10506 235TH PL SW.PDFlill I . iiiiiii3917
10506 235TH PL SW
0
ADDRESS:
TAX ACCOUNT/PARCEL NUMBER: t---Z
BUILDING PERMIT (NEW STRUCTURE):
COVENANTS (RECORDED)
CRITICAL AREAS :�CA"-,gDETERMINATION: ❑ Conditional Waiver ❑ Study RequiredXWaiver
DISCRETIONARY PERMIT #'S:
DRAINAGE PLAN DA'
PARKING AGREEMENTS DATED:
EASEMENT(S) RECORDED FOR:
PERMITS
PLANNING DATA CHECKLIST DATED:
SCALED PLOT PLAN DATED:
SEWER LID FEE $:
SHORT PLAT FILE: LOT:
SIDE SEWER AS BUILT DATED:
SIDE SEWER PERMIT(S) #:
GEOTECH REPORT DATED:
STREET USE / ENCROACHMENT PERMIT #:
WATER METER TAP CARD DATED:
LID #:
BLOCK:
LATEMP\DST's\Forms\Street File Checklist.doc
** 600 ' 39bd 1ti101 **
1* •
Critical Areas Checklist CA File Nod?00'7�-'
Site Information (soils/topography/hydrology/vegetation)
1. Site Address/Location: 3 5- 'Al s r` J
2. Property Tax Account Number: -7--% D o 6 7-o / 0 0
3. Approximate Site Size (acres or square feet): 2
4. is this site currently developed? Y yes; no.
If yes; how is site developed?
5. Describe the general site topography. Check all that apply.
^� Flat: less than 5-feet elevation change over entire site.
Rolling slopes on site generally less than 15% (a vertical rise of 10-feet over a horizontal
distance of 66-feet).
Hilly: slopes present on site of more than 15% and less than 30% (a vertical rise of 10-feet
over a horizontal distance of 33 to 66-feet).
Steep: grades of greater than 30% present on site (a vertical rise of 10-feet over a horizontal
distance of less than 33-feet).
Other (please describe):
6. Site contains areas of year-round standing water: t7 0 ; Approx. Depth:
7. Site contains areas of seasonal standing water: /10 ; Approx. Depth
What season(s) of the year?
S. Site is in the floodway J'i D floodplain of a water course.
9. Site contains a creek or an area where water flows across the grounds surface? Flows are year-round?
)I o Flows are seasonal? A_ (What time of year? 01 15 ).
10. Site is primarily: forested : meadow ; shrubs ; mixed x
urban landscaped ()awn, shrubs etc)
11. Obvious wetland is present on site: N Ip
For City Staff Use Only
1. Plan Check Number,p>irable?
2 Sibe is Zoned? C51,
_
j 3 SCS mapped soli type(s)? Qf t� rG ivy GnC CvM P
4. Critical Areas inventory or C.A map indicates Critical Area on site?
C u n j (r cif 1-01 ", Sy v Z► . f'°Ss b % J "
5. Site within designated earth subsidence landslide hazard area? A112
DETERMINATION
Reviewed
Critical Amas ChecWisL&G/2.17.2004
!�ara • �nu�
6
#]P20
City of Edmonds
Development Services Department
Planning Division
Phone: 425.771.0220
Fax: 425.771.0221
The Critical Areas Checklist contained on this form is to
be filled out by any person preparing a Development
Permit Application for the City of Edmonds prior to
his/her submittal of the application to the City.
The purpose of the Checklist is to enable City staff to
determine whether any poteatW Critical Areas are, or
may be, present on the subject property. The information
needed to complete the Checklist should be easily
available from observations of the site or data available at
City Hall (Critical areas inventories, maps, or soil
surveys).
0
Date Received: la
City Receipt#:
Critical Areas File #*C-RA DOD7401rog
Critical Areas Checklist Fee:
Date Mailed to Applicant:
A property owner, or his/her authorized representative,
must fill out the checklist, sign and date it, and submit it
to the City. The City will review the checklist, make a
precursory site visit, and make a determination of the
subsequent steps necessary to complete a development
permit apptication_
Please submit a vicinity map, along with the signed copy
of this form to assist City staff in finding and locating the
specific piece of property described on this form. In
addition, the applicant shall include other pertinent
information (e.g. site plan, topography map, etc.) or
studies in conjunction with this Checklist to assistant staff
in completing their preliminary assessment of the site.
I` The undersigned applicant, and his/her/its heirs, and assigns, in consideration on the processing of the application agrees
to release, indemnify, -defend and hold the City of Edmonds harmless from any and all damages, including reasonable
attorney's fees, arising from any action or infraction based in whole or pad upon false, misleading, inaccurate or
incomplete information furnished by the applicant, his/her/its agents or employees.
By my signature, i certify that the information and exhibits herewith submitted are true and correct to the best of my
1 1' 'on on the behalf of the owner as listed below.
am authorized to fit knowledge and that 1 0
SIGNATURE of APPLICANT/AGMfr DATE
Property Owner's Authorization
By my signature, I ce ' I have authorized the above Applicant/Agent to apply for the subject land use application,
and grant my permissio for the publiSoffi an the staff of the City of Edmonds to enter the subject property for the
purposes of inspection Sathis li n.
