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Home My WebLink AboutRPT- Boun SP TIR 2016.11.21 (stamped and signed) BOUN SHORT PLAT SITE ADDRESS: 1024 Duvall Ave NE, Renton, Washington SECTION 10/TOWNSHIP 23 NORTH, RANGE 5 EAST, W.M. Technical Information Report (___________________________) Associated Permit Number Prepared For: Warring Properties Contact: Socheat “Kent” Khnor 845 106th Ave, Suite 200 Bellevue, WA 98003 Date Prepared: November 21, 2016 Prepared By: Drew T. Young, EIT Reviewed By: Brandon M. Loucks, P.E. Beyler Consulting LLC 7602 Bridgeport Way W, #3D Lakewood, WA 98499 253.301.4157 CONTACT phone: 253-301-4157 fax: 253-336-3950 info@beylerconsulting.com beylerconsulting.com LAKEWOOD OFFICE 7602 Bridgeport Way W #3D Lakewood, WA 98499 ISSAQUAH OFFICE 455 Rainier Blvd N Issaquah, WA 98027 Plan. Design. Manage. CIVIL & STRUCTURAL ENGINEERING | LAND SURVEYING | PLANNING PROJECT MANAGEMENT | FEASIBILITY | PERMIT EXPEDITING Page 1 Boun Short Plat TABLE OF CONTENTS I. PROJECT OVERVIEW ................................................................ 2 Project Description ...................................................................... 2 Figure 1. TIR Worksheet ............................................................ 4 Figure 2. Location Map .............................................................. 12 Figure 3. Drainage Basins, Subbasins, and Site Characteristics ....... 13 Figure 4. Soils Map ................................................................... 16 II. CONDITIONS AND REQUIREMENTS SUMMARY ....................... 17 III. OFFSITE ANALYSIS ................................................................ 22 3.1.1 Task 1 - Study Area Definition and Maps ......................... 22 3.1.2 Task 2 - Resource Review ............................................. 22 3.1.3 Task 3 - Field Inspection ............................................... 23 3.1.4 Task 4 - Drainage System Description and Problem Descriptions ............................................................................. 34 3.1.5 Task 5 - Mitigation of Existing or Potential Problems .......... 34 IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ................................................................................... 35 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN ...................... 59 VI. SPECIAL REPORTS AND STUDIES ........................................... 63 VII. OTHER PERMITS ..................................................................... 63 VIII. CSWPPP ANALYSIS AND DESIGN ........................................... 63 IX. BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT ................................................................................. 63 X. OPERATION AND MAINTENANCE MANUAL .............................. 63 XI. APPENDICES .......................................................................... 64 APPENDIX A – OFFSITE STUDY MAPS............................................... APPENDIX B – DOWNSTREAM SYSTEM TABLE AND MAPS ................... APPENDIX C – BOND QUANTITIES WORKSHEETS/COST DATA AND INVENTORY .................................................................................. APPENDIX D – DRAFT BMP COVENANT ............................................. APPENDIX E – CSWPPP REPORT ...................................................... Page 2 Boun Short Plat I. PROJECT OVERVIEW Project Description The proponent of the Boun Short Plat proposes to subdivide an undeveloped parcel, with the exception of an abandoned shed building that is to be removed as part of this project, located in the City of Renton, King County Washington. The King County parcel number for the property is 102305-9139. The project parcel is approximately 57,677 sf, 1.32 acres in size. The parcel is zoned Residential 8 (R-8) according to the City of Renton Zoning Map effective as of July 1, 2015. The allowed density range in the R-8 zone is a minimum of 4.0 dwelling units per net acre (DUA) to a maximum of 8.0 DUA. The Boun Short Plat proposes to subdivide the current parcel into 7 single-family lots equating to a proposed density of 5.29 DUA. The proposed lots range in size from the smallest being 5,098 sf in size and the largest being 6,453 sf in size. A single stormwater tract will be created with this subdivision for the purpose of stormwater treatment and mitigation for the development. The remaining area will be dedicated to the City of Renton for public right-of-way use. The property is adjacent to Duvall Ave NE to the east, single family parcels to the south and north, and Chelan Ave NE to the west. The proposed project is keeping consistent with neighboring land use characteristics. The site will be accessed through two separate access points. The first access will be an extension of Chelan Place NE, an existing 20’ alleyway, from the south boundary to the north boundary of the project parcel. This access way will be developed into a 16’ paved alley within a 20’ wide right-of-way dedication which meets the current City of Renton street standards for alleys. An additional access point to Chelan Ave NE will be provided in the east to west direction through a 16’ paved alley within a 20’ public access and utilities easement. Half street frontage improvements will be included along the west and east boundary of the project site. The west half of Duvall Avenue NE will be improved to current City of Renton Standards for principle arterials by providing two 11-foot travel lanes, a 5-foot bike lane, vertical curb and gutter, an 8-foot wide planter strip, an 8-foot wide sidewalk and a 2-foot maintenance area behind the sidewalk. This will require a 3.5-foot right-of-way dedication along the east boundary line of the project parcel. Chelan Avenue NE will be improved to two separate variations of the current City of Renton Standards for Residential Access Streets. Starting from the south boundary of the project site, the east half of Chelan Avenue NE will be improved to provide a 12-foot travel lane, vertical curb and gutter, an 8-foot wide planter strip, and a 5-foot wide sidewalk for approximately 120 feet. At this point, the Residential Access Street will transition into a Limited Residential Access Street which consists of a 20- foot paved roadway, vertical curb and gutter, an 8-foot wide planter strip, and a 5-foot sidewalk. This road section will be constructed north until it reaches the north boundary line of the project. To incorporate these improvements, an 18’ right of way dedication will be necessary along a portion of the northwest boundary of the project parcel. An 18’ wide section of right-of-way north of the project site will not be improved as part of this project. As a condition of preliminary plat approval (LUA16-00124), a road standards modification will be submitted concurrently with the Utility Construction Permit to allow for the 18’ wide section of right-of-way to remain undeveloped. This project is subject to the 2009 King County Surface Water Design Manual (King Manual) and the City of Renton amendments to the Manual (Renton Manual). Per Figure 1.1.2.A of the Renton Manual, the Boun Short Plat project is subject to a full drainage review meeting core requirements #1 through #8 and special requirements #1 through #6. Page 3 Boun Short Plat It has been determined that the site consists of two separate threshold discharges areas. Threshold Discharge Area #1 (West Basin) consists of a majority of the project site area that naturally discharges stormwater to the southwest corner of the parcel. Threshold Discharge Area #2 (A-East Basin, B-North basin) consists of a small portion of land along the east boundary which naturally discharges stormwater east to an existing swale within Duvall Ave NE (TDA 2.A) and the 18’ wide panhandle section of land located north of the project site that naturally discharges stormwater to the northwest (TDA 2.B). A drainage adjustment, per Section 1.4 of the Renton Manual, is proposed to combine a portion of threshold discharge area #2.A with threshold discharge area #1. See section III and IV of this report for further details. Page 4 Boun Short Plat Figure 1. TIR Worksheet KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2009 Surface Water Design Manual 1/9/2009 1 Part 1 PROJECT OWNER AND PROJECT ENGINEER Part 2 PROJECT LOCATION AND DESCRIPTION Project Owner ________________________ Phone ______________________________ Address ____________________________ ____________________________________ Project Engineer ______________________ Company ___________________________ Phone ______________________________ Project Name _________________________ DDES Permit # ________________________ Location Township ______________ Range ________________ Section ________________ Site Address __________________________ _____________________________________ Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS Landuse Services Subdivison / Short Subd. / UPD Building Services M/F / Commerical / SFR Clearing and Grading Right-of-Way Use Other _______________________ DFW HPA COE 404 DOE Dam Safety FEMA Floodplain COE Wetlands Other ________ Shoreline Management Structural Rockery/Vault/_____ ESA Section 7 Part 5 PLAN AND REPORT INFORMATION Technical Information Report Site Improvement Plan (Engr. Plans) Type of Drainage Review (circle): Date (include revision dates): Date of Final: Full / Targeted / Large Site ___________________ ___________________ ___________________ Type (circle one): Date (include revision dates): Date of Final: Full / Modified / Small Site __________________ __________________ __________________ Part 6 ADJUSTMENT APPROVALS Type (circle one): Standard / Complex / Preapplication / Experimental / Blanket Description: (include conditions in TIR Section 2) ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ Date of Approval: ______________________ KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2009 Surface Water Design Manual 1/9/2009 2 Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes / No Start Date: _______________________ Completion Date: _______________________ Describe: _________________________________ _________________________________________ _________________________________________ _________________________________________ _________________________________________ Part 8 SITE COMMUNITY AND DRAINAGE BASIN Community Plan : _________________________________ Special District Overlays: __________________________________________________________ Drainage Basin: ___________________________________ Stormwater Requirements: ________________________________________________________ Part 9 ONSITE AND ADJACENT SENSITIVE AREAS River/Stream _______________________ Lake _____________________________ Wetlands ___________________________ Closed Depression ___________________ Floodplain __________________________ Other ______________________________ ___________________________________ Steep Slope ______________________ Erosion Hazard ___________________ Landslide Hazard __________________ Coal Mine Hazard __________________ Seismic Hazard ___________________ Habitat Protection __________________ _________________________________ Part 10 SOILS Soil Type _________________ _________________ _________________ _________________ Slopes _________________ _________________ _________________ _________________ Erosion Potential _________________ _________________ _________________ _________________ High Groundwater Table (within 5 feet) Other ________________________ Sole Source Aquifer Seeps/Springs Additional Sheets Attached KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2009 Surface Water Design Manual 1/9/2009 3 Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE Core 2 – Offsite Analysis_________________ Sensitive/Critical Areas___________________ SEPA________________________________ Other_________________________________ _____________________________________ LIMITATION / SITE CONSTRAINT _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ Additional Sheets Attached Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Threshold Discharge Area: (name or description) Core Requirements (all 8 apply) Discharge at Natural Location Number of Natural Discharge Locations: Offsite Analysis Level: 1 / 2 / 3 dated:__________________ Flow Control (incl. facility summary sheet) Level: 1 / 2 / 3 or Exemption Number ____________ Small Site BMPs ___________________________________ Conveyance System Spill containment located at: _________________________ Erosion and Sediment Control ESC Site Supervisor: Contact Phone: After Hours Phone: Maintenance and Operation Responsibility: Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Liability Provided: Yes / No Water Quality (include facility summary sheet) Type: Basic / Sens. Lake / Enhanced Basicm / Bog or Exemption No. ______________________ Landscape Management Plan: Yes / No Special Requirements (as applicable) Area Specific Drainage Requirements Type: CDA / SDO / MDP / BP / LMP / Shared Fac. / None Name: ________________________ Floodplain/Floodway Delineation Type: Major / Minor / Exemption / None 100-year Base Flood Elevation (or range): ______________ Datum: Flood Protection Facilities Describe: Source Control (comm./industrial landuse) Describe landuse: Describe any structural controls: KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2009 Surface Water Design Manual 1/9/2009 4 Oil Control High-use Site: Yes / No Treatment BMP: ________________________________ Maintenance Agreement: Yes / No with whom? ____________________________________ Other Drainage Structures Describe: Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION Clearing Limits Cover Measures Perimeter Protection Traffic Area Stabilization Sediment Retention Surface Water Collection Dewatering Control Dust Control Flow Control MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION Stabilize Exposed Surfaces Remove and Restore Temporary ESC Facilities Clean and Remove All Silt and Debris, Ensure Operation of Permanent Facilities Flag Limits of SAO and open space preservation areas Other ______________________ Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch) Flow Control Type/Description Water Quality Type/Description Detention Infiltration Regional Facility Shared Facility Flow Control BMPs Other ________________ ________________ ________________ ________________ ________________ ________________ Biofiltration Wetpool Media Filtration Oil Control Spill Control Flow Control BMPs Other ________________ ________________ ________________ ________________ ________________ ________________ ________________ KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2009 Surface Water Design Manual 1/9/2009 3 Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE Core 2 – Offsite Analysis_________________ Sensitive/Critical Areas___________________ SEPA________________________________ Other_________________________________ _____________________________________ LIMITATION / SITE CONSTRAINT _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ Additional Sheets Attached Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Threshold Discharge Area: (name or description) Core Requirements (all 8 apply) Discharge at Natural Location Number of Natural Discharge Locations: Offsite Analysis Level: 1 / 2 / 3 dated:__________________ Flow Control (incl. facility summary sheet) Level: 1 / 2 / 3 or Exemption Number ____________ Small Site BMPs ___________________________________ Conveyance System Spill containment located at: _________________________ Erosion and Sediment Control ESC Site Supervisor: Contact Phone: After Hours Phone: Maintenance and Operation Responsibility: Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Liability Provided: Yes / No Water Quality (include facility summary sheet) Type: Basic / Sens. Lake / Enhanced Basicm / Bog or Exemption No. ______________________ Landscape Management Plan: Yes / No Special Requirements (as applicable) Area Specific Drainage Requirements Type: CDA / SDO / MDP / BP / LMP / Shared Fac. / None Name: ________________________ Floodplain/Floodway Delineation Type: Major / Minor / Exemption / None 100-year Base Flood Elevation (or range): ______________ Datum: Flood Protection Facilities Describe: Source Control (comm./industrial landuse) Describe landuse: Describe any structural controls: KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2009 Surface Water Design Manual 1/9/2009 4 Oil Control High-use Site: Yes / No Treatment BMP: ________________________________ Maintenance Agreement: Yes / No with whom? ____________________________________ Other Drainage Structures Describe: Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION Clearing Limits Cover Measures Perimeter Protection Traffic Area Stabilization Sediment Retention Surface Water Collection Dewatering Control Dust Control Flow Control MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION Stabilize Exposed Surfaces Remove and Restore Temporary ESC Facilities Clean and Remove All Silt and Debris, Ensure Operation of Permanent Facilities Flag Limits of SAO and open space preservation areas Other ______________________ Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch) Flow Control Type/Description Water Quality Type/Description Detention Infiltration Regional Facility Shared Facility Flow Control BMPs Other ________________ ________________ ________________ ________________ ________________ ________________ Biofiltration Wetpool Media Filtration Oil Control Spill Control Flow Control BMPs Other ________________ ________________ ________________ ________________ ________________ ________________ ________________ KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2009 Surface Water Design Manual 1/9/2009 5 Part 15 EASEMENTS/TRACTS Part 16 STRUCTURAL ANALYSIS Drainage Easement Covenant Native Growth Protection Covenant Tract Other Cast in Place Vault Retaining Wall Rockery > 4’ High Structural on Steep Slope Other Part 17 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 attached Technical Information Report. To the best of my knowledge the information provided here is accurate. Signed/Date Page 12 Boun Short Plat Figure 2. Location Map Page 13 Boun Short Plat Figure 3. Drainage Basins, Subbasins, and Site Characteristics Figure 3.1 – Existing Conditions Map Figure 3.2 – Proposed Conditions Map MBMBSS~SHEET OFJOB NUMBERNO. DESCRIPTION INIT. DATE DRAWN BY:CHECKED BY: SCALE: HORZ:VERT: DATE:CIVIL & STRUCTURAL ENGINEERING | LAND SURVEYING | PLANNING PROJECT MANAGEMENT | FEASIBILITY | PERMIT EXPEDITING LAKEWOOD OFFICE7602 Bridgeport Way W #3D Lakewood, WA 98499 phone: 253-301-4157 fax: 253-336-3950 ISSAQUAH OFFICE 455 Rainier Blvd NIssaquah, WA 98027phone: 425-392-8055fax: 425-392-0108 beylerconsulting.com BEYLER CONSULTING Plan. Design. ManageFIGURE 3.11EXISTING BASIN MAP BOUN SHORT PLAT BASIN MAPS CITY OF RENTON,WASHINGTON16-2061A PORTION OF SECTION 10, TOWNSHIP 23 NORTH, 5 WEST, W.M.DUVALL AVE NE CHELAN AVE NE THRESHOLD DISCHARGEAREA #1(WEST BASIN)(46,236 SF)(1.06 ACRES)THRESHOLD DISCHARGEAREA #2.A(EAST BASIN)(8,771 SF)(0.20 ACRES)BOUN SHORT PLATEXISTING BASIN MAPSCALE: 1" = 40'2040040THRESHOLD DISCHARGE AREA #2.B(NORTH BASIN)(2,669 SF)(0.061 ACRES)TO REMAIN UNDEVELOPED ANDDEDICATED TO CITY OF RENTONAS PUBLIC RIGHT OF WAY(MODIFICATION REQUEST #NATURAL DISCHARGELOCATION #1(EXISTING CATCH BASIN)NATURAL DISCHARGELOCATION #2.A(EXISTING SWALE)NATURAL DISCHARGELOCATION #2.B(SHEET FLOW TO NATIVEVEGETATION- NO APPARENTDISCHARGE LOCATION)BASIN AREA CALCULATIONSTHRESHOLD DISCHARGE AREA #1ONSITE (WEST BASIN)TOTAL BASIN AREA: 48,706 SF (1.12 ACRES)IMPERVIOUS (EXISTING SHED): 330 SFPERVIOUS (LAWN/GRASS): 48,376 SFOFFSITE (CHELAN AVE NE)TOTAL BASIN AREA: 4,148 SF (0.95 ACRES)IMPERVIOUS (ASPHALT): 1,577 SFPERVIOUS (LAWN/GRASS): 2,571 SFTHRESHOLD DISCHARGE AREA #2.AONSITE (EAST BASIN)TOTAL BASIN AREA: 6,302 SF (0.14 ACRES)PERVIOUS (LAWN/GRASS): 6,302 SFOFFSITE (DUVALL AVE NE)TOTAL BASIN AREA: 8,432 SF (0.19 ACRES)IMPERVIOUS (ASPHALT): 6,375 SFPERVIOUS (LAWN/SWALE): 2,057 SFTHRESHOLD DISCHARGE AREA #2.BONSITE (NORTH BASIN)TOTAL BASIN AREA: 2,669 SF (0.06 ACRES)IMPERVIOUS (GRAVEL DRIVEWAY): 789 SFPERVIOUS (LAWN/GRASS): 1,880 SFTHRESHOLD DISCHARGE AREA #1(OFFSITE)(4,148 SF)(0.095 ACRES)THRESHOLD DISCHARGE AREA #2.A(OFFSITE)(8,432 SF)(0.19 ACRES) LOT 45,966 SFLOT 55,658 SFLOT 65,638 SFTRACT A7,253 SFLOT 76,453 SFLOT 25,751 SFLOT 15,098 SFLOT 35,893 SFMBMBSS~434436438438 438438434 SHEET OFJOB NUMBERNO. DESCRIPTION INIT. DATE DRAWN BY:CHECKED BY: SCALE: HORZ:VERT: DATE:CIVIL & STRUCTURAL ENGINEERING | LAND SURVEYING | PLANNING PROJECT MANAGEMENT | FEASIBILITY | PERMIT EXPEDITING LAKEWOOD OFFICE7602 Bridgeport Way W #3D Lakewood, WA 98499 phone: 253-301-4157 fax: 253-336-3950 ISSAQUAH OFFICE 455 Rainier Blvd NIssaquah, WA 98027phone: 425-392-8055fax: 425-392-0108 beylerconsulting.com BEYLER CONSULTING Plan. Design. ManageFIGURE 3.21PROPOSED BASIN MAP BOUN SHORT PLAT BASIN MAPS CITY OF RENTON,WASHINGTON16-2061A PORTION OF SECTION 10, TOWNSHIP 23 NORTH, 5 WEST, W.M.DUVALL AVE NE CHELAN AVE NE THRESHOLDDISCHARGE AREA #1(WEST BASIN)(50,746 SF)(1.16 ACRES)BOUN SHORT PLATPROPOSED BASIN MAPSCALE: 1" = 40'2040040THRESHOLD DISCHARGE AREA #2.B(NORTH BASIN)(2,665 SF)(0.061 ACRES)TO REMAIN UNDEVELOPED ANDDEDICATED TO CITY OF RENTONAS PUBLIC RIGHT OF WAY(MODIFICATION REQUEST #NATURAL DISCHARGELOCATION #1(RELOCATED CATCHBASIN)NATURAL DISCHARGELOCATION #2.A(EXISTING SWALE)THRESHOLD DISCHARGEAREA #2.A(EAST BASIN)(409 SF)(0.009 ACRES)BASIN AREA CALCULATIONSTHRESHOLD DISCHARGE AREA #1ONSITE (WEST BASIN)TOTAL BASIN AREA: 50,746 SF (1.16 ACRES)IMPERVIOUS (PGIS: ASPHALT/DWAY): 8,944 SFIMPERVIOUS (ROOFTOPS): 18,802 SFPERVIOUS (LAWN/GRASS): 23,000 SFONSITE (VAULT BY-PASS)TOTAL BASIN AREA: 3,559 SF (0.082 ACRES)IMPERVIOUS (PGIS: ASPHALT/SWALK): 1,973 SFPERVIOUS (PLANTER STRIP): 1,586 SFOFFSITE (VAULT BY-PASS)TOTAL BASIN AREA: 2,528 SF (0.058 ACRES)IMPERVIOUS (PGIS: ASPHALT): 2,049 SFPERVIOUS (PLANTER STRIP): 479 SFOFFSITE (CHELAN AVE NE)TOTAL BASIN AREA: 1,620 SF (0.037 ACRES)IMPERVIOUS (ASPHALT): 1,576 SFPERVIOUS (LAWN/GRASS): 44 SFVAULT SIZING CALCULATIONS:TO DETENTION/WQ VAULT:TOTAL IMPERVIOUS: 27,746 SF (0.637 ACRES)TOTAL PERVIOUS: 23,000 SF (0.528 ACRES)VAULT BYPASS AREA CALCULATIONS:TO BYPASS DETENTION/WQ VAULT:TOTAL IMPERVIOUS: 4,022 SF (0.09 ACRES)TOTAL PERVIOUS: 2,065 SF (0.05 ACRES)THRESHOLD DISCHARGE AREA #2.AONSITE (EAST BASIN)TOTAL BASIN AREA: 409 SF (0.009 ACRES)IMPERVIOUS (SIDEWALK): 297 SFPERVIOUS (MAINTENANCE STRIP): 112 SFOFFSITE (DUVALL AVE NE)TOTAL BASIN AREA: 8,432 SF (0.19 ACRES)IMPERVIOUS (ASPHALT): 6,869 SFPERVIOUS (PLANTER STRIP): 1,563 SFTHRESHOLD DISCHARGE AREA #2.BONSITE (NORTH BASIN)TOTAL BASIN AREA: 2,669 SF (0.06 ACRES)IMPERVIOUS (GRAVEL DRIVEWAY): 789 SFPERVIOUS (LAWN/GRASS): 1,880 SFNATURAL DISCHARGELOCATION #2.B(SHEET FLOW TO NATIVEVEGETATION- NO APPARENTDISCHARGE LOCATION)THRESHOLD DISCHARGE AREA #1(OFFSITE)(1,620 SF)(0.037 ACRES)THRESHOLD DISCHARGEAREA #2.A(OFFSITE)(8,432 SF)(0.19 ACRES)THRESHOLD DISCHARGE AREA #1(ONSITE- VAULT BYPASS)(3,559 SF)(0.082 ACRES)THRESHOLD DISCHARGE AREA #1(OFFSITE-VAULT BYPASS)(2,528 SF)(0.058 ACRES) Page 16 Boun Short Plat Figure 4. Soils Map Page 17 Boun Short Plat II. CONDITIONS AND REQUIREMENTS SUMMARY The Boun Short Plat, File No. LUA16-000124; SHPL-A, is APPROVED WITH CONDITIONS and subject to the following conditions: 1. The width of Lot 7 shall be increased to comply with the minimum 50-foot lot width requirement of the R-8 zone. 2. A demolition permit shall be obtained for the removal of the detached accessory structure, and all required inspections shall be completed prior to the recording of the short plat. 3. A detailed landscape plan shall be submitted at the time of Utility Construction Permit Review. The detailed landscape plan shall include an 8-foot wide landscaping strip between the curb and sidewalk along the full length of the Chelan Avenue NE and Duvall Avenue NE frontages or a modification request to reduce the landscape strip shall be submitted and approved in accordance with RMC 4-9-250D at the time of Utility Construction Permit Review. 