5901 23RD DR W SEAWAY CORP 3C 2025-07-29

I I. Project Overview 1 This Stormwater Site Plan is designed to fulfill the requirements established by the City of Everett's Drainage Ordinance for the following proposed development by Northshore Christian Church. The 44.8 acre site is located north of 60th Street NW on both sides of 23rd Drive W. The aerial photograph (Figure 1) shows the location of this site. Of the total 44.8 acres, 18.5 acres drains to Powder Mill Gulch, 9.1 acres drains north onto the adjacent plat, and 17.2 acres drains to Narbeck Creek. A total of 18.17 acres is proposed to be developed. 13.46 acres of this developed area drains to Powder Mill Gulch and 4.71 acres drains north to the adjacent plat. All Tables and Figures referenced in this report can be found in the Everett Stormwater Management Manual. II. Preliminary Conditions Summary Except for an existing gravel road and sewer line that extend in line with 23rd Drive, the site is undeveloped. The entire site is vegetated with a dense second growth forest of trees and understory of brush (Table 1-5.6, wood or forestland young second growth or brush). Figure 1 shows the existing cover on the site and surrounding properties. From the Soil Survey of Snohomish County Area, Washington, soils in this area are Alderwood Gravelly Sandy Loam (Table 1-5.5, Hydrologic Soil Group C). The topographical map (Figure 2) shows the natural drainage patterns on the site and surrounding properties. Figure 3 shows the drainage patterns of the existing sub-basins within the site. Overall, the site slopes to the north, with the east 17.2 acres of the site draining into Narbeck Creek, the west 18.5 acres draining to Powder Mill Gulch, and the northwest 9.1 acres draining onto the adjacent plat. The division lines of the three basins are shown on Figures 1, 2 & 3. A portion of the site draining toward Narbeck Creek is only going to be developed into ball fields at this time. Therefore, drainage calculations for that portion of the site are not accounted for in this report. Subsurface drainage pipes will direct groundwater to the proposed pond. If that area is developed to more intensity in the future, detention will need to be designed with outfall into Narbeck Creek. The basins to be developed total 27.6 acres. Of the 27.6 acres, 18.17 acres is proposed to be developed. 13.46 acres of this developed area drains to Powder Mill Gulch and 4.71 acres drains to the adjacent plat. The remaining 9.43 acres of the 27.6 acres is either buffer (landscaping & NGPA) or retention pond. The west and north sides of the site abut residentially developed property. The west half of the south side of the site abuts 60th Street. The east half of the south side of the site, (east of 23rd Drive) abuts undeveloped commercial property or Narbeck creek/buffer. The east side of the site abuts Narbeck creek buffer. Site conditions as seen on Figure 2 show that there is little drainage which can enter onto the site from surrounding properties. North of the site, drainage flows away from the site. As described above, drainage onsite flows towards the respective creeks on the east and west sides of the site and toward the adjacent plat to the north. Therefore, there is only potential for drainage to enter the site across the south property line. I