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Understanding TMDLs: A primer for permit writersU.S. Environmental Protection Agency
1
Module Objectives
• Provide a basic understanding of the TMDL program
• Illustrate the technical steps in developing TMDLs• Discuss typical approaches for developing TMDLs• Highlight connection between TMDLs and NPDES
permits
2
Module Roadmap
• Definition of a TMDL• Clean Water Act context• TMDL Elements• TMDL Development Process• Emerging or Evolving Issues• Tips for Engaging in the TMDL Process• Resources
3
What is a TMDL?
• Greatest amount of loading that a water can receive without violating water quality standards (i.e., loading capacity). [40 CFR 130.2(f)]
TMDL =WLAi + LAi + MOS
WLAi: Sum of waste load allocations for existing and future point sources
LAi: Sum of load allocations for existing and future nonpoint and background sourcesMOS: Margin of safety
4
What is a TMDL?• WLAs set pollutant
loading cap for point sources
• LAs set pollutant loading cap for nonpoint sources
• Reserve capacity sets aside allocation for future development
• Margin of Safety (MOS) allocation accounts for uncertainty 5
Point Source #1
Point Source #2
Nonpoint Source #1
Nonpoint Source #2
MOS
Reserve Capacity
Mortgage
Water &Electricity
Groceries &Other
Essentials
Car Payments
Contingencies
SavingsAccount
6
Adopt Water Quality Standards
Monitor and Assess Waters
List Impaired & Threatened Waters
Develop TMDLs(TMDL = WLA + LA + MOS)
Control Point Sources via NPDES Permits
Manage Nonpoint Sources through Grants,
Partnerships and Voluntary Programs
Trading
CWA 303(a)–(c)40 CFR 103.3
40 CFR 103.4
CWA 303(d)40 CFR 103.7
CWA 303(d)40 CFR 103.7
CWA 303(e)40 CFR 103.540 CFR 103.6
Steps in the Water Quality-based Approach of the Clean Water Act
Relevant Statutes and Regulations
Water Quality Standards
• Designated use (e.g., aquatic life, recreation, drinking water)
• Water quality criteria to protect uses• Narrative or numeric• Magnitude, duration, frequency (e.g., DO: 5 mg/L daily
minimum; fecal coliform: 200 counts/100 mL 30-day geometric mean)
• Antidegradation provisions • General implementation policies
7
Monitoring and Assessment• Establish monitoring programs to assess
the quality of waters• Include physical, chemical and biological data• Include appropriate quality assurance and control• Support a variety of CWA programs:
• Abatement and control• Water quality standards• TMDLs• NPDES • Waterbody health
8
Adopt Water Quality Standards
Monitor and Assess Waters
List Impaired & Threatened Waters
Develop TMDLs(TMDL = WLA + LA + MOS)
303(d) List of Impaired Waters• Identify waters that do not meet WQS after:
• Technology-based effluent limitations• More stringent effluent limitations• Other pollution control requirements
• Include a priority ranking for all listed segments• Identify TMDLs scheduled for next 2 years • Identify the pollutants causing or expected to cause
violations of the applicable WQS• Provide documentation to support determination
to list or not to list its waters9
303(d) List of Impaired Waters (cont.)• Developed every 2 years• Submitted to EPA for review/approval• Available on state websites and summarized on
EPA’s TMDL website: www.epa.gov/owow/tmdl
10
Integrated Report
303(d) list (impaired/threatened waters)305(b) report (overall health of waterbodies)314 report (health of lakes/reservoirs)
11
Integrated Report
Since 2002, due April 1, every even-numbered year
Reporting guidance issued for each listing cycle (2002, 2004, 2006 and 2008):http://www.epa.gov/owow/tmdl/guidance.html
Integrated Report (cont.)
