Contents

Introduction .................................................................................................................................................. 1

Section A. Numeric Post-Construction Standards in MS4 Permits............................................................... 3

Section B. Water Quality-Based Effluent Limits in MS4 Permits................................................................13

1. Listing of applicable TMDLS, WLAS, and the affected MS4s...........................................................14

2. Numeric limits and other quantifiable approaches for the specific pollutants of concern ............15

3. Required implementation of specific stormwater controls or management measures.................20

4. Other types of water quality-based requirements..........................................................................24

4.1 Permitting Authority Review and Approval of TMDL Plans ....................................................24

4.2 Monitoring/Modeling Requirements......................................................................................29

4.3 TMDL-Related Annual Reporting Requirements.....................................................................33

5. Requirements for discharges to impaired waters prior to TMDL approval ....................................35

i 
Introduction

Although much progress has been made since the 

first stormwater regulations were promulgated in 

1990, significant challenges remain in protecting 

waterbodies from the impact of stormwater 

discharges. Urban-related stormwater has been 

identified as the source of impairment for tens of 

thousands of miles of rivers, streams, and coastal 

shorelines, as well as hundreds of thousands of 

acres of lakes, reservoirs and ponds in the United 

States. These impairments are largely due to the 

expansion of the built environment, which removes 

vegetation, alters the natural infiltration capability 

of the land, generates the discharge of pollutants, 

and leads to stream erosion. 

National Pollutant Discharge Elimination System 

(NPDES) permitting authorities are employing a 

variety of different requirements in their municipal 

separate storm sewer system (MS4) permits to 

combat these problems. Permitting authorities 

have included numeric performance and/or design 

standards in MS4 permits to control discharges 

from new development and redevelopment. In addition, numeric effluent limitations have been 

expressed as water quality-based effluent limits (WQBELs) for specific pollutant parameters 

based on applicable wasteload allocations (WLAs) or other water quality objectives. Many 

permits also include requirements for the MS4 to implement specific management measures 

that are consistent with approved Total Maximum Daily Loads (TMDLs) or with the need to 

protect impaired waters prior to TMDL development.

To develop this compendium, the U.S. Environmental Protection Agency (EPA) reviewed all 

state and EPA-issued individual and general MS4 final permits issued up to June 2014. The 

review focused on MS4 permitting approaches that incorporated retention-based postconstruction standards. It also focused on permitting approaches that directly implement 

TMDLs through numeric requirements or pollutant-specific management measures, or a 

combination of both. MS4 permits were also reviewed to determine how permitting authorities 

measured progress of implementation of WQBEL requirements through such measures as 

review and approval of implementation plans, monitoring/modeling, and reporting 

MS4 Permit Universe

250 individual MS4 permits cover 

approximately 855 Phase I MS4s. 

54 general MS4 permits cover 

approximately 6,589 Phase II MS4s. 

100 individual MS4 permits cover 

approximately 106 Phase II MS4s. 

3 watershed MS4 permits cover 

approximately 3 Phase I and 40 

Phase II MS4s. 

Regulated MS4s are typically cities, 

counties, towns, and villages; 

however, Phase II MS4s also include 

nontraditional MS4s such as public 

universities, departments of 

transportation, hospitals and prisons.

The universe of the Phase II MS4 

program changes every 10 years 

according to the U.S. Census Bureau 

definition of urbanized area.

1 
requirements. Finally, MS4 permit approaches were identified that dealt with discharges to 

impaired waters prior to TMDL approval.

This compendium presents examples of 

different permitting approaches that EPA 

found in its nationwide review by 

describing, and in some cases excerpting, 

language from permits. The compendium 

is divided into two major sections. Section 

A provides examples of permits that 

implement numeric post-construction 

performance and/or design standards, 

and Section B presents different 

permitting approaches to address 

impaired waters and TMDLs. Note that a 

number of the permits identified in the 

compendium are featured in more than 

one of the categories.

EPA notes that this compendium is intended to serve as a snapshot of permitting approaches. 

EPA anticipates that as permits are reissued in the coming months and years, the information in 

this compendium will need to be updated to include new examples or modified information. 

EPA has an interest in ensuring the accuracy of the information contained in this document, and 

therefore welcomes input on any aspect of this compendium at any time. The Agency will 

update the compendium as needed based on the comments received. EPA notes that the 

inclusion of any particular permit example should not be read as an Agency endorsement of the 

entire approach taken in that permit. In addition, this document does not impose any new 

legally binding requirements on EPA, states, or the regulated community, and does not confer 

legal rights or impose legal obligations upon any member of the public. EPA made every 

attempt to ensure the accuracy of the examples included in this document; however, in the 

event of a conflict between this compendium and any statute, regulation, or permit, the 

statute, regulation or permit controls. For more information about the NDPES Stormwater 

Program visit www.epa.gov/npdes/stormwater. 

Parking island bioretention

Stafford County, Virginia 

(Credit: Abby Hall/EPA) 

2 
Numeric Post-Construction Standards Section A

Section A. Numeric Post-Construction Standards in 

MS4 Permits

Many states have developed 

performance and/or design 

standards to control postconstruction stormwater 

discharges from newly 

developed and redeveloped 

sites. MS4 permits in 33 states 

have conditions implementing 

numeric performance standards. 

A comprehensive list of state 

standards for post-construction 

stormwater standards is 

provided at

www.epa.gov/npdes/pubs/sw_st

ate_summary_standards.pdf. 

Many states have implemented numeric, retention-based performance standards for newly 

developed and redeveloped sites. These standards typically require or encourage using

infiltration, evapotranspiration, or harvest practices to control a specified volume of 

stormwater. Volume retention is critical to reduce pollutant loads of all water quality 

parameters and to reduce erosion of the receiving waterbody. It also provides multiple 

community benefits by treating stormwater as a resource. Retention-based performance 

standards have been expressed in various ways. Some retention standards have been 

expressed as a volume of rainfall, a percentile storm event, or a ground water recharge volume

that must be retained. The following permits are examples of MS4 permits that implement such 

standards (listed by EPA Region). 

Parking lot bioretention

(Credit: Abby Hall/EPA) 

REGION 1 

Connecticut

The 2013 Phase I City of Stamford, Connecticut, MS4 permit requires that the permittee 

incorporate the use of runoff reduction and low impact development (LID) practices into their 

land use regulations to meet a goal of maintaining post-development runoff conditions similar 

to pre-development runoff conditions. Specifically, for all new development and 

redevelopment sites with a currently developed effective impervious cover of less than 40%, 

3 
Numeric Post-Construction Standards Section A

the applicant must design the site to retain the entire water quality volume for the site. For 

redevelopment of sites with an effective impervious cover of 40% or more, a developer shall 

design the site to retain on-site half the water quality volume for the site. In the 2004 

Connecticut Stormwater Quality Manual, the recommended water quality volume is the runoff 

volume for 90% of the average annual storm events, which is equivalent to the runoff 

associated with the first inch of rainfall. Any new Stamford MS4 discharge that is within 500 

feet of the tidal wetland must discharge through a system designed to retain the volume of 

stormwater runoff generated by one inch of rainfall from the MS4 within the discharge's 

drainage area. See Section 6.A.3.a.iii.

Permit available upon request: Chris.Stone@ct.gov

Vermont

The 2012 Vermont general permit for discharges from small MS4s requires permittees to 

implement and enforce the requirements in the 2002 Vermont Stormwater Management 

Manual for new development and redevelopment. The manual includes a ground water 

recharge volume standard that is determined as a function of annual pre-development 

recharge for a given soil group, average annual rainfall volume, and amount of impervious 

cover at a site. The ground water recharge standard can be met by one of two methods, or a 

combination of both. The first is designated as the percent volume method, and is based on 

infiltrating the recharge volume using one or more approved structural stormwater treatment 

practices. The second method is designated as the percent area method, and is based on 

draining runoff from some or all of the site impervious area through one or more approved 

nonstructural stormwater treatment practices. The manual also includes a water quality 

treatment standard that requires water quality treatment of 90% of annual storms based on 

removing total suspended solids (TSS) and total phosphorus (TP). The State of Vermont directly 

regulates post-construction stormwater runoff from activities that result in creation of new or 

expansion of existing impervious surface of more than an acre; regardless of whether the site 

discharges to an MS4 or directly to a waterbody. Consequently, the MS4 program must only 

regulate those sites that fall below the impervious cover threshold but disturb at least one acre 

of land or less if it is a part of a common plan of development. See Section IV.H.5.e.

REGION 2

New Jersey 

The 2009 New Jersey general permit for discharges from small MS4s requires permittees to 

implement and enforce a program to address stormwater runoff from new development and 

redevelopment and adopt ordinances according to state stormwater management rule, N.J.A.C. 

7:8-4, to control stormwater from nonresidential development and redevelopment projects. In 

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Numeric Post-Construction Standards Section A

addition, the permittee must ensure that any residential development and redevelopment 

projects that are subject to the Residential Site Improvement Standards for stormwater 

management (N.J.A.C. 5:21-7) comply with those standards. The New Jersey standard for 

ground water recharge requires that 100% of the average annual pre-construction ground

water recharge volume for the site is maintained. For the purpose of calculating runoff 

coefficients and ground water recharge, there is a presumption that the pre-construction 

condition of a site or portion thereof is a wooded land use with good hydrologic condition. This 

ground water recharge requirement does not apply to previously developed portions of sites in 

urban redevelopment areas. The New Jersey standard for water quality provides that 

stormwater management measures are to be designed to reduce the post-construction load of 

TSS in stormwater runoff generated from the water quality design storm by 80% of the 

anticipated load from the developed site, expressed as an annual average. See Part I.F.3.

