HomeMy WebLinkAboutRS_TIR_Sierra_Homes_SP_230306_v2.pdf
Western Washington Division Eastern Washington Division
165 NE Juniper St., Ste 201, Issaquah, WA 98027 407 Swiftwater Blvd, Cle Elum, WA 98922
Phone: (425) 392-0250 Fax: (425) 391-3055 Phone: (509) 674-7433 Fax: (509) 674-7419
www.EncompassES.net
PRELIMINARY TECHNICAL INFORMATION REPORT
For
Sierra Homes Short Plat
702 Nile Avenue NE
Renton, WA 98059
November 2, 2022
Revised March 1, 2023
Prepared by:
Ian Dahl
Encompass Engineering Job No. 21706
Prepared For:
Dan Finkbeiner
Sierra Homes
PO Box 3069
Issaquah, WA 98027
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Table of Contents
I. PROJECT OVERVIEW ................................................................................................................ 1
II. CONDITIONS AND REQUIREMENTS SUMMARY ...................................................................... 6
III. OFFSITE ANALYSIS .................................................................................................................. 10
IV. FLOW CONTROL, LOW IMPACT DEVELOPMENT AND WATER QUALITY FACILITY ANALYSIS
AND DESIGN ........................................................................................................................... 17
V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN ..................................................................... 20
VI. SPECIAL REPORTS AND STUDIES ............................................................................................ 20
VII. OTHER PERMITS ..................................................................................................................... 20
VIII. CSWPP ANALYSIS AND DESIGN .............................................................................................. 20
IX. BOND QUANTITIES, FACILITY SUMMARIES AND DECLARATION of COVENANT ................... 20
X. OPERATION AND MAINTENANCE MANUAL .......................................................................... 20
List of Figures
Figure 1 – TIR Worksheet
Figure 2 – Vicinity Map
Figure 3 – Soils Map and Legend
Figure 4 – Existing Conditions Map
Figure 5 – Developed Conditions Map
Figure 6 – Drainage Review Flow Chart
Figure 7 – Downstream Map
Appendix A
Geotechnical Evaluation by Cobalt Geosciences dated October 4, 2021
Appendix B
Wetland Reconnaissance for 702 Nile Ave, Renton WA by Altmann Oliver Associates, LLC dates
December 10, 2021
Appendix C
Arborist Report by Layton Tree Consulting, LLC dated October 26, 2022
Tree & Construction Memo by Layton Tree Consulting, LLC dated February 21, 2023
Appendix D
WWHM Output
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I. PROJECT OVERVIEW
Project: 702 Nile Avenue Short Plat
Site Address: 702 Nile Avenue NE, Renton, WA 98059 (See Vicinity Map)
Tax Parcel #: 112305-9002
Zoning District: R-4 (Single Family Residential)
Site Area: 31,998 SF (0.73 AC)
Site Location: The site is in the City of Renton within the SW quarter of Section 11,
Township 23 North, Range 5 East, W.M, King County, Washington. The
site is located on the south side of NE 7th Place, and on the east side of
Nile Ave NE.
Figure 2: Vicinity Map
Pre-developed Site Conditions:
The project site is located in the City of Renton on a 31,998 SF (0.73 AC) lot that is zoned R-4 (single-family
residential). The site is accessed from Nile Avenue NE, south of the intersection of Nile Avenue NE and NE
7th Place. The site is bordered to the west by Nile Avenue NE, to the north by NE 7th Place, and to the east
and south by single family residences. Additionally, there is a Category III Wetland bordering the
southeastern corner of the site.
The site is currently developed with a single-family residence accessed from Nile Avenue NE via a gravel
driveway on the western side of the site. The property is located within the Lower Cedar River and May
Creek drainage basin, within the Cedar River/Lake Washington watershed. Runoff exits the site from two
separate natural discharge areas (NDA’s: A & B). NDA A is on the western portion of the site, where runoff
sheet flows towards Nile Ave NE and enters the City of Renton storm system. NDA B is located in the
southeastern portion of the site where runoff sheet flows offsite towards an adjacent wetland.
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Stormwater is ultimately discharged to Lake Washington, located approximately 3 miles west of the site.
See full downstream analysis in Section III of this Technical Information Report (TIR).
An Existing Conditions Map is included as Figure 4 at the end of this Section.
Critical Areas:
Per the Wetland Reconnaissance report by Altmann Oliver Associates, included as Appendix B, a Category
III Wetland borders the southeastern corner of the site, but its enhanced buffer does not encroach on the
property. No other critical areas have been identified on or adjacent to the site.
Soils:
Per the US Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS) Web Soil
Survey (WSS) information, the entire project site is underlain with Alderwood gravelly sandy loam, 8 to 15
percent slopes (See Figure 3 below). A Geotechnical Evaluation prepared by Cobalt Geosciences
(Appendix A) confirms this soil classification across the site, with the discovery of weathered and
unweathered glacial till. According to the Geotechnical Evaluation, full infiltration of stormwater is
infeasible, however limited infiltration is feasible with the soil classification of “Loamy Sand.”
Figure 3: Soil Map and Legend
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Developed Site Conditions
The project proposes the development of three (3) single-family lots within the 31,998 SF (0.73 AC) parcel.
Lot 1 is 9,214 SF and is proposed along the eastern portion of the site, Lot 2 is 9,417 SF and is proposed in
the central portion of the site, and Lot 3 is 9,733 SF and is proposed along the western portion of the site.
A 3,634 SF stormwater tract is proposed in the southwest corner of the site. All three lots will have
driveway access off NE 7th Place.
The parcel is zoned R-4, which allows for a maximum building coverage of 35% and a maximum impervious
surface coverage of 50%. For the preliminary design of the lots, a maximum building coverage was
assumed, with the coverage on Lot 1 limited by setback requirements. The rooftop areas used for
stormwater calculations are 3,225 SF for Lot 1, 3,296 SF for Lot 2, and 2,788 SF for Lot 3. Additionally,
1,611 SF of on-site driveway, 820 SF of off-site driveway, and 215 SF of walkway are proposed, bringing
the total proposed new/replaced impervious for the site to 12,574 SF.
Stormwater runoff from Lots 1-3 will be collected and conveyed to an 88’x16’ CMP Detention Tank,
located within a stormwater tract in the southwest corner of the site. Please refer to Section IV of this TIR
for additional discussion. To maintain the existing downstream drainage patterns to the off-site wetland,
and equivalent area of lawn in the developed condition will be graded towards the southeast corner of
the site. Please refer to Core Requirement # 9 in Section II and Section IV of this TIR for additional
discussion on stormwater BMPs. A Developed Conditions Map is provided as Figure 5 at this end of this
Section.
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II. CONDITIONS AND REQUIREMENTS SUMMARY
The 2022 City of Renton Surface Water Design Manual (RSWDM) was utilized to determine and address
all core and special requirements. Based on the criteria specified in Figure 1.1.2.A of the RSWDM, the
project falls under Full Drainage Review. Per Section 1.1.2.4 of the RSWDM, the project must meet all nine
(9) core and all six (6) special requirements. See Figure 6 below for more information on how the type of
drainage review was determined.
Figure 6: Drainage Review Flow Chart
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Core Requirements
Core Requirement #1: Discharge at the Natural Location
The proposed development runoff will follow existing drainage patterns that flow towards the
City of Renton storm system on Nile Avenue NE and NE 7th Place as well as southeast towards the
adjacent offsite wetland. In order to avoid downstream impact to the wetland, the existing site
was evaluated to quantify the amount of runoff tributary to the wetland. Based on the
topographic survey, 7,096 SF of lawn areas were found to drain to the wetland in the southeastern
portion of the site. In the post-developed condition, an equivalent amount of lawn area will be
graded towards the wetland to retain the same downstream drainage conditions. See Figure 4-
Existing Conditions Map as well as the Level 1 Downstream Analysis in Section III of this TIR for a
complete description of the existing drainage paths.
Core Requirement #2: Downstream Analysis
A Level 1 Downstream analysis has been completed for the site and no existing or potential
problems have been identified. This analysis is included in Section III of this TIR.
Core Requirement #3: Flow Control Facilities
Based on the City of Renton’s flow control application map, the project site is located within the
Duration Flow Control Standard (Forested Conditions). Flow control facilities are required to
match the developed peak discharge rates to historical (forested) site conditions over the range
of flows extending form 50% of the 2-year up to the full 50-year flow and match the peaks for the
2- and 10-year return periods.
An 88’x16’ CMP Detention Tank, with a 78” diameter is proposed to meet stormwater
requirements. This stormwater facility will be located in the southwest corner of the site within a
stormwater tract. Please refer to Section IV of this TIR for additional discussion.
Core Requirement #4: Conveyance System
Conveyance in compliance with the requirements detailed in Section 1.2.4.1 of the City of Renton
2022 SWDM will be provided with final engineering.
Core Requirement #5: Construction Stormwater Pollution Prevention
The limits of construction for the project are less than 1 acre. A temporary erosion and sediment
control (TESC) plan providing details on best management practices (BMPs) to be implemented
during construction is included in the engineering plan set. A Construction Stormwater Pollution
Prevention Plan (CSWPPP) will be provided with final engineering. Please refer to Section VIII of
this TIR for additional discussion.
Core Requirement #6: Maintenance and Operations
An Operation and Maintenance Manual will be provided with final engineering.
Core Requirement #7: Financial Guarantees and Liability
The owner will arrange for any financial guarantees and liabilities required by the permit.
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Core Requirement #8: Water Quality Facilities
In accordance with Section 1.2.8.1.A of the RSWDM, Basic Water Quality Treatment is not
required for this project as new plus replaced pollution generating impervious surfaces (PGIS) do
not exceed 5,000 SF, meeting exemption 1. This preliminary design accounts for a total of
approximately 2,431 SF of driveway area, which is below the 5,000 SF threshold.
Core Requirement #9: Flow Control BMPs
This project is classified as a small subdivision; therefore, it is subject to the Small Subdivision
Project BMP Requirements detailed in Section 1.2.9.3.1 in the RSWDM. Although implementation
of individual lot BMPs is not required until building permit application, BMPs have been
considered for the future improvements on Lots 1-3 based on Section 1.2.9.2 and of the RSWDM.
See Section IV of this TIR for further discussion and flow control analysis.
Impervious Surface BMPs
Full Dispersion: Infeasible for Lots 1-3. An 100-foot native vegetated flowpath segment is not
available on these sites.
Full Infiltration: Infeasible for Lots 1-3. The Geotechnical Evaluation by Cobalt Geosciences dated
October 4, 2021 (Appendix A) states that the site is underlain by weathered and unweathered
glacial till that becomes denser with depth.
Limited Infiltration: The Geotechnical Evaluation by Cobalt Geosciences dated October 4, 2021
(Appendix A) states that limited infiltration is feasible with the classification of loamy sand, with
the stipulation that an overflow system is provided. For rainfall regions greater than SeaTac 1.0,
a 2-foot wide gravel trench must be 48.3 feet in length in loamy sand soils to mitigate 1,000 SF of
impervious surface.
To avoid downstream impacts to the wetland per Core Requirement #1, limited infiltration
trenches will be located on the northern portion of the site and overflow to the on-site storm
system. Three 10’x10’ gravel filled trenches have been designed to mitigate runoff from a total of
2,515 SF of rooftop area. A 48.3-foot by 2-foot trench has a surface area of 96.6 SF; therefore,
96.6 SF of gravel infiltration trench can infiltrate up to 1,000 SF of impervious area. A 10’x10’
trench has 100 SF of surface area and therefore can infiltrate up to (300/96.6)x 1,000=3,105.6 SF
of impervious area. This is larger than the 2,515 SF of tributary rooftop area.
Rain Gardens/Bioretention: Infeasible for Lots 1 and 2. BMP’s relying on full infiltration are not
feasible as described above.
Permeable Pavement: Infeasible for Lots 1 and 2. BMP’s relying on full infiltration are not feasible
as described above.
Basic Dispersion: Basic Dispersion is infeasible for Lots 1-3. Directing rooftop runoff towards the
backyard lawn areas will increase runoff towards the off-site wetland, which is prohibited per
Section 1.2.2.1.1 of the RSWDM.
For projects that will result in an impervious surface coverage on the buildable portion of the
site/lot greater than 65%, on-site BMPs must be applied to 20% of target impervious surfaces.
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12,574 SF of impervious area is anticipated to be constructed on-site. BMPs have been sized to
mitigate up to 2,515 SF. This accounts for 2,515/12,574= 20.0% of target impervious surfaces.
Therefore, this requirement has been met.
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Special Requirements
Special Requirement #1: Other Adopted Area-Specific Requirements
Critical Drainage Area – N/A
Master Drainage Plan – N/A
Basin Plan – N/A
Lake management Plan – N/A
Shared Facility Drainage Plan – N/A
Special Requirement #2: Flood Hazard Area Delineation
The limits of this project do not lie within a delineated FEMA 100-year floodplain.
Special Requirement #3: Flood Protection Facilities
This project does not rely on or propose to modify/construct a new flood protection facility.
Special Requirement #4: Source controls
The project is a single-family residential development; therefore, this requirement is not
applicable.
Special Requirement #5: Oil Control
This project is not considered high-use in need of oil control.
Special Requirement #6: Aquifer Protection Area
The site is not located within an Aquifer Protection Area per the Groundwater Protection Areas
Map in the RSWDM.
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III. DOWNSTREAM ANALYSIS
A Level 1 Downstream analysis has been conducted per the requirements in Section 1.2.2.1 of the
RSWDM. Please see Tasks 1 through 4 below for a summary of the results.
Task 1: Define and Map the Study Area
The area of analysis extends approximately a quarter-mile downstream from the natural discharge areas.
This site includes two NDA’s – one being on the western side of the side, and the other being near the
southeastern corner of the site. These two NDA’s converge in under a quarter-mile, therefore creating
one threshold discharge area. A Downstream Map is provided in Figure 7 below.
Figure 7: Downstream Map
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Task 2: Review All Available Information on the Study Area
Per King County resources, there have been no significant drainage complaints within a quarter-mile
downstream of the site.
Task 3: Field Inspect the Study Area
A field inspection was performed by Encompass Engineering & Surveying on March 16, 2022. Please refer
to Task 4 for a detailed description of the downstream drainage system and analysis.
Task 4: Describe the Drainage System
Runoff from the site is split into two Natural Discharge Areas (A & B), however these flowpaths converge
within a ¼ mile downstream of the site, creating one Threshold Discharge Area for the site. NDA A is
located on the western side of the site, where runoff sheet flows off the driveway towards Nile Ave NE
(A1). Before reaching Nile Ave, the runoff enters a private area drain that conveys the runoff to the catch
basin located on the intersection of NE 7th Place and Nile Ave NE (A2). Once entering the City of Renton
public stormwater system, the runoff starts being conveyed parallel with Nile Ave NE to the south. After
about 400 FT, the runoff passes by NE 7th Court and continues running to the south (A3). After another
400 FT, the public stormwater system intersects with NE 6th Street (A4/B5) which is also where NDA B
converges with NDA A.
NDA B is located in the southeastern portion of the site, and runoff generally sheet flows off-site to the
south in this area (B1). Once exiting the site, the runoff begins to converge into the wetland located just
southeast of the site (B2). The runoff travels through the wetland for approximately 500 FT to the south
before entering a catch basin at the southern edge of the wetland (B3). This catch basin conveys the runoff
into the City of Renton public stormwater system where it begins to travel southwest along Orcas Ave NE.
After 200 FT along Orcas Ave NE, the runoff enters a stormwater detention pond (B4). The outlet is on the
western side of the pond, where it then gets conveyed back into the City of Renton public stormwater
system and converges with NDA A on Nile Ave NE (A4/B5).
After NDA A and NDA B converge, the runoff continues running parallel with Nile Ave NE to the south for
around 300 FT before passing by the intersection of NE 5th Place and Nile Ave NE (A5/B6). Approximately
300 FT past NE 5th Place the downstream analysis was completed, just over ¼ mile downstream of the site
(A6/B7). Please refer to Figure 7 above, for the approximate location of identified drainage features.
Photographs from the site visit are included below.
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Element A1 – Runoff sheet flows towards the western edge of the site
Element A2 – Type 2 CB located just northwest of property corner
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Element A3 – Type 1 CB conveying stormwater south along Nile Ave NE
Element A4/B5 – Type 1 CBs at NE 6th St. & Nile Ave NE (convergence point)
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Element B1 – Runoff sheet flows southeast through lawn towards property edge
Element B2 – Runoff converges into the offsite wetland located just southeast of the site
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Element B3 – Runoff enters CB at southern end of wetland
Element B4 – Stormwater detention pond located southwest of the wetland
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Element A5/B6 – Stormwater passes by NE 5th Place/continues flowing south on Nile Ave NE
Element A6/B7 – 12” concrete culvert along eastern side of Nile Ave NE (1/4 mile limit)
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IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN
Part A: Existing Site Hydrology
This property is located within the Lower Cedar River and May Creek drainage basin, within the Cedar
River/Lake Washington watershed. The 31,998 SF (0.73 AC) site is currently developed with a single-family
residence accessed from Nile Ave NE via a gravel driveway on the western side of the site. Stormwater
runoff from the site sheet flows off site from two different NDA’s (NDA A & B). NDA A is on the western
portion of the site, where runoff sheet flows towards Nile Ave NE and enters the City of Renton st orm
system. NDA B is located in the southeastern portion of the site where runoff sheet flows offsite towards
an adjacent wetland. Stormwater is ultimately discharged to Lake Washington, located approximately 3
miles west of the site. See full downstream analysis in Section III of this Technical Information Report (TIR).
The Geotechnical Evaluation prepared by Cobalt Geosciences (Appendix A) confirms the NRCS Alderwood
gravelly sandy loam soil classification and has determined that the site is only feasible for limited
infiltration due to the presence of glacial till.
