HomeMy WebLinkAboutGEO2022-00030 - GEO Geological Review - 4/18/2021 -�.L � o2Z-0t)0 9
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RECEIVED
MAR 282022
Geotechnical Report 615 W. Alder Street
Griffin Single Family Residence
161 N Colony Surf Drive, Lilliwaup
Parcel No. 32309-14-00030 - OOb'1 )
Mason County, Washington
April 18, 2021
Project#2139
Prepared For:
Bryan Griffin
10650 NE 9th Place, Unit 1227
Bellevue, WA 98004
Prepared By:
Envirotech Engineering
PO Box 984
Belfair, Washington 98528
Phone: 360-275-9374
SX ;
4/18/2021
MASON COUNTY
COMMUNITY SERVICES Geotechnical Report
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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 Bryan Griffin Parcel# 32309-14-00030
Site Address 161 N Colony Surf Drive
(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 40
(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) 15
(d) Recommended buffers from the landslide hazard areas shoreline bluffs and the tops of other slopes.
Located on page(s) 18
(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) 18
(12) Recommendations for the preparation of structural mitigation or details of other proposed mitigation.
Located on page(s) 19
(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
t tY nr- Report,dated April 18,2021 and entitled Griffin Single
'
Family Residence, meets all the requirements of the Mason
z
County Resource Ordinance,Geologically Hazardous Areas
Section, is complete and true,that the assessment
demonstrates conclusively that the risks posed by the landslide
s, Al k r hazard can be mitigated through the included geotechnical
4/18/2021 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 2of2
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............................................................................................................................................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.....................................................................................................11
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...........................................15
5.2.3 Retaining Wall Backfill.............................................................................................................16
5.2.4 Wet Weather Considerations....................................................................................................16
5.2.5 Building Pads............................................................................................................................16
5.3 BUILDING AND FOOTING SETBACKS.................................................................................................17
5.4 SURFACE AND SUBSURFACE DRAINAGE...........................................................................................17
5.5 VEGETATION BUFFER AND CONSIDERATIONS.................................................................................18
5.6 TEMPORARY AND PERMANENT EROSION CONTROL.......................................................................18
5.7 SEPTIC DRAINFIELDS........................................................................................................................18
5.8 STRUCTURAL MITIGATION...............................................................................................................19
6.0 CLOSURE.............................................................................................................................................20
Appendix A-Site Plan
Appendix B -Soil Information
Appendix C-Slope Stability
Appendix D—Erosion Control
Appendix E—Drainage Details
1.0 INTRODUCTION
Envirotech Engineering (Envirotech) has completed a geotechnical investigation for a planned
single family residence located at 161 N Colony Surf Drive, identified as parcel number 32309-
14-00030, 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 February 10,
2021. 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 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 1-or 2-story single family residence,new
on-site septic system, and other ancillary features typical of this type of development.
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
Envirotech Engineering Geotechnical Report
PO Box 984 page 1 Parcel 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
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 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.
Project
}
}
Vicinity Map from Mason County Website
Envirotech Engineering Geotechnical Report
PO Box 984 page 2 Parcel 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
2.0 SURFACE CONDITIONS
Information pertaining to the existing surface conditions for the project was gathered on February
10, 2021 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 is vacant. 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. The maximum critical slope is approximately 71% with a vertical relief of
about 40 feet.
Critical ascending slopes, with grades exceeding 40% appear to be within 300 feet of the planned
development. The maximum critical slope is approximately 70% with a vertical relief of about
120 feet.
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 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
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.
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.
N
A
Aerial Photo from Mason County Website
Envirotech Engineering Geotechnical Report
PO Box 984 page 4 Parcel 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
3.0 SUBSURFACE INVESTIGATION
Information on subsurface conditions pertaining to the project was primarily gathered on
February 10, 2021 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 3 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 48 inches, and very
dense soils from 48 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 "Interactive Geologic Map" by the Washington Department of Natural Resources classifies
the Project as glacial drift,Qgic. General captions are as follows:
Envirotech Engineering Geotechnical Report
PO Box 984 page 5 Parcel 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
Geologic Unit Symbol;Qgic
Geologic Unit Age:Pleistocene
Geologic Unit Name:Vashon ice-contact deposits
Unfit Oescription:Diamiclon,cobbty pebble gravel,silty sandy till,silty pebble gravel,and pebbly sue,with minor send and silt;yellow-tan to
gray,loose to very dense:clasts subangular to subrounded;variously sorted:massive to well stratified,accompanied by stagnant-ice features,
such as kettles,hummocky topography,eskers(separately mapped as unit age where distinct),and subglacial orSubaenal outwash channels.
