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Total Maximum Daily Loads (TMDLs) are a requirement of the Clean Water Act. States must identify waters that are impaired and must develop TMDLs for those impaired by pollutants. A TMDL is a calculation of the maximum amount of a pollutant that a water body can receive and still meet water quality standards. The list of impaired waters requiring a TMDL is called the 303(d) list and can be found in Volume 2 of the Integrated Report. Waters are 303(d) listed for specific designated uses. Designated uses for surface waters are:
- warm water aquatic habitat
- cold water aquatic habitat
- primary contact recreation
- secondary contact recreation
- domestic water supply
- outstanding state resource water
The TMDL Section of the Water Quality Branch is responsible for producing the 303(d) list, collecting chemical and biological data in upstream areas and tributaries to known impaired waters and developing TMDL documents to allocate allowable loads of pollutants to sources
TMDL Defined
The term TMDL can refer to several related concepts:
A TMDL is a calculation of the maximum amount of a pollutant that a stream or lake can receive and still meet water quality standards. Technically, TMDL=WLA + LA + MOS where the allowable load (TMDL) is equal to the wasteload allocation (WLA or allowable load for KPDES-permitted sources) plus the load allocation (LA for sources that do not have a KPDES permit) and a Margin of Safety (MOS) to account for uncertainty.
A TMDL may also refer to a written report, which includes detailed assessment information of site-specific impaired waters, watershed information, data analysis, the calculated amount of an allowable pollutant load and the allocation of the allowable load to sources.