HomeMy WebLinkAboutGEO2024-00043 Geotech Report FPA - GEO General - 3/23/2024 �E2011- 00Gq
Geotechnical Report
,Johns Prairie Mine Expansion — Unit 1
3560 E Johns Prairie Road, Shelton
Parcel No. 32009-09-02000
Mason County, Washington
March 23, 2024
Project#24029
Prepared For:
Manke Family Resources,LLC
PO Box 1302
Shelton, Washington 98584
Prepared By:
Envirotech Engineering, PLLC
PO Box 984
Belfair, Washington 98528
Phone: 360-275-9374
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MASON COUNTY Submittal Checklist
COMMUNITY SERVICES Geotechnical Report
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Instructions:
This checklist must be submitted with a Geotechnical Report and completed,signed, and stamped by the licensed
professional(s)who prepared the Geotechnical Report for review by Mason County pursuant to the Mason County
Resource Ordinance. If an item is found not applicable,the report should explain the basis for the conclusion.
Note: Unless specifically documented. this report does not provide compliance to the International Residential
Code Sections R403.1.7 for foundations on or adjacent to slopes, Section R403.1.8 for expansive soils or section
1808.7.1 of the International Building Code Section for Foundations on or adjacent to slopes.
Applicant/Owner Manke Family Resources, LLC Parcel# 32009-09-02000
Site Address 3500 E Johns Prairie Road, Shelton
(1) (a) A discussion of general geologic conditions in the vicinity of the proposed development,
Located on page(s) 5
(b) A discussion of specific soil types,
Located on page(s) 6
(c) A discussion of ground water conditions,
Located on page(s) 7
(d) A discussion of the upslope geomorphology,
Located on page(s) 3
(e) A discussion of the location of upland waterbodies and wetlands,
Located on page(s) 3
(f) A discussion of history of landslide activity in the vicinity, as available in the referenced maps and
records.
Located on page(s) 8
(2) A site plan which identifies the important development and geologic features.
Located on Map(s)_Geotechnical Site Plan—Appendix A
(3) Locations and logs of exploratory holes or probes.
Located on Map(s) Geotechnical Site Plan and Soil Logs(Appendix B)
(4) The area of the proposed development,the boundaries of the hazard,and associated buffers and
setbacks shall be delineated(top, both sides,and toe)on a geologic map of the site.
Located on Map(s) Geotechnical Site Plan
(5) A minimum of one cross section at a scale which adequately depicts the subsurface profile,and
which incorporates the details of proposed grade changes.
Located on Map(s) Soil Profile (Appendix B)
(6) A description and results of slope stability analyses performed for both static and seismic loading
conditions.Analysis should examine worst case failures.The analysis should include the Simplified
Bishop's Method of Circles.The minimum static safety factor is 1.5,the minimum seismic safety
factor is 1.1,and the quasi-static analysis coefficients should be a value of 0.15.
Located on page(s) 10 Page 1 of 39
(7) (a) Appropriate restrictions on place'ment of drainage features,
Located on page(s) „1�_I4 LV
(b) Appropriate restrictions on placement of septic drain fields,
Located on page(s) A (S LV
(c) Appropriate restrictions on placement of compacted fills and footings,
Located on page(s) (3 Lya
(d) Recommended buffers from the landslide hazard areas shoreline bluffs and the tops of other slopes.
Located on page(s) � I`4 Ld
(e) Recommended setbacks from the landslide hazard areas shoreline bluffs and the tops of other slopes.
Located on page(s) ;4 1 q 1.II
(8) Recommendations for the preparation of a detailed clearing and grading plan which specifically identifies
vegetation to be removed,a schedule for vegetation removal and replanting, and the method of vegetation
removal. I
Located on page(s)A LV
(9) Recommendations for the preparation of a detailed temporary erosion control plan which identifies the specific
mitigating measures to be implemented during construction to protect the slope from erosion, landslides and
harmful construction methods.
Located on page(s) 34 14 LV
(10) An analysis of both on--site and off-site impacts of the proposed development.
Located on page(s) I I o
(11) Specifications of final development conditions such as,vegetative management,drainage,erosion control,and
buffer widths.
Located on page(s)o+*-Q ,... L.V
(12) Recommendations for the preparation of structural mitigation or details of other proposed mitigation.
Located on page(s) X ( 5 L.V
(13) A site map drawn to scale showing the property boundaries,scale, north arrow,and the location and nature
of existing and proposed development on the site.
