BLD2021-0090+Geotech Report+1.21.2021_10.24.04_AM+2000908Group Northwest, Inc.
December 301h, 2020
Mr. Thang Nguyen
7300 — 176th St SW
Edmonds, WA
Email: TNguyen98005&gmail.com
Phone: (253) 486-9154
Subject: Geotechnical Evaluation
Backyard Deck & Geologic Hazard Areas
7300 —176th St SW
Edmonds, WA
Dear Mr. Nguyen,
Geotechnieal Engineers, Geologists
& Environmental Specialists
G-5330
Per your request, GEO Group Northwest, Inc. has completed a geotechnical evaluation of the
backyard deck and geologic hazard areas located at the above -subject property in Edmonds,
Washington.
SITE DESCRIPTION
The project site is a currently occupied, single-family residential lot in northern Edmonds,
Washington, as illustrated in Plate I — Site location Map. The parcel is trapezoid shaped and
comprises approximately 11,326 square feet (0.26 acres). The existing residence occupies the
northern region of the lot closest to 176th Street Southwest. The backyard is level near the
eastern property line, however begins to slope southwest at moderate to steep inclinations down
to a gully at the southern property line, and slopes west at low to moderate inclinations to the
western property line. The site is bordered by residential developed properties to the west, south,
and east, and by 176th Street Southwest to the north. Construction of an elevated deck attached
to the southwest corner of the residence has been started earlier this year, but is currently halted
per the direction of the City of Edmonds.
13705 Bel -Red Road • Bellevue, Washington 98005
Phone 425/649-8757 • Fax 425/649-8758
December 30th, 2020 G-5330
7300 — 176th St SW, Edmonds, WA Page 2
GEOLOGIC OVERVIEW
According to the geologic mapping of the area, the site soils are identified as Vashon subglacial
till (Qvt) from the Fraser Glaciation. Vashon subglacial till deposits typically consist of non -
stratified mixtures of sand, silt, and gravel that were deposited beneath the Vashon glacier during
the Fraser glaciation time period (late Pleistocene) that ended approximately 13,000 years ago.
As a result of being consolidated by the glacial ice, glacial till deposits are typically dense to
very dense and relatively impermeable.
SITE INVESTIGATION
On December loth, 2020, Mr. Garrett Dean, Staff Engineering Geologist from our firm, visited
the site to perform a visual reconnaissance of the property and investigate the subsurface soil
conditions. Two exploratory borings, HA-1 and HA-2, were drilled using a hand -operated auger.
The boring locations are illustrated on Plate 2 — Site Plan.
Soils encountered consisted of a layer of medium dense topsoil to a depth of approximately 10 to
12 inches, underlain by weathered glacial till consisting of medium dense to dense silty sand
with variable amounts of subrounded gravel, and cobbles. Denser, less weathered glacial till was
found at depths between 1.5 and 2.4 feet in the borings. Groundwater seepage was not
encountered during our investigation. For a more detailed description of the soils encountered,
please refer to the hand auger boring logs in Attachment 1.
Elevated Backyard Deck
We evaluated the deck's construction during our visit. We observed that the deck is
approximately 12 feet wide by 19 feet long, and elevated approximately 10 feet above the ground
surface at the tallest extent. The deck attaches to the western side of the south face of the
existing residence. The floor of the deck is slatted and allows water to pass through to the
ground below. The deck is supported on 6 inch by 6 inch timber posts bracketed to cubic
concrete footings which are directly underlain by very dense, native glacial till. It is our opinion
that the deck is well -supported from a geotechnical standpoint.
GEO Group Northwest, Inc.
December 30th, 2020 G-5330
7300 — 176th St SW, Edmonds, WA Page 3
Landslide Hazard Area
City of Edmonds GIS mapping indicates that a landslide hazard area is present on the project
property and extends onto portions of adjacent properties to the west and east. This area is
indicated on Plate 2 — Site Plan, and Plate 3 — Geologic Hazard Areas Mapping.
