REVIEWED BLD BLD2020-0965+Geotechnical_Report+9.17.2020_2.04.18_PMJuly 19, 2017
ES-5323
Ms. Kari Johannessen
10727 — 226th Street Southwest
Edmonds, Washington 98002
Subject: Geotechnical Evaluation
Johannessen Short Plat
10727 — 226t" Street Southwest
Edmonds, Washington
Reference: Lovell-Sauerland & Associates, Inc.
Preliminary Development Plan, dated April 21, 2008
Earth
I Solutions
NWac
Earth Solutions NW LLC
• Geotechnical Engineering
• Construction Monitoring
• Environmental Sciences
Department of Ecology (DOE)
2012 Stormwater Management Manual for Western Washington (SMMWM)
Amended December 2014
United States Department of Agriculture
Natural Resources Conservation Service
Online Web Soil Survey (WSS) resource
James P. Minard
Geologic Map of the Edmonds East and
Washington, 1983
Dear Ms. Johannessen:
Part of the Edmonds West Quadrangles
As requested, Earth Solutions NW, LLC (ESNW) has prepared this infiltration and geotechnical
evaluation letter for the proposed development.
Project Description
The subject site located at 10727 — 226th Street Southwest in Edmonds, Washington, as
illustrated on the Vicinity Map (Plate 1). The site consists of one residential tax parcel
(Snohomish County parcel number 27032500310300) totaling approximately 2.35 acres of land
area. The property is currently developed with a single-family residence and associated
improvements located in the northwestern portion of the site; the remainder of the site consists
primarily of yard areas and lightly forested land.
-1805 - 136th Place N.E., Suite 201 • Bellevue, WA 98005 0 (425) 449-4704 • FAX (425) 449-4711
Ms. Kari Johannessen ES-5323
July 19, 2017 Page 2
Within the site, there is a knoll occupying the northwestern half of the site (existing residence).
The ground drops off at about 8 to 38 percent grade to a low-lying, nearly level portion of the
site. The subject site is bordered to the north, east, and west by residential structures and to
the south by 2261" Street Southwest.
Based on the site development plan provided to us, the existing single-family residential
structure will remain and two new single-family residential structures will be constructed within
the southern portion of the site. We anticipate grading activities will include cuts and fills to
establish the planned building alignment. Based on the existing grades, we estimate cuts to
establish building pad and foundation subgrade elevations will be on the order of five feet or
less. However, grading plans were not available at the time this letter was prepared. Drywells
will be incorporated into site designs as a means of stormwater management for new
impervious surfaces. Site improvements will also include underground utility installations.
At the time this letter was prepared, specific building load values were not available. However,
we anticipate the proposed residential structure will consist of relatively lightly loaded wood
framing supported on conventional foundations. Based on our experience with similar
developments, we estimate wall loads on the order of one to two kips per lineal foot and slab -
on -grade loading of 150 pounds per square foot (psf).
If the above design assumptions are incorrect or change, ESNW should be contacted to review
the recommendations in this evaluation. ESNW should review the final design to verify the
geotechnical recommendations provided in this letter have been incorporated into the plans.
Subsurface Conditions
As part of this geotechnical evaluation, An ESNW representative observed, logged, and
sampled two test pits on June 29, 2017, excavated at accessible locations within the proposed
development area. The approximate locations of the test pits are depicted on Plate 2 (Test Pit
Location Plan). Please refer to the test pit logs provided in Appendix A for a more detailed
description of subsurface conditions. Representative soil samples collected at the test pit
locations were analyzed in general accordance with the Unified Soil Classification System
(USCS) and United States Department of Agriculture (USDA) methods and procedures.
Topsoil and Fill
Topsoil was observed extending to depths of approximately 4 to 6 inches below existing
grades. The topsoil was characterized by dark brown color and fine organic material.
Significant fill deposits were not encountered at the test pit locations during our fieldwork. Fill
may be present, however, within proximity to existing structural improvements. Where fill is
encountered during construction, ESNW should be consulted to evaluate the suitability for
reuse as structural fill.
