APPROVED STM Stormwater Report 01-19-2021BLD2019-1553
IEC10
INSIGHT ENGINEERING CO.
RESUB
Jan 21 2021
CITY OF EDMONDS
DEVELOPMENT SERVICES
DEPARTMENT
Applicant:
Gregory Hoy & Midori Oka
2630 77t" Ave SE Unit A515
Mercer Island, WA 98040
STORMWATER SITE PLAN
For
Hoy Residence
Prepared for
The City of Edmonds
121 5th Ave N
Edmonds, WA 98020
425-771-0220
Project Site Location:
8051 184" St SW
Edmonds, WA -98026
APPLIES WITH APPLICABLE
CITY STROMWATER CODE
Contact:
IECO
P.O. Box 1478
Everett, WA98206
425-303-9363
Tax Id: 27041800103800
IECO Project: 19-1023
Certified Erosion and Sedimentation Control Lead:
To be named by contractor
Stormwater Site Plan Prepared By:
Ryan J. Korte
Stormwater Site Plan Preparation Date:
November 15, 2019
Revised Date:
January 19, 2021
Approximate Construction Date:
January 1, 2021
P.O Box 1478 Everett, WA 98206 • P: 425.303.9363
info@insightengineering.net
01 /21 /2021
TABLE OF CONTENTS
1.0 Executive Summary................................................................................................................3
1.1 Minimum Requirements Summary..............................................................................................7
2.0 Existing Conditions.................................................................................................................9
3.0 Offsite Analysis.....................................................................................................................14
3.1 Upstream Analysis.....................................................................................................................14
3.2 Downstream Analysis................................................................................................................14
4.0 Developed Conditions..........................................................................................................18
5.0 Site Hydraulic Analysis.........................................................................................................20
5.1 Existing Basin Summary............................................................................................................20
5.2 Developed Basin Summary
........................................................................................................20
6.0 Appendix...............................................................................................................................21
Figures
Figure1 - Vicinity Map.................................................................................................................6
Figure2 - Soil Map......................................................................................................................10
Figure3 - Downstream Analysis Map 1....................................................................................16
Figure 4 - Downstream Analysis Map 2....................................................................................17
Insight Engineering Co. - Stormwater Site Plan
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Acronyms and Abbreviations
BLA
Boundary Line Adjustment
BMP
Best Management Practices
DOE
Department of Ecology
ECDC
Edmonds Community Development Code
EDDS
Engineering Design and Development Standards
ESC
Erosion and Sediment Control
IECO
Insight Engineering Company
MR
Minimum Requirement
SWPPP
Stormwater Pollution Prevention Plan
SWMMWW
Stormwater Management Manual for Western Washington
TESC
Temporary Erosion and Sediment Control
WWHM
Western Washington Hydrology Model
Insight Engineering Co. - Stormwater Site Plan
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1.0 Executive Summary
The proposed project Hoy Residence is located at 8051 184th St SW, Edmonds,
Washington. More generally, the site is in Section 18, Township 27 North, and Range 4 East of
the Willamette Meridian in Snohomish County, Washington. Please refer to the Vicinity Map
attached later in the section. This project is subject to the City of Edmond's 2017 requirements and
the requirements defined in DOE's 2014 SWMMWW.
The site area is 0.38 acres. The site is currently undeveloped and exists as lawn and large
evergreen trees. The site contains one drainage basin that slopes moderately to the north. Please
refer to the downstream analysis map for more details. There are no critical areas located on the
site. Per NRCS survey of Snohomish County, the project site contains Alderwood soils that have
a hydrologic classification of Type "C". Please refer to the soils map and descriptions attached
later in this report for more details.
The project site is zoned as RS-10. The proposal is to construct a new single-family home,
garage, and ADU with a total roof area of 4,895 SF. Access to the site will be through an access
easement to the south connecting to 184th St SW. The total proposed hard surface area will be
8,625 SF.
Per Figure 3.1, (Flow Chart for Determining Requirements for Development) from the
2017 Edmonds Stormwater Addendum, Minimum requirements # 1 through 9 shall apply for this
project. See section 1.1 for Minimum Requirements Summary included later in this report. Flow
control requirements are exempt as the proposed development will increase the site's peak
discharge by 0.03 CFS which is less than the 0.1 CFS threshold (using hourly timesteps) requiring
flow control. MR #6 water quality is exempt as the total PGHS is only 3,100 SF which is less than
the threshold of 5,000 SF.
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Per ECDC 18.30.060.D.5.d Minimum Requirement #5: On -site Stormwater Management, the
following roof BMPs must be considered in the following order: Full Dispersion or Full
Infiltration, Rain Gardens or Bioretention, Downspout Dispersion Systems, Perforated Stub -out
Connections, and Detention Vaults or Pipes. Full infiltration was the first BMP deemed feasible
and will be implemented using permeable pavement per BMP T5.15 and an infiltration trench per
BMP T5.10A. A bubble -up catch basin has been provided to allow for overflow from the
infiltration trench. Overflow will drain to the north to continue its natural drainage pathway. The
infiltration trench will store and fully infiltrate stormwater to continue its natural drainage
pathway, therefore, no runoff is expected to leave the site. Please refer to Appendix A for tables
detailing BMP feasibility. According to the Underground Injection Control (UIC) program:
Chapter 173-218 WAC, the proposed infiltration trench must be registered as a UIC.
Per ECDC 18.30.060.D.5.d Minimum Requirement #5: On -site Stormwater Management,
the BMPs for other hard surfaces must be considered in the following order: Full Dispersion,
Permeable Pavement or Rain Gardens, Sheet Flow Dispersion, Detention Vault or Pipe. Permeable
Pavement was the first BMP deemed feasible and will be implemented per BMP T5.15 for the
driveway area. The patio areas will be collected via yard drains and conveyed to the infiltration
trench. Please refer to Appendix A for tables detailing BMP feasibility.
The roof drains and patio yard drains will drain to the infiltration trench. The driveway area
will be paved using permeable pavement. Post -Construction Soil Quality and Depth BMP T.5.13
is proposed to provide onsite stormwater management for the pervious areas of the site.
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Flow Chart for Determining Requirements for Development.
Ducs the project result in 2,000 square feet, or greater, of new plus replaced hard surface area?
OR
Dees the land disturbing activity total 7,000 square feet or greater?
Yes No
Minimum requirements No. I through 5 apply Minimum requirement No. 2 applies
Next Question
Dues the project add 5,000 square feet or more of new plus replaced hard surfaces?
OR
Convert 0.75 acres or more of vegetation to lawn or landscaped areas?
OR
Convert 2.5 acres or more of native vegetat ion to pasture?
No
Yes
Is this a road related project`
111 Minimum Requirements
ii pply to the new and replaced
hard surfaces and converted
vegetation areas_
All Minimum Requiren-iunts
apply to the new hard surfaces
and converted vegetation areas.
Yes
Insight Engineering Co. - Stormwater Site Plan
Yee
Does the project add
5,000 square feet or H
more of new hard
surfaces'
Yes
Dc) new hard surfaces add 50%car
more to the existing hard surtacc�,
within the project limits?
No
No
I No additional I
requirements.
11/15/19
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FIGURE]. VICINITYMAP
Taken from Snazzy Maps
INSIGHT ENGINEERING CO.
P.O. Box 1478Everett, WA98206
425-303-9363, 425-303-9362 f.
Info@insightengineering.net
Insight Engineering Co. - Stormwater Site Plan
Figure 1 -Vicinity May
Hoy Residence
Edmonds, Washington
SCALE: DATE 1/21/21 JOB#: 19-1023
NTS
BY FILE NAME:
RJK 19-1023/doc/Stormwater Site Plan
11/15/19
1.1 Minimum Requirements Summary
MR : Minimum Requirement
SWPPP : Stormwater Pollution Prevention Plan
MR #1 Stormwater Site Plan Narrative: The Stormwater Site Plan preparation follows the City
of Edmonds 2017 requirements and in accordance with DOE's 2014 SWMMWW. Refer to the
executive summary within Section 1.0.
MR #2 SWPPP Narrative: A SWPPP has been included in the Appendix A under Section 6.
MR #3 Water Pollution Source Control for New Development: No source control pollutants
pertain to the proposed single-family project; therefore, no BMPs are required for the project.
MR #4 Preservation of Natural Drainage Systems and Outfalls: The runoff from the site will
be fully infiltrated, therefore no runoff is anticipated to leave the site. The downstream public
channel should not experience any future flooding problems.
MR #5 Onsite Stormwater Management: Per ECDC 18.30.060.D.5.d Minimum Requirement
#5: On -site Stormwater Management, the following roof BMPs must be considered in the
following order: Full Dispersion or Full Infiltration, Rain Gardens or Bioretention, Downspout
Dispersion Systems, Perforated Stub -out Connections, and Detention Vaults or Pipes. Full
infiltration was the first BMP deemed feasible and will be implemented using permeable pavement
per BMP T5.15 and an infiltration trench per BMP T5.10A. A bubble -up catch basin has been
provided to allow for overflow from the infiltration trench. Overflow will drain to the north to
continue its natural drainage pathway. The infiltration trench will store and fully infiltrate
Stormwater to continue its natural drainage pathway, therefore, no runoff is expected to leave the
site. Please refer to Appendix A for tables detailing BMP feasibility. According to the
Underground Injection Control (UIC) program: Chapter 173-218 WAC, the proposed infiltration
trench must be registered as a UIC.
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Per ECDC 18.30.060.D.5.d Minimum Requirement #5: On -site Stormwater Management,
the BMPs for other hard surfaces must be considered in the following order: Full Dispersion,
Permeable Pavement or Rain Gardens, Sheet Flow Dispersion, Detention Vault or Pipe. Permeable
Pavement was the first BMP deemed feasible and will be implemented per BMP T5.15 for the
driveway area. The patio areas will be collected via yard drains and conveyed to the infiltration
trench. Please refer to Appendix A for tables detailing BMP feasibility.
The roof drains and patio yard drains will drain to the infiltration trench. The driveway area will
be paved using permeable pavement. Post -Construction Soil Quality and Depth BMP T.5.13 is
proposed to provide onsite stormwater management for the pervious areas of the site.
MR #6 Runoff Treatment: MR #6 water quality is exempt as the total PGHS is only 3,100 SF
which is less than the threshold of 5,000 SF.
MR #7 Flow Control:. Flow control requirements are exempt as the proposed development will
increase the site's peak discharge by 0.03 CFS which is less than the 0.1 CFS threshold (using
hourly timesteps) requiring flow control.
MR #8 Wetlands protection: There are no wetlands present on site and the site will not
discharge to a wetland area.
MR #9 Operations and Maintenance: An Operations and Maintenance Manual is provided
under the Appendix E.
Insight Engineering Co. - Stormwater Site Plan
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2.0 Existing Conditions
The proposed project Hoy Residence is located at 8051 184th St SW, Edmonds,
Washington. More generally, the site is in Section 18, Township 27 North, and Range 4 East of
the Willamette Meridian in Snohomish County, Washington.
The site area is 0.38 acres. The site is currently undeveloped and exists as lawn and large
evergreen trees. The site contains one drainage basin that slopes moderately to the north. Please
refer to the downstream analysis map for more details. There are no critical areas located on the
site. Per NRCS survey of Snohomish County, the project site contains Alderwood soils that have
a hydrologic classification of Type "C". Please refer to the soils map and descriptions attached
later in this report for more details.
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FIGURE 2. SOIL MAP
f I 1
• e , i
4
SOILS LEGEND
5— Alderwood-Urban land complex, 2 to 8 percent slopes
6— Alderwood-Urban land complex, 8 to 15 percent slopes
Figure 2 - Soil May
03Mf Hoy Residence
Edmonds, Washington
ISIGHT ENGINEERING CO. SCALE: DATE: 1/21/21 JOB#: 19-1023
NONE
P.O. Box 1478 Everett, WA 98206 FILE NAME:
425-303-9363, 425-303-9362 f.
