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Home My WebLink AboutRS_Prelim_TIR_201201_v1.pdfCivil Engineers ● Structural Engineers ● Landscape Architects ● Community Planners ● Land Surveyors Preliminary Technical Information Report PREPARED FOR: Lakhpal Brar 8054 South 132nd Street Renton, WA 98178 PROJECT: Brar Short Plat 8054 South 132nd Street Renton, WA 98178 2200320.10 PREPARED BY: Ella Anguiano Project Engineer REVIEWED BY: Scott Kaul, PE Project Manager DATE: November 2020 Preliminary Technical Information Report PREPARED FOR: Lakhpal Brar 8054 South 132nd Street Renton, WA 98178 PROJECT: Brar Short Plat 8054 South 132nd Street Renton, WA 98178 2200320.10 PREPARED BY: Ella Anguiano Project Engineer REVIEWED BY: Scott Kaul, PE Project Manager DATE: November 2020 I hereby state that this Preliminary Technical Information Report for the Brar Short Plat project has been prepared by me or under my supervision, and meets the standard of care and expertise that is usual and customary in this community for professional engineers. I understand that City of Renton does not and will not assume liability for the sufficiency, suitability, or performance of drainage facilities prepared by me. 11/06/2020 Preliminary Technical Information Report Brar Short Plat i 2200320.10 Table of Contents 1.0 Project Overview.........................................................................................................................1-1 1.1 Purpose and Scope .........................................................................................................1-1 1.2 Existing Conditions ..........................................................................................................1-1 1.3 Post-Development Conditions .........................................................................................1-1 Section 1.0 Figures Figure 1-1 .........TIR Worksheet Figure 1-2 .........Site Location Map Figure 1-3 .........Drainage Basin Map Figure 1-4 .........USDA Soils Survey 2.0 Conditions and Requirements Summary.................................................................................2-1 2.1 Core Requirements..........................................................................................................2-1 2.1.1 CR 1 – Discharge at the Natural Location ..........................................................2-1 2.1.2 CR 2 – Offsite Analysis.......................................................................................2-1 2.1.3 CR 3 – Flow Control ...........................................................................................2-1 2.1.4 CR 4 – Conveyance System...............................................................................2-1 2.1.5 CR 5 – Construction Stormwater Pollution Prevention.......................................2-1 2.1.6 CR 6 – Maintenance and Operations .................................................................2-1 2.1.7 CR 7 – Financial Guarantees and Liability .........................................................2-1 2.1.8 CR 8 – Water Quality Facilities...........................................................................2-1 2.1.9 CR 9 – Onsite Best Management Practices (BMPs) ..........................................2-2 2.1.10 SR 1 – Other Adopted Area-Specific Requirements...........................................2-2 2.1.11 SR 2 – Flood Hazard Area Delineation...............................................................2-2 2.1.12 SR 3 – Flood Protection Facilities.......................................................................2-2 2.1.13 SR 4 – Source Controls......................................................................................2-3 2.1.14 SR 5 – Oil Control...............................................................................................2-3 2.1.15 SR 6 – Aquifer Protection Area...........................................................................2-3 Section 2.0 Figures Figure 2-1 .........Flood Insurance Rate Map Figure 2-2 .........City of Renton Groundwater Protection Areas 3.0 Offsite Analysis...........................................................................................................................3-1 3.1 Task 1 – Study Area Definition and Maps .......................................................................3-1 3.2 Task 2 – Resource