Publication Summary

The Upper Chehalis watershed has been identified as a major source of fecal coliform bacteria to the Lower Chehalis watershed that includes Grays Harbor. Within the Upper Chehalis watershed, fecal coliform concentrations in excess of the water quality criteria are widespread.

A comprehensive evaluation of fecal coliform data in the Upper Chehalis River was completed, and target reductions were established for the mainstem segments of the Upper Chehalis River and its tributaries.

Implementation strategies recommended include (1) implementing and improving best management practices for nonpoint sources, (2) replacing failing on-site sewage treatment systems, and (3) developing a monitoring strategy to evaluate the effectiveness of the TMDL implementation measures.

The Upper Chehalis watershed has been identified as a major source of fecal coliform bacteria to the Lower Chehalis watershed that includes Grays Harbor. Within the Upper Chehalis watershed, fecal coliform concentrations in excess of the Washington State water quality criteria are widespread. To improve water quality, best management practices (e.g., fencing riparian corridors, implementing dairy waste management, re-vegetating riparian areas) have been implemented at select locations. A total maximum daily load (TMDL) for fecal coliform bacteria also has been completed for a major sub-watershed, the Black River. However, areas of non-compliance remain in the Upper Chehalis watershed.

This document provides a comprehensive evaluation of fecal coliform data for the Upper Chehalis River and its tributaries. All available data from sources within and outside the Department of Ecology were considered. Year-round data were used for evaluating trends; however, data from the most critical periods, when bacteria levels were highest, were used to calculate reduction goals. Target reductions necessary to bring bacterial concentrations down to water quality standards were established at selected segments using the statistical roll-back method.

Implementation strategies recommended include (1) implementing and improving best management practices for nonpoint sources, (2) replacing failing on-site sewage treatment systems, and (3) developing a monitoring strategy to evaluate the effectiveness of the TMDL implementation measures.

Discharges from seven major permitted facilities also were considered in this TMDL study. All of the facilities were determined to be meeting water quality standards, so no further bacteria reductions were recommended for these facilities.

The Data Appendix is provided above as a data supplement (zip file) in Excel.