HomeMy WebLinkAboutGEO2011-00076 - GEO Geological Review - 10/26/2011 GEO
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 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 Name:
Permit Parcel#'s:
Date(s) of the Document(s) reviewed: O �i
1. A discussion of geologic conditions in the general vicinity of the proposed development, with geologic unit
designation based on referenced maps.
OK? %-"� 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? t� Comment:
(d) A discussion of the upslope geomorphology,
OK? ✓ Comment:
(e) A discussion 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? VZ 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 7-p-m
ent, etc.).
OK? Comment:
5. A discussion of e 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 lightof the proposed development.
OK? ✓ Comment: lye
7. A recommendation by the preparer whether a Geotechnical Report should be required to further evaluate site
conditions and a proposed develop nt of the subject�ro rty.
OK? Comment: d, fe(v/vi iY1_K.�'r'('
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 boundari of the landslide hazard area (top, both sides, and toe),
OK? Comment: ZZ
(c) the associated buffers (top, both side�nd toe)
OK? Comment:
(d) building or other setbacks (top, both si eels, 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 sed development on the site.
OK? 17 Comment:
Are the Documents signed and stamped? C By whom? ��
License#: License e.
FIRST REVIEW proved ❑ Need more info.
If not approved, what i the next action/recommendation for further action?
Reviewed by , on . Time spent in review:
�I
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
� -o2o [
Mason County Department of Community Development
Submittal Checklist For a Geotechnical Assessment
Instructions:
This checklist must be submitted with a Geotechnical Report and completed, signed, and stamped by the
licensed professional(s)who prepared the Geotechnical 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 Dante and Lea del Pilar Parcel# 32232-50-53004
Site Address 16 E Tacoma St, Union, Washington, 98592
(1) A discussion of general geologic conditions in the general vicinity of the
proposed development, with geologic unit designation based
on reference maps.
Located on page(s) Page Pages 1 -2
(2) (a) A discussion of the groundwater conditions at the site,
Located on page(s) Page 2
(b) A discussion of the estimated depth to water
Located on page(s) Page 3
(c) A discussion of the quantity of surface seepage
Located on page(s) Page 3
(d) A discussion of the upslope geomorphology
Located on page(s) Page 1
(e) A discussion of location of upland waterbodies and wetlands.
Located on page(s) Page 3
(3) The approximate depth to hard or competent soil, e.g. glacial till or outwash sand.
Located on Map(s) Page 3
(4) A discussion of any geomorphic expression of past slope instability (presence of
hammocky ground or ground cracks, terraced topography indicative of landslide block
movement, bowed or arched trees indicating downslope movement, etc.).
Located on Map(s) Page 3
(5) A discussion of the history of landslide activity, as available in the
referenced maps and records.
Located on Map(s) Page 3
(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 Map(s) Page 3
Disclaimer: Mason County does not certify the quality of the work done in this Geotechnical
Assessment.
Page 1 of 2 Form Effective June 2008
(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.
Located on page(s) Page 3
(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 Maps No Hazard Area within 300-ft.
(b) the boundaries of the landslide hazard area (top, both sides, and toe),
Located on Map(s) No Hazard Area within 300-ft
(c) the associated buffers(top, both sides, and toe).
Located on Map(s) No Hazard Area within 300-ft
(d) building or other setbacks(top,both sides, and toe).
Located on Map(s) Plan Sheet 2
(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 Maps Plan Sheet 2
I, Alan A. Tahia, P.E. hereby certify under penalty of perjury that I am a civil engineer licensed in the
State of Washington with specialized knowledge of geotechnical/geological engineering or a geologist or
engineering geologist licensed in the State of Washington with special knowledge of the local conditions. I
also certify that the Geotechnical Assessment, dated October 261h, 2011 , and entitled
Dante and Lea del Pilar Geotechnical Assessment meets all the requirements of the Mason
County Resource Ordinance, Landslide Hazard 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. (Signature and Stamp)
T
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IONAL E�G�
Disclaimer: Mason County does not certify the quality of the work done in this Geotechnical
Assessment.
Page 2 of 2 Form Effective June 2008
TAHJA ENGINEERING, Inc.
