Water: Total Maximum Daily Loads (303d)
Draft Guidance for Water Quality-based Decisions: The TMDL Process (Second Edition), EPA-841-D-99-001, August 1999
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This document provides guidance to States, Territories and authorized Tribes exercising responsibility under section 303(d) of the Clean Water Act concerning the development of lists of waterbodies not meeting water quality standards and TMDLs for such waterbodies. It also provides guidance to the public and the regulated community on how EPA intends to exercise its discretion in implementing section 303(d) and its regulations regarding lists of impaired waterbodies and TMDLs. The guidance is designed to implement national policy on these issues. The document does not, however, substitute for section 303(d) of the Clean Water Act or EPA's regulations; nor is it a regulation itself. Thus, it does not impose legally-binding requirements on EPA, States, Territories, authorized Tribes or the regulated community, and may not apply to a particular situation based upon the circumstances. EPA and State, Territorial and authorized Tribal decisionmakers retain the discretion to adopt approaches on a case-by-case basis that differ from this guidance where appropriate. EPA may change this guidance in the future.
Address/Email for Comments:
EPA solicits comments on the "Draft Guidance for Water Quality-based Decisions: The TMDL Process (Second Edition)." Send written comments on the proposed TMDL Guidance to: TMDL Guidance, U.S. Environmental Protection Agency, Mail Code 4503F, 401 M Street, S.W., Washington, DC 20460. As of August 23, 1999, EPA will also accept comments electronically. Comments should be sent to the following email address at: firstname.lastname@example.org. Electronic comments must be submitted as an ASCII or WordPerfect file avoiding the use of special characters and any form of encryption. No confidential business information (CBI) should be sent via email. EPA requests that commenters submit any references cited in their comments. All comments must be postmarked by October 22, 1999, which ends the 60 day comment period. No facsimiles (faxes) will be accepted.
Please note: In order to provide the public and all stakeholders an adequate period of time to fully analyze the issues and prepare comprehensive comments, we are extending the comment period an additional 90 days for a total comment period of 150 days. The extended comment period deadline is now January 20, 2000. Please send your written comments to the Comment Clerk for the TMDL Program Rule, Water Docket (W-98-31), U.S. Environmental Protection Agency, 401 M Street, S.W., Washington, DC 20460 by January 20, 2000.
Chapter 1. Introduction provides an overview of § 303(d) program activities,the process for identifying impaired or threatened waters, and the proceduresfor establishing total maximum daily loads (TMDLs). The regulatory frameworkand essential definitions are reviewed. Issues associated with interpretingthe regulation and the implications for States, Territories, and authorizedTribes in carrying out the requirements of the § 303(d) program are described.
- The TMDL process
- Answers to frequently asked questions
Chapter 2. Identifying Impaired and Threatened Waterbodies and Setting Priorities for Establishing TMDLs discusses the process by which impaired or threatened waters are identified and listed under § 303(d) of the Clean Water Act (CWA). Included in this chapter are the scope of the listing process (waters that must be included); the contents of the § 303(d) list; the process by which States, Territories, and authorized Tribes can add or remove waters from the list; documentation of methodologies used in the listing process; and priority ranking of impaired or threatened waters and scheduling of TMDL establishment.
- Statutory and regulatory requirements
- The listing process
- The four parts of the § 303(d) list submittal
- How monitoring supports the § 303(d) listing process
- Public participation
- EPA actions
Chapter 3. Establishing and Implementing TMDLs discusses the establishment and implementation of the TMDL. Included in this chapter are factors that must be considered when establishing a TMDL, the components of a TMDL analysis, planning for implementation and monitoring, the required elements of an approvable TMDL submittal, and the implementation process.
