REPORT - 988717 Weis Residence Edmonds.pdf
April 24, 2017
Mr. James Weis
50 Mill Plain Road
Danbury, CT 06811
jweis@techair.com
Geotechnical Site Assessment
Residential Development
16630 74 th Place West
Edmonds, Washington
NGA File No. 988717
Dear Mr. Weis:
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We are pleased to submit the attached Site Assessment 16630 74 Place
West Edmonds
within the site and provides recommendations for the proposed site improvements. Our services were
completed in general accordance with the proposal signed by you on April 9, 2017.
The site is situated on a 0.92-acre rectangular lot, composed of a moderate northwest-facing slope that
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descends from the eastern property line to the western property line along 76 Avenue West. Two gently
sloping terraces break the slope in the central and eastern part of the property. Stilthouse Creek and a
tributary stream meander in and out of the northern property line. A dilapidated, concrete structure and
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driveway are located near the eastern property line and are adjacent to 74 Place West. The proposed
development plan includes the demolition of the existing structure, and the construction of a new single-
family residence within the property. Final grading or drainage plans have not been developed at the time
this report was prepared.
We explored the site with five hand-auger boreholes extending to depths in the range of 1.5 to 5.5 feet
below the existing ground surface. Our explorations indicated that the terraced areas are generally underlain
by loose to medium dense, fine to medium sand with trace gravel soils that we interpreted as native glacial
soilsat depth.
We concluded that the site was generally compatible with development. We recommend that the new
structure be founded on the medium dense or better native glacial soils for bearing capacity and settlement
considerations. These soils were generally encountered at depths between 3.0 and 5.0 feet below existing
ground surface on terraces, and is assumed to be deeper on slopes. We should note that localized areas of
deeper unsuitable soils and/or undocumented fill could be encountered at this site and exposed at the
proposed foundation subgrade elevations, depending on final site grading and development plans. This
Geotechnical Site Assessment NGA File No. 988717
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16630 74 Place West April 24, 2017
Edmonds, Washington Summary - Page 2
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condition would require additional excavations in foundation, slab, and pavement areas to remove the
unsuitable soils. In the attached report, we have also included recommendations for site grading, temporary
slopes, retaining walls, erosion control, and site drainage.
We should be retained to discuss our recommendations with your design team, and 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
in the explorations, to provide recommendations for design changes should the conditions revealed during
the work differ from these anticipated, and to evaluate whether or not earthwork and foundation installation
activities comply with contract plans and specifications.
We appreciate the opportunity 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 ............................................................................................................................................ 1
SITE CONDITIONS ...................................................................................................................... 2
Surface Conditions .................................................................................................................... 2
Subsurface Conditions .............................................................................................................. 2
CONCLUSIONS AND RECOMMENDATIONS ....................................................................... 3
General ...................................................................................................................................... 3
GEOLOGIC HAZARDS ASSESSMENT ................................................................................... 4
Erosion Control and Slope Protection Measures ...................................................................... 5
Site Preparation and Grading .................................................................................................... 5
Temporary and Permanent Slopes ............................................................................................ 6
Foundation Support .................................................................................................................. 7
Structural Fill ............................................................................................................................ 8
Slab-on-Grade ........................................................................................................................... 9
Pavements ................................................................................................................................. 9
Site Drainage ............................................................................................................................ 9
USE OF THIS REPORT ............................................................................................................. 10
List of Figures
Figure 1 Vicinity Map
Figure 2 Site Plan
Figure 3 Cross Section A-
Figure 4 Cross Section B-
Figure 5 Soil Classification Chart
Figures 6 and 7 Logs of Exploration
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Site Assessment
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16630 74 Place West
Edmonds, Washington
INTRODUCTION
This report presents the results of our geotechnical site assessment of the potential single-family residential
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development project on the property located at 16630 74 Place West in Edmonds, Washington, as shown
on the Vicinity Map in Figure 1. The parcel contains relatively steep slopes, and has consequently been
mapped as an erosion hazard area by the City of Edmonds. The current parcel number on file for the
property is 00513100009500.
