Edmonds Waterfront Restoration Pilot Infiltration Test Technical Memorandum.pdfDraft Technical Memorandum
TO: Mr. John Barker, Principal
FROM: Annabel Warnell, EIT and Steven R. Wright, PE
DATE: May 16, 2018
RE: Supplemental Geotechnical Engineering Services
Edmonds Waterfront Restoration
Pilot Infiltration Test Investigation
Edmonds, Washington
Introduction
This technical memorandum summarizes the results of supplemental geotechnical engineering
services that Landau Associates, Inc. (LAI) provided in support of the Edmonds Waterfront Restoration
project, located at 220 Railroad Avenue in Edmonds, Washington (site). The general project location is
shown on Figure 1.
This technical memorandum has been prepared based on information provided by representatives of
Barker Landscape Architects, PS, the Edmonds Senior Center, and the City of Edmonds (City); our
review of available subsurface information for the project area; data collected during our field
investigation; our familiarity with geologic conditions in the vicinity of the site; and our experience
with similar projects.
Project Understanding
We understand the City plans to restore a portion of the shoreline by removing an existing bulkhead
that supports a fill area near the Edmonds Senior Center. The fill area is currently occupied by a
parking lot and a section of waterfront walkway. The walkway will be relocated landward to align
approximately with the existing walkways on each side of the parking lot, and an upper tidal pocket
beach area will be constructed where the existing bulkhead and fill are currently located. Current
plans show proposed improvements consisting of the following elements:
— two beach access stairways, one located at each end of the new walkway section
— reorientation of the parking lot
— minor modifications to the water system
— a pile -supported bulkhead near the new walkway section
— new drainage and bioretention facilities.
As currently planned, the proposed bioretention facilities will have a minimum depth of 36 inches and
be located along the eastern edge of the project site (i.e., near Railroad Avenue).
LANDAU
ASSOUATES 130 2nd Avenue South • Edmonds, Washington 98020 • (425) 778-0907
DRAFT Landau Associates
Scope of Services
LAI was subcontracted by Barker Landscape Architects, PS, who is completing design of the project on
behalf of the City, to complete a supplemental subsurface investigation at the site and develop
geotechnical conclusions and recommendations regarding the infiltration characteristics of the site
soils. The supplemental geotechnical services described herein were provided in general accordance
with the scope of services outlined in our proposal for supplemental geotechnical engineering
services, dated April 24, 2018.
Existing Site Conditions
The following sections summarize subsurface conditions observed in the vicinity of the proposed
bioretention facilities at the time of our investigation. Interpretations of site conditions are based on
our review of available information, as well as the results of our site reconnaissance and subsurface
explorations.
Subsurface Soil Conditions
Subsurface conditions in the vicinity of the proposed bioretention facilities were explored by
excavating two test pits (PIT-1 and PIT-2) 6.4 and 6.2 feet (ft) below ground surface (bgs), respectively,
on May 2, 2018. The approximate locations of our explorations are shown on Figure 2. Each
representative soil type observed in our explorations was described using the soil classification system
shown on Figure 3. Figure 4 presents summary logs of the conditions observed during our field
investigation.
Fill was observed in both test pits beneath existing surface conditions (i.e., up to about 1 ft of topsoil).
The upper portion of the fill generally consisted of gravelly sand with silt, trash, and brick debris. The
fill transitioned to black and silty for approximately 4 inches at 2.2 and 2.0 ft bgs in test pits PIT-1 and
PIT-2, respectively. Beneath this layer, the fill consisted of sand with varying gravel content in a
medium dense and moist condition that was observed to the maximum depths of our test pits.
Groundwater Conditions
At the time of our May 2018 supplemental field investigation, groundwater seepage was observed in
test pit PIT-1 at 6.4 ft bgs. Groundwater was not observed in test pit PIT-2. The groundwater
conditions reported herein and on the test pit logs are for the specific locations and date indicated
and may not be indicative of other locations and/or times. Groundwater conditions will vary
depending on local subsurface conditions, weather conditions, and other factors, with maximum
groundwater levels generally occurring during late winter and early spring.
