This article's lead sectionmay be too short to adequately summarize the key points. Please consider expanding the lead to provide an accessible overview of all important aspects of the article.(April 2022)
The Clean Water Act requires that state environmental agencies complete TMDLs for impaired waters and that the United States Environmental Protection Agency (EPA) review and approve / disapprove those TMDLs.[4] Because both state and federal governments are involved in completing TMDLs, the TMDL program is an example of cooperative federalism. If a state doesn't take action to develop TMDLs, or if EPA disapproves state-developed TMDLs, the EPA is responsible for issuing TMDLs. EPA published regulations in 1992 establishing TMDL procedures.[5] Application of TMDLs has broadened significantly in the last decade to include many watershed-scale efforts, including the Chesapeake Bay TMDL.[6] TMDLs identify all point source and nonpoint source pollutants within a watershed.[4]
State inventories
The Clean Water Act requires states to compile lists of water bodies that do not fully support beneficial uses such as aquatic life, fisheries, drinking water, recreation, industry, or agriculture; and to prioritize those water bodies for TMDL development. These inventories are known as "303(d) lists" and characterize waters as fully supporting, impaired, or in some cases threatened for beneficial uses.[7]
Planning process
Beneficial use determinations must have sufficient credible water quality data for TMDL planning.
Throughout the U.S., data are often lacking adequate spatial or temporal coverage to reliably establish the sources and magnitude of water quality degradation.
TMDL planning in large watersheds is a process that typically involves the following steps:
Watershed characterization—understanding the basic physical, environmental, and human elements of the watershed.
Impairment status—analyzing existing data to determine if waters fully support beneficial uses
Data gaps and monitoring report—identification of any additional data needs and monitoring recommendations
Source assessment—identification of sources of pollutants, and magnitude of sources.
Load allocation—determination of natural pollutant load, and load from human activities (i.e. diffuse nonpoint sources and point discharges).
Set targets—establishment of water quality targets intended to restore or maintain beneficial uses.
TMDL implementation plan—a watershed management strategy to attain established targets.[7]
Water quality targets
The purpose of water quality targets is to protect or restore beneficial uses and protect human health. These targets may include state/federal numerical water quality standards or narrative standards, i.e. within the range of "natural" conditions. Establishing targets to restore beneficial uses is challenging and sometimes controversial. For example, the restoration of a fishery may require reducing temperatures, nutrients, sediments, and improving habitat.[7]
Necessary values for each pollutant target to restore fisheries can be uncertain. The potential for a water body to support a fishery even in a pristine state can be uncertain.
Background
Calculating the TMDL for any given body of water involves the combination of factors that contribute to the problem of nutrient concentrated runoff. Bodies of water are tested for contaminants based on their intended use. Each body of water is tested similarly but designated with a different TMDL. Drinking water reservoirs are designated differently from areas for public swimming and water bodies intended for fishing are designated differently from water located in wildlife conservation areas. The size of the water body also is taken into consideration when TMDL calculating is undertaken. The larger the body of water, the greater the amounts of contaminants can be present and still maintain a margin of safety. The margin of safety (MOS) is numeric estimate included in the TMDL calculation, sometimes 10% of the TMDL, intended to allow a safety buffer between the calculated TMDL and the actual load that will allow the water body to meet its beneficial use (since the natural world is complex and several variables may alter future conditions). TMDL is the end product of all point and non-point source pollutants of a single contaminant. Pollutants that originate from a point source are given allowable levels of contaminants to be discharged; this is the waste load allocation (WLA). Nonpoint source pollutants are also calculated into the TMDL equation with load allocation (LA).[7]
Calculation
The calculation of a TMDL is as follows:
where WLA is the waste load allocation for point sources, LA is the load allocation for nonpoint sources, and MOS is the margin of safety.[8][2][3][9]
Load allocations
Load allocations are equally challenging as setting targets. Load allocations provide a framework for determining the relative share of natural sources and human sources of pollution.
The natural background load for a pollutant may be imprecisely understood. Industrial dischargers, farmers, land developers, municipalities, natural resource agencies, and other watershed stakeholders each have a vested interest in the outcome.[7]
Implementation
To implement TMDLs with point sources, wasteload allocations are incorporated into discharge permits for these sources.[10] The permits are issued by EPA or delegated state agencies under the National Pollutant Discharge Elimination System (NPDES). Nonpoint source discharges (e.g. agriculture) are generally in a voluntary compliance scenario. The TMDL implementation plan is intended to help bridge this divide and ensure that watershed beneficial uses are restored and maintained. Local watershed groups play a critical role in educating stakeholders, generating funding, and implementing projects to reduce nonpoint sources of pollution.[7]
Guidance for Water Quality-Based Decisions: The TMDL Process (PDF) (Report). Washington, D.C.: U.S. Environmental Protection Agency (EPA). April 1991. EPA 440/4-91-001.
