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..s. /ð- // 1.4.1 Project Design Changes For clarification, none of the cost increases associated with design changes are being driven by the Task Force recommendations. Several design changes were required for the recycled water distribution facilities as design progressed from conceptual-level design to pre-design. Specifically, the size of the standby potable water connection for the storage tank at SBSA was increased to improve system reliability, a jack-and-bore crossing of Union Pacific Railroad tracks was added in the Seaport area, and a booster pump station was added to the system to ensure adequate system pressure throughout the system for the life of the project. The necessity of the booster pump station, which would be located in the vicinity of the Highway 101/Redwood Shores Parkway interchange, is still under evaluation pending finalization of operational strategies and system pressure data. The pump station was added to the updated cost estimate to ensure it is included in the financing plan and to provide a conservative overall project cost estimate for City Council. The recycled water treatment facilities underwent several significant design changes between conceptual-level design and final design. The City and SBSA sought many of these design improvements to ensure the facilities would be sufficiently robust and flexible to effectively produce, store, and distribute recycled water over the course of its intended 1 DO-year design life. The increased costs also include possible future expansion of the storage and distribution facilities. Other design changes resulted as solutions to structural and environmental issues. The following design changes caused treatment facility costs to increase: . The pump station was originally planned to be outdoors, but was revised to be fully enclosed in a structure due to concerns about noise from large pumps operating at night. . The elevation of the structures was limited to an elevation of 120 feet due to concerns over visual impacts to adjacent residential areas, associated with the requirement that a use permit be obtained for development of facilities on the SBSA "buffer" land parcel. This required constructing the structures with a much more horizontal and larger footprint, resulting in more expensive construction. . Standby emergency power for the pumping facilities was added to improve system reliability. . Storage tank size and configuration was modified and increased to provide for up to three days of continuous peak day demand. The goal was to ensure system reliability (especially for non-irrigation, year-around users like industrial and commercial cooling customers) and to reduce the probability of using the potable water backup supply to meet customer needs if SBSA production of recycled water is interrupted. The original project envisioned serving mostly irrigation customers, so some short-duration interruptions of service were assumed to be acceptable. . The tanks were originally designed to be circular tanks but are now rectangular cast-in-place concrete structures due to seismic and other structural considerations associated with construction on some of the deepest Bay muds in the San Francisco Bay Area. . The chlorine contact chamber will be covered with a concrete roof to prevent contamination of the water from birds. Redwood City Recycled Water Project Progress Report 2005 Redwood City Recycled Water Task Force Recommendations - Final Report p:lpw-proj\2004\0468025...., recycled retrofit & support svcllask 11 program supportltask force status report\linal reportlprogress report on ff recommendationsJinal.doc Page 3