HomeMy WebLinkAboutGeological Assessment - GEO General - 2/19/2014 Geological Assessment
for
Beisley, Inc. Single Family Residential Property
321 NE Anchor Drive
Parcel No. 12330-50-00088
Mason County, Washington
February 19, 2014
Project#1418
Prepared For:
Beisley, Inc. A-OrLYnE
PO Box 2355 G � sT9r
Belfair, Washington 98528
Prepared By:
Envirotech Engineering a,P0 Ric s s�°
G
PO Box 984 SS/�NALE�
Belfair, Washington 98528
Phone: 360-275-9374
Fax: 360-275-4789
Mason County Department of Community Development
SubmMW Chaeklist For a Geological Assessment
Instructions:
This checkhstwRist be submitted with a Geological Assessrnentand completed,signed, and
stamped by the licensed professionai(s)who prepared the Geological Assessment for review by
Mason County pursuant to the Mason County Resource Ordinance. If an item found to be not
applicable,the report should explain the basis for the conclusion.
Applicant/Owner 9a_;4r. n CI. Parcel# /Z33o-SO-OARS S
SfteAddress 32 f Ali Anc4vr OriVt 13e.(Qr
(1) A discussion of geologic conditions in the generatvidnky of the
proposed development,with geologic unit designation based
on referenced maps.
Located on page(s)
(2) (a)A discussion of the ground water conditions at the site,
Located on page(s) 9
discussion of the ed de
pth epth to water
(b) Located on pages) `r'
(c) A discussion of the quartffty of surface seepage
Located on page(s)
9
(d) A discussion of the upslope geomorphology
Located on page(s) S-
(a) A discussion of location of and waterbodies and wetlands.
Located on page(s)
5
(3) The approximate depth to hard or dense competent soil,e.g.glacial till or outwash sand.
Located on page(s) 13
(4) A discussion of any geomorphic expression of past slope instability(presence of
hummocky ground or ground decks,terraced topography indicative of landslide dolt
movemen(bowed or arched trees indicating downslope movement, etc.).
Located on page(s) S'
(5 A dismission of the history of landslide activity in the vicinity,as available in the
referenced maps and records.
Located on page(s) /0 , /
(6) An opinion on whether the proposed development is within the landslide hazard area or
its associated buffer or setback and the potential for landslide activity at the site in light of
k the proposed development.
Located on page(s) /0
(7 A recommendation by the preparer whether a Geotechnical Report should be required to
further evaluate site conditions and the proposed development of the subject property.
Page 1 of 2 Forth Effective June 2008
■
Located on page(s) /v
(a) If the presence of a hazard is determined within 300 feet of the ro
then the following are cw6ated•on a geologic malt' a rtra P p�development,
(a) the area orthe propose dev on a gM p'
Located on Map(s) r
(b),the boun(1artes of the landslide hazard area(tOR both sides. and toe).
Located on Maps) 5: ,, p/�
(c) the associated buffers T.both sides,and toe)
Located on Map(s) a
(d) building or other setbacks(to .both skies, and foe).
Located on Maps)
(9 A she map drawn to scale showing the property boundaries,scale, north arrow, and the
location and nature of e�stinngg and posed development on the site.
Located on Maps) S.l_p
I. / -lll ���yle � � _ .
Penally of perjury that 1 ahr a civil ;i hereby certify under
engineer licensed in the Stale of Wash$rgtcm with sPacMWwed
lmowled in of geotechNcal/geological en9fieertn9 or a geologist orenginsering geologist
licensed in the State of Washington with apecial knoWedge of the local conditions. I also certify
that the Geological Assessment,dated
Ir rr ,/----�.�._, and entitled
rr�y
Mn n ,ny Ra9Durce Ordinance, wrests 811 the requirements of the
assessment demonstrates ly rde Hazard Section, is compete and true,that the
mitigated through the Included g�that
designposed by the landSWO hazard can be
Mitigated in such a manner as to reccmmerrdstlons,and that all hazards are
(Signature and,Stamp) prevent harm to property and public health and safety.
