Driessen geotech rptN
tilain Office
1731 I — 135i° AveNE, A-500
Woodinville, %VA 98072
(425) 486-1669 - FAX (425) 481-2510
February 4, 2020
Mr. Peter Driessen
9229 Olympic View Drive
Edmonds, Washington
Via Email: n3ssctiCioginail,coln
NELSON GEOTECHNICAL
ASSOCIATES, INC.
GEOTECHNICAL ENGINEERS & GEOLOGISTS
Geotechnical Comment Response Letter
Driessen Property Residence Development
9229 Olympic View Drive
Edmonds, Washington
NGA File No. 1063618
Dear Mr. Driessen:
llncinecring-Gcology Branch
5526 Indualry Lane, 42
East wenateliec. NVA 98802
(509) 665-7696. 1 AX (509) 665-7692
This letter presents the results of our geotechnical engineering review of the plans and comment response
for your proposed residence project located at 9229 Olympic View Drive in Edmonds, Washington.
INTRODUCTION
We previously prepared a geotechnical report for the proposed residence development dated December 5,
2018. Project plans consist of demolishing the existing site structures and constructing a new single-
family residence in the same approximate location. We understand that concerns have been raised by the
City of Edmonds regarding geotechnical aspects of the proposed site development. The city's comments
were documented in a letter dated November 18, 2019. For our use in preparing this letter, we were
provided with a site plan titled "Driessen Residence," dated December 16, 2019 and prepared by CASA
Architecture. In the following section, we summarize the geotechnical concern raised by the City of
Edmonds, followed by our response.
CITY OF EDMONDS REVIEW COMMENT AND OUR RESPONSE
Comment 1:
Please update the December 5, 2018 report to address the specific improvements proposed including the
grading and rockeries within the identified 25 foot geotechnical setback recommended from the bottom
of the southern slope. Lf) , Ci r - ]
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Geotechnical Comment Response Letter
Driessen Residence
Edmonds, Washington
NGA File No. 1063619
February 4, 2020
Page 2
Response:
Based on review of the provided plans and discussions with your architect, we understand that there is an
existing up to three foot tall rockery wall immediately south of the existing residence within the
southeastern portion of the site. We also understand that the existing rockery is proposed to be extended
to the west as a part of the proposed residence development. The existing rockery is located within the
25-foot recommended setback area and the new proposed rockery wall extension will also be located
within the recommended 25-foot setback. The proposed rockery wall extension will be located
approximately 15- to 20-feet from the toe of the steep slope and will have a maximum height of three feet
tall. We understand that the rockery will mostly be supporting a cut excavation and minimal fill
placement will result of constructing the rockery extension. In our opinion, the proposed three foot tall
rockery wall extension within the previously recommended 25-foot setback from the toe of the steep
southern slopes is feasible from a geotechnical standpoint. We recommend that the proposed grading
activities associated with the rockery wall installation be localized to the proposed rockery wall area and
be kept to a minimum. The steep slopes and areas within 15-feet of the toe of the steep slopes should
remain undisturbed. Areas disturbed during the installation of the rockery wall extension should be
protected from erosion as discussed in our previous report. Disturbed areas should also be stabilized and
revegetated immediately after grading activities are completed.
CLOSURE
All recommendations provided in our previous report regarding site development should be strictly
followed. We should be retained to review development plans once they have been finalized. We
recommend that NGA be retained to provide monitoring and consultation services during construction to
confirm that the conditions encountered are consistent with those indicated by the explorations, to
provide recommendations for design changes should the conditions revealed during the work differ from
those anticipated, and to evaluate whether or not earthwork activities comply with contract plans and
specifications.
We trust this memorandum should satisfy your needs at this time. Please contact us if you have any
questions or require additional services.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Comment Response Letter
Driessen Residence
Edmonds, Washington
NGA File No. 1063618
February 4, 2020
Page 3
We appreciate the opportunity to provide service to you on this project. Please contact us if you have
any questions regarding this letter or require further information.
Sincerely,
NELSON GEOTECHNICAL ASSOCIATES, INC.
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LEE S. BELLAH
Lee S. Bellah, LG
Project Geologist
Khaled M. Shawish, PE
Principal
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NELSON GEOTECHNICAL ASSOCIATES, INC.
N A
Main Office
17311 -- 135` Ave NE, A-500
Woodinville, WA 98072
(425) 486-1669 • FAX (425) 481-2510
December 5, 2018
Mr, Peter Driessen
9229 Olympic View Drive
Edmonds, Washington
NELSON GEOTECHNICAL
ASSOCIATES, INC.
GEOTECHNICAL ENGINEERS & GEOLOGISTS
Geotechnical Engineering Evaluation
Driessen Property Residence Development
9229 Olympic View Drive
Edmonds, Washington
NGA File No. 1063618
Dear Mr. Driessen:
Engineering -Geology Branch
5526 Industry Lanc, #2
East Wenatchee, WA 98802
(509) 665-7696 FAX (509) 665-7692
We are pleased to submit the attached report titled "Geotechnical Engineering Evaluation — Driessen
Property Residence Development — 9229 Olympic View Drive — Seattle, Washington." This report
summarizes our observations of the existing surface and subsurface conditions within the properties, and
provides general recommendations for the proposed site development. Our services were completed in
general accordance with the proposal signed by you on October 29, 2018.
The site is currently occupied by a single-family residence within the central portion of the site. The
ground surface within the property is relatively level to gently sloping from the south to the north.
However, a steep north -facing slope is located directly above and to the south of the property that
descends from the northern shoulder of Olympic View Drive down to the property. We understand that
the proposed development plan will likely include removal of the existing residence and construction of a
new single-family residence within the same approximate location. We have been requested to provide a
geotechnical evaluation of the proposed development. Final grading and stormwater plans were not
available at the time this report was prepared. We should be retained to review final development plans,
including plans for site grading, retaining walls, and drainage prior to construction.
We also understand that stormwater generated within the property may be directed to onsite infiltration
systems, if feasible. We performed one small-scale pilot infiltration test (PIT) in accordance with the
2014 Department of Ecology {DOE) Stormwater Management in Western W_ ashington manual to
determine the design of infiltration or detention facilities. The subsurface soils generally consisted of
medium dense or better fine to medium sand with silt and gravel that we interpreted as native glacial
outwash soils. Based on our field-testing results, we have concluded that the site soils are conducive for
traditional stormwater infiltration.
We explored the subsurface soil conditions throughout the site and steep slope to the south of the site with
three trackhoe excavated test pits and two hand tool excavations. One of the trackhoe excavated
explorations was utilized for the onsite infiltration testing. Our explorations indicated that the site was
generally underlain by undocumented fill soils with competent native glacial outwash deposits at
relatively shallow depths.
CITY COPY DECEIVED
OCT 17 Zo,s
$LD2C��a-13Z� BUILDING
Geotechnical Engineering Evaluation NGA File No. 1063618
Driessen Property Residence Development December 5, 2018
Edmonds, Washington Summary - Page 2
It is our opinion that the proposed site development is feasible from a geotechnical engineering
standpoint, provided that our recommendations for site development are incorporated into project plans.
hi general, the native glacial deposits underlying the site should adequately support the planned structure.
