HomeMy WebLinkAboutGEOtechnical Report - BLD Engineering / Geo-tech Reports - 4/3/2024 Geotechnical Report
Littlejohn Single Family Residential Properties
241 — 221 NE Circle Drive, Tahuya
Parcel No. 32214-52-05007 & -05008
Mason County, Washington
April 3, 2024
Project#24083
Prepared For:
Heather Littlejohn
182 NE Lake Drive
Tahuya, Washington 98588
Prepared By:
Envirotech Engineering
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 siopes.
Applicant/Owner Heather Littlejohn Parcel# 32214-52-05007&32214-52-05008
Site Address 241 &221 NE Circle Drive.Tahuya
(1) (a) A discussion of general geologic conditions in the vicinity of the proposed development,
Located on page(s) 5
(b) A discussion of specific soil types,
Located on page(s) 6
(c) A discussion of ground water conditions,
Located on page(s) 7
(d) A discussion of the upslope geomorphology,
Located on page(s) 3
(e) A discussion of the location of upland waterbodies and wetlands,
Located on page(s) 3
(f) A discussion of history of landslide activity in the vicinity,as available in the referenced maps and
records.
Located on page(s)- 8
(2) A site plan which identifies the important development and geologic features.
Located on Map(s) Site Plan-Appendix A
(3) Locations and logs of exploratory holes or probes.
Located on Map(s) Site Plan and Soil Logs(Appendix B)
(4) The area of the proposed development,the boundaries of the hazard,and associated buffers and
setbacks shall be delineated(top,both sides,and toe)on a geologic map of the site.
Located on Map(s) Site Plan
(5) A minimum of one cross section at a scale which adequately depicts the subsurface profile,and
which incorporates the details of proposed grade changes.
Located on Map(s) Soil Profile(Ag ndix B)_
(6) A description and results of slope stability analyses performed for both static and seismic loading
conditions.Analysis should examine worst case failures.The analysis should include the Simplified
Bishop's Method of Circles.The minimum static safety factor is 1.5,the minimum seismic safety
factor is 1.1,and the quasi-static analysis coefficients should be a value of 0.15.
Located on page(s) 9 Page 1 of 36
(7) (a) Appropriate restrictions on placement of drainage features,
Located on page(s) 17
(b) Appropriate restrictions on placement of septic drain fields,
Located on page(s) 18
(c) Appropriate restrictions on placement of compacted fills and footings,
Located on page(s) 13 and 15
(d) Recommended buffers from the landslide hazard areas shoreline bluffs and the tops of other slopes.
Located on page(s) 17
(e) Recommended setbacks from the landslide hazard areas shoreline bluffs and the tops of other slopes.
Located on page(s) 16
(8) Recommendations for the preparation of a detailed clearing and grading plan which specifically identifies
vegetation to be removed,a schedule for vegetation removal and replanting,and the method of vegetation
removal.
Located on page(s) 17
(9) Recommendations for the preparation of a detailed temporary erosion control plan which identifies the specific
mitigating measures to be implemented during construction to protect the slope from erosion,landslides and
harmful construction methods.
Located on page(s) 10
(10) An analysis of both on-site and off-site Impacts of the proposed development.
Located on page(s) 12
(11) Specifications of final development conditions such as,vegetative management,drainage,erosion control,and
buffer widths.
Located on page(s) 17-18
(12) Recommendations for the preparation of structural mitigation or details of other proposed mitigation.
Located on page(s) 18
(13) A site map drawn to scale showing the property boundaries,scale,north arrow,and the location and nature
of existing and proposed development on the site.
Located on Map(s) Site Plan
1,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
V CLYDE sr Report,dated April 3,2024,and entitled Littlejohn Single
Family Residential Properties,meets all the requirements of
a the Mason County Resource Ordinance,Geologically
Hazardous Areas Section, is complete and true,that the
cR�° a assessment demonstrates conclusively that the risks posed by
the landslide hazard can be mitigated through the included
4/3/24
geotechnical design recommendations,and that all hazards
Disclaimer;Mason County does not are mitigated in such a manner as to prevent harm to property
certify the quality of the work done in and public health and safety.
this Geotechnical Report.
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
11 GENERAL OBSERVATIONS..................................................................................................................3
2.2 TOPOGRAPHY.....................................................................................................................................3
2.2.1 Upslope Geomorphology............................................................................................................3
2.3 SURFACE DRAINAGE..........................................................................................................................3
2.3.1 Upslope Water Bodies................................................................................................................3
2.4 SLOPE AND EROSION OBSERVATIONS...............................................................................................4
3.0 SUBSURFACE INVESTIGATION......................................................................................5
3.1 FIELD METHODS,SAMPLING AND FIELD TESTING...........................................................................5
3.2 GENERAL GEOLOGIC CONDITIONS...................................................................................................5
3.3 SPECIFIC SUBSURFACE CONDITIONS.................................................................................................6
3.3.1 Groundwater............................................................................................................................... 7
4.0 ENGINEERING ANALYSES AND CONCLUSIONS...................»..».............................................8
4.1 SLOPE STABILITY...............................................................................................................................8
4.1.1 Slope Stability Analysis..............................................................................................................9
4.2 EROSION............................................................................................................................................10
4.3 SEISMIC CONSIDERATIONS AND LIQUEFACTION..............................................................................10
4.3.1 Liquefaction..............................................................................................................................10
4.4 LANDSLIDE'EROSION AND SEISMIC HAZARDS CONCLUSIONS........................................................11
4.5 LATERAL EARTH PRESSURES...........................................................................................................11
4.6 ON-SITE AND OFF-SITE IMPACTS.....................................................................................................11
5.0 ENGINEERING RECOMMENDATIONS.......................»...............................................................12
5.1 BUILDING FOUNDATION RECOMMENDATIONS.................................................................................12
5.1.1 Bearing Capacity.......................................................................................................................12
5.1.2 Settlement..................................................................................................................................13
5.1.3 Concrete Slabs-on-Grade..........................................................................................................13
5.2 EARTHWORK CONSTRUCTION RECOMMENDATIONS.......................................................................13
5.2.1 Excavation.................................................................................................................................13
5.2.2 Placement and Compaction of Native Soils and Engineered Fill...........................................14
5.2.3 Retaining Wall Backfill.............................................................................................................15
5.2.4 Wet Weather Considerations....................................................................................................15
5.2.5 Building Pads............................................................................................................................15
5.3 BUILDING AND FOOTING SETBACKS.................................................................................................15
5.4 SURFACE AND SUBSURFACE DRAINAGE...........................................................................................16
5.5 VEGETATION BUFFER AND CONSIDERATIONS.................................................................................16
5.6 TEMPORARY AND PERMANENT EROSION CONTROL.......................................................................17
5.7 SEPTIC DRAINFIELDS........................................................................................................................17
5.8 STRUCTURAL MITIGATION...............................................................................................................17
6.0 CLOSURE...........................................».....................................................»......_...............................18
Appendix A-Site Plan
Appendix B-Soil Information
Appendix C-Slope Stability
Appendix D—Erosion Control
Appendix E—Drainage Details
1.0 INTRODUCTION
Envirotech Engineering (Envirotech) has completed a geotechnical investigation for a planned
single family residence located at 241 & 221 NE Circle Drive, identified as parcel numbers
32214-52-05005, -05006, Mason County, Washington. See the vicinity map on the following
page for a general depiction of the site location.
An initial geotechnical evaluation of the project was conducted by Envirotech on March 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.