New York

The 2010 New York general permit for discharges from small MS4s requires permittees to 

develop and implement a program to address stormwater runoff from new development and 

redevelopment that ensures projects meet applicable standards in the New York State 

Stormwater Management Design Manual. The New York standard for new development 

requires runoff reduction be met by infiltration, ground water recharge, reuse, recycle, or 

evaporation of 100% of the post-development water quality volume unless specific physical site 

limitations prohibit or limit the use of infiltration or ground water recharge. This runoff 

reduction requirement is designed to replicate pre-development hydrology by maintaining preconstruction infiltration, peak runoff flow, and discharge volume. The water quality volume is 

calculated based on the amount of runoff equivalent to 90% rain event and the percent of 

impervious cover created at a site. This requirement can be accomplished by applying on-site 

green infrastructure techniques, standard stormwater management practices with runoff 

reduction capacity, and effective site planning. Redevelopment projects are encouraged to 

comply with the runoff reduction standard; however, it is not a requirement. Instead, 

alternative sizing criteria and stormwater management controls have been developed for 

redevelopment activities. See Parts VII.A.5 and VIII.A.5. 

REGION 3

West Virginia

The 2009 West Virginia general permit for discharges from small MS4s requires permittees to 

implement and enforce site design standards for all new development and redevelopment 

disturbing one acre or more. The site design standards require management measures that 

keep and manage on-site the first inch of rainfall from a 24-hour storm preceded by 48 hours of 

no measurable precipitation. This first inch of rainfall must be 100% managed with no discharge 

5 
Numeric Post-Construction Standards Section A

to surface waters, unless one of the two alternatives specified in the permit, off-site mitigation 

and payment in lieu, are met. See Part II.C.B.5.a.ii. 

Washington, DC

The 2011 District of Columbia Phase I MS4 (DC MS4) permit requires the design, construction, 

and maintenance of stormwater controls to achieve on-site retention of 1.2 inches of 

stormwater from a 24-hour storm with a 72-hour antecedent dry period through 

evapotranspiration, infiltration and/or stormwater harvesting and use for new development 

and redevelopment projects greater than or equal to 5,000 square feet. See Section 4.1.1. 

Maryland

Maryland has two general permits, one for municipalities and one for state and federal 

agencies, for discharges from small MS4s that require that stormwater management for new 

development and redevelopment be addressed for any proposed project that disturbs 5,000 

square feet or more of earth. Because Maryland has a stormwater management program in 

place that regulates new development and redevelopment projects, the state considers 

compliance with the state statute to be compliance with this minimum control measure, this 

general permit, and federal regulations. Permittees shall comply with all state and local laws, 

regulations, ordinances, and procedures relating to stormwater management. In addition, 

permittees must implement and comply with the principles, methods, and practices found in 

the 2000 Maryland Stormwater Design Manual, Volumes 1 and 2. The manual specifies that 

environmental site design (ESD) shall be implemented to the maximum extent practicable

(MEP) to mimic pre-development conditions. The standard for characterizing pre-development 

runoff characteristics for new development projects is woods in good hydrologic condition. ESD 

practices are to be used to the MEP to meet the required water quality volume and the ground

water recharge volume. The water quality volume is defined as the runoff volume from the 1-

inch rain event in the Maryland Eastern Rainfall Zone and 0.9 inch in the Maryland Western 

Rainfall Zone. The manual includes a redevelopment policy that provides flexibility and 

alternative requirements for sites with more than 40% impervious area. See Part III.E. 

The Phase I MS4 permits in Maryland [Anne Arundel County (2014), Charles County (2002), 

Carroll County (2005), Frederick County (2002), Harford County (2004), Howard County (2005), 

Montgomery County (2010), Prince George’s County (2014), City of Baltimore (2013), and 

Baltimore County (2013)] also require by reference that the permittee implement the 

stormwater management design policies, principles, methods, and practices found in the 2000 

Maryland Stormwater Design Manual or other innovative stormwater management 

technologies approved by MDE. See Part III.E.1. 

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Numeric Post-Construction Standards Section A

Delaware

The 2013 New Castle County, Delaware, MS4 permit requires permittees to implement a 

program to address stormwater from post-development sites as prescribed under the Delaware 

Sediment and Stormwater regulations. In general, the Delaware Sediment and Stormwater 

regulations require stormwater controls sized according to the Resource Protection Event. The 

design parameter for the Resource Protection Event shall be the annualized runoff volume 

(RPv) produced by a storm having a 99% probability of occurring annually (i.e., the 1-year 

event) based on post-developed conditions. For new development, the RPv shall be reduced to 

an equivalent 0% effective imperviousness. For redevelopment, the RPv shall be reduced to an 

equivalent 70% of the existing effective imperviousness. The RPv shall be further reduced to an 

equivalent wooded condition for any existing meadow or wooded areas within the limit of 

disturbance based on the 2007 Delaware Land Use/Land Cover data. See Part II.A.4. 

REGION 4

Tennessee 

The 2010 Tennessee general permit for discharges from small MS4s requires for new 

development and redevelopment projects greater than or equal to one acre, management 

measures that are designed, built, and maintained to infiltrate, evapotranspire, harvest and/or 

use, at a minimum, the first inch of every rainfall event preceded by 72 hours of no measurable 

precipitation. This first inch of rainfall must be 100% managed with no stormwater runoff being 

discharged to surface waters. See Section 4.2.5.2.1. 

The 2011 Phase I City of Chattanooga, Tennessee, and the 2012 Phase I City of Nashville, 

Tennessee, MS4 permits include runoff reduction standards which require, in combination or 

alone, management measures that are designed, built, and maintained to infiltrate, 

evapotranspire, harvest, and/or use, at a minimum, the first inch of every rainfall event 

preceded by 72 hours of no measurable precipitation. The permittee may develop incentive 

standards for redevelopment and/or to increase use of green infrastructure best management 

practices (BMPs) while allowing flexibility for developers and designers to meet development 

standards. Such incentive standards are subject to certain criteria and may not exceed a 

maximum reduction of 50% of the required volume. For projects that cannot meet 100% of the 

runoff reduction requirement, the remainder must be treated prior to discharge with a 

technology documented to remove 80% TSS. See Section 3.2.5.2. 

Kentucky

The 2011 Phase I Louisville and Jefferson County, Kentucky, MS4 permit requires the 

development of an ordinance that requires water quality control measures to infiltrate, 

7 
Numeric Post-Construction Standards Section A

evapotranspirate, harvest, and reuse at least the equivalent runoff produced from an 80th

percentile storm (e.g., 0.75 inches). See Part II.B.5. 

REGION 5

Minnesota 

The 2013 Minnesota general permit for 

discharges from small MS4s requires 

permittees to develop and implement a postconstruction stormwater management 

program that requires new development 

projects to meet a standard of no net increase 

from pre-project conditions of stormwater 

discharge volume, TSS, and TP. Redevelopment 

projects are required to meet a standard of a 

net reduction from pre-project conditions of 

stormwater discharge volume, TSS, and TP. See 

Part III.D.5. Parking lot tree pit in Maplewood, Minnesota

(Credit: Alisha Goldstein/EPA)

Wisconsin

The 2014 Wisconsin general permit for 

discharges from small MS4s requires 

permittees to implement a program for new 

development and redevelopment that 

includes an ordinance or other regulatory 

mechanism that establishes postconstruction performance standards 

equivalent to those contained in Wisconsin’s 

administrative code NR 151.122 through 

151.126, and 151.242 through 151.246. The 

infiltration performance standard in 

Wisconsin’s code is based on the 

imperviousness of the site. For example, sites 

with low imperviousness or development 

with less than 40% connected 

imperviousness such as parks, cemeteries, 

and low-density residential development, must infiltrate sufficient runoff volume so that the 

post-development infiltration volume shall be at least 90% of the pre-development infiltration 

volume, based on an average annual rainfall. For sites with 40%–80% connected 

Wisconsin also has a numeric standard 

that applies to the entire MS4 not only to new 

development and redevelopment:

The 2014 Wisconsin general permit for 

discharges from small MS4 requires 

permittees to meet at minimum a 20% 

reduction in the annual average mass of TSS

discharging from the MS4 to surface waters of 

the state as compared to implementing no 

stormwater management controls. Source 

area controls, structural stormwater 

management practices, and nonstructural 

control practices implemented to achieve the 

20% reduction in TSS shall be maintained. 

See Section 2.7.1

8 
Numeric Post-Construction Standards Section A

imperviousness, such as medium- and high-density residential, multi-family development, 

industrial and institutional development, and office parks, the post-development infiltration 

volume shall be at least 75% of the pre-development infiltration volume. For sites greater than 

80% connected imperviousness, such as commercial strip malls, shopping centers, and 

commercial downtowns, the post-development infiltration volume shall be at least 60% of the 

pre-development infiltration volume. See Section 2.5. 

