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Water: Total Maximum Daily Loads (303d)

Chapter 1 - Introduction And Executive Summary


Guidance for Water Quality-Based Decisions:
The TMDL Process

Purpose and Summary

The purpose of this guidance document is to explain the programmatic elements and requirements of the TMDL process as established by section 303(d) of the Clean Water Act and by EPA's Water Quality Planning and Management Regulations (40 CFR Part 130). A TMDL, or total maximum daily load, is a tool for implementing State water quality standards and is based on the relationship between pollution sources and in-stream water quality conditions. The TMDL establishes the allowable loadings or other quantifiable parameters for a waterbody and thereby provides the basis for States to establish water quality-based controls. These controls should provide the pollution reduction necessary for a waterbody to meet water quality standards.

Section 303(d) of the Act establishes the TMDL process to provide for more stringent water quality-based controls when technology-based controls are inadequate to achieve State water quality standards. When implemented according to this guidance, the TMDL process can broaden the opportunity for public participation, expedite water quality-based National Pollutant Discharge Elimination System (NPDES) permitting, and lead to technically sound and legally defensible decisions for attaining and maintaining water quality standards. In addition, the TMDL process provides a mechanism for integrating the management of both the point and nonpoint pollution sources that together may contribute to a waterbody's impairment.

Chapter Two of this guidance document provides a description of the TMDL process in the context of the water quality-based approach to pollution reductions. This approach includes the identification and priority ranking of water quality-limited waters, the targeting and scheduling of high priority waters, the development of TMDLs, and the implementation of control actions that should result in the attainment of water quality standards. Assessment for water quality standards attainment provides the information needed to identify water quality-limited waters and for the evaluation of the TMDL and control actions.

The development and implementation of the TMDL establishes the link between water quality standards assessment and water quality-based control actions. The third chapter of this document describes how a State should proceed with developing TMDLs once waters are targeted for action and then how to implement them. Special consideration is given to such issues as adequacy of data and information, how to consider nonpoint source contributions, and when to use a modified approach, called the phased approach, that results in a TMDL with special requirements. Implementation of the TMDL is discussed in terms of the mechanisms that are available to reduce both point and nonpoint loads.

The final chapter of this guidance describes the specific roles and responsibilities that the States and EPA have in implementing CWA section 303(d). EPA review and approval of lists of waters submitted by the States, the priority rankings of these waters, and the TMDLs are set forth in the Water Quality Planning and Management Regulation. This guidance presents a detailed discussion of the submission of lists and TMDLs, and the review and approval processes. The States' responsibility to involve the public in the TMDL process is also highlighted in this chapter. The value and importance of public participation is also emphasized throughout the document.

This guidance focuses on the programmatic aspects rather than the technical issues of the TMDL process. Numerous technical guidance manuals have been developed by EPA to assist States in calculating wasteload allocations (WLA). A list of these manuals can be found in Appendix A along with a description of other relevant guidance documents. A brief description of selected technical considerations can be found in Appendix D and information about EPA supported models can be found in Appendix E. The other appendices provide the reader with useful and relevant information such as descriptions of related water quality programs (Appendix B) and a general outline of an EPA/State agreement for TMDL development (Appendix F).

Policies and Principles

To achieve the water quality goals of the Clean Water Act, EPA's first objective is to ensure that technology-based controls on point sources are established and maintained. Where such controls are insufficient to attain and maintain water quality standards, water quality-based controls are required. Under the authority of section 303(d) of the Clean Water Act, EPA expects States to develop TMDLs for their water quality-limited waters where technology-based effluent limitations or other legally required pollution control mechanisms are not sufficient or stringent enough to implement the water quality standards applicable to such waters.

More intensive assessments of water quality and an evaluation of pollution sources should be conducted where water quality standard violations occur or where indications of declining water quality or habitat loss are observed. A TMDL should be developed and appropriate control actions taken on all pollution sources and follow-up monitoring should be conducted to assure that water quality standards are met. If follow-up monitoring indicates that water quality standards are not or will not be met, a revised TMDL is required.

Lack of information about certain types of pollution problems (for example, those associated with nonpoint sources or with certain toxic pollutants) should not be used as a reason to delay implementation of water quality-based controls. When developed according to a phased approach, the TMDL can be used to establish load reductions where there is impairment due to nonpoint sources or where there is a lack of data or adequate modeling. EPA regulations provide that load allocations for nonpoint sources may be based on "gross allotments" (40 CFR 130.2(g)) depending on the availability of data and appropriate techniques for predicting loads. In addition, before approving a TMDL in which some of the load reductions are allocated to nonpoint sources in lieu of additional load reductions allocated to point sources, there must be specific assurances that the nonpoint source reductions will in fact occur. Therefore, this guidance provides that in specific situations, the TMDL must include a schedule for the implementation of control mechanisms, monitoring, and assessment of standards attainment. If standards are not attained, a TMDL revision is required. Data collected through monitoring would then be useful in revising the TMDL. While this phased approach requires additional monitoring of waterbody to evaluate the effectiveness of nonpoint source management measures or more stringent effluent limitations, it does not delay the establishment of such control mechanisms where there is a lack of information.


