The report never specifically addresses the issue of primary vs. secondary treatment in Puget Sound, but it does offer solid facts that show it is wise to provide secondary treatment. It does not flush out twice a day, as The Times' article states. The average age of the water in the main part of Puget Sound is 150 days, and 50 percent of the water moving north is recirculated back into the Sound. The report also says 70 percent of the lead and 40 percent of the copper and zinc discharged into Puget Sound never leave. In fact, almost all the particles discharged into the Sound never leave, but instead sink to the bottom within two weeks - a strong argument for secondary treatment.
Primary treatment removes the solid material from wastewater and minimal amounts of toxicants.
Secondary treatment uses natural organisms and aeration, much like bubbling in streams, to further clean the wastewater. The organisms essentially detoxify the water by removing remaining solids and metals and organic chemicals, such as detergents and pesticides. Our West Point and Renton plants successfully remove 95 percent of the pollutants before the wastewater is piped far out and deep into Puget Sound. It is a scientific fact that the water quality in Puget Sound has improved since the '80s, when we all were alarmed by dead whales and reports of bottom fish with liver lesions. While it is too early to see changes in all of Puget Sound, scientists do say that secondary treatment of sewage by the communities bordering Puget Sound will result in a 5 percent reduction in discharge of toxicants.