HomeMy WebLinkAboutGEO2015-00038 for BLD2015-00788 - BLD Engineering / Geo-tech Reports - 9/18/2015 ��DZO15- oa ��
RECEIVER
PLANNING SEP Z 12015
426 W. CEDAR ST.
Geotechnical Report
for
Goodwin Residence
111 E. Warren Drive
Parcel No. 32232-55-00026
Mason County, Washington
September 18, 2015
Project#15131
Prepared For:
Gerald Goodwin
P.O. Box 542 G�P�L LA°E sT9T
Union, Washington 98592
Prepared By:
Envirotech Engineering �0A' �Fc 43045
TYE-
PO Box 984 SS��NALE�G
Belfair, Washington 98528
Phone: 360-275-9374
Maas--F COU""Y 7eoaltnent of CorntnU"ifv Deyaioprnen[
Z!AjU n;,,Ia` Chxeckiisi Gr 7 i9eolt'cflntCal l�eAi�i%
instructions:
This checklist rnust be submitted with a Geotecnricai Report and completed_signed; and stamped by the
heel tseCi iiraFBS$i^ua si(S).r1hC prepaFed t_he Geotechnicd Report for review by Mason County pL suanit t0
Z h a 1 as0,1 v o•Iit zwJi;ii:, vs;iu�arzGB. _tee: cie.ri3tCi to be a of sppH �tie, sie tej7ori si7GU:U v�'.'.}rla.1
the basis for i e coric-iusion-
AppiicanUUivner PXrw (9,29d w;I Parcels 3
=T r►` Jr i
Site riurdi ess C
(1) (a)A discussion of general gedlogic conditions in the vicinity of the proposed development,
Located on page(s)
C b) Al discussifl t 0i.3PeC1PC s r,—; S
Located on pagers;
(c) A discussion of ground water conditions
Located on page(si 7
(d) A discussion o;the upslopee geo.mmrphology
`Ocaied On page(s) 3
(e) A discussion of .he 1--caiion of upland viate:i?odies and wetlands
Located or page(s) !�
(i ,� CitSCuSSiLr. �e i Story or iandstide activity in the acrivhy in the vicinity,as avail2bte in fhe
referenced maps and records
L., Ld or. pagers' i
(2) A site plan%thich identifies the im:^:,I;ant development and geologic features.
o
(3) Locations and legs of ex loratm!ho es or pro es_
UP, Wiap.
(4) i bi area of the proposed development, the boundaries of the hazard, and associated buffers and
tb seacks shall be delineated(top: both sides,and toe)on a geologic map of the site.
L.ca ed off: Map's,, P/Qyl
(5) A:nin`sn'um of one cross seczcn at a scale 1.uhid-t adequately depicts the subsurface profile, and
which in_corsp-or3"as fbe de`-ails-of proposed grade changes.
L-vuate-6 Of, Nlap(s J r j {�r�{-;t e-
(6) = r w cr,nticn fin^r--s•_,::5�'_`Si<;ps S ability lys s pelf"Urmed�;� sta:fi _~
F e...,J aitt7 e!3 .�E="_.c al,�'
annditions_Analysis should enamirle worst oaseaf�aaures_1-he anal:s Smuld include the
;. rli isP. -!Aau 2 s vH1as_%te.atii3il mra s i a rc saf"ei4ir acbr is ,i h a rnki hn!a;i
se'smsic saf-N,factor is !-I-and}fie gi=asi-sir_anaryfsic flY tents should ire a v-allue of GA5_
Located on pages) /1
(I) ;21 .I i)or opriai8 r es>rictioins fir?eiac-s~jent of drainage features
Loco€ed on page(s) i 7
fFia) .t=ccr cr aC-:-a- icrions cr: of se !-ic di-a n%elds
Located on page(s) 19
- -
ti_i �u;�-t vf3r- ie i esti ict`i/o�i is flit P,lacei-3eni of compacted Ms and footings
Located on 7atiets)_!"
Page i of 2 Form Effective June 2008
Disciairna-,: "Olason County does not certify The Ott-jiby of the t,vOrk done it
00
(d) Recommended buffers from ffie landslide hazard areas shoreiine-bluffs and the tops of other
siopes on me proper'ru.
Located on page(s) /
(e) Recommended setbacks from the landslide hazard areas shoreline bluffs and the tops of
oilier siopes on the properiv_
Locates: or.page(s) 17
(u) Receorm—nendafions Tor the preparation of a cieisited clearing and grading pion wsiuflt speci EC;iallY
idea' les vegetation to be removed, a schedule for vegetation removal and replanting, and the
method of vegetation removal-
. Located on page(s)
(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
siope Jfi am erosion, iandsiides and harmful construction methods.
Located on page(s) i/.
(-iu) An anaiysis Of both Grl-site and off-site impacts or'the proposed development.
Located on page(s) 13
(i i) jpSGlfiCaiiOnS or final development conditions such as,vegetative manage;neni, drainage,
erosion control, and buffer widths_
Located on page(s)
(12) Recommendations for the preparation of structural mitigation or details of-other proposed
n;Higatio^-
Located an page(s) /
(IX1 iL s=iR m?p draIAM E_SC-Ble showing the property.boundaries,scale.-nert+h ai-o ,and the location
and nature of existing and proposed development on the site.
