Drainage_Report-dated_3-16-16.pdfRj".'4v� n (o cc I -L
r
0JFAJM'4GEREP0JFT
for
RECEIVED
�, MAR 2C) 9016
19125 94 Ave West
Edmonds, WA 98020 ` ' VELOPMENT SERVIC'E,;
COUNTER
CSP Engineering PFN 15-036
City of Edmonds PFN
March 16, 2016
f
CSP f17,
q�lMme
rl)7g
Civil Engineering Design and Consulting
1037 NE6ShSt#153
Seattle, WA 98115
Phone. 206 406 9965
email@cspengineering.com
www.cspengineering.com
Project Overview
Two single family residences are proposed in conjunction with a 4 lot short plat of a 1.66 acre combined Site Parcel
situated in the Fruitdale Watershed. Impervious and permeable hardscape surface for the project is estimated to be
approximately 4,500 sf (0.10 acres) per lot and will be comprised of NPGIS roof area, PGIS driveway asphalt pavement,
PGPS driveway permeable pavement, and NPGIS walkway. The proposed improvements will disturb —0.37 acres. Soils
are classified generally as SAND underlain by advance Outwash (Liu & Associates Inc. January 30, 2016 Geotechnical
Investigation). The project will create greater than 5,000 sf of impervious surface and will disturb less than 1.0 acre in
land and is therefore classified as a Category 2 Small Site Project.
Small Site Minimum Requirement #1— Preparation of Stormwater Site Plan
This report combined with the final Stormwater & Grading/Construction SWPP Plans address this requirement.
Small Site Minimum Requirement #2 — Construction Stormwater Pollution Prevention Plan
This report combined with the final Stormwater & Grading/Construction SWPP Plans address this requirement.
Small Site Minimum Requirement #3 — Source Control of Pollution
Specific source controls are not required for single family residential sites.
Small Site Minimum Requirement #4 — Preservation of Natural Drainage Systems and Outfalls
The proposed development preserves the natural drainage systems and outfalls.
Small Site Minimum Requirement #5 — Onsite Stormwater Management
Onsite stormwater management BMPs will be implemented to the maximum extend feasible through the use of
permeable pavement, infiltration trenches, and the implementation of BMP T5.13 post -construction soil amendment.
In-situ infiltration tests (Liu & Associates Inc. January 30, 2016 Geotechnical Investigation) indicate suitable soils for
permeable pavements and infiltration facilities.
Small Site Minimum Requirement #6 — Runoff Treatment
The total of new and replaced effective pollution -generating impervious surface (PGIS) is less than 5,000 sf and
pollution -generating pervious surfaces (PGPS) is less than three-quarters (3/4) of an acre therefore stormwater
treatment facilities are not applicable.
Small Site Minimum Requirement #7 — Flow Control
Stormwater flow control is accomplished by utilizing permeable pavement and onsite infiltration. WWHM3 modeling
of PGIS roof areas, estimated to be 2,500 sf (0.06 acres) per lot, show 100% mitigation utilizing a 34 If x 5' deep x 3'
wide infiltration trench. Permeable pavement is given a 100% Flow Control Credit pursuant to Table 4 — Flow Control
Credits for Permeable Pavement of the City of Edmonds Development Information #E728. Non mitigated PGIS
pavement and impervious walkways are estimated to be —900 sf (0.02 acres) per lot.
WWHM3 modeling, analyzed on a per lot basis, of 0.06 acres of roof area mitigated via infiltration trench and 0.02
acres of non -mitigated impervious surface generate the following peak flows:
2 -year storm = 0.005 cfs
10 -year storm = 0.008 cfs
100 -year storm = 0.013 cfs
Pursuant to Table 4-5 Edmonds Stormwater Code Supplement, allowable release rates, also analyzed on a per lot basis,
of 4,500 sf (0.10 acres) of impervious surface are as follows:
2 -year storm @ 0.07 cfs per acre of impervious surface = 0.007 cfs
10 -year storm @ 0.25 cfs per acre of impervious surface = 0.025 cfs
1 of 26
100 -year storm @ 0.45 cfs per acre of impervious surface = 0.045 cfs
WWHM3 software modeling was calculated unitizing "Puget East 36" precipitation time series and a long term design
infiltration rate 2.5 inches per hour (Liu & Associates Inc. January 30, 2016 Geotechnical Investigation).
Small Site Minimum Requirement #8 — Wetland Protection
No wetlands are known to be located within % mile of the subject site.
Small Site Minimum Requirement #9 — Operation and Maintenance
Operation and maintenance will be performed by the homeowner as directed by the engineer of record upon
completion of the project.
Small Site Minimum Requirement #10 — Offsite Analysis and Mitigation
Non -mitigated impervious surfaces (driveway approaches and walkways) will sheet -flow to vegetated areas adjacent
to the street frontage pavement for dispersion/infiltration. Due to the small areas and resultant flows significant
impacts to the downstream system are not anticipated.
Small Site Minimum Requirement #11— Financial Liability
The site in not known to be located within a Critical Area triggering the requirement of a performance bond.
2 of 26
Appendix
1,000 2,000 4,000 61,600 8,000
�afbul Park
ftmt Park 8
F kAjAdaile
5o ov
re
2100d, Sw w
Vicinity/Basin Map
0 1,000 2,,000 4w. a„000 6, ODD 8,0Ov
00
�
m' jv�
1 in 2,000 It
No wanwn,� of my aut, hduding amuracy, Wriess, or mwIftni abIlly amompnV MIs AwNd.
