be used to
determine impairments, and many monitoring programs
already include measurements for chlorophyll a.
Several states have adopted chlorophyll a concentrations
as standards or as goals for lake quality. Oregon has set
an endpoint of 10 pg/L for natural lakes that thermally
stratify and 15 pg/L for natural lakes that do not
thermally stratify, to identify waterbodies where
phytoplankton may impair uses (NALMS, 1992).
Similarly, North Carolina uses a target of 40 pg/L for
warm waters and 15 pg/L for cold waters (NALMS,
1992). On the regional level, Raschke (1994) has
proposed a mean growing-season limit of 15 pg/L for
water supply impoundments in the southeastern United
States and a value of 25 pg/L for waterbodies primarily
used for other purposes (e.g., viewing pleasure, safe
swimming, fishing, boating).
First Edition: November 1999
4-5
-------
Identification of Water Quality Indicators and Target
Chlorophyll a might not be an appropriate indicator
where use impairment is more closely related to
excessive macrophyte growth. The relationship between
nutrient concentrations and chlorophyll response also
may be highly variable and difficult to predict. Laws
and Chalup (1990), for example, have shown that
growth rate and chlorophyll a respond differently under
nutrient-limited conditions and under nutrient-saturated
(light-limited) conditions.
Periphyton biomass
Periphyton biomass directly measures the biomass of
attached algae. Periphyton biomass can be measured
either qualitatively (e.g., no visible growths on hand-
held stones) or quantitatively (e.g., ash-free dry weight
or milligrams of chlorophyll a per square meter) (Quinn,
1991). The primary advantage of this measurement is
that it directly reflects the water quality characteristic
that impairs use. In this way, biomass indicators force
managers to focus on all of the factors that contribute to
periphyton growth, instead of relying only on nutrient
controls to provide relief. One disadvantage associated
with using periphyton biomass as an indicator is the cost
and difficulty associated with its monitoring. Further,
developing predictive relationships between nutrient
load and periphyton biomass can present considerable
challenges because well-known and validated water
Indicators and Target Values in the Clark Fork River, Montana
Dense mats of filamentous algae and heavy growths of diatom algae have caused problems recently with the irrigation and
recreational uses of the Clark Fork River in western Montana. Segments of the river have been placed on the state's list of
impaired waters, and several studies have been conducted to determine the extent and magnitude of the excessive algae
production and to develop nutrient level and biological response criteria (Ingman, 1992).
As a preliminary step toward TMDL development, nutrient assessment indicators for the Clark Fork River were developed by
the Nutrient Target Subcommittee of the Tri-State Implementation Council. Because Montana does not have statewide
numeric criteria for nutrients, development of these indicators was based on a review of academic studies, literature values,
and public input. The subcommittee selected a summer mean algal biomass chlorophyll a concentration of 100 mg/m2 as
distinguishing between the impaired and unimpaired condition of the river.
To determine the nutrient concentrations that would keep algal growths below this level, the subcommittee relied on several
sources of information:
• The University of Montana conducted a series of experiments to measure water quality response to various concentrations
of nitrogen and phosphorus (Watson et al., 1990). Artificial stream channels were constructed and fed with Clark Fork
River water that was spiked with various concentrations of each nutrient. The response of algal growth rates and of
maximum standing crops to changes in nutrient levels was carefully measured. The experimental findings indicated that
levels of attached diatom algae in the middle of the Clark Fork River would be reduced if concentrations of soluble reactive
phosphorus were held below 30 jug/L and concentrations of soluble nitrogen levels were held below 250 jug/L
• Clark Fork water quality measurements for total nitrogen, total phosphorus, and chlorophyll a were entered into a
regression model that contained data from more than 200 distinct river sites (Dodds and Smith, 1995). The results
indicated that if summer mean total nitrogen concentrations were held below 350 jug/L, chlorophyll a concentrations should
not exceed 100 mg/m2 in most areas of the Clark Fork. The corresponding summer mean total phosphorus concentration
recommended by this regression approach was 45.5 jug/L
• Another method of estimating the required nutrient concentrations was to set them equal to nutrient concentrations in
reaches of the Clark Fork where algae are not a frequent problem. Based on this "reference site" technique, the proposed
summer target levels were 6 ji/g/L or less for soluble phosphorus and 30 ji/g/L or less for soluble nitrogen (Ingman, 1992).
These concentration ranges are typical of relatively unimpaired portions of the Clark Fork during July through September.
Based on the information from these various sources, the subcommittee adopted nutrient target values of 300 ji/g/L total
nitrogen, 20 jug/L total phosphorus upstream from Missoula, and 39 jug/L total phosphorus downstream from Missoula. The
subcommittee said that one reason for choosing these relatively conservative target values was to explicitly account for a
margin of safety.
The subcommittee also noted in its report that, although the management focus would be on the total form of these nutrients,
both total and soluble forms should be monitored to give the best picture of bioavailability and of the breakdown between
point and nonpoint sources.
4-6
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
quality models are not available. Relying on periphyton
biomass also may neglect the important role of emergent
macrophytes in stream nutrient cycling.
Transparency
Because of its simplicity and low cost, Secchi depth is
likely the most widely used surrogate for estimating
algal biomass and, subsequently, trophic state (Michaud,
1991). It is, however, a much more indirect measure and
subject to interferences from a variety of sources (e.g.,
fine sediment). Secchi depth correlates to chlorophyll a
concentrations (Rast and Lee, 1978) and is a particularly
important measure because the public easily perceives
water clarity. Secchi depth might be a reliable indicator
of the trophic state of a waterbody, provided that its
water clarity depends primarily on algal biomass (i.e.,
the amounts of inorganic turbidity and color present in
the water column are negligible).
Macrophyte coverage or density
Newbry et al. (1981) recommend using macrophyte
coverage percentage as a potential nutrient enrichment
indicator in lakes and reservoirs. Specifically, for the
portion of a waterbody with a depth of 2 meters or less,
the indicator would be the percentage of the waterbody
impaired by macrophyte growth during peak recreation
use. Other researchers have suggested a similar
approach, but a somewhat deeper cutoff point (Porcella,
1989). This indicator might be particularly appropriate
for those shallow lakes and reservoirs where users are
aware of and sensitive to changes in the abundance and
distribution of macrophytes (e.g., the southeastern
United States). One confounding issue related to
macrophyte density is the positive relationship between
increasing water clarity and the extent of macrophyte
beds (Quinn, 1991).
Biological indicators
Several states have used biological indicators to assess
water quality. For example, the Ohio EPA uses the
index of biotic integrity (IBI) to assess the aquatic life in
its rivers and streams (Hughes et al., 1992), and many
states use fish yield to indicate the health of their
fisheries. Proposed biological indicators have attempted
to incorporate information on fish, benthic invertebrates,
zooplankton assemblages, algae, macrophytes, etc.
EPA's Rapid Bioassessment Protocols (Plafkin et al,
1989) also are used frequently as a cost-effective
approach to evaluating whether a stream is supporting
aquatic life uses. An advantage of using biological
indicators is that they are not as subject to time
variability as are chemical pollutants (NALMS, 1992).
The difficulty in quantifying the linkage between
biological indicators and source loadings, however, can
present problems for their use in developing TMDLs.
Most importantly, their use in developing TMDLs
requires (1) knowledge of the appropriate reference or
unimpaired conditions and (2) ability to discriminate
between effects of nutrient enrichment and other factors,
including physical habitat condition, on biotic integrity.
It also may be difficult to establish a target value for a
biological indicator representing impairment in a stream.
Algal biomass above nuisance levels often can produce
wide diel swings in pH. For example, pH levels in
gravel-bottom rivers with large periphyton biomass can
be as high as 10, which severely restricts the ability of
stream organisms to function normally. pH is very
inexpensive and easy to monitor and can be sampled by
nontechnical personnel. Because aquatic organisms are
most sensitive to extreme pH levels rather than daily
means, monitoring should include afternoon hours when
pH is likely to be at its maximum. A difficulty
associated with this parameter is that factors other than
eutrophication (e.g., turbulence, light, temperature)
might affect water acidity.
Nutrient ratios
Ratios of the summenwinter concentration of soluble
nutrients might indicate the relative intensity of algal
activity in a particular stream. The intensity of algal
activity could be estimated by evaluating the fraction of
the nutrient supply (winter, nongrowth period) assumed
to be removed and incorporated by algae (winter-
summer soluble concentration). It should be noted,
however, that the use of this approach assumes that
ground water and upstream inflow concentrations are
constant between summer and winter (which might not
be a valid assumption for many watersheds). Ratios of
total to soluble nutrients in winter, compared with
summer, would provide a similar index of algal use, but
would account for changing inflow concentrations (i.e.,
First Edition: November 1999
4-7
-------
Identification of Water Quality Indicators and Target
of total nutrients). Such indicators have not yet been
tested in streams and therefore would require some
evaluation.
Others
Numerous other water quality measurements potentially
could serve as nutrient overenrichment indicators. Some
of these might be appropriate for certain regions or for
specific waterbodies with unique considerations. Many
of the following measurements are not ideal indicators
because they describe conditions that might be unrelated
to nutrient loading. They might best be used in
combination with some of the other measurements
described previously.
• Odor and taste indicators
• Total and volatile suspended solids concentrations
• Dissolved organic material
• Extent of submerged aquatic vegetation
• Benthic community metabolism
• Sediment composition (organics, size fraction,
nutrients, profile, sediment fluxes)
• Secondary production (meiofauna,
macroinvertebrates, fish)
• Production and respiration
• Aesthetics (foam, scum)
Recommendation: For many nutrient TMDLs, it might
be appropriate to have an indicator directly tied to
nutrient loadings (e.g., phosphorus or nitrogen) and one
or more indicators that more directly relate to the
designated uses (e.g., algal biomass or dissolved oxygen
concentration). Moreover, for large watersheds with
complex problems, it might be useful to choose several
indicators to gauge water quality. A "nested approach"
of selecting certain, perhaps more costly indicators for
critical subwatersheds and of using more easily
monitored indicators in other subwatersheds is one way
to address this dilemma.
Although selecting the indicator or indicators is
necessarily a site-specific decision, Figure 4-2 provides
some guidance for which of various indicators might be
most appropriate for different types of waterbodies and
several representative designated uses. Note that
phosphorus and nitrogen are included in each case
because of their primary role in stimulating nuisance
plant growth. Because indicator selection requires a
careful consideration of the unique mix of issues,
opportunities, and characteristics present in each
watershed, TMDL developers are encouraged to use this
information as a starting point and to consult key
references and local experts in the final selection of
indicators.
4. What target value will be used and how does
it compare to existing conditions?
For each indicator used in developing a nutrient TMDL,
a desired or target condition must be established to
provide measurable environmental management goals
and a clear linkage to attaining water quality standards.
As mentioned previously, target values for some
indicators already will be established directly through
numerical criteria in water quality standards. Otherwise,
various mechanisms determine an appropriate target
value, including comparing the conditions in the listed
water to those at an appropriate reference site,
conducting user surveys, using an existing trophic
classification system, and comparing to literature values.
Note that all of these methods require some
interpretation of what constitutes an impaired versus an
unimpaired condition. In many cases, this determination
is subjective. For example, different persons might have
different opinions of which chlorophyll a concentration
is associated with the recreational impairment of a
reservoir. Regardless of the method used to establish
the indicator value, it is important to solicit comment
from as many stakeholders as possible, including the
public and regulatory agencies. Stakeholder comment is
an important component of the Watershed Approach
(USEPA, 1996b), and it can be particularly useful for
interpreting narrative standards. For instance, in a
stream designated for support of a cold-water fishery, a
biological indicator aimed at assessing the health and
diversity of the fish population could be refined into a
quantitative target based on stakeholder consensus as to
what constitutes a sufficiently viable fishery.
Factors to consider in establishing target
conditions
Degree of experience applying the indicator(s) in the area
or in similar settings
Where local experience has been gained in applying
nutrient indicators, it is often possible to identify target
4-8
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Nutrient
Impaired
Waterbody
Lake or Reservoir*
River or Stream
Most
Sensitive
Designated
Use
Most
Sensitive
Designated
Use
Aquatic Life
Recreation
Water Supply
Aquatic Life
Recreation
Water Supply
1. Dissolved Oxygen
2. Biological Indicators
3. Transparency
4. Total Phosphorus
5. Total Nitrogen, DIN
1. Chlorophyll a 1. Chlorophyll a
2. Macrophyte Coverage 2. Transparency
3. Transparency 3. Total Dissolved Solids
4. Total Phosphorus 4. Total Phosphorus
5. Total Nitrogen, DIN 5. Total Nitrogen, DIN
1. Biological Indicators
2. Periphyton Biomass
3. Dissolved Oxygen
4. pH
5. Soluble Reactive P
6. Total Nitrogen, DIN
1. Periphyton Biomass 1. Periphyton Biomass
2. Transparency
3. Soluble Reactive P
4. Total Nitrogen, DIN
2. Total Dissolved Solids
3. Soluble Reactive P
4. Total Nitrogen, DIN
Includes plankton-dominated rivers
Figure 4-2. Guidelines for selecting indicators based on waterbody type and several representative designated uses
conditions through analysis of historical conditions or
reference stream conditions in relatively high quality
parts of the watershed. Where less local or directly
analogous experience is available, it might be
appropriate to establish more conservative targets.
Variability of conditions in the watershed
The larger the study area for the TMDL and the more
heterogeneous the waterbody characteristics in the
watershed, the more important it will be to consider
establishing multiple target conditions for the TMDL. It
may be useful to stratify the targets based on spatial
distinctions (e.g., fast-flowing versus slow-moving
reaches, main stems vs. tributaries). Similarly, it may be
appropriate to account for seasonal variations in setting
target conditions (e.g., require that a stricter target
condition apply to peak growing periods).
Margin of safety considerations
Factors to consider in defining the margin of safety
include the expected accuracy or reliability of the
indicator for the designated use of concern and the
degree to which the use is impaired.
Comparison to reference sites
One method for establishing target values is through a
comparison to reference sites. This is typically done by
comparing data collected from the impaired site with
data from one or more similar sites not impaired or
"least impacted." It might also include comparing
current data from the impaired site to historic data from
the site before the impairment. Conditions at the
reference site (e.g., nutrient concentrations) can be
interpreted as approximate target values for the TMDL.
A disadvantage to this approach is that it might not
First Edition: November 1999
4-9
-------
Identification of Water Quality Indicators and Target
always establish the actual conditions beyond which
impairment is expected. Reference sites may represent
the completely unaffected state, a relatively unaffected
state, or increasing degrees of existing impact, as
deemed appropriate. Selection of an appropriate
reference site should reflect a clear understanding of the
overall system of which the receiving water is a part.
User surveys
Minnesota and Vermont have surveyed users to
determine indicator target values, especially in lakes and
reservoirs (Heiskary, 1989; Heiskary and Wilson, 1989;
Smeltzer and Heiskary, 1990). This approach is
especially useful when the impaired designated use of
the waterbody is recreation. Survey results can correlate
with simultaneous water quality measurements to
establish a range of values between acceptable and
unacceptable conditions. If 90 percent of those surveyed
agree that their aesthetic enjoyment of a lake is impaired
at chlorophyll a concentrations exceeding 30 pg/L, this
value represents a possible biomass target value. The
survey approach recognizes that the overall water
quality of a waterbody is highly subjective and may vary
considerably by region or user group.
Comparison to an existing classification system
A third means of identifying site-specific target values
for nutrient TMDLs is through comparison with an
existing classification system. The Carlson trophic
status classification system is a good example of an
existing classification systems for lakes (see box on
next page).
For the development of site-specific nutrient criteria, the
trophic classification system can be used to evaluate the
condition of the waterbody (trophic status), determine
the water quality goal (e.g., oligotrophic), and help
determine the appropriate nutrient target value. Several
approaches have been taken to develop a trophic state
classification system based on the value of certain
commonly measured water quality parameters (e.g., total
phosphorus, chlorophyll a, Secchi depth, and
hypolimnetic oxygen depletion) and general
limnological relationships. Ideally, observed water
quality values can be compared to these established
classification systems to determine the trophic status of
any particular waterbody. (This comparison assumes, of
User Surveys in Lake Champlain, Vermont
In 1991 Vermont established numeric eutrophication
criteria for Lake Champlain based on the
relationship between a variety of trophic parameters
and user perceptions of lake aesthetics and
recreational viability (Smeltzer, 1992). This example
illustrates one way of assessing use attainment of
narrative standards and a method for setting target
values once an indicator has been chosen.
The Vermont Department of Environmental
Conservation (VDEC) supervises a volunteer
monitoring program of Lake Champlain. Since
1987, the volunteers participating in the program
have completed a user survey form each time a
water quality sample is taken. The frequency
distributions produced from the surveys and
associated water quality data were analyzed to
establish quantitative relationships between the
trophic parameters and user responses. This
process includes two steps. First, the survey data
are used to define "algal nuisance" in terms of
instantaneous values for the trophic parameters.
The second step is to analyze the distribution of
water quality data over time and choose a mean
water quality value that produces an acceptable
frequency of the instantaneous value.
Using an algorithm developed by Walker (1985),
VDEC considered the statistical distribution of
measurements over time to derive seasonal mean
water quality values corresponding to an acceptably
low frequency occurrence of nuisance conditions.
The Vermont Water Resources Board used this
methodology to establish a total phosphorus
criterion of 14 ji/g/L for portions of Lake Champlain.
This result corresponds to a 1 percent frequency of
occurrence of a "moderate" nuisance condition.
course, that trophic status can link directly to use
impairment. For instance, many reservoirs in the
southeastern United States are naturally borderline
eutrophic.) One such classification system is in
Table 4-2. As Vollenweider and Kerekes (1980)
observed, these values are subject to overlap between
different categories and, therefore, the parameters serve
more as relative indicators than as discrete descriptors.
4-10
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Carlson Trophic Status Index
A frequently used bio mass-related trophic status index is that developed by Carlson (1977). Carlson's trophic status
index (TSI) uses Secchi depth (SD), chlorophyll a (Chi), and total phosphorus (TP), each producing an independent
measure of trophic state. Index values range from approximately 0 (ultraoligotrophic) to 100 (hypereutrophic). The
index is scaled so that TSI = 0 represents a Secchi transparency of 64 m. Each halving of transparency represents
an increase of 10 TSI units. For example, a TSI of 50 represents a transparency of 2 m, the approximate division
between oligotrophic and eutrophic lakes (Olem and Flock, 1990). A TSI is calculated from each of Secchi depth,
chlorophyll concentration, and phosphorus concentration (Carlson, 1977; Carlson and Simpson, 1996):
TSI (Chi) = 30.6+ 9.81 In (Chi)
TSI (TP) = 4.15+ 14.42 In (TP)
TSI (SD) = 60-14.41 In(SD)
Trophic state indices can be used to infer trophic state of a lake and whether algal growth is nutrient or light limited.
If the three indices are approximately equal, then phosphorus limits algal growth. If the three are not equal, then other
interpretations exist (see related box). The following classification can be used to interpret the TSI:
TSI < 40
35 < TSI < 45
TSI > 45
TSI > 60
most oligotrophic lakes
mesotrophic lakes
eutrophic lakes
hypertrophic lakes
A trophic status index also has been developed for total nitrogen (TN) (Kratzer and Brezonik, 1981; Carlson, 1992):
TSI (TN) = 54.45 + 14.43 In (TN)
When considering the results of TSI calculations, one should recall the assumptions on which the carbon formulae
are based: 1) Secchi transparency is a function of phytoplankton biomass; 2) phosphorus is the factor limiting algal
growth; and 3) total phosphorus concentration directly correlates with algal biomass (Davenport, 1983)
For a more complete discussion of trophic state indices and their interpretation, see Carlson (1992) and Carlson and
Simpson (1996).
Table 4-2. Trophic status classification (for lakes) by Vollenweider and Kerekes (1980
Water Quality Parameter
Total phosphorus
Total nitrogen
Chlorophyll a
Peak chlorophyll a
Secchi depth (m)
Oligotrophic
mean
8
660
1.7
4.2
9.9
range (n)
3-18(21)
310-1,600
0.3-4.5 (22)
1.3-11 (16)
5.4-28(13)
Mesotrophic
mean
27
750
4.7
16
4.2
range (n)
11-96(19)
360-1 ,400
3-11 (16)
5-50(12)
1.5-8.1 (20)
Eutrophic
mean
84
1900
14
43
2.4
range (n)
16-390(71)
390-6,100
2.7-78 (70)
1 0-280 (46)
0.8-7.0 (70)
Note: Units are ji/g/L (or mg/m3), except for Secchi depth; means are geometric annual means (Iog10), except for
peak chlorophyll a.
First Edition: November 1999
4-11
-------
Identification of Water Quality Indicators and Target
Table 4-3. A trophic status classification based on water quality parameters
Water Quality
Total P (fjg/L)
Chlorophyll a (ji/g/L)
Secchi disc depth (m)
Hypolimnetic oxygen (% of
saturation)
Oligotrophic
< 10
<4
4
>80
Mesotrophic
10-20
4-10
2-4
10-80
Eutrophic
>20
>10
<2
<10
Source
USEPA(1974)
USEPA(1974)
USEPA(1974)
USEPA(1974)
Source: Adapted from Novotny and Olem, 1994.
Vollenweider (1968) and Sawyer (1947) categorized
trophic status according to phosphorus concentration.
Lakes with phosphorus concentrations below 10 pg/L
are classified as Oligotrophic, phosphorus concentrations
between 10 and 20 pg/L are indicative of mesotrophic
lakes, and eutrophic lakes have phosphorus
concentrations exceeding 20 pg/L. This classification is
consistent with the data from the National
Eutrophication Survey (USEPA, 1974), which also used
several other parameters in the classification system
(Table 4-3). Note that much of the work conducted on
trophic status classification systems has focused on
northern, temperate lakes. Applying these systems to
lakes in other regions, rivers, streams, or reservoirs must
therefore be done carefully. Although the ranges
identified in Tables 4-2 and 4-3 can serve as a starting
point, analysts should investigate the availability of local
studies. Raschke (1994), for example, gathered data for
17 small southeastern piedmont impoundments to
establish a management relationship between algal
bloom frequency and seasonal mean chlorophyll a
concentrations. Based on the bloom frequency analysis,
literature values, and experience, Raschke proposed a
mean growing season limit of < 15 /ig/L chlorophyll a
for attaining drinking water supply use in small
southeastern impoundments. For other uses, such as
fishing and swimming, a mean growing season limit of
<25 /ig/L is recommended1.
Literature values
Several authors have suggested potential target values
for nutrient indicators. Welch et al. (1988),
summarizing 22 studies in U.S. and Swedish streams,
suggest that "a biomass range of 100-150 mg
chlorophyll a/m2 may represent a critical level for an
aesthetic nuisance." Moreover, EPA's 1986 criterion
document (USEPA, 1986a) specifies target values for
nitrate when it relates to toxic effects on fish. The
report concludes that nitrate-nitrogen concentrations at
or below 90 mg/L should protect warm-water fishes,
while concentrations at or below 0.06 mg/L should
protect salmonid fish. (Note that the guideline for
salmonids is based on very limited data, and many
natural salmonid waters have nitrate concentrations
It should be noted, however, that these limits are not achievable in
many southeastern United States impoundments, and a target value
will need to be evaluated on a site-specific basis.
Interpretations of deviations from typical
conditions associated with TSI values
TSI Relationships Possible Interpretation
TSI (CHL) = TSI (SD)
TSI (CHL) > TSI (SD)
TSI (TP) = TSI (SD) >
TSI (CHL)
TSI (SD) = TSI (CHL)
> TSI (TP)
TSI (TP) > TSI (CHL)
= TSI (SD)
Algae dominate light
attenuation
Large particulates, such as
Aphanizomenon flakes,
dominate
Nonalgal particulate or
dissolved color dominate light
attenuation
Phosphorus limits algal
biomass (TN/TP ratio greater
than 33:1)
Zooplankton grazing,
nitrogen, or some factor other
than phosphorus limits algal
biomass
4-12
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
exceeding this level.) This document also suggests as a
guideline to prevent nuisance algal growths that total
phosphates as phosphorus should not exceed 0.1 mg/L in
any stream or other flowing water or exceed 0.05 mg/L
in any stream at the point where it enters a lake or
reservoir.
Golterman (1975) suggests that, in general,
eutrophication may occur in surface waters that have
nitrate-nitrogen concentrations above 0.3 mg/L and
phosphate-phosphorus concentrations above 0.02 mg/L.
Experiments in phosphorus-limited flowing systems
suggest that very low soluble reactive phosphorus (SRP)
concentrations may be required to avoid periphytic
biomass at nuisance levels. For example, less than 1
pg/L SRP was recommended for the Spokane River
(Welch et al., 1989), and less than 25 pg/L SRP from
experiments in laboratory channels (Horner et al., 1983).
Best professional judgment
It is sometimes infeasible to develop numerical targets
based on the methods described above because
inadequate information is available or relationships
between the designated uses and the selected indicators
are not well understood. In this case, it might be
feasible to develop target values based on the best
professional judgment of resource professionals
involved in TMDL development. To ensure that these
targets are defensible, analysts are advised to:
• Consult with several experts with local experience
rather than relying on a single opinion.
• Thoroughly document the thinking underlying the
target, including assumptions, related experience, or
other factors considered in identifying the targets.
• Remember that targets must be set at levels believed
to result in full support of the impaired designated
uses (i.e., water quality "improvements" may be
inadequate).
Recommendation: The target value(s) for the chosen
indicator(s) can be established using a variety of
approaches. The most technically defensible approach
should consider the water quality standard, the available
data, and the current understanding of the system.
5. What changes does the proposed rule speak
to?
On August 23, 1999, EPA published proposed rules that
specify that approvable TMDLs must include at a
minimum ten elements. Within the water quality
indicators and target values step, an approvable TMDL
will need to include the following information:
1. Identification of the pollutant for which the
TMDL is being established and quantification of
the maximum pollutant load that may be present
in the waterbody and still ensure attainment and
maintenance of water quality standards; and
2. Identification of the amount or degree by which
the current pollutant load in the waterbody
deviates from the pollutant load needed to attain
or maintain water quality standards.
RECOMMENDATIONS FOR SELECTING WATER
QUALITY INDICATORS AND TARGET VALUES
• If available, the numeric standard should be used as
the TMDL indicator and target value.
• If numerical criteria are not available, or if
supplemental indicators are needed, the TMDL
developer should base selection on both scientific or
technical considerations and practicality and cost
considerations. The selection must necessarily
consider site-specific factors, although Figure 4-2
provides general guidelines.
• The target value for the chosen indicator can be
based on: comparison to similar but unimpaired
waters; user surveys; empirical data summarized in
classification systems; literature values; or best
professional judgment.
RECOMMENDED READING
(Note that the full list of references for this section is at
the end of the document.)
• Carlson, R., and J. Simpson. 1996. A coordinator's
guide to volunteer lake monitoring methods. North
American Lake Management Society and the
Educational Foundation of America.
First Edition: November 1999
4-13
-------
Identification of Water Quality Indicators and Target
Duda, A.M., M.L. Iwanski, R.J. Johnson, and J.A.
Jaksch. 1987. Numerical standards for managing
lake and reservoir water quality. Lake and
Reservoir Management 3:1-21.
NALMS,1992. Developing eutrophication standards
for lakes and reservoirs. A report prepared by the
Lake Standards Subcommittee, May 1992. North
American Lake Management Society, Alachua, FL.
USEPA. 1998a. National strategy for the
development of regional nutrient criteria. EPA 822-
R-98-002. U.S. Environmental Protection Agency,
Office of Water, Washington, DC.
4-14
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Source Assessment
Objective: Characterize the type, magnitude, and
location of sources of nutrient loading to the
waterbody.
Procedure: Compile an inventory of all possible
sources of nutrients to the waterbody. Sources may
be identified through assessment of maps, data,
reports, or field surveys. It is likely that a
combination of techniques will be needed,
depending on the complexity of the source loading
and watershed delivery processes. After compiling
an inventory, use monitoring, statistical analysis,
modeling, or a combination of methods to determine
the relative magnitude of source loadings, focusing
on the primary and controllable sources of nutrients.
OVERVIEW
The source assessment is needed to evaluate the
type, magnitude, timing, and location of loading to
an impaired waterbody. It further describes the
sources initially identified during the problem
identification. The source assessment determines
nutrient inputs, measured as loads or concentrations,
that will support the formulation of the load
allocation and the wasteload allocation of the
TMDL. Several factors should be considered in
conducting the source assessment. These factors
include identifying the various types of sources
(e.g., point, nonpoint, background, atmospheric), the
relative location and magnitude of loads from the
sources, the transport mechanisms of concern (e.g,
runoff, infiltration), and the time scale of loading to
the waterbody (i.e., duration and frequency of
nutrient discharge to receiving waters).
The evaluation of loading typically uses a variety of
techniques, including relying on existing monitoring
data, doing simple calculations, spreadsheet
analysis using empirical methods, or a range of
computer modeling systems. The selection of the
appropriate technique is an outgrowth of the
problem identification and watershed
characterization performed during the initial phase
of TMDL development.
A TMDL should include an evaluation of all the
significant sources contributing to the nutrient loading of the
waterbody. The detail of the assessment will vary, however,
depending on the overall approach best suited to the site-
specific conditions. The selection of the appropriate method
for estimating loads should be based on the complexity of
the problem, time constraints, the availability of resources
and monitoring data, and the management objectives under
consideration. Generally, it is advantageous to select the
simplest method that addresses the questions at hand, uses
existing monitoring information, and considers the available
resources and time constraints for completing the TMDL.
This section of the protocol describes various types of
sources, identifies procedures for characterizing loadings,
and introduces a process for selecting a source assessment
technique.
QUESTIONS TO CONSIDER FOR THE SOURCE
ASSESSMENT
1. What sources are contributing to the problem and
how can they best be characterized?
Individual nutrient sources in the watershed should be
inventoried to develop a targeted approach for estimating
and eventually allocating loads. The inventory should
include an evaluation of the processes, pathways, and
potential effects that the loads might have on the waterbody
and the TMDL indicator or indicators that have been
Key Questions to Consider for
the Source Assessment
1. What sources are contributing to the problem and
how can they best be characterized?
2. How should sources be grouped to facilitate load
estimation and TMDL allocation?
3. What are the primary processes or delivery
mechanisms from the various source categories
under consideration?
4. What is the appropriate level of spatial and
temporal detail for determination of the source
loading?
5. What analysis techniques are appropriate for
estimating the source loads?
6. What changes does the proposed rule speak to?
First Edition: November 1999
5-1
-------
Source Assessment
selected. The goal of the inventory is to understand
both the individual and aggregate effects of the
sources.
A source inventory is performed by dividing the
sources in the watershed into manageable
categories, or groupings, that can be further
examined to determine nutrient delivery
mechanisms. A first step is to divide the watershed
into broad land use categories that are known to
generate nutrients, such as agricultural or industrial
land uses. Specific operations within each broad
category should also be identified. For example,
agricultural land uses can be subdivided by type of
productive livestock or crop then further subdivided
such as cattle farming, dairy production, row crops,
etc. In some circumstances it might be warranted to
further subdivide these operations into specific
waste generating activities such as manure
generation. Dairy production, for example, would
include manure storage, spreading, and milking
parlor wash water. Sources of information that can
be used to identify and document these activities
include land use maps, aerial photographs, local
conservation organizations, tax maps, field surveys,
and point source discharge permits.
The initial inventory can be entered into a table or
database for more effective management. The
inventory also can be mapped or summarized at the
subwatershed level to determine the resolution and
scale of analysis that should be conducted. The
depth (or detail) of the inventory is a function of the
size of the watershed, the magnitude of the
impairment, the variability of the sources in the
watershed, and other specific considerations (e.g.,
time and resources available).
Once the sources within the watershed have been
inventoried and mapped, each activity should be
evaluated to determine its individual pollutant
generating mechanisms, processes, and potential
magnitude. This evaluation will include identifying
the primary mechanisms of transmission
(atmospheric deposition, erosion, snowmelt, ground
water, etc.), the variability of loadings (steady,
rainfall or snowmelt related, seasonal, etc.), and the
significance of biochemical and physical processes
(nitrification, denitrification, adsorption, etc.).
Figure 5-1 identifies several common sources and pathways
associated with nutrient loading to a reservoir.
Recommendation: Develop a comprehensive list of the
potential nutrient sources to the waterbody. Use the list of
potential sources and the watershed inventory to identify
actual sources and to develop a plan for estimating their
magnitude. Use GIS or maps to document the location of
sources and the processes important for delivery to the
waterbody.
2. How should sources be grouped to facilitate load
estimation and TMDL allocation?
The grouping of the various source categories should be
carefully considered during the source assessment stage of
TMDL development. The appropriate selection of the
various loading categories will facilitate completion of the
subsequent analytical and allocation steps. The grouping of
source categories can be by type, ownership, subwatershed,
distance from the stream, etc. The source category
groupings should consider the relative magnitude of the
loads, potential management options, and economic
considerations. The sources should be grouped to highlight a
recognizable link between the source categories and the
allocation of loads.
Another factor to consider when grouping sources is the
degree to which various sources contribute bioavailable or
other forms of a nutrient. This is especially important for
phosphorus because some sources might contribute largely
nonbioavailable phosphorus and therefore a reduction in
their loadings will not be as significant as would a
comparable reduction
in loads of
bioavailable
phosphorus. As
mentioned in Section
1, this might be a
significant issue in
rivers because the
shorter residence times
(compared to lakes) do
not allow for effective
decomposition of
organic phosphorus.
Similarly, loads of
highly refractory
Factors to Consider for
Grouping Sources
Delivery mechanisms
Type and location of sources
relative to waterbody of
concern
Management options under
consideration
Social, political, and economic
factors
Physical characteristics of the
watershed including slope,
geology, soils, and drainage
network
5-2
First Edition: November 1999
-------
Scale
Assumptions
Phosphorus limited
Reservoir indicator is chlorophyll a
Annual averaging period
Edge
of Field
Cropland
Erosion
Pasture
Washoff
Agriculture
Impervious Area
Buildup/Washoff
|
Pervious Area
Erosion
|
Urban
1
Direct Inputs
Septic Systems
Land-Based
Point Sources
Stream/River
Reservoir
Instream Phosphorus
Transport
n .
Reservoir
Analytic
Technique
Loading Rate
Models (such as
screening method)
Used to Estimate
Average Annual Load
Estimates of
to River Groun
i
d Water
' >
i i
from Literature/
Monitoring
f
Delivery Estimated
From Monitoring
Empirical Model
Relating Phosphorus
Concentration to
Chlorophyll a
Figure 5-1. Common mechanisms and sources associated with nutrient loading to a reservoir.
organic nitrogen may need to be weighted
differently from loads of biovailable inorganic
nitrogen.
3. What are the primary processes or delivery
mechanisms from the various source
categories under consideration?