Unit Qglc ranges in thickness from a few to tens of feet and is mapped over a large part of the fluted upland surface on both sides of Hood
Canal and against the Olympic Mountains below a break in slope at approximately 1250 ft elevation.Where lacking more recognizable
stagnant-ice features,unit tic is commonly a triable:but compact,sungladai melt-out till that appears permeable Typically distinguished
from lodgment till by its apparent roughness in lidar shaded-relief and its association with other stagnant-ice features.It crudely corresponds
with areas mapped by Haugerud(2009b)as a rippled;fluted glaciated surface(his unit gfr)on the Kitsap Peninsula.Unit Qgic ties directly on
top of alter material or basalt and may include more oxidized,locally derived deposits.It rarely is found on recognizable Fraser-age advance
glacial deposits,and in this quadrangle does not appear to have a Vashon-age lodgment tiff beneath as found on Bainbridge Island(Maugerud.
2005).Though it can be found in fluted drumlins(indicating subglacial emplacement)as a diamict,it lacks subtorizonlat foliation,is permeable,
and is less competent than a'typical`subglacial lodgment till,it may be related to tilts found by Laprade(2003)in the Seattle area See
additional discussion in Contreras and others(2012a:b):
3 Project
24k Surface Geology n;
Pleistocene continental glacial drift
200 m
600 ft
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
Envirotech Engineering Geotechnical Report
PO Box 984 page 6 Parcel 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
locations. Soils for this project were primarily described utilizing the Unified Soil Classification
System(USCS)and the Soil Conservation Service(SCS)descriptions.
Within test pit locations, soils within the upper 3 feet of natural ground were generally observed
to be moist,brown silty sand with gravel (SM). Soils below the upper 3 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.
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, Hf, with 30% - 45% slopes. The soil designations are depicted in the aerial photograph
below, and descriptions are provided in Appendix B of this report.
A
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 150 feet directly below the property at the building pad location. Surface
seepage or 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 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
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 `Unstable' 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:
Project
Geofogic Hazard Layers
t S#a a StaWtttp•`JOE Coastai Zone Alas
A ' Unstable-rcceM 54ide
: : hT
Map from Mason County Website
Envirotech Engineering Geotechnical Report
PO Box 984 page 8 Parcel 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
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:
Project
„ _� $ails-Hydrlc Sails
x.s.
Soils-highly u t*soils
Soils-Hlghly Erax ible Sails
E
W#stside Siape Stabitiry Model{EPj
moderate siege instatiltty
Hi<o Ssop--lr iltfy
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 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 3 feet soil depth
Soil unit weight: 132 pcf
Angle of internal friction: 30 degrees
Cohesion: 200 psf
Envirotech Engineering Geotechnical Report
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Ph. 360-275-9374 April 18,2021
Soils below 3 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 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, 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 Hood Canal Fault Zone, which is approximately 0.5 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.
Envirotech Engineering Geotechnical Report
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Belfair,Washington 98528 Mason County,Washington
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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
Envirotech Engineering Geotechnical Report
PO Box 984 page 11 Parcel 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
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 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
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
Recommendations provided in this section account for the site development of a typical one- or
two-story, single family residential structure. 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 structure can be established on
shallow, continuous or isolated 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 15 inches shall be placed at a minimum of 18 inches below the existing
ground surface atop unyielding soils. For a columnar load of no more than 3 tons, a
circular or square isolated foundation diameter or width shall be at least 24 inches.
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 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
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
Interior slabs, if utilized, should be supported on a minimum of 4 inches of compacted
coarse, granular material (Retained on U.S. Sieve #10 or greater) that is placed over
undisturbed, competent native subgrade or engineered fill per the Earthwork
Recommendations Section below.
The recommendations for interior concrete slabs-on-grade as presented herein are only
relevant for the geotechnical application of this project. Although beyond the scope of
this report, concrete slabs should also be designed for structural integrity and
environmental reliability. This includes vapor barriers or moisture control for mitigating
excessive moisture in the building.
5.2 Earthwork Construction Recommendations
Founding material for building 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.
Envirotech Engineering Geotechnical Report
PO Box 984 page 14 Parcel 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
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.
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.
FOOTING
COMPACTED
NATIVE SOILS'
OR ENGINEERED 1
FILL I
Trt1 11YTSTtED SU
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
Envirotech Engineering Geotechnical Report
PO Box 984 page 15 Parcel 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
and fill slopes shall be limited to a slope of 2:1, unless otherwise approved by an
engineer.
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 lh 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. 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 consisting of built-up fill, if utilized, shall be constructed per the fill
placement and compaction recommendations as presented above. Built-up fill shall be
limited to no more than 4 feet in height. Both engineered fill and native soils may be used
for building pads. Building pad slopes shall be no steeper than 2:1 for both compacted
engineered fill and re-compacted native soils used as fill. Building pad fill shall be
"keyed" into the existing subgrade to a depth of at least 2 feet below the existing ground
surface. The term "keyed," as used here, implies that the interface between the building
pad and subgrade is horizontally level.Alternatively,building pads may be keyed into the
subgrade to the above specified depth, and stepped. Stepped fill should be keyed into the
subgrade at a minimum width of 10 feet. All footings shall be located at least 5 feet away
from the top of the engineered fill slope.
Envirotech Engineering Geotechnical Report
PO Box 984 page 16 Parcel 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
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 30 feet footing
setback from the face of the nearby descending slopes exceeding 40%. See the figure below and
the Site Plan in Appendix A for an illustration of the setbacks.