Info@insightengineering.net BY.719-1023/ doc/Stormwater Site Plan
Insight Engineering Co. - Stormwater Site Plan
11/15/19
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Snohomish County Area, Washington
5—Alderwood-Urban land complex, 2 to 8 percent slopes
Map Unit Setting
• National map unit symbol: 2hz9
• Elevation: 50 to 800 feet
• Mean annual precipitation: 25 to 60 inches
• Mean annual air temperature: 48 to 52 degrees F
• Frost -free period: 180 to 220 days
• Farmland classification: Not prime farmland
Map Unit Composition
• Alderwood and similar soils: 60 percent
• Urban land: 25 percent
• Minor components: 15 percent
• Estimates are based on observations, descriptions, and transects of the mapunit.
Description of Alderwood
Setting
• Landform: Till plains
• Parent material: Basal till
Typical profile
• HI - 0 to 7 inches: gravelly ashy sandy loam
• H2 - 7 to 35 inches: very gravelly ashy sandy loam
• H3 - 35 to 60 inches: gravelly sandy loam
Properties and qualities
• Slope: 2 to 8 percent
• Depth to restrictive feature: 20 to 40 inches to densic material
• Natural drainage class: Moderately well drained
• Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately
low (0.00 to 0.06 in/hr)
• Depth to water table: About 18 to 36 inches
• Frequency of flooding: None
• Frequency of ponding: None
• Available water storage in profile: Low (about 3.0 inches)
Interpretive groups
• Land capability classification (irrigated): None specified
• Land capability classification (nonirrigated): 4s
• Hydrologic Soil Group: B
• Forage suitability group: Limited Depth Soils (G002XN302WA)
• Hydric soil rating: No
Minor Components
Mckenna
• Percent of map unit: 5 percent
• Landform: Depressions
• Hydric soil rating: Yes
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Norma, undrained
• Percent of map unit: 5 percent
• Landform: Depressions
• Hydric soil rating: Yes
Terric medisaprists, undrained
• Percent of map unit: 5 percent
• Landform: Depressions
• Hydric soil rating: Yes
6—Alderwood-Urban land complex, 8 to 15 percent slopes
Map Unit Setting
• National map unit symbol: 2hzn
• Elevation: 50 to 800 feet
• Mean annual precipitation: 25 to 60 inches
• Mean annual air temperature: 48 to 52 degrees F
• Frost -free period: 180 to 220 days
• Farmland classification: Not prime farmland
Map Unit Composition
• Alderwood and similar soils: 60 percent
• Urban land: 25 percent
• Minor components: 5 percent
• Estimates are based on observations, descriptions, and transects of the mapunit.
Description of Alderwood
Setting
• Landform: Till plains
• Parent material: Basal till
Typical profile
• HI - 0 to 7 inches: gravelly ashy sandy loam
• H2 - 7 to 35 inches: very gravelly ashy sandy loam
• H3 - 35 to 60 inches: gravelly sandy loam
Properties and qualities
• Slope: 8 to 15 percent
• Depth to restrictive feature: 20 to 40 inches to densic material
• Natural drainage class: Moderately well drained
• Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately
low (0.00 to 0.06 in/hr)
• Depth to water table: About 18 to 36 inches
• Frequency of flooding: None
• Frequency of ponding: None
• Available water storage in profile: Low (about 3.0 inches)
Interpretive groups
• Land capability classification (irrigated): None specified
• Land capability classification (nonirrigated): 4s
• Hydrologic Soil Group: B
• Forage suitability group: Limited Depth Soils (G002XN302WA)
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• Hydric soil rating: No
Minor Components
Norma, undrained
• Percent of map unit: 5 percent
• Landform: Drainageways
• Hydric soil rating: Yes
Insight Engineering Co. - Stormwater Site Plan
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3.0 Offsite Analysis
A site reconnaissance was performed by Brian Kalab of Insight Engineering on October
28, 2019 to verify the downstream flow paths and observe any drainage problems downstream of
the site. The sky was partly cloudy with a temperature of 40 degrees.
The site area is 0.38 acres. The site is currently undeveloped and exists as lawn and large
evergreen trees. The site contains one drainage basin that slopes moderately to the north.
3.1 Upstream Analysis
Based on the site reconnaissance and the topographic survey of the site, the upstream flows
appear to be minimal. Refer to the Downstream Analysis Map attached in the next page for more
details.
3.2 Downstream Analysis
The existing site drains to the north to follow the contour of the site and flows through the
neighboring properties at the addresses of 8117 182nd St SW, 8115 182nd St SW, 18218 801h Ave
W, and 18208 80th Ave W. The flow path flows towards structures and over lawn area on all four
properties as well as runs over driveways on 18218 and 18208 80th Ave W. The flow path from
the site to the drainage system along 80th Ave W is about 370 ft. The runoff flows north on 80th
Ave for about 220 ft through a series of 12" concrete pipes. Along the west side of 80th Ave the
flow travels north through a large grassy area for about 50-feet to a catch basin. The flow then
travels via 12-inch concrete pipe to flow north for 120-feet then continues north 225-feet through
a grass ditch. The flow then transitions back into a 12-inch concrete pipe for another 240-feet
north. The flow then turns east along 180th St SW and flows for approximately 625-feet through a
series of grass ditches and 12-inch concrete pipes. The flow then crosses beneath Olympic View
Dr via an 18 in concrete pipe for about 40-feet. The 18-inch pipe then outlets to a ditch that flows
275-feet to Perrinville Creek. Perrinville Creek flows north unrestricted for about a mile from the
site to discharge into the Puget Sound.
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This is where the downstream analysis was concluded. There did not appear to be any restrictions
or erosional problems downstream of the site.
In the developed state, the runoff from the driveway will infiltrate into the ground and will
follow the natural drainage pathway. Runoff from the roof and patios will be collected into the
infiltration trench located to the north of the proposed home. The proposed grading will not cause
any changes to the direction of the flow path because it will continue to cause the stormwater to
flow to the north. A bubble -up catch basin has been provided to allow for overflow from the
infiltration trench. Overflow will drain to the north to continue its natural drainage pathway. The
infiltration trench will store and fully infiltrate stormwater to continue its natural drainage
pathway, therefore, no runoff is expected to leave the site.
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FIGURE 3. DOWNSTREAM ANALYSIS MAP 1
[MI
mmffr3
INSIGHT ENGINEERING CO
P.O. Box 1478 Everett, WA 98206
425-303-9363, 425-303-9362 f.
Info@insightengineering.net
A
Map taken from City of Edmonds GIs
Figure 3 - Downstream Analysis Map
Hoy Residence
Edmonds, Washington
ISCALE:DATE: 1/21/21 JOB #: 19-1023
ONE I I I
I FILE NAME:
BY: RJK 19-1023/doc/Stormwater Site Plan
Insight Engineering Co. - Stormwater Site Plan 11/15/19
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FIGURE 4. DOWNSTREAM ANALYSIS MAP 2
IEC
INSIGHT ENGINEERING CO
P.O. Box 1478 Everett, WA 98206
425-303-9363, 425-303-9362 f.
Info@insightengineering.net
Map taken from City of Edmonds GIS
Figure 4 - Downstream Analysis Map
Hoy Residence
Edmonds, Washington
ISCALE:DATE: 1/21/21 JOB #: 19-1023
ONE I I I
I FILE NAME:
BY: RJK 19-1023/doc/Stormwater Site Plan
Insight Engineering Co. - Stormwater Site Plan 11/15/19
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4.0 Developed Conditions
The proposed project Hoy Residence is located at 8051 184th St SW, Edmonds,
Washington. More generally, the site is in Section 18, Township 27 North, and Range 4 East of
the Willamette Meridian in Snohomish County, Washington. Per NRCS survey of Snohomish
County, the project site contains Alderwood soils that have a hydrologic classification of Type
«C„
The project site is zoned as RS-10. The proposal is to construct a new single-family home,
garage, and ADU with a total roof area of 4,895 SF. Access to the site will be through an access
easement to the south connecting to 184th St SW.
Per ECDC 18.30.060.D.5.d Minimum Requirement #5: On -site Stormwater Management, the
following roof BMPs must be considered in the following order: Full Dispersion or Full
Infiltration, Rain Gardens or Bioretention, Downspout Dispersion Systems, Perforated Stub -out
Connections, and Detention Vaults or Pipes. Full infiltration was the first BMP deemed feasible
and will be implemented using permeable pavement per BMP T5.15 and an infiltration trench per
BMP T5.10A. A bubble -up catch basin has been provided to allow for overflow from the
infiltration trench. Overflow will drain to the north to continue its natural drainage pathway. The
infiltration trench will store and fully infiltrate stormwater to continue its natural drainage
pathway, therefore, no runoff is expected to leave the site. Please refer to Appendix A for tables
detailing BMP feasibility. According to the Underground Injection Control (UIC) program:
Chapter 173-218 WAC, the proposed infiltration trench must be registered as a UIC.
Per ECDC 18.30.060.D.5.d Minimum Requirement #5: On -site Stormwater Management,
the BMP's for other hard surfaces must be considered in the following order: Full Dispersion,
Permeable Pavement or Rain Gardens, Sheet Flow Dispersion, Detention Vault or Pipe. Permeable
Pavement was the first BMP deemed feasible and will be implemented per BMP T5.15 for the
Insight Engineering Co. - Stormwater Site Plan
11/15/19
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driveway area. The patio areas will be collected via yard drains and conveyed to the infiltration
trench. Please refer to Appendix A for tables detailing BMP feasibility.
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5.0 Site Hydraulic Conditions
Per NRCS survey of Snohomish County, the project site contains Alderwood soils that have a
hydrologic classification of Type "C".
Site Area = 0.36 Acres (15,602 SF)
Clearing Limit = 0.38 Acres (16,402 SF)
5.1 Existing Basin Summary
Site Area = 0.36 Acres
Clearing Limit = 0.38 Acres
The entire existing basin was modeled as forested.
Refer to the Existing Basin Map and the following pages for more details.
5.2 Developed Basin Summary
Site Area
Clearing Limit
Impervious:
= 0.36 Acres
= 0.38 Acres
Roof Area
= 0.11 Acres (4,895 SF)
Driveway (Onsite)
= 0.05 Acres (2,300 SF)
Driveway (Offsite)
= 0.02 Acres ( 800 SF)
PatioiWalkway
= 0.02 Acres ( 630 SF)
Total Impervious
= 0.20 Acres (8,625 SF)
Pervious:
Pervious Area (Lawn) = 0.38 - 0.20 = 0.18 Acres
Refer to the Developed Basin Map and the following pages for more details.
Insight Engineering Co. - Stormwater Site Plan
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POSRION PROPERTY LINE
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20 2' I SCALE: 1" — 20'
I ENT
RANCE
NCENI
ENTRA6
"-02'59 E 27041800104000 � � I 0 10 20
3.68' TRENCH DAM MP.) /8041
I
�N"-28i
5 54w , I 1 DE VEL OPED BASIN MAP
6.0 Appendix
A. Minimum Requirement #5 Bmp Feasibility
C. Stormwater Pollution Prevention Plan
D. Geotech Report
E. Operation & Maintenance Manual
Insight Engineering Co. - Stormwater Site Plan
11/15/19
-21-
A. MINIMUM REQUIREMENT #5 BMP FEASIBILITY
Roof BMPs (List #1)
Per ECDC 18.30.060.D.5.d Minimum Requirement #5
BMP
Feasibility
BMP Feasibility Conditions
T5.30 Full Dispersion
Infeasible
Full Dispersion is infeasible because of the
required flow path and preserved vegetation area
could not be achieved.
T5.10A Downspout
Feasible
Downspout Full Infiltration has been considered
Full Infiltration
and deemed feasible. Permeable pavers and an
infiltration trench will both be used to infiltrate
roof runoff.