Various mechanisms transmit nutrients to receiving
waters. The following section provides a
description of the primary pathways of nutrient
loading, with brief descriptions of key mechanisms
or factors to consider when estimating loads.
Surface water
Surface water runoff occurs when the sources of
contaminants (such as manure or chemicals) directly
wash into receiving waters or when sediment
particles absorb contaminants and then transport
them during storm or snowmelt events. The types of
soils and vegetation directly influence the absorption rate of
nutrients into the soils. Land management practices, such as
grazing patterns and no-till planting, also have effects on the
rate of erosion and nutrient concentration (Doran et al,
1981). Enrichment rates of nutrients in soils that wash into
receiving waters during storm or snowmelt events can be
based on potency factors of the parent soils (Novotny and
Chesters, 1981). Table 5-1 provides example literature
values for dissolved nutrients in agricultural runoff.
Ground water
Ground water contamination from nutrients can occur from
various sources, including septic systems, fertilizer
application, animal waste, waste-lagoon sludge, and soil
mineralization (Boyce et al., 1976; Kreitler, 1975; Moody,
1990; Spalding and Exner, 1991; cited in Gosselin et al.,
1997). Estimating loading from septic systems is typically
conducted by using a per-capita nutrient load estimate from
literature values and a characterization of the number and
location of regional septic treatment systems. Additionally,
some knowledge of the local soil's ability to retain nitrogen
First Edition: November 1999
5-3
-------
Source Assessment
Table 5-1. Example literature values for dissolved nutrients in agricultural runoff
Land Use
Fallow3
Corna
Small grainsa
Haya
Pasture"
Barnyardsb
Nitrogen (nig/L)
2.6
2.9
1.8
2.8
3.0
29.3
Phosphorus (nig/L)
0.10
0.26
0.30
0.15
0.25
5.10
Snowmelt runoff from manured landc
Corn
Small grains
Hay
12.2
25.0
36.0
1.9
5.0
8.7
TJornbush et al. (1974); "Edwards et al. (1972); cGilbertson et al. (1979).
and phosphorus is used to estimate how much of the
per-capita load reaches surface water sources
through ground water transport. In the absence of
site-specific monitoring information, per-capita
nutrient loading and soil retention rates can be
estimated from literature values and professional
judgment.
Quantifying loads from fertilizer application, animal
waste, waste-lagoon sludge, and soil mineralization
through ground water transport works best using
site-specific monitoring information. Without
monitoring information, however, literature surveys
and professional judgment may be used to
characterize loading from these sources. Because of
the complex relationship between factors
contributing to ground water concentrations of
nutrients, literature values should be used
cautiously. Factors influencing nutrient levels in
ground water can include land use, characteristics of
ground water flow, local soil quality and conditions,
landscape characteristics, well construction, and
distance of point sources from the waterbody.
Atmospheric deposition
Inputs of nutrients in rainfall may be a significant
source of loading in larger lake and reservoir
systems. Rainfall inputs can be particularly important when
the waterbody is large compared to the watershed area
drained. Quantifying rainfall sources of nutrients involves
estimating average seasonal rainfall, the surface area of the
waterbody of concern, and estimates of nutrient
concentration in the rainfall. Nutrient concentrations in
rainfall can be measured through monitoring or by using
literature values. Dryfall, deposited from dry-weather
airborne organic material, also may be an important source
of loading. Dryfall inputs may vary with local land uses
along the shore, so if dryfall monitoring is conducted,
several site-specific samples should be obtained (USEPA,
1983). Dryfall sources of nutrient loading also may be
quantified through monitoring information or from literature
values.
Sediment release (phosphorus)
Under certain conditions, bottom sediments can be
important sources of phosphorus to the overlying waters of
lakes and impoundments, particularly if the lake or
impoundment is shallow or has an anaerobic hypolimnium
(Chapra, 1997). Phosphorus flux from sediment deposits is
strongly affected by sediment composition and oxygen
levels in the water column; sediment release can contribute
significant nutrient loadings during low-oxygen conditions.
Typically, larger lakes and reservoirs are susceptible to low
oxygen levels during periods of stratification, which usually
5-4
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
occurs in mid- to late-summer in monomictic
systems. For dimictic systems, low oxygen also can
occur under the ice in winter. Under low-oxygen
conditions, phosphorus may be released from the
sediment layer, entering the water column and
contributing to loading. Indicators of potential
nutrient loading from sediment sources might
include probable high concentrations of phosphorus
in the sediment and known low-oxygen conditions
in the waterbody, or evidence of algal blooms
following turnover in the late summer or early fall.
Without site-specific monitoring information,
literature values can be used to estimate phosphorus
loading from the sediment. Such values should be
used very cautiously, because the loading parameter
will be site-specific, depending on the iron content
and other sediment characteristics. Note that
sediment release will change over time in response
to changes in loadings. Where the sediment release
comprises a significant portion of the system load, it
should be modeled. Model frameworks are
available to compute sediment phosphorus release
(e.g., Nurnberg, 1988, Seo and Canale, 1999).
Background or natural sources
Natural or background inputs of nitrogen and
phosphorus in stream and river systems will
contribute to increased nutrient concentrations.
Typically, such sources can be estimated from
regional reference streams. Reference sites are
relatively undisturbed by human influences or
represent least-impaired conditions; their levels of
nitrogen and phosphorus reflect background loading
from stream erosion, wild animal wastes, leaf fall
and other natural or background processes. If
possible, reference streams should be located in
similar geophysical and hydrologic watersheds,
having similar stream morphology and stream order.
A wide variety of state and local agencies may
collect information about reference streams.
Without site-specific or regional reference stream
information, literature values may be used to
estimate background sources. Some literature
values from the National Eutrophication Study are
shown in Table 5-2.
4. What is the appropriate level of spatial and
temporal detail for determination of the source
loading?
A broad range of issues, including availability of data, time
and resource constraints, relative significance of the source
loading, influence of geographic issues, and the need to
quantify episodic versus steady-state problems will
determine the appropriate level of detail for the source
analysis.
Availability of data
When a large amount of data is available, a more detailed
analysis might be appropriate for estimating sources. In
situations with minimal site-specific monitoring
information, and time or resource constraints preclude long-
term or expensive monitoring plans, simplified loading
analysis using literature values and simple methods may be
used. If other TMDLs or watershed-based studies have been
conducted in the area, these should be the prototype to
develop and calibrate the source analysis.
Time scale
One of the first questions to address in selecting an
appropriate source assessment technique is the time scale of
the problem to be considered. Examining a problem that
occurs only at low-flow periods might require primarily an
estimate of the loads delivered during a critical low-flow
condition. This calculation may be based on gauging station
records or a simplified analysis of contributing sources.
Low-flow conditions are
often dominated by point-
source discharges and
baseflow (ground water)
sources. In this situation,
source loadings may be
quantified by a
combination of in-stream
monitoring and point-
source discharge records.
For those situations where
low-flow nonpoint sources
are believed to be
significant (e.g., because of
septic systems or irrigation
return flows), these sources also will need to be estimated.
Factors to Consider in
Determining the Level of
Detail for the Analysis
• Data availability
• Time scale
• Spatial scale
• Delivery mechanisms
• Land use types
• Management activities
considered
• Value of resource and
management cost
First Edition: November 1999
5-5
-------
Source Assessment
Table 5-2. Mean dissolved nutrients measured in streamflow by the National Eutrophication Survey
Watershed Type
Concentrations (nig/L)
Eastern
United States
Central
United States
Western
United States
Total Inorganic Nitrogen
>90% Forested
>75% Forested
>50% Forested
>50% Agriculture
>75% Agriculture
>90% Agriculture
0.19
0.23
0.34
1.08
1.82
5.04
0.06
0.10
0.25
0.65
0.80
0.77
0.07
0.07
0.18
0.83
1.70
0.71
Total Orthophosphorus
>90% Forested
>75% Forested
>50% Forested
>50% Agriculture
>75% Agriculture
>90% Agriculture
0.006
0.007
0.013
0.029
0.052
0.067
0.009
0.012
0.015
0.055
0.067
0.085
0.012
0.015
0.015
0.083
0.069
0.104
Source: Omernik, 1977.
Another category of time scale are those waters
where longer-term loadings are of concern. In
receiving waters with longer residence times,
including some lakes and estuaries, it is appropriate
to estimate loads monthly or even annually.
Techniques appropriate for these situations include
unit-loading rate calculations and use of simple
models or methods. For evaluation of monthly
loadings, with some year-to-year variability, mid-
range models (or those that combine empirical
approaches with some aspects of modeling) can be
used.
Episodic load estimates might be needed in
waterbodies with short residence times and will
require the consideration of a series of individual
storms or a continuous (hourly or daily) simulation
of the loading processes. Simulation models can
consider loadings from rainfall- and snowmelt-
driven processes continuously. Interpretation of the time-
variable loads can be used to examine the frequency and
magnitude of loading.
Phasing
Later phases of a TMDL may include consideration of more
complex analysis methods, including conducting additional
monitoring or modeling to confirm or modify the original
estimates.
Recommendation: In general, a steady-state analysis should
be widely useful for developing a nutrient TMDL. Point
sources, sediment oxygen demand, ground water inflows,
and upstream background loads are approximately constant
or can be adequately averaged (USEPA, 1995a). A dynamic
analysis might be justified when standards require that
minimum dissolved oxygen levels be maintained at all times
5-6
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
and nutrient loads are known to cause varied levels
of dissolved oxygen in the stream.
5. What analysis techniques are appropriate
for estimating the source loads?
A range of analytical tools and methods is available
for estimating nutrient loads, depending on the
appropriate time scale and available resources.
They include the use of monitoring data, empirical
methods, and computer models. Consider the
following factors when selecting a tool to estimate
nutrient loads:
• Availability of data and funds to support data
collection
• Familiarity with the analysis tool
• Staff support
• Degree of accuracy required
• Physical, chemical, and biological processes to
consider
Monitoring data
Site-specific monitoring data can help to determine
load estimates when water quality and flow
measurements are readily available. Monitoring at
gauging stations, upstream of the area of concern,
can help to estimate the boundary conditions or
loads. Many gauging stations have long-term
records of flow; however, monitoring for nutrient
and related chemical concentrations (e.g.,
biochemical oxygen demand) is much less frequent.
Depending on the particular station, the monitoring
frequency might range from several samples per
year to several per month. Load estimates at the
station typically derive from a relationship between
the flow and associated nutrient concentration. This
relationship, represented by a regression equation,
can be used to calculate the total estimated load or
to develop a series of upstream boundary conditions.
Because significant increases in nutrient inputs may
occur during wet-weather flows, sufficient dry-
weather flow and concentration data should be
collected to avoid overestimating load contributions
during wet-weather periods. Nutrient input then can
be estimated by multiplying an average flow by the
flow-weighted concentration or by a regression
equation of nutrient input effect on flow. Also note that
monitoring data can be combined with stream water quality
modeling to estimate nonpoint sources. For example,
Warwick et al., (1997) interpreted data collected by the
Nevada Division of Environmental Protection with a
modified version of WASP5 (a dynamic in-stream water
quality simulation program) to estimate nonpoint source
loads for a complex river and channel portion of the Carson
River.
The advantage of using monitoring data is that it is a quick,
easy, and inexpensive method. One disadvantage is that
specific sources of loading are difficult to characterize (i.e.,
the monitoring data alone do not necessarily identify the
loads associated with the various source categories).
Another limitation of using monitoring information is that
the method provides little information for areas outside the
monitoring station drainage area.
Empirical methods
Empirical methods use statistical relationships to relate land
use to loadings. For example, EPA has published
probability-distribution graphs for various pollutants at sites
across the country in Results of the Nationwide Urban
Runoff Program (USEPA, 1983). These graphs can be used
to estimate event mean concentration (EMC) levels; such
estimates are best taken from sites with similar geological,
hydrologic, and physiographic patterns to the area under
consideration. Straightforward spreadsheet analysis, using
values and equations from previous studies, then may be
used to estimate loadings, given a set of EMC and flow
volume measurements. Calculation of pollutant loading in
this manner necessitates a large data set to best capture the
probability distribution of pollutant concentrations at a
given locale; the probability distribution of the EMC is used
to provide upper and lower estimates of contaminant
loading. Without comprehensive site-specific water quality
measurements, statistical methods may be used to determine
probable EMC levels for a given source. An example of
typical phosphorus and nitrogen loading rates is provided in
Table 5-3.
In the Albemarle-Pamlico case study described on the
following page, a literature search was conducted to obtain
high, medium, and low estimates of export coefficients for
the various land use categories in the basin. Export
coefficients are average annual unit-area nutrient loads
associated with various land uses. The percentage of land in
First Edition: November 1999
5-7
-------
Source Assessment
Table 5-3. Typical phosphorus and nitrogen loading ranges for various land uses.
Land Use
Roadway
Commercial
Single-family low
density
Single-family
high density
Multifamily
residential
Forest
Grass
Pasture
Total Phosphorus (kg/ha-y)
Minimum
0.59
0.69
0.46
0.54
0.59
0.10
0.01
0.01
Maximum
1.50
0.91
0.64
0.76
0.81
0.13
0.25
0.25
Median
1.10
0.80
0.55
0.65
0.70
0.11
0.13
0.13
Total Nitrogen (kg/ha-y)
Minimum
1.3
1.6
3.3
4.0
4.7
1.1
1.2
1.2
Maximum
3.5
8.8
4.7
5.6
6.6
2.8
7.1
7.1
Median
2.4
5.2
4.0
5.8
5.6
2.0
4.2
4.2
Multiply loadings in kg/ha-y by 0.89 to get Ib/acre-y.
As with all literature values, this table should be used discriminately and only in the absence of site-specific data.
Source: Horner et al., 1994.
Source Assessment in Albemarle-Pamlico Estuary, North Carolina and Virginia
In a study of the Albemarle and Pamlico Sounds, a screening analysis of the A-P watersheds was conducted to determine
which watersheds were contributing the most excess nutrients to surface waters (NCDEHNR, 1993). The Albemarle-Pamlico
source assessment demonstrates use of simple empirical equations combined with GIS tools. The analysis, developed by
North Carolina Department of Environment, Health, and Natural Resources (NCDEHNR), Division of Environmental
Management (NCDEM), used a combination of export coefficients, nutrient mass balances and GIS analysis to calculate
preliminary nutrient loadings from the 68 North Carolina and 44 Virginia watersheds in the study area.
Point source discharges were identified from Discharger Monitoring Reports through NCDEM and the Virginia Water Control
Board. Nitrogen and phosphorus inputs were determined by using the median value of monthly records of flow and
concentration data. The discharges were identified by latitude and longitude coordinates and entered into a GIS system.
The watershed boundaries were overlaid onto this map to locate each discharge site by watershed.
Nonpoint sources were calculated in two ways: (1) using export coefficients for each land use, and (2) by estimating
agricultural inputs through a more detailed mass balance approach. In the first method, LANDSAT land use and cover data
were used to identify types of land use in the basin. This information was entered into a GIS system to determine how much
of each land use was contained in each watershed. A literature review of export coefficients was used to generate high,
medium, and low estimates of loading from each land use category. Land use areas were multiplied by the appropriate
export coefficients to determine loading for each of the 68 watersheds.
A mass balance approach also was used to further refine nonpoint source loadings from agricultural areas in the 16 gauged
watersheds of the study area. This approach attempted to balance and account for the input, output, and storage of nutrients
in each watershed. Inputs into the mass balance included fertilizer, precipitation, livestock wastes, and nitrogen fixation.
Outputs included the nutrients in harvested crops, soil fixation, denitrification, loss to swamp forests, and river export.
Estimates of nutrient flux were determined by a combination of literature searches, professional judgment, and estimates of
county-specific information, such as livestock numbers. For example, livestock inputs were determined using county
estimates of livestock data combined with per-animal estimates of nutrient generation to calculate total production. Based on
literature review and professional judgment, 3 percent, 5 percent, and 10 percent were chosen as the low, most likely, and
high estimates of the percentage of nutrients entering the water.
5-8
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
each land use category was multiplied by the export
coefficients to determine estimates of nutrient
loading for each watershed in the basin.
A mass balance approach also may be used to
estimate nutrient loading. In this method, estimates
of nutrient inputs, outputs, and storage are used to
determine loadings. Flow-gauging information is
required to assist in the estimate of nutrient fluxes.
Literature values can be used to estimate inputs and
outputs for each category of nutrient supply or loss.
In the Albemarle-Pamlico study, literature values
were used to estimate inputs and outputs: inputs
included fertilizer application, precipitation,
livestock wastes, and nitrogen fixation; outputs
included the nutrients in harvested crops, soil
fixation, denitrification, loss to swamp forests, and
river export. To complete the mass balance, a
storage term can be used to account for the
differences in inputs and outputs to the system; such
differences might be attributable to soil, ground
water, and biomass nutrient storage.
Computer models
The development of TMDLs often requires the use
of watershed loading models to evaluate the effects
of land uses and practices on pollutant loading to
waterbodies. These loading models typically are
divided into categories (i.e., simple, mid-range, or
complex) based on complexity, operation, time step,
and simulation technique. Simple methods are
usually used for studies that are not data intensive,
whereas complex methods may be long-term
approaches that require extensive resources,
monitoring, and calibration. Mid-range methods
combine techniques of both, often bridging the gap
in data and available resources.
Figure 5-2 depicts a decision process for the
selection of the appropriate tool for nutrient loading
assessment and TMDL development in cases where
modeling techniques are deemed necessary. The
flowchart identifies a series of key decision points
that can help guide the user in the selection of the
appropriate model.
Simple methods
Simple methods are compilations of expert judgment and
empirical relationships between physiographic
characteristics of the watershed and pollutant export. They
may use existing literature values, and typically can be
applied by using a spreadsheet program or hand-held
calculator. Simple models and methods are often used when
data limitations and budget and time constraints preclude the
use of more sophisticated methods. Simple models are
probably most appropriate for load estimates in the
following instances:
1. Only rough or relative estimates of nutrient loadings and
limited predictive capability are needed.
2. The water quality problems of concern occur seasonally
or annually (i.e., simple methods are not usually
appropriate where loadings of shorter duration are
important).
The major advantage of simple methods is that they can
provide a rapid means of identifying critical loading areas
with minimal effort and data requirements. The major
disadvantage of using most simple methods is that the
assumptions used provide only gross estimates of nutrient
loads and are of limited value for determining loads on a
seasonal or finer time scale. Another disadvantage is that
the methods are of limited use for evaluating the effect of
control measures.
Examples of readily available simple models or methods
include EPA Screening Procedures, the Simple Method, the
USGS Regression Method, and the Watershed spreadsheet
model. Application of a simple method should use locally
derived default data (e.g., EMCs, monitoring, loading
analysis) or data from areas with similar physical
characteristics. Site-specific monitoring data should be used
whenever possible to check the accuracy of the predictions.
For example, the predicted load can be compared with
monitoring data at a gauging station. Some simple methods
are best applied to smaller watersheds, because they do not
consider transport processes or losses.
The Simple Method may be used to estimate pollutant
concentration runoff from urban drainage areas and is based
on storm event calculations. Runoff is estimated using
runoff coefficients for the fraction of rainfall converted to
runoff. A correction factor is used to account for those
storms that do not produce runoff. Pollutant concentrations
First Edition: November 1999
5-9
-------
Source Assessment
Time Scale of Waterbody
Response to Loads
Steady State
Low Flow
Short Term Dynamic
(Monthly/Annual)
(Hours/Days/Months)
Estimate Loading/Baseline
Conditions at Specified
Flow
Simple Method
USGS Statistical
Loading Rate
Mid-Range/
Complex
Monitoring/
Statistical
Methods
Simple/Load
Estimation
1
' 1
r i
u
Urban
P8
GWLF
SWMM
....— —-—. J
Rural
GWLF
SWAT/
SWRRB
r
U
1 Mixed
II GWLF
1 BASINS
J
Urban
SWMM
SLAM
HSPF/BASINS
Rural II Mixed
SWAT/ I HSPF/BASINS
SWRRB
HSPF/BASINS
Figure 5-2. Decision tree with preferred model selection options
5-10
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
in runoff depend on the land use activity and can be
obtained from sampling programs such as the
National Urban Runoff Program (NURP) or from
site-specific monitoring data. Potential applications
of the Simple Method are to estimate pollutant
loading from an uncontrolled development site or to
estimate expected extreme concentrations that will
occur over a specified time period. The Simple
Method is best adapted for use in small watersheds
of less than 1 square mile.
EPA Screening Procedures can be used to assess
point and nonpoint source loadings and atmospheric
deposition loads. Agricultural nonpoint loads are
based on the Universal Soil Loss Equation (USLE),
the Soil Conservation Service (SCS, now the
Natural Resource Conservation Service [NRCS])
runoff curve number procedure, and loading
functions using enrichment ratios. Urban nonpoint
loads are estimated using the buildup-washoff
concept (the buildup-washoff concept accounts for
incremental buildup of nutrients between storms).
Receiving water analyses use a mass balance
approach that assumes steady-state conditions.
Accuracy is limited when default parameters are
substituted for site-specific data. The procedure
neglects seasonal variation in predicting annual
loadings and considers only steady-state conditions
for receiving water analysis.
The USGS Regression Method is an example of a
statistical or empirical method. This method
estimates source loading as a function of land-use,
percentage of imperviousness, drainage area, mean annual
rainfall, and mean minimal monthly temperature. The USGS
Regression Method gives mean storm event pollutant loads
and corresponding confidence intervals. The USGS
Regression Method is used to estimate pollutant
concentration from urbanized watersheds and relies upon a
statistical approach to estimate annual, seasonal, or storm
event mean pollutant loads. The method uses regression
equations for estimating mean storm event pollutant loads,
and it provides users with a confidence interval to bracket
estimates of loading. The method is valid only for areas
where regression coefficients are obtainable (i.e., regional
transferability is limited). The method applies to smaller
watersheds.
The Watershed method is a spreadsheet application for
estimating urban, rural noncropland, and rural cropland
loads. Urban loads are calculated from point estimates of
flow and concentration, rural noncropland loads are
estimated by unit area, and rural cropland loads are based on
the Universal Soil Loss Equation. The method was applied
to estimate loading from point sources, CSOs, septic tanks,
rural cropland, and noncropland rural sources for the
Delavan Lake watershed in Wisconsin (Walker et al., 1989).
The spreadsheet program also can be used to calculate
program costs and cost-effectiveness per unit load nutrient
reduction.
The Federal Highway Administration Model (FHWA) is a
screening-level statistical model to estimate nutrient
loadings and the variability of loadings as estimated from
runoff volume distributions and event mean concentrations
for the median runoff event at highway or urban sites.
Simple Method
Metropolitan Washington Council of Governments
777 North Capitol Street
Suite 300
Washington, DC 20002
(202) 962-3200
EPA Screening Procedure
National Technical Information Services
5285 Port Royal Road
Springfield, VA 22161
(703) 487-4650
Refer to document number
NTIS P.B. 86122496
(EPA/600/6-85/002a).
USGS Regression Method
U.S. Geological Survey
430 National Center
Reston, VA 22092
(703) 648-5892
Watershed
U.S. Geological Survey
6417 Normandy Lane
Madison, Wl 53719-1133
(608)821-3853
Federal Highway Administration Model
Office of Engineering and Highways
Federal Highway Administration
6300 Georgetown Pike
First Edition: November 1999
5-11
-------
Source Assessment
USGS Regression Method for Estimating Source Loadings
The regression approach USGS researchers developed is based on a statistical description of historic records of storm runoff
responses on a watershed level (Tasker and Driver, 1988). This method may be used for rough preliminary calculations of
annual pollutant loads when data and time are limiting. Simple regression equations were developed using available monitoring
data for pollutant discharges at 76 gauging stations in 20 states. Separate equations are given for 10 pollutants, including for
dissolved and total nutrients. Input data include drainage area, percentage imperviousness, mean annual rainfall, general land
use pattern, and mean minimum monthly temperature. Application of this method provides storm-mean pollutant loads and
corresponding confidence intervals. The general form of the regression model follows:
W = 10
[a + b/DA + clA + dMAR + eMJT + fX2]
BCF
where:
W = mean load, in pounds, associated with a runoff event
DA = drainage area in square miles
IA = impervious area, in percentage of DA
MAR = mean annual rainfall, inches
MJT = mean minimum January temperature, in degrees Fahrenheit
X2 = land-use indicator variable
BCF = bias correction factor
The appropriate regression coefficients for a, b, c, d, e, and f can be obtained from Tasker and Driver (1988). For example, to
compute the mean annual load of total nitrogen, in pounds, at a 0.5-mi2 basin that is 90 percent residential with impervious area
of 30 percent and in a region where the mean number of storms per year is 79, first compute the mean load for a storm, W, using
the appropriate regression coefficients. Plugging in the values from Tasker and Driver (1988) provides a mean load, in pounds,
of 16.9. The mean annual load can be calculated by multiplying this value by 79, the average number of storms per year, to yield
a mean annual load of 1,335 pounds of total nitrogen per year.
Selected values from Tasker and Driver (1988).
Dependent
Variable
Total N
Total
NH3+N
Total P
Dissolved
P
Regression
Constant
a
- 0.2433
- 0.7282
- 1 .3884
-1.3661
SORT (DA)
b
1 .6383
1.6123
2.0825
1.3955
IA
c
0.0061
0.0064
-
-
MAR
d
-
0.0226
0.0234
-
MJT
e
-
-0.0210
-0.0213
-
X2
f
- 0.442
- 0.4345
-
-
Bias
Correction
Factor
1.345
1.277
1.314
1.469
Rainfall is converted to runoff, using a runoff
coefficient calculated from the percentage of
impervious land use. Pollutant buildup is based on
traffic volumes and surrounding area characteristics.
The model is used to evaluate lake and stream
impacts for stormwater discharges and provides an
uncertainty analysis of runoff and pollutant
concentrations or loads. The method does not consider the
soluble fraction of pollutants or the precipitation and settling
of phosphorus in lakes. The Federal Highway
Administration has used the FHWA model to evaluate the
impacts of storm-water runoff from highways and their
surrounding drainage areas.
5-12
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Mid-range methods
Mid-range methods attempt a compromise between
the empiricism of the simple methods and the
complexity of detailed mechanistic models. Mid-
range methods are probably most appropriate for
load estimates for the following conditions:
• Nonpoint or storm-driven sources are the
primary concern.
• Slightly more detailed assessment is needed.
• The water quality problems of concern require
the evaluation of specific storms or monthly or
annual variability.
• Available data and resources are insufficient to
support the development of a more detailed
model formulation.
The advantage of mid-range watershed-scale models
is that they evaluate nutrient sources and impacts
over broad geographic scales and therefore can
assist in defining target areas for mitigation
programs in a watershed. Several mid-range models
are designed to interface with geographic
information systems, which greatly facilitate
parameter estimation (e.g., AGNPS). Greater
reliance on site-specific data gives mid-range
models a relatively broad range of regional
applicability. However, the use of simplifying
assumptions or default values can limit the accuracy
of their predictions to within about an order of
magnitude (Dillaha, 1992) and can restrict their
analysis to relative comparisons.
Site-specific monitoring data should be used
whenever possible to verify the predictions. For
example, the predicted load can be compared with
monitoring data at a sampling station to test the
accuracy of the predictions.
The Generalized Watershed Loading Functions
(GWLF) model can be used to estimate nutrient
loads from urban and agricultural watersheds,
including septic systems (Haith et al., 1992).
GWLF is based on simple runoff, sediment and
ground water relationships combined with empirical
chemical parameters. It evaluates streamflow,
nutrients, soil erosion and sediment yield values
from complex watersheds. Runoff is calculated with
the NRCS curve number equation. Urban nutrient
loads are calculated by exponential accumulation and wash-
off functions. Nutrient loads from septic systems are
calculated by estimating the per capita daily load from each
type of septic system considered and the number of people
in the watershed served by each type. GWLF can apply to
relatively large watersheds with multiple land uses and point
sources. It tracks total and dissolved nutrients and sediment.
Stormwater storage and treatment are not considered. It has
been used in an 85,000-hectare watershed from the West
Branch Delaware River Basin in New York using a 3-year
period of record (Haith and Shoemaker, 1987). GWLF also
has been used for TMDL development in the Tar-Pamlico
Basin of North Carolina. Input data requirements are daily
precipitation and temperature data, runoff source areas,
transport parameters including runoff curve numbers, soil-
loss factor, evapotranspiration-cover coefficient, erosion
product, ground water recession and seepage coefficients,
sediment delivery ratio, and chemical parameters including
urban nutrient accumulation rates, dissolved nutrient
concentrations in runoff, and solid-phase nutrient
concentrations in sediment.
The Agricultural Nonpoint Source Pollution Model 98
(AGNPS 98) is a joint USDA NRCS and Agricultural
Research Service system of computer models developed to
predict nonpoint source pollutant loadings within
agricultural watersheds. It contains a continuous simulation,
surface runoff model designed for risk and cost/benefit
analyses. The set of computer programs consists of (1)
input generation and editing, as well as associated
databases; (2) the "annualized" science and technology
pollutant loading model (AnnAGNPS); and (3) output
reformatting and analysis. The model allows the
Mid-Range Methods:
List of Contacts
GWLF Model
Department of Agricultural and Biological Engineering
Cornell University
Ithaca, NY 14853
(607) 255-2802
AGNPS
USDA NRCS National Water and Climate Center
Water Science and Technology Team
11710BeltsvilleDrive
Suite 125
Beltsville, MD 20705
www.sedlab.olemiss.edu/index.html
First Edition: November 1999
5-13
-------
Source Assessment
comparison of the effects of implementing various
conservation alternatives within a watershed.
However, AGNPS lacks nutrient transformation and
in-stream processes and needs further field testing
for its pollutant transport component. Input data
requirements include topography and soil
characteristics, meteorologic data, land-use data
(cropping history and nutrient applications), point
source data, and a global parameter for
characterizing channel geometry and stream length.
AGNPS output includes storm runoff volume and
peak rate, sediment output (various sediment
parameters such as sediment yield and
concentration) and pollutant concentration and load.
Nutrient concentrations from feedlots and other
point sources can be modeled, and individual feedlot
potential ratings also can be derived using the
model.
Detailed methods
Detailed methods provide the best representation of
the current understanding of watershed processes
affecting pollution generation. Detailed models
depict how watershed processes change
continuously over time rather than relying on
simplified terms for rates of change (Addiscott and
Wagenet, 1985). Algorithms in detailed models
more closely simulate the physical processes of
infiltration, runoff, pollutant accumulation, in-
stream effects, and ground water and surface water
interaction. Detailed models provide information
on source loadings from specific portions of
watersheds and can predict the effect of different
management practices. The input and output of
detailed models also have greater spatial and
temporal resolution. If appropriately applied,
Model Calibration, Validation, and Verification
Calibration: model testing with known input and output
to adjust or estimate factors.
Validation: comparison of model results with an
independent data set (without further adjustment).
Verification: examination of the numerical technique in
the computer code to ascertain that it truly represents
the conceptual model with no inherent numerical
problems.
See Reckhowand Chapra, 1983, Chapra, 1997, or
Oreskes et. al, 1994, for more information.
models such as HSPF and SWMM can accurately estimate
pollutant loads and the expected impacts on water quality.
New interfaces developed for HSPF and SWMM, and links
with GISs, can facilitate the use of complex models for
environmental decision-making. However, their added
accuracy might not always justify the amount of effort and
resources they require. Detailed methods are probably most
appropriate for load estimates when:
• More explicit analysis of the runoff and pollutant
transport processes is required.
• The water quality problems of concern require the
consideration of short-term (i.e, hours, days) and time-
variable effects.
• A higher degree of accuracy and refinement are required
for the load estimates because of the complexity of the
watershed system or the cost of potential controls.
The advantages of using detailed models are that they can
provide relatively accurate predictions of variable flows and
water quality at numerous points within a watershed if
properly applied and calibrated. The additional accuracy
they provide, however, comes at the expense of considerably
more time and resources. Detailed models also require
significantly longer implementation time, because they
usually require an appropriate model calibration, validation,
and verification procedure to document model accuracy.
Formulation and calibration may require a data monitoring
and collection strategy.
Better Assessment Science Integrating Point and Nonpoint
Sources (BASINS) is a multipurpose environmental analysis
system developed by EPA's Office of Water to help
regional, state, tribal, and local agencies perform watershed-
and water quality-based studies. BASINS integrates data on
water quality and quantity, land uses, and point and
nonpoint source loading, providing the ability to perform
preliminary assessments of any watershed in the continental
United States.
Three models are integrated into BASINS within an
Arc View GIS environment. The Nonpoint Source Model
(NPSM) estimates land-use-specific nonpoint source
loadings for selected pollutants in a watershed (cataloging
unit or user-defined subwatershed scale). QUAL2E is a
one-dimensional, steady-state water quality and
eutrophication model that allows fate and transport
modeling for both point and nonpoint source loadings.
TOXIROUTE is a screening-level stream routing model that
5-14
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
performs simple dilution and decay calculations
under mean or low-flow conditions for a stream
system within a given watershed (cataloging unit).
Arc View geographic data preparation, selection
routines, and visual output streamline the use of the
models, and a postprocessor is provided to
graphically display model results.
The Hydrological Simulation Program-Fortran
(HSPF) model is used to calculate pollutant load and
transport from complex watersheds to receiving
waters. HSPF provides capabilities for continuous
and storm event simulation. Input data
requirements include continuous rainfall,
evapotranspiration, temperature, and solar intensity
records. Many other parameters need to be
specified in the HSPF model, although some default
values are available. The model output includes a
time series of the runoff flow rate, sediment load,
nutrient and pesticide concentrations, and water
quantity and quality at any location in the
watershed. The Chesapeake Bay Program has used
HSPF to model total watershed contributions of
flow, sediment, and nutrients to the tidal region of
the bay (Donigian et al., 1990; Donigian and
Patwardhan, 1992).
DR3M-QUAL, a multi-event urban runoff quality
model, may be used to assess urban storm water
pollutant loads and simulates impervious areas,
pervious area, and precipitation contributions to
runoff quality and the effects of street sweeping or
detention storage. Variation of runoff quality is
simulated for user-specified storm runoff periods.
Between these storms, a daily accounting of the
accumulation and washoff of water quality
constituents is maintained. Input data requirements
include: daily rainfall, evaporation and storm-event
rainfall at a constant time step; subcatchment data
including area, imperviousness, length, slope,
roughness, and infiltration parameters; trapezoidal
or circular channel dimensions and kinematic wave
parameters; stage-area-discharge relationships for
storage basins; and water quality parameters,
including buildup and washoff coefficients. Model
output includes time series of runoff hydrographs
and quality graphs (concentration or load versus
time) at any location in the drainage system,
summaries for storm events, and graphical output of
water quality and quantity analysis.
