This article provides short notes on Total Maximum Daily Loads (TMDL).
A Total Maximum Daily Load (TMDL) is the maximum amount of a pollutant that a body of water can receive while sill meeting water can receive while still meeting water quality standards.
Alternatively, TMDL is an allocation of that water pollutant deemed acceptable to the subject receiving waters.
States must identify waters and establish Total Maximum Loads to protect them. This includes identification of needed load reductions within a watershed from agricultural producers and other nonpoint sources.
TMDLs have been used extensively by the United States Environmental Protection Agency (EPA) and state environmental agencies in implementing the CWA (Clean Water Act) by establishing maximum pollution limits for industrial wastewater dischargers. EPA published regulations in 1992 establishing producers. This process incorporates both point source and nonpoint sources pollutants within a watershed.
Calculating the TMDL for any given body of water involves the combination of factors that contribute the problem of nutrient concentrated runoff. Bodies of water are tested for contaminants based on their intended use. Each body of water is tested similarly but designated with a different TMDL.
Drinking water reservoirs are designated differently than areas for public swimming and water bodies intended for fishing are designated differently than water located in wildlife conservation areas. The size of the water body also is taken into consideration when TMDL calculating is undertaken.
The larger the body of water, the greater the amounts of contaminants can be present and still maintain a Margin of Safety. The Margin of Safety (MOS) is the nutrients allowed to be present in a body of water and have it still meet state water quality requirements for its intended use.
TMDL is the end product of all point and non-point source of pollutants of a single contaminant. Pollutants that originate from a point source are given allowable levels of contaminants to be discharged; this is the Waste Load Allocation (WLA). Nonpoint source pollutants are also calculated into the TMDL equation with Load Allocation (LA).
The calculation of a TMDL is as follows:
TMDL = WLA + LA + MOS