Located on Map(s) Geotechnical Site Plan
I, Michael Staten,hereby certify under penalty of perjury that I am a civil engineer licensed in the State of Washington
with specialized knowledge of geotechnical/geological engineering or a geologist or engineering geologist licensed in
the State of Washington with special knowledge of the local conditions. I also certify that the Geotechnical
CLYDF sr Report,dated March 23, 2024 ,and entitled Johns
Prairie Mine Expansion — Unit 1 meets all the
9
requirements of the Mason County Resource Ordinance,
R 43045 �, Geologically Hazardous Areas Section, is complete and true,
�rs'r NA 3/23/24 that the assessment demonstrates conclusively that the risks
posed by the landslide hazard can be mitigated through the
Disclaimer: Mason County does not included geotechnical design recommendations,and that all
certify the quality of the work done in hazards are mitigated in such a manner as to prevent harm to
this Geotechnical Report. property and public health and safety. Page 2 of 2
TABLE OF CONTENTS
1.0 INTRODUCTION................................................................................................................................. l
1.1 PROJECT INFORMATION.................................................................................................................... 1
1.2 PURPOSE OF INVESTIGATION AND SCOPE OF WORK........................................................................ 1
2.0 SURFACE CONDITIONS...........................»......................................»...............................................3
2.1 TOPOGRAPHY.....................................................................................................................................3
2.1.1 Upslope Geomorphology............................................................................................................3
2.2 SURFACE DRAINAGE..........................................................................................................................3
2.2.1 Upland Water Bodies.................................................................................................................3
2.3 SLOPE AND EROSION OBSERVATIONS...............................................................................................3
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............................................................................................................................... 7
3.4 SOILS TESTING AND PROPERTIES......................................................................................................7
3.4.1 INFILTRATION RATES......................................................................................................................7
4.0 ENGINEERING ANALYSES AND CONCLUSIONS......................................................................8
4.1 SLOPE STABILITY............................................................................................................................... 8
4.1.1 Slope Stability Analysis.............................................................................................................10
4.2 EROSION............................................................................................................................................I I
4.3 SEISMIC CONSIDERATIONS AND LIQUEFACTION..............................................................................11
4.3.1 Liquefaction..............................................................................................................................11
4.4 LANDSLIDE,EROSION AND SEISMIC HAZARDS CONCLUSIONS........................................................12
4.5 ON-SITE AND OFF-SITE IMPACTS.....................................................................................................12
5.0 ENGINEERING RECOMMENDATIONS........................................................................................13
5.1 BUILDING FOUNDATION RECOMMENDATIONS.................................................................................13
5.2 EARTHWORK CONSTRUCTION RECOMMENDATIONS.......................................................................13
5.2.1 Excavation.................................................................................................................................13
5.2.2 Placement and Compaction of Native Soils and Engineered Fill...........................................13
5.3 BUILDING AND FOOTING SETBACKS.................................................................................................14
5.4 SURFACE AND SUBSURFACE DRAINAGE...........................................................................................14
5.5 VEGETATION BUFFER AND CONSIDERATIONS.................................................................................14
5.6 TEMPORARY AND PERMANENT EROSION CONTROL.......................................................................14
5.7 SEPTIC DRAINFIELDS........................................................................................................................15
5.8 STRUCTURAL MITIGATION...............................................................................................................15
5.9 TIMBER HARVESTING RECOMMENDATIONS....................................................................................15
6.0 CLOSURE.............................................................................................................................................16
Appendix A—Geotechnical Site Plan
Appendix B -Soil Information
Appendix C-Slope Stability
1.0 INTRODUCTION
Envirotech Engineering, PLLC. (Envirotech) has completed this geotechnical report for a
property located at 3500 E Johns Prairie Road, Shelton, identified as parcel number
32009-09-02000 in Mason County, Washington.
As presented herein, this report includes information pertaining to the project in this
Introduction Section; observations of the property and surrounding terrain in the Surface
Conditions Section; field methods and soil descriptions in the Subsurface Investigation
Section; supporting documentation with relation to slope stability, erosion, seismic
considerations, and lateral earth pressures in the Engineering Analyses and Conclusions
Section; and, recommendations for foundation, settlement, earthwork construction,
retaining walls, erosion control, drainage, and vegetation in the Engineering
Recommendations Section.
An initial geotechnical evaluation of the project was conducted by Envirotech on January
25, 2024. It was determined that slopes in excess of 40% with a vertical relief of at least
10 feet were present within 300 feet of the planned development. Based on this site
characteristic, the proposed development will require a geotechnical report pursuant to
Landslide Hazard Areas of Mason County Resource Ordinance (MCRO) 8.52.140.
During the site visit by Envirotech, surface and subsurface conditions were assessed.
After completion of the field work and applicable project research, Envirotech prepared
this geotechnical report which, at a minimum, conforms to the applicable MCRO.
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 clear cut logging in support of expanding the existing Johns Prairie Mine .
Approximate site development footprint with relation to existing geological site features
are illustrated in the Geological Site Plan in Appendix A of this report.
1.2 Purpose of Investigation and Scope of Work
The purpose of this geotechnical investigation is to assess geological hazards, and
evaluate the project in order to provide geotechnical recommendations that should be
implemented during development. The investigation included characterizing the general
project surface and subsurface conditions, and evaluating the suitability of the soils to
support the planned site activities.
In order to fulfill the purpose of investigation, the geotechnical program completed for
the proposed improvements of the project include:
• Review project information provided by the project owner and/ or owner's
Envirotech Engineering Geotechnical Report
PO Box 984 page 1 Parcel 32009-09-02000
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 23, 2024
representative. This included Geotechnical Evaluations by Associated Earth
Sciences and McLucas& Associates;
• Conduct a site visit to document the site conditions that may influence the
construction and performance of the proposed improvements of the project;
• Define general subsurface conditions of the site by observing subsoils within test
pits and/ or cut banks, review geological maps for the general area, research
published references concerning slope stability, and review water well reports
from existing wells near the project;
• Collect bulk samples,as applicable, at various depths and locations;
• Perform soils testing to determine selected index and/or engineering properties of
the site soils;
• Complete an engineering analysis supported by the planned site alterations, and
the surface and subsurface conditions that were identified by the field
investigation, soil testing, and applicable project research; and,
• Establish conclusions based on findings, and make recommendations for
drainage, slope stability, erosion control, earthwork construction requirements,
and other considerations.
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Envirotech Engineering Geotechnical Report
PO Box 984 page 2 Parcel 32009-09-02000
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 23, 2024
2.0 SURFACE CONDITIONS
Information pertaining to the existing surface conditions for the project was gathered on
January 25, 2024 by a representative with Envirotech. During the site visit, site features
were documented that may reveal potential geological hazards.
This Surface Conditions Section provides information on topography,drainage and slope/
erosion conditions for the project and surrounding areas. An aerial photo of the project
and immediate vicinity is provided on the following page.
