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Total Maximum Daily Load (TMDL)

The Environmental Protection Agency (EPA) requires Washington State Department of Ecology (Ecology) to develop a TMDL for each water body segment that does not meet state water quality standards for a specific pollutant. A TMDL:

  • Identifies pollution problems in a watershed.
  • Specifies how much pollution needs to be reduced or eliminated.
  • Provides targets and strategies to achieve clean water.

TMDLs in WSDOT's NPDES Municipal Stormwater Permit

The NPDES Municipal Stormwater Permit requires WSDOT to comply with requirements in applicable TMDLs approved by the EPA. Ecology, WSDOT’s Municipal Stormwater Permit administrator, reissued WSDOT's permit in March 2014. The permit includes 28 TMDLs statewide (pdf 933 kb).

TMDL Requirements

The requirements that WSDOT needs to comply with differ in each TMDL.  Appendix 3 (pdf 108 kb) of the permit lists WSDOT’s required action items and includes a flow chart of the programmatic approach.

WSDOT's Programmatic Approach

The fecal coliform programmatic approach was developed to streamline the development of TMDL implementation plans and ensure WSDOT is required to perform applicable and appropriate actions. The programmatic approach (pdf 191 kb) has been revised to apply to other TMDL pollutants (i.e. temperature, sediment, nutrients). It is applicable when evidence exists that WSDOT is a significant contributor of the pollutant of concern in the watershed. Evidence includes stormwater sampling data or some other actionable information.

WSDOT's programmatic approach includes:

  • Inventory of highway discharge locations.
  • Illicit discharge detection and elimination (IDDE).
  • Visual source identification.
  • Identification of maintenance issues (if applicable to the pollutant of concern).

Standard operating procedures (SOPs) describe WSDOT's data collection methods when implementing the programmatic approach in TMDL areas:

Standard Operating Procedure for Data Collection in TMDL Areas (pdf 478 kb)

Summary Reports

Reports that summarize findings are submitted to the Department of Ecology for each TMDL that requires WSDOT to implement the programmatic approach. To date, reports have been submitted for the following TMDLs:

  • Bear-Evans Creek
  • Green River
  • Hangman Creek
  • Issaquah Creek Basin
  • Little Bear Creek
  • Newaukum Creek
  • Oakland Bay
  • Palouse River
  • Puyallup River
  • Salmon Creek
  • Snoqualmie River
  • South Fork Palouse
  • Swamp Creek Basin
  • Stillaguamish River
  • Totten/Eld and Skookum Inlets Tributaries
  • Upper Naches River and Cowiche Creek
  • Whatcom Creek Watershed


For more information on TMDLs, contact WSDOT's TMDL Lead Elsa Pond (360)570-6654 or refer to Ecology's TMDL website.