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Water Supply and Storage Requirements
<br />As part of this study, existing and future demands for the entire City were reviewed.
<br />Demands assumptions given in Table 13-1 were used to project out the water
<br />demands for each of the development scenarios given in this study. The City's average
<br />day demand, which is based on a historical 5-year average, is 2,194,000 gallons per
<br />day (gpd) or 1,523 gallons per minute (gpm). The City's peak day demand, which is
<br />also based on a historical 5-year average is 5,455,000 gpd (3,788 gpm).
<br />According to AWWA, it is typical to recommend that the City have an approximate
<br />storage capacity equal to the average day demand plus a fire flow equalization
<br />amount. For purposes of this study, a fire flow of 3,500 gallons per minute for 3 hours
<br />(630,000 gallons) was added to the average day demand to determine the required
<br />storage capacity for the entire City. Therefore, 2,824,000 gallons is required for the
<br />City's water storage. Currently, the City has approximately 3,750,000 gallons in
<br />elevated storage.
<br />According to 10-State Standards, a City should be able to provide a water supply in the
<br />amount of their peak day demands with their largest well out of service (firm
<br />capacity). The City of Elk River has a firm capacity for the entire City of 5,500 gpm,
<br />with Well No. 8 having a capacity of 1,300 gpm out of service.
<br />Both the water storage and well supply capacities for the entire City are sufficient for
<br />the entire City's water demands. However, the City's water system is split into two
<br />pressure zones, the high pressure zone is located in the north portions of the City and
<br />the low pressure zone is located in the south portion of the City. The AUAR study area
<br />is located in the low pressure zone. The low pressure zone and high pressure zone
<br />are connected by three booster stations.
<br />The City's water model was provided by Elfering and Associates for the low pressure
<br />zone. According to the water model provided the existing average day demand for the
<br />low pressure zone is 999,000 gpd (694 gpm) and the peak day demand is 3,936,000
<br />gpd (2,733 gpm) (Elfering used a peak day factor of 3.94 which is higher than the
<br />City's historical peak factor). Only Wells 2, 3, and 4 and the Gary Street and Freeport
<br />Towers are located within the low pressure zone; therefore, the low pressure zone
<br />has a storage capacity of 2,000,000 gallons and a total well capacity of 3,600,000 gpd
<br />(2,500 gpm). In the model provided by Elfering, the total low pressure zone well
<br />capacity was used during the peak day calculations. As shown, the low pressure zone
<br />has sufficient storage capacity for the low pressure zone's average day demand plus a
<br />fire flow capacity of 630,000 gallons, which results in a required storage capacity of
<br />1,629,000 gallons. The total low pressure zone well supply capacity, however, cannot
<br />accommodate the peak day demands from the low pressure zone as a stand alone
<br />system and therefore, Elfering directed us to include a supply of 700 gpm flow be
<br />added to the model to mimic the supply that is available from the high pressure zone
<br />through the opening of the City's Pressure Reducing Valves (PRV's). This resulted in a
<br />total water supply to the low zone of 3,200 gpm. Once this was added to the water
<br />model, there was sufficient well capacity provided to the low pressure zone on the
<br />existing peak day.
<br />City of Elk River
<br />Draft Alternative Urban Areawide Review
<br />July 2011
<br />Page 34 of 84
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