### MEMORANDUM UN I TED STATES ENVIRONMENTAL PROT ECTION AGENCY WASHINGTON, D.C

. 20460



## NOV 2 6 

## 201 4

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 ca us es streambank erosion, flooding, sewer overflows , and basement backups. The decreased natural infil tration ofrainwater reduces groundwater recharge, depleting

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### 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 s tormwater discharges , effluent limits be expressed as best management practices (BMPs) or other s imilar 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 so urc es (see Box 1 

### in the attachment for specific examples). Monitoring of the impacts of stormwater 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 stormwater permits. Notwit h standing these developments , stormwater 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 th eir 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 stormwater 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 permits 3 

### and industrial and construction storm water discharge permits. As a result of comments received and informed by the reviews of EPA and state-i ssued stormwater permits, EPA is in this memorandum replacing the

1 See generally Urban Stormwater Management in the United States (National Research Counci l, 2009), particularly th e discussion in Chapter 3, Hydrologic, Geomorphic, and Biological Effects ofUrbanization on Watersheds. 2 Stormwater discharg e 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 stormwater 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 , Lo s Angeles County , CA , and the Alabama Dept. o f Transportation, among many others. See also Secti on 4

.2 (Monitoring/Modeling Requirements) ofEPA's Municipal S e

parate Storm Sewer System P ermits: Post-Construction P e1jormance Standards & Wate r 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 Com pendium, 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 feas ible, numeric effluent limitations in NPDES permits for stormwater di scharges;

• 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 ofwater 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, 1 999)

. 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, ifthe 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 demons trates 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 ofpermits 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 level s, etc

. "

### 4
EPA also recent ly completed a review of state-issued N PDES 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 provi s ions shown in the MS4 Compendium. For example, some permits are requiring as an effl ue nt limi tation compliance with a numeric or narrative WQS, whi le others require the implementation of specific BMP s 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 ofpermitting approaches in state-issued industrial and construction stormwater permits in early 20 1 5.
Permits for MS4 Di scharges
The CWA prov ides that stormwa ter permits for MS4 discharges "shall require controls to reduce the discharge of pollutants to the maximum extent practicable

... and s uch 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 (9t h Cir. 1999)

. The 2002 memorandum stated "EPA expects that most WQBELs for NPDES -regula ted municipal and small construction storm water discharges will be in the form of BMPs , and that numeric limitations will be used only in rare instance s." As demonstrated in the MS4 Compendium, NPDES permitting authorities are using various forms of clear, specific , and measurable requirements , a nd , where feasible , numeric effluent limitations in order to establish a more objective and acc ountable 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 limitations 5 

### 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 ofthe attachment)

. WQBELs in 

### MS4 permits can be expressed as system- w ide requi rements rather than as individual discharge locatio n 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 app licable TMDLs, WLA s, and the affected MS4s; (2) numeric limits and other quantifiab le approaches for specific pollutants of concern; (3) requirements to implement spec ific stormwater controls or managem ent 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 pr ior to TMDL approval. 5 For the purpose of this m emorandum , and in the context ofNPDES permits for stormwater discharges , "nume ri c " effluent limitations refer to limitations with a quantifiable or measurable parameter related to a pollutant (or pollutants). Numeric WQB ELs 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 stormwater 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 establi sh 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 wit h 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 D i scharges
The CW A requi res that permits for stormwater discharges associated with industrial activity comply with section 301 ofthe 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 ofthe 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 example s.
Permits should contain clear, specific, and measurable element s associated with BMP implementation (e

. g., s chedule 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 ofwater quality standards. Permitting authori ties 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 wou ld typically require the permittee to take ad ditional 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 stormwater 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 b e applicable to your discharge. The benchmark concentrations are not effluent limitations; a benchmark exceedance, therefore, is not a permit vio lation. 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 la rge 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 requi rements 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 feas ible, 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 decis ion as to how to express the WQBEL(s) , either as numeric effluent lim itations or as BMPs, with clear, specific, and measurable elements , should be based on an analysi s of the specific facts and circumstances surrounding the permit, and/or the underlying WLA, including the nature ofthe stormwa ter 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 imp lementing BMPs can be tracked. Improved knowledge of BMP effectiveness gained since 2002 7 

### should be reflected in the demonstration and supporting rationale that implementation ofthe BMPs will attain water quality standards and be consistent with WLAs.
EPA 's regulations at40 CFR 

### § 122.47 govern the use ofcom pl iance schedules in NPDES permits. Centra l 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 NPDE S 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 C FR 