2.1 Topography
The topographic information provided in this section was extrapolated from a public lidar
source, and incorporated observations and GIS measurements. See the Geological Site
Plan in Appendix A for an illustration of the general slope indicators with respect to the
planned development.
Maximum sloping grades within 300 feet of the proposed development area with a
vertical relief in excess of at least 10 feet were observed to be 48% on the property, with
slopes exceeding 60% beyond.
2.1.1 Upslope Geomorphology
The landform that is upland from property is considered a hillside and crest 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.
2.2 Surface Drainage
The majority of the stormwater runoff originating upslope from the anticipated
development is expected to be minimal . Significant scour, erosion and sediment
transport was not apparent near the project.
2.2.1 Upland Water Bodies
There are no water bodies or wetlands located upslope from the planned
development that would significantly influence the project.
2.3 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:
Envirotech Engineering Geotechnical Report
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Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 23, 2024
• 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.
Several bowing characteristics of the evergreens were observed indicted slow downhill
creep. Severe slope instability indicators or other significant mass wasting on the
property or within the general vicinity of the project were not observed. Indications of
past mass wasting or deep-seated slope problems were not observed during the site visit.
This was for the observed area of land clearing only. Indications of shallow landsliding
was observed at the base of the slope beyond the project limits, apparently due to
highway cuts.
Aerial Photo from Mason County Website
Envirotech Engineering Geotechnical Report
PO Box 984 page 4 Parcel 32009-09-02000
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 23, 2024
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 January 25, 2024
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. See Appendix B for a soil profile cross-sections, soil logs, and other
appropriate information as necessary.
3.1 Field Methods,Sampling and Field Testing
Information on subsurface conditions for the project was accomplished by reviewing
several soil log information in the area including well logs, septic logs, and other
applicable geotechnical investigations. Information on subsurface conditions also
included reviewing geological maps within the project vicinity. No soil samples were
collected for this project.
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. More specifically for the project location, a caption
from the Washington State Department of Natural Resources is as follows:
MapUnit: Qgo
Age: Quaternary
Name: Undifferentiated outwash
Description: Recessional and proglacial stratified sand, gravel, and cobbles with minor
silt and clay interbeds deposited in delta, ice-contact, beach, and meltwater stream
environments; may include advance outwash.
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.
Envirotech Engineering Geotechnical Report
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Ph. 360-275-9374 March 23, 2024
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 assessed.
The project is primarily composed of undisturbed, native soils, without indications of fill.
For engineering purposes, these native soils are presented below.
Soils within the upper 180 feet of natural ground are primarily moist, poorly graded
gravels and sands (GP and SP) . Soils below this upper soil strata were observed to be
strongly cemented glacial till, locally known as hardpan. The hardpan is believed to
extend to depths of at least 50 feet. This is based on nearby well reports, site geology,
and/or knowledge of the general area.
Expanded and specific subsurface descriptions, other than what is provided in this
section, are provided within additional soil information located in Appendix B of this
report. The Boring Log provided in the appendix that is closest to this project was
originated by McLucas & Associates in 1997.
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 Grove
gravelly sandy loam with 30% -45% slopes. See the soil map below.
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Soil Survey From USDA Natural Resources Conservation Service
Envirotech Engineering Geotechnical Report
PO Box 984 page 6 Parcel 32009-09-02000
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 23, 2024
3.3.1 Groundwater
From the water well report(s) and knowledge of the general area, permanent
groundwater is at least 150 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.
3.4 Soils Testing and Properties
Visual classification of soils was performed in the field at all observed soil profiles.
Visual classifications were performed in accordance with the American Standards for
Testing and Materials (ASTM D2488).
The general results from the visual classification are presented above in the Subsurface
Conditions Section. Specifically, soils within the upper strata primarily consisted of
approximately 45% gravel, 50% sand-sized soils, and 5% fines with no plasticity
indicating a very low content of clay within the fine fraction. Minor variations observed
during the visual classification of particle size content (i.e. gravel, sand, fines), or isolated
pockets within the soil stratification were insignificant in relation to the overall
engineering properties of the soil.
Based on the fines content, erodibility of the site soils is considered to be low. However,
soils on disturbed steep slopes are more apt to erode than disturbed soils on flatter slopes.
Based on the fines content and fraction of clay within the fines content, settleability of the
site soils is expected to be fast. Permeability is expected to be high for this site due
significance of moderate density, poorly graded granular soils.
3.4.1 Infiltration Rates
Infiltration rates are based on the Soil Grain Size Analysis Method as outlined in
the 2012 Stormwater Management Manual for Western Washington. Based on
soil characteristics and the aforesaid drainage manual, infiltration was determined
to be 25.5 in/hr per the the following:
Logio(Ksdt) _-1.57+1.90DIo+0.015136o—0.0131390—2.08ffnes
Kim= saturated hydraulic conductivity, cm/sec
Dio= soil sample 10%finer by weight, min
D6o=soil sample 60%finer by weight, min
D90=soil sample 90% finer by weight, min
ffines= soil fraction passing#200 seive, by weight, min
Envirotech Engineering Geotechnical Report
PO Box 984 page 7 Parcel 32009-09-02000
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 23, 2024
4.0 ENGINEERING ANALYSES AND CONCLUSIONS
The following section includes slope stability, erosion, seismic considerations, and
impacts to both on-site and off-site properties.
4.1 Slope Stability
Landslides are natural geologic processes, and structures near slopes possess an inherent
risk of adverse settlement, sliding or structural damage due to these processes.