PRINCIPLES
Biennial Submission of Lists. Every two years, States will submit their required 303(d) identification of water quality-limited waters still needing TMDLs including a priority ranking of waterbodies to EPA. These lists may be included with a State's biennial 305(b) report or as a separate report submitted at the same time as the 305(b) report.

Priority TMDLs. Along with the biennial submission of 303(d) lists, States will identify high priority waters targeted for TMDL development over the next two years.

Approach for TMDL Development. When specific criteria are met, a TMDL with additional specifications for monitoring and implementation under the phased approach should be developed to provide for immediate pollution reduction and for collection of additional information.

Implementation of Controls Based on TMDLs. States will continue to improve and maintain point source controls through WLAs and NPDES permits while implementing and maintaining nonpoint source controls through LAs and State or local requirements.

Nonpoint Source Controls. LAs for nonpoint sources will be accompanied by a description of nonpoint source load reduction goals and the procedure for reviewing and revising nonpoint source controls. Such descriptions will be referenced in reviewing TMDLs for approval.

Time Schedule. TMDLs will be developed on a schedule negotiated with EPA Regional offices. Time schedules for the review of TMDLs will also be negotiated with EPA Regional offices, but will occur within the statutory requirement of 30 days.

Geographic Targeting. States should develop TMDLs that account for both point and nonpoint sources on a geographically targeted waterbody basis. Geographically targeted waterbodies could include segments, basins, and watersheds as defined by the States.

Threatened Good Quality Waters. States are expected to include threatened good quality waters in their identification and prioritization of waters still needing TMDLs.

Public Participation. States are expected to ensure appropriate public participation in the TMDL development and implementation process.

Environmental Indicators. States should measure the effectiveness of control actions by monitoring changes in ambient water quality or biological conditions. Measuring environmental progress or showing environmental results is a critical need and has become a key element in EPA's strategic planning process.

As required by the Clean Water Act, States are to identify and report to EPA their water quality-limited waters. These waters are to be identified according to the provisions established in EPA's Water Quality Management and Planning Regulation at 40 CFR 130.7(b). The identified waters should include those impaired due to point and nonpoint sources and may include threatened good quality waters. EPA is establishing with this guidance that States should submit to EPA, in conjunction with the 305(b) water quality assessment reports, in April of 1992, the list of water quality-limited waters that still require TMDLs. Every two years thereafter, a State should update its list of 303(d) waters and submit it with the 305(b) report. This guidance describes in detail the identification process and the specific information that should be submitted to EPA.

As required by the Clean Water Act, States are to rank by priority all waters needing TMDLs. Since each State has a unique organizational arrangement for the protection of water quality, this guidance does not prescribe how a State should set its priorities. However, priority ranking should result in the identification of targeted waterbodies for which immediate TMDL development should be undertaken. In the biennial submission of their updated list of 303(d) waters, EPA expects States to identify the waters targeted for TMDL development in the forthcoming two years.

Historically, the water quality-based pollution control program has focused on reducing the load of chemical contaminants (e.g. nutrients, biochemical oxygen demand, metals) to waterbodies. EPA has defined the terms load, loading capacity, and load allocation in regulations and technical guidance documents so that wasteload allocations can be calculated. Chemical contaminant problems will continue to constitute a major portion of pollution control efforts and the terms "load" and "load reduction" are used throughout this document. However, it is becoming increasingly apparent that in some situations water quality standards -- particularly designated uses and biocriteria -- can only be attained if non-chemical factors such as hydrology, channel morphology, and habitat are also addressed. EPA recognizes that it is appropriate to use the TMDL process to establish control measures for quantifiable non-chemical parameters that are preventing the attainment of water quality standards. Control measures, in this case, would be developed and implemented to meet a TMDL that addresses these parameters in a manner similar to chemical loads. As methods are developed to address these problems, EPA and the States will incorporate them into the TMDL process.

The principles established by EPA in this guidance reflect these policies and reaffirm the existing regulatory requirements. They are intended to help States manage their surface water quality programs in a manner consistent with the intent and requirements of section 303(d) of the CWA and the Water Quality Planning and Management Regulations in 40 CFR 130. These principles are discussed throughout this guidance.

