APVD RESUB 4-BLD2024-0235+Storm_Drainage_Report+12.13.2024_8.53.18_AM+4668579BLD2024-0235 RESUB
Dec 13 2024
CITY OF EDMONDS
DEVELOPMENTSERVICES
DEPANTMENT
STORM DRAINAGE REPORT
For
Proposed Single -Family Residence
For: Mr. Douglas Subcleff
Located at
8816 189t" Place SW, Edmonds, WA 98026 Tax
Parcel Number: 00728600000300
Prepared by:
Effective Engineering PLLC
CIVIL ENGINEERING/CONSULTING
8627 NE 180t" Street
Bothell, Washington 98011
Phone: (206) 303-7639
Fax: (425) 658-9203
E-mail: admin@effectiveengineeringpllc.com
12-11-2024
1
COMPLIES WITH APPLICABLE
CITY STORMWATER CODE
EE2020-112
01 /03/2025
Table of Contents
Drainage Report
Project Overview
3
Preparation of Stormwater Site Plans 5
Construction Stormwater Pollution Prevention 6
Appendix A
Figure II-3.22: Silt Fence
14
Figure II-3.1: Stabilized Construction Access 15
Table V-A.5: Maintenance Standards - Catch Basins and Detention
Typical Detention Tank
Flow Control Structure
Cobalt GeoSciences Geotechnical Report 2-18-23
2 EE2020-112
Project Overview
The site is vacant land on the South -East Corner of 89th Ave W and 189th PL SW. The site
located at, 8816 189th Place SW, Edmonds, WA 98026 and the tax parcel number is:
00728600000300. The site is undeveloped with just a gravel driveway and shed, and there no
significant trees. The site is covered with grass. The site has 5% to 20% +/- slope down from east
to west. The site is bordered to west, south, and east by single family residents and to the north
by 189th PL SW.
There is a 3 foot+/- concrete block wall on the west property line dividing the site from the lower
neighboring lot to the west.
There appears to be no drainage issues upstream or downstream. Per our site visit, there is no
sign of any water going on or off of the site.
Per the Cobalt Geo-Sciences Report dated 2-18-23 (see attached) the soils are glacial till and
infiltration is not feasible.
Anew multi -story house and concrete driveway will be constructed on the 12, 462.83 sf (0.29
acre) site. See the site plan and Okimoto Architecture plan sheets for detail. The proposed
surfaces are as followed:
Proposed Building Roof with overhang(sf)
2940
Concrete driveway (sf)
1460
Patio covered by roof 278 sf
Road and sidewalk patch
133
Total Proposed impervious area (sf)
4,533
Total Proposed Impervious coverage
35.3%
Clearing limit area = 10,548sf;
Per the City of Edmonds and the 2019 DOE SWMMWW drainage control will be provided for
this Categoryl project per List 1. Per Cobalt soil report, the soils are Glacial till and infiltration is
infeasible. Since infiltration is infeasible and there is not room for dispersion, we will use a
direct connection to the storm drain in 189th PI SW for the roof and driveway drains. See the
drainage plan for detail. Due to the Glacial Till soils and depth of the drainage lines a Perforated
pipe connection is infeasible due to high winter ground water. Therefore we will install a
Stormwater Detention System using 201f of 48 inch O pipe and Control Manhole
According to Figure I-3.1 in the Department of Ecology Stormwater Management Manual,
minimum requirements # 1 through #5 apply to the new and replaced hard surfaces.
3 EE2020-112
Figure 1-3.1: Flow Chart for Determining Requirements for New
Development
start Here
Does the Site have 35% Yi See Redevelopment Project
or more of existing hard Threst+olds and the Figure 'FAow
Chan for Deterr wwv
surface coverage?
Riagwramwus for Redeveloper",
Does the Project convert 3/4
acres or more of vegetation to
Does the Project result in lawn or landscaped areas, or
5,000 square teat, or NO convert 2.5 acres or more of
greater, of new plus native vegetation to pasture?
replaced hard surface
area? NO
1 Yes VW
Does the Project result in 2,000
t square feet, or greater, of new plus
All Minimum Requirements replaced hard surface area?
apply to the new and replaced
hard surfaces and converted �� JNO
vegetation areas
Does the Project have land
[:Minimum Requirernartts I" disturbing activities of 7,000
rr,.d
ough X5 apply to the new Y4"square feet or greater"
replaced hard surfacesnd the land disturbed- �Na
Minimum Requirement 62
awl".
Itlltr� Flow Chart for Determining Requirements for
I New Development
t)FPAR-MFNT OF RlwaedMarch 2'1v_
ECOLOGY Please aae tom -M,rw acy. we gowrbcyrgnr nod ar aovnillm noboa tnawtno pennesions.
Stale of wast+lngton tmftbon d rary and
2019 Stormwater Management Manual for Western Washington
Volume 1- Chapter 3 - Page 89
4 EE2020-112
Minimum Requirement #1: Preparation of Stormwater Site Plans ...................2
Minimum Requirement #2: Construction Stormwater Pollution Prevention
(SWPP) .
Minimum Requirement #3: Source Control of Pollution..................................2
Minimum Requirement #4: Preservation of Natural Drainage Systems and
Outfalls...............................................................................................................2
Minimum Requirement #5: On -site Stormwater Management .... Minimum
Requirement #1: Preparation of Stormwater Site Plans
Stormwater Site Plans will be provided per I-3.4.1 of the 2019 DOE Stormwater
Management Manual for Western Washington.
Minimum Requirement #2: Construction Stormwater Pollution Prevention
(SWPP)
Element 1: Preserve Vegetation/Mark Clearing Limits
Mark clearing limits BMP C103 will be the extent of the property line.
Element 2: Establish Construction Access
Stabilized construction access will be constructed. This can be seen on the Erosion
Control Plan BMP C-105 Stabilized Construction Entrance.
Element 3: Control Flow Rates
Best Management Practices will be provided to the extent feasible Per Cobalt soil report,
the soils are Glacial till (see the Cobalt soil report). We will use regular concrete pavement for
the driveway and a direct connection through a perforated pipe connection to the storm drain in
189th PL SW for the roof downspouts as there is no room for dispersion and the soils are not
suitable for infiltration. A new catch basin will be installed to connect drainage from the house to
the existing drainage in 189th Place SW. It is shown in the drainage plan. A sediment trap will be
used during construction to remove silt and control flow rates. Mulching of exposed soil will also
be used to control flow rates. Disturbed soil will be amended per SD632
5 EE2020-112
Element 4: Install Sediment Controls
A silt fence BMP C233 will be installed and additional sediment control features will be
made based on Cobalt soil report. A sediment trap will be installed.
Element 5: Stabilize Soils
The disturbed soil will be treated per BMP T5.13 for soil quality and depth and
BMP C 121 for Mulching and BMP C-120 for seeding.
Element 6: Protect Slopes
If Slope protection is needed use BMP C-123 plastic covering and then BMP C 121
Mulching and BMP C-120 Seeding.
Element 7: Protect Drain Inlets
The existing catch basin on 189th PI SW will be protected with storm drain inlet
protection, use BMP C220 Storm Drain Inlet Protection. All new catch basins installed no this
project will be provided with inlet protection during construction.
Element 8: Stabilize Channels and Outlets
There are no channels on this project.
Element 9: Control Pollutants
There are no special pollutants on this project as this is small site PGS = 1424sf <
5,OOOsf. Measures will be taken to control saw cutting and concrete placing to avoid pollution.
Use as needed BMP C 150 Materials on Hand:
BMP C 151 Concrete Handling
BMP C152 Saw -cutting and Surfacing Pollution Prevention
BMP C 15 3 Materials delivery, Storage and containment
BMP C 154 Concrete washout area
Element 10: Control De -Watering
Per soil report, If Dewatering should be needed on this project use a sediment trap if there is
sufficient space. If space is limited, other filtration methods will need to be incorporated.
The sediment trap is sized per Q=CIA= 0.9x0.24xl.3= 0.28cfs for the 2 year storm runoff
Sediment trap = 2080sf x 0.28cfs = 582.4sf minimum surface area per Fig II-3.26 Sediment Trap
6 EE2020-112
Element 11: Maintain BMPs
The owner will be responsible for maintaining the BMP's on this project per chapter 4 of
Volume II of 2019 DOE.
Element 12: Manage the Project
The owner will be responsible for managing the project.
Element 13: Protect Low Impact Development BMPs
All low impact development BMPs will be followed be the owner.
Minimum Requirement #3: Source Control of Pollution
Objective: the intent of source control BMPs is to prevent stormwater from coming in contact
with pollutants. They are a cost-effective means of reducing pollutants in stormwater and,
therefore should be a first consideration in all projects. There are no significant sources of
pollution on this SFR project. Roof runoff will be routed through a Stormwater Detention System
prior to being discharged to the piped drainage system in 189th PI SW. The driveway will be
made of concrete pavement and its runoff will be collected by a catch basin or it will sheet flow
onto the adjacent grass yard. All disturbed soil will be amended with compost per SD642 and
BPM C121
Mulching and grass planted per BMP C-120 As there is less than 5,000sf of PGS on this project
it meets the minimum area exemption. Reference BMP S411 for Landscaping and Lawns. The
Stormwater Control manhole will provide some pollution protection by allowing sediments to
settle and oils to rise.
Minimum Requirement #4: Preservation of Natural Drainage Systems and
Outfalls
Objective: to preserve and utilize natural drainage systems to the fullest extent because of the
multiple stormwater benefits these systems provide; and to prevent erosion at and downstream of
the discharge location.
The area of this project has been heavily disturbed by suburban development. Surrounding
properties on 189th PL SW drain to the street where flow is collected by an underground storm
drainage system. Lots to the west and south do not drain any significant amount of water onto
this site.