The Storm Water Management Model (SWMM) simulates
overland water quantity and quality produced by storms in
urban watersheds. Several modules or blocks are included
to model a wide range of quality and quantity watershed
processes. Model components include rainfall and runoff
processes, water quality analysis, and point-source inputs.
Either continuous or storm event simulation is possible, with
variable and user-specified time steps (wet and dry weather
periods). Input data requirements include rainfall
hyetographs, antecedent conditions, land use, topography,
soil characteristics, dry-weather flow, hydraulic inputs
(gutters or pipes), pollutant accumulation and washoff
parameters, and hydraulic and kinetic parameters. Model
output includes time series of flow, stage, and constituent
concentrations at any location in the watershed. Seasonal
and annual summaries are available.
Detailed Methods: List of Contacts
BASINS
EPA OST (4305)
Standards and Applied Science Division
401 M Street, SW
Washington, DC 20460
(202) 260-9821
http://www.epa.gov/ostwater/BASINS/
DR3M-QUAL
415 National Center
Mail stop 437
U.S. Geological Survey
Reston, VA20192
(703)648-5313
http://water.usgs.gov/software/
HSPF and SWMM
Model Distribution Coordinator
CEAM USEPA
960 College Station Road
Athens, GA 30605-2700
ftp://ftp.epa.gov/epa_ceam/wwwhtml/software.htm
6. What changes does the proposed rule speak to?
On August 23, 1999, EPA published proposed rules that
specify that approvable TMDLs must include at a minimum
ten elements. Within the source assessment step, an
approvable TMDL will need to include an identification of
the source categories, source subcategories, or individual
sources of the pollutant for which the wasteload allocations
and load allocations are being established.
First Edition: November 1999
5-15
-------
Source Assessment
RECOMMENDATIONS FOR SOURCE
ASSESSMENT
• Using all available information, develop a
comprehensive list of the potential and actual
nutrient sources to the waterbody of concern.
Develop a plan for identifying and accounting
for the load originating from the identified
sources in the watershed.
• Use GIS or maps to document the location of
sources and the processes important for delivery
to the waterbody.
• Group sources into some appropriate
management unit (e.g., by delivery mechanism
or common characteristics) for evaluation using
the available resources and analytical tools.
• Ideally, monitoring data should be used to
estimate the magnitude of loads from various
sources. Without such data, some combination
of literature values, best professional judgment,
and appropriate analytical tools or models will
be necessary. In general, the simplest approach
that provides meaningful predictions should be
used.
• In general, a steady-state analysis should be
widely useful for developing a nutrient TMDL.
Point sources, sediment oxygen demand, ground
water inflows, and upstream background loads
are approximately constant or can be adequately
averaged (USEPA, 1995c).
RECOMMENDED READING
(Note that the full list of references for this section
is included at the end of the document.)
• Novotny, V., and H. Olem. 1994. Water
quality: Prevention, identification, and
management of diffuse pollution. Van Nostrand
Reinhold Company, New York, NY.
• USEPA. 1983. Results of the Nationwide
Urban Runoff Program. NTISPB84-185552.
U.S. Environmental Protection Agency, Water
Planning Division, Washington, DC.
• USEPA. 1986b. Stream sampling for
wasteload allocation applications. EPA 625/6-
86-013. U.S. Environmental Protection Agency, Office
of Research and Development, Washington, DC.
USEPA. 1990. The lake and reservoir restoration
guidance manual. EPA-440/4-90-006. U.S.
Environmental Protection Agency, Office of Water,
Washington, DC.
USEPA. 1991b. Modeling of nonpoint source water
quality in urban and nonurban areas. EPA/600/3-
91/039. U.S. Environmental Protection Agency,
Washington, DC.
USEPA. 1992b. A quick reference guide: Developing
nonpoint source load allocations for TMDLs. EPA 841-
B-92-001. U.S. Environmental Protection Agency,
Washington, DC.
USEPA. 1997a. Compendium of tools for watershed
assessment and TMDL development. EPA841-B-97-
006. U.S. Environmental Protection Agency, Office of
Wetlands, Oceans, and Watersheds, Washington, DC.
5-16
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Linkage Between Water Quality Targets and Sources
Objective: Define a linkage between the selected water
quality targets and the identified pollutant sources to
characterize total assimilative capacity for nutrient
loading or total load reduction needed.
Procedure: Determine the cause-and-effect relationship
between the water quality target and the identified
pollutant sources through data analysis, best
professional judgment, models, or previously
documented relationships. Use the linkage to determine
what loadings or nutrient concentration are acceptable to
achieve the desired level of water quality. Develop
approaches for determining an appropriate margin of
safety.
OVERVIEW
One of the essential components of developing a TMDL
is to establish a link or relationship between predicted
nutrient loads and the numeric indicators that have been
chosen to measure the attainment of uses. Once this link
has been established, it is possible to determine the total
capacity of the waterbody to assimilate nutrient loadings
while still supporting its designated uses, and allowable
loads can be allocated among the various pollutant
sources. The linkage is essentially used to answer the
question: How much nutrient loading reduction is
necessary to attain the desired water quality (as
evaluated through numeric targets)? The link can be
established by using one or more analytical tools.
Ideally, the link can be based on a long-term set of
monitoring data that allows the TMDL developer to
associate certain waterbody responses to flow and
loading conditions. More often, however, the link must
be established by using a combination of monitoring
data, statistical and analytical tools (including
simulation models), and best professional judgment.
This section provides recommendations of the
appropriate techniques that can be used when
establishing the source-indicator link. As with the
prediction of pollutant source loadings, the analysis can
be conducted using methods that range from the simple
to the complex. This section also provides guidance for
selecting specific analytical tools, given certain
conditions, and provides brief descriptions of these tools
with their advantages and disadvantages for developing
nutrient TMDLs. Readers should note that there are
other analytical tools in addition to those described here,
which have been selected for their availability,
applicability to a wide range of conditions, and history
of use. Several other documents are referenced at the
end of this section for additional information.
KEY QUESTIONS TO CONSIDER FOR LINKAGE
BETWEEN WATER QUALITY TARGETS AND
SOURCES
1. Considering the indicator to be evaluated,
available monitoring data, hydraulic
characteristics of the system, and temporal
and spatial factors, what is an appropriate
level of analysis?
Choice of an analytical tool to link the nutrient loads to
the TMDL indicator(s) depends on the interaction of
several technical and practical factors. Several
suggestions on how to address these factors were
included in the numeric targets and source assessment
sections and are not repeated here. Other key factors to
consider in determining the appropriate level of analysis
for TMDL linkages include the following:
• Physical and hydraulic characteristics of the
waterbody (e.g., lake versus stream).
• Temporal representation needs. (Are seasonal
averages sufficient, or must dynamic events on a
shorter time scale be evaluated?)
Key Questions to Consider for Linkage of
Water Quality Targets and Sources
1. Considering the indicator to be evaluated,
available monitoring data, hydraulic
characteristics of the system, and temporal
and spatial factors, what is an appropriate
level of analysis?
2. Considering the advantages and
disadvantages of various approaches, what
is the appropriate technique to establish a
relationship between sources and water
quality response?
First Edition: November 1999
6-1
-------
Linkage Between Water Quality Targets and Sources
• Spatial representation needs. (Are there significant
spatial variations in the indicator and does spatial
variability in the waterbody need to be represented?)
• User requirements (including availability of
resources, time constraints, and staff familiarity with
specific analysis techniques).
• Stakeholder interests and outreach needs.
• Degree of accuracy needed.
Indicators and sources can be linked at many different
levels of complexity in the TMDL process. In some
cases, previously documented empirical relationships
such as those described in Section 3 (Identification of
Water Quality Indicators and Target Values) can be
used. For example, the Carlson Trophic Status Index
(Carlson, 1977) can be used to predict the in-lake
chlorophyll concentrations associated with various total
phosphorus concentrations. In other cases, literature
values or best professional judgment might be sufficient
to describe the linkage. Simplified computer models
often can be used to easily apply these empirical
relationships or literature values. Under certain
conditions, more sophisticated simulation models might
need to be used for more detailed analysis.
In many cases, the TMDL process commences without
sufficient data to support application of sophisticated
modeling techniques. Analysis of the linkage for many
nutrient TMDLs will start with the use of simple steady-
state concentration-response analyses for scoping the
problem. If the simple representation of the linkage is
unsatisfactory because the uncertainties in the analysis
are too great, additional, more sophisticated methods can
be used for the analysis. The process of moving from
simple, lower cost representations to more complex,
higher cost representations can be viewed as a ladder.
How far is it necessary to climb? This determination
must be made as a trade-off among cost (and available
resources), priority of the TMDL, the complexity and
type of processes under consideration, and accuracy
(acceptable size of the margin of safety). The exact
specification of the steps of this ladder will vary from
waterbody to waterbody. For instance, there are times
when a high-priority TMDL involves a high level of
detail (e.g., multiple episodic loadings), but an empirical
simplified model coupled with a high margin of safety is
acceptable because the level of point source treatment
and nonpoint source management practices required are
well within the financial capability of the watershed
community. There are also instances where increasing
the level of detail, although increasing cost, yields no
corresponding reduction in uncertainty.
2. Considering the advantages and
disadvantages of various approaches, what is
the appropriate technique to establish a
relationship between sources and water
quality response?
Because of the interaction of the factors identified
above, it is not possible to specify an appropriate
technique or model choice using a "cookbook"
approach, although some general considerations
applicable to this decision are summarized in the
decision tree shown in Figure 6-1.
This decision tree first distinguishes between streams
and rivers (dominantly advective systems) and lakes and
reservoirs (dominantly dispersive systems). Note that
Waters Impaired Primarily
by Point Sources
In instances where the primary source of nutrients
is point sources, the source-indicator link can be
established using a traditional design condition
approach that relies on steady-state analytical
methods. The approach works because, with
constant loads, the maximum impact is expected
to occur at low flows. EPA's Technical Guidance
Manual for Performing TMDLs and Waste Load
Allocations provides information on developing
TMDLs for this type of situation.
Technical Guidance Manual for Performing
TMDLs. Book II, Streams and Rivers: Part 1.
BOD/Dissolved Oxygen and Nutrient/
Eutrophication (EPA823-B-97-002)
Technical Guidance Manual for Performing Waste
Load Allocations. Book IV, Lakes, Reservoirs, and
Impoundments: Chapter 2. Nutrient/
Eutrophication Impacts (EPA 440/4-84-019)
To order these documents, contact the National
Service Center for Environmental Publications at
(800) 490-9198 or
http://www.epa.gov/ncepihom/index.html
6-2
First Edition: November 1999
-------
Waterbody with
Nutrient Impairment
Stream or River
Instream Impacts
Greater Impacts in
Receiving Lake
Periphyton /
Macrophyte
Dominated
Plankton-Dominated
Concentration/
Response
Relationships
WASPS
CE-QUAL-RIV1
CE-QUAL-W2
HSPF
AQUATOX
Dynamic
WASPS
CE-QUAL-W2
CE-QUAL-ICM
Figure 6-1. Decision tree for selecting an appropriate model technique
First Edition: November 1999
6-3
-------
Linkage Between Water Quality Targets and Sources
this distinction is not always clear-cut; some short-
residence reservoirs behave more like rivers. Streams
and rivers are then subdivided into systems dominated
by planktonic algae and systems dominated by
periphyton or macrophytes. Again, the distinction
between the two types might blur in the real world. On
each pathway, choices will need to be made regarding
the complexity of the chosen technique. Finally, an
example selection of available techniques or models is
included at each terminal branch. Again, final choice of
an appropriate technique or model will require careful
examination of the properties of the individual
techniques to match analytical requirements of the
assessment.
Some detailed comments are warranted about several
portions of this decision tree. First, note there is a
connection from the "streams" branch back to the
"lakes" branch. In many cases, the nutrient loads that
impair rivers and streams also result in impairment in
the lakes, reservoirs, or estuaries into which the rivers
and streams discharge. Because of longer residence
times, the receiving waterbody may be more sensitive
than the river. If, ultimately, more stringent allocations
will be required to protect this receiving water, it makes
sense to base the analysis and TMDL on the most
sensitive impacted water. Whether the resulting TMDL
also protects the less sensitive river can be determined
later.
Note also the absence of any sophisticated models for
periphyton-dominated rivers and streams. At present,
detailed predictive modeling of periphyton-dominated
systems is limited by poor understanding of their growth
processes, and this is an identified area for future
research. Simplified representations of periphyton are
within HSPF. The USGS has a water quality model
(USGS-QW, Bauer et al, 1979) that simulates attached
algae. This model was applied to a section of the south
Platte River, Colorado (Spahr and Blakely, 1985).
QUAL2E also has been applied where attached algae
must be simulated by applying a benthic sink, rather
than a source of ammonia nitrogen (Paschal and
Mueller, 1991). Finally, Warwick et al. (1997) have
modified WASP5 to simulate attached algae, with
applications on the Carson and Truckee rivers.
Special consideration also will be needed for analysis of
streams in semiarid areas. In alluvial valley sections of
semiarid streams, surface flow is typically seasonal or
ephemeral, and during much of the year the dominant
flow in areas of thick alluvium occurs in the subsurface
hyporheic zone. Studies of a Sonoran desert stream
(Valett et al., 1990) revealed that average interstitial
water volume was nearly four times that of surface
water and contained levels of nutrients substantially
higher than those observed in surface water. In such
areas, observations of surface water concentrations can
provide a very incomplete picture of total nutrient
cycling in the stream.
Descriptions of Various Approaches anil Their
Advantages anil Disadvantages1
Concentration and Response Relationships
For lakes and reservoirs, a strong quantitative
framework has been developed during the past two
decades that allows for the prediction of algal biomass
and other associated water quality parameters from
nutrient loading and water column nutrient
concentrations. (Refer to the Indicators section of this
document for more complete discussions of these
frameworks.) These concentration-response
relationships are based on a large set of empirical data
and have proven to be useful management techniques
worldwide. For many lakes and reservoirs, the link
between pollutant sources and water quality response
required for TMDL development can be based on these
relationships. When using this type of approach, TMDL
developers should consider the types of waterbodies
included in the empirical databases they are using and
apply them to their situation accordingly. For example,
much of the work on trophic status classification
systems has focused on northern, temperate lakes;
applications of these techniques to other regions must
therefore be done carefully. Moreover, users should
understand that such correlations are usually highly
uncertain, which must be considered when they are used
to establish TMDLs.
Compared to lakes and reservoirs, much less work has
been done to develop empirical models for periphyton
biomass in natural streams and rivers (e.g., Biggs and
Further summary information on available models is in the
Compendium of Tools for Watershed Assessment and TMDL
Development (USEPA, 1997a)
6-4
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Close, 1989 and Lohman et al., 1992, as cited in Dodds
and Smith, 1995). One example is presented by Dodds
and Smith (1995), who report on constructing a database
containing data from more than 200 distinct sites or
rivers throughout North America, Europe, and New
Zealand. They found that total nitrogen and total
phosphorus concentrations were more highly correlated
to stream chlorophyll than were nonnutrient factors such
as latitude, temperature, stream gradients, or
hydrodynamics. They also found that total nitrogen and
phosphorus more highly correlate with algal growth than
soluble reactive phosphorus and dissolved inorganic
nitrogen. Applying their results to the Clark Fork River,
the authors suggest that summer mean total nitrogen
concentrations should not exceed 350 ^g/L and total
phosphorus 45.5 ^g/L to keep chlorophyll
concentrations below 350 mg/m2.
Simulation models
If an appropriate concentration-response relationship
cannot link indicators and sources, an appropriate
simulation model can be used. A key aspect of model
identification is the complexity, cost, and effort of
implementation, which must be balanced against the
benefits achieved by using the model to estimate the
TMDL (refer to the Problem Identification section
above). Public understanding and communication also
can be crucial to choosing an analytical technique. This
is particularly important for TMDLs that must rely on
voluntary management measures to control nonpoint
loads. Using a model that is overly complex, poorly
documented, not peer reviewed, proprietary, or not well
known will increase the difficulty of understanding,
communicating, and gaining acceptance of the results.
The following brief descriptions identify relevant
characteristics of available models with their advantages
and disadvantages for application to developing nutrient
TMDLs.
CE-QUAL-RIV1. The Hydrodynamic and Water
Quality Model for Streams (CE-QUAL-RIV1) was
developed to simulate water quality conditions
associated with the highly unsteady flows that can occur
in regulated rivers. The model has two submodels for
hydrodynamics (RIV1H) and water quality (RIV1Q).
Output from the hydrodynamic solution is used to drive
the water quality model. Water quality constituents
modeled include temperature, dissolved oxygen,
carbonaceous biochemical oxygen demand, organic
nitrogen, ammonia nitrogen, nitrate nitrogen, and
soluble reactive phosphorus. The effects of algae and
macrophytes on water quality also can be included as
external forcing functions specified by the user. A
limitation of CE-QUAL-RIV1 is that it is applicable
only to situations where flow is predominantly one-
dimensional.
QUAL2E. The Enhanced Stream Water Quality Model
(QUAL2E), originally developed in the early 1970s, is a
one-dimensional water quality model that assumes
steady-state flow but allows simulation of diel variations
in temperature or algal photosynthesis and respiration
(Brown and Barnwell, 1987.) QUAL2E represents the
stream as a system of reaches of variable length, each
subdivided into computational elements of the same
length in all reaches. The basic equation used in
QUAL2E is the one-dimensional advection-dispersion
mass transport equation. An advantage of QUAL2E is
that it includes components that allow quick
implementation of uncertainty analysis using sensitivity
analysis, first-order error analysis, or Monte Carlo
simulation. The model has been used widely for stream
wasteload allocations and discharge permit
determinations in the United States and other countries.
QUAL2E has been applied where attached algae need to
be simulated by applying a benthic sink rather than a
source of ammonia nitrogen (Paschal and Mueller,
1991). EPA's Office of Science and Technology
developed a Microsoft Windows-based interface for
QUAL2E that facilitates data input and output
evaluation, and QUAL2E is one of the models included
in EPA's Better Assessment Science Integrating Point
and Nonpoint Sources (BASINS).
WASPS. WASP5 is a general-purpose modeling system
for assessing the fate and transport of conventional and
toxic pollutants in surface waterbodies. Its EUTRO5
submodel is designed to address eutrophication
processes and has been used in a wide range of
regulatory and water quality management applications.
The model may be applied to most waterbodies in one,
two, or three dimensions and can be used to predict
time-varying concentrations of water quality
constituents. It might be somewhat limited for lake
applications by a lack of internal temperature
simulation. The model reports a set of parameters,
including dissolved oxygen concentration, carbonaceous
biochemical oxygen demand (CBOD), ultimate CBOD,
phytoplankton, carbon, chlorophyll a, total nitrogen,
First Edition: November 1999
6-5
-------
Linkage Between Water Quality Targets and Sources
total inorganic nitrogen, ammonia, nitrate, organic
nitrogen, total inorganic nitrogen, organic phosphorus,
and inorganic phosphorus. Although zooplankton
dynamics are not simulated in EUTRO5, their effect can
be described by user-specified forcing functions. Lung
and Larson (1995) used EUTRO5 to evaluate
phosphorus loading reduction scenarios for the Upper
Mississippi River and Lake Pepin, while Warwick et al.
(1997) have modified WASP5 to simulate attached
algae, with applications on the Carson and Truckee
rivers, respectively.
EUTROMOD. EUTROMOD, a spreadsheet-based
watershed and lake modeling procedure developed for
eutrophication management, emphasizes uncertainty
analysis. The model estimates nutrient loading, various
trophic state parameters, and trihalomethane
concentration using data on land use, pollutant
concentrations, and lake characteristics. The model was
developed using empirical data from EPA's national
eutrophication survey, with trophic state models used to
relate phosphorus and nitrogen loading to in-lake
nutrient concentrations. The phosphorus and nitrogen
concentrations then are related to maximum chlorophyll
level, Secchi depth, dominant algal species,
hypolimnetic dissolved oxygen status, and
trihalomethane concentration. EUTROMOD allows for
uncertainty analysis by considering the error in
regression equations using an annual mean precipitation
and coefficient of variation to account for hydrologic
variability. EUTROMOD is limited in its application
because it is designed for watersheds in the southern
United States and it provides predictions only of
growing season averages.
PHOSMOD. PHOSMOD uses a modeling framework
described by Chapra and Canale (1991) for assessing the
impact of phosphorus loading on stratified lakes. A total
phosphorus budget for the water layer is developed with
inputs from external loading, and recycling from the
sediments, and considering losses from flushing and
settling. The sediment-to-water recycling depends on
the levels of sediment total phosphorus and
hypolimnetic oxygen concentration, the latter estimated
with a semi-empirical model. PHOSMOD can be used
to make daily or seasonal analyses and was developed to
assess long-term dynamic trends. Output includes
tabular and graphical output of lake total phosphorus,
percentage of total phosphorus in sediment,
hypolimnetic dissolved oxygen concentrations, and days
of anoxia.
BATHTUB. BATHTUB applies a series of empirical
eutrophication models to morphologically complex
lakes and reservoirs. The program performs steady-state
water and nutrient balance calculations in a spatially
segmented hydraulic network that accounts for
advective and diffusive transport, and nutrient
sedimentation. Eutrophication-related water quality
conditions (total phosphorus, total nitrogen, chlorophyll
a, transparency, and hypolimnetic oxygen depletion) are
predicted using empirical relationships derived from
assessment of reservoir data (Walker, 1985, 1986).
Applications of BATHTUB are limited to steady-state
evaluation of relationships between nutrient-loading,
transparency and hydrology, and eutrophication
responses. BATHTUB has been cited as an effective
tool for lake and reservoir water quality assessment and
management, particularly where data are limited (Ernst
etal., 1994).
CE-QUAL-W2. CE-QUAL-W2 is a two-dimensional,
longitudinal and vertical water quality model that can be
applied to most waterbody types. It includes both a
hydrodynamic component (dealing with circulation,
transport, and deposition) and a water quality
component. The hydrodynamic and water quality
routines are directly coupled, although the water quality
routines can be updated less frequently than the
hydrodynamic time step to reduce the computational
burden in complex systems. Water quality constituents
that can be modeled include algae, dissolved oxygen,
ammonia-nitrogen, nitrate-nitrogen, phosphorus, total
inorganic carbon, and pH.
Several limitations are associated with using CE-QUAL-
W2 to model nutrient overenrichment in lakes and
reservoirs. Because the model assumes lateral
homogeneity, it is best suited for relatively long and
narrow waterbodies that exhibit strong longitudinal and
vertical water quality gradients. It might be
inappropriate for large waterbodies. The model also has
only one algal compartment, and algal succession,
zooplankton, and macrophytes cannot be modeled.
The Hydrological Simulation Program - FORTRAN
(HSPF). HSPF is a comprehensive package developed
by EPA for simulating water quantity and quality for a
6-6
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
wide range of organic and inorganic pollutants from
agricultural watersheds (Bicknell et al., 1993). The
model uses continuous simulations of water balance and
pollutant generation, transformation, and transport.
Time series of the runoff flow rate, sediment yield, and
user-specified pollutant concentrations can be generated
at any point in the watershed. The model also includes
in-stream quality components for nutrient fate and
transport, biochemical oxygen demand, dissolved
oxygen, pH, phytoplankton, zooplankton, and benthic
algae. Statistical features incorporated into the model
allow for frequency-duration analysis of specific output
parameters. Data requirements for HSPF can be
extensive, and calibration and verification are
recommended. The program is maintained on IBM
microcomputers and DEC/VAX systems. Because of its
comprehensive nature, the HSPF model requires highly
trained personnel. It is recommended that its application
to real case studies be a team effort. The model has
been extensively used for both screening-level and
detailed analyses. Moore et al. (1992) describe an
application to model BMP effects on a Tennessee
watershed. Scheckenberger and Kennedy (1994) discuss
how HSPF can be used in subwatershed planning.
CE-QUAL-ICM. CE-QUAL-ICM incorporates
detailed algorithms for water quality kinetics and can be
applied to most waterbodies in one, two, or three
dimensions. Interactions among input variables are
described in 80 partial differential equations that apply
more than 40 parameters (Cerco and Cole, 1993).
Model outputs include temperature; inorganic suspended
solids; diatoms; blue-green algae (and other
phytoplankton); dissolved, labile, and refractory
components of particulate organic carbon; organic
nitrogen; organic phosphorus; ammonium; nitrate and
nitrite; total phosphate; and dissolved oxygen. Although
the model has full capabilities to simulate state-of-the-
art water quality kinetics, it is potentially limited by
available data for calibration and verification. The
model also might require significant technical expertise
in aquatic biology and chemistry to be used
appropriately.
It should be pointed out that few models described in
this section are able to mechanistically simulate
sediment oxygen demand (SOD). That is, most of the
models represent SOD as a constant input parameter.
Such models are not able to simulate how SOD may
change following reduction in loads, and it is necessary
to either assume that SOD remains unchanged or impose
an empirical relationship between SOD and the load
reduction (see Chapra, 1997). In fact, the relationship is
likely to be nonlinear, and to have a slow response time.
As discussed in Section 2, SOD is an important factor in
nutrient TMDLs because significant nutrient load can be
released from anoxic bottom sediments. Modelers
CE-QUAL-RIV1, CE-QUAL-W2,
and CE-QUAL-ICM
U.S. Army Corps of Engineers Waterways
Experiment Station
3909 Halls Ferry Road
Vicksburg, MS 39180
(601)634-3670
BASINS/QUAL2E (Windows)
EPA OST (4305)
Standards and Applied Science Division
401 M Street, SW
Washington, DC 20460
(202) 260-9821
http://www.epa.gov/OST/BASINS/
QUAL2E (DOS)
Center for Exposure Assessment Modeling (CEAM)
USEPA
960 College Station Road
Athens, GA 30605-2700
(706)355-8400
ftp://ftp.epa.gov/epa_ceam/wwwhtml/software.htm
WASPS and HSPF
CEAM USEPA
960 College Station Road
Athens, GA 30605-2700
(706) 355-8400
ftp://ftp.epa.gov/epa_ceam/wwwhtml/software.htm
EUTROMOD and PHOSMOD
North American Lake Management Society
PO Box 5443
Madison, Wl 53705
(608) 233-2836
BATHTUB
U.S. Army Corps of Engineers Waterways
Experiment Station
3909 Halls Ferry Road
Vicksburg, MS 39180
(601)634-3659
http://www.wes.army.mil/el/elmodels/
First Edition: November 1999
6-7
-------
Linkage Between Water Quality Targets and Sources
should recognize that holding SOD constant when
evaluating various allocation scenarios might result in
conservative predictions (i.e., SOD is likely to decrease
if loads are reduced), while assumptions of a linear
decline with load may overestimate improvements.
RECOMMENDATIONS FOR LINKAGE BETWEEN
WATER QUALITY TARGETS AND SOURCES
• Select an appropriate technique on a site-specific
basis and consider the nature of the indicator to be
evaluated, hydraulic characteristics of the
waterbody, user requirements, and relevant temporal
or spatial representation needs.
• Use all available and relevant data; ideally, the
linkage will be supported by monitoring data,
allowing the TMDL developer to associate
waterbody responses to flow and loading conditions.
• Most nutrient TMDLs will start with the use of
simple steady-state concentration-response
relationships to scope the problem. If the simple
representation of the linkage is unsatisfactory, more
sophisticated techniques can be used. Figure 6-1
displays recommended models for several types of
waterbodies and use impairments.
• When selecting a technique to establish a
relationship between sources and water quality
response, generally use the simplest technique that
adequately addresses the factors identified above.
How can the expected accuracy of models be
estimated?
An important step in the model calibration and
validation process is to make some sort of estimate,
either qualitative or quantitative, of the accuracy or
reliability of model predictions. This estimate, of
course, will be an important factor in deciding how to
use the model results in the estimation of the TMDL.
The basic point is that models produce only an
approximation of reality. Model predictions cannot be
any better than the calibration and validation effort, and
will always have some uncertainty associated with the
output. If model predictions are to be the basis of
decisions, it is essential to have some understanding of
the uncertainty associated with the model prediction.
For instance, suppose a model predicts an instream
chlorophyll a concentration of 20 pg/L given a certain
set of flow and nutrient loading conditions. However,
the model prediction is not exact, as sampling of the
stream during those flow and loading conditions would
likely demonstrate. The model must thus provide
additional information specifying how much variability
to expect around the "most likely" prediction of 20.
Obviously, it makes a significant difference if the
answer is "likely between 15 and 25" or "likely between
10 and 100."
Evaluating these issues involves the closely related
concepts of model accuracy and reliability. "Accuracy"
can be defined as a measure of the agreement between
the model predictions and observations. "Reliability" is
a measure of confidence in model predictions for a
specific set of conditions and for a specified confidence
level. Unfortunately, it is not easy to assess relative
accuracy among models. The formality and degree to
which model reliability must be assessed will vary case-
by-case, from narrative statements to detailed
quantitative analysis. A quantitative analysis is usually
advisable when model results are used as the major basis
for significant management decisions.
In terms of the probability that the numeric targets of the
TMDL will be exceeded, consider two separate sources
of temporal variability, natural variability and model
uncertainty. Natural variability concerns the variability
in loading and waterbody response that occurs as a
result of precipitation sequences, and so on. Model
uncertainty adds an additional layer of "noise." For
instance, the simulated response to a precipitation
sequence may not be quite right. The probability of
exceedances from natural variability alone can be
assessed through continuous simulation over a
sufficiently long period of precipitation and flow
records. However, assessment of the risk of impairment
to a waterbody should also consider the accuracy of the
model.
In the following sections, we provide a brief review of
techniques available to assess the reliability, or
uncertainty, associated with simulation model
predictions. Many different techniques are used to
assess model reliability. This review focuses on three of
the most commonly used methods: sensitivity analysis,
first-order analysis, and Monte Carlo simulation. Listed
in increasing order of complexity and detail, each
method is useful for specific purposes. Many published
reports document model reliability analysis techniques
6-8
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
(e.g., IAEA, 1989; Cox and Baybutt, 1981; Inman and
Helton, 1988; Marin, et al., 1989).
Sensitivity Analysis
Sensitivity analysis is the least sophisticated and easiest
analysis of the three to conduct. However, this ease of
use produces only rudimentary results. Consequently,
sensitivity analysis is best suited to preliminary
reliability analysis and model selection and screening.
The object of a sensitivity analysis is most clearly
described by its name. This method is used primarily to
assess the sensitivity of model output to perturbations of
individual model parameters. The means of conducting
such an analysis are fairly straightforward. First,
identify one or more parameter of interest. In most
cases, all of the model parameters are chosen for the
analysis. Vary each selected parameter through its range
of values, while holding all other parameters at their
median, or "best-estimate" values, and calculate the
model output for each scenario. In many cases, it is
sufficient to run the model with the selected parameter
at only two points, its realistic upper and lower bounds.
The analysis is then repeated for each parameter
identified earlier. If the model output varies
considerably for a given parameter, that parameter is
determined to have a large effect on the uncertainty in
model output. If the effect is small, the model is
determined to be less sensitive to the parameter.
First-Order Analysis
First-order analysis (also called variance or analytical
uncertainty propagation) is a slightly more sophisticated
approach to assessing model reliability. It is used to
determine the variance of the model output as a function
of the variances and covariances of model inputs and
parameters. Like sensitivity analysis, variance
propagation examines the effects of uncertainty in
individual parameters on the model prediction; however,
first-order analysis produces a numerical estimate of the
additional variability. If the modeler can reasonably
assume (and justify) a specific distribution on the
predicted values (e.g., a normal distribution), then this
estimated variance can be used to compute confidence
intervals for estimated values.
Depending on the nature of the model, the variance
associated with one parameter may propagate through
the model very differently from the variance of another
parameter with the same level of uncertainty. That is,
uncertainty in "important" parameters will have a
relatively large effect on the uncertainty associated with
model prediction, while less important variables will
have a smaller impact. Clearly then, the effect of
variance propagation depends on both the uncertainty
associated with model parameters and the structure of
the model itself.
Monte Carlo Simulation Analysis
The third method, Monte Carlo simulation, is a form of
probabilistic uncertainty analysis. The objective of this
method is to build up an empirical picture of the
complete distribution function of model output over the
possible range of input parameters. Evaluation of the
distribution function is accomplished by a "brute force"
approach, involving running the model over and over
with randomly varied parameter values and collecting
the results.
The Monte Carlo method yields not only a variance
estimate but also a probability distribution for the model
prediction. This distribution is an important piece of
information, allowing the modeler to compute interval
estimates and draw probability-based conclusions about
the model output.
To use the Monte Carlo technique, the modeler first
assigns probability distributions to each parameter.
These distributions should be based on a solid
combination of past experience, preliminary data
screening, and expert opinion. No inherent restrictions
are placed on the form of these distributions, making
Monte Carlo analysis an easily generalized technique.
After distributions for the parameters are specified, the
Monte Carlo simulation model randomly generates a
parameter value from the appropriate distribution and
inserts these values into the model equations, yielding a
predicted value. Autocorrelation in time series
parameters can be represented by using a moving
average or autoregressive approach, in which the next
estimate depends on the prior values or the random
component of the prior estimate. This process is
repeated many (several hundred or thousand) times,
from which a sample cumulative probability distribution
is generated for the model output. This distribution
reflects the overall response to the overall variability or
uncertainty in the input parameters.
First Edition: November 1999
6-9
-------
Linkage Between Water Quality Targets and Sources
For water quality simulations, it is important to
recognize that cross-correlation frequently exists
between different input variables. For instance, there is
often a lagged correlation between ambient temperature
and pH, so that the highest temperatures will not
coincide generally with the lowest pH values. Failure to
represent such cross-correlation can lead to erroneous
conclusions. This problem can be resolved by
generating the correlated parameters simultaneously
from their joint distribution, which, however, requires an
estimate of the cross-correlation structure. The
mathematical techniques for addressing these issues are
outside the scope of this document but have been
extensively covered elsewhere (see, for instance,
Hammersley and Handscomb, 1964; Loucks et al., 1981;
Bras and Rodriguez-Iturbe, 1985).
The Monte Carlo technique provides several advantages
over the previously discussed approaches to reliability
analysis. Most importantly, this method provides the
modeler with a probability distribution for model
prediction, rather than simply an estimate of its variance.
This distribution forms the basis for computing various
estimates (e.g., mean, median, 95th percentile) and
appropriate confidence intervals for these estimates. As
mentioned above, the Monte Carlo method also can
apply to a wide variety of circumstances. For example,
its use is not restricted to linear models, wide classes of
distributions may be used for input parameters, and the
computations are very straightforward. However, these
advantages do not come without some cost. Most
notably, the modeler must specify distributions for the
input parameters. Careful thought must be put into
assigning these distributions, as they form the basis for
the model output distribution. A frequent criticism of
conclusions drawn from a Monte Carlo simulation
revolves around the choice of parameter distributions.