Ylen¢
Soils Map
7'
�;J
PROJECT
”
4' u 4
vpv
I` N
T T 4
110,
4�w- ig
o",
wo
�w'
Slope Map
3 of 26
Western Washington Hydrology Model
PROJECT REPORT
Project Name: 15-036 KNOB HILL INFL
Site Address: 19125 94TH AVE W
City
EDMONDS, WA 93020
Report Date
3/1.6/2016
MGS Regoin
Data Start
1943/10/01
Data End
1997/09/30
DOT Data Number: 00
WWHM3 Version:
PREDEVELOPED LAND USE
Name ROOF - PER LOT
Bypass: No
GroundWater: No
Pervious Land Use Acres
Impervious Land Use Acres
ROOF TOPS FLAT 0.06
Element Flows To:
Surface Interflow
Gravel Trench Bed 1, Gravel.. Trench Bed 1,
Name I Gravel Trench Bed 1
Bottom Length: 34ft.
Bottom Width : 3ft.
Trench bottom slope 1: 0.001 To 1
Trench Left side slope 0: 0 To 1
Trench right side slope 2: 0 To 1
Material thickness of first layer : 4
Pour Space of material for first layer
Material thickness of second layer : 0
Pour Space of material for second layer
Material thickness of third layer : 0
Pour Space of material for third layer
Infiltration On
Infiltration rate 2.5
Infiltration saftey factor 1
Discharge Structure
Riser Height: 4 ft.
Riser Diameter: 12 in.
Element Flows To:.
Outlet 1 Outlet 2
0.4
0
0
Groundwater
Gravel Trench Bed Hydraulic Table
Stave(ft) Area(acr) Volume(axcr-ft) Dschra(cfs) Infilt(ofs)
4 of 26
O-OOO
0.002
0.000
0,000
0.000
0-056
0.002
0.000
0,000
0.006
0.111
8.002
0.000
0.000
0.006
0.I57
0,002
0.080
0.000
0.006
0.222
0.002
0.000
0.000
0.005
0.278
0.002
0.000
0.000
0.006
0.333
0.002
0.008
0.000
0.006
0.389
0.002
0.000
0.000
0.006
0.444
0.002
0.000
0.000
0.006
0.500
0.002
0.000
0.000
0.006
0.556
0.002
0-00I
0,000
0.006
0.611
0.002
0.00I
0.000
0.006
0,667
0,002
0-001
0,000
0.005
0.722
0.002
0.00I
0.000
0.006
0.778
0.002
0.001
0,000
0.006
0-855
0.002
0.001
0.000
0.006
0.889
0-002
0.001
0.000
0.006
0,944
0.002
0.001
0.000
0.006
1.000
0.002
0.001
0.000
0.006
1.056
0-002
0.001
0.000
0.006
1.111
0,002
0.001
0-000
0.006
1.I67
0.002
0.002.
0-000
0.006
1.222
0.002
0.001
0.000
0.006
1.278
0.002
0,00I
0.000
0.006
1.]3]
0-002
0.001
0.000
0.006
1.389
0.002
0.00I
0,000
0.006
1.444
0.002
0.001
0-000
0.006
1.500
0.002
0.001
0-000
0-000
1-556
0,002
0-00I
0.000
0.006
1.611
0.002
0.002
0.000
0.006
1.667
0.002
0.003
0.000
0.006
1.722
0.003
0.002
0.000
0-006
1.778
0.002
0.002
0.000
0.006
1.833
0.002
0,002
0.000
0.006
1.889
0.002
0.002
0.000
0.006
1,944
0.002
0.002
0.000
0.006
2.000
0.002
0.002
0.000
0.006
2-056
0.002
0,002
0.000
O'OOG
3.I1I
0.002
0,002
0.000
0.006
2.167
0.002
0.002
0.000
0.006
2-222
0.002
0.002
0.000
0.006
2-278
0.002
0.002
0,000
O-OOG
2.333
0.002
0.002
0,000
0.006
2.389
0.002
0.003
0.000
0.006
3.444
0,002
0.002
0.000
0.006
3.500
0.002
0,002
0.000
0.006
2.556
0.002
0.002
0-000
0.008
2.61I
0.002
0.002
0.000
0.006
2.667
0.002
0.002
0.000
0.006
2.722
0.002
0.003
0.000
0.006
2.778
0.002
0.003
0.000
0.006
2.833
0.003
0.003
0.000
0.006
2.889
0.002
0,003
0.000
0.006
2.944
0.002
0.083
0.000
0.000
5.000
0.002
0.003
0.000
0.006
3,056
0.002
0.003
0.000
0.006
3.I11
0.002
0.003
0.000
0.006
3.167
0.002
0.003
0.000
0.006
3,222
0,002
0.003
0.000
0.006
5.278
0.002
0.005
8.000
0.006
3.333
0.002
0.005
0.000
0.006
3,389
0-002
0.003
0.000
0,006
5.444
0.002
0.003
0.000
0.006
5 of 26
3.500
0.002
0.003
0.000
0.006
3.556
0.002
0.003
0.000
0^006
5.611
0,002
0,003
0.000
0.006
3.567
0.002
0.005
0.000
0-006
3.722
0.002
0.003
0,000
0,006
3,778
0.002
0,004
0,000
0.006
3.833
0.002
0.004
0.000
0,006
5.889
0.002
0.004
0.000
0.006
3.944
0.002
0.004
0.000
0,006
4,000
0.002
0.004
0.000
0.006
4-056
0.002
0.004
0.128
0.O06
4.111
0.002
0.004
0.361
0.006
4.167
0.002
0.004
0.663
0.006
4.222
0.002
0^004
1^020
0.006
4.278
0,002
0.001
1,426
0.006