12
Category Description
1 All designated uses met
2 Some, but not all, uses met
3 Cannot determine if any uses met (insufficient data)
4 Impaired/threatened – TMDL not needed
4a TMDL completed
4b TMDL alternative
4c Non-pollutant causes
5 Impaired/threatened by pollutant –TMDL needed
Section 303(d) List
TMDL Roles
• States develop TMDLs for each “pollutant/waterbody combination”
• Public review and comment• EPA reviews/approves
• If disapprove, EPA develops TMDL• EPA has developed TMDLs in response to court orders or
at request of states
13
Adopt Water Quality Standards
Monitor and Assess Waters
List Impaired & Threatened Waters
Develop TMDLs(TMDL = WLA + LA + MOS)
The TMDL Program Today• 71,000+ impairments (waterbody-
pollutant combinations)• Top 10 Listed Impairments
1. Pathogens2. Metals3. Nutrients4. Organic enrichment/
low DO5. Sediment6. PCBs7. Mercury8. pH9. Impaired biota10. Turbidity
As of January 2012
14
TMDL Elements• Water Quality Standards• Loading capacity
• Mass per time, toxicity or other appropriate measure (40 CFR 130.2(f) and 130.2(i))
• WLAs (40 C.F.R. §130.2(h)) • LAs (40 CFR 130.2(g))
• Range from reasonably accurate estimates to gross allotments• MOS (CWA 303(d)(1)(C), 40 CFR 130.7(c)(1))
• Implicit or explicit (USEPA 1991)• Critical conditions (40 CFR 130.7(c)(1)) • Seasonal variation (CWA 303(d)(1)(C), 40 CFR 130.7(c)
(1)) 15
TMDL Elements (cont.)
• Reasonable assurance• When impaired by a blend of point and nonpoint sources,
provide "reasonable assurances" that LAs will be achieved (USEPA 1991)
• Future growth or sources• Daily load (Grumbles 2006)
• TMDLs should be expressed in terms of daily time increments
• TMDLs may include alternative, non-daily load expressions to facilitate implementation of WQS 16
9. Monitoring Plan+
10. Implementation Plan+
4. LAs*5. WLAs*6. MOS*7. Seasonal Variation*8. Reasonable Assurance+
TMDL Process
17
Problem Understanding
Stak
ehol
der I
nvol
vem
ent &
Pub
lic P
artic
ipati
on
Linkage between Loading and Waterbody Response
Allocation Analysis
TMDL Report and Submittal
1. Description of waterbody, pollutant of concern, pollutant sources, and priority ranking
2. WQS and numeric WQ target*
3. Loading Capacity*(including critical conditions*)
11. Public Participation*
Elements in a TMDL Submittal
* Required by regulation (40 CFR 130.7)+ Recommended through guidance
From Guidelines for Reviewing TMDLs under Existing Regulations issued in 1992 (May 20, 2002): http://www.epa.gov/owow/tmdl/guidance/final52002.html
Implementation and Monitoring Plan
TMDL Target Identification
Source Assessment
Problem Understanding – Questions to Answer• What was the basis for listing
(e.g., supporting data)?• What pollutant is causing the problem?• Under what conditions does the problem occur
(i.e., critical conditions)?• What characteristics of the waterbody and/or its
watershed might be exacerbating or mitigating the problem?
• What are the known or potential sources?• What efforts to protect the watershed
are already underway?18
Problem Understanding – Data Compilation & Analysis• Data Compilation
• Waterbody monitoring data• Point source monitoring data • Watershed data and GIS coverages • Previous studies
• Data Analysis• What is the problem? • Where does it occur? • When does it occur? • How does it occur? 19
Data Analysis – Impairment Analysis• Confirm impairment• Understand magnitude/frequency of
exceedances
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Running geomean Fecal coliform NTE WQC Geomean WQC
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DUCHESNE RIVER
ROCK CREEKDUCHESNE R, WEST FORK
CURRANT CREEK
INDIAN
CANYO
N CREEK
ANTELO
PE CR
EEK
NUTTERS CAN
YON
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STRAWBERRY RIVERDUCHESNE RIVER
UINTA RIVER
WHITER OCKS RIVE R
COTT ONWOOD CREEKDRY GULCH CREEK
RED CREEK
PIGEON WATER CREEK
LAKE FORK CREEK
Y ELLOWSTONE RIVER
STRAWBERRYRESERVOIR
Average TDS#S 0 - 135#S 135 - 290#S 290 - 616#S 616 - 998
#S 998 - 2013
Data Analysis – Spatial Analysis Examples
21
Data Analysis – Spatial Analysis Examples (cont.)
