HomeMy WebLinkAboutGEO2018-00023 - GEO Geological Review - 2/24/2018 ,
GEOZI�I� - ���
Mason County Review Checklist
For a Geological Assessment
Instructions:
This checklist is intended to assist Staff in the review of a Geological Assessment. The Assessment 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 Assessment is also reviewed for clarity and consistency. If the drawings,
discussion or recomme
ndations 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 Name: L-)n QU.r�
Permit#: Parcel#'s:
Date(s)of the Document(s) reviewed:
1. A discussion of geologic conditions in the general vicinity of the proposed development, with geologic unit
designation based on referenced maps.
OK?X_Comment:
2. (a) A discussion of the ground water conditions at the site,
OK? Comment:
(b) A discussion of the estimated depth to water,
OK?_)� Comment:
(c) A discussion of the quantity of surface seepage,
OK? 'y Comment:
(d) A discussion of the upslope geomorphology,
OK? X Comment:
(e) A discussion of location of upland waterbodies and wetlands.
OK? Comment:
3. The approximate depth to hard or dense competent soil, e.g. glacial till or outwash sand.
OK?_X Comment:
4. A discussion of any geomorphic expression of past slope instability (presence of hummocky ground or ground
cracks, terraced topography indicative of landslide block movement, bowed or arched trees indicating
downslope movement, etc.).
OK? X_Comment:
5. A discussion of the history of landslide activity in the vicinity, as available in the referenced maps and records.
OK? _Comment:
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 the proposed development.
OK? _Comment:
7. A recommendation b the pre parer p p arer whether a Geotechnical Report should be required to further evaluate site
conditions and the proposed development of the subject property.
OK? _Comment:
8. If the presence of a hazard is determined within 300 feet of the proposed development, then the following are
delineated on a geologic map/site map:
Page 1 of 2 Form Effective June 2008
(a) the area of the proposed development,
OK? Comment:
(b) the boundaries of the landslide hazard area (top, both sides, and toe),
OK? — Comment:
(c) the associated buffers (top, both sides, and toe)
OK? Comment:
(d) building or other setbacks (top, both sides, and toe).
OK? Comment:
9. A site map drawn to scale showing the property boundaries, scale, north arrow, and the location and nature of
existing and pro osed development on the site.
OK? Comment:
Are the Documents signed and stamped?—Y— By whom? VG 1 GE C 6u&o
License#: License type: PC
FIRST REVIEW Approved ❑ Need more info.
If not approved, what is the next action/recommendation for further action?
Reviewed by on IZ7// Time spent in review: �� m
SECOND REVIEW/UPDATE ❑ Approved ❑ Need more info.
If not approved, what is the next action/recommendation for further action?
Reviewed by on . Time spent in second review:
THIRD REVIEW/ UPDATE ❑ Approved ❑ Need more info.
If not approved, what is the next action/recommendation for further action?
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
MASON COUNTY Submittal Checklist
COMMUNITY SERVICES Geological Assessment
Bulldiag,Pfinning,EnYi(onmental Health,Community Hoahh
Instructions:
This checklist must be submitted with a Geological Assessment and completed,signed, and stamped by the licensed
professional(s)who prepared the Geological Assessment for review by Mason County pursuant to the Mason County
Resource Ordinance. If an item is found not applicable,the report should explain the basis for the conclusion.
Note:Unless specifically documented,this report does not provide compliance to the International Residential Code Sections
R403.1.7 for foundations on or adjacent to slopes,Section R403.1.8 for expansive soils or section 1808.7.1 of the International
Building Code Section for Foundations on or adjacent to slopes.
Applicant/Owner l Parcel# -Jor)4 CI= '
ti01v.,i6
Site Address XXA )EI S7 I' `"1 , 11r P
(1) A discussion of geologic conditions in the general vicinity 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,
F'1
Located on page(s)��,
(b) A discussion of the estimated depth to water,
Located on page(s)
(c) A discussion of the quantity of surface seepage,
Located on page(s) �r'
(d) A discussion of the upslope geomorphology,
Located on page(s) i
(e) A discussion of location of upland waterbodies and wetlands.
Located on page(s)",
(3) The approximate depth to hard or dense competent soil,e.g.glacial till or outwash sand.
