CANOD.pdfCity of Edmonds
Critical Area Notice of Decision
Applicant:
Property Owner:
Critical Area File #:
C) tcepPermit
Number:
20 oz 5
Site Location:
Parcel Number:
Project Description:
Arid,
,
0
❑ Conditional Waiver. No critical area report is required for the project described above,
1. There will be no alteration of a Critical Area or its required buffer,
2. The proposal is an allowed activity pursuant to ECDC 23.40.220, 23.50.220, and/or
23.80.040,
3. The proposal is exempt pursuant to ECDC 23.40.230,
F -I Erosion Hazard. Project is within erosion hazard area. Applicant must prepare an erosion and
sediment control plan in compliance with ECDC 18,30.
ACritical Area Report Required. The proposed project is within a critical area and/or a critical area
buffer and a critical area report is required. A critical area report has been submitted and evaluated
for compliance with the following criteria pursuant to ECDC 23.40,160:
I The proposal minimizes the impact on critical areas in accordance with ECDC 23,40,120,
Mitigation sequencing;
2. The proposal does not pose an unreasonable threat to the public health, safety, or welfare
on or off the development proposal site;
3. The proposal is consistent with the general purposes of this title and the public interest;
4. Any alterations permitted to the critical area are mitigated in accordance with ECDC
23.40.110, Mitigation requirements.
5. The proposal protects the critical area functions and values consistent with the best
available science and results in no net loss of critical functions and values; and
6. The proposal is consistent with other applicable regulations and standards.
❑ Unfavorable Critical Area Decision. The proposed project is not exempt or does not adequately
mitigate its impacts on critical areas and/or does not comply with the criteria in ECDC 23.40.1,60 and
the provisions of the City of Edmonds critical area regulations. See attached findings of
noncompliance,
X,
E2' -', Favorable Critical Area Decision. The proposed project as described above and as shown on the
attached site plan meets or is exempt from the criteria in ECDC 23,40.160, Review Criteria, and
complies with the applicable provisions of the City of Edmonds critical area regulations. Any
subsequent changes to the proposal shall void this decision pending re -review of the proposal.
F -I Conditions. Critical Area specific condition(s) have been applied to the pen -nit number referenced
above, See referenced permit number for specific condition(s),
V
Reviewer Signature Date
Appeals: Any decision to approve, condition, or deny a development proposal or other activity based on the
requirements of critical area regulations may be appealed according to, and as part of, the appeal procedure, if any,
for the permit or approval involved.
Revised 12/16/2010
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Dennis K BrUce, RE.
M.S.C.E., M.B.A. Geotechnical /Civil Engineer
July 29, 2011 RECEIVE&
APR - 2 201?
City of Edmonds DIVE Lc�)PO�F,,,'i Sr-F,I\flCEa', C,"rR,
c/o Greg Gorsuch TY OF EWONDS
9207 Olympic View Drive
Edmonds, Washington 98026
Subject: Geotechnicall Evaluation — Foundation Recommendations
Proposed House Addition Project
9207 Olympic View Drive
This engineering report presents the results of a geotechnical evaluation of the
Gorsuch house and property at 9207 Olympic View Drive, Edmonds, Washington. This
evaluation was required due to owner concerns, as well as City of Edmonds
requirements for critical areas - potential hazard zones.
_REFERENCLES:
* Site plan with existing structure and proposed modest addition plans
* Addition plans (furnished by owner)
* Site photographs by D. Bruce, P.E.
8_AQK
jQBQUND:
'The overall Gorsuch property is rectangular in shape with approximately fifty feet
(50') of frontage, and approximately two hundred feet (200') of depth. (See survey and
site plan).
Currently, the existing residence occupies the eastern -most portion of the
property in the "flatter" portion of the property. The western portion of the property
contains steep slopes (greater than 40%), that slope downward to the Burlington
Northern Railroad right-of-way.
This engineer understands that Mr. Gorsuch proposes to construct a second
story addition, and in conjunction, construct a slight lower level addition (see plans).
SOILS * FOUNDATIONS a SITE DEVELOPMENT 0 INSPECTION a DRAINAGE 11 OF - SIGN & PEFFMIT 0 LEGAL
P.O. Box 55502 - Shoreline, WA 98155 - (206) 546-9217 - FAX (206) 546-8442
City • Edmonds
Re: Gorsuch Property
July 29, 2011
Page 2
T FINITEMNIpil 11111
Visual evaluation of the property by this engineer revealed no evidence of an
geotechnical distress: no slides, no soil tension cracks, nor any evidence of erosion
degradation. As stated, the western portion • this lot slopes steeply downward to t
railroad right-of-way and Puget Sound. I
The steep slope is heavily vegetated, with no evidence of erosional degradation.
