22-102749-UP-Geotechnical Report-06-15-2022-V1South Sound Geotechnical Consulting
P.O. Box 39500, Lakewood, WA 98496 (253) 973-0515
June 18, 2021
35000 Pacific Hwy South, LLC
3106 Sumner Tapps Hwy East, Suite A
Lake Tapps, WA 98391
Attention: Mr. Eric Corliss
Subject: Geotechnical Engineering Report – Infiltration Assessment
Plant 2 Relocation
35000 and 35050 Pacific Hwy South
Federal Way, WA
SSGC Project No. 21041
Mr. Corliss,
South Sound Geotechnical Consulting (SSGC) has completed an infiltration assessment for the Plant 2
Relocation at the above addressed property in Federal Way, Washington in support of design of
stormwater facilities. Our services have been completed in general conformance with our proposal
P21052 (dated May 10, 2021) and authorized per signature of our agreement for services. Our scope of
services included completion of one pilot infiltration test and one test pit, laboratory testing, engineering
analyses, and preparation of this report.
PROJECT INFORMATION
The site is on the east side of Pacific Highway South and encompasses four parcels. A new concrete plant
is planned on the lots. Preliminary plans have stormwater control facilities in the southwest portion of the
site (on the 35050 lot). Infiltration facilities are planned to assist in stormwater control.
SITE CONDITIONS
The proposed stormwater facility area is currently used as an access drive into the property and parking
area for trailers. A short retaining wall (on the order of 2 to 3 feet) is along the sidewalk that borders the
western boundary and Pacific Highway South. The access drive rises from street level to the overall
generally level property elevation.
SUBSURFACE CONDITIONS
Subsurface conditions were characterized by completing one infiltration test and one test pit on May 27,
2021. Test holes were advanced to final depths between 7 and 11 feet below existing ground surface.
Approximate locations of the explorations are shown on Figure 1, Exploration Plan. A summary
description of observed subgrade conditions is provided below. Logs of t he test holes are provided in
Appendix A.
Infiltration Assessment SSGC
Plant 2 Relocation
Federal Way, Washington
SSGC Project No. 21041
June 18, 2021
2
Soil Conditions
Fill was observed below the surface in the test holes and extended to depths between 1.5 to 2.5
feet. Fill consisted of mixed silt, sand, and gravel with variable debris. Native soil below the fill
consisted of silty sand with gravel and occasional cobbles. This soil was in a dense condition
closer to the surface, grading to medium dense with depth. It extended to the base of the test
holes.
Groundwater Conditions
Groundwater was not observed in the test holes at the time of excavation. No visual evidence of
perched seasonal groundwater (such as mottling) was observed. Groundwater levels will vary
throughout the year based on seasonal precipitation and on- and off-site drainage patterns.
Geologic Setting
Native soils on the property are mapped as Vashon recessional outwash per the USGS “Geologic
Map of the Poverty Bay 7.5’ Quadrangle, King and Pierce Counties, Washington”. These soils
reportedly formed in recessional glacial outwash. However, native soils were not characteristic
of recessional outwash and appeared to represent sandy drift or till.
INFILTRATION CHARACTERISTICS
One small-scale Pilot Infiltration Test (PIT) were completed in general conformance with the 2016 King
County Surface Water Design Manual to assess infiltration potential in the native soils. Results of the
infiltration test is presented in Table 1.
Table 1. Infiltration Test Results
Infiltration
Test No.
Depth of
Test
from Surface
(feet)
Soil Type
Field
Infiltration Rate
(in/hr)
Corrected
Infiltration
Rate
(in/hr)
Correction
Factors*
(Fg/Ft/Fp)
PIT-1 8 Silty SAND with
gravel 4.5 2.0 (1.0/0.5/0.9)
*Correction Factors from the 2016 KCSWDM.
The infiltration test was completed at a depth of 8 feet as we are unaware of planned finish grades of the
proposed concrete plant, and to ensure the test was completed below the base of the retaining wall along
the Pacific Hwy South sidewalk. Based on field results, we recommend a design rate of 2 inches per hour
(in/hr) for the soil at the tested depth. Native soils in the test pit in the north side of the proposed
stormwater facility appeared similar.
Groundwater was not observed in the test holes to a depth of 11 feet below existing grades. Evidence of
seasonal perched groundwater (such as mottling) was not observed in the test holes. Groundwater is not
Infiltration Assessment SSGC
Plant 2 Relocation
Federal Way, Washington
SSGC Project No. 21041
June 18, 2021
3
anticipated to affect stormwater facilities in this area of the site. In addition, following completion of the
infiltration test, the test hole was advanced to a depth of 11 feet with no evidence of ponded water
introduced during the test.