- Statutory and regulatory requirements
- The required elements of the TMDL submittal
- The components of the TMDL establishment process
- How monitoring supports the TMDL establishment process
- Public participation
- EPA actions
List of Tables
List of Figures
The objective of the TMDL process is to systematically identify impaired or threatened waterbodies and the pollutant(s) causing the impairment and ultimately establish a scientifically-based strategy-a TMDL-for correcting the impairment or eliminating the threat and restoring the waterbody. A schematic of the listing and TMDL establishment process is shown in Figure 1-1. States, Territories, and authorized Tribes are required to identify and establish a priority ranking for waterbodies not meeting water quality standards. They must then establish a TMDL for each of these waterbodies. The U.S. Environmental Protection Agency (EPA) reviews the list and TMDLs. If the EPA disapproves the list or TMDLs or if the State, Territory, or authorized Tribe fails to establish the list or TMDLs, EPA will list waterbodies and establish TMDLs for them. The TMDL process allows for alternative point and nonpoint source control strategies that provide decision makers with an opportunity to compare the cost-effectiveness and efficiency of different pollutant reduction activities or controls and the social and economic benefits of alternative allocation approaches.
Successful use of the TMDL process to develop an effective strategy to improve water quality requires accurately defining the problem, characterizing the impaired waterbody and all pollutants contributing to the impairment, and understanding the political and economic constraints that affect implementation and acceptance of the TMDL. Establishment of TMDLs rests on the following premises:
- The total pollutant load to a waterbody is derived from point, nonpoint, and background sources.
- Pollutant loads can be transported into a waterbody directly through effluent discharge, bank and bar erosion (in streams, rivers, estuaries, and lakes), recirculation (e.g., nutrients in lakes, estuaries, and wetlands), solar heating, atmospheric deposition, and groundwater flows or indirectly by overland flow caused by snowmelt or precipitation.
- The technical approach used to develop the TMDL will vary according to the nature of the problem, pollutant of concern, type of waterbody, types and number of pollutant sources, and political and economic constraints that affect a specific watershed.
TMDLs are required to consider the effect of processes that contribute pollutants to a waterbody. These processes may relate to thermal changes, critical flow conditions, sedimentation, and riparian and channel processes. Control measures to implement TMDLs, therefore, are not limited to National Pollutant Discharge Elimination System (NPDES) permits, but may also include State, Territorial, Tribal, and local authorities and actions to reduce nonpoint source pollution.
It is necessary to become familiar with several terms used throughout this guidance. These definitions will be discussed in greater detail in later chapters.
- Critical conditions
- The critical condition can be thought of as the "worst case" scenario of environmental conditions in the waterbody in which the loading expressed in the TMDL for the pollutant of concern will continue to meet water quality standards. Critical conditions are the combination of environmental factors (e.g., flow, temperature, etc.) that results in attaining and maintaining the water quality criterion and has an acceptably low frequency of occurrence.
- Impaired waterbody
- Any waterbody of the United States that does not attain water quality standards (designated uses, numeric and narrative criteria and antidegradation requirements defined at 40 CFR 131), due to an individual pollutant, multiple pollutants, pollution, or an unknown cause of impairment. Where a waterbody receives a thermal discharge from one or more point sources, "impaired" means that the waterbody does not have or maintain a balanced indigenous population of shellfish, fish, and wildlife.
- Load allocation
- The portions of a TMDL's maximum allowable pollutant load allocated to nonpoint sources of a pollutant, including atmospheric deposition or natural background sources.
- Margin of safety (MOS)
- A required element of a TMDL that accounts for uncertainty and lack of knowledge. An MOS may be expressed as unallocated assimilative capacity or conservative analytical assumptions used in establishing the TMDL and its maximum allowable pollutant load (e.g., derivation of numeric loads, modeling assumptions, or effectiveness of proposed management actions).
- Dredged spoil, solid waste, incinerator residue, sewage, garbage, sewage sludge, munitions, chemical wastes, biological materials, radioactive materials, heat, wrecked or discarded equipment, rock, sand, cellar dirt, and industrial, municipal, and agricultural waste discharged into water. This term does not mean (A) "sewage from vessels" within the meaning of § 312 of the Clean Water Act or (B) water, gas, or other material that is injected into a well to facilitate production of oil or gas, or water derived in association with oil or gas production and disposed of in a well, if the well used either to facilitate production or for disposal purpose is approved by authority of the State in which the well is located, and if that the State determines that such injection or disposal will not result in the degradation of ground or surface water resources. (See CWA § 502(6).) EPA believes this definition encompasses drinking water contaminants regulated under § 1412 of the Safe Drinking Water Act and may be discharged to waters of the United States that are source waters of one or more public water systems. Source water is any water reaching the intake of a public water system.
