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RS_Prelim_TIR_210429_v2.pdf
Civil 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 Ryan Inouye, PE Project Engineer REVIEWED BY: Scott Kaul, PE Project Manager DATE: November 2020 Revised April 2021 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 Ryan Inouye, PE Project Engineer REVIEWED BY: Scott Kaul, PE Project Manager DATE: November 2020 Revised April 2021 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. 04/29/2021 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 Figure 3-2 .........Downstream Drainage 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) ........................................................................4-2 4.1.4 Flow Control System (Part D).............................................................................4-3 4.2 Water Quality System (Part E).........................................................................................4-3 Section 4.0 Figures Figure 4-1 .........City of Renton Flow Control Application Map – Reference 15-A Figure 4-2 .........Predeveloped and Developed Basin Maps Figure 4-3 .........Preliminary WWHM Flow Control Calculations 5.0 Conveyance System Analysis and Design...............................................................................5-1 Section 5.0 Figures Figure 5-1 .........Frontage Conveyance Check 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 Flow Control Duration 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 Level One Downstream Analysis has been conducted. The analysis includes: 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 south 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. Refer to Figure 3-2 for Downstream Drainage Map. 3.3 Task 3 – Field Inspection A Level 1 downstream analysis was performed on February 16, 2021. The downstream drainage path was field inspected for existing drainage problems. The analysis concluded there are no existing drainage problems within 0.25 mile of site discharge to the City conveyance system. 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. 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 Figure 3-2.........Downstream Drainage 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. 2,400400 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. THIS MAP IS NOT TO BE USED FOR NAVIGATIONWGS_1984_Web_Mercator_Auxiliary_Sphere Notes None 02/15/2021 Legend 272 0 136 272 Feet Information Technology - GIS RentonMapSupport@Rentonwa.gov City and County Labels City and County Boundary Addresses Parcels Network Structures Access Riser Inlet Manhole Utility Vault Clean Out Unknown Control Structures Pump Stations Discharge Points Water Quality Detention Facilities Pond Tank Vault Bioswale Wetland Other Stormwater Mains Culverts Open Drain Virtual Drainlines Facility Outlines Private Network Structures Access Riser Inlet Manhole Clean Out Utility Vault Unknown Private Control Structures Private Pump Stations Private Discharge Points Private Water Quality Private Detention Facilities Tank Wetland Filter Strip Infiltration Trench Vault Pond Bioswale Stormtech Chamber Other Private Pipes Private Culverts Private Open Drain Private Facility Outlines Fences Inactive Structures Inactive Pipes Inactive Water Quality Inactive Detention Facilities PROJECT SITE 1/4 MILE DOWNSTREAM 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 southeast corner of the site will be maintained. The Western Washington Hydrology Model (WWHM) was used to model the existing site and tributary basin area. The Predeveloped Basin Map (Figure 4-2) shows the basin limits evaluated for flow control. Upstream property is tributary to the project site and is referred to as The Pass-Through Basin. The offsite Pass-Through Basin is modeled as existing conditions. The Onsite Basin area includes the proposed improvements within the parcel and along the frontage (but excludes the existing residence that will remain). The onsite basin is modeled as forest to establish the target predeveloped flow control requirements. The existing residence to remain is referred to as The Developed – Basin Swap Area. This basin is not included in existing conditions hydrology but is shown as a reference for the developed conditions basin modeling. The existing building and improvements on Lot 1 will remain. 4.1.2 Developed Site Hydrology (Part B) Runoff will be collected in and conveyed to a treatment and detention system 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 will increase. The increased stormwater runoff will be detained, thus meeting the Flow Control Standard. Preliminary WWHM calculations are included as Figure 4-3. The Developed Basin Map (Figure 4-2) shows the basin limits evaluated for flow control. The Pass-Through Basin matches existing cover conditions for the upstream tributary runoff. The Onsite Basin assumes full buildout of the short plat with all associated impervious surfaces (excluding the frontage improvements that are not feasible to detain). All landscape and lawn areas will meet the Soil Amendment Criteria, as outlined in CRSWDM Appendix C, Section C.2.13.1. The Soil Amendment section clarifies that areas meeting the design guidelines for Soil Amendment can be modeled as pasture. All lawn areas are proposed to meet Soil Amendment requirements; therefore, all lawn areas are modeled as pasture. The project will retain Lot 1 improvements; therefore, Lot 1 does not require flow control. However, because this area can be detained, it will be routed through the detention system in-lieu of the frontage improvements, which are not feasible to detain. The project will detain an equivalent area to the proposed new and replaced surfaces. The flow control durations for the proposed site will be determined using the existing and developed surface areas shown below. Preliminary Technical Information Report Brar Short Plat 4-2 2200320.10 Table 1 – Predeveloped vs. Developed Modeled Site Hydrology Basin (acres)Predeveloped Developed Pass-Through Forest 0.598 -- Pervious (Pasture)-0.254 - Pervious (Lawn)--0.99 Impervious 0.022 0.366 0.12 4.1.3 Performance Standards (Part C) Area-Specific Flow Control Facility Standard The project is in a Flow Control Duration Standard (Forested Conditions) 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. New impervious surfaces, new pervious surfaces, and replaced impervious surfaces require flow control treatment. Because of the topography of the site, a portion of the frontage improvements cannot be detained onsite for flow control. A basin swap is proposed to provide flow control for an equivalent area. 0.049 acre of the frontage will bypass the detention system. The existing improvements on Lot 1 are included in flow control to mitigate for the bypass area. The Basin Swap area exceeds the 0.049 acre required for mitigation; therefore, the excess area is modeled as passing through the detention system (0.022 acre of impervious surfacing). The 0.022 acre of pass-through area is included in both the predeveloped and developed scenarios. Refer to the Developed Basin Map (Figure 4-2) for the Detention Bypass Basin and the proposed Basin Swap. The Pass-Through Basin north of the site does not require mitigation. The drainage from the Pass-Through Basin will be routed through the detention system; therefore, the basin is included in both the predeveloped and developed basins. 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 basin prior to discharge from the site. The unit will be sized according the GULD approval and the manufacturer’s recommendations. 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. Preliminary Technical Information Report Brar Short Plat 4-3 2200320.10 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. WWHM calculations are provided in Figure 4-3 showing the flow duration standard is met. The required detention volume is 4,560 cubic feet (0.11 ac-ft). Our preliminary design provides a 4-foot deep system with approximately 5,880 cubic feet. (0.13 ac-ft) of storage. The design is 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. Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 4.0 Figures Figure 4-1.........City of Renton Flow Control Application Map – Reference 15-A Figure 4-2.........Predeveloped and Developed Basin Maps Figure 4-3.........Preliminary WWHM Flow Control Calculations PROJECT SITE N BRAR SHORT PLAT PREDEVELOPED CONDITIONS GRAPHIC SCALE 0 50 100 1" = 50 FEET 25 Q:\2020\2200320\10_CIV\CAD\EXHIBITS\20210427 - Basin Map-Predeveloped.dwg PASS-THROUGH BASIN PERVIOUS: 0.99 ACRE IMPERVIOUS: 0.12 ACRE ONSITE BASIN WWHM MODEL PERVIOUS: 0.598 ACRE IMPERVIOUS: 0.0 ACRE DEVELOPED - BASIN SWAP AREA PERVIOUS: 0.016 ACRE IMPERVIOUS: 0.055 ACRE (0.022 ACRE OF IMPERVIOUS AREA IS MODELED AS PASS THROUGH) N BRAR SHORT PLAT DEVELOPED CONDITIONS GRAPHIC SCALE 0 50 100 1" = 50 FEET 25 Q:\2020\2200320\10_CIV\CAD\EXHIBITS\20210427 - Basin Map.dwg PASS-THROUGH BASIN PERVIOUS: 0.99 ACRE IMPERVIOUS: 0.12 ACRE DETENTION BYPASS BASIN PERVIOUS: 0.016 ACRE IMPERVIOUS: 0.033 ACRE BASIN SWAP PERVIOUS: 0.016 ACRE IMPERVIOUS: 0.055 ACRE (0.022 ACRE OF IMPERVIOUS AREA IS MODELED AS LOT 1 PASS THROUGH) ONSITE BASIN PERVIOUS: 0.254 ACRE IMPERVIOUS: 0.344 ACRE WWHM2012 PROJECT REPORT Detention_Brar 4/27/2021 12:26:30 PM Page 2 General Model Information Project Name:Detention_Brar Site Name:Brar Site Address: City: Report Date:4/27/2021 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.000 Version Date:2019/09/13 Version:4.2.17 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year Detention_Brar 4/27/2021 12:26:30 PM Page 3 Landuse Basin Data Predeveloped Land Use Predeveloped Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Mod 0.299 C, Forest, Steep 0.299 Pervious Total 0.598 Impervious Land Use acre Impervious Total 0 Basin Total 0.598 Element Flows To: Surface Interflow Groundwater Detention_Brar 4/27/2021 12:26:30 PM Page 4 Upstream Pass Through Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Mod 0.99 Pervious Total 0.99 Impervious Land Use acre ROOF TOPS FLAT 0.07 DRIVEWAYS FLAT 0.05 Impervious Total 0.12 Basin Total 1.11 Element