HomeMy WebLinkAboutGEO2023-00092 - GEO Geological Review - 7/28/2023 NNIN�
PI.A RECEIVED
NOV 2 8 2023
615 W. Alder Street
Geological Assessment
Knight Single Family Residential Property
140 NE Seitz Dr, Belfair
Parcel No. 12330-33-90029
Mason County, Washington
July 28, 2023
Project#23223
Prepared For:
Matthew & Brittany Knight
PO Box 4
Wauna, WA 98395
Prepared By:
Envirotech Engineering
PO Box 984
Belfair, Washington 98528
Phone: 360-275-9374
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07/28/2023
MASON COUNTY Submittal Checklist
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COMMUNITY SERVICES Geological Assessment
&uldutq,Glammmg,Envitontn.MA Health,Comnountty Hr-.tlth
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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.
Applicant/Owner Matthew&Brittany Knight Parcel# 12330-33-90029
Site Address 140 NE Seitz Dr
(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 page(s) 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) 10
(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) n/a
(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.
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 07/28/2023 ,and entitled Kniaht 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 health and safety.
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07/28/2023
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.................................................................................................................................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 Upland Water Bodies.................................................................................................................3
2A SLOPE AND EROSION OBSERVATIONS...............................................................................................4
3.0 SUBSURFACE INVESTIGATION....................................................................................................5
3.1 FIELD METHODS,SAMPLING AND FIELD TESTING...........................................................................5
3.2 GEOLOGIC CONDITIONS....................................................................................................................5
3.3 SPECIFIC SUBSURFACE CONDITIONS.................................................................................................5
3.3.1 Groundwater...............................................................................................................................6
4.0 ENGINEERING CONCLUSIONS......................................................................................................7
4.1 LANDSLIDE ITAZARDS.........................................................................................................................7
4.1.1 Landslides and Slope Stability Analysis.................................................................................... 8
4.1.2 Surface and Subsurface Drainage............................................................................................8
4.2 EROSION HAZARDS............................................................................................................................8
4.3 SEISMIC HAZARDS..............................................................................................................................9
4.4 OTHER CONSIDERATIONS..................................................................................................................9
5.0 CLOSURE.............................................................................................................................................10
Appendix A-Site Plan
Appendix B-Soil Information
1.0 INTRODUCTION
Envirotech Engineering, PLLC. (Envirotech) has completed this geological assessment for a
residential property located at 140 NE Seitz Dr, identified as parcel number 12330-33-90029 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 July
14,2023.It was determined that natural slopes between 15%and 40%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 confirm 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 proponent 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 1 Parcel 12330 33 90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28 2023
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Envirotech Engineering Geological Assessment
PO Box 994 page 2 Parcel 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
2.0 SURFACE CONDITIONS
Information pertaining to the existing surface conditions for the project was gathered on July 14,
2023 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 surrounded by residential
development. NE Seitz extends along the north side of the property. Vegetation on and near the
property has been mostly cleared with some remaining fir trees and other 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 26% with a vertical relief of approximately 35 feet. An isolated area of slopes
over 40%with a low vertical relief was observed at the base of the property due to a combination
of the neighbor's driveway cut and some fill.
2.2.1 Upslope Geomorphology
Ascending grades are generally located to the east 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 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
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 sediments 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.
rr
A
{
50 100 200 300
NINE now—
Aerial Photo from Mason County
Envirotech Engineering Geological Assessment
PO Box 984 page 4 Parcel 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
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 July 14, 2023 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.
3.2 Geologic Conditions
In general, soils at the project are composed of materials from glacial advances. The geologic
conditions as presented in the"Geologic Map of Washington,"compiled by J.Eric Schuster,2002
indicates Quaternary sediments, Qg. Quaternary sediments are generally unconsolidated deposits,
and dominantly deposited from glacial drift, including alluvium deposits. This project is located
within the Puget Lowland.Typically,"lower tertiary sedimentary rocks unconformably overlie the
Crescent Formation."as revealed in the Geologic Map.Initial sedimentary rocks were formed from
shales,sandstones and coal deposits from rivers.During the Quaternary period,the Puget Lowland
was covered by numerous ice sheets, with the most recent being the Fraser glacier with a peak of
approximately 14,000 years ago. Upon the glacial retreat, the landscape was formed by glacial
erosion glacial drift deposits.
