U.S. Environmental Protection Agency

U.S. Environmental Protection Agency
Understanding WLA Implementation in NPDES Permits: A Primer for TMDL Developers Welcome to this presentation on understanding the implementation of wasteload allocations, or WLAs, through National Pollutant Discharge Elimination System or, NPDES, permits. This presentation is one of three Web-based training modules on the topic of total maximum daily loads, or TMDLs, and the NPDES program sponsored by the U.S. Environmental Protection Agency. While it isn’t necessary to complete the other modules in this Web-based training series, the information in those modules do cover fundamental TMDL and NPDES permitting issues that are related to the topics addressed in this presentation. If you have questions on TMDL or permitting topics, consider viewing those presentations as well. Before we get started with the presentation, I’d like to cover one housekeeping item. All the materials used in this presentation have been reviewed by U.S. EPA staff for technical accuracy. TMDL development and implementation and NPDES permitting are governed by the existing requirements of the Federal Water Pollution Control Act, known as the Clean Water Act, and U.S. EPA’s implementing regulations. These statutory and regulatory provisions contain legally binding requirements. The information in this presentation is not binding. Furthermore, it supplements, and does not modify, existing U.S. EPA policy, guidance, and training on TMDLs and NPDES permitting. U. S. EPA may change the contents of this presentation in the future. Let’s first take a look at the objectives for this module. U.S. Environmental Protection Agency

Module Roadmap What is the regulatory context for implementing TMDL requirements in NPDES permits? How are effluent limits developed from wasteload allocations (WLAs)? How might other NPDES permit components be affected by a TMDL? What are some technical and policy challenges related to implementing TMDLs in NPDES permits? In this module, we have several learning objectives as we consider implementing TMDL requirements in NPDES permits. First, we will want to establish the regulatory context. We will briefly look at the structure of the NPDES program and review what the NPDES regulations say about WLAs calculated as part of a TMDL. Second, we will consider how effluent limitations in NPDES permits are calculated from WLAs, whether those WLAs come from a TMDL, or if they are determined in some other manner. Third, we will look at how components of an NPDES permit other than effluent limitations might be affected by TMDL requirements. Finally, we will consider some important technical and policy challenges that can complicate the implementation of TMDLs through NPDES permits.

What is a TMDL? TMDL = SWLAi + SLAi + MOS
Greatest amount of loading that a water can receive without violating water quality standards (i.e., loading capacity). [40 CFR 130.2(f)] TMDL = SWLAi + SLAi + MOS SWLAi: Sum of waste load allocations for existing and future point sources SLAi: Sum of load allocations for existing and future nonpoint and background sources MOS: Margin of safety Before we start talking about TMDL implementation, let’s make sure we are on the same page about what TMDLs are. TMDLs are developed for impaired waterbodies, or those waterbodies that do not meet their applicable water quality standards. In essence, TMDLs are “pollutant budgets” for a specific waterbody that if met would result in attainment of water quality standards. This allowable load is the TMDL, and is also known as the loading capacity. TMDLs are also required to include a safety factor as an extra measure of environmental protection, taking into account uncertainties associated with estimating the pollutant sources and their effect on the waterbody. This is referred to as the margin of safety. Once the loading capacity has been identified (with the margin of safety factored in), the TMDL is allocated among sources. Those sources regulated by the NPDES program, referred to as point sources, receive wasteload allocations, or WLAs. Sources not regulated by the NPDES program, referred to as nonpoint sources, and natural background, receive load allocations, or LAs. This concept is often illustrated with this equation showing that the TMDL is the sum of the individual wasteload allocations and load allocations as well as the incorporation of the margin of safety.

Typical Components of a TMDL
WLAs set pollutant loading cap for point sources LAs set pollutant loading cap for nonpoint sources Reserve capacity sets aside allocation for future development Margin of Safety (MOS) allocation accounts for uncertainty Reserve Capacity Point Source #1 MOS Point Source #2 Nonpoint Source #2 Another way to think of this concept is seeing the TMDL as a “pie” where the sum of all of the slices equals the total load that can be discharged to the waterbody. The portions of the TMDL pie assigned to point sources are the WLAs. Every point source that discharges to a water for which a TMDL has been developed receives a WLA. A point source’s WLA places a cap on the amount of pollutant that a particular point source can discharge to the waterbody and are implemented through NPDES permits. The portions of the TMDL pie assigned to nonpoint sources or background loads are the LAs. Other portions of the TMDL pie can include an allocation set aside to allow for future development, typically referred to as the reserve capacity. This is not required, but sometimes is included so that the TMDL doesn’t have to be reopened to accommodate new sources. Another portion of the TMDL pie might include an allocation for the Margin of Safety. The Margin of Safety can also be addressed through conservative assumptions in the TMDL calculations rather than as an explicit portion of the loading capacity. Nonpoint Source #1

TMDL Process EPA Recommended Elements in a TMDL Submittal
1. Description of waterbody, POC pollutant sources, and priority ranking Problem Understanding TMDL Target Identification Source Assessment 2. Water Quality Standards and numeric WQ target* Loading Capacity- Linking WQ and Sources* (including critical conditions*) Linkage between Loading and Waterbody Response 4. Load Allocations (LAs)* 5. Wasteload Allocations (WLAs)* 6. Margin of Safety (MOS)* 7. Seasonal Variation* Stakeholder Involvement & Public Participation Allocation Analysis This flow chart illustrates the required elements of a TMDL that will go to EPA for review and approval and the TMDL development process. This module focuses on how to implement element number 5, wasteload allocations, or WLAs, assigned to point sources regulated under the NPDES program. If you want more detailed information on the TMDL Process, you can review Module 1, Understanding TMDLs: A Primer for Permit Writers. If you are ready to focus on WLA implementation through NPDES permits, we’ll start by taking a look at the NPDES statutory and regulatory framework. 8. Reasonable Assurances+ 9. Monitoring Plan+ 10. Implementation Plan+ Implementation and Monitoring Plan TMDL Report and Submittal 11. Public Participation* * Required by regulation (40 CFR 130.7) + Recommended through guidance From Guidelines for Reviewing TMDLs under Existing Regulations issued in 1992 (May 20, 2002):

Overview of the NPDES Program
NPDES Statutory and Regulatory Framework CWA section 301(a) and 40 CFR 122.1(b) All point sources Discharging pollutants Into waters of the United States Must obtain an NPDES permit from EPA or an authorized state, territory, or tribe The scope of the NPDES permit program is provided in the NPDES regulations found in the Code of Federal Regulations at 40 CFR 122.1(b). This regulation states that the NPDES Program requires permits for the discharge of pollutants from any point source into waters of the United States. The terms “point source,” “pollutants,” and “waters of the United States” have been established, defined and interpreted by either the Clean Water Act, the NPDES regulations, or the courts. If you are interested in how these terms are defined within the NPDES program, check the EPA Web site for additional training that provides more detail on the structure of the NPDES program. For our purposes here, it is sufficient to know that such discharges must obtain an NPDES permit. NPDES Permit Writers' Workshop: Module 1

Overview of the NPDES Program
What is a Permit? A permit is a license that is issued by the government granting permission to do something that would be illegal in the absence of the permit (e.g., driver’s license) There is no right to a permit and it is revocable for cause (e.g., reckless driving) An NPDES permit is a license to discharge and can be revoked for cause That does bring up a very basic question, “What is a permit?” A good dictionary definition of permit is, “Permission, especially in written form; or, a document or a certificate giving permission to do something; or, a license or a warrant.” A very common example of a permit would be a driver’s license. A driver’s license provides the government’s permission to an individual to operate a specific class of motor vehicle. Without the government’s permission, it is illegal to drive. Of course you can still do it, but if you get caught driving without a license; you’re probably going to be in serious trouble. Similarly, an NPDES permit provides permission to an owner or operator of a point source, allowing them to discharge pollutants to waters of the United States. Again, a point source facility could discharge pollutants to waters of the United States without a permit, but if it gets caught, there can be some severe penalties including both monetary and possible incarceration. An NPDES permit is also like a driver’s license in that it spells out conditions under which a discharge is permissible. A driver’s license might limit or “condition” your operation of a vehicle so that you can drive only when you wear corrective lenses or perhaps only during daylight hours. The types of conditions that must be or may be included in an NPDES permit can be quite a bit more complicated and are based on the requirements established in the Clean Water Act and NPDES regulations. By understanding that a permit is a license, like a driver’s license, it becomes clear that one of the fundamental principles of the Clean Water Act is that an NPDES permit allowing a facility to discharge is a privilege, not a right, and that privilege (in other words, the NPDES permit), like a driver’s license, may be revoked for cause. When we talk about NPDES permit program authorization it sounds very straightforward. That, of course, is not the case. When a state requests authorization to implement the NPDES program, it does not always request or receive authorization for the whole program. By the whole program, I mean all components of the NPDES program. NPDES Permit Writers' Workshop: Module 1

