HomeMy WebLinkAboutGEO2023-00072 - GEO General - 9/19/2023 6jEb 26Z3 - 000-7Z.
RECEIVED
S'I:-P 19 20?3
615 W. Nder Street
Geotechnical & Shoreline Report
Bulkhead — Dock — Shoreline Access
30- 40- & 50 N Sundown Dr, Hoodsport
Parcel Nos. 42318-50-00013, -00014, -00015
Mason County, Washington
July 7, 2023
Project#22329
Prepared For:
Mason Webb, et al
46808 286th Ave SE
Enumclaw, WA 98022
Prepared By:
Envirotech Engineering
PO Box 984
Belfair, Washington 98528
Phone: 360-275-9374
V C.LY'pF 3T
r ,p 43045
fiGISTERE'
SSO\AL£�C
7/7/2023
Tuc,h5 . OLbb • ,�ahnsu��
MASON COUNTY Submittal C;ec
( COMMUNITY SERVICES Geotechnical Report
INlllnmp.IMntun4 llrrrtnnmi'nu111rnfln,tMmn Wny lla•nn
Instructions:
This checklist must be submitted with a Geotechnical Report and completed,signed, and stamped by the licensed
professional(s)who prepared the Geotechnical Report for review by Mason County pursuant to the Mason County
Resource Ordinance. If an item is found not applicable,the report should explain the basis for the conclusion.
Note:Unless specifically documented,this report does not provide compliance to the International Residential Code
Sections R403.1.7 for foundations on or adjacent to slopes,Section R403.1.8 for expansive soils or section 1808.7.1
of the International Building Code Section for Foundations on or adjacent to slopes.
Applicant/Owner Mason Webb et al Parcel# 42318-50-00013,-00014, -00015
Site Address 30-40-&50 N Sundown Dr
(1) (a) A discussion of general geologic conditions in the vicinity of the proposed development,
Located on page(s) 5
(b) A discussion of specific soil types,
Located on page(s) 6
(c) A discussion of ground water conditions,
Located on page(s) 7
(d) A discussion of the upslope geomorphology,
Located on page(s) 3
(e) A discussion of the location of upland waterbodies and wetlands,
Located on page(s) 3
(f) A discussion of history of landslide activity in the vicinity,as available in the referenced maps and
records.
Located on page(s) 8
(2) A site plan which identifies the important development and geologic features.
Located on Map(s) Site Plan—Appendix A
(3) Locations and logs of exploratory holes or probes.
Located on Map(s) Site Plan and Soil Logs(Appendix B)
(4) The area of the proposed development,the boundaries of the hazard,and associated buffers and
setbacks shall be delineated (top,both sides,and toe)on a geologic map of the site.
Located on Map(s) Site Plan
(5) A minimum of one cross section at a scale which adequately depicts the subsurface profile, and
which incorporates the details of proposed grade changes.
Located on Map(s) Soil Profile(Appendix B)
(6) A description and results of slope stability analyses performed for both static and seismic loading
conditions.Analysis should examine worst case failures.The analysis should include the Simplified
Bishop's Method of Circles.The minimum static safety factor is 1.5,the minimum seismic safety
factor is 1.1,and the quasi-static analysis coefficients should be a value of 0.15.
Located on page(s) 9 Page 1 of 35
(7) (a) Appropriate restrictions on placement of drainage features,
Located on page(s) 16
(b) Appropriate restrictions on placement of septic drain fields,
Located on page(s) 17
(c) Appropriate restrictions on placement of compacted fills and footings,
Located on page(s) 15
(d) Recommended buffers from the landslide hazard areas shoreline bluffs and the tops of other slopes.
Located on page(s) 17
(e) Recommended setbacks from the landslide hazard areas shoreline bluffs and the tops of other slopes.
Located on page(s) 16
(8) Recommendations for the preparation of a detailed clearing and grading plan which specifically identifies
vegetation to be removed,a schedule for vegetation removal and replanting,and the method of vegetation
removal.
Located on page(s) 17
(9) Recommendations for the preparation of a detailed temporary erosion control plan which identifies the specific
mitigating measures to be implemented during construction to protect the slope from erosion, landslides and
harmful construction methods.
Located on page(s) 10
(10) An analysis of both on-site and off-site impacts of the proposed development.
Located on page(s) 11
(11) Specifications of final development conditions such as,vegetative management,drainage,erosion control,and
buffer widths.
Located on page(s) 16
(12) Recommendations for the preparation of structural mitigation or details of other proposed mitigation.
Located on page(s) 17
(13) A site map drawn to scale showing the property boundaries, scale, north arrow, and the location and nature
of existing and proposed development on the site.
Located on Map(s) Site Plan
I, Michael Staten,hereby certify under penalty of perjury that I am a civil engineer licensed in the State of Washington
with specialized knowledge of geotechnical/geological engineering or a geologist or engineering geologist licensed in
the State of Washington with special knowledge of the local conditions. I also certify that the Geotechnical
CLYDZ S Report, dated July 7,2023 and entitled Bulkhead—Dock—
Asri,,t T�Tn Shoreline Access, meets all the requirements of the Mason
> County Resource Ordinance, Geologically Hazardous Areas
Section, is complete and true,that the assessment
r 43o45)_ demonstrates conclusively that the risks posed by the landslide
rc• STEt���' r
tsS�oNAL hazard can be mitigated through the included geotechnical
7/7/2023 design recommendations,and that all hazards are mitigated in
Disclaimer:Mason County does not such a manner as to prevent harm to property and public
certify the quality of the work done in health and safety.
this Geotechnical Report.