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10
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1,000
Jan-95 Feb-95 Mar-95 Apr-95 May-95 Jun-95 Jul-95 Aug-95 Sep-95 Oct-95 Nov-95 Dec-95
TS
S (
mg
/L)
Station 3 - Upstream Station 4 - Downstream
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Station 3 (upstream) - TSS (mg/L)
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am
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S (
mg
/L)
1:1
Data Analysis – Temporal Analysis Examples
23
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1000
10000
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Fec
al C
olifo
rm (
#/10
0 m
L)
25th-75th Percentile Mean, Min, Max Median Not-To-Exceed Standard
1
10
100
1000
10000
Jan-00 Jul-00 Jan-01 Jul-01 Jan-02 Jul-02 Jan-03 Jul-03 Jan-04 Jul-04
Tu
rbid
ity
(ntu
)
Upstream Downstream
Data Analysis – Relationship among Parameters• Evaluate relationship among pollutants
contributing to impairment(s) (e.g., sediment and phosphorus)
• Evaluate relationship among pollutants and other water quality response measures (e.g., nutrients and DO)
• Evaluate water quality and other waterbody conditions (e.g., flow, temperature, depth)
24
Data Analysis – Water Quality and Flow Example
25
Time-series of Flow and Fecal Coliform Data
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10,000
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-88
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Fecal coliform (#/100 mL) Flow (cfs)
Flow Duration Curve and Corresponding Fecal Coliform
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1,200
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Flow Duration Interval
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00
mL
)
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6,000
Flo
w (
cfs
)
FC Flow
Regression - Flow vs. Fecal Coliform
R2 = 0.5466
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1200
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Flow (cfs)
Fe
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)
Water Quality Target Identification – Goals• Understand applicable water quality
standards• Identify numeric target for calculation of loading
capacity• Based on numeric water quality criterion (e.g., 750 ug/l
aluminum)• Based on interpretation of narrative criterion
26
Water Quality Target Identification – Process • Select an indicator
• Consistent with WQS and impairment
• Quantifiable• Compatible with local conditions, critical conditions, sources
• Select a target value• Reference sites• Historical or background
conditions• Literature/guidance values• Functional relationships (e.g., algal mass & total phosphorus,
TSS & measures of fishery health)
27
A measurable parameter for which a target value can be set to represent attainment of WQS (e.g., nitrogen, TSS)
Value or magnitude (e.g., concentration) established for indicator; level at which WQS will be supported
Water Quality Target Identification – Examples• Sediment – “no adverse impacts to aquatic life”
• TSS concentration (literature values, reference conditions, background/historical data)
• Loading target based on reference conditions• Biology – “maintain healthy benthic communities”
• Stressor Identification to identify pollutant• Identify target based on statistical analysis, literature values,
reference conditions, etc. • Nutrients – “not in concentrations that cause
objectionable conditions…”• Concentration or loading target for limiting nutrient (modeling,
statistical analysis of stressor-response, literature values, reference conditions, background/historical data)
28
Source Assessment – Goals
• Identify potential point and nonpoint sources (type, location, pollutants, etc.)
• Understand how sources affect waterbody condition (e.g., delivery mechanisms)
• Understand relative magnitude or influence of major sources
29
30
• Point sources: • Discharge effluent through
discrete conveyance such as pipes or man-made ditches
• Permitted through NPDES
Source Assessment – Types of Sources
31
www.epa.gov/owm
Source Assessment – Types of Sources (cont.)• Nonpoint sources:
• Diffuse pollution sources (i.e., without a single point of origin or not introduced into a receiving stream from a specific outlet)
• Generally carried from the land surface to waterbodies through stormwater runoff
• Not permitted through NPDES
32
www.epa.gov/owow/nps
Source Assessment – Process• Identify potential nonpoint sources
• Field surveys, land use coverages, aerial photos, previous studies, local knowledge
• Location, pollutants, activity types/timing• Identify potential point sources
• NPDES PCS/ICIS, state permitting staff• Facility and permit information (e.g., type, design flow,
pollutants discharged, permit limits, etc.)• Use results of data analysis to identify primary sources
expected to be contributing to impairment• Identify source dynamics that need to be represented
in linkage analysis 33
34
Atmospheric DepositionPasturesCropland Watering
Livestock
MS4 Stormwater
Permitted Industrial
FacilityWWTP
Expe
cted
Sou
rces
Base flowsHigh flows, storm events
Precipitation-driven Inputs•Build-up and wash-off of pollutants•Surface water runoff
Direct Inputs•Arbitrary, sometimes constant, discharge•Discrete, direct discharge to waterbodies
= NPS= PS
Del
iver
y M
echa
nism
Criti
cal L
oadi
ngCo
nditi
ons
Linkage Analysis – Goals
• Evaluate receiving water response to pollutant loadings
• Establish “link” between sources and water quality standards
• Identify loading capacity
35
Linkage Analysis – Process
• Select approach• Apply approach• Establish “existing” loading and conditions• Calculate loading capacity
36
Linkage Analysis – Approach Selection
37
User and ApplicationConsiderations
• What experience or training is required to apply the approach?