7 EE2020-112
The only outfall for this site is to the street piped drainage system. The piped drainage system in
189m Pl SW flows west from the existing SDMH through a 12" 0 pipe The pipe drains down
189th PI SW to the west to 92"d Avenue West and then appears to drain north and to Puget Sound
within a mile of the site. A 12" 0 pipe has more than adequate capacity 4cfs min, to handle the
flow from this site and basin. See downstream drainage map below:
Minimum Requirement #5: On -site Stormwater Management
Objective: to use practices distributed across a development that reduce the amount of disruption.
of the natural hydrologic characteristics of the site.
We will use list 1 for this Category 1 project
The site has already been cleared of natural vegetation. The yard area will be re -landscaped after
construction with grass and other landscaping plans and will have Post Construction Quality and
Depth Soil Amendments per .BMP T5.13.
The roof drains will be routed to the piped storm drainage system in 189th Pl SW through a catch
basin and 201f of 48"0 Pipe and a Control Manhole for Stormwater Detention. The driveway will
use regular concrete pavement. Grading of the site will be kept to a minimum.
8 EE2020-112
Per List 1 for Roof drainage:
A. Full Dispersion cannot be used as there is not a 100 foot natural vegetated flow path
B. Downspout infiltration cannot be used as the Geotechnical report states infiltration is
infeasible as there is not 3 feet of permeable soil above the restrictive layer.
C. Raingardens are and Bio-Retention are infeasible as all infiltration is infeasible per the
Geotech Report as the design infiltration rate is less than 0.3 in/hr
D. Downspout dispersion is infeasible as there is not an adequate 50 foot vegetated flow
path
E. Detention will be used using 201f of 48" 0 Pipe and a Control Manhole.
F. A Perforated Pipe Connection will not be used due to the impervious soil and restrictive
layer.
For Other Hard Surfaces: A. Full dispersion is infeasible as there is not a 100foot
natural vegetated flow path.
B. Full Infiltration or Pervious Pavement is infeasible as the Geotechnical report states that
infiltration is infeasible due to low permeability (less than 0.3 in/hr) and high
groundwater.
C. Raingardens are infeasible as the Geotechnical Report states that infiltration is infeasible
on the site and the soil has low permeability of less than 0.3 in/hr..
D. Bio-Retention- Is infeasible because soil ha low permeability of less than 0.3 in/hr.
E. Sheet Flow and Concentrated Flow Dispersion is infeasible as there is not an adequate 10
foot vegetated flow path.
F. A detention tank using 201f of 48" Diameter pipe, and a Control Manhole will be used. A
catch basin in the driveway will be installed at the north property line to collect runoff
from the driveway and rout it into the Stormwater Detention System. Per the Edmonds
Stormwater Addendum 6.3.1 the required storage is 2% of the hard surface area or
4,400sf x 0.02 x 3ft = 264 CF of storage required.
We will use 20 feet of 48" 0 pipe @ 12.56 cf/ft = 251.2 cf and 41f of 36" pipe @ 7cf/lf =
28cf = 279cf provided
Other Requirements
No other special requirements, such as re -zones, variances, adjustments or SEPA mitigations are
not required for this site.
Area Description = Lot = 12,462.83 sf vacant lawn
9 EE2020-112
Impervious = new house roof area of house = 2,940sf
Driveway and garage apron paving = 1,460sf
Sidewalk Patch in ROW = 133sf
Total impervious on site area = 4,400sf
Total % impervious = 35.3%
New Lawn = 7,742.83sf
Total Hard Surface = 4,533sf including off site
5.1 Low Impact Development Best Management Practices
As Minimum Requirements 1 through 5 are required on this project, List #1: On -site Stormwater
Management BMPs for Projects Triggering Minimum Requirements #1 through #5. As no BMPs
are feasible we will use a Stormwater Detention Tank connection to the piped Storm Drainage
System in 189th Place SW. The downstream drainage system is piped to Puget Sound, less than 1
mile away, and capacity is adequate to pass the flows from this site.
Lawn and Landscaped Areas
Post -Construction Soil Quality and Depth
Areas disturbed by construction and not built upon will be treated according to SD-642 prior to
landscaping.
A direct connection to the storm drain in 189th P1 SW will not be made as a perforated pipe
connection is infeasible per the Geotech Report, as groundwater is expected at approximately 3
feet below grade and the invert of our storm drain pipe outlet is over 4 feet below grade and 1
foot of separation between groundwater and the bottom of the Perforated Pipe Connection trench
is required per the DOE SWMMWW.
5. CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN
Per Minimum Requirement #2, all new development and redevelopment projects are responsible
for preventing erosion and discharge of sediment and other pollutants into receiving waters. This
is achieved through:
Project Requirements - Construction SWPPP Elements See Minimum Requirement #2
6. CONVEYANCE SYSTEM ANALYSIS AND DESIGN- NA there are no conveyance pipes on
this project
10 EE2020-112
Conclusions and Recommendations
In summary, the best management practice for stormwater runoff on this development is a direct
connection to the piped drainage system in 189th PL SW for the roof and driveway through a direct
pipe connection. The driveway will be made of regular concrete pavement. All construction Erosion
Control BMPs will be followed and Site Plans/ESC Plans will be provided. Pollutants will be
controlled with this system as well. The Cobalt soil report will provide more information about the
soils and recommendations on foundation design, retaining walls, and construction field reviews.
Appendix
Silt Fence detail
Stabilized Construction Entrance Detail
Maintenance for Catch Basins
Cobalt GeoSciences Report dated 2-18-23
Detention Tank Detail
11 EE2020-112
2" x 2" WOOD/STEEL
FILTER FABRIC SECURED
TO 2" x 2" 14 GA
WIRE FABRIC EQUAL
NATIVE BACKFILL MATERIAL
FILTER FABRIC MATERIAL IN CONTINOUS ROLLS
USE STAPLES OR WIRE RINGS TO ATTACH
FABRIC TO WIRE
2" x 2" WOOD/STEEL POSTS-,
r�
WIRE MESH FENCE
TO SUPPORT FILTER
FABRIC
BURY BOTTOM OF FILTER
MATERIAL S' TO 12'
NOTES,
I CONTRACTOR/DEVELOPER SHALL MAINTAIN AND ENSURE PROPER
EROS" CONTROL THROUGHOUT PROJECT CITY INSPECTION REQUIRED ON
2 SILT FENCE TO BE PLACED DOWNSLOPE OF CONSTRUCTION ALL EROSION CONTROL METHODS
A 'NlrY BEFORE OTHER WORK CAN BEGIN
�r REVIWN DATE
CITY OF EDMONDS FILTER FABRIC FENCE JMUARY 20Ia
FILTRATION SYSTEMS
PUBLIC WORKS STANDARD
DEPARTMENT DETAIL
,AC3'% APPROVED BY R. ENOLISH E R — 9 00
12 EE2020-112
.LS
A
TH
IN
DE FULL WIDTH
GR£SS/EGRESS
DETAIL NOTES:
u THE MINIMUM LENGTH SHALL BE EXTENDED AS NECESSARY TO ENSURE MATERIAL IS NOT TRACKED OFF SITE
AND/OR INTO THE PUBLIC RIGHT-OF-WAY
O ATB DRIVEWAY RAMP AND/OR SITE ACCESS ROAD 15- WIDE MIN. SEE TABLE BELOW FOR REQUIRED LENGTH.
NOTES:
1 SURFACE WATER - ALL SURFACE WATER FLOWING OR DIVERTED TOWARD CONSTRUCTION ENTRANCES SHALL BE PIPED
ACROSS THE ENTRANCE IF PIPING IS IMPRACTICAL, A MOUNTABLE BERM WITH 51 SLOPES WILL BE PERMITTED
2 MAINTENANCE - THE ENTRANCE SHALL BE MAINTA)NED IN A CONDITION WHICH WILL PREVENT TRACKING OR FLOWING
OF SEDIMENT OFF SITE AND/OR ONTO PUBLIC RIGHT—OF-WAY THIS MAY REQUIRE PERIODIC TOP DRESSING WITH
ADDIT►ONAL QUARRY SPALLS AS CONDITIONS DEMAND AND REPAIR AND/OR CLEANOUT OF ANY MEASURES USED TO
TRAP SEDIMENT ALL SEDIMENT SPILLED, DROPPED, WASHED OR TRACKED OFF SITE AND/OR ONTO PUBLIC
RIGHT-OF-WAY MUST BE REMOVED IMMEDIATELY
3 WHEELS SHALL BE CLEANED TO REMOVE SEDIMENT PRIOR TO LEAVING THE SITE WHEN WASHING IS USED, IT SMALL
BE DONE ON AN AREA STABILIZED WITH QUARRY SPALLS AND WHICH DRAINS INTO AN APPROVED SEDIMENT TRAPPING
DEVICE
4. INSPECTION AND NEEDED MAINTENANCE SHALL BE PROVIDED AFTER EACH RAIN.
PROJECT
SIZE
MIN LENGTH OF (FEET)
QUARRY SPALLS-
< 1/4 ACRE
30
< 1 ACRE
50
< 3 ACRE
100
> 3 ACRE
100
• PROVIDE ATB OR ASPHALT
TRANSITION WHERE FRONTAGE
ROAD IS AN ARTERIAL
LENGTH TO BE DETERMINED
BY CITY INSPECTOR CITY INSPECTION REQUIRED ON
ALL EROSION CONTROL METHODS
BEFORE OTHER WORK CAN BEGIN
CITY OF EDMONDS STABILIZED CONSTRUCTION JANUARY 201a
ENTRANCE
r PUBLIC WORKS ";I,DiLRD
DEPARTMENT DLTAIL
-> APPROVED BY R. E► G ISM E R - 9 01
13
EE2020-112
Table V-A.S1 Maintenance Standards - Catch Basins
ainnsnce
Defect
Conditions When Maintenance Is Needed
"mai m- Is p
Results expected W��Mer-
Res
component
Trash ordrbds which is located immediately In front of the catch bssln opening or is blocking lnletllng capacity of the basin by morethan 10%.
