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Home My WebLink AboutR0-14 - Drainage ReportPRELIMII{ARYTECHII\ICAL II{FORMATIOI{ REPORTFOR7th Street Short PtatRenton, 'WashingtonJuly 2019Prepared for:Jagadeshwar Gattu14716 NE 76th StreetRedmondo WA 98052Prepared by:William Qi, DesignerReviewed By:Eric N. Oehler, Project ManagerCara Visintainer, P.8., Senior Project Manager128LtREPORT #1,7234 TABLE OF CONTENTS PAGE 1.0 PROJECT OVERVIEW ................................................................................................................... 1 2.0 CONDITIONS AND REQUIREMENTS SUMMARY ................................................................. 19 2.1 Analysis of the Nine Core Requirements .................................................................................... 19 2.2 Analysis of Special Requirements .............................................................................................. 23 3.0 OFF-SITE ANALYSIS ................................................................................................................... 25 3.1 Study Area Definition and Maps ................................................................................................ 25 3.2 Resource Review ........................................................................................................................ 25 3.3 Drainage System Description and Problem Descriptions ........................................................... 26 3.4 Mitigation of Existing or Potential Problems .............................................................................. 26 4.0 STORMWATER ANALYSIS AND DESIGN ............................................................................... 35 4.1 Existing Site Hydrology .............................................................................................................. 35 4.2 Developed Site Hydrology .......................................................................................................... 35 4.3 Performance Standards ............................................................................................................... 36 4.4 Water Quality System ................................................................................................................. 37 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN .............................................................. 45 6.0 SPECIAL REPORTS AND STUDIES ........................................................................................... 48 7.0 OTHER PERMITS ......................................................................................................................... 81 8.0 CSWPP ANALYSIS AND DESIGN ............................................................................................. 82 9.0 BOND QUANTITIES..................................................................................................................... 84 10.0 OPERATIONS AND MAINTENANCE MANUAL ..................................................................... 85 LIST OF FIGURES Figure 1.1 – Technical Information Report (TIR) Worksheet .................................................................. 4 Figure 1.2 – Vicinity Map ......................................................................................................................... 12 Figure 1.3 – Pre-developed Basin Map ..................................................................................................... 14 Figure 1.4 – Developed Basin Map .......................................................................................................... 16 Figure 1.5 – Soil Map and Descriptions ................................................................................................... 17 Figure 3.1 – FEMA Map ........................................................................................................................... 31 Figure 3.2 – Sensitive Ares Map ............................................................................................................... 33 Figure 3.3 – Offsite Analysis Drainage System Table .............................................................................. 35 Figure 3.4 – Downstream Analysis Maps ................................................................................................. 37 Figure 4.1 – WWHM Report .................................................................................................................... 42 Figure 4.2 – Stormfilter Sizing ................................................................................................................. 51 Figure 5.1 – LDD Computer Output ......................................................................................................... 56 Figure 6.1 – Geotechnical Engineer’s Report ........................................................................................... 61 Page | 1 1.0 PROJECT OVERVIEW The 7th Street Short Plat project consists of a single 27,705 sq.ft. (0.64-acres) parcel, addressed 3605 NE 7th Street, Renton, WA 98056, in the jurisdictional boundary of the City of Renton (King County Tax Parcel# 8011100135). The project also lies within a portion of the NW ¼ of the SE ¼ of Section 9, Township 23 North, Range 5 East. Refer to Figure 1.2 – Vicinity Map within this section. The site is generally rectangular and contains an existing single-family residence and detached garage along with gravel drive, which are proposed to be removed along with this project. The remainder of the site is covered with dense vegetation, and slopes from the east to the west at an approximate gradient ranging from 5% to 10% with isolated areas up to 30%. The property is surrounded by single-family developments to the south, north, east and west. To the north the property abuts 7th NE Street of which a single-family residence is located across the street. According to Natural Resources Conservation Service (NRCS), site soils consist of Arents, Alderwood material, 6 to 15 percent slopes. According to the Geotechnical report conducted by Earth Solutions NW, LLC (ESNW) on August 20, 2018, the native soils were classified primarily as silty sand with gravel, consistent with the typical makeup of glacial till deposits. Based on their infiltration tests and observation of variable soil conditions, neither full or limited infiltration is feasible. The project proposes the construction of 3 lots for single-family residence, frontage improvements, private access road, driveways and associated utilities. The site improvements are designed per the 2017 City of Renton Surface Water Design Manual (Manual) and its amendments to the 2016 King County Surface Water Design Manual. The project site is located in the East Lake Washington-Renton Drainage Basin resulting in 0.37 acres of new and replaced impervious surface. According to Fig. 1.1.2.A, the proposed single-family residential project requires a Direct Drainage Review. Therefore, all nine core requirements and six special requirements apply. A detention vault and a Contech stormfilter are proposed for flow control and water quality control. A TIR work sheet has been included in Figure 1.1 of this section. Page | 2 Figure 1.1 – Technical Information Report (TIR) Worksheet CITY OF RENTON SURFACE WATER DESIGN MANUAL 2017 City of Renton Surface Water Design Manual 12/12/2016 8-A-1 REFERENCE 8-A TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Part 2 PROJECT LOCATION AND DESCRIPTION Phone ___________________________________ Project Name __________________________ CED Permit # ________________________ Location Township ________________ Range __________________ Section _________________ Site Address __________________________ _____________________________________ Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS Land Use (e.g., Subdivision / Short Subd.) Building (e.g., M/F / Commercial / SFR) 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 (check one): Date (include revision dates): Date of Final: Targeted Simplified Large Project Directed Plan Type (check one): Date (include revision dates): Date of Final: Full Modified Simplified __________________ __________________ __________________ Project Owner __Jagadeshwar Gattu ___________7th Street Short Plat 23N 05E 9 3605 N.E. 7th Street Renton, WA 98056 x x Address __14716 NE 76th Street_________ _______________Redmond, WA 98052__________________________ Project Engineer ________Eric N. Oehler___________________ Company _______CES NW Inc.