Earth Solutions NW, LLC
Ms. Kari Johannessen
July 19, 2017
Native Soil
ES-5323
Page 3
Underlying the topsoil, soil conditions at the test pit locations were observed to consist of poorly
graded gravel with sand and poorly graded sand (USCS: GP and SP, respectively) outwash
deposits. The native soil deposits were generally observed to be in a medium dense condition
beginning at depths of approximately one to three feet below existing grades.
Geologic Setting
The referenced geologic map indicates the project location is underlain by Vashon advance
outwash (Qva). The advance outwash is characterized primarily as sand and gravel deposit.
The soil conditions observed at the test pit locations are generally consistent with the geologic
mapping.
Groundwater
Groundwater was not encountered at the test pit locations at the time of our exploration.
Perched seepage, however, may be encountered during site grading activities, particularly
during the winter, spring, and early summer months. It is noted that groundwater seepage rates
and elevations fluctuate depending on many factors, including precipitation duration and
intensity, the time of year, and soil conditions. In general, groundwater flow rates are higher
during the wetter, winter months. Based on subsurface conditions observed, we do not
anticipate groundwater will impact the proposed infiltration facilities.
Geotechnical Considerations
Based on the results of our investigation, the proposed single-family structures can be
supported on conventional spread and continuous footings bearing on undisturbed competent
native soil, compacted native soil, or new structural fill. Based on the soil conditions
encountered at the test sites, competent native soils suitable for support of foundations should
be encountered beginning at depths of approximately one to three feet below existing grades.
The soils encountered at the test pit locations generally have a low to moderate sensitivity to
moisture based on the fines content of the soil. Compaction of the soil to the levels necessary
for use as structural fill may be difficult during wet weather conditions. Where loose or
unsuitable soil conditions are encountered at foundation subgrade elevations during site
preparation activities, compaction of the soils to the specifications of structural fill, or
overexcavation and replacement with granular structural fill will be necessary. Structural fill
should consist of suitable granular soils compacted to 95 percent of Modified Proctor (ASTM
D1557). Organic material exposed at foundation subgrade elevations must be removed and
grades restored with structural fill.
Earth Solutions NW, LLC
Ms. Kari Johannessen ES-5323
July 19, 2017 Page 4
Provided the structures will be supported as described above, the following parameters can be
used for design of the new foundations:
• Allowable soil bearing capacity 2,500 psf
Passive earth pressure 300 pcf (equivalent fluid)
• Coefficient of friction 0.40
A one-third increase in the allowable soil bearing capacity can be assumed for short-term wind
and seismic loading conditions.
With structural loading as expected, total settlement in the range of one inch is anticipated, with
differential settlement of about one-half inch. The majority of the settlements should occur
during construction, as dead loads are applied.
Seismic Considerations
The 2015 IBC recognizes ASCE for seismic site class definitions. In accordance with Table
20.3-1 of ASCE, Minimum Design Loads for Buildings and Other Structures, Site Class D,
should be used for design.
In our opinion, the site is not susceptible to liquefaction. The native soil relative density and the
absence of an established shallow groundwater table are the primary bases for this opinion.
Drainage
Surface grades must be designed to direct water away from the buildings. The grade adjacent
to the buildings should be sloped away from the buildings at a gradient of at least 2 percent for
a horizontal distance of at least four feet. In our opinion, perimeter footing drains should be
installed at or below the invert of the building footings. ESNW can reevaluate the need for
footing drains during construction, if requested.
Infiltration Evaluation
We understand stormwater will likely be managed by infiltration drywells located near the
southern area of the subject site. The referenced 2014 Stormwater Management Manual for
Western Washington (2014 SMMWW) was consulted, as required.
As indicated in the Subsurface section of this letter, native soils encountered during our
fieldwork were characterized primarily sand and gravel, outwash deposits. Based on the results
of USDA textural analyses, the native soils were classified primarily as slightly to extremely
gravelly sand with fines contents of about 0.1 to 0.9 percent (irrespective of gravel content).
Earth Solutions NW, LLC
Ms. Kari Johannessen ES-5323
July 19, 2017 Page 5
In -situ testing was completed in accordance with the Small-scale Pilot Infiltration Test (PIT)
procedure, as outlined in Volume III, Chapter 3, Page 526 of the 2014 SMMWW. The testing
was completed at depths of approximately four feet below existing grades at TP-1 and
approximately four -and -one-half feet at TP-2. The testing was completed within the native sand
and gravel outwash soils. The in -situ rate obtained during testing was 62 inches per hour at
TP-1 and 55 inches per hour at TP- 2.
