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HomeMy WebLinkAboutRS_TIR_20210215_v2 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 Page | 1 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 Page | 2 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 Page 1 of 3 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 Page 2 of 3 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 Page 3 of 3 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