4.333
0.002
0.005
1.874
0.006
4.389
0.002
0.005
2.362
0,006
4.444
0.002
0.005
2.886
0,006
4.500
0.002
0.005
3.443
0.006
4.556
0.002
0^005
4.033
0.006
4.611
0.002
0.005
4.653
0.000
4.667
0.002
0,005
5.50I
0,006
4.723
0.002
0.005
5.978
0.006
4.778
0.002
0.006
6.680
0,006
4,833
0.002
0.006
7.409
0.006
4.889
0.002
0,006
8.162
0.006
4.944
0.002
0,006
8.939
0.006
5.000
0.002
0.006
9.739
0.006
Nam ma : 0O0MZTZGATEo IMPERVIOUS SURFACE - PER LOT
Bypass: No
GroundWater: No
Pervious Acres
Impervious Land Use Acres
DRIVEWAYS umoo o.nu
Element nlmmo To:
Surface Iutezflow Groundwater
Name : EXISTING - PER LOT'
Bypass: No
GroundWater: No
Pervious Laud Use Acres
u`o, Forest, Mod -1
Impervious Land UAcres
Element Flows To/
Surface zotezflow Groundwater
6of 26
MITIGATED LAND USE
uauuLrazo RESULTS
Flow Frequency Return Periods for ezedaveloped. POC #1
Return Period
Flow(cfs)
2 year
0.022812
5 year
0.030791
10 year
0.038495
25 year
8.044187
50 year
0.050303
100 year
0.056733
Flow Frequency Return Periods for Mitigated, POC #1
Return Period
Flo
u year
0.005141
5 year
0.008881
10 year
0'008II7
25 year
0'009777
50 year
0'0I1087
100 year
0.012482
Yearly Peaks for Precen,eloped and Mitigated' POC #1
7 o 26
1950
0.019
0.004
195I
0.033
0.007
1952
0.023
0.006
1953
0.019
0.004
1954
0.026
0.006
1955
0.033
0.008
1956
0.027
0.006
1957
0.014
0.003
1958
0,023
0.005
1959
0.04I
0.009
I960
0,023
0.005
1961
0,016
0.004
1962
0.052
0.012
1963
0.023
0.005
1.964
0.036
0.008
1965
0.018
0.004
1966
0.015
0.004
1957
0.0I5
0.004
1968
0.055
0.012
1969
0.030
0.007
1970
0.037
8.009
I871
0.018
0,004
1973
0.025
0,006
1973
0.042
0.010
1974
0.020
0.006
1975
0^029
0.007
1976
0,023
0.005
1977
0.02I
0.005
1978
0.017
0.004
1979
0.015
0.003
1980
0.034
0.007
I981
0.015
8.004
1982
0.019
0^004
7 o 26
l983
1984
1985
l986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
Ranked
Rank
2
3
4
5
6
7
8
9
IO
ll
12
13
14
15
16
17
IB
19
20
21
22
23
24
25
26
27
28
29
30
31
]2
35
34
35
35
37
]H
39
40
41
42
43
0.020
O -O22
0.020
0.031
0.029
0.028
0.023
0.024
0.015
0.017
0.019
0.019
0.013
0.019
0.022
0.028
Yearly Peaks for
Predeveloped
0.0562
O -O523
0.0424
0.0406
0.0367
0.0363
O.O]37
0.0335
O-O33I
0.0308
0.0302
0.0294
0.0291
0.0281
0.0277
0.0273
0.0258
0.0257
0.0254
0.0235
0-O2]4
0.0234
0.0230
0.0229
0.0226
0.0225
0.0216
0.0216
0.0210
0.0205
0.0204
0.0194
0.0192
0.0191
0.0190
0.0190
0.0189
0.0182
0.0176
0.0171
0.0169
0.0163
0.0155
0.005
0.005
0.005
0.007
0.006
0.006
0.005
0.005
0.003
0.004
0.004
0.004
0.003
0.004
0.005
0.006
eredeveIoped and
Mitigated
0.0124
0.0119
0.0095
0.0093
0.0085
0.0078
0.0075
0.0072
0.0069
0.0067
0.0065
0.0065
0.0065
0.0064
0.0060
0.0059
0.0058
0.0058
0.0057
0.0057
0.0054
0.0053
0.0052
0.0052
0.0050
0.0050
0.0049
0.0049
0.0047
0.0046
0.0045
0.0045
0.0045
0.0042
0.0042
0.0041
0.0041
0.0041
0.0040
0.0040
0.0039
0.0039
0.0037
2�Ml
8of28
44
0,0152
0.0037
45
0,0151
0.0037
46
0,0149
0.0034
47
0.0I49
0.0033
48
0.0137
0.003I
49
0,0I34
0.0029
Tbe Fa( �ili� �,,, EY\S3I,D.
Flow(CFS) Precev Dev :Percentage Pass/:Fail
0.0II4
678
2
0
Pass
0.0II8
604
2
0
Pass
0.0I22
538
l
0
Pass
0.0I36
434
O
O
Pass
0.0130
456
0
0
Pass
0.0I34
413
0
O
Pass
0.0I38
374
O
0
Pass
0.0I42
327
O
O
Pass
0.0.145
391
O
O
Pass
0.01.49
265
0
0
Pass
0.01.53
244
O
O
Pass
0.01.57
217
0
O
Pass
0.0I5I
1.93
0
O
Pass
0.0.165
176
O
0
Paso
0.0I69
I51
O
O
Pass
0,0173
I30
O
O
Pass
0.01.77
1.1.7
O
O
Pass
0.0I8I
I06
O
0
Pass
0.0I95
lOO
0
0
Pass
0.0I89
86
O
O
Pass
0.0193
76
O
0
Pass
0.01.97
70
O
O
Pass
0.0200
65
0
O
Pass
0.0204
59
O
O
Pass
0.0208
55
O
O
Pass
0^02l2
52
0
O
Pass
0. 0216
5.1
U
O
Pass
0.0220
48
0
O
Pass
0.0224
46
O
O
Pass
0.0228
41.
