HomeMy WebLinkAboutGEO2021-00021 for BLD2021-00338 - BLD Permit / Conditions - 7/3/2019 2oz I - ooa z 1
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MAR 0 9 2021
PLANNING 615 W. Alder Street
Geotechnical Report
Ethridge Retaining Wall & RV Pad
8980 E State Route 106, Union
Parcel No. 32235-31-00190
Mason County, Washington
July 3, 2019
Project#1973
Prepared For:
Richard and Laura Ethridge
8980 E State Route 106
Union, Washington 98592
Prepared By:
Envirotech Engineering
PO Box 984
Belfair, Washington 98528
Phone: 360-275-9374
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MASON COUNTY 1;i fhmittP= f';hP01i t
Ili COMMUNITY SERVICES Geotechnical Report
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 Richard and Laura Ethridge Parcel# 32235-31-00190
Site Address 8980 E State Route 106
(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, 11
(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 of36
(7) (a) Appropriate restrictions on placement of drainage features,
Located on page(s) 17
(b) Appropriate restrictions on placement of septic drain fields,
Located on page(s) 18
(c) Appropriate restrictions on placement of compacted fills and footings,
Located on page(s) 13 and 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 - 12
(11) Specifications of final development conditions such as,vegetative management,drainage, erosion control,and
buffer widths.
Located on page(s) 17- 18
(12) Recommendations for the preparation of structural mitigation or details of other proposed mitigation.
Located on page(s) 18
(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
4 cLYOP Report,dated July 3,2019, and entitled Ethridge Retaining
A��,F wnsf��.sr1y� Wall&RV Pad, meets all the requirements of the Mason
County Resource Ordinance,Geologically Hazardous Areas
Section, is complete and true,that the assessment
demonstrates conclusively that the risks posed by the landslide
04,�ss GIST roti4L��v hazard can be mitigated through the included geotechnical
7/3/19 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.................................................................................................................................I
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
GE O SER
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............................................................................................................................................10
4.3 SEISMIC CONSIDERATIONS AND LIQUEFACTION..............................................................................10
4.3.1 Liquefaction..............................................................................................................................11
4.4 LANDSLIDE,EROSION AND SEISMIC HAZARDS CONCLUSIONS........................................................11
4.5 LATERAL EARTH PRESSURES...........................................................................................................11
4.6 ON-SITE AND OFF-SITE IMPACTS.....................................................................................................1 1
5.1 FOUNDATION RECOMMENDATIONS..................................................................................................13
5.1.1 Bearing Capacity.......................................................................................................................13
5.1.2 Settlement..................................................................................................................................14
5.1.3 Parking Concrete Slabs-on-Grade or Asphalt..........................................................................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 BackjW............................................................................................................16
5.2.4 Wet Weather Considerations....................................................................................................16
5.3 BUILDING AND FOOTING SETBACKS.................................................................................................16
5.4 SURFACE AND SUBSURFACE DRAINAGE...........................................................................................16
5.5 VEGETATION BUFFER AND CONSIDERATIONS.................................................................................17
5.6 TEMPORARY AND PERMANENT EROSION CONTROL.......................................................................17
5.7 SEPTIC DRAINFIELDS........................................................................................................................17
5.8 STRUCTURAL MITIGATION...............................................................................................................17
6.0 CLOSURE.............................................................................................................................................18
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 a planned
RetainingWall and RV ad located at 8980 E State Route 106,identified as parcel number 32235-
P
31-00190, 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 May 22,2019. 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) 17.01.100. 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
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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
Information pertaining to the planned development of the project was provided by the proponent
of the property.The planned development consists of a new RV pad and retaining wall in order to
have sufficient parking grade 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
concerning slope stability, and review water well reports from existing wells near the
Envirotech Engineering Geotechnical Report
PO Box 984 page 1 Parcel 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
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.
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Vicinity Map from Mason County Website
Envirotech Engineering Geotechnical Report
PO Box 984 page 2 Parcel 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
2.0 SURFACE CONDITIONS
Information pertaining to the existing surface conditions for the project was gathered on May 22,
2019 by a representative with Envirotech. During the site visit, 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 property has an existing single-family residence and existing driveway. Vegetation
on and near the project consists primarily of secondary growth firs, cedars, 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 ascending slopes,with grades exceeding 40% appear to be within 300 feet of the planned
development. The maximum critical slope is approximately 87% with a vertical relief of about 90
feet.
Descending grades are generally located to the north 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
Significant runoff originating upslope of the development sheet flows and runs onto the property.
Excessive scour or erosion were not observed within the immediate vicinity of the planned
development.However, water plants and seepage was observed.
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 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
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.
Except for saturated subsoils,these slope instability indicators or other 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.
91
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Aerial Photo from Mason County Website
Envirotech Engineering Geotechnical Report
PO Box 984 page 4 Parcel 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
3.0 SUBSURFACE INVESTIGATION
Information on subsurface conditions pertaining to the project was primarily gathered on May 22,
2019 by a representative 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 5 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 generally indicated loose to medium dense soils in the upper 60 inches, and very
dense soils from 60 inches to the depth of terminus.
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 Skokomish Valley and Union 7.5-minute Quadrangles,Mason County,
Washington' by Michael Polenz, Jessica L. Czajkowski, Gabriel Legorreta Paulin, Trevor A.
Conteras, Brendon A. Miller, Maria E. Martin, Timothy J. Walsh, Robert L. Logan, Robert J.