Flows To: Surface Interflow Groundwater Detention_Brar 4/27/2021 12:26:30 PM Page 5 Lot 1 Pass Through Bypass:No GroundWater:No Pervious Land Use acre Pervious Total 0 Impervious Land Use acre ROOF TOPS FLAT 0.022 Impervious Total 0.022 Basin Total 0.022 Element Flows To: Surface Interflow Groundwater Detention_Brar 4/27/2021 12:26:30 PM Page 6 Mitigated Land Use Developed Basin Bypass:No GroundWater:No Pervious Land Use acre C, Pasture, Mod 0.254 Pervious Total 0.254 Impervious Land Use acre ROADS MOD 0.172 ROOF TOPS FLAT 0.172 Impervious Total 0.344 Basin Total 0.598 Element Flows To: Surface Interflow Groundwater Vault 1 Vault 1 Detention_Brar 4/27/2021 12:26:30 PM Page 7 Pass Through Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Mod 0.99 Pervious Total 0.99 Impervious Land Use acre ROOF TOPS FLAT 0.07 DRIVEWAYS FLAT 0.05 Impervious Total 0.12 Basin Total 1.11 Element Flows To: Surface Interflow Groundwater Vault 1 Vault 1 Detention_Brar 4/27/2021 12:26:30 PM Page 8 Lot 1 Pass Through Bypass:No GroundWater:No Pervious Land Use acre Pervious Total 0 Impervious Land Use acre ROOF TOPS FLAT 0.022 Impervious Total 0.022 Basin Total 0.022 Element Flows To: Surface Interflow Groundwater Vault 1 Vault 1 Detention_Brar 4/27/2021 12:26:30 PM Page 9 Routing Elements Predeveloped Routing Detention_Brar 4/27/2021 12:26:30 PM Page 10 Mitigated Routing Vault 1 Width:12 ft. Length:95 ft. Depth:5 ft. Discharge Structure Riser Height:4 ft. Riser Diameter:18 in. Orifice 1 Diameter:1.25 in.Elevation:0 ft. Orifice 2 Diameter:0.8 in.Elevation:2.67 ft. Orifice 3 Diameter:0.45 in.Elevation:3.5 ft. Element Flows To: Outlet 1 Outlet 2 Vault Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)Infilt(cfs) 0.0000 0.026 0.000 0.000 0.000 0.0556 0.026 0.001 0.010 0.000 0.1111 0.026 0.002 0.014 0.000 0.1667 0.026 0.004 0.017 0.000 0.2222 0.026 0.005 0.020 0.000 0.2778 0.026 0.007 0.022 0.000 0.3333 0.026 0.008 0.024 0.000 0.3889 0.026 0.010 0.026 0.000 0.4444 0.026 0.011 0.028 0.000 0.5000 0.026 0.013 0.030 0.000 0.5556 0.026 0.014 0.031 0.000 0.6111 0.026 0.016 0.033 0.000 0.6667 0.026 0.017 0.034 0.000 0.7222 0.026 0.018 0.036 0.000 0.7778 0.026 0.020 0.037 0.000 0.8333 0.026 0.021 0.038 0.000 0.8889 0.026 0.023 0.040 0.000 0.9444 0.026 0.024 0.041 0.000 1.0000 0.026 0.026 0.042 0.000 1.0556 0.026 0.027 0.043 0.000 1.1111 0.026 0.029 0.044 0.000 1.1667 0.026 0.030 0.045 0.000 1.2222 0.026 0.032 0.046 0.000 1.2778 0.026 0.033 0.047 0.000 1.3333 0.026 0.034 0.049 0.000 1.3889 0.026 0.036 0.050 0.000 1.4444 0.026 0.037 0.051 0.000 1.5000 0.026 0.039 0.051 0.000 1.5556 0.026 0.040 0.052 0.000 1.6111 0.026 0.042 0.053 0.000 1.6667 0.026 0.043 0.054 0.000 1.7222 0.026 0.045 0.055 0.000 1.7778 0.026 0.046 0.056 0.000 1.8333 0.026 0.048 0.057 0.000 1.8889 0.026 0.049 0.058 0.000 1.9444 0.026 0.050 0.059 0.000 2.0000 0.026 0.052 0.060 0.000 2.0556 0.026 0.053 0.060 0.000 4,560 CU FT REQUIRED Detention_Brar 4/27/2021 12:26:30 PM Page 11 2.1111 0.026 0.055 0.061 0.000 2.1667 0.026 0.056 0.062 0.000 2.2222 0.026 0.058 0.063 0.000 2.2778 0.026 0.059 0.064 0.000 2.3333 0.026 0.061 0.064 0.000 2.3889 0.026 0.062 0.065 0.000 2.4444 0.026 0.064 0.066 0.000 2.5000 0.026 0.065 0.067 0.000 2.5556 0.026 0.066 0.067 0.000 2.6111 0.026 0.068 0.068 0.000 2.6667 0.026 0.069 0.069 0.000 2.7222 0.026 0.071 0.073 0.000 2.7778 0.026 0.072 0.076 0.000 2.8333 0.026 0.074 0.078 0.000 2.8889 0.026 0.075 0.080 0.000 2.9444 0.026 0.077 0.081 0.000 3.0000 0.026 0.078 0.083 0.000 3.0556 0.026 0.080 0.084 0.000 3.1111 0.026 0.081 0.086 0.000 3.1667 0.026 0.082 0.087 0.000 3.2222 0.026 0.084 0.089 0.000 3.2778 0.026 0.085 0.090 0.000 3.3333 0.026 0.087 0.091 0.000 3.3889 0.026 0.088 0.092 0.000 3.4444 0.026 0.090 0.094 0.000 3.5000 0.026 0.091 0.095 0.000 3.5556 0.026 0.093 0.097 0.000 3.6111 0.026 0.094 0.099 0.000 3.6667 0.026 0.096 0.100 0.000 3.7222 0.026 0.097 0.102 0.000 3.7778 0.026 0.098 0.103 0.000 3.8333 0.026 0.100 0.104 0.000 3.8889 0.026 0.101 0.106 0.000 3.9444 0.026 0.103 0.107 0.000 4.0000 0.026 0.104 0.108 0.000 4.0556 0.026 0.106 0.318 0.000 4.1111 0.026 0.107 0.698 0.000 4.1667 0.026 0.109 1.186 0.000 4.2222 0.026 0.110 1.750 0.000 4.2778 0.026 0.112 2.363 0.000 4.3333 0.026 0.113 2.998 0.000 4.3889 0.026 0.114 3.626 0.000 4.4444 0.026 0.116 4.221 0.000 4.5000 0.026 0.117 4.758 0.000 4.5556 0.026 0.119 5.217 0.000 4.6111 0.026 0.120 5.589 0.000 4.6667 0.026 0.122 5.876 0.000 4.7222 0.026 0.123 6.097 0.000 4.7778 0.026 0.125 6.374 0.000 4.8333 0.026 0.126 6.594 0.000 4.8889 0.026 0.127 6.807 0.000 4.9444 0.026 0.129 7.014 0.000 5.0000 0.026 0.130 7.214 0.000 5.0556 0.026 0.132 7.409 0.000 5.1111 0.000 0.000 7.600 0.000 Detention_Brar 4/27/2021 12:26:30 PM Page 12 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:1.588 Total Impervious Area:0.142 Mitigated Landuse Totals for POC #1 Total Pervious Area:1.244 Total Impervious Area:0.486 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.159116 5 year 0.252714 10 year 0.323511 25 year 0.42264 50 year 0.503379 100 year 0.589959 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.073424 5 year 0.131825 10 year 0.187213 25 year 0.281927 50 year 0.374649 100 year 0.490456 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.278 0.062 1950 0.292 0.072 1951 0.172 0.191 1952 0.090 0.051 1953 0.068 0.048 1954 0.124 0.059 1955 0.130 0.085 1956 0.151 0.064 1957 0.192 0.065 1958 0.101 0.063 Detention_Brar 4/27/2021 12:27:10 PM Page 13 1959 0.090 0.055 1960 0.186 0.166 1961 0.139 0.061 1962 0.068 0.045 1963 0.144 0.059 1964 0.139 0.059 1965 0.194 0.062 1966 0.096 0.049 1967 0.288 0.080 1968 0.189 0.055 1969 0.169 0.060 1970 0.143 0.055 1971 0.182 0.062 1972 0.256 0.098 1973 0.079 0.055 1974 0.180 0.053 1975 0.207 0.079 1976 0.142 0.059 1977 0.112 0.039 1978 0.140 0.058 1979 0.101 0.046 1980 0.352 0.092 1981 0.135 0.053 1982 0.308 0.332 1983 0.156 0.067 1984 0.103 0.051 1985 0.130 0.054 1986 0.173 0.114 1987 0.162 0.147 1988 0.062 0.052 1989 0.058 0.040 1990 0.583 0.442 1991 0.387 0.263 1992 0.124 0.054 1993 0.075 0.057 1994 0.052 0.035 1995 0.116 0.068 1996 0.292 0.240 1997 0.189 0.228 1998 0.141 0.054 1999 0.425 0.093 2000 0.158 0.057 2001 0.084 0.040 2002 0.246 0.104 2003 0.231 0.046 2004 0.326 0.351 2005 0.160 0.069 2006 0.160 0.067 2007 0.526 0.339 2008 0.373 0.482 2009 0.223 0.099 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.5828 0.4817 2 0.5265 0.4425 3 0.4255 0.3509 Detention_Brar 4/27/2021 12:27:10 PM Page 14 4 0.3872 0.3395 5 0.3728 0.3318 6 0.3516 0.2633 7 0.3256 0.2397 8 0.3083 0.2276 9 0.2918 0.1909 10 0.2917 0.1659 11 0.2880 0.1467 12 0.2785 0.1135 13 0.2557 0.1045 14 0.2463 0.0987 15 0.2312 0.0981 16 0.2226 0.0929 17 0.2072 0.0922 18 0.1942 0.0853 19 0.1916 0.0802 20 0.1895 0.0786 21 0.1893 0.0723 22 0.1864 0.0688 23 0.1818 0.0678 24 0.1799 0.0675 25 0.1734 0.0668 26 0.1722 0.0650 27 0.1688 0.0644 28 0.1616 0.0628 29 0.1604 0.0622 30 0.1599 0.0619 31 0.1583 0.0616 32 0.1558 0.0607 33 0.1512 0.0602 34 0.1442 0.0594 35 0.1426 0.0592 36 0.1422 0.0589 37 0.1412 0.0588 38 0.1403 0.0584 39 0.1390 0.0567 40 0.1388 0.0567 41 0.1349 0.0554 42 0.1302 0.0553 43 0.1297 0.0550 44 0.1243 0.0549 45 0.1240 0.0544 46 0.1163 0.0543 47 0.1124 0.0540 48 0.1025 0.0530 49 0.1014 0.0530 50 0.1010 0.0520 51 0.0957 0.0508 52 0.0898 0.0508 53 0.0896 0.0487 54 0.0843 0.0483 55 0.0795 0.0460 56 0.0755 0.0456 57 0.0681 0.0448 58 0.0676 0.0400 59 0.0623 0.0398 60 0.0576 0.0389 61 0.0522 0.0350 Detention_Brar 4/27/2021 12:27:10 PM Page 15 Detention_Brar 4/27/2021 12:27:10 PM Page 16 Duration Flows The Facility PASSED Flow(cfs)Predev Mit Percentage Pass/Fail 0.0796 2220 2139 96 Pass 0.0838 1936 1837 94 Pass 0.0881 1591 1433 90 Pass 0.0924 1372 1138 82 Pass 0.0967 1186 914 77 Pass 0.1010 1032 750 72 Pass 0.1052 852 487 57 Pass 0.1095 747 256 34 Pass 0.1138 636 233 36 Pass 0.1181 528 214 40 Pass 0.1224 455 204 44 Pass 0.1266 404 195 48 Pass 0.1309 346 184 53 Pass 0.1352 300 166 55 Pass 0.1395 276 157 56 Pass 0.1438 248 142 57 Pass 0.1481 216 131 60 Pass 0.1523 198 123 62 Pass 0.1566 182 120 65 Pass 0.1609 161 116 72 Pass 0.1652 143 108 75 Pass 0.1695 131 102 77 Pass 0.1737 126 96 76 Pass 0.1780 116 88 75 Pass 0.1823 106 83 78 Pass 0.1866 101 82 81 Pass 0.1909 93 75 80 Pass 0.1951 82 72 87 Pass 0.1994 80 69 86 Pass 0.2037 77 63 81 Pass 0.2080 70 61 87 Pass 0.2123 65 58 89 Pass 0.2166 63 54 85 Pass 0.2208 61 50 81 Pass 0.2251 58 48 82 Pass 0.2294 58 46 79 Pass 0.2337 55 46 83 Pass 0.2380 52 46 88 Pass 0.2422 48 43 89 Pass 0.2465 47 42 89 Pass 0.2508 42 38 90 Pass 0.2551 40 38 95 Pass 0.2594 38 35 92 Pass 0.2636 36 33 91 Pass 0.2679 35 30 85 Pass 0.2722 33 27 81 Pass 0.2765 32 26 81 Pass 0.2808 30 24 80 Pass 0.2850 28 23 82 Pass 0.2893 26 22 84 Pass 0.2936 23 21 91 Pass 0.2979 23 20 86 Pass 0.3022 20 20 100 Pass MEETS FLOW CONTROL STANDARDS Detention_Brar 4/27/2021 12:27:10 PM Page 17 0.3065 19 20 105 Pass 0.3107 18 19 105 Pass 0.3150 17 17 100 Pass 0.3193 16 17 106 Pass 0.3236 15 14 93 Pass 0.3279 14 13 92 Pass 0.3321 13 12 92 Pass 0.3364 13 12 92 Pass 0.3407 13 11 84 Pass 0.3450 13 10 76 Pass 0.3493 13 10 76 Pass 0.3535 12 7 58 Pass 0.3578 12 7 58 Pass 0.3621 10 6 60 Pass 0.3664 9 6 66 Pass 0.3707 7 6 85 Pass 0.3749 6 6 100 Pass 0.3792 6 6 100 Pass 0.3835 6 6 100 Pass 0.3878 6 5 83 Pass 0.3921 5 4 80 Pass 0.3964 5 4 80 Pass 0.4006 5 4 80 Pass 0.4049 5 4 80 Pass 0.4092 5 3 60 Pass 0.4135 5 2 40 Pass 0.4178 5 2 40 Pass 0.4220 4 2 50 Pass 0.4263 3 2 66 Pass 0.4306 3 2 66 Pass 0.4349 3 2 66 Pass 0.4392 3 2 66 Pass 0.4434 3 1 33 Pass 0.4477 2 1 50 Pass 0.4520 2 1 50 Pass 0.4563 2 1 50 Pass 0.4606 2 1 50 Pass 0.4648 2 1 50 Pass 0.4691 2 1 50 Pass 0.4734 2 1 50 Pass 0.4777 2 1 50 Pass 0.4820 2 1 50 Pass 0.4863 2 0 0 Pass 0.4905 2 0 0 Pass 0.4948 2 0 0 Pass 0.4991 2 0 0 Pass 0.5034 2 0 0 Pass Detention_Brar 4/27/2021 12:27:10 PM Page 18 Water Quality Water Quality BMP Flow and Volume for POC #1 On-line facility volume:0 acre-feet On-line facility target flow:0 cfs. Adjusted for 15 min:0 cfs. Off-line facility target flow:0 cfs. Adjusted for 15 min:0 cfs. FINAL WQ SIZING TO BE PROVIDED WITH FINAL ENGINEERING Detention_Brar 4/27/2021 12:27:10 PM Page 19 LID Report Detention_Brar 4/27/2021 12:27:39 PM Page 20 Model Default Modifications Total of 0 changes have been made. PERLND Changes No PERLND changes have been made. IMPLND Changes No IMPLND changes have been made. Detention_Brar 4/27/2021 12:27:39 PM Page 21 Appendix Predeveloped Schematic Detention_Brar 4/27/2021 12:27:40 PM Page 22 Mitigated Schematic Detention_Brar 4/27/2021 12:27:42 PM Page 23 Predeveloped UCI File RUN GLOBAL WWHM4 model simulation START 1948 10 01 END 2009 09 30 RUN INTERP OUTPUT LEVEL 3 0 RESUME 0 RUN 1 UNIT SYSTEM 1 END GLOBAL FILES <File> <Un#> <-----------File Name------------------------------>*** <-ID-> *** WDM 26 Detention_Brar.wdm MESSU 25 PreDetention_Brar.MES 27 PreDetention_Brar.L61 28 PreDetention_Brar.L62 30 POCDetention_Brar1.