__________________________ Phone ______253-848-4282_____________________________ x x x Full _________6.9.2019_ __________________ __________________ REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 12/12/2016 2017 City of Renton Surface Water Design Manual8-A-2 Part 6 SWDM ADJUSTMENT APPROVALS Type (circle one): Standard / Blanket Description: (include conditions in TIR Section 2) ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ Approved Adjustment No. ______________________ Date of Approval: _______________________ Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes / No Start Date: _______________________ Completion Date: _______________________ Describe: _________________________________ _________________________________________ _________________________________________ Re: SWDM 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 ________________________ Lake ______________________________ Wetlands ____________________________ Closed Depression ____________________ Floodplain ___________________________ Other _______________________________ _______________________________ Steep Slope __________________________ Erosion Hazard _______________________ Coal Mine Hazard ______________________ Seismic Hazard _______________________ Habitat Protection ______________________ _____________________________________ East Lake Washington-Renton Landslide Hazard ______________________ REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2017 City of Renton Surface Water Design Manual 12/12/2016 Ref 8-A-3 Part 10 SOILS Soil Type ______________________ ______________________ ______________________ ______________________ Slopes ________________________ ________________________ ________________________ ________________________ Erosion Potential _________________________ _________________________ _________________________ _________________________ High Groundwater Table (within 5 feet) Other ________________________________ Sole Source Aquifer Seeps/Springs Additional Sheets Attached Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE Core 2 – Offsite Analysis_________________ Sensitive/Critical Areas__________________ SEPA________________________________ LID Infeasibility________________________ 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 (include facility summary sheet) Standard: _______________________________ or Exemption Number: ____________ On-site BMPs: _ Conveyance System Spill containment located at: _____________________________ Erosion and Sediment Control / Construction Stormwater Pollution Prevention CSWPP/CESCL/ESC Site Supervisor: _____________________ Contact Phone: _________________________ After Hours Phone: _________________________ Perforated stub-out connections NA AmC - Arents, Alderwood 6-15% REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 12/12/2016 2017 City of Renton Surface Water Design Manual8-A-4 Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) 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 summary sheet) Type (circle one): Basic / Sens. Lake / Enhanced Basic / Bog or Exemption No. _______________________ Special Requirements (as applicable): Area Specific Drainage Requirements Type: SDO / MDP / BP / 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:Detention Vault REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2017 City of Renton Surface Water Design Manual 12/12/2016 Ref 8-A-5 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 Control Pollutants Protect Existing and Proposed BMPs/Facilities Maintain Protective 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 BMPs/Facilities, restore operation of BMPs/Facilities as necessary Flag limits of sensitive areas 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 Regional Facility Shared Facility On-site BMPs Other Vegetated Flowpath Wetpool Filtration Oil Control Spill Control On-site BMPs Other ________________ ________________ ________________ ________________ ________________ ________________ ________________ Part 15 EASEMENTS/TRACTS Part 16 STRUCTURAL ANALYSIS Drainage Easement Covenant Native Growth Protection Covenant Tract Other ____________________________ Cast in Place Vault Retaining Wall Rockery > 4ƍ High Structural on Steep Slope Other _______________________________ x x x X X X X X X X X X X X X Infiltration x Detention Vault___ ________________ ________________ ________________ Connections______ Storm Filter x x x Perforated stub-out REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEETTECHNICAL INFORMATION REPORT (TIR) WORKSHEETSigned/Datel, or a civil engineer under my superv¡sion, have visited the site. Actual site conditions as observed wereincorporated into this worksheet and the attached Technical lnformation Report. To the best of myknowledge the infornption providg{ her¡ is accurate.(' l"rt" lVñbv 7't't qPaTtl7 SIGNATURE OF PROFESSIONAL ENG¡NEER12^2/20168-A-62017 City of Renton Surface Water Design Manual Page | 8 Figure 1.2 – Vicinity Map 4,514 376 7th Street Short Plat 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. Vicinity Map 9/11/2018 Legend 2560128 THIS MAP IS NOT TO BE USED FOR NAVIGATION Feet Notes 256 WGS_1984_Web_Mercator_Auxiliary_Sphere Information Technology - GIS RentonMapSupport@Rentonwa.gov Page | 10 Figure 1.3 – Pre-developed Basin Map Page | 11 Figure 1.4 – Developed Basin Map Page | 13 Figure 1.5 – Soils Map and Descriptions Soil Map—King County Area, Washington (Soil Map of 7th Street Short Plat) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/11/2018 Page 1 of 3526039052604005260410526042052604305260440526045052604605260470526048052604905260500526039052604005260410526042052604305260440526045052604605260470526048052604905260500562440562450562460562470562480562490562500562510562520 562440 562450 562460 562470 562480 562490 562500 562510 562520 47° 29' 41'' N 122° 10' 15'' W47° 29' 41'' N122° 10' 11'' W47° 29' 38'' N 122° 10' 15'' W47° 29' 38'' N 122° 10' 11'' WN Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84 0 25 50 100 150 Feet 0 5 10 20 30 Meters Map Scale: 1:575 if printed on A portrait (8.5" x 11") sheet. Soil Map may not be valid at this scale. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Unit Polygons Soil Map Unit Lines Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Spoil Area Stony Spot Very Stony Spot Wet Spot Other Special Line Features Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: King County Area, Washington Survey Area Data: Version 13, Sep 7, 2017 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jul 8, 2014—Jul 15, 2014 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Soil Map—King County Area, Washington (Soil Map of 7th Street Short Plat) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/11/2018 Page 2 of 3 Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI AmC Arents, Alderwood material, 6 to 15 percent slopes 0.9 100.0% Totals for Area of Interest 0.9 100.0% Soil Map—King County Area, Washington Soil Map of 7th Street Short Plat Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/11/2018 Page 3 of 3 King County Area, Washington AmC—Arents, Alderwood material, 6 to 15 percent slopes Map Unit Setting National map unit symbol: 1hmsq Elevation: 50 to 660 feet Mean annual precipitation: 35 to 60 inches Mean annual air temperature: 50 degrees F Frost-free period: 150 to 200 days Farmland classification: Not prime farmland Map Unit Composition Arents, alderwood material, and similar soils: 100 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Arents, Alderwood Material Setting Landform: Till plains Parent material: Basal till Typical profile H1 - 0 to 26 inches: gravelly sandy loam H2 - 26 to 60 inches: very gravelly sandy loam Properties and qualities Slope: 6 to 15 percent Depth to restrictive feature: 20 to 40 inches to densic material Natural drainage class: Moderately well drained Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.06 in/hr) Depth to water table: About 16 to 36 inches Frequency of flooding: None Frequency of ponding: None Available water storage in profile: Very low (about 2.3 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4s Hydrologic Soil Group: B/D Hydric soil rating: No Data Source Information Soil Survey Area: King County Area, Washington Survey Area Data: Version 13, Sep 7, 2017 Map Unit Description: Arents, Alderwood material, 6 to 15 percent slopes---King County Area, Washington Soil Map of 7th Street Short Plat Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/11/2018 Page 1 of 1 Page | 19 2.0 CONDITIONS AND REQUIREMENTS SUMMARY The project is subject to Direct Drainage Review as dictated by the Manual’s Core Requirements No. 1 through 9, and Special Requirements No. 1 through 6. 2.1 Analysis of the Nine Core Requirements Core Requirement No. 1: Discharge at the Natural Location Intent: To prevent adverse impacts to downstream properties caused by diversion of flow from one flowpath to another, and to discharge in a manner that does not significantly impact downhill properties or drainage systems. Diversions can cause greater impacts (from greater runoff volumes) than would otherwise occur from new development discharging runoff at the natural location. Diversions can also impact properties that rely on runoff water to replenish wells and ornamental or fish ponds. Response: Historically, runoff from the site sheet flows southwest of the site, and the overflow flows into the catch basin of the neighboring single-family residence. The project proposes to control its runoff with the use of a detention vault. Runoff from the site will route to the southwest corner of the parcel, and then will be discharged into the existing conveyance system located in NE 7th Place through proposed drainage pipe. The following table summarizes the basin areas and stormwater flows: Existing Basin Area (Acres) 0.71 Developed Basin Area (Acres) 0.71 100-year Predeveloped Flow Rate (CFS) 0.100 100-year Developed Flow Rate (CFS) 0.079 Core Requirement No. 2: Off-Site Analysis Intent: To identify and evaluate offsite flooding, erosion, and water quality problems that may be created or aggravated by the proposed project, and to ensure appropriate measures are provided for preventing creation or aggravation of those problems. In addition, this requirement is intended to ensure appropriate provisions are made, as needed, to mitigate other identified impacts associated with the quantity and quality of surface and storm water runoff from the project site (e.g., impacts to the hydrology of a wetland as may be identified by a "critical area report" per RMC 4-3-050). Page | 