MEMORANDUM 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

NOV 2 6 2014 

OFFICE OF WATER 

SUBJECT: Revisions to the November 22,2002 Memorandum "Establishing Total Maximum 

Daily Load (TMDL) Wasteload Allocations (WLAs) for Storm Water Sources 

FROM: 

TO: 

and NPDES Permit Requirements Based on LAs" 

Andrew D. Sawyers, Director 

Office of Wastewater Management 

Benita Best-Wong, Director 

Office of Wetlands, Oceans and Water 

Water Division Directors 

Regions 1 - 10 

This memorandum updates aspects of EPA's November 22,2002 memorandum from 

Robert H. Wayland, III, Director of the Office of Wetlands, Oceans and Watersheds, and James 

A. Hanlon, Director of the Office of Wastewater Management, on the subject of"Establishing 

Total Maximum Daily Load (TMDL) Wasteload Allocations (WLAs) for Storm Water Sources 

and NPDES Permit Requirements Based on Those WLAs" (hereafter "2002 memorandum''). 

Today's memorandum replaces the November 12, 2010, memorandum on the same subject; the 

Water Division Directors should no longer refer to that memorandum for guidance. 

This memorandum is guidance. It is not a regulation and does not impose legally binding 

requirements on EPA or States. EPA and state regulatory authorities should continue to make 

permitting and TMDL decisions on a case-by-case basis considering the particular facts and 

circumstances and consistent with applicable statutes, regulations, and case law. The 

recommendations in this guidance may not be applicable to a particular situation. EPA may 

change or revoke this guidance at any time. 

Background 

Stormwater discharges are a significant contributor to water quality impairment in this 

country, and the challenges from these discharges are growing as more land is developed and 

more impervious surface is created. Stormwater discharges cause beach closures and 

contaminate shellfish and surface drinking water supplies. The increased volume and velocity of 

stormwater discharges causes streambank erosion, flooding, sewer overflows, and basement 

backups. The decreased natural infiltration of rainwater reduces groundwater recharge, depleting 

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2 

our underground sources of drinking water. 1 There are stormwater management solutions, such 

as green infrastructure, that can protect our waterbodies from stormwater discharges and, at the 

same time, offer many other benefits to communities. 

Section III of the 2002 memorandum recommended that for NPDES-regulated municipal 

and small construction storm water discharges, effluent limits be expressed as best management 

practices (BMPs) or other similar requirements, rather than as numeric effluent limits. The 2002 

memorandum went on to provide guidance on using "an iterative, adaptive management BMP 

approach" for improving stormwater management over time as permitting agencies, the regulated 

community, and other involved stakeholders gain more experience and knowledge. EPA 

continues to support use of an iterative approach, but with greater emphasis on clear, specific, 

and measurable permit requirements and, where feasible, numeric NPDES permit provisions, as 

discussed below. 

Since 2002, States and EPA have obtained considerable experience in developing 

TMDLs and WLAs that address stormwater sources (see Box 1 in the attachment for specific 

examples). Monitoring of the impacts of storm water discharges on water quality has become 

more sophisticated and widespread.2 The experience gained during this time has provided better 

information on the effectiveness of stormwater controls to reduce pollutant loadings and address 

water quality impairments. In many parts of the country, permitting agencies have issued several 

rounds of storm water permits. Notwithstanding these developments, storm water discharges 

remain a significant cause of water quality impairment in many places, highlighting a continuing 

need for more meaningful WLAs and more clear, specific, and measurable NPDES permit 

provisions to help restore impaired waters to their beneficial uses. 

With this additional experience in mind, on November 12, 2010, EPA issued a 

memorandum updating and revising elements of the 2002 memorandum to better reflect current 

practices and trends in permits and WLAs for storm water discharges. On March 17, 2011, EPA 

sought public comment on the November 2010 memorandum and, earlier this year, completed a 

nationwide review of current practices used in MS4 permits3 and industrial and construction 

storm water discharge permits. As a result of comments received and informed by the reviews of 

EPA and state-issued storm water permits, EPA is in this memorandum replacing the 

