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City of Pleasanton 4.0 Water Agency Background Final Water Supply Assessment Stoneridge Drive Specific Plan Amendment and Staples Ranch Project Cottonwood Creek. Just northeast of the current Pleasanton city limits, the Arroyo Las Positas joins the Arroyo Mocho. Figure 4 shows the Arroyo systems in Zone 7's service area. 5.1.1 Water Treatment and Capacity Zone 7 currently operates two water treatment plants (WTP), Del Valle WTP and Patterson Pass WTP. Total surface water treatment design capacity is 55 mgd. At present, Zone 7 is in the final design, permitting and pre-bid stages of constructing a third WTP in the Altamont Hills. The Altamont WTP will initially treat 24 mgd and but is being planned to expand up to 42 mgd as needed over the next 20 years. When all three WTPs are operating at capacity, Zone 7 will be capable of producing up to 98 mgd. Zone 7 also operates seven wells located in Pleasanton within three well fields - with a combined peak pumping capacity of 32 mgd. In order to ensure proper distribution of both its treated surface water and groundwater well supplies, Zone 7 also manages a regional pipeline transmission and conveyance system used to transport potable water supplies to the retail water agencies. 5.2 City of Pleasanton Service Area and Water System The City of Pleasanton's Water Department supplies water to approximately 22,000 residential, commercial, industrial, governmental, and landscape irrigation customers throughout the city limits.' The City's water supply system is primarily dependent on the supply of water available from Zone 7 sources (supplying approximately 75 - 80 percent of the City's annual water demand). The City's transmission and distribution system connects with Zone 7's water conveyance pipelines at seven metering locations (turnouts) located throughout the City. The City also operates three municipal groundwater wells to supplement the purchased supplies. These wells supply the remaining 20 - 25 percent of total annual City water demand. The City's service area is shown in Figure 5. 5.3 Water Supply Setting 5.3.1 Climate Pleasanton's climate is best described as Mediterranean, characterized by hot, dry summers and cool, moist winters. Annual precipitation in the region varies from 24 to 28 inches in the western portions of the Livermore-Amador Valley to approximately 14 inches in the more arid, eastern locations. Table 5-1 shows the average annual precipitation, evapotranspiration and irrigation demands in and around the project area. Personal Communication with City of Pleasanton Utilities Department, October 2007. P:\Projects - WP OnIy411182.01 Staples Ranch WSA\FinallFinal WSA.doc 5-3