Because the infiltration rate obtained from in -situ testing is considered to be a short-term rate,
correction factors must be applied in order to determine a long-term design rate. The correction
factors outlined below were used in accordance with Table III-3.3.1 of the 2014 SMMWW
outlined in Volume III, Chapter 3, Page 529. The correction factors, along with the measured
infiltration rate, were incorporated into the following equation: Ksat design = Ksat initial x CFI x
CFt x CF,,,.
• Measured (Ksat initial) 55 inches per hour
• Site variability CF„ = 0.75
■ Test method CFt = 0.5
■ Degree of influent control CFm = 0.9
Long-term design infiltration rate (Ksat design) 18 inches per hour
The design infiltration rate is applicable to facilities located in proximity to the infiltration test
locations. Should revised locations be pursued, ESNW should be contacted to perform
additional in -situ testing, as necessary. We recommend incorporating emergency overflow
provisions in the facility designs.
ESNW should be retained to observe the construction of infiltration facilities on the subject site
in order to confirm soil conditions are as anticipated. Supplementary geotechnical
recommendations may be provided at the time of construction, where necessary.
Drywell Sizing
Typical drywell sizing recommendations are based on the USDA classifications of the soils
observed at the proposed bottom of facility. The referenced 2014 SMMWW provides sizing
criteria for soils considered generally suitable for full infiltration (medium to coarse sands and
gravels). Extremely gravelly sand was identified at the proposed bottom of facility locations.
For sizing of roof runoff infiltration drywells, the site soils should be designed as course sands.
In our opinion, the soils observed at the approximate bottom of facilities should be considered
suitable for full infiltration applications. As stated in Volume II, Chapter 3, Page 454 of the DOE
stormwater manual, drywells placed within coarse sands must have at least 360 cubic feet of
gravel for every 1,000 square feet of tributary impervious surface. It is our opinion that an
overflow should be incorporated into facility designs.
Earth Solutions NW, LLC
Ms. Kari Johannessen
July 19, 2017
On -site Stormwater Management
ES-5323
Page 6
Pursuant to City of Edmonds stormwater management requirements, implementation of on -site
stormwater BMPs are required for proposed developments in accordance with specified
thresholds, standards, and lists. The intent of BMP implementation is to infiltrate, disperse, and
retain stormwater runoff on site to the extent feasible. We understand the proposed
development intends to add over 5,000 square feet of new hard surface and therefore must
comply with Minimum Requirements (MRs) 1 through 9, as outlined on Pages 42 through 70 of
Volume I of the referenced stormwater manual. MR 5 concerns on -site stormwater
management, and the viability of specific BMPs are to be evaluated for each type of proposed
surface. The table below summarizes our evaluation of the required BMPs for MR 5, as
outlined in the referenced stormwater manual, from a geotechnical standpoint. It is instructed in
the referenced stormwater manual that BMPs are to be considered in the order listed (from top
to bottom) for each surface type, and the first BMP that is determined to be viable should be
used. For completeness, however, we have evaluated each listed BMP for the proposed
surface types.
AM
Lawns and Landscaped Areas
T5.13: Post -construction soil quality and depth
(Volume V, Chapter 5)
P,--r-
T5.30: Full dispersion (Volume V, Chapter 5)
T5.10A: Downspout full infiltration systems
(Volume III, Chapter 3)
T7.30: Bioretention (Volume V, Chapter 7)
T5.14A: Rain Gardens (Volume V, Chapter 5)
T5.10B: Downspout dispersion systems
(Volume III, Chapter 3)
T5.10C: Perforated stub -out connections
(Volume III, Chapter 3)
T5.30: Full dispersion (Volume V, Chapter 5)
le?
Yes
or Infeasiibilitv Criteria
None. No slopes greater than 33 percent
are present.
No
The proposed project will
not preserve at
least 65 percent of the site.
Based on results of the
PIT, a design
Yes
infiltration rate of 18
in/hr can be
considered for design.
