HomeMy WebLinkAboutGEO2021-00073 BLD2025-00122 SFR - BLD Engineering / Geo-tech Reports - 7/1/2021 00673
PLANNING
Geological Assessment
Allen Single Family Residential Property
XXX E Williams Road, Allyn
Parcel No. 12229-24-00010
Mason County, Washington
October 26, 2020
Project#20182
Prepared For:
Tiffani Allen
Prepared By:
Envirotech Engineering
PO Box 984
Belfair, Washington 98528
Phone: 360-275-9374
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10/26/2020
MASON COUNTY )hmitttai ;~` f�Ckiist
COMMUNITY SERVICES Geological Assessment
E"wV%Manning.Emmonmentai Heaitn,Community Heafth
NOW
Instructions:
This checklist must be submitted with a Geological Assessment and completed, signed, and stamped by the licensed
professional(s)who prepared the Geological Assessment 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.
ApplicanvOwner Tiff ant Allen Parcel# 12229-24 00010
Site Address XXX E Williams Ave
(1) A discussion of the geologic conditions in the general vicinity of the proposed development,with geologic unit
designation based on referenced maps.
Located on page(s) 5
(2) (a) A discussion of ground water conditions,
Located on page(s) 6
(b) A discussion of the estimated depth to water,
Located on page(s) 6
(c) A discussion of the quantity of surface seepage,
Located on page(s) 6
(d) A discussion of the upslope geomorphology,
Located on page(s) 3
(e) A discussion of location of upland waterbodies and wetlands
Located on page(s) 3
(3) The approximate depth to hard or dense,competent soil,e.g.glacial till or outwash sand.
Located on page(s) 5
(4) A discussion of any geomorphic expression of past slope instability(presence of hummocky ground
or ground cracks,terraced topography indicative of landslide block movement, bowed or arched trees
indicating downslope movement,etc)
Located on page(s) 4
(5) A discussion of the history of landslide activity in the vicinity, as available in the referenced maps and
records.
Located on page(s) 7
(6) An opinion on whether the proposed development is within the landslide hazard area or its associated buffer or
setback and the potential for landslide activity at the site in light of the proposed development.
Located on pages) 7
(7) A recommendation by the preparer whether a Geotechnical Report should be required to further evaluate site
conditions and the proposed development of the subject property.
Located on page(s) 12
(8) If the presence of a hazard is located within 300 feet of the proposed development,then the following are
delineated on a geologic map/site map:
(a) The area of proposed development,
Located on map(s) n/a
(b) The boundaries of the landslide hazard area(top,both sides,and toe).
Located on map(s) n/a
(c) The associated buffers(top,both sides,and toe),
Located on map(s) n/a
(d) Building or other setbacks(top,both sides,and toe).
Located on map(s) nia
(8) 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 (Appendix A)
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 Geological Assessment
dated ___October 26,2020 , and entitled Allen Single Family Residential Property , 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 hazard can be mitigated
through the included geotechnical design recommendations,and that all hazards are mitigated in such a manner as
to prevent harm to property and public healtn and safety.
C O'Uf, 9
` 43"5
10/26/2'020
Disclaimer:Mason County does not certify the quality of
the work done in this Geological Assessment.
Page 2 of 2
TABLE OF CONTENTS
1.0 INTRODUCTION...»............................»...............»............................................................................. I
1.1 PROJECT INFORMATION............................................................................................ 1
1.2 PURPOSE OF L`VVFSTIGATION AND SCOPE OF WORK........................................................................
2.0 SURFACE CONDITIONS....................................................................................................................3
2.1 GENERAL OrsFRVATIONS......................................................................................... . 3
........................
