Understanding Total Maximum Daily Loads with Stormwater Sources and theNPDES Stormwater Permitting Process

U.S. Environmental Protection Agency

Learning Objectives

• Provide an overview of TMDLs and NPDES stormwater permitting

• Provide an understanding of how TMDL writers can address stormwater in TMDL development

• Provide an understanding of how NPDES permit writers can develop permits to implement TMDLs

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Presentation Roadmap

• Overview of the TMDL program • Overview of the NPDES stormwater permitting

process • Basics of TMDL and stormwater permit integration• What’s different about TMDLs for stormwater

sources?• What’s different about stormwater permits to

implement TMDLs? • Quiz 3

Overview of Total Maximum Daily Loads (TMDLs)

• Wasteload allocations (WLAs) set loading cap for point sources

• Load allocations (LAs) set loading cap for nonpoint sources

• Reserve capacity sets aside allocation for future development

• Margin of Safety (MOS) allocation accounts for uncertainty

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Point Source #1

Point Source #2

Point Source #3

Nonpoint Source #1Nonpoint

Source #2

Nonpoint Source #3

Nonpoint Source #4

MOS

ReserveCapacity

Wasteload Allocations (WLAs)

• WLA used to determine WQBEL

• WQBEL implemented through NPDES permits

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Point Source #1

Point Source #2 – WLA

MOS

ReserveCapacity

Point Source #3

Nonpoint Source #1Nonpoint

Source #2

Nonpoint Source #3

Nonpoint Source #4

Brief Overview of Regulated Stormwater Sources• Three primary types of sources (40 CFR 122.26(a)

and 122.26(b))• Municipal separate storm sewer systems (MS4s)• Construction • Industrial

• Other sources as designated by the permitting authority

• Two types of NPDES stormwater permits• Individual • General

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Types of NPDES Permits

• Individual Permit• 1 application submitted

1 permit issued• Appropriate where

discharger needs site-specific permit conditions

Public Notice and Public CommentsPublic Notice and Public Comments

Administrative RecordAdministrative Record

Permit ApplicationPermit Application

Draft Permit and Fact Sheet Development• Effluent Limits• Monitoring Conditions• Standard Conditions• Special Conditions

Draft Permit and Fact Sheet Development• Effluent Limits• Monitoring Conditions• Standard Conditions• Special Conditions

Final PermitFinal Permit

Types of NPDES Permits

• General Permit• 1 permit issued many

applications submitted• Appropriate where multiple

dischargers require relatively uniform permit conditions Public Notice and Public CommentsPublic Notice and Public Comments

Administrative RecordAdministrative Record

Identify Need and Collect DataIdentify Need and Collect Data

Draft Permit and Fact Sheet Development• Effluent Limits• Monitoring Conditions• Standard Conditions• Special Conditions

Draft Permit and Fact Sheet Development• Effluent Limits• Monitoring Conditions• Standard Conditions• Special Conditions

Final PermitFinal Permit

Notice of Intent (NOI) to be CoveredNotice of Intent (NOI) to be Covered

Overview of Regulated Stormwater Sources: MS4s• Not just municipalities• Phase I MS4s

• Based on population served (100,000+)• Individual permit with detailed application process

• Phase II MS4s• Small regulated MS4s within the boundaries of an

‘urbanized area’ or designated by permit authority• Two permit types

• MS4 general permit with 6 minimum control measures• Individual permit under special circumstances 9

Overview of Regulated SW Sources: Construction• Phase I: disturb 5 acres or more • Phase II: disturb between one and 5 acres• Permit types

• Construction General Permit (CGP)• Individual permits are an option under certain conditions

• Discharge to impaired waters• Reasonable potential to cause or contribute to water

quality standard exceedance

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Overview of Regulated SW Sources: Industrial Activity• Eleven categories of industrial activity• Covered under multi-sector general permit (MSGP),

although individual permits are an option under certain conditions

• Able to certify to a condition of no exposure in lieu of permit coverage

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Permitting Other SW Sources: Residual Designation• Authorizes NPDES permitting authorities to

designate other stormwater sources for permit coverage• Cause or contribute to water quality standard excursion• Significant contributor of pollutants to surface waters

• Implications for how TMDLs are developed that include both regulated and currently unregulated stormwater sources

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Let’s Review. . .