20 Response: The project is proposing to detain all stormwater runoff from developed site and frontage improvement area, and will release runoff at pre-developed rates and durations based on a forested cover condition of the site. This is going to result in lower peak flows from the site; therefore, no off-site flooding or erosion problems will be created or aggregated by this project. A Level One Downstream Analysis is located within Section 3.0 of this report. Core Requirement No. 3: Flow Control Intent: To ensure the minimum level of control needed to protect downstream properties and resources from increases in peak, duration, and volume of runoff generated by new development. The level of control varies depending on location and downstream conditions identified under Core Requirement #2. Response: The project is proposing a detention vault for flow control. Please refer Section 4.0 of flow control calculations. Core Requirement No. 4: Conveyance System Intent: To ensure proper design and construction of engineered conveyance system elements. Conveyance systems are natural and engineered drainage facilities that collect, contain, and provide for the flow of surface and storm water. This core requirement applies to the engineered elements of conveyance systems—primarily pipes, culverts, and ditches/channels. Response: Pipe Systems: The proposed conveyance system is comprised of privately owned roof downspout pipes, which connect to the proposed perforated stub-out connections, and a series of storm drainage pipes connecting from the proposed catch basins to the public drainage system in NE 7th Place. The conveyance system is sized to convey the 100-year developed peak flow analyzed using LDD’s Manning Calculator in Section 5.0 of this report. Culverts: There are no proposed culverts for this development. Ditches/Channels: There are no proposed ditches/Channels for this development. Core Requirement No. 5: Temporary Erosion and Sediment Control Intent: To prevent the transport of sediment and other impacts, like increased runoff, related to land disturbing activities. Erosion of disturbed areas on construction sites can result in excessive Page | 21 sediment transport to adjacent properties and to surface waters. This sediment can result in major adverse impacts, such as flooding from obstructed drainage ways, smothering of salmonid spawning beds, algal blooms in lakes, and exceedances of state water quality standards for turbidity. These impacts can also result from the increased runoff generated by land disturbing activities on construction sites. Response: A Temporary Erosion and Sedimentation Control (TESC) Plan will be prepared as part of the Construction Plans. The TESC Plan will prevent the transport of sediment to streams, wetlands, lakes, drainage systems, and adjacent properties in accordance with all the applicable standards of 2017 City of Renton Surface Water Design Manual. Core Requirement No. 6: Maintenance and Operations Intent: To ensure that the maintenance responsibility for drainage facilities is clearly assigned and that these facilities will be properly maintained and operated in perpetuity. Response: The onsite stormwater components will be located within private property and will be maintained by the homeowners. The Flow Control Covenant and maintenance standards for the privately maintained drainage components will be provided along with the final engineering plan submittal. Core Requirement No. 7: Financial Guarantees and Liability Intent: To ensure financial guarantees are posted to sufficiently cover the cost of correcting, if necessary, incomplete or substandard drainage facility construction work, and to warrant for two years the satisfactory performance and maintenance of those newly constructed drainage facilities. Core Requirement #7 is also intended to ensure that a liability policy is provided that protects the proponent and the City from any damages relating to the construction or maintenance of required drainage facilities by private parties. Response: Bond Quantities will be provided along with the final engineering plan submittal. Core Requirement No. 8: Water Quality Intent: To require an efficient, cost-effective level of water quality treatment tailored to the sensitivities and resource protection needs of the downstream receiving water to which the project site drains, or, in the case of infiltration, protection of the receiving groundwater system. Response: The project proposes 8,276 sq. ft. of new pollution impervious surfaces (PGIS). A stormfilter with three (3) 18’’ ZPG cartridges will be provided upstream of the detention vault for basic water quality control. Page | 22 Core Requirement No. 9: On-site BMPs Intent: To provide mitigation of hydrologic impacts that are not possible/practical to mitigate with a flow control facility. Such impacts include increases in runoff volumes and peak discharges and decreases in groundwater recharge. Increased runoff volume and peak discharges leads to higher and more variable stream velocities at low flows and more frequent water level fluctuations in streams and wetlands. This causes wash-out and stranding of aquatic species, algal scour and washout of organic matter, loss of vegetation diversity and habitat quality, and disruption of cues for spawning, egg hatching, and migration. Decreased groundwater recharge reduces water supply for human use and summer base flows in streams, which is critical to water temperature, salmonid use of smaller streams, and the habitat quality of mainstem side channels and wetlands used for spawning, rearing, and flood refuge. On-site BMPs seek to reduce runoff volumes and flashiness and increase groundwater recharge by reducing imperviousness and making use of the pervious portions of development sites to maximize infiltration and retention of stormwater onsite. Thus, the goal is to apply on-site BMPs to new impervious surfaces, new pervious surfaces, and replaced impervious surfaces, to the maximum extent feasible without causing flooding or erosion impacts. Response: According to Section 1.2.9.2 of the Manual, the project is on a site that is larger than 22,000 sq. ft., therefore, large lot BMP requirements apply. Project proposes perforated pipe connections (C.2.11) to control its roof runoff. The following is an evaluation of each BMP as required by Section 1.2.9.2.2 of the Manual: 1. Full Dispersion: Full Dispersion BMP was deemed infeasible since there was not a 100-ft flow path available onsite. 2. Full Infiltration: Full Infiltration BMP was deemed infeasible due to the low infiltration capacity of onsite soils according to the onsite soil infiltration tests shown in geotechnical report. Limited Infiltration: Limited Infiltration BMP was deemed infeasible due to the low infiltration capacity of onsite soils according to the onsite soil infiltration tests shown in geotechnical report. Bioretention: Page | 23 Bioretention BMP was deemed infeasible due to the low infiltration capacity of onsite soils according to the onsite soil infiltration tests shown in geotechnical report. Permeable Pavement: Permeable Pavement BMP was deemed infeasible due to the low infiltration capacity of onsite soils according to the onsite soil infiltration tests shown in geotechnical report. 3. Basic Dispersion: Basic Dispersion BMP was deemed infeasible for roof area since there was not a 25 feet flow path available on site for the dispersion trench (C.2.4.4). Basic Dispersion BMP was deemed infeasible for driveways since there was not a 10 feet flow path available for dispersion. 4. Soil Moisture Holding Capacity Protection: All new pervious surface area will be protected in accordance with the soil amended BMP as detailed in Appendix C, Section C.2.13 of the Manual. 5. Perforated Pipe Connection: A 10 ft. perforated stub-out connection will be provided for runoff from the rooftop as detailed in Appendix C, Section C.2.11 of the Manual. 2.2 Analysis of Special Requirements Special Requirement No. 1: Other Adopted Area-Specific Requirements Response: The following is a list of other possible adopted area-specific requirements according to the Manual: Master Drainage Plan – The area is not part of a master drainage plan. Basin Plans – This site is located within the East Lake Washington-Renton drainage basin. No additional requirements have been identified. Salmon Conservation Plan – The site is located within the WRIA 8 Chinook Salmon Conservation Plan Area. No additional requirements apply. Flood Hazard Reduction Plan Updates – This project does not appear to be within a Flood Hazard Area; therefore, this plan does not apply. Page | 24 Shared Facility Drainage Plan – The project does not propose to connect to a shared detention facility system or create a shared facility; therefore, this plan does not apply. Special Requirement No. 2: Flood Hazard Area Delineation Response: The proposed site is not located within the 100-year floodplain or flood hazard area. Please refer to the FEMA map within Section 3.0 of this report. Special Requirement No. 3: Flood Protection Facilities Response: Special Requirement No. 3 is not applicable to the proposed site since the site will not affect any existing flood protection facilities. Special Requirement No. 4: Source Control Response: Special Requirement No. 4 only applies to commercial site development permits. Since this site is a single-family residential, this requirement does not apply. Special Requirement No. 5: Oil Control Response: Special Requirement No. 5 does not apply to the site since it is not classified as a high-use site. Special Requirement No. 6: Aquifer Protection Area Response: The project is not located within either Aquifer Protection Area Zone 1 or Zone 2; therefore, this requirement does not apply. Page | 25 3.0 OFF-SITE ANALYSIS 3.1 Study Area Definition and Maps The City of Renton requires a summary of the upstream drainage basin, and one-quarter mile downstream drainage analysis. Under predeveloped condition, stormwater from a portion of south side of NE 7th Street flows to the site from the north property line, which sheet flows to the existing landscape area. Under developed condition, stormwater from the frontage improvement areas (i.e., roadway, sidewalk, landscape) will be collected by two proposed catch basins and conveyed to the proposed detention vault onsite. 