REGION 6

New Mexico

The 2012 Phase I MS4 permit for the City of Albuquerque, Albuquerque Metropolitan Arroyo 

Flood Control Authority (AMAFCA), New Mexico Department of Transportation (NMDOT), and 

University of New Mexico (UNM) requires the implementation and enforcement, via ordinance 

and/or other enforceable mechanism(s), of site design standards that capture the 90th

percentile storm event runoff to ensure the hydrology associated with new development and 

redevelopment sites mimic the pre-development hydrology of the previously undeveloped site. 

See Part I.C.5.b.

REGION 8

Montana

The 2009 Montana general permit for discharges from small MS4s requires, for new 

development and redevelopment projects greater than or equal to one acre, the 

implementation of LID practices that infiltrate, evapotranspire, or capture for reuse the runoff 

generated from the first 0.5 inches of rainfall from a 24-hour storm preceded by 48 hours of no 

measurable precipitation. See Part II.B.5. 

REGION 9

California

The 2013 California general permit for discharges from small MS4s requires that new 

development and redevelopment projects are designed to evapotranspire, infiltrate, harvest

and use, and biotreat stormwater to meet at least one of the following hydraulic sizing design 

criteria: volumetric criteria (approximately the 85th percentile 24-hour storm runoff event or 

the volume of annual runoff required to achieve 80% or more capture) or flow-based criteria 

(the flow of runoff produced from a rain event equal to at least 0.2 inches per hour intensity; or 

the flow of runoff produced from a rain event equal to at least two times the 85th percentile 

hourly rainfall intensity). See Section E.12.e.ii.c. 

9 
Numeric Post-Construction Standards Section A

Los Angeles County, CA

The 2012 Los Angeles County MS4 permit requires that each permittee shall require applicable 

new development and redevelopment projects to retain on-site the stormwater quality design 

volume defined as the runoff from: (1) the 0.75-inch, 24-hour rain event or (2) the 85th 

percentile, 24-hour rain event, whichever is greater. When evaluating the potential for on-site 

retention, each permittee shall consider the maximum potential for evapotranspiration from 

green roofs and rainfall harvest and use. Alternative compliance measures are allowed where 

meeting the standard is shown to be technically infeasible or where a project has been 

determined to provide an opportunity to replenish regional groundwater supplies at an off-site 

location. Alternative compliance measures include on-site biofiltration, off-site infiltration, a 

proposed ground water replenishment project, an off-site retrofit project such as green streets, 

parking lot retrofits, green roofs, and rainfall harvest and use, or participate in a regional 

stormwater mitigation program. The permittee must also require applicable new development 

and redevelopment projects within natural drainage systems to implement hydrologic control 

measures, to minimize changes in post-development hydrologic stormwater runoff discharge 

rates, velocities, and duration. This shall be achieved by maintaining the project’s pre-project 

stormwater runoff flow rates and durations. See Part VI.D.7.c.

San Francisco, CA

The 2009 San Francisco Bay Regional Water Board Municipal Permit requires permittees to 

require applicable new development and redevelopment projects to treat 100% of the design 

storm runoff with LID treatment measures (harvesting and reuse, infiltration, 

evapotranspiration, or biotreatment) on-site or with LID treatment measures at an alternate

stormwater treatment facility. The design storm is defined to meet at least one of the following 

hydraulic sizing design criteria: (1) volume hydraulic design basis (treat stormwater runoff equal 

to approximately the 85th percentile 24-hour storm runoff event or the volume of annual 

runoff required to achieve 80% or more capture); (2) flow hydraulic design basis (treat (a) 10% 

of the 50-year peak flowrate; (b) the flow of runoff produced by a rain event equal to at least 

two times the 85th percentile hourly rainfall intensity; or (c) the flow of runoff resulting from a 

rain event equal to at least 0.2 inches per hour intensity); or (3) combination flow and volume 

design basis (treat at least 80% of the total runoff over the life of the project). See Sections 

C.3.c and C.3.d. 

San Diego, CA

The 2013 San Diego Regional MS4 permit requires the permittee to require applicable new 

development and redevelopment projects to implement LID BMPs that are designed to retain 

(i.e. intercept, store, infiltrate, evaporate, and evapotranspire) on-site the pollutants contained 

10
Numeric Post-Construction Standards Section A

in the volume of stormwater runoff produced from a 24-hour, 85th percentile storm event 

(design capture volume), with the potential to implement off-site alternative compliance 

projects that will have a greater overall water quality benefit for the watershed than if the 

project were to implement structural BMPs on-site. In addition, the permittee must require 

implementation of on-site BMPs to manage hydromodification that may be caused by 

stormwater runoff discharged from a project as follows: (1) post-project runoff conditions 

(flow rates and durations) must not exceed pre-development runoff conditions by more than 

10% (for the range of flows that result in increased potential for erosion, or degraded instream 

habitat downstream of the project); and (2) avoid critical sediment yield areas, or implement 

measures that allow critical coarse sediment to be discharged to receiving waters, such that 

there is no net impact to the receiving water. See Part II.E.3.c. 

REGION 10

Anchorage, AK

The 2010 Anchorage, Alaska, individual MS4 permit requires that for new development and 

redevelopment projects that result in a land disturbance of 10,000 square feet or more, 

management measures that keep and manage the runoff generated from the first 0.52 inches 

of rainfall from a 24-hour event preceded by 48 hours of no measureable precipitation. The 

ordinance or regulatory mechanism must require that the first 0.52 inches of rainfall be 100% 

managed with no discharge to surface waters, except in circumstances described in the permit. 

Runoff volume reduction can be achieved by canopy interception, soil amendments, 

evapotranspiration, rainfall harvesting, engineered infiltration, extended filtration, and/or any 

combination of such practices. See Part II.B.2. 

Washington

The 2013 Western Washington general permit for discharges from small MS4s and the 2013 

Washington Phase I MS4 permit require permittees to implement LID performance standards 

for certain newly developed and redeveloped sites. The standard requires that stormwater 

discharges match developed discharge durations to pre-developed durations for the range of 

pre-developed discharge rates from 8% of the 2-year flow to 50% of the 2-year flow. See 

Appendix I, Section 4.5. 

Oregon 

The 2011 Phase I Portland, Oregon, MS4 permit requires new development and redevelopment 

projects that create or replace 500 square feet of impervious surface to capture and treat 80% 

of the annual average runoff volume, based on a documented local or regional rainfall 

11
Numeric Post-Construction Standards Section A

frequency and intensity. The program must prioritize and include LID, green infrastructure, or 

equivalent design and construction approaches. See Schedule A.4.f. 

The 2010 Phase I Salem, 2010 Phase I Gresham/Fairview, 2010 Phase I Multnomah, 2011 

Phase 1 Eugene, and the 2012 Phase I Clackamas County, Oregon, MS4 permits have the same 

standard, but it applies to new development and redevelopment projects of varying site size 

thresholds.

12
Water Quality-Based Effluent Limitations Section B

Section B. Water Quality-Based Effluent Limits in MS4 

Permits 

This section presents examples of different 

types of permit requirements that are 

based on TMDLs or concern for impaired 

waters. The permits EPA reviewed showed 

that permitting authorities are taking a 

variety of different approaches to 

establishing WQBELs in their MS4 permits. 

Although some water quality-based 

requirements in these permits are in the 

form of numeric effluent limits, others are 

expressed as specific control measures 

that must be implemented to be 

consistent with applicable water quality 

standards or WLAs. 

Permeable pavement and bioretention in 

Albuquerque, New Mexico

(Photo courtesy of AridLID.org)

Overall, EPA found that nearly all MS4 permits include at least some language addressing 

impaired waters. For the purposes of presenting the different types of permitting approaches 

found in EPA’s survey, this compendium organizes the examples into the following categories:

1. Listing of applicable TMDLs, WLAs, and/or the affected MS4s

2. Numeric effluent limits and other quantifiable approaches for the specific pollutants of 

concern1

3. Required implementation of specific stormwater controls or management measures

4. Other types of water quality-based requirements

a. Permitting Authority Review and Approval of TMDL Plans

b. Monitoring/Modeling Requirements

c. TMDL-Related Annual Reporting Requirements

5. Requirements for discharges to impaired waters prior to TMDL approval

1 The use of the term pollutant of concern in this compendium refers to the pollutant parameter(s) for which a 

waterbody is listed as impaired under section 303(d) of the Clean Water Act or for which a TMDL has been 

approved or established by EPA.

13

 
Water Quality-Based Effluent Limitations Section B

1. Listing of applicable TMDLS, WLAS, and the affected MS4s

A first step in determining whether additional permit requirements are necessary as a result of 

an approved or established TMDL is to establish whether any TMDLs or WLAs apply to the MS4s 

being permitted. Although many permits have placed the responsibility for making this 

determination on the MS4 permittee, several permits have instead included information on 

which TMDLs and WLAs apply and which MS4s are affected directly in the permit. This 

approach reduces the amount of work required of the permittee in interpreting TMDL 

documents, and provides greater clarity for the permittee in understanding what water qualityrelated requirements may apply. The following are examples of this approach. 