SIGNATURE OF OWNER DATE Zi 'D Z
Owner/Appileant:
�OY► nj�'e r K ri14 �
Name
Street Address
City State Zip
Telephone: 266 77 `7-91'`�
Email address (optional):
Ap 'cant Rep • tiv
Name p
S t Address
City rc✓f - S '/, Zip
Telephone: ` s, — `� O
Email Address (optional):
LIU & ASSOCIATES, INC.
Geotechnical Engineering Engineering Geology Earth Science
April 8, 2008
Mr. Ron Steinman
Boulevard Park Place
2805 South 125 h Street
Seattle, WA 98168
Dear Mr. Steinman:
Subject: Geotechnical Engineering Study
Proposed 2-Lot Short Plat
10506 — 235 b Place SW
Edmonds, Washington
L&A Job No. 8AO31
INTRODUCTION
APR a 8 2098
BUILDING DEPT-
We have completed a geotechnical engineering study for the subject plat site located at the above
address in Edmonds, Washington. The general location of the plat site is shown on Plate 1 —
Vicinity Map. We understand that the proposed development for the site is to plat it into two
single-family residential building lots, with a new residence to be constructed on each lot. The
purpose of this study is to characterize the subsurface conditions of the site, evaluate feasibility
of onsite stormwater disposal, and provide geotechnical recommendations for onsite stormwater
disposal systems (if feasible), grading, erosion mitigation, surface and ground water drainage
control, and foundation design and construction for the proposed development of the site.
Presented in this report are our findings, conclusion and recommendations.
PROJECT DESCRIPTION
For our use in this study, you provided us with a topographic survey and plat plan of the subject
site. The proposed development of the site is to plat it into two lots. We understand that the
existing house on Lot 1 (the east lot) will be demolished, and that a new residence will be
19213 Kenlake Place NE - Kenmore, Washington 98028
Phone (425) 483-9134 - Fax (425) 486-2746
�iREE'� FILE
April 8, 2008
Proposed 2-Lot Short Plat
L&A Job No. 8AO31
Page 2
constructed on each of the two lots. The terrain within the site is mostly gently to very gently
Sloped. We understand that _grading or the proposed development.,of.the__site_.will .generally
follow the existing contours with minimal cut and fill required. The new residences will be
accessed via paved driveways from 235 h Place SW. Storm runoff collected over impervious
surfaces of each of the two new residences is to be disposed onsite into an individual infiltration
trench along the north side of the site.
SCOPE OF SERVICES
To achieve the above purposes, our scope of services for this study comprises specifically the
following:
1 Review the geologic and soil conditions at the site based on a published geologic map.
2. Explore the subsurface conditions of the site with backhoe test pits to a firm bearing soil
stratum or to the maximum depth (about 10 feet) capable of by the backhoe used in
excavating the test pits, whichever occurs first.
3. Perform necessary geotechnical analyses, evaluate feasibility of onsite stormwater
disposal, and provide geotechnical recommendations for onsite stormwater disposal (if
feasible), grading, erosion mitigation, surface and ground water drainage control,
foundation design and construction, etc., based on subsurface conditions encountered in
the test pits and results of our geotechnical analyses.
4. Prepare a written report to present our findings, conclusions, and recommendations.
SITE CONDITIONS
SURFACE CONDITIONS
The site is a rectangle -shaped tract of land. It is situated on a broad, very gentle, north -trending
valley in southwestern Edmonds. The site is bounded by 235th Place SW to the north, backed
LIU & ASSOCIATES, INC.
April 8, 2008
Proposed 2-Lot Short Plat
L&A Job No. 8AO31
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into a wooded vacant land to the south, and adjoined by residential developments to the east and
west. It has a frontage of about 177 lineal_ feet along 2351` Place SW and is about 145 feet deep.
There is a low-lying area traversing roughly southwest -northeast through the middle of the site.
The terrain within the site generally slopes gently to very gently at about 2.5 to 12.5 percent
grade from its northwest and southeast corners down towards this low-lying area, except at the
northwest corner of the site where it steepens up to about 30 percent grade. The site is currently
occupied by anexisting single-family residence in about its northwestern quarter. The area
surrounding the existing house is mostly covered by lawn grass and shrubs. The remaining area
of the site is dotted by tall, mature, evergreen trees with thick underbrush.
GEOLOGIC SETTING
The Geologic Map of the Edmonds East and Part of the Edmonds West Quadrangles,
Washington, by James P. Minard, published by U. S. Geological Survey in 1983, was referenced
for the geologic and soil conditions at the residence site. According to this publication, the
surficial soil unit at and in the vicinity of the site is mapped as Advance Outwash (Qva).
The geology of the Puget Sound Lowland has been modified by the advance and retreat of
several glaciers in the past and subsequent deposits and erosion. The latest glacier advanced to
the Puget Sound Lowland is referred to as the Vashon Stade of the Fraser Glaciation, which has
occurred during the later stages of the Pleistocene Epoch and retreated from the region some
14,500 years ago.
The advance outwash soil unit is composed of stratified sand and gravel with minor amounts of
silt and clay, deposited by the meltwater of and subsequently overridden by advancing glacial ice.