No Trash a debris located immediately in fruit of
Trash or debris Onthe basin) that exceeds 60 percent of the sump depth as measured front the bottom of basin to Invert of the lowest pipe Into or out of the
catch basin man grate opening.
basin, but In no case less than a minimum of sb( Inches clearance from the debris surface to the Invert of the lowest pipe.
No trash or debris in the catch basin.
Trash B Debris
Trash a debris In try Inlet or outlet pipe blocking more than 113 of its height.
Inlet and outlet pipes free of trash m debris.
Dead animals avegetation that could generate odors that could cause complaints or dangerous gases (e.g., methane).
No dead animals or vegetation present within the
catch basin.
Sediment (In the basin) that exceeds 60 percent of the sump depth as measured from the bottom of basin to Invert of the lowest pipe Into gout of the
Sediment
basin, but In no case less than a minimum of 6 Inches clearance from the sediment surface to the Invert afthe lowest pipe.
No sediment in the catch basin
General
Strudure Damagete
Top slab has holes larger than 2 square inches or cracks widathan 1/4 inch. gntet is to make sure n, mrtlenel is running into basin).
Top slab is free of hales antl cracks.
Frame end/arTap Slab
Frame not sitting gush on top slab, i.e., separation of more than 314 inch of the from from the top stab. Fremerrat securely attached
Frame is sitting flush an the riser rings atop slab
and grimy attached.
Fractures orCracks In
Maintenance personjudges met structure is unsound.
Basin reaced areIced to design standards.
a
Basin Walls/Bottom
Grua fillet has separated or cracked widerthan 112 inch and longerttmn l foot at the joint of cry inletfoutlet pipe or any evidence of soil particles entering
pipe is regmuted and secure at basin wall.
catch basin through cracks.
Settlement/ MII
If failure of basin has created a safety, function, ordesign problem.
Basin replaced orrepeired to design standards.
alignment
Vegetation growing saws and blocking mare than 10% or the basin opening.
No vegetation blocking opening to basin.
Vegetation
Vegetation growing in inlet/outlet pipe joints that is more than six inches tall and Ins than abr inches apart.
No vegetation or root growth present.
Contamination and Pol-
IWion
See Table V-A.1: Maintenance Standards - Detention Ponds
No pollutlen present.
Cover Not in Piece
Covers missing manly partially in place. Any open catch basin requires maintenance.
Covedgrate Is In pli meets design standards,
end Is secured
Catch Basin
Looking Mechanism
Mechanism cannot be opened by one maintenance person with properteds. Bolts into Items have less then 1/2 inch of thread
Mechanism opens with propertools.
Cover
Not Working
CoverDificubto
One maintenance person cannot remove lid afterapplying normal lifting pressure.
Covercm bere—ad byonemnirterenceper-
Remove
(intent is keep coverfr m sealing off access to mairten uri
Son.
Ladder
Ladder Rurpe Unsafe
Ladder Is wands dueto missing rungs, not securely attached to basin well. misalignment. mat. cracks, orsharp edges.
Ladder meets design dandadsand allows maln-
teeence person safe access.
Grate opening Unsafe
Gretewah opening widerthen 7/8 inch.
Grate opening meets design standards.
Metal Grates
Trash and Debris
Thai and debts that is blocking mare it=20% of grate surface inletting capacity.
Grate free of trash and debris.
(ItApplicablo)
DrnagetlorMieeing.
Crate missing or broken members)of the grate.
Grate Is In place, meets the design standards, and
Is Installed and aligned with the III path.
2019 StormwaterManagement Manual for Western Washington
Volume V-AppendiA - Page 1009
G Stormwater Control Operations and Maintenance Requirements
No. 3 -
Detention Pipes and
Vaults
Recommended
Conditions When Results Expected
Yalrnenanos
Inspection
Maintenance is When Maintenance
convonent
Frequency'
A E
Defeo or Probfera
Needed is Performed
Facility - Genera:
Contaminants and
I!I Any evidence of ~
• Materials removed
Requirements
pollution
contaminants or
and disposed of
f
pollution such as oil,
according to
gasoline, concrete
applicable
slurries, or paint
regulations
• Source control
SMPs
implemented d
appropriate
• No contaminants
present other than
a surface oil film
Pipe or Vault Storage
B. W. E
Trash and debris
Any trash and debris
No trash or debris in
Area
accumulated in vault
vault or pipe
or pipe (includes
floatables and non-
Peatables)
A
Sediment
Accumulated
All sediment removed
accumulation
sediment depth
from storage area
exceeds 10 percent
of the diameter of the
storage area for
%length of storage
vault or any point
depth exceeds
15 percent of
diameter
Pipe or Vault
A
Plugged air vent
Any blockage of the
Pipe or vault freely
Structure
vent
vents
A
Pipe bent out of Any part of vaulUplpe
Pipe or vault repaired
shape is bent out of shape
or replaced to design
more than 10 percent
of its design shape
A
Gaps between • A gap WKW than
No water or soil
sections, damaged r, inch at the joint
entering pipe or vault
joints or cracks or of any pipe or vault
through joints or walls
tears in wall sections
• Any evidence of
sod particles
entering the pipe
or vault at a joint or
Itla+ough a wall
Stornwater Manual
July 2021
Directors' Rule 10-202110"-200
G-11
15 EE2020-112
Appendix G Stormwater Control Operations and Maintenance Requirements
No. 3 - Detention Pipes and Vaults
Recommended Conditions When Rewlts Expected
Maintenance btepWdon Maintenance is When Maintenance
Component Frequenctfl Defect or Problem Needed Is Performed
Vault Structure
A
Damage to wall,
• Cracks wider than
Vault sealed and
frame, bottom_ andlor
'S Inch
structurally sound
top slab
• Any evxlersce of
aor an" the
structure through
cracks
• Qualified
Inspection
personiei
determines that
the vault is not
structurally sound
InIet'Outlet Pipes
A
Sediment
Sediment filling 1 G or
InleVoutlet pipes dear
accumulation
more of the pipe
of sediment
B. W, E
Trash and debris Trash and debris
No trash or debris In
accumulated In
pipes
inleVoutlet pipes
(includes floatables
and non-lloatables)
A
Damaged
• Cracks wider than
No cracks more than
''12 inch at the joint
'/-inch wide at the
of the inletfouttet
joint of the inleUoullet
pipes
pipe
• Any evidence of
"entering at the
joints of the
inletfouttel pipes
Access Maintenance
A
CoverAid not in place
• Cdveriid Is
Maintenance hole
Hole
rwswV or arty
access coverllid in
partially in place
place and secure
• Any open
maintenance hole
requires
Immediate
maintenance
A
Locking mechanism
• Mechanism cannot
Mechanism opens
not working
be opened by one
with proper tools
maintenance
person with proper
tools
a Bolts cannot be
seated
• Self -ticking
coverrad does not
work
pvectors' Rule 10 202 t r Dww,2W
G-12
Stormwaker M,ir of
Ally 2021
16 EE2020-112
Appendix G Stormwater Control Operations and Maintenance Requirements
No. 3 - Detention Pipes and Vaults
Ree mntandod Conditions When RowRs Expected
Maintenance hlspeclfon Maintenance is When Maintenance
Component Frequency" Defect or Problem Needed IS Performed
Access Maintenance
A
Coverilid dtfficult to
One maintenance
Coveolid can be
Hole (continued)
remove
person cannot
removed and
remove covenhd after
reinstalled by one
applying 80 ibs of lift
maintenance person
A
Ladder rungs unsafe
Missing rungs,
Ladder meets design
misalignment. rust. or
standards and allows
Cracks
maintenance person
safe access
Large Access
A
Damaged or difficult
Large access doors
Replace or repair
Doors'Plate
to open
or plates cannot be
access door so it can
openeWremoved
opened as designed
using normal
equipment
A
Gaps. does not cover
Large access doors
Doors close flat and
completely
not flat and7or access
covers access
opening not
opening completely
completely covered
A
Lifting nngs missing,
Lkting rings not
Lifting rings sufficient
rusted
capable of Willing
to Itft or remove door
weight of door or
or plate
plate
' Inspachm frequency
A - Amory. B * Bonnuatly, M - Moritfsy. E - Recommend thal addWral inspections be pertained as appropriate after rnalor
eremts (e g., >1 inch of prenprtation in 24 nours or envtrormmiat ncdent that causes mrtamnant n4rumse. 0 = Ouadady {four
bmr^, per ya . W = Recrxnrnand that at -east one inWamon ocw dung IN wet maran, pra+eraety ahar hoes have bst Moir
1 cm Pets
Uormrvater N-brit at
July 2021
Directors' Rule 10.2021IONW-200
G-11
17 EE2020-112
Appendix G Stormwater Control Operations and Maintenance Requiremerits
No. 4 -Flow Control Structure & Control Device
Recommended Condition When ftesWts Expected
Maintenance Inspection Maintenance is When Maintenance
component Frequency' Defect or Problem Needed is Performed
The Flow Control Structure and Control Device shall conform with design criteria shown upon the approved plane
or the design standards In place at the time of oonstrucban. This Inctudees but is not bmited to, orchoe dlameter(s),
onfloe elevation(s) overflow elevation. Reference Standard Plans No. 270, 271. and 272.
Structure
A
Trash and debris
Trash or debris of
No trash or debris
more than i6 cubic
blocking or potentially
foot which is located
blocking entrance to
immediately in front
structure
of the sbttclure
opening or is blocking
capacity of the
structure by more
than 10 percent
Trash or debrs In the
No trash or debris in
structure that
the structure
exceeds 113 the
depth from the
bottom of basin to
Invert the lowest pipe
Into or out of the
basin.