WWHM 2012 was used to model the existing condition using target surfaces per Section 1.2.3 of the 2022
RSWDM. 7,096 SF of lawn area tributary to the off-site wetland has been removed from the model, as an
equivalent size of lawn area in the proposed condition will be graded towards the wetland to avoid
downstream impacts.
Part B: Developed Site Hydrology
The project proposes the development of three (3) single-family lots within the 31,998 SF (0.73 AC) parcel.
Lot 1 is 9,214 SF and is proposed along the eastern portion of the site, Lot 2 is 9,417 SF and is proposed in
the central portion of the site, and Lot 3 is 9,733 SF and is proposed along the western portion of the site.
All three lots will have driveway access off NE 7th Place. Using the maximum lot coverage of 35%, or the
maximum coverage based on building setbacks, a rooftop area of 3,225 SF was used fo r Lot 1, 3,296 SF
for Lot 2, and 2,788 SF for Lot 3. An additional 1,611 SF of on-site driveway, 820 SF of off-site driveway,
and 215 SF of walkway are proposed, bringing the total proposed new/replaced impervious for the site to
12,574 SF.
Limited infiltration via three 10’x10’ gravel filled trenchs is proposed for a total of 2,515 SF of rooftop area.
The remainder of impervious surfaces will be conveyed to an 88’x16’ CMP Detention Tank, with a 78”
diameter. This stormwater facility will be located in the southwest corner of the site within a stormwater
tract, and discharge to a proposed manhole located on Nile Ave NE.
WWHM 2012 was used to model the proposed condition using target surfaces per Section 1.2.3 of the
2022 RSWDM, not including the 7,096 SF of lawn area tributary to the off-site wetland. No modeling credit
was given as the on-site BMPs will be privately maintained. A summary of the existing and developed
analyses is provided in the table below.
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Existing Conditions Areas
Measured Modeled
Condition Area (AC) Area (AC)
Lawn: 0.49
Forest: 0.58
Driveway 0.15
Roof 0.09
Total Area: 0.73 0.58
Existing Conditions Model
Developed Conditions Areas
Measured Modeled
Condition Area (AC) Area (AC)
Lawn: 0.43 0.28
Roof: 0.21 0.21
Walkway/Patio: 0.02 0.02
Driveway: 0.07 0.07
Total Area: 0.73 0.58
Developed Conditions Model
Part C: Performance Standards
Based on the City of Renton’s flow control application map, the project site is located within the Duration
Flow Control Standard (Forested Conditions). Flow control facilities are required to match the developed
peak discharge rates to historical (forested) site conditions over the range of flows extending form 50% of
the 2-year up to the full 50-year flow and match the peaks for the 2- and 10-year return periods. However,
the site meets flow control exemption 2 per Section 1.2.3.1.A of the RSWDM, and flow control facilities
are not required.
This project is classified as a small subdivision; therefore, it is subject to the Small Subdivision Project BMP
Requirements detailed in Section 1.2.9.3.1 in the RSWDM. Although implementation of individual lot
BMPs is not required until building permit application, BMPs have been considered for the future
improvements on Lots 1 and 2 based on Section 1.2.9.2 and of the RSWDM. The site falls within a Basic
Water Quality treatment area in accordance with Section 1.2.8.1.A of the RSWDM, however new plus
replaced impervious pollution generating areas within the project site is under 5,000 SF and therefore
water quality treatment is not required.
Part D: Flow Control System
Flow control will be provided by a Contech 88’x16’ CMP Detention Tank, with a 78” diameter. This
stormwater facility will be located in the southwest corner of the site within a stormwater tract, and
discharge via a control structure to a proposed manhole located on Nile Ave NE. Per WWHM modeling,
the required storage of the system is 0.204 ac-ft, or 8,886 CF. 8,891 CF of storage is provided with this
system. Please refer to Appendix B for a copy of the full WWHM data output.
Part E: Water Quality System
In accordance with Section 1.2.8.1.A of the RSWDM, Basic Water Quality Treatment is not required for
this project as new plus replaced pollution generating impervious surfaces (PGIS) do not exceed 5,000
SF, meeting exemption 1. 2,431 SF of driveway is proposed on this project.
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V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN
A conveyance system analysis will be provided with final engineering
VI. SPECIAL REPORTS AND STUDIES
• Geotechnical Evaluation by Cobalt Geosciences dated October 4, 2021
• Wetland Reconnaissance for 702 Nile Ave, Renton WA by Altmann Oliver Associates, LLC dates
December 10, 2021
• Arborist Report by Layton Tree Consulting, LLC dated October 26, 2022
• Trees & Construction Memo by Layton Tree Consulting, dated February 21, 2023
VII. OTHER PERMITS
• Civil Construction Permit
• Final Short Plat
• Building Permits
• Right-of-Way Use Permit
VIII. CSWPP ANALYSIS AND DESIGN
A CSWPPP will be provided with final engineering.
IX. BOND QUANTITIES, FACILITY SUMMARIES AND DECLARATION of
COVENANT
Bond Quantities, Facility Summary and Declaration of Covenant to be provided with Final Engineering.
X. OPERATION AND MAINTENANCE MANUAL
An Operation and Maintenance Manual to be provided with Final Engineering.
Appendix A
Geotechnical Evaluation by Cobalt Geosciences dated October 4, 2021
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, Washington 98028
www.cobaltgeo.com (206) 331-1097
October 4, 2021
Dan Finkbeiner
danfinkbeiner@comcast.net
RE: Geotechnical Evaluation
Proposed Residential Development
702 Nile Avenue
Renton, Washington
In accordance with your authorization, Cobalt Geosciences, LLC has prepared this letter to
discuss the results of our geotechnical evaluation at the referenced site.
The purpose of our evaluation was to provide recommendations for foundation design, grading,
and earthwork.
Site Description
The site is located at 702 Nile Avenue NE in Renton, Washington. The site consists of one
irregularly shaped parcel (No. 1123059002) with a total area of 31,996 square feet.
The property is developed with a residence and large accessory building and gravel driveway. The
remainder of the property is undeveloped and vegetated with grasses, bushes, blackberry vines,
and sparse trees.
The site slopes gently downward to the south at minimal magnitudes and relief. The site is
bordered to the north by NE 7th Place, to the east and south by residential properties, and to the
west by Nile Avenue NE.
The proposed development includes up to three new residences and driveways. Stormwater will
include infiltration or other systems depending on feasibility. Site grading may include cuts and
fills of 3 feet or less and foundation loads are expected to be light. We should be provided with
the final plans to verify that our recommendations remain valid and do not require updating.
Area Geology
The Geologic Map of King County, indicates that the site is underlain by Vashon Glacial Till.
Vashon Glacial Till includes dense mixtures of silt, sand, clay, and gravel. These deposits become
denser with depth and are nearly impermeable.
Soil & Groundwater Conditions
As part of our evaluation, we excavated one test pit and two hand borings, where accessible.
There were numerous utilities that limited access to all areas with an excavator. The explorations
encountered approximately 6 inches of topsoil and vegetation underlain by about 1 to 2 feet of
medium dense, silty-fine to medium grained sand with debris (Fill). This layer was underlain by
2 to 3 feet of loose to medium dense, silty-fine to medium grained sand with gravel (Weathered
Glacial Till). These materials were underlain by dense, silty-fine to medium grained sand with
gravel and cobbles (Glacial Till), which continued to the termination depths of the explorations.
October 4, 2021
Page 2 of 10
Geotechnical Evaluation
www.cobaltgeo.com (206) 331-1097
Groundwater was not encountered in the explorations. The soils became dense and mottled
approximately 4.5 to 5.5 feet below grade. Groundwater could be present 4 to 5 feet below grade
during the wet season.
Water table elevations often fluctuate over time. The groundwater level will depend on a variety
of factors that may include seasonal precipitation, irrigation, land use, climatic conditions and
soil permeability. Water levels at the time of the field investigation may be different from those
encountered during the construction phase of the project.
Erosion Hazard
The Natural Resources Conservation Services (NRCS) maps for King County indicate that the site
is underlain by Alderwood gravelly sandy loam (8 to 15 percent slopes). These soils would have a
slight to moderate erosion potential in a disturbed state depending on the slope magnitude.
It is our opinion that soil erosion potential at this project site can be reduced through landscaping
and surface water runoff control. Typically, erosion of exposed soils will be most noticeable
during periods of rainfall and may be controlled by the use of normal temporary erosion control
measures, such as silt fences, hay bales, mulching, control ditches and diversion trenches. The
typical wet weather season, with regard to site grading, is from October 31st to April 1st. Erosion
control measures should be in place before the onset of wet weather.
Seismic Hazard
The overall subsurface profile corresponds to a Site Class D as defined by Table 1613.5.2 of the
International Building Code (IBC). A Site Class D applies to an overall profile consisting of
stiff/medium dense soils within the upper 100 feet.
We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to
obtain values for SS, S1, Fa, and Fv. The USGS website includes the most updated published data
on seismic conditions. The following tables provide seismic parameters from the USGS web site
with referenced parameters from ASCE 7-10 and 7-16.
Seismic Design Parameters (ASCE 7-10)
Site
Class
Spectral
Acceleration
at 0.2 sec. (g)
Spectral
Acceleration
at 1.0 sec. (g)
Site
Coefficients
Design Spectral
Response Parameters
Design
PGA
Fa Fv SDS SD1
D 1.387 0.521 1.0 1.5 0.925 0.521 0.569
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Seismic Design Parameters (ASCE 7-16)
Site
Class
Spectral
Acceleration
at 0.2 sec. (g)
Spectral
Acceleration
at 1.0 sec. (g)
Site
Coefficients
Design Spectral
Response Parameters
Design
PGA
Fa Fv SDS SD1
D 1.387 0.475 1.0 Null 0.925 Null 0.591
Additional seismic considerations include liquefaction potential and amplification of ground
motions by soft/loose soil deposits. The liquefaction potential is highest for loose sand with a
high groundwater table. The site has a relatively low likelihood of liquefaction. For items listed
as “Null” see Section 11.4.8 of the ASCE.
Conclusions and Recommendations
General
The site is underlain by fill and at depth by weathered and unweathered glacial till that becomes
denser with depth. The proposed residential structures may be supported on shallow foundation
systems bearing on medium dense or firmer native soils or on structural fill placed on the native
soils. Local overexcavation or recompaction of loose weathered native soils and fill may be
necessary depending on the proposed elevations and locations of the new footings.
Infiltration is generally feasible in the weathered glacial till. Any system should have overflow to
an suitable discharge point or dispersion location. We should be provided with the plans for
review.
Site Preparation
Trees, shrubs and other vegetation should be removed prior to stripping of surficial organic-rich
soil and fill. Based on observations from the site investigation program, it is anticipated that the
stripping depth will be 6 to 18 inches. Deeper excavations will be necessary below large trees and
in any areas underlain by undocumented fill.
The native soils consist of silty-sand with gravel. Most of the native soils may be used as
structural fill provided they achieve compaction requirements and are within 3 percent of the
optimum moisture. Some of these soils may only be suitable for use as fill during the summer
months, as they will be above the optimum moisture levels in their current state. These soils are
variably moisture sensitive and may degrade during periods of wet weather and under equipment
traffic.
Imported structural fill should consist of a sand and gravel mixture with a maximum grain size of
3 inches and less than 5 percent fines (material passing the U.S. Standard No. 200 Sieve).
Structural fill should be placed in maximum lift thicknesses of 12 inches and should be compacted
to a minimum of 95 percent of the modified proctor maximum dry density, as determined by the
ASTM D 1557 test method.
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Temporary Excavations
Based on our understanding of the project, we anticipate that the grading could include local cuts
on the order of approximately 3 feet or less for foundation placement. Temporary excavations
should be sloped no steeper than 1.5H:1V (Horizontal:Vertical) in loose native soils and fill and
1H:1V in medium dense native soils. If an excavation is subject to heavy vibration or surcharge
loads, we recommend that the excavations be sloped no steeper than 2H:1V, where room permits.
Temporary cuts should be in accordance with the Washington Administrative Code (WAC) Part
N, Excavation, Trenching, and Shoring. Temporary slopes should be visually inspected daily by a
qualified person during construction activities and the inspections should be documented in daily
reports. The contractor is responsible for maintaining the stability of the temporary cut slopes
and reducing slope erosion during construction.
Temporary cut slopes should be covered with visqueen to help reduce erosion during wet weather,
and the slopes should be closely monitored until the permanent retaining systems or slope
configurations are complete. Materials should not be stored or equipment operated within 10 feet
of the top of any temporary cut slope.
Soil conditions may not be completely known from the geotechnical investigation. In the case of
temporary cuts, the existing soil conditions may not be completely revealed until the excavation
work exposes the soil. Typically, as excavation work progresses the maximum inclination of
temporary slopes will need to be re-evaluated by the geotechnical engineer so that supplemental
recommendations can be made. Soil and groundwater conditions can be highly variable.
Scheduling for soil work will need to be adjustable, to deal with unanticipated conditions, so that
the project can proceed and required deadlines can be met.
If any variations or undesirable conditions are encountered during construction, we should be
notified so that supplemental recommendations can be made. If room constraints or
groundwater conditions do not permit temporary slopes to be cut to the maximum angles allowed
by the WAC, temporary shoring systems may be required. The contractor should be responsible
for developing temporary shoring systems, if needed. We recommend that Cobalt Geosciences
and the project structural engineer review temporary shoring designs prior to installation, to
verify the suitability of the proposed systems.
Foundation Design
The proposed structures may be supported on shallow spread footing foundation systems bearing
on undisturbed dense or firmer native soils or on properly compacted structural fill placed on the
suitable native soils. Any undocumented fill and/or loose native soils should be removed and
replaced with structural fill below foundation elements. Structural fill below footings should
consist of clean angular rock 5/8 to 4 inches in size. We should verify soil conditions during
foundation excavation work.
For shallow foundation support, we recommend widths of at least 16 and 24 inches, respectively,
for continuous wall and isolated column footings supporting the proposed structure. Provided
that the footings are supported as recommended above, a net allowable bearing pressure of 2,000
pounds per square foot (psf) may be used for design.
A 1/3 increase in the above value may be used for short duration loads, such as those imposed by
wind and seismic events. Structural fill placed on bearing, native subgrade should be compacted
to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Footing
excavations should be inspected to verify that the foundations will bear on suitable material.
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Exterior footings should have a minimum depth of 18 inches below pad subgrade (soil grade) or
adjacent exterior grade, whichever is lower. Interior footings should have a minimum depth of 12
inches below pad subgrade (soil grade) or adjacent exterior grade, whichever is lower.
If constructed as recommended, the total foundation settlement is not expected to exceed 1 inch.
Differential settlement, along a 25-foot exterior wall footing, or between adjoining column
footings, should be less than ½ inch. This translates to an angular distortion of 0.002. Most
settlement is expected to occur during construction, as the loads are applied. However, additional
post-construction settlement may occur if the foundation soils are flooded or saturated. All
footing excavations should be observed by a qualified geotechnical consultant.
Resistance to lateral footing displacement can be determined using an allowable friction factor of
0.40 acting between the base of foundations and the supporting subgrades. Lateral resistance for
footings can also be developed using an allowable equivalent fluid passive pressure of 225 pounds
per cubic foot (pcf) acting against the appropriate vertical footing faces (neglect the upper 12
inches below grade in exterior areas). The frictional and passive resistance of the soil may be
combined without reduction in determining the total lateral resistance.
Care should be taken to prevent wetting or drying of the bearing materials during construction.
Any extremely wet or dry materials, or any loose or disturbed materials at the bottom of the
footing excavations, should be removed prior to placing concrete. The potential for wetting or
drying of the bearing materials can be reduced by pouring concrete as soon as possible after
completing the footing excavation and evaluating the bearing surface by the geotechnical engineer
or his representative.
Concrete Retaining Walls
The following table, titled Wall Design Criteria, presents the recommended soil related design
parameters for retaining walls with a level backslope. Contact Cobalt if an alternate retaining wall
system is used. This has been included for new cast in place walls, if proposed.
Wall Design Criteria
“At-rest” Conditions (Lateral Earth Pressure – EFD+) 55 pcf (Equivalent Fluid Density)
“Active” Conditions (Lateral Earth Pressure – EFD+) 35 pcf (Equivalent Fluid Density)
Seismic Increase for “At-rest” Conditions
(Lateral Earth Pressure)
21H* (Uniform Distribution) 1 in 2,500 year
event
Seismic Increase for “At-rest” Conditions
(Lateral Earth Pressure)
14H* (Uniform Distribution) 1 in 500 year event
Seismic Increase for “Active” Conditions
(Lateral Earth Pressure)
7H* (Uniform Distribution)
Passive Earth Pressure on Low Side of Wall
(Allowable, includes F.S. = 1.5)
Neglect upper 2 feet, then 275 pcf EFD+
Soil-Footing Coefficient of Sliding Friction (Allowable;
includes F.S. = 1.5)
0.40
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*H is the height of the wall; Increase based on one in 500 year seismic event (10 percent probability of being exceeded in
50 years),
+EFD – Equivalent Fluid Density
The stated lateral earth pressures do not include the effects of hydrostatic pressure generated by
water accumulation behind the retaining walls. Uniform horizontal lateral active and at-rest
pressures on the retaining walls from vertical surcharges behind the wall may be calculated using
active and at-rest lateral earth pressure coefficients of 0.3 and 0.5, respectively. A soil unit weight
of 125 pcf may be used to calculate vertical earth surcharges.
To reduce the potential for the buildup of water pressure against the walls, continuous footing
drains (with cleanouts) should be provided at the bases of the walls. The footing drains should
consist of a minimum 4-inch diameter perforated pipe, sloped to drain, with perforations placed
down and enveloped by a minimum 6 inches of pea gravel in all directions.
