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Arborist Report Page 1 of 6
Renton Technical College 2200871.40
May 5, 2023
ARBORIST REPORT
TO: Planning Division
City of Renton
1055 South Grady Way
Renton, WA 98055
Eric Lara
Project Manager
Engineering & Architectural Services
Washington State Department of
Enterprise Services
DATE OF VISIT: April 5, 2023
PROJECT NO.: 221079.40
CC: PROJECT NAME: Renton Technical College
Tree Inventory
FROM: Stuart Johnson
ISA Certified Arborist #PN8124A
Qualified Tree Risk Assessor
AHBL INC.
Tacoma - (253) 383-2422
LOCATION: 3000 4th Ave NE, Renton, WA 98056
ASSIGNMENT AND SCOPE OF REPORT:
This report is provided for Renton Technical College, for the southern portion of campus including parcel #7227800500, which
is bordered by Monroe Avenue on the east, NE 4th St. to the south, and both Jefferson Ave NE and Kirkland Ave NE to the
west. The parcel inventoried has a total area of 643,654 square feet, which includes at least nine buildings, several parking
lots, and their associated grounds. Barry Baker of Renton Technical College and Eric Lara of Washington State Department of
Enterprise Services requested an assessment and recommendations for (9) existing trees located immediately north of
Building F. This report satisfies the requirements for Arborist Reports included in Renton Municipal Code, Chapter 8, Section
4-8-120 under Submittal Requirements and is intended to accompany the required Routine Vegetation Management Permit.
The scope of this report is to provide the following:
• An inventory of all trees within the project area, including size and species
• A visual tree assessment for health and condition
• Recommendations regarding which trees should be removed or retained
METHODOLOGY
This assessment evaluated (9) significant trees greater than 6 inches in diameter breast height (DBH) in the south campus
area. Tree species were identified and mapped to determine the number, distribution, and condition of existing trees on
campus. Observations were limited to visual inspection from ground level and each tree’s health was evaluated using a 1-5
scale where 1 = dead, 2 = poor, 3 = fair, 4 = good, 5 = excellent condition. Significant structural defects or characteristics
including decay, poor crown condition, dieback and a history of failure were noted. Limits of disturbance are determined based
on a combination of the critical root zone and driplines of the trees. The tree inventory and evaluation criteria are based on the
International Society of Arboriculture (ISA) Best Management Practices – Tree Inventories, Second Edition (2013) by Jerry
Bond.
Arborist Report Page 2 of 6
Renton Technical College 2200871.40
May 5, 2023
OBSERVATIONS
Tree Species: The nine trees included in this inventory are all Thuja plicata (Western red cedar) trees. This large
evergreen native conifer has a strong pyramidal form and can reach well over 100 feet tall by 30 feet wide in an urban
setting. Preferred site conditions are part sun/shade and adequate soil moisture.
Tree Conditions: Trees #217 - #225 are located in between Buildings F and H in a planting strip along the north
exterior wall of Building F (see attached Tree Removal Plan). The planting strip is approximately 23’ wide, with 9’ of
mulched planting bed then a small curb and to the north, an approximately 13’ wide lawn area. The distance between
the Building F north wall and the south end of the trunk and root flare ranges from 18”-24”. Of the (9) trees, (5) are in
fair condition and (4) are in good condition. Additionally, (4) of the trees are considered Landmark Trees according to
RMC definitions. The estimated whole tree height is approximately 40’ and trunk diameter ranges from 17” – 33”
D.B.H (see attached data sheet for more detailed information). The (9) canopies have been raised up to 14’+ and
extend south over approximately a 10’ wide by 150’ long portion of the Building F roof.
Trees #220, #221, #222, #223, #224, all Western red cedar, are in fair condition, based on their structure and health.
These trees all exhibit thinning crowns, lower-than-normal vigor, as well as a heavy set of cones.