�.v�:.�r=oit ri-airstsi S� F1`c-r,
t, 4i G j�cam-' C_ hereby c =5'under Penalty of
pedur'y*mt i are a civi'i engineer iicensec in-die jtaTc of Washington 1+ifM spemalmea Knowiedge of
•• - "3"i or ca ged ist or en fi is-.—w8i tst 111ce tse as H a�'�c di
�vY2tasiriiGccfc�avfvt��sc.ai a'i{3IT's t t a a '�
'`-_
Report.dated `��lgf/� ,apd er:u led 6Pa4cAp ca
(j DodWr✓1 �Sr�G?/' - Qe"ia'rx'ii the 9�r'tx�*itF�ee�va i=:c alrc5{iit
C-o onty Resomw Ordhtance.Lards-fide w-F6 SecHan.-is comple a and cede,Mat tie assessme-it
demonstrates conclus;veiy ifia=r-he risks posed by file tandsllde hazards can be mitigated through the
Su
ii3C1l1Qe�i�ao'eccar7}ea;a!deli r aae:t�ca¢ea8viaii=_��tS,and mar-ali h uas a-e BiiflugaE�Eli ral a tManner as
IP
Page 2 of 2 Form Effecfive.lune 2006
b?3sc!almen Masrn County does not^_erMr v':e quality of the wort:done In this Gsuta&,nIcaf:?; �-
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.................................................................................................................4
2.4 SLOPE AND EROSION OBSERVATIONS................................................................................................4
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.............................................................................................................11
4.2 EROSION............................................................................................................................................11
4.3 SEISMIC CONSIDERATIONS AND LIQUEFACTION.............................................................................12
4.3.1 Liquefaction..............................................................................................................................12
4.4 LANDSLIDE,EROSION AND SEISMIC HAZARDS CONCLUSIONS.......................................................13
4.5 LATERAL EARTH PRESSURES...........................................................................................................13
4.6 ON-SITE AND OFF-SITE IMPACTS.....................................................................................................13
5.0 ENGINEERING RECOMMENDATIONS.......................................................................................14
5.1 BUILDING FOUNDATION RECOMMENDATIONS................................................................................14
5.1.1 Bearing Capacity......................................................................................................•................14
5.L2 Settlement..................................................................................................................................IS
5.1.3 Concrete Slabs-on-Grade..........................................................................................................1 S
5.2 EARTHWORK CONSTRUCTION RECOMMENDATIONS......................................................................15
5.2.1 Excavation.................................................................................................................................1 S
5.2.2 Placement and Compaction of Native Soils and Engineered Fill...........................................16
5.2.3 Retaining Wall Backfdl............................................................................................................17
5.2.4 Wet Weather Considerations....................................................................................................17
5.3 BUILDING AND FOOTING SETBACKS.................................................................................................17
5.4 SURFACE AND SUBSURFACE DRAINAGE...........................................................................................17
5.5 VEGETATION BUFFER AND CONSIDERATIONS.................................................................................18
5.6 TEMPORARY AND PERMANENT EROSION CONTROL.......................................................................18
5.7 SEPTIC DRAINFIELDS........................................................................................................................19
5.8 STRUCTURAL MITIGATION...............................................................................................................19
6.0 CLOSURE............................................................................................................................................20
Appendix A-Site Plan
Appendix B-Soil Information
Appendix C-Slope Stability
Appendix D—Erosion Control
1.0 INTRODUCTION
Envirotech Engineering (Envirotech) has completed a geotechnical investigation for a planned
single family residence located at I I I E Warren Drive, identified as parcel number 32232-55-
00026, Union, Mason County, Washington. See the vicinity map on the following page for a
general depiction of the site location.
The geotechnical investigation was conducted at the request of the proponent of the property,
Gerald Goodwin, in support of the proposed development as detailed below. The proposed
development,as provided herein,and the surrounding area that may influence the development,is
identified throughout this report as the Project.
An initial geotechnical evaluation of the Project was conducted by Envirotech on August 31,
2015. 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 during the geotechnical investigation. Other Project information was obtained by
Envirotech. There is no current development on 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 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.
11 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:
Envirotech Engineering 111 E Warren Drive
PO Box 984 page 1 Parcel 32232-55-00026
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 September 18,2015
• 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
references concerning slope stability, and review water well reports from existing wells
near the Project;
• Collect bulk samples 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
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Vicinity Map from Mason County Website
Envirotech Engineering 111 E Warren Drive
PO Box 984 page 2 Parcel 32232-55-00026
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 September 18,2015
1 �
2.0 SURFACE CONDMONS
Information pertaining to the existing surface conditions for the Project was gathered on August
31, 2015 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
The property is accessed from Warren Drive,an existing paved roadway. The Project is currently
undeveloped land as previously mentioned. The access road extends near the north property line,
and Hood Canal borders the property to the south. Beyond the property, rural residential
development exists. Vegetation on and near the Project consists primarily of secondary growth
firs and shrubbery common to this area of the Pacific Northwest. Vegetation has been mostly
cleared, and approximately 2 feet of fill material is located to the east of the planned
development. There was no fill material obseved at the project footprint. 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%, approximately 166 feet to the southeast
of the planned development. The maximum critical slope is approximately 64% with a vertical
relief of approximately 118 feet.
Ascending grades are generally located to the west of the planned development. These slopes are
relatively minor within 300 feet of the Project,with no apparent slope grades of at least 10%.
2.2.1 Upslope Geomorphology
The upland area of the property and beyond is generally situated on a crest 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.
Envirotech Engineering 111 E Warren Drive
PO Box 984 page 3 Parcel 32232-55-00026
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 September 18,2015
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.
