2013-0919 Meadowview Grading peer review.pdfhuolu , n°niirunni�°ntn� �j,rui I, m w,
September 24, 2013
HWA Project No. 2012-089-21 Task 700
City of ]Edmonds
Public Works: Engineering Department
121 Fifth Avenue North
Edmonds, Washington 98020
Attention: Mr. Leif Bjorback
Building Official
Subject: GEOTECHNICAL REVIEw ESLl`IA
Proposed 5 —Lot Short Plat-Meadowview Estates
15620 72nd Avenue West
Edmonds, Washington
City Project No. 001.000.62.524.20.41.00
Dear Mr. Bjorback,
As requested, HWA GeoSciences Inc. (HWA) previously undertook and completed a
completeness review of the submittal prepared by Mr. Kent Halvorson regarding the proposed
construction of 4 new residences and driveway on an existing 3.22 acre lot within Edmonds,
Washington. The subject property is located at 15620 72"d Avenue West and is within the Earth
Subsidence and Landslide Hazard Area of North Edmonds. We understand that the current
application is for drainage, road, and utility installation with associated grading for lot line
adjustment only. Building construction plans and structural design calculations were not
included in this submittal. This letter acknowledges that submittal package we have reviewed is
now complete containing the items listed below. In addition, we provide review and comment
on portions of the submittal package concerned with geology or geotechnical engineering.
The following documents were submitted for use during our geologic review:
Completeness Reviert, ESLHA, Proposed 5-Lot Short Plat 1lleadowvieiv Estates, 15620
72"d Avenue Vest, Edmonds (Prepared by HWA GcoSciences Inc, July, 29, 2013) (1
copy).
Completeness Revietiv Pre -Application Formfor Earth Subsidence Landslide Hazard
Area Projects (Prepared by Kent and Susan Halvorson, July 2013) (1
21312 30th Drive ` II,
copy).
City of Edmonds Environmental Checklist #P71 (Prepared by Kent and
Susan Halvorson on July 13, 2013). (1 copy).
S'uitc 110
Bodic1l,, WA 9802 p /010
'h+ 425374,0106
Em 425.72E1.27H
lvlvder.ulw agc"xonk
September 24, 2013
HWA Project No. 2012-089-21 Task 700
® North Edmonds Earth Subsidence and Landslide Hazard Areas Map (May 2006,
Landau) -with parcel area annotated (1 copy), accompanied by North Edmonds Earth
Subsidence and Landslide Hazard Area Summary Report, Edmonds, Washington
(Landau, 2007) (1 copy).
® Vicinity Map (Prepared by LDC, July 2013) (3 copies).
® Topographical Map and Survey (Prepared by LDC, July 19, 2013) (1 copy).
® Land Clearing/Tree Cutting Plan (Prepared by LDC, August 9, 2013) (1 copy)
® Geotechnical Engineering Study, Proposed Five -Lot short Plat, 15620-72"d Avenue YVest,
Edmonds, Washington (Prepared by Geotech Consultants, July 12, 2013) (1 copy).
® Civil Construction Plan Sheets Including: CS-01 Cover sheet, ER-01 TESC Plan, ER-02
TESC Notes and Details, RD-01 Grading, Road and Utility Plan, RD-02 Road and
Utility Plan, DT-01 and DT-02 Notes and Details (all Prepared by LDC, July 17, 2013) (1
copy).
® Small Site Storm Drainage Report (Prepared by LDC, July 16, 2013) (1 copy).
® Stormwater Pollution Prevention Plan (SWPP-Prepared by LDC July 15, 2013) (1 copy).
® Lead Design Professional Designation and Statement, Meadowview Estates. (Prepared
by Daniel P. Carmody, P.E. of LDC on July 15,2013) (1 copy).
® Applicant/Owner Liability & landslide Acknowledgement, Meadowvieiv Estates
(Prepared and signed by Mr. Kent Halverson on July 15, 2013) (1 copy).
® Geotechnical Hazard Identification/Declaration and Mitigation Statement of Risk -
Proposed Five -lot Short Plat, Meadowview Estates, 15620-72"d Avenue West, Edmonds,
Washington.( Prepared by Geotech Consultants, July 19, 2013) (1 copy).