The mapped landslide hazard area on the property is restricted to the southern portion of the
property which slopes south to a shallow gully. The hazard area is approximately 43 feet south
of the existence residence footprint. This slope area is shown as having a height of up to
approximately 26 feet. Edmonds GIS mapping indicates the upper 14 feet of slope descends at
an inclination of less than or equal to approximately 46 percent grade, while the bottom 12 feet
slopes at an inclination less than or equal to approximately 27 percent grade. Per ECDC
23.80.020(B), the upper portion of the slope area meets the criteria for designation as a landslide
hazard area based on its inclination and height (criteria #4 and #8 in the code section).
Erosion Hazard Area
City of Edmonds GIS mapping indicates that an erosion hazard area is present on the property
and onto portions of adjacent properties to the north, west, south, and east. These areas are
indicated in Plate 3 — Geologic Hazard Areas Mapping.
According to information obtained from the USDA Natural Resources Conservation Service
(MRCS), surface soils on slopes with inclinations between 2 and 8 percent on the property are
mapped as Alderwood-Urban land complex series soils. These soils typically consist of gravelly
sandy loam and have a parent material of basal glacial till. Nearby developed area to the west is
mapped as having Alderwood series soils on slopes with inclinations between 15 to 30 percent.
These soils typically consist of gravelly sandy loam and have a parent material of glacial drift or
outwash over dense glacio-marine deposits, according to NRCS. Soils information is attached as
Attachment 2 to this report.
Hazard Evaluation
The presence of a typical topsoil horizon underlain with dense to very dense, native glacial till at
shallow depths in the project site is indicative of minimal previous site grading. In our opinion,
past modification of the landslide hazard designated slope is unlikely to have occurred. The
slope is mantled with trees, ivy and other ground cover, which provides protection against soil
movement or erosion. The recently -constructed deck protrudes 19 feet south from the southwest
GEO Group Northwest, Inc.
December 30th, 2020 G-5330
7300 — 176th St SW, Edmonds, WA Page 4
corner of the existing residence, 24 feet north of the mapped landslide hazard. The deck
construction has not added any impervious surface area, as the flooring is slatted and free -
draining. The distance from the landslide hazard, minimal bearing pressure, presence of very
dense native soils underlying the footings, and the absence of additional impervious surface area
to the project site are mitigating factors regarding potential impacts to the site's geologic hazard
areas. It is our opinion that the deck has not reduced the factor of safety for landslide
occurrences below the limits of 1.5 for static conditions and 1.2 for dynamic conditions on slopes
at the project site or adjacent properties.
Hazard Mitigation
We do not anticipate adverse impact to critical areas due to the deck construction, however, our
recommended measures to mitigate the potential for landsliding or erosion associated with the
project include the following:
- Retention of vegetation and ground cover on the slope to provide protection against soil
movement or erosion.
CONCLUSIONS
We understand that construction of the subject backyard deck has been halted due to the lack of a
building permit. After investigation of the deck construction, subsurface condition, and geologic
hazard areas, it is our opinion that the deck is well -supported and bears on very dense, native
glacial till. In our opinion, the risk of the backyard deck adversely affecting the geologic hazard
areas on the subject or neighboring properties can be considered negligible.
GEO Group Northwest, Inc.
December 30th, 2020 G-5330
7300 — 176th St SW, Edmonds, WA Page 5
LIMITATIONS
The findings and recommendations stated herein are based on field observations, our experience
on similar projects and our professional judgment. The recommendations presented herein are
our 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 and within the project schedule and budget constraints. No warranty is
expressed or implied. In the event that site conditions are found to differ from those described in
this report, we should be notified so that the relevant recommendations in this report can be
reevaluated and modified if appropriate.
CLOSING
We appreciate the opportunity to provide you with geotechnical engineering services for this
project. Please do not hesitate to contact us if you have any questions regarding this report.
Sincerely,
GEO Group Northwest, Inc.
Garrett Dean, G.I.T.
Staff Engineering Geologist
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4 pF WA�yl�9 �
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William Chang, P.E.
Principal Engineer
GEO Group Northwest, Inc.
December 30th, 2020 G-5330
7300 — 176th St SW, Edmonds, WA Page 6
Plates and Attachment:
Plate I — Site Location Map
Plate 2 — Site Plan
Plate 3 — Geologic Hazard Areas Mapping
Attachment I — USCS Soil Classification and Hand Auger Boring Logs
Attachment 2 — NRCS Soil Mapping
GEO Group Northwest, Inc.
