Vanir provided extensive pre-construction services, full construction management and inspection for this design-build marine outfall project, which won eight industry awards. Vanir’s QA/QC support covered onshore and oﬀshore work plus oﬀsite locations for pipe fabrication. The project was completed two years ahead of the contracted completion date and within budget.
The outfall begins as an 84” ID steel pipe connecting onshore to conveyance tunnels that extend back 12 miles to the treatment plant. Shortly after leaving the shoreline, the 84” ID pipe branches at a steel wye to two, 5,000 LF, 63” OD HDPE lines. The HDPE pipe terminates at a water depth of 600 feet in Puget Sound, with the last 250 feet of each pipe being diﬀuser pipe.
The onshore and near shore pipe was installed in an open-cut trench, which was sheeted up to a water depth of 30 feet and unsheeted thereafter to -80 Mean Lower Low Water. From 80 feet deep to
the end of the line, the HDPE pipe was bottom laid. Over a 72-hour period, the two pre-assembled HDPE lines were ﬂoated into place and installed using controlled submergence by ﬂooding the pipeline while it was under 60 tons of tension.