Cation Exchange Capacity (CEC) and organic content tests were completed on a soil sample from the
base of the infiltration test elevation in the test holes. Test results are summarized in Table 2.
Table 2. CEC and Organic Content Results
Test Location CEC Results
(milliequivalents)
CEC Required*
(milliequivalents)
Organic Content
Results (%)
Organic
Content
Required* (%)
PIT-1 5.3 ≥ 5 1.02 ≥1.0
* Per the 2016 KCSWDM.
CEC and organic content of the tested sample satisfy county requirements.
REPORT CONDITIONS
This report has been prepared for the exclusive use of 3500 Pacific Hwy South, LLC and their agents for
specific application to the project discussed and has been prepared in accordance with generally accepted
geotechnical engineering practices in the area. No warranties, either express or i mplied, are intended or
made. The analysis and recommendations presented in this report are based on observed soil conditions
and test results at the indicated locations, and from other geologic information discussed. This report
does not reflect variations that may occur across the project limits, or due to the modifying effects of
drainage patterns or weather.
This report was prepared for the planned type of development of the site as discussed herein. It is not
valid for third party entities or alternate types of development on the site without the express wr itten
consent of SSGC. If development plans change, we should be notified to review those changes and
modify our recommendations, as necessary.
The scope of services for this project does not include any environmental or biological assessment of the
site including identification or prevention of pollutants, hazardous materials, or conditions. Other studies
should be completed if the owner is concerned about the potential for contamination or pollution.
N
South Sound Geotechnical Consulting
P.O. Box 39500
Lakewood, WA 98496
(253) 973-0515
Figure 1 – Exploration Plan
Plant 2 Relocation
Federal Way, WA
SSGC Project #21041
Approximate Test Pit Location
PIT - 1
TP - 1
PIT - 1
Approximate Infiltration Test Location
Scale: NTS
Base map from drawing titled “Site Plan – Plant
2 Relocation”, by Apex Engineering, dated
2-1-21.
Legend
PIT-1
TP-1
Infiltration Assessment SSGC
Plant 2 Relocation
Federal Way, Washington
SSGC Project No. 21041
June 18, 2021
5
Appendix A
Field Exploration Procedures
Infiltration Assessment SSGC
Plant 2 Relocation
Federal Way, Washington
SSGC Project No. 21041
June 18, 2021
6
Field Exploration Procedures
Our field exploration for this project included one small-scale Pilot Infiltration Test (PIT) and one test pit
completed on May 27, 2021. Approximate locations of the explorations are shown on Figure 1,
Exploration Plan. The exploration locations were determined by pacing from site features. Ground
surface elevations referenced on the logs were inferred from topography from Google Earth satellite
imagery. Exploration locations and elevations should be considered accurate only to the degree implied by
the means and methods used.
A private excavating contractor subcontracted to SSGC dug the infiltration test holes. Select soil samples
were collected and stored in moisture tight for further assessment and laboratory testing. Explorations
were backfilled with excavated soils and tamped when completed. Please note that backfill in the
explorations will likely settle with time. Backfill located in building or pavement areas should be re-
excavated and recompacted, or replaced with structural fill.
The following logs indicate the observed lithology of soils and other materials observed in the
explorations at the time of excavation. Where a soil contact was observed to be gradational, our log
indicates the average contact depth. Our logs also indicate the approximate depth to groundwater (where
observed at the time of excavation), along with sample numbers and approximate sample depths. Soil
descriptions on the logs are based on the Unified Soil Classification System.
Project: Plant 2 Relocation SSGC Job # 21041 EXPLORATION LOGS PAGE 1 OF 1
Location: 35050 Pacific Hwy S., Federal Way, WA
EXPLORATION LOGS FIGURE A-1
South Sound Geotechnical Consulting PIT-1, TP-1 Logged by: THR
Infiltration Test PIT-1
Depth (feet) Material Description
0 – 2.5
2.5 – 11
Fill: Silt, sand, gravel with some debris (asphalt, brick,
plastic sheeting): Loose to medium dense, moist, brown.
Silty SAND with gravel and occasional cobble: Dense
grading medium dense, moist, gray grading brown at 4 feet.
(SM) (Sample S-1 @ 8 feet)
Test hole completed at approximately 11 feet on 5/27/21.
Infiltration test run at 8 feet.
Groundwater not observed at time of excavation.
Piezometer set in test hole.
Approximate surface elevation: 252 feet
Test Pit TP-1
Depth (feet) Material Description
0 – 1.5
1.5 – 7
Fill: Silt, sand, and gravel: Loose to medium dense, moist,
brown.
