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Ms. Sue Polka
<br />June 2, 2017
<br />Page 3
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<br />particularly improvements pertaining to the extension into the TCAAP site. The following summarizes the
<br />WSB modeling results:
<br />
<br />- Booster Station Pumps: The existing booster station has two pumps, each with a nominal
<br />capacity of 1,500 gallons per minute (gpm). The proposed west side booster station was sized to
<br />meet the future maximum day demands in the north pressure zone under the assumption that
<br />only one pump at each station operates under normal conditions. Therefore, the west side
<br />booster station was modeled to be identical to the east side station, with one 1,500 gpm pump
<br />running and the second pump available as a backup to provide redundancy.
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<br />- Water Storage: Additional water storage is needed to serve the projected water demands of the
<br />City’s north pressure zone. The future average day demands in the north pressure zone are
<br />expected to increase to 1.47 million gallons per day (MGD) by 2030, assuming a ten-year build
<br />out of the TCAAP site with construction beginning in 2020. The volume of storage required for a
<br />water distribution system is determined by examining many variables, including operational
<br />needs, fire flow needs, equalization volume and firm supply capacity.
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<br />Under normal conditions, required minimum fire flow is determined by evaluating the exposure,
<br />occupancy, construction materials, and interior sprinkler system flow rates of each individual
<br />building. Since this information is not readily available, the recommended minimum fire flow rate
<br />for the TCAAP site was conservatively assumed to be 3,500 gpm. This fire flow was
<br />approximated based on the Insurance Service Office (ISO) and the American Water Works
<br />Association (AWWA) standards and recommendations.
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<br />The projected calculations used for determining the existing and future storage needs for the
<br />City’s north pressure zone are shown in Table 1.
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<br /> Table 1: North Pressure Zone Water Storage Volume Requirements
<br />
<br />Year 2017 Year 2019 Year 2030
<br />3 Hour
<br />Fire
<br />3 Hour
<br />Fire
<br />3 Hour
<br />Fire
<br />A Average Daily Water Use (gpd) 560,000 630,000 1,470,000
<br />
<br />B Maximum/Average Day Ratio 3 3 3
<br />C Maximum Day Water Use (gpd) (A x B) 1,680,000 1,890,00 4,410,000
<br />D Maximum Day Water Use in gpm 1,167 1,313 3,063
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<br />E Firm Pumping Supply Capacity in gpm 1,500 4,500 4,500
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<br />F ISO Design Fire Fighting Rate in gpm 3,500 3,500 3,500
<br />G Fire Fighting Duration in Hours 3 3 3
<br />H Design Fire Fighting Volume in gal (F x G x 60min/hour) 630,000 630,000 630,000
<br />
<br />I Total Coincident Demand in gpm (D + F) 4,667 4,813 6,563
<br />J Required Draft from Storage in gpm (I - E) 3,167 313 2,063
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<br />K Adjusted Fire Fighting Storage in gal (G x 60 min/hr x J) 570,060 56,000 371,000
<br />L Equalization Storage in gal/day (C x 25%) 420,000 472,500 1,102,500
<br />M Total Storage Need in gal (K + L) 990,060 528,500 1,473,500
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<br />N Existing Storage Capacity in gal 500,000 500,000 500,000
<br />O Additional Storage Capacity Needed in gal (M – N) 490,060 28,500 973,500
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