HomeMy WebLinkAboutRS_Report Geotechnical_666 Stevens Ave NW_2026-04-27
13705 Bel-Red Road · Bellevue, Washington 98005
Phone 425/649-8757 · Fax 425/649-8758
November 25, 2025 G-6355
Arturo Medina
666 Stevens Ave NW
Renton, WA 98057
Subject: Geotechnical Engineering Investigation
Proposed Addition
666 – Stevens Avenue Northwest
Renton, Washington 98057
Dear Arturo:
In accordance with our contract with you dated October 7, 2025, we have investigated the
subsurface conditions at the subject property and prepared the following geotechnical report for
the proposed addition at the subject property.
SITE AND PROJECT DESCRIPTION
Site Description
The project site (Parcel No. 420240-0011) is located west of Renton Municipal Airport, as
shown on the attached Plate 1 – Vicinity Map. The project site is approximately rectangular-
shaped, with its major axis oriented approximately east-west. The project site is approximately
4,800 square feet (0.11 acres).
In general, topography at the project site is relatively flat near the site’s eastern and western
limits, and has been regraded near the center of the site, with a maximum elevation of
approximately 148 feet near the site’s western limit, and a minimum elevation of approximately
144 feet near the site’s eastern limit. The project site is currently developed, with an
approximately 720 square feet single-family residence with a daylight basement near the center
of the site, and an approximately 500 square feet detached garage near the site’s eastern limit.
Other areas at the site are landscaped, including grass groundcover, small trees, and shrubs
around the perimeter of the project site. An approximately 50 feet long rockery with an average
height of approximately 5.5 feet and maximum height of 6.0 feet is located east of the existing
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GEO Group Northwest, Inc.
residence and south of the detached garage along the project site’s southern limit. An
approximately 6.0 feet tall cast-in-place concrete wall is located near the northwest corner of the
existing residence, and extends onto the neighboring residential property.
The project site is accessed by Stevens Ave NW, along the site’s western limit, as well as by an
Lind Ave NW along the site’s eastern limit. The project site is bounded by developed residential
lots to the north and south.
Project Description
Based on our discussions with the project’s design team, it is our understanding that construction
of an addition to the existing residence is proposed. The proposed addition is anticipated to be
located west of the existing residence, and is not anticipated to result in more than 2,000 square
feet of new or replaced impervious surfaces at the project site. The proposed addition is
anticipated to be constructed at or near the existing site elevations at the proposed project area.
The proposed addition is not anticipated to have a basement, and the addition is anticipated to be
supported on conventional concrete footings, if appropriate. Stormwater generated from the
proposed addition is anticipated to be collected and directed towards the existing stormwater
system for the residence, and discharged to an approved discharge location.
GEOLOGIC CONDITIONS
The published geologic map1 for the region indicates that the project site and its vicinity are
underlain by Quaternary-age recessional stratified drift (Qit) deposits. Recessional stratified drift
deposits typically consist of well-sorted sands and gravel that were deposited in drainage
channels issuing from the retreating glacial lobe towards the end of the Vashon glaciation period,
which occurred approximately 12 thousand years ago.
SUBSURFACE INVESTIGATION
Subsurface Investigation
On October 15th, 2025, a geologist with our firm visited the project site to perform a visual
reconnaissance of the project site & its vicinity, as well as to investigate the subsurface soil
conditions. Two exploratory borings were excavated with hand tools. The approximate locations
1 Mullineaux, D.R., 1965, Geologic map of the Renton quadrangle, King County, Washington, U.S. Geological
Survey, Geologic Quadrangle Map GQ-405, 1:24,000.
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GEO Group Northwest, Inc.
of each boring and test hole are illustrated on the attached Plate 2- Site Plan. During excavation
of each boring, samples of the encountered soils were collected for further analysis at our office.
Soils encountered in boring HA-1 consisted of loose to medium dense light silty sand with gravel
to a depth of 1.5 feet below ground surface (bgs), underlain by medium dense light brown silty
sand to a depth of approximately 2.5 feet bgs. Loose to medium dense brown silty sand was
encountered at depths below approximately 2.5 feet bgs in boring HA-1. Advancement of boring
HA-1 was terminated at approximately 3.5 feet bgs due to equipment refusal on cobbles. We
used a ½” diameter steel T-probe to probe the soils encountered at the bottom of boring HA-1
and probed approximately 10.0 inches. Based on the results of the probing, loose soils are
anticipated below approximately 3.5 feet bgs in boring HA-1.