Clean Water Act Section 303(d)

Section 303(d) of the Act (see next page) requires States to identify waters that do not or are not expected to meet applicable water quality standards with technology-based controls alone. Waters impacted by thermal discharges are also to be identified. States are required to establish a priority ranking for these waters, taking into account the pollution severity and designated uses of the waters.

Once the identification and priority ranking of water quality-limited waters are completed, States are to develop TMDLs at a level necessary to achieve the applicable State water quality standards. Completed TMDLs must allow for seasonal variations and a margin of safety that accounts for any lack of knowledge concerning the relationship between effluent limitations and water quality.

States are required to submit to EPA the "waters identified and loads established" for review and approval by EPA. If disapproved, EPA will establish the TMDLs at levels necessary to implement the applicable water quality standards. For waters that are not identified under sections 303(d)(1)(A) and (1)(B) as being water quality-limited, States are to estimate TMDLs for information purposes.

Subsections 4(A) and (B) were added to CWA section 303(d) with the 1987 amendments in order to ensure consistency with the water quality standards process for use classification and with the NPDES antibacksliding requirements.


FEDERAL WATER POLLUTION CONTROL ACT
Section 303(d)
(1)(A) Each State shall identify those waters within its boundaries for which the effluent limitations required by section 301(b)(1)(A) and section 301(b)(1)(B) are not stringent enough to implement any water quality standard applicable to such waters. The State shall establish a priority ranking for such waters, taking into account the severity of the pollution and the uses to be made of such waters.

(B) Each State shall identify those waters or parts thereof within its boundaries for which controls on thermal discharges under section 301 are not stringent enough to assure protection and propagation of a balanced indigenous population of shellfish, fish, and wildlife.

(C) Each State shall establish for the waters identified in paragraph (1)(A) of this subsection, and in accordance with the priority ranking, the total maximum daily load, for those pollutants which the Administrator identifies under section 304(a)(2) as suitable for such calculation. Such load shall be established at a level necessary to implement the applicable water quality standards with seasonal variations and a margin of safety which takes into account any lack of knowledge concerning the relationship between effluent limitations and water quality.

(D) Each State shall estimate for the waters identified in paragraph (1)(B) of this subsection the total maximum daily thermal load required to assure protection and propagation of a balanced, indigenous population of shellfish, fish and wildlife. Such estimates shall take into account the normal water temperatures, flow rates, seasonal variations, existing sources of heat input, and the dissipative capacity of the identified waters or parts thereof. Such estimates shall include a calculation of the maximum heat input that can be made into each such part and shall include a margin of safety which takes into account any lack of knowledge concerning the development of thermal water quality criteria for such protection and propagation in the identified waters or parts thereof.

(2) Each State shall submit to the Administrator from time to time, with the first such submission not later than one hundred and eighty days after the date of publication of the first identification of pollutants under section 304(a)(2)(D), for his approval the waters identified and the loads established under paragraphs (1)(A), (1)(B), (1)(C), and (1)(D) of this subsection. The Administrator shall either approve or disapprove such identification and load not later than thirty days after the date of submission. If the Administrator approves such identification and load, such State shall incorporate them into its current plan under subsection (e) of this section. If the Administrator disapproves such identification and load, he shall not later than thirty days after the date of such disapproval identify such waters in such State and establish such loads for such waters as he determines necessary to implement the water quality standards applicable to such waters and upon such identification and establishment the State shall incorporate them into its current plan under subsection (e) of this section.

(3) For the specific purpose of developing information, each State shall identify all waters within its boundaries which it has not identified under paragraph (1)(A) and (1)(B) of this subsection and estimate for such waters the total maximum daily load with seasonal variations and margins of safety, for those pollutants which the Administrator identifies under section 304(a)(2) as suitable for such calculation and for thermal discharges, at a level that would assure protection and propagation of a balanced indigenous population of fish, shellfish and wildlife.

(4) LIMITATIONS ON REVISION OF CERTAIN EFFLUENT LIMITATIONS.--

(A) STANDARD NOT ATTAINED.--For waters identified under paragraph (1)(A) where the applicable water quality standard has not yet been attained, any effluent limitation based on a total maximum daily load or other waste load allocation established under this section may be revised only if (i) the cumulative effect of all such revised effluent limitations based on such total maximum daily load or waste load allocation will assure the attainment of such water quality standard, or (ii) the designated use which is not being attained is removed in accordance with regulations established under this section.