We visited the site on April 6 and 13, 2017 to observe the existing conditions. The property is rectangular
in shape, and approximately 0.92 acres in area. It is bordered to the north and south by existing single-
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family residences, and to the east and west by 74 Place West and 76 Avenue West, respectively. Intended
development plans consist of demolishing an existing structure, and constructing a new single-family
residence within one of the terrace areas within the property with associated access drive and utilities.
SCOPE
The purpose of this study was to explore and characterize the site surface and subsurface conditions, and
provide general recommendations for site development. Our services were completed in general accordance
with our proposal signed by you on April 9, 2017 and consisted of the following general tasks:
1. A review of available soil and geologic maps of the area.
2. Mapping the conditions on the slope, performing shallow hand-tool excavations (hand augers)
as necessary to prepare cross-sections and qualitatively evaluate current slope stability
conditions.
3. Performing grain-size sieve analysis on soil samples, as necessary.
4. Providing our opinions regarding the steep slope conditions.
5. Providing preliminary recommendations for foundation support and embedment.
6. Providing preliminary recommendations for earthwork.
7. Providing preliminary recommendations for temporary and permanent slopes.
8. Providing preliminary recommendations for retaining walls, if needed.
9. Providing preliminary recommendations for slab and pavement subgrade preparation.
10. Providing preliminary recommendations for site drainage and erosion control.
11. Documenting the results of our findings, conclusions, and recommendations in a written
geotechnical report.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Site Assessment NGA File No. 988717
16630 74 th Place West April 24, 2017
Edmonds, Washington Page 2
SITE CONDITIONS
Surface Conditions
The parcel is roughly rectangular in shape, approximately 115feet wide and 350feet long covering
approximately 0.92 acres, as shown on the Schematic Site Plan in Figure 2. The property generally slopes
steeply down to the northwest with a total vertical relief of about 80 feet across relatively steep pitches of
approximately 22 to 24 degrees (40 to 44 percent grade) and two gently sloping terraces. Each is about 70
feet in width, as shown on Cross Sections A-- (Figures 3 and 4). During the study, a tributary
stream to Stilthouse Creek was observed to flow westward along the northern width of the property, and
meandered across the property line within the ravine to the north. On the western property line, a pond of
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stagnant water several inches deep was observed adjacent to 76 Avenue West, and appears to originate
from runoff and controlled in elevation by a culvert beneath the road, which is elevated approximately four
feet by a concrete block and soldier pile retaining system, as shown on Cross Section A-.
A dilapidated, concrete structure and driveway are located near the eastern property line and adjacent to
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74 Place West. Except for the structure, the property is undeveloped and occupied by a variety of trees,
including mature western red cedar, alder, and big leaf maple trees, with an understory of English ivy,
western swordfern, salal, blackberry brambles, and other shrubs. Some building materials, construction
debris, and scattered pieces of garbage are also present on the property.
Subsurface Conditions
Geology:
The Geologic map of the Edmonds East and part of the Edmonds West quadrangles, Washington
(MF-1541), by James P. Minard, (USGS, 1983) was reviewed for this site. The site is mapped as Quaternary
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glacial deposits of till (Qvt) near 76 Avenue West, and Transitional Beds (Qtb) to the east, near 74 Place
West. In this area, glacial till is a thick unit composed of a mixture of clay, silt, sand, and gravels. It is
typically dense due to the weight of the overriding glacier which deposited the material as it travelled.
Transitional Beds are relatively finer in grain size, and contain mainly fine sand, silt, and clay. From our
explorations, it appears that the onsite soils fit the description of the mapped glacial deposits.
Explorations:
The subsurface conditions within the site were investigated on April 13, 2017 by excavating
five explorations with a hand auger and other hand tools. The approximate locations of the explorations are
shown on the Schematic Site Plan in Figure 2. Geologists from Nelson Geotechnical Associates, Inc. (NGA)
conducted the explorations, collected samples of the soils encountered, and maintained a log of the
explorations. The soils were visually classified in general accordance with the Unified Soil Classification
System, presented as Figure 5. The logs of the explorations are presented in Figures 6 and 7. We present a
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Site Assessment NGA File No. 988717
16630 74 th Place West April 24, 2017
Edmonds, Washington Page 3
brief summary of the subsurface conditions in the paragraph below. For a detailed description of the
subsurface conditions, the exploration logs should be reviewed.