1 See generally Urban Stormwater Management in the United States (National Research Council, 2009), particularly 

the discussion in Chapter 3, Hydrologic, Geomorphic, and Biological Effects of Urbanization on Watersheds. 2 Stormwater discharge monitoring programs have expanded the types pollutants and other indices (e.g., biologic 

integrity) being evaluated. This information is being used to help target priority areas for cleanup and to assess the 

effectiveness of storm water BMPs. There are a number of noteworthy monitoring programs that are ongoing, 

including for example those being carried out by Duluth, MN, Capitol Region Watershed District, MN, Honolulu, 

HI, Baltimore or Montgomery County, MD, Puget Sound, WA, Los Angeles County, CA, and the Alabama Dept. of 

Transportation, among many others. See also Section 4.2 (Monitoring/Modeling Requirements) of EPA's Municipal 

Separate Storm Sewer System Permits: Post-Construction Pe1jormance Standards & Water Quality-Based 

Requirements- A Compendium of Permitting Approaches (EPA, June 20 14), or "MS4 Compendium" available at 

hnp://water.epa.gov/polwaste/npdes/stormwater/upload/sw ms4 compendium.pdf, for other examples of note. 3 See EPA's MS4 Permit Compendium, referenced in the above footnote. 
3 

November 2010 memorandum, updating aspects of the 2002 memorandum and providing 

additional information in the following areas: 

• Including clear, specific, and measurable permit requirements and, where feasible, 

numeric effluent limitations in NPDES permits for stormwater discharges; 

• Disaggregating stormwater sources in a WLA; and · 

• Designating additional stormwater sources to regulate and developing permit limits for 

such sources. 

Including Clear, Specific, and Measurable Permit Requirements and, Where Feasible, 

Numeric Effluent Limitations in NPDES Permits for Stormwater Discharges 

At the outset of both the Phase I and Phase II stormwater permit programs, EPA provided 

guidance on the type of water quality-based effluent limits (WQBELs) that were considered most 

appropriate for stormwater permits. See Interim Permitting Policy for Water Quality-Based 

Limitations in Storm Water Permits [61 FR 43761 (August 26, 1996) and 61 FR 57425 

(November 6, 1996)] and the Phase II rulemaking preamble 64 FR 68753 (December 8, 1999). 

Under the &pproach discussed in these documents, EPA envisioned that in the first two to three 

rounds of permit issuance, storm water permits typically would require implementation of 

increasingly more effective best management practices (BMPs). In subsequent stormwater 

permit terms, if the BMPs used during prior years were shown to be inadequate to meet the 

requirements of the Clean Water Act (CW A), including attainment of applicable water quality 

standards, the permit would need to contain more specific conditions or limitations. 

There are many ways to include more effective WQBELs in permits. In the spring of 

2014, EPA published the results of a nationwide review of current practices used in MS4 permits 

in Municipal Separate Storm Sewer Systems Permits: Post-Construction Performance Standards 

& Water Quality-Based Requirements- A Compendium of Permitting Approaches (June 2014). 

This MS4 Compendium demonstrates how NPDES authorities have been able to effectively 

establish permit requirements that are more specifically tied to a measurable water quality target, 

and includes examples of permit requirements expressed in both numeric and non-numeric form. 

These approaches, while appropriately permit-specific, each share the attribute of being 

expressed in a clear, specific, and measurable way. For example, EPA found a number of permits 

that employ numeric, retention-based performance standards for post-construction discharges, as 

well as instances where permits have effectively incorporated numeric effl.uent limits or other 

quantifiable measures to address water quality impairment (see the attachment to this 

memorandum). 

EPA has also found examples where the applicable WLAs have been translated into 

BMPs, which are required to be implemented during the permit term to reflect reasonable further 

progress towards meeting the applicable water quality standard (WQS). Incorporating greater 

specificity and clarity echoes the approach first advanced by EPA in the 1996 Interim Permitting 

Policy, which anticipated that where necessary to address water quality concerns, permits would 

be modified in subsequent terms to include "more specific conditions or limitations (which] may 

include an integrated suite of BMPs, performance objectives, narrative standards, monitoring 

triggers, numeric WQBELs, action levels, etc." 
4 

EPA also recently completed a review of state-issued NPDES industrial and construction 

permits, which also revealed a number of examples where WQBELs are expressed using clear, 

specific, and measurable terms. Permits are exhibiting a number of different approaches, not 

unlike the types of provisions shown in the MS4 Compendium. For example, some permits are 

requiring as an effluent limitation compliance with a numeric or narrative WQS, while others 

require the implementation of specific BMPs that reduce the discharge of the pollutant of 

concern as necessary to meet applicable WQS or to implement a WLA and/or are requiring their 

permittees to conduct stormwater monitoring to ensure the effectiveness of those BMPs. EPA 

intends to publish a compendium of permitting approaches in state-issued industrial and 

construction storm water permits in early 2015. 

