CANOD.pdfCity of Edmonds
Critical Area Notice of Decision
Applicant:
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Owner:
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Critical Area FilePermit
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Number:
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Site Location:
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Project Description:
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❑ 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,
❑ Erosion Hazard. Project is within erosion hazard area. Applicant must prepare an erosion and
sediment control plan in compliance with ECDC 18.30.
0- Critical 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 23.40.160 and
the provisions of the City of Edmonds critical area regulations. See attached findings of
noncompliance,
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,
[--J Conditions. Critical Area specific condition(s) have been applied to the permit number referenced
above. See referenced permit number for specific condition(s).
Reviewer
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evi er-
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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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i.,3-ootechnical Engineering ancl Earth Sciences
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RECEIVED
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CO[INITR
SUBJECT: GEOLOGICALLY HAZARDOUS AREAS EVALUATIO
Proposed Residence Replacement
723 Hanna Park Road
Edmonds, Washington
Project No. 12-110-01 1
Dear Erik and Tamara,
This report presents our geotechnical evaluations and recommendations for
construction of the subject proposed residence. Our services are provided in
accordance with the scope and conditions of our proposal dated March 28, 2012.
We have been provided a site survey and development plans and elevations prepared
by Prentiss Architects. We understand that the proposed new two story residence with
attached garage will generally be located over the site of the existing house on the lot
but will be a somewhat smaller footprint. A new driveway addition will be constructed
along the east side of the residence. The proposed residence will be supported near
existing grade with a slab -on -grade floor.
Review of Edmonds ECA Inventory mapping indicates that the site lies in an erosion
hazard area and the west slope is considered to be a landslide hazard but the site is
not indicated to be within a seismic hazard area.
We have not been provided any structural load information, but based on our
experience we expect that bearing wall loads will be on the order of 2 to 3 kips per foot
and column loads are expected to range from about 10 to 20 kips. If actual structural
loads exceed the above values by more than 25%, this office should be notified.
Nelson April 16, 2012
SCOPE OF WORK
Our work has included site reconnaissance, subsurface explorations, engineering
evaluations and the preparation of this report. The scope of work included the following
specific tasks:
o Review of published geologic mapping and Edmonds ECA Inventory Maps
of geologically hazardous Areas maps for the site vicinity.
o Performed a site reconnaissance to observe conditions on the site and on
the adjacent bluff slope within the BNR right-of-way.
o Performed hand auger borings to explore the subsoil conditions at the
new residence site. Approximate locations of the borings are shown on
Figure 2 and logs of the borings are included in Appendix A.
o Performed engineering evaluations of the surface and subsurface
conditions observed and developed geotechnical recommendations for
foundation design and construction including slope setbacks plus
geotechnical recommendations general site development.
o Prepared this geotechnical report summarizing our findings and
geotechnical recommendations for site development including foundation
design and construction, subgrade preparation, erosion control and
drainage control.
OBSERVED SITE CONDITIONS
Surface Conditions
Our site observations and explorations were made on 4/6/12. The property is located
on the west side of Hanna Park Road situated between the road and the Burlington
Northern Railroad ROW to the west. Topographically the site is located in a nearly flat
terrace area above the northwesterly facing coastal bluff which drops down to the
railroad tracks as shown in Figures 1 and 2. The proposed residence will be located
within the upper terrace area where the existing house is currently located and will be
bordered on the north and south by neighboring residential property within the terrace
area and on the west by the very steep coastal bluff slope as shown in Figure 2.
The proposed building site area is on the upper terrace is currently occupied by the
existing residence and is well vegetated with lawns and shrubs. In addition the eastern
area of the property includes many trees including several fir trees ranging from about 2
to 2.5 feet in diameter.
Project No. 12-110-01 Page 2
Nelson April 16, 2012
Our observations of the existing bluff slope indicates that it is also well vegetated with
grass and ivy and occasional blackberries. Based on our field measurements, the bluff
slope is about 25 feet in vertical height and is very steep with slope angles ranging from
about 50 to 55 degrees. We did not observe any evidence of sliding or erosion of the
bluff slope or on the upper site.
Subsoil Conditions
We drilled four hand auger borings at the approximate locations shown on Figure 2.
Detailed logs of the our borings are presented in Appendix A.