CLY4
�N
Assessment-
DisclaknOr Mason County does not certify the quality of the work done in this Geological
Page 2 of 2
Form Effective June 2008
APPENDIX A
{ SITE PLAN
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APPENDIX B
SOIL INFORMATION
F
Mason County, Washington
Ee—Everett gravelly loamy sand, 5 to 15 percent slopes
Map Unit Setting
• Elevation: 50 to 500 feet
• Mean annual precipitation: 55 to 90 inches
• Mean annual air temperature: 48 to 50 degrees F
• Frost-free period. 160 to 180 days
Map Unit Composition
• Everett and similar soils: 100 percent
Description of Everett
Setting
• Landtbrm: Terraces
• Parent material: Glacial outwash
Properties and qualities
• Slope: 5 to 15 percent
• Depth to restrictive feature: More than 80 inches
• Drainage class: Somewhat excessively drained
• Capacity of the most limiting layer to transmit water(Ksat): High to very high
(5.95 to 19.98 in/hr)
• Depth to water table: More than 80 inches
• Frequency of flooding: None
• Frequency of ponding: None
• Available water capacity: Very low (about 2.5 inches)
Interpretive groups
• Farmland classification: Farmland of statewide importance
• Land capability(nonirrigated): 4s
• Hydrologic Soil Group: A
• Other vegetative classification: Unnamed (G002XN402WA)
Typical profile
• 0 to 7 inches: Gravelly ashy loamy sand
• 7 to 21 inches: Extremely gravelly sand
• 21 to 60 inches: Very gravelly sand
Description — Map Unit Description
i
TEST PIT LOG
TEST PIT NUMBER TP-1
PROJECT: Beisley Geological Assessment DATE OF LOG: 02/12/2014
PROJECT NO: 1418 LOGGED BY: MCS
CLIENT: Beisley, Inc. EXCAVATOR: N/A
LOCATION: Parcel 12330-50-00088 DRILL RIG: None
Mason County, Washington ELEVATION: N/A
INITIAL DEPTH OF WATER: N/A FINAL DEPTH OF WATER: N/A
STANDARD PENETRATION TEST
SOIL STRATA,
DEPTH SAMPLERS USCS DESCRIPTION LL Pi CURVE
DEPTH N
AND TEST DATA 10 30 50
0 ....... ..........................................
-=•� SP Light brown,moist,medium dense SAND
with GRAVEL.Gravel is fine and
subrounded.Non plastic.
1 -
rV
2
3
GP Coarse GRAVEL with medium coarse
SAND.Non plastic.
O0
4 00
5 OO
001
very dense
6
Excavation terminated at approximately6.0 feet
7
8
9
10
No Groundwater Encountered ENVIROTECH ENGINEERING
Geotechnical Engineering
This in/wmation peftin;only to do bodng and d Wd not be
interpreted as being indi*w of ft sixes sRe.
f e one)neb and rtaeb'Qepy with wpwtram rb frT—23.a�? .
..., ataeebe WATER. WELL REPORT
'—d MGD+�� � or WASEDPOMMIC Permit tb. ....
(I) OWNER: Nie.___ky1L g_Uti.lsties Inc. wddP.0_1ox 29.�►.P�4];bQ,yN jDq�n gg�7p
C (P) LOCATION OF WELL camty w�^ ..NE-,A.-SE-a svc_3a-r-23 w.
dBearive Md dlemmr teem raw er eaad(etMee eoen.r f -East quarter corner
(3) PROPOSED US& Domadto p"lnd=UW D 10oaicbat D (18) WELL LOG.
Niniswaem D Ton!Wou D 0o w D esw�O`°�0°ewrai'.w 61F*°*mw ft6h eWT Oct 01 E y ew.mr r'�
3 Owb*ee Ammo at webt * I stem"o...fr.tmc at,art aW carry to7 rah ehaepr.r lbntattom.
y (4) TYPE OF WORE (u mr team aW).... __-- - 11A^�'a•- !anal TO
New wi 0 tmmed-Dos Hraa O Dm aaetl D tSbta)a Dom O "
C a.remumed D ih,hvy D JWM D
C
c (5) DISIXIMON& maxwr of ._$ taehea
�O DrRtad_i aim--- D(om.t.ametr.a--A 33tr R --
M (i) CONSTRUCTION DETAIIAk
Cad bj fashMad: t3 •Dram.free, 0 a to _ae 61
( MUWdM t7 Dram.tram_ m.m_A
webs"@ Dtem.from —_n m_to All 171.