Permits for MS4 Discharges 

The CWA provides that stormwater permits for MS4 discharges "shall require controls to 

reduce the discharge of pollutants to the maximum extent practicable ... and such other 

provisions as the Administrator or the State determines appropriate for the control of such 

pollutants." CWA se·ction 402(p)(3)(B)(iii). Under this provision, the NPDES permitting 

authority has the discretion to include requirements for reducing pollutants in stormwater 

discharges as necessary for compliance with water quality standards. Defenders of Wildlife v. 

Browner, 191 F.3d 1159, 1166 (9th Cir. 1999). 

The 2002 memorandum stated "EPA expects that most WQBELs for NPDES-regulated 

municipal and small construction storm water discharges will be in the form of BMPs, and that 

numeric limitations will be used only in rare instances." As demonstrated in the MS4 

Compendium, NPDES permitting authorities are using various forms of clear, specific, and 

measurable requirements, and, where feasible, numeric effluent limitations in order to establish a 

more objective and accountable means for reducing pollutant discharges that contribute to water 

quality problems.4 Where the NPDES authority determines that MS4 discharges have the 

reasonable potential to cause or contribute to a water quality standard excursion, EPA 

recommends that the NPDES permitting authority exercise its discretion to include clear, 

specific, and measurable permit requirements and, where feasible, numeric effluent limitations5 

as necessary to meet water quality standards. 

NPDES authorities have significant flexibility in how they express WQBELs in MS4 

permits (see examples in Box l of the attachment). WQBELs in MS4 permits can be expressed 

as system-wide requirements rather than as individual discharge location requirements such as 

4 The MS4 Compendium presents examples of different permitting approaches that EPA has found during a 

nationwide review of state MS4 permits. Examples of different WQBEL approaches in the MS4 Compendium 

include permits that have (I) a list of applicable TMDLs, WLAs, and the affected MS4s; (2) numeric limits and 

other quantifiable approaches for specific pollutants of concern; (3) requirements to implement specific stormwater 

controls or management measures to meet the applicable WLA; (4) permitting authority review and approval of 

TMDL plans; (5) specific impaired waters monitoring and modeling requirements; and (6) requirements for 

discharges to impaired waters prior to TMDL approval. 5 For the purpose of this memorandum, and in the context ofNPDES permits for stormwater discharges, "numeric" 

effluent limitations refer to limitations with a quantifiable or measurable parameter related to a pollutant (or 

pollutants). Numeric WQBELs may include other types of numeric limits in addition to end-of-pipe limits. Numeric 

WQBELs may include, among others, limits on pollutant discharges by specifying parameters such as on-site 

storm water retention volume or percentage or amount of effective impervious cover, as well as the more traditional 

pollutant concentration limits and pollutant loads in the discharge. 
5 

effluent limitations on discharges from individual outfalls. Moreover, the inclusion of numeric 

limitations in an MS4 permit does not, by itself, mandate the type of controls that a permittee 

will use to meet the limitation. 

EPA recommends that NPDES permitting authorities establish clear, specific, and 

measurable permit requirements to implement the minimum control measures in MS4 permits. 

With respect to requirements for post-construction stormwater management, consistent with 

guidance in the 1999 Phase II Rule, EPA recommends, where feasible and appropriate, numeric 

requirements that attempt to maintain pre-development runoff conditions ( 40 CFR § 

122.34(b)(5)) be incorporated into MS4 permits. EPA's MS4 Compendium features examples 

from 17 states and the District of Columbia that have already implemented retention 

performance standards for newly developed and redeveloped sites. See Box 2 of the attachment 

for examples. 