General Permits

California

The 2013 California small MS4 permit includes tables showing applicable TMDLs, the MS4s 

covered by WLAs, the applicable WLA, and individualized TMDL implementation requirements 

for each affected MS4. See Attachment G. 

Minnesota 

The Minnesota Pollution Control Agency includes on its website the Master List MS4 Permit 

TMDLs Spreadsheet that identifies TMDLs and associated WLAs that apply to its regulated 

MS4s. See the Permit tab.

Washington

The 2013 Western Washington small MS4 permit identifies each TMDL within the permit area 

and all affected MS4 permittees. See Appendix 2. The permit also states that “For applicable 

TMDLs not listed in Appendix 2, compliance with this Permit shall constitute compliance with 

the TMDL.” See Section S7.B.

Individual Permits

Anchorage, AK

The 2010 Anchorage, Alaska, MS4 permit fact sheet includes a list of completed TMDLs that 

identifies the pollutants of concern and percent reduction needed. 

Contact state for permit.

14
Water Quality-Based Effluent Limitations Section B

Menomonee Watershed, Wisconsin

The 2012 Menomonee Watershed Permit for Milwaukee, Wisconsin, and 10 other MS4 

permittees includes a table that lists all of the impaired waterbodies in the Menomonee River 

Watershed, the pollutants of concern, and the contributing MS4. See Table 1. 

Prince George’s County, MD

The 2014 Prince George’s County, Maryland, MS4 permit provides an attachment, which 

includes a three-page list of EPA-approved TMDLs in the County. See Attachment B. 

2. Numeric limits and other quantifiable approaches for the 

specific pollutants of concern

NPDES permits for MS4 discharges have included numeric effluent limitations for specific 

parameters based on an applicable TMDL WLA. Some examples of MS4 permits with numeric 

effluent limitations and other quantifiable approaches include the following. 

General Permits 

California

The 2013 California general permit for discharges from small MS4s incorporates numeric WLAs 

that apply to individual small MS4s. Although the permit states that these numeric WLAs (for 

fecal coliform, sediment, and pesticides) apply to the named MS4s, it provides near-term 

actions, in the form of specific management measures, which constitute the bulk of what the 

permittee must do to be consistent with the WLAs. For example, for the Pajaro River TMDL and 

Implementation Plan for sediment, four MS4 permittees are prohibited from discharging 

sediment to the listed waterbodies in excess of the incorporated WLAs (Table 1). The 

allocations represent a 90% reduction in sediment loading to each waterbody from urban 

roads. See Attachment G –Region Specific Requirements, Regional Water Board Approved 

TMDLs—where urban runoff is listed as a source.

Table 1. Pajaro River TMDL for Sediment

Applicable MS4s Major Subwatershed

Metric Tons of Sediment 

Per Year

City of Morgan Hill

City of Gilroy

City of Hollister

City of Watsonville

Tres Pinos 1

San Benito 100

Llagas 787

Uvas 139

Upper Pajaro 161

Corralitos 284

Mount of Pajaro River 191

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Water Quality-Based Effluent Limitations Section B

Virginia

The 2013 Virginia general permit for discharges from small MS4s requires permittees 

discharging to the Chesapeake Bay watershed to reduce loadings of nitrogen, phosphorus, and 

TSS from existing developed lands (pre-June 30, 2009) by 5% of its modeled share by the permit 

expiration date. The permit also requires a 5% offset of increased loads from new and 

grandfathered construction projects disturbing one or more acres for which an average land 

cover condition greater than 16% impervious cover was used in the design of post-development 

stormwater facilities. The general permit includes tables with loading rates to be used by the 

permittee to calculate required load reductions from existing sources. Load reductions are to 

be accomplished through the implementation of a Chesapeake Bay TMDL Action Plan that 

outlines the means and methods by which the permittee will achieve the required reductions. 

For this permit term, the permit states that compliance with these requirements “represents 

adequate progress for this state permit term towards achieving TMDL WLAs consistent with the 

assumptions and requirements of the TMDL.” See Sections I.C, I.C.2.a.5, Tables 3.a–3.d, I.C.2.a.7 

and 8, and I.C.3. In the Watershed Implementation Plan for the Chesapeake Bay TMDL, Virginia 

committed to a phased approach to reducing nitrogen, phosphorus, and TSS from the MS4 and 

will include additional loading reductions in the next two permits terms.

Individual Permits

Arlington County, VA

The 2013 Arlington County, Virginia, MS4 permit has the same pollutant reduction 

requirements for nitrogen, phosphorus, and TSS as the 2013 Virginia small MS4 general permit 

(described above). The Arlington County MS4 permit also requires the permittee to identify and 

submit to the state at least seven retrofit projects within its watershed retrofit plans that will 

be implemented within County rights-of-way or on County property within 60 months of permit 

issuance. The MS4 is also required to:

• Plant a minimum of 2,000 trees on County lands and develop a program to distribute a 

minimum of 2,000 trees to private property owners.

• Have funding to accommodate a minimum of 200 participants in the StormwaterWise 

Landscape program, which provides cost-sharing and technical assistance for the 

installation of small-scale BMPs to reduce stormwater runoff from private properties.

See Parts I.B.2.c and I.D.1.b. 

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Water Quality-Based Effluent Limitations Section B

California Permits

Lake Tahoe, CA

The 2011 Lake Tahoe, California, MS4 permit, covering the City of South Lake Tahoe, and 

portions of El Dorado County and Placer County in the Lake Tahoe Hydrologic Unit, requires 

each permittee to reduce fine sediment particle (FSP), TP and total nitrogen (TN) loads by 10%, 

7%, and 8%, respectively, by September 30, 2016. These percentage reduction requirements 

were applied to each of the permittee’s baseline load of FSP, TP, and TN to determine the 

maximum load allowance for each permittee to meet the 5-year load reduction requirements. 

See Section IV.B and Table IV.B.1.

Los Angeles County, CA

The 2012 Los Angeles County, California, systemwide permit requires permittees to comply 

with numeric WQBELs based on WLAs in approved TMDLs. The permit includes comprehensive 

provisions to achieve WLAs from applicable TMDLs, including interim and final WQBELs and 

corresponding compliance schedules consistent with the state-adopted TMDL Implementation 

Plan, compliance monitoring, and reporting requirements, and for each pollutant of concern. 

For example, Attachment L of the permit prescribes final and interim WQBELs that apply to 

MS4s discharging to the Santa Clara River. The attachment includes WQBELs for nitrogen, 

chloride, trash, and E. coli that are consistent with the WLAs from approved TMDLs for the 

Santa Clara River watershed. 

For the interim WQBELs, the permit includes several alternatives from which the permittees 

can choose to demonstrate compliance. A permit can demonstrate compliance with the 

applicable interim WQBEL in any of the following ways:

• There are no violations of the interim WQBEL for the pollutant of concern at the 

permittee’s applicable MS4 outfalls;

• There are no exceedances of the applicable receiving water limitation for the pollutant 

of concern in the receiving water at or downstream of the permittee’s outfalls;

• There is no direct or indirect discharge from the permittee’s MS4 to the receiving water 

subject to the interim WQBEL and/or the receiving water limitation for the pollutant of 

concern;

• The permittee has submitted and is fully implementing an approved Watershed 

Management Program (WMP) or an Enhanced Watershed Management Program

(EWMP), which requires among other things that the permittee include multi-benefit 

regional projects that retain through infiltration or capture and reuse the stormwater 

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Water Quality-Based Effluent Limitations Section B

volume from the 85th percentile, 24-hour storm for the drainage areas tributary to 

these projects.

See Parts VI.C and E, and Attachments L – R.

Orange County, CA

The 2009 Orange County, California, MS4 permit establishes a number of different numeric 

WQBELs that affect MS4s discharging to certain watersheds. For instance, for MS4s discharging 

to the Newport Watershed, the permit requires compliance with WLAs for metals (cadmium, 

copper, lead, zinc, mercury, and chromium), organochlorine compounds, and selenium. See 

Section XVIII.B.4. Note that the original TMDLs for these constituents included no 

implementation plans or compliance schedules for attainment. During development of the 

modified TMDL, which will include an implementation plan, the permittees are required to 

continue working towards meeting the WLAs. In addition, for TMDLs with implementation 

plans, the permit includes WLAs that are required to be met as soon as 2013 (e.g., recreational 

standards for fecal coliform), but by no later than 2019 (e.g., shellfish standards for fecal

coliform). See Section XVIII.C. Other numeric WLAs are required in Section XVIII.D for diazinon, 

chloropyrifos, TN, TP, and sediment. Note that, according to the permitting authority, the WLAs 

for these constituents have already been achieved. Compliance with the WLAs is to be 

determined by receiving water monitoring. Where monitoring reveals that the WLAs are 

exceeded, the permittees are required to evaluate and submit to the permitting authority 

within 12 months of the exceedances a proposal for implementing additional BMPs. See Section 

XVIII.E.

San Diego, CA

The 2013 San Diego Regional MS4 permit contains numeric effluent limitations for diazinon, 

dissolved copper, TN, TP, lead, zinc, and indicator bacteria, which are consistent with applicable 

TMDL WLAs. The permit identifies for each applicable TMDL information about the TMDL 

(waterbodies, adoption dates); which MS4 co-permittees are affected; final compliance 

requirements (final compliance dates, receiving water and/or effluent limitations, BMP 

requirements, and final TMDL compliance determination); interim compliance requirements; 

and specific monitoring and assessment requirements. See Attachment E.