Foundations should be advanced through any loose soils down to the competent native bearing soils
interpreted to underlie the site, for bearing capacity and settlement considerations. These soils should
generally be encountered approximately three to four feet below the existing ground surface, based on our
explorations. If loose soils or undocumented fill are encountered in unexplored areas of the site, they
should be removed and replaced with structural fill for foundation and pavement support. Final grading
and stormwater plans were not available at the time this report was prepared. We should be retained to
review final development plans, including plans for site grading, retaining walls, and drainage prior to
construction.
It is also our opinion that the soils that underlie the site and form the core of the slopes within the vicinity
and to the south of the site should be stable with respect to deep-seated earth movements, due to their
inherent strength and slope geometry. However, there is a potential for shallow sloughing and erosion
events to occur and impact the subject property. Based on our site observations, it is also our opinion that
the proposed structure setback of 25-feet from the toe of the steep slope to the south of the property
should provide adequate protection for the proposed structures against shallow failures originating on the
steep slopes above and to the south. We should be consulted if design changes are made and the proposed
setback is reduced.
In the attached report, we have also included recommendations for site grading, foundation support,
retaining walls and site drainage. We recommend that Nelson Geotechnical Associates (NGA) be
retained to review the geotechnical aspects of the project plans prior to construction. We also recommend
that NGA be retained to provide monitoring and consultation services during construction to confirm that
the conditions encountered are consistent with those indicated by the explorations, to provide
recommendations for design changes should the conditions revealed during the work differ from those
anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with
contract plans and specifications.
It has been a pleasure to provide service to you on this project. Please contact us if you have any
questions regarding this report or require further information.
Sincerely,
NELSON GEOTECHNICAL ASSOCIATES, INC.
Khaled M. Shawish, PE
Principal
TABLE OF CONTENTS
INTRODUCTION.............................................................................................................1
SCOPE............................................................................................................................... I
SITECONDITIONS......................................................................................................... 2
SurfaceConditions ....... ....................... :.... __.... :........ ,....... :..:..... .................... ..............
2
SubsurfaceConditions.................................................................................................. 3
Hydrogeologic Conditions......................................................................... ..............
3
SENSITIVE AREA EVALUATION............................................................................... 4
SeismicHazard.............................................................................................................
4
ErosionHazard.............................................................................................................
5
Landslide Hazard/Slope Stability.................................................................................
5
CONCLUSIONS AND RECOMMENDATIONS.......................................................... 5
General.........................................................................................................................
5
Erosion Control and Slope Protection Measures.........................................................
7
Site Preparation and Grading....................................................................................... 8
Temporary and Permanent Slopes............................................................................... 9
StructureSetbacks........................................................................................................
9
Foundations................................................................................................................
10
RetainingWalls..........................................................................................................
11
StructuralFill..............................................................................................................
12
Slab -on -Grade., ... ...........................................................................................
13
Pavements...................................................................................................................
13
Utilities................................................................................................................ I ......
14
Stormwater Infiltration.................................................................................
14
SiteDrainage..............................................................................................................
15
CONSTRUCTION MONITORING.............................................................................16
USE OF THIS REPORT................................................................................................16
LIST OF FIGURES
Figure 1 —Vicinity Map
Figure 2 — Site Plan
Figure 3 — Cross -Section A -A'
Figure 4 — Cross -Section B-B'
Figure 5 — Soil Classification Chart
Figures 6 and 7 —Exploration Logs
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Driessen Property Residence Development
9229 Olympic View Drive
Edmonds, Washington
INTRODUCTION
This report presents the results of our geotechnical engineering investigation and evaluation of the
planned residence development project in Edmonds, Washington. The project site is located at 9229
Olympic View Drive in Edmonds, Washington, as shown on the Vicinity Map in Figure 1. The purpose
of this study is to explore and characterize the site's surface and subsurface conditions and to provide
geotechnical recommendations for the planned site development.
The site is currently occupied by a single-family residence within the central portions of the site. The
ground surface within the property is relatively level to gently sloping from the south to the north.
However, a steep north -facing slope is located directly above and to the south of the property that
descends from the northern shoulder of Olympic View Drive down to the property. We understand that
the proposed development plan will likely include removal of the existing residence and construction of a
new single-family residence within the same approximate location. Specific development or grading plans
were not available at the time this report was prepared. The existing site layout is shown on the
Schematic Site Plan in Figure 2.
We understand that stormwater generated within the property may be directed to onsite infiltration
systems, if feasible. We have also been requested to evaluate the infiltration capacity of the site soils
within the property. The City of Edmonds utilizes the 2014 Department of Lcoia (DOE) t at r
Management in Western W-whingtQn manual to determine the design of infiltration or detention facilities.
According to this manual, long-term design infiltration rates for this site are to be determined by
performing on -site infiltration testing consisting of the Small Pilot Infiltration Test (PIT).
SCOPE
The purpose of this study is to explore and characterize the site surface and subsurface conditions, and
provide general recommendations for site development. Specifically, our scope of services includes the
following:
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1063618
Driessen Property Residence Development December 5, 2018
Edmonds, Washington Page 2
1. Review available soil and geologic maps of the area.
2. Explored the subsurface soil and groundwater conditions within the vicinity of the steep
slope with trackhoe excavated test pits. Trackhoe was provided by NGA.
3. Map the conditions on the site slopes, perform hand -tool excavations, and evaluate
current slope stability conditions.
4. Provide recommendations for foundation support, including minimum foundation
embedment.
5. Provide recommendations for deep foundation support, as needed.
6. Provide recommended structure setbacks from the steep slope.
7. Provide recommendations for earthwork.
8. Provide recommendations for temporary and permanent slopes.
9. Provide recommendations for slab subgrade preparation.
10. Determine feasibility of on -site stormwater infiltration.
11. Provide long-term design infiltration rates based on one on -site Small Scale Pilot
Infiltration Test (PIT) per the 2014 DOE Stormwater Manual. Location and depth of test
to be determined by civil engineer. Water for the test was secured by client.
12. Provide recommendations for infiltration system installation.
13. Provide recommendations for site drainage.
14. Provide recommendations for long-term slope protection and maintenance.
15. Document the results of our findings. Conclusions, and recommendations in a written
geotechnical report.
SITE CONDITIONS
Surface Conditions
The site consists of an irregular -shaped parcel covering approximately 0.45 acres. The site is currently
occupied by a single-family residence within the central portion of the property. The site is accessed by a
concrete, U-shaped driveway along the western property line. Vegetation surrounding the developed
portions of the site consists of landscaping plants, grass yard areas, and few young to mature trees.