The "Geologic Map of the Belfair 7.5-minute Quadrangle, Mason, Kitsap and Pierce Counties,
Washington" by Michael Polenz, Katelin Alldritt, Nicholas J. Heheman, Isablle Y. Sarikhan, and
Robert L.Logan,July 2009,provides the following caption(s)for the project area:
Qgic Sand,gravel,lodgment till,and flow till;minor silt and day beds;tan to gray;variably
sorted;loose to compact;massive to well stratified;locally includes over-steepened beds
that typically reflect sub-ice flow,but their dip may
Qgt Unsorted,urstratffied(but locally banded)mix of day,silt sand,and gravel;typically
supported by a sandy matrix;mostly gray but locally ranging to tan,light brown,or
orange;typically unweathered;lodgment tin compact
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
Envirotech Engineering Geological Assessment
PO Box 984 page 5 Parcel 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
engineering properties of the soil, susceptibility for potential landslides, erosion and seismic
hazards may be assessed.
The project is primarily composed of undisturbed, native soils, without indications of substantial
fill near the planned building area. Some fill was present away from the building area. 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 5 feet of natural ground were observed to be moist, brown silty sand with
gravel (SM). 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 Indianola loamy sand,Ic,with 15%
to 30% slopes, and Everett gravelly loamy sand, Ee, with 5% to 15% slopes. See the soil map
below,and the applicable SCS soil profile(s)in Appendix B of this report.
�4. «.
105 210 420 630
F
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 100 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.
Envirotech Engineering Geological Assessment
PO Box 984 page 6 Parcel 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
4.0 ENGINEERING CONCLUSIONS
The following sections present engineering assessments and conclusions concerning the project.
These conclusions have been made available based on the planned construction activities as
outlined in the Introduction Section of this report;general observations of drainage and topography
as summarized in the Surface Conditions Section; and soil conditions that were identified by the
field investigation and soils testing as outlined in the Subsurface Investigation Section.Conclusions
for the Project that is provided herein, includes pertinent information for landslide, erosion and
seismic hazards.
4.1 Landslide Hazards
For the planned development, as provided in the Introduction Section of this report, it is
Envirotech's opinion that the proposed development is not subjected to or cause adverse impacts
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 slope movements that may be damaging to life or property.
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 speck site geology or soils.A resource map from DNR is provided below:
Envirotech Engineering Geological Assessment
PO Box 984 page 7 Parcel 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
'N
A
1 Z
■ Mo(knate Slope Instability
. High Sbpe Instability
Highly Erodible Soils
I ® HydliC Sons
lip ® Highly Unstable Soils
Map from Washington State Department of Natural Resources
4.1.1 Landslides and Slope Stability Analysis
Past landslide activity or high slope instability indicators near the proposed development
were 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 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).
Envirotech Engineering Geological Assessment
PO Box 984 page 8 Parcel 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
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.
4.3 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
0.50g 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.
There are no known faults beneath this project. The nearest Class `A' or 'B' fault to this property
is the Tacoma fault.This fault is Class `B',and is located approximately 2 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.
Envirotech Engineering Geological Assessment
PO Box 984 page 9 Parcel 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
5.0 CLOSURE
Based on the project information and site conditions as presented in this report, it is Envirotech's
opinion that additional geotechnical studies are not required to further evaluate this project.
Due to the inherent natural variations of the soil stratification and the nature of the geotechnical
subsurface exploration, there is always a possibility that soil conditions encountered during
construction are different than those described in this report. Therefore, it is recommended that
Envirotech is promptly notified if project and subsurface conditions found on-site are not as
presented in this report so that we can re-evaluate our recommendations.
This report presents a geological/geotechnical assessment, and is intended only for the owner,or
owners' representative. Furthermore, this report is only valid for the project information and
location described herein.