NOTE: It is essential that all storm water discharge occur away f the steep
slope face. This requirement may entail all storm water lines to be extend all the
way to the bottom of slope.
Again, the Gorsuch property reveals no evidence of any erosional degradation.
In order to augment the existing site geotechnical information, soil test holes
were hand -dug by this engineer in the Vicinity of the proposed modest "foundation bump
out". i• hand -dug test holes verified similar sub -grade conditions, namely:
0" to 6" Lawn, organics, roots, and organic silt
6" to 32" (bottom of test hole- Extremely dense glacial till
impossible to hand dig any
deeper)
No groundwater was encountered in either • the 2 test holes. Both test hole
walls remained vertical and .• No sloughing • caving occurred.
Additionally, numerous examples of the exposed underlying extremely dense
glacial till are evident under the existing deck zone.
Log 6-M Uf &1 &11
Based on the findings of this investigation, and experience with numerous similar
sites in the area, the Gorsuch property at 9207 Olympic View Drive, Edmonds, is
geotechnically appro for the proposed nominal house footprint addition, subject to
the following:
City of Edmonds
R. Gorsuch Property
July 29, 2011
Page 3
Setback distances: Geotechnically, the proposed nominal additional footprint is
approved, as indicated on the project plans. Do not construct any house
foundation elements closer than twenty-five feet (25.0') from the existing top -of -
slope (existing fence line).
I RN LOUNLIR I Mrk I A MRS73K I I F. I W� I W_Mr�' MWL'u ly I ut I VUL-M..-M 10 1 L -Not, a
• Standard reinforced continuous and spread footings. Allowable bearing
pressure: 3,000 p.s.f.
® Equivalent fluid pressure of 35 p.c.f. is recommended for any retaining wall
design provided drainage zone is inspected and verified by this engineer.
® For retaining wall design, use friction factor of 0.55 and passive pressure of 350
P.O.
• Geotechnical inspections by this engineerprior to any foundation concrete
placement.
The proposed structure can be supported on conventional continuous and spread
footings bearing on undisturbed native soils or on structural fill placed above native
soils. See the later sub -section entitled General Earthwork and Structural Fill for
structural fill placement and compaction recommendations. Continuous and individual
spread footings should have minimu widths of eighteen (18) and twenty-four (24)
inches, respectively, and should be bottomed at least eighteen (18) inches below the
lower adjacent finish ground surface.
Depending on the final site grades, some over -excavation may be required below
footings to expose competent native soils. Unless lean concrete is used to fill the over
excavated hole, the width of the over -excavation at the bottom must be at least as wide
as the sum of two times the depth of the over -excavation and the footing width. For
example, an over -excavation extending two feet below the bottom of a three-foot wide
footing must be at least seven feet wide at the base of the excavation.
Footings constructed according to the above recommendations may be designe'l'
for an allowable soil bearing pressure of two thousand (2,000) pounds per square foot
(p.s.f.). A one-third increase in this design bearing pressure may be used when
City of Edmonds
Re: Gorsuch Property
July 29, 2011
Page 4
considering short-term wind or seismic loads. For the above design criteria, it is
anticipated that total post -construction settlement of footings founded on competent,
native soils (or on structural fill up to five (5) feet in thickness) will be about one-half
inch, with differential settlements on the order of one-quarter inch.
Lateral loads due to wind or seismic forces may be resisted by friction between
the foundations and the bearing soils, or by passive earth pressure acting on the
vertical, embedded portions of the foundations. For the latter condition, the foundations
must either be poured directly against undisturbed soil or the backfill placed around the
outside of the foundation must be level structural fill. We recommend the following
design values be used for the foundation's resistance to lateral loading:
■
- I a F 11171
Coefficient of Friction 0.55
Passive Earth Pressure 350 p.c.f.
(1) p.c.f. is pounds per cubic foot.
(2) Passive earth pressure is computed using the equivalent fluid density.
We recommend that a safety factor of at least 1.5 be used for design of
foundation's resistance to lateral loading.
Slab -on -grade floors may be supported on undisturbed, competent native soils or
:tn structural fill. The slabs may be supported on the existing soils provided these soils
can be re -compacted prior to placement of the free -draining sand or gravel underneath
the slab. This sand and gravel layer should be a minimum of four (4) inches thick. We
also recommend using a vapor barrier such as 6 -mil. plastic membrane beneath the
slab with minimum overlaps of 12 inches for sealing purposes.
FT
M115011
Retaining walls backfilled on one side only should be designed to resist lateral
earth pressures imposed by the soils retained bylthese structures. The following
City of Edmonds
Re: Gorsuch Property
July 29, 2011
Page 5
recommended design parameters are Tor wa ess T =177,MTM'
which restrain level backfill:
Val- .__
Active Earth Pressure"
Passive Earth Pressure
Coefficient of Friction
Soil Unit Weight
IN
M
(1) p.c.f. is pounds per cubic foot
(2) Active and passive earth pressures are computed using equivalent fluid
densities.
