APPROVED STM BLD2020-1129+Storm_Drainage_Report+10.21.2020_1.39.01_PMRAM Engineering
Memorandum
To: City of Edmonds Date: October 6, 2020
Engineering Division
From: Rob Long, PE
RAM Engineering
Subject: Select Homes 7th Ave S Short Plat- Lot 21055 7t" Ave S
Stormwater Memo
RAM Job No. 19-037
This memo provides a summary of the stormwater drainage control system for Lot 2 of the Select Homes 2-Lot
Short Plat (PLN2020-0019). Due to the anticipated site grading and existing fills present onsite infiltration and
dispersion BMPs are not feasible; thus, a detention pipe is the viable stormwater hard surface BMP for the
individual lots. Therefore, the roof top and other hard surfaces will be managed by a detention pipe system
designed in accordance with the Edmonds Stormwater Addendum (per (ECDC 18.30.030.D.5.d). In accordance
with Edmonds Code, lawn and landscape areas will be managed by post -construction soil quality and depth soil
amendments (per BMP T5.13).
The rooftop and "other hard surfaces" (driveway, walk/patio, and portion of the alley and ROW improvements
areas) will total 4,350 sf and will be managed by an onsite detention pipe (per Edmonds Stormwater
Addendum, 6.3.1). The 4,350 sf of hard surface will require 35 ft of 36" pipe (4,350 sf x 0.008=34.8) for BMP
mitigation. The detention pipe will be constructed onsite, along the west boundary of the lot; see the Civil Site
plan for layout and construction details of the detention pipe system.
Below is a stormwater control summary table for Lot 2:
Stormwater Control Summary:
Project Site Category: Category 2 (part of the Select Homes 2-Lot Short Plat PLN2020-0019)
Discharge Location: City's Municipal Separate Storm Sewer System (MS4)
Type of Area
Square Footage
Stormwater Facility
Lawn and Landscape
3,763 sf
Soil Amendments (BMP T5.13)
Roofs (Hard Surface)
2,970 sf
Detention Pipe (ECDC 18.30.030.D.5.d)
Other Hard Surfaces
880 sf
Detention Pipe (ECDC 18.30.030.D.5.d)
ROW/Alley
500 sf
25% Retrofit
0 SF
None
Select Homes 7th Ave S Short Plot- Lot 21055 7th Ave S Page 2 of 2
Stormwater Memo
RAM lob No. 19-037
Select Homes 7th Ave S Short Plat Lot 2 Hard Surface Summary:
Roof = 2,970 sf
Driveway = 520 sf
Sidewalk/Patio = 360 sf
ROW/Alley = 500 sf
Total = 4,350 sf
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