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 11 PERLND 12 PERLND 17 IMPLND 4 IMPLND 5 COPY 501 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<----------Title----------->***TRAN PIVL DIG1 FIL1 PYR DIG2 FIL2 YRND 1 Predeveloped MAX 1 2 30 9 END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 501 1 1 END TIMESERIES END COPY GENER OPCODE # # OPCD *** END OPCODE PARM # # K *** END PARM END GENER PERLND GEN-INFO <PLS ><-------Name------->NBLKS Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 11 C, Forest, Mod 1 1 1 1 27 0 12 C, Forest, Steep 1 1 1 1 27 0 17 C, Lawn, Mod 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 11 0 0 1 0 0 0 0 0 0 0 0 0 12 0 0 1 0 0 0 0 0 0 0 0 0 17 0 0 1 0 0 0 0 0 0 0 0 0 Detention_Brar 4/27/2021 12:27:42 PM Page 24 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 11 0 0 4 0 0 0 0 0 0 0 0 0 1 9 12 0 0 4 0 0 0 0 0 0 0 0 0 1 9 17 0 0 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO PWAT-PARM1 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** 11 0 0 0 0 0 0 0 0 0 0 0 12 0 0 0 0 0 0 0 0 0 0 0 17 0 0 0 0 0 0 0 0 0 0 0 END PWAT-PARM1 PWAT-PARM2 <PLS > PWATER input info: Part 2 *** # - # ***FOREST LZSN INFILT LSUR SLSUR KVARY AGWRC 11 0 4.5 0.08 400 0.1 0.5 0.996 12 0 4.5 0.08 400 0.15 0.5 0.996 17 0 4.5 0.03 400 0.1 0.5 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 11 0 0 2 2 0 0 0 12 0 0 2 2 0 0 0 17 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 11 0.2 0.5 0.35 6 0.5 0.7 12 0.2 0.3 0.35 6 0.3 0.7 17 0.1 0.25 0.25 6 0.5 0.25 END PWAT-PARM4 PWAT-STATE1 <PLS > *** Initial conditions at start of simulation ran from 1990 to end of 1992 (pat 1-11-95) RUN 21 *** # - # *** CEPS SURS UZS IFWS LZS AGWS GWVS 11 0 0 0 0 2.5 1 0 12 0 0 0 0 2.5 1 0 17 0 0 0 0 2.5 1 0 END PWAT-STATE1 END PERLND IMPLND GEN-INFO <PLS ><-------Name-------> Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 4 ROOF TOPS/FLAT 1 1 1 27 0 5 DRIVEWAYS/FLAT 1 1 1 27 0 END GEN-INFO *** Section IWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** 4 0 0 1 0 0 0 5 0 0 1 0 0 0 END ACTIVITY PRINT-INFO Detention_Brar 4/27/2021 12:27:42 PM Page 25 <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* 4 0 0 4 0 0 0 1 9 5 0 0 4 0 0 0 1 9 END PRINT-INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** 4 0 0 0 0 0 5 0 0 0 0 0 END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC 4 400 0.01 0.1 0.1 5 400 0.01 0.1 0.1 END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN 4 0 0 5 0 0 END IWAT-PARM3 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS 4 0 0 5 0 0 END IWAT-STATE1 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** Predeveloped *** PERLND 11 0.299 COPY 501 12 PERLND 11 0.299 COPY 501 13 PERLND 12 0.299 COPY 501 12 PERLND 12 0.299 COPY 501 13 Upstream Pass Through*** PERLND 17 0.99 COPY 501 12 PERLND 17 0.99 COPY 501 13 IMPLND 4 0.07 COPY 501 15 IMPLND 5 0.05 COPY 501 15 Lot 1 Pass Through*** IMPLND 4 0.022 COPY 501 15 ******Routing****** END SCHEMATIC NETWORK <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** COPY 501 OUTPUT MEAN 1 1 48.4 DISPLY 1 INPUT TIMSER 1 <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** END NETWORK RCHRES GEN-INFO RCHRES Name Nexits Unit Systems Printer *** # - #<------------------><---> User T-series Engl Metr LKFG *** Detention_Brar 4/27/2021 12:27:42 PM Page 26 in out *** END GEN-INFO *** Section RCHRES*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # HYFG ADFG CNFG HTFG SDFG GQFG OXFG NUFG PKFG PHFG *** END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ******************* PIVL PYR # - # HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB PIVL PYR ********* END PRINT-INFO HYDR-PARM1 RCHRES Flags for each HYDR Section *** # - # VC A1 A2 A3 ODFVFG for each *** ODGTFG for each FUNCT for each FG FG FG FG possible exit *** possible exit possible exit * * * * * * * * * * * * * * *** END HYDR-PARM1 HYDR-PARM2 # - # FTABNO LEN DELTH STCOR KS DB50 *** <------><--------><--------><--------><--------><--------><--------> *** END HYDR-PARM2 HYDR-INIT RCHRES Initial conditions for each HYDR section *** # - # *** VOL Initial value of COLIND Initial value of OUTDGT *** ac-ft for each possible exit for each possible exit <------><--------> <---><---><---><---><---> *** <---><---><---><---><---> END HYDR-INIT END RCHRES SPEC-ACTIONS END SPEC-ACTIONS FTABLES END FTABLES EXT SOURCES <-Volume-> <Member> SsysSgap<--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # tem strg<-factor->strg <Name> # # <Name> # # *** WDM 2 PREC ENGL 1 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 1 IMPLND 1 999 EXTNL PREC WDM 1 EVAP ENGL 0.76 PERLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 IMPLND 1 999 EXTNL PETINP END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** COPY 501 OUTPUT MEAN 1 1 48.4 WDM 501 FLOW ENGL REPL END EXT TARGETS MASS-LINK <Volume> <-Grp> <-Member-><--Mult--> <Target> <-Grp> <-Member->*** <Name> <Name> # #<-factor-> <Name> <Name> # #*** MASS-LINK 12 PERLND PWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 12 MASS-LINK 13 PERLND PWATER IFWO 0.083333 COPY INPUT MEAN END MASS-LINK 13 MASS-LINK 15 IMPLND IWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 15 Detention_Brar 4/27/2021 12:27:42 PM Page 27 END MASS-LINK END RUN Detention_Brar 4/27/2021 12:27:42 PM Page 28 Mitigated UCI File RUN GLOBAL WWHM4 model simulation START 1948 10 01 END 2009 09 30 RUN INTERP OUTPUT LEVEL 3 0 RESUME 0 RUN 1 UNIT SYSTEM 1 END GLOBAL FILES <File> <Un#> <-----------File Name------------------------------>*** <-ID-> *** WDM 26 Detention_Brar.wdm MESSU 25 MitDetention_Brar.MES 27 MitDetention_Brar.L61 28 MitDetention_Brar.L62 30 POCDetention_Brar1.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 14 IMPLND 2 IMPLND 4 PERLND 17 IMPLND 5 RCHRES 1 COPY 1 COPY 501 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<----------Title----------->***TRAN PIVL DIG1 FIL1 PYR DIG2 FIL2 YRND 1 Vault 1 MAX 1 2 30 9 END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 501 1 1 END TIMESERIES END COPY GENER OPCODE # # OPCD *** END OPCODE PARM # # K *** END PARM END GENER PERLND GEN-INFO <PLS ><-------Name------->NBLKS Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 14 C, Pasture, Mod 1 1 1 1 27 0 17 C, Lawn, Mod 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 14 0 0 1 0 0 0 0 0 0 0 0 0 17 0 0 1 0 0 0 0 0 0 0 0 0 Detention_Brar 4/27/2021 12:27:42 PM Page 29 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 14 0 0 4 0 0 0 0 0 0 0 0 0 1 9 17 0 0 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO PWAT-PARM1 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** 14 0 0 0 0 0 0 0 0 0 0 0 17 0 0 0 0 0 0 0 0 0 0 0 END PWAT-PARM1 PWAT-PARM2 <PLS > PWATER input info: Part 2 *** # - # ***FOREST LZSN INFILT LSUR SLSUR KVARY AGWRC 14 0 4.5 0.06 400 0.1 0.5 0.996 17 0 4.5 0.03 400 0.1 0.5 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 14 0 0 2 2 0 0 0 17 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 14 0.15 0.4 0.3 6 0.5 0.4 17 0.1 0.25 0.25 6 0.5 0.25 END PWAT-PARM4 PWAT-STATE1 <PLS > *** Initial conditions at start of simulation ran from 1990 to end of 1992 (pat 1-11-95) RUN 21 *** # - # *** CEPS SURS UZS IFWS LZS AGWS GWVS 14 0 0 0 0 2.5 1 0 17 0 0 0 0 2.5 1 0 END PWAT-STATE1 END PERLND IMPLND GEN-INFO <PLS ><-------Name-------> Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 2 ROADS/MOD 1 1 1 27 0 4 ROOF TOPS/FLAT 1 1 1 27 0 5 DRIVEWAYS/FLAT 1 1 1 27 0 END GEN-INFO *** Section IWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** 2 0 0 1 0 0 0 4 0 0 1 0 0 0 5 0 0 1 0 0 0 END ACTIVITY PRINT-INFO <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* 2 0 0 4 0 0 0 1 9 4 0 0 4 0 0 0 1 9 Detention_Brar 4/27/2021 12:27:42 PM Page 30 5 0 0 4 0 0 0 1 9 END PRINT-INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** 2 0 0 0 0 0 4 0 0 0 0 0 5 0 0 0 0 0 END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC 2 400 0.05 0.1 0.08 4 400 0.01 0.1 0.1 5 400 0.01 0.1 0.1 END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN 2 0 0 4 0 0 5 0 0 END IWAT-PARM3 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS 2 0 0 4 0 0 5 0 0 END IWAT-STATE1 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** Developed Basin*** PERLND 14 0.254 RCHRES 1 2 PERLND 14 0.254 RCHRES 1 3 IMPLND 2 0.172 RCHRES 1 5 IMPLND 4 0.172 RCHRES 1 5 Pass Through*** PERLND 17 0.99 RCHRES 1 2 PERLND 17 0.99 RCHRES 1 3 IMPLND 4 0.07 RCHRES 1 5 IMPLND 5 0.05 RCHRES 1 5 Lot 1 Pass Through*** IMPLND 4 0.022 RCHRES 1 5 ******Routing****** PERLND 14 0.254 COPY 1 12 IMPLND 2 0.172 COPY 1 15 IMPLND 4 0.172 COPY 1 15 PERLND 14 0.254 COPY 1 13 PERLND 17 0.99 COPY 1 12 IMPLND 4 0.07 COPY 1 15 IMPLND 5 0.05 COPY 1 15 PERLND 17 0.99 COPY 1 13 IMPLND 4 0.022 COPY 1 15 RCHRES 1 1 COPY 501 16 END SCHEMATIC NETWORK <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** COPY 501 OUTPUT MEAN 1 1 48.4 DISPLY 1 INPUT TIMSER 1 Detention_Brar 4/27/2021 12:27:42 PM Page 31 <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** END NETWORK RCHRES GEN-INFO RCHRES Name Nexits Unit Systems Printer *** # - #<------------------><---> User T-series Engl Metr LKFG *** in out *** 1 Vault 1 1 1 1 1 28 0 1 END GEN-INFO *** Section RCHRES*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # HYFG ADFG CNFG HTFG SDFG GQFG OXFG NUFG PKFG PHFG *** 1 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ******************* PIVL PYR # - # HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB PIVL PYR ********* 1 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO HYDR-PARM1 RCHRES Flags for each HYDR Section *** # - # VC A1 A2 A3 ODFVFG for each *** ODGTFG for each FUNCT for each FG FG FG FG possible exit *** possible exit possible exit * * * * * * * * * * * * * * *** 1 0 1 0 0 4 0 0 0 0 0 0 0 0 0 2 2 2 2 2 END HYDR-PARM1 HYDR-PARM2 # - # FTABNO LEN DELTH STCOR KS DB50 *** <------><--------><--------><--------><--------><--------><--------> *** 1 1 0.02 0.0 0.0 0.5 0.0 END HYDR-PARM2 HYDR-INIT RCHRES Initial conditions for each HYDR section *** # - # *** VOL Initial value of COLIND Initial value of OUTDGT *** ac-ft for each possible exit for each possible exit <------><--------> <---><---><---><---><---> *** <---><---><---><---><---> 1 0 4.