Reso13 PC 13-09 2859 Initial Study Mitigated Negative Declaration Kensington

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— Coverage of soil, equipment, and supplies that could contribute non- visible pollution prior to rainfall events or perform monitoring of runoff. — Perform monitoring of discharges to the stormwater system. MM HYD 1-9: The developer will submit a copy of the draft SWPPP to the City of Redwood City for review and approval prior to construction of the project site. The certified SWPPP will be posted at the site and will be updated to reflect current site conditions. Post-Construction Impacts Implementation of the project will result in an increase in pollutant loads due to an approximate 13 percent increase in impermeable surfaces on the site. The project site will still contribute the same types of stormwater runoff pollutants as the existing development. Street and parking area runoff often carries grease, oil, and trace amounts of heavy metals into natural drainages. Runoff from landscaping can carry pesticides,herbicides, and fertilizers. Although the amounts of these pollutants ultimately discharged into the waterways are unknown, over time they could be substantial. The existing and proposed square footages of pervious and impervious surfaces are shown on Table 3,below. The existing project site is approximately 46,026 square feet23, of which approximately 61 percent is currently comprised of impervious surfaces. The proposed project will replace 28,299 square feet of impervious surface on-site and add an additional 5,878 square feet of impervious surfaces. The remaining 11,919 square feet of area will be open space comprised of pervious surface and landscaping. The project will result in a net increase in impervious surfaces on the site, so implementation of the proposed project could increase the amount of runoff and pollution flowing into the storm drain system. TABLE 3 Pervious and Im ervious Surfaces On-Site in s uare feet Site Surface Existing % Project % Net % Conditions Conditions Difference Im ervious Building Footprint 6,099 13 18,292 40 12,193 27 Parking/ Sidewalks/Patios/Paths 22,130 48 15,815 34 -6,315 -14 Subtotal 28,229 61 34,107 74 5,878 13 Pervious Landsca in 17,797 39 11,919 26 -5,878 -13 Total 46,026 100 46,026 100 Because the project will replace more than 10,000 square feet of impervious surface area on the project site,the project must comply with the City of Redwood City's Stormwater Management and Discharge Control Program and the SWRCB NPDES permit. In order to meet these requirements, the project will include the following measure to reduce runoff pollutant loads: 23 One acre equals 43,560 square feet. Kensington Assisted Living Facility Project 57 Initial Study Redwood City Apri12013