Review..............................................................................................3-1 3.3 Task 3 – Field Inspection.................................................................................................3-1 3.4 Task 4 – Drainage System Description and Problem Descriptions.................................3-1 Preliminary Technical Information Report Brar Short Plat ii 2200320.10 Section 3.0 Figures Figure 3-1 .........City of Renton Effective FEMA Flood Insurance Rate Map 4.0 Flow Control and Water Quality Facility Analysis and Design...............................................4-1 4.1 Flow Control.....................................................................................................................4-1 4.1.1 Existing Site Hydrology (Part A) .........................................................................4-1 4.1.2 Developed Site Hydrology (Part B).....................................................................4-1 4.1.3 Performance Standards (Part C) ........................................................................4-1 4.1.4 Flow Control System (Part D).............................................................................4-2 4.2 Water Quality System (Part E).........................................................................................4-2 Section 4.0 Figures Figure 4-1 .........City of Renton Flow Control Application Map – Reference 15-A Figure 4-2 .........Preliminary MGSFlood Flow Control Calculations 5.0 Conveyance System Analysis and Design...............................................................................5-1 6.0 Special Reports and Studies.....................................................................................................6-1 Section 6.0 Figures Figure 6-1 .........Geotechnical Engineering Report 7.0 Other Permits..............................................................................................................................7-1 8.0 CSWPPP Analysis and Design..................................................................................................8-1 9.0 Bond Quantities, Facility Summaries, and Declaration of Covenant ....................................9-1 10.0 Operations and Maintenance Plan..........................................................................................10-1 11.0 Conclusion................................................................................................................................11-1 Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 1 Project Overview Preliminary Technical Information Report Brar Short Plat 1-1 2200320.10 1.0 Project Overview 1.1 Purpose and Scope This report accompanies the civil engineering plans and documents for the Brar Short Plat project site, a proposed residential development project located at 8054 South 132nd Street in the city of Renton, King County, Washington. The project site comprises Parcel No. 2144800460, which is 0.75 acre in size. The site is bordered to the north and west by private residential parcels, to the south by South 132nd Street, and to the east by a new residential development under construction. See Figure 1-1 for the TIR Worksheet and Figure 1-2 for a Site Location map. The site is located within the jurisdiction of City of Renton, which has amended the 2016 King County Surface Water Design Manual (KCSWDM) as the 2016 City of Renton Surface Water Design Manual (CRSWDM). Per the CRSWDM, the Peak Rate Flow Control Standard shall be met, along with the Basic Enhanced Water Quality Treatment Menu. 1.2 Existing Conditions The site currently has an existing residence in its southern portion and an outbuilding centrally located onsite. The remainder of the site is primarily pasture. There are several existing trees on the eastern side of the site and within the existing residence’s front yard. Generally, the site slopes to the south parallel to the east and west parcel boundaries. The slope is moderately steep at about 15%. The existing property discharges to the public right-of-way on South 132nd Street. The existing drainage patterns have been analyzed and are discussed in detail in the Level One Downstream Analysis (see Section 3.0). 