T5.IOB Downspout
NA
Dispersion
T5.IOC Perforated
N/A
Stub -out Connections
Detention Pipe or Vault
N/A
Other Hard Surface BMPs (List #1)
Per ECDC 18.30.060.D.5.d Minimum Requirement #5
BMP
Feasibility
BMP Feasibility Conditions
T5.30 Full Dispersion
Infeasible
Full Dispersion is infeasible because of the lack
of preserved vegetated could not be achieved for
this MR zoned project.
Permeable Pavement or
Feasible
Permeable Pavement has been considered feasible
Rain Gardens
and will be used for hard surfaces.
T5.12 Sheet Flow
N/A
Dispersion
Detention Pipe or Vault
N/A
Insight Engineering Co. - Stormwater Site Plan
11/15/19
-22-
Insight Engineering Co. - Stormwater Site Plan
11/15/19
-23-
WWH?
PROJECT
General Model Information
Project Name: Hoy Residence
Site Name:
Hoy Residence
Site Address:
XX 81 st Ave W
City:
Edmonds
Report Date:
11 /14/2019
MGS Region:
Puget East
Data Start:
1901 /10/1
Data End:
2058/09/30
Timestep:
Hourly
DOT Data Number03
Version Date:
2018/03/08
Version:
4.2.14
POC Thresholds
Low Flow Threshold for POC1: 50 Percent of the 2 Year
High Flow Threshold for POC1: 50 Year
Hoy Residence 11/14/2019 3:08:45 PM Page 2
Landuse Basin
Data
Predeveloped Land
Use
Predeveloped
Bypass:
No
GroundWater:
No
Pervious Land Use
acre
C, Forest, Mod
0.38
Pervious Total
0.38
Impervious Land Use
acre
Impervious Total
0
Basin Total
0.38
Element Flows To:
Surface Interflow Groundwater
Hoy Residence 11/14/2019 3:08:45 PM Page 3
Mitigated Land Use
Roof/Patios
Bypass:
No
GroundWater:
No
Pervious Land Use
acre
Pervious Total
0
Impervious Land Use
acre
ROOF TOPS FLAT
0.11
SIDEWALKS FLAT
0.02
Impervious Total
0.13
Basin Total
0.13
Element Flows To:
Surface Interflow Groundwater
Gravel Trench Bed 1 Gravel Trench Bed 1
Hoy Residence 11/14/2019 3:08:45 PM Page 4
Driveway
Bypass: No
Impervious Land Use acre
DRIVEWAYS MOD LAT 0.07
Element Flows To:
Outlet 1 Outlet 2
Permeable Pavement 1
Hoy Residence 11/14/2019 3:08:45 PM Page 5
Lawn
Bypass:
Yes
GroundWater:
No
Pervious Land Use
acre
C, Lawn, Mod
0.18
Pervious Total
0.18
Impervious Land Use
acre
Impervious Total
0
Basin Total
0.18
Element Flows To:
Surface Interflow
Groundwater
Hoy Residence 11/14/2019 3:08:45 PM Page 6
Routing Elements
Predeveloped Routing
Hoy Residence 11/14/2019 3:08:45 PM Page 7
Mitigated Routing
Gravel Trench Bed 1
Bottom Length:
Bottom Width:
Trench bottom slope 1:
Trench Left side slope 0:
Trench right side slope 2:
Material thickness of first layer:
Pour Space of material for first layer:
Material thickness of second layer:
Pour Space of material for second layer
Material thickness of third layer:
Pour Space of material for third layer:
Infiltration On
Infiltration rate:
Infiltration safety factor:
Total Volume Infiltrated (ac-ft.):
Total Volume Through Riser (ac-ft.):
Total Volume Through Facility (ac-ft.):
Percent Infiltrated:
Total Precip Applied to Facility:
Total Evap From Facility:
Discharge Structure
Riser Height: 0 ft.
Riser Diameter: 0 in.
Element Flows To:
Outlet 1 Outlet 2
80.00 ft.
12.00 ft.
0 To 1
0 To 1
0 To 1
3.5
0.3
0
0
0
0
0.35
1
49.327
0
49.327
100
0
0
Gravel Trench Bed Hydraulic Table
Stage(feet)
Area(ac.)
Volume(ac-%)
Discharge(cfs)
Infilt(cfs)
0.0000
0.022
0.000
0.000
0.000
0.0389
0.022
0.000
0.000
0.007
0.0778
0.022
0.000
0.000
0.007
0.1167
0.022
0.000
0.000
0.007
0.1556
0.022
0.001
0.000
0.007
0.1944
0.022
0.001
0.000
0.007
0.2333
0.022
0.001
0.000
0.007
0.2722
0.022
0.001
0.000
0.007
0.3111
0.022
0.002
0.000
0.007
0.3500
0.022
0.002
0.000
0.007
0.3889
0.022
0.002
0.000
0.007
0.4278
0.022
0.002
0.000
0.007
0.4667
0.022
0.003
0.000
0.007
0.5056
0.022
0.003
0.000
0.007
0.5444
0.022
0.003
0.000
0.007
0.5833
0.022
0.003
0.000
0.007
0.6222
0.022
0.004
0.000
0.007
0.6611
0.022
0.004
0.000
0.007
0.7000
0.022
0.004
0.000
0.007
0.7389
0.022
0.004
0.000
0.007
0.7778
0.022
0.005
0.000
0.007
0.8167
0.022
0.005
0.000
0.007
0.8556
0.022
0.005
0.000
0.007
0.8944
0.022
0.005
0.000
0.007
Hoy Residence 11/14/2019 3:08:45 PM Page 8
0.9333
0.022
0.006
0.000
0.007
0.9722
0.022
0.006
0.000
0.007
1.0111
0.022
0.006
0.000
0.007
1.0500
0.022
0.006
0.000
0.007
1.0889
0.022
0.007
0.000
0.007
1.1278
0.022
0.007
0.000
0.007
1.1667
0.022
0.007
0.000
0.007
1.2056
0.022
0.008
0.000
0.007
1.2444
0.022
0.008
0.000
0.007
1.2833
0.022
0.008
0.000
0.007
1.3222
0.022
0.008
0.000
0.007
1.3611
0.022
0.009
0.000
0.007
1.4000
0.022
0.009
0.000
0.007
1.4389
0.022
0.009
0.000
0.007
1.4778
0.022
0.009
0.000
0.007
1.5167
0.022
0.010
0.000
0.007
1.5556
0.022
0.010
0.000
0.007
1.5944
0.022
0.010
0.000
0.007
1.6333
0.022
0.010
0.000
0.007
1.6722
0.022
0.011
0.000
0.007
1.7111
0.022
0.011
0.000
0.007
1.7500
0.022
0.011
0.000
0.007
1.7889
0.022
0.011
0.000
0.007
1.8278
0.022
0.012
0.000
0.007
1.8667
0.022
0.012
0.000
0.007
1.9056
0.022
0.012
0.000
0.007
1.9444
0.022
0.012
0.000
0.007
1.9833
0.022
0.013
0.000
0.007
2.0222
0.022
0.013
0.000
0.007
2.0611
0.022
0.013
0.000
0.007
2.1000
0.022
0.013
0.000
0.007
2.1389
0.022
0.014
0.000
0.007
2.1778
0.022
0.014
0.000
0.007
2.2167
0.022
0.014
0.000
0.007
2.2556
0.022
0.014
0.000
0.007
2.2944
0.022
0.015
0.000
0.007
2.3333
0.022
0.015
0.000
0.007
2.3722
0.022
0.015
0.000
0.007
2.4111
0.022
0.015
0.000
0.007
2.4500
0.022
0.016
0.000
0.007
2.4889
0.022
0.016
0.000
0.007
2.5278
0.022
0.016
0.000
0.007
2.5667
0.022
0.017
0.000
0.007
2.6056
0.022
0.017
0.000
0.007
2.6444
0.022
0.017
0.000
0.007
2.6833
0.022
0.017
0.000
0.007
2.7222
0.022
0.018
0.000
0.007
2.7611
0.022
0.018
0.000
0.007
2.8000
0.022
0.018
0.000
0.007
2.8389
0.022
0.018
0.000
0.007
2.8778
0.022
0.019
0.000
0.007
2.9167
0.022
0.019
0.000
0.007
2.9556
0.022
0.019
0.000
0.007
2.9944
0.022
0.019
0.000
0.007
3.0333
0.022
0.020
0.000
0.007
3.0722
0.022
0.020
0.000
0.007
3.1111
0.022
0.020
0.000
0.007
3.1500
0.022
0.020
0.000
0.007
Hoy Residence 11/14/2019 3:08:45 PM Page 9
3.1889
0.022
0.021
0.000
0.007
3.2278
0.022
0.021
0.000
0.007
3.2667
0.022
0.021
0.000
0.007
3.3056
0.022
0.021
0.000
0.007
3.3444
0.022
0.022
0.000
0.007
3.3833
0.022
0.022
0.000
0.007
3.4222
0.022
0.022
0.000
0.007
3.4611
0.022
0.022
0.000
0.007
3.5000
0.022
0.023
0.000
0.007
Hoy Residence 11/14/2019 3:08:45 PM Page 10
Permeable Pavement 1
Pavement Area:0.0712 acre.Pavement Length:62.00 ft.
Pavement Width:
50.00 ft.
Pavement slope 1:0.02 To 1
Pavement thickness:
0.334
Pour Space of Pavement:
0.12
Material thickness of second layer:
2.5
Pour Space of material for second layer:
0.03
Material thickness of third layer:
0
Pour Space of material for third layer:
0
Infiltration On
Infiltration rate:
0.35
Infiltration safety factor:
1
Total Volume Infiltrated (ac-ft.):
52.21
Total Volume Through Riser (ac-ft.):
0
Total Volume Through Facility (ac-ft.):
52.21
Percent Infiltrated:
100
Total Precip Applied to Facility:
0
Total Evap From Facility:
1.737
Element Flows To:
Outlet 1 Outlet 2
Permeable Pavement Hydraulic Table
Stage(feet)
Area(ac.)
Volume(ac-ft.)