3.2 Resource Review  Adopted Basin Plans: This site is located within the East Lake Washington – Renton drainage basin. According to the City’s GIS Map Viewer the site is tributary to Cedar River, and ultimately Lake Washington.  Floodplain and Floodway FEMA Maps: Per the FEMA map number 53033C0981F the site is located in Zone X and is not located within the 100-year floodplain. Please see the FEMA map within this section.  Offsite Analysis Report: No other offsite analysis reports were located.  Sensitive Areas Folios: Based on a review of the Renton and King County Sensitive Areas Maps and Land Survey, it was found that the subject site does not contain any seismic hazards, flood hazards, erosion hazards, wildlife network, aquafer protection zone, or coal mines.  United States Department of Agriculture King County Soils Survey: Based on the NRCS soils map for this area, the entire site is located within AmC-Arents, Alderwood material, 6-15% slopes, AmC soils are typically underline by gravelly sandy loam 0 to 26-inches then to very gravelly sandy loam from 26 to 60-inches. These soils are classified as type C and have low capacity to transmit water.  Wetlands Inventory Maps: Based on a review of the Renton and King County maps there are no onsite or adjacent offsite wetlands.  Washington State DOE List of Polluted Waters: There are no polluted waters within 1-mile of the project site. Page | 26  Erosion and Landslide Maps: As shown in the sensitive area map, a small moderate slope area exists in the south of the site. A temporary erosion control and a retaining wall are proposed to prevent erosion and landslide, respectively. 3.3 Drainage System Description and Problem Descriptions The project site slopes from east to west at an approximate rate of 5% to 10% with isolated areas up to 30%. The current runoff from the existing house and detached garage disperses to the western portion of the site. The overflow from the site flows into the existing storm drainage system within Pierce Pl. NE and NE 6th Ct. to the west of the property. Under developed condition, the project is proposing to detain all stormwater runoff from developed area of the site and frontage improvements, and release runoff matching 50% of the 2-year peak flow up to full 50-year peak flow of the pre-developed basin (forested condition). The drainage from the detention vault will route to the southwest corner of the site and ultimately discharge to the existing conveyance within NE 7th Place, and then flows to the 12-inch drainage pipe along Olympia Ave NE to the South. The runoff then flows southernly into the 30-inch private stormwater main within Olympia Ave NE and Monroe Ave. The stormwater continue flows southernly for approximately 0.50 miles to NE 2nd Street, then discharges to Cedar River and eventually flows into Lake Washington. No off-site flooding or erosion problems will be created or aggregated by this project due to the proposed detention vault. An Offsite Analysis Drainage System Table is included within this section for reference. 3.4 Mitigation of Existing or Potential Problems There are no existing problems that need mitigation due to the construction of this project. The runoff from the site will be controlled with a proposed detention vault of 10,800 cubic feet storage volume, which will release runoff matching 50% of the 2-year peak flow up to full 50- year peak flow of the pre-developed basin (forested condition). Therefore, no potential problems will be aggravated by this project. Page | 27 Figure 3.1 – FEMA Map D :::: ,,::::,,,,SUNSETNESTREETAVENUE H I LLS 6 8 ZONE XDAYTON1ST SENE SE SHELTON8 3AVENUEPLACE STREET ACCESSS T R E E T PLACE STREET55AVENUE 8 1 SERENTON AVENUE NES E 3RD NE AVENUEINDEXSE 6 4 NE STR EETKIRKLAND PLACE SE6TH COUR T STREET 3RD 2ND 6TH STREET NEN EAVENUENE AVENU E NEGLENWOOD CEDAR 7TH SEHARRINGTONCHELANNE 530088 6TH STREET EDMONDS AVENUE NEAMZONE X Bridge NE PLACE ¥k405 N ENEDRIVEPARK 10THBOULEVARD ST R E E T STREET PLACEPLACE AVENENE2 N D PLACE STREET S T R E E T ZONE XNE 10 AVENUE NESTREET 7 T H PLACE 2ND DRIVE STREET UNIONSUNSET 49S U N S ET 8 T H RIVER6017 131ST4TH P L A C E NE5TH NE PLAC E OLYMPIAAVENUE NEPLACEAVENUE144TH SE D RIVE AVENUESENE 5TH ZONEFERNDALEPLACENE 6TH NE 7TH 5TH 9TH 136TH6TH STREET C HE L A N A V EN UE S EAVENUE1ST AVENUE ZONE X NE 10TH PLACE 50 W IN D S OR 58STREET PLACE SE 8 T H INDEXNE 6T HAVENUEZONE X 2ND 5TH CT2ND DUVALLNES E AVEAVENUEAVENUESTREET7TH A VEN U E A VENUE KING COUNTY 10TH HARRINGTONSE JEFFERSONP L A C E 6TH 66 STREET NE SE 135TH IN DEX APAO80 1ST NEAVENUEPLACE QUEENPLACE ZONE AE NE 8TH SE 10TH NE 8 T H EDMONDSPLA C E AVENUEP L A C E ZONE X 4THPLAC E6TH CHELANNE NE 5TH NE G L E N WOOD5TH AVENUEBREMERTONROADSTREETS T R E E TNENEOLYMPIA 54PLACE5TH STREETINDEXZONE AE NE PLA C E NE 5TH STREET 5TH STREETNESENEPLACEAVENUE530071 3 R D 1 41ST67 S ENE SHEL TONN E VASHON5THSTREET PLACEPLACE NECEDAR RIVER PLACE NENE TACOMA PLACE PLACE AVENUEZONE X 52 STREET STREET NE UNINCORPORATED AREASVASHON SENE 79 3 R D 21LYNNWOOD4TH 2ND SE BREME R TON STREET S E OLYMPIANE 6TH N E NE 7TH RAILROAD53STREET N E NE NE 5TH RENTONCITY OF RENTON CAMAS DRIVE SE 11THNEAVENUE6THPIERCE AVE SEINDEXQUEENSENE NE S E NE PLACENE 133RDMONROEC O URT NESTREET SE N E 6 T H SE 9TH VASHONNESTREET AVENUECOURT PROFILE BASELINE AVENUESTREET SEAVENUENE9TH 116TH 1 S T ZONE X 6 5 7TH SE CEDAR MAPLEAVENUEINDEXFERNDALE Footbridge A IANAVENUEPLACE BREMERTONP L ACE8TH AVENUE NENE 57WI NDSORI NDEXN E 6 T H NEPLACE NEZONE X 5TH C O U R T ZONE X NE AVENUE SE22 STREETCOURTCIRCLE 9TH SENE SE PLACEHIGHWAY LAN E NEASHELTONROAD6TH NEP L A C E ZONE AEPLACENEPLACEAEINDEX3RD NE 4T H BREMERTONP L A C E SY5646 PLACE NEAVENUE NE 7TH TRAIL NE ST R EE TRENTON DIST CTNENENEFERNDALEPINES T R E E TEDMONDSSEAVENUENE SE 16 NE NE N E FERNDALE SESHELTON 5TH NE ROADNE S T R EETSTREET NE NE N E NE 9TH NENE ZONE X ZONE X PLACE NECOURTZONE X COURT 132ND AVE SEAVENUE PROFILE BASELINE SE 15 138THPLACE 9 ROYALLANE 5THNESTREET STREET 63SE 77 SE 61ST R E D MONDNE9TH 10TH TACOMANE7TH NERID G E NEACCESS ROADNEAHAGVALLEY 82 4 T H RAILROAD FERNDALE S EUNIONPLACE 51 PLACE NE9TH NENE NEWPORTCEDAR RIVER ZONE X STREET AVENUEPLAC E 10TH P LA C E PLACEAVENUE G L ENWOODNE PLACE7THAVENUEBREMERTONSTREET COURT SE 59148TH 4TH 3RD CTNENE QUEEN567TH NE 9TH AEAVENUESTREET NE 4TH PLACE ACNE AV ENUE 6TH 130THCOURT DIST2NDPLACE STR E E T NE NEFERNDALEBOULEVARDZONE X CT AVENUE SESEAC62NE STREETA J NE 10TH STREET NE CT NE 20 NE 2NDFE RNDALE8 EVERGREEN 3RDAVENUE PLACEPLAVENUE NE Riverview ParkBridge COURTPIERCE NEN EZONE X NEJEFFERSONW AY C O U R TNENENE AVENUEAVENUE SEREDMOND SESE2ND SE INDE XAVENUE NENES ECOURTACCESS AFA D STREETNEAVENUESE STREET SE 125TH SE SEAVENUEPLACE COURT 140TH WAY SE86 ZONE X 84SE 124TH SEAVENUE 69ROYAL INDEX 141ST H IL L S SE 87PLACEAVENUE NESE 140TH S E 116TH 136THAVENUESTREET140TH 1 4 1 S T 140THABSTREET 530088 PLACE 530088 STREET STREET 125TH SENE SEAVENUE NEZONEAE AVENUE143RDAVE SESTR E ET STREET 141STNE 4TH 150THSTREET SE9188PLACE85 H A RRIN GTON SEAVENUE SECITY OFAVENUE 22 STREET NE 9TH 144TH STREET STREET SESTREET 142NDSE 90144THS T R E ET 530088 AQ133RD 143RDSTREET SES E HOQUIAMRENTON 143RD86SESEAVENUEDUVALL 15 NE 4THLANE AVENUESE SE SE 141S TSESTREET ZONE X142NDPLACE 132ND SE STREET SE SE141STNE 4TH CITY OF RENTON138TH SE140THJERICHOCEDARAVENUE SE10 132ND AR143RDSEST SE SE SE126TH NE139THPLACE 122ND 83AVENUESE PLACE RIVERSENE 4TH STREET 142ND13 4 T H139TH STREET ST STREET AVENUESE1 3 1 ST 139THSTREET SE SE 146TH STREET 121ST AS118TH SE AVENUESE AVENUESE 135TH ZONE X HOQUIAMSE 129TH SE PROFILE BASELINE 530088 NE 6TH NE 4TH CITY OF RENTON 89SE STREETAVENUESTREET ZONE X138TH AVENUE SESE 140TH STREETAVENUECITY OF RENTON 142ND HILLS151STDRIVEBEACON AS88SE 90WAY SE ZONE X 85WAY SE78 WAY SE87 89WAY140TH134THZONE X 133RDAVED R IVE91ZONEAE ZONE X 140TH 140TH 140THWAYNESE NE 10TH MONTEREY NEPARKING DRIVE3RD C O URTSUNSET C OURT 47C EMETARY AAZNERIVERSTREET RAILROADNEWA YNENE 8TH BLAINEBOULEVARDNE44ZONE AE 8THWINDS O R ZONEX S CITY OF RENTONKENWORTH PLACE PLACECOURT NEPLACE4THABERDEEN AVENUE NEBLAINEZONE AE MT.OLIVETCAMAS BEACON ZONE X 4 5DRIVEHOUSER S E H OUS E RNEA VENU E W A Y NEWAYAVENUESE BRONSONBL AINEABERDEEN 9TH STREET PLACE 3 R D NOTE: MAP AREA SHOWN ON THIS PANEL IS LOCATED WITHIN TOWNSHIP 23 NORTH, RANGE 5 EAST.43SUNSETD R IV ECAPRINE 10THRIVER STREET NPLACE NENE NEPLACE8TH ZONE X ¥k405 CEDARVALLEY STREET NE RAILROAD 530088 ZONE X S T R E E T AVENUE8TH ZONE XGRAND EYS E NE SEAVENUENEWAYNE 9 TH 4 6 TRAIL MAPLE PLACE P A R KBRONSONNE BYPASSNE¥k405 7TH NCED A RSE2ND NE8 DRIVEWAYNEBOULEVARD 7THHIGHWAYMONTEREY BLAI NEW AY LOT NEDR6 THN E 2N D RIVER STREET STREETPLACEAVENUER AIL R O A DCIRCLE 6TH PLACE NE 6TH COURT VUEMONTHOUSERN48SE 138TH STR BEACON WAY NOTE: MAP AREA SHOWN ON THIS PANEL IS LOCATED WITHIN TOWNSHIP 23 NORTH, RANGE 5 EAST.S NOTE: MAP AREA SHOWN ON THIS PANEL IS LOCATED WITHIN TOWNSHIP 23 NORTH, RANGE 5 EAST. Ñ Ñ Ñ Ñ Ñ Ñ Ñ Ñ 134TH AVE SESE 149THSTREET ZONE X ZONE AO(DEPTH 1')135TH AVE SE SOOS CREEK PARK AND TRAIL ZONE X ZONE X ZONE X PROFILE BASELINE JOINS PANEL 0983 JOINS PANEL 0668 JOINS PANEL 0982JOINS PANEL 09775261000mN . 