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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