Located on page(s) y
(4) A discussion of any geomorphic expression of past slope instability(presence of hummocky ground or ground
cracks,terraced topography indicative of landslide block movement, bowed or arched trees indicating
downslope movement,etc.).
Located on page(s) -2,
(5) A discussion of the history of landslide activity in the vicinity, as available in the referenced maps and records.
Located on page(s)
(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 the proposed development.
Located on page(s)
(7) A recommendation by the preparer whether a Geotechnlcal Report should be required to further evaluate site
conditions and the proposed development of the subject property.
Rev.February 2018
i
Located on page(s)
(8) If the presence of a hazard is determined within 300 feet of the proposed development,then the following are
delineated on a geologic map/site map:
(a) the area of the proposed development,
Located on Map(s) 0/4
(b) the boundaries of the landslide hazard area(top, both sides,and toe),
Located on Map(s) 04i
(c) the associated buffers top, both sides,and toe),
i�
Located on Map(s) /
(d) building or other setbacks (top, both sides,and toe).
Located on Map(s) A214
(9) A site map drawn to scale showing the property boundaries, scale, north arrow, and the location and nature of
existing and proposed development on the site.
Located on Map(s) rite
hereby certify under penalty of perjury that I am a
civil engineer licensed in the State of Washington with specialized knowledge of geotechnical/geological engineering
or a geologist or engineering geologist licensed in the State of Washington with special knowledge of the local
conditions. I also certify that the Ge logical Assessment, dated rE� and entitled
J ) 1
h - c7c' .�� �;t�s'S>' ; r i , �',} P•�h/1,C v� L"o �r meets all the
requirements of the Mason County Resource Ordinance,Geologically Hazardous Areas Section, is complete and true,
that the assessment demonstrates conclusively that the risks posed by the landslide hazard can be mitigated through
the included geotechnical design recommendations, and that all hazards are mitigated in such a manner as to prevent
harm to property and public health and safety.
r NYAs
(Signature and Stamp)
Page 2 of 2
Disclaimer.Mason County does not certify the quality of the work done In this Geological Assessment.
DE-CIVIL, PLLC
P.O. Box 446
F Tacoma,WA 98401
Ph(253)228-0513
www.de-civil.com
February 24, 2018
Mr. Dale Dowler Geologic Assessment: Landslide
7516—50'Street W Hazard Geotechnical Letter
University Place.,WA 98467 XXX East 4th Street
Mason County,Washington
C/o Mr. Mike Spingola PN:322325-2-0014&0016
Job: 18-037 Spingola.LHGL
INTRODUCTION
This report presents the results of our geotechnical investigation for the proposed residential building to be
located at XXX East 4th Street in Mason County, Washington. The general location of the site is shown on the
attached Site Vicinity Map, Figure 1.
Our understanding of the project is based on our discussions with you, and our January 25, 2018 site visit. We
understand that you are in the process of applying for a building permit for a new residence to be located on
the currently undeveloped parcel(s).The building will be situated in the west side of the site the north end of
the undeveloped lot. The building will most likely be comprised of concrete and wood frame construction.
Clearing and grading is expected to be limited to that required to develop sufficient access to the new building
site.
SCOPE
The purpose of our services is to evaluate the surface and subsurface conditions at the site as a basis for assessing
potential adverse impacts to and from the slopes located within the site area. We understand that because of
the height and inclination of the slopes on the site,a geotechnical assessment is being required by Mason County
to address geologic hazards at the site. Specifically,our scope of services for the project included the following:
1. Visiting the site and conducting a geologic reconnaissance to assess the site's soil,groundwater,
and slope conditions.
2. Assessing the landslide hazards in accordance with the current Mason County ordinances.
No subsurface explorations or laboratory testing were completed as part of this assessment. However,we were
able to observe the near surface soil conditions in exposed soils on the site and review available septic test pit
records.
The services described in this report were prepared under the responsible charge Glen Coad, PE. Mr. Coad
meets the qualifications contained in the Mason County codes to prepare a landslide hazard geological
assessment. Mr. Coad understands the requirements of the current Landslide Hazard Area Chapter and the
definitions of the applicable terms contained within it. Individuals under the responsible charge of Mr. Coad
has performed a landslide hazard geotechnical assessment, conducted a field investigation, and researched
available historic records on the above referenced site. In our opinion,the scope of services completed for this
project is adequate to meet the requirements of the Department and it does not appear that an active
landslide hazard area exists within 300 feet of the site.
