Environmental Health - Toxic Substances
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Total Maximum Daily Load (TMDL)
Total Maximum Daily Load (TMDL) - "A TMDL is a calculation of the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards, and an allocation of that load among the various sources of that pollutant. Pollutant sources are characterized as either point sources that receive a wasteload allocation (WLA), or nonpoint sources that receive a load allocation (LA)." - U.S. Environmental Protection Agency, 2011
Total Maximum Daily Load (TMDL) - "A TMDL addresses the sum of all point source loads ('waste load allocation' [WLA]) and loads associated with nonpoint sources ('load allocation' [LA]). TMDL=WLA+LA+MOS." - U.S. Environmental Protection Agency, 2010
Total Maximum Daily Load (TMDL) - "'TMDL' stands for Total Maximum Daily Load, and refers to the total quantity (or load) of a pollutant that a stream can carry and still conform to designated uses and fishable/swimmable water quality. TMDL also refers to a regulatory process that States, Territories, and authorized Tribes use to determine allowable pollutant concentrations in streams." - Shipp and Cordy, 2002
Total Maximum Daily Load (TMDL) - "Total Maximum Daily Loads (TMDLs) must be developed for each impaired water body. TMDLs are actions to restore clean water by examining water quality problems, identifying sources of pollutants, and specifying actions that create solutions. TMDLs define how much of a pollutant a water body can tolerate and still meet water quality standards." - Clean Estuary Partnership
Text in brackets ("[text]") are additions by the editor.
Waste Load Allocation (WLA) - "Amount of pollutant from existing point sources (e.g., sewage treatment plant; industrial facility; stormwater)." - U.S. Environmental Protection Agency, 2010
Load Allocation (LA) - "Amount of pollutant from existing nonpoint sources and natural background (e.g., farm runoff; atmospheric mercury)." - U.S. Environmental Protection Agency, 2010
Margin of Safety (MOS) - "Part of TMDL allocated to uncertainty in analysis." - U.S. Environmental Protection Agency, 2010
USGS Information on TMDLs
Related Science Feature Articles
More Information on TMDLs
Clean Estuary Partnership, Information on the San Francisco Bay--Mercury TMDL.
Shipp, A., and Cordy, G.E., 2002, The USGS role in TMDL assessments: U.S. Geological Survey Fact Sheet FS-130-01.
U.S. Environmental Protection Agency, 2010, Fact sheet--Total maximum daily loads: U.S. Environmental Protection Agency, Fact Sheet EPA841-F-10-001.
U.S. Environmental Protection Agency, 2011, What is a TMDL?: U.S. Environmental Protection Agency, access date June 3, 2011.
Disclaimer: The definitions on this page are provided for information purposes only, and do not indicate endorment by the U.S. Geological Survey.