APPROVED STM RESUB2 BLD2023-1534+Storm_Drainage_Report+7.23.2024_4.05.16_PM+4396656RESUB BLD2023-1534
Jul 23 2024
CITY OF EDMONDS
DEVELOPMENT SERVICES
DEPARTMENT
Drainage Report
94th Ave SFR
for
APPLICANT/CONTACT/CONTRACTOR
Landsverk Quality Homes, Inc.
24113 56th Ave W
Mountlake Terrace, WA 98020
Attn: Joseph Rowett
425.742.2742
joseph@lqh-inc.com
SITE LOCATION:
18809 941h AVE W
Edmonds, WA 98020
Tax Parcel: 00434600004608
9
� - �•i Pt
Prepared by:
Omega Engineering, Inc
2707 Wetmore Ave
Everett, WA 98201
425.903.4852
joe@omega-eng.com
Checked by:
Joseph M. Smeby, P.E.
Job No: 23-0406
April 2023
Revised: April 2024
COMPLIES WITH APPLICABLE
CITY STORMWATER CODE
08/20/2024
TABLE OF CONTENTS
TABLEOF CONTENTS.......................................................................................................1
LISTOF FIGURES...............................................................................................................2
1. INTRODUCTION & SITE CLASSIFICATION...............................................................3
2. MR#1: PREPARATION OFSTORMWATER SITE PLANS...........................................4
3. MR#2: CONSTRUCTION STORMWATER POLUTION PREVENTION .......................4
A. SITE GRADING/EROSION CONTROL RISK ASSESSMENT.....................................5
B. SWPPP MINIMUM ELEMENTS...................................................................................5
5. MR#4: PRESERVATION OF NATURAL DRAINAGE SYSTEM...................................7
6. MR#5: ON -SITE STORMWATER MANAGEMENT......................................................8
7. OPERATION AND MAINTENANCE MANUAL.........................................................9
8. SUMMARY....................................................................................................................9
APPENDIX......................................................................................................A
9411 Ave SFR 23-0406
April 2024 Page 1
LIST OF FIGURES
ITEM PAGE
FIGURE 1 VICINITY MAP......................................................................................... 10
FIGURE 2 EXISTING DRAINAGE BASIN MAP ....................................................... 11
FIGURE 3 DEVELOPED DRAINAGE BASIN MAP .................................................. 12
9411 Ave SFR 23-0406
April 2024 Page 2
INTRODUCTION & SITE CLASSIFICATION
This document is intended to provide engineering information necessary to support the
building permit application submittal to the City of Edmonds for the new SFR and driveway
proposed on this site. The site currently is undeveloped and consists of pasture. The
project parcel is 0.31 acres. Access to the site will be from the existing private driveway to
the west off of 94th Ave W.
The total area of disturbance including both clearing and grading does not exceed 3/4 acres
and the new total impervious surfaces do not exceed 5,000 sf. Therefore, this project is
classified as a category 1 project and only minimum requirements 1-5 will apply. This
determination was made using figure 3.1 of the Edmonds Stormwater Addendum.
The proposed project will create 4,510 sf of new plus replaced hard surfaces. All of the
new and replaced hard surfaces will be mitigated using on -site stormwater management
BMPs including a perforated stub out connection and amended soils. For this project it is
estimated that 250 CY of cut and 250 CY of fill will be needed to construct and grade the
proposed site. All on -site drainage improvements have been designed to meet or exceed
the 2019 DOE Stormwater Management Manual as well as the 2022 Edmonds
Stormwater Addendum.
The site is located at 18809 94th Ave W, Edmonds, WA 98020, and in Section 13,
Township 27 N, Range 3 E, Willamette Meridian. See Figure 1 - Vicinity Map.
941h Ave SFR 23-0406
April 2024 Page 3
Figure 1-3.1: Flow Chart for Determining Requirements for New
Development
Start Here
Does the Site have 35%
or more of existing hard
surface coverage?
No
Does the Project result in
5,000 square feet, or
greater, of new plus
replaced hard surface
area?
Yes
All Minimum Requirements
apply to the new and replaced
hard surfaces and converted
vegetation areas.
DEPARTMENT OF
ECOLOGY
State of Washington
Yes See Redevelopment Project
Thresholds and the Figure Flow
Chart for Determining
Requirements for Redevelopment".