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SITE LOCATION MAP
Group Northwest, Inc. NGUYEN RESIDENCE
- Geotechnical Engineers, Geologists, & 7300 - 176TH ST SW
Environmental Scientists EDMONDS, WASHINGTON
SCALE NONE DATE 12/30/2020 1 MADE GD CHKD WC I JOB NO. G-5330 I PLATE 1
Approximate
Property Line
Boring Number & ❑ Erosion Hazard
Approximate Location Critical Area 0 20' 40'
HA-1
❑ Landslide Hazard Approx. Scale: 1 inch = 20 feet
This Plan Adapted From City of Edmonds GIS, 2020 Critical Area
SITE PLAN
Group Northwest, Inc. NGUYEN RESIDENCE
- Geotechnical Engineers, Geologists, & 7300 - 176TH ST SW
Environmental Scientists EDMONDS, WASHINGTON
SCALE AS SHOWN DATE 12/30/2020 1 MADE GD j CHKD WC I JOB NO. G-5330 I PLATE 2
City of Edmonds
Geologic Hazard Areas Mapping
'
�.
3�
Legend
Creeks
® Seismic Hazard Areas
Earth Subsidence and Landslide 1
L! Minimum Buffer Adjace nt to Hat
Wetlands
Wetlands Boundary
— - Wetland 90undA-S Not Com plu[et
MMM
,0
o Wetland Known Ex--
ElvadPlains
A
Lj
39
AE
M
_
�
q
®
® l'F
.ry
❑ x
asp
3� .in:S
•37 i
Contour Lines t
.35-8
Q mod• ' rp1
— t D. e
1410
Landslide Hazard Area 40%
rr
❑ Severe Erasion Hazard 15%-40%
a
❑ Erosion Hazard Areas 15%-40%
1: 379
4�
Notes
7300 - 176th St SW, Edmonds. WA
0 31.57 63.1 Feet
S� 47.0 This map is a user generated static output from an Internet mapping sire and is for
WG5. 1984 Web Mercator Auailia ry, Sphere
reference only. D. to layers that appea r on this map may or may no[ he actuate,
—rrent,orotherwisereliable-
City of Edmonds
THIS MAP
IS NOT TO RE USED FOR DESIGN OR CONSTRUCTION
Source: City of Edmonds GIS.
GEOLOGIC HAZARD AREAS MAPPING
Group Northwest, Inc.
NGUYEN RESIDENCE
7300 - 176TH ST SW
_ Geotechnical Engineers, Geologists, &
Environmental Scientists
EDMONDS, WASHINGTON
SCALE: As Shown
DRAWN: GD
CHECKED: WC
DATE: 12/30/2020
1 PROJECT NO.: G-5330
I PLATE 3
LEGEND OF SOIL CLASSIFICATION AND PENETRATION TEST
MAJOR DIVISION
COARSE
GRAINED
SOILS
More Than Half
by Weight Larger
Than No. 200
Sieve
FINE-GRAINED
SOILS
More Than Half
by Weight
Smaller Than No.
200 Sieve
CLEAN
GRAVELS
GRAVELS
(little or no
fines)
(More Than Half
Coarse Grains
Larger Than No.
DIRTY
4 Sieve)
GRAVELS
(with some
fines)
CLEAN
SANDS
SANDS
(little or no
(More Than Half
fines)
Coarse Grains
Smaller Than No.