Topography within the site is generally relatively level to gently sloping from east to west. To the south
of the property a steep north -facing slope descends to the southern property line from the northern
shoulder of Olympic View Drive at inclinations in the range of 32 to 35 degrees (63 to 70 percent) as
shown on Cross Sections A -A' and B-B' in Figures 3 and 4. The overall height of the steep slope is
approximately 10 to 13 feet. The existing residence setback from the toe of the steep slope is
approximately 25-feet. We did not observe surface water or seepage emitting from the site slopes within
the site during our visit on November 2, 2018. We also did not observe any indications of recent slope
movement within or near the subject property during our site visit.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No, 1063618
Driessen Property Residence Development December 5, 2018
Edmonds, Washington Page 3
Subsurface Conditions
Geology: The geologic units for the overall site are shown on Geologic map of the EdMonds East and
part of the Edmonds West quadrangles, Washington, by Minard, J.P. (USGS, 1983). The site is mapped
as Transitional Beds (Qtb) with Vashon till (Qvt) and Advance Outwash (Qva) in the near vicinity. The
transitional beds seem to grade upward into the base of the overlying advance outwash at some localities.
Till is generally described as a non -sorted mixture of clay, silt, sand, pebbles, cobbles, and boulders, all in
variable amounts. The advance outwash is described as mostly clean gray pebbly sand. Our explorations
typically encountered surficial undocumented fill/topsoil underlain by fine to medium sand with varying
amounts of silt and gravel, which we interpreted as native advance outwash soils at depth.
Explorations: The subsurface conditions within the site were explored on November 2, 2018 with three
test pit explorations within the proposed residence area along with two band tool explorations within the
steep slope area to the south of the site. The approximate locations of our explorations are shown on the
Site Plan in Figure 2.
A geologist from NGA was present during the explorations, examined the soils and geologic conditions
encountered, obtained samples of the different soil types, and maintained logs of the explorations. The
soils were visually classified in general accordance with the Unified Soil Classification System, presented
in Figure 5. The logs of our explorations are attached to this report and are presented as Figures 6 and 7.
We present a brief summary of the subsurface conditions in the following paragraph. For a detailed
description of the subsurface conditions, the exploration logs should be reviewed.
At the surface of Infiltration Pit 1, Test Pit 1 and 2, and Hand Augers 1 and 2, we generally encountered
approximately 3.0 to 5.0 feet of dark brown to brown, silty fine to medium sand with varying amounts of
gravel, roots, organics, and charcoal, which we interpreted as undocumented fill soils. Underlying the
undocumented fill in all of our explorations, we encountered gray to gray -brown, fine to medium sand
with varying amounts of silt and gravel, which we interpreted as native glacial outwash deposits.
Infiltration Pit 1, Test Pit 1 and 2, and Hand Augers 1 and 2 were terminated at respective depths of 6.0,
6.0, 5.5, 7.0, and 6.0 feet below the existing ground surface.
Hydrogeologic Conditions
We did not encounter groundwater within our explorations. If groundwater is encountered during
construction we would interpret this water to be perched water. Perched water occurs when surface water
infiltrates. Perched water does not represent a regional groundwater "table" within the upper soil
horizons. Perched water tends to vary spatially and is dependent upon the amount of rainfall. We would
expect the amount of perched groundwater to decrease during drier times of the year and increase during
wetter periods.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Driessen Property Residence Development
Edmonds, Washington
SENSITIVE AREA EVALUATION
Seismic Hazard
NGA File No. 1063618
December 5, 2018
Page 4
The 2018 International Building Code (IBC) seismic design section provides a basis for seismic design
of structures. Table 1 below provides seismic design parameters for the site that are in conformance
with the 2018 IBC, which specifies a design earthquake having a 2% probability of occurrence in 50
years (return interval of 2,475 years), and the 2008 USGS seismic hazard maps.
Table 1— 2018 IBC Seismic Design Parameters
Site Class
Spectral Acceleration
Spectral Acceleration
Site Coefficients
Design Spectral
at 0.2 sec. (g)
at 1.0 sec. (g)
Response
%
S1
Parameters
Fa
F„
SDs
SD1
r—D
1.288
0.505
1.000
1.500
0.859
0.505
The spectral response accelerations were obtained from the USGS Earthquake Hazards Program
Interpolated Probabilistic Ground Motion website (2008 data) for the project latitude and longitude.
The site, and portions of the greater Edmonds area, are contained within the South Whidbey Island Fault
Zone (SWIFZ): an active, shallow region of seismicity within central Puget Sound stretching from the
Strait of Juan de Fuca to North Bend. Information published in 2013 by the Department of Natural
Resources suggests the SW1FZ last ruptured less than 2,700 years ago, and that the fault zone can produce
a M7.5 earthquake. In our opinion, the risk of a surface fault rupture within this specific site is low, given
available data.
Hazards associated with seismic activity include liquefaction potential and amplification of ground
motion by soft deposits. Liquefaction is caused by a rise in pore pressures in a loose, fine sand deposit
beneath the groundwater table. The competent glacial soils interpreted to underlie the site have a low
potential for liquefaction or amplification of ground motion.
The competent glacial deposits interpreted to form the core of the site slopes above and to the south of the
property are considered stable with respect to deep-seated slope failures. However, the overlying loose
surficial materials and the fill located on the slope to the south of the property have the potential for
shallow sloughing failures during seismic events. Such events should not affect the planned development
provided the foundations along with the proposed structure setbacks and slope stabilization measures are
designed as described in this report.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1063618
Driessen Property Residence Development December 5, 2018
Edmonds, Washington Page 5
Erosion Hazard
The criteria used for determination of the erosion hazard for affected areas include soil type, slope
gradient, vegetation cover, and groundwater conditions. The erosion sensitivity is related to vegetative
cover and the specific surface soil types, which are related to the underlying geologic soil units. The
Natural Resources Conservation Service (MRCS) lists the site as Alderwood gravelly sandy loam, 15 to
30 percent slopes with a moderate erosion hazard. Based on experience with other projects in the area, it
is our opinion that the erosion hazard for site soils should be low in areas where the site is not disturbed.
Landslide Hazard/Slope Stability
The criteria used for evaluation of landslide hazards include soil type, slope gradient, and groundwater
conditions. The property is generally situated on a gently sloping ground with a steep north -facing slope
descending to the southern property line from the northern shoulder of Olympic view Drive at gradients in
the range of 32 to 35 degrees (63 to 70 percent). The overall height of the steep slope above the property
is approximately 10 to 13 feet. We did not observe evidence of significant slope instability within the
steep slopes to the south of the property during our investigation, such as deep-seated landsliding. We
also did not observe groundwater seepage or signs of recent erosion or sloughing on the steep slopes to
the south of the site at the time of our visit.
The core of the slopes above and to the south of the site are inferred to consist primarily of competent
glacial deposits. Relatively shallow sloughing failures as well as surficial erosion are natural processes
and should be expected on the steeper slopes during extreme weather conditions. It is our opinion that
while there is potential for erosion, soil creep, and shallow failures within the loose surficial soils on the
steep slopes, there is not a significant potential for deep-seated slope failures under current site
conditions. Proper site grading and drainage as well as adequate foundation placement and setbacks as
recommended in this report should help maintain current stability conditions.