2.4 Slope and Erosion Observations
The slope grades 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.
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Aerial Photo from Mason County We site
Envirotech Engineering 111 E Warren Drive
PO Box 984 page 4 Parcel 32232-55-00026
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 September 18,2015
3.0 SUBSURFACE INVESTIGATION
Information on subsurface conditions pertaining to the Project was primarily gathered on August
31, 2015 by a representative with Envirotech. Specific 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 extending to depths of up to 6 feet below the existing 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 24 inches, and very
dense soils from 24 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 Shelton 1:100,000 Quadrangles, Mason County, Washington" by,
Robert L.Logan,June 2003,provides the following caption(s)for the project area:
Envirotech Engineering 111 E Warren Drive
PO Box 984 page 5 Parcel 32232-55-00026
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 September 18,2015
Qapa Alpine out%%ash, pre—late Wisconshian 011eistocene}—Stratified
sand, gravel, and cobbles; in the Quinault basin,clasts consist of
sandstone and less-abundant basalt from the Olympic Mountains core
and peripheral rocks; in streams draining the southern and southeast-
ern Olympics,clasts consist primarily of Crescent Formation basalt
with less-abundant Olympic-core sandstone; may include peat, silt,
and clay, and may be capped by weathered loess; clasts are generally
more rounded than those in till and lack facets and striations; poorly
to moderately sorted, gray to subtle yellow with wispy orange weath-
ering.
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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 Soil Conservation Service(SCS)descriptions.
Envirotech Engineering 111 E Warren Drive
PO Box 984 page 6 Parcel 32232-55-00026
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 September 18,2015
The Project is currently composed of native soils without indications of borrowed fill. Within test
pit locations,soils within the upper 2 feet of natural ground were observed to be fill. Soils located
below 2 feet of natural ground to a depth of 4 feet were observed to be moist, brown silty sand
with gravel(SM). Soils below the upper 4 feet layer to a depth of terminous were observed to be
mostly grey, low moisture, silty sand with gravel (SM), locally known as hardpan. The hardpan
may extend to depths approximately 48 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 Loam,
Aa,0% - 5% 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.
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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
f e property location. Surface seepage
is at least 50 feet directly below the p perry at the building pad oc
or perched groundwater at shallow depths was not observed on-site,nor indicated on the
well reports. However, some groundwater is expected to flow directly above the hardpan
on occasion.
Envirotech Engineering 11 I E Warren Drive
PO Box 984 page 7 Parcel 32232-55-00026
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 September 18,2015
4.0 ENGINEERING ANALYSES AND CONCLUSIONS
The following sections present engineering analyses and conclusions with relation to the existing
conditions and proposed improvements of the Project. This section includes slope stability,
erosion, seismic considerations, lateral earth pressures, 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, excessive and/or repeated surficial slope
movements, if not repaired, may represent a threat to the structural integrity of the slope. If this
situation does arise, the slope shall be inspected by a geotechnical engineer. Subsequently,
maintenance may be required in order to prevent the possibility of further surficial or deep seated
slope movements that may be damaging to life and property.
According to the Coastal Zone Atlas of Mason County, Washington, the Project is within and
near terrain labeled `Stable' and `Intermediate' regarding potential landslide activity. Stable
slopes are generally not prone to landslides due to small grades and accommodating geology.
Historically, intermediate terrains have no known landslides. However, this site is considered
inherently hazardous due the existing geology and/ or topography, and additional analyses and
recommendations concerning the slopes are presented herein. A Stability Map from the Coastal
Zone Atlas for the general area of this Project is provided below:
Envirotech Engineering i 11 E Warren Drive
PO Box 984 page 8 Parcel 32232-55-00026
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 September 18,2015
V 5
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Project
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5
Map from Washington State Department of Ecology Website
According to the Resource Map from the Washington State Department of Natural Resources
(DNR), the Project is not within terrain labeled `highly unstable' relating to soils. DNR labeled
portions of this project as medium and high slope instability with relation to slopes. This
delineation is primarily dependent upon slopes and convergence. Secondly, lithology and
precipitation are modeled within this delineation. In summary, this designation is based on
mapping without field observations or knowledge of the specific site geology or soils. A
Resource Map from the DNR Forest Practices Application Review System is provided below:
Envirotech Engineering 111 E Warren Drive
PO Box 984 page 9 Parcel 32232-55-00026
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 September 18,2015
t
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■ �.� Project
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Resource Map from Washington State Department of Natural Resources Website
SOILS—On Resource Map only
Hydric Soils
HigWy Unstable
Higlily Erodible
Fighly Unstable
Fiahh-Erodible
No Data or Gravel
Pits
SLOPE—On Resource Map onk
Medium Slope
Instabilit-:
High Slope Instati1r:
Envirotech Engineering 111 E Warren Drive
PO Box 984 page 10 Parcel 32232-55-00026
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 September 18,2015
4.1.1 Slope Stability Analysis
Based on site geology, a non-circular slope stability analysis should be performed.
However, the Simplified Bishop Method (circular analysis), as presented herein, was
utilized. Although the method of circles does not fit the site conditions, Envirotech
certifies that our analysis is more conservative for these project conditions than other
conforming slope stability models. For this Project and level of geotechnical
investigation, our conclusions or recommendations would not be changed by this
variation in analysis.Where applicable,our slope stability analysis utilizes the subsurface
angle of repose.