18-037 Spingola.LHGL
February 24,2018
Page 2
SITE CONDITIONS
Surface Conditions
The subject parcel is located at XXX East 4th Street in Mason County, Washington. The parcels are somewhat
irregular in shape and measure approximately 160 feet in length (north to south) by 130 feet in width (east to
west)and encompasses approximately 0.47 acres when combined. The lots have been largely cleared of trees
at some point in the past.Access to the site is from East 4th Street, a public road. The west area of the site is
moderately sloped with grades of 10 to 15 percent with a steeply sloped area along the east side of the property.
This steeply sloped area appeared to be 30 to 50 percent grade with an overall elevation height of 20 to 30 feet.
The slope was well vegetated with trees and appeared to be in a stable condition.The site is bounded by similar
residential properties on the south, north,west and east.
No seepage was observed at the time of our site visit. No evidence of deep-seated slope instability was observed
at the site or the adjacent areas at the time of our site visit. No erosion, or other soil movement was observed
at the time of our site visit. At the time of our site visit the property was well vegetated with trees,grass, and
shrubs.
Site Soils
The Natural Resource Conservation Service Web Soil Survey for Pierce County mapped the soils in the area of
the site as Alderwood gravelly sandy loam (Aa & Ad). The Alderwood soils are derived from glacial till under
conifers typically have very low infiltration capabilities. Slopes generally range from 0 to 15 percent and 30 to
50 percent and are listed as having a Slight and Severe erosion hazard respectively. Based on our site
observations we anticipate that dense till soils are present at depths of 4 feet or less. A copy of the NRCS Web
Soil Survey map for the site vicinity is attached as Figure 2.
Site Geology
The Geologic Map of the Skokomish Valley and Union 7.5 minute Quadrangle, Mason County, Washington by
Micheal Polenz, Jessica L. Czajkowski, Gabriel Legorreta Pulin, Trevor A. Contretas, Bendan A. Miller, Maria E.
Martin,Timothy J. Walsh, Robert L. Logan, Robert J. Carson, Chris N.Johnson, Rian H.Skov,Shannon A. Mahan
and Cody R. Cohan, June 2010 (Revised 2011) indicates that the site is underlain by Vashon glacial till (Qgtt).
This glacial soil was deposited during the most recent Vashon Stade of the Fraser Glaciation, approximately
12,000 to 15,000 years ago.The glacial till consists of a mixture of clay,silt,sand,and gravel that was deposited
at the base of the prehistoric continental glacial ice mass and were subsequently over-ridden. Glacial soils
overridden by glacial ice can be considered over-consolidated, which typically exhibit high strength and low
compressibility characteristics.An excerpt of the above referenced map in included as Figure 3.
The Puget Sound Coastal Zones Atlas has the site mapped as "S" for Stable with outlying areas marked with a
"I" Intermediate slope stability,see Figure 4 Coastal Zones Atlas.
No groundwater seepage was observed on the site or adjacent areas.
Landslide Hazard Indicators—per Mason County,Chapter 8
The Code of Ordinances for Mason County, Chapter 8,Section 52,Article 140 states that a landslide hazard area
is any of the following:
A. Areas with an indications of earth movement such as debris slides,earthflows,slumps,and rock falls.
B. Areas with artificial over steepened or un-engineered slopes. i.e.,cuts or fills.
C. Areas with slopes containing soft or potentially liquefiable soils.
D. Areas over steepened or otherwise unstable as a result of stream incision,stream bank erosion,and
undercutting by wave action.
E. Slopes greater than fifteen percent(8.5 degrees)and having the following:
18-037 Spingola.LHGL
February 24,2018
Page 3
a. Hillsides intersecting geologic contacts with a relatively permeable sediment overlying a
relatively impermeable sediment or bedrock(e.g.,sand overlying clay);and
b. Springs of groundwater seepage.
F. Any area with a slope of forty percent or steeper and with a vertical relief often or more feet except
areas composed of consolidated rock. A slope is delineated by establishing its toe and top and
measured by averaging the inclination over at least ten feet of vertical relief.