2.2 TOPOGRAPHY... 3
2.2.1 Upslope Geomorphology...................................................... .............................................3
2.3 SURFACE DRAINAGE....................................................................................................................... 3
2.3.1 Upland Water Bodies.......................................................................................................... 3
2.4 SLOPE AND EROSION ORSFRVATIONS...............................................................................................4
3.0 SUBSURFACE INVESTIGATION...............................................................»............................
........S
3.1 FIELD METHODS,SAMPLING AND FIELD TESTING...........................................................................5
3.2 GEOLOGIC CONDITIONS............................................................................................................... S
3.3 SPECIFIC SURSURFACF CONDITIONS.................................................................................................6
3.3.1 Groundwater...........................................................................................................................:... 7
4.0 ENGINEERING CONCLUSIONS.....»............»..»...........................»..».».........................................8
4.1 LA.NDSLWE HAZARDS.........................................................................................................................8
4.1.1 landslides and Slope Stability Analysis...................................................................................10
4.1.2 Surface and.Subsurface Drainage...........................................................................................10
4.2 EROSION HAZARDS..................................................................................................................... .10
4.3 SEISMIC HAZARDS.............................................................................................................................11
4.4 OTHER CONSIDERATIONS.................................................................................................................11
5.0 CLOSURE..........................................................».................................................................................12
Appendix A-Site Plan
Appendix B-Soil Information
i "
1.0 INTRODUCTION
Envirotech Engineering, PLLC. (Envirotech) has completed this geological assessment for a
residential property located at XXX Williams Road, identified as parcel number 12229-244MIO
in Mason County, Washington. As presented herein, this assessment includes information
pertaining to the Project in this Introduction Section; observations of the property and
surrounding terrain in the Surface Conditions Section; field methods and soils descriptions in the
Subsurface Investigation Section; and, assessments for landslides, erosion, seismic hazards, and
other considerations in the Conclusions Section.
An initial geological/ geotechnical evaluation of the project was conducted by Envirotech on
October 10, 2020. It was determined that natural slopes between 15% and 40%n were present
within 300 feet of the project. Due to these slope grades, a geological assessment is required
pursuant to landslide hazard areas of the Mason County Resource Ordinance(MCRO).
During the evaluation and site visit by Envirotech, surface and subsurface conditions were
assessed in order to determine if further geotechnical studies are required. After completion of the
field work and applicable Project research,Envirotech prepared this geological assessment.
1.1 Project Information
Information pertaining to the project was provided by the proponent of the property, and
observations from a field visit by Envirotech.The proposed development is expected to consist of
a new single family residence, on-site septic system, and other ancillary features typical of this
type of development. Approximate site development with relation to existing site features are
illustrated in the Site Plan in Appendix A of this report.
1.2 Purpose of Investigation and Scope of Work
The purpose of this geological assessment was to evaluate the project in order to contirm that the
proposed development is outside of any landslide hazard area and its associated buffers and
setbacks as determined in the MCRO. The investigation included characterizing the general
project surface and subsurface conditions,and evaluating the suitability of the soils to support the
planned site development. In order to fulfill the purpose of investigation, the geological/
geotechnical program completed for the proposed improvements of the Project include:
• Review project information provided by the pmponent of the project;
• Conduct a site visit to document the site conditions that may influence the construction
and performance of the proposed improvements;
• Define general subsurface conditions of the site by observing soils within test pit
excavations, review well logs from existing wells near the Project, and evaluate
geological and hazard maps depicting the site geology for the vicinity of the project;
• Perform soils testing.such as visual classifications, to determine selected index properties
of the soils;
• Complete an engineering assessment supported by planned site alterations and the surface
and subsurface conditions that were identified by the field investigation, soil testing, and
applicable project research;and,
• Establish engineering conclusions based on findings and anticipated development.
Envirotech Engineering Geological Assessment
PO Box 984 page I Parcel 1 2229-24-000 1 0
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 October 26,2020
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Vicinity Map from Mason County Website
Envirotech Engineering Geological Assessment
PO Box 984 page 2 Parcel 12229-24-00010
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 October 26,2020
2.0 SURFACE CONDITIONS
Information pertaining to the existing surface conditions for the project was gathered on October
10, 2020 by a representative with Envirotech. During the site visit, site features were documented
that may influence construction or reveal potential geological hazards. This Surface Conditions
Section provides information on general observations, vegetation, topography, drainage and
slope/erosion conditions for the project and surrounding areas.
2.1 General Observations
The property is currently vacant land with few improvements and surrounded by residential
development. Vegetation on and near the property consists primarily of maples, hemlocks, 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 for an illustration of the general slope indicators with respect to the planned
development.
Descending slopes exceeding 15% are located on and beyond the property. Average slope grades
are approximately 10% with a vertical relief of approximately 20 feet.