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 Geological Assessment
PO Box 984 page 10 Parcel 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
APPENDIX A
SITE PLAN
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TEST PIT LOG
TEST PIT NUMBER TP-1
PROJECT: SFR Geological Assessment DATE OF LOG: 07/14/2023
PROJECT NO: 23223 LOGGED BY: MCS
CLIENT: Knight EXCAVATOR: N/A
LOCATION: Parcel 12330-33-90029 DRILL RIG: None
Mason County,Washington ELEVATION: N/A
INITIAL DEPTH OF WATER: N/A FINAL DEPTH OF WATER: N/A
SOIL STRATA, STANDARD PENETRATION TEST
DEPTH SAMPLERS USCS DESCRIPTION LL PI CURVE
AND TEST DATA DEPTH N 10 30 SO
0
SM Brown,moist,medium dense SILTY
SAND with GRAVEL.Gravel is fine and
subrounded.Sand is primarily coarse.
1 Non plastic.
2
3
4
5 Excavation terminated at approximately
5.0 feet
8
7
8
9
10
No Groundwater Encountered ENVIROTECH ENGINEERING
This intonation pertains only to this boring and should nor be Geotechnical Engineering
mtorpreted as being Odo&NP or the entre.aYo.
Map Unit Description:Indianola loamy sand.15 to 30 percent slopes—Mason County.
Washington
Mason County, Washington
lc—Indianola loamy sand,15 to 30 percent slopes
Map Unit Setting
National map unit symbol: 2t639
Elevation: 0 to 980 feet
Mean annual precipitation: 30 to 81 inches
Mean annual air temperature: 48 to 50 degrees F
Frost-free period: 170 to 210 days
Farmland classification., Farmland of statewide importance
Map Unit Composition
Indianola and similar soils: 85 percent
Minor components: 15 percent
Estimates are based on observations,descriptions.and transects of
the mapunit.
Description of Indianola
Setting
Landform: Eskers,kames,terraces
Landform position(two-dimensional): Backslope
Landform position(three-dimensional): Side slope
Down-slope shape: Linear
Across-slope shape: Linear
Parent material: Sandy glacial outwash
Typical profile
011-0 to 1 inches: slightly decomposed plant material
A-1 to 6 inches: loamy sand
Bwf-6 to 17 inches. loamy sand
Bw2-17 to 27 inches: sand
BC-27 to 37 inches: sand
C-37 to 60 inches: sand
Properties and qualities
Slope: 15 to 30 percent
Depth to restrictive feature: More than 80 inches
Natural drainage class: Somewhat excessively drained
Capacity of the most limiting layer to transmit water(Ksat): High to
very high(5,95 to 99.90 iNhr)
Depth to water table: More than 80 inches
Frequency of flooding: None
Frequency of ponding: None
Available water storage in profile: Low(about 3.9 inches)
Interpretive groups
Land capability classification(irrigated): 6e
Land capability classification(nonirrigated): 4e
Hydrologic Soil Group: A
i so,% Natural Resourees Web Soil Surrey M2rz019
Conservation Service National Cooperative Soil Survey PSP 1 d 2
Map Unit Descripliom Indianola loamy sand.15 to 30 percent slopes--Mason County.
Washington
Forage suitability group: Droughty Soils(G002XS401 WA),
Droughty Soils(0002XN402WA)
Hydric soil rating. No
Minor Components
Alderwood
Percent of map unit: 8 percent
Landform: Ridges,hills
Landform position(two-dimensional). Backslope
Landform position(three-dimensional): Side slope,nose slope,tali
Down-slope shape: Linear,convex
Across-slope shape: Convex
Hydric soil rating: No
Everett
Percent of map unit: 5 percent
Landform: Karnes,eskers,moraines
Landform position(two-dimensional): Backslope
Landform position(three-dimensional): Side slope
Down-slope shape: Convex
Across-slope shape: Convex
Hydric soil rating: No
Norma
Percent of map unit: 2 percent
Landform: Depressions,drainageways
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
i,i N Natural Resources Web Sal Survey OrM2019
-� Conservation Service National Cooperative Soa Survey Pegs 2 of 2
Map Unit Description:Everett gravelly loamy sand.5 to 15 percent slopes...Mason County.
