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C.E.S. NW Inc. Civil Engineering & Surveying TECHNICAL INFORMATION REPORT FOR 7 TH STREET SHORT PLAT A PRIL 2021 PREPARED FOR: JAGADESHWAR G ATTU 14716 NE 76TH STREET R ENTON, WA 98052 PREPARED BY: ERIC OEHLER, PROJECT MANAGER C.E.S. NW, I NC. 429 29TH STREET NE, SUITE D PUYALLUP, WA 98372 (253) 848-4282 DEVELOPMENT ENGINEERING Nathan Janders 05/25/2021 SURFACE WATER UTILITY jfarah 05/25/2021 TE CHINICAL INFORMATIOI\ REPORTFOR7th Street Short PlatRenton, 'WashingtonJuly 2020Revised September 2020Revised April 2021Prepared for:Jagadeshwar Gattu14716 NE 76tn streetRedmond, WA 98052Prepared by:Eric Oehler, Project ManagerReviewed By:Fred Brown, P.E., Senior Project Manager,úpLl4ttTtoREPORT #17234 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 .............................................................................................. 24 3.0 OFF-SITE ANALYSIS ................................................................................................................... 26 3.1 Study Area Definition and Maps ................................................................................................ 26 3.2 Resource Review ........................................................................................................................ 26 3.3 Drainage System Description and Problem Descriptions ........................................................... 27 3.4 Mitigation of Existing or Potential Problems .............................................................................. 27 4.0 STORMWATER ANALYSIS AND DESIGN ............................................................................... 35 4.1 Existing Site Hydrology .............................................................................................................. 35 4.2 Developed Site Hydrology .......................................................................................................... 36 4.3 Performance Standards ............................................................................................................... 37 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 – Conveyance Calculations ..................................................................................................... 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 at 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 rectangular in shape and contains an existing single-family residence and detached garage along with a gravel driveway that is accessed from NE 7th Street. Both the existing house and detached garage will be removed as part of site construction. The remainder of the site is mostly covered in grass with some bushes/shrubs located along the west boundary line. There is one fir tree located onsite along with two fir trees and one maple tree that are located along the north boundary line and just inside of the existing NE 7th Street right of way. All existing trees will be removed during site construction. The site generally 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 NE 7th Street with single-family residences 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 nor limited infiltration is feasible. The project proposes the construction of 3 lots for single-family residences, 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 in the East Lake Washington-Renton Drainage Basin resulting in 0.45 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 cement concrete detention vault and CONTECH catch basin stormfilter are proposed for flow control and water quality treatment, respectively. 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) WORKSHEETl, or a civil engineer under my supervision, 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 information provided here is accurate.Signed/DatePa¡t17 SIGNATURE OF PROFESSIONAL ENGINEER12il2/20t68-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 SITE Page | 10 Figure 1.3 – Pre-developed Basin Map Page | 11 Figure 1.4 – Developed Basin Maps 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 flow path 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 fishponds. Response: Historically, runoff from the site sheet flows in a southwesterly direction and the overflow likely flows into the existing storm drainage system located within NE 6th Court and Pierce Place NE. The project proposes to control its runoff with the use of a detention vault centrally located within the site. Discharge from the detention vault will exit the site near the southwest corner within a below ground tightlined storm drainage system consisting of storm structures and storm pipes. The proposed storm drainage system will cross the adjacent parcels south of the site within a proposed 