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T ECHNICAL I NFORMATION R EPORT
C ENTRAL I SLAND S HORT P LAT
3413 NE 7 TH S TREET
R ENTON, W ASHINGTON 98056
The Concept Group
4701 SW Admiral Way, Ste 353 ● Seattle, WA 98116 ● (206) 446-1291
TDR Category 1 Report
Central Island Short Plat 3413 NE 7th Street
RENTON, WASHINGTON 98056
REVISIONS
August 19, 2020 Original Submission
November 20, 2020 1st Revision
Developer/Owner
Contact: Brian Le
Address: 3413 NE 7th Street; Renton, WA 90856
Phone: (206) 427-2193
Professional Preparing TIR
Name: Anna Nguyen, P.E.
Company: The Concept Group
Address: 4701 SW Admiral Way, Ste 353; Seattle, WA 98116
Phone: (206) 446-1291
Email: anna@conceptbusinessgroup.com
I certify that this technical information report and all attachments were prepared
either by me or my technical staff working directly under my supervision.
DocuSign Envelope ID: CDCD483A-D56F-4B5D-8BEE-2255EC560695
Table of Contents
SECTION 1: PROJECT OVERVIEW ............................................................................................................................................. 1
SITE INFORMATION .......................................................................................................................................................................... 1
EXISTING CONDITIONS...................................................................................................................................................................... 1
PROPOSED CONDITIONS ................................................................................................................................................................... 1
SECTION 2: CONDITIONS AND REQUIREMENTS ...................................................................................................................... 2
DESIGN STANDARDS ........................................................................................................................................................................ 2
CORE REQUIREMENT #5: EROSION AND SEDIMENT CONTROL .................................................................................................................. 2
CORE REQUIREMENT #6: MAINTENANCE AND OPERATIONS .................................................................................................................... 2
CORE REQUIREMENT #7: FINANCIAL GUARANTEES AND LIABILITY ............................................................................................................. 2
SPECIAL REQUIREMENT #1: OTHER ADOPTED REQUIREMENTS ................................................................................................................. 2
SPECIAL REQUIREMENT #2: FLOOD HAZARD AREA DELINEATION.............................................................................................................. 2
SPECIAL REQUIREMENT #3: FLOOD PROTECTION FACILITIES .................................................................................................................... 2
SPECIAL REQUIREMENT #4: SOURCE CONTROL ..................................................................................................................................... 2
SECTION 3: PROPOSED BMP’S & MAINTENANCE GUIDELINES ................................................................................................ 3
PROPOSED ON-SITE BMP’S .............................................................................................................................................................. 3
MAINTENANCE GUIDELINES .............................................................................................................................................................. 3
SECTION 4 – CSWPP ANALYSIS AND DESIGN ........................................................................................................................... 4
ESC PLAN ANALYSIS AND DESIGN (PART A) ......................................................................................................................................... 4
CSWPP PLANS DESIGN (PART B) ...................................................................................................................................................... 5
SECTION 5 – BOND QUANTITIES, FACILITIES SUMMARIES, AND DECLARATION OF COVENANT .............................................. 6
Appendices
Appendix A: Civil Plan Set
Appendix B: Maintenance and Operations Manual
Central Islands Short Plat –TDR Category 1 Report November 2020
The Concept Group Page 1
SECTION 1: PROJECT OVERVIEW
The property is located at 3413 NE 7th Street in the City of Renton, Washington. There
is currently one (1) single family residence on the property. The project proposes to short
plat the existing parcel into three (3) total single-family residential lots. The existing
structures on the property will remain. Proposed improvements include the construction
of two (2) new single-family structures, a private access driveway/road, associated
utilities and stormwater management facilities.
Site Information
Location: 3413 NE 7th Street; Renton, WA
Size: 28,669 sq ft (approximately 0.66 acre)
City, County, State: Renton, King County, Washington
Governing Agency: City of Renton
Design Criteria: 2017 City of Renton Surface Water Design Manual
Existing Conditions
There is currently one (1) single family residence on the property. Surface water infiltrates
to native soils with the overflow sheet flowing south towards NE 7th Place. Existing
impervious surface coverage is detailed in Table 1 below. Existing impervious to remain.
