The District has established robust seismic design guidelines following the American Lifelines Alliance (ALA) guidance. The design objective for the critical segments of the SLA that cross active seismic faults is to withstand an event with a 2-percent chance of occurrence in 50 years (2PE50, or 2,475-year return interval for the Wasatch Fault Zone in this location). This is defined in the ALA guidance as a Pipe Function Class IV (the highest class recognized). The District’s performance objective is to maintain pressure integrity during an event, at a minimum, and to remain undamaged if possible. The “damaged but intact” scenario is more likely for larger-diameter pipe (>60 inches) and larger return intervals (2,475 years). The following table describes damage scenarios for pre- and post-mitigation efforts for the SLA.