Based on results of the
PIT, a design
Yes
infiltration rate of 18
in/hr can be
considered for design.
No
Proper setbacks and vegetated flow paths
are not available.
Yes
None.
No
T5.15: Permeable pavement (Volume V,
Chapter 5) Yes
T7.30: Bioretention (Volume V, Chapter 7) Yes
T5.14A: Rain Gardens (Volume V, Chapter 5)
T5.12: Sheet flow dispersion
T5.11: Concentrated flow dispersion (Volume
V, Chapter 5)
No
The proposed project will not preserve at
least 65 percent of the site.
Based on results of
the
PIT,
a design
infiltration rate of
18
in/hr
can be
considered for design.
Based on results of
the
PIT,
a design
infiltration rate of
18
in/hr
can be
considered for design.
Sheet flow dispersion and concentrated
flow dispersion may be feasible, however,
proper setbacks and vegetated flow paths
may not be available.
Earth Solutions NW, LLC
Ms. Kari Johannessen
July 19, 2017
Utility Support and Trench Backfill
ES-5323
Page 7
In our opinion, the native soils anticipated to be exposed in utility excavations should generally
be considered suitable for support of utilities. Organic or highly compressible soils encountered
in the trench excavations should not be used for supporting utilities. The native soils should
generally be suitable for use as structural trench backfill. Moisture conditioning of the soils will
likely be necessary prior to use as structural backfill. Utility trench backfill should be placed and
compacted to 95 percent of the modified proctor, or to the presiding jurisdiction specifications.
Limitations
The recommendations and conclusions provided in this geotechnical evaluation letter are
professional opinions consistent with the level of care and skill that is typical of other members
in the profession currently practicing under similar conditions in this area. A warranty is not
expressed or implied. Variations in the soil and groundwater conditions observed at the test pit
locations may exist, and may not become evident until construction. ESNW should reevaluate
the conclusions in this geotechnical evaluation letter if variations are encountered.
Should you require additional information, or have questions, please call.
Sincerely,
EARTH SOLUTIONS NW, LLC
Adam Z. Shier, G.I.T.
Staff Geologist
Attachments: Plate 1 - Vicinity Map
Plate 2 - Test Pit Location Plan
Test Pit Logs
Grain Size Distribution
cc: Leif Helleren Construction, Inc.
Attention: Mr. Leif Helleren (Email only)
F;
"cZ i NAL
Henry T. Wright, P.E.
Senior Project Engineer
Earth Solutions NW, LLC
iNd rN
'M Pon
N
rL W 3k
25 Eeiv
J394 rL M —w:F!,?
IS!
3—
L
3N �4
hMW SV.C•X
35
3-:
FL ST rL
a
X
AF
PL n
X le H
IIUAII r I
)ki&ni��' LF1
yjyft:k JA, 2-
NO mv-
9A. .
PirwL a —:F
y.
Arp% FL a
_% :�
YA
3! .1--
rJ
.75 Ile
&w-7.r.
91
ZML i--Jw
—
K 5.57 Er
4w r
244GTK ST
;r T26.V" T, = N K R1II!&K.Tr`(W'fflYT"F F
C C
�53;,H , Y. sA
LN 1 S�16 NjL IMIFY!
NMI)h L M
Jw 17%
ip 1, sr-�!
'Vam7 it K.
awn
%mTnts r 11 H %r
■ UhD ti
py M CA"
Sf
I OFMIT gym - I
#
H rH
FP
PJDjffi hM
W,
in
.4&
nil �Vls LL4 LU 9r. V—
M
% t4w PAGO -tf '4,
9 1�
= MH Mill Iffn Air
IN
tip IwIST
vCjrI1 a;L
CAAI:
ID
sr A h ST 105FH 5T
114L
U2
%R LI
hvw IylI U, ME:
OFri i'N
Ney A IN, 'ME 1-r C lzin, %I L,
.WFH�
)r
% mmyj 1 51 vini:E
Rr %% I; M
Reference: NORTH
Snohomish County, Washington
Map 474 Oil!
