A TMDL
(Total Maximum Daily Load) is a calculation of the maximum amount of a pollutant that a waterbody can receive and still meet
the designated use. A designated use, such as drinking water supply
or contact recreation (swimming), is met when specific water quality
criteria set by States, Territories or Tribes are met. Section 303 of the
Clean Water Act defines a TMDL to be the sum of the allowable loads of a single pollutant from all contributing point and nonpoint sources. The calculation must include a margin of safety to ensure that the waterbody can be used for the purposes the State has designated. The calculation must also account for seasonal variation in water quality.
A TMDL also includes the allocation of the load back to the original point
and nonpoint sources.
Calculating TMDLs is a complex
process often aided by a model application such as WARMF.
With a model, stakeholders can use environmental data to track pollution
back to the original source and predict current and future scenarios. Once
the TMDL is set, models are helpful during the allocation phase which may
involve load reduction strategies such as best management practices (BMPs)
or treatment plant upgrades. Because TMDL calculation is a
stakeholder-driven process, models often serve as useful communication
tools during the development of viable alternatives and consensus
building.
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Muddy Creek of the Cheat River
Basin with acid mine drainage.
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