San Francisco, CA

The 2009 San Francisco Bay Regional MS4 permit requires the permittee to implement trash 

load reduction plans and actions to reduce trash loads from their MS4 by 40% by 2014, 70% by 

2017, and 100% by 2022.

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Water Quality-Based Effluent Limitations Section B

Prince George’s County, MD

The 2014 Prince George’s County, Maryland, MS4 permit requires the County to develop a work 

plan within one year to address the Anacostia Trash TMDL, which estimates that 170,628 

pounds of trash will need to be removed annually. The work plan must include a detailed 

schedule, trash reduction benchmarks in years two and four, and methods of implementation. 

The County must also develop accounting methods to quantify annual trash reductions. 

The permit also requires restoration plans for waters with approved TMDLs. The restoration 

plans must address the stormwater WLA for all EPA-approved TMDLs in the County. An annual 

TMDL assessment report is required to be submitted to the permitting authority. In addition, 

the permit requires the County, within the 5-year permit term, to achieve reductions in 

discharges consistent with the Chesapeake Bay TMDL by restoring 20% of the previously 

developed impervious land with little or no controls. See similar requirements in the 2014 Anne 

Arundel County, Maryland, MS4 permit (Parts IV.E.2.a and VI.A).

Note that Maryland has five other Phase I MS4 permits [Charles County (2002), Carroll County 

(2005), Frederick County (2002), Harford County (2004), and Howard County (2005)] that are 

required during their current administratively extended permit term to restore 10% of the 

County’s impervious surface area that was identified during the previous permit term. These 

permits also require permittees to begin to implement an additional 10% restoration during the 

permit term for a total goal of 20% restoration. The permit further requires monitoring to 

determine the effectiveness of the restoration efforts toward achieving water quality.

See Parts IV.D.4, IV.E, and VI.A. See similar requirements in Parts IV.E and VI of both the 2013 

Baltimore County, Maryland, MS4 permit and the 2013 Baltimore City, Maryland, MS4 permit. 

Honolulu, HI

The 2011 Honolulu City/County MS4 permit requires compliance with the “urban source 

wasteload allocation” based on different TMDLs in table format including applicable allocations; 

existing loads; and reductions needed for TN, TP, and TSS. See Sections F.3.b and F.3.b.1 

through F.3.b.6.

Washington, DC

The 2011 DC MS4 permit requires the permittee to remove 103,188 pounds of trash annually. 

Reductions must be made through a combination of the following approaches:

• Direct removal from waterbodies (e.g., stream cleanups, skimmers) 

• Direct removal from the MS4 (e.g., catch basin cleanout, trash racks) 

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Water Quality-Based Effluent Limitations Section B

• Direct removal prior to entry to the MS4 (e.g., street sweeping)

• Prevention through additional disposal alternatives (e.g., public trash/recycling collection)

• Prevention through waste reduction practices, regulations, and/or incentives (e.g., bag

fees)

The MS4 is also required to achieve the following numeric requirements:

• Implement retrofits for stormwater discharges from a minimum of 18,000,000 square

feet of impervious surfaces during the permit term. A minimum of 1,500,000 square

feet of this objective must be in transportation rights-of-way;

• Achieve a minimum net annual tree planting rate of 4,150 plantings annually within the

DC MS4 area, with the objective of a District-wide urban tree canopy coverage of 40%

by 2035. The annual total tree planting shall be calculated as a net increase, such that

annual mortality is also included in the estimate. Trees must be planted in accordance

with the Planting Specifications issued by the International Society of Arboriculture as

appropriate to the site conditions; and

• Install at a minimum 350,000 square feet of green roofs on District properties during the

term of the permit (including schools and school administration buildings).

See Sections 4.1.5.4, 4.1.6.2, 4.1.7.2, and 4.10.1. 

3. Required implementation of specific stormwater controls or

management measures

EPA found several examples of permits that require their MS4 permittees to implement specific 

BMPs or other management measures to ensure consistency with the applicable TMDLs. This 

approach provides both the permitting authority and the permittee with measurable 

performance measures that can be readily tracked, and it provides both parties with the ability 

to understand what actions constitute reasonable further progress towards achieving the TMDL 

and protecting water quality.

General Permits 

California

The 2013 California general permit for discharges from small MS4s includes additional 

(narrative) stormwater control requirements that are deemed by the permitting authority to be

consistent with applicable TMDLs. These requirements are individualized for each pollutant of

concern, and different requirements apply to each impaired watershed and contributing MS4

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Water Quality-Based Effluent Limitations Section B

dischargers. For instance, to be consistent with the Napa River pathogens WLA for municipal 

stormwater, the permit requires the six affected MS4s to educate the public about pathogen 

impacts and ways to reduce pathogen discharges, and to develop and implement programs to 

reduce/eliminate fecal coliform loading from pet wastes, among other requirements. See 

Attachment G.

Minnesota 

The 2013 Minnesota general permit for discharges from small MS4s requires each regulated 

small MS4 to submit a compliance schedule with their permit application showing what BMPs

will be implemented and when during the permit term to address applicable WLAs, and target 

dates for when the WLAs will be achieved. Note that the state provides public notice and an 

opportunity to comment on each permit application. See Section II.D.6.f.

Pennsylvania

The 2013 Pennsylvania general permit for discharges from small MS4s requires that permittees 

develop, submit for approval, and ensure implementation of an MS4 TMDL Plan that is 

designed to achieve pollutant reductions requirements of the applicable WLAs. The permit 

provides permittees with a list of nine alternative TMDL Control Measures for permittees to 

consider for reducing pollutants consistent with applicable WLAs. See Section II.F.1 (NOI 

Instructions).

Washington

The 2013 Western Washington Phase II 

Municipal Stormwater Permit includes 

tables that establish additional 

watershed-specific actions that are 

required of each named MS4. The actions 

are differentiated based on the 

applicable TMDL and pollutant of 

concern. See Appendix 2.

Street-side swale and pervious concrete sidewalk 

in Seattle, Washington

(Credit: Abby Hall/EPA)

The 2014 Washington State Department 

of Transportation (WDOT) MS4 permit

includes specific mandated action items 

for WDOT that are associated with 

individual TMDLs. For example, to 

implement the Hangman Creek Fecal Coliform, Temperature, TSS/Turbidity TMDL, WDOT is 

required to take the following actions by deadlines specified in the permit:

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Water Quality-Based Effluent Limitations Section B

• Within WDOT’s right-of-way inside the TMDL boundary, identify illicit sources of 

bacteria and sediment discharges to the stormwater conveyance system. A priority list 

of stream crossings and stormwater discharge locations to Hangman Creek are 

identified;

• If stormwater discharges that transport bacteria over natural background levels to listed 

receiving waters are found from sources within WSDOT’s right-of-way and control, 

WSDOT will apply BMPs from their Stormwater Management Program Plan (SWMPP) or 

perform remediation to correct bacteria discharges;

• To address TSS and turbidity, WSDOT will work to prevent sediment from entering area 

waterways along SR 27 (in upper watershed) and SR 195 rights-of-way. WSDOT will 

prioritize problem areas and work with individual property owners to prevent sediment 

from entering area waterways via WSDOT’s MS4; and

• Evaluate whether stormwater discharges contribute to elevated temperature issued, 

and, if so, take steps to reduce the adverse thermal stormwater discharge impacts to 

Hangman Creek or its tributaries.

See Appendix 3 (Applicable TMDL Requirements).

Individual Permits

Denver, CO

The 2009 Denver, Colorado, MS4 permit identifies specific requirements that apply to 

discharges to Segment 14 of the Upper South Platte River Basin associated with WLAs from the 

approved E. coli TMDL. The permit requires the permittee to identify outfalls with dry weather 

flows and to identify outfalls of concern; to monitor priority outfalls of concern for flow rates 

and E. coli densities; to implement a system maintenance program for listed priority basins 

(which includes storm sewer cleaning and sanitary sewer investigations); to install markers at 

least 90% of storm drain inlets in areas with public access; and to conduct a public outreach 

program focused on sources that contribute E. coli loads to the MS4. See Part I.B.1.f.

The permit also requires the permittee to develop and implement new programs and BMPs, in 

addition to the activities described above, to reduce dry weather discharges of E. coli to the 

extent necessary so that by the end of the compliance period, dry weather discharges from 

MS4 outfalls of concern do not contribute to an exceedance of the E. coli standard (do not 

exceed an E. coli density of 126 cfu per 100 ml for a geometric mean of all samples collected at 

a specific outfall in a 30-day period). The permit includes a compliance schedule for meeting 

this requirement by November 30, 2018. See Part I.B.1.f.

Contact state for permit.

