Publication Summary

The Upper Chehalis River Basin TMDL, developed by the Washington State Department of Ecology, is being established for surface water temperature standard exceedences that are caused almost entirely by solar radiation. Temperature is a measure of heat, which is considered a pollutant under Section 502(6) of the Clean Water Act. Heat generated by the amount of solar radiation from sunlight reaching the stream provides energy to raise water temperatures. Contributions of heat from municipal and industrial point sources in the Upper Chehalis River are small, but they have been addressed in this TMDL through wasteload allocations. This TMDL is designed to address impairments due to surface water temperature increases on nine water quality-limited streams (representing 19 segments) located in the watershed and provide goals for protection of all remaining streams. Streamside shade is used as a surrogate measure for water temperature. Use of surrogate measures is allowed by federal regulations (40 CFR 130.3) and the July 1998 Report to the Federal Advisory Committee on the TMDL Program (EPA-100-R-98-006). A decrease in shade increases incoming solar radiation and the resultant heat transfer to the stream. A more complete description of the factors influencing stream system temperatures appears in Appendix E.