Page 2 of 2
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
2.2.1 Upslope Geomorphology.............................................................................................................................3
2.3 SURFACE DRAINAGE.............................................................................................................................................3
2.3.1 Upslope Water Bodies..................................................................................................................................3
2.4 SLOPE AND EROSION OBSERVATIONS...................................................................................................................4
3.0 SUBSURFACE INVESTIGATION........................................................................................................................5
3.1 FIELD METHODS,SAMPLING AND FIELD TESTING...............................................................................................5
3.2 GENERAL GEOLOGIC CONDITIONS.......................................................................................................................5
3.3 SPECIFIC SUBSURFACE CONDITIONS.....................................................................................................................6
3.3.1 Groundwater................................................................................................................................................7
4.0 ENGINEERING ANALYSES AND CONCLUSIONS.........................................................................................8
4.1 SLOPE STABILITY..................................................................................................................................................8
4.1.1 Slope Stability Analysis...............................................................................................................................9
4.2 EROSION................................................................................................................................................................9
4.2.1 Shoreline Recession...................................................................................................................................10
4.3 SEISMIC CONSIDERATIONS AND LIQUEFACTION.................................................................................................10
4.3.1 Liquefaction...............................................................................................................................................10
4.4 LANDSLIDE,EROSION AND SEISMIC HAZARDS CONCLUSIONS...........................................................................11
4.5 LATERAL EARTH PRESSURES..............................................................................................................................11
4.6 ON-SITE AND OFF-SITE IMPACTS.......................................................................................................................12
5.0 ENGINEERING RECOMMENDATIONS.........................................................................................................13
5.1 BUILDING FOUNDATION RECOMMENDATIONS....................................................................................................13
5.1.1 Bearing Capacity.......................................................................................................................................13
5.1.2 Settlement...................................................................................................................................................14
5.1.3 Concrete Slabs-on-Grade..........................................................................................................................14
5.2 EARTHWORK CONSTRUCTION RECOMMENDATIONS..........................................................................................14
5.2.1 Excavation.................................................................................................................................................14
5.2.2 Placement and Compaction of Native Soils and Engineered Fill............................................................14
5.2.3 Retaining Wall Backflll.............................................................................................................................15
5.2.4 Wet Weather Considerations.....................................................................................................................16
5.2.5 Building Pads.............................................................................................................................................16
5.3 BUILDING AND FOOTING SETBACKS...................................................................................................................16
5.4 SURFACE AND SUBSURFACE DRAINAGE..............................................................................................................16
5.5 VEGETATION BUFFER AND CONSIDERATIONS....................................................................................................16
5.6 TEMPORARY AND PERMANENT EROSION CONTROL...........................................................................................17
5.7 SEPTIC DRAiNFIELDs..........................................................................................................................................17
5.8 STRUCTURAL MITIGATION.................................................................................................................................17
5.9 SHORELINE DEVELOPMENT................................................................................................................................17
5.9.1 Alternative Approaches.............................................................................................................................19
5.9.2 Mitigation Measures..................................................................................................................................20
6.0 CLOSURE............................................................................................................................................................21
Appendix A-Site Plan
Appendix B-Soil Information
Appendix C-Slope Stability
Appendix D—Erosion Control
1.0 INTRODUCTION
Envirotech Engineering (Envirotech) has completed a geotechnical investigation for planned
development located at 30-40-&50 N Sundown Dr,identified as parcel numbers 42318-50-00013,
-00014, & -00015, Mason County, Washington. See the vicinity map on the following page for a
general depiction of the site location.
An initial geotechnical evaluation of the project was conducted by Envirotech on July 17, 2022.It
was determined that slopes in excess of 40% with a vertical relief of at least 10 feet were present
within 300 feet of the planned development. Based on this site characteristic, the proposed
development will require a geotechnical report pursuant to Landslide Hazard Areas of Mason
County Resource Ordinance (MCRO) 8.52.140. During the site visit by Envirotech, surface and
subsurface conditions were assessed. After completion of the field work and applicable project
research, Envirotech prepared this geotechnical report which, at a minimum, conforms to the
applicable MCRO.
As presented herein, this report includes information pertaining to the project in this Introduction
Section; observations of the property and surrounding terrain in the Surface Conditions Section;
field methods and soil descriptions in the Subsurface Investigation Section; supporting
documentation with relation to slope stability, erosion, seismic considerations, and lateral earth
pressures in the Engineering Analyses and Conclusions Section; and, recommendations for
foundation, settlement, earthwork construction, retaining walls, erosion control, drainage, and
vegetation in the Engineering Recommendations Section.
1.1 Project Information
Currently, all 3 properties are fully developed. Lot 15 has a permitted bulkhead that has failed or
currently failing. The planned development consists of a rock bulkhead along all 3 property
shorelines, and docks for each residence. In addition, a wood staircase is planned so that Lot 13
and Lot 14 may access the shoreline. Due to government regulations, armoring of the entire
shoreline is not permitted.Approximate building footprint and other proposed features with relation
to existing site conditions are illustrated on the Site Map provided in Appendix A of this report.
1.2 Purpose of Investigation and Scope of Work
The purpose of this geotechnical investigation is to assess geological hazards, and evaluate the
project in order to provide geotechnical recommendations that should be implemented during
development.The investigation included characterizing the general project surface and subsurface
conditions,and evaluating the suitability of the soils to support the planned site activities.
In order to fulfill the purpose of investigation,the geotechnical program completed for the proposed
improvements of the project include:
• Review project information provided by the project owner and/or owner's representative;
• Conduct a site visit to document the site conditions that may influence the construction and
performance of the proposed improvements of the project;
• Define general subsurface conditions of the site by observing subsoils within test pits and/
or cut banks, review geological maps for the general area, research published references
Envirotech Engineering Geotechnical Report
PO Box 984 page 1 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
concerning slope stability, and review water well reports from existing wells near the
project;
• Collect bulk samples,as applicable,at various depths and locations;
• Perform soils testing to determine selected index and/or engineering properties of the site
soils;
• Complete an engineering analysis supported by the planned site alterations,and the surface
and subsurface conditions that were identified by the field investigation, soil testing, and
applicable project research; and,
• Establish conclusions based on findings, and make recommendations for foundations,
drainage, slope stability, erosion control, earthwork construction requirements, and other
considerations.
N X a y
Lake
Cushman
Project
Aff
p Lake Cushman
State Park
Prospect
Ridge
IT 1
Cushman
M(
J, HMI !
0 60001=eet 4 _
Vicinity Map from Mason County
Envirotech Engineering Geotechnical Report
PO Box 984 page 2 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
2.0 SURFACE CONDITIONS
Information pertaining to the existing surface conditions for the project was gathered on July 17,
2022, and February 15, 2023 by representatives with Envirotech.During the site visits,the type of
geotechnical investigation was assessed, site features were documented that may influence
construction,and site features were examined that may be influenced by construction.This Surface
Conditions Section provides information on general observations,vegetation,topography,drainage
and observed slope/erosion conditions for the project and surrounding areas that may impact the
project.
2.1 General Observations
Currently, the parcels are fully developed with existing single family residences, septic systems,
and an existing bulkhead in places. Vegetation on and near the project consists primarily of
secondary growth firs, maples and other trees and shrubbery common to this area of the Pacific
Northwest.An aerial photo of the project and immediate vicinity is provided on the following page.