4. A Final Tree Retention Plan shall be submitted at the time of Utility Construction Permit Review. The Final Tree Retention Plan shall include minimum 2-inch caliper replacement trees within the onsite 10-foot landscape strip. The Final Tree Retention Plan shall be submitted to the Current Planning Project Manager for review and approval. 5. A modification request shall be submitted and approved for the proposed waiver of frontage improvements along the 18-foot wide panhandle north of the project site. The modification request shall be submitted at the time of Utility Construction Permit Review. 6. Access for Lots 1-7 shall be provided via the alley (Chelan Place NE). The front façade of the houses to be constructed on Lots 1-4 shall Duvall Avenue NE and the front façade of the houses to be constructed on Lots 5-7 shall face Chelan Avenue NE. A note to this effect shall be recorded on the face of the Short Plat map. 7. The width of the alley shall be revised to comply with the City’s adopted street standards, or a modification to these standards shall be requested at the time of Utility Construction Permit Review. Page 18 Boun Short Plat Review of Eight Core Requirements and Six Special Requirements The following comments are a review of the Core and Special Requirements per the 2009 King County Surface Water Stormwater Manual with City of Renton Amendments (where applicable). Core Requirement No. 1 Discharge at the Natural Location Threshold Discharge Area #1 Under existing conditions, the site’s topography suggests that stromwater runoff within threshold discharge area #1 sheet flows to the southwest over densely vegetated land cover consisting of various types of grass and brush. Any accumulated runoff is allowed to overflow onto Chelan Ave NE into an existing catch basin near the southwest corner of the project parcel. Under developed conditions, stormwater will sheet flow over impervious surfaces and be collected within a closed conveyance system. Rooftop runoff will be directly tightlined to this conveyance system. The closed conveyance system will route stormwater to a combined water quality and detention vault. The proposed stormwater vault will ultimately discharge stormwater to the catch basin located in Chelan Avenue NE near the southwest corner of the project site, matching the current natural discharge location. Threshold Discharge Area #2-A Under existing conditions, threshold discharge area #2-A which is located along the east boundary of the project parcel allows stormwater to sheet flow towards an existing conveyance swale located along the west side of Duvall Ave NE. This swale flows north along the western portion of Duvall Avenue NE. Under developed conditions, a portion of threshold discharge area #2-A will be allowed to sheet flow towards Duvall Ave NE. Accumulated runoff will be collected within a closed conveyance system and will be tightlined to a riprap discharge pad located just north of the project site within the existing drainage swale, meeting the natural discharge location of threshold discharge area #2-A. The remaining portion of threshold discharge area #2-A will sheet flow west towards the closed conveyance system of Threshold Discharge Area #1. This stormwater will be collected, mitigated and released at the natural discharge location of Threshold Discharge Area #1. A drainage adjustment will be submitted to the City of Renton at time of Utility Construction Permit Review for approval to discharge this portion of Threshold Discharge Area #2-A at a location other than the natural discharge location. A reference to this approval will be added to this report once reviewed and approved by the City of Renton. Threshold Discharge Area #2-B Currently, there are no proposed planned improvements to this TDA. Therefore, this requirement is not applicable at this time. Core Requirement No 2 Offsite Analysis The project proposes to discharge stormwater within both threshold discharge areas to the May Creek drainage basin. A Level 1 offsite analysis has been completed for each of the two threshold discharge areas. Further narrative of this analysis can be found in Section III of this report. Core Requirement No 3 Flow Control Flow Control Facility Analysis and Design has been broken into two parts, part 1: Threshold Discharge Area #1 discussing the threshold area tributary to proposed onsite vault system, and Threshold Discharge Area #2, discussing the north and east portions of the onsite and offsite tributary area and improvements. Please refer to the Basin Maps in Figure 3, depicting areas as described herein. Page 19 Boun Short Plat Threshold Discharge Area #1 Flow Control Facility (1.2.3.1.B): The proposed project is located within the Flow Control Duration Standard – Matching Forested Site Conditions area. This level of flow control requires new impervious and pervious surfaces, that are not fully dispersed, to flow to a flow control facility that matches the flow durations of predeveloped rates for forested (historic) site conditions over the range of flows extending from 50% of the 2-year up to the full 50-year flow. To satisfy this requirement, an underground detention vault is proposed to detain onsite runoff to historic flow control levels per Section 1.2.3.1.B. See Section IV of this report for forested site conditions flow control performance standards and detention analysis. Flow Control BMPs (1.2.3.2): In addition to flow control facility requirements, implementation of flow control BMPs as part of this “subdivision” project is incentive-based per Section 1.2.3.3 of the Renton Manual. However, if the applicant wishes to implement or make provision for implementation of BMPs as part of the subdivision project for purposes of receiving the BMP credits then the requirements outlined in Section 5.2.2.1 must be met depending on the site location of the proposed BMPs. Based on a site evaluation, it has been determined that dispersion and infiltration is infeasible based on proposed lot size and existing soil conditions. The applicant proposes to implement a restricted footprint for the seven (7) lots following section C.2.9.2 of the King Manual. See Part C of Section IV of this report for the Small Lot BMP performance standards and further analysis of the proposed BMPs. Flow Control Bypass (1.2.3.2.E): A flow control bypass facility per Section 1.2.3.2.E of the Renton Manual is also proposed. The project proposes to bypass a small amount of targeted onsite impervious area within Tract A which provides access to Chelan Ave NE as well as the proposed offsite improvements of Chelan Ave NE. The bypass of this target area is necessary due to grading constraints of the site. The onsite flow control facility was sized to incorporate a reduction in allowed flow release to match historic durations for 50% of the 2-year through 50-year peaks at the downstream point of compliance, Catch Basin 1. See Section IV for further detail. Threshold Discharge Area #2 (2-A & 2-B) Flow Control Facility (1.2.3.1.B): The proposed project is located within the Flow Control Duration Standard – Matching Forested (Historic) Site Conditions area. This is required unless an exception applies to the proposed site conditions. Per Section 1.2.3.1.B – Exemption #2 of the Renton Manual, the facility requirement in Flow Control Duration Standard Matching Forested Site Conditions Areas is waived for any threshold discharge area in which there is less than a 0.1 cfs difference in the sum of developed 100-year peak flows for those target surfaces subject to this requirement and the sum of forested (historic) site conditions 100-year peak flows for the same surface areas. The developed conditions for this Threshold Discharge Area do not exceed a 0.1 cfs difference in the sum of developed 100-year peak flows for those target surfaces subject to the flow control facility requirement and the sum of historic (forested) site conditions 100-year peak flows for the same surface areas. Thus, flow control is not required for this threshold discharge area per section 1.2.3.1.B of the Renton Manual. See Section IV of this report for details and a table of the target areas. Core Requirement No. 4 Conveyance System New pipes systems will be designed with sufficient capacity to convey and contain, at minimum, the 25-year peak flow. See Section V of this report for the conveyance analysis. Page 20 Boun Short Plat Core Requirement No. 5 Erosion and Sediment Control This development is expected to be constructed in a single phase. Please see Appendix E for the prepared CSWPPP, and sheets C2-C3 in the prepared Construction Plans. Core Requirement No. 6 Maintenance and Operations It is anticipated that the proposed stormwater system will be owned and operated by the City of Renton. Therefore, operations and maintenance recommendations can be made upon request by the City of Renton. Core Requirement No. 7 Financial Guarantees and Liability Financial guarantees can be made available to the City upon request. Core Requirement No. 8 Water Quality Water Quality Facility Analysis and Design has been broken into two parts, part 1: Threshold Discharge Area #1 discussing the threshold area tributary to proposed onsite vault system, and Threshold Discharge Area #2, discussing the north and east portions of the onsite and offsite tributary area and improvements. Please refer to the Basin Maps in Figure 3, depicting areas as described herein. Threshold Discharge Area #1 Treatment Facility (1.2.8) This TDA is located within a Basic Water Quality treatment area as designated by the City of Renton and is not subject to the requirements of Enhanced Water Quality as it is not a Commercial, Industrial or Multifamily land use or a road project with an expected average daily traffic (ADT) count of 7,500. The developed conditions of TDA #1 exceed the 5,000 sf of proposed pollution generating impervious (PGIS) surface area exemption per Section 1.2.8.1 of the Renton Manual. Therefore, the project proposes to satisfy the basic water quality treatment requirement through the use of an onsite combined detention/wetvault located near the southwest corner of the project parcel to provide treatment for onsite runoff. See Section IV of this report for further description of the treatment system. Untreated Discharge (Treatment Bypass) (1.2.8.2) This TDA proposes to bypass a small portion of the proposed onsite and the entire offsite target pollution-generating surface that would need to be pumped to be treated by the required water quality facility. Per Section 1.2.8.2 of the Renton Manual, the following criteria must be met; 1) treatment of the constrained area by filter strip, biofiltration, or a linear sand filter is not feasible, and a treatment trade as described above is not possible. 2) The untreated target surface is less than 5,000 square feet of new PGIS and is less than 5,000 square feet of new plus replaced PGIS on a redevelopment. 3) Any target PGPS within the area to be released untreated shall be addressed with a landscape management plan. The project proposes 4,022 sf of target PGIS which is less than the 5,000 sf threshold to allow for Untreated Bypass. See Section IV of this report for further description of the untreated discharge. Threshold Discharge Area #2 (2-A & 2-B) Treatment Facility (1.2.8) This TDA is located within a Basic Water Quality treatment area as designated by the City of Renton and is not subject to the requirements of Enhanced Water Quality as it is not a Commercial, Industrial or Multifamily land use or a road project with an expected average daily traffic (ADT) count of 7,500. The developed conditions of TDA #2 do not exceed the 5,000 sf of proposed pollution generating impervious (PGIS) surface area exemption per Page 21 Boun Short Plat Section 1.2.8.1 of the Renton Manual. Therefore, a treatment facility is not required within threshold discharge area #2. Special Requirement No. 1 Other Adopted Area-Specific Requirements This project is not in a designated Critical Drainage Area. This special requirement is not applicable. Special Requirement No. 2 Flood Hazard Area Delineation The project does not contain or is not adjacent to a flood hazard area for a river, stream, lake, wetland, closed depression, or marine shoreline that is within the 100-year floodplain according to King County and FEMA. Special Requirement No. 3 Flood Protection Facilities This project does not rely on any flood protection facility such as a levee or revetment nor will construct a new flood protection facility. Special Requirement No. 4 Source Control This project does not require a commercial building or commercial site development permit. This special requirement is not applicable. Special Requirement No. 5 Oil Control This project is not defined as a high-use site nor is a redevelopment project proposing $100,000 or more of improvements to an existing high-use site. This special requirement is not applicable. Special Requirement No. 6 Aquifer Protection Area This project is not in a designated Aquifer Protection Area (APA). This special requirement is not applicable. Page 22 Boun Short Plat III. OFFSITE ANALYSIS An offsite analysis report has been prepared per Section 1.2.2, Core Requirement #2. This is to identify and evaluate offsite flooding, erosion, and water quality problems that may be created or aggravated by the proposed project. The primary component of this offsite analysis report is the downstream analysis. The second component of the report is to evaluate the upstream drainage system to verify that significant flooding and erosion impact will not occur as a result of the project. 3.1 DOWNSTREAM ANALYSIS The following Level 1 downstream analysis is a review of the drainage system up to a mile downstream of the site. The four tasks outlined under this review are: Task 1 – Define and map the study area Task 2 – Review all available information on the study area Task 3 - Field inspect the study area Task 4 - Drainage System Description and Problem Descriptions Task 5 – Mitigation of Existing or Potential Problems 3.1.1 Task 1 - Study Area Definition and Maps The project is located in the May Creek Drainage Sub-Basin within the Lake Washington/Cedar River Watershed. The drainage study area is approximately a mile-long path encompassing the site's downstream corridor. See Appendix A for maps of the basic study area. The site is currently unimproved, with the exception of an abandoned shed, surrounded by single family residential uses on all sides. 3.1.2 Task 2 - Resource Review The following resources have been reviewed for the downstream analysis. This is a review of available information on the downstream area at least a mile downstream. Sources include the City of Renton GIS maps, King County GIS maps, and geotechnical studies. Adopted Basin Plan  The site is located in the May Creek Drainage Sub-Basin within the Cedar River/Lake Washington Watershed (WRIA Cedar Sammamish (8)) Sensitive Area (See Appendix A for Sensitive Area Maps)  Erosion- None Mapped  Seismic – None Mapped  Landslide – None Mapped  Coal Mine – None Mapped  Streams and Wetlands Map – None Mapped  Susceptible to Groundwater Contamination – None Mapped  100-year flood plain – According to King County iMAP and the FEMA Flood Maps, the 100-year flood plain is not located near the project property. Drainage Complaints and Studies King County –Relevant DNRP drainage complaints within 1 mile of the downstream corridor of each threshold discharge area within the last 10 years were searched. TDA #1 There are currently no open complaints within the downstream corridor nor are there any relevant drainage complaints that were made within Page 23 Boun Short Plat the last 10 years. Going beyond a Level 1 analysis (within the last 15 years), a single complaint pertaining specifically to a water quality cross connection was made in regards to the regional stormwater pond in 2004. See Appendix A for a drainage complaint map of the downstream corridor. TDA #2 There are currently no open complaints within the downstream corridor nor are there any relevant drainage complaints that were made within the last 10 years. Going beyond a Level 1 analysis (within the last 15 years), a single complaint was made in 2003 in regards to a potential septic tank dumping that was leaching into the roadside swale along Duvall Ave NE, just north of the site. See Appendix A for a drainage complaint map of the downstream corridor. 