2.2.1 Upslope Geomorphology
Ascending grades are generally located to the south of the planned development. This
slope is relatively minor within 300 feet of the Project, with no apparent slope grades of
at least 15%. The upland area of the property is situated on a hillside and crest.
Landforms are primarily of glacial origin with centuries of weathering overburden.
Additional geomorphology that is pertinent to both upslope and downslope areas are
provided in the Subsurface Investigation Section of this report_
2.3 Surface Drainage
The majority of the stormwater runoff originating upslope from the anticipated development is
expected to be minimal to moderate. Significant scour, erosion and sediment transport was not
apparent near the project.
2.3.1 Upland Water Bodies
There are no apparent water bodies or wetlands located upslope from the planned
development that would significantly influence the Project.
Envirotech Engineering Geological Assessment
PO Box 984 page 3 Parcel 12229-244M 10
Belfair,Washington 98528 Mason County, Washington
Ph. 360-275-9374 October 26,2020
•
2.4 Slope and Erosion Observations
The existing moderate slopes near the Project signal a potential landslide or erosion hazard area.
Some indicators that may suggest past slope movements include:
• Outwash of sedimcnts near the bottom of the slope,
• Fissures, tension cracks or naturally 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_
The above mentioned indicators, or other signs of significant mass wasting on the property or
within the general vicinity of the Project were not observed or discovered during research.
Indications of past landslides, current unstable slopes, deep-seated slope problems, or surficial
slope failures were not observed during the site visit.
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Aerial Photo from Mason County Website
Envirotech Engineering Geological Assessment
PO Box 984 page 4 Parcel 12229-24-00010
Belfair,Washington 98S28 Mason County,Washington
Ph. 360-275-9374 October 26,2020
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3.0 SUBSURFACE INVESTIGATION
Information on subsurface conditions pertaining to the project was gathered during research and a
site reconnaissance.The site visit was accomplished on October 10,2020 by a representative with
Envirotech. Specific information on field methods, sampling, field testing, subsurface conditions,
and results from soil testing are presented in this section of the report. Appendix B has pertinent
information on subsurface conditions for the Project,including test pit log(s)representative of the
site soils,and water well report(s)originating from the subject property and/or nearby properties.
3.1 Field Methods,Sampling and Field'Testing
Information on subsurface conditions for the Project was accomplished by probing anticipated
foundation areas with hand tools, and observing soils within test pit excavations and/ or earth
cuts. Information on subsurface conditions also included reviewing geological maps within the
Project vicinity, and water well reports originating from nearby properties. No soil samples were
collected for this Project. Envirotech measured the relative density of the in-situ soils by gauging
the resistance of hand tools.
12 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, Qx. 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 Vaughn 7.5-minute Quadrangle, Pierce and Mason Counties,
Washington'by Robert L.Logan and Timothy J.Walsh,December 2007,provides the following
caption(s)for the project area:
Envirotech Engineering Geological Assessment
PO Box 984 page 5 Parcel 12229-24-00010
Belfair,Washington 98529 Mason County,Washington
Ph. 360-275-9374 October 26.2020
Vashon till—Unsorted,uriaratified(but locally banded)mix of clay.silt.
sand,and gravel. typically supported by a sandy matrix.mostly gray but
locally ranging to tan,light brown,or orange.typically unweathered.
lodgment till compact.with well-developed facies resembling concrete.
but near die surface commionly hackly and(or)looser and covered by 1 to
6 ft of loose ablation till:deposited directly by glacial ice and commonly
includes clasts or clumps plucked Coin underlying units.Clasts are
commonly striated and faceted.with angular or rounded edges. Boulders
are ge ncially sparse within the till but large(erratic)boulders of plutonic
or metamorphic rock are common on till surfaces. Some exposures include
interbands and lenses of sand and gravel.locally with shears and joints.