Site Conditions: Trees #218-#222 were planted directly over top of a storm drain lateral pipe. The storm pipe
connects the three Building F roof drain downspouts to the main storm pipe running north/south along Kirkland Ave
NE via a catch basin and lateral line with clean-outs. Roots from trees #217 - #225 are impacting the storm pipes and
causing documented damage to SDCB 3078 and its stem lines since at least 2015 (see attached Tree Removal Plan
and Exhibit 2.1). All nine trees are directly over top of existing storm pipes or within 3 feet of the storm pipe system
components such as the downspouts, cleanouts, and yard drains.
DISCUSSION AND RECOMMENDATIONS
Tree roots are biologically optimized organs responsible for uptake of water along with dissolved elements and
compounds. They are opportunistic and are stimulated, elongate, and divide more rapidly as moisture levels and soil
conditions approach optimal levels for the species. In most cases, roots seldom break pipes and then enter them. In
most situations roots enter through joints or cracks and breaks in the pipe assembly. Cracks can occur due to
differential settling or failure of joints and may release oxygenated water into the soils. Once roots meet this, they can
quickly start to divide rapidly to capitalize on newly available resources. Species compatibility and site selection are
critical to ensuring that urban trees can live long lives and achieve their full ecosystem service potential. According to
current best practice sources, such as the City of Seattle Urban Forestry Department, Thuja plicata trees should be
planted a minimum of 20’ from buildings and 5’ from underground utilities. The City of Renton Approved Tree List &
Spacing Guidelines 2022 Edition also states that large maturing trees (such as western red cedar), should be used in
8’ or wider planting strips and should be located a minimum of 5’ from underground utilities. Furthermore, the Arbor
Day Foundation’s Tree Planting Guide advises that large maturing trees should be planted at least 20’ from a
structure wall. By these current standards, the (9) trees in question were planted too close to the building and its
associated utilities, increasing the likelihood of damage to infrastructure. The observed condition of trees #220-#224
signal that the trees are experiencing an elevated level of stress, possibly the result of their roots being in contact with
both the building F foundation as well as the asphalt paving to the north.
The potential for roots to impact the Building F foundation is also a concern with potential costly impacts such as
water damage to interior spaces. Tree roots can disrupt building foundations by exploiting existing cracks and through
soil movement and sinking. No visible signs of disruption to the existing Building F masonry wall were observed.
Visible damage to adjacent concrete extruded curb and asphalt paving is occurring where roots from tree #217 are
growing north and east towards the storm drain catch basin.
Additionally, and of concern to campus safety, the narrow corridor in between Buildings F and H is heavily canopied.
These and other large evergreen trees, produce at times a dark space on campus and contribute to a lack of visibility
through this commonly used space where students and staff travel through. The failure of the storm drain system in
this area has and will continue to result in potentially hazardous conditions should the pipes be damaged to the extent
that water is impounded and backs up onto pedestrian paving.
Arborist Report Page 3 of 6
Renton Technical College 2200871.40
May 5, 2023
Previous Mitigation Efforts:
Starting back in 2015, due to observed standing water and poor drainage in this area, the college worked with a
plumbing contractor to inspect the storm drain lines and found them to be obstructed with tree roots. On two
occasions in 2015 plumbing contractors were hired by the college to remove and replace portions of private storm
pipe. Re-routing three roof drain downspouts into an existing catch basin provided a period where drainage structures
operated successfully. Additional maintenance performed since that time has included cable lining or “snaking” as
well as “hydro jetting” of the lines. Mechanical snaking is a process by which a drain snake with a long cable and
cutting tip is extended through the drainpipe with the tip working to cut through and remove blockages. Hydro-jetting,
where a high-pressure water jet is sent through pipes can remove excess buildup of material and roots. These
activities can prove useful in reducing blockages but would need to be done every 6 months (per plumbing
contractor’s recommendations).
Over the last 8 years the college has spent at least $11,494 repairing and replacing the storm drain system due to
root intrusion and damage. These practical attempts to mitigate the damage without tree removal have been
unsuccessful.
Alternatives to Tree Removal:
As part of the tree removal permit criteria an exploration of reasonable alternatives to removal is required. To date,
alternatives employed to resolve the drainage issues have included mechanical snaking, hydro-jetting, and pipe
replacement, including re-routing portions of the lines as stated in the previous paragraph. To consider this as
preventative maintenance would require regular inspection by camera, followed up by snaking, hydro-jetting, or
chemical root treatment on a regular basis. Due to the quantity and proximity of the trees to the drainpipe, this work
was recommended to be completed twice a year, at an approximate cost of $1200-$2000 annually.