Permits for Industrial Stormwater Discharges 

The CW A requires that permits for stormwater discharges associated with industrial 

activity comply with section 301 of the Act, including the requirement under section 

301(b)(l)(C) to contain WQBELs to achieve water quality standards for any discharge that the 

permitting authority determines has the reasonable potential to cause or contribute to a water 

quality standard excursion. CWA section 402(p)(3)(A), 40 CFR § 122.44(d)(l)(iii). When the 

permitting authority determines, using the procedures specified at 40 CFR § 122.44(d)(l)(ii), that 

the discharge causes or has the reasonable potential to cause or contribute to an in-stream 

excursion of the water quality standards, the permit must contain WQBELs as stringent as 

necessary to meet any applicable water quality standard for that pollutant. EPA recommends that 

NPDES permitting authorities use the experience gained in developing WQBELs to design 

effective permit conditions to create objective and accountable means for controlling stormwater 

discharges. See box 3 in the attachment for examples. 

Permits should contain clear, specific, and measurable elements associated with BMP 

implementation (e.g., schedule for BMP installation, frequency of a practice, or level of BMP 

performance), as appropriate, and should be supported by documentation that implementation of 

selected BMPs will result in achievement of water quality standards. Permitting authorities 

should also consider including numeric benchmarks for BMPs and associated monitoring 

protocols for estimating BMP effectiveness in stormwater permits. Benchmarks can support an 

adaptive approach to meeting applicable water quality standards. While exceeding the 

benchmark is not generally a permit violation, exceeding the benchmark would typically require 

the permittee to take additional action, such as evaluating the effectiveness of the BMPs, 

implementing and/or modifying BMPs, or providing additional measures to protect water 

quality. 6 Permitting authorities should consider structuring the permit to clarify that failure to 

implement required corrective action, including a corrective action for exceeding a benchmark, is 

a permit violation. EPA notes that, as many storm water discharges are authorized under a general 

permit, NPDES authorities may find it more appropriate where resources allow to issue 

6 For example, Part 6.2.1 of EPA's 2008 MSGP provides: "This permit stipulates pollutant benchmark 

concentrations that may be applicable to your discharge. The benchmark concentrations are not effluent limitations; 

a benchmark exceedance, therefore, is not a permit violation. Benchmark monitoring data are primarily for your use 

to determine the overall effectiveness of your control measures and to assist you in knowing when additional 

corrective action(s) may be necessary to comply with the effluent limitations .. . " 
6 

individual permits that are better tailored to meeting water quality standards for large industrial 

stormwater discharges with more complex stormwater management features, such as multiple 

outfalls and multiple entities responsible for permit compliance. 

All Permitted Stormwater Discharges 

As stated in the 2002 memorandum, where a State or EPA has established a TMDL, 

NPDES permits must contain effluent limits and conditions consistent with the assumptions and 

requirements ofthe WLAs in the TMDL. See 40 CFR § 122.44(d)(l)(vii)(B). Where the TMDL 

includes WLAs for stormwater sources that provide numeric pollutant loads, the WLA should, 

where feasible, be translated into effective, measurable WQBELs that will achieve this objective. 

This could take the form of a numeric limit, or of a measurable, objective BMP-based limit that 

is projected to achieve the WLA. For MS4 discharges, CWA section 402(p)(3)(B)(iii) provides 

flexibility for NPDES authorities to set appropriate deadlines for meeting WQBELs consistent 

with the requirements for compliance schedules in NPDES permits set forth in 40 CFR § 122.47. 

The permitting authority's decision as to how to express the WQBEL(s), either as 

numeric effluent limitations or as BMPs, with clear, specific, and measurable elements, should 

be based on an analysis of the specific facts and circumstances surrounding the permit, and/or the 

underlying WLA, including the nature of the stormwater discharge, available data, modeling 

results, and other relevant information. As discussed in the 2002 memorandum, the permit's 

administrative record needs to provide an adequate demonstration that, where a BMP-based 

approach to permit limitations is selected, the BMPs required by the permit will be sufficient to 

implement applicable WLAs. Permits should also include milestones or other mechanisms where 

needed to ensure that the progress of implementing BMPs can be tracked. Improved knowledge 

of BMP effectiveness gained since 2002 7 should be reflected in the demonstration and 

supporting rationale that implementation of the BMPs will attain water quality standards and be 

consistent with WLAs. 

