HomeMy WebLinkAboutGEO2019-00094 - BLD Engineering / Geo-tech Reports - 6/22/2018 Geotechnical Report
for
Williams Single Family Residence
51 E Westlake Drive S, Allyn
Parcel No. �"n'
Mason County, Washington
June 22, 2018
Project#1884
Prepared For:
Tyson Williams
12580 Schaefer Road , cL),�,.
Schertz, Texas 78108
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Prepared By:
Envirotech Engineering, PLLC
PO Box 984
Belfair, Washington 98528
Phone: 360-275-9374
r
MASON COUNTY
COMMUNITY SERVICES
Building,Planning,Environmental Health,Community Health Geotechnical Report
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 Intemational
Building Code Section for Foundations on or adjacent to slopes.
Applicant/Owner Tyson Williams Parcel# 12219-50-00067
Site Address 50 E Westlake Drive S, Allyn
(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, APPROVED
Located on page(s) 6 MASON COUNTY DCD PLANNING.
(c) A discussion of ground water conditions. SITE PLAN REQUIRED TO BE ON SITE
CH GES SUBJET TO APPROVAL
Located on page(s) 7
(d) A discussion of the upslope geomorphology..
y Date -
Located on page(s) 3
(e) A discussion of the location of upland waterbodies and wetlands,
Located on page(s) 3
(f) A discussion of history of landslide activity in the vicinity, as available in the referenced maps and records.
Located on page(s) 8
(2) A site plan which identifies the important development and geologic features.
Located on Map(s) Site Plan —Appendix A
(3) Locations and logs of exploratory holes or probes.
Located on Map(s) Site Plan and Soil Logs (Appendix B)
(4) The area of the proposed development, the boundaries of the hazard, and associated buffers and setbacks shall
be delineated (top. both sides, and toe)on a geologic map of the site.
Located on Map(s) Site Plan
(5) A minimum of one cross section at a scale which adequately depicts the subsurface profile, and which
incorporates the details of proposed grade changes.
Located on Map(s) Soil Profile (Appendix B)
(6) A description and results of slope stability analyses performed for both static and seismic loading conditions.
Analysis should examine worst case failures. The analysis should include the Simplified Bishop's Method of
Circles. The minimum static safety factor is 1.5. the minimum seismic safety factor is 1.1, and the quasi-static
analysis coefficients should be a value of 0.15.
Located on page(s) 9
Rev. February 2018
(7) (a) Appropriate restrictions on placement of drainage features,
Located on page(s) 15
(b) Appropriate restrictions on placement of septic drain fields.
Located on page(s) 17
(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) 16
(e) Recommended setbacks from the landslide hazard areas shoreline bluffs and the tops of other slopes.
Located on page(s) 15
(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) 16
(9) Recommendations for the preparation of a detailed temporary erosion control plan which identifies the specific
mitigating measures to be implemented during construction to protect the slope from erosion, landslides and
harmful construction methods.
Located on page(s) 10
(10) An analysis of both on-site and off-site impacts of the proposed development.
Located on page(s) 11
(11) Specifications of final development conditions such as, vegetative management, drainage. erosion control. and
buffer widths.
Located on page(s) 15 - 17
(12) Recommendations for the preparation of structural mitigation or details of other proposed mitigation.
Located on page(s) 17
(13) A site map drawn to scale showing the property boundaries, scale, north arrow, and the location and nature of
existing and proposed development on the site.
Located on Map(s) Site Plan
I, Michael Staten. hereby certify under penalty of perjury that I am a civil engineer licensed in the State of Washington
with specialized knowledge of geotechnicallgeological 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
Report dated June 22, 2018. and entitled Williams Single
,3111��� Family Residence, meets all the requirements of the Mason
County Resource Ordinance, Geologically Hazardous Areas
w Section, is complete and true,that the assessment
demonstrates conclusively that the risks posed by the landslide
a % p hazard can be mitigated through the included geotechnical
4,04: a
' design recommendations,and that all hazards are mitigated in
such a manner as to prevent harm to property and public health
and safety.
Page 2 of 2
Disclaimer: Mason County does not certify the quality of the work done in this Geotechnical Report.
Table of Contents
1.0 INTRODUCTION................................................«..................................................................................................I
1.1 PROJECT INFORMATION........................................................................................................................................1
1.2 PURPOSE OF INVESTIGATION AND SCOPE OF WORK.............................................................................................1
2.0 SURFACE CONDITIONS...................................».............................................................................................»...3
2.1 GENERAL OBSERVATIONS.....................................................................................................................................3
2.2 TOPOGRAPHY........................................................................................................................................................3
2.2.1 Upslope Geomorphology..............................................................................................................................3
2.3 SURFACE DRAINAGE..............................................................................................................................................3
2.3.1 Upslope Water Bodies..................................................................................................................................3
2.4 SLOPE AND EROSION OBSERVATIONS....................................................................................................................4
3.0 SUBSURFACE INVESTIGATION........................................................................................................................5
3.1 FIELD METHODS,SAMPLING AND FIELD TESTING................................................................................................5
3.2 GENERAL GEOLOGIC CONDITIONS.......................................................................................................................5
3.3 SPECIFIC SUBSURFACE CONDITIONS.....................................................................................................................6
3.3.1 Groundwater.................................................................................................................................................7
4.0 ENGINEERING ANALYSES AND CONCLUSIONS.....»..».......»..................».....»....».................
...........„.......8
4.1 SLOPE STABILITY..................................................................................................................................................8
4.1.1 Slope Stability Analysis................................................................................................................................9
4.2 EROSION..............................................................................................................................................................10
4 2.1 Shoreline Recession................................................................... ......10
..........................................................
4.3 SEISMIC CONSIDERATION'S AND LIQUEFACTION.................................................................................................10
43.1 Liquefaction................................................................................................................................................11
4.4 LANDSLIDE,EROSION AND SEISMIC HAZARDS CONCLUSIONS............................................................................11
4.5 LATERAL EARTH PRESSURES..............................................................................................................................1 1
4.6 ON-SITE AND OFF-SITE IMPACTS........................................................................................................................11
5.0 ENGINEERING RECOMMENDATIONS.........................................................................................................12
5.1 BUILDING FOUNDATION RECOMMENDATIONS....................................................................................................12
5.L I Bearing Capadty........................................................................................................................................
