Brackett's Corner Geotechnical Investigation.pdfNorthwest, Geotechnical Engineers, Geologistsroa4�
&Environmental Scientists
W — . ...- — ---- --' . ------ ----
December 1, 2015
Mr. Jake Lyon
Pride Ventures
P.O. Box 429
Edmonds, WA 98020
also via: jake@prideventuresllc.com
Subject: INFILTRATION EVALUATION - SOIL CONFIRMATION
PROPOSED TO TOMES
8000 - 212"m ST SW
EDMONDS, WASHINGTON
G-3995
Ref: "Geotechnical Investigation, Townhome Buildings, 80' Avenue W and 2121' Street SW,
Edmonds, Washington, L&A Jon No. 15-058", Liu & Associates, Inc., June 15 2015.
Dear Mr. Lyon:
Per your request GEO Group Northwest, Inc., has prepared the following letter to document soil
conditions at the proposed infiltration system location for the proposed townhome development.
SITE AND PROJECT DESCRIPTION
The subject site is a currently developed lot containing three buildings. Based upon plans
prepared by Lovell- Sauerland & Associates, Inc., we understand that the proposed development
at the site is for a new 14 -building residential development. The site stormwater is proposed to
be infiltrated at a series of infiltration trenches located along the north and east sides of the
property boundaries. The bottom of the infiltration trenches are proposed to be at an elevation of
438.1 which ranges from approximately 8.9 to 9.9 feet below the existing site elevations at the
trench locations. The proposed development and infiltration layout is shown on the attached
Plate 1- Site Plan.
GEO Group Northwest, Inc.
13240 NE 20th Street, Suite 10 • Bellevue, Washington 98005
Phone 425/649-8757 - Fax 425/649-8758
December 1, 2015 G-3995
8000 - 212'h St SW, Edmonds, Washington Page 2
INFILTRATION EVALUATION BY OTHERS
In June of 2015 Liu and Associates, Inc. (L&A) prepared the referenced Geotechnical Report in
which infiltration rates were provided based upon gradational analysis of soils collected at two
test pits (TP -1 and TP -3) located at the east side of the lot in the general vicinity of the proposed
infiltration near the east property boundary. L&A described soils at the site as consisting of
Vashon Till (Qvt) overlying Advance Outwash (Qva). L&A described the soils observed at the
lower portions the test pits as being the Advance Outwash (Qva). For soil samples from depths
of 6.5-7.5 feet and 8.0-9.0 feet L&A recommended a design infiltration rate (Ks.,) not to exceed
2.0 inches/hour. GEO Group Northwest, Inc., has reviewed the Liu and Associates report.
CITY COMMENTS
Based upon discussions with Mr. Jake Lyons of Pride Ventures LLC we understand that the City
of Edmonds has concerns regarding whether or not the site soil conditions at the northern side of
the property match those which were tested at the east side of the lot and whether or not the
design infiltration rate is acceptable for infiltration trenches which are proposed near the north
side of the property. A written explanation of the City's comments was not provided.
SUBSURFACE CONDITIONS
On November 18, 2015 a representative of GEO Group Northwest, Inc., visited the site to
observe soils at test pits excavated by the project owner. Two test pits labled TP -G1 and TP -G2
were excavated at the north side of the property at the approximate locations shown on the
attached Plate 1- Site Plan. The test pits were located at or near the proposed location of the
northern infiltration trenches. Soils observed at the test pits consist of gravelly silty SAND soils
with varying amounts of cobbles and boulders which grade to sandier soils with less silt content
below depths of around 5 to 6 -feet below ground surface (bgs). The apparent unweathered
Vashon Till soils are present below depths of 2 to 3.5 feet bgs. The deeper sandier soils appear
to be a sandier portion of the Till or the underlying Advance Outwash soils. A log of the
observed soils is attached as Plate A2 - Test Pit Logs. The test pits TP-Gl and TP -G2 were
excavated to depths of 10 -feet and 6.25 -feet bgs, respectively, and no groundwater seepage was
observed at these depths. The test pit TP -G2 was limited in depth due to encountering existing
utilities at the sides of the trench. Soil samples were collected from the test pit TP -G1 at depths
of 7, 9 and 10 -ft bgs.
GEO Group Northwest, Inc.