PO Box 235, Hoodsport, WA 98548
(360) 877-9512
Mason County DCD
PO Box 279
Shelton, WA 98584
Dante & Lea del Pilar
19906 SE 277t' St
Kent, WA 98042-8552
Cell; (253) 740-5311
RE: Geotechnical Assessment
16 E Tacoma St
Union, WA 98592
Mason Co. Prcl No. 32232-50-53004
Mason Co. Case No.s BLD2011-00659
INTRODUCTION
I was contacted in September of this year by Lea del Pilar who requested my assistance in developing
a geotechnical assessment or report to address landslide stability issues relating to the improvement of
the del Pilar property in Union Washington, Mason County. The del Pilars are in the process of
replacing a previously existing residence and garage which have recently been demolished in
preparation of their currently proposed property improvements.
Slopes on the property were investigated and the —170' x 130' parcel was found to be located in an
area whose upslope geomorphology may be described as hilly, with slopes measuring— 15% along
the property's southerly (upland) boundary and slopes averaging approximately 25% towards the
McReavy Road, State Route 105 and Hood Canal to the north of the property.
Mason County's Resource Ordinance(MCRO) requires geotechnical investigation and reporting of
properties with slopes exceeding 15%and more than 10 feet of vertical relief. Property improvements
and ground disturbing activities within 300 feet of slopes exceeding 40%, or within 300 feet of slopes
exhibiting instability are required to have a geotechnical report level document prepared to determine
where the property may safely be developed, and/or what mitigation measures may be needed or
required to safely develop property either within an area classified as a landslide hazard area, or within
the hazard areas' buffer(s). No indications of instability were found, so it is my opinion that the
property should be investigated under the requirements of a geotechnical assessment.
The following nine elements are required to be addressed in geotechnical assessments prepared to
meet Mason County's geotechnical assessment requirements.
1. SURFACE AND GEOLOGIC CONDITIONS: The site is located in an area identified below
on the Geologic Map of Shelton 1:100,000 Quadrangle, Washington as a location on Hood Canal's
south shore area in the town of Union accessed off of the McReavy Road and East Tacoma Street.
' DNR OFR2003-15 Geologic Map of Shelton 1:100,000 Quadrangle,Washington
File: C: ProjectslDel PilarlGeo-Assmnt 1 of 4 10/26/201 1
TAHJA ENGINEERING, Inc.
PO Box 235, Hoodsport, WA 98548
(360) 877-9512
cent
1 Dow Mtn aw ' °po _
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The map reveals that the soils on the del Pilar property are classified as Continental Glacial Deposits
of the Fraser Glaciation, Vashon Stade(Qga& Qgt). Inspection of the Soil Survey of Mason County
found the site to be located in an area with an Alderwood gravelly sandy loam(Ac) soil type,which
is identified in the County's Critical Resource Ordinance as susceptible to severe erosion when
disturbed. As such a site specific Sediment and Erosion Control Plan(E&S)is required to be
prepared for and followed in the site's development. The site already has an existing access to the
site off of 4"h Street serving the property from E Tacoma Street which is weathered in and adequate
in its current condition.
Inspection of Washington State Department of Ecology's Coastal Atlas landslide hazard section
found the del Pilar property and surrounding area classified as stable. No history of landslides are
reported or evident on the property itself or anywhere in the neighborhood surrounding the del Pilar
property. The geological soils descriptions of the site's soils are as follows;
Advance outwash, late Wisconsinan (Pleistocene)—Glaciofluvial
sand and gravel and lacustrine clay, silt,and sand deposited during
the advance of glaciers; sandy units commonly thick, well sorted and
fine grained, with interlaycred coarser sand,gravel,and cobbles and
silt rip-up lag deposits at their base; may contain nonglacial sedi-
ments; generally overlain by rill.
Till,late Wisconsinan(Pleistocene)--Unsorted, unstratified, highly
compacted mixture of clay,silt,sand gravel,and boulders deposited
by glacial ice of the Puget lobe;gray;may contain interbedded strati-
fied sand, silt, and gravel;sand-size fraction is very angular and con-
tains abundant polycrystalline quartz,which distinguishes this unit
from alpine till; cobbles and boulders are commonly striated and(or)
faceted; although unweathered almost everywhere,may contain cob-
bles or small boulders of deeply weathered granitic rock.
File:C.lProjectsDel PdarlGeo-Assmnt 2 of 4 10/26/2011
TAHJA ENGINEERING, Inc.
