Total Maximum Daily Loads (TMDL)


Definition - What does Total Maximum Daily Loads (TMDL) mean?

Total maximum daily load (TMDL) is a calculation of the maximum amount of pollutant that a waterway can contain to stay within water quality standards. Sources of pollutants are categorized as either point or non-point. Point sources include all sources of pollutant that are subject to the National Pollutant Discharge Elimination System (NPDES). These include wastewater treatment facilities, and stormwater discharges. Non-point sources include all remaining sources of pollutant, including natural background sources.

Safeopedia explains Total Maximum Daily Loads (TMDL)

The Total Maximum Daily Load must take into account seasonal changes in water quality. It also includes a margin of safety (MOS) to account for the effect that pollutant reduction in meeting water quality standards. The TDML calculation is:


WLA refers to the sum of wasteload allocations (point sources). LA refers to the sum of load allocations (non-point sources and background sources). MOS refers to the margin of safety.

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