12
5.1.2 Settlement...................................................................................................................................................13
5.1.3 Concrete Stabs-on-Grade...........................................................................................................................13
5.2 EARTHWORK CONSTRUCTION RECOMMENDATIONS...........................................................................................13
5.2.1 Excavation..................................................................................................................................................13
5.2.2 Placement and ConFacdon ojNative Soils and Engineered Fill.............................................................13
5.2.3 Retaining Waft BackJill..............................................................................................................................14
S.2.4 Wet Weather Considerations......................................................................................................................1 S
5.2.5 Building Pads.............................................................................................................................................1 S
5.3 BUILDING AND FOOTING SETBACKS....................................................................................................................15
5.4 SURFACE AND SuBs RiFACE DRAINAGE...............................................................................................................1 S
5.5 VEGETATION BUFFER AND CONSIDERATIONS.....................................................................................................16
5.6 TEMPORARY AND PERMANENT EROSION CONTROL...........................................................................................16
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 51 E Westlake Drive S, identified as parcel number 12219-50-
00067, 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 April 17, 2018.
It was determined that slopes in excess of 40% with a vertical relief of at least 10 feet were
present within 300 feet of the planned development. Based on this site characteristic, the
proposed development will require a geotechnical report pursuant to Landslide Hazard Areas of
Mason County Resource Ordinance (MCRO) 17.01.100. During the site visit by Envirotech,
surface and subsurface conditions were assessed. After completion of the field work and
applicable project research, Envirotech prepared this geotechnical report which, at a minimum,
conforms to the applicable MCRO.
As presented herein, this report includes information pertaining to the project in this Introduction
Section; observations of the property and surrounding terrain in the Surface Conditions Section;
field methods and soil descriptions in the Subsurface Investigation Section; supporting
documentation with relation to slope stability, erosion, seismic considerations, and lateral earth
pressures in the Engineering Analyses and Conclusions Section; and, recommendations for
foundation, settlement, earthwork construction, retaining walls, erosion control, drainage, and
vegetation in the Engineering Recommendations Section.
1.1 Project Information
Information pertaining to the planned development of the project was provided by the proponent
of the property. The planned development consists of a 1- or 2-story single family residence, and
other ancillary features typical of this type of development. Approximate building footprint and
other proposed features with relation to existing site conditions are illustrated on the Site Map
provided in Appendix A of this report.
1.2 Purpose of Investigation and Scope of Work
The purpose of this geotechnical investigation is to assess geological hazards, and evaluate the
project in order to provide geotechnical recommendations that should be implemented during
development. The investigation included characterizing the general project surface and
subsurface conditions, and evaluating the suitability of the soils to support the planned site
activities.
In order to fulfill the purpose of investigation, the geotechnical program completed for the
proposed improvements of the project include:
• Review project information provided by the project owner and/ or owner's
representative;
• Conduct a site visit to document the site conditions that may influence the construction
and performance of the proposed improvements of the project;
• Define general subsurface conditions of the site by observing subsoils within test pits
and/ or cut banks, review geological maps for the general area, research published
Envirotech Engineering. PLLC _ 51 E Westlake Drive S
PO Box 984 page 1 Parcel 12219-50-00067
Belfair. Washin-ton 98528 Mason Count, Washington
Ph. 360-275-9374 June 22,2018
/ L
references concerning slope stability, and review water well reports from existing wells
near the project;
• Collect bulk samples,as applicable,at various depths and locations;
• Perform soils testing to determine selected index and/or engineering properties of the site
soils;
• Complete an engineering analysis supported by the planned site alterations, and the
surface and subsurface conditions that were identified by the field investigation, soil
testing,and applicable project research; and,
• Establish conclusions based on findings, and make recommendations for foundations,
drainage, slope stability, erosion control, earthwork construction requirements, and other
considerations.
Project
7
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Vicinity Map from Mason County Website
Envirotech Engineering. PLLC 51 E Westlake Drive S
PO Box 984 page 2 Parcel 12219-50-00067
Belfair. Washington 98528 Mason County. Washington
Ph. 360-275-9374 June 22.2018
2.0 SURFACE CONDITIONS
Information pertaining to the existing surface conditions for the project was gathered on April 17,
2018 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 an existing driveway. Vegetation on and near the project
consists primarily of secondary growth firs, maples, and other trees and shrubbery common to
this area of the Pacific Northwest. An aerial photo of the project and immediate vicinity is
provided on the following page.
2.2 Topography
The topographic information provided in this section was extrapolated from a public lidar source,
and incorporated observations and field measurements. Where necessary, slope verification
included measuring slope lengths and inclinations with a cloth tape and inclinometer. See the Site
Plan in Appendix A in this report for an illustration of general topography with respect to the
planned development.
Critical descending slopes, with grades exceeding 40% appear to be within 300 feet of the
planned development. The maximum critical slope is approximately 42% with a vertical relief of
about 25 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.
2.3 Surface Drainage
Runoff originating upslope of the development is mostly diverted away from the property by
accommodating topography. Excessive scour, erosion or other indications of past drainage
problems were not observed within the immediate vicinity of the planned development.
2.3.1 Upslope Water Bodies
There are no apparent water bodies or wetlands located upslope from the planned
development that would significantly influence the project.
Envirotech Engineering, PLLC 51 E Westlake Dri,,e S
PO Box 984 page 3 Parcel 12219-50-00067
Belfair. Washington 98528 Mason County, Washington
Ph. 360-275-9374 June 22,2018
2.4 Slope and Erosion Observations
The slope gradients near the project signal a potential landslide or erosion hazard area. Some
indicators that may suggest past slope movements include:
• Outwash of sediments near the bottom of the slope,
• Fissures, tension cracks, hummocky ground or stepped land masses on the face or top of
the slope,and parallel to the slope,
• Fine, saturated subsurface soils,
• Old landslide debris.
• Significant bowing or leaning trees, or,
• Slope sloughing or calving.
These slope instability indicators or other significant mass wasting on the property or within the
general vicinity of the project were not observed or discovered during research. Indications of
past landslides, current unstable slopes, deep-seated slope problems, or surficial slope failures
were not observed during the site visit.
low-
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Aerial Photo from Google Website
Envirotech Engineering. PLLC 51 E Westlake Drive S
PO Box 984 v pa e-+ Parcel 12219-50-00067
Belfair. Washinuton 98528 Mason County, Washington
Ph. 360-275-9374 June 22,2018
- r
3.0 SUBSURFACE INVESTIGATION
Information on subsurface conditions pertaining to the project was primarily gathered on April
17,2018 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 4.5 feet below the natural ground
surface. Information on subsurface conditions also included reviewing geological maps
representing the general vicinity of the project.
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 24 inches, and very
dense soils from 48 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, Qe. Quaternary sediments are generally unconsolidated
deposits, and dominantly deposited from glacial drift, including alluvium deposits. This project is
located within the Puget Lowland. Typically, "lower tertiary sedimentary rocks unconformably
overlie the Crescent Formation."as revealed in the Geologic Map. Initial sedimentary rocks were
formed from shales, sandstones and coal deposits from rivers. During the Quaternary period, the
Puget Lowland was covered by numerous ice sheets,with the most recent being the Fraser glacier
with a peak of approximately 14,000 years ago. Upon the glacial retreat, the landscape was
formed by glacial erosion glacial drift deposits.
