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RS_Preliminary_Storm_Report_240301_v1
Sophie Jo Short Plat Preliminary TIR & Level 1 Downstream Analysis February 28, 2024 Prepared for Schneider Family Homes 6510 Southcenter Blvd #1 Tukwila, WA 98188 Submitted by ESM Consulting Engineers, LLC 33400 8th Avenue S, Suite 205 Federal Way, WA 98003 253.838.6113 tel 253.838.7104 fax www.esmcivil.com 02/29/2024 Table of Contents Section 1. Project Overview Section 2. Conditions and Requirements Summary Section 3. Off-Site Analysis Section 4. Flow Control & Water Quality Facility Analysis and Design Section 5. Conveyance System Analysis and Design Section 6. Special Reports and Studies Section 7. Other Permits Section 8. ESC Analysis and Design Section 9. Bond Quantities, Facility Summaries, & Declaration of Covenant Section 10. Operations and Maintenance Manual List of Figures 1.1 TIR Worksheet 1.2 Vicinity Map 1.3A Existing Drainage Basin 1.3B Developed Drainage Basin 1.4 Soils Map 3.1 Water Quality Assessment Map (DOE) 3.2 Downstream Study Area 3.3 Field Study Area Appendix Appendix A Hydrology Model Output Appendix B Geotechnical Study Appendix C Additional Documents (None at this time) \\esm8\engr\esm-jobs\441\004\023\stormreport\sophie jo short plat.docx Sophie Jo Short Plat Page 1 February 28, 2024 Preliminary TIR 1. Project Overview The proposed Sophie Jo Short Plat project is a 3-lot plat with associated utilities, street improvements, sidewalk, and stormwater infrastructure. The purpose of this report is to encapsulate the documents and analysis in accordance with the 2022 City of Renton Surface Water Design Manual (RSWDM). Stormwater Review: The project is subject to a Full Drainage Review according to Section 1.1.2.4 of the RSWDM. The proposed development will result in greater than 2,000 sf of new plus replaced impervious surfaces but less than 50 acres of new impervious surface. A Full Drainage Review consists of reviewing Core Requirements #1-9 and Special Requirements #1-5 as outlined in Figure 1.1.2.A of the RSWDM. A discussion of these requirements can be found in Section 2 of this report. Existing Site: The proposed Sophie Jo Short Plat project site is located in the Southeast Quarter of Section 19, Township 23 N, Range 05 E, W.M., situated on one parcel, The site is located at the southeast corner of the intersection between S 21st ST and Smithers Ave S in the City of Renton, within the urban growth area, Zoned R-8. Parcel (722200-0110): 20,010 sf (0.46 ac) is currently undeveloped and does not have an address assigned to the property. The property is rectangular in shape, approximately 290’ x 74’. Adjacent to the Parcel is 21st St (Neighborhood Collector Arterial) to the north, 2114 Smithers Ave S (a single-family home) to the south, the Zetterberg Project (Medium Density, Single-Family development) to the East, and Smithers Ave S (Residential Access) to the west. The property has remained undeveloped and vegetated with trees and underbrush. The grades across the property slope down towards the west central area of the site at grades approximately 5%. Overall, the site is flat to moderately sloped with approximately 6 feet of vertical relief. There are no known critical areas on or adjacent to the project site. Proposed improvements: The plat infrastructure improvements include 3 single family lots and a joint use driveway tract used for a shared access between lots 2 and 3, and a stormwater detention vault. Additional site improvements include public right-of-way, road and sidewalk, improvements, associated utilities, including new sewer and water services, and landscaping. The improvements are currently slated to be built in one phase. Stormwater will be collected and conveyed by a series of pipes and catch basins. A flow control facility, an underground detention vault, is proposed to meet the flow control standards associated with this project. The design of the stormwater management/flow control facility mitigation includes implementation of a mitigation trade to meet the required flow control standard for the area. This treatment trade had been mapped and included with the basin maps in this Section. Refer to Section 4 for further discussion of the existing and proposed hydrology, performance criteria, and design details. Sophie Jo Short Plat Page 2 February 28, 2024 Preliminary TIR Geotechnical: A geotechnical study has been