2013 Water System Plan, Volume II - Seattle City Clerk's Office - City ...

pipelines to lower pressure zones to drive turbines that turn pumps to lift water from the
same source to other higher pressure zones. These turbines can provide water to five of
the six pressure zones that rely on pumps. The turbines are used regularly and controlled
remotely from SPU’s system control center. These non-electric pumping facilities
provide water from gravity-fed ground level storage or from transmission pipelines
operating at pressures lower than the zone’s.
Table 1 below summarizes how supply to each of the six pumped-only zones would be
maintained in the event of an extended regional power outage through a combination of
gravity supply at first, and alternative pumping later. The amount of gravity standby
storage provides adequate time to remotely or locally activate the non-electric pumping
facilities, even under peak day demands. However, delivery to Magnolia 480, Queen
Anne 530 and Volunteer 530 would be limited to the capacity of Lincoln Turbine, and
emergency curtailments to reduce demands to indoor use only would be needed in these
areas if a widespread power outage were to occur during peak season.
C. CONCLUSION
In conclusion, SPU has analyzed the performance of the water system under the above
emergencies. Results show that at least five days of indoor water use can be met through
year 2040 and possibly beyond. If the emergency were to occur during peak
consumption periods, such as the summer irrigation season, SPU will request its
customers to curtail discretionary water use until the emergency has been resolved.
SPU will make storage sizing and decommissioning decisions consistent with this
emergency scenario based model for system storage reliability. Storage that is deemed
necessary will be maintained (e.g., regular recoating, cleaning, sanitary surveys,
structural inspections, etc) and storage that is deemed unnecessary will be physically
disconnected from the system. Some decommissioned steel storage may be kept in a
‘mothballed’ state (e.g., aesthetic painting on the outside and left standing).
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