The backfill adjacent to and extending a lateral distance behind the walls at least 2 feet should
consist of free-draining granular material. All free draining backfill should contain less than 3
percent fines (passing the U.S. Standard No. 200 Sieve) based upon the fraction passing the U.S.
Standard No. 4 Sieve with at least 30 percent of the material being retained on the U.S. Standard
No. 4 Sieve. The primary purpose of the free-draining material is the reduction of hydrostatic
pressure. Some potential for the moisture to contact the back face of the wall may exist, even with
treatment, which may require that more extensive waterproofing be specified for walls, which
require interior moisture sensitive finishes.
We recommend that the backfill be compacted to at least 90 percent of the maximum dry density
based on ASTM Test Method D1557. In place density tests should be performed to verify
adequate compaction. Soil compactors place transient surcharges on the backfill. Consequently,
only light hand operated equipment is recommended within 3 feet of walls so that excessive stress
is not imposed on the walls.
Stormwater Management Feasibility
The site is underlain by weathered and unweathered glacial till. These soils become denser with
depth. The dense till acts as a restrictive layer on which groundwater can seasonally develop. The
site is also underlain by areas of fill. The fill and dense till are not suitable for infiltration;
however, the weathered till can be suitable for some infiltration.
We performed a small scale pilot infiltration test (PIT) in TP-1. The test was performed in general
accordance with the Washington State Department of Ecology stormwater manual. The results
are as follows:
Test
Number
Test
Depth (ft)
Measured
Infiltration
Rate (in/hr)
Correction Factors Design
Infiltration
Rate
(in/hr) CFV CFT CFM
TP-1 3.0 1.0 0.8 0.5 0.9 0.35
The design infiltration rate was determined by applying correction factors to the measured
infiltration rate as prescribed in Volume III, Section 3.3.6 of the DOE. The measured rate must
be reduced through appropriate correction factors for site variability (CFV), uncertainty of test
method (CFT), and degree of influent control (CFM) to prevent siltation and bio-buildup.
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Systems should consist of shallow trenches located downgradient of any residences. Any system
should penetrate into the weathered till but have at least 12 inches of clearance above mottled
soils and dense till. Systems should have adequate overflow for seasonal fluctuations in storm
events. We can provide additional input once the site plans have been prepared. We must be on
site to verify soil conditions at trench locations. The soils are consistent with the Loamy Sand
designation from the King County Surface Water Design Manual
We should be provided with final plans for review to determine if the intent of our
recommendations has been incorporated or if additional modifications are needed.
Slab-on-Grade
We recommend that the upper 12 inches of the native soils within slab areas be re-compacted to
at least 95 percent of the modified proctor (ASTM D1557 Test Method).
Often, a vapor barrier is considered below concrete slab areas. However, the usage of a vapor
barrier could result in curling of the concrete slab at joints. Floor covers sensitive to moisture
typically requires the usage of a vapor barrier. A materials or structural engineer should be
consulted regarding the detailing of the vapor barrier below concrete slabs. Exterior slabs
typically do not utilize vapor barriers.
The American Concrete Institutes ACI 360R-06 Design of Slabs on Grade and ACI 302.1R-04
Guide for Concrete Floor and Slab Construction are recommended references for vapor barrier
selection and floor slab detailing.
Slabs on grade may be designed using a coefficient of subgrade reaction of 210 pounds per cubic
inch (pci) assuming the slab-on-grade base course is underlain by structural fill placed and
compacted as outlined in Section 8.1. A 4- to 6-inch-thick capillary break layer should be placed
over the prepared subgrade. This material should consist of pea gravel or 5/8 inch clean angular
rock.
A perimeter drainage system is recommended unless interior slab areas are elevated a minimum
of 12 inches above adjacent exterior grades. If installed, a perimeter drainage system should
consist of a 4-inch diameter perforated drain pipe surrounded by a minimum 6 inches of drain
rock wrapped in a non-woven geosynthetic filter fabric to reduce migration of soil particles into
the drainage system. The perimeter drainage system should discharge by gravity flow to a
suitable stormwater system.
Exterior grades surrounding buildings should be sloped at a minimum of one percent to facilitate
surface water flow away from the building and preferably with a relatively impermeable surface
cover immediately adjacent to the building.
Erosion and Sediment Control
Erosion and sediment control (ESC) is used to reduce the transportation of eroded sediment to
wetlands, streams, lakes, drainage systems, and adjacent properties. Erosion and sediment
control measures should be implemented, and these measures should be in general accordance
with local regulations. At a minimum, the following basic recommendations should be
incorporated into the design of the erosion and sediment control features for the site:
Schedule the soil, foundation, utility, and other work requiring excavation or the disturbance
of the site soils, to take place during the dry season (generally May through September).
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However, provided precautions are taken using Best Management Practices (BMP’s), grading
activities can be completed during the wet season (generally October through April).
All site work should be completed and stabilized as quickly as possible.
Additional perimeter erosion and sediment control features may be required to reduce the
possibility of sediment entering the surface water. This may include additional silt fences, silt
fences with a higher Apparent Opening Size (AOS), construction of a berm, or other filtration
systems.
Any runoff generated by dewatering discharge should be treated through construction of a
sediment trap if there is sufficient space. If space is limited other filtration methods will need
to be incorporated.
Utilities
Utility trenches should be excavated according to accepted engineering practices following OSHA
(Occupational Safety and Health Administration) standards, by a contractor experienced in such
work. The contractor is responsible for the safety of open trenches. Traffic and vibration adjacent
to trench walls should be reduced; cyclic wetting and drying of excavation side slopes should be
avoided. Depending upon the location and depth of some utility trenches, groundwater flow into
open excavations could be experienced, especially during or shortly following periods of
precipitation.
In general, silty and sandy soils were encountered at shallow depths in the explorations at this
site. These soils have low cohesion and density and will have a tendency to cave or slough in
excavations. Shoring or sloping back trench sidewalls is required within these soils in excavations
greater than 4 feet deep.
All utility trench backfill should consist of imported structural fill or suitable on site soils. Utility
trench backfill placed in or adjacent to buildings and exterior slabs should be compacted to at
least 95 percent of the maximum dry density based on ASTM Test Method D1557. The upper 5
feet of utility trench backfill placed in pavement areas should be compacted to at least 95 percent
of the maximum dry density based on ASTM Test Method D1557. Below 5 feet, utility trench
backfill in pavement areas should be compacted to at least 90 percent of the maximum dry
density based on ASTM Test Method D1557. Pipe bedding should be in accordance with the pipe
manufacturer's recommendations.
The contractor is responsible for removing all water-sensitive soils from the trenches regardless of
the backfill location and compaction requirements. Depending on the depth and location of the
proposed utilities, we anticipate the need to re-compact existing fill soils below the utility
structures and pipes. The contractor should use appropriate equipment and methods to avoid
damage to the utilities and/or structures during fill placement and compaction procedures.
CONSTRUCTION FIELD REVIEWS
Cobalt Geosciences should be retained to provide part time field review during construction in
order to verify that the soil conditions encountered are consistent with our design assumptions
and that the intent of our recommendations is being met. This will require field and engineering
review to:
Monitor and test structural fill placement and soil compaction
Observe bearing capacity at foundation locations
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Observe slab-on-grade preparation
Monitor foundation drainage placement
Observe excavation stability
Geotechnical design services should also be anticipated during the subsequent final design phase
to support the structural design and address specific issues arising during this phase. Field and
engineering review services will also be required during the construction phase in order to
provide a Final Letter for the project.
CLOSURE
This report was prepared for the exclusive use of Dan Finkbeiner and his appointed consultants.
Any use of this report or the material contained herein by third parties, or for other than the
intended purpose, should first be approved in writing by Cobalt Geosciences, LLC.
The recommendations contained in this report are based on assumed continuity of soils with
those of our test holes and assumed structural loads. Cobalt Geosciences should be provided with
final architectural and civil drawings when they become available in order that we may review our
design recommendations and advise of any revisions, if necessary.
Use of this report is subject to the Statement of General Conditions provided in Appendix A. It is
the responsibility of Dan Finkbeiner who is identified as “the Client” within the Statement of
General Conditions, and its agents to review the conditions and to notify Cobalt Geosciences
should any of these not be satisfied.
Sincerely,
Cobalt Geosciences, LLC
10/4/2021
Phil Haberman, PE, LG, LEG
Principal
October 4, 2021
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Statement of General Conditions
USE OF THIS REPORT: This report has been prepared for the sole benefit of the Client or its
agent and may not be used by any third party without the express written consent of Cobalt
Geosciences and the Client. Any use which a third party makes of this report is the responsibility
of such third party.
BASIS OF THE REPORT: The information, opinions, and/or recommendations made in this
report are in accordance with Cobalt Geosciences present understanding of the site specific
project as described by the Client. The applicability of these is restricted to the site conditions
encountered at the time of the investigation or study. If the proposed site specific project differs
or is modified from what is described in this report or if the site conditions are altered, this report
is no longer valid unless Cobalt Geosciences is requested by the Client to review and revise the
report to reflect the differing or modified project specifics and/or the altered site conditions.
STANDARD OF CARE: Preparation of this report, and all associated work, was carried out in
accordance with the normally accepted standard of care in the state of execution for the specific
professional service provided to the Client. No other warranty is made.
INTERPRETATION OF SITE CONDITIONS: Soil, rock, or other material descriptions, and
statements regarding their condition, made in this report are based on site conditions
encountered by Cobalt Geosciences at the time of the work and at the specific testing and/or
sampling locations. Classifications and statements of condition have been made in accordance
with normally accepted practices which are judgmental in nature; no specific description should
be considered exact, but rather reflective of the anticipated material behavior. Extrapolation of in
situ conditions can only be made to some limited extent beyond the sampling or test points. The
extent depends on variability of the soil, rock and groundwater conditions as influenced by
geological processes, construction activity, and site use.
VARYING OR UNEXPECTED CONDITIONS: Should any site or subsurface conditions be
encountered that are different from those described in this report or encountered at the test
locations, Cobalt Geosciences must be notified immediately to assess if the varying or unexpected
conditions are substantial and if reassessments of the report conclusions or recommendations are
required. Cobalt Geosciences will not be responsible to any party for damages incurred as a result
of failing to notify Cobalt Geosciences that differing site or sub-surface conditions are present
upon becoming aware of such conditions.
PLANNING, DESIGN, OR CONSTRUCTION: Development or design plans and
specifications should be reviewed by Cobalt Geosciences, sufficiently ahead of initiating the next
project stage (property acquisition, tender, construction, etc), to confirm that this report
completely addresses the elaborated project specifics and that the contents of this report have
been properly interpreted. Specialty quality assurance services (field observations and testing)
during construction are a necessary part of the evaluation of sub-subsurface conditions and site
preparation works. Site work relating to the recommendations included in this report should only
be carried out in the presence of a qualified geotechnical engineer; Cobalt Geosciences cannot be
responsible for site work carried out without being present.
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
www.cobaltgeo.com
cobaltgeo@gmail.com
SITE PLAN
FIGURE 1
N
Proposed Three Lot Development
702 Nile Avenue NE
Renton, Washington
TP-1
Subject Property
HB-1 HB-2
Subject Property TP-1
PT
Well-graded gravels, gravels, gravel-sand mixtures, little or no fines
Poorly graded gravels, gravel-sand mixtures, little or no fines
Silty gravels, gravel-sand-silt mixtures
Clayey gravels, gravel-sand-clay mixtures
Well-graded sands, gravelly sands, little or no fines
COARSE
GRAINED
SOILS
(more than 50%
retained on
No. 200 sieve)
Primarily organic matter, dark in color,
and organic odor Peat, humus, swamp soils with high organic content (ASTM D4427)HIGHLY ORGANIC
SOILS
FINE GRAINED
SOILS
(50% or more
passes the
No. 200 sieve)
MAJOR DIVISIONS SYMBOL TYPICAL DESCRIPTION
Gravels
(more than 50%
of coarse fraction
retained on No. 4
sieve)
Sands
(50% or more
of coarse fraction
passes the No. 4
sieve)
Silts and Clays
(liquid limit less
than 50)
Silts and Clays
(liquid limit 50 or
more)
Organic
Inorganic
Organic
Inorganic
Sands with
Fines
(more than 12%
fines)
Clean Sands
(less than 5%
fines)
Gravels with
Fines
(more than 12%
fines)
Clean Gravels
(less than 5%
fines)
Unified Soil Classification System (USCS)
Poorly graded sand, gravelly sands, little or no fines
Silty sands, sand-silt mixtures
Clayey sands, sand-clay mixtures
Inorganic silts of low to medium plasticity, sandy silts, gravelly silts,
or clayey silts with slight plasticity
Inorganic clays of low to medium plasticity, gravelly clays, sandy clays,
silty clays, lean clays
Organic silts and organic silty clays of low plasticity
Inorganic silts, micaceous or diatomaceous fine sands or silty soils,
elastic silt
Inorganic clays of medium to high plasticity, sandy fat clay,
or gravelly fat clay
Organic clays of medium to high plasticity, organic silts
Moisture Content Definitions
Grain Size Definitions
Dry Absence of moisture, dusty, dry to the touch
Moist Damp but no visible water
Wet Visible free water, from below water table
Grain Size Definitions
Description Sieve Number and/or Size
Fines <#200 (0.08 mm)
Sand
-Fine
-Medium
-Coarse
Gravel
-Fine
-Coarse
Cobbles
Boulders
#200 to #40 (0.08 to 0.4 mm)
#40 to #10 (0.4 to 2 mm)
#10 to #4 (2 to 5 mm)
#4 to 3/4 inch (5 to 19 mm)
3/4 to 3 inches (19 to 76 mm)
3 to 12 inches (75 to 305 mm)
>12 inches (305 mm)
Classification of Soil Constituents
MAJOR constituents compose more than 50 percent,
by weight, of the soil. Major constituents are capitalized
(i.e., SAND).
Minor constituents compose 12 to 50 percent of the soil
and precede the major constituents (i.e., silty SAND).
Minor constituents preceded by “slightly” compose
5 to 12 percent of the soil (i.e., slightly silty SAND).
Trace constituents compose 0 to 5 percent of the soil
(i.e., slightly silty SAND, trace gravel).
Relative Density Consistency
(Coarse Grained Soils) (Fine Grained Soils)
N, SPT, Relative
Blows/FT Density
0 - 4 Very loose
4 - 10 Loose
10 - 30 Medium dense
30 - 50 Dense
Over 50 Very dense
N, SPT, Relative
Blows/FT Consistency
Under 2 Very soft
2 - 4 Soft
4 - 8 Medium stiff
8 - 15 Stiff
15 - 30 Very stiff
Over 30 Hard
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
www.cobaltgeo.com
cobaltgeo@gmail.com
Soil Classification Chart Figure C1
Test Pit &
Hand Boring
Logs
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
www.cobaltgeo.com
cobaltgeo@gmail.com
Test Pit TP-1
Date: September, 2021
Contractor: Jim
Depth: 10’
Elevation: Logged By: PH Checked By: SC
Groundwater: None
Material Description
Moisture Content (%)Plastic
Limit
Liquid
Limit
10 20 30 400 50
1
2
3
4
5
6
DCP Equivalent N-Value
7
8
9
10
SM
Dense to very dense, silty-fine to medium grained sand with gravel,
mottled yellowish brown to grayish brown, moist. (Glacial Till)
End of Test Pit 10’
Topsoil/Grass
Proposed Residences
702 Nile Avenue NE
Renton, Washington
Hand Boring HB-1
Date: September, 2021
Contractor: Cobalt
Depth: 6’
Elevation: Logged By: PH Checked By: SC
Groundwater: None
Material Description
Moisture Content (%)Plastic
Limit
Liquid
Limit
10 20 30 400 50
1
2
3
4
5
6
DCP Equivalent N-Value
7
8
9
10
Dense to very dense, silty-fine to medium grained sand with gravel,
mottled yellowish brown to grayish brown, moist. (Glacial Till)
SM
End of Hand Boring 6’
Topsoil/Vegetation
SM Loose to medium dense, silty-fine to medium grained sand with
gravel, dark yellowish brown, dry to moist. (Weathered Glacial Till)
Loose to medium dense, silty-fine to medium grained sand with
gravel, dark yellowish brown, dry to moist. (Weathered Glacial Till)
SM
SM Loose to medium dense, silty-fine to medium grained sand with
gravel and debris, dark yellowish brown, dry to moist. (Fill)
Loose to medium dense, silty-fine to medium grained sand with
gravel and debris, dark yellowish brown, dry to moist. (Fill)
SM
Test Pit &
Hand Boring
Logs
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
www.cobaltgeo.com
cobaltgeo@gmail.com
Proposed Development
16127 Cascadian Way
Bothell, Washington
Hand Boring HB-2
Date: September, 2021
Contractor: Cobalt
Depth: 6’
Elevation: Logged By: PH Checked By: SC
Groundwater: None
Material Description
Moisture Content (%)Plastic
Limit
Liquid
Limit
10 20 30 400 50
1
2
3
4
5
6
DCP Equivalent N-Value
7
8
9
10
Dense to very dense, silty-fine to medium grained sand with gravel,
mottled yellowish brown to grayish brown, moist. (Glacial Till)
SM
End of Hand Boring 6’
Topsoil/Vegetation
SM Loose to medium dense, silty-fine to medium grained sand with
gravel, dark yellowish brown, dry to moist. (Weathered Glacial Till)
Loose to medium dense, silty-fine to medium grained sand with
gravel and debris, dark yellowish brown, dry to moist. (Fill)
SM
Attachment
Cobalt Geosciences, LLC
PO Box 1792
North Bend, WA 98045
(206) 331-1097
www.cobaltgeo.com
phil@cobaltgeo.com
Appendix B
Wetland Reconnaissance for 702 Nile Ave, Renton WA by Altmann Oliver Associates, LLC dates
December 10, 2021
December 10, 2021
AOA-6482
Dan Finkbeiner
danfinkbeiner@comcast.net
SUBJECT: Wetland Reconnaissance for 702 Nile Ave, Renton, WA
Parcel 112305-9002 (PRE21-000056)
Dear Dan:
On November 16, 2021, I conducted a wetland reconnaissance on and adjacent to
the subject property utilizing the methodology outlined in the May 2010 Regional
Supplement to the Corps of Engineers Wetland Delineation Manual: Western
Mountains, Valleys, and Coast Region (Version 2.0).