completed by Development Engineering, PLLC., dated September 7, 2017. Three exploration pits were dug across the project site. See Figure 1.4 for the Soils Map provided by Development Engineering for test pit locations. In summary, the three test pits had uniform subsurface conditions that confirmed the general geological mapping stratigraphy. The soils generally consisted of a minimum of 24 to 36 inches of weathered silty sand and gravel over a dense sandstone layer. No groundwater seepage was observed in any of the test pits, although based on soil observations it is anticipated that during periods of heavy rainfall the upper soils would become saturated. Based on the soil findings, the subsurface conditions observed in the test pits are not favorable for infiltration of significant volumes of project stormwater This is due primarily to the site soil’s relatively high fines content, and shallow groundwater observed in the test pits. A copy of Development Engineering’s report has been included In Appendix B. CITY OF RENTON SURFACE WATER DESIGN MANUAL 2022 City of Renton Surface Water Design Manual 6/22/2022 8-A-1 REFERENCE 8-A TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Part 2 PROJECT LOCATION AND DESCRIPTION Project Owner _____________________________ Phone ___________________________________ Address __________________________________ _________________________________________ Project Engineer ___________________________ Company _________________________________ Phone ___________________________________ Project Name __________________________ CED Permit # ________________________ Location Township ________________ Range __________________ Section _________________ Site Address __________________________ _____________________________________ Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS Land Use (e.g., Subdivision / Short Subd.) Building (e.g., M/F / Commercial / SFR) Grading Right-of-Way Use Other _______________________ DFW HPA COE 404 DOE Dam Safety FEMA Floodplain COE Wetlands Other ________ Shoreline Management Structural Rockery/Vault/_____ ESA Section 7 Part 5 PLAN AND REPORT INFORMATION Technical Information Report Site Improvement Plan (Engr. Plans) Type of Drainage Review (check one): Date (include revision dates): Date of Final: Full Targeted Simplified Large Project Directed __________________ __________________ __________________ Plan Type (check one): Date (include revision dates): Date of Final: Full Modified Simplified __________________ __________________ __________________ Schneider Family Homes 6510 Southcenter Blvd #1 Tukwila, WA 98188 Brandon Loucks ESM Consulting Engineers (253) 838-6113 Sophie Jo Short Plat 23 N 05 E 19 x x x x x REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 6/22/2022 2022 City of Renton Surface Water Design Manual 8-A-2 Part 6 SWDM ADJUSTMENT APPROVALS Type (circle one): Standard / Blanket Description: (include conditions in TIR Section 2) ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ Approved Adjustment No. ______________________ Date of Approval: _______________________ Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes / No Start Date: _______________________ Completion Date: _______________________ Describe: _________________________________ _________________________________________ _________________________________________ Re: SWDM Adjustment No. ________________ Part 8 SITE COMMUNITY AND DRAINAGE BASIN Community Plan: ____________________________________________________________________ Special District Overlays: ______________________________________________________________ Drainage Basin: _____________________________________________________________________ Stormwater Requirements: _____________________________________________________________ Part 9 ONSITE AND ADJACENT SENSITIVE AREAS River/Stream ________________________ Lake ______________________________ Wetlands ____________________________ Closed Depression ____________________ Floodplain ___________________________ Other _______________________________ _______________________________ Steep Slope __________________________ Erosion Hazard _______________________ Landslide Hazard ______________________ Coal Mine Hazard ______________________ Seismic Hazard _______________________ Habitat Protection ______________________ _____________________________________ REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2022 