- The man-made or man-induced alteration of the chemical, physical, biological, and radiological integrity of water.
- Reasonable assurance
- Reasonable assurance means that you demonstrate that each wasteload allocation and load allocation in a TMDL will be implemented. For point sources regulated under section 402 of the Clean Water Act, you must demonstrate reasonable assurance by procedures that ensure that enforceable NPDES permits (including coverage to individual sources under a general NPDES permit) will be issued expeditiously to implement applicable wasteload allocations for point sources. For nonpoint sources you must demonstrate reasonable assurance by specific procedures and mechanisms that ensure load allocations for nonpoint sources will be implemented for that waterbody. Specific procedures and mechanisms for nonpoint sources must apply to the pollutant for which the TMDL is being established, must be implemented expeditiously, and must be supported by adequate funding. Examples of specific procedures and mechanisms which may provide reasonable assurances for nonpoint sources include State, Territorial, and authorized Tribal regulations, local ordinances, performance bonds, contracts, cost share agreements, memoranda of understanding, site specific voluntary actions, and compliance audits of best management practices.
- Thermal discharge
- The discharge of the pollutant heat from a point source.
- Threatened waterbody
- Any waterbody of the United States that currently attains water quality standards (designated uses, numeric and narrative criteria and antidegradation requirements defined at 40 CFR 131), but for which existing and readily available data and information on adverse declining trends or anticipated load measures indicate that water quality standards will likely be exceeded by the time the next list is required to be submitted to EPA. Where a waterbody is threatened by a thermal discharge, threatened means that the waterbody has a balanced indigenous population of shellfish, fish, and wildlife, but adverse declining trends indicate that a balanced indigenous population of shellfish, fish, and wildlife will not be maintained.
- Total maximum daily load (TMDL)
- TMDLs are written plans and analyses established to ensure that the waterbody will attain and maintain water quality standards (existing uses, designated uses, numeric and narrative criteria and antidegradation requirements defined at 40 CFR 131) including consideration of reasonably foreseeable increases in pollutant loads. TMDLs must be established for waterbodies on Part 1 of your list of impaired and threatened waterbodies and must contain the following ten elements: (1) the name and geographic location of the impaired or threatened waterbody for which the TMDL is being established; (2) identification of the pollutant and quantification of the pollutant load that may be present in the waterbody and still allow attainment and maintenance of water quality standards; (3) identification of the amount or degree by which the pollutant load in the waterbody deviates from the target representing attainment or maintenance of water quality standards; (4) identification of source categories, source subcategories or individual sources of the pollutant for which wasteload and load allocations are being established; (5) wasteload allocations for pollutants from point sources; (6) load allocations for pollutants from nonpoint sources; (7) a margin of safety; (8) consideration of seasonal variation; (9) an allowance for future growth which accounts for reasonably foreseeable increases in pollutant loads; and (10) an implementation plan.
- Wasteload allocation
- The portions of a TMDL's pollutant load allocated to a point source of a pollutant.
- A geographically defined portion of navigable waters, waters of the contiguous zone, and ocean waters under the jurisdiction of the United States, including segments of rivers, streams, lakes, wetlands, coastal waters, and ocean waters.
What is the § 303(d) list?
The § 303(d) list is a list of all impaired or threatened waters within the jurisdiction of a State, Territory, or authorized Tribe. EPA believes that the list required under § 303(d)(1) of the Clean Water Act provides a comprehensive public accounting of all impaired or threatened waterbodies, regardless of the cause or source of the impairment or threat. An impaired waterbody is one that does not attain water quality standards (including designated uses, narrative and numeric criteria, and antidegradation requirements defined at 40 CFR 131), due to an individual pollutant, multiple pollutants, pollution, or an unknown cause of impairment. Where a waterbody receives a thermal discharge from one or more point sources, impaired means that the waterbody does not have or maintain a balanced indigenous population of shellfish, fish, and wildlife. A threatened waterbody is one that currently attains water quality standards but existing and readily available data and information on adverse declining trends indicate that water quality standards will likely be exceeded by the time the next list is required to be submitted to EPA.
States, Territories, and authorized Tribes must list impaired or threatened waterbodies regardless of the source of the impairment. The source of the impairment might be from point sources, nonpoint sources, atmospheric deposition, or a combination of these. Impaired or threatened waterbodies must be listed regardless of whether the pollutant or source of pollution is known.