STRUCTURE
TOP OF
SLOPE SLOPE
tACE
SETBACK --- 1 FOOTING
From the illustration above, structures may be located closer to the top of slope by extending the
foundation deep enough to maintain the recommended setback. In addition, the required setback
may be reduced by mitigation,and subsequently would require additional geotechnical studies.
The minor critical slopes next to the roadway may be modified with a driveway, and retained
with walls or daylight basement walls. If modified, excess fills or cuts with relation to the home
should be reviewed by Envirotech.
5.4 Surface and Subsurface Drainage
Positive drainage should be provided in the final design for all planned residential buildings.
Drainage shall include sloping the ground surface, driveways and sidewalks away from the
project structures. All constructed surface and subsurface drains should be adequately maintained
during the life of the structure. If drainage problems occur during or after construction, additional
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,
and that roof downspout dispersion on splash blocks are employed. Recommended drainage
details are provided in Appendix E of this report.
Envirotech Engineering Geotechnical Report
PO Box 984 page 17 Parcel 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
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 or within
a distance of 10 feet beyond the top of the slope. 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. See the Site Plan in Appendix A of this report for a depiction of
the vegetation buffer.
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 Drannfields
Septic drainfields were considered in our geotechnical evaluation.This includes septic drainfields
with relation to the observed soil conditions, expected vegetation removal, and existing and
proposed topography. Based on the aforesaid parameters, the septic drainfields are not expected
to adversely influence critical slopes with some restrictions. This is also based on compliance
with all recommendations in this report.
This includes maintaining geotechnical setbacks as presented in this report. We recommend
extending lateral lengths as much as possible to spread the effluent,and utilize at least 8 doses per
day to minimize impacts to the slope.
Envirotech Engineering Geotechnical Report
PO Box 984 page 18 Parcel 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
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 19 Parcel 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
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 20 Parcel 32309-14-00030
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 18,2021
APPENDIX A
SITE PLAN
SCRLLE' 1 INCH = 150 FEET
0�5- 15C
APPROXIMATE TOP OF CRITICAL
SLOPE EXCEEDING 40%
B
FTE TILE OF PRTEPlfALLY
'��/,�✓/ /UNSTAI!<.E Sl.'OPE
A f ,r,N FT Ct14RTRUICTIT i RET'Rd&K FROM TOE
,� / OF CRIT]CAl 3LOfA•:
/
MINO R CRITICAL
-! SLOPES V/ LOV
.x 6 RELIEF
PERTY LINE
30 FT CONSTRUCTION SETBACK FROM TOP
TRI 3F CRITICAL
jI /APPROXIMATE TOE OF CRITICAL SLOPE
BUIL g f EXCEEDING 40Z
AREA r ,
.T
10 FT VEGETATION REIgVAI:----- " A
BUFFER FROM TOP Or CRITICAL - aS f p1
SLOPE /\ /
APPROXIMATE TOP OF CRITICAL
SLOPE EXCEEDING 4011 {. Tf O's°f0 I.MATI�b
FIrTF SINGLE FAHILY RESIEEI1.j,.E
I r z-ls% I iYg a T s Wm Fm`T I sr AAAL "TALrI
IIek�YI:TFT A ALTFId TivF$MY AE UTR,M—x N TRII: GEOTE4:P MIC6L REPORT
4ECTEZAILE`etl.r ;T.
EIIXG1BJW WrRA WIT r10 F BY M I Uri I AND X&%fF1T10 G i N CCX It+Y SURF DRIVE
CONTGaFRB MERE EXTRAPIIt,i7FA FROM A EXPLTC ED 5IAlRGE.AMD PARCEL Oe'309--14—O0030
INCORPORATED FIELD RfEA9�.REM€NTS AS EXPLAINED IN THE GEIIIECMNRAL LEGEND N \F 1T9
REPORT
8. Bot+NDARIES VERY NCr PREPARED 3Y A L% SURVEYOR,LOCATIONSTEMPORARY FMINEERr
IS STB FEATURES THE ARE SHOVN NFRE,SUCH 0 AT TOP OF&LOPES,TCE +-J--{-aO57OIN GUMIRIi. EN i 9C EFItSiNEERIMD
OF SLOOPES,WATER FEATURES, ETC.,. WITH RELAMN T PROPERTYO THE PROPERTY
LINES MUST BE VERIFIED BY THE OYNER RECCIMMSNDATIONO IN THE ---- - SLmw TNWCATOR RELFA 9.VASWNG7GH 4a7 Y
GXUTE:CWILAL REPIBiT PRUYClk SErBACK5,ThA IRS,Ik'I?''110 ErE Vr H 36[1-r-'J3Y4
RELATION TO GEELOCiIC FEA URES,NOT PROPERTY LINES S THESE 4EDLOGIE ,-==' EIILSTIMI LONTIBJR
FEAP s MAY B LOCATED 014 THE SUB.3ECT PROPERTY GR H=RING TPI8 TEST ITT I SITE PLAN
APPENDIX B
SOIL INFORMATION
� . . . .