Federal and State Roles
Module 2: Scope and Regulatory Framework of the NPDES Program Federal and State Roles Before NPDES program authorization: EPA issues permits EPA conducts compliance and monitoring activities EPA enforces State must grant or waive CWA section 401 certification After NPDES program authorization: State implements as above No CWA section 401 certification is required EPA oversees program administration Another basic question is “Who is responsible for drafting and issuing NPDES permits?” Who does a potential discharger need to deal with to apply for and receive approval to discharge? The answer is, “It depends on the location of the discharge.” The first thing to determine is whether the state where a discharge is located is “authorized” to administer the NPDES program. This authorization (sometimes incorrectly referred to as delegation) is granted by EPA to a state, territory, or tribe if it can demonstrate that it has the legal authority, implementation procedures, and resources necessary to run the program. Regulations in 40 CFR Part 123 address this authorization. Authorization is no small effort and it can take years to get this approval. If the state does not have authorization to administer the NPDES program, EPA will be the permitting authority. Where EPA is the permitting authority, the EPA Regional office is responsible for issuing the permits, taking enforcement actions, and conducting inspections and monitoring visits as necessary. If a state has authorization, then it is the permitting authority and it performs all of the day-to-day permit issuance. In this case, EPA acts in an oversight role, providing review and guidance for the state’s program. Under certain circumstances, such as when EPA objects to a permit or a state fails to enforce the requirements of a permit, EPA might determine that the state action is insufficient and may issue its own permit or perform other program functions. Remember, territories and tribes are considered to be like states and, as such, must also go through the approval process to implement the NPDES program for the territory or tribe. When we talk about NPDES permit program authorization it sounds very straightforward. That, of course, is not the case. When a state requests authorization to implement the NPDES program, it does not always request or receive authorization for the whole program. By the whole program, I mean all components of the NPDES program. Instructors’ Manual

NPDES Permit Types, Coverage, and Emerging Program Areas
4/17/2017 Permit Components Components of All Permits Industry-Specific Components Municipal-Specific Components Cover Page Effluent Limitations Effluent Guidelines Case by Case Limitations Secondary Equivalent to Secondary Technology-based Water Quality-based Monitoring and Reporting Special Conditions This slide gives us a graphical representation of the five basic components of NPDES permits. Cover Page – This simply tells who is issuing the permit, who is receiving the permit, what statutes and regulations apply, and provides the effective and expiration dates for the permit. Effluent Limitations – These are very important and will include consideration of technology-based and water quality-based requirements. Monitoring and Reporting – This section tells the permittee when, where, how, and how much monitoring it must conduct and how to report the results. Special Conditions – This includes special monitoring and studies, best management practices, compliance schedules, special programs. This component will be dependent on the type of permit being requested. Standard Conditions – These are important boilerplate requirements that are included in ALL permits Additional Monitoring / Special Studies Pretreatment Municipal Sewage Sludge CSOs Best Management Practices Compliance Schedules Standard Conditions NPDES Permit Writers' Course: Module 3

Types of NPDES Permits—Individual
NPDES Permit Types, Coverage, and Emerging Program Areas 4/17/2017 Types of NPDES Permits—Individual 1 application submitted permit issued Appropriate where facility-specific permit conditions (e.g., effluent limitations, management practices, monitoring and reporting) are needed Application Individual Permit Having defined what a permit is, who issues permits, and how a permit is broken down into its component parts, we can take a look at the “types” of permits that are authorized under the NPDES regulations. EPA and state permitting authorities can provide permit coverage to different types of point sources in one of two ways. They can either develop a unique permit for each discharger or an “umbrella” permit that covers a large number of similar dischargers. We call these two types of coverage individual permits and general permits. Let’s first discuss what we mean by an individual permit. Well, an individual permit is just what it sounds like. An individual facility gets its own unique permit designed for its specific discharge or discharges. For example, ACME, Inc. has a process wastewater discharge to Pristine Creek. ACME completes a permit application that describes its operation and discharge, provides appropriate effluent data, and requests a permit to allow it to discharge. The permitting authority reviews the application, collects all the information it can about the facility, the discharge, and the receiving water, and crafts and issues a permit that is unique to the ACME, Inc. facility and provides specific conditions that ACME must meet. An individual permit is well suited for situations where the characteristics of the facility and the receiving water are unique, and where site-specific effluent limits and other permit conditions are needed. NPDES Permit Writers' Course: Module 3

Types of NPDES Permits—General
NPDES Permit Types, Coverage, and Emerging Program Areas 4/17/2017 Types of NPDES Permits—General Authorized at 40 CFR 1 permit issued many Notices of Intent submitted Appropriate where multiple, similar sources (e.g., same category, similar process) within the same geographic area require permit coverage sources have similar discharges and would require the same or similar permit conditions Permit must identify: area of coverage sources covered NOI process Now, let’s talk about general permits. The requirements for general permits are found at 40 CFR General permits are appropriate to use where there are multiple, similar sources with similar discharges that would result in similar permit conditions. Examples of this might include construction stormwater discharges, seafood processing, and placer mining. With general permits, the permit writer develops one permit that covers multiple dischargers and each discharger prepares and submits a notice of intent, or NOI. The NOI serves as the general permit application and is how a discharger notifies the permitting authority that they wish to have permit coverage. In addition to the required components of all NPDES permits, the general permit must include the following: the area of coverage, the sources covered, and a description of the notice of intent process. General Permit NOIs NPDES Permit Writers' Course: Module 3

TMDLs and Permit Components
NPDES Permit Types, Coverage, and Emerging Program Areas 4/17/2017 TMDLs and Permit Components Components of All Permits Industry-Specific Components Municipal-Specific Components Cover Page Effluent Limitations Effluent Guidelines Case by Case Limitations Technology-based Secondary Equivalent to Secondary Water Quality-based Monitoring and Reporting Special Conditions As we consider the implementation of TMDLs in NPDES permits, we are going to spend most of our time looking at how TMDLs affect the development of effluent limitations, particularly water quality-based effluent limitations, referred to as WQBELs. It is important to note that implementing TMDL requirements in NPDES permits might also affect permit components other than just the effluent limitations. We will briefly discuss some monitoring and reporting requirements, special conditions, and standard conditions of NPDES permits as well. However, for now, let’s turn our attention to development of water quality-based effluent limitations. Additional Monitoring / Special Studies Pretreatment Municipal Sewage Sludge CSOs Best Management Practices Compliance Schedules Standard Conditions NPDES Permit Writers' Course: Module 3

Relationship Between WQ Standards and Effluent Limitations
Water Quality Standards Relationship Between WQ Standards and Effluent Limitations Numeric WQ Criteria Magnitude Duration Frequency Narrative WQ Criteria Effluent Limitations Magnitude Averaging Period Water quality standards apply in the waterbody and the permit limits typically apply at the discharge point. So how does a permit writer examine the applicable numeric and narrative water quality criteria that apply to a particular waterbody and determine if WQBELs are necessary to protect those water quality standards? If there is a reasonable potential for a discharge to cause, or contribute to an excursion above any state water quality standard then a WQBEL is required to be developed. If so, the permit writer calculates WQBELS from water quality standards. To do this, the permit writer needs to have a way to “translate” between water quality criteria and effluent limitations. This translation is complicated by the fact that numeric water quality criteria often are made up of a magnitude; duration; and a frequency. That is… How much of the pollutant can be present? How long is the allowable period of exposure? and How frequently can the pollutant be present at the given magnitude and duration and water quality standards still be attained? Effluent limitations, on the other hand, have a calculated magnitude at an averaging period that is specified in the NPDES regulations. Narrative water quality criteria generally are qualitative statements and do not have any numeric expression of magnitude, duration, and frequency, further complicating the translation into effluent limitations. Permit writers calculate end-of-pipe water quality-based effluent limitations where necessary to ensure that water quality standards are attained in the receiving water.

Where do TMDLs fit in? So, where do TMDLs fit into this process of translating water quality standards into end-of-pipe effluent limitations?

40 CFR (d)(1)(vii) (vii) When developing water quality-based effluent limits under this paragraph the permitting authority shall ensure that: The level of water quality to be achieved by limits on point sources established under this paragraph is derived from and complies with all applicable water quality standards; and Effluent limits developed to protect a narrative water quality criterion, a numeric water quality criterion, or both, are consistent with the assumptions and requirements of any available wasteload allocation for the discharge prepared by the State and approved by EPA pursuant to 40 CFR The answer is that TMDLs can limit the amount of a specific pollutant that can be legally discharged into a waterbody as WLAs for point sources. According to federal regulations, WQBELs in an NPDES permit must be “consistent with the assumptions and requirements of any available wasteload allocation for the discharge” that is part of an approved TMDL. This regulation directly ties an NPDES permit to implementation of a TMDL. So, in effect, the TMDL helps to translate water quality standards into NPDES effluent limitations through the wasteload allocation process.

