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HomeMy WebLinkAboutF_Sunset Terrace_TIR_180326.pdf Technical Information Report SUNSET TERRACE DEVELOPMENT BUILDING 1 (AKA COLPITTS SITE 9/10) Prepared for Colpitts Development and City of Renton, WA Prepared by Osborn Consulting, Inc. 1800 112th Ave NE, Suite 220E Bellevue, WA 98004 (425) 451-4009 Final: March 2018 3-26-18 LUA-15000159 PR-16000306 U-16002232 R-4003 FINAL IN COMPIANCE WITH CITY OF RENTON STANDARDS DEVELOPMENT ENGINEERING Ann Fowler 03/30/2018 SURFACE WATER UTILITY rstraka 04/02/2018 Technical Information Report i Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) T ABLE OF C ONTENTS Section I Project Overview ........................................................................................................... 1 Project Description ....................................................................................................................... 1 Proposed Improvements .............................................................................................................. 1 Existing Drainage System ............................................................................................................ 6 Proposed Drainage System ......................................................................................................... 6 Soils ............................................................................................................................................. 7 Section II Conditions and Requirements Summary ................................................................... 8 Core Requirements ...................................................................................................................... 8 Core Requirement 1: Discharge at Natural Location ............................................................... 8 Core Requirement 2: Offsite Analysis ...................................................................................... 8 Core Requirement 3: Flow Control .......................................................................................... 8 Core Requirement 4: Conveyance System .............................................................................. 9 Core Requirement 5: Erosion and Sediment Control ............................................................... 9 Core Requirement 6: Maintenance and Operations ................................................................ 9 Core Requirement 7: Financial Guarantees & Liability ............................................................ 9 Core Requirement 8: Water Quality ......................................................................................... 9 Special Requirements .................................................................................................................. 9 Special Requirement 1: Other Adopted Area-Specific Requirements ..................................... 9 Special Requirement 2: Floodplain/Floodway Delineation ....................................................... 9 Special Requirement 3: Flood Protection Facilities ................................................................. 9 Special Requirement 4: Source Control ................................................................................. 10 Special Requirement 5: Oil Control ........................................................................................ 10 Special Requirement 6: Aquifer Protection Area ................................................................... 10 Section III Off-site Analysis ........................................................................................................ 11 Task 1: Study Area Definition and Maps ................................................................................... 11 Task 2: Resource Review .......................................................................................................... 11 Task 3: Field Inspection ............................................................................................................. 12 Task 4: Drainage System Description and Problems Description ............................................. 13 Task 5: Mitigation of Existing or Potential Problems .................................................................. 13 Section IV Flow Control and Water Quality Facility Analysis and Design ............................. 14 Existing Site Hydrology (Part A) ............................................................................................. 14 Developed Site Hydrology (Part B) ........................................................................................ 14 Performance Standards (Part C) ........................................................................................... 15 Flow Control System (Part D) ................................................................................................ 16 Water Quality System (Part E) ............................................................................................... 18 Section V Conveyance System Analysis and Design .............................................................. 19 Section VI Special Reports and Studies ................................................................................... 22 Section VII Other Permits ........................................................................................................... 23 Section VIII CSWPPP Analysis and Design .............................................................................. 24 ESC Plan Analysis and Design (Part A) ................................................................................ 24 Stormwater Pollution Prevention and Spill (SWPPS) Plan Design (Part B) ........................... 26 ESC Site Inspection Forms .................................................................................................... 29 Technical Information Report ii Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) CWSPPP Worksheet Forms / Cleanup Report ...................................................................... 34 Section IX Bond Quantities, Facility Summaries, and Declaration of Covenant ................... 35 Bond Quantities Worksheet ................................................................................................... 35 Flow Control and Water Quality Facility Summary Sheet and Sketch ................................... 35 Declaration of Covenant for Privately Maintained Flow Control and WQ Facilities................ 35 Declaration of Covenant for Privately Maintained Flow Control BMPs .................................. 35 Section X Operations and Maintenance Manual. ..................................................................... 36 References ................................................................................................................................... 39 Appendices A – Permit Plans B – WWHM Detention Sizing Results and TESC Sizing Results C – Geotechnical Report D – Flow Control BMPs Requirement Figures 1 – TIR Worksheet………………………………………………………………………………………..2 2 – Site Location…………………………………………………………………………………………..4 3 – Drainage Basins, Subbasins, and Site Characteristics…………………………………………..4 4 – Soils…………………………………………………………………………………………………....5 6 - Map of the proposed conditions…………………....………………………....…………………....15 7 – Section of the Detention Vault showing volume calculation…………………....……………....16 8 – Manning Conveyance Calculation for Existing Downstream Pipe………………………..…....19 9 – Manning Conveyance Calculation for Proposed Vault Outfall Pipe…………………………....19 10 – Manning Conveyance Calculation for Interceptor Ditch …………………....………………....24 Technical Information Report 1 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) SECTION I PROJECT OVERVIEW Project Description This Technical Information Report (TIR) summarizes the stormwater requirements and the proposed stormwater management practices governing the design for the proposed Sunset Terrace Development Colpitts Site 9/10. The TIR worksheet is shown in Figure 1. The proposed improvement is located adjacent to King County’s new Renton Highlands Library between NE Sunset Blvd, NE 10th St, Sunset Lane NE and Harrington Ave NE, in the City of Renton, King County, Washington (Figure 2). The proposed improvement lot is 26,313 square feet and will include a six-story mixed use residential and commercial building with associated structured parking. Proposed Improvements The development provides these elements:  Creation of six-story mixed use building and associated structured parking  Drainage detention system  Sidewalk improvements to the property line Technical Information Report 2 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) Figure 1, page 1 of 2 King County Department of Development and Environmental Services TECHNICAL INFORMATION REPORT (TIR) WORKSHEET PART 1 PROJECT OWNER AND PROJECT ENGINEER PART 2 PROJECT LOCATION AND DESCRIPTION Project Owner Colpitts Development Project: Sunset Terrace Development Colpitts Site 9/10 Address 1015 37th Ave E, Seattle, WA, 98112 Location Phone 206-322-1381 Township 23N Project Engineer Robert Parish, PE Range 5E Company Osborn Consulting, Inc. Section 9 Address/Phone 1800 112th Ave NE, Suite 220E, Bellevue, WA 98004 (425) 451-4009 PART 3 TYPE OF PERMIT APPLICATION PART 4 OTHER REVIEWS AND PERMITS  Subdivision  DFW HPA  Shoreline Management  Short Subdivision  COE 404  Rockery  Grading  DOE Dam Safety  Structural Vaults  Commercial  FEMA Floodplain  Other - Building  Other Mixed-Use  COE Wetlands PART 5 SITE COMMUNITY AND DRAINAGE BASIN Community: Renton, King County, WA Drainage Basin: Johns Creek Drainage Basin PART 6 SITE CHARACTERISTICS  River  Floodplain  Stream  Wetlands  Critical Stream Reach  Seeps/Springs  Depressions/Swales  High Groundwater Table  Lake  Groundwater Recharge  Steep Slopes  Other (Portion of Property in Aquifer Protection Zone) PART 7 SOILS Soil Type Slopes Erosion Potential Erosive Velocities Fill 0-4% Slight Silty Sand (USCS SP/SM) - Till 0-4% Slight  Additional Sheets Attached Technical Information Report 3 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) Figure 1, page 2 of 2 King County Department of Development and Environmental Services TECHNICAL INFORMATION REPORT (TIR) WORKSHEET PART 8 DEVELOPMENT LIMITATIONS REFERENCE LIMITATION/SITE CONSTRAINT  Downstream Analysis  Flow Control Standards Level 1 Flow Control plus 100 year peak matching  Wetlands and Stream Report   Additional Sheets Attached PART 9 ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION  Sedimentation Facilities  Stabilize Exposed Surface  Stabilized Construction Entrance  Remove and Restore Temporary ESC Facilities  Perimeter Runoff Control  Clean and Remove All Silt and Debris  Clearing and Grading Restrictions  Ensure Operation of Permanent Facilities  Cover Practices  Flag Limits of SAO and open space preservation areas  Construction Sequence  Other  Other PART 10 SURFACE WATER SYSTEM  Grass Lined Channel  Tank  Infiltration Method of Analysis  Pipe System  Vault  Depression WWHM  Open Channel  Energy Dissipater  Flow Dispersal Compensation/Mitigation  Dry Pond  Wetland  Waiver of Eliminated Site Storage  Wet Pond  Stream  Regional Detention Brief Description of System Operation Detention, connecting to existing storm drain in ROW Facility Related Site Limitations Reference Facility Limitation PART 11 STRUCTURAL ANALYSIS PART 12 EASEMENTS/TRACTS  Cast in Place Vault  Drainage Easement  Retaining Wall  Access Easement  Rockery > 4' High  Native Growth Protection Easement  Structural on Steep Slope  Tract  Other - Building Other PART 14 SIGNATURE OF PROFESSIONAL ENGINEER I or a civil engineer under my supervision have visited the site. Actual site conditions as observed were incorporated into this worksheet and the attachments. To the best of my knowledge the information provided here is accurate. Signed/Date KCLSLIBRARYBASINBOUNDARY(0.606 ACRES)BUILDING FOUNDATIONMATCHES LOT PROPERTY LINE(ZERO SETBACK LOT)FIGURE 3. DRAINAGE BASINS, SUBBASINS, AND SITECHARACTERISTICS below.RENTON, WASHINGTON / /31417RENTON, WASHINGTON / /31417 Technical Information Report 4 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) Note: There are no geographic features and critical areas adjacent to the site. Figure 2: Site Location (NTS) Sunset Terrace Building 1 Site Limits of downstream study Technical Information Report 5 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) Figure 4: Soils (NTS) Approx boundary of aquifer protection zone 2 Ragnar-Indianola association – Outwash (Per USDA Soil Map) Fill Soils over Till (Per Geotechnical Study) Note: No Areas are draining to the site Sunset Terrace Building 1 Site KCLSLIBRARYBASINBOUNDARY(0.606 ACRES)BUILDING FOUNDATIONMATCHES LOT PROPERTY LINE(ZERO SETBACK LOT)FIGURE 5. EXISTING SITE HYDROLOGY (PART A) below.RENTON, WASHINGTON / /31417RENTON, WASHINGTON / /31417 KCLSLIBRARYBASINBOUNDARY(0.606 ACRES)BUILDING FOUNDATIONMATCHES LOT PROPERTY LINE(ZERO SETBACK LOT)FIGURE 6. DEVELOPED SITE HYDROLOGY (PART B) below.RENTON, WASHINGTON / /51017RENTON, WASHINGTON / /51017 Technical Information Report 6 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) Existing Drainage System The project site is a former Renton Housing Authority site. The property currently sits upon fill materials and glacial till, and has recently demolished three two-story multi-family residential buildings. In addition to the buildings, the project site contained mainly lawn, with a few trees and sidewalks connecting entranceways to the sidewalks along Sunset Lane NE and Harrington Ave NE. See Table 1 for a breakdown of the area. Currently, storm drainage runoff originating from within the limits of the property is routed via catch basins and storm drains to an existing Right of Way (ROW) storm drain system in Sunset Lane NE and Harrington Avenue NE to the Sunset Blvd NE that is routed down Sunset Boulevard NE toward Lake Washington. The project site property slopes northeast to southwest. The high point of the property is on the northeast end of the property at approximately elevation 340 NAVD 88. The low point is at the southwest end of the property at approximately elevation 336 NAVD 88. Table 1: Existing Areas Surface Onsite Area (acres) Bypass Area (acres) Total Area (acres) Pervious 0.3695 Landscaping 0.290 0.0795 Impervious 0.3652 Buildings, walkways and roads 0.316 0.0492 Total Site 0.7347 Proposed Drainage System The project proposes to remove the existing improvements and construct a new building and sidewalks. See Table 2 for a breakdown of the proposed areas. As part of these improvements, a detention vault will provide flow control prior to flowing in to the existing storm drain system in the Harrington Ave NE ROW that connects to the existing Sunset Blvd NE storm drain and flows along Sunset Blvd NE toward Lake Washington. Technical Information Report 7 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) The City of Renton’s February 2010 Surface Water Design Manual Amendment to the 2009 King County Surface Water Design Manual was used to determine that the project requires a Full Drainage Review. The project adds 2,000 SF or more of new impervious surface, therefore all core requirements and special requirements must be met, if applicable. To comply with the requirements, a detention vault located in the underground parking structure is proposed. No water quality treatment is proposed as the roof and sidewalk are non-pollution generating surfaces. See Appendix A for a plan view of the proposed system. See Appendix B for a summary of the sizing calculations from WWHM. Table 2: Proposed Areas Surface Onsite Area (acres) Bypass Area (acres) Total Area (acres) Pervious 0.0424 Landscaping 0 0.0424 Impervious 0.6923 Buildings and walkways 0.606 0.0239 Porous concrete sidewalk 0.0624 Total Site 0.7347 Refer to the plans in Appendix A for drainage areas and existing/proposed storm drainage systems. Soils The soils within the project site are fill soils on top of glacially compacted very dense silty sand that has a negligible permeability and the same properties glacial till. These soils are consistent across the site as summarized in the Geotechnical Engineering Report included in Appendix C. Technical Information Report 8 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) SECTION II CONDITIONS AND REQUIREMENTS SUMMARY The project is a mixed-use project that replaces more than 2,000 SF of impervious surface. As requested by the City of Renton, a Drainage Report has been completed, with the documented requirements below. Requirements follow the Full Drainage Review as specified Table 1.1.2.A in the City of Renton’s February 2010 Amendment to King County’s 2009 Surface Water Design Manual Core Requirements Core Requirement 1: Discharge at Natural Location Runoff from the site will continue to flow to the existing storm drain system in the ROW that flows into Lake Washington. Core Requirement 2: Offsite Analysis See Section III for the findings of the Level 1 offsite analysis. Core Requirement 3: Flow Control Per Reference 11-A of the City of Renton’s February 2010 Amendment to King County’s 2009 Surface Water Design Manual, the site is located in a Peak Rate Flow Control Standard (existing Site Conditions) area. The project will utilize a detention vault system to provide flow control to provide peak rate flow control to match the existing 2, 10 and 100-yr peak runoff rates. See Section IV below. To meet the Flow Control BMP requirement, the project will install porous pavement in the Right-of Way. See Section IV below and Appendix D. Since the Flow Control BMP will be installed in the ROW which bypasses the detention system, the project will need to demonstrate compliance with Section 1.2.3.2.E of the City of Renton’s February 2010 Amendment to King County’s 2009 Surface Water Design Manual. See Section IV below. Technical Information Report 9 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) Core Requirement 4: Conveyance System All conveyance systems have been designed for the 25-year peak flow. See Appendix B for a summary of the calculations. Core Requirement 5: Erosion and Sediment Control Temporary and permanent erosion and sediment control plans will be implemented as described in Section VIII. A Temporary Erosion and Sediment Control Plan is included within the construction documents and is attached in Appendix A. The construction documents also require the permanent stabilization be provided through paving and landscape. Core Requirement 6: Maintenance and Operations An Operations and Maintenance Manual is included in Section X. Core Requirement 7: Financial Guarantees & Liability To be provided by the owner prior to start of construction. Core Requirement 8: Water Quality No pollution generating surfaces are proposed as part of this project, therefore, no water quality treatment is proposed. See Section IV below. Special Requirements Special Requirement 1: Other Adopted Area-Specific Requirements Apart from the Sunset Terrace Master Site plan, there are no other known Adopted Area-Specific Requirements for the site. Special Requirement 2: Floodplain/Floodway Delineation The proposed project is not within or adjacent to an identified floodplain or floodway. Special Requirement 3: Flood Protection Facilities There is no existing or proposed flood protection facility included on the project. Technical Information Report 10 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) Special Requirement 4: Source Control No existing or proposed water quality pollutant hazard per the King County Stormwater Pollution Prevention Manual is currently known to be associated with the proposed building. The project’s Temporary Erosion and Sediment Control Plan will address measures to reduce pollutant hazards resulting from construction activities. Special Requirement 5: Oil Control The project does not qualify as a high use site therefore this requirement is not applicable. Special Requirement 6: Aquifer Protection Area The northern half of the project area is in an Aquifer Protection Zone per the City of Renton Sensitive Areas Map. The project is not planning to infiltrate stormwater onsite. Technical Information Report 11 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) SECTION III OFF-SITE ANALYSIS This project falls within the Johns Creek Drainage Basin, as identified by the City of Renton. Runoff from the project is directed to an existing storm drain pipe network that direct discharges to Lake Washington. A Level One Offsite Analysis was completed. No existing or potential problems were identified during this off- site analysis. Task 1: Study Area Definition and Maps The majority of runoff from the proposed project area is collected and detained. The property slopes from northeast to southwest. The high point of the property is on the northeast corner of the property at approximately elevation 340 NAVD 88. The low point is at the southwest corner of the property at approximately elevation 336 NAVD 88. Any overland runoff originating from the