II
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. . . . . . . . . . . . +i.
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§ 2a .
TEST PIT LOG
TEST PIT NUMBER TP-1
PROJECT:Griffin Geotechnical Report DATE OF LOG: 2/10/2021
PROJECT NO: 2139 LOGGED BY: RJM
CLIENT: Bryan Griffin EXCAVATOR: N/A
LOCATION: 161 N Colony Surf Drive DRILL RIG: None
Mason County,Washington ELEVATION: N/A
INITIAL DEPTH OF WATER: N/A FINAL DEPTH OF WATER: N/A
SOIL STRATA, STANDARD PENETRATKSN TEST
DEPTH SAMPLERS USCS DESCRIPTION LL P1 CURVE
AND TEST DATA DEPTH N 10 30 50
Q. F ..4 ..--._1111 ..1.1..1...1................
SM Brown,moist SILTY SAND with gravel,
medium dense.Gravel is well-graded
and subrounded.Sand is medium and
coarse.Non plastic
-2
Light brown,low moisture,very dense
g „ 'hardpan
Excavation terminated at approximately 3
feet
4
5
e
7
9
10
No Groundwater Encountered ENVIROTECH ENGINEERING
This inama<rorr peta+ns only to ttrs bohng acrd shoelki-rot be Geotechnical Engineering
inteip eted as being rt*ctt a of the entire sFe.
Map Unit Oaa r lion Hoodsportgravelly sandy loam.30 to 45 percent slopes--Mason
County,Washington
Mason County,Washington
Ht—Hoodsport gravelly sandy loam,30 to 45 percent slopes
Map Unit Setting
National map unit symbol. 2hkz
Elevation: 0 to 920 tee!
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 transacts of
the mapunit.
Description of Hoodsport
Setting
Landform.'Till plains.
Parent material:Basal till
Typical profile
HI-0105 inches: gravelly medial sandy loam
112-5 to 24 inches: very gravelly medial sandy loam
113-24 to 60 inches: gravelly sandy loam
Properties and qualities
Slope:30 to 45 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:Noire
Frequency of ponding_None
Available water capacity.Very low(about 4.6 inches)
interpretive groups
Land capability classIfication(irrigated): None specified
Land capability classification(noni igated): 8e
Hydrologic Soil Group: BID
Hydric soul rating. No
Data Source Information
Sod Survey Area: Mason County,Washington
Survey Area Data: Version 16,Jun 4,2020
t M Natural Resources Web Soil Survey 4!170A21
Conservation Service National Cooperative Soil Surrey Page I of 1
Map Unit Description Alderwood gravelly sandy loam,15 to 30 percent slopes--Mason
County,wash- ton
Forage suitability group: Limited Depth Soils(GO02XS301 WA),
Limited Depth Soils(GO02XF303WA).Limited Depth Soils
(GO02XN302WA)
Hydre soil rating: No
Minor Components
Everett
Percent of map unit: 5 percent
Landform: Karnes,eskers,moraines
Landform position(two-dimensional): Backsiope
Landform position(three-dimensional): Side slope
Down-slope shape: Convex
Across-slope shape: Convex
Hydric soil rating: No
Indianola
Percent of map unit: 5 percent
Landform: Eskers,kames.terraces
Landform position(three-dimensional): Tread
Down-slope shape: Linear
Across-slope shape: Linear
lydnc soil rating: No
Shalcar
Percent of map unit: 3 percent
Landform: Depressions
Landform position(three-dimensional): Dip
Down-slope shape: Concave
Across-slope shape; Concave
Hydnc soil rating Yes
Norma
Percent of map unit 2 percent
Landform: Depressions,drainageyvays
Landform position(three-dimensional): Dip
Down-slope shape: Concave,linear
Across-slope shape: Concave
Hydric soil rating: Yes
Data Source Information
Soil Survey Area: Mason County,Washington
Survey Area Data: Version 14.Sep 10.2018
t5 Naturar Reswxcee Web Sat Survey 12/10O018
Conservator Service National Cooperative Soil Survey Page 2 of 2
rile ONgtnal and First Copy with WATER WELL REPORT Appheetion No. .,... _. ......„.
1 x�epy
7Nrd Copy—Drnter's Copy STATE OF WAl IG )N fAsrattt xo..... _ ..
(1) OWNER N. h +S t{�+rl r.... ladrar. �t +� /5p'at ► +.y.�J'c ��$�,..
(2) LOCATION OF WELL
a
Beans uut_dfstaeror from aecgon or subdivlston corner
(3) PROPOSED USE: Domeaie fYtndustriei ❑ Muwetpai❑ (19) WELLS LOG:
Irrigation t7 That Well ❑ Other ❑ Formation; xnb.by color,ehorocter,sae of macerl.0 aid tt:ticare.cod
N 017i4%,thkwarnmoofasuu�tke sod iedtbe bled and note a a1 toe o g toeore
' (4) TYPE OF WORK: Owners number of welt e*trV Jog eaeb ril4050 of 7ormtoo
t!f mores than one1,.... .,.�,•-.�<...,,............... s[ATlAIAL � FROM t'O
New wen ffi Method:Dui O Bored lJ
Deepe"d ❑ gable I< DA"n Q .Ld_ .LIL.