• What level of effort is needed for application?
• What are the data needs?• What is the expected cost
(of necessary software and of time and labor for application)?
ProgrammaticConsiderations
• What is the schedule?• Are there existing tools available for
the waterbody/watershed?• Are there any planned future uses for
the approach (e.g., linkage to other analyses, implementation planning)?
• Are there proven and acceptedmethods applied for
similar
projects?TechnicalConsiderations
• What are the applicable water quality criteria?
• What are the impairments and critical conditions?
• What are the sources and their behavior and characteristics?
• How are the multiple sources, impaired waterbodies or impairments related?
Approach Selection
38
Technical needs of approach
Technical considerations for approach selection
Water quality criteria and TMDL targets
Impairments and critical conditions
Sources
Spatial Needs
Time-scale Needs
Processes to Include
Are different criteria or TMDL targets applicable in different locations within the watershed?
What are the duration and frequency of applicable criteria or targets?
Is criterion based on pollutant level (e.g., concentration) or a measure of response or condition (e.g., flow, habitat quality, eutrophication)?
What are the pollutants?
How many impaired segments are being addressed?
What are the location and distribution of impaired segments?
What is the timing associated with impairment (e.g., instantaneous vs. chronic or cumulative effects)?
Are there any temporal trends to capture (e.g., seasonality in waterbody conditions)?
Is meeting the target dependent on or affected by multiple waterbody measures (e.g., nutrient levels, temperature, pH)?
What are the waterbody critical conditions for loading response (e.g., dynamic, flow variable vs. steady-state)?
If dealing with multiple pollutants, how are they related?
What type of sources/land uses exist in the watershed?
What are the location and distribution of sources?
At what level do the sources need to be isolated (e.g., gross loading vs. land use specific loading)?
Are the effects due to cumulative or acute loading conditions?
Are there temporal variations in source loading (e.g., due to weather patterns, seasonal activities)?
At what temporal scale do the sources need to be estimated?
What is the source loading behavior (e.g., precipitation-driven, direct discharge)?
Do sources impact multiple impaired segments (i.e., need for in-stream routing and transport)?
Does the analysis need to evaluate individual and/or cumulative impact of sources?
Types of Approaches – Examples • Mass balance• Load duration• Modeling
• Watershed• Receiving water
39
Types of Approaches – Mass Balance
Inputs – Losses = Outputs
•Relies on the assumption of conservation of mass into a waterbody•Identifies the allowable load input to meet water quality target after the consideration of losses•Typically “back-calculates” allowable loads based on target concentrations and waterbody volume
40
Types of Approaches – Mass Balance Example• Large river impaired by PCBs• Monitoring confirmed two major sources
• Permitted industrial facility• Permitted runoff from landfill
• Developed a spreadsheet model to represent a simplified mass balance for the system
41
Types of Approaches – Mass Balance Example (cont.)
42
Upstream Boundary
Industrial facility outfall
Tributary #2
Landfill runoff
Tributary #1
Downstream Boundary
(flow, concentration)
(flow, concentration)
(flow, concentration)
(flow, concentration)
Types of Approaches – Mass Balance Example (cont.)
