by Kirby Lindsay
Monica Van der Vieren, of King County Community Relations, has confirmed that while the Fremont Siphon is nearing the end of its design – the original construction took place between 1907 and 1913 - the county has no reason to expect the pipeline to fail prior to rehabilitation or replacement, on its current schedule. If a problem is detected, Van der Vieren wrote by e-mail, King County will respond rapidly. They monitor the siphon regularly, and gave it particular attention during recent record rainfalls.
Information for the Community
During the meeting Bill Cranston, a consulting project manager from MWH Global, explained that engineers envisioned 32 alternative plans to replace, repair or rehabilitate the original siphon. Then, through a fatal flaw review that assessed many factors, they narrowed the list down to four options that will be further developed, with community input.
Two of these options involve replacement of the current siphon (located west of the Fremont Bridge, near the terminus of 2nd Avenue NW) by establishing a new pipeline crossing approximately 200’ west. Nearly identical, the only difference in these options concerns the method of tunneling. One uses remote microtunneling, while the other calls for hand-mining.
A third option also builds a microtunnel as a temporary by-pass, while workers would rehabilitate the original siphon. Afterwards, the county would have this extra tunnel for future uses.
The fourth option diverges broadly from the others – and is both much cheaper and much riskier. The siphon runs under the canal through a 375’ concrete utility corridor, filled with water. The corridor also contains a City of Seattle water main and Comcast cable lines, and this option may require removal of these shared utilities.
The proposal suggests encasing the siphon – two pipes, one of 60” diameter and the other of 48” – in concrete. Then, as the pipes deteriorate, and the flow (hopefully) carries away the pieces, two intact concrete pipes remain. This option, unlike the others, has a design life of only 50 years and, should anything go wrong, it would require extremely expensive emergency repairs.
Input From the Community
A single plan for siphon repair should come in early 2011 – after a continued community comment period. Project design, environmental review and permitting will be done from 2011 to 2014. A tentative schedule for construction has the starting date set for late 2014, with the duration depending on the plan chosen.
The County has seriously considered the community impacts from this large-scale construction project, to be done in a high density, high traffic area. It will require relocation of the Burke-Gilman Trail for up to 1 ½ years. As often as possible, they want to find mitigation measures, and plan to establish a 24/7 hotline during construction for potential complaints and comments from neighbors.
King County already has a website – including the meeting presentation - for this project. Van der vieren has given out her e-mail and phone number (206/263-7301) for community comments. Van der vieren and the other representatives at the meeting, including Fremont resident Pam Elardo, the King County Wastewater West Section Manager, volunteered to provide information, but they also want to hear from the community – and hope to address concerns before they become crises.
©2010 Kirby Lindsay. This column is protected by intellectual property laws, including U.S. copyright laws. Reproduction, adaptation or distribution without permission is prohibited.