Subsoils encountered in our explorations included a variable depth of fill and weathered
natural soils overlying stiff and dense natural soils. The fill and weathered soils ranged
from about 2 to 3.5+ feet thick at our borings locations. Fill soils were encountered to
depths of about 2 to 2.5 feet at the HA -2 and HA -3 boring locations and included silty
sand and clayey silt soils with charcoal. The underlying natural soils included clayey
silt, sandy silt, clayey sand and silty sand which became stiff to hard at depths of about
1.5 to 2 feet below the natural ground surface (below the existing fill soils).
Ground Water Conditions
Ground water was encountered in borings HA -1, HA -2 and HA -4 at depths of 35", 28"
and 27" respectively. No free ground water was observed in HA -3 to the maximum
auger depth of 5.5 feet but the subsoils at HA -3 and at all locations above the water
table were field classified as moist to very moist.
Measured moisture contents of the soil samples from HA -2 and HA -3 typically ranged
from about 15 to 29 percent and moisture contents of samples from HA -1 and HA -4
ranged from about 11 to 17 percent.
Project No. 12-110-01 Page 3
Nelson
SITE EVALUATIONS
Site Geology
April 16, 2012
Review of published geologic mapping (Figure 1) indicates that the surface soils in the
site vicinity (Qw) are older deposits of the Whidbey Formation, pre -dating the Fraser
glaciation that ended about 13,500 to 15,000 years ago. The Whidbey formation
deposits were glacially consolidated during the Fraser Glaciation. The Whidbey
formation is described as interglacial sediments which are typically bedded, compact,
medium to coarse-grained sands.
Geologic Hazards
Review of Edmonds ECA Inventory mapping indicates that geologic hazards mapped
within 200 feet of the site are limited to erosion hazard and landslide hazard. The site
is not indicated to be within a seismic hazard area.
Landslide Hazard Assessment
The existing bluff slope that borders the west side of the site is considered to meet the
criteria for Landslide Hazard Areas presented in 23.80.020 B of the Edmonds code
based upon its height and very steep inclination.
Based upon our surface observations, combined with our shallow explorations and
review of the geologic map of Figure 1, the bluff is composed of very dense/hard
glacially consolidated soils. Our observations of the existing bluff slope surface and
the area above the slope revealed no evidence of deep seated instability of the slope
nor any current shallow instability on the site or on the adjacent properties. In addition,
review of the geologic map of Figure 1 shows no major landslides mapped within the
area included on Figure 1 (more than 1 mile radius around the site).
As with all hillside development, you the owner must be aware of and accept the risk
that future slope failures may occur and may result in damage to your property and/or
neighboring property. In our opinion, the bluff slope is stable with regard to gross or
deep seated stability of the glacially consolidated deposits. However considering the
very steep slope inclination, in our opinion there is a moderate to high risk of future
shallow skin failures or sloughing of the bluff slope face over time. In general shallow
slope failures are most likely to occur during the winter and spring months due to
increased soil moisture conditions and during earthquake shaking due to the additional
dynamic loads on the slope.
The risk of structure damage resulting from a shallow slope failure varies with the
distance from the slope. In general to minimize risk, structures should be set back from
the top of adjacent steep slopes as far as practical within the constraints of the
Project No. 12-110-01 Page 4
Nelson April 16, 2012
development plans. As a minimum we recommend a 20 foot buffer + 15 foot setback
from the top of slope for the structure (total buffer + setback = 35 feet). Provided that
the structure is located behind our recommended minimum buffer and setback and
supported on undisturbed dense/stiff natural soils, future shallow skin failures and
sloughing of the bluff slope should have no impact on the proposed structure. Review
of Figure 2 indicates that the combined buffer + setback from the top of bluff for the
proposed house location ranges from about 36 feet at the NW corner to about 70 feet
at the SW corner and therefore more than meets our recommended minimum buffer +
setback.
In our opinion provided that the recommendations of this report are incorporated into
the design and construction procedures, the proposed residence will not adversely
impact the subject property or adjacent properties and will not adversely impact other
geologic hazard areas.