(B) STANDARD ATTAINED.--For waters identified under paragraph (1)(A) where the quality of such waters equals or exceeds levels necessary to protect the designated use for such waters or otherwise required by applicable water quality standard, any effluent limitation based on a total maximum daily load or other waste load allocation established under this section, or any water quality standard established under this section, or any other permitting standard may be revised only if such revision is subject to and consistent with the antidegradation policy established under this section.


Water Quality Planning and Management Regulation

EPA's Water Quality Planning and Management Regulation at 40 CFR Part 130 establishes the program and policies that implement CWA section 303(d) requirements. Section 130.7 describes the TMDL process and the State's responsibility for identifying waters still requiring TMDLs, setting priorities and developing TMDLs, submitting the waters identified with priority rankings and the TMDLs to EPA for approval, and the incorporation of the TMDLs into the State's Water Quality Management Plan.

To implement the program, the regulation establishes the following definitions for loading capacity, load allocation, wasteload allocation, total maximum daily load, water quality-limited segments and water quality-limited segments still requiring TMDLs. A definition for margin of safety (MOS) is also provided.

Loading capacity (LC) -- The greatest amount of loading that a water can receive without violating water quality standards. (40 CFR 130.2(f))

Load allocation (LA) -- The portion of a receiving water's loading capacity that is attributed either to one of its existing or future nonpoint sources of pollution or to natural background sources. Load allocations are best estimates of the loading, which may range from reasonably accurate estimates to gross allotments, depending on the availability of data and appropriate techniques for predicting the loading. Wherever possible, natural and nonpoint source loads should be distinguished. (40 CFR 130.2(g))

Wasteload allocation (WLA) -- The portion of a receiving water's loading capacity that is allocated to one of its existing or future point sources of pollution. WLAs constitute a type of water quality-based effluent limitation. (40 CFR 130.2(h))

Total maximum daily load (TMDL) -- The sum of the individual WLAs for point sources and LAs for nonpoint sources and natural background. If a receiving water has only one point source discharger, the TMDL is the sum of that point source WLA plus the LAs for any nonpoint sources of pollution and natural background sources, tributaries, or adjacent segments. TMDLs can be expressed in terms of either mass per time, toxicity, or other appropriate measure that relate to a State's water quality standard. If Best Management Practices (BMPs) or other nonpoint source pollution control actions make more stringent load allocations practicable, then WLAs can be made less stringent. Thus, the TMDL process provides for nonpoint source control tradeoffs. (40 CFR 130.2(i))

In practice, the terms TMDL and WLA have at times been incorrectly used interchangeably instead of considering both LA and WLA as components of a TMDL. A TMDL, as referenced in this guidance, includes both WLAs and LAs, established in accordance with EPA's regulations.

Water quality-limited segments -- Those water segments that do not or are not expected to meet applicable water quality standards even after the application of technology-based effluent limitations required by sections 301(b) and 306 of the Act. (40 CFR 130.2(j)) Technology-based controls include, but are not limited to, best practicable control technology currently available (BPT) and secondary treatment.

Water quality-limited segments still requiring TMDLs -- Segments identified through a process established by paragraph 130.7(b)(1) of EPA's Water Quality Planning and Management Regulation. Waters need TMDLs when certain specified pollution reduction requirements (identified in the regulation under subparagraphs (b)(1)(i), (ii), and (iii)) are not stringent enough to implement water quality standards for such waters. The specified pollution controls include technology-based effluent limitations required by sections 301(b) and 306 of the Clean Water Act and other appropriate requirements that can provide a more stringent level of treatment than federally-required technology-based effluent limitations. (40 CFR 130.7(b)(1))

This document contains the terms 303(d) waters and 303(d) lists. These waters (and waters on the 303(d) lists) are those water quality-limited segments that still require TMDLs as defined by the regulation. Thus, a water segment that meets its water quality standards after the implementation of water quality-based control actions would retain its water quality-limited status but would no longer be on a State's 303(d) list of waters still requiring TMDLs.

Margin of Safety (MOS) -- A required component of the TMDL that accounts for the uncertainty about the relationship between the pollutant loads and the quality of the receiving waterbody. (CWA section 303(d)(1)(C)) The MOS is normally incorporated into the conservative assumptions used to develop TMDLs (generally within the calculations or models) and approved by EPA either individually or in State/EPA agreements. If the MOS needs to be larger than that which is allowed through the conservative assumptions, additional MOS can be added as a separate component of the TMDL (in this case, quantitatively, a TMDL = LC = WLA + LA + MOS).


Table of Contents Chapter 1 Chapter 2 Chapter 3
Chapter 4 Appendix A Appendix B Appendix C
apd ape apf apg
acro sections

 

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