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Mercer Island crews find unrecorded access points, stop Lake Washington overflow after lake‑line blockage
Summary
City crews traced a late‑February blockage between Pump Stations 10 and 11, located previously unrecorded lake‑line access points, jetted and cleared a roughly 150‑foot clog of grease and rags, and restored Pump Station 10; staff plan GIS updates, CCTV inspection of the reach and design‑ready emergency permitting.
City utility staff told the Mercer Island Utility Board on March 10 that a late‑February high‑wet‑well alarm at Pump Station 10 revealed a downstream blockage between Pump Stations 10 and 11 that caused an overflow into Lake Washington. Crews located two previously unrecorded lake‑line access points near Covenant Shores, ran a 1,000‑foot jetter hose and cleared an estimated 150‑foot blockage of grease, diapers and rags. Pump Station 10 was restored to normal operation and the city reported the overflow to King County Public Health, the Washington Department of Ecology and impacted residents.
Jason (utility staff) and Alan Hunter, the city’s utility operations manager, described the response: SCADA alarms alerted staff overnight, crews first attempted to clear the clay with local access but could not reach the clog. A jetter truck with about 1,000 feet of hose was brought in; staff also used metal detectors and probes to locate access points that were not recorded in the GIS system. Alan said the jetter head scoured and cleared the blockage and crews then backed down remnants at Pump Station 11.
Staff emphasized the limits of available equipment: typical jetter reels of this size use up to about 1,000 feet of hose and longer reaches may require barges or specialized arrangements to access lake‑line segments. City staff said they borrowed contractor equipment for this event and acknowledged fortunate circumstances — including a senior crew member who recalled where access had been installed — helped stop the overflow quickly.
As next steps, the city plans to update GIS records, perform a CCTV inspection of the section between Pump Stations 10 and 11 now that access is confirmed, evaluate maintenance frequency and flow‑metering options, and prepare design‑ready emergency access and permit packages so future responses do not wait months for external approvals. Staff noted that emergency permitting with federal and state agencies can take several months and that streamlining those approvals for pre‑designed access would reduce risk and response time.
Board members praised crews for rapid work and strong community engagement — including an EOC‑coordinated ask for reduced residential usage during the event — and asked staff to return with data on event frequency and any recommended capital work to increase access and resilience.