Erosion Hazard Assessment
The USDA soil mapping of the site area indicates the onsite soils to be Alderwood-
Urban land complex, 2 to 8 percent slopes. Per the criteria for Erosion Hazard Areas
presented in 23.80.020 A of the Edmonds code, the upper site is not considered an
erosion hazard area due to the very minor surface gradients which are much less than
15 percent plus the fact that we did not observe any visible evidence of ground water
seepage on the site. However the bluff slope is considered to be an erosion hazard per
the criteria due to the very steep gradients of the bluff.
Currently the property is well vegetated and we observed no indication of seepage or
ongoing erosion areas on the upper site or on the bluff slope. Based on our site
explorations the subsoils are generally silt -clay and silt -sand mixtures and are
considered to have a moderate erosion potential if exposed to concentrated water flow
in graded or disturbed areas. We have provided recommendations for drainage control
and erosion control during and after construction to prevent uncontrolled water flow
over the site and bluff slope surfaces. In our opinion, erosion risk should be low if our
recommendations are followed.
Seismic Considerations
Although the site is not mapped as a seismic hazard area, the Puget Sound region is a
seismically active area and you should be aware of the potential for seismic shaking
and associated secondary effects. About 17+ moderate to large earthquakes (M5 to
M7+) have occurred in the Puget Sound and northern Cascades region since 1872 (140
years) including the 2/28/01 M6.8 Nisqually earthquake and it is our opinion that the
proposed structure will very likely experience significant ground shaking during its
useful life.
Project No. 12-110-01 Page 5
Nelson April 16, 2012
The site lies only about 5 miles southwest of the mapped fault zone of the South
Whidbey Island fault which also has a postulated maximum credible earthquake
magnitude of 7.0 to 7.5. The recurrence intervals of large earthquakes on the South
Whidbey fault (SWF) is not known but recent data indicates that a earthquake on the
order of M6.5 to 7.0 occurred on the SWF about 3000 years ago and smaller events
occur more frequently as evidenced by the 5.3 event on May 2, 1996 which was
attributed to that fault.
Based on a recently published study by the USGS, the site is also located about 18
miles north of the inferred east -west trending Seattle fault zone which passes through
Seattle and trends along the 1-90 corridor. The Seattle fault has a postulated maximum
credible earthquake magnitude on the order of 7.0. The Seattle fault has been
documented to have moved at its west end (Bainbridge Island) about 1000 to 1100
years ago and evidence of movement at the east end has also recently been
documented. Some experts feel that the recurrence interval between large events on
the Seattle Fault may be on the order of several thousands of years but our calculations
indicate it may be on the order of 1200 to 1400 years.
Another recent study (2004) of the Vashon-Tacoma area presents evidence for the
east -west trending Tacoma Fault which is indicated to pass through the south end of
Vashon and the middle of Maury Island about 32 miles south of the site. The study
suggests that the Tacoma Fault and the Seattle fault may be linked at depth.
In addition to Puget Sound seismic sources, a great earthquake event (M8 to M9+) has
been postulated for the Cascadia Subduction Zone (CSZ) along the northwest Pacific
coast of Oregon, Washington and Canada. The current risk of a future CSZ event is
not known at this time. Published reports have indicated recurrence intervals for a CSZ
event to range from as little as 100-200 years to as long as 1000+ years and the time of
the last event is reported to have been about 312 years ago.
The 2009 International Building Code (IBC) requires consideration of a spectral
acceleration level with probability of exceedance of 2 percent in 50 years for seismic
structural design. This corresponds to about a 2475 -year recurrence interval
earthquake ground motion. Based on the short period spectral response accelerations
presented in Figure 1613.5(1) of the 2009 IBC, adjusted as per equations 16-36, 16-38
and factored as per section 1803.5.12(2), we estimate the IBC peak ground
acceleration for soils design at this site to be about 0.33g. Please note that the 0.33g
peak ground acceleration includes the additional reduction factor of section
1803.5.12(2) and is not intended for structural analyses. This site is considered a Site
Class C for structural design.
Considering the stiff/very dense to hard nature of the natural soils recommended for
foundation support, it is our opinion that the potential for damage due to liquefaction,
lateral spreading and seismically induced settlement is nil. The onsite slope is
considered to have a moderate to high potential for induced shallow failures depending
on the earthquake magnitude and shallow ground water conditions at the time of the
Project No. 12-110-01 Page 6
Nelson April 16, 2012
earthquake but deep seated stability should be adequate even considering the 0.33g
IBC peak acceleration.
