19-104208-Geotechnical (Soils) Report-06-26-2020-V1
Shoreline Geotechnical Assessment
Grealish Bulkhead Replacement
212 SW 292nd Street
Parcel No. 1196000121
Federal Way, Washington
June 20, 2020
Project #2090
Prepared For:
Amy Grealish
212 SW 292nd Street
Federal Way, Washington 98023
Prepared By:
Envirotech Engineering, PLLC
PO Box 984
Belfair, Washington 98528
Phone: 360-275-9374
6/20/20
TABLE OF CONTENTS
1.0 INTRODUCTION ................................................................................................................................. 1
1.1 PROJECT INFORMATION .................................................................................................................... 1
1.2 PURPOSE OF INVESTIGATION AND SCOPE OF WORK ........................................................................ 1
2.0 SURFACE CONDITIONS.................................................................................................................... 3
2.1 GENERAL OBSERVATIONS.................................................................................................................. 3
2.2 TOPOGRAPHY ..................................................................................................................................... 3
2.3 SURFACE DRAINAGE AND HYDROLOGY ............................................................................................ 3
2.4 SLOPE AND EROSION OBSERVATIONS ............................................................................................... 3
3.0 SUBSURFACE INVESTIGATION ..................................................................................................... 5
3.1 FIELD METHODS, SAMPLING AND FIELD TESTING ........................................................................... 5
3.2 GEOLOGIC CONDITIONS .................................................................................................................... 5
3.3 SPECIFIC SUBSURFACE CONDITIONS ................................................................................................. 6
3.3.1 Groundwater and Hydrogeology ............................................................................................... 7
4.0 ENGINEERING CONCLUSIONS & RECOMMENDATIONS ...................................................... 8
4.1 LANDSLIDE HAZARDS AND EFFECTS OF PROPOSED DEVELOPMENT ............................................... 8
4.2 EROSION HAZARDS ............................................................................................................................ 9
4.3 SEISMIC HAZARDS .............................................................................................................................. 9
4.4 CONCLUSIONS AND RECOMMENDATIONS FOR THE PROPOSED DEVELOPMENT .............................. 9
4.4.1 Alternative Approaches .............................................................................................................10
4.4.2 Mitigation Measures .................................................................................................................10
5.0 CLOSURE .............................................................................................................................................11
Appendix A - Site Plan
_____________________________________________________________________________________
Envirotech Engineering Shoreline Geotechnical Assessment
PO Box 984 page 1 212 SW 292nd Street
Belfair, Washington 98528 Federal Way, Washington
Ph. 360-275-9374 June 20, 2020
1.0 INTRODUCTION
Envirotech Engineering, PLLC (Envirotech) has completed this shoreline geotechnical
assessment for a proposed bulkhead repair/ replacement located at 212 SW 292nd Street,
identified as parcel number 1196000121 in Federal Way, Washington. As presented herein, this
assessment includes information pertaining to the project in this Introduction Section;
observations of the property and surrounding terrain in the Surface Conditions Section; soils and
geological descriptions in the Subsurface Investigation Section; and, assessments and
considerations for the development of this project in the Conclusions and Recommendations
Section.
1.1 Project Information
Information pertaining to the project was provided by the proponent of the property. The
proposed project is planned to consist of a bulkhead replacement on the Puget Sound. The
existing wall is failing. The existing bulkhead consists of reinforced concrete of approximately 3
feet in height and about 54 feet in length. The proposed bulkhead is a reinforced concrete wall of
6 feet in height. The purpose of the wall is to benefit the integrity of the existing residential
structures neighboring both sides of the property. Approximate site development with relation to
site features are illustrated in the Site Map in Appendix A.
1.2 Purpose of Investigation and Scope of Work
The purpose of this shoreline geotechnical assessment was to evaluate the proposed project with
relation to erosion, geologic hazards, shoreline alternatives, site adequacy, and geological and
hydrological impacts to the property and adjacent/ downstream properties.
In order to fulfill the purpose of investigation, the geotechnical program completed for the
proposed improvements include:
• Review project information provided by the proponent of the property;
• Conduct a site visit to document the site conditions that may influence the construction
and performance of the proposed improvements;
• Define general subsurface conditions of the site by observing near surface soils and
review soil/ geological maps for the vicinity of the project;
• Complete an engineering assessment supported by planned site alterations and the surface
and subsurface conditions that were identified by the field investigation, soil testing, and
applicable project research; and,
• Establish engineering conclusions and recommendations based on findings and the
anticipated development.
