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.