CONCLUSIONS AND RECOMMENDATIONS
General
It is our opinion that the planned residential development within the site is feasible from a geotechnical
standpoint. It is also our opinion that the soils that underlie the site and form the core of the steep slopes
along and to the south of the subject site should be stable with respect to deep-seated earth movements,
due to their inherent strength and slope geometry. Proper erosion and drainage control measures as
recommended in this report should reduce this potential. Our explorations indicated that the site is
generally underlain by competent native glacial deposits at depth. The native glacial deposits encountered
at depth should provide adequate support for foundation, slab, and pavement loads. We recommend that
the planned structures be designed utilizing shallow foundations. Footings should extend through any
loose soil or undocumented fill soils and be founded on the underlying medium dense or better native
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1063618
Driessen Property Residence Development December 5, 2018
Edmonds, Washington Page 6
deposits, or structural fill extending to these soils. The competent soil deposits should typically be
encountered approximately three to four feet below the existing surface, based on our explorations. We
should note that localized areas of deeper unsuitable soils and/or undocumented fill could be encountered
at this site. This condition would require additional excavations in foundation, slab, and pavement areas
to remove the unsuitable soils.
Based on our site observations, it is also our opinion that the proposed structure setback of 25-feet from
the toe of the steep slopes that terminate on the southern property line should provide adequate protection
for the proposed structure against shallow failures originating on the steeper slopes above and help
maintain the existing stability of the slopes.
Specific development plans for the site were not available at the time this report was prepared. Proposed
grading within should minimize cuts and fills on or near the sloping portions of the site. All cuts and fills
should be supported using retaining walls. We should be retained to review grading and retaining wall
plans once development plans are finalized. Under no circumstances should fill be placed on any slopes
without engineering analysis and specific recommendations by NGA.
All grading operations and drainage improvements planned as part of this development should be planned
and completed in a matter that enhances the stability of the steep slopes, not reduces it. Excavation spoils
associated with the residence excavations should not be stockpiled near the site slopes or be allowed to
encroach on the slopes. Also, all runoff generated within the site should be collected and routed into a
permanent discharge system and not be allowed to flow over the slopes. Future vegetation management
on the slopes should be the subject of a specific evaluation and a plan approved by City of Edmonds. The
site slopes should be monitored on an ongoing basis, especially during the wet season and after seismic
events for any signs of instability, and corrective actions promptly taken should any signs of instability be
observed. Lawn clipping and any other household trash or debris should never be allowed to reach the
slopes.
The soils encountered on this site are considered moisture -sensitive and will disturb easily when wet. To
lessen the potential impacts of construction on the slopes and to reduce cost overruns and delays, we
recommend that construction take place during the drier summer months. If construction takes place
during the rainy months, additional expenses and delays should be expected. Additional expenses could
include the need for placing erosion control and temporary drainage measures to protect the slopes, the
need for placing a blanket of rock spalls on exposed subgrades, and construction traffic areas prior to
placing structural fill, and the need for importing all-weather material for structural fill.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1063619
Driessen Property Residence Development December 5, 2018
Edmonds, Washington Page 7
We recommend that NGA be retained to review final project plans and provide consultation regarding
structure placement, site grading, and foundation support. We also recommend that NGA be retained to
provide monitoring and consultation services during construction to confirm that the conditions
encountered are consistent with those indicated by the explorations, to provide recommendations for
design changes should the conditions revealed during the work differ from those anticipated, and to
evaluate whether or not earthwork and foundation installation activities comply with contract plans and
specifications.
Erosion Control and Slope Protection Measures
The erosion hazard for the on -site soils is interpreted as moderate but the actual hazard will be dependent
on how the site is graded and how water is allowed to concentrate. Best Management Practices (BMPs)
should be used to control erosion. Areas disturbed during construction should be protected from erosion.
Erosion control measures may include diverting surface water away from the stripped or disturbed areas.
Silt fences and/or straw bales should be erected to prevent muddy water from leaving the site or flowing
over the slopes. Stockpiles should be covered with plastic sheeting during wet weather and stockpiled
material should be kept away from the steep slope near the southern property line. Disturbed areas should
be planted as soon as practical and the vegetation should be maintained until it is established. The erosion
potential for areas not stripped of vegetation should be low to moderate.
Protection of the steep slope areas should be performed as required by the City of Edmonds. Specifically,
we recommend that slopes adjacent to the southern property line not be disturbed or modified through
placement of any fill or removal of the existing vegetation. No additional material of any kind should be
placed on either slope or be allowed to reach the slopes, such as excavation spoils, lawn clippings, and
other yard waste, trash, and soil stockpiles. Vegetation should not be removed from the slopes.
Replacement of vegetation should be performed in accordance with City of Edmonds code. Any
proposed development within the slope setback area, other than light decks or patios, should be the
subject of a specific geotechnical evaluation. Under no circumstances should water be allowed to
concentrate on the slopes.
The clearing of vegetation within the area of the proposed residential developments should not affect
slope stability, provided the disturbed areas outside the building are revegetated as soon as practical and
protected from erosion. In areas that are disturbed during or after construction, planting, hydro seeding,
and/or straw mulching are effective ways to minimize erosion and allow vegetation to be re-established
rapidly.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1063618
Driessen Property Residence Development December 5, 2018
Edmonds, Washington Page 8
Site Preparation and Grading
After erosion control measures are implemented, site preparation should consist of stripping any loose
soils and undocumented fill to expose medium dense or better native soil in foundation, slab -on -grade,
and pavement areas. The stripped materials should be removed from the site or stockpiled for later use as
landscaping fill. Based on our observations, we anticipate stripping depths of three to four feet,
depending on the specific locations. However, additional stripping may be required if areas of deeper
undocumented fill and/or loose soil are encountered in unexplored areas of the site.
If the ground surface, after site stripping, should appear to be loose, it should be compacted to a non -
yielding condition. Areas observed to pump or weave during compaction should be over -excavated and
replaced with properly compacted structural fill or rock spalls. If loose soils are encountered in any slab
areas, the loose soils should be removed and replaced with rock spalls or granular structural fill. If
significant surface water flow is encountered during construction, this flow should be diverted around
areas to be developed, and the exposed subgrades should be maintained in a semi -dry condition.
This site is underlain by moisture -sensitive soils. Due to these conditions, special site stripping and
grading techniques might be necessary, especially if grading is attempted in wet weather. These could
include using large excavators equipped with wide tracks and a smooth bucket to complete site grading
and promptly covering exposed subgrades with a layer of crushed rock for protection. If wet conditions
are encountered or construction is attempted in wet weather, the subgrade should not be compacted as this
could cause further subgrade disturbance. In wet conditions, it may be necessary to cover the exposed
subgrade with a layer of crushed rock as soon as it is exposed to protect the moisture sensitive soils from
disturbance by machine or foot traffic during construction. The prepared subgrade should be protected
from construction traffic and surface water should be diverted around prepared subgrade. Shallow
groundwater, if encountered, should be intercepted with cut-off drains and routed around the planned
grading area, or the groundwater should be controlled with sump -pumps or dewatering systems. Failure
to follow these recommendations could cause erosion and failures on the slopes, as well as result in
inadequate subgrades.