Deposits of garbage
No condition present
exceeding 1 cubic
which would attract or
foot in volume
support the breeding
of insects or rodents
A
Sediment
Sediment exceeds
Sump of structure
60 percent of the
contains no sediment
depth from the
bottom of the
structure to the Invert
of the lowest pipe into
or out of the structure
or the bottom of the
control dunce section
or is within 6 inches
of the Invert of the
lowest pipe Into or out
of the structure or the
bottom of the control
device section
pvectors' Rule 10 20211DWW,2W
G-14
Ynrmwatar M.ir of
Ally 2021
18 EE2020-112
Appendix G Stormwater Control Operations and Maintenance Requirements
No. 4 - Flow Control
Structure & Control Device
Recommended
Condition When
Remits Expected
h sintenance
Inspection
Maintenance is
When Maintenance
Component
Frequency'
Defect or Problem Needed
Is Performed
Frame is even wltn
Structure (continued)
A
Damage to frame Corner of frame
and,or top slab extends more than
curb
2% inch past curb face
Into the street (If
applicable)
Top slab is free of
Top slab has holes
f larger than
holes and cracks
2 square inches or
cracks wider than
inch
Frame is sitting flush
Frame not sitting
i Oush on top slab, Le.,
on top slab
separation of more
than % Inch of the
frame from the top
stab
A
Cracks in walls or
• Cracks wider than
Structure is sealed
bottom
'/, inch and loner
and structurally
than 3 feet
sound
• Any evidence of
soil particles
entering structure
through cracks
• Ma.+tenanoe
person judges that
structure 4
unsound
• Cracks wider than
No cracks more than
'rS inch and longer
'/.-inch wide at the
than 1 foot at the
joint of inlevouttet
Joint of any
pipe
InleuoutW pipe
• Any eviiisence of
sod particles
entering structure
dough cracks
A
Settlements
Structure has settled
Basin replaced or
misalignment
more than 1 inch or
repaired to design
has rotated more
standards
than 2 inches out of
alignment
Uormwater Manual
July 2021
Owectors' Rule 10.2021 rpww-200
G-1S
19 EE2020-112
Appendix G Stormwater Control Operations and Maintenance Requirements
No. 4 - Flow Control
Structure & Control Device
Recommended
Condition When
faowksExpected
Yalntenance
Inspection
Maintenance is
When Maintenance
Component
Frequency'
Defect or Problem Needed
is Performed
Structure (conbnued)
A
Damaged pope pints • Cracks wider than
No cracks more than
,S Inch at the Joint
%-inch wide at the
of the inleVoutlet
Joint of inleVoutlet
pipes
pipes
• Any evidence of
sod entering the
structure at the
Joint of the
inleVoutlet pipes
A, E
Contaminants and Any evidence of
• Materials removed
pollution contaminants or
and disposed of
pollution such as oil,
acocirding to
gasoline, concrete
applicable
slurries. or paint
regulations
• Source control
BMPs
implemented if
appropriate
• No contaminants
present other than
a surface oil film
A
Ladder rungs missing
Ladder is unsafe due
Ladder meets design
or unsafe
to missing rungs,
standards and allows
misalignment, rust,
maintenance person
Cracks, or sharp
safe access-
�edges
Control Device
A
Damaged or missing
i Riser section is not
securely attached to
T section securely
attached to wall and
structure wall and
outlet pipe
outlet pipe structure
should support at
least 1,000 Ibs of up
or down pressure
Structure is not in
Structure in correct
upright position (alb*
position
up to 10 percent from
plumb)
Connections to outlet
Connections to outlet
pipe are not
pipe are water tight;
watertight or show
structure repaired or
signs of delenorated
replaced and works
grout
as designed
Any holes —other
Structure has no
than designed
holes other than
holes in the
designed holes
structure
(hectors' Rule 10 20211DWW,2W
G-16
Ynrmwarer M,irmal
Aiiy 2021
20 EE2020-112
Appendix G Stormwater Control Operations and Maintenance Requirements
No. 4 - Flow Control
Structure &
Control Device
Recommended
Condition When
RewltsExpected
Maintenance
Inspection
Maintenance is
When Maintenance
Component
Freouencyi
Defect or Problem
Damaged or missing
Needed
Cleanout gate is
Is Performed
Replace cleanout
Spear Gate
A
id appecable)
missing
gate
Cleanoul gate is not
Gate is watertight and
watertight
works as designed
Gate cannot be
Gale moves up and
moved up and dawn
down easily and is
by one maintenance
watertight.
person
ChairVrod leading to
Chain is in place and
gate is missing or
works as designed.
damaged.
Orifice Plate
A
Damaged or missing
Control device is not
Plate Is In place and
working property due
works as designed.
to missing, out of
place, or bent onfice
f plats.
A
Obstructions
Any trash. debris,
Plate is free of all
sediment, or
obstructions and
vegetation blocking
works as designed
the date
Overflow Pipe
A
Obstructions
I Any trash or debns
Pipe is free of all
blocking (or having
obstructions and
the potential of
works as designed
blocking) the overflow
pipe
A
Deformed or
Lip of overflow pipe is
Overflow pipe does
damaged lip
bent or deformed
not allow overflow at
an elevation lower
than design
Inlet/Outlet Pipe
A
Sediment
Sediment haling V3 or
Inletloutlet pipes dear
accumulation
more of the pipe
of sediment
B. W, E
Trash and debris
Trash and debris
No trash or debris in
accumulated in
pipes
inleVoutlel pipes
(includes flostables
and non•flostables)
A
Damaged
• Cracks wider then
No cracks more than
V. Inch at the Joint
'/.-inch wide at the
of the InleVoutlet
pint of the InleVoutiet
pipes
P►Pe
• Any evidence of
sod entering at the
Joints of the
InleVoubet pipes
Uormwater AAan&AM
July 2021
owectors, Rule 10-20211OwW200
G•17
21 EE2O2O-112
Appendix G Stormwater Control Operations and Maintenance Requiremerits
No. 4 - Flow Control Structure & Control Device
Recommended Condition When RestfRs Expected
Maintenance Inspection Maintenance is When Maintenance
Component Frequency' Defect or Problem Needed Is Performed
Metal Grates A Unsafe grate opening Grate with opening Grate opening meets
C
IIf Applicable) wider than 718 inch design standards
8, W. E
Trash and debris
Trash and debris that
Grate free of trash
is blocking more than
and debris. footnote
20 percent of grate
to guidelines for
surface
disposal
A
Damaged or missing
Grate missing or
Grate Is In place and
broken member(s) of
meets design
the grate
standards
Maintenance Hole
A
CoverAid not in place
is Cover&d is
CoverAid protects
Coverlid
missiing or only
opening to structure
partially on place
• Any open
structure
requires urgent
maintenance
A
Locking mechanism
• Mechanism cannot
Mechanism opens
Not Working
be opened by one
with proper tools
mantenance
person with proper
toots
• Bolts cannot be
seated
is Self4ocltrg
ooverAld does not
wat
A
Coventid difficult to
One maintenance
Cover!1id can be
Remove
person cannot
removed and
rerllo na coveOid after
reinstalled by one
applying 80 Ibs of lift
maintenance person
Inspection frequency:
A = Annually. 8 = Bannuaey M = Monthly. E = Remmin rend that addrlronal Inspections be performed as appropriate alter major
evems (e.g., >t Inch of precipitation In 24 hours or environmental ncideot mat causes contemnant release, o - Quarterly (four
braes per year): W • Recommend that at beet one inspeCiOn occur during the wet season, preferably after trees have lost their
INVes
(hrectors' Rule 10 202 t r Dww,2W
G-18
Vnrmwarer M.irmal
Ally 2021
22 EE2020-112
Appendix G Stormwater Control Operations and Maintenance Requirements
No. 5 - Catch
Basins and Maintenance
Holes
Recommended
Condition When
Rowks Expected
Maintenance
Inspection
Maintenance is
When Maintenance
component
Frequency'
Defect of Problem
Sediment
Needed
Sediment exceeds
is Performed
Sump of catch basin
Structure
A
60 percent of the
contains no sediment
depth from the
bottom of the catch
basin to the covert o1
the lowest pipe Into or
out of the catch basin
or Is within 6 Inches
of the invert of the
lowest pipe Into or out
of the catch basin
B. W, E
Trash and It 1h in
Trash or debris of
No trash or debris
more than !6 cubic
blocking or potentially
foot which is located
blocking entrance to
immediatoty in front
catch basin
of the catch basin
opening or is blocking
capacity of the catch
basin by more than
10 percent
A
Trash or debns In the
No trash or debris in
catch basin that
the catch basin
exceeds 113 the
depth from the
bottom of basin to
Invert the lowest pipe
Into or out of the
basin
A
Dead animals or
No dead animals or
vegetation that could
vegetation present
generate odors that
within catch basin
could cause
complaints or
dangerous gases
(e g. methane
A
Deposits of garbage
No condition present
exceeding 1 cubic
which would attract or
foot in volume
support the !reeding
i
of Insects or rodents
Uormwater AranuM
July 2021
Directors' Itule 10.2021 rpww-200
G-19
23 EE2020-112
Appendix G Stormwater Control Operations and Maintenance Requiremerits
No. 5 - Catch
Basins and Maintenance Holes
Recommended
Condition When
Reattlts Expected
Itilalnlenanoe
Inspection
Maintenance is
When Maintenance
COatpooent
Frequency'
Defect or Problem Needed
is Performed
Frame Is even wrtn
Structure (continued)
A
Damage to frame Corner of frame
anCU'or top slab extends more than
curb
2% inch past curb face
Into the street (tf
applicable).