Recondtuonad❑ BataryCl Jetted !t^o�a y#°
O (9) DIMENSIONS: Dtamveerpf west _ l�GJt75r2�f3ltgG�7CL4+►i 1�
QDriuta_ II'1/ ....st. Depth or teo,ptetad wn l tad• `� _.__. __TPA *ni ��R 'i' "t o
two (6) CONSTRUCTION DETA1t,S: /r
C rn.m.f:dm .m Zn.'.vx. --
o Threaded❑ Dram_fratt ........n,to.. _. n _. .:.__., _-
Wefded
t>a Periorationa: Yee❑ xa,(C
Type of perforator Used....,_..........,._....< .,.. ...... . ,.._.W.»__.
a. SIZE of pertorapm»,._.:.._..,..._.,,..:......In.by_._.,._...._...,...«,,in.
r .,......._ .._perforations from_.,,,_......._......ft.to „.... ft.
_...._,..«__,.perforatiOM from,...,...._... ft.to.. ..... ft. ......--..�..
perforaaene from......_... n.to.._..M.._..._...ft.
Sereema Y»❑ xo k .
Q M.nuLetttrm'a Natht,...........,...........»...._....._.. „_......_._,......
Type,........ ... .__,_..._-Model No_._..._..^....
41 Dram..._,._._.._Slot sloe.. ...._.Dam_____.-.ft.to..__,.._.._.ft.
'� Gravel packed: Yea❑ Nol,�. Star M gaaft:....__...____..._
Oravoi piaeed tram ..... h..to. __...........ft.
Surface seal: Ym)� No❑ To ghat d t LL,.. tt.
...........
Did soy suet& contain unuaeble wstert Yaa I1 No _
Type of watery......._..__...__.__....,.Daptb of Nsaf►-..—..__._..,._
z Method of aeafnt chat. __..<,. _ ._. __..
N (7) PUMP: eranufacturar'a xarru.,,......._. .._._.______.._.Y.., «._
type'
(8) WATER LEVELS �,d'u'rmsaa&Cea s»wti°i
Stalk bed l .. .ft below top of welt Data. .. - ..
,,,,, Arteetan preoure.....................lb..per#dusre imtt Data .......
o Art hat,water is controlled by.. ..'
'o (Cap.pure,etc.) .r
(8S DrrwdowItn amount water level to
) WELL TESTS towered trotow atanr revel Work started.._�...e^_^.. iR.J.,it Completed ..!_,.�..A( IR.j_3
w Was a pump teat made? Yes❑ No Co'tt yq,by vdtomt ..........
Yield: PlJmin.with rl.drawaown otter hre. WELL DRILLERS STATEMENT:
This well was drifted under my jurisdiction and this report Is
true to the best of my knowledge and belief.
Recovery data (umd ts{ten as hero wince
pump ail olD iwMMr level
tlf meaaaced from writ tnp to water hvelt
Time Water Least l Time water f.teet Tlms wooer fwvat Nom$-.-.•.. Fe-an, l tY l.! .....<.S.r'" ...._.....
fPeseon.6rfn or torporattonY or prtat)
............_....�_ » ..._.. __... .._._. _.. Afld ... � tfof v Lft�
d ...R...._........ _., .....,
v.t.dr.wdom.Rdr_ ».
Bstier test . WJtRat.trap.e4-. La. ...`.,.... ,&wan ISrtliteY
ArtMan flow...._.._.__-... _..._. ._&Aso. DaN.._.__.__...._.._ »._......._. 'f-
try �
Temperature of water._..._Was►chemical analysts msdat to.Cj Na, Lceaae No,.......: ........Daft,...../,..._ ....,......„...,,
APPENDIX C
SLOPE STABILITY
1 . 00
1 10
1 _ 201
1. . 30
11 . 40
1 _ 50
x . 1 . 60
1 . 70
1 . 80
90
2 . 0O
r� x
r. jet Grffsn Repeart
DaLtafi1E; DynamicAnalysss
Ai- 1ys s _ 8i ahc V
% , 00
?yd2«<?y2d < « 1 . 10
± . 20
J- 30
140
. 1 . 50
?J2 }1 , 60
1 . 70
-1 . 80
L
\ �z
. .�
2=o) ct , Griffin R+p =t
Dtafi1 = S iic Pn. 1ySiZ
nly«ia = 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
e5 rT
DIRECTIEIN OF---•r DUSTINfa
WATEI FLUW JND SURFACE
ar
N.T.S.
2'x2' WOOD POST (TYP) GEOTEXTILE FABRIC
OR EQUIVALENT OR BETTER AND WIRE MESH
6 FT MAX, O.C.
EXISTI6
GROJND Ft CE
12* DEEP, 8' WE y rr
TRENCH FILLED WITH
3/4' TD 1 1/2" } es Fr
WASHED GRAVEL OR VEG T i' _ __
BOTTOM EXTENTS OF
GEOTEXTILE FABRIC SILT FENCE DETAI
N.T.S.