Due to their generally granular composition, the advance outwash deposits are of moderately
high permeability and drains well. Because they were glacially overridden, the advance outwash
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April 8, 2008
Proposed 2-Lot Short Plat
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deposits are generally dense to very dense in its natural, undisturbed state, except the top 2 to 4
_ _ . _ feet,_where_ exposed -on. slopes_which..may be_ weathered_to a loose to medium. -dense- state.__ The- _
advance outwash deposits can stand in steep natural slopes and man-made cuts for extended
period when undisturbed. Where exposed on slopes with poor vegetation cover and subjected to
storm runoff or groundwater seepage, the advance outwash deposits may be gradually eroded and
slough and redeposit to a flatter inclination. The underlying fresh advance outwash deposits in
their native, undisturbed state can provide good foundation support with little settlement
expected for light to moderate residential structures.
SOIL CONDITIONS
Subsurface conditions of the site were explored with six test pits. The test pits were excavated
on March 26, 2008, to depths from 6.5 to 7.0 feet with a track -mounted backhoe. The
approximate locations of the test pits are shown on Plate 2 - Site and Exploration Location Plan.
The test pits were located with either a tape measure or by visual reference to existing
topographic features in the field and on the topographic survey map, and their locations should be
considered only accurate to the measuring method used.
A geotechnical engineer from our office was present during subsurface exploration, who
examined the soil and geologic conditions encountered and completed logs of test pits. Soil
samples obtained from each soil unit in the test pits were visually classified in general
accordance with United Soil Classification System, a copy of which is presented on Plate 3.
Detailed descriptions of soils encountered during site exploration are presented in test pit logs on
Plates 4 through 6.
The soil conditions encountered by the test pits are quite uniform throughout the site. The test
pits encountered a layer of loose organic topsoil, from 8 to 15 inches thick. The topsoil is
underlain by a layer of weathered soils of brown to light -brown, medium -dense, slightly silty,
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April 8, 2008
Proposed 2-Lot Short Plat
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fine to medium sand, with various amount of gravel and occasional cobble, from 1.5 to 3.2 feet
thick. Underlying this layer of weathered-soils.to_the_depths.explored.is a fresh advance outwash
deposit of light -gray, medium -dense to dense, fine to medium sand with a trace of gravel.
GROUNDWATER CONDITION
Groundwater seepage was not encountered in any of the test pits excavated on the site. The layer
of weathered soils and the underlying fresh advance outwash deposit are both of high
permeability, and would allow stormwater to seep through easily.- It is our opinion that
groundwater under the site should be at such depth that it would have minimal impact on the
construction of the proposed development of the site or on the proper functioning of the proposed
infiltration trenches.
DISCUSSIONS AND RECOMMENDATIONS
GENERAL
Based on the soil and groundwater conditions encountered in our subsurface explorations, it is
our opinion that the site is suitable for the proposed development from the geotechnical
engineering viewpoint, provided that the recommendations in this report are fully implemented
and observed during construction.
The surficial unsuitable soils, including topsoil and loose soils in the root zone, should be
completely stripped down to the light -gray fresh advance outwash deposit within the building
pads of the proposed new residences, and down to the brown to light -brown weathered soils in
areas of the driveways. If properly prepared, the fresh advance outwash soils should be capable
of providing adequate foundation support to the proposed new residences, and the weathered
soils should be able to adequately support the driveways. The gravelly sandy soils of the
weathered soil layer and the underlying advance outwash deposit are of high permeability. These
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soil layers will be able to adequately support infiltration trenches to dispose onsite storm runoff
collected over_ impervious surfaces of the new residences.
GEOLOGIC HAZARDS AND AUTIGATION
Landslide Hazard
The terrain of the subject site is generally gently to very -gently sloped, and the site is underlain at
shallow depth by medium -dense to dense, fresh, advance outwash soils of moderate to high shear
strength. Therefore, the potential for deep-seated landslides to occur on the , site should be
minimal.
Erosion Hazard
The topsoil and loose surficial soils mantling the site are of low resistance against erosion. The
erosion potential, however, will be greatly reduced by the mostly gentle to very -gentle terrain of
the site. To further mitigate the erosion potential of the site, the vegetation cover outside of
construction limits should be preserved and maintained. Unpaved exposed ground within the site
resulted from construction activities should be a soon as possible. Concentrated stormwater
should not be disposed uncontrolled onto the ground within the site. Stormwater over
impervious surfaces, such as roofs and paved driveways, should be captured with underground
drain line systems connected to roof downspouts and catch basins installed in the driveways.
Water collected by these underground drainage systems should be tightlined to discharge into a
storm sewer or a suitable stormwater disposal facility, such as infiltration trenches.
Seismic Hazard
The Puget Sound region is in an active seismic zone. The site of mostly gentle to very -gentle
terrain is underlain at shallow depth by medium -dense to dense, fresh, advance outwash soils of
moderate to high shear strength. There is also a lack of extensive, static, groundwater table at
shallow depth under the site. Therefore, the potential for seismic hazards, such as liquefaction
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and lateral soil spreading, to occur on the site should be minimal. The proposed new residences,
however, should be_ designed_ for seismic. forces induced by potential strong earthquakes. Based _____
on the soil conditions encountered by the test pits, it is our opinion that Seismic Use Group I and
Site Class D should be used in the seismic design of the proposed residences in accordance with
the 2003 International Building Code (IBC).