O
0
Pass
0.0252
38
O
O
Pass
0.0236
34
0
0
Pass
0,0240
33
0
0
Dass
0.0244
35
O
O
Pass
0.0288
31
O
O
Pass
0.0252
31
O
O
Bsao
0.0256
28
0
O
Pass
0.0259
25
O
O
Pass
0.0253
24
O
O
Pass
0.0367
34
0
O
Paso
0.0271
23
0
0
Pass
0.0275
22
O
O
Paso
0.0279
21
O
0
Pass
0.0293
20
0
D
Pass
0.0287
20
O
O
Pass
0.029I
20
O
O
2aae
0,0285
IR
O
0
Pass
0.0299
17
O
O
Paso
0.0303
1.4
O
O
gaoe
0.0307
14
O
O
Pass
9of2G
0.0311
12
10
0
Pass
0.0314
12
0
Pass
0.0318
3. 2
0
P a ss
0.0322
12
0
Pass
0.0326
11
0
Pass
0.0330
11
0
0
Pass
0.0334
10
0
Pass
0.0338
8
0
Pass
0.0342
8
C3
0
Pass
0.0346
8
0
0
Pass
0.0350
8
0
0
Pass
0.0354
8
0
Pass
0.0358
8
ID
Pass
0.0362
7
0
0
Pass
0.0366
6
0
0
Pass
0.0369
5
0
Pass
0.0373
5
Pass
0.0377
5
10
Pass
0.0381
5
0
Pass
0.0385
5
0
0
Pass
0.0389
5
0
0
Pass
0.0393
5
0
0
Pass
0.0397
5
0
Pass
0.0401
5
0
Pass
0.0405
4
0
0
Pass
0.0409
3
0
l
Pass
0.0413
3
0
0
Pass
0.0417
3
0
Pass
0.0421
3
0
Pass
0.0424
2
Ck
0
Pass
0.0428
2
0
Ca
Pass
0.0432
2
Pass
0.0436
2
0
0
Pass
0.0440
2
0
0
Pass
0.0444
2
a. s a
0.0448
2
0
0
Pass
0.0452
2
0
Pass
0.0456
2
0
0
Pass
0.0460
2
0
0
Pass
0.0464
2
0
C3
Pass
0.0468
2
Pass
0.0472
2
0
Pass
0.0476
2
0
0
Pass
0.0479
2
0
Pass
0.0483
2
0
Pass
0.0487
2
0
0
Pass
0.0491
2
0
Pass
0.0495
2
0
Pass
0.0499
2
lC)
0
Pass
0.0503
2
0
0
Pass
Water Quality BMP Flow and Volume for POC 1,
On-line facility volume: 0 acre-feet
On-line facility target flow: 0 cfs.
Adjusted for 15 min: 0 efs.
Off-line facility target flow: 0 cfs.
Adjusted for 15 min: 0 cfs.
PerInd and Imp1nd Changes
No changes have been made.
10 of 26
This program and accompanying documentation is provided 'as-is' without warranty of any kind, The entire risk
regarding the performance and results of this program is assumed by the user. Clear Creek Solutions and the
Washington State Department of Ecology disclaims all warranties, either expressed or implied, including but not
Limited. to implied warranties of program and accompanying documentation. In no event shall Clear Creek
Solutions and/or the Washington State Department of Ecology be liable for any damages whatsoever (including
without limitation to damages for loss of business profits, loss of business information, business interruption,
and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions or the
Washington State Department of Ecology has been advised of the possibility of such damages..
11 of 26
1.11t1f & ASSOC IATES,
Geotechnical Engineering Engineering Geology
January 30, 2016
Mr. Bill Linton
45 Pine Street, #304.
Edmonds, WA 98020
Dear.Mr. Linton:
Subje& In Situ Infiltration Tests
Linton Plat
1.91,25 94th Avenue West & 9302 .- 192nd Place West
Edrn0Dds, Washington
L Job No. l6-001.
INTRODUCTION
Eanth Science
We understand a 4 -lot plat residential development project is proposed for the sul�ject
properties located at the above addresses in Edmonds, Washington. The subject
properties are to be platted into four building lots, with the existing residences at the
above addresses (Lots I and 4) to remain and with new single-family residences to be
constructed on the other two lots (]Lots 2 and 3). We also understand onsite stonnwater
disposal by infiltration into the ground is being considered for the proposed development,
At your request, we have completed a geotechnical investigation and conducted in-situ
infiltration tests for the proposed new residences to be constructed on Lots 2 and 3. The
purpose for this investigation and infiltration tests is to characterize subsurface (soil and
groundwater) conditions of l..,ots 2 and 3 and provide reconimendations for onsite
stormwater disposal by infiltration for the proposed. new residences. Presented in this
report are our findings of subsurtace conditions, infiltration test results, and. sten water
disposal recommendations.
19213 l`K nl IIRlace NE - Kenmore, Washington 98028
Phone (425) 483-9134 - Fax (425) 486-2746
12 of 26
january 30, 2016
Linton Plat
L&A.Job No. 16-001
Page 2
PROJECT DESCRIPTION
`]'he subject plat site is situated on the lower portion of a gentle, westerly -declining slope.
A short, distance further to the west the slope becomes steeper. Storrnwater collected over
impervious surfaces of the proposed new residences is to be disposed with infiltration
facilities to be installed along the downhill side of each of Lots 2 and 3.