Till forms a locally patchy and seemingly randomly distributed cover up to
a several tens of feet thick.with a thickness of t to 20 ft most common. It
typically dominates.but is also locally discontinuous on. fluted surfaces.
with individual dnuulius measuring 0.1 to 0.3 nni wide by 0.8 to 1.3 mi
long and the long axis aligned with the direction of ice flow.Till typically
is in sllatp. wwouf6rinable contact with underlying toms.most commonly
advance outwash(uuut Qga and subunit). Unit Qgt lies stratigraphically
below unit Qgo. It may include unrecognized exposures of older till.a
map boundary mismatch between unit Qgt on this map and unit Qgo,.on
the Vaughn quadrangle to the south(Logan and Walsh.20071 may have
resulted from a map-production error in the northwest corner of the
�auglm map(Josh Logan.Wash.Divn.of Geology and Earth Resources.
oral corm a n.. 2009).
3.3 Specific Subsurface Conditions
The following subsurface conditions are estimated descriptions of the project subgrade utilizing
information from the depth of penetration at all testing, sampling, observed and investigated
locations. Soils for this project were described utilizing the Unified Soil Classification System
(USCS). Using the USCS in conjunction with estimated relative densities and other anticipated
engineering properties of the soil, susceptibility for potential landslides, erosion and seismic
hazards may be msessed.
The project is primarily composed of undisturbed, native soils, without indications of substantial
fill. Competent bearing soils were encountered at 12 inches below the existing native ground
surface in locations where the ground was probed. For engineering purposes, these native soils
consist of distinguishable layers,as presented below.
Soils within the upper 4 feet of natural ground were observed to be primarily moist, brown silty
sand with clay (SM). Soils were denser with depth. 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(SCS), the site soils are described as Sinclair shotty loam,
Envimtech Engineering Geological Assessment
PO Box 984 page 6 Parcel 12229-24-00010
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 (ktnber 26,2020
S,,, with 5% - 15% slopes. See the soil map below, and the applicable SCS soil profile(s) 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 rel"(s)and knowledge of the general area,permanent groundwater
is at least 50 feet below the current ground surface. Surface seepage or perched
groundwater at shallow depths was not observed on-site, nor indicated on the well
reports. However, some seasonal groundwater is expected to flow directly above the
hardpan on occasion.
Env►rotech Engineering Geological Assessment
PO Box 984 page 7 Parcel 12229-24-00010
Belfair,Washington 99529 Mason County.Washington
Ph. 360-275-9374 October 26,2020
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4.0 ENGINEERING CONCLUSIONS
The following sections present engineering assessments and conclusions concerning the project.
These conclusions have been [Wade available based on the planned construction activities as
outlined in the Introduction Section of this report; general observations of drainage and
topography as summarized in the Surface Conditions Section; and, soil conditions that were
identified by the field investigation and soils testing as outlined in the Subsurface Investigation
Section. Conclusions for the Project that is provided herein, includes pertinent information for
landslide,erosion and seismic hazards.
4.1 Landslide Hazards
For the planned development, as provided in the Introduction Section of this report, it is
F.nvirotech's opinion that the proposed development is not subjected to or cause adverse imparts
to a landslide hazard area or its associated buffer or setback as defined in the MCRO. This
conclusion is based on the contents provided in this report.
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. 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, excessive and/or repeated surficial slope
movements, if not repaired, may represent a threat to the structural integrity of the slope.
Maintenance of the slope should be completed if the situation does arise in order to prevent the
possibility of further surficial or deep seated glope movements that may tx: da►caging to life or
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. Stable
slopes are generally not prone to landslides due to small grades and accommodating geology.
Historically, intermediate terrains have no known landslides. A site specific analyses and
conclusions concerning the slopes are presented herein. A Stability Map from the Coastal Zone
Atlas for the general area of this Project may be found below.