property flows toward the southwest side of the property and would enter the roadway drainage system along Sunset Blvd NE. The flow continues southwest. According to the City of Renton Maps, the flow direct discharges into Lake Washington. These limits fall within Renton, King County, Washington. The proposed project is located within Section 9 of Township 23 North, Range 5 East, WM in King County, Washington. The site is located in the Cedar River/Lake Washington Watershed. Task 2: Resource Review The following resources have been reviewed for existing or potential problems in the study area. Geotechnical Evaluation Geotech Consultants Inc performed a geotechnical analysis of the site. Refer to Appendix C for the report. Renton Flow Control Per the City of Renton, the site shall provide Level 1 Flow Control. Technical Information Report 12 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) FEMA Map Review The FEMA map for the project area was reviewed and showed no floodplains or floodways within or near the project limits. Wetlands The City of Renton Sensitive Areas Map showed no wetlands at the site. Streams The City of Renton Sensitive Areas Map does not list any creeks or streams in the vicinity of the project. Erosion Hazard The project site is not indicated on the City of Renton Critical Erosion Hazard Area map. There is no Critical Erosion Hazard Area within a quarter mile radius of the project site. Landslide Hazard The project site is not indicated as a Landslide Hazard Area. There is no Landslide Hazard Area within a quarter mile radius of the project site. Seismic Hazard Areas The project site is not indicated as a Seismic Hazard Area. Task 3: Field Inspection The resource review identified no previously identified problems. The field visit was completed on 5/7/2012, the weather was clear, 65-degrees, there had been no rain for at least 48 hours. The finding of the field visit was checked again on 7/5/2016 (sunny, 65-degrees, with no rain in the past 24-hours) confirmed the project’s basin boundary and that the northern portion of the site drains into the existing piped drainage system in Sunset Lane NE where it flows 55-feet to the south-west to the 18-inch diameter storm drain in Harrington Ave NE. From here it flows about 170-feet to the 30-inch storm drain in Sunset Blvd NE. The southern portion of the site drains into the existing piped drainage system on Sunset Blvd NE, approximately 75 ft upstream of the 30-inch storm drain. The 30-inch storm drain follows Sunset Blvd NE to the west turn to the northwest as is Technical Information Report 13 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) continues down the hill at approximately 8% slope about 1,320-feet to Edmonds Avenue through a series of Type 2-drianage structures. Edmonds Avenue was the limits of the field inspection, see Figure 2. No existing or potential problems were identified during the field inspection. Task 4: Drainage System Description and Problems Description The drainage system is described above in Task 1 and 3. No existing or potential problems were identified during this study. Task 5: Mitigation of Existing or Potential Problems There are no existing or potential problems identified on or near the proposed project site. The project site development will not increase storm flow rates to create or exacerbate any existing drainage problems. Mitigation will be provided by a detention vault, in compliance with the City Drainage Requirements. Technical Information Report 14 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) SECTION IV FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN Existing Site Hydrology (Part A) The site currently sits upon fill materials and glacial till. Site has recently demolished three two-story multi-family residential buildings. In addition to the buildings, the project site contained mainly lawn, with a few trees and sidewalks connecting entranceways to the sidewalks along Sunset Lane NE and Harrington Ave NE. There are no natural streams and natural drainage features, including wetlands on the site. See Figure 5 for the map of the existing conditions. See Table 1: Existing Onsite Areas for summary of the areas. Developed Site Hydrology (Part B) The project proposes to construct a new building and sidewalks. As part of these improvements, a detention vault will provide flow control prior to flowing in to the existing storm drain system in the Harrington Ave NE right of way. The Harrington Ave NE storm drain connects to the existing Sunset Blvd NE storm drain matching the existing flow path from the site. The City of Renton’s February 2010 Surface Water Design Manual Amendment to the 2009 King County Surface Water Design Manual (The City’s Manual) was used to determine that the project requires a Full Drainage Review. The project adds 2,000 SF or more of new impervious surface, therefore all core requirements and special requirements must be met, if applicable. To comply with the requirements, a detention vault located in the underground parking structure is proposed. No water quality treatment is proposed as the roof and sidewalk are non-pollution generating surfaces. To meet the Flow Control BMP requirement, the project will install porous pavement in the Right-of Way. See Appendix A for a plan view of the proposed system. See Appendix B for a summary of the sizing calculations from WWHM. Technical Information Report 15 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) Refer to the plans in Appendix A for drainage areas and existing/proposed storm drainage systems. See Figure 6 for the map of the proposed conditions. See Table 2: Proposed Areas for summary of the areas. Performance Standards (Part C) Onsite Area Area-specific flow control facility standard: Per Reference 11-A of the City of Renton’s February 2010 Amendment to King County’s 2009 Surface Water Design Manual (The City’s Manual), the site is located in a Peak Rate Flow Control Standard (existing Site Conditions) area. The project will utilize a detention vault system to provide flow control to provide peak rate flow control to match the existing 2, 10 and 100-yr peak runoff rates. See Section IV Part D below. Conveyance system capacity standards: Per Section 1.2.4 of The City’s Manual, the piped conveyance system serving the project shall convey the 25-year event with 6-inches freeboard with the top of the drainage structure, and the 100- year event with no freeboard. In addition it shall meet the headwater requirements in Section 4.3.1 of The City’s Manual Land use-specific water quality requirement: Per Section 1.2.8.1, the project meet the surface area exception, since ether will be less than 5,000 SF of new plus replaced PGIS. The proposed used of the project (mixed using commercial and housing) does not trigger any special requirements for source control per Section 1.3.4 since all future operations will occur within the building. In addition the project does is not an high-use site, therefore oil control per Section 1.3.5 is not required. ROW Bypass Area Since the only available space for the Flow Control BMP requirement is in the ROW (See Appendix D) improvements in the ROW would have to bypass the detention system and demonstrate compliance with demonstrate compliance with Section 1.2.3.2.E of the City of Renton’s February 2010 Amendment to King County’s 2009 Surface Water Design Manual. See Section IV Part D below. Technical Information Report 16 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) Flow Control System (Part D) Onsite Area As noted above, peak rate flow control is proposed for the project matching existing site conditions 2, 10 and 100-yr peak-rate runoff for areas draining to constructed (man-made) drainage systems. Flow Control will be mitigated as noted on the Drainage Control Plan (Sheet C3.0 and C3.1)in Appendix A, using an detention vault located in the south-west corner of the parking level 1 coupled with a flow control device. The vault will be part of the building structure but will be accessible from outside the building. The detention volume was designed in accordance with Section 5.3.3 of the 2009 KCSWDM as follows: • Vault was designed as a flow through system. • The bottom of the vault has a V with 5% side slopes. • The invert is elevated to provide at least 6-inches of sediment storage. • The outflow constrictor meet the applicable requirements. • The vault is designed by the structural engineer and it part of the building structural plans. • Adequate access is provided to the vault with venting. • The depth of the vault is less than 20-feet and greater then 7-feet. • The vault access is about 20-feet from the road WWHM was used to size the orifice and overflow riser, per Appendix B the orifices are greater than 0.25 inches, For the overflow riser, the following equation per 2009 King County Surface Water Design Manual, figure 5.3.4.H was used to verify overflow capacity Qweir= 9.739 DH3/2 = 9.739 x (8/12) x (0.5)3/2 = 2.29 cfs Qorifice= 3.782 D2H1/2 = 3.782 x (8/12)2 x (0.5)1/2 = 1.19 cfs Both of these values exceed the expected 100-year Post Developed Un-Mitigated peak flow as listed in Table 3 below. Technical Information Report 17 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) Figure 7 – Section of the Detention Vault showing volume calculation (NTS) Per 2009 King County Surface Water Design Manual section 3.3.4 the project includes a volumetric safety factor as follows: WWHM 100-year stage = 5.4 feet = 853.2 CF Facility storage depth = 6.25 feet = 966 CF Volumetric Safety Factor = (966 CF – 853.2 CF) / 853.2 CF = 13% >10% Below in Table 3 is a summary of the peak flows (15-minute time series) for pre- developed, post-developed, and mitigated conditions. Additional WWHM results are located in Appendix B. Technical Information Report 18 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) Table 3: Summary of Peak Flows Condition 2-Year (cfs) 10-Year (cfs) 100-Year (cfs) Pre-Developed 0.1397 0.2171 0.3285 Post Developed Un-Mitigated (for conveyance design) 0.2309 0.3329 0.4694 Post Developed Mitigated 0.1341 0.2007 0.3074 To meet the Flow Control BMP requirement, the project will add at least 2,639 SF of porous pavement and landscaping in the Right-of Way. See Appendix D. ROW Bypass Area Since the area needed to meet the Flow Control BMP will bypass the onsite detention area Section 1.2.3.2.E of the City of Renton’s February 2010 Amendment to King County’s 2009 Surface Water Design Manual will be addressed as follows: Section 1.2.3.2.E.1 – The point