Washington
Mason County,Washington
Ee—Everett gravelly loamy sand,5 to 15 percent slopes
Map Unit Setting
National map unit symbol: 2hk7
Elevation: 50 to 500 feet
Mean annual precipitation: 55 to 90 inches
Mean annual air temperature: 48 to 50 degrees F
Frost-free period: 160 to 180 days
Farmland classification: Prime farmland if irrigated
Map Unit Composition
Everett and similar soils:100 percent
Estimates are based on observations,descriptions,and transects of
the mapunit.
Description of Everett
Setting
Landform.Terraces
Parent material.Glacial outwash
Typical profile
HI-0 to 7 inches: gravelly ashy loamy sand
H2-7 to 21 inches. extremely gravelly sand
H3-21 to 60 inches. very gravelly sand
Properties and qualities
Slope:5 to 15 percent
Depth to restrictive feature:More than 80 inches
Drainage class.Somewhat excessively drained
Capacity of the most limiting layer to transmit water(Ksat).High to
very high(5.95 to 19.98 in/hr)
Depth to water table:More than 80 inches
Frequency of flooding:None
Frequency of ponding:None
Available water supply,0 to 60 inches: Very low(about 2.5 inches)
Interpretive groups
Land capability classification(irrigated): None specified
Land capability classification(nonirrigated): 4s
Hydrologic Soil Group: A
Ecological site: F002XA004WA-Puget Lowlands Forest
Forage suitability group: Droughty Soils(G002XN402WA)
Other vegetative classification: Droughty Soils(G002XN402WA)
tub Nab"Nd"Wase — Web Sod Surrey 3flFV Z3
i Cauarvad"- -, NatKWW Cooperative Sop Survey Pape 1 Of 2
Map Unit Description Everett gravelly loamy sand,5lo 15 percent slopes—.Mason County,
Wash"ton
Hyddc soil rating No
Data Source Information
Soil Survey Area: Mason County,Washington
Survey Area Data. Version 18,Sep 8,2022
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• IDf!AODyrIDMAL SKKM O NLCXMARY) 4
Geological Assessment
Knight Single Family Residential Property
140 NE Seitz Dr, Belfair
Parcel No. 12330-33-90029
Mason County, Washington
July 28, 2023
Project#23223
Prepared For:
Matthew & Brittany Knight
PO BoxWauna, FEP
Wauna, WA 98395Prepared By 8Envirotech Engineering —_J
PO Box 984
Belfair, Washington 98528
Phone: 360-275-9374
� CLYOe S
%t
s , /63Ui5 _
07/28/2023
I
® MASON COUNTY S!?hmittril f h =rkliSt
COMMUNITY SERVICES Geological Assessment
InatruMlons:
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.i6 for expensive soils or section 1608.7.1
of the International Building Code Section for Foundations on oradjecent to slopes.
Applicant/Owner Matthew 6 Brittany Knight Parcel If 12330-33-90029
Site Address 140 NE Seitz Or
(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 ups"geomorphology,
Located on page(s) 3
(a) A discussion of location of upland waterbodles and wellands.
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 page(s) 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) 10
(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 saes,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) n/a
(9) A site map drawn to scale showing the property bounden",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 07/28/2023 ,and entitled Knight 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 geolechnical design recommendations,and that all hazards are mitigated in such a manner as
to prevent harm to property and public health and safety.
F a r 1
pf FCWIT l w"
c,"1 07/28/2023
Disclaimer:Mason County does not ce"the quality of
the work done in this Geological Assessment.
Peg&2 of 1
TABLE OF CONTENTS
1.0 INTRODUCI'ION._._........._._............._....._.............__...................._._...................................1
1.1 PROJRCr INFOINtA77ON.................................................................................................................... 1
1.2 PuRPosa of DwEmGATION ANDSCOPE OF WORR........................................................................ 1
2.0 SURFACE CONDITIONS......_......._ ..„_„__,, ,,,,,,,,_,,,,,,,,_—3
2.1 GENERAL OBSERVATIONS..................................................................................................................3
2.2 TOp()GRAPFtV.....................................................................................................................................3
2.2.1 Upslope Geomorpholpay............................................................................................................3
23 SURFACEDRAINAGE..........................................................................................................................3
2.3.1 Upland Wider Bodies 3
.......................................................