December 1, 2015 G-3995
8000 - 212` St SW, Edmonds, Washington Page 3
GRADATIONAL ANALYSIS AND INFILTRATION RATE
Gradational analysis was performed for one sample S-3 collected from the test pit TP -G1 at a
depth of 10 -feet below ground surface (bgs). The results of this analysis are attached as Plate 2 -
Gradational Analysis. Based upon the gradational analysis for the S-3 soil we have used the
Soil Grain Size Analysis Method from the 2012 WDOE Stormwater Management Manual for
Western Washington (formula below) to calculate the estimated initial infiltration rate of Ksat =
17.1 inches/hour.
loglo (1 s,,) = -1.57 + 1.90 (D,o) + 0.015 (D60) - 0.013 (D90) - 2.08 (fees)
Similar to the L&A report we recommend applying a factor of safety of 4 to determine the design
infiltration rate, which in this case is Design Ksal = 4.3 inches/hour.
CONCLUSIONS AND RECOMMENDATIONS
It is our opinion that the soils observed at the test pits at the north side of the site are similar to
those observed at the east side of the property and that the recommended design infiltration rates
are appropriate for the proposed infiltration system. Our analysis indicates a faster infiltration
rate than the L&A report, however, we recommend using the slower value of 2 inches/hour due
to the likelihood of some site variability. We recommend that the proposed infiltration system be
designed and constructed in accordance with the referenced report by Liu and Associates.
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.
Adam Gaston
Project Engineer
Wil'
Principal
1
n
cc; Julian Liu - Liu and Associates - julianliu100@yahoo.com
GEO Group Northwest, Inc.
tit " W
' I,:.
oz
N aV O
tl4 1
,. 1 .....�.............- ...-- � -.....,..............._.........-._-- O W
tln�
M.
fly, p
9 g� �b a xri
u
It oil
Is
.a„a
I
f �
�4 W dl �. I
lr t "111111 ',�
� f
qq��pp °,,M I I �, ,��w�'rv,�... I'. ,. ..,.- kr + ix » « � •",w „x �. ., ,.......... y u n
Jin
I
M
4m iN6MmfU fYb k'1AfM
ry i FFF�++
4 lot
rA
p u
p�
Ih w �. mw .,.. m.Yw •, �. L.. ... ......... �,,. '"I.a, .,.J
W � 'tial
v
............
m
M
x d�ii,pp
yy` A"W
r-I �
m 0
I
Particle Size Distribution Report
�3A Coars�E20.8
Gravel
0.0 4.8 �
l7RRIIY JILC - 111111_
.,.. % Sand _.
... _,... __ . e .... ... � .
Coaras Madlum Fins
12.5 21.6 25.8
SIEVE PERCENT SPEC' PASS?
SI2E FINER PERCENT (X=NO)
�2't 100.0
l" 96.3
3/411 95.2
3/8" 86.0
#4 74.4
#10 61.9
#40 40.3
#60 29.8
#100 21.7
#200 14.5
#270 11.5
#325 9.8
(no specification provided)
Source of Sample: 0-3995 Lyon Depth: 10 ft
Sample 14uniber, T -PI
G'"roup Northwest. In,,
VJITO NE 20th Suit Suit. 10. BeILv , WA "kSAW
Pho 425*49-8757 PAX 4251649-9759
Emil �twb Y1remvwpnwxw:.It
SCALE: NTS DATE: 12-1-15 MADE: AG
Gray, Glacial Till
Silt
% Fines
14.5
Date: l l /20/l 5
GRADATIONAL ANALYSIS
8000 - 212TH ST SW
EDMONDS, WASHINGTON
JOB NO.: G-3995
PLATE: 2
PL= NP
l.= NV
PI-
Ge dents.
D90= 12.1405
D85= 8,9813
D60= 1.7246
D50= 0.7817
0330= 0,2521
D15= 0.0799
D10= 0.0460
C= 37.52
Cc= 0.80
9-Lals, l LcAtiqu
USCS= SM
AASHTO=
A -1-b
Remarks
Sampled: 11/18/15, Received: 11/19/15
Tested: 11/19115
Equipment: 53, 58, 66, 112
Date: l l /20/l 5
GRADATIONAL ANALYSIS
8000 - 212TH ST SW
EDMONDS, WASHINGTON
JOB NO.: G-3995
PLATE: 2
LEGEND OF SOIL CLASSIFICATION AND PENETRATION TEST
UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)
MAJOR DIVISION GROUP
UL TYPICAL DESCRIPTION J LABORATORY CLASSIFICATION CRITERIA
SYMB
WELL GRADED GRAVELS, GRAVEL -SAND Cu = (D60 / D10) grealerthan 4
CLEAN GWTELE OR NO FINES ween Cc = (0302) / (D10 , D60) bet1 and 3
GRAVELS
l MIXTURE. LI DETERMINE
PERCENTAG.... .