of convergence will be about 200-feet which is within a quarter-mile downstream of the facility's project site discharge point. Section 1.2.3.2.E.2 – The increase in the existing site conditions 100-year peak discharge from the area of bypassed target surfaces is 0.014 cfs, less than the 0.4 cfs limit. Section 1.2.3.2.E.3 – The bypassed runoff will not create a significant adverse impact to downstream drainage systems. Section 1.2.3.2.E.4 – The bypassed area added to the onsite area will not exceed the 5,000 SF of new plus replaced PGIS. Section 1.2.3.2.E.5 – The existing site conditions 100-year peak discharge from the area of bypassed target surfaces will increase by about 0.014 cfs less than 0.1 cfs, therefore compensatory mitigation by a flow control facility is not needed. Water Quality System (Part E) As noted above, the proposed project does not include any pollution generating surfaces, so no water quality treatment is proposed. Technical Information Report 19 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) SECTION V CONVEYANCE SYSTEM ANALYSIS AND DESIGN The un-mitigated peak flows for the proposed conveyance pipes were modeled using the Western Washington Hydrologic Model (WWHM) with a 15-minute time step (See Table 4). All WWHM findings are shown in Appendix B. Plan views of the system is shown on sheets C3.0 and C3.1 of the plans found in Appendix A. Table 4: Conveyance Peak Flows Condition 25-Year Flow (cfs) 100-Year Flow (cfs) Post Developed Un-Mitigated (for conveyance design) 0.3865 0.4694 For the existing system, the full flow capacity flow for existing stormwater downstream pipes in Harrington Avenue NE (note: these pipe will be installed as part of the City’s Sunset Lane Project that is currently under construction) was calculated using Manning's equation, results are shown in Table 5, Figure 8 and Figure 9. This information was used for the backwater analysis shown in Table 6 to verify that the pipe system will still function with more then 6-inches of freeboard when the existing pipes in the ROW are flowing full. Table 5: Summary of Conveyance Calculations Location From To Size (in) Slope (%) Mannings n Full flow capacity (cfs) Peak Vel (fps) Existing Harrington Downstream SD CB#22 CB#21 18 0.50 0.014 6.90 3.90 Proposed SD from project to ROW Vault CB#22 8 1.00 0.013 1.18 3.44 Technical Information Report 20 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) Figure 8 – Manning Conveyance Calculation for Existing Downstream Pipe Figure 9 – Manning Conveyance Calculation for Proposed Vault Outfall Pipe Technical Information Report 21 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) Table 6: Backwater Analysis Method for the Proposed pipe systems Technical Information Report 22 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) SECTION VI SPECIAL REPORTS AND STUDIES See Appendix C for the Geotechnical report See Architectural/Structural plans for the vault design Technical Information Report 23 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) SECTION VII OTHER PERMITS N/A Technical Information Report 24 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) SECTION VIII CSWPPP ANALYSIS AND DESIGN ESC Plan Analysis and Design (Part A) See proposed ESC plan and Erosion control notes on the Demolition, and Erosion Sediment Control Plan (Sheet 4) in Appendix A. As discussed in the project overview of the TIR, the proposed improvement is located adjacent to King County’s new Renton Highlands Library between NE Sunset Blvd, NE 10th St, Sunset Lane NE and Harrington Ave NE, in the City of Renton, King County, Washington. The contractor shall implement Erosion and Sediment control (ESC) measures during construction according to the City of Renton and King County Drainage Requirements. The proposed erosion control plan includes a stabilized construction entrance, inlet protection, chain link fencing, sediment trap/portable storage tanks, straw wattles, slope protections, interceptor swales, silt fence and sump pumps (to be located and sized by the contractor to meet field conditions). Approximate sizing of the portable storage tanks/baker tank was based upon 2009 King County Surface Water Design Manual , section D.3.5.1 for Sediment Trap as follows: 2 Year Peak = 0.140 CFS (assuming a fully disturbed site) Surface Area = 2080 x 2 year peak flow = 2080 x 0.140 CFS = 291 SF Volume = 291 SF x 5 feet depth = 1456 CF Dewatering Orifice Diameter = (per section D.3.5.2 for Sediment Pond) Ao = As(2h)0.5/(0.6 x 3600 x T x g0.5) = 4.81(10-6) x As x (h)0.5 = 4.81(10-6) x 291 x (3.5)0.5 = 0.0026 SF D =13.54(Ao0.5) = 13.54(0.00260.5) = 0.69 inches = 1 inch minimum per King County. Technical Information Report 25 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) Over flow riser = 100 Year Peak Flow= 0.328 CFS (assuming a fully disturbed site) Freeboard = 1-ft Per 2009 King County Surface Water Design Manual, figure 5.3.4.H, the minimum size for the over flow riser shall be 10-inches Due to the depth of the excavation, a pump will be required to drain the Sediment Pond/ portable storage tanks. This pump should be sized to convey the 100-year peak flow and be equipped with a functioning automated on/off switch. Interceptor swales per City of Renton Standard Plan 217.10 have a flow capacity of 21.56 CFS, see Figure 10, which exceeds the expected 100-year peak flow rate from the project site. Figure 10 – Manning Conveyance Calculation for Interceptor Ditch Actual sizing of the portable storage tanks/baker tank and pumps and all other erosion control facilities will depend on the contractor's approach, construction sequence and operations. Per the erosion control notes on the plans the control is required to upgrade the erosion control facilities as needed to keep the site in compliance. The 24-hour ESC contact for the project will be identified by the contractor prior to start of construction at the pre-construction meeting. Per the erosion control notes Technical Information Report 26 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) on the plans, at the pre-construction meeting the contractor is required to provide for City approval a SWPPP and erosion control plans detailing the construction approach and sequence to keep the site compliant. Stormwater Pollution Prevention and Spill (SWPPS) Plan Design (Part B) As part of construction the contractor shall provide a SWPPS plan utilizing BMP’s from Washington State Department of Ecology’s 2012 Stormwater Management Manual the that will detail, at a minimum, the following pollution generating activities typically associated with construction: Storage and Handling of Liquids Leaks and spills of pollutant materials during handling and storage are the primary sources of pollutants. Once the liquids to be stored and handled onsite are identified and the types and sizes of containers are specified, secondary containment methods can be sized. The following BMP’s can be used to safely store and handle liquids onsite: S427 BMPs for Storage of Liquid, Food Waste, or Dangerous Waste Containers S412 BMP’s for Loading and Unloading Areas for Liquid and Solid Material Storage and Stockpiling of Construction Materials and Wastes Contact between outside bulk materials (i.e. gravel, sand, topsoil, etc) and stormwater can cause leachate, and erosion of the stored materials. Contaminants may include TSS, BOD, organics, and dissolved salts (sodium, calcium, and magnesium chloride, etc.). Once construction materials and wastes that may be generated or stockpiled onsite are identified, cover measures and containers can be specified to keep rainwater from contacting construction materials and wastes that can contribute pollutants to storm, surface and ground water. The following BMP’s can be utilized to safely store and stockpile construction materials and wastes: S429 BMPs for Storage or Transfer (Outside) of Solid Raw Materials, Byproducts, or Finished Products BMP C153 Material Delivery, Storage and Containment Technical Information Report 27 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) Fueling The method of onsite fueling for construction equipment shall be specified, the type and size of tanks described, containment methods for fuel spills described, and lighting and signage plan for evening fueling described using the following BMP’s: S419 BMPs for Mobile Fueling of Vehicles and Heavy Equipment Maintenance, Repairs, and Storage of Vehicles and Equipment Maintenance and repair areas shall be identified by the contractor. Use of drip pans or plastic beneath vehicles is required. Methods of collection, storage and disposal of vehicle fluid will be described and signs will be posted in areas designated for vehicle maintenance stating that no vehicle washing may occur in the area. The following BMP’s can be utilized for proper maintenance, repair and storage of vehicles and equipment: S414 BMPs for Maintenance and Repair of Vehicles and Equipment S421 BMPs for Parking and Storage of Vehicles and Equipment S431 BMPs for Washing and Steam Cleaning Vehicles/Equipment/Building Structures Concrete Saw Cutting, Slurry, and Washwater Disposal If possible, truck washout areas shall be located outside the Aquifer Protection Area. If truck washout areas are located within an Aquifer Protection Area, the washout area must be lined with an impervious membrane. Once truck washout areas and areas for rinsing hand tools are identified, the size of pumps necessary to collect and contain slurry and washwater can be specified and the methods for collecting, treating, and disposal of wastewater from exposed aggregate processes, concrete grinding and saw cutting, and new concrete washing and curing water can be described. The following BMP’s can be implemented for this work: BMP C106 Wheel Wash BMP C151 Concrete Handling BMP C152 Sawcutting and Surfacing Pollution Prevention BMP C154 Concrete Washout Area S431 BMPs for Washing and Steam Cleaning Vehicles/Equipment/Building Structures Technical Information Report 28 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) Handling of pH Elevated Water New concrete vaults/structures may cause collected water to have an elevated pH. This water cannot be discharged to storm or surface water until neutralized. Water can be treated, neutralized and disposed of using the following BMP’s: BMP C252 High pH Neutralization Using CO2 BMP C253 pH Control for High pH Water Application of Chemicals including Pesticides and Fertilizers It is not known at this time if the contractor will apply any chemicals on the site. If