HomeMy WebLinkAboutMcCarthy Revision Letter 191231
December 31, 2019
State Department of Ecology
Northwest Regional Office
3190 160th Ave SE
Bellevue, WA 98008
Subject: Shoreline Exemption - LUA18-000653
McCarthy Landscape Project
Dear Sir or Madam:
We are writing to inform the Department of Ecology that a revision to the subject shoreline exemption
has been submitted to the City and approved as a non-substantive change. The applicant, Jason
Laskelle of May Creek Landscaping, submitted a request for a revision to the Shoreline Exemption sent
to DOE on October 23rd 2018.
Revision Summary: The approved Shoreline Exemption (LUA18-000653) for landscaping that would
occur within Reach D of the Lake Washington Shoreline Jurisdiction, mapped with a Shoreline
Residential designation has been proposed to be amended. Originally, the project involved landscaping
a hillside with slope stabilizing plants. During the course of work it was determined by Zipper Geo,
geotechnical consultants, that the slope was in danger of failure and needed to be stabilized with
retaining walls. The applicant is still eligible for a shoreline exemption due to the emergency nature of
the stabilization activities as described in a geotechnical report by Zipper Geo, dated September 6th
2019 (Exhibit 2). Due to this, the scope of the project expanded to include a two-tier pin pile retaining
wall system. The proposed retaining walls would impede current erosion hazards along Lake
Washington Blvd and result in permanently stabilizing the slope. The applicant has proposed an
updated landscaping plan (Exhibit 3) with plants that will act as a screen for the retaining walls while
mitigating erosion and encouraging soil stability. These plants include Euonymus japonicus ‘Green
Spire’, Arbutus unedo ‘Compacta’, Rosa rugosa ‘Hansa’, Cornus sericea ‘Kelseyi’, Lonicera pileata, and
Frangaria chiloensis.
Analysis: Per WAC 173-27-100, changes are substantive if they materially alter the project in a
manner that relates to its conformance to the terms and conditions of the permit, the master
program and/or the policies and provisions of chapter 90.58 RCW. The proposed revisions
above are in conformance with the terms and conditions of the permit, the master program
and policies, therefore the City has determined a permit Revision is not required for the above
changes.
Please contact me at (425) 430-7246 or bgillia@rentonwa.gov if you have any questions or need
additional information.
Respectfully,
Brittany Gillia
Assistant Planner
Enclosure: Site Plan
Zipper Geo, geotechnical reports
Planting Plan
FIGUREJob No.Zipper Geo Associates, LLC19019 36th Ave. W.,Suite ELynnwood, WASHT. of11NEIGHBORHOOD DETAIL MAP2041.01DATE: AUGUST 20191MCCARTHY RESIDENCE SLOPE STABILIZATION3403 BURNETT AVENUE NORTHRENTON, WASCALE IN FEET010010050PROJECT SITEN 34TH ST.N 35TH ST.BURNETT AVE. N
LAKE WA BLVD. N