All explorations encountered a surficial layer of organic-rich topsoil between 0.5 and 2.0 feet thick.
Underlying the surficial topsoil, explorations encountered brown or tan, silty fine to medium sand with
trace gravel in Hand Augers 3 through 5, and brown, silty fine to medium sand in Hand Augers 1 and 2 on
the slope. Hand Augers 1 through 3 exposed medium dense conditions at the depths explored, while Hand
Auger 4 and Hand Auger 5 exposed loose conditions at depth. Hand Augers 1 through 3 were terminated
in medium dense, gravelly deposits at depths between 3.0 and 5.5 feet below the existing ground surface.
Hand Auger 4 and Hand Auger 5 were terminated in loose deposits between 1.5 and 3.5 feet below the
ground surface due to the loose conditions and groundwater seepage.
Hydrologic:
Surficial water features were observed on the site and in the vicinity. A tributary stream to
Stilthouse Creek flows westwards in a moderate to steep-sloped ravine on the northern side of the property,
as shown on the Site Plan in Figure 2. Stagnant water approximately 2 3 inches in depth was observed to
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pond adjacent to the elevated 76 Avenue West. This structure may be impeding or reducing flow from the
stagnant pond, which may have originated by runoff or hydraulically nonconductive material below.
We observed moderate groundwater seepage within HA-4 at approximately 2.0 feet below the existing
ground surface. Moderate groundwater seepage was also encountered in Hand Auger 5 at a depth of 0.75
feet below the existing ground surface.
We anticipate that any groundwater encountered near the surface is in a perched condition. Perched water
occurs when the water infiltrates through less dense, more permeable soils and accumulates on the top of
the upper soil horizons. Perched water tends to vary spatially and is dependent on the amount of
precipitation. Perched water tends to flow laterally above the impermeable layer and may daylight on the
slope in the form of seasonal seepage.
CONCLUSIONS AND RECOMMENDATIONS
General
It is our opinion that development of the property is feasible from a geotechnical standpoint, provided that
our recommendations are incorporated into the design and construction of this project. We believe that site
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constraints, especially groundwater conditions, adjacent to 76 Avenue West may require supplementary
planning and support before development in that area can feasibly occur.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Site Assessment NGA File No. 988717
16630 74 th Place West April 24, 2017
Edmonds, Washington Page 4
Geologic Hazards Assessment
Seismic Hazard:
We reviewed the 2015 International Building Code (IBC) for seismic site classification
for this project. Based on sites with similar geology, we expect that soils overlying the loose to medium
dense surface soils are dense to very dense. These conditions best fit the IBC description for Site Class C.
Hazards associated with seismic activity include liquefaction potential and amplification of ground motion.
Liquefaction is caused by a rise in pore pressures in a loose, fine sand deposit beneath the groundwater
table. Because a groundwater table is not present near the ground surface and also because the relative
density of soils interpreted to underlie the site is predominately medium dense or better (below weathered
or disturbed surface soils), it is our opinion that the risk of liquefaction and amplification of ground motion
is low.
The potential exists for seismically-induced shallow and deep-seated failures to occur on the steep slope at
this site. However, based on geologic mapping and observations of surface features at this and adjoining
sites, the risk of failure does not appear to be greater than what would be expected on similar sites within
the topographic zone between the top of the slope and the beach in this area of the City of Edmonds. Based
on the limited information, the soils interpreted to underlie the site are considered to be relatively stable
with respect to deep-seated slope failures.
Erosion Hazard:
The criteria used for determining the erosion hazard for the site soils includes 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 Soil Survey of Snohomish County Area, Washington, by the Soil Conservation Service (SCS) was
reviewed to determine the erosion hazard of the on-site soils. The site surface soils were classified using
the SCS classification system as Alderwood gravelly sandy loam, 15 to 30 percent slopes. These soils are
listed as having a moderate hazard of water erosion. It is our opinion that these soils should have a slight
to low hazard for erosion in areas that are not disturbed and where the vegetation cover is not removed.
Surficial erosion is a natural process and was occurring on the steep ravine slopes at the time of our visit.
