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HomeMy WebLinkAboutRS__TIR_230403_v1 www.furrengineering.com Stormwater Site Plan/Report Grant Place Townhomes 1600 Grant Avenue S Renton, WA 98055 Permit #: Parcel # 202305-9052 For: Satwant Singh 15 S Grady Way Ste. 527 Renton, WA 98057 (206) 391-3311 April 3, 2023 Revised: Prepared by: R. Elliott, E.I.T. FES Project #20069 4/3/2023 R G G N A F U R SE F ORP I ANO EL T S GE SI N ERE DEEATDSNTAWFO . SAHI INREENOTR46937 FES Project 22061 TOC TABLE OF CONTENTS 1.0 PROJECT OVERVIEW ................................................................................................ 2 Technical Information Report (TIR) Worksheet ........................................................... 3 Vicinity Map ................................................................................................................ 8 2.0 CONDITIONS AND REQUIREMENTS SUMMARY ..................................................... 9 2.1 Analysis of the Nine (9) Core Requirements ....................................................... 10 2.2 Analysis of the Five Special Requirements ......................................................... 12 2.3 Conditions of Approval ........................................................................................ 13 3.0 OFFSITE ANALYSIS ................................................................................................. 14 Downstream Map ...................................................................................................... 17 Downstream Table .................................................................................................... 18 4.0 FLOW CONTROL, LOW IMPACT DEVELOPMENT (LID) AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ...................................................................... 19 4.1 VAULT ANALYSIS .............................................................................................. 19 4.2 WATER QUALITY SYSTEM ............................................................................... 22 Developed Conditions Exhibit ................................................................................... 23 StormFilter Detail ...................................................................................................... 24 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN................................................. 36 6.0 SPECIAL REPORTS AND STUDIES ......................................................................... 37 7.0 OTHER PERMITS ...................................................................................................... 38 8.0 CSWPP ANALYSIS AND DESIGN ............................................................................ 39 9.0 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT ................................................................................................................................ 40 10.0 OPERATIONS AND MAINTENANCE MANUAL ........................................................ 41 Appendix A: Pacific Engineering Downstream Analysis ............................................... 52 Appendix B: Geotechnical Report ................................................................................... 53 Appendix C: As-Built Survey Drawings ........................................................................... 54 Page 2 1.0 PROJECT OVERVIEW This project proposes the construction of eight townhouse buildings on a single 92,828 sf (2.131 ac) parcel (no. 202305-9052) located at 1600 Grant Ave. S, Renton, WA 98055. This project is the continuation of an expired plat (civil permit no. U16004475); currently, the site is partially developed with several constructed buildings, building foundations, utilities, and rough-graded alley. Stormwater onsite is collected by the onsite storm system and conveyed into a combined detention/wetvault, which discharges through a Contech StormFilter manhole and into the municipal storm system within Grant Ave. Low Impact Development (LID) BMPs are generally infeasible onsite due to unsuitable soils, high/perched groundwater, and the amount of completed construction onsite. A letter from a licensed geotechnical engineer has been added to the 2005 geotechnical investigation to confirm site conditions and to approve construction to continue as proposed. The City of Renton has amended the 2021 King County Stormwater Design Manual (KCSWDM) to create the 2022 City of Renton Surface Water Design Manual (CoRSWDM), which serves as the governing document for stormwater management within the city. This report shall serve to comply with the updated requirements of this manual and the Renton Municipal Code. KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Project Owner Phone _____ Address Project Engineer Company ____ Phone _______ Part 2 PROJECT LOCATION AND DESCRIPTION Project Name _ DLS-Permitting Permit #_____ Location Township Range _ Section _ Site Address _______ Part 3 TYPE OF PERMIT APPLICATION □ Land use (e.g.,Subdivision / Short Subd. / UPD) □ Building (e.g.,M/F / Commercial / SFR) □ Clearing and Grading □ Right-of-Way Use □ Other ___________________________ Part 4 OTHER REVIEWS AND PERMITS1 □ DFW HPA □ COE CWA 404 □ ECY Dam Safety □ FEMA Floodplain □ COE Wetlands □ Other _________ □ Shoreline Management □ Structural Rockery/Vault/______ □ ESA Section 7 Part 5 PLAN AND REPORT INFORMATION Technical Information Report Type of Drainage Review (check one): Date (include revision dates): Date of Final: □ □ □ □ □ Full Targeted Simplified Large Project Directed Site Improvement Plan (Engr. Plans) Plan Type (check one): Date (include revision dates): Date of Final: □ Full □ Modified □ Simplified Part 6 SWDM ADJUSTMENT APPROVALS Type (circle one): Standard / Experimental /Blanket Description: (include conditions in TIR Section 2) Approved Adjustment No._ _ Date of Approval: __________________________ 1 DFW: WA State Dept. of Fish and Wildlife. HPA: hydraulic project approval. COE: (Army) Corps of Engineers. CWA: Clean Water Act. ECY: WA State Dept. of Ecology. FEMA: Federal Emergency Management Agency. ESA: Endangered Species Act. 2021 Surface Water Design Manual 1 Last revised 7/23/2021 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes / No Start Date: Describe: Completion Date:Re: KCSWDM Adjustment No. 