Supplemental Geotechnical Engineering Services May 16, 2018
Edmonds Waterfront Restoration 2
DRAFT
Landau Associates
Infiltration Testing
Two small-scale pilot infiltration tests (PITs) were performed in test pits PIT-1 and PIT-2 in general
accordance with Appendix B of the 2017 Edmonds Community Development Code. The bottom surface
area of each PIT was approximately 24 square feet. The general procedure for conducting each PIT
involved:
— excavating the test pit to the anticipated base depth of the proposed bioretention facility
(PIT-1 and PIT-2 were performed at depths of 3.4 and 3.2 ft bgs, respectively)
— installing a vertical measuring rod marked in 1/10-ft increments near the center of the test pit
— adding water to the test pit to establish a water depth of approximately 1 ft
— maintaining water in the test pit for a "pre-soak period" to saturate the anticipated receptor
soils of the bioretention facility
— installing a pressure transducer at the base of the test pit to continuously record water levels
— adjusting the flow rate to maintain a stabilize water level in the test pit
— turning off the inflow of water and recording the depth of water in the test pit over time with
the pressure transducer and measuring rod
— excavating an additional 3 ft below the PIT base to observe if water had mounded on
hydraulic restrictive layers or continued to flow deep into the subsurface.
The results of our infiltration testing are summarized in the following section of this technical
memorandum.
Conclusions and Recommendations
In order to estimate long-term (design) infiltration rates, correction factors in Table B.1 of the 2017
ECDC were applied to the measured (field) infiltration rates to account for site variability and number
of tests conducted (CFv = 0.33), the test method used (CFt = 0.5), and the degree of influent control to
prevent siltation and bio-buildup (CFm = 0.9).
A value of CFm = 0.9 assumes that maintenance to remove sediment build-up will be conducted on
the facilities when performance drops to 90 percent of the intended design. If this is inconsistent with
the planned maintenance schedule for the proposed facilities, the recommended design infiltration
rates presented below should be reduced.
Table 1 summarizes the results of our PIT investigation. Based on the conditions observed in our
explorations, the results of our field investigation, and applicable correction factors provided by the
2017 ECDC, we recommend assuming design infiltration rates of 0.3 and 2.0 inches per hour at the
approximate locations of PIT-1 and PIT-2, respectively, for soils at the anticipated base depth of the
proposed bioretention facilities. Groundwater seepage was observed in PIT-1 at 6.3 ft bgs. No other
hydraulic restricting layers were observed in our explorations.
Supplemental Geotechnical Engineering Services May 16, 2018
Edmonds Waterfront Restoration 3
DRAFT
Landau Associates
Table 1. Summary of Pilot Infiltration Test Results
PIT Designation
PIT-1
PIT-2
in/hr = inches per hour
PIT = Pilot infiltration test
Field Infiltration Rate
(in/hr)
2.0
14.0
Use of This Technical Memorandum
Recommended Design
Infiltration Rate
(in/hr)
0.3
MCI
Landau Associates, Inc. prepared this technical memorandum for the exclusive use of Barker
Landscape Architects, PS, the Edmonds Senior Center, and the City of Edmonds for specific application
to the Edmonds Waterfront Restoration project in Edmonds, Washington. Use of this technical
memorandum by others or for another project is at the user's sole risk. Within the limitations of
scope, schedule, and budget, our services have been conducted in accordance with generally
accepted practices of the geotechnical engineering profession; no other warranty, express or implied,
is made. We trust this technical memorandum provides you with sufficient information to proceed
with the design of the project. If you have questions or require clarification on any of the items
discussed above, please call the undersigned at (425) 778-0907.
LANDAU ASSOCIATES, INC.