PROVIDE FULL WIDTH
3/4 IN TO 1 1/ .jNed INGRESS/EGRESS
CRUSHED GRAVEL
PLACED AT 6 IN
MINIMUM DEPTH
WELL-DRAINED
SOILS
0.02 IN/MIN F U E"aN
R=25 FT MIN
t
Access ROAD _
STABILIZED CONSTRUCTION ENTRANCE
N.T.S.
C,O.rml.INDTESU
JErtro Tti3E LOf
"X—M"THE T . E II"It7a �1 AML)71t 13&t T rlPW"i1B..J IA ��HO$a�t8
PIS "7G" 1MA71C11l 7l 1IRH.T flTU L.7F1Zt1ThQ.Itm STALL O ` #, i .0F
L IIwA *JI3E T GIW1 L FAEI.Ar XJCH Al NA In TEl.flTT Ll.
ALL ECM NBA SEINKE r 1SSCH•§HL FACIL17 1 APIB BEY)CEZ S HALL Z LEVEL IPA1ZII A9E
TI11TAILY A W a1 BATELT TAJWL Zr tllAR, tl.I.l[POW WITH FLY FINE SLBBFAL ,
ALL I3IX4 ATS1 �lT STL rAEO.I17E$4B*V B ILL Z LEFT 14 Pt SHR ACE PEIRFM ALL WtAlT1BT7
IIITIL THE LVSL OPE AREAS HAVE I mBE0B01LY BT 11.ZEZ OR TO THE SLOPE
i.WFAl 4TElJ.Al s aw"maim.AHm ULD Al
1VE$ AT THE RAHTE Or A1I
4. O EAcEIE ETWB1 MTY I AH01 4 Al WELL
lS.L T BI l HAVE SEEN CF VI T01 O7 L1 Al0IAl TTOK AM OTPIF,E O4WBZ Al TO
AcrrifTTiN WO FLRTTF TAm 22 40710 PATO TT7TI A HTOS[EA AI£B F0101 r THE TANIr ST
II EODXE TIE IatTTIID w ALL GEUT
p AR:m T Ala I 1LmIu DcvI I A M a. I.,
O TO THE T OF HEAR r : DamS J. ,a.E I TIC TREATi,
VILL OR..T TT A.GOSPTABEE ULROO4I SW BETOTHE OF A TfMGH &FER"T11SSFIRD IE IC Al LAlB A000ZOBS TI]
MAY tVER IT TB Ill'HE OATETEST or RE17014.ANTI OIULII Al OBMSSEI0,BSMLY
URORER1TO BUT MUST ALSO Al • aTED 41TH MOW NETT'1TI3 AD.f.TEEOOT TO VATER AOIDES NUtO Wsn.A
OTHTfz srnrL, TTDEMTT≥�FTf
THE FU.Lm tr . aEI 4q r. FOR EM
I SEASUN(NAY Tt4W SEPTER?'BER Al —THE CLEANING or LAMA.P4CLUSINS THE TONTRU..OR A COUNTY APPROVED ALTERNATE IEEB NITITTBE,
VAL OF F)rsl c VE(ETAIWOO OR OTHHER DRO.ACS COVER,*1ST HE LIMITED III
Y AS b(JCH LAND AS CAN RECEZVF APPRO'RI4TD PROTECTIVE 1TIVM OR Al PIL+URTit2E PLOITY MEOMTIC
WISE STATOLI7TB.AFTER HAVING BEEN Z'LEAfEB ER OTHERWISE DISTURBED. NAME 19 WEBGHTIXI (71) 1''1)
Y NO LATER THAN SEPTEMSEW 30 OF A GIVEN YEAR,U"I.ESS IMMtETO:ATE
AOILIZATICN IS$6'ECFIED IN DIE EROSION AHD SE000ENT CONI OL PLPAN,ALL RESTER MAGAIISTIS AL$A} ID 92 SO
REAS CLEARED OR OTHERWISE DISTURBED MUST BE APPROPRIATELY STABILIZED ANNUAL RYE(LIOLYUM I LTIF ERUM> 40 98 90
UGH THE USE OF MULCHING,NETTING,PLASTIC SHEETING,ERROSIN BLANKETS, CHEWING FESUE 40 97 80
REE DRAINING MATERIAL,ETC., BY SEPTEMBER 30 OR SOONER PER THE APPROVED (FESTUCA RUBRA(OMMUTATA>
AN OF ACTION.UNLESS OTHERWISE APPROVED BY THE COUNTY, SEEDING (JAMESTOWN, HAMMER. SHADOW,KOKET>
RSEIZING AND MULCHING Or CLEARED OR OTHERWISE DISTURBED AREAS SHALL BE WHITE DUTCH CLOVER 10 96 90
H£D DURING THE FOLLOWING PERIODS!MARCH 1 TO MAY 15, AND AUGUST 15 TO (TRIFOLIUM MEPENS>
TOBER L SEEDING AFTER OCTOBER 1 WILL BE DONE WHEN PHYSICAL COMPLETION
THE PROJECT IS D4MDMENT AND THE ENVIROMENTAL CONDITIONS ARE CONDUCIVE MULCHING
SATISFACTORY GROWTH IN THE EVENT THAT PERANENT STABILIZATION IS NOT
SIDLE,AN ALTERNATIVE METH13D OF GROUND COVER, SUCH AS MULCHING,NETTING,L MATERIALS USED FOR MULCHING ARE RECOMMENDED TO BE WOOD
ASTIC SHEETING, EROSION BLANKETS,ETC., MUST BE INSTALLED BY NO LATER THAN FIBER CELLILOSE,AND 510,1.11 BE APPLIED AT A RATE OF 1000
EPTEMBER 30. POUNDS PER ACRE.
