APPROVED STM RESUB3 BLD2022-0750+Storm_Drainage_Report+6.8.2023_2.03.24_PM+3597790RESUB
Jun 09 2023
CITY OF EDMONDS
DEVELOPMENT SERVICES
DEPARTMENT
STORMWATER REPORT
CITY OF EDMONDS
For
Abedalla Residence
7815 202nd PI SW
Edmonds, WA 98026
May 31, 2023
W co o
T
.10 ,Q 39374
�I ST6R�,tl�'
SSION
Prepared By:
Edward Mecum
Jared Foulk
Prepared For:
Niran Abedalla
10951 SE 162nd St
Bellevue, WA 98006
Civil Engineering & Development Services
1375 NW Mall St, STE 3; Issaquah, WA 98027
(425) 821-5038 Email: Info@G2CIVIL.COM COMPLIES ST RMWATWITH APPLICABLECODE
CITY STORMWATER CODE
06/16/2023
Niran Abedalla Technical Information Report
TABLE OF CONTENTS
A. Project Overview.................................................................................................1
B. Minimum Requirements....................................................................................4
FIGURES
Figure 1: Vicinity Map
Figure 2: Soils Map
Figure 3: Flow Chart for Determining Requirements for New Development
APPENDICES
Appendix A: Riley Group Infiltration Assessment
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A. Project Overview
Existing Conditions
The site is located at 7815 202nd PI SW in Edmonds, WA, Tax Parcel No. 00401300000400. The
property is 7,216 SF (approximately 0.17 AC) and bordered to the north, east, and west by single-
family residences and to the south by 202nd PI SW. The project site slopes from northwest to the
southeast at an average grade of approximately 1%. The downstream receiving system is Pine
Ridge Park Creek and ultimately Puget Sound. The site is currently developed with a single-family
residence, shed, and is vegetated with lawn areas, shrubs, and a few trees. The site is accessed
from an existing driveway from 202nd PI SW. The site soils are mapped as Alderwood-Urban land
complex, 8 to 15 percent slopes.
Runoff from the site sheet flows to the south into a roadside swale located on the northern
portion of 202nd PL SW.
Proposed Conditions
The project incorporates the construction of on and off -site infrastructure to support the
construction of a new single-family residence. The new residence will access in the existing
driveway location on 202nd PI SW via a new 20' wide pervious concrete driveway. The proposed
site areas are provided below.
Summary of Proposed Site Improvements:
Surface Type
Area (SF)
Onsite Roof
2,624
Total Impervious:
2,624
Pervious Driveway
516
Pervious Walkways
113
Total Area:
3,253
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Figure 1: Vicinity Map
m 3 199th St SW
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202nd PI SW
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203rd St SW
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2041h St SW E EET H
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?p4th PI SW
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205Mi StSW q a ---- `}--.
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2061h St S 206yt St SW
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2
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Figure 2: Soils Map
4 w
r rl'
gills,
40
1
� S-
- .-"'
k Snohomish County Area, Washington (WA661)
— " Snohomish County Area, Washington O
(WA661)
Map Acres Percent of
Unit Map Unit Name in AOI AOI
Symbol
5 Alderwood-Urban 0.5 100.0%
land complex, 2
to 8 percent
slopes
Totals for Area of 0.5 100.00/0
Interest
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B. Minimum Requirements
The existing impervious surface coverage is less than 35%, therefore the project is classified as
new development. The Department of Ecology's Figure 1-2.4.1: Flow Chart for Determining
Requirements for New Development (Figure 3, page 7) was utilized to determine the project
requirements relative to stormwater management. The project adds less than 5,000 sq. ft. of new
impervious surface but more than 2,000 sq. ft. of new plus replaced impervious surface,
therefore minimum requirements 1 through 5 apply to the project.
Implementing Minimum Requirements #1- #5
Minimum Requirement No. 1— Preparation of Stormwater Site Plan
A stormwater site plan is included in the permit submittal.
Minimum Requirement No. 2 — Construction Stormwater Pollution Prevention Plan
All new development and redevelopment projects in which new, replaced, or new plus replaced
impervious surfaces total 2,000 square feet or more, shall comply with Construction SWPPP
Elements #1 through #13. A CSWPPP has been incorporated into the Stormwater Site Plans.