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 END HYDR-INIT END RCHRES SPEC-ACTIONS END SPEC-ACTIONS FTABLES FTABLE 1 92 4 Depth Area Volume Outflow1 Velocity Travel Time*** (ft) (acres) (acre-ft) (cfs) (ft/sec) (Minutes)*** 0.000000 0.026171 0.000000 0.000000 0.055556 0.026171 0.001454 0.009994 0.111111 0.026171 0.002908 0.014134 0.166667 0.026171 0.004362 0.017310 0.222222 0.026171 0.005816 0.019988 0.277778 0.026171 0.007270 0.022347 0.333333 0.026171 0.008724 0.024480 0.388889 0.026171 0.010178 0.026442 0.444444 0.026171 0.011631 0.028268 0.500000 0.026171 0.013085 0.029982 0.555556 0.026171 0.014539 0.031604 0.611111 0.026171 0.015993 0.033147 0.666667 0.026171 0.017447 0.034620 Detention_Brar 4/27/2021 12:27:42 PM Page 32 0.722222 0.026171 0.018901 0.036034 0.777778 0.026171 0.020355 0.037394 0.833333 0.026171 0.021809 0.038707 0.888889 0.026171 0.023263 0.039976 0.944444 0.026171 0.024717 0.041207 1.000000 0.026171 0.026171 0.042401 1.055556 0.026171 0.027625 0.043563 1.111111 0.026171 0.029079 0.044695 1.166667 0.026171 0.030533 0.045799 1.222222 0.026171 0.031987 0.046876 1.277778 0.026171 0.033440 0.047930 1.333333 0.026171 0.034894 0.048961 1.388889 0.026171 0.036348 0.049970 1.444444 0.026171 0.037802 0.050960 1.500000 0.026171 0.039256 0.051931 1.555556 0.026171 0.040710 0.052884 1.611111 0.026171 0.042164 0.053820 1.666667 0.026171 0.043618 0.054740 1.722222 0.026171 0.045072 0.055645 1.777778 0.026171 0.046526 0.056535 1.833333 0.026171 0.047980 0.057412 1.888889 0.026171 0.049434 0.058275 1.944444 0.026171 0.050888 0.059126 2.000000 0.026171 0.052342 0.059964 2.055556 0.026171 0.053796 0.060792 2.111111 0.026171 0.055249 0.061608 2.166667 0.026171 0.056703 0.062413 2.222222 0.026171 0.058157 0.063208 2.277778 0.026171 0.059611 0.063993 2.333333 0.026171 0.061065 0.064769 2.388889 0.026171 0.062519 0.065536 2.444444 0.026171 0.063973 0.066293 2.500000 0.026171 0.065427 0.067042 2.555556 0.026171 0.066881 0.067783 2.611111 0.026171 0.068335 0.068516 2.666667 0.026171 0.069789 0.069241 2.722222 0.026171 0.071243 0.073927 2.777778 0.026171 0.072697 0.076370 2.833333 0.026171 0.074151 0.078391 2.888889 0.026171 0.075605 0.080194 2.944444 0.026171 0.077058 0.081856 3.000000 0.026171 0.078512 0.083418 3.055556 0.026171 0.079966 0.084902 3.111111 0.026171 0.081420 0.086324 3.166667 0.026171 0.082874 0.087693 3.222222 0.026171 0.084328 0.089019 3.277778 0.026171 0.085782 0.090306 3.333333 0.026171 0.087236 0.091559 3.388889 0.026171 0.088690 0.092782 3.444444 0.026171 0.090144 0.093977 3.500000 0.026171 0.091598 0.095148 3.555556 0.026171 0.093052 0.097591 3.611111 0.026171 0.094506 0.099255 3.666667 0.026171 0.095960 0.100774 3.722222 0.026171 0.097414 0.102211 3.777778 0.026171 0.098867 0.103589 3.833333 0.026171 0.100321 0.104922 3.888889 0.026171 0.101775 0.106218 3.944444 0.026171 0.103229 0.107481 4.000000 0.026171 0.104683 0.108717 4.055556 0.026171 0.106137 0.318200 4.111111 0.026171 0.107591 0.698922 4.166667 0.026171 0.109045 1.186555 4.222222 0.026171 0.110499 1.750379 4.277778 0.026171 0.111953 2.363402 4.333333 0.026171 0.113407 2.998200 4.388889 0.026171 0.114861 3.626701 4.444444 0.026171 0.116315 4.221498 4.500000 0.026171 0.117769 4.758028 4.555556 0.026171 0.119223 5.217348 Detention_Brar 4/27/2021 12:27:42 PM Page 33 4.611111 0.026171 0.120676 5.589382 4.666667 0.026171 0.122130 5.876568 4.722222 0.026171 0.123584 6.097856 4.777778 0.026171 0.125038 6.373961 4.833333 0.026171 0.126492 6.594321 4.888889 0.026171 0.127946 6.807474 4.944444 0.026171 0.129400 7.014084 5.000000 0.026171 0.130854 7.214720 5.055556 0.026171 0.132308 7.409875 END FTABLE 1 END FTABLES EXT SOURCES <-Volume-> <Member> SsysSgap<--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # tem strg<-factor->strg <Name> # # <Name> # # *** WDM 2 PREC ENGL 1 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 1 IMPLND 1 999 EXTNL PREC WDM 1 EVAP ENGL 0.76 PERLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 IMPLND 1 999 EXTNL PETINP END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** RCHRES 1 HYDR RO 1 1 1 WDM 1004 FLOW ENGL REPL RCHRES 1 HYDR STAGE 1 1 1 WDM 1005 STAG ENGL REPL COPY 1 OUTPUT MEAN 1 1 48.4 WDM 701 FLOW ENGL REPL COPY 501 OUTPUT MEAN 1 1 48.4 WDM 801 FLOW ENGL REPL END EXT TARGETS MASS-LINK <Volume> <-Grp> <-Member-><--Mult--> <Target> <-Grp> <-Member->*** <Name> <Name> # #<-factor-> <Name> <Name> # #*** MASS-LINK 2 PERLND PWATER SURO 0.083333 RCHRES INFLOW IVOL END MASS-LINK 2 MASS-LINK 3 PERLND PWATER IFWO 0.083333 RCHRES INFLOW IVOL END MASS-LINK 3 MASS-LINK 5 IMPLND IWATER SURO 0.083333 RCHRES INFLOW IVOL END MASS-LINK 5 MASS-LINK 12 PERLND PWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 12 MASS-LINK 13 PERLND PWATER IFWO 0.083333 COPY INPUT MEAN END MASS-LINK 13 MASS-LINK 15 IMPLND IWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 15 MASS-LINK 16 RCHRES ROFLOW COPY INPUT MEAN END MASS-LINK 16 END MASS-LINK END RUN Detention_Brar 4/27/2021 12:27:42 PM Page 34 Predeveloped HSPF Message File Detention_Brar 4/27/2021 12:27:42 PM Page 35 Mitigated HSPF Message File Detention_Brar 4/27/2021 12:27:42 PM Page 36 Disclaimer Legal Notice 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. 2005-2021; All Rights Reserved. Clear Creek Solutions, Inc. 6200 Capitol Blvd. Ste F Olympia, WA. 98501 Toll Free 1(866)943-0304 Local (360)943-0304 www.clearcreeksolutions.com Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 5 Conveyance System Analysis and Design Preliminary Technical Information Report Brar Short Plat 5-1 2200320.10 5.0 Conveyance System Analysis and Design All onsite conveyance systems will be sized to meet the requirements of Chapter 4 of the CRSWDM. Conveyance calculations will be provided with the final engineering design. Stormwater improvements will reduce discharge from the site by providing flow control. The 100-year discharge rate from the detention system is approximately 0.5 cfs. The conveyance line along the frontage consists of two 12-inch pipes at 1.46% and 0.83%. The Flow Master program is used to evaluate the most restrictive 0.83% slope pipe with a full flow capacity of 4.2 cfs (refer to Figure 5-1). The 0.5 cfs from the site is well within the 4.2 cfs conveyance capacity of the system. The existing conveyance system along the frontage appears to be adequately sized for the developed conditions. Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 5.0 Figures Figure 5-1.........Frontage Conveyance Check 2215 North 30th Street Suite 300 Tacoma, WA 98403 253.383.2422 TEL 253.383.2572 FAX BRAR SHORT PLAT - 2200320.10 FRONTAGE CONVEYANCE CHECK 5-1 Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 6 Special Reports and Studies Preliminary Technical Information Report Brar Short Plat 6-1 2200320.10 6.0 Special Reports and Studies A Geotechnical Engineering Report, dated August 3, 2020, by South Sound Geotechnical Consulting is included as Figure 6-1. Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 6.0 Figures Figure 6-1.........Geotechnical Engineering Report South Sound Geotechnical Consulting August 3, 2020 LSB Petroleum, LLC 11706 - 164th Ave SE Renton, WA 98059 Attention: Mr. Lakhpal Brar Subject: Geotechnical Engineering Report Brar Short Plat 8054 S. 132nd Street Renton, Washington SSGC Project No. 20058 Ms. Brar, South Sound Geotechnical Consulting (SSGC) has completed a geotechnical assessment for the planned short plat on the above addressed property in Renton, Washington. Our services have been completed in general conformance with our proposal P20050 (dated June 23, 2020) and authorized per signature of our agreement for services. Our scope of services included completion of five test pits, one infiltration test, laboratory testing, engineering analyses, and preparation of this report. PROJECT INFORMATION The project property is on the north side of S. 132nd Street and encompasses approximately 0.75 acres. It is rectangular with the long axis trending in a north-south direction. A single-family residence currently occupies the southern portion. One shop/garage structure is in the northwestern portion. The property is on a south-facing slope with elevation change on the order of 30 feet (+/-) per Google satellite imagery. Proposed development includes short plating the property into four individual lots. We understand the existing residence will remain as one of the lots. Conventional spread footing foundations are anticipated for support of new structures with concrete slab-on-grade garage floors. SUBSURFACE CONDITIONS Subsurface conditions were characterized by completing four test pits and one infiltration test on the site on July 8, 2020. Test holes were advanced to final depths between 6 and 10 feet below existing ground surface. Approximate locations of the test pits and infiltration test site are shown on Figure 1, Exploration Plan. Logs of these explorations are provided in Appendix A. A summary description of observed subgrade conditions is provided below. Geotechnical Engineering Report SSGC Brar Short Plat – S. 132nd St Renton, WA SSGC Project No. 20058 August 3, 2020 2 Soil Conditions Fill was observed at the surface in two of the test pits and extended to depths of about 1 to 1.5 feet. It consisted of loose silt, sand, and gravel and likely sourced from the property during construction of existing improvements. Topsoil was below the fill (and