The site soils are considered to be moisture -sensitive and will disturb easily when wet. We recommend
that construction take place during the drier summer months if possible. However, if construction takes
place during the wet season, additional expenses and delays should be expected due to the wet conditions.
Additional expenses could include the need for placing a blanket of rock spalls on exposed subgrades,
construction traffic areas, and paved areas prior to placing structural fill. Wet weather grading will also
require additional erosion control and site drainage measures. Some of the on -site soils may be suitable
for use as structural fill, depending on the moisture content of the soil at the time of construction. NGA
NELSON GEOTECHN/CAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Driessen Property Residence Development
Edmonds, Washington
NGA File No. 1063618
December 5, 2018
Page 9
should be retained to evaluate the suitability of all on -site and imported structural fill material during
construction.
Temporary and Permanent Slopes
Temporary cut slope stability is a function of many factors, including the type and consistency of soils,
depth of the cut, surcharge loads adjacent to the excavation, length of time a cut remains open, and the
presence of surface or groundwater. It is exceedingly difficult under these variable conditions to estimate
a stable, temporary, cut slope angle. Therefore, it should be the responsibility of the contractor to
maintain safe slope configurations at all times as indicated in OSHA guidelines for cut slopes.
The following information is provided solely for the benefit of the owner and other design consultants and
should not be construed to imply that Nelson Geotechnical Associates, Inc. assumes responsibility for job
site safety. Job site safety is the sole responsibility of the project contractor.
For planning purposes, we recommend that temporary cuts in the upper surficial and undocumented fill
soils be no steeper than 2 Horizontal to 1 Vertical (21-1:IV). Temporary cuts in the competent native
glacial soils at depth should be no steeper than 1.511:IV. If significant groundwater seepage or surface
water flow were encountered, we would expect that flatter inclinations would be necessary. We
recommend that cut slopes be protected from erosion. The slope protection measures may include
covering cut slopes with plastic sheeting and diverting surface runoff away from the top of cut slopes.
We do not recommend vertical slopes for cuts deeper than four feet, if worker access is necessary. We
recommend that cut slope heights and inclinations conform to appropriate OSHA/WISHA regulations.
Permanent cut and fill slopes should be no steeper than 2H:1V. However, flatter inclinations may be
required in areas where loose soils are encountered. Permanent slopes should be vegetated and the
vegetative cover maintained until established.
Structure Setbacks
Uncertainties related to building along the top and toe of steep slopes are typically addressed by the use of
building setbacks. The purpose of the setback is to establish a "buffer zone" between the structure and
the top and toe of the slope so that ample room is allowed for normal slope recession during a reasonable
life span of the structure. In a general sense, the greater the setback, the lower the risk of slope failures to
impact the structure. From a geological standpoint, the setback dimension is based on the slope's
physical characteristics, such as slope height, slope angle, material composition, and hydrology. Other
factors such as historical slope activity, rate of regression, and the type and desired life span of the
development are important considerations as well.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1063618
Driessen Property Residence Development December 5, 2018
Edmonds, Washington Page 10
Based upon the conditions described above, it is our opinion that the potential for shallow sloughing -type
failures during severe weather exists on the steeper slopes in the vicinity of the site. We understand the
proposed setback for the new residence will be approximately 25 feet from the toe of the slope along the
southern property line. It is our opinion that a total setback distance of 25 feet between the proposed
structures and toe of steep slopes located to the south of the site should provide adequate protection
against normal shallow failures originating on the steep slopes above the proposed structures. This
setback is adequate with the understanding that the slopes are not altered during or after construction.
Temporary cuts into the slope could destabilize the slope and as such, any excavations near the slope
should be specifically evaluated and approved by NGA.
Protection of the setback and steep slope areas should be performed as required by the City of Edmonds.
Specifically, we recommend that the setback area and site slopes not be disturbed or modified through
placement of any fill or removal of the existing vegetation. No material of any kind should be placed
within the setback area or be allowed to reach the slopes, such as excavation spoils, lawn clippings,
debris, and soil stockpiles. Any sloping areas disturbed during construction should be planted as soon as
practical to reduce the potential for erosion. The new vegetation should be maintained until it is
established. Replacement of vegetation should be performed in accordance with City of Edmonds code.
Under no circumstances should water be allowed to concentrate on the slope.
Foundations
Conventional shallow spread foundations should be placed on competent native glacial soils, or be
supported on structural fill or rock spalls extending to these soils. Competent native soils should be
encountered approximately three to four feet below ground surface based on our explorations. Where
undocumented fill or less dense soils are encountered at footing bearing elevation, the subgrade should be
over -excavated to expose suitable bearing soil. The over -excavation may be filled with structural fill, or
the footing may be extended down to the competent native glacial soils. If footings are supported on
structural fill, the fill zone should extend outside the edges of the footing a distance equal to one half of
the depth of the over -excavation below the bottom of the footing.
Footings should extend at least 18 inches below the lowest adjacent finished ground surface for frost
protection and bearing capacity considerations. Foundations should be designed in accordance with the
2018 IBC. Footing widths should be based on the anticipated loads and allowable soil bearing pressure.
Water should not be allowed to accumulate in footing trenches. All loose or disturbed soil should be
removed from the foundation excavation prior to placing concrete.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Driessen Property Residence Development
Edmonds, Washington
NGA File No. 1063618
December 5, 2018
Page 11
For foundations constructed as outlined above, we recommend an allowable design bearing pressure of
not more than 2,000 pounds per square foot (psf) be used for the design of footings founded on the
competent native glacial deposits or structural fill extending to the competent native material. The
foundation bearing soil should be evaluated by a representative of NGA. We should be consulted if
higher bearing pressures are needed. Current IBC guidelines should be used when considering increased
allowable bearing pressure for short-term transitory wind or seismic loads. Potential foundation
settlement using the recommended allowable bearing pressure is estimated to be less than 1-inch total and
%Z-inch differential between adjacent footings or across a distance of about 20 feet, based on our
experience with similar projects.
Lateral loads may be resisted by friction on the base of the footing and passive resistance against the
subsurface portions of the foundation. A coefficient of friction of 0.35 may be used to calculate the base
friction and should be applied to the vertical dead load only. Passive resistance may be calculated as a
triangular equivalent fluid pressure distribution. An equivalent fluid density of 200 pounds per cubic foot
(pcf) should be used for passive resistance design for a level ground surface adjacent to the footing. This
level surface should extend a distance equal to at least three times the footing depth. These recommended
values incorporate safety factors of 1.5 and 2.0 applied to the estimated ultimate values for frictional and
passive resistance, respectively. To achieve this value of passive resistance, the foundations should be
poured "neat" against the native glacial deposits or compacted fill should be used as backfill against the
front of the footing. We recommend that the upper one foot of soil be neglected when calculating the
passive resistance.