3.1.3 Task 3 - Field Inspection A site visit was performed on July 18, 2016 for the purpose of analyzing the proposed project site and its upstream and downstream corridor. The weather and conditions were light rain and cloudy. A description of the drainage path is described below. See Appendix B for downstream reach locations. THRESHOLD DISCHARGE AREA #1 (West Basin) Upstream The subject site sits on a high point with very little runoff crossing the site from adjacent properties. The site’s topography suggests that stormwater runoff from the site is divided and sheets flows to the southwest and to the northeast. The westerly portion of the site drains to the southwest into an existing catch basin within public right of way (Chelan Ave NE). Downstream Runoff contributing to the downstream corridor from the project site consists of the generated runoff from the improved roadway and rooftop of the project site. The following is a discussion of the downstream corridor from threshold discharge area #1’s natural discharge location. See Appendix B for a Summary of each reach including: pipe size, length, and material as well as a map of each reach’s location. Downstream Legend - Surface Flow Arrow - Closed Conveyance Flow Arrow - Closed Conveyance Flow Arrow (Tributary) Page 24 Boun Short Plat Reach 1 0’ The runoff generated from the project parcel sheet flows southeast and is collected within a Type 1 Catch Basin (Facility ID# 178992) within Chelan Ave NE. Photo 1: Site topography facing northeast from Chelan Ave NE towards Project Site. Reach 2 0’ – 31’ Stormwater is collected within an existing Type 1 Catch Basin (Facility ID# 178992) and conveyed west within a 12-inch CPEP Storm Main sloped at 3.21% (R-332511). At time of site visit, the pipe did not seem to be flowing at capacity nor were flooding problems observed. Photo 2: Facing North on Chelan Ave NE. Stormwater flows south within closed conveyance system. Project Site Ex. CB - Type 1 ID: 178992 Ex. CB - Type 1 ID: 178992 Ex. CB - Type 1 ID: 116933 N Page 25 Boun Short Plat Reach 3 31’ – 180’ Stormwater is collected within an existing Type 1 Catch Basin (Facility ID# 116931) and conveyed southwest within a 12-inch CPEP Storm Main sloped at 0.52% (R-332511). At time of site visit, the pipe did not seem to be flowing at capacity nor were flooding problems observed. Photo 3: Facing northwest on Chelan Ave NE. Stormwater flows southwest within closed conveyance system. Reach 4 180’ – 275’ Stormwater is collected within an existing Type 2-54” Catch Basin (Facility ID# 175753) and conveyed west within a 60-inch CMP WQ Tank (R-332511). This WQ facility is privately owned and operated. Photo 4: Facing north on NE 10th Street. Stormwater flows west within closed conveyance system/WQ Facility. Ex. CB - Type 1 ID: 116931 N Ex. WQ Facility ID: 175753 Page 26 Boun Short Plat Reach 5 275’ – 395’ Stormwater is discharged to an existing Type 2 Catch Basin (Facility ID# 116930) and conveyed west within a 12-inch of unknown material storm main (R-332511). It should be noted that per as-built R-332511, the storm main connection is incorrectly shown to connect to the existing sanitary sewer within NE 10th Street. Photo 5: Facing West on NE 10th Street. Stormwater flows west within closed conveyance system. Reach 6 395’ – 477’ Stormwater is collected within a Type 2 Catch Basin (Facility ID# 116927) and conveyed north within a 12-inch CPEP Storm Main (D-22661A) sloped at 4.86%. This portion of pipe discharges into a regional stormwater facility which was developed as part of the NE 10th Street/Anacortes Ave NE Detention Pond and Storm System Improvement Project. Photo 6: Facing West on NE 10th Street. Stormwater is collected within Type II Catch Basin and conveyed north within closed conveyance system. Ex. CB - Type 2 ID: 116930 Ex. CB - Type 2 ID: 116930 Page 27 Boun Short Plat Reach 7 477’ – 825’ Stormwater is detained within a combined water quality and detention pond. Stormwater is then released at a controlled flow rate from an existing Type II-54” Catch Basin (Facility ID# 115504) and conveyed south within an 18- inch CPEP Storm Main (D-22661A) sloped at 0.20%. Stormwater is collected within a Type 2-48” Catch Basin (Facility ID# 115505) and conveyed southwest within an 18-inch CPEP Storm Main (D-22661A) sloped at 0.20%. From this location, stormwater is convey back into NE 10th Street public right of way to a Type 2-48” Catch Basin (Facility ID# 116923) (D-226618). Reach 8 825’ – 1,003’ Stormwater is conveyed west from the Type 2 Catch Basin within an 18-inch CPEP Storm Main (D-226618) sloped at 0.24%. Photo 7: Facing Northwest on NE 10th Street. Stormwater is collected in Type II catch basin and conveyed west within closed conveyance system. Ex. CB - Type 2 ID: 116923 Page 28 Boun Short Plat Reach 9 1,003’ – 1,038’ Stormwater is collected within a Type 2 Catch Basin and conveyed west within an 18-inch CPEP Storm Main (D-226618) sloped at 0.14%. Photo 8: Facing Northeast on NE 10th Street. Stormwater is collected in Type II catch basin and conveyed west within closed conveyance system. Additional flow enters the conveyance system from a type I catch basin located to the north of the type 2 catch basin. Reach 10 1,038’ – 1,138’ Stormwater is collected within a Type 2 Catch Basin located at the intersection of NE 10th Street and Anacortes Ave NE and conveyed north within a 30-inch CPEP Storm Main (D-226617) sloped at 0.39%. Photo 9: Facing Northwest at intersection of NE 10th Street and Anacortes Ave NE. Stormwater is collected in Type II catch basin and conveyed north within closed conveyance system. Additional flow enters the conveyance system from storm main east of this location. Ex. CB - Type 2 ID: 116903 Ex. CB - Type 2 ID: 116902 Page 29 Boun Short Plat Reach 11 1,138’ – 1,258’ Stormwater is collected within a Type 2 Catch Basin located approximately 100 feet north of the intersection of NE 10th Street and Anacortes Ave NE. Stormwater is conveyed north within a 30-inch CPEP Storm Main (D-226617) sloped at 0.40%. Photo 10: Facing North along Anacortes Ave NE. Stormwater is collected in Type II catch basin and conveyed north within closed conveyance system. Reach 12 1,258’ – 1,333’ Stormwater is collected within a Type 2 Catch Basin (Facility ID# 116900) within Anacortes Ave NE and conveyed north within a 30-inch CPEP Storm Main (D-226617) sloped at 0.41%. Completing the downstream analysis ¼ of a mile downstream from the project site natural discharge location. Photo 11: Facing North along Anacortes Ave NE. Stormwater is collected in Type II catch basin and conveyed north within closed conveyance system. Ex. CB - Type 2 ID: 116901 Ex. CB - Type 2 ID: 116900 N N Ex. CB - Type 2 ID: 116895 ¼ mile downstream Page 30 Boun Short Plat THRESHOLD DISCHARGE AREA #2.A (East Basin) Upstream The subject site sits on a high point with very little runoff crossing the site from adjacent properties. The site’s topography suggests that stormwater runoff from the site is divided and sheets flows to the southwest and to the northeast. The easterly portion of the site drains to the northeast into an existing conveyance swale within public right of way (Duvall Ave NE). Downstream Runoff contributing to the downstream corridor from the project site consists of the generated runoff from the existing asphalt within Duvall Ave NE and proposed sidewalk. The following is a discussion of the downstream corridor from threshold discharge area #2.A’s natural discharge location. See Appendix B for a Summary of each reach including: pipe size, length, and material as well as a map of each reach’s location. Reach 1 0’ The runoff generated from the project parcel sheet flows northwest and is collected within an existing roadside conveyance swale (Facility ID# 450085) located along the east boundary of the project parcel. Stormwater is conveyed north. Photo 12: Facing northwest along Duvall Ave NE. Stormwater sheet flows east within project parcel and enters existing conveyance swale along the east boundary of the site. Project Site Ex. Conveyance Swale ID: 450085 Page 31 Boun Short Plat Reach 2 0’- 695’ Stormwater is conveyed north within the conveyance swale along Duvall Ave NE. Stormwater passes through a series of CMP culverts that were installed under various driveways along this segment of flow path. The swale is well established with various land covers. No evidence erosion or flooding were observed at time of site visit. Garbage and other types of debris were found at various locations along the swale which could cause potential issues if not cleaned. Photo 13: Facing northwest along Duvall Ave NE. Stormwater shallow channel flows within the swale. Stormwater flows north. Reach 3 695’- 753’ Stormwater is collected within a 12-inch concrete culvert (Facility ID# 700093). The inlet to concrete culvert had a small amount of sedimentation build up and leaf debris. Photo 14: Facing west along Duvall Ave NE. Shallow channel flow enters concrete culvert. Debris that could potential disrupt channel flow Ex. Conc. Culvert (Facility ID #700093) Page 32 Boun Short Plat Reach 3 753’- 835’ Stormwater is collected within a Type 1 Catch Basin (Facility ID# 130734). Stormwater is convey north within a 12-inch concrete pipe. Photo 15: Facing west along Duvall Ave NE. Stormwater is conveyed north within a Type 1 CB. Reach 4 835’- 883’ Stormwater is collected within a Type 1 Catch Basin (Facility ID# 130735). Stormwater is convey north within a 12-inch concrete pipe. Photo 16: Facing west along Duvall Ave NE. Stormwater is conveyed north within a Type 1 CB. Ex. CB - Type 1 ID: 130734 Ex. CB - Type 1 ID: 130735 Page 33 Boun Short Plat Reach 5 883’- 1103’ Stormwater is collected within a Type 1 Catch Basin (Facility ID# 130736). Stormwater is convey north within a 12-inch concrete pipe. The 12-inch concrete pipe is sloped at 3.4% (R-147402). Photo 17: Facing northwest along Duvall Ave NE. Stormwater is conveyed north within a Type 1 CB. Reach 6 1103’- 1402’ Stormwater is collected within a Type 1 Catch Basin (Facility ID# 130794). Stormwater is convey north within a 12-inch concrete pipe. The 12-inch concrete pipe is sloped at 1.3% (R-147402). Completing the downstream analysis ¼ of a mile downstream from the project site natural discharge location. Photo 18: Facing southwest along Duvall Ave NE. Stormwater is conveyed north within a Type 1 CB. Ex. CB - Type 1 ID: 130736 Ex. CB - Type 1 ID: 130794 Page 34 Boun Short Plat 3.1.4 Task 4 - Drainage System Description and Problem Descriptions There are no apparent drainage complaints in the vicinity of the project site. However, during the downstream analysis, a problem was identified with releasing stormwater within Threshold Discharge Area #1 to an existing water quality facility that was installed to treat stormwater for the Vuong Short Plat (Project R-332511). Any increase in stormwater above the design water quality flow rate would cause the facility to improperly function. Mitigation of this downstream problem is necessary to allow the project vault to discharge to the downstream network. 3.1.5 Task 5 - Mitigation of Existing or Potential Problems To mitigate the downstream issue identified in Task 4, a flow splitter is proposed to bypass flows higher than the water quality flow rate of the existing water quality facility to the downstream network. See Section IV of this report for further details. Page 35 Boun Short Plat IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN The stormwater flow control and water quality facilities were designed in accordance with the 2009 King County Surface Water Design Manual (King Manual) and the City of Renton amendments to the Manual (Renton Manual). Threshold Discharge Area #1 Existing Site Hydrology (Part A-1) Threshold Discharge Area #1 is comprised of approximately 80% (46,236 sf) of the project parcel. Under existing conditions, the site is currently undeveloped with exception to an abandoned barn that is located near the northern boundary line of the parcel. The site’s topography suggests that stormwater runoff within threshold discharge area #1 sheet flows to the southwest over densely vegetated land cover consisting of various types of grass and brush. There is approximately six (6) feet of vertical relieve across the site with an average slope around 5%. Any accumulated runoff is allowed to overflow onto Chelan Ave NE into an existing catch basin near the southwest corner of the project parcel. Developed Site Hydrology (Part B-1) Under developed conditions, a drainage adjustment will allow for nearly the entire site (50,746 sf) to drain to Threshold Discharge Area #1. Stormwater will sheet flow over impervious areas and be collected within a closed conveyance system. Rooftop runoff will be directly tightlined to this conveyance system. The closed conveyance system then will route stormwater to a combined water quality and detention vault for treatment and flow control. The disturbance on site will include construction clearing and grading, construction of 2 public alley ways, associated utilities (sewer, water, storm, power, etc.), required landscaping buffers and tree replacement, and eventually seven single-family houses with an associated driveway. To account for this future development, an estimated impervious area equating to the maximum impervious allowed per table 4-2-110A was utilized to size stormwater facilities. It is proposed that each driveway and roof drain connection will be collected and conveyed to the stormwater facility. Tables 4.1 and 4.2 break down the historic site conditions and developed site conditions TABLE 4.1 – Historic Site Conditions – Threshold Discharge Area #1 Sub-basin Total sf (ac) Impervious sf (ac) Till Grass sf (ac) Till Forest sf (ac) Threshold Discharge Area #1 (On-site) 46,236 (1.06) 0 0 46,236 (1.06) Threshold Discharge Area #1 (Off-site) 2,528 (0.05) 0 0 2,528 (0.05) Threshold Discharge Area #2.A (On-site) (Drainage Adjustment) 8,362 (0.19) 0 0 8,362 (0.19) TOTAL AREAS 57,126 (1.31) 0 0 57,126 (1.31) Page 36 Boun Short Plat TABLE 4.2 – Developed Conditions – Threshold Discharge Area #1 Sub-basin Total sf (ac) Impervious sf (ac) Till Grass sf (ac) Till Forest sf (ac) Threshold Discharge Area #1 (to Vault)* (includes TDA 2.A area per Drainage Adjustment) 50,746 (1.16) 27,746 (0.637) 23,000 (0.528) 0 Threshold Discharge Area #1 (On-site Bypass) 1,111 (0.026) 376 (0.009) 735 (0.017) 0 Threshold Discharge Area #1 (Off-site Bypass) 4,976 (0.114) 3,559 (0.082) 1,417 (0.032) 0 TOTAL 56,833 (1.305)31,681 (0.727) 25,152 (0.577) 0 (0) * The area reflects the site area after ROW dedication Performance Standards (Part C-1) Flow Control Facility: Performance standards for flow control design use Table 1.2.3.1 of the Manual. The site is located in the Flow Control Duration Standard – Matching Forested Site Conditions as designated by the City of Renton Flow Control Applications Map. This level of control is necessary for runoff from target surfaces (new impervious and pervious surfaces not fully dispersed) within the threshold discharge area. An underground detention vault has been proposed to detain runoff to the historic flow control levels per the Manual. Table 1.2.3.2 of the Manual indicates the level of flow control required based on the flow control area and the identified downstream problems, if any. This project did not identify any downstream problems and being located in the Flow Control Duration Standard Matching Forested Site Conditions (conservation flow control area) shall apply: historic site conditions Level 2 flow control standard, which matches historic durations for 50% of 2-year through 50-year peaks and matches historic 2-year and 10-year peaks. Target surfaces: new impervious, new pervious per Section 1.2.3.1 page 1-34 of the Manual. Flow Control BMPs: In addition to flow control facility requirements, implementation of flow control BMPs as part of this “subdivision” project is optional per Section 5.2.2.1 of the Manual. However, if the applicant wishes to implement or make provisions for implementation of BMPs as part of the subdivision project for purposes of receiving the BMP credits, then the requirements outlined in Section 5.2.2.1 must be met depending on the site location of the proposed BMPs. Based on a site evaluation, it has been determined that full dispersion/infiltration and basic dispersion/partial infiltration is not feasible. Per Section 5.2.1.1 Small Lot BMP Requirements of the Manual, one or more BMPs must be applied to (or used to mitigate for) an impervious area equal to at least 10% of site/lot for site/lot sizes up to 11,000 square feet. The project proposes to utilize a restricted footprint to satisfy the Small Lot BMP implementation requirement. Utilizing Section C.2.9.2 – Restricted Footprint of the manual, the following lot coverage areas were determined. Page 37 Boun Short Plat TABLE 4.3 – Restricted Footprint (C.2.9.2) Lot Number Lot Size (sf) Allowed Impervious (sf per Zoning – 65%) Restricted Imp. Area (55% or 10% site area) (sf) Lot 1 5,098 3,314 2,804 Lot 2 5,751 3,738 3,163 Lot 3 5,893 3,830 3,241 Lot 4 5,966 3,878 3,281 Lot 5 5,658 3,678 3,112 Lot 6 5,638 3,665 3,101 Lot 7 6,453 4,194 3,600 Water Quality The project is located within a Basic Water Quality treatment area as designated by the King County 2009 Water Quality Application Maps and is not subject to the Enhanced Basic WQ menu per Section 1.2.8.1.A of the Manual. The goal of Basic WQ treatment is 80% removal of total suspended solids. To satisfy this treatment requirement, the project proposed a combined detention/wetvault located in the southwest corner of the project to provide treatment for onsite. See Part E of this section for analysis of the water quality facilities. Stormwater Conveyance The conveyance system capacity standards require that new conveyance systems contain the 25-year peak flow and ensure that the 100-year event does not create a severe flooding or erosion problem. See Section V of this report for the conveyance analysis per Core Requirement #4. Flow Control Systems (Part D-1) To address the increased runoff impact of the parcel, stormwater runoff from the proposed development will be mitigated by an underground detention vault in the southwest corner of the property within a dedicated Tract. As identified in Section III – Downstream Analysis of this report, a modification to the downstream drainage network is necessary to allow for the vault to discharge to the existing storm main within Chelan Ave NE. The existing type 1 catch basin near the northwest corner of the intersection of Chelan Ave NE and NE 10th Street will be replaced with a larger type 2 – 60” catch basin to allow for the use of an orifice flow splitter. Vault The detention portion of the combination detention and water quality facility was designed under Section 5.3.3.1 of the Manual. The vault was designed to discharge flow under the Flow Control Duration Standard – Matching Forested Site Conditions as discussed in Part C of this section. The facility was sized according to HSPF methodology using King County Runoff Time Series (KCTRS) software per Section 3.2.2 of the Manual. The vault will have a primary control structure designed to discharge stormwater per the flow control requirements. The flow control system utilizes a flow-restrictor tee with multiple orifices as shown in Figure 5.3.4.D of the Manual. The detention portion of the vault is 4.5 feet deep. The vault is broken into a two detention chambers due to site constraints. The first chamber (combined WQ and Detention) is 17.25’Wx107.5’L, approximately a 6:1 length to width ratio. The second chamber (detention only) is approximately 17.25’Wx107.5’L, having a total surface area of 3,708 sf (3,700 sf required) The total provided volume within the vault is 16,686 cf. Page 38 Boun Short Plat This volume is based on several factors. The size of the contributing basin, the type of ground cover, and any applicable flow control BMP facility sizing credits listed in Table 5.2.2.A of the Manual. See Table 4.4 for the vault basin areas used for input into KCTRS. As part of flow control BMP requirements, at least 10% of each individual lot size must be mitigated using an applicable Flow Control BMP type to receive Flow Control Sizing Credits. Due to site constraints, a restricted footprint of the allowed impervious for each lot will be incorporated into the site design to meet the Flow Control BMP requirement. These credits are reflected in the table below. Due to grading constraints of the site, portions of Tract A target pervious and impervious surfaces as well as off-site right of way improvements of Chelan Ave NE target surfaces cannot be collected within the proposed stormwater vault. A mitigation of target surfaces that bypass the facility was incorporated into the sizing the detention vault, as allowed per section 1.2.3.2.E of the manual. A point of compliance analysis was completed within KCRTS to ensure that the controlled stormwater release of the vault combined with the uncontrolled bypass flow equates to less than or equal to historic site stormwater durations from ½ of the 2-year storm event through the 50-year storm event. TABLE 4.4 – Design Vault Basin Areas Sub-basin Total Area sf (ac) Impervious sf (ac) Till Grass sf (ac) Till Forest sf (ac) Threshold Discharge Area #1 - Onsite 50,746 (1.165) 27,746 (0.637) 23,000 (0.528) - Threshold Discharge Area #1 – Onsite (Bypass) 1,111 (0.026) 376 (0.009) 735 (0.017) - Threshold Discharge Area #1 – Offsite (Bypass) 4,976 (0.114) 3,559 (0.082) 1,417 (0.032) - TOTAL Area to Vault 50,746 (1.165) 27,746 (0.637) 23,000 (0.528) - TOTAL Area to Bypass Vault 6,087 (0.139) 3,935 (0.090) 2,152 (0.049) - TABLE 4.5 – Vault Volume Summary Vault Function Storage Interval Required Volume (cf) Provided Volume (cf) Sediment Storage 422.66–424.3 - - Water Quality 424.3-429.3 3,687 9,272 Detention 429.3-433.8 16,650 16,689 Freeboard 433.8-434.3 - 1,854 Page 39 Boun Short Plat Control Structure (Primary Discharge Control) The control structure was designed to use multiple orifices in order to discharge flow at a conservative flow control release rate. Flow through these offices may be determined at any given elevation through the following equations listed in Section 5.3.4.2 of the Manual: ghCAQ2, (Orifice) Where C = 0.62, A is the area of the orifice in square feet, g is the gravity constant, and h is the headwater in feet, and 2/3739.9 DHQweir, (Weir) Where D equals the diameter of the riser (18 inches) TABLE 4.6 – Flow Summary Vault Stage Elevation Head, h (ft) Flow Rate, Q (cfs) 429.3 0.0 0.000 430.3 1.0 0.007 431.3 2.0 0.010 432.3 3.0 0.013 433.3 4.0 0.050 434.8 4.5 0.069 Primary Overflow The primary overflow is the overflow weir on the 18-inch diameter control riser. The weir is intended as a safety measure if any of the orifices are plugged. The bottom of the weir (top of riser) is set at the peak detention volume storage depth. Per Table 3.2 of the Manual, KCRTS with 15-minute time steps is to be used to calculate the peak flow if the majority of the tributary area is detained. Per section 5.3.1.1 of the Manual, the 100-year, 15-minute developed peak must be able to bypass the control structure. The developed 100-yr, 15-minute peak flow = 1.02 cfs. See the following pages for KCRTS output. The freeboard necessary above the top of the riser to allow for primary overflow is determined from the weir equation as shown above. ))(5.1(739.906.1 2/3Hcfs, H = 0.173 ft = 2.1” Six inches of freeboard have been provided above the top of riser in the vault. Page 40 Boun Short Plat KCRTS Peak Flow Output (15-minute time steps) Flow Frequency Analysis Time Series File:dev-15min.