SITE PREPARATION AND GENERAL GRADING
The vegetation within construction limits should be cleared and their roots thoroughly grubbed.
The existing house on the site to be demolished should also have its foundations removed.
Surficial topsoil and unsuitable soils in the root zone should be stripped down to the layer of
weathered soils within the driveways, and down to the fresh advance outwash soils within the
building pads of the new residences. The exposed soils in excavated areas should be compacted
to a non -yielding state with a vibratory roller compactor and proof -rolled with a fully loaded
dumptruck or watertruck. The onsite surficial soils contain a high percentage of fines and are
sensitive to moisture. A layer of clean quarry spalls placed over excavated areas and areas of
frequent traffic, such as entrance to the site, may be required to protect the subgrade soils from
disturbance by construction traffic.
TEMPORARY EROSION AND DRAINAGE CONTROL
During construction, storm runoff, if any, should be intercepted with ditches or interceptor trench
drains, as required, with collected water discharged into temporary storage and settling ponds.
Only clean and clear water in the settling pond may be released into a nearby storm inlet, if
available. The storm inlet should be covered with a filter sock and the filter socks should be
cleaned frequently to prevent clogging. The filter socks should be removed after the completion
of construction work for the proposed development of the site. Silt fences should be erected
along the downhill boundaries of the site to prevent sediment from being transported onto
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April 8, 2008
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adjoining properties or the street by storm runoff. The bottom of filter fabric of the silt fence
should be anchored in a_trench filled with gravel._
EXCAVATION AND FILL SLOPES
Under no circumstance should excavation slopes be greater than the limits specified by local,
state and federal safety regulations if workers have to perform construction work in excavated
areas. Unsupported temporary cuts greater than 4 feet in height should be no steeper than 1H:1 V
in the surficial topsoil and weathered soils and no steeper than 3/4H:1 V in the underlying
medium -dense to dense, fresh, advance outwash soils. Permanent cut banks, if any, should be no
steeper than 2-1/4H:1V in the surficial topsoil and weathered soils, and no steeper than 2H:1 V in
the underlying medium -dense to dense, fresh, advance outwash soils.
Permanent fill embankments required to support structural or traffic load, if any, should be
constructed with compacted structural fill placed over undisturbed, proof -rolled, medium -dense
to dense, fresh, advance outwash soils after the surficial unsuitable soils are completely stripped.
Permanent fill placed over sloping ground steeper than 20% grade should be structurally
supported. Sloping ground steeper than 15% grade should be benched with vertical steps not
exceeding 4 feet after stripping of the surficial unsuitable soils and prior to constructing
permanent fill embankments. The slope of permanent fill embankments should be no steeper
than 2H:1 V. Upon completion, the sloping faces of permanent fill embankments should be
thoroughly compacted to a non -yielding state with a hoe -pack.
The soil units and stability of cut banks should be verified by a geotechnical engineer during
excavation. The above recommended cut and fill slopes are under the assumption that
groundwater seepage will not be encountered during construction. If groundwater seepage is
encountered, the construction should be immediately halted and the slope stability re-evaluated.
The slopes may have to be flattened and other measures taken to stabilize the slopes. Surface
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runoff should not be allowed to flow uncontrolled over the top of cut or fill slopes. Permanent
cut slopes or fill embankments should be -vegetated _as.soon as possible for long-term stability,
and should be covered with clear plastic sheets, as required, to protect them from stormwater
until the vegetation is fully established.
STRUCTURAL FILL
Structural fill is the fill that supports structural or traffic load. Structural fill should consist of
clean soils free of organic and other deleterious substances and with particles not larger than four
inches. Structural fill should have a moisture content within one percent of its optimum moisture
content at the time of placement. The optimum moisture content is the water content in the soil
that enable the soil to be compacted to the highest dry density for a given compaction effort. The
onsite, clean, silty fine sand soils may be used for structural fill only if their moisture content can
be controlled to near their optimum moisture content at the time of placement. Imported material
to be used as structural fill should be clean, free -draining, granular soils containing no more than
5 percent by weight finer than the No. 200 sieve based on the fraction of the material passing No.
4 sieve, and should contain particles no larger than four inches.
The ground over which structural fill is to be placed should be prepared in accordance with
recommendations in the SITE PREPARATION AND GENERAL GRADING and
EXCAVATION AND FILL SLOPES sections of this report. Structural fill should be placed in
lifts no more than 10 inches thick in its loose state, with each lift compacted to a minimum
percentage of the maximum dry density determined by ASTM D1557 (Modified Proctor Method)
as follows:
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April 8, 2008
Proposed 2-Lot Short Plat
L&A Job No. 8A031
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Application
-- Within building pads and under foundations
Roadway/driveway subgrade
Retaining wall backfill
Utility trench backfill
BUILDING FOUNDATIONS
% of Maximum Dry Density
- _ 95%. — --
95% for top 3 feet and 90% below
92%
95% for top 4 feet and 90% below
Conventional footing foundations may be used to support the proposed new residences. The
footing foundations should be placed on or into undisturbed, medium -dense to dense, fresh,
advance outwash soils, or on compacted structural fill constructed over these competent basal
soils. To reach the fresh advance outwash soils, excavation depths of 3.0 to 4.0 feet below
existing grade would be required. Footing bearing soils exposed at bottom of footing trenches
should be compacted to a non -yielding state with a vibratory compactor, and should be covered
and protected with a minimum 4-inch layer of compacted 2-inch-minus crushed rock as required.