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, slope verification
included measuring slope lengths and inclinations with a cloth tape and inclinometer. See the Site
Plan in Appendix A in this report for an illustration of general topography with respect to the
planned development.
Critical descending slopes,with grades exceeding 40%appear to be within 300 feet of the planned
development. Although nearly vertical slopes were observed, the average critical slope is
approximately 72% with a vertical relief of about 70 feet total.
Ascending grades are generally located to the east of the planned development. These slopes are
relatively minor within 300 feet of the project,with no apparent slope grades of at least 15%.
2.2.1 Upslope Geomorphology
The upland area of the property and beyond is generally situated on a hillside of glacial
origin.
2.3 Surface Drainage
Runoff originating upslope of the development is mostly diverted away from the property by
accommodating topography. Excessive scour, erosion or other indications of past drainage
problems were not observed within the immediate vicinity of the planned development.
2.3.1 Upslope Water Bodies
There are no apparent water bodies or wetlands located upslope from the planned
development that would significantly influence the project.
Envirotech Engineering Geotechnical Report
PO Box 984 page 3 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
2.4 Slope and Erosion Observations
The slope gradients near the project signal a potential landslide or erosion hazard area. Some
indicators that may suggest past slope movements include:
• Outwash of sediments near the bottom of the slope,
• Fissures, tension cracks,hummocky ground or stepped land masses on the face or top of
the slope,and parallel to the slope,
• Fine, saturated subsurface soils,
• Old landslide debris,
• Significant bowing or leaning trees,or,
• Slope sloughing or calving.
Deep-seated slope problems were not observed during the site visit.The upper bank and shoreline
bank of Lake Cushman is currently eroding.Most of the failure is shallow erosion due to the over-
steepened, exposed soils. Larger blocks of landslides from bluff peel-off is evident. Shoreline
dynamics from high water elevation of the lake erodes the lower bank. Freeze/thaw erodes both
the upper and lower banks.
N
A
h ..
U
0 90 Feet
Aerial Photo from Mason County
Envirotech Engineering Geotechnical Report
PO Box 984 page 4 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
3.0 SUBSURFACE INVESTIGATION
Information on subsurface conditions pertaining to the project was primarily gathered on July 17,
2022 and February 15, 2023 by representatives with Envirotech. Applicable information on field
methods, sampling, field testing,general geologic conditions, specific subsurface conditions, and
results from soil testing are presented in this section of the report.Appendix B of this report includes
pertinent information on subsurface conditions for the project,such as subsoil cross-section(s),test
pit log(s), and applicable water well report(s).Water well reports were utilized to estimate ground
water levels, and if sufficient, were used in identifying subsoil types. Applicable test pit locations
are depicted on the Site Plan provided in the appendix of this report.
3.1 Field Methods,Sampling and Field Testing
Information on subsurface conditions for the project was accomplished by examining soils within
test pits and/or nearby banks extending to depths of up to 4 feet below the natural ground surface.
Information on subsurface conditions also included reviewing geological maps representing the
general vicinity of the project,and water well reports originating from nearby properties.
Soil samples were not obtained from this project. Envirotech measured the relative density of the
near-surface in-situ soils by gauging the resistance of hand tools. Within testing locations, field
testing results indicated variable loose to very dense soils. The upper bank soils were very dense,
as well as some places near the surface of the beach. The soils within the bench located between
the upper bank and shoreline bank were tested to be loose.
3.2 General 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 "Geologic Map of the Hoodsport 7.5-minute Quadrangle, Mason County, Washington" by
Michael Polenz, Brendan A. Miller, Nigel Davies,Benjamin B.Perry, Kenneth P. Clark,Timothy
J. Walsh, Robert J. Carson, and Jonathan F. Hughes, August 2012, provides the following
caption(s)for this project:
Unit Age Description
- -
Qgim Pleistocene Deposits as described for master unit Qgic but interpreted as end moraine of
the northern-sourced Puget lobe ice sheet. Moraines are typically marked by
abundant ablation till,but that trend was not apparent where we observed the
unit.
Envirotech Engineering Geotechnical Report
PO Box 984 page 5 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
N Qaf QIS
0
€t
f.
wtr
0 180 Feet .sup,
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 primarily described utilizing the Unified Soil Classification
System(USCS) and the Soil Conservation Service(SCS)descriptions.
The project is currently composed of native soils without indications of fill.Within the upper bank,
soils within the upper 4 feet of natural ground were generally observed to be moist, brown silty
sand with gravel(SM) over at least 20 feet of poorly graded sand(SP) with layers of clay with silt
(CL).
The relative densities of the soil within selected test pits are provided above in Section 3.1.
Expanded and specific subsurface descriptions, other than what is provided in this section, are
provided in the soil logs located in Appendix B of this report.
According to the"Soil Survey of Mason County,"by the United States Department of Agriculture,
Soil Conservation Service,the site soils are described as Hoodsport gravelly sandy loam, He, with
15% to 30% slopes, and Hoodsport stony sandy loam, Hg, with 5% to 15% slopes. The soil
Envirotech Engineering Geotechnical Report
PO Box 984 page 6 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
designations are depicted in the aerial photograph below, and descriptions are provided in
Appendix B of this report.
r.�
}.
0 40 80 160 240
Fee
Soil Survey from USDA Natural Resources Conservation Service
3.3.1 Groundwater
From the water well report(s) and knowledge of the general area, permanent groundwater
is at least 50 feet directly below the property at the building pad location. Surface seepage
was observed within 2 places along the shoreline. Perched groundwater at shallow depths
was not observed on-site,nor indicated on the well reports.
Envirotech Engineering Geotechnical Report
PO Box 984 page 7 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
4.0 ENGINEERING ANALYSES AND CONCLUSIONS
The following section includes slope stability,erosion,seismic considerations,and impacts to both
on-site and off-site properties.
4.1 Slope Stability
Landslides are natural geologic processes, and structures near slopes possess an inherent risk of
adverse settlement, sliding or structural damage due to these processes. Geotechnical engineering
cannot eliminate these risks for any site with sloping grades because gravity is constantly inducing
strain on the sloping soil mass. Excessive wet weather and/or earthquakes will exacerbate these
strains. Geotechnical engineering considers excessive wet weather and `design' earthquakes in
order to provide an acceptable factor of safety for developing on or near sloping terrain with relation
to current engineering protocol. These factors of safeties are based on engineering standards such
as defining engineering properties of the soil, topography, water conditions, seismic acceleration
and surcharges.Surface sloughing or other types of surficial slope movements usually do not affect
the deep-seated structural capability of the slope.However,repeated surficial slope movements,if
not repaired, may present a threat to the structural integrity of the slope. If any slope movement
arises, the slope should be inspected by an engineer. Subsequently,maintenance may be required
in order to prevent the possibility of further surficial or deep seated slope movements that may be
damaging to life and property.