City of Renton Surface Water Design Manual 6/22/2022 Ref 8-A-3 Part 10 SOILS Soil Type ______________________ ______________________ ______________________ ______________________ Slopes ________________________ ________________________ ________________________ ________________________ Erosion Potential _________________________ _________________________ _________________________ _________________________ High Groundwater Table (within 5 feet) Other ________________________________ Sole Source Aquifer Seeps/Springs Additional Sheets Attached Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE Core 2 – Offsite Analysis_________________ Sensitive/Critical Areas__________________ SEPA________________________________ LID Infeasibility________________________ Other________________________________ _____________________________________ LIMITATION / SITE CONSTRAINT _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ Additional Sheets Attached Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Threshold Discharge Area: (name or description) Core Requirements (all 9 apply): Discharge at Natural Location Number of Natural Discharge Locations: Offsite Analysis Level: 1 / 2 / 3 dated:__________________ Flow Control (include facility summary sheet) Standard: _______________________________ or Exemption Number: ____________ Conveyance System Spill containment located at: _____________________________ Erosion and Sediment Control / Construction Stormwater Pollution Prevention CSWPP/CESCL/ESC Site Supervisor: _____________________ Contact Phone: _________________________ After Hours Phone: _________________________ Maintenance and Operation Responsibility (circle one): Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Liability Provided: Yes / No 09/26/2023 Detention Vault #1 TBD 5%NoBeaurite REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 6/22/2022 2022 City of Renton Surface Water Design Manual 8-A-4 Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Water Quality (include facility summary sheet) Type (circle one): Basic / Sens. Lake / Enhanced Basic / Bog or Exemption No. _______________________ On-site BMPs Describe: Special Requirements (as applicable): Area Specific Drainage Requirements Type: SDO / MDP / BP / Shared Fac. / None Name: ________________________ Floodplain/Floodway Delineation Type (circle one): Major / Minor / Exemption / None 100-year Base Flood Elevation (or range): _______________ Datum: Flood Protection Facilities Describe: Source Control (commercial / industrial land use) Describe land use: Describe any structural controls: Oil Control High-Use Site: Yes / No Treatment BMP: _________________________________ Maintenance Agreement: Yes / No with whom? _____________________________________ Other Drainage Structures Describe: #1e REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2022 City of Renton Surface Water Design Manual 6/22/2022 Ref 8-A-5 Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION Clearing Limits Cover Measures Perimeter Protection Traffic Area Stabilization Sediment Retention Surface Water Collection Dewatering Control Dust Control Flow Control Control Pollutants Protect Existing and Proposed BMPs/Facilities Maintain Protective BMPs / Manage Project MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION Stabilize exposed surfaces Remove and restore Temporary ESC Facilities Clean and remove all silt and debris, ensure operation of Permanent BMPs/Facilities, restore operation of BMPs/Facilities as necessary Flag limits of sensitive areas and open space preservation areas Other _______________________ Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch) Flow Control Description Water Quality Description On-site BMPs Description Detention Infiltration Regional Facility Shared Facility Other _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ Vegetated Flowpath Wetpool Filtration Oil Control Spill Control Other _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ Full Dispersion Full Infiltration Limited Infiltration Rain Gardens Bioretention Permeable Pavement Basic Dispersion Soil Amendment Perforated Pipe Connection Other _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ x x x x x x x x x x x x x x Vault REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 6/22/2022 2022 City of Renton Surface Water Design Manual 8-A-6 Part 15 EASEMENTS/TRACTS Part 16 STRUCTURAL ANALYSIS Drainage Easement