Table 1: Existing Impervious Surfaces (SF)
House (to remain) 2,074
Driveway (to remain) 356
Total 2,430
Proposed Conditions
The project proposes to short plat the existing parcel into a total of three (3) single family
residential lots. Proposed improvements include the construction of two (2) new single-
family structures, private access road, associated utilities and stormwater management
facilities.
Each new residential lot is assumed to consist of 4,000 sq ft of new impervious surface,
of which, 400 - 600 sq ft is PGIS driveway. The remainder of the property will consist of
landscape and lawns.
Table 2: Proposed New Impervious Surfaces (SF)
Lot 2 & Lot 3 (house + driveway, assumed max) 8,000
Private Road 4,797
Frontage Improvement 867
Total New Impervious Surface 13,664
Central Islands Short Plat –TDR Category 1 Report November 2020
The Concept Group Page 2
SECTION 2: CONDITIONS AND REQUIREMENTS
Design Standards
The 2017 City of Renton Surface Water Design Manual, as adopted from the 2016 King
County Surface Water Design Manual sets forth the drainage requirements for this
project. The project is subject to Targeted – Category 1 Drainage Review which requires
the project to address Core Requirement #5 and Special Requirements #1 through #4 of
the SWM. In addition, per the Conditions of Approval of the Short Plat, Core
requirements #6 and #7 must also be addressed.
Core Requirement #5: Erosion and Sediment Control
All erosion and sediment control measures shall be governed by the requirements of the
City of Renton and the King County Surface Water Manual. An Erosion and
Sedimentation Control plan has been prepared to assist the contractor in complying with
these requirements and designed to prevent sediment-laden run-off from leaving the site
during construction. Refer to Section 4 for the ESC analysis and Appendix A for the
Erosion Control plans and details.
Core Requirement #6: Maintenance and Operations
Maintenance and operations of all drainage facilities located within the private
residential property is the responsibility of the applicant or property owner. Refer to
Section 3 for a discussion of the proposed BMP’s and Appendix B for the Maintenance
and Operations Manual.
Core Requirement #7: Financial Guarantees and Liability
Proposed BMP’s are privately owned and maintained. A construction bond will be
posted for all propose and existing utilities constructed under the expired permit
U15005689. Upon completion of construction, a two-year maintenance bond will also
be posted for all new and existing utilities constructed under the expired permit
U15005689.
Special Requirement #1: Other Adopted Requirements
Based on available data at the time this report was prepared, there are no one Special
Adopted Requirements for this project.
Special Requirement #2: Flood Hazard Area Delineation
Based on FEMA Flood Map # FM53033C0981F the project area is located in Zone X, a
500-year flood plain.
Special Requirement #3: Flood Protection Facilities
This project is exempt from Special Requirement #3 because it does not rely on an
existing flood protection facility or propose to modify/construct new protection facilities.
Special Requirement #4: Source Control
This project does not exceed the water quality requirement threshold; therefore, it is
exempt from Special Requirement #4.
Central Islands Short Plat –TDR Category 1 Report November 2020
The Concept Group Page 3
SECTION 3: PROPOSED BMP’S & MAINTENANCE GUIDELINES
Proposed On-site BMP’s
The project utilizes Better Site Design by generally matching existing grades where
feasible. Existing trees and other vegetation around the site perimeter will be preserved
where possible to help minimize disturbance to the hydrologic cycle. Native soils in all
disturbed pervious areas will be amended with compost.
Lawn and Landscaped Areas
Within the limits of site disturbance, duff and topsoil will be retained in an undisturbed
state and stockpiled for later use to stabilize and amend soils throughout the Site.
Postconstruction soil amendment will meet the requirements of the 2017 City of Renton
Surface Water Design Manual.