As presented herein,this report includes information pertaining to the project in this Introduction
Section; observations of the property and surrounding terrain in the Surface Conditions Section;
field methods and soil descriptions in the Subsurface Investigation Section; supporting
documentation with relation to slope stability, erosion, seismic considerations, and lateral earth
pressures in the Engineering Analyses and Conclusions Section; and, recommendations for
foundation, settlement, earthwork construction, retaining walls, erosion control, drainage, and
vegetation in the Engineering Recommendations Section.
1.1 Project Information
Information pertaining to the planned development of the project was provided by the proponent
of the property.The planned development consists of a 1-or 2-story single family residence,new
on-site septic system, and other ancillary features typical of this type of development.
Approximate construction envelope and other proposed features with relation to existing site
conditions are illustrated on the Site Map provided in Appendix A of this report.
1.2 Purpose of Investigation and Scope of Work
The purpose of this geotechnical investigation is to assess geological hazards, and evaluate the
project in order to provide geotechnical recommendations that should be implemented during
development. The investigation included characterizing the general project surface and
subsurface conditions, and evaluating the suitability of the soils to support the planned site
activities.
In order to fulfill the purpose of investigation, the geotechnical program completed for the
proposed improvements of the project include:
• Review project information provided by the project owner and/ or owner's
representative;
• Conduct a site visit to document the site conditions that may influence the construction
and performance of the proposed improvements of the project;
• Define general subsurface conditions of the site by observing subsoils within test pits
Envirotech Engineering Geotechnical Report
PO Box 984 page 1 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
and/ or cut banks, review geological maps for the general area, research published
references concerning slope stability, and review water well reports from existing wells
near the project;
• Collect bulk samples,as applicable,at various depths and locations;
• Perform soils testing to determine selected index and/or engineering properties of the site
soils;
• Complete an engineering analysis supported by the planned site alterations, and the
surface and subsurface conditions that were identified by the field investigation, soil
testing,and applicable project research;and,
• Establish conclusions based on findings, and make recommendations for foundations,
drainage, slope stability,erosion control,earthwork construction requirements, and other
considerations.
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Vicinity Map from Mason County Website
Envirotech Engineering Geotechnical Report
PO Box 984 page 2 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
2.0 SURFACE CONDITIONS
Information pertaining to the existing surface conditions for the project was gathered on March
25, 2025 by a representative with Envirotech. During the site visit, the type of geotechnical
investigation was assessed, site features were documented that may influence construction, and
site features were examined that may be influenced by construction. This Surface Conditions
Section provides information on general observations, vegetation, topography, drainage and
observed slope/ erosion conditions for the project and surrounding areas that may impact the
project.
2.1 General Observations
Currently, the property is vacant with evidence of past clearing. Vegetation on and near the
project consists primarily of secondary growth firs and shrubbery common to this area of the
Pacific Northwest. An aerial photo of the project and immediate vicinity is provided on the
following page.
2.2 Topography
The topographic information provided in this section was extrapolated from a public lidar source,
and incorporated observations and field measurements. Where necessary, slope verification
included measuring slope lengths and inclinations with a cloth tape and inclinometer. See the Site
Plan in Appendix A in this report for an illustration of general topography with respect to the
planned development.
Critical descending slopes, with grades exceeding 40% appear to be within 300 feet of the
planned development. The maximum critical slope is approximately 45% with a vertical relief of
about 30 feet.
Ascending grades are generally located to the east of the planned development. These slopes are
relatively minor within 300 feet of the project,with no apparent slope grades of at least 15%.
2.2.1 Upslope Geomorphology
The upland area of the property and beyond is generally situated on a hillside of glacial
origin.
23 Surface Drainage
Runoff originating upslope of the development is mostly diverted away from the property by
accommodating topography. Dry Pond is located beyond the slope toe. Excessive scour, erosion
or other indications of past drainage problems were not observed within the immediate vicinity of
the planned development.
23.1 Upslope Water Bodies
There are no apparent water bodies or wetlands located upslope from the planned
development that would significantly influence the project.
Envirotech Engineering Geotechnical Report
PO Box 984 page 3 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
2A Slope and Erosion Observations
The slope gradients near the project signal a potential landslide or erosion hazard area. Some
indicators that may suggest past slope movements include:
• Outwash of sediments near the bottom of the slope,
• Fissures,tension cracks,hummocky ground or stepped land masses on the face or top of
the slope,and parallel to the slope,
• Fine,saturated subsurface soils,
• Old landslide debris,
• Significant bowing or leaning trees,or,
• Slope sloughing or calving.
These slope instability indicators or other significant mass wasting on the property or within the
general vicinity of the project were not observed or discovered during research. Indications of
past landslides, current unstable slopes, deep-seated slope problems, or surficial slope failures
were not observed during the site visit.
27
261.NE CIRCLE t
241 NE CRCLE DR
E CIRCLE DR 221 NE CIRCLE DR
Aerial Photo from Mason County GIS Website
Envirotech Engineering Geotechnical Report
PO Box 984 page 4 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
3.0 SUBSURFACE INVESTIGATION
Information on subsurface conditions pertaining to the project was primarily gathered on March
25,2024 by a representative with Envirotech.Applicable information on field methods,sampling,
field testing, general geologic conditions, specific subsurface conditions, and results from soil
testing are presented in this section of the report. Appendix B of this report includes pertinent
information on subsurface conditions for the project, such as subsoil cross-section(s), test pit
log(s), and applicable water well report(s). Water well reports were utilized to estimate ground
water levels,and if sufficient,were used in identifying subsoil types.Applicable test pit locations
are depicted on the Site Plan provided in the appendix of this report.
3.1 Field Methods,Sampling and Field Testing
Information on subsurface conditions for the project was accomplished by examining soils within
test pits and/ or nearby banks extending to depths of up to 3 feet below the natural ground
surface. Information on subsurface conditions also included reviewing geological maps
representing the general vicinity of the project, and water well reports originating from nearby
properties.
Soil samples were not obtained from this project.Envirotech measured the relative density of the
near-surface in-situ soils by gauging the resistance of hand tools. Within testing locations, field
testing results generally indicated loose to medium dense soils in the upper 36 inches, and very
dense soils from 36 inches to the depth of terminous.
3.2 General Geologic Conditions
In general, soils at the project are composed of materials from glacial advances. The geologic
conditions as presented in the "Geologic Map of Washington," compiled by J. Eric Schuster,
2002 indicates Quaternary sediments, Qg. Quaternary sediments are generally unconsolidated
deposits,and dominantly deposited from glacial drift,including alluvium deposits.This project is
located within the Puget Lowland. Typically, "lower tertiary sedimentary rocks unconformably
overlie the Crescent Formation."as revealed in the Geologic Map.Initial sedimentary rocks were
formed from shales, sandstones and coal deposits from rivers. During the Quaternary period,the
Puget Lowland was covered by numerous ice sheets,with the most recent being the Fraser glacier
with a peak of approximately 14,000 years ago. Upon the glacial retreat, the landscape was
formed by glacial erosion glacial drift deposits.
The "Geologic Map of the Lilliwaup 7.5-minute Quadrangle, Mason County, Washington" by
Trevor A. Contreras, Gabriel Legorreta Paulin,Jessica L. Czajkowsld,Michael Polenz,Robert L.
Logan, Robert J. Carson, Shannon A. Mahan, Timothy J. Walsh, Chris N.Johnson, and Rian H.