The "Geologic Map of the Belfair 7.5-minute Quadrangle, Mason, Kitsap and Pierce Counties,
Washington" by Michael Polenz, Katelin Alldritt, Nicholas J. Hehemann, Isablle Y. Sarikhan,
and Robert L.Logan,July 2009, provides the following caption(s)for the project area:
Envirotech Engineering. PLLC J 51 E Westlake Drive S
PO Box 984 page 5 Parcel 12219-50-00067
Belfair. Washington 98528 Mason County, Washington
Ph. 360-275-9374 June 22.2018
Ogt Vashou till—unsorted. unstratified(but locally banded.) mix of clay. silt.
saiid. and gravel, tvpically supported by a sandv nianix. mostly gray but
locall-v rangilig to tii. light brown. or orange. typicilly unweathered,
lodgment till compact. With well-developed ficies resembling concrete.
but clear the surface conlnlon1v hackl•and (or) looser and covered by I to
6 ft of loose ablation till. deposited directlt- b1• elacial ice and eoninionly
includes clasts or chiIllps plucked from underlying units C lasts are
conullon1v strtited and faceted. with angular or rounded edges Boulders
are generally sparse within the till but large (erratic)boulders of plutonic
or nietainorphic rock are conullon on till surfaces Some exposuies include
interbands and lenses of sand and 21 ivel. locally with ,hears and touits.
Till forins a locally pitchy and seerlullgly randomly distributed covet tip to
a several tens of feet thick. with a thickness of> to 20 ft inost coilulion It
typically dominates. but is also locally discontinuous on, fluted surfaces.
with individual drunllun, measuring 0 1 to 0 3 nil wide by 0 S to 1 3 till
long and the lone ams aligned with the direction of ice floe\-. Till tvpicilly
is ui sharp, wicontorinible contact will underIvina units. illo4t conlilloilly
advance outwash (unit Qga and subunit) Unit Qgt lie- Stratigraplucill'
below unit Qgo It nmy include unrecognized exposures of older till.A
inap boundary Illismatch between unit Qgt on this nlap aIld unit Qgos on
the V allelul quadiangle to the south (Logan and NValsh. 21007)tllay 11,zve
resulted from a neap-production error in the northwest confer of the
Vaughn niap(Josh Logan. Wash Divn. of Geology and Earth Resources.
oral coiluawl . 2,009)
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Project
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Geological Map Department of Natural Resources Washington State
3.3 Specific Subsurface Conditions
The following subsurface conditions are estimated descriptions of the project subgrade utilizing
information from the depth of penetration at all testing, sampling, observed and investigated
locations. Soils for this project were primarily described utilizing the Unified Soil Classification
Envirotech Engineering. PLLC 51 E Westlake Drive S
PO Box 984 page 6 Parcel 12219-50-00067
Belfair, Washington 98528 Mason County. Washington
Ph. 360-275-9374 June 22.2018
System(USCS)and the Soil Conservation Service(SCS)descriptions.
The project is currently composed of native soils without indications of fill. Within test pit
locations, soils within the upper 4 feet of natural ground were generally observed to be moist,
brown silty sand with gravel (SM). Soils below the upper 4 feet layer were observed to be mostly
grey, low moisture, silty sand with gravel (SM), locally known as hardpan. The hardpan may
extend to depths greater than 50 feet. This is based on nearby well reports, site geology, and/ or
knowledge of the general area.
The relative densities of the soil within selected test pits are provided above in Section 3.1.
Expanded and specific subsurface descriptions, other than what is provided in this section, are
provided in the soil logs located in Appendix B of this report.
According to the "Soil Survey of Mason County," by the United States Department of
Agriculture, Soil Conservation Service, the site soils are described as Alderwood Gravelly Sandy
Loam, Ab, with 8% - 15% slopes, and Alderwood Gravelly Sandy Loam, A,, with 15% - 30%
slopes. The soil designations are depicted in the aerial photograph below, and descriptions are
provided in Appendix B of this report.
>,f 71
1
Soil Survey From USDA Natural Resources Conservation Service
3.3.1 Groundwater
From the water well report(s)and knowledge of the general area, permanent groundwater
is at least 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.PLLC 51 E Westlake Drive S
PO Box 984 page 7 Parcel 12219-50-00067
Belfair, Washington 98528 Mason County, Washington
Ph. 360-275-9374 June 22.2018
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.
The project is not located within the coastal atlas zone.
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:
1
1
t-. Project �-
Resource Map from Washington State Department of Natural Resources Website
Envirotech Engineering. PLLC 51 E Westlake Drive S
PO Box 984 page 8 Parcel 12219-50-00067
Belfair. Washington 98528 Mason County, Washington
Ph. 360-275-9374 June 22.2018
1 1
SOILS—On Resource Uy only
H,Aric Sods
Highly Unstable
Hi2hly Erodible
Hithh:'nstai;le d:
10 Data or Gravel
Pits
SLOPE—On Resource alas onh
Medium Slope
Instability
High Slope Instability
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 5 feet soil depth
Soil unit weight: 135 pcf
Angle of internal friction: 34 degrees
Cohesion: 0 psf
Soils below 5 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 1.6 and 1.1, respectively.
See the slope stability information in Appendix C for a depiction of input parameters and
example of outputs.
Envirotech Engineering. PLLC 51 E Westlake Drive S
PO Box 984 page 9 Parcel 12219-50-00067
Belfair. Washington 98528 Mason County. Washington
Ph. 360-275-9374 June 22,2018
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.
4.2.1 Shoreline Recession
The Project is not located along a shoreline.
4.3 Seismic Considerations and Liquefaction
There are no known faults beneath this project. The nearest Class 'A' or Class 'B' fault to this
property is the Tacoma Fault Zone, in which is approximately 3700 feet 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.
Envirotech Engineering. PLLC 51 E Westlake Drive S
PO Box 984 page 10 Parcel 12219-50-00067
Belfair, Washington 98528 Mason County, Washington
Ph. 360-275-9374 June 22,2018
4.3.1 Liquefaction
The potential for liquefaction is believed to be very low to low for this project. This is
based, in part, on the subsurface conditions such as soil characteristics and the lack of a
permanent shallow water table. Subgrade characteristics that particularly contribute to
problems caused from liquefaction include submerged, confined, poorly-graded granular
soils (i.e. gravel, sand, silt). Although gravel- and silt-sized soil particles could be
problematic, fine and medium grained sands are typically subjected to these types of
seismic hazards. No significant saturated sand stratifications are anticipated to be within
the upper 50 feet of the subsoil for this project.