What is a Wasteload Allocation?
Calculating WQBELs What is a Wasteload Allocation? Wasteload Allocation (WLA): the portion of a receiving water’s loading capacity that is allocated to one of its existing or future point sources Before we go on, let’s review the definition of a “wasteload allocation.” A WLA can be defined as the portion of a receiving water’s loading capacity that is allocated to one of its existing or future point sources. Now let’s look at how a permit writer would determine an appropriate wasteload allocation to use as a basis for developing effluent limitations. The WLA can come directly from a TMDL, or the permit writer can derive the WLA from applicable water quality criteria, such as aquatic life and human health. In the next several slides, we are going to examine several cases where WLAs can be developed and utilized by permit writers. NPDES Permit Writers' Workshop: Module 6

Calculating WQBELs WLA from a TMDL WLA = portion of the receiving water’s TMDL allocated to a specific point source We are going to now go through an example of a TMDL that has been developed for an impairment due to sediments. A wasteload allocation for total suspended solids (TSS) has been developed for our point source, Smalltown POTW. As we mentioned, the wasteload allocation is the portion of the TMDL for TSS that has been allocated to the POTW. NPDES Permit Writers' Workshop: Module 6

Calculating WQBELs from WLAs
Calculating Effluent Limits TMDLs are often comprised of load allocations for non-point sources as well as WLAs point sources Loadings can include more constant discharges from point sources and dynamic discharges from non-point sources due to, for example, stormwater events It is important to determine how the WLA is expressed in the TMDL So here is an example of a fairly common type of TMDL, one that has been developed for an impaired waterbody due to sediments. In many instances, there can be loadings from point and non-point sources that vary based on weather conditions. WLAs from point sources are typically less variable from those associated with non-point source discharges due to stormwater events. It is very important to read the TMDL carefully to determine how the WLA for a particular point source is expressed.

Assume the daily loading for the TMDL is equivalent to a maximum daily limit (MDL) as expressed in an NPDES permit. So, starting from the WLA in the TMDL, what is the process to calculate the MDL that would go in a NPDES permit? The MDL is developed as follows: The WLA is used to calculate the long term average (LTA). The MDL is calculated from the LTA. In our example, our POTW has a WLA for TSS of 50 mg/L. Now actual loadings from a POTW for TSS are not static but variable, just not as variable as those from non-point sources. Where the non-point source loadings are highly correlated to stormwater events, loadings from POTWs are less so. For this example, we will assume the daily loadings for the TMDL are equivalent to the maximum daily limit (MDL) that will be developed for the POTW’s NPDES permit. We will take the TSS WLA assigned to the POTW and calculate a MDL for that facility. So how do we do that? We will follow the EPA recommendations for water quality-based permitting for toxics in the Technical Support Document for Water Quality-based Toxics Control or TSD. Specifically, the TSD provides a detailed statistical procedure for characterizing pollutant concentrations in effluent based on a limited data set and accounting for the variability of that effluent. When we discuss calculating effluent limits for a toxic parameter in our next example, we will provide more detail in the statistical approach recommended in the TSD. For this example, we will take the TSS WLA for this POTW, calculate the LTA and then derive a MDL for TSS for our POTW.

Module 6D: Developing Chemical-specific WQBELs
4/17/2017 Calculate LTAs WLA multipliers [0.52 - z] e CV = 0.6 WLA = 50 mg/L = 99th percentile value LTA = 50 mg/L x _______ = mg/L CV 95th 99th percentile percentile 0.1 0.853 0.797 0.2 0.736 0.643 0.3 0.644 0.527 0.4 0.571 0.440 0.5 0.514 0.373 0.6 0.468 0.321 0.7 0.432 0.281 Our WLA is a never to be exceeded value. If the WLA is in the “99th percentile” position, then the lognormal distribution would look something like this……with 99 percent of the expected values BELOW the calculated wasteload allocation. In effect, this distribution requires the facility to perform in a manner which, on average may be much lower than the wasteload allocation, and which assures that 99 percent of the time its effluent concentration is less than the wasteload allocation. In other words, even on its bad days, the facility shouldn’t exceed the wasteload allocation, and, therefore, will not exceed the criteria in the receiving water. In this example, assume that the WLA is fixed at the 99th percentile and assume that the coefficient of variation (CV) = The CV is simply the standard deviation of the data set divided by the mean. Where are limited data values, generally less than 10, EPA recommends a default CV of 0.6 be used. These are described in more detail in the TSD. In addition, your state will probably have detailed procedures on which CV and percentiles to use. Be sure to follow your state’s procedures. What is the multiplier? 0.321 We multiply the WLA (50 mg/L) by the multiplier of to get an LTA of mg/L. 0.8 0.403 0.249 0.9 0.379 0.224 1.0 0.360 0.204 1.1 0.344 0.187 1.2 0.330 0.174 1.3 0.319 0.162 1.4 0.310 0.153 1.5 0.302 0.144 1.6 0.296 0.137 1.7 0.290 0.131 1.8 0.285 0.126 1.9 0.281 0.121 2.0 0.277 0.117 NPDES Permit Writers' Course

4/17/2017 Calculate the MDL LTA multipliers [ e z 2 ] MDL MDL = 99th percentile value CV = 0.6 MDL = mg/L x = 50 mg/L 95th 99th CV percentile percentile 0.1 1.17 1.25 0.2 1.36 1.55 0.3 1.55 1.90 0.4 1.75 2.27 0.5 1.95 2.68 0.6 2.13 3.11 0.7 2.31 3.56 0.8 2.48 4.01 0.9 2.64 4.46 The TSD provides a table based on a lognormal distribution of effluent values that gives multipliers for calculating a maximum daily limit from the LTA. We have to know the CV and the desired percentile value for the MDL. The TSD recommends setting the MDL at the 99th percentile, but different permitting authorities may use a different percentile. Check your permitting procedures. Using the table from the TSD, we are going to set the MDL at the 99th percentile. Assuming a CV of 0.6, what is our multiplier? Our multiplier is 3.11. We multiply the LTA (16.05 mg/L) by 3.11 and get an MDL of 50 mg/L. You will notice that this is the same as our WLA from the TMDL. That is because we are using a similar averaging period, the loading from the TMDL being equivalent to the daily maximum limit in the NPDES permit. Is this always the case, no! In our next example we will go through what a permit writer must do when calculating WQBELs from load allocations based on differing averaging periods. So the MDL we just calculated is the only limit we need to put in the permit right? No, we also need to compare the water quality-based effluent limits (WQBELs) we develop to applicable technology-based effluent limits (TBELs) and the more stringent limit is placed in the permit. For a POTW, the secondary treatment standards are applicable and prescribe an average monthly limit (AML) for TSS of 30 mg/L and a weekly average limit of 45 mg/L. These limits are for different periods than the MDL so we would include all 3 effluent limits. The AML and weekly effluent limit satisfy the TBELs and the MDL satisfies the TMDL. 1.0 2.78 4.90 1.1 2.91 5.34 1.2 3.03 5.76 1.3 3.13 6.17 1.4 3.23 6.56 1.5 3.31 6.93 1.6 3.38 7.29 1.7 3.45 7.63 1.8 3.51 7.95 1.9 3.56 8.26 2.0 3.60 8.55 NPDES Permit Writers' Course

Step 2: Calculate Long-Term Averages (LTAs) and Select Lowest
Calculating WQBELs Steps in Developing Chemical-Specific WQBELs from Aquatic Life Criteria Step 1: Determine Wasteload Allocation (WLA) from Aquatic Life Water Quality Criterion Step 2: Calculate Long-Term Averages (LTAs) and Select Lowest In this instance, we are going to use the example of a pollutant that has applicable aquatic life criteria. Again, it is common for pollutants to have multiple criterion apply to them, which lead to multiple WLAs. Different criterion use different averaging periods and critical conditions, therefore we need a way to “translate” the results of the WLAs into a common basis for analysis, Here is a simple flow chart outlining a process for developing water quality-based effluent limitations for aquatic life criteria where no TMDL exists for that pollutant. The specific process we will describe is based on the guidance in USEPA’s Technical Support Document for Water Quality-based Toxics Control, which we will refer to as the Technical Support Document or TSD. We will apply this guidance to our examples using acute aquatic life criteria expressed as 1-hour average criteria and chronic aquatic life criteria expressed as 4-day average criteria. These averaging periods are typical for many aquatic life criteria for toxic pollutants. We would use similar procedures for aquatic life criteria with different averaging periods (for example, a 30-day average) or for other types of criteria, such as human health criteria, but the procedures would differ in some important details. Consider reviewing the Technical Support Document for more information. Looking at the water quality-based effluent limit development process for most aquatic life criteria, our first step is determining acute and chronic wasteload allocations from the applicable acute and chronic aquatic life criteria for the pollutant of concern. Step 3: Calculate Maximum Daily Limit (MDL) and Average Monthly Limit (AML)* *Other averaging periods used where appropriate (e.g., instantaneous maximum and instantaneous minimum for pH) NPDES Permit Writers' Workshop: Module 6