Geotechnical engineering cannot eliminate these risks for any site with sloping grades
because gravity is constantly inducing strain on the sloping soil mass. Excessive wet
weather and/ or earthquakes will exacerbate these strains. Geotechnical engineering
considers excessive wet weather and `design' earthquakes in order to provide an
acceptable factor of safety for developing on or near sloping terrain with relation to
current engineering protocol.These factors of safeties are based on engineering standards
such as defining engineering properties of the soil, topography, water conditions, seismic
acceleration and surcharges. Surface sloughing or other types of surficial slope
movements usually do not affect the deep-seated structural capability of the slope.
However, repeated surficial slope movements, if not repaired, may present a threat to the
structural integrity of the slope. If any slope movement arises, the slope should be
inspected by an engineer. Subsequently, maintenance may be required in order to prevent
the possibility of further surficial or deep seated slope movements that may be damaging
to life and property.
According to the Coastal Zone Atlas of Mason County, Washington, the project is within
and near terrain labeled `Stable' and `Intermediate' regarding potential landslide activity.
Descriptions of these mapping units may be found in the aforesaid Atlas. A Stability Map
from the Coastal Zone Atlas for the general area of this project is provided below:
Envirotech Engineering Geotechnical Report
PO Box 984 page 8 Parcel 32009-09-02000
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 23, 2024
Project r_ � lY
5
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Map from Washington State Department of Ecology Website
According to the Resource Map from the Washington State Department of Natural
Resources (DNR), the project is not within terrain labeled `highly unstable' relating to
soils. DNR labeled portions of this project as medium and high slope instability with
relation to slopes. A Resource Map from the DNR Forest Practices Application Review
System is provided below:
Envirotech Engineering Geotechnical Report
PO Box 984 page 9 Parcel 32009-09-02000
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 23, 2024
ff
Project
r
S Puget Sound
Resource Map from Washington State Department of Natural Resources Website
4.1.1 Slope Stability Analysis
The Simplified Bishop Method, utilizing `STABLE' software, was used to
analyze the static stability of the site slopes. Seismic conditions were estimated
utilizing worst case scenario values from the static analysis, a quasi-static analysis
coefficient of at least 0.15, and applying the applicable values to STABLE
software. Various radii's and center points of the circle were automatically
selected, and produced factor of safeties in a graphical and tabular format. Worst
case scenario values were used in the slope stability analysis in regards to
topography, surcharges, water content, internal friction and cohesion of the site
soils. STABLE software has been repeatedly checked with manual calculations,
and consistently proved to be a very conservative program. The following soil
properties were used in the analysis, and are based on observed conditions, known
geology, and/or published parameters:
Soil unit weight: 132 pcf
Angle of internal friction: 36 degrees
Cohesion: 0 psf
Based on the slope stability analysis, unacceptable factors of safety could be
present on and near the critical slope, but do not reflect proposed conditions. For
Envirotech Engineering Geotechnical Report
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Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 23, 2024
this project, slope stability will be improved due to unloading weight from the top
of slope, therefore minimum factor of safeties for static and dynamic conditions
were estimated to be at least 1.5 and 1.1, respectively. See the slope stability
information in Appendix C for a depiction of minimum factors of safety away
from the project.
4.2 Erosion
Based on the USCS description of the project soils, the surface soils are considered
moderately erodible. According to the Resource Map from the Washington State DNR, as
provided above, the project is not within terrain labeled `highly erodible.' This project is
not within an erosion hazard area as defined by the MCRO. Erosion hazard areas are
those with USDA SCS designations of River Wash (Ra), Coastal Beaches (Cg),
Alderwood Gravelly Sandy Loam on slopes 15% or greater(Ac and Ad), Cloquallum Silt
Loam on slopes 15% or greater (Cd), Harstine Gravelly Sandy Loam on slopes 15% or
greater(Hb), and Kitsap Silt Loam on slopes 15% or greater(Kc).
Due to the type and magnitude of development, full erosion control plans are required for
this project. Temporary and permanent erosion control measures are required for site
development, and shall be provided in a stormwater management plan.
4.3 Seismic Considerations and Liquefaction
There are no known faults beneath this project. The nearest Class `A' or 'B' fault to this
property is the Olympia Structure Fault , which is not located on the property or adjacent
properties. This information is supported by the USGS Quaternary Fault and Fold
Database for the United States.
Potential landslides due to seismic hazards have been considered, and are addressed in
the Slope Stability Analysis Section provided earlier in this report.
4.3.1 Liquefaction
The potential for liquefaction is believed to be low for this project. This is based,
in part, on the subsurface conditions such as soil characteristics and the lack of a
permanent shallow water table. Subgrade characteristics that particularly
contribute to problems caused from liquefaction include submerged, confined,
poorly-graded granular soils (i.e. gravel, sand, silt). Although gravel- and silt-
sized soil particles could be problematic, fine and medium grained sands are
typically subjected to these types of seismic hazards. No significant saturated sand
stratifications are anticipated to be within the upper 50 feet of the subsoil for this
project.
Envirotech Engineering Geotechnical Report
PO Box 984 page I 1 Parcel 32009-09-02000
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 23, 2024
4.4 Landslide,Erosion and Seismic Hazards Conclusions
DNR did indicate historic landslide activity near the project in the form of a dormant,
relict deep seated landslide. Mapped slope conditions, as delineated by the Departments
of Ecology and/or Natural Resources, were considered in our slope stability assessment.
Based on the proximity and severity of mapped delineations with respect to the proposed
development, results of the aforesaid slope stability analysis, observed surface conditions,
and other pertinent information, it is our opinion that the proposed development may
occur in accordance with the recommendations in this geotechnical report.