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 0.1,
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 4 feet soil depth
Soil unit weight: 130 pcf
Angle of internal friction: 34 degrees
Cohesion: 40 psf
Soils below 4 feet in depth
Soil unit weight: 140 pcf
Angle of internal friction: 40 degrees
Cohesion: 400 psf
Based on the slope stability analysis, minimum factors of safety were determined to be
less than 1.5 relative to static slope failures, and less than 1.1 with relation to seismic
conditions. These factors of safety were primarily limited to the face of the slope, and 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 2.5 and 1.9, 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 not within terrain labeled `highly erodible.' This Project is within an erosion hazard
area as defined by the MCRO. Erosion hazard areas are those with USDA SCS designations of
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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).
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 contain
specific erosion control options recommended for this Project. Additional erosion control
measures than what is initially established may need to be employed if excessive erosion occurs
during construction, or required by the prevailing agency. Complete 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.
4.3 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 Hood Canal Fault Zone, in which is approximately 3 miles to the northwest 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
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.
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� Ili
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.
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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. 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. Foundations should not bear on
existing on-site fill.
For a bearing capacity requirement of no more than 1500 psf, a minimum continuous
footing width of 12 inches(15 inches for 2 story buildings)shall be placed at a minimum
of 12 inches below the existing ground surface. 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
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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.
5.13 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.
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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
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.
&FOOTINGC❑MPACTEDNATIVE S❑ILS❑R ENGINEEREDFILL
1 1-1
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
90% 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.
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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
Although the subsoil characteristics do not pose a great risk in regards to saturation,
additional provisions may be required during prolonged wet weather. Every precaution
should be made in order to prevent free moisture from saturating and ponding within
excavations. If the bottom of excavations used for footing placement changes from a
moist and dense characteristic as presented in this report to loose, saturated conditions,
then these soils become unsuitable for foundation bearing material. If this situation
occurs, a geotechnical engineer should be notified, or these soils should be completely
removed and replaced with suitable compacted material as presented above.
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 65 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.
STRUCTURE
TOP OF
SLOPE SLOPE
FACE _
I I—I I '
�— — SETBACK —� FOOTING
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
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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 roof infiltration is dispersed using either splash blocks or a
trench located at least 10 feet downslope from the proposed house, conforming to the Mason
County Small Parcel Stormwater Plan. One splash block is needed per 700 sq. ft. of roof.
Recommended dispersion locations are delineated on the Site Plan in Appendix A.
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 is an excellent measure to minimize surficial slope movements and erosion on slope
faces and exposed surfaces. By removing trees, the root strength is decreased over time, thereby
lowering the `apparent' cohesion of the soil. Transpiration is decreased, which results in
additional groundwater, increased pore water pressure and less cohesion/ friction of the soil
particles. Stormwater runoff also increases, and, fewer plants will create less absorption of the
force from raindrops,thereby creating the potential for erosion hazards.
Vegetation Buffer—Vegetation shall not be removed from the face of the critical slope or within
a distance of 50 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
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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 Map in Appendix A depicts the recommended locations for erosion control
facilities to be installed,if 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. The following Surface and Subsurface Drainage Section may
have additional recommendations with relation to permanent erosion for surface drainage
features.
5.7 Septic Drainfields
The approximate location of the septic drainfield is presented 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.
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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
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Ph. 360-275-9374 September 18,2015
APPENDIX A
SITE PLAN
EErPROPOSED HOUSE
EXISTING GRADE
SILTY SAND W/
GRAVEL (SM)
,--A-9-�&:
WERY DENSE GULLY
GLACIAL TILL'
o LJ
0
SECTION A-A
PROJECT/ OWNER/ LOCATIONi
SINGLE FAMILY RESIDENCE
GE❑TECHNICAL REPORT
GOODWIN
PARCEL 32232-55-00026
MASON COUNTY, WASHINGTON
NOTES,
ENGINEER,
1) MINOR GRADE CHANGES REQUIRED IN ORDER TO ACHIEVE ENVIROTECH ENGINEERING
POSITIVE DRAINAGE PO BOX 984
2) THE SOIL PROFILE IS ACCURATE FOR THE DEPTH OF BELFAIR, WASHINGTON 98528
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
APPENDIX B
SOIL INFORMATION
TEST PIT LOG
TEST PIT NUMBER TP-1
PROJECT: Goodwin Geotechnical Report DATE OF LOG: 8/31/2015
PROJECT NO: 15131 LOGGED BY: MCS
CLIENT: Gerald Goodwin EXCAVATOR: N/A
LOCATION: Parcel 32232 55 00026 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
Fill,
1 - -
2
SM Brown, moist, loose to medium dense
SILTY SAND with GRAVEL. Gravel is
course and subrounded. Sand is mostly
3 medium. Low plasticity.
4 .............. .....................................................................................
SM Very dense glacial till.