EPA's regulations at40 CFR § 122.47 govern the use of compliance schedules in 

NPDES permits. Central among the requirements is that the effluent limitation(s) must be met 

"as soon as possible." 40 CFR § 122.47(a)(l). As previously discussed, by providing discretion 

to include "such other provisions" as deemed appropriate, CWA section 402(p)(3)(B)(iii) 

provides flexibility for NPDES authorities to set appropriate deadlines towards meeting 

WQBELs in MS4 permits consistent with the requirements for compliance schedules in NPDES 

permits set forth in 40 CFR § 122.47. See Defenders of Wildlife v Browner, 191 F.3d at 1166. 

EPA expects the permitting authority to document in the permit record the basis for determining 

that the compliance schedule is "appropriate" and consistent with the CW A and 40 CFR § 

122.47. Where a TMDL has been established and there is an accompanying implementation plan 

that provides a schedule for an MS4 to implement the TMDL, or where a comprehensive, 

integrated plan addressing a municipal government's wastewater and stormwater obligations 

under the NPDES program has been developed, the permitting authority should consider such 

schedules as it decides whether and how to establish enforceable interim requirements and 

interim dates in the permit. 

7 See compilation of current BMP databases and summary reports available at 

http://water.epa.gov/infrastructure/greeninfrastructure/gi performance.cfrn, which has compiled current BMP 

databases and summary reports. 
7 

EPA notes that many permitted storm water discharges are covered by general 

permits. Permitting authorities should consider and build into general permits requirements to 

ensure that permittees take actions necessary to meet the WLAs in approved TMDLs and address 

impaired waters. A general permit can, for example, identify permittees subject to applicable 

TMDLs in an appendix, and prescribe the activities that are required to meet an applicable 

WLA. 

Lastly, NPDES permits must specify monitoring requirements necessary to determine 

compliance with effluent limitations. See CWA section 402(a)(2); 40 CFR 122.44(i). The permit 

could specify actions that the permittee must take if the BMPs are not performing properly or 

meeting expected load reductions. When developing monitoring requirements, the NPDES 

authority should consider the variable nature of storm water as well as the availability of reliable 

and applicable field data describing the treatment efficiencies of the BMPs required and 

supporting modeling analysis. 

Disaggregating Stormwater Sources in a WLA 

In the 2002 memorandum, EPA said it "may be reasonable to express allocations for 

NPDES-regulated stormwater discharges from multiple point sources as a single categorical 

wasteload allocation when data and information are insufficient to assign each source or outfall 

individual WLAs." EPA also said that, "[i]n cases where waste load allocations are developed for 

categories of discharges, these categories should be defined as narrowly as available information 

allows." Furthermore, EPA said it "recognizes that the available data and information usually are 

not detailed enough to determine waste load allocations for NPDES-regulated stormwater 

discharges on an outfall-specific basis." 

EPA still recognizes that"[ d]ecisions about allocations of pollutant loads within a TMDL 

are driven by the quantity and quality of existing and readily available water quality data," but 

has noted the difficulty of establishing clear, specific, and measurable NPDES permit limitations 

for sources covered by WLAs that are expressed as single categorical or aggregated wasteload 

allocations. Today, TMDL writers may have more information-such as more ambient 

monitoring data, better spatial and temporal representation of stormwater sources, and/or more 

permit-generated data-than they did in 2002 to develop more disaggregated TMDL WLAs. 

Accordingly, for all these reasons, EPA is again recommending that, "when information 

allows," WLAs for NPDES-regulated stormwater discharges be expressed "as different WLAs 

for different identifiable categories" (e.g., separate WLAs for MS4 and industrial stormwater 

discharges). In addition, as EPA said in 2002, "[t]hese categories should be defined as narrowly 

as available information allows (e.g., for municipalities, separate WLAs for each municipality 

and for industrial sources, separate WLAs for different types of industrial storm water sources or 

dischargers)." EPA does not expect states to assign WLAs to individual MS4 outfalls; however, 

some states may choose to do so to support their implementation efforts. These recommendations 

are consistent with the decision in Anacostia Riverkeeper, Inc. v. Jackson, 2011 U.S. Dist. Lexis 

80316 (July 25, 2011 ). 

