Fremont Siphon Pipeline Replacement
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17 March, 2015: Preparations are under way ahead of a scheduled summer launch of the 2.15m diameter Herrenknecht microtunneling machine that will excavate twin tunnels beneath the Lake Washington ship canal in Seattle. Up to 220 million gal/day of combined sewage and stormwater, from an area of 100 square miles, currently pass through the existing 48in and 60in diameter cast iron pipes that were built in the early 1900s and set inside a concrete-lined tunnel. That infrastructure is now past its useful service life, explains King County Project Representative Marty Noble. The Federally mandated gravity-fed inverted siphon solution will ensure that CSO overflows into Lake Washington canal are cut in line with the provisions of the Environment Protect Act.

Second canal crossing for Seattle sewer upgrade - TunnelTalk, November 2012
Ballard siphon replacement project - TunnelCast, October 2013


Fremont Siphon Pipeline Replacement

Sterling Noren reporting for TunnelCast
Location: Lake Washington ship canal, Seattle, Washington
Dimensions: 2 x 465ft (142m) x 60in (152cm) micro tunnels beneath the Lake Washington ship canal
Type: CSO wastewater tunnel to replace twin cast iron pipes, built in 1907–1913.
Owner: King County Department of Natural Resources and Parks Wastewater Treatment Division
Project value: US$21,722,000
Launch/retrieval shafts: 80ft (24m) deep x 30ft (9m) diameter
Excavation method: Herrenknecht Microtunneling machine, 2145mm o.d, specially designed for 4.5 bar groundwater pressure
Main Contractor: Stellar J Construction
Tunnel Subcontractor: Northwest Boring
Shaft Construction: Malcolm Drilling