4.4 Landslide,Erosion and Seismic Hazards Conclusions
DNR 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, PLLC 51 E Westlake Drive S
PO Box 984 page 1 1 Parcel 12219-50-00067
Belfair, Washington 98528 Mason County, Washington
Ph. 360-275-9374 June 22,2018
5.0 ENGINEERING RECOMMENDATIONS
The following sections present engineering recommendations for the proposed improvements of
the project. These recommendations have been made available based on the planned
improvements as outlined in the Introduction Section of this report; general observations
including drainage and topography as recapitulated in the Surface Conditions Section; soil/
geologic conditions that were identified from the geotechnical investigation that is summarized in
the Subsurface Investigation Section; and, project research, analyses and conclusions as
determined in the Engineering Analysis and Conclusions Section. Recommendations for the
project that is provided herein, includes pertinent information for building foundations, earthwork
construction, building and/ or footing setbacks, drainage, vegetation considerations, and erosion
control.
5.1 Building Foundation Recommendations
Recommendations provided in this section account for the site development of a typical one- or
two-story, single family residential structure. The recommended allowable bearing capacities and
settlements as presented below, consider the probable type of construction as well as the field
investigation results by implementing practical engineering judgment within published
engineering standards. Evaluations include classifying site soils based on observed field
conditions and soil testing for this project. After deriving conservative relative densities, unit
weights and angles of internal friction of the in-situ soils, the Terzhagi ultimate bearing capacity
equation was utilized for determining foundation width and depth. Foundation parameters
provided herein account for typical structural pressures due to the planned type of development.
A structural analysis is beyond the scope of a geotechnical report, and a structural engineer may
be required to design specific foundations and other structural elements based on the soil
investigation. Stepped foundations are acceptable, if warranted for this project. Continuous,
isolated, or stepped foundations shall be horizontally level between the bottom of the foundation
and the top of the bearing strata. The frost penetration depth is not expected to extend beyond 12
inches below the ground surface for this project under normal circumstances and anticipated
design features.
5.1.1 Bearing Capacity
Existing in-situ soils for this project indicates that the structure can be established on
shallow, continuous or isolated footings. Foundations shall be established on relatively
undisturbed native soil that is competent and unyielding. Alternatively, foundations may
be constructed on selective re-compacted native soil or compacted engineered fill as
described in the Earthwork Construction Recommendations Section of this report.
For a bearing capacity requirement of no more than 1500 psf, a minimum continuous
footing width of 13 inches(17 inches for 2-story structures)shall be placed at a minimum
of 24 inches below the existing ground surface atop unyielding soils. For a columnar load
of no more than 3 tons,a circular or square isolated foundation diameter or width shall be
at least 24 inches. Foundation recommendations are made available based on adherence
to the remaining recommendations that are provided in this report. Alterations to the
aforementioned foundation recommendations may be completed upon a site inspection by
a geotechnical engineer after the foundation excavation is completed.
Envirotech Engineering, PLLC 51 E Westlake Drive S
PO Box 984 page 12 Parcel 12219-50-00067
Belfair. Washington 98528 Mason County, Washington
Ph. 360-275-9374 June 22,2018
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.
5.2.2 Placement and Compaction of Native Soils and Engineered Fill
For engineered fill or disturbed native soils that will be utilized as fill material directly
beneath foundations, observation and/ or geotechnical testing is required prior to
Envirotech Engineering, PLLC 51 E Westlake Drive S
PO Box 984 rake I, Parcel 1 22 1 9-50-00067
Belfair. Washington 98528 Mason County, Washington
Ph. 360-275-9374 June 22,2018
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.
FD❑TING
COMPACTED
NATIVE SOILS
FOR
ILL ENGINEERED j' t
1
411
II 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 IN, Finer(by weight)
6" 100
Y 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.
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
Em irotech Enaineering.PLLC 51 E Westlake Drive S
PO Box 984 page 14 Parcel 1 22 1 9-50-00067
Belfair. Washington 98528 Mason County, Washington
Ph. 360-275-9374 June 22.2018
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.
5.2.5 Building Pads
Building pads are not expected for this project
5.3 Building and Footing Setbacks
Provided that assumptions relating to construction occur and recommendations are followed as
presented in this report, the factor of safety for slope stability is sufficient for a 18 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.
Iri S 7 R,J,-T-kE
J.
From the illustration above, structures may be located closer to the top of slope by extending the
foundation deep enough to maintain the recommended setback. In addition, the required setback
may be reduced by mitigation, and subsequently would require additional geotechnical studies.
5.4 Surface and Subsurface Drainage
Positive drainage should be provided in the final design for all planned residential buildings.
Drainage shall include sloping the ground surface, driveways and sidewalks away from the
project structures. All constructed surface and subsurface drains should be adequately maintained
during the life of the structure.If drainage problems occur during or after construction, additional
engineered water mitigation will be required immediately. This may include a combination of
swales, berms,drain pipes, infiltration facilities, or outlet protection in order to divert water away
from the structures to an appropriate protected discharge area. Leakage of water pipes, both
drainage and supply lines,shall be prevented at all times.
Envirotech Engineering.PLLC 51 E Westlake Drive S
PO Boa 984 page 15 Parcel 12219-50-00067
Belfair. Washington 98528 Mason County. Washington
Ph. 360-275-9374 June 22,2018
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 8 feet beyond the top of the slope. However, any tree deemed hazardous to life or
property shall be removed. If tree removal is necessary, then stumps and roots shall remain in
place. and the underbrush and soil shall remain undisturbed as much as possible. Any disturbed
soil shall be graded and re-compacted in order to restore the terrain similar to preexisting
conditions and drainage patterns. See the Site Plan in Appendix A of this report for a depiction of
the vegetation buffer.
5.6 Temporary and Permanent Erosion Control
Erosion control during construction should include minimizing the removal of vegetation to the
least extent possible. Erosion control measures during construction may include stockpiling
cleared vegetation, silt fencing, intercepting swales, berms, straw bales, plastic cover or other
standard controls. Although other controls may be used, if adequate, silt fencing is presented in
this report as the first choice for temporary erosion control. Any erosion control should be located
down-slope and beyond the limits of construction and clearing of vegetation where surface water
is expected to flow. If the loss of sediments appears to be greater than expected, or erosion
control measures are not functioning as needed, additional measures must be implemented
immediately. See Appendix D for sketches and general notes regarding selected erosion control
measures. The Site Plan in Appendix A depicts the recommended locations for erosion control
facilities to be installed as necessary.
Permanent erosion control 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
Envirotech Engineering. PLt.0 51 F Westlake Drive S
PO Box 984 page 16 Parcel 12219-50-00067
Belfair. Washington 98528 Mason County. Washington
Ph. 360-275-9374 June 22.2018
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 project is expected to connect to a public sewer system.
5.8 Structural Mitigation
With respect to landslide alleviation or slope improvements, structural mitigation is not necessary
for this project. This determination is based on the anticipated improvements of the project,
engineering conclusions,and compliance with all recommendations provided in this report.