Covenant Native Growth Protection Covenant Tract Other ____________________________ Cast in Place Vault Retaining Wall Rockery > 4′ High Structural on Steep Slope Other _______________________________ Part 17 SIGNATURE OF PROFESSIONAL ENGINEER I, or a civil engineer under my supervision, have visited the site. Actual site conditions as observed were incorporated into this worksheet and the attached Technical Information Report. To the best of my knowledge the information provided here is accurate. ____________________________________________________________________________________ Signed/Date x Shared Access King Vicin ity M ap Date: 9 /25 /20 23 Notes: Th e infor matio n in clu de d on t his map has been comp ile d b y Kin g Count y staf f from a variety of source s an d is su bject to cha ng ewithout n otice. Kin g Co unt y makes no re present ations o r wa rra nties, exp re ss o r im plied , a s to accu ra cy, complet en ess, t ime lin ess,or rig hts to the use of such informa tion . This d ocu me nt is not intended for u se as a survey pr od uct. King Cou nty shall n ot be lia blefor a ny g en er al, sp ecial, indirect, incide ntal, o r conse qu en tial damag es including , but not limited to , lost revenu es or lo st profitsresulting from th e use or m isu se of t he info rmat ion cont aine d on this map . An y sale of this map or in formation o n t his map isprohibited except by written p er mission of King County.± SITE Figure 1.2 - P W W WWS S S DRAWING:JOB NO.DATE:DRAWN:SHEET OF(425) 297-9900(253) 838-6113www.esmcivil.comLand PlanningLandscape ArchitectureLand SurveyingProject ManagementPublic WorksCivil EngineeringΚ Κ ΒΕδχδθκ ςξ+ ς≅ 87//2223// 7σγ ≅υδ Ρ+ Ρτησδ 1/4Β Ν Μ Ρ Τ Κ Σ Η Μ Φ ∆ Μ Φ Η Μ ∆ ∆ Θ ΡFEDERAL WAYLYNNWOOD\\\\esm8\\ENGR\\ESM-JOBS\\441\\004\\023\\StormReport\\Resources\\CAD Basin Maps\\PREDEVELEOPED BASIN.dwg2/29/2024 3:52 PMPlotted:File:Plotted By: Devon WatermanΡΒΓΜ∆ΗΧ∆Θ ΓΝΛ∆ΡΡΝΟΓΗ≅ ΙΝ ΡΓΝΘΣ ΟΚ≅ΣPREDEVELOPED BASIN MAP (BEFORE MITIGATION TRADE)441-004-023DEVON WATERMAN10/24/20231 1 ON SITE: AREA OF NEW TARGET (NEW & REPLACED SURFACES) (20,691 SF) FRONTAGE: AREA OF NEW TARGET (NEW & REPLACED SURFACES) (7,968 SF) ΕΗΦΤΘ∆ 0−2≅ , ΟΘ∆Χ∆Υ∆ΚΝΟ∆Χ Α≅ΡΗΜ Λ≅Ο ,Α∆ΕΝΘ∆ ΛΗΣΗΦ≅ΣΗΝΜ ΣΘ≅Χ∆ , NOTE: REFER TO TABLE 4.1 FOR PROJECT AREAS LEGEND ΡΒ≅Κ∆9 0! < 0 2/& 15 30 µRIDGE10ΡΣ ΡΣ Ρ ΡΛΗΣΓ∆ΘΡ ≅Υ∆ Ρ P W W WWS S S DRAWING:JOB NO.DATE:DRAWN:SHEET OF(425) 297-9900(253) 838-6113www.esmcivil.comLand PlanningLandscape ArchitectureLand SurveyingProject ManagementPublic WorksCivil EngineeringΚ Κ ΒΕδχδθκ ςξ+ ς≅ 87//2223// 7σγ ≅υδ Ρ+ Ρτησδ 1/4Β Ν Μ Ρ Τ Κ Σ Η Μ Φ ∆ Μ Φ Η Μ ∆ ∆ Θ ΡFEDERAL WAYLYNNWOOD\\\\esm8\\ENGR\\ESM-JOBS\\441\\004\\023\\StormReport\\Resources\\CAD Basin Maps\\PREDEVELEOPED BASIN.dwg2/29/2024 3:52 PMPlotted:File:Plotted By: Devon WatermanΡΒΓΜ∆ΗΧ∆Θ ΓΝΛ∆ΡΡΝΟΓΗ≅ ΙΝ ΡΓΝΘΣ ΟΚ≅ΣPREDEVELOPED BASIN MAP (AFTER MITIGATION TRADE)441-004-023DEVON WATERMAN10/24/20231 1 FRONTAGE: NON-TARGET AREA PROPOSED FOR MITIGATION FOR TRADE OF A PORTION OF THE TARGET FRONTAGE (2,916 SF) ΕΗΦΤΘ∆ 0−2Α , ΟΘ∆Χ∆Υ∆ΚΝΟ∆Χ Α≅ΡΗΜ Λ≅Ο ,≅ΕΣ∆Θ ΛΗΣΗΦ≅ΣΗΝΜ ΣΘ≅Χ∆ , ON SITE: AREA OF NEW TARGET (NEW & REPLACED SURFACES) (24,848 SF) FRONTAGE: AREA OF NEW TARGET (NEW & REPLACED SURFACES) (1,075 SF) NOTE: REFER TO TABLE 4.1 FOR PROJECT AREAS LEGEND ΡΒ≅Κ∆9 0! < 0 2/& 15 30 µRIDGE10ΡΣ ΡΣ Ρ ΡΛΗΣΓ∆ΘΡ ≅Υ∆ Ρ P POWER VAULT W W WW0 2ΣΘ≅ΒΣ ≅1 DRAWING:JOB NO.DATE:DRAWN:SHEET OF(425) 297-9900(253) 838-6113www.esmcivil.comLand PlanningLandscape ArchitectureLand SurveyingProject ManagementPublic WorksCivil EngineeringΚ Κ ΒΕδχδθκ ςξ+ ς≅ 87//2223// 7σγ ≅υδ Ρ+ Ρτησδ 1/4Β Ν Μ Ρ Τ Κ Σ Η Μ Φ ∆ Μ Φ Η Μ ∆ ∆ Θ ΡFEDERAL WAYLYNNWOOD\\\\esm8\\ENGR\\ESM-JOBS\\441\\004\\023\\StormReport\\Resources\\CAD Basin Maps\\DEVELEOPED BASIN.dwg2/29/2024 3:53 PMPlotted:File:Plotted By: Devon WatermanΡΒΓΜ∆ΗΧ∆Θ ΓΝΛ∆ΡΡΝΟΓΗ≅ ΙΝ ΡΓΝΘΣ ΟΚ≅ΣDEVELOPED BASIN MAP441-004-023DEVON WATERMAN10/24/20231 1 FLOW CONTROL TARGET AREA BYPASS (1,075 SF) DETENTION VAULT TRIBUTARY BASIN (24,848 SF) DETENTION VAULT TRIBUTARY BASIN NON-TARGET TRADED AREA (2,916 SF) ΕΗΦΤΘ∆ 0−2Β , Χ∆Υ∆ΚΝΟ∆Χ Α≅ΡΗΜ Λ≅Ο ,≅ΕΣ∆Θ ΛΗΣΗΦ≅ΣΗΝΜ ΣΘ≅Χ∆ , ΡΒ≅Κ∆9 0! < 0 2/& 15 30 µ NOTE: REFER TO TABLE 4.2 FOR PROJECT AREAS LEGEND 7222000106 7222000105 7222000070 98882000109888200020RIDGE10ΡΣ ΡΣ Ρ ΡΛΗΣΓ∆ΘΡ ≅Υ∆ Ρ Approximate Site Location Not to Scale DE-CIVIL, PLLC P.O. Box 446 Tacoma, WA 98401 Ph (253) 228-0513 www.de-civil.com USDA Web Soil Survey Schneider SP 7XX S 21st Street Renton