What is the format of the list?
Part 1: Waterbodies impaired or threatened by a pollutant as defined in 40 CFR 130.2(d).
Part 2: Waterbodies impaired or threatened by pollution as defined by CFR § 130.2(c), but not impaired or threatened by one or more pollutants.
Part 3: Waterbodies for which EPA has approved or established a TMDL for one or more pollutants, but where water quality standards have not yet been attained.
Part 4: Waterbodies that are impaired, but for which implementation of best practicable control technology for point sources and secondary treatment for publicly owned treatment works are expected to result in attainment of water quality standards by the next listing cycle.
The § 303(d) list has four parts. Waterbodies impaired or threatened by pollutants are placed on Part 1 of the list, and a TMDL is required for each waterbody and pollutant combination. Once a TMDL has been established, the waterbody and pollutant combination is moved to Part 3 of the list until water quality standards are attained. Waterbodies impaired or threatened due to pollution are listed on Part 2 of the list. No TMDL is required for these waterbody and pollution combinations. Part 4 of the list consists of waterbody and pollutant combinations for which implementation of best practicable control technology for point sources and secondary treatment for publicly owned treatment works are expected to result in attainment of water quality standards by the next listing cycle. No TMDL is required for these waterbody and pollutant combinations as long as water quality standards are attained before the next listing cycle. Otherwise, the waterbody and pollutant combination must be included on Part 1 unless there is documentation that failing to attain standards is due to failure to comply with applicable technology-based requirements.
How long do waterbodies stay on the list?
Once a waterbody has been identified as impaired or threatened by a specific pollutant and placed on the § 303(d)(1) list, that waterbody and pollutant combination must remain on the list until water quality standards are attained. It does not matter whether a waterbody has been assigned to Part 1, 2, 3, or 4 of the list. All impaired or threatened waterbodies on the list must remain on the list until new data and information indicate that the waterbody has attained water quality standards and is no longer impaired or is no longer threatened.
What type of information is used to generate the list of impaired or threatened waters?
EPA regulations require that States, Territories, and authorized Tribes assemble all existing and readily available data and information to develop a list of impaired or threatened waterbodies (40 CFR 130.22). EPA regulations also explain that existing and readily available data must include, but is not limited to the data and information included in the following:
- Most recent EPA-approved § 303(d) list.
- Most recent § 305(b) report.
- CWA § 319 nonpoint source assessments.
- Drinking water source water assessments under § 1453 of the Safe Drinking Water Act, where the assessment results demonstrate for one or more pollutants regulated as drinking water contaminants under § 1412 that either a water quality standard has been exceeded, or is at risk of being exceeded, or the concentration of a pollutant has increased since use of the waterbody as a public water supply began.
- Dilution calculations, trend analyses, or predictive models for determining the physical, chemical, or biological integrity of streams, rivers, lakes, and estuaries.
- Data, information, and water quality problems reported by local, State, Territorial, or Federal agencies, Tribal governments, members of the public, and academic institutions.
Existing and readily available data and information includes both monitored data and evaluated data and information. Although it is usually preferable to base listing decisions on monitored data, there are situations where the decision may be based solely or primarily on evaluated data and information. In these cases, there must be assurances that the evaluated data and information are reliable and are in accordance with applicable data collection and/or quality assurance/quality control (QA/QC) program requirements.
What is a TMDL?
TMDLs are written plans and analyses established to ensure that the waterbody will attain and maintain water quality standards (designated uses, numeric and narrative criteria and antidegradation requirements defined at 40 CFR 131) including consideration of reasonably foreseeable increases in pollutant loads. TMDLs must be established for waterbodies on Part 1 of the list of impaired or threatened waterbodies.
The total maximum daily load (TMDL) process is an essential element of the water quality-based approach to watershed management. It links the development and implementation of control measures to attainment of water quality standards. Through the establishment and implementation of a TMDL, pollutant loadings from all sources are estimated; links are established between pollutants, sources, and impacts on water quality; allowable pollutant loads can be allocated to each source; and appropriate control mechanisms can be established or modified so that water quality standards can be achieved.