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.304 6 8/27/01 18:00 1.02 1 100.00 0.990 0.224 8 1/05/02 15:00 0.690 2 25.00 0.960 0.690 2 12/08/02 17:15 0.429 3 10.00 0.900 0.244 7 8/23/04 14:30 0.425 4 5.00 0.800 0.425 4 11/17/04 5:00 0.374 5 3.00 0.667 0.374 5 10/27/05 10:45 0.304 6 2.00 0.500 0.429 3 10/25/06 22:45 0.244 7 1.30 0.231 1.02 1 1/09/08 6:30 0.224 8 1.10 0.091 Computed Peaks 0.909 50.00 0.980 KCRTS Vault Output Page 41 Boun Short Plat Flow Frequency Analysis Time Series File:pre.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.082 2 2/09/01 18:00 0.105 1 100.00 0.990 0.022 7 1/06/02 3:00 0.082 2 25.00 0.960 0.061 4 2/28/03 3:00 0.063 3 10.00 0.900 0.002 8 3/24/04 20:00 0.061 4 5.00 0.800 0.036 6 1/05/05 8:00 0.053 5 3.00 0.667 0.063 3 1/18/06 20:00 0.036 6 2.00 0.500 0.053 5 11/24/06 4:00 0.022 7 1.30 0.231 0.105 1 1/09/08 9:00 0.002 8 1.10 0.091 Computed Peaks 0.097 50.00 0.980 Flow Frequency Analysis Time Series File:dev.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.202 6 2/09/01 2:00 0.412 1 100.00 0.990 0.160 8 1/05/02 16:00 0.245 2 25.00 0.960 0.244 3 2/27/03 7:00 0.244 3 10.00 0.900 0.169 7 8/26/04 2:00 0.214 4 5.00 0.800 0.204 5 10/28/04 16:00 0.204 5 3.00 0.667 0.214 4 1/18/06 16:00 0.202 6 2.00 0.500 0.245 2 10/26/06 0:00 0.169 7 1.30 0.231 0.412 1 1/09/08 6:00 0.160 8 1.10 0.091 Computed Peaks 0.357 50.00 0.980 Flow Frequency Analysis Time Series File:bypass.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.027 6 2/09/01 2:00 0.053 1 100.00 0.990 0.022 8 1/05/02 16:00 0.034 2 25.00 0.960 0.031 3 2/27/03 7:00 0.031 3 10.00 0.900 0.024 7 8/26/04 2:00 0.028 4 5.00 0.800 0.028 4 10/28/04 16:00 0.028 5 3.00 0.667 0.028 5 1/18/06 16:00 0.027 6 2.00 0.500 0.034 2 10/26/06 0:00 0.024 7 1.30 0.231 0.053 1 1/09/08 6:00 0.022 8 1.10 0.091 Computed Peaks 0.047 50.00 0.980 Page 42 Boun Short Plat Retention/Detention Facility Type of Facility: Detention Vault Facility Length: 60.83 ft Facility Width: 60.83 ft Facility Area: 3700. sq. ft Effective Storage Depth: 4.50 ft Stage 0 Elevation: 0.00 ft Storage Volume: 16650. cu. ft Riser Head: 4.50 ft Riser Diameter: 18.00 inches Number of orifices: 3 Full Head Pipe Orifice # Height Diameter Discharge Diameter (ft) (in) (CFS) (in) 1 0.00 0.52 0.016 2 3.50 1.35 0.049 4.0 3 4.10 0.50 0.004 4.0 Top Notch Weir: None Outflow Rating Curve: None Stage Elevation Storage Discharge Percolation (ft) (ft) (cu. ft) (ac-ft) (cfs) (cfs) 0.00 0.00 0. 0.000 0.000 0.00 0.01 0.01 37. 0.001 0.001 0.00 0.02 0.02 74. 0.002 0.001 0.00 0.03 0.03 111. 0.003 0.001 0.00 0.04 0.04 148. 0.003 0.002 0.00 0.05 0.05 185. 0.004 0.002 0.00 0.15 0.15 555. 0.013 0.003 0.00 0.25 0.25 925. 0.021 0.004 0.00 0.35 0.35 1295. 0.030 0.004 0.00 0.45 0.45 1665. 0.038 0.005 0.00 0.55 0.55 2035. 0.047 0.005 0.00 0.65 0.65 2405. 0.055 0.006 0.00 0.75 0.75 2775. 0.064 0.006 0.00 0.85 0.85 3145. 0.072 0.007 0.00 0.95 0.95 3515. 0.081 0.007 0.00 1.05 1.05 3885. 0.089 0.008 0.00 1.15 1.15 4255. 0.098 0.008 0.00 1.25 1.25 4625. 0.106 0.008 0.00 1.35 1.35 4995. 0.115 0.009 0.00 1.45 1.45 5365. 0.123 0.009 0.00 1.55 1.55 5735. 0.132 0.009 0.00 1.65 1.65 6105. 0.140 0.009 0.00 1.75 1.75 6475. 0.149 0.010 0.00 1.85 1.85 6845. 0.157 0.010 0.00 1.95 1.95 7215. 0.166 0.010 0.00 2.05 2.05 7585. 0.174 0.010 0.00 2.15 2.15 7955. 0.183 0.011 0.00 2.25 2.25 8325. 0.191 0.011 0.00 2.35 2.35 8695. 0.200 0.011 0.00 Page 43 Boun Short Plat 2.45 2.45 9065. 0.208 0.011 0.00 2.55 2.55 9435. 0.217 0.012 0.00 2.65 2.65 9805. 0.225 0.012 0.00 2.75 2.75 10175. 0.234 0.012 0.00 2.85 2.85 10545. 0.242 0.012 0.00 2.95 2.95 10915. 0.251 0.013 0.00 3.05 3.05 11285. 0.259 0.013 0.00 3.15 3.15 11655. 0.268 0.013 0.00 3.25 3.25 12025. 0.276 0.013 0.00 3.35 3.35 12395. 0.285 0.013 0.00 3.45 3.45 12765. 0.293 0.014 0.00 3.50 3.50 12950. 0.297 0.014 0.00 3.51 3.51 12987. 0.298 0.014 0.00 3.53 3.53 13061. 0.300 0.015 0.00 3.54 3.54 13098. 0.301 0.017 0.00 3.56 3.56 13172. 0.302 0.020 0.00 3.57 3.57 13209. 0.303 0.023 0.00 3.58 3.58 13246. 0.304 0.027 0.00 3.60 3.60 13320. 0.306 0.029 0.00 3.61 3.61 13357. 0.307 0.031 0.00 3.63 3.63 13431. 0.308 0.032 0.00 3.73 3.73 13801. 0.317 0.038 0.00 3.83 3.83 14171. 0.325 0.043 0.00 3.93 3.93 14541. 0.334 0.047 0.00 4.03 4.03 14911. 0.342 0.051 0.00 4.10 4.10 15170. 0.348 0.053 0.00 4.11 4.11 15207. 0.349 0.054 0.00 4.12 4.12 15244. 0.350 0.055 0.00 4.13 4.13 15281. 0.351 0.055 0.00 4.14 4.14 15318. 0.352 0.056 0.00 4.24 4.24 15688. 0.360 0.060 0.00 4.34 4.34 16058. 0.369 0.064 0.00 4.44 4.44 16428. 0.377 0.067 0.00 4.50 4.50 16650. 0.382 0.069 0.00 4.60 4.60 17020. 0.391 0.534 0.00 4.70 4.70 17390. 0.399 1.380 0.00 4.80 4.80 17760. 0.408 2.480 0.00 4.90 4.90 18130. 0.416 3.780 0.00 5.00 5.00 18500. 0.425 5.250 0.00 5.10 5.10 18870. 0.433 6.680 0.00 5.20 5.20 19240. 0.442 7.210 0.00 5.30 5.30 19610. 0.450 7.700 0.00 5.40 5.40 19980. 0.459 8.170 0.00 5.50 5.50 20350. 0.467 8.600 0.00 5.60 5.60 20720. 0.476 9.020 0.00 5.70 5.70 21090. 0.484 9.420 0.00 5.80 5.80 21460. 0.493 9.800 0.00 5.90 5.90 21830. 0.501 10.170 0.00 6.00 6.00 22200. 0.510 10.530 0.00 6.10 6.10 22570. 0.518 10.870 0.00 6.20 6.20 22940. 0.527 11.200 0.00 6.30 6.30 23310. 0.535 11.530 0.00 6.40 6.40 23680. 0.544 11.840 0.00 6.50 6.50 24050. 0.552 12.150 0.00 Page 44 Boun Short Plat Hyd Inflow Outflow Peak Storage Stage Elev (Cu-Ft) (Ac-Ft) 1 0.20 0.07 4.48 4.48 16579. 0.381 2 0.41 0.07 4.38 4.38 16223. 0.372 3 0.24 0.04 3.69 3.69 13668. 0.314 4 0.21 0.01 3.05 3.05 11282. 0.259 5 0.24 0.06 4.29 4.29 15864. 0.364 6 0.20 0.01 2.88 2.88 10671. 0.245 7 0.16 0.01 2.90 2.90 10723. 0.246 8 0.17 0.01 1.43 1.43 5296. 0.122 Hyd R/D Facility Tributary Reservoir POC Outflow Outflow Inflow Inflow Target Calc 1 0.07 0.03 ******** ******* 0.08 2 0.07 0.05 ******** 0.10 0.09 3 0.04 0.03 ******** ******* 0.04 4 0.01 0.03 ******** ******* 0.04 5 0.06 0.03 ******** ******* 0.08 6 0.01 0.03 ******** ******* 0.03 7 0.01 0.02 ******** ******* 0.03 8 0.01 0.02 ******** ******* 0.03 ---------------------------------- Route Time Series through Facility Inflow Time Series File:dev.tsf Outflow Time Series File:rdout POC Time Series File:dsout Inflow/Outflow Analysis Peak Inflow Discharge: 0.413 CFS at 6:00 on Jan 9 in Year 8 Peak Outflow Discharge: 0.068 CFS at 20:00 on Feb 9 in Year 1 Peak Reservoir Stage: 4.48 Ft Peak Reservoir Elev: 4.48 Ft Peak Reservoir Storage: 16579. Cu-Ft : 0.381 Ac-Ft Add Time Series:bypass.tsf Peak Summed Discharge: 0.093 CFS at 9:00 on Jan 9 in Year 8 Point of Compliance File:dsout.tsf Flow Duration from Time Series File:rdout.tsf Cutoff Count Frequency CDF Exceedence_Probability CFS % % % 0.001 28578 46.605 46.605 53.395 0.534E+00 0.003 6557 10.693 57.298 42.702 0.427E+00 0.005 7915 12.908 70.205 29.795 0.298E+00 0.007 7315 11.929 82.135 17.865 0.179E+00 0.009 4253 6.936 89.070 10.930 0.109E+00 0.011 3741 6.101 95.171 4.829 0.483E-01 0.012 2011 3.280 98.451 1.549 0.155E-01 0.014 693 1.130 99.581 0.419 0.419E-02 0.016 37 0.060 99.641 0.359 0.359E-02 0.018 22 0.036 99.677 0.323 0.323E-02 Page 45 Boun Short Plat 0.020 18 0.029 99.706 0.294 0.294E-02 0.022 15 0.024 99.731 0.269 0.269E-02 0.024 9 0.015 99.746 0.254 0.254E-02 0.026 8 0.013 99.759 0.241 0.241E-02 0.028 16 0.026 99.785 0.215 0.215E-02 0.029 17 0.028 99.812 0.188 0.188E-02 0.031 2 0.003 99.816 0.184 0.184E-02 0.033 10 0.016 99.832 0.168 0.168E-02 0.035 9 0.015 99.847 0.153 0.153E-02 0.037 6 0.010 99.856 0.144 0.144E-02 0.039 5 0.008 99.865 0.135 0.135E-02 0.041 5 0.008 99.873 0.127 0.127E-02 0.043 7 0.011 99.884 0.116 0.116E-02 0.045 4 0.007 99.891 0.109 0.109E-02 0.047 5 0.008 99.899 0.101 0.101E-02 0.048 6 0.010 99.909 0.091 0.913E-03 0.050 7 0.011 99.920 0.080 0.799E-03 0.052 10 0.016 99.936 0.064 0.636E-03 0.054 6 0.010 99.946 0.054 0.538E-03 0.056 5 0.008 99.954 0.046 0.457E-03 0.058 5 0.008 99.962 0.038 0.375E-03 0.060 4 0.007 99.969 0.031 0.310E-03 0.062 5 0.008 99.977 0.023 0.228E-03 0.064 5 0.008 99.985 0.015 0.147E-03 0.065 3 0.005 99.990 0.010 0.978E-04 0.067 2 0.003 99.993 0.007 0.652E-04 Flow Duration from Time Series File:dsout.tsf Cutoff Count Frequency CDF Exceedence_Probability CFS % % % 0.001 28043 45.732 45.732 54.268 0.543E+00 0.003 8072 13.164 58.896 41.104 0.411E+00 0.006 8986 14.654 73.550 26.450 0.264E+00 0.008 6637 10.824 84.374 15.626 0.156E+00 0.010 4721 7.699 92.073 7.927 0.793E-01 0.013 2621 4.274 96.347 3.653 0.365E-01 0.015 1275 2.079 98.426 1.574 0.157E-01 0.017 354 0.577 99.004 0.996 0.996E-02 0.020 208 0.339 99.343 0.657 0.657E-02 0.022 85 0.139 99.481 0.519 0.519E-02 0.024 60 0.098 99.579 0.421 0.421E-02 0.027 38 0.062 99.641 0.359 0.359E-02 0.029 36 0.059 99.700 0.300 0.300E-02 0.031 33 0.054 99.754 0.246 0.246E-02 0.034 23 0.038 99.791 0.209 0.209E-02 0.036 12 0.020 99.811 0.189 0.189E-02 0.038 14 0.023 99.834 0.166 0.166E-02 0.040 11 0.018 99.852 0.148 0.148E-02 0.043 5 0.008 99.860 0.140 0.140E-02 0.045 8 0.013 99.873 0.127 0.127E-02 0.047 8 0.013 99.886 0.114 0.114E-02 0.050 6 0.010 99.896 0.104 0.104E-02 0.052 4 0.007 99.902 0.098 0.978E-03 0.054 7 0.011 99.914 0.086 0.864E-03 Page 46 Boun Short Plat 0.057 7 0.011 99.925 0.075 0.750E-03 0.059 5 0.008 99.933 0.067 0.669E-03 0.061 9 0.015 99.948 0.052 0.522E-03 0.064 7 0.011 99.959 0.041 0.408E-03 0.066 5 0.008 99.967 0.033 0.326E-03 0.068 4 0.007 99.974 0.026 0.261E-03 0.070 3 0.005 99.979 0.021 0.212E-03 0.073 3 0.005 99.984 0.016 0.163E-03 0.075 3 0.005 99.989 0.011 0.114E-03 0.077 3 0.005 99.993 0.007 0.652E-04 0.080 2 0.003 99.997 0.003 0.326E-04 0.082 1 0.002 99.998 0.002 0.163E-04 Duration Comparison Anaylsis Base File: pre.tsf New File: dsout.tsf Cutoff Units: Discharge in CFS -----Fraction of Time----- ---------Check of Tolerance------- Cutoff Base New %Change Probability Base New %Change 0.018 | 0.97E-02 0.90E-02 -6.9 | 0.97E-02 0.018 0.017 -2.6 0.023 | 0.63E-02 0.48E-02 -24.7 | 0.63E-02 0.023 0.020 -12.2 0.028 | 0.50E-02 0.33E-02 -33.4 | 0.50E-02 0.028 0.022 -19.1 0.033 | 0.37E-02 0.22E-02 -40.8 | 0.37E-02 0.033 0.026 -20.4 0.038 | 0.29E-02 0.17E-02 -41.0 | 0.29E-02 0.038 0.030 -21.5 0.043 | 0.22E-02 0.14E-02 -36.3 | 0.22E-02 0.043 0.033 -23.2 0.048 | 0.15E-02 0.11E-02 -24.7 | 0.15E-02 0.048 0.040 -15.9 0.053 | 0.10E-02 0.98E-03 -4.8 | 0.10E-02 0.053 0.050 -3.8 0.057 | 0.64E-03 0.72E-03 12.8 | 0.64E-03 0.057 0.059 3.5 0.062 | 0.34E-03 0.46E-03 33.3 | 0.34E-03 0.062 0.065 4.1 0.067 | 0.23E-03 0.28E-03 21.4 | 0.23E-03 0.067 0.070 4.4 0.072 | 0.16E-03 0.18E-03 10.0 | 0.16E-03 0.072 0.073 1.3 0.077 | 0.82E-04 0.65E-04 -20.0 | 0.82E-04 0.077 0.076 -1.4 0.082 | 0.16E-04 0.16E-04 0.0 | 0.16E-04 0.082 0.083 0.9 Maximum positive excursion = 0.004 cfs ( 6.1%) occurring at 0.061 cfs on the Base Data:pre.tsf and at 0.065 cfs on the New Data:dsout.tsf Maximum negative excursion = 0.010 cfs (-23.8%) occurring at 0.041 cfs on the Base Data:pre.tsf and at 0.031 cfs on the New Data:dsout.tsf ---------------------------------- Route Time Series through Facility Inflow Time Series File:dev.tsf Outflow Time Series File:rdout POC Time Series File:dsout Inflow/Outflow Analysis Peak Inflow Discharge: 0.413 CFS at 6:00 on Jan 9 in Year 8 Peak Outflow Discharge: 0.068 CFS at 20:00 on Feb 9 in Year 1 Peak Reservoir Stage: 4.48 Ft Peak Reservoir Elev: 4.48 Ft Peak Reservoir Storage: 16579. Cu-Ft Page 47 Boun Short Plat : 0.381 Ac-Ft Add Time Series:bypass.tsf Peak Summed Discharge: 0.093 CFS at 9:00 on Jan 9 in Year 8 Point of Compliance File:dsout.tsf Flow Duration from Time Series File:rdout.tsf Cutoff Count Frequency CDF Exceedence_Probability CFS % % % 0.001 28578 46.605 46.605 53.395 0.534E+00 0.003 6557 10.693 57.298 42.702 0.427E+00 0.005 7915 12.908 70.205 29.795 0.298E+00 0.007 7315 11.929 82.135 17.865 0.179E+00 0.009 4253 6.936 89.070 10.930 0.109E+00 0.011 3741 6.101 95.171 4.829 0.483E-01 0.012 2011 3.280 98.451 1.549 0.155E-01 0.014 693 1.130 99.581 0.419 0.419E-02 0.016 37 0.060 99.641 0.359 0.359E-02 0.018 22 0.036 99.677 0.323 0.323E-02 0.020 18 0.029 99.706 0.294 0.294E-02 0.022 15 0.024 99.731 0.269 0.269E-02 0.024 9 0.015 99.746 0.254 0.254E-02 0.026 8 0.013 99.759 0.241 0.241E-02 0.028 16 0.026 99.785 0.215 0.215E-02 0.029 17 0.028 99.812 0.188 0.188E-02 0.031 2 0.003 99.816 0.184 0.184E-02 0.033 10 0.016 99.832 0.168 0.168E-02 0.035 9 0.015 99.847 0.153 0.153E-02 0.037 6 0.010 99.856 0.144 0.144E-02 0.039 5 0.008 99.865 0.135 0.135E-02 0.041 5 0.008 99.873 0.127 0.127E-02 0.043 7 0.011 99.884 0.116 0.116E-02 0.045 4 0.007 99.891 0.109 0.109E-02 0.047 5 0.008 99.899 0.101 0.101E-02 0.048 6 0.010 99.909 0.091 0.913E-03 0.050 7 0.011 99.920 0.080 0.799E-03 0.052 10 0.016 99.936 0.064 0.636E-03 0.054 6 0.010 99.946 0.054 0.538E-03 0.056 5 0.008 99.954 0.046 0.457E-03 0.058 5 0.008 99.962 0.038 0.375E-03 0.060 4 0.007 99.969 0.031 0.310E-03 0.062 5 0.008 99.977 0.023 0.228E-03 0.064 5 0.008 99.985 0.015 0.147E-03 0.065 3 0.005 99.990 0.010 0.978E-04 0.067 2 0.003 99.993 0.007 0.652E-04 Flow Duration from Time Series File:dsout.tsf Cutoff Count Frequency CDF Exceedence_Probability CFS % % % 0.001 28043 45.732 45.732 54.268 0.543E+00 0.003 8072 13.164 58.896 41.104 0.411E+00 0.006 8986 14.654 73.550 26.450 0.264E+00 0.008 6637 10.824 84.374 15.626 0.156E+00 0.010 4721 7.699 92.073 7.927 0.793E-01 Page 48 Boun Short Plat 0.013 2621 4.274 96.347 3.653 0.365E-01 0.015 1275 2.079 98.426 1.574 0.157E-01 0.017 354 0.577 99.004 0.996 0.996E-02 0.020 208 0.339 99.343 0.657 0.657E-02 0.022 85 0.139 99.481 0.519 0.519E-02 0.024 60 0.098 99.579 0.421 0.421E-02 0.027 38 0.062 99.641 0.359 0.359E-02 0.029 36 0.059 99.700 0.300 0.300E-02 0.031 33 0.054 99.754 0.246 0.246E-02 0.034 23 0.038 99.791 0.209 0.209E-02 0.036 12 0.020 99.811 0.189 0.189E-02 0.038 14 0.023 99.834 0.166 0.166E-02 0.040 11 0.018 99.852 0.148 0.148E-02 0.043 5 0.008 99.860 0.140 0.140E-02 0.045 8 0.013 99.873 0.127 0.127E-02 0.047 8 0.013 99.886 0.114 0.114E-02 0.050 6 0.010 99.896 0.104 0.104E-02 0.052 4 0.007 99.902 0.098 0.978E-03 0.054 7 0.011 99.914 0.086 0.864E-03 0.057 7 0.011 99.925 0.075 0.750E-03 0.059 5 0.008 99.933 0.067 0.669E-03 0.061 9 0.015 99.948 0.052 0.522E-03 0.064 7 0.011 99.959 0.041 0.408E-03 0.066 5 0.008 99.967 0.033 0.326E-03 0.068 4 0.007 99.974 0.026 0.261E-03 0.070 3 0.005 99.979 0.021 0.212E-03 0.073 3 0.005 99.984 0.016 0.163E-03 0.075 3 0.005 99.989 0.011 0.114E-03 0.077 3 0.005 99.993 0.007 0.652E-04 0.080 2 0.003 99.997 0.003 0.326E-04 0.082 1 0.002 99.998 0.002 0.163E-04 Vault - Flow Control Performance Evaluation (Per Section 3.2.2) 1. The post-developed flow duration curve lies strictly below the predevelopment curve at the lower limit of the range of control (between 50% of the 2-year and the 2- year). Requirement Satisfied - The dsout (combined flow duration of release of vault and bypass structure) duration curve lies strictly below the target duration curve. 2. At any duration within the range of control, the post-development flow is less than 1.1 times the predevelopment flow. Requirement Satisfied – After running a flow durations comparison analysis, a maximum positive excursion found among the range of control was less than 10%. 3. The target duration curve may not be exceeded along more than 50% of the range of control. Requirement Satisfied - After running a flow duration’s comparison analysis, 5 of the 14 flow duration cutoff values (50%) were exceeded. Page 49 Boun Short Plat 4. The peak flow at the upper end of the range of control (historical 50-year) may not exceed predeveloped levels by more than 10%. Requirement Satisfied – Peak flows at the upper end of the range of control do not exceed predeveloped flow levels by greater than 10%. Flow Splitter (Catch Basin #12) The following flow splitter was sized, in part, utilizing stormwater calculations that were completed during the development of the Vuong Short Plat, prepared by Touma Engineers. For further information about this stormwater system, see below. The flow splitter was sized utilizing Section 6.2.5 of the King County Manual. Per 6.2.5.1, orifice flow splitters shall be sized per Section 5.3.4.2. Qwq=CAorifice(2gh)^0.5 Where Qwq=0.11 cfs (Water Quality Flow Rate Per Vuong Short Plat) C = 0.62 (for plate orifice) G = 32.2 (ft/s2) H = Hydraulic Head (overflow elevation – outlet IE) = 429.37 - 427.87 = 1.5’ Solve A = 0.11/(0.62*(2*32.2*1.5)^0.5) = 0.0181 ft2 Solve for r = ϖr2 = (0.181/ϖ)^0.5 = 0.0759’ Solve for d = 2r = 2*0.0759 = 0.1518’ = 1.82” A 1.82” diameter orifice shall be installed at the bottom of the riser tee within the proposed type 2-60” catch basin. See sheet C5 of the plan set for further flow splitter details. Flow Splitter Flow Capacity Check: Per Section 6.2.5.2 – Design Criteria Item 3, the maximum head shall be minimized to flow in excess of the water quality design flow. Specifically, flow to the WQ facility at the 100-year water surface shall not increase the design WQ flow by more than 10%. To analyze the flow splitter at the 100-year storm event, the rational method was utilized to calculate a 100-year storm event flow rate for both the Boun Short Plat and Vuong Short Plat which are tributary to this conveyance point. An assumed time of concentration was utilized of 6.3 minutes (minimum). Vuong Short Plat Total Sub-Basin Area = 1.13 acres (per Approved TIR) Impervious = 0.83 acres Pervious = 0.30 acres Boun Short Plat Total Sub-Basin Area = 1.31 acres Impervious = 0.73 acres Pervious = 0.58 acres Total contributing Sub-Basin Areas: Total Impervious = 1.56 acres Total Pervious = 0.88 acres Page 50 Boun Short Plat Rational Method Equation Qr=CIrA Where Cc= (C1A1+C2A2+C3A3+….CnAn)/At Cc = (1.56 acres * 0.90 (per Table 3.2.1.A) + 0.88 acres * 0.25 (per Table 3.2.1.A))/2.44 Cc = 0.67 unitless Where Ir = Pr *ir; Pr = the total precipitation at the project site for the 24-hour duration storm event for a given return frequency. Per Figure 3.2.1.D for the 100-Year Storm Event, Pr = 3.9 inches. ir = (Ar)(Tc)(-br), where Ar = 2.61, Br = 0.63 per Table 3.2.1.B. ir = 2.61*6.3-0.63 ir = 0.8186 Ir = 3.9” * 0.8186 = 3.19 Q100 = 0.67*3.19*2.44 = 5.22 cfs Per Figure 5.3.4.H – Riser Inflow Curves, an approximate increase of 0.36’ of head will be necessary to pass the 100-year storm event through the top of the overflow riser with utilizing a 30” (2.5’) standpipe riser. However, a correction needs to be made to this figure to account for the minor flow that will leave the facility through the WQ facility orifice outlet. The following equation was derived to account for this flow loss. Q100 = 9.739 DH3/2 + CAorifice(2gh)^0.5 5.22 cfs = 9.739 * 2.5 * H3/2 + 0.62* 0.0181 (2*32.2*h)^0.5 Solving for H, H = 0.36’ Verify that the change of 0.36’ in head does not increase the amount of flow to WQ facility >10%. A modified flow splitter is proposed at Catch Basin #12 to allow for the overflow elevation of the WQ facility to be 0.4’ higher than the overflow elevation of the downstream network outlet. This will allow for water to flow into the downstream network prior to allowing water to surcharge the water quality facility. The change in flow between the WQ flow rate and the 100-year storm event is the following (note: overflow above the 12” tee is not allowed, therefore weir flow was ignored): Qorifice=CAorifice(2gh)^0.5 = 0.62*0.0181*(2*32.2*(1.5+.36))^0.5 = 0.122 Percent Difference = (0.122 – 0.11)/0.123 = 0.976 = 9.7% < 10% Therefore, a 30” standpipe will have the capacity to convey the 100-year storm event without increase the amount of flow conveyed to the WQ facility by more than 10%. See Plan Sheet C5 of the accompanying plan set for further details. 