WLA from TMDL WLA Widgets-R-Us Nonpoint Source ABC, Inc. Smalltown
Calculating WQBELs WLA from TMDL Widgets-R-Us Nonpoint Source ABC, Inc. WLA Smalltown POTW Nonpoint Source Let’s assume that we are writing an NPDES permit for ABC, Incorporated. One way to determine a WLA for ABC, Incorporated is to consider this facility in the context of its entire watershed. A TMDL could give us WLAs for each of the point sources in the watershed after considering how they are related to one another and to a common waterbody of concern affected by each of them. Acme Gadgets Water body of Concern NPDES Permit Writers' Workshop: Module 6

WLA from a TMDL WLA = portion of the TMDL allocated to a specific point source If a TMDL or other watershed analysis has been developed for the pollutant of concern for the receiving water, a WLA for the point source in our example, ABC, Inc., might already have been determined. The WLA is the portion of the TMDL for the pollutant of concern that has been allocated to ABC, Incorporated. So, as we have just seen, when developing water quality-based effluent limitations for ABC, Incorporated, the regulations require that these limitations be consistent with the assumptions and requirements of the available wasteload allocation for ABC, Inc., from the approved TMDL.

WLA for a Single Facility
Calculating WQBELs WLA for a Single Facility Local water quality impacts Single point source Other sources considered in “background” Determine the maximum allowable discharge (i.e., the WLA) for the single facility A second permitting scenario that is common for toxic pollutants is where we need to address a single point source. Here, sources other than our permittee, ABC, Inc., are simply considered as contributing to the upstream presence of the pollutant prior to considering the contribution from ABC, Inc. NPDES Permit Writers' Workshop: Module 6

Determining WLAs QrCr-QsCs WLA = Cd = Qd
Calculating WQBELs Determining WLAs Mass-Balance Equation: QsCs + QdCd = QrCr Q = Flow (mgd or cfs) C = Pollutant concentration (mg/l) Mass = [Concentration] [Flow] To determine the WLA: We are assuming that there is not a WLA for this pollutant from an approved TMDL. In these cases, permit writers typically use a fairly simple water quality model, such as a simple mass-balance equation, to model a single discharge and determine the wasteload allocation for the pollutant of concern. Here is the mass-balance equation rearranged to solve for the concentration of the discharge. This value will be the wasteload allocation for ABC, Inc. QrCr-QsCs Qd WLA = Cd = NPDES Permit Writers' Workshop: Module 6

Module 9: Coal Mining WQBELs-Calculate WQBELs Calculating WQBELs from WLAs WLAs represent a point source’s allocated share of the waterbody’s pollutant loading and should, as appropriate, be translated into a WQBEL for that source WLAs derived directly from water quality criteria through TMDLs, watershed analyses, or facility-specific analyses might be expressed as daily allocation or have the same duration as criteria WQBELs derived from WLAs using EPA or state-specific limit development procedures must be consistent with assumptions used to derive applicable WLAs [40 CFR (d)(1)(vii)(B)] typically have different duration/averaging period than WLAs We have discussed two different ways that a WLA could be derived: 1) from a TMDL and 2) from a facility-specific analysis. It is important for us to keep in mind that, however a WLA is developed, it provides information that should guide the development of a WQBEL. WLAs are derived directly from water quality criteria and their expression, such as a concentration or load, and their duration, whether daily, monthly or even annual, can vary by TMDL. How the LAs and WLAs are expressed is based on a number of considerations, including the water quality criteria, the nature of the water quality impairment, and the type and behavior of major sources. While WQBELs must be consistent with the assumptions used to derive applicable WLAs, they typically are expressed in different terms than WLAs. It is important to note that, consistent with the NPDES regulations, most WQBELs for continuous discharges are expressed as average monthly limits and maximum daily limits. Consequently, there are statistical procedures to calculate these WQBELs from WLAs (expressed as 1-hour or 4-day averages) NPDES Permit Writers' Specialty Course: Coal Mine Permitting

Module 8: Coal Mining WQBELs-Determine the Need for WQBELs Calculating WQBELs from WLAs Follow permitting authority procedures to calculate WQBELs from WLAs permitting authority regulation, policy, or guidance EPA’s Technical Support Document for Water Quality-based Toxics Control (TSD) uses a statistical analysis that assumes effluent data follow a lognormal distribution Most states that administer the NPDES permits program will have some detailed procedures for calculating WQBELs from WLAs. However, EPA has established its recommendations for water quality-based permitting for toxics in the Technical Support Document for Water Quality-based Toxics Control or TSD. Specifically, the TSD provides a detailed statistical procedure for characterizing pollutant concentrations in effluent based on a limited data set and accounting for the variability of that effluent. The procedures use a statistical analysis that assumes that effluent data follow what’s called a “lognormal distribution.” For any permitting situation where effluent concentrations tend to follow a lognormal distribution, permit writers can use procedures similar to those developed by EPA, and published in the TSD, to derive effluent limits from a WLA, provided by a TMDL or calculated directly for an individual point source. In addition, the TSD provides procedures for developing WQBELs for environmental data that are normally distributed or a delta-lognormal distribution. NPDES Permit Writers' Specialty Course: Coal Mine Permitting

Calculating WQBELs Steps in Developing Chemical-Specific WQBELs from Aquatic Life Criteria Step 1: Determine Wasteload Allocation (WLA) from Aquatic Life Water Quality Criterion Step 2: Calculate Long-Term Averages (LTAs) and Select Lowest Using these procedures, the next step after determining the appropriate wasteload allocation (or reviewing the WLA from an approved TMDL) is to calculate the long-term average effluent concentration that will ensure that the wasteload allocation is met. Step 3: Calculate Maximum Daily Limit (MDL) and Average Monthly Limit (AML)* *Other averaging periods used where appropriate (e.g., instantaneous maximum and instantaneous minimum for pH) NPDES Permit Writers' Workshop: Module 6

Module 8: Coal Mining WQBELs-Determine the Need for WQBELs
Key Terms Lognormal Distribution: the probability distribution of any random variable whose logarithm is normally distributed Relative Frequency: the fraction or ratio of the number of observations in a category or class to the total number of observations Lognormal Distribution Relative Frequency To understand how that works, we need to define some key terms. A lognormal distribution is a probability distribution of any random variable whose logarithm is normally distributed. Two features of the lognormal distribution that you might notice right away are: The concentration values are at or above zero. In other words, there is no such thing as a negative concentration. The right hand tail of the curve is asymptotic to the x-axis. In other words, statistically, there is no upper limit to the potential concentration of the pollutant in the effluent. However, as we move up the x-axis (which represents concentration), the chance of these higher values occurring becomes negligible. Concentration NPDES Permit Writers' Specialty Course: Coal Mine Permitting

Module 8: Coal Mining WQBELs-Determine the Need for WQBELs
Key Terms (continued) Long-term Average (LTA): for a continuous random variable (in our case, pollutant concentration), the value at which the area under the distribution curve to the left of the value equals the area under the distribution curve to the right of the value Coefficient of Variation (CV): a statistical measure of the relative variation of a distribution or set of data (in our case, pollutant concentrations) calculated as the standard deviation divided by the mean The curve itself can be described using a couple of terms of art: The first is the Long Term Average or LTA. The Long Term average is the point on the x-axis that bisects the area under the curve. Because the curve is skewed to the upper end values, the LTA is nearly always to the right of the peak of the curve. The second term of art, is the “coefficient of variation” or CV. The CV is calculated as the standard deviation of the data divided by the mean and represents a measure of the relative distribution or variation of the data around that long-term average. NPDES Permit Writers' Specialty Course: Coal Mine Permitting