Water should not be allowed to accumulate in excavated footing trenches. Disturbed soils in
footing trenches should be completely removed or thoroughly re -compacted prior to pouring
concrete for the footings.
If the above recommendations are followed, our recommended design criteria for footing
foundations are as follows:
s Allowable soil bearing pressure, including dead and live loads, should be no greater than
3,000 psf for footings poured on or into the undisturbed, fresh, medium -dense to dense,
fresh, advance outwash soils, and no more than 2,500 psf on structural fill constructed
over these competent basal soils. The footing bearing soils should be verified onsite by a
geotechnical engineer after the footing trenches have been excavated and before the
footings are poured.
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April 8, 2008
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• The minimum depth to bottom of perimeter footings below adjacent final exterior grade
should be no less than 18 inches. The minimum depth to bottom of the interior footings
below top of floor slab should be no less than 12 inches.
• The minimum width should be no less than 16 inches for continuous footings, and no less
than 24 inches for individual footings, except those footings supporting light -weight
decks or porches.
A one-third increase in the above recommended allowable soil bearing pressure may be used
when considering short-term, transitory, wind or seismic loads. For footing foundations designed
and constructed per recommendations above, we estimate that the maximum total post -
construction settlement of the buildings should be 3/4 inch or less and the differential settlement
across building width should be 1/2 inch or less.
Lateral loads on buildings can be resisted by the friction force between the foundations and the
subgrade soils or the passive earth pressure acting on the below -grade portion of the foundations.
For the latter, the foundations must be poured "neat" against undisturbed soils or backfilled with
a clean, free -draining, compacted structural fill. We recommend that an equivalent fluid density
(EFD) of 325 pcf (pounds per cubic foot) for the passive earth pressure be used for lateral
resistance. The above passive pressure assumes that the backfill is level or inclines upward
behind the foundations for a horizontal distance at least twice the depth of the foundations below
final grade. A coefficient of friction of 0.60 between the foundations and the subgrade soils may
be used. These are unfactored values, and a proper factor of safety should be used in calculating
the resisting forces against lateral loads on the buildings.
BASEMENT AND RETAINING WALLS
Basement walls restrained horizontally at the top are considered unyielding and should be
designed for a lateral soil pressure under the at -rest condition; while retaining walls free to move
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April 8, 2008
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at the top should be designed for a lateral soil pressure under the active condition. We
recommend that a lateral soil pressure_ of 45_ pcf EFD be used for the design of basement walls
with level or descending backslope and 35 pcf EFD for retaining walls with level or descending
backslope. For ascending backslopes, an additional pressure of 0.75 pcf EFD per degree of the
angle of backslopes above the horizontal should be added to the above recommended pressures
for the design of basement and retaining walls. To counter the above active or at -rest pressure, a
passive lateral soil pressure of 325 pcf EFD may be used, except that the passive pressure within
the top 12 inches of the finish subgrade should be ignored. The above passive pressure assumes
that the backfill is level or inclines upward away from the walls. The above lateral soil pressures
are under the assumption that groundwater behind the walls is fully drained. To resist against
sliding, the friction force between the footings and the subgrade soils may be calculated based on
a coefficient of friction of 0.60. The above soil parameters are ultimate values, and proper
factors of safety should be used in the design of the basement and retaining walls against sliding
and overturning failures. Basement walls or retaining walls may be supported on footing
foundations seated on or into the underlying medium -dense to dense, fresh, advance outwash
soils with an allowable soil bearing pressure not to exceed 3,000 psf.
A vertical drainage blanket consisting of at least 12-inch-thick free -draining pea gravel or washed
gravel should be placed against basement and retaining walls to prevent accumulation of
groundwater behind and buildup of hydrostatic pressure against the walls. The remaining
backfill behind the vertical drainage blanket should consist of structural fill constructed per
recommendations in the STRUCTURAL FILL section of this report. The top 12 inches of
backfill should consist of compacted, clean, onsite soils. The backfill material for the basement
and retaining walls should be compacted with a hand -operated compactor. Heavy compaction
equipment should not be allowed closer to the walls than a horizontal distance equal to the wall
height. A footing drain, as recommended in the DRAINAGE CONTROL section of this report,
should also be provided for basement and retaining walls.
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April 8, 2008
Proposed 2-Lot Short Plat
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SLAB -ON -GRADE FLOORS
Slab -on -grade floors, if used, should be placed on firm subgrade soils prepared as outlined in the
SITE PREPARATION AND GENERAL EARTHWORK and the STRUCTURAL FILL sections
of this report. Where moisture control is critical, the slab -on -grade floors should be placed on a
capillary break which is in turn placed on the compacted subgrade. The capillary break should
consist of a minimum four -inch -thick layer of free -draining gravel or crushed rock containing no
more than 5% by weight passing the No. 4 sieve. We recommend that a vapor barrier, such as a
6-mil plastic membrane, be placed over the capillary break to keep moisture from migrating
upwards.