Roof Surface Areas
Infiltration Drywells are proposed for this project. Drywells have been designed to
mitigate onsite runoff for each of the new lots, infiltrating 100% of the 100-year
developed flow, with an overflow release rate of 0.00 cfs. The proposed drywell will
have minimum bottom surface area of 170 SF x 4.0 feet in depth. Final drywell sizing
will be provided during the building permit phase.
Private Access Driveway
Permeable Pavement is proposed for the private access driveway which has already been
constructed under the expired permit U15005689.
Maintenance Guidelines
Maintenance and operations of all drainage facilities (infiltration drywells and permeable
pavement) located within the private residential properties is the responsibility of
property owner. Proper maintenance is important for adequate functioning of the
stormwater facilities. If it is unclear whether a problem exists, contact a Professional
Engineer. Excerpts from the 2016 KCSWDM for maintenance guidelines are included in
the Maintenance and Operations Manual in Appendix B.
Central Islands Short Plat –TDR Category 1 Report November 2020
The Concept Group Page 4
SECTION 4 – CSWPP ANALYSIS AND DESIGN
ESC Plan Analysis and Design (Part A)
All erosion and sediment control measures shall be governed by the requirements of the
City of Renton and the King County Surface Water Manual. An Erosion and
Sedimentation Control plan has been prepared to assist the contractor in complying with
these requirements and designed to prevent sediment-laden run-off from leaving the site
during construction. Refer to Appendix C for Erosion Control plans and details.
The erosion potential of the site is influenced by four major factors: soil characteristics,
vegetative cover, topography, and climate. Erosion/ sedimentation control is achieved
by a combination of structural measures, cover measures, and construction practices that
are tailored to fit the specific site.
Construction Sequence and Procedure
Prior to the start of any grading activity upon the site, all erosion control measures,
including installation of a stabilized construction entrance, shall be installed in
accordance with the construction documents.
The best construction practice will be employed to properly clear and grade the site and
to schedule construction activities. The planned construction sequence for the
construction of the site is as follows:
1. INSTALL CATCH BASIN PROTECTION IF REQUIRED.
2. INSTALL CONSTRUCTION ENTRANCE IF REQUIRED.
3. INSTALL PERIMETER PROTECTION (SILT FENCE, BRUSH BARRIER, ETC.).
4. MAINTAIN EROSION CONTROL MEASURES IN ACCORDANCE WITH APPENDIX D
OF THE SURFACE WATER DESIGN MANUAL AND MANUFACTURER'S
RECOMMENDATIONS.
5. RELOCATE EROSION CONTROL MEASURES OR INSTALL NEW MEASURES SO
THAT AS SITE CONDITIONS CHANGE THE EROSION AND SEDIMENT CONTROL IS
ALWAYS IN ACCORDANCE WITH THE CITY'S EROSION AND SEDIMENT
CONTROL STANDARDS.
6. COVER ALL AREAS THAT WILL BE UNWORKED FOR MORE THAN SEVEN DAYS
DURING THE DRY SEASON OR TWO DAYS DURING THE WET SEASON WITH
STRAW, WOOD FIBER MULCH, COMPOST, PLASTIC SHEETING OR EQUIVALENT.
7. STABILIZE ALL AREAS THAT REACH FINAL GRADE WITHIN SEVEN DAYS.
8. SEED OR SOD ANY AREAS TO REMAIN UNWORKED FOR MORE THAN 30 DAYS.
9. UPON COMPLETION OF THE PROJECT, ALL DISTURBED AREAS MUST BE
STABILIZED AND BMPS REMOVED IF APPROPRIATE.
Trapping Sediment
Structural control measures will be used to reduce erosion and retain sediment on the
construction site. The control measures will be selected to fit specific site and seasonal
conditions. The following items will be used to control erosion and sedimentation
processes:
• Temporary gravel construction entrance
• Filter fabric fences (Silt fences)
• Ground cover measures such as straw cover and/or hydroseeding
Central Islands Short Plat –TDR Category 1 Report November 2020
The Concept Group Page 5
• Inlet protection
Vehicle tracking of mud off-site shall be avoided. Installation of a gravel construction
entrance will be installed at a location to enter the site. The entrances are a minimum
requirement and may be supplemented if tracking of mud onto public streets becomes
excessive.