2A SLom AND EROSION OnsmvATIONS...............................................................................................4
3.0 SUBSURFACE DrMTIGATION....._.._.._.... .....................„,.,,,„„_„_,-„_,_,,,._,..,,,,.._5
3.1 FIRLD METRODS�SAMPUNG AND FITLD TanING...........................................................................5
32 GEOLOGIC Common....................................................................................................................5
33 SPECIFIC SUBSURFACE CONDITIONS.................................................................................................5
3.3.1 Groundwater...............................................................................................................................6
4.0 ENGINEERING CONCLUSIONS_._._..............«._._..........._.._.... 7
4.1 LANDSLMEHAZARDS.........................................................................................................................7
4.1.1 Landslides and Slope Stability Andyala....................................................................................8
4.1.2 Surface and Subsurface DmbW.............................................................................................8
42 ERostON HAzARss...................................................................................................................................................................................................................................8
43 SEDc[LZa . 9
A OTHR CONSIDERA17ONS.......................................................................................... . 9
5.0 CLOSURE.............._..........
_.....-.............._.-.........................«....._........................._.».....-............10
Appendix A-Sile Plan
Appendix B-Soil Information
1.0 INTRODUCTION
Envirotech Engineering, PLLC. (Envirotech) has completed this geological assessment for a
residential property located at 140 NE Seitz Dr, identified as parcel number 12330-33-90029 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 July
14,2023.It was determined that natural slopes between 15%and 40%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 Envimtech,sufface 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,Envirmech 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 Envirmech.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 confirm 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 proponent 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 1 Parcel 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
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Envinnech Engineering Geological Assessment
PO Box 984 page 2 Parcel 12330-33-90029
Belfair,Washington 98528 Mason Comty,Washington
Ph. 360-275-9374 July 28,2023
2.0 SURFACE CONDITIONS
Information pertaining to the existing surface conditions for the project was gathered on July 14,
2023 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 surrounded by residential
development. NE Seitz extends along the north side of the property. Vegetation on and near the
property has been mostly cleared with some remaining fir trees and other 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 26% with a vertical relief of approximately 35 feet. An isolated area of slopes
over 40% with a low vertical relief was observed at the base of the property due to a combination
of the neighbor's driveway cut and some fill.
2.2.1 Upslope Geomorphology
Ascending grades are generally located to the east 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 downsiope areas are provided in the
Subsurface Investigation Section of this report.
2.3 Surface Drainage
The majority of the stonnwater 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 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
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 sediments 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.
f
so ioo rao aoo
F
Aerial Photo from Mason County
Envirotech Engineering Geological Assessment
PO Box 984 page 4 parcel 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
3.0 SUBSURFACE WMI7IGATION
Information on subsurface conditions pertaining to the project was gathered during research and a
site reconnaissance. The site visit was accomplished on July 14, 2023 by a representative with
Envirotil 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,SampBng 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.
3.2 Geologic Conditions
In general, soils at the project are composed of materials from glacial advances. The geologic
conditions as presented in the"Geologic Map of Washington,"compiled by J.Eric Schuster,2002
indicates Quaternary sediments, %. 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 unconfonnably overlie the
Crescent Formation."as revealed in the Creologic 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 Belfair 7.5-minute Quadrangle, Mason, Kitsap and Pierce Counties,
Washington' by Michael Polenz, Katelin Alldrift, Nicholas J. Hellman, Isablle Y. Sarikhan,and
Robert L. Logan,July 2009,provides the following caption(s) for the project area:
urit oawipnan
Q is Sand,gravel, lodgment till,and flow till; tumor silt and clay beds:tan to gray, variably
carted; loose to compact; massive to well stratified; locally includes over-steepened beds
that typically reflect woke flow,but their dip may
Qn unsorted,umtabfied(but locally banded)mix of clay,silt, and,and gavel;typically
suploortetl by a sandy matdx;mostly gray but locally ranging to tan,light brown,or
earge;typiraay unweathered;lodgment till compact
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
Envlmtech Engineering Geological Assessment
PO Box 984 page 5 Parcel 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
engineering properties of the soil, susceptibility for potential landslides, erosion and seismic
hazards may be assessed.