The following information may be used as a guide by the county to indicate areas that have a higher likelihood of
meeting the classification criteria previously listed:
A. The areas identified on the Mason County Soil Survey Map as having slopes greater than fifteen
percent.
B. The areas identified on the Coastal Zone Atlas,Volume 9,of Mason County,Washington as:
a. Unstable—"U"
b. Unstable Old Slides—"UOS"
c. Unstable Recent Slides—"URS"
d. Intermediate Slopes—"I"
e. Modified Slopes—"M"
C. The areas identified as Class 2, 3,4,or 5 of the maps: "Relative Slope Stability of the Southern Hood
Canal Area, Washington" by M. Smith and R.J. Carson, Washington State Department of Natural
Resources, Division of Earth Resources, 1977; `The Geological Map of North Central Mason County,
Washington," by R.J. Carson 1976, U.S.Geologic Survey OFR 76-2.
D. Areas mapped as landslide deposits (Map Unit Qls) on the" Geologic map of the Longbranch 7.5-
minute quadrangle,Thurston, Pierce, and Mason Counties, Washington by R. L. Logan, T.J. Walsh,
and Michael Polenz. One sheet,scale 2:24,000,2003;Geologic map of the Squaxin Island 7.5-minute
quadrangle, Mason and Thurston Counties,Washington, by R. L. Logan, Michael Polenz,T.J. Walsh,
and H. W. Schasse. One sheet, scale 1:24,000, 2003; Geologic map of the Shelton 7.5-minute
quadrangle, Mason and Thurston Counties, Washington, by H. W. Schasse, R. L. Logan, Michael
Polenz,and T.J. Walsh. One sheet,scale 1:24,000, 2003;and Geologic map of the Summit Lake 7.5-
minute quadrangle,Thurston and Mason Counties,Washington, by R.L. Logan and T.J.Walsh. Forty-
two by thirty-six inch.Color sheet,scale 1:24,000,2004.
CONCLUSIONS
Based on our site evaluation,it is our opinion that the site is suitable for the future construction of the proposed
residence and related appurtenances. It is also our opinion that an active landslide hazard area does not exist
on or within 300 feet of the site.
Landslide Hazard Indicators—per Pierce Mason County Chapter 8
Mason County, Chapter 8, Section 52, Article 140 uses the above referenced checklist to define a landslide
hazard area. Based on our observations of the site and review of published information,we offer the following
comments.
No evidence of landslide activity, or significant erosion was observed at the site at the time of our site visit.
Some slopes steeper than 15 percent were observed on or near the site, but no intersecting contacts were
observed or are mapped in the site vicinity. There were some slopes steeper than 40 percent with more than
10 feet in height located on the site. We did observe slopes greater than 30 percent with more than 10 feet of
height on the site associated with native slopes east of the building site. It is anticipated that the future building
will not be located within the height of the slope divided by three (approximately 10 feet), therefore it is
anticipated that it will be able to meet prescriptive setback requirements. If these requirements cannot be met
we will be available to provide additional recommendations or setback reduction criteria. Some clearing and
18-037 Spingola.LHGL
February 24,2018
Page 4
grading may occur on the steeper slopes occurring on the site. Provided appropriate soil erosion control and
site stabilizing measures are employed, we do not anticipate that it will be a limiting feature to site
development. No groundwater seepage was observed at the site. No planes of weakness or rockfall hazards
were observed at the site. No other landslide hazard criteria were observed at the site or the immediate
adjacent areas.
LIMITATIONS
We have prepared this report for the Dowler's and members of the design team for use in evaluating a portion
of this project. Subsurface conditions described herein are based on our observations of exposed soils on the
parcel. This report may be made available to regulatory agencies or others, but this report and conclusions
should not be construed as a warranty of subsurface conditions. Subsurface conditions can vary over short
distances and can change with time.
Within the limitations of scope, schedule and budget, our services have been executed in accordance with
generally accepted practices in this area at the time this report was prepared. No warranty,express or implied,
should be understood.
We trust this is sufficient for your current needs. Should you have any questions, or require additional
information, please contact us at your earliest convenience.
