August 9, 1999
In a joint meeting of the Kenmore and Lake Forest Park city councils on Aug. 2, John Stack and Mary Rumpf of ST Engineering presented the findings of their study of the feasibility and impacts of the King County regional wastewater service plan and the alternative proposal by the King County Council. The cost of the independent study was shared by the two councils.
According to ST Engineering, the original wastewater plan called for all northeast county wastewater to be conveyed by the existing lake line trunk pipeline from Kenmore to Matthew's Beach in Seattle and from there to the West Point Treatment Plant (WTP). It was planned that as the region grew, a second line would be added next to the first.
Metro balances its flows to two treatment plants. Some of the north end flows are sent to the East Treatment Plant in Redmond in the winter and then to the west in the summer. This is necessary because of the huge volume of storm water that enters Seattle's combined sewers during winter storms. In 1984, the courts ordered Metro to upgrade the West Point Treatment Plant in Seattle to provide secondary treatment of wastewater. This reduced the future capacity of WTP.
The lake line capacity at Matthew Park pump station is 26mgd (million gallons per day). During the 1996-97 holiday storm, severe overflows occurred near the Kenmore pump station and near the lake line just downstream from the McAlleer-Lyon trunk. At Sheridan Beach in Lake Forest Park, sewage backed up into a number of homes.
The study reported that Metro plans to build a third treatment plant north of Lake Washington with plans to complete construction by the year 2010. To prevent future major problems, Metro would add an additional 10 million gallon storage facility at North Creek pump station and at another site. This storage would be capable of reducing peak flows to the capacity of the lake line through the year 2010. In the event that the new treatment plant was not on line by then, Metro would add an additional 10 million gallon storage for a total of 20 million gallons of additional storage. This, the report concluded, would handle 20-year storm flows through the year 2015.
However, there are concerns about the plan. King County Councilmembers Maggie Fimia and Rob McKenna have voiced their fears about the tightness of the construction schedule; they doubt that site procurement and construction can be completed by 2010. They feel the currently possible expansion of the West Point treatment plant and the construction of the second lake line as originally planned would give King County greater flexibility and a higher degree of safety against future overflows.
Stack and Rumpf pointed out that the lake line is the smallest part of the current pipeline and flow can quadruple during a rain storm in a wastewater system.
"Conveyance versus storage is the decision to be made," John Stack, president of ST Engineering concluded. "The costs of both proposals vary and the effect of each plan is different. Either plan would work to stop the currently foreseen overflow. However, storage can only by used up to a point. Eventually, you have to convey the waste to a treatment facility. This is not a deductive logic issue. At some point, you have to make a choice."
"Overflow is the major concern," Steve Anderson, Kenmore City Manager observed.
Both councils will review the study and decide which proposal their cities should endorse.