A. Sieve)
DIRTY
SANDS
(with some
fines)
SILTS
Liquid Limit
(Below A -Line on
< 50%
Plasticity Chart,
Liquid Limit
Negligible
Organic)
> 50%
CLAYS
Liquid Limit
(Above A -Line on
< 30%
Plasticity Chart,
Liquid Limit
Negligible
Organic)
> 50%
Liquid Limit
ORGANIC
< 50%
SILTS & CLAYS
(Below A -Line on
Plasticity chart)
Liquid Limit
> 50%
UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)
GROUP
LABORATORY
SYMBOL
TYPICAL DESCRIPTION
CLASSIFICATION
CRITERIA
WELL GRADED GRAVELS, GRAVEL -SAND
Cu =(D60/D10) greaterthan 4
GW
MIXTURE, LITTLE OR NO FINES
DETERMINE
Cc = (D30 * D30 / D10 / D60) between 1 and 3
POORLY GRADED GRAVELS, AND GRAVEL -SAND
GP
MIXTURES LITTLE OR NO FINES
PERCENTAGES OF
NOT MEETING ABOVE REQUIREMENTS
GRAVEL AND SAND
FROM GRAIN SIZE
ATTERBERG LIMITS BELOW
GM
SILTY GRAVELS, GRAVEL -SAND -SILT MIXTURES
DISTRIBUTION
CONTENT
"A" LINE.
CURVE.
COARSE GRAINED
OF FINES
EXCEEDS
or P.I. LESS THAN 4
CLAYEY GRAVELS, GRAVEL -SAND -CLAY
ATTERBERG LIMITS ABOVE
GC
MIXTURES
SOILS ARE CLASSIFIED
12%
"A" LINE.
AS FOLLOWS:
<5% Fine Grained:
or P.I. MORE THAN 7
WELL GRADED SANDS, GRAVELLY SANDS,
Cu = (D60 / D10) greater than 6
SW
LITTLE OR NO FINES
GW, GP, SW, SP
> Fine Grained:
Cc= (D30 * D30 / D10 / D60) between 1 and 3
POORLY GRADED SANDS, GRAVELLY SANDS,
SP
LITTLE OR NO FINES
GGMM, GC, SM, SC;
SFine
NOT MEETING ABOVE REQUIREMENTS
ATTERBERG LIMITS BELOW
SM
SILTY SANDS, SAND -SILT MIXTURES
se dual
Grainined:d: use
symbols.
CONTENT
"A" LINE
OF FINES
EXCEEDS
with P.I. LESS THAN 4
ATTERBERG LIMITS ABOVE
SC
CLAYEY SANDS, SAND -CLAY MIXTURES
12%
"A" LINE
with P.I. MORE THAN 7
INORGANIC SILTS, ROCK FLOUR, SANDY SILTS
60
MIL
OF SLIGHT PLASTICITY
INORGANIC SILTS, MICACEOUS OR
50
MH
DIATOMACEOUS, FINE SANDY OR SILTY SOIL
o
INORGANIC CLAYS OF LOW PLASTICITY,
W 40
CL
GRAVELLY, SANDY, OR SILTY CLAYS, CLEAN
0
CLAYS
U30
CH
INORGANIC CLAYS OF HIGH PLASTICITY, FAT
CLAYS
H
5 2D
OL
ORGANIC SILTS AND ORGANIC SILTY CLAYS OF
a
LOW PLASTICITY
10
7
OH
ORGANIC CLAYS OF HIGH PLASTICITY
4
0
A -Line _1
FL.AITICITY CHART FOR
PASSING NO. 40
SIEVE
CH or OH
CL or OL
4-ML
MH or OH
OL or ML
0 10
HIGHLY ORGANIC SOILS Pt PEAT AND OTHER HIGHLY ORGANIC SOILS LIQUID LIMIT (% )
SOIL PARTICLE SIZE
FRACTION
U.S. STANDARD SIEVE
Passing
Retained
Sieve
Size
(mm)
Sieve
Size
(mm:
SILT / CLAY
#200
0.075
SAND
FINE
MEDIUM
COURSE
#40
410
#4
0.425
0
4.75
#200
940
#10
0.075
0.425
2
GRAVEL
FINE
COURSE
19
76
#4
4.75
19
COBBLES
76 mm to 203 mm
BOULDERS
> 203 mm
ROCK
FRAGMENTS
> 76 mm
ROCK
>0.76 cubic meter in volume
GENERAL GUIDANCE OF SOIL ENGINEERING PROPERTIES
FROM STANDARD PENETRATION TEST (SPT)
SANDY SOILS
SILTY & CLAYEY SOILS
Blow
Relative
Friction
Blow
Unconfined
Counts
Density
Angle
Description
Counts
Strength
Description
N
%
0, degree
N
qu, tsf
0-4
0 -15
Very Loose
< 2
< 0.25
Very soft
4-10
15 - 35
26 - 30
Loose
2-4
0.25 - 0.50
Soft
10 - 30
35 - 65
28 - 35
Medium Dense
4-8
0.50 - 1.00
Medium Stiff
30 - 50
65 - 85
35 - 42
Dense
8 - 15
1.00 - 2.00
Stiff
> 50
85 - 100
38 - 46
Very Dense
15 - 30
2.00 - 4.00
Very Stiff
> 30
> 4.00
Hard
Group Northwest, Inc.