5
6
Excavation terminated at approximately
6.0 feet
7
8
9
110
No Groundwater Encountered ENVIROTECH ENGINEERING
This information pertains only to this boring and should not be Geotechnical Engineering
interpreted as being indicitive 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: 20 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
Bw1 - 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(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
LSDA Natural Resources Web Soil Survey 9/14/2015
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
Other vegetative classification: Limited Depth Soils
(G002XN302WA), Limited Depth Soils(G002XS301 WA),
Limited Depth Soils(G002XF303WA)
Minor Components
Indianola
Percent of map unit: 5 percent
Landform: Karnes, hillslopes, terraces, eskers
Landform position (two-dimensional): Summit, backslope
Landform position (three-dimensional): Crest, side slope, tread
Down-slope shape: Convex, linear
Across-slope shape: Convex, linear
Ecological site: Thuja plicata-Pseudotsuga menziesii/Gaultheria
shallon/Polystichum munitum (F002XN903WA)
Other vegetative classification: Droughty Soils(G002XN402WA)
Everett
Percent of map unit: 5 percent
Landform: Kames, moraines, eskers
Landform position(two-dimensional): Backslope
Landform position(three-dimensional): Side slope
Down-slope shape: Convex
Across-slope shape: Convex
Other vegetative classification: Droughty Soils(G002XN402WA)
Shalcar
Percent of map unit: 3 percent
Landform: Depressions
Landform position (three-dimensional): Dip
Down-slope shape: Concave
Across-slope shape: Concave
Other vegetative classification: Wet Soils(G002XN102WA)
Norma
Percent of map unit: 2 percent
Landform: Depressions, drainageways
Landform position(three-dimensional): Dip
Down-slope shape: Concave, linear
Across-slope shape: Concave
Other vegetative classification: Wet Soils(G002XS101 WA)
Data Source Information
Soil Survey Area: Mason County, Washington
Survey Area Data: Version 10, Sep 30, 2014
usD,% Natural Resources Web Soil Survey 9/14/2015
Conservation Service National Cooperative Soil Survey Page 2 of 2
APPENDIX C
SLOPE STABILITY
O O O O O O O O O O O
O H N m 1 In w (` w m O
. . . . . . . . . . .
rl rl ri r-1 rl r� ri ri r1 r-I N
N
O
z
HUa
3H0
AHD
0 � y
0 H -H
(7Npq �
a
a
.. .. a U
0
0
0
(n 4
H .H £
0 •rl 01 n
0 W >i0
0 v 011
04
1 00
1 10
1 20
1 . 30
1 40
1 50
1 60
1 70
1 _ 80
1 90
62 . O 0
58
P r o j e c t G O O D W T N
Datafi1e OYNAMTC
A n a 1 y s i a B i s h o p
STABLE-2002 MZ A....1.1- L-1
STABLE Slope Stability Analysis System
New User
Project GOODWIN
Datafile: DYNAMIC Bishop
STABLE Version 9.03.00u
Bishop
TITLE
DYNAMIC
UNITS (Metric/Imperial) = I
GEOMETRY DEFINITION
POINTS
NO. X Y
1 0.000 0.000
2 166.000 0.000
3 348.000 -118.000
4 398.000 -118.000
5 0.000 -4.000
6 166.000 -4.000
7 348.000 -122.000
8 398.000 -122.000
9 39.800 0.000
10 56.560 0.000
11 73.320 0.000
12 90.070 0.000
13 106.830 0.000
14 123.590 0.000
15 140.350 0.000
16 157.110 0.000
17 173.860 -5.100
18 190.620 -15.960
19 207.380 -26.830
20 224.140 -37.690
21 240.890 -48.560
22 257.650 -59.420
23 274.410 -70.290
24 291.170 -81.150
25 307.930 -92.020
26 324.680 -102.880
27 341.440 -113.750
28 358.200 -118.000
LINES
Lo X Hi X SOIL
1 2 1
2 3 1
3 4 1
5 6 2
6 7 2
7 8 2
SOILS
SOIL NAME LINETYPE-PEN COHESION FRICTION UNIT WT.
STABLE02002 MZ Associates Ltd Printed on: 14/09/15 @ 16:23:32 Page: 1
STABLE Slope Stability Analysis System
New User
Project GOODWIN
Datafile: DYNAMIC Bishop
1 SILTY SAND 0.00 40.0 34.000
2 HARDPAN 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
POINT PORE PRESSURES
POINT PRESSURE
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
SLIP DIRECTION (+/- X) = +
SLIP-CIRCLES
AUTOMATIC
Circle Centre Grid Extremities
318.400
+++++++++++++++
+ +
39.800 * * 358.200
+ +
+++++++++++++++
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 Circles 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 MZAssociates Ltd Printed on: 14/09/15 @ 16:23:32 Page: 2
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 E 6 FT MAX. O.C. 0.5 FT
BEFORE PLACING GRAVEL 2'x2'x5' WOOD POST OR �— 6 FT —�
12' DEEP, 8' WIDE TRENCH EQUIVALENT OR BETTER EXISTING
FILLED WITH 3/4' TO 1 1/2' GROUND SURFACE
2
WASHED GRAVEL or VEGETAT N T
2.5 FT 12' DEEP, 8' WIDE
DIRECTION OF EXISTING TRENCH FILLED WITH 1 T
WATER FLOW GROUND SURFACE 2.5 FT
12' 3/4' TO 1 1/2'
2.5 FT WASHED GRAVEL OR
VEGETATION
�g- BOTTOM EXTENTS OF
,�7_ F
GEOTEXTILE FABRIC SILT FENCE - DETAIL
SILT FENCE - CROSS SECTION N.T.S.
GENERAL NOTES- N.T.S. HAY OR STRAW MATTING
1. SHOULD THE TEMPORARY EROSION AND SEDIMENT CONTROL MEASURES SHOWN ON 1. STRAW SHALL BE AIR DRIED, AND FREE FROM WEED SEEDS AND
COARSE MATERIAL.
THESE PLANS PROVE TO BE INADEQUATE DURING CONSTRUCTION, THE CONTRACTOR
SHALL INSTALL ADDITIONAL EROSION AND SEDIMENT CONTROL FACILITIES. 2. APPLY AT APPROXIMATELY 75 TO 100 POUNDS PER 1000 SQUARE
FEET OF GROUND.