15-ft. wide private storm drainage easement before discharging into the existing storm drainage system located in NE 7th Place. The following table summarizes the basin areas and stormwater flows: Existing Basin Area (Acres) 1.03 Developed Basin Area (Acres) 1.03 100-year Predeveloped Flow Rate (CFS) 0.23 100-year Developed Flow Rate (CFS) 0.09 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 Page | 20 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). Response: The project is proposing to detain all stormwater runoff from the developed site and release runoff at pre-developed rates and durations based on a forested cover condition of the site. Stormwater runoff from the frontage improvements will not be conveyed to the proposed detention vault however this area has been accounted for in its design as a bypass basin. 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 a privately owned storm drainage system. The proposed storm drainage system will be a below ground tightlined system consisting of storm structures and storm pipes. The proposed onsite storm drainage system and the proposed storm drainage system crossing the adjacent parcels to the south will be private. The private storm drainage system will consist of storm structures, storm pipes, detention vault, and catch basin stormfilter. The proposed private storm drainage system will collect and convey stormwater runoff from the developed site to the proposed detention vault prior to ultimately discharging to the existing storm Page | 21 drainage system located in NE 7th Place. The conveyance system is sized to convey the 100-year developed peak flow analyzed using the Rational Method 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 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 has been prepared as part of the civil 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 has been provided. 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. Page | 22 Response: Bond Quantities have been provided along with the formal civil construction 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 to construct approximately 0.19 acres of new onsite pollution generating impervious surfaces (PGIS). A catch basin stormfilter with one (1) 27” ZPG cartridge will be provided upstream of the detention vault for basic water quality treatment. 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 will create lots that are smaller than 22,000 sq. ft., therefore, small lot BMP requirements apply. 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. Page | 23 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: 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: Perforated Pipe Connection BMP was deemed infeasible due to the low infiltration capacity of onsite soils according to the onsite soil infiltration tests shown in geotechnical report. Page | 24 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. 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. Page | 25 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 | 26 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 conditions, stormwater from a portion of the south side of NE 7th Street flows to the site along the north property line, which sheet flows to the existing landscape area. Under the developed condition, stormwater from the frontage improvement areas (i.e., roadway, sidewalk, landscape) will be collected by the proposed curb and gutter and conveyed to the west approximately 115 feet where it will be collected by an existing catch basin. 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 | 27 Erosion and Landslide Maps: As shown in the sensitive area map, a small moderate slope area exists in the southern portion of the site. Temporary erosion control and a permanent 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 conditions, the project is proposing to detain all stormwater runoff from the developed onsite area 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. Stormwater runoff 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 continues to flow 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 having 8,000 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 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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 PRELIMINARY 9/15/2017 SITE 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 SITE 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 SITE A B C D E F G 1/4 Miles downstream Page | 35 4.0 STORMWATER ANALYSIS AND DESIGN 4.1 Existing Site Hydrology The existing site is rectangular in shape, covered with mostly grass, a few trees, and sporadic areas of bushes/shrubs. 