Envirotech Engineering. PLI.0 51 E Westlake Drive S
PO Box 984 page 17 Parcel 1 22 1 9-50-00067
Belfair. Washington 98528 Mason County. Washin-ton
Ph. 360-275-9374 June 22,2018
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
Robert McNearny, E.I.T. Michael Staten,P.E.
Staff Engineer Geotechnical Engineer
Envirotech Engineering.PLLC 51 E Westlake Drive S
PO Box 984 page 18 Parcel 12219-50-00067
Belfair. Washington 98528 Mason County, Washington
Ph. 360-275-9374 June 22.2018
APPENDIX A
SITE PLAN
CONSTRUCTION
ENVELOPE SCALE: 1,=40'
rml -
0 10 20 40
/T P
/ STREAM
SILT FENCE DISSIPATION TEE
1D' CONSTRUCTION SETBACK ---' PROPSED DRAINAGE
TICiHTLINE TO STREAM
8' VEGETATED BUFFER �
-- TOE Elf- SLOPE
TOP OF SLOPE / EXCEEDING 4%
EXCEEDING 40'/.
PROJECT/ OWNER/ LOCATION-
NOTES
1, EROSION CONTROL MAY BE REQUIRED FOR THIS SITE, GENERAL LOCATIONS SINGLE FAMILY RESIDENCE
ARE DEPICTED, AND ALTERNATIVES MAY BE UTILIZED AS EXPLAINED IN THE GEOTECHNICAL REPORT
GEOTECHNICAL REPORT.
2. CONTOURS WERE NOT PREPARED BY A LICENSED LAND SURVEYOR. WILLIAMS
CONTOURS WERE EXTRAPOLATED FROM A PUBLIC LIDAR SOURCE, AND 51 E WESTLAKE DRIVE S
INCORPORATED FIELD MEASUREMENTS AS EXPLAINED IN THE GEOTECHNICAL LEGEND PARCEL 12219-50-00067
REPORT. MASON COUNTY WASHINGTON
3. BOUNDARIES WERE NOT PREPARED BY A LICENSED SURVEYOR. LOCATIONS TEMPORARY ENGINEER-
OF SITE FEATURES THAT ARE SHOWN HERE, SUCH AS TOP OF SLOPES, TOE EROSION CONTROL ENVIROTECH ENGINEERING
OF SLOPES, WATER FEATURES, ETC.., WITH RELATION TO THE PROPERTY P❑ BOX 984
LINES MUST BE VERIFIED BY THE OWNER. RECOMMENDATIONS IN THE SLOPE INDICATOR BELFAIR, WASHINGTON 98528
GEOTECHNICAL REPORT PROVIDE SETBACKS, BUFFERS, DEPTHS, ETC.. WITH 360-275-9374
RELATION TO GEOLOGIC FEATURES, NOT PROPERTY LINES, THESE GEOLOGIC EXISTING CONTOUR
FEATURES MAY BE LOCATED ON THE SUBJECT PROPERTY OR NEIGHBORING TP TEST PIT SITE. PLAN
PROPERTIES.
1 �
APPENDIX B
SOIL INFORMATION
VERTICAL AND HORIZONTAL SCALE,
SCALE: I"=20'
0 5 10 20 J
PROPOSED STRUCTURE
EXISTING GRADE
-- ---- -----� SILTY SAND
W/ GRAVEL (SM)
VERY DENSE \ ��
GLACIAL TILL
SECTION A-A
PROJECT/ ❑WNER/ LOCATION,
SINGLE FAMILY RESIDENCE
GEOTECHNICAL REPORT
WILLIAMS
51 E WESTLAKE DRIVE S
PARCEL 12219-50-00067
MASON COUNTY, WASHINGTON
NOTES
ENGINEER
1) MINOR GRADE CHANGES REQUIRED IN ❑RDER TO ACHIEVE ENVIROTECH ENGINEERING
POSITIVE DRAINAGE PO BOX 984
2) THE SOIL PROFILE IS ACCURATE FOR THE DEPTH OF BELFAIR, WASHINGTON 98529
THE OBSERVED TEST PITS AT THE SPECIFIED LOCATIONS. 360-275-9374
LOWER DEPTHS ARE BASED ON SITE GEOLOGY,
WELL LOG(S), AND/OR EXPERIENCE IN THE GENERAL AREA. SOIL PROFILE
TEST PIT LOG
TEST PIT NUMBER TP-1
PROJECT: Williams Geotechnical Report DATE OF LOG: 4/18/2018
PROJECT NO: 1884 LOGGED BY: MCS
CLIENT: Tyson Williams EXCAVATOR: N/A
LOCATION: Parcel 12219-50-00067 DRILL RIG: None
Mason County, Washington ELEVATION: N/A
INITIAL DEPTH OF WATER: N/A FINAL DEPTH OF WATER: N/A
SOIL STRATA. STANDARD PENETRATION TEST
DEPTH SAMPLERS USCS DESCRIPTION LL PI CURVE
AND TEST DATA DEPTH N 10 30 50
0 . . . . . . .
SM Brown; moist. loose to medium dense
SILTY SAND with GRAVEL. Gravel is
primarily well-graded and subangular.
1 Sand is mostly medium. Low plasticity.
2
3
4
Light brown, dense
Excavation terminated at approximately
5 4.5 feet
6
7
8
9
10
No Groundwater Encountered ENVIROTECH ENGINEERING
This information pertains only to this boring and should not be Geotechnical Engineering
interpreted as being indicative of the entire site.
Map Unit Description:Alderwood 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 statewide importance
Map Unit Composition
Alderwood and similar soils: 85 percent
Minor components: 15 percent
Estimates are based on observations descriptions, and transects of
the mapunit.
Description of Alderwood
Setting
Landform: Ridges. hills
Landform position (two-dimensional): Backslope
Landform position (three-dimensional): Side slope; nose slope. talf
Down-slope shape. Linear. convex
Across-slope shape: Convex
Parent material. Glacial drift and/or glacial outwash 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
2Cdl -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(Ksat): Very
low to moderately low (0.00 to 0.06 in/hr)
Depth to water table: About 18 to 37 inches
Frequency of flooding: None
Frequency of ponding: None
Available water storage in profile: Very low (about 2.7 inches)
Interpretive groups
Land capability classification (irrigated): None specified
Land capability classification (nonirrigated): 4e
Hydrologic Soil Group: B
21, Natural Resources Web Soil Survey 6/22/2018
Conservation Service National Cooperative Soil Survey Page 1 of 2
Map Unit Description:Alderwood gravelly sandy loam, 15 to 30 percent slopes—Mason
County Washington
Forage suitability group. Limited Depth Soils (G002XN302WA).