Geotechnical Engineers, Geologists,
& Environmental Scientists
13240 NE 20th Street, Suite 12 Bellevue, WA 98005
Phone (425) 649-8757 Fax (425) 649-8758 ATTACH, 1
HAND -AUGER BORING: HA-1
LOGGED BY GD LOG DATE: 12/10/2020
GROUND ELEV. 383 feet+/ -
DEPTH
ft.
USCS
SOIL DESCRIPTION
SAMPLE
No.
Water
%
OTHER TESTS/
COMMENTS
Silty SAND, dark brown, medium dense, damp; organic -rich,
F S 1
21.6
Probe 8" at 0'
SPA
with some subrounded gravel, and roots
�
SM
(topsoil) /
--------------------------
Probe2"at1.3'
2
SPA
Silty SAND, grayish brown, dense to very dense, damp; with
S2
9.3
Probe 1" at 1.9'
subrounded gravel and some cobbles
SM
(glacial till)
Probe 0.5
3
S3
9.5
at 2.4'
Total depth = 2.7 feet
4
No groundwater encountered.
5
6
7
LOGGED BY GD
HAND -AUGER BORING: HA-2
LOG DATE: 12/2/2020
GROUND ELEV. 381 feet+/ -
DEPTH
ft.
USCS
SOIL DESCRIPTION
SAMPLE
No.
Water
%
OTHER TESTS/
COMMENTS
SP/
Silty SAND, dark brown, medium dense, damp; organic -rich,
Probe 8" at 0'
1
SM
with some subrounded gravel, and roots
— —
(topsoil) f
-----------------------
Probe 1" at 1.1'
2
SP/
Silty SAND, brown, dense to very dense, damp; with
S1
9,8
Probe 0.5„
SM
subrounded gravel and some cobbles
at 1.7'
(glacial till)
3
Total depth = 2.4 feet
No groundwater encountered.
4
5
6
7
Group Northwest, Inc.
Geotechnical Engineers, Geologists, &
Environmental Scientists
HAND AUGER BORING LOGS
SINGLE-FAMILY RESIDENCE
7300 - 176TH ST SW
EDMONDS, WASHINGTON
JOB NO. G-5330 DATE 12/30/20 ATTACH. 1
NV
549600
47o 50'27'N
Soil Map —Snohomish County Area, Washington
(7300 - 176th St SW, Edmonds, WA)
549MO 549760 549840 549920 550000 550080
550160
nif. I id J.'t t"Ih i
4W
47o 50' 11" N
549600 549680 549760 549840 549920 550000 550080 550160
Map Scale: 1:3,560 if printed on A landscape (11" x 8.5") sheet.
I Meters
N '50
Web Mencatloo rn200 300
Feet
0 150 300 600 900
Map projection or Comer coordinates: WGS84 Edge tics: LTrM Zone ION WGS84
usDA Natural Resources Web Soil Survey
Conservation Service National Cooperative Soil Survey
550240
550240
rym
5503M
�w I 47o 59 27" N
R
I
50'11" N
550320
12/29/2020
Page 1 of 3
MAP LEGEND
Area of Interest (AOI)
0
Area of Interest (AOI)
Soils
0
Soil Map Unit Polygons
rwr
Soil Map Unit Lines
0
Soil Map Unit Points
Special
Point Features
Vo
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
.14
Gravelly Spot
0
Landfill
Lava Flow
Marsh or swamp
+
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
4
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
oa
Sodic Spot
Soil Map —Snohomish County Area, Washington
(7300 - 176th St SW, Edmonds, WA)
MAP INFORMATION
Spoil Area
The soil surveys that comprise your AOI were mapped at
1:24,000.