43
Dissolved Particulate
Water
Sediment
Sediment/WaterInterface
OUTFLOW
Res
uspe
nsio
n
(upstream, tributaries,
direct sources)
INFLOW
Types of Approaches – Mass Balance Example (cont.)• Reduce source contributions until achieve
criteria• Allocate to primary sources and background based
on successful scenario• WLA as concentration and annual load
44
Types of Approaches – Load Duration• Uses observed flows and water quality target
to establish a flow-variable curve of loading capacities
• Builds on using flow duration curves, which evaluate cumulative frequency of historic flow data
• Multiply target concentration by observed flows to create a “loading capacity curve”
45
Types of Approaches – Load Duration (cont.)• Plotted with existing loads to identify needed
reductions
46
Existing load: 290,022 G-org/day
Loading capacity: 90,511 G-org/day
Load reduction: 69%
Types of Approaches – Load Duration (cont.)
47
Loading CapacityLoading Capacity minus MOS
MS4 WLA
WWTP WLA
LA
Types of Approaches – Watershed Models• Watershed hydrologic and water quality
processes• Some simulate only the land-based processes• Some include linked river segments and simulate in-
stream transport and water quality processes• Include direct inputs (e.g., septics, point sources)
• Vary in the level of detail (e.g., processes, simulation timestep)
• Range in complexity from the use of empirically based loading functions (e.g., GWLF) to physically based simulations (e.g., HSPF)
48
Types of Approaches – Receiving Water Models• Simulate conditions within a receiving
waterbody (e.g., lake, stream, estuary) • Based on representation of physical, chemical
and biological processes• Typically include inputs as user-defined boundary
conditions (monitoring data, watershed model output)• Steady-state or dynamic models
• Steady-state: operate under a single, nonvariable flow condition with constant inputs (e.g., design or critical flow)
• Dynamic models: time-variable simulation• Varies in level of complexity in spatial detail (1-, 2-, or
3-D)49
Futu
re G
row
th (3
)
Load
ing
Capa
city
Total Load
Load Reduction
Perm
itted
Con
ditio
ns (2
)
TMDL
Sce
nario
C
TMDL
Sce
nario
BTM
DL S
cena
rio A
Existi
ng C
ondi
tions
(1)
Futu
re G
row
th (3
)
Types of Approaches – Modeling Process
50
Load
ing
Capa
city
Total Load
Load Reduction
Perm
itted
Con
ditio
ns (2
)
TMDL
Sce
nario
C
TMDL
Sce
nario
BTM
DL S
cena
rio A
Existi
ng C
ondi
tions
(1)
Allocation Analysis – Goals
• Allocate loading capacity among WLAs, LAs and MOS• Meet legal requirements• Facilitate implementation
• Identify necessary source load reductions
51
Allocation Analysis – Decisions• Identify appropriate expression of allocations
• Mass per time, toxicity, “other appropriate measure”
• Determine how to include MOS• Implicit as conservative assumptions• Explicit portion of load
• Determine whether future growth requires allocation• “Reserved” portion of load for future NPS or point
sources• Based on amount of certain land areas (e.g., future
conversion of ag to urban) 52
Allocation Analysis – Decisions (cont.)• Identify appropriate spatial or source scale of
allocations• Location of impaired segment(s)• Location/distribution of sources• Location of monitoring stations• Areas of targeted implementation
• Identify appropriate time scale for allocations• Expression of water quality standards• Nature of impairment/impact (e.g., acute vs. chronic)• Temporal variations in loading• Implications for monitoring or implementation• If non-daily, also include daily
53
Allocation Analysis – Process
• Identify potential allocation scenarios• Equal concentrations• Equal percent removal • Target sources
• Relative impact of individual sources (e.g., sensitivity)• Potential for multiple benefits (e.g., control multiple pollutants from one
source)• “Controllability” of sources• Stakeholder priorities
54
Allocation Analysis – Process (cont.)• Represent different combinations of source
reductions that all meet WQS
55
0.000