Top slab is free of
Top slab has holes
f larger than
holes and cracks
2 square inches or
cracks wider than
'/. inch.
Frame Is sitting flush
Frame not sitting
flush on top slab, Le.,
on top stab.
separation of more
then % Inch of the
frame from the top
stab
A
Cracks in walls or
• Cracks wider than
Catch basin is sealed
bottom
% Inch and longer
and structurally
than 3 feet
sound
• Any evidence of
sw particles
onterwhg catch
basin through
cracks
• Maintenance
person judges that
etch basin Is
unsound
• Cracks wider than
No cracks more than
`f, Inch and k]ngar
'/. inch wide at the
than 1 foot at tre
joint of intelloutlet
joint of any
pipe
InleVoutlN pipe
• Any evidence of
sot particles
entering catch
basin through
cracks
A
Settlement/
Catch basin has
Basin replaced or
misalignment
settled more than
repaired to design
t inch or has notated
standards
more than 2 inches
out of alignment
phrectors' Rule 10 202 t 1 Dww,2W
G-20
Yrxmwater M.ir of
Ally 2021
24 EE2020-112
Appendix G Stormwater Control Operations and Maintenance Requirements
Unintenanoe
Structure (continued) I A
No. 5 - Catch Basins and Maintenance Holes
Recommended Condition When Itlnufts. Expected
Inspection Maintenance is When Maintenance
A. E
InleVOutset Pipe I A
ILW,E
A
Catch Basin Cutlet A
Trap
(Reference Standard
Plan No. 267)
A
Uormwater Manaaa
July 2021
Defect or Problem
Needed
is Performed
No cracks more than
[13 Ti3aP pipe joints • Cracks wider then
!6 inch at the joint
% inch wide at the
of the inleVoutlet
joint of inleVouLW
pipes
pipes
. Any evidence of
soi entering the
catch basin at the
joint of the
inleVouttet popes
• Materials removed
Contaminants and Any evidence of
pollution
contaminants or
and disposed of
1 pollution such as oil,
according to
gasoline, concrete
applicable
slurries. or paint
regulations
• Source contra
BMPs
implemented d
appropriate
• No contaminants
present other than
a surface oil film
Sediment
Sediment filling V3 or
InleVoutlet pipes dear
accumulation
more of the pipe
of sediment
Trash and debris
fresh and debris
No trash or debris in
accumulated in
pipes
Wevoutlet pipes
(includes floatables
and non-1lostables)
• Cracks wider than
No cracks more than
Damaged
Y: inch at the joint
Y.-inch wide at the
of the InlevoutkN
joint of the InleVoutlet
pipes
pipe
• Any evidence of
sW entering at the
joints of the
inleVoutW pipes
Missing
When the required
Outlet trap Installed
outlet trap is not
and prevents
installed upon the
flostables from being
outlet pipe
discharged
Permanently installed
When the trap is
Outlet trap removable
grouted to the outlet
for maintenance and
pipe and is not
inspecfion
removable to allow
for maintenance and
Directors' Rule 10.2021 rpww-200
G-21
25 EE2020-112
Appendix G Stormwater Control Operations and Maintenance Requirements
No. 5 - Catch
Basins and Maintenance Holes
Recommended
Condition When
Reins Expected
Maintenance Inspection
Maintenance is
When Maintenance
Component Frequency'
Defect or Problem Needed
Damaged Cracks, broken
Its Performed
Water will be
Catch Basin Outlet
A
Trap
welds, seams or any
discharged from the
(Reference Standard
other conditions that
submerged portion of
Plan f4o. 267)
i allows water to be
the trap
(continued)
discharged from other
than the submerged
portion of the trap
Metal Grates
A
Unsafe grate opening Grate with opening
Grate opening meets
(Catch Basins)
wider than T8 inch
design standards
8, W. E
Trash and debris
I Trash and debris that
Grate free of bash
{ Is blocking more than
and detins. footnote
120 percent of grate
to guidelines for
surface
disposal
A
Damaged or missing
• Grate missing or
Grate is in place and
broken member(s)
meets design
of the grate
standards
• Any open
structure
requires urgent
maintenance
Maintenance Hole
A
CoverAid not in place
• Coven'id Is
CoverAd protects
Cover, -Lid
messing or only
opening to structure
partially in place
• Any open
structure
requires urgent
maintenance
A
Locking mechanism
Mechanism opens
• Artv.hanmm cannot
Not Working
be opened by one
with proper tools
maintenance
person with proper
tools
• Bolts cannot be
seated
• Self-iocking
cover -led does not
work
A
Coveolid difficult to
One maintenance
CoverAtd can be
remove
person cannot
removed and
remove coverAid after
reinstalled by one
applying 80 lbs, of hft
maintenance person
inspection frequency
A * Amunly. B - Biannuaity, M - Monl iy, E + Recommend that a1d4ional inspections be performed as appropriate after mator
m4was (a g., ,1 inch of precipitation in 24 hours or envirorrnentar oxidant that causes mrvamnant m4aase O - Ouarteny (four
hone^. per year). W = Recommend Mat at feast one tnstmclson occur during the war see*snn, preferaotV char Irani Rave lost their
leaves
(hrectors' Rule 10 20211 Dww,2W
G-22
Vormwarer M.in,tal
Ally 2021
26 EE2020-112
Figure V-12.16: Typical Detention Vault
%ttmeaa oper" win 06114A NOTE. AN vawi wee s semi be wOun W ofan
eonMrod apses vw *q Mom PON
Af—
5, r 10' opww 101 vauia
2000 SF or Gnats hoot avert
optponal S it 10'
access vault mew
be used in Imr d
OW a�oossa
01111101 IA
frames, gralm, and round sold moors
nwdperl'ORAIN' vah locking boas
well range —ELL
- - 1—
MDt
dargn_ s- _
-
lbw. reaIndor
-- Handholds, — r
M.-ph ra Nods, {
•rvn
-- - cylocM d outlet
that lass than dr.ebped
Section A -A 100•Tn decOn lore
floor grate with 2' r 2'
1' Irwtnwrm hinged access dove (V
r %' golvamted metal
hers)
Nob n
1 All medal parts must be oonpson renaYani Sseal pads must ba gaNant.ad and asphaa ctnrlad i Traafnwwt 1 or bMW),
2 Provide vmler stop at as cast -on -place oonstpuctnorr )oaft Precast vauts shal have approved rubber gasket system
3 Vauds < 10' vale must use nemuvable lints
1 Pralabnoatod vaunt sections may require structural modif"i m to support S' - 10' opnnrV over mate vauh AiatnalOv*,
access wn be tvLwderl vur is sde vealibub as shown
NOT TO SCALE
w
DEPARTMENT OF
ECOLOGY
iState of O.bar`.mgton
Typical Detention Vault
Rev v ad ,lies 2016
Please sec mrFr.%'Aww.wy. war ycwotvpjryhl wrd lop mpyrghl not re mck.dng per mstnorn,
bnt:pl- ullydtnMy anddruclartrw
2019 Stormwater Management Manual for Western Washington
Volume V - Chapter 12 - Page 991
27 EE2020-112
FLOW CONTROL �I 4 5"r
STRUCTURE
NON -SHRINK GROUT
PVC PIPE•
1'-G' MAX
CONTROL DEVICE
EL*
ASSEMBLY TO BE
COUPLING PVC PIPE
REMOVABLE FROM
(OPTIONAL)-\ STUB• I
INSIDE THE FCS I
PVC PIPE'
SET SCREW TO
PREVENT ROTATION
INVERT*
TEE•
GASKET (TYP) J
' I
SPOOL*
Z
I ELBOti'•
PVC ADAPTER* W/
CROSS
DOUBLE GASKET
AND ADHESIVE
BONDED SAND FINISH
ON EXTERIOR MIN 7" LONG
DRILLED ORIFICE
CAULK SPACE BETWEEN
IN PVC INSIDECAP PLUG
a!
PVC ADAPTER AND PIPE STUB CONNECTION at
CONTROL DEVICE ORIFICE°WkT
ER'
L
DETAL
DRILLED
ORIFICE
CONNECTION AND 0
LADDER OR HAND HOLDS -
DU•
CONTROL DEVICE
POLYPROPYLENE
PVC INSIDE
(SEE DETAIL A)
CAP PLUG•
1
OUTLET PIPE
CINCH ANCHOR
ALLOWABLE OUTLET LOCATION
(180' to 315')
WIRE ROPE
CUP (SS)
FINISHED GRADE
CATCH BASJN TYPE n
COE STO DTL
-
DEF
//j/ �pEFORMED
V-NOTCH WEIR AS NEEDED•ER
STEEL
D-300A
OVERFLOW ELEV`+ALUMINUM)
ROD (ST OR
SUPPORT (2 REO'D)AL
ORIFICE
LENGTH 10 FIT
ED•PVC
RA
PIPE &X
CROSS
FLOW CONTROL
STRUCTURE
CONTROL DEVICESEE
DETAIL ADETENTION
PIPE
PIPE SUPPORT
(LENGTH, DIAMETER,
DETAL @
DIAMFTFR•
MATERIAL TYPE) -
FLOW CONTROL STRUCTURE
SHOWN W/ TYPE 2 CATCH BASIN
(DETAILS A & B SHALL APPLY TO ALL DESIGNS
NOTES; WHERE A SHLAR GATE WOULD OTHERWISE APPLY)
• SPECIFIC DESIGN INFORMATION AS INDICATED ON APPROVED CONSTRUCTION DRAWINGS
INVERT OF DETENTION PIPE IN STRUCTURE SHALL BE EQUAL TO OR HIGHER THAN THE INVERT OF THE OUTLET PIPE
PRIVATELY -OWNED CONTROL STRUCTURES SHALL NOT BE PLACED IN CITY RIGHT-OF-WAY
•• SEE COE STD DTL SO-3006
�r REVISION DATE
CITY OF EDMONDS FLOW CONTROL SEPTUM 2023
STRUCTURE
r PUBLIC WORKS (FCS) STANDARD
DEPARTMENT DETAIL
APPROVED HY R. ENGLISH S D- 3 0 1
W
EE2020-112
COBALT
G E 0 S C I E N C E S
February 18, 2023
Douglas and Amy Subcleff
Dsubcleff(&_gmail.com
C/O Richard Okimoto
raoarch(&outlook.com
RE: Geotechnical Evaluation
Proposed Residence
89o8189th Place SW
Edmonds, Washington
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 geotechnical evaluation at the referenced site.