chemicals are to be applied, a list of chemicals that may be used on the project site shall be provided and where and how the chemicals will be applied and stored will be described. If chemicals are to be applied on site, the following BMP’s should be implemented: S411 BMPs for Landscaping and Lawn/Vegetation Management BMP C153 Material Delivery, Storage and Containment Technical Information Report 29 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) ESC Site Inspection Forms The Contractor shall regularly conduct site inspection to verify compliance with permit requirements. The results of each site inspection shall be summarized in an inspection report or checklist that is entered into or attached to the site log book. It is suggested that the inspection report or checklist be included in this appendix to keep monitoring and inspection information in one document, but this is optional. However, it is mandatory that this SWPPS and the site inspection forms be kept on-site at all times during construction, and that inspections be performed and documented as outlined below. At a minimum, each site inspection report or checklist shall include: a) Inspection date/times. b) Weather information: general conditions during inspection, approximate amount of precipitation since the last inspection, and approximate amount of precipitation within the last 24 hours. c) A summary or list of all BMPs that have been implemented, including observations of all erosion/sediment control structures or practices. d) The following shall be noted: i. locations of BMPs inspected, ii. locations of BMPs that need maintenance, iii. the reason maintenance is needed, iv. locations of BMPs that failed to operate as designed or intended, and v. locations where additional or different BMPs are needed, and the reason(s) why e) A description of stormwater discharged from the site. The presence of suspended sediment, turbid water, discoloration, and/or oil sheen shall be noted, as applicable. f) A description of any water quality monitoring performed during inspection, and the results of that monitoring. g) General comments and notes, including a brief description of any BMP repairs, maintenance or installations made as a result of the inspection. h) A statement that, in the judgment of the person conducting the site inspection, the site is either in compliance or out of compliance with the terms and conditions of the CSCP and the NPDES permit. If the site Technical Information Report 30 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) inspection indicates that the site is out of compliance, the inspection report shall include a summary of the remedial actions required to bring the site back into compliance, as well as a schedule of implementation. i) Name, title, and signature of person conducting the site inspection or clean up; and the following statement: “I certify under penalty of law that this report is true, accurate, and complete, to the best of my knowledge and belief”. When the site inspection indicates that the site is not in compliance with any terms and conditions of the NPDES permit, the Contractor/Permittee shall take immediate action(s) to: stop, contain, and clean up the unauthorized discharges, or otherwise stop the noncompliance; correct the problem(s); implement appropriate BMPs, and/or conduct maintenance of existing BMPs; and achieve compliance with all applicable standards and permit conditions. In addition, if the noncompliance causes a threat to human health or the environment, the Contractor/Permittee shall comply with the Noncompliance Notification requirements in Special Condition S5.F of the permit. Technical Information Report 31 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) SITE INSPECTION CHECKLIST (Page 1 of 3) Project ____________________ Permit No. ___________ Inspector _________ Date and Time ____________ Overall Need Site BMPs Condition Repair? Comments/Observations Clearing Limits ●Buffer Zones around sensitive areas G F P Y N ● G F P Y N ● G F P Y N Construction Access/Roads ●Stabilized site entrance G F P Y N ●Stabilized roads/parking area G F P Y N ● G F P Y N Control Flow Rates ●Swale G F P Y N ●Dike G F P Y N ●Sediment pond G F P Y N ●Sediment trap G F P Y N ● G F P Y N ● G F P Y N Install Sediment Controls ●Sediment pond/trap G F P Y N ●Silt fence G F P Y N ●Straw bale barriers G F P Y N ● G F P Y N ● G F P Y N ● G F P Y N Preserve Vegetation/Stabilize Soils ●Nets and blankets G F P Y N ●Mulch G F P Y N ●Seeding G F P Y N ● G F P Y N ● G F P Y N Protect Slopes ●Terrace G F P Y N ●Pipe slope drains G F P Y N ● G F P Y N ● G F P Y N Protect Drain Inlets ●Inserts G F P Y N ● G F P Y N ● G F P Y N Stabilize Channels and Outlets ●Conveyance channels G F P Y N ●Energy dissipators G F P Y N ● G F P Y N Control Pollutants ●Chemical Storage Area covered G F P Y N ●Concrete handling G F P Y N ●Any spills? G F P Y N Control De-watering ● G F P Y N G=Good F=Fair P=Poor Y=Yes N=No Technical Information Report 32 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) SITE INSPECTION CHECKLIST (Page 2 of 3) Project ____________________ Permit No. ___________ Inspector _________ Date and Time ____________ Will existing BMPs need to be modified or removed, or other BMPs installed? YES NO IF YES, list the action items to be completed on the following table: Actions to be Completed Date Completed/ Initials 1. 2. 3. 4. 5. Describe current weather conditions Approximate amount of precipitation since last inspection: __________ inches and precipitation in the past 24 hours*: __________inches *based on an on-site rain gauge or local weather data. Describe discharging stormwater, if present. Note the presence of suspended sediment, “cloudiness”, discoloration, or oil sheen. Was water quality sampling part of this inspection? YES NO If yes, record results in the Water Quality Monitoring Form Sampling Location Turbidity (NTU) pH (Standard Units) Meets Standards? (Y/N) Notes Technical Information Report 33 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) SITE INSPECTION CHECKLIST (Page 3 of 3) Project ____________________ Permit No. ___________ Inspector _________ Date and Time ___________ Date and time of the last calibration of sampling equipment: ________________________________ Is the site in compliance with the SWPPP and the permit requirements? YES NO If no, indicate tasks necessary to bring site into compliance on the “Actions to be Completed” table above, and include dates each job WILL BE COMPLETED. If no, has the non-compliance been reported to Dept. of Ecology? YES NO If no, should the SWPPP be modified: YES NO Is Dept. of Ecology was notified, indicate the date, time, contact name and phone number below: Date: ____________________________________ Time: ____________________________________ Contact Name: ____________________________________ Phone #: ___________________________________ Sign the following certification: “I certify that this report is true, accurate, and complete, to the best of my knowledge and belief.” Inspection completed on:____________ by: (print+signature)___________________ Title/Qualification of Inspector:______________________ Technical Information Report 34 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) CWSPPP Worksheet Forms / Cleanup Report The Contractor shall provide specifics on spill prevention and cleanup and must include the following information in addition to any activity-specific information in Subsection A above related to spill prevention: 1. List the possible sources of a spill and identify the BMPs to be used for each source to prevent a spill. 2. Identify personnel responsible for spill prevention and cleanup and clearly list the responsibilities of each person identified. Contact information for these personnel must be clearly identified in the report and on the SWPPS site plan. 3. Describe the procedures to be used for monitoring spill prevention BMPs and for responding to a spill incident, including keeping records/reports of all inspections and spills (see attached worksheets that may be used). 4. Identify where spill response materials will be stored. Make reference to the SWPPS site plan for location information. 5. Identify disposal methods for contaminated water and soil after a spill. 2009 Surface Water Design Manual (CSWPP Forms) 1/9/2009 Page 1 BMP Implementation Completed by: Title: Date: Develop a plan for implementing each BMP. Describe the steps necessary to implement the BMP (i.e., any construction or design), the schedule for completing those steps (list dates), and the person(s) responsible for implementation. BMPs Description of Action(s) Required for Implementation Scheduled Milestone and Completion Date(s) Person Responsible for Action Good Housekeeping 1. 2. 3 1. 2. 3. Preventive Maintenance 4. 1.SpillPrevention andEmergency Cleanup 2. 3. Inspections 1. 2. 3. 2009 Surface Water Design Manual (CSWPP Forms) 1/9/2009 Page 2 BMPs Description of Action(s) Required for Implementation Schedule Milestone and Completion Date(s) Person Responsible for Action Source Control BMPs 1. 2. 3 4. 5. 6. 7. 8. Treatment BMPs 1. 2. 3. 4. Emerging technologies 1. 2. Flow Control BMPs 3. 4. 