Soils encountered in boring HA-2 consisted of loose brown silty sand to a depth of
approximately 1.0 feet bgs, underlain by medium dense olive brown silty sand with gravel to a
depth of approximately 2.5 feet bgs in boring HA-2. Dense olive brown silty sand was
encountered at depths between approximately 2.5 and 3.0 feet bgs in boring HA-2. Loose to
medium dense brown gravelly sand with silt was encountered at depths below approximately 3.0
feet bgs in boring HA-2. Advancement of boring HA-2 was terminated at approximately 5.0 feet
bgs due to equipment refusal on cobbles. We used a ½” diameter steel T-probe to probe the soils
encountered at the bottom of boring HA-2 and probed approximately 4.0 inches. Based on the
results of the probing, medium dense soils are anticipated below approximately 5.0 feet bgs in
boring HA-2. No groundwater was encountered during the advancement of either boring.
We interpret the sandy soils encountered below approximately 1.5 feet bgs in boring HA-1 to be
relatively weathered horizon of recessional stratified drift, overlain by fill soils with inconsistent
densities. We interpret gravelly sand encountered below approximately 3.0 feet bgs in boring
HA-2 to be a relatively weathered horizon of recessional stratified drift, overlain by fill soils with
inconsistent densities. For a more detailed description of the soils encountered during our
subsurface investigation, please refer to the boring logs on the attached Appendix A – USCS Soil
Classification & Boring Logs.
GEOLOGIC HAZARD AREA INVESTIGATION AND EVALUATION
Geologic hazard areas are areas which may be susceptible to erosion, landslides, or soil
liquefaction during seismic events due to their topography or subsurface conditions. The City of
Renton regulates development within geologic hazard areas to minimize the long-term impact
development may have on the functionality of geologically hazardous areas. Development
standards for each geologic hazard area can be found in the City of Renton’s Municipal Code
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GEO Group Northwest, Inc.
Chapter 4-3-050G. The approximate locations of mapped geologic hazard areas at the project
site and its vicinity are illustrated on Plate 3 – Geologic Hazard Map.
Sensitive and Protected Slopes
Based on our review of geologic hazard mapping by the City of Renton, sensitive and protected
slopes are mapped within 50 feet of the project site’s eastern limit. Areas in the project site’s
vicinity that are mapped as having sensitive and protected slopes by the City of Renton are
located on two vacant residential parcels east of the project site. The sensitive and protected
slopes extend beyond the two vacant residential parcels to Rainier Ave N, localized to a gulch
that is bounded by NW 7th Street and NW 6th Street.
It is our understanding that the proposed project area is located outside of the protected slope’s
structure setback, and no disturbance to the sensitive or protected slopes is proposed. As such,
we anticipate that the proposed addition will not increase the threat of the geological hazard to
adjacent properties beyond the pre-development condition, will not adversely impact other
critical areas, and the proposed addition can be safely accommodated on the site, provided our
geotechnical recommendations are properly incorporated into the project’s design and
implemented during construction.
It is also our opinion that soil erosion at the project site can be mitigated through temporary and
permanent erosion control measures and control of surface water runoff. Our recommendations
for appropriate construction BMPs and erosion control are provided in the Conclusions and
Recommendations section of this report.
SITE SEISMIC DESIGN CLASSIFICATION
Per the procedures specified in ASCE Standard 7-16, the project site can be assigned a seismic
design classification as Site Class D (stiff soil profile). This conclusion is based on review of the
geologic mapping of the site vicinity, the conditions encountered in the borings advanced on the
site, and our understanding and interpretation of deeper subsurface condition at the site. Seismic
design parameters applicable for the site are as follows:
SS = 1.462g SMS = 1.462g SDS = 0.975g
S1 = 0.499g
The peak ground acceleration for the site, adjusted for the assigned site class, is 0.685g per
current seismic hazard design mapping and calculations conforming to ASCE Standard 7-16.
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GEO Group Northwest, Inc.
CONCLUSIONS AND RECOMMENDATIONS
Based upon the results of our study, it is our professional opinion that the site is geotechnically
suitable for the proposed addition without increasing the risk of slope instability or soil erosion at
the project site or adjacent properties. Based on the results of our subsurface investigation, the
project site is underlain with medium dense, recessional stratified drift deposits that are
consistent with available geologic mapping of the vicinity. These competent native soils are
anticipated to be found at depths below approximately 5.0 feet bgs at the location of the
proposed addition. Details of our recommendations regarding the geotechnical aspects of the
proposed addition’s construction and proposed site improvements are described in the following
sections of this report.
Site Preparation and General Earthwork
Grading and earthwork for the project should be limited to the minimum amount required to
achieve final site grades. At the start of construction, the project area should be cleared of all
organic soils and debris, if present. These materials should be hauled off site or used for
landscaping as appropriate; they should not be used as backfill for the project.
Erosion Control
Prior to the start of construction, temporary erosion and sedimentation controls (TESCs) should
be installed to prevent the flow of sediment-laden runoff from the site and to minimize the
potential for on-site soil erosion. Temporary erosion and sedimentation controls, such as straw
wattles or silt fencing should be installed down-gradient of areas disturbed during construction
activity to prevent sediment-laden surface runoff from being discharged off the project site.
