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86 The project component is expected to qualify for a 50 percent exemption under Special Project Category “B” (Larger Infill Projects) of the San Mateo Countywide Water Pollution Prevention Program. This means that the project would be 50 percent exempt (in storm drainage volume) from County low impact development (LID) requirements because the project component would: (1) be located in a municipality’s designated central business district, downtown core area or downtown core zoning district, neighborhood business district or comparable pedestrian-oriented commercial district, or historic preservation site and/or district; (2) create and/or replace more than 0.5 acres of impervious area and less than 2.0 acres; (3) include no surface parking, except for incidental parking for emergency access, ADA access, and passenger or freight loading zones; (4) have at least 85 percent coverage of the entire site by permanent structures; the remaining 15 percent portion of the site may be used for safety access, parking structure entrances, trash and recycling service, utility access, pedestrian connections, public uses, landscaping and stormwater treatment; and (5) have a minimum density of either 50 dwelling units per acre (for residential projects) or a Floor Area Ratio (FAR) of 2:1 (for commercial projects) - mixed use projects may use either criterion (Project applicant “C.3 and C.6 Development Review Checklist, San Mateo Countywide Water Pollution Prevention Program,” R. Hansen, CBG, undated). However, the project component would only use six percent of the project component site’s impervious surface runoff, which would be treated via media filtration; the remaining 94 percent would be treated using LID measures. This proposed exemption is subject to City review and approval. The project site is approximately 87 percent impervious and occupied by two existing structures, connected by a covered walkway, and surface parking. There would be a net decrease in total impervious surface area with development of the proposed project component, including an increase in building rooftop area that would be offset by a reduction in impervious sidewalk, patios, paths, driveways, streets, and uncovered parking, with a net change of an 882 SF decrease in total impervious surface area. The proposed project component would decrease total impervious surface area by 882 SF (pre-project impervious surface area of 35,995 SF; minus post-project impervious surface area of 35.113 SF = 882 SF). There would be an increase in building rooftop area (from pre-project 8,198 SF to post-project 31,923 SF) and decreases in impervious sidewalk, patios, paths, driveways, streets, and uncovered parking (from pre-project 27,798 SF to post-project 3,190). However, the post-development impervious surface area (35,113 SF) would be less than the pre-development impervious surface area (35,995 SF) (Project applicant “C.3 and C.6 Development Revise Checklist, San Mateo Countywide Water Pollution Prevention Program,” R. Hansen, CBG, undated). The project’s preliminary storm water control plan (Plan Sheet C.6, 10/30/23) identifies 12 drainage management areas (DMA): 10 are onsite (DMA-1, DMA-2, DMA-3, DMA-4, DMA-5, DMA-6, DMA-7, DMA-8, DMA-11, and DMA-12), and two are offsite (DMA-9 and DMA-10). In addition, an “alternate” preliminary stormwater control plan (Plan Sheet C.6.1, 10/30/23) has been provided by the project component applicant. This alternative plan includes a 13th DMA (DMA-13) and slightly different overall configuration; the alternate plan is described in more detail following this description of the proposed stormwater control plan. The DMAs can be generalized by their treatment control measures: DMA-1 through DMA-5 would convey runoff from the roof and podium deck to flow-through planters containing bio-retention media; these planters would be located at the ground level with the exception of DMA-3, where the flow-through planter would be located on the podium. DMA-6, which is the uncovered ground-level building courtyard area, would convey runoff through internal plumbing to an onsite media filter. DMA-7, DMA-8, DMA-11, and DMA-12 would contain runoff from the perimeter of the project component site as well as the podium deck, and would be self-retaining areas. DMA-9 and DMA-10, treating the Woodside Road frontage and sidewalk as well as a small portion of onsite sidewalk, would use Silva Cells (see “847 Woodside Road - Narrative Discussion of Low Impact Development Feasibility/Infeasibility” prepared by the applicant; undated). The Silva Cell system provides space for uncompacted soil that supports tree root growth while allowing for the ground to naturally absorb and filter stormwater. Each “cell” would consist of an open frame formed with a base and posts that connect to a top “deck.” This frame would allow stormwater (rainwater) to filter through the soil while providing physical support for ground-level sidewalk and nearby loads. More specifically, the DMAs provide treatment as follows (see Plan Sheet C.6 for all DMA locations and the “Preliminary Treatment Control Measure Summary” on the plan sheet for DMA specifications):  DMA-1: 5,219 SF of impervious area and 161 SF of pervious area; located in the northeastern part of the project component site; required bioretention is 161 SF, and treatment proposed is 161 SF. Stormwater runoff from DMA-1 would be treated using a flow-through planter.  DMA-2: 8,773 SF of impervious area and 377 SF of pervious area; located adjacent to and south of DMA-7 and extending into the center of the site; required bioretention is 352 SF, and treatment proposed is 377 SF. Stormwater runoff from DMA-2 would be treated using a flow-through planter. ATTY/RESO.0074/CC RESO 847 WOODSIDE (CEQA) - EXHIBIT 1 - CEQA CONSISTENCY CHECKLIST REV: 10-23-24 VR Page 86 of 135