Perfwat%im tar Q No
` zyvaaeradfetetar is HDifa raw86 It:
0 st>O:ar pa,emattac ey ,�. 2 _ d 874 we
3D—p.mraaW from�g�a m N Ave
parlmmttme erase 1tI_a.m a
prsmttsr from�—a.m ESL s
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Dram._ate nr r_tom—a.to a. 221
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Cc Gravel packs& Ym.D No p it M er+.eb:
GM eeb tdaea0 fro. rem tt.
3 Surface seek vw m ROD Tb what dot mr _s
mil"wave to"w nnl t..Awnt -, r= .
ODid on, atom aadtle mmaable setters Yr O No D Rbtn 87ir ft re t(+ (
z 7"0 or waawr—_ Dope at Scan-- 7 Qg (,to l .•r _
Method of"am Nam uR 1 O 1 i R t n
O (7) PUMP., tr—�7aryyq� t o ra '
do rypv;
a (8) WATER LEVEL& eve leaeb.... _ 50 - :•.. __ ,
mettle mva .....-- -_—_..-_!L hNrw up of waY na fa
ATSAAM w+.rum-- a Per eaueae had Dae___—
W ArmYam water le amtraD"w (CA*.vatva etc.)
w0 (9) WELL TEST& Drawdo le ammae. teem le
a+ lowr.d"' o,..mne m a'r wen(emron.7=29 m ZL. ursw (a• &z16 _1&ZL
= We,a pump tea"Mar Yee D Nop N yW,by
YI hew: Sal./min.WM tt drawdown otter hm. WELL DRILLERS STAT899ENT:
" .. This wept wet driUmd under ray)urledletien and Oft report le
true to the but of aq knowledte and bellel.
Recovery dam Inrr ^ r ono wave pone rraed o� (waam level
gl "same Rem.r�to"stem mat Stoic ui D Co. Inc.
O TM" wear raver r(a.. vacs feet t•me warn ravel NADr..._......._A.._.F�inA__.-_.-.._._.._....-................_....
__..
piemom,a.m,r eore enaa) (Type r primp
y ___..._....____........_ ..
M--
....... .___..�_ ...... AddtWe..._._....._..._._____.t_ ._._-•_.__^_.----._..._.___._..._
...........
Daa ae tea �wYm-.-4—a dww*e am ... [&lnad)- .. (w�W-nrllMrj�.�------------•
ttebtee tee _
tamperaUm at v zw___Was a ahamhat anatrab madam yr IR me D Llown
Chemical is by others
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TABLE OF CONTENTS
1.0 INTRODUCTION...................««.....................«........._...........................«...................................1
1.1 PROJECT INFORMATION.....................................................................................................................1
1.2 PURPOSE OF INVESTIGATION AND SCOPE OF WORK.........................................................................1
2.0 SURFACE CONDITIONS.«....«...........«.................................«. .........«...................................«.«3
2.1 GENERAL OBSERVATIONS..................................................................................................................3
2.2 TOPOGRAPHY......................................................................................................................................4
2.2.1 Upsiope Geonwrpkology.............................................................................................................4
2.3 SURFACEDRAINAGE...........................................................................................................................4
2.3.1 Upland Wafer Bodles..................................................................................................................4
2.4 SLOPE AND EROSION OBSERVATIONS................................................................................................4
3.0 SUBSURFACE INVESTIGATION«.«............«..................................................................................5
3.1 FIELD METHODS SAMPLING AND FIELD TESTING............................................................................5
3.2 GEOLOGICCONDITIONS.....................................................................................................................5
3.3 SPECIFIC SUBSURFACE CONDITIONS..................................................................................................7
3.3.1 Groundwater...............................................................................................................................8
4.0 ENGINEERING CONCLUSIONS«.«.«..........................................««.....«........«................................9
4.1 LANDSLIDE HAZARDS.........................................................................................................................9
4.L1 Landslides and Slope Stability Analysis...................................................................................11
4.L2 Surface and Subsurface Drainage...........................................................................................12
4.2 EROSION HAZARDS...........................................................................................................................12
4.3 SEISMIC HAZARDS............................................................................................................................12
4.4 ENGINEERING CONSIDERATIONS.....................................................................................................13
5.0 CLOSURE«....«...................................................................«...........................«........«««..«...........«.14
Appendix A-Site Plan
Appendix B-Soil Information
1.0 INTRODUCTION
Envirotech Engineering (Envirotech) has completed this geological assessment for a residential
property located at 321 NE Anchor Drive,identified as parcel number 12330-50-00088 in Belfair,
Mason County, Washington (Project). As presented herein, this assessment includes information
pertaining to the Project in this Introduction Section; observations of the property and
surrounding terrain in the Surface Conditions Section; field methods and soils descriptions in the
Subsurface Investigation Section; and, assessments for landslides, erosion, seismic hazards, and
other considerations in the Conclusions Section.