Limited Depth Soils (G002XF303WA), Limited Depth Soils
(G002XS301 WA)
Hydric soil rating: No
Minor Components
Everett
Percent of map unit: 5 percent
Landform: Kames. eskers. moraines
Landform position (two-dimensional): Backslope
Landform position (three-dimensional): Side slope
Down-slope shape: Convex
Across-slope shape: Convex
Hydric soil rating: No
Indianola
Percent of map unit: 5 percent
Landform: Kames, terraces. eskers
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: Drainageways. depressions
Landform position (three-dimensional): Dip
Down-slope shape: Linear. concave
Across-slope shape: Concave
Hydric soil rating: Yes
Data Source Information
Soil Survey Area. Mason County, Washington
Survey Area Data: Version 13. Sep 7. 2017
UriNatural Resources Web Soil Survey 512212018
Conservation Service National Cooperative Soil Survey Page 2 of 2
APPENDIX C
SLOPE STABILITY
STABLE Slope Stability Analysis System
New User
Project : WILLIAMS
Datafile: STATIC Bishop
STaB:E "version 9.03.00u
Bishop
«r+rx.rrr.r.r•r.rr.r.xrr..r«««.r...rrr.r:*.•.++.+....:...«
TITLE
STATIC
UNITS (Metric/Imperial) I
++rrrr++rrxr.rrrr+rrrxxrrr+x:xrrrxxrrrxx+rir+xr++rrx++rxxr
GEOMETRY DEFINITION
POINTS
NO. X Y
1 0.000 0.000
2 50.000 0.000
3 110.000 -25.000
4 120.000 -25.000
5 0.000 -4.000
6 50.000 -4.000
7 110.000 -29.000
6 120.000 -29.000
9 12.000 0.000
10 17.050 0.000
11 22.110 0.000
12 27.160 0.000
13 32.210 0.000
14 37.260 0.000
15 42.320 0.000
16 47.370 0.000
17 52.420 -1.010
18 57.470 -3.110
19 62.530 -5.220
20 67.580 -7.320
21 72.630 -9.430
22 77.680 -11.540
23 82.740 -13.640
24 87.790 -15.750
25 92.840 -17.850
26 97.890 -19.960
27 102.950 -22.060
28 108.000 -24.110
LINES
Lo X Hi X SOIL
1 2 1
2 3 1
3 4 -
5 6 2
6 7 2
7 8 2
r rrrrrr++r++tr+xrrrrrxxrr.rrrx.rxrrrxexr.x+rrxxxrrxr rrrrx+
SOZLS
SOIL NAME LINETYPE-PEN COHESION FRICTION UNIT WT.
STABLES'2002 MZAssociates Ltd Printed on: 22/06118 @ 13:48:14 Page• 1
STABLE Slope Stability Analysis System
New User
Project WILLIAMS
Datafile: STATIC Bishop
1 SM CONTINUOUS-BLACK 0.00 32.0 '-34.0c0
2 HP CONTINUOUS-BLUE 400.00 40.0 140.000
PORE PRESSURE SPECIFICATION
SOIL PIEZO RU EXCESS
Y/N/P Value Value
1 N 0.000 0.000
2 N 0.000 0.000
PIEZOMETRIC SURFACE
POINT
POINI PORE PRESSURES
POINT PRESSURE
SLIP DIRECTION (+/- X) - +
SLIP-CIRCLES
AUTOMATIC
Circle Centre Grid Extremities
96.000
12.000 + } 108.000
0.000
X spacing -- no. of cols (max 10)- 10
Y spacing -- no. of rows (max 20)- 20
Grid 1 Circles through point 9
Grid 2 Circles through point 10
Grid 3 Circles through point 11
Grid 4 Ci:cles through point 12
Grid 5 Circles through point 13
Grid 6 Circles through point 14
Grid 7 Circles through point 15
Grid 8 Circles through point 16
Grid 9 Circles through point 17
Grid 10 Circles through point 18
Grid 11 Circles through point 19
Grid 12 Circles through point 20
Grid 13 Circles through point 21
Grid 14 Circles through point 22
STABLE02002 MZ Associates Ltd Printed on: 22'06'18 @ 13:48:14 Page: 2
1 . 00
1 _ 1 O
1 . 2 O
1 _ 3 O
x 5; 1 . 40
1 . 50
1 . 6 O
1 . 7 0
1 . 80
1 _ 90
2 _ 00
n:*r
.---------
4_� O- 8 _ 506
0...
L�roject. WTLL2AMS
Datafile STATIC
Analysts B3.sY,op
f 1
1 7 O
1 . 2 O
1 . 30
1 _ 7 O
1 . 80
1 . 9 O
�c
o : 2 _ OO
i
d
't^
1 . 238
Project: WSLLSAMS
Datafile DYNAM=C
Ana 7_y op
APPENDIX D
EROSION CONTROL
GEOTEXTILE FABRIC GEOTEXTILE FABRIC
BET
WRAP AROUND TRENCH 2'x2' WOOD POST AND WIRE MESH
TO AT LEAST ENTIRE OR EQUIVALENT OR BETTER
BOTTOM OF TRENCH 2 6 FT MAX. O.C. 0.5 FT
BEFORE PLACING GRAVEL 21x2'x5' WOOD POST OR 6 FT -----I
12' DEEP, 8' WIDE TRENCH EQUIVALENT OR BETTER EXISTING
FILLED WITH 3/4' TO 1 1/2'1 GROUND SURFACE 2 T I
WASHED GRAVEL or VEGETATION 1
AnApeppal
DIRECTION OF --y y 2.5jFt 12' DEEP, 8' WIDEINNER
WATER FLOW EXISTING GROUND SURFACE TRENCH FILLED WITH 1 T
12' 3/4' TO 1 1/2' 2.5 FT
+ WASHED GRAVEL OR
2,SfFT
VEGETATION
8•f- BOTTOM EXTENTS OF
GEOTEXTILE FABRIC SILT FENCE - DETAIL
SILT FENCE - CROSS SECTION N.T.S.
N.T.S. HAY OR STRAW MATTING
ENERAL NOTES- 1. STRAW SHALL BE AIR DRIED, AND FREE FROM WEED SEEDS AND
COARSE MATERIAL.
SHOULD THE TEMPORARY EROSION AND SEDIMENT CONTROL MEASURES SHOWN ON 2. APPLY AT APPROXIMATELY 75 TO 100 POUNDS PER 1000 SQUARE
HESE PLANS PROVE TO BE INADEQUATE DURING CONSTRUCTION, THE CONTRACTOR FEET OF GROUND.
HALL INSTALL ADDITIONAL EROSION AND SEDIMENT CONTROL FACILITIES, 3. MINIMUM THICKNESS SHALL BE 2 INCHES.