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 □Steep Slope □ Lake □Erosion Hazard □ Wetlands □Landslide Hazard □ Closed Depression □Coal Mine Hazard □ Floodplain □Seismic Hazard □ Other □Habitat Protection □ Part 10 SOILS Soil Type Slopes Erosion Potential □ High Groundwater Table (within 5 feet) □ Sole Source Aquifer □ Other ______________ _______________________ □ Seeps/Springs □ Additional Sheets Attached 2021 Surface Water Design Manual 2 Last revised 7/23/2021 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE LIMITATION / SITE CONSTRAINT □ Core 2 - Offsite Analysis____________________ _________________________________ □ Sensitive/Critical Areas _____________________ _________________________________ □ SEPA _____________________________________ _________________________________ □ LID Infeasibility____________________________ _________________________________ □ Other _____________________________________ _________________________________ □ □ 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 (include facility Level: 1 / 2 / 3 or Exemption Number ______________ summary sheet)Flow Control BMPs Conveyance System Spill containment located at: Erosion and Sediment Control /CSWPP/CESCL/ESC Site Supervisor: Construction Stormwater Pollution Prevention Contact Phone: After Hours Phone: Maintenance and Operation Responsibility (circle one): Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Liability Provided: Yes / No Water Quality (include facility Type (circle one): Basic / Sens. Lake / Enhanced Basic / Bog summary sheet)or Exemption No. Landscape Management Plan: Yes / No For Entire Project:Total Replaced Impervious surfaces on the site % of Target Impervious that had a feasible FCBMP Total New Pervious Surfaces on the site Repl. Imp. on site mitigated w/flow control facility implemented Repl. Imp. on site mitigated w/water quality facility Repl. Imp. on site mitigated with FCBMP 2021 Surface Water Design Manual 3 Last revised 7/23/2021 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Special Requirements (as applicable): Area Specific Drainage Requirements Type: CDA / SDO / MDP / BP / LMP / Shared Fac. / None Name: Floodplain/Floodway Delineation Type (circle one): Major / Minor / Exemption / None 100-year Base Flood Elevation (or range): Datum: Flood Protection Facilities Describe: Source Control (commercial / industrial land use) Describe land use: Describe any structural controls: 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 ^ Protection of Flow Control BMP Facilities (existing and proposed) ^ Maintain BMPs / Manage Project 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, restore operation of Flow Control BMP Facilities as necessary ^ Flag limits of SAO and open space preservation areas ^ Other 2021 Surface Water Design Manual 4 Last revised 7/23/2021 Page 8 Vicinity Map Scale: none. PROJECT SITE Page 9 2.0 CONDITIONS AND REQUIREMENTS SUMMARY Per KCSWDM Section 1.1, Figure 1.1.2.A: Flow Chart for Determining Type of Drainage Review Required, this project is required to comply with Full Drainage Review per Section 1.1.2.4: Therefore, this project must comply with all nine core requirements in Section 1.2 and all five special requirements in Section 1.3. Page 10 2.1 Analysis of the Nine (9) Core Requirements 2.1.1 Core Requirement #1: Discharge at the Natural Location This project is a continuation of an expired permit, with a previously-designed stormwater system onsite discharging from the site into the municipal storm system through the existing manhole in Grant Ave. This project proposes discharge through this system. Therefore, the existing drainage pattern is maintained under the developed condition. See Section 3.4 of this report. 2.1.2 Core Requirement #2: Offsite Analysis See Section 3.0: Offsite Analysis. 2.1.3 Core Requirement #3: Flow Control Per King County iMap, Conservation Flow Control is required for this site. Therefore, per Table 1.2.3.A, the historic site conditions Level 2 flow control standard shall apply. A previously-installed vault, designed by others, shall be used to provide the required level of flow control. See Section 4.1: Vault Analysis. 2.1.4 Core Requirement #4: Conveyance System Conveyance shall be primarily through 12” CMP pipe; see Section 5.0: Conveyance System Analysis and Design. 2.1.5 Core Requirement #5: Erosion and Sediment Control A Temporary Erosion and Sediment Control (TESC) plan is included separately as a part of this submittal. 2.1.6 Core Requirement #6: Maintenance and Operations Maintenance and operations instructions from the KCSWDM are provided in Section 10.0 of this report. 2.1.7 Core Requirement #7: Financial Guarantees and Liability Bond quantity analysis will be provided separately at final approval. 2.1.8 Core Requirement #8: Water Quality Because this project proposes the development of a multifamily project, Enhanced Basic Water Quality is required per CoRSWDM Section 1.2.8.1(A). Water quality will be provided by a two-facility treatment train consisting of a combined detention/wet vault and a ConTech Stormfilter with ZPG filters. See Section 4.2: Water Quality System. 2.1.9 Core Requirement #9: Flow Control BMPs This project was evaluated per CoRSWDM Section 1.2.9.2.2: Large Lot BMP Requirements: 1. Full dispersion: Dispersion is not feasible on this project due to insufficient vegetated flowpath. 2. Full infiltration of roof runoff: Infiltration is not feasible on this project due to unsuitable soils and high/perched groundwater. 