BLD2022-1087+STORMWATER MEMO+8.15.2022_1.26.20_PM+3051190RAM Engineering
To: City of Edmonds
Engineering Division
From: Rob Long, PE
RAM Engineering
Memorandum
Date: July 20, 2022
Subject: Select Homes 2-Lot Short Plat at 7922 2O3rd St SW(PLN2O21-0039)- Lot 1
Lot 1 Stormwater Memo
RAM Job No. 20-020
This memo provides a summary of the stormwater drainage control system for Lot 1 of the Select Homes 2-Lot
Short Plat at 7922 203rd St SW(PLN2021-0039). A site -specific geotechnical evaluation recommends infiltration
as the stormwater control measure, in addition, BMP T5.13: Post -Construction Soil Quality and Depth shall be
applied to all disturbed pervious areas of the project site. The proposed roof top and "other hard surfaces"
(driveway, patio, walks, etc.) will be managed by joint (Lot 1 and 2) infiltration trench located under the shared
driveway for the project.
The joint infiltration trench has been designed to account for both Lot 1 and Lot 2 hard (impervious) surfaces of
the short plat; the infiltration system design accommodates 3,650 sf of hard surface from Lot 1 (per Short Plat
Civil Design). The proposed hard surface of Lot 1 consists of 2,670 sf of roof area, 600 sf driveway, and 380 sf of
uncovered walk and patio.
Below is a stormwater control summary table for Lot 1:
Stormwater Control Summary:
Project Site Category: Category 2 (part of the 203rd St SW 2-Lot Short Plat)
Discharge Location: On -site Infiltration
Type of Area
Square Footage
Stormwater Facility
Lawn and Landscape
4,079 sf
Soil Amendments (BMP T5.13)
Roof
2,670 sf
Infiltration Trench
Hard Surfaces
980 sf
Infiltration Trench
(Driveway, Walk and Patio)
25% Retrofit
0 SF
None
P M Engineering 19109 36"Ave W, Suite 100 Lynnwood WA 98036 (425) 678-6960 RAMengineeringinc.com
Select Homes 2-Lot Short Plat at 7922 203'd St SW- Lot 1 Page 2 of 2
Stormwater Memo
RAM lob No. 20-020
Select Homes 203rd St SW Short Plat Lot 1 Hard Surface Summary:
Roof = 2,670 sf
Driveway = 600 sf
Sidewalk/Patio = 380 sf
Total = 3,650 sf
25' DRAINAGE & JOINT Ny
U7ILITY EASEMENT (TYP) o
h � I
15' PRIVATE
ACCESS
27041900112600 EASEMENT wl
DRIVEWAY = 600 s#
INSTALLED AS PART OF zl
SHORT PLAT
PART OF 77-IE 203RD ST SW
SHORT PLAT (PLN2021-0039)
4" PVC F0077NG
4_ I DRAIN & 1.0Z MIN
GARAGE
FF 426.0 ! PROPOSED HOUSE
v'A'7F 8,579 5F MAIN FF 427.50
�� 7,341 SF (NET)
ROOF = 2,670 sf
DRY U11L111L15
k mar .
SDCO
COVERED
IE 424.0 PA770
8920 55'W 10'
V
PVC ROOF
DRAIN ® 1.0Z MIN
1 I
CONNECT TO
r I
STORM STUB
IE 422.2E
IE 421.2E
10' PRIVATE
SEWER
EASEMENT
PETER
7i
ED
7/ZO/200Z
PKAM Engineering 19109 36" Ave W, Suite 100 Lynnwood WA 98036 (425) 678-6960 RAMengineeringinc.com