Skov,June 2010,provides the following caption(s)for the project area:
Vashou lodgment all—Sand.pebbles_cobbles.silt.and clay id:amucton).gray.convact.clasts
subaneular to rounded.unsorted and unstratified:includes northern-and local-source material.
Envirotech Engineering Geotechnical Report
PO Box 984 page 5 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
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Geological Map Department of Natural Resources Washington State
33 Specific Subsurface Conditions
The following subsurface conditions are estimated descriptions of the project subgrade utilizing
information from the depth of penetration at all testing, sampling, observed and investigated
locations. Soils for this project were primarily described utilizing the Unified Soil Classification
System(USCS)and the Natural Resource Conservation Service(NRCS)descriptions.
The project is currently composed of native soils without indications of fill. Within test pit
locations, soils within the upper 3 feet of natural ground were generally observed to be moist,
brown silty sand with gravel (SM).Soils below the upper 3 feet layer were observed to be mostly
grey, low moisture, silty sand with gravel (SM), locally known as hardpan. The hardpan may
extend to depths greater than 50 feet. This is based on site geology, and/ or knowledge of the
general area.
The relative densities of the soil within selected test pits are provided above in Section 3.1.
Expanded and specific subsurface descriptions, other than what is provided in this section, are
provided in the soil logs located in Appendix B of this report.
According to the "Soil Survey of Mason County," by the United States Department of
Agriculture, Soil Conservation Service,the site soils are described as Alderwood Gravelly Sandy
Loam, An, with 6% - 15% slopes, and Alderwood Gravelly Sandy Loam, Ar, with 15% - 30%
slopes. The soil designations are depicted in the aerial photograph below, and descriptions are
provided in Appendix B of this report.
Envirotech Engineering Geotechnical Report
PO Box 984 page 6 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
A
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Soil Survey From USDA Natural Resources Conservation Service
33.1 Groundwater
From knowledge of the general area, permanent groundwater is at least 50 feet directly
below the property at the building pad location. Surface seepage or perched groundwater
at shallow depths was not observed on-site,nor indicated on the well reports.
Envirotech Engineering Geotechnical Report
PO Box 984 page 7 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
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 represent 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 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:
Project
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Envirotech Engineering Geotechnical Report
PO Box 984 page 8 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
Resource Map from Washington State Department of Natural Resources Website
�OIL�—Ct::Rego•.::ce\lsp c::::
_i•:drk Sods
Hid*Unstable
Hi¢hh•Erodible
Fiahh•Crstable
Hiahh•Erodible
No Data or Gravel
Pits
SLOPE—9n Res o•u:ce Nrzo oab
_'� edimzi Slope
Istabdity
High Sl,pt Instabdit-,
4.1.1 Slope Stability Analysis
The Simplified Bishop Method, utilizing `STABLE' software, was used to analyze the
static stability of the site slopes. Seismic conditions were estimated utilizing worst case
scenario values from the static analysis,a quasi-static analysis coefficient of at least 0.15,
and applying the applicable values to STABLE software. Various radii's and center
points of the circle were automatically selected, and produced factor of safeties in a
graphical and tabular format. Worst case scenario values were used in the slope stability
analysis in regards to topography, surcharges, water content, internal friction and
cohesion of the site soils. STABLE software has been repeatedly checked with manual
calculations, and consistently proved to be a very conservative program. The following
soil properties were used in the analysis, and are based on observed conditions, known
geology,and/or published parameters:
Upper 3 feet soil depth
Soil unit weight: 132 pcf
Angle of internal friction: 30 degrees
Cohesion: 0 psf
Soils below 3 feet in depth
Soil unit weight: 140 pcf
Angle of internal friction: 40 degrees
Cohesion: 400 psf
Based on the slope stability analysis, unacceptable factors of safety could be present on
and near the critical slope,but do not reflect conditions where development is expected to
occur. For this project, at the location of the proposed development, minimum factor of
safeties for static and dynamic conditions were estimated to be 1.51 and 1.11,
Envirotech Engineering Geotechnical Report
PO Box 984 page 9 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
respectively. See the slope stability information in Appendix C for a depiction of input
parameters and example of outputs.
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 within terrain labeled `highly erodible.' This Project is not within an erosion hazard
area as defined by the MCRO. Erosion hazard areas are those with USDA SCS designations of
River Wash (Ra), Coastal Beaches (Cg), Alderwood Gravelly Sandy Loam on slopes 15% or
greater (Ac and Ad), Cloquallum Silt Loam on slopes 15% or greater (Cd), Harstine Gravelly
Sandy Loam on slopes 15%or greater(Hb),and Kitsap Silt Loam on slopes 15%or greater(Kc).
It is our opinion that minor erosion control recommendations provided in this report is sufficient
for the development of this project, and additional engineered erosion control plans are not
required. Temporary and permanent erosion control measures are required for site development.
Extents of temporary erosion control will mostly depend on the timeliness of construction,
moisture content of the soil,and amount of rainfall during construction. Soil erosion typical to the
existing site conditions and planned disturbance of the project include wind-borne silts during dry
weather, and sediment transport during prolonged wet weather. Sediment transport could be from
stormwater runoff or tracking off-site with construction equipment.
The Temporary and Permanent Erosion Control Section (Section 5.6) of this report consist of
specific erosion controls to be implemented. Additional erosion control information and
specifications may be found in the latest addition of the "Stormwater Management Manual for
Western Washington,"prepared by the Washington State Department of Ecology Water Quality
Program.
43 Seismic Considerations and Liquefaction
There are no known faults beneath this project. The nearest Class `A' or Class V fault to this
property is the Tacoma Fault Zone,in which is approximately 2 miles to the south of this project.
This information is based on the USGS Quaternary Fault and Fold Database for the United States.
Potential landslides due to seismic hazards have been considered, and are addressed in the Slope
Stability Analysis Section provided earlier in this report.
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.
43.1 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
Envirotech Engineering Geotechnical Report
PO Box 984 page 10 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
shallow water table. Subgrade characteristics that particularly contribute to problems
caused from liquefaction include submerged, confined, poorly-graded granular soils (i.e.
gravel,sand,silt). Although gravel-and silt-sized soil particles could be problematic,fine
and medium grained sands are typically subjected to these types of seismic hazards. No
significant saturated sand stratifications are anticipated to be within the upper 50 feet of
the subsoil for this project.
4.4 Landslide,Erosion and Seismic Hazards Conclusions
DNR did not indicate historic landslide activity near the project. Mapped slope conditions, as
delineated by the Departments of Ecology and/ or Natural Resources, were considered in our
slope stability assessment. Based on the proximity and severity of mapped delineations with
respect to the proposed development, results of the aforesaid slope stability analysis, observed
surface conditions, and other pertinent information, it is our opinion that the proposed
development may occur in accordance with the recommendations in this geotechnical report.
4.5 Lateral Earth Pressures
Lateral earth pressures exerted through the backfill of a retaining wall are dependent upon several
factors including height of retained soil behind the wall, type of soil that is retained, degree of
backfill compaction, slope of backfill, surcharges, hydrostatic pressures, earthquake pressures,
and the direction and distance that the top of the wall moves. Significant retaining structures are
not anticipated for this project. If retaining walls are later planned for this project, prescriptive
requirements from the County should be adhered to. For retaining structures with a height
exceeding County prescriptive requirements, additional design parameters must be accounted for
in the retaining wall analysis, and recommendations should only be provided by a qualified
engineer after the type of backfill is acquired, inclination of backfill slope is estimated, and the
final wall height is determined.
