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99 The Housing Component would incorporate traditional low impact development (LID) treatment measures in the onsite stormwater system design to meet Provision C.3 permit and San Mateo Countywide Stormwater Pollution Prevention Program (SMCSWPPP) requirements (Plan Set, Sheet C-6.1, 11/2022). Stormwater from the site would be treated with a combination of bioretention areas, Silva Cells areas, and self-treating landscape areas. Each bioretention area is sized according to C.3 Technical Guidance. The Housing Component would manage stormwater runoff in 14 drainage management areas (DMA), which include a combination of on-site and off-site DMAs. Nine (9) of the 14 DMAs would treat runoff in bioretention areas, three DMAs would treat runoff in self-retaining landscape areas, and the remaining two DMAs (offsite) would treat runoff via the Silva Cell system. The Housing Component site is approximately 93 percent impervious. Site cover consists of existing buildings, driveways and paved internal roadways (for the self-storage facility), and landscaping. The Housing Component build out would result in 28,197 SF of onsite impervious surface area, compared to 32,767 SF of onsite impervious surface area under existing conditions (Plan Set, Sheet C-6.1, 11/2022). Therefore, there would be a net decrease in total impervious surface area amounting to 4,570 SF. Post-construction onsite pervious surface area would amount to 6,876 SF. All stormwater data and components provided by the Housing Component applicant are subject to review, approval, and onsite inspection by the City. The Housing Component would be subject to these standard requirements as conditions of project component approval. As a result of Focused GPU standards and the City requirements described above, the proposed Housing component would have a less than significant impact and would not generate additional stormwater drainage impacts beyond those analyzed in the Focused GPU program EIR. Therefore, this Housing component would be consistent with the analysis in the Focused GPU EIR because it would not create new impacts or increase impacts, and there is no new information of substantial importance for CEQA purposes. b. The City of Redwood City does not currently rely on groundwater as a water supply source. Groundwater impacts were analyzed in the Focused GPU EIR and were determined to be less than significant impacts because Redwood City did not then have and had no intention of using groundwater as a water supply, so future development within the planning area would not have caused a depletion of groundwater supplies. Additionally, because future developments would largely be constructed on previously developed land, there would not be a substantial increase in impervious surfaces. Because the Focused GPU implementation would not substantially decrease water supplies or interfere substantially with groundwater recharge, this impact was found to be less than significant. Implementation of the proposed Housing Component would not require substantial amounts of water such that it would result in substantially depleted groundwater supplies (see item XIX[b] [water supply] of this checklist). Under the State’s Sustainable Groundwater Management Act (SGMA), medium and high priority groundwater basins are required to prepare a Groundwater Sustainability Plan (GSP). The Housing Component site is located in the San Mateo Plain Subbasin – Santa Clara Valley Basin, which according to the City of Redwood City 2020 Urban Water Management Plan (UWMP) has been ranked as a “very low priority” basin and is therefore not subject to the requirements of SGMA. In addition, as discussed in item (a) above, there would be a net decrease in impervious surface area. Therefore, the proposed Housing Component would not substantially decrease groundwater supplies or interfere substantially with groundwater recharge such that the project component would impede sustainable groundwater management of the basin. The Focused GPU program EIR (Focused GPU program EIR pp. 4.10-18 through 4.10-19) concluded that although the City is currently evaluating groundwater as a potential future emergency or back-up supply source, there is no guarantee that future development projects would use groundwater for water supply, and instead would rely on potable water purchased from SFPUC (distributed by the City) and recycled water from the City. The Focused GPU program EIR also concluded that increases in new impervious areas associated with future development within the City, including the Housing Component, would be expected to be minimal and would not be expected to interfere substantially with groundwater recharge. Therefore, the Housing Component would not substantially decrease water supplies or interfere substantially with groundwater recharge such that the Housing Component would impede sustainable groundwater management of the basin. This impact would be less than significant. This component would be consistent with the analysis in the Focused GPU EIR because it would not create new impacts or increase impacts, and there is no new information of substantial importance for CEQA purposes. c. As discussed in the Focused GPU program EIR (pp. 4.10-19 and 4.10-21), development facilitated by the Focused GPU would occur in areas of the City that are currently developed, and increases in impervious surfaces would be relatively minimal (i.e., new impervious surfaces would generally replace existing impervious surfaces and either result in a decrease in impervious surface area due to more extensive use of stormwater control measures or result in a small net increase in impervious surface area). As discussed in item (a) above and the subparts below, the proposed Housing Component would therefore not substantially alter the existing drainage pattern of project component site. In addition, the rate or amount of surface runoff would not be substantially increased by new development because ATTY/RESO.0031/CC RESO CEQA GUIDELINES (901 EL CAMINO REAL) REV: 04-22-25 VR Page 99 of 148