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 side 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 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. There is approximately 0.35 acres of offsite area that is contributory to the proposed onsite storm drainage systems. This area has been accounted for in the sizing of the detention vault, water quality treatment device, and conveyance calculations. 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 (offsite – bypass) C, Lawn, Mod 0.03 Driveway (offsite – bypass) Roads/Mod 0.01 Grass (offsite – contributory) C, Lawn, Flat 0.31 Roofs (offsite – contributory) Roof Tops/Flat 0.04 Total 1.03 Table 4.1- Pre-Developed Basin Summary The 15-minutes pre-developed peak flows for the existing basin (1.03-acre) are as follows (from WWHM report attached): Q2= 0.060-cfs Q10= 0.122-cfs Q25= 0.161-cfs Q100= 0.229-cfs Page | 36 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, private access, detention vault, utilities, driveways, sidewalks, landscaping, and 3 single-family residences. Frontage improvements include curb, gutter, 8-foot landscape planter, and 5-foot sidewalk on the south side of NE 7th Street. The total disturbed area will cover approximately 0.68 acres both onsite and offsite. As previously mentioned, there is approximately 0.35 acres of offsite area that is contributory to the proposed onsite storm drainage systems. As a result, this area has been accounted for in the sizing of the detention vault, water quality treatment device, and conveyance calculations. Upon completion of the project, impervious surfaces covering the site include approximately 0.12-acre of private access road, 0.07-acre of driveways, 0.04-acre of sidewalks, etc. and 0.19- 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 Landscape C, Pasture, Flat 0.22 Private Access Road Roads/Flat 0.12 Roof Surfaces Roof Tops/Flat 0.19 Driveways Driveways/Flat 0.07 Sidewalks Sidewalks/Flat 0.04 Grass (offsite – contributory) C, Lawn, Flat 0.31 Roofs (offsite – contributory) Roof Tops/Flat 0.04 Total 0.99 Area WWHM Land-use Acres Landscape (offsite – bypass) C, Pasture, Mod 0.01 Road (offsite – bypass) Roads/Mod 0.01 Sidewalk (offsite – bypass) Sidewalk/Mod 0.02 Total 0.04 Table 4.2- Post Developed Basin Summary The 15-minutes post-developed peak flows for the developed onsite basin (0.99-acre) are as follows (WWHM report): Q2= 0.035 cfs Q10= 0.057 cfs Page | 37 Q25= 0.070 cfs Q100= 0.092 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). 4.4 Water Quality System The project proposes to construct approximately 0.19 acre of new onsite pollution generating impervious surfaces (PGIS). A catch basin stormfilter with one (1) 27” ZPG cartridge will be provided upstream of the detention vault for basic water quality treatment. Page | 39 Figure 4.1 – WWHM reports WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: 7th Street Short Plat Site Name: Detention Vault Sizing Calculation Site Address: City: Report Date: 11/4/2020 Gage: Seatac Data Start: 1948/10/01 Data End: 2009/09/30 Precip Scale: 1.00 Version Date: 2019/09/13 Version: 4.2.17 ___________________________________________________________________ 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, Lawn, Flat .31 C, Lawn, Mod .03 Pervious Total 0.98 Impervious Land Use acre ROADS MOD 0.01 ROOF TOPS FLAT 0.04 Impervious Total 0.05 Basin Total 1.03 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name: Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Pasture, Flat .22 C, Lawn, Flat .31 Pervious Total 0.53 Impervious Land Use acre ROADS FLAT 0.12 ROOF TOPS FLAT 0.23 DRIVEWAYS FLAT 0.07 SIDEWALKS FLAT 0.04 Impervious Total 0.46 Basin Total 0.99 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Vault 1 Vault 1 ___________________________________________________________________ Name: Vault 1 Width: 20 ft. Length: 40 ft. Depth: 11 ft. Discharge Structure Riser Height: 10 ft. Riser Diameter: 18 in. Orifice 1 Diameter: 0.6875 in. Elevation: 0 ft. Orifice 2 Diameter: 0.625 in. Elevation: 5.6 ft. Orifice 3 Diameter: 0.5 in. Elevation: 6.8 ft. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Vault Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.018 0.000 0.000 0.000 0.1222 0.018 0.002 0.004 0.000 0.2444 0.018 0.004 0.006 0.000 0.3667 0.018 0.006 0.007 0.000 0.4889 0.018 0.009 0.009 0.000 0.6111 0.018 0.011 0.010 0.000 0.7333 0.018 0.013 0.011 0.000 0.8556 0.018 0.015 0.011 0.000 0.9778 0.018 0.018 0.012 0.000 1.1000 0.018 0.020 0.013 0.000 1.2222 0.018 0.022 0.014 0.000 1.3444 0.018 0.024 0.014 0.000 1.4667 0.018 0.026 0.015 0.000 1.5889 0.018 0.029 0.016 0.000 1.7111 0.018 0.031 0.016 0.000 1.8333 0.018 0.033 0.017 0.000 1.9556 0.018 0.035 0.017 0.000 2.0778 0.018 0.038 0.018 0.000 2.2000 0.018 0.040 0.019 0.000 2.3222 0.018 0.042 0.019 0.000 2.4444 0.018 0.044 