4.6 On-Site and Off-Site Impacts
From a geotechnical position, it is Envirotech's opinion that the subject property and adjacent
properties to the proposed development should not be significantly impacted if all
recommendations in this report are followed. This opinion is based on the expected site
development, existing topography, existing nearby development,land cover, and adhering to the
recommendations presented in this report. Future development or land disturbing activities on
neighboring properties or properties beyond adjacent parcels that are upslope and/or downslope
from the subject property could cause problems to the subject property. For this reason, future
development or land disturbance near the subject property should be evaluated by a geotechnical
engineer.
Envirotech Engineering Geotechnical Report
PO Box 984 page 11 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
5.0 ENGINEERING RECOWAENDATIONS
The following sections present engineering recommendations for the proposed improvements of
the project. These recommendations have been made available based on the planned
improvements as outlined in the Introduction Section of this report; general observations
including drainage and topography as recapitulated in the Surface Conditions Section; soil/
geologic conditions that were identified from the geotechnical investigation that is summarized in
the Subsurface Investigation Section; and, project research, analyses and conclusions as
determined in the Engineering Analysis and Conclusions Section. Recommendations for the
project that is provided herein,includes pertinent information for building foundations,earthwork
construction, building and/or footing setbacks, drainage, vegetation considerations, and erosion
control.
5.1 Building Foundation Recommendations
Recommendations provided in this section account for the site development of a typical one- or
two-story, single family residential structure. The recommended allowable bearing capacities and
settlements as presented below, consider the probable type of construction as well as the field
investigation results by implementing practical engineering judgment within published
engineering standards. Evaluations include classifying site soils based on observed field
conditions and soil testing for this project. After deriving conservative relative densities, unit
weights and angles of internal friction of the in-situ soils,the Terzhagi ultimate bearing capacity
equation was utilized for determining foundation width and depth. Foundation parameters
provided herein account for typical structural pressures due to the planned type of development.
A structural analysis is beyond the scope of a geotechnical report, and a structural engineer may
be required to design specific foundations and other structural elements based on the soil
investigation. Stepped foundations are acceptable, if warranted for this project. Continuous,
isolated, or stepped foundations shall be horizontally level between the bottom of the foundation
and the top of the bearing strata. The frost penetration depth is not expected to extend beyond 12
inches below the ground surface for this project under normal circumstances and anticipated
design features.
5.1.1 Bearing Capacity
Existing in-situ soils for this project indicates that the structure can be established on
shallow, continuous or isolated footings. Foundations shall be established on relatively
undisturbed native soil that is competent and unyielding. Alternatively,foundations may
be constructed on selective re-compacted native soil or compacted engineered fill as
described in the Earthwork Construction Recommendations Section of this report.
For a bearing capacity requirement of no more than 1500 psf, a minimum continuous
footing width of 12 inches(15 inches for 2-story structures)shall be placed at a minimum
of 18 inches below the existing ground surface atop unyielding soils.For a columnar load
of no more than 3 tons,a circular or square isolated foundation diameter or width shall be
at least 24 inches. Foundation recommendations are made available based on adherence
to the remaining recommendations that are provided in this report. Alterations to the
Envirotech Engineering Geotechnical Report
PO Box 984 page 12 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
aforementioned foundation recommendations may be completed upon a site inspection by
a geotechnical engineer after the foundation excavation is completed.
5.1.2 Settlement
Total and differential settlement that a structure will undergo depends primarily on the
subsurface conditions,type of structure, amount and duration of pressure exerted by the
structure, reduction of pore water pressure, and in some instances,the infiltration of free
moisture. Based on the expected native soil conditions, anticipated development, and
construction abides by the recommendations in this report, the assumed foundation
system may undergo a maximum of 1.0 inch total settlement,and a maximum differential
settlement of 0.75 inch.
5.1.3 Concrete Slabs-on-Grade
Interior slabs, if utilized, should be supported on a minimum of 4 inches of compacted
coarse, granular material (Retained on U.S. Sieve #10 or greater) that is placed over
undisturbed, competent native subgrade or engineered fill per the Earthwork
Recommendations Section below.
The recommendations for interior concrete slabs-on-grade as presented herein are only
relevant for the geotechnical application of this project. Although beyond the scope of
this report, concrete slabs should also be designed for structural integrity and
environmental reliability. This includes vapor barriers or moisture control for mitigating
excessive moisture in the building.
5.2 Earthwork Construction Recommendations
Founding material for building foundations shall consist of undisturbed native soils to the
specified foundation depths. Compacted engineered fill, or selective re-compacted native soils
may be used to the extents provided in this Earthwork Construction Recommendations Section.
The following recommendations include excavations, subgrade preparation, type of fill, and
placement of fill for building foundations.
5.2.1 Excavation
Excavation is recommended to remove any excessive organic content or other deleterious
material, if present, beneath foundations and to achieve appropriate foundation depth.
Additional sub-excavation will be required for this project if the soils below the required
foundation depth are loose, saturated, not as described in this report, or otherwise
incompetent due to inappropriate land disturbing, or excessive water trapped within
foundation excavations prior to foundation construction.All soils below the bottom of the
excavation shall be competent, and relatively undisturbed or properly compacted fill. If
these soils are disturbed or deemed incompetent, re-compaction of these soils below the
anticipated footing depth is necessary. Excavations shall be completely dewatered,
compacted, and suitable before placement of additional native soil, engineered fill or
structural concrete.
Envirotech Engineering Geotechnical Report
PO Box 984 page 13 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
511 Placement and Compaction of Native Soils and Engineered Fill
For engineered fill or disturbed native soils that will be utilized as fill material directly
beneath foundations, observation and/ or geotechnical testing is required prior to
foundation construction. The following placement and compaction requirements are
necessary.
For disturbed native soils or engineered fill beneath foundations, limits of compacted or
re-compacted fill shall extend laterally from the bottom edge of the foundation at a rate of
one horizontal foot for each foot of compacted or re-compacted fill depth beneath the
foundation.See the illustration below.
FOOTING
COMPACTED
NATIVE SOILS
OR ENGINEERED I
FILL
1
UNDISTURBED SUBGRADE
Both engineered fill and native soils used as compacted fill should be free of roots and
other organics, rocks over 6 inches in size, or any other deleterious matter. Because of
moisture sensitivity, importing and compacting engineered fill may be more economical
than compacting disturbed native soils. Engineered fill shall include having the soils
retained on the No. 4 sieve crushed (angular), and should consist of the following
gradation:
U.S.Standard Sieve %Finer(by weight)
6" 100
3" 60—100
No.4 20—60
No.200 0-8
Table 1
Partical Size Distribution of Engineered Fill
Compaction shall be achieved in compacted lifts not to exceed 6 inches for both native
soils and engineered fill,respectively.Each lift should be uniformly compacted to at least
95% of the modified Proctor maximum dry density (ASTM D 1557) and within 3% of
optimum moisture content. Each lift surface should be adequately maintained during
construction in order to achieve acceptable compaction and inter-lift bonding.
Temporary earth cuts and temporary fill slopes exceeding 4 feet in height should be
limited to a slope of 2:1 (horizontal:vertical). Utility trenches or other confined
excavations exceeding 4 feet should conform to OSHA safety regulations. Permanent cut
and fill slopes shall be limited to a slope of 2:1, unless otherwise approved by an
engineer.