5260000mN . 5259000mN . 5258000mN . 563000mE 7 562000mE 7 47° 28' 07.5" 122° 09' 22.5"47° 28' 07.5" 122° 11' 15" 47° 30' 00" 122° 11' 15"47° 30' 00" 122° 09' 22.5" COMMUNITY NUMBER PANEL SUFFIX CONTAINS: (SEE MAP INDEX FOR FIRM PANEL LAYOUT) Federal Emergency Management Agency FLOOD INSURANCE RATE MAPFIRM MAP REPOSITORIESRefer to Map Repositories list on Map Index EFFECTIVE DATE OF COUNTYWIDEFLOOD INSURANCE RATE MAPSeptember 29, 1989 EFFECTIVE DATE(S) OF REVISION(S) TO THIS PANELMay 16, 1995 - to update map format.(Date of Revision) - to change Base Flood Elevations, to update corporate limits, to add roads and road names, to update the effects of wave action, to change Special Flood Hazard Areas, to change zone designations and to incorporate previously issued Letters of Map Revision. For community map revision history prior to countywide mapping, refer to the CommunityMap History table located in the Flood Insurance Study report for this jurisdiction. To determine if flood insurance is available in this community, contact your insurance agentor call the National Flood Insurance Program at 1-800-638-6620. Notice to User: The Map Number shown belowshould be used when placing map orders; theCommunity Number shown above should beused on insurance applications for the subject community. MAP REVISED MAP NUMBER53033C0981G KING COUNTY,WASHINGTONAND INCORPORATED AREAS KING COUNTY 530071 0981 GRENTON, CITY OF 530088 0981 G NFIP NATIONAL FLOOD INSURANCE PROGRAMPANEL 0981G PANEL 981 OF 1700 250 10000FEET 150 3000METERS MAP SCALE 1" = 500'500 150 NOTES TO USERS This map is for use in administering the National Flood Insurance Program. It doesnot necessarily identify all areas subject to flooding, particularly from local drainagesources of small size. The community map repository should be consulted forpossible updated or additional flood hazard information. To obtain more detailed information in areas where Base Flood Elevations (BFEs)and/or floodways have been determined, users are encouraged to consult the FloodProfiles and Floodway Data and/or Summary of Stillwater Elevations tables containedwithin the Flood Insurance Study (FIS) Report that accompanies this FIRM. Usersshould be aware that BFEs shown on the FIRM represent rounded whole-footelevations. These BFEs are intended for flood insurance rating purposes only andshould not be used as the sole source of flood elevation information. Accordingly,flood elevation data presented in the FIS Report should be utilized in conjunction withthe FIRM for purposes of construction and/or floodplain management. Coastal Base Flood Elevations shown on this map apply only landward of 0.0’North American Vertical Datum of 1988 (NAVD 88). Users of this FIRM should beaware that coastal flood elevations are also provided in the Summary of StillwaterElevations table in the Flood Insurance Study Report for this jurisdiction. Elevationsshown in the Summary of Stillwater Elevations table should be used for constructionand/or floodplain management purposes when they are higher than the elevationsshown on this FIRM. Boundaries of the floodways were computed at cross sections and interpolatedbetween cross sections. The floodways were based on hydraulic considerations withregard to requirements of the National Flood Insurance Program. Floodway widthsand other pertinent floodway data are provided in the Flood Insurance Study Reportfor this jurisdiction. Certain areas not in Special Flood Hazard Areas may be protected by flood controlstructures. Refer to Section 2.4 "Flood Protection Measures" of the Flood InsuranceStudy Report for information on flood control structures for this jurisdiction. The projection used in the preparation of this map was Universal TransverseMercator (UTM) zone 10. The horizontal datum was NAD 83, GRS 1980spheroid. Differences in datum, spheroid, projection or UTM zones used in theproduction of FIRMs for adjacent jurisdictions may result in slight positionaldifferences in map features across jurisdiction boundaries. These differences do notaffect the accuracy of this FIRM. Flood elevations on this map are referenced to the North American Vertical Datum of1988. These flood elevations must be compared to structure and ground elevationsreferenced to the same vertical datum. For information regarding conversionbetween the National Geodetic Vertical Datum of 1929 and the North AmericanVertical Datum of 1988, visit the National Geodetic Survey website athttp://www.ngs.noaa.gov or contact the National Geodetic Survey at the followingaddress: NGS Information ServicesNOAA, N/NGS12National Geodetic SurveySSMC-3, #92021315 East-West HighwaySilver Spring, Maryland 20910-3282(301) 713-3242 To obtain current elevation, description, and/or location information for bench marksshown on this map, please contact the Information Services Branch of the NationalGeodetic Survey at (301) 713- 3242, or visit its website at http://www.ngs.noaa.gov. Base Map information shown on the FIRM was derived from multiplesources. Base map files were provided in digital format by King County GIS, WADNR, WSDOT, and Pierce County GIS. This information was compiled at scales of1:12,000 to 24,000 during the time period of 1994-2012. The profile baselines depicted on this map represent the hydraulic modeling baselines that match the flood profiles in the FIS report. As a result of improved topographic data, the profile baseline, in some cases, may deviate significantly from the channel centerline or appear outside the SFHA. Based on updated topographic information, this map reflects more detailed andup-to-date stream channel configurations and floodplain delineations thanthose shown on the previous FIRM for this jurisdiction. As a result, the FloodProfiles and Floodway Data tables for multiple streams in the FloodInsurance Study Report (which contains authoritative hydraulic data) may reflectstream channel distances that differ from what is shown on the map. Also, the road to floodplain relationships for unrevised streams may differ from what isshown on previous maps. Corporate limits shown on this map are based on the best data available at the timeof publication. Because changes due to annexations or de-annexations may haveoccurred after this map was published, map users should contact appropriatecommunity officials to verify current corporate limit locations. Please refer to the separately printed Map Index for an overview map of thecounty showing the layout of map panels; community map repository addresses;and a Listing of Communities table containing National Flood Insurance Programdates for each community as well as a listing of the panels on which each communityis located. For information on available products associated with this FIRM visit the MapService Center (MSC) website at http://msc.fema.gov. Available products mayinclude previously issued Letters of Map Change, a Flood Insurance Study Report,and/or digital versions of this map. Many of these products can be ordered orobtained directly from the MSC website. If you have questions about this map, how to order products, or the NationalFlood Insurance Program in general, please call the FEMA Map InformationeXchange (FMIX) at 1-877-FEMA-MAP (1-877-336-2627) or visit the FEMAwebsite at http://www.fema.gov/business/nfip. Zone D boundary Floodway boundary 1% Annual Chance Floodplain Boundary 0.2% Annual Chance Floodplain Boundary *Referenced to the North American Vertical Datum of 1988 D !!!!!!!!!!!!!!LEGEND SPECIAL FLOOD HAZARD AREAS (SFHAs) SUBJECT TOINUNDATION BY THE 1% ANNUAL CHANCE FLOOD ZONE A ZONE AE ZONE AH ZONE AO ZONE AR ZONE A99 ZONE V ZONE VE ZONE X FLOODWAY AREAS IN ZONE AE OTHER FLOOD AREAS OTHER AREAS ZONE XZONE D The 1% annual chance flood (100-year flood), also known as the base flood, is the flood that hasa 1% chance of being equaled or exceeded in any given year. The Special Flood Hazard Area isthe area subject to flooding by the 1% annual chance flood. Areas of Special Flood Hazardinclude Zones A, AE, AH, AO, AR, A99, V, and VE. The Base Flood Elevation is the water-surfaceelevation of the 1% annual chance flood. No Base Flood Elevations determined. Base Flood Elevations determined. Flood depths of 1 to 3 feet (usually areas of ponding); Base Flood Elevationsdetermined. Flood depths of 1 to 3 feet (usually sheet flow on sloping terrain); averagedepths determined. For areas of alluvial fan flooding, velocities also determined. Special Flood Hazard Areas formerly protected from the 1% annual chanceflood by a flood control system that was subsequently decertified. ZoneAR indicates that the former flood control system is being restored to provideprotection from the 1% annual chance or greater flood.Area to be protected from 1% annual chance flood by a Federal floodprotection system under construction; no Base Flood Elevations determined. Coastal flood zone with velocity hazard (wave action); no Base Flood Elevationsdetermined. Coastal flood zone with velocity hazard (wave action); Base Flood Elevationsdetermined. The floodway is the channel of a stream plus any adjacent floodplain areas that must be