According to the Resource Map from the Washington State Department of Natural Resources
(DNR), the project is not within terrain labeled `highly unstable' relating to soils. DNR labeled
portions of this project as medium and high slope instability with relation to slopes. A Resource
Map from the DNR Forest Practices Application Review System is provided below:
N MAN
A ■ i
Project
Moderate Slope Instability
■ High Slope Instability
® Highly Erodible Soils
® Hydric Soils
1 i ® Highly Unstable Soils
0 240 Feet
Resource Map from Washington State Department of Natural Resources
Envirotech Engineering Geotechnical Report
PO Box 984 page 8 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
4.1.1 Slope Stability Analysis
The Simplified Bishop Method, utilizing `STABLE' software, was used to analyze the
static stability of the site slopes. Seismic conditions were estimated utilizing worst case
scenario values from the static analysis, a quasi-static analysis coefficient of at least 0.15,
and applying the applicable values to STABLE software. Various radii and center points
of the circle were automatically selected,and produced factor of safeties in a graphical and
tabular format. Worst case scenario values were used in the slope stability analysis in
regard to topography, surcharges, water content, internal friction and cohesion of the site
soils. STABLE software has been repeatedly checked with manual calculations, and
consistently proved to be a very conservative program.The following soil properties were
used in the analysis, and are based on observed conditions, known geology, and/or
published parameters:
Upper 4 feet soil depth
Soil unit weight: 132 pcf
Angle of internal friction: 30 degrees
Cohesion: 200 psf
Soils below 4 feet in depth
Soil unit weight: 140 pcf
Angle of internal friction: 40 degrees
Cohesion: 400 psf
For this project, at the location of the proposed development, minimum factor of safeties
for static and dynamic conditions were estimated to be less than 1.5 and 1.1, respectively.
See the slope stability information in Appendix C for a depiction of minimum factors of
safety.
4.2 Erosion
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,as provided above,the
project is not within terrain labeled `highly erodible.' This project is not within an erosion hazard
area as defined by the MCRO. Erosion hazard areas are those with USDA SCS designations of
River Wash (Ra), Coastal Beaches (Cg), Alderwood Gravelly Sandy Loam on slopes 15% or
greater(Ac and Ad),Cloquallum Silt Loam on slopes 15%or greater(Cd),Harstine Gravelly Sandy
Loam on slopes 15%or greater(Hb), and Kitsap Silt Loam on slopes 15%or greater(Kc).
It is our opinion that minor erosion control recommendations provided in this report is sufficient
for the development of this project, and additional engineered erosion control plans are not
required. Temporary and permanent erosion control measures are required for site development.
Extents of temporary erosion control will mostly depend on the timeliness of construction,moisture
content of the soil, and amount of rainfall during construction. Soil erosion typical to the existing
site conditions and planned disturbance of the project include wind-borne silts during dry weather,
Envirotech Engineering Geotechnical Report
PO Box 984 page 9 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
and sediment transport during prolonged wet weather. Sediment transport could be from
stormwater runoff or tracking off-site with construction equipment.
The Temporary and Permanent Erosion Control Section (Section 5.6) of this report consist of
specific erosion controls to be implemented. Additional erosion control information and
specifications may be found in the latest addition of the "Stormwater Management Manual for
Western Washington," prepared by the Washington State Department of Ecology Water Quality
Program.
4.2.1 Shoreline Recession
Due to the close proximity of a shoreline,an evaluation of the shoreline recession rate for
this project was completed. The future shoreline regression will be zero on the subject
property with ordinary care and maintenance of a bulkhead that extends the entire extents
of the property. Without a bulkhead, we anticipate future shoreline regression to be less
than 10 feet within a 50-year span. However, neighboring property owners account for
nearly 12 inches per year of lower bank shoreline erosion. The upper bank is expected to
have an average regression of less than 5 feet within a 50-year span.
4.3 Seismic Considerations and Liquefaction
There are no known faults beneath this project. The nearest Class `A' or Class `B' fault to this
property is the Hood Canal fault zone, which is approximately 3 miles to the southeast of this
project.This information is based on the USGS Quaternary Fault and Fold Database for the United
States.
Potential landslides due to seismic hazards have been considered, and are addressed in the Slope
Stability Analysis Section provided earlier in this report.
Soils immediately below the expected foundation depth for this project are generally Type D,
corresponding to the International Building Code (IBC) soil profiles. According to the IBC, the
regional seismic zone is 3 for this project. The estimated peak ground acceleration ranges from
0.50g to 0.60g.This estimation is based on the United States Geological Survey(USGS)National
Seismic Hazard project in which there is an estimated 2%probability of exceedance within the next
50 years.
4.3.1 Liquefaction
The potential for liquefaction is believed to be low for this project. This is based,in part,
on the subsurface conditions such as soil characteristics and the lack of a permanent
shallow water table. Subgrade characteristics that particularly contribute to problems
caused from liquefaction include submerged, confined, poorly-graded granular soils (i.e.
gravel, sand, silt).Although gravel-and silt-sized soil particles could be problematic,fine
and medium grained sands are typically subjected to these types of seismic hazards. No
significant saturated sand stratifications are anticipated to be within the upper 50 feet of
the subsoil for this project.
Envirotech Engineering Geotechnical Report
PO Box 984 page 10 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
4.4 Landslide,Erosion and Seismic Hazards Conclusions
DNR did not indicate historic landslide activity near the project. DoE mapped a landslide to the
north of the parcels. Mapped slope conditions, as delineated by the Departments of Ecology and/
or Natural Resources, were considered in our slope stability assessment. The upper bank is
experiencing some landsliding as previously described. Based on the proximity and severity of
mapped delineations with respect to the proposed development, results of the aforesaid slope
stability analysis, observed surface conditions, and other pertinent information, it is our opinion
that the proposed development may occur in accordance with the recommendations in this
geotechnical report.It shall be known to the property owners that shorelines pose a unique risk of
earth movements.The proposed development in this report is ordinary shoreline development and
could be vulnerable to future landslides just as it is for virtually all shoreline property owners.
Completely alleviating landslide risks along shorelines are usually not feasible due to constraints
and government ordinances. This geotechnical report does not provide complete stabilization.