Respectfully submitted,
Development Engineering, PLLC
�r GL
~ ti
n
Owner
WGC
Doc ID:18-037 Spingola.LHGL
Attachments: Figure 1:Vicinity Map
Figure 2:USDA Soils Map
Figure 3:USGS Geological Map
Figure 4:Coastal Zones Atlas
Figure 5:Site Plan
�`tlglon
rr N
b
W Yy
C elee"ADr-....i Pant C-tlsNCrA�c
E PlrtatS�- - -_.@ g➢�9++a Arc-
-_.
u^Ridge Rn
E%30
x�O
d
Es 1
Approximate Site Location
Not to Scale
I
DE-CIVIL, PLLC
D P.O. Box 446 Site Vicinity Map
Tacoma,WA 98401 Dowler Residence
Ph(253)228-0513 XXX East 4th Street
www.de-civii.com
Mason County, Washington
Job No:18-03' February 2018 Figure 1
Sal Map--Mason County`Nasnington
A _
r Q= C= 4ZI'S 4= 4= - 4Q2W 4MO s�d:
r-
{
('Y+f C3.
y. K.. _. �;jam'•�p 'y ! +
ti 7�
I
muse � ;. a.,..,�•..�::t.:i<- ..:. C: 4r ns"
i
�' 14p5ak�111Afpitidm Abid+�!(11'•B.573st
c a m +® m
we
c ra 3110 ® um
/V "$w'Y w.b'ram can.—*n k-WGS84 EdWb:urM Z-1GN WGSo4
111 Natwal Resources Web Sat Survey 2/24/2018
-mm Conservation Service Nabonal Cooperative Sal Survey Page 1 of 3
Approximate Site Location 0
WNot to Scale
DE-CIVIL, PLLC USDA Soils Map
D P.O. Box 446
Tacoma,WA 98401 Dowler Residence
Ph(253)228-0513 XXX East 4th Street
www.de-civil.com Mason County, Washington
Job No:18-037 February 2018 Figure 2
O
i e 7 i
i (I
I
r d„�
BWl 2. gMISf 0
Mud i14--l� ` i'•d„i$ i
pi0.1 of
Qbr,•--
7 K O M l . S H s �' l . Q
PUop
_ v-
L A T r$ 9a ' �f $7
�I
� 1 •, of� �., �. y ., � r� :�� r_y t t��r:.�,.�.
1, Oaf $ ,
.l .F -_ram Q ' •'-�,J� ✓.�_ J „i�' _ :.
7 , ,,,ypp►'���
Opo
1 x
1 :.�.Y. r t!//Il,r, ..{•.._,�,,.l���lt�'Jl ."'�J •� ... Y``�t j/. A;
Approximate Site Location 0
I
Not to Scale
DE-CIVIL, PLLC
P.O.Box 446 Geological Map
Tacoma,WA 98401 Dowler Residence
Ph(253)228-0513 XXX East 4th Street
www.de-civil.com
Mason County, Washington
I
Job No:18-037 February 2018 Figure 3
i
d
Approximate Site Location
Not to Scale
T` DE-CIVIL, PLLC Slope Stability Map
P.O. Box 446
Tacoma,WA 98401 Dowler Residence
Ph(253)228-0513 XXX East 4t'' Street
www.de-civil.com
Mason County, Washington
Job No:18-037 February 2018 Figure 4
- ST�uE.GRRi.Sota
3�IL'3a.
4li110n County Dept. ►faith S v C�
APPROY O
(CIS-
n
(J
o a1I.
CrLEhREI, AIeEA
E
Ate 1"• 10
TEST BOLES
Not to Scale
DE-CIVIL PLLC
Site Plan
P.O.Box 446
D Tacoma,WA 98401 Dowler Residence
th
Ph(253)228-0513 XXX East 4 Street
www.de-civil.com
Mason County, Washington
Job No:18-037 February 2018 Figure 5
i
DE-CIVIL, PLLC
P.O. Box 446
Tacoma,WA 98401
Ph (253) 228-0513
www.de-civil.com
February 24, 2018
Mr. Dale Dowler Geologic Assessment: Landslide
7516—50th Street W Hazard Geotechnical Letter
University Place., WA 98467
Mason County, Washington
C/o Mr. Mike Spingola PN: 322325-2-0014&0016
Job: 18-037 Spingola.LHGL
INTRODUCTION
This report presents the results of our geotechnical investigation for the proposed residential building to be
located at XXX East 4th Street in Mason County, Washington. The general location of the site is shown on the
attached Site Vicinity Map, Figure 1.