PO Box 235, Hoodsport, WA 98548
(360) 877-9512
2. DISCUSSION OF GROUNDWATER CONDITIONS AT THE SITE; The general slope of
the property to the north and towards Hood Canal keeps the property fairly well drained and dry. The
area encompassing the del Pilar property is mainly glacial till(Qgt),which typically acts as an
impermeable restrictive layer extending to depths of 30 to 50-ft or more with the water table located
beneath the till layer. The immediate area around the del Pilar site are identified as advance outwash
materials which agrees with inspection of the surface soils at the site as gravelly sand and loam. Minor
seepage was apparent in the southeast area of the del Pilar property where the property has been
leveled down below the original ground's till layer. Surface water runoff from the site is generally
intercepted in the 40' Street ditch located along the southerly side of 4th Street. Groundwater in the area
is typically coincident with the Hood Canal sea level elevation or lower,roughly 200 feet below the
ground surface at the del Pilar property.No upland waterbodies or wetlands were found on or near the
del Pilar property.
3. APPROXIMATE DEPTH TO HARD OR COMPETENT SOIL: Most of the del Pilar
property has been cleared and leveled in the past and compacted from past residential use of the
property. The glacial outwash soil material is moderately deep(2 to 3 feet below the surface)on the
24%f neighborhood slope. Compaction of the central area of the del Pilar site has produced a
compacted dense bearing soil generally within a foot of the ground's surface. The Geologic Map of
Shelton 1:100,000 Quadrangle Map indicates the presence of a glacial till beneath the site at a shallow
depth(usually less than 5-feet). The loamy gravelly sand residing above the till layer is moderately
dense,and should provide adequate bearing for standard residential foundations.
4. DISCUSSION OF GEOMORPHIC EXPRESSION OF PAST SLOPE INSTABILITY: The
del Pilar property and properties surrounding the site display no evidence of recent slope instability or
earth movement. As a portion of the Geologic Map of Shelton 1:100,000 Quadrangle on page 2
reveals,the del Pilar property is located in the vicinity of several fault lines identified on the map as
(1) the terminus of two faults emanating from the north and terminating approximately 10+miles to
the northwest of the del Pilar property on the north side of Dow Mountain(2) a fault line which
follows Hood Canal is located approximately 3 miles north and west of the del Pilar site. The presence
of these features does not represent an unusual hazard, and standard seismic analysis of the site is
intended to anticipate potential tectonic impacts. The Washington State Department of Ecology
Coastal Atlas indicates that the del Pilar property is located in a stable area.
5. DISCUSSION OF THE HISTORY OF LANDSLIDE ACTIVITY IN THE VICINITY:
Inspection of the Coastal Zone Atlas covering this area found the del Pilar property and surrounding
area to be characterized as stable.No documented history of instability was found in the project area.
6. AN OPINION ON WHETHER THE PROPOSED DEVELOPMENT IS WITHIN THE
LANDSLIDE HAZARD AREA OR ITS ASSOCIATED BUFFER OR SETBACK: The del Pilar
property,in my opinion is not in a landslide hazard area. Literature references and my personal site
inspection all support my opinion that this property is not on or near a landslide hazard area.
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: A geotechnical report level
File:C.IProjectslDel PilarlGeo-Assmnt 3 of 4 10/26/2011
TAHJA ENGINEERING, Inc.
PO Box 235,Hoodsport, WA 98548
(360) 877-9512
investigation of the property does not appear warranted from the observations and findings already
made.
8. IF THE PRESENCE OF A HAZARD IS DETERMINED WITHIN 300 FEET OF THE
PROPOSED DEVELOPMENT,THEN THE AREA OF THE PROPOSED DEVELOPMENT,
BOUNDARIES OF THE HAZARD,AND ASSOCIATED BUFFERS AND SETBACKS SHALL BE
DELINEATED(TOP, BOTH SIDES,AND TOE)ON A GEOLOGIC MAP/SITE MAP. No
landslide hazard areas have been found either on or within 300 feet of the property.
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: This report includes a site plan which contains the
required information.
Summary,
The del Pilars have indicated they intend to build on the footprint or foundation of the existing garage
foundation with a garage and second floor apartment. The existing concrete foundation may be
salvageable, but the garage elevation walls should be constructed to shear panel specifications, and the
concrete floor may be topped with a new slab.
This concludes my assessment of the Dante and Lea del Pilar property located in the Union
community of Mason County, Washington. In brief, it is my opinion that the property and proposed
improvements are not in jeopardy from instability or earth movements, and should be allowed to
proceed without additional landslide stability investigation or reporting. Please feel free to contact me
if there are any additional concerns or issues required to be addressed by Mason County's Resource
Ordinance 17.01.100— 104.
Sincerely,
F WA
a7784�0' w�
��' ��GIs�
�SSI0 L F,
Alan A. Tahja, P.E.