In addition to ground shaking and geotechnical secondary hazards, coastal sites are
also subject to the non -geotechnical related hazard of tsunami waves which was so
graphically demonstrated by the recent 12/26/04 tsunami in the Indian Ocean and the
3/11/11 tsunami that devastated Japan. Tsunamis are long -wavelength, long -period sea
waves that can be caused by vertical displacements of the sea floor which are typically
generated by large seismic events. Although tsunamis waves generally have wave
heights less than 1 meter in deep water areas, wave heights exceeding 20 meters can
develop as the wave enters shallow coastal waters.
Historically tsunamis have caused only minor damage in Washington, primarily in the
coastal areas from Grays Harbor to Long Beach where wave heights of about 13 to 15
feet high came ashore from the tsunamis triggered by the 1964 Alaska earthquake. At
Neah Bay on the Strait of Juan de Fuca, six smaller tsunamis waves generated by
distant seismic events were recorded between 1946 and 1986.
There is also geologic evidence of a pre -historic tsunamis within Puget Sound that likely
occurred about 1100 years ago. This tsunamis is thought to have been generated by a
large seismic event on the Seattle Fault which runs from Bainbridge Island eastward to
near North Bend. In addition geologists have found evidence along the Washington
coast they believe indicates a tsunamis was generated by a great Cascadia Subduction
Zone (CSZ) earthquake about 300 years ago.
We cannot assess the risk of tsunamis related damage to your site except to consider
that it is less than the general risk of earthquake damage related to ground shaking.
Future tsunamis may be generated by distant earthquakes across the Pacific Ocean,
from earthquakes in Alaska and the Aleutian Islands, from a great CSZ earthquake off
the Washington coast or from a local earthquake in the Puget Sound region.
Tsunamis risk at your site is somewhat reduced by its location within Puget Sound
which provides some protection from Pacific Ocean tsunamis waves and by the 30+
foot high shoreline which would provide protection from smaller tsunami wave heights.
A tsunamis resulting from a local earthquake could come ashore within minutes of the
earthquake that generates it. We recommend that when a future large earthquake
occurs that you evacuate the subject residence immediately and go to higher ground at
least 100 feet above the beach level and remain there until authorities determine that
there is no tsunamis hazard.
Structure Support
In our opinion, the existing fill and loose/soft weathered soils are not suitable for
foundation support. Therefore the new foundations must extend through the fill and
weathered soils into the underlying natural bearing soils encountered at depths of about
Project No. 12-110-01 Page 7
Nelson April 16, 2012
3.5 to 4 feet below ground at our boring locations. We recommend that foundations for
the proposed residence be extended through the existing loose/soft fill soils to bear
within the underlying very dense/stiff/hard natural soils and that the foundations have
the minimum 35 foot buffer + setback from the top of the bluff slope.
As an alternative to deep spread footings to penetrate fill and unsuitable soils
foundation loads may be transferred from the recommended minimum foundation
depths to the recommended bearing soils by a monolith of lean concrete.
Recommendations for spread footings optionally supported on a lean concrete monolith
are presented in the RECOMMENDATIONS section of this report.
Construction Considerations
It should be noted that we encountered ground water above the recommended
foundation bearing soils at the HA -1 and HA -2 locations. De -watering will likely be
required for foundation construction excavations, depending upon the time of year.
RECOMMENDATIONS
The following presents our recommendations for design and construction of
foundations, site grading, site drainage, erosion control and observations and testing
during construction.
Spread Footing Foundations
Conventional spread footings founded on undisturbed dense/stiff natural soils should
provide good support for the proposed residence. Footings should be at least 18
inches wide and all footings should be behind the minimum 35 foot horizontal buffer +
setback from the top of bluff slope. Footings should also be setback beyond a 1:1 (h:v)
projection from adjacent lower footings. Footing design may be based on a maximum
allowable bearing pressure of 2000 psf for both square and continuous footings.