Our understanding of the project is based on our discussions with you, and our January 25, 2018 site visit. We
understand that you are in the process of applying for a building permit for a new residence to be located on
the currently undeveloped parcel(s). The building will be situated in the west side of the site the north end of
the undeveloped lot. The building will most likely be comprised of concrete and wood frame construction.
Clearing and grading is expected to be limited to that required to develop sufficient access to the new building
site.
SCOPE
The purpose of our services is to evaluate the surface and subsurface conditions at the site as a basis for assessing
potential adverse impacts to and from the slopes located within the site area. We understand that because of
the height and inclination of the slopes on the site,a geotechnical assessment is being required by Mason County
to address geologic hazards at the site. Specifically, our scope of services for the project included the following:
1. Visiting the site and conducting a geologic reconnaissance to assess the site's soil,groundwater,
and slope conditions.
2. Assessing the landslide hazards in accordance with the current Mason County ordinances.
No subsurface explorations or laboratory testing were completed as part of this assessment. However,we were
able to observe the near surface soil conditions in exposed soils on the site and review available septic test pit
records.
The services described in this report were prepared under the responsible charge Glen Coad, PE. Mr. Coad
meets the qualifications contained in the Mason County codes to prepare a landslide hazard geological
assessment. Mr. Coad understands the requirements of the current Landslide Hazard Area Chapter and the
definitions of the applicable terms contained within it. Individuals under the responsible charge of Mr. Coad
has performed a landslide hazard geotechnical assessment, conducted a field investigation, and researched
available historic records on the above referenced site. In our opinion,the scope of services completed for this
project is adequate to meet the requirements of the Department and it does not appear that an active
landslide hazard area exists within 300 feet of the site.
18-037 Spingola.LHGL
February 24, 2018
Page 2
SITE CONDITIONS
Surface Conditions
The subject parcel is located at XXX East 4th Street in Mason County, Washington. The parcels are somewhat
irregular in shape and measure approximately 160 feet in length (north to south) by 130 feet in width (east to
west) and encompasses approximately 0.47 acres when combined. The lots have been largely cleared of trees
at some point in the past. Access to the site is from East 4th Street, a public road. The west area of the site is
moderately sloped with grades of 10 to 15 percent with a steeply sloped area along the east side of the property.
This steeply sloped area appeared to be 30 to 50 percent grade with an overall elevation height of 20 to 30 feet.
The slope was well vegetated with trees and appeared to be in a stable condition.The site is bounded by similar
residential properties on the south, north, west and east.
No seepage was observed at the time of our site visit. No evidence of deep-seated slope instability was observed
at the site or the adjacent areas at the time of our site visit. No erosion, or other soil movement was observed
at the time of our site visit. At the time of our site visit the property was well vegetated with trees, grass, and
shrubs.
Site Soils
The Natural Resource Conservation Service Web Soil Survey for Pierce County mapped the soils in the area of
the site as Alderwood gravelly sandy loam (Aa & Ad). The Alderwood soils are derived from glacial till under
conifers typically have very low infiltration capabilities. Slopes generally range from 0 to 15 percent and 30 to
50 percent and are listed as having a Slight and Severe erosion hazard respectively. A copy of the NRCS Web
Soil Survey map for the site vicinity is attached as Figure 2.
Site Geology
The Geologic Map of the Skokomish Valley and Union 7.5 minute Quadrangle, Mason County, Washington by
Micheal Polenz, Jessica L. Czajkowski, Gabriel Legorreta Pulin, Trevor A. Contretas, Bendan A. Miller, Maria E.
Martin,Timothy J. Walsh, Robert L. Logan, Robert J. Carson, Chris N.Johnson, Rian H. Skov, Shannon A. Mahan
and Cody R. Cohan, June 2010 (Revised 2011) indicates that the site is underlain by Vashon glacial till (Qgtt).
This glacial soil was deposited during the most recent Vashon Stade of the Fraser Glaciation, approximately
12,000 to 15,000 years ago.The glacial till consists of a mixture of clay, silt, sand,and gravel that was deposited
at the base of the prehistoric continental glacial ice mass and were subsequently over-ridden. Glacial soils
overridden by glacial ice can be considered over-consolidated, which typically exhibit high strength and low
compressibility characteristics. An excerpt of the above referenced map in included as Figure 3.