Calculate LTA Assume a lognormal distribution of effluent data
Calculating WQBELs Calculate LTA Assume a lognormal distribution of effluent data WLA is never to be exceeded Characterize never to be exceeded by an upper bound value (e.g., WLA is the 99th percentile concentration on the lognormal effluent distribution) Knowing the WLA and a (coefficient of variation) CV, calculate the LTA For this presentation, we’ll assume that our data follow a lognormal distribution, and we’ll use the wasteload allocations that we’ve already calculated to determine the long-term averages. Recall that our wasteload allocation calculations “modeled” the amount of a pollutant that could be discharged to the receiving water under critical conditions and NOT cause an exceedance of the applicable criterion. That also means that, if the facility discharges above the WLA under critical conditions, then there’s a likelihood that an exceedance of the criterion would occur. We certainly don’t want that to happen. Therefore, we’ll consider the WLA as a value that is “never to be exceeded.” Knowing that our lognormal statistical distribution is mathematically “unbound” on the upper end, it is impossible to find a point on the distribution that will “never to be exceeded.” So, we’ll have to assume that the wasteload allocation occurs at some upper bound value on this distribution—such as the 99th percentile. EPA’s Technical Support Document provides guidance on how a state might establish an acceptable “upper bound”, but ultimately, it is the state or EPA permitting authority that selects the appropriate percentile, usually through regulation, policy, or guidance. Now we can use the coefficient of variation to define the lognormal data distribution, and from that distribution, we can calculate a long term average corresponding to each of the wasteload allocations. NPDES Permit Writers' Workshop: Module 6

Goal: Reduce Concentration Below WLA
Calculating WQBELs Goal: Reduce Concentration Below WLA Distribution that Meets WLA Requirement Relative Frequency Now here’s what the process looks like graphically. First, we plot our calculated wasteload allocation on the “x-axis.” This is a fixed value which we’ve said is “never to be exceeded.” If we define “never to be exceeded as the “99th percentile” position, then our lognormal distribution would look something like this ……with 99 percent of the expected values BELOW the calculated wasteload allocation. In effect, this distribution requires the facility to perform in a manner which, on “average” may be much lower than the wasteload allocation, and which assures that 99 percent of the time its effluent concentration is less than the wasteload allocation. In other words, even on its “bad days” the facility shouldn’t exceed the wasteload allocation, and, therefore, will not exceed the criteria in the receiving water. X WLA Concentration NPDES Permit Writers' Workshop: Module 6

Characterize Distribution by LTA and CV
Calculating WQBELs Characterize Distribution by LTA and CV Relative Frequency CV LTA WLA X Concentration Since we have established that the data follow a lognormal statistical distribution, we can calculate the relationship between the WLA (at the 99th percentile) and the LTA (or “mean value”) based on the coefficient of variation. EPA has provided tables in the Technical Support Document for calculating this relationship between the 99th percentile value and the Long Term Average based on the coefficient of variation of the data. The Technical Support Document recommends that we use a Coefficient of Variation of 0.6 if we have less than 10 samples from this facility. If we have 10 or more samples, we can compute Coefficient of Variation as the standard deviation divided by the mean. Our next slide shows how the LTA is calculated based on a chronic WLA. NPDES Permit Writers' Workshop: Module 6

4/17/2017 Calculate LTAs WLA multipliers [ 0.5   2 - z Chronic CV = 0.6 WLA(chronic) = 1.5 mg/L = 99th percentile value LTA(chronic) = 1.5 mg/L x _______ = mg/L ] e CV 95th 99th percentile percentile 0.1 0.922 0.891 0.2 0.853 0.797 0.3 0.791 0.715 0.4 0.736 0.643 0.5 0.687 0.581 0.6 0.644 0.527 0.7 0.606 0.481 0.8 0.571 0.440 In this example, we will assume that the chronic WLA is fixed at the 99th percentile and assume that CV is equal to These are described in more detail in the TSD. The equations and the multipliers are slightly different between the equations for calculating an LTA from the chronic WLA and the acute WLA because the chronic WLA is a 4-day average value and the acute WLA is a single (one-day) value. What is the multiplier? 0.527 We multiply the chronic WLA (1.5 mg/L) by the multiplier of to get to an LTA of 0.79 mg/L. We would follow a similar procedure to determine the acute LTA or human health LTA. 0.9 0.541 0.404 1.0 0.514 0.373 1.1 0.490 0.345 1.2 0.468 0.321 1.3 0.449 0.300 1.4 0.432 0.281 1.5 0.417 0.264 1.6 0.403 0.249 1.7 0.390 0.236 1.8 0.379 0.224 1.9 0.369 0.214 2.0 0.360 0.204 NPDES Permit Writers' Course

Calculating WQBELs Steps in Developing Chemical-Specific WQBELs from Aquatic Life Criteria Step 1: Determine Wasteload Allocation (WLA) from Aquatic Life Water Quality Criterion Step 2: Calculate Long-Term Averages (LTAs) and Select Lowest After a permit writer has defined the desired frequency distribution for the effluent in terms of the long-term average and coefficient of variation of pollutant concentrations, he or she can use that information to calculate effluent limitations expressed as a maximum daily limit and an average limit, generally an average monthly limit. Step 3: Calculate Maximum Daily Limit (MDL) and Average Monthly Limit (AML)* *Other averaging periods used where appropriate (e.g., instantaneous maximum and instantaneous minimum for pH) NPDES Permit Writers' Workshop: Module 6

4/17/2017 Calculate MDL and AML Use the lognormal distribution to calculate the MDL and AML from the lowest LTA uses upper-bound estimates for both MDL (e.g., 99th percentile) and AML (e.g., 95th percentile) ties AML to planned frequency of monitoring allows comparison to technology-based limits We set both the maximum daily limit, referred to as the MDL, and the average monthly limit, referred to as the AML, at upper-bound values on the effluent concentration distribution curve. The MDL is at the 99th percentile The AML is at the 95th percentile These percentiles are consistent with EPA’s recommendations in the TSD and with EPA’s approach to establishing effluent guidelines The value we calculate for the AML also depends on how frequently we plan to have the facility monitor for that parameter. After we calculate the MDL and AML, we have effluent limitations that we can compare to the technology-based limitations. Why do we need to compare to technology based limits? Because it's the law. We must use the more stringent of the technology or water quality-based limits as the applicable limits in our NPDES permit. NOTE: Regulations at (d) require average monthly and maximum daily limits for non-municipals and average monthly and average weekly limits for POTWs, unless impractical. EPA guidance in TSD is that average weekly limits are impractical for toxics. Why? Might miss a one day spike in toxicity that can impact aquatic life. NPDES Permit Writers' Course

Calculate MDL and AML from the LTA
Module 6D: Developing Chemical-specific WQBELs 4/17/2017 Calculate MDL and AML from the LTA CV Relative Frequency This slide shows the relationship between LTA and AML and MDL . Notice that the MDL and AML are upper-bound values on the lognormal distribution curve. LTA AML MDL Concentration NPDES Permit Writers' Course

4/17/2017 Step 4: Calculate MDL and AML LTA multipliers [ e z 2 ] MDL MDL = 99th percentile value CV = 0.6 MDL = mg/L x = 1.8 mg/L 95th 99th CV percentile percentile 0.1 1.17 1.25 0.2 1.36 1.55 0.3 1.55 1.90 0.4 1.75 2.27 0.5 1.95 2.68 0.6 2.13 3.11 0.7 2.31 3.56 0.8 2.48 4.01 0.9 2.64 4.46 To facilitate our effluent limitation calculations, the TSD provides a table based on a lognormal distribution of effluent values that gives multipliers for calculating a maximum daily limit, or MDL, from the LTA. We have to know the CV and the desired percentile value for the MDL. Note that the equation is just the reciprocal of the equation used in Step 1 for calculating an LTA from the 1-day WLA. The TSD recommends setting the MDL at the 99th percentile, but different permitting authorities may use a different percentile. Check your permitting procedures. Using the table from the TSD, we are going to set the MDL at the 99th percentile. Assuming a CV of 0.6, what is our multiplier? Our multiplier is 3.11. We multiply the LTA (0.58 mg/L) by 3.11 and get an MDL of 1.8 mg/L. Note: In this case, the MDL happens to be the same as the acute WLA. This situation occurs because we originally set the WLA at a 99th percentile value (and treated it as having a daily averaging period), back calculated an LTA from that acute WLA, then chose the acute LTA as the basis for our limits and went back to a 99th percentile value for the MDL. So, we started with a 99th percentile of daily values and ended up back at that same 99th percentile of daily values.) 1.0 2.78 4.90 1.1 2.91 5.34 1.2 3.03 5.76 1.3 3.13 6.17 1.4 3.23 6.56 1.5 3.31 6.93 1.6 3.38 7.29 1.7 3.45 7.63 1.8 3.51 7.95 1.9 3.56 8.26 2.0 3.60 8.55 NPDES Permit Writers' Course