Annabel Warnell, EIT
Senior Staff EIT
Steven R. Wright, PE
Principal
AMW/SZW/rgm
[\\ED MDATA01\PROJECTS\1738\001\R\PITTEC MEMO\EDMONDS WATERFRONT RESTORATION PILOT INFILTRATION TEST TECHNICAL M EMORANDUM.DOCXi
Supplemental Geotechnical Engineering Services May 16, 2018
Edmonds Waterfront Restoration 4
DRAFT
Landau Associates
Attachments: Figure 1. Vicinity Map
Figure 2. Site and Exploration Plan
Figure 3. Soil Classification System and Key
Figure 4. Logs of Test Pits (PIT-1 and PIT-2)
Supplemental Geotechnical Engineering Services May 16, 2018
Edmonds Waterfront Restoration 5
Puget Sound
Project Location
FA
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Miles
Data Source: Esri 2012
Edmonds Waterfront Restoration
LANDAU Edmonds, Washington
ASSOCIATES
PF/
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220th StSW — J =__
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Vicinity Map
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1
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Edmonds Senior Center
Legend
PIT-1 ® Approximate Pilot Infiltration Test Location and Designation
0 40 80
Scale in Feet
Source: Goo le Earth Pro, 2018
Edmonds Waterfront Restoration
Edmonds, Washington
Figure
Site and Exploration Plan 2
MAJOR
DIVISIONS
Soil Classification System
Uscs
GRAPHIC LETTER
SYMBOL SYMBOL"I'
TYPICAL
DESCRIPTIONS (2)(3)
GRAVEL AND
CLEAN GRAVEL
o ° o ° IQ
GW
Well -graded gravel; graveVsand mixture(s); little or no fines
0
GRAVELLY SOIL
(Little or no fines)
Poorly graded gravel; graveVsand mixture(s); little or no fines
D o ° ° ° 0,
GP
0 �>
(More than
Silty gravel; graveVsand/siltmixture(s)
GRAVEL WITH FINES
GM
ZE Z
coarse fraction retained
(Appreciable amount of
°
Q 0 N
on No. 4 sieve)
fines)
GC
Clayey gravel; gravel/sand/clay mixture(s)
d
LO z°
SAND AND
CLEAN SAND
SW
Well -graded sand; gravelly sand; little or no fines
Cl) t t
SANDY SOIL
(Little or no fines)
Poorly graded sand; gravelly sand; little or no fines
SP
Q 0`o
SAND WITH FINES
SM
m
OU
(More than 50%of
Silty sand; sand/silt mixture(s)
@
coarse fraction passed
(Appreciable amount of
SC
through No. 4 sieve)
fines)
Clayey sand; sand/clay mixture(s)
p
ML
Inor anic silt and veryfine sand; rock flour; silty or clayey fine
sand or clayey silt with slight plasticity
t
SILT AND CLAY
CL
U) 0 w N
Inorganic clay of low to medium plasticity; gravelly clay; sandy
y'w
0 o m a)
(Liquid limit less than 50)
clay; silty clay; lean clay
QL
Z o E >N
N
Organic silt; organic, silty clay of low plasticity
(a
r " (D
MH
Inorganic silt; micaceous or diatomaceous fine sand
mN
(D0.-
SILT AND CLAY
ul co0
CH
Inorganic clay of high plasticity; fat clay
Z E
LL
(Liquid limit greater than 50)
Organic clay of medium to high plasticity; organic silt
OH
HIGHLY ORGANIC SOIL
PT
Peat; humus; swamp soil with high organic content
GRAPHIC LETTER
OTHER MATERIALS SYMBOL SYMBOL TYPICAL DESCRIPTIONS
PAVEMENT
' ".:
AC or PC
Asphalt concrete pavement or Portland cement pavement
ROCK
RK
Rock (See Rock Classification)
WOOD
i7o
WD
Wood, lumber, wood chips
DEBRIS
DB
Construction debris, garbage
Notes: 1. USCS letter symbols correspond to symbols used by the Unified Soil Classification System and ASTM classification methods. Dual letter symbols
(e.g., SP-SM for sand or gravel) indicate soil with an estimated 5-15% fines. Multiple letter symbols (e.g., ML/CL) indicate borderline or multiple soil
classifications.
2. Soil descriptions are based on the general approach presented in the Standard Practice for Description and Identification of Soils (Visual -Manual
Procedure), outlined in ASTM D 2488. Where laboratory index testing has been conducted, soil classifications are based on the Standard Test
Method for Classification of Soils for Engineering Purposes, as outlined in ASTM D 2487.
3. Soil description terminology is based on visual estimates (in the absence of laboratory test data) of the percentages of each soil type and is defined
as follows:
Primary Constituent: > 50% - "GRAVEL," "SAND," "SILT," "CLAY," etc.
Secondary Constituents: > 30% and < 50% - "very gravelly," "very sandy," "very silty," etc.
> 15% and < 30% - "gravelly," "sandy," "silty," etc.
Additional Constituents: > 5% and < 15% - "with gravel," "with sand," "with silt," etc.
< 5% - "with trace gravel," "with trace sand," "with trace silt," etc., or not noted.
4. Soil density or consistency descriptions are based on judgement using a combination of sampler penetration blow counts, drilling or excavating
conditions, field tests, and laboratory tests, as appropriate.