Based on the subsoil conditions encountered at our boring locations footing
embedment depths are expected to range from about 3.5 to 4 feet below the existing
surface. As an alternative to deep spread footings to penetrate fill and unsuitable
soils, foundation loads may be transferred from the recommended minimum foundation
depths to the recommended bearing soil embedment by a monolith of lean concrete
having a minimum compressive strength of 1000 psi. The width of an un -reinforced
lean concrete monolith should be at least as wide as the footing or at least one-third of
the monolith height, whichever is greater. Reinforced monoliths should be designed by
a structural engineer. A suitable width trench should be excavated with a smooth
Project No. 12-110-01 Page 8
Nelson April 16, 2012
edged excavator bucket (no teeth) to expose and clean the very stiff/hard bearing soil
surface (no personnel in the trench) under observation by our office and backfilled as
soon as possible (at least the. same day) with the lean concrete to the footing elevation.
Settlement of the structure is expected to be within tolerable limits for this type of
construction. For example, the estimated settlement of a 18 inch wide continuous
footing carrying a load of 3 kips/ft. is on the order of 1/2 inch. Maximum differential
settlement within the proposed structure is expected to be on the order of 1/4 inch.
Settlements are expected to occur primarily during construction.
Resistance to lateral loads can be assumed to be provided by friction acting at the base
of foundations and by passive earth pressure. A coefficient of friction of 0.4 may be
assume with the dead load forces in contact with on-site soils. An allowable static
passive earth pressure of 150 psf per foot of depth may be used for the sides of
footings poured against undisturbed weathered soils or properly compacted fill.
The vertical and lateral bearing values indicated above are for the total dead load plus
frequently applied live loads. For short duration dynamic loading caused by seismic or
wind forces, the vertical bearing values may be increased by 50 percent and allowable
lateral passive pressures may be increased by 33 percent.
Site Grading
Site grading is expected to be limited primarily to excavation for construction of
foundations and subgrade preparation for slabs and driveway. Footing excavations are
expected to be about 3.5 to 4 feet deep. Excavation and fill placement within slab and
pavement subgrade areas is expected to be about 1 to 2 feet.
Site Preparation: Existing vegetation, debris, existing fill and/or loose or soft soils
should be stripped from the areas that are to be graded. During rough grading, excess
soils should be hauled off site and no material should be placed on the slope. Soils
containing more than 1% by weight of organics may be used in planter areas, but
should not be used for fill beneath slab or pavement areas. Stumps, debris and trash
should be removed from the site. Subsoil conditions on the site may vary from those
encountered in our explorations. Therefore, the soils engineer should observe the
prepared areas prior to placement of any new fills.
Temporary Excavations: Based on the subsurface conditions encountered in our
borings, it is our opinion that temporary excavations in natural soils above the ground
water may be made vertically to depths of 4 feet. Deeper temporary excavations that
personnel will enter should be made at slope gradients no steeper than 1:1
(horizontal: vertical). Excavations that extend below the ground water table should be
de -watered and should be made no steeper than 1.5:1 (h:v). It should be noted that the
contractor is responsible for safety and maintenance of construction slopes.
Project No. 12-110-01 Page 9
Nelson April 16, 2012
Structural Fill: In our experience the onsite soils will be moisture sensitive with regard to
compactability for structural fill and the existing silt soils are considered to be generally
too wet for adequate compaction, particularly the silt/clay soils. Excavated sand and
gravel soils are considered technically suitable for general structural fill provided that
they can be dried back adequately for compaction. If moisture contents are too high at
the time of grading, adequate compaction may be very difficult to impossible requiring
the use of clean sand and gravel import material with less than about 10 percent fines
for adequate compaction.
General structural fill should be placed in horizontal lifts not exceeding 8 inches in loose
thickness and compacted to at least 90% of the maximum dry density as determined by
the ASTM D1557 test method. Loose and disturbed soils, form -work and debris should
be removed prior to placing structural fill or backfill.
Pavement and Slab Subgrade Preparation: Pavements and slabs -on -grade should be
supported on a properly compacted structural fill subgrade (below slab/pavement and
base course) over firm/medium dense, non-organic natural soils. All topsoil and
loose/soft weathered soils in subgrade areas should be stripped as required to remove
all organic and loose/soft soils and expose firm/medium dense natural soils (up to a
maximum of 24 inches below final subgrade) and the stripped soils should be replaced
with properly compacted structural fill. Proper subgrade compaction should be verified
by field density testing by a qualified testing laboratory.
