Publication Summary

During 2003-2005, a monitoring study was conducted to determine the effectiveness of Total Maximum Daily Load (TMDL) clean-up efforts in the lower Snoqualmie River basin. Results show that bacteria levels have improved at most sites, but more effort is needed to meet water quality standards. Dissolved oxygen levels in the mainstem Snoqualmie have generally remained the same. More study is needed to determine if dissolved oxygen TMDL targets are met during the August-October critical period. Report recommendations include (1) specific studies to determine sources of water pollution, and (2) additional pollution-control actions.

The Washington State Department of Ecology (Ecology) is required under Section 303(d) of the federal Clean Water Act to develop and implement Total Maximum Daily Loads (TMDLs; water cleanup plans) for impaired waters in the state. Ecology is also required to evaluate the effectiveness of the water cleanup plan in achieving the needed improvement in water quality.

During 2003-05, Ecology conducted this study to determine the effectiveness of cleanup efforts in the Snoqualmie River watershed. The study analyzes the effectiveness of 1994-2004 TMDL implementation activities in protecting and restoring water quality.

Water quality in the Snoqualmie River has improved, but more effort is needed to ensure that Washington State water quality standards and TMDL targets are met. Dissolved oxygen levels in the mainstem Snoqualmie have generally remained the same. More study is needed to determine if dissolved oxygen TMDL targets are met. Bacteria levels in the mainstem and most of the tributaries have improved. The mainstem Snoqualmie River nearly meets standards for fecal coliform, but many tributaries do not meet fecal coliform standards. Higher nutrient levels and low dissolved oxygen levels in some of the tributaries may be associated with high bacterial inputs.

Ecology sampled wastewater from three wastewater treatment plants (WWTPs) for this 2003-05 study, but the amount of data collected was insufficient to determine compliance. Review of monitoring data submitted as part of WWTP National Pollutant Discharge Elimination System permits revealed compliance with the target control recommendations in the TMDL. Higher bacteria and nutrient levels were measured downstream of the City of North Bend and its WWTP.

This report recommends that local governments continue existing pollution-control actions in the Snoqualmie watershed. The study also shows that additional pollution controls are needed through on-site sewage system surveys, agricultural practice surveys, and stormwater pollution-control activities.

Link to EIM data for User Study ID GONW0001