Tools to interpret and implement

On March 29, 2019, we issued a short-term modification to the WAC 173-201A-200(1)(f) total dissolved gas (TDG) criteria for areas on the lower Snake and lower Columbia rivers.

On Dec. 30, 2019, we formally adopted revisions to the TDG criteria for the Columbia and Snake rivers.

The Chelan Public Utility District is requesting revisions to the water quality standards for the Chelan River. These revisions include:

• Aquatic life use designation to reflect highest attainable use in the river
• Site-specific temperature and dissolved oxygen criteria that protect the proposed aquatic life use designation

We hope to initiate the public process for this rulemaking with a rule announcement (CR-101) later this year. This decision to announce a CR-101 must first be approved by Ecology's director.

Application materials:

• Application cover letter
• Chelan River Use Attainability Analysis report

Ecology response letter:

• Ecology letter to Chelan Public Utility District, Feb. 18, 2020

Mixing zones are areas adjacent to an effluent outfall or in-water activity where water mixing causes dilution of the effluent with the receiving water. Permitted dischargers may have a specified boundary at the outside edge of the mixing zone where they must meet the water quality standards.

Site-specific criteria are criteria adopted for a waterbody that is different from the established criteria based on local conditions and/or key species. The site-specific criteria should fully protect existing and attainable uses for the waterbody.

A water quality offset is a tool used to reduce pollution levels for a specific water quality parameter in a waterbody in order to allow new or expanded permitted discharges.

Intake credits is a procedure for establishing effluent limits that takes into account the amount of a pollutant that is already present. When a facility releases a discharge into the same water body the pollutant must be equal or less than the starting level.