USEPA Office of Water - TMDL Program Results Analysis Fact Sheet 3 - May 5, 2009
             Fact Sheet:   Total  Maximum  Daily  Loads
               TOTAL MAXIMUM DAILY LOAD (TMDL) and the CLEAN WATER ACT

The goal of the Clean Water Act (CWA) is to restore and maintain the chemical, physical, and biological integrity of our
nation's waters. Under CWA section 303(d), states, territories, and authorized tribes are required to develop lists of
waterbody segments impaired by a pollutant and needing a TMDL.

A TMDL is a technical calculation of the maximum load of a pollutant a waterbody can receive and still meet water
quality standards. A TMDL addresses the sum of all point source loads ("waste load allocation") and loads associated
with nonpoint sources ("load allocation"). Tens of thousands of TMDLs have been developed nationwide since 1995.
                                  TMDL = WLA + LA + MOS


                                  WLA Waste Load Allocation
                                  Amount of pollutant from
                                  existing point sources (e.g.,
                                  sewage treatment plant;
                                  industrial facility;
                                  stormwater)


                                  LA Load Allocation
                                  Amount of pollutant from
                                  existing nonpoint sources
                                  and natural background
                                  (e.g., farm runoff;
                                  atmospheric mercury)
                Adopt Water Quality Standards
                   Monitor & Assess Water F
              List Impaired & Threatened Waters
                Develop TMDLs including load
                   and wasteload allocations
                      Implement the TMDL
In general, the CWA requires states to establish water quality standards for waters
within their borders by designating specific uses for their waters (designated uses)
and establishing criteria by which to
protect those uses, control pollutant                    Over 37,000 TM DLs Completed
sources, and monitor and assess
water quality.
                                  MOS Margin of Safety
                                  Part of TMDL allocated to
                                  uncertainty in analysis

States are responsible for submitting
biennial lists [section 303(d) lists of
impaired waters] and water quality
assessment reports [section 305(b)
reports] to the Environmental
Protection Agency (EPA).

States develop TMDLs for listed waters
in accordance with priority ranking.
EPA provides an 8 to 13 year time
frame to complete the development
of a TMDL once a waterbody is listed.
These loading limits, when fully
implemented, should ensure that the
state's waters achieve the relevant
water quality standards.

                                       40,000
5/5/09
            # of TMDLs per fiscal year • Cumulative # of TMDLs

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                    USEPA Office of Water - TMDL Program Results Analysis Fact Sheet 3 - May 5, 2009
       Nonpoint Source, Point Source, and Mixed TMDLs
     44%
                                                      ED Nonpoint
                                                        Source
                                                       I Point Source
                                                      • Combination
                                                        of Point and
                                                        Nonpoint
                                                        Sources
               TMDLs established for nonpoint
               sources far outnumber those
               completed for point sources. This
               trend mirrors nonpoint source causes
               of impairment dominating states'
               impaired waters lists.
               These  nonpoint source TMDLs are
               especially challenging to implement,
               as the  Clean Water Act is limited to
               voluntary controls (e.g., best
               management practices) on nonpoint
               sources.
A partial list of TMDLs by pollutant from the Assessment, TMDL Tracking and Implementation System (ATTAINS) appears
below. For the full list, visit http://iaspub.epa.gov/waters10/attains nation  cy.control?p report type=T.
                                      National Cumulative TMDLs by Pollutant
                                        This chart includes TMDLs since October 1, 1995.

                                                Description of this table
                      NOTE: Click on the underlined "Pollutant Group" value to see a detailed list of pollutants. Click on the
                      underlined "Number of TMDLs" value to see a listing of those TMDLs for the pollutant Group.

                                                                          Number of Causes of
                                 Pollutant Group
                      Mercury
                      Metals (other than Mercury)
                      Organic Enrichment/Oxygen Depletion
                 	Temperature	

Prolific TMDL development has occurred for some types of TMDLs, such as mercury and pathogen TMDLs, because of:
    •   numerous listings of specific causes of impairment on state impaired waters lists,
    •   templates created by EPA regions or states which greatly increase TMDL development efficiency, and
    •   EPA guidance issued regarding TMDL development for specific, common pollutants.
                       Mercury
                   Pathogens
  • Ranks second nationally in causes of waterbody
    impairment
  • EPA approved the Northeast Regional Mercury TMDL
    - a multi-state effort - in fiscal year 2008. This TMDL
    covers over 5,000 mercury-impaired waterbodies in
    New Hampshire as well as waterbodies in the
    remaining New England states and New York
    (http://www.epa.gov/owow/tmdl/examples/mercury.html
    , http://www.epa.gov/region1/eco/tmdl/approved.html)
  • Similarly, in MN, over 1,000 TMDLs were approved
    within a statewide mercury TMDL effort.
  • To assist other states, EPA has developed information
    on approaches to mercury:
    -^   Listing Waters Impaired by Atmospheric Mercury
        Under Clean Water Act Section 303(d)
        (http://www.epa.gov/owow/tmdl/mercury5m/)
    -^   TMDLs Where Mercury Loadings are
        Predominantly from Air Deposition TMDL
        checklist document
        (http://www.epa.gov/owow/tmdl/pdf/document me
        rcury tmdl elements.pdf)
• Rank first nationally in causes of waterbody impairment
• Several EPA regions use an approval checklist, which
 compresses information from potentially lengthy
 decision rationales to simpler, briefer documents. Also,
 state-specific, general decision rationales applicable to
 all bacteria TMDLs in the state are utilized.
• EPA has developed information on approaches to
 addressing pathogens in TMDLs:
 -^    Options for Expressing Daily Loads in TMDLs
       (http://www.epa.gov/owow/tmdl/draft daily  loads
       tech.pdf)
 -^    Total Maximum Daily Loads with Stormwater
       Sources: A Summary of 17 TMDLs
       (http://www.epa.gov/owow/tmdl/17 TMDLs Stor
       mwater Sources.pdf)
 -^    An Approach for Using Load Duration Curves in
       the Development of TMDLs
       (http://www.epa.gov/owow/tmdl/duration  curve  g
       uide  aug2007.pdf)
 -^    Protocol for Developing Pathogen  TMDLs
       (http://www.epa.gov/owow/tmdl/pathogen all.pdf)
 For more information: TMDL Home Page http://www.epa.gov/owow/tmdl/. Contact: Sarah Furtak (202) 566-1167. furtak.sarah@epa.gov

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