Root barrier installation or root pruning as alternative strategies are not feasible since most of the trees are directly on
top of the pipes or close enough that extensive excavation in the critical root zone would be costly work and present
the significant possibility of causing serious damage to the trees in question. It is for these reasons that industry
standards recommend large size trees be kept sufficiently separated from utilities. With sufficient clearance, root
removal and excavation can safely occur further out in the critical root zone, making tree retention more feasible.
Root exclusion strategies as listed above would carry a higher likelihood of causing whole tree failure as significant
structural roots would need to be removed. This root removal would be destabilizing to the already asymmetrical root
plates growing up against the Building F foundation. For these reasons further extensive trenching within the critical
root zones to employ further root exclusion strategies is not a reasonable recommendation.
Additional work to repeatedly replace sections of drainpipe would both be costly and impactful to the trees. These
costs represent an unreasonable financial burden the college would need to expend, in perpetuity, to maintain a safe
campus environment. Eventually, storm water from the building F roof must enter the main line west of building F to
exit the vicinity, requiring underground piping within the critical root zone of the 9 existing trees. Alternatives for below
ground modifications to tree roots or pipes carry significant costs, financially as well as in potential adverse impacts to
the trees, rendering them unreasonable.
Date Damage Observed Mitigation Action Cost Impact to Tree
03/27/2015 Standing water, roof
drains not operating
properly
Excavate 1 downspout
line. Replace 4’ section of
pipe and add clean-out.
$3,293
(Exhibit 2.1)
Moderate-Excavation, soil
compaction, and root
removal within critical root
zone.
08/26/2015 Standing water, roof
drains not operating
properly
Excavate 2 downspout
lines. Trench to re-route
pipes into existing catch
basin.
$8,201
(Exhibit 2.2)
Significant- Excavation,
soil compaction from
equipment, significant root
removal within critical root
zone.
Arborist Report Page 4 of 6
Renton Technical College 2200871.40
May 5, 2023
Damage Potential Mitigation
Action
Cost Impact to Tree Maintenance
Outcome
• Buckling asphalt • Replace 25 SF
asphalt
$750 Minimal if grind and
overlay
5-year effective solution,
replace as needed.
• Broken concrete
curb
• Replace concrete
curb
$500 Minimal 5-year effective solution,
replace as needed
• Catch basin root
intrusion
• Replace catch basin $3000 Moderate, due to
excavation proximity to
tree
10-year effective solution
• Storm drain-
pipe intrusion
• Camera Inspection,
Annually
$250 Minimal, loss of roots
only within pipe
1-year solution
• Snake every 6
months
$350 Minimal, loss of roots
only within pipe
.5-year solution
• Hydro-jet every 6
months
$750 Minimal, loss of roots
only within pipe
.5-year solution
• Chemical herbicide
treatment in pipes
$500 Moderate over long
period of time, loss of
roots only within pipe
.5-year solution
• Replace pipe $3000-
$8000
Significant, due to
excavation proximity to
tree and root loss
5–10-year solution
• Linear Root Barrier
installation along
pipe route
$3000 Significant, due to
excavation proximity to
tree and root loss
10-year solution
• Root pruning along
pipe route
$3000 Significant, due to
excavation proximity to
tree and root loss
5-year solution
• Storm drain
downspout
connection
intrusion
• Replace pipe and
clean-out structures
$3000-
$8000
Significant, due to
excavation proximity to
tree and root loss
5–10-year solution
Proposed Tree Removal:
The continued damage to utilities is a direct result of the nine large species trees with extensive root systems being
located too close to the adjacent building, and utilities. Reasonable alternatives to tree removal have been attempted
by the college and have not provided a long-term solution. Without a viable mitigation strategy, nine Western red
cedar trees numbered #217-#225, located north of Building F are recommended for removal.