below the surface in the remaining excavations) and ranged in thickness from about 6 inches to 1 foot at the test locations. Native soil below the topsoil consisted of an upper silty sand with variable gravel. This soil was in a loose condition and ranged in thickness from about 6 inches to 2 feet, where present. An interpreted weathered glacial till was below the upper soil and consisted of silty sand with gravel and occasional cobbles in a loose to medium dense condition. This weathered zone extended to depths between 3 and 46feet. Dense glacial till was below the weathered zone and extended to the termination depths of the explorations. Groundwater Conditions Groundwater was not observed in the test holes at the time of excavation. However, mottling of the upper native silty sand and weathered till layer implies perched groundwater conditions during the wetter seasons of the year. The presence of dense glacial till can create perched groundwater in the upper soils. Groundwater levels will vary throughout the year based on seasonal precipitation and on- and off-site drainage patterns. Geologic Setting Soils within the development area have been classified by the NRCS in the Soil Survey of King County, Washington. Surface soils are mapped as Alderwood gravelly sandy loam. This soil is described as forming in glacial till. Native soils observed in the test holes appear to consist of a thin layer of alluvium over glacial till, conforming to the mapped soil type. GEOTECHNICAL DESIGN CONSIDERATIONS Development for the proposed plat is considered feasible based on observed soil conditions in the test pits. Properly prepared native soils can be used for support of conventional spread footing foundations, floor slabs, and pavements. Infiltration to assist in stormwater control will be difficult at this site. The presence of dense glacial till at fairly shallow depth will limit infiltration to lateral flow through the upper silty sand and weathered till horizons. Infiltration systems will be limited to shallow dispersion facilities as allowed by the city. Recommendations presented in the following sections should be considered general and may require modifications at the time of construction. They are based upon the subsurface conditions observed in the test pits and the assumption that finish site grades will not be substantially different than existing grades. It should be noted subsurface conditions across the site can vary from those depicted on the exploration logs and can change with time. It should be expected that fill of unknown type and thickness may be Geotechnical Engineering Report SSGC Brar Short Plat – S. 132nd St Renton, WA SSGC Project No. 20058 August 3, 2020 3 present due to historic uses of this site. Therefore, proper site preparation will depend upon the weather and soil conditions encountered at the time of construction. We recommend SSGC review final plans and further assess subgrade conditions at the time of construction, as warranted. General Site Preparation Site grading and earthwork should include procedures to control surface water runoff. Grading the site without adequate drainage control measures may negatively impact site soils, resulting in increased export of impacted soil and import of fill materials, t hereby potentially increasing the cost of the earthwork and subgrade preparation phases of the project. Site grading should include removal (stripping) of fill and topsoil or very loose or soft soils in building and pavement areas. Topsoil/fill extended to depths ranging from about 6 inches to 2 feet in the observed test holes, but may be deeper in other areas. Final stripping depths can only be determined at the time of construction. Subgrades should consist of firm, undisturbed native soils following stripping. General Subgrade Preparation Subgrades in building footprints and pavement areas should consist of firm, undisturbed native soils. We recommend exposed subgrades in building and conventional pavement areas are proofrolled using a large roller, loaded dump truck, or other mechanical equipment to assess subgrade conditions following stripping. Proofrolling efforts should result in the upper 1 foot of subgrade soils in building and conventional pavement areas achieving a compaction level of at least 95 percent of the maximum dry density (MDD) per the ASTM D1557 test method. Wet, loose, or soft subgrades that cannot achieve this compaction level should be removed (over-excavated) and replaced with structural fill. The depth of over-excavation should be based on soil conditions at the time of construction. A representative of SSGC should be present to assess subgrade conditions during proofrolling. Grading and Drainage Positive drainage should be provided during construction and maintained throughout the life of the development. Surface water should not be allowed to flow into construction excavations or fill areas. Structural Fill Materials The suitability of soil for use as structural fill will depend on the gradation and moisture content of the soil when it is placed. Soils with higher fines content (soil fraction passing the U.S. No. 200 sieve) will become sensitive with higher moisture content. It is often difficult to achieve adequate compaction if soil moisture is outside of optimum ranges for soils that contain more than about 5 percent fines. Geotechnical Engineering Report SSGC Brar Short Plat – S. 132nd St Renton, WA SSGC Project No. 20058 August 3, 2020 4 Site Soils: Topsoil and existing fill are not considered suitable for use as structural fill. Native soils contain sufficient fines (silt and clay) that make them moisture sensitive and difficult to use as structural fill. These soils would have to be moisture conditioned within optimal moisture content to use as structural fill. Optimum moisture is considered within about +/- 2 percent of the moisture content required to achieve the maximum dry density (MDD) per the ASTM D-1557 test method. If moisture content is higher or lower than optimum, soils would need to be dried or wetted prior to placement as structural fill. Import Fill Materials: We recommend imported structural fill placed during dry weather consist of material which meets the specifications for Gravel Borrow as described in Section 9-03.14(1) of the 2018 Washington State Department of Transportation (WSDOT) Specifications for Road, Bridge, and Municipal Construction manual (Publication M 41-10). Gravel Borrow should be protected from disturbance if exposed to wet conditions after placement. During wet weather, or for backfill on wet subgrades, import soil suitable for compaction in wetter conditions should be provided. Imported fill for use in wet conditions should conform to specifications for Select Borrow as described in Section 9-03.14(2), or Crushed Surfacing per Section 9-03.9(3) of the 2018 WSDOT M-41 manual, with the modification that a maximum of 5 percent by weight shall pass the U.S. No. 200 sieve for these soil types. Structural fill placement and compaction is weather-dependent. Delays due to inclement weather are common, even when using select granular fill. We recommend site grading and earthwork be scheduled for the drier months of the year. Frozen soil is not suitable as structural fill. Structural Fill Placement We recommend structural fill is placed in lifts not exceeding about 10 inches in loose measure. It may be necessary to adjust lift thickness based on site and fill conditions during placement and compaction. Finer grained soil used as structural fill and/or lighter weight compaction equipment may require significantly thinner lifts to attain required compaction levels. Granular soil with lower fines contents could potentially be placed in thicker lifts (1 foot maximum) if they can be adequately compacted. Structural fill should be compacted to attain the recommended levels presented in Table 1, Compaction Criteria. Geotechnical Engineering Report SSGC Brar Short Plat – S. 132nd St Renton, WA SSGC Project No. 20058 August 3, 2020 5 Table 1. Compaction Criteria Fill Application Compaction Criteria* Footing areas 95 % Upper 2 feet in pavement areas, flatwork, and utility trenches 95 % Below 2 feet in pavement areas, flatwork, and utility trenches 92 % Utility trenches or general fill in non-paved or -building areas 90 % *Per the ASTM D 1557 test method. Trench backfill within about 2 feet of utility lines should not be over-compacted to reduce the risk of damage to the line. In some instances, the top of the utility line may be within 2 feet of the surface. Backfill in these circumstances should be compacted to a firm and unyielding condition. We recommend fill procedures include maintaining grades that promote drainage and do not allow ponding of water within the fill area. The contractor should protect compacted fill subgrades from disturbance during wet weather. In the event of rain during structural fill placement, the exposed fill surface should be allowed to dry prior to placement of additional fill. Alternatively, the wet soil can be removed. We recommend consideration is given to protecting haul routes and other high traffic areas with free-draining granular fill material (i.e. sand and gravel containing less than 5 pe rcent fines) or quarry spalls to reduce the potential for disturbance to the subgrade during inclement weather. Structural fill placed on sloping ground should be constructed using a benched (stairstep) methodology. Benches should be cut level or with a slight downward incline into the slope in firm native soil. Benches should be wide enough to accommodate a minimum 20-ton vibratory roller and be a maximum of about two feet high. Earthwork Procedures Conventional earthmoving equipment should be suitable for earthwork at this site. Earthwork may be difficult during periods of wet weather or if elevated soil moisture is present. Excavated site soils may not be suitable as structural fill depending on the soil moisture content and weather conditions at the time of earthwork. If soils are stockpiled and wet weather is anticipated, the stockpile should be protected with securely