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Water Quality-Based Effluent Limitations Section B

Florida Phase I MS4 Permits

Florida’s Phase I MS4 permits require permittees that discharge to waterbodies with an 

approved TMDL and a Basin Management Action Plan (BMAP) to comply with the provisions of 

the BMAP and report on the status of BMAP implementation with each annual report. For 

waterbodies with an approved TMDL, but no BMAP, the MS4 permittee is required to submit 

for review and approval a TMDL prioritization schedule within 6 months of the permit effective 

date. At a minimum, the highest priority TMDL is to have a plan to address the pollutant of 

concern by the end of the permit cycle. See, for example, Parts VIII. B.2 and B.3.a of the Pinellas 

and Miami-Dade permits.

Florida’s permits also include specific requirements for fecal coliform TMDL waters that do not 

have a BMAP. In these cases, the MS4 permittee is required to develop and submit a bacterial 

pollution control plan with specific elements such as bacteria source tracking and a pet waste 

management program. The bacteria pollution control plan is to be implemented in accordance 

to the schedule within the approved plan. The permittees are required to submit a status 

report with each annual report. See, for example, Part VIII.B.4 of the Pinellas and Miami-Dad 

permits.

Contact state for permits.

San Francisco, CA

The 2009 San Francisco Bay Regional Stormwater MS4 Permit includes narrative and numeric

WQBELs for trash, mercury, polychlorinated biphenyls, pesticides, copper, polybrominated 

diphenyl ether, and selenium. The permit requires interim milestones and pollutant-specific 

control measures that are consistent with the implementation actions identified in the 

applicable WLA. (For “urban stormwater,” see pages 15–16 of the Basin Plan Amendments to 

the San Francisco Basin Water Quality Control Plan, 

www.swrcb.ca.gov/sanfranciscobay/water_issues/programs/TMDLs/sfbaymercury/Adopted_B

PA_080906.pdf.) For example, the San Francisco Basin Water Quality Control Plan for mercury 

includes interim and final milestones of 120 kilograms per year (kg/yr) loading by February 2018 

and 82 kg/yr by February 2028. The permit incorporates both the aggregate WLA and the 

interim loading milestone, as well as implementation requirements that are identified in the 

TMDL Implementation Plan, including requirements to:

(1) Implement a mercury source control program; 

(2) Implement a monitoring system to quantify mercury loads and loads reduced; 

(3) Monitor methylmercury in discharges; 

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Water Quality-Based Effluent Limitations Section B

(4) Conduct a fate and transport study; and

(5) Develop an allocation sharing mechanism.

See Sections C-9 through C-14.

4. Other types of water quality-based requirements

A number of permits exhibit alternative means of ensuring consistency with applicable TMDLs, 

other than by adopting numeric requirements or implementing specific stormwater controls. 

The following permitting approaches are illustrative of these types of requirements. 

4.1 Permitting Authority Review and Approval of TMDL Plans

Several permitting authorities require that their permittees develop a TMDL Plan (or the TMDL 

component of the overall stormwater management program [SWMP] document) and submit it 

for review and/or approval. The benefit of this type of approach is that through the permitting 

authority review there is an additional level of assurance that the proposed plan will be

consistent with the assumptions and requirements of any available WLA in an approved TMDL.

General Permits 

Vermont

The 2012 Vermont general permit for discharges from small MS4s requires permittees that 

discharge to a stormwater-impaired water with an approved TMDL to submit, within 3 years of 

the permit issuance date, a Flow Restoration Plan for state review and approval.

Pennsylvania

The 2013 Pennsylvania general permit for discharges from small MS4s requires permittees 

discharging to impaired waters for which a TMDL has been approved to submit with their notice 

of intent (NOI) for review and approval by the permitting authority an MS4 TMDL Plan designed 

to achieve pollutant reductions consistent with the applicable WLA. The permit requires that

[P]ermittees must include the reductions in pollutant loads attained by implementation of 

control measures or BMPs, broken down measure by measure or BMP by BMP. Permittees must 

have physical pollutant removal measures installed on-the-ground in time for their successful 

operation to be documented in the periodic report or the progress report submitted at the end 

of the third year of coverage under this permit. Additional measurable substantial progress with 

installation of physical pollutant removal measures must be documented in the reports 

submitted with the next successive renewal NOI or application for a renewal permit. 

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Water Quality-Based Effluent Limitations Section B

A further description of these reports is found in the NOI Instructions. The permit also requires 

that MS4 TMDL Plans and Designs be signed and sealed by a professional engineer holding a 

valid license in good standing from the state. See Section II.F (NOI Instructions) and Part C.1 

(Authorization to Discharge).

Virginia

The 2013 Virginia general permit for discharges from small MS4s requires that permittees 

discharging to the Chesapeake Bay watershed submit a Chesapeake Bay TMDL Action Plan 

within 24 months of the permit effective date for review and approval by the permitting 

authority. Unless specifically denied in writing by the department, TMDL Action Plans and 

updates developed in accordance with this section of the permit become effective and

enforceable 90 days after the date received by the department. The Chesapeake Bay TMDL 

Action Plans must include the following: 

• A review of the current MS4 program to identify new or modified legal authorities to 

meet these requirements;

• An estimate of the annual pollutant of concern loads discharged from the existing 

sources based loading rates specified in the permit;

• A determination of the total pollutant load reductions necessary to reduce the annual 

pollutant of concern loads from existing sources;

• The management practices and retrofit programs that will be utilized to meet the 

required load reductions and a schedule to achieve those reductions. The schedule 

should include annual benchmarks to demonstrate the ongoing progress in meeting the 

reductions; and

• The means and methods to offset the increased loads from new sources that disturb 

one or more acres as a result of the utilization of an average land cover condition 

greater than 16% impervious cover for the design of post-development stormwater 

management facilities. The permittee must use tables in the permit to develop the 

equivalent pollutant load for nitrogen and TSS. The permittee must offset 5% of the 

calculated increased load from these new sources during the permit cycle.

See Table 1 and Section I.C.2. 

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Water Quality-Based Effluent Limitations Section B

Georgia 

The 2012 Georgia general permit for discharges from small MS4s requires existing permittees 

discharging to impaired waters with an approved TMDL to develop and submit for review and 

approval to the permitting authority an Impaired Waters Plan (for MS4s with a population of <

10,000) or a Monitoring and Implementation Plan (for MS4s with a population of > 10,000). 

• The Impaired Waters Plan, which must be submitted by a specific date, must include a 

list of the impaired waters and the pollutant(s) of concern, a map showing the locations 

of the impaired waters and all MS4 outfalls discharging to those waters, BMPs that will 

be implemented to address each pollutant of concern, and a schedule for implementing 

the BMPs. 

• The Monitoring and Implementation Plan, which also must be submitted by a specified 

date, must identify where wet weather monitoring will occur, sample type, frequency, 

schedule to begin monitoring, and a description of the BMPs that will be implemented 

to address each pollutant of concern.

See Sections 4.4.1 and 4.4.2. 

Minnesota 

The 2013 Minnesota general permit for discharges from small MS4s requires each applicant to 

submit its Stormwater Pollution Prevention Program (SWPPP) document to the permitting 

authority, including a compliance schedule for addressing applicable WLAs with the following 

required elements:

• Interim milestones, expressed as BMPs or progress toward implementation of BMPs to 

be achieved during the term of this permit

• Dates for implementation of interim milestones

• Strategies for continued BMP implementation beyond the term of this permit

• Target dates the applicable WLA(s) will be achieved

See Sections II.D.6 and III.E.

California

The 2013 California general permit for discharges from small MS4s requires some of its 

permittees, for specific TMDLs, to submit for review and approval a plan to minimize, control, 

and preferably prevent the discharge of the pollutant of concern.

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Water Quality-Based Effluent Limitations Section B

Individual Permits

Arlington Country, VA

The 2013 Arlington County, Virginia, MS4 permit has the same requirement as the 2013 Virginia 

small MS4 general permit to submit a Chesapeake Bay TMDL Action Plan within 24 months of 

the permit effective date for review and approval by the permitting authority (described 

above). See Part I.D.1.b.

Denver, CO 

The 2009 Denver, Colorado, MS4 permit identifies specific requirements that apply to 

discharges to Segment 14 of the Upper South Platte River basin associated with WLAs from the 

approved E. coli TMDL. The permit requires the permittee to submit to the state an E. coli

control plan, which, among other things, must include requirements for the permittee to 

identify outfalls with dry weather flows and to identify outfalls of concern; to monitor priority 

outfalls of concern for flow rates and E. coli densities; to implement a system maintenance 

program for listed “priority basins” (which includes storm sewer cleaning and sanitary sewer 

investigations); to install markers for at least 90% of storm drain inlets in areas with public 

access; to conduct a public outreach program focused on sources that contribute E. coli loads to 

the MS4; and to develop and implement additional programs and BMPs as necessary to ensure 

that dry weather discharges from MS4 outfalls of concern by November 30, 2018, do not 

contribute to an exceedance of the E. coli standard (do not exceed an E. coli density of 126 cfu 

per 100 ml for a geometric mean of all samples collected at a specific outfall in a 30-day 

period). See Part I.B.1.f.

Contact state for permit.

Los Angeles Country, CA

The 2012 Los Angeles County, California, systemwide permit provides permittees with the 

option of demonstrating compliance with interim WQBELs by implementing a state-approved 

WMP or EWMP. The permit specifies what each WMP or EWMP must include to be approvable. 