Silty SAND with gravel and occasional cobble: Dense
grading medium dense, moist, gray grading brown at 3 feet.
(SM)
Test pit completed at approximately 7 feet on 5/27/21.
Groundwater not observed at time of excavation.
Approximate surface elevation: 252 feet
Infiltration Assessment SSGC
Plant 2 Relocation
Federal Way, Washington
SSGC Project No. 21041
June 18, 2021
7
Appendix B
Laboratory Testing and Results
Infiltration Assessment SSGC
Plant 2 Relocation
Federal Way, Washington
SSGC Project No. 21041
June 18, 2021
8
Laboratory Testing
Organic content and cation exchange capacity (CEC) testing on a sample from the base of the PIT test
hole was completed by Northwest Agricultural Consultants of Kennewick, Washington. Results of the
laboratory testing are included in this appendix.
2545 W Falls Avenue
Kennewick, WA 99336
509.783.7450
www.nwag.com
lab@nwag.com
Sample ID Organic Matter Cation Exchange Capacity
Pit-1, S-1 1.02% 5.3 meq/100g
Method ASTM D2974 EPA 9081
South Sound Geotechnical Consulting
PO Box 39500
Lakewood, WA 98496
Report: 55334-1-1
Date: June 3, 2021
Project No: 21041
Project Name: Corliss Plant
UNIFIED SOIL CLASSIFICATION SYSTEM
Criteria for Assigning Group Symbols and Group Names Using Laboratory TestsA Soil Classification
Group
Symbol
Group NameB
Coarse Grained Soils
More than 50% retained
on No. 200 sieve
Gravels
More than 50% of coarse
fraction retained on
No. 4 sieve
Clean Gravels
Less than 5% finesC
Cu 4 and 1 Cc 3E GW Well-graded gravelF
Cu 4 and/or 1 Cc 3E GP Poorly graded gravelF
Gravels with Fines
More than 12% finesC
Fines classify as ML or MH GM Silty gravelF,G, H
Fines classify as CL or CH GC Clayey gravelF,G,H
Sands
50% or more of coarse
fraction passes
No. 4 sieve
Clean Sands
Less than 5% finesD
Cu 6 and 1 Cc 3E SW Well-graded sandI
Cu 6 and/or 1 Cc 3E SP Poorly graded sandI
Sands with Fines
More than 12% finesD
Fines classify as ML or MH SM Silty sandG,H,I
Fines Classify as CL or CH SC Clayey sandG,H,I
Fine-Grained Soils
50% or more passes the
No. 200 sieve
Silts and Clays
Liquid limit less than 50
inorganic PI 7 and plots on or above “A” lineJ CL Lean clayK,L,M
PI 4 or plots below “A” lineJ ML SiltK,L,M
organic Liquid limit - oven dried 0.75 OL Organic clayK,L,M,N
Liquid limit - not dried Organic siltK,L,M,O
Silts and Clays
Liquid limit 50 or more
inorganic PI plots on or above “A” line CH Fat clayK,L,M
PI plots below “A” line MH Elastic SiltK,L,M
organic Liquid limit - oven dried 0.75 OH Organic clayK,L,M,P
Liquid limit - not dried Organic siltK,L,M,Q
Highly organic soils Primarily organic matter, dark in color, and organic odor PT Peat
A Based on the material passing the 3-in. (75-mm) sieve
B If field sample contained cobbles or boulders, or both, add “with cobbles
or boulders, or both” to group name.
C Gravels with 5 to 12% fines require dual symbols: GW -GM well-graded
gravel with silt, GW -GC well-graded gravel with clay, GP-GM poorly
graded gravel with silt, GP-GC poorly graded gravel with clay.
D Sands with 5 to 12% fines require dual symbols: SW -SM well-graded
sand with silt, SW -SC well-graded sand with clay, SP-SM poorly graded
sand with silt, SP-SC poorly graded sand with clay
E Cu = D60/D10 Cc =
6010
2
30
DxD
)(D
F If soil contains 15% sand, add “with sand” to group name.
G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM.
HIf fines are organic, add “with organic fines” to group name.
I If soil contains 15% gravel, add “with gravel” to group name.
J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay.
K If soil contains 15 to 29% plus No. 200, add “with sand” or “with
gravel,” whichever is predominant.
L If soil contains 30% plus No. 200 predominantly sand, add
“sandy” to group name.
M If soil contains 30% plus No. 200, predominantly gravel,
add “gravelly” to group name.
N PI 4 and plots on or above “A” line.
O PI 4 or plots below “A” line.
P PI plots on or above “A” line.
Q PI plots below “A” line.