As a result, sensitivity to the choice of parameter
distributions is an important issue to consider;
unfortunately, the effect of different distributional
choices is difficult to assess. A second potential
problem lies in the computer-intensive nature of the
analysis. For large, complex models with disperse
parameter distributions, Monte Carlo analysis may be
computationally infeasible. Stratified sampling
techniques (e.g., Latin hypercube sampling) may be used
to reduce the effort required to obtain a representative
approximation of the cumulative distribution frequency.
Several popular environmental fate and transport models
are currently available with Monte Carlo analysis
capability (such as QUAL2E). Others may be modified
to perform such a function, with level of effort
dependent on the clarity and structure of the original
computer code. Hession et al., (1996) describe the
application of the Monte Carlo analysis to the
EUTROMOD model for a TMDL for Wister Lake,
Oklahoma.
RECOMMENDED READING
(Note that the full list of references for this section is at
the end of the document.)
• Chapra, S. 1997. Surface Water-Quality Modeling.
The McGraw-Hill Companies, Inc.
• Thomann, R.V., and J.A. Mueller. 1987. Principles
of Surface Water Quality Modeling and Control.
Harper & Row, New York.
• USEPA. 1980. Technical Guidance Manual for
Performing Waste Load Allocations - Simplified
Analytical Method for Determining NPDES Effluent
Limitations for POTWs Discharging into Low-flow
Streams. U.S. Environmental Protection Agency,
Office of Water Regulations and Standards,
Monitoring and Data Support Division, Washington,
DC.
• USEPA. 1984a. Technical Guidance Manual for
Performing Waste Load Allocations. Book II,
Streams and Rivers. Chap. 1, Biochemical oxygen
demand/dissolved oxygen. EPA 440/4-84-020.
U.S. Environmental Protection Agency, Office of
Water, Washington, DC.
• USEPA. 1984b. Technical Guidance Manual for
Performing Waste Load Allocations. Book IV,
Lakes and impoundments. Chap. 2,
Nutrient/eutrophication impacts. EPA 440/4-84-
019. U.S. Environmental Protection Agency, Office
of Water, Washington, DC.
• USEPA. 1984c. Technical Guidance Manual for
Performing Waste Load Allocations. Book II,
Streams and Rivers. Chap. 2,
Nutrient/eutrophication impacts. EPA 440/4-84-021.
6-10
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
U.S. Environmental Protection Agency, Office of
Water, Washington, DC.
USEPA. 1985. Rates, Constants, and Kinetic
Formulations in Surface Water Quality Modeling,
EPA/600/3-85/040. U.S. Environmental Protection
Agency, Washington, DC.
USEPA. 1987. Technical Guidance Manual for
Performing Waste Load Allocations. Book VI,
Design Conditions. Chap.l, Stream design flow for
steady state modeling. EPA 440/4-87-004. U.S.
Environmental Protection Agency, Washington, DC.
USEPA. 1997a. Compendium of Tools for
Watershed Assessment and TMDL Development.
EPA841-B-97-006. U.S. Environmental Protection
Agency, Washington, DC.
USEPA. 1997c. Technical Guidance Manual for
Performing Waste Load Allocations. Book II,
Streams and Rivers. Part 1, BOD/DO and
nutrients/eutrophication. EPA823-B-97-002. U.S.
Environmental Protection Agency, Office of Water,
Washington, DC.
First Edition: November 1999 6-11
-------
Linkage Between Water Quality Targets and Sources
6-12
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Allocations
Objective: Using total assimilative capacity developed
in the linkage component, develop recommendations for
the allocation of loads among the various point and
nonpoint sources, while accounting for uncertainties in
the analyses (i.e., MOS) and, in some cases, a reserve
for future loadings.
Procedure: Determine the allocations based on a
determination of the acceptable loading (loading
capacity), the margin of safety, and the estimated loads
from significant sources. The available load is then
allocated among the various sources.
OVERVIEW
A TMDL consists of the sum of individual wasteload
allocations (WLAs) for point sources and load
allocations (LAs) for both nonpoint sources and natural
background levels for a given waterbody. The sum of
these components must result in the attainment of water
quality standards for that waterbody. The TMDL also
must include a margin of safety (MOS), either implicitly
or explicitly, that accounts for the uncertainty in the
relationship between pollutant loads and the quality of
the receiving waterbody. Conceptually, this definition is
denoted by the equation:
TMDL = S WLAs + S LAs + (MOS)
To establish a TMDL, the administering agency must
find an acceptable combination of allocations that
adequately protects water quality standards. However,
deciding how to divide the assimilative capacity of a
given waterbody among sources can be a challenging
task. Issues that affect the allocation process include:
• Economics
• Political considerations
• Feasibility
• Equitability
• Types of sources and management options
• Public involvement
• Implementation
• Limits of technology
• Variability in loads, effectiveness of BMPs
Although there is more than one approach to
establishing TMDLs, typical steps in the allocation
process are addressed in the following sections.
KEY QUESTIONS TO CONSIDER FOR ALLOCATIONS
1. What are the steps for completing the
allocations?
The first step in establishing a TMDL is to specify the
methods to use to incorporate an MOS. Section 303(d)
of the CWA requires TMDLs to include "a margin of
safety which takes into account any lack of knowledge
concerning the relationship between effluent limitations
and water quality." Given that TMDLs address both
point source allocations (WLAs) and nonpoint source
allocations (LAs), this concept may be extended to
cover uncertainty in BMP effectiveness in addition to
effluent limitations.
There are two basic methods for incorporating the MOS
(USEPA, 199 la; 1999):
• Implicitly incorporate the MOS using conservative
model assumptions to develop allocations or
• Explicitly specify a portion of the total TMDL as
the MOS and use the remainder for allocations.
In many cases, the MOS is incorporated implicitly. In
these cases, the conservative assumptions that account
for the MOS should be identified. An explicit
calculation, including evaluation of uncertainty in the
linkage analysis, has the advantage of clarifying the
assumptions that go into the MOS determination.
Key Questions to Consider for Allocations
1. What are the steps for completing the allocations?
2. How should candidate allocations be evaluated?
3. How can TMDLs be translated into controls?
4. How should issues of equitability and fairness be
addressed?
5. How should stakeholders be involved?
6. What changes does the proposed rule speak to?
First Edition: November 1999
7-1
-------
Example Allocation
Suppose the linkage analysis indicates that protection of uses in a lake requires a phosphorus TMDL equivalent
to 250,000 kg/yr (685 kg/day) total P. Current P load to the lake is estimated to be 300,000 kg/yr. Of this total
existing load, 200,000 kg/yr is derived from agricultural nonpoint sources (assuming reasonable worst-case
contributions) and 100,000 from two point sources (wastewater treatment plants contributing 75,000 and 25,000
kg/yr respectively). Because the existing load exceeds the TMDL, further reductions are required. The state
also has decided to apply an MOS of 10 percent on the TMDL to account for uncertainties in the analysis,
equivalent to 25,000 kg/yr. An analysis of the effectiveness of supporting additional BMPs for agriculture
suggests that a net P loading reduction of 33 percent can be obtained. Thus, the tentative LAs for the NPS are
200,000 x (1 - 0.33) = 134,000 kg/yr. The sum of the WLAs needed to meet the TMDL may then be calculated
from
I WLAs = TMDL - I LAs - MOS =
250,000 - 134,000 - 25,000 = 91,000 kg/yr.
The WLAs must then be adjusted to equal this sum.
The state has decided to impose reductions on point sources proportional to their current percentage
contribution to the total point source loads. These percentage contributions are 75 percent and 25 percent for
the two WWTPs, respectively. The revised WLAs can then be calculated as follows:
WWTP A: 75% x 91,000 = 68,250 kg/yr
WWTP B: 25% x 91,000 = 22,750 kg/yr
Permit conditions may then be written to ensure attainment of these WLAs as annual averages.
2. How should candidate allocations be
evaluated?
TMDLs by definition are combinations of WLAs and
LAs that allocate assimilative capacity to achieve water
quality standards. The first step in the evaluation is to
determine which segments and sources require
allocation adjustment to achieve water quality standards.
The actual adjustment to allocations likely will be based
on the administering agencies' policies and procedures.
For instance, should reductions be spread out across all
sources or apply to only a few targeted sources? Each
agency may have its own criteria for making these
decisions (e.g., magnitude of impact, degree of
management controls now in place, feasibility,
probability of success, cost, etc.). The following
subsections provide information on the types of factors
that might need to be considered when making
allocation decisions in cases where technology-based
controls on point sources alone are not sufficient to meet
water quality standards and thus a TMDL is required.
Assessing alternatives
Each allocation strategy under consideration will need
to be tested using the linkage analysis (Section 6) to
evaluate the potential effectiveness of the proposed
alternative. The analysis might need to include
consideration of the seasonal or annual variability in
loadings, particularly where significant contributions are
made by precipitation-driven nonpoint sources. As
alternative allocation strategies are developed, it might
be necessary to reassess the adequacy of the selection of
targets and linkages.
Achieving a balance between WLAs anil LAs
An appropriate balance should be struck between point
source (PS) and nonpoint source (NPS) controls in
establishing the formal TMDL components. Finding a
balance between WLAs and LAs involves the evaluation
of several factors. First, the manager needs to know
how the loads causing the impairment are apportioned
7-2
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
between PS and NFS. Is one source dominating the
other? Imposition of controls should reflect the
magnitude of the source, where possible. For instance,
if a pollutant load from NFS was found to be 80 percent
of the total loading to a problem area and a 40 percent
overall reduction in loading was needed, necessary load
reductions cannot be achieved through point source
controls alone.
Managers also must consider the differences in terms of
nutrient availability among the various sources. For
example, an agricultural source might be a relatively
large contributor of total phosphorus load, but if the
phosphorus load remains largely in nonbioavailable
form within the impaired waterbody segment, a
reduction in loading is likely to have less of an impact.
In general, it is advisable to develop the TMDF in terms
of total phosphorus (because of the possibility of
transformation from unavailable to available
phosphorus), but in some cases allocations to individual
sources might need to be prorated based on the
refractory nature of their phosphorus contribution.
3. How can TMDLs be translated into controls?
Translate WLAs into NPDES permit requirements
The National Pollutant Discharge Elimination System
(NPDES) permit is the mechanism for translating WLAs
into enforceable requirements for point sources. The
NPDES Program is established in section 402 of the
Clean Water Act (CWA). Under the NPDES program,
permits are required for the discharge of pollutants from
most point source discharges into the waters of the
United States (see 40 CFR Parti22 for applicability).
Although an NPDES permit authorizes a point source
facility to discharge, it also subjects the permittee to
legally enforceable requirements set forth in the permit.
40 CFR 122.44(d)(l)(vii)(B) requires effluent limits to
be consistent with WLAs in an approved TMDL.
One way WLAs are translated into permits is through
effluent limitations. Effluent limitations impose
restrictions on the quantities, rates of discharge, and
concentrations of specified pollutants in the point source
discharge. Effluent limitations reflect either minimum
federal or state technology-based guidelines or levels
needed to protect water quality, whichever is more
stringent. By definition, TMDLs involve WLAs more
stringent than technology-based limits to protect water
quality standards, and are therefore used to establish
appropriate effluent limitations. Effluent limitations
may be expressed either as numerical restrictions on
pollutant discharges or as best management practices
when numerical limitations are infeasible (40 CFR
122.44(k)). 40 CFR 122.45(d) requires numerical
NPDES effluent limitations for continuous discharges to
be expressed, unless impracticable, as average weekly
and average monthly discharge limitations for publicly
owned treatment works (POTWs) and as daily
maximums and monthly averages for other dischargers.
Translate LAs into implementation plans
Unlike NPDES permits for point sources, there are no
corresponding permit requirements for nonpoint
sources. Instead, load allocations are addressed, where
necessary, through implementation of BMPs. However,
implementation of BMPs generally occurs through
voluntary and incentive programs, such as government
cost-sharing. Therefore, when establishing nonpoint
source load allocations within a TMDL, the TMDL
development documentation should show (1) there is
reasonable assurance that nonpoint source controls will
be implemented and maintained or (2) nonpoint source
reductions are demonstrated through an effective
monitoring program (USEPA, 199la; 1999).
Although LAs may be used to target BMP
implementation within a watershed, translation of LAs
into specific BMP implementation programs can be a
problem. One reason for this difficulty is that often
many agencies are involved in BMP implementation,
rather than a single oversight agency, as for NPDES
permits. In addition to numerous landowner-operators,
BMP implementation can typically include federal,
state, and local involvement. Often, the objectives of
the varying agencies are different, which makes
coordination difficult.
Moreover, it is not always easy to predict the
effectiveness of BMPs. TMDL strategies heavily
dependent on loading reductions through LAs should
include long-term watershed water quality monitoring
programs to evaluate BMP effectiveness.
First Edition: November 1999
7-3
-------
4. How should issues of equitability and fairness
be addressed?
One issue that arises in distributing assimilative capacity
is equitability among allocations. Chadderton et al.
(1981) provide an examination of a variety of methods
to establish WLAs among interacting discharges. Five
methods were reviewed for a situation involving five
interacting discharges of biochemical oxygen demand
(BOD):
• Equal percentage removal or equal percentage
treatment.
• Equal effluent concentration.
• Equal incremental cost above minimum treatment
(normalized for volumetric flow rate).
• Effluent concentration inversely proportional to
pollutant mass inflow rate.
• Modified optimization (i.e., least cost solution that
includes the minimum treatment requirements of the
technology-based controls).
A comparison of the methods was made based on cost,
equity, efficient use of stream assimilative capacity, and
sensitivity to stream quality data. The authors
concluded that "equal percentage] treatment" was
preferable in the example studied because of the
method's insensitivity to data errors and accepted use by
several states. Although such a method could be used to
strike a balance between various point sources or (in
some cases) between similar nonpoint sources, it is
unlikely to be feasible for balancing between point and
nonpoint sources. The other methods cited by
Chadderton et al. (1981), or combinations thereof, might
be preferable under different circumstances.
5. How should stakeholders be involved?
Following federal regulations for water quality
management planning (40 CFR Part 130), TMDLs
should be available for public comment. For TMDL
strategies to succeed, however, those parties likely to be
affected by the TMDL (i.e., the stakeholders) should
also participate in the TMDL development process.
Effective communication is a key element of the public
participation process. Stakeholders should be made
aware of and engaged in the decisions regarding priority
status of a waterbody, the modeling results or data
analyses used to establish TMDLs for the waterbody,
and the pollutant control strategies resulting from the
TMDL (i.e., WLAs and LAs).
Methods for Communicating
TMDLs to Stakeholders
Issue public notices.
Hold public meetings or hearings.
Circulate basin or watershed plans for public review.
Use educational and outreach programs to expand
general knowledge of the TMDL process.
SUMMARY
The allocation step translates the TMDL into allowable
loads, distributed among the various sources, and
accounts for a margin of safety. Allocations are
required for both point sources (WLAs) and nonpoint
sources (LAs) and must include either an implicit or
explicit margin of safety. Point source wasteload
allocations are translated into NPDES permit
requirements; nonpoint sources load allocations are
translated into implementation plans. The TMDL
implementation plan for point and nonpoint sources
can be submitted with the TMDL, but it is not an
element of the actual TMDL and is not approved or
disapproved by EPA. Because the allocations will
involve issues such as equity, economics, and political
considerations, it is important that the administering
agency involve stakeholders throughout development of
the TMDL.
6. What changes does the propose rule speak
to?
On August 23, 1999, EPA published proposed rules that
specify that approvable TMDLs must include at a
minimum ten elements. Within the allocation step, an
approvable TMDL will need to include the following
information:
1. Wasteload allocations to each industrial and
municipal point source permitted under §402 of the
Clean Water Act discharging the pollutant for which
the TMDL is being established ; wasteload
allocations for storm water, combined sewer
overflows, abandoned mines, combined animal
7-4
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
feeding operations, or any other discharges subject
to a general permit may be allocated to categories of
sources, subcategories of sources or individual
sources; pollutant loads that do not need to be
allocated to attain or maintain water quality
standards may be included within a category of
sources, subcategory of sources or considered as
part of background loads; and supporting technical
analyses demonstrating that wasteload allocations
when implemented, will attain and maintain water
quality standards;
2. Load allocations to nonpoint sources of a pollutant,
including atmospheric deposition or natural
background sources. If possible, a separate load
allocation must be allocated to each source of
natural background or atmospheric deposition; load
allocations may be allocated to categories of
sources, subcategories of sources or individual
sources. Pollutant loads that do not need to be
allocated may be included within a category of
sources, subcategory of sources or considered as
part of the background load, supporting technical
analyses must demonstrate that load allocations,
when implemented, will attain and maintain water
quality standards;
3. A margin of safety expressed as unallocated
assimilative capacity or conservative analytical
assumptions used in establishing the TMDL; e.g.,
derivation of numeric targets, modeling
assumptions, or effectiveness of proposed
management actions which ensures attainment and
maintenance of water quality standards for the
allocated pollutant;
4. Consideration of seasonal variation and high and
low flow conditions such that water quality
standards for the allocated pollutant will be met
during all design environmental conditions;
5. An allowance for future growth which accounts for
reasonably foreseeable increases in pollutant loads;
and
6. An implementation plan, which may be developed
for one or a group of TMDLs.
Minimum Elements of an Approvable Implementation
Plan
Whether an implementation plan is for one TMDL or a
group of TMDLs, it must include at a minimum the
following eight elements:
• Implementation actions/management measures: a
description of the implementation actions and/or
management measures required to implement the
allocations contained in the TMDL, along with a
description of the effectiveness of these actions
and/or measures in achieving the required pollutant
loads or reductions.
• Time line: a description of when activities necessary
to implement the TMDL will occur. It must include
a schedule for revising NPDES permits to be
consistent with the TMDL. The schedule must also
include when best management practices and/or
controls will be implemented for source categories,
subcategories and individual sources. Interim
milestones to judge progress are also required.
• Reasonable assurances: reasonable assurance that
the implementation activities will occur. Reasonable
assurance means a high degree of confidence that
wasteload allocations and /or load allocations in
TMDLs will be implemented by Federal, State or
local authorities and /or voluntary action. For point
sources, reasonable assurance means that NPDES
permits (including coverage under applicable
general NPDES permits) will be consistent with any
applicable wasteload allocation contained in the
TMDL. For nonpoint sources, reasonable assurance
means that nonpoint source controls are specific to
the pollutant of concern, implemented according to
an expeditious schedule and supported by reliable
delivery mechanisms and adequate funding.
• Legal or regulatory controls: a description of the
legal authorities under which implementation will
occur (as defined in 40 CFR 130.2(p)). These
authorities include, for example, NPDES, Section
401 certification, Federal Land Policy and
Management programs, legal requirements
associated with financial assistance agreements
under the Farm Bills enacted by Congress and a
broad variety of enforceable State, Territorial, and
First Edition: November 1999
7-5
-------
authorized Tribal laws to control nonpoint source
pollution.
• Time required to attain water quality standards: an
estimate of the time required to attain water quality.
The estimates of the time required to attain and
maintain water quality standards must be specific to
the source category, subcategory or individual
source and tied to the pollutant for which the TMDL
is being established. It must also be consistent with
the geographic scale of the TMDL, including the
implementation actions.
• Monitoring plan: a monitoring or modeling plan
designed to determine the effectiveness of the
implementation actions and to help determine
whether allocations are met. The monitoring or
modeling plan must be designed to describe whether
allocations are sufficient to attain water quality
standards and how it will be determined whether
implementation actions, including interim
milestones, are occurring as planned. The
monitoring approach must also contain an approach
for assessing the effectiveness of best management
practices and control actions for nonpoint sources.
• Milestones for attaining water quality standards: a
description of milestones that will be used to
measure progress in attaining water quality
standards. The milestones must reflect the pollutant
for which the TMDL is being established and be
consistent with the geographic scale of the TMDL,
including the implementation actions. The
monitoring plan must contain incremental,
measurable milestones consistent with the specific
implementation action and the time frames for
implementing those actions.
• TMDL revision procedures: a description of when
TMDLs must be revised. EPA expects that the
monitoring plan would describe when failure to
meet specific milestones for implementing actions
or interim milestones for attaining water quality
standards will trigger a revision of the TMDL.
Recommendations for Allocations
• The method of incorporating the Margin of Safety
(i.e., implicitly or explicitly) should be identified.
• Allocations should reflect the relative size and
magnitude of sources, where possible, and represent
an appropriate and feasible balance between WLAs
and LAs.
• Allocations should be accompanied by adequate
documentation to provide reasonable assurance that
water quality standards will be attained.
• Affected stakeholders should help to develop
allocations.
RECOMMENDED READING
(Note that the full list of references for this section is at
the end of the document.)
• Chadderton, R.A., A.C. Miller, and A.J. McDonnell.
1981. Analysis of waste load allocation procedures.
Water Resources Bulletin 17(5):760-766.
• Thomann, R.V., and J.A. Mueller. 1987. Principles
of surface water quality modeling and control.
Harper & Row, New York, NY.
• USEPA. 1991a. Guidance for water quality-based
decisions: The TMDL process. EPA 440/4-91-001.
U.S. Environmental Protection Agency, Assessment
and Watershed Protection Division, Washington,
DC.
• USEPA. 1993. Guidance specifying management
measures for sources of nonpoint pollution in
coastal waters. EPA 840-B-92-002. U.S.
Environmental Protection Agency, Office of Water,
Washington, DC.
• USEPA. 1995c. Watershed protection: A project
focus. EPA 841-R-95-003. U.S. Environmental
Protection Agency, Office of Water, Washington,
DC
• USEPA 1999. Draft guidance for water quality-
based decisions: The TMDL process (second
edition). EPA 841-D-99-001. U.S. Environmental
Protection Agency, Washington, DC.
7-6
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Follow-up Monitoring and Evaluation
Objective: Define the monitoring and evaluation plan to
validate the Total Maximum Daily Load (TMDL),
assess the adequacy of control actions to implement the
TMDL, and provide a basis for reviewing and revising
TMDL elements or control actions in the future.
Procedure: Identify the key questions that a monitoring
plan needs to address, and evaluate monitoring options
and implement the monitoring program. Describe the
specific monitoring plan, including timing and location
of monitoring activities, parties responsible for
monitoring, and quality assurance and quality control
procedures. Describe the schedule for reviewing
monitoring results and considering the need for TMDL
or action plan revisions, and discuss the adaptive
management approach to take. The monitoring
component of a TMDL results in a description of
monitoring and adaptive management plan objectives,
methods, schedules, and responsible parties.
OVERVIEW
TMDL submittals should include a monitoring plan to
determine whether the TMDL has attained water quality
standards and to support any revisions to the TMDL that
might be required. Follow-up monitoring is
recommended for all TMDLs, given the uncertainties
inherent in TMDL development (USEPA 1991a; 1997b;
1999). The rigor of the monitoring plan should depend
on the confidence in the TMDL analysis: a more
rigorous monitoring plan should be included for TMDLs
with more uncertainty and where the environmental and
economic consequences of the decisions are most
significant. This section discusses key factors to
consider in developing the monitoring plan and suggests
additional sources of guidance on monitoring plan
development.
Models often can prove useful in evaluating the results
of monitoring. Because weather and other watershed
process drivers usually are not identical before and after
implementation, it is difficult to compare monitoring
data results. The monitoring must consider that
situation. If models are calibrated to conditions before
and after implementation, they then can be run for the
post-implementation period assuming implementation
practices are not applied. This approach can facilitate
the evaluation of the relative effectiveness of different
implementation approaches and the adequacy of
different TMDL components.
KEY QUESTIONS TO CONSIDER FOR FOLLOW-UP
MONITORING AND EVALUATION
1. What key factors influence monitoring
plan design?
Key factors to consider in developing the TMDL
monitoring plan include the following:
Need to evaluate specific TMDL elements
TMDL problem identification, indicators, numeric
targets, pollutant estimates, and allocations may need to
be reevaluated to determine if they are accurate and
effective. The monitoring plan should define specific
questions to be answered about these elements through
the collection of monitoring information. Potential
questions include the following:
• Are the selected indicators capable of detecting
designated use impacts of concern and responses to
control actions?
• Have baseline or background conditions been
adequately characterized?
• Are the numeric targets set at levels that reasonably
represent the appropriate desired conditions for
designated uses of concern?
• Have all important pollutant sources been identified?
• Have pollutant sources been accurately estimated?
Key Questions to Consider for Follow-up
Monitoring and Evaluation
1. What key factors influence monitoring plan
design?
2. What is in an appropriate monitoring plan?
3. What is an appropriate adaptive management
plan, including review and revision schedule?
4. What constitutes an adequate monitoring
plan?
5. What changes does the proposed rule speak
to?
First Edition: November 1999
8-1
-------
Follow-up Monitoring and Evaluation
• Has the linkage between pollutant sources and
impacts to the waterbody been accurately
characterized?
• Have other watershed processes (e.g., hydrology) that
affect nutrient production or that impact designated
uses been accurately described?
• Where reference sites were used to help determine
TMDL targets and load reduction needs, were
reference site conditions accurately described?
• Were models or methods used for the TMDL
accurately calibrated, validated, verified?
Not all questions will be appropriate for all TMDL
monitoring plans because the degree of uncertainty for
different TMDL elements will vary case-by-case.
Need to evaluate implementation actions
It is often important to determine whether actions
identified in the implementation plan actually were
carried out (implementation monitoring) and whether
these actions were effective in attaining TMDL
allocations (effectiveness monitoring). Specific
questions to answer concerning implementation actions
should be part of the monitoring plan.
Stakeholder goals for monitoring efforts
Watershed stakeholders often participate in follow-up
monitoring and stakeholder interests should be
considered in devising monitoring plans.
Existing monitoring activities, resources, anil
capabilities
Analysts should identify existing and planned
monitoring activities to coordinate TMDL monitoring
needs with other planned efforts, particularly for a long-
term monitoring program, large study areas, or if the
water quality agency's monitoring resources are limited.
Staff capabilities and training should also be considered,
to ensure that monitoring plans are feasible.
Practical constraints to monitoring
Monitoring options are often limited by practical
constraints (e.g., problems with access to monitoring
sites and concerns about indirect impacts of monitoring
on habitat). Other factors influencing the design of
monitoring plans and different types of monitoring that
are of interest for TMDLs are discussed in detail in
MacDonaldetal. (1991).
Types of monitoring
Several types of monitoring may be considered in
developing the monitoring plan (modified from
MacDonaldetal., 1991).
• Baseline monitoring. Baseline monitoring describes
existing conditions and provides a basis for future
comparisons. This type of monitoring is not always
necessary for the monitoring plan. Usually, some
baseline data already exist and were considered
during TMDL development.
• Implementation monitoring. This type of monitoring
would ensure that identified management actions
(such as specific BMPs or resource restoration or
enhancement projects) are undertaken. This
information also would be analyzed as a factor that
influences the conclusions from the trend monitoring.
• Project or effectiveness monitoring. Specific projects
undertaken in the context of the TMDL or separate
from the TMDL but potentially affecting water
quality conditions for the watershed area under
consideration should be monitored both to determine
their immediate effects and the effects on the water
quality downstream of the project.
• Trend monitoring. This type of monitoring assesses
the effectiveness of management actions and the
changes in conditions over time relative to the
baseline and identified target values. Trend
monitoring is the primary type of follow-up
monitoring, assuming the other elements of the
TMDL are appropriately developed. It would
address the changing conditions in the waterbody that
result from TMDL-specific activities and other land
management activities over time. This is the most
critical component of the monitoring program,
because it also serves to document progress toward
achieving the desired water quality conditions.
• Validation monitoring. This type of monitoring is
used to re-evaluate the selection of indicators,
numeric targets, and source analysis methods.
8-2
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
2. What is in an appropriate monitoring plan?
The first step in developing an appropriate monitoring
and adaptive management plan is to clarify the goals of
the monitoring program. It may be possible to
accomplish several of these monitoring goals
simultaneously. For example, the primary need in most
TMDLs will be to document progress toward achieving
the numeric targets. During this process, the additional
information collected may lead to a better understanding
of the processes, suggesting a revision to the pollutant
source analysis that would better pinpoint the nutrient
problem and lead to faster attainment of water quality
improvements; or, maybe a particular restoration or
enhancement project did not produce the desired effects
and it should be changed.
The relationships between the monitoring plan and the
TMDL's numeric targets, source analysis, linkages, and
allocations, and the implementation plan, should be
addressed. Specific questions to be answered should be
articulated as monitoring hypotheses, and the plan
should explain how the monitoring program will answer
those questions. Any assumptions should be explained.
The monitoring plan's approach to both episodic events
and continuous effects should be explained, and the
likely effects of episodic events should be discussed.
The design can be delineated by source type, by
geographic area, or by ownership parcel.
The monitoring methods to be used should be described
and the rationale for selecting these methods provided.
Monitoring locations and frequencies should be defined,
and the parties responsible for conducting the
monitoring should be listed (if known).
An appropriate Quality Assurance Project Plan should
be developed, detailing the sampling methods, selection
of sites, and analysis methods consistent with accepted
quality assurance and quality control practices. The
monitoring plan should be peer reviewed, if possible.
(For more information see USEPA, 1994a, 1994b.)
3. What is an appropriate adaptive management
plan, including review and revision schedule?
The plan should contain a section that addresses the
adaptive management component. This section should
discuss when and how the TMDL will be reviewed. If
possible, the plan should describe criteria to guide
TMDL review and revision. For example, the plan
could identify expected levels of progress toward
meeting TMDL numeric targets at the initial review,
stated as interim numeric targets or interim load
reduction expectations. The plan also could identify
"red flag" thresholds for key indicators that would
signal fundamental dangers to designated uses and
perhaps trigger a more in-depth review of the TMDL
and implementation plan's components.
The adaptive management component need not schedule
every TMDL review ever needed; it should be adequate
to indicate an estimated frequency of review and specify
a date for the initial review. Reliably forecasting how
often TMDL reviews will be needed would be difficult,
especially where problems are likely to take several
years (or more) to solve.
4. What constitutes an adequate monitoring
plan?
The monitoring and adaptive management plan is a
required component of TMDLs developed under the
phased approach. The plan should incorporate each
component discussed above, with adequate rationale for
the selected monitoring and adaptive management
approach. If it is infeasible to develop the monitoring
plan in detail at the time of TMDL adoption, it may be
adequate to identify the basic monitoring goals, review
the time frame, and identify responsible parties while
committing to develop the full monitoring plan in the
near future. The plan should clearly indicate the
monitoring goals and hypotheses, parameters to monitor,
the locations and frequency of monitoring, the
monitoring methods to use, schedule for review and
potential revision, and the parties responsible for
implementing the plan.
5. What changes does the proposed rule speak
to?
On August 23, 1999, EPA published proposed rules that
specify that approvable TMDLs must include at a
minimum ten elements. Within the monitoring step, an
approvable TMDL will need to include a monitoring
plan as part of the implementation plan. The monitoring
plan needs to determine the effectiveness of control
actions and/or management measures being
implemented and whether the TMDL is working, as well
as a procedure that will be followed if components of a
First Edition: November 1999
8-3
-------
Follow-up Monitoring and Evaluation
TMDL must be refined. The plan should clearly
indicate the monitoring goals and hypotheses, the
parameters to be monitored, the locations and frequency
of monitoring, the monitoring methods to be used, the
schedule for review and potential revision, and the
parties responsible for implementing the plan. It must
contain incremental, measurable targets consistent with
the specific implementation action and the time frames
for implementing those actions. This information is
needed to adequately assess whether the specified
actions are sufficient to attain water quality standards.
The following are key factors to consider when
developing a TMDL monitoring plan:
• Need to evaluate specific TMDL components. TMDL
problem identification, indicators, numeric targets,
source estimates, and allocations might need
reevaluation to determine whether they are accurate
and effective. The monitoring plan should define
specific questions to be answered about these
components through the collection of monitoring
information
• Need to evaluate implementation actions. It is often
important to determine whether actions identified in
the implementation plan were actually carried out
(implementation monitoring) and whether these
actions were effective in attaining TMDL allocations
(effectiveness monitoring). Specific questions to be
answered concerning implementation actions should
be articulated as part of the monitoring plan.
• Stakeholder goals for monitoring efforts. Watershed
stakeholders often participate in follow-up
monitoring and their interests should be considered in
devising monitoring plans.
• Existing monitoring activities, resources, and
capabilities. Analysts should identify existing and
planned monitoring activities to address TMDL
monitoring needs in concert with these efforts,
particularly where a long-term monitoring program is
envisioned, the study area is large, or water quality
agency monitoring resources are limited. Staff
capabilities and training should also be considered to
ensure that monitoring plans are feasible.
• Practical constraints to monitoring. Monitoring
options can be limited by practical constraints (e.g.,
Characteristics of Effective Monitoring Plans
Quantifiable in approach. Results must be
discernible over time, to compare them to
previous or reference conditions.
Appropriate in scale and application and
relevant to designated uses and the TMDL
methods.
Adequately precise, reproducible by
independent investigators, and consistent with
scientific understanding of the problems and
solutions.
Able to distinguish among many different
factors or sources (e.g., pasture washoff,
cropland erosion, urban runoff, septic systems).
Versatile. Generally looks at the problem from
many different perspectives.
Understandable to the public and supported by
stakeholders.
Feasible and cost-effective.
Anticipates potential future conditions and
climatic influences.
Minimally disruptive to the designated uses
during data collection.
Conducive to reaching and sustaining
conditions that support the designated uses.
problems with access to monitoring sites and
concerns about indirect impacts of monitoring on
habitat).
RECOMMENDATIONS FOR FOLLOW-UP
MONITORING AND EVALUATION
• Clearly identify the goals of the monitoring program.
• Define specific questions to answer about the
evaluation of individual TMDL elements.
• If possible, coordinate with other existing or planned
monitoring activities.
• Determine which type(s) of monitoring (e.g.,
implementation, trend) is (are) appropriate for
accomplishing the desired goals.
• Develop an appropriate quality assurance plan;
follow-up monitoring should be designed to yield
defensible data that can support future analysis.
8-4
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
RECOMMENDED READING
(Note that the full list of references for this section is at
the end of the document.)
• MacDonald, L., A.W. Smart, and R.C. Wissmar.
1991. Monitoring guidelines to evaluate effects of
forestry activities on streams in the Pacific
Northwest and Alaska. EPA 910/9-91-001. U.S.
Environmental Protection Agency, Region 10,
Nonpoint Source Section, Seattle, WA.
• USEPA. 1990. Monitoring lake and reservoir
restoration. EPA 440/4-90-007. U.S. Environmental
Protection Agency, Office of Water, Washington,
DC.
• USEPA. 1992c. Monitoring guidance for the national
estuary program. EPA 842 B-92-004.
U.S. Environmental Protection Agency, Washington,
DC.
• USEPA. 1996c. Nonpoint source monitoring and
evaluation guide. November 1996. U.S.