Stockpiled soils should be covered with plastic sheeting. The temporary erosion and sediment
controls should be maintained during the progress of the project until the ground disturbance
activities have been completed and the disturbed areas have been stabilized.
Concentrated surface water should not be allowed to flow into excavations. Any accumulated
surface water should be directed toward settlement or collection points for treatment and
discharge, as appropriate for the site conditions, per a construction stormwater management plan.
Water should not be allowed to stand in any area where concrete slabs or footings are to be
constructed. During construction, loose surfaces should be sealed at night by compacting the
surface to reduce the potential for moisture infiltration into the soils.
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For permanent erosion control, disturbed soils that are not covered with impervious surfacing
should be landscaped and mulched upon completion of the site work.
Temporary Excavations and Slopes
Under no circumstances should temporary excavation slopes be greater than the limits specified
in local, state, and national government safety regulations, except as discussed below or when
being evaluated by the geotechnical engineer.
We anticipate that shallow temporary excavations may be made from the existing grade for the
proposed residence’s foundation footings. We recommend that cuts which are greater than four
(4) feet in height should be sloped at inclinations no steeper than 1H:1V (Horizontal:Vertical).
Evidence of seasonal groundwater seepage was observed during our subsurface investigation and
may be encountered during periods of heavy rainfall during construction. If water seepage or
other adverse conditions are encountered, the geotechnical engineer should observe and evaluate
these conditions, and temporary cuts in these soils may need to be made at shallower inclinations
when recommended by the geotechnical engineer. If groundwater seepage accumulates in
temporary excavations, we recommend that groundwater be directed to one or more temporary
‘sump’ locations onsite for collection and treatment before being discharged to an approved
stormwater collection system.
Permanent Slopes
Permanent un-reinforced slopes should be inclined no steeper than 2.5H:1V. Permanent un-
reinforced slopes that are to be mowed or maintained should be inclined no steeper than 3H:1V.
Subgrade Preparation
Soils in areas to receive structural fill, concrete footings or concrete slabs should be prepared to a
firm, unyielding condition. The prepared subgrade should be observed and approved by the
geotechnical engineer. Any detected soft spots or disturbed areas should be compacted or
excavated and replaced with compacted structural fill or crushed rock as directed by the
geotechnical engineer.
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GEO Group Northwest, Inc.
Structural Fill
All fill material used to achieve design site elevations below concrete footings or slabs should
meet the requirements for structural fill. During wet weather conditions, we recommend that
material to be used as structural fill should have the following specifications:
1. Be free draining, granular material containing no more than five (5) percent fines (silts
and clay-size particles passing a No. 200 mesh sieve);
2. Be free of organic material and other deleterious substances, such as construction debris
and garbage;
3. Have a maximum particle size of three (3) inches in diameter.
All fill material should be placed at or slightly above the optimum moisture content. The
optimum moisture content is the water content in soil that enables the soil to be compacted to the
greatest dry density for a given compaction effort.
Based upon our subsurface investigation, the near surface site soils consisted of sandy soils
which may be appropriate for use as structural fill. Due to the fine-grained gradation of the site
soils, additional compaction efforts should be anticipated to achieve the necessary degree of
compaction for their use as structural fill. If structural fills are required to achieve design site
elevations, then we recommend the use of an imported granular fill material which may provide
more uniformity and be easier to compact to the required structural fill specifications, especially
during periods of wet weather.
Structural fill underneath concrete slabs or footings, should be compacted to at least ninety-two
(92) percent of the material’s maximum dry density, as determined by ASTM Test Designation
D-1557-91 (Modified Proctor). Structural fill placed within twelve (12) inches of finish grade
should be compacted to at least ninety-five (95) percent of the material’s maximum dry density.
Structural fill material should be spread and compacted in lifts that are ten (10) inches or less in
thickness in an uncompacted state. The compacted fill material should be field tested by using
ASTM Designations D2922 and D3017, Nuclear probe method, to verify that the required degree
of compaction has been achieved, or be approved by the geotechnical engineer.
We recommend that GEO Group Northwest, Inc. be retained to evaluate the suitability of
structural fill material and to monitor the compaction of structural fill material during
construction for quality assurance of the earthwork.
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GEO Group Northwest, Inc.
Addition Support
The proposed addition can be supported on conventional concrete footings founded on the site’s
native medium dense or denser soils, or on a compacted, structural fill underlain with the site’s
native, medium dense or denser soils. These competent native soils are anticipated to be found at
depths below approximately 5.0 feet bgs at the location of the proposed addition. Native soils
encountered above approximately 5.0 feet bgs at the location of the proposed addition may be
compacted with heavy equipment (i.e., hoe-pack) to the required structural fill specifications.