DRIVEWAY PAVEMENT
Performance of driveway pavement is critically related to the conditions of the underlying
subgrade soils. We recommend that the subgrade soils under the driveways be treated and
prepared as described in the SITE PREPARATION AND GENERAL EARTHWORK and
STRUCTURAL FILL sections of this report. Topsoil and unsuitable soils in the root zone
should be stripped down to medium -dense weathered soils within the footprints of driveways.
Prior to placing base material, the exposed subgrade soils should be compacted to a non -yielding
state with a vibratory compactor and proof -rolled with a piece of heavy construction equipment,
such as a fully -loaded dumptruck or watertruck. Any areas with excessive flexing or pumping
should be over -excavated and re -compacted or replaced with compacted structural fill.
We recommend that a minimum 4-inch layer, compacted, crushed rock base (CRB), consisting of
7/8-inch crushed rock, be constructed over the above prepared subgrade soils. This crushed rock
base should be topped by 3-inch-thick Class B asphalt concrete (AC) or 4-inch-thick concrete
pavement.
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April 8, 2008
Proposed 2-Lot Short Plat
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Page 14
ONSITE STORMWATER DISPOSAL
Feasibility of Onsite Stormwater Disposal
Infiltration trenches to be constructed along the south side of the site are proposed for stormwater
disposal for the new residences. The predominantly sandy soils of the layer of weathered soils
and the underlying fresh advance outwash deposit are of high permeability and will be able to
adequately support infiltration trenches for onsite stormwater disposal.
Design of Infiltration Trenches
The advance outwash soil unit shown on the above -reference geologic map and encountered by
the test pits is also mapped as "Soil Type 17 — Everett Gravelly Sandy Loam 0 to 8 percent
slopes", according to Soil Map Sheet 56 in the Soil Survey of Snohomish County Area,
Washington, published by United States Department of Agriculture, Soil Conservation Services
(SCS). Table 14 in this publication lists the permeability of this soil type to be from 6.0 to 20.0
iph (inches per hour). Based on our experience and infiltration tests conducted in this soil unit,
the in -situ infiltration rate in this clean fine to medium sand deposits with various amount of
gravel and occasional cobble should be in the range from 40 to 80 iph. We recommend that an
infiltration rate not to exceed 7.5 iph be used for the design and sizing of the infiltration trenches
to be used to dispose stormwater for the new residences.
Construction of Infiltration Trenches
The infiltration trenches should be located on the downhill side of adjacent buildings, and should
be set back at least 5 feet from the buildings and property lines. Stormwater collected over
impervious surfaces should be routed into an oil -water separator/sediment control structure
before being discharged into the infiltration trenches.
Our recommendations for construction of the infiltration trenches with a single dispersion pipe is
presented on Plate 7. The infiltration trenches should be at least 24 inches wide. The bottom of
LIU & ASSOCIATES, INC.
April 8, 2008
Proposed 2-Lot Short Plat
L&A Job No. 8AO31
Page 15
infiltration trenches should be excavated at least 6 inches into the underlying fresh advance
outwash deposit which lies about-3 to 4 _feet below the existing ground surface. The side walls of
the trenches should be lined with a layer of non -woven filter fabric. The trenches are then filled
with clean washed 3/4 to 1-1/2 inch gravel or crushed rock to within about 8 inches of the finish
grade. The dispersion pipes should be constructed of 4-inch rigid or 6-inch flexible perforated
PVC pipes and laid level in the gravel or crushed rock filled trench at about 12 inches below the
top of trenches. At such elevation, the dispersion pipes should have sufficient separation from
winter high groundwater level. The gravel or crushed rock fill should be densified to a non -
yielding state with a concrete vibrator. The top of the gravel or crushed rock fill should also be
covered with the filter fabric liner. The remaining trenches should then be filled with compacted
onsite clean sandy soils.
DRAINAGE CONTROL
Building Footprint Excavation
Excavation of building footprints for the proposed new residences, if encountering groundwater,
should have the bottom of excavation sloped and ditches excavated along the bases of cut banks
to direct groundwater seepage to flow into a sump pit from which water can be pumped out of
the pit into a nearby storm inlet. A layer of 2-inch crushed rocks should be placed over firm
subgrade soils under footings, as required, to protect the soils from disturbance by construction
equipment and foot traffic. This crushed rock base should be built to a few inches above
groundwater level, but not less than 6 inches thick. The crush rock base should be compacted in
12-inch lifts to a non -yielding state with a vibratory mechanical compactor.
Building Footing Drains
A subdrain should be installed around the perimeter footings of each of the proposed new
residences to minimize accumulation of groundwater under the buildings. The subdrains should
consist of a 4-inch-minimum-diameter, perforated, rigid, drain pipe, laid a few inches below the
LIU & ASSOCIATES, INC.
April 8, 2008
Proposed 2-Lot Short Plat
L&A Job No. 8AO31
Page 16
bottom of perimeter footings. The trenches and the drain lines should have a sufficient gradient
(0.5% minimum) to generate flow by gravity. The drain lines should be embedded in washed
gravel completely wrapped in non -woven filter fabric to within about 12 inches of finish grade.
The remaining trenches may be backfilled with on -site impervious soils. Water collected by the
perimeter footing subdrains should be tightlined, separately from the roof and surface stormwater
drain systems, to discharge into a storm drain or a suitable stormwater disposal facility, such as
infiltration trenches.