The purpose of our evaluation was to provide recommendations for foundation design, grading,
and earthwork.
Site Description
The site is located at 89o8 189th Place SW in Edmonds, Washington. The site consists of one
rectangular shaped parcel (No. 007286o000O3OO) with a total area of about 0.29 acres (Figure
1).
The property is developed with a short driveway, shed, and local modular block walls near the
north margin. The remainder of the property is undeveloped and vegetated with grasses, bushes,
and sparse trees.
The site slopes downward from east to west at magnitudes of 5 to 20 percent and relief of about 15
feet. There is a 2 to 3 feet tall rockery near the east property line (facing west) and a 2 to 3 feet
concrete wall near the west property line (facing west).
The site is bordered to the east, west, and south by residences, and to the north by 189th Place SW.
The proposed development includes a new residence with daylight basement and driveway.
Stormwater will include infiltration or other systems depending on feasibility.
Site grading may include cuts and fills of 10 feet or less and foundation loads are expected to be
light. We should be provided with the final plans to verify that our recommendations remain
valid and do not require updating.
Area Geology
The Geologic Map of the Edmonds East Quadrangle, indicates that the site is underlain by Vashon
Glacial Till.
Vashon Glacial Till includes mixtures of silt, sand, clay, and gravel. These materials are usually
impermeable and are typically dense to very dense below a weathered zone.
www.cobaltgeo.com (2o6) 331-1097
February 18, 2023
Page 2 of ii
Geotechnical Evaluation
Soil & Groundwater Conditions
As part of our evaluation, we excavated two test pits within the property, where accessible.
The explorations encountered approximately 6 inches of grass and topsoil underlain by
approximately 2.25 to 3.25 feet of loose to medium dense, silty -fine to medium grained sand with
gravel trace cobbles (Weathered Glacial Till). These materials were underlain by dense to very
dense, silty -fine to fine grained sand trace gravel (Vashon Glacial Till), which continued to the
termination depths of the explorations. The till was partially to well cemented in most areas.
Groundwater was not encountered during the exploration work; however, the shallow soils were
mottled. There is a chance that perched groundwater as interflow may develop on the denser till
during the wet season. The depth to groundwater, if present, would likely be 3 to 8 feet. One or
more monitoring wells would be required to determine the depth to any seasonal groundwater.
Water table elevations often fluctuate over time. The groundwater level will depend on a variety
of factors that may include seasonal precipitation, irrigation, land use, climatic conditions and
soil permeability. Water levels at the time of the field investigation may be different from those
encountered during the construction phase of the project.
Erosion Hazard
The Natural Resources Conservation Services (NRCS) maps for Snohomish County indicate that
the site is underlain by Alderwood-Urban land complex (2 to 8 percent slopes) and McKenna
gravelly silt loam (o to 8 percent slopes) . In general, these soils have a slight to moderate erosion
potential in a disturbed state.
It is our opinion that soil erosion potential at this project site can be reduced through landscaping
and surface water runoff control. Typically, erosion of exposed soils will be most noticeable
during periods of rainfall and may be controlled by the use of normal temporary erosion control
measures, such as silt fences, hay bales, mulching, control ditches and diversion trenches. The
typical wet weather season, with regard to site grading, is from October 31st to April ist. Erosion
control measures should be in place before the onset of wet weather.
Seismic Hazard
The overall subsurface profile corresponds to a Site Class D as defined by Table 1613.5.2 of the
International Building Code (IBC). A Site Class D applies to an overall profile consisting of
medium dense to very dense soils within the upper ioo feet.
We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to
obtain values for Ss, Sl, F,, and F,,. The USGS website includes the most updated published data
on seismic conditions. The following tables provide seismic parameters from the USGS web site
with referenced parameters from ASCE 7-16.
www.cobaltgeo.com (2o6) 331-1097
February 18, 2023
Page 3 of 11
Geotechnical Evaluation
Seismic Design Parameters (ASCE 7-16)
Site
Spectral
Spectral
Site
Design Spectral
Design
Class
Acceleration
Acceleration
Coefficients
Response Parameters
PGA
at 0.2 sec. (g)
at 1.o sec. (g)
Fa
F,
SDs
SD1
D
1.298
0.459
1.0
Null
o.865
Null
0.555
Additional seismic considerations include liquefaction potential and amplification of ground
motions by soft/loose soil deposits. The liquefaction potential is highest for loose sand with a
high groundwater table. The site has a low likelihood of liquefaction. For items listed as "Null"
see Section 11.4.8 of the ASCE.
Conclusions and Recommendations
General
The site is underlain by weathered and unweathered glacial till which becomes denser with depth.
There may be local areas of fill in some areas of the site associated with prior grading of nearby
properties.
The proposed residential structure may be supported on a shallow foundation system bearing on
medium dense or firmer native soils or on structural fill placed on the native soils. Local
overexcavation of loose weathered native soils may be necessary depending on the proposed
elevations and locations of the new footings.
Widespread infiltration is not feasible due to the presence of a shallow restrictive layer and areas
of groundwater. The subsurface soil becomes very dense and fine grained and act as an aquitard
or restrictive layer.
We recommend utilizing dispersion systems (if there is space) or detention with direct/perforated
connection to City infrastructure. We can provide additional input once a civil site plan has been
prepared.
Site Preparation
Trees, shrubs and other vegetation should be removed prior to stripping of surficial organic -rich
soil and fill. Based on observations from the site investigation program, it is anticipated that the
stripping depth will be 6 to 18 inches. Deeper excavations will be necessary below foundation
systems and in any areas underlain by undocumented fill.
The native soil consists of silty -sand with gravel. Most of the native soils may be used as
structural fill provided, they achieve compaction requirements and are within 3 percent of the
optimum moisture. Some of these soils may only be suitable for use as fill during the summer
months, as they will be above the optimum moisture levels in their current state. These soils are
variably moisture sensitive and may degrade during periods of wet weather and under equipment
traffic.
www.cobaltgeo.com (2o6) 331-1097
February 18, 2023
Page 4 of ii
Geotechnical Evaluation
Imported structural fill should consist of a sand and gravel mixture with a maximum grain size of
3 inches and less than 5 percent fines (material passing the U.S. Standard No. 200 Sieve).
Structural fill should be placed in maximum lift thicknesses of 12 inches and should be compacted
to a minimum of 95 percent of the modified proctor maximum dry density, as determined by the
ASTM D 1557 test method.
Temporary Excavations
Based on our understanding of the project, we anticipate that the grading could include local cuts
on the order of approximately io feet or less for foundation and utility placement. Any deeper
temporary excavations should be sloped no steeper than 1.5H:1V (Horizontal:Vertical) in loose
native soils and fill, 1H:1V in medium dense native soils and 3/411:1V in dense to very dense
native soils. If an excavation is subject to heavy vibration or surcharge loads, we recommend that
the excavations be sloped no steeper than 2H:1V, where room permits.
Temporary cuts should be in accordance with the Washington Administrative Code (WAC) Part
N, Excavation, Trenching, and Shoring. Temporary slopes should be visually inspected daily by a
qualified person during construction activities and the inspections should be documented in daily
reports. The contractor is responsible for maintaining the stability of the temporary cut slopes
and reducing slope erosion during construction.
Temporary cut slopes should be covered with visqueen to help reduce erosion during wet weather,
and the slopes should be closely monitored until the permanent retaining systems or slope
configurations are complete. Materials should not be stored or equipment operated within io feet
of the top of any temporary cut slope.
Soil conditions may not be completely known from the geotechnical investigation. In the case of
temporary cuts, the existing soil conditions may not be completely revealed until the excavation
work exposes the soil. Typically, as excavation work progresses the maximum inclination of
temporary slopes will need to be re-evaluated by the geotechnical engineer so that supplemental
recommendations can be made. Soil and groundwater conditions can be highly variable.
Scheduling for soil work will need to be adjustable, to deal with unanticipated conditions, so that
the project can proceed and required deadlines can be met.
If any variations or undesirable conditions are encountered during construction, we should be
notified so that supplemental recommendations can be made. If room constraints or
groundwater conditions do not permit temporary slopes to be cut to the maximum angles allowed
by the WAC, temporary shoring systems may be required. The contractor should be responsible
for developing temporary shoring systems, if needed. We recommend that Cobalt Geosciences
and the project structural engineer review temporary shoring designs prior to installation, to
verify the suitability of the proposed systems.
Foundation Design
The proposed residence may be supported on a shallow spread footing foundation system bearing
on undisturbed medium dense or firmer native soils or on properly compacted structural fill
placed on suitable native soils. Any undocumented fill and/or loose native soils should be
removed and replaced with structural fill below foundation elements. Structural fill below
footings should consist of clean angular rock 5/8 to 4 inches in size. We should verify soil
conditions during foundation excavation work.
www.cobaltgeo.com (2o6) 331-1097
February 18, 2023
Page 5 of ii
Geotechnical Evaluation
For shallow foundation support, we recommend widths of at least 16 and 24 inches, respectively,
for continuous wall and isolated column footings supporting the proposed structure. Provided
that the footings are supported as recommended above, a net allowable bearing pressure of 2,500
pounds per square foot (psf) may be used for design.