Environmental Protection Agency, Office of Water,
Washington, DC.
First Edition: November 1999 8-5
-------
Follow-up Monitoring and Evaluation
Considerations for Monitoring Algal Biomass and Nutrients in Streams and Rivers
The following information on monitoring considerations for streams and rivers was prepared for use in one of the guidance
documents being drafted as part of EPA's National Strategy for the Development of Regional Nutrient Criteria (USEPA,
1998a). Guidance for monitoring nutrients and algae in lakes and reservoirs is available from Monitoring Lake and Reservoir
Restoration (USEPA, 1990), and other sources.
Attached algal biomass can vary greatly in time and space within the same stream. Thus, the number of replicates required to
reduce the standard error of mean biomass to a reasonable percentage can be too large to be practical. To reduce
variability, the focus should be on algal sampling in the part of the stream where algae is most likely to conflict with
designated uses. For rivers with unwadable depths, sampling must be confined to the wadable portions. For streams and
rivers shallow enough to be wadable during the growing season, it may be possible to sample randomly across the entire
width of the stream if the resulting sample variability is acceptable. If variability is too large, the focus should be on an
indicator zone with a delimited range of water velocity, depth, and substrate size.
In general, it is recommended to collect 20 replicate samples and to analyze at least 10 of them to determine the variability in
the data. (The second 10 then may be analyzed, should the standard error for the first 10 be too large.) For a few years, it is
advisable to analyze all samples collected until the number of samples required to detect changes and trends of the desired
magnitude has been determined.
Once criteria for algal biomass have been established, certain sampling considerations must be addressed to obtain
meaningful samples.
How can algal criteria be applied to samples that come from only certain depths of the stream? British Columbia has
developed the following algal biomass criteria for small wadable streams (Nordin, 1985): 50 mg/l of chlorophyll a to protect
aesthetics and 100 mg/l to protect against undesirable changes in the stream community. Nordin, the principal author of
these criteria, agreed that it was reasonable to apply the aesthetic criteria to the wadable portion of larger rivers. The level
necessary to protect aquatic life is likely to be system-specific and is best evaluated by determining how algal biomass
affects dissolved oxygen, pH, and aquatic communities.
How large an area should be characterized when assessing whether a reach exceeds a quantitative criterion? To ensure
that a reasonably representative portion of a reach is sampled, replicate samples should be distributed over a reach of at
least 100 m. Before selecting a point for sampling, a researcher should walk a few hundred meters upstream and
downstream to ensure that the preferred sampling point is not atypical of the reach being characterized. Low altitude aerial
photos taken on a sunny day in mid-to-late growing season are very useful to determine the longitudinal extent of conditions
similar to those at the sampling site. Floating the stream by boat can serve a similar purpose.
For how long must algal biomass exceed criteria to be considered unacceptable? Attached algal biomass does not change
as rapidly as water column parameters. Hence, one sample a month (from June to September) is probably adequate to
assess algal biomass. If only two samplings can be afforded, the period likely to contain the highest biomass levels should be
bracketed. However, such a sampling scheme may be unacceptable if both sample values exceed aesthetic criteria. If algal
biomass is high enough to cause excessive dissolved oxygen or pH fluctuations that violate water quality standards or that
release toxins at unacceptable levels, then the time frames for those water quality violations should be used to judge the
acceptability of algal biomass levels. As an example, some states might regard the exceedance of algal biomass criteria
once in 10 years (i.e., only during the 10-year low-flow) as acceptable, but more frequent exceedances may be deemed
unacceptable.
Monitoring for nutrients attempts to determine the seasonal pattern in nutrient levels and how they related to algal biomass
levels. The following offers some ideas for when and where to most efficiently sample nutrients.
When should samples be taken? Annual total nutrient loading is unlikely to be a good predictor of river algal biomass
because growth may be poor during the periods of highest loading (from scour and turbidity). River algal growth is likely to
relate to nutrient levels during the season of greatest algal growth. Nutrient sampling should be conducted monthly to
bimonthly during the season of greatest nutrient loading and during the season of greatest algal growth. Comparison of
nutrient levels between the seasons of greatest and least algal growth helps to determine how much of the loading algae take
up. Hence, some nutrient sampling also should occur during the season of lowest algal biomass levels (at least three
samplings spread over the period). Many nutrient monitoring programs are based on quarterly sampling. However,
year-to-year variations in the window of high flows, the period of high nutrient uptake and algal growth, and the period of algal
sloughing at the end of the growing season make detecting long-term trends from quarterly samples very difficult.
Where to sample: Nutrient levels may vary greatly throughout a river system, necessitating numerous sampling sites. To
quantify sources and loads, monitoring stations for nutrients in rivers should be located upstream and downstream of major
sources of nutrients or of diluting waters (e.g., discharges, development, tributaries, areas of major groundwater inputs).
Source: Watson, 1997.
8-6 First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Assembling the TMDL
Objective: Clearly identify the components of a TMDL
submittal to support adequate public participation and to
facilitate TMDL review and approval.
Procedure: Compile all pertinent information used to
develop the TMDL and prepare the final submittal. The
final submittal should document all of the major
assumptions and analyses.
OVERVIEW
It is important to clearly identify the "pieces" of the
TMDL submittal and to show how they fit together to
provide a coherent planning tool that can lead to
attaining water quality standards for nutrient-related
water quality impairments. Where TMDLs derive from
other analyses or reports, it is helpful to develop a
separate document or chapter that ties together the
TMDL components and shows where background
information can be found.
RECOMMENDATIONS FOR CONTENT OF
SUBMITTALS
Section 303(d) of the CWA and EPA's implementing
regulations specify that a TMDL consists of the sum of
WLAs for future and existing point sources and LAs for
future and existing nonpoint sources and natural
background, considering seasonal variation and a
margin of safety. These loads are established at levels
necessary to implement applicable water quality
standards with seasonal and interannual variation and a
margin of safety. Experience indicates, however, that
information in addition to the statutory and regulatory
requirements is useful to support adequate public
participation and to facilitate EPA review and approval.
As partners in the TMDL development process, it is in
the best interest of the state and EPA to work together to
determine how much supporting information the TMDL
submittal needs.
Recommended Minimum Submittal Information
The following outlines suggestions for TMDL
submittals:
1. Submittal Letter
• Each TMDL submitted to EPA should be
accompanied by a submittal letter stating that
the submittal is a draft or final TMDL submitted
under §303(d) of the CWA for EPA review and
approval.
2. Problem Statement
• Waterbody name and location.
• A map is especially useful if information
displayed indicates the area covered by the
TMDL (e.g., watershed boundary or upper and
lower bounds on the receiving stream segment)
and the location of sources.
• Waterbody §303(d) list status (including
pollutant covered by the TMDL and priority
ranking).
• Watershed description (e.g., predominant land
cover or land use, geology and hydrology).
3. Applicable Water Quality Standards and Water
Quality Numeric Targets
• Description of applicable water quality
standards, including designated use(s) affected
by the pollutant of concern, numeric or narrative
standard, and the antidegradation policy.
• If the TMDL is based on a target other than a
numeric water quality standard, describe the
process used to derive the target.
4. Pollutant Assessment
• Source inventory with location of
Background
Point sources
Nonpoint sources
• Supporting documentation for the analysis of
pollutants loads from each source.
First Edition: November 1999
9-1
-------
Assembling the TMDL
5. Linkage Analysis
• Rationale for the analytical method used to
establish the cause-and-effect relationship
between the numeric target and the identified
pollutant sources.
• Supporting documentation for the analysis (e.g.,
basis for assumptions, strengths and weaknesses
in the analytical process, results from water
quality modeling).
6. TMDL and Allocations
• Total Maximum Daily Load (TMDL)1
The TMDL is expressed as the sum of the
WLAs, the LAs, and the MOS (if an explicit
MOS is included).
If the TMDL is expressed in terms other
than mass per time, explain the selection of
the other appropriate measure.
• Wasteload Allocations (WLAs)2
Loads allocated to existing and future point
sources.
An explanation of any WLAs based on the
assumption that loads from a nonpoint
source will be reduced.
If no point sources are present, list the WLA
as zero.
• Load Allocations (LAs)2
Loads allocated to existing and future
nonpoint sources.
Loads allocated to natural background
(where possible to separate from nonpoint
sources).
If there are no nonpoint sources or natural
background, list the LA should as zero.
• Seasonal Variation1
Description of the method chosen to
consider seasonal and interannual variation.
• Margin of Safety1
An implicit MOS is considered through
conservative assumptions in the analysis. To
justify this type of MOS, an explanation of
the conservative assumptions used is
needed.
An explicit MOS is incorporated by setting
aside a portion of the TMDL as the MOS.
7.
8.
9.
Required by statute.
2
Required by regulation.
• Critical Conditions2
Critical conditions associated with flow,
loading, designated use impacts, and other
water quality factors.
Follow-Up Monitoring Plan
• Recommended component for TMDLs.
Public Participation2
• Description of public participation process used.
• Summary of significant comments received and
the responses to those comments.
Implementation Plan
• Implementation plans are needed before TMDL
approval if they are necessary to provide
reasonable assurance that the load allocations
contained in the TMDL will be achieved.
Supplementary TMDL Submittal Information
In addition to the information described above, TMDL
submittals can be improved by preparing supplemental
information, including a TMDL summary memorandum,
a TMDL executive summary, a TMDL technical report,
and an administrative record. The effort required to
develop these documents should be minimal because
they are largely a repackaging of information contained
in the TMDL submittal. For example, the TMDL
executive summary would be prepared for the TMDL
technical report but would also be ideal for press
releases or distribution to the public.
The TMDL summary memorandum provides an
overview of all the essential regulatory elements of a
TMDL submittal. This overview can facilitate
regulatory and legal review. The summary memo should
include the following information:
• Waterbody (name, size) and location
• Pollutant of concern
• Primary pollutant source(s)
• Applicable water quality standards
• Major data and information sources
• TMDL establishment
• WLA, LA, MOS, critical condition, seasonality,
background concentrations
• Implementation
• Reasonable assurance
9-2
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
• Follow-up monitoring
• Public participation
The TMDL executive summary provides an overview of
the TMDL, the conclusions and implications, the
analyses, and the background. This document is useful
for public information, news releases, and public
hearing announcements.
The TMDL technical report provides a compilation of
the information sources, technical analyses,
assumptions, and conclusions. This document provides
a summary of the technical basis and rationale used in
deriving the TMDL. A sample report outline might
include the following sections:
1. Executive Summary
2. Introduction
3. TMDL Indicators and Numeric Targets
4. Water Quality Assessment
5. Source Assessment
6. Linking the Sources to the Indicators and Targets
7. Allocation
8. Implementation
9. Monitoring
10. References
The administrative record provides the technical
backup, sources of information, calculations, and
analyses used in deriving the TMDL. A typical
administrative record might include the following:
• Spreadsheets
• Modeling software, input and output files
• References
• Reports
• Paper calculations
• Maps (working copies)
Public Participation
Public participation is a requirement of the TMDL
process and is vital to a TMDL's success. The August
23, 1999, proposed regulation states that the public must
be allowed at least 30 days to review and comment on a
TMDL prior to its submission to EPA for review and
approval. In addition, with its TMDL submittal, a state,
territory, or authorized tribe must provide EPA with a
summary of all public comments received regarding the
TMDL and the State's, Territory's, or authorized
Tribe's response to those comments, indicating how the
comments were considered in the final decision.
EPA believes, however, that stakeholders can contribute
much more than their comments on a specific TMDL
during the public review process. Given the
opportunity, stakeholders can contribute credible, useful
data and information about an impaired or threatened
water body. They may also be able to raise funds for
monitoring or to implement a specific control action
and/or management measure.
More importantly, stakeholders can offer insights about
their community that may ensure the success of one
TMDL allocation strategy over an alternative, as well as
the success of follow-up monitoring and evaluation
activities. Stakeholders possess knowledge about a
community's priorities, how decisions are made locally,
and how different residents of a watershed interact with
one another. A thorough understanding of the social,
political, and economic issues of a watershed is as
critical to successful TMDL development as an
understanding of the technical issues. States, territories,
and authorized tribes can create a sense of ownership
among watershed residents and "discover" innovative
TMDL strategies through a properly managed public
participation process.
Each state, territory and authorized tribe is required to
establish and maintain a continuing planning process
(CPP) as described in section 303(e) of the Clean Water
Act. A CPP contains, among other items, a description
of the process that the state, territory or authorized tribe
uses to identify waters needing water quality based
controls, a priority ranking of these waters, the process
for developing TMDLs, and a description of the process
used to receive public review of each TMDL. EPA
encourages states, territories, and authorized tribes to
use their CPP as the basis for establishing a process for
public participation, involvement, and in many cases
leadership, in TMDL establishment. On a watershed
level, the continuing planning process allows programs
to combine or leverage resources for public outreach and
involvement, monitoring and assessment, development
of management strategies, and implementation.
First Edition: November 1999
9-3
-------
Assembling the TMDL
RECOMMENDED READING
(Note that the full list of references for this section is at
the end of the document.)
• USEPA. 1991a. Guidance for water quality-based
decisions: The TMDL process. EPA 440/4-91-001.
U.S. Environmental Protection Agency, Assessment
and Watershed Protection Division, Washington,
DC.
• USEPA \999.Draft guidance for water quality-
based decisions: The TMDL process (second
edition). EPA 841-D-99-001. U.S. Environmental
Protection Agency, Washington, DC.
9-4
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
APPENDIX: Case Studies
Laguna de Santa Rosa, California, TMDL
Chatfield Basin, Colorado, TMDL
First Edition: November 1999
-------
Appendix: Case Studies
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
TMDL Summary: Laguna de Santa Rosa, California
Waterbody Type:
Pollutant:
Designated Uses:
Size of Waterbody:
Size of Watershed:
Water Quality Standards:
Indicators:
Analytical Approach:
Introduction
Stream
Nutrients
Various
Approximately 12 miles
255 square miles
0.025 mg-N/L un-ionized
ammonia
7.0 mg/L minimum
dissolved oxygen
concentration
Same as above
Load-response relationship
The TMDL developed for the Laguna de Santa Rosa
illustrates the steps that can be taken to address a
waterbody impaired by elevated total nitrogen and
ammonia and by low dissolved oxygen levels. The plan
TMDL Submittal Elements
Loading Capacity: Varies by season
Load Allocation: Varies by season
Wasteload Allocation: Varies by season
Seasonal Variation: Varies by season
Margin of Safety:
Implicit through conservative
assumptions
is consistent with a phased-approach TMDL: estimates
are made of needed reductions of pollutant loads, load-
reduction controls are implemented, and water quality is
monitored for plan effectiveness. Flexibility is built
into the plan so that load reduction targets and control
actions can be reviewed if monitoring indicates
continuing water quality problems.
Problem Identification
A cover memo should describe the waterbody as it is
identified on the state's section 303(d) list, the pollutant
of concern, and the priority ranking of the waterbody.
The TMDL submittal must include a description of the
point, nonpoint, and natural background sources of the
pollutant of concern, including the magnitude and
location of the sources. The TMDL submittal should
also contain a description of any important assumptions,
such as (1) the assumed distribution of land use in the
watershed; (2) population characteristics, wildlife
resources, other relevant characteristics affecting
pollutant characterization and allocation, as applicable;
(3) present and future growth trends, if this factor was
taken into consideration in preparing the TMDL; (4)
explanation and analytical basis for expressing the
TMDL through surrogate measures, if applicable.
Laguna de Santa Rosa is a tributary of the Russian River
and is located near the city of Santa Rosa, California.
The Laguna is home to salmonid and trout species and is
a resource for recreational fisheries. However, the
Laguna de Santa Rosa was listed on California's section
303(d) list of impaired waterbodies in 1992, 1994, and
1996. It was listed because of seasonal high ammonia
and low dissolved oxygen levels caused by excessive
nutrient loadings. High levels of un-ionized ammonium
exceeded EPA's existing criterion of 0.025 mg-N/L
(USEPA, 1986). (Levels of un-ionized ammonia above
0.025 mg-N/L are considered toxic to fish.) Low levels
of dissolved oxygen in the Laguna were also detected,
violating the North Coast Region's Basin Plan objective
of 7.0 mg/L for minimum dissolved oxygen.
Description of the Applicable Water Quality
Standards and Numeric Water Quality Target
The TMDL submittal must include a description of the
applicable state water quality standard, including the
designated use(s) of the waterbody, the applicable
numeric or narrative water quality criterion, and the
antidegradation policy. This information is necessary
for EPA to review the load and wasteload allocation
required by the regulation. A numeric water quality
First Edition: November 1999
Appendix-1
-------
Appendix: Case Studies
target for the TMDL (a quantitative value used to
measure whether the applicable water quality standard
is attained) must be identified. If the TMDL is based on
a target other than a numeric water quality criterion, the
submittal must include a description of the process used
to derive the target.
EPA's numeric criterion of 0.025 mg-N/L for un-ionized
ammonia was used as the target value for the total
ammonia indicator. Ammonia exists in water in either
the ionic state or the un-ionized state. The percentage
of measured total ammonia present in the toxic un-
ionized state is a function of pH and temperature. As
pH and temperature rise so does the relative percentage
of total ammonia in the un-ionized state. The TMDL
analysis assumes a conservative temperature of 24 °C
and a pH of 8 in establishing the total ammonia target.
These temperature and pH levels are worst-case
conditions for ammonia toxicity and are rarely observed
during the year in the Laguna; the target value for the
indicator therefore implicitly accounts for a margin of
safety.
Source Assessment
High algal productivity is common in the Laguna.
Algal growth depends on an adequate supply of two
nutrients, nitrogen and phosphorus. Historically high
nitrogen concentrations in the Laguna's water column
and the prevalence of many typical pollutant sources led
investigators to suspect a nutrient loading problem in
the watershed (Morris, 1995). Algal Growth Potential
Studies conducted characterized the algal growth in the
Laguna's water as being limited by nitrogen (Roth and
Smith, 1992, 1993, 1994).
Two section 205 (j) studies were conducted to determine
the sources of nitrogen in the watershed. North Coast
Regional Water Quality Control Board (NCRWQCB)
staff conducted the first study in 1989-91, and it
concluded that urban runoff, animal waste runoff, and
wastewater from the city of Santa Rosa's Subregional
Wastewater Reclamation Plant are sources of nitrogen,
including ammonia. A subsequent 205(j) study
conducted by the city of Santa Rosa in 1991-93
estimates the waste loads of nitrogen and organic matter
from each loading sector in the watershed, including
loads from septic systems, open space, agricultural
operations, urban runoff, and wastewater from the
Subregional Plant. Total loads of nitrogen and ammonia
for the various loading sectors are estimated for each
season and further disaggregated spatially by four
distinct watershed areas. For example, the watershed
area between Trenton-Heraldsburg Road and
Guerneville Road has total estimated wintertime loads
of 772,576 pounds total nitrogen. Twenty-four percent
of the load is attributed to urban runoff, 32 percent to
wastewater sources, 10 percent to non-irrigated
agricultural sources, 25 percent to dairy farm sources, 2
percent to dairy pond overflows, 4 percent to septic
loadings, and the remaining 3 percent to open space
runoff.
NCRWQCB staff reduced the septic loading estimates
from the 1991-93 205(j) study by 58 percent, citing
overly conservative assumptions used by the city (e.g.,
the city's assumptions included an excessive estimate of
wastewater flow per capita). Septic waste load
estimates used in the TMDL may still be too high
because the TMDL assessment assumes, probably
incorrectly, that all wastewater discharged through
septic systems reaches the Laguna, even those systems
at the edge of the watershed (Strauss, 1995). The
strategy outlined by NCRWQCB staff commits to a
more intensive study of septic system discharges and
transport to the Laguna to better characterize septic
loading.
Loading Capacity — Linking Water Quality and
Pollutant Sources
As described in EPA guidance, a TMDL describes the
loading capacity of a waterbody for a particular
pollutant. EPA regulations define loading capacity as
the greatest amount of loading that a waterbody can
receive without violating water quality standards (40
CFR 130.2(f)). The TMDL submittal must describe the
rationale for the analytical method used to establish the
cause-and-effect relationship between the numeric target
and the identified pollutant sources. In many
circumstances, a critical condition must be described
and related to physical conditions in the waterbody (40
CFR 130.7(c)(l)). Supporting documentation for the
analysis must also be included, including the basis for
assumptions, strengths and weaknesses in the analytical
process, and results from water quality modeling, so that
EPA can properly review the elements of the TMDL
required by the statute and regulations.
Appendix-2
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
High ammonia levels in the Laguna are the result of
inputs of nitrogen in various forms. The NCRWQCB
focused on controlling the supply of nitrogen to the
Laguna as a means of controlling ammonia. The un-
ionized ammonia goal was converted into numeric
concentration-based targets for total nitrogen and total
ammonia using the conservative temperature and pH
assumptions for partitioning un-ionized ammonia
discussed above.
At night, in the absence of light, algae use oxygen in a
respiration reaction. As algae levels increase, so does
the corresponding respiration oxygen demand. When
respiration demands exceed oxygen transfer rates across
the water surface, low levels of dissolved oxygen can
result. Since nitrogen is the limiting nutrient for algal
growth in the basin, NCRWQCB focused on controlling
the supply of nitrogen to the Laguna as a means of
controlling the growth of algae and thus increasing the
levels of dissolved oxygen in the river. Direct actions
to increase the levels of dissolved oxygen in the Laguna
are infeasible due to both technical challenges and the
complex interaction of factors that affect oxygen supply
and demand. Because of insufficient information
relating nutrient levels to dissolved oxygen and algae
levels directly, NCRWQCB used the un-ionized
ammonia goal to derive loading reductions in nitrogen.
NCRWQCB staff expect that reductions in total
nitrogen will result in reductions in total ammonia, total
phosphate, and organic matter. Reductions in these
parameters are expected to reduce algal growth, which
is in turn expected to increase levels of dissolved
oxygen in the water. NCRWQCB staff have continued
to monitor dissolved oxygen levels in the Laguna and
will modify nitrogen loading reduction goals if
minimum goals are not attained in the first phase of the
TMDL.
The numeric concentration-based targets for total
nitrogen and total ammonia were combined with
seasonal flow information at each attainment point in
the watershed to derive total permissible loading targets
for each area by season.
Allocations
EPA regulations require that a TMDL include
wasteload allocations (WLAs), which identify the
portion of the loading capacity allocated to existing and
future point sources (40 CFR 130.2(g)). If no point
sources are present or the TMDL recommends a zero
WLA for point sources, the WLA must be listed as zero.
The TMDL may recommend a zero WLA if the state
determines, after considering all pollutant sources, that
allocating only to nonpoint sources will still result in
attainment of the applicable water quality standard. In
preparing the WLA, it is not necessary that every
individual point source have a portion of the allocation
of pollutant loading capacity. It is necessary, however,
to allocate the loading capacity among individual point
sources as necessary to meet the water quality standard.
The TMDL submittal should also discuss whether a
WLA is based on an assumption that loads from a
nonpoint source or sources will be reduced. In such
cases, the state needs to demonstrate reasonable
assurance that the nonpoint source reductions will occur
within a reasonable time.
EPA regulations also require that a TMDL include load
allocations (LAs), which identify the portion of the
loading capacity allocated to existing and future
nonpoint sources and to natural background (40 CFR
130.2(h)). Load allocations may range from reasonably
accurate estimates to gross allotments (40 CFR
130.2(g)). Where it is possible to separate natural
background from nonpoint sources, separate LAs should
be made and described. If there are neither nonpoint
sources nor natural background or the TMDL
recommends a zero LA, an explanation must be
provided. The TMDL may recommend a zero LA if the
state determines, after considering all pollutant sources,
that allocating only to point sources will still result in
attainment of the applicable water quality standard.
The statute and regulations require that a TMDL include
a margin of safety to account for any lack of knowledge
concerning the relationship between effluent limitations
and water quality (CWA § 303(d)(l)(C), 40 CFR
130.7(c)(l)). EPA 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.
First Edition: November 1999
Appendix-3
-------
Appendix: Case Studies
The statute and regulations require that a TMDL be
established with seasonal variations. The state must
describe the method chosen for including seasonal
variations in the TMDL (CWA § 303(d)(l)(C), 40 CFR
Several allocation scenarios were developed for the
Laguna TMDL, each satisfying total permissible
seasonal loading targets for each of the four areas. A
period of public review allowed for stakeholder input,
resulting in selection of an appropriate scenario that
allocated responsibilities for nutrient loading reduction
equitably and allowed for phased implementation.
Criteria used for allocating load reductions were to
• Meet water quality goals.
• Best represent the Laguna flow and pollutant
loading dynamics.
• Provide a reasonable time frame for stakeholders to
make load reduction adjustments.
• Provide reasonable and achievable load reductions.
Targeted load reductions were implemented through
allocations among
• Nonpoint source nutrient discharge reduction
projects.
• Urban stormwater load reductions.
• Municipal wastewater plant upgrades in Santa Rosa.
• Septic system upgrades.
NCRWQCB staff divided the Laguna watershed into
four areas and established attainment points at the
downstream end of each reach. They developed
seasonal loads for each of the four areas. Seasonal
loads were developed because variation in seasonal
flow patterns is an important factor in determining
nutrient concentrations in the Laguna. NCRWQCB
staff relied on flow information gathered in May 1991
to December 1993 in making load allocations; two of
the three years were dry years and are probably
representative of the longer-term flow record (Strauss,
1995).
Table 1 summarizes the existing and targeted reduction
loads for one attainment point during the summer
season. Implementation of the TMDL should result in
attainment of narrative and numeric surface water
quality standards in the Laguna during most times of the
year (Morris, 1995, cited in Smith, 1995). Although the
planned load reduction activities will not be fully
effective in meeting the summertime nitrogen reduction
target goals, this is partly due to the overly high summer
septic system load estimates. Actual loading from the
septic systems is suspected to be much lower than
originally estimated (Morris, 1995). Further studies to
more accurately characterize the septic loading
parameters are under way.
Table 1. Summer allocations for total nitrogen
(pounds/season) forTrenton-Heraldsburg Road attainment
point. Annual loads are composed of seasonal (winter,
spring, summer, fall) loads distributed among four separate
attainment points.
Pollutant Source
Urban
Wastewater
Nonirrigated
Dairy Agriculture
Dairy Pond
Septic
Open Space
Total
Estimated Existing Load
647
0
987
584
13,727
33,170
390
49,505
Allocation
0
0
987
0
0
33,170
390
34,547
Monitoring Plan
EPA's 1991 document Guidance for Water Quality-
Based Decisions: The TMDL Process (EPA 440/4-91-
001) calls for a monitoring plan when a TMDL is
developed under the phased approach. The guidance
provides that a TMDL developed under the phased
approach also needs to provide assurances that nonpoint
source control measures will achieve expected load
reductions. The phased approach is appropriate when a
TMDL involves both point and nonpoint sources and the
point source WLA is based on an LA for which
nonpoint source controls need to be implemented.
Therefore, EPA's guidance provides that a TMDL
developed under the phased approach should include a
monitoring plan that describes the additional data to be
collected to determine if the load reductions required by
the TMDL lead to attainment of water quality standards.
NCRWQCB has developed a plan to monitor water
quality at each of the four attainment points throughout
each season. NCRWQCB collects water quality
samples biweekly and during storm events. In addition,
Appendix-4
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
continuous remote monitoring is conducted for
dissolved oxygen, pH, conductance, and temperature at
monthly intervals. The monitoring evaluates Laguna
water quality and informs the future direction of the
TMDL plan.
Statistical methods are used to evaluate water quality
compliance with the USEPA criterion for un-ionized
ammonia and the Basin Plan minimum objective for
dissolved oxygen. The minimum dissolved oxygen
objective is considered obtained if median and 90th
percentile values of dissolved oxygen concentrations are
maintained above 7.0 mg/L, as determined with
cumulative frequency distributions. A staged method
was used to evaluate un-ionized ammonia goals,
specifying the percentage of measurements that must
meet the EPA criterion per the following schedule:
1. Sixty percent of the measurements must be below
the EPA criterion by July 1996.
2. Seventy percent must be below the EPA criterion by
July 1998.
3. Eighty percent must be below the EPA criterion by
July 2000.
The water quality data are evaluated using cumulative
distribution plots and t-tests of the mean of seasonal
measurements compared to the USEPA criterion for un-
ionized ammonia. Thus far the monitoring has
indicated that the TMDL's interim goals have been
attained (Otis, 1999).
Implementation Plans
On August 8, 1997, EPA's Bob Perciasepe issued a
memorandum, "New Policies for Establishing and
Implementing Total Maximum Daily Loads (TMDLs),"
which directs EPA regions to work in partnership with
states to achieve nonpoint source load allocations
established for 303(d)-listed waters impaired solely or
primarily by nonpoint sources. To this end, the
memorandum asks that regions assist states in
developing implementation plans that include
reasonable assurances that the nonpoint source load
allocations established in TMDLs for waters impaired
solely or primarily by nonpoint sources will in fact be
achieved; a public participation process; and
recognition of other relevant watershed management
processes. Although implementation plans are not
approved by EPA, they help establish the basis for
EPA's approval of TMDLs.
The Waste Reduction Strategy for the Laguna de Santa
Rosa includes a description of the actions that will take
place to implement the TMDL. These include
• Grant program aimed at reducing waste inputs from
confined animal operations.
• Stormwater runoff program.
• NPDES permit program.
• Voluntary actions organized by the Laguna
Watershed Coordinated Resource Management and
Planning Task Force.
Reasonable Assurances
EPA guidance calls for reasonable assurances when
TMDLs are developed for waters impaired by both point
and nonpoint sources or for waters impaired solely by
nonpoint sources. In a water impaired by both point and
nonpoint sources, where a point source is given a less
stringent wasteload allocation based on an assumption
that nonpoint source load reductions will occur,
reasonable assurance must be provided for the TMDL to
be approvable. This information is necessary for EPA to
review the load and wasteload allocations required by
the regulation.
In a water impaired by solely by nonpoint sources,
reasonable assurances are not required for a TMDL to
be approvable. For such nonpoint source-only waters,
states are encouraged to provide reasonable assurances
regarding achievement of load allocations in the
implementation plans described in section 7, above. As
described in the August 8, 1997, Perciasepe
memorandum, such reasonable assurances should be
included in state implementation plans and "may be non-
regulatory, regulatory, or incentive-based, consistent
with applicable laws and programs."
References
Morris, C.N. 1995. Waste reduction strategy for the
Laguna de Santa Rosa. Prepared for the California
Regional Water Quality Control Board, North Coast
Region, Santa Rosa, CA. March.
Otis, P. 1999. Personal communication. March 30.
First Edition: November 1999
Appendix-5
-------
Appendix: Case Studies
Roth, J.C., and D.W. Smith. 1992. Final report: 1990-
1991 Laguna de Santa Rosa water quality monitoring
program. January.
Roth, J.C., and D.W. Smith. 1993. Final report: 1991-
1992 Laguna de Santa Rosa water quality monitoring
program. May.
Roth, J.C., and D.W. Smith. 1994. Final report: 1992-
1993 Laguna de Santa Rosa water quality monitoring
program. May.
Smith, D. 1995. Memo describing analysis to support
approval of TMDLs for Laguna de Santa Rosa, Water
Management Branch, Region 9, U.S. Environmental
Protection Agency, San Francisco,CA. May.
Strauss, A. 1995. Approval letter for TMDL submittal,
Water Management Branch, Region 9, U.S.
Environmental Protection Agency, San Francisco, CA.
May.
USEPA. 1986. Quality criteria for water. EPA 440/5-
86-001. U.S. Environmental Protection Agency,
Washington, DC.
USEPA. 1997. New policies for establishing and
implementing Total Maximum Daily Loads (TMDLs).
Memorandum sent by Robert Perciasepe, Assistant
Administrator. August 8, 1997.
Contact: Dave Smith, Region 9 TMDL Coordinator
United States Environmental Protection Agency
75 Hawthorne Street • San Francisco, CA 94105
(415) 744-2012 • smith.davidw@epa.gov
Appendix-6
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
TMDL Summary: Chatfield Basin, Colorado
Waterbody Type:
Pollutant:
Designated Uses:
Size of Waterbody:
Size of Watershed:
Water Quality Standards:
Indicators:
Analytical Approach:
Reservoir
Phosphorus
Recreation, Aquatic Life,
Water Supply, Agriculture
1,450 acres
3,000 square miles
Narrative
17 pg/L chlorophyll a
27 jug/L total phosphorus
from July to September
Jones-Bachman Model;
Canfield-Bachman Model
Introduction
Chatfield Reservoir is a U.S. Army Corps of Engineers
facility located on the South Platte River just southwest
of Denver, Colorado. The reservoir was completed in
1976 for purposes of flood protection for the
metropolitan Denver area following the disastrous
South Platte flood of 1965. Since that time, Chatfield
Reservoir, which is now the primary attraction of a state
park, has become increasingly popular as a recreational
facility and concern over possible decreases in water
quality due to upstream nutrient loadings has arisen.
The upstream watershed, called here the "Chatfield
Basin" and shown in Figure 1, encompasses a total area
TMDL Submittal Elements
Loading Capacity: 59,000 Ibs/yr total phosphorus
20,000 Ibs/yr reduction from NPS
128,000 Ibs/yr reduction from PS
Load Allocation:
Wasteload Allocation:
Seasonal Variation:
Margin of Safety:
Loads are specified on an annual
basis
Implicit through conservative
assumptions
of approximately 3,000 square miles and covers portions
of six counties. It includes the headwaters of the South
Platte River and extends westward to the continental
divide and south nearly to Colorado Springs. The South
Platte River portion of the basin is largely undeveloped
and includes portions of the Pike National Forest and the
Mount Evans Wilderness area. Some small urban areas
and agricultural uses are also present. The eastern
portion of the Chatfield Basin comprises the Plum Creek
watershed, approximately 300 square miles in area.
Problem Identification
The TMDL submittal must include a description of the
point, nonpoint, and natural background sources of the
pollutant of concern, including the magnitude and
location of the sources. The TMDL submittal should
also contain a description of any important assumptions,
such as (1) the assumed distribution of land use in the
watershed; (2) population characteristics, wildlife
resources, other relevant characteristics affecting
pollutant characterization and allocation, as applicable;
(3) present and future growth trends, if this factor was
taken into consideration in preparing the TMDL; (4)
explanation and analytical basis for expressing the
TMDL through surrogate measures, if applicable.
A Clean Lakes Study for Chatfield Reservoir performed
in 1984 (DRCOG, 1984) stated: "The existing water
quality of the reservoir is adequate for its designated
purposes [recreation, aquatic life, water supply, and
agriculture] and only minor concerns have occurred
regarding water quality" and "The purpose of the
Chatfield Reservoir Clean Lakes Study ... is different
from the purpose of most clean lake studies in that it
attempted to prevent an adverse situation from occurring
instead of studying how to resolve an existing one."