Carson, Chris N. Johnson, Rian H. Skov, Shannon A. Mahan, and Cody R. Cohan, June 2010,
provides the following caption(s)for the project area:
Allutlum fan deposits—Cobbles.pebbles,sand,silt.and boulders:poorly sorted and stratified:
forms concentric lobes where streams emerge from valleys;relict where Qoaf.
Qapd Pre-Fraser Olymplc-source glaclai dtlft,undfilded—Till and outwash consisting of cobbles
and pebbles with occasional boulders and sandy to clayey matrix.
aPre-Fraser
Olympic-sourrt outwash gravel---Cobble to pebble gravel with sandy to clayey
imatrix:grav to lielht orange-brown;conhpam clasts mostly subrounded:nhoderately sorted.
Envirotech Engineering Geotechnical Report
PO Box 984 page 5 Parcel 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3, 2019
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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 test pit
locations, soils within the upper 5 feet of natural ground were generally observed to be moist to
saturated,brown silty sand with gravel (SM). Soils below the upper 5 feet layer were observed to
be mostly grey,low moisture, silty sand with gravel(SM),locally known as hardpan.The hardpan
may extend to depths greater than 50 feet. This is based on nearby well reports, site geology,and/
or knowledge of the general area.
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.
Envirotech Engineering Geotechnical Report
PO Box 984 page 6 Parcel 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
According to the"Soil Survey of Mason County,"by the United States Department of Agriculture,
Soil Conservation Service, the site soils are described as Alderwood Gravelly Sandy Loam, Ad,
with 30% - 50% slopes. The soil designations are depicted in the aerial photograph below, and
descriptions are provided in Appendix B of this report.
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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 30 feet directly below the property at the building pad location. Surface seepage
was noted on the face of the critical slope. 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 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
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 Coastal Zone Atlas of Mason County,Washington,the project is within and near
terrain labeled `Stable' and `Intermediate' regarding potential landslide activity. Descriptions of
these mapping units may be found in the aforesaid Atlas. A Stability Map from the Coastal Zone
Atlas for the general area of this project is provided below:
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Map from Washington State Department of Ecology Website
Envirotech Engineering Geotechnical Report
PO Box 984 page 8 Parcel 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
According to the Resource Map from the Washington State Department of Natural Resources
(DNR),the project is 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:
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Resource Map from Washington State Department of Natural Resources Website
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's 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
regards 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 5 feet soil depth
Soil unit weight: 132 pcf
Angle of internal friction: 30 degrees
Cohesion: 200 psf
Envirotech Engineering Geotechnical Report
PO Box 984 page 9 Parcel 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
Soils below 5 feet in depth
Soil unit weight: 140 pcf
Angle of internal friction: 40 degrees
Cohesion: 400 psf
Based on the slope stability analysis, unacceptable factors of safety could be present on
and near the critical slope,but do not reflect conditions where development is expected to
occur. For this project, at the location of the proposed development, minimum factor of
safeties for static and dynamic conditions were estimated to be at least 1.5 and 1.1,
respectively.See the slope stability information in Appendix C for a depiction of minimum
factors of safety away from the project.
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 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,
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.
4.3 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 Tacoma Fault Zone, in which is approximately 3 miles to the northeast 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.
Envirotech Engineering Geotechnical Report
PO Box 984 page 10 Parcel 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
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.
4.4 Landslide,Erosion and Seismic Hazards Conclusions
DNR indicated historic landslide activity near the project. Mapped slope conditions, as delineated
by the Departments of Ecology and/or Natural Resources, were considered in our slope stability
assessment. 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.
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.A structural or geotechnical professional should design retaining walls based on
specific conditions.
Soil parameters for the structural design of retaining walls may be estimated as 134 pounds per
cubic foot(pcf)and 118 pcf for engineered fill and native soils,respectively.The angle of internal
friction may be estimated as 36 degrees and 32 degrees for engineered fill and native soils,
respectively. These soil parameters are based on soil type and placement conforming to the
Earthwork Construction Recommendations Section in this report.
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
Envirotech Engineering Geotechnical Report
PO Box 984 page 11 Parcel 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
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 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
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
P J
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 Foundation Recommendations
Recommendations provided in this section account for the site development of a typical concrete
reinforced or block retaining wall.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. Stepped foundations are acceptable, if
warranted for this project.Continuous, isolated,or stepped foundations shall be horizontally level
between the bottom of the foundation and the top of the bearing strata.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 wall structure can be established on
shallow, continuous footings. Foundations shall be established on relatively undisturbed
native soil that is competent and unyielding.Alternatively,foundations may be constructed
on selective re-compacted native soil or compacted engineered fill as described in the
Earthwork Construction Recommendations Section of this report.
For a bearing capacity requirement of no more than 1500 psf, a minimum continuous
footing width of 24 inches shall be placed at a minimum of 24 inches below the existing
ground surface atop prepared, unyielding soils. Foundation recommendations are made
available based 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.
Envirotech Engineering Geotechnical Report
PO Box 984 page 13 Parcel 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
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 Parking Concrete Slabs-on-Grade or Asphalt
Both cement concrete slabs or asphalt should be supported on a minimum of 24 inches of
compacted coarse,granular material(Retained on U.S. Sieve#10 or greater)that is placed
over prepared, competent native subgrade located at least 24 inches below the current
ground surface or engineered fill per the Earthwork Recommendations Section below.