anchored plastic sheeting. If stockpiled soils become wet and unusable, it will become necessary to import clean, granular soils to complete wet weather site work. Wet or disturbed subgrade soils should be over-excavated to expose firm, non-yielding, non-organic soils and backfilled with compacted structural fill. We recommend the earthwork portion of this project be completed during extended periods of dry weather. If earthwork is completed during the wet season (typically October through April) it may be necessary to take extra measures to protect subgrade soils. Geotechnical Engineering Report SSGC Brar Short Plat – S. 132nd St Renton, WA SSGC Project No. 20058 August 3, 2020 6 If earthwork takes place during freezing conditions, we recommend the exposed subgrade is allowed to thaw and re-compacted prior to placing subsequent lifts of structural fill. Alternatively, the frozen soil can be removed to unfrozen soil and replaced with structural fill. The contractor is responsible for designing and constructing stable, temporary excavations (including utility trenches) as required to maintain stability of excavation sides and bottoms. Excavations should be sloped or shored in the interest of safety following local and federal regulations, including current OSHA excavation and trench safety standards. Temporary excavation cuts should be sloped at inclinations of 1.5H:1V (Horizontal:Vertical) or flatter, unless the contractor can demonstrate the safety of steeper cut slopes. It should be noted outwash soils have the tendency to cave into open excavations. Shoring may be necessary for deeper utility trenches on this site. Permanent cut and fill slopes should be inclined at grades of 2H:1V, or flatter. A geotechnical engineer and accredited materials testing firm should be retained during the construction phase of the project to observe earthwork operations and to perform necessary tests and observations during subgrade preparation, placement and compaction of structural fill, and backfilling of excavations. Foundations Foundations can be placed on firm native soils or on a zone of structural fill above prepared subgrades as described in this report. The following recommendations are for conventional spread footing foundations: Bearing Capacity (net allowable): 3,000 pounds per square foot (psf) for footings supported on firm native soils or structural fill over native subgrades prepared as described in this report. Footing Width (Minimum): 16 inches (Strip) 24 inches (Column) Embedment Depth (Minimum): 18 inches (Exterior) 12 inches (Interior) Settlement: Total: < 1 inch Differential: < 1/2 inch (over 30 feet) Allowable Lateral Passive Resistance: 325 psf/ft* (below 12 inches) Allowable Coefficient of Friction: 0.40* *These values include a factor of safety of approximately 1.5. The net allowable bearing pressures presented above may be increased by one-third to resist transient, dynamic loads such as wind or seismic forces. Lateral resistance to footings should be ignored in the upper 12-inches from exterior finish grade unless restricted. Geotechnical Engineering Report SSGC Brar Short Plat – S. 132nd St Renton, WA SSGC Project No. 20058 August 3, 2020 7 Foundation Construction Considerations All foundation subgrades should be free of water and loose soil prior to placing concrete , and should be prepared as recommended in this report. Concrete should be placed soon after excavating and compaction to reduce disturbance to bearing soils. Should soils at foundation level become excessively dry, disturbed, saturated, or frozen, the affected soil should be removed prior to placing concrete. We recommend SSGC observe foundation subgrades prior to placement of concrete. Foundation Drainage Ground surface adjacent foundations should be sloped away to facilitate drainage. We recommend footing drains are installed around perimeter footings. Footing drains should include a minimum 4- inch diameter perforated rigid plastic or metal drain line installed along the exterior base of the footing. The perforated drain lines should be connected to a tight line pipe that discharges to an approved storm drain receptor. The drain line should be surrounded by a zone of clean, free-draining granular material having less than 5 percent passing the No. 200 sieve or meeting the requirements of section 9-03.12(2) “Gravel Backfill for Walls” in the 2018 WSDOT (M41-10) manual. The free- draining aggregate zone should be at least 12 inches wide and wrapped in filter fabric. The granular fill should extend to within 6 inches of final grade where it should be capped with compacted fill containing sufficient fines to reduce infiltration of surface water into the footing drains. Alternately, the ground surface can be paved with asphalt or concrete. Cleanouts are recommended for maintenance of the drain system. On-Grade Floor Slabs On-grade floor slabs should be placed on native soils or structural fill prepared as described in this report. We recommend a modulus subgrade reaction of 175 pounds per square inch per inch (psi/in) for native soil or compacted granular structural fill over properly prepared native soil. We recommend a capillary break is provided between the prepared subgrade and bottom of slab. Capillary break material should be a minimum of 4 inches thick and consist of compacted clean, free- draining, well graded coarse sand and gravel. The capillary break material should contain less than 5 percent fines, based on that soil fraction passing the U.S. No. 4 sieve . Alternatively, a clean angular gravel such as No. 7 aggregate per Section 9-03.1(4) C of the 2018 WSDOT (M41-10) manual could be used for this purpose. We recommend positive separations and/or isolation joints are provided between slabs and foundations, and columns or utility lines to allow independent movement where needed. Backfill in interior trenches beneath slabs should be compacted in accordance with recommendations presented in this report. Geotechnical Engineering Report SSGC Brar Short Plat – S. 132nd St Renton, WA SSGC Project No. 20058 August 3, 2020 8 A vapor retarder should be considered beneath concrete slabs that will be covered with moisture sensitive or impervious coverings (such as tile, wood, etc.), or when the slab will support equipment or stored materials sensitive to moisture. We recommend the slab designer refer to ACI 302 and/or ACI 360 for procedures and limitations regarding the use and placement of vapor retarders. Seismic Considerations Recommended seismic parameters and values in Table 2 are based on the 2015 International Building Code (IBC). Table 2. Seismic Parameters PARAMETER VALUE 2015 International Building Code (IBC) Site Classification1 D Ss Spectral Acceleration for a Short Period 1.46 S1 Spectral Acceleration for a 1-Second Period 0.546g Fa Site Coefficient for a Short Period 1.00 Fv Site Coefficient for a 1-Second Period 1.50 1 Note: In general accordance with 2015 International Building Code, Section 1613.3.1 for risk categories I,II,III. IBC Site Class is based on the estimated characteristics of the upper 100 feet of the subsurface profile. Ss, S1, Fa, and Fv values based on the OSHPD Seismic Design Maps website. Liquefaction Soil liquefaction is a condition where loose, typically granular soils located below the groundwater surface lose strength during ground shaking, and is often associated with earthquakes. The Seattle Hazard Explorer website does not show the site in a liquefaction prone area. Native soils consist of principally dense to very dense glacially consolidated materials at relatively shallow depth. The risk of liquefaction at this site is considered low for the design level earthquake. Lateral Earth Pressures We anticipate retaining walls may be required in portions of the development. Below grade or retaining walls will be subject to lateral earth pressures. Subgrade walls are typically designed for “active” or “at- rest” earth pressure conditions. Active earth pressure is commonly used for design of free-standing cantilever retaining walls and assumes lateral movement at the top of the wall of around 0.002H to 0.004H, where H is the height of the wall. The at-rest condition assumes no wall movement. Geotechnical Engineering Report SSGC Brar Short Plat – S. 132nd St Renton, WA SSGC Project No. 20058 August 3, 2020 9 We anticipate most walls will retain native outwash or new structural fill to accommodate final site grades. The following recommended earth pressures (Table 3) should be applied as a triangular distribution starting at the top of the wall (for active and at-rest) and bottom of wall (for passive) and assume: ▪ Backfill behind walls is level and no surcharge loads will be applied; ▪ Drainage is provided behind the wall to prevent the development of hydrostatic pressures. Table 3. Lateral Earth Pressures Soil Type Earth Pressure Coefficient* Equivalent Fluid Pressure (pcf)* Loose Native Soils (0 to 4 feet) Active: 0.36 At-rest: 0.53 Passive: 2.80 Active: 40 At-rest: 55 Passive: 300 Dense Glacial Till (Below 4 feet) Active: 0.25 At-rest: 0.38 Passive: 350 Active: 30 At-rest: 45 Passive: 350 * A factor of safety of about 1.5 should be applied to these values. Additional lateral pressure should be added to these values to model surcharges such as adjacent structures, sloped backfill behind the wall, traffic, construction equipment, or seismic loads. We recommend an active seismic pressure of 5H psf (where H is the height of the subgrade wall) and an at- rest seismic pressure of 8H. The effects of other surcharge loads should be accounted for as appropriate. Wall Backfill Backfill behind retaining walls should consist of granular material that satisfies the criteria of Section 9-03.12(2) “Gravel Backfill for Walls” per the 2018 WSDOT (M 41-10) manual, or as approved by the engineer. Wall backfill should be placed in lifts not exceeding 8 inches and compacted with hand-operated compaction equipment. Compaction of wall backfill should be between 90 to 92 percent of the maximum dry density (MDD) per the ASTM D1557 test method within 3 feet of the back of the wall. At a distance