Element 1— Mark Clearing Limits — Clearing limits at the property lines will be delineated with silt
fence and orange construction fencing.
Element 2 — Establish Construction Access — The existing driveway will provide adequate access
during construction, however a quarry spall construction entrance will be provided.
Element 3 — Control Flow Rates — Given the existing topography and small scope of work, there
will be minimal flows generated during construction and flow rates will not be controlled.
Element 4 — Install Sediment Controls— Silt fencing will be constructed and is expected to provide
construction stormwater sediment control during construction.
Element 5 — Stabilize Soils — Stockpiled or unworked soils will be protected during construction
by covering with plastic or temporary or permanent seeding. All exposed soils will be landscaped
or seeded at the conclusion of the project.
Element 6 — Protect Slopes — Cut/fill slopes are not anticipated but if necessary will be protected
as required.
Element 7 — Protect Drain Inlets — The existing and newly constructed conveyance system inlets
will be protected during construction if warranted.
Element 8 — Stabilize Channels and Outlets — There are no existing or proposed surface channels
or outfalls.
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Element 9 — Control Pollutants — The small size of this project will limit the opportunity for
discharge of pollutants. Waste/demolition debris will not be stockpiled, fueling will be done off -
site and concrete trucks will be washed out off -site.
Element 10—Control De -watering— De -watering is not anticipated, as construction will take place
during the dry season.
Element 11 — Maintain BMPs — BMPs will be maintained as necessary to assure continued
functioning.
Element 12 — Manage the Project — An inspector (sites less than 1 acre) will be present or on call
to ensure BMPs are maintained and assess effectiveness of ESC measures. Rainy season
requirements will be implemented if necessary.
Element 13 — Protect Low Impact Development BMPs —The locations of the proposed infiltration
trench in the rear of the house and permeable pavement for the driveway, walkway and rear slab
shall be protected from compaction to the maximum extent feasible during construction. Orange
construction fencing shall be provided around the location for the proposed infiltration trench.
Minimum Requirement No. 3 — Source Control of Pollution
S411— BMPs for Landscaping and Lawn/Vegetation Management will be implemented.
Minimum Requirement No. 4— Preservation of Natural Drainage Systems and Outfalls
The natural drainage pattern for the site will be maintained. The surface runoff from the
proposed impervious surfaces will be collected and routed to an onsite infiltration trench.
Minimum Requirement No. 5 — On -Site Stormwater Management
The project triggers Minimum Requirements #1-5 therefore, On -Site Stormwater Management
BMPs from List #1 will be implemented to the maximum extent feasible. Please see below for the
feasibility evaluation of the BMPs from List #1 by surface type.
Lawn and Landscaped Areas:
1. Post Construction Soil Quality and Depth — This BMP is feasible and will be
implemented per City of Edmonds Standard Detail SD-642 for all disturbed and
converted vegetated areas.
Roofs:
1. Full Dispersion and Downspout Full Infiltration Systems — Infiltration is feasible and
will be implemented for the proposed roof area per City of Edmonds Standard Detail
SD-636 and Department of Ecology BMP T5.10A.
2. Raingarden or Bioretention — N/A, all impervious areas have been mitigated.
3. Downspout Dispersion Systems — N/A, all impervious areas have been mitigated.
4. Perforated Stub -out Connection — N/A, all impervious areas have been mitigated.
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Other Hard Surfaces:
1. Full Dispersion — Infeasible. The minimum flow path length of 100 LF cannot be met.
2. Permeable Pavement, Rain Garden, or Bioretention —Permeable pavement is feasible
and will be implemented for the proposed walkway and driveway.
3. Sheet Flow Dispersion — N/A, hard surfaces will be mitigated with permeable
pavement.
Summary — Post construction soil quality and depth will be implemented for all proposed
pervious areas. Downspout full infiltration will be implemented for the proposed roof area and
permeable pavement will be used for the proposed walkway and driveway.