Envirotech Engineering Geotechnical Report
PO Box 984 page 14 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
5.2.3 Retaining Wall Backfill
As previously mentioned, significant retaining structures are not anticipated for this
project. However, if used, native soils may be used as retaining wall backfill for this
project. Backfill may also consist of engineered fill or borrow materials approved by a
geotechnical engineer. Placement, compaction and extents of retaining wall backfill
should also be specified by a geotechnical engineer or qualified professional.
5.2.4 Wet Weather Considerations
Due to the types of subsurface soils, additional provisions may be required during
prolonged wet weather. Every precaution should be made in order to prevent free
moisture from saturating the soils within excavations. If the bottom of excavations used
for footing placement changes from a moist and dense/hard characteristic as presented in
this report to muck or soft, saturated conditions, then these soils become unsuitable for
foundation bearing material. If this situation occurs, a geotechnical engineer should be
notified, and these soils should be completely removed and replaced with compacted
engineered fill or suitable native material as presented in this section.
5.25 Building Pads
Building pads for this project, if utilized, shall be constructed per the fill placement and
compaction recommendations as presented above. Both engineered fill and native soils
may be used for building pads. Building pad slopes shall be no steeper than 2:1 for both
compacted engineered fill and re-compacted native soils used as fill. Building pad fill
shall be"keyed"into the existing subgrade to a depth of at least 2 feet below the existing
ground surface. The term "keyed," as used here, implies that the interface between the
building pad and subgrade is horizontally level. Alternatively, building pads may be
keyed into the subgrade to the above specified depth,and stepped. Stepped fill should be
keyed into the subgrade at a minimum width of 10 feet. All footings shall be located at
least 5 feet away from the top of the engineered fill slope.
53 Building and Footing Setbacks
Provided that assumptions relating to construction occur and recommendations are followed as
presented in this report, the factor of safety for slope stability is sufficient for a 15 feet footing
setback from the face of the nearby descending slopes exceeding 40%. See the figure below and
the Site Plan in Appendix A for an illustration of the setbacks.
S-RUC T;kE
ILP OF
SLOPE
_.IIT.I_.''..
� 1
F SETE,4:K I FOOTING
Envirotech Engineering Geotechnical Report
PO Box 984 page 15 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
Setbacks may be encroached by extending all foundations to the top of hardpan estimated to be
approximately 3 feet below the existing ground surface.
5A Surface and Subsurface Drainage
Positive drainage should be provided in the final design for all planned residential buildings.
Drainage shall include sloping the ground surface, driveways and sidewalks away from the
project structures.All constructed surface and subsurface drains should be adequately maintained
during the life of the structure.If drainage problems occur during or after construction,additional
engineered water mitigation will be required immediately. This may include a combination of
swales,berms,drain pipes,infiltration facilities,or outlet protection in order to divert water away
from the structures to an appropriate protected discharge area. Leakage of water pipes, both
drainage and supply lines,shall be prevented at all times.
If impervious thresholds are exceeded per Mason County 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.
Both footing perimeter drains and roof drains are required for this project. Subsurface water
intercepted in the footing perimeter drains, and stormwater collected from roof drains shall be
separately tight-lined to the recommended outlet. Roof and foundation drains may share a
tightline if an above ground drainage outlet is allowable and a backflow preventer is installed
within the pipe system in order to prevent roof water from entering the foundation area.
For this project, we recommend that an above ground outlet is located beyond the toe of the
critical slope. An energy dissipater is required at the outlet. Recommended outlet locations are
delineated on the Site Plan in Appendix A, and drainage details are provided in Appendix E of
this report.
5.5 Vegetation Buffer and Considerations
For this project, we believe that a detailed clearing and grading plan is not warranted unless
Mason County thresholds are exceeded, and basic vegetation management practices should be
adhered to.
Vegetation Buffer—Vegetation shall not be removed from the face of the critical slope or within
a distance of 5 feet beyond the top of the slope. However, any tree deemed hazardous to life or
property shall be removed. If tree removal is necessary, then stumps and roots shall remain in
place, and the underbrush and soil shall remain undisturbed as much as possible. Any disturbed
soil shall be graded and re-compacted in order to restore the terrain similar to preexisting
conditions and drainage patterns. See the Site Plan in Appendix A of this report for a depiction of
the vegetation buffer.
Envirotech Engineering Geotechnical Report
PO Box 984 page 16 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
5.6 Temporary and Permanent Erosion Control
Erosion control during construction should include minimizing the removal of vegetation to the
least extent possible. Erosion control measures during construction may include stockpiling
cleared vegetation, silt fencing, intercepting swales, berms, straw bales, plastic cover or other
standard controls. Although other controls may be used, if adequate, silt fencing is presented in
this report as the first choice for temporary erosion control.Any erosion control should be located
down-slope and beyond the limits of construction and clearing of vegetation where surface water
is expected to flow. If the loss of sediments appears to be greater than expected, or erosion
control measures are not functioning as needed, additional measures must be implemented
immediately. See Appendix D for sketches and general notes regarding selected erosion control
measures. The Site Plan in Appendix A depicts the recommended locations for erosion control
facilities to be installed as necessary.
Permanent erosion control may also be necessary if substantial vegetation has not been
established within disturbed areas upon completion of the project. Temporary erosion control
should remain in place until permanent erosion control has been established. Permanent erosion
control may include promoting the growth of vegetation within the exposed areas by mulching,
seeding or an equivalent measure. Selected recommendations for permanent erosion control are
provided in Appendix D. Additional erosion control measures that should be performed include
routine maintenance and replacement,when necessary, of permanent erosion control, vegetation,
drainage structures and/or features.
5.7 Septic Drainfields
The approximate location of the septic drainfield is presented within the building limits on the
Site Plan in Appendix A of this report.Based on the septic drainfield location with relation to the
existing and proposed topography,the drainfields are not expected to adversely influence critical
slopes.This is also based on compliance with all recommendations in this report.
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. If
setback encroachments are needed, then deeper foundations are required per the
recommendations in this report.
Envirotech Engineering Geotechnical Report
PO Box 984 page 17 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
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 En""g""i��neering
�.vr1vc.
Robert McNearny,E.I.T. Michael Staten,P.E.
Staff Engineer Geotechnical Engineer
Envirotech Engineering Geotechnical Report
PO Box 984 page 18 NE Circle Drive
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 April 3,2024
Xvrid MLIS
v IUC[Nad4fv
i
NOTE: ALL SEPTIC
DRAINFIELDS VJST BE TOE OF SLOPE
INSTALLED WITHIN THE EXCEEDING 4,3% N
C❑NSTRUCTI❑N ENVELOPE
SCALEI
C I® 1
s
I
~ FT DIFFt:SER
EE
,os
A
a• SLID PVC
PIPE
SILT FENCE
EXISTING
DRIVEWAY +
i
�TpI � !