County, Washington Job No: 17-166 September 2017 Figure 3 Sophie Jo Short Plat Page 9 February 28, 2024 Preliminary TIR 2. Conditions and Requirements Summary The project is subject to a Full Drainage Review according to Section 1.1.2.4 of the RSWDM. The proposed development will result in greater than 2,000 sf of new plus replaced impervious surfaces but less than 50 acres of new impervious surface. A Full Drainage Review consists of reviewing Core Requirements #1-9 and Special Requirements #1-5 as outlined in Table 1.1.2.A of the RSWDM. Review of the 9 Core Requirements and 5 Special Requirements This section describes how the project will meet the RSWDM Core and Special Requirements. Core Requirement No. 1 Discharge at the Natural Location The project site is made up of a single threshold discharge area with one natural discharge location. The site naturally drains toward the northeastern corner of the property. All runoff generated from the developed basin will discharge to the northeast corner of the site and enter an existing storm system. See Figure 1.3A for the natural discharge location. Core Requirement No. 2 Off-site Analysis An off-site analysis of the project has been completed and documented in Section 3 of this report. Core Requirement No. 3 Flow Control The site is located within a Conservation Flow Control Area, matching forested site conditions, requiring at minimum Level 2 flow control standards per Section 1.2.3.1.B of the RSWDM and the City of Renton Flow Control Application map. The flow control standard will be met through the use of an underground detention system in a shared access tract to release stormwater at approved rates to the natural discharge location. Refer to Section 4 for more information. Core Requirement No. 4 Conveyance System The new conveyance network will be analyzed and designed with sufficient capacity to convey and contain the 25-year and 100-year peak flow events. Stormwater conveyance calculations will be provided in Section 5 during the final preparations of the construction plans/final engineering documents. Core Requirement No. 5 Erosion and Sediment Control Erosion and sediment controls to prevent the transport of sediment from the project site to downstream drainage facilities, water resources, and adjacent properties will be provided on the construction plans and discussed the Erosion and Sediment Control Report. Core Requirement No. 6 Maintenance and Operations The Operations and Maintenance manual will be included with the final TIR as requested by the city. Core Requirement No. 7 Financial Guarantees and Liability All drainage facilities constructed or modified for projects will comply with the financial guarantee requirement. Financial guarantees will be provided to the city as required. Sophie Jo Short Plat Page 10 February 28, 2024 Preliminary TIR Core Requirement No. 8 Water Quality The proposed project, a single-family development, is located within a Basic WQ treatment area. After analysis of the proposed and future build-out land use areas, the development falls under Core Requirement #8, Exemption #1, less than 5,000 sf of new plus replaced PGIS will be created and less than 3/4 acre of new PGPS will be added. Refer to Table 4.2 for a breakdown of the new plus replaced PGIS area proposed. Core Requirement No. 9 Flow Control BMP’s All applicable Flow Control BMPs are listed and discussed in Section 4 of this report. Special Requirement No. 1 Other Adopted Area-Specific Requirements There are no known master drainage plans, basin plans, salmon conservation plans, stormwater compliance plans, flood hazard reduction plan updates, or shared facility drainage plans for this project. Special Requirement No. 1 does not apply. Special Requirement No. 2 Flood Hazard Area Delineation There is no known flood hazard on or around the project site. Special Requirement No. 2 does not apply. Special Requirement No. 3 Flood Protection Facilities The developed project site is not protected by an existing flood protection facility. The proposed site improvements do not include the modification of an existing flood protection facility. Special Requirement No. 3 does not apply. Special Requirement No. 4 Source Control The site is a residential development and is not subject to this requirement. Special Requirement No. 4 does not apply. Special Requirement No. 5 Oil Control The project does not have a “high-use