The focus of the reconnaissance was to: 1) confirm no wetlands or streams on the
subject property, 2) verify that the previously delineated and surveyed boundary of
the off-site wetland to the southeast (Wetland A) had not changed, and 3) rate
Wetland A per current conditions to determine the current buffer requirement.
1.0 EXISTING ON-SITE CONDITIONS
The site is currently developed with a single-family residence/church and associated
storage building and mowed yard. No native or hydrophytic plant communities were
observed on the property. Borings taken throughout the site revealed high chroma
non-hydric soils and there was no evidence of ponding or prolonged soil saturation
anywhere on the property.
Based on the site review there are no wetlands or streams located on the property.
2.0 WETLAND A
Wetland A is a forested Depressional Hydrogeomorphic (HGM) wetland located off-site
to the southeast. The wetland was delineated and surveyed as part of the adjacent
Weston North residential development. Off-site conditions do not appear to have
significantly changed and the previously surveyed wetland boundary appears to remain
accurate.
Dan Finkbeiner December 10, 2021 Page 2 of 2
Wetland A previously met the criteria for a Category III wetland with 3 Habitat Points
and this rating has not changed (Attachment A). Category III wetlands with 3
Habitat Points currently require a standard 75-foot buffer adjacent non low impact
land uses per RMC 4-3-050.G.2.
As part of the Weston North development, a shed located in the buffer was removed
and the degraded buffer enhanced with native plantings and placed within a protective
tract (Tract A). The enhanced buffer does not encroach into the subject property
(Attachment B).
If you have any questions regarding the wetland reconnaissance, please give me a call.
Sincerely,
ALTMANN OLIVER ASSOCIATES, LLC
John Altmann
Ecologist
Attachments
Wetland name or number A
Name of wetland (or ID #):Date of site visit:11/16/2021
Rated by Trained by Ecology? Yes No Date of training 03/08 & 03/15
HGM Class used for rating Wetland has multiple HGM classes? Yes No
NOTE: Form is not complete with out the figures requested (figures can be combined ).
Source of base aerial photo/map
OVERALL WETLAND CATEGORY III (based on functions or special characteristics )
1. Category of wetland based on FUNCTIONS
Category I - Total score = 23 - 27 Score for each
Category II - Total score = 20 - 22 function based
X Category III - Total score = 16 - 19 on three
Category IV - Total score = 9 - 15 ratings
(order of ratings
is not
important )
M L 9 = H, H, H
H L 8 = H, H, M
M L Total 7 = H, H, L
7 = H, M, M
6 = H, M, L
6 = M, M, M
5 = H, L, L
5 = M, M, L
4 = M, L, L
3 = L, L, L
2. Category based on SPECIAL CHARACTERISTICS of wetland
X
Depressional & Flats
RATING SUMMARY – Western Washington
List appropriate rating (H, M, L)
HydrologicImproving
Water Quality
MSite Potential
Landscape Potential
Habitat
H
FUNCTION
Parcel 112305-9002
Altmann
King County iMAP
Coastal Lagoon
Interdunal
Value
Score Based on
Ratings 7 7 3 17
M
CHARACTERISTIC Category
Estuarine
Wetland of High Conservation Value
Bog
Mature Forest
Old Growth Forest
None of the above
Wetland Rating System for Western WA: 2014 Update
Rating Form - Effective January 1, 2015 1 WSDOT Adapted Form - March 2, 2015
Wetland name or number A
Maps and Figures required to answer questions correctly for
Western Washington
Depressional Wetlands
Map of: Figure #
Cowardin plant classes Previous
Hydroperiods Previous
Location of outlet (can be added to map of hydroperiods )Previous
Boundary of area within 150 ft of the wetland (can be added to another figure )B
Map of the contributing basin Previous
1 km Polygon: Area that extends 1 km from entire wetland edge - including
polygons for accessible habitat and undisturbed habitat
Screen capture of map of 303(d) listed waters in basin (from Ecology website)C
Screen capture of list of TMDLs for WRIA in which unit is found (from web)D
Riverine Wetlands
Map of: Figure #
Cowardin plant classes
Hydroperiods
Ponded depressions
Boundary of area within 150 ft of the wetland (can be added to another figure )
Plant cover of trees, shrubs, and herbaceous plants
Width of unit vs. width of stream (can be added to another figure )
Map of the contributing basin
1 km Polygon: Area that extends 1 km from entire wetland edge - including
polygons for accessible habitat and undisturbed habitat
Screen capture of map of 303(d) listed waters in basin (from Ecology website)
Screen capture of list of TMDLs for WRIA in which unit is found (from web)
Lake Fringe Wetlands
Map of: Figure #
Cowardin plant classes
Plant cover of trees, shrubs, and herbaceous plants
Boundary of area within 150 ft of the wetland (can be added to another figure )
1 km Polygon: Area that extends 1 km from entire wetland edge - including
polygons for accessible habitat and undisturbed habitat
Screen capture of map of 303(d) listed waters in basin (from Ecology website)
Screen capture of list of TMDLs for WRIA in which unit is found (from web)
Slope Wetlands
Map of: Figure #
Cowardin plant classes
Hydroperiods
Plant cover of dense trees, shrubs, and herbaceous plants
Plant cover of dense, rigid trees, shrubs, and herbaceous plants
(can be added to another figure )
Boundary of area within 150 ft of the wetland (can be added to another figure )
1 km Polygon: Area that extends 1 km from entire wetland edge - including
polygons for accessible habitat and undisturbed habitat
Screen capture of map of 303(d) listed waters in basin (from Ecology website)
Screen capture of list of TMDLs for WRIA in which unit is found (from web)
A
S 3.1, S 3.2
S 3.3
S 4.1
S 2.1, S 5.1
To answer questions:
H 1.1, H 1.4
H 1.2
S 1.3
H 2.1, H 2.2, H 2.3
L 3.1, L 3.2
L 3.3
H 2.1, H 2.2, H 2.3
R 3.1
R 3.2, R 3.3
To answer questions:
L 1.1, L 4.1, H 1.1, H 1.4
H 1.2
R 1.1
R 2.4
R 1.2, R 4.2
R 4.1
R 2.2, R 2.3, R 5.2
H 2.1, H 2.2, H 2.3
L 1.2
L 2.2
D 1.1, D 4.1
D 2.2, D 5.2
D 4.3, D 5.3
H 2.1, H 2.2, H 2.3
D 3.1, D 3.2
D 3.3
To answer questions:
H 1.1, H 1.4
To answer questions:
D 1.3, H 1.1, H 1.4
D 1.4, H 1.2
Wetland Rating System for Western WA: 2014 Update
Rating Form - Effective January 1, 2015 2 WSDOT Adapted Form - March 2, 2015
Wetland name or number A
For questions 1 -7, the criteria described must apply to the entire unit being rated.
1. Are the water levels in the entire unit usually controlled by tides except during floods?
NO - go to 2 YES - the wetland class is Tidal Fringe - go to 1.1
1.1 Is the salinity of the water during periods of annual low flow below 0.5 ppt (parts per thousand)?
NO - Saltwater Tidal Fringe (Estuarine)YES - Freshwater Tidal Fringe
NO - go to 3 YES - The wetland class is Flats
If your wetland can be classified as a Flats wetland, use the form for Depressional wetlands.
3. Does the entire wetland unit meet all of the following criteria?
NO - go to 4 YES - The wetland class is Lake Fringe (Lacustrine Fringe)
4. Does the entire wetland unit meet all of the following criteria?
The wetland is on a slope (slope can be very gradual ),
The water leaves the wetland without being impounded.
NO - go to 5 YES - The wetland class is Slope
5. Does the entire wetland unit meet all of the following criteria?
The overbank flooding occurs at least once every 2 years.
NO - go to 6 YES - The wetland class is Riverine
NOTE: The Riverine unit can contain depressions that are filled with water when the river is not flooding.
If your wetland can be classified as a Freshwater Tidal Fringe use the forms for Riverine wetlands.
If it is Saltwater Tidal Fringe it is an Estuarine wetland and is not scored. This method cannot be
used to score functions for estuarine wetlands.
The vegetated part of the wetland is on the shores of a body of permanent open water (without any
plants on the surface at any time of the year) at least 20 ac (8 ha) in size;
The water flows through the wetland in one direction (unidirectional) and usually comes from seeps.
It may flow subsurface, as sheetflow, or in a swale without distinct banks.
NOTE: Surface water does not pond in these type of wetlands except occasionally in very small and shallow
depressions or behind hummocks (depressions are usually <3 ft diameter and less than 1 ft deep).
The unit is in a valley, or stream channel, where it gets inundated by overbank flooding
from that stream or river,
2. The entire wetland unit is flat and precipitation is the only source (>90%) of water to it.
Groundwater and surface water runoff are NOT sources of water to the unit.
HGM Classification of Wetland in Western Washington
If hydrologic criteria listed in each question do not apply to the entire unit being rated, you probably have a unit
with multiple HGM classes. In this case, identify which hydrologic criteria in questions 1 - 7 apply, and go to
Question 8.
At least 30% of the open water area is deeper than 6.6 ft (2 m).
Wetland Rating System for Western WA: 2014 Update
Rating Form - Effective January 1, 2015 3 WSDOT Adapted Form - March 2, 2015
Wetland name or number A
NO - go to 7 YES - The wetland class is Depressional
NO - go to 8 YES - The wetland class is Depressional
NOTES and FIELD OBSERVATIONS:
Salt Water Tidal Fringe and any other
class of freshwater wetland
HGM class to
use in rating
Riverine
Depressional
Lake Fringe
If you are still unable to determine which of the above criteria apply to your wetland, or if you have more than
2 HGM classes within a wetland boundary, classify the wetland as Depressional for the rating.
Riverine
Treat as
ESTUARINE
Slope + Lake Fringe
Depressional + Riverine along stream
within boundary of depression
Depressional + Lake Fringe
Riverine + Lake Fringe
NOTE: Use this table only if the class that is recommended in the second column represents 10% or more of
the total area of the wetland unit being rated. If the area of the HGM class listed in column 2 is less than 10%
of the unit; classify the wetland using the class that represents more than 90% of the total area.
HGM classes within the wetland unit
being rated
Slope + Riverine
Slope + Depressional
Depressional
Depressional
7. Is the entire wetland unit located in a very flat area with no obvious depression and no overbank flooding?
The unit does not pond surface water more than a few inches. The unit seems to be maintained by high
groundwater in the area. The wetland may be ditched, but has no obvious natural outlet.
8. Your wetland unit seems to be difficult to classify and probably contains several different HGM classes. For
example, seeps at the base of a slope may grade into a riverine floodplain, or a small stream within a
Depressional wetland has a zone of flooding along its sides. GO BACK AND IDENTIFY WHICH OF THE
HYDROLOGIC REGIMES DESCRIBED IN QUESTIONS 1-7 APPLY TO DIFFERENT AREAS IN THE UNIT
(make a rough sketch to help you decide). Use the following table to identify the appropriate class to use for
the rating system if you have several HGM classes present within the wetland unit being scored.
6. Is the entire wetland unit in a topographic depression in which water ponds, or is saturated to the surface, at
some time during the year? This means that any outlet, if present, is higher than the interior of the wetland.
Wetland Rating System for Western WA: 2014 Update
Rating Form - Effective January 1, 2015 4 WSDOT Adapted Form - March 2, 2015
Wetland name or number A
D 1.1. Characteristics of surface water outflows from the wetland:
points = 3
points = 2
points = 1
points = 1
Yes = 4 No = 0
Wetland has persistent, ungrazed, plants > 95% of area points = 5
Wetland has persistent, ungrazed, plants > ½ of area points = 3
Wetland has persistent, ungrazed plants > 1/10 of area points = 1
Wetland has persistent, ungrazed plants < 1/10 of area points = 0
D 1.4. Characteristics of seasonal ponding or inundation:
This is the area that is ponded for at least 2 months. See description in manual.
Area seasonally ponded is > ½ total area of wetland points = 4
Area seasonally ponded is > ¼ total area of wetland points = 2
Area seasonally ponded is < ¼ total area of wetland points = 0
Total for D 1 Add the points in the boxes above 9
Rating of Site Potential If score is: 12 - 16 = H 6 - 11 = M 0 - 5 = L Record the rating on the first page
D 2.1. Does the wetland unit receive stormwater discharges?Yes = 1 No = 0 1
Yes = 1 No = 0
D 2.3. Are there septic systems within 250 ft of the wetland?Yes = 1 No = 0 1
Source Yes = 1 No = 0
Total for D 2 Add the points in the boxes above 3
Rating of Landscape Potential If score is: 3 or 4 = H 1 or 2 = M 0 = L Record the rating on the first page
Yes = 1 No = 0
Yes = 1 No = 0
Yes = 2 No = 0
Total for D 3 Add the points in the boxes above 1
Rating of Value If score is: 2 - 4 = H 1 = M 0 = L Record the rating on the first page
1
0
Water Quality Functions - Indicators that the site functions to improve water quality
D 1.0. Does the site have the potential to improve water quality?
2
Wetland has an unconstricted, or slightly constricted, surface outlet
that is permanently flowing
Wetland has an intermittently flowing stream or ditch, OR highly
constricted permanently flowing outlet.
Wetland is a depression or flat depression (QUESTION 7 on key)
with no surface water leaving it (no outlet).
Wetland is a flat depression (QUESTION 7 on key), whose outlet is
a permanently flowing ditch.
2
D 2.0. Does the landscape have the potential to support the water quality function of the site?
DEPRESSIONAL AND FLATS WETLANDS
D 3.3. Has the site been identified in a watershed or local plan as important
for maintaining water quality (answer YES if there is a TMDL for the basin in
which the unit is found )?
D 1.2. The soil 2 in below the surface (or duff layer) is true clay or true organic
(use NRCS definitions ).
D 1.3. Characteristics and distribution of persistent plants (Emergent, Scrub-shrub, and/or
Forested Cowardin classes):
D 2.4. Are there other sources of pollutants coming into the wetland that are
not listed in questions D 2.1 - D 2.3?
D 3.1. Does the wetland discharge directly (i.e., within 1 mi) to a stream, river,
lake, or marine water that is on the 303(d) list?
D 2.2. Is > 10% of the area within 150 ft of the wetland in land uses that
generate pollutants?
D 3.2. Is the wetland in a basin or sub-basin where an aquatic resource is on the 303(d) list?
D 3.0. Is the water quality improvement provided by the site valuable to society?
1
0
0
0
5
Wetland Rating System for Western WA: 2014 Update
Rating Form - Effective January 1, 2015 5 WSDOT Adapted Form - March 2, 2015
Wetland name or number A
D 4.1. Characteristics of surface water outflows from the wetland:
points = 4
points = 2
points = 1
points = 0
Marks of ponding are 3 ft or more above the surface or bottom of outlet points = 7
Marks of ponding between 2 ft to < 3 ft from surface or bottom of outlet points = 5
Marks are at least 0.5 ft to < 2 ft from surface or bottom of outlet points = 3
The wetland is a “headwater” wetland points = 3
Wetland is flat but has small depressions on the surface that trap water points = 1
Marks of ponding less than 0.5 ft (6 in)points = 0
The area of the basin is less than 10 times the area of the unit points = 5
The area of the basin is 10 to 100 times the area of the unit points = 3
The area of the basin is more than 100 times the area of the unit points = 0
Entire wetland is in the Flats class points = 5
Total for D 4 Add the points in the boxes above 8
Rating of Site Potential If score is: 12 - 16 = H 6 - 11 = M 0 - 5 = L Record the rating on the first page
D 5.1. Does the wetland unit receive stormwater discharges?Yes = 1 No = 0 1
D 5.2. Is > 10% of the area within 150 ft of the wetland in land uses that generate excess runoff?
Yes = 1 No = 0
Yes = 1 No = 0
Total for D 5 Add the points in the boxes above 3
Rating of Landscape Potential If score is: 3 = H 1 or 2 = M 0 = L Record the rating on the first page
points = 2
points = 1
Flooding from groundwater is an issue in the sub-basin.points = 1
points = 0
There are no problems with flooding downstream of the wetland.points = 0
Yes = 2 No = 0
Total for D 6 Add the points in the boxes above 1
Rating of Value If score is: 2 - 4 = H 1 = M 0 = L Record the rating on the first page
DEPRESSIONAL AND FLATS WETLANDS
D 6.0. Are the hydrologic functions provided by the site valuable to society?
The wetland captures surface water that would otherwise flow down-gradient into areas
where flooding has damaged human or natural resources (e.g., houses or salmon redds):
Flooding occurs in a sub-basin that is immediately down-
gradient of unit.
Surface flooding problems are in a sub-basin farther down-
gradient.
Hydrologic Functions - Indicators that the site functions to reduce flooding and stream degradation
D 4.0. Does the site have the potential to reduce flooding and erosion?
2
Wetland is a depression or flat depression with no surface water
leaving it (no outlet)
Wetland has an unconstricted, or slightly constricted, surface outlet
that is permanently flowing
Wetland has an intermittently flowing stream or ditch, OR highly
constricted permanently flowing outlet
Wetland is a flat depression (QUESTION 7 on key), whose outlet is
a permanently flowing ditch
3
D 5.0. Does the landscape have the potential to support hydrologic function of the site?
1
1
D 5.3. Is more than 25% of the contributing basin of the wetland covered with intensive human
land uses (residential at >1 residence/ac, urban, commercial, agriculture, etc.)?