• Three types of regulated stormwater sources• MS4s (Phase II MS4 GP)• Industrial (MSGP)• Construction (CGP)

• Other sources using RDA• Stormwater sources assigned WLAs • WLAs translated to WQBELs in permits

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Basics of TMDL & Stormwater Permit Integration• WLAs for regulated stormwater sources

• Needed to promote effective implementation• As specific for each regulated stormwater source as

possible

• NPDES stormwater permits must be consistent with assumptions and requirements of WLAs

• TMDL and permit writers should work together throughout the process

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TMDL Process

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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. Water Quality Standards and numeric WQ target*

4. Load Allocations (LAs)*5. Wasteload Allocations (WLAs)*6. Margin of Safety (MOS)*7. Seasonal Variation*

3. Loading Capacity- Linking WQ and Pollutant Sources*

(including critical conditions*)

8. Reasonable Assurances+

9. Monitoring Plan+

10. Implementation Plan+

11. Public Participation*

EPA Recommended 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

Problem Understanding

TMDL Target Identification

Source Assessment

Understanding SW Effects

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Precipitation

Interception

Infiltration

Percolation

Transpiration

EvaporationSurfaceRunoff

GroundwaterReturn Flow

Understanding SW Effects

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Understanding SW Effects

• Altered stream hydrology (“water quantity”)• Higher peak flows• Increased runoff volume• Lower base flows

• Increased pollutant loading (“water quality”)• Higher runoff volumes • Exposure to stormwater sources• Less opportunity for filtering

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Impairment Characterization

• Waters impaired by stormwater sources often listed for:• Biological impairment • Habitat alteration

• Focus on multiple pollutants and combined effects• Look at indicators of stormwater impacts

• Flow patterns• Degraded biology/habitat• Imperviousness

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Establishing Water Quality Targets• Water quality targets include…

• Indicator• Associated target value

• Water quality targets for TMDLs with SW sources• Consider multiple stressors due to changes in flow and

increased pollutant loads• Could lead to use of a surrogate target, such as

impervious cover, that represents combined SW effects20

Stormwater Source Assessment

• Challenging boundary issues• Snapshot in time

• Construction sites ephemeral in nature• Industrial source no-exposure status could change

• Less familiar point source databases• eNOI • state-specific stormwater database

• Data generated by sources varies by type and permit requirement

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Understanding Spatial Boundaries of SW Sources • MS4 system boundary ≠

municipal jurisdictional boundary• Phase II regulated small MS4s

only within urbanized area boundary

• Industrial and construction sources can be found in and out of MS4 boundaries

MS4 Generated Information

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TMDL Approach Selection

• Similar approaches to consider• Impairment/source specific information to consider

• Use of a surrogate target such as IC or flow volume• Boundary/location of stormwater sources• Behavior of stormwater sources • Critical conditions

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Categorizing Stormwater WLAs• WLAs for other point sources are presented for

each individual point source facility

• For regulated stormwater sources, TMDL writers might face challenges that limit their ability to provide individual WLAs for each regulated stormwater source

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Challenges for Categorizing Stormwater Source WLAs

• Data availability • Boundary issues • Varied implementation approaches

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Residual Designation Authority and WLAs• Include language in the TMDL about potential

changes in regulatory status• Currently unregulated stormwater sources have load

allocations• Use of RDA to change designation means load allocation

becomes a wasteload allocation

• No need for TMDL resubmission• Might require WLA refinement• Change in overall loading cap would be subject to

approval 27

Options for Categorizing and Expressing WLAs

• Individual by each regulated stormwater source

• Categorical by each type of stormwater source

• Aggregated for all stormwater sources

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Individual WLAs by Source: Overview