Discharge(cfs) Infilt(cfs)
0.0000
0.071
0.000
0.000
0.000
0.0315
0.071
0.000
0.000
0.025
0.0630
0.071
0.000
0.000
0.025
0.0945
0.071
0.000
0.000
0.025
0.1260
0.071
0.000
0.000
0.025
0.1574
0.071
0.000
0.000
0.025
0.1889
0.071
0.000
0.000
0.025
0.2204
0.071
0.000
0.000
0.025
0.2519
0.071
0.000
0.000
0.025
0.2834
0.071
0.000
0.000
0.025
0.3149
0.071
0.000
0.000
0.025
0.3464
0.071
0.000
0.000
0.025
0.3779
0.071
0.000
0.000
0.025
0.4094
0.071
0.000
0.000
0.025
0.4408
0.071
0.000
0.000
0.025
0.4723
0.071
0.001
0.000
0.025
0.5038
0.071
0.001
0.000
0.025
0.5353
0.071
0.001
0.000
0.025
0.5668
0.071
0.001
0.000
0.025
0.5983
0.071
0.001
0.000
0.025
0.6298
0.071
0.001
0.000
0.025
0.6613
0.071
0.001
0.000
0.025
0.6928
0.071
0.001
0.000
0.025
0.7242
0.071
0.001
0.000
0.025
0.7557
0.071
0.001
0.000
0.025
0.7872
0.071
0.001
0.000
0.025
0.8187
0.071
0.001
0.000
0.025
0.8502
0.071
0.001
0.000
0.025
0.8817
0.071
0.001
0.000
0.025
0.9132
0.071
0.002
0.000
0.025
0.9447
0.071
0.002
0.000
0.025
Hoy Residence 11/14/2019 3:08:45 PM Page 11
0.9762
0.071
0.002
0.000
0.025
1.0076
0.071
0.002
0.000
0.025
1.0391
0.071
0.002
0.000
0.025
1.0706
0.071
0.002
0.000
0.025
1.1021
0.071
0.002
0.000
0.025
1.1336
0.071
0.002
0.000
0.025
1.1651
0.071
0.002
0.000
0.025
1.1966
0.071
0.002
0.000
0.025
1.2281
0.071
0.002
0.000
0.025
1.2596
0.071
0.002
0.000
0.025
1.2910
0.071
0.002
0.000
0.025
1.3225
0.071
0.002
0.000
0.025
1.3540
0.071
0.002
0.000
0.025
1.3855
0.071
0.003
0.000
0.025
1.4170
0.071
0.003
0.000
0.025
1.4485
0.071
0.003
0.000
0.025
1.4800
0.071
0.003
0.000
0.025
1.5115
0.071
0.003
0.000
0.025
1.5430
0.071
0.003
0.000
0.025
1.5744
0.071
0.003
0.000
0.025
1.6059
0.071
0.003
0.000
0.025
1.6374
0.071
0.003
0.000
0.025
1.6689
0.071
0.003
0.000
0.025
1.7004
0.071
0.003
0.000
0.025
1.7319
0.071
0.003
0.000
0.025
1.7634
0.071
0.003
0.000
0.025
1.7949
0.071
0.003
0.000
0.025
1.8264
0.071
0.003
0.000
0.025
1.8578
0.071
0.004
0.000
0.025
1.8893
0.071
0.004
0.000
0.025
1.9208
0.071
0.004
0.000
0.025
1.9523
0.071
0.004
0.000
0.025
1.9838
0.071
0.004
0.000
0.025
2.0153
0.071
0.004
0.000
0.025
2.0468
0.071
0.004
0.000
0.025
2.0783
0.071
0.004
0.000
0.025
2.1098
0.071
0.004
0.000
0.025
2.1412
0.071
0.004
0.000
0.025
2.1727
0.071
0.004
0.000
0.025
2.2042
0.071
0.004
0.000
0.025
2.2357
0.071
0.004
0.000
0.025
2.2672
0.071
0.004
0.000
0.025
2.2987
0.071
0.004
0.000
0.025
2.3302
0.071
0.005
0.000
0.025
2.3617
0.071
0.005
0.000
0.025
2.3932
0.071
0.005
0.000
0.025
2.4246
0.071
0.005
0.000
0.025
2.4561
0.071
0.005
0.000
0.025
2.4876
0.071
0.005
0.000
0.025
2.5191
0.071
0.005
0.000
0.025
2.5506
0.071
0.005
0.000
0.025
2.5821
0.071
0.006
0.000
0.025
2.6136
0.071
0.006
0.000
0.025
2.6451
0.071
0.006
0.000
0.025
2.6766
0.071
0.006
0.000
0.025
2.7080
0.071
0.007
0.000
0.025
2.7395
0.071
0.007
0.000
0.025
2.7710
0.071
0.007
0.000
0.025
Hoy Residence 11/14/2019 3:08:45 PM Page 12
2.8025 0.071 0.008 0.000
2.8340 0.071 0.008 0.000
0.025
0.025
Hoy Residence 11/14/2019 3:08:45 PM Page 13
Analysis Results
POC 1
0
to 100
+ Predeveloped
Predeveloped Landuse Totals for POC #1
Total Pervious Area:
0.38
Total Impervious Area:
0
Mitigated Landuse Totals
for POC #1
Total Pervious Area:
0.18
Total Impervious Area:
0.271166
0 -1
os , z
x Mitigated
Flow Frequency Method: Log Pearson Type III 17B
Flow Frequency Return Periods for Predeveloped. POC #1
Return Period
Flow(cfs)
2 year
0.006482
5 year
0.010763
10 year
0.013192
25 year
0.015726
50 year
0.017257
100 year
0.01853
Flow Frequency Return Periods for Mitigated. POC #1
Return Period
Flow(cfs)
2 year
0.007958
5 year
0.014221
10 year
0.019762
25 year
0.02863
50 year
0.036781
100 year
0.046424
Annual Peaks
Annual Peaks for Predeveloped
and Mitigated. POC #1
Year
Predeveloped
Mitigated
1902
0.009
0.007
1903
0.003
0.003
1904
0.008
0.019
1905
0.003
0.004
1906
0.001
0.003
1907
0.010
0.012
1908
0.006
0.007
1909
0.007
0.008
1910
0.012
0.014
1911
0.006
0.007
Cumulative Pro6a6ility
0 000,
e m 20 ao so TO ao , ob " eea i o
Hoy Residence 11/14/2019 3:08:45 PM Page 14
1912
0.024
0.039
1913
0.009
0.007
1914
0.002
0.033
1915
0.003
0.004
1916
0.005
0.007
1917
0.002
0.003
1918
0.006
0.006
1919
0.004
0.004
1920
0.006
0.007
1921
0.006
0.006
1922
0.007
0.010
1923
0.006
0.009
1924
0.003
0.003
1925
0.003
0.004
1926
0.005
0.006
1927
0.007
0.006
1928
0.005
0.007
1929
0.011
0.013
1930
0.006
0.006
1931
0.006
0.006
1932
0.004
0.007
1933
0.005
0.007
1934
0.015
0.020
1935
0.005
0.005
1936
0.008
0.008
1937
0.008
0.015
1938
0.007
0.006
1939
0.000
0.003
1940
0.005
0.011
1941
0.006
0.006
1942
0.008
0.013
1943
0.003
0.010
1944
0.009
0.023
1945
0.006
0.007
1946
0.006
0.009
1947
0.004
0.004
1948
0.013
0.012
1949
0.011
0.012
1950
0.006
0.005
1951
0.007
0.006
1952
0.022
0.035
1953
0.018
0.030
1954
0.005
0.007
1955
0.004
0.005
1956
0.003
0.003
1957
0.007
0.006
1958
0.018
0.019
1959
0.011
0.014
1960
0.004
0.005
1961
0.011
0.031
1962
0.005
0.007
1963
0.002
0.004
1964
0.005
0.030
1965
0.013
0.013
1966
0.002
0.005
1967
0.005
0.012
1968
0.007
0.006
1969
0.005
0.007
Hoy Residence 11/14/2019 3:09:08 PM Page 15
1970
0.008
0.013
1971
0.014
0.014
1972
0.009
0.055
1973
0.010
0.013
1974
0.007
0.010
1975
0.016
0.027
1976
0.006
0.016
1977
0.004
0.003
1978
0.012
0.016
1979
0.003
0.009
1980
0.006
0.011
1981
0.006
0.008
1982
0.004
0.006
1983
0.010
0.012
1984
0.003
0.010
1985
0.006
0.013
1986
0.005
0.006
1987
0.010
0.015
1988
0.008
0.006
1989
0.006
0.005
1990
0.008
0.007
1991
0.006
0.009
1992
0.009
0.012
1993
0.007
0.006
1994
0.013
0.011
1995
0.003
0.003
1996
0.015
0.013
1997
0.007
0.006
1998
0.006
0.010
1999
0.000
0.001
2000
0.005
0.010
2001
0.003
0.004
2002
0.012
0.024
2003
0.007
0.007
2004
0.008
0.009
2005
0.011
0.019
2006
0.004
0.005
2007
0.005
0.011
2008
0.006
0.006
2009
0.004
0.005
2010
0.003
0.006
2011
0.004
0.004
2012
0.006
0.011
2013
0.005
0.008
2014
0.003
0.004
2015
0.014
0.036
2016
0.002
0.003
2017
0.011
0.011
2018
0.020
0.021
2019
0.022
0.027
2020
0.007
0.015
2021
0.009
0.012
2022
0.003
0.011
2023
0.007
0.010
2024
0.027
0.047
2025
0.005
0.005
2026
0.010
0.010
2027
0.004
0.009
Hoy Residence 11/14/2019 3:09:08 PM Page 16
2028
0.002
0.003
2029
0.007
0.007
2030
0.015
0.015
2031
0.004
0.003
2032
0.003
0.004
2033
0.003
0.003
2034
0.004
0.005
2035
0.016
0.015
2036
0.008
0.009
2037
0.001
0.004
2038
0.010
0.014
2039
0.001
0.002
2040
0.003
0.006
2041
0.004
0.007
2042
0.017
0.018
2043
0.007
0.010
2044
0.010
0.009
2045
0.006
0.008
2046
0.007
0.007
2047
0.005
0.005
2048
0.006
0.006
2049
0.006
0.009
2050
0.004
0.006
2051
0.006
0.018
2052
0.004
0.005
2053
0.006
0.006
2054
0.012
0.029
2055
0.002
0.005
2056
0.002
0.004
2057
0.004
0.004
2058
0.005
0.005
Ranked Annual Peaks
Ranked Annual Peaks for Predeveloped and
Rank
Predeveloped
Mitigated
1
0.0273
0.0545
2
0.0244
0.0473
3
0.0223
0.0392
4
0.0217
0.0364
5
0.0203
0.0354
6
0.0180
0.0325
7
0.0179
0.0314
8
0.0169
0.0303
9
0.0162
0.0302
10
0.0156
0.0285
11
0.0154
0.0272
12
0.0151
0.0269
13
0.0147
0.0244
14
0.0143
0.0234
15
0.0136
0.0206
16
0.0131
0.0204
17
0.0129
0.0193
18
0.0129
0.0190
19
0.0123
0.0188
20
0.0123
0.0185
21
0.0120
0.0180
22
0.0118
0.0163
23
0.0113
0.0160
Mitigated. POC #1
Hoy Residence 11/14/2019 3:09:08 PM Page 17
24
0.0112
0.0152
25
0.0112
0.0152
26
0.0110
0.0151
27
0.0107
0.0146
28
0.0107
0.0146
29
0.0105
0.0142
30
0.0103
0.0141
31
0.0102
0.0139
32
0.0101
0.0135
33
0.0099
0.0135
34
0.0098
0.0135
35
0.0095
0.0132
36
0.0095
0.0128
37
0.0089
0.0127
38
0.0089
0.0127
39
0.0088
0.0127
40
0.0085
0.0124
41
0.0085
0.0123
42
0.0084
0.0123
43
0.0083
0.0122
44
0.0083
0.0117
45
0.0082
0.0117
46
0.0078
0.0115
47
0.0078
0.0113
48
0.0076
0.0112
49
0.0076
0.0111
50
0.0075
0.0110
51
0.0074
0.0106
52
0.0074
0.0105
53
0.0073
0.0105
54
0.0071
0.0105
55
0.0071
0.0104
56
0.0070
0.0102
57
0.0070
0.0101
58
0.0069
0.0101
59
0.0069
0.0100
60
0.0068
0.0098
61
0.0068
0.0096
62
0.0068
0.0096
63
0.0068
0.0093
64
0.0067
0.0093
65
0.0067
0.0091
66
0.0066
0.0091
67
0.0065
0.0090
68
0.0064
0.0087
69
0.0063
0.0087
70
0.0063
0.0085
71
0.0063
0.0085
72
0.0062
0.0084
73
0.0062
0.0079
74
0.0062
0.0078
75
0.0062
0.0078
76
0.0061
0.0076
77
0.0060
0.0075
78
0.0060
0.0075
79
0.0060
0.0075
80
0.0060
0.0074
81
0.0059
0.0074
Hoy Residence 11/14/2019 3:09:08 PM Page 18
82
0.0059
0.0073
83
0.0059
0.0073
84
0.0059
0.0073
85
0.0059
0.0073
86
0.0058
0.0071
87
0.0058
0.0071
88
0.0057
0.0071
89
0.0056
0.0068
90
0.0056
0.0067
91
0.0056
0.0067
92
0.0055
0.0067
93
0.0055
0.0067
94
0.0054
0.0066
95
0.0053
0.0065
96
0.0053
0.0064
97
0.0052
0.0064
98
0.0051
0.0063
99
0.0051
0.0063
100
0.0050
0.0063
101
0.0050
0.0063
102
0.0049
0.0062
103
0.0049
0.0062
104
0.0048
0.0060
105
0.0048
0.0060
106
0.0048
0.0060
107
0.0046
0.0060
108
0.0046
0.0059
109
0.0045
0.0058
110
0.0045
0.0057
111
0.0044
0.0057
112
0.0044
0.0057
113
0.0043
0.0056
114
0.0043
0.0056
115
0.0042
0.0056
116
0.0042
0.0056
117
0.0041
0.0054
118
0.0040
0.0054
119
0.0040
0.0054
120
0.0040
0.0053
121
0.0039
0.0052
122
0.0038
0.0051
123
0.0038
0.0051
124
0.0037
0.0050
125
0.0037
0.0048
126
0.0037
0.0047
127
0.0037
0.0047
128
0.0034
0.0046
129
0.0033
0.0045
130
0.0033
0.0045
131
0.0032
0.0045
132
0.0031
0.0044
133
0.0031
0.0043
134
0.0031
0.0043
135
0.0031
0.0043
136
0.0030
0.0042
137
0.0029
0.0041
138
0.0029
0.0040
139
0.0029
0.0039