Does the Project convert 3/a
acres or more of vegetation to
_ lawn or landscaped areas, or
NO convert 2.5 acres or more of
native vegetation to pasture?
Yes
Minimum Requirements #1
through #5 apply to the new
and replaced hard surfaces
and the land disturbed.
Does the Project result in 2,000
square feet, or greater, of new plus
replaced hard surface area?
Yes Y I No
Does the Project have land
disturbing activities of 7,000
square feet or greater?
No
Minimum Requirement #2
applies.
Flow Chart for Determining Requirements for
New Development
Revised March 2019
Please see http://www.ecy.wa.go✓%opyright.html for copyright notice including permissions,
limitation of liability, and disclaimer.
2019 Stormwater Management Manual for Western Washington
Volume 1- Chapter 3 - Page 89
2. MR#1: PREPARATION OF STORMWATER SITE PLANS
As noted in Section 1 of this report this project is only subject to minimum requirements 1-
5. Therefore, this drainage design has been prepared to address the requirements
contained in the 2019 DOE manual, 2022 Edmonds Stormwater Addendum and applicable
handouts. The engineering plan set submitted to the City for review along with this report
contains the required information. This document is intended to provide the supporting
information to justify the sizing of the BMPs and detail how the design of the selected
BMPs meet the required standards.
The runoff from the proposed SFR roof surfaces will be directed to a perforated stub out
connection. The runoff from the new driveway will be collected and conveyed along with
the roof runoff to a detention pipe west of the new SFR. The detention system will
discharge to the existing conveyance system within the north side of the property within
the existing retention easement. The existing storm system drains to the northwest and
leaves the property near the northwest corner before turning west through an easement
along the north side of parcel 00434600004602 and ultimately connects to the existing
conveyance system within 94th Ave W.
3. MR#2: CONSTRUCTION STORMWATER POLUTION
PREVENTION
Clearing, grading, and temporary erosion and sediment control plans have been prepared
as part of the drainage plan drawings. However, since a construction site is dynamic it will
be necessary to reassess the erosion control BMP's during construction and install
additional measures when necessary.
Proposed temporary measures possible for this project will include the following BMP's:
• Installation of stabilized construction entrance (existing driveway to be used as
construction entrance, to be modified as needed).
• Retention of Existing Vegetation
• Straw mulch, hydroseed or other mulching and planting method to stabilized
unworked areas.
• Silt fencing
Permanent measures to reduce or eliminate erosion or water quality degradation will
include the following BMP's:
• Permanent landscaping in pervious areas.
• Limiting cut and fill slopes to 2:1 maximum and 3:1 maximum where exposed to
standing water.
• Routine maintenance and inspection of the grounds and response to developing
problems.
The listed erosion control BMP's will be engineered for anticipated conditions in
compliance with DOE guidelines. With proper installation, maintenance and inspection the
proposed BMP's should result in minimal impact to the surrounding environment. The City
retains the authority by code to require additional measures should the existing measures
prove insufficient.
94th Ave SFR 23-0406
April 2024 Page 4
A. SITE GRADING/EROSION CONTROL RISK ASSESSMENT
Area proposed to be cleared/worked:
0.27 acres
Average slope for the site:
13%
Erosion Hazard of Soil
High
Critical Areas downslope
No
Site is upstream of an ESA Stream
No
Based on the above information and the fact that the slope of the site is moderate and
construction site runoff will filter through the soil, and that if site conditions warrant,
additional BMP's can be implemented as corrective measures the Risk Category for this
site is High Risk.
B. SWPPP MINIMUM ELEMENTS
1: Mark Clearing Limits
The first step in the "Construction Sequence" included on the clearing and grading plan
sheets is for the limits of clearing to be flagged and to have construction fencing (BMP
C103) placed along the limits prior to any other construction activity.
2: Establish Construction Access
The SWPPP calls for the stabilized construction access (BMP C105) to be placed at the
location of the proposed driveway. Contractor to modify entrance as needed.
3: Control Flow Rates
This project will use straw wattles (BMP C235) to provide flow control for small sites per
DOE SWMMWW Vol II. This BMP can be installed around the site where runoff is found
to concentrate to provide additional flow control.