kept free ofencroachment so that the 1% annual chance flood can be carried without substantial increases inflood heights. Areas of 0.2% annual chance flood; areas of 1% annual chance flood withaverage depths of less than 1 foot or with drainage areas less than 1 squaremile; and areas protected by levees from 1% annual chance flood. Areas determined to be outside the 0.2% annual chance floodplain. Areas in which flood hazards are undetermined, but possible. CBRS areas and OPAs are normally located within or adjacent to Special Flood Hazard Areas. CBRS and OPA boundary Boundary dividing Special Flood Hazard Area Zones and boundary dividing Special Flood Hazard Areas of different Base Flood Elevations, flood depths, or flood velocities. Base Flood Elevation value where uniform within zone; elevation infeet* Cross section line Transect line Geographic coordinates referenced to the North American Datum of1983 (NAD 83) Western Hemisphere 1000-meter Universal Transverse Mercator grid values, zone 104989000m N Bench mark (see explanation in Notes to Users section of this FIRMpanel) River Mile Base Flood Elevation line and value; elevation in feet* COASTAL BARRIER RESOURCES SYSTEM (CBRS) AREAS OTHERWISE PROTECTED AREAS (OPAs) 513 (EL 987) 45° 02’ 08”, 93° 02’ 12” DX5510 M1.5 A A 23 23 Page | 29 Figure 3.2 – Sensitive Areas Map 2,400 200 City of Renton Print map Template 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 10/16/2018 Legend 136068 THIS MAP IS NOT TO BE USED FOR NAVIGATION Feet Notes 136 WGS_1984_Web_Mercator_Auxiliary_Sphere Information Technology - GIS RentonMapSupport@Rentonwa.gov Erosion hazard - high Floodway Special Flood Hazard Areas (100 year flood) Landslide Very High High Moderate Unclassified Slope City of Renton >15% & <=25% >25% & <=40% (Sensitive) >40% & <=90% (Protected) >90% (Protected) Environment Designations Natural Shoreline High Intensity Shoreline Isolated High Intensity Shoreline Residential Urban Conservancy Jurisdictions Streams (Classified) <all other values> Type S Shoreline Type F Fish Type Np Non-Fish Type Ns Non-Fish Seasonal Page | 31 Figure 3.3 – Offsite Analysis Drainage System Table CITY OF RENTON SURFACE WATER DESIGN MANUAL2017 City of Renton Surface Water Design Manual12/12/2016Ref 8-B-1REFERENCE 8-BOFF-SITE ANALYSIS DRAINAGE SYSTEM TABLECITY OF RENTON SURFACE WATER DESIGN MANUAL, CORE REQUIREMENT #2Basin:Subbasin Name:Subbasin Number:DateSymbolDrainage Component Type, Name, and SizeDrainage Component DescriptionSlopeDistance from Site DischargeExisting ProblemsPotential ProblemsObservations of Field Inspector, Resource Reviewer, or ResidentSee mapType: sheet flow, swale, stream, channel, pipe, pond, flow control/treatment/on-site BMP/facilitySize: diameter, surface areadrainage 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 erosionTributary area, likelihood of problem, overflow pathways, potential impactsEast Lake Washington-Renton7th Street Short Plat10/16/2018ABCDEFGPipePipePipePipePipePipePipe4.311.622.050.530.770.741.033796528911,1041,2191,3281,511NoneNone10'' in Diameter12'' in Diameter12'' in Diameter30'' in Diameter30'' in Diameter30'' in Diameter30'' in DiameterNoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNone Page | 33 Figure 3.4 – Downstream Analysis Map 4,514752 7th Street Short Plat 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. THIS MAP IS NOT TO BE USED FOR NAVIGATIONWGS_1984_Web_Mercator_Auxiliary_Sphere Notes None 10/17/2018 Legend 512 0 256 512 Feet Information Technology - GIS RentonMapSupport@Rentonwa.gov Water Service Areas Wastewater Service Areas Network Structures Inlet Manhole Utility Vault Unknown Structure Control Structure Pump Station Discharge Point Water Quality Detention Facilities Pond Tank Vault Wetland Stormwater Main Culvert Open Drains Facility Outline Private Network Structures Inlet Manhole Utility Vault Unknown Structure Private Control Structure Private Discharge Point Private Water Quality Private Detention Facilities Pond Tank Vault Wetland Private Pipe Private Culvert Private Open Drains Private Facility Outline Fence Special Assessment Districts Points of Interest Parks Waterbodies Streets 2015.sid Red: Band_1 Green: Band_2 Blue: Band_3 CacheExtent_144K Page | 35 4.0 STORMWATER ANALYSIS AND DESIGN 4.1 Existing Site Hydrology The existing site is, generally, rectangular in shape, covered with trees, grass and blackberries. Historically, a 676 sq.ft. roof area of single-family home was onsite with lawns and one detached 855 sq.ft garage and 1,200 sq.ft. gravel drive, which will be demolished as part of this project. The site slopes from northeast to southwest at approximate rates of 5% to 10%, at the west of the site the slopes exceed 20% while continuing to slope downward from east to west. Overall, the existing site has an elevation range of 412-ft near the northeast corner to 400-ft near the southwest corner near the west property line of the site. The onsite soils are Arents, Alderwood material, 6 to 15 percent slopes (RmC). According to the geotechnical report conducted by ESNW on August 20, 2018, the native soils were classified primarily as silty sand with gravel, consistent with the typical makeup of glacial till deposits. A Pre-developed Basin Map is included in Section 1 of this report. The land-use of the pre- developed basin is as follows: Area WWHM Land-use Acres Till Forest C, Forest, Mod 0.64 Grass (frontage) C, Pasture, Mod 0.04 Roadway (frontage) Road, Mod 0.03 Total 0.71 Table 4.1- Pre-Developed Basin Summary The 15-minutes pre-developed peak flows for the basin (0.71-acre) are as follows (from WWHM report attached): Q2= 0.03-cfs Q10= 0.06-cfs Q25= 0.07-cfs Q100= 0.10-cfs 4.2 Developed Site Hydrology Limits of site disturbance will include installation of sediment and erosion control Best Management Practices (BMPs), construction of frontage improvements, driveways, detention Page | 36 vault, utilities, landscaping and 3 single-family residences. Frontage improvements include curb, gutter, 8-foot planter and 5-foot sidewalk on the southern side of NE 7th Street. The total disturbed area will cover approximately 0.71 acres both onsite and off. Upon completion of the project, impervious surfaces covering the site include approximately 0.11-acre of access road, 0.08-acre of driveways, and 0.15-acre of new rooftops. Please refer to the Developed Basin Map in Section 1 of this report. The land-use of the post-developed basin is as follows: Area WWHM Land-use Acres Access Road Roads, Flat 0.11 Roof Roof Tops, Flat 0.15 Driveway Driveways, Flat 0.08 Lawn C, Lawn, Flat 0.30 Road (frontage) Roads, Flat 0.04 Sidewalk (frontage) Sidewalk, Flat 0.02 Landscape (frontage) C, Lawn, Flat 0.01 Total 0.71 Table 4.2- Post Developed Basin Summary The 15-minutes post-developed peak flows for the basin (0.71-acre) are as follows (WWHM report): Q2= 0.013 cfs Q10= 0.034 cfs Q25= 0.049 cfs Q100= 0.079 cfs 4.3 Performance Standards The site does not have the proper flow paths and soils for either full dispersion or infiltration. The runoff of the site will flow to the detention vault, which is sized to match 50% of the 2-year peak flow up to the full 50-year peak flow of the existing site condition (forested). Page | 37 4.4 Water Quality System The project proposes 8,276 sq. ft. of new PGIS. A Contech Stormfilter is proposed for basic stormwater treatment, the detailed calculation of the stormfilter sizing is shown in this Section below. Page | 39 Figure 4.1 – WWHM reports WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: Detention Vault 6.7.2019 Site Name: 7th St. SP Site Address: 3605 NE 7th Street City : Renton Report Date: 6/7/2019 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2019/04/13 Version : 4.2.16 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Mod .64 C, Pasture, Mod .04 Pervious Total 0.68 Impervious Land Use acre ROADS MOD 0.03 Impervious Total 0.03 Basin Total 0.71 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Lawn, Flat .31 Pervious Total 0.31 Impervious Land Use acre ROADS FLAT 0.15 ROOF TOPS FLAT 0.15 DRIVEWAYS FLAT 0.08 SIDEWALKS FLAT 0.02 Impervious Total 0.4 Basin Total 0.71 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Vault 1 Vault 1 ___________________________________________________________________ Name : Vault 1 Width : 22.8146761986609 ft. Length : 45.6293523973221 ft. Depth: 11 ft. Discharge Structure Riser Height: 10 ft. Riser Diameter: 18 in. Orifice 1 Diameter: 0.33 in. Elevation: 0 ft. Orifice 2 Diameter: 0.79 in. Elevation: 6.67 ft. Orifice 3 Diameter: 0.5 in. Elevation: 8.04125000000003 ft. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Vault Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.023 0.000 0.000 0.000 0.1222 0.023 0.002 0.001 0.000 0.2444 0.023 0.005 0.001 0.000 0.3667 0.023 0.008 0.001 0.000 0.4889 0.023 0.011 0.002 0.000 0.6111 0.023 0.014 0.002 0.000 0.7333 0.023 0.017 0.002 0.000 0.8556 0.023 0.020 0.002 0.000 0.9778 0.023 0.023 0.002 0.000 1.1000 0.023 0.026 0.003 0.000 1.2222 0.023 0.029 0.003 0.000 1.3444 0.023 0.032 0.003 0.000 1.4667 0.023 0.035 0.003 0.000 1.5889 0.023 0.038 0.003 0.000 1.7111 0.023 0.040 0.003 0.000 1.8333 0.023 0.043 0.004 0.000 1.9556 0.023 0.046 0.004 0.000 2.0778 0.023 0.049 0.004 0.000 2.2000 0.023 0.052 0.004 0.000 2.3222 0.023 0.055 0.004 0.000 2.4444 0.023 0.058 0.004 0.000 2.5667 0.023 0.061 0.004 0.000 2.6889 0.023 0.064 0.004 0.000 2.8111 0.023 0.067 0.005 0.000 2.9333 0.023 0.070 0.005 0.000 3.0556 0.023 0.073 0.005 0.000 3.1778 0.023 0.075 0.005 0.000 3.3000 0.023 0.078 0.005 0.000 3.4222 0.023 0.081 0.005 0.000 3.5444 0.023 0.084 0.005 0.000 3.6667 0.023 0.087 0.005 0.000 3.7889 0.023 0.090 0.005 0.000 3.9111 0.023 0.093 0.005 0.000 4.0333 0.023 0.096 0.005 0.000 4.1556 0.023 0.099 0.006 0.000 4.2778 0.023 0.102 0.006 0.000 4.4000 0.023 0.105 0.006 0.000 4.5222 0.023 0.108 0.006 0.000 4.6444 0.023 0.111 0.006 0.000 4.7667 0.023 0.113 0.006 0.000 4.8889 0.023 0.116 0.006 0.000 5.0111 0.023 0.119 0.006 0.000 5.1333 0.023 0.122 0.006 0.000 5.2556 0.023 0.125 0.006 0.000 5.3778 0.023 0.128 0.006 0.000 5.5000 0.023 0.131 0.006 0.000 5.6222 0.023 0.134 0.007 0.000 5.7444 0.023 0.137 0.007 0.000 5.8667 0.023 0.140 0.007 0.000 5.9889 0.023 0.143 0.007 0.000 6.1111 0.023 0.146 0.007 0.000 6.2333 0.023 0.149 0.007 0.000 6.3556 0.023 0.151 0.007 0.000 6.4778 0.023 0.154 0.007 0.000 6.6000 0.023 0.157 0.007 0.000 6.7222 0.023 0.160 0.011 0.000 6.8444 0.023 0.163 0.014 0.000 6.9667 0.023 0.166 0.017 0.000 7.0889 0.023 0.169 0.018 0.000 7.2111 0.023 0.172 0.020 0.000 7.3333 0.023 0.175 0.021 0.000 7.4556 0.023 0.178 0.023 0.000 7.5778 0.023 0.181 0.024 0.000 7.7000 0.023 0.184 0.025 0.000 7.8222 0.023 0.186 0.026 0.000 7.9444 0.023 0.189 0.027 0.000 8.0667 0.023 0.192 0.029 0.000 8.1889 0.023 0.195 0.031 0.000 8.3111 0.023 0.198 0.033 0.000 8.4333 0.023 0.201 0.035 0.000 8.5556 0.023 0.204 0.036 0.000 8.6778 0.023 0.207 0.038 0.000 8.8000 0.023 0.210 0.039 0.000 8.9222 0.023 0.213 0.040 0.000 9.0444 0.023 0.216 0.041 0.000 9.1667 0.023 0.219 0.042 0.000 9.2889 0.023 0.222 0.044 0.000 9.4111 0.023 0.224 0.045 0.000 9.5333 0.023 0.227 0.046 0.000 9.6556 0.023 0.230 0.047 0.000 9.7778 0.023 0.233 0.048 0.000 9.9000 0.023 0.236 0.049 0.000 10.022 0.023 0.239 0.102 0.000 10.144 0.023 0.242 0.919 0.000 10.267 0.023 0.245 2.175 0.000 10.389 0.023 0.248 3.562 0.000 10.511 0.023 0.251 4.790 0.000 10.633 0.023 0.254 5.646 0.000 10.756 0.023 0.257 6.215 0.000 10.878 0.023 0.260 6.695 0.000 11.000 0.023 0.262 7.143 0.000 11.122 0.023 0.265 7.564 0.000 11.244 0.000 0.000 7.963 0.000 ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.68 Total Impervious Area:0.03 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.31 Total Impervious Area:0.4 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.02924 5 year 0.044231 10 year 0.05567 25 year 0.071902 50 year 0.085325 100 year 0.099924 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.012853 5 year 0.024027 10 year 0.033787 25 year 0.049117 50 year 0.062915 100 year 0.078921 ___________________________________________________________________ Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.041 0.007 1950 0.042 0.020 1951 0.051 0.046 1952 0.021 0.006 1953 0.016 0.019 1954 0.022 0.007 1955 0.033 0.007 1956 0.030 0.026 1957 0.031 0.007 1958 0.024 0.008 1959 0.022 0.007 1960 0.043 0.027 1961 0.024 0.022 1962 0.015 0.006 1963 0.023 0.015 1964 0.030 0.021 1965 0.026 0.022 1966 0.020 0.008 1967 0.047 0.018 1968 0.029 0.007 1969 0.027 0.008 1970 0.025 0.017 1971 0.027 0.007 1972 0.041 0.038 1973 0.020 0.024 1974 0.029 0.010 1975 0.036 0.007 1976 0.028 0.007 1977 0.013 0.005 1978 0.022 0.018 1979 0.020 0.005 1980 0.062 0.034 1981 0.021 0.007 1982 0.043 0.023 1983 0.030 0.008 1984 0.019 0.006 1985 0.013 0.006 1986 0.041 0.013 1987 0.040 0.026 1988 0.016 0.007 1989 0.018 0.006 1990 0.098 0.033 1991 0.058 0.039 1992 0.026 0.014 1993 0.021 0.006 1994 0.012 0.005 1995 0.027 0.023 1996 0.066 0.043 1997 0.048 0.038 1998 0.023 0.007 1999 0.063 0.035 2000 0.024 0.007 2001 0.016 0.004 2002 0.029 0.018 2003 0.044 0.007 2004 0.042 0.034 2005 0.031 0.007 2006 0.031 0.024 2007 0.078 0.047 2008 0.086 0.033 2009 0.045 0.021 ___________________________________________________________________ Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.0981 0.0465 2 0.0858 0.0463 3 0.0784 0.0435 4 0.0662 0.0387 5 0.0633 0.0379 6 0.0621 0.0377 7 0.0583 0.0351 8 0.0508 0.0337 9 0.0476 0.0336 10 0.0471 0.0335 11 0.0447 0.0326 12 0.0437 0.0274 13 0.0433 0.0265 14 0.0425 0.0256 15 0.0419 0.0242 16 0.0416 0.0238 17 0.0412 0.0234 18 0.0408 0.0234 19 0.0407 0.0224 20 0.0404 0.0220 21 0.0359 0.0211 22 0.0331 0.0208 23 0.0314 0.0205 24 0.0311 0.0192 25 0.0308 0.0184 26 0.0304 0.0183 27 0.0304 0.0179 28 0.0295 0.0174 29 0.0293 0.0153 30 0.0293 0.0144 31 0.0291 0.0130 32 0.0279 0.0103 33 0.0272 0.0077 34 0.0271 0.0076 35 0.0271 0.0076 36 0.0263 0.0075 37 0.0260 0.0074 38 0.0247 0.0074 39 0.0245 0.0074 40 0.0241 0.0073 41 0.0240 0.0073 42 0.0235 0.0073 43 0.0225 0.0072 44 0.0222 0.0072 45 0.0222 0.0069 46 0.0220 0.0068 47 0.0212 0.0068 48 0.0208 0.0067 49 0.0208 0.0067 50 0.0203 0.0067 51 0.0201 0.0066 52 0.0197 0.0063 53 0.0193 0.0063 54 0.0180 0.0061 55 0.0163 0.0060 56 0.0161 0.0060 57 0.0158 0.0058 58 0.0150 0.0054 59 0.0130 0.0054 60 0.0129 0.0052 61 0.0115 0.0043 ___________________________________________________________________ Stream Protection Duration POC #1 The Facility PASSED The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0146 9313 7676 82 Pass 0.0153 8277 7099 85 Pass 0.0160 7386 6586 89 Pass 0.0168 6583 6051 91 Pass 0.0175 5863 5525 94 Pass 0.0182 5281 5020 95 Pass 0.0189 4748 4539 95 Pass 0.0196 4282 4094 95 Pass 0.0203 3850 3681 95 Pass 0.0210 3484 3268 93 Pass 0.0218 3148 2892 91 Pass 0.0225 2866 2627 91 Pass 0.0232 2597 2348 90 Pass 0.0239 2334 2097 89 Pass 0.0246 2108 1884 89 Pass 0.0253 1904 1740 91 Pass 0.0260 1729 1549 89 Pass 0.0268 1560 1404 90 Pass 0.0275 1401 1257 89 Pass 0.0282 1261 1171 92 Pass 0.0289 1134 1084 95 Pass 0.0296 1031 1007 97 Pass 0.0303 945 936 99 Pass 0.0310 869 873 100 Pass 0.0318 788 795 100 Pass 0.0325 729 702 96 Pass 0.0332 673 576 85 Pass 0.0339 600 505 84 Pass 0.0346 537 452 84 Pass 0.0353 485 406 83 Pass 0.0360 430 371 86 Pass 0.0368 383 332 86 Pass 0.0375 340 294 86 Pass 0.0382 296 259 87 Pass 0.0389 260 224 86 Pass 0.0396 227 206 90 Pass 0.0403 197 183 92 Pass 0.0410 166 165 99 Pass 0.0418 147 141 95 Pass 0.0425 136 121 88 Pass 0.0432 119 101 84 Pass 0.0439 105 77 73 Pass 0.0446 93 63 67 Pass 0.0453 80 48 60 Pass 0.0460 69 24 34 Pass 0.0468 58 0 0 Pass 0.0475 52 0 0 Pass 0.0482 42 0 0 Pass 0.0489 33 0 0 Pass 0.0496 31 0 0 Pass 0.0503 30 0 0 Pass 0.0510 27 0 0 Pass 0.0518 24 0 0 Pass 0.0525 22 0 0 Pass 0.0532 20 0 0 Pass 0.0539 19 0 0 Pass 0.0546 16 0 0 Pass 0.0553 16 0 0 Pass 0.0560 15 0 0 Pass 0.0568 14 0 0 Pass 0.0575 12 0 0 Pass 0.0582 11 0 0 Pass 0.0589 10 0 0 Pass 0.0596 9 0 0 Pass 0.0603 9 0 0 Pass 0.0610 9 0 0 Pass 0.0618 9 0 0 Pass 0.0625 8 0 0 Pass 0.0632 8 0 0 Pass 0.0639 7 0 0 Pass 0.0646 7 0 0 Pass 0.0653 7 0 0 Pass 0.0660 7 0 0 Pass 0.0668 6 0 0 Pass 0.0675 5 0 0 Pass 0.0682 5 0 0 Pass 0.0689 5 0 0 Pass 0.0696 5 0 0 Pass 0.0703 5 0 0 Pass 0.0710 5 0 0 Pass 0.0718 5 0 0 Pass 0.0725 5 0 0 Pass 0.0732 5 0 0 Pass 0.0739 5 0 0 Pass 0.0746 5 0 0 Pass 0.0753 5 0 0 Pass 0.0760 4 0 0 Pass 0.0768 4 0 0 Pass 0.0775 4 0 0 Pass 0.0782 4 0 0 Pass 0.0789 3 0 0 Pass 0.0796 3 0 0 Pass 0.0803 3 0 0 Pass 0.0810 3 0 0 Pass 0.0818 3 0 0 Pass 0.0825 3 0 0 Pass 0.0832 3 0 0 Pass 0.0839 3 0 0 Pass 0.0846 3 0 0 Pass 0.0853 3 0 0 Pass _____________________________________________________ ___________________________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0.0585 acre-feet On-line facility target flow: 0.0639 cfs. Adjusted for 15 min: 0.0639 cfs. Off-line facility target flow: 0.0357 cfs. Adjusted for 15 min: 0.0357 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 79.57 N 0.00 Total Volume Infiltrated 79.57 0.00 0.00 0.00 0.00 0% No Treat. Credit Compliance with LID Standard 8 Duration Analysis Result = Failed ___________________________________________________________________ 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. 2005-2019; All Rights Reserved. Page | 40 Figure 4.2 – Stormfilter Sizing 11835 NE Glenn Widing Dr., Portland OR 97220 Toll-free: 800.548.4667 Fax: 800.561.1271 ©2012 Contech Engineered Solutions LLC www.conteches.com Page 1 of 1 TS-P026 Size and Cost Estimate Prepared by Renna Esmabe on June 10, 2019 7th Street Short Plat – Stormwater Treatment System Renton, WA Information provided:  Total contributing area = 0.71 acre  Impervious area = 0.37 acre  Water quality flow, Qwq = 0.036 cfs  Peak hydraulic flow rate, Qpeak = <1 cfs  Presiding agency = Renton, WA Assumptions:  Media = ZPG cartridges  Drop required from RIM to outlet = 2.3’ minimum Size and cost estimates: The StormFilter is a flow-based system, and therefore, is sized by calculating the peak water quality flow rate associated with the design storm. The water quality flow rate was calculated by using SBUH and provided to Contech Engineered Solutions LLC. The StormFilter for this site was sized based on treatment flow rate of 0.036 cfs. To accommodate this treatment flow rate, Contech Engineered Solutions recommends using a steel three-cartridge CatchBasin StormFilter (see attached detail). The estimated cost of this size system is $13,900, complete and delivered to the jobsite. The contractor is responsible for setting the CatchBasin StormFilter and all external plumbing. The steel CatchBasin StormFilter has an internal bypass capacity of 1.0 cfs, which does not exceed the peak flows from this site. Project Name:7th Street Short Plat Site Designation:Date:6/10/19 County or Independent City:Renton Designer:RPE State:WA Flow Based Data: Peak Design Flow (cfs) Water Quality Flow (cfs) Annual Rainfall (inches) Total Drainage Area, A (ac) Post Development Impervious Area, AI (ac) Pervious Area, AP (ac) TSS Removal By Pretreatment Agency Required TSS % Removal Required TSS Removal Efficiency of Filter Percent Runoff Capture Mean Annual Runoff, Vt (ft3) Event Mean Concentration of Pollutant, EMC (mg/L) Annual Mass Load, Mtotal (lbs) Flow Based Filter Sizing: Mass to be Captured by System (lbs) Filter Type Structure Type Cartridge Height Media Type Cartridge Flow Rate, gpm/sf Allowable Load Per Cartridge (lbs) Cartridges Required Recommended Model TSS Treatment Capacity (lbs) Maximum Water Quality Flow 44 0.71 0.37 0.036 StormFilter Catchbasin (Steel) 90% 52,971 69.40 3 SFCB3 1.00 gpm/sf ZPG <1 50% 60% 0.34 0.95 0.25 80% 231.34 70 108.00 0.05 cfs 18'' 36 Page | 45 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN The 100-year unmitigated peak flow rate (0.40 cfs) as determined by WWHM stormwater model is used to check the conveyance system. The minimum pipe diameter, material type and slope is as follows: 12-inch ADS N-12 at 0.51 percent. Using LDD’s Manning Calculator, a Mannings Coefficient (n) of 0.012 and the aforementioned pipe parameter results in a full flow rate of 2.75 cfs; therefore, the proposed system has sufficient capacity to convey the 100-year, 15-minute flow rate. Page | 46 Figure 5.1 – LDD Computer Output Manning Pipe Calculator Given Input Data: Shape ........................... Circular Solving for ..................... Flowrate Diameter ........................ 