A 1/3 increase in the above value may be used for short duration loads, such as those imposed by
wind and seismic events. Structural fill placed on bearing, native subgrade should be compacted
to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Footing
excavations should be inspected to verify that the foundations will bear on suitable material.
Exterior footings should have a minimum depth of 18 inches below pad subgrade (soil grade) or
adjacent exterior grade, whichever is lower. Interior footings should have a minimum depth of 12
inches below pad subgrade (soil grade) or adjacent exterior grade, whichever is lower.
If constructed as recommended, the total foundation settlement is not expected to exceed 1 inch.
Differential settlement, along a 25-foot exterior wall footing, or between adjoining column
footings, should be less than 1/2 inch. This translates to an angular distortion of 0.002. Most
settlement is expected to occur during construction, as the loads are applied. However, additional
post -construction settlement may occur if the foundation soils are flooded or saturated. All
footing excavations should be observed by a qualified geotechnical consultant.
Resistance to lateral footing displacement can be determined using an allowable friction factor of
0.4o acting between the base of foundations and the supporting subgrades. Lateral resistance for
footings can also be developed using an allowable equivalent fluid passive pressure of 250 pounds
per cubic foot (pcf) acting against the appropriate vertical footing faces (neglect the upper 12
inches below grade in exterior areas). The frictional and passive resistance of the soil may be
combined without reduction in determining the total lateral resistance.
Care should be taken to prevent wetting or drying of the bearing materials during construction.
Any extremely wet or dry materials, or any loose or disturbed materials at the bottom of the
footing excavations, should be removed prior to placing concrete. The potential for wetting or
drying of the bearing materials can be reduced by pouring concrete as soon as possible after
completing the footing excavation and evaluating the bearing surface by the geotechnical engineer
or his representative.
Concrete Retaining Walls
The following table, titled Wall Design Criteria, presents the recommended soil related design
parameters for retaining walls with a level backslope. Contact Cobalt if an alternate retaining wall
system is used. This has been included for new cast in place walls, if any are proposed.
Wall Design Criteria
"At -rest" Conditions (Lateral Earth Pressure — EFD+)
55 pcf (Equivalent Fluid Density)
"Active" Conditions (Lateral Earth Pressure — EFD+)
35 pcf (Equivalent Fluid Density)
Seismic Increase for "At -rest" Conditions
(Lateral Earth Pressure)
14H* (Uniform Distribution)
Seismic Increase for "Active" Conditions
(Lateral Earth Pressure)
7H* (Uniform Distribution)
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February i8, 2023
Page 6 of ii
Geotechnical Evaluation
Passive Earth Pressure on Low Side of Wall
Neglect upper 2 feet, then 275 pcf EFD'
(Allowable, includes F.S. = 1.5)
Soil -Footing Coefficient of Sliding Friction (Allowable;
0.40
includes F.S. = 1.5)
'H is the height of the wall; Increase based on one in 500 year seismic event (io percent probability of being exceeded in
50 years),
,EFD — Equivalent Fluid Density
The stated lateral earth pressures do not include the effects of hydrostatic pressure generated by
water accumulation behind the retaining walls. Uniform horizontal lateral active and at -rest
pressures on the retaining walls from vertical surcharges behind the wall may be calculated using
active and at -rest lateral earth pressure coefficients of 0.3 and 0.5, respectively. A soil unit weight
Of 125 pcf may be used to calculate vertical earth surcharges.
To reduce the potential for the buildup of water pressure against the walls, continuous footing
drains (with cleanouts) should be provided at the bases of the walls. The footing drains should
consist of a minimum 4-inch diameter perforated pipe, sloped to drain, with perforations placed
down and enveloped by a minimum 6 inches of pea gravel in all directions.
The backfill adjacent to and extending a lateral distance behind the walls at least 2 feet should
consist of free -draining granular material. All free draining backfill should contain less than 3
percent fines (passing the U.S. Standard No. 200 Sieve) based upon the fraction passing the U.S.
Standard No. 4 Sieve with at least 30 percent of the material being retained on the U.S. Standard
No. 4 Sieve. The primary purpose of the free -draining material is the reduction of hydrostatic
pressure. Some potential for the moisture to contact the back face of the wall may exist, even with
treatment, which may require that more extensive waterproofing be specified for walls, which
require interior moisture sensitive finishes.
We recommend that the backfill be compacted to at least go percent of the maximum dry density
based on ASTM Test Method D1557. In place density tests should be performed to verify
adequate compaction. Soil compactors place transient surcharges on the backfill. Consequently,
only light hand operated equipment is recommended within 3 feet of walls so that excessive stress
is not imposed on the walls.
Stormwater Management Feasibility
The site is underlain by weathered to unweathered glacial till. We determined the infiltration rate
of subsurface soils with a small scale PIT in TP-1.
The design infiltration rate was determined by applying correction factors to the observed
infiltration rate as prescribed in Volume III, Section 3.3.6 of the DOE. The observed rate must be
reduced through appropriate correction factors for site variability (CFv), uncertainty of test
method (CFA and degree of influent control (CFM) to prevent siltation and bio-buildup.
It should be noted that construction traffic or other disturbance to the target infiltration area
could compact the soil, which may decrease the effective infiltration rates. The correction factors
and resulting design infiltration rate are also shown in the table below.
www.cobaltgeo.com (2o6) 331-1097
February 18, 2023
Page 7 of 11
Geotechnical Evaluation
Test
Test
Measured
Correction Factors
Design
Number
Depth (ft)
Infiltration
Infiltration
Rate (in/hr)
Rate
CFv
CFT
CFM
(in/hr)
TP-1
4.0
0.5
0.5
0.5
0.9
0.11
Widespread infiltration is not feasible due to the shallow soil conditions (dense mottled till) and
potential for seasonal groundwater at shallow depths.
In general, permeable pavements are feasible for use in the upper, weathered glacial till soils,
where some infiltration is possible. We recommend that these systems be located in areas with
cuts of 1 foot or less and downslope of the new residence. Areas should be stripped of topsoil and
any fill, verified by the geotechnical engineer to be stable, and then prepared with clean angular
rock and finished pavements. These areas must not be compacted by traffic, equipment, or
surcharge loads. These areas should be left natural until ready for completion. A typical
infiltration rate (factored) for the weathered till ranges from 0.3 to 0.7 inches per hour.
We anticipate that stormwater will be managed using direct or perforated connection to City
infrastructure. Local dispersion devices may be feasible if there is adequate space. We can
provide additional input regarding other systems if they are being considered.
We should be provided with final plans for review to determine if the intent of our
recommendations has been incorporated or if additional modifications are needed. We must be
on site to verify soil conditions at permeable pavement locations.
Slab -on -Grade
We recommend that the upper 12 inches of the existing native soils within slab areas be re -
compacted to at least 95 percent of the modified proctor (ASTM D1557 Test Method).
Often, a vapor barrier is considered below concrete slab areas. However, the usage of a vapor
barrier could result in curling of the concrete slab at joints. Floor covers sensitive to moisture
typically requires the usage of a vapor barrier. A materials or structural engineer should be
consulted regarding the detailing of the vapor barrier below concrete slabs. Exterior slabs
typically do not utilize vapor barriers.
The American Concrete Institutes ACI 36olt-o6 Design of Slabs on Grade and ACI 302.1R-04
Guide for Concrete Floor and Slab Construction are recommended references for vapor barrier
selection and floor slab detailing.
Slabs on grade may be designed using a coefficient of subgrade reaction of 18o pounds per cubic
inch (pci) assuming the slab -on -grade base course is underlain by structural fill placed and
compacted as outlined above. A 4- to 6-inch-thick capillary break layer should be placed over the
prepared subgrade. This material should consist of pea gravel or 5/8 inch clean angular rock.
A perimeter drainage system is recommended unless interior slab areas are elevated a minimum
Of 12 inches above adjacent exterior grades. If installed, a perimeter drainage system should
consist of a 4-inch diameter perforated drain pipe surrounded by a minimum 6 inches of drain
rock wrapped in a non -woven geosynthetic filter fabric to reduce migration of soil particles into
www.cobaltgeo.com (2o6) 331-1097
February i8, 2023
Page 8 of ii
Geotechnical Evaluation
the drainage system. The perimeter drainage system should discharge by gravity flow to a
suitable stormwater system.
Exterior grades surrounding buildings should be sloped at a minimum of one percent to facilitate
surface water flow away from the building and preferably with a relatively impermeable surface
cover immediately adjacent to the building.
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.
• 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.
Utilities
Utility trenches should be excavated according to accepted engineering practices following OSHA
(Occupational Safety and Health Administration) standards, by a contractor experienced in such
work. The contractor is responsible for the safety of open trenches. Traffic and vibration adjacent
to trench walls should be reduced; cyclic wetting and drying of excavation side slopes should be
avoided. Depending upon the location and depth of some utility trenches, groundwater flow into
open excavations could be experienced, especially during or shortly following periods of
precipitation.
In general, silty soils were encountered at shallow depths in the explorations at this site. These
soils have low cohesion and density and will have a tendency to cave or slough in excavations.
Shoring or sloping back trench sidewalls is required within these soils in excavations greater than
4 feet deep.
All utility trench backfill should consist of imported structural fill or suitable on site soils. Utility
trench backfill placed in or adjacent to buildings and exterior slabs should be compacted to at
least 95 percent of the maximum dry density based on ASTM Test Method D1557. The upper 5
feet of utility trench backfill placed in pavement areas should be compacted to at least 95 percent
of the maximum dry density based on ASTM Test Method D1557. Below 5 feet, utility trench
backfill in pavement areas should be compacted to at least 90 percent of the maximum dry
density based on ASTM Test Method D1557. Pipe bedding should be in accordance with the pipe
manufacturer's recommendations.
www.cobaltgeo.com (2o6) 331-1097
February iS, 2023
Page 9 of ii
Geotechnical Evaluation
The contractor is responsible for removing all water -sensitive soils from the trenches regardless of
the backfill location and compaction requirements. Depending on the depth and location of the
proposed utilities, we anticipate the need to re -compact existing fill soils below the utility
structures and pipes. The contractor should use appropriate equipment and methods to avoid
damage to the utilities and/or structures during fill placement and compaction procedures.