4: Install Sediment Controls
This site and SWPPP proposes to construct/maintain silt fencing (BMP C233) along the
downslope sides of the project area along with the use of wattles (BMP C235). These
features are intended to minimize the opportunity for sediment to leave the site via
stormwater or on vehicles. The construction of these features is one of the first items
required in the "Construction Sequence".
5: Stabilize Soils
The "Construction Sequence" calls for the stabilization of soils that remain unworked for
certain lengths of time based on the time of year. Stabilization techniques may include but
not limited to mulching (C121), plastic sheeting or hydroseeding, notes have been added
to the plan regarding protection for the stock pile area if necessary. A stockpile area has
been identified on the SWPPP and is setback a minimum of 20-feet from any down slope
property line.
6: Protect Slopes
All disturbed slopes on site during construction are required to be protected with mulch
(BMP C121) or other means as specified in the construction sequence. No concentrated
runoff or significant amounts of sheet flow will be directed to new cut or fill slopes during
construction.
94th Ave SFR 23-0406
April 2024 Page 5
7: Protect Drain Inlets
All new drain inlets shall be protected using inlet protection (BMP C220) such as filter
socks/temporary sediment traps during construction.
8: Stabilize Channels and Outlets
No new channels or outlets are proposed for this site.
9: Control Pollutants
No outside chemicals are expected to be necessary for the construction of this project. All
vehicles working on and around the site would need to meet the State requirements for
emissions. Vehicle fueling locations will be used to limit the potential impacts from any
spills.
10: Control Dewatering
Dewatering will not be necessary for this project. However, the detention system will be in
place during construction to collect any dewatering runoff.
11: Maintain BMPs
The construction supervisor will be responsible for maintaining all BMPs during
construction and working with the City to relocate or add BMPs as necessary as site
conditions change.
12: Manage the Project
It will be the responsibility of the Contractor and Developer to manage this project and
coordinate with the City Inspector and Engineer.
Inspection and Monitoring:
Site inspections shall be done by a person who is knowledgeable in the principles and
practices of erosion and sediment control. The person must have skills to first assess the
site conditions and construction activities that could impact the quality of stormwater, and
second assess the effectiveness of erosion and sediment control measures used to
control the quality of stormwater discharges.
Whenever inspection and/or monitoring reveals that the BMPs identified in the
Construction SWPPP are inadequate, due to the actual discharge of or potential to
discharge a significant amount of any pollutant, appropriate BMPs or design changes shall
be implemented as soon as possible.
Maintaining an Updated Construction SWPPP:
The construction SWPPP shall be retained on -site or within reasonable access to the site.
The SWPPP shall be modified whenever there is a change in the design, construction,
operation, or maintenance at the construction site that has, or could have, a significant
effect on the discharge of pollutants to waters of the state.
The SWPPP shall be modified if, during inspections or investigations conducted by the
owner/operator, or the applicable local or state regulatory authority, it is determined that
the SWPPP is ineffective in eliminating or significantly minimizing pollutants in stormwater
discharges from the site. 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 days following inspection.
94th Ave SFR 23-0406
April 2024 Page 6
13: Protect Low Impact Development BMPs
The area for the future perforated stubout connection will be protected with construction
fencing to protect that area from compaction/disturbance.
4. MR#3: SOURCE CONTROL OF POLLUTION
The City of Edmonds Stormwater Supplement and DOE Drainage manual was reviewed to
determine if the proposed land -use for this project required any site -specific source control
BMPs to be constructed. All single-family residential projects shall, at a minimum,
incorporate BMPs from DOE SWMMWW Volume IV, S411 — BMPs for Landscaping and
Lawn/Vegetation Management. The BMPS from this section that shall be utilized for this
project area:
• Select the right plants for the planting location based on proposed use, available
maintenance, soil conditions, sun exposure, water availability, height, sight factors,
and space available.
• Ensure the plants selected for planting are not on the noxious weed list.
• Do not dispose of collected vegetation into waterways or storm sewer systems.
• Do not blow vegetation or other debris into the drainage system.
• Dispose of collected vegetation by composting or recycling.