Stony Spot
Very Stony Spot
Warning: Soil Map may not be valid at this scale.
Wet Spot
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
Other
line placement. The maps do not show the small areas of
.-
Special Line Features
contrasting soils that could have been shown at a more detailed
scale.
Water Features
Streams and Canals
Please rely on the bar scale on each map sheet for map
measurements.
Transportation
Rails
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
rwr
Interstate Highways
Coordinate System: Web Mercator (EPSG:3857)
US Routes
Maps from the Web Soil Survey are based on the Web Mercator
L
Major Roads
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Local Roads
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
Background
.
Aerial Photography
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Snohomish County Area, Washington
Survey Area Data: Version 22, Jun 4, 2020
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Sep 2, 2018—Sep
25, 2018
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
USDA Natural Resources Web Soil Survey 12/29/2020
Conservation Service National Cooperative Soil Survey Page 2 of 3
Soil Map —Snohomish County Area, Washington
7300 - 176th St SW, Edmonds, WA
Map Unit Legend
Map Unit Symbol
Map Unit Name
Acres in AOI
Percent of AOI
3
5
Alderwood gravelly sandy
loam, 15 to 30 percent
slopes
21.1
43.0%
57.0%
Alderwood-Urban land
complex, 2 to 8 percent
slopes
28.0
Totals for Area of Interest
49.1
100.0%
usDA Natural Resources Web Soil Survey 12/29/2020
Conservation Service National Cooperative Soil Survey Page 3 of 3
Map Unit Description: Alderwood gravelly sandy loam, 15 to 30 percent slopes ---Snohomish
County Area, Washington
Snohomish County Area, Washington
3—Alderwood gravelly sandy loam, 15 to 30 percent slopes
Map Unit Setting
National map unit symbol: 2t627
Elevation: 0 to 1,000 feet
Mean annual precipitation: 25 to 60 inches
Mean annual air temperature: 46 to 52 degrees F
Frost -free period: 160 to 240 days
Farmland classification: Farmland of statewide importance
Map Unit Composition
Alderwood and similar soils: 85 percent
Minor components: 15 percent
Estimates are based on observations, descriptions, and transects of
the mapunit.
Description of Alderwood
Setting
Landform: Ridges, hills
Landform position (two-dimensional): Backslope
Landform position (three-dimensional): Side slope, nose slope, talf
Down -slope shape: Linear, convex
Across -slope shape: Convex
Parent material: Glacial drift and/or glacial outwash over dense
glaciomarine deposits
Typical profile
A - 0 to 7 inches: gravelly sandy loam
Bw1 - 7 to 21 inches: very gravelly sandy loam
Bw2 - 21 to 30 inches: very gravelly sandy loam
Bg - 30 to 35 inches: very gravelly sandy loam
2Cd1 - 35 to 43 inches: very gravelly sandy loam
2Cd2 - 43 to 59 inches: very gravelly sandy loam
Properties and qualities
Slope: 15 to 30 percent
Depth to restrictive feature: 20 to 39 inches to densic material
Drainage class: Moderately well drained
Capacity of the most limiting layer to transmit water (Ksat): Very low
to moderately low (0.00 to 0.06 in/hr)
Depth to water table: About 18 to 37 inches
Frequency of flooding: None
Frequency of ponding: None
Available water capacity. Very low (about 2.7 inches)
Interpretive groups
Land capability classification (irrigated): None specified
Land capability classification (nonirrigated): 4e
Hydrologic Soil Group: B
usDA Natural Resources Web Soil Survey 12/29/2020
Conservation Service National Cooperative Soil Survey Page 1 of 2
Map Unit Description: Alderwood gravelly sandy loam, 15 to 30 percent slopes ---Snohomish
County Area, Washington
Forage suitability group: Limited Depth Soils (G002XF303WA),
Limited Depth Soils (G002XN302WA), Limited Depth Soils
(G002XS301 WA)