An initial geological/geotechnical evaluation of the Project was conducted by Envirotech without
the property owner or owner's representative on February 12, 2014. It was determined that
natural slopes between 15% and 400/a were present within 300 feet of the Project. Due to these
slope grades,a geological assessment is required pursuant to landslide hazard areas of the Mason
County Resource Ordinance(MCRO).
During the evaluation and site visit by Envirotech, surface and subsurface conditions were
assessed in order to determine if further geotechnical studies are required.After completion of the
field work and applicable Project research,Envirotech prepared this geological assessment.
1.1 Project Information
Information pertaining to the Project was provided by the property owner's representative, and
observations from a field visit by Envirotech.The property consists of an unimproved driveway.
The proposed development is expected to consist of a new single family residence and on-site
septic features.Approximate site development with relation to existing site features are illustrated
in the Site Map in Appendix A.
1.2 Purpose of Investigation and Scope of Work
The purpose of this geological assessment was to evaluate the Project in order to confirm that the
proposed development is outside of any landslide hazard area and its associated buffers and
setbacks as determined in the MCRO. The investigation included characterizing the general
Project surface and subsurface conditions,and evaluating the suitability of the soils to support the
planned site development. In order to fulfill the purpose of investigation, the geological/
geotechnical program completed for the proposed improvements of the Project include:
• Review project information provided by the Project owner's representative;
• Conduct a site visit to document the site conditions that may influence the construction
and performance of the proposed improvements;
• Define general subsurface conditions of the site by observing soils within test pit
excavations, review well logs from existing wells near the Project, and evaluate
geological maps depicting the site geology for the vicinity of the Project;
• Perform soils testing,such as visual classifications,to determine selected index properties
of the soils;
• Complete an engineering assessment supported by planned site alterations and the surface
and subsurface conditions that were identified by the field investigation, soil testing, and
applicable Project research,and,
• Establish engineering conclusions based on findings and anticipated Project.
Envirotech Engineering Beisley,Inc.Geological Assessment
Ph.360-275-9374 page 1 Parcel 12330-50-M88
Fax:360-2754789 Belfair,Mason County,Washington
February 19,2014
Ni FERN WAY
a� Project
Larson Lake y
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A-�J W 4 NE SEIrZ DRa� / ,ro JF—
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Vicinity Mapfrom Mason County Website.
Envirotech Engineering Beisley, Inc.Geological Assessment
Ph. 360-275-9374 page 2 Parcel12330-50-00088
Fax:360-2754789 Beifair, Mason County, Washington
February 19,2014
2.0 SURFACE CONDITIONS
Information pertaining to the existing surface conditions for the Project was gathered on February
12, 2014 by Michael Staten, geotechnical engineer with Envirotech. During the site visit, site
features were documented that may influence construction or reveal potential geological hazards.
This Surface Conditions Section provides information on general observations, vegetation,
topography,drainage and slope/erosion conditions for the Project and surrounding areas.
2.1 General Observations
The Project is currently vacant cleared for development with an existing driveway. The property
and neighboring properties have some fill and earth cuts.NE Anchor Drive extends along the east
side of the property, and Hood Canal is located over 1900 feet to the south. Vegetation on and
near the property consists primarily of 2w growth firs, blackberry, 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.
Project
s
a
Aerial Map from Mason County Website.
Envirotech Engineering Beisley,Inc.Geological Assessment
Ph. 360-275-9374 page 3 Parcel 12330-50-00088
Fax:360-2754789 Belfair,Mason County, Washington
February 19,2014
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
Map in Appendix A for an illustration of the general slope indicators with respect to the planned
development.
Descending slopes exceeding 15% are located on and beyond the property. Average slope grades
are approximately 20% with a vertical relief of approximately 70 feet. Cut and fill slopes on and
near the property have grades of over 60%vertical reliefs of nearly 10 feet.