1.3 Post-Development Conditions The project proposes a four-lot subdivision; the existing residence will remain as Lot 1. The buildable area within each lot ranges from 2,020 to 2,840 square feet. Each lot will be constructed with a paved driveway from a private shared access driveway. Stormwater will be collected in closed conveyances and treated by a proprietary (basic) stormwater treatment device prior to discharging to the public storm system in South 132nd Street. This will maintain the natural discharge point for stormwater leaving the site. Refer to Figure 1-3 for a Drainage Basin Map and Figure 1-2 for a Site Location Map. Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 1.0 Figures Figure 1-1.........TIR Worksheet Figure 1-2.........Site Location Map Figure 1-3.........Drainage Basin Map Figure 1-4.........USDA Soils Survey Lakhpal Brar 8054 S 132nd St, Renton, WA 98178 Matt Weber AHBL, Inc. 253.383.2422 8054 S 132nd St, Renton, 98178 Brar Short Plat 13 23 4 November 2020 November 2020 Cedar River/Lake Washington Sub Basin The City of Renton Peak Flow Rate Control Standard and Basic Water Quality Ur N/A N/A Slopes exceeding 15% East Valley Road public stormwater system and wetland east of site 2 TBD TBD Peak Rate Flow Control Standard TBD Commercail Conveyance pipes, catch basins, Bioretention cell, and treatment unit. Treatment Unit 2215 North 30th Street Suite 300 Tacoma, WA 98403 253.383.2422 TEL 253.383.2572 FAX BRAR SHORT PLAT VICINITY MAP FIGURE 1-2 Soil Map—City of Seattle, Washington (Soil Map) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/5/2020 Page 1 of 35259310525932052593305259340525935052593605259370525938052593905259400525941052593105259320525933052593405259350525936052593705259380525939052594005259410557920557930557940557950557960557970557980557990558000 557920 557930 557940 557950 557960 557970 557980 557990 558000 47° 29' 8'' N 122° 13' 52'' W47° 29' 8'' N122° 13' 48'' W47° 29' 4'' N 122° 13' 52'' W47° 29' 4'' N 122° 13' 48'' 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: 1:543 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 1:12,000. 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: City of Seattle, Washington Survey Area Data: Version 4, Jun 4, 2020 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jun 29, 2019—Jul 21, 2019 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—City of Seattle, Washington (Soil Map) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/5/2020 Page 2 of 3 Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 3056 Urban land-Alderwood complex, 5 to 12 percent slopes 0.4 49.1% 5020 Beausite-Alderwood-Urban land complex, 12 to 35 percent slopes 0.4 50.9% Totals for Area of Interest 0.7 100.0% Soil Map—City of Seattle, Washington Soil Map Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/5/2020 Page 3 of 3 City of Seattle, Washington 3056—Urban land-Alderwood complex, 5 to 12 percent slopes Map Unit Setting National map unit symbol: 2xtbd Elevation: 20 to 540 feet Mean annual precipitation: 30 to 40 inches Mean annual air temperature: 48 to 52 degrees F Frost-free period: 180 to 240 days Farmland classification: Not prime farmland Map Unit Composition Urban land:60 percent Alderwood and similar soils:15 percent Minor components:25 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Urban Land Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 8 Hydric soil rating: No Description of Alderwood Setting Landform:Hills Landform position (two-dimensional):Backslope, summit, shoulder Landform position (three-dimensional):Crest, side slope, nose slope Down-slope shape:Linear Across-slope shape:Convex Parent material:Glacial drift and/or glacial outwash over dense glaciomarine deposits Typical profile A - 0 to 7 inches: gravelly sandy loam Bw1 - 7 to 21 inches: very gravelly sandy loam Bw2 - 21 to 30 inches: very gravelly sandy loam Bg - 30 to 35 inches: very gravelly sandy loam 2Cd1 - 35 to 43 inches: very gravelly sandy loam 2Cd2 - 43 to 59 inches: very gravelly sandy loam Properties and qualities Slope:5 to 12 percent Depth to restrictive feature:20 to 39 inches to densic material Drainage class:Moderately well drained Map Unit Description: Urban land-Alderwood complex, 5 to 12 percent slopes---City of Seattle, Washington Soil Data Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/5/2020 Page 1 of 2 Capacity of the most limiting layer to transmit water (Ksat):Very low to moderately low (0.00 to 0.01 in/hr) Depth to water table:About 18 to 35 inches Frequency of