If placement of structural fill beneath the addition’s footings is required to achieve design grades,
we recommend that the compacted structural fill placed beneath the addition’s footings extends
from the base of the footing downward as imaginary planes (interior and exterior) inclined no
steeper than 1H:1V away from the footing to the approved subgrade. This recommendation is
illustrated on Plate 4 - Typical Footing Drain.
Our recommended design criteria for concrete footings constructed on dense native soils or on
structural fill underlain with native soils are provided below.
Concrete Footing Foundations
Concrete footings should bear directly on a suitable subgrade, or on a pad of structural fill placed
on such a subgrade. Our recommended design criteria for concrete footing foundations are as
follows:
- Allowable bearing pressure, including all dead and live loads:
Undisturbed, Medium dense (or denser) native soil = 2,000 psf
Structural fill placed on medium dense (or denser) native soil = 2,000 psf
- Minimum depth to bottom of interior footings below top of floor slab = 12 inches
- Minimum width of wall footings = 16 inches
- Minimum lateral dimension of column footings = 24 inches
- Estimated post-construction settlement = ½ inch
- Estimated post-construction differential settlement across addition width = ½ inch
A one third increase in the above allowable bearing pressures can be used when considering
short-term transitory wind or seismic loads. Lateral loads against the building foundations can be
resisted by friction between the foundation and the supporting compacted building pad or by
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passive earth pressure acting on the buried portions of the foundations. For the latter case, the
foundations must be poured “neat” against the existing undisturbed soil or be backfilled with
compacted structural fill. Our recommended parameters are as follows:
- Passive Earth Pressure (Lateral Resistance)
350 pcf, equivalent fluid weight, for structural fill or competent undisturbed
native soil.
- Coefficient of Friction (Friction Factor)
0.35 for structural fill or competent undisturbed native soil
We recommend that GEO Group Northwest, Inc. be retained to observe excavations for the
addition’s footings prior to installation of the footings to verify whether exposed soils will be
able to support the design allowable soil bearing capacity, and that construction of the footings
conforms with the recommendations presented in this report. Soil bearing verification may also
be required by the governing municipality.
Concrete Slabs-on-grade
It is our understanding that concrete slab-on-grade floors are proposed for the project. Concrete
slab-on-grade floors should be constructed on a firm, dense, and unyielding subgrade. During
preparation of the slab subgrade, any areas of the subgrade that have been disturbed by
construction activity should either be re-compacted or excavated and replace with compacted
structural fill. We recommend that structural fill placed below slab-on-grade floors conform to
the earthwork and grading recommendations provided in this report.
To avoid build-up of moisture on the subgrade, concrete slabs should be placed on a capillary
break, which is in turn placed on the prepared subgrade. The capillary break should consist of a
layer at least six (6) inches thick, of free-draining crushed rock or gravel containing no more than
five (5) percent material passing a No. 4 sieve. A vapor barrier, such as a 6-mil plastic
membrane, should be placed over the capillary break and sealed to minimize water vapor
transmission upward through the slab, if post-construction vapor transmission is undesirable.
Subsurface Drainage
We recommend footing drains be installed around the exterior perimeter of the addition. Footing
drains should consist of a four (4) inch minimum diameter perforated rigid drain pipe laid with
perforations downwards, at or slightly above the bottom of the footing with a gradient sufficient
to generate flow. The drain line should be bedded on, surrounded by, and covered with a free-
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GEO Group Northwest, Inc.
draining aggregate material. The drain rock and drain line should each be completely surrounded
by a geotextile filter fabric, Mirafi 140N or equivalent. Once the footing drains are installed, the
excavation should be backfilled with a compacted fill material. The footing drains should be
tight lined to discharge to an approved storm water collection system.
Under no circumstances should roof downspout drain lines be connected to the footing drainage
system. All roof downspout drain lines must be separately tight lined to discharge into the
approved storm water collection system. We recommend that sufficient cleanouts be installed at
strategic locations to allow for periodic maintenance of the footing drains and downspout drains.
For footing drain design details, please refer to the attached Plate 4 - Typical Footing Drain.
Surface Drainage
During construction, stormwater should not be allowed to stand in areas where footings or slabs
are to be constructed. Final site grades should provide drainage away from the building
structures.
We do not anticipate an adverse impact to the site’s stormwater drainage will result from the
proposed construction. We recommend that storm water drainage from impervious areas be
collected into one or more tight-line systems which convey the water to an approved stormwater
system. Storm water should not be permitted to develop into concentrated flows on the ground
surface, because concentrated flows can lead to increased soil erosion and rutting.
LIMITATIONS
This report has been prepared for the specific application to this site for the exclusive use of
Arturo Medina, and their authorized representatives. Any use of this report by other parties is
solely at that party’s own risk. We recommend that this report be included in its entirety in the
project contract documents for reference during construction.
Our findings and recommendations stated herein are based on field observations, our experience
and judgement. The recommendations are our professional opinion 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, and within the budget
constraint. No warranty is expressed or implied. In the event that soil conditions not anticipated
in this report are encountered during site development, GEO Group Northwest, Inc. should be
notified and the above recommendations should be re-evaluated.