The existing or potential outflow from the wetland is so constrained
by human or natural conditions that the water stored by the wetland
cannot reach areas that flood. Explain why
1
0
3
D 4.2. Depth of storage during wet periods: Estimate the height of ponding above the bottom of
the outlet. For wetlands with no outlet, measure from the surface of permanent water or if dry, the
deepest part.
D 4.3. Contribution of the wetland to storage in the watershed: Estimate the ratio of the area of
upstream basin contributing surface water to the wetland to the area of the wetland unit itself.
D 6.1. The unit is in a landscape that has flooding problems. Choose the description that best
matches conditions around the wetland unit being rated. Do not add points. Choose the highest
score if more than one condition is met.
D 6.2. Has the site been identified as important for flood storage or flood
conveyance in a regional flood control plan?
Wetland Rating System for Western WA: 2014 Update
Rating Form - Effective January 1, 2015 6 WSDOT Adapted Form - March 2, 2015
Wetland name or number A
HABITAT FUNCTIONS - Indicators that site functions to provide important habitat
H 1.0. Does the site have the potential to provide habitat?
Aquatic bed 4 structures or more: points = 4
Emergent 3 structures: points = 2
Scrub-shrub (areas where shrubs have > 30% cover)2 structures: points - 1
Forested (areas where trees have > 30% cover)1 structure: points = 0
If the unit has a Forested class, check if :
H 1.2. Hydroperiods
Permanently flooded or inundated 4 or more types present: points = 3
Seasonally flooded or inundated 3 types present: points = 2
Occasionally flooded or inundated 2 types present: points = 1
Saturated only 1 types present: points = 0
Permanently flowing stream or river in, or adjacent to, the wetland
Seasonally flowing stream in, or adjacent to, the wetland
Lake Fringe wetland 2 points
Freshwater tidal wetland 2 points
H 1.3. Richness of plant species
If you counted:> 19 species points = 2
5 - 19 species points = 1
< 5 species points = 0
H 1.4. Interspersion of habitats
These questions apply to wetlands of all HGM classes.
The Forested class has 3 out of 5 strata (canopy, sub-canopy, shrubs, herbaceous,
moss/ground-cover) that each cover 20% within the Forested polygon
1
H 1.1. Structure of plant community: Indicators are Cowardin classes and strata within the
Forested class. Check the Cowardin plant classes in the wetland. Up to 10 patches may be
combined for each class to meet the threshold of ¼ ac or more than 10% of the unit if it is smaller
than 2.5 ac. Add the number of structures checked.
None = 0 points Low = 1 point Moderate = 2 points
All three diagrams
in this row are
HIGH = 3 points
0
Check the types of water regimes (hydroperiods) present within the wetland. The water regime
has to cover more than 10% of the wetland or ¼ ac to count (see text for descriptions of
hydroperiods ).
0
Count the number of plant species in the wetland that cover at least 10 ft2.Different patches of the same species can be combined to meet the size threshold and you do
not have to name the species. Do not include Eurasian milfoil, reed canarygrass, purple
loosestrife, Canadian thistle 1
Decide from the diagrams below whether interspersion among Cowardin plants classes
(described in H 1.1), or the classes and unvegetated areas (can include open water or mudflats)
is high, moderate, low, or none. If you have four or more plant classes or three classes and open
water, the rating is always high.
Wetland Rating System for Western WA: 2014 Update
Rating Form - Effective January 1, 2015 7 WSDOT Adapted Form - March 2, 2015
Wetland name or number A
H 1.5. Special habitat features:
Large, downed, woody debris within the wetland (> 4 in diameter and 6 ft long)
Standing snags (dbh > 4 in) within the wetland
Total for H 1 Add the points in the boxes above 5
Rating of Site Potential If Score is: 15 - 18 = H 7 - 14 = M 0 - 6 = L Record the rating on the first page
H 2.0. Does the landscape have the potential to support the habitat function of the site?
H 2.1 Accessible habitat (include only habitat that directly abuts wetland unit ).
Calculate:
0.9 % undisturbed habitat + (0 % moderate & low intensity land uses / 2 ) = 0.9%
If total accessible habitat is:
> 1/3 (33.3%) of 1 km Polygon points = 3
20 - 33% of 1 km Polygon points = 2
10 - 19% of 1 km Polygon points = 1
< 10 % of 1 km Polygon points = 0
H 2.2. Undisturbed habitat in 1 km Polygon around the wetland.
Calculate:
14.4 % undisturbed habitat + (11.2 % moderate & low intensity land uses / 2 ) = 20%
Undisturbed habitat > 50% of Polygon points = 3
Undisturbed habitat 10 - 50% and in 1-3 patches points = 2
Undisturbed habitat 10 - 50% and > 3 patches points = 1
Undisturbed habitat < 10% of 1 km Polygon points = 0
H 2.3 Land use intensity in 1 km Polygon: If
> 50% of 1 km Polygon is high intensity land use points = (-2)
≤ 50% of 1km Polygon is high intensity points = 0
Total for H 2 Add the points in the boxes above -1
Rating of Landscape Potential If Score is: 4 - 6 = H 1 - 3 = M < 1 = L Record the rating on the first page
Site meets ANY of the following criteria:points = 2
It has 3 or more priority habitats within 100 m (see next page)
It is mapped as a location for an individual WDFW priority species
Site has 1 or 2 priority habitats (listed on next page) with in 100m points = 1
Site does not meet any of the criteria above points = 0
Rating of Value If Score is: 2 = H 1 = M 0 = L Record the rating on the first page
0
1
-2
H 3.0. Is the habitat provided by the site valuable to society?
H 3.1. Does the site provide habitat for species valued in laws, regulations, or policies? Choose
only the highest score that applies to the wetland being rated .
It provides habitat for Threatened or Endangered species (any plant
or animal on the state or federal lists)
It is a Wetland of High Conservation Value as determined by the
Department of Natural Resources
0
Invasive plants cover less than 25% of the wetland area in every stratum of plants (see
H 1.1 for list of strata )
Undercut banks are present for at least 6.6 ft (2 m) and/or overhanging plants extends
at least 3.3 ft (1 m) over a stream (or ditch) in, or contiguous with the wetland, for at
least 33 ft (10 m)
Stable steep banks of fine material that might be used by beaver or muskrat for denning
(> 30 degree slope) OR signs of recent beaver activity are present (cut shrubs or trees
that have not yet weathered where wood is exposed )
At least ¼ ac of thin-stemmed persistent plants or woody branches are present in areas
that are permanently or seasonally inundated (structures for egg-laying by amphibians )
3
Check the habitat features that are present in the wetland. The number of checks is the number
of points.
It has been categorized as an important habitat site in a local or
regional comprehensive plan, in a Shoreline Master Plan, or in a
watershed plan
Wetland Rating System for Western WA: 2014 Update
Rating Form - Effective January 1, 2015 8 WSDOT Adapted Form - March 2, 2015
Wetland name or number A
Aspen Stands: Pure or mixed stands of aspen greater than 1 ac (0.4 ha).
Herbaceous Balds: Variable size patches of grass and forbs on shallow soils over bedrock.
Cliffs: Greater than 25 ft (7.6 m) high and occurring below 5000 ft elevation.
http://wdfw.wa.gov/publications/00165/wdfw00165.pdf or access the list from here:
http://wdfw.wa.gov/conservation/phs/list/
Caves: A naturally occurring cavity, recess, void, or system of interconnected passages under the
earth in soils, rock, ice, or other geological formations and is large enough to contain a human.
Note: All vegetated wetlands are by definition a priority habitat but are not included in this list because they are
addressed elsewhere.
WDFW Priority Habitats
Count how many of the following priority habitats are within 330 ft (100 m) of the wetland unit: NOTE : This
question is independent of the land use between the wetland unit and the priority habitat.
Biodiversity Areas and Corridors: Areas of habitat that are relatively important to various species
of native fish and wildlife (full descriptions in WDFW PHS report ).
Old-growth/Mature forests: Old-growth west of Cascade crest – Stands of at least 2 tree species,
forming a multi-layered canopy with occasional small openings; with at least 8 trees/ac (20 trees/ha)
> 32 in (81 cm) dbh or > 200 years of age. Mature forests – Stands with average diameters
exceeding 21 in (53 cm) dbh; crown cover may be less than 100%; decay, decadence, numbers of
snags, and quantity of large downed material is generally less than that found in old-growth; 80-200
years old west of the Cascade crest.
Priority habitats listed by WDFW (see complete descriptions of WDFW priority habitats, and the counties in
which they can be found, in: Washington Department of Fish and Wildlife. 2008. Priority Habitat and Species
List. Olympia, Washington. 177 pp.
Oregon White Oak: Woodland stands of pure oak or oak/conifer associations where canopy
coverage of the oak component is important (full descriptions in WDFW PHS report p. 158 – see
web link above ).
Riparian: The area adjacent to aquatic systems with flowing water that contains elements of both
aquatic and terrestrial ecosystems which mutually influence each other.
Westside Prairies: Herbaceous, non-forested plant communities that can either take the form of a
dry prairie or a wet prairie (full descriptions in WDFW PHS report p. 161 – see web link above ).
Instream: The combination of physical, biological, and chemical processes and conditions that
interact to provide functional life history requirements for instream fish and wildlife resources.
Nearshore: Relatively undisturbed nearshore habitats. These include Coastal Nearshore, Open
Coast Nearshore, and Puget Sound Nearshore. (full descriptions of habitats and the definition of
relatively undisturbed are in WDFW report – see web link on previous page ).
Snags and Logs: Trees are considered snags if they are dead or dying and exhibit sufficient decay
characteristics to enable cavity excavation/use by wildlife. Priority snags have a diameter at breast
height of > 20 in (51 cm) in western Washington and are > 6.5 ft (2 m) in height. Priority logs are > 12
in (30 cm) in diameter at the largest end, and > 20 ft (6 m) long.
Talus: Homogenous areas of rock rubble ranging in average size 0.5 - 6.5 ft (0.15 - 2.0 m),
composed of basalt, andesite, and/or sedimentary rock, including riprap slides and mine tailings. May
be associated with cliffs.
Wetland Rating System for Western WA: 2014 Update
Rating Form - Effective January 1, 2015 9 WSDOT Adapted Form - March 2, 2015
EagleView Technologies, Inc.
0 1,000 2,000 3,000 4,000500
US Feet
Subject Property Parcel: 112305-9002
Approximate Wetland A Rating Unit
1 Km Habitat Classification Polygon
Accessible Relatively Undisturbed Habitat 0.9%%
Accessible Low_Moderate Intensity Habitat 0.0%
Relativley Undisturbed Habitat 13.5%
Low_Moderate Intensity Habitat 11.2%
High Intensity Habitat 74.4%
Figure A AOA - 6482City of Renton
Parcel 112305-9002
King County, EagleView Technologies, Inc.
0 125 250 375 50062.5
US Feet
Subject Property Parcel: 112305-9002
Approximate Wetland A Rating Unit
150' Pollution Assessment Polygon
Pollution Generating Surfaces 77.3%
Figure B AOA - 6482City of Renton
Parcel 112305-9002
Figure C
Sources: Esri, HERE, Garmin, Intermap, increment P Corp., GEBCO, USGS,FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, EsriJapan, METI, Esri China (Hong Kong), (c) OpenStreetMap contributors, and
December 10, 2021
0 0.5 10.25Miles
K
Assessed Water/SedimentWater
Category 5 - 303d
Category 4C
Category 4B
Category 4A
Category 2
Category 1
Sediment
Category 5 - 303d
Category 4C
Category 4B
Category 4A
Category 2
Category 1
Figure D
Sources: Esri, HERE, Garmin, Intermap, increment P Corp., GEBCO, USGS,FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, EsriJapan, METI, Esri China (Hong Kong), (c) OpenStreetMap contributors, and
December 10, 2021
0 0.25 0.50.125Miles
K
Assessed Water/SedimentWater
Category 5 - 303d
Category 4C
Category 4B
Category 4A
Category 2
Category 1
Sediment
Category 5 - 303d
Category 4C
Category 4B
Category 4A
Category 2
Category 1
WQ Improvement ProjectsApproved
In Development
Appendix C
Arborist Report by Layton Tree Consulting, LLC dated October 26, 2022
Trees & Construction Memo by Layton Tree Consulting, LLC dated February 21, 2022
LAYTON TREE CONSULTING, LLC
It’s all about trees……
PO BOX 572, SNOHOMISH, WA 98291-0572 * 425-220-5711 * bob@laytontreeconsulting.com
ARBORIST REPORT
702 Nile Avenue NE
Renton, WA
Report Prepared by:
Bob Layton
Registered Consulting Arborist #670
Certified Arborist #PN-2714A
April 14, 2022
Updated October 26, 2022
Arborist Report – 702 Nile Ave NE
Page 2 Layton Tree Consulting LLC April 14, 2022
Updated October 26, 2022
Table of Contents
Assignment.................................................................................................................................................... 3
Description .................................................................................................................................................... 3
Methodology ................................................................................................................................................. 3
Judging Condition...................................................................................................................................... 4
Observations ................................................................................................................................................. 4
Discussion/Recommendations ...................................................................................................................... 4
Tree Protection Recommendations .............................................................................................................. 5
Tree Protection Measures ............................................................................................................................ 5
Tree Density-Tree Replacement - Updated .................................................................................................. 6
Arborist Disclosure Statement ...................................................................................................................... 8
Attachments
Photos, pages 9 - 12
Tree Summary Table
Tree Plan Map
City of Renton – Approved Tree List
Arborist Report – 702 Nile Ave NE
Page 3 Layton Tree Consulting LLC April 14, 2022
Updated October 26, 2022
Assignment
Layton Tree Consulting, LLC was asked to compile an Arborist Report for one parcel in Renton. The
subject property is located at 702 Nile Avenue NE. The purpose of the report is to satisfy City
requirements regarding tree retention regulations associated with the proposed redevelopment of the
property.
My assignment is to prepare a written report on present tree conditions, and to provide appropriate
recommendations for the protection of retained or protected trees during development.
This report covers all of the criteria set forth under the City of Renton’s tree regulations, Municipal Code
Section 4-4-130 - Tree Retention and Land Clearing Regulations. The property is zoned R4, requiring the
retention of 30% of the existing significant trees.
Date of Field Examination: April 6, 2022
Description
There are few trees on the subject property. The site is mostly open and covered in lawn and gravel. The
adjacent rights-of-way of NE 7th Place and Nile Avenue NE have been recently landscaped. Several trees,
shrubs and ground covers have been planted in recent years.
Five significant trees were identified on the property. A significant tree is any tree with a caliper of at least
6-inches or alder or cottonwood tree at least 8-inches. The subject trees are all fruit trees.
Trees have been previously marked with a numbered aluminum tag attached to the lower trunk. These
same tag numbers are used for this report. Tree numbers correspond with the numbers on the attached
Tree Summary Table and Tree Plan Map.
An additional five off-site trees were also assessed. These are all mature apple trees located within a
proximity of the south property line. They are located within an access tract.
Methodology
Each tree in this report was visited. Tree diameters were measured by tape. The tree heights were
measured using a Spiegel Relaskop. Each tree was visually examined for defects and vigor. The tree
assessment procedure involves the examination of many factors:
• The crown or canopy of the tree is examined for current vigor/health by examining the foliage for
appropriate color and density, the vegetative buds for color and size, and the branches for structural
form and annual shoot growth; and the overall presence of limb dieback and/or any disease issues.
• The trunk or main stem of the tree is inspected for decay, which includes cavities, wounds, fruiting
bodies of decay (conks or mushrooms), seams, insect pests, bleeding or exudation of sap, callus
development, broken or dead tops, structural defects and unnatural leans. Structural defects can
include but are not limited to excessive or unnatural leans, crooks, forks with V-shaped crotches,
multiple attachments.
Arborist Report – 702 Nile Ave NE
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Updated October 26, 2022
• The root collar and exposed surface roots are inspected for the presence of decay, insect damage, as
well as if they have been injured or wounded, undermined or exposed, or the original grade has
been altered.
Judging Condition
The three condition categories are described as follows:
Good – free of significant structural defects, no disease concerns, minor pest issues, no significant root
issues, good structure/form with uniform crown or canopy, foliage of normal color and density, average or
normal vigor, will be wind firm if isolated or left as part of a grouping or grove of trees, suitable for its
location
Fair – minor to moderate structural defects not expected to contribute to a failure in near future, no disease
concerns, moderate pest issues, no significant root issues, asymmetric or unbalanced crown or canopy,
average or normal vigor, foliage of normal color, moderate foliage density, will be wind firm if left as part of
a grouping or grove of trees, cannot be isolated, suitable for its location
Poor – major structural defects expected to cause fail in near future, disease or significant pest concerns,
decline due to old age, significant root issues, asymmetric or unbalanced crown or canopy, sparse or
abnormally small foliage, poor vigor, not suitable for its location
The attached Tree Summary Table provides specific information on tree sizes and dripline measurements.
Observations
The subject trees are all fruit trees. The majority (#947, #949 and #952) are mature apple trees. Most
have developed significant trunk decay which is common for the species. Vigor is good. Trees have
been well-maintained (pruned) in the past. These are in ‘fair’ condition.
Tree #1 is a semi-mature pear. It has been recently heavily pruned/cut back. See pictures below. It has
developed typical form and is of fairly good vigor. Condition is ‘fair’.
Tree #2 is a young cherry fruit tree variety. It has developed decent structural form and is of good vigor.
Condition is ‘fair’.
Off-site/Neighboring Trees
These are all mature apple trees. #951 and #953 have extensive decay within the trunks. The
remainder have developed moderate internal decay. Vigor remains good. These are all low risk due to
size. Continued retention is feasible. Tree #953 is a boundary line tree.