Envirotech Engineering Geological Assessment
PO Box 984 page 8 Parcel 12229-24-00010
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 October 26.2020
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Map from Washington State Department of Ecology Website
According to the Department of Natural Resources (DNR) "LHZ—Final A-1 Map— Landslide
Inventory—Mason Watershed,by Sarikhan,et. al., May 2007,"previous landslide activity is not
recorded near the project. Per the Resource Map from DNR, the Project is not within terrain
labeled `highly unstable' or 'highly erodible' relating to soils. DNR labeled portions of this
project as medium to high slope instability with relation to slopes. This delineation is primarily
dependent upon slopes and convergence. Secondly, lithology and precipitation are modeled
within this delineation. In summary, this designation is based on mapping without field
observations or knowledge of the specific site geology or soils. A resource map from DNR is
provided below:
Envirotech Engineering Geological Assessment
PO Box 984 page 9 Parcel 12229-24-00010
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 October 26,2020
i
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Pr(lject
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/ ~ Soils-Hydoc Sods
Soils.Highly Unslablo Soils
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Westside Slops Sub111ry Model tl`pi
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Map from Washington State Department of Natural Resources Website
4.1.1 Landslides and Slope Stability Analysis
Past landslide activity or high slope instability indicators near the proposed development
was not revealed during the project research. In addition,detrimental landslide activity or
potential high landslide indicators were not observed during the site visit as outlined in
the Surface and Subsurface Conditions Sections of this report. Due to these factors, and
existing/proposed conditions,a slope stability analysis was not deemed necessary for this
project. Considering the planned construction as summarized in the Introduction Section
of this report; the aforementioned surface and subsurface conditions for the project; the
slope stability assessment provided herein; and the Engineering Conclusions provided
later in this report, it is our opinion that the project is not within a landslide hazard area,
and that the proposed site alterations will not encourage a landslide hazard.
4.1.2 Surface and Subsurface Drainage
This project does not appear to experience significant subsurface drainage or surface
runoff. It is our opinion that groundwater or surface drainage is not a limiting factor for
this Project.
4.2 Erosion Hazards
Based on the USCS description of the Project soils, the surface soils are considered moderately
erodible. According to the Resource Map from the Washington State DNR, 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
Envirotech Engineering Geological Assessment
PO Box 984 page 10 Parcel 12229-24-00010
Belfair,Washington 99Q9 Mason County.Washington
Ph. 360-275-9374 October 26.2020
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slopes 15% or greater (Ac and Ad), Cloquallum Silt Loam on slopes 15% or greater (Cd),
iHarstine Gravelly Sandy Loam on slopes 15% or greater (Hb), and Kitsap Silt Loam on slopes
15%or greater(Kc).
Temporary and/or permanent erosion control measures may be required for any site when land
disturbance is involved. 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 conditions and planned disturbance of this Project include wind-borne silts during dry
weather, and sediment transport during prolonged wet weather. Sediment transport of disturbed
soils could be from stormwater runoff or tracking off-site with construction equipment. Although
an engineered erosion control plan is not warranted for this project, Best Management Practices
(BMP's) should be employed during and after construction. Ordinary BMP's includes silt
fencing,protection of drainage outlets and vegetating denuded areas.
Erosion control information and specifications may be found in the applicable "Stormwater
Management Manual for Western Washington,"prepared by the Washington State Department of
Ecology Water Quality Program.
43 Seismic Hazards
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
0.509 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.
There are no known faults beneath this project. The nearest Class 'A' or'B' fault to this property
is the Tacoma Fault Zone. This fault is a Class 'B', and is located approximately .5 miles to the
south of the Project. This information is supported by the USGS Quaternary Fault and Fold
Database for the United States.
The potential for liquefaction and other earthquake induced hazards are believed to be low for
this project. This is based on subsurface conditions such as soil characteristics and the lack of a
permanent and substantial shallow water table. Subgrade characteristics that particularly
contribute to problems caused by seismic events include submerged and confined, poorly-graded
granular soils. Although gravel- and silt-sized soil particles could be problematic, fine and
medium grained sands are typically subjected to these types of seismic hazards.
4.4 Other Considerations
Conclusions in this report are based on the type and location of the anticipated development,and
existing on-site and off-site conditions. Site development that significantly deviates from the
anticipated improvements presented in this report, or nearby development that influences this
Project may require geotechnical design recommendations. If foundations are located on slopes
exceeding 15%, we recommend that the footing is extended to a depth of at least 2.5 feet below
the top of ground surface as measured from the downslope edge of the foundation.
Envirotech Engineering Geological Assessment
PO Box 984 page 11 Parcel 12229-24-00010
Belfair,Washington 98528 Mason County,Washington'
Ph. 360-275-9374 October 26.2020
II
5.0 CLOSURE
Based on the project information and site conditions as presented in this report, it is Envirotech's
opinion that additional geotechnical studies are not required to further evaluate this project.