5.2 Earthwork Construction Recommendations
Founding material for both walls and parking areas 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 organic laden, or otherwise incompetent due to inappropriate land
disturbing. All soils below the bottom of the excavation shall be prepared as follows, or
properly compacted fill over prepared subgrade. If these soils are disturbed or deemed
incompetent, re-compaction of these soils below the anticipated footing depth or parking
pad is necessary. Excavations shall be completely dewatered, compacted, and suitable
before placement of additional native soil,engineered fill or structural concrete. Subgrade
preparation at the bottom of the excavation includes compaction if the soils are relatively
dry with a 90 pound `jumping jack' making a minimum of 5 passes. If soils are saturated
or too wet for proper compaction,2-inch to 4-inch crushed ballast should be placed per the
following section.
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 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
For disturbed native soils or engineered fill beneath foundations, limits of compacted or
g P
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.
FOOTING
COMPACTED
NATIVE SOILS
OR ENGINEERED t
FILL
1
UN�[STURBED SUBGRA)lE
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 be the 2 to 6 inch crushed
ballast as described above or 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. Except for crushed ballast, 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.Crushed ballast shall be compacted using loaded construction equipment
until subgrade is firm and unyielding.
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.
Envirotech Engineering Geotechnical Report
PO Box 984 page 15 Parcel 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
5.2.3 Retaining Wall Backfill
Native soils may be used as retaining wall backfill for this project if the total wall height is
4 feet or less and the recommendations below are followed.Native soils for retaining walls
exceeding 4 feet in height must be approved by the local authority or evaluated by an
engineer. Backfill may consist of engineered fill, as presented in this report, or borrow
material approved by a geotechnical engineer. Compaction of these materials shall be
achieved in compacted lifts of about 12 inches. Each lift should be uniformly compacted
to at least 85%, and no more than 90% of the modified Proctor maximum dry density
(ASTM D 1557). If pavement or building loads are planned to be located within retaining
wall backfill,then 90%compaction is required.In addition,heavy construction equipment
should be at a distance of at least Vi the wall height. Over-compaction and limiting heavy
construction equipment should be prevented to minimize the risk of excess lateral earth
pressure on the retaining structure. Envirotech recommends that retaining wall backfill is
compacted with light equipment such as a hand-held power tamper.If clean,coarse gravel
soils are utilized as engineered fill, and surcharges will not influence the retaining wall,
compaction may be achieved by reasonably densifying granular soils with construction
equipment.
5.2.4 Wet Weather Considerations
Due to the types of subsurface soils, additional provisions may be required during
prolonged wet weather. We strongly encourage that work is performed during the dry
season of the year.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.
5.3 Building and Footing Setbacks
Due to the type of project,building setbacks are not required.
5.4 Surface and Subsurface Drainage
Positive drainage should be provided to allow surface water to travel towards its natural drainage
path. Retaining walls shall include drainage collection within the backfill, and the outlet should
daylight with gravity flow.
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.
Envirotech Engineering Geotechnical Report
PO Box 984 page 16 Parcel 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
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 upslope.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, and the underbrush and soil shall remain undisturbed as
much as possible.Any disturbed 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. Although other controls may be used, if adequate, silt fencing is presented in this report
as the first choice for temporary erosion control.Any erosion control should be located down-slope
and beyond the limits of construction and clearing of vegetation where surface water is expected to
flow. If the loss of sediments appears to be greater than expected,or erosion control measures are
not functioning as needed, additional measures must be implemented immediately. See Appendix
D for sketches and general notes regarding selected erosion control measures. The Site Plan in
Appendix A depicts the recommended locations for erosion control facilities to be installed as
necessary.
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. Selected recommendations for permanent erosion control are provided in Appendix D.
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 existing,and not part of this project.
5.8 Structural Mitigation
With respect to landslide alleviation or slope improvements, structural mitigation is not necessary
for this project. This determination is based on the anticipated improvements of the project,
engineering conclusions,and compliance with all recommendations provided in this report.
Envirotech Engineering Geotechnical Report
PO Box 984 page 17 Parcel 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
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 Legarza,M.S. Michael Staten,P.E.
Staff Geologist Geotechnical Engineer
Envirotech Engineering Geotechnical Report
PO Box 984 page 18 Parcel 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
APPENDIX A
SITE PLAN
SUILS1 MEDIUM DENSE SILTY SAND WITH GRAVEL SCALE I INCH Go rEET
(SM) OVERLYING VERY DENSE GLACIAL TILL
0 15�n
PRO"0SCE DRIVEWAY
EXISTING DRIVEWAv
E STATE ROJTE 106 'I
A APPROXIMATE TOE OF
i r
SLOPE EXCEEDING 40%
i
P
EXISTING SINGLE RpPpSED RV PAD
"AMILY RESIDENCE 40 /
PROPOSED 6 FT RETAINING
_ N �
EXISTING GARAGE ba N WALL
1t
A'
EXISTING SEPTIC—"'z
DRAINFIELD
moo' g �d
NOTES PROJECT/ INNER/ LOCATION,
1. EROSION CONTROL MAY BE REQUIRED FOR THIS SITE. GENERAL LOCATIONS SINGLE FAMILY RESIDENCE
ARE DEPICTED, AND ALTERNATIVES MAY BE UTILIZED AS EXPLAINED IN THE GEOTECHNICAL REPORT
GEOTLCHNICA. REPOR7
I!.CONTOURS WERE. NOT PREPARED BY A LICENSED LAND SURVEYOR. ETHRIDGE
CONTOURS WERE EXTRAPOLATED FROM A PUBLIC LIDAR SOURCE, AND 8980 E STATE RTE 106
INCORPORATED FIELD MEASUREMENTS AS EXPLAINED 1N THE GE.OIECHNICAL LEGEND PARCEL 32235-31-00190
REPORT.