site” characteristic and is not a redevelopment of a high-use site. Special Requirement No. 5 does not apply. A “high-use site” is a commercial or industrial site that typically generates or is subject to runoff containing high concentrations of oil due to high traffic turnover, on-site vehicle or heavy or stationary equipment’s use, or the frequent transfer of liquid petroleum or coal derivative products. Sophie Jo Short Plat Page 11 February 28, 2024 Preliminary TIR 3. Level 1 Off-Site Analysis This narrative is to provide a Level 1 Downstream Analysis for the proposed Sophie Jo Short Plat development per Core Requirement #2, Section 1.2.2 of the 2021 City of Renton Surface Water Design Manual (RSWDM). The analysis is to identify and evaluate offsite flooding, erosion, and water quality problems that may be created or aggravated by the proposed project. The primary component of this offsite analysis is the downstream corridor. The second component is to evaluate the upstream drainage system to verify any offsite run-on that may impact the project. The following Level 1 downstream analysis is a qualitative survey of the downstream system of the project site and is composed of the following four tasks: Task 1 – Define and map the study area Task 2 – Downstream Resource Review for 1-mile downstream Task 3 – Field Inspection Task 4 – Drainage System Description and Problem Descriptions Task 1: Study Area Definition and Maps The drainage study area is approximately a one-mile-long path encompassing the site’s downstream corridor. See Figure 3.2 for a map of the basic study area. The study area also includes a 1/4-mile downstream field investigation of stormwater released from the project site. See Figure 1.3A for the Existing Site Conditions Exhibit and Figure 3.3 for a map of the downstream field investigation. Task 2: Resource Review Flow Control Map According to the City of Renton Flow Control Applications Map, the project is located within the Conservation Flow Control Area, matching forested site conditions, and required to comply with Level 2 Flow Control Standards. Site Soils A geotechnical study has been completed by Development Engineering, PLLC., dated September 7, 2017. Three exploration pits were dug across the project site. See Figure 1.4 for the Soils Map provided by Development Engineering for test pit locations. In summary, the three test pits had uniform subsurface conditions that confirmed the general geological mapping stratigraphy. The soils generally consisted of a minimum of 24 to 36 inches of weathered silty sand and gravel over a dense sandstone layer. No groundwater seepage was observed in any of the test pits, although based on soil observations it is anticipated that during periods of heavy rainfall the upper soils would become saturated. Based on the soil findings, the subsurface conditions observed in the test pits are not favorable for infiltration of significant volumes of project stormwater as stated in the geotechnical study. This is due primarily to the site soil’s relatively high fines content, and shallow groundwater observed in the test pits. A copy of Development Engineering’s report has been included with the submittal package. Sophie Jo Short Plat Page 12 February 28, 2024 Preliminary TIR Resource Overview According to available information at the time of writing: Drainage Basin: The site drains into the S 21st ST Right of Way Stormwater Conveyance System. Streams: There are no known mapped or identified streams through or adjacent to the project site Erosion Hazard: None mapped. According to the Geotechnical report prepared by Development Engineering, dated September 07, 2017, the site is not considered an erosion hazard area as defined by the City of Renton. Landslide Hazard Area: None mapped. According to the Geotechnical report prepared by Development Engineering, dated September 07, 2017, the site does not contain Landslide Hazard Areas as defined by City of Renton. Lakes: None mapped 100 Year Floodplain The Federal emergency Management Agency prepared maps for all areas within the City of Federal Way. These maps can be found on the FEMA website. Panel #53033C0979G, effective 08/19/2020 depicts the areas, if any, subject to flooding in the vicinity of this project. By inspection of this map, the project is located in Zone X, which is designated as areas outside the 0.2 percent annual chance floodplain. Downstream