### § 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 establi shed 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 ava ilable at http: //water.epa.gov/infrastructure /greeninfrastructure /gi performance.cfrn , which has comp il ed 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 reliab le 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 s tormwater discharges from multiple point sources as a single categorical wasteload allocation when data and information are in sufficient to assign each source or outfall individual WLAs." EPA also said that, " [i]n cases where wasteload allocations are developed for categories of discharges, these categories should be defined as narrowly as available informa tion allows." Furthermore, EPA said it "recognizes that the available data and information usually are not detailed enough to determine waste lo ad allocations for NPDES -regul ated stormwater discharges on an outfall-specific basis. "
EPA s till recognizes that"[d]ecis ions 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 stormwa ter 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 j urisdictional

### 8 boundaries, land use and growth projections, and locations of storm water controls and infrastructure, to facilitate disaggregation. TMDLs have used diff erent 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 subwatershed 8 

### 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 ofan 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 des ignated sources to be subject to NPDES permits. Section 402(p)(6) provides EPA with authority to identify additional stormwater di scharges as needing a permit.
In addition to the stormwater dis charge s specifically identified as needing an NPDES permit, the CW A and the NPDES regulation s 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 lo ad 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 stormwater 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 permi t but may be required to obtain an NPDES permit in the

8 Wissahickon Creek Siltat ion 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.htm l and Upper M i nnehaha 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 allocatio n 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" 

### i f the stormwater discharge from the source were required to obta in NPDES permit coverage. S uch language would help e nsure that the allocation is properly characterized by the permit writer should the source ' s regulatory status change. This will help the permit writer devel op limitations for the NPDES permit applicable to the newly permitted source t hat are cons istent 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 Divis ion, or Tom Wall , Director of the Assessment and Watershed Protect ion Division

.

cc: Assoc iation of C le an Water Administrators TMDL Program Branch Chiefs , Region s 1

- 10 NPDES Permits Branch Chiefs , Region s 1

- 10 Attachment: MS4 and Industria l 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 ach ieved within a set timeframe. For example: Reduce fine sediment particles, total phosphorus , and total nitrogen loads by I0 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 of40 percent by 203S (20 II Washington , DC MS4 permit) Di scharges fr om the MS4 must not cause or contribute to exceedance s of receiv ing 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 expre s sions 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 reasonab le 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 reasonab ly 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 subbas in s, 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 discharge s to Segment 14 of the Upper South Platte River Basin associated w ith 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 w ith both numeric and non-numeric expressions ofthe WQBEL : Discharges of trash from the MS4 to the LA River must be reduced to zero by Sept. 20 16. Permittees also have the op tion of complying via the in stallation 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 opportunitie s 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 perm it: Keep and manage on site the first o ne inch of rainfa ll from a 2 4 -hour storm preceded by 48 hours of no measurab le precipitation. 20 II DC Phase I MS4 permit: Achieve on-site retention of I .2" of stormwat er 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 90 1h percentile storm event runoff to mimic the predevelopment hydrology of the previously undeveloped site. 20 I0 Anchorage , AK Phase I MS4 permit: Keep and manage the runoff generated from the first 0.52 inches ofrainfall 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 di scharge durations to pre-developed durations for the range of pre-deve loped 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 (20 13 Hawaii MSGP) Beginning July I , 20 I0, permittees discharging to impaired waters without an EPA-approved TMDL shall comply with the following effluent limits (based on state WQS), including (for examp le): 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 Wash ington 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 s ite) , or no more than 5 NTU above background turbidity when the background turb idi t y is 50 NTU or less, or no more than a I 0% increase in turbidity when background rurb idity is more than 50 NTU. Discharges to waterbodies on the 303(d) list (Category 5) for high pH must comply with the numer ic 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 ofthe p ollutant(s) of concern will meet instream water quality criteria at the po int 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 perm its) In addition to other applicable WQBELs, there shall be no discharge that causes visible oil sheen, and no discharge offloating solids or persistent foam in other than trace amounts. Persistent foam is foam that does not dis s ipate 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-imp aired 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 immediate ly, but in no case later than 7 days after the construction activity in that portion of the site has temporari ly or permanently ceased (as compared to 14 days for no -impaired waters); (2) temporary sediment basins must meet specified design standards ifthey will serve an area of 5 or more acres (as compared to 10 or more acres for other s ites); (3) retain a water quality volume of l inch ofrunoff 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 imp lement one or more of the following practices:(!) compost berms , compost blankets, or compost socks; (2) erosion control mats; (3) tackifiers used w ith a perimeter control BMP ; (4) a natural buffer of 50 feet (horizontally) p lus 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)