This proactive, as opposed to reactive, management
attitude is still applicable today. Since 1984, the
growing-season average chlorophyll a goal (discussed
below) for the reservoir has never been exceeded.
Nonetheless, the continued presence of significant levels
of phosphorus in the reservoir and the concomitant
possibility of nuisance algal blooms have resulted in a
growing awareness of the need for proactive
management. Indeed, Douglas County, which composes
First Edition: November 1999
Appendix-7
-------
Appendix: Case Studies
Figure 1. Chatfield Basin and Plum Creek Study Area
a portion of the watershed, is one of the most rapidly
developing areas in the nation. Given the rapid
urbanization in the watershed and the desire to preserve
the historically good quality of water in the reservoir,
the Chatfield Basin Authority ("the Authority," an inter-
governmental water quality management agency) has
embarked on a long-term TMDL program. Elements of
that program include the following:
• Water quality standard. Establish a growing season
average (July-September) in-reservoir total
phosphorus standard protective of good historical
water quality.
• TMDL. Phosphorus has been assumed to be the
nutrient of primary concern, and the estimated 1995
total annual raw load (i.e., no existing upstream
removal) to the reservoir from the entire basin under
1-in-10-year high-runoff conditions is
approximately 207,000 pounds. Determine the Total
Maximum Annual Load (TMAL) that will just meet
this standard; that is, determine how much of the
207,000-pound load must be removed.
• WLA/LA. Determine an appropriate distribution of
the TMAL between and among point sources and
nonpoint sources.
This management program has been under way for
nearly a decade, and the Authority's approaches to these
objectives are discussed in this paper.
Description of the Applicable Water Quality
Standards and Numeric Water Quality Target
The TMDL submittal must include a description of the
applicable state water quality standard, including the
designated use(s) of the waterbody, the applicable
numeric or narrative water quality criterion, and the
antidegradation policy. This information is necessary
for EPA to review the load and wasteload allocation
required by the regulation. A numeric water quality
target for the TMDL (a quantitative value used to
measure whether the applicable water quality standard is
attained) must be identified. If the TMDL is based on a
target other than a numeric water quality criterion, the
submittal must include a description of the process used
to derive the target.
The water quality variable of concern in Chatfield
Reservoir is chlorophyll a. The Authority, through the
Denver Regional Council of Governments (DRCOG),
has determined that maintaining growing-season average
chlorophyll a concentrations of 17 ^g/L is an
appropriate management target (DRCOG, 1984).
Because chlorophyll a itself is not input to a waterbody
from point and nonpoint sources, the regulatory and
management focus is on total phosphorus, which has
been assumed to be the algal-limiting nutrient (or can be
forced to be such through sufficient control). Thus, to
set an in-reservoir, numerical, regulatory standard on
total phosphorus such that the chlorophyll a goal is
achieved, a quantitative relationship between total
phosphorus and chlorophyll a was investigated.
The model DRCOG selected was the Jones-Bachman
model (Jones and Bachman, 1976) which, when
calibrated to Chatfield Reservoir, relates the two
variables as
CHL = 0.1413*TP
1.46
(1)
where CHL is the chlorophyll a concentration
and total phosphorus is the total phosphorus
concentration (//g/L). The parameters of equation (1)
were estimated from a single, paired chlorophyll a/total
phosphorus sample, the only data available at the time of
the study (1982). By specifying 17 pg/L for chlorophyll
a in equation (1), the regulatory total phosphorus
standard was determined by solving the equation for
total phosphorus, resulting in a growing season average,
Appendix-8
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
in-reservoir concentration of 27 /ng/L. (It should be
noted that more recent data have shown that model (1)
significantly overpredicts observed chlorophyll a
concentrations, given observed total phosphorus
concentrations. Thus, the current 27 pg/L standard is
regarded as conservative. Future in-reservoir modeling
activities are planned to develop a better relationship
between the two variables and a more appropriate
standard.)
Source Assessment
The current target value for nutrient management
activities in the basin is the 27 pg/L total phosphorus
standard in the reservoir. Sources of total phosphorus
loads to the reservoir include point sources, nonpoint
sources, and baseload (dry weather) inflows from both
the South Platte and Plum Creek subbasins. Although
the Plum Creek subbasin is the much smaller of the two,
it contributes the great majority of the total phosphorus
load due to its relatively higher state of development. In
addition, there are several reservoirs upstream of
Chatfield Reservoir in the South Platte subbasin and
these reservoirs effectively serve as nutrient removal
mechanisms so that little additional phosphorus removal
is practicable in the South Platte subbasin. For these
reasons, those point and nonpoint sources of total
phosphorus amenable to further management control as
part of the TMDL process are essentially limited to the
Plum Creek subbasin.
Loading Capacity — Linking Water Quality and
Pollutant Sources
As described in EPA guidance, a TMDL describes the
loading capacity of a waterbody for a particular
pollutant. EPA regulations define loading capacity as
the greatest amount of loading that a waterbody can
receive without violating water quality standards (40
CFR 130.2(f)). The TMDL submittal must describe the
rationale for the analytical method used to establish the
cause-and-effect relationship between the numeric
target and the identified pollutant sources. In many
circumstances, a critical condition must be described
and related to physical conditions in the waterbody (40
CFR 130.7(c)(l)). Supporting documentation for the
analysis must also be included, including the basis for
assumptions, strengths and weaknesses in the analytical
process, and results from water quality modeling, so
that EPA can properly review the elements of the TMDL
required by the statute and regulations.
The Jones-Bachman model (equation (1)) relates in-
reservoir total phosphorus concentrations to chlorophyll
a concentrations on a growing season average basis. For
phosphorus management purposes, it is also necessary to
relate total phosphorus concentrations to annual total
phosphorus loadings to the reservoir. The model
selected for this purpose (DRCOG, 1982) was the
Canfield-Bachman model (Canfield and Bachman,
1981) which, when parameterized to the 1982 data pair
and using a 1-in-10-year reservoir inflow, is expressed
as
TP = 17(0.82 * L-589 + 59.4) (2)
where TP is the in-reservoir total phosphorus
concentration (//g/L) and L is the annual areal
phosphorus loading (mg/m2/yr). The first term in the
denominator of (2) is a settling term. The second term
reflects the flushing effect of annual inflow. Solving
equation (2) for the total phosphorus standard (27 pg/L)
results in an allowable annual areal load of 4,900
mg/m2/yr, or an annual load of 59,000 pounds. Thus,
59,000 pounds is the estimated TMAL not to be
exceeded in 90 percent of years.
Allocations
EPA regulations require that a TMDL include wasteload
allocations (WLAs), which identify the portion of the
loading capacity allocated to existing and future point
sources (40 CFR 130.2(g)). If no point sources are
present or the TMDL recommends a zero WLA for point
sources, the WLA must be listed as zero. The TMDL
may recommend a zero WLA if the state determines,
after considering all pollutant sources, that allocating
only to nonpoint sources will still result in attainment of
the applicable water quality standard. In preparing the
WLA, it is not necessary that every individual point
source have a portion of the allocation of pollutant
loading capacity. It is necessary, however, to allocate
the loading capacity among individual point sources as
necessary to meet the water quality standard. The
TMDL submittal should also discuss whether a WLA is
based on an assumption that loads from a nonpoint
source or sources will be reduced. In such cases, the
state needs to demonstrate reasonable assurance that the
First Edition: November 1999
Appendix-9
-------
Appendix: Case Studies
nonpoint source reductions will occur within a
reasonable time.
EPA regulations also require that a TMDL include load
allocations (LAs), which identify the portion of the
loading capacity allocated to existing and future
nonpoint sources and to natural background (40 CFR
130.2(h)). Load allocations may range from reasonably
accurate estimates to gross allotments (40 CFR
130.2(g)). Where it is possible to separate natural
background from nonpoint sources, separate LAs should
be made and described. If there are neither nonpoint
sources nor natural background or the TMDL
recommends a zero LA, an explanation must be
provided. The TMDL may recommend a zero LA if
the state determines, after considering all pollutant
sources, that allocating only to point sources will still
result in attainment of the applicable water quality
standard.
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
effluent limitations and water quality (CWA §
303(d)(l)(C), 40 CFR 130.7(c)(l)). EPA 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.
The statute and regulations require that a TMDL be
established with seasonal variations. The state must
describe the method chosen for including seasonal
variations in the TMDL (CWA § 303(d)(l)(C), 40 CFR
Current annual loads (raw) in the Chatfield Basin have
been estimated at approximately 207,000 pounds and
the TMAL is estimated at 59,000 pounds, both under 1-
in-10 annual inflow conditions. The annual load that
must be reduced from point and nonpoint sources is
then the difference, or approximately 148,000 pounds.
Thus, the point source/nonpoint source load allocation
issue for the Plum Creek subbasin is: How should the
59,000 pound TMAL be allocated among point sources
(there are six) and between point and nonpoint sources
so that total treatment costs are minimized? This section
addresses that issue using an optimization approach.
Because of the present uncertainty surrounding the
TMAL, the optimal (minimum cost) removals for point
sources and nonpoint sources are expressed as functions
rather than as single values. (In the future, under
possibly different TMAL conditions, these functions can
be used for point source/nonpoint source load
allocations.)
Treatment Costs
Twenty-year present worth treatment cost functions
were developed for both point sources and nonpoint
sources. Point source costs included only the additional
costs (capital and operating) to remove phosphorus by
chemical means and were based on data from USEPA
(1987) and Murphy and Associates (1983). Nonpoint
source treatment costs assumed that stormwater
detention basins were the preferred best management
practice (BMP) type and were based on data provided by
Schueler (1987).
Optimal Point Source WLA
An optimization analysis was first performed to develop
the minimum cost wasteload allocation function for
point sources only. This optimization determined, for
any given total annual load removed by point sources,
the least cost means of attaining this removal among the
six point source dischargers. The marginal cost
principle was the basis of the optimization such that a
given annual load removed was allocated among the
dischargers in accordance with their marginal treatment
costs. The result of this analysis was a function yielding
minimum present worth point source treatment cost as a
function of total annual phosphorus load removed
among the dischargers (Figure 2).
Optimal Nonpoint Source LA
Similarly, a function relating minimum treatment costs
for nonpoint sources only as a function of total annual
nonpoint source load removed was developed. Given
that some 40 discrete (noncontiguous) urbanized areas
exist within the Plum Creek Study Area, this
optimization problem was essentially whether to build
40 individual detention basins, one regional detention
Appendix-10
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
50 100 150
Animal Load Removed
(1000 D>)
Figure 2. PS and NFS Minimum Cost Functions
basin, or some number in between. This optimization
problem was originally formulated as a mixed-integer
linear program, but proved prohibitively time-
consuming to solve. Instead, a more conventional
approach was taken wherein a limited number of
alternatives were individually costed and the minimum
selected. A single, regional detention basin was
determined to be the optimal configuration.
Under the assumption that nonpoint source controls
should be protective of the reservoir during 90 percent
of years, a time series of runoff events representing the
1-in-10-year hydrology was developed. Phosphorus
loads were also developed for these events, and the
design time series was then routed through the regional
detention basin for each of a variety of alternative basin
volumes. For each alternative basin volume, the routed
time series of runoff and phosphorus loads resulted in a
total annual load removed by the detention basin. The
result of the analysis thus yielded minimum nonpoint
source treatment costs as a function of total annual load
removed among nonpoint sources only (Figure 2).
Perhaps surprisingly, the optimal nonpoint source
(NFS) cost function in Figure 2 reveals much higher
costs for NFS phosphorus control than point source
(PS) controls. This cost difference is attributable to at
least the following factors: (1) the use of structural
BMPs, (2) the choice of capturing runoff from the 1-in-
10 runoff year instead of a more typical year, and (3)
the relative ineffectiveness of detention basin
phosphorus removal (assumed at 45 percent). It is not
known to what extent these relative cost differences
might also apply in other watersheds.
Optimal PS/NPS LA
The optimal point source and nonpoint source load
allocation functions are shown together in Figure 2.
Each represents the minimum cost of removing load
from that source only. The question is then: What is the
function representing optimal allocation between point
sources and nonpoint sources?
The optimal point source/nonpoint source load
allocation function was developed by solving a series of
nonlinear programming models. The decision variables
were: X1 = annual load removed by point sources and
X2 = annual load removed by nonpoint sources (during
90th percentile year). The objective function was MIN
[Cos^Xj) + Cost(X2)] where Cos^Xj) is the minimum
present worth cost function for point sources, discussed
previously, and Cost(X2) is the minimum present worth
cost function for nonpoint sources, also discussed
previously. Constraints on the optimization model were
that Xj plus X2 equal the total annual load removed and,
further, that X1 and X2 must be less than or equal to
technological upper limits.
The nonlinear programming model was solved for a
variety of total annual loads removed. The resulting
minimum cost point source/nonpoint source load
allocation function is shown in Figure 3 and the
resulting allocation between point sources and nonpoint
sources in Figure 4. Interestingly, but perhaps not
surprisingly given the high nonpoint source costs, point
sources are used exclusively to remove phosphorus up to
an annual removal of approximately 128,000 pounds.
Beyond this, it becomes economical to begin removing
some of the additional load by using detention basins.
Thus, of the currently estimated 148,000 pound annual
load to be removed, the first 128,000 pounds would
most economically be achieved by the point sources
with the remaining 20,000 pounds to be removed by a
regional detention basin. The 128,000 pound point
source WLA corresponds to a uniform effluent
concentration among all six dischargers of
approximately 0.5 mg/L. (Given the study assumptions
and uncertainties, this concentration is not considered to
be significantly different from the 1.0 mg/L effluent
First Edition: November 1999
Appendix-11
-------
Appendix: Case Studies
0 50 100 150 200
Annual Load Removed
(1000 ft)
Figure 3. Minimum Cost Function
concentration that had already been established by the
Colorado Water Quality Control Commission.)
Monitoring Plan for TMDLs Developed Under the
Phased Approach
EPA's 1991 document Guidance for Water Quality -
Based Decisions: The TMDL Process (EPA 440/4-91-
001), calls for a monitoring plan when a TMDL is
developed under the phased approach. The guidance
provides that a TMDL developed under the phased
approach also needs to provide assurances that nonpoint
source control measures will achieve expected load
reductions. The phased approach is appropriate when a
TMDL involves both point and nonpoint sources and
the point source WLA is based on an LA for which
nonpoint source controls need to be implemented.
Therefore, EPA's guidance provides that a TMDL
developed under the phased approach should include a
monitoring plan that describes the additional data to be
collected to determine if the load reductions required by
the TMDL lead to attainment of water quality standards.
Monitoring efforts are continuing both in-reservoir and
in the watershed. Specific monitoring objectives
include trend analysis (total phosphorus and chlorophyll
a), BMP effectiveness, standard compliance, and data
collection to support future modeling.
Implementation Plans
On August 8, 1997, EPA's Bob Perciasepe issued a
memorandum, "New Policies for Establishing and
Implementing Total Maximum Daily Loads (TMDLs),"
which directs EPA regions to work in partnership with
states to achieve nonpoint source load allocations
established for 303(d)-listed waters impaired solely or
primarily by nonpoint sources. To this end, the
memorandum asks that regions assist states in
developing implementation plans that include
reasonable assurances that the nonpoint source load
allocations established in TMDLs for waters impaired
solely or primarily by nonpoint sources will in fact be
achieved; a public participation process; and recognition
of other relevant watershed management processes.
Although implementation plans are not approved by
EPA, they help establish the basis for EPA's approval of
TMDLs.
Water quality in Chatfield Reservoir has been relatively
good historically, and the management program for
Chatfield Reservoir and the Plum Creek Basin is
fortunate to find itself in a proactive position. Future
TMDL-related activities intend to maintain this good
quality, despite increasing urban pressures in the
watershed. These future activities include the
following:
• Refinement of the TMAL estimate and margin of
safety. The 59,000-pound TMAL currently
recognized is believed to be too conservative and, if
true, functions as an implicit margin of safety.
Future in-reservoir nutrient/chlorophyll a modeling
140
120
100
LA so
(1000 lb>«o
40
ao
o
PS
1WS
50 100 150 300
Annual Load Re moved
(1000 ft)
Figure 4. Optimum Load Allocation Schedule.
Appendix-12
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
is planned to refine the TMAL estimate and the
corresponding total phosphorus standard. It is
anticipated that this modeling effort will include an
uncertainty analysis that will result in an explicit
margin of safety. The improved TMAL estimate
will also permit a more precise determination of the
cost-effective point source/nonpoint source load
allocation, based on the schedule shown in Figure 4.
• BMP implementation. Despite the current
uncertainty in the TMAL and concomitant
uncertainty in the cost-effective point
source/nonpoint source load allocation, the
Authority is moving forward with implementation
of BMPs in the watershed. Two structural BMPs, a
Lemna system (in which duckweed is used to
remove nutrients) and a constructed wetland, have
been brought on-line in recent years. In addition,
existing erosion and sediment control ordinances
are being given more enforcement attention.
Reasonable Assurances
EPA guidance calls for reasonable assurances when
TMDLs are developed for waters impaired by both
point and nonpoint sources or for waters impaired solely
by nonpoint sources. In a water impaired by both point
and nonpoint sources, where a point source is given a
less stringent wasteload allocation based on an
assumption that nonpoint source load reductions will
occur, reasonable assurance must be provided for the
TMDL to be approvable. This information is necessary
for EPA to review the load and wasteload allocations
required by the regulation.
In a water impaired solely by nonpoint sources,
reasonable assurances are not required for a TMDL to
be approvable. For such nonpoint source-only waters,
states are encouraged to provide reasonable assurances
regarding achievement of load allocations in the
implementation plans described above. As described in
the August 8, 1997, Perciasepe memorandum, such
reasonable assurances should be included in state
implementation plans and "may be non-regulatory,
regulatory, or incentive-based, consistent with
applicable laws and programs."
Comment on Optimal PS/NPS Load Allocation
Methodology
The USEPA funded the development of the optimal load
allocation methodology highlighted in this case study.
This funding was provided in an effort not only to assist
water quality management in the Chatfield Basin, but
also to assess the potential for use of optimization
technology in TMDL activities for other watersheds.
The Chatfield Basin application demonstrates that there
is indeed an economical balance between point source
and nonpoint source responsibilities in meeting a
TMDL, and significant savings are possible when this
balance is known. (The current 1.0 mg/L point source
effluent limit in the Chatfield Basin resulted from an
appeal, based on cost-effectiveness arguments, by the
Authority to the Colorado Water Quality Control
Commission to relax a previously required, very
stringent effluent limit of 0.2 mg/L. If the 0.2 mg/L limit
had remained a requirement of the load allocation, the
resulting point source load removal would be 134,000
pounds, leaving 14,000 pounds to be removed from the
nonpoint sources to achieve the TMAL. This load
allocation would cost approximately 37 percent more
than the optimal load allocation based on 0.5 mg/L
effluent limits.)
In addition to the potential load allocation cost savings
offered by an optimization approach, a broader
conclusion might have emerged from this pilot study.
There seems to be a prevailing belief in the watershed
management community that removal of nonpoint
source pollutants constitutes essentially a panacea for
water quality problems because nonpoint source
removal is regarded as generally less expensive than
point source controls. However, the results of this study
suggest that structural nonpoint source control is not
nearly as cost-effective as might have been previously
believed: a relatively high level of point source
phosphorus removal is economically efficient before
structural nonpoint source controls are appropriate.
Thus, perhaps the real value of this study lies not so
much in guiding phosphorus allocation between point
sources and nonpoint sources controlled by structural
BMPs, but rather in quantifying the economic costs of
failing to prevent nonpoint source pollution in the first
place. If source controls, such as erosion control or
agricultural BMPs, are not in place and effective at
preventing nonpoint source pollution, structural controls
First Edition: November 1999
Appendix-13
-------
Appendix: Case Studies
such as the detention basins used in this study become
necessary. As demonstrated here, this after-the-fact
treatment is very expensive.
References
Canfield, D.E., andR.W. Bachman. 1981. Prediction of
total phosphorus concentrations, chlorophyll a, and
Secchi depths in natural and artificial lakes. Canadian
Journal of Fisheries and Aquatic Science, Vol. 38.
Denver Regional Council of Governments (DRCOG).
1984. Chatfield Reservoir Clean Lake Study. April.
Jones, J.R., and R.W. Bachman. 1976. Prediction of
phosphorus and chlorophyll levels in lakes. Journal
Water Pollution Control Federation 48(9), September.
Murphy and Associates. 1983. Construction costs for
wastewater treatment plants: 1973 -1982. Murphy and
Associates, Denver, CO. June.
Schueler, T.R. 1987. Controlling urban runoff: A
practical manual for planning and designing urban
BMPs. Prepared for the Washington Metropolitan
Water Resources Planning Board, Washington, DC.
USEPA. 1987. Handbook—Retrofitting POTWsfor
phosphorus removal in the Chesapeake Bay drainage
basin. EPA/625/6-87/017. U.S. Environmental
Protection Agency, Water Engineering Research
Laboratory, Cincinnati, OH.
Woodward-Clyde. 1992. Nonpoint source management
plan for the Chatfield Basin, Colorado.
Contact: Bruce Zander, Region 8 TMDL Coordinator
United States Environmental Protection Agency
999 18th Street • Denver, CO 80202-2405
zander.bruce@epa.gov
Appendix-14
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
References
Addiscott, T.M., and R.J. Wagenet. 1985. Concepts of
solute leaching in soils: A review of modeling
approaches. Journal of Soil Science 36:411-424.
Auer, M.T., R.P. Canale, J.M. Graham, H.C. Grundler,
J.P. Hoffman, and Y. Matsuoka. 1982. Ecological
studies and mathematical modeling of Cladophora in
Lake Huron. Journal of Great Lakes Research 8(1):
73-143.
Bauer, D.P., M.E. Jennings, and I.E. Miller. 1979.
One-dimensional steady-state stream water quality
model. U.S. Geological Survey Water Resources
Investigations Report 79-45. 215 pp.
Bicknell, B. R., J. C. Imhoff, J. L. Kittle, A. S.
Donigian, and R. C. Johanson. 1993. Hydrological
Simulation Program - FORTRAN (HSPF): User's
manual for release 10.0.
Biggs, B.J.F., and M.E. Close. 1989. Periphyton biomass
dynamics in gravel bed rivers: the relative effects of
flows and nutrients. Freshwater Biology 22:209-231.
Biggs, B. J. F. 1995. The contribution of disturbance,
catchment geology and land use to the habitat template
of periphyton in stream ecosystems. Freshwater Biology
33:419-438.
Bisson, P.A., G.H. Reeves, R.E. Bilby, and R.J. Naiman.
1997. Watershed management and Pacific salmon:
Desired future conditions. In Pacific salmon and their
ecosystems—Status and future options, ed. D.J. Stouder,
P.A. Bisson, and R.J. Naiman. Chapman and Hall,
1997.
Bothwell, M.L. 1985. Phosphorus limitation of lotic
periphyton growth rates: An intersite comparison using
continuous-flow throughs (Thompson River system;
British Columbia). Limnology and Oceanography
30:527-542.
Bothwell, M.L. 1988. Growth rate responses of lotics
periphytic diatoms to experimental phosphorus
enrichment—the influence of temperature and light.
Canadian Journal of Fish and Aquatic Sciences 45:261 -
270.
Boyce, J.S., J. Muir, A.P. Edwards, E.G. Seim, and R.A.
Olson, 1976. Geologic nitrogen in Pleistocene loess of
Nebraska. Journal of Environmental Quality 5(l):93-96.
Bras, R.L., and I. Rodgriguez-Iturbe. 1985. Random
functions and hydrology. Addison-Wesley, Reading,
MA.
Brick, C., and J. Moore. 1996. Diel variation of trace
metals in the upper Clark Fork River, Montana.
Environmental Science and Technology 30(6): 1953-60.
Brown, L.C., and T.O. Barnwell. 1987. The enhanced
stream water quality model QUAL2E and QUAL2E-
UNCAS: Documentation and user manual. EPA600/3-
87/007, U.S. Environmental Protection Agency, Athens,
GA.
Butcher, J.B., and S. Covington. 1995. Dissolved
oxygen analysis with temperature dependence. Journal
of Environmental Engineering 121(10): 756-759.
Carlson, R.E. 1977. A trophic state index for lakes.
Limnology and Oceanography 22:361-369.
Carlson, R.E. 1980. More complications in the
chlorophyll-Secchi disk relationship. Limnology and
Oceanography 25:378-382.
Carlson, R.E. 1992. Expanding the trophic state
concept to identify non-nutrient limited lakes and
reservoirs. In Proceedings of a National Conference on
Enhancing the States' Lake Management Programs.
Monitoring and Lake Impact Assessment, Chicago, IL,
pp. 59-71.
Carlson, R.E., and J. Simpson. 1996. A coordinator's
guide to volunteer lake monitoring methods. North
American Lake Management Society and the
Educational Foundation of America.
Cerco, C.F., and T. Cole. 1993. Three-dimensional
eutrophication model of the Chesapeake Bay. Journal
of Environmental Engineering 119(6): 1006-1025.
First Edition: November 1999
References-1
-------
Chadderton, R.A., A.C. Miller, and AJ. McDonnell.
1981. Analysis of waste load allocation procedures.
Water Resources Bulletin 17(5):760-766.
Chapra, S., andR.P. Canale. 1991. Long-term
phenomenological model of phosphorus and oxygen for
stratified lakes. Water Research 25(6):707-715.
Chapra, S. 1997. Surface water-quality modeling. The
McGraw-Hill Companies, Inc.
Chessman, B.C., P.E. Hutton, and J.M. Burch. 1992.
Limiting nutrients for periphyton growth in sub-alpine,
forest, agricultural and urban streams. Freshwater
Biology 28:349-361.
Cole, T.M., andE.M. Buchak. 1995. CE-QUAL-W2: A
two-dimensional, laterally averaged, hydrodynamic and
water quality model, Ver. 2.0. Instructional Report EL-
95 Draft. U.S. Army Corps of Engineers, Waterway
Experiment Station, Vicksburg, MS.
Cox, D.C., and P.C. Baybutt. 1981. Methods for
uncertainty analysis: A comparative survey. Risk
Analysis 1(4): 251-258.
Davenport, T. 1983. Water resource data in trend
analysis for the Blue Creek watershed project, Pike
County, Illinois Phase III. DWDC, IEPA, Springfield,
IL. 264 pp.
Dillaha, T.A. 1992. Nonpoint source modeling for
evaluating the effectiveness of best management
practices. NWQEP Notes 52:5-7. National Water Quality
Evaluation Project, North Carolina State University
Water Quality Group, Raleigh, NC.
Dodds, W.K., and V.H. Smith. 1995. Managing excess
chlorophyll levels in the Clark Fork River with nutrient
controls. A report presented to the Montana Department
of Health and Environmental Sciences. Revised April 1,
1995.
Dodds, W.K., V.H. Smith, and B. Zander. 1997.
Developing nutrient targets to control benthic
chlorophyll levels in streams: A case study of the Clark
Fork River. Water Research 31:1738-1750.
Donigian, A.S., Jr., B.R. Bicknell, L.C. Linker, J.
Hannawald, C. Chang, and R. Reynolds. 1990.
Chesapeake Bay Program Watershed Model application
to calculate bay nutrient loadings: Preliminary Phase I
findings and recommendations. Prepared by AQUA
TERRA Consultants for the U.S. Chesapeake Bay
Program, Annapolis, MD.
Donigian, A.S., Jr., and A.S. Patwardhan. 1992.
Modeling nutrient loadings from croplands in the
Chesapeake Bay Watershed. In Proceedings of water
resources sessions at Water Forum '92, Baltimore,
Maryland, August 2-6, 1992, pp. 817-822.
Doran, J.V., J.S. Schepes, andN.P. Swanson. 1981.
Chemical and bacteriological quality of pasture runoff.
Journal of Soil and Water Conservation 36(3):166-171.
Dornbush, J.N., J.R. Anderson, L.L. Harms. 1974.
Quantification of pollutants in agricultural runoff. EPA-
660/2-74-005, U.S. Environmental Protection Agency,
Washington, DC.
Duda, A.M., M.L. Iwanski, R.J. Johnson, and J.A.
Jaksch. 1987. Numerical standards for managing lake
and reservoir water quality. Lake and Reservoir
Management 3:1-27.
Dunne, T., and L.B. Leopold. 1978. Water in
environmental planning. W.H. Freeman and Company,
New York, NY.
Edwards, W.M., E.G. Simpson, M.H. Frere. 1972.
Nutrient content of barnyard runoff water. Journal of
Environmental Quality 1(4):401-405.
Ernst, M.R., W. Frossard, and J.L. Mancini. 1994. Two
eutrophication models make the grade. Water
Environment and Technology, November, pp. 15-16.
Gilbertson, C.B., F.A. Norstadt, A.C. Mathers, R.F.
Holt, A.P. Barnett, T.M. McCalla, C.A. Onstadt, and
R.A. Young. 1979. Animal waste utilization on crop
land and pasture land. EPA-600/2-79-059. U.S.
Environmental Protection Agency, Washington, DC.
References-2
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Golterman, H.L. 1975. Physiological limnology: An
approach to the physiology of lake ecosystems. Elsevier
Scientific Publishing Company, New York, NY. 489 pp.
Gosselin, D.C., J. Headrick, R. Tremblay, X.H. Chen, S.
Summerside. 1997. Domestic well water quality in rural
Nebraska. Groundwater Monitoring and Remediation
17:2-97.
Haith, D.A., and L.L. Shoemaker. 1987. Generalized
watershed loading functions for stream flow nutrients.
Water Resources Bulletin 107(EEI): 121:137.
Haith, D.A., R. Mandel, and R.S. Wu. 1992. GWLF -
Generalized watershed loading functions, Ver. 2.0-
User's manual. Department of Agricultural
Engineering, Cornell University, Ithaca, NY.
Hammersley, J.M., and D.C. Handscomb. 1964. Monte
Carlo methods. Methuen, London.
Heiskary, S.A., 1989. Lake protection through
standards: A state's viewpoint. In Water quality
standards for the 21st century: Proceedings of a
national conference. U.S. Environmental Protection
Agency, Office of Water, Washington, DC, pp. 117-121.
Heiskary, S.A., and C.B. Wilson. 1989. The regional
nature of lake water quality across Minnesota: An
analysis for improving resource management. Journal of
the Minnesota Academy of Science 55(l):71-77.
Hession, W.C., D.E. Storm, C.T. Haan, K.H. Reckhow,
M.D. Smolen. 1996. Risk analysis of total maximum
daily loads in an uncertain environment using
EUTROMOD. Journal of Lake and Reservoir
Management 12(3):331-347.
Horner, R.R., E.B. Welch, and R.B. Veenstra. 1983.
Development of nuisance periphytic algae in laboratory
streams in relation to enrichment and velocity. In
Periphyton of freshwater ecosystems, ed. R.G. Wetzel.
Dr. W. Junk Publishers, The Hague, Netherlands, pp.
121-124.
Horner, R.R., E.B. Welch, M.R. Seeley, and J.M.
Jacoby. 1990. Responses of periphyton to changes in
current velocity, suspended sediment and phosphorus
concentration. Freshwater Biology 24: 215-232.
Horner, R.R., J.J. Skupien, E.H. Livingston, H.E.
Shaver. 1994. Fundamentals of urban runoff
management: technical and institutional issues. Terrene
Institute in cooperation with USEPA. Washington, DC.
Hughes, R.M., T.R. Whittier, S.A. Thiele, J.E. Pollard,
D.V. Peck, S.G. Paulsen, D. McMullen, J. Lazorchak,
D.P. Larsen, W.L. Kinney, P.R. Kaufmann, S. Hedtke,
S.S. Dixit, G.B. Collins, and J.R. Baker. 1992. Lake and
stream indicators for the United States Environmental
Protection Agency's Environmental Monitoring and
Assessment Program. In Ecological Indicators, Volume
1. Elsevier Applied Science, pp. 305-335.
Ingman, G.L. 1992. A rationale and alternatives for
controlling nutrients and eutrophication problems in the
Clark Fork river basin. State of Montana, Department of
Health and Environmental Sciences, Water Quality
Bureau.
Inman, R.L., and J.C. Helton. 1988. An investigation of
uncertainty and sensitivity analysis techniques for
computer models. Risk Analysis 8(1): 71-90.
International Atomic Energy Agency (IAEA). 1989.
Evaluating the reliability of predictions made using
environmental transfer models. Environmental Safety
Series No. 100. IAEA, Vienna.
Kratzer, C.R., and P.L. Brezonik. 1981. A Carlson-type
trophic state index for nitrogen in Florida lakes. Water
Resources Bulletin 17:713-715.
Kreitler, C.W. 1975. Determining the source of nitrate
in groundwater by nitrogen isotope studies: Report of
investigations no. 83, University of Texas at Austin,
Bureau of Economic Geology.
Laws, E.A., and M.S. Chalup. 1990. A microalgal
growth model. Limnology and Oceanography
35(3):597-608.
First Edition: November 1999
References-3
-------
Lohman, K., J.R. Jones, and B.D. Perkins. 1992. Effects
of nutrient enrichment and flood frequency on
periphyton biomass in northern Ozark streams.
Canadian Journal of Fisheries and Aquatic Science
49:1198-1205.
Loucks, D.P., J.R. Stedinger, andD.A. Haith. 1981.
Water resource systems planning and analysis.
Prentice-Hall, Englewood Cliffs, NJ.
Lung, W., and C.E. Larson. 1995. Water quality
modeling of the upper Mississippi River and Lake
Pepin. Journal of Environmental Engineering
121(10):691-699.
MacDonald, L., A.W. Smart, and R.C. Wissmar. 1991.
Monitoring guidelines to evaluate effects of forestry
activities on streams in the Pacific Northwest and
Alaska. EPA 910/9-91-001. U.S. Environmental
Protection Agency, Region 10, Nonpoint Source
Section, Seattle, WA.
Maki, A.W., D.B. Porcella, and R.H. Wendt. 1983. The
impact of detergent phosphorus bans on receiving water
quality. Water Resources 18(7):893-903.
Marin, C.M., M.A. Medina, and J.B. Butcher, J.B. 1989.
Monte Carlo analysis and Bayesian decision theory for
assessing the effects of waste sites on ground water, I:
theory. Journal of Contaminant Hydrology 5: 1-13.
Michaud, J. P. 1991. A citizen's guide to understanding
and monitoring lakes and streams. The Department of
Ecology Publications Office, Olympia, WA.
Moody, D.W. 1990. Ground water contamination in the
United States. Journal of Soil & Water Conservation
45 (2): 170-179
Moore, L.W., C. Y. Chew, R.H. Smith, and S. Sahoo.
1992. Modeling of best management practices on North
Reelfoot Creek, Tennessee. Water Environment
Research 64(3):241-247.
