20121120073927324.pdfLANDAU
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TECHNICAL MEMORANDUM ENVAMMENK I GE07L{:}BQCAI I NANM RENES
TO: Leonard Yarberry, Building Official
City of Edmonds Development Services Department, Building Division
FROM: Chad T. McMullen P.E. and Dennis R. Stettler, P.E.
DATE: November 19, 2012
RE: GEOTECHNICAL PEER REVIEW
EARTH SUBSIDENCE AND LANDSLIDE HAZARD AREA - PRE2012 - 0032
OLSON SFR —15500 75T" PLACE WEST
EDMONDS, WASHINGTON
This technical memorandum provides our geotechnical peer review for the permit submittal
package that was submitted to the City of Edmonds (City) for the proposed referenced development
within the Earth Subsidence and Landslide Hazard Area (ESLHA) of North Edmonds. The submittal
consists of a two document packets—one stamped "Received August 23, 2012" and one stamped
"Received October 1, 2012." The former packet was submitted for completeness review by the City; the
latter packet contains a replacement set of architectural -structural drawings, an updated structural
calculations packet, and an executed agreement with BNSF for stormwater tightline construction and
discharge onto the railroad's right-of-way. For the purpose of this peer review, we reference the more
recent architectural and structural documents. We previously performed a geotechnical completeness
review (summarized in a technical memorandum to the City, dated August 30, 2012) of the August 23,
2012 submittal documents. The purpose of the current geotechnical peer review is to review portions of
the submittal package and assess its compliance with City development and building permit requirements
as contained in Edmonds Community Development Code (ECDC) Chapters 19.10 and 23.80. This
geotechnical peer review was accomplished in accordance with Task Order No. 12-03 of Landau
Associates' On -Call Geotechnical Engineering Services Agreement with the City.
We have received the following information forwarded by the City for review:
August 23, 2012 Submittal Documents:
® Architectural/Structrtral Plan Set (14 Sheets, including architectural and structural plans,
elevations, and details) prepared by Architectural Design Associates, dated August 20, 2012.
Includes geotechnicaUlandslide risk statements signed and sealed by geotechnical and
structural engineers on Title Sheet T1.0.
® Site Plan (Sheet SPLO) listed in sheet index of Architectural Plan Set (above) but not bound;
encountered loose in submittal packet. Dated July 11, 2011.
® Landscape Plan Set and Tree Hazard Evaluation packet, including Re -vegetation and Tree
Mitigation Plan (drawing L1.0), Signiftcant Tree Inventory and Tree Preservation Plait
130 2nd Avenue South e Edmonds, WA 98020 e (425) 778-0907 ® fax (425) 778-6409 o www.landauinc.com
(drawing L2.0). Hannsen & Associates. Plans dated August 13, 2012. Packet data sheets
(16 total) dated August 4, 2012.
• Civil Plan Set (6 Sheets, including TESC plan, SWPP plan, road and storm drainage plan
and details, and sewer/water plan) prepared by J.C. McDonnell Engineering, PC. Issued
August 10, 2012.
• Storm Drainage Study for George Olson SFR. J.C. McDonnell & Associates. August 8,
2012 revision date.
• Olson Property Geotechnical Hazard Assessment. Letter from J.C. McDonnell Engineering,
PC to City of Edmonds Building Department deferring geotechnical risk statement to Nelson
Geotechnical Associates, Inc. (geotechnical risk statement is made and sealed by NGA on
Title Sheet [T1.0] of Architectural Plan Set, above). Dated August 20, 2012.
• Revised Geotechnical Engineering Report, 15500 75`r' Place West, Edmonds, Washington,
Prepared for Mr. George Olson. Report prepared by Nelson Geotechnical Associates, Inc.,
dated July 15, 2011.
• Covenant of Notification and Indemnification/Hold Harmless. Assessor's Tax Parcel ID
00500900000103 signed by George M. Olson and Virginia A. Olson, dated August 17, 2012.
• North Edmonds Earth Subsidence and Landslide Hazard Areas Map (with property location
noted and signed certification as to property location), by James Thomas, Project Architect,
dated August 17, 2012.
• Engineering Survey for George Olson, prepared by Metron and Associates, dated December,
2010.
• Completed City of Edmonds Traffic Impact Analysis Worksheet. Undated.
• Gravity Calculations, #2011-26, George and Ginger Olson. Architectural Design Associates.
Dated August 27, 2011.
• Structural Calculation Packets by Mitchell Engineering, Inc., including soldier pile/lagging
design calculations (packet date: March 10, 2011) and foundation, slab, shearwall, and other
structural design calculations (packet date June 30, 2011). Signed and sealed.
• Applicant/Owner liability and landslide risk acknowledgement signed by George M. Olson
and Virginia A. Olson, dated August 17, 2012, with notarized attachment dated August 21,
2012.
• Affidavit of Earth Subsidence Landslide Hazard Area Permit Posting. Dated and notarized
August 21, 2012.