Discussion/Recommendations
The owner desires to remove the five property fruit trees and establish new trees in their place. Fruit
trees are of low retention value. A mix of new coniferous and deciduous species will ultimately be much
more beneficial to the surrounding area over the long-term. New tree plantings will replace the lost
tree canopy within a few years and ultimately surpass the canopy coverage that would have been
retained by meeting the 30% retention requirement in a very short time.
Arborist Report – 702 Nile Ave NE
Page 5 Layton Tree Consulting LLC April 14, 2022
Updated October 26, 2022
The attached map shows the extent of driplines of subject trees. Position a tree protection barrier just
beyond the driplines of neighboring trees as shown on the map. Follow the tree protection
recommendations and measures as outlined below.
Trees #951 and #953 are in poor condition due to extensive trunk decay. However, these can be
retained at low risk due to their small size.
Tree Protection Recommendations
Tree protection fencing shall be positioned around any retained and/or protected trees prior to site
demolition or bringing any heavy equipment onto the site. This will help to define clearing limits and
protect soils and surface roots.
Any roots damaged during site work outside of the tree protection fenced area shall be pruned clean at
sound tissue prior to backfilling or finishing areas. Sound tissue is where the root is undamaged and the
bark is completely intact with the root. This will help roots to seal off potential decay and allow them to
sprout new growth. Any disturbed areas near protected trees shall be watered weekly during the dry
season of June through September. This will help to create a favorable environment for new root
growth and reduce the overall stress associated with root loss and disturbance.
Simply finish the landscape within the driplines by maintaining the existing lawn. Maintain the existing
grades inside tree protection areas. Keep large plantings, irrigation trenching and construction of
hardscapes outside of tree protection areas. All landscape work within the tree protection zone shall be
completed by hand-labor only.
Tree Protection Measures
The following guidelines are recommended to ensure that the designated space set aside for the
retained trees is protected and construction impacts are kept to a minimum. Tree Protection Standards
have been set forth under RMC 4-4-130 H. Performance Standards for Land Development/Building
Permits; 9. Protection Measures During Construction. Review this code section prior to the start of
work.
• Tree protection fencing shall be erected per prior to moving any heavy equipment on site. Doing
this will set clearing limits and avoid compaction of soils within root zones of retained trees.
• Excavation limits shall be laid out in paint on the ground to avoid over excavating.
• To establish sub grade for foundations, curbs and pavement sections near the trees, soil should
be removed parallel to the roots and not at 90-degree angles to avoid breaking and tearing
roots that lead back to the trunk within the drip-line. Any roots damaged during these
excavations should be exposed to sound tissue and cut cleanly with a saw.
• Areas excavated within the drip-line of retained trees should be thoroughly irrigated weekly
during dry periods.
Arborist Report – 702 Nile Ave NE
Page 6 Layton Tree Consulting LLC April 14, 2022
Updated October 26, 2022
• Preparations for final landscaping shall be accomplished by hand within the drip-lines of
retained trees. Large equipment shall be kept outside of the tree protection zones at all times.
Tree Density-Tree Replacement - Updated
Consult with your City planner on final tree replacement/landscape requirements. Per the following
code sections as underlined below.
H. PERFORMANCE STANDARDS FOR LAND DEVELOPMENT PERMITS:
1. Protected Trees: Trees required to be retained or planted pursuant to this subsection H1 are
considered protected trees, as defined in RMC 4-11-200, Definitions T. Protected trees shall be retained
or planted as follows:
a. Minimum Tree Retention Requirements: Properties subject to an active land development permit
shall retain a minimum of thirty percent (30%) of all significant trees on site.
b. Tree Credit Requirements: With the exception of interior remodels not involving any building
addition, removal of trees, or alteration of impervious areas, properties subject to an active land
development permit shall comply with all of the following minimum tree credit requirements, and apply
the tree credit value table in subsection H1bv of this Section:
i. Tree credit requirements shall apply at a minimum rate of thirty (30) credits per net acre.
ii. Either tree retention or a combination of tree retention and supplemental tree planting (with new
small, medium, or large tree species) shall be provided to meet or exceed the minimum tree credits
required for the site.
iii. Supplemental tree planting shall consist of new small, medium, or large species trees, as defined in
RMC 4-11-200, Definitions T. The supplemental trees shall be planted with a minimum size of two-inch
(2") caliper, or evergreen trees with a minimum size of six feet (6') tall. The Administrator shall have the
authority to approve, deny, or restrict the tree species for proposed supplemental trees.
iv. Within subdivisions, location of supplemental tree replanting shall be prioritized within tree tract(s)
versus individual lots.
v. Tree credit value for each tree, existing or new, is assigned as shown in the following table:
e. Replacement Requirements: As an alternative to retaining trees, the Administrator may authorize the
planting of replacement trees on the site if it can be demonstrated to the Administrator’s satisfaction
that an insufficient number of trees can be retained.
i. Replacement Criteria: Replacement planting in lieu of minimum tree retention may be granted for
situations where:
Arborist Report – 702 Nile Ave NE
Page 7 Layton Tree Consulting LLC April 14, 2022
Updated October 26, 2022
(a) There are special circumstances related to the size, shape, topography, location, or surroundings of
the subject property; or
(b) The strict application of the code would prevent reasonable use of property; or
(c) The strict application of the code would prevent compliance with minimum density requirements of
the zone; or
(d) The project is a short plat with four (4) or fewer lots.
ii. Replacement Quantity and Standards: When the minimum number of protected trees cannot be
retained, replacement trees with at least a two-inch (2") caliper, or evergreen trees at least six feet (6')
tall, shall be planted based on the tree credit value of each protected tree removed pursuant to the
table shown in subsection H1b of this Section. The protected trees used for calculating required credit
replacement shall be determined based on the priority order of the significant trees proposed for
removal on site. Replacement trees shall not contribute to the total credits required pursuant to
subsection H1b of this Section. The City may require a surety or bond to ensure the survival of
replacement trees.
iii. Replacement Tree Species: The Administrator shall have the authority to approve, deny, or restrict
the tree species for proposed replacement trees.
f. Fee in Lieu: When the Administrator determines that it is infeasible to replace or supplement trees on
the site, payment into the City’s Urban Forestry Program fund may be approved in an amount of money
approximating the current market value of the replacement trees and the labor to install them. The City
shall determine the value of replacement trees.
Minimum Tree Density is 30 tree credits per net acre. The property is 31,996 sq.ft. requiring a minimum
of 22 tree credits. To satisfy the tree density requirement, the planting of 10 new medium species
(worth 1 tree credit each) and 6 new large species (worth 2 tree credits each) is recommended.
The City’s approved tree list is attached. Replacement tree species shall be chosen from this list. Plant
new trees in areas where they can fully mature without conflicting with new improvements. Work with
a landscape architect to select species and locations appropriate for the site. Consult with your city
planner on final tree replacement requirements and species selections.
Arborist Report – 702 Nile Ave NE
Page 8 Layton Tree Consulting LLC April 14, 2022
Updated October 26, 2022
Arborist Disclosure Statement
Arborists are tree specialists who use their education, knowledge, training and experience to examine
and assess trees, recommend measures to enhance the beauty and health of trees, and attempt to
reduce the risks associated with living near trees. Clients may choose to accept or disregard the
recommendations of the arborist, or to seek additional advice.
Arborists cannot detect every condition that could possibly lead to the structural failure of a tree. Trees
are living organisms that grow, respond to their environment, mature, decline and sometimes fail in
ways we do not fully understand. Conditions are often hidden within trees and below ground.
Arborists cannot guarantee that a tree will be healthy and/or safe under all circumstances, or for a
specified period of time. Likewise, remedial treatments, like any medicine, cannot be guaranteed.
Treatment, pruning and removal of trees may involve considerations beyond the scope of the arborist’s
services such as property boundaries, property ownership, site lines, disputes between neighbors, and
other issues. Arborists cannot take such considerations into account unless complete and accurate
information is disclosed to the arborist. An arborist should then be expected to reasonably rely upon
the completeness and accuracy of the information provided.
Trees can be managed, but they cannot be controlled. To live near trees is to accept some degree of
risk. The only way to eliminate all risk associated with trees is to eliminate all trees
Arborist Report – 702 Nile Ave NE
Page 9 Layton Tree Consulting LLC April 14, 2022
Updated October 26, 2022
Photo Documentation
Tree #1 on left, #2 on right
Looking west across back of property, Tree #952 on immediate left
Arborist Report – 702 Nile Ave NE
Page 10 Layton Tree Consulting LLC April 14, 2022
Updated October 26, 2022
Looking east across back of property, Tree #947 in foreground
Looking east at off-site trees in access tract
Arborist Report – 702 Nile Ave NE
Page 11 Layton Tree Consulting LLC April 14, 2022
Updated October 26, 2022
Tree #951 – lower trunk, extensive decay
Tree #953 – lower trunk, extensive decay
Arborist Report – 702 Nile Ave NE
Page 12 Layton Tree Consulting LLC April 14, 2022
Updated October 26, 2022
NE 7th PL ROW adjacent to subject property
Nile Ave NE ROW adjacent to subject property
Layton Tree Consulting LLC
For:Sierra Homes
Site:702 Nile Ave NE - Renton
Tree Summary Table
Date:
Tree/DBH Height
Tag #Species (inches)(feet)Condition Comments Proposal
N S E W
1 pear 10 15 4 8 8 4 Fair recently cut back Remove
2 cherry-fruit 6 14 7 5 8 7 Fair decent form Remove
952 apple 17,15 (23)25 15 16 17 18 Fair typical, moderate trunk decay Remove
949 apple *13 18 13 10 10 11 Fair typical, decent form Remove
947 apple *12 21 11 10 12 12 Fair typical, moderate trunk decay Remove
Neighboring/Off-site Trees
946 apple 12,9 (15)27 11 15 12 13 Fair typical, moderate trunk decay Protect
948 apple 9 22 5 12 8 4 Fair poor form Protect
950 apple *22 29 13 13 12 15 Fair typical, moderate trunk decay Protect
951 apple *26 31 8 15 17 13 Poor extensive trunk decay, low risk Protect
953 apple 18 25 6 13 12 12 Poor extensive trunk decay, low risk Protect
Dripline measurements from face of trunk
* - caliper measurement at one-foot above ground
Drip-Line / Limits of Disturbance
(feet)
4/6/2022
Calculated DBH: the DBH is parenthesis is the square root of the sum of the dbh for each
individual stem squared (example with 3 stems: dbh = square root [(stem1)2 +(stem2)2
APPROVED TREE LIST – Small, Medium, and Large
H:\CED\Data\Forms-Templates\Self-Help Handouts\Planning\treeslist_march2010.doc P. 1
In the City of Renton there is an overabundance of maple and cherry species. According to the most recent street tree inventory, maples
currently comprise 35% and cherry 24% of all species. To reduce a catastrophic loss of species, experts agree that 10% o r less of any species
or cultivar exist within a street tree population. Because of this, planting maple or cherry trees within the right -of-way is discouraged.
SMALL TREES:
30 feet in height or less
Botanical name / Common Name
Mature
Height
in Feet
Mature
Spread
in Feet Fall Color Comments
Acer buergeranum / Trident Maple 20 20
yellow
orange
and red
Adaptable to urban environments. Decidiuous: prefers moist, well-drained soils:
tolerates infertile sites. Drought tolerant.
Acer campestre / Hedge Maple 30 30 yellow
Deciduous; prefers moist, rich soils; slow growing tree tolerant of air pollution
and soil compaction; yellow fall color; cultivars available including Queen
Elizabeth maple (‘Evelyn’) with dark green, glossy foliage.
Acer circinatum / Vine Maple 20-25 10
orange
and red
Deciduous; prefers moist, well-drained soils; tolerates seasonal saturation and
varying soil types; drought tolerant once established; bushy shrub or small tree;
most often multi-trunked and does well in small groups; white flowers April-
June.
Acer ginnala 'Flame' / Amur Maple 20 20 red
Deciduous; prefers moist, well-drained soils, but is tolerant of drought; is often
multi-trunked, but can be pruned to a single stem; rounded form; fragrant,
yellowish-white flowers in spring; cultivars are available such as ‘Flame’ and
‘Embers’ with differing fall colors. Select or prune for single stem; can be multi-
trunked.
Acer grandidentatum 'Schmidt' / Rocky Mt.
Glow Maple 25+ 15 intense
Acer griseum / Paperback Maple 25 20 scarlet
Deciduous; prefers moist, well-drained soils, but is moderately drought tolerant;
bronze peeling bark provides year-round visual interest; often multitrunked, but
can be trained to a single stem; slow growing; disease and pest resistant.
Smooth, peeling, cinnamon colored bark.
APPROVED TREE LIST – Small, Medium, and Large
H:\CED\Data\Forms-Templates\Self-Help Handouts\Planning\treeslist_march2010.doc P. 2
Botanical name / Common Name
Mature
Height
in Feet
Mature
Spread
in Feet Fall Color Comments
Acer palmatum / Japanese Maple 20 24
yellow,
orange,
red
Prefers moist, well-drained soils; deciduous; slow to moderate growth rate;
multi-trunked with spreading branches; intolerant of inundation but moderately
drought resistant; vibrant fall colors; many cultivars available including ‘Emperor
I’, ‘Katsura’, and ‘Osakazuki’. Hundreds of varied cultivars. Can be slow growing.
Acer saccharum 'Apollo' 25 10
yellow,
orange Prefers well drained soils, but grows in varying soils; hearty.
Acer platanoides 'Globosum' / Globe
Norway Maple 20 18 yellow
Moist soils preferred, but tolerates drought and seasonal inundation; tolerant of
urban pollution; dense, compact, round form; slow-growing deciduous tree with
brilliant fall color; shallow root system may make mowing under the tree slightly
difficult; good selection for locations under power lines; another cultivar well
suited for such a location is A. platanoides ‘Almira,’ reaching only 20-25 ft.
Rounded top, and compact growth.
Acer truncatum / Purpleblow maple 20-25 20-25
Prefers moist, well-drained soil, but drought tolerant; very cold hardy deciduous
tree; moderate growth rate; yellow flowers in spring; an additional maple
cultivar of interest is 'Pacific sunset'.
Acer truncatum x A. platanoides 'Warren's
Red' / Pacific Sunset 30 25
yellow-
orange/
red
Acer Triflorum - Roughbark maple 25-30 20-25
apricot,
gold
Deciduous; prefers moist soils, but somewhat drought tolerant once established;
rough, knobby trunk provides interest in winter; disease and pest resistant; non-
aggressive roots do not damage sidewalks or driveways.
Amelanchier grandiflora 'Princess Diana' 20 15 bright red Good for limited space.
Amelanchier x grandiflora 'Autumn
Brilliance' Serviceberry 20 15
red or
yellow
Moist to dry, well-drained soils; small tree; drought tolerant; white clustered
flowers in spring; also try 'Princess Diana' for bright red fall color and the slightly
taller 'Robin Hill' (20-30 feet). Reliable bloom.
Amelanchier laevis ' lustre' / Luster
Serviceberry 25 25
red or
yellow
Moist to dry, well-drained soils; small tree; drought tolerant; white clustered
flowers in spring.
APPROVED TREE LIST – Small, Medium, and Large
H:\CED\Data\Forms-Templates\Self-Help Handouts\Planning\treeslist_march2010.doc P. 3
Botanical name / Common Name
Mature
Height
in Feet
Mature
Spread
in Feet Fall Color Comments
Arbutus 'Marina' 25 15 evergreen
Good substitute for Pacific Madrone. May exceed 25' height under some site
conditions.
Carpinus caroliniana / American hornbeam 20-30 20-20
Deciduous; prefers moist, rich soils; grows near saturated areas but is only
weakly tolerant of saturation; blooms March-May; slow growing; deep coarse
laterally spreading roots; medium life span; also consider Carpinus japonica
(Japanese hornbeam).
Cercis canadensis / Eastern Redbud 25 30 yellow
Deciduous; prefers moist, rich soils; tolerant of shade; somewhat drought
resistant, but not in full sun; purple-lavender flowers; medium longevity; often
multi-trunked; shallow, fibrous roots become deeper on drier sites; fairly short-
lived; blooms March-May. Blooms before leaves are out.
Cornus kousa 'Chinensis' / Chinese Kousa
Dogwood 20 20
reddish to
scarlet
Prefers moist soils; tolerant of varying soil types; moderate growth rate;
deciduous; white flowers in June and large red fruits that resemble a raspberry
in September; red to maroon fall color; more disease resistant than other
dogwoods; many additional cultivars available. Most resistant to disease of the
dogwoods.
Crataegus crus-galli 'Inermis' / Thornless
Cockspur Hawthorn 25 30
orange to
scarlet Red persistent fruit.
Crataegus x lavalii / Lavalle Hawthorne 28 20
bronze,
coppery
red
Deciduous; prefers moist, well-drained soil, but tolerant of varying soil types;
white flowers in spring; fruit can be a bit messy. Thorns on younger trees.
Crataegus phaenopyrum / Washington
Hawthorn 25 20 scarlet Thorny.
Fraxinus pennsylvanica 'Johnson' /
Leprechaun Ash 18 16 yellow
Prefers moist, well-drained soils; deciduous: slow to moderate growth rate;
tolerant of inundation but moderately drought resistant. A miniature in every
way.
Magnolia x loebneri 20 20 yellow Several cultivars.
Magnolia grandiflora 'Little Gem' 15 10 evergreen Useful where larger varieties are inappropriate.
Magnolia grandiflora 'Victoria' 25 20 evergreen
APPROVED TREE LIST – Small, Medium, and Large
H:\CED\Data\Forms-Templates\Self-Help Handouts\Planning\treeslist_march2010.doc P. 4
Botanical name / Common Name
Mature
Height
in Feet
Mature
Spread
in Feet Fall Color Comments
Malus spp. / Flowering crabapple 15-25 6-15
Selection should be based on disease resistance to apple scab and fireblight.