In general, states are encouraged to disaggregate the WLA when circumstances allow 

to facilitate implementation. TMDL writers may want to consult with permit writers and local 

authorities to collect additional information such as sewer locations, MS4 jurisdictional 
8 

boundaries, land use and growth projections, and locations of storm water controls and 

infrastructure, to facilitate disaggregation. TMDLs have used different approaches to 

disaggregate stormwater to facilitate MS4 permit development that is consistent with the 

assumptions and requirements of the WLA. For example, some TMDLs have used a 

geographic approach and developed individual WLAs by subwatershed8 or MS4 boundary 

(i.e., the WLA is subdivided by the relative estimated load contribution to the subwatershed 

or the area served by the MS4). TMDLs have also assigned percent reductions9 of the loading 

based on the estimated wasteload contribution from each MS4 permit holder. Where 

appropriate, EPA encourages permit writers to identify specific shares of an applicable 

wasteload allocation for specific permittees during the permitting process, as permit writers 

may have more detailed information than TMDL writers to effectively identify reductions for 

specific sources. 

Designating Additional Stormwater Sources to Regulate and Developing Permit Limits for 

Such Sources 

The 2002 memorandum states that "stormwater discharges from sources that are not 

currently subject to NPDES regulation may be addressed by the load allocation component of a 

TMDL." Section 402(p)(2) ofthe Clean Water Act (CWA) requires industrial stormwater 

sources, certain municipal separate storm sewer systems, and other designated sources to be 

subject to NPDES permits. Section 402(p)(6) provides EPA with authority to identify additional 

stormwater discharges as needing a permit. 

In addition to the stormwater discharges specifically identified as needing an NPDES 

permit, the CW A and the NPDES regulations allow for EPA and NPDES authorized States to 

designate additional stormwater discharges for regulation. See: 

40 CFR §§122.26 (a)(9)(i)(C), (a)(9)(i)(D), (b)(4)(iii), (b)(7)(iii), (b)(15)(ii) and 122.32(a)(2). 

Accordingly, EPA encourages permitting authorities to consider designation of stormwater 

sources in situations where coverage under NPDES permits would, in the reasonable judgment of 

the permitting authority and, considering the facts and circumstances in the waterbody, provide 

the most appropriate mechanism for implementing the pollution controls needed within a 

watershed to attain and maintain applicable water quality standards. 

If a TMDL had previously included a newly permitted source as part of a single 

aggregated or gross load allocation for all unregulated stormwater sources, or all unregulated 

sources in a specific category, the NPDES permit authority could identify an appropriate 

allocation share and include a corresponding limitation specific to the newly permitted 

storm water source. EPA recommends that any additional analysis used to identify that share and 

develop the corresponding limit be included in the administrative record for the permit. The 

permit writer's additional analysis would not change the TMDL, including its overall loading 

cap. 

In situations where a stormwater source addressed in a TMDL's load allocation is not 

currently regulated by an NPDES permit but may be required to obtain an NPDES permit in the 

8 Wissahickon Creek Siltation TMDL (Pennsylvania) www.eoa.gov/reg3wapd/trndl/pa trndl/wissahickonlindex.htm. 9 Liberty Bay Watershed Fecal Coliform Bacteria TMDL (Washington). 

hups://fortrcss.wa.gov/ecy/publications/SummaryPages/ 131 00 14.html and Upper Minnehaha Creek Watershed Nutrients and 

Bacteria TMDL (Minnesota) http://www.pca.state.nm.us/index.php/vicw-documcnt.html?gid=20792 
9 

future, the TMDL writer should consider including language in the TMDL explaining that the 

allocation for the storrnwater source is expressed in the TMDL as a "load allocation" contingent 

on the source remaining unpermitted, but that the " load allocation" would later be deemed a 

"wasteload allocation" if the stormwater discharge from the source were required to obtain 

NPDES permit coverage. Such language would help ensure that the allocation is properly 

characterized by the permit writer should the source's regulatory status change. This will help 

the permit writer develop limitations for the NPDES permit applicable to the newly permitted 

source that are consistent with the assumptions and requirements of the TMDL's allocation to 

that source. 

