10521 19TH AVE SE 2022-05-23 - Laserfiche WebLink

Silver Lake Plaza Minimum Requirement # 1: Stormwater Site Plan Executive Summary The proposed 0.94 Acre development site consists entirely of clearing/grading for the construction of a new two story mixed use commercial building with associated parking and drainage improvements. The proposed building is designed to contain a restaurant, hair salon, and office space. Access to the site is to be provided directly from 19t" Avenue SE located directly west of the site. All new utilities are to be provided by existing services within 19t' Avenue SE. Total new/replaced hard surfaces for the site have been calculated at 32,302 sf. with approximately 22,430 sf. of that consisting of PGIS. All new/replaced hardscape area to consist of effective runoff. 8,597 sf. of new landscape area also to be installed for the project. As a result of these amounts, project triggers analysis of Minimum Requirements 1-9 of the 2014 DOE SWDM. Due to the infeasibility of on -site infiltration and dispersion measures, drainage management for new on -site runoff, along with approximately 0.16 Acres of upstream lawn runoff entering the site, will be provided by an underground pipe detention system, with a post -detention large linear sand filter (providing enhanced treatment), along the south side of the site beneath the proposed parking and drive aisle areas. The controlled and treated runoff is to discharge into the public drainage system along the east side of 19th Avenue SE, maintaining the natural discharge location for the site. The longest proposed conveyance route to the detention system is 123 lineal feet. Refer to sections MR#6 and MR#7 for more detailed design and analysis of water quality treatment and flow control design. The project is to be designed according to the Amended 2014 Stormwater Management Manual for Western Washington (SWMMWW) and the City of Everett Design and Construction Standards and Specifications. Conveyance system design is to be based on Section 4-2 of the City of Everett DCSS. Existing Conditions Summary The site consists of two parcels with one tax number and contains existing unmaintained vegetation. The site and immediately adjacent areas tend to slope westerly toward 19th Avenue SE at slopes ranging from 3% to 12%. Runoff from the site and areas upstream of the site is intercepted by the existing public storm drainage system along 19th Avenue SE. This public system conveys runoff southerly, eventually discharging into Silver Lake. WESTERN ENGINEERS, INC. 2 PROJECT: 15-1415-A