DESIGNED:SCALE:CHECKED:DRAWN:DATE:SHEETJOB NO.OFBYDESCRIPTIONDATENO.PLOT DATE:DRAWING19019 36th Avenue West, Suite E |Lynnwood, WA 98036PH: (425) 582-9928 | Fax: (425) 582-9930 | www.zippergeo.comSUBMITTAL RECORD8/26/19LAST EDIT:RobZ:\Projects\2001 - 2050\2041 McCarthy Residence\2041.01 McCarthy Residence\Working File\Drafting\2041.01 Plans REV 3.dwgRAR4/25/19-INITIAL RELEASE6MCCARTHY RESIDENCE SLOPE STABILIZATION3403 BURNETT AVENUE NORTHRENTON, WASHINGTON8/8/192041.01TAJRARRARRAR7/25/19-REDESIGN W/PIN PILE WALLS - INITIAL RELEASE8/26/19RAR8/8/191REVISED PER CITY REVIEW COMMENTSRAR8/26/192REVISION TO ADDRESS PLANNING COMMENTSAS SHOWNCONTACT INFORMATION:CLIENT:MARY MCCARTHY3403 BURNETT AVENUE NORTHRENTON, WA 98327(253) 720-0126LANDSCAPE ARCHITECT:FRANCINE M DAY LANDSCAPE ARCHITECTURE700 NW 42ND STREET, #409SEATTLE, WA 98107(206) 930-7493GEOTECHNICAL ENGINEER:ZIPPER GEO ASSOCIATES, LLC19019 36TH AVE. WEST, SUITE ELYNNWOOD, WA 98036(425) 582-9928CONTACT: Robert Ross, P.E.rross@zippergeo.comSHEET INDEXC1.0 - SITE AND TESC PLANC2.0 - TESC NOTES AND DETAILSC3.0 - GRADING AND DRAINAGE PLANC3.1 - DETAILSC3.2 - DETAILSC3.3 - DETAILSAPPROXIAMTE SCALE IN FEET051010BASEMAP FROM TOPOGRAPHIC SURVEY BY TYEE SURVEYORS DATED 6/14/18 AND MODIFIED BY ZGAINSTALL CATCHBASIN FILTERHATCHED AREA INDICATESAPPROXIMATE LIMITS OF SLOPESTABILIZATION WORK3403 BURNETT AVENUENORTHPROPOSED RETAINING WALLSEXISTING ROCKERY
TEMPORARY EROSION AND SEDIMENT CONTROL GENERAL NOTESPART 1 - GENERAL1.THE SUCCESS OF THIS PROJECT IS HIGHLY DEPENDANT ONCONTROL OF SURFACE WATER RUNOFF INTO THE WORKAREA TO PREVENT EROSION AND FURTHER DESTABILIZATIONOF THE SLOPE.2.COMPLETION OF THIS PROJECT WILL REQUIRE TEMPORARILYREMOVING VEGETATION FROM A STEEP SLOPE. THEEXPOSED SURFACE MUST BE PROTECTED FROM EXPOSURETO DIRECT RAINFALL AND SURFACE WATER RUNOFF TO THEEXTENT POSSIBLE DURING CONSTRUCTION. IF WETWEATHER IS EXPECTED (DEFINED AS FORECAST RAINFALLGREATER THAN 0.25 INCHES IN A 12 HOUR PERIOD), AT THEEND OF EACH WORK DAY, THE SLOPE SHALL BE COVEREDWITH ANCHORED PLASTIC SHEETING. AREAS OF THE SITETHAT WILL BE UN-WORKED FOR MORE THAN TWO DAYSSHOULD BE COVERED WITH ANCHORED PLASTIC SHEETING.DEPENDING ON THE CONSTRUCTION PROGRESS, THERE MAYBE A NEED TO TEMPORARILY DELAY WORK AT THE SITE IFHEAVY RAINFALL IS FORECAST. TEMPORARY WORK DELAYSDURING CONSTRUCTION WILL BE EVALUATED ON ACASE-BY-CASE BASIS THROUGH OBSERVATION OF SITECONDITIONS BY ZIPPER GEO ASSOCIATES IN COORDINATIONWITH THE CONTRACTOR.3.CONSTRUCTION EROSION CONTROL MEASURES MUST BE INPLACE AND APPROVED BY THE ENGINEER AND CITY PRIOR TOANY EARTH DISTURBANCE.4.THE IMPLEMENTATION OF THE TEMPORARY EROSION ANDSEDIMENT CONTROL (TESC) PLANS AND THE CONSTRUCTION,MAINTENANCE, REPLACEMENT AND UPGRADING OF THE TESCFACILITIES IS THE RESPONSIBILITY OF THE CONTRACTORUNTIL ALL CONSTRUCTION IS APPROVED AND SITE ISPERMANENTLY STABILIZED.5.THE CONTRACTOR SHALL PROVIDE AND MAINTAINTEMPORARY SEDIMENTATION COLLECTION FACILITIES TOENSURE THAT SEDIMENT-LADEN WATER DOES NOT ENTERTHE PUBLIC