2009 Surface Water Design Manual (CSWPP Forms) Page 1 1/9/2009 Material Inventory Completed by: Title:Date: List materials handled, treated, stored, or disposed of at the project site that may potentially be exposed to precipitation or runoff.Quantity (Units) Likelihood of contact with stormwater Past Spill or Used Produced Stored If Yes, describe reason Leak MaterialPurpose/Location (indicate per/wk. or yr.) Yes No 2009 Surface Water Design Manual (CSWPP Forms) Page 1Potential Pollutant Source Identification Completed by: Title:Date:List all potential stormwater pollutants from materials handled, treated, or stored on-site. Potential Stormwater Pollutant Stormwater Pollutant Source Likelihood of pollutant being present in your stormwater discharge. If yes, explain 2009 Surface Water Design Manual (CSWPP Forms) Page 1List of Significant Spills and Leaks Completed by: Title:Date:List all spills and leaks of toxic or hazardous pollutants that were significant but are not limited to, release of oil or hazardous substances in excess of reportable quantities. Although not required, we suggest you list spills and leaks of non-hazardous materials. Description Response Procedure Date(month/day/year) Location (asindicated on site map) Type of Material Quantity Source, If Known Reason for Spill/Leak Amount of Material Recovered Material No longerexposed to Stormwater (Yes/No)Preventive Measure Taken 2009 Surface Water Design Manual (CSWPP Forms) Page 1 1/9/2009 Employee Training Completed by:Title:Date:Describe the annual training of employees on the SWPPP, addressing spill response, good housekeeping, and material management practices. Training Topics 1.) LINE WORKERS Brief Description of Training Program/Materials (e.g., film, newsletter course) Schedule for Training (list dates) Attendees Spill Prevention and Response Good Housekeeping Material Management Practices 2.) P2 TEAM: SWPPP Implementation Monitoring Procedures 2009 Surface Water Design Manual (CSWPP Forms) 1/9/2009 Page 1 Pollution Prevention Team Completed by: ______________________ Title: ______________________________ Date: ______________________________ Responsible Official: Title: Team Leader: Office Phone: Cell Phone #: Pager #: Responsibilities: (1) Title: Office Phone: Pager #: Cell Phone: Responsibilities: (2) Title: Office Phone: Pager #: Cell Phone #: Responsibilities: Technical Information Report 35 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) SECTION IX BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT Bond Quantities Worksheet See attached. Flow Control and Water Quality Facility Summary Sheet and Sketch To be provided after approval of the plans Declaration of Covenant for Privately Maintained Flow Control and WQ Facilities To be provided after approval of the plans Declaration of Covenant for Privately Maintained Flow Control BMPs To be provided after approval of the plans Technical Information Report 36 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) SECTION X OPERATIONS AND MAINTENANCE MANUAL. Project: Sunset Terrace Development Building 1 – (AKA Colpitts Site 9/10) Prepared for: Colpitts Development The attached Operation and Maintenance checklist is intended to provide guidance to the owner(s) for the operation and maintenance of the drainage and the stormwater detention system at the Sunset Terrace Development. The owner is responsible for maintenance of storm drainage facilities within the property. The owner is not responsible for maintenance within the public right-of- way. This manual cannot anticipate every problem, but provide a checklist for the most anticipated maintenance items. The stormwater system should be regularly maintained on an annual basis during the summer prior to the start of the "rainy season" at the end of September. When operating normally, the system should not have any surface ponding of stormwater and the detention system should fully drain (except for the 4-foot sump) within 24-hours after a storm event. If either of these are not true then the system should be reviewed using the maintenance checklist to determine the problem. For additional and updated maintenance information visit the King County Storm resources at: http://www.kingcounty.gov/environment/waterandland/stormwater.aspx or the Washington State Department of Ecology's web-site at: http://www.ecy.wa.gov/programs/wq/wqhome.html Below is a summary of each component of the storm drainage system: Detention Vault The vault in located in the south-west corner of the level 1 parking lot (see attached plan) at the corner of Harrington Ave NE and Sunset Lane NE. The vault is only accessible through a maintenance hole located outside the building in the sidewalk. The purpose of the vault is to use the flow control device (see below) to temporarily store stormwater runoff from the building roof to reduce the peak stormwater runoff flows. See the attached “NO. 3 – DETENTION TANKS AND VAULTS” checklist for items to be reviewed during the inspection. Technical Information Report 37 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) If any maintenance is required inside the vault, then the owner shall used only personnel with current confined space entry certification to enter the vault. Prior to personnel entering the vault, the maintenance hole and three vents shall be opened and used for forced air venting. Flow control structure The flow control structure is located in the vault and is visible from the maintenance hole. The flow control structure consists of a 12-inch diameter vertical riser pipe with two orifices sized to only let through a limited flow of stormwater runoff. The lowest orifice is submerged in the sump located under the bottom of the riser, the second is located under the elbow that is attached to the riser pipe near the top of the riser pipe. If the orifices are blocked, the Stormwater Vault can be drained to allow cleaning by opening a shear gate. This is done by pulling on the handle attached to the top rung underneath the lid. The shear gate shall be closed after cleaning. See attached “NO. 4 – CONTROL STRUCTURE/FLOW RESTRICTOR” checklist for items to be reviewed during the inspection. Connection to the City System The detention system is connected via a storm water drain to the City’s storm water system in the intersection of Harrington Ave NE and Sunset Lane NE. The owner is not responsible to maintain the maintenance hole in the public right-of- way that the project’s storm drain connects to. See attached “NO. 6 – CONVEYANCE PIPES” checklist for items to be reviewed during the inspection. Right of Way Porous Pavement and Landscaping The project includes approximately 3,000 SF of pervious concrete sidewalk and adjacent landscape strip in the Right of Way along Sunset Boulevard. See attached “NO. 11 – GROUNDS (LANDSCAPING)” and “NO. 30 – PERMEABLE PAVEMENT BMP” checklist for items to be reviewed during the inspection. Below is a stormwater inspection form and checklists to be completed each year at the time of the inspection and when any maintenance is performed on the storm drain system. A copy of all the completed forms and checklists shall be kept on site in a log book for review by the City. Technical Information Report 38 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) STORMWATER INSPECTION FORM O.K. Not O.K. Condition, Corrective Action, General Notes Detention Vault Flow control structure Conveyance pipes Porous Pavement and Landscape Strip Comments: Was any waste disposed? If so where? Inspection completed by: ____________________ (Signature) ___________________ (Job Title) ________ (Date) Notes: • Attached completed checklists. • Keep a copy of all the completed forms and checklists on site in a log book for review by the City. APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 2009 Surface Water Design Manual – Appendix A 1/9/2009 A-5 NO. 3 – DETENTION TANKS AND VAULTS Maintenance Component Defect or Problem Conditions When Maintenance is Needed Results Expected When Maintenance is Performed Trash and debris Any trash and debris which exceed 1 cubic foot per 1,000 square feet (this is about equal to the amount of trash it would take to fill up one standard size office garbage can). In general, there should be no visual evidence of dumping. Trash and debris cleared from site. Noxious weeds Any noxious or nuisance vegetation which may constitute a hazard to County personnel or the public. Noxious and nuisance vegetation removed according to applicable regulations. No danger of noxious vegetation where County personnel or the public might normally be. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations.Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Site Grass/groundcover Grass or groundcover exceeds 18 inches in height. Grass or groundcover mowed to a height no greater than 6 inches. Trash and debris Any trash and debris accumulated in vault or tank (includes floatables and non-floatables). No trash or debris in vault. Tank or Vault Storage Area Sediment accumulation Accumulated sediment depth exceeds 10% of the diameter of the storage area for ½ length of storage vault or any point depth exceeds 15% of diameter. Example: 72-inch storage tank would require cleaning when sediment reaches depth of 7 inches for more than ½ length of tank. All sediment removed from storage area. Plugged air vent Any blockage of the vent. Tank or vault freely vents. Tank bent out of shape Any part of tank/pipe is bent out of shape more than 10% of its design shape. Tank repaired or replaced to design. Tank Structure Gaps between sections, damaged joints or cracks or tears in wall A gap wider than ½-inch at the joint of any tank sections or any evidence of soil particles entering the tank at a joint or through a wall. No water or soil entering tank through joints or walls. Vault Structure Damage to wall, frame, bottom, and/or top slab Cracks wider than ½-inch, any evidence of soil entering the structure through cracks or qualified inspection personnel determines that the vault is not structurally sound. Vault is sealed and structurally sound. Sediment accumulation Sediment filling 20% or more of the pipe. Inlet/outlet pipes clear of sediment. Trash and debris Trash and debris accumulated in inlet/outlet pipes (includes floatables and non-floatables). No trash or debris in pipes. Inlet/Outlet Pipes Damaged Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering at the joints of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of the inlet/outlet pipe. APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 1/9/2009 2009 Surface Water Design Manual – Appendix A A-6 NO. 3 – DETENTION TANKS AND VAULTS Maintenance Component Defect or Problem Conditions When Maintenance is Needed Results Expected When Maintenance is Performed Cover/lid not in place Cover/lid is missing or only partially in place. Any open manhole requires immediate maintenance. Manhole access covered. Locking mechanism not working Mechanism cannot be opened by one maintenance person with proper tools. Bolts cannot be seated. Self-locking cover/lid does not work. Mechanism opens with proper tools. Cover/lid difficult to remove One maintenance person cannot remove cover/lid after applying 80 lbs of lift. Cover/lid can be removed and reinstalled by one maintenance person. Access Manhole Ladder rungs unsafe Missing rungs, misalignment, rust, or cracks. Ladder meets design standards. Allows maintenance person safe access. Damaged or difficult to open Large access doors or plates cannot be opened/removed using normal equipment. Replace or repair access door so it can opened as designed. Gaps, doesn't cover completely Large access doors not flat and/or access opening not completely covered. Doors close flat and covers access opening completely. Large access doors/plate Lifting Rings missing, rusted Lifting rings not capable of lifting weight of door or plate. Lifting rings