Infiltration Trench Sizing:
A review of the site soil conditions was conducted by Riley Group. Per the geotechnical
investigation, the soils on the site are conducive to infiltration and characterized as outwash
sands and gravel. Therefore, an infiltration trench is proposed and will be located along the
northwest of the project site. Refer to Appendix A: Riley Group Infiltration Assessment for
additional soil information.
Per Volume III, Section 3.1.1 — Downspout Full Infiltration Systems (BMP T5.10A) of the DOE
Manual, for sites with medium sand, 30 LF of trench is required per 1,000 SF of roof area. This is
equivalent to 90 CF of trench per 1,000 SF of roof area (30 LF x 2' Wide x 1.5' Deep = 90 CF).
Therefore;
Roof Area = 2,624 SF
Required Infiltration Trench = 90 CF x (2,624 SF / 1,000 SF) = 236.2 CF
Proposed Infiltration Trench = 40' Long x 4' Wide x 1.5' Deep = 240 CF
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Figure 1-3.1: Flow Chart for Determining Requirements for New
Development
Raft Hen
Does the Site have 35"K
or more of amr, 'g hard
surface coverage?
Does the Project result in
5,000 square feet, a
greater, of new plus
replaced hard surface
area?
Yes
All Minimum Requirements
apply to the new and replaced
hard surfaces and converted
vegetation areas.
Yes
See Redevelopment Project
Thresholds and the Fgure *How
Chart for Peferntirtatg
Requirements For Redevwbpmen .
Does the Profed convert i;
acres or more of vegetation to
lawn or landscaped areas, or
o corrmt 2.5 acres or more of
native vegetation to peshre?
No
/You$
Does the Project result In 2,000
:yu.t•e feet, or greater, of new plus
rcplaoed hard surface area?
�No
Minimum Rsquirw ants #1
through 45 apply to the new
and replaced hard surfaces
and the land disturbed.
Does the Proliect have land
disturbing aairrties of 7,000
Yes square feet or greater?
No
Minimum Requirement 42
applies.
—� Flow Chart for Determining Requirements for
New Development
DEPARTMENT OF Ruossed Mach `Ju
ECOLOGYP1. gowboprtgfv riftVkr copyrigM not co uxd i.dng parmaxince.
state of washinglonj limllabon of liability and CW*r w
2019 Stormwater Management Manual for Westem Washington
Volume 1- Chapter 3 - Page 89
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Niran Abedalla Technical Information Report
C. Off -Site Analysis
Project Name: Niran Abedalla
Site Address: 7815 202nd PL SW
King County Tax Parcel: 00401300000400
Adopted Basin Plan: The site is located within the Kelsey Creek Drainage Basin.
Upstream Tributary Area: There are no significant areas tributary to the site.
Downstream Analysis:
A field review of the downstream conditions was performed on November 21, 2021. The weather was
cloudy, and the temperature was approximately 60 degrees. A visual reconnaissance was performed
utilizing information obtained from the City of Edmonds GIS Mapping and the on -site survey. Please refer
to the storm drainage mapping exhibits that follow for a depiction of the downstream drainage conditions.
Site Photo
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Niran Abedalla Technical Information Report
Runoff from the site currently sheet flows to the southwest towards 202"d PI SW where it enters the
existing public conveyance system approximately 130 feet west of the site. The existing conveyance
system within 202"d PI SW directs runoff to the west via a series of catch basins and closed pipes for 615
feet. Runoff is then redirected north along 81s' Ave W for 145 feet, then west through residential areas
for 550 feet to 202"d PI SW. Runoff then continues west along 202"d PI SW for 195 feet, then south along
83rd Ave W for 300+ feet and the end of the downstream analysis. The field reconnaissance was
terminated as the % mile point analysis was met.
Downstream Concerns & Effects of Proposed Project: Developed runoff generated from the developed
site will be collected, infiltrated and conveyed via overflow to the existing public conveyance system
within 202"d PI SW. The downstream appears capable of conveying the release rates associated with the
project. Significant impacts to the downstream system are not anticipated, as no signs of drainage related
problems were observed during the field reconnaissance.
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,Mi 10 9 R
Riley Group Infiltration Assessment