CONSTRUCTION FIELD REVIEWS
Cobalt Geosciences should be retained to provide part time field review during construction in
order to verify that the soil conditions encountered are consistent with our design assumptions
and that the intent of our recommendations is being met. This will require field and engineering
review to:
■ Monitor and test structural fill placement and soil compaction
■ Observe bearing capacity at foundation locations
■ Observe slab -on -grade preparation
■ Monitor foundation drainage placement
■ Observe excavation stability
Geotechnical design services should also be anticipated during the subsequent final design phase
to support the structural design and address specific issues arising during this phase. Field and
engineering review services will also be required during the construction phase in order to
provide a Final Letter for the project.
CLOSURE
This report was prepared for the exclusive use of Doug Subcleff and his appointed consultants.
Any use of this report or the material contained herein by third parties, or for other than the
intended purpose, should first be approved in writing by Cobalt Geosciences, LLC.
The recommendations contained in this report are based on assumed continuity of soils with
those of our test holes and assumed structural loads. Cobalt Geosciences should be provided with
final architectural and civil drawings when they become available in order that we may review our
design recommendations and advise of any revisions, if necessary.
Use of this report is subject to the Statement of General Conditions provided in Appendix A. It is
the responsibility of Doug Subcleff who is identified as "the Client" within the Statement of
General Conditions, and its agents to review the conditions and to notify Cobalt Geosciences
should any of these not be satisfied.
www.cobaltgeo.com (2o6) 331-1097
February 18, 2023
Page io of ii
Geotechnical Evaluation
Sincerely,
Cobalt Geosciences, LLC
, "ON
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54896
TONAL
12/9/2022
Phil Haberman, PE, LG, LEG
Principal
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www.cobaltgeo.com (2o6) 331-1097
February 18, 2023
Page n of n
Geotechnical Evaluation
Statement of General Conditions
USE OF THIS REPORT: This report has been prepared for the sole benefit of the Client or its
agent and may not be used by any third party without the express written consent of Cobalt
Geosciences and the Client. Any use which a third parry makes of this report is the responsibility
of such third parry.
BASIS OF THE REPORT: The information, opinions, and/or recommendations made in this
report are in accordance with Cobalt Geosciences present understanding of the site specific
project as described by the Client. The applicability of these is restricted to the site conditions
encountered at the time of the investigation or study. If the proposed site specific project differs
or is modified from what is described in this report or if the site conditions are altered, this report
is no longer valid unless Cobalt Geosciences is requested by the Client to review and revise the
report to reflect the differing or modified project specifics and/or the altered site conditions.
STANDARD OF CARE: Preparation of this report, and all associated work, was carried out in
accordance with the normally accepted standard of care in the state of execution for the specific
professional service provided to the Client. No other warranty is made.
INTERPRETATION OF SITE CONDITIONS: Soil, rock, or other material descriptions, and
statements regarding their condition, made in this report are based on site conditions
encountered by Cobalt Geosciences at the time of the work and at the specific testing and/or
sampling locations. Classifications and statements of condition have been made in accordance
with normally accepted practices which are judgmental in nature; no specific description should
be considered exact, but rather reflective of the anticipated material behavior. Extrapolation of in
situ conditions can only be made to some limited extent beyond the sampling or test points. The
extent depends on variability of the soil, rock and groundwater conditions as influenced by
geological processes, construction activity, and site use.
VARYING OR UNEXPECTED CONDITIONS: Should any site or subsurface conditions be
encountered that are different from those described in this report or encountered at the test
locations, Cobalt Geosciences must be notified immediately to assess if the varying or unexpected
conditions are substantial and if reassessments of the report conclusions or recommendations are
required. Cobalt Geosciences will not be responsible to any parry for damages incurred as a result
of failing to notify Cobalt Geosciences that differing site or sub -surface conditions are present
upon becoming aware of such conditions.
PLANNING, DESIGN, OR CONSTRUCTION: Development or design plans and
specifications should be reviewed by Cobalt Geosciences, sufficiently ahead of initiating the next
project stage (property acquisition, tender, construction, etc), to confirm that this report
completely addresses the elaborated project specifics and that the contents of this report have
been properly interpreted. Specialty quality assurance services (field observations and testing)
during construction are a necessary part of the evaluation of sub -subsurface conditions and site
preparation works. Site work relating to the recommendations included in this report should only
be carried out in the presence of a qualified geotechnical engineer; Cobalt Geosciences cannot be
responsible for site work carried out without being present.
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Test Pit
Location
Provided Site Plan
Not to Scale
Cobalt Geosciences, LLC
Proposed Residence
SITE
P.O. Box 82243
Kenmore, wa
COBALT�\8
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9 9
PLAN
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(206) 331-1097
Edmonds, Washington
FIGURE 1
www.cobaltgeo.com
cobaltgeo@gmaitcom
Slab on Grade
Basement or Shallow Foundation Wall
12" Free Draining Backfill and/or Drainage Mat
Attached to Wall
Backfill Soils Compacted
per Geotechnical Report
4" Diameter Perforated Pipe
-- --�H H
Native Soils Benched
as Required
Filter Fabric Over Rock
(Mirafi 14oN)
3//4" Washed Rock or
Clean Angular Rock
Not to Scale
Cobalt Geosciences, LLC
PO Box 1792
Typical Foundation Drain Detail Attachment North Bend, WA 98045
• _ (2o6) 331-1097
GEOSCIENCES www.cobaltgeo.com
Philpcobaltgeo.com
Unified Soil Classification System (USCS)
MAJOR DIVISIONS
SYMBOL
TYPICAL DESCRIPTION
Clean Gravels
Gw
Well -graded gravels, gravels, gravel -sand mixtures, little or no fines
Gravels
(more than 50%
(less than 5%
fines)
GP
Poorly graded gravels, gravel -sand mixtures, little or no fines
COARSE
GRAINED
SOILS
of coarse fraction
retained on No. 4
sieve)
Gravels with
Fines
(more than 12%
fines)
GM
Silty gravels, gravel -sand -silt mixtures
GC
Clayey gravels, gravel -sand -clay mixtures
(more than 50%
retained on
Clean Sands
:•: sw
Well -graded sands, gravelly sands, little or no fines
No. 200 sieve)
Sands
(50% or more
of coarse fraction
(less than 5%
fines)
sP
Poorly graded sand, gravelly sands, little or no fines
passes the No. 4
sieve)
Sands with
Fines
sM
Silty sands, sand -silt mixtures
(more than 12%
fines)
sc
Clayey sands, sand -clay mixtures
ML
Inorganic silts of low to medium plasticity, sandy silts, gravelly silts,
FINE GRAINED
(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
Organic rganic
oL
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
elastic silt
CH
Inorganic clays of medium to high plasticity, sandy fat clay,
or gravelly fat clay
Organic
OHOrganic
clays of medium to high plasticity, organic silts
HIGHLY ORGANIC
SOILS
Primarily organic matter, dark in color,
and organic odor
PT
Peat, humus, swamp soils with high organic content (ASTM D4427)
Classification of Soil Constituents
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 (o.o8 mm)
Sand
-Fine
#200 to #40 (o.o8 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)
1 Moisture Content Definitions 1
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, WA 98028
Soil Classification Chart
Figure Ci
(2o6) 331-1097
_
www.cobaltgeo.com
cobaltgeo(&gmail.com
Test Pit TP-1
Date: January 2023
Depth: 8'
Groundwater: None
Contractor: Jim
Elevation:
Logged By: PH Checked By: SC
N
0)
o
-0Plastic
Moisture Content (%)
I Liquid
U
U
U
L
E
Limit Limit
T
C
N
Material Description
D
o
?
o
DCP Equivalent N-Value
G
0 10 20 30 40 50
—
—
Topsoil/Grass
------
1
----
__
GSM
--------------------------------------------
Loose to medium dense, silty -fine to medium grained sand with gravel,
locally mottled reddish brown to yellowish brown, moist.
2
(Weathered Glacial Till)
3
------
4
----
--
SM
---------------------------------------------
Dense to very dense, silty -fine to medium grained sand with gravel,
mottled yellowish brown to grayish brown, moist. (Glacial Till)
5
Till was cemented
6
7
End of Test Pit 8'
9
10
Test Pit TP-2
Date: January 2023
Depth: 6'
Groundwater: None
Contractor: Jim
Elevation:
Logged By: PH Checked By: SC
—
NJ0
0)
o
-
Moisture Content (%)
Plastic Liquid
=
U
L
E
3
Limit Limit
�
�
N
Material Description
?
o
DCP Equivalent N-Value
o
C
0 10 20 30 40 50
1
SM
Loose to medium dense, silty -fine to medium grained sand with gravel,
mottled reddish brown to yellowish brown, moist.
2
(Weathered Glacial Till)
-----
—3
----
SM
---------------------------------------------
Dense to very dense, silty -fine to medium grained sand with gravel,
yellowish brown to grayish brown, moist. (Glacial Till)
4
Locally cemented
5
End of Test Pit 8'
7
8
9
10
Cobalt Geosciences, LLC
Proposed Residence
Test Pit
P.O. Box 82243
Kenmore, WA 98028
COBALT
89o8189th Place SW
Logs
(2o6) 331-1097
GEOSCIENCES
Edmonds, Washington
www.cobaltgeo.com
cobaltgeo(digmail.com