Hoy Residence 11/14/2019 3:09:08 PM Page 19
140
0.0028
0.0039
141
0.0028
0.0038
142
0.0027
0.0036
143
0.0026
0.0036
144
0.0026
0.0035
145
0.0025
0.0034
146
0.0024
0.0034
147
0.0024
0.0033
148
0.0024
0.0033
149
0.0023
0.0033
150
0.0022
0.0033
151
0.0020
0.0032
152
0.0017
0.0032
153
0.0013
0.0031
154
0.0013
0.0029
155
0.0005
0.0029
156
0.0003
0.0023
157
0.0001
0.0015
Hoy Residence 11/14/2019 3:09:08 PM Page 20
Duration Flows
Flow(cfs)
Predev
Mit
Percentage
Pass/Fail
0.0032
12741
8274
64
Pass
0.0034
11578
7286
62
Pass
0.0035
10528
6433
61
Pass
0.0037
9599
5685
59
Pass
0.0038
8785
5083
57
Pass
0.0039
8068
4551
56
Pass
0.0041
7430
4042
54
Pass
0.0042
6845
3609
52
Pass
0.0044
6296
3253
51
Pass
0.0045
5809
2941
50
Pass
0.0047
5329
2649
49
Pass
0.0048
4899
2382
48
Pass
0.0049
4511
2157
47
Pass
0.0051
4167
1946
46
Pass
0.0052
3845
1768
45
Pass
0.0054
3545
1629
45
Pass
0.0055
3273
1496
45
Pass
0.0056
3026
1368
45
Pass
0.0058
2803
1261
44
Pass
0.0059
2615
1176
44
Pass
0.0061
2443
1093
44
Pass
0.0062
2290
1029
44
Pass
0.0064
2118
961
45
Pass
0.0065
1985
896
45
Pass
0.0066
1868
837
44
Pass
0.0068
1762
764
43
Pass
0.0069
1652
715
43
Pass
0.0071
1562
657
42
Pass
0.0072
1478
609
41
Pass
0.0073
1393
558
40
Pass
0.0075
1324
522
39
Pass
0.0076
1243
496
39
Pass
0.0078
1172
461
39
Pass
0.0079
1119
425
37
Pass
0.0081
1053
394
37
Pass
0.0082
1000
369
36
Pass
0.0083
953
347
36
Pass
0.0085
901
324
35
Pass
0.0086
868
300
34
Pass
0.0088
833
283
33
Pass
0.0089
799
266
33
Pass
0.0090
774
251
32
Pass
0.0092
740
239
32
Pass
0.0093
717
223
31
Pass
0.0095
688
212
30
Pass
0.0096
658
202
30
Pass
0.0098
630
195
30
Pass
0.0099
598
188
31
Pass
0.0100
565
180
31
Pass
0.0102
539
170
31
Pass
0.0103
513
158
30
Pass
0.0105
487
148
30
Pass
0.0106
465
139
29
Pass
0.0107
447
134
29
Pass
Hoy Residence 11/14/2019 3:09:08 PM Page 21
0.0109
435
131
30
Pass
0.0110
413
126
30
Pass
0.0112
402
121
30
Pass
0.0113
375
119
31
Pass
0.0115
360
112
31
Pass
0.0116
343
108
31
Pass
0.0117
326
101
30
Pass
0.0119
310
98
31
Pass
0.0120
292
94
32
Pass
0.0122
279
92
32
Pass
0.0123
264
89
33
Pass
0.0124
254
85
33
Pass
0.0126
237
85
35
Pass
0.0127
225
82
36
Pass
0.0129
216
77
35
Pass
0.0130
203
72
35
Pass
0.0132
185
71
38
Pass
0.0133
176
68
38
Pass
0.0134
166
65
39
Pass
0.0136
156
60
38
Pass
0.0137
140
60
42
Pass
0.0139
128
60
46
Pass
0.0140
120
59
49
Pass
0.0141
112
57
50
Pass
0.0143
99
54
54
Pass
0.0144
95
54
56
Pass
0.0146
85
54
63
Pass
0.0147
79
52
65
Pass
0.0149
77
51
66
Pass
0.0150
73
50
68
Pass
0.0151
66
49
74
Pass
0.0153
61
45
73
Pass
0.0154
54
43
79
Pass
0.0156
47
43
91
Pass
0.0157
44
42
95
Pass
0.0158
39
40
102
Pass
0.0160
36
38
105
Pass
0.0161
34
38
111
Faii
0.0163
31
38
122
Fail
0.0164
29
36
124
Fail
0.0165
27
36
133
Fail
0.0167
27
35
129
Fail
0.0168
25
34
136
Fail
0.0170
21
32
152
Fail
0.0171
21
32
152
Fail
0.0173
19
32
168
Fail
The development has an increase in flow durations
from 1 /2 Predeveloped 2 year flow to the 2 year flow
or more than a 10% increase from the 2 year to the 50
year flow.
Hoy Residence 11/14/2019 3:09:08 PM Page 22
Water Quality
Water Quality BMP Flow and Volume for POC #1
On-line facility volume:
0 acre-feet
On-line facility target flow:
0 cfs.
Adjusted for 15 min:
0 cfs.
Off-line facility target flow:
0 cfs.
Adjusted for 15 min:
0 cfs.
Hoy Residence 11/14/2019 3:09:08 PM Page 23
LID Report
LID Technique
Usedfor
Total Volume
Volume
Infiltration
Cumulative
Percent
Waterfluality
Percent
Comment
Treatment?
Needs
Through
Volume
Volume
Volume
Water Quality
Treatment
Facility
(ac-ft)
Infiltration
Infiltrated
Treated
(ac-ft)
(ac-ft)
Credit
Gravel Trench Bed 1 PQC
❑
44.89
❑
100.00
Permeable Pavement 1 POC
❑
47.51
❑
100.00
Total Volume Infiltrated
92.40
0.00
0.00
100.00
0.00
0%
No Treat.
Credit
❑uration
Compliance with LI❑
Analysis
Standard 8% oft-yrto 50% of
Result =
2 yr
Failed
Hoy Residence 11/14/2019 3:09:08 PM Page 24
Model Default Modifications
Total of 0 changes have been made.
PERLND Changes
No PERLND changes have been made.
IMPLND Changes
No IMPLND changes have been made.
Hoy Residence 11/14/2019 3:09:25 PM Page 25
Appendix
Predeveloped Schematic
ter,, lPredevelopec
0.38ac
Hoy Residence 11/14/2019 3:09:25 PM Page 26
Mitigated Schematic
0
Hoy Residence 11/14/2019 3:09:34 PM Page 27
C. STORMWATER POLLUTION PREVENTION PLAN
This Stormwater Pollution Prevention Plan (SWPPP) has been prepared as part of the
Construction stormwater permit requirements for the project Hoy Residence located at 8051 184th
St SW, Edmonds, Washington. Itis located in Section 18, Township 27 North, and Range 4 East
of the Willamette Meridian in Snohomish County, Washington. The site area is 0.38 acres. The
site is currently undeveloped and exists as lawn and large evergreen trees. The site contains one
drainage basin that slopes moderately to the north. Please refer to the downstream analysis map
for more details. There are no critical areas located on the site. Per NRCS survey of Snohomish
County, the project site contains Alderwood soils that have a hydrologic classification of Type
"C". Please refer to the soils map and descriptions attached later in this report for more details.
The site area is 0.36 acres. The site is currently undeveloped and exists as lawn and large
evergreen trees. The site contains one drainage basin that slopes moderately to the north. Please
refer to the downstream analysis map for more details. There are no critical areas located on the
site. Per NRCS survey of Snohomish County, the project site contains Alderwood soils that have
a hydrologic classification of Type "C". Please refer to the soils map and descriptions attached
later in this report for more details.
The project site is zoned as RS-10. The proposal is to construct a new single-family home,
garage, and ADU with a total roof area of 4,895 SF. Access to the site will be through an access
easement to the south connecting to 184th St SW. The total proposed hard surface area will be
8,625 SF.
The roof drains and patio yard drains will drain infiltration trench. The driveway area will
be paved using permeable pavement. Post -Construction Soil Quality and Depth BMP T.5.13 is
proposed to provide onsite stormwater management for the pervious areas of the site.
The purpose of this SWPPP is to describe the proposed construction activities and all temporary
and permanent erosion and sediment control (TESC) measures, pollution prevention measures,
inspection/monitoring activities, and recordkeeping that will be implemented during the proposed
construction project. The objectives of the SWPPP are to:
Insight Engineering Co. - Stormwater Site Plan
11/15/19
-24-
1. Implement Best Management Practices (BMPs) to prevent erosion and
sedimentation, and to identify, reduce, eliminate or prevent stormwater
contamination and water pollution from construction activity.
2. Prevent violations of surface water quality, ground water quality, or
sediment management standards.
3. Prevent, during the construction phase, adverse water quality impacts
including impacts on beneficial uses of the receiving water by controlling
peak flow rates and volumes of stormwater runoff at the Permittee's outfalls
and downstream of the outfalls.
This SWPPP was prepared using the Ecology SWPPP Template. This SWPPP was prepared based
on the requirements set forth in the Construction Stormwater General Permit and in the Stormwater
Management Manual for Western Washington (SWMMWW 2005).
The 13 BMP Elements
Element #1— Mark Clearing Limits
To protect adjacent properties and to reduce the area of soil exposed to construction, the
limits of construction will be clearly marked before land -disturbing activities begin.
Element #2 — Establish Construction Access
Construction access or activities occurring on unpaved areas shall be minimized, yet
where necessary, access points shall be stabilized to minimize the tracking of sediment
onto public roads, and wheel washing, street sweeping, and street cleaning shall be
employed to prevent sediment from entering state waters.
Install the temporary construction entrance, according to the approved construction plans,
prior to any clearing or grading activities. Maintain until the access road is paved.
Element #3 — Control Flow Rates
In order to protect the properties and waterways downstream of the project site,
stormwater discharges from the site will be controlled. In general, discharge rates of
stormwater from the site will be controlled where increases in impervious area or soil
compaction during construction could lead to downstream erosion, or where necessary to
meet local agency stormwater discharge requirements.
Element #4 — Install Sediment Controls
Install silt fencing, according to the approved plans, prior to any clearing or grading activities.
Maintain until all construction activities are completed.
Install catch basin filters, according to the approved construction plans, as catch basins become
operable. Maintain until all construction activities are completed.
Insight Engineering Co. - Stormwater Site Plan
11/15/19
-25-
Element #5 — Stabilize Soils
Exposed and un-worked soils shall be stabilized with the application of effective BMPs to prevent
erosion throughout the life of the project.