^United States. Clean Water Act, sec. 303(d), 33 U.S.C. § 1313(d)
^ abNational Research Council (2001). Assessing the TMDL Approach to Water Quality Management (Report). Washington, DC: National Academies Press. doi:10.17226/10146. ISBN978-0-309-07579-4.
^ abNational Academies of Sciences, Engineering and Medicine (2019). Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff (Report). National Academies Press. doi:10.17226/25473. ISBN978-0-309-49376-5.
^ ab"Overview of Identifying and Restoring Impaired Waters under Section 303(d) of the CWA". Impaired Waters and TMDLs. EPA. 2021-09-20.
^EPA. "Water Quality Planning and Management: Total maximum daily loads (TMDL) and individual water quality-based effluent limitations". Code of Federal Regulations,40 CFR 130.7.
^Chesapeake Bay TMDL Executive Summary (PDF) (Report). EPA. 2010-12-29.
^ abcdef"Overview of Total Maximum Daily Loads". EPA. 2021-09-20.
^A. Shirmohammadi; I. Chaubey; R. D. Harmel; D. D. Bosch; R. Muñoz-Carpena; C. Dharmasri; A. Sexton; M. Arabi; M. L. Wolfe; J. Frankenberger; C. Graff; T. M. Sohrabi (2006). "Uncertainty in TMDL Models". Transactions of the American Society of Agricultural and Biological Engineers. 49 (4): 1033–1049. doi:10.13031/2013.21741. hdl:10919/48202.
^Granato, Gregory E.; Jones, Susan Cheung (2017). "Estimating Total Maximum Daily Loads with the Stochastic Empirical Loading and Dilution Model". Transportation Research Record. Transportation Research Board; National Academies of Sciences, Engineering and Medicine. 2638: 104–112. doi:10.3141/2638-12. S2CID 116016432. 2638.
^"Chapter 6: Water Quality-Based Effluent Limitations". NPDES Permit Writers' Manual (Report). EPA. September 2010. EPA 833-K-10-001.
External links
EPA TMDL Program
EPA's AskWATERS Expert Query Tool - data on TMDLs
EPA Water Quality Standards Program
Stochastic Empirical Loading and Dilution Model Documentation Page - US Geological Survey
August 22, 2023
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This article s lead section may be too short to adequately summarize the key points Please consider expanding the lead to provide an accessible overview of all important aspects of the article April 2022 A total maximum daily load TMDL is a regulatory term in the U S Clean Water Act describing a plan for restoring impaired waters that identifies the maximum amount of a pollutant that a body of water can receive while still meeting water quality standards 1 2 3 Contents 1 State and federal agency responsibilities 2 State inventories 3 Planning process 3 1 Water quality targets 3 2 Background 3 3 Calculation 3 4 Load allocations 4 Implementation 5 See also 6 References 7 External linksState and federal agency responsibilities EditThe Clean Water Act requires that state environmental agencies complete TMDLs for impaired waters and that the United States Environmental Protection Agency EPA review and approve disapprove those TMDLs 4 Because both state and federal governments are involved in completing TMDLs the TMDL program is an example of cooperative federalism If a state doesn t take action to develop TMDLs or if EPA disapproves state developed TMDLs the EPA is responsible for issuing TMDLs EPA published regulations in 1992 establishing TMDL procedures 5 Application of TMDLs has broadened significantly in the last decade to include many watershed scale efforts including the Chesapeake Bay TMDL 6 TMDLs identify all point source and nonpoint source pollutants within a watershed 4 State inventories EditThe Clean Water Act requires states to compile lists of water bodies that do not fully support beneficial uses such as aquatic life fisheries drinking water recreation industry or agriculture and to prioritize those water bodies for TMDL development These inventories are known as 303 d lists and characterize waters as fully supporting impaired or in some cases threatened for beneficial uses 7 Planning process EditBeneficial use determinations must have sufficient credible water quality data for TMDL planning Throughout the U S data are often lacking adequate spatial or temporal coverage to reliably establish the sources and magnitude of water quality degradation TMDL planning in large watersheds is a process that typically involves the following steps Watershed characterization understanding the basic physical environmental and human elements of the watershed Impairment status analyzing existing data to determine if waters fully support beneficial uses Data gaps and monitoring report identification of any additional data needs and monitoring recommendations Source assessment identification of sources of pollutants and magnitude of sources Load allocation determination of natural pollutant load and load from human activities i e diffuse nonpoint sources and point discharges Set targets establishment of water quality targets intended to restore or maintain beneficial uses TMDL implementation plan a watershed management strategy to attain established targets 7 Water quality targets Edit The purpose of water quality targets is to protect or restore beneficial uses and protect human health These targets may include state federal numerical water quality standards or narrative standards i e within the range of natural conditions Establishing targets to restore beneficial uses is