3, BOUNDARIES WERE NOT PREPARED BY A LICENSED SURVEYOR. LOCATIONS TEMPOIARY ENGINEER;
� SITE FEATURES THAT ARE SOWN HERE. SUCH AS TOP O' SLOPES, TOE +++EROSIMTEMPOR CONTOR. ENGINEER; ENGINEERING
Or SLCOPES, WATER rEATURES, ETC., WITH RELATION TO THE PROPERTY PO BOX ECH
LINES MUST BE VERIFIED BY 7NE OWNER RECOW&NDATIONS IN THE �. SLOPE INDICATOR BELFAIR, VASH1NGi0N 98520
GEOTFCHNICAL REPORT PROVIDE SETBACKS, BUFFERS, DEPTHS, ETC.. WITH 360I-AIR, 37�
RELATION TO GEOLOGIC FEATURES, NOT PROPERTY LINES. THESE GEOAG(C - Ex1ST1NG CONTOUR.
FLATURLS MAY BE LOCATED ON THE SUBJECT PROPERTY OR NEIGHBORING TP1 7T T pl, SITE PLAN
RTIES.
NOI.LVMOANa 'IIOS
S XIUN2[ddV
MEDIUM DENSE SILTY SAND
WITH GRAVEL (SM)
EXISTING GRADE
$b�
PROPOSED 6FT
b�
RETAINING WALL
PROPOSED RV PAD-
PROPOSED FILL---
DENSE GLACIAL TILL
�CTIIl/Ir-A
PQ.ECT/DVWRi ILCATWO
SINGLE FAMILY RESIDENCE
CEOTECHNICAL REPatT
cTMR K&
P*AICEL 3"35 31 OoIYJ
why w^sm CmNry. V*swGTm
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2TK� MOA.L a#=MTE FEW TK arm Q 3E IMP&ME PC FA 9V
TIC alsEwm TUT P(TS At TIC SPCCOTID LWATum �E1F�lt.VASI@1G7D�9W'!
LMOU 971M AW PAO 01 UX GEMW. Y�O�7YY-737�
vHLL L.Oup,**WM EwWaDcE M TIE QDEML MEA SOIL PROFILE
TEST PIT LOG
TEST PIT NUMBER TP-1
PROJECT: Ethridge Geotechnical Report DATE OF LOG: 4';2212019
PROJECT NO: 1973 LOGGED BY: RJM
CLIENT: Laura and Richard Ethridge EXCAVATOR: NSA
LOCATION: 8980 E State Route 106 DRILL RIG: None
Mason County. Washington ELEVATION: N-A
INITIAL DEPTH OF WATER: N:A FINAL DEPTH OF WATER: NIA
STANDARD PENETRATION TEST
SOIL STRATA
DEPTH SAMPLERS L;SCS DESCRIPTION LL PI CURVE
AND TEST DATA DEPTH N 10 30 50
0
SM Medium brown,moist,medium dense
SILTY SAND with GRAVEL Gravel is
primarily well-graded and subrounded
I Sand is mostly medium No plasticity
3
a 17.
.S
Light brown,very dense glacial till(c3±5'
5 Excavation terminated at approximately 5
feet
6
7
9
9
10
No Groundwater Encountered ENVIROTECH ENGINEERING
7hia m!ormalron perta;ns or,Fy to lima borrg and ahouid not bs Geotechnical Engineering
mte,p,eted as bang indtobve or the entve site
Map Unit Description Alderwood gravelly sandy loam 30 to 50 percent slopes--Mason
Court:,lkashmgton
Mason County. Washington
Ad—Alderwood gravelly sandy loam. 30 to 50 percent slopes
Map Unit Setting
National map unit symbol 2t628
Elevation 50 to 800 feet
P leaf r annual precipitation 25 to 60 inches
Mean annual air temperature 46 to 52 degrees F
Frost-free period 160 to 240 days
Farmland classification Not prime farmland
Map Unit Composition
Aldetwoocl and similar soils 80 percent
Minor components 20 percent
Estimates are based on observations,descriptions,and transacts of
the mapunit.