2. ALL EROSION AND SEDIMENT CONTROL FACILITIES AND DEVICES SHALL BE
INSPECTED DAILY AND IMMEDIATELY MAINTAINED, IF NECESSARY. 3. MINIMUM THICKNESS SHALL BE 2 INCHES.
3. ALL EROSION AND SEDIMENT CONTROL FACILITIES AND DEVICES SHALL BE LEFT IN4. HAY OR STRAW IS SUBJECT TO BLOWING. KEEP MOIST OR TIED
PLACE UNTIL THE UPSLOPE AREAS HAVE BEEN PERMANENTLY STABILIZED. DOWN.
TEMPORARY EROSION CONTROL NOTES, PERMANENT EROSION CONTROL NOTES-
OR ALL AREAS WHICH HAVE BEEN STRIPPED OF VEGETATION OR EXPERIENCED LAND SEEDING FOR RAW SLOPES
DISTURBING ACTIVITIES, AND WHERE NO FURTHER WORK IS ANTICIPATED FOR A 1. BEFORE SEEDING, INSTALL NEEDED SURFACE RUNOFF CONTROL
PERIOD EXCEEDING THE LISTED CRITERIA BELOW, ALL DISTURBED AREAS MUST BE MEASURES SUCH AS GRADIENT TERRACES, INTERCEPTOR DIKES,
IMMEDIATELY STABILIZED WITH MULCHING, GRASS PLANTING OR OTHER APPROVED STALES, LEVEL SPREADERS AND SEDIMENT BASINS.
EROSION CONTROL TREATMENT APPLICABLE TO THE TIME OF YEAR. GRASS SEEDING 2, THE SEED BED SHALL BE FIRM WITH FAIRLY FINE SURFACE,
ALONE WILL ONLY BE ACCEPTABLE DURING THE MONTHS OF APRIL THROUGH FOLLOWING SURFACE ROUGHENING. PERFORM ALL OPERATIONS ACCROSS
SEPTEMBER. HOWEVER, SEEDING MAY PROCEED WHENEVER IT IS IN THE INTEREST OF OR PERPENDICULAR TO THE SLOPE.
THE 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 TO
ONLY AS MUCH LAND AS CAN RECEIVE APPROPRIATE PROTECTIVE COVER OR BE FOSTER AND PROTECT THE ROOT STRUCTURE.
OTHERWISE STABILIZED, AFTER HAVING BEEN CLEARED OR OTHERWISE DISTURBED , 5, SEED BEDS PLANTED BETWEEN NE NE ER 1 AND APRIL 30,
B
BY NO LATER THAN SEPTEMBER 30 OF A GIVEN YEAR. UNLESS IMMEDIATE GEOTEARMORING OF THE SEED BED WILL BE NECESSARY, (e.g.,
STABILIZATION IS SPECIFIED IN THE EROSION AND SEDIMENT CONTROL PLAN, ALL 6. FER FERTILIZERS
JUTE MAT, CLEAR PLASTIC COVERING).
AREAS CLEARED OR OTHERWISE DISTURBED MUST BE APPROPRIATELY STABILIZED 6. FERTILIZERS ARE TO BE USED ACCORDING IZ SUPPLIERS'
THROUGH THE USE OF MULCHING, NETTING, PLASTIC SHEETING, EROSION BLANKETS, RECOMMENDATIONS. AMOUNTS SHOULD T MINIMIZED, ESPECIALLY
FREE DRAINING MATERIAL, ETC., BY SEPTEMBER 30 OR SOONER PER THE APPROVED ADJACENT TO WATER BODIES AND WETLANDS.
PLAN OF ACTION. UNLESS OTHERWISE APPROVED BY THE COUNTY, SEEDING, USE THE FOLLOWING RECOMMENDED SEED MIXTURE FOR EROSION
FERTILIZING AND MULCHING OF CLEARED OR OTHERWISE DISTURBED AREAS SHALL BE CONTROL, OR A COUNTY APPROVED ALTERNATE SEED MIXTURE.
PERFORMED DURING THE FOLLOWING PERIODS: MARCH I TO MAY 15, AND AUGUST 15 TO
OCTOBER 1. SEEDING AFTER OCTOBER 1 WILL BE DONE WHEN PHYSICAL COMPLETION PROPORTIONS PURITY GERMINATION
OF THE PROJECT IS IMMINENT AND THE ENVIROMENTAL CONDITIONS ARE CONDUCIVE NAME BY WEIGHT(%) (%) (X)
TO SATISFACTORY GROWTH. IN THE EVENT THAT PERANENT STABILIZATION IS NOT
POSSIBLE, AN ALTERNATIVE METHOD OF GROUND COVER, SUCH AS MULCHING, NETTING, REDTOP (AGROSTIS ALBA) 10 92 90
PLASTIC SHEETING, EROSION BLANKETS, ETC., MUST BE INSTALLED BY NO LATER THAN ANNUAL RYE (LOLIUM MULTIFLORUM) 40 98 90
SEPTEMBER 30. CHEWING FESUE 40 97 80
(FESTUCAIN THE EVENT THAT CONSTRUCTION ACTIVITIES OR OTHER SITE DEVELOPMENT (JAMESTO RUBRA COM, S ADO
ACTIVITIES ARE DISCONTINUED FOR AT LEAST 4 CONSECUTIVE DAYS, THE WHITE
BANNER, SHADOW, KOKET)
OWNER/CONTRACTOR SHALL BE RESPONSIBLE FOR THE INSPECTION OF ALL EROSION WHITE DUTCH CLOVER 10 96 90
AND SEDIMENT CONTROL FACILITIES IMMEDIATELY AFTER STORM EVENTS, AND AT (TRIFOLIUM REPENS)
LEAST ONCE EVERY WEEK. THE OWNER/ CONTRACTOR SHALL BE RESPONSIBLE FOR MULCHING
THE MAINTENANCE AND REPAIR OF ALL EROSION AN SEDIMENT CONTROL FACILITIES.
