Publication Summary

This study began in late summer 1994 by characterizing receiving waters in the vicinity of six small municipal wastewater treatment plants discharging to the central basin of Puget Sound. The purposes of the study were to: 1) conduct mixing zone analyses and provide the input data and modeling results to permit managers; and 2) establish whether there is a need for costly site-specific data versus more readily available regional data.

This study began in late summer 1994 by characterizing receiving waters in the vicinity of six small municipal wastewater treatment plants discharging to the central basin of Puget Sound. The purposes of the study were to: 1) conduct mixing zone analyses and provide the input data and modeling results to permit managers; and 2) establish whether there is a need for costly site-specific data versus more readily available regional data.

The study concluded that: 1) it is better to use regional stratification data sets like the ones available from Ecology′s Ambient Monitoring Program than to attempt site-specific measurements of stratification; 2) it is better to collect a complete data set of site-specific current measurements; but if it will not be complete, then 3) the better approach is to conduct sensitivity analyses for acute and chronic mixing zones using a fine resolution of currents over a large range of values. A number of the important findings from this study were incorporated into Ecology′s Guidance for Conducting Mixing Zone Analyses.