2.4(LCH SH0.L,D BE APPLIES INN ALL AREAS WITH EXPOSED SLOPES
THE EVENT'GHAT E ZT1IR ACTIVUSDI OR OTHER BITE OREMEW THAN TAL
AK FOR AT LEAST 4 BARB.THE 3 NOE FT S9ERLS Al USE).1BHHBT.ISATELV AFTER SEE INE OR I1
SHALL Al POD01EIEE FIR THE D10- OF ALL IUI AREAS WZi1 CADET Al SEEDED EEAORE OF THE SEASON.ALL
1sJAT*B.FACILITIES OSEBIMELY AFTER STmmm Tom.Am AT AREAS IAl1HO YILOUI SMALL Al LOVFREB IT L
tI EVERY U8. OF ALL£1010110 AN T .FACILITIES.
=711BFR I THRO ANAL Al—ON SITES'DIERE
STISIZTIDE ACTIVITY 01 IN PEU,THE ELEMIMO Or LOOM THE I FOTH TTATY# F IXlE TO HI i Y
VELMIOR SHALL BE LWES
AS 050CM LAN AREA AS^ OR IT 6B `VI 1 a'97yorX B Knr3 m OR '181.1 BE
EVEWA 046.101*105.4 IS TED 001W f OR AM SEDIOSSOT P IDIITTE'B IF'1 ffi.T F*A*.E MI LO OOT(L.ORAL SAME!LOAM,
OFOWI'OFF-BITE IS OBSERVED SILT LOB'*ANHBY CLAY LOA11.LAY LOAPB,
4.B1W SHALL Al C S11 TO THE lE ISBETISETUBI
VEIP MAT OR AlBTAISLIT 9 7001.IETT A O BIN II m Illy"IR RII
REE E ,E S BASS T
5(1101 rEVE AFER 7B 1T4 6LLIT T son..
F 6A IIfJ°514, L
rX TTE son..ALL
T ARE XM rd=SMAL'BE IN PLA E
1 FENLTNG,SEDIMENT TRAPS,SEIRHUENT PISHDS,ETC., WILL NUT Al VIEWED AS
DEOUATE COVER IN AND 13F THEMSELVES.IN THE EVENT THAT ANY LAND AREA NOT
ING ACTIVELY WORKED REMAINS UNPROTECTED OR HAS NOT BEEN APPROPRIATELY
TABILIZED 5 DAYS AFTER HAVING BEEN CLEARED,ALL CONSTRUCTION ACTIVITY Od
SITE,EXCEPT FOR APPROVED EROSION AND SEDIMENT CONTROL ACTIVITY. SHALL
MIEDIATELY CEASE UNTIL SUCH A TOME AS AFOREMENTIONED LAND AREA HAS BEEN
PPROPRIATELY PROTECTED OR STABILIZED.
STTCKPLE MANAGEMENT
L STOCKPILE SMALL BE STAND,IZE0(WITH PLASTIC COVERING OR OTHER APPROVED DEVICE)DAILY BETWEEN NOVEMBER I AND MARCH
31,
2.IN ANY SEASON,SEDIMENT LEA RING FROM STOCK PILES MUST BE PREVENTED.
3.TOPSOIL SHNLL NOT BE PLACED WHILE IN A FR02O4 ON MUDDY CONDITION,WHEN THE SUBGRADE IS EXCESSIVELY WET,ON WHEN
CONDITIONS EXIST THAT MAY OTHERWISE HE STRIt mAL TO PROPER GRADING OF PR POSED SODDING OR 555104 2.
MRogV .'01IMLOD65 SR aw THE IEHO TO ME TORIONLED .L Al ENDTAR4D AI,I'IT*01 TO TIE 5.980165Ki
T MATERIAL SHAL1 BE 4 70114 10 5514TH SPILLS T4 TTT 4.P403H FM RESIDENTIAL*03651 FAMILY LENS 141 Y Al
TLTA- WITH I 11654 TTT t INCH (STATE ST °Arty SETTXIBO
t.THE HILL.7E AT LEAST Al L ICS 7HO�'%(tea L0141FEET L FEET �WITH LEO THAN I ACRE OF
LIYTUROED SOLI, WIDTH SHALL.BE F'LL WIDTH OF THE VEHICLE INGRESS AND EGRESS AREA.BMALI.ETH'PADS MAY 1E APPROVED
FOR SINGLE-FAMILY RESIDENTIAL AND SMALL COMMERCIAL SITES,
3.ADDITIONAL ROCK SHALL BE ADDED PERIODICALLY TO MAINTAIN PROPER FUNCTION OF THE PAD.
