Comprehensive Sewer Plan in line for an update in Tumwater

The City of Tumwater is working to refresh its comprehensive sewer plan, which was last updated 10 years ago. 

The Tumwater Public Works Committee advanced a service provider agreement with Carollo Engineers for $474,416. The committee made the decision at a meeting on Thursday, Nov. 21.

Tumwater Water Resources Department Program Manager Patrick Soderberg said the update would help the city assess its current sewer system and prepare for future demand.  

To evaluate the current system, Soderberg said Carollo would begin by creating basins at lift stations or at convergence points of sewer lines to monitor flow levels during dry and wet seasons.

The firm would also develop a hydraulic model to stimulate how wastewater flows through the pipes. The model would account for infiltration and inflow, which happens when groundwater gets into the sewer line during wet season. 

The findings would inform a capital improvement plan, which would detail the needed maintenance, repairs and upgrades for the system.  

The plan would also include a financial component to evaluate the revenue required to maintain the system and to recommend a five-year rate schedule.

Council member Eileen Swarthout asked whether the plan would include the sewer lines beneath Interstate 5. Soderberg said it does. He noted close attention would be paid to those lines, which have been flagged before because of certain limiting factors. 

Swarthout also asked whether the plan includes opportunities for service extension, specifically mentioning 70th Avenue. Soderberg affirmed, saying Carollo’s work would inform them of service areas they can grow into while identifying limitations. 

With the committee’s endorsement, Carollo’s contract is going to be forwarded to the city council for approval at a Dec. 2 meeting. If approved, the project would take more than 30 months to complete with money coming from the city’s sanitary sewer fund.