The Puget Sound Coastal Zones Atlas has the site mapped as "S" for Stable with outlying areas marked with a
"I" Intermediate slope stability, see Figure 4 Coastal Zones Atlas.
No groundwater seepage was observed on the site or adjacent areas.
Landslide Hazard Indicators—per Mason County,Chapter 8
The Code of Ordinances for Mason County, Chapter 8, Section 52, Article 140 states that a landslide hazard area
is any of the following:
A. Areas with an indications of earth movement such as debris slides,earthflows,slumps, and rock falls.
B. Areas with artificial over steepened or un-engineered slopes. i.e., cuts or fills.
C. Areas with slopes containing soft or potentially liquefiable soils.
D. Areas over steepened or otherwise unstable as a result of stream incision, stream bank erosion, and
undercutting by wave action.
E. Slopes greater than fifteen percent(8.5 degrees) and having the following:
18-037 Spingola.LHGL
February 24, 2018
Page 3
a. Hillsides intersecting geologic contacts with a relatively permeable sediment overlying a
relatively impermeable sediment or bedrock(e.g., sand overlying clay); and
b. Springs of groundwater seepage.
F. Any area with a slope of forty percent or steeper and with a vertical relief often or more feet except
areas composed of consolidated rock. A slope is delineated by establishing its toe and top and
measured by averaging the inclination over at least ten feet of vertical relief.
The following information may be used as a guide by the county to indicate areas that have a higher likelihood of
meeting the classification criteria previously listed:
A. The areas identified on the Mason County Soil Survey Map as having slopes greater than fifteen
percent.
B. The areas identified on the Coastal Zone Atlas,Volume 9, of Mason County,Washington as:
a. Unstable—"U"
b. Unstable Old Slides—"UOS"
c. Unstable Recent Slides—"URS"
d. Intermediate Slopes—"I"
e. Modified Slopes—"M"
C. The areas identified as Class 2, 3, 4, or 5 of the maps: "Relative Slope Stability of the Southern Hood
Canal Area, Washington" by M. Smith and R.J. Carson, Washington State Department of Natural
Resources, Division of Earth Resources, 1977; "The Geological Map of North Central Mason County,
Washington," by R.J. Carson 1976, U.S.Geologic Survey OFR 76-2.
D. Areas mapped as landslide deposits (Map Unit Qls) on the" Geologic map of the Longbranch 7.5-
minute quadrangle, Thurston, Pierce, and Mason Counties, Washington by R. L. Logan, T. J. Walsh,
and Michael Polenz. One sheet,scale 2:24,000, 2003; Geologic map of the Squaxin Island 7.5-minute
quadrangle, Mason and Thurston Counties, Washington, by R. L. Logan, Michael Polenz, T.J. Walsh,
and H. W. Schasse. One sheet, scale 1:24,000, 2003; Geologic map of the Shelton 7.5-minute
quadrangle, Mason and Thurston Counties, Washington, by H. W. Schasse, R. L. Logan, Michael
Polenz, and T.J. Walsh. One sheet, scale 1:24,000, 2003; and Geologic map of the Summit Lake 7.5-
minute quadrangle,Thurston and Mason Counties,Washington,by R. L. Logan and T.J.Walsh. Forty-
two by thirty-six inch.Color sheet,scale 1:24,000, 2004.
CONCLUSIONS
Based on our site evaluation, it is our opinion that the site is suitable for the future construction of the proposed
residence and related appurtenances. It is also our opinion that an active landslide hazard area does not exist
on or within 300 feet of the site.
Landslide Hazard Indicators—per Pierce Mason County Chapter 8
Mason County, Chapter 8, Section 52, Article 140 uses the above referenced checklist to define a landslide
hazard area. Based on our observations of the site and review of published information, we offer the following
comments.
No evidence of landslide activity, or significant erosion was observed at the site at the time of our site visit.