DRAINAGE SYSTEM. AS CONSTRUCTIONPROGRESSES AND UNEXPECTED (SEASONAL) CONDITIONSDICTATE, MORE TEMPORARY SEDIMENTATION COLLECTIONFACILITIES MAY BE REQUIRED TO PREVENT VIOLATINGAPPLICABLE WATER STANDARDS. THEREFORE, DURING THECOURSE OF CONSTRUCTION IT SHALL BE THE OBLIGATIONAND RESPONSIBILITY OF THE CONTRACTOR TO ADDRESS ANYNEW CONDITIONS THAT MAY BE CREATED BY THEIRACTIVITIES AND TO PROVIDE ADDITIONAL FACILITIES THATMAY BE NEEDED TO PROTECT ADJACENT PROPERTIES.6.THE TESC FACILITIES SHOWN ON THESE PLANS MUST BECONSTRUCTED IN CONJUNCTION WITH ALL CLEARING ANDGRADING ACTIVITIES, AND IN SUCH A MANNER AS TO ENSURETHAT SEDIMENT-LADEN WATER DOES NOT LEAVE THE SITE,ENTER THE DRAINAGE SYSTEM, OR VIOLATE APPLICABLEWATER STANDARDS.7.NO SEDIMENT SHALL BE TRACKED INTO THE STREET ORPAVED SURFACES. SEDIMENT SHALL BE REMOVED FROMTRUCKS AND EQUIPMENT PRIOR TO LEAVING THE SITE. IN THEEVENT OF FAILURE OF THE EROSION CONTROL SYSTEMRESULTING IN SEDIMENT BEING TRACKED ONTO PAVEDSURFACES, THE CONTRACTOR SHALL IMMEDIATELYIMPLEMENT MEASURES TO CORRECT THE SITUATION, ANDVACUUM STREET SWEEPING SHALL BE EMPLOYED ON ANEMERGENCY BASIS. IF VACUUM STREET SWEEPING VEHICLESARE UTILIZED, THEY SHALL BE OF THE TYPE THAT REMOVESTHE SEDIMENT FROM THE PAVEMENT. WASHING OF THESTREETS WILL NOT BE ALLOWED WITHOUT PRIOR CITY OFRENTON APPROVAL.8. AREAS NOT WORKED FOR MORE THAN 2 DAYS SHALL BECOVERED WITH ANCHORED PLASTIC SHEETING.PART 1 - GENERAL CONT.9.NO SEDIMENT SHALL BE ALLOWED TO ENTER ANY CATCHBASIN WITHIN THE SITE, OR ADJACENT PROPERTIES. IN THEEVENT OF A FAILURE OF THE TESC PLAN THAT RESULTS INSEDIMENT ENTERING A CATCH BASIN, THE CONTRACTORSHALL REMOVE ALL SUCH SEDIMENT IMMEDIATELY.10.DISTURBED SOILS THAT ARE EXPOSED TO SURFACE RUNOFFSHALL BE IMMEDIATELY STABILIZED WITH TESC MEASURESAND APPROVED BY THE ENGINEER AND CITY.11.THE TESC FACILITIES SHALL BE INSPECTED DAILY BY THECONTRACTOR AND MAINTAINED AS NECESSARY TO ENSURETHEIR CONTINUED FUNCTIONING.12.CATCH BASINS IN THE STREET SHALL BE INSPECTED BY THECONTRACTOR DAILY. WATER LEAVING THE SITE DURINGCONSTRUCTION, INCLUDING WATER CARRIED BY TRUCKS,SHALL BE CLEAN. THE CONTRACTOR SHALL CLEAN CITYCATCH BASINS AND IMPLEMENT EXTRA SEDIMENTATIONCONTROL MEASURES IF NECESSARY AND AS DIRECTED BYTHE CITY OF RENTON INSPECTOR/DOE INSPECTOR AT NOADDITIONAL EXPENSE TO OWNER.13.THE TESC FACILITIES SHALL BE MAINTAINED UNTILPERMANENT EROSION CONTROL (REVEGETATION WITHTREES, SHRUBS, GROUND COVER, ETC.) PER THEAPPOROVED PLANS IS IN PLACE.14.WHERE SEEDING FOR TEMPORARY EROSION CONTROL ISUSED, FAST GERMINATING GRASSES SHALL BE APPLIED ATAN APPROPRIATE RATE.15.WHERE STRAW MULCH FOR TEMPORARY EROSION CONTROLIS USED, IT SHALL BE APPLIED AT A MINIMUM THICKNESS OFTWO INCHES.16.THE CONTRACTOR IS SOLELY RESPONSIBLE FOR ALL MEANSAND METHODS AND SEQUENCING OF TESC MEASURES ANDENSURING WATER QUALITY REQUIREMENTS ARE MET.PART 2 - TEMPORARY EXCAVATION STABILITY1.A TEMPORARY EXCAVATION WILL BE REQUIRED TO REMOVELOOSE SOIL FROM AN