For restrained walls which cannot deflect at least 0.002 times the wall
height, a uniform lateral pressure of one hundred (100 p.s.f. should be
added to the active equivalent fluid pressure).
The values given above are to be used for design of permanent foundation and
retaining walls only. An appropriate safety factor should be applied when designing ti
walls. We recommend using a safety factor of at least 1.5 for overturning and sliding. .
The above design values do not include the effects of any hydrostatic pressures
behind the walls and assume that no surcharge slopes or loads will be placed above the
walls. If these conditions exist, then those pressures should be added to the above
lateral pressures. Also, if sloping backfill is desired behind the walls, then we will need
to be given the wall dimensions and slope of the backf ill in order to provide the
appropriate design earth pressures.
Heavy construction equipment should not be operated behind retaining and
foundation walls within a distance equal to the height of the wall, unless the walls ar
designed for the additional lateral pressures resulting from the equipment. Placerne
and compaction of retaining wall backfill should be accomplished with hand -operate
equipment. I
City of Edmonds
Re: Gorsuch Property
July 29, 2011
Page 6
I
Backfill placed within eighteen (18) inches of any retaining or foundation walls
should be free -draining structural fill containing no organics. This backfill should contain
no more than five (5) percent silt or clay particles and have no particles greater than four
(4) inches in diameter. The percentage of particles passing the No. 4 sieve should be
between twenty-five (25) and seventy (70) percent. Due to their high silt content, if the
native soils are used as backfill, a drainage composite, such as Mirafi and Enkadrain,
should be placed against the retaining walls. The drainage composites should be
hydraulically connected to the foundation drain system. The purpose of these backfill
requirements is to assure that the design criteria for the retaining wall is not exceeded
because of a build-up of hydrostatic pressure behind the wall. The subsection entitled
General Earthwork and Structural Fill contains recommendations regarding placement
and compaction of structural fill behind retaining and foundation walls.
EXCAVATION AND SLOPES:
At the time of this investigation and report, it is understood that maximum
excavation depths for the nominal house addition will be less than three feet (3.0') in
depth. Thus, no temporary shoring is Muired.
In no case should excavation slopes be greater than the limits specified in local,
state and national government safety regulations. Temporary cuts up to a height of
four (4.0') feet deep in unsaturated soils may be vertical. For temporary cuts having a
height greater than four (4.0') feet, the cut should have an inclination no steeper than
1:1 (Horizontal:Vertical) from the top of the slope to the bottom of the excavation. Under
specific recommendations by the geotechnical engineer, excavation cuts may be
modified for site conditions. All permanent cuts into native soils should be inclined no
steeper than 2:1 (H:V). Fill slopes should not exceed 2H:1 V. It is important to note that
sands do cave suddenly, and without warning. The contractors should be made aware
of this potential hazard.
Water should not be allowed to flow uncontrolled over the top of any temporary or
permanent slope. All permanently exposed slopes should be seeded with an
appropriate species of vegetation to reduce erosion and improve stability of the surficial
layer of soil.
City of Edmonds
Re: Gorsuch Property
July 29, 2011
Page 7
Footing drains are recommended at the base of all footings and retaining walls.
These drains should be surrounded by at least six (6) inches of one -inch -minus washed
rock wrapped in non -woven geotextile filter fabric (Mirafi 140N, Supac 4NP, or similar
material). At the highest point, the perforated pipe invert should be at least as low as
the bottom of the footing and it should be sloped for drainage. All roof and surface
water drains must be kept separate from the foundation drain system.
No groundwater was observed in either of the 2 test holes during the fieldwork.
Seepage into the planned excavation is possible, and likely if excavation occurs during
winter months, and if encountered should be drained away from the site by use of
drainage ditches, perforated pipe, French drains, or by pumping from sumps
interconnected by shallow connector trenches at the bottom of the excavation.
The excavation of the site should be graded so that surface water is directed off
the site and away from the tops of slopes. Water should not be allowed to stand in any
area where foundations, slabs, or pavements are to be constructed. Any exposed
slopes to be covered with plastic to minimize erosion. Final site grading in areas
adjacent to buildings should be sloped at least two (2) percent away from the building,
except where the area adjacent to the building is paved.
GENERAL EARTHWORK AND STRUCTURAL FILL:
The proposed building and pavement areas should be stripped and cleared of all
surface vegetation, all organic matter, and other deleterious material. The stripped or
removed materials should not be mixed with any materials to be used as structural fill.