ALL EROSION AND SEDIMENT CONTROL FACILITIES AND DEVICES SHALL BE 4. HAY OR STRAW IS SUBJECT TO BLOWING. KEEP MOIST OR TIED
NSPECTED DAILY AND IMMEDIATELY MAINTAINED, IF NECESSARY. DOWN.
ALL EROSION AND SEDIMENT CONTROL FACILITIES AND DEVICES SHALL BE LEFT IN
LACER NTIERO EONPCOQTROAREAS HAVE BEEN PERMANENTLY STABILIZED, PERMANENT EROSION CONTROL NOTES,
EMPS.
OR ALL AREAS WHICH HAVE BEEN STRIPPED OF VEGETATION OR EXPERIENCED LAND SEEDING FOR RAW SLOPES
ISTURBING ACTIVITIES, AND WHERE NO FURTHER WORK IS ANTICIPATED FOR A 1. BEFORE SEEDING, INSTALL NEEDED SURFACE RUNOFF CONTROL
ERIOD EXCEEDING THE LISTED CRITERIA BELOW, ALL DISTURBED AREAS MUST BE MEASURES SUCH AS GRADIENT TERRACES, INTERCEPTOR DIKES,
MMEDIATELY STABILIZED WITH MULCHING, GRASS PLANTING OR OTHER APPROVED SWALES, LEVEL SPREADERS AND SEDIMENT BASINS.
ROSION CONTROL TREATMENT APPLICABLE TO THE TIME OF YEAR. GRASS SEEDING 2. THE SEED BED SHALL BE FIRM WITH FAIRLY FINE SURFACE,
%LONE WILL ONLY BE ACCEPTABLE DURING THE MONTHS OF APRIL THROUGH FOLLOWING SURFACE ROUGHENING, PERFORM ALL OPERATIONS ACCROSS
EPTEMBER. HOWEVER, SEEDING MAY PROCEED WHENEVER IT IS IN THE INTEREST OF OR PERPENDICULAR TO THE SLOPE.
HE OWNER/CONTRACTOR, BUT MUST ALSO BE AUGMENTED WITH MULCHING, NETTING 3. SEEDING RECOMMENDATIONS, AS SHOWN BELOW, AND SHOULD BE
R OTHER APPROVED TREATMENT. APPLIED AT THE RATE OF 120 POUNDS PER ACRE.
DRY SEASON (MAY 1 THRU SEPTEMBER 30) -- THE CLEARING OF LAND, INCLUDING THE 4. SEED BEDS PLANTED BETWEEN MAY i AND OCTOBER 31 WILL
REMOVAL OF EXISTING VEGETATION OR OTHER GROUND COVER, MUST BE LIMITED TO REQUIRE IRRIGATION AND OTHER MAINTENANCE AS NECESSARY T❑
NLY AS MUCH LAND AS CAN RECEIVE APPROPRIATE PROTECTIVE COVER OR BE FOSTER AND PROTECT THE ROOT STRUCTURE.
THERWISE STABILIZED, AFTER HAVING BEEN CLEARED OR OTHERWISE DISTURBED , 5. SEED BEDS PLANTED BETWEEN N 1 AND APRIL 30,
ARMORING OF THE SEED BED WILL BE NE
BE NE ER
Y NO LATER THAN SEPTEMBER 30 OF A GIVEN YEAR. UNLESS IMMEDIATE NECESSARY, (e.g.,
TABILIZATION IS SPECIFIED IN THE EROSION AND SEDIMENT CONTROL PLAN, ALL GEOTEXTILES, JUTE MAT, CLEAR PLASTIC COVERING),
REAS CLEARED OR OTHERWISE DISTURBED MUST BE APPROPRIATELY STABILIZED 6. FERTILIZERS ARE TO BE USED ACCORDING SUPPLIERS'
HROUGH THE USE OF MULCHING, NETTING, PLASTIC SHEETING, EROSION BLANKETS, RECOMMENDATIONS, AMOUNTS SHOULD MINIMIZED, ESPECIALLY
REE DRAINING MATERIAL, ETC., BY SEPTEMBER 30 OR SOONER PER THE APPROVED ADJACENT T❑ WATER BODIES AND WETLANDS,
LAN OF ACTION. UNLESS ❑THERWISE APPROVED BY THE COUNTY, SEEDING, USE THE FOLLOWING RECOMMENDED SEED MIXTURE FOR EROSION
ERTILIZING AND MULCHING OF CLEARED OR OTHERWISE DISTURBED AREAS SHALL BE CONTROL, OR A COUNTY APPROVED ALTERNATE SEED MIXTURE.
ERFORMED DURING THE FOLLOWING PERIODS: MARCH 1 TO MAY 15, AND AUGUST 15 TO
CTOBER 1. SEEDING AFTER OCTOBER 1 WILL BE DONE WHEN PHYSICAL COMPLETION PROPORTIONS PURITY GERMINATION
F THE PROJECT IS IMMINENT AND THE ENVIROMENTAL CONDITIONS ARE CONDUCIVE NAME BY WEIGHT(%) (7) (%)
0 SATISFACTORY GROWTH. IN THE EVENT THAT PERANENT STABILIZATION IS NOT
OSSIBLE, AN ALTERNATIVE METHOD OF GROUND COVER, SUCH AS MULCHING, NETTING, REDTOP (AGROSTIS ALBA) 10 92 90
LASTIC SHEETING, EROSION BLANKETS, ETC., MUST BE INSTALLED BY NO LATER THAN ANNUAL RYE (LOLIUM MULTIFLORUM) 40 98 90
EPTEMBER 30. CHEWING FESUE 40 97 80
N THE EVENT THAT CONSTRUCTION ACTIVITIES OR OTHER SITE DEVELOPMENT (JAMESTOFESTUCA N, BARUBRA BANNECOMMUR,
ADO
CTIVITIES ARE DISCONTINUED FOR AT LEAST 4 CONSECUTIVE DAYS, THE WHITE
BANNER, SHADOW, KOKET)
WNER/CONTRACTOR SHALL BE RESPONSIBLE FOR THE INSPECTION OF ALL EROSION WHITE DUTCH CLOVER 10 96 90
ND SEDIMENT CONTROL FACILITIES IMMEDIATELY AFTER STORM EVENTS, AND AT <TRIFOLIUM REPENS>
EAST ONCE EVERY WEEK, THE OWNER/ CONTRACTOR SHALL BE RESPONSIBLE FOR MULCHING
HE MAINTENANCE AND REPAIR OF ALL EROSION AN SEDIMENT CONTROL FACILITIES.
ET SEASON (OCTOBER I THRU APRIL 30) -- ON SITES WHERE UNINTERUPTED 1. MATERIALS USED FOR MULCHING ARE RECOMMENDED TO BE WOOD
pNSTRUCTION ACTIVITY IS IN PROGRESS, THE CLEARING OF LAND, INCLUDING THE FIBER CELLULOSE, AND SHOULD BE APPLIED AT A RATE OF 1000
REMOVAL OF EXISTING VEGETATION AND OTHER GROUND COVER, SHALL BE LIMITED POUNDS PER ACRE.