Active stream channel erosion was being caused by the flow of Stilthouse Creek and its tributary stream in
the northern portion of the property.
Landslide Hazard/Slope Stability:
The criteria used for evaluation of landslide hazards include soil type,
slope gradient, and groundwater conditions. The central portion and western end of the property are
characterized by a steep northwest-facing slope. In addition, the property is located immediately south of
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Site Assessment NGA File No. 988717
16630 74 th Place West April 24, 2017
Edmonds, Washington Page 5
the designated Meadowdale Landslide Complex, which has experienced prevalent documented failures,
and was augmented by extensive monitoring and drainage improvements by the City of Edmondsover the
past four decades. Weathered and disturbed surface soils on the steep slope have the potential for shallow
sloughing failures triggered by severe weather or seismic events.
It is our opinion that there is potential for erosion, soil creep, and shallow failures within loose surficial
soils on the slope. Proper site grading and drainage should help maintain current stability conditions. In
addition, the potential may exist for deep-seated failures to occur at this site. However, based on geologic
mapping and observations of surface features at this and adjoining sites, the risk of failure does not appear
to be greater than what would be expected on similar sites between the beach and top terrace within this
area of the City of Edmonds. Further explorations, such as deep soil borings, would be required to refine
the risk of deep-seated slope failures.
Erosion Control and Slope Protection Measures
The erosion hazard for the on-site soils is listed as moderate throughout the property. The actual hazard will
depend on how the site is graded and how water is managed. 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 stripped or disturbed areas and not
allowing water to concentrate and flow uncontrolled. Silt fences and/or straw bales should be erected to
prevent muddy water from leaving the site or flowing toward the steep slope. Stockpiles should be covered
with plastic sheeting during wet weather. Disturbed areas should be planted as soon as practical and the
vegetation should be maintained until it is established. Replacement of vegetation should be performed in
accordance with City of Edmonds guidelines. The erosion potential for areas not stripped of vegetation
should be slight to low.
In the long term, we recommend that the site development activities be concentrated on the benches, and
that steep slopes be disturbed as little as practical. No material of any kind should be placed on the steeper
slope, or be allowed to reach them, such as excavation spoils, lawn clippings and other yard waste, trash,
and soil stockpiles. Any proposed future development should be reviewed by NGA for the need to conduct
a specific geotechnical evaluation, as needed. Under no circumstances should water be allowed to
concentrate on the steep slopes. The slopes should be monitored during wet weather and corrective
measures promptly implemented should any signs of slope distress or instability be observed.
Site Preparation and Grading
After initial erosion control measures are implemented, site preparation should consist of stripping areas to
be developed of all organic matter, organic-laden topsoil, and soil with abundant roots. Some of the stripped
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Site Assessment NGA File No. 988717
16630 74 th Place West April 24, 2017
Edmonds, Washington Page 6
materials may be stockpiled for later reuse in landscaped areas; excess materials should be removed and
disposed of offsite.
We recommend that areas that are at grade, or will be supporting fill, foundations, concrete slabs, or
pavements be scarified to a depth of at least 12 inches (after stripping) to identify buried roots or any
unsuitable materials and to create more uniform conditions. Roots and other unsuitable materials should be
removed and the scarified soils should be moisture-conditioned as needed and recompacted to the
requirements of structural fill described below.
The timing of earthwork with respect to seasonal variations in the environment will have some effect on
the behavior of the native onsite soils. The amount of silt in the soil indicates that the soils are somewhat
moisture sensitive and may be difficult to compact if they are overly wet. We recommend that construction
take place during the drier summer and early autumn months, if possible. If construction takes place during
the rainy season, additional expenses and delays should be expected due to overly wet conditions.
Temporary and Permanent Slopes
Temporary excavation 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 water 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 since they are continuously at the job site, able to observe the soil and
groundwater conditions encountered, and able to monitor the nature and condition of the 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 all temporary cuts be no steeper than 2 Horizontal to 1 Vertical
(2H: 1V). If groundwater seepage is encountered, we expect that flatter inclinations may be necessary.