Concrete slabs and pavements should have 2 -way reinforcement and should have
frequent construction joints to reduce. the potential for cracking. Risk of cracking can
be reduced by placing frequent construction joints, placing 2 -way reinforcement steel,
and by additional excavation and replacement of the existing subgrade with new
structural fill. Interior concrete slabs should be underlain by a capillary break
consisting of a polyethylene vapor barrier of at least 6 mil thickness.
Utility Trenches: Buried utility conduits should be bedded and backfilled around the
conduit in accordance with the project specifications. Where conduit underlies concrete
pavement or slabs -on -grade, the backfill above the pipe should be placed and
compacted in accordance with the recommendations for structural fill. If clean granular
fill is used for trench backfill it should be capped with 6 inches of onsite silty soils in
non -paved areas.
Drainage Control
Surface drainage on the site should be controlled, collected and discharged to the
storm drain system or to a non-erosive discharge point below the bluff slope. No
uncontrolled water flow should be allowed on the site or towards the bluff slope.
Adequate positive drainage should be provided away from the structure to area drains
to prevent water from ponding and to reduce percolation of water into subsoils.
Project No. 12-110-01 Page 10
Nelson April 16, 2012
Granular backfill should be capped with paving or 6 inches of onsite silty soils. A
desirable slope for surface drainage is 2% in landscaped areas and 1 % in paved areas.
Roof drains for the proposed new residence and out buildings should be tightlined into
the storm drain system (no discharge on the ground surface) or to a non-erosive
discharge point below the bluff slope. New subsurface drains should consist of a four -
inch minimum diameter perforated PVC drain pipe placed in at least one cubic foot of a
washed drain gravel per lineal foot and the drain gravel should be encapsulated with
Mirafi 140N filter fabric or equivalent..
Temporary ditches and sumps should be provided during construction as required to
collect surface runoff and/or subsurface seepage in the construction area. Silt ladened
water from construction drainage should be de -silted via an approved de -silting system
prior to discharge into the storm drain system.
Erosion Control
Onsite materials are expected to be moderately erodible when exposed to concentrated
water flow therefore drainage should be controlled to prevent concentrated flows.
Exposed soils and stockpiles should be covered during heavy rainfall and no soil should
be placed on the bluff slope or within the slope buffer. Siltation fences or other suitable
detention devices should be provided around soil stockpiles and around the lower sides
of exposed soil areas during construction to control the transport of eroded material.
The lower edge of the silt fence fabric should have "J" shaped embedment in a trench
extending at least 12 inches below the ground surface.
Exposed final graded soil areas should be covered with a non-erosive surface covering
or planted immediately with grass and deep rooted plants to provided permanent
erosion control. In addition we recommend that the exposed soil surfaces of the site be
temporarily covered with straw mulch or other suitable erosion resistant material during
the wet season (11/1 through 3/31) if final erosion control measures are not completed
before 11 /1.
Observations and Testing During Construction
Recommendations presented in this report are based on the assumption that soil and
foundation conditions exposed during construction will be observed by our office so that
any necessary design changes or supplements may be made. Footing excavations
should be observed to verify bearing soils plus recommended minimum embedment
and slope setbacks. All subsurface drain systems should be observed by our office to
verify proper construction. Proper pavement and slab subgrade preparation and
structural fill placement and compaction should be observed by our office and verified
with field and laboratory density testing by a qualified testing laboratory.
Project No. 12-110-01 Page 11
Nelson April 16, 2012
uncontrolled water flow should be allowed, especially over the bluff slope. Adequate
positive drainage should be provided away from the structure to area drains to prevent
water from ponding and to reduce percolation of water into subsoils. Granular backfill
should be capped with paving or 6 inches of onsite silty soils. A desirable slope for
surface drainage is 2% in landscaped areas and 1 % in paved areas.
Roof drains for the proposed new residence and out buildings should be tightlined into
the storm drain system (no discharge on the ground surface) or to a non-erosive
discharge point below the bluff slope. New subsurface drains should consist of a four -
inch minimum diameter perforated PVC drain pipe placed in at least one cubic foot of a
washed drain gravel per lineal foot and the drain gravel should be encapsulated with
Mirafi 140N filter fabric or equivalent..