3.2.1 RATIONAL METHOD 2009 Surface Water Design Manual 1/9/2009 3-13 TABLE 3.2.1.A RUNOFF COEFFICIENTS - "C" VALUES FOR THE RATIONAL METHOD General Land Covers Single Family Residential Areas* Land Cover C Land Cover Density C Dense forest Light forest Pasture Lawns Playgrounds Gravel areas Pavement and roofs Open water (pond, lakes, wetlands) 0.10 0.15 0.20 0.25 0.30 0.80 0.90 1.00 0.20 DU/GA (1 unit per 5 ac.) 0.40 DU/GA (1 unit per 2.5 ac.) 0.80 DU/GA (1 unit per 1.25 ac.) 1.00 DU/GA 1.50 DU/GA 2.00 DU/GA 2.50 DU/GA 3.00 DU/GA 3.50 DU/GA 4.00 DU/GA 4.50 DU/GA 5.00 DU/GA 5.50 DU/GA 6.00 DU/GA 0.17 0.20 0.27 0.30 0.33 0.36 0.39 0.42 0.45 0.48 0.51 0.54 0.57 0.60 * Based on average 2,500 square feet per lot of impervious coverage. For combinations of land covers listed above, an area-weighted "Cc:x At" sum should be computed based on the equation Cc: x At = (C1 x A1) + (C2 x A2) + ...+(Cn x An), where A8 = (A1 + A2 + ...+An), the total drainage basin area. TABLE 3.2.1.B COEFFICIENTS FOR THE RATIONAL METHOD "iR" EQUATION Design Storm Return Frequency aR bR 2 years 5 years 10 years 25 years 50 years 100 years 1.58 2.33 2.44 2.66 2.75 2.61 0.58 0.63 0.64 0.65 0.65 0.63 TABLE 3.2.1.C kR VALUES FOR Tt USING THE RATIONAL METHOD Land Cover Category kR Forest with heavy ground litter and meadow 2.5 Fallow or minimum tillage cultivation 4.7 Short grass pasture and lawns 7.0 Nearly bare ground 10.1 Grassed waterway 15.0 Paved area (sheet flow) and shallow gutter flow 20.0 3.2.1 RATIONAL METHOD 2009 Surface Water Design Manual 1/9/2009 3-17 FIGURE 3.2.1.D 100-YEAR 24-HOUR ISOPLUVIALS SNOHOMISH COUNTY KING COUNTY KING COUNTY PIERCE COUNTY KIRKLAND REDMOND REDMOND DUVALL WOODINVILLEBOTHELL MERCERISLAND RENTON TUKWILA SEATTLE SEATTLE BURIEN NORMANDY PARK SEATAC BELLEVUE NEWCASTLE ISSAQUAH SNOQUALMIE CARNATION NORTH BEND SEATTLE SHORELINE MEDINA BEAUXARTS CLYDEHILL YARROW POINTHUNTSPOINT LAKEFOREST PARK FEDERAL WAY PACIFICMILTON ALGONA AUBURN KENT KENT DES MOINES BLACK DIAMOND ENUMCLAW KENT Vashon Island MauryIsland COVINGTON MAPLEVALLEY 520 522 104 5 522 405 908 900 167 169 515 516 509 518 509 90 405 405 99 5 5 900 90 99 99 99 509 161 164 167 18 18 18 516 169 169 410 520 Elliott Bay LakeSamm amishLakeWashington P ugetSound CedarRiver Green River Whi t eRi ver Sa mmami shRiverSnoqualmie River 0 2 4 Miles N 100-Year 24-Hour Precipitation in Inches WESTERN KING COUNTY 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.83. 9 3.93.94.0 4.04.05.04.14.24.34.44.55.55.5 6.0 6.56.56.04.1 4.2 4.3 4. 4 4.54.6 5.3.4 CONTROL STRUCTURES — METHODS OF ANALYSIS 2009 Surface Water Design Manual 1/9/2009 5-47 Riser Overflow The nomograph in Figure 5.3.4.H may be used to determine the head (in feet) above a riser of given diameter and for a given flow (usually the 100-year peak flow for developed conditions). FIGURE 5.3.4.H RISER INFLOW CURVES 1 10 100 0.1 1 10HEAD IN FEET (measured from crest of riser) Qweir=9.739 DH3/2 Qorifice=3.782 D2H1/2 Q in cfs, D and H in feet Slope change occurs at weir-orifice transition Q (cubic feet per second)18 21 24 27 30 42 487254 10 12 15 33 36 RISER DIAMETER (inches) WATERQUALITYThefollowingcalculationistodeterminewaterqualityvolume,itisbasedon1/3of2-yearstorm,whichis2/3=0.67”.The0.67”precipitationisusedforcomputingthewaterqualityvolume.SBUWSCSMETHODFORCOMPUTINGRUNOFFHYDROGRAPHSTORMOPTIONS:1-S.C.S.TYPE-lA2-7-DAYDESIGN STORM3-STORM DATAFILESPECIFYSTORMOPTION:1S.C.S.TYPE-lARAINFALLDISTRIBUTIONENTER:FREQ(YEAR),DURATION(HOUR),PRECIP(INCHES)1,24,0.67S.C.S.TYPE-lADISTRiBUTION1-YEAR24-HOURSTORM.67hTOTALPRECIP.*********ENTER:A(PERV),CN(PERV),A(IMPERV),CN(IMPERV),TCFORBASINNO.I0.3,86,0.83,98,6.3DATAPRINT-OUT:AREA(ACRES)PERVIOUSIMPERVIOUSTC(MINUTES)ACNACN1.1.386.0.898.06.3PEAK-Q(CFS)T-PEAK(HRS)VOL(CU-FT).117.8314961496cu.ft.isrequired.Itisproposedtoconstructunderground60-inchpipetostorethecalculatedwaterqualityvolume.Cross-sectionareaof60-inchpipelessthebottomandtop6-inchesis16.02s.fRefertosketchonfollowingsheetLengthof60-inchpipeis1496/16.02=93.33 IfUSE95.00ifof6Oinch Page 55 Boun Short Plat Water Quality System (Part E-1) The project is located within a Basic Water Quality treatment area as discussed in Part C in this Section. To satisfy this treatment requirement, the project proposes a combined detention/wetvault located in the southwest corner of the project to provide basic treatment for onsite runoff. Vault (Water Quality) The proposed water quality wetvault for the site has been sized to obtain adequate particulate removal efficiency per section 6.4.1.1 of the Manual. This is based on the volume of the wetvault in relation to the volume of stormwater runoff from the mean annual storm, VB/VR. For basic water quality vaults, this ratio, vault volume/mean annual storm, shall equal at least 3. The sizing of the wetvault is accomplished by first determining the acreage of pervious and impervious areas. These values are used to calculate the treatment runoff volumes by multiplying the acreage of each surface type by the mean annual storm (0.04 feet, per Figure 6.4.1.A of the Manual). Runoff factors are also applied to each surface type, 0.25 for grass and 0.90 for impervious. The sum of the grass and impervious runoff volumes is the total runoff volume from the mean annual storm, VR. To calculate the minimum required volume of the wetpool (VB), the mean annual runoff volume (VR) was multiplied by 3. Grass runoff = (23,000 sf)(0.04’)(0.25) = 230 cf Impervious runoff = (27,746 sf)(0.04’)(0.90) = 999 cf Forest runoff= (0 sf)(0.039’)(0.10)= 0 cf Total runoff volume, VR = 230 cf + 999 cf + 0 cf = 1,229 cf Total basin volume, VB = 1,229 cf x 3 = 3,687 cf The water quality portion of the vault is 17.25’Wx107.5’L, a 6:1 length to width ratio. The proposed depth of the wetvault is 5.00 feet. This provides a total volume of 9,270 cf. See sheet C8 of the engineering plan set for vault dimensions and details. Threshold Discharge Area #2 (2.A & 2.B) Existing Site Hydrology (Part A-2) Threshold Discharge Area #2 is comprised of approximately 20% (11,440 sf) of the project parcel. This includes 8,771 sf of area near the southeast corner of the project parcel and 2,669 sf of project area which consists of an 18-foot strip of land to be dedicated as part of this project. Under existing conditions, Threshold Discharge Area 2.A (the eastern portion of the project site) is currently undeveloped. The site’s topography suggests this portion of land sheet flows to the northeast over densely vegetated land cover consisting of various types of grass and brush. There is approximately six (3) feet of vertical relieve across the site with an average slope around 5%. Any accumulated runoff is allowed to enter a stormwater conveyance swale within Duvall Ave NE near the northeast corner of the project parcel. Threshold Discharge Area 2.B (the 18’ strip of land located near the northwest corner of the project site) is currently undeveloped with the exception of an existing gravel driveway. The site’s topography suggests this portion of land sheet flows to the northwest over vegetated land cover consisting of short lawn. There is approximately one (1) foot of vertical relieve across the site with an average slope around 2%. Any accumulated runoff would flow Page 56 Boun Short Plat northwest along the western edge of the existing gravel access road. Threshold Discharge Area 2.A and 2.B join approximately ½ of a mile downstream of the project site. Developed Site Hydrology (Part B-2) Under developed conditions, a drainage adjustment will allow for a large portion of the Threshold Discharge Area 2.A (8,362 sf) to drain to Threshold Discharge Area #1. The remaining 409 sf will allow stormwater to sheet flow over impervious areas and be collected within a closed conveyance system within Duvall Ave NE. The closed conveyance system will discharge to a rock outfall pad just north of the project site to the existing stormwater ditch. The disturbance within threshold discharge area #2 will include construction clearing and grading, construction of right of way improvements within Duvall Ave NE, associated utilities (storm, power, etc.), required landscaping buffers, and tree replacement. Tables 4.7 and 4.8 break down the historic site conditions and developed site conditions TABLE 4.7 – Historic Site Conditions – Threshold Discharge Area #2 Sub-basin Total sf (ac) Impervioussf (ac) Till Grass sf (ac) Till Forest sf (ac) Threshold Discharge Area #2.A - Onsite 8,771 (0.20) 0 0 8,771 (0.20) Threshold Discharge Area #2.A – Offsite (Historic Conditions) 8,432 (0.19) 0 0 8,432 (0.19) Threshold Discharge Area #2.B 2,669 (0.06) 0 0 2,669 (0.06) TOTAL 19,872 (0.456) 0 0 19,872 (0.456) TABLE 4.8 – Developed Conditions – Threshold Discharge Area #2 Sub-basin Total sf (ac) Impervioussf (ac) Till Grass sf (ac) Till Forest sf (ac) Threshold Discharge Area #2.A - Onsite 409 (0.009) 297 (0.006) 112 (0.003) 0 Threshold Discharge Area #2.A – Offsite (Existing Conditions w/ Planter Strip Addition) 8,432 (0.19) 6,869 (0.16) 1,563 (0.03) 0 Threshold Discharge Area #2.B 2,669 (0.06) 789 (0.02) 1,880 (0.04) 0 TOTAL 11,510 (0.26) 7,955 (0.18) 3,555 (0.08) 0 (0) * The area reflects the site area after ROW dedication Page 57 Boun Short Plat Performance Standards (Part C-2) Flow Control Facility: The proposed project is located within the Flow Control Duration Standard – Matching Historic Site Conditions area: Match developed discharge durations to historic (forested) duration for the range of pre-developed discharge rates from 50% of the 2-year peak flow up to the full 50-year peak flow. The above is required unless a flow control exception applies to the proposed site conditions. Per Section 1.2.3.1.B – Exception 2, The facility requirement in Flow Control Duration Standard Matching Forested Site Conditions Areas is waived for any threshold discharge area in which there is no more than 0.1-cfs difference in the sum of the developed 100-year peak flows for those target surfaces subject to this requirement and the sum of forested (historic) site conditions 100-year peak flows for the same surface areas. The developed conditions do not exceed a 0.1 cfs difference in the sum of developed 100- year peak flows for those target surfaces subject to the flow control facility requirement and the sum of historic site conditions 100-year peak flows for the same surface areas. Thus flow control is not required for this threshold discharge area per section 1.2.3.1.B of the Renton Manual. Part D of this section for analysis output comparing the pre and post flow rates. Water Quality The project is located within the Basic Water Quality treatment area as designated by the King County 2009 Water Quality Application Maps and is not subject to the Enhanced Basic WQ menu per Section 1.2.8.1.A of the Manual. The goal of Basic WQ treatment is 80% removal of total suspended solids. This is required unless an applicable exemption to Core Requirment #8 applies. This threshold discharge area meets the treatment exemption for surface area per Section 1.2.8 Exemptions. The proposed conditions will not increase PGIS surface areas within Threshold Discharge Area #2. The proposed conditions will include the construction of 297 sf of sidewalk impervious (not recognized as PGIS per the Manual) and 112 sf of pervious area. Therefore, a water quality facility for TDA #2.A is not proposed at this time. Stormwater Conveyance The conveyance system capacity standards require that new conveyance systems contain the 25-year peak flow and ensure that the 100-year event does not create a severe flooding or erosion problem. See Section V of this report for the conveyance analysis per Core Requirement #4. Flow Control Systems (Part D-2) As mention in part C-2, a flow control facility is not required for this TDA. Flow calculations for each basin condition subject to the flow control analysis were analyzed at the 100-year storm event. See Table 4.9 and 4.10 below and following page for basin areas and KCRTS output. TABLE 4.9 – Historic Site Conditions – Threshold Discharge Area #2.A – Target Surfaces Sub-basin Total sf (ac) Impervious sf (ac) Till Grass sf (ac) Till Forest sf (ac) Threshold Discharge Area #2.A - Onsite 409 (0.009) 0 0 409 (0.009) Page 58 Boun Short Plat TABLE 4.10 – Developed Site Conditions – Threshold Discharge Area #2.A – Target Surfaces Sub-basin Total sf (ac) Impervious sf (ac) Till Grass sf (ac) Till Forest sf (ac) Threshold Discharge Area #2.A - Onsite 409 (0.009) 297 (0.007) 112 (0.002) 0 Flow Frequency Analysis Time Series File: hist.tsf Project Location: Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.001 2 2/09/01 2:00 0.001 1 100.00 0.990 0.000 6 11/28/01 14:00 0.001 2 25.00 0.960 0.001 3 2/28/03 3:00 0.001 3 10.00 0.900 0.000 7 3/03/04 19:00 0.001 4 5.00 0.800 0.000 8 11/17/04 16:00 0.001 5 3.00 0.667 0.001 4 1/18/06 16:00 0.000 6 2.00 0.500 0.001 5 11/24/06 5:00 0.000 7 1.30 0.231 0.001 1 1/09/08 6:00 0.000 8 1.10 0.091 Computed Peaks 0.001 50.00 0.980 Flow Frequency Analysis Time Series File: dev.tsf Project Location: Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.002 5 2/09/01 2:00 0.004 1 100.00 0.990 0.002 7 1/05/02 16:00 0.003 2 25.00 0.960 0.002 3 12/08/02 18:00 0.002 3 10.00 0.900 0.002 8 8/26/04 2:00 0.002 4 5.00 0.800 0.002 6 10/28/04 16:00 0.002 5 3.00 0.667 0.002 4 1/18/06 16:00 0.002 6 2.00 0.500 0.003 2 10/26/06 0:00 0.002 7 1.30 0.231 0.004 1 1/09/08 6:00 0.002 8 1.10 0.091 Computed Peaks 0.003 50.00 0.980 The difference at the 100-year storm event frequency is 0.003 cfs (0.004-0.001) which is less than the 0.1 cfs increase requirement. Therefore, a flow control facility is not required in Threshold Discharge Area #2. Page 59 Boun Short Plat V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN Onsite The conveyance system was designed per Section 3 and 4 of the Manual. Table 3.2 of the Manual suggests that the Rational Method of analysis is required for undetained areas for tributary areas less than 10 ac. To analyze the proposed systems, the Rational Method was used based on:  QR = CIRA  King county I.D.F. Family (2009 Manual)  25 and 100-year 24-hour storm event flow  Runoff coefficients  Appropriate Manning’s number The Rational Method was used per section 3.2.1. of the Manual. The runoff coefficients, ‘C’ values were taken from Table 3.2.1.A. A C value of 0.9 was used for the roofed surface and a conservative time of concentration value of 6.3 minutes was used. This is a low travel time, but will provide relatively higher flow rate. Conveyance Pipes The new stormwater conveyance system has been proposed to convey runoff in a way that does not impact the drainage basin of the existing site. A conveyance and backwater analysis for the proposed project have been calculated as shown on the following page. Stormwater runoff will drain to catch basins and then flow through varying diameter storm pipes. All new pipes are to be designed with sufficient capacity to convey and contain at minimum the 25-year peak flow and not cause a flooding nuisance during a 100-year storm event. If for larger storms that may overtop the storm structures, all stormwater will be isolated on site. LOT 45,966 SFLOT 55,658 SFLOT 65,638 SFTRACT A7,253 SFLOT 76,453 SFLOT 25,751 SFLOT 15,098 SFLOT 35,893 SFSS~434436438438 438438434 SHEET OFJOB NUMBERNO. DESCRIPTION INIT. DATE DRAWN BY:CHECKED BY: SCALE: HORZ:VERT: DATE:CIVIL & STRUCTURAL ENGINEERING | LAND SURVEYING | PLANNING PROJECT MANAGEMENT | FEASIBILITY | PERMIT EXPEDITING LAKEWOOD OFFICE7602 Bridgeport Way W #3D Lakewood, WA 98499 phone: 253-301-4157 fax: 253-336-3950 ISSAQUAH OFFICE 455 Rainier Blvd NIssaquah, WA 98027phone: 425-392-8055fax: 425-392-0108 beylerconsulting.com BEYLER CONSULTING Plan. Design. ManageEXHIBIT1CONVEYANCE MAP BOUN SHORT PLAT BASIN MAPS CITY OF RENTON,WASHINGTON16-2061A PORTION OF SECTION 10, TOWNSHIP 23 NORTH, 5 WEST, W.M.DUVALL AVE NE CHELAN AVE NE BOUN SHORT PLATCONVEYANCE MAPSCALE: 1" = 30'1530030NATURAL DISCHARGELOCATION #1(RELOCATED CATCHBASIN)NATURAL DISCHARGELOCATION #2.A(EXISTING SWALE)CB #6SUB-BASIN #6SUB BASIN AREA = 47,846 SFIMPERVIOUS AREA = 26,885 SFPERVIOUS AREA = 20,961 SFCB #4CB #5SUB-BASIN #5SUB-BASIN AREA = 2,899 SFIMPERVIOUS AREA = 1,289 SFPERVIOUS AREA = 1,610 SFCB #3CB #2CB #1CB #7CB #8OUTLET #1EX. CB #SUB-BASIN #8SUB-BASIN AREA = 3,917 SFIMPERVIOUS AREA = 2,927 SFPERVIOUS AREA = 990 SFSUB-BASIN #7SUB-BASIN AREA = 1,264 SFIMPERVIOUS AREA = 964 SFPERVIOUS AREA = 300 SFSUB-BASIN #2SUB-BASIN AREA = 2,529 SFIMPERVIOUS AREA = 1,598 SFPERVIOUS AREA = 931 SFSUB-BASIN #9SUB-BASIN AREA = 8,687 SFIMPERVIOUS AREA = 6,775 SFPERVIOUS AREA = 1,912 SFSUB-BASIN #11SUB-BASIN AREA = 1,005 SFIMPERVIOUS AREA = 838 SFPERVIOUS AREA = 167 SFCB #9CB #10CB #11LINK 1LINK 2LINK 3LINK 4LINK 5LINK 6LINK 7LINK 8LINK 9LINK 10LINK 11LINK 12 COMPOSITE A C*A Tc i25 I25 Q25 (basin)Q25 (accum.)DIA. MATERIAL SLOPE QFULL VFULL V25 RThetaDEPTHd/D PIPE FROM TO (ac) C (ac) C C (ac) (Min.) cfs cfs in. n ft/ft cfs fps fps radians ft LINK‐1 CB11 CB10 0.00 0.25 0.02 0.9 0.79 0.02 0.02 6.3 0.804 2.774 0.050 0.050 8 0.012 0.005 0.97 2.78 1.49 0.07 1.65 0.10667 0.16 LINK‐2 CB10 CB9 0.00 0.25 0.00 0.9 0.00 0.00 0.00 6.3 0.804 2.774 0.000 0.050 12 0.012 0.005 2.72 3.47 1.56 0.08 1.41 0.12 0.12 LINK‐3 CB9 OUTLET #2 0.04 0.25 0.16 0.9 0.76 0.20 0.15 6.3 0.804 2.774 0.419 0.469 12 0.012 0.006 2.90 3.70 2.76 0.16 2.23 0.28 0.28 LINK‐4 CB8 CB7 0.02 0.25 0.07 0.9 0.74 0.09 0.07 6.3 0.804 2.774 0.183 0.183 12 0.012 0.010 3.87 4.93 2.65 0.10 1.65 0.16 0.16 LINK‐5 CB7 CB2 0.01 0.25 0.02 0.9 0.75 0.03 0.02 6.3 0.804 2.774 0.060 0.243 12 0.012 0.010 3.87 4.93 2.85 0.11 1.75 0.18 0.18 LINK‐6 CB6 CB4 0.48 0.25 0.62 0.9 0.62 1.10 0.68 6.3 0.804 2.774 1.875 2.301 12 0.012 0.010 3.87 4.93 5.71 0.31 2.90 0.56 0.56 LINK‐7 CB5 CB4 0.04 0.25 0.03 0.9 0.54 0.07 0.04 6.3 0.804 2.774 0.099 0.099 12 0.012 0.027 6.33 8.06 3.63 0.08 1.41 0.12 0.12 LINK‐8 CB4 CB3 0.00 0.25 0.00 0.9 0.00 0.00 0.00 6.3 0.804 2.774 0.000 2.401 12 0.012 0.046 8.27 10.54 9.26 0.21 2.66 0.38 0.38 LINK‐9 CB3 Vault*0.00 0.25 0.00 0.9 0.00 0.00 0.00 6.3 0.804 2.774 0.000 2.401 12 0.012 0.022 5.77 7.35 7.08 0.24 2.98 0.46 0.46 LINK‐10 Vault* CB2 0.00 0.25 0.00 0.9 0.00 0.00 0.00 6.3 0.804 2.774 0.000 2.401 12 0.012 0.011 4.01 5.10 5.92 0.31 2.90 0.56 0.56 LINK‐11 CB2 CB1 0.02 0.25 0.04 0.9 0.66 0.06 0.04 6.3 0.804 2.774 0.106 2.750 12 0.012 0.010 3.87 4.93 6.72 0.40 2.62 0.63 0.63 LINK‐12 CB 1 OUTLET #1 0.00 0.25 0.00 0.9 0.00 0.00 0.00 6.3 0.804 2.774 0.000 2.750 12 0.012 0.010 3.95 5.03 6.40 0.36 2.74 0.6 0.6 (1) (2) (3) (4) (5) (6) (7) (8)(9)(10) (11) (12)(13)(14)(15)(16)(17)(18)(19) (20) Q Length Pipe Size n Value Outlet IE Inlet IE Barrel Area Vf Barrel Velocity Head TW Elev. Friction Loss Entr. HGL Elev. Entr. Head Loss Exit Head Loss Outlet Cont. Elev. Inlet Cont. Elev. Appr. Vel. Head Bend Head Loss Junction Head Loss HW Rim El Diff. PIPE FROM TO (cfs) (ft) (in) (ft) (ft) (sqft) (fps) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) LINK‐12 OUTLET #1 CB1 2.75 25 12 0.012 428.52 428.78 0.79 3.50 0.190 429.62 0.08 429.70 0.10 0.190 429.98 429.88 ‐0.19 0.24 0.00 430.03 432.29 2.26 LINK‐11 CB1 CB2 2.75 8 12 0.012 428.78 428.86 0.79 3.50 0.190 430.03 0.02 430.05 0.10 0.190 430.34 429.96 ‐0.15 0.18 0.01 430.39 432.36 1.97 LINK‐10 CB2 Vault*2.40 41 12 0.012 428.86 429.30 0.79 3.06 0.145 430.03 0.12 430.15 0.07 0.145 430.37 430.35 0.00 0.00 0.00 430.37 433.38 3.01 LINK‐9 Vault* CB3 2.40 9 12 0.012 427.30 427.50 0.79 3.06 0.145 433.80 0.04 433.84 0.07 0.145 434.05 428.60 ‐0.15 0.18 0.00 434.09 437.19 3.10 LINK‐8 CB3 CB4 2.40 21 12 0.012 427.83 428.79 0.79 3.06 0.145 434.09 0.10 434.20 0.07 0.145 434.41 429.89 ‐0.13 0.17 0.01 434.45 436.84 2.39 LINK‐7 CB4 CB5 0.10 120 12 0.012 428.79 432.00 0.79 0.13 0.000 434.45 0.00 434.46 0.00 0.000 434.46 432.00 0.00 0.00 0.00 434.46 436.29 1.83 LINK‐6 CB4 CB6 2.30 64 12 0.012 428.79 429.43 0.79 2.93 0.133 434.46 0.17 434.63 0.07 0.133 434.83 430.33 0.00 0.00 0.00 434.83 436.48 1.65 LINK‐5 CB2 CB7 0.24 47 12 0.012 428.86 429.33 0.79 0.31 0.001 430.37 0.01 430.37 0.00 0.001 430.38 429.33 0.00 0.00 0.00 430.37 432.83 2.46 LINK‐4 CB7 CB8 0.18 39 12 0.012 429.33 429.72 0.79 0.23 0.001 430.37 0.00 430.38 0.00 0.001 430.38 429.72 0.00 0.00 0.00 430.38 432.93 2.55 LINK‐3 OUTLET #2 CB9 0.47 16 12 0.012 434.90 434.99 0.79 0.60 0.006 435.61 0.00 435.61 0.00 0.006 435.62 434.99 0.00 0.00 0.00 435.62 437.16 1.54 LINK‐2 CB9 CB10 0.05 190 12 0.012 434.99 435.93 0.79 0.06 0.000 435.62 0.00 435.62 0.00 0.000 435.62 435.93 0.00 0.00 0.00 435.93 438.38 2.45 LINK‐1 CB10 CB11 0.05 22 8 0.012 435.93 436.05 0.35 0.14 0.000 435.93 0.00 435.93 0.00 0.000 435.93 436.05 0.00 0.00 0.00 436.05 437.75 1.70 BOUN SHORT PLAT BACKWATER CALCULATION SHEET (25 YEAR) LOCATION *Vault TW Elevation = Top Detention = 433.80 BOUN SHORT PLAT CONVEYANCE SYSTEM ANALYSIS AND SIZING TABLE USING THE RATIONAL METHOD (25 YEAR) LOCATION PERVIOUS IMPERVIOUS *Vault Modelled as a flow through structure at full capacity COMPOSITE A C*A Tc i100 I100 Q100 (basin)Q100 (accum.)DIA. MATERIAL SLOPE QFULL VFULL V100 RThetaDEPTHd/D PIPE FROM TO (ac) C (ac) C C (ac) (Min.) cfs cfs in. n ft/ft cfs fps fps radians ft LINK‐1 CB11 CB10 0.00 0.25 0.02 0.9 0.79 0.02 0.02 6.3 0.819 3.192 0.058 0.058 8 0.012 0.005 0.97 2.78 1.60 0.07 1.75 0.12 0.18 