_____________________________________________________________________________________
Envirotech Engineering Shoreline Geotechnical Assessment
PO Box 984 page 2 212 SW 292nd Street
Belfair, Washington 98528 Federal Way, Washington
Ph. 360-275-9374 June 20, 2020
Vicinity Map from King County Website
Project
_____________________________________________________________________________________
Envirotech Engineering Shoreline Geotechnical Assessment
PO Box 984 page 3 212 SW 292nd Street
Belfair, Washington 98528 Federal Way, Washington
Ph. 360-275-9374 June 20, 2020
2.0 SURFACE CONDITIONS
Information pertaining to the existing surface conditions for the project was gathered on May 28,
2020 by a representative with Envirotech. During the site visit, site features were documented that
may influence construction or reveal potential geological or hydrologic hazards. This Surface
Conditions Section provides information on general observations, vegetation, topography,
drainage and slope/ erosion conditions for the project and surrounding areas.
2.1 General Observations
The project is currently developed with a single family residence, driveway, bulkhead, and other
ancillary features typical of this type of development. Vegetation consists mainly of urban
landscaping. Beach flora or fauna was not observed at the time of our site visit. The existing
concrete bulkhead has cracks and allowed scour within its backfill. Foundation undermining of
the structure on the eastern neighboring parcel was observed. It is also reported that basement
flooding occurs on the western neighboring parcel. Envirotech observed that inadequate height of
the subject bulkhead may be the primary contributor of the flooding. An aerial photo of the
project and immediate vicinity is provided below.
2.2 Topography
The topographic information provided in this section was extrapolated from a public lidar source,
and incorporated observations and field measurements, where necessary. Slopes are relatively
mild near the existing residence and bulkhead area. Slopes are approximately 60% with a vertical
relief of about 35 feet between the home and bulkhead.
2.3 Surface Drainage and Hydrology
Surface water such as streams or wetlands do not appear to affect the property. The ordinary high
water mark of the Puget Sound is approximately 4 feet from the face of the existing bulkhead.
Significant scour behind the existing bulkhead was observed. Significant beach erosion or
sediment transport on the beach was not apparent within the immediate vicinity of the project. It
is apparent that the bulkhead area to the slope toe is within the FEMA flood zone.
2.4 Slope and Erosion Observations
Signs of significant mass wasting on the property or within the general vicinity of the project
were not observed or discovered during research. Indications of past landslides, current unstable
slopes, deep-seated slope problems, or surficial slope failures were not observed during the site
visit.
_____________________________________________________________________________________
Envirotech Engineering Shoreline Geotechnical Assessment
PO Box 984 page 4 212 SW 292nd Street
Belfair, Washington 98528 Federal Way, Washington
Ph. 360-275-9374 June 20, 2020
Aerial Photo from King County Website
_____________________________________________________________________________________
Envirotech Engineering Shoreline Geotechnical Assessment
PO Box 984 page 5 212 SW 292nd Street
Belfair, Washington 98528 Federal Way, Washington
Ph. 360-275-9374 June 20, 2020
3.0 SUBSURFACE INVESTIGATION
Information on subsurface conditions pertaining to the project was gathered during research and a
site reconnaissance. The site visit was accomplished on May 28, 2020 by a representative with
Envirotech. Specific information on field methods, sampling, field testing, subsurface conditions,
and results from soil testing are presented in this section of the report.
3.1 Field Methods, Sampling and Field Testing
Information on subsurface conditions for the project was accomplished by probing the project
area with hand tools. Information on subsurface conditions also included reviewing geological
and other soil mapping/ logging within the vicinity of the property. Envirotech measured the
relative density of the in-situ soils by gauging the resistance of hand tools.
3.2 Geologic Conditions
In general, soils at the project are composed of materials from glacial advances. The geologic
conditions as presented in the “Geologic Map of Washington,” compiled by J. Eric Schuster,
2002 indicates Quaternary sediments, Qg. Quaternary sediments are generally unconsolidated
deposits, and dominantly deposited from glacial drift, including alluvium deposits. This project is
located within the Puget Lowland. Typically, “lower tertiary sedimentary rocks unconformably
overlie the Crescent Formation.” as revealed in the Geologic Map. Initial sedimentary rocks were
formed from shales, sandstones and coal deposits from rivers. During the Quaternary period, the
Puget Lowland was covered by numerous ice sheets, with the most recent being the Fraser glacier
with a peak of approximately 14,000 years ago. Upon the glacial retreat, the landscape was
formed by glacial erosion glacial drift deposits.