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GEO Group Northwest, Inc.
ADDITIONAL SERVICES
GEO Group Northwest recommends that it be retained to perform a review of the final design
and specifications of the proposed addition to verify that our geotechnical recommendations are
properly interpreted and incorporated into the design and construction documents and are
appropriate for the finalized configuration of the proposed construction.
We also recommend that we be retained to provide geotechnical monitoring and testing services
during construction to verify that construction work is completed in compliance with the
recommendations in this report and the project plans. As part of these services, we will be
available to discuss and recommend design changes, if needed, in the event that unanticipated
site conditions are encountered or occur during construction.
CLOSING
We appreciate the opportunity to provide you with geotechnical engineering services for this
project. If you have any questions, or if we may be of further service, please do not hesitate to
contact us.
Sincerely,
GEO GROUP NORTHWEST, INC.
Dated: 11/25/2025
Andrew Hoff, G.I.T. William Chang, P.E.
Staff Engineering Geologist Principal Engineer
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GEO Group Northwest, Inc.
Attachments:
- Plate 1 – Vicinity Map
- Plate 2 – Site Plan
- Plate 3 – Geologic Hazard Map
- Plate 4 – Typical Footing Drain
- Appendix A – USCS Soil Classification & Boring Logs
Source: King County iMap, 2025
SCALE NONE DATE 11/25/2025 MADE AH CHKD WC JOB NO.G-6355 PLATE 1
VICINITY MAP
PROPOSED ADDITION
666 STEVENS AVE NW
RENTON, WA 98057
Geotechnical Engineers, Geologists, &
Environmental Scientists
GEO Group Northwest, Inc.
PROJECT SITE
N
Source: Renton GIS, 2025 SCALE As Shown DATE 11/25/25 MADE AH CHKD WC JOB NO.G-6355 PLATE 2
SITE PLAN
PROPOSED ADDITION
666 STEVENS AVE NW
RENTON, WA 98057
Geotechnical Engineers, Geologists, & Environmental Scientists
GEO Group Northwest, Inc.
Approx. Scale: 1 inch = 15'
15'0 30'
LEGEND
N
HAND AUGER NUMBER AND
APPROXIMATE LOCATIONHA-#
EXISTING RESIDENCE
(APPROX.)
PROPOSED ADDITION
(APPROX.)
EXISTING GARAGE
(APPROX.)
HA-1
HA-2
Source: Renton GIS, 2025 SCALE As Shown DATE 11/25/25 MADE AH CHKD WC JOB NO.G-6355 PLATE 3
GEOLOGIC HAZARD MAP
PROPOSED ADDITION
666 STEVENS AVE NW
RENTON, WA 98057
Geotechnical Engineers, Geologists, & Environmental Scientists
GEO Group Northwest, Inc.
Approx. Scale: 1 inch = 25'
25'0 50'
LEGEND
N
EXISTING RESIDENCE
(APPROX.)
PROPOSED ADDITION
(APPROX.)EXISTING GARAGE
(APPROX.)S 123RD ST
ST
E
V
E
N
S
A
V
E
N
W
SCALE:NONE DATE:11/24/2025 MADE:AH CHKD:WC JOB NO.G-6355 PLATE 4
FOOTING DRAIN DETAIL
PROPOSED ADDITION
666 STEVENS AVE NW
RENTON, WA 98057
NOT TO SCALE
DRAINLINE
Minimum 4-inch diameter
slotted or perforated PVC
pipe (perforations facing
down); lay pipe to have
sufficient gradient toward
discharge location
GEOTEXTILE FILTER FABRIC
Non-woven geotextile filter fabric
(Mirafi 140 NL, or equivalent),
wrapped around the drain rock
WASHED DRAIN ROCK
Bedded entirely around the
drain line, minimum 1-foot
wide column behind wall
FOOTING BACKFILL
Compacted soil general
backfill, or structural fill
where applicable (refer to
notes below)
FLOOR SLAB
CAPILLARY BREAK
NOTES:
1.) Perforated or slotted rigid PVC pipe should be tight jointed and laid with perforations or slots down,
and with positive gradient toward discharge location(s). The pipe should be placed at or slightly
above the elevation of the bottom of the footing. Do not replace rigid PVC pipe with flexible
corrugated plastic pipe.
2.) Do not connect other drainage lines to the footing drain lines. Drain line cleanouts should be
installed at appropriate locations to allow inspection and maintenance of the lines after construction.
3.) If the backfill will support sidewalks, driveways, patios, or other structures, it should be compacted
to at least 90% of its maximum dry density based on the Modified Proctor test method, except that
the top 12 inches of the backfill should be compacted to at least 95% of the maximum dry density.
4.) The geotextile filter fabric should be placed around the drain rock as shown, and not wrapped
directly around the pipe.