0.020 0.000 2.5667 0.018 0.047 0.020 0.000 2.6889 0.018 0.049 0.021 0.000 2.8111 0.018 0.051 0.021 0.000 2.9333 0.018 0.053 0.022 0.000 3.0556 0.018 0.056 0.022 0.000 3.1778 0.018 0.058 0.022 0.000 3.3000 0.018 0.060 0.023 0.000 3.4222 0.018 0.062 0.023 0.000 3.5444 0.018 0.065 0.024 0.000 3.6667 0.018 0.067 0.024 0.000 3.7889 0.018 0.069 0.025 0.000 3.9111 0.018 0.071 0.025 0.000 4.0333 0.018 0.074 0.025 0.000 4.1556 0.018 0.076 0.026 0.000 4.2778 0.018 0.078 0.026 0.000 4.4000 0.018 0.080 0.026 0.000 4.5222 0.018 0.083 0.027 0.000 4.6444 0.018 0.085 0.027 0.000 4.7667 0.018 0.087 0.028 0.000 4.8889 0.018 0.089 0.028 0.000 5.0111 0.018 0.092 0.028 0.000 5.1333 0.018 0.094 0.029 0.000 5.2556 0.018 0.096 0.029 0.000 5.3778 0.018 0.098 0.029 0.000 5.5000 0.018 0.101 0.030 0.000 5.6222 0.018 0.103 0.032 0.000 5.7444 0.018 0.105 0.034 0.000 5.8667 0.018 0.107 0.036 0.000 5.9889 0.018 0.110 0.038 0.000 6.1111 0.018 0.112 0.039 0.000 6.2333 0.018 0.114 0.040 0.000 6.3556 0.018 0.116 0.041 0.000 6.4778 0.018 0.119 0.042 0.000 6.6000 0.018 0.121 0.043 0.000 6.7222 0.018 0.123 0.044 0.000 6.8444 0.018 0.125 0.046 0.000 6.9667 0.018 0.127 0.049 0.000 7.0889 0.018 0.130 0.050 0.000 7.2111 0.018 0.132 0.052 0.000 7.3333 0.018 0.134 0.053 0.000 7.4556 0.018 0.136 0.055 0.000 7.5778 0.018 0.139 0.056 0.000 7.7000 0.018 0.141 0.057 0.000 7.8222 0.018 0.143 0.058 0.000 7.9444 0.018 0.145 0.059 0.000 8.0667 0.018 0.148 0.060 0.000 8.1889 0.018 0.150 0.061 0.000 8.3111 0.018 0.152 0.062 0.000 8.4333 0.018 0.154 0.063 0.000 8.5556 0.018 0.157 0.064 0.000 8.6778 0.018 0.159 0.065 0.000 8.8000 0.018 0.161 0.066 0.000 8.9222 0.018 0.163 0.067 0.000 9.0444 0.018 0.166 0.068 0.000 9.1667 0.018 0.168 0.069 0.000 9.2889 0.018 0.170 0.070 0.000 9.4111 0.018 0.172 0.071 0.000 9.5333 0.018 0.175 0.071 0.000 9.6556 0.018 0.177 0.072 0.000 9.7778 0.018 0.179 0.073 0.000 9.9000 0.018 0.181 0.074 0.000 10.022 0.018 0.184 0.127 0.000 10.144 0.018 0.186 0.944 0.000 10.267 0.018 0.188 2.200 0.000 10.389 0.018 0.190 3.587 0.000 10.511 0.018 0.193 4.815 0.000 10.633 0.018 0.195 5.671 0.000 10.756 0.018 0.197 6.239 0.000 10.878 0.018 0.199 6.719 0.000 11.000 0.018 0.202 7.167 0.000 11.122 0.018 0.204 7.589 0.000 11.244 0.000 0.000 7.988 0.000 ___________________________________________________________________ Name: Basin 2 Bypass: Yes GroundWater: No Pervious Land Use acre C, Pasture, Mod .01 Pervious Total 0.01 Impervious Land Use acre ROADS MOD 0.01 SIDEWALKS MOD 0.02 Impervious Total 0.03 Basin Total 0.04 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.98 Total Impervious Area:0.05 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.54 Total Impervious Area:0.49 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.059521 5 year 0.094657 10 year 0.121881 25 year 0.160852 50 year 0.193268 100 year 0.228641 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.03505 5 year 0.047454 10 year 0.056717 25 year 0.069675 50 year 0.080281 100 year 0.091739 ___________________________________________________________________ Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.098 0.033 1950 0.108 0.034 1951 0.079 0.069 1952 0.037 0.027 1953 0.027 0.027 1954 0.045 0.029 1955 0.057 0.033 1956 0.058 0.037 1957 0.070 0.035 1958 0.040 0.029 1959 0.037 0.027 1960 0.079 0.060 1961 0.053 0.032 1962 0.024 0.023 1963 0.051 0.030 1964 0.056 0.032 1965 0.068 0.031 1966 0.037 0.026 1967 0.109 0.038 1968 0.061 0.034 1969 0.055 0.030 1970 0.051 0.030 1971 0.067 0.036 1972 0.092 0.046 1973 0.033 0.028 1974 0.061 0.030 1975 0.077 0.037 1976 0.055 0.031 1977 0.037 0.025 1978 0.045 0.029 1979 0.035 0.028 1980 0.129 0.047 1981 0.045 0.031 1982 0.112 0.062 1983 0.049 0.033 1984 0.037 0.026 1985 0.042 0.029 1986 0.073 0.048 1987 0.072 0.053 1988 0.028 0.026 1989 0.023 0.023 1990 0.232 0.062 1991 0.145 0.064 1992 0.049 0.031 1993 0.034 0.027 1994 0.021 0.021 1995 0.048 0.033 1996 0.122 0.068 1997 0.080 0.064 1998 0.050 0.034 1999 0.160 0.043 2000 0.055 0.029 2001 0.029 0.031 2002 0.082 0.048 2003 0.086 0.033 2004 0.110 0.077 2005 0.064 0.034 2006 0.064 0.033 2007 0.203 0.076 2008 0.154 0.084 2009 0.089 0.044 ___________________________________________________________________ Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.2322 0.0843 2 0.2028 0.0767 3 0.1598 0.0763 4 0.1536 0.0692 5 0.1451 0.0680 6 0.1291 0.0641 7 0.1217 0.0640 8 0.1119 0.0619 9 0.1101 0.0617 10 0.1095 0.0595 11 0.1080 0.0526 12 0.0978 0.0477 13 0.0925 0.0476 14 0.0890 0.0470 15 0.0863 0.0460 16 0.0819 0.0437 17 0.0798 0.0427 18 0.0788 0.0378 19 0.0786 0.0373 20 0.0775 0.0371 21 0.0729 0.0362 22 0.0715 0.0347 23 0.0698 0.0341 24 0.0682 0.0340 25 0.0672 0.0340 26 0.0641 0.0338 27 0.0635 0.0335 28 0.0613 0.0334 29 0.0606 0.0333 30 0.0582 0.0332 31 0.0568 0.0329 32 0.0560 