SCOPE OF SERVICES
Our proposed scope of services ror this geotechnical investigation comprises specifically
the following -
1. Review geologic and soil conditions at the site based on a published geologic map.
1Excavate test pits up to about 8 feet (Jeep (maximairt depth capable by the backb[oe
used in digging test pits) to explore subsurt4ce conditions in proposed infiltration
facility areas of Lots 2 and 3. Perform an in-situ infiltration tests on these lots, in
suitable infiltratable soil layer(s) if encountered, The tests will be conducted in
accordance with the requirements and procedure outlined in Washington State
Department of Ecology 2005 Ste mini Mann qtqpt Manual I'm Western
Washington.
3. Prepare a. written report to present our findings of subsurface conditions of
proposed. infiltration facility area, infiltration test results, and recommendations for
design and construction of infiltration -trenches.,
SITE CONDITIONS
Surface Condition
The general location of the project site is shown on Plate I -- Vicinity Map. The plat site
is situated on a gentle, westerly -declining slope,. 'It is bounded by 192nd Place SW to the
LIU &.ASSOCIATES, INC.
13 of 26
January 30, 2016
Linton Plat
L&A Job No. 16-001
Page 3
north, 192nd Street SW to the south, and 94th Avenue W to the west, and is adjoined by a
single-family residence to the east. The area to be platted into Lots 2 and 3 spans
between 192nd Place SW and 192nd Street SW and is sandwiched between the two
existing residences on the site. This area is currently vacant, but is a landscaped, garden -
like open space. This open space generally slopes down westerly gently with cross slopes
down to the north and south from a ridge down the middle of the site,
Geologic Setting
The (Jeologic–Mall_ '(1111onds l""Ist and [laq ofthe L'tin'tonds Wes )�L,, <� 5,yj
.__Mall.._ _L__ ......... — - ----- __ . . ......... . __ __ - .. .. .. ....... _... - L 'L
)Yqts, in t_q-QI i , by James 11. Minard, published by U. S. Geological Survey in 1983, was
referenced for the geologic and soil conditions at the project site. According to this
publication, the surficial soil units at and in the vicinity of the project site are mapped as
Advance Outwash (Qva) on the downhill side overlain by Vashon Till (Qvt) on the uphill
side of the project site.
The geology of the Puget Sound Lowland has been modified by the advance and retreat of
several glaciers in the past and subsequent deposits and erosion. The latest glacier
advanced to the Puget Sound Lowland is referred to as the Vashon Stade of the Fraser
Glaciation, which has occurred during the later stages of the Pleistocene Epoch and
retreated from the region some 12,500 years ago.
The deposits of the Vashon till soil unit were plowed directly under glacial ice during the
most recent glacial period as the glacier advanced over an eroded, irregular surface of
older formations and sediments. This soil unit is composed of a mixture of unsorted clay,
LIU & ASSOCIATES, INC.
14 of 26
January 30, 2016
Linton Plat
L&A. Job No. 16 001
Page 4
silt., sand, gravel, and scattered cobbles and boulders. The Vashon till soil over the top
two to three feet is non-nally weathered to a medi uni- dense state, and is moderately
permeable and compressible, 'Fhe underlying fresh till soil, commonly refierred to as
"'hard pan", is very -dense and cemented. The Vast" on till soil unit, however, was not
encountered by the test pits excavated on the site.
The deposits cel` the advance outwash soil unit, normally underlying the Vashon till soil
unit, are co posed ofstratified sand and gravel with very minor arnount of silt and clay,
deposited by the rneltwater of advancing glacial ice cal' the last glacier then overridden by
the still advancing glacier. Due to their generally granular composition, the advance
outwash deposits are of t' high permeability and drains fairly well, The advance
outwash deposits are generally dense to very dense in their natural, undisturbed state. The
underlying fresh advance outwash deposits in their native, undisturbed state can provide
good tbundation support with little settlement expected for light to moderately heavy
structures.
Soil Condition
Subsurface conditions in [tie proposed infiltration facility areas of Lots 2 and 3 were
explored with test pits. These test pits were excavated on January 20, 2016, with a
rubber -tracked backhoe, to depths of 7.5 to 8.5 feet. The approximate locations orthc test
pits are shown on Plate 2 -- Site and Exploration Location Plan. The test pits were located
with either a tape ineasure or by 'visual refierence to existing topographic, features in the
field and. on the topographic survey map, and their locations should be considered as offly
accurate to the kneasuring rnethod used.
MU & ASSOCIATES, INC.
15 of 26
January 30, 2016
Unton Plat
L&A Job No. 16-001
Page 5
A geotechnical engineer from our office was present during subsurface exploration,
examined the soil and geologic conditions encountered, and completed logs of the test
pits. Soil samples obtained ftom each soil layer in the test pits were visually classified in
genenal accordance with United Soil Classification System, a copy of which is presented
on Plate 3. 1)etailed descriptions of soil layers encountered during site exploration are
presented in test pit logs on plate 4.
Both test pits encountered a layer of topsoil, about 8 to10 inches thick, Underlying the
topsoil is a layer of weathered soil of brown, loose to medium -dense, silty fine sand, from
1.8 to 3.8 feet thick., This weathered soil layer is underlain to the depths explored by a
light -brown tur light gray, medium -dense to dense, fine to ruediurn sand deposit, which
appears to be of advance our ash.
G'R0UNDWX'rER CONDITION
Groundwater was not encountered by either test pit excavated on the site. The advance
oulwash soil underlying the site at shallow depth is of" rnoderately-1.1igh permeability and
would allow stormwater to seep thrOLDgh easily.
IN-SFIV INFILTRATION TESTS
In Situ Infiltration "rest Pit
We performed two in-siCa infiltration tests, one on each of'],ants 2 and 3, on January 20,
2016, in the proposed infiltration facility areas of the lots. The iDfiltration test pits, IT -1
and IT -2 on the lots, were located next, to the test pits on the lots, as shown on Plate 1
1AU & ASSOCIATES, INC.