Structural fill is defined as any fill placed under the building, behind permanent
retaining or foundation walls, or in other areas where the underlying soils needs to
support loads. This engineer should observe site conditions during and after excavation
prior to placement of any structural fill.
All structural fill should be placed in horizontal lifts with a moisture content at or
near the optimum moisture content. The optimum moisture content is that moisture
content which results in the greatest compacted dry density. The moisture content of fill
soils is very important and must be closely controlled during the filling and compaction
N�
City of Edmonds
Re: Gorsuch Property
July 29, 2011
Page 8
The allowable thickness of the fill lift will depend on the material type, compaction
equipment, and the number of passes made to compact the lift. In no case should the
lifts exceed twelve (12) inches in loose thickness. The following table presents
recommended relative compaction for structural fill:
F1,*T_=_ . 111110T.T��
Compaction
95%
K�-
Where: Minimum relative compaction is the ratio, expressed in percentages,
the compacted dry density to the maximum dry density, as determined in
accordance with ASTM Test Designation D-1 557-78 (Modified Proctor). I
If grading activities take place during wet weather, or when the silty, on-site soils
are wet, site preparation costs may be higher because of delays due to rains and the
potential need to import granular fill. The on-site soils are generally silty and thus are
moisture sensitive. Grading operations will be difficult when the moisture content of
these soils exceeds the optimum moisture content.
Moisture sensitive soils will also be susceptible to excessive softening and
�_IMT" isture content is I ireater than
the optimum moisture content.
Ideally, structural fill, which is to be placed in wet weather, should consist of a
granular soil having no more than five (5) percent silt or clay particles. The percentage
of particles passing the No. 200 sieve should be measured from that portion of the soil
passing the three -quarter -inch sieve.
The use of "some" on-site soils for fill material may be accepta if the upper
organic materials are segregated and moisture contents are monitored by engineering
insR'ction.
J"
City of Edmonds <
Re: Gorsuch Property
,July 29, 201'l
Page 9
DRAINAGE CQNTRQLS:
No drainage problems were evident with the existing Gorsuch residence and
property.
NOTE: As stated earlier, do n
1_A§9w any collected storm water to "dump" on
the slope face itself. It isffb
.1sential wes that all storm ater discharge linbe verified as
1_
-functional, and be extended all the.myAy to the bottom of slope.
All foundation concrete (footings, stem walls, slabs, any retaining walls, etc.)
shall have a minimum cement content of 5-1/2 sacks per cubic yard of concrete mix.
—EDMONDS COMMUNITY DEVEOPMENT
LCO _ — _DE-SEQ
Buffer Requirement: As stated in this report, no foundation elements may be
constructed within 25.0 feet (horizontally) of the top -of -slope. The proposed
building plans indicate that the modest addition will comply with the City of
Edmonds requirement for a forty foot (40') setback.
Alterations: This project dom--not alter the designated erosion / landslide hazard
area.
This house addition project will not increase surface water discharge or
sedimentation to adjacent properties beyond pre -development conditions.
0 The addition project will not decrease slope stability on adjacent properties.
Is This addition project will riot adversely impact other critical areas.
This proposed addition project shall not decrease the factor of safety for landslide
occurrences below the limits of 1.5 (for static conditions) and 1.2 (for dynamic
conditions).
0 The improvement is "clustered" in that it is a simple house addition project.
City of Edmonds
Re: Gorsuch Property
July 29, 2011
Page 10
® The house addition project does minimize alterations to the natural contour of the
slope. See plans.
® House addition project does n impact the steep vegetated westerly slope.
® This addition project does not result in greater risk or any need for increased
buffers on neighboring properties.
• The existing natural slope is not impacted by this project.
The recommendations of this report are only valid when key geotechnical
2spects are inspected by this engineer during construction:
• Soil cuts
• Foundation sub -grade verification
• Any retaining wall, or rockery placement
• Any fill placement
• Subsurface drainage installation
• Temporary and permanent erosion control measures
,; jI Ti ul
The proposed Gorsuch house addition at 9207 Olympic View Drive, Edmonds,
Washington is geotechnically approved when constructed in accordance with the
recommendations herein, compliance with City of Edmonds approved plans and
requirements, and key geotechnical inspections during construction.
The findings and recommendations of this report were prepared in accordance
with generally accepted professional engineering principles and practice. No other
warranty, either express or implied, is made. The conclusions are based on the results
of the field exploration and interpolation of subsurface conditions between explored
locations. If conditions are encountered during construction that appear to be different
than those described in this report, this engineer should be notified to observe the
situation and review and verity or modify the recommendations.
City of Edmonds
Fie: GorSUCh Property
July 29, 2011
Page `I 'I
It there are any questions, do not hesitate to call.
DMB:vlb
cc: Greg Gorsuch
k",
Dennis M. Bruce, P.E.
Geotechnical / Civil Engineer