Arborist Report Page 5 of 6
Renton Technical College 2200871.40
May 5, 2023
CONCLUSIONS
Nine existing site trees numbered #217-#225 should be removed to prevent further damage to the existing storm drain utilities.
Reasonable alternatives to tree removal have shown to be unsuccessful in mitigating the damage caused by these trees. The
spatial constraints on site highly limit possible alternatives for conveying storm water from Building F to the public system. For
these reasons the trees in question should be removed.
The recommendations in this report reflect the current development proposal. Any changes made regarding the location, size,
or extent of impact of the construction of the proposed buildings, utilities, landscaping, and driveways will require further
assessment to meet the requirements of the City of Renton Tree Retention and Land Clearing code.
The recommendations in this report are based on the current conditions of the existing trees dated February 15th, 2023, and
their current associated preservation values. Should the conditions and/or health of the trees decline prior to construction
activities, an additional assessment may be needed.
Prepared by
Stuart Johnson
AHBL INC.
Certified Arborist
ISA #PN-8124N
sjohnson@ahbl.com
253-383-2422
Attached: Glossary of Terms, Tree Removal Plan, Data table, Exhibits.
End of Arborist Report SJ/
c: Craig Skipton - AHBL
Kristin Kildall- AHBL
\\ahbl.com\data\Projects\2021\2210791\40_LAN\NON_CAD\2_SPECS_REPORTS\Arborist Report\20230301 - Arborist Report - RTC - 2210791.40.docx
Arborist Report Page 6 of 6
Renton Technical College 2200871.40
May 5, 2023
Attachment 1. Glossary of Arboricultural Terms
DBH: Diameter at Breast Height (measured 4.5 ft. above the ground line on the high side of the tree).
Branch bark ridge: The raised area of bark in the branch crotch that marks where the branch and parent
material meet.
Branch collar: The swollen area at the base of a branch.
Cambium: The dividing layer of cells that forms sapwood (xylem) to the inside and inner bark (phloem) to the
outside.
Closure: The process of woundwood covering a cut or other tree injury.
Crown: The leaves and branches of a tree measured from the lowest branch on the trunk to the top of the tree.
Crown Cleaning: Selective pruning to remove dead, diseased, and/or broken branches.
Crown Raising: Selective pruning to remove lower limbs and provide vertical clearance.
Crown Reduction: Selective pruning to decrease height and/or spread.
Decay: The degradation of woody tissue caused by microorganisms.
Establishment: The point after planting when a tree’s root system has grown sufficiently into the surrounding soil
to support shoot growth and anchor the tree.
Heading Cut: 1. Cutting a currently growing or a 1-year old shoot, back to a bud. 2. Cutting an older branch of
stem back to a stub in order to meet a defined structural objective. 3. Cutting an older branch or stem back to a
lateral branch not large enough to assume apical dominance in order to meet a defined structural objective.
Heading may or may not be an acceptable pruning practice, depending on the application.
Interfering Branches: Crossing, rubbing, or upright branches that have the potential to damage tree structure
and/or health.
Internodal cut: A cut located between lateral branches or buds.
Lateral Branch: A shoot or stem growing from a parent branch or stem.
Leader: A dominant or co-dominant, upright stem.
Parent Branch or Stem: A tree trunk, limb, or prominent branch from which shoots or stems grow.
Phloem: Inner bark conduction tissues that transport organic substances, primarily carbohydrates, from leaves
and stems to other parts of the plant.
Pruning: The selective removal of plant parts to meet specific goals and objectives.
Restoration: Selective pruning to improve the structure, form, and appearance of trees that have been severely
headed, vandalized, or damaged.
Thinning: Selective pruning to reduce density of live branches.
Wound: An opening that is created when the bark of a live branch or stem is penetrated, cut, or removed.
Xylem: Wood tissue. Active xylem is sapwood; inactive xylem is heartwood.
DATA TABLE - Renton Technical College Arborist Report
217 Western red cedar Thuja plicata 33"40'18'4 Full Sun Remove 12 Landmark tree, 1.5' from Bldg F foundation, Split trunk at 18", 2 stems
218 Western red cedar Thuja plicata 17"40'16'4 Full Sun Remove 7 1.5' from Bldg F foundation
219 Western red cedar Thuja plicata 12"40'16'4 Full Sun Remove 6 1.5' from Bldg F foundation
220 Western red cedar Thuja plicata 21"40'18'3 Full Sun Remove 8 1.5' from Bldg F foundation, Thin crown, Heavy cone production, 3 stems.