The “Interactive Geologic Map” from the Department of Natural Resources provides the
following caption(s) for the project area:
Geologic Unit Label: Qvrs
Publisher: USGS
Publication Number: SIM 2854
Quadrangle Name: Poverty Bay
Symbology: Pleistocene glaciolacustrine deposits
Geologic Unit Description
Geologic Unit Age: Pleistocene
Geologic Unit Name: Vashon Stade recessional coarse-grained lacustrine deposits
Unit Description: Composed of coarse-grained sand, forming crude terraces as high as
about 30 m (100 ft) above Poverty Bay. Probably subaqueous deposits of
streams flowing into one of ice-dammed lakes that filled trough of Puget
Sound late in ice recession
Age-Lithology: Pleistocene glaciolacustrine deposits
_____________________________________________________________________________________
Envirotech Engineering Shoreline Geotechnical Assessment
PO Box 984 page 6 212 SW 292nd Street
Belfair, Washington 98528 Federal Way, Washington
Ph. 360-275-9374 June 20, 2020
Geological Map Department of Natural Resources Washington State
3.3 Specific Subsurface Conditions
The following subsurface conditions are estimated descriptions of the project subgrade utilizing
information from the depth of penetration at all testing, sampling, observed and investigated
locations. Soils for this project were described utilizing the Unified Soil Classification System
(USCS). Using the USCS in conjunction with estimated relative densities and other anticipated
engineering properties of the soil, susceptibility for potential landslides, erosion and seismic
hazards may be assessed.
Soils within the upper 12 inches below the existing beach grade were observed to be primarily
moist to wet, loose, poorly graded sand with gravel (SP) overlying dense soils. Upland soils
appeared to be silty sand with gravel that was medium dense to dense.
According to the “Soil Survey of King County,” by the United States Department of Agriculture,
Soil Conservation Service (SCS), the site soils are described as Indianola loamy sand, with 5% -
15% slopes. See the soil map below, and the applicable SCS soil profile(s) in Appendix B of this
report.
_____________________________________________________________________________________
Envirotech Engineering Shoreline Geotechnical Assessment
PO Box 984 page 7 212 SW 292nd Street
Belfair, Washington 98528 Federal Way, Washington
Ph. 360-275-9374 June 20, 2020
Soil Survey From USDA Natural Resources Conservation Service
3.3.1 Groundwater and Hydrogeology
Permanent groundwater is expected to be at least 30 feet directly below the ground
surface near the lowlands of the property. Groundwater at shallow depths or surface
seepage was not observed at the time of our site visit.
_____________________________________________________________________________________
Envirotech Engineering Shoreline Geotechnical Assessment
PO Box 984 page 8 212 SW 292nd Street
Belfair, Washington 98528 Federal Way, Washington
Ph. 360-275-9374 June 20, 2020
4.0 ENGINEERING CONCLUSIONS & RECOMMENDATIONS
The following sections present engineering assessments and conclusions concerning the project.
These conclusions have been made available based on the planned construction activities as
outlined in the Introduction Section of this report; general observations of drainage and
topography as summarized in the Surface Conditions Section; and, soil conditions that were
identified by the field investigation and soils testing as outlined in the Subsurface Investigation
Section. Conclusions for the project that is provided herein, includes pertinent information for
landslide, erosion and seismic hazards.
4.1 Landslide Hazards and Effects of Proposed Development
According to the Coastal Zone Atlas of King County, Washington, the project is within and near
terrain labeled ‘Stable’ and ‘Intermediate’ regarding potential landslide activity. Stable slopes are
generally not prone to landslides due to small grades and accommodating geology. Historically,
intermediate terrains have no known landslides. A Stability Map from the Coastal Zone Atlas for
the general area of this project may be found below.
Map from Washington State Department of Ecology Website
Past landslide activity or high slope instability indicators near the proposed development was not
revealed during the project research. In addition, detrimental landslide activity or potential high
Project
_____________________________________________________________________________________
Envirotech Engineering Shoreline Geotechnical Assessment
PO Box 984 page 9 212 SW 292nd Street
Belfair, Washington 98528 Federal Way, Washington
Ph. 360-275-9374 June 20, 2020
landslide indicators were not observed during the site visit as outlined in the Surface and
Subsurface Conditions Sections of this report.
4.2 Erosion Hazards
Based on the USCS description of the project soils, the surface soils are considered moderately
erodible. According to the Resource Map from the Washington State DNR, the project is not
within terrain labeled ‘highly erodible.’
It is our opinion that this property has a high susceptibility risk for future shoreline erosion if the
bulkhead completely fails. It is also our opinion that the proposed development will not
encourage significant erosion.
4.3 Seismic Hazards
There appears to be a fault near the property to the north identified as the Tacoma Fault Zone.