R
TOP OF SLOPE '
EXCEEDING 40% ; �TP2'
5' VEuETATED
BUFFER L
e N� C❑NSTRa[:TION
IS' CONSTRUCTION SETBACK ENVEL❑PE
4
BLILDING SETBACKS MAY
BE ENCROACHED PER
THE GEOTECHNICAL REPORT
I
!voTTrs�
EmMD4('MPOI MAY HE REWJId=D FEN Nis SITE cE!!p&LOCATDa
ARE DCnICTEE, L%D FLTMATNES 4A- BC CTILVEI AS EVLAM IN M r
CEOTECHNICAL REMY'
e,:ONT(KA's WERE sOT rwE+AeEU Er A LI;:Eh%Et LAMD SLRVEVR
MNTOuRS WERE rXTRAFOLATED FROM A 'JRLIC LMAR SOURCC,A41 ------ i 1N-ORP074rED rELu W-AS:;PEME-.TS AS C•�LAINEE IA THE EOTE,-d=AL UE(EyD
REvO+ _
3.MAD"
E+[ES WE NOT PRE-'AvLl. 1+A LI..E%NEI :GRVErOk.La ATOMS --- E`:CINEE4
'OF 'ITE FEATJRES THAT A4E 'HOW%HERE SLC O TCM'ORAR��
H AS TO"BF SLO
ES. TOE 1134 rU C:Cl.TRDL
:OF SLT'ES. WATER FEAT4 kE:; E7r... +ITH+ELATOh TO THE r•A-'EH r, EN✓IROTE:M EMSIME .W.,
LMS.usT EE vERlrsu x ,E OWVER.kE-0-K%b-TIO\. If.THE SLOPE MKATni �O EDx ear
-CEOTECHMCAL REP[9-PROYIBE SETBACKS. VFFEPS. BE'TH:. ETC..WITH mLrmc YAsmamH 98526
!RELATIQY TO�--,EOLCY N FEAT+E%.KOT SAKI? ,L1 E%'. THENE IULOI.I:. E•ISTMc rDu D,w 'it9-2t�-47/A 7
rEATJRES MAr BE LCLATEL a%THE SLFJELT "D E' • O, NEI�:HFA.'n.,
URGER-lEs, TP Tm PIT SITE PLAN
APPENDIX B
SOIL INFORMATION
ra,:w as mmapffft sc"
VULD 11a3T-v
PROPOSED STRUCTURE
EXISTING GRADE
�— EXISTING GRADE
SILTY SAND W/
GRAVEL CSN>
VERY DENSE
GLACIAL TILL
qS�
SE:'TID% A-A
norc.�
11 K%W LRADE"%CES A M) RED IN MDEP TO 4".NIEVE E46I4EE4.
PDsITIvE G+AIN41 E ENvIN 9b4 DI EN.dvEE+iv:,
PO BO% ee4
i INC SOIL i)reILE Is AA:LAAiE FOR I IE fLO OF HELFAIR VA%HINfTOh *- x
THE CiSCRVED FEET PITS AT THE SPE:FIED LD,^.4iIINi, TFC-,�i-"74
LOW"CE'�iNS WE D<SED ON SITC CEDLDL•.
vELL LD:.:xl. 4%l:•DR F:-ERiEWE 14 THE :CNE.AL aRD.
..OIL :'kOFILE
Map Unit Description-Aidenvood gravelly sandy loam.15 to 30 percent slopes--Mason
County,Washington
Mason County, Washington
Ac—Alderwood gravelly sandy loam, 15 to 30 percent slopes
Map Unit Setting
National map unit symbol: 2t627
Elevation: 0 to 1,000 feet
Mean annual precipitation: 25 to 60 inches
Mean annual air temperature: 46 to 52 degrees F
Frost-free period: 160 to 240 days
Farmland classification: Farmland of state.%ide importance
Map Unit Composition
Atdert.00d and similar sods: 85 percent
Minor components: 15 percent
Estimates are based on observations,descriptions.and transec's of
the mapunit.
Description of Alderwood
Setting
Landform: Ridges,hills
Landform position(two-dimensional): Backsiope
Landform position(three-dimensional): Side slope.nose slope,tall
Down-slope shape: Linear,convex
Across-slope shape: Convex
Parent material: Glacial drift andior glacial ouh:ash over dense
glaciomarine deposits
Typical profile
A-0 to 7 inches: gravelly sandy loam
Bwl-7 to 21 inches: very gravelly sandy loam
Bw2-21 to 30 inches: very gravelly sandy loam
Bg-30 to 35 inches: very gravelly sandy loam
2Cd1-35 to 43 inches: very gravelly sandy loam
2Cd2-43 to 59 inches: very gravelly sandy loam
Properties and qualities
Slope: 15 to 30 percent
Depth to restrictive feature: 20 to 39 inches to densic material
Natural drainage class: Moderately well drained
Capacity of the most limiting layer to transmit water(Ksal): Very
low to moderately low(0.00 to 0.06 inthr)
Depth to water table: About 18 to 37 inches
Frequency of flooding: None
Frequency of ponding: None
Available stater storage in profile: Very low(about 2.7 inches i
Interpretive groups
Land capability classification(imga!ed1: None specified
Land capability classification(nonirrigated;: 4e
Hydrologic Soil Group: B
Natural Resources Web Sojl Survey 12 10.2018
Conservation Service Nalionol Cooperative Sod Survey Page t Ot?
Map Unit Description.Aderwood gravelly sandy loam.15 to 30 percent slopes---Mason
County,Washington
Forage suitability group: Limited Depth Soils(G002XS301 WA),
Limited Depth Soils(0002XF303WA),Limited Depth Soils
(G002XN302WA)
Hydnc soil rating. No
Minor Components
Everett
Percent of map unit: 5 percent
Landform: Kames,eskers,moraines
Landform position(two-dimensional): eacks�ope
Landform position(three-dimensional.: Side slope
Down-slope shape: Convex
Across-slope shape: Convex
Hydric soil rating. No
Indianola
Percent of map unit. 5 percent
Landform: Eskers,kames,terraces
Landform position(three-dimensional): Tread
Down-slope shape: Linear
Across-slope shape: Linear
Hydric soil rating: No
Shalcar
Percent of map unit: 3 percent
Landform: Depressions
Landform position(three-dimensional): Dip
Down-slope shape: Concave
Across-slope shape: Concave
Hydric soil rating. Yes
Norma
Percent of map unit. 2 percent
Landform: Depressions.drainage.vays
Landform position(three-dimensional;: Dio_
Doi'm-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
Ntlursr Resources Web Soil Survey 12 10201H
Comervirtion Service National Cooperative Soil Survev Pape 2 of
APPENDIX C
SLOPE STABILITY
r
0
a
0
it
O w m J P N a W N r 0
-- - ---------_---- - ---------------------------- -_. ...... . _ 0 0�_Q_..Q-g
j
i
i'
0 0 0 0 0 0 0 0 0 0 0
C H N M 4 n O i` M 1� 0
. . . . . .
APPENDIX D
EROSION CONTROL
GEOTEXTILE FABRIC
WRAP AROUND TRENCH
TO AT LEAST ENTIRE
BOTTOM OF TRENCH
BEFORE PLACING GRAVEL 2'x2'x5' WOOD POST OR
12' DEEP, 8' WIDE TRENCH EQUIVALENT OR BETTER
FILLED WITH 3/4' TO 1 1/2' — 7'
WASHED GRAVEL OR VEGETATION I
DIRECTION OF 11 2Z h
WATER FLOW EXISTING
2 GROUND SURFACE
2.5 rt
SILT FENCE - CROSS SECTION
N.T.S.
2'x2' WOOD POST <TYrl) GE13TEXTILE FABRIC
OR EQUIVALENT OR BETTER AND WIRE MESH
@ 6 FT MAX. O.C,
�-- 6 FT t m FT
EXISTING II
GROUND SURFACE
Wl
12' DEEP, 8' WIDE
TRENCH FILLED WITH 3/4' TO 1 1/2' a5 FT
WASHED GRAVEL OR VEG TI
BOTTOM EXTENTS OF
GEOTEXTILE FABRIC SILT F N G - DETAI
N.T.S.