However, the rock bulkhead is accepted practice to mitigate shoreline erosion. A bulkhead will
provide a small amount of protection to the upper bank by not allowing the buttress to erode.
However,the upper bank will continue to experience slow regression over time.This could be very
subtle, or it could have 5 feet or so blocks of earth peel off at any given moment. If this occurs,
then additional earth movement of this nature within the same location is not expected for decades.
4.5 Lateral Earth Pressures
Retaining walls may be utilized for this project. The lateral earth pressures exerted through the
backfill of a retaining wall are dependent upon several factors including height of retained soil
behind the wall, type of soil that is retained, degree of backfill compaction, slope of backfill,
surcharges,hydrostatic pressures,earthquake pressures, and the direction and distance that the top
of the wall moves.
An equivalent fluid unit weight used for structural design may be estimated as the product of the
backfill soil unit weight and the earth pressure coefficient for at-rest pressures. Retaining walls
should be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of the
following:
At-Rest Active
Native Soils 49 pcf 32 pcf
Engineered Fill Soils 45 pcf 28 pcf
The values provided above shall be increased by 1 pcf for every 1 degree of backfill/natural slope
angle. These equivalent fluid unit weight values do not include lateral earth pressures induced by
earthquakes,groundwater,or surcharges from live loads.Earthquake pressures should be added to
the wall analysis,and treated as an inverted pressure triangle where the resultant pressure is located
at 2/3 of the wall height,or other method approved by a structural engineer.The following resultant
earthquake pressures as a function of the wall height(H)may be utilized:
Envirotech Engineering Geotechnical Report
PO Box 984 page 11 Parcel 42318-50-00013,-00014, -00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
At-Rest Active
Native Soils 15AH psf 9.811 psf
Engineered Fill Soils 13.611 psf 8.2H psf
See the Earthwork Construction Recommendations Section for details concerning the use of native
soils, engineered fill and placement of backfill.
4.6 On-Site and Off-Site Impacts
From a geotechnical position, it is Envirotech's opinion that the subject property and adjacent
properties to the proposed development should not be significantly impacted if all
recommendations in this report are followed. This opinion is based on the expected site
development, existing topography, existing nearby development, land cover, and adhering to the
recommendations presented in this report. Future development or land disturbing activities on
neighboring properties or properties beyond adjacent parcels that are upslope and/or downslope
from the subject property could cause problems to the subject property. For this reason, future
development or land disturbance near the subject property should be evaluated by a geotechnical
engineer.
Envirotech Engineering Geotechnical Report
PO Box 984 page 12 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
5.0 ENGINEERING RECOMMENDATIONS
The following sections present engineering recommendations for the proposed improvements of
the project.These recommendations have been made available based on the planned improvements
as outlined in the Introduction Section of this report; general observations including drainage and
topography as recapitulated in the Surface Conditions Section; soil/geologic conditions that were
identified from the geotechnical investigation that is summarized in the Subsurface Investigation
Section;and,project research,analyses and conclusions as determined in the Engineering Analysis
and Conclusions Section. Recommendations for the project that is provided herein, includes
pertinent information for building foundations, earthwork construction, building and/ or footing
setbacks, drainage,vegetation considerations, and erosion control.
5.1 Building Foundation Recommendations
The recommended allowable bearing capacities and settlements as presented below, consider the
probable type of construction as well as the field investigation results by implementing practical
engineering judgment within published engineering standards.Evaluations include classifying site
soils based on observed field conditions and soil testing for this project.After deriving conservative
relative densities, unit weights and angles of internal friction of the in-situ soils, the Terzhagi
ultimate bearing capacity equation was utilized for determining foundation width and depth.
Foundation parameters provided herein account for typical structural pressures due to the planned
type of development. A structural analysis is beyond the scope of a geotechnical report, and a
structural engineer may be required to design specific foundations and other structural elements
based on the soil investigation. The frost penetration depth is not expected to extend beyond 12
inches below the ground surface for this project under normal circumstances and anticipated design
features.
5.1.1 Bearing Capacity
Existing in-situ soils for this project indicates that the bulkhead structure can be established
6 inches into cemented hardpan if located within the upper 24 inches. The bulkhead shall
be founded at least 24 inches below the surface atop unyielding, undisturbed soils if
hardpan is not encountered.If hardpan is not encountered,a geotechnical inspector should
verify the competency of the founding soils.
Staircase and landing foundations within 5 feet from the top of slope should be anchored
at least 4 feet below the final ground surface. Staircase foundations located within the
bench area between the upper bank and shoreline shall utilize piers or other deep
foundations as designed by the structural engineer.
Alternatively, foundations may be constructed on selective re-compacted native soil or
compacted engineered fill that is atop firm,unyielding soils as described in the Earthwork
Construction Recommendations Section of this report.Additional geotechnical criteria will
be required for this option,and depends on the location of the fill and the structure that the
fill is supporting.
Undisturbed, unyielding foundation soils for this project have an allowable bearing
capacity of not more than 1500 psf.Foundation recommendations are made available based
Envirotech Engineering Geotechnical Report
PO Box 984 page 13 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
on adherence to the remaining recommendations that are provided in this report.
Alterations to the aforementioned foundation recommendations may be completed upon a
site inspection by a geotechnical engineer after the foundation excavation is completed.
5.1.2 Settlement
Total and differential settlement that a structure will undergo depends primarily on the
subsurface conditions, type of structure, amount and duration of pressure exerted by the
structure, reduction of pore water pressure, and in some instances, the infiltration of free
moisture. Based on the expected native soil conditions, anticipated development, and
construction abides by the recommendations in this report,the assumed foundation system
may undergo a maximum of 1.0 inch total settlement, and a maximum differential
settlement of 0.75 inch.
5.1.3 Concrete Slabs-on-Grade
Concrete slabs are not an element of this project.
5.2 Earthwork Construction Recommendations
Founding material for foundations shall consist of undisturbed native soils to the specified
foundation depths.Compacted engineered fill, or selective re-compacted native soils may be used
to the extents provided in this Earthwork Construction Recommendations Section. The following
recommendations include excavations, subgrade preparation,type of fill, and placement of fill for
building foundations.
5.2.1 Excavation
Excavation is recommended to remove any excessive organic content or other deleterious
material, if present, beneath foundations and to achieve appropriate foundation depth.
