The ITR report notes there are no active fault crossings in the Delta conveyance alignment and that seismic demands are not extreme compared to other projects, and DCA indicated it agreed on that statement. Why are we building tunnels if seismic issues are not a concern?

Home > FAQs > The ITR report notes there are no active fault crossings in the Delta conveyance alignment and that seismic demands are not extreme compared to other projects, and DCA indicated it agreed on that statement. Why are we building tunnels if seismic issues are not a concern?

Can members have a list of soil conditioners considered for use? What is the composition of soil conditioners?

June 12, 2020

Would tunnel segments still be lowered into the tunnel from launch shafts even if there was a maintenance shaft available?

June 12, 2020

The ITR report’s note reflects the fact that the current tunnel corridors do not contain active faults and tunneling options themselves would not be uniquely affected by seismic considerations. It was not expressing any opinion regarding the need for or benefit of Delta Conveyance for providing increased seismic reliability to the State Water Project. On this point, in 2014 the U.S. Geological Survey (USGS) estimated that there was a 72% probability of a magnitude 6.7 or greater earthquake (a “major event”) occurring in the San Francisco Bay Area by 2043. Levees in portions of the Delta could be at risk of failure in the event of a “major event,” such as an earthquake of at least magnitude 6.7. If the levee failures occur in portions of the western, central or southern Delta, the reliability of freshwater SWP diversions at Clifton Court Forebay could be compromised.