NCDEHNR. 1993. Neuse River basinwide water quality
management plan. North Carolina Department of
Environmental, Health, and Natural Resources, Division
of Environmental Management, Water Quality Section.
Adopted February 11, 1993.
Newbold, J.D., R.V. O'Neill, J.W. Elwood, and W. Van
Winkle. 1982. Nutrient spiraling in streams:
implications for nutrient limitation and invertebrate
activity. The American Naturalist 120:628-652.
Newbry, B.W., R.A. Jones, and G.F. Lee. 1981.
Assessment and analysis of eutrophication of Tennessee
river system impoundments. Proceedings ASCE
Symposium on Surface Water Impoundments. American
Society of Civil Engineers, pp. 413-424.
Nordin, R.N. 1985. Water quality criteria for nutrients
and algae. Water Quality Unit, Resource Quality
Section, Water Management Branch, B.C. Ministry of
Environment, Victoria, British Columbia, Canada. May
1985.
NALMS. 1992. Developing eutrophication standards
for lakes and reservoirs. A report prepared by the Lake
Standards Subcommittee, May 1992. North American
Lake Management Society, Alachua, EL.
Novotny, V., and B. Chesters. 1981. Handbook on
nonpoint pollution: Sources and management. Van
Nostrand and Reinhold Company, New York, NY.
Novotny, V., and H. Olem. 1994. Water quality:
Prevention, identification, and management of diffuse
pollution. Van Nostrand Reinhold Company, New York,
NY.
Nurnberg, O.K. 1988. Prediction of phosphorus release
rates from total and reductant-soluble phosphorus in
lake sediments. Canadian Journal of Fisheries and
Aquatic Science 45: 453-462.
Olem, H., and G. Flock, eds. 1990. Lake and reservoir
restoration guidance manual. 2nd ed. EPA 440/4-90-
006. Prepared by North American Lake Management
References-4
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Society for the U.S. Environmental Protection Agency,
Washington, DC.
Omernik, J.M. 1977. Nonpoint source-stream nutrient
level relationships: A nationwide study. EPA600/3-77-
105. U.S. Environmental Protection Agency, Corvallis,
OR.
Oreskes, N., K. Shrader-Frechette, and K. Belitz. 1994.
Verification, validation and confirmation of numerical
models in the earth sciences. Science 263(5147):641-
646.
Paschal, J.E., Jr., and O.K. Mueller. 1991. Simulation of
water quality and the effects ofwastewater effluent on
the South Platte River from Chatfield Reservoir through
Denver, Colorado. Water-Resources Investigations
Report 91-016. U.S. Geological Survey, Denver, CO.
Plafkin, J.L., M.T. Harbour, K.D. Porter, S.K. Gross,
and R.M. Hughes. 1989. Rapid bioassessmentprotocols
for use in streams and rivers: Benthic
macroinvertebrates and fish. EPA/440/4-89/001. U.S.
Environmental Protection Agency, Office of Water,
Washington, DC.
Porcella, D. 1989. Lake protection through standards. In
Water Quality Standards for the 21st Century:
Proceedings of a National Conference. U.S.
Environmental Protection Agency, Office of Water,
Washington, DC, pp. 129-130.
Power, M.E. 1990. Effects of fish in river food webs.
Science 250:811-814.
Quinn, J.M. 1991. Guidelines for the control of
undesirable biological growths in water. Consultancy
report no. 6213/2. Water Quality Centre, Hamilton, New
Zealand.
Raschke, R.L. 1994. Phytoplankton bloom frequencies
in a population of small southeastern impoundments.
Lake and Reservoir Management 8(2): 205-210.
Rast, W., and G.F. Lee. 1978. Summary analysis of the
North American (U.S. Portion) OECD eutrophication
project: Nutrient loading-lake response relationships
and trophic state indices. EPA-600-3/78-008. U.S.
Environmental Protection Agency, Corvallis
Environmental Research Laboratory, Corvallis, OR.
Reckhow, K.H., and S.C. Chapra. 1983. Engineering
approaches for lake management. Vol. 1: Data analysis
and empirical modeling. Butterworths Publishing,
Boston, MA. 340 pp.
Sawyer, C.H. 1947. Fertilization of lakes by agricultural
and urban drainage. New England Water Works
Association 61:109-127.
Scheckenberger, R.B., and A.S. Kennedy. 1994. The use
of HSPF in subwatershed planning. In Current practices
in modeling the management of stormwater impacts, ed.
W. James. Lewis Publishers, Boca Raton, FL, pp. 175-
187.
Seeley, M.R. 1986. Use of artificial channels to study
the effects of nutrients, velocity and turbidity on
periphyton. M.Sc. thesis. University of Washington,
Seattle.
Seo, D. and R.P. Canale. 1999. Analysis of sediment
characteristics and total phosphorus models for Shagawa
Lake. Journal of Environmental Engineering 125(4):
346-350.
Smeltzer, E. 1992. Developing eutrophication standards
for Lake Champlain from user survey data. Vermont
Department of Environmental Conservation, Water
Quality Division, Waterbury, VT. July.
Smeltzer, E., and S.A. Heiskary. 1990. Analysis and
applications of lake user survey data. Lake and
Reservoir Management 6(1): 109-118.
Smith, R.L. 1990. Ecology and field biology. 4th ed.
Harper Collins Publishers, New York, NY.
Spahr, N.E., and S.R. Blakely. 1985. Effects of
waste-water effluent on the South Platte River from
Littleton to Denver. U.S. Geological Survey Water
Resources Investigations Report 85-4124. 97 pp.
First Edition: November 1999
References-5
-------
Spalding, R.G., and M.E. Exner. 1991. Nitrate
contamination in the contiguous United States. NATO
ASI Series 30:13-8.
Steinman, A.D. 1996. Effects of grazers on freshwater
benthic algae. In Algal ecology: Freshwater benthic
ecosystems, ed. R.J. Stevenson, M.L. Bothwell, and R.L.
Lowe, Academic Press, San Diego, CA., pp. 341-373.
Straub, C.P. 1989. Practical handbook of environmental
control. CRC Press, Inc., Boca Raton, EL.
Tasker, G.D., and N.E. Driver. 1988. Nationwide
regression models for predicting urban runoff water
quality at unmonitored sites. Water Resources Bulletin
24(5):1091-1101.
Thomann, R.V., and J.A. Mueller. 1987. Principles of
surface water quality modeling and control. Harper and
Row, NY.
USEPA. 1974. The relationship of phosphorus and
nitrogen to the trophic state of Northeast and North-
Central lakes and reservoirs. National Eutrophication
Survey working paper no. 23. U.S. Environmental
Protection Agency, Washington, DC.
USEPA. 1980. Technical guidance manual for
performing waste load allocations - Simplified
analytical method for determining NPDES effluent
limitations for POTWs discharging into low-flow
streams. U.S. Environmental Protection Agency, Office
of Water Regulations and Standards, Monitoring and
Data Support Division, Washington, DC.
USEPA. 1983. Results of the nationwide urban runoff
program. NTIS PB84-185552. U.S. Environmental
Protection Agency, Washington, DC.
USEPA. 1984a. Technical guidance manual for
developing Total Maximum Daily Loads. Book II,
Streams and rivers, Part 1, Biochemical oxygen
demand/dissolved oxygen and nutrients/eutrophication).
EPA 440/4-84-020. U.S. Environmental Protection
Agency, Washington, DC.
USEPA. 1984b. Technical guidance manual for
performing waste load allocations. Book IV, Lakes,
Reservoirs, and Impoundments: Chapter 2.
Nutrient/Eutrophication impacts. EPA 440/4-84-019.
U.S. Environmental Protection Agency, Washington,
DC.
USEPA. 1984c. Technical guidance manual for
performing waste load allocations. Book II, Streams and
Rivers. Chap. 2, Nutrient/Eutrophication impacts. EPA
440/4-84-021. U.S. Environmental Protection Agency,
Office of Water, Washington, DC.
USEPA 1985. Rates, constants, and kinetics
formulations in surface water quality modeling.
EPA/600/3-85/040. U.S. Environmental Protection
Agency, Washington, DC.
USEPA. 1986a. Quality criteria for water. EPA 440/5-
86-001. U.S. Environmental Protection Agency,
Washington, DC.
USEPA. 1986b. Stream sampling for wasteload
allocation applications. EPA 625/6-86-013. U.S.
Environmental Protection Agency, Office of Research
and Development, Washington, DC.
USEPA 1987. Technical guidance manual for
performing waste load allocations. Book VI, Design
Conditions, Chapter 1, Stream Flow Design for Steady
State Modeling. EPA 440/4-87-004. U.S.
Environmental Protection Agency, Washington, DC.
USEPA. 1990. Monitoring lake and reservoir
restoration. EPA 440/4-90-007. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
USEPA. 1991a. Guidance for water quality-based
decisions: The TMDLprocess. EPA 440/4-91-001. U.S.
Environmental Protection Agency, Assessment and
Watershed Protection Division, Washington, DC.
References-6
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
USEPA. 1991b. Modeling of nonpoint source water
quality in urban and non-urban areas. EPA/600/3-
91/039. U.S. Environmental Protection Agency,
Washington, DC.
USEPA. 1992a. Environmental impacts of storm-water
discharges. EPA 841-R-92-001. U.S. Environmental
Protection Agency, Washington, DC.
USEPA. 1992b. A quick reference guide: Developing
nonpoint source load allocations for TMDLs. EPA 841-
B-92-001. U.S. Environmental Protection Agency,
Washington, DC.
USEPA. 1992c. Monitoring guidance for the national
estuary pro gram. EPA 842 B-92-004.
U.S. Environmental Protection Agency, Washington,
DC.
USEPA. 1993. Guidance specifying management
measures for sources of nonpoint pollution in coastal
waters. EPA 840-B-92-002. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
USEPA. 1994a. EPA requirements for quality assurance
project plans for environmental data operations. EPA
QA/R-5. U.S. Environmental Protection Agency,
Quality Assurance Management Staff, Washington, DC.
Draft Interim Final, August 1994.
USEPA. 1994b. Guidance for the data quality objectives
process. EPA QA/G-4. EPA/600/R96/055. U.S.
Environmental Protection Agency, Office of Research
and Development, Washington, DC.
USEPA. 1995a. Technical guidance manual for
developing TMDLs. Book II: Streams and rivers, Part 1:
Biological oxygen demand/dissolved oxygen and
nutrients/eutrophication. EPA823-B-95-007. U.S.
Environmental Protection Agency, Office of Water,
Washington, DC.
USEPA, 1995b. Watershed protection: A statewide
approach. EPA 841-R-95-001. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
USEPA. 1995c. Watershed protection: A project focus.
EPA 841-R-95-003. U.S. Environmental Protection
Agency, Office of Water, Washington, DC.
USEPA. 1996a. TMDL development cost estimates:
Case studies of 14 TMDLs. EPA-R-96-001. U.S.
Environmental Protection Agency, Office of Water,
Washington, DC.
USEPA. 1996b. Watershed approach framework. EPA
840-S-96-001. U.S. Environmental Protection Agency,
Office of Water, Washington, DC.
USEPA. 1996c. Nonpoint source monitoring and
evaluation guide. November 1996. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
USEPA. 1997a. Compendium of tools for watershed
assessment and TMDL development. EPA841B-97-006.
U.S. Environmental Protection Agency, Office of
Wetlands, Oceans, and Watersheds, Washington, DC.
USEPA. 1997b. New policies for establishing and
implementing Total Maximum Daily Loads (TMDLs).
Memorandum sent by Robert Perciasepe, Assistant
Administrator. August 8, 1997.
USEPA. 1997c. Technical guidance manual for
performing waste load allocations. Book II: Streams
and rivers. Parti: Biological oxygen demand/dissolved
oxygen and nutrients/eutrophication. EPA823-B-97-
002. U.S. Environmental Protection Agency, Office of
Water, Washington, DC.
USEPA. 1998a. National strategy for the development
of regional nutrient criteria. EPA 822-R-98-002. U.S.
Environmental Protection Agency, Office of Water,
Washington, DC.
USEPA. 1998b. 1998 Update of ambient water quality
criteria for ammonia. EPA 822-R-98-008. U.S.
Environmental Protection Agency, Washington, DC.
USEPA 1999. Draft Guidance for Water Quality-based
Decisions: The TMDL Process (Second Edition). EPA
First Edition: November 1999
References-?
-------
841-D-99-001. U.S. Environmental Protection Agency,
Washington, DC.
Valett, H.M., S.G. Fisher, and E.H. Stanley. 1990.
Physical and chemical characteristics of the hyporheic
zone of a Sonoran Desert stream. Journal of the North
American Benthological Society 9(3):201-215.
Vollenweider, R.A. 1968. Scientific fundamentals of the
eutrophication of lakes and flowing waters, with
particular reference to nitrogen and phosphorus as
factors in eutrophication. DAS/CSI/68.27. Organization
of Economic Cooperation and Development, Paris.
Vollenweider, R.A., and J.J. Kerekes. 1980.
Background and summary results of the OECD
cooperative program on eutrophication. In International
Symposium on Inland Waters and Lake Restoration.
EPA 440/5-81-010. U.S. Environmental Protection
Agency, Washington, DC.
Walker, W.W. 1985. Statistical basis for mean
chlorophyll a criteria. In Lake and reservoir
management: Practical applications pp. 57-62. North
American Lake Management Society.
Walker, W.W. 1986. Empirical methods for predicting
eutrophication in impoundments; Report 4, Phase II:
Applications Manual. Technical Report E-81-9. U.S.
Army Engineer Waterways Experiment Station,
Vicksburg, MS.
Walker, J.F., S.A. Pickard, and W.C. Sonzogni. 1989.
Spreadsheet watershed modeling for nonpoint source
pollution management in a Wisconsin basin. Water
Resources Bulletin 25(1): 139-147.
Warwick, J.J., D. Cockrum, and M. Horvath. 1997.
Estimating non-point source loads and associated water
quality impacts. Journal of Water Resources Planning
and Management 123(5):302-310.
Watson, S., and E. McCauley, and J.A. Downing. 1992.
Sigmoid relationship between phosphorus, algal
biomass, and algal community structure. Canadian
Journal of Fish and Aquatic Science 49:2605-2610.
Watson, V. 1997. Monitoring considerations in setting
regional nutrient and algal biomass criteria. Unpublished
manuscript.
Watson, V.J., P. Berlind, and L. Bahls. 1990. Control of
algal standing crop by P and N in the Clark Fork River.
In Proceedings of the 1990 Clark Fork River
Symposium, University of Montana, MT.
Welch, E.B., J.M. Jacoby, R.R. Homer, and M.R.
Seeley. 1988. Nuisance biomass levels of periphytic
algae in streams. Hydrobiologia, 157:161-168.
Welch, E.B., R.R. Horner, and C.R. Patmont. 1989.
Prediction of nuisance periphytic biomass: A
management approach. Water Research 23(4): 401-405.
Welch, E.B., J.M. Quinn, C.W. Hickey. 1992.
Periphyton biomass related to point-source nutrient
enrichment in seven New Zealand streams. Water
Resources 26(5):669-675.
Wetzel, R.G. 1983. Limnology. 2nded. Saunders
College Publishing. Fort Worth, TX.
Wright, R.M., and A.J. McDonnell. 1986. Macrophyte
growth in shallow streams: Field investigations. Journal
of Environmental Engineering 112:967-982.
References-8
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
KEY TO ACRONYMS
AGNPS Agricultural Nonpoint Source SCS
Pollution Model SRP
ANSWERS Areal Nonpoint Source Watershed SD
Environment Response Simulation SWAT
BASINS Better Assessment Science Integrating SWMM
Point and Nonpoint Sources SWRRBWQ
BLM Bureau of Land Management
BMP best management practice TMDL
BOD Biochemical Oxygen Demand TP
CFR Code of Federal Regulations TSI
CREAMS Chemical, Runoff, and Erosion from TSS
Agricultural Management Systems USDA
CWA Clean Water Act
DR3M Multi-Event Urban Runoff Quality USDOI
Model
DO Dissolved Oxygen USEPA
EMAP Environmental Monitoring and
Assessment Program USES
FEMAT Federal Ecosystem Management USGS
Team USLE
FHWA Federal Highway Administration WLA
GIS Geographic Information System
GWLF Generalized Watershed Loading WQS
Functions WWTP
HSPF Hydrologic Simulation Program-
Fortran
LA load allocation (for nonpoint sources
in TMDLs)
MOS margin of safety, a required TMDL
element
NALMS North American Lake Management
Society
NAWQA National Water Quality Assessment
project led by USGS
NPDES National Pollutant Discharge
Elimination System
NFS nonpoint source
NRCS Natural Resource Conservation
Service
NTU nephelometric turbidity units
PL-566 Public Law 566, which established the
USDA Small Watersheds program
QA/QC Quality Assurance/Quality Control
RBP rapid bioassessment protocol
RUSLE revised universal soil loss equation
Soil Conservation Service
Soluble Reactive Phosphorus
Secchi Disc
Soil Water Assessment Tool
Storm Water Management Model
Simulator for Water Resources in
Rural Basins- Water Quality
total maximum daily load
Total Phosphorus
Trophic Status Index
total suspended solids
United States Department of
Agriculture
United States Department of the
Interior
United States Environmental
Protection Agency
United States Forest Service
United States Geological Survey
universal soil loss equation
waste load allocation (for point
sources in TMDLs)
water quality standards
wastewater treatment plant
First Edition: November 1999
Acronyms-1
-------
Acronyms
Acronyms-2
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
GLOSSARY
Acute toxicity. A chemical stimulus severe enough to
rapidly induce an effect; in aquatic toxicity tests, an
effect observed within 96 hours or less is considered
acute. When referring to aquatic toxicology or human
health, an acute effect is not always measured in terms
of lethality.
Adsorption-desorption. Adsorption is the process by
which nutrients such as inorganic phosphorus adhere to
particles via a loose chemical bond with the surface of
clay particles. Desorption is the process by which
inorganic nutrients are released from the surface of
particles back into solution. Adsorption differs from
absorption in that absorption is the assimilation or
incorporation of a gas, liquid, or dissolved substance
into another substance.
Advanced secondary treatment. Biological or
chemical treatment processes added to a secondary
treatment plant, including conventional activated sludge
to increase the removal of solids and biochemical
oxygen demand (BOD). Typical removal rates for
advanced secondary plants are on the order of 90
percent removal of solids and BOD.
Advanced waste treatment (AWT). Wastewater
treatment process that includes combinations of physical
and chemical operation units designed to remove
nutrients, toxic substances, or other pollutants.
Advanced, or tertiary, treatment processes treat effluent
from secondary treatment facilities using processes such
as nutrient removal (nitrification, denitrification),
filtration, or carbon adsorption. Tertiary treatment plants
typically achieve about 95 percent removal of solids and
BOD in addition to removal of nutrients or other
materials.
Advection. Bulk transport of the mass of discrete
chemical or biological constituents by fluid flow within
a receiving water. Advection describes the mass
transport due to the velocity, or flow, of the waterbody.
Aerobic. Environmental conditions characterized by the
presence of dissolved oxygen; used to describe
biological or chemical processes that occur in the
presence of oxygen.
Algae. Any organisms of a group of chiefly aquatic
microscopic nonvascular plants; most algae have
chlorophyll as the primary pigment for carbon fixation.
As primary producers, algae serve as the base of the
aquatic food web, providing food for zooplankton and
fish resources. An overabundance of algae in natural
waters is known as eutrophication.
Algal bloom. Rapidly occurring growth and
accumulation of algae within a body of water. It usually
results from excessive nutrient loading and/or a sluggish
circulation regime with a long residence time. Persistent
and frequent blooms can result in low-oxygen
conditions.
Algal growth. Algal growth is related to temperature,
available light, and the available abundance of inorganic
nutrients (N, P, Si). Algal species groups (e.g., diatoms,
greens, etc.) are typically characterized by different
maximum growth rates.
Algal respiration. Process of endogenous respiration
of algae in which organic carbon biomass is oxidized to
carbon dioxide.
Algal settling. Process in which phytoplankton cells
(algae) are lost from the water column by physical
sedimentation of the cell particles. Algal biomass lost
from the water column is then incorporated as sediment
organic matter and undergoes bacterial and biochemical
reactions, releasing nutrients and consuming dissolved
oxygen.
Allocations. That portion of a receiving water's loading
capacity attributed to one of its existing or future
pollution sources (nonpoint or point) or to natural
background sources. (A wasteload allocation [WLA] is
that portion of the loading capacity allocated to an
existing or future point source, and a load allocation
[LA] is that portion allocated to an existing or future
nonpoint source or to natural background levels. Load
allocations are best estimates of the loading, which can
range from reasonably accurate estimates to gross
allotments, depending on the availability of data and
appropriate techniques for predicting loading.)
First Edition: November 1999
Glossary-1
-------
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 on 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.
Ammonia toxicity. Under specific conditions of
temperature and pH, the un-ionized component of
ammonia can be toxic to aquatic life. The un-ionized
component of ammonia increases with pH and
temperature.
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. See also Anaerobic.
Anthropogenic. Pertains to the [environmental]
influence of human activities.
Antidegradation Policies. Policies that are part of each
state's water quality standards. These policies are
designed to protect water quality and provide a method
of assessing activities that might affect the integrity of
waterbodies.
Aquatic classification system. Assigns a classification
to a waterbody reflecting the water quality and the
biological health (integrity). The classification is
determined through use of biological indices (see IBI).
Examples of classifications include oligosaprobic
(cleanest water quality) and polysaprobic (highly
polluted water).
Aquatic ecosystem. Complex of biotic and abiotic
components of natural waters. The aquatic ecosystem is
an ecological unit that includes the physical
characteristics (such as flow or velocity and depth), the
biological community of the water column and benthos,
and the chemical characteristics such as dissolved
solids, dissolved oxygen, and nutrients. Both living and
nonliving components of the aquatic ecosystem interact
and influence the properties and status of each
component.
Assimilative capacity. The amount of contaminant
load that can be discharged to a specific waterbody
without exceeding water quality standards or criteria.
Assimilative capacity is used to define the ability of a
waterbody to naturally absorb and use a discharged
substance without impairing water quality or harming
aquatic life.
Attached algae. Photosynthetic organisms that remain
in a stationary location by attachment to hard rocky
substrate. Attached algae, usually present in shallow
hard-bottom aquatic environments, can significantly
influence nutrient uptake and diurnal oxygen variability.
Autotroph. An organism that derives cell carbon from
carbon dioxide. The conversion of carbon dioxide to
organic cell tissue is a reductive process that requires a
net input of energy. The energy needed for cell synthesis
is provided by either light or chemical oxidation.
Background levels. Levels representing the chemical,
physical, and biological conditions that would result
from natural geomorphological processes such as
weathering or dissolution.
Bacteria. Single-celled microorganisms. Bacteria of
the coliform group are considered the primary indicators
of fecal contamination and are often used to assess water
quality.
Bacterial decomposition. Breakdown by oxidation, or
decay, of organic matter by heterotrophic bacteria.
Bacteria use the organic carbon in organic matter as the
energy source for cell synthesis.
BASINS (Better Assessment Science Integrating
Point and Nonpoint Sources). A computer-run tool
that contains an assessment and planning component
that allows users to organize and display geographic
information for selected watersheds. It also contains a
modeling component to examine impacts of pollutant
loadings from point and nonpoint sources and to
characterize the overall condition of specific watersheds.
Glossary-2
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
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.
Benthic ammonia flux. The process by which decay of
organic matter within the sediments of a natural water
results in the release of ammonia nitrogen from the
interstitial water of sediments to the overlying water
column. Benthic release, or regeneration, of ammonia is
an essential component of the nitrogen cycle.
Benthic organisms. Organisms living in, or on, bottom
substrates in aquatic ecosystems.
Benthic photosynthesis. Synthesis of cellular carbon
by algae attached to the bottom of a natural water
system. Benthic photosynthesis typically is limited to
shallow waters in which light is available at the bottom.
Best practicable control technologies (BPT). Effluent
limitations that are based on the average performance of
the best existing plants in an industry.
Best management practices (BMPs). Methods,
measures, or practices determined to be reasonable and
cost-effective means for a landowner to meet certain,
generally nonpoint source, pollution control needs.
BMPs include structural and nonstructural controls and
operation and maintenance procedures.
Bioaccumulation. The process by which a compound
is taken up by an aquatic organism, both from water and
through food.
Bioassessment. Biological assessment; the evaluation
of an ecosystem using integrated assessments of habitat
and biological communities in comparison to
empirically defined reference conditions.
Bioavailability. A measure of the physicochemical
access that a toxicant has to the biological processes of
an organism. The less the bioavailability of a toxicant,
the less its toxic effect on an organism.
Biochemical oxygen demand (BOD). The amount of
oxygen per unit volume of water required to bacterially
or chemically oxidize (stabilize) the oxidizable matter in
water. Biochemical oxygen demand measurements are
usually conducted over specific time intervals (5, 10, 20,
30 days). The term BOD generally refers to a standard
5-day BOD test. BOD = CBOD + NBOD.
Biological criteria. Also known as biocriteria,
biological criteria are narrative expressions or numeric
values of the biological characteristics of aquatic
communities based on appropriate reference conditions.
Biological criteria serve as an index of aquatic
community health.
Biomass. The amount, or weight, of a species, or group
of biological organisms, within a specific volume or area
of an ecosystem.
Boundary conditions. Values or functions representing
the state of a system at its boundary limits.
Calcareous. Pertaining to or containing calcium
carbonate.
Calibration. The process of adjusting model
parameters within physically defensible ranges until the
resulting predictions give a best possible good fit to
observed data.
Carbonaceous Biological Oxygen Demand (CBOD).
Refers to the oxygen demand associated with the
oxidation of organic carbon.
Carlson trophic status index (TSI). Index based on
the correlations between the clarity or transparency
expressed by the Secchi disc depth, algal concentrations
expressed by chlorophyll a, and the spring, or average
annual, total phosphorus concentrations. Identifies
waterbodies as oligotrophic, mesotrophic, eutrophic, or
hypertrophic.
Cation exchange capacity. The sum total of
exchangeable cations that a soil can adsorb. Expressed
in centimoles per kilogram of soil (or of other adsorbing
material such as clay.)
Channel. A natural stream that conveys water; a ditch
or channel excavated for the flow of water.
Chloride. An atom of chlorine in solution; an ion
bearing a single negative charge.
First Edition: November 1999
Glossary-3
-------
Chlorophyll. A group of green photosynthetic pigments
that occur primarily in the chloroplast of plant cells. The
amount of chlorophyll a, a specific pigment, is
frequently used as a measure of algal biomass in natural
waters.
Chronic toxicity. Toxicity impact that lingers or
continues for a relatively long period of time, often
one-tenth of an organism's life span or longer. Chronic
effects could include mortality, reduced growth, or
reduced reproduction.
Cladophora. Filamentous green algae often associated
with conditions of nutrient enrichment in both lakes and
streams. Cladophora can be a particular problem where
dense mats might physically interfere with water supply
and recreational uses.
Clean Lakes Projects. The principal federal program
dealing with the restoration of degraded lakes.
Clean Water Act (CWA). The Clean Water Act
(formerly referred to as the Federal Water Pollution
Control Act or Federal Water Pollution Control Act
Amendments of 1972), Public Law 92-500, as amended
by Public Law 96-483 and Public Law 97-117, 33
U.S.C. 1251 et seq. The Clean Water Act (CWA)
contains a number of provisions to restore and maintain
the quality of the nation's water resources. One of these
provisions is section 303(d), which establishes the
TMDL program.
Coastal Zone. Lands and waters adjacent to the coast
that exert an influence on the uses of the sea and its
ecology, or whose uses and ecology are affected by the
sea.
Combined sewer overflows (CSOs). Discharge of a
mixture of storm-water and domestic waste when the
flow capacity of a sewer system is exceeded during
rainstorms. CSOs discharged to receiving water can
result in contamination problems that may prevent the
attainment of water quality standards.
Combined sewer system (CSS). Sewer system that
receives both domestic wastewater and storm water and
conducts the mixture to a treatment facility.
Completely mixed condition. A condition in which no
measurable difference in the concentration of a pollutant
exists across a transect of the waterbody (e.g., the
concentration does not vary by 5 percent).
Concentration. Amount of a substance or material in a
given unit volume of solution; usually measured in
milligrams per liter (mg/L) or parts per million (ppm).
Concentration-based limit. A limit based on the
relative strength of a pollutant in a waste stream, usually
expressed in milligrams per liter (mg/L).
Conservative substance. A substance that does not
undergo any chemical or biological transformation or
degradation in a given ecosystem.
Contamination. The act of polluting or making impure;
any indication of chemical, sediment, or biological
impurities.
Continuous discharge. A discharge that occurs without
interruption throughout the operating hours of a facility,
except for infrequent shutdowns for maintenance,
process changes, or other similar activities.
Conventional pollutants. As specified under the Clean
Water Act, conventional contaminants include
suspended solids, coliform bacteria, high biochemical
oxygen demand, pH, and oil and grease.
Cost-share program. A program that allocates project
funds to pay a percentage of the cost of constructing or
implementing a best management practice. The
remainder of the costs are paid by the producer (s).
Cross-sectional area. Wet area of a waterbody normal
to the longitudinal component of the flow.
Critical condition. The critical condition can be
thought of as the "worst case" scenario of environmental
conditions in the waterbody in which the loading
expressed in the TMDL for the pollutant of concern will
continue to meet water quality standards. Critical
conditions are the combination of environmental factors
(e.g., flow, temperature, etc.) that results in attaining and
maintaining the water quality criterion and has an
acceptably low frequency of occurrence.
Glossary-4
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Decay. The gradual decrease in the amount of a given
substance in a given system due to various sink
processes including chemical and biological
transformation, dissipation to other environmental
media, or deposition into storage areas.
Decomposition. Metabolic breakdown of organic
materials; the formation of by-products of
decomposition releases energy and simple organic and
inorganic compounds. See also Respiration.
Denitrification. The process of decomposition of
nitrites and nitrates (by bacteria) that results in the
eventual release of nitrogen gas into the atmosphere.
Design stream flow. The stream flow used to conduct
steady-state wasteload allocation modeling.
Designated uses. Those uses specified in water quality
standards for each waterbody or segment whether or not
they are being attained.
Deterministic model. A model that does not include
built-in variability: same input will always result in the
same output.
Detritus. Any loose material produced directly from
disintegration processes. Organic detritus consists of
material resulting from the decomposition of dead
organic remains.
Diagenesis. Production of sediment fluxes as a result of
the flux of particulate organic carbon in the sediment
and its decomposition. The diagenesis reaction can be
thought of as producing oxygen equivalents released by
various reduced species.
Diatoms. Single-celled or colonial algae with siliceous
cell walls; important component of phytoplankton.
Diel. Involving a 24-hour period.
Dilution. The addition of some quantity of less-
concentrated liquid (water) that results in a decrease in
the original concentration.
Dimictic. Describes lakes and reservoirs that freeze
over and normally go through two stratification and
mixing cycles within a year.
Direct runoff. Water that flows over the ground
surface or through the ground directly into streams,
rivers, and lakes.
Discharge. Flow of surface water in a stream or canal,
or the outflow of groundwater from a flowing artesian
well, ditch, or spring. Can also apply to discharge of
liquid effluent from a facility or to chemical emissions
into the air through designated venting mechanisms.
Discharge Monitoring Report (DMR). Report of
effluent characteristics submitted by a municipal or
industrial facility that has been granted an NPDES
discharge permit.
Discharge permits (under NPDES). A permit issued
by the U.S. EPA or a state regulatory agency that sets
specific limits on the type and amount of pollutants that
a municipality or industry can discharge to a receiving
water; it also includes a compliance schedule for
achieving those limits. The permit process was
established under the National Pollutant Discharge
Elimination System, under provisions of the Federal
Clean Water Act.
Dispersion. The spreading of chemical or biological
constituents, including pollutants, in various directions
at varying velocities depending on the differential in-
stream flow characteristics.
Dissolved oxygen (DO). The amount of oxygen
dissolved in water. This term also refers to a measure of
the amount of oxygen available for biochemical activity
in a waterbody, an indicator of the quality of that water.
Dissolved oxygen sag. Longitudinal variation of
dissolved oxygen representing the oxygen depletion and
recovery following a waste load discharge into a
receiving water.
Diurnal. Actions or processes that have a period or a
cycle of approximately one tidal-day or are completed
within a 24-hour period and that recur every 24 hours.
Domestic wastewater. Also called sanitary wastewater,
consists of wastewater discharged from residences and
from commercial, institutional, and similar facilities.
First Edition: November 1999
Glossary-5
-------
Drainage basin. A part of a land area enclosed by a
topographic divide from which direct surface runoff
from precipitation normally drains by gravity into a
receiving water. Also referred to as a watershed, river
basin, or hydrologic unit.
Dynamic model. A mathematical formulation
describing and simulating the physical behavior of a
system or a process and its temporal variability.
Dynamic simulation. Modeling of the behavior of
physical, chemical, and/or biological phenomena and
their variations over time.
Ecoregion. A physical region defined by its ecology,
which includes meteorological factors, elevation, plant
and animal species composition, landscape position, and
soils.
Ecosystem. An interactive system that includes the
organisms of a natural community association together
with their abiotic physical, chemical, and geochemical
environment.
Effluent. Municipal sewage or industrial liquid waste
(untreated, partially treated, or completely treated) that
flows out of a treatment plant, septic system, pipe, etc.
Effluent guidelines. The national effluent guidelines
and standards specify the achievable effluent pollutant
reduction that is attainable based upon the performance
of treatment technologies employed within an industrial
category. The National Effluent Guidelines Program
was established with a phased approach whereby
industry would first be required to meet interim
limitations based on best practicable control technology
currently available for existing sources (BPT). The
second level of effluent limitations to be attained by
industry was referred to as best available technology
economically achievable (BAT), which was established
primarily for the control of toxic pollutants.
Effluent limitation. Restrictions established by a state
or EPA on quantities, rates, and concentrations in
pollutant discharges.
Effluent plume. Delineates the extent of contamination
in a given medium as a result of a distribution of
effluent discharges (or spills). Usually shows the
concentration gradient within the delineated areas or
plume of flow of contaminants.
Empirical model. Use of statistical techniques to
discern patterns or relationships underlying observed or
measured data for large sample sets. Does not account
for physical dynamics of waterbodies.
Endpoint. An endpoint (or indicator/target) is a
characteristic of an ecosystem that may be affected by
exposure to a stressor. Assessment endpoints and
measurement endpoints are two distinct types of
endpoints commonly used by resource managers. An
assessment endpoint is the formal expression of a valued
environmental characteristic and should have societal
relevance (an indicator). A measurement endpoint is the
expression of an observed or measured response to a
stress or disturbance. It is a measurable environmental
characteristic that is related to the valued environmental
characteristic chosen as the assessment endpoint. The
numeric criteria that are part of traditional water quality
standards are good examples of measurement endpoints
(targets).
