Mixing Zone Studies - All wastewater treatment plants are required to conduct mixing zone studies for facility planning and development of NPDES permit limits. Cosmopolitan Engineering staff conducted mixing zone studies for numerous wastewater discharges to rivers and estuaries, including 40 of the 59 municipal WWTP outfalls to Puget Sound, and 39 discharges to area rivers.

A common element of outfall analysis and mixing zone studies into marine waters is a Shellfish Closure Zone Analysis. The Washington State Dept. of Health (Health) establishes shellfish closure zones for all existing and proposed outfall anticipated to impact shellfish beds of the State. Cosmopolitan has worked with Health in the development of shellfish closure zones for a number of projects.

Field Studies - Cosmopolitan Engineering has planned and executed water quality field studies for analyzing the impacts of point and nonpoint discharges to surface waters. Field studies have included water and sediment chemistry, oceanographic water properties for mixing zone studies, dive inspections of marine biota and structures, and effluent tracer studies.

TMDL Studies - Cosmopolitan Engineering has participated in the development and technical review of all of the major TMDL models developed in Western Washington Rivers. Most of these studies have been conducted for a consortium of the affected local parties. Work has included modeling and model verification field studies. A few recent TMDL projects include:

Snohomish Estuary TMDL Model Verification Studies - Snohomish County

Puyallup River TMDL Mediation - Pierce County

Willapa River TMDL - Pacific County

Chehalis River TMDL Model Review - Lewis County

Skagit River TMDL Model Development and Wasteload Allocations - Mt. Vernon