greater than 3 feet behind the back of the wall, backfill can be compacted using conventional rollers, with backfill compacted to at least 92 percent of the MDD (ASTM D1557). Wall Drainage Drainage should be provided behind subgrade walls to reduce the potential for hydrostatic pressure developing against the wall and to reduce the risk of groundwater from entering subgrade floors. We recommend a minimum 12-inch wide zone of free draining granular soil (WSDOT Section 9- 03.12(4), or as approved by the design engineer) is placed directly behind the wall. Alternatively, Geotechnical Engineering Report SSGC Brar Short Plat – S. 132nd St Renton, WA SSGC Project No. 20058 August 3, 2020 10 an approved drainage mat can be used behind the wall. A perforated rigid plastic drainpipe at least 6-inches in diameter should be installed behind the base of the wall within 6-inches of the bottom of the footing. The drain line should be surrounded with the free-draining granular soil zone and sloped to provide flow to an approved storm water receptor. The granular fill zone should extend to within 1 foot of final grade of the wall, where it should be capped with compacted low permeable fill containing sufficient fines to reduce infiltration of surface water into the drainage zone. A filter fabric (such as Mirafi 140N, or other approved material) should be placed between native soils and the granular drain material to limit siltation into the drainage zone. Cleanouts are recommended for maintenance of the drain system. Infiltration Characteristics We understand stormwater control will use infiltration facilities. General assessment of infiltration potential of native soils was performed by completing one small-scale Pilot Infiltration Test (PIT) in the proposed storm tract per the 2016 King County Surface Water Design Manual. Test PIT-1 was completed in the upper native silty sand. Results of the infiltration test are presented in Table 3. Table 3. Infiltration Test Results Infiltration Test No. Depth of Test from Surface (feet) Soil Type Field Infiltration Rate (in/hr) Corrected Infiltration Rate (in/hr) Correction Factors* (Fg/Ft/Fp) PIT-1 2 Alluvium/Weathered Till 3 1.2 (1.0/0.5/0.8) * Correction Factors from the 2017 City of Renton Surface Water Design Manual. Correction factors applied to the field rate per equation 5-11 of the County Manual. The tested infiltration rate from PIT-1 is considered appropriate for the soil tested. However, the presence of dense glacial till below the alluvium/weathered till will form a barrier to vertical groundwater flow. We interpret the infiltration rate to be reflective of mostly horizontal flow through the upper soils. Infiltration facilities planned in the upper 3 to 4 feet of site soils should be restricted to shallow dispersion systems as the dense glacial till is considered a barrier which should be accounted for in design . An infiltration rate of 1.2 inches per hour is recommended for dispersion systems in the upper silty sand and weathered till. No infiltration should be accounted for in the dense (unweathered) glacial till. Cation Exchange Capacity (CEC) and organic content test were completed on samples from the two test holes in the storm track area to assess treatment characteristics of the upper outwash soil. Test results are summarized in Table 4. Geotechnical Engineering Report SSGC Brar Short Plat – S. 132nd St Renton, WA SSGC Project No. 20058 August 3, 2020 11 Table 4. CEC and Organic Content Results Test Location, Depth Soil Type CEC Results (milliequivalents) CEC Required* (milliequivalents) Organic Content Results (%) Organic Content Required* (%) PIT-1, 2 feet Alluvium 10 ≥ 5 2.79 ≥1.0 *Per the 2017 City of Renton Surface Water Design Manual. CEC and organic test results satisfy City criteria on the tested soil. Conventional Pavement Sections Subgrades for conventional pavement areas should be prepared as described in the “Subgrade Preparation” section of this report. Subgrades below pavement sections should be graded or crowned to promote drainage and not allow for ponding of water beneath the section. If drainage is not provided and ponding occurs, the subgrade soils could become saturated, lose strength, and result in premature distress to the pavement. In addition, the pavement surfacing should also be graded to promote drainage and reduce the potential for ponding of water on the pavement surface. Minimum recommended pavement section for private driveways are presented in Table 5. Pavement sections in public right-of-ways (S. 132nd Street) should conform to City of Renton requirements for the road designation. Table 5. Preliminary Pavement Sections Traffic Area Minimum Recommended Pavement Section Thickness (inches) Asphalt Concrete Surface1 Portland Cement Concrete Aggregate Base Course2 Subbase Aggregate3 Driveways 2 - 4 12 1 1/2 –inch nominal aggregate hot-mix asphalt (HMA) per WSDOT 9-03.8(1) 2 Crushed Surfacing Base Course per WSDOT 9-03.9(3) 3 Native granular soils compacted to 95% of the ASTM D1557 test method, or Gravel Borrow per WSDOT 9-03.14(1) or Crushed Surfacing Base Course WSDOT 9-03.9(3) Conventional Pavement Maintenance The performance and lifespan of pavements can be significantly impacted by future maintenance. The above pavement sections represent minimum recommended thicknesses and, as such, periodic maintenance should be completed. Proper maintenance will slow the rate of pavement deterioration and will improve pavement performance and life. Preventative maintenance consists of both localized maintenance (crack and joint sealing and patching) and global maintenance (surface Geotechnical Engineering Report SSGC Brar Short Plat – S. 132nd St Renton, WA SSGC Project No. 20058 August 3, 2020 12 sealing). Added maintenance measures should be anticipated over the lifetime of the pavement section if any existing fill or topsoil is left in-place beneath pavement sections. Geologic Hazard Area Discussion The City of Renton’s COR Map for critical areas identifies the south-facing slope as having inclinations between 15 and 25 percent which satisfies criteria per Title IV, Chapter 3 of the City of Renton Municipal Code (RMC) as a regulated slope. The slope is not mapped as a high erosion hazard. Landslide Hazard Native soils on site slopes consist of a relatively thin layer of alluvium, over weathered glacial till, over dense to very dense glacial till. No evidence of recent landslide activity was apparent on site slopes or near the property at the time of our fieldwork. In addition, we are unaware of active landslides within 300 feet of the property. The proposed development should not adversely impact slope stability on the site or on adjacent properties. Erosion Hazard Native glacial soils on the site mapped by the USDA are considered to have a moderate potential to erosion. We observed no evidence of excessive erosion on the property, including the west- facing slope. Regarding planned development, it is our opinion that Best Management Practices (BMP) for erosion control (silt fencing, straw bales, etc) can be utilized such that the risk of off - site transport of sediment is limited during construction. Additional erosion control measures may be necessary if earthwork is scheduled during the wetter seasons. All erosion control provisions should follow City of Renton regulations to reduce the risk of off-site transport of sediments. Exposed soils following construction should be vegetated as soon as possible. REPORT CONDITIONS This report has been prepared for the exclusive use of Mr. Lakhpal Brar and his agents for specific application to the project discussed, and has been prepared in accordance with generally accepted geotechnical engineering practices in the area. No warranties, either express or i mplied, are intended or made. The analysis and recommendations presented in this report are based on observed soil conditions and test results at the indicated locations, and from other geologic information discussed. This report does not reflect variations that may occur across the site, or due to the modifying effects of construction or weather or other natural events. The nature and extent of such variations may not become evident until during or after construction. If variations appear, we should be immediately notified so that further evaluation and supplemental recommendations can be provided. N South Sound Geotechnical Consulting P.O. Box 39500 Lakewood, WA 98496 (253) 973-0515 Figure 1 – Exploration Plan Brar Short Plat Renton, WA SSGC Project #20058 Approximate Test Pit Location PIT - 1 TP - 1 PIT - 1 Approximate Infiltration Test Location Scale: NTS Base map from plan titled “Brar Short Plat - Plot Plan”, by Kaul Design Architecture, PLLC, undated. Legend TP-1 PIT-1 TP-2 TP-3 TP-4 Geotechnical Engineering Report SSGC Brar Short Plat – S. 132nd St Renton, WA SSGC Project No. 20058 August 3, 2020 A-1 Appendix A Field Exploration Procedures and Exploration Logs Geotechnical Engineering Report SSGC Brar Short Plat – S. 132nd St Renton, WA SSGC Project No. 20058 August 3, 2020 Field Exploration Procedures Our field exploration for this project included four test pits and one infiltration test completed on July 8, 2020. The approximate locations of the explorations are shown on Figure 1, Exploration Plan. The exploration locations were determined by pacing from site features. Ground surface elevations referenced on the logs were inferred from topography from Google Earth satellite imagery. Exploration locations and elevations should be considered accurate only to the degree implied by the means and methods used. A private excavation company subcontracted to SSGC dug the test holes. Soil samples were collected and stored in moisture tight for further assessment and laboratory testing. Explorations were backfilled with excavated soils and tamped when completed. Please note that backfill in the explorations will likely settle with time. Backfill material located in building areas should be re-excavated and recompacted, or replaced with structural fill. The following logs indicate the observed lithology of soils