flooding:None Frequency of ponding:None Available water capacity:Very low (about 2.7 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4s Hydrologic Soil Group: A Hydric soil rating: No Minor Components Everett Percent of map unit:10 percent Landform:Hills Landform position (two-dimensional):Shoulder, backslope Landform position (three-dimensional):Side slope, crest Down-slope shape:Linear Across-slope shape:Convex Hydric soil rating: No Mckenna Percent of map unit:10 percent Landform:Terraces Landform position (three-dimensional):Tread Down-slope shape:Concave Across-slope shape:Concave Hydric soil rating: Yes Kitsap Percent of map unit:5 percent Landform:Terraces Landform position (three-dimensional):Tread Down-slope shape:Linear Across-slope shape:Linear Hydric soil rating: No Data Source Information Soil Survey Area: City of Seattle, Washington Survey Area Data: Version 4, Jun 4, 2020 Map Unit Description: Urban land-Alderwood complex, 5 to 12 percent slopes---City of Seattle, Washington Soil Data Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/5/2020 Page 2 of 2 City of Seattle, Washington 5020—Beausite-Alderwood-Urban land complex, 12 to 35 percent slopes Map Unit Setting National map unit symbol: 2xtbw Elevation: 20 to 540 feet Mean annual precipitation: 30 to 40 inches Mean annual air temperature: 48 to 52 degrees F Frost-free period: 180 to 240 days Farmland classification: Not prime farmland Map Unit Composition Beausite and similar soils:50 percent Alderwood and similar soils:25 percent Urban land:20 percent Minor components:5 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Beausite Setting Landform:Hillslopes Landform position (two-dimensional):Shoulder, backslope, summit Landform position (three-dimensional):Side slope, crest, nose slope Down-slope shape:Convex Across-slope shape:Convex Parent material:Glacial drift mixed with colluvium and/or residuum derived from sandstone or conglomerate Typical profile Oi - 0 to 2 inches: slightly decomposed plant material Oe - 2 to 3 inches: moderately decomposed plant material A - 3 to 5 inches: gravelly sandy loam Bw1 - 5 to 9 inches: very gravelly sandy loam Bw2 - 9 to 17 inches: very gravelly sandy loam Bw3 - 17 to 25 inches: very gravelly sandy loam C - 25 to 36 inches: very gravelly sandy loam 2R - 36 to 59 inches: bedrock Properties and qualities Slope:12 to 35 percent Depth to restrictive feature:24 to 39 inches to lithic bedrock Drainage class:Well drained Capacity of the most limiting layer to transmit water (Ksat):Moderately high to high (1.42 to 7.09 in/hr) Depth to water table:More than 80 inches Frequency of flooding:None Frequency of ponding:None Map Unit Description: Beausite-Alderwood-Urban land complex, 12 to 35 percent slopes---City of Seattle, Washington Soil Data Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/5/2020 Page 1 of 3 Available water capacity:Very low (about 2.9 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 6e Hydrologic Soil Group: B Hydric soil rating: No Description of Alderwood Setting Landform:Hills Landform position (two-dimensional):Backslope, summit, shoulder Landform position (three-dimensional):Crest, side slope, nose slope Down-slope shape:Linear Across-slope shape:Convex Parent material:Glacial drift and/or glacial outwash over dense glaciomarine deposits Typical profile A - 0 to 7 inches: gravelly sandy loam Bw1 - 7 to 21 inches: very gravelly sandy loam Bw2 - 21 to 30 inches: very gravelly sandy loam Bg - 30 to 35 inches: very gravelly sandy loam 2Cd1 - 35 to 43 inches: very gravelly sandy loam 2Cd2 - 43 to 59 inches: very gravelly sandy loam Properties and qualities Slope:12 to 35 percent Depth to restrictive feature:20 to 39 inches to densic material Drainage class:Moderately well drained Capacity of the most limiting layer to transmit water (Ksat):Very low to moderately low (0.00 to 0.01 in/hr) Depth to water table:About 18 to 35 inches Frequency of flooding:None Frequency of ponding:None Available water capacity:Very low (about 2.7 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 6e Hydrologic Soil Group: A Hydric soil rating: No Description of Urban Land Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 8 Hydric soil rating: No Map Unit Description: Beausite-Alderwood-Urban land complex, 12 to 35 percent slopes---City of Seattle, Washington Soil