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<br />system would need to be of a type approved by the Bay Area Stormwater Management Agencies Association
<br />(BASMAA). This proposed exemption is subject to City review and approval.
<br /> The project component site is about 89 percent impervious and almost entirely occupied by the existing office building
<br />and parking. There would be a net increase in total impervious surface area because part of the proposed project
<br />component site includes approximately 7,474 square feet of existing impervious surface area (the Spring/Marshall
<br />parklet and adjacent undeveloped patch), which would be a part of the parcel assembly to create the 1.6-acre site for
<br />the project component. Applicant-proposed stormwater treatment for the project component would is discussed below.
<br /> The project component’s storm water management plan (Sandis, p. 2 and “Attachment I: Stormwater Capacity
<br />Calculations”; Plan Sheet TM6.0, 11/9/23) identifies four onsite drainage management areas (DMAs): DMA-1,
<br />DMA-2, DMA-3, and DMA-4; the plan also identifies six offsite DMAs: DMA-A, DMA-B, DMA-C, DMA-D,
<br />DMA-E, and DMA-F. In addition, to meet stormwater discharge 10-year pre-development standards, the project
<br />component proposes to route stormwater to detention tanks in the basement (two stormwater tanks would be located
<br />on Basement Level 1) after being treated by either flow-through planters or media filters. (Sandis “Appendix F: LID
<br />Reduction Narrative”; Plan Sheet A3, 11/9/23).
<br /> Onsite DMAs. All onsite DMAs except DMA-4 would be treated using flow-through planters; DMA-4 would be
<br />treated via media filter, located in the building basement. For stormwater treatment purposes, the flow-through planters
<br />are considered LID but the media filters are not. (See Plan Sheet TM6.0 for locations.)
<br /> DMA-1, a 8,652 SF (0.20 AC) area, located along the northern part of the project component site; required
<br />treatment area is 327 SF, and treatment proposed is 338 SF.
<br /> DMA-2, a 11,383 SF (0.26 AC) area, located in the north-central part of the project component site; required
<br />treatment area is 437 SF, and treatment proposed is 457 SF.
<br /> DMA-3, a 21,953 SF (0.50 AC) area, located just off center toward the west, in the middle part of the project
<br />component site; required treatment area is 821 SF, and treatment proposed is 965 SF.
<br /> DMA-4, a 27,881 SF (0.64 AC), located along the eastern and southern parts of the project component site; the
<br />treatment would be via media filter. Stormwater runoff from DMA-4, which includes the building terraces and
<br />the public commons area, would be collected via roof drains and area drains (for the commons area), conveyed
<br />via piping to the media filters.
<br /> Total onsite stormwater area (impervious plus pervious) = 69,869 SF (1.6 AC); total onsite stormwater area required
<br />to be treated = 1,585 SF; total onsite stormwater area treatment proposed = 1,760 SF.
<br /> Offsite DMAs. All offsite DMAs would be treated using silva cells or a similar product, per City of Redwood City
<br />green infrastructure standards. The Silva Cell system, or a similar product, would be proposed to treat the stormwater
<br />runoff from the public right-of-way that drains to the project component frontage, including curb inlets, which will
<br />collect stormwater runoff and then convey it to Silva Cells and for street tree locations. The Silva Cell system provides
<br />space for uncompacted soil that supports tree root growth while allowing for the ground to naturally absorb and filter
<br />stormwater. Each “cell” would consist of an open frame formed with a base and posts that connect to a top “deck.”
<br />This frame would allow stormwater (rainwater) to filter through the soil while providing physical support for ground-
<br />level sidewalk and nearby loads. The support would reduce impacts on roots from compaction, and thereby allow tree
<br />roots to grow naturally, which would extend the health and life of the tree (Sandis, pp. 2 and 4; Plan Sheets TM6.0
<br />and TM6.1, 11/9/23). The Silva Cell system, or an equally effective product, is proposed for 28 street trees: six on
<br />Broadway, eight on Main Street, eight on Walnut Street, and six on Marshall Street. (See Plan Sheet TM6.0 for
<br />locations.)
<br /> DMA-A, a 5,580 SF (0.13 AC) area, located adjacent to the northeastern part of the project component site;
<br />required treatment area is 220 SF, and treatment proposed is 273 SF.
<br /> DMA-B, a 2,578 SF (0.06 AC) area, located adjacent to part of the eastern part of the project component site;
<br />required treatment area is 98 SF, and treatment proposed is 145 SF.
<br /> DMA-C, a 4,921 SF (0.11 AC) area, located adjacent to the southeastern and part of the eastern part of the project
<br />component site; required treatment is 190 SF, and treatment proposed is 221 SF.
<br /> DMA-D, a 5,720 SF (0.13 AC) area, located adjacent to the southwestern part of the project component site;
<br />required treatment area is 223 SF, and treatment proposed is 232 SF.
<br /> DMA-E, a 5,697 SF (0.13 AC) area, located adjacent to the western part of the project component site; required
<br />treatment is 224 SF, and treatment proposed is 241 SF.
<br /> DMA-F, a 9,135 SF (0.21 AC) area, located adjacent to the northwestern part of the project component site;
<br />required treatment area is 358 SF, and treatment proposed is 429 SF.
<br />ATTY/RESO.0074/CC RESO 847 WOODSIDE (CEQA) - EXHIBIT 1 - CEQA CONSISTENCY CHECKLIST
<br />REV: 10-23-24 VR
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