Some slopes steeper than 15 percent were observed on or near the site, but no intersecting contacts were
observed or are mapped in the site vicinity. There were some slopes steeper than 40 percent with more than
10 feet in height located on the site. We did observe slopes greater than 30 percent with more than 10 feet of
height on the site associated with native slopes east of the building site. It is anticipated that the future building
will not be located within the height of the slope divided by three (approximately 10 feet), therefore it is
anticipated that it will be able to meet prescriptive setback requirements. If these requirements cannot be met
we will be available to provide additional recommendations or setback reduction criteria. Some clearing and
18-037 Spingola.LHGL
February 24, 2018
Page 4
grading may occur on the steeper slopes occurring on the site. Provided appropriate soil erosion control and
site stabilizing measures are employed, we do not anticipate that it will be a limiting feature to site
development. No groundwater seepage was observed at the site. No planes of weakness or rockfall hazards
were observed at the site. No other landslide hazard criteria were observed at the site or the immediate
adjacent areas.
LIMITATIONS
We have prepared this report for the Dowler's and members of the design team for use in evaluating a portion
of this project. Subsurface conditions described herein are based on our observations of exposed soils on the
parcel. This report may be made available to regulatory agencies or others, but this report and conclusions
should not be construed as a warranty of subsurface conditions. Subsurface conditions can vary over short
distances and can change with time.
Within the limitations of scope, schedule and budget, our services have been executed in accordance with
generally accepted practices in this area at the time this report was prepared. No warranty,express or implied,
should be understood.
We trust this is sufficient for your current needs. Should you have any questions, or require additional
information, please contact us at your earliest convenience.
Respectfully submitted,
Development Engineering, PLLC
WA
t J '•vyr �
Glen Coad, P
Owner
WGC
Doc ID:18-037 Spingola.LHGL
Attachments: Figure 1:Vicinity Map
Figure 2:USDA Soils Map
Figure 3:USGS Geological Map
Figure 4:Coastal Zones Atlas
II
)on
yr_
b
c
H
W �
36o,...._.._
PYik
_r.GreaYthn69'--�yy {{-Inlier Are
f'59
rag—A—
_ 1 1
JJj� on'idg<_N!.
e
3 s
a = I
Approximate Site Location
Not to Scale
DE-CIVIL, PLLC
D P.O. Box 446 Site Vicinity Map
Tacoma, WA 98401 Dowler Residence
Ph(253) 228-0513 XXX East 4th Street
www.de-civil.com
Mason County, Washington
Job No:18-037 February 2018 Figure 1
i
Sal Map--Mason County.Wasbington
m,mot �+m ® aso ago a ,�
ar
.�
.i .
j
.:
t „
�t
E j
l n
Ab
cc c
Aij
CA
jo
r
Ac
+'
P L"S A t► � --�'
VI® Z.
Z z
� lAp.,ale:1:11AFpiridm Atr>�pe(IS'xas)3et
ti N 0 u
� m I® Z10
F�
0
1'bG7pr VAbl4Otr Cona muxir»:V.CSa6 Edg ti-l111A7a-1Qi WCi51j4
i tire.% Natural Resources Web Soil Survey 2242018
�i Conservation Service National Cooperative Soil Survey Page 1 of 3
Approximate Site Location (D
n
Not to Scale
I
DE-CIVIL, PLLC USDA Soils Map
P.O. Box 446
.J Tacoma,WA 98401 Dowler Residence
Ph (253)228-0513 XXX East 4 t h Street
www.de-civil.com
Mason County, Washington
Job No:18-037 February 2018 Figure 2
I T,n si
8M9 L
Mud M 12-1
af
O
QPUoP
I at
/
J y •�
QPUOP
hi-I
Q9aQmw ;
i
Approximate Site Location
Not to Scale
DE-CIVIL, PLLC
Geological Map
P.O. Box 446
Tacoma,WA 98401 Dowler Residence
Ph(253) 228-0513 XXX East 4th Street
www.de-civil.com
Mason County, Washington
Job No:18-037 February 2018 Figure 3
i
i
i
r" E SF��ke St
Rd
E Wand Dr
Approximate Site Location
Not to Scale
DE-CIVIL, PLLC
Slope Stability Map
P.O. Box 446
Tacoma,WA 98401 Dowler Residence
Ph (253) 228-0513 XXX East 4th Street
www.de-civil.com
Mason County, Washington
Job No:18-037 February 2018 Figure 4