Permeable Pavement
Permeable pavement surfaces will be installed during the final stage of construction to
limit potential damage to the surface. Once installed, permeable pavement must be
inspected after a major storm to make sure it is working properly. Prolonged ponding or
standing water on the pavement surface is a sign that the system is defective and may
need to be replaced. To help extend the useful life of the system, the surface of the
permeable pavement should be kept clean and free of leaves, debris, and sediment
through regular sweeping or vacuum sweeping.
During construction, permeable pavement surface will be temporarily covered with a
tarp to prevent potential damage to the surface and plugging of the permeable pavement
subsurface layers.
CSWPP Plans Design (Part B)
Project does not require a CSWPPP since it proposes to disturb less than 1 acre of land.
Central Islands Short Plat –TDR Category 1 Report November 2020
The Concept Group Page 6
SECTION 5 – BOND QUANTITIES, FACILITIES SUMMARIES, AND
DECLARATION OF COVENANT
Proposed BMP’s are privately owned and maintained. A construction bond has been be
posted for all proposed utilities under the expired permit U15005689. This bond will be
transferred to the new construction permit upon permit issuance.
Upon completion of construction, a two-year maintenance bond will also be posted for
all new and existing utilities constructed under the expired permit U15005689.
The Declaration of Covenant is included with the Maintenance and Operations Manual
in Appendix B
Central Island SP –Technical Information Report
The Concept Group Appendices
Appendix A
Civil Plan Set
Central Island SP –Technical Information Report
The Concept Group Appendices
Appendix B
Maintenance & Operations Manual
OPERATIONS & MAINTENANCE MANUAL
FOR
Central Island Short Plat
3413 NE 7th Street
RENTON, WASHINGTON 98056
Operations & Maintenance Manual Prepared By
The Concept Group
4701 SW Admiral Way, PMB # 353
Seattle, Washington 98116
Anna Nguyen, P.E.
AUGUST 19, 2019
TABLE OF CONTENTS
1.0 INTRODUCTION ....................................................................................................... 1
2.0 STORMWATER BMPS ............................................................................................. 1
2.1 Infiltration Drywells ............................................................................................ 1 2.2 Permeable Pavement ....................................................................................... 2
Appendices
Appendix A – Declaration of covenant
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1.0 INTRODUCTION
This Operations and Maintenance Manual (O&M) has been prepared as part of the stormwater permit requirements for the Central Island Short Plat project located in Renton, Washington. The site is located at 3413 NE 7th Street, in the City of Renton,
Washington.
Maintenance and operations of all drainage facilities located within the private residential properties is the responsibility of the applicant or property owner. Proper maintenance is important for adequate functioning of the stormwater facilities. If it is unclear whether a problem exists, contact a Professional Engineer.
A Declaration of Covenant is recorded for this project. Refer to Appendix A.
2.0 STORMWATER BMPS
2.1 Infiltration Drywells
Your property contains a stormwater management flow control BMP (best management practice) called "full infiltration," which was installed to mitigate the stormwater quantity and quality impacts of some or all of the impervious surfaces on your property. Full
infiltration is a method of soaking runoff from impervious area (such as paved areas and
roofs) into the ground. If properly installed and maintained, full infiltration can manage runoff so that a majority of precipitation events are absorbed. Infiltration devices, such as gravel filled trenches, drywells, and ground surface
depressions, facilitate this process by putting runoff in direct contact with the soil and
holding the runoff long enough to soak most of it into the ground. To be successful, the soil condition around the infiltration device must be reliably able to soak water into the ground for a reasonable number of years.
The infiltration devices used on your property include the following as indicated on the
flow control BMP site plan:
• gravel filled drywells
The size, placement, and composition of these devices as depicted by the flow control
BMP site plan and design details must be maintained and may not be changed without written approval either from the City of Renton. Infiltration devices must be inspected annually and after major storm events to identify
and repair any physical defects. Maintenance and operation of the system should focus
on ensuring the system's viability by preventing sediment-laden flows from entering the device. Excessive sedimentation will result in a plugged or non-functioning facility. If the infiltration device has a catch basin, sediment accumulation must be removed on a yearly basis or more frequently if necessary. Prolonged ponding around or atop a device may
indicate a plugged facility. If the device becomes plugged, it must be replaced. Keeping
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the areas that drain to infiltration devices well swept and clean will enhance the longevity of these devices. For roofs, frequent cleaning of gutters will reduce sediment loads to these devices.