16 of 26
January 30, 2016
Unto n Plat
]L IQ Job No, 16-001
Page 6
The bottom of the infiltration test pits was excavated to about 12 to 18 inches into the
targeted advance outwash sand soil. Groundwater was not encountered by these pits,
Dirnensions of the in test pits and soil condition at bottom of the pits are
presented in the table below�
Infiltration Test Procedure
rl 'he in-situ infiltration tests were conducted in accordance with the procedure oudined in
Washington State Department of Ecology 20,12 Storinwater_M11flap,
Wcsllcnl!, W0shjJ11gjq!,r�. The infiltration test pits were first filled with water for hours to
soak the soils underneath the pits. Clear tap water was used in the tests. The infiltration
tests were then conducted in the pits by falling head method. The advance our ash sand
soil is of high pertneability that it took a long period to soak the soil under the pits and to
accumulate enough water in the pits to do the tests. A. steel bar was placed across the top
of the test pits and water levels from the steel bar were measured it] the beginning and at
the end of a 30-ininute test period®
LIAJ & ASSOCIATES, INC
17 of 26
TEST PIT SIZE AND SOIL CONDITION
. . . ..
Test
. ......
Pit
............
Description of Soff
No.
Size . ..... ....
at IBottornm of Test Pit
rt -....1
4.33° x 6,67'
Ught-gray, medium AND,
x 3.75' deep
. ..
trace time gravel
. . . . . ..... .. .. ............
F-2
4.75'x 6.83'
1 ught gray, fine to medium
x 5.5" deep
SAND, trace fine gravel
Infiltration Test Procedure
rl 'he in-situ infiltration tests were conducted in accordance with the procedure oudined in
Washington State Department of Ecology 20,12 Storinwater_M11flap,
Wcsllcnl!, W0shjJ11gjq!,r�. The infiltration test pits were first filled with water for hours to
soak the soils underneath the pits. Clear tap water was used in the tests. The infiltration
tests were then conducted in the pits by falling head method. The advance our ash sand
soil is of high pertneability that it took a long period to soak the soil under the pits and to
accumulate enough water in the pits to do the tests. A. steel bar was placed across the top
of the test pits and water levels from the steel bar were measured it] the beginning and at
the end of a 30-ininute test period®
LIAJ & ASSOCIATES, INC
17 of 26
January 30, 2016
Linton Plat
L Job No. 16-001
Page 7
,rest. Results
The initial. infiltration rate of each testt Ksat initw5 in. inches per hour (iph), was thus
deterrnined. The results of the infiltration tests are 1,wesented in the table below -
Test
Water 1.... ev
Elapsed
InUtraborn
Infiltration
Rate, K,,,t j,,jtj.j
K'
Rate bK'at
No,
Begun End
Time,
Kn.
In./Hr.
ln./Hr.
l T- 1
22-3/4"
36-118"
1 30
2675
775
IT -2
33....1 /4'"
43-3/8"
............... .
30
20.25
5487
- - ----]
a Measure
- ---------
d from a steel bar placed across top of pfts
b Ksat :---
C FT x Ksag , where C IFT = C Fv
x C Ft x CF E
RECOMMENDA,r]'ONS
Design Infiltration Rate
As shown in the equation above, the K,,t inffiA values determined by the infiltration tests
are to be modified according to correction factors include: site variability and number of
locations tested (CFF), uncertainty of test method (CF,), and degree of influent control to
prevent. siltation and bio buildup (CF,,,), are to be applied on K,,,, jjt�.j value to get the
design infiltration rate, K -,,,t. According Table 3.3.1 of the DOE Manual, C.F, = 0.33 to
1.0, CFI — 0.5 for small scale test, and CF... = 0.9. Use a middle value 0.65 for CF, thus,
CFI� =-. (0,65) (0.5) (0.9) = 0.29. The K,,,t value for the infiltration test was thus calculated
LIQ & ASSOCIATES, IN( -
18 of 26
January 30, 2016
Linton Plat
L&A Job No, 16-001
Page 8
and is shown in the table above. Based on the above analysis and on the conservative
side, we recommend an infiltration rate no more than 2.5 iph of the targeted advance
out ash deposit be used for design of proposed infiltration trenches in the areas of the
test pits and infiltration tests,
Infiltration Trench Construction
Infiltration trenches to be used for onsite story-nwater disposal should be set back at least 5
feet from property lines and 8 feet from adjacent building footing foundations or utility
trenches. The bottom of infiltration trenches should be at least 1.5 feet lower than
adjacent building footing foundations and utility trenches.
Infiltration trenches should be cut at least one foot into the targeted light -gray advance
outwash soil of medium sand to fine to medium sand with trace gravel into which
stormwater is to be dispersed. To reach this target soil stratum the trenches would have to
be excavated to about 3.5 feet or deeper in the vicinity of Test Pit TP -I and Infiltration
Test IT- 1, and to about 5.5 feet or deeper in the vicinity of Test Pit TP -2 and Infiltration
Test IT -2. The condition of the soil unit at bottom of infiltration trenches should be
verified by a geotechnical engineer during construction. The stability of the trench cut
banks should also be verified by a geotechnical engineer during excavation.
Infiltration trenches should be at least 24 inches wide, The side walls of the trenches
should be lined with a layer of non -woven filter fabric (l4 IR 140NS), The trenches
are then filled with clean washed 3/4 to 1-1/2 inch gravel or crushed rock to within about
12 to 15 inches of the top of trenches. The dispersion pipes should be constructed of 4-
LIU & ASSOCIATES, INC.