AREA IN THE SOUTHERN PORTION OFTHE SLOPE. TEMPORARY EXCAVATION SLOPE STABILITY IS AFUNCTION OF MANY FACTORS, INCLUDING: GROUNDWATERSEEPAGE, THE TYPE AND DENSITY OF THE VARIOUS SOILSTRATA, THE DEPTH OF CUT; SURCHARGE LOADINGSADJACENT TO THE EXCAVATION, AND THE LENGTH OF TIMETHE EXCAVATION REMAINS OPEN.2.AS THE CONTRACTOR IS CONTINUOUSLY PRESENT AT THESITE AND ABLE TO CONTINUOUSLY OBSERVE SITECONDITIONS, THE CONTRACTOR SHOULD BE RESPONSIBLEFOR MAINTENANCE OF SAFE SLOPES AND WORKER SAFETY.WE RECOMMEND THE CONTRACTOR CONTINUOUSLYOBSERVE TEMPORARY EXCAVATIONS FOR INDICATIONS OFINSTABILITY SUCH AS SOIL SLUMPS, GROUNDWATERSEEPAGE AT THE SURFACE OF THE SLOPE, AND CRACKS ORDOWN SETTING OF THE GROUND SURFACE AT THE TOP OFTHE SLOPE OR ALONG ANY PORTION OF THE SLOPE. IF SIGNSOF INSTABILITY ARE OBSERVED, THE CONTRACTOR SHALLSTOP WORK AND CONTACT ZIPPER GEO ASSOCIATESIMMEDIATELY FOR FURTHER OBSERVATION ANDRECOMMENDATIONS.3.ZIPPER GEO ASSOCIATES (ZGA) SHALL PROVIDE PERIODICOBSERVATION OF GRADING AND RESTORATION AS ITPROCEEDS. ZGA SHALL OBSERVE THE SITE AND TEMPORARYEXCAVATIONS IMMEDIATELY AFTER A RAINFALL EVENTTOTALING 0.5 INCHES OR MORE IN A 24 HOUR PERIOD.TEMPORARY PLASTIC COVERINGCATCH BASIN INSERTDESIGNED:SCALE:CHECKED:DRAWN:DATE:SHEETJOB NO.OFBYDESCRIPTIONDATENO.PLOT DATE:DRAWING19019 36th Avenue West, Suite E |Lynnwood, WA 98036PH: (425) 582-9928 | Fax: (425) 582-9930 | www.zippergeo.comSUBMITTAL RECORD8/26/19LAST EDIT:RobZ:\Projects\2001 - 2050\2041 McCarthy Residence\2041.01 McCarthy Residence\Working File\Drafting\2041.01 Plans REV 3.dwgRAR4/25/19-INITIAL RELEASE6MCCARTHY RESIDENCE SLOPE STABILIZATION3403 BURNETT AVENUE NORTHRENTON, WASHINGTON8/8/192041.01TAJRARRARRAR7/25/19-REDESIGN W/PIN PILE WALLS - INITIAL RELEASE8/26/19RAR8/8/191REVISED PER CITY REVIEW COMMENTSRAR8/26/192REVISION TO ADDRESS PLANNING COMMENTSNOT TO SCALE
19019 36th Avenue West, Suite E Lynnwood, Washington 98036 (425) 582-9928
Zipper Geo Associates, LLC
Geotechnical and Environmental Consulting
Project No. 2041.01
August 26, 2019
Mary McCarthy
3403 Burnett Avenue North
Renton, WA 98105
Subject: Land Use Code Modification Request
McCarthy Slope Stabilization
3403 Burnett Avenue North
Renton, WA
Dear Ms. McCarthy:
Zipper Geo Associates, LLC prepared retaining wall construction plans and stability calculations for the
proposed slope stabilization project located on your property dated August 8th , 2019. The City of
Renton Land Use department reviewed those plans and indicated that modifications to the plans are
required in order to meet Section 4-4-040.2.e.i and 4-4-040.2.f of the Renton Municipal Code (the
Code). It is not feasible to meet those requirements and the purpose of this letter is to provide required
information in support of a Land Use Code Modification Request as required and described in the
Renton Planning Division’s Submittal Requirements, Modification document. The requested
information or reference to it is provided below.