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Tips: Individual WLAs by Source

• Ensure consistency between source characterization and source WLAs

• Provide information and assumptions about each source

• Provide estimated baseline load for each source• Present WLA to support implementation

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Categorical WLAs by Source Type: Overview

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Tips: Categorical WLAs by Source Type• Create regulated stormwater source inventory

• Indicate which regulated stormwater sources are included under each category

• Provide recommendations for sub-allocating the categorical WLAs

• Provide rationale for using this approach 32

Single Aggregated WLA for All Stormwater Sources: Overview

33

Tips: Single Aggregated WLA for All Stormwater Sources• Create regulated stormwater source inventory

• Indicate which regulated stormwater sources are included under the aggregated WLA

• Provide recommendations for sub-allocating the aggregated WLA

• Provide rationale for using this approach 34

Mixing WLA Options

• Select options best suited to sources• Data availability• Permit requirements and implementation strategies

• Consider other options for further categorizing WLAs• Subwatershed• Dry weather/wet weather

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WLA Challenges and Considerations by Source

Type

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MS4 WLA Challenges

• Regulated area based on system boundary

• Regulated area might have pockets that don’t drain to the regulated system

• Regulated area might contain nested sources

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Charles River Pathogen TMDL MS4 WLA • Includes 35 MS4s • Assigns two WLAs to all MS4s for

each type of surface waters• Expresses WLA as colonies/day• Calculated WLA using flow data

from areas with impervious cover• Captures combined sewer areas• Presented on a segment-by-

segment basis 38

Wissahickon Creek Siltation TMDL MS4 WLAs

• Covers 16 MS4s in five subwatersheds

• Estimates loads for five subwatersheds and distributes among MS4s

• Contains existing load, WLA, percent reduction for each MS4

• Presents WLAs by subwatershed in appendix 39

Shingle Creek Chloride TMDL MS4 WLAs

• Covers deicing activities by multiple MS4s• Nine municipalities• One county• MN Dept. of Transportation

• Includes categorical MS4 WLA• Allows implementation

flexibility40

Construction Source WLA Challenges

• Varied timeframes for construction activities

• Change in source type after activity ends

• Activities located in MS4 boundary

• Activities located outside MS4 boundary41

Potomac Drains (WV) Sediment TMDL Construction WLAs• Identified 176 regulated

construction sources at outset of TMDL

• Updated information during process with new active and pending permits

• Assigns individual WLAs to 297 regulated construction sources

• Includes future growth allowance

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Industrial WLA Challenges• Regulated industrial stormwater

sources might be located in the MS4 boundary

• Regulated industrial stormwater sources might have a no exposure certification

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Columbia Slough TMDLs Industrial WLAs• Lead TMDL (1998)• Aggregated WLA for

permitted industrial area• Provides an approach for

industrial facilities to calculate their individual WLA• Unit-area basis• Dependent on flow conditions 44

Photo: Mark Gamba http://www.portlandmonthlymag.com/travel-and-outdoors/articles/1008-features-oasis/

Gauley River Watershed TMDL Industrial WLAs• Iron/TSS WLAs (2008)

• Loads (lbs/yr)• Concentrations (mg/L)

• Individual WLA assigned to each industrial facility• Facilities have iron and TSS