This fault is a Class ‘B,‘ and is located less than 1/8 mile to the north of the project. This
information is supported by the USGS Quaternary Fault and Fold Database for the United States.
The potential for liquefaction are believed to be low for this project. According to the Interactive
Geologic Map of Washington, liquefaction susceptibility is very low within the vicinity of this
project. This is also based on subsurface conditions such as soil characteristics and the lack of a
permanent and substantial shallow water table. Subgrade characteristics that particularly
contribute to problems caused by seismic events include submerged and confined, poorly-graded
granular soils. Although gravel- and silt-sized soil particles could be problematic, fine and
medium grained sands are typically subjected to these types of seismic hazards.
4.4 Conclusions and Recommendations for the Proposed Development
The property appears adequate for the proposed development as described in this report because,
in our opinion, the project will not have a negative impact on geological, hydrological or
shoreline dynamics with respect to current conditions. Since the bulkhead replacement consists of
nearly the same type, location, and size, it is our opinion that there will be virtually no negative
impacts to the property, neighboring properties, or down-current properties from the proposed
development.
The replacement of the bulkhead will be beneficial to the neighboring single family residential
structures on both sides of the subject property. For the property to the west, basement flooding
has been reported. Extending the height of the bulkhead to 6 feet from 3 feet will match the
height of the neighboring bulkhead and mitigate water from overtopping. In addition, extending
the bulkhead height will also mitigate the current foundation undermining occurring on the
existing structure on the property to the east.
Conclusions in this report are based on the type and location of the anticipated development, and
existing on-site and off-site conditions. Site development that significantly deviates from the
anticipated improvements presented in this report, or future nearby development that influences
this project may require geotechnical design recommendations.
_____________________________________________________________________________________
Envirotech Engineering Shoreline Geotechnical Assessment
PO Box 984 page 10 212 SW 292nd Street
Belfair, Washington 98528 Federal Way, Washington
Ph. 360-275-9374 June 20, 2020
4.4.1 Alternative Approaches
Alternative approaches were considered in our geotechnical assessment. These
alternatives include a do-nothing approach, and alternative construction materials.
The do-nothing alternative will allow for additional wall failure, and additional damaging
effects to the neighboring structures.
Envirotech believes that the concrete bulkhead is more suitable than rock armoring or
soft shore protection. Rock would be cantered, and will provide an overall different
configuration that would change shoreline dynamics and hydrogeologic conditions with
respect to both existing and proposed conditions. Soft armoring such as logs and root
wads are not advised for this project. This is due to the close proximity of the structure to
the east, and the lack of height that soft shore could provide. In addition, rapid
deterioration of the loose backfill materials would occur without hard armoring deflecting
waves, tidal action and storm surges.
4.4.2 Mitigation Measures
A replacement bulkhead with additional height is the best science available in order to
mitigate site specific damages that are already occurring.
Since the planned armoring is virtually the same type and location as the existing
bulkhead, this alone is mitigation in order to maintain current conditions and shoreline
dynamics. In conclusion, there will be no adverse impacts to off-site properties from the
planned bulkhead replacement with relation to existing condition.
_____________________________________________________________________________________
Envirotech Engineering Shoreline Geotechnical Assessment
PO Box 984 page 11 212 SW 292nd Street
Belfair, Washington 98528 Federal Way, Washington
Ph. 360-275-9374 June 20, 2020
5.0 CLOSURE
Based on the project information and site conditions as presented in this report, it is Envirotech’s
opinion that additional geotechnical studies are not required to further evaluate this project.
Due to the inherent natural variations of the soil stratification and the nature of the geotechnical
subsurface exploration, there is always a possibility that soil conditions encountered during
construction are different than those described in this report. Therefore, it is recommended that
Envirotech is promptly notified if project and subsurface conditions found on-site are not as
presented in this report so that we can re-evaluate our recommendations.
This report presents a geological/ geotechnical assessment, and is intended only for the owner, or
owners’ representative. Furthermore, this report is only valid for the project information and
location described herein. Significant geological or property changes prior to the implementation
of this project could render this report outdated, and will require additional geotechnical studies.
The services described in this report were prepared under the responsible charge of Michael
Staten, a professional engineer with Envirotech. Michael Staten has appropriate education and
experience in the field of geotechnical engineering in order to assess landslide hazards, erosion
hazards, earthquake hazards, and shoreline dynamics.
Please contact Michael Staten at 360-275-9374 if you have any questions, comments, or require
additional information.
Sincerely,
Envirotech Engineering
Michael Staten, P.E.
Geotechnical Engineer
APPENDIX A
SITE PLAN