Temporary ditches and sumps should be provided to as required to collect surface
runoff and/or subsurface seepage in the construction area. Silt ladened water from
construction drainage should be de -silted via an approved de -silting system prior to
discharge into the storm drain system.
Erosion Control
Onsite materials are expected to be moderately erodible when exposed to concentrated
water flow therefore drainage should be controlled to prevent concentrated flows.
Exposed soils and stockpiles should be covered during heavy rainfall and no soil should
be placed on the bluff slope or within the slope buffer. Siltation fences or other suitable
detention devices should be provided around soil stockpiles and around the lower sides
of exposed soil areas during construction to control the transport of eroded material.
The lower edge of the silt fence fabric should have "J" shaped embedment in a trench
extending at least 12 inches below the ground surface.
Exposed final graded soil areas should be covered with a non-erosive surface covering
or planted immediately with grass and deep rooted plants to provided permanent
erosion control. In addition we recommend that the exposed soil surfaces of the site be
temporarily covered with straw mulch or other suitable erosion resistant material during
the wet season (11/1 through 3/31) if final erosion control measures are not completed.
Observations and Testing During Construction
Recommendations presented in this report are based on the assumption that soil and
foundation conditions exposed during construction will be observed by our office so that
any necessary design changes or supplements may be made. Footing excavations
should be observed to verify bearing soils plus recommended minimum embedment
and slope setbacks. All subsurface drain systems should be observed by our office to
verify proper construction. Proper pavement and slab subgrade fill placement and
Project No. 12-110-01 Page 11
Nelson
r4X@3TFI3
April 16, 2012
This report was prepared for specific application to this project and for the exclusive use
of Erik and Tamara Nelson and their representatives. The findings and conclusions of
this report were prepared in accordance with the skill and care ordinarily exercised by
local members of the geotechnical profession currently practicing under similar
conditions. We make.no other warranty, either express or implied.
Variations may exist in site conditions between those described in this report and actual
conditions encountered during construction. Based on our experience, it is our opinion
that some variation in the continuity and depth of subsoil deposits and ground water
levels should be anticipated due to natural deposition variations and site grading. Due
to seasonal moisture changes, ground water conditions should be expected to change
with time. Care should be exercised when interpolating or extrapolating subsurface
soils and ground water conditions between or beyond our borings and borings
Unanticipated subsurface conditions commonly occur and cannot be prevented by
merely making explorations and performing reconnaissance. Such unexpected
conditions frequently require additional expenditures to achieve a properly constructed
project. If conditions encountered appear to be different from those indicated in this
report, our office should be notified.
Respectfully submitted,
GEOSPECTRUM
�'
James A. Doolittle
Principa
.. -
•.l Engineer
Encl:
• --
Encl: Figures 1 and 2
Appendix A
Dist: 2/Addressee
No. 12-110-01
�..
FEZ
Page 12
t
ref: "Geologic Map of the Edmonds East and Part
of the Edmonds West Quadrangles,
Washington", USGS MF -1541, by James P.
Minard 1983 Scale: 1"= 2000' SITE VICINITY GEOLOGIC MAP
GEOSPECTRUM CONSULTANTS, INC.
GaotBchnlco/ Englnaor/ng and Earth Sc -!®"cos
Proposed Residence Replacement
723 Hanna Park Road
Edmonds, Washington
Proj. NO2-110 1 Date 4/12 1 Figure 1
P
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SITE CONDITIONS & EXPLORATION PLAN
Proposed Residence Replacement
GEOSPECTRUM CONSULTANTS, INC. 723 Hanna Park Road
Edmonds, Washington
Er7g71r7dRqr1r-)g7 and Ecrrth I Proj. No. 12-1101 Date 4/12 1 Figure 2
APPENDIX A
FIELD EXPLORATION
Our field exploration included a site reconnaissance and subsurface exploration
program. During the site reconnaissance, the surface site conditions were noted, and
the locations of the hand auger borings were approximately determined.
The hand auger borings were approximately located using the existing carport corners
as a reference. Elevations at the exploration locations were estimated based on the
topographic mapping included on Figure 2.
The borings were advanced using hand excavation tools. Soils were continuously
logged and classified in the field by visual examination, in accordance with the ASTM
Soil Classification system.