For example, each EWMP must, among other things:

• Prioritize water quality issues resulting from stormwater/non-stormwater discharges to 

the receiving water within each Watershed Management Area; 

• Identify and implement strategies, control measures, and BMPs to ensure that 

discharges (1) achieve applicable WQBELs; (2) do not cause or contribute to 

exceedances of receiving water limitations; and (3) do not include non-stormwater 

discharges that are prohibited;

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Water Quality-Based Effluent Limitations Section B

• Execute an integrated monitoring program to determine progress towards achieving

applicable limitations and/or action levels;

• Modify strategies, control measures, and BMPs as necessary based on analysis of

monitoring data to ensure applicable WQBELs and receiving water limitations and other

milestones are achieved in the required timeframes;

• Include multi-benefit regional projects to ensure that MS4 discharges achieve

compliance with all final WQBELs and do not cause or contribute to exceedances of

receiving water limitations by retaining through infiltration or capture and reuse the

stormwater volume of the 85th percentile, 24-hour storm for the drainage areas

tributary to the multi-benefit regional projects; and

• Maximize the effectiveness of funds through analysis of alternatives and section and

sequencing of actions needed to address human health and water quality-related

challenges and noncompliance.

The permittee is considered in compliance with the interim WQBELs if it:

• Provides timely notice of its intent to develop a WMP or EWMP;

• Meets all deadlines for development of the WMP or EWMP;

• For the area covered by the program, targets implementation of watershed control

measures in its existing SWMP to address known contributions of pollutants from MS4

discharges that cause or contribute to exceedances of receiving water limitations;

• Demonstrates reasonable assurance (through a peer-reviewed quantitative modeling

approach) that implementation of the actions/projects proposed in the WMP or EWMP

will achieve WQBELs and receiving water limitations by required deadlines;

• Receives final approval of the WMP or EWMP;

• Fully implements its approved WMP or EWMP, including all proposed actions/projects,

per the approved time schedules; and

• Periodically adapts its WMP or EWMP, when necessary, if monitoring data indicate that

expected water quality outcomes are not being achieved.

See Parts VI.C and E, and Attachments L – R. 

Montgomery County, MD 

The 2010 Montgomery County, Maryland, MS4 permit requires the permittee to submit to 

the state for review and approval a plan for each EPA-approved TMDL for the portion of a 

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Water Quality-Based Effluent Limitations Section B

watershed covered by the permit. The plans must include the actions and deadlines to meet 

the required pollutant load reduction benchmarks and WLAs within the specified timeframe. 

See Part III.J.2. 

Prince George’s Country, MD

The 2014 Prince George’s County, Maryland, MS4 permit requires the permittee to submit for 

review and approval by the state a restoration plan for each WLA approved by EPA prior to the 

permit’s effective date. The permit requires that each restoration plan: (1) include the final date 

for meeting applicable WLAs and a detailed schedule for implementing all structural and 

nonstructural measures necessary for meeting applicable WLAs; (2) provide detailed cost 

estimates for individual projects, programs, controls, and plan implementation; (3) evaluate 

and track implementation of restoration plans toward meeting established benchmarks, 

deadlines, and stormwater WLAs; and (4) develop an ongoing iterative process for focusing in 

on areas where the WLAs are not being met according to benchmarks and deadlines 

established as part of the County’s watershed assessments. Note that in another section of the 

permit, the County is required to specify pollutant load reduction benchmarks for each 

watershed that demonstrate progress toward meeting all applicable stormwater WLAs. See 

Sections III.E.1.b.v and E.2. 

Washington, DC

The 2011 DC MS4 permit requires the permittee to submit for review and approval no later 

than 30 months after the effective date of the permit modification a consolidated TMDL 

Implementation Plan to address all TMDL WLAs applicable to District waters, with a focus on 

15 specific TMDLs affecting the MS4’s discharge, but also to evaluate other pollutants of 

concern for which relevant WLAs exist. Further, the permittee is required to submit an annual 

updated Consolidated TMDL Implementation Plan to account for any new or revised TMDL 

WLAs. See Section 4.10. 

4.2 Monitoring/Modeling Requirements

A number of permits are starting to require their MS4s, which are identified and assigned 

allocations in TMDLs, to monitor2 for the associated pollutant(s) of concern or, in others, to 

model the effects of stormwater controls on the discharge of pollutant(s) of concern. Some of 

these requirements are specific to the pollutant parameter, while others dictate that the 

2 Note that while many Phase I MS4 permits include monitoring requirements, these have generally not been, until 

relatively recently, included for the purposes of implementing TMDLs.

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Water Quality-Based Effluent Limitations Section B

permittee establish a monitoring program of its own to determine progress towards meeting 

applicable WLAs. 

General Permits 

California

The 2013 California general permit for discharges from small MS4s includes tailored 

requirements for monitoring in certain watersheds. The permit specifies which permittees are 

affected by the tailored requirements, and the receiving streams where the monitoring must be 

performed. In some watersheds, the monitoring is intended to establish baseline pollutant 

loading information, while in a number of others, the monitoring program (which is submitted 

to the state as part of a Wasteload Allocation Attainment Program) is intended show whether 

the MS4’s program is meeting interim targets or WLA-based limits. In a number of watersheds, 

in addition to the effluent monitoring requirements, permittees are required to submit a 

quantifiable numeric analysis demonstrating that the BMPs selected for implementation will 

likely achieve the applicable WLA according to the schedule for implementing the TMDL, based 

on modeling, published BMP pollutant removal performance estimates, best professional 

judgment, and/or other available tools. See, for example, the permit requirements for the San 

Lorenzo River TMDL for sediment in Appendix G. See Attachment G– Region Specific 

Requirements, Regional Water Board Approved TMDLs—where urban runoff is listed as a 

source. 

Georgia 

The 2012 Georgia general permit for discharges from small MS4s requires permittees with a 

population of > 10,000 that discharge to an impaired water either with or without an approved 

TMDL to implement a monitoring plan for all pollutants of concern. The monitoring plan, which 

must be submitted to the permitting authority for review and approval, is required to specify 

the sampling locations, sample type and frequency, implementation schedule, and the BMPs 

that will be implemented to control and reduce the pollutants of concern. Annual reports are 

required to include an assessment of the data trends for each pollutant of concern. The 

assessment must initially include a characterization of baseline conditions to determine the 

effectiveness of the BMPs employed and what, if any, additional adaptive BMP measures may 

be necessary to return the waters to comply with state water quality standards. See Section 

4.4.2. 

Pennsylvania

The 2013 Pennsylvania general permit for discharges from small MS4s requires permittees to 

report on the progress of implementation of applicable MS4 TMDL Plans by submitting to the 

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permitting authority either annual or progress reports. (Further description of reports found in 

NOI Instructions.) The permit requires the reports to include the reductions in pollutant load 

attained by implementation of the TMDL control measures and BMPs, broken down measure 

by measure and BMP by BMP. The report must demonstrate that measurable progress toward 

meeting the required pollutant load reductions are being achieved and are consistent with the 

conditions and assumptions of the applicable TMDL. See Section II.F.2 (NOI Instructions).

Washington

The 2013 Western Washington small MS4 general permit requires a number of its permittees to 

conduct discharge or surface water monitoring for fecal coliform and to electronically submit 

the results to the state. See Appendix 2. 

Individual Permits

Atlanta, GA

Georgia’s Phase I MS4 permits require MS4s to propose a monitoring and implementation plan 

for each pollutant of concern. The plan must include a map showing the monitoring locations 

and must specify the sample type and frequency. Each annual report shall include an 

assessment of the data trends for each pollutant of concern. The assessment shall initially 

include a characterization of baseline conditions to determine the effectiveness of the BMPs 

employed and what, if any, additional adaptive BMP measures may be necessary to return the 

waterbody to compliance with state water quality standards. See, for example, Part 3.3.7 of the 

Bibb County, GA MS4 permit and Part III.E. of the Atlanta, Georgia, permit.

Permits available upon request: Frances.Carpenter@dnr.state.ga.us

Nashville, TN

The 2012 Nashville, Tennessee, MS4 permit includes specific monitoring instructions for waters 

impaired for siltation and/or habitat alteration, and pathogens. For example, for siltation and 

habitat alteration impairments, biological stream sampling must be performed utilizing the 

Semi-Quantitative Single Habitat Method (October 2006). For pathogen impairments, samples 

must be performed using methods identified in the permitting authority’s Quality System 

Standard Operating Procedure for Chemical and Bacteriological Sampling of Surface Waters 

(December 2009), and they must include the collection of 5 samples and corresponding flow 

measurements, within a 30-day period and must be performed between June through 

September (Summer). The permit also requires Visual Stream Surveys and Impairment 

Inventories on streams impaired for siltation, habitat alteration, and pathogens immediately 

upstream and downstream of each MS4 outfall to identify and prioritize MS4 stream 

impairment sources. See 4.1 and 4.2. 

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Water Quality-Based Effluent Limitations Section B

Florida Phase I Permits

Florida’s Phase I MS4 permits require the MS4 for waterbodies with an approved TMDL, but 

without a BMAP, to submit to the state for review and approval a TMDL monitoring and 

assessment plan within one year. The permits specify the minimum elements of the plan, which 

include:

• Develop a table showing the annual loadings currently discharged from outfalls into 

waterbodies with an adopted TMDL;

• Rank the outfalls, based on total annual loading of the pollutant(s) of concern, 

discharging into each waterbody with an adopted TMDL; and

• Based on a review of sediment and biological monitoring results from the past, validate 

the results of the loading assessment that identifies the highest priority outfalls. 