5. MR#4: PRESERVATION OF NATURAL DRAINAGE SYSTEM
The runoff from the existing on -site basin drains in a northwestern direction towards the
western property lines. It flows onto the adjacent property and continues west following the
topography. Runoff is collected by the catch basin to the west on 94th Ave W,
approximately 130 feet from the project parcel. Out of this catch basin, a 12-inch concrete
pipe carries the runoff north into a catch basin at the intersection of 94th Ave W and 187th
St SW. From there the runoff flows out into an unnamed stream which travels northwest
for approximately 500-feet.
That this point the stream is collected by a 12" CMP pipe and conveyed north and then
west to the Olympic View Dr R/W where it connects with the existing conveyance system
in the roadway. This is the '/4 mile downstream point for this project and the downstream
analysis was concluded here. The unnamed stream noted for this downstream continues
northwest and ultimately discharges into Puget Sound.
The neighboring property to the east is developed with a SFR, driveway and landscaping.
Much of that parcel is flat in the landscaped areas near the common property line with this
project. Review of available information on -site indicates that the drainage from the hard
surfaces on that parcel are collected and tightlined and do not contribute to surface flows
toward this parcel. Therefore, only the landscaped areas from that parcel contribute to the
upstream surface flows tributary to this parcel.
The site grading on the east side of this parcel will be done to ensure that upstream runoff
is still allowed to flow onto this parcel as in the existing condition while directing the flows
94th Ave SFR 23-0406
April 2024 Page 7
away from the new foundation as required by the project Geotech. The runoff will be
directed north between the new foundation and existing east property line around the
building where it will be allowed to then flow northwest through the site as in the existing
conditions.
6. MR#5: ON -SITE STORMWATER MANAGEMENT
Per the 2019 DOE manual, and the Edmonds Addendum Appendix A the following BMPs
were considered, and the highest priority BMP found feasible was selected.
Lawn and Landscaped Areas:
1) Post -construction soil quality and depth: Required and selected. Sheet 4 of the
plan set provides both the location of the soil that shall be amended, as well as
notes to inform the contractor how to amend the soil.
Roofs:
1) Full Dispersion: Full dispersion was found to be infeasible due to not having the
required flow path. There is also not enough native vegetation on -site to meet the
requirements of full dispersion.
2) Downspout Full Infiltration Systems: Full infiltration was found to be infeasible by
the project Geotech due to excessive depths of undocumented fill.
3) Bioretention or Rain Gardens: Not feasible due to excessive fill depths per project
Geotech.
4) Downspout Dispersion Systems: The minimum vegetated flow paths can be
achieved on this lot. However, the Geotech advised that any runoff should be
collected and directed to the City infrastructure to prevent water from entering the
adjacent properties' foundation. Sheet flow dispersion is infeasible.
5) Detention Vaults and Pipes/Tanks: This BMP is feasible on this site and has been
selected for this project.
Per Section 6.3.1 of the 2022 Edmonds Stormwater Addendum, a 36-inch
detention pipe shall be sized using the equation L = 0.008*A, where A is equal to
the contributing hard surface area. For a contributing roof, driveway and walk area
of 4,510, the required 36" diameter pipe length is 36.1 feet. Therefore, a 40 LF 36"
diameter pipe shall be used, connected to the 54" diameter Type 2 CB with control
structure to meet the detention requirements of Minimum Requirement #5.
6) Perforated Stubout Connection: Not required, higher priority BMP found feasible.
94th Ave SFR 23-0406
April 2024 Page 8
Other Hard Surfaces:
1) Full Dispersion: Infeasible (See above).
2) Permeable Pavement: Infeasible as outlined in Geotechnical Report for this
project.
3) Bioretention or Rain Gardens: Infeasible (See above).
4) Sheet Flow Dispersion: The minimum vegetated flow paths can be achieved on
this lot. However, the Geotech advised that any runoff should be collected and
directed to the City infrastructure to prevent water from entering the adjacent
properties' foundation. Sheet flow dispersion is infeasible.
5) Concentrated Flow Dispersion: Similar to sheet flow dispersion, concentrated flow
dispersion is infeasible for this project.
6) Detention Vaults and Pipes: Feasible and selected. See detention pipe sizing
above for all hard surface runoff proposed for this project.
The proposed driveway which totals approximately (670 sf) will be collected in a
yard drain and directed to the same SDMH on -site described above. Refer to sheet
3 of the plans for more information.