Attached: Topographic Plan Sheets
File:C:ProjectslDel PilaHGeo-Assmnt 4 of 4 10/26/201 1
Rev# Description Date TAHJA ENGINEERING,INC. SITE PLAN
Alan Tahja,P.E. Dante&Les del Pilar del PUar
PO Box 235 19906 SE 277th St „
Hoodspor4 WA 98548 Keck WA 98042-8552 1 of2
Mason Co.Prel No.:32232-50-53004 (360)877-9512 cell (253) 740-5311
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_________ Property Line— 170'
4th Street
25'Front Yard Bldg Setback Line ,-�„ M b y
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General Septic System I Demolished location to be
Tank&Drainfield Area :a Garage& utilized in new I 0 w
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Foundations I v `o `
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24 g rjo '�d1'a.e Line—170'
3D784�O w� SCALE: 1"=30' �-1 Fir&Hem [ 17
1STER �1 o io 20 30 Stumps N
`S10NALE� 20'Back Yard Bldg Setback Line °,
Requested 10'Back Yard Bldg Setback �'
16 E Tacoma Street, Uni Washington
TBLD2011-00659
00
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————————————— —————— ------ PP b
4th Street
____ ____________________ _____- _----- ----- ----
Stabilized Construction �— —————
Entrance(Existing) s,�� N �
I Ecology BMP C105 s' �°' I � '�
I N 4� i y q
Ulm I 36"dia. 0 4o w e ter
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Silt Fence Installation(BMI#C 3)
Location-Install&maintaih un 'I b
disturbed construction area as be ome � �N
permanently stabilized wit4 vegeta'on 1 a 's N F4
or gravel. I
I `pg RA I Stormwater BMPs repres nt Best gement � e NJ Practices as promoted in Washingto tate Q O0 ZI
Dept.of Ecology's Stormwater man a for w $ p
_ Previous Western Washington(2019). cO0„ b
I ---- Gii&ence ——————————— ti
I Recommended Stan&arAotes for r sion
3t)7g4 �� L--- Control Plans follow thislplan sh t.
cy ------- -------
ST
ZONAL E T OO
24 to 30"dia. Stormwater Note; All measures necessary to
Fir&Hem contain stormwater silt&turbidity within the k Q,
Stumps construction area are mandatory.Silt or turbidity c ~
SCALE: I"=30' detectable off-site is an infraction of Ecology and
0 10 20 30 16 E Tacoma Street, Unio Washington Mason County stormwater management regulations.
Appendix II-A
Recommended Standard Notes for Erosion Control Plans
The following standard notes are suggested for use in erosion control plans. Local jurisdictions
may have other mandatory notes for construction plans that are applicable. Plans should also
identify with phone numbers the person or firm responsible for the preparation of and
maintenance of the erosion control plan.
Standard Notes
Approval of this erosion/sedimentation control (ESC) plan does not constitute an approval of
permanent road or drainage design (e.g. size and location of roads, pipes, restrictors, channels,
retention facilities, utilities, etc.).
The implementation of these ESC plans and the construction, maintenance, replacement, and
upgrading of these ESC facilities is the responsibility of the applicant/contractor until all
construction is completed and approved and vegetation/landscaping is established.
The boundaries of the clearing limits shown on this plan shall be clearly flagged in the field
prior to construction. During the construction period, no disturbance beyond the flagged
clearing limits shall be permitted. The flagging shall be maintained by the applicant/contractor
for the duration of construction.
The ESC facilities shown on this plan must be constructed in conjunction with all clearing and
grading activities, and in such a manner as to insure that sediment and sediment laden water do
not enter the drainage system, roadways, or violate applicable water standards.
The ESC facilities shown on this plan are the minimum requirements for anticipated site
conditions. During the construction period, these ESC facilities shall be upgraded as needed for
unexpected storm events and to ensure that sediment and sediment-laden water do not leave the
site.
The ESC facilities shall be inspected daily by the applicant/contractor and maintained as
necessary to ensure their continued functioning.
The ESC facilities on inactive sites shall be inspected and maintained a minimum of once a
month or within the 48 hours following a major storm event. At no time shall more than one
foot of sediment be allowed to accumulate within a trapped catch basin. All catch basins and
conveyance lines shall be cleaned prior to paving. The cleaning operation shall not flush
sediment laden water into the downstream system.
Stabilized construction entrances shall be installed at the beginning of construction and
maintained for the duration of the project. Additional measures may be required to insure that
all paved areas are kept clean for the duration of the project.
February 2005 Volume 11— Construction Stormwater Pollution Prevention A-1
8-2 Volume 11— Construction Stormwater Pollution Prevention February 2005