0 AS MUCH LAND AREA AS CAN BE COVERED OR STABILIZED WITHIN 24 HOURS IN 2. MULCH SHOULD HE APPLIED IN ALL AREAS WITH EXPOSED SLOPES
HE EVENT A MAJOR STORM IS PREDICTED AND/ OR EROSION AND SEDIMENT GREATER THAN 2:1 <HORIZONTAIMMED ICAL).
TRANSPORT OFF-SITE IS OBSERVED. 3. MULCHING SHOULD BE USED IMMEDIATELY AFTER SEEDING OR IN
AREAS WHICH CANNOT BE SEEDED BECAUSE OF THE SEASON, ALL
IL
L CLEARED OR DISTURBED AREAS SHALL RECEIVE APPROPRIATE PROTECTIVE AREAS REQUIRING MULCH SHALL BE COVERED BY NOVEMBER 1.
OVER OR BE ❑THERWISE STABILIZED, SUCH AS MULCHING, NETTING, PLASTIC
HEETING, EROSION BLANKETS, FREE DRAINING MATERIAL, ETC., WITHIN 5 DAYS AFTER
AVING BEEN CLEARED OR OTHERWISE DISTURBED IF NOT BEING ACTIVELY WORKED.
ILT FENCING, SEDIMENT TRAPS, SEDIMENT PONDS, ETC., WILL NOT BE VIEWED AS
DEQUATE COVER IN AND OF THEMSELVES. IN THE EVENT THAT ANY LAND AREA NOT
EING ACTIVELY WORKED REMAINS UNPROTECTED OR HAS NOT BEEN APPROPRIATELY
TABILIZED 5 DAYS AFTER HAVING BEEN CLEARED, ALL CONSTRUCTION ACTIVITY ON
HE SITE, EXCEPT FOR APPROVED EROSION AND SEDIMENT CONTROL ACTIVITY, SHALL
MMEDIATELY CEASE UNTIL SUCH A TIME AS AFOREMENTIONED LAND AREA HAS BEEN
PPROPRIATELY PROTECTED OR STABILIZED.
ILT FENCE
PROJECT/ OWNER/ LOCATION
GEOTEXTILE FILTER FABRIC TYPE SHALL BE PER SPECIFIED IN THE 'STORMWATER MANAGEMENT MANUAL SINGLE FAMILY RESIDENCE
-OR THE PUGET SOUND BASIN,' OR APPLICABLE COUNTY STANDARDS
GEOTEXTILE FILTER FABRIC SHALL BE PURCHASED IN A CONTINUOUS ROLL CUT TO THE LENGTH OF GEOTECHNICAL REPORT
ACH BARRIER TO AVOID USE OF JOINTS. IF JOINTS ARE NECESSARY, FILTER FABRIC SHALL BE SPLICED WILLIAMS
OGETHER ONLY AT A SUPPORT POST WITH A MINIMUM 6-INCH OVERLAP AND SECURELY FASTENED AT 51 E WESTLAKE DRIVE S
BOTH ENDS TO THE POST, PARCEL 12219-50-00067
. STANDARD FILTER FABRIC SHALL BE FASTENED USING V STAPLES OR TIE WIRES (HOG RINGS) 8 4 IN MASON COUNTY, WASHINGTON
PACING,
4. POSTS SHALL BE SPACED AND PLACED AT DEPTHS INDICATED IN THE DETAILS ON THIS SHEET, AND ENGINEER-
RIVEN SECURELY INTO THE GROUND. ENVIROTECH ENGINEERING
. WIRE MESH SHALL BE 2'X2'X14 GAUGE OR EQUIVILENT. THE WIRE MESH MAY BE ELIMINATED IF PO BOX 984
XTRA-STRENGTH FILTER FABRIC (MONOFILAMENT), AND CLOSER POST SPACING IS USED. BELFAIR, WASHINGTON 98528
. A TRENCH SHALL BE EXCAVATED ACCORDING TO THE DETAILS ON THIS SHEET ALONG THE LINE OF THE 360-275-9374
❑STS AND UPSLOPE FROM THE SILT FENCE.
7. SILT FENCES SHALL BE LOCATED DOWNSLOPE FROM THE CLEARING LIMITS OF THE PROJECT. EROSION CONTROL
f 1 •
APPENDIX E
DRAINAGE DETAILS
-------------
STEEL CLAMPS (TYP)
CORRUGATED TIGHTLINE 10 FT MIN SPACING SE REELNCH DIAMETER
6-INCH MIN. DIAMETER SECURELY FASTENED T❑ PIPE
LEVEL SECTION
3FT DIFFUSER TEE
TWO 6-FOOT
ANCHORS (TYP), r NOTES.
k4 REBAR OR 1. IT IS STRONGLY SUGGESTED TO
EQUIVALENT 3 IT MIN UTILIZE A HEAT WELDED HIGH DENSITY
POLYETHYLENE (HDPE) PIPE IN LIEU OF
CORRUGATED PLASTIC PIPE.
2. IF PLASTIC PIPE IS USED, FREQUENT
INSPECTION (BI-ANNUALY), AND
NECESSARY MAINTENANCE IS REQUIRED.
TIGHTLINE DETAIL 3. HOLE DIAMETER SHALL BE I INCH FOR
N.T.S. 6-INCH TEES, AND 2 INCHES FOR 12-INCH
TEES.
4. HOLE SPACING SHALL BE EQUAL TO
(1.5 X HOLE DIAMETER).
5. DIAMETER OF TEE SHALL EQUAL
DIAMETER OF TIGHTLINE PIPE.
��O
�y
NO HOLES OPPOSITE
OF PIPE
0
o° ° DRILL HOLES
IN FRONT HALF
0 0 ° OF TEE ONLY
3 FT (4) 6' 84 REBARS
SCREW CAP OR BENT OVER TEE AS
BOLTED FLANGE, SHOWN. ALTERNATE
EACH END ANCHORING BETWEEN PROJECT/ OWNER/ LOCATION,
FRONT AND BACK OF SINGLE FAMILY RESIDENCE
TEE.
GEOTECHNICAL REPORT
DEFFUSER TEE DETAIL, WILLIAMS
N.T.S. 51 E WESTLAKE DRIVE S
LEGEND PARCEL 12219-50-00067
MASON COUNTY WASHINGTON
TEMPORARY ENGINEER-
EROSION CONTROL ENVIROTECH ENGINEERING
PO BOX 984
SLOPE INDICATOR BELFAIR, WASHINGTON 98528
EXISTING CONTOUR 360-275-9374
TP TEST PIT DRAINAGE