2006 Water Comprehensive Plan - City of Bellevue

increase in demand anticipated due to growth that is expected in downtown Bellevue. Both theEast and South Operating Areas have a surplus of total required storage, through build-out.As part of this Comprehensive Plan update, a new storage capacity analysis was completed toprovide an updated basis for addressing the West Operating Area deficiency. The storageevaluation method for each operating area used in the previous Water Comprehensive Plan wasalso used in the recent calculation. The results presented here presume the following conditions:• Bellevue is supplied water from multiple sources.• Supply sources have sufficient capacity to meet maximum day demands.• Supply sources have sufficient capacity to meet average day demand with the largestsource out of service.• Nesting of fire flow and standby storage components is not utilized. (Nesting allows forthe same storage volume to be used for both fire flow and standby uses. So the requiredstorage volume for both is equal to whichever storage component is larger.)To evaluate storage adequacy for the years 2011 and 2025 (six- and twenty-year planninghorizons) and projected build-out, as shown in the tables, the following procedures werefollowed:• The number of Equivalent Residential Units (ERUs) and the maximum day demandwere derived from the population and demand analysis performed in Chapter 4• Existing storage for each operating area was identified and listed.• Required standby storage was calculated as 200 gallons per ERU.• Equalizing storage was calculated as 20 percent of the peak day demand.• The appropriate level of fire flow was included (5,500 gpm for all operating areas).• The total storage requirement was calculated as the sum of the three values calculatedabove.• Available storage was compared to required storage to determine the level of storageexcess or deficiency.• System analysis was conducted to evaluate system improvements to meet requiredstorage needs.The result of future water conservation activities and their impact on the storage requirementswithin Bellevue have not been specifically addressed. The only portion of the calculation ofstorage requirements that would be impacted by a decrease in demand is equalizing storage,calculated as 20 percent of the maximum day demand. For example, a decrease in maximumday demand of 100,000 gpd would result in a decease in storage requirements of 20,000 gallons.8-9