8102 EVERGREEN WAY EVERETT 4 CORNERS 2025-08-06

Four Corners Short Plat Stormwater Site Plan SECTION 8 — PERMANENT STORMWATER CONTROL PLAN A. Off -Site Analysis A field inspection was performed on Friday, July 5, 2019 on a sunny day with a temperature of approximately 80 degrees. The site is developed and has been previously cleared for the use of various commercial business that are currently located on the project site. There are areas of the site covered with brush and grass, but the majority of the site appears to be covered with impervious surface in the form of buildings, asphalt, and gravel surfaces. On -site Drainage Basin The project site can be split up into two distinct drainage basins. The southern basin, consisting of the Everett Medical Clinic, flows due west to a separate stormwater pond. The remainder of the project site flows northeast and is collected via a series of below grade conveyance system. The project site primarily discharges to an existing Swale in the north east corner of the project site, that is discharged to the below grade system in 79th Place SE and Evergreen Way. Downstream Basin The project site is surrounded by public roadways on all sides, Beverly Lane to the west, 791h Place SE to the north, Evergreen Way to the east, and SR526 (Boeing Freeway) to the south. The detention/treatment facility on the south side of the property discharges to the public system below grade in the Beverly Lane right-of-way. This system traverses north, below grade before combining with the western portion of the 791h Place SE right-of-way system. The conveyance system continues to traverse north through a series of below grade systems. The Beverly Lane system eventually discharges to Beverly Lake approximately 1/2 mile north of the project site. The swale in the north east portion of the site discharges to the eastern system within 79th Place SE right- of-way. This system traverses east and connects to the stormwater system within the Evergreen Way right-of- way. The Evergreen way conveyance system traverses north within the right-of-way. Upstream Basin The project site is surrounded by public roadways on all sides, Beverly Lane to the west, 79th Place SE to the north, Evergreen Way to the east, and SR526 (Boeing Freeway) to the south. Each of the right-of-ways are fully developed with stormwater collection and conveyance systems. No upstream basins are anticipated with this project. B. Existing Hydrology The existing site was previously developed with the construction of the Andersons Shopping Center. The site has historically been a large commercial building with associated parking. After reviewing historical aerials, the shopping center and parking lot was developed prior to 1969. In 1999, the northeast portion of the site was redeveloped with a McDonalds Restaurant. The Geotech and storm drainage report from that redevelopment is attached in Appendix D. As stated in the attached stormwater report, the existing site stormwater was collected and routed via a below grade conveyance system to the low point of the property, the north east corner of the project site. The entire shopping center parcel, along with the restaurant parcel stormwater are currently combined and discharge to an existing vegetative swale in the northeast corner of the property. The swale discharges to the below grade stormwater system located within the 791h Place SE right-of-way which is then routed to the Evergreen right-of-way. CPH Project No. 0024-18-042 October 23, 2020 CPIH CONSULTANTS Page 15