7. OPERATION AND MAINTENANCE MANUAL
The Property Owner will be responsible for maintaining the stormwater and landscaping
facilities within this development. Specific problems can be recorded along with the
appropriate action taken.
Routine inspections and maintenance will improve the long-term performance of the
stormwater facilities. If at any time you are unsure if a problem exists or how to address a
specific problem, contact a Professional Engineer.
8. SUMMARY
As documented in this report the proposed improvements for this project trigger minimum
requirements 1-5 to be addressed for stormwater mitigation. Stormwater management
techniques have been incorporated into the design to mitigate for the proposed site
changes. Therefore, the stormwater design for this project has met or exceeded all the
applicable minimum requirements.
94th Ave SFR 23-0406
April 2024 Page 9
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23-0406
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1 OF 1
APPENDIX A
ADDITIONAL STUDIES, CALCS &
SITE PHOTOS
COBALT
G E 0 S C I E N C E S
September 2, 2022
Landsverk Quality Homes
Attn: Duane Landsverk & Joseph Rowett
24113 56th Avenue West
Mountlake Terrace, Washington
RE: Geotechnical Evaluation
Proposed Residence
187xx 94th Avenue West
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,
stormwater management, grading, and earthwork.
Site Description
The site is located at 187xx 94th Avenue West in Edmonds, Washington. The site consists of one
rectangular parcel (No. 00434600OO46o8) with a total area of about 0.32 acres, and a smaller
parcel that is the access easement from 94th Avenue West (No. 004346o00046o1).
The site is currently undeveloped and partially vegetated with weeds and grasses. The site slopes
downward from east to west at magnitudes of 5 to 15 percent and relief of about 13 feet.
The site is and bordered on all sides by residences with local access driveways.
The proposed development includes a new residence and driveway. Stormwater will include
infiltration or other systems depending on feasibility.
Site grading may include cuts and fills of 3 feet or less and foundation loads are expected to be
light.
We note that the project is ready to begin; therefore, some of our recommendations may not be
required as part of design or construction. We have included them in case modifications are
proposed.
Area Geology
The Geologic Map of the Edmonds East and West Quadrangles, 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
September 2, 2022
Page 2 of 10
Geotechnical Evaluation
Soil & Groundwater Conditions
As part of our evaluation, we excavated three test pits within the property areas, where accessible.
The explorations encountered approximately 6 inches of grass and topsoil underlain by
approximately 6.5 to at least 10.5 feet of loose to medium dense, silty -fine to medium grained
sand with gravel and poorly graded sand with variable amounts of debris (Fill). These materials
were underlain by medium 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
locally well cemented.
Groundwater was not encountered; however, the soils below the fill were locally mottled. There is
a chance that light volumes of groundwater may develop on the denser glacial till at variable
depths below the site. Groundwater would most likely be present during the wet season and
either within the fill and/or on the denser till.
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 King County indicate that the site
is underlain by Alderwood Urban land complex (8 to 15 percent slopes). These soils would have a
slight to moderate erosion potential in a disturbed state depending on the slope magnitude.
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 1st. Erosion
control measures should be in place before the onset of wet weather.
Seismic Hazard
The overall subsurface profile below the fill 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 too 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.
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Page 3 of 10
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
0.458
1.0
Null
o.865
Null
0.554
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 significant areas of undocumented fill along with weathered and
unweathered glacial till which becomes denser with depth. 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.
It is necessary to remove all undocumented fill from below the building pad and foundation areas
as part of development. Suitable fills may be used to replace these materials; however, the
underlying medium dense till must be exposed and benched prior to fill placement. Fill removal
should extend outward at a 1H:1V envelope from the edges of all foundation elements.
Widespread infiltration of runoff is not feasible based on the soil and anticipated groundwater
conditions. We recommend perforated or tightline connection of runoff devices to City
infrastructure. There does not appear to be adequate space for dispersion trenches. We can
provide additional recommendations upon request.
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 former
foundation areas in any areas underlain by undocumented fill.
The native soils consist of silty -sand with gravel and the fill includes poorly graded sand as well as
silty -sand with debris. The poorly graded sands and native soils are likely suitable for use as fill
provided all debris and organic materials are removed. These 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.