PROVIDE FULL WIDTH
3/4 IN TO 1 i/2-IN,rt INGRESS/EGRESS
CRUSHED GRAVEL
PLACED AT 6 IN
MINIMUM DEPTH
WELL-DR4I-D
SOILS
-042 IN/MIN F"�TM
R=25 FT MIN
4 —
e<'CESS Rd0
STABILIZED CONSTRUCTION ENTRANCE
N.T.S.
ENERAL.NOTES, PERMANENT EROSION CONTROL NOTES
SHOULD THE TEMPORARY EROSION 414D SEDIMENT LOYTRM MEASURES SHOWN ON SEEDING FOR RAW SLOPES
fESE PLANS PROVE TO BE INADEQUATE CJR14G CONSTRUCTION,THE CONTRACTOR L BEFORE SEEDING,INSTALL NEECED SURFACE RUNOFF CONTRA.
MALL INSTALL ADDITIONAL EROSION A.4D SECIMENT CONTROL FACILITIES. MEASURES SUCH AS GRADIENT TERRACES,INTERCEPTOR DIKES,
ALL EROSION AND SEDIMENT CONTROL FACILITIES A4D DEVICES SHALL BE SWALES,LEVEL SPREADERS AND SEDIMENT BASINS.
I.NSPECTED DAILY AND IMMEDIATELY MAINTAINED,IF NECESSARY. P.THE SEED BED SHALL BE FIRM WITH FAIRLY FINE SURP4CE.
ALL EROSION AND SEDIMENT CONTROL FACILITIES ANC DEVICES SHALL FE LEFT IN FOLLOWING SJRFACE ROUGFENINI..PERFORM ALL OPERATIONS ACC40S
LACE UNTIL THE UPSLOFE AREAS HAVE BEEN PERMANENTLY STABILIZED. OR PERPENDICULAR TO THE SLOPE.
MPORARY EROSION CONTROL NOTES- 3.SEEDING RECOMMENDATIONS,AS SHOWN BELOW, AND SH13JLE BE
APPLSEO AT THE RATE OF 120 POJNES PER ACRE
R ALL AREAS WHICH HAVE BEEN STRIPPED OF VEGETATION OR EXPERIENCED LAND 4. SEEDQXRE BEDS PLANATMN D TTEENMMAY I AND CTOBERAS 31 wDLTO
]STURBING ACTIVITIES.AND WHERE NO FURTHER WORK A OR ANTICIPATED F A FOSTER AND PROTECT THE ROOT STRUCTURE,
R:OD EXCEEDING THE LISTED CRITERIA BELOW,ALL, DISTURBED AREAS MUST BE 5.SEED BEDS PLANTED BETWEEN NOVEMBER 1 AND APRIL 30,
MMEDIATELY STABILIZED WITH MULCHING,GRASS PLANTING OR OTHER APPROVED ARMORING OF THE SEED BED WILL BE NECESSARY,(e.g..
ROSIUN CONTROL TREATMENT APPLICABLE TO THE TIME OF YEAR -RASS SEEDING GEOTEX71LES, JUTE M4T. CLEAR PLASTIC COVERING),
ONE WILL ONLY BE ACCEPTABLE DURING THE MONTHS OF APRIL THROUGH 6,FERTILIZERS ARE TO BE USED ACCORDING TO SUPPLIERS'
EHE PTEMBER.HOWEVER, SEEDING MAY PROCEED WHENEVER IT IS IN THE INTEREST OL RECOMMENDATIONS.AMOUNTS SHO..LD BE MINIMIZED,ESPECIALLY
OWNER/CONTRACTIR, BLT MJST ALSO BE AUGMENTED WITH MULCHING, NETTING 41.;ACENT TO WATER BODIES AND WETLANDS.
R OTHER APPROVED TREATMENT.
RY SEASON(MAY 1 THRU SEPTEMBER 30)-- THE CLEARING OF LAND. INCLULING TFE CSETTHEROL.OR 1 LING RECOMMENDED APP'Q EC SEED M:IXTUREEFOR ETOSWR
MOVAL OF EXISTING VEGETATION OR OTHER GROUND COVER.MUST BE LIMITED TO
NLY AS MUCH LAND AS CAN RECEIVE APPROPRIATE PROTECTIVE COVER OR BE PROPORTIONS PURITY GERMINATO
HERWISE STABILIZED,AFTER HAVING BEEN CLEARED OR OTHERWISE DISTURBED NAME BY WEIGHTW (X) W
Y N13 LATER THAN SEPTEMBER 30 13F A GIVEN YEAR.UNLESS IMMEDIATE
'TABA]ZATION IS SPECIFIED IN THE EROSION AND SEDIMENT CONTROL PLAN, ALL REETOP(AGROSTIS ALBA) 10 92 90
REAS CLEARED 13R OTHERWISE DISTURBED MUST BE APPROPRIATELY STABILIZED ANNUAL RYE (LOLIUM MULTIFLORUM) 4C 98 90
ROUTiH THE USE OF MULCHING.NETTING,PLASTIC SHEETING,EROSION BLANKETS, CHEWING FESLE 40 97 BO
REE DRAINING MATERIAL, ETC., BY SEPTEMBER 30 OR SOONER PER 114E APPROVED (FESTUCA RUBRA COMMUTATA)
AN OF ACTION, UNLESS QRE7RWISE APPROVED BY T-E COUNTY, SEEDING, (JAVESTOWN, BANNER, SHADOW, KOKET)
RTILIZING AND MULCHING OF CLEARED OR OTHERWISE DISTJRPEO AREAS SHALL BE WHITE DUTCH CLOVER 10 96 90
RFORMED DURING THE FOLLOWING PERIODS,MARCH 1 TO PAY 15,AND AUGUST L5 TO (TRIFOLIJM REPENS)
CTOBER L SEEDING AFTER O:TOBER 1 WILL BE DINE WHEN-MYSICAL COMPLETION
THE PROJECT IS IMMINENT AND THE ENVIWENTAL CONDITIONS ARE CONDUCIVE M..LCHONG
SATISFACTORY GROWTH IN THE EVENT THAT PERANENT STABILIZATION IS NUT
SSIBLE, AN ALTERNATIVE METHOD OF GROUND COVER, SU^H AS MULCHO\G, NETTING,L MATERIALS USED FOR MULCHING ARE RECOMMENDED TO BE WIND
ASTIC SHEETING,EROSION BLANKETS,ETC.,MUST BE INSTALLED BY NO LATER THAN FIBER CELLULOSE. AND SHlxLC BE APPLIED AT A RATE OF 1C00
PTEMBER 3C.
PO.,\ESA PER ACRE.
2,MULCH SHOULD BE APPLIED IN ALL AREAS WITH EXPOSED SLOPES
N THE EVENT THAT CONSTRUCTION ACTIVITIES IN OTHER SITE DEVELOPMENT _BEATER -HAN bl(HQRIZONTAL,VER7ICAL).