4.5 On-Site and Off-Site Impacts
From a geotechnical position, it is Envirotech's opinion that the subject property and
adjacent properties to the proposed development should not be significantly impacted if
all recommendations in this report are followed. This opinion is based on the expected
site development, existing topography, existing nearby development, land cover, and
adhering to the recommendations presented in this report. Future development or land
disturbing activities on neighboring properties or properties beyond adjacent parcels that
are upslope and/or downslope from the subject property could cause problems to the
subject property. For this reason, future development or land disturbance near the subject
property should be evaluated by a geotechnical engineer.
Envirotech Engineering Geotechnical Report
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Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 23, 2024
5.0 ENGINEERING RECOMMENDATIONS
The following sections present engineering recommendations for the proposed site
alterations. These recommendations have been made available based on the planned
improvements as outlined in the Introduction Section of this report; general observations
including drainage and topography as recapitulated in the Surface Conditions Section;
soil/ geologic conditions that were identified from the geotechnical investigation that is
summarized in the Subsurface Investigation Section; and, project research, analyses and
conclusions as determined in the Engineering Analysis and Conclusions Section.
Recommendations for the project that is provided herein, includes pertinent information
for building foundations, earthwork construction, building and/ or footing setbacks,
drainage, vegetation considerations,and erosion control.
5.1 Building Foundation Recommendations
Construction of buildings are not planned at this time. Applicable logging roads and
landings are addressed later in this report.
5.2 Earthwork Construction Recommendations
Earthwork may be needed for temporary logging roads and landings. The following
recommendations include parameters for earth cuts and fills.
5.2.1 Excavation
Excavation may be required for road cuts, and it is recommended to remove any
excessive organic content or other deleterious material, if present, near the ground
surface. Excavations for road cuts and landings should be limited to a slope of
1:1, and not more than 4 feet in height. We recommend a full bench cut for
temporary roads if planned within the hillside. Landings should not be allowed on
the hillside. Mine cuts after logging takes place shall be per the mining
geotechnical report.
5.2.2 Placement and Compaction of Native Soils and Engineered Fill
For disturbed native soils or engineered fill beneath road foundations, the fill
should be compacted to a firm, unyielding condition. Furthermore, fill should be
compacted in lifts not to exceed 12 inches, and compacted to 90% compaction
relative to the modified Proctor.
Fill heights should be limited to 4 feet, and fill slopes should be not steeper than
2:1.
Envirotech Engineering Geotechnical Report
PO Box 984 page 13 Parcel 32009-09-02000
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 23,2024
5.3 Building and Footing Setbacks
Since permanent structures are not an element of this project, setbacks for buildings or
other structures do not apply.
5.4 Surface and Subsurface Drainage
If impervious thresholds are exceeded per the prevailing agency code, then engineered
stormwater management plans are required for this project. The drainage engineer must
coordinate with a geotechnical engineer for input with relation to slope stability prior to
submitting drainage plans. If stormwater management plans are not required for this
project, then the following recommendations should be followed.
For this project, we recommend that infiltration is avoided in order to maintain slope
stability. Rock cribs and/ or slash berms per the drainage engineer is recommended to
manage stormwater for this project.
5.5 Vegetation Buffer and Considerations
For this project, we believe that a detailed clearing and grading plan is warranted since
thresholds are exceeded.
Vegetation Buffer — Vegetation removal from the steep slope is part of this project.
Therefore, buffers are not required. See Section 5.9 below for additional
recommendations.
5.6 Temporary and Permanent Erosion Control
From a geotechnical position, ordinary temporary and permanent erosion control is
sufficient for this project. Extents of temporary erosion control will mostly depend on the
timeliness of construction, moisture content of the soil, and amount of rainfall during
construction. Soil erosion typical to the existing site conditions and planned disturbance
of the Project include wind-borne silts during dry weather, and sediment transport during
prolonged wet weather. Sediment transport could be from stormwater runoff or tracking
off-site with construction equipment. Erosion control during construction should include
minimizing the removal of vegetation to the least extent possible. Erosion control
measures during construction may include stockpiling cleared vegetation, silt fencing,
intercepting swales, berms, straw bales, plastic cover or other standard controls.
Temporary erosion control should remain in place until permanent erosion control has
been established. Permanent erosion control may include promoting the growth of
vegetation within the exposed areas by mulching, seeding or an equivalent measure.
Envirotech Engineering Geotechnical Report
PO Box 984 page 14 Parcel 32009-09-02000
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 23, 2024
Additional 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.
5.7 Septic Drainfields
Septic drainfields will not be constructed at this time, and therefore not an element of this
project.
5.8 Structural Mitigation
With respect to landslide alleviation or slope improvements, structural mitigation is not
necessary for this project. This determination is based on the anticipated improvements of
the project, engineering conclusions, and compliance with all recommendations provided
in this report.
5.9 Timber Harvesting Recommendations
It is understood that timber harvesting is to be completed prior to any other site disturbing
activities. Envirotech recommends drainage accommodations for this project due to the
planned logging. Envirotech completed this and is provided under a separate cover.
Logging roads and landings shall follow the Earthwork Recommendations provided in
Section 5.2 of this report.
Conventional equipment such as skidders and crawlers may be used for this project. Logs
should be elevated on one end when dragging across the site, although dragging should
be minimized as much as possible. Recommendations in this report are provided as a cost
efficient way to alleviate erosion problems that may arise from this disturbance.
Since timber removal will be done to accommodate expansion of the gravel mine,
permanent erosion control is not needed. However, denuded soils shall be temporarily
stabilized immediately per the drainage plan.
Although not expected (especially water concerns), some conditions that may need
immediate attention upon tree removal includes excessive erosion, scour, sloughing,
significant changes to drainage patterns, new springs, new seepages or isolated areas of
ground saturation. Envirotech should be notified if unforeseen conditions arise.