challenging and sometimes controversial For example the restoration of a fishery may require reducing temperatures nutrients sediments and improving habitat 7 Necessary values for each pollutant target to restore fisheries can be uncertain The potential for a water body to support a fishery even in a pristine state can be uncertain Background Edit Calculating the TMDL for any given body of water involves the combination of factors that contribute to the problem of nutrient concentrated runoff Bodies of water are tested for contaminants based on their intended use Each body of water is tested similarly but designated with a different TMDL Drinking water reservoirs are designated differently from areas for public swimming and water bodies intended for fishing are designated differently from water located in wildlife conservation areas The size of the water body also is taken into consideration when TMDL calculating is undertaken The larger the body of water the greater the amounts of contaminants can be present and still maintain a margin of safety The margin of safety MOS is numeric estimate included in the TMDL calculation sometimes 10 of the TMDL intended to allow a safety buffer between the calculated TMDL and the actual load that will allow the water body to meet its beneficial use since the natural world is complex and several variables may alter future conditions TMDL is the end product of all point and non point source pollutants of a single contaminant Pollutants that originate from a point source are given allowable levels of contaminants to be discharged this is the waste load allocation WLA Nonpoint source pollutants are also calculated into the TMDL equation with load allocation LA 7 Calculation Edit The calculation of a TMDL is as follows T M D L W L A L A M O S displaystyle TMDL WLA LA MOS where WLA is the waste load allocation for point sources LA is the load allocation for nonpoint sources and MOS is the margin of safety 8 2 3 9 Load allocations Edit Load allocations are equally challenging as setting targets Load allocations provide a framework for determining the relative share of natural sources and human sources of pollution The natural background load for a pollutant may be imprecisely understood Industrial dischargers farmers land developers municipalities natural resource agencies and other watershed stakeholders each have a vested interest in the outcome 7 Implementation EditTo implement TMDLs with point sources wasteload allocations are incorporated into discharge permits for these sources 10 The permits are issued by EPA or delegated state agencies under the National Pollutant Discharge Elimination System NPDES Nonpoint source discharges e g agriculture are generally in a voluntary compliance scenario The TMDL implementation plan is intended to help bridge this divide and ensure that watershed beneficial uses are restored and maintained Local watershed groups play a critical role in educating stakeholders generating funding and implementing projects to reduce nonpoint sources of pollution 7 See also EditWastewater quality indicators Water pollution Water quality modellingReferences EditGuidance for Water Quality Based Decisions The TMDL Process PDF Report Washington D C U S Environmental Protection Agency EPA April 1991 EPA 440 4 91 001 United States Clean Water Act sec 303 d 33 U S C 1313 d a b National Research Council 2001 Assessing the TMDL Approach to Water Quality Management Report Washington DC National Academies Press doi 10 17226 10146 ISBN 978 0 309 07579 4 a b National Academies of Sciences Engineering and Medicine 2019 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff Report National Academies Press doi 10 17226 25473 ISBN 978 0 309 49376 5 a b Overview of Identifying and Restoring Impaired Waters under Section 303 d of the CWA Impaired Waters and TMDLs EPA 2021 09 20 EPA Water Quality Planning and Management Total maximum daily loads TMDL and individual water quality based effluent limitations Code of Federal Regulations 40 CFR 130 7 Chesapeake Bay TMDL Executive Summary PDF Report EPA 2010 12 29 a b c d e f Overview of Total Maximum Daily Loads EPA 2021 09 20 A Shirmohammadi I Chaubey R D Harmel D D Bosch R Munoz Carpena C Dharmasri A Sexton M Arabi M L Wolfe J Frankenberger C Graff T M Sohrabi 2006 Uncertainty in TMDL Models Transactions of the American Society of Agricultural and Biological Engineers 49 4 1033 1049 doi 10 13031 2013 21741 hdl 10919 48202 Granato Gregory E Jones Susan Cheung 2017 Estimating Total Maximum Daily Loads with the Stochastic Empirical Loading and Dilution Model Transportation Research Record Transportation Research Board National Academies of Sciences Engineering and Medicine 2638 104 112 doi 10 3141 2638 12 S2CID 116016432 2638 Chapter 6 Water Quality Based Effluent Limitations NPDES Permit Writers Manual Report EPA September 2010 EPA 833 K 10 001 External links EditEPA TMDL Program EPA s AskWATERS Expert Query Tool data on TMDLs EPA Water Quality Standards Program Stochastic Empirical Loading and Dilution Model Documentation Page US Geological Survey The Center for TMDL and Watershed Studies at Virginia Tech Retrieved from https en wikipedia org w index php title Total maximum daily load amp oldid 1086917686, wikipedia, wiki, book, books, library,