The project is primarily composed of undisturbed, native soils, without indications of substantial
fill near the planned building area.Some fill was present away from the building area. Competent
hearing 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 5 feet of natural ground were observed to be moist,brown silty sand with
gravel (SM). 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 Indianola loamy sand,Ic,with 15%
to 30% slopes, and Everett gravelly loamy sand, Ee, with 5% to 15% slopes. See the soil map
below,and the applicable SCS soil profile(s)in Appendix B of this report.
i
ios z+o azo szo
Fee
Soil Survey from USDA Natural Resources Conservation Service
3.3.1 Groundwater
From the water well report(s)and knowledge of the general area,permanent groundwater
is at least 100 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.
Envirotech Engineering Geological Assessment
PO Box 984 page 6 Parcel 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
4.0 ENGINEERING CONCLUSIONS
The following sections present engineering assessments and conclusions concerning the project.
These conclusions have been made available based on the planned construction activities as
outlined in the Introduction Section of this report;general observations of drainage and topography
as summarized in the Surface Conditions Section; and soil conditions that were identified by the
field investigation and soils testing as outlined in the Subsurface Investigation Section.Conclusions
for the Project that is provided herein, includes pertinent information for landslide, erosion and
seismic hazards.
4.1 Landslide Hazards
For the planned development, as provided in the Introduction Section of this report, it is
Envirotech's opinion that the proposed development is not subjected to or cause adverse impacts
to a landslide ha—rd 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 sail,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 farther
surficial or deep seated slope movements that may be damaging to life or property.
According to the Department of Natural Resources (DNR) "11-1Z - 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 7 Parcel 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
I Z
` ■ rh.Y.am sbee IngxNnry
■ HIM S Onteb "
■ ® HIII*EIWU.Solis
®
■ rvM m dis
p �t
r® HHIM U.W.E 11
Map from Washington State Deparonent of Natural Resources
4.1.1 Landslides and Slope Stability Analysis
Past landslide activity or high slope instability indicators near the proposed development
were not revealed during the project research.In addition,detrimental landslide activity M
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.
42 Erosion Hazards
Based on the USCS description of the Pmject 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 deemed 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).
Envirotech Engineering Geological Assessment
PO Box 984 page 8 Parcel 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 36M75-9374 July 28,2023
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 (BBC) soil profiles. According to the BBC, 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.
There are no known faults beneath this project.The nearest Class 'A' or 'B' fault to this property
is the Tacoma fault This fault is Class `B',and is located approximately 2 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.
4A 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.
Envirotech Engineering Geological Assessment
PO Box 984 page 9 Parcel 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
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, them is always a possibility that soil conditions encountered during
construction are different than those described in this report. Therefore, it is recommended that
Envirotech is promptly notified if project and subsurface conditions found on-site are not as
presented in this report so that we can re-evaluate our recommendations.
This report presents a geological/geotechnical assessment, and is intended only for the owner, or
owners' representative. Furthermore, this report is only valid for the project information and
location described herein.
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 Geological Assessment
PO Box 994 page 10 Parcel 12330-33-90029
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 July 28,2023
APPENDIX A
SITE PLAN
N
PROPERTY
+i LINE
s�
iy
C
L
CL
Cy 9t
PROPOSED \
r C BUILDING
AREA
eiy
rv�
o SINULEE FAMILY
Irian.