Envirotech Engineering Geotechnical Report
PO Box 984 page 15 Parcel 32009-09-02000
Belfair,Washington 98528 Mason County, Washington
Ph. 360-275-9374 March 23, 2024
6.0 CLOSURE
Based on the project information provided by the owner, the proposed development, and
site conditions as presented in this report, it is Envirotech's opinion that additional
geotechnical studies are not required to further evaluate this project.
Due to the inherent natural variations of the soil stratification and the nature of the
geotechnical subsurface exploration, there is always a possibility that soil conditions
encountered during construction are different than those described in this report. It is not
recommended that a qualified engineer performs a site inspection during earthwork
construction unless fill soils will influence the impending foundation. However, if native,
undisturbed subsurface conditions found on-site are not as presented in this report, then a
geotechnical engineer should be consulted.
This report presents geotechnical design guidelines, and is intended only for the owner,
or owners' representative, and location of project described herein. This report should not
be used to dictate construction procedures or relieve the contractor of his responsibility.
Any and all content of this geotechnical report is only valid in conjunction with the
compliance of all recommendations provided in this report. Semantics throughout this
report such as `shall,' `should' and `recommended' imply that the correlating design
and/or specifications must be adhered to in order to potentially protect life and/ or
property. Semantics such as `suggested' or `optional' refer that the associated design or
specification may or may not be performed, but is provided for optimal performance. The
recommendations provided in this report are valid for the proposed development at the
issuance date of this report. Changes to the site other than the expected development,
changes to neighboring properties, changes to ordinances or regulatory codes, or
broadening of accepted geotechnical standards may affect the long-term conclusions and
recommendations of this report.
The services described in this report were prepared under the responsible charge of
Michael Staten, a professional engineer with Envirotech. Michael Staten has appropriate
education and experience in the field of geotechnical engineering in order to assess
landslide hazards,earthquake hazards, and general soil mechanics.
Please contact Michael Staten at 360-275-9374 if you have any questions, comments, or
require additional information.
Sincerely,
Envirotech Engineering
'Ifr S
Michacl Staten, P.E.
Geotechnical Engineer
Envirotech Engineering Geotechnical Report
PO Box 984 page 16 Parcel 32009-09-02000
Belfair,Washington 98528 Mason County, Washington
Ph. 360-275-9374 March 23, 2024
APPENDIX A
GEOTECHNICAL SITE PLAN
4
SCALE, I MH-25D FEET
D �50
E APPRx. TOP CRITICAL SLOPE
MI \\
EXISTING MISN.G ROAD TO BE r 6
USED FOR LOGGING CGl { /
hj J4 / OARLAND DAY
LOGGDvG LIMITS MUST BE AT
LEAST IC FEET FROM PROPERTY
LINES AND 200 FEET FROG MHHV �
f OO ' �Amx. MHHV a
TOE OF CRITICAL SLOPE
LOGGING] LIMITS z x<
(4PPRX) i ��•
SETBACKS OR VEGETATION
D_FFERS FROM SLOPES ARE
+SOT REUUIRCII. SEE REPORI.
E S74TE ROUTE 3
i
�/PROPERr- LINE
TPt� t
NOTES-
L CONTOURS WEPE NOT -REPARED BY A LICEvSEB LAND S+..RvEYOR
ONTOIFS WERE rx-.APdATI_➢FRO"A PUBLff. LTEAR SO.1RrE,AND
INCIPPOFATEE FI11D MEASIIRENENTS AS FYPLA]NEr. 1N THE rEERE::HNUAL
4UMPT LEGDrD
:. DO..NBAHIES vERE NOT PwfYAREB Iv A LL:ENS£D SURVEYOR LELATIEM
OF SITE FEATURES THAT A.E SHOWN HERE.SUCH AS TIP OF SLOr£S TOE .,tl.�nl, Ehra"cER
OF "LOSES, 'WATER FEATURES.ETC.. WITH RELATION 70 TIE KOPF- ENVIROTECH ENIHEERI-C
LINES HJS7 BE VEiNFIED BY THE OWNER. RE OIMEIiD►71UNS IN THE .-OC" Ea..11N_ -0111J-1 PO Box 9@4
:,EOTECMI]CAL REPORT 'ROVIDE SETBA:KS, BLFFDR'a, [EMS, ETC. WITH it';H TE-:T 'IT BELFAIR, WASHIN15TON 9020
RELATION TD GI3ZOSIL' FEAT.".ES,NOT FRCFCRIY LINES.THESE LEDLIIJL .364-275-9374
FEATURES -AY BE LOCATEL ON THE S.BJECT PROAERTY OR-EIGHBIMN; BI N ,OR L�,,��,
PROPERTIES. SITE PLAN
APPENDIX B
SOIL INFORMATION
vaRl[N.AMO w®RtO)rigT.�N.n
DLRC 101110
EX. MINE ROAD
EXTENTS OF
LOGGING
MATERIAL TO BE MINED 3, t
SR 3
EX. GRAVEL MINE S :' ;'''; ";: . _ry<;'
RECESSIONA OUTWA hi���• '��• '• OAKLAND
y' `t. � �,�•.'t
OSIT$ iy�'- •- _�,�•„�, BAY
SECTION A-A
ENmEER
EIMROTECN ENwastm
PO BOX 904
BELFAIR. VASHMION 905M
W-275-9914
SOIL PROFILE
FROJECT= MANM JOHNS PRAIRIE LEGEND
CLIM: 5/21/97 TIME: 2:30 P.M. SARDY GRAVF.L
P)EUNG NO: 11
ELEVATTC24: 197' 5" WELL SORTED SAND
i'PAGE No: 1
ISTA^.IC WATER IXVEL: 156' SILT - CLAM
DRILL TYPE: REVERSE CIRCLI"..ATION
S"PLING- CONT MUS
MDR OCK
It
57�ZiTA E)EPTH DESCRIPTION
i', •r 0 0-20' Topsoil dlstvrbed by Woad grading. Ylry d P/
wre (•oil aoiaGnxc) , vrry dart gra7ish brown, silty,
�f•: r 1S
- ..ry clean, tlar.e and wed. aanAy (mitwr 11t1a}
a :.• Rpradom. 1--3, wall-graded pcElrla-:o-granola gxa-1,
Qi eC740 or gravelly sand. tbTa. a mesh SO,D$. -200 mah 2.25-
-. c granvls• pzodominate-
i �i, •soes 10-15',
'` •. g: to
r s
•
••• O.'3.