1. Pre-Application Meeting Summary: A formal pre-application meeting was not held. However,
email correspondence with Ms. Vanessa Dolbee was completed and through that
correspondence, Ms. Dolbee has indicated that it appears the modification can be approved.
2. Wavier Form: No waiver form was provided.
3. Land Use Permit Master Application Form: A land use permit master application form was
previously submitted and is also attached to this letter.
4. Fees: Fees have not been submitted, however Ms. Dolbee has indicated the fee will be
determined after the Modification submittal information has been received.
5. Project Narrative: The project will consist of constructing a two-tiered retaining wall and
associated landscaping on a slope located along the west side of the subject property. The
slope is currently experiencing erosion and shallow landslide instability. The purpose of the
retaining walls and landscaping is to permanently stabilize the slope. Detailed information
regarding the geometry of the proposed retaining walls and landscaping can be found on the
attached plans.
6. Justification for the Modification Request to Section 4-4-040.2.e.i: Section 4-4-040.2.e.i of
the Code requires that “The width of a terrace shall be equal to the height of the tallest abutting
retaining wall; however, the minimum terrace width shall be two feet (2').” The tallest abutting
retaining wall under the current proposal is 4 feet. As such, this section of the Code would
require a minimum terrace width of 4 feet. Under the current proposal, a terrace width of only
Zipper Geo Associates, LLC
McCarthy Slope Stabilization
Project No. 2041.01
August 26, 2019
19023 36th Avenue West, Suite D Lynnwood, Washington 98036 (425) 582-9928
Page 2
3 diverging to 4 feet can be provided for approximately the south half of the upper proposed
retaining wall (Wall 2). The only feasible retaining wall system that can work at this site due to
access constraints is one installed with hand-carried equipment as currently proposed. The
proposed wall system is at it’s structural limit. Moving Wall 2 down-slope to provide the 4 foot
terrace width for the entire wall length would result in inadequate structural capacity for the
lower wall (Wall 1) as the upper wall would begin to impose passive lateral earth pressures on
the lower wall therefor requiring a wall with larger structural elements that cannot be installed
with hand-carried equipment. Adding capacity to the lower wall through installation of
additional piles is not feasible as the piles are spaced as close as reasonably feasible such that
they do not interact therefore reducing capacity. Using machined equipment to install larger
structural elements is not feasible as the existing home blocks access to the area from the top
and such equipment would have inadequate reach from the bottom.
Justification for the Modification Request to Section 4-4-040.2.f: Section 4-4-040.2.f of the
Code requires that “For land area that is not between two (2) retaining walls (i.e., not a terrace),
the lower soil grade (i.e., ground at the bottom of a retaining wall’s exposed surface) and the
upper soil grade (i.e., ground at the top a retaining wall) abutting a retaining wall shall be level
for a horizontal distance (measured perpendicularly to the wall) equaling one foot (1') for every
one foot (1') in height of the retaining wall.” This section would require a level grade at the
bottom of the lower wall (Wall 1) extending 4 feet from the wall face. A gently sloping grade
extending only 3 feet from the wall face can be provided under the current proposal. Providing
a level grade distance of 4 feet would require the height of Wall 1 to be increased or the tier
width between Walls 1 and 2 to be decreased. For similar reasons under the justification for
Section 4-4-040.2.e.i, a 4 feet level grade distance cannot be provided. The current proposal is
at it’s structural limit.