0.0328 33 0.0553 0.0323 34 0.0546 0.0319 35 0.0546 0.0315 36 0.0527 0.0315 37 0.0514 0.0314 38 0.0514 0.0310 39 0.0498 0.0305 40 0.0494 0.0303 41 0.0486 0.0302 42 0.0477 0.0302 43 0.0454 0.0298 44 0.0451 0.0293 45 0.0447 0.0290 46 0.0419 0.0288 47 0.0402 0.0288 48 0.0374 0.0287 49 0.0373 0.0283 50 0.0371 0.0279 51 0.0369 0.0274 52 0.0368 0.0273 53 0.0348 0.0271 54 0.0339 0.0265 55 0.0330 0.0263 56 0.0288 0.0257 57 0.0275 0.0257 58 0.0274 0.0253 59 0.0244 0.0232 60 0.0227 0.0228 61 0.0206 0.0213 ___________________________________________________________________ Stream Protection Duration POC #1 The Facility PASSED The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0298 5330 4481 84 Pass 0.0314 4569 3508 76 Pass 0.0331 3972 3071 77 Pass 0.0347 3407 2774 81 Pass 0.0364 2926 2520 86 Pass 0.0380 2528 2286 90 Pass 0.0397 2182 2082 95 Pass 0.0413 1916 1833 95 Pass 0.0430 1666 1574 94 Pass 0.0446 1457 1320 90 Pass 0.0463 1263 1148 90 Pass 0.0479 1136 1045 91 Pass 0.0496 1000 945 94 Pass 0.0512 880 845 96 Pass 0.0529 768 745 97 Pass 0.0545 672 661 98 Pass 0.0562 562 563 100 Pass 0.0578 486 449 92 Pass 0.0595 417 370 88 Pass 0.0611 355 304 85 Pass 0.0628 310 258 83 Pass 0.0644 269 209 77 Pass 0.0661 231 161 69 Pass 0.0677 202 123 60 Pass 0.0694 180 87 48 Pass 0.0711 161 46 28 Pass 0.0727 147 22 14 Pass 0.0744 126 9 7 Pass 0.0760 110 5 4 Pass 0.0777 99 2 2 Pass 0.0793 87 1 1 Pass 0.0810 81 1 1 Pass 0.0826 75 1 1 Pass 0.0843 71 1 1 Pass 0.0859 68 0 0 Pass 0.0876 64 0 0 Pass 0.0892 56 0 0 Pass 0.0909 52 0 0 Pass 0.0925 49 0 0 Pass 0.0942 46 0 0 Pass 0.0958 43 0 0 Pass 0.0975 41 0 0 Pass 0.0991 37 0 0 Pass 0.1008 36 0 0 Pass 0.1024 33 0 0 Pass 0.1041 30 0 0 Pass 0.1057 30 0 0 Pass 0.1074 27 0 0 Pass 0.1090 24 0 0 Pass 0.1107 21 0 0 Pass 0.1123 19 0 0 Pass 0.1140 17 0 0 Pass 0.1156 16 0 0 Pass 0.1173 16 0 0 Pass 0.1189 16 0 0 Pass 0.1206 16 0 0 Pass 0.1222 15 0 0 Pass 0.1239 14 0 0 Pass 0.1256 14 0 0 Pass 0.1272 13 0 0 Pass 0.1289 13 0 0 Pass 0.1305 12 0 0 Pass 0.1322 11 0 0 Pass 0.1338 11 0 0 Pass 0.1355 10 0 0 Pass 0.1371 10 0 0 Pass 0.1388 10 0 0 Pass 0.1404 8 0 0 Pass 0.1421 8 0 0 Pass 0.1437 8 0 0 Pass 0.1454 7 0 0 Pass 0.1470 6 0 0 Pass 0.1487 6 0 0 Pass 0.1503 6 0 0 Pass 0.1520 6 0 0 Pass 0.1536 5 0 0 Pass 0.1553 5 0 0 Pass 0.1569 5 0 0 Pass 0.1586 5 0 0 Pass 0.1602 4 0 0 Pass 0.1619 4 0 0 Pass 0.1635 4 0 0 Pass 0.1652 4 0 0 Pass 0.1668 3 0 0 Pass 0.1685 3 0 0 Pass 0.1701 3 0 0 Pass 0.1718 2 0 0 Pass 0.1734 2 0 0 Pass 0.1751 2 0 0 Pass 0.1768 2 0 0 Pass 0.1784 2 0 0 Pass 0.1801 2 0 0 Pass 0.1817 2 0 0 Pass 0.1834 2 0 0 Pass 0.1850 2 0 0 Pass 0.1867 2 0 0 Pass 0.1883 2 0 0 Pass 0.1900 2 0 0 Pass 0.1916 2 0 0 Pass 0.1933 2 0 0 Pass ___________________________________________________________________ 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. 2005-2020; All Rights Reserved. Page | 40 Figure 4.2 – Stormfilter Sizing WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: 7th Street Short Plat Site Name: Stormfilter #1 Water Quality Calculation (CB Stormfilter) Site Address: City: Report Date: 9/11/2020 Gage: Seatac Data Start: 1948/10/01 Data End: 2009/09/30 Precip Scale: 1.00 Version Date: 2019/09/13 Version: 4.2.17 ___________________________________________________________________ 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, Flat .78 Pervious Total 0.78 Impervious Land Use acre Impervious Total 0 Basin Total 0.78 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name: Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Pasture, Flat .2 C, Lawn, Flat .31 Pervious Total 0.51 Impervious Land Use acre ROADS FLAT 0.12 ROOF TOPS FLAT 0.04 DRIVEWAYS FLAT 0.07 SIDEWALKS FLAT 0.04 Impervious Total 0.27 Basin Total 0.78 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.78 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.51 Total Impervious Area:0.27 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.022933 5 year 0.036017 10 year 0.043432 25 year 0.051287 50 year 0.056148 100 year 0.060282 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.128666 5 year 0.174349 10 year 0.207108 25 year 0.251445 50 year 0.286667 100 year 0.323813 ___________________________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0.0495 acre-feet On-line facility target flow: 0.0449 cfs. Adjusted for 15 min: 0.0449 cfs. Off-line facility target flow: 0.0248 cfs. Adjusted for 15 min: 0.0248 cfs. ___________________________________________________________________ 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. 