•.O. r � 20-40' Chin! t0 vary claax, very dark gssyish row
�_ •O light-to-s•d. clay caat�•d, well-QYYd*d ] (Pxdam 1•-1
• + •••• yebblrto-gramllr gravely. Prydea. coarse and m*d.
.•••�• • sand, or sandy yrav'al_ OTo. a mash 4911. -200 ralo !.fit.
Ocaa•ional s' �bble•. Trcu. 25-90', p Y
i p. ca• �25 gsaval or granular coarse aatrd.
•s.r.r.
- rr•
3
NOTES;
Votae At south and of •ontAarn kettle, half way dowm road.
Clavation 107' b'- SRL 1"',
?4r." s AM*0asatee, I.'
Ip.O. lloz 33S2, l,aoay, Mi. D2309 1360) 352-2y49
PRO�XCT: KNNrM. JOHNS PRAIRIE LEGEND
DAIS: 3/27/97 Q'
TIME: 2:-30 p.n. SANDY GpJkVSL
FJpRING NO, 11
LLEVATlaaa: 187' S" WELL SKIRTED SAND
PAGE NO, 2 ="
iSTATIC WATER LEVEL: 356' SILT - CLAY
DRILL TYPE: Td VERSE CIF CUTATICK
SAMPLING: OWTINUOUS +•fi BEDROCK
STRATA DEPTH DESCRIPTIO[Q
pee-�
• CP
0-0-0 -0
�• ••�
• • w•+• 40-55' Chang* to eet, vanity Aaxk groyieb brawn, very
•` +'ar cleao, silt and slay mated, 6•- cobbiy )-illux), prsdem.
a a~•a: sled. and aoaxae/very ems+ tam -2T
• !+•O• Weil a4+d, 4"_
!• • )P • _•-) pmft1+-tO" r&ftu1a gravel. **0. —mt 79t-
+��.` : -200 wash 1.8%. Ftm 45-50', lea granelu a mz. smad-
O'er•�b
0-a ..o.
p i r':O• 55-751 Net, very dark ¢raieb brown, mod. Clay eiatad,
spa R• j Olean, pradom. oo"aa tad mod. candy, 21- pehbla a-
a a • -
ir—*I. Grrvel rounded from 70-751. +No. 9 mrsb
.. !•• fit. -200 mra?t 2A%.
•th•..
HmB
NaLu--" : Aisoci-tam, Zara.
P.Q. Pa: 535.2, Lacey, wa. 9&509 (360) 352-2149 -
I�ROJBCT- HAHn JOWS PRAIRIE yEG.
DAM 5/27/97 .
0
Tim: 2n30 p.m. SANDY GRAVEL
DORIHG NO: 11
EIXVAT70N: 107' S� :;• RBLL SMTED SAND
PAGE NO: 3 ---
STR.IC WATER I.FVE7_-, 156' SILT - CLAY
DRILL TV -. REVERSE CIRCULATION
sAHPLn(G: CON'TI-XIUS ]BEDROCK
STRATA MPTH IMSCRIPT:ObZ --.
a � • - 60
•p•s •
s'
■lpmoo
e.!
ae o•a
75-95' Chanym to wat (not sat.), elaAnar isacerial (clay
�py gone) _ otherwise no wmjor Change trtm above. Gravel core
.4 �'• anrjular and ■asv COW eq. 71 FCedL . ccaraa and mad.
sandy, coh ly, 3-- (pred e. 1.'26+-)r pebble- etea-gtahttic
gravel_ +Zfo. 1 mash 11%. -2co aesh $.Oi. Troga 85-40' ,
••• back to clay coatings, wars lovnded gravel, and 6"-
�p a�• aolble■ £zoo 90-y5 , no —M low; a granule Travel, as
• •'` +O sliavw. w(th pebbles and a navel_.•Qa.a Pe' 9
•• ••
4 �•
10 iRt
9Q
NOTBS:
Nmtocas a issocistaw, Ibc.
P.O. Box $352, Zacer, va. P&WP fJcoJ SU-2349
pRWECT: NWKE JOHNS PRAIRIE LEGMD
PATE: 5/27/97
TIME: 2:30 p.m. SANDY GRAVEL
BORING NO: it
$LEVATION: 1071 5" - 1RLL SORTED SAND
4An NO: 4 _-
STATIC RATER LZVEL: ISV SILT - CLAY
DRILL TYPE' RWERSE CIACUIATIM
SAMMING: 0004TIMMS :; BSI7R0�.K
STRATA DEPTH DESCRIHT£JN
•:
. I,a
►t:p's
9$-100, ChaaQs to Wet, d_:tY, fioe-ty �a tea=*v
•��'�'s;. assvty, vubsaanded Lshbleq> nl+ grsvel. +no' seah
'''�, • 100-130- Change to wry daTX q;ayiah L-wown. wt. zed.
"� • 9'- tp."Aam. V-).