Apply temporary hydro -seed to exposed and un-worked soils, according to the approved
construction plans, as needed to prevent erosion during site grading. Apply permanent hydro -seed
to areas at final grade as site grading is completed.
Apply mulching to exposed and un-worked soils, according to the approved construction plans, as
needed to prevent erosion during site grading. Maintain until site grading is completed and
permanent hydro -seed is applied.
Cover stockpiles with plastic sheeting, according to the approved construction plans, as needed to
prevent erosion during site grading. Maintain until stockpiles are removed from site.
Element #6 — Protect Slopes
All cut and fill slopes will be designed, constructed, and protected in a manner than minimizes
erosion. The following specific BMPs will be used to protect slopes for this project.
Element #7 — Protect Drain Inlets
All storm drain inlets and culverts made operable during construction shall be protected to prevent
unfiltered or untreated water from entering the drainage conveyance system. However, the first
priority is to keep all access roads clean of sediment and keep street wash water separate from
entering storm drains until treatment can be provided.
Element #8 — Stabilize Channels and Outlets
Where site runoff is to be conveyed in channels, or discharged to a stream or some other natural
drainage point, efforts will be taken to prevent downstream erosion.
Element #9 — Control Pollutants
All pollutants, including waste materials and demolition debris, that occur onsite shall be handled
and disposed of in a manner that does not cause contamination of stormwater. Good housekeeping
and preventative measures will be taken to ensure that the site will be kept clean, well organized,
and free of debris.
Element #10 — Control Dewatering
There will be no dewatering expected as part of this proposal. If it occurs, Baker tanks will be
used for dewatering.
Element #11— Maintain BMPs
All temporary and permanent erosion and sediment control BMPs shall be maintained and
repaired as needed to assure continued performance of their intended function. Maintenance and
repair shall be conducted in accordance with each particular BMP's specifications. Visual
monitoring of the BMPs will be conducted at least once every calendar week and within 24 hours
of any rainfall event that causes a discharge from the site. If the site becomes inactive, and is
temporarily stabilized, the inspection frequency will be reduced to once every month. All
Insight Engineering Co. - Stormwater Site Plan
11/15/19
-26-
temporary erosion and sediment control BMPs shall be removed within 30 days after the final
site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped
sediment shall be removed or stabilized on site. Disturbed soil resulting from removal of BMPs
or vegetation shall be permanently stabilized.
Element #12 — Manage the Proiect
Erosion and sediment control BMPs for this project have been designed based on the following
principles:
Design the project to fit the existing topography, soils, and drainage patterns; Emphasize erosion
control rather than sediment control; Minimize the extent and duration of the area exposed; Keep
runoff velocities low; Retain sediment on site; Thoroughly monitor site and maintain all ESC
measures and Schedule major earthwork during the dry season. The SWPPP shall be modified as
necessary to include additional or modified BMPs designed to correct problems identified.
Revisions to the SWPPP shall be completed within seven (7) days following the inspection.
Element #13 — Protect On -site Stormwater Management BMPs for Runoff from Roofs and
Other Hard Surfaces
On -site stormwater management BMPs used for runoff from roofs and other hard
surfaces include: full dispersion, roof downspout full infiltration or dispersion
systems, perforated stubout connections, rain gardens, bioretention systems,
permeable pavement, sheetflow dispersion, and concentrated flow dispersion. The
areas on the site to be used for these BMPs shall be protected from siltation and
compaction during construction by sequencing the construction in a fashion to
install these BMPs at the latter part of the construction grading operations, by
excluding equipment from the BMPS and the associated areas, and by using the
erosion and sedimentation control BMPs listed below. Additional requirements for
protecting these BMPs during the construction process, testing functionality, and
restoring functionality are needed at the final stage of the construction process.
Relevant BMPs
BMP C102: Buffer Zone BMP
C 103: High Visibility Fence BMP
C200: Interceptor Dike and Swale BMP
C201: Grass -lined Channels BMP
C207: Check Dams BMP
C208: Triangular Silt Dike BMP
C231: Brush Barrier BMP
Insight Engineering Co. - Stormwater Site Plan
11/15/19
-27-
C233: Silt Fence BMP
C234: Vegetated Strip
Insight Engineering Co. - Stormwater Site Plan
11/15/19
-28-
D. GEOTECH REPORT
Insight Engineering Co. - Stormwater Site Plan
11/15/19
-29-
COBALT
GEOSCIENCES
April 27, 2019
Mr. Paul King
Paul.judgeandassociates ogmail.com
RE: Stormwater Feasibility Evaluation
Proposed Single -Family Residence
8045 —184th Street SW
Parcel No. 270418o0103800
Edmonds, Washington
Dear Mr. King,
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, Washington 98028
In accordance with your authorization, Cobalt Geosciences, LLC has prepared this letter to
discuss the results of our stormwater feasibility evaluation at the referenced site.
The purpose of our evaluation was to determine the feasibility of utilizing infiltration devices for
stormwater runoff management.
Site and Project Description
The site is located at 8045 — 184th Street SW in Edmonds, Washington. The site consists of one
nearly rectangular shaped parcel with a total area of about 0.46 acres.
The property consists of an undeveloped parcel surrounded on all sides by residential properties.
There is an access easement near the southwest corner of the property. The site is nearly level to
slightly undulating and vegetated with grasses, ferns, bushes/shrubs, and sparse evergreen and
deciduous trees.
The project includes construction will include a new multi -story residence with garage and
crawlspace area. Stormwater management may include dispersion, detention, or infiltration
facilities depending on feasibility.
Area Geology
The Geologic Map of Edmonds East and West Quadrangle indicates that the site is near the
contacts between Vashon Glacial Till and Vashon Advance Outwash.
Vashon Glacial Till is typically characterized by an unsorted, non -stratified mixture of clay, silt,
sand, gravel, cobbles and boulders in variable quantities. These materials are typically dense and
relatively impermeable. The poor sorting reflects the mixing of the materials as these sediments
were overridden and incorporated by the glacial ice.
Vashon Advance Outwash consists of glacially consolidated sand and gravel with variable
amounts of silt deposited in front of the advancing glaciers approximately 15,000 years ago.
These deposits are commonly overlain by Vashon Glacial Till.
www.cobaltgeo.com (2o6) 331-1097
April 27, 2019
Page 2 of 3
Stormwater Feasibility Evaluation
Soil & Groundwater Conditions
As part of our evaluation, we excavated and sampled two hand borings up to 8 feet below grade.
Figure 1 shows the general location of the hand borings. Exploration logs are attached at the end
of this letter report.
Both hand borings encountered approximately 6 inches of grass and topsoil underlain by
approximately 3.5 to 4.5 feet of loose to medium dense, silty -fine to medium grained sand with
gravel (Weathered Glacial Till). This layer was underlain by dense, silty -fine to medium grained
sand trace to with gravel (Glacial Till?), which continued to the termination depths of the hand
borings.
Groundwater not encountered in the hand borings. Groundwater is not anticipated to be present
within at least 12 inches of the bottom of the infiltration trenches excavated up to a depth of 4 feet
below grade.
Stormwater Management Feasibility
We understand that stormwater runoff will flow into infiltration trenches within the property at
two or more locations.
We performed an in situ infiltration test in HB-1 at a depth of 3 feet below grade. Following
testing and application of correction factors for site variability (0.33), testing (0.5), and influent
control (0.9), the infiltration rate was determined to be 0.35 inches per hour. This is just above
the minimum that the Washington State Department of Ecology considers feasible.
We recommend that the bottom of the trenches be situated within native soils consistent with
those described on the attached logs. We recommend a maximum trench/system depth of 4 feet
below grade. Local loosening of the native soils may be required up to 2 feet below the bottom of
system elevations. We recommend locating systems at least 40 feet apart and at least io feet from
property lines. We should be on site to confirm soil conditions and provide additional
recommendations if necessary.
Erosion and Sediment Control
Erosion and sediment control (ESQ is used to reduce the transportation of eroded sediment to
wetlands, streams, lakes, drainage systems, and adjacent properties. Erosion and sediment
control measures should be implemented, and these measures should be in general accordance
with local regulations. At a minimum, the following basic recommendations should be
incorporated into the design of the erosion and sediment control features for the site:
• Schedule the soil, foundation, utility, and other work requiring excavation or the disturbance
of the site soils, to take place during the dry season (generally May through September).
However, provided precautions are taken using Best Management Practices (BMP's), grading
activities can be completed during the wet season (generally October through April).
• All site work should be completed and stabilized as quickly as possible.
• Additional perimeter erosion and sediment control features may be required to reduce the
possibility of sediment entering the surface water. This may include additional silt fences, silt
fences with a higher Apparent Opening Size (AOS), construction of a berm, or other filtration
systems.
www.cobaltgeo.com (206) 331-1097
April 27, 2019
Page 3 of 3
Stormwater Feasibility Evaluation
• Any runoff generated by dewatering discharge should be treated through construction of a
sediment trap if there is sufficient space. If space is limited other filtration methods will need
to be incorporated.
Closure
The information presented herein is based upon professional interpretation utilizing standard
practices and a degree of conservatism deemed proper for this project. We emphasize that this
report is valid for this project as outlined above and for the current site conditions, and should not
be used for any other site
Sincerely,
Cobalt Geosciences, LLC
H0NYy�!
44 WASy���d
54896 /.
Exp. 6-26-2020
Phil Haberman, PE, LG, LEG
Principal
PH/sc
www.cobaltgeo.com (2o6) 331-1097
HB-i N
9 Approximate Hand Boring Location A
ised Single -Family Residence
8045 -184th Street SW
Edmonds, Washington
SITE PLAN
FIGURE i
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
www.cobaltgeo.com
cobaltgeo ft ail.com
Unified Soil Classification System (USCS)
MAJOR DIVISIONS SYMBOL
TYPICAL DESCRIPTION
GW
Clean Gravels
Well -graded gravels, gravels, gravel -sand mixtures, little or no fines
Gravels
(more than 50%
(less than 5% _ GP
fines)
Poorly graded gravels, gravel -sand mixtures, little or no fines
COARSE
GRAINED
SOILS
of coarse fraction
retained on No. 4
sieve)
GM
Gravels with
Fines
(more than 12% GC
fines)
Silty gravels, gravel -sand -silt mixtures
Clayey gravels, gravel -sand -clay mixtures
(more than 50%
retained on
;°e sw
Clean Sands
Well -graded sands, gravelly sands, little or no fines
No. 200 sieve)
Sands
(50% or more
of coarse fraction
(less than 5% SP
fines)
Poorly graded sand, gravelly sands, little or no fines
passes the No. 4
sieve)
sM
Sands with Fines
Silty sands, sand -silt mixtures
(more than 12% sc
fines)
Clayey sands, sand -clay mixtures
ML
Inorganic silts of low to medium plasticity, sandy silts, gravelly silts,
FINE GRAINED
SOILS
(50% or more
Silts and Clays
(liquid limit less
than 50)
Inorganic cL
or clayey silts with slight plasticity
Inorganic clays of low to medium plasticity, gravelly clays, sandy clays
silty clays, lean clays
oL
Organic
Organic silts and organic silty clays of low plasticity
passes the
MH
Inorganic silts, micaceous or diatomaceous fine sands or silty soils,
No. 200 sieve)
Silts and Clays
(liquid limit 50 or
more)
Inorganic CH
elastic silt
Inorganic clays of medium to high plasticity, sandy fat clay,
or gravelly fat clay
OH
Organic
Organic clays of medium to high plasticity, organic silts
HIGHLY ORGANIC
SOILS
primarily organic matter, dark in color, PT
and organic odor
Peat, humus, swamp soils with high organic content (ASTM D4427)
1 Classification of Soil Constituents 1
MAJOR constituents compose more than 50 percent,
by weight, of the soil. Major constituents are capitalized
(i.e., SAND).