Slope the surface to drain
away from the wall
FOOTING
FOOTING DRAIN DETAIL
Geotechnical Engineers, Geologists, &
Environmental Scientists
GEO Group Northwest, Inc.
STRUCURAL FILL (If reqd.)
Compacted structural fill should
extend downward at 1H:1V planes
to the approved subgrade
1H:1V (45 deg.)
CLEAN
GRAVELS
GW
(little or no
fines)GP
DIRTY
GRAVELS
GM
(with some
fines)GC
CLEAN
SANDS
SW
(little or no
fines)SP
DIRTY
SANDS
SM
(with some
fines)SC
Liquid Limit
< 50%ML
Liquid Limit
> 50%MH
Liquid Limit
< 50%CL
Liquid Limit
> 50%CH
Liquid Limit
< 50%OL
Liquid Limit
> 50%OH
Pt
Sieve Size
(mm)Sieve Size
(mm)
SILT / CLAY #200 0.075
SAND 0 - 4 0 -15 Very Loose < 2 < 0.25 Very soft
FINE #40 0.425 #200 0.075 4 - 10 15 - 35 26 - 30 Loose 2 - 4 0.25 - 0.50 Soft
MEDIUM #10 2.00 #40 0.425 10 - 30 35 - 65 28 - 35 Medium Dense 4 - 8 0.50 - 1.00 Medium Stiff
COARSE #4 4.75 #10 2.00 30 - 50 65 - 85 35 - 42 Dense 8 - 15 1.00 - 2.00 Stiff
GRAVEL > 50 85 - 100 38 - 46 Very Dense 15 - 30 2.00 - 4.00 Very Stiff
FINE 0.75" 19 #4 4.75 > 30 > 4.00 Hard
COARSE 3" 76 0.75" 19
COBBLES
BOULDERS
ROCK
FRAGMENTS
ROCK PLATE A1Fax (425) 649-8758
Description
Bellevue, WA 98005
Blow Counts
N
Relative
Density, %
Friction Angle
φ, degrees Description Blow Counts
N
Unconfined
Strength qu,
tsf
76 mm to 203 mm
> 203 mm
> 76 mm 13705 Bel-Red Rd
>0.76 cubic meter in volume Phone (425) 649-8757
HIGHLY ORGANIC SOILS PEAT AND OTHER HIGHLY ORGANIC SOILS
SOIL PARTICLE SIZE GENERAL GUIDANCE FOR ENGINEERING PROPERTIES OF SOILS, BASED ON STANDARD
PENETRATION TEST (SPT) DATA
FRACTION
U.S. STANDARD SIEVE
Passing Retained SANDY SOILS SILTY & CLAYEY SOILS
CLAYEY GRAVELS, GRAVEL-SAND-CLAY
MIXTURES
GC: ATTERBERG LIMITS ABOVE "A" LINE.
or P.I. MORE THAN 7
INORGANIC CLAYS OF LOW PLASTICITY,
GRAVELLY, SANDY, OR SILTY CLAYS, CLEAN
CLAYS
Less Than Half by
Weight Larger
Than No. 200
Sieve
INORGANIC CLAYS OF HIGH PLASTICITY, FAT
CLAYS
ORGANIC SILTS
& CLAYS
(Below A-Line on
Plasticity Chart)
ORGANIC SILTS AND ORGANIC SILTY CLAYS OF
LOW PLASTICITY
ORGANIC CLAYS OF HIGH PLASTICITY
FINE-GRAINED
SOILS
SILTS
(Below A-Line on
Plasticity Chart,
Negligible
Organics)
INORGANIC SILTS, ROCK FLOUR, SANDY SILTS
OF SLIGHT PLASTICITY
INORGANIC SILTS, MICACEOUS OR
DIATOMACEOUS, FINE SANDY OR SILTY SOIL
CLAYS
(Above A-Line on
Plasticity Chart,
Negligible
Organics)
More Than Half
by Weight Larger
Than No. 200
Sieve
SANDS WELL GRADED SANDS, GRAVELLY SANDS,
LITTLE OR NO FINES CONTENT
OF FINES BELOW
5%
Cu = (D60 / D10) greater than 6
Cc = (D30)2 / (D10 * D60) between 1 and 3
(More Than Half
Coarse Fraction is
Smaller Than No.