4,IF THE PAD DOES NOT AX(IUATELY REMOVE THE MUD FROM THE VEHICLE WHEELS, THE WHEELS SHALL BE HOSED OFF BEFORE
THE VEHICLE ENTERS A PAVED STREET.THE WASHING SHALL BE DONE ON AN AREA COVERED WITH CRUSHED ROCK AND WASH
WATER SMALL DRAIN TO A SEDIMENT RETENTION FACILITY OR TH2OC44 A SILT FENCE.
LI PSHD:E
FTANVARIT
TILE FILTER PARHIC TYPE:$HM,BE PER SPECIFIES 3$THE'STUDWAM MAMACEIIEIOS NARW L.
INd 6T 11*881 IfASIH7"OH ASW 1 E 015.84(5 STA PAHtIID
TILE FILTER FABRIC SHALL Al PIllEHASEIO IN A C US RRL CUT TO THE LEMITH OF
RIER TI]AVOID USE OF.RUNTS IF£10115 ARE H SSA*V,FLIER FABRI^,SHALL Al SPLICES
MY AT A SS T POST WITHH A MSHIIEDI 4-INCH OVETLAR WALE SECIALLY FASTENED AT
5 TO THE POST,
510141505.7 FILTER FABRIC SMALL BC BANTERED IRON)3 STAPLES OR TIE WIRES 04405 WIN.TE,T 8 4 IN
SHHA L TE WAE£D AND PLAIDED AT 3EPTHE lNLI1:ATED IN THHE.DETAILS 074 THIS SHEET;AND
scamELY INTO TICESH SHALL BE 2'X2`%14 GAUGE OR ELBUIVILENT,THE WIRE MESH NAY BE ELIMINATED ID'
XTRA-STRENGTH FILTER FABRIC (MONOF•RAMENT). AND CLOSER POST SPACING IS USED.
A TRENCH SHALL BE EXCAVATED ACCORDING TO THE DETAILS ON THIS SHEET ALONG THE LINE OF THE
TS AND UPSLOPE FROM THE SILT FENCOL
SILT FENCES SHALL HE LOCATED DIWNSLOPE FROM THE CLEARING LIMITS OF THE PROJECT,
APPENDIX D
DRAINAGE DETAILS
HOUSE
ROOF DOWNSPOUT
SERVES UP TO
700 SF OF ROOF
._. _
50 FT MIN
VEGETATED
FLOW PATH
DOWNSPOUT
EXTENSION
ROOF DOWNSPQUT AND SPLASH BLOCK DETAILS
N.T.S.
Ev�vi roter,h Evl,gI eerLvug, PLLC.
ceotechvcat &V"Vl rovLwtel�.taL r ratiwage t�adwa�
September 18,2021
Bryan Griffin
10650 9th Place NE,Unit 1227
Bellevue,Washington 98004
Reference: Geotechnical Report Addendum#1
161 N. Colony Surf Drive,Lilliwaup,Washington
Dear Mr. Griffin,
Envirotech Engineering, PLLC has completed this geotechnical report addendum for the referenced
project. It is planned to have a home on the referenced parcel 32309-14-00030,and the septic drainfield to
serve the development to be located on the neighboring parcel 32309-14-00070. The subject of this
addendum is to address the parcel with the planned septic system, and provide additional details for fill on
the property.
A site visit to the additional parcel was conducted by Envirotech on September 16, 2021 in order to
evaluate geological hazards, and identify the feasibility of constructing a septic system. The 2d parcel is
nearly identical,in general, to the one located at 161 N Colony Surf Drive(parent parcel) with relation to
slopes and geology. It is our opinion that septic installation may commence on the 2°d parcel. Based on
our slope stability analysis, the septic system construction should follow the guidelines in the
geotechnical report for setbacks and maintain vegetation buffers.
Without mitigation, fill material should be less than 4 feet in height, and located outside of the 30-foot
setback for buildings as presented in the geotechnical report. Fills used to support structures are to be
placed and compacted per Section 5.2.5 of the report. Any fill (structural or yard) may exceed 4 feet in
height and/or encroach the setback,but not the vegetation buffer,if the fill is benched into the underlying
cemented hardpan in a manner presented in Section 5.2.5. This requires removal of the upper few feet of
soils,and creating a level bench in the hardpan prior to filling and compacting.
Thank you for the opportunity to work on this project. If you have any questions or need any further
assistance,please contact Michael Staten at 360-275-9374.
Sincerely,
Envirotech Engineering
cLYo
xr�a5Tt, C
9/18/21
Michael Staten,P.E.
Project Director
PD gox984
4f r, wastltwgtovS528
Off: 30-275934
Cell.: 3&O-ro8y-(O45
ewv%rotech@geotechwical�w fo.covu,