The existing underwater lake line at Mercer Island was prone to damage and badly deteriorated, and the existing pump stations had reached the end of their service lives. This project used two construction contracts to correct these problems and mitigate environmental impacts to Lake Washington. As the construction manager, Vanir managed the replacement of 7,000 LF of existing sanitary sewer lines with new gravity and force mains along the northwest shoreline of Mercer Island; development of 42 lateral connections from the underwater line to beachfront properties; construction of a new pump station; decommissioning of two existing pump stations; and shoreline and property restoration.
Construction challenges included: a) maintaining service to multi-million dollar homes on the existing gravity sewers and keeping existing force mains active while installing and connecting to the new system in an underwater environment, and b) managing excavation and dewatering issues for the 55-foot deep pump station on the shore of Lake Washington.
Saving the project
When initial bids exceeded the city’s budget, the city retained Vanir to find a way to save the project. The Vanir team collaborated with the owner, engineer and contractors to refine the design, reallocate risk, re-estimate the cost, repackage the scope into two contracts and re-bid. New bids came in about $2 million under the new budget and contracts were awarded.