2005-2020; All Rights Reserved. Size and Cost Estimate 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-P027 Prepared by Renna Esmabe on September 17, 2020 7th Street Short Plat – Stormwater Treatment System Renton, WA Information provided: Total contributing area = 0.78 ac Impervious area = 0.27 ac Water quality flow, Qwq = 0.0248 cfs Peak hydraulic flow rate, Qpeak = 0.32 cfs Presiding agency = City of Renton, WA Assumptions: Media = ZPG cartridge Cartridge flow rate = 11.25 gpm Drop required from inlet to outlet = 3.05’ minimum Size and cost estimates: The StormFilter is a flow-based system, and is therefore sized by calculating the peak water quality flow rate associated with the design storm. The water quality flow rate was calculated by the consulting engineer using WWHM and was provided to Contech Engineered Solutions LLC for the purposes of developing this estimate. Contech has reviewed and determined that the offline WQ flow rate is representative of the 91% runoff volume that is required for basic treatment. The StormFilter for this site was sized based on a water quality flow rate of 0.0248 cfs. To accommodate this flow rate, Contech Engineered Solutions recommends using a 1-cartridge StormFilter catch basin unit. The estimated cost of this system is approximately $11,100 complete and delivered to the job site. This estimate assumes that the unit follows the standard design. Typically the steel StormFilter catch basin units have internal bypass capacities of 1.0 cfs. If the peak discharge off the site is expected to exceed this rate, we recommend placing a high-flow bypass upstream of the StormFilter system. Contech Engineered Solutions could provide our high-flow bypass, the StormGate, which provides a combination weir-orifice control structure to limit the flow to the StormFilter. The estimated cost of this structure is $4,000. The final cost would depend on the actual depth and size of the unit. CONTECH Stormwater Solutions Inc. Engineer: Date 9/17/2020 Site Information StormFilter #1 Project Name 7th Street Short Plat Project State Washington Project Location Renton Drainage Area, Ad 0.78 ac Impervious Area, Ai 0.27 ac Pervious Area, Ap 0.51 % Impervious 35% Runoff Coefficient, Rc 0.36 Water quality flow 0.02 cfs Peak storm flow 0.32 cfs Filter System Filtration brand StormFilter Cartridge height 27 in Specific Flow Rate 1.00 gpm/ft2 Flow rate per cartridge 11.3 gpm SUMMARY Number of Cartridges 1 Determining Number of Cartridges for Flow Based Systems ©2006 CONTECH Stormwater Solutions contechstormwater.com 1 of 1 Page | 45 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN The 100-year unmitigated peak flow rate (1.71 cfs) as determined by the Rational Method has been used to check the conveyance system. The minimum pipe diameter, material type and slope are as follows: 12-inch ADS N-12 at 0.50 percent. Using a Mannings Coefficient (n) of 0.012 and the aforementioned pipe parameter results in a full flow rate of 1.73 cfs at a flow depth of 0.64-feet. Therefore, the proposed conveyance system has sufficient capacity to convey the flow produced by the 100-year, 24-hour storm event. Page | 46 Figure 5.1 – Conveyance Calculations 3.2.1 RATIONAL METHOD FIGURE 3.2.1.D 100-YEAR 24-HOUR ISOPLUVIALS 2016 Surface Water Design Manual 6/15/2016 3-19 3.2.1 RATIONAL METHOD TABLE 3.2.1.A RUNOFF COEFFICIENTS - "C" VALUES FOR THE RATIONAL METHOD General Land Covers Single Family Residential Areas* Land Cover C Land Cover Density C Dense forest Light forest Pasture Lawns Playgrounds Gravel areas Pavement and roofs Open water (pond, lakes, wetlands) 0.10 0.15 0.20 0.25 0.30 0.80 0.90 1.00 0.20 DU/GA (1 unit per 5 ac.) 0.40 DU/GA (1 unit per 2.5 ac.) 0.80 DU/GA (1 unit per 1.25 ac.) 1.00 DU/GA 1.50 DU/GA 2.00 DU/GA 2.50 DU/GA 3.00 DU/GA 3.50 DU/GA 4.00 DU/GA 4.50 DU/GA 5.00 DU/GA 5.50 DU/GA 6.00 DU/GA 0.17 0.20 0.27 0.30 0.33 0.36 0.39 0.42 0.45 0.48 0.51 0.54 0.57 0.60 * Based on average 2,500 square feet per lot of impervious coverage. For combinations of land covers listed above, an area-weighted "Cc x At" sum should be computed based on the equation Cc x At = (C1 x A1) + (C2 x A2) + ...+(Cn x An), where A8 = (A1 + A2 + ...+An), the total drainage basin area. TABLE 3.2.1.B COEFFICIENTS FOR THE RATIONAL METHOD "iR" EQUATION Design Storm Return Frequency aR bR 2 years 5 years 10 years 25 years 50 years 100 years 1.58 2.33 2.44 2.66 2.75 2.61 0.58 0.63 0.64 0.65 0.65 0.63 TABLE 3.2.1.C kR VALUES FOR Tt USING THE RATIONAL METHOD Land Cover Category kR Forest with heavy ground litter and meadow 2.5 Fallow or minimum tillage cultivation 4.7 Short grass pasture and lawns 7.0 Nearly bare ground 10.1 Grassed waterway 15.0 Paved area (sheet flow) and shallow gutter flow 20.0 2016 Surface Water Design Manual 4/24/2016 3-15 Rational Method - 100 Year Storm Event Total Conveyance Basin Area = 0.99 Acres Storm Event 100 yr Precip (Pr)3.9 Area Basin area 0.46 AC 0.31 AC 0.22 AC C Table 3.2.1A 0.9 0.25 0.2 ar Table 3.2.1B 2.61 2.61 2.61 br Table 3.2.1B 