Lakeline Reach 1 Capacity Improvements
Project Details
Reach 1, located along the east side of the Island, begins at 4266 E Mercer Way and terminates at King County’s South Metro Pump Station, (PS-KCS), 9603 SE 72nd Street. This reach includes City pump stations PS 25, PS 24, PS 23, and PS 22, as well as approximately 13,350 feet of 8- to 14-inch cast iron lakeline. The lakeline itself runs adjacent to 170 properties and under 150 docks.
Background
Mercer Island’s sewer collection system includes approximately 105 miles of gravity mains, 2,400 manholes, 17 pump stations, and one flush station. A key component of the system is the lakeline—a series of low-pressure sewer mains located 5 to 100 feet offshore that convey wastewater along the island’s perimeter. The lakeline collects flows from both residential connections and pump stations, ultimately discharging to King County’s North Metro (PS-KCN) and South Metro (PS-KCS) pump stations for off-island treatment.
The lakeline is divided into five hydraulically distinct segments, or “reaches.” The condition of Reach 1 is currently unknown, primarily due to the lack of access points, which has prevented inspection, maintenance, and upgrades since its original installation in 1966. This absence of condition data underscores the need for a comprehensive assessment and long-term planning to address potential capacity and reliability issues.
Description
The purpose of this project is to provide comprehensive engineering design and support services for the Lakeline Reach 1 Capacity Improvements Project. This is a complex, multi-year effort focused on identifying and addressing system deficiencies within Reach 1 to ensure reliable flow capacity and prevent future Sanitary Sewer Overflows (SSOs). Anticipated activities include data collection, planning, field reconnaissance, surveying, condition assessment, modeling and analysis, permitting, and design and engineering support for preliminary, small-scale, and full-scale construction efforts. The work will be delivered in clearly defined phases to address priority needs and accommodate evolving conditions.
Project Timeline
Planning/Design: August 2025 – June 2027
Construction Timeframe: June 2027 – December 2028
Estimated Budget
$3,099,208
Contact:
Christopher Marks, Utilities Engineer, 206-677-1027; chris.marks@mercerisland.gov
Status Updates
June 13, 2025
On May 12, the City issued a Request for Qualifications (RFQ) seeking statements of qualifications (SOQs) from engineering firms for design and support services related to the Lakeline Reach 1 Capacity Improvements Project. This week, following a thorough evaluation of the submitted SOQs, the City identified Tetra Tech as the most qualified firm. Contract negotiations are currently underway.