WET SEASON (OCTOBER 1 THRU APRIL 30) -- ON SITES WHERE UNINTERUPTED 1. MATERIALS USED FOR MULCHING ARE RECOMMENDED TO BE WOOD
FIBER CELLULOSE, AND SHOULD BE APPLIED AT A RATE OF 1000
CONSTRUCTION ACTIVITY IS IN PROGRESS, THE CLEARING OF LAND, INCLUDING THE
REMOVAL OF EXISTING VEGETATION AND OTHER GROUND COVER, SHALL BE LIMITED POUNDS PER ACRE.
2. MULCH SHOULD BE APPLIED IN ALL AREAS WITH EXPOSED SLOPES
TO AS MUCH LAND AREA AS CAN BE COVERED OR STABILIZED WITHIN 24 HOURS IN
GREATER THAN 24 (HORIZONTAL—VERTICAL).
THE EVENT A MAJOR STORM IS PREDICTED AND/ OR EROSION AND SEDIMENT
IMMEDIATELY
TRANSPORT OFF-SITE IS OBSERVED. 3. MULCHING SHOULD BE USED MMEDIATELY AFTER SEEDING OR IN
AREAS WHICH CANNOT BE SEEDED BECAUSE OF THE SEASON. ALL
ALL CLEARED OR DISTURBED AREAS SHALL RECEIVE APPROPRIATE PROTECTIVE AREAS REQUIRING MULCH SHALL BE COVERED BY NOVEMBER 1.
COVER OR BE OTHERWISE STABILIZED, SUCH AS MULCHING, NETTING, PLASTIC
SHEETING, EROSION BLANKETS, FREE DRAINING MATERIAL, ETC., WITHIN 5 DAYS AFTER
HAVING BEEN CLEARED OR OTHERWISE DISTURBED IF NOT BEING ACTIVELY WORKED.
SILT FENCING, SEDIMENT TRAPS, SEDIMENT PONDS, ETC., WILL NOT BE VIEWED AS
ADEQUATE COVER IN AND OF THEMSELVES. IN THE EVENT THAT ANY LAND AREA NOT
BEING ACTIVELY WORKED REMAINS UNPROTECTED OR HAS NOT BEEN APPROPRIATELY
STABILIZED 5 DAYS AFTER HAVING BEEN CLEARED, ALL CONSTRUCTION ACTIVITY ON
THE SITE, EXCEPT FOR APPROVED EROSION AND SEDIMENT CONTROL ACTIVITY, SHALL
IMMEDIATELY CEASE UNTIL SUCH A TIME AS AFOREMENTIONED LAND AREA HAS BEEN
APPROPRIATELY PROTECTED OR STABILIZED.
SILT FENCE
PROJECT/ OWNER/ LOCATION-
1. GEOTEXTILE FILTER FABRIC TYPE SHALL BE PER SPECIFIED IN THE 'STORMWATER MANAGEMENT MANUAL SINGLE FAMILY RESIDENCE
FOR THE PUGET SOUND BASIN,' OR APPLICABLE COUNTY STANDARDS
2. GEOTEXTILE FILTER FABRIC SHALL BE PURCHASED IN A CONTINUOUS ROLL CUT TO THE LENGTH OF GE❑TECHNICAL REPORT
EACH BARRIER TO AVOID USE OF JOINTS. IF JOINTS ARE NECESSARY, FILTER FABRIC SHALL BE SPLICED GOODWIN
TOGETHER ONLY AT A SUPPORT POST WITH A MINIMUM 6-INCH OVERLAP AND SECURELY FASTENED AT PARCEL 32232-55-00026
BOTH ENDS TO THE POST. MASON COUNTY, WASHINGTON
3. STANDARD FILTER FABRIC SHALL BE FASTENED USING 1' STAPLES OR TIE WIRES (HOG RINGS) 2 4 IN
SPACING.
4. POSTS SHALL BE SPACED AND PLACED AT DEPTHS INDICATED IN THE DETAILS ON THIS SHEET, AND ENGINEERt
DRIVEN SECURELY INTO THE GROUND. ENVIROTECH ENGINEERING
5. WIRE MESH SHALL BE 2'X2'X14 GAUGE OR EQUIVILENT, THE WIRE MESH MAY BE ELIMINATED IF PO BOX 984
EXTRA-STRENGTH FILTER FABRIC (MONOFILAMENT), AND CLOSER POST SPACING IS USED. BELFAIR, WASHINGTON 98528
6. A TRENCH SHALL BE EXCAVATED ACCORDING TO THE DETAILS ON THIS SHEET ALONG THE LINE OF THE 360-275-9374
POSTS AND UPSLOPE FROM THE SILT FENCE.