Minor constituents compose 12 to 50 percent of the soil
and precede the major constituents (i.e., silty SAND).
Minor constituents preceded by "slightly" compose
5 to 12 percent of the soil (i.e., slightly silty SAND).
Trace constituents compose o to 5 percent of the soil
(i.e., slightly silty SAND, trace gravel).
Relative Density
(Coarse Grained Soils)
Consistency
(Fine Grained Soils)
N, SPT,
Relative
N, SPT,
Relative
Blows/FT
Density
Blows/FT
Consistency
0-4
Very loose
Under 2
Very soft
4 -10
Loose
2-4
Soft
10 - 30
Medium dense
4-8
Medium stiff
30 - 50
Dense
8 -15
Stiff
Over 50
Very dense
15 - 30
Very stiff
Over 3o
Hard
Grain Size Definitions
Description
Sieve Number and/or Size
Fines
<#200 (0.08 mm)
Sand
-Fine
#200 to #40 (0.08 to 0.4 mm)
-Medium
#40 to #10 (0.4 to 2 MM)
-Coarse
#10 to #4 (2 to 5 mm)
Gravel
-Fine
#4 to 3/4 inch (5 to 19 mm)
-Coarse
3/4 to 3 inches (19 to 76 mm)
Cobbles
3 to 12 inches (75 to 305 mm)
Boulders
>12 inches (305 mm)
Moisture Content Definitions
Dry Absence of moisture, dusty, dry to the touch
Moist Damp but no visible water
Wet Visible free water, from below water table
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA98028 Soil Classification Chart Figure C1
(206) 331-1097
_ www.cobalt eg o.com
cobaltgeo(d-) gmail.com
Log of Hand Boring HB-1
Date: April 23, 2019
Depth: 8'
Initial Groundwater: N/A
Contractor:
Elevation: N/A
Sample Type: Grab
Method: Hand Auger
Logged By: PH Checked By: SC
Final Groundwater: N/A
U)
J
o
4
Moisture Content (%)
Plastic Liquid
_ >
U
-
E
N
Limit Limit
o
Material Description
0
?
o
SPT N-Value
G
0 10 20 30 40 50
Vegetation/Topsoil
---
_
----
--
---
SM
---------------------------------------------
Loose to medium dense, silty -fine to medium grained sand
with gravel, dark yellowish brown to yellowish brown,
moist. (Weathered Glacial Till)
—2
—3
—4
----
--
--
SM
---------------------------------------------
Dense, silty -fine to medium grained sand,
yellowish brown to grayish brown, moist. (Glacial Till?)
—b
—7
End of Hand Boring 8'
—9
— 10
Cobalt Geosciences, LLC
Proposed Residence
Hand
P.O. Box 82243
COBALT8045
- 184th Street SW
Boring
(2o6) 331- 097 8028
GEOSCIENCES
Edmonds, Washington
Log
www.cobaltgeo.com
cobaltgeo ftmail.com
Log of Hand Boring HB-2
Date: April 23, 2019
Depth: 6'
Initial Groundwater: N/A
Contractor:
Elevation: N/A
Sample Type: Grab
Method: Hand Auger
Logged By: PH Checked By: SC
Final Groundwater: N/A
U)
J
o
4
Moisture Content (%)
Plastic Liquid
_ >
U
-
E
N
Limit Limit
o
Material Description
0
?
o
SPT N-Value
G
0 10 20 30 40 5
Vegetation/Topsoil
----
- 1
----
--
---
SM
--------------------------------------------
Loose to medium dense, silty -fine to medium grained sand
with gravel and cobbles, dark yellowish brown to
yellowish brown, moist. (Weathered Glacial Till)
—2
—3
SM
Dense, silty fine to medium grained sand
yellowish brown to grayish brown, moist. (Glacial Till?)
—5
End of Hand Boring 6'
—7
—8
—9
— 10
Cobalt Geosciences, LLC
Proposed Residence
Hand
P.O. Box 82243
COBALT8045
- 184th Street SW
Boring
(2o6) 331- 097 8028
GEOSCIENCES
Edmonds, Washington
Log
www.cobaltgeo.com
cobaltgeo ftmail.com
E. OPERATION & MAINTENANCE MANUAL
Insight Engineering Co. - Stormwater Site Plan
11/15/19
-30-
No. 2 — Infiltration
Maintenance
Defect
Conditions When Maintenance Is
Results Expected When
Component
Needed
Maintenance Is
Performed
General
Trash & Debris
See "Detention Ponds" (No. 1).
See "Detention Ponds"
(No. 1).
Poisonous/Noxious
See "Detention Ponds" (No. 1).
See "Detention Ponds"
Vegetation
(No. 1).
Contaminants and
See "Detention Ponds" (No. 1).
See "Detention Ponds"
Pollution
(No. 1).
Rodent Holes
See "Detention Ponds" (No. 1).
See "Detention Ponds"
(No. 1)
Storage Area
Sediment
Water ponding in infiltration pond after
Sediment is removed
rainfall ceases and appropriate time
and/or facility is cleaned
allowed for infiltration. Treatment basins
so that infiltration system
should infiltrate Water Quality Design Storm
works according to
Volume within 48 hours, and empty within
design.
24 hours after cessation of most rain
events.
(A percolation test pit or test of facility
indicates facility is only working at 90% of
its designed capabilities. Test every 2 to 5
years. If two inches or more sediment is
present, remove).
Filter Bags (if
Filled with
Sediment and debris fill bag more than 1/2
Filter bag is replaced or
applicable)
Sediment and
full.
system is redesigned.
Debris
Rock Filters
Sediment and
By visual inspection, little or no water flows
Gravel in rock filter is
Debris
through filter during heavy rain storms.
replaced.
Side Slopes of
Erosion
See "Detention Ponds" (No. 1).
See "Detention Ponds"
Pond
(No. 1).
Emergency
Tree Growth
See "Detention Ponds" (No. 1).
See "Detention Ponds"
Overflow Spillway
(No. 1).
and Berms over 4
feet in height.
Piping
See "Detention Ponds" (No. 1).
See "Detention Ponds"
(No. 1).
Emergency
Rock Missing
See "Detention Ponds" (No. 1).
See "Detention Ponds"
Overflow Spillway
(No. 1).
Erosion
See "Detention Ponds" (No. 1).
See "Detention Ponds"
(No. 1).
Pre -settling
Facility or sump
6" or designed sediment trap depth of
Sediment is removed.
Ponds and Vaults
filled with Sediment
sediment.
and/or debris
Volume V — Runoff Treatment BMPs — December 2014
4-35
No. 5 — Catch Basins
Maintenance
Defect
Conditions When Maintenance is Needed
Results Expected When
Component
Maintenance is
performed
General
Trash &
Trash or debris which is located immediately
No Trash or debris located
Debris
in front of the catch basin opening or is
immediately in front of
blocking inletting capacity of the basin by
catch basin or on grate
more than 10%.
opening.
Trash or debris (in the basin) that exceeds 60
No trash or debris in the
percent of the sump depth as measured from
catch basin.
the bottom of basin to invert of the lowest
pipe into or out of the basin, but in no case
less than a minimum of six inches clearance
from the debris surface to the invert of the
lowest pipe.
Trash or debris in any inlet or outlet pipe
Inlet and outlet pipes free
blocking more than 1/3 of its height.
of trash or debris.
Dead animals or vegetation that could
No dead animals or
generate odors that could cause complaints
vegetation present within
or dangerous gases (e.g., methane).
the catch basin.
Sediment
Sediment (in the basin) that exceeds 60
No sediment in the catch
percent of the sump depth as measured from
basin
the bottom of basin to invert of the lowest
pipe into or out of the basin, but in no case
less than a minimum of 6 inches clearance
from the sediment surface to the invert of the
lowest pipe.
Structure
Top slab has holes larger than 2 square
Top slab is free of holes
Damage to
inches or cracks wider than 1/4 inch
and cracks.
Frame and/or
Top Slab
(Intent is to make sure no material is running
into basin).
Frame not sitting flush on top slab, i.e.,
Frame is sitting flush on
separation of more than 3/4 inch of the frame
the riser rings or top slab
from the top slab. Frame not securely
and firmly attached.
attached
Fractures or
Maintenance person judges that structure is
Basin replaced or repaired
Cracks in
unsound.
to design standards.
Basin Walls/
Bottom
Grout fillet has separated or cracked wider
Pipe is regrouted and
than 1/2 inch and longer than 1 foot at the
secure at basin wall.
joint of any inlet/outlet pipe or any evidence of
soil particles entering catch basin through
cracks.
Settlement/
If failure of basin has created a safety,
Basin replaced or repaired
Misalignment
function, or design problem.
to design standards.
Vegetation
Vegetation growing across and blocking more
No vegetation blocking
than 10% of the basin opening.
opening to basin.
Vegetation growing in inlet/outlet pipe joints
No vegetation or root
that is more than six inches tall and less than
growth present.
six inches apart.
Contamination
See "Detention Ponds" (No. 1).
No pollution present.
and Pollution
Volume V — Runoff Treatment BMPs — December 2014
4-38
No. 5 — Catch Basins
Maintenance
Defect
Conditions When Maintenance is Needed
Results Expected When
Component
Maintenance is
performed
Catch Basin
Cover Not in
Cover is missing or only partially in place.
Catch basin cover is
Cover
Place
Any open catch basin requires maintenance.
closed
Locking
Mechanism cannot be opened by one
Mechanism opens with
Mechanism
maintenance person with proper tools. Bolts
proper tools.
Not Working
into frame have less than 1/2 inch of thread.
Cover Difficult
One maintenance person cannot remove lid
Cover can be removed by
to Remove
after applying normal lifting pressure.
one maintenance person.
(Intent is keep cover from sealing off access
to maintenance.)
Ladder
Ladder Rungs
Ladder is unsafe due to missing rungs, not
Ladder meets design
Unsafe
securely attached to basin wall,
standards and allows
misalignment, rust, cracks, or sharp edges.
maintenance person safe
access.
Metal Grates
Grate opening
Grate with opening wider than 7/8 inch.
Grate opening meets
(If Applicable)
Unsafe
design standards.
Trash and
Trash and debris that is blocking more than
Grate free of trash and
Debris
20% of grate surface inletting capacity.
debris.
Damaged or
Grate missing or broken member(s) of the
Grate is in place and
Missing.
grate.
meets design standards.
No. 6 — Debris Barriers (e.g., Trash Racks)
Maintenance
Defect
Condition When Maintenance is
Results Expected When
Components
Needed
Maintenance is Performed
General
Trash and
Trash or debris that is plugging more
Barrier cleared to design flow
Debris
than 20% of the openings in the barrier.
capacity.
Metal
Damaged/
Bars are bent out of shape more than 3
Bars in place with no bends more
Missing
inches.
than 3/4 inch.
Bars.
Bars are missing or entire barrier
Bars in place according to design.
missing.
Bars are loose and rust is causing 50%
Barrier replaced or repaired to
deterioration to any part of barrier.
design standards.
Inlet/Outlet
Debris barrier missing or not attached to
Barrier firmly attached to pipe
Pipe
pipe
Volume V — Runoff Treatment BMPs — December 2014
4-39
No. 22 - Maintenance Standards and Procedures for Permeable Pavement.
Note that the inspection and routine maintenance frequencies listed below are recommended by Ecology. They do not supersede or replace the municipal stormwater permit requirements for inspection frequency required of
municipal stormwater permittees for "stormwater treatment and flow control BMPs/facilities."