2.2.1 Upslope Geomorphology
Ascending grades are generally located to the northwest of the planned development.
This slope grades within 300 feet of the Project and are of at least 30% in some locations.
The upland area of the property is situated on a hillside. Landforms are primarily of
glacial origin with centuries of weathering overburden. Additional geomorphology that is
pertinent to both upslope and downslope areas are provided in the Subsurface
Investigation Section of this report.
23 Surface Drainage
The neighbor's drainage outlet is in close proximity to the property line. Significant scour,
erosion and sediment transport was not apparent near the Project.
23.1 Upland Water Bodies
There are no apparent water bodies or wetlands located in immediate vicinity upslope
from the planned development that would significantly influence the Project. Larson
Lake is located at approximately 2200 feet to the northwest direction of the property.
2A Slope and Erosion Observations
The existing moderate slopes near the Project signal a potential landslide or erosion hazard area.
Some indicators that may suggest past slope movements include:
• Outwash of sediments near the bottom of the slope,
• Fissures, tension cracks or naturally stepped land masses on the face or top of the slope,
and parallel to the slope,
• Fine, saturated subsurface soils,
• Old landslide debris,
• Significant bowing or leaning trees,or,
• Slope sloughing or calving.
The above mentioned indicators, or other signs of significant mass wasting on the property or
within the general vicinity of the Project were not observed or discovered during research.
Indications of past landslides, current unstable slopes, deep-seated slope problems, or surficial
slope failures were not observed during the site visit.
Envirotech Engineering Beisley,Inc.Geological Assessment
Ph. 360-275-9374 page 4 Parcel 12330-50-00088
Fax: 360-2754789 Belfair, Mason County, Washington
Febmary 19,2014
3.0 SUBSURFACE INVESTIGATION
Information on subsurface conditions pertaining to the Project was gathered during research and a
site reconnaissance. The site visit was accomplished on February 12, 2014 by Michael Staten,
geotechnical engineer with Envirotech. Specific information on field methods, sampling, Feld
testing, subsurface conditions, and results from soil testing are presented in this section of the
report. Appendix B has pertinent information on subsurface conditions for the Project, including
test pit log(s)representative of the site soils, and water well report(s)originating from the subject
property and/or nearby properties.
3.1 Field Methods,Sampling and Field Testing
Information on subsurface conditions for the Project was accomplished by probing anticipated
foundation areas with hand tools, and observing soils within test pit excavations and/ or earth
cuts. Information on subsurface conditions also included reviewing geological maps within the
Project vicinity,and water well reports originating from nearby properties.No soil samples were
collected for this Project. Envirotech measured the relative density of the in-situ soils by gauging
the resistance of hand tools.
3.2 Geologic Conditions
In general, soils at the project are composed of materials from glacial advances. The geologic
conditions as presented in the "Geologic Map of Washington," compiled by J. Eric Schuster,
2002 indicates Quaternary sediments, QB. 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 Beisley,Inc. Geological Assessment
Ph.360-275-9374 page 5 Parcel12330-50.00088
Fax: 360-275-4789 Belfair,Mason County, Washington
February 19,2014
., . .
b Q
4 D r
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Geologic Map USGS Website.