® Covenant of Notification and Indemnification/Hold Harmless (prepared by Mr. Kent
Halvorson on July 23, 2013) (1 copy).
® Affidavit of "Notice of Application Posted at Job Site" Signed by Dylan Gerhardstein, on
July 22, 2013. (1 copy).
Currently, Building Construction Plans and Structural Calculations and a Declaration by the
Lead Structural Engineer have not been submitted. We understand this is likely because the
current permit application is only for site grading and utility installation. However with regard to
the specific geotechnical and critical areas elements of the ESLHA permit submittal checklist the
submittal meets the minimum compliance requirements except in terms of copies required for
submittal as noted on the attached checklist.
GEOTECHNICAL REVIEW
In general, the submittal package is complete as to form, and prepared in accordance with local
generally accepted geotechnical engineering practices. Below we provide comments with regard
to certain geologic and geotechnical aspects of the project described in the submittal documents:
Checklist Item 6 Topographic Map: Proposed structures are not delineated. Map to be updated
when structural plans are submitted for review in the future.
Halvorson Geotechnical Review ESLHA 2 HWA GeoSciences Inc.
September 24, 2013
HWA Project No. 2012-089-21 Task 700
Checklist Item 7 Land Clearing/Tree Cutting Plan: Sheet TR-01 in current submittal package.
This plan appears to meet the general requirements per COE Handout P#46. Tree removal
appears to be restricted to the footprint for the new driveway and adjacent slope cut. However, it
is not clear if the geotechnical engineer has reviewed the proposed tree cutting plan and
determined whether, in his opinion, it creates any slope stability issues or if a
landscape/restoration plan should be devised to mitigate potential long term erosion impacts.
Checklist Item 8 Geotechnical Report: In general, the report appears to meet the generally
accepted engineering practices; however the following omissions are noted:
1) On page 1, Site Conditions Chapter, Surface section of the report, a 40-foot wide
landslide that occurred in 1997 is discussed. If known it would be useful to have the
location of the slide marked in the Site Plan.
2) It appears that geologic interpretations were made, however, there is no indication that
the report was reviewed or approved by a geologist as required in COE Chapter
19.10.030G (4).
3) The report discusses static and seismic stability of the slope with regard to deep-seated
movement, but fails to provide an estimate of the rate of episodic bluff retreat expected
(potentially caused by isolated slides such as occurred in 1997 and/or soil softening due
to fieeze-thaw, wetting and drying, etc) for periods of 25 and 125 years as required in
COE Chapter 19.10.030G (6).
Checklist Item 9. Civil Construction Plan Sheets: In general, the plan sheets are complete as to
form. The following comments are provided for consideration
1) Sheet ER-01: It appears that the clearing limits extend into the area that the geotechnical
engineer recommended not be disturbed (see Page 6, 1 st Par. of the geotechnical report).
Does the geotechnical engineer have any concerns or require special provisions to be
observed when construction encroaches into this area?
2) Sheet RD-02: The proposed grade of the storm drain section between CB-3 and CB-2 is
extremely steep (25.25%). It is likely that the trench backfill will act as a French drain
and collect and convey infiltrating/shallow ground water seepage down toward CB-2
where the inclination and direction of the trench changes abruptly creating the potential
for localized wet soil conditions that spread towards the steep slope. At this location
consideration might be given to inclusion of perforated trench drain tied into CB-2.
CLOSURE
Within the limitations of scope, schedule and budget, our review of geotechnical and critical
areas elements of the submittal package was completed in accordance with generally accepted
principles and practices in this area at the time this letter was prepared. We make no other
warranty either express or implied.
rol
Halvorson Geotechnical Review ESLHA 3 HWA GeoSciences Inc.
September 24, 2013
HWA Project No. 2012-089-21 Task 700
We appreciate the opportunity to be of service. If you have any questions regarding this report,
please do not hesitate to contact either of the undersigned at (425) 774-0106.
Sincerely,
HWA GEOSCIENCES INC.
Steven E. Greene, L.G., L.E.G.
Principal Engineering Geologist
Vice -President
Halvorson Geoteclmical Review ESLHA 4 HWA GeoSeiences Inc.