By The Thomas Guide
Rand McNally
32nd Edition 4
k: :z
IF, 1z
NOTE: This plate may contain areas of color. ESNW cannot be Drwn. MRS Date 07/19/2017 Proj. No. 5323
responsible for any subsequent misinterpretation of the information
resulting from black & white reproductions of this plate. Checked AZS I Date July 2017 Plate 1
226TH STREET S.W.
- — - - — - — - - — - - — -
I I
I I I
I I I
I
I I
I
LEGEND
TP-1 Approximate Location of
— ■ — ESNW Test Pit, Proj. No
ES-5323, June 2017
I LSubject Site
__
Existing Building
Proposed Building
NORTH
0 30 60 120
1 "=60'
Scale in Feet
NOTE: The graphics shown on this plate are not intended for design
purposes or precise scale measurements, but only to illustrate the
approximate test locations relative to the approximate locations of
existing and / or proposed site features. The information illustrated
is largely based on data provided by the client at the time of our
study. ESNW cannot be responsible for subsequent design changes
or interpretation of the data by others.
NOTE: This plate may contain areas of color. ESNW cannot be
responsible for any subsequent misinterpretation of the information
resulting from black & white reproductions of this plate.
�coc
ca a O
a � �
O
U
U N
O
J U)
o-0
a o
n E
oLU
�w
Drwn. By
M RS
Checked By
AZS
Date
07/19/2017
Proj. No.
5323
Plate
2
Earth Solutions l VVLLC
SOIL CLASSIFICATION CHART
MAJOR DIVISIONS
SYMBOLS
TYPICAL
GRAPH LETTER
DESCRIPTIONS
CLEAN
Gw
WELL -GRADED GRAVELS. GRAVEL -
GRAVEL
GRAVELS
*►r
MIXTURES, LITTLE OR NO
AND
FSAND INES
GRAVELLY
SOILS
a
° ❑QO"C?
POORLY -GRADED GRAVELS,
(LITTLE OR NO FINES
a o a o GP
GRAVEL- SAND MIXTURES, LITTLE
❑ c0
OR NO FINES
COARSE
a
GRAINED
SOILS MORETHAN%
GRAVELS WITH
GM
SILTY GRAVELS, GRAVEL - SAND -
SE
FINES
�#
a
Q
SILT MIXTURES
FRACTION
RETAINED ON NO.
4 SIEVE
(APPREAMOUNT CI ABLECLAYEY
GC
GRAVELS, GRAVEL - SAND -
FINES
CLAY MIXTURES
MORE THAN 50% SAND
CLEAN SANDS
Sw
WELL -GRADED SANDS, GRAVELLY
SANDS, LITTLE OR NO FINES
OF MATERIAL IS AND
LARGERTHAN SANDY
NO.200 SIEVE SOILS
SIZE
(LITTLE OR NO FINES)
SP
POORLY -GRADED SANDS,
GRAVELLY SAND, LITTLE OR NO
FINES
SANDS WITH
FINES
=
SM
SILTY SANDS, SAND -SILT
MIXTURES
MORE THAN 50%
OF COARSE
FRACTION
PASSING ON NO.
4 SIEVE
FINES) LE
SC
CLAYEY SANDS, SAND -CLAY
AMOUNT OF
M X URES
INORGANIC SILTS AND VERY FINE
ML
SANDS, ROCK FLOUR, SILTY OR
CLAYEY FINE SANDS OR CLAYEY
SILTS WITH SLIGHT PLASTICITY
r+�-
INORGANIC CLAYS OF LOW TO
MEDIUM PLASTICITY, GRAVELLY
SILTS
LIQUID LIMIT
FINE AND
GRAINED CLAYS LESS THAN 50
CLAYS, SANDY CLAYS, SILTY
SOILS
CLAYS, LEAN CLAYS
OL
ORGANIC SILTS AND ORGANIC
—
SILTY CLAYS OF LOW PLASTICITY
MORE THAN S
OF MATERIALL I
MH
INORGANIC SILTS, MICACEOUS OR
DIATOMACEOUS
SMALLER THANN
FINE SAND OR
NO.200 SIEVE
SILTY SOILS
SIZE
SILTS
AND IN
CHLIQUID
INORGANIC CLAYS OF HIGH
GREATER THAN 50
EATER
CLAYS
PLASTICITY
OH I
ORGANIC CLAYS OF MEDIUM TO
HIGH PLASTICITY, ORGANIC SILTS
HIGHLY ORGANIC SOILS
P�'
PEAT, HUMUS, SWAMP SOILS WITH
HIGH ORGANIC CONTENTS
DUAL SYMBOLS are used to indicate borderline soil classifications.