3. Where (1) and (2) are infeasible, the following BMPs must be evaluated for feasibility: Page 11 a. Full infiltration: Infiltration is not feasible on this project due to unsuitable soils and high/perched groundwater. b. Limited infiltration: Infiltration is not feasible on this project due to unsuitable soils and high/perched groundwater. c. Bioretention: Bioretention is not feasible due to unsuitable soils and high/perched groundwater. d. Permeable Pavement: Permeable pavement is not feasible due to unsuitable soils and high/perched groundwater and slopes greater than 5%. 4. All target surfaces not mitigated by Requirements (1), (2), and (3) above must be mitigated to the maximum extent feasible using Basic Dispersion. Dispersion is not feasible due to insufficient vegetated flow path. 5. For projects that will result in an impervious surface coverage on the buildable portion of the site/lot of less than 45%, flow control BMPs must be applied to 50% of target impervious surfaces. There are no feasible flow control BMPs from requirements (1), (2), (3), and (4) above. Native Growth Retention Credit shall be applied to the proposed 2,595 square-foot native growth protection area (NGPA). Page 12 2.2 Analysis of the Five Special Requirements 2.2.1 Special Requirement No. 1: Other Adopted Area-Specific Requirements.  Critical Drainage Areas (CDAs): There are no CDAs adopted in King County at this time.  Master Drainage Plans (MDPs): This project is not a part of an MDP.  Basin Plans (BPs): This project is subject to the City of Renton Shoreline Master Program.  Salmon Conservation Plans (SCPs): This project is subject to the requirements of the WRIA 9 Salmon Habitat Plan.  Stormwater Compliance Plans (SWCPs): This project is subject to the provisions of the 2022 King County Stormwater Management Program Plan (SWMP).  Lake Management Plans (LMPs): No known LMPs apply to this project.  Hazard Mitigation Plan: This project is subject to the requirements of the King County FHMP and the City of Renton’s Hazard Mitigation Plan.  Shared Facility Drainage Plans (SFDPs): This project is not subject to shared facility drainage requirements. 2.2.2 Special Requirement No. 2: Flood Hazard Area Delineation. There are no flood hazards on or adjacent to the site; see Section 3.2 of this report. 2.2.3 Special Requirement No. 3: Flood Protection Facilities. N/A 2.2.4 Special Requirement No. 4: Source Control. N/A 2.2.5 Special Requirement No. 5: Oil Control. N/A Page 13 2.3 Conditions of Approval Reserved. Page 14 3.0 OFFSITE ANALYSIS A Level 1 Downstream Analysis was performed by Pacific Engineering Design, LLC, and is attached to this report as Appendix A. 3.1 Task 1: Define and Map the Study Area. See the Downstream Map at the end of this section. 3.2 Task 2: Review All Available Information on the Study Area King County iMap was used to review the site and the area approximately ½ mile downstream: Category Project Site Within ¼ mi. downstream Environmentally Sensitive Areas Tributary basin (2005 CAO) Lower Lower Potential landslide hazard areas No No Potential landslide hazard areas 50- foot buffer No No Landslide hazards, incorporated KC No No Potential steep slope hazard areas No No Basin condition (2005 CAO) Low Low Shoreline condition (2005 CAO) N/A N/A Erosion hazard (1990 SAO) Yes No Seismic hazard (1990 SAO) No No Coal Mine hazard (1990 SAO) Yes Yes Stream (1990 SAO) No Unclassified Wetland (1990 SAO) No No Sensitive area notice on title No No Chinook distribution No No Wildlife network No No Channel migration hazard areas No No Flooding info River gages N/A N/A Flood photos N/A N/A River miles from flood patrol map book N/A N/A River facilities N/A N/A Flood phases N/A N/A Elevation certificates N/A N/A Letter of Map Amendment and Revisions N/A N/A FEMA cross-sections N/A N/A FEMA FIRM panels 53033C0979G 53033C0979G FEMA floodway N/A N/A FEMA 100-year floodplain N/A N/A FEMA 500-year floodplain N/A N/A FEMA area with reduced risk due to levee No No Regulatory floodplain No No King County sea level rise risk area No No Groundwater Groundwater sources N/A N/A Groundwater quality sampling sites No No Groundwater management areas South King County South King County Page 15 Category Project Site Within ¼ mi. downstream Areas susceptible to groundwater contamination Low Low Critical aquifer recharge area No No Sole source aquifer No No Wellhead protection areas – one year time of travel No No Wellhead protection areas – five years time of travel No No Wellhead protection areas – ten years time of travel Yes Yes Water service area City of Renton City of Renton Hydrography and Hydrology Hydrogauges N/A N/A Lake buoy N/A N/A Lakes and large rivers N/A N/A Streams N/A N/A Drainage basin Black River Black River Water resource inventory areas Duwamish-Green (09) Duwamish-Green (09) River Corridor Mapping Historical Landslides No No Fans and debris flows No No Rock fall No No Deep-seated landslide No No Shallow debris slides No No Noxious weeds No No Stormwater Services Stormwater Facilities N/A N/A Drainage studies N/A N/A Neighborhood drainage projects N/A N/A Surface water engineering projects N/A N/A Drainage complaints N/A N/A Surface Water Design Manual Flow control N/A N/A Water quality N/A N/A The City of Renton’s GIS resources were also reviewed: Category Project Site Within ¼ mi. downstream Coalmines Severity: Moderate Severity: Moderate Erosion Hazard Severity: High Severity: High Flood N/A N/A Landslide Hazard Severity: Moderate Severity: Moderate Regulated Slopes >15%, ≤25% >15%, ≤25% >25%, ≤40% Seismic Hazard Areas No No Seismic Faults Yes Yes Regulated Shoreline N/A N/A Wetlands N/A N/A Wellhead Protection Area N/A N/A Streams (classified) N/A Thunder Hills Creek Classification Type: Np – Non-Fish Water Feature Type: Stream Page 16 3.3 Task 3: Field Inspect the Study Area A site visit was performed by Dean A. Furr of Furr Engineering Services to confirm the findings of the downstream analysis performed by Pacific Engineering. See Appendix A: Pacific Engineering Downstream Analysis. 