October 23, 2012 Submittal Documents:
• Resubmitted Architectural/Structural Plan Set (14 Sheets, including architectural and
structural plans, elevations, and details) prepared by Architectural Design Associates,
revised date September 26, 2012. Includes geotechnical/landslide risk statements signed and
sealed (photocopies) by geotechnical and structural engineers on Title Sheet T1.0
• Resubmitted Gravity Calculation and Structural Calculation packets by Architectural Design
Associates (ADA) and Mitchell Engineering, Inc., respectively. With ADA coversheet dated
September 26, 2012.
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Executed Pipeline License between BNSF Railway Company and George and Virginia
Olson. Jones Land LaSalle Brokerage. Cover letter dated August 22, 2012, with transmittal
sheet by ADA, dated September 26, 2012.
The documents submitted appear to meet the minimum required application submittals identified
in Section 19.10.030 of the Development Code. The following sections provide our specific geotechnical
peer review comments.
GEOTECHNICAL REPORT
The geotechnical report provides a reasonably comprehensive evaluation and discussion of site
conditions and risks, and provides geotechnical recommendations for design. The report appears to
adequately document existing site conditions based upon field reconnaissance and subsurface
explorations, and acknowledges the occurrence of landsliding within the ELSHA and the risk potential for
future landsliding at and in the vicinity of the subject parcel. However, the report contains the following
language (page 6):
This site and the overall site vicinity lies within an ancient landslide area. The site
and vicinity have been relatively stable for a very long period of time, and
development in the area has taken place in the farm of single-family residences
and roadways. Although the likelihood of the ancient slide to become active in the
foreseeable future is very low, extreme environmental conditions coupled with
inadequate human practices could re -activate the ancient landslide. Stich
external factors could include severe and elongated weather events and/or
significant seismic activity.
We are concerned that the above paragraph understates the risk posed by the site. The statement
that "the site and vicinity have been relatively stable for a very long period of time ..." ignores the recent
landslide that has occurred on the site and the history of multiple landslides within the North Edmonds
ESLHA that have occurred within the last 70+ years (some relatively close to this site). The above
quotation appears to convey a reduced level of risk that is contrary to what historical experience within
the ELSHA would suggest. We recommend that NGA revisit the landslide risk conditions at this site
and also provide a clear statement of risk and their assessment of the stability of the site and whether it
is their professional opinion that the site meets the criteria for "Stable" as defined in ECDC
19.10.020.0. (including the estimated probability of earth movement) as restated below:
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"Stable" shall mean that the risk of damage to the proposed development, or to adjacent
properties, from soil instability is minimal subject to the conditions set forth in the reports
developed under the requirements of ECDC ,19.10.030 and the proposed development will not
increase the potential for soil movement.
In the event that any site has an underlying risk of movement based upon deep-seated earth
movement or large-scale earth failure which is not susceptible to correction by on-site
improvements, such hazard shall not render a site proposed for single-family residences to be
presumed unstable for the purpose of this provision if the geotechnical engineer of record and
recommendation of any peer reviewer confirm the risk of probability of earth movement is 30
percent or less within a 25 -year period.
In order to meet the definition of "stable" the geotechnical report shall include identified hazards
for the property and the mitigation measures proposed to reduce or correct the hazards along
with measures taken to mitigate potential impacts from the remaining hazards, including all on -
and off-site measures taken to correct or reduce the risk. These shall be fully disclosed to the
applicant and future owners, heirs and assigns in the covenant required to be executed in
accordance with provisions of this chapter, in which case the defined risk may be approved as an
acceptable condition.
Landslide debris consisting of loose to medium dense colluvium is reported as extending up to
about 15 ft below existing grades on the site. The footprint of the proposed structure is located in the
uppermost third of the slide debris extents, and the current site layout appears to be similar to the layout
contemplated at the time of the geotechnical report preparation. The proposed design would excavate a
portion of the slide mass to create a level grade within the building footprint and would transmit structure
loads (via deep foundations) to competent soil underlying the slide mass. These appear to be reasonable
design strategies.
Deep foundations consisting of about 25 -ft long, 16 to 24 -inch diameter drilled piers are
recommended in the report; 25 -ft long, 18 -inch diameter augercast piles are indicated on the project
drawings for support of building loads. Smaller, isolated column loads (from exterior decks and
stairways) are supported primarily by pin -pile groups. The lowest building floor consists of a structural
slab supported by augercast piles connected by grade -beams.
Recommendations for site and roof drainage include collection and conveyance to the base of the
steep slope, along the BNSF right-of-way.
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CIVIL PLANS AND STORM DRAINAGE STUDY
Inspection, maintenance, and regular reporting of TESC measures by the Geotechnical Engineer
of Record are required [see the City ESLHA Temporary Erosion and Sediment Control (TESC)
Requirements]. The pre -construction meeting needs to include the Geotechnical Engineer of Record (see
City ESLHA TESC Requirements). On Sheet Cl, subheading "Construction Sequence," the
Geotechnical Engineer of Record is identified as Nelson Geotechnical Inc (NGA). However, in the
subheading "Engineer's Notes," Cornerstone Geotechnical Inc. is identified as providing geotechnical
engineering for the project. We recommend that the notes be revised appropriately. Alternatively, if a
different geotechnical engineer is retained for the construction phase (i.e., other than NGA), the new
geotechnical engineer must submit statements of agreement or disagreement [and recommended
changes] to the project design, in accordance with 19.10.080(B).