7. SILT FENCES SHALL BE LOCATED DOWNSLOPE FROM THE CLEARING LIMITS OF THE PROJECT. ER❑SI❑N CONTROL
MASON COUNTY
DEPARTMENT OF COMMUNITY DEVELOPMENT
Planning Division
P O Box 279, Shelton, WA 98584
(360)427-9670
Geotechnical ReportReview Acceptance Letter
October 14, 2015
JERRY GOODWIN
PO BOX 542
UNION WA 98592
Case No.: GE02015-00038
Parcel No.: 322325500026
Proiect Description: NEW SFR WITH ATTACHED GARAGE
The Geotechnical Report for JERRY GOODWIN has been received and reviewed by the Planning
Department. The report was prepared by Michael C. Staten dated 9/18/2015.
Based on the certification provided by the licensed engineer/geologist, the referenced
Geotechnical Report was prepared in general accordance with the requirements in the Mason
County Resource Ordinance, Landslide Hazard Areas 17.01.100.E.5. Mason County considers the
review valid until such time as scope of project, site conditions, and/or regulations change. Should
the scope of work, site conditions, and/or regulations change after the original review, then an
addendum from the original author of the report may be required to address these changes. The
report would only be re-reviewed if a permit for development were submitted after these changes
occur. Mason County does not certify the quality of the work done in this Geotechnical Report.
Please contact me at (360) 427-9670, ext. 365 if you have questions.
Sincerely,
/// k 0�- 0-"-4
Allan Borden
Land Use Planner
Mason County Planning Department
Comments: Geo Tech brought in today by applicant - removing HOLD from record and sending
to PLANNER for review
10/14/2015 Page 1 of 1 GE02015-00038
Mason County Review Checklist
For a Geotechnicai Report
Instructions:
This checklist is intended to assist Staff in the review of a Geotechnical Report. The Geotechnical Report
is reviewed for completeness with respect to the Resource Ordinance. If an item is found to be not
applicable, the Report should explain the basis for the conclusion.The Report is also reviewed for clarity
and consistency. If the drawings, discussion, or recommendations are not understandable, they should be
clarified. If they do not appear internally consistent or consistent with the.application or observations on
site, this needs to be corrected or explained. If resolution is not achieved with the author, staff should
refer the case to the Planning Manager or Director.
Applicant's N e:.
Permit# S 'vU7p ' Parcel# Z 5!�- oo
lc
Date(s) of the ocum nt(seview d:5f
(1) (a)A discu sion of general geologic conditions in the vicinity of the proposed development,
OK? on
(b) A di c sion of specific soil types
OK?Comment: _.
(c) A disc sion of ground water conditions. ,
OK? V Comment:
(d) A discu. ion of the uPslope geomorphology
OK? Comment:
(e) A discu ion of the location of upland waterbodies and wetlands
_
OK?Comment:
(f) A discussion of history of landslide activity in the activity in the.vicinity; as available in the
OK?refere ed maps and records Q
Comment: O 4
(2) A site plan w ch identifies the i ortant d velopment and geologic features.
OK? mment:
(3) Locations d logs of exploratory holeg or probes.
OK? Comment:
(4) The area of the proposed development,the boundaries of the hazard, and associated buffers and
setbacks s,4ail be delineate�,(to ,both 'des, and toe)on a geologic map of the site.
OK? V Comment: vti
(5) A minimum of one cross section at . scale which adequately depicts the subsurface profile, and
which incorporates the deta' f proposed gr a hanges.
OK? ✓Comment:
(6) A description and results of slope sta 'ity a. lyses performed for both static and seismic loading
conditions.Analysis should examine worst case failures. The analysis should include the
Simplified Bish p's Method of Circles. The minimum static safety factor is 1.5, the minimum
seismic safe factor is 1.1. and the uasi-static analysis coeffients should be a value of 0.15.
OK? Comment: a, r�
(7) (a)Approp to restrictions on la ement of drainage features
OK?Comment:
(b) Appropriate restrictions on placement of septic drain fields
OK? Comment:
(c) Appropn restrictions on placement of compacted fills and footings
OK? . Comment:
(d) Recommended buffers from the landslide hazard areas shoreline bluffs and the tops of other
slopes on the property.
Page 1 of 2 Form Effective June 2008
OK? Comment:
(e) Recomme ed setbacks from the landslide hazard areas shoreline bluffs and the tops of
other sippes on the prop
OK? Comment:
(8) Recommendations for the p eparation of a detailed clearing and grading plan which specifically
identifies ve etation to be removed, a schedule for vegetation removal and replanting, and the
method of egetation removal.
OK? Comment:
(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 e;pltion, landslides and harmful construction methods.
OK? l/Comment:
(10) An analysis of both on-site and off-site impacts of the proposed development.
OK?_ Comment:
(11) Specifications of final development conditions such as, vegetative management, drainage,
erosion corLtrol, and buffer widths. /� C G
OK? Comment: /' j 1 -
(12) Recommendations for the preparat on of structural mitigation or details of other proposed
mitigation. p 6 CI
OK?Comment: T
(13) A site map drawn to scale sho ng the property boundaries, scale, north arrow, and the location
and nature existing and pr e ment on the site.
OK?Comment:
Are the Documents signed and stamp d?
a. Type and #of License:
Knot approved, what is the next action/recommendatiori for further action? r
Reviewed by , on
Time spent in review.
SECOND REVIEW/ UPDATE: .
Reviewed by , on
Time spent in second review:
THIRD REVIEW/ UPDATE:
Reviewed by , on
Time spent in third review:
Disclaimer: Mason County does not certify the quality of the work done in this Geological Assessment
Page 2 of 2 Form Effective June 2008