Data Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/5/2020 Page 2 of 3 Minor Components Mckenna Percent of map unit:5 percent Landform:Terraces Landform position (three-dimensional):Tread, dip Down-slope shape:Concave Across-slope shape:Concave Hydric soil rating: Yes Data Source Information Soil Survey Area: City of Seattle, Washington Survey Area Data: Version 4, Jun 4, 2020 Map Unit Description: Beausite-Alderwood-Urban land complex, 12 to 35 percent slopes---City of Seattle, Washington Soil Data Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/5/2020 Page 3 of 3 Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 2 Conditions and Requirements Summary Preliminary Technical Information Report Brar Short Plat 2-1 2200320.10 2.0 Conditions and Requirements Summary 2.1 Core Requirements 2.1.1 CR 1 – Discharge at the Natural Location There is one basin within the site in one Threshold Discharge Area (TDA). All core requirements are required for this TDA. The natural discharge location of this TDA is maintained. 2.1.2 CR 2 – Offsite Analysis A preliminary downstream analysis is included in Section 3.0 below. A full Level One Downstream Analysis will be performed for the final Technical Information Report. The analysis will include: Defining and mapping the study area. Reviewing available information on the study area. Field inspecting the study area. 2.1.3 CR 3 – Flow Control The project is in a Flow Control Duration Standard and is within the West Lake Washington – Seattle South Drainage Basin. This flow control standard requires discharges to match predeveloped forested site conditions. Flow control is discussed in further detail in Section 4.0, Flow Control and Water Quality Facility Analysis and Design. 2.1.4 CR 4 – Conveyance System The proposed conveyance system will be designed to meet the requirements outlined in Section 1.2.4 of the CRSWDM. Refer to Section 5.0 for more information. 2.1.5 CR 5 – Construction Stormwater Pollution Prevention Onsite land disturbance will consist of clearing the undeveloped portion of the site, demolition of the existing onsite outbuilding, and regrading of the site for three future homes. A Construction Stormwater Pollution Prevention Plan (CSWPPP) will be included with the final engineering design. 2.1.6 CR 6 – Maintenance and Operations Maintenance and operations of all drainage facilities are the responsibility of the owner. A completed Operations and Maintenance Plan will be included with the final engineering design. 2.1.7 CR 7 – Financial Guarantees and Liability All financial guarantee and liability requirements will be met by the owner and will be provided with the final engineering design. This project will provide a Drainage Facilities Restoration and Site Stabilization Financial Guarantee. 2.1.8 CR 8 – Water Quality Facilities The project site is subject to the Basic Water Quality Treatment Menu per the CRSWDM. Design of these water quality facilities is discussed in Section 4.0. Preliminary Technical Information Report Brar Short Plat 2-2 2200320.10 2.1.9 CR 9 – Onsite Best Management Practices (BMPs) The Brar Short Pat project is classified as a Large Lot per Section 1.2.9.2 of the CRSWDM. The proposed project site will meet the Large Lot BMP Requirements outlined in Section 1.2.9.2.2 of the CRSWDM. Below is a discussion of the list approach for each type of surface proposed on the site. Landscape Areas Post Construction Soil Quality and Depth will be used. Impervious Areas Full Dispersion is not feasible because the development cannot maintain the required vegetated flow path area. Full Infiltration and Full Infiltration of Roof Runoff are not feasible because the existing soils that are able to infiltrate are relatively shallow and cannot support infiltration due to the site’s steep slope. Runoff will flow laterally and negatively impact downstream lots. Limited Infiltration is not feasible because the existing soils that are able to infiltrate are relatively shallow and cannot support infiltration due to the site’s step slope. Any runoff that may infiltrate at grade will flow laterally into the adjacent foundation of the lower lots. Bioretention per Onsite BMP standards is not feasible because the facilities would not be able to be designed on slopes less than 8%. Permeable Pavement is not feasible because the site slopes exceed 10%. Permeable pavement is not ideal for slopes exceeding 5%. Basic Dispersion is not feasible because there is not a vegetated flow path of 50 feet. Reduced Impervious Surface Credit is not feasible for this site. Native Growth Retention Credit and Tree Retention Credit are not feasible to achieve the required residential density on this project and serve the site with utilities. Perforated Pipe Connection is not feasible because the existing fill and alluvial soils cannot support infiltration. 