Qgic Vashon glacial ice-contact deposits—Sand, gravel, lodgment till, and flow till; minor silt and clay
beds; tan to gray; variably sorted; loose to compact; massive to well stratified; locally includes over-
steepened beds that typically reflect sub-ice flow, but their dip may, along with small-scale shears, also
have developed as collapse features or due to glaciotectonic and tectonic deformation; formed in the
presence of meltwater alongside ice, generally toward the end of the glaciation, and is thus commonly
accompanied by stagnant-ice features, such as kettles and less-orderly hummocky topography, eskers(also
separately mapped as subunit Qge), and subglacial or subaerial outwash channels. Deposits and
morphologies that support conceptual association with both ice and meltwater are common in the map area
and suggest that where unit Qgic is mapped in the presence of fluted topography,it is commonly only a few
Envirotech Engineering Beisley,Inc.Geological Assessment
Ph.360-275-9374 page 6 Parcel12330-50-00088
Fax: 360-275-4789 Belfair, Mason County, Washington
February 19,2014
feet thick and locally could have been mapped as undifferentiated drift(unit Qgd). Elsewhere,the unit may
be over 100 ft thick. Unit Qgic also includes poorly consolidated till commonly accompanied by
underlying, angular sand and noted as "sub-glacially reworked till' by Laprade (2003) (see Geologic
Setting), especially in fluted areas that lack dead-ice features. See unit Qgo and Fig. 4 for discussion of
similarities between units Qgic and Qgo (and its subunits Qgos, Qgof, and Qgol). A discrepancy between
this map and the Vaughn quadrangle to the south resulted where Logan and Walsh (2007) mapped
undifferentiated Quaternary deposits (unit Qu) because they lacked field exposures and geomorphic signs
of the dead-ice deposits that are apparent north of the boundary. Dead-ice topography north of the boundary
also reveals a sandy deposit mapped as unit Qgos by Logan and Walsh (2007) to be a facies within unit
Qgic. Locally divided into:
Qge Vashon glacial eskers—Sand and gravel; tan to brown; loose; moderately to well sorted; moderately
to well rounded with good porosity and permeability;deposited subglacially by Vashon melt-water in areas
occupied by stagnant ice;forms low,elongate,sinuous hills that seem to rest like slugs on fluted
uplands or subglacial outwash channels and locally can be seen to merge into channel incisions (Fig. 1).
One such transition causes a map boundary mismatch between unit Qgic on this map and unit Qgoe(esker)
on the Vaughn quad to the south (Logan and Walsh, 2007). Some polygons of this unit abut against unit
Qgic in the Lake Wooten quadrangle to the west(Derkey and Hehemann,2009),where eskers are noted by
linear symbols over unit Qgic. The underlying interpretation is identical.
3.3 Specific Subsurface Conditions
The following subsurface conditions are estimated descriptions of the Project subgrade utilizing
information from the depth of penetration at all testing, sampling, observed and investigated
locations. Soils for this project were described utilizing the Unified Soil Classification System
(USCS). Using the USCS in conjunction with estimated relative densities and other anticipated
engineering properties of the soil, susceptibility for potential landslides, erosion and seismic
hazards may be assessed.
The Project is primarily composed of undisturbed, native soils, with indications of isolated fill as
previously mentioned. Competent bearing soils were encountered at 18 inches below the existing
native ground surface in locations where the ground was probed. Fill areas were loose and
unconsolidated—not suitable for foundations. For engineering purposes,these native soils consist
of distinguishable layers,as presented below.
Soils within the upper 3 feet of natural ground were observed to be primarily moist, light brown
medium dense sand with fine gravel (SP). Soils below the upper 3 feet SP layer were observed to
be coarse gravel with medium coarse sand(GP). Soils below the upper 6 feet GP layer were very
dense SM. Expanded and specific subsurface descriptions, other than what is provided in this
section,are provided in the soil logs located in Appendix B of this report.
According to the "Soil Survey of Mason County," by the United States Department of
Agriculture, Soil Conservation Service (SCS), the site soils are described as Everett gravelly
loamy sand, E,, 5 to 15 percent slopes. See the soil map below, and the applicable SCS soil
profile(s)in Appendix B of this report.
Envirotech Engineering Beisley,Inc.Geological Assessment
Ph.360-275-9374 page 7 Parcel 12330-50-00088
Fax: 360-2754789 BeMir,Mason County, Washington
February 19,2014
Soil Surveyfrom 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 140 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 Beisley,Inc. Geological Assessment
Ph.360-275-9374 page 8 Parcel12330-50-00088
Fax: 360-2754789 Belfair, Mason County,Washington
February 19,2014
4.0 ENGINEERING CONCLUSIONS
The following sections present engineering assessments and conclusions concerning the Project.
These conclusions have been made available based on the planned construction activities as
outlined in the Introduction Section of this report; general observations of drainage and
topography as summarized in the Surface Conditions Section; and, soil conditions that were
identified by the field investigation and soils testing as outlined in the Subsurface Investigation
Section. Conclusions for the Project that is provided herein, includes pertinent information for
landslide, erosion and seismic hazards.
4.1 Landslide Hazards
For the planned development, as provided in the Introduction Section of this report, it is
Envirotech's opinion that the proposed development is not subjected to or cause adverse impacts
to a landslide hazard area or its associated buffer or setback as defined in the MCRO. This
conclusion is based on the contents provided in this report.