Due to the inherent natural variations of the soil stratification and the nature of the geotechnical
subsurface exploration, there is always a possibility that soil conditions encountered during
construction are differcnt than thosc: dcwribcd ui this report. Thca-cfurc, it is tuuuttnendcd that
Envirotech is promptly notified if project and subsurface conditions found on-site are not as
presented in this report so that we can re-evaluate our recommendations.
This report presents a geological/geotechnical assessment, and is intended only for the owner, or
owners' representative. Furthermore, this report is only valid for the project information and
location described herein.
The services descrihed 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 Geological Assessment
PO Box 984 page 12 Parcel 12229-24-00010
Belfair,Washington 98528 Hasson County. Washington
Ph. 360-275-9374 October 26,2020
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APPENDIX A
SITE PLAN
I
SCA._- 1 INCH• LID FEET
OUTLI[V RUN_DARLC ,_•RV=RTl LX
AREA
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Po �!S
PROJECT/OWNERI LICATION
SINGLE FAM:_Y PROPERTY
GEOLOGICAL ASSESSMENT
ALLEN
N07E3. RXi E WILLIAMS RD
1 SLOPE INDICATORS WERE FIELI HEASIKD DT ENVIR07ECM,ANC/OR PARCEL 122P9-24-03C'.0
EXTRAPOLATED FROM A•IIKIC LIIAR SONICE WHERE APPWANIA-E, MASON
2.IWNDARIES ON THIS SIT[ PLAN WERE Pal PREPARED BY A LICENSED
SIIIVEYOR LOCATIONS OFSITE TEATURCS AND GEOLOGICAL/ SUBsk-WACE LEGEND ENCIN[Em
DESIGMATiOMS AS SHOWN HERE,WITH K 1)LATUN TO THE PERTT _IMES ENVIROTECH ENGINELRINC
MAT DE VERIFIED BY 'w 06**t THE CONCLUSIONS AND PO BOX 96A
RECbR(NDATIWS PROVIDED IN THE GECTECHNTCAL/GEOLOGICAL REPORT —'� fLORE INDICATOR BELFAIR, WASMINGTC%96529
OL
ARC BASED O1 GEOLOGIC AND
SPECIFIC SUISiAFACE FEATURES THAT MY
K LOCATED ON AND?� THE PRDKRTT.AND ARE NOT NECESSARILY P PROBE 3RA-2�S-9374
BASED OIF OF PNWRT•LINES SHOWN ON THIS SITE PLAN TPI t[ST PIT SITE PLAN
I ,
i
APPENDIX B
SOIL INFORMATION
I
TEST PIT LOG
TEST PIT NUMBER TP-1
PROJECT: SFR Geological Assessment DATE OF LOG: 10110/2020
PROJECT NO: 20182 LOGGED BY: MCS
CLIENT: Allen EXCAVATOR: N/A
LOCATION: Parcel 12229-24-00010 DRILL RIG: None
Mason County,Washington ELEVATION: NiA
INITIAL DEPTH OF WATER: N/A FINAL DEPTH OF WATER: N/A
SOIL 57RATA, STANDARD PEhETAArtptN TEST
DEPTH SAMPLERS USCS DESCRIPTION II PI CURVE
AND TEST DATA KPTH N t0 JO 50
0
t SM Brown,moor.medium dense SILTY
SAND with CLAY
t
2
3
4 Exawation terminated at app mwnai*
4 0 feet
5
6
7
B
8
10
No(;mn**aw Encountered ENVIROTECH ENGINEERING
rhv++bf�mbm 0*to on 6mv and**Lm nd ee Geotectrncel Engffwwm
.K«re�ee as bem wxk 6*an».I+b.9b
Map 11M t1.saPlian Se�doa shay bear,S b 15 pereod slope--�taaon(;only,
WaaMrx2tnn ,
Mason County, Washington
So—Sinclair shotty loam,5 to 15 percent slopes
Map Unit Sefting
Nattanal map unit svntbd 2tm7
Ekwatiorn 0 to AX)toet
Akron annual pre of,itabon 25 k)50 inches
AMran Minna/au tenyhwattnw 5n dogrpws F
Frost-free period 200 days
farmland cla=hcvtan Farmland of statewide itnoonan e
Map Unit Composition
Sinclair a cl sirndar sits 100 percent
Fstrnotes are Lased on observotrons.desc:riptioris and transacts of
the mainurilt
Description of Sinclair
Setting
:_andform TO plain
Typical profit
H1-010 11 rrtd*s. gravelly loarn
H2-It to 35 mxfts very gravely barn
H3-35 to 60 kichi S. gravelly sarxly kam
Properties and quaitUes
FAX* 51n 15 pArm"
rknplh to ranfmf P f"un; 28 to 42 Incr*s to denslC rmaterwi
Diamiaye aa" KWof ately wall drained
Caparity of the most Mrrntmp layer to transmit water(XsW) Very low