Enhancement. In the context of restoration ecology,
any improvement of a structural or functional attribute.
Environmental Monitoring and Assessment Program
(EMAP). A USEPA program to monitor and assess the
ecological health of major ecosystems, including surface
waters, forests, near-coastal waters, wetlands,
agricultural lands, arid lands, and the Great Lakes, in an
integrated, systematic manner. Although EMAP has
been curtailed somewhat during recent years, the
program is designed to operate at regional and national
scales, for decades, and to evaluate the extent and
condition of entire ecological resources by using a
common sampling framework to sample approximately
12,500 locations in the conterminous United States.
Epiphyte. A plant that grows above the ground,
supported nonparasitically by another plant or object,
and deriving its nutrients and water from rain, the air,
dust, etc.
Estuary. Brackish-water area influenced by the tides
where the mouth of a river meets the sea.
Glossary-6
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Estuarine number. A nondimensional parameter
accounting for decay, tidal dispersion, and advection
velocity; used for classification of tidal rivers and
estuarine systems.
Eutrophication. The natural aging process during
which a lake, estuary, or bay evolves into a bog or marsh
and eventually disappears. During the later stages of
eutrophication the waterbody is choked by abundant
plant life as the result of increased amounts of nutritive
compounds such as nitrogen and phosphorus. Human
activities can accelerate the process of nutrient
enrichment in waterbodies, resulting in accelerated
biological productivity (growth of algae and weeds) and
an undesirable accumulation of algal biomass.
Eutrophication model. A mathematical formulation
that describes the advection, dispersion, and biological,
chemical, and geochemical reactions that influence the
growth and accumulation of algae in aquatic
ecosystems. Models of eutrophication typically include
one or more species groups of algae; inorganic and
organic nutrients (N, P); organic carbon; and dissolved
oxygen.
Existing use. Use actually attained in the waterbody on
or after November 28, 1975, whether or not it is
included in the water quality standards (40 CFR 131.3).
Fate of pollutants. Physical, chemical, and biological
transformation in the nature and changes of the amount
of a pollutant in an environmental system.
Transformation processes are pollutant-specific.
Because they have comparable kinetics, different
formulations for each pollutant are not required.
Feedlot. A confined area for the controlled feeding of
animals. Tends to concentrate large amounts of animal
waste that cannot be absorbed by the soil and, hence,
may be carried to nearby streams or lakes by rainfall
runoff.
First-order kinetics. The type of relationship
describing a dynamic reaction in which the rate of
transformation of a pollutant is proportional to the
amount of that pollutant in the environmental system.
Flocculation. The process by which suspended
colloidal or very fine particles are assembled into larger
masses or floccules that eventually settle out of
suspension.
Fluvial geomorphology. The effect of rainfall and
runoff on the form and pattern of riverbeds and river
channels.
Flux. Movement and transport of mass of any water
quality constituent over a given period of time. Units of
mass flux are mass per unit time.
Forcing functions. External empirical formulation used
to provide input describing a number of processes.
Typical forcing functions include parameters such as
temperature, point and tributary sources, solar radiation,
and waste loads and flow.
Geochemical. Referring to chemical reactions
involving earth materials such as soil, rocks, and water.
Geomorphology. The study of the evolution and
configuration of landforms.
Gradient. The rate of change of the value of one
quantity with respect to another; for example, the rate of
decrease of temperature with depth in a lake.
Ground water. The supply of fresh water found
beneath the earth's surface, usually in aquifers, which
supply wells and springs. Because ground water is a
major source of drinking water, there is growing concern
over contamination from leaching agricultural or
industrial pollutants and leaking underground storage
tanks.
Half-saturation constant. Nutrient concentration at
which the growth rate of the population of a species or
group of species is half the maximum rate.
Half-saturation constants define the nutrient uptake
characteristics of different phytoplankton species. Low
half-saturation constants indicate the ability of the algal
group to thrive under nutrient-depleted conditions.
Heterotroph. An organism that uses organic carbon for
the formation of cell tissue, e.g., is unable to synthesize
organic compounds from inorganic substrates for food
and must consume organisms or their products. Bacteria
are examples of heterotrophs; photosythesizing
organisms are not.
First Edition: November 1999
Glossary-7
-------
Hydrodynamic model. Mathematical formulation used
in describing fluid flow of circulation, transport, and
deposition processes in receiving water.
Hydrograph. A graph showing variation of stage
(depth) or discharge in a stream over a period of time.
Hydrologic cycle. The circuit of water movement from
the atmosphere to the earth and its return to the
atmosphere through various stages or processes, such as
precipitation, interception, runoff, infiltration, storage,
evaporation, and transpiration.
Hydrology. The study of the distribution, properties,
and effects of water on the earth's surface, in the soil
and underlying rocks, and in the atmosphere.
Hydrolysis. A chemical reaction that occurs between a
substance and water, resulting in the cleaving of a
molecular bond and the formation of new bonds with
components of the water molecule; a reaction of water
with a salt to create an acid or a base.
Hyetograph. Graph of rainfall rate versus time during a
storm event.
Hypolimnetic oxygen depletion rate. Describes
changing dissolved oxygen concentrations with respect
to time in the hypolimnion (lowest stratum) of lakes and
reservoirs. Dissolved oxygen concentrations in the
hypolimnion are especially significant because of their
effect on fish.
Hyporheic. The volume of saturated sediment beneath
and beside streams and rivers where ground water and
surface water mix.
Index of Biotic Integrity (IBI). An index that uses
measurements of the distribution and abundance or
absence of several fish species types in each waterbody
for comparison. A portion of a waterbody is compared
to a similar, unimpacted waterbody in the same
ecoregion.
Indicator. A measurable quantity that can be used to
evaluate the relationship between pollutant sources and
their impact on water quality.
Indicator organism. An organism used to indicate the
potential presence of other (usually pathogenic)
organisms. Indicator organisms are usually associated
with the other organisms, but are usually more easily
sampled and measured.
Indirect discharge. A nondomestic discharge
introducing pollutants to a publicly owned treatment
works.
Infiltration capacity. The capacity of a soil to allow
water to infiltrate into or through it during a storm.
Initial mixing zone. The region immediately
downstream of an outfall where effluent dilution
processes occur. Because of the combined effects of the
effluent buoyancy, ambient stratification, and current,
the prediction of initial dilution can be complex.
In situ. In place; in situ measurements consist of
measurements of components or processes in a full-scale
system or a field, rather than in a laboratory.
Irrigation. Applying water or wastewater to land areas
to supply the water and nutrient needs of plants.
Irrigation return flow. Surface and subsurface water
that leaves a field after the application of irrigation
water.
Kinetic processes. Description of the rates and modes
of changes in the transformation or degradation of a
substance in an ecosystem.
Land application. Discharge of wastewater onto the
ground for treatment or reuse. See also Irrigation.
Leachate. Water that collects contaminants as it
trickles through wastes, pesticides, or fertilizers.
Leaching can occur in farming areas, feedlots, and
landfills and can result in hazardous substances entering
surface water, ground water, or soil.
Leachate collection system. A system that gathers
leachate and pumps it to the surface for treatment.
Light saturation. The optimal light level for algae and
macrophyte growth and photosynthesis.
Glossary-8
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Loading, Load, Loading rate. The total amount of
material (pollutants) entering the system from one or
multiple sources; measured as a rate in weight per unit
time.
Load allocation (LA). The portion of a receiving
water's loading capacity attributed either to one of its
existing or future nonpoint sources of pollution or to
natural background sources. Load allocations are best
estimates of the loading, which can range from
reasonably accurate estimates to gross allotments,
depending on the availability of data and appropriate
techniques for predicting the loading. Wherever
possible, natural and nonpoint source loads should be
distinguished. (40 CFR 130.2(g))
Loading capacity (LC). The greatest amount of
loading a water can receive without violating water
quality standards.
Low-flow (7Q10). 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.
Macrophyton. The larger aquatic plants of all types.
They are sometimes attached to the waterbody bottom
(benthic), sometimes free-floating, sometimes totally
submersed, and sometimes partially emergent. Complex
types usually have true roots, stems, and leaves; the
macroalgae are simpler but may have stem- and leaf-like
structures.
Margin of safety (MOS). A required component of the
TMDL that accounts for the uncertainty about the
relationship between the pollutant loads and the quality
of the receiving waterbody (CWA section 303(d)(l)(C)).
The MOS is normally incorporated into the conservative
assumptions used to develop TMDLs (generally within
the calculations or models) and approved by EPA either
individually or in state/EPA agreements. If the MOS
needs to be larger than that which is allowed through the
conservative assumptions, additional MOS can be added
as a separate component of the TMDL (in this case,
quantitatively, a TMDL = LC = WLA + LA + MOS).
Mass balance. An equation that accounts for the flux of
mass going into a defined area and the flux of mass
leaving the defined area. The flux in must equal the flux
out.
Mass loading. The quantity of a pollutant transported to
a waterbody.
Mass wasting. Downslope transport of soil and rocks
due to gravitational stress.
Mathematical model. A system of mathematical
expressions that describe the spatial and temporal
distribution of water quality constituents resulting from
fluid transport and the one or more individual processes
and interactions within some prototype aquatic
ecosystem. A mathematical water quality model is used
as the basis for waste load allocation evaluations.
Maximum depth. The greatest depth of a waterbody.
Mean depth. Volume of a waterbody divided by its
surface area.
Meiofauna. Microorganisms that can be caught in
sieves with holes of a certain size.
Mineralization. The transformation of organic matter
into a mineral or an inorganic compound.
Mitigation. Actions taken to avoid, reduce, or
compensate for the effects of environmental damage.
Among the broad spectrum of possible actions are those
which restore, enhance, create, or replace damaged
ecosystems.
Monitoring. Periodic or continuous surveillance or
testing to determine the level of compliance with
statutory requirements and/or pollutant levels in various
media or in humans, plants, and animals.
Monomictic. Describes lakes and reservoirs that are
relatively deep, do not freeze over during the winter
months, and undergo a single stratification and mixing
cycle during the year. These lakes and reservoirs
usually become destratified during the mixing cycle,
most often in the fall of the year.
Monte Carlo simulation. A stochastic modeling
technique that involves the random selection of sets of
input data for use in repetitive model runs. Probability
First Edition: November 1999
Glossary-9
-------
distributions of receiving water quality concentrations
are generated as the output of a Monte Carlo simulation.
Narrative criteria. Nonquantitative guidelines that
describe the desired water quality goals.
National Pollutant Discharge Elimination System
(NPDES). The national program for issuing, modifying,
revoking and reissuing, terminating, monitoring, and
enforcing permits, and imposing and enforcing
pretreatment requirements, under sections 307, 402, 318,
and 405 of the Clean Water Act.
N/P ratio. The ratio of nitrogen to phosphorus in an
aquatic system. The ratio is used as an indicator of the
nutrient limiting conditions for algal growth; also used
as an indicator for the analysis of trophic levels of
receiving waters.
Natural waters. Flowing water within a physical
system that has developed without human intervention,
in which natural processes continue to take place.
Nitrate (NO3) and Nitrite (NO2). Oxidized nitrogen
species. Nitrate is the form of nitrogen preferred by
aquatic plants.
Nitrification. The oxidation of ammonium salts to
nitrites (via Nitrosomonas bacteria) and the further
oxidation of nitrite to nitrate (via Nitrobacter bacteria).
Nitrifier organisms. Bacterial organisms that mediate
the biochemical oxidative processes of nitrification.
Nitrogen. A nutrient assimilated by plants which
promotes growth. The most bioavailable forms of
nitrogen are nitrate (NO3), nitrite (NO2), and ammonia
(NH3).
Nitrogenous biochemical oxygen demand (NBOD).
The oxygen demand associated with the oxidation of
ammonia.
Nonpoint source. Pollution that originates from
multiple sources over a relatively large area. Nonpoint
sources can be divided into source activities related to
either land or water use including failing septic tanks,
improper animal-keeping practices, forest practices, and
urban and rural runoff.
Numeric targets. A measurable value determined for
the pollutant of concern which, if achieved, is expected
to result in the attainment of water quality standards in
the listed waterbody.
Numerical model. Model that approximates a solution
of governing partial differential equations which
describe a natural process. The approximation uses a
numerical discretization of the space and time
components of the system or process.
Nutrient. A primary element necessary for the growth
of living organisms. Carbon dioxide, nitrogen, and
phosphorus, for example, are required nutrients for
phytoplankton growth.
Nutrient limitation. A deficit of a nutrient (e.g.,
nitrogen and phosphorus) required by microorganisms to
metabolize organic substrates.
One-dimensional (1-D) model. A mathematical model
defined along one spatial coordinate of a natural water
system. Typically, 1-D models are used to describe the
longitudinal variation of water quality constituents along
the downstream direction of a stream or river. In writing
the model, it is assumed that the cross-channel (lateral)
and vertical variability is relatively homogenous and
can, therefore, be averaged over those spatial
coordinates.
Organic matter. The organic fraction that includes
plant and animal residue at various stages of
decomposition, cells and tissues of soil organisms, and
substances synthesized by the soil population.
Commonly determined as the amount of organic
material contained in a soil or water sample.
Organic nitrogen. Nitrogen in a form that is bound to
an organic compound.
Organic phosphorous. Phosphorus in a form that is
bound to an organic compound.
Orthophosphate. Phosphorus in a form that is most
readily available to plants. It consists of the species
H2PO42 , HPO42 , and PO43 . (Also known as soluble
reactive phosphorus (SRP).)
Glossary-10
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Outfall. The point where water flows from a conduit,
stream, or drain.
Oxidation. The chemical union of oxygen with metals
or organic compounds accompanied by a removal of
hydrogen or another atom. It is an important factor for
soil formation and permits the release of energy from
cellular fuels.
Oxygen demand. Measure of the dissolved oxygen
used by a system (microorganisms) in the oxidation of
organic matter. (See also Biochemical oxygen
demand.)
Oxygen depletion. A deficit of dissolved oxygen in a
water system due to oxidation of organic matter.
Oxygen saturation. The natural or artificial reaeration
or oxygenation of a water system (water sample) to
bring the level of dissolved oxygen to maximum
capacity. Oxygen saturation is greatly influenced by
temperature, elevation, and other water characteristics.
Partitioning coefficient. A constant symbolizing the
ratio of the concentration of a solute in the upper of the
two liquid phases in equilibrium to its concentration in
the lower phase. Chemicals in solution are partitioned
into dissolved and particulate adsorbed phases based on
their corresponding sediment-to-water partitioning
coefficient.
Peak runoff. The highest value of the stage or
discharge attained by a flood or storm event; also
referred to as flood peak or peak discharge.
Periphyton. Microscopic underwater plants and animals
that are firmly attached to solid surfaces such as rocks,
logs, pilings, and other structures.
Permit. An authorization, license, or equivalent control
document issued by EPA or an approved federal, state,
or local agency to implement the requirements of an
environmental regulation; e.g., a permit to operate a
wastewater treatment plant or to operate a facility that
may generate harmful emissions.
Permit Compliance System (PCS). Computerized
management information system that contains data on
NPDES permit-holding facilities. PCS keeps extensive
records on more than 65,000 active water-discharge
permits on sites located throughout the nation. PCS
tracks permit, compliance, and enforcement status of
NPDES facilities.
Phased approach. Under the phased approach to
TMDL development, load allocations and wasteload
allocations are calculated using the best available data
and information recognizing the need for additional
monitoring data to accurately characterize sources and
loadings. The phased approach is typically employed
when nonpoint sources dominate. It provides for the
implementation of load reduction strategies while
collecting additional data.
Phosphorus. A nutrient assimilated by plants which
promotes growth. The most bioavailable form of
phosphorus is soluble reactive phosphorus (SRP), also
known as orthophosphate.
Photosynthesis. The biochemical synthesis of
carbohydrate-based organic compounds from water and
carbon dioxide using light energy in the presence of
chlorophyll. Photosynthesis occurs in all plants,
including aquatic organisms such as algae and
macrophytes. Photosynthesis also occurs in primitive
bacteria such as blue-green algae.
Phytoplankton. A group of generally unicellular
microscopic plants characterized by passive drifting
within the water column. See Algae.
Plankton. Group of generally microscopic plants and
animals passively floating, drifting, or swimming
weakly. Plankton include the phytoplankton (plants) and
zooplankton (animals).
Point source. Pollutant loads discharged at a specific
location from pipes, outfalls, and conveyance channels
from either municipal wastewater treatment plants or
industrial waste treatment facilities. Point sources can
also include pollutant loads contributed by tributaries to
the main receiving water stream or river.
Pollutant. Dredged spoil, solid waste, incinerator
residue, sewage, garbage, sewage sludge, munitions,
chemical wastes, biological materials, radioactive
materials, heat, wrecked or discarded equipment, rock,
sand, cellar dirt, and industrial, municipal, and
First Edition: November 1999
Glossary-11
-------
agricultural waste discharged into water. (CWA section
502(6)).
Pollution. Generally, the presence of matter or energy
whose nature, location, or quantity produces undesired
environmental effects. Under the Clean Water Act, for
example, the term is defined as the man-made or man-
induced alteration of the physical, biological, chemical,
and radiological integrity of water.
Pool. Portion of a stream with reduced current velocity,
often with deeper water than surrounding areas and with
a smooth surface.
Postaudit. A subsequent examination and verification
of a model's predictive performance following
implementation of an environmental control program.
Pretreatment. The treatment of wastewater to remove
or reduce contaminants prior to discharge into another
treatment system or a receiving water.
Primary productivity. A measure of the rate at which
new organic matter is formed and accumulated through
photosynthesis and chemosynthesis activity of producer
organisms (chiefly, green plants). The rate of primary
production is estimated by measuring the amount of
oxygen released (oxygen method) or the amount of
carbon assimilated by the plant (carbon method).
Primary treatment. A basic wastewater treatment
method that uses settling, skimming, and (usually)
chlorination to remove solids, floating materials, and
pathogens from wastewater. Primary treatment typically
removes about 35 percent of biochemical oxygen
demand (BOD) and less than half of the metals and toxic
organic substances.
Privately owned treatment works. Any device or
system that is (a) used to treat wastes from any facility
whose operator is not the operator of the treatment
works and (b) not a publicly owned treatment works.
Public comment period. The time allowed for the
public to express its views and concerns regarding
action by EPA or states (e.g., a Federal Register notice
of a proposed rule-making, a public notice of a draft
permit, or a Notice of Intent to Deny).
Publicly owned treatment works (POTW). Any
device or system used in the treatment (including
recycling and reclamation) of municipal sewage or
industrial wastes of a liquid nature that is owned by a
state or municipality. This definition includes sewers,
pipes, or other conveyances only if they convey
wastewater to a POTW providing treatment.
Raw sewage. Untreated municipal sewage.
Reaction rate coefficient. Coefficient describing the
rate of transformation of a substance in an
environmental medium characterized by a set of
physical, chemical, and biological conditions such as
temperature and dissolved oxygen level.
Reaeration. The net flux of oxygen occurring from the
atmosphere to a body of water with a free surface.
Receiving waters. Creeks, streams, rivers, lakes,
estuaries, ground-water formations, or other bodies of
water into which surface water and/or treated or
untreated waste are discharged, either naturally or in
man-made systems.
Reserve capacity. Pollutant loading rate set aside in
determining stream waste load allocation, accounting for
uncertainty and future growth.
Residence time. Length of time that a pollutant remains
within a section of a stream or river. The residence time
is determined by the streamflow and the volume of the
river reach or the average stream velocity and the length
of the river reach.
Respiration. Biochemical process by means of which
cellular fuels are oxidized with the aid of oxygen to
permit the release of the energy required to sustain life;
during respiration, oxygen is consumed and carbon
dioxide is released.
Restoration. Return of an ecosystem to a close
approximation of its presumed condition prior to
disturbance.
Riffle. A rocky shoal or sand bar located just below the
surface of the water.
Glossary-12
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
Riparian areas. Areas bordering streams, lakes, rivers,
and other watercourses. These areas have high water
tables and support plants that require saturated soils
during all or part of the year. Riparian areas include
both wetland and upland zones.
Riparian vegetation. Hydrophytic vegetation growing
in the immediate vicinity of a lake or river closely
enough so that its annual evapotranspiration constitutes
a factor in the lake or river regime.
Riparian zone. The border or banks of a stream.
Although this term is sometimes used interchangeably
with floodplain, the riparian zone is generally regarded
as relatively narrow compared to a floodplain. The
duration of flooding is generally much shorter, and the
timing less predictable, in a riparian zone than in a river
floodplain.
Roughness coefficient. A factor in velocity and
discharge formulas representing the effects of channel
roughness on energy losses in flowing water. Manning's
"n" is a commonly used roughness coefficient.
Rotating biological contactor (RBC). A wastewater
treatment process consisting of a series of closely
spaced rotating circular disks of polystyrene or
polyvinyl chloride. Attached biological growth is
promoted on the surface of the disks. The rotation of
the disks allows contact with the wastewater and the
atmosphere to enhance oxygenation.
Runoff. That part of precipitation, snowmelt, or
irrigation water that runs off the land into streams or
other surface water. It can carry pollutants from the air
and land into receiving waters.
Scoping modeling. A method of approximation that
involves simple, steady-state analytical solutions for a
rough analysis of the problem.
Scour. To abrade and wear away. Used to describe the
weathering away of a terrace or diversion channel or
streambed. The clearing and digging action of flowing
water, especially the downward erosion by stream water
in sweeping away mud and silt on the outside of a
meander or during flood events.
Secchi depth. A measure of light penetration into a
waterbody that is a function of the absorption and
scattering of light in water. Secchi depth is
operationally defined as the depth at which a white disc
is indistinguishable from the surrounding water or the
black and white quadrants of a black and white disc are
indistinguishable from one another when the disc is
lowered into the water.
Secondary treatment. The second step in most
publicly owned waste treatment systems, in which
bacteria consume the organic parts of the waste. It is
accomplished by bringing together waste, bacteria, and
oxygen in trickling filters or in the activated sludge
process. This treatment removes floating and settleable
solids and about 90 percent of the oxygen-demanding
substances and suspended solids. Disinfection is the
final stage of secondary treatment. (See Primary
treatment, Tertiary treatment.)
Sediment oxygen demand (SOD). The solids
discharged to a receiving water are partly organics, and
upon settling to the bottom, they decompose
anaerobically as well as aerobically, depending on
conditions. The oxygen consumed in aerobic
decomposition represents another dissolved oxygen sink
for the waterbody.
Septic system. An on-site system designed to treat and
dispose of domestic sewage. A typical septic system
consists of a tank that receives waste from a residence or
business and a system of tile lines or a pit for disposal of
the liquid effluent (sludge) that remains after
decomposition of the solids by bacteria in the tank; must
be pumped out periodically.
Sewage fungus. Proliferations of bacteria and/or fungi
that may form feathery, cotton-wool-like growths in
streams and rivers that have high concentrations of
dissolved organic compounds.
Sewer. A channel or conduit that carries wastewater
and storm water runoff from the source to a treatment
plant or receiving stream. Sanitary sewers carry
household, industrial, and commercial waste. Storm
sewers carry runoff from rain or snow. Combined
sewers handle both.
First Edition: November 1999
Glossary-13
-------
Simulation. The use of mathematical models to
approximate the observed behavior of a natural water
system in response to a specific known set of input and
forcing conditions. Models that have been validated, or
verified, are then used to predict the response of a
natural water system to changes in the input or forcing
conditions.
Sinuosity. The degree to which a river or stream bends.
Slope. The degree of inclination to the horizontal.
Usually expressed as a ratio, such as 1:25 or 1 on 25,
indicating one unit vertical rise in 25 units of horizontal
distance, or in a decimal fraction (0.04), degrees (2
degrees 18 minutes), or percent (4 percent).
Soluble reactive phosphorus. Form of phosphorus that
is most readily available to plants. It consists of the
species H2PO42 , HPO42 , and PO43 . (Also known as
orthophosphate.)
Sorption. The adherence of ions or molecules in a gas
or liquid to the surface of a solid particle with which
they are in contact.
Spatial segmentation. A numerical discretization of
the spatial component of a system into one or more
dimensions; forms the basis for application of numerical
simulation models.
Stabilization pond. A large earthen basin used for the
treatment of wastewater by natural processes involving
the use of both algae and bacteria.
Steady-state model. Mathematical model of fate and
transport that uses constant values of input variables to
predict constant values of receiving water quality
concentrations. Model variables are treated as not
changing with respect to time.
Stoichiometric ratio. Mass-balance-based ratio for
nutrients, organic carbon, and algae (e.g.,
nitrogen-to-carbon ratio).
STORET. U.S. Environmental Protection Agency
national water quality database for STORage and
RETrieval (STORET). Mainframe water quality
database that includes physical, chemical, and biological
data measured in waterbodies throughout the United
States.
Storm runoff. Storm water runoff, snowmelt runoff,
and surface runoff and drainage; rainfall that does not
evaporate or infiltrate the ground because of impervious
land surfaces or a soil infiltration rate lower than rainfall
intensity, but instead flows onto adjacent land or into
waterbodies or is routed into a drain or sewer system.
Stratification (of waterbody). Formation of water
layers each with specific physical, chemical, and
biological characteristics. As the density of water
decreases due to surface heating, a stable situation
develops with lighter water overlaying heavier and
denser water.
Streamflow. Discharge that occurs in a natural channel.
Although the term "discharge" can be applied to the
flow of a canal, the word "streamflow" uniquely
describes the discharge in a surface stream course. The
term "streamflow" is more general than "runoff since
streamflow may be applied to discharge whether or not
it is affected by diversion or regulation.
Stream restoration. Various techniques used to
replicate the hydrological, morphological, and
ecological features that have been lost in a stream
because of urbanization, farming, or other disturbance.
Stressor. Any physical, chemical, or biological entity
that can induce an adverse response.
Substrate. Bottom sediment material in a natural water
system.
Surface area. The area of the surface of a waterbody;
best measured by planimetry or the use of a geographic
information system.
Surface runoff. Precipitation, snowmelt, or irrigation
water in excess of what can infiltrate the soil surface and
be stored in small surface depressions; a major
transporter of nonpoint source pollutants.
Surface water. All water naturally open to the
atmosphere (rivers, lakes, reservoirs, ponds, streams,
impoundments, seas, estuaries, etc.) and all springs,
Glossary-14
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
wells, or other collectors directly influenced by surface
water.
Suspended solids or load. Organic and inorganic
particles (sediment) suspended in and carried by a fluid
(water). The suspension is governed by the upward
components of turbulence, currents, or colloidal
suspension. Suspended sediment usually consists of
particles smaller than 0.1 mm, although size may vary
according to current hydrological conditions. Particles
between 0.1 mm and 1 mm may move as suspended or
be deposited (bedload).
Technology-based standards. Effluent limitations
applicable to direct and indirect sources that are
developed on a category-by-category basis using
statutory factors, not including water quality effects.
Temperature coefficient. Rate of increase in an
activity or process over a 10 degree Celsius increase in
temperature. Also referred to as the Q10.
Tertiary treatment. Advanced cleaning of wastewater
that goes beyond the secondary or biological stage,
removing nutrients such as phosphorus, nitrogen, and
most biochemical oxygen demand (BOD) and suspended
solids.
Thalweg. Deepest part of a stream channel.
Three-dimensional (3-D) model. Mathematical model
defined along three spatial coordinates where the water
quality constituents are considered to vary over all three
spatial coordinates of length, width, and depth.
Topography. The physical features of a geographic
surface area including relative elevations and the
positions of natural and man-made features.
Total Kjeldahl nitrogen (TKN). The total of organic
and ammonia nitrogen in a sample, determined by the
Kjeldahl method.
Total Maximum Daily Load (TMDL). The sum of the
individual wasteload allocations (WLAs) for point
sources, load allocations (LAs) for nonpoint sources and
natural background, plus a margin of safety (MOS).
TMDLs can be expressed in terms of mass per time,
toxicity, or other appropriate measures that relate to a
state's water quality standard.
Total nitrogen (TN). The total amount of nitrogen in a
sample, including organic nitrogen, nitrate (NO3), nitrite
(NO2), and ammonia (NH4).
Total phosphorus (TP). The total amount of
phosphorus in a sample, including both organic and
inorganic forms. In most lakes, the organic forms of
phosphorus make up a large majority of the total
phosphorus.
Toxic substances. Those substances, such as
pesticides, plastics, heavy metals, detergent, solvent, or
any other natural or man-made materials, that are
poisonous, carcinogenic, or otherwise directly harmful
to human health and the environment.
Transit time. In nutrient cycles, the average time that a
substance remains in a particular form; the ratio of
biomass to productivity.
Transport of pollutants (in water). Transport of
pollutants in water involves two main processes: (1)
advection, resulting from the flow of water, and (2)
dispersion, or transport due to turbulence in the water.
Tributary. A lower order-stream compared to a
receiving waterbody. "Tributary to" indicates the largest
stream into which the reported stream or tributary flows.
Trophic state. A classification of the condition of a
waterbody pertaining to the availability of nutrients.
Trophic states include oligotrophy (nutrient-poor),
mesotrophy (intermediate nutrient availability),
eutrophy (nutrient-rich), and hypertrophy (excessive
nutrient availability).
Turbidity. A measure of opacity of a substance; the
degree to which light is scattered or absorbed by a fluid.
Turbulent flow. A flow characterized by agitated and
irregular, random-velocity fluctuations.
Turbulence. A type of flow in which any particle may
move in any direction with respect to any other particle
and not in a smooth or fixed path. Turbulent water is
agitated by cross currents and eddies. Turbulent velocity
First Edition: November 1999
Glossary-15
-------
is that velocity above which turbulent flow will always
exist and below which the flow may be either turbulent
or laminar.
Two-dimensional (2-D) model. A mathematical model
defined along two spatial coordinates where the water
quality constituents are considered averaged over the
third remaining spatial coordinate. Examples of 2-D
models include descriptions of the variability of water
quality properties along (a) the length and width of a
river that incorporates vertical averaging of depth, or (b)
the length and depth of a river that incorporates lateral
averaging across the width of the waterbody.
Uncertainty factors. Factors used in the adjustment of
toxicity data to account for unknown variations. Where
toxicity is measured on only one test species, other
species may exhibit more sensitivity to that effluent. An
uncertainty factor would adjust measured toxicity
upward and downward to cover the sensitivity range of
other, potentially more or less sensitive species.
Unstratified. Indicates a vertically uniform or
well-mixed condition in a waterbody. See also
Stratified.
Use Attainability Analysis (UAA). A structured
scientific assessment of the factors affecting the
attainment of the use, which may include physical,
chemical, and economic factors as described in the Code
of Federal Regulations section 131.10(g). (40 CFR
131.3)
Validation (of a model). Process of determining how
well the mathematical model's computer representation
describes the actual behavior of the physical processes
under investigation. A validated model will have also
been tested to ascertain whether it accurately and
correctly solves the equations being used to define the
system simulation.
Verification (of a model). Testing the accuracy and
predictive capabilities of the calibrated model on a data
set independent of the data set used for calibration.
Volatilization. Process by which chemical compounds
are vaporized (evaporated) at given temperature and
pressure conditions by gas transfer reactions. Volatile
compounds have a tendency to partition into the gas
phase.
Wasteload allocation (WLA). The portion of a
receiving water's loading capacity that is allocated to
one of its existing or future point sources of pollution.
WLAs constitute a type of water quality-based effluent
limitation (40 CFR 130.2(h)).
Wastewater. Usually refers to effluent from a sewage
treatment plant. See also Domestic wastewater.
Wastewater treatment. Chemical, biological, and
mechanical procedures applied to an industrial or
municipal discharge or to any other sources of
contaminated water to remove, reduce, or neutralize
contaminants.
Water quality. The biological, chemical, and physical
conditions of a waterbody. It is a measure of a
waterbody's ability to support beneficial uses.
Water quality-based effluent limitations (WQBEL).
Effluent limitations applied to dischargers when
technology-based limitations alone would cause
violations of water quality standards. Usually WQBELs
are applied to discharges into small streams.
Water quality-based permit. A permit with an
effluent limit more stringent than one based on
technology performance. Such limits might be
necessary to protect the designated use of receiving
waters (e.g., recreation, irrigation, industry, or water
supply).
Water quality criteria. Levels of water quality
expected to render a body of water suitable for its
designated use, composed of numeric and narrative
criteria. Numeric criteria are scientifically derived
ambient concentrations developed by EPA or states for
various pollutants of concern to protect human health
and aquatic life. Narrative criteria are statements that
describe the desired water quality goal. Criteria are
based on specific levels of pollutants that would make
the water harmful if used for drinking, swimming,
farming, fish production, or industrial processes.
Water quality-limited segments. Those water
segments which do not or are not expected to meet
Glossary-16
First Edition: November 1999
-------
Protocol for Developing Nutrient TMDLs
applicable water quality standards even after the
application of technology-based effluent limitations
required by sections 301(b) and 306 of the Clean Water
Act (40 CFR 130.290)). Technology-based controls
include, but are not limited to, best practicable control
technology currently available (BPT) and secondary
treatment.
Zero-order kinetics. Describes a reaction with a
constant rate of pollutant depletion per unit time.
Zooplankton. Very small animals (protozoans,
crustaceans, fish embryos, insect larvae) that live in a
waterbody and are moved passively by water currents
and wave action.
Water quality standard. Law or regulation that
consists of the beneficial designated use or uses of a
waterbody, the numeric and narrative water quality
criteria that are necessary to protect the use or uses of
that particular waterbody, and an antidegradation
statement.
Watershed-based trading. Watershed-based trading is
an efficient, market-driven approach that encourages
innovation in meeting water quality goals, but remains
committed to enforcement and compliance
responsibilities under the Clean Water Act. It involves
trading arrangements among point source dischargers,
nonpoint sources, and indirect dischargers in which the
"buyers" purchase pollutant reductions at a lower cost
than what they would spend to achieve the reductions
themselves. Sellers provide pollutant reductions and
may receive compensation. The total pollution
reduction, however, must be the same or greater than
what would be achieved if no trade occurred.
Watershed protection approach (WPA). The U.S.
EPA's comprehensive approach to managing water
resource areas, such as river basins, watersheds, and
aquifers. WPA has four major features—targeting
priority problems, stakeholder involvement, integrated
solutions, and measuring success.
Watershed-scale approach. A consideration of the
entire watershed, including the land mass that drains
into the aquatic ecosystem.
Watershed. A drainage area or basin in which all land
and water areas drain or flow toward a central collector
such as a stream, river, or lake at a lower elevation.
Wetlands. An area that is saturated by surface water or
ground water with vegetation adapted for life under
those soil conditions, as in swamps, bogs, fens, marshes,
and estuaries.
First Edition: November 1999
Glossary-17
-------
Glossary
Glossary-18
First Edition: November 1999
------- |