Landslides are natural geologic processes, and structures near slopes possess an inherent risk of
adverse settlement, sliding or structural damage due to these processes. Geotechnical engineering
cannot eliminate these risks for any site with sloping grades because gravity is constantly
inducing strain on the sloping soil mass. Excessive wet weather and/ or earthquakes will
exacerbate these strains. Geotechnical engineering considers excessive wet weather and `design'
earthquakes in order to provide an acceptable factor of safety for developing on or near sloping
terrain. These factors of safeties are based on engineering standards such as defining engineering
properties of the soil,topography,water conditions, seismic acceleration and surcharges.
Surface sloughing or other types of surficial slope movements usually do not affect the deep-
seated structural capability of the slope. However, excessive and/or repeated surficial slope
movements, if not repaired, may represent a threat to the structural integrity of the slope.
Maintenance of the slope should be completed if the situation does arise in order to prevent the
possibility of further surficial or deep seated slope movements that may be damaging to life or
property.
According to the Coastal Zone Atlas of Mason County, Washington, the Project is within and
near terrain labeled `Stable' 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. A site specific analyses and conclusions concerning the slopes
are presented herein. A Stability Map from the Coastal Zone Atlas for the general area of this
Project may be found below.
Envirotech Engineering Beisley,Inc.Geological Assessment
Ph.360-275-9374 page 9 Parcel 12330-50-00088
Fax:360-2754789 Belfair, Mason County, Washington
February 19,2014
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According to the Department of Natural Resources (DNR) "LHZ — Final A-1 Map — Landslide
Inventory—Mason Watershed, by Sarikhan, et. al., May 2007," previous landslide activity is not
recorded near the project. Per the Resource Map from DNR, the Project is not within terrain
labeled `highly unstable' or `highly erodible' relating to soils. DNR labeled portions of this
project as medium slope instability with relation to slopes. This delineation is primarily
dependent upon slopes and convergence. Secondly, lithology and precipitation are modeled
within this delineation. In summary, this designation is based on mapping without field
observations or knowledge of the specific site geology or soils. A resource map from DNR is
provided below:
Envirotech Engineering Beisley,Inc.Geological Assessment
Ph. 360-275-9374 page 10 Parcel 12330-50-00088
Fax: 360-275-4789 Belfair,Mason County,Washington
February 19,2014
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4.1.1 Landslides and Slope Stability Analysis
Past landslide activity or high slope instability indicators near the proposed development
was not revealed during the Project research. In addition, detrimental landslide activity or
potential high landslide indicators were not observed during the site visit as outlined in
the Surface and Subsurface Conditions Sections of this report. Due to these factors, and
existing/proposed conditions,a slope stability analysis was not deemed necessary for this
Project. Considering the planned construction as summarized in the Introduction Section
of this report; the aforementioned surface and subsurface conditions for the Project; the
slope stability assessment provided herein; and the Engineering Conclusions provided
later in this report, it is our opinion that the Project is not within a landslide hazard area,
and that the proposed site alterations will not encourage a landslide hazard.
Envirotech Engineering Beisley, Inc. Geological Assessment
Ph.360-275-9374 page 11 Parcel 12330-50-00088
Fax:360-275-4789 Belfair,Mason County,Washington
February I9,2014
4.1.2 Surface and Subsurface Drainage
Although neighboring outlets directly affect the property, it does not appear to cause
landsliding. Minor erosion is expected. If these outlets become problematic, Envirotech
should be contacted for possible solutions. See the Engineering considerations provided
later in this report for roof runoff mitigation.
4.2 Erosion Hazards
Based on the USCS description of the Project soils, the surface soils are considered moderately
erodible. According to the Resource Map from the Washington State DNR, as provided above,
the Project is not within terrain labeled `highly erodible.' This Project is not within an erosion
hazard area as defined by the MCRO. Erosion hazard areas are those with USDA SCS
designations of River Wash (Ra), Coastal Beaches (Cg), Alderwood Gravelly Sandy Loam on
slopes 15% or greater (Ac and Ad), Cloquallum Silt Loam on slopes 15% or greater (Cd),
Harstine Gravelly Sandy Loam on slopes 15% or greater (Hb), and Kitsap Silt Loam on slopes
15%or greater(Kc).