12.0000 in Depth ........................... 10.0000 in Slope ........................... 0.0051 ft/ft Manning's n ..................... 0.0120 Computed Results: Flowrate ........................ 2.7962 cfs Area ............................ 0.7854 ft2 Wetted Area ..................... 0.6994 ft2 Wetted Perimeter ................ 27.6063 in Perimeter ....................... 37.6991 in Velocity ........................ 3.9983 fps Hydraulic Radius ................ 3.6480 in Percent Full .................... 83.3333 % Full flow Flowrate .............. 2.7564 cfs Full flow velocity .............. 3.5095 fps Critical Information Critical depth .................. 8.9556 in Critical slope .................. 0.0064 ft/ft Critical velocity ............... 4.7447 fps Critical area ................... 0.6390 ft2 Critical perimeter .............. 24.7609 in Critical hydraulic radius ....... 3.7162 in Critical top width .............. 12.0000 in Specific energy ................. 1.1043 ft Minimum energy .................. 1.1195 ft Froude number ................... 0.8640 Flow condition .................. Subcritical WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: TESC Site Name: 7th St. SP Site Address: 3605 NE 7th Street City : Renton Report Date: 6/7/2019 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2019/04/13 Version : 4.2.16 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Mod .64 C, Pasture, Mod .04 Pervious Total 0.68 Impervious Land Use acre ROADS MOD 0.03 Impervious Total 0.03 Basin Total 0.71 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Lawn, Flat .31 Pervious Total 0.31 Impervious Land Use acre ROADS FLAT 0.15 ROOF TOPS FLAT 0.15 DRIVEWAYS FLAT 0.08 SIDEWALKS FLAT 0.02 Impervious Total 0.4 Basin Total 0.71 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.68 Total Impervious Area:0.03 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.31 Total Impervious Area:0.4 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.02924 5 year 0.044231 10 year 0.05567 25 year 0.071902 50 year 0.085325 100 year 0.099924 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.172917 5 year 0.227272 10 year 0.265349 25 year 0.315942 50 year 0.35549 100 year 0.396672 ___________________________________________________________________ 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. 2005-2019; All Rights Reserved. Page | 48 6.0 SPECIAL REPORTS AND STUDIES  Geotechnical Report, prepared by ENSW dated September 28, 2018. Page | 49 Figure 6.1 – Geotechnical Engineer’s Report EarthSolutionsNWLLC EarthSolutionsNWLLC 1805 -136th Place N.E.,Suite 201 Bellevue,WA 98005 (425)449-4704 Fax (425)449-4711 www.earthsolutionsnw.com Geotechnical Engineering Construction Observation/Testing Environmental Services GEOTECHNICAL ENGINEERING STUDY PROPOSED SHORT PLAT 3605 NORTHEAST 7 STREET RENTON,WASHINGTON ES-6261 TH Geotechnical Engineering,Construction Observation/Testing and Environmental Services Drwn.CAM Checked CGH Date Sept.2018 Date 09/26/2018 Proj.No.6261 Plate 1 Earth Solutions NWLLCEarthSolutionsNWLLC EarthSolutionsNWLLC Vicinity Map 7th Street Short Plat Renton,Washington Reference: King County,Washington Map 626 By The Thomas Guide Rand McNally 32nd Edition NORTH NOTE:This plate may contain areas of color.ESNW cannot be responsible for any subsequent misinterpretation of the information resulting from black &white reproductions of this plate. SITE Geotechnical Engineering,Construction Observation/Testing and Environmental Services Drwn.CAM Checked CGH Date Sept.2018 Date 09/26/2018 Proj.No.6261 Plate 2 Earth Solutions NWLLCEarthSolutionsNWLLC EarthSolutionsNWLLC n.e.7th street queenavenuen.e.House Garage 400 400 405 405 410 410 TP-1 TP-2 TP-3 TP-4 TP-5 NOTE:This plate may contain areas of color.ESNW cannot be responsible for any subsequent misinterpretation of the information resulting from black &white reproductions of this plate. NOTE:The graphics shown on this plate are not intended for design purposes or precise scale measurements,but only to illustrate the approximate test locations relative to the approximate locations of existing and /or proposed site features.The information illustrated is largely based on data provided by the client at the time of our study.ESNW cannot be responsible for subsequent design changes or interpretation of the data by others. LEGEND Approximate Location of ESNW Test Pit,Proj.No. ES-6261,Aug.2018 Subject Site Existing Building TP-1 NOT -TO -SCALE NORTH Test Pit Location Plan 7th Street Short Plat Renton,Washington Drwn.CAM Checked CGH Date Sept.2018 Date 09/26/2018 Proj.No.6261 Plate 3 Earth Solutions NWLLCEarthSolutionsNWLLC EarthSolutionsNWLLC Geotechnical Engineering,Construction Observation/Testing and Environmental Services Retaining Wall Drainage Detail 7th Street Short Plat Renton,Washington NOTES: Free-draining Backfill should consist of soil having less than 5 percent fines. Percent passing No.4 sieve should be 25 to 75 percent. Sheet Drain may be feasible in lieu of Free-draining Backfill,per ESNW recommendations. Drain Pipe should consist of perforated, rigid PVC Pipe surrounded with 1-inch Drain Rock. LEGEND: Free-draining Structural Backfill 1-inch Drain Rock 18"Min. Structural Fill Perforated Rigid Drain Pipe (Surround in Drain Rock) SCHEMATIC ONLY -NOT TO SCALE NOT A CONSTRUCTION DRAWING Drwn.CAM Checked CGH Date Sept.2018 Date 09/26/2018 Proj.No.6261 Plate 4 Earth Solutions NWLLCEarthSolutionsNWLLC EarthSolutionsNWLLC Geotechnical Engineering,Construction Observation/Testing and Environmental Services Footing Drain Detail 7th Street Short Plat Renton,Washington Slope Perforated Rigid Drain Pipe (Surround in Drain Rock) 18"Min. NOTES: Do NOT tie roof downspouts to Footing Drain. Surface Seal to consist of 12"of less permeable,suitable soil.Slope away from building. LEGEND: Surface Seal:native soil or other low-permeability material. 1-inch Drain Rock SCHEMATIC ONLY -NOT TO SCALE NOT A CONSTRUCTION DRAWING Page | 81 7.0 OTHER PERMITS The following permits and/or approvals are thought to be required as part of this project:  Postmaster Approval  Grading permit  Right of Way Permit Page | 82 8.0 CSWPP ANALYSIS AND DESIGN TESC measures are put into place to prevent sediment from leaving the site. The proposed TESC plan, Construction Pollution Prevention Plan, includes and is not limited to the following guidelines set in the Manual and the City Amendments to Appendix D of the 2016 King County Surface Water Design Manual in order to comply with Core Requirement No. 5. Clearing Limits – The clearing limits are on the engineering plans and will be flagged in the field. Cover Measures – Cover measures are specified on the TESC plan set and will be implemented in the field as necessary. These cover measures include mulching, temporary seeding, and plastic covering. Perimeter Protection –The silt fence and clearing limits will be shown on the TESC plans and implemented in the field. The silt fence is placed on the downslope side of the property. During construction no runoff shall leave the site. Traffic Area Stabilization – Traffic area stabilization will be addressed by a stabilized construction entrance. Sediment Retention – Retention will be established by silt fences around the perimeter and catch basin inserts that will control of the on-site sediment-laden water. Dust Control – Dust control by splinklering will be provided as needed. Wet Season Construction: Infrastructure construction will be conducted in the summer months. Any construction planned during the wet season will be according to King County and the City of Renton standards. Construction Within Sensitive Areas and Buffers: There are no onsite sensitive areas or buffers. Maintenance: Maintenance requirements are detailed in the TESC notes on the engineering plans. Final Stabilization: Upon completion of the project, all disturbed areas will be stabilized and Best Management Practices removed if appropriate. Page | 84 9.0 BOND QUANTITIES The City of Renton Bond Quantity Worksheet will be included along with the final engineering plan submittal. Page | 85 10.0 OPERATIONS AND MAINTENANCE MANUAL The drainage facilities on this project will be maintained by the homeowners. Maintenance instructions will be provided along with the final engineering plan submittal.