GRAVELS f (little or no GP POORLY GRADED GRA ES OF NOT MEETING ABOVE R
I VELS, AND GRAVEL SAND GRAVEL AND SAND
(More Than Had r fines) MIXTURES LITTLE OR NO FINES FROM GRAIN SIZE REQUIREMENTS
COARSE-
GRAINED SOILS Coarse Grains - __ DISTRIBUTION
Larger Than No. 4 CURVE ATTERBERG LIMITS BELOW
Sieve) DIRTY GM SILTY GRAVELS GRAVEL -SAND -SILT MIXTURES 'A' LINE.
GRAVELS I CONTENT or P I LESS THAN 4
OF FINES -
(with some CLAYEY GRAVELS, GRAVEL -SAND -CLAY EXCEEDS 12lines) GCS MIXTURES COARSE GRAINED ATTERBERG
LINE ABOVE
SOILS ARE or P -I. MORE THAN 7
AS
SANDS CLEAN SW WELL GRADED SAND . FINES _ GRAVELLY
SANDS, LIITLE CLASSIFIED FOLLOWS: = (13 070 10) greater ethan
en Band 3
( SANDS (D3 )
. , ._ .,m.. ... ............_____.._„.w ,
(More Than Had � ` „
CGrains (little or no POORLY GRADED SANDS, GRAVELLY SANDS, < 5% Fine Grained:
MoreThan Hall by oarse SP N07 MEETING ABOVE REQUIREMENTS
Weigh Larger 49mager Than No. 4 lines) LITTLE OR NO FINES GW, GP, SW, SP
Sieve) ....... _..... _ .�,..-.,�,,,,,,,, , ,,,,, ,.e,. ......�..,m-�-. .._.,�..,... ®,�....... .........-
Than No. 200 SiATTER.BERG LIMITS BELOW
Sieve DIRT. SM SILTY SANDS, SAND -SILT MIXTURES > 121/ Fine Grained: 'A' LINE
SANDS GM, GC, SM, SC CONTENT OF wgh P. 1. LESS THAN 4
— ,.... ... ,.m.,. ,...,. r ,�......... ..._..-__......-.,,,, FINES
(with some
5 to 11/ Fine EXCEEDS 12% ATTERBERG LIMITS ABOVE
Ones) Sc CLAYEY SANDS, SAND -CLAY MIXTURES Grained use dual "A' LINE
symbols with P.1, MORE THAN 7
Liquid quid Limit INORGANIC SILTS, ROCK FLOUR, SANDY SILTS
(Below A -Line on
SILTS 50 PLASTICITY CHART A Une OF SLIGHT PLASTICITY 60 -..- -
W
FINE-GRAINED Negligible organic) Llquidg� , . m ...� , ......._-.. C LT ,....,,_........ ..
_
Limit INORGANIC SILTS, MICACEOUS OR FOR SOIL PASSINGI I
SOILS > 50% MH DIATOMACEOUS, FINE SANDY OR SILTY SOIL 50 NO. 40 SIEVE .•._..11. ”"' """ °"
- -- ------------------...w nw .., .... o CH or OH
INORGANIC CLAYS OF LOW PLASTICITY, X 40 .-..
CLAYS Uq<30% CL GRAVELLY, SANDY, OR SILTY CLAYS, CLEAN O
(Above A -Line on CLAYS Z
.. ........ 30
Plecticity Chart, --- ..... .. ...-....._.... } ._-
Negligible Organic) Liquid Umit INORGANIC CLAYS OF HIGH PLASTICITY, FAT F—
>
SM. CH CLAYS FCL or OL
More Than Hag by ,_ ,.. •........ , -.._.._........ ....,....,,. .. ......... .................:
20 ..