SINGMILY PROPERTY
cEn.pG1LAL ASSESSMENT
zNwr
T,o
: s >arz v
m.a ma»-smn
LEGENC [l[SCP
nwmaax eanMeeec
-i atPl Nc�'i 9 MF rM
� a�a.zn-air x�aw aevv
rnr rrt SITE CLAN
APPENDIX B
SOIL INFORMATION
TEST PIT LOG
TEST PIT NUMBER TP-1
PROJECT: SFR Geological Assessment DATE OF LOG: 0711 VM23
PROJECT NO: 23223 LOGGED BY: MCS
CLIENT: Knight EXCAVATOR: WA
LOCATION: Parcel 1233Q3MW29 DRILL RIG: None
Mason County,Washington ELEVATION: WA
INITIAL DEPTH OF WATER: WA FINAL DEPTH OF WATER: WA
MIL STRATA STAIDMDDEXE1RA1gHTE$i
DEPTH SAMPLERS USCS DESCRIPTION LL PI LURVE
PND TEST DATA DEPTH N 10 30 EO
0
SM BrowM1 mast,medium sense SILTY
SAND was GRAVEL Gmm�nl is fire aM
Non plastic
stic Send is Drlmenly muse.
� Non Dkafic.
2
J ji
A
S E.Yation remtlmleB as ,nxwrao*
sorest
e
7
e
a
10
No crwnewalert�coumcea ENVIROTECH ENGINEERING
mvnmmwro��enane onirro ins mmg aw aiam,wae Geolschni®I E,inssbg
niemarenazmno ame awem.
MV.abnYaT:bMI4Y aaa,sb.1ab30{Mtrki-Mau, .
sassi
Mason County,Washington
Ic-4ndianola loamy sand, 15 to 30 percent slopes
Map Unit Sallie,
National map unit symbol 2r839
Elevation: 0 to 980 feet
Mean annual preopdefion: W to 81 inches
Mean annual air IempmaNrs: 48 to W degrees F
Frost-hoe permd: 17010210 days
Farmland GassiAcalbn: Famlland of sNtawee importance
Map Unit Co npoaplon
Monson.and similar sal": 65 percent
Minor components: 15 percent
Estimates ere based on observotgns.de"cnpflora,and transacts of
the respond
Description of Indianola
Saturn,
Lardbrm: Eskers,Mamas,taneces
Landau.poet.(Iwodie.niot ial): Bekslopa
Lemaorm position(Mree-dimensionall: Side slope
Donn-vqx she, linear
Across-slope shape: Linear
Panel reasons. Sandy glaaal oulwash
Typleal proHla
Di-0 her 1 arches: Sligh,y decwnposed plant material
A-116 Mches: loamy sand
Bwf-6lo 17 inches: loamy send
Bw2.1I027inchas sand
BC-211031 inches: sand
C-37b60inahas: sand
PropMMs and yuali le s
Slope: 15 to 3o parcent
Depth to rastoca.feature: More then inches
Natural drainage class. $pMwhet axoassivay drained
Caption of the most kraals,layer to tevenut euder(Ksap: Hlghto
vary high(5 95 to 99.90 inm)
Depth M water table: More than 80 incbes
Ffaguenryaflooding.' Who
Frequam olpondirg: No.
Avaibbis water Morena in PrMrM: Low(about 3.9 imhoe)
Intl rpreavc groups
Landcapabdifyclassi(tan(in,tWend 6e
Lend eelvbl0ly GassdKetbn(rlmlrrlgafetlf 4a
Hydrdoglo Soil Group' A
`.vaf XebrM saww Mypyy gyyy fl1}/N18
i Caaxvra i 112
Mf Wi pwpba�kW W b^Y vtl,exist MYrl rMr♦•a—Morn CµNY.
NYW^YM
Faragesuilaslitygraup Droughty Sods(G002XSs01WA),
Droughty Soils(GrX12XWMA)
HyUfa sal is,, No
Minor Compnrleme
AlEerw000
Pementofmap unit Bpercent
toopeom: Rose,hills
LanCform poshpn(Aro-Cimansapay Backsk,m
Laneherm pos i n(three4imensonel): Side slope nose slope,tall
Does,slope shape: Linear.convex
Across-slope shape' Convex
Hytlrlc soil reho, No
EvereH
Percent mromp ems 5 percent
Lerxllorm: Kames.eskers,moraines
LeM/mnposi(lon(Modimensionel): Beckebpe
LaMrwmpostionphreaoismoponap: Side slope
Down-s iee shape: Convex
Across-sbpeshape. Convex
Hydricsoilmlag: No
Norm
Pemenl of map uNl: 2 Portent
Landtmm.' Depressions,Cramagevrays
Lampe—poser(fhme-Oimensanall: Dlp
Dawn-since space: concave,linear
Across-sage shape: Concave
Hydorseilralirg Yes
Data Source Information
Sal Survey Area: Mason Counly,Washington
Survey Area Data: version 14,Sep 1G.2018
Nwtls-- a.,S 5u,in 6Q8N1a
J� ess—ebnenYke s iC a ona rope errve..ae 1u wY Pegp2o12
Yp Utiprvf4crt Ew�FIprM`/bmy mrb.5b t5 pwwm Ywe-Heron Covxy.