Penetration tests were performed in the hand auger borings using a 1/2 -inch diameter
penetrometer and a 27.5 -pound driving hammer falling 24 inches. Recorded blows for
12 -inches of penetration are shown on the hand auger boring summary sheets.
Logs of the hand auger borings are presented on the boring summary sheets A-1 and
A-2. The hand auger boring summaries include descriptions of the soils and pertinent
field data. Soil consistency and moisture conditions indicated on the logs are
interpretations based on the conditions observed in the field. Boundaries between soil
strata indicated on the logs are approximate and actual transitions between strata may
be gradual.
Logged by JAD
Date: 4/6/12
Depth Blows Class. Soil Description
0 sod/topsoil
............... .....................
1 SM Silty fine Sand
with occ gravel
2 4
3-
4— 20
5--
61 7
Elevation:42.5'
Consistency Moisture Color W(%) Comments
SM Silty Sand, v. fine w/trace clay -
� ne pd
grave,1.1......... ................
becomes more gravelly edium
Tnse/
ense
Maximum depth 5 feet. Auger ref sal on gray
Ground water at 35 inches after 3. hours.
Logged by JAD
Date: 4/6/12
Depth Blows Class. Soil Description
0
1
2
3
4
5
6
7
Em
ra -
ro n
at 3.5 feet.
Elevation: 41.5
Consistency Moisture Color W(%) Comments
ML Clayey Silt soft moist o�lt
r
with organics to v�n
Ta
re - rn
very
moist 25.0
Clayey/Silty Sand, v. fine loose wet red-brn 15.1
7 w/occ gravel brown
blue -
Tedium gray
GEOSPECTRUM CONSULTANTS, INC. Proposed Residence Replacement
723 Hanna Park Road
Geotechnical Engineering and Earth Sciences Edmonds, Washington
Proj. No. 12-110 Date 4/12 Figure A-1
ense
21.6
20
75+
....................
dense
Maximum depth 6.5 ft.
Ground water encountered at 28".
GEOSPECTRUM CONSULTANTS, INC. Proposed Residence Replacement
723 Hanna Park Road
Geotechnical Engineering and Earth Sciences Edmonds, Washington
Proj. No. 12-110 Date 4/12 Figure A-1
HAND AUGER BORING.
Logged by JAD
Date: 4/6/12 Elevation:41.0'
Depth Blows Class. Soil Description Consistency Moisture Color W(%) Comments
0
1
2
3
4
5
6
7
Logged by JAD
Date: 4/6/12
Depth Blows Class. Soil Description
0-
1
2
3
4
5
6
7
Elevation: 40.0
Consistency Moisture Color W(%) Comments
SM
Silty fine Sand
ith coarse sand
occ gravel
loose
moist
to
very
moist
very
b{own
dark
brown
&black
21.6
ML
Clayey Silt with fine sand
s?ft
moylQd
3
wet
firm
moist
Per 0Ybrn
28.6
Silty Sand, f -c, w/trace clay
& gravel to 2"
dose
de se
mottlipd
Peel rn
ML
Sandy Silt, very fine
stiff
gray
14
Maximum auger depth 2.5 ft.
25.8
9
Ground water at approximately 27
.
Maximum depth 7 feet. No groun
water encl
ntered.
Logged by JAD
Date: 4/6/12
Depth Blows Class. Soil Description
0-
1
2
3
4
5
6
7
Elevation: 40.0
Consistency Moisture Color W(%) Comments
GEOSPECTRUM CONSULTANTS, INC. Proposed Residence Replacement
723 Hanna Park Road
Geotechnical Engineering and Earth Sciences Edmonds, Washington
Proj. No. 12-11OT Date 4/12 1 Figure A-1
sod/topsoil
loose
moist
very,
moist
brown
16.1
S il/
Silty SangjSandy Silt
i i S
occ. or any to
80+
wet
12.7
Silty Sand, f -c, w/trace clay
& gravel to 2"
dose
de se
mottlipd
Peel rn
Maximum depth 3.5 ft.
Maximum auger depth 2.5 ft.
Ground water at approximately 27
.
GEOSPECTRUM CONSULTANTS, INC. Proposed Residence Replacement
723 Hanna Park Road
Geotechnical Engineering and Earth Sciences Edmonds, Washington
Proj. No. 12-11OT Date 4/12 1 Figure A-1