2.1.10 SR 1 – Other Adopted Area-Specific Requirements To our knowledge, no adopted area-specific requirements are applicable to the project site. 2.1.11 SR 2 – Flood Hazard Area Delineation Flood Insurance Rate Map 53033C0976G was consulted for this project and shows the project site within the Zone X area, which is described as areas determined to be outside of the 500-year floodplain. Refer to Figure 2-1 of this section for the Flood Insurance Rate Map. 2.1.12 SR 3 – Flood Protection Facilities The project site does not contain, nor is it adjacent to, any existing flood protection facilities. Project improvements do not include flood protection measures. Preliminary Technical Information Report Brar Short Plat 2-3 2200320.10 2.1.13 SR 4 – Source Controls The proposed project is classified as a residential site. Water quality source controls applicable to the project site shall be evaluated and applied as described in the King County Stormwater Pollution Prevention Manual (KCSWPPM) and Renton Municipal Code IV. 2.1.14 SR 5 – Oil Control The project is not considered a high-use site; therefore, it is not subject to oil control requirements. 2.1.15 SR 6 – Aquifer Protection Area According to the City of Renton Public Works Department Groundwater Protection Areas map, Reference 15-B of the CRSWDM, the site is not located within an aquifer protection area. Refer to Figure 2-2 for the above referenced map. Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 2.0 Figures Figure 2-1.........Flood Insurance Rate Map Figure 2-2.........City of Renton Groundwater Protection Areas USGS The National Map: Orthoimagery. Data refreshed October, 2020. National Flood Hazard Layer FIRMette 0 500 1,000 1,500 2,000250 Feet Ü SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT SPECIAL FLOOD HAZARD AREAS Without Base Flood Elevation (BFE) Zone A, V, A99 With BFE or DepthZone AE, AO, AH, VE, AR Regulatory Floodway 0.2% Annual Chance Flood Hazard, Areas of 1% annual chance flood with average depth less than one foot or with drainage areas of less than one square mileZone X Future Conditions 1% Annual Chance Flood HazardZone X Area with Reduced Flood Risk due to Levee. See Notes.Zone X Area with Flood Risk due to LeveeZone D NO SCREEN Area of Minimal Flood Hazard Zone X Area of Undetermined Flood HazardZone D Channel, Culvert, or Storm Sewer Levee, Dike, or Floodwall Cross Sections with 1% Annual Chance 17.5 Water Surface Elevation Coastal Transect Coastal Transect Baseline Profile Baseline Hydrographic Feature Base Flood Elevation Line (BFE) Effective LOMRs Limit of Study Jurisdiction Boundary Digital Data Available No Digital Data Available Unmapped This map complies with FEMA's standards for the use of digital flood maps if it is not void as described below. The basemap shown complies with FEMA's basemap accuracy standards The flood hazard information is derived directly from the authoritative NFHL web services provided by FEMA. This map was exported on 10/20/2020 at 2:06 PM and does not reflect changes or amendments subsequent to this date and time. The NFHL and effective information may change or become superseded by new data over time. This map image is void if the one or more of the following map elements do not appear: basemap imagery, flood zone labels, legend, scale bar, map creation date, community identifiers, FIRM panel number, and FIRM effective date. Map images for unmapped and unmodernized areas cannot be used for regulatory purposes. Legend OTHER AREAS OF FLOOD HAZARD OTHER AREAS GENERAL STRUCTURES OTHER FEATURES MAP PANELS 8 B 20.2 The pin displayed on the map is an approximate point selected by the user and does not represent an authoritative property location. 