Tolerant of prolonged soil saturation; short lived; tolerant of drought and
seasonally saturated soils; deciduous; white or faintly pink flowers in spring;
numerous Malus species and cultivars provide a variety of foliage and flower
colors, forms and fruit.
Malus 'Adirondack' 18 8 yellow Red fruit. Excellent scab resistance.
Malus 'Red Barron' 18 8 yellow Good for narrow spaces. Red berries.
Malus 'Golden Raindrops' 18 13 yellow Abundant yellow fruit.
Malus 'Tschonoskii' 28 14 scarlet Sparse green fruit, pyramidal.
Parrotia persica / Persian Parrotia 30 20
yellow-
orange
red
Moist to dry soils; drought tolerant when established, deciduous tree with
moderate growth rate; brilliant fall color; often multi-trunked, but can be
trained to have just one; tolerates urban pollution and soil compaction; surface
roots do not generally cause problems; virtually disease and pest-free.
Pranus 'Frankthrees' / Mt. St. Helens Plum 20 20 Purple foliage.
Prunus 'Newport' / Newport Plum 20 20
reddish to
scarlet Purple red foliage.
Prunus cerasifera 'Krauter Vesuvius' /
Flowering Plum 30 15 Upright growth, darkest foliage of the plums.
Prunus cerasifera 'Thundercloud' / Plum 20 20 Dark purple foliage.
Prunus x hillieri 'Spire' 30 10
orange
red
Prunus 'Snowgoose' / Snow Goose Cherry 20 20 Upright when young, spreading when older.
Prunus serrulata 'Amanogawa' / Flowering
Cherry 20 6 bronze Particularly useful for very narrow planting strips.
Prunus serrulata 'Shirofugen' / Japanese
flowering cherry 25 25
Deciduous flowering tree; moist, well-drained soils; double pink to white blooms
in spring; vigorous grower; additional desirable choices include P. serrulata
‘Snowgoose’, ‘Kwanzan’, and ‘Shirotae’.
Prunus x yedoensis 'Akebono' / Flowering
Cherry 25 25 yellow
APPROVED TREE LIST – Small, Medium, and Large
H:\CED\Data\Forms-Templates\Self-Help Handouts\Planning\treeslist_march2010.doc P. 5
Botanical name / Common Name
Mature
Height
in Feet
Mature
Spread
in Feet Fall Color Comments
Quercus Ilex / Holly Oak 20 20
Prefers moist soils, but grows in varying soils; hearty, slow-growing evergreen
tree; light pink flowers May-June; pruning will keep tree small for a hedge,
without pruning may grow considerably larger – not appropriate under utility
lines; tolerates salt water spray. Prune to keep small, leave it alone to grow
large.
Styrax japonica / Japanese Snowbell 25 25 yellow Plentiful, green 1/2 inch seeds.
Styrax obassia / Fragrant Snowbell 30 25
Prefers moist, well-drained soil but tolerates wide variations; fragrant with
flowers; twisting bark. Try other Styrax species.
APPROVED TREE LIST – Small, Medium, and Large
H:\CED\Data\Forms-Templates\Self-Help Handouts\Planning\treeslist_march2010.doc P. 6
MEDIUM TREES:
30 to 50 feet in height
Botanical name / Common Name
Mature
Height
in Feet
Mature
Spread
in Feet Fall Color Comments
Acer campestre 'Evelyn' / Queen Elizabeth
Maple 35 30 yellow More upright branching than the species.
Acer platanoides 'Columnar' / Columnar
Norway maple 40 15 yellow
Deciduous; adapts to varying soils; upright or columnar in form making this
cultivar a better choice for narrow locations; tolerant of drought and seasonal
inundation; tolerates urban pollution and displays brilliant fall color; shallow
rooting necessitates locating at least 4-6 feet from sidewalks and driveways to
prevent heaving of pavement. Good close to buildings.
Acer truncatum x A. platanoides
'Klethsform' / Norwegian Sunset 35 25
yellow-
orange/
red
Acer rubrum 'Bowhall' / Bowhall Maple 40 15
yellow
orange
Acer rubrum 'Karpick' / Karpick Maple 35-40 20
yellow to
orange May work under very high powerlines with arborist's approval.
Acer rubrum 'Scarsen' / Scarlet Sentinel
Maple 40 20
yellow
orange
Acer rubrum / Red Maple 35-50 15-40
Deciduous tree known for fall color; prefer wet or moist soils; fast growing with
roots that may heave sidewalks or interfere with mowing; many cultivars of
varying heights available including: A. rubrum, 'Armstrong', 'Bowhall', 'Karpick',
'Scarsen', and 'Red Sunset'.
Betula jacquemontii / Jacquemontii Birch 40 30 yellow White bark makes for good winter interest.
Carpinus betulus 'Fastigiati' / Pyramidal
European Hornbeam 35 25 yellow
Fagus sylvatica 'Dawyck Purple' / Dawyck
Purple Beech 40 12
Purple foliage.
APPROVED TREE LIST – Small, Medium, and Large
H:\CED\Data\Forms-Templates\Self-Help Handouts\Planning\treeslist_march2010.doc P. 7
Botanical name / Common Name
Mature
Height
in Feet
Mature
Spread
in Feet Fall Color Comments
Fraxinus americana 'Autumn Applause' /
Ash 40 25 purple
Deciduous; prefers moist, well-drained soils; dense, wide spreading canopy;
long-lived; purple fall color; moderate growth rate; also try F. Americana
'Junginger'.
Fraxinus oxycarpa 'Raywood' / Raywood
Ash 35 25
reddish
purple
Pyrus calleryana 'Aristocrat' / Pear 40 45 red
Pyrus calleryana 'Chanticleer' / Flowring
Pear 40 15
Deciduous tree that grows well in a variety of soil types; orange to reddish fall
color; white flowers in spring; additional cultivars of interest include P.
calleryana 'Redspire' and 'Aristocrat'.
Pyrus calleryana 'Redspire' / Pear 40 45 red
Pyrus calleryana 'Autumn Blaze' / Pear 30 25 scarlet Vigorous.
Ginko biloba 'Autumn Gold' / Maidenhair
tree 45 35 yellow
Moist soils; deciduous ornamental tree; fast growing and long-lived; tolerant of
urban pollution, summer drought and winter inundation; showy fall color; grows
in soils of varying quality; provides dense canopy; additional cultivars available.
Ginko biloba 'Princeton Sentry' 40 15 yellow Very narrow growth.
Gleditsia triacanthos inermis 'Shademaster'
/ Shademaster Thornless Honeylocust 45 35 yellow
Deciduous; prefers moist, rich soils, but will grow in varying soil types; a
thornless cultivar tolerant of drought and seasonal inundation; adapts to urban
pollution and displays vigorous growth; deciduous tree with showy yellow fall
color; additional cultivars available such as ‘Imperial,’ which grows 30-35 feet,
‘Moraine,’ and ‘Rubylace’. Do not confuse with 'Sunburst'.
Koelreuteria paniculata / Goldenrain Tree 20-35 10-30 yellow
Deciduous; prefers moist well-drained soils, but is tolerant of poor soils; medium
rate of growth and longevity; tolerant of periods of drought and seasonal
inundation; tolerates urban pollution; provides a dense, wide-spreading canopy.
Midsummer blooming.
Oxydendron arboreum / Sourwood 35 12
reddish
purple Consistent and brilliant fall color.
Prunus sargentii 'Columnarus' 35 15
orange to
orange
red The cherry with the best fall color.
APPROVED TREE LIST – Small, Medium, and Large
H:\CED\Data\Forms-Templates\Self-Help Handouts\Planning\treeslist_march2010.doc P. 8
Botanical name / Common Name
Mature
Height
in Feet
Mature
Spread
in Feet Fall Color Comments
Quercus 'Crimschmidt' / Crimson Spire Oak 45 15 Hard to find.
Robinia x ambigua 'Idahoensis' / Pink Idaho
Locust 35 25 yellow Fragrant flowers.
Tilia americana 'Redmond' 35 20 yellow Pyramidal, needs water.
Tilia cordata 'Chancole' / Chancelor Linden 35 20 yellow Pyramidal.
Tilia cordata 'De Groot' / Linden 30-50 20 yellow Compact, suckers less than other Lindens.
Tilia cordata 'Greenspire' / Greenspire
Linden 40 30 yellowish Symmetrical pyramidal form.
Tilia cordata 'Littleleaf' / Littleleaf Linden 30-50 30
Deciduous; prefers moist, well-drained soils, but tolerant of a variety of soil
types; tolerant of wind and urban pollution; fast growing and long-lived;
tolerates summer drought and seasonal inundation; provides a dense canopy; C.
cordata is the hardiest Linden; many forms available including, T. cordata
‘Chancellor’, ‘Corzam’, and ’Greenspire’.
APPROVED TREE LIST – Small, Medium, and Large
H:\CED\Data\Forms-Templates\Self-Help Handouts\Planning\treeslist_march2010.doc P. 9
LARGE TREES:
50 feet in height or taller
Botanical name / Common Name
Mature
Height
in Feet
Mature
Spread
in Feet Fall Color Comments
Acer freemanli / Autumn Blaze Maple 50 40 orange
Abies grandis / Grand Fir 100 40
Evergreen; tolerant of fluctuating water tables and floods; medium rate of
growth; root structure depends on site conditions – shallow in moist areas, deep
taproot in drier conditions.
Acer nigrum 'Green Colunm' / Green
Column Maple 50 20
yellow to
orange Good close to buildings.
Acer platanoides 'Emerald Queen' 50 40 yellow
Deciduous; fast growing with an erect, spreading form; prefers moist soils, but is
tolerant of summer drought and seasonal inundation; tolerates urban pollution;
avoid locating near structures due to shallow, vigorous rooting; additional
cultivars available including A. platanoids ‘Parkway’.
Acer pseudoplatanus / Sycamore maple 40-60 25-40
Deciduous; prefers moist, well-drained soils but is adaptable to may soil types;
tolerates summer drought and seasonal inundation; tolerant of urban pollution
with a moderate growth rate; sturdy, resistant to wind and salt spray; a number
of cultivars are available including: A. pseudoplatanus ‘Atropurpureum,’ ‘
Brilliantissimum,’ ‘Cox’ (Lustre), and ‘Puget Pink’.
Acer saccharum 'Bonfire' 50 40
bright
orange
red Fastest growing sugar maple.
Acer saccharum 'Commemoration' 50 35
orange to
orange-
red Resistant to leaf tatter.
Acer saccharum 'Green Mountain' 45 35
red to
orange
Acer saccharum / Sugar maple 60-75 35
yellow,
orange
Deciduous; prefers moderately moist, well-drained soils; long-lived and tolerant
of urban pollutants; slow to medium growth rate; needs large planting area; a
variety of cultivars available including Acer saccharum ‘Legacy’.
APPROVED TREE LIST – Small, Medium, and Large
H:\CED\Data\Forms-Templates\Self-Help Handouts\Planning\treeslist_march2010.doc P. 10
Botanical name / Common Name
Mature
Height
in Feet
Mature
Spread
in Feet Fall Color Comments
Calocedrus decurrens / Incense cedar 75-90 10-20
Evergreen; tolerant of poor soils; drought tolerant after established; tolerant of
wind and urban conditions; narrow growth habit makes this a good choice for
smaller spaces and ideal for screening, fragrant tree; slow growing and long-
lived.
Carpinus betulus / European Hornbeam 40-60 30-40
Deciduous tree: tolerant of urban pollution and poor soils; cultivars available
and suggested include 'Fasigiata' (30-40 ft height) and 'Franz Fontaine' (30-35 ft
height).
Cedrus deodara / Deodar cedar 40-60 20-40
Evergreen; prefers moist, well-drained soils, but drought tolerant when
established; fairly fast growing and long lived; dense, wide spreading canopy;
attractive cultivars available.
Cercidiphyllum japonicum / Katsura Tree 40-60 20-40
apricot,
orange
Deciduous; requires moist soil and does not do well on hot dry sites. Leaves are
heart-shaped.
Cercidiphyllum japonicum / Katsura Tree 40 40
yellow to
orange
Fagus sylvatica / Green Beech 50 40 bronze Silvery-grey bark.
Fraxinus american 'Autumn Purple' /
Autumn Purple White Ash 60-80 50-70
to a dark
purple
Deciduous; prefers moist well-drained soils but tolerates a range of soil types;
Also try 'Rosehill'.
Fraxinus latifolia / Oregon Ash 40-80 30
Deciduous; saturated, ponded or moist soils; flood tolerant; small green-white
flowers; tolerant of poor soils.
Fraxinus pennsylvanica / Green Ash 50 40
Deciduous; prefers moist soils; fast growth rate; salt, seasonal drought and
urban pollution; numerous cultivars including'Patmore' (50-60 ft. height),
'Summit' (to 45 ft. height), and 'Urbanite' (to 50 ft. height).
Fraxinus pennsylvanica 'Patmore' /
Patmore Ash 45 35 yellow Extremely hardy, may be seedless.
Fraxinus pennsylvanica 'Urbanite' / Ash 50 40
deep
bronze
Gleditsia triacanthos inermis 'Skyline' /
Skyline Thornless Honeylocust 60-70 40 yellow
Deciduous; prefers moist soils, but will grow in poor soils; tolerant of drought,
seasonal inundation, and urban pollution; occasionally fruit pods can create
litter during winter months; thornless. Do not confuse with 'Sunburst'.
APPROVED TREE LIST – Small, Medium, and Large
H:\CED\Data\Forms-Templates\Self-Help Handouts\Planning\treeslist_march2010.doc P. 11
Botanical name / Common Name
Mature
Height
in Feet
Mature
Spread
in Feet Fall Color Comments
Gymnocladus dioicus espresso / Espresso
Kentucky Coffeetree 50 35 yellow Deciduous; drought and variable soil tolerant; seedless.
Liquidamber styraci fleia / American
sweetgum 60-75 40
Deciduous; prefers moist well-drained soils but tolerant of poor soils; drought
tolerant after established; avoid major roadways and restricted sites. Many
cultivars available.
Liriodendron tulipifera / Tulip Tree 60-80 30-60 yellow
Deciduous; prefers moist, deep, well-drained soils, but tolerates poor soils; fast
growing; needs large growing area, lower growing cultivars available such as
'Columnar'. Fast-growing tree.
Metasequoia glyptostoboides / Dawn
redwood 70-100 25
Deciduous; prefers moist, deep, well-drained soils, but tolerates compacted and
poor soils; long-lived, fast growing conifer; tolerant of seasonal inundation and
drought; can grow in standing water; needles turn russet in the fall; needs large
growing area; lower growing cultivars available such as M. glyptostroboides
‘Gold Rush’ and ‘Sheridan Spire’.
Nothofagus antartica / Southern Beech 50 35 none Rugged twisted branching and petite foliage.
Nyssa sylvatica / Tupelo 70+ 20
apricot to
bright red Handsomely chunky bark.
Picca omorika / Serbian spruce 50-60 20-25
Slow growing; tolerant of varying soils and urban pollution; moderately drought
tolerant once established; elegant evergreen spruce, good for narrow locations;
lower growing cultivars available.
Pseudotsuga menziesii / Douglas fir 75-120 40
Evergreen conifer; moist to dry soils; long-lived with a medium to fast rate of
growth; tolerant of summer drought, winter inundation, and poor soils;
withstands wind and urban pollution; provides a nice canopy, but potential
height will restrict placement.
Quercus coccinea / Scarlet oak 50-60 45
brilliant
scarlet to
red
Deciduous; grows in a variety of soil types; long-lived with a moderate growth
rate; tolerant of summer drought and urban pollution; does not tolerate
saturated soils or shade.
APPROVED TREE LIST – Small, Medium, and Large
H:\CED\Data\Forms-Templates\Self-Help Handouts\Planning\treeslist_march2010.doc P. 12
Botanical name / Common Name
Mature
Height
in Feet
Mature
Spread
in Feet Fall Color Comments
Quercus macrocarpa / Burr oak 70-80 30-40
Prefers moist soils, but is adaptable to varying soils; slow growing and long-lived;
rugged looking deciduous tree; tolerant of seasonal drought and inundation;
tolerates urban pollution and city conditions; provides a wide-spreading, dense
canopy.
Quercus phellos / Willow oak 60-70 50
Deciduous; prefers moist, well-drained soils, but grows in a wide range of soils
types; long-lived tree with moderate growth rate and fibrous root system;
tolerant of seasonal drought and inundation, as well as urban pollution; provides
a wide-spreading, dense canopy; small delicate leaves.
Quercus palustris 'Crownright' 80 40 More upright form of Pin Oak.
Quercus robar / English oak 40-60+ 40
Prefers well-drained soil; slow to moderate growth rate; long-lived deciduous
tree; tolerant of seasonal drought and inundation; tolerates urban pollution,
poor soils and constrained root space; susceptible to powdery mildew; many
varieties and cultivars available including: ‘Concordia,’ ‘Fastigiata,’ ‘Foliis
Variegatis, and ’Westminster Globe.’
Quercus rubra / Northern red oak 60-75 50
Prefers moist, well-drained soils, but drought tolerant when established;
tolerates seasonal inundation, urban pollution and salt spray; moderate rate of
growth and longevity; provides a dense, wide-spreading canopy; susceptible to
oak wilt fungus.
Quercus shumardii / Shumard's oak to 70 50
Prefers moist, well-drained soils; deciduous, long-lived tree; tolerant of seasonal
drought and inundation, urban pollution and poor soils.
Taxodium distichum / Bald cypress to 75 40
Deciduous conifer; wet, mucky soils; tolerant of summer drought and seasonal
flooding; will grow in poor soils; slow growing; long-lived with a wide-spreading
canopy; roots do not appear to lift sidewalks as readily as other species; prune
lower branches for sight-lines; cultivars include T. distichum ‘Shawnee Brave’.