benchmark values under MSGP • Facilities that meet benchmarks

not considered a significant source

• Assigning WLA necessary to allow SW discharge under MSGP

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NPDES Permit Components

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Components of All Permits

Cover PageCover Page

Special ConditionsSpecial Conditions

Monitoring and ReportingMonitoring and Reporting

Effluent LimitationsEffluent Limitations

Additional Monitoring / Special StudiesAdditional Monitoring / Special Studies

Best Management PracticesBest Management Practices

Standard ConditionsStandard Conditions

Compliance SchedulesCompliance Schedules

Technology-basedTechnology-based

Water Quality-basedWater Quality-based

NPDES Permit Components Affected by TMDLs

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Components of All Permits

Cover PageCover Page

Special ConditionsSpecial Conditions

Monitoring and ReportingMonitoring and Reporting

Effluent LimitationsEffluent Limitations

Additional Monitoring / Special StudiesAdditional Monitoring / Special Studies

Best Management PracticesBest Management Practices

Standard ConditionsStandard Conditions

Compliance SchedulesCompliance Schedules

Technology-basedTechnology-based

Water Quality-basedWater Quality-based

48

40 CFR 122.44(d)(1)(vii)(vii) When developing water quality-based effluent limits under this paragraph the permitting authority shall ensure that:(A)The level of water quality to be achieved by limits on point sources established under this paragraph is derived from and complies with all applicable water quality standards; and(B)Effluent limits developed to protect a narrative water quality criterion, a numeric water quality criterion, or both, are consistent with the assumptions and requirements of any available wasteload allocation for the discharge prepared by the State and approved by EPA pursuant to 40 CFR 130.7.

Effluent Limits in Stormwater Permits• Numeric limits

• Pollutant loads and concentrations• Numeric parameters acting as surrogates for pollutants

(i.e., impervious cover or flow)

• Narrative BMP limits • Selected to meet the WLA• Possibly includes requirement to monitor BMP

performance against benchmarks49

Options for Numeric Effluent Limits in Stormwater Permits• Develop water quality-based effluent limitations

(WQBELs)

• Incorporate WLA as numeric effluent limit (e.g., bacteria concentration or sediment percent reduction)

50

Options for Narrative Effluent Limits in Stormwater Permits• Require implementation of BMPs in the permit

• Based on documented pollutant removal effectiveness• Consider numeric performance benchmarks

• Incorporate specific BMPs identified in the TMDL or implementation plan

• Hybrid approach: meet narrative limits or be subject to numeric limits

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Monitoring in Stormwater Permits

• Visual• BMP installation inspections• Discharges• In-stream

• Analytical monitoring • Discharge/Outfall• BMP performance (flow, pollutant removal)

• Ambient

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Compliance Schedules in Stormwater Permits • Compliance schedule and interim limits might be

necessary • BMP implementation over time to meet WLA• Time needed for compliance with numeric effluent limit

• Consult EPA’s memorandum “Compliance Schedules for Water Quality Based Effluent Limits in NPDES Permits” http://www.epa.gov/npdes/pubs/memo_complianceschedules_may07.pdf) 53

WLAs to MS4 Permit Example: Washington D.C. MS4 Permit

• Permit includes two different types of WQBELs that are linked to applicable TMDLs1. Numeric effluent limit: Requires annual removal of

103,188 lbs of trash as defined by Anacostia River Watershed Trash TMDL

2. Other TMDL requirements• Permit lists 15 TMDLs for BOD, fecal coliform, TSS, oil and grease, organics

and metals, PCBs, trash, nutrients • For all WLAs assigned to the DC MS4, the permittee to develop and

submit a TMDL Implementation Plan for review and approval within 30 months of permit issuance (Section 4.10.3) 54

TMDL Implementation Plan Requirements (Section 4.10.3)• Schedule of WLA attainment with interim milestones if longer

than 5 years

• Numeric benchmarks• Specify annual pollutant load reductions• Extent of controls to achieve benchmarks• Modeling to show how controls will achieve WLA

• Submit within 30 months of effective date for EPA review and approval• EPA will incorporate approved plan as enforceable permit provisions• Annual updates as needed to include new WLAs• If insufficient progress is shown during permit term from effluent

monitoring, adjustments to the Implementation Plan must be made within 6 months

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Determining Applicability of the TMDL to SW Permits

• Permitting staff makes determination• General permit application process guides

permittee to determine:• Receiving waterbody• If receiving water is impaired or subject to a TMDL

• General permit contains list of TMDLs and applicable waterbodies

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Considerations for Implementation Planning

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Tools to Support Implementation Planning• BMP Performance Evaluation Tool (EPA Region 1)