Additional sub-excavation will be required for this project if the soils below the required
foundation depth are loose, saturated, not as described in this report, or otherwise
incompetent due to inappropriate land disturbing, or excessive water trapped within
foundation excavations prior to foundation construction.All soils below the bottom of the
excavation shall be competent, and relatively undisturbed or properly compacted fill. If
these soils are disturbed or deemed incompetent, re-compaction of these soils below the
anticipated footing depth is necessary. Excavations shall be completely dewatered,
compacted, and suitable before placement of additional native soil, engineered fill or
structural concrete.
5.2.2 Placement and Compaction of Native Soils and Engineered Fill
For engineered fill or disturbed native soils that will be utilized as fill material directly
beneath foundations, observation and/ or geotechnical testing is required prior to
foundation construction. The following placement and compaction requirements are
necessary.
Envirotech Engineering Geotechnical Report
PO Box 984 page 14 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
For disturbed native soils or engineered fill beneath foundations, limits of compacted or
re-compacted fill shall extend laterally from the bottom edge of the foundation at a rate of
one horizontal foot for each foot of compacted or re-compacted fill depth beneath the
foundation. See the illustration below.
F❑❑TING
COMPACTED
NATIVE S❑ILS
OR ENGINEERED 1
FILL I
II UNDISTURBED SUBGRADE1
Both engineered fill and native soils used as compacted fill should be free of roots and
other organics, rocks over 6 inches in size, or any other deleterious matter. Because of
moisture sensitivity, importing and compacting engineered fill may be more economical
than compacting disturbed native soils. Engineered fill shall include having the soils
retained on the No. 4 sieve crushed (angular), and should consist of the following
gradation:
U.S.Standard Sieve %Finer(by weight)
6" 100
3" 60— 100
No.4 20—60
No.200 0-8
Table 1
Particle Size Distribution of Engineered Fill
Compaction shall be achieved in compacted lifts not to exceed 6 inches for both native
soils and engineered fill,respectively. Each lift should be uniformly compacted to at least
95% of the modified Proctor maximum dry density (ASTM D 1557) and within 3% of
optimum moisture content. Each lift surface should be adequately maintained during
construction in order to achieve acceptable compaction and inter-lift bonding.
Temporary earth cuts and temporary fill slopes exceeding 4 feet in height should be limited
to a slope of 2:1 (horizontal:vertical). Utility trenches or other confined excavations
exceeding 4 feet should conform to OSHA safety regulations.Permanent cut and fill slopes
shall be limited to a slope of 2:1,unless otherwise approved by an engineer.
5.2.3 Retaining Wall Backfill
Retaining wall backfill shall be designed by the structural engineer for walls. Any other
backfill needed for development is not expected.
Envirotech Engineering Geotechnical Report
PO Box 984 page 15 Parcel 42318-50-00013,-00014, -00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
5.2.4 Wet Weather Considerations
Due to the types of subsurface soils, additional provisions may be required during
prolonged wet weather.Every precaution should be made in order to prevent free moisture
from saturating the soils within excavations. If the bottom of excavations used for footing
placement changes from a moist and dense/hard characteristic as presented in this report
to muck or soft, saturated conditions, then these soils become unsuitable for foundation
bearing material. If this situation occurs, a geotechnical engineer should be notified, and
these soils should be completely removed and replaced with compacted engineered fill or
suitable native material as presented in this section.
5.2.5 Building Pads
Building pads for this project are not expected.
5.3 Building and Footing Setbacks
Provided that assumptions relating to construction occur and recommendations are followed as
presented in this report,the factor of safety for slope stability is sufficient for a zero feet footing
setback from the top and toe of the nearby critical slope exceeding 40%.
5.4 Surface and Subsurface Drainage
If drainage problems occur during or after construction, engineered water mitigation will be
required immediately. This may include a combination of swales, berms, drain pipes, infiltration
facilities, or outlet protection in order to divert water away from the structures to an appropriate
protected discharge area.Leakage of water pipes,both drainage and supply lines,shall be prevented
at all times.
If impervious thresholds are exceeded per the prevailing agency code,then engineered stormwater
management plans are required for this project. The drainage engineer must coordinate with a
geotechnical engineer for input with relation to slope stability prior to submitting drainage plans.
If stormwater management plans are not required for this project, then the following
recommendations should be followed.
For this project, we recommend that infiltration is avoided in order to maintain slope stability.
Special provisions for the proposed development are not necessary.
5.5 Vegetation Buffer and Considerations
For this project, we believe that a detailed clearing and grading plan is not warranted unless the
prevailing agency thresholds are exceeded, and basic vegetation management practices should be
adhered to.
Vegetation Buffer — Vegetation shall not be removed from the face of the critical slope unless
minimally needed for development. However,any tree deemed hazardous to life or property shall
be removed. If tree removal is necessary, then stumps and roots shall remain in place (where
feasible),and the underbrush and soil shall remain undisturbed as much as possible.Any disturbed
Envirotech Engineering Geotechnical Report
PO Box 984 page 16 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
soil shall be graded and re-compacted in order to restore the terrain similar to preexisting conditions
and drainage patterns.
5.6 Temporary and Permanent Erosion Control
Erosion control during construction should include minimizing the removal of vegetation to the
least extent possible.Erosion control measures during construction may include stockpiling cleared
vegetation, silt fencing, intercepting swales, berms, straw bales, plastic cover or other standard
controls.
Permanent erosion control is necessary if substantial vegetation has not been established within
disturbed areas upon completion of the project. Temporary erosion control should remain in place
until permanent erosion control has been established. Permanent erosion control may include
promoting the growth of vegetation within the exposed areas by mulching,seeding or an equivalent
measure. Additional erosion control measures that should be performed include routine
maintenance and replacement,when necessary,of permanent erosion control,vegetation,drainage
structures and/or features.
5.7 Septic Drainfields
Septic drainfields are not an element of this project.
5.8 Structural Mitigation
With respect to landslide alleviation or slope improvements, structural mitigation is not necessary
for this project. As stated, shoreline development presents a unique risk that must be incurred by
the property owners. This determination is based on the anticipated improvements of the project,
engineering conclusions, and compliance with all recommendations provided in this report. See
Section 4.4 of this report for specific details on existing landslide potential for this project.
5.9 Shoreline Development
The property appears adequate for the proposed development as described in this report because,
in our opinion, the project will not have a significant negative impact on geological,hydrological
or shoreline dynamics with respect to current conditions. In addition, the bulkhead is needed for
protection of the proposed docks.We recommend that the entire frontage of all 3 properties consists
of new and replaced hard armoring per the rational below:
• Lot 13 is less than 20 feet wide at the shoreline,and the entire shoreline of Lot 13 must be
protected in order to protect the dock.