A detailed maintenance checklist is included in Appendix B.
2.2 Permeable Pavement
Permeable pavement reduces the amount of rainfall that becomes runoff by allowing water to seep through the pavement into a free-draining gravel or sand bed, where it can
be infiltrated into the ground.
The permeable pavement used on your property include the following as indicated on the flow control BMP site plan:
• porous asphalt
The area covered by permeable pavement as depicted by the flow control BMP site plan and design details must be maintained as permeable pavement and may not be changed without written approval either from the City of Renton.
Permeable pavements must be inspected after one major storm each year to make sure it is working properly. Prolonged ponding or standing water on the pavement surface is a sign that the system is defective and may need to be replaced. If this occurs, contact the pavement installer or the City of Renton. A typical permeable pavement system has a life
expectancy of approximately 25-years. To help extend the useful life of the system, the
surface of the permeable pavement should be kept clean and free of leaves, debris, and sediment through regular sweeping or vacuum sweeping. The owner is responsible for the repair of all ruts, deformation, and/or broken paving units.
APPENDIX A – DECLARATION OF COVENANT
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Return Address:
City Clerk’s Office
City of Renton
1055 S Grady Way
Renton, WA 98057
DECLARATION OF COVENANT AND EASEMENT FOR INSPECTION
AND MAINTENANCE OF DRAINAGE FACILITIES AND ON-SITE BMPS
Grantor:
Grantee: City of Renton
Legal Description:
Assessor's Tax Parcel ID#:
IN CONSIDERATION of the approved City of Renton (check one of the following)
residential building permit, commercial building permit, clearing and grading permit,
subdivision permit, or short subdivision permit for application file No.
LUA/SWP_______________________ relating to the real property ("Property") described above, the
Grantor(s), the owner(s) in fee of that Property, hereby covenants(covenant) with the City of Renton, a
political subdivision of the state of Washington, that he/she(they) will observe, consent to, and abide by
the conditions and obligations set forth and described in Paragraphs 1 through 9 below with regard to the
Property, and hereby grants(grant) an easement as described in Paragraphs 2 and 3. Grantor(s) hereby
grants(grant), covenants(covenant), and agrees(agree) as follows:
1. The Grantor(s) or his/her(their) successors in interest and assigns ("Owners ") shall at their
own cost, operate, maintain, and keep in good repair, the Property's drainage facilities constructed as
required in the approved construction plans and specifications __________ on file with the City of
Renton and submitted to the City of Renton for the review and approval of permit(s)
_____________________________. The property's drainage facilities are shown and/or listed on Exhibit
A. The property’s drainage facilities shall be maintained in compliance with the operation and
maintenance schedule included and attached herein as Exhibit B. Drainage facilities include pipes,
channels, flow control facilities, water quality facilities, on-site best management practices (BMPs) and
other engineered structures designed to manage and/or treat stormwater on the Property. On-site BMPs
include dispersion and infiltration devices, bioretention, permeable pavements, rainwater harvesting
systems, tree retention credit, reduced impervious surface footprint, vegetated roofs and other measures
designed to mimic pre-developed hydrology and minimize stormwater runoff on the Property.
2. City of Renton shall have the right to ingress and egress over those portions of the Property
necessary to perform inspections of the stormwater facilities and BMPs and conduct maintenance
activities specified in this Declaration of Covenant and in accordance with the Renton Municipal Code.