Modification Compliance: We interpret that the primary intent of the land use requirements
under the sections in which modifications are requested is one of aesthetics. It is our opinion
the proposed modification substantially meets the land use element by providing 3 of the 4
feet required and is the minimum adjustment needed to allow for the proposed retaining wall
system. Providing 3 of the 4 feet will still allow for landscaping and an aesthetically pleasing
finished product. The proposed modification allows for safety and environmental protection
by stabilizing an otherwise relatively unstable slope. The proposed modification will not be
injurious to other properties in the vicinity as it still provides a majority of the requirements.
The modification is justified and required based on reasons cited above. The modification will
not create adverse impacts to other properties as it provides a majority of the requirements.
7. Neighborhood Detail Map: See attached.
8. Site Plan: See attached plans.
9. Architectural Elevations: See attached plans.
Zipper Geo Associates, LLC
McCarthy Slope Stabilization
Project No. 2041.01
August 26, 2019
19023 36th Avenue West, Suite D Lynnwood, Washington 98036 (425) 582-9928
Page 3
Respectfully submitted,
Zipper Geo Associates, LLC
Robert A. Ross, P.E.
Principal
8/26/19
19019 36th Avenue West, Suite E Lynnwood, Washington 98036 (425) 582-9928
Zipper Geo Associates, LLC
Geotechnical and Environmental Consulting
Project No. 2041.01
September 6, 2019
Mary McCarthy
3403 Burnett Avenue North
Renton, WA 98105
Subject: Land Use Emergency Exemption
McCarthy Slope Stabilization
3403 Burnett Avenue North
Renton, WA
Dear Ms. McCarthy:
Zipper Geo Associates, LLC prepared retaining wall construction plans and stability calculations for the
proposed slope stabilization project located on your property dated August 8th , 2019. The City of
Renton Land Use department was apparently unaware of the emergency nature of this project. After
correspondence with Ms. Vanessa Dolbee, City of Renton Planning Manager regarding the emergency
nature of this project, Ms. Dolbee has requested additional information in order to grant the project a
temporary emergency exemption from certain land use code requirements. The purpose of this letter
is to provide the requested information such that the city will grant an exemption and the work can be
completed prior to the beginning of the upcoming rainy season.
In our opinion, the area in which the work is proposed is currently unstable and presents an
unacceptable level of risk to the safety of the public who use the street below the slope and an
unacceptable risk of damage to the McCarthy property. Evidence of this risk is clearly observable on
the slope, primarily characterized by cracks on the surface of the slope indicating failure. We highly
recommend the work outlined in our August 8th, 2019 plans be implemented as soon as possible and
absolutely prior to the onset of the coming rainy season.
In accordance with Section 4-3-050, C of the Renton Municipal Code (the Code), work of an emergency
nature is permitted within critical areas and their associated buffers provided that the criteria outline
in Section 4-3-050, C, footnote 27 is met. Our comments regarding the footnote 27 criteria are
provided below.
• 27 A: As discussed above, It is our opinion an unacceptable threat to life or sever loss of
property will occur if an emergency permit is not granted. The slope is unstable as discussed
above.
• 27 B: It is our opinion the anticipate threat may occur before permit can be issued or modified
under the procedures otherwise required by this Section and other applicable laws. If the slope
is left in its current condition and exposed to rainfall or rising groundwater levels as a result of
rainfall, further failure may occur depositing landslide debris in the roadway below and further
Zipper Geo Associates, LLC
McCarthy Slope Stabilization
Project No. 2041.01
September 6, 2019
19023 36th Avenue West, Suite D Lynnwood, Washington 98036 (425) 582-9928
Page 2
destabilization of the land beyond the top of the slope. It is our understanding that under the
procedures otherwise required by this section of the Code and other sections, a permit would
not likely be granted until after the upcoming rainy season begins.