LINK‐2 CB10 CB9 0.00 0.25 0.00 0.9 0.00 0.00 0.00 6.3 0.819 3.192 0.000 0.058 12 0.012 0.005 2.72 3.47 1.39 0.06 1.29 0.1 0.1 LINK‐3 CB9 OUTLET #2 0.04 0.25 0.16 0.9 0.76 0.20 0.15 6.3 0.819 3.192 0.482 0.539 12 0.012 0.006 2.90 3.70 2.76 0.16 2.23 0.28 0.28 LINK‐4 CB8 CB7 0.02 0.25 0.07 0.9 0.74 0.09 0.07 6.3 0.819 3.192 0.211 0.211 12 0.012 0.010 3.87 4.93 2.44 0.09 1.53 0.14 0.14 LINK‐5 CB7 CB2 0.01 0.25 0.02 0.9 0.75 0.03 0.02 6.3 0.819 3.192 0.069 0.280 12 0.012 0.010 3.87 4.93 3.03 0.12 1.85 0.2 0.2 LINK‐6 CB6 CB4 0.48 0.25 0.62 0.9 0.62 1.10 0.68 6.3 0.819 3.192 2.157 2.648 12 0.012 0.010 3.87 4.93 6.28 0.36 2.74 0.6 0.6 LINK‐7 CB5 CB4 0.04 0.25 0.03 0.9 0.54 0.07 0.04 6.3 0.819 3.192 0.114 0.114 12 0.012 0.027 6.33 8.06 3.23 0.06 1.29 0.1 0.1 LINK‐8 CB4 CB3 0.00 0.25 0.00 0.9 0.00 0.00 0.00 6.3 0.819 3.192 0.000 2.763 12 0.012 0.046 8.27 10.54 9.50 0.21 2.74 0.4 0.4 LINK‐9 CB3 Vault*0.00 0.25 0.00 0.9 0.00 0.00 0.00 6.3 0.819 3.192 0.000 2.763 12 0.012 0.022 5.77 7.35 7.28 0.25 3.10 0.49 0.49 LINK‐10 Vault* CB2 0.00 0.25 0.00 0.9 0.00 0.00 0.00 6.3 0.819 3.192 0.000 2.763 12 0.012 0.011 4.01 5.10 6.50 0.36 2.74 0.6 0.6 LINK‐11 CB2 CB1 0.02 0.25 0.04 0.9 0.66 0.06 0.04 6.3 0.819 3.192 0.122 3.165 12 0.012 0.010 3.87 4.93 7.71 0.49 2.36 0.69 0.69 LINK‐12 CB 1 OUTLET #1 0.00 0.25 0.00 0.9 0.00 0.00 0.00 6.3 0.819 3.192 0.000 3.165 12 0.012 0.010 3.95 5.03 7.69 0.47 2.41 0.68 0.68 (1) (2) (3) (4) (5) (6) (7) (8)(9)(10) (11) (12)(13)(14)(15)(16)(17)(18)(19) (20) Q Length Pipe Size n Value Outlet IE Inlet IE Barrel Area Vf Barrel Velocity Head TW Elev. Friction Loss Entr. HGL Elev. Entr. Head Loss Exit Head Loss Outlet Cont. Elev. Inlet Cont. Elev. Appr. Vel. Head Bend Head Loss Junction Head Loss HW Rim El Diff. PIPE FROM TO (cfs) (ft) (in) (ft) (ft) (sqft) (fps) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) LINK‐12 OUTLET #1 CB1 3.16 25 12 0.012 428.52 428.78 0.79 4.03 0.252 429.62 0.07 429.69 0.13 0.252 430.07 430.03 ‐0.25 0.32 0.00 430.14 432.29 2.15 LINK‐11 CB1 CB2 3.16 8 12 0.012 428.78 428.86 0.79 4.03 0.252 430.14 0.02 430.16 0.13 0.252 430.54 430.11 ‐0.19 0.24 0.01 430.60 432.36 1.76 LINK‐10 CB2 Vault*2.76 41 12 0.012 428.86 429.30 0.79 3.52 0.192 430.14 0.13 430.26 0.10 0.192 430.55 430.40 0.00 0.00 0.00 430.55 433.38 2.83 LINK‐9 Vault* CB3 2.76 9 12 0.012 427.30 427.50 0.79 3.52 0.192 433.80 0.05 433.85 0.10 0.192 434.13 428.60 ‐0.19 0.24 0.00 434.18 437.19 3.01 LINK‐8 CB3 CB4 2.76 21 12 0.012 427.83 428.79 0.79 3.52 0.192 434.18 0.13 434.32 0.10 0.192 434.60 429.89 ‐0.18 0.22 0.01 434.66 436.84 2.18 LINK‐7 CB4 CB5 0.11 120 12 0.012 428.79 432.00 0.79 0.15 0.000 434.66 0.01 434.66 0.00 0.000 434.66 432.00 0.00 0.00 0.00 434.66 436.29 1.63 LINK‐6 CB4 CB6 2.65 64 12 0.012 428.79 429.43 0.79 3.37 0.177 434.66 0.18 434.85 0.09 0.177 435.11 430.48 0.00 0.00 0.00 435.11 436.48 1.37 LINK‐5 CB2 CB7 0.28 47 12 0.012 428.86 429.33 0.79 0.36 0.002 430.55 0.01 430.56 0.00 0.002 430.56 429.33 0.00 0.00 0.00 430.56 432.83 2.27 LINK‐4 CB7 CB8 0.21 39 12 0.012 429.33 429.72 0.79 0.27 0.001 430.56 0.00 430.56 0.00 0.001 430.57 429.72 0.00 0.00 0.00 430.57 432.93 2.36 LINK‐3 OUTLET #2 CB9 0.54 16 12 0.012 434.90 434.99 0.79 0.69 0.007 435.61 0.01 435.62 0.00 0.007 435.63 434.99 0.00 0.00 0.00 435.63 437.16 1.53 LINK‐2 CB9 CB10 0.06 190 12 0.012 434.99 435.93 0.79 0.07 0.000 435.63 0.00 435.63 0.00 0.000 435.63 435.93 0.00 0.00 0.00 435.93 438.38 2.45 LINK‐1 CB10 CB11 0.06 22 8 0.012 435.93 436.05 0.35 0.17 0.000 435.93 0.00 435.93 0.00 0.000 435.93 436.05 0.00 0.00 0.00 436.05 437.75 1.70 BOUN SHORT PLAT BACKWATER CALCULATION SHEET (100 YEAR) LOCATION *Vault TW Elevation = Top Detention = 433.80 BOUN SHORT PLAT CONVEYANCE SYSTEM ANALYSIS AND SIZING TABLE USING THE RATIONAL METHOD (100 YEAR) LOCATION PERVIOUS IMPERVIOUS *Vault Modelled as a flow through structure at full capacity Page 63 Boun Short Plat VI. SPECIAL REPORTS AND STUDIES Geotechnical Report Geotechnical Report, Proposed Boon-Phany Short Plat October 12, 2015; Prepared by PanGEO Incorporated VII. OTHER PERMITS Existing Permits: There are currently no other permits that effect the drainage submittal or the Technical Information Report. Future Permits: NPDES Permit Building Permit for Each Lot VIII. CSWPPP ANALYSIS AND DESIGN Please refer to Appendix E for the prepared CSWPPP IX. BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT A completed Bond Quantities Worksheet can be found in Appendix D. X. OPERATION AND MAINTENANCE MANUAL A Maintenance and Operations Manual will be provided upon request/at a later date when plans are closer to approval. XI. APPENDICES APPENDIX A – OFFSITE STUDY MAPS 3,983 332 COR Critical Areas Map - Regulated Slopes This map is a user generated static output from an Internet mapping site and is for reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. None 8/29/2016 Legend 2260 113 THIS MAP IS NOT TO BE USED FOR NAVIGATION Feet Notes 226 WGS_1984_Web_Mercator_Auxiliary_Sphere Information Technology - GIS RentonMapSupport@Rentonwa.gov City and County Boundary Other City of Renton Addresses Parcels Slope City of Renton >15% & <=25% >25% & <=40% (Sensitive) >40% & <=90% (Protected) >90% (Protected) Slope King County >15% & <=25% >25% & <=40% >40% & <=90% >90% 3,983 332 COR Critical Areas Map - Seismic This map is a user generated static output from an Internet mapping site and is for reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. None 8/29/2016 Legend 2260 113 THIS MAP IS NOT TO BE USED FOR NAVIGATION Feet Notes 226 WGS_1984_Web_Mercator_Auxiliary_Sphere Information Technology - GIS RentonMapSupport@Rentonwa.gov City and County Boundary Other City of Renton Addresses Parcels Seismic Hazard Areas 3,983 332 COR Critical Areas Map - Wellhead Protection Areas This map is a user generated static output from an Internet mapping site and is for reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. None 8/29/2016 Legend 2260 113 THIS MAP IS NOT TO BE USED FOR NAVIGATION Feet Notes 226 WGS_1984_Web_Mercator_Auxiliary_Sphere Information Technology - GIS RentonMapSupport@Rentonwa.gov City and County Boundary Other City of Renton Addresses Parcels Wellhead Protection Area Zones Zone 1 Zone 1 Modified Zone 2 3,983 332 COR Critical Areas Map - Wetland This map is a user generated static output from an Internet mapping site and is for reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. None 8/29/2016 Legend 2260 113 THIS MAP IS NOT TO BE USED FOR NAVIGATION Feet Notes 226 WGS_1984_Web_Mercator_Auxiliary_Sphere Information Technology - GIS RentonMapSupport@Rentonwa.gov City and County Boundary Other City of Renton Addresses Parcels Wetlands Date: 8/29/2016 ±The information included on this map has been compiled by King County staff from a variety of sources and issubject to change without notice. King County makes no representations or warranties, express or implied,as to accuracy, completeness, timeliness, or rights to the use of such information. This document is not intendedfor use as a survey product. King County shall not be liable for any general, special, indirect, incidental, orconsequential damages including, but not limited to, lost revenues or lost profits resulting from the use or misuseof the information contained on this map. Any sale of this map or information on this map is prohibited except bywritten permission of King County. Legend Parcels Erosion hazard(1990 SAO) Seismic hazard(1990 SAO) Landslide hazard(1990 SAO) Coal mine hazard(1990 SAO) class 1 class 2 perennial class 2 salmonid class 3 unclassified Wetland (1990SAO) Sensitive areanotice on title Chinookdistribution Wildlife network severe moderate King County Critical Areas Map Date: 8/29/2016 ±The information included on this map has been compiled by King County staff from a variety of sources and issubject to change without notice. King County makes no representations or warranties, express or implied,as to accuracy, completeness, timeliness, or rights to the use of such information. This document is not intendedfor use as a survey product. King County shall not be liable for any general, special, indirect, incidental, orconsequential damages including, but not limited to, lost revenues or lost profits resulting from the use or misuseof the information contained on this map. Any sale of this map or information on this map is prohibited except bywritten permission of King County. Legend Parcels Bonded Commercial-MF Commercial-SF Construction DOT FMD Regional Residential Drainagecomplaints King County Drainage Complaints Map APPENDIX B – DOWNSTREAM SYSTEM TABLE AND MAPS 1,991 166 Threshold Discharge Area #1 - Downstream Map This map is a user generated static output from an Internet mapping site and is for reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. 8/29/2016 Legend 1130 56 THIS MAP IS NOT TO BE USED FOR NAVIGATION Feet Notes 113 WGS_1984_Web_Mercator_Auxiliary_Sphere Information Technology - GIS RentonMapSupport@Rentonwa.gov City and County Boundary Other City of Renton Addresses Parcels Wetlands Network Structures Inlet Manhole Utility Vault Unknown Structure Control Structure Pump Station Discharge Point Water Quality Detention Facilities Pond Tank Vault Wetland Pipe Culvert Open Drains Virtual Drainline Facility Outline Private Network Structures 1,991 166 Threshold Discharge Area #1 - Downstream Map 2 This map is a user generated static output from an Internet mapping site and is for reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. 8/29/2016 Legend 1130 56 THIS MAP IS NOT TO BE USED FOR NAVIGATION Feet Notes 113 WGS_1984_Web_Mercator_Auxiliary_Sphere Information Technology - GIS RentonMapSupport@Rentonwa.gov City and County Boundary Other City of Renton Addresses Parcels Wetlands Network Structures Inlet Manhole Utility Vault Unknown Structure Control Structure Pump Station Discharge Point Water Quality Detention Facilities Pond Tank Vault Wetland Pipe Culvert Open Drains Virtual Drainline Facility Outline Private Network Structures OFF-SITEANALYSISDRAINAGE SYSTEMTABLESURFACEWATER DESIGNMANUAL,COREREQUIREMENT#2Basin:Subbasin Name: Subbasin Number:Symbol DrainageComponent Type, Name, and Size DrainageComponentDescriptionSlopeDistancefrom site dischargeExistingProblemsPotentialProblemsObservations of field inspector, resource reviewer, or resident see map Type: sheet flow, swale, stream, channel, pipe, pond; Size: diameter, surface area drainage basin, vegetation, cover, depth, type of sensitive area, volume %¼ ml = 1,320 ft. constrictions, under capacity, ponding, overtopping, flooding, habitat or organism destruction, scouring, bank sloughing, sedimentation, incision, other erosion tributary area, likelihood of problem, overflow pathways, potential impacts 3,983 332 Threshold Discharge Area #2.A - Downstream Map 1 This map is a user generated static output from an Internet mapping site and is for reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. 9/1/2016 Legend 2260 113 THIS MAP IS NOT TO BE USED FOR NAVIGATION Feet Notes 226 WGS_1984_Web_Mercator_Auxiliary_Sphere Information Technology - GIS RentonMapSupport@Rentonwa.gov City and County Boundary Other City of Renton Addresses Parcels Network Structures Inlet Manhole Utility Vault Unknown Structure Control Structure Pump Station Discharge Point Water Quality Detention Facilities Pond Tank Vault Wetland Pipe Culvert Open Drains Facility Outline Private Network Structures Inlet Manhole 3,983 332 Threshold Discharge Area #2.A - Downstream Map 2 This map is a user generated static output from an Internet mapping site and is for reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. 9/1/2016 Legend 2260 113 THIS MAP IS NOT TO BE USED FOR NAVIGATION Feet Notes 226 WGS_1984_Web_Mercator_Auxiliary_Sphere Information Technology - GIS RentonMapSupport@Rentonwa.gov City and County Boundary Other City of Renton Addresses Parcels Network Structures Inlet Manhole Utility Vault Unknown Structure Control Structure Pump Station Discharge Point Water Quality Detention Facilities Pond Tank Vault Wetland Pipe Culvert Open Drains Facility Outline Private Network Structures Inlet Manhole OFF-SITEANALYSISDRAINAGE SYSTEMTABLESURFACEWATER DESIGNMANUAL,COREREQUIREMENT#2Basin:Subbasin Name: Subbasin Number:Symbol DrainageComponent Type, Name, and Size DrainageComponentDescriptionSlopeDistancefrom site dischargeExistingProblemsPotentialProblemsObservations of field inspector, resource reviewer, or resident see map Type: sheet flow, swale, stream, channel, pipe, pond; Size: diameter, surface area drainage basin, vegetation, cover, depth, type of sensitive area, volume %¼ ml = 1,320 ft. constrictions, under capacity, ponding, overtopping, flooding, habitat or organism destruction, scouring, bank sloughing, sedimentation, incision, other erosion tributary area, likelihood of problem, overflow pathways, potential impacts APPENDIX C – BOND QUANTITIES WORKSHEETS/COST DATA AND INVENTORY Planning Division |1055 South Grady Way – 6th Floor | Renton, WA 98057 (425) 430‐7200••Section I: Project Information•••Section II: Bond Quantities Worksheets•• Section II.a EROSION CONTROL (Stabilization/Erosion Sediment Control (ESC))• Section II.b TRANSPORTATION (Street and Site Improvements)• Section II.c DRAINAGE (Drainage and Stormwater Facilities): • Section II.d WATER ‐ONLY APPLICABLE IF WATER SERVICE IS PROVIDED BY CITY OF RENTON• Section II.e SANITARY SEWER ‐ ONLY APPLICABLE IF SEWER SERVICE IS PROVIDED BY CITY OF RENTON••••••Section III. Bond Worksheet• This section calculates the required Permit Bond for construction permit issuance as well as the required Maintenance Bond for project close‐out submittals to release the permit bond on a project. All unit prices include labor, equipment, materials, overhead and profit. Complete the 'Quantity' columns for each of the appropriate section(s). Include existing Right‐of‐Way (ROW), Future Public Improvements and Private Improvements.The 'Quantity Remaining' column is only to be used when a project is under construction. The City allows one (1) bond reduction during the life of the project with the exception of the maintenance period reduction.Excel will auto‐calculate and auto‐populate the relevant fields and subtotals throughout the document. Only the 'Quantity' columns should need completing.Additional items not included in the lists can be added under the "write‐in" sections. Provide a complete description, cost estimate and unit of measure for each write‐in item. Note: Private improvements, with the exception of stormwater facilities, are not included in the bond amount calculation, but must be entered on the form. Stormwater facilities (public and private) are required to be included in the bond amount.BOND QUANTITY WORKSHEET INSTRUCTIONSThis worksheet is intended to be a "working" copy of the bond quantity worksheet, which will be used throughout all phases of the project, from initial submittal to project close‐out approval. Submit this workbook, in its entirety, as follows:The following forms are to be completed by the engineer/developer/applicant as applicable to the project: The Bond Worksheet form will auto‐calculate and auto‐populate from the information provided in Section I and Section II.This section includes all pertinent information for the projectSection II contains a separate spreadsheet TAB for each of the following specialties: (1) electronic copy and (2) hard copies of the entire workbook for civil construction permit submittal. Hard copies are to be included as part of the Technical Information Report (TIR).(1) electronic copy and (1) hard copy of the entire workbook for final close‐out submittal.This section must be completed in its entiretyInformation from this section auto‐populates to all other relevant areas of the workbookPage 1 of 14Ref 8‐H Bond Quantity WorksheetINSTRUCTIONSUnit Prices Updated: 03/2016Version: 06/2016Printed 11/21/2016 Planning Division |1055 South Grady Way – 6th Floor | Renton, WA 98057 (425) 430‐7200Date Prepared: Name:PE Registration No:Firm Name:Firm Address:Phone No.Email Address:Project Name: Project Owner:CED Plan # (LUA):Phone:CED Permit # (U):Address: Site Address:Street Intersection:Addt'l Project Owner:Parcel #(s):Phone:Address: Clearing and grading greater than or equal to 5,000 board feet of timber? Yes/No:NOWater Service Provided by:If Yes, Provide Forest Practice Permit #:Sewer Service Provided by: SITE IMPROVEMENT BOND QUANTITY WORKSHEETPROJECT INFORMATIONCITY OF RENTONCITY OF RENTON1 Select the current project status/phase from the following options: For Approval ‐ Preliminary Data Enclosed, pending approval from the City; For Construction ‐ Estimated Data Enclosed, Plans have been approved for contruction by the City; Project Closeout ‐ Final Costs and Quantities Enclosed for Project Close‐out SubmittalEngineer Stamp Required (all cost estimates must have original wet stamp and signature)Clearing and Grading Utility ProvidersN/AProject Location and Description Project Owner InformationBoun Short PlatBellevue, WA 98004102305‐9139Kent Khnor ‐ Warring Properties16‐000124, SHPL‐A 206‐715‐982611/21/2016Prepared by:FOR APPROVALProject Phase 1Brandon@BeylerConsulting.comBrandon Loucks50085Beyler Consulting LLC7602 Bridgeport Way W, STE D Lakewood, WA 98253‐301‐41571012 Duvall Avenue NE Renton, WA 98059845 106th Ave, Suite 200NE 10th Street & Duvall Ave NE########Abbreviated Legal Description:THE EAST HALF OF THE SOUTHWEST QUARTER OF THE NORTHWEST QUARTER OF SECTION 10, TOWNSHIP 23 NORTH, RANGE 5 EAST, WILLAMETTE MERIDIAN, IN KING COUNTY, WASHINGTON;EXCEPT THE SOUTH 200 FEET; ANDPage 2 of 14Ref 8‐H Bond Quantity WorksheetSECTION I PROJECT INFORMATIONUnit Prices Updated: 06/14/2016Version: 06/14/2016Printed 11/21/2016 CED Permit #:########UnitReference # Price Unit Quantity CostBackfill & compaction‐embankmentESC‐16.50$ CYCheck dams, 4" minus rockESC‐2SWDM 5.4.6.380.00$ EachCatch Basin ProtectionESC‐335.50$ Each 12426.00Crushed surfacing 1 1/4" minusESC‐4WSDOT 9‐03.9(3)95.00$ CYDitchingESC‐59.00$ CYExcavation‐bulkESC‐62.00$ CY 15483,096.00Fence, siltESC‐7SWDM 5.4.3.11.50$ LF 480720.00Fence, Temporary (NGPE)ESC‐81.50$ LFGeotextile FabricESC‐92.50$ SYHay Bale Silt TrapESC‐100.50$ EachHydroseedingESC‐11SWDM 5.4.2.40.80$ SYInterceptor Swale / DikeESC‐121.00$ LFJute MeshESC‐13SWDM 5.4.2.23.50$ SYLevel SpreaderESC‐141.75$ LFMulch, by hand, straw, 3" deepESC‐15SWDM 5.4.2.12.50$ SYMulch, by machine, straw, 2" deepESC‐16SWDM 5.4.2.12.00$ SYPiping, temporary, CPP, 6"ESC‐1712.00$ LFPiping, temporary, CPP, 8"ESC‐1814.00$ LFPiping, temporary, CPP, 12"ESC‐1918.00$ LFPlastic covering, 6mm thick, sandbaggedESC‐20SWDM 5.4.2.34.00$ SYRip Rap, machine placed; slopesESC‐21WSDOT 9‐13.1(2)45.00$ CY 4180.00Rock Construction Entrance, 50'x15'x1'ESC‐22SWDM 5.4.4.11,800.00$ EachRock Construction Entrance, 100'x15'x1'ESC‐23SWDM 5.4.4.13,200.00$ Each 13,200.00Sediment pond riser assemblyESC‐24SWDM 5.4.5.22,200.00$ EachSediment trap, 5' high berm ESC‐25SWDM 5.4.5.119.00$ LF 24456.00Sed. trap, 5' high, riprapped spillway berm section ESC‐26SWDM 5.4.5.170.00$ LF 302,100.00Seeding, by handESC‐27SWDM 5.4.2.41.00$ SYSodding, 1" deep, level groundESC‐28SWDM 5.4.2.58.00$ SYSodding, 1" deep, sloped groundESC‐29SWDM 5.4.2.510.00$ SYTESC SupervisorESC‐30110.00$ HR 4440.00Water truck, dust controlESC‐31SWDM 5.4.7140.00$ HRUnitReference # Price Unit Quantity CostEROSION/SEDIMENT SUBTOTAL: 10,618.00SALES TAX @ 9.5% 1,008.71EROSION/SEDIMENT TOTAL: 11,626.71(A)SITE IMPROVEMENT BOND QUANTITY WORKSHEETFOR EROSION & SEDIMENT CONTROLDescription No.