1:6,000 122°14'9"W 47°29'18"N 122°13'31"W 47°28'53"N Esri, HERE, Garmin, (c) OpenStreetMap contributor s, and the GIS usercommunity Zone 1 Zone 1 Modified Zone 2 Renton Water District ³    Data Sources: City of Renton, King County, ESRI This document is a graphic representation, not guaranteedto survey accuracy, and is based on the best informationavailable as of the date shown. This map is intended forCity display purposes only. Coordinate System: NAD 1983 HARN StatePlane Washington North FIPS 4601 FeetProjection: Lambert Conformal ConicDatum: North American 1983 HARN Date: 05/15/2020 0 0.5 10.25 Miles       Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 3 Offsite Analysis Preliminary Technical Information Report Brar Short Plat 3-1 2200320.10 3.0 Offsite Analysis 3.1 Task 1 – Study Area Definition and Maps One TDA exists for the site. All core requirements are required. The site drains to the southwest and discharges to the existing public stormwater system. The existing discharge point will be maintained. The northern neighboring property contributes stormwater to the onsite basin area while the property to the east is the only upstream developed area within the same TDA. 3.2 Task 2 – Resource Review The following resources were reviewed to determine if there are any existing or potential problems in the study area: Adopted Basin Plans: The project lies within the Lower Cedar River Basin and is subject to the Lower Cedar River Basin and Nonpoint Pollution Action Plan. Requirements for the Lower Cedar River Basin will be followed where applicable. Offsite Analysis Reports: AHBL staff has not located offsite analysis reports for projects near the Brar Short Plat. FEMA Map: FEMA Flood Insurance Rate Map 53033C0976 G, dated August 19, 2020 (see Figure 2-1), indicates that the project site lies outside the categorized flood zones. City of Renton Effective FEMA Flood Insurance Rate Map: The project site is not located in a Flood Hazard Zone (see Figure 3-1). Topographic survey. Renton online GIS Map. 3.3 Task 3 – Field Inspection A full field inspection of the downstream area will be performed prior to final design. 3.4 Task 4 – Drainage System Description and Problem Descriptions Stormwater runoff discharges to the public storm system within South 132nd Street. The entire system is within 12-inch closed conveyance pipes. This drainage discharges to a seasonal creek that eventually discharges to Lake Washington, over 1 mile downstream from the site. There are no known signs of flooding, overtopping, or erosion. A full field inspection of the downstream will be performed prior to final design. Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 3.0 Figures Figure 3-1.........City of Renton Effective FEMA Flood Insurance Rate Map RentonKent Newcastle King CountyTukwilaMercer Island Bellevu e Lake Washington Lake Youngs Panther Lake Lake Boren Cedar RiverBlack River May Creek Springbrook Creek Cougar MountainCougar Mountain Coal Creek ParkCoal Creek Park Cedar River Natural ZoneCedar River Natural Zone May Creek ParkMay Creek Park Soos Creek Park and TrailSoos Creek Park and Trail Black River Riparian ForestBlack River Riparian Forest McGarvey Open SpaceMcGarvey Open Space Maplewood Community ParkMaplewood Community Park ValleyValley BensonBenson HighlandsHighlands West HillWest Hill East PlateauEast Plateau SE 192ND STTALBOT RD S140TH AVE SERAI N I E R A V E S EAST VALLEY RDSE 168TH ST RENTON A V E S116TH AVE SENE 12TH STE M ERCER WAY148TH AVE SENE 7TH S T84TH AVE SHOQUIAM AVE NENEWCASTLE W AY W M E RCER WAY S 128TH ST SW 41ST ST PARK AVE N128TH AVE SESE JONES R D E VALLEY HWYSE 72ND ST SE 164TH ST NILE AVE NEN 10TH S T SE 183RD S TUNION AVE NE156TH AVE SEUNION AVE SENE 2ND ST 148TH AVE SESE 164TH STLIND AVE SWUNION AVE NE116TH AVE SESW 7TH ST N 8TH ST EDMONDS AVE NEPUGET DR S E NE 27TH ST 156TH AVE SERENTON AVE S BENSON RD SMONROE AVE NE116TH AVE SENE 4TH ST SR 515 SUNS E T BLV D N E PARK AVE NM APLE VALLEY HWY SW 43RD ST NE 3RD STLOGAN AVE NSW SU NSET BLVD SW GRADY W A Y N 3RD STRAINIER AVE N140TH WAY S ESR 167108TH AVE SEN 6TH ST S 2ND S T 108TH AVE SESR 515[^405 [^405 Effective FEMA FloodInsurance Rate Map µ Legend Renton City Limits Zone AE, A, AH, AO - Regulatory Zone X - Non Regulatory 0 0.5 10.25 Miles Public Works - Surface Water UtilityPrint Date: 11/05/2012 Data Sources: City of Renton, FEMA FIRM revised May 16, 1995.Cedar River flood hazard area updated with FEMA Cedar RiverLOMR (Case No. 06-10-B569P) approved December 4, 2006. This document is a graphic representation, not guaranteedto survey accuracy, and is based on the best informationavailable as of the date shown. This map is intended forCity display purposes only. Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 4 Flow Control and Water Quality Facility Analysis and Design Preliminary Technical Information Report Brar Short Plat 4-1 2200320.10 4.0 Flow Control and Water Quality Facility Analysis and Design 4.1 Flow Control 4.1.1 Existing Site Hydrology (Part A) The existing site is developed with two existing buildings, asphalt, and gravel areas. The site is mostly pervious surfaces. The natural discharge location at the southwest corner of the site will be maintained. MGSFlood was used to model the existing site and determine peak flows. 4.1.2 Developed Site Hydrology (Part B) Runoff will be collected in and conveyed to a treatment and detention device located in the southern section of the property. After being treated and detained, the stormwater runoff will be discharged to the public storm system in South 132nd Street. The project is in a Flow Control Duration Standard and is within the West Lake Washington – Seattle South Drainage Basin (see Figure 4-1). This standard requires that developed flows match to predeveloped forested conditions. Under proposed conditions, net impervious area is planned to increase. The increased stormwater runoff will be detained, thus meeting the Flow Control Standard. Preliminary MGSFlood peak flow calculations are included as Figure 4-2. The annual peak flows and durations for the proposed site will be determined using the existing and developed surface areas shown below. Table 1 – Existing vs. Developed Site Hydrology for West Basin West Basin (acres)Predeveloped Proposed Pervious 0.581 0.272 Impervious 0.059 0.369 4.1.3 Performance Standards (Part C) Area-Specific Flow Control Facility Standard The project is in a Flow Control Duration Standard and is within the West Lake Washington – Seattle South Drainage Basin (see Figure 4-1). This standard requires that developed flows match to predeveloped forested conditions. Conveyance System Capacity Standards The onsite stormwater networks will be sized to convey and contain the 25-year peak flow and the 100-year runoff event, and may not create or aggravate a severe flooding problem or severe erosion problem, as described in Section 1.2.2 of the CRSWDM. Water Quality Treatment Menu In accordance with the 2016 CRSWDM, onsite flows will be treated to specifications provided by the Basic Water Quality standards. The goal of this treatment menu is to reduce total suspended solids (TSS) by 80%. A proprietary treatment unit with General Use Level Designation (GULD) approval for basic treatment will be used to treat stormwater from the west basin prior to discharge from the site. The unit will be sized according the GULD approval and the manufacturer’s recommendations. Preliminary Technical Information Report Brar Short Plat 4-2 2200320.10 Source Controls The proposed project consists of new residential houses and driveways, along with the existing residence and updated driveway. Source control and erosion and sediment control measures during construction will be included in a CSWPPP to be submitted with the final engineering design. Post-construction source controls will be included in an Operation and Maintenance Plan to be submitted with the final engineering design. Oil Controls Not applicable. 4.1.4 Flow Control System (Part D) A StormTank or StormChamber detention system is proposed to detain developed runoff and release it to match to the flow duration standard. MGSFlood calculations are provided in Figure 4-2 showing that the proposed peak flow rates match predeveloped, forested conditions. Our preliminary design estimates that a 3-foot deep system with approximately 1,760 square feet of storage will be adequate to control runoff from this site. 4.2 Water Quality System (Part E) In accordance with the 2016 CRSWDM, onsite flows will be treated to specifications provided by the Basic Water Quality standards. The goal of this treatment menu is to reduce total suspended solids (TSS) by 80%. A proprietary treatment unit with GULD approval for basic treatment will be used to treat stormwater prior to discharge from the site. The unit will be sized according the GULD approval and the manufacturer’s recommendations.