If you have any questions please feel free to contact us or Deborah Nagle, Director of the 

Water Permits Division, or Tom Wall, Director of the Assessment and Watershed Protection 

Division. 

cc: Association of Clean Water Administrators 

TMDL Program Branch Chiefs, Regions 1 - 10 

NPDES Permits Branch Chiefs, Regions 1 - 10 

Attachment: MS4 and Industrial Stormwater Permit Examples 
lO 

ATTACHMENT: MS4 and Industrial Stormwater Permit Examples 

BOX 1. Examples ofWQBELs in MS4 Permits: 

I. Numeric expression of the WQBEL: The MS4 Permit includes a specific, quantifiable performance 

requirement that must be achieved within a set time frame. For example: 

Reduce fine sediment particles, total phosphorus, and total nitrogen loads by I 0 percent, 7 percent, 

and 8 percent, respectively, by September 30, 2016 (20 II Lake Tahoe, CA MS4 permit) 

Restore within the S-year permit term 20 percent of the previously developed impervious land (2014 

Prince George's County, MD MS4 permit) 

Achieve a minimum net annual planting rate of 4, ISO planting annually within the MS4 area, with 

the objective of an MS4-wide urban tree canopy of 40 percent by 203S (20 II Washington, DC MS4 

permit) 

Discharges from the MS4 must not cause or contribute to exceedances of receiving water limits for 

Diazinon of 0.08~-tg/L for acute exposure (I hr averaging period) or O.OS~-tg/L for chronic exposure 

(4-day averaging period), OR must not exceed Diazinon discharge limits of0.072 ~-tg/L for acute 

exposure or 0.04S~-tg/L for chronic exposure (20 13 San Diego, CA Regional MS4 permit) 

2. Non-numeric expressions of the WQBEL: The MS4 Permit establishes individualized, watershed-based 

requirements that require each affected MS4 to implement specific BMPs within the permit term, which 

will ensure reasonable further progress towards meeting applicable water quality standards. 

To implement the corrective action recommendations of the Issaquah Creek Basin Water Cleanup 

Plan for Fecal Coliform Bacteria (part of the approved Fecal Coliform Bacteria TMDL for the 

Issaquah Creek Basin), King County is required during the permit term to install and maintain animal 

waste education and/or collection stations at municipal parks and other pennittee owned and operated 

lands reasonably expected to have substantial domestic animal use and the potential for stormwater 

pollution. The County is also required to complete lODE screening for bacteria sources in SO percent 

of the MS4 subbasins, including rural MS4 subbasins, by February 2, 2017 and implement the 

activities identified in the Phase I permit for responding to any illicit discharges found (20 13 Western 

Washington Small MS4 General Permit) 

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

approved£. coli TMDL, the MS4 must identify outfalls with dry weather flows; monitor priority 

outfalls for flow rates and E. coli densities; implement a system maintenance program for listed 

priority basins (which includes storm sewer cleaning and sanitary sewer investigations); install 

markers on at least 90% of storm drain inlets in areas with public access; and conduct a public 

outreach program focused on sources that contribute E. coli loads to the MS4. By November 30, 

2018, dry weather discharges from MS4 outfalls of concern must not contribute to an exceedance of 

the E. coli standard ( 126 cfu per I 00 ml for a geometric mean of all samples collected at a specific 

outfall in a 30-day period) (2009 Denver, CO MS4 Permit) 

3. Hybrid approach with both numeric and non-numeric expressions of the WQBEL: 

Discharges of trash from the MS4 to the LA River must be reduced to zero by Sept. 20 16. Permittees 

also have the option of complying via the installation of defined "full capture systems" to prevent 

trash from entering the MS4 (2012 Los Angeles County, CA MS4 Permit). 

To attain the shared, load allocation of 27,000 metric tons/year of sediment in the Napa River 

sediment TMDL, municipalities shall determine opportunities to retrofit and/or reconstruction of road 

crossings to minimize road-related sediment delivery (:S SOO cubic yards/mile per 20-year period) to 

stream channels (20 13 CA Small MS4 General Permit). 
l l 

Box 2. Examples of Retention Post Construction Standards for New and Redevelopment in MS4 

Permits 

2009 WV small M$4 permit: Keep and manage on site the first one inch of rainfall from a 24-hour 

storm preceded by 48 hours of no measurable precipitation. 

20 II DC Phase I MS4 permit: Achieve on-site retention of I .2" of storm water from a 24-hour storm 

with a 72-hour antecedent dry peri.od through evapotranspiration, infiltration and/or stormwater 

harvesting. 

2012 Albuquerque, NM Phase I MS4 permit: Capture the 901

h percentile storm event runoff to mimic 

the predevelopment hydrology of the previously undeveloped site. 