yYllµn
Mason County,Washington
Ee—Everett gravelly loamy sand, 5 to 15 percent slopes
Map Unit Setting
Nafe nag map prof symbol 2hk7
Elevation: 50 to 500 feet
Mean annual pratipifatbn: 55 to 90 inches
Mean annual air lempenfun: Cy,to 50 cashes F
Frost fine peniod 160 t.1e0 aays
Farmlare"asSiWatbn: Pnmafannland ifimgated
Map Unit compoanin
Everett and similar soils:100 percent
Estimates are based on observations,dascnpgns,and fnnaeers of
the mapunit
Dexnpion of Evantt
Setting
Lerneffi. Tenaces
Parent materle,Glacial ouWash
Typical proeb
HI-01.7volah, gravelly.shi loamy send
H2-7ro 21 inches: exlretrely gravelly send
H3-2IIo60inchea: verygravellysand
Prop.rti.a and gualalee
Slope:5 to 15 percent
DepP ro nstricfive feature:Mon Nan 80 heroes
Drainage on. Somewhat excessively drained
Cement,of the mosf Ilmdirg leyero Iansmd water fKa g),High to
very high(5,95 to 19.981Nhr)
Depth to watenable:More than 80 inches
Fn,inni,offlacch,:None
Frepuency of pending.None
Available wafer supply,0 to 60 inches: Vary are,(about 2.5 i hea)
Inrerpretia.group.
Landrypa6lirydaasinea(lon(Lngafed): NonespacNed
Landwpedldytlassir heruloniagared): 4s
Hydrologic Soil Group: A
Eauagiralaite FW2XA0NWA-Puget Lowlands Forest
Fongesuifabilitygnevo, Droughty Solis(G002%N002WA)
Othervag.fttivedaadbc.b. Droughty Soils(G002%N<02WAI
Lzq eeNY 0.ww— yebsaasur / yt NN ]
i Emwetlwi$m gWrW Colaayy gy5/yaf Pegelort
IYp W pevgm'.EwreagrMy kemY uN,5 b 151m'eM Wqn—Mxm GUMy.
V/az�mWn
Hypnc arod ruling: No
Data Source Information
$al Survey n a: Mason county.Washington
Surrey Data. Veregn 18.Sep B,2022
ViM rwarwe. NYa 9MfrFA .1.
s wsw.rmanva war ceeo«n..sa sn+r r 2o12
_ ," WATER WELL REPORT
arAee ro waeaumox
UI OWN@ nm..➢m.Cas[eel AeY.i05S 3GASY(x%i DE. 5E fort om;hmd
8 ItI I AWN OF WIele u+vNum-...__.___..__._.Ei Ef- Al oes.30. r73-».a-7.p:.
Kx.....r am uuuxe:7 wawa e+.ueanwen.vs+
=y 0I PROPOSED US& mmrw a terra.D r.wrr D (14) WEnLL�+LOG:
x"..am o Tr x
— lel TYPE OF WOaK :,i�^mew•^vr..�..M. urmL Peq V»
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me...t aid e;xaVal Yitb mare__
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GnVel eeeW: rwD wA arn••n
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90 If) PUMP: 4te6[ml --
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.• IM HELL T6T5: wr'..°�'i1.w�»u�..:.. ... w
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i' rww�^ew dn��eiWi�mYAixbn.M lM:..Mxlb
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r _ Aee». Belfai YQ(�� 99529
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