Once the monitoring and assessment plan is approved, the permits require storm event 

monitoring for a minimum of seven storm events at the top-ranked outfall identified in the plan 

to validate the estimates of annual pollutant loadings. A final report summarizing the results 

must be submitted for review and approval by the state. See, for example, Parts VIII.B.3.b and c 

of the 2013 Pinellas and 2011 Miami-Dade Phase I MS4 permits. 

Contact state for permit.

Prince George’s County, MD

The 2014 Prince George’s County, Maryland, MS4 permit requires the permittee to conduct 

monitoring to track progress toward meeting TMDLs, specifically chemical, physical, and 

biological monitoring in the Bear Branch watershed and an assessment of the effectiveness of 

stormwater controls for stream channel protection in the Black Branch watershed. The permit 

includes specific protocols to be followed based on the type of monitoring. For each annual 

report, the permittee must submit information on the results of the monitoring as well as 

pollutant load reductions related to applicable WLAs. See Part IV.F and V.A. See also similar 

requirements in Part IV.F of the 2013 Baltimore County, MD MS4 permit. 

Tucson, AZ

The 2011 Tucson, Arizona, MS4 permit requires the MS4 to conduct monitoring at least two 

times during the first year of the permit to evaluate the effectiveness of control measures by 

comparing the phosphorus loads in stormwater with the applicable WLAs in the TMDL. The 

target value for ortho-phosphorus based on the WLA in the TMDL is 0.139 lbs/day minus the 

load contributed by the added ground water. See Part 6.2. 

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Contact state for permit.

4.3 TMDL-Related Annual Reporting Requirements

Several permits require MS4s that are subject to TMDLs to report on progress made towards 

implementing required management measures related to the TMDL. These approaches provide 

the permitting authority with data and other information that can be used to determine what 

kind of progress is being made towards achievement of the TMDL. The following are examples 

of this type of requirement. 

General Permits 

Arizona

The 2002 Arizona general permit for discharges from small MS4s requires as part of the annual 

report for permittees to include a description and schedule for implementation of additional 

BMPs that may be necessary, based on monitoring results, to ensure compliance with 

applicable TMDLs. See Section V.G.1.f. 

Arkansas

The 2009 Arkansas general permit for discharges from small MS4s requires permittees to report 

on progress on program implementation and reducing the pollutant of concern and updates to 

measurable goals for the pollutant of concern reduction program elements. See Section 3.4.5. 

California

The 2013 California general permit for discharges from small MS4s requires permittees to 

report annually on the status of implementation of specific TMDL components. The report must 

include: (1) A description of BMPs implemented, including types, number, and locations; (2) An 

assessment of the effectiveness of implemented BMPs in progressing towards attainment of 

WLAs within the TMDLs’ specified timeframes; (3) All monitoring data, including a statistical 

analysis of the data to assess progress towards attainment of WLAs within the TMDLs’ specified 

timeframes; and (4) Based on results of the effectiveness assessment and monitoring, a 

description of the additional BMPs that will be implemented to attain WLAs within the TMDLs 

specified timeframes. See Section E.15.d. 

Georgia 

The 2012 Georgia general permit for discharges from small MS4s requires MS4 permittees with 

populations over 10,000 that discharge to impaired waters with or without a TMDL to include 

an assessment of the data trends for each pollutant of concern in their annual reports. The 

initial annual report must also include a characterization of baseline conditions to determine 

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the effectiveness of the BMPs employed and what, if any, additional adaptive BMP measures 

may be necessary to return the waters to compliance with state water quality standards. See 

Section 4.4.2. 

Minnesota 

The 2013 Minnesota general permit for discharges from small MS4s requires the following to be 

included in the annual report: (1) a list of all BMPs being applied to achieve the applicable WLA 

(including a unique identifier and geographic coordinate); (2) stage of implementation for each 

BMP; (3) updated estimate of the cumulative reductions in loading achieved for each pollutant 

of concern; and (4) updated narrative describing any adaptive management strategies used for 

making progress to achieve applicable WLA. See Part III.E and IV.B. The state also provides 

specific TMDL reporting forms and training for using the forms. 

Nevada

The 2010 Nevada general permit for discharges from small MS4s requires permittees to include 

in their annual reports an update on all control measures being implemented to address 

applicable WLAs, and estimated reductions of pollutants of concern. See Section II.B.2.e and f. 

Individual Permits 

Prince George’s Country, MD

The Prince George’s County, Maryland, MS4 permit requires the permittee to submit an annual 

TMDL assessment report that includes complete descriptions of the analytical methodology 

used to evaluate the effectiveness of the County’s restoration plans toward achieving 

implementation of EPA-approved TMDLs. The County is also required to provide: (1) estimated 

net changes in pollutant load reductions from all completed water quality improvement 

projects, enhanced stormwater management programs, and alternative stormwater control 

initiatives; (2) a comparison of the net change in pollutant load reductions with the established 

benchmarks, deadlines, and applicable stormwater WLAs; (3) itemized costs for completed 

projects, programs, and initiatives to meet established pollutant reduction benchmarks and 

deadlines; (4) cost estimates for completing all projects, programs, and alternatives necessary 

for meeting applicable stormwater WLAs; and (5) a description of additional watershed 

restoration actions that can be enforced when benchmarks, deadlines, and applicable 

stormwater WLAs are not being met or when projected funding is inadequate. See Section 

III.E.4. 

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5. Requirements for discharges to impaired waters prior to 

TMDL approval

Several permits identified specific actions that must be taken to address impaired waters prior 

to completion of an approved TMDL. The following examples exhibited this approach. 

General Permits 

Arkansas

The 2009 Arkansas general permit for discharges from small MS4s specifies required actions 

that must be taken by permittees that discharge to impaired waters for nutrients, bacteria, or 

other pollutants of concern prior to the completion of the TMDL. For instance, for bacteria 

impairments, the permittee is required to take the following actions:

• Within 1 year, identify potential significant sources of bacteria entering the MS4;

• Within 2 years, develop and implement a public education program to reduce the 

discharge of bacteria in municipal stormwater contributed by: (1) pets, recreation and 

exhibition livestock, and zoos; and (2) on-site wastewater treatment systems;

• Within 2 years, review results from the Illicit Discharge Detection and Elimination (IDDE) 

program and modify as necessary to prioritize the detection and elimination of 

discharges contributing bacteria to the MS4; and

• Include in annual reports updates to measurable goals for bacteria reduction program 

elements. 

See Sections 3.4.5 and 3.4.5.2. 

California 

The 2013 California general permit for discharges from small MS4s requires permittees to 

implement additional procedures for discharges to impaired waters:

• For the construction site inventory, provide the location of the project with respect to 

all waterbodies listed as impaired for sediment and turbidity (Section E.10.a); and

• For the post-construction BMP condition assessment, the permittee is required to give 

higher priority for maintenance to BMPs designed to remove pollutants for which the 

receiving water is impaired (Section E.12.ii.b). 

In addition, permittees that discharge to waters listed as impaired where urban runoff is listed 

as a source must consult with the permitting authority within one year of permit coverage to 

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Water Quality-Based Effluent Limitations Section B

assess whether monitoring is necessary and, if so, the appropriate monitoring plan. Section 

E.13.c. 

Georgia 

The 2012 Georgia general permit for discharges from small MS4s requires existing permittees 

discharging to impaired waters to develop and submit for review and approval to the 

permitting authority an Impaired Waters Plan (for MS4s with a population of < 10,000) or a 

Monitoring and Implementation Plan (for MS4s with a population of > 10,000). 

• The Impaired Waters Plan, which must be submitted by a specific date, must include a 

list of the impaired waters and the pollutant(s) of concern, a map showing the locations 

of the impaired waters and all MS4 outfalls discharging to those waters, BMPs that will 

be implemented to address each pollutant of concern, and a schedule for implementing 

the BMPs. 

• The Monitoring and Implementation Plan, which also must be submitted by a specified 

date, must identify where wet weather monitoring will occur, sample type, frequency, 

schedule to begin monitoring, and a description of the BMPs that will be implemented 

to address each pollutant of concern.

The permittee is also required to annually check whether an impaired water within its 

permitted area has been added to the latest 305(b)/303(d) list. Newly listed waters must be 

addressed in the plan and the SWMP must be revised accordingly. See Section 4.4.2. 

Individual Permits

Baton Rouge, LA

The 2009 Baton Rouge, Louisiana, permit requires the MS4 to develop an Interim Pollutant 

Reduction Plan for discharges of a pollutant on a 303(d) list prior to completion of a TMDL. 

Specific activities and dates are specified when the pollutant is a nutrient constituent, for 

bacteria, or another pollutant (for example, identify potential sources of nutrient pollutant 

within 1 year, develop a public education program for residential/commercial uses of fertilizers 

within 2 years, develop a program to reduce discharge of nutrients from municipal facilities 

within 2 years, etc.). See Part II.B.1.

Contact state for permit.

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