4/17/2017 Step 4: Calculate MDL and AML LTA multipliers [z - 0.52 n ] e 95th percentile 99th percentile AML AML Value = 95th percentile CV = 0.6 Number of = 8 (assume 2x/wk-Samples sampling) AML = mg/L x = mg/L CV n=1 n=2 n=4 n=8 n=30 n=1 n=2 n=4 n=8 n=30 0.1 1.17 1.12 1.08 1.06 1.03 1.25 1.18 1.12 1.08 1.04 0.2 1.36 1.25 1.17 1.12 1.06 1.56 1.37 1.25 1.18 1.08 0.3 1.55 1.38 1.26 1.18 1.09 1.90 1.59 1.40 1.27 1.13 0.4 1.75 1.52 1.36 1.25 1.12 2.27 1.83 1.55 1.37 1.18 0.5 1.96 1.66 1.45 1.31 1.16 2.68 2.09 1.72 1.48 1.23 0.6 2.13 1.90 1.55 1.38 1.19 3.11 2.37 1.90 1.59 1.28 0.7 2.31 1.94 1.65 1.45 1.22 3.56 2.66 2.08 1.71 1.33 0.8 2.48 2.07 1.75 1.52 1.26 4.01 2.96 2.27 1.83 1.39 0.9 2.64 2.20 1.85 1.59 1.29 4.46 3.28 2.48 1.96 1.44 1.0 2.78 2.33 1.95 1.66 1.33 4.90 3.59 2.68 2.09 1.50 The TSD provides a similar table for the AML. To determine the appropriate multiplier, we need to know the CV and the desired percentile value for the AML. In addition, we need to know how many samples per month we will require the permittee to collect to determine its monthly average. The more samples in the average, the lower the multiplier and the lower the AML. Does this make sense? Yes. As you collect more samples, the average of those samples should get closer to the mean value of the distribution, which is the LTA. So, as the number of samples that make up the monthly average increases, the ratio of the AML to the LTA (i.e., the multiplier) gets closer to 1.0. These limit calculations assume that when the permittee collects samples, the concentrations will be on the high end of the distribution and the average will move down as more samples are collected. Using the table from the TSD, we set the AML at the 95th percentile. The TSD recommends selecting the 95th percentile for the AML. This approach parallels the process for developing effluent limitations guidelines. We will base our AML calculation on a monitoring frequency of 8 samples per month. In other words, the AML will define the limit for an average of eight samples per month. Assuming a CV of 0.6, what is our multiplier? Our multiplier is 1.38 We multiply the LTA (0.58 mg/L) by 1.38 and get an MDL of 0.8 mg/L. 1.1 2.91 2.45 2.04 1.73 1.36 5.34 3.91 2.90 2.23 1.56 1.2 3.03 2.56 2.13 1.80 1.39 5.76 4.23 3.11 2.37 1.62 1.3 3.13 2.67 2.23 1.87 1.43 6.17 4.55 3.34 2.52 1.68 1.4 3.23 2.77 2.31 1.94 1.47 6.56 4.86 3.56 2.66 1.74 1.5 3.31 2.86 2.40 2.00 1.50 6.93 5.17 3.78 2.81 1.80 1.6 3.38 2.95 2.48 2.07 1.54 7.29 5.47 4.01 2.96 1.87 1.7 3.45 3.03 2.56 2.14 1.57 7.63 5.77 4.23 3.12 1.93 1.8 3.51 3.10 2.64 2.20 1.61 7.95 6.06 4.46 3.28 2.00 1.9 3.56 3.17 2.71 2.27 1.64 8.26 6.34 4.68 3.43 2.07 2.0 3.60 3.23 2.78 2.33 1.68 8.55 6.61 4.90 3.59 2.14 NPDES Permit Writers' Course

4/17/2017 Calculated WQBELs We calculated the following WQBELs: Maximum Daily Limit = 1.8 mg/L Average Monthly Limit = 0.80 mg/L Our maximum daily limit is 1.8 mg/L while our average monthly limit is 0.80 mg/L. NPDES Permit Writers' Course

Recap of WLA to WQBEL Examples
Understand your state’s procedures for calculating WQBELs Not all states follow EPA’s TSD methodology WLAs – are derived directly from water quality criteria Expression - concentration or load Duration - daily, monthly or even annual Both can vary by TMDL Most WQBELs for continuous, non-municipal discharges are expressed as average monthly limits and maximum daily limits So what should we take away from these examples? First, know and follow your state’s procedures for calculating WQBELS, they may or may not follow EPA’s TSD methodology. It’s important to understand how your agency’s procedures work so that the WLAs from TMDLs can be implemented into NPDES permits. Also, remember that WLAs are derived directly from water quality criteria and their expression, such as a concentration or load, and their duration, whether daily, monthly or even annual, can vary by TMDL. However, NPDES regulations require that most WQBELs for continuous non-municipal discharges are expressed as average monthly limits and maximum daily limits. It’s important to understand how you need to get from here to there as far as taking a WLA and developing a WQBEL that satisfies state and federal regulations. And, once again, permit writers and TMDL developers need to communicate to ensure WLAs from TMDLs can be implemented into NPDES permits.

What challenges arise when implementing WLAs from TMDLs in an NPDES permit?
That seems straightforward enough, but things are not always as straightforward as they seem. When implementing WLAs from a TMDL in an NPDES permit, there are situations that present some interesting challenges to permit writers and opportunities for collaboration between TMDL developers and permit writers.

NPDES Effluent Limitations and TMDLs: Implementation Challenges
Different WLAs for the same point source Seasonal or annual WLAs Varying discharge and receiving water flows WLAs in general permits New and expanding discharges Our first implementation challenge occurs when we have different wasteload allocations that apply to the same point source for the same pollutant. Let’s see how this might happen.

Different WLAs for the Same Point Source
Calculating WQBELs Different WLAs for the Same Point Source Widgets-R-Us Nonpoint Source ABC, Inc. WLA? Receiving Water Smalltown POTW Nonpoint Source Here is the example of a watershed with multiple point and nonpoint sources that we considered previously. Recall that we were considering how a wasteload allocation is established for ABC, Inc., assuming that it is discharging the pollutant of concern. And remember that ABC, Inc. is upstream of the waterbody of concern. If we develop a TMDL to ensure that the water quality criteria for the pollutant of concern are attained in this downstream waterbody, the permit writer should have a wasteload allocation for ABC, Inc. But, is that the only wasteload allocation? What if ABC, Inc. discharges into a receiving water that also has water quality criteria for the pollutant of concern? If the permit writer determines that the discharge of that pollutant from ABC, Inc. has the reasonable potential to cause, or contribute to, an excursion above that criterion in the receiving water, a facility-specific WLA will likely be determined. Acme Gadgets Water body of Concern NPDES Permit Writers' Workshop: Module 6

Different WLAs for the Same Point Source (continued)
WQBELs must be derived from and comply with ALL applicable water quality standards 40 CFR (d)(1) vii) When developing water quality-based effluent limits under this paragraph the permitting authority shall ensure that: The level of water quality to be achieved by limits on point sources established under this paragraph is derived from and complies with all applicable water quality standards The regulations require that permits limits include effluent limits that are derived from and comply with all applicable water quality standards. So, the water quality-based effluent limitations developed for ABC, Inc. must meet water quality standards in both the immediate receiving water and the downstream water body for which the TMDL was calculated. That might mean that the facility is subject to effluent limits more stringent than or in addition to the limits derived from the TMDL wasteload allocation to protect the immediate receiving water for the discharge.

Different WLAs for the same point source Seasonal or annual WLAs Varying discharge and receiving water flows WLAs in general permits New and expanding discharges Another challenge comes when TMDLs include seasonal or annual wasteload allocations. For many TMDL pollutants, such as nutrients and sediment, primary threats to achieving water quality standards can depend on cumulative load. In addition, the accuracy of pollutant loading estimates for these parameters generally increases as the length of the calculation period increases. Establishing longer-term allocations and implementing and tracking control of such pollutants over a longer period of time are appropriate given the chronic nature of the pollutant loading and resulting impairments. For these reasons, many approved TMDLs have been expressed as maximum monthly, seasonal, or annual loads in addition to daily loads. Let’s take a look at why this presents an implementation challenge for permit writers.

Seasonal or Annual WLAs
Continuous discharges 40 CFR (d) requires average monthly and average weekly or maximum daily limits as the norm Use TSD procedures (modified as appropriate) to calculate effluent limits from WLAs < 30 days duration EPA has made exceptions where WLAs are longer-term “Chesapeake Bay Annual Nutrient Limits Memorandum” The first concern is regulatory in nature, and it applies to continuous discharges, such as municipal wastewater treatment plants and many industrial discharges. The regulations require that, as a norm, effluent limits for continuous discharges be expressed as average monthly and average weekly or maximum daily limits. This requirement presents a challenge when implementing seasonal or annual wasteload allocations. As we discussed earlier, the procedures from the Technical Support Document for Water Quality-based Toxics Control for calculating water quality-based effluent limitations are designed to implement water quality criteria and wasteload allocations with a monthly or shorter averaging period. However, the regulation does provide some flexibility. It requires average monthly and average weekly or maximum daily effluent limits unless expressing limits in those averaging periods is “impracticable.” In a 2004 memorandum on nutrient limits in the Chesapeake Bay watershed, EPA supported using annual effluent limitations to meet nutrient-related criteria in the Chesapeake Bay and its tidal tributaries. EPA acknowledged that it is impracticable to express effluent limitations for nitrogen and phosphorus discharges in the Bay watershed developed to address nutrient criteria in terms of average monthly, average weekly, or maximum daily limitations because of a number of issues. One of the critical issues identified was that EPA and states were developing wasteload allocations for point source discharges to the Bay and its tributaries expressed as annual loads to achieve water quality standards for the Chesapeake Bay.

