Guidance for Conducting Mixing Zone Analyses

The Washington State Department of Ecology has developed "Guidance for Conducting Mixing Zone Analyses," Appendix C (PDF) of the Permit Writer’s Manual. Its purpose is to fill in most of the knowledge gaps so that consultants and Ecology’s permit managers will be able to operate and communicate from the same, uniformly high, level of understanding and expertise needed to produce quality mixing-zone analyses. It accomplishes this by providing the specific, detailed information that is needed to select the correct values for the effluent and receiving water parameters, select the appropriate model, and determine when a dye study should be used.

In order for the mixing zone guidance to be most useful, it’s essential to have a prior working knowledge of how water quality-based effluent limits are developed in Washington state. This knowledge can be gained through reading and understanding the Water Quality Standards for Surface Waters of the State of Washington (in particular the subparts on Toxic Substances and Mixing Zones) and the Department of Ecology’s Permit Writer’s Manual (in particular Chapters 6 and 7) —and through experience. 

For more information on the mixing zone guidance, contact:

Anise Ahmed, P.E.
WA State Dept. of Ecology
PO Box 47600
Olympia, WA 98504-7600
Telephone: (360) 407-6767
FAX: (360) 407-6884
E-mail: anise.ahmed@ecy.wa.gov

For more information on the Permit Writer's Manual, contact:

Vince McGowan
WA State Dept of Ecology
PO BOX 47600
Olympia WA 98504-7600
Telephone: (360) 407-6433
FAX: (360) 407-6426
E-mail: vincent.mcgowan@ecy.wa.gov

For more information on the Water Quality Standards, contact:

Susan Braley
WA State Dept of Ecology
PO BOX 47600
Olympia WA 98504-7600
Telephone: (360) 407-6414
FAX: (360) 407-6426
E-mail: susan.braley@ecy.wa.gov