3.4 Task 4: Describe the Drainage System Site drainage is collected into a vault, which discharges into the municipal storm system in Grant Ave. Water is discharged through a 15-inch culvert across Grant Ave, then sheet-flows northwest along a vegetated path. See the downstream map and table at the end of this section. ABC D PROJECT SITE ph 206.890.8291 4715 142nd Pl. SW #B, Edmonds, WA 98026 GRANT PLACE TOWNHOMESDOWNSTREAM MAPRCE 4/3/2023 20069 DOWNSTREAM FLOWPATH N STORM STRUCTURE Downstream Table Symbol Drainage Component Type, Name, and Size Drainage Component Description Slope Distance from site discharge Existing Problems Potential Problems Observations 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 mi = 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. A Site discharge — — N/A — Onsite SWPPP measures in place during construction. A→B 12” CMP conveyance 28 N/A N/A B Type 2 storm drain manhole 28 N/A N/A B→C 15” CMP culvert 96 N/A N/A C Culvert outlet 96 N/A Damage from wildlife, overgrowth by vegetation C→D Sheet flow 1,320 N/A N/A D Terminus of downstream analysis 1,320 N/A — Page 19 4.0 FLOW CONTROL, LOW IMPACT DEVELOPMENT (LID) AND WATER QUALITY FACILITY ANALYSIS AND DESIGN This project is a continuation of an expired plat and is currently partially-constructed. Refer to civil permit no. U16004475 for previous site conditions. Table 1, below, shows a breakdown of proposed project areas: PROP. ON-SITE DEVELOPMENT sf ac DISTURBED AREA 92,828 2.131 IMPERVIOUS 65,000 1.492 TOWNHOUSE ROOFS 28,161 0.646 ALLEY/DRIVEWAYS 24,620 0.565 CONCRETE WALKWAYS/CURB+GUTTER 8,857 0.203 RETAINING WALLS 736 0.017 ASPHALT VAULT ACCESS 653 0.015 GRASSCRETE VAULT ACCESS 1,973 0.045 PERVIOUS (NGPA) 2,595 0.060 PERVIOUS (LS) 25,233 0.579 PROP. FRONTAGE DEVELOPMENT sf ac DISTURBED AREA 2,636 0.061 IMPERVIOUS 1,548 0.036 SIDEWALK/CURB+GUTTER 1,131 0.026 DRIVEWAYS 417 0.010 PERVIOUS (LS) 1,088 0.025 Table 1: Proposed project area breakdown. See the Developed Conditions Exhibit at the end of this section. An onsite storm system, designed by others, has been installed. In order to ensure that the existing system will be sufficient to provide the required level of flow control and water quality, analysis was performed according to the 2022 CoRSWDM using WWHM 2012 modelling software. 4.1 VAULT ANALYSIS The combined detention/wetvault will be used to meet both flow control and water quality requirements; see Section 4.3: Water Quality System. WWHM 2012 was used to model the site using the inputs in Table 3, below: Page 20 WWHM INPUTS AC PREDEVELOPED - SITE 2.110 C, FOREST, MOD 2.110 PREDEVELOPED – GRANT AVE FRONTAGE 0.082 C, FOREST, MOD 0.082 PREDEVELOPED - OFFSITE UPSTREAM 0.220 C, FOREST, MOD 0.220 DEVELOPED - ONSITE 2.110 C, FOREST, MOD 0.060 C, PASTURE, MOD 0.563 C, LAWN, MOD 0.045 ROADS/FLAT 0.554 ROOF TOPS/FLAT 0.658 DRIVEWAYS/MOD 0.012 SIDEWALKS/FLAT 0.217 DEVELOPED - GRANT AVE (BYPASS) 0.082 C, PASTURE, MOD 0.037 DRIVEWAYS/MOD 0.018 SIDEWALKS/FLAT 0.027 DEVELOPED - OFFSITE UPSTREAM (BYPASS) 0.220 C, FOREST, MOD 0.220 DEVELOPED - TOTAL 2.192 Table 3: WWHM inputs. The existing (historic) condition is modelled as forest, using hydrologic soil group C. Run-on from the upstream area and from the frontage improvements to Grant Ave. are considered bypass. The existing 90.06-foot long, 40.08-foot wide vault was modelled with a live storage depth of 8 feet, using a rectangular-notched, single-orifice control structure with the following parameters: RISER HEIGHT (FT) 8 RISER DIAMETER (IN) 18 RISER TYPE NOTCHED NOTCH TYPE RECTANGULAR NOTCH HEIGHT (FT) 2.0 NOTCH WIDTH (FT) 0.01 ORIFICE NUMBER DIAMETER (IN) HEIGHT (FT) 1 0.78 0 Table 4: Control structure data. The existing vault and the proposed control structure passed; therefore, the existing vault and the proposed control structure will be sufficient to provide the required level of flow control for this project. The following flow rates were calculated: Page 21 FLOW FREQUENCY FLOW (CFS) 501 PREDEVELOPED 701 DEVELOPED, UNMITIGATED 801 DEVELOPED, MITIGATED 2 Year 0.0718 0.5886 0.0386 5 Year 0.1177 0.7480 0.0612 10 Year 0.1472 0.8568 0.0811 25 Year 0.1822 0.9985 0.1130 50 Year 0.2065 1.1073 0.1426 100 Year 0.2292 1.2190 0.1780 Increase in 100-year return period flow rate: 0.9898 Table 5: Calculated flow rates. See the WWHM printout at the end of this section. This vault is designed to discharge flows up to the water quality rate of 0.2384 cfs, with a 12” storm pipe discharging into a ConTech StormFilter manhole at an invert elevation (IE) of 290.87; see Section 4.2: Water Quality System. A second outlet discharges into a manhole downstream of the StormFilter, with an IE of 295.57. Flows then enter into the municipal storm system within Grant Ave. The available live storage and dead storage volumes were calculated based upon as-built drawings produced by Tyee Surveyors; see Appendix C: As-Built Drawings. Table 2, below, summarizes the as-built floor and inside roof elevations. Vault access no. Inside roof elevation (ft) Floor elevation (ft) 1 299.71 286.55 2 299.52 286.44 3 299.73 286.21 4 299.71 285.28 5 299.72 285.58 6 299.73 284.92 7 299.71 284.91 8 299.67 284.89 average 299.69 285.60 Table 2: As-built vault elevations. Using the average inside roof elevation and the average floor elevation calculated above, an effective high water surface (HWS) elevation may be determined, given 0.5 ft freeboard: 𝐻𝑊𝑆= 299.69 − 0.5 = 299.19 Similarly, a bottom water quality surface (BWQS) may be determined, given 0.5 of sediment storage: 𝐵𝑊𝑄𝑆= 285.60 + 0.5 = 286.10 Given a surveyed water quality invert elevation of 290.87, the total effective live and dead storage may be calculated: 299.19 − 290.87 = 8.32 𝑓𝑡 𝑙𝑖𝑣𝑒 𝑠𝑡𝑜𝑟𝑎𝑔𝑒 290.87 − 286.10 = 4.77 𝑓𝑡 𝑑𝑒𝑎𝑑 𝑠𝑡𝑜𝑟𝑎𝑔𝑒 Page 22 Therefore, the as-built vault provides additional storage over the modelled live storage depth of 8.0 feet and dead storage depth of 4.0 feet, which were sufficient to meet flow control and water quality requirements. 