We recommend that cut slopes be protected from erosion. Measures taken may include covering cut slopes
with plastic sheeting and diverting surface runoff away from the top of cut slopes. Excavated material
should not be stockpiled any closer than 10 feet from the top of the cuts. We do not recommend vertical
slopes for cuts deeper than 4 feet if worker access is necessary. We recommend that cut slope heights and
inclinations conform to WISHA/OSHA standards. If the above inclinations cannot be met due to site
constraints and/or worker access issues, we recommend that shoring be considered for temporary cuts. We
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Site Assessment NGA File No. 988717
16630 74 th Place West April 24, 2017
Edmonds, Washington Page 7
are available to provide specific recommendations for temporary shoring, if desired, once the foundation
design hasbeen finalized.
Permanent cut and fill slopes should be no steeper than 2H:1V. Permanent slopes should be planted and the
vegetative cover should be maintained until it is established. We should review plans for this project and
visit the site to evaluate any excavations that are deeper than about 4 feet.
Foundation Support
Conventional shallow spread foundations should be placed on medium dense or better native soils, or be
supported on structural fill or rock spalls extending to those soils. Medium dense soils should be
encountered approximately 3 to 5 feet below the ground surface on terraces based on our explorations. If
less dense soils are encountered at the 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 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
2015 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.
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 medium
dense or better native soils or structural fill extending to the competent native material. The foundation
bearing soil should be evaluated by a representative of NGA. 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 ½-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
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Site Assessment NGA File No. 988717
16630 74 th Place West April 24, 2017
Edmonds, Washington Page 8
(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
structural fill should be used to backfill against the
front of the footing. We recommend that the upper 1 foot of soil be neglected when calculating the passive
resistance.
Structural Fill
General:
Fill placed beneath foundations, concrete slabs, 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
Site Preparation and Grading
receive the fill should be suitably prepared as described in the subsection
of this report prior to beginning fill placement.
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 3 inches. All-weather structural fill
should contain no more than 5 percent fines (soil finer than U.S. No. 200 sieve, based on that fraction
passing the U.S. 3/4-inch sieve). The use of on-site soils as structural fill should be feasible, but will be
dependent on moisture content of the material at the time construction takes place. We should be retained
to evaluate proposed structural fill material prior to placement.
Fill Placement:
Following subgrade preparation, placement of structural fill may proceed. All fill
placements should be accomplished in uniform lifts up to 8 inches thick. Each lift should be spread evenly
and be thoroughly compacted prior to placement of subsequent lifts.
All structural fill underlying building areas, concrete floor slabs, 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 (Modified Proctor) procedure.
The moisture content of the soils to be compacted should be within about ± 2 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.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Site Assessment NGA File No. 988717
16630 74 th Place West April 24, 2017
Edmonds, Washington Page 9
Slab-on-Grade
Site Preparation and
Slabs-on-grade should be supported on subgrade soils prepared as described in the
Grading
subsection of this letter. We recommend that all floor slabs be underlain by at least six inches of
free-draining gravel with less than 3 percent by weight of the material passing the U.S. No. 200 Sieve 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 (including gravel-surfacing) subgrade preparation and structural filling where required, should
Site Preparation and Grading Structural Fill
be completed as recommended in the and subsections of
this letter. Pavement subgrade should be proof-rolled with a heavy, rubber-tired piece of equipment, to
identify soft or yielding areas that require repair.
Site Drainage
Surface Drainage:
The finished ground surface should be graded such that runoff is directed to an
appropriate stormwater discharge management system. Water should not be allowed to collect in any areas
where footings, slabs, or pavements are to be constructed. Final site grades should allow for drainage away
from structures. We suggest that the finished ground be sloped at a minimum gradient of 3 percent, for a
distance of at least 10 feet away from structures and access drives. Surface water from paved areas should
be collected and routed through an appropriate discharge system.
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 from the excavation and routed to a suitable discharge point. Water should not be
allowed to flow over the steep slope.