Thuja plicata / Western red cedar 200+ 60
Moist to swampy soils; evergreen tree tolerant of seasonal flooding and
saturated soils; a good tree for screening; long-lived; cultivars ‘Pumilio’ and
‘Cuprea’ are shorter versions, ‘Aurea’ and ‘Atrovirens’ have distinctive foliage.
Tilia americana x euchlora 'Redmond' /
Redmond Linden 50 35 yellow
Prefers moist, rich soils, but tolerant of a variety of soils; tolerant of seasonal
drought and inundation, urban pollution and poor soils; deciduous tree
resistant; also try 'Sentry' and 'Boulevard'.
APPROVED TREE LIST – Small, Medium, and Large
H:\CED\Data\Forms-Templates\Self-Help Handouts\Planning\treeslist_march2010.doc P. 13
Botanical name / Common Name
Mature
Height
in Feet
Mature
Spread
in Feet Fall Color Comments
Tilia plalyphyllos / Bigleaf linden 60-80 60
Prefers moist, well-drained soils, but grows in a variety of soil types; deciduous
tree with medium growth rate; long-lived; tolerant of seasonal drought and
inundation; tolerates urban pollutants; provides a wide-spreading, dense
canopy; yellowish-white flowers attract bees.
Tilia tomentosa / Silver Linden 40-75 25-45
Deciduous; prefers moist, well-drained soils, but drought tolerant when
established; urban tolerant. Cultivars include 'sterlay' and 'Green Mountain'.
Ulmus ssp. / Elm hybrids 50-60 35-50 yellow
Deciduous; prefers moist, well-drained soils, but drought tolerant; rapid grower;
a hybrid elm resistant to Dutch elm disease; suggested hybrids include
‘Accolade’, ‘Homestead’ and ‘Pioneer’.
Ulmus 'Homestead' / Homestead Elm 60 35 yellow
Ulmus parvifolia / Lace Bark Elm 50 40
Deciduous; prefers moist, well drained soils but tolerant of soil types and hot dry
conditions. Flaking bark of orange, gray, green and brown color. Several cultivars
including 'Allee' and 'Bosque'.
Ulmus 'Pioneer' / Pioneer Elm 60 50 yellow Resistant to Dutch elm disease.
Umbellularia californica / Oregon myrtle 40-75+ to 50
Prefers moist, well-drained soils; slow growing evergreen tree with aromatic
leaves; tolerates seasonal drought and inundation; tolerant of urban pollution;
provides a wide spreading, dense canopy; resistant to pests and disease; good
for tall hedges or, when trunks are thinned, as a street tree; requires summer
watering until established.
LAYTON TREE CONSULTING, LLC
It’s all about trees……
PO BOX 572, SNOHOMISH, WA 98291-0572 * 425-220-5711 * bob@laytontreeconsulting.com
TREES & CONSTRUCTION MEMO
To: Ian Dahl, Encompass Engineering
From: Bob Layton
CC: Dan Finkbeiner, Sierra Homes
Date: February 21, 2023
Re: 702 Nile Ave NE – Off-Site Tree Retention/Protection Memo
Dear Mr. Dahl,
I have reviewed the final site plan for the 702 Nile Avenue NE project and the city comments
regarding impacts to off-site apple Trees #946, #948 and #950. A snap-shot of the site plan is
attached.
In order to adequately protect the off-site apple trees, the detention tank will need to be shifted
3-feet north to provide a ‘no-disturbance’ or protection zone of 6-feet from the property line.
There will be some impacts to outer dripline areas on the north side but these are not expected
to have any adverse impacts on tree health. Apple trees are quite hardy and have good relative
tolerance to construction impacts. The condition of the subject trees is expected to remain
unchanged so long as the following protection measures are adhered to.
Protection Measures
Tree protection fencing shall be positioned around protected trees per the attached map prior
to site demolition or bringing any heavy equipment onto the site. This will help to define
clearing limits and protect soils and surface roots.
Soils shall be cut and pulled back away from the trees to avoid tearing and shredding roots
inside the protection area. Any roots from protected trees damaged during site work outside of
the tree protection areas shall be pruned clean at sound tissue prior to backfilling or finishing
areas. Sound tissue is where the root is undamaged and the bark is completely intact with the
root. This will help roots to seal off potential decay and allow them to sprout new growth. Any
February 21, 2023 702 Nile Ave NE – Tree Protection
Page 2 LAYTON TREE CONSULTING, LLC
disturbed areas near protected trees shall be watered weekly during the dry season of mid-May
through mid-October. Thoroughly water the outer dripline areas every 7 to 10 days to maintain
a favorable environment for new root growth and to reduce the degree of stress associated with
the site changes.
Equipment shall be kept outside of tree protection areas at all times. Any branches that are
damaged during site work shall be properly pruned.
Maintain the existing grades with the protection areas. Finish the landscape within the driplines
of protected trees by simply maintaining the existing lawn or covering the area within the
dripline with a +/- 4-inch layer of organic mulch. Keep irrigation trenches, large plantings or
other improvements outside of the tree protection areas.
Please let me know if you have any questions or need further assistance.
Sincerely,
Bob Layton
Registered Consulting Arborist #670
ISA Certified Arborist #PN-2714A
ISA Tree Risk Assessment Qualified
Attachments:
Snap-shot of Site Plan/Tree Plan Map
February 21, 2023 702 Nile Ave NE – Tree Protection
Page 3 LAYTON TREE CONSULTING, LLC
ARBORIST DISCLOSURE STATEMENT
Arborists are tree specialists who use their education, knowledge, training and experience to
examine and assess trees, recommend measures to enhance the beauty and health of trees, and
attempt to reduce the risks associated with living near trees. Clients may choose to accept or
disregard the recommendations of the arborist, or to seek additional advice.
Arborists cannot detect every condition that could possibly lead to the structural failure of a
tree. Trees are living organisms that grow, respond to their environment, mature, decline and
sometimes fail in ways we do not fully understand. Conditions are often hidden within trees
and below ground. Arborists cannot guarantee that a tree will be healthy and/or safe under all
circumstances, or for a specified period of time. Likewise, remedial treatments, like any
medicine, cannot be guaranteed.
Treatment, pruning and removal of trees may involve considerations beyond the scope of the
arborist’s services such as property boundaries, property ownership, site lines, disputes
between neighbors, and other issues. Arborists cannot take such considerations into account
unless complete and accurate information is disclosed to the arborist. An arborist should then
be expected to reasonably rely upon the completeness and accuracy of the information
provided.
Trees can be managed, but they cannot be controlled. To live near trees is to accept some
degree of risk. The only way to eliminate all risk associated with trees is to eliminate all trees.
Appendix D
WWHM Output
WWHM2012
PROJECT REPORT
21706 WWHM 3/1/2023 3:23:56 PM Page 2
General Model Information
Project Name:21706 WWHM
Site Name:
Site Address:
City:
Report Date:3/1/2023
Gage:Seatac
Data Start:1948/10/01
Data End:2009/09/30
Timestep:15 Minute
Precip Scale:1.167
Version Date:2021/08/18
Version:4.2.18
POC Thresholds
Low Flow Threshold for POC1:50 Percent of the 2 Year
High Flow Threshold for POC1:50 Year
21706 WWHM 3/1/2023 3:23:56 PM Page 3
Landuse Basin Data
Predeveloped Land Use
Basin 1
Bypass:No
GroundWater:No
Pervious Land Use acre
C, Forest, Flat 0.58
Pervious Total 0.58
Impervious Land Use acre
Impervious Total 0
Basin Total 0.58
Element Flows To:
Surface Interflow Groundwater
21706 WWHM 3/1/2023 3:23:56 PM Page 4
Mitigated Land Use
Basin 1
Bypass:No
GroundWater:No
Pervious Land Use acre
C, Lawn, Flat 0.28
Pervious Total 0.28
Impervious Land Use acre
ROOF TOPS FLAT 0.21
DRIVEWAYS FLAT 0.07
SIDEWALKS FLAT 0.02
Impervious Total 0.3
Basin Total 0.58
Element Flows To:
Surface Interflow Groundwater
Contech CMP 1 Contech CMP 1
21706 WWHM 3/1/2023 3:23:56 PM Page 5
Routing Elements
Predeveloped Routing
21706 WWHM 3/1/2023 3:23:56 PM Page 6
Mitigated Routing
Contech CMP 1
Element Flows To:
Outlet 1 Outlet 2
21706 WWHM 3/1/2023 3:23:56 PM Page 7
Analysis Results
POC 1
+ Predeveloped x Mitigated
Predeveloped Landuse Totals for POC #1
Total Pervious Area:0.58
Total Impervious Area:0
Mitigated Landuse Totals for POC #1
Total Pervious Area:0.28
Total Impervious Area:0.3
Flow Frequency Method:Log Pearson Type III 17B
Flow Frequency Return Periods for Predeveloped. POC #1
Return Period Flow(cfs)
2 year 0.022658
5 year 0.037355
10 year 0.048512
25 year 0.064104
50 year 0.07675
100 year 0.090241
Flow Frequency Return Periods for Mitigated. POC #1
Return Period Flow(cfs)
2 year 0.011987
5 year 0.01741
10 year 0.021864
25 year 0.028607
50 year 0.034531
100 year 0.041312
Annual Peaks
Annual Peaks for Predeveloped and Mitigated. POC #1
Year Predeveloped Mitigated
1949 0.028 0.010
1950 0.032 0.012
1951 0.047 0.030
1952 0.016 0.009
1953 0.013 0.011
1954 0.019 0.011
1955 0.029 0.011
1956 0.024 0.012
1957 0.022 0.011
1958 0.022 0.011
21706 WWHM 3/1/2023 3:24:29 PM Page 8
1959 0.019 0.010
1960 0.036 0.018
1961 0.018 0.012
1962 0.012 0.008
1963 0.018 0.011
1964 0.022 0.011
1965 0.017 0.012
1966 0.015 0.010
1967 0.034 0.011
1968 0.020 0.010
1969 0.019 0.010
1970 0.016 0.011
1971 0.021 0.011
1972 0.036 0.014
1973 0.017 0.012
1974 0.019 0.011
1975 0.027 0.011
1976 0.019 0.011
1977 0.007 0.009
1978 0.016 0.012
1979 0.010 0.008
1980 0.051 0.032
1981 0.015 0.011
1982 0.035 0.013
1983 0.024 0.011
1984 0.015 0.009
1985 0.009 0.010
1986 0.038 0.012
1987 0.035 0.013
1988 0.015 0.009
1989 0.009 0.010
1990 0.097 0.017
1991 0.044 0.014
1992 0.018 0.012
1993 0.018 0.009
1994 0.007 0.008
1995 0.024 0.012
1996 0.055 0.031
1997 0.044 0.049
1998 0.016 0.010
1999 0.060 0.015
2000 0.017 0.012
2001 0.004 0.008
2002 0.024 0.013
2003 0.032 0.010
2004 0.037 0.027
2005 0.025 0.011
2006 0.025 0.012
2007 0.072 0.054
2008 0.076 0.032
2009 0.034 0.012
Ranked Annual Peaks
Ranked Annual Peaks for Predeveloped and Mitigated. POC #1
Rank Predeveloped Mitigated
1 0.0970 0.0536
2 0.0763 0.0487
3 0.0718 0.0318
21706 WWHM 3/1/2023 3:24:29 PM Page 9
4 0.0604 0.0318
5 0.0553 0.0309
6 0.0507 0.0296
7 0.0466 0.0268
8 0.0437 0.0175
9 0.0437 0.0172
10 0.0379 0.0149
11 0.0374 0.0140
12 0.0362 0.0140
13 0.0356 0.0134
14 0.0352 0.0131
15 0.0348 0.0129
16 0.0344 0.0125
17 0.0343 0.0124
18 0.0324 0.0124
19 0.0323 0.0124
20 0.0294 0.0124
21 0.0277 0.0123
22 0.0270 0.0118
23 0.0255 0.0118
24 0.0246 0.0118
25 0.0242 0.0117
26 0.0239 0.0117
27 0.0235 0.0116
28 0.0235 0.0114
29 0.0222 0.0114
30 0.0220 0.0114
31 0.0216 0.0113
32 0.0207 0.0113
33 0.0201 0.0113
34 0.0194 0.0111
35 0.0192 0.0111
36 0.0191 0.0110
37 0.0189 0.0110
38 0.0187 0.0109
39 0.0183 0.0109
40 0.0181 0.0106
41 0.0177 0.0106
42 0.0176 0.0105
43 0.0169 0.0105
44 0.0168 0.0104
45 0.0165 0.0104
46 0.0163 0.0103
47 0.0161 0.0100
48 0.0156 0.0099
49 0.0156 0.0098
50 0.0153 0.0096
51 0.0150 0.0096
52 0.0148 0.0095
53 0.0147 0.0095
54 0.0132 0.0094
55 0.0123 0.0094
56 0.0100 0.0090
57 0.0094 0.0088
58 0.0089 0.0085
59 0.0072 0.0084
60 0.0066 0.0083
61 0.0044 0.0080
21706 WWHM 3/1/2023 3:24:29 PM Page 10
21706 WWHM 3/1/2023 3:24:29 PM Page 11
Duration Flows
The Facility PASSED
Flow(cfs)Predev Mit Percentage Pass/Fail
0.0113 18469 16681 90 Pass
0.0120 16114 11082 68 Pass
0.0127 14316 6832 47 Pass
0.0133 12694 4395 34 Pass
0.0140 11182 2421 21 Pass
0.0146 9886 1850 18 Pass
0.0153 8819 1650 18 Pass
0.0160 7843 1496 19 Pass
0.0166 7007 1368 19 Pass
0.0173 6297 1232 19 Pass
0.0179 5679 1148 20 Pass
0.0186 5174 1071 20 Pass
0.0193 4703 984 20 Pass
0.0199 4280 910 21 Pass
0.0206 3903 835 21 Pass
0.0212 3527 786 22 Pass
0.0219 3183 743 23 Pass
0.0226 2864 700 24 Pass
0.0232 2592 654 25 Pass
0.0239 2353 616 26 Pass
0.0245 2141 572 26 Pass
0.0252 1953 529 27 Pass
0.0259 1796 480 26 Pass
0.0265 1669 424 25 Pass
0.0272 1517 367 24 Pass
0.0278 1344 331 24 Pass
0.0285 1222 305 24 Pass
0.0292 1123 280 24 Pass
0.0298 1042 252 24 Pass
0.0305 969 220 22 Pass
0.0312 910 195 21 Pass
0.0318 838 175 20 Pass
0.0325 766 168 21 Pass
0.0331 704 151 21 Pass
0.0338 634 141 22 Pass
0.0345 571 127 22 Pass
0.0351 488 120 24 Pass
0.0358 425 114 26 Pass
0.0364 376 107 28 Pass
0.0371 341 103 30 Pass
0.0378 307 96 31 Pass
0.0384 270 92 34 Pass
0.0391 235 86 36 Pass
0.0397 196 78 39 Pass
0.0404 171 72 42 Pass
0.0411 145 67 46 Pass
0.0417 125 64 51 Pass
0.0424 107 60 56 Pass
0.0430 95 58 61 Pass
0.0437 84 55 65 Pass
0.0444 71 51 71 Pass
0.0450 61 49 80 Pass
0.0457 55 45 81 Pass
21706 WWHM 3/1/2023 3:24:29 PM Page 12
0.0464 45 43 95 Pass
0.0470 40 39 97 Pass
0.0477 37 32 86 Pass
0.0483 35 29 82 Pass
0.0490 29 20 68 Pass
0.0497 25 19 76 Pass
0.0503 22 18 81 Pass
0.0510 17 16 94 Pass
0.0516 15 14 93 Pass
0.0523 11 11 100 Pass
0.0530 9 8 88 Pass
0.0536 8 0 0 Pass
0.0543 8 0 0 Pass
0.0549 8 0 0 Pass
0.0556 7 0 0 Pass
0.0563 7 0 0 Pass
0.0569 7 0 0 Pass
0.0576 7 0 0 Pass
0.0582 7 0 0 Pass
0.0589 7 0 0 Pass
0.0596 7 0 0 Pass
0.0602 6 0 0 Pass
0.0609 5 0 0 Pass
0.0616 5 0 0 Pass
0.0622 5 0 0 Pass
0.0629 4 0 0 Pass
0.0635 4 0 0 Pass
0.0642 4 0 0 Pass
0.0649 4 0 0 Pass
0.0655 4 0 0 Pass
0.0662 4 0 0 Pass
0.0668 4 0 0 Pass
0.0675 4 0 0 Pass
0.0682 4 0 0 Pass
0.0688 4 0 0 Pass
0.0695 3 0 0 Pass
0.0701 3 0 0 Pass
0.0708 3 0 0 Pass
0.0715 3 0 0 Pass
0.0721 2 0 0 Pass
0.0728 2 0 0 Pass
0.0734 2 0 0 Pass
0.0741 2 0 0 Pass
0.0748 2 0 0 Pass
0.0754 2 0 0 Pass
0.0761 2 0 0 Pass
0.0768 1 0 0 Pass
21706 WWHM 3/1/2023 3:24:29 PM Page 13
Water Quality
Water Quality BMP Flow and Volume for POC #1
On-line facility volume:0 acre-feet
On-line facility target flow:0 cfs.
Adjusted for 15 min:0 cfs.
Off-line facility target flow:0 cfs.
Adjusted for 15 min:0 cfs.
21706 WWHM 3/1/2023 3:24:29 PM Page 14
LID Report
21706 WWHM 3/1/2023 3:25:07 PM Page 15
Model Default Modifications
Total of 0 changes have been made.
PERLND Changes
No PERLND changes have been made.
IMPLND Changes
No IMPLND changes have been made.
21706 WWHM 3/1/2023 3:25:07 PM Page 16
Appendix
Predeveloped Schematic
21706 WWHM 3/1/2023 3:25:08 PM Page 17
Mitigated Schematic