5900 36TH AVE W 2025-01-06 - Laserfiche WebLink

SOUNDVIEW TECHNOLOGY CENTER EVERETT, WA PERMANENT STORMWATER CONTROL PLAN EXISTING SITE HYDROLOGY The total site is approximately 39 acres with only 26.36 acres being developed. The site is currently unoccupied consisting of grass and shrubs, modeled as 100% forested. It is comprised of 4 existing basins (A, B, C and D). Basin A and D receive existing upstream tributary flows of 1.55 acres (A) and 2.31 acres (D) forested area that will not be routed to the onsite storm drainage system. See Table 2 below for existing conditions of the on-site basin areas. Table 2 Existing Conditions Basin Area (AC) Description Grade 6.19 Basin A - Forest, previously cleared Steep 12.18 Basin B - Forest, previously cleared Steep 6.26 Basin C - Forest, previously cleared Steep 1.73 Basin D - Forest, previously cleared Steep 26.36 Total Basin Area DEVELOPED SITE HYDROLOGY The proposed site development will consist of paved parking and drive aisles, concrete walkways, three buildings, and landscaping/pervious surface. The project has limited frontage improvements, proposing to replace the existing curb/gutter and sidewalk around the cul-de-sac bulb. The project site is 26.35 acres of total development area to 5 detention systems. All the basins will contain areas/flows from the proposed development. The Per Earth Solutions NW report dated Feb. 9, 2017 it is infeasible to infiltrate and no LID measures will be applied to the proposed stormwater system except for BMP 5.13 Post- Construction Quality and Depth. See Table 3 for proposed conditions of the on-site basins and vaults. Table 3 Proposed Conditions Basin Total Total Hard Surface PGHS (AC) NPGHS Converted Vaults Area (AC) (AC) Vegetated Area (AC) (AC) A 6.19 6.19 0 6.19 0 #2 B 12.18 9.81 6.66 3.15 2.37 #3 &#5 C 6.26 5.35 4.52 0.83 0.91 #4 D 1.73 1.73 0 1.73 0 #1 26.36 Total Basin Area SEPTEMBER 23, 2022 STORMWATER DRAINAGE REPORT PAGE 22