LTIVITIES ARE DISCONTINUED FOR AT LEAST 4 CONSECJTIVE DAYS, THE 3.MULCHING SHOULD BE USED IMMEDIATELY AFTER SEEDING OR IN
VNER/CONTRACTOR SHALL BE RESPONSIBLE FOR THE INSPECTION IF ALL EROSION AREAS WHICH CANNOT BE SEEDED BECAUSE OF THE SEASON,ALL
ND SEDIMENT CONTROL FACILITIES IMMEDIATELY AFTER STORM EVENTS, AND AT AREAS REQUIRING MULCH SHALL BE COVERED BY NOVEMBER L
LAST ONCE
ELZN CTOR MC FHEMAINTENNCE AND REPAIR IF ALL EROSION AN SEDIMENT CONTROL F4ILITIES,
TpPSObiNG
ET SEASON (OCTOBER I THRU APRIL 20)—ON SITES WHERE UNINTERUPTEO T C.:E TO HIGHLY
OF DENSE E
INSTRUCTION ACTIVITY IS IN PROGRESS. THE CLEARING OF LAND, INCLUDING THE EXPOSED SOBS.L TOPSOIL SHOULD BE USED FOR THIS PRp_E'-
MOVAL EXISTING VEGETATION AND OTHER GROLNC COVER.SHALL BE LIMITED
13 AS MUCH LAND AREA AS CAN BE COVERED OR STABBIZEC WITHIN 24 HOVERS IN 2 TOPSOIL SHOULD BE PLACED ON SLOPES NOT EXCEEDING bL
EVENT A MAJOR STORM IS PREDICTED AND/OR EROSION AND SEDIMENT 3.STRIPPING AND STOCKPILING ON-SITE SOBS SHALL ONLY BE
RANSPpRT IFF-SITE IS OBSERVED. PERMITTED IF TUPSOB IS FRIABLE AND LOAMY (LOAM,SANDY LOAM,
SILT LOAM, SANDY CLAY LOAM,CLAY LOAM%
ALL CLEARED OR DISTURBED AREAS SMALL RECEIVE APPROPRIATE PROTECTIVE 4,STRIPPING SHALL BE CONFINED TO THE IMMEDIATE CONSTRUCTION
OVER OR BE OTHERWISE STABILIZED,SJCH AS MULCHING, NETTING,PLASTIC AREAS A FOUR TO SIX INCH STRIPPING DEPTH IS .AMMON, BUT
HEETING,EROSION BLANKETS, FREE DRAINING MATERIAL.ETC„ WITHIN 5 DAYS AFTER DEPTH MAY VARY DEPENDING ON THE PARTICLLAR SOIL.ALL
WING BEEN CLEARED OF OTHERWISE DISTURBED IF NOT BEING ACTIVELY WORKED, SURFACE RUNOFF CONTROL STRUCTURES SHALL BE 1% PLACE BEFORE
ILT FENCING, SEDIMENT TRAPS, SEDIMENT PONDS,ETC., WILL NUT BE VIEWED AS STRIPPING.
DEDUATE COVER IN AND OF THEMSELVES.IN THE EVENT THAT ANY LAND AREA NUT
ING ACTIVELY WORKED REMAINS UMPRpTECTED IN HAS NOT BEEN APPROPRIATELY
TABILI2ED 5 DAYS AFTER HAVING BEEN CLEARED,AIL CONSTRUCTION ACTIVITY IN
SITE,EXCEPT FOR APPROVED EROSION AND SEDIMENT CONTROL ACTIVITY,SHALL
MMEDIATELY CEASE UNTIL SUCH A TIME AS AFOREMENTIONEC LANE AREA OAS SEEN
PPROPRIATELY PROTECTED OR STABILIZED.
STaKPLE MANAGEvm
1.STOCKPOJE SHALL BE STABILIZED(WITH PLASTIC ZOVERING OR OTHER APPRDVEC DEICE)DAILY HLTWQN NOVEMBER;AND MARCH
31.
I:IN ARY SEASON,SEDIMENT LEACHING FROM STOCK PIES M-ST BE PREVENTEL
3 TOPSOIL SHALL NUT HE PLACED WHILE IN A FROZEN IR MMuCDY CO%DITIDN,WHEN THE SLBGRACE IS EXCESSIVELY WET,IF WHEN
CDNttrm NS EXIST THAT MAY OTHERWISE BE CETR:MEMTAL TO PROPER GRADIMG Ot PROPOSED Mr,,..OR SEED, .
4.PREVIOUSLY ESTABLISHED r.RADES 1H THE AREAS TO HE TO'SOLEC SHALL BE MAINTAIEC ACCORDING TO THE APPROVED PUNS
STABILIZED C04STRLCTMN ENTRANCE
L MATERIAL SHALL BE 4 INCH TO B INCH QJARRY SPALLS(4 TO 6 INCH FOR RESIDENTIAL SINGLE FAMILY LOTS)AYE MAY BE
TOP-DRESSED WITH L INCH TO 3 INCH ROCK (STATE STANDARD SPECIFICATIONS. SECTION 8-15.)
2.THE ROCK PAD SHALL BE AT LEAST 12 INCHES THICK AND 50 FEET LONG(20 FEET Fdt SITES WITH LESS THAN 1 ACRE OF
DISTURBED SOB>.WIDTH SHALL BE F.AL WITH OF THE VEHICLE INGRESS AND EGRESS AREA.SMALLER PACS MAY BE APPROVED
FOR SINGLE-FAMILY RESIDENTIAL ANE SMALL COMMERCIAL SITES
3.ADDITIONAL ROCK SHALL BE ACDEC PERIOII'ALLY TO MAINTAIN PROPER FUNCTION OF THE PAD.
4.IF THE PAD DOLS NOT ACE=JATELY REMOVE THE MUD FROM THE VEHICLE WHEELS. THE WHEELS SHALL BE HOSED OFF BEFORE
THE VEHICLE ENTERS A PAVES STREET, THE WASHING SHALL BE DONE ON AN AREA COVERED WITH CRUSHED ROCK AND WASH
WATER SHALL DRAIN TO A SECDlEvT RETENTION FACILITY OR THROUGH A SILT FENCE.
ILT FENCE
GEOTE%TILE FILTER FABRIC TYPE SHALL BE PER SPECIFIED IN TIC'STORMWATER MANAGEMENT MA\,;AL
OR THE PUGET SOLND BASIN; OR APPLICABLE COUNTY STANDARDS
GEUTEXTILE FILTER FABRIC SHALL FE PURCHASED IN A CONTINUOUS ROLL CUT TO THE LENGTH IF
ACH BARRIER TO AVMC USE OF .:DINTS.IF JOINTS ARE NECESSARY,FILTER FABRIC SHALL BE SPLICED
OGETHER ONLY AT A SUPPOR? POST WITH A MINIMUM 6-INCH OVERLAP AND SECURELY FASTENED AT
OTH ENDS TO THE POST.
,STANDARD FILTER FABRIC SHALL BE FASTENED USING I'STAPLES OR TIE WIRES (HOG RINGS) 9 4 IN
PACING,
POSTS SHALL BE SPACED AND PLACED AT DEPTHS INDICATED IN THE DETAILS ON THIS SHEET,AND
RIVEN SECJRELY INTO THE GROUND,
WIRE MESH SHALL BE 2'XP'X14 GAUCE OR 0UIVILENT,THE WIRE MESH MAY BE ELIMINATED IF
XTRA-STRENSTH FILTER FABRIC(MONOFILAMENT),AND CLOSER POST SPACING IS USED.
A TRENCH SHALL BE EXCAVATED ACCORMN.,TO THE DETAILS ON THIS SHEET ALONG THE LINE OF THE
13STS AND J-SLOPE FROM THE SILT FENCE
Z.SILT FENCES SHALL BE LOCATED DOWNSL.O-E FROM THE CLEARING LV41TS OF THE PRO.)ECT.
APPENDIX E
DRAINAGE DETAILS
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