19 of 26
January 30, 2016
Linton Plat
L&A Job No. 16-001
pia :.nlae 9
inch rigid PVC pipes and laid level in the gravel or crushed rock filled trenches at about 2
feet below top of the trenches. 'nic top off' tine gravel or crushed rock fill should also be
covered with the filter fabric liner. The remaining trenches should then be backfilled
onsite clean sandy soil, The gravel or crushed rock fill should be placed in lifts no more
than 10 inches tf ick in loose state, with each lift compacted to a non-yieldingstate with a
vibratory mechanical compactor, The compaction and densification of trench fill is
critical if it is to support driveways, Stonnwater Captured over paved driveways should
be routed into a catch basin equipped with an od-water separator before being released
into infiltration trenches. The trenches of tightlines conveying stormwater fi,orn the
residences to irffiltration trenches should be constructed with an impervious collar or
barrier, such as lean concrete or clay dart'i, to prevent backflow of water rrorn infiltration
trenches to the residences.
If maintaining groundwater quality is critical, the bottom of trenches should be filled with
a nimirnuiri 18 -inch layer of uncornpacted amended soil. The amended soil should
contain 40 percent (by volume) of compost, mixed with clean medium -to -coarse sand, to
achieve an organic content of at least 10% by dry weight.
LIMITATIONS
This report has been prepared for the specitic application to the subject prqject for the
exclusive use by Mr. Bill Linton, and his associates, representatives, consultants and
contractors. The conclusions and in terpretat ions in this report, however, should not be
construed as a warranty of the subsurface conditions. The scope of this report does not
LI U & ASSOCIATES, INC.
20 of 26
January 30, 2016
Linton Plat
L&A. Job No. 16-001
Page 10
include services related to construction safety precautions and our recommendations are
not. intended to direct the contractor's methods, techniques, sequences or procedures,
except as specifically described in this report for design consideratiorm.
Our recommendations and conclusion are based on the geologic and soil conditions
encountered by the test pits excavated on the site, the infiltration test results, and our
experience and engineering judgment. The conclusions and recommendations are
professional opinions derived in a manner consistent with the level of care and skill
ordinarily exercised by other members of the profession currently practicing under similar
conditions in this area. No warranty, expressed or implied, is made.
The actual subsurface conditions of the site may vary from those encountered by the test
pits. The nature and extent of such variations may not become evident until construction
starts. If variations appear then, we should be retained to re. -evaluate the
recommendations of this report, and to verify or modify them in writing prior to
proceeding lbrther with the construction of the infiltration facilities. A. copy of thisreport
should be provided to the contractor of infiltration trenches for compliance with the
recommendations in this report. Infiltration trench construction work of the pr(�ject
shou ld. be observed and monitored by a geotechnical engineer to ensure compliance with
the recommendations in this report..
1AU & ASSOCIATES, INC.
21 of 26
January 30, 2016
Linton Plat
L&A Job No. 16-001
Page 11
We are pleased to be of service to you on this project. Please feel free to contact us if you
have questions regarding this report or need further consultation.
Four plates attached
J. S. (Julian) Liu, Ph.D., P.E.
Principal
LIU & ASSOCIATES, INC.
22 of 26
P , PONWS
-, 1iu
61MCK1--FFS
LANDiNb-
xx
✓
qj/
�J,
sw
I.
OP A00K `PK
ILA,'
PW
rm-
rs 17
JIM
I S sw
sw
S!,'�
, 11"i '�J
1B8TH
sl s
YNb W,
.Yal
4
p -7111� - Y"
u PL
RROJE,.
100 11
sn
. . . . . . . .. .. .. .. . ..... . .. .. .. .. . ..... FL 1915T 5T
C'N
zz
�.,. ...._, _,. W ¢rte �. �v�ws�, r�rp
Q�f
J1 3, 1920 ST, SW_
. Grj,,A)
AF
61 "i
196111 S
T� 614
4b& l if1' DT
. . . . . . . . . . . .
u7 a dr
�Y,
MF LODY LN
0
J
v r)
L!Jj
6 !iL SW Uj
�i�sp
v r" WY
2 OOTH 51 SW
GRTKA 11 V I STA
4�
J1
LN
d w
OWL
LWA w SIERRA
ifytiv s I TTAA)
W,
P4
s t z�, . . .......
:1 vj w�
24/ IC1 , �:,
pR PRAGUE
''PINE
d, r P ov �E ")WOE
LIU & ASSOCIAT'ES, INC. L I N � U N 11' U -k I
19125 - 94TH AVE W & 9302 - 192ND PLACE W
Geotechnical Engineering - Engineering Geology - Earth Science EDMONDS, WASHINGTON
23 of 26
PNOW L
70 �
A
-�T
T r,a�d
A41 G94-
pl, S
-
v w
VICINITY MAP
LIU & ASSOCIAT'ES, INC. L I N � U N 11' U -k I
19125 - 94TH AVE W & 9302 - 192ND PLACE W
Geotechnical Engineering - Engineering Geology - Earth Science EDMONDS, WASHINGTON
23 of 26
LI U & ASSOCIATES, INC.
Geotechnical Engineering - Engineering Geology ° Earth Science
I 'El I tA I
LINTON PLAT
9302 192ND PL SW & 19125 94TH AVE W
EDMONDS, WASHINGTON
24 of 26
i u � i
wwwwmww w
UNIFIED Il CLASSIFICATION SYSTEM
MAJOR DIVISIONS
... ..... ....