(A)WRITE‐IN‐ITEMS Page 3 of 14Ref 8‐H Bond Quantity WorksheetSECTION II.a EROSION_CONTROLUnit Prices Updated: 06/14/2016Version: 06/14/2016Printed 11/21/2016 CED Permit #:########Existing Future Public PrivateRight‐of‐Way Improvements Improvements(D) (E)Description No. Unit Price Unit Quant. Cost Quant. Cost Quant. Cost Quant. CostGENERAL ITEMS Backfill & Compaction‐ embankment GI‐1 6.00$ CYBackfill & Compaction‐ trench GI‐2 9.00$ CY 2502,250.003002,700.00Clear/Remove Brush, by hand (SY) GI‐3 1.00$ SYBollards ‐ fixed GI‐4 240.74$ EachBollards ‐ removable GI‐5 452.34$ EachClearing/Grubbing/Tree Removal GI‐6 10,000.00$ Acre 0.232,300.001.111,000.00Excavation ‐ bulk GI‐7 2.00$ CYExcavation ‐ Trench GI‐8 5.00$ CY 2501,250.003001,500.00Fencing, cedar, 6' high GI‐9 20.00$ LFFencing, chain link, 4' GI‐10 38.31$ LFFencing, chain link, vinyl coated, 6' high GI‐11 20.00$ LFFencing, chain link, gate, vinyl coated, 20' GI‐12 1,400.00$ EachFill & compact ‐ common barrow GI‐13 25.00$ CYFill & compact ‐ gravel base GI‐14 27.00$ CYFill & compact ‐ screened topsoil GI‐15 39.00$ CYGabion, 12" deep, stone filled mesh GI‐16 65.00$ SYGabion, 18" deep, stone filled mesh GI‐17 90.00$ SYGabion, 36" deep, stone filled mesh GI‐18 150.00$ SYGrading, fine, by hand GI‐19 2.50$ SYGrading, fine, with grader GI‐20 2.00$ SY 641012,820.00Monuments, 3' Long GI‐21 250.00$ EachSensitive Areas Sign GI‐22 7.00$ EachSodding, 1" deep, sloped ground GI‐23 8.00$ SYSurveying, line & grade GI‐24 850.00$ Day 21,700.0054,250.0032,550.00Surveying, lot location/lines GI‐25 1,800.00$ Acre 11,800.00Topsoil Type A (imported) GI‐26 28.50$ CYTraffic control crew ( 2 flaggers ) GI‐27 120.00$ HRTrail, 4" chipped wood GI‐28 8.00$ SYTrail, 4" crushed cinder GI‐29 9.00$ SYTrail, 4" top course GI‐30 12.00$ SYConduit, 2" GI‐31 5.00$ LF 5002,500.00Wall, retaining, concrete GI‐32 55.00$ SFWall, rockery GI‐33 15.00$ SF 1752,625.00SUBTOTAL THIS PAGE:7,700.00 10,750.00 30,795.00(B)(C)(D)(E)SITE IMPROVEMENT BOND QUANTITY WORKSHEETFOR STREET AND SITE IMPROVEMENTSQuantity Remaining (Bond Reduction) (B) (C)Page 4 of 14Ref 8‐H Bond Quantity WorksheetSECTION II.b TRANSPORTATIONUnit Prices Updated: 06/14/2016Version: 06/14/2016Printed 11/21/2016 CED Permit #:########Existing Future Public PrivateRight‐of‐Way Improvements Improvements(D) (E)Description No. Unit Price Unit Quant. Cost Quant. Cost Quant. Cost Quant. CostSITE IMPROVEMENT BOND QUANTITY WORKSHEETFOR STREET AND SITE IMPROVEMENTSQuantity Remaining (Bond Reduction) (B) (C)ROAD IMPROVEMENT/PAVEMENT/SURFACINGAC Grinding, 4' wide machine < 1000sy RI‐1 30.00$ SYAC Grinding, 4' wide machine 1000‐2000sy RI‐2 16.00$ SYAC Grinding, 4' wide machine > 2000sy RI‐3 10.00$ SYAC Removal/Disposal RI‐4 35.00$ SY 29510,325.00Barricade, Type III ( Permanent ) RI‐5 56.00$ LF 16896.00Guard Rail RI‐6 30.00$ LFCurb & Gutter, rolled RI‐7 17.00$ LFCurb & Gutter, vertical RI‐8 12.50$ LF 190023,750.00Curb and Gutter, demolition and disposal RI‐9 18.00$ LF 50900.00Curb, extruded asphalt RI‐10 5.50$ LFCurb, extruded concrete RI‐11 7.00$ LFSawcut, asphalt, 3" depth RI‐12 1.85$ LF 8321,539.20Sawcut, concrete, per 1" depth RI‐13 3.00$ LFSealant, asphalt RI‐14 2.00$ LF 8321,664.00Shoulder, gravel, 4" thick RI‐15 15.00$ SYSidewalk, 4" thick RI‐16 38.00$ SY 30011,400.00Sidewalk, 4" thick, demolition and disposal RI‐17 32.00$ SYSidewalk, 5" thick RI‐18 41.00$ SYSidewalk, 5" thick, demolition and disposal RI‐19 40.00$ SYSign, Handicap RI‐20 85.00$ EachStriping, per stall RI‐21 7.00$ EachStriping, thermoplastic, ( for crosswalk ) RI‐22 3.00$ SFStriping, 4" reflectorized line RI‐23 0.50$ LF 610305.00Additional 2.5" Crushed Surfacing RI‐24 3.60$ SY 50180.00HMA 1/2" Overlay 1.5" RI‐25 14.00$ SYHMA 1/2" Overlay 2" RI‐26 18.00$ SYHMA Road, 2", 4" rock, First 2500 SY RI‐27 28.00$ SYHMA Road, 2", 4" rock, Qty. over 2500SY RI‐28 21.00$ SYHMA Road, 4", 6" rock, First 2500 SY RI‐29 45.00$ SY 27012,150.0065029,250.00HMA Road, 4", 6" rock, Qty. over 2500 SY RI‐30 37.00$ SYHMA Road, 4", 4.5" ATB RI‐31 38.00$ SYGravel Road, 4" rock, First 2500 SY RI‐32 15.00$ SYGravel Road, 4" rock, Qty. over 2500 SY RI‐33 10.00$ SYThickened Edge RI‐34 8.60$ LF 1301,118.00SUBTOTAL THIS PAGE:62,033.20 31,264.00 180.00(B)(C)(D)(E)Page 5 of 14Ref 8‐H Bond Quantity WorksheetSECTION II.b TRANSPORTATIONUnit Prices Updated: 06/14/2016Version: 06/14/2016Printed 11/21/2016 CED Permit #:########Existing Future Public PrivateRight‐of‐Way Improvements Improvements(D) (E)Description No. Unit Price Unit Quant. Cost Quant. Cost Quant. Cost Quant. CostSITE IMPROVEMENT BOND QUANTITY WORKSHEETFOR STREET AND SITE IMPROVEMENTSQuantity Remaining (Bond Reduction) (B) (C)PARKING LOT SURFACING No.2" AC, 2" top course rock & 4" borrow PL‐1 21.00$ SY2" AC, 1.5" top course & 2.5" base course PL‐2 28.00$ SY4" select borrow PL‐3 5.00$ SY1.5" top course rock & 2.5" base course PL‐4 14.00$ SYSUBTOTAL PARKING LOT SURFACING:(B)(C)(D)(E)LANDSCAPING & VEGETATION No.Street Trees LA‐1 225.00$ Each 122,700.00173,825.00Median Landscaping LA‐2 35.00$ Each 632,205.00Right‐of‐Way Landscaping LA‐3Wetland Landscaping LA‐4SUBTOTAL LANDSCAPING & VEGETATION:2,700.00 6,030.00(B)(C)(D)(E)TRAFFIC & LIGHTING No.Signs TR‐1Street Light System ( # of Poles) TR‐2 2,000.00$ Each 36,000.00Traffic Signal TR‐3Traffic Signal Modification TR‐4SUBTOTAL TRAFFIC & LIGHTING:6,000.00(B)(C)(D)(E)WRITE‐IN‐ITEMSSUBTOTAL WRITE‐IN ITEMS:STREET AND SITE IMPROVEMENTS SUBTOTAL: 78,433.20 42,014.00 37,005.00SALES TAX @ 9.5% 7,451.15 3,991.33 3,515.48STREET AND SITE IMPROVEMENTS TOTAL: 85,884.35 46,005.33 40,520.48(B)(C)(D)(E)Page 6 of 14Ref 8‐H Bond Quantity WorksheetSECTION II.b TRANSPORTATIONUnit Prices Updated: 06/14/2016Version: 06/14/2016Printed 11/21/2016 CED Permit #:########Existing Future Public PrivateRight‐of‐Way Improvements Improvements(D) (E)Description No. Unit Price Unit Quant. Cost Quant. Cost Quant. Cost Quant. CostDRAINAGE (CPE = Corrugated Polyethylene Pipe, N12 or Equivalent) For Culvert prices, Average of 4' cover was assumed. Assume perforated PVC is same price as solid pipe.) Access Road, R/D D‐1 26.00$ SY 481,248.00* (CBs include frame and lid)Beehive D‐2 90.00$ EachThrough‐curb Inlet Framework D‐3 400.00$ EachCB Type I D‐4 1,500.00$ Each 710,500.0011,500.00CB Type IL D‐5 1,750.00$ EachCB Type II, 48" diameter D‐6 2,300.00$ Each 12,300.0024,600.0012,300.00 for additional depth over 4' D‐7 480.00$ FT 157,200.00125,760.0083,840.00CB Type II, 54" diameter D‐8 2,500.00$ Each for additional depth over 4' D‐9 495.00$ FTCB Type II, 60" diameter D‐10 2,800.00$ Each 12,800.00 for additional depth over 4' D‐11 600.00$ FT 21,200.00CB Type II, 72" diameter D‐12 6,000.00$ Each for additional depth over 4' D‐13 850.00$ FTCB Type II, 96" diameter D‐14 14,000.00$ Each for additional depth over 4' D‐15 925.00$ FTTrash Rack, 12" D‐16 350.00$ Each 1350.00Trash Rack, 15" D‐17 410.00$ EachTrash Rack, 18" D‐18 480.00$ EachTrash Rack, 21" D‐19 550.00$ EachCleanout, PVC, 4" D‐20 150.00$ EachCleanout, PVC, 6" D‐21 170.00$ Each 71,190.00Cleanout, PVC, 8" D‐22 200.00$ EachCulvert, PVC, 4" (Not allowed in ROW)D‐23 10.00$ LFCulvert, PVC, 6" (Not allowed in ROW)D‐24 13.00$ LFCulvert, PVC, 8" (Not allowed in ROW)D‐25 15.00$ LFCulvert, PVC, 12" (Not allowed in ROW)D‐26 23.00$ LFCulvert, PVC, 15" (Not allowed in ROW)D‐27 35.00$ LFCulvert, PVC, 18" (Not allowed in ROW)D‐28 41.00$ LFCulvert, PVC, 24" (Not allowed in ROW)D‐29 56.00$ LFCulvert, PVC, 30" (Not allowed in ROW)D‐30 78.00$ LFCulvert, PVC, 36" (Not allowed in ROW)D‐31 130.00$ LFCulvert, CMP, 8" D‐32 19.00$ LFCulvert, CMP, 12" D‐33 29.00$ LFSUBTOTAL THIS PAGE:24,350.00 13,050.00 7,388.00(B) (C) (D) (E)SITE IMPROVEMENT BOND QUANTITY WORKSHEETFOR DRAINAGE AND STORMWATER FACILITIESQuantity Remaining (Bond Reduction) (B) (C)Page 7 of 14Ref 8‐H Bond Quantity WorksheetSECTION II.c DRAINAGEUnit Prices Updated: 06/14/2016Version: 06/14/2016Printed 11/21/2016 CED Permit #:########Existing Future Public PrivateRight‐of‐Way Improvements Improvements(D) (E)Description No. Unit Price Unit Quant. Cost Quant. Cost Quant. Cost Quant. CostSITE IMPROVEMENT BOND QUANTITY WORKSHEETFOR DRAINAGE AND STORMWATER FACILITIESQuantity Remaining (Bond Reduction) (B) (C)DRAINAGE (Continued)Culvert, CMP, 15" D‐34 35.00$ LFCulvert, CMP, 18" D‐35 41.00$ LFCulvert, CMP, 24" D‐36 56.00$ LFCulvert, CMP, 30" D‐37 78.00$ LFCulvert, CMP, 36" D‐38 130.00$ LFCulvert, CMP, 48" D‐39 190.00$ LFCulvert, CMP, 60" D‐40 270.00$ LFCulvert, CMP, 72" D‐41 350.00$ LFCulvert, Concrete, 8" D‐42 42.00$ LFCulvert, Concrete, 12" D‐43 48.00$ LFCulvert, Concrete, 15" D‐44 78.00$ LFCulvert, Concrete, 18" D‐45 48.00$ LFCulvert, Concrete, 24" D‐46 78.00$ LFCulvert, Concrete, 30" D‐47 125.00$ LFCulvert, Concrete, 36" D‐48 150.00$ LFCulvert, Concrete, 42" D‐49 175.00$ LFCulvert, Concrete, 48" D‐50 205.00$ LFCulvert, CPE, 6" (Not allowed in ROW)D‐51 14.00$ LFCulvert, CPE, 8" (Not allowed in ROW)D‐52 16.00$ LFCulvert, CPE, 12" (Not allowed in ROW)D‐53 24.00$ LFCulvert, CPE, 15" (Not allowed in ROW)D‐54 35.00$ LFCulvert, CPE, 18" (Not allowed in ROW)D‐55 41.00$ LFCulvert, CPE, 24" (Not allowed in ROW)D‐56 56.00$ LFCulvert, CPE, 30" (Not allowed in ROW)D‐57 78.00$ LFCulvert, CPE, 36" (Not allowed in ROW)D‐58 130.00$ LFCulvert, LCPE, 6" D‐59 60.00$ LFCulvert, LCPE, 8" D‐60 72.00$ LFCulvert, LCPE, 12" D‐61 84.00$ LFCulvert, LCPE, 15" D‐62 96.00$ LFCulvert, LCPE, 18" D‐63 108.00$ LFCulvert, LCPE, 24" D‐64 120.00$ LFCulvert, LCPE, 30" D‐65 132.00$ LFCulvert, LCPE, 36" D‐66 144.00$ LFCulvert, LCPE, 48" D‐67 156.00$ LFCulvert, LCPE, 54" D‐68 168.00$ LFSUBTOTAL THIS PAGE:(B) (C) (D) (E)Page 8 of 14Ref 8‐H Bond Quantity WorksheetSECTION II.c DRAINAGEUnit Prices Updated: 06/14/2016Version: 06/14/2016Printed 11/21/2016 CED Permit #:########Existing Future Public PrivateRight‐of‐Way Improvements Improvements(D) (E)Description No. Unit Price Unit Quant. Cost Quant. Cost Quant. Cost Quant. CostSITE IMPROVEMENT BOND QUANTITY WORKSHEETFOR DRAINAGE AND STORMWATER FACILITIESQuantity Remaining (Bond Reduction) (B) (C)DRAINAGE (Continued)Culvert, LCPE, 60" D‐69 180.00$ LFCulvert, LCPE, 72" D‐70 192.00$ LFCulvert, HDPE, 6" D‐71 42.00$ LFCulvert, HDPE, 8" D‐72 42.00$ LFCulvert, HDPE, 12" D‐73 74.00$ LFCulvert, HDPE, 15" D‐74 106.00$ LFCulvert, HDPE, 18" D‐75 138.00$ LFCulvert, HDPE, 24" D‐76 221.00$ LFCulvert, HDPE, 30" D‐77 276.00$ LFCulvert, HDPE, 36" D‐78 331.00$ LFCulvert, HDPE, 48" D‐79 386.00$ LFCulvert, HDPE, 54" D‐80 441.00$ LFCulvert, HDPE, 60" D‐81 496.00$ LFCulvert, HDPE, 72" D‐82 551.00$ LFPipe, Polypropylene, 6" D‐83 84.00$ LFPipe, Polypropylene, 8" D‐84 89.00$ LFPipe, Polypropylene, 12" D‐85 95.00$ LFPipe, Polypropylene, 15" D‐86 100.00$ LFPipe, Polypropylene, 18" D‐87 106.00$ LFPipe, Polypropylene, 24" D‐88 111.00$ LFPipe, Polypropylene, 30" D‐89 119.00$ LFPipe, Polypropylene, 36" D‐90 154.00$ LFPipe, Polypropylene, 48" D‐91 226.00$ LFPipe, Polypropylene, 54" D‐92 332.00$ LFPipe, Polypropylene, 60" D‐93 439.00$ LFPipe, Polypropylene, 72" D‐94 545.00$ LFCulvert, DI, 6" D‐95 61.00$ LFCulvert, DI, 8" D‐96 84.00$ LFCulvert, DI, 12" D‐97 106.00$ LFCulvert, DI, 15" D‐98 129.00$ LFCulvert, DI, 18" D‐99 152.00$ LFCulvert, DI, 24" D‐100 175.00$ LFCulvert, DI, 30" D‐101 198.00$ LFCulvert, DI, 36" D‐102 220.00$ LFCulvert, DI, 48" D‐103 243.00$ LFCulvert, DI, 54" D‐104 266.00$ LFCulvert, DI, 60" D‐105 289.00$ LFCulvert, DI, 72" D‐106 311.00$ LFSUBTOTAL THIS PAGE:(B) (C) (D) (E)Page 9 of 14Ref 8‐H Bond Quantity WorksheetSECTION II.c DRAINAGEUnit Prices Updated: 06/14/2016Version: 06/14/2016Printed 11/21/2016 CED Permit #:########Existing Future Public PrivateRight‐of‐Way Improvements Improvements(D) (E)Description No. Unit Price Unit Quant. Cost Quant. Cost Quant. Cost Quant. CostSITE IMPROVEMENT BOND QUANTITY WORKSHEETFOR DRAINAGE AND STORMWATER FACILITIESQuantity Remaining (Bond Reduction) (B) (C)Specialty Drainage ItemsDitching SD‐1 9.50$ CYFlow Dispersal Trench (1,436 base+) SD‐3 28.00$ LF French Drain (3' depth) SD‐4 26.00$ LFGeotextile, laid in trench, polypropylene SD‐5 3.00$ SYMid‐tank Access Riser, 48" dia, 6' deep SD‐6 2,000.00$ EachPond Overflow Spillway SD‐7 16.00$ SYRestrictor/Oil Separator, 12" SD‐8 1,150.00$ EachRestrictor/Oil Separator, 15" SD‐9 1,350.00$ EachRestrictor/Oil Separator, 18" SD‐10 1,700.00$ EachRiprap, placed SD‐11 42.00$ CY 8336.00Tank End Reducer (36" diameter) SD‐12 1,200.00$ EachInfiltration pond testing SD‐13 125.00$ HRPermeable Pavement SD‐14Permeable Concrete Sidewalk SD‐15Culvert, Box __ ft x __ ft SD‐16SUBTOTAL SPECIALTY DRAINAGE ITEMS:336.00(B) (C) (D) (E)STORMWATER FACILITIES (Include Flow Control and Water Quality Facility Summary Sheet and Sketch)Detention Pond SF‐1 Each Detention Tank SF‐2 Each Detention Vault SF‐3 65,000.00$ Each 165,000.00Infiltration Pond SF‐4 Each Infiltration Tank SF‐5 Each Infiltration Vault SF‐6 Each Infiltration Trenches SF‐7 Each Basic Biofiltration Swale SF‐8 Each Wet Biofiltration Swale SF‐9 Each Wetpond SF‐10 Each Wetvault SF‐11 37,000.00$ Each 137,000.00Sand Filter SF‐12 Each Sand Filter Vault SF‐13 Each Linear Sand Filter SF‐14 Each StormFilter SF‐15 Each Rain Garden SF‐16 Each SUBTOTAL STORMWATER FACILITIES:102,000.00(B) (C) (D) (E)Page 10 of 14Ref 8‐H Bond Quantity WorksheetSECTION II.c DRAINAGEUnit Prices Updated: 06/14/2016Version: 06/14/2016Printed 11/21/2016 CED Permit #:########Existing Future Public PrivateRight‐of‐Way Improvements Improvements(D) (E)Description No. Unit Price Unit Quant. Cost Quant. Cost Quant. Cost Quant. CostSITE IMPROVEMENT BOND QUANTITY WORKSHEETFOR DRAINAGE AND STORMWATER FACILITIESQuantity Remaining (Bond Reduction) (B) (C)WRITE‐IN‐ITEMSWI‐1WI‐2WI‐3WI‐4WI‐5WI‐6WI‐7WI‐8WI‐9WI‐10WI‐11WI‐12WI‐13WI‐14WI‐15SUBTOTAL WRITE‐IN ITEMS:DRAINAGE AND STORMWATER FACILITIES SUBTOTAL: 24,686.00 13,050.00 109,388.00SALES TAX @ 9.5% 2,345.17 1,239.75 10,391.86DRAINAGE AND STORMWATER FACILITIES TOTAL: 27,031.17 14,289.75 119,779.86(B) (C) (D) (E)Page 11 of 14Ref 8‐H Bond Quantity WorksheetSECTION II.c DRAINAGEUnit Prices Updated: 06/14/2016Version: 06/14/2016Printed 11/21/2016 CED Permit #:########Existing Future Public PrivateRight‐of‐Way Improvements Improvements(D) (E)Description No. Unit Price Unit Quant. Cost Quant. Cost Quant. Cost Quant. CostConnection to Existing Watermain W‐1 2,000.00$ Each 24,000.00Ductile Iron Watermain, CL 52, 4 Inch Diameter W‐2 50.00$ LFDuctile Iron Watermain, CL 52, 6 Inch Diameter W‐3 56.00$ LF 15840.00Ductile Iron Watermain, CL 52, 8 Inch Diameter W‐4 60.00$ LF 38523,100.00Ductile Iron Watermain, CL 52, 10 Inch Diameter W‐5 70.00$ LFDuctile Iron Watermain, CL 52, 12 Inch Diameter W‐6 80.00$ LFGate Valve, 4 inch Diameter W‐7 500.00$ EachGate Valve, 6 inch Diameter W‐8 700.00$ Each 1700.00Gate Valve, 8 Inch Diameter W‐9 800.00$ Each 43,200.00Gate Valve, 10 Inch Diameter W‐10 1,000.00$ EachGate Valve, 12 Inch Diameter W‐11 1,200.00$ EachFire Hydrant Assembly W‐12 4,000.00$ Each 14,000.00Permanent Blow‐Off Assembly W‐13 1,800.00$ Each 11,800.00Air‐Vac Assembly, 2‐Inch Diameter W‐14 2,000.00$ EachAir‐Vac Assembly, 1‐Inch Diameter W‐15 1,500.00$ EachCompound Meter Assembly 3‐inch Diameter W‐16 8,000.00$ EachCompound Meter Assembly 4‐inch Diameter W‐17 9,000.00$ EachCompound Meter Assembly 6‐inch Diameter W‐18 10,000.00$ EachPressure Reducing Valve Station 8‐inch to 10‐inch W‐19 20,000.00$ EachWATER SUBTOTAL:4,000.00 33,640.00SALES TAX @ 9.5% 380.00 3,195.80WATER TOTAL: 4,380.00 36,835.80(B) (C) (D) (E)SITE IMPROVEMENT BOND QUANTITY WORKSHEETFOR WATERQuantity Remaining (Bond Reduction) (B) (C)Page 12 of 14Ref 8‐H Bond Quantity WorksheetSECTION II.d WATERUnit Prices Updated: 06/14/2016Version: 06/14/2016Printed 11/21/2016 CED Permit #:########Existing Future Public PrivateRight‐of‐Way Improvements Improvements(D) (E)Description No. Unit Price Unit Quant. Cost Quant. Cost Quant. Cost Quant. CostClean Outs SS‐1 1,000.00$ Each 77,000.00Grease Interceptor, 500 gallon SS‐2 8,000.00$ EachGrease Interceptor, 1000 gallon SS‐3 10,000.00$ EachGrease Interceptor, 1500 gallon SS‐4 15,000.00$ EachSide Sewer Pipe, PVC. 4 Inch Diameter SS‐5 80.00$ LFSide Sewer Pipe, PVC. 6 Inch Diameter SS‐6 95.00$ LF 15014,250.00Sewer Pipe, PVC, 8 inch Diameter SS‐7 105.00$ LF 20321,315.00Sewer Pipe, PVC, 12 Inch Diameter SS‐8 120.00$ LFSewer Pipe, DI, 8 inch Diameter SS‐9 115.00$ LFSewer Pipe, DI, 12 Inch Diameter SS‐10 130.00$ LFManhole, 48 Inch Diameter SS‐11 6,000.00$ Each 212,000.00Manhole, 54 Inch Diameter SS‐13 6,500.00$ EachManhole, 60 Inch Diameter SS‐15 7,500.00$ EachManhole, 72 Inch Diameter SS‐17 8,500.00$ EachManhole, 96 Inch Diameter SS‐19 14,000.00$ EachPipe, C‐900, 12 Inch Diameter SS‐21 180.00$ LFOutside Drop SS‐24 1,500.00$ LSInside Drop SS‐25 1,000.00$ LSSewer Pipe, PVC, ____ Inch Diameter SS‐26Lift Station (Entire System) SS‐27 LSSANITARY SEWER SUBTOTAL:54,565.00SALES TAX @ 9.5% 5,183.68SANITARY SEWER TOTAL: 59,748.68(B) (C) (D) (E)SITE IMPROVEMENT BOND QUANTITY WORKSHEETFOR SANITARY SEWERQuantity Remaining (Bond Reduction) (B) (C)Page 13 of 14Ref 8‐H Bond Quantity WorksheetSECTION II.e SANITARY SEWERUnit Prices Updated: 06/14/2016Version: 06/14/2016Printed 11/21/2016 Planning Division |1055 South Grady Way – 6th Floor | Renton, WA 98057 (425) 430‐7200Date:Name:Project Name: PE Registration No:CED Plan # (LUA):Firm Name:CED Permit # (U):Firm Address:Site Address:Phone No.Parcel #(s):Email Address:Project Phase: Site Restoration/Erosion Sediment Control Subtotal (a) (a)11,626.71$ Existing Right‐of‐Way Improvements Subtotal (b) (b)90,264.35$ Future Public Improvements Subtotal (c) (c)142,589.81$ Stormwater & Drainage Facilities Subtotal (d) (d)161,100.78$ Bond Reduction (Quantity Remaining)2(e) (e)‐$ Site RestorationCivil Construction PermitMaintenance Bond78,790.99$ Bond Reduction2Construction Permit Bond Amount 3Minimum Bond Amount is $10,000.001 Estimate Only ‐ May involve multiple and variable components, which will be established on an individual basis by Development Engineering.2 The City of Renton allows one request only for bond reduction prior to the maintenance period. Reduction of not more than 70% of the original bond amount, provided that the remaining 30% willcover all remaining items to be constructed. 3 Required Bond Amounts are subject to review and modification by Development Engineering.* Note: The word BOND as used in this document means any financial guarantee acceptable to the City of Renton.** Note: All prices include labor, equipment, materials, overhead and profit. T(P +R ‐ S)Prepared by:Project InformationCONSTRUCTION BOND AMOUNT */**(prior to permit issuance)253‐301‐4157Brandon@BeylerConsulting.comBoun Short Plat16‐000124, SHPL‐A1012 Duvall Avenue NE Renton, WA 98059102305‐9139FOR APPROVAL########7602 Bridgeport Way W, STE D Lakewood, WA 98335608,372.47$ P (a) x 150%SITE IMPROVEMENT BOND QUANTITY WORKSHEET BOND CALCULATIONS11/21/2016Brandon Loucks50085Beyler Consulting LLCR((b)+(c)+(d)) x 150%EST1((b) + (c) + (d)) x 20%‐$ MAINTENANCE BOND */**(after final acceptance of construction)11,626.71$ 90,264.35$ 590,932.41$ 17,440.07$ ‐$ 142,589.81$ 161,100.78$ S(e) x 150%Page 14 of 14Ref 8‐H Bond Quantity WorksheetSECTION III. BOND WORKSHEETUnit Prices Updated: 06/14/2016Version: 06/14/2016Printed 11/21/2016 APPENDIX D – DRAFT BMP COVENANT APPENDIX E – CSWPPP REPORT BOUN SHORT PLAT SITE ADDRESS: 1012 DUVALL AVE NE RENTON, WA 98059 SECTION 32, TOWNSHIP 24 N., RANGE 05 E., W.M. Construction Stormwater Pollution Prevention Plan Prepared for: Warring Properties Contact: Kent Khnor 845 106th Ave, Suite 200 Federal Way, WA 98003 Date Prepared: October 5, 2016 Prepared by: Drew Young, EIT Reviewed by: Brandon M. Loucks, P.E. Beyler Consulting 7602 Bridgeport Way W #3D Lakewood, WA 98499 253.301.4157 Project Number: 16-206 Project Name: Boun Short Plat RPT-CSWPPP-Boun Short Plat 2016.10.05 Page 2 of 10 TABLE OF CONTENTS I. Construction Pollution Prevention Plan .................................... 3 Section 1 – Project Overview ........................................................ 3 Section 3 – Existing Site Conditions ............................................... 4 Section 4 – Adjacent Areas ........................................................... 4 Section 5 – Critical Areas ............................................................. 4 Section 6 – Soils ......................................................................... 4 Section 7 – Potential Erosion Problems ........................................... 4 Section 8 – Construction Stormwater Pollution Prevention Elements ... 5 Section 9 – Construction Phasing .................................................. 9 Section 10 – Construction Schedule ............................................... 9 Section 11 – Financial/Ownership Responsibilities .......................... 10 Section 12 – Engineering Calculations .......................................... 10 Section 13 – Conclusion ............................................................. 