Runoff Over Impervious Surfaces
Storm runoff over impervious surfaces, such as roofs and paved driveways, should be collected
by underground drain line systems connected to downspouts and by catch basins. Stormwater
thus collected should be tightlined to discharge into a storm drain or a suitable stormwater
disposal facility, such as infiltration trenches. .
Surface Drainage
Water should not be allowed to stand in any areas where footings, on -grade -slabs, or pavement is
to be constructed. Finish ground surface, except paved areas, should be graded to direct surface
runoff away from the proposed buildings. We recommend the finish ground be sloped at a
gradient of 3 percent minimum for a distance of at least 10 feet away from the buildings, except
in the areas to be paved.
Cleanouts
Sufficient number of cleanouts at strategic locations should be provided. for the underground
drain line systems. The underground drain line systems should be maintained periodically to
prevent clogging.
LIU & ASSOCIATES, INC.
April 8, 2008
Proposed 2-Lot Short Plat
L&A Job No. 8AO31
Page 17
LUMTATIONS
This report -has been prepared for the specific application to the subject project for the exclusive
use by Mr. Ron Steinman and his associates, representatives, consultants and contractors. We
recommend that this report, in its entirety, be included in the project contract documents for the
information of the prospective contractors for their estimating and bidding purposes and for
compliance to the recommendations in this report during construction. The conclusions and
interpretations in this report, however, should not be construed as a warranty of the subsurface
conditions. The scope of this study does not include services related to construction safety
precautions and our recommendations are not intended to direct the contractor's methods,
techniques, sequences or procedures, except as specifically described in this report for design
considerations.
Our recommendations and conclusions are based on soil conditions encountered in the test pits,
our engineering analyses, and our experience and engineering judgment. The conclusions and
recommendations are professional opinions derived in a manner consistent with the level of care
and skill ordinarily exercised by other members of the profession currently practicing under
similar conditions in this area. No warranty, expressed or implied, is made.
The actual subsurface conditions encountered during construction may vary from those
encountered in the test pits. The nature and extent of such variations may not become evident
until construction starts. If variations occur then, we should be retained to re-evaluate the
recommendations of this report, and to verify or modify them in writing prior to further
construction.
LIU & ASSOCIATES, INC.
April 8, 2008
Proposed 2-Lot Short Plat
L&A Job No. 8AO31
Page 18
CLOSURE
We are pleased to be of service to you on this project. Please feel free to call us if you- have any . _
questions regarding this report or need further consultation.
Seven plates attached
Yours very truly,
LIU & ASSOCIATES, INC.
J. S. (Julian) Liu, Ph.D., P.E.
Consulting Geotechnical Engineer
LIU & ASSOCIATES, INC.
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VICINITY MAP
g ru & ASS®C* ffAT ES9 WC.
2-LOT SHORT PLAT
10506 - 235TH PLACE SW
EDMONDS, WASHINGTON
_
Geotechnical Engineering • Engineering Geology Earth Science
JOB NO. BA031 I DATE 4/4/2008 I PLATE 1
Dow
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ILIU & ASSOCIATES, OTC
Geotechnical Engineering _ Engineering Geology • Earth Science
SITE AND EXPLORATION LOCATION PLAN
2-LOT SHORT PLAT
10506 - 235TH PLACE SW
EDMONDS, WASHINGTON
JOB NO. 8AO31 I DATE 4/4/2008 1 PLATE 2
UNIFIED SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS
GROUP
GROUP NAME
SYMBOL
GRAVEL
CLEAN
GW
WELL -GRADED GRAVEL, FINE TO COARSE GRAVEL
GP
POORLY -GRADED GRAVEL
COARSE-
MORE THAN 50% OF
GRAVEL
GRAVEL WITH
GM
SILTY GRAVEL
GRAINED
COARSE FRACTION
SOILS
RETAINED ON NO.4 SIEVE
FINES
GC
CLAYEY GRAVEL
SAND
CLEAN
SW
WELL -GRADED SAND, FINE TO COARSE SAND
SP
POORLY -GRADED SAND
MORE THAN 50%
MORE THAN 50% OF
SAND
SAND WITH
SM
SILTY SAND
RETAINED ON THE
COARSE FRACTION
NO.200 SIEVE
PASSING NO.4 SIEVE
FINES
SC
CLAYEY SAND
FINE-
SILT AND CLAY
INORGANIC
ML
SILT
CL
CLAY
GRAINED
LIQUID LIMIT
ORGANIC
OL
ORGANIC SILT, ORGANIC CLAY
SOILS
LESS THAN 50%
MORE THAN 50%
SILTY AND CLAY
INORGANIC
MH
SILT OF HIGH PLASTICITY, ELASTIC SILT
CH
CLAY OF HIGH PLASTICITY, FAT CLAY
PASSING ON THE
LIQUID LIMIT
ORGANIC
OH
ORGANIC SILT, ORGANIC SILT
NO.200 SIEVE
50% OR MORE
-T-
HIGHLY ORGANIC SOILS
PT
PEAT AND OTHER HIGHLY ORGANIC SOILS
NOTES:
SOIL MOISTURE MODIFIERS:
1. FIELD CLASSIFICATION IS BASED ON VISUAL E)MMINATION
DRY - ABSENCE OF MOISTURE, DUSTY, DRY TO
OF SOIL IN GENERAL ACCORDANCE WITH ASTM D2488-83.