4.2 WATER QUALITY SYSTEM Enhanced Basic Level Water Quality will be provided by a treatment train of a combined wet/detention vault and a Stormfilter unit. WWHM was used to calculate the required water quality volume of 0.2033 ac•ft (8,856 cf); see the WWHM printout at the end of this section. Given the effective dead storage depth, calculated in Section 4.1, above, of 4.77 feet, the vault provides a total volume of 17,218 cf of dead storage, and is therefore sufficient to meet the required water quality volume for the first stage of the treatment train. The second stage of the treatment train shall consist of a ConTech StormFilter manhole. This product is approved for General Use Level for Basic Treatment by the Washington State Department of Ecology, using either PhosphoSorb or ZPG media. See the StormFilter detail at the end of this section. Each cartridge has a through-flow rate of 7.5 gpm (0.0165 cfs). Per WWHM, the mitigated flow rate (i.e., the discharge flow rate from the vault into the StormFilter) is equal to 0.0315 cfs. Therefore, two cartridges will provide a flow rate of 0.0330 cfs and will be sufficient to treat the required water quality flow rate from the vault of 0.0207 cfs. PARCEL AREA 92,828 SF ON-SITE DISTURBED AREA 92,828 SF OFF-SITE DISTURBED AREA 2,636 SF ph 206.890.8291 4715 142nd Pl. SW #B, Edmonds, WA 98026 RCE 4/3/2023 20069 GRANT PLACE TOWNHOMESDEVELOPED CONDITIONS EXHIBITROOF ASPHALT (ONSITE) CONCRETE (ONSITE) GRASSCRETE ASPHALT (OFFSITE) CONCRETE (OFFSITE) LEGEND N INSIDE HEIGHT6' [1829 mm] TYPICALHYDRAULIC DROP(H) INLET INV.TO OUTLET INV.OUTLET FLOATABLES BAFFLE INLET PIPE INLET CONTRACTOR TO GROUT TO FINISHED GRADE GRADE RING/RISERS SECTION A-A PLAN VIEW STANDARD OUTLET RISER FLOWKIT: 41A FLOW KIT OUTLET SUMP HDPE OUTLET RISER TOP SLAB ACCESS SEE FRAME AND COVER DETAIL STORMFILTER CARTRIDGE OUTLET SUMP FLO W Ø5'-0" [Ø1524 mm] I.D. MANHOLE STRUCTURE (Ø6'-0" [Ø1829 mm]) O.D. A A FOR M AINTENANCE C A L L 1 .8 0 0 .3 3 8.1122 www.contechES.com T MClean w a t e r s t a r t s her e FRAME AND COVER (DIAMETER VARIES) N.T.S. FOR M AINTENANCE C A L L 1 .8 0 0 .3 3 8.1122 www.contechES.com T MClean w a t e r s t a r t s her e FRAME AND COVER (DIAMETER VARIES) N.T.S. SFMH60 STORMFILTER STANDARD DETAILwww.contechES.com GENERAL NOTES 1.CONTECH TO PROVIDE ALL MATERIALS UNLESS NOTED OTHERWISE. 2.DIMENSIONS MARKED WITH ( ) ARE REFERENCE DIMENSIONS. ACTUAL DIMENSIONS MAY VARY. 3.FOR SITE SPECIFIC DRAWINGS WITH DETAILED VAULT DIMENSIONS AND WEIGHTS, PLEASE CONTACT YOUR CONTECH ENGINEERED SOLUTIONS LLC REPRESENTATIVE. www.ContechES.com 4.STORMFILTER WATER QUALITY STRUCTURE SHALL BE IN ACCORDANCE WITH ALL DESIGN DATA AND INFORMATION CONTAINED IN THIS DRAWING. 5.STRUCTURE SHALL MEET AASHTO HS-20 LOAD RATING, ASSUMING EARTH COVER OF 0' - 5' [1524 mm] AND GROUNDWATER ELEVATION AT, OR BELOW, THE OUTLET PIPE INVERT ELEVATION. ENGINEER OF RECORD TO CONFIRM ACTUAL GROUNDWATER ELEVATION. CASTINGS SHALL MEET AASHTO M306 AND BE CAST WITH THE CONTECH LOGO. 6.FILTER CARTRIDGES SHALL BE MEDIA-FILLED, PASSIVE, SIPHON ACTUATED, RADIAL FLOW, AND SELF CLEANING. RADIAL MEDIA DEPTH SHALL BE 7-INCHES [178 mm]. FILTER MEDIA CONTACT TIME SHALL BE AT LEAST 38 SECONDS. 7.SPECIFIC FLOW RATE IS EQUAL TO THE FILTER TREATMENT CAPACITY (gpm) [L/s] DIVIDED BY THE FILTER CONTACT SURFACE AREA (sq ft)[m2]. 8.STORMFILTER STRUCTURE SHALL BE PRECAST CONCRETE CONFORMING TO ASTM C-478 AND AASHTO LOAD FACTOR DESIGN METHOD. INSTALLATION NOTES A.ANY SUB-BASE, BACKFILL DEPTH, AND/OR ANTI-FLOTATION PROVISIONS ARE SITE-SPECIFIC DESIGN CONSIDERATIONS AND SHALL BE SPECIFIED BY ENGINEER OF RECORD. B.CONTRACTOR TO PROVIDE EQUIPMENT WITH SUFFICIENT LIFTING AND REACH CAPACITY TO LIFT AND SET THE STORMFILTER STRUCTURE. C.CONTRACTOR TO INSTALL JOINT SEALANT BETWEEN ALL STRUCTURE SECTIONS AND ASSEMBLE STRUCTURE. D.CONTRACTOR TO PROVIDE, INSTALL, AND GROUT INLET PIPE(S). E.CONTRACTOR TO PROVIDE AND INSTALL CONNECTOR TO THE OUTLET RISER STUB. STORMFILTER EQUIPPED WITH A DUAL DIAMETER HDPE OUTLET STUB AND SAND COLLAR. IF OUTLET PIPE IS LARGER THAN 8 INCHES [200 mm], CONTRACTOR TO REMOVE THE 8 INCH [200 mm] OUTLET STUB AT MOLDED-IN CUT LINE. COUPLING BY FERNCO OR EQUAL AND PROVIDED BY CONTRACTOR. F.CONTRACTOR TO TAKE APPROPRIATE MEASURES TO PROTECT CARTRIDGES FROM CONSTRUCTION-RELATED EROSION RUNOFF. STORMFILTER DESIGN NOTES CARTRIDGE HEIGHT SPECIFIC FLOW RATE (gpm/sf) [L/s/m2] CARTRIDGE FLOW RATE (gpm) [L/s] RECOMMENDED HYDRAULIC DROP (H) 27" [686 mm]18" [458 mm]LOW DROP 3.05' [930 mm]2.3' [700 mm]1.8' [550 mm] STORMFILTER TREATMENT CAPACITY IS A FUNCTION OF THE CARTRIDGE SELECTION AND THE NUMBER OF CARTRIDGES. THE STANDARD MANHOLE STYLE IS SHOWN WITH THE MAXIMUM NUMBER OF CARTRIDGES (4). VOLUME SYSTEM IS ALSO AVAILABLE WITH MAXIMUM 4 CARTRIDGES. Ø5'-0" [1524 mm] MANHOLE STORMFILTER PEAK HYDRAULIC CAPACITY IS 1.0 CFS [28.3 L/s] . IF THE SITE CONDITIONS EXCEED 1.0 CFS [28.3 L/s] AN UPSTREAM BYPASS STRUCTURE IS REQUIRED. CARTRIDGE SELECTION 18.79 [1.19]12.53 [0.79]8.35 [0.54] 2 [1.30] 22.5 [1.42]11.25 [0.71]15 [0.95]10 [0.63]5 [0.32]7.5 [0.44] 1.67* [1.08]1 [0.65] * 1.67 gpm/sf [1.08 L/s/m2] SPECIFIC FLOW RATE IS APPROVED WITH PHOSPHOSORB® (PSORB) MEDIA ONLY 2 [1.30]1.67* [1.08]1 [0.65]2 [1.30]1.67* [1.08]1 [0.65] STRUCTURE ID WATER QUALITY FLOW RATE (cfs) [L/s] PEAK FLOW RATE (cfs) [L/s] RETURN PERIOD OF PEAK FLOW (yrs) NUMBER OF CARTRIDGES REQUIRED MEDIA TYPE (PERLITE, ZPG, PSORB) PIPE DATA:I.E.MATERIAL DIAMETER INLET PIPE #1 INLET PIPE #2 OUTLET PIPE SITE SPECIFIC DATA REQUIREMENTS WIDTH HEIGHTANTI-FLOTATION BALLAST NOTES/SPECIAL REQUIREMENTS: RIM ELEVATION CARTRIDGE FLOW RATE * PER ENGINEER OF RECORD