sufficient to lift or remove door or plate. APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 2009 Surface Water Design Manual – Appendix A 1/9/2009 A-7 NO. 4 – CONTROL STRUCTURE/FLOW RESTRICTOR Maintenance Component Defect or Problem Condition When Maintenance is Needed Results Expected When Maintenance is Performed Trash or debris of more than ½ cubic foot which is located immediately in front of the structure opening or is blocking capacity of the structure by more than 10%. No Trash or debris blocking or potentially blocking entrance to structure. Trash or debris in the structure that exceeds 1/3the depth from the bottom of basin to invert the lowest pipe into or out of the basin. No trash or debris in the structure. Trash and debris Deposits of garbage exceeding 1 cubic foot in volume. No condition present which would attract or support the breeding of insects or rodents. Sediment Sediment exceeds 60% of the depth from the bottom of the structure to the invert of the lowest pipe into or out of the structure or the bottom of the FROP-T section or is within 6 inches of the invert of the lowest pipe into or out of the structure or the bottom of the FROP-T section. Sump of structure contains no sediment. Corner of frame extends more than ¾ inch past curb face into the street (If applicable). Frame is even with curb. Top slab has holes larger than 2 square inches or cracks wider than ¼ inch. Top slab is free of holes and cracks. Damage to frame and/or top slab Frame not sitting flush on top slab, i.e., separation of more than ¾ inch of the frame from the top slab. Frame is sitting flush on top slab. Cracks wider than ½ inch and longer than 3 feet, any evidence of soil particles entering structure through cracks, or maintenance person judges that structure is unsound. Structure is sealed and structurally sound. Cracks in walls or bottom Cracks wider than ½ inch and longer than 1 foot at the joint of any inlet/outlet pipe or any evidence of soil particles entering structure through cracks. No cracks more than 1/4 inch wide at the joint of inlet/outlet pipe. Settlement/ misalignment Structure has settled more than 1 inch or has rotated more than 2 inches out of alignment. Basin replaced or repaired to design standards. Damaged pipe joints Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering the structure at the joint of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of inlet/outlet pipes. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Structure Ladder rungs missing or unsafe Ladder is unsafe due to missing rungs, misalignment, rust, cracks, or sharp edges. Ladder meets design standards and allows maintenance person safe access. T section is not securely attached to structure wall and outlet pipe structure should support at least 1,000 lbs of up or down pressure. T section securely attached to wall and outlet pipe. Structure is not in upright position (allow up to 10% from plumb). Structure in correct position. Connections to outlet pipe are not watertight or show signs of deteriorated grout. Connections to outlet pipe are water tight; structure repaired or replaced and works as designed. FROP-T Section Damage Any holes—other than designed holes—in the structure. Structure has no holes other than designed holes. Cleanout Gate Damaged or missing Cleanout gate is missing. Replace cleanout gate. APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 1/9/2009 2009 Surface Water Design Manual – Appendix A A-8 NO. 4 – CONTROL STRUCTURE/FLOW RESTRICTOR Maintenance Component Defect or Problem Condition When Maintenance is Needed Results Expected When Maintenance is Performed Cleanout gate is not watertight. Gate is watertight and works as designed. Gate cannot be moved up and down by one maintenance person. Gate moves up and down easily and is watertight. Chain/rod leading to gate is missing or damaged. Chain is in place and works as designed. Damaged or missing Control device is not working properly due to missing, out of place, or bent orifice plate. Plate is in place and works as designed. Orifice Plate Obstructions Any trash, debris, sediment, or vegetation blocking the plate. Plate is free of all obstructions and works as designed. Obstructions Any trash or debris blocking (or having the potential of blocking) the overflow pipe. Pipe is free of all obstructions and works as designed. Overflow Pipe Deformed or damaged lip Lip of overflow pipe is bent or deformed. Overflow pipe does not allow overflow at an elevation lower than design Sediment accumulation Sediment filling 20% or more of the pipe. Inlet/outlet pipes clear of sediment. Trash and debris Trash and debris accumulated in inlet/outlet pipes (includes floatables and non-floatables). No trash or debris in pipes. Inlet/Outlet Pipe Damaged Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering at the joints of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of the inlet/outlet pipe. Unsafe grate opening Grate with opening wider than 7/8 inch. Grate opening meets design standards. Trash and debris Trash and debris that is blocking more than 20% of grate surface. Grate free of trash and debris. footnote to guidelines for disposal Metal Grates (If Applicable) Damaged or missing Grate missing or broken member(s) of the grate. Grate is in place and meets design standards. Cover/lid not in place Cover/lid is missing or only partially in place. Any open structure requires urgent maintenance. Cover/lid protects opening to structure. Locking mechanism Not Working Mechanism cannot be opened by one maintenance person with proper tools. Bolts cannot be seated. Self-locking cover/lid does not work. Mechanism opens with proper tools. Manhole Cover/Lid Cover/lid difficult to Remove One maintenance person cannot remove cover/lid after applying 80 lbs. of lift. Cover/lid can be removed and reinstalled by one maintenance person. APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 2009 Surface Water Design Manual – Appendix A 1/9/2009 A-11 NO. 6 – CONVEYANCE PIPES AND DITCHES Maintenance Component Defect or Problem Conditions When Maintenance is Needed Results Expected When Maintenance is Performed Sediment & debris accumulation Accumulated sediment or debris that exceeds 20% of the diameter of the pipe. Water flows freely through pipes. Vegetation/roots Vegetation/roots that reduce free movement of water through pipes. Water flows freely through pipes. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Damage to protective coating or corrosion Protective coating is damaged; rust or corrosion is weakening the structural integrity of any part of pipe. Pipe repaired or replaced. Pipes Damaged Any dent that decreases the cross section area of pipe by more than 20% or is determined to have weakened structural integrity of the pipe. Pipe repaired or replaced. Trash and debris Trash and debris exceeds 1 cubic foot per 1,000 square feet of ditch and slopes. Trash and debris cleared from ditches. Sediment accumulation Accumulated sediment that exceeds 20% of the design depth. Ditch cleaned/flushed of all sediment and debris so that it matches design. Noxious weeds Any noxious or nuisance vegetation which may constitute a hazard to County personnel or the public. Noxious and nuisance vegetation removed according to applicable regulations. No danger of noxious vegetation where County personnel or the public might normally be. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Vegetation Vegetation that reduces free movement of water through ditches. Water flows freely through ditches. Erosion damage to slopes Any erosion observed on a ditch slope. Slopes are not eroding. Ditches Rock lining out of place or missing (If Applicable) One layer or less of rock exists above native soil area 5 square feet or more, any exposed native soil. Replace rocks to design standards. APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES NO. 11 – GROUNDS (LANDSCAPING) Maintenance Component Defect or Problem Conditions When Maintenance is Needed Results Expected When Maintenance is Performed Site Trash or litter Any trash and debris which exceed 1 cubic foot per 1,000 square feet (this is about equal to the amount of trash it would take to fill up one standard size office garbage can). In general, there should be no visual evidence of dumping. Trash and debris cleared from site. Noxious weeds Any noxious or nuisance vegetation which may constitute a hazard to County personnel or the public. Noxious and nuisance vegetation removed according to applicable regulations. No danger of noxious vegetation where County personnel or the public might normally be. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Grass/groundcover Grass or groundcover exceeds 18 inches in height. Grass or groundcover mowed to a height no greater than 6 inches. Trees and Shrubs Hazard Any tree or limb of a tree identified as having a potential to fall and cause property damage or threaten human life. A hazard tree identified by a qualified arborist must be removed as soon as possible. No hazard trees in facility. Damaged Limbs or parts of trees or shrubs that are split or broken which affect more than 25% of the total foliage of the tree or shrub. Trees and shrubs with less than 5% of total foliage with split or broken limbs. Trees or shrubs that have been blown down or knocked over. No blown down vegetation or knocked over vegetation. Trees or shrubs free of injury. Trees or shrubs which are not adequately supported or are leaning over, causing exposure of the roots. Tree or shrub in place and adequately supported; dead or diseased trees removed. 