Within each TMDL is a carefully identified allowable pollutant load. This pollutant load is the amount of a pollutant that may be contributed to a waterbody and still allow that waterbody to attain and maintain water quality standards. The allowable pollutant load is equivalent to the sum of wasteload allocations for point sources, load allocations for nonpoint sources, a margin of safety sufficient to account for uncertainty and lack of knowledge, and allowances for future growth.
What are the required elements of a TMDL submittal?
Ten discrete elements are required as part of a TMDL submittal:
- The name and geographic location of the impaired or threatened waterbody for which the TMDL is being established, as well as the geographic location of upstream waterbodies that contribute the pollutant for which the TMDL is being established (40 CFR 130.33(b)(1)).
- Identification of the pollutant for which the TMDL is being established and quantification of the target load of the pollutant that may be present in the waterbody and still ensure attainment and maintenance of water quality standards (designated uses, numeric and narrative criteria and antidegradation requirements defined at 40 CFR 131) (40 CFR 130.33(b)(2)).
- Identification of the amount or degree by which the current pollutant load in the waterbody deviates from the target representing attainment or maintenance of water quality standards (designated uses, numeric and narrative criteria and antidegradation requirements defined at 40 CFR 131) (40 CFR 130.33(b)(3)).
- Identification of the source categories, source subcategories, or individual sources of the pollutant for which the wasteload allocations and load allocations are being established consistent with 40 CFR 130.2(f) and 130.2(g) (40 CFR 130.33(b)(4)).
- Wasteload allocations to each industrial and municipal point source permitted under §402 of the Clean Water Act discharging the pollutant for which the TMDL is being established ; wasteload allocations for storm water, combined sewer overflows, abandoned mines, combined animal feeding operations, or any other discharges subject to a general permit may be allocated to categories of sources, subcategories of sources or individual sources; pollutant loads that do not need to be allocated to attain or maintain water quality standards (minor or remotely located) may be included within a category of sources, subcategory of sources or considered as part of background loads; and supporting technical analyses demonstrating that wasteload allocations when implemented, will attain and maintain water quality standards (40 CFR 130.33(b)(5)).
- Load allocations, ranging from reasonably accurate estimates to gross allotments, to nonpoint sources of a pollutant, including atmospheric deposition or natural background sources; if possible, a separate load allocation should be allocated to each source of a pollutant, where this is not possible, load allocations may be allocated to categories of sources, subcategories of sources; pollutant loads that do not need to be allocated (minor or remotely located) may be included within a category of sources, subcategory of sources or considered as part of background loads; and supporting technical analyses demonstrating that load allocations, when implemented, will attain and maintain water quality standards (40 CFR 130.33(b)(6))
- A margin of safety expressed as unallocated assimilative capacity or conservative analytical assumptions used in establishing the TMDL; e.g., derivation of numeric targets, modeling assumptions, or effectiveness of proposed management actions which ensures attainment and maintenance of water quality standards for the allocated pollutant (40 CFR 130.32(b)(7)).
- Consideration of seasonal variation such that water quality standards will be met for the allocated pollutant during all seasons of the year (40 CFR 130.33(b)(8)).
- An allowance for future growth which accounts for reasonably foreseeable increases in pollutant loads (40 CFR 130.33(b)(9)).
- An implementation plan, which may be developed for one or a group of TMDLs (40 CFR 130.33(b)(10)).
As part of each TMDL, States, Territories, and authorized Tribes are also required to submit a summary of all public comments on the TMDL and responses to those comments. Responses must indicate whether the agency agreed or disagreed with each comment and why, as well as how comments were considered in the final decision (40 CFR 130.37(b)). States, Territories, and authorized Tribes should include a cover/submittal letter when submitting a TMDL to EPA for approval.
For what types of impairments are TMDLs established?
TMDLs are established for impairments or threats to a waterbody caused by identifiable pollutants, as defined by the CWA. TMDLs are not established for impairments or threats to a waterbody that are caused by pollution only (no identifiable pollutant). If it is unknown whether the cause of impairment is a pollutant or some type of pollution, EPA expects the waterbody to be included on Part 1 of the § 303(d) list and the pollutant(s) to be identified when TMDL establishment is initiated.