CARTRIDGE HEIGHT (SEE TABLE ABOVE) ** * *** *** *** * * * * * * * * 800-338-1122 513-645-7000 513-645-7993 FAX 9025 Centre Pointe Dr., Suite 400, West Chester, OH 45069THIS PRODUCT MAY BE PROTECTED BY ONE OR MORE OF THE FOLLOWING U.S. PATENTS: 5,322,629; 5,524,576; 5,707,527; 5,985,157; 6,027,639; 6,649,048; RELATED FOREIGN PATENTS, OR OTHER PATENTS PENDING. Page 25 WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: 20069 - vault design Site Name: Grant Avenue Townhomes Site Address: 1600 Grant Ave S City : Renton, WA Report Date: 3/17/2023 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2021/08/18 Version : 4.2.18 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : SITE Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Mod 2.131 Pervious Total 2.131 Impervious Land Use acre Impervious Total 0 Basin Total 2.131 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ Name : UPSTREAM Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Mod .22 Page 26 Pervious Total 0.22 Impervious Land Use acre Impervious Total 0 Basin Total 0.22 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ Name : FRONTAGE Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Mod .061 Pervious Total 0.061 Impervious Land Use acre Impervious Total 0 Basin Total 0.061 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : SITE Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Mod .06 C, Lawn, Mod .045 C, Pasture, Mod .579 Pervious Total 0.684 Page 27 Impervious Land Use acre ROADS FLAT 0.565 ROOF TOPS FLAT 0.646 DRIVEWAYS MOD 0.015 SIDEWALKS FLAT 0.22 Impervious Total 1.446 Basin Total 2.13 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Vault 1 Vault 1 ___________________________________________________________________ Name : FRONTAGE Bypass: No GroundWater: No Pervious Land Use acre C, Pasture, Mod .037 Pervious Total 0.037 Impervious Land Use acre DRIVEWAYS MOD 0.018 SIDEWALKS FLAT 0.027 Impervious Total 0.045 Basin Total 0.082 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Vault 1 Vault 1 ___________________________________________________________________ Name : UPSTREAM Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Mod .22 Pervious Total 0.22 Impervious Land Use acre Page 28 Impervious Total 0 Basin Total 0.22 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Vault 1 Vault 1 ___________________________________________________________________ Name : Vault 1 Width : 40.8 ft. Length : 90.06 ft. Depth: 9 ft. Discharge Structure Riser Height: 8 ft. Riser Diameter: 18 in. Notch Type: Rectangular Notch Width: 0.010 ft. Notch Height: 2.250 ft. Orifice 1 Diameter: 0.78 in. Elevation: 0 ft. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Vault Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.084 0.000 0.000 0.000 0.1000 0.084 0.008 0.005 0.000 0.2000 0.084 0.016 0.007 0.000 0.3000 0.084 0.025 0.009 0.000 0.4000 0.084 0.033 0.010 0.000 0.5000 0.084 0.042 0.011 0.000 0.6000 0.084 0.050 0.012 0.000 0.7000 0.084 0.059 0.013 0.000 0.8000 0.084 0.067 0.014 0.000 0.9000 0.084 0.075 0.015 0.000 1.0000 0.084 0.084 0.016 0.000 1.1000 0.084 0.092 0.017 0.000 1.2000 0.084 0.101 0.018 0.000 1.3000 0.084 0.109 0.018 0.000 1.4000 0.084 0.118 0.019 0.000 1.5000 0.084 0.126 0.020 0.000 1.6000 0.084 0.135 0.020 0.000 1.7000 0.084 0.143 0.021 0.000 1.8000 0.084 0.151 0.022 0.000 1.9000 0.084 0.160 0.022 0.000 2.0000 0.084 0.168 0.023 0.000 2.1000 0.084 0.177 0.023 0.000 Page 29 2.2000 0.084 0.185 0.024 0.000 2.3000 0.084 0.194 0.025 0.000 2.4000 0.084 0.202 0.025 0.000 2.5000 0.084 0.210 0.026 0.000 2.6000 0.084 0.219 0.026 0.000 2.7000 0.084 0.227 0.027 0.000 2.8000 0.084 0.236 0.027 0.000 2.9000 0.084 0.244 0.028 0.000 3.0000 0.084 0.253 0.028 0.000 3.1000 0.084 0.261 0.029 0.000 3.2000 0.084 0.269 0.029 0.000 3.3000 0.084 0.278 0.030 0.000 3.4000 0.084 0.286 0.030 0.000 3.5000 0.084 0.295 0.030 0.000 3.6000 0.084 0.303 0.031 0.000 3.7000 0.084 0.312 0.031 0.000 3.8000 0.084 0.320 0.032 0.000 3.9000 0.084 0.329 0.032 0.000 4.0000 0.084 0.337 0.033 0.000 4.1000 0.084 0.345 0.033 0.000 4.2000 0.084 0.354 0.033 0.000 4.3000 0.084 0.362 0.034 0.000 4.4000 0.084 0.371 0.034 0.000 4.5000 0.084 0.379 0.035 0.000 4.6000 0.084 0.388 0.035 0.000 4.7000 0.084 0.396 0.035 0.000 4.8000 0.084 0.404 0.036 0.000 4.9000 0.084 0.413 0.036 0.000 5.0000 0.084 0.421 0.036 0.000 5.1000 0.084 0.430 0.037 0.000 5.2000 0.084 0.438 0.037 0.000 5.3000 0.084 0.447 0.038 0.000 5.4000 0.084 0.455 0.038 0.000 5.5000 0.084 0.463 0.038 0.000 5.6000 0.084 0.472 0.039 0.000 5.7000 0.084 0.480 0.039 0.000 5.8000 0.084 0.489 0.040 0.000 5.9000 0.084 0.497 0.042 0.000 6.0000 0.084 0.506 0.044 0.000 6.1000 0.084 0.514 0.047 0.000 6.2000 0.084 0.523 0.050 0.000 6.3000 0.084 0.531 0.053 0.000 6.4000 0.084 0.539 0.056 0.000 6.5000 0.084 0.548 0.060 0.000 6.6000 0.084 0.556 0.064 0.000 6.7000 0.084 0.565 0.067 0.000 6.8000 0.084 0.573 0.071 0.000 6.9000 0.084 0.582 0.076 0.000 7.0000 0.084 0.590 0.080 0.000 7.1000 0.084 0.598 0.085 0.000 7.2000 0.084 0.607 0.105 0.000 7.3000 0.084 0.615 0.112 0.000 7.4000 0.084 0.624 0.119 0.000 7.5000 0.084 0.632 0.126 0.000 7.6000 0.084 0.641 0.134 0.000 7.7000 0.084 0.649 0.141 0.000 2-year flow rate: 0.0386 cfs Page 30 7.8000 0.084 0.658 0.149 0.000 7.9000 0.084 0.666 0.157 0.000 8.0000 0.084 0.674 0.165 0.000 8.1000 0.084 0.683 0.667 0.000 8.2000 0.084 0.691 1.570 0.000 8.3000 0.084 0.700 2.667 0.000 8.4000 0.084 0.708 3.798 0.000 8.5000 0.084 0.717 4.805 0.000 8.6000 0.084 0.725 5.568 0.000 8.7000 0.084 0.733 6.059 0.000 8.8000 0.084 0.742 6.506 0.000 8.9000 0.084 0.750 6.891 0.000 9.0000 0.084 0.759 7.254 0.000 9.1000 0.084 0.767 7.601 0.000 9.2000 0.000 0.000 7.931 0.000 ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:2.412 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.941 Total Impervious Area:1.491 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.071818 5 year 0.11768 10 year 0.147168 25 year 0.182246 50 year 0.206543 