• 27 C: The standards and criteria for nonemergency activities have been incorporated into the
proposed measures. Specifically, the proposed structural solution meets typical safety factor
requirements and the area will be replanted.
With regard to time requirements, the work can be completed within 90 days. However, footnote 27
requires the area be restored to original condition. This is not feasible. The proposed work cannot be
removed as the area would then become unstable. This work is required to permanently stabilize the
slope and is the only feasible alternative we have been able to develop considering other code
requirements and site access constraints as previously discussed.
With regards to Shoreline Regulations, emergency construction is allowed under similar circumstances
as critical areas. The above information provides a basis for emergency construction as related to
Shoreline Regulations. As required by Shoreline, Critical Areas, and other code regulations, we will
continue to pursue any permits which would have been required for the work absent the above-
described emergency situation.
Respectfully submitted,
Zipper Geo Associates, LLC
Robert A. Ross, P.E.
Principal
Copies:
Vanessa Dolbee (City of Renton) – 1 electronic copy, Scott Warlick (City of Renton) – 1 electronic copy,
Jennifer Henning (City of Renton) – 1 electronic copy, Brianne Bannwarth (City of Renton) – 1 electronic
copy, Brittany Gillia (City of Renton) – 1 electronic copy, Jason Laskelle (May Creek Landscaping) – 1
electronic copy
9/6/19
19019 36th Avenue West, Suite E Lynnwood, Washington 98036 (425) 582-9928
Zipper Geo Associates, LLC
Geotechnical and Environmental Consulting
Project No. 2041.01
October 18, 2019
Mary McCarthy
3403 Burnett Avenue North
Renton, WA 98105
Subject: Short and Long Term Impacts
McCarthy Slope Stabilization
3403 Burnett Avenue North
Renton, WA
Dear Ms. McCarthy:
Zipper Geo Associates, LLC prepared retaining wall construction plans and stability calculations for the
proposed slope stabilization project located on your property dated August 8th , 2019. The City of
Renton granted an emergency exemption to begin the work prior to obtaining all of the necessary
permits due to the emergency nature of the project. As a condition to granting the exemption, the
City will not finalize the permit until a Shoreline Permit, Critical Areas Permit, and a Wall Modification
have been approved. In order to further process the required additional permits/approvals, the City
has requested a narrative describing the short and long term impacts the project may have on adjacent
properties. The purpose of this letter is to provide that narrative.
Short Term Impacts
The project involves earth work on a steep slope with areas of relatively unstable soils. The work will
expose soils highly susceptible to erosion. Additionally, the work could result in shallow landslides in
the unstable soils. The potential impacts of erosion are deposition and transport of sediment off-site.
The potential impacts of landslides include safety concerns for the traveling public along Lake
Washington Boulevard below and potentially destabilizing areas along the sides and tops of the slope.
The project plans were developed to mitigate the potential short term impacts through the use of
temporary erosion and sediment control measures and observation of construction by a geotechnical
engineer from Zipper Geo Associates. The work is currently proceeding and the mitigation measures
outlined in the plans are proving successful at mitigating the potential short term impacts.
Long Term Impacts
The long term impacts of the project are, in our opinion, beneficial to neighboring properties.
Specifically, prior to construction, the slope was over-steepened, covered with invasive plant species,
and contained areas of unstable soils. The project will stabilize an otherwise unstable slope, which if
failed, would have negative impacts on adjacent properties. The project will remove invasive species
and replace them with non-invasive species therefore increasing the potential for biodiversity in the
area. As such, we do not foresee negative long term impacts associated with the work.
Zipper Geo Associates, LLC
McCarthy Slope Stabilization
Project No. 2041.01
October 18, 2019
19023 36th Avenue West, Suite D Lynnwood, Washington 98036 (425) 582-9928
Page 2
We trust this information meets the City’s current request. If we can be of further assistance, please
contact us.
Respectfully submitted,
Zipper Geo Associates, LLC
Robert A. Ross, P.E.
Principal
Copies:
Vanessa Dolbee (City of Renton) – 1 electronic copy, Jason Laskelle (May Creek Landscaping) – 1
electronic copy
10/18/19