10 **EROSION CONTROL RESPONSIBILITY** The Construction Stormwater Polllution Prevention Plan should be kept onsite with a copy of the plans at all time. The objective is to control erosion and prevent sediment and other pollutants from leaving the site during the construction of the project. The owner or assigned contractor shall be responsible for maintaining erosion control Best Management Practices during construction. All BMPs shall be inspected, maintained, and repaired as needed to assure continued performance of their intended function. The owner or contractor shall identify a Certified Erosion and Sediment Control Lead. This person shall be on-site or on-call at all times. The Erosion Control Lead information shall be inserted into this report. The CSWPP shall be modified, if during inspection or investigations conducted by the owner/operator, or the applicable local or state regulatory authority, it is determined that the CSWPPP is ineffective in elimination or significantly minimizing pollutants in stormwater discharges from the site. The CSWPPP shall be modified as necessary to include additional or modified BMPs designed to correct problems identified. Revisions to the SWPPP shall be completed within seven (7) calendar days following the inspection. Construction site operators are required to be covered by a Construction Stormwater General Permit through the Department of Ecology if they are engaged in clearing, grading, and excavating activities that disturb one or more acres and discharge stormwater to surface waters of the state. Smaller sites may also require coverage if they are part of a larger common plan of development that will ultimately disturb one acre or more. Page 3 of 10 I. Construction Pollution Prevention Plan Section 1 – Project Overview The proponent of the Boun Short Plat proposes to subdivide an undeveloped parcel, with the exception of an abandoned shed building that is to be removed as part of this project, located in Renton, King County Washington. The King County parcel number for the property is 102305-9139. The project parcel is approximately 57,677 sf, 1.32 acres in size. The parcel is zoned Residential 8 (R-8) according to the City of Renton Zoning Map effective as of July 1, 2015. The allowed density range in the R-8 zone is a minimum of 4.0 dwelling units per net acre (DUA) to a maximum of 8.0 DUA. The Boun Short Plat proposes to subdivide the current parcel into 7 single-family lots equating to a proposed density of 6.80 DUA. The proposed lots range in size from the smallest being 5,098 sf in size and the largest being 6,453 sf in size. A single stormwater tract will be created with this subdivision for the purpose of stormwater treatment and mitigation for the development. The remaining area will be dedicated to the City of Renton for public right-of-way use. The property is adjacent to Duvall Ave NE to the east, single family parcels to the south and north, and Chelan Ave NE to the west. The proposed project is keeping consistent with neighboring land use characteristics. The site will be accessed through two separate access points. The first access will be an extension of Chelan Place NE, an existing 20’ alleyway, from the south boundary to the north boundary of the project parcel. This access way will be developed into a 16’ paved alley within a 20’ wide right-of-way dedication which meets the current City of Renton street standards. An additional access point to Chelan Ave NE will be provided in the east to west direction through a 16’ paved alley within a 20’ public access and utilities easement. Half street frontage improvements will be included along the west and east boundary of the project site. The west half of Duvall Avenue NE will be improved to current City of Renton Standards for principle arterials by providing two 11-foot travel lanes, a 5-foot bike lane, vertical curb and gutter, an 8-foot wide planter strip, an 8-foot wide sidewalk and a 2-foot maintenance area behind the sidewalk. This will require a 3.5-foot right-of-way dedication along the east boundary line of the project parcel. Chelan Avenue NE will be improved to two separate variations of the current City of Renton Standards for Residential Access Streets. Starting from the south boundary of the project site, the east half of Chelan Avenue NE will be improved to provide a 12-foot travel lane, vertical curb and gutter, an 8-foot wide planter strip, and a 5-foot wide sidewalk for approximately 120 feet. At this point, the Residential Access Street will transition into a Limited Residential Access Street which consists of a 20-foot paved roadway, vertical curb and gutter, an 8-foot wide planter strip, and a 5-foot sidewalk. This road section will be constructed north until it reaches the north boundary line of the project. To incorporate these improvements, an 18’ right of way dedication will be necessary along a portion of the northwest boundary of the project parcel. An 18’ wide section of right-of-way north of the project site will not be improved as part of this project. As a condition of preliminary plat approval (LUA16-00124), a road standards modification will be submitted concurrently with the Utility Construction Permit to allow for the 18’ wide section of right-of-way to remain undeveloped. This project is subject to the 2009 King County Surface Water Design Manual (King Manual) and the City of Renton amendments to the Manual (Renton Manual). Per Figure 1.1.2.A of the Renton Manual, the Boun Short Plat project is subject to a full drainage review meeting core requirements #1 through #8 and special requirements #1 through #6. Page 4 of 10 It has been determined that the site consists of two separate threshold discharges areas. Threshold discharge area #1 consists of a majority of the project site area that naturally discharges stormwater to the southwest corner of the project site. Threshold discharge area #2 consists of a small portion of land along the east boundary which naturally discharges stormwater east to an existing swale with Duvall Ave NE and the 18’ wide panhandle section of land located north of the project site that naturally discharges stormwater to the northwest. A drainage adjustment, per Section 1.4 of the Renton Manual, is proposed to combine a small portion of threshold discharge area #2 with threshold discharge area #1. See section III and IV of this report for further details. Section 2 – Erosion Control Specialist It will be responsibility of the owner and/or the contractor to regularly inspect and maintain the proposed erosion control BMPs, and will take additional measures, as necessary, to respond to changing site conditions. Should it become necessary, the engineer will be made available in providing recommendations for additional erosion control measures to the site. Section 3 – Existing Site Conditions Currently, the parcel is undeveloped with the exception of an abandoned shed building that is to be removed as part of this project. The project is composed of two (2) threshold discharge areas. The site has a localized high point near the south central portion of the property. Water sheet flows southwest and northeast from this high point with an overall vertical relieve of 5 feet. Several existing utility service connections (sewer, storm, water, power, cable, etc.) are located within the existing right of way boundary of Chelan Ave NE and Duvall Ave NE. There are no known vegetative buffers, floodplains, wetlands, geologic hazard areas, streams, creeks, ponds, ravines, or well protection areas present within or near the project area. Section 4 – Adjacent Areas The property is adjacent to Duvall Ave NE to the east, single family parcels to the south and north, and Chelan Ave NE to the west. The proposed project is keeping consistent with neighboring land use characteristics. Section 5 – Critical Areas King County GIS mapping and City of Renton GIS mapping were utilized to determine critical areas that may be located on or near the project site. There are no known vegetative buffers, floodplains, wetlands, geologic hazard areas, streams, creeks, ponds, ravines, or well protection areas present within or near the project area. Section 6 – Soils The Soil Conservation Service Soil Survey shows that the project area soils are comprised of Alderwood Gravelly Sandy Loam (Map Unit Symbol: AgC). Alderwood Gravelly Sandy Loam soils are generally derived from glacial drift and/or glacial outwash over dense glaciomarine deposits and are moderately well drained that range in slope from 8 to 15 percent. Page 5 of 10 Section 7 – Potential Erosion Problems Due to the existing stabilized ground cover and the site consisting of slopes between 0 to 5 percent, it is anticipated the site will be adequately protected from potential erosion problems. Care shall be given to stockpiled materials during construction to minimize the potential for erosion. Catch basins shall be fitted with inlet silt protections, both on-site and off-site, to protect the existing stormwater management systems. The existing drainage swale along Duvall Ave NE shall be protected from erosion, at a minimum, with silt perimeter fencing along cleared/graded areas. To minimize any potential erosion problems, Grade roads/driveways and construct bases as soon as possible. Cover any unworked soil during extended times of no construction activity. Keep as much construction traffic as possible on the road base and off open soils to avoid compaction of the native soils. Silt fences or other BMPs that are capable of retaining water shall be utilized to retain silt laden runoff to the project area. Section 8 – Construction Stormwater Pollution Prevention Elements Element 1: Mark Clearing Limits Prior to beginning land disturbing activities, including clearing and grading, all clearing limits, sensitive areas and their buffers, and trees that are to be preserved within the construction area shall be clearly marked, both in the field and on the plans, to prevent damage and offsite impacts Plastic, metal, or stake wire fence may be used to mark the clearing limits. The duff layer, native top soil, and natural vegetation shall be retained in an undisturbed state to the maximum extent practicable. If it is not practicable to retain the duff layer in place, it should be stockpiled on-site, covered to prevent erosion, and replaced immediately upon completion of the ground disturbing activities Suggested BMPs: BMP: Preserving Natural Vegetation BMP D.3.1.1: High Visibility Plastic or Metal Fence BMP D.3.3.1: Silt Fence Element 2: Establish Construction Access Construction vehicle access should utilitize the proposed stabilized construction entrance within the project clearing limits. Contractor shall restrict movement in and out of the site to one entrance and one exit. When a construction entrance is not preventing sediment from being tracked onto pavement, a wheel wash should be considered. If sediment is tracked off site, the public roads shall be cleaned thoroughly at the end of each day. During wet weather, public roads may need to be cleaned more frequently to prevent sediment from entering water of the state. Suggested BMPs: BMP D.3.4.1: Stabilized Construction Entrance/Exit BMP D.3.4.2: Construction Road/Parking Area Stabilization Page 6 of 10 Element 3: Control Flow Rates Properties and waterways downstream from development sites shall be protected from erosion due to increases in the volume, velocity, and peak flow rate of stormwater runoff from the project site. Temporary interceptor swales will be installed, as necessary, to direct runoff during construction to the temporary sediment trap located along the west boundary of the project site. Depending on the longitudinal slope of the swale, rock check dams will be placed to control flow rates of runoff. Suggested BMPs: BMP D.3.6.1: Interceptor Dike and Swale BMP D.3.6.4: Check Dams BMP D.3.5.1: Sediment Trap BMP D.3.6.5: Outlet Protection Element 4: Install Sediment Controls Prior to leaving a construction site, stormwater runoff from disturbed areas shall pass through a sediment removal BMP. Runoff from fully stabilized areas may be discharged without a sediment removal BMP. Full stabilization means the use of erosion products or vegetative cover that will fully prevent soil erosion. Suggested BMPs: BMP D.3.5.1: Sediment Trap BMP D.3.3.1: Silt Fence Element 5: Stabilize Soils The following constraints will apply. From October 1 through April 30, no soils shall remain exposed and unworked for more than 2 days. From May 1 to September 30, no soils will remain exposed and unworked for more than 7 days. This condition will apply to all soils on site, whether at final grade or not. The areas outside of the roadway will be stabilized with mulch, grass planting or other approved erosion control treatment during the construction phase. Suggested BMPs BMP D.3.2.1: Surface Roughening BMP D.3.2.6: Temporary and Permanent Seeding BMP D.3.2.2: Mulching BMP D.3.2.3: Nets and Blankets BMP D.3.2.4: Plastic Covering BMP D.3.2.7: Sodding BMP D.3.2.9: Compost Blankets BMP D.3.8: Dust Control Page 7 of 10 Element 6: Protect Slopes Design and construct cut and fill slopes in a manner that will minimize erosion. If found necessary to aid in surface water routing during construction, temporary interceptor swales shall be excavated to slope any developed runoff to a sediment trap or pond. Rock check dams shall be placed at regular intervals to reduce slope runoff velocities within the temporary inceptor swales. Exposed soils on slopes shall be stabilized as specified in Element 5. Suggested BMPs: BMP D.3.2.6: Temporary and Permanent Seeding BMP D.3.2.2: Mulching BMP D.3.2.3: Nets and Blankets BMP D.3.6.4: Check Dams Element 7: Protect Drain Inlets All storm drain inlets made operable during construction shall be protected so that stormwater runoff shall not enter the conveyance system without first being filtered or treated to remove sediment. Existing downstream catch basins located within the vicinity of the project site shall be protected using storm drain inlet protection. After installation of grated inlets on the property, these structures shall be provided a form of inlet protection. Suggested BMPs BMP D.3.5.3: Storm Drain Inlet Protection Element 8: Stabilize Channels and Outlets All temporary stormwater channels shall be stabilized to limit the erosion potential during construction. Temporary on-site conveyance channels shall be designed, construction and stabilized to prevent erosion. When the permanent outlets are installed, they shall be protected with washed rock/rip rap for erosion protection. Suggested BMPs BMP D.3.6.4: Check Dams BMP D.3.6.5: Outlet Protection Element 9: Control Pollutants Control of pollutants are the responsibility of the construction superintendent. Maintenance and repair of heavy equipment and vehicles involving oil changes, hydraulic system drain down, solvent and de-greasing cleaning operations, fuel tank drain down and removal, and other activities that may result in discharge or spillage of pollutants to the ground or into stormwater runoff must be conducted using spill prevention measures, such as drip pans. Contaminated surfaces will be cleaned immediately following any discharge or spill incident. The superintendent will be expected to use his best judgment in addressing any and all Page 8 of 10 conditions that are potentially damaging to the environment. Emergency repairs may be performed on-site using temporary plastic placed beneath and, if raining, over the vehicle. All pollutants, including waste materials and demolition debris that occur on-site during construction will be handled and disposed of in a manner that does not cause contamination of stormwater. Cover, containment, and protection from vandalism will be provided for all chemicals, liquid products, petroleum products, and non-inert wastes present on the site. Suggested BMPs BMP C151: Concrete Handling (2015 Washington State DOE Manual) BMP C152: Sawcutting and Surfacing Pollution Prevention (2015 DOE Manual) BMP C153: Material Delivery, Storage and Containment (2015 DOE Manual) Element 10: Control De-Watering De-watering is not anticipated. However, if encountered, de-watering shall be discharged into a closed conveyance system for discharge from the site. The water resulting from construction site de-watering activities must be treated prior to discharge or disposed in a manner that is consistent with the City of Renton Manual. Highly turbid or otherwise contaminated dewatering water, such as from construction equipment operation will be handled separately from stormwater. Element 11: Maintain BMPs All temporary and permanent erosion and sediment control BMPs shall be maintained and repaired as needed to assure continued performance of their intended function. All maintenance and repair will be conducted in accordance with standard procedures for the BMPs. Sediment control BMPs will be inspected weekly or after a runoff-producing storm event during the dry season and daily during the wet season. All temporary erosion and sediment control BMPs will be removed within 30 days after final site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped sediment shall be removed or stabilized on site. Disturbed soil areas resulting from removal of BMPs or vegetation will be permanently stabilized with mulch, grass planting or other approved erosion control treatment. Suggested BMPs BMP C150: Materials On Hand (2015 DOE Manual) BMP C160: Certified Erosion and Sediment Control Lead (2015 DOE Manual) Element 12: Manage the Project Site construction will be performed after the erosion and sediment control measures have been constructed. Preparation for site grading and earthwork should include procedures intended to drain ponded water and control surface water runoff. Grading the site without adequate drainage control measures may negatively impact site soil. From October 1 through April 30, clearing, grading, and other soil disturbing activities shall only be permitted if the transport of sediment from the construction site to receiving waters will be prevented through a combination of favorable site and weather conditions, Page 9 of 10 limitations on extent of activity, and proposed erosion and sediment control measures. The Contractor and/or owner should stop the permitted activity if sediment leaves the construction site causing a violation of the surface water quality standard or if erosion and sediment control measures are not adequately maintained. Trenches should be opened only immediately prior to construction and the trenches will be backfilled immediately after any required testing or inspections of the installed improvements. Trenching spoils will be treated as other disturbed earthwork and measures will be taken to cover or otherwise stabilize the material, as required. All BMPs shall be inspected, maintained, and repaired as needed to assure continued performance of their intended function. Section 9 – Construction Phasing The recommended construction sequence will include these steps in this order, but some portions of the steps may be performed out of sequence as conditions require. The Construction Sequence is as follows: 1. The contractor shall become familiar with the property, construction drawings and geotechnical conditions on site. The contractor shall meet with the developer, civil engineer, and any other design professional to review the physical constraints affecting the proposed construction. 2. The contractor shall schedule and attend a pre-construction meeting with the City of Renton prior to preforming any site work. 3. For each phase of work, the project surveyor shall flag the limits of clearing and grading, and the contractor shall install all temporary erosions control measures. 4. When TESC measures are approved by the City inspector, install site improvements. 5. Proceed with site improvements making adjustments to the Erosion Control measures as needed. 6. Install final soil stabilization/amendments in areas where final grades have been achieved and future disturbance can be avoided. 7. Hydroseed or place straw mulch on any other disturbed areas. 8. Once the threat of erosion has passed, and all construction is complete, the remaining erosion control measure may be removed with approval from the City inspector. 9. All permanent drainage facilities shall be cleaned of any sediment and construction debris. Sediment laden water shall not be flushed downstream. All storm drainage facilities shall be protected in place from construction activity via brightly flagged stakes or, if necessary, temporary construction fencing. Section 10 – Construction Schedule The project is intended to begin construction in the Spring of 2017. Special consideration is required for source control during the wet season period, which may include phased construction, materials available for immediate stabilization of denuded areas and diligent review of site for noted erosion concerns. Page 10 of 10 Section 11 – Financial/Ownership Responsibilities The property owner will be responsible for bonds and other required securities for this project. Section 12 – Engineering Calculations Sediment Trap Calculations 15-Minute Peak Flow Calculations using KCRTS Flow Frequency Analysis Time Series File:dev-15min.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.304 6 8/27/01 18:00 1.02 1 100.00 0.990 0.224 8 1/05/02 15:00 0.690 2 25.00 0.960 0.690 2 12/08/02 17:15 0.429 3 10.00 0.900 0.244 7 8/23/04 14:30 0.425 4 5.00 0.800 0.425 4 11/17/04 5:00 0.374 5 3.00 0.667 0.374 5 10/27/05 10:45 0.304 6 2.00 0.500 0.429 3 10/25/06 22:45 0.244 7 1.30 0.231 1.02 1 1/09/08 6:30 0.224 8 1.10 0.091 Computed Peaks 0.909 50.00 0.980 SA = FS (Q2-year/Vs) = 2 * (0.304/.00096) = 633.3 sf = 634 sf See sheet C2 of the plan set for sediment trap location and details. Section 13 – Conclusion Erosion control procedures as described in this report and illustrated on the design plans, if properly implemented, should mitigate anticipated erosion effects from the development of this project. The success of erosion control measures is usually related to the Contractor’s attention to maintenance of such measures. However, in some instances, even with proper attention being paid to erosion control, measures such as those shown on the plans are unable to prevent the discharge of turbid water. In this event, secondary measures may be required. These additional BMPs are provided in Appendix D of the 2009 King County Surface Water Design Manual and Volume 2 of the 2012 edition of the Washington State Department of Ecology Stormwater Management Manual for Western Washington.