Admin Order 58-20-26 - Laserfiche WebLink

Home Browse Search

Ballantyne Consulting, LLC Hazard Assessment and Mitigation of Lifeline Systems Ballantyne Consulting LLC • 1915 63rd St. NE • Tacoma, WA 98422 • 206‐226‐7496 dbballan@comcast.net • BallantyneConsulitng.com FINAL Technical Memorandum Date: June 30, 2016 From: Donald Ballantyne, PE To: Teri Higgins, City of Eugene Subject: Seismic Assessment of Wastewater Collection and Conveyance System 1.Introduction This Technical Memorandum describes the seismic assessment conducted by Ballantyne Consulting, LLC of the City of Eugene, Oregon (Eugene) sewage collection and conveyance system. The work was done as a subconsultant to West‐Yost. Eugene staff provided GIS support. Eugene provides collection and conveyance of wastewater but does not provide treatment. The system consists of about 3.65 million feet of sewer pipe ranging in size from eight‐ to seventy‐two‐inches in diameter. This planning level assessment evaluated the expected performance of these sewers. There are 26 wastewater pump stations in the system. This assessment evaluated five of the older more typical pump stations. The assessment evaluated the expected performance of a moment magnitude 9.0 (Mw9.0) Cascadia Subduction Zone (CSZ) earthquake on the system. Earthquake ground motion, liquefaction and landslide probabilities and permanent ground deformations (PGD) were obtained from the Oregon Department of Geology and Mineral Industries (DOGAMI), using the planning level earthquake hazard data that was developed for the Oregon Resilience Plan. It is the intent that the findings of this evaluation be incorporated into the Eugene Wastewater Comprehensive Plan. 2.Regional Seismicity and the Cascadia Subduction Zone Earthquake The CSZ is the most significant earthquake source zone that can impact Eugene. A CSZ event is expected to have similar impacts as the 2011 Japanese Tohoku Earthquake. The postulated Mw9.0 CSZ fault runs about 600 miles from mid‐Vancouver Island in Canada south to Eureka California. Starting at one end, it would take about 5 minutes for it to “un‐zip”, resulting in ground shaking for that duration along its length. The CSZ fault zone is located off the Pacific coast shore line, on‐the‐order of 100 miles distant from Eugene, so strong shaking has attenuated by the time it reaches the City. The CSZ has traditionally been considered to have a 500‐year recurrence interval with an event breaking its entire length with a magnitude on the order of Mw9.0. The last event occurred in 1,700 AD. Multiple smaller events would also be possible breaking adjacent segments of the fault. In recent years, Dr. Chris Goldfinger, at Oregon State University, has studied turbidites along the CSZ and concluded that there is a shorter recurrence interval in southern segment of the CSZ. In the segment 2020 Eugene Wastewater Master Plan Appendix A-1 Appendix A