THE TOUCH
2. SOIL CLASSIFICATION USING LABORATORY TESTS IS BASED
SLIGHTLY MOIST - TRACE MOISTURE, NOT DUSTY
ON ASTM D2487-83.
MOIST - DAMP, BUT NO VISIBLE WATER
3. DESCRIPTIONS OF SOIL DENSITY OR CONSISTENCY ARE
VERY MOIST- VERY DAMP, MOISTURE FELT TO THE TOUCH
BASED ON INTERPRETATION OF BLOW -COUNT DATA, VISUAL
WET - VISIBLE FREE WATER OR SATURATED,
APPEARANCE OF SOILS, AND/OR TEST DATA.
USUALLY SOIL IS OBTAINED FROM BELOW
WATER TABLE
LIU & ASSOCIATES, INC.
UNIFIED SOIL CLASSIFICATION SYSTEM
Geotechnical Engineering • Engineering Geology . Earth Science
PLATE 3
TEST PIT NO.
Logged By: JSL Date: 3/26/2008
1
Ground El. ±
Depth
uses
Sample
w
Other
ft.
CLASS.
Soil Description
No.
%
Test
OL
Duff on surface
1
Dark -brown, loose, organic, slightly silty, fine SAND, with
SP/SM
abundant roots to,3/4-inch diameter, moist OPSOIL
2
Brown, medium -dense, slightly silty, fine to medium SAND, trace
gravel and occasional cobble, few roots, slightly moist
3
4
Light -gray, medium -dense to dense, fine to medium SAND, trace
SP
5
gravel, slightly moist (fresh ADVANCE OUTWASH)
6
7
8
9
Test pit terminated at 7.0 ft, groundwater not encountered.
10
TEST PIT NO. 2
Logged By: JSL Date: 3/26/2008
Ground EL ±
Depth
USCS
Sample
W
Other
ft.
CLASS.
Soil Description
No.
%
Test
OL
Oak brush and duff on surface
1
Dark -brown, loose, organic, slightly silty, fine SAND, with
SP
abundant roots to 1/4-inch diameter, moist TOPSOIL)
2
Light -brown, medium -dense, fine to medium SAND, trace gravel
and occasional cobble, slightly moist
3
4
Light -gray, medium -dense to dense, fine to medium SAND, trace
SP
gravel, slightly moist (fresh ADVANCE OUTWASH)
5
6
7
8
9
Test pit terminated at 7:0 ft, groundwater not encountered.
10
LIU & ASSOCIATES, INC.
Geotechnical Engineering - Engineering Geology - Earth Science
TEST PIT LOGS
2-LOT SHORT PLAT
10506 - 235TH PLACE SW
EDMONDS, WASHINGTON
JOB NO. 8A031 DATE 4/4/2008 1 PLATE 4
root
vA—
drain
PLAN VIEW
NTS 4' rigid or 6' flexible
perforated pipe
................................................
infiltration trench sump w/solid lid
PLAN VIEW root drain
overflow
4' rigid or 6' flexible splash block
j- perforated pipe
-- -•
v..-••--....
o Q
_
I
y o Q o°° C
p washed rock �, _ 4
" 00
1' mm 5A' min
I
t' min
1 1 /2 -3/4"
o 00
varies
A
fine mesh CB sump w/solid lid
screen
•
tJo a-wovla�
604-1 PAC TaP
4a
t
4
v a �4a4
t 4-"IZIGIDotZ
I(
ddv
�ttrXlQ�I-l;
Z
4�
410vp0 a
I -PIPS
_
� 0 � � da
1n145a1tsp fZo�
3142r
MS01MTo.
GOP'
SECTION A
St�.N D
NTS
INFILTRATION TRENCH - SINGLE DISPERSION PIPE
ILrU & ASSOCUTES9 ffN C.
2-LOT SHORT PLAT
10506 - 235TH PLACE SW
Geotechnicat Engineering • Engineering Geology • Earth Science_
EDMONDS, WASHINGTON
JOB NO. 8A031 I DATE 4/5/2008 1 PLATE 7
April 8, 2008
Proposed 2-Lot Short Plat
L&A Job No. 8A031
Page 18
CLOSURE
We are pleased to be of service to you on this project. Please feel free to call us if you have any
questions regarding this report or need further consultation.
Seven plates attached
! 27589
SlQNAL '
e rP-1 MEs 7 / 17 /
Yours very truly,
L SSOCIATES, INC.
J. S. (Julian) Liu, Ph.D., P.E.
Consulting Geotechnical Engineer
1Lff U & ASSOC I hU L ES, ff C.
NOTICE:
No warranty of accuracy.
The information shown on the attached map(s)
was compiled for use by the City of Edmonds,
its Employees and Consultants. The City of
Edmonds does not warrant the accuracy of
anything set forth on these map(s). Any person
or entity requesting a copy should conduct an
independent inquiry regarding the information
shown on the map(s), including, but not limited
to, the location of any sewer stub shown. Such
sewer stubs may or may not exist and may or
may not exist at the location shown. Neither
the City of Edmonds nor its employees or
officers shall be liable for the information given
on map(s), nor for any one representation
provided based upon said map(s).