0.63 0.63 0.63 Tc Time of concentraton 6.3 6.3 6.3 ir ar*Tc^(-br) 0.82 0.82 0.82 Ir Pr x ir 3.19 3.19 3.19 Total Q C x Ir x A 1.32 cfs 0.25 cfs 0.14 cfs 1.71 cfs 12" Storm Pipe @ 0.50% (Flattest slope of the 12" storm pipes that conveys entire total conveyance basin) Flow Capacity Calcs. (manning's) Bold Numbers entered directly Pipe Dia. (D)12.00 " 12.00 " 12.00 " Manning's n (n)0.014 0.012 0.014 Slope (S)0.50% 0.50% 0.50% Depth (Y)1.00' 1.00' 0.64' Qactual 2.34 cfs 2.73 cfs 1.73 cfs Vactual 2.979 fps 3.475 fps 3.260 fps 12" Storm Pipe @ 0.50%. Flattest 12" storm pipe that conveys entire 0.99 acre developed conveyance basin. Q = 1.486/ n x R x S 2/3 1/2 Filename GENERAL.xls Tab Pipe Flows 9/18/2020 1:10 PM > 1.71 CFS (100-yr. 24-hr. Storm Event) 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 15365 N.E. 90th Street, Suite 100 • Redmond, WA 98052 • (425) 449-4704 • FAX (425) 449-4711 Earth Solutions NW LLC Geotechnical Engineering, Construction Observation/Testing and Environmental Services July 16, 2020 ES-6261.01 Kalapas Homes, LLC 14716 Northeast 76th Street Redmond, Washington 98052 Attention: Mr. Pavan Narkulla Subject: Detention Vault Design Recommendations Proposed Residential Short Plat 3605 Northeast 7th Street Renton, Washington Reference: Earth Solutions NW, LLC Geotechnical Engineering Study Project No. ES-6261, dated September 28, 2018 CES NW, Inc. Project No. 17234, dated June 30, 2020 Private Access Tract “A” Plan & Profile, Sheet C7 Stormwater Detention Vault Plan & Sections, Sheet C9 Water Main Extension and Side Sewer Plan, Sheet C11 Dear Mr. Narkulla: Earth Solutions NW, LLC (ESNW) has prepared this geotechnical evaluation letter to provide detention vault design parameters for the proposed short plat. This letter was prepared in general accordance with our proposal (PSA-6261.01) dated June 22, 2020 and authorized by you on June 25, 2020. Project Description The subject site is located southeast of the Northeast 7th Street and Pierce Place Northeast intersection, in Renton, Washington. Proposed redevelopment plans include construction of single-family homes sites and related infrastructure improvements. We understand that a stormwater detention vault (vault) will be constructed in the central site area. Review of the referenced plan sets indicate grade cuts of about 16 feet will be required to achieve design subgrade elevations for the vault. If the above design assumptions are incorrect or change, ESNW should be contacted to review the recommendations provided in this letter. ESNW should review final designs to confirm that our geotechnical recommendations have been incorporated into final site plans. Kalapas Homes, LLC ES-6261.01 July 16, 2020 Page 2 Earth Solutions NW, LLC Subsurface Conditions Topsoil was generally encountered in the upper 4 to 12 inches of existing grades at the test pit locations. Fill was encountered at TP-5 during our August 2018 exploration and was characterized as silty sand in a medium dense and damp condition, extending to an exposure depth of about three feet below the ground surface (bgs). Underlying topsoil and local fill, native soils were primarily classified as silty sand with gravel (USCS: SM), consistent with the typical makeup of glacial till deposits. The silty sand was characterized as loose to medium dense in the upper three to six feet of existing grades. Thereafter, the native soil was encountered in a dense to very dense conditions, extending to the maximum exploration depth of about eight-and-one-half feet bgs. In general, native soils were encountered in a damp to moist condition. Groundwater Perched groundwater seepage was not encountered during our August 2018 exploration. Perched seepage zones are common within glacial deposits and may develop and subside with changing rainfall patterns and amounts. On this basis, groundwater intrusion may be encountered within the vault excavation. Groundwater seepage rates and elevations fluctuate depending on many factors, including precipitation duration and intensity, the time of year, and soil conditions. In general, groundwater flow rates are higher during the wetter, winter months. The contractor must be prepared to manage groundwater entering the excavation. Detention Vault Recommendations With respect to detention vault construction, competent support conditions for the proposed vault foundation are likely to be provided within the dense to very dense portion of the encountered glacial till deposit. Based on our observation, such bearing conditions will likely be encountered beginning at depths between about three and six feet bgs. We understand that grade cuts of about 16 feet will be required to achieve design footing elevations. On this basis, we anticipate dense