4 Sieve)
POORLY GRADED SANDS, GRAVELLY SANDS,
LITTLE OR NO FINES
CLEAN SANDS NOT MEETING ABOVE
REQUIREMENTS
SILTY SANDS, SAND-SILT MIXTURES
CONTENT OF FINES
EXCEEDS 12%
ATTERBERG LIMITS BELOW "A" LINE
with P.I. LESS THAN 4
CLAYEY SANDS, SAND-CLAY MIXTURES ATTERBERG LIMITS ABOVE "A" LINE
with P.I. MORE THAN 7
COARSE-
GRAINED SOILS
GRAVELS
(More Than Half
Coarse Fraction is
Larger Than No. 4
Sieve)
WELL GRADED GRAVELS, GRAVEL-SAND
MIXTURE, LITTLE OR NO FINES CONTENT
OF FINES BELOW
5%
SOIL CLASSIFICATION & PENETRATION TEST DATA EXPLANATION
UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)
MAJOR DIVISION GROUP
SYMBOL TYPICAL DESCRIPTION LABORATORY CLASSIFICATION CRITERIA
Cu = (D60 / D10) greater than 4
Cc = (D30)2 / (D10 * D60) between 1 and 3
POORLY GRADED GRAVELS, AND GRAVEL-SAND
MIXTURES LITTLE OR NO FINES
CLEAN GRAVELS NOT MEETING ABOVE
REQUIREMENTS
SILTY GRAVELS, GRAVEL-SAND-SILT MIXTURES CONTENT
OF FINES EXCEEDS
12%
GM: ATTERBERG LIMITS BELOW "A" LINE.
or P.I. LESS THAN 4
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70 80 90 100
PL
A
S
T
I
C
I
T
Y
I
N
D
E
X
(
%
)
LIQUID LIMIT (%)
CL-ML
CL MH or OH
U-Line
PLASTICITY CHART
FOR SOIL PASSING
NO. 40 SIEVE
7
4
CH
Geotechnical Engineers, Geologists, &
Environmental Scientists
GEO Group Northwest, Inc.
ML
A-Line
MLor OL
LOGGED BY AH LOG DATE:10/15/2025
DEPTH SAMPLE Water OTHER TESTS/
ft. USCS SOIL DESCRIPTION No. % COMMENTS
1
2
3
4
5
6
7
LOGGED BY AH LOG DATE:10/15/2025
DEPTH SAMPLE Water OTHER TESTS/
ft. USCS SOIL DESCRIPTION No. % COMMENTS
1
2
3
4
5
6
7
HAND AUGERED BORING LOG
PROPOSED ADDITION
666 STEVENS AVE NW
RENTON, WA 98057
JOB NO. DATE 11/25/25 PLATE A2
HAND AUGERED BORING NO: HA-1
HAND AUGERED BORING NO: HA-2
G-6355
Total depth of boring = 42.0" bgs (below ground surface)
- Equipment refusal on cobble
- No groundwater seepage observed
Geotechnical Engineers, Geologists, &
Environmental Scientists
GEO Group Northwest, Inc.
SM
Probe 5-6"
Probe 3"
Probe 10"
Probe 10"
Probe 9"
SM
Total depth of boring = 60.0" bgs (below ground surface)
- Equipment refusal on cobble
- No groundwater seepage observed
Probe 12"
Probe 12"
S-1
Probe 4"
SM
S-1
Probe 18"
S-2SM
S-2Olive brown SILTY SAND WITH GRAVEL, fine sand, fine
subrounded gravel, medium dense, dry; small roots at 2.0'
Grass groundcover underlain by light brown SILTY SAND WITH
GRAVEL, fine sand, mostly fine to coarse subrounded gravel, loose to
medium dense, dry; abundant rootlets.
S-3SMBrown SILTY SAND, very fine to fine sand, dry, loose to medium
dense, dry; rootlets present, occasional cobbles.
Probe 8"
Probe 4"
Brown SILTY SAND, fine sand, loose, dry; abundant rootlets, trace
fine subrounded gravel.
Olive brown SILTY SAND, sand is fine, dense, dry; trace coarse
subrounded gravel present, weakly cemented.
SM
Same as above; light gray SILT nodules present, decrease gravel.
Light brown to light gray SILTY SAND, very fine to fine sand, medium
dense, dry; trace fine subrounded gravel, cemented.
S-3
S-4SMBrown GRAVELLY SAND WITH SILT, fine to medium sand, fine to
coarse subrounded gravel, loose to medium dense, dry; rootlets and
minor oxide staining at 4.0'
Same as above; becomes medium dense, increased silt.
DEPARTMENT OF COMMUNITY
AND ECONOMIC DEVELOPMENT
Page 1 of 3 | Published: 6/4/2025
Development Engineering Division | 1055 South Grady Way | Renton, WA 98057 | 425-430-7240
Website: rentonwa.gov
ENGINEERING IMPROVEMENT DETERMINATION
RESULTS
Published : 6/4/2025
Project Address/Location: _____________________________ Parcel #(s): ________________________________
Determination results are based on the information provided by the Applicant. Deviations from the submitted information may require
that a new Determination Request form be submitted and result in additional requirements.
ROADWAY IMPROVEMENTS
Street Name(s): __________________________ Roadway Classification(s): ___________________________
NO Right of Way Dedication and NO Street Frontage Improvements Required as the project falls within
RMC 4-6-060 Street Standards exemption criteria.