Seasonal or Annual WLAs (continued)
Annual or seasonal WLAs could be implemented as effluent limits Annual or seasonal loading requirement Annual or seasonal average concentration Supplement with limits or milestones that have shorter averaging periods as appropriate See Draft Options for Expressing Daily Loads in TMDLs (USEPA 2007) Use TSD procedures (modified as appropriate) to calculate effluent limits from WLAs < 30 days duration Where a TMDL includes annual or seasonal wasteload allocations that achieve water quality standards, it could be appropriate to implement wasteload allocations as annual or seasonal limits, either in the form of a total loading or average concentration depending on how the wasteload allocation is expressed. Again, the nature of the pollutant and potential environmental and human impacts need to be taken into consideration when determining if annual or seasonal limits are appropriate. A permit writer should follow their particular State’s policy and guidance in determining the appropriate time periods for effluent limitations.

Seasonal or Annual WLAs (continued)
Non-continuous discharges 40 CFR (e) requires that discharges be particularly described and limited considering, as appropriate Frequency Total mass Maximum rate of discharge of pollutants Prohibition or limitation by mass, concentration, or other measure Finally, it is worth noting that for non-continuous discharges, such as batch discharges or wet-weather discharges, the regulations provide flexibility and allow an appropriate expression of effluent limits that is source-specific. The discharge should be specifically described and limited considering, as appropriate, frequency of discharge, total mass discharge, maximum rate of discharge of pollutants during the discharge, and prohibition or limitation by mass, concentration, or some other measure.

Different WLAs for the same point source Seasonal or annual WLAs Varying discharge and receiving water flows WLAs in general permits New and expanding discharges Wet weather discharges, such as municipal and industrial stormwater, present several unique challenges when incorporating TMDL requirements in NPDES permits. A number of these challenges are addressed in the third module of this series of Web presentations on the TMDL and NPDES programs. In this module, however, we will consider discharges that might occur during both wet and dry weather and how to implement TMDLs that assign different allocations to these sources under different effluent or receiving water flow conditions.

Varying Discharge and Receiving Water Flows
Tiered limits common in NPDES permits Limits can be tiered based on: Changes in effluent flow (e.g., +/- 20%) Changes in receiving water flow (summer vs. winter; storm event vs. dry weather) TMDL and the permit should clearly state conditions for moving between tiers Pollutant and flow measurement and reporting essential Tiered limitations are not uncommon in NPDES permits. Technology-based effluent limitations derived from production-based effluent guidelines may be tiered to account for seasonal changes in production or anticipated growth or decline in production. For example, a food processor might switch production processes between the summer and fall and, therefore, would have effluent limits based on different effluent guideline requirements for each season. Or, a facility might anticipate that, during the course of its five-year permit term, it will increase production by 50 percent. That increase in production would lead to an increase in limits calculated from production-based effluent guidelines. Multiple limits could be included in the facilities permits, with the higher limits triggered by a specified percent increase in production. Similarly, where a TMDL accounts for changes in effluent or receiving water flow due to process changes or changes in climatic conditions, NPDES permits can account for the changes through tiered limits. For example, allocations and, therefore, effluent limits could be tiered to account for changes in effluent flow of 20 percent or more, which would be consistent with EPA’s recommendations for changes in production levels that could be used to trigger tiered limits. In addition, wasteload allocations and effluent limits could vary seasonally or when receiving water conditions are above or below a specified flow, such as the 7Q10 low flow. The important thing for TMDL developers and permit writers to remember is that where varying allocations are assigned under varying flow conditions and effluent limits are written to meet the different flow regimes, both the TMDL and the permit should clearly state the conditions under which the different “tiers” apply. In addition, the permit should include requirements to measure and report not only pollutant concentrations or loads, but also effluent or receiving water flows, as appropriate, in order to demonstrate that conditions for moving to another tier have been met. In addition, TMDL developers should be aware of the wastewater treatment technology being utilized where “tiered” WLAs apply. Biological treatment systems typically are not able to respond rapidly to frequently changing WLAs. It is very important that TMDLs and NPDES permits clearly state the conditions under which different “tiers” apply.

Different WLAs for the same point source Seasonal or annual WLAs Varying discharge and receiving water flows WLAs in general permits New and expanding discharges The next challenge we want to think about is how to address wasteload allocations in general permits. General permits are used to cover a variety of point source categories, including many stormwater and other wet weather point sources. General permits can cover sources within a watershed, an entire state, or sometimes multiple states. Implementing TMDLs and wasteload allocations designed to achieve water quality standards for a specific water body is a challenge when writing general permits.

WLAs in General Permits
Depending on the geographic coverage and nature of the sources, options include: Require facilities with WLAs to obtain individual permits Apply a consistent set of requirements to all sources demonstrated to meet the WLA Categorical WLAs Best management practices or numeric requirements Include some requirements that apply to all sources and individual requirements to implement WLA “Hybrid” permitting approach Example: EPA Region 10 general permit for some aquaculture facilities in Idaho In some cases, the locations of sources are so widespread and the potentially applicable TMDLs and wasteload allocations are just too numerous to accommodate within a single general permit. The permit writer might have to include in the “Applicability” section of the general permit a condition stating that any source that has been assigned a wasteload allocation as part of an approved TMDL must apply for an individual permit. On the other hand, some wasteload allocations can be more readily translated into effluent limits that could be used to control multiple sources within the same category and covered under a general permit. Some TMDLs assign categorical wasteload allocations to a group of stormwater discharges. These wasteload allocations might be translated into “across the board” pollutant reduction targets or into best management practice requirements that could be applied to all sources in a particular category along with numeric targets that assess progress toward meeting the wasteload allocation. More details on these types of wasteload allocations and permit requirements are presented in the third module of this series. Finally, in some cases, it might be possible for a general permit to include requirements that apply to all sources that might seek coverage under the permit and also include requirements, based on a TMDL, that apply only to certain sources specified in the permit. In a sense, this is a hybrid of the general and individual permitting approaches. EPA Region 10 has used this approach in issuing its general permit for Idaho cold water and warm water aquaculture facilities (also known as concentrated aquatic animal production facilities) that have been provided wasteload allocations in a TMDL approved by EPA as of the effective date of the permit. This permit even incorporates seasonal effluent limits and provisions to allow water quality trading.

Different WLAs for the same point source Seasonal or annual WLAs Varying discharge and receiving water flows WLAs in general permits New and expanding discharges Finally, we will look at the challenges presented by addressing implementation of TMDLs in permits for new and expanding discharges.

New and Expanding Discharges:
Existing TMDLs: Reserve capacity Trading TMDL revision Pre TMDL: Criteria end-of-pipe No discharge How a permit writer addresses new and expanding discharges in impaired waters depends on whether there is an existing TMDL or if a TMDL has not yet been developed and approved. In both cases, there are options that may be available dependent on the policies and guidance for each particular state. Permit writers are urged to follow their state’s policy and work with their EPA Regional Office in determining how to permit these types of dischargers.

