AgdaPkt 2018-01-22 Joint SA PFA - Laserfiche WebLink

Browse Search

CIVIL ENrIN ® S A N D ' S SURVEYOS PLANNERS EERS Site Assessment Studv 8.C. - Page 29 January 12, 2018 Harbor View — Inner Harbor June 2015). The Inner Harbor Specific Plan Utilities Engineering Report was utilized to analyze the existing utilities on the project site along with costs and calculations for this site assessment. These utilities include Potable Water, Recycled Water, Sanitary Sewer, and Storm Drain which run along Blomquist Street and Maple Street with various laterals extending into the project site. SANITARY SEWER Sanitary Sewer Facilities consist of gravity main and forced main, with existing gravity laterals running through the project site. A 10" gravity pipe runs across the project site north to south, continuing across highway 101. The existing force main along Blomquist runs to the Maple street pump station. Both the gravity and the force main flow north to be treated at the Silicon Valley Clean Water Wastewater Treatment Plant in Redwood Shores. Typical sanitary sewer loads that can be expected are estimated based on an average demand per area for a typical Electronics/engineering and design office. This average demand factor is applied for both the Proposed Project building area and the Base Project building area giving an average flow of 215,894 gallons per day (gpd) and 151,126 gpd, respectively. Applying a peak flow factor to the average flow gives a peak flow of 1.34 cubic feet per second (cfs) and 0.94 cfs for the Proposed and Base Project, respectively. Existing gravity 10" main, 8" and 6" lateral are then used to calculate the existing capacity of the gravity sewer lines on site. Redwood City Design Criteria are assumed for pipe slopes, flow elevation at peak flow condition, as well as design velocity range. The calculated accumulative existing capacity for peak flow is 2.01 cfs. This capacity is large enough to take on the both the Proposed and Base Project, though additional upstream loads on the system are not accounted for in the calculation. In order for sanitary sewer facilities to be utilized within the Proposed Project, 456 LF of 10" line needs to be removed and 861 LF installed in order to reroute sewer line around the proposed buildings B1 and B2 at a cost of $ 73,028 to the developer. Assuming the Base Project is designed around the existing lines and no re-routing is necessary, there is a possibility there will be no additional cost to the developer. In either scenario there will be no additional cost to the city. STORM DRAINAGE The proposed project site is located within two separate watersheds, the Oddstad and Seaport Boulevard watersheds. The existing storm drain system within the project area has a 30" main running along Blomquist to the Oddstad pump station and then discharging into Steinberger Creek. The existing system is likely designed to convey the 10 -year design storm while current City of Redwood City standards require a 100 -year design storm. Calculations for the proposed and Base Project were completed for the 100 -year — 10 minute duration storm in the project location. Peak discharge for the Proposed and Base Project are 45.44 cfs and 48.75 cfs, respectively. The capacity of the 33" main is larger than both the Proposed and Base Project at 56.38 cfs. This is assuming all flow for the site goes into the storm drain. A more realistic approximation Page 13 1700 S. Winchester Boulevard I Campbell, CA 95008 1 P. 408.636.0900 1 F. 408.636.0999 / www.sandis.net