Right of Way Dedication and/or Street Frontage Improvements Required per RMC 4-6-060.
Modified Right of Way Dedication and/or Street Frontage Improvements Recommended.
Fee-in-Lieu Allowed for Street Frontage Improvements (see City Fee Schedule for $/LF of frontage)
666 Stevens Ave NW 4202400011
Stevens Ave NW KC Urban Collector Arterial
4
DEPARTMENT OF COMMUNITY
AND ECONOMIC DEVELOPMENT
Page 1 of 3 | Published: 6/4/2025
Development Engineering Division | 1055 South Grady Way | Renton, WA 98057 | 425-430-7240
Website: rentonwa.gov
ENGINEERING IMPROVEMENT DETERMINATION
RESULTS
Published : 6/4/2025
Project Address/Location: _____________________________ Parcel #(s): ________________________________
Determination results are based on the information provided by the Applicant. Deviations from the submitted information may require
that a new Determination Request form be submitted and result in additional requirements.
ROADWAY IMPROVEMENTS
Street Name(s): __________________________ Roadway Classification(s): ___________________________
NO Right of Way Dedication and NO Street Frontage Improvements Required as the project falls within
RMC 4-6-060 Street Standards exemption criteria.
Right of Way Dedication and/or Street Frontage Improvements Required per RMC 4-6-060.
Modified Right of Way Dedication and/or Street Frontage Improvements Recommended.
Fee-in-Lieu Allowed for Street Frontage Improvements (see City Fee Schedule for $/LF of frontage)
666 Stevens Ave NW 4202400011
Lind Ave NW Residential
4
4
The project fronts Lind Ave NW along the east property line. This segment of Lind Ave NW is a dead
end residential access street with an existing right of way width of 30 feet which includes a paved
width of 20 feet. To meet the City's complete street standards for residential access streets,
minimum right of way is 60 feet per City code 4-6-060, half street improvements shall include a
pavement width of 32 feet (16 feet from centerline), a 0.5 foot curb, an 8 foot planting strip, a 5 foot
sidewalk, street trees and storm drainage improvements.
However, the city will support a modification to retain the existing frontage and a modification
request shall be required.
ENGINEERING IMPROVEMENT DETERMINATION RESULTS (CONT’D)
Page 2 of 3 | Published: 6/4/2024
Project Address/Location: _____________________________ Parcel #(s): _________________________________
Determination results are based on the information provided by the Applicant. Deviations from the submitted information may
require that a new Determination Request form be submitted and result in additional requirements.
STORM DRAINAGE REVIEW TYPE (See City of Renton Surface Water Design Manual Figure 1.1.2.A for
Reference)
Basic Drainage Evaluation (Less than 2,000 Square Feet of New or Replaced Impervious Surface)
Simplified Drainage Review (Renton Surface Water Design Manual, Appendix C)
Targeted Drainage Review due to ____________________________________________________
Directed Drainage Review
For information on review type and submittal requirements, please see here.
ANTICIPATED SUBMITTAL ITEMS
Required Waived All Checklists/Studies/Reports Required Unless Waived by City Staff
_____ Civil Construction Permit Application
_____ Residential Drainage Application
_____ Deed of Dedication
_____ Real Estate Excise Tax Affidavit (REETA) – (See Example REETA Form)
_____ Modification Application and Supporting Documents
_____ Fee-in-Lieu of Street Improvements Application
_____ Soils Report (See Renton Surface Water Design Manual Appendix C, Section C.1.3)
_____ Written Drainage Assessment (See Example Simplified Drainage Review)
_____ Storm Drainage Covenant (See Example Storm Drainage Covenant)
_____ Water Availability from:
_____ Sewer Availability from:
RESULT PROVIDED BY:
Determination expires six (6) months following the date of the Determination Results provided that City codes have not
changed within this period that would affect this determination. A new Determination Request will need to be submitted
following this expiration. The applicant is cautioned that information contained in this summary is preliminary and non-
binding and may be subject to modification and/or concurrence by official City decision-makers.
RESOURCES
Definitions
Renton Surface Water Design Manual (RSWDM)
City of Renton Standard Details
City of Renton Forms
Electronic File Standards
666 Stevens Ave NW 4202400011
4
4
4
4
4
4
4
4
4
4
4
4
ENGINEERING IMPROVEMENT DETERMINATION RESULTS (CONT’D)
Note: This handout shall not be used as a substitute for code and regulations. The applicant is responsible for compliance with all codes and regulations,
whether or not described in this document.
Page 3 of 3 | Published: 6/4/2024
Project Address/Location: _____________________________ Parcel #(s): _________________________________
Determination results are based on the information provided by the Applicant. Deviations from the submitted information may
require that a new Determination Request form be submitted and result in additional requirements.
INFORMATION PROVIDED BY APPLICANT:
666 Stevens Ave NW 4202400011