Retaining Walls
Specific grading plans for this project were not available at the time this report was prepared, but
retaining walls may be incorporated into project plans. In general, the lateral pressure acting on
subsurface retaining walls is dependent on the nature and density of the soil behind the wall, the amount
of lateral wall movement which can occur as backfill is placed, wall drainage conditions, and the
inclination of the backfill. For walls that are free to yield at the top at least one thousandth of the height
of the wall (active condition), soil pressures will be less than if movement is limited by such factors as
wall stiffness or bracing (at -rest condition). We recommend that walls supporting horizontal backfill and
not subjected to hydrostatic forces, be designed using a triangular earth pressure distribution equivalent to
that exerted by a fluid with a density of 40 pcf for yielding (active condition) walls, and 60 pcf for non -
yielding (at -rest condition) walls. A seismic design loading of 8H should also be included in the wall
design. It represents the total height of the wall.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1063618
Driessen Property Residence Development December 5, 2018
Edmonds, Washington Page 12
These recommended lateral earth pressures are for a drained granular backfill and are based on the
assumption of a horizontal ground surface behind the wall for a distance of at least the subsurface height
of the wall, and do not account for surcharge loads. Additional lateral earth pressures should be
considered for surcharge loads acting adjacent to subsurface walls and within a distance equal to the
subsurface height of the wall. This would include the effects of surcharges such as traffic loads, floor slab
loads, slopes, or other surface loads. We could consult with the structural engineer regarding additional
loads on retaining walls during final design, if needed.
The lateral pressures on walls may be resisted by friction between the foundation and subgrade soil, and
by passive resistance acting on the below -grade portion of the foundation. Recommendations for
frictional and passive resistance to lateral loads are presented in the Foundations subsection of this
report.
All wall backfill should be well compacted as outlined in the Structural Fill subsection of this report.
Care should be taken to prevent the buildup of excess lateral soil pressures due to over -compaction of the
wall backfill. This can be accomplished by placing wall backfill in 8-inch loose lifts and compacting the
backfill with small, hand -operated compactors within a distance behind the wall equal to at least one-half
the height of the wall. The thickness of the loose lifts should be reduced to accommodate the lower
compactive energy of the hand -operated equipment. The recommended level of compaction should still
be maintained.
Permanent drainage systems should be installed for retaining walls. Recommendations for these systems
are found in the Subsurface Drainage subsection of this report. We recommend that we be retained to
evaluate the proposed wall drain backfill material and observe installation of the drainage systems.
Structural Fill
General: Fill placed beneath foundations, pavement, or other settlement -sensitive structures should be
placed as structural fill. Structural fill, by definition, is placed in accordance with prescribed methods and
standards, and is monitored by an experienced geotechnical professional or soils technician. Field
monitoring procedures would include the performance of a representative number of in -place density tests
to document the attainment of the desired degree of relative compaction. The area to receive the fill
should be suitably prepared as described in the Site Preparation and Grading subsection prior to
beginning fill placement.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1063619
Driessen Property Residence Development December 5, 2018
Edmonds, Washington Page 13
Materials: Structural fill should consist of a good quality, granular soil, free of organics and other
deleterious material, and be well graded to a maximum size of about three inches. All-weather fill should
contain no more than five -percent fines (soil finer than U.S. No. 200 sieve, based on that fraction passing
the U.S. 3/4-inch sieve). Some of the more granular on -site soils may be suitable for use as structural fill,
but this will be highly dependent on the moisture content of these soils at the time of construction. Rock
fragments should be crushed to no larger than 3-inch particle size if intended for use as structural fill. We
should be retained to evaluate all proposed structural fill material prior to placement.
Fill Placement: Following subgrade preparation, placement of structural fill may proceed. All filling
should be accomplished in uniform lifts up to eight inches thick. Each lift should be spread evenly and be
thoroughly compacted prior to placement of subsequent lifts. All structural fill underlying building areas
and pavement subgrade should be compacted to a minimum of 95 percent of its maximum dry density.
Maximum dry density, in this report, refers to that density as determined by the ASTM D-1557
Compaction Test procedure. The moisture content of the soils to be compacted should be within about
two percent of optimum so that a readily compactable condition exists. It may be necessary to over -
excavate and remove wet soils in cases where drying to a compactable condition is not feasible. All
compaction should be accomplished by equipment of a type and size sufficient to attain the desired degree
of compaction and should be tested.
Slab -on -Grade
Slabs -on -grade should be supported on subgrade soils prepared as described in the Site Preparation and
Grading subsection of this report. We recommend that all floor slabs be underlain by at least six inches
of free -draining gravel with less than three percent by weight of the material passing Sieve #200 for use
as a capillary break. We recommend that the capillary break be hydraulically connected to the footing
drain system to allow free drainage from under the slab. A suitable vapor barrier, such as heavy plastic
sheeting (6-mil minimum), should be placed over the capillary break material. An additional 2-inch-thick
moist sand layer may be used to cover the vapor barrier. This sand layer may be used to protect the vapor
barrier membrane and to aid in curing the concrete.
Pavements
Pavement subgrade preparation and structural filling where required, should be completed as
recommended in the Site Preparation and Grading and Structural Fill subsections of this report. The
pavement subgrade should be proof -rolled with a heavy, rubber -tired piece of equipment, to identify soft
or yielding areas that require repair. The pavement section should be underlain by a minimum of six
inches of clean granular pit run or crushed rock. We should be retained to observe the proof -rolling and
recommend repairs prior to placement of the asphalt or hard surfaces.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1063618
Driessen Property Residence Development December 5, 2018
Edmonds, Washington Page 14
Utilities
We recommend that underground utilities be bedded with a minimum 12 inches of pea gravel prior to
backfilling the trench with on -site or imported backfill material. Trenches within settlement sensitive
areas should be compacted to 95% of the modified proctor as described in the Structural Fill subsection
of this report. Trenches located in non-structural areas should be compacted to a minimum 90% of the
maximum dry density. Trench backfill compaction should be tested.
Stormwater Infiltration
General: The 2014 Denartment of Ecology (DOE) Stormwater Management in Western Washington
manual was utilized to determine the long-term design infiltration rate of the site soils. According to this
manual, on -site infiltration testing consisting of the Small -Scale Pilot Infiltration Test (PIT) was used to
determine the long-term design infiltration rates. We conducted one small-scale PIT within Infiltration
Pit 1 as shown on the attached Site Plan in Figure 2. The subsurface soil generally consisted of gray, fine
to medium sand with silt and gravel, which we interpreted as native, glacial outwash soils.
The test was conducted within a pit that measured 4.0-feet long by 3.0-feet wide by 6.0-feet deep. As
soon as the infiltration pit was excavated, the pit was filled with at least 12 inches of water and we began
the soaking period of the PIT for approximately 6-hours. At this time, the water flow rate into the hole
was monitored with a Great Plains Industries (GPI) TM 075 water flow meter for the pre-soak period.
After the 6-hour soaking period was completed, the water level was maintained at a depth of
approximately 12-inches for one hour for the steady-state period. The flow rate for Infiltration Pit 1
stabilized at 0.383 gallon per minute (22.98 gallons per hour). This equated to an approximate infiltration
rate of 3.07 inches per hour. The water was shut off after the steady-state period and monitored every 15
minutes for one hour. After one hour, the water level within the pit had decreased by 4 inches, resulting
in a measured infiltration rate of 4.0 inches per hour.
