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1 <br />t <br />I <br />J <br />i <br />0 <br />SOUNDVIEW TECHNOLOGY CENTER EVERETT, WA <br />PERMANENT STORMWATER CONTROL PLAN <br />EXISTING SITE HYDROLOGY <br />The total site is approximately 39 acres with only 25.82 acres being developed. The site is currently <br />unoccupied consisting of grass and shrubs, modeled as 100% forested. It is comprised of 4 existing <br />basins (A, B, C and D). Basin A and D receive existing upstream tributary flows of 1.55 acres (A) and 2.31 <br />acres (D) forested area that will not be routed to the onsite storm drainage system. See Table 2 below for <br />existing conditions of the on -site basin areas. <br />Table 2 <br />Existing <br />Conditions <br />Basin Area (AC) <br />Description <br />Grade <br />6.01 <br />Basin A - Forest, previously <br />cleared <br />Steep <br />11.98 <br />Basin B - Forest, previously <br />cleared <br />Steep <br />6.13 <br />Basin C - Forest, previously <br />cleared <br />Steep <br />1.70 <br />Basin D -Forest, <br />previouslycleared <br />Steep <br />25.82 <br />Total Basin Area <br />DEVELOPED SITE HYDROLOGY <br />The proposed site development will consist of paved parking and drive aisles, concrete walkways, 4 <br />buildings, and landscaping/pervious surface. The project has limited frontage improvements, proposing to <br />replace the existing curb/gutter and sidewalk around the cul-de-sack bulb. The project site is 25.82 acres <br />of total development area to 5 detention systems. All the basins will contain areas/flows from the <br />proposed development. The Per Earth Solutions NW report dated Feb. 9, 2017 it is infeasible to infiltrate <br />and no LID measures will be applied to the proposed stormwater system except for BMP 5.13 Post - <br />Construction Quality and Depth. See Table 3 for proposed conditions of the on -site basins and vaults. <br />Table 3 <br />Proposed Conditions <br />Area (AC) <br />Description <br />Grade <br />Basin A — Vault #2 Building A — 17,900 SF <br />Flat Roof <br />6.01 <br />B — 90,400 SF <br />C — 24,300 SF <br />D — 129,200 SF <br />= 6.01ac imp. total <br />Basin B — Vault #3 (lower surface area — 2.68ac lawn <br />Steep Lawn, Mod. Roads, <br />11.98 <br />and 7.87ac imp.) <br />and Flat Sidewalks <br />= 9.55ac total <br />Vault #5 Building D — 106,000 SF <br />Flat Roof <br />= 2.43ac total <br />6.13 <br />Basin C — Vault #4 (upper surface area — 0.59ac lawn <br />Flat Lawn, Sidewalks, & <br />and 5.28ac imp.) <br />Roads <br />= 6.13ac total <br />Basin D — Storm Chamber System #1 <br />1.70 <br />Building A — 74,400 SF <br />Flat Roof <br />= 1.70ac total <br />25.82 <br />Total Basin Area <br />IMAY 23, 2017 STORMWATER DRAINAGE REPORT PAGE 19 <br />