Other vegetative classification: Limited Depth Soils
(G002XF303WA), Limited Depth Soils (G002XN302WA),
Limited Depth Soils (G002XS301 WA)
Hydric soil rating: No
Minor Components
Everett
Percent of map unit: 5 percent
Landform: Eskers, moraines, kames
Landform position (two-dimensional): Backslope
Landform position (three-dimensional): Side slope
Down -slope shape: Convex
Across -slope shape: Convex
Hydric soil rating: No
Indianola
Percent of map unit: 5 percent
Landform: Eskers, kames, terraces
Landform position (three-dimensional): Tread
Down -slope shape: Linear
Across -slope shape: Linear
Hydric soil rating: No
Shalcar
Percent of map unit: 3 percent
Landform: Depressions
Landform position (three-dimensional): Dip
Down -slope shape: Concave
Across -slope shape: Concave
Hydric soil rating: Yes
Norma
Percent of map unit: 2 percent
Landform: Drainageways, depressions
Landform position (three-dimensional): Dip
Down -slope shape: Linear, concave
Across -slope shape: Concave
Hydric soil rating: Yes
Data Source Information
Soil Survey Area: Snohomish County Area, Washington
Survey Area Data: Version 22, Jun 4, 2020
usDA Natural Resources Web Soil Survey 12/29/2020
Conservation Service National Cooperative Soil Survey Page 2 of 2
Map Unit Description: Alderwood-Urban land complex, 2 to 8 percent slopes ---Snohomish
County Area, Washington
Snohomish County Area, Washington
5—Alderwood-Urban land complex, 2 to 8 percent slopes
Map Unit Setting
National map unit symbol: 2hz9
Elevation: 50 to 800 feet
Mean annual precipitation: 25 to 60 inches
Mean annual air temperature: 48 to 52 degrees F
Frost -free period: 180 to 220 days
Farmland classification: Not prime farmland
Map Unit Composition
Alderwood and similar soils: 60 percent
Urban land: 25 percent
Minor components: 15 percent
Estimates are based on observations, descriptions, and transects of
the mapunit.
Description of Alderwood
Setting
Landform: Till plains
Parent material: Basal till
Typical profile
H1 - 0 to 7 inches: gravelly ashy sandy loam
H2 - 7 to 35 inches: very gravelly ashy sandy loam
H3 - 35 to 60 inches: gravelly sandy loam
Properties and qualities
Slope: 2 to 8 percent
Depth to restrictive feature: 20 to 40 inches to densic material
Drainage class: Moderately well drained
Capacity of the most limiting layer to transmit water (Ksat): Very low
to moderately low (0.00 to 0.06 in/hr)
Depth to water table: About 18 to 36 inches
Frequency of flooding: None
Frequency of ponding: None
Available water capacity. Low (about 3.0 inches)
Interpretive groups
Land capability classification (irrigated): None specified
Land capability classification (nonirrigated): 4s
Hydrologic Soil Group: B
Forage suitability group: Limited Depth Soils (G002XN302WA)
Other vegetative classification: Limited Depth Soils
(G002XN302WA)
Hydric soil rating: No
usDA Natural Resources Web Soil Survey 12/29/2020
Conservation Service National Cooperative Soil Survey Page 1 of 2
Map Unit Description: Alderwood-Urban land complex, 2 to 8 percent slopes ---Snohomish
County Area, Washington
Minor Components
Terric medisaprists, undrained
Percent of map unit: 5 percent
Landform: Depressions
Other vegetative classification: Wet Soils (G002XN102WA)
Hydric soil rating: Yes
Norma, undrained
Percent of map unit: 5 percent
Landform: Depressions
Other vegetative classification: Wet Soils (G002XN102WA)
Hydric soil rating: Yes
Mckenna
Percent of map unit: 5 percent
Landform: Depressions
Other vegetative classification: Wet Soils (G002XN102WA)
Hydric soil rating: Yes
Data Source Information
Soil Survey Area: Snohomish County Area, Washington
Survey Area Data: Version 22, Jun 4, 2020
usDA Natural Resources Web Soil Survey 12/29/2020
Conservation Service National Cooperative Soil Survey Page 2 of 2