Recommended Frequency a
Component
Condition when Maintenance is Needed
Action Needed
Inspection
Routine
(Standards)
(Procedures)
Maintenance
Surface/Wearing Course
Permeable
A, S
Runoff from adjacent pervious areas deposits soil, mulch or
. Clean deposited soil or other materials from permeable pavement or other adjacent surfacing
Pavements, all
sediment on paving
. Check if surface elevation of planted area is too high, or slopes towards pavement, and can be regraded (prior to regrading,
protect permeable pavement by covering with temporary plastic and secure covering in place)
• Mulch and/or plant all exposed soils that may erode to pavement surface
Porous asphalt or
A or B
None (routine maintenance)
Clean surface debris from pavement surface using one or a combination of the following methods:
pervious concrete
. Remove sediment, debris, trash, vegetation, and other debris deposited onto pavement (rakes and leaf blowers can be used
for removing leaves)
• Vacuum/sweep permeable paving installation using:
o Walk -behind vacuum (sidewalks)
o High efficiency regenerative air or vacuum sweeper (roadways, parking lots)
o ShopVac or brush brooms (small areas)
• Hand held pressure washer or power washer with rotating brushes
Follow equipment manufacturer guidelines for when equipment is most effective for cleaning permeable pavement. Dry
weather is more effective for some equipment.
Ab
Surface is clogged:
. Review the overall performance of the facility (note that small clogged areas may not reduce overall performance of facility)
Ponding on surface or water flows off the permeable
. Test the surface infiltration rate using ASTM C1701 as a corrective maintenance indicator. Perform one test per installation,
pavement surface during a rain event (does not infiltrate)
up to 2,500 square feet. Perform an additional test for each additional 2,500 square feet up to 15,000 square feet total. Above
15,000 square feet, add one test for every 10,000 square feet.
• If the results indicate an infiltration rate of 10 inches per hour or less, then perform corrective maintenance to restore
permeability. To clean clogged pavement surfaces, use one or combination of the following methods:
• Combined pressure wash and vacuum system calibrated to not dislodge wearing course aggregate.
• Hand held pressure washer or power washer with rotating brushes
• Pure vacuum sweepers
Note: If the annual/biannual routine maintenance standard to clean the pavement surface is conducted using equipment from
the list above, corrective maintenance may not be needed.
A
Sediment present at the surface of the pavement
. Assess the overall performance of the pavement system during a rain event. If water runs off the pavement and/or there is
ponding then see above.
• Determine source of sediment loading and evaluate whether or not the source can be reduced/eliminated. If the source
cannot be addressed, consider increasing frequency of routine cleaning (e.g., twice per year instead of once per year).
Summer
Moss growth inhibits infiltration or poses slip safety hazard
. Sidewalks: Use a stiff broom to remove moss in the summer when it is dry
• Parking lots and roadways: Pressure wash, vacuum sweep, or use a combination of the two for cleaning moss from
pavement surface. May require stiff broom or power brush in areas of heavy moss.
A
Major cracks or trip hazards and concrete spalling and
. Fill potholes or small cracks with patching mixes
raveling
. Large cracks and settlement may require cutting and replacing the pavement section. Replace in -kind where feasible.
Replacing porous asphalt with conventional asphalt is acceptable if it is a small percentage of the total facility area and does
not impact the overall facility function.
• Take appropriate precautions during pavement repair and replacement efforts to prevent clogging of adjacent porous
materials
a Frequency: A= Annually; B= Biannually (twice per year); S = Perform inspections after major storm events (24-hour storm event with a 10-year or greater recurrence interval).
b Inspection should occur during storm event.
Volume V — Runoff Treatment BMPs — December 2014
4-60
No. 22 (continued) - Maintenance Standards and Procedures for Permeable Pavement.
Recommended Frequency a
Component
Condition when Maintenance is Needed
Action Needed
Inspection
Routine
(Standards)
(Procedures)
Maintenance
Surface/Wearing Course (cont'd)
Interlocking concrete
A or B
None (routine maintenance)
Clean pavement surface using one or a combination of the following methods:
paver blocks and
. Remove sediment, debris, trash, vegetation, and other debris deposited onto pavement (rakes and leaf blowers can be used
aggregate pavers
for removing leaves)
• Vacuum/sweep permeable paving installation using:
o Walk -behind vacuum (sidewalks)
o High efficiency regenerative air or vacuum sweeper (roadways, parking lots)
o ShopVac or brush brooms (small areas)
• Note: Vacuum settings may have to be adjusted to prevent excess uptake of aggregate from paver openings or joints.
Vacuum surface openings in dry weather to remove dry, encrusted sediment.
A b
Surface is clogged:
. Review the overall performance of the facility (note that small clogged areas may not reduce overall performance of facility)
Ponding on surface or water flows off the permeable
. Test the surface infiltration rate using ASTM C1701 as a corrective maintenance indicator. Perform one test per installation,
pavement surface during a rain event (does not infiltrate)]
up to 2,500 square feet. Perform an additional test for each additional 2,500 square feet up to 15,000 square feet total. Above
15,000 square feet, add one test for every 10,000 square feet.
• If the results indicate an infiltration rate of 10 inches per hour or less, then perform corrective maintenance to restore
permeability.
• Clogging is usually an issue in the upper 2 to 3 centimeters of aggregate. Remove the upper layer of encrusted sediment,
and fines, and/or vegetation from openings and joints between the pavers by mechanical means and/or suction equipment
(e.g., pure vacuum sweeper).
• Replace aggregate in paver cells, joints, or openings per manufacturer's recommendations
A
Sediment present at the surface of the pavement
. Assess the overall performance of the pavement system during a rain event. If water runs off the pavement and/or there is
ponding, then see above.
• Determine source of sediment loading and evaluate whether or not the source can be reduced/eliminated. If the source
cannot be addressed, consider increasing frequency of routine cleaning (e.g., twice per year instead of once per year).
Summer
Moss growth inhibits infiltration or poses slip safety hazard
. Sidewalks: Use a stiff broom to remove moss in the summer when it is dry
• Parking lots and roadways: Vacuum sweep or stiff broom/power brush for cleaning moss from pavement surface
A
Paver block missing or damaged
Remove individual damaged paver blocks by hand and replace or repair per manufacturer's recommendations
A
Loss of aggregate material between paver blocks
Refill per manufacturer's recommendations for interlocking paver sections
A
Settlement of surface
May require resetting
Open -celled paving
A or B
None (routine maintenance)
. Remove sediment, debris, trash, vegetation, and other debris deposited onto pavement (rakes and leaf blowers can be used
grid with gravel
for removing leaves)
• Follow equipment manufacturer guidelines for cleaning surface.
A b
Aggregate is clogged:
• Use vacuum truck to remove and replace top course aggregate
Ponding on surface or water flows off the permeable
. Replace aggregate in paving grid per manufacturer's recommendations
pavement surface during a rain event (does not infiltrate)]
A
Paving grid missing or damaged
. Remove pins, pry up grid segments, and replace gravel
• Replace grid segments where three or more adjacent rings are broken or damaged
• Follow manufacturer guidelines for repairing surface.
A
Settlement of surface
May require resetting
A
Loss of aggregate material in paving grid
Replenish aggregate material by spreading gravel with a rake (gravel level should be maintained at the same level as the
plastic rings or no more than 1/4 inch
above the top of rings). See manufacturer's recommendations.
A
Weeds present
. Manually remove weeds
• Presence of weeds may indicate that too many fines are present (refer to Actions Needed under "Aggregate is clogged" to
address this issue)
a Frequency: A= Annually; B= Biannually (twice per year); S = Perform inspections after major storm events (24-hour storm event with a 10-year or greater recurrence interval).
b Inspection should occur during storm event.
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No. 22 (continued) - Maintenance Standards and Procedures for Permeable Pavement.
Recommended Frequency a
Component
Condition when Maintenance is Needed
Action Needed
Inspection
Routine
(Standards)
(Procedures)
Maintenance
Surface/Wearing Course (cont'd)
Open -celled paving
A or B
None (routine maintenance)
. Remove sediment, debris, trash, vegetation, and other debris deposited onto pavement (rakes and leaf blowers can be used
grid with grass
for removing leaves)
• Follow equipment manufacturer guidelines for cleaning surface.
A b
Aggregate is clogged:
. Rehabilitate per manufacturer's recommendations.
Ponding on surface or water flows off the permeable
pavement surface during a rain event (does not infiltrate)]
A
Paving grid missing or damaged
. Remove pins, pry up grid segments, and replace grass
• Replace grid segments where three or more adjacent rings are broken or damaged
• Follow manufacturer guidelines for repairing surface.
A
Settlement of surface
. May require resetting
A
Poor grass coverage in paving grid
. Restore growing medium, reseed or plant, aerate, and/or amend vegetated area as needed
• Traffic loading may be inhibiting grass growth; reconsider traffic loading if feasible
As needed
None (routine maintenance)
. Use a mulch mower to mow grass
A
None (routine maintenance)
• Sprinkle a thin layer of compost on top of grass surface (1/2" top dressing) and sweep it in
• Do not use fertilizer
A
Weeds present
. Manually remove weeds
• Mow, torch, or inoculate and replace with preferred vegetation
Inlets/Outlets/Pipes
Inlet/outlet pipe
A
Pipe is damaged
Repair/replace
A
Pipe is clogged
Remove roots or debris
Underdrain pipe
Clean pipe as
Clean orifice at least
Plant roots, sediment or debris reducing capacity of
. Jet clean or rotary cut debris/roots from underdrain(s)
needed
biannually (may
underdrain (may cause prolonged drawdown period)
. If underdrains are equipped with a flow restrictor (e.g., orifice) to attenuate flows, the orifice must be cleaned regularly
need more frequent
cleaning during wet
season)
Raised subsurface
Clean pipe as
Clean orifice at least
Plant roots, sediment or debris reducing capacity of
. Jet clean or rotary cut debris/roots from underdrain(s)
overflow pipe
needed
biannually (may
underdrain
. If underdrains are equipped with a flow restrictor (e.g., orifice) to attenuate flows, the orifice must be cleaned regularly
need more frequent
cleaning during wet
season)
Outlet structure
A, S
Sediment, vegetation, or debris reducing capacity of outlet
. Clear the blockage
structure
. Identify the source of the blockage and take actions to prevent future blockages
a Frequency: A= Annually; B= Biannually (twice per year); S = Perform inspections after major storm events (24-hour storm event with a 10-year or greater recurrence interval).
b Inspection should occur during storm event.
Volume V — Runoff Treatment BMPs — December 2014
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No. 22 (continued) - Maintenance Standards and Procedures for Permeable Pavement.
Recommended Frequency a
Component
Condition when Maintenance is Needed
Action Needed
Inspection
Routine
(Standards)
(Procedures)
Maintenance
Inlets/Outlets/Pipes (cont'd)
Overflow
B
Native soil is exposed or other signs of erosion damage are
Repair erosion and stabilize surface
present at discharge point
Aggregate Storage Reservoir
Observation port
A, S
Water remains in the storage aggregate longer than
If immediate cause of extended ponding is not identified, schedule investigation of subsurface materials or other potential
anticipated by design after the end of a storm
causes of system failure.
Vegetation
Adjacent large shrubs
As needed
Vegetation related fallout clogs or will potentially clog voids
. Sweep leaf litter and sediment to prevent surface clogging and ponding
or trees
. Prevent large root systems from damaging subsurface structural components
Once in May and
Vegetation growing beyond facility edge onto sidewalks,
Edging and trimming of planted areas to control groundcovers and shrubs from overreaching the sidewalks, paths and street
Once in September
paths, and street edge
edge improves appearance and reduces clogging of permeable pavements by leaf litter, mulch and soil.
Leaves, needles, and
In fall (October to
Accumulation of organic debris and leaf litter
Use leaf blower or vacuum to blow or remove leaves, evergreen needles, and debris (i.e., flowers, blossoms) off of and away
organic debris
December) after leaf
from permeable pavement
drop (1-3 times,
depending on
canopy cover)
a Frequency: A= Annually; B= Biannually (twice per year); S = Perform inspections after major storm events (24-hour storm event with a 10-year or greater recurrence interval).
b Inspection should occur during storm event.
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