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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 3 feet or less for foundation and most of the utility placement. Any
deeper temporary excavations should be sloped no steeper than 1.511:1V (Horizontal:Vertical) in
loose native soils and fill, 111:1V in medium dense native soils and 3/41-1:1V 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. If groundwater is
encountered, temporary excavations may need to be decreased to 1.5H:1V or lower.
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 structure 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 the suitable native soils. Any undocumented fill and/or loose native soils should be
removed and replaced with structural fill below foundation elements.
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Geotechnical Evaluation
It is necessary to remove all undocumented fill from below the building pad and foundation areas
as part of development. Suitable fills may be used to replace these materials; however, the
underlying medium dense till must be exposed and benched prior to fill placement. Fill removal
should extend outward at a 1H:1V envelope from the edges of all foundation elements.
We should verify soil conditions during foundation excavation work. Alternatively, pin piles
could be used to support building foundations to limit the need for overexcavation. We can
provide recommendations upon request.
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 2,000
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
0.40 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 225 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.
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Geotechnical Evaluation
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)
21H* (Uniform Distribution) 1 in 2,500 year
event
Seismic Increase for "At -rest" Conditions
(Lateral Earth Pressure)
14H* (Uniform Distribution)1 in 500 year event
Seismic Increase for "Active" Conditions
(Lateral Earth Pressure)
7H* (Uniform Distribution)
Passive Earth Pressure on Low Side of Wall
(Allowable, includes F.S. = 1.5)
Neglect upper 2 feet, then 225 pcf EFD+
Soil -Footing Coefficient of Sliding Friction (Allowable;
includes F.S. = 1.5)
0.40
'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),
IEFD — 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.
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Geotechnical Evaluation
Stormwater Management Feasibility
Infiltration is not feasible at this site due to the very significant depths of undocumented fill. The
fill is over 10 feet thick in places and is underlain by relatively dense glacial till. The glacial till is
mottled and acts as a restrictive layer. Runoff would likely migrate laterally to the west, and into
adjacent residence's crawlspaces and/or basement areas.
Due to the fill and sloping conditions, we do not recommend shallow systems as the runoff will
degrade the fills and likely cause issues on downslope properties.
We recommend collection of runoff from new impervious surfaces with direct or perforated
connection to City infrastructure. We can provide additional recommendations upon request.
Slab -on -Grade
We anticipate that all fill will be removed and replaced with structural fill for any slab on grade
areas. We recommend that the upper 12 inches of the native soils within slab areas below the fill
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 36oR-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
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 (ESC) 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:
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Geotechnical Evaluation
• 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 and sandy 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.
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:
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Geotechnical Evaluation
■ 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 Landsverk Quality Homes and their 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 Landsverk Quality Homes 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.
Sincerely,
Cobalt Geosciences, LLC
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9/2/2022
Phil Haberman, PE, LG, LEG
Principal
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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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Pipe piles should consist of Schedule 40 galvanized steel with mechanical couplers for splices. Battered
piles may be necessary to provide lateral support to the structures.
The number of piles required depends on the magnitude of the design load. Allowable axial compression
capacities of 6, 1o, and 15 tons may be used for the 3-, 4-, and 6-inch diameter pin piles, respectively, with
an approximate factor of safety of 2 for piles driven to refusal. Penetration resistance required to achieve
the (refusal) capacities will be determined based on the hammer used to install the pile. Tensile capacity of
pin piles should be ignored in design calculations.
It is our experience that the driven pipe pile foundations should provide adequate support with total
settlements on the order of or less.
For 3-, 4-, and 6-inch pin piles, the following table is a summary of driving refusal criteria for different
hammer sizes that are commonly used:
Hammer
3" Pile Refusal
4" Pile Refusal
6" Pile Refusal
Hammer
Weight (lb) /
Criteria
Criteria
Criteria
Model
Blows per
(s/inch
(s/inch
(s/inch
minute
penetration)
penetration)
penetration)
Hydraulic
850 / 900
10
16
TB 325
Hydraulic
11100 / 900
6
10
20
TB 425
Hydraulic
2,000 / 600
3
4
10
TB 725X
Hydraulic
3,000 / 500
6
TB 830X
Please note that these refusal criteria were established empirically based on previous load tests on 3-, 4-,
and 6-inch pin piles. Contractors may select a different hammer for driving these piles and propose a
different driving criterion. In this case, it is the contractor's responsibility to demonstrate to the
geotechnical engineer's satisfaction that the design load can be achieved based on their selected equipment
and driving criteria.