Drainage Complaints Relevant drainage complaints within the downstream corridor within the last 10-years were searched. After searching for publicly documented complaints, it was found that there are currently no relevant open or closed drainage complaints from the last 10 years. Sophie Jo Short Plat Page 13 February 28, 2024 Preliminary TIR Water Quality Assessment The Department of Ecology Water Quality Assessment 303(d)/305(b) lists were reviewed to see if there are any known downstream water quality concerns. Waters whose beneficial uses are impaired by pollutants that require a water improvement project are placed in the polluted water category (Category 5) and put on the 303(d) list. The 305(b) lists all waters and all categories. Pollutants of concern could be Bacteria, Dissolved oxygen, temperature, metals, phosphorus, turbidity, or high pH. Discharge from the project site is tributary to an unnamed Creek approximately 2,000 feet downstream of the project (tributary to Lake Washington). According to the assessment, pollutants of this unnamed creek are classified as Category 5. Category 5 parameters are: Bioassessment indicating degraded biological integrity. Designated water quality problems There are no designated water quality problems known at this time. Downstream Corridor The downstream corridor consists of one flow path, flowing east on S 21st Street’s closed conveyance system for 270 ft before entering the Benson Dr South’s closed conveyance system. The stormwater travels north towards Lake Washington for roughly a quarter mile before being deposited into a densely forested area. After this point, water exiting the densely forested area will collect in an unnamed stream to be later collected by a series of conveyance systems before entering Lake Washington. The following is a narrative of the two natural downstream flow paths and combined flow path documented during the field analysis. Task 3: Field Inspection (Level 1 Inspection) A site visit was conducted on September 26, 2023, by ESM Consulting Engineers for the purpose of analyzing the project site and its upstream and downstream corridors. The weather conditions were heavy rain and thunderstorms, approximately 50°F. The ground surface was wet. Continuous flow was observed through the downstream conveyance network from upstream tributaries. A description of the drainage path is provided below. Refer to Figure 3.3 at the end of this section for a map of the downstream reaches and point locations. Upstream and onsite runoff The project site has limited potential for upstream run-on. Based on the topography conditions, the project parcel receives upstream run-on from adjacent properties. The project parcel is covered in moderately dense to dense forest areas consisting of young and mature trees. The entire area including the project property and adjacent roadways are tributary to Lake Washington. There is a channel running through roadside edges of the property and presumed that most stormwater is conveyed east through this channel into the S 21st St right-of-way at the natural discharge location. Sophie Jo Short Plat Page 14 February 28, 2024 Preliminary TIR Upstream Inspection Pictures taken at Points 1-3 on Smithers Ave S are shown below. Additional points along the adjacent right-of-way of the existing stormwater conveyance system are also shown throughout the field investigation narrative. Refer to Figure 3.3 for a map of point locations. Photo Photo Description Point #1 – Looking north along Smithers Ave S. Point #2 – Looking north along Smithers Ave S. Sophie Jo Short Plat Page 15 February 28, 2024 Preliminary TIR Point #3 – Looking south at the Smithers S Discharge into the property. Pictures taken at Points 4-9 on the Property are shown below. Point #4 – Looking north at the start of the existing conveyance ditch on site. Sophie Jo Short Plat Page 16 February 28, 2024 Preliminary TIR Point #5 – Rounding the southeast corner of the intersection between S 21st St and Smithers Ave S along the on-site conveyance ditch. Point #6 – Looking east along S 21st St. Sophie Jo Short Plat Page 17 February 28, 2024 Preliminary TIR Point #7 - Looking east along S 21st St. Point #8 - Looking east along S 21st St. Sophie Jo Short Plat Page 18 February 28, 2024 Preliminary TIR Point #9 - Looking south at the Discharge point of the Property into the conveyance network of S 21st St. Sophie Jo Short