Drilling and Sampling Key Field and Lab Test Data
SAMPLER TYPE SAMPLE NUMBER & INTERVAL
Code Description
a 3.25-inch O.D., 2.42-inch I.D. Split Spoon
b 2.00-inch O.D., 1.50-inch I.D. Split Spoon
c Shelby Tube
d Grab Sample
e Single -Tube Core Barrel
f Double -Tube Core Barrel
g 2.50-inch O.D., 2.00-inch I.D. WSDOT
h 3.00-inch O.D., 2.375-inch I.D. Mod. California
i Other - See text if applicable
1 300-lb Hammer, 30-inch Drop
2 140-lb Hammer, 30-inch Drop
3 Pushed
4 Vibr000re (Rotosonic/Geoprobe)
5 Other - See text if aoolicable
Code
PP = 1.0
Sample Identification Number
TV = 0.5
PID = 100
Recovery Depth Interval
W = 10
1�J
4 Sample Depth Interval
D = 120
-200 = 60
J
Portion of Sample Retained
GS
for Archive or Analysis
AL
GT
CA
Groundwater
V Approximate water level at time of drilling (ATD)
♦ Approximate water level at time other than ATD
Description
Pocket Penetrometer, tsf
Torvane, tsf
Photoionization Detector VOC screening, ppm
Moisture Content, %
Dry Density, pcf
Material smaller than No. 200 sieve, %
Grain Size - See separate figure for data
Atterberg Limits - See separate figure for data
Other Geotechnical Testing
Chemical Analysis
Edmonds Waterfront Figure
1ALANDAU Restoration Soil Classification System and Key
ASSOCIATES Edmonds, Washington
c�
0
a
0)
W
r
0
0
PIT-1
SAMPLE DATA
SOIL PROFILE
GROUNDWATER
75 Excavation Method: Rubber -tired Backhoe
a
o Z @ H :°
rn � Ground Elevation (fty Not Measured
� a m a o
r u Excavated By: City of Edmonds
m ca a
CL U
`� Logged By: AMW
w rn 06 U) H
Z)
— 0
SM
Ivy over brown, silty, gravelly, fine to coarse
-
SAND with organics (loose, moist)
-
(TOPSOIL)
SP-
-
SM
Gray -brown, gravelly, fine to coarse SAND with
—2
silt and brick debris (medium dense, moist)
_
S-1 =
d
SM
(FILL) /
_
SP
\ -Grades to light brown / /^
-
S-2=
d
\ Black, silty, fine to coarse SAND with gravel /
—4
\(medium dense, moist) /
-------------------
-
Gray -brown, fine to coarse SAND with gravel
-
(medium dense, moist)
-
-PIT performed at 3.4 ft bgs
—6
S-3
d
-Grades to gray Y
� Groundwater Seepage at 6.4
Test Pit Completed
05/02/18
-
Total Depth
of Test
Pit = 6.4 ft.
PIT-2
SAMPLE DATA SOIL GROUNDWATER
a '5 Excavation Method: R i d er-tBackhoe
o Z @ :° U) T Ground Elevation (ft):
Not Measured
a m a o .2U) Excavated By: City of Edmonds
CL
M_ ca a
o w U) 06 U)� c� Z)Logged ��
0 SM Ivy over brown, silty, fine to coarse SAND with
grave nd organics (loose, moist)
SP (TOPSOIL) Groundwater not encountered.
Brown, gravelly, fine to coarse SAND with trash
2 (medium dense, moist)
SK \ \ (FILL)
SP J /
S-1 I d Black, silty, fine to coarse SAND with gravel and /
brick debris (medium dense, moist) /
\------------------
4 Light brown, gravelly, fine to coarse SAND
(medium dense, moist)
-Grades to gray
-PIT performed at 3.2 ft bgs
g S-2 d
Test Pit Completed 05/02/18
Total Depth of Test Pit = 6.2 ft.
8
Notes: 1. Stratigraphic contacts are based on field interpretations and are approximate.
2. Reference to the text of this report is necessary for a proper understanding of subsurface conditions.
3. Refer to "Soil Classification System and Key" figure for explanation of graphics and symbols.
Edmonds Waterfront Figure
1ALANDAU Restoration Log of Test Pits /�
ASSOCIATES Edmonds, Washington `