The discussion in the text of this report is necessary for a proper understanding of the nature
of the material presented in the attached logs.
Earth Solutions NW TEST PIT NUMBER TP-1
1805 - 136th Place N.E., Suite 201
Bellevue, Washington 98005 PAGE 1 OF 1
VAN
Telephone: 425-449-4704
Fax: 425-449-4711
CLIENT Kari Johannessen PROJECT NAME Johannessen Short Plat
PROJECT NUMBER ES-5323 PROJECT LOCATION Edmonds, Washington
DATE STARTED 6/29/17 COMPLETED 6/29/17 GROUND ELEVATION TEST PIT SIZE
EXCAVATION CONTRACTOR CLE GROUND WATER LEVELS:
EXCAVATION METHOD AT TIME OF EXCAVATION ---
LOGGED BY AZS CHECKED BY HTW AT END OF EXCAVATION ...
NOTES Depth of Topsoil & Sod 4": soil AFTER EXCAVATION ---
I W
HW
U
_
W_
TESTS
(6
° O
MATERIAL DESCRIPTION
Q" a=
�
Qz
0
TPSL
� '
0.5 Dark brown, TOPSOIL
Tan silty SAND with gravel, medium dense, moist
MC = 6.60%
SM
MC = 3.20%
2 U
Gray poorly graded GRAVEL with sand, medium dense, damp
a �9
Op
p a�
MC = 3.00%
Fines = 0.90%
Qb
[USDA Classification: extremely gravelly SAND]
5
GP
O
° O�
�b
�a
- -
° R4
Ob
o [�"
-becomes moist
� �
-
MC = 11.70%
9.0
Test Pit terminated at 9.0 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
Bottom of test pit at 9.0 feet.
Earth Solutions NW TEST PIT NUMBER TP-2
1805 - 136th Place N.E., Suite 201
Bellevue, Washington 98005 PAGE 1 OF 1
Tax
Telephone: 425-449-4704
Fax: 425-149-4711
CLIENT Kari Johannessen PROJECT NAME Johannessen Short Plat
PROJECT NUMBER ES-5323 PROJECT LOCATION _ Edmonds, Washington
DATE STARTED 6/29/17 COMPLETED 6/29/17 GROUND ELEVATION TEST PIT SIZE
EXCAVATION CONTRACTOR CLE GROUND WATER LEVELS:
EXCAVATION METHOD AT TIME OF EXCAVATION —
LOGGED BY AZS CHECKED BY HTW AT END OF EXCAVATION --
NOTES Depth of Topsoil & Sod 6": grass AFTER EXCAVATION ---
w
U
_
a
�W
TESTS
U
a 0
MATERIAL DESCRIPTION
Q
a=
vd
az
=
rn
0
TPSL
..
0.5 Dark brown TOPSOIL, roots
Brown silty SAND with gravel, medium dense, moist
- -
MC = 7.60%
SM
MC = 2.80%
2.0
Gray poorly graded GRAVEL with sand, medium dense, damp
o Qa
°i7V
MC = 2.30%
b0�
[USDA Classification: extremely gravelly SAND]
5
Fines = 0.20%
P
° C50
a D
)Q
a°
7.0
Gray poorly graded SAND, medium dense, moist
-
SP
MC = 16.60%
9.0 [USDA Classification: slightly gravelly SAND]
Fines = 0.10%
Test pit terminated at 9.0 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
Bottom of test pit at 9.0 feet.
Ld
31�1
1
I
INS
�llil�ii
iA
millillin
millillin
llmmiiiiiiimmiiiiiii,s-
lismillillismillillinm
lins�ii
lillin
diil
1
I111
iiiiiiinm
�m
USDA: Gray Extremely Gravelly Sand. USCS: GP with Sand.
TP-2 9.0oft.
USDA: Gray Slightly Gravelly Sand. USCS: SP.
0
■