to very dense glacial till to be exposed at the vault subgrade. Although perched groundwater seepage may be encountered within the excavation, we do not anticipate that measures to counter hydrostatic uplift will need to be included in the vault design. With respect to temporary slopes, the upper three to six feet of loose to medium dense soil should be considered a Type C soil, while the dense to very dense soil beneath should be considered a Type A soil. These designations correlate with temporary slope inclinations of 1.5H:1V (Type C) and 0.75H:1V (Type A). If adequate slope setbacks cannot be achieved, temporary shoring may be necessary in order to facilitate vault construction activities. ESNW can provide temporary shoring recommendations upon request. A zone of free-draining rock or a sheet drain must be provided behind the vault walls with a rigid perforated PVC drain pipe placed at the base of the vault walls. If the bottom of the vault is too low to gravity flow to an outlet, the drain (and associated drain rock or sheet drain) should be raised to a point where it can gravity flow to an outlet. The portion of the vault walls located below the drain pipe must be designed for hydrostatic pressure. Kalapas Homes, LLC ES-6261.01 July 16, 2020 Page 3 Earth Solutions NW, LLC The following values can be used for design of the vault: • Allowable soil bearing capacity 5,000 psf* •Active earth pressure (yielding condition) 35 pcf (equivalent fluid) 80 pcf (hydrostatic condition) •At-rest earth pressure (restrained condition) 55 pcf 100 pcf (hydrostatic condition) •Traffic lateral surcharge for passenger 70 psf (rectangular distribution) vehicles (where applicable) •Passive earth pressure 350 pcf (equivalent fluid) •Coefficient of friction 0.40 •Seismic surcharge 6H *Value is for dense native soil anticipated to be exposed beginning at depths of about three to six feet or more belowexisting grades. ESNW should review the vault design to confirm the recommendations provided in this letter are followed and provide supplemental recommendations, where necessary. Prior to mass excavation activities for the proposed vault, ESNW, the client, and the contractor, should observe a test pit excavation within the vault location. The test pit should extend at least to the subgrade elevation of the vault footing. This exploration will assist in determining appropriate slope inclinations and allow for evaluation of groundwater conditions in the area. The test pit should be performed during the construction phase of the project. Additional Services The recommendations and conclusions provided in this recommendation letter are professional opinions consistent with the level of care and skill that is typical of other members in the profession currently practicing under similar conditions in this area. A warranty is not expressed or implied. Variations in soil and groundwater conditions observed at the test pit locations may exist and may not become evident until construction. ESNW should reevaluate the conclusions provided in this geotechnical evaluation letter if variations are encountered. ESNW should have an opportunity to review final site designs with respect to the geotechnical recommendations provided in this letter. ESNW should also be retained to provide earthwork observation, testing, and further consultation services during development and construction. Kalapas Homes, LLC ES-6261.01 July 16, 2020 Page 4 Earth Solutions NW, LLC We trust this letter meets your current needs. Should you have questions regarding the content herein, or require additional information, please call. Sincerely, EARTH SOLUTIONS NW, LLC Chase G. Halsen, L.G. Kyle R. Campbell, P.E. Project Geologist Principal Engineer 07/16/2020 07/16/2020 Page | 81 7.0 OTHER PERMITS The following permits and/or approvals are thought to be required as part of this project: Postmaster Approval 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 civil construction 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 has been shown on the TESC plans and will be 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 water sprinkler will be provided as needed. Wet Season Construction: Infrastructure construction will be conducted generally in the spring/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 | 83 Page | 84 9.0 BOND QUANTITIES The City of Renton Bond Quantity Worksheet has been included with the civil construction plan submittal. Page | 85 10.0 OPERATIONS AND MAINTENANCE MANUAL The drainage facilities on this project will be maintained by the homeowners. Maintenance instructions have been included in the Operations and Maintenance Manual for Drainage Facilities (Attachment “A”) submitted with the civil construction plans.