Are TMDLs established for specific pollutants?
TMDLs are established for the specific waterbody and pollutant combinations that States, Territories, and authorized Tribes identify on Part 1 of their § 303(d) lists. Separate TMDLs are required for each waterbody and pollutant combination, although States, Territories, and authorized Tribes are encouraged to establish TMDLs for multiple waterbodies within the same watershed in a coordinated manner.
TMDLs can also be established by using an appropriate surrogate for a broader type of impairment on a specific waterbody. The key is to frame the problem in a way that ties all aspects of TMDL establishment back to the pollutant and waterbody of concern. For example, acceptable surrogate targets for a TMDL that is developed to address violation of temperature criteria might be increasing the percent of stream cover or improving the channel morphology (e.g., establishing a smaller width-depth ratio and a more stable meander pattern). However, to be an acceptable surrogate indicator for the TMDL, a quantitative relationship between the surrogate indicator and the pollutant (in this case heat) must be established. This might require a detailed explanation about how stream cover or width-depth ratio is related to temperature. For example, streams that have a larger width-depth ratio tend to be shallow and wide, exposing more water volume to solar heating than streams that are deeper and narrower, supporting analysis and documentation justifying this approach is required..
At what geographic scale are TMDLs established?
There are no fixed rules regarding the appropriate size or scale of a TMDL. The geographic scale will vary considerably with the scope of the problem to be addressed and the location of sources that contribute to the problem. TMDLs may vary in scale from the entire basin to the watershed of small headwater streams to individual stream segments contaminated by a particular pollutant discharged by a limited number of sources. A TMDL might be too large if its size and complexity preclude meaningful monitoring, evaluation, and implementation. By contrast, a TMDL might be too small if its geographic scale is defined so narrowly that the entire problem area is not included in the analysis, and in particular if all sources contributing to the problem are not identified and addressed.
TMDLs can be developed for waterbodies of various sizes ranging from single stream reaches to whole basins well over 1,000 square miles in size. The geographic scale of the TMDL is primarily a function of
- Specific impairment or threat to designated use(s)
- Type of waterbody that is impaired
- Spatial distribution of use impairments
- Pollutant source locations
- Scale of similar assessment and planning efforts under way for the waterbody
Where impairments occur throughout a watershed, it is recommended that the analysis be conducted for smaller, more homogenous analytical units (subwatersheds). For example, specific impaired river reaches might require detailed TMDLs to address individual sources. If this subwatershed approach is chosen, care should be taken to apply consistent methodologies within a basin from one subwatershed to the next so that an additive approach can eventually be applied to the larger basin.
How long do you have to establish all required TMDLs?
TMDLs for high-priority waterbody and pollutant combinations should be completed prior to completion of medium- and low-priority waterbody and pollutant combinations on Part 1 of the § 303(d) list (40 CFR 130.31(1)). TMDLs for all waterbody and pollutant combinations must be completed no later than 15 years after their initial placement on Part 1 of the § 303(d) list (40 CFR 130.31(2)). EPA expects States, Territories, and authorized Tribes to schedule establishment of TMDLs in a manner that will ensure the workload is reasonably distributed over the entire duration of the schedule (40 CFR 130.31(3)).
How can stakeholders and the interested public be involved and contribute to the § 303(d) listing and TMDL establishment process?
Public participation is a required component of the TMDL process and is often vital to a TMDL's success. Stakeholders can contribute credible, useful data and information about impaired or threatened waterbodies. They can also contribute more than their approval or disapproval for a specific TMDL. They might be able to raise funds for monitoring or to implement a specific control measure. More importantly, stakeholders can offer insights about their community that might ensure the success of one TMDL allocation strategy where an alternative strategy might fail, as well as the success of follow-up monitoring and evaluation activities.
Why is implementation essential to the successful TMDL?
To be effective in improving water quality, a TMDL must be more than an estimation of necessary pollutant reductions; it must be implemented. Therefore, every approved TMDL must include an implementation plan that explains the techniques that will be used to meet the load reductions identified. The plan also provides the mechanism for tracking the implementation of management measures and point source controls and monitoring the various relevant indicators of water quality conditions. Evaluation of the milestones identified in the implementation plan can be used to determine whether progress is being made toward meeting water quality standards.