•�'+''i. s11t snd clay voted, poorly-graded
•o¢ :: pa�l�-��9=aadia_ gravallY. fiaa-t�-caarer aaad
do +�i• SPredvra, Mad. and QOatall . +10. 4 ash 45%. -200 nrs16
•�. . . 3.39. Frmm 100-105'. sand is ElMr. Furs. 1610-115`
a4 to.. egptaics 311- rock. lsen 11i-1ST`• ats� Pebbles &n4
�p: I' -, —egad We4311-60Ltad, 1111lfr, ■R& aea dinar..L.
. wi ayi
d Q�t• •
. ins
. a •
•O�ati•�
P T. -
1,20
WTE S: -
MbLnase i Aaacciafte, znc.
1P.C. M" 5-M, I.saq►, Ya. 906"9 (J"j 312-2149
PrtojECT: XWKE JOHNS PRAIRIE Licaum
DATE: 5/27/97 0'
TIME: 2=30 p.m. GAMY ,GPAVZL
BORING NO: 11
EUVAT I ON: 167, 5" .: WZ" SORTED SAND
PAGE NO: 5
STATIC WATER LEVEL: 156' 8W - cxjky
[)RILL TYPE: PZWRSE CIRCULATION
SAMPLING., CONTINWJS ��r. SBmm
STV.kTA DEPTR 7ESCRIPTTON —
•i16M 120
f
i rL�
• D -
a♦Y,� 130-110' CAaaga to vexT dart gragi&b hrown, att.
moderately alaaa, besvy Milt and clay a"tod. wobbly
�..;,.� t�s�1, ilae-meciiwa-oq�igci�e eapa�r, 9•- iRna�, i.s^-1 .
• Q,e •� yebbl«-� ram! gsatnel, or Sra"J y .and. +140. 4
as Q.:a t►ash 49.74_ -200 wwab 5.7%. prey 138-140' . maoh dirtiefr
with �µnd-at. clay. a" IifM and Mad. tam dims minor.
• � 4
C 41-
..
• +�•."eL 144-190' Very dark Qc-riak brown, Vet, v.ry siltyl
•%D A elm" (beat? fin- WmWa11k/clay o0atinga) , 6'-
'e• mib1t. pelt-�-9rafrale gcsv lly. warts+-Pd Us-
.: lima amd, or Sandy 9xavm2. *No. 1
s.• araaa 10.2%. eantaL" clay bslla. flea. -AS-150', ealY
Vow-
&-e and vtTy oeara* sand and Is" axis'.
VMS:
fiTlsloeM S A.-aciatea, Inc.
P.O. loaf d312, LOOL-Y, V4. 9dS09 f390J 3-T919
M)JECT: MANKE JOHNS PRAIRIE LEGEND —
DATE: 5/27/97
TIME: 2:30 p.m. ,Q• SANDY GRK%9CL
BORING NO:
ELEVATIOLV: 157, 5^ WELL SORTED Fi r
FA= W: 6 --
STATIC RATER I Nr9L: 156' - SILT - C1AY
DRII,T. TYkz': REVERSE CIRCULATION •�;+
S MVLrM: CONITIMOUR �'� SEDYMCK
STRATA DEPTH DESCRIPTION
t31 4 1b0-165' Very "wt. Oliva bv6Ne, VMM7 diwty, ■"tY/
{ elrywX, prodam. eoarp and waved. saudY, oobbly (20),
well-g236ed 31- {psado•_ z•-) pabblo-paa-graauls
•Q•�� Qrsvc]. t11o. { mesh 956. -200 maed, 6.9%.
r
Nam'
r••t: �__
•ram =�
w
.�•e:• 165-170' Daft alive-brown, eaturatod, andudtia
b0aaltie, very oobk=y, pred=n. oorrs♦ sandy. aim�a
s 1.25" (pradom. gzammle) 93r4hvel. +17a. a sash 59.41h.
♦ -200 a zb 3.01k. Good orbshwd rook source.
�b Q,f
•«gyp.•. . ^1?0-i@S' Dark oliv*-hroan, saturated, +.s11-yiwcMd .�•-
P�^d• - q;raval with wilt and well-gwodwd L1rw-to-eeasae ■und.
t Ezom 170-175, hit clay and te.er sand, but "tidal
cio•anad up again iroa 175-190', ttiv. 6 Pooh S9.3%.
•• -i0G mesh 6.71.
9'ii+rpL�
b
,e e
e+p•
NOTES: -
MC7aeam i Associates, zoo,
PeRoj9CT: HAMM jama8 PPAIRn LEGEND
DM: 5/21/97 �
Tna: 2:30 P.M. &ANDY G7MVEL
BORIM No: 11
ZlSVm6TXO 1: 1071 5^ WELL gpRTED sANC
pwx NO: 7
STATIC WATER LBYEL: 156' —— GILT - CLAY
DRILL T'Epg: pj=M CIR UtATiCH 'E:.
BZMWCIK
SAWLING: CMNTIt7MUS
6TjtATA DEPTH D88CRY_PTI
t: w 19�J
1Sl-106' Dan" blrr�OsaY laa,�strin+(T) clay.
^ matte® of boring it 196'. StaLLc irate: level 1591.
r
'ab / ` �rsPCiatea, IRc
f.V. Boor 555.7, Lacey, xa. 98�U9 f36U) 3s?-.Z319
Test Pit#1
0-6 ft SP/GP Poorly graded sand and gravel
Test Pit#2
0-3 ft SP/GP Poorly graded sand and gravel
APPENDIX C
SLOPE STABILITY
1- .00
.4O
. SO
. 7O
. RO. 9O
O. 62
Slope Stability: Dynamic
.00
1 10
. 7 0
1 . 30
. 40
1 . so
1 1 GO
1 70
7 Sit U
1
I O O
i
tl
O . 96
Slope Stability: Static