We recommend the use of footing drains around structures. Footing drains should be installed at least 1
foot below planned finished floor elevation. Footing drains should discharge into tightlines leading to an
appropriate collection and discharge point away from the slope, 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 Site Assessment NGA File No. 988717
16630 74 th Place West April 24, 2017
Edmonds, Washington Page 10
USE OF THIS REPORT
NGA has prepared this report for Mr. James Weis and his agents, for use in the planning and preliminary
design of a single-family residence on this site only. Additional geotechnical engineering analyses and
evaluations may be needed once a specific concept is developed to determine if it is compatible with
prevailing site conditions. Our scope does not include services related to construction safety precautions
procedures, except as specifically described in our letter for consideration in design. There are possible
variations in subsurface conditions between the explorations and also with time. Our 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.
All people who own or occupy homes on hillsides should realize that landslide movements are always a
possibility. The homeowner should periodically inspect the slope, especially after a winter storm. If distress
is evident, a geotechnical engineer should be contracted for advice on remedial/preventative measures. The
probability that land sliding will occur is substantially reduced by the proper maintenance of drainage
control measures at the site. Therefore, the homeowner should take responsibility for performing such
maintenance. Consequently, we recommend that a copy of our letter be provided to any future homeowners
if the property is sold.
We recommend that NGA be retained to provide additional analyses and evaluations during the design
phase and to provide monitoring and consultation services during construction to confirm that the
conditions encountered are consistent with expectations. NGA can provide recommendations for design
changes should the conditions revealed during the work differ from those anticipated, and to evaluate
whether or not construction 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 letter was
prepared. No other warranty, express 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 Site Assessment NGA File No. 988717
16630 74 th Place West April 24, 2017
Edmonds, Washington Page 11
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.
Carston T. Curd, GIT
Staff Geologist
Timothy D. Huntting, PE
Senior Engineer
CTC:TDH:sg
Seven Figures Attached
NELSON GEOTECHNICAL ASSOCIATES, INC.
VICINITY MAP
Not to Scale
Project
Site
N:\\2017 NGA Project Folders\\9887-17 Weis Residence Development Edmonds\\Drafting\\VM.dwg
Edmonds, WA
Nelson Geotechnical
Project Number
No.DateRevisionByCK
G
Weis Residence
Associates, Inc.
NA
988717
DPNCTC
14/19/17Original
Development
Geotechnical Engineers & Geologists
Vicinity Map
Figure 1
Snohomish County (425) 339-1669
17311-135th Ave. NE, A-500
Woodinville, WA 98072
Wenatchee/Chelan (509) 665-7696
(425) 486-1669 / Fax 481-2510
www.nelsongeotech.com
100
Approximate Scale: 1 inch = 50 feet
W
l
P
A'
h
t
4
7
50
Approximate location of tributary
HA-4
0
B'B
HA-3
Schematic Site Plan
HA-1
Reference: Site plan based on field measurements, observations, and aerial photo review.
HA-2
Number and approximate
N:\\2017 NGA Project Folders\\9887-17 Weis Residence Development Edmonds\\Drafting\\SP.dwg
location of hand auger
HA-5
Approximate locationApproximate location
of cross-section
of property line
LEGEND
Approximate location of
Stilthouse Creek
A
76th Ave W
A'
HA-1
A
Project Number Nelson Geotechnical
No.DateRevisionByCK
G
Weis Residence
Associates, Inc.
NA
988717
4/19/17OriginalDPNCTC
1
Development
Geotechnical Engineers & Geologists
Schematic Site Plan
Figure 2
17311-135th Ave. NE, A-500Snohomish County (425) 337-1669
Woodinville, WA 98072Wenatchee/Chelan (509) 665-7696
(425) 486-1669 / Fax 481-2510www.nelsongeotech.com
Stratigraphic conditions are interpolated between
the explorations. Actual conditions may vary.
East
200
350300
400250
350
A'
Elevations are arbitrary.
74th Pl W
300
NOTES:
2)
1)
Reference: Cross Section is based on field measurements using a hand-held clinometer and 100-ft tape measure.
250
Existing House
HA-1
200
Silty Sand (SM)
Distance (feet)
150
HA-2
100
Ponded water
Retaining Wall
N:\\2017 NGA Project Folders\\9887-17 Weis Residence Development Edmonds\\Drafting\\CS.dwg
?
76th Ave W
50
HA-5
HA-1
Exploration
?
