Publication Summary

Water quality problems have been identified in the Chehalis River basin of Southwest Washington for at least 30 years. The Water Quality Program of the Washington State Department of Ecology has requested a review of historical data, with the object of identifying needs for additional study; and, if appropriate, establishing the total maximum daily load (TMDL) of pollutants contributing to water quality problems.

Water quality problems have been identified in the Chehalis River basin of Southwest Washington for at least 30 years. The Water Quality Program of the Washington State Department of Ecology has requested a review of historical data, with the object of identifying needs for additional study; and, if appropriate, establishing the total maximum daily load (TMDL) of pollutants contributing to water quality problems.

The Chehalis River displays the hydrologic characteristics typical of Western Washington rivers with minimal snowmelt input. Critical low flows occur in late summer, and high flows are associated with intense rainfall. Ambient data show long-term and widespread problems with low dissolved oxygen and high water temperatures during summer low flows, and elevated bacteria counts and turbidity during winter high flows. Certain metals appear to exceed chronic toxicity criteria, although data quality problems limit the certainty of that observation. Many special studies have been conducted in the Chehalis River system. These studies have examined sediment loading, oxygen problems in the mainstem Chehalis River between Centralia and Chehalis; water quality problems in the Black River; and problems on smaller tributaries, including Hanaford, Dillenbaugh, Salzer, and Wildcat Creeks.

The review of historical data supports the development of a TMDL for bacteria and dissolved oxygen. A special study and basin action plan is recommended to improve Chehalis River system water temperatures. Needs are identified for additional study of turbidity, toxicity, metals, local water quality problems on small tributaries, and near-field compliance of permitted dischargers with the Washington State Water Quality Standards.