In accordance with the 2014 Denarlment of EeoloU (DOE-) Stormwater Management in Western
Washington, correction factors of 0.7, 0.5, and 0.9 for CFI,, CFt, and the long-term conductivity loss
factor, respectively were applied to the field measured infiltration rate. A total correction factor of 0.315
was applied to the field infiltration rate obtained from the falling head portion of Infiltration Pit 1 to
determine the long-term design infiltration rate for the granular outwash soils across the site.
Using the above correction factor and the measured infiltration rate of 4.0 inches per hour, we calculated
a long-term design infiltration rate of approximately 1.26 inches per hour. In our opinion, a long-term
design infiltration rate of 1.26 inches per hour could be utilized to design the on -site infiltration systems
within the native glacial outwash soils at depth throughout the site.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1063618
Driessen Property Residence Development December 5, 2018
Edmonds, Washington Page 15
We recommend the base of any infiltration systems be advanced through the upper soils and be founded
within the native glacial outwash soils encountered at depth. We did not encounter groundwater
throughout the site to the depths explored. The storm water management systems within this site should
be sized and designed in accordance with the stormwater manual and with the provided long-term design
infiltration rate of 1.26 inches per hour. We recommend that any proposed infiltration systems be located
as to not negatively impact any proposed or existing nearby structures and/or properties and also meet all
required setbacks from existing property lines, structures, sensitive areas and steep slopes in accordance
with the Snohomish County Drainage Manual. Any proposed on -site infiltration systems should be
located outside the proposed 25-foot setback from the toe of the steep slope.
Site Drainage
Surface Drainage: Final site grades should allow for drainage away from site slopes and away from the
planned residence areas. We suggest that the finished ground be sloped at a minimum gradient of three
percent for a distance of at least 10 feet away from the building. Runoff generated on this site should be
collected and routed into a permanent discharge system. This should include all downspouts and runoff
generated on all hard surfaces and yards areas. Under no circumstances should water be allowed to flow
uncontrolled over the slopes. Water should not be allowed to collect in any area where footings or slabs
are to be constructed.
Subsurface Drainage: If groundwater is encountered during construction, we recommend that the
contractor slope the bottom of the excavation and collect the water into ditches and small sump pits where
the water can be pumped out of the excavation and routed into a suitable outlet. We recommend that the
residence down spouts and footing drains be tightlined to an appropriate discharge location.
We recommend the use of footing drains around structures. Footing drains should be installed at least one
foot below planned finished floor elevation. The drains should consist of a minimum 4-inch-diameter,
rigid, slotted or perforated, PVC pipe surrounded by free -draining material wrapped in a filter fabric. We
recommend that the free -draining material consist of an 18-inch-wide zone of clean (less than three -
percent fines), granular material placed along the back of walls. Washed rock is an acceptable drain
material, or drainage composite may be used instead. The free -draining material should extend up the
wall to one foot below the finished surface. The top foot of soil should consist of low permeability soil
placed over plastic sheeting or building paper to minimize the migration of surface water or silt into the
footing drain. Footing drains should discharge into tightlines leading to an appropriate collection and
discharge point with convenient cleanouts to prolong the useful life of the drains. Roof drains should not
be connected to wall or footing drains.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1063618
Driessen Property Residence Development December 5, 2018
Edmonds, Washington Page 16
CONSTRUCTION MONITORING
We should be retained to provide construction monitoring services during the earthwork phase of the
project to evaluate subgrade conditions, temporary cut conditions, fill compaction, and drainage system
installation.
USE OF THIS REPORT
NGA has prepared this report for Mr. Peter Driessen and his agents, for use in the planning and design of
the development on these sites only. The scope of our work does not include services related to
construction safety precautions and our recommendations are not intended to direct the contractors'
methods, techniques, sequences, or procedures, except as specifically described in our report for
consideration in design. There are possible variations in subsurface conditions between the explorations
and also with time. Our report, conclusions, and interpretations should not be construed as a warranty of
subsurface conditions. A contingency for unanticipated conditions should be included in the budget and
schedule. We recommend that we be retained to review the project plans after they have been developed
to determine that recommendations in the report were incorporated into project plans.
All people who own or occupy homes on or near hillsides should realize that landslide movements are
always a possibility. The landowner should periodically inspect the slope, especially after a winter storm
or seismic event. If distress is evident, a geotechnical engineer should be contacted for advice on
remedial/preventative measures. The probability that landsliding will occur is substantially reduced by
the proper maintenance of drainage control measures at the site (the runoff from the roofs should be led to
an approved discharge point). Therefore, the homeowner should take responsibility for performing such
maintenance. Consequently, we recommend that a copy of our report be provided to any future
homeowners of the property if the home is sold.
We recommend that NGA be retained to review final plans prior to construction. We also recommend
that NGA be retained to provide monitoring and consultation services during construction to confirm that
the conditions encountered are consistent with those indicated by the explorations, to provide
recommendations for design changes should the conditions revealed during the work differ from those
anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with
contract plans and specifications. We should be contacted a minimum of one week prior to construction
activities and could attend pre -construction meetings if requested.
Within the limitations of scope, schedule, and budget, our services have been performed in accordance
with generally accepted geotechnical engineering practices in effect in this area at the time this report was
prepared. No other warranty, expressed or implied, is made. Our observations, findings, and opinions are
a means to identify and reduce the inherent risks to the owner. o-o-o
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Driessen Property Residence Development
Edmonds, Washington
NGA File No. 1063618
December 5, 2018
Page 17
It has been a pleasure to provide service to you on this project. If you have any questions or require
further information, please call.
Sincerely,
NELSON GEOTECHNICAL ASSOCIATES, INC.
44 4-/a/i,
Alex B. Rinaldi, GIT
Staff Geologist H
poo;[ vvash�
2883
I LEE S. BELLAH I
Lee S. Bellah, LG
Project Geologist
Maher A. Shebl, PhD, PE, M.ASCE
Senior Engineer
ABR:LSB:MAS:dy
Seven Figures Attached
NELSON GEOTECHNICAL ASSOCIATES, INC.
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No.
Date
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1063618
Driessen Property
NGA ASSOCIATES, INC.
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Figure 1
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Number and approximate
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_ Number and approximate Scale: 1 inch = 30 feet
location of hand auger
Reference: Site Plan based on a plan dated June 12, 2018 titled "Topographic Survey," prepared by Pacific Geornatic Services, Inc.
9
Project Number NELSON GEOTECHNICAL No. Date Revision By CK 2
1063618 Driessen Property NGA ASSOCIATES, INC. 1 1117118 Original DPN ABR s
Site Plan GEOTECHNICAL ENGINEERS & GEOLOGISTS
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---r 200
190
180
170
160
(VOTES:
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2) Elevations are approximate.
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NOTES:
1) Stratigraphic conditions are interpolated between
the explorations. Actual conditions may vary.
2) Elevations are approximate.
a hand-held clinometer and 100-ft taae measure.