• Lot 14 is approximately 55 feet wide at the shoreline,and hard armoring should extend the
entire property to protect its dock plus the dock on Lot 13 since the shoreline frontage is
insufficient on Lot 13 for adequate protection.
• Lot 15 is reported by Mason County to have a legal permitted bulkhead. Due to the recent
failures,hard armoring should be re-established on Lot 15.
• Hard armoring is important on all 3 lots due to the very loose shoreline soils.As previously
mentioned, a neighboring property owner has attested to about 12 inches of bank erosion
per year. Partial bulkheads to protect the docks would have a high probability of backfill
Envirotech Engineering Geotechnical Report
PO Box 984 page 17 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
erosion wrapping around the backside of the bulkheads causing failure. See the photos
below.
- F Y r {
t t y 1
-x
N
f�
Large mass of loose soils slumping along lower shoreline
�s
J
.A
'f
ry
Failing rock protection and exposed earth eroding
Envirotech Engineering Geotechnical Report
PO Box 984 page 18 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
!Y
L !
1
L,1 1` lY
T
- �� .4a. ,yy y •ri
OR
Rigr_7
Loose earth slumping along shoreline
Since the bulkhead is partially a replacement, within a small cove with existing shoreline
protection, it is our opinion that there will be virtually no impacts to the property, neighboring
properties,or down-current properties from the proposed development.
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.
5.9.1 Alternative Approaches
Alternative approaches were considered in our geotechnical assessment.These alternatives
include a do-nothing approach, and alternative construction materials.
Envirotech Engineering Geotechnical Report
PO Box 984 page 19 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
The do-nothing alternative will allow for immanent and complete backfill failure that
would provide no protection to the docks.
Envirotech believes that the rock armoring is more suitable than concrete or soft shore
protection. Rock will not impede groundwater flow, would be cantered, and will provide
an overall positive configuration that would not significantly 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 rapid
deterioration of the loose backfill materials that is currently occurring with existing soft
shore armoring.
5.9.2 Mitigation Measures
Measures to mitigate potential site specific and cumulative geological and hydrological
impacts of the proposed development are provided herein in order to mitigate adverse
impacts to adjacent and down-current properties.
Since the planned armoring is virtually the same type and location as the existing/ pre-
existing bulkhead, this alone is mitigation in order to maintain current conditions on Lot
15. In conclusion,there will be no adverse impacts to off-site properties from the planned
bulkhead replacement and new bulkhead on Lots 13 and 14 with relation to existing
condition due to the small cove and existing protection within the cove.
Envirotech Engineering Geotechnical Report
PO Box 984 page 20 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
6.0 CLOSURE
Based on the project information provided by the owner, the proposed development, 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.It is not recommended that a qualified
engineer performs a site inspection during earthwork construction unless fill soils will influence
the impending foundation.However,if native,undisturbed subsurface conditions found on-site are
not as presented in this report,then a geotechnical engineer should be consulted.
This report presents geotechnical design guidelines,and is intended only for the owner,or owners'
representative, and location of project described herein. This report should not be used to dictate
construction procedures or relieve the contractor of his responsibility.
Any and all content of this geotechnical report is only valid in conjunction with the compliance of
all recommendations provided in this report. Semantics throughout this report such as `shall,'
`should' and `recommended' imply that the correlating design and/or specifications must be
adhered to in order to potentially protect life and/ or property. Semantics such as `suggested' or
`optional' refer that the associated design or specification may or may not be performed, but is
provided for optimal performance. The recommendations provided in this report are valid for the
proposed development at the issuance date of this report.Changes to the site other than the expected
development, changes to neighboring properties, changes to ordinances or regulatory codes, or
broadening of accepted geotechnical standards may affect the long-term conclusions and
recommendations of this report.
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, earthquake hazards,
and general soil mechanics.
Please contact Michael Staten at 360-275-9374 if you have any questions, comments, or require
additional information.
Sincerely,
Envirotech Engineering
Jessica Smith,M.S. Michael Staten,P.E.
Staff Geologist Geotechnical Engineer
Envirotech Engineering Geotechnical Report
PO Box 984 page 21 Parcel 42318-50-00013,-00014,-00015
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 7,2023
APPENDIX A
SITE PLAN
SCAL£ 1 [\CY � 67 fEET
o L3 30 bo
LAKE CUSHMAN
APPRX. LOW WATER
ELEVATION
PROPOSED ^~��,• / -—ORDINARY HIGH
WATER (OHW) &
DOCK (TYP) TOP OF BANK '� � TOE OF DANK
yNEV FLOCK BULKHEAD
.' FOR -230 LF a 10 FT
HIGH MAX. SEE DETAILS
NOTES.