to Moderately low(0,00 to 0.06 irvhrl
Depth to writer t lik Atwitrt 18 to 30 niche;
f repuency of flooding None
Frequarncy of pcytding None
Available water capoctty Low(about 3,F inches)
h+terpretive groups
Land copobldy claesthcation(irrtgnted) None spectfieA
Land capability dassihcahon(noon rrgated) 4s
Hydrofuya%&W&cxv B
Forage cuitabdity group Lmnitod Cloth Sous jGW2XN302WA)
Ofliet vegetative daWcabon Limited Depth Sous
(0002XN.302WA)
Nvrfnc::al rating No
Data Source Information
Sod Stavey Area Mason County.Washington
Survey Area Data Version 16..)un 4,2020
V.� McAxe1 Reeovrr Wvb Sal Swvrc 142a2020
Canserwaoe SelVip WaOonal Cooperates Sod Survey page 1 of n
GEO 26zI - 6 Q o -13
Mason County Review Checklist
For a Geological Assessment
Instructions:
This checklist is intended to assist Staff in the review of a Geological Assessment. The Assessment 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 Assessment 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: L L f
Permit#: al_O Z0 21 — Q 14 L j Parcel#'s: 122 Z 9- '2,-) 0 00)U
Date(s)of the Document(s) reviewed: -I — 2��
1. A discussion of geologic conditions in the general vicinity of the proposed development, with geologic unit
designation bas on referenced maps.
OK? Comment:
2. (a) A discussio of the ground water conditions at the site,
OK? Comment:
(b) A discussi n of the estimated depth to water,
OK? Comment:
(c) A discussion of the quantity of surface seepage,
OK? Comment:
(d) A discussi n of the upslope geomorphology,
OK? Comment:
(e) A discus si n of location of upland waterbodies and wetlands.
OK? Comment.
3. The approximate depth to hard or dense competent soil, e.g. glacial till or outwash sand.
OK? ✓✓ Comment:
4. A discussion of any geomorphic expression of past slope instability (presence of hummocky ground or ground
cracks, terraced topography indicative of landslide block movement, bowed or arched trees indicating
downslope mo ement, etc.).
OK? Comment:
5. A discussiont the history of landslide activity in the vicinity, as available in the referenced maps and records.
OK? Comment.
& An opinion on whether the proposed development is within the landslide hazard area or its associated buffer or
setback and tpe potential for landslide activity at the site in light of the proposed development.
OK? 7 Comment:
7. A recommend abon by the preparer whether a Geotechnical Report should be required to further evaluate site
conditions and a proposed development of the subject property.
OK? Comment:
8. If the presence of a hazard is determined within 300 feet of the proposed development, then the following are
delineated on a geologic map/site map:
Page 1 of 2 Form Effective June 20
(a) the area of,the proposed development,
OK? Comment:
(b) the boun ries of the landslide hazard area(top, both sides, and toe),
OK? Comment:
(c) the associated buffers(top, both sides, and toe)
OK? Comment:
(d) building or other setbacks(top, both sides, and toe).
OK? Ai A Comment:
9. 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.
OK? S Comment:
Are the Documents signed and stamped? �5 By whom?
License A30 Y 5 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.
If not approved, what is the next action/recommendation for further action?
Reviewed by on . Time spent in second review:
THIRD REVIEW/UPDATE ❑ Approved ❑ Need more info.
If not approved, what is the next action/recommendation for further action?
Reviewed by on . Time spent in third review
Disclaimer. Mason County does not certify the quality of the work done in this Geological Assessment
Page 2 of 2 Form Effective June 2008