Description of Alderwood
Setting
Landform' Ridges,hills
Landforni positron(hvo-dimensional) Backsiope
Landform position(three-dimensional): Side slope.nose slope talf
Down-slope shape Linear,convex
Across-slope shape Convex
Parent material Glacial drift and!or glacial oulwash over dense
glociomarine deposits
Typical profile
A-0 to 7 inches gravelly sandy loam
Bw 1-7 to 21 inches very gravelly sandy loan)
Bw2-21 to 30 inches very gravelly sandy loam
Bg-30 to 35 inches very gravelly sandy loam
2Cd t-35 to 43 inches very gravelly sandy loam
2Cd2-43 to 59 inches very gravelly sandy loam
Properties and qualities
Slope 30 to 50 percent
Depth to restrictive feature 20 to 39 inches to densic material
Natural drainage class Moderately well drained
Capacity of the most tirniting layer to transmit water(Ksat) Very
low to moderately low(0.00 to 0.06 inihr)
Depth to water table About 18 to 37 inches
Frequency of flooding None
Frequency of ponding None
Available water storage in profile Very low(about 2 7 inches)
Interpretive groups
Laixl capability classification(irrigated) None specified
Land capability classification(nonirrigated). 7e
Hydrologic Soil Group 8
I,\ Natural Resources web Sod Survey 61 12r2019
41111111111111111 Conservation Service National Cooperatr,s Sod Survey Page t of 2
Map Unit Description Alderwocd gravelly sandy loam,30 to 50 percent slopes--Mason
County.Washington
Hydric soil rating No
Minor Components
Everett
Percent of neap unit 10 percent
Landform Kames,eskers,moraines
Landform position(two-dimensional) Backslope
Landform position(three-dimensional) Side slope
Down-slope shape. Convex
Across-.slope shape Convex
Hydric sal rating No
Indianola
Percent of neap unit 5 percent
Leindfornr Eskers,kames,terraces
Landform position(three-dimensional): Tread
Down-slope shape Linear
Across-slope shape Linear
Hydric sod rating No
Shalcar
Percent of map rind: 3 percent
Landfornn: Depressions
Landform position(three-cliniensional) Dip
Down-slope shape. Concave
Across-slope shape Concave
Hydric sod rating Yes
Norma
Percent of map unit; 2 percent
La ndfonm Depressions drainageways
Landform position(three-dimensional): Dip
Down-slope shape Concave,linear
Across-slope shape Concave
Hydric sod rating Yes
Data Source Information
Soil Survey Area Mason County,Washington
Survey Area Data Version 14,Sep 10.2018
si,� Natural Resources Neb Sod Survey 6112l2019
Conservation Service National Cooperative Sod Survey Page 2 of 2
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APPENDIX C
SLOPE STABILITY
1. . 00
1 . 1 O
1 . =O
1 . 30
1 . 40
1 . 50
160
1 . 70
1 80
1 . 9 O
2 . 00
Project Ethridge Project
Datagilo Dynamic Analysis
Analysis Bishop
Envirotech Engineering Geotechnical Report
PO Box 984 page 1 Parcel 32235-31-00190
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 3,2019
1 . O O
1 . 1 0
1 . O
1 . 3 0
1 . 40
1 . 50
l . 60
1 . 70
1 . 80
1 . 90
. O O
7^B
Pro�act Ethridge Prajact
Datafile� static Analysis
Analysis Bishop
APPENDIX D
EROSION CONTROL
GEOTEXTILE FABRIC
WRAP AROUND TRENCH
TO AT LEAST ENTIRE
BOTTOM OF TRENCH
BEFORE PLACING GRAVEL 2'x2'x5' WOOD POST OR
12' DEEP, 8' WIDE TRENCH EQUIVALENT OR BETTER
FILLED WITH 3/4• TO 1 1/2'
WASHED GRAVEL OR VEGETAT�N
DIRECTION OF r z�Fr
WATER FLOW EXISTING
GROUND SURFACE
T ¢e►T
SILT FENCE - CROSS SECTION
N,T.S.
2'x2' WOOD POST (TYP) GEOTEXTILE FABRIC
OR EQUIVALENT OR BETTER AND WIRE MESH
2 6 FT MAX. O C.
6f1 I r O.�FT
EXISTING IL
GROUND SURFACE
e
12' DEEP, 8' WIDE
TRENCH FILLED WITH an
3/4' TO 1 1/2' 23 FT
WASHED GRAVEL OR VEG TI �L
BOTTOM EXTENTS OF
GEOTEXTILE FABRIC SILT FENCE - DETAIL
N.T.S.
PROVIDE FULL WIDTH
3/4 IN TO 1 I/2�N�FT INGRESS/EGRESS
CRUSHED GRAVEL
PLACED AT 6 IN
MINIMUM DEPTH
WELL—DRAINED
SOILS
^0.02 IN/MIN FULL NTH
R-25 FT MIN
q
ACCcs: ROAD
STAB LI ED CONSTRUCTION ENTRANCE
N.T.S.
PER-ANENT EROSION CONTROL NOTES,
AL NOTES-
SEEM' FOR RAW SLOPES
SHIELD THE TEMPORARY EROSION AND SEDIMENT CONTROL MEASURES SHOWN ON
GCSE PLANS PROVE TO BE INADEOuATE MING CONSTRUCTION, THE CONTRACTOR L BEFORE SEEDING, INSTALL NEEDED SURFACE RUNOFF CONTROL
CHILL INSTALL ADDITIONAL EROSION AND SEDIMENT CONTRA,FACILITIES. MEASURES SUCH AS GRADIENT TERRACES,INTERCEPTOR DIKES,
ALL CROSmN AND SEDIMENT CONTROL rAr-nx 1ES AND DEVICES SMALL BE SVALES, LEVEL SPREADERS AND SEDIMENT BASINS.
NSPCCTED DAILY AND MMEDDATELY MAINTAINED,7 NECESSARY, 2.THE SEED BED SMALL BE FIRM WITH FAIRLY FINE SURFACE,
1.ALL EROSION AND SEDIMENT CONTROL FACILITIES AND DEVICES SHALL BE LEFT IN FO LOVING SURFACE ROUGHENING.PERFORM ALL OPERATIOPIS ACCROs
LACE UNTIL THE UPSL13PE AREAS HAVE DUN PERMANENTLY STABILIZED. OR PERPENDICULAR TO THE SLOPE.