0.200
0.400
0.600
0.800
1.000
1.200
1.400
Oct
-95
Apr-96
Oct-9
6
Apr-9
7
Oct
-97
Apr-98
Oct
-98
Apr-9
9
Oct
-99
Apr-00
Oct
-00
Apr-01
Oct
-01
Tota
l Nit
rog
en (
mg
/L)
TMDL Target Baseline Scenario A Scenario B Scenario C
Scena rio A
Forest40%
Ag
17%
Urban
16%
Septics
5%
Resident ial16%
WWTP6%
Sce nario B
Forest
36%
Ag11%
Urban25%
Septics4%
WWTP4%
Resident ial
20%
Sce nario C
Forest
40%
Ag
11%
Urban25%
Sept ics2%
WW TP2%
Resident ial20%
Percent of total TMDL load
Reasonable Assurance
• Required in mixed-source TMDLs — with nonpoint and point sources
• Provides assurance that NPS reductions will occur• Should be case-specific • Can utilize an adaptive management approach
toward meeting WQS
56
TMDL Implementation
• Nonpoint Sources:• No federal regulatory enforcement program • State/local NPS management programs (few w/
regulatory enforcement)
• Point Sources:• Permits enforceable under CWA through NPDES • Issued by EPA or states w/ delegated authority
57
Translating WLAs into Permits
• Permit writers should, as appropriate, translate WLAs to water quality-based effluent limitations (WQBELs)• WLAs
• Derived directly from water quality criteria through TMDLs, watershed analyses, or facility-specific analyses
• Expression can vary (concentration vs. load; daily, monthly, annual)
• WQBELs• Derived from WLAs using EPA or state-specific limit development
procedures• Must be consistent with assumptions used to derive applicable WLAs [40
CFR 122.44(d)(1)(vii)(B)]• Typically have different duration/averaging period than WLAs
58
Translating WLAs into Permits
59
Step 1: Determine Wasteload Allocation (WLA) from Aquatic Life Water Quality Criterion
Step 2: Calculate Long-Term Averages (LTAs) and Select Lowest
Step 3: Calculate Maximum Daily Limit (MDL) and Average Monthly Limit (AML)*
*Other averaging periods used where appropriate (e.g., instantaneous maximum and instantaneous minimum for pH)
Steps in Developing Chemical-Specific WQBELs from Aquatic Life Criteria
TMDL Monitoring Plans• Recommended through EPA guidance• Provides data to demonstrate water quality
improvements associated with TMDL implementation
• Supports adaptive management• Choose approach appropriate to TMDL goals and
targets• Before/after control study • Paired watershed study• Upstream/downstream study• Trend monitoring 60
Emerging or Evolving Issues
• Regulated stormwater (subject of Module 3)• Nutrient criteria• Climate change• PCBs• Invasive species• Ocean acidification• Water quality trading• TMDL revisions/reopening
61
Tips for Engaging in the TMDL Process• Understand format/content of your state’s 303(d)
list• Review TMDL development schedule• Provide data and information on point sources• Provide input on selection of linkage analysis
approach and how point sources are represented• Participate in allocation analysis• Understand that the WLA in a TMDL may not
provide the most stringent effluent limit 62
Resources• Technical Resources
• TMDL Process and Background • Guidance for Water Quality-based Decisions: The TMDL Process. EPA 440/4-91-001. • Protocol for Developing Sediment TMDLs. EPA 841-B-99-004. • Protocol for Developing Pathogen TMDLs. EPA 841-R-00-002.• Protocol for Developing Nutrient TMDLs. EPA 841-B-99-007.
• Modeling for TMDLs• Compendium of Tools for Watershed Assessment and TMDL Development. EPA841-B-97-006. • TMDL Model Evaluation and Research Needs. EPA/600/R-05/149.
• Special Topics• Options for Expressing Daily Loads in TMDLs. Draft: June 22, 2007. • Handbook for Developing Watershed TMDLs. Draft: December 15, 2008. • TMDLs to Stormwater Permits Handbook. Draft: November 2008. • An Approach for Using Load Duration Curves in the Development of TMDLs. EPA 841-B-07-006• PCB TMDL Handbook. EPA 841-R-11-006
• www.epa.gov/owow/tmdl (under TMDL Technical Resources)• Policy and Guidance Resources (listing, special issues)
• www.epa.gov/owow/tmdl (under TMDL Guidance) 63
PROPERTIES
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