Temporary and/ or permanent erosion control measures may be required for any site when land
disturbance is involved. Erosion control will mostly depend on the timeliness of construction,
moisture content of the soil, and amount of rainfall during construction. Soil erosion typical to the
existing conditions and planned disturbance of this Project include wind-borne silts during dry
weather, and sediment transport during prolonged wet weather. Sediment transport of disturbed
soils could be from stormwater runoff or tracking off-site with construction equipment. Although
an engineered erosion control plan is not warranted for this project, Best Management Practices
(BMP's) should be employed during and after construction. Ordinary BMP's includes silt
fencing,protection of drainage outlets and vegetating denuded areas.
Erosion control information and specifications may be found in the applicable "Stormwater
Management Manual for Western Washington,"prepared by the Washington State Department of
Ecology Water Quality Program.
43 Seismic Hazards
Soils immediately below the expected foundation depth for this Project are generally Type D,
corresponding to the International Building Code (IBC) soil profiles. According to the IBC, the
regional seismic zone is 3 for this Project. The estimated peak ground acceleration ranges from
0.50g to 0.60g.This estimation is based on the United States Geological Survey(USGS)National
Seismic Hazard Project in which there is an estimated 2% probability of exceedance within the
next 50 years.
There are no known faults beneath this Project. The nearest Class `A' or 'B' fault to this property
is the Tacoma Fault Zone. This fault is a Class `A,` and is located approximately 6 miles to the
south of the Project. This information is supported by the USGS Quaternary Fault and Fold
Database for the United States.
The potential for liquefaction and other earthquake induced hazards are believed to be low for
this Project. This is based on subsurface conditions such as soil characteristics and the lack of a
permanent and substantial shallow water table. Subgrade characteristics that particularly
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February 19,2014
contribute to problems caused by seismic events include submerged and confined poorly-graded
granular soils. Although gravel- and silt-sized soil particles could be problematic, fine and
medium grained sands are typically subjected to these types of seismic hazards.
4.4 Engineering Considerations
Conclusions in this report are based on the type and location of the anticipated development, and
existing on-site and off-site conditions.Roof drainage for this project should have an outlet above
ground, and located downslope as much as possible. An outlet with rip-rap lined channel between
the driveway and property line is recommended.
Existing fill should be removed and replaced with engineered fill,or foundations should extend to
at least 18"below bottom of fill.
Although slopes are currently stable, development could induce instability. For this reason,
buildings should be located at least 10 feet from top of descending slopes. Encroachment of this
10-foot setback may occur by deepening foundations an additional depth of 12 inches per every
1-foot of setback reduction.
Site development that significantly deviates from the anticipated improvements presented in this
report, or nearby development that influences this Project may require gectechnical design
recommendations.
Envirotech Engineering Beisley, Inc.Geological Assessment
Ph. 360-275-9374 page 13 Parcel 12330-50-00088
Fax:360-2754789 Belfair, Mason County,Washington
February 19,2014
5.0 CLOSURE
Based on the project information and site conditions as presented in this report, it is Envirotech's
opinion that additional geotechnical studies are not required to further evaluate this Project.
Due to the inherent natural variations of the soil stratification and the nature of the geotechnical
subsurface exploration, there is always a possibility that soil conditions encountered during
construction are different than those described in this report. Therefore, it is recommended that
Envirotech is promptly notified if project and subsurface conditions found on-site are not as
presented in this report so that we can re-evaluate our recommendations.
This report presents a geological/geotechnical assessment, and is intended only for the owner, or
owners' representative. Furthermore, this report is only valid for the project information and
location described herein.
The services described in this report were prepared under the responsible charge of Michael
Staten, a professional engineer with Envirotech. Michael Staten has appropriate education and
experience in the field of geotechnical engineering in order to assess landslide hazards,
earthquake hazards,and general soil mechanics.
Please contact Michael Staten at 360-275-9374 if you have any questions, comments, or require
additional information.
Sincerely,
Envirotech Engineering
Michael Staten,P.E.
Geotechnical Engineer
Envirotech Engineering Beisley, Inc.Geological Assessment
Ph.360-275-9374 page 14 Parcel12330-50-00088
Fax:360-275-4789 Belfair,Mason County, Washington
February 19,2014