3. SEEDING RECOMMENDATIONS, AS SHOWN INOJOW, AND SHOULD BE
MPORARY EROSION CONTROL NOTES( APPLIED AT THE RATE OF 120 POUNDS PER ACRL
4. SEED BEDS PLANTED BETWEEN MAY 1 AND OCTOBER 31 WILL
OR ALL AREAS WHICH NAVE BEEN STRIPPED OF VEGETATION OR EXPERIENCED LAND REQUIRE IRRIGATION AND OTHER MAINTENANCE AS NECESSARY TO
1STURBING ACTOv1T1ES, AND WHERE NO FURTHER WORK IS ANTICIPATED FOR A FOSTER AND PROTECT THE ROOT STRUCTURE
R:OD EXCEEDING M LISTED CRITERIA BELOW, ALL DISTURBED AREAS MUST BE 5. SEED KOS PLANTED BETWEEN NOVEMBER L AND APRIL 30,
MMEDIATELY STABILIZED WITH MULCHING, GRASS PLANTMG OR OTHER APPROVED ARMORING ff THE SEED BCD WILL BE NECESSARY, (e.g.,
ROSION CONTRA. TREATMENT APPLICABLE TO THE TIME OF YEAR. GRASS SEEDING GEOTEXTILEs, JUTE NAT, CLEAR PLASTIC COVERING).
NE WILL ONLY BE ACCEPTABLE DURING THE MONTHS 13F APRIL THROUGH 6.FERTILIZERS ARE TO BE USED ACCORDING TO SUPPLIERS'
EPTEMBER. HOWEVER, SEEDING MAY PROCEED WHENEVER IT IS M THE INTEREST OF RECOMMENDATIONS. AMOUNTS SHOL➢ BE MINIMIZED,ESPECIALLY
OWNER/CONTRACTOR, BUT MUST ALSO BE AUGMENTED WITH MULCHING, NETTING ADJACENT TO WATER BODIES AND WETLANDS.
OTHER APPROVED TREATMENT.
USE THE FAlOVING RECOMMENDED SEED MIXTURE FOR EROsM
RY SEASON (MAY 1 THRU SEPTEMBER 30) — THE CLEARING OF LAND, INCLUDING THE CONTROL, OR A C13JNTY APPROVED ALTERNATE SEED MIXTURE.
MOVAL OF EXISTING vrmTATON OR OTHER GROR.D COVER, MUST BE LIMITED TO
Y AS MUCH LAND AS CAN RECEIVE APPROPRIATE PROTECTIVE COVER OR BE PROPORTIONS PURITY GERPINA
THERVISE STABILIZED, AFTER HAVING TEEN CLEARED OR OTHERWISE DISTURBED NAME BY WEIGHT(%) (%) (X>
Y NO LATER THAN SEPTEMBER 30 OF A GIVEN YEAR. UNLESS IMMEDIATE
TAKLJzATIDR Is SPECIFIED M THE EROSION AND SEDIMENT CONTROL PLAN, ALL RCDTOP (AGROSTIS ALBA) LO 92 90
AS CLEARED OR OTHERWISE DISTURBED MUST BE APPROPRIATELY STABILIZED ANNUAL RYE (LOLIUM MU..T7FLIRUM) 40 98 90
MwOuGH THE USE OF MULCHING, N£TT7NG, PLASTIC SHEETING,MS04 BLANKETS, CHEWING FESuE 40 97 80
WEE DRAINING MATERIAL, ETC., BY SEPTEMBER 30 OR SOONER PER THE APPROVED (FESTUCA RUBRA COMMUTATA)
N TV ACTION. UNLESS OTHERVISE APPROVED BY THE COUNTY, SEEDMG, (JAMESTOVN, BANNER, SHADOW, kOkET)
R1ILIZINNG AND MULCHING OF CLEARED OR OTHERWISE DISTURBED AREAS SHALL BE WHITE DUTCH CLOVER SO % 90
RFORNED DURING THE FOLLOWING PERIODS)MARCH 1 TO MAY 15, AND AUGUST 15 TO (TRIFOLIUM REPENS)
TIMBER L SEEDING AFTER OCTOBER 1 WILL BE DONE WHEN PHYSICAL COMPLETION
THE PROJECT IS IMMINENT AND THE ENVIRO(HTAL CONDITIONS ARE C04D-JC" MULCHING
El SATISFACTORY GROWTH IN INC EVENT THAT PERANINT sTABILIZATION IS NOT
SS11LE, AN ALTERNATIVE METHOD OF GROUND COVER, SUCH AS MULCHING, NETTD4G,L MATERIALS USED FOR MULCHING ARE RECE0004DED TO BE WOOD
STIC SHEETING, ER13SMN BLANKETS, ETC., MUST BE INSTALLED BY N13 LATER THAN FIBER CELLULOSE, AND SHOULD BE APPLIED AT A RATE OF 1C00
TEMBER 30. POUNDS PER ACRE
2. MULCH SHOULD BE APPLIED IN ALL AREAS WITH EXPOSED SLOPES
HE T EVENT THAT CONSTRUCTION ACTIVITIES OR OTHER SITE DEv[LOPNdNT GREATER -HAW 211 (MEIRIZONTAL-VERTICAL),
CTIVITICS ARE DISCONTINUED FOR AT LEAST 4 CONSECUTIVE DAYS THE 3. MULCHING SHOULD BE USED IMMEDIATELY AFTER SEEDING OR IN
WNER/CONTRACTOR SHAD_ BE RESPONSIBLE FOR THE INSPECTION& ALL EROSION AREAS WHICH CANNOT BE SEEDED BECAUSE OF THE SEASON, ALL
NO SEDIMENT CONTROL FACILITIES IMMEDIATELY AFTER STORM EVENTS, AND AT AREAS REQUIRING MULCH SMALL BE COVERED BY NOVEMBER 1.