GROUP GROUP NAME
SYMBOL
GRA VEL CLEAN
4a �� WELL -G RAD GRAVEL, FINE TO COARSE GRAVEL i
COARSE- MORE THAN 50% OF GRAVEL
G POORLY -GRADED GRAVEL
GRAINED COARSE FRACTION GRAVEL WITH IGM
SILTY GRAVEL
ON NO.4 SIEVE
SOILS RETAINED RETAINEDY
SFIN
----_
_ .... CLAYEY GRAVEL
SAND CLEAN
SW WELL -GRADED SAND, FINE TO COARSE SAND
MORE THAN 50% MORE THAN 50°x° OF SAND
SF POORLY -GRADED SAND -
RETAINED ON THE COARSE FRACTION SAND WITH
-__-
SSI SILTY SAND
NO,
NO. 200 SIEVE PASSING NO. 4 SIEVE
FINES
SC CLAYEY SAND
FINE- SILT AND CLAY INORGANIC
L SILT
GRAINED LIQUID LINT
CL CLAY
SOILS LESS THAN 50°!° CRtAIVI
OL C7FtGAfVIC SILT, ORGANIC CLAY _......_mm_..
MORE THAN 50% I SILTY ANIS CLAY INORGANIC
MH SILT OF HIGH PLASTICITY, ELASTIC SILT
..�.�...."__...___.....__-....__....�v....�_�.,„�„'
PASSING ON THE i
LIQUID LINT
H CLAY OF HIGH PLASTICITY, FAT CLAY
NO, 200 SIEVE 50% OR MORE
I
ORGANIC
� � � �....e_..-......-.-.. _._
OH ORGANIC SILT, (ORGANIC SILT
HIGHLY ORGANIC SC3ILS
�8�1 � �I PEATAND OTHER HIGHLY ORGANIC SOILS^^-..�.
NOTES:
SOIL MOISTURE MODIFIERS:
1. FIELD CLASSIFICATION IS BASED ON VISUAL EXAMINATION
DRY - ABSENCE OF MOISTURE, DUSTY, DRY TO
OF SOIL IN GENERAL ACCORDANCE WITH ASTM D24$£I-83.
THE TOUCH
2.. "MOIL CLASSIFICATION USING LABORATORY TESTS IS BASED
SLIGHTLY MOIST - TRACE MOISTURE, NOT DUSTY
ON ASTM D2457-53,
MOIST - DAMP, BUT NO VISIBLE WATER
3, DESCRIPTIONS OF SOIL DENSITY OR CONSISTENCY ARE
VERY MOIST - VERY DAMP, MOISTURE FELT TO THE TOUCH
BASED ON INTERP'RET'ATION OF BLOW -COUNT DATA, VISUAL
WET- VISIBLE FREE WATER OR SATURATED,
APPEARANCE OF SOLS, AND/OR TEST DATA.
USUALLY SOIL IS OBTAINED FROM BELOW
WATER TABLE
1..AU'& 'I”"E , INC.
UNIFIED SOIL CLASSIFICATION SYSTEM
Geotechnical Engineering • Engineering Geology Earth Science
PLATE 3
25 of 26
TES I,,,, P1 °°IIr NO. 1
"III" T P1„,I,,,, 2
Logged 6y: JSL Cute: 1/20/2016 Ground El. mml:
__�... �.....,_� �... ........._........_.
depth !lSE
p Sample w Other
[CLASS,
Soil Descri tion No, % gest
OLDark-brown louse, organic, silty fine SAND, some roots, mois_ t ” ...._ � . .. � �...�.__.
SM Brown, medium -devise, silty fine SAND, moist, occasional roots,
2 moist
s
4
5 S Light brown to light -grey medium -dense
to dense, fine to i^nediurn
SAND, trace gravel, moist (ADVANCE OUTWAShl)
6
7
8
1 q t
Test pit terminated at &5 ft: groundwater not encountered.
TEST FAIT LOGS
9302 192ND PL SW & 19125 94TH AVE
Geotechnical Engineering - Engineering Geology � Earth Science I S WASHINGTON
J�I� NO16W001 DATE 1/2a/2a1s L...ATE
26 of 26
Logged
y:
JSL Cate: 1/20/2016
Ground El.
Cbepth
uses
Sample
w
Cather
ft, ._
cLA zea.
_ _ _ _ _Soil_ Description
No.
%
Test
y ,ii�undai�t ror�t,>
GUN�j_--_..-.._._______—._.__.___.__..___.,
SP/SM
Brown, loose to medium -dense, slightly silty, fine SAND, trace
2
gravel, some roots, moist
t -
iS
t__.._ m.. -. _ ediurro sASVCi, w...
.6g- k -brown to Ig' -t --gray, medium -donee to dense, me"d'i .,. ' -._
trace gravel, slightly -moist (ADVANCE Cal! ASH)
5
6
7
_m
Test pit terminated at 7.5 ; groundwater not encountered.
r�
tq
"III" T P1„,I,,,, 2
Logged 6y: JSL Cute: 1/20/2016 Ground El. mml:
__�... �.....,_� �... ........._........_.
depth !lSE
p Sample w Other
[CLASS,
Soil Descri tion No, % gest
OLDark-brown louse, organic, silty fine SAND, some roots, mois_ t ” ...._ � . .. � �...�.__.
SM Brown, medium -devise, silty fine SAND, moist, occasional roots,
2 moist
s
4
5 S Light brown to light -grey medium -dense
to dense, fine to i^nediurn
SAND, trace gravel, moist (ADVANCE OUTWAShl)
6
7
8
1 q t
Test pit terminated at &5 ft: groundwater not encountered.
TEST FAIT LOGS
9302 192ND PL SW & 19125 94TH AVE
Geotechnical Engineering - Engineering Geology � Earth Science I S WASHINGTON
J�I� NO16W001 DATE 1/2a/2a1s L...ATE
26 of 26