TMDLs and Permit Components
NPDES Permit Types, Coverage, and Emerging Program Areas 4/17/2017 TMDLs and Permit Components Components of All Permits Industry-Specific Components Municipal-Specific Components Cover Page Effluent Limitations Effluent Guidelines Case by Case Limitations Technology-based Secondary Equivalent to Secondary Water Quality-based Monitoring and Reporting Special Conditions Before we wrap up this presentation, let’s take a quick look at some of the other components that might be affected by implementing TMDL requirements in an NPDES permit. Additional Monitoring / Special Studies Pretreatment Municipal Sewage Sludge CSOs Best Management Practices Compliance Schedules Standard Conditions NPDES Permit Writers' Course: Module 3

Monitoring and Reporting
Effluent monitoring frequency based on type of limits Compliance with numeric limits Assess effectiveness of BMPs Interim monitoring and reporting where limits are seasonal or annual Monitoring and reporting to implement tiered limits (e.g., effluent and receiving water flow) Self-monitoring and reporting requirements are included in almost all NPDES permits. In effect, we require monitoring of pollutants limited in the permit so that the permittee can demonstrate compliance with its limits. Hopefully, that’s the case; however, if the monitoring demonstrates noncompliance, then the data can be used as the basis for an enforcement action. In addition to compliance assessment, monitoring may also serve to provide data for the permitting authority or the public regarding treatment efficiency and to more accurately characterize effluents during the permit reissuance process. Reports of self-monitoring results on special forms called “Discharge Monitoring Reports” are used to establish compliance or non-compliance with effluent limitations. For permits where best management practices might be used to implement wasteload allocations from a TMDL, the results of self-monitoring can be used to assess the effectiveness of BMPs in attaining the required wasteload allocations. In addition, we mentioned previously that permit writers should include interim monitoring and reporting, for example, monthly, where a permit contains annual or seasonal effluent limits derived from annual or seasonal wasteload allocations. Interim monitoring allows both the permittee and the permitting authority to assess whether or not the permittee is likely to meet the longer-term requirement. Also, we previously mentioned the possible need for monitoring and reporting changes in effluent and receiving water flow if a permit includes tiered limits to implement TMDL requirements that apply under varying flow conditions.

Special Conditions Additional monitoring Best management practices
Studies to support future TMDL development or revision Monitoring to demonstrate WQ standards attainment Best management practices Implement WLAs for some sources Must be consistent with the assumptions and requirements of the WLA Compliance schedules Gives the permittee time to comply with a final WQBEL Final limits must be derived from and comply with water quality standards Interim milestones required if compliance schedule exceeds one year Site-specific special conditions are used in a permit to address issues that are not readily addressed through numeric effluent limitations and routine self-monitoring to demonstrate compliance. We refer to the types of special conditions applicable to all types of dischargers, both industrial and municipal, as the “ABCs” of special conditions. “A,” additional monitoring, or sometimes special studies. They could be used to require monitoring that would support future TMDL development or revision, such as dilution and mixing modeling, ambient pollutant monitoring, and biomonitoring, to name a few examples. Special ambient monitoring requirements might be included in permits to help assess whether assumptions of the TMDL are correct and whether allocations in the TMDL are sufficient to achieve water quality standards. Speaking of best management practices, they are the “B” in our ABCs. We already mentioned the fact that BMPs might be used in some permits to implement wasteload allocations from a TMDL, as long as those BMPs are consistent with the assumptions and requirements of the wasteload allocations. Finally, the “C.” This stands for compliance schedules. In a permit, a compliance schedule gives the permittee time to come into compliance with a final water quality-based effluent limit, including water quality-based effluent limits derived from TMDL wasteload allocations. The final limit must appear in the permit along with interim milestones if the compliance schedule exceeds one year. If a TMDL recommends specific monitoring or BMPs that should be implemented in NPDES permits, those requirements should be clearly stated within the TMDL. Permit writers and TMDL developers are encouraged to collaborate in developing those requirements.

Module 10: Standard Conditions of NPDES Permits
40 CFR —Conditions applicable to all permits 40 CFR —Additional conditions applicable to specified categories of NPDES permits States, tribes, or territories might have more stringent requirements For TMDL implementation, some important standard conditions include: Property rights [122.41(g)] Duty to provide information [122.41(h)] Permit transfers [122.41(l)(3)] Standard conditions establish the legal basis of the permit. They also include certain provisions that EPA wants in all permits to ensure consistency. The federal regulations are very clear that these conditions must be in every permit, and this requirement applies to state-issued permits as well as EPA-issued NPDES permits, though states may modify the standard conditions to make them more stringent. A few important standard conditions that might impact TMDL implementation include: Property rights, which indicates that the permit does not convey any property rights of any sort or any exclusive privilege. Thus, implementation of a wasteload allocation in an NPDES permit does not mean that the wasteload allocation becomes the permittee’s “property.” Duty to provide information, which indicates that the permittee must furnish, within a reasonable time, any information needed to determine compliance with the permit or to determine whether there is cause to modify, revoke and reissue, or terminate the permit. The permittee also must furnish, on request, copies of records that must be kept as required by the permit. This provision could be important if a regulatory authority needs information from the permittee to determine whether the wasteload allocations assigned under a TMDL are adequate to achieve attainment of water quality standards or whether the wasteload allocations and, therefore, the effluent limits in the permit, should be modified. Last but not least, permit transfers can occur after proper notice is provided to the regulatory authority. The standard condition in (l)(3) notes that the regulatory authority may require modification or revocation and reissuance of the permit to change the name and incorporate other requirements as might be necessary under the Clean Water Act. This provision would give the regulatory authority an opportunity, if it so desired, to reconsider the wasteload allocation assigned to the facility at the time of the transfer. For facilities discharging to impaired waters with WLAs assigned to them, the permit writer should contact the TMDL developers informing them of the permit transfer. Instructors’ Manual

When the Job is “Finished”
Permit modifications [40 CFR ] New information Reopener Anti-backsliding See Chapter 7 of the U.S. Environmental Protection Agency NPDES Permit Writers’ Manual (2010) Wow. That’s a lot of information and those are a lot of considerations that go into implementing TMDLs and wasteload allocations in NPDES permits. When that process is complete, can a permit writer take it easy? Well, not exactly. If new information becomes available that was not available at the time of permit issuance and this information would have justified different permit conditions at that time, this new information might be sufficient cause under 40 CFR to modify or revoke and reissue the permit with different effluent limitations. Any changes to limits that were derived from a wasteload allocation from a TMDL must remain consistent with the assumptions and requirements of that wasteload allocation. The permitting authority would need to demonstrate this consistency in the permit record when making the modification. Another possible reason for permit modification might be the completion of a TMDL during the permit term. Often, permits will include a specific reopener that puts the permittee “on notice” that completion of a TMDL would constitute a basis for modifying the permit to implement the requirements of that TMDL. One final note, any permit changes would need to meet all of the anti-backsliding requirements of the Clean Water Act and NPDES regulations. Briefly, effluent limits in reissued permits need to be as stringent as in previous permits unless specific conditions are met. We don’t have time to discuss anti-backsliding in this presentation, but you can see Chapter 7 of the NPDES Permit Writers’ Manual if you want to know more about how these provisions are implemented in permits.

Tips for a TMDL Practitioner Involved in the NPDES Permitting Process
Consult with permitting staff on available data and information for different steps in TMDL development Source Identification Specific WLAs Understand how WLAs are traditionally translated into permit limits within your State Discuss assumptions made in developing the TMDL (assume constant loadings throughout the year, assume seasonal loading, etc.) Review the NPDES permit development schedule So what can we take away from this module? Here are some tips for TMDL developers who are involved in the NPDES permitting process First, a great deal of data and information on point source dischargers are collected as part of the NPDES permitting program. Historical effluent data, influent waste stream information, descriptions of wastewater treatment systems, and ambient receiving water data can be contained in the permit files. In addition, more and more States are collecting data electronically which makes utilizing these data and information easier than ever. Analyzing permit files and communicating with permit writers will also allow you to understand how WLAs are translated into water quality-based effluent limits within your State. If a TMDL is being developed for a particular water body or stream segment, it is also a good idea to talk about the NPDES permit development schedule for any point source dischargers to the impaired waterbody. If there are permits coming up for reissuance or perhaps a permit application for a new discharger has been received, effective dialogue between the TMDL and permitting groups can result in more effective TMDLs and NPDES permits.

Tips for a TMDL Practitioner Involved in the NPDES Permitting Process –cont-
Talk with NPDES permit writers concerning the types of information that could be in a TMDL that would be helpful in developing permit limits and conditions Monitoring requirements Specific BMPs Take into account facilities’ treatment processes in developing tiered or variable WLAs in a TMDL Biological treatment systems take time to reach steady state conditions Be clear in describing when different tiers or requirements apply Permitting and TMDL staff should work together throughout the TMDL development and NPDES permitting processes This communication can also lead to the inclusion of certain information or requirements that would be helpful to permit writers in developing effluent limits and conditions. These could include specific BMPs for the discharger or monitoring requirements. Finally, permit writers and TMDL developers can ensure that there is clarity in TMDLs and permits when tiered limits apply. The key is that effective communication among both groups can lead to greater environmental protection.

Resources Federal Statutes and Regulations Government Printing Office (GPO): U.S. Code Code of Federal Regulations Federal Register National Pollutant Discharge Elimination System (NPDES) EPA NPDES Training EPA NPDES Permit Writers’ Manual EPA NPDES Outreach EPA NPDES Regulations EPA NPDES Permit Program Basics EPA NPDES Water Permitting 101 This slide provides a list of resources related to the information presented in this module. Most of the resources are available at EPA’s NPDES permitting web page at Now it is time to take a brief quiz based on the information we’ve discussed.

Permit module

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