City of Renton shall provide at least 30 days written notice to the Owners that entry on the Property is
THUONG PHAM
STEWARTS HIGHLAND ACRE TRS
801110-0110
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planned for the inspection of drainage facilities. After the 30 days, the Owners shall allow the City of
Renton to enter for the sole purpose of inspecting drainage facilities. In lieu of inspection by the City, the
Owners may elect to engage a licensed civil engineer registered in the state of Washington who has
expertise in drainage to inspect the drainage facilities and provide a written report describing their
condition. If the engineer option is chosen, the Owners shall provide written notice to the City of Renton
within fifteen days of receiving the City’s notice of inspection. Within 30 days of giving this notice, the
Owners, or engineer on behalf of the Owners, shall provide the engineer’s report to the City of Renton. If
the report is not provided in a timely manner as specified above, the City of Renton may inspect the
drainage facilities without further notice.
3. If City of Renton determines from its inspection, or from an engineer’s report provided in
accordance with Paragraph 2, that maintenance, repair, restoration, and/or mitigation work is required to
be done to any of the drainage facilities, City of Renton shall notify the Owners of the specific
maintenance, repair, restoration, and/or mitigation work (Work) required pursuant to the Renton
Municipal Code. The City shall also set a reasonable deadline for the Owners to complete the Work, or to
provide an engineer’s report that verifies completion of the Work. After the deadline has passed, the
Owners shall allow the City access to re-inspect the drainage facilities unless an engineer’s report has
been provided verifying completion of the Work. If the Work is not completed within the time frame set
by the City, the City may initiate an enforcement action and/or perform the required maintenance, repair,
restoration, and/or mitigation work and hereby is given access to the Property for such purposes. Written
notice will be sent to the Owners stating the City’s intention to perform such work. This work will not
commence until at least seven (7) days after such notice is mailed. If, within the sole discretion of the
City, there exists an imminent or present danger, the seven (7) day notice period will be waived and
maintenance and/or repair work will begin immediately.
4. The Owners shall assume all responsibility for the cost of any maintenance, repair work, or
any measures taken by the City to address conditions as described in Paragraph 3. Such responsibility
shall include reimbursement to the City within thirty (30) days of the receipt of the invoice for any such
work performed. Overdue payments will require payment of interest at the maximum legal rate allowed
by RCW 19.52.020 (currently twelve percent (12%)). If the City initiates legal action to enforce this
agreement, the prevailing party in such action is entitled to recover reasonable litigation costs and
attorney’s fees.
5. The Owners are required to obtain written approval from City of Renton prior to filling,
piping, cutting, or removing vegetation (except in routine landscape maintenance) in open vegetated
stormwater facilities (such as swales, channels, ditches, ponds, etc.), or performing any alterations or
modifications to the drainage facilities referenced in this Declaration of Covenant.
6. Any notice or consent required to be given or otherwise provided for by the provisions of this
Agreement shall be effective upon personal delivery, or three (3) days after mailing by Certified Mail,
return receipt requested.
7. With regard to the matters addressed herein, this agreement constitutes the entire agreement
between the parties, and supersedes all prior discussions, negotiations, and all agreements whatsoever
whether oral or written.
8. This Declaration of Covenant is intended to protect the value and desirability and promote
efficient and effective management of surface water drainage of the real property described above, and
shall inure to the benefit of all the citizens of the City of Renton and its successors and assigns. This
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Declaration of Covenant shall run with the land and be binding upon Grantor(s), and Grantor's(s')
successors in interest, and assigns.
9. This Declaration of Covenant may be terminated by execution of a written agreement by the
Owners and the City that is recorded by King County in its real property records.
IN WITNESS WHEREOF, this Declaration of Covenant for the Inspection and Maintenance of
Drainage Facilities is executed this _____ day of ____________________, 20_____.
GRANTOR, owner of the Property
GRANTOR, owner of the Property
STATE OF WASHINGTON )
COUNTY OF KING )ss.
On this day personally appeared before me:
, to me known to be the individual(s) described in
and who executed the within and foregoing instrument and acknowledged that they signed the same as
their free and voluntary act and deed, for the uses and purposes therein stated.
Given under my hand and official seal this _____ day of ____________________, 20_____.
Printed name
Notary Public in and for the State of Washington,
residing at
My appointment expires