APPROVED STM BLD2020-1128+Storm_Drainage_Report+10.20.2020_3.49.09_PMRAM Engineering RECEIVED BLD2020-1128
oct.27 2020 Memorandum
To: City of Edmonds DEVELOPMENT OPARTMENRVICES Date: October 6, 2020
Engineering Division
From: Rob Long, PE
RAM Engineering
Subject: Select Homes 7th Ave S Short Plat- Lot 1
Stormwater Memo
RAM Job No. 19-037
COMPLIES WITH APPLICABL
CITY STORMWATER CODE
Fir.
This memo provides a summary of the stormwater drainage control system for Lot 1 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 4,250 sf and will be managed by an onsite detention pipe (per Edmonds
Stormwater Addendum, 6.3.1). The 4,250 sf of hard surface will require 34 ft of 36" pipe (4,250 sf x 0.008) 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 1:
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)
2,960 sf
Detention Pipe (ECDC 18.30.030.D.5.d)
Other Hard Surfaces
790 sf
Detention Pipe (ECDC 18.30.030.D.5.d)
ROW/Alley
500 sf
25% Retrofit
0 SF
None
Select Homes 71h Ave S Short Plat- Lot 1 105 fir Street
Stormwater Memo
RAM lob No. 19-037
Page 2 of 2
Select Homes 7th Ave S Short Plat Lot 1 Hard Surface Summary:
Roof = 2,960 sf
Driveway = 500 sf
Sidewalk/Patio = 290 sf
ROW/Alley = 500 sf
Total = 4,250 sf
l0/6/2020
RAM Engineering 1653113 th Ave W, Suite A108 Lynnwood WA 98037 (425)678-6960 RAMengineeringinc.com