and other materials observed in the explorations at the time of excavation. Where a soil contact was observed to be gradational, our log indicates the average contact depth. Our logs also indicate the approximate depth to groundwater (where observed at the time of excavation), along with sample numbers and approximate sample depths. Soil descriptions on the logs are based on the Unified Soil Classification System. Project: Brar Short Plat SSGC Job # 20058 TEST PIT LOGS PAGE 1 OF 3 Location: S. 132nd Street, Renton, WA TEST PIT LOGS FIGURE A-1 South Sound Geotechnical Consulting PIT-1, TP-1 through TP-4 Logged by: THR Infiltration Test PIT-1 Depth (feet) Material Description 0 – 1 1 – 6 6 – 10 Topsoil Silty SAND with occasional gravel: Loose to medium dense moist, brownish gray. (SM) (Sample S-1 @ 3 feet) Silty SAND with gravel: Dense to very dense, moist, gray. (SM) (Glacial Till) Test hole completed at approximately 10 feet on 7/8/20. Infiltration test completed at 2.5 feet. Groundwater not observed at time of excavation. Approximate surface elevation: 250 feet Test Pit TP-1 Depth (feet) Material Description 0 – 0.5 0.5 – 1.5 1.5 – 3 3 – 6 Topsoil Silty SAND: Loose, moist, orangish brown. (SM) Silty SAND with occasional gravel and cobbles: Medium dense to dense, moist, mottled orange-gray. (SM) (Weathered Glacial Till) Silty SAND with gravel and cobbles: Very dense, moist, gray. (SM) (Glacial Till) Test pit completed at approximately 6 feet on 7/8/20. Groundwater not observed at time of excavation. Approximate surface elevation: 275 feet Project: Brar Short Plat SSGC Job # 20058 TEST PIT LOGS PAGE 2 OF 3 Location: S. 132nd Street, Renton, WA TEST PIT LOGS FIGURE A-1 South Sound Geotechnical Consulting PIT-1, TP-1 through TP-4 Logged by: THR Test Pit TP-2 Depth (feet) Material Description 0 – 0.5 0.5 – 2.5 2.5 – 4 4 – 6 Topsoil Silty SAND: Loose, moist, orangish brown. (SM) Silty SAND with occasional gravel and cobbles: Medium dense to dense, moist, mottled orange-gray. (SM) (Weathered Glacial Till) Silty SAND with gravel and cobbles: Very dense, moist, gray. (SM) (Glacial Till) Test pit completed at approximately 6 feet on 7/8/20. Groundwater not observed at time of excavation. Approximate surface elevation: 273 feet Test Pit TP-3 Depth (feet) Material Description 0 – 1.5 1.5 – 2 2 – 3 3 – 4 4 – 6 Fill: Silt, sand, and occasional gravel: Loose, moist, light brown. Topsoil Silty SAND: Loose, moist, orangish brown. (SM) Silty SAND with some gravel: Medium dense, moist, mottled orange-gray. (SM) (Weathered Glacial Till) SAND with silt and occasional gravel: Dense to very dense, moist, gray. (SM) (Glacial Till) Test pit completed at approximately 6 feet on 7/8/20. Groundwater not observed at time of excavation. Approximate surface elevation: 255 feet Project: Brar Short Plat SSGC Job # 20058 TEST PIT LOGS PAGE 3 OF 3 Location: S. 132nd Street, Renton, WA TEST PIT LOGS FIGURE A-1 South Sound Geotechnical Consulting PIT-1, TP-1 through TP-4 Logged by: THR Test Pit TP-4 Depth (feet) Material Description 0 – 1 1 – 1.5 1.5 – 2 2 – 4 4 – 6 Fill: Silt, sand, and occasional gravel: Loose, moist, brown. Topsoil Silty SAND: Loose, damp, orangish brown. (SM) Silty SAND with some gravel: Medium dense, moist, mottled orange-gray. (SM) (Weathered Glacial Till) Silty SAND with gravel and occasional cobble: Dense to very dense, moist, gray. (SM) (Glacial Till) Test pit completed at approximately 6 feet on 7/8/20. Groundwater not observed at time of excavation. Approximate surface elevation: 262 feet Geotechnical Engineering Report SSGC Brar Short Plat – S. 132nd St Renton, WA SSGC Project No. 20058 August 3, 2020 C-1 Appendix B Laboratory Testing and Results Geotechnical Engineering Report SSGC Brar Short Plat – S. 132nd St Renton, WA SSGC Project No. 20058 August 3, 2020 B-1 Laboratory Testing Select soil samples were tested for organic content and cation exchange capacity (CEC) by Northwest Agricultural Consultants of Kennewick, Washington. Results of the laboratory testing are included in this appendix. 2545 W Falls Avenue Kennewick, WA 99336 509.783.7450 www.nwag.com lab@nwag.com Sample ID Organic Matter Cation Exchange Capacity PIT-1, S-1 2.79% 10.0 meq/100g Method ASTM D2974 EPA 9081 South Sound Geotechnical Consulting PO Box 39500 Lakewood, WA 98496 Report: 51979-1-1 Date: July 14, 2020 Project No: 20058 Project Name: Brar UNIFIED SOIL CLASSIFICATION SYSTEM Criteria for Assigning Group Symbols and Group Names Using Laboratory TestsA Soil Classification Group Symbol Group NameB Coarse Grained Soils More than 50% retained on No. 200 sieve Gravels More than 50% of coarse fraction retained on No. 4 sieve Clean Gravels Less than 5% finesC Cu 4 and 1 Cc 3E GW Well-graded gravelF Cu 4 and/or 1 Cc 3E GP Poorly graded gravelF Gravels with Fines More than 12% finesC Fines classify as ML or MH GM Silty gravelF,G, H Fines classify as CL or CH GC Clayey gravelF,G,H Sands 50% or more of coarse fraction passes No. 4 sieve Clean Sands Less than 5% finesD Cu 6 and 1 Cc 3E SW Well-graded sandI Cu 6 and/or 1 Cc 3E SP Poorly graded sandI Sands with Fines More than 12% finesD Fines classify as ML or MH SM Silty sandG,H,I Fines Classify as CL or CH SC Clayey sandG,H,I Fine-Grained Soils 50% or more passes the No. 200 sieve Silts and Clays Liquid limit less than 50 inorganic PI 7 and plots on or above “A” lineJ CL Lean clayK,L,M PI 4 or plots below “A” lineJ ML SiltK,L,M organic Liquid limit - oven dried 0.75 OL Organic clayK,L,M,N Liquid limit - not dried Organic siltK,L,M,O Silts and Clays Liquid limit 50 or more inorganic PI plots on or above “A” line CH Fat clayK,L,M PI plots below “A” line MH Elastic SiltK,L,M organic Liquid limit - oven dried 0.75 OH Organic clayK,L,M,P Liquid limit - not dried Organic siltK,L,M,Q Highly organic soils Primarily organic matter, dark in color, and organic odor PT Peat A Based on the material passing the 3-in. (75-mm) sieve B If field sample contained cobbles or boulders, or both, add “with cobbles or boulders, or both” to group name. C Gravels with 5 to 12% fines require dual symbols: GW -GM well-graded gravel with silt, GW -GC well-graded gravel with clay, GP-GM poorly graded gravel with silt, GP-GC poorly graded gravel with clay. D Sands with 5 to 12% fines require dual symbols: SW -SM well-graded sand with silt, SW -SC well-graded sand with clay, SP-SM poorly graded sand with silt, SP-SC poorly graded sand with clay E Cu = D60/D10 Cc = 6010 2 30 DxD )(D F If soil contains 15% sand, add “with sand” to group name. G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM. HIf fines are organic, add “with organic fines” to group name. I If soil contains 15% gravel, add “with gravel” to group name. J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay. K If soil contains 15 to 29% plus No. 200, add “with sand” or “with gravel,” whichever is predominant. L If soil contains 30% plus No. 200 predominantly sand, add “sandy” to group name. M If soil contains 30% plus No. 200, predominantly gravel, add “gravelly” to group name. N PI 4 and plots on or above “A” line. O PI 4 or plots below “A” line. P PI plots on or above “A” line. Q PI plots below “A” line. Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 7 Other Permits Preliminary Technical Information Report Brar Short Plat 7-1 2200320.10 7.0 Other Permits Required permits for the project include a Preliminary and Final Short Plat application, Right-of- Way and Site Grading Permits, and City of Renton residential building permits. Because this site is less than 1.0 acre, a National Pollutant Discharge Elimination System (NPDES) permit through Department of Ecology will not be required. Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 8 CSWPPP Analysis and Design Preliminary Technical Information Report Brar Short Plat 8-1 2200320.10 8.0 CSWPPP Analysis and Design A CSWPPP will be included with the final engineering design. Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 9 Bond Quantities, Facility Summaries, and Declaration of Covenant Preliminary Technical Information Report Brar Short Plat 9-1 2200320.10 9.0 Bond Quantities, Facility Summaries, and Declaration of Covenant The required forms will be included with the final engineering design. Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 10 Operations and Maintenance Plan Preliminary Technical Information Report Brar Short Plat 10-1 2200320.10 10.0 Operations and Maintenance Plan The drainage facilities detailed in this report will be privately owned and maintained. A detailed Operations and Maintenance Plan will be included with the final engineering design. Preliminary Technical Information Report Brar Short Plat 2200320.10 Section 11 Conclusion Preliminary Technical Information Report Brar Short Plat 11-1 2200320.10 11.0 Conclusion The Brar Short Plat site has been designed to meet the 2016 King County Surface Water Design Manual (KCSWDM), amended by City of Renton as the 2016 City of Renton Surface Water Design Manual (CRSWDM). The site uses water quality facilities to treat stormwater draining from the site. It was determined using these criteria that: The site will meet the City’s Flow Duration Standard to match forested conditions. Water quality facilities will be designed to meet the required Enhanced Basic Water Quality Treatment Level for the site. Pipe networks will be designed to be of adequate size to effectively convey the 25-year storm event and to contain the 100-year storm event. This analysis is based on data and records either supplied to or obtained by AHBL. These documents are referenced within the text of the analysis. The analysis has been prepared using procedures and practices within the standard accepted practices of the industry. We conclude that this project, as schematically represented, will not create any new problems within the downstream drainage system. This project will not noticeably aggravate any existing downstream problems due to either water quality or quantity. AHBL, Inc. Ryan Inouye, PE Project Engineer EMA/RI/lsk November 2020 Revised April 2021 Q:\2020\2200320\WORDPROC\Reports\20210429 Rpt (Prelim TIR) 2200320.10.docx