Hand Auger Designation
A
0
Groundwater Level
Geologic Contact
During Exploration
(approximate)
250
300200
350
400
West
Arbitrary Elevation (feet)
Nelson Geotechnical
No.DateRevisionByCK
Project Number
G
Weis Residence
Associates, Inc.
NA
988717
4/19/17OriginalDPNCTC
1
Development
Geotechnical Engineers & Geologists
Cross-Section A-A'
Figure 3
437 East Penny Road
17311-135th Ave. NE, A-500
Woodinville, WA 98072
Wenatchee, WA 98801
(425) 486-1669 / Fax 481-2510
(509) 665-7696
Stratigraphic conditions are interpolated between
the explorations. Actual conditions may vary.
300
340
360
380320
North
140
B'
Elevations are arbitrary.
120
NOTES:
2)
1)
Reference: Cross Section is based on field measurements using a hand-held clinometer and 100-ft tape measure.
100
80
Distance (feet)
HA-4
60
Silty Sand (SM)
40
Existing House
N:\\2017 NGA Project Folders\\9887-17 Weis Residence Development Edmonds\\Drafting\\CS.dwg
?
20
HA-1
HA-3
Exploration
?
Hand Auger Designation
B
0
Groundwater Level
Geologic Contact
During Exploration
South
(approximate)
300
360340
380320
Arbitrary Elevation (feet)
Nelson Geotechnical
No.DateRevisionByCK
Project Number
G
Weis Residence
Associates, Inc.
NA
988717
4/19/17OriginalDPNCTC
1
Development
Geotechnical Engineers & Geologists
Cross-Section B-B'
Figure 4
437 East Penny Road
17311-135th Ave. NE, A-500
Woodinville, WA 98072
Wenatchee, WA 98801
(425) 486-1669 / Fax 481-2510
(509) 665-7696
UNIFIED SOIL CLASSIFICATION SYSTEM
GROUP
GROUP NAME
MAJOR DIVISIONS
SYMBOL
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
WITH FINES
SOILS
NO. 4 SIEVE
GC
CLAYEY GRAVEL
CLEAN
SW
WELL-GRADED SAND, FINE TO COARSE SAND
SAND
SAND
SP
POORLY GRADED SAND
MORE THAN 50 %
MORE THAN 50 %
RETAINED ON
OF COARSE FRACTION
SAND
SM
SILTY SAND
NO. 200 SIEVE
PASSES NO. 4 SIEVE
WITH FINES
SC
CLAYEY SAND
ML
SILT AND CLAY
SILT
FINE -
INORGANIC
CL
CLAY
GRAINED
LIQUID LIMIT
LESS THAN 50 %
ORGANIC
OL
ORGANIC SILT, ORGANIC CLAY
SOILS
MH
SILT OF HIGH PLASTICITY, ELASTIC SILT
SILT AND CLAY
INORGANIC
MORE THAN 50 %
CH
PASSES
CLAY OF HIGH PLASTICITY, FLAT CLAY
LIQUID LIMIT
NO. 200 SIEVE
N:\\2017 NGA Project Folders\\9887-17 Weis Residence Development Edmonds\\Drafting\\SC.dwg
50 % OR MORE
ORGANIC
OH
ORGANIC CLAY, ORGANIC SILT
HIGHLY ORGANIC SOILS
PT
PEAT
NOTES:
1) Field classification is based on visualSOIL MOISTURE MODIFIERS:
examination of soil in general
Dry - Absence of moisture, dusty, dry to
accordance with ASTM D 2488-93.
the touch
2) Soil classification using laboratory tests
Moist - Damp, but no visible water.
is based on ASTM D 2488-93.
Wet - Visible free water or saturated,
3) Descriptions of soil density or
usually soil is obtained from
consistency are based on
below water table
interpretation of blowcount data,
visual appearance of soils, and/or
test data.
Project Number Nelson Geotechnical
No.DateRevisionByCK
G
Weis Residence
Associates, Inc.