20 I 0 Anchorage, AK Phase I MS4 permit: 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. 

2013 Western WA small MS4 permit: Implement low impact development performance standards to 

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. 
12 

BOX 3. Examples of WQBELs in Industrial (including Construction) Stormwater Permits; 

I. Numeric expression of the WQBEL: The permit includes a specific, quantifiable performance 

requirement that must be achieved: 

Pollutant concentrations shall rtot exceed the stormwater discharge limits specified in the permit 

(based on state WQS), including (for example): Cadmium-0.003 mg/1; Mercury-0.0024 mg/1; 

Selenium-0.02 mg/1 (2013 Hawaii MSGP) 

Beginning July I, 20 I 0, permittees discharging to impaired waters without an EPA-approved TMDL 

shall comply with the following effluent limits (based on state WQS), including (for example): 

Turbidity-25 NTU; TSS-30 mg/1; Mercury-0.0021 mg/1; Phosphorus, Ammonia, Lead, Copper, Zincsite-specific limits to be determined at time ofpermit coverage (2010 Washington MSGP) 

If discharging to waters on the 303(d) list (Category 5) impaired for turbidity, fine sediment, or 

phosphorus, the discharge must comply with the following effluent limit for turbidity: 25 NTU (at 

the point of discharge from the site), or no more than 5 NTU above background turbidity when the 

background turbidity is 50 NTU or less, or no more than a I 0% increase in turbidity when 

background rurbidity is more than 50 NTU. Discharges to waterbodies on the 303(d) list (Category 

5) for high pH must comply with the numeric effluent limit of pH 6.5 to 8.5 su (2010 Washington 

CGP) (2010 Washington CGP) 

2. Narrative expression of the WQBEL: The permit includes narrative effluent limits based on applicable 

WQS: 

New discharges or new dischargers to an impaired water are not eligible for permit coverage, unless 

documentation or data exists to show that (I) all exposure of the pollutant(s) of concern to 

stormwater is prevented; or (2) the pollutant(s) of concern are not present at the facility; or (3) the 

discharge of the pollutant(s) of concern will meet instream water quality criteria at the point of 

discharge (for waters without an EPA-approved TMDL), or there is sufficient remaining WLAs in an 

EPA-approved TMDL to allow the discharge and that existing dischargers are subject to compliance 

schedules to bring the waterbody into attainment with WQS (20 II Vermont MSGP; similar 

requirements in RI, NY, MD, VA, WV, SC, AR, TX, KS, NE, AZ, CA, AK, OR, and WA permits) 

In addition to other applicable WQBELs, there shall be no discharge that causes visible oil sheen, and 

no discharge of floating solids or persistent foam in other than trace amounts. Persistent foam is foam 

that does not dissipate within one half hour of point of discharge (20 14 Maryland MSGP) 

3. Requirement to implement additional practices or procedures for discharges to impaired waters: 

For sediment-impaired waters (without an approved TMDL), the permittee is required to maintain a 

minimum 50-foot buffer zone between any disturbance and all edges of the receiving water (2009 

Kentucky CGP) 

For discharges to impaired waters, implement the following: (I) stabilization of all exposed soil areas 

immediately, but in no case later than 7 days after the construction activity in that portion of the site 

has temporarily or permanently ceased (as compared to 14 days for no-impaired waters); (2) 

temporary sediment basins must meet specified design standards if they will serve an area of 5 or 

more acres (as compared to 10 or more acres for other sites); (3) retain a water quality volume of l 

inch of runoff from the new impervious surfaces created by the project (though this volume reduction 

requirement is for discharges to all waters, not just impaired waters) (2013 Minnesota CGP). 

If the. site discharges to a water impaired for sediment or turbidity, or to a water subject to an EPAapproved TMDL, the permittee must implement one or more of the following practices:(!) compost 

berms, compost blankets, or compost socks; (2) erosion control mats; (3) tackifiers used with a 

perimeter control BMP; (4) a natural buffer of 50 feet (horizontally) plus 25 feet (horizontally) for 5 

degrees of slope; (5) water treatment by electro-coagulation, flocculation, or filtration; and/or (6) 

other substantially equivalent sediment or turbidity BMP approved by the state (2010 Oregon CGP)