ST ONCE EVERY WEEK. THE OWNER/ CONTRACTOR SHALL BE RESPONSIBLE FOR
HE MAINTENANCE AND REPAIR IIF ALL EROSION AN SEDIMENT CONTROL FACILITIES. TOPSCHLING
T SEASON (OCTOBER 1 THRU APRIL 30) —ON SITES WHERE UNINNTERUPTED L TDeSOA SHOULD BE USfD FQR 'Hli PROJECT puE TO MI:,ILr
ONSTRUCTION ACTIVITY IS IN PROGRESS, THE CLEARING OF LAND, INCLUDING THE DENSE AL SOD SOILS.
NOVAL OF EXISTING VEGETATION AND OTHER GRAND COVER, SHALL BE LIMITED ON SLOPES 40T EXCEEDING 2 PLACED L
2, TOPSOIL SHOULD BEE
AS MUCH LAND AREA AS CAN BE COVERED OR STABILIZED WITHIN 24 HOJRS IN 3, STRIPPING AND STOCKPILINGPLACED
ON-SITE SONS SMALL ONLY BE
EVENT A MAJOR STORM IS PREDICTED AND/ OF EROSION AND SEDIMENT PERMITTED II TOPSOIL IS FRIABLE AND LOAMY (LOAM, SANDY LOAM,
RAHSPORT OFF-SITE IS OBSERVED. SILT LOAM, SANDY CLAY LOAM, CLAY LOAM),
LL CLEARED OR DISTURBED AREAS SHALL RECEIVE APPROPRIATE PROTECTIVE 4, STRIPPING SHALL BE CONFINED TO THE IMMEDIATE CONSTRJCTMN
OVER OR BE OTHERWISE STABILIZED, SJCH AS MULCHING, NETTING, PLASTIC OVER A FAIR TO SIX INCH STRIPPING DEPTH IS COMMON, BUT
DEPTHHEETING, EROSION BLANKETS, FREE DRAINING MATERIAL,ETC,. WITHIN 5 DAYS AFTER SURFACE MAY VARY ONTR13 S OF THE PARTICULAR SOP.ALL
AVING BEEN CLEARED OR OTHERWISE DISTURBED I'' NOT BEING ACTIVELY WORKER SURFACE RUNOFF LONTR[L STRUCTURES SHIAIl IE IN PUCE BEFORE
ILT FENCING, SEDI-ENT TRAPS, SEDIMENT PONDS,LTC„ WILL NOT K VIEWED AS STRIPPING.
DEQUATE COVER IN AND OF THEMSELVES, IN THE EVENT THAT ANY LAND AREA NOT
NG ACTIVELY WORKED REH(AMS UNPROTECTED ON MS NOT BEEN APPROPRIATELY
TABLVED 5 DAYS AFTER HAVING BEEN CLEWED,ALL CONSTRUCTION ACTIVITY ON
HE SITE,EXCEPT FOR APPROVED EROSION AND SEDIMENT CONTROL ACTIVITY, SMALL
IMMEDIATELY CEASE UNTIL SUCH A TIME AS A►ORE ENTIC ED LAND AREA PAS BEEN
PPROPRIATELY PRCIMCTED OR STABILIZED.
STQCI:BLj MANV~
SrECKOPE SMALL K STARLRCD(VSM PLASTIC CRVCeING ON UnCR APPRRVEt KVK;O DAILY WTVRLN)OvEMKR I ANB MARCH
3L
I:N ANY SDASON,SEDIMENT LFA[HNO FROM STOCK PILLS Wu3T K PREVENTED.
1 TOPSOIL SMALL MIFT BE PLACED WHILE IN A FROZCN OR MUDDY CONDITION, WHEN THE SUBGRADE IS CxCESSIVELY WET,0R WHEN
COTQr BINS rXIST THAT WAY OTHERWISE K IBITRIMWAL TO PRIIOER GRADI4G OF PROPOSED SOOtING OR SQDI4G.
4.PREVIOUSLY ESTABLInED GRAMS a THE AREAS TO K TOPSOLEt SMALL K M.AINT"t ACCORDING TO THE APPROVED PLANS.
STABILIZED CMSTRLCTMK ENTRANCE
L MATERIAL SHALL BE 4 INCH TO 8 INCH QUARRY SPALLS (4 TO 6 INCH IM RESIDENTIAL SINGLE FAMILY LOTS) AND WAY BE
TOP-DRESSED WITH 1 INCH TO 3 INCH ROCK (STATE STANDARD SPECIFICATIONS, SECTION 8-150
2. THE ROCK PAO SHALL BE AT LEAST 12 INCHES THICK AND 50 FEET LONG (20 FEET FOR SITES WITH LESS THAN 1 ACRE OF
DISTURBED SOIL), WIDTH SMALL E'C FULL WIDTH OF THE VEHICLE INGRESS AND EGRESS AREA, SMALLER PADS MAY BE APPROVED
FOR SINGLE-FAMILY RESIDENTIAL AND SMALL COMMERCIAL SITES.
3.ADDITIONAL ROCK SHALL BE ADDED PERIOEICALLY TO MAINTAIN PROPER FUNCTION or THE PAD,
4,IF THE PAD DOZES NOT ADEGJATELY REMOVE THE NUD FROM THE VEHICLE WHEELS, THE WHEELS SMALL BE HOSED OFF BEFORE
THE VEHICLE ENTERS A PAVED STREET. THE WASHING SHALL DE DONE ON AN AREA COVERED WITH CRUSHED ROCK AND WASH
WATER SHALL DRAIN TO A SEVD+CNT RETENTION FACILITY OR T17R000H A SILT FENCE.