fp
-TOE OF BANK
r'
r '- 7OP OF 'ANK
' / r (APPRX)
X"o. / PROPOSED STA�pls
_ -- TP7e� APPRX HOME
EXIST G. - - OCATION
PATH t RX PA
�CEL YP)
j 1 42318-50- 014
ZERO VEGETATTON PUFFER, t I 0.,4V SUND N
REMOVAL OF VEG=TAT1 FRO 1 \ P i2 EL
CRITICAL SLOPE NOT PEZNITTCD_ P�`tRLT ti'� 4231'8750-00013
UNLESS AS ALL13VED IN S Lr=.�
GEOTECHN1CAL REPORT , 42318E150-00015 � 30 N SUNDOWN ➢
COIiSeRUCFION SETSfrCKS FROM50 N Sl,2Ni)PWN DR'+. •___� �-�._
TOP OF CRITICAL SLOPE DO NOT j
APPLY. SEE REPORT
t
SM�ia
-'Ti
FRO.ECT/OWNER/LMATIW,
Z C13N,TMJQS WERE NOT NEPARED§Y A LICENSED LAND SURVEMIL SINGLE FAMILY RESIDENCE
CDNTMiRS WERE E,XTRAFa'ATCD MEN A PUiL.t'LIDAR sO.IRCE,A-NO G1=OTECWNIC/L REPORT
INCDTPORATEB FIELD MEASUtEHENTS AS ExPLA'INED IK TIC GEOTEQN1 AL
REFORT. vE9R
ROJNDARrLS WERE NETS PREPARED BY A LICZNSEO VURVEYER.IA'ATEONS 30-'50 N V.NCOYN CREVE
Or SSTE F'+CATLC[ES THA'• ME SHIOWN PULE.SUL'FI AS TD'IF SLOVES.11K �LE E;END PA110EL 42319-30•{06LS.-C13014.-0811
O SLOEF S, WATER F ATLR3S,ETC,WITH RELAT304 TO THE P502ERTY WASEN V.111MY. VAS"IY N
LL%FF W=T RE V.-R1F ET'gY T.E 9,,Wk RECDHgN`ATIENS IX THE EN3INEEA
G`OYECWIt.,AL REPORT PPavIDT SL73.4:ICS,9LF'FEAS.DL'PTHS. EIG.WITH RLO'i INDICATCR ENVIREMN Et a1N:Fa7TNG
R LATTOV TO GEM= FEEAT5EnZ NOT PROPERTY LINES-7AESE GEOLOMC Pp P0X 58/
FEATLRES MAY 7E LOCATED ON TIIE S B.CCT PRORUTT OR%EfZNDMP4 T,FC— EXISTUK,C[KTOUY BEL>`REIt. W4vfINLTOM 9834-18
PROPERTIES, f TP31@ TEST PIT 350-273-9374
SITE PLAN
APPENDIX B
SOIL INFORMATION
o,Ulr..L A+a EOttlINUL CALL
t otH=40 FEET
9 Lo 29 49
STAIRCASE
EARTH CUT AS
NEEDED FOR MEDIUM DENSE SILTY SAND
STAIRCASE WITH GRAVEL (SM)
C❑NSTRUCTION
PIN PILES FOR
F❑UNDAIT❑NS WITHIN BENCH
AREA BETWEEN UPPER BANK
AND SHORELINE
VERY DENSE ALPINE
GLACIAL DEPOSITS (SM)
LAKE _
CUSHMAN
LOOSE LANDSLIDE DEPOSITS AND TALUS
ROCK BULKHEAD
SECnON A-A
FROECT/OVNE R/USATEQI
SINGLE FA14ILY RESIDENCE
GE❑TECHNICAL REPORT
VEHR, ET AL
30-;A0 N Sc'NGOVW CRTVE
PAttCEL+23L"Q-000t5.-00M,-C➢0L3
MA801E CENNTY,VASHIWjMN
EN3DEER
EVVLEQECCH EN5314MRING
PO➢0" "4
BELFAER,VASHPi M 99VO
S❑IL PROFILE
TEST PIT LOG
TEST PIT NUMBER TP-1
PROJECT: S=R Geological Assessment DATE OF LOG: 0711712022
PROJECT NO: 22329 LOGGED BY! NICS
C'_IENT: 'Gebb EXCAVATOR: MA
LOCATION: Parcel4231&50�-300'4 DRILL RIG: None
Mason County,Washington ELEVATION: N,A
INITIAL DEPTH OF WATER: NA FINAL DEPTH OF WATER: NIA
SOILS1RAIA, ill +iJtE`aE'nl'i�YiEr'
C=PL^ SAMPLERS USCS DESCRIPTION LL PI CilR'JE
AND TEST CATA DEPTH �! '0 20 0
.........................I................
St.t S ca rr�fsL rrcalum dense SILI"Y
S.wtdD W.h GWrtL,Grayrl Is flno and
- :uhroun3ed.Sand Is primally ecnrse,
1 Non Clasth
r -
3 '
i
<:.\.. . ....................-----.......................
S.. Brown,low mols;ure,ve-y dense
p FOORLY GRACE-D SAND,Srnd is
'Y -dai:Ay meafurr..Nar,plastl.,
5 i y
�t g3g
"i-
9
L Layer of vary hard clay with.:III r,Ci 1
Liu
Bank ex;rn--v:rr 10 R
NoCroundrrate-En;ourrered ENVIRflTECH ENGINEERING
r..'x r.«y r-I,-}A'j-%j OtM Geotectmltal EnginrcihO
.vtr"N--.= S^Cf"i d-"a eras SR.
Map Unit Description:Hoodsport stony sandy loam,5 to 15 percent slopes—Mason County,
Washington
Mason County,Washington
Hg—Hoodsport stony sandy loam,5 to 15 percent slopes
Map Unit Setting
National map unit symbol., 2h10
Elevation: 330 to 1,480 feet
Mean annual precipitation: 60 inches
Mean annual air temperature: 50 degrees F
Frost-free period: 150 to 175 days
Farmland classification: Not prime farmland
Map Unit Composition
Hoodsport and similar soils:100 percent
Estimates are based on observations,descriptions,and transects of
the mapunit.
Description of Hoodsport
Setting
Landform:Till plains
Parent material.,Basal till
Typical profile
H1-0 to 5 inches: stony medial sandy loam
H2-5 to 24 inches: very gravelly medial sandy loam
H3-24 to 60 inches: gravelly sandy loam
Properties and qualities
Slope:5 to 15 percent
Depth to restrictive feature:20 to 40 inches to densic material
Drainage class:Moderately well drained
Capacity of the most limiting layer to transmit water(Ksat):Very low
to moderately low(0.00 to 0.06 in/hr)
Depth to water table:About 18 to 36 inches
Frequency of flooding:None
Frequency of ponding:None
Available water supply,0 to 60 inches: Very low(about 1.6 inches)
Interpretive groups
Land capability classification(irrigated): None specified
Land capability classification(nonirrigated): 6s
Hydrologic Soil Group: B/D
Ecological site: F002XA005WA-Puget Lowlands Moist Forest
Forage suitability group: Limited Depth Soils(G002XF303WA)
Other vegetative classification: Limited Depth Soils
(G002XF303WA)
USDA Natural Resources Web Soil Survey 1/23/2023
i Conservation Service National Cooperative Soil Survey Page 1 of 2
Map Unit Description:Hoodsport stony sandy loam,5 to 15 percent slopes—Mason County,
Washington
Hydric soil rating: No
Data Source Information
Soil Survey Area: Mason County,Washington
Survey Area Data: Version 18,Sep 8,2022
LsDA Natural Resources Web Soil Survey 1/23/2023
Conservation Service National Cooperative Soil Survey Page 2 of 2
APPENDIX C
SLOPE STABILITY
' 1_ 00 }
1_20
1 _3 O
40
so
1_ 60
1 1 .70 1
8 O
1
=2 _ OO
V
Y�
a r of e c t _ web b Repo r't
DaLai"i.L� pyi,a miC Tnalysig
an a i y s i s B i s h op
/ 1.00
1.1 O
1.2 0
1.30
/ 1.40
1 1 .50
1_60 I
1 .70
1.so
1.90
=2.00
0-000
I
Pro e c t We bb Re p o r t
Data file Static Ana l.ys:i.c:
Analysis Bishop