4/24/2016 2016 Surface Water Design Manual – Appendix A A-16 APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES NO. 30 – PERMEABLE PAVEMENT BMP Maintenance Component Defect or Problem Conditions When Maintenance is Needed Results Expected When Maintenance is Performed Preventative Surface cleaning/ vegetation control Media surface vacuumed or pressure washed annually, vegetation controlled to design maximum. Weed growth suggesting sediment accumulation. No dirt, sediment, or debris clogging porous media, or vegetation limiting infiltration. Porous Concrete, Porous Asphaltic Concrete, and Permeable Pavers Trash and debris Trash and debris on the pavement interfering with infiltration; leaf drop in fall season. No trash or debris interfering with infiltration. Sediment accumulation Sediment accumulation on the pavement interfering with infiltration; runoff from adjacent areas depositing sediment/debris on pavement. Pavement infiltrates as designed; adjacent areas stabilized. Infiltration rate Pavement does not infiltrate at a rate of 10 inches per hour. Pavement infiltrates at a rate greater than 10 inches per hour. Ponding Standing water for a long period of time on the surface of the pavement. Standing water infiltrates at the desired rate. Broken or cracked pavement Pavement is broken or cracked. No broken pavement or cracks on the surface of the pavement. Settlement Uneven pavement surface indicating settlement of the subsurface layer. Pavement surface is uniformly level. Moss growth Moss growing on pavement interfering with infiltration. No moss interferes with infiltration. Inflow Inflow to the pavement is diverted, restricted, or depositing sediment and debris on the pavement. Inflow to pavement is unobstructed and not bringing sediment or debris to the pavement. Underdrain Underdrain is not flowing when pavement has been infiltrating water. Underdrain flows freely when water is present. Overflow Overflow not controlling excess water to desired location; native soil is exposed or other signs of erosion damage are present. Overflow permits excess water to leave the site at the desired location; Overflow is stabilized and appropriately armored. Permeable Pavers Broken or missing pavers Broken or missing paving blocks on surface of pavement. No missing or broken paving blocks interfering with infiltration. Level surface Uneven surface due to settlement or scour of fill in the interstices of the paving blocks. Pavement surface is uniformly level. Compaction Poor infiltration due to soil compaction between paving blocks. No soil compaction in the interstices of the paver blocks limiting infiltration. Dead grass Grass in the interstices of the paving blocks is dead. Healthy grass is growing in the interstices of the paver blocks. Inspection Frequency Annually and after large storms, and as needed seasonally to control leaf drop, evergreen needles etc. Permeable pavement is functioning normally. 4/24/2016 2016 Surface Water Design Manual – Appendix A A-38 Technical Information Report 39 Sunset Terrace Development – Building 1 (aka Colpitts Site 9/10) REFERENCES King County 2009 King County Surface Water Design Manual City of Renton 2010 City of Renton Amendments to the King County Surface Water Design Manual http://rentonwa.gov/uploadedFiles/Government/PW/UTILITIES/Surface_W ater/City%20Amendments%20to%20the%20King%20County%20Surface% 20Water%20Design%20Manual.pdf Department of Ecology 2012 Stormwater Management Manual for Western Washington APPENDIX A PERMIT PLANS COVER SHEET below.RENTON, WASHINGTON / /51017RENTON, WASHINGTON / /51017SUNSET TERRACE DEVELOPMENT - BUILDING 1CONSTRUCTION SETSHEET INDEXSHEET # SHEET TITLEB15001398, B16002230, B16002234, U16002232, LUA 15-000159,LUA 13-001114, LUA 10-052, LUA 14-001475, 5A-A, 5A-M, CUP GENERAL NOTES below.RENTON, WASHINGTON / /51017RENTON, WASHINGTON / /51017CITY OF RENTON - SURFACE WATER DRAINAGE NOTES AND SPECIFICATIONS’’“”CITY OF RENTON - SANITARY SEWER NOTES AND SPECIFICATIONS’’ CITY OF RENTON - WATER UTILITY NOTES AND SPECIFICATIONS’“” “” “” “” ’’ KCLSLIBRARYEROSION AND SEDIMENT CONTROL PLAN below.EROSION CONTROL NOTESRENTON, WASHINGTON / /51017RENTON, WASHINGTON / /51017RECOMMENDED CONSTRUCTION SEQUENCE KCLSLIBRARYDEMOLITION PLAN below.RENTON, WASHINGTON / /51017RENTON, WASHINGTON / /51017 EROSION CONTROL DETAILS below.RENTON, WASHINGTON / /51017RENTON, WASHINGTON / /510171 EROSION CONTROL DETAILS below.RENTON, WASHINGTON / /51017RENTON, WASHINGTON / /51017 EROSION CONTROL DETAILS below.RENTON, WASHINGTON / /51017RENTON, WASHINGTON / /510171 9/10 COLPITTSFFE=336.50LOWER GARAGE FFE=317.25KCLSLIBRARYGRADING PLAN below.RENTON, WASHINGTON / /51017RENTON, WASHINGTON / /51017 / /42716 9/10 COLPITTSFFE=336.50GARAGE FFE=317.25KCLSLIBRARYDRAINAGE CONTROL PLAN below.RENTON, WASHINGTON / /51017RENTON, WASHINGTON / /51017 BUILDINGDRAINAGE DETAILS below.RENTON, WASHINGTON / /51017RENTON, WASHINGTON / /51017 ****************DRAINAGE DETAILS below.RENTON, WASHINGTON / /51017RENTON, WASHINGTON / /51017 UTILITIES PLAN below.RENTON, WASHINGTON / /51017RENTON, WASHINGTON / /51017 UTILITY DETAILS below.RENTON, WASHINGTON / /51017RENTON, WASHINGTON / /51017 UTILITY DETAILS below.RENTON, WASHINGTON / /51017RENTON, WASHINGTON / /51017 UTILITY DETAILS below.RENTON, WASHINGTON / /51017RENTON, WASHINGTON / /51017 S000 SHORING PLANS100 STRUCTURAL GENERAL NOTESS101 STRUCTURAL GENERAL NOTESS200 FOUNDATION / PARKING LEVEL 3 PLAN S201F PARKING LEVEL 2 CONCRETE FRAMING PLANS202F PARKING LEVEL 1 CONCRETE FRAMING PLANS202R PARKING LEVEL 1 CONCRETE REINFORCING PLANS201R PARKING LEVEL 2 CONCRETE REINFORCING PLANS203F LOFT LEVEL FRAMING PLANS203R LOFT LEVEL CONCRETE REINFORCING PLANS204F RESIDENTIAL LEVEL 1 CONCRETE FRAMING PLANS204R RESIDENTIAL LEVEL 1 CONCRETE REINFORCING PLANS204W RESIDENTIAL LEVEL 1 WOOD FRAMING PLANS205 RESIDENTIAL LEVEL 2 WOOD FRAMING PLANS206 RESIDENTIAL LEVEL 3 WOOD FRAMING PLANS207 RESIDENTIAL LEVEL 4 WOOD FRAMING PLANS208 RESIDENTIAL LEVEL 5 WOOD FRAMING PLANS209 ROOF FRAMING PLANS300 TYPICAL FOUNDATION and CONCRETE FRAMING DETAILSS301 TEMPORARY EXCAVATION SHORING DETAILS and SECTIONSS302 BASEMENT WALL SECTIONSS303 BASEMENT WALL SECTIONSS304 BASEMENT WALL SECTIONSS305 BASEMENT WALL SECTIONSS400 TYPICAL P.T. and CONCRETE REINFORCING DETAILSS401 CONCRETE COLUMN SCHEDULES and REINFORCING DETAILSS402 TYPICAL CMU AND CONCRETE DETAILSS403 CONCRETE BEAM SCHEDULES404 TYPICAL VENEER DETAILSS405 TYPICAL CANOPY DETAILSS406 TYPICAL LIGHT GA. FRAMING DETAILSS407 CONCRETE BEAM SCHEDULES408 CONCRETE SHEARWALL DETAILS & SCHEDULES5.1 TYPICAL WOOD FRAMING DETAILSS5.2 WOOD SHEARWALLS SCHEDULE and DETAILSS5.3 TYPICAL WOOD FRAMING SECTIONSS5.4 TYPICAL STEEL & WOOD FRAMING SECTIONSS5.5 TYPICAL DECK FRAMING SECTIONS & DETAILS APPENDIX B WWHM DETENTION SIZING RESULTS AND TESC SIZING RESULTS Below are the peak flows for the following scenarios: • 501 POC 1 Pre developed Flow (the existing condition) • 701 Inflow to POC 1 Mitigated (The pre-mitigated condition – aka the flow into the vault) • 801 POC 1 Mitigated Flow (the mitigated condition) APPENDIX C GEOTECHNICAL REPORT APPENDIX D FLOW CONTROL BMPS REQUIREMENT SUNSET TERRACE MF PROJECT (SUNSET TERRACE - 9/10 SITE) - B16002230 FLOW CONTROL BMP VARIANCE REQUEST 1 Dear Ms. Fowler: The Sunset Terrace MF Project (Sunset Terrace - 9/10 Site) - B16002230 requests a variance to the Flow Control BMP requirement as described in Section 1.2.3.3 and 5.2.1.3 of the City of Renton Amendments to the King County Surface Water Design Manual. In summary, the project is a “zero setback” building which occupies the entire parcel. As a result, there are no opportunities on the project parcel for rainwater infiltration into the native soils. Below are the results of our analysis. Per section 5.2.1.3-Large Lot High Impervious BMP Requirements, the project falls under section 5.2.1.3 by occupying an area greater than 22,000 SF and is greater than 45% impervious. Section 5.2.1.3 has three items to evaluate for this project, they are: 1. Full Dispersion: is not feasible, there is no native vegetated surface on the developed site. 2. Flow Control BMPs: Since the site is 100% impervious, flow control BMPs must be applied to 10% of the site (2,639 SF). The Flow Control BMPs are evaluated as follows. • Full Infiltration per Section 5.4, Due to building occupying the entire site, this is not feasible due to the following: o Access requirements (5.3.2.1)  The maximum depth of the facility would exceed 20-feet. o Setbacks (5.4.3.1)  The facility would be located under the building, hence not meeting 20-feet setback requirements • Limited Infiltration per Appendix C, Section C.2.3, Due to building occupying the entire site, this is not feasible due to the following: o Setbacks (C.2.2.2)  The facility would be located under the building, hence not meeting 5-feet setback requirements • Basic Dispersion per Appendix C, Section C.2.4, Per section C.2.4.1, the project does not have any landscape to create a vegetated flowpath segment, hence this is not feasible. DATE MARCH 17, 2017 TO ANN FOWLER, CITY OF RENTON CC KENT SMUTNY, VEER ARCHITECTS FROM ROBERT PARISH, PE, OSBORN CONSULTING, INC. SUBJECT SUNSET TERRACE MF PROJECT (SUNSET TERRACE - 9/10 SITE) - B16002230 FLOW CONTROL BMP VARIANCE REQUEST SUNSET TERRACE MF PROJECT (SUNSET TERRACE - 9/10 SITE) - B16002230 FLOW CONTROL BMP VARIANCE REQUEST 2 • Rain Garden per Appendix C, Section C.2.5, o Per section C.2.5.1:  Due to building occupying the entire site, this is not feasible as the project does not have any landscape to create a raingarden. o Per section C.2.4.1  The facility would not be able to meet 5-feet building or property line setback requirements • Permeable Pavement per Appendix C, Section C.2.6, Due to building occupying the entire site, this is not feasible. • Rainwater Harvesting per Appendix C, Section C.2.7, o Per section C.2.7.2:  the system would need to be 6,600 CF or 10ft x 10ft x 66ft, there is no room on the site for a tank, hence this is not feasible.  There is also not enough landscaping on the project to benefit from the stored water. o This BMP has been removed from the 2016 KCSWDM list of flow control BMPs. • Vegetated Roof o This BMP has been removed from the 2016 KCSWDM list of flow control BMPs. • Reduced Impervious Surface Credit per Appendix C, Section C.2.9, Due to building occupying the entire site, this option is not feasible. • Native Growth Retention Credit per Appendix C, Section C.2.10. There is no native vegetated surface to be protected. 3. Roof downspouts infiltration: Not possible as all downspouts would infiltrate under the building. Since there are no feasible onsite flow control BMP’s, in order to comply with the Flow Control BMP requirement, the project requests to construct at least 2,639 SF of pervious concrete sidewalk with an adjacent 7.5-ft to 9.5-ft wide landscape strip in the public right of way along Sunset Boulevard. This area is currently within the project limits of the future Sunset Boulevard project where the City is planning to replace the existing condition with new sidewalk and landscaping. The proposed area is shown in the attached plan. Please contact me with any questions in regards to this request. Sincerely, Robert Parish, PE Osborn Consulting, Inc. 9/10 COLPITTSFFE=336.50GARAGE FFE=317.25KCLSLIBRARYDRAINAGE CONTROL PLAN below.RENTON, WASHINGTON / /3 14 17RENTON, WASHINGTON / /3 14 17Proposed Flow Control BMP: 1,640 SF LandscapingProposed Flow Control BMP: 3,058 SF Pervious Concrete Sidewalk