A structural engineer shall perform the structural design of the pile including spacing and reinforcing
steel. The structural engineer also should determine the buckling load for the slender piles and make sure
that is not exceeded.
A 200 percent load test should be performed on 3 percent of the total piles. This test consists of increasing
the load on a test pile in 25 percent increments up to 200 percent of the design load. This load is held for 1
hour and deflections are measured on a dial gauge (to the hundredths or lower) for each load up to 200
percent. The pile should be unloaded in 25 percent increments.
Lateral resistance for footings can be developed using battered piles or an allowable equivalent fluid passive
pressure of 225 pounds per cubic foot (pcf) acting against the appropriate vertical footing faces (neglect the
upper 12 inches below grade in exterior areas).
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SITE MAP
FIGURE
P.O. Box 82243
Kenmore, WA 98028
(206)
www.cobaltgeo.com
cobaltgeo(&gmail.com
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: August 2022
Depth: 10'
Groundwater: None
Contractor: Client provided
Elevation: N/A
Logged By: PH
Checked By: SC
N
0)
o
Moisture Content (%)
u
Q
E
Plastic I
Limit
I Liquid
Limit
�
�
L
Material Description
DCP Equivalent N-Value
o
C
?
o
0
0 10
20 30 40 50
Cobalt Geosciences, LLC
Proposed Residence
P.O. Box 82243
COBALT
187xx 94th Avenue West
Test Pit
Kenmore, WA 98028
(2o6) 331-1097
GEOSCIENCES
Edmonds, Washington
Logs
www.cobaltgeo.com
cobaltgeopgmail.com
Topsoil and Grass __________________________
1
,•
SP
Loose to medium dense, fine to medium grained sand trace gravel
yellowish brown to grayish brown, dry. (Fill)
2
Caving
4
'
ys+ • ,ti :
6
• ••1 1
End of Test Pit 10'
Test
Pit
TP-2
Date: August 2022
Depth: 10'
Groundwater: None
Contractor: Client provided
Elevation: N/A
Logged By: PH
Checked By: SC
N
0)
o
Moisture Content (%)
u
Q
E
Plastic I
Limit
I Liquid
Limit
�
�
L
Material Description
DCP Equivalent N-Value
o
C
?
o
G
0 10
20 30 40 50ff
Cobalt Geosciences, LLC
Proposed Residence
P.O. Box 82243
COBALT
18�xx 94th Avenue West
Test Pit
Kenmore, WA 98028
(2o6) 331-1097
"
Edmonds, Washington
Logs
www.cobaltgeo.com
cobaltgeopgmail.com
_______Topsoil
and Grass
1
SM
Loose to medium dense, silty -fine to fine grained sand with gravel and
'
debris, olive gray to grayish brown. (Fill)
2
3
4
5
6
7
8
SM
dim Meudense, silty -fine to medium grained sand with gravel,
mottled yellowish brown, moist. (Weathered Glacial Till)
End of Test Pit 10'
Test
Pit
TP-3
Date: August 2022
Depth. 8'
Groundwater: None
Contractor: Client provided
Elevation: N/A
Logged By: PH
Checked By: SC
N
0)
o
Moisture Content (%)
u
Q
E
Plastic I
Limit
I Liquid
Limit
�
�
L
Material Description
DCP Equivalent N-Value
o
C
?
o
G
0 10
20 30 40 50
Cobalt Geosciences, LLC
Proposed Residence
P.O. Box 82243
COBALT
18�xx 94th Avenue West
Test Pit
Kenmore, WA 98028
(2o6) 331-1097
GEOSCIENCES
Edmonds, Washington
Logs
www.cobaltgeo.com
cobaltgeopgmail.com
Topsoil and Grass ____________ _ ______________
1
, ,
SM
Loose to medium dense, silty -fine to fine grained sand with gravel and
debris, olive gray to grayish brown. (Fill)
2
3
4
5
6
SM
Medium dense, silty -fine to medium grained sand with gravel,
mottled yellowish brown, moist. (Weathered Glacial Till)
End of Test Pit 8'
9
10