• Can estimate BMP pollutant load removal or size a BMP to meet specific pollutant removal target

• www.epa.gov/region1/npdes/stormwater/

• SUSTAIN (EPA ORD)• Identifies most cost-effective combinations of BMP type,

location and size to meet specific flow and water quality targets

• www.epa.gov/nrmrl/wswrd/wq/models/sustain/

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WLAs to MS4 Permit Example: San Francisco Bay TMDLs

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San Francisco Bay TMDL: WLAs for PCBs and Mercury• PCB and Mercury TMDLs

• Identify “urban stormwater” as a source that contribute to the impairment

• Allocate county-wide loads for those identified as sources of urban stormwater discharges

• TMDL Implementation Plans • Provide a 20-year timeline for meeting the WLAs• Specify what must be included in NPDES permits • Require implementation of BMPs designed to achieve

WLA• Specify requirements for permit reissuance

• based on an updated effectiveness of BMPs• include technically feasible and cost-efficient controls to

attain WLAs

60

San Francisco Bay PCB and Mercury TMDL Implementation Plans• PCBs Implementation Plan

• 1st permit cycle – implement BMP pilots• 2nd permit cycle – implement BMPs that protect

strategic locations and develop plan to attain allocations

• Mercury Implementation Plan • Identifies specific permit requirements that must

be included in urban stormwater permits • Example: develop and implement mercury source

control program; monitor levels of methymercury in discharges 61

San Francisco Bay MS4 Permit (2009)• Permit covers stormwater discharges from multiple

municipalities and local agencies

• Includes both the minimum regulatory requirements (i.e., MS4 “six minimum measures”) and TMDL-based requirements (Sections C.9-C.14) for all impairment pollutants• Pesticides, mercury, PCBs, copper• Trash

• TMDL requirements in permit are directly linked to the Implementation Plans for each of the impairment pollutants

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WLAs to SW Permit Limits: Mercury

SW WLAs• Assigned to 12 urban SW

dischargers, listed by county or MS4 entity

• 20 yr deadline to achieve WLA with interim milestone

• Specifies that NPDES permits must require sources to implement BMPs designed to achieve WLA, including a set of minimum requirements• Implement mercury source

control program• Implement monitoring system

to quantify load reductions• Monitor methylmercury in

discharges• Fate and transport study• Develop allocation sharing

mechanism

Permit Limits• Incorporates specific aggregate

WLA and interim loading milestone • 20 yr deadline for attainment of

aggregate WLA and 10 yr deadline for interim loading milestone

• WQBEL in permit match requirements set out in Implementation Plan

• Additional WQBELs:• Pilot projects to evaluate municipal

sediment removal practices, on-site treatment systems through retrofits, and pollution abatement programs in stormwater conveyances 63

Tips for TMDL Developers and NPDES Stormwater Permit Writers• Work together throughout the TMDL

development process• Promotes data sharing • Encourages programmatic information exchange

• Identify all stormwater sources in the watershed affecting an impaired waterbody• MS4s, traditional and non-traditional• Construction site in and out of MS4• Industrial facilities in and out of MS4

64

Tips for TMDL Developers and NPDES Stormwater Permit Writers• Address data gaps by developing suite of

monitoring requirements for TMDLs and permits

• Express WLAs to promote effective implementation

• One WLA per stormwater source, if adequate data

• Talk to NPDES stormwater permitting staff about implementation details 65

Tips for TMDL Developers and NPDES Stormwater Permit Writers• Determine whether to prescribe BMPs and

where (TMDL v. permit)• Assist stormwater permittees in finding

impaired waterbodies and associated TMDL information • Direct permittees to WLAs related to their

discharges• Provide guidance on BMP selection where

narrative effluent limits are used 66

Resources

Technical assistance from EPA: www.epa.gov/owow/tmdl/stormwater/ Summary of State PracticesSummary of 17 TMDLs with SW

sourcesUnderstanding TMDL Requirements

for MS4s Stormwater TMDL Implementation

Support Manual 67

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