Sewer Overflow Reduction Project

On August 22, 2022, authorization was granted by Council to apply for funding from the Washington State Public Works Board (PWB) and Water Quality Combined (WQC) funding programs for low interest loans for the Sewer Overflow Improvement Project. The project would accomplish the following improvements:

1. Replace influent screens in the WWTP headworks building with high flow screens at 451 Semanski St S.

2. Replace three existing sewer lift stations with a single new sewer lift station. The design will include approximately 3,000 feet of gravity sewer and about 4,000 feet of force main. The gravity sewers will be located within existing public rights of way and will divert flows from the three existing lift stations to the new lift station. The location of the project is shown in the attached map.

On February 27, 2023, Council approved a loan from the PWB for the Sewer Overflow Improvement project in the amount of $4,400,000. The PWB loan will be used for the lift station and WWTP headworks influent screen replacement portion of the project. A Department of Ecology (DOE) loan in the amount of $3,450,000 has been awarded for financing the gravity and force main conveyance portion of the lift station project.

Increasing the capacity of the headworks screen will allow all four headworks pumps to be operated simultaneously so more flow to be taken into the WWTP, rather than backing flows up into the upstream collection system. Lowering hydraulic grades in the collection system will reduce WWTP bypasses and collection system overflows. The new lift station and discharge force main will be sized to fully convey sewer flows to the station and significantly reduce the occurrence of sewer overflows currently experienced from the existing sewer lift stations. The headworks screen replacement has a direct benefit to the new lift station by reducing the hydraulic grade in the collection system where the lift station discharges. The gravity sewer extension required to eliminate the existing lift station would only allow seven existing properties the opportunity to connect to sewer and all but one are already on septic system. Therefore there is no economic growth driver behind the project.

From 2023 through 2026, a total of $1.4M in annual debt service that the City has been paying on the WWTP upgrade completed in 2009 will be fully retired. The reduction in debt service will exceed the new debt service that the City is adding in 2025, including this project. The interest rate for the DOE loan is 1.2% for a 20-year term with no local cost share requirement.

The schedule for completing the project depends on whether delays due to permitting and material supply issues can be kept to a minimum. Ideally the project would be finished in the fall of 2025. Large projects such as the Sewer Overflow Improvement Project require outside financing to spread out the cost impact.

On January 22, 2024, the City will hold a hearing at the City Council meeting on January 22 to discuss the DOE project/agreement publicly and take comments.  Comments may also be submitted to Scott Woodbury at swoodbury@ci.enumclaw.wa.us or by calling 253-261-1937.

Map