Weight Smaller Liquid Limit ORGANIC SILTS AND ORGANIC SILTY CLAYS OF n- MH a OH
Than No. 200 ORGANIC SILTS 8 / OL LOW PLASTICITY 10
a . ,� . ,
Sieve CLAYS
w
..............w..._.....,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, r 7
x MIL
(Below A-Une on 4
OH ORGANIC CLAYS OF HIGH PLASTICITY mrt
Placticity Chart) Uqumd OV --- - •--�
> 501/6 0 10 20 30 40 0 60 70 80 90 100 110
LIQUID LIMIT (%)
HIGHLY ORGANIC SOILS Pt PEAT AND OTHER HIGHLY ORGANIC SOILS
SOIL PARTICLE SIZE
'..�..., . a,,. �.... ............... ___ .................... n GENERAL GUIDANCE OF SOIL ENGINEERING PROPERTIES FROM STANDARD PENETRATION TEST (SPT)
U.S. STANDARD SIEVE
FRACTION Passing Retained SANDY SOILS SILTY & CLAYEY SOILS
Ste..
ve Size Sieve Size Blow Relative i Friction Blow Unconfined
....... _ mm) Counts Density Angle Description Counts Strength Description
SILT / CLAY #200 0.075 N % (0, degree N qu, isf
.-,., $ ... _... -,. _.... -. ,...m.. ...mm .....v..- _ -..,
wa
.�4. ... 0-15.. .e_ ,,. ............�, Very Loose ------
w.. ...... �., ........,__...-...... _.- .... ................
2 0.25 V ry 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 #40 0.425 10-30 35.65 28-35 Medium Dense 4-11 0..50. 1.00 Medium Stiff
COARSE #4 4.75 1 #10 2 30-50 65-85 36-42 Dense 8-15 1.00.2,00 Stiff
> 50 85-100 38-46 Very Dense 15- 30 2.00.4.00 Very Stiff
FINE 19 #4 4,75 > 30 > 4.00 Hard
COARSE 76 k 19
COBBLES 76mm to 203 mm
130ULUE.. ...... .... ..... _.---_.... _ ...... Group Northwest, Inc.
RS > 203 mm
Geotachnical Engineers, Geologists, &
CK Erwlronmental Scientists
FRA oMENT3 > 76 mm
_ 13240 NE 20th Street, Suite 10 Bellevue, WA 98005
ROCK >0.76 cubic meter in volume Phone (425) 649.8757 Fax (425) 649-8758 PLATE Al
TEST PIT NO. TP -G1
TEST PIT NO. TP -G2
LOGGED BY AG TEST PIT DATE: 11/18/2015
DEPTH SAMPLE Water OTHER TESTS/
ft. USCS SOIL DESCRIPTION No. % COMMENTS
SM Brown/orangish gravelly silty SAND with occasional cobbles, moist,
medium dense
SM Tan gravelly silty fine SAND with some cobbles and occasional
boulders, moist, dense, cementation at 6' bgs (TILL)
5
Total depth of test pit = 6.25 feet bgs
No groundwater seepage observed
10
15
,Group Northwest, Inc.
Geotechnical Engineers, Geologists, $
Environmental Scientists
TEST PIT LOGS
PROPOSED TOWNHOMES
5000 - 212TH ST SW
EDMONDS, WASHINGTON
LOGGED
BY
AG TEST PIT DATE: 11/18/2015
DEPTH
SAMPLE
Water
OTHER TESTS/
ft.
USCS
SOIL DESCRIPTION
No.
%
COMMENTS
SM
Brown gravelly silty SAND with some cobbles and occasional
boulders, moist, medium dense to dense
SM-
-Light brown gravelly silty fine SAND and occasional boulders, moist,
5
cementation, nta on, dense (TILL)
SM
Grading to sandier soil at T bgs
S-1
S-2
10
S-3
Total depth of test pit = 10 feet below ground surface (bgs)
No groundwater seepage observed
15
TEST PIT NO. TP -G2
LOGGED BY AG TEST PIT DATE: 11/18/2015
DEPTH SAMPLE Water OTHER TESTS/
ft. USCS SOIL DESCRIPTION No. % COMMENTS
SM Brown/orangish gravelly silty SAND with occasional cobbles, moist,
medium dense
SM Tan gravelly silty fine SAND with some cobbles and occasional
boulders, moist, dense, cementation at 6' bgs (TILL)
5
Total depth of test pit = 6.25 feet bgs
No groundwater seepage observed
10
15
,Group Northwest, Inc.
Geotechnical Engineers, Geologists, $
Environmental Scientists
TEST PIT LOGS
PROPOSED TOWNHOMES
5000 - 212TH ST SW
EDMONDS, WASHINGTON