221 Western red cedar Thuja plicata 17"40'18'3 Full Sun Remove 7 1.5' from Bldg F foundation, Thin crown, Heavy cone production
222 Western red cedar Thuja plicata 23"40'18'3 Full Sun Remove 9 1.5' from Bldg F foundation, Thin crown, Heavy cone production, 2 stems.
223 Western red cedar Thuja plicata 27"40'18'3 Full Sun Remove 10 Landmark tree, 1.5' from Bldg F foundation, Split trunk at 24", 2 stems
224 Western red cedar Thuja plicata 27"40'18'3 Full Sun Remove 10 Landmark tree, 1.5' from Bldg F foundation, 3'x1' wound on stem from previous branch failure.
225 Western red cedar Thuja plicata 25"40'18'4 Full Sun Remove 10 Landmark tree, 1.5' from Bldg F foundation
DBH Species
Scientific name
Species
Common name#
Overall
Crown
Health
NotesOverall
Height
Crown
Width
Tree Credit
Value Exposure Primary Maintenance
Page 1 of 1
PHOTO EXHIBITS RENTON TECHNICAL COLLEGE ARBORIST REPORT
PAGE 1
TREES #217-225
PHOTO EXHIBITS RENTON TECHNICAL COLLEGE ARBORIST REPORT
PAGE 2
TREE #224 TREES #217-223
TREE #224 TREE #223
PHOTO EXHIBITS RENTON TECHNICAL COLLEGE ARBORIST REPORT
PAGE 3
TREES #224 AND #225 TREE #220
TREE #217 TREES #217-#220
Invoice
Tech:STEVE
Due Date:4/26/2015
March 27, 2015
Invoice
453930Invoice #:
Job Date:3/27/2015
13701 24th St E Ste C-9
Sumner, WA 98390
253-987-7980
www.theplumbinganddrainco.com
Renton Technical College
3000 NE 4th St
Building F Downspouts
Renton, WA 98056
Job Name:Bill To:
3000 NE 4th St
Renton, WA 98056
425-235-2372 425-235-2387 425-235-2471 425-235-5839
Description of Services and Work Rendered:
Renton Technical College
Issue of work:
Repair storm line.
Description of repair provided:
Dug up around in front of downspout out 6' to 90. Removed 4' section of pipe. clogged with roots. Installed new
pipe with 2 way clean out backfilled. Cabled line out to other obstruction downstream 10' under tree in 10" line.
Barry gone till 3/30 will call and left him know other obstruction will be at additional cost.
Additional Recommendation:
6 month jetter maintenance.
1 year labor and material warranty
3007.68 $3,293.41
THANK YOU FOR YOUR BUSINESS, WE APPRECIATE IT VERY MUCH!
Subtotal Sales Tax Total
285.73
Invoice
Date
8/26/2015
Invoice #
A13843
Bill To
Renton Technical College
c/o Barry Baker
3000 NE 4th Street
Renton, WA 98056
Job Site
3000 NE 4th Street
Renton, WA 98056
BOB OATES SEWER ROOTER, LLC.
600 W Nickerson St
Seattle, WA 98119
Comm/Res
C
Terms
Net 15
Technician
AF
Sales Rep
Aaron Flint Aaron Flint
MarketingOriginal Call Slip
N/A
Total
Balance Due
Subtotal
Sales Tax
Payments/Credits
Description AmountClassQtyRate
Excavation Original Proposal - Re-route two
downspouts into existing catch basin on private
property.
Estimated project duration - 2 days
* Machine rental - 2 days x $350/day
700.00TExcavation1 700.00
* Labor - two man prevailing wage - 2 days x
$2800/day
5,600.00TExcavation15,600.00
Materials 1,190.00TExcavation1 1,190.00
$8,201.55
$8,201.55
$7,490.00
$711.55
$0.00