UNIFIED SOIL CLASSIFICATION SYSTEM
GROUPSYMBOL
MAJOR DIVISIONS
GROUP NAME
CLEAN
GW
WELL -GRADED, FINE TO COARSE GRAVEL
COARSE-
GRAVEL
GRAVEL
GP
POORLY -GRADED GRAVEL
GRAINED
MORE THAN 50 %
GRAVEL
GM
SILTY GRAVEL
OF COARSE FRACTION
RETAINED ON
SOILS
NO.4 SIEVE
WITH FINES
GC
CLAYEY GRAVEL
SAND
CLEAN
SW
WELL -GRADED SAND, FINE TO COARSE SAND
SAND
SP
POORLY GRADED SAND
MORE THAN 50 %
RETAINED ON
MORE THAN 50 %
NO.200 SIEVE
OF COARSE FRACTION
SAND
SM
SILTY SAND
PASSES NO.4 SIEVE
SC
CLAYEY SAND
WITH FINES
FINE -
SILT AND CLAY
ML
SILT
INORGANIC
GRAINED
LIQUID LIMIT
CL
CLAY
LESS THAN 50 %
SOILS
ORGANIC
OL
ORGANIC SILT, ORGANIC CLAY
SILT AND CLAY
MH
SILT OF HIGH PLASTICITY, ELASTIC SILT
INORGANIC
MORE THAN 50 %
PASSES
LIQUID LIMIT
CH
CLAY OF HIGH PLASTICITY, FAT CLAY
NO. 200 SIEVE
50 % OR MORE
ORGANIC
OH
ORGANIC CLAY, ORGANIC SILT
HIGHLY ORGANIC SOILS
PT
PEAT
NOTES:
1) Field classification is based on visual SOIL MOISTURE MODIFIERS:
examination of soil in general
accordance with ASTM D 2488-93. Dry - Absence of moisture, dusty, dry to
the touch
2) Soil classification using laboratory tests
Moist - Damp, but no visible water
is based on AST M D 2488-93.
3) Descriptions of soil density or Wet - Visible free water or saturated,
consistency are based on usually soil is obtained from
interpretation of blowoount data, below water table
visual appearance of soils, and/or
test data.
Project Number
NELSON GEOTECHNICAL
No.
Date
Revision
By
CK
1063618
Driessen Property
Soil Classification Chart
-�N
"" � ��-. ASSOCIATES, INC.
GEOTECHNICAL ENGINEERS & GEOLOGISTS
,
„n„s
original
DPN
neR
Figure 5
Woad)nN"a 0"" Eee/ Wenelehee CO..
17311-135lh Ave NE,A-500 5526 Indudry Lane, M2
WoedhlNYa, WA 86012 Eed Wenekhee, WA OBB02
(4251488-166g /'.:481-2510— ndeongeoleoh— A) 665?MI Fee: N5-760
LOG OF EXPLORATION
DEPTH (FEET)
USC SOIL DESCRIPTION
INFILTRATION PIT
ONE
0.0-4.0
LIGHT TO DARK BROWN, SILTY FINE TO MEDIUM SAND WITH GRAVEL, ROOTS, ORGANICS,
AND TRACE DRAIN ROCK (LOOSE TO MEDIUM DENSE, MOIST) fflLL
4.0 - 6.0
SP-SM GRAY TO GRAY -BROWN, FINE TO MEDIUM SAND WITH SILT, GRAVEL, AND TRACE IRON -OXIDE
STAINING (MEDIUM DENSE TO DENSE, MOIST)
SAMPLE WAS NOT COLLECTED
GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED
TEST PIT CAVING WAS NOT ENCOUNTERED
TEST PIT WAS COMPLETED AT 6.0 FEET ON 11/2/2018
TEST PIT ONE
0.0-1.2
LIGHT TO DARK BROWN, SILTY FINE TO MEDIUM SAND WITH GRAVEL, ROOTS, AND ORGANICS
(LOOSE TO MEDIUM DENSE, MOIST) (FILLI
1.2-3.0
ORANGE -BROWN TO BROWN, SILTY FINE TO MEDIUM SAND WITH SCATTERED ROOTS,
CHARCOAL, AND ORGANICS (MEDIUM DENSE, MOIST) (FILLI
3.0- 6.0
SP-SM GRAY, FINE TO MEDIUM SAND WITH SILT AND GRAVEL (MEDIUM DENSE TO DENSE, MOIST)
SAMPLE WAS COLLECTED AT 6.0 FEET
GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED
TEST PIT CAVING WAS NOT ENCOUNTERED
TEST PIT WAS COMPLETED AT 6.0 FEET ON 11/2/2018
TEST PIT TWO
0.0-3.0
BROWN TO DARK BROWN, SILTY FINE TO MEDIUM SAND WITH GRAVEL, ROOTS, AND
ORGANICS (LOOSE TO MEDIUM DENSE, MOIST) FI
3.0- 5.5
SP-SM GRAY, FINE TO MEDIUM SAND WITH SILT AND GRAVEL (MEDIUM DENSE TO DENSE, MOIST)
SAMPLE WAS COLLECTED AT 5.0 FEET
GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED
TEST PIT CAVING WAS NOT ENCOUNTERED
TEST PIT WAS COMPLETED AT 5.5 FEET ON 11/2/2018
HAND AUGER ONE
0.0-5.0
BROWN TO DARK BROWN, SILTY FINE TO MEDIUM SAND WITH GRAVEL, ROOTS, AND
ORGANICS (LOOSE TO MEDIUM DENSE, MOIST) (FILL
5.0 - 7.0
SP-SM LIGHT BROWN TO GRAY, FINE TO MEDIUM SAND WITH SILT AND GRAVEL
(MEDIUM DENSE TO DENSE, MOIST)
SAMPLE WAS COLLECTED AT 6.5 FEET
GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED
HAND AUGER CAVING WAS NOT ENCOUNTERED
HAND AUGER WAS COMPLETED AT 7.0 FEET ON 11/2/2018
ABR:KMS NELSON GEOTECHN/CAL ASSOCIATES, INC.
FILE NO 1063618
FIGURE 6
LOG OF EXPLORATION
DEPTH (FEET) USC SOIL DESCRIPTION
HAND AUGER TWO
0.0-4.8 BROWN TO DARK BROWN, SILTY FINE TO MEDIUM SAND WITH GRAVEL, ROOTS, CHARCOAL
AND ORGANICS (LOOSE TO MEDIUM DENSE, MOIST) (MIL)
4.8 - 6.0 SP-SM LIGHT BROWN TO GRAY, FINE TO MEDIUM SAND WITH SILT AND GRAVEL
(MEDIUM DENSE TO DENSE, MOIST)
SAMPLE WAS NOT COLLECTED
GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED
HAND AUGER CAVING WAS NOT ENCOUNTERED
HAND AUGER WAS COMPLETED AT 6.0 FEET ON 11/2/2018
ABR:KMS NELSON GEOTECHNICAL ASSOCIATES, INC.
FILE NO 1063618
FIGURE 7