100 year 0.229238 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.039775 5 year 0.063964 10 year 0.085035 25 year 0.118559 50 year 0.149341 100 year 0.185839 ___________________________________________________________________ Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated Page 31 1949 0.083 0.030 1950 0.098 0.037 1951 0.157 0.145 1952 0.049 0.027 1953 0.040 0.033 1954 0.061 0.034 1955 0.098 0.033 1956 0.079 0.045 1957 0.063 0.033 1958 0.070 0.036 1959 0.060 0.030 1960 0.108 0.080 1961 0.060 0.037 1962 0.037 0.026 1963 0.051 0.034 1964 0.072 0.035 1965 0.048 0.039 1966 0.046 0.032 1967 0.110 0.036 1968 0.062 0.033 1969 0.060 0.032 1970 0.048 0.034 1971 0.055 0.035 1972 0.119 0.107 1973 0.053 0.039 1974 0.059 0.035 1975 0.081 0.032 1976 0.058 0.034 1977 0.009 0.028 1978 0.049 0.036 1979 0.030 0.025 1980 0.140 0.119 1981 0.044 0.033 1982 0.091 0.041 1983 0.078 0.035 1984 0.047 0.028 1985 0.028 0.028 1986 0.123 0.038 1987 0.109 0.060 1988 0.043 0.028 1989 0.028 0.028 1990 0.260 0.082 1991 0.138 0.072 1992 0.056 0.037 1993 0.055 0.028 1994 0.018 0.024 1995 0.079 0.037 1996 0.182 0.141 1997 0.141 0.149 1998 0.034 0.028 1999 0.154 0.075 2000 0.055 0.035 2001 0.010 0.024 2002 0.063 0.038 2003 0.095 0.030 2004 0.101 0.112 2005 0.075 0.034 Page 32 2006 0.085 0.042 2007 0.197 0.207 2008 0.240 0.114 2009 0.112 0.039 ___________________________________________________________________ Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.2601 0.2070 2 0.2396 0.1486 3 0.1966 0.1446 4 0.1821 0.1410 5 0.1569 0.1188 6 0.1541 0.1140 7 0.1405 0.1117 8 0.1402 0.1071 9 0.1379 0.0818 10 0.1231 0.0796 11 0.1191 0.0751 12 0.1117 0.0722 13 0.1103 0.0601 14 0.1086 0.0447 15 0.1083 0.0419 16 0.1013 0.0415 17 0.0981 0.0395 18 0.0976 0.0393 19 0.0948 0.0388 20 0.0909 0.0384 21 0.0845 0.0384 22 0.0827 0.0374 23 0.0815 0.0374 24 0.0788 0.0368 25 0.0786 0.0366 26 0.0778 0.0364 27 0.0751 0.0356 28 0.0722 0.0356 29 0.0705 0.0353 30 0.0635 0.0349 31 0.0635 0.0348 32 0.0621 0.0347 33 0.0611 0.0346 34 0.0604 0.0341 35 0.0604 0.0340 36 0.0595 0.0340 37 0.0585 0.0339 38 0.0582 0.0337 39 0.0563 0.0335 40 0.0550 0.0334 41 0.0547 0.0332 42 0.0547 0.0329 43 0.0528 0.0329 44 0.0509 0.0320 45 0.0492 0.0319 46 0.0492 0.0317 47 0.0485 0.0304 48 0.0479 0.0304 Page 33 49 0.0469 0.0302 50 0.0461 0.0283 51 0.0440 0.0283 52 0.0429 0.0282 53 0.0398 0.0281 54 0.0371 0.0279 55 0.0344 0.0279 56 0.0298 0.0276 57 0.0284 0.0272 58 0.0278 0.0258 59 0.0185 0.0254 60 0.0098 0.0243 61 0.0085 0.0238 ___________________________________________________________________ Stream Protection Duration POC #1 The Facility PASSED The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0359 17085 13109 76 Pass 0.0376 15481 9146 59 Pass 0.0394 14070 5375 38 Pass 0.0411 12801 4254 33 Pass 0.0428 11567 3799 32 Pass 0.0445 10517 3501 33 Pass 0.0463 9561 3251 34 Pass 0.0480 8750 3024 34 Pass 0.0497 8034 2860 35 Pass 0.0514 7345 2704 36 Pass 0.0531 6733 2560 38 Pass 0.0549 6192 2423 39 Pass 0.0566 5726 2246 39 Pass 0.0583 5309 2089 39 Pass 0.0600 4924 1960 39 Pass 0.0618 4569 1827 39 Pass 0.0635 4235 1691 39 Pass 0.0652 3951 1561 39 Pass 0.0669 3643 1436 39 Pass 0.0687 3388 1295 38 Pass 0.0704 3133 1205 38 Pass 0.0721 2915 1102 37 Pass 0.0738 2706 1028 37 Pass 0.0756 2488 961 38 Pass 0.0773 2314 901 38 Pass 0.0790 2136 829 38 Pass 0.0807 1972 767 38 Pass 0.0824 1824 703 38 Pass 0.0842 1702 652 38 Pass 0.0859 1577 602 38 Pass 0.0876 1442 583 40 Pass 0.0893 1325 568 42 Pass 0.0911 1232 553 44 Pass 0.0928 1147 538 46 Pass 0.0945 1083 519 47 Pass Page 34 0.0962 1020 506 49 Pass 0.0980 947 495 52 Pass 0.0997 885 475 53 Pass 0.1014 824 455 55 Pass 0.1031 761 436 57 Pass 0.1049 725 425 58 Pass 0.1066 676 399 59 Pass 0.1083 627 356 56 Pass 0.1100 589 320 54 Pass 0.1117 552 287 51 Pass 0.1135 506 253 50 Pass 0.1152 471 228 48 Pass 0.1169 427 209 48 Pass 0.1186 388 194 50 Pass 0.1204 356 181 50 Pass 0.1221 329 172 52 Pass 0.1238 297 159 53 Pass 0.1255 270 149 55 Pass 0.1273 242 139 57 Pass 0.1290 219 130 59 Pass 0.1307 197 121 61 Pass 0.1324 174 109 62 Pass 0.1342 152 100 65 Pass 0.1359 130 91 70 Pass 0.1376 119 85 71 Pass 0.1393 104 77 74 Pass 0.1410 95 64 67 Pass 0.1428 84 57 67 Pass 0.1445 75 49 65 Pass 0.1462 69 42 60 Pass 0.1479 61 37 60 Pass 0.1497 54 32 59 Pass 0.1514 46 28 60 Pass 0.1531 39 23 58 Pass 0.1548 29 22 75 Pass 0.1566 25 20 80 Pass 0.1583 22 19 86 Pass 0.1600 20 16 80 Pass 0.1617 17 15 88 Pass 0.1635 14 12 85 Pass 0.1652 12 8 66 Pass 0.1669 8 6 75 Pass 0.1686 7 4 57 Pass 0.1703 7 4 57 Pass 0.1721 7 4 57 Pass 0.1738 6 4 66 Pass 0.1755 6 4 66 Pass 0.1772 6 4 66 Pass 0.1790 6 4 66 Pass 0.1807 6 4 66 Pass 0.1824 5 2 40 Pass 0.1841 5 2 40 Pass 0.1859 5 2 40 Pass 0.1876 5 2 40 Pass 0.1893 5 2 40 Pass 0.1910 5 2 40 Pass 0.1928 5 2 40 Pass Page 35 0.1945 4 2 50 Pass 0.1962 4 2 50 Pass 0.1979 3 2 66 Pass 0.1996 3 2 66 Pass 0.2014 3 2 66 Pass 0.2031 3 2 66 Pass 0.2048 3 2 66 Pass 0.2065 3 2 66 Pass _____________________________________________________ ___________________________________________________________________ 0701 Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0.2033 acre-feet On-line facility target flow: 0.2384 cfs. Adjusted for 15 min: 0.2384 cfs. Off-line facility target flow: 0.1338 cfs. Adjusted for 15 min: 0.1338 cfs. 0801 Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0.0625 acre-feet On-line facility target flow: 0.0317 cfs. Adjusted for 15 min: 0.0317 cfs. Off-line facility target flow: 0.0207 cfs. Adjusted for 15 min: 0.0207 cfs. ___________________________________________________________________ LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft.) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Vault 1 POC N 256.14 N 0.00 Total Volume Infiltrated 256.14 0.00 0.00 0.00 0.00 0% No Treat. Credit Compliance with LID Standard 8 Duration Analysis Result = Passed ___________________________________________________________________ Perlnd and Implnd Changes No changes have been made. ___________________________________________________________________ This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2023; All Rights Reserved. Page 36 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN The constructed stormwater conveyance system onsite consists typically of 12” corrugated storm pipe and was analyzed using Manning’s equation in order to ensure sufficient capacity. 𝑄=1.49 𝑛∗𝐴∗𝑅௛ ଶ ଷ ∗𝑆 ଵ ଶ where 𝑛= Manning’s coefficient = 0.012 𝑄= cross-sectional average velocity 𝐴= area 𝑅௛ = hydraulic radius 𝑆= pipe slope The most constrained pipe in the system shall be considered; see Appendix C: As-Built Survey drawings. Given: 𝐴= 0.785 sf 𝑅௛ = 4” 𝑆= 0.041 𝑄=1.49 0.012 ∗ 0.785 ∗(4) ଶ ଷ ∗(0.041) ଵ ଶ = 7.842 𝑐𝑓𝑠 at 100% pipe capacity, and 4.705 cfs at 60% capacity. Given 100-year peak flows of 1.219 cfs, each component of the conveyance system is sufficient to convey peak flows at 60% capacity. Additionally, discharge from the vault must be considered, based upon the most constrained pipe: 𝑄=1.49 0.012 ∗ 0.785 ∗ (4) ଶ ଷ ∗(0.002) ଵ ଶ = 1.669 𝑐𝑓𝑠 at 100% pipe capacity, and 1.002 cfs at 60% capacity. Therefore, all pipes downstream of the vault shall have sufficient capacity to convey the peak flows of 0.1780 cfs. Page 37 6.0 SPECIAL REPORTS AND STUDIES Geotechnical Engineering Evaluation prepared by Nelson Geotechnical Associates, dated June 10, 2005. Attached to this report as Appendix B. Page 38 7.0 OTHER PERMITS Land Use Building (Multi-family) Clearing and Grading Right-of-Way Use Page 39 8.0 CSWPP ANALYSIS AND DESIGN A Stormwater Pollution and Prevention Plan (SWPPP) is submitted separately per the Department of Ecology. The requirements of the KCSWDM are satisfied as follows: 1. Clearing limits. Clearing limits are delineated on the Temporary Erosion and Sediment Control Plan and shall be marked onsite with high-visibility fencing. 2. Cover measures. Temporary and permanent cover measures shall be provided to protect disturbed areas, e.g., plastic covering, hydroseeding, etc. 3. Perimeter protection. Silt fencing shall be used to filter sediment downstream of disturbed areas. 4. Traffic area stabilization. A stabilized construction entrance has been constructed. 5. Sediment retention: The proposed vault is being used to collect sediment during construction. Silt fencing shall provide sediment retention at the perimeter of the site. 6. Surface water collection. The proposed vault shall be used to collect surface water. 7. Dewatering control. Dewatering is not anticipated as a part of this project. 8. Dust control. Dust control shall be provided by sprinkling, if required. 9. Flow control. Flow control shall be provided by the proposed vault. 10. Control pollutants: The following BMPs shall be employed to control pollutants, per KCSWDM D.2.2:  Concrete handling  Concrete washout area  Sawcutting and surfacing pollution prevention  Material delivery, storage, and containment  pH control for high pH water  Maintain protective BMPs  Manage the project 11. Protect existing and proposed flow control BMPs. This project does not include existing or proposed flow control BMPs requiring protection. 12. Maintain BMPs. Maintenance of BMPs shall be the responsibility of the Certified Erosion and Sediment Control Lead (CESCL), to be appointed by the contractor. 13. Manage the project. Coordination and timing of site development activities relative to ESC concerns shall be the responsibility of the CESCL. During the wet season (October 1 to April 30) any site with exposed soils shall be subject to the "Wet Season Requirements" contained in the ESC Standards. In addition to the ESC cover measures, these provisions include covering any newly-seeded areas with mulch and seeding as much disturbed area as possible during the first week of October to provide grass cover for the wet season. Prior to obtaining final construction approval, the site shall be stabilized, structural ESC measures (such as silt fences and sediment traps) shall be removed, and drainage facilities shall be cleaned as specified in the ESC Standards. Page 40 9.0 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT Submitted separately. Page 41 10.0 OPERATIONS AND MAINTENANCE MANUAL Page 42 Page 43 Page 44 Page 45 Page 46 Page 47 Page 48 Page 49 Page 50 Page 51 Page 52 APPENDIX A: PACIFIC ENGINEERING DOWNSTREAM ANALYSIS Page 53 APPENDIX B: GEOTECHNICAL REPORT Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, Washington 98028 www.cobaltgeo.com (206) 331-1097 March 3, 2023 Satwant Singh pmvrsingh@gmail.com RE: Permit Renewal Proposed Townhomes 1600 Grant Avenue South Renton, Washington In accordance with your authorization, Cobalt Geosciences, LLC has prepared this letter to discuss permit renewal. We note that much of the planned construction is nearly completed. It is our opinion that the construction can continue per plan. Based on our observations at the site and observations during periodic site visits during grading, we recommend routing runoff from impervious surfaces to the detention system. Infiltration systems are not feasible at this site due to several factors. These include the presence of glacial till soils which are nearly impermeable and act as an aquitard; location and elevations of new buildings (possible intrusion behind walls and into buildings); presence of shallow perched groundwater in many areas (zero to minimal clearance above groundwater); presence of newer structural fills over the native soils (not suitable to infiltrate into fills), and slope magnitudes generally in excess of 15 percent in most locations. We anticipate that final landscaping and any additional planned grading/construction will occur per the approved plans during the upcoming dry grading season. Sincerely, Cobalt Geosciences, LLC Phil Haberman, PE, LG, LEG 3/3/2023 Principal PH/sc Page 54 APPENDIX C: AS-BUILT SURVEY DRAWINGS