On Sheet Cl, the circled symbol "IT" is shown on the Site TESC & Grading Plan and on the
TESC Legend, though "IT" is not defined (Interceptor Trench?) and its dimensions/extents are not
apparent. A Temporary Interceptor Trench Section is included on this sheet. Please clarify the intent of
these plan items.
On Sheet Cl, a stockpile is noted between the top of the steep slope and the residence footprint.
From the geotechnical design report, pp. 11:
Site preparation should also consist of stripping any organic topsoil and/or
loose/soft soils in areas that will support foundations, slabs -on -grade, pavement, or
structural fill. The stripped material should not be stockpiled in any area between
the top of the slope and the residence footprint.
The stockpile location does not satisfy the recommendations of the geotechnical report. The
location of stockpiling should be modified to accommodate the geotechnical recommendations.
A statement of adequacy of the proposed TESC and grading designs, as required by
19.10.040(C), is signed and sealed by NGA on the Architectural Plan Set.
STRUCTURAL DESIGN
Plan Sheet SP1.0 shows the location of a replacement wall for a failing wall near the northeast
property line and structural calculation sheets for a soldier pile and lagging wall are provided. However,
a structural detail is not provided in the structural plan set that we reviewed. We recommend that the
plans include the location and structural details for the soldier pile retaining wall.
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LANDSCAPE DESIGN
Harmsen & Associates conducted a tree inventory and condition survey for the project and
prepared landscaping plans which appear to be in general accordance with ECDC 23.40. Reported
conditions include numerous downhill -leaning trees with overweighted trunks due to ivy loads or poor
growth habit. Twenty-one trees will be removed within the construction footprint of the residence; an
additional eleven trees were identified as hazard trees and will be removed. The code specifies that trees
removed within critical areas be replaced at a rate of two -to -one. On the Re -vegetation and Tree
Mitigation Plan (Sheet L1.0), only 21 replacement trees are shown. One additional tree is necessary to
mitigate removal of eleven hazard trees located outside of the construction footprint. Replacement tree
species include vine maple, serviceberry, pacific dogwood, douglas fir, and excelsa cedar. Some of these
species are identified by the Department of Ecology as well-suited for erosion control and slope
stabilization; we must defer to the landscape architect's expertise concerning the suitability of the other
selected species for these design functions.
A drought -tolerant grass seed blend is specified for long-term erosion control around the
developed portion of the parcel. Automatic sprinklers or other irrigation systems are not specified on the
landscaping plans.
REQUIRED STATEMENTS AND DECLARATIONS
We reviewed the submittal package and confirmed that the statements and declarations from the
design professional as required by the City for development within the ESLHA are included in the
following documents:
• Covenant of Notification and Indemnification/Hold Harmless. Assessor's Tax Parcel ID
00500900000103 signed by George M. Olson and Virginia A. Olson, dated August 17, 2012.
• Structural engineer declaration stating awareness and understanding of landslide risks is
made, signed, and sealed on the Architectural/Structural plan set by Mitchell Engineering.
• Geotechnical hazard acknowledgement, mitigation, minimal risk statement, and declared
review and approval of the project's structural and civil design elements, is made, signed, and
sealed on the Architectural/Structural plan set by NGA.
• A signed and stamped risk statement is not made by the project civil engineer, J.C.
McDonnell Engineering. In the Olson Property Geotechnical Hazard Assessment letter to the
City, J.C. McDonnell argues that such a risk statement would be outside his scope of
expertise and is more appropriately made by the geotechnical engineer. J.C. McDonnell
Engineering does state that the development of the civil and drainage plans has followed the
recommendations of the Project Geotechnical Engineer and those plans have been reviewed
by Nelson Geotechnical. In our opinion, this statement adequately addresses the required
statement from the Civil Engineer as contained in ECDC 19.10.040.C.
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• Applicant/Owner liability and landslide risk acknowledgement signed by George M. Olson
and Virginia A. Olson, dated August 17, 2012, with notarized attachment dated August 21,
2012.
• Affidavit of Earth Subsidence Landslide Hazard Area Permit Posting. Dated and notarized
August 21, 2012.
In general, the statements and declarations have been appropriately addressed, although the City
should consider whether the deferred statement of risk approach proposed by the civil engineer is
acceptable.
This technical memorandum has been prepared for use by the City of Edmonds in evaluating the
adequacy of permit submittal documents related to the proposed Olson single family residence at 15500
75`h Place West. The focus of this review was the geotechnical aspects of the application. The purpose of
the review was to assess the adequacy of the application documents for compliance with City
requirements contained in ECDC 23.80 and ECDC 19.10 and conformance with conventionally accepted
geotechnical engineering practices. This geotechnical peer review by Landau Associates does not lessen
the requirements for the applicant's geotechnical consultant and other design professionals to prepare an
appropriate design for the site conditions.
We appreciate this opportunity to be of service to the City. Please contact us if you have any
questions or if we may be of further service.
CTM/DRS/rgm
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LANDAU ASSOCIATES