NA
988717
DPNCTC
14/19/17Original
Development
Geotechnical Engineers & Geologists
Soil Classification Chart
Figure 5
Snohomish County (425) 337-1669
17311-135th Ave. NE, A-500
Woodinville, WA 98072
Wenatchee/Chelan (509) 665-7696
(425) 486-1669 / Fax 481-2510
www.nelsongeotech.com
LOG OF EXPLORATION
DEPTH (FEET) USCSOIL DESCRIPTION
HAND AUGER ONE
0.0 –2.0DARK BROWN/BLACK SILTY FINE TO MEDIUM SAND WITH ORGANICS (TOPSOIL); (LOOSE;
MOIST)
2.0 –3.5SMBROWN SILTY FINE TO MEDIUM SAND; (LOOSE TO MEDIUM DENSE; MOIST)
SAMPLES WERE COLLECTED AT 1, 2, AND 3.5 FEET.
GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED.
HAND AUGER CAVING WAS NOT ENCOUNTERED.
HAND AUGER WAS TERMINATED AT 3.5 FEET ON 4/13/17 DUE TO A ROCK.
HAND AUGER TWO
0.0 –0.5DARK BROWN/BLACK SILTY FINE TO MEDIUM SAND WITH ORGANICS (TOPSOIL); (LOOSE;
MOIST)
0.5 –2.0SMBROWN/RED HUE SILTY FINE TO MEDIUM SAND WITH TRACE GRAVEL; (LOOSE TO MEDIUM
DENSE; MOIST)
2.0 –5.5SMBROWN SILTY FINE TO MEDIUM SAND; (MEDIUM DENSE; MOIST)
SAMPLES WERE COLLECTED AT 1.5, 2.5, AND 5 FEET.
GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED.
HAND AUGER CAVING WAS NOT ENCOUNTERED.
HAND AUGER WAS TERMINATED AT 5.5 FEET ON 4/13/17 DUE TO A ROCK.
HAND AUGER THREE
0.0 –1.25DARK BROWN/BLACK SILTY FINE TO MEDIUM SAND WITH ORGANICS (TOPSOIL); (LOOSE;
MOIST)
1.25 –3.0SMBROWN/DARK BROWN SILTY FINE TO MEDIUM SAND WITH TRACE GRAVEL AND ORGANICS;
(LOOSE TO MEDIUM DENSE; MOIST)
SAMPLE WAS COLLECTED AT 3 FEET.
GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED.
HAND AUGER CAVING WAS NOT ENCOUNTERED.
HAND AUGER WAS TERMINATEDAT 3 FEET ON 4/13/17 DUE TO A ROCK.
HAND AUGER FOUR
0.0 –1.75DARK BROWN/BLACK SILTY FINE TO MEDIUM SAND WITH ORGANICS (TOPSOIL); (LOOSE;
MOIST)
1.75 –3.5SMBROWN/TAN SILTY FINE TO MEDIUM SAND WITH TRACE GRAVEL; (LOOSE; MOIST TO WET)
SAMPLES WERE COLLECTED AT 1.5, 2.5, AND 4 FEET.
GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 2 FEET.
HAND AUGER CAVING WAS NOT ENCOUNTERED.
HAND AUGER WAS TERMINATED AT 3.5 FEET ON 4/13/17 DUE TO THE INABILITY TO REMOVE
MATERIAL WITH AUGER.
EAF:TDH:ctc NELSON GEOTECHNICAL ASSOCIATES, INC.
FILE NO9887-17
FIGURE6
LOG OF EXPLORATION
DEPTH (FEET) USCSOIL DESCRIPTION
HAND AUGER FIVE
0.0 –0.5DARK BROWN/BLACK SILTY FINE TO MEDIUM SAND WITH ORGANICS (TOPSOIL); (LOOSE;
MOIST)
0.5 –1.5SMBROWN/TAN SILTY FINE TO MEDIUM SAND WITH TRACE GRAVEL; (LOOSE; WET)
SAMPLES WERE COLLECTED AT 1.0 FEET.
GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 0.75 FEET.
HAND AUGER CAVING WAS NOT ENCOUNTERED.
HAND AUGER WAS TERMINATED AT 1.5 FEET ON 4/13/17 DUE TO THE INABILITY TO REMOVE
MATERIAL WITH AUGER.
EAF:TDH:ctc NELSON GEOTECHNICAL ASSOCIATES, INC.
FILE NO9887-17
FIGURE7