Response to Comments - Presidio Trust

any increase in storm water flow from the project site to the City’s combined sewer system may have onthe number or volume of combined sewer discharges. “The analyses should evaluate the capacity of theexisting PHSH District sanitary sewer mains, the amount of storm water infiltration expected from thearea, the amount of storm water runoff the Project will generate, and the conditions under which theestimated sanitary and storm water flows will contribute to combined sewer discharges from the SFPUCwest-side sewer system. An evaluation of historical sewer capacity problems when previous use of thesite was at a maximum, historical sanitary flow volume, and the estimated average sanitary flow rate fromthis site at project completion” should be determined.Response UT-4 – In response to the comment, the wastewater and storm drainage analysis in the DraftSEIS was expanded to include a comparison of the runoff projections included in the planning for theCity’s Richmond Transport project with current runoff projections for the PHSH district. This analysisconcluded that the PHSH district was included in the planning for the Richmond Transport Project. TheCity’s 1971 Master Plan for Wastewater Management, which served as the basis for the RichmondTransport Project, assigned an average runoff coefficient of 0.54 for the area tributary to the RichmondTransport (which includes the PHSH district). The 1971 Master Plan resulted in an estimated peak flowof 15.4 cubic feet per second (cfs) compared to the resultant peak flow of 11.4 cfs using the 1994 PresidioStorm Water Management Plan. Both estimates were based on a 10-year, 30-minute storm with anintensity of 0.67 inch per hour. This confirms that there is sufficient capacity in the San Francisco PublicUtilities Commission (SFPUC) system to accommodate runoff from the PHSH district without increasingcombined sewer discharges over planned levels. All alternatives would include storm water reductionmeasures described in Mitigation Measure UT-7 Storm Water Reduction, which include limitingimpervious surfaces and other infiltration techniques. Additionally, during design infrastructure upgradesto the PHSH district, areas of infiltration to the sewer system will be addressed and other storm waterminimization measures will be identified (see Response to Comment OT-1), which would further reduceimpacts on the SFPUC west-side sewer system.UT-5. Water Supply and DemandThe SFPUC asserted that its San Francisco Urban Water Management Plan projection of Presidio dailywater demand of one million gallons per day (mgd) is not a guaranteed water allocation for the Presidioand may need to be revised downward.Response UT-5 – The SFPUC’s comments are noted. The Trust is a retail water customer of the SFPUC.As such, it is vital that Presidio water demands are incorporated into the SFPUC’s regional water demandplanning. The Trust currently purchases supplemental water from the SFPUC when the Trust’s localsupplies are not sufficient to meet peak demands. As the Trust implements proposed land uses,restoration efforts, demolition, and other activities consistent with the PTMP, the Trust will continue torely on the SFPUC for a portion of the Presidio’s water needs. The Presidio’s projected water demandswill vary over the course of the year from 0.75 to 1.93 million gallons per day (mgd), with a projectedannual consumption of approximately 445 million gallons resulting in an average daily demand ofapproximately 1.22 mgd. The Trust’s on-site supplies (Lobos Creek) typically supply between 0.7 andPublic Health Service Hospital Response to Comments 69