ILT FENCE
GEOTCXTILE FILTER FABRIC TAPE SHALL BE PER SPECIFIED IN THE 'STURMWATER MANAGEMENT 4AN-41.
THE PUGET SOUND BASIN,' OR APPLICABLE COUNTY STANDARDS
GEOTEXTILE FILTER FABRIC SHALL BE PURCHASED IN A CONTINUOUS R0.L CUT TO THE LENGTH OF
H BARRIER TO AVOID JSE OF JOINTS.7 JOINTS ARE NECESSARY, FILTER FABRIC SHALL BE SPLICED
ETHER ONLY AT A SUPPORT POST WITH A MINIMUM 6-INCH OVERLAP AND SECURELY FASTENED AT
OTH ENDS TO THE POST.
. STANDARD FILTER IABRIC SMALL BE FASTbED USING 1' STAPLES OR TIE WIRES <HOG RINGS) B 4 IN
PALM.
POSTS SMALL BE SPAM AND PLACED AT DEPTHS INDICATED M THE DETAILS ON THIS SHEET, AND
RIVEN SECURELY INTO THE GROUND,
. WIRE MESH SHALL It 2'X2'X14 GAUGE OR EQUIVIENT. THE WIRE MESH MAY BE ELIMINATED IF
XIRA-STRE4:,TH FILTER FABRIC 010471LANENT), AND CLOSER POST SPACING IS USED.
A TRENCH SHALL BE EXCAVATED AccOW014(,TO THE DETAILS ON THIS S'FW ALONG THE LINE OF THE
OSTS AND J+SLONE rROM THE SILT FENCE
Z, SILT FEN::ES SHALL BC LOCATED DOHNSLEK FROM THE ('LEAW:N(,LIMITS OF THE PROJECT,
GEo 2021 - O0C)L_)l
Mason County Review Checklist
for a Geotechnical Report
Instructions:
This checklist is intended to assist Staff in the review of a Geotechnical Report. The Geotechnical Report is reviewed
for completeness with respect to the Resource Ordinance. If an item is found to be not applicable, the Report should
explain the basis for the conclusion. The Report is also reviewed for clarity and consistency. If the drawings,
discussion, or recommendations are not understandable, they should be clarified. If they do not appear internally
consistent or consistent with the application or observations on site, this needs to be corrected or explained. If
resolution is not achieved with the author, staff should refer the case to the Planning Manager or Director.
Applicant's Name: �'t���� 11r
Permit#: ��-��01-1— 0033� Parcel 3 223� '31��� 1 � U
Date(s) of the Document(s) reviewed: 3 _ ( `(
1. (a) A discussi n of general geologic conditions in the vicinity of the proposed development,
OK? Comment:
(b) A discussionof specific soil types
OK? ��// Comment:
(c) A discussio of ground water conditions
OK? V Comment:
(d) A discussionjf the upslope geomorphology
OK? Comment:
(e) A discussio of the location of upland waterbodies and wetlands
OK? Comment:
(f) A discussion�of history of landslide activity in the vicinity, as available in the referenced maps and records
OK? ! ��// Comment:
2. A site plan at identifies the important development and geologic features.
OK? �J Comment:
3. Locations d logs of exploratory holes or probes.
U. Comment:
4. The area f the proposed development, the boundaries of the hazard, and associated buffers and setbacks shall
be deline ted (top, both sides, and toe) on a geologic map of the site.
OK? Comment:
5. A minimum of one cross section at a scale which adequately depicts the subsurface profile, and which
incorporat the details of proposed grade changes.
OK? Comment:
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 c effients should be a value of 0.15.
OK? V Co ment:
7. (a) Appropri restrictions on placement of drainage features
OK? Comment:
(b) Appropriat restrictions on placement of septic drain fields
OK? Comment:
(c) Appropriat restrictions on placement of compacted fills and footings.
OK? Comment:
Page 1 of 2 Form Effective June 2008
1
(d) Recomm nded buffers from the landslide hazard areas shoreline bluffs and the tops of other slopes.
OK? Comment:
(e) Recom nded setbacks from the landslide hazard areas shoreline bluffs and the tops of other slopes.
OK? Comment:
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.
OK? Comment:
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 onstruction methods.
OK? Comment:
10. An anal is of both on-site and off-site impacts of the proposed development.
OK? Comment:
11. Specifications of final development conditions such as, vegetative management, drainage, erosion control, and
buffer widths.
OK? Comment:
12. Recomrryendations for the preparation of structural mitigation or details of other proposed mitigation.
U. ✓ Comment:
13. A site m p drawn to scale showing the property boundaries, scale, north arrow, and the location and nature of
existing nd proposed development on thesite.
OK? Comment: .�ltC iLA
-J
M T Are the Documents signed and stamped? 1I3 t By whom? �G �}1r L k}��
License#: H3 0L4( License type:
FIRST REVIEW ❑ Approved ❑ Need more info.
If not approved, what is the next action/recommendation for further action?
Reviewed by , on . Time spent in review:
SECOND REVIEW/ UPDATE ❑ Approved ❑ Need more info.
Reviewed by , on . Time spent in second review:
THIRD REVIEW/ UPDATE ❑ Approved ❑ Need more info.
Reviewed by , on . Time spent in third review:
Disclaimer: Mason County does not certify the quality of the work done in this Geotechnical Report.
Page 2 of 2 Form Effective June 2008