Plat Page 19 February 28, 2024 Preliminary TIR Natural Discharge Point #1 Reach 1A (0’ –270’) – Upon leaving the site, stormwater enters in the S 21st St right-of-way conveyance network through an inlet (see Point #9) to a catch basin along the roadway (Point #10). This inlet is the Discharge Point for the site. From this point, stormwater heads east along S 21st St towards Benson Dr S. No signs of any conveyance nuisances or flooding problems were observed. Photo Photo Description Point #10 – Discharged stormwater from site enters S 21st St conveyance system heading east along S 21st St. Sophie Jo Short Plat Page 20 February 28, 2024 Preliminary TIR Point #11 – looking east along S 21st St. Point #12 – looking east along S 21st St heading to the intersect with Benson Dr S. Sophie Jo Short Plat Page 21 February 28, 2024 Preliminary TIR Reach 2 (270’ – 1500’) – Stormwater enters the Benson Dr S conveyance system and starts heading north along the Benson Dr S right of way. The Benson Dr S conveyance system discharges into a densely forested area to connect into a stream later downstream. Photo Photo Description Point #13 – Looking northeast at the intersection of S 21st St and Benson Dr S Point #14 – Looking north along Benson Dr S. Sophie Jo Short Plat Page 22 February 28, 2024 Preliminary TIR Point #15 - Looking north along Benson Dr S. Point #16 – Looking east into the densely forested area assumed to be the discharge point for the Benson Dr S conveyance system. Sophie Jo Short Plat Page 23 February 28, 2024 Preliminary TIR Task 4: Drainage Description and Problem Descriptions The downstream drainage system is largely comprised of a 12” tightline system. See Task 3 for a narrative of the downstream flow path for a quarter mile downstream of the site and a description of each reach. Downstream Drainage Problems There are no known or observed conveyance system nuisance problems, severe erosion, or flooding problems. Downstream Water Quality Problems Discussed in Task 2 of the Offsite Analysis, a biological integrity problem was noted approximately half a mile downstream. A detailed parameter has not been identified. This potential water quality problem is beyond the quarter mile threshold to warrant mitigation as suggested in the KCRSWDM Section 1.2.2.3. See Figure 3.1 below for a map of the classified 303(d) areas downstream of the project site. Figure 3.1 – Water Quality Assessment Kin g Date : 10 /2/20 23 Notes: The informati on included on this map has been c ompil ed by King County s taff from a variety of sources and issubject to change without notice. King County makes no repr esentations or warr anties, ex press or implied,as to accurac y, completeness, timel iness, or rights to the us e of such information. T hi s doc ument i s not intendedfor use as a s urvey product. Ki ng County shall not be l iable for any general , special, indirect, incidental, orconsequential damages i ncl uding, but not li mited to, lost revenues or los t profits resulting from the us e or mi sus eof the information contained on this map. Any sale of thi s map or informati on on this map is prohi bited exc ept bywritten permi ss i on of Ki ng County. Leg end Pa rc els Po tentiallandslide ha za rdareas (20 16 , s eeexplanation--->) Er os ion h az ar d(19 90 SAO) Se ism ic ha za rd(19 90 SAO) Co al mine h az ar d(19 90 SAO) St rea m (19 90 SA O) cla ss 1 cla ss 2 pe ren nia l cla ss 2 sa lmon id cla ss 3 unc las s ifie d Wetlan d (1 99 0SAO) Se ns itive a re anotice on title FEMA flo odw ay FEMA 100 ye arfloodplain FEMA 500 ye arfloodplain FEMA are a withreduced r isk du eto le ve e Dr aina gecomplaints Figure 3.2 - D ownstream Study Area ± 1/4 Mile Downstream 1/2 Mile Downstream 1 Mile Downstream Site 1995-0868 Type: WQA Problem: DUMPING Closed: 4/21/1996 2012-0717 Type: CUST Problem: WQAI Closed: 12/18/2012 2,257 188 Figure 3.3 - Field Study Area 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. Field conditions were Thunderstorms and Heavy Rain. Figure corresponds to narrative written for downstream analysis. 10/2/2023 Legend 128064 THIS MAP IS NOT TO BE USED FOR NAVIGATION Feet Notes 128 WGS_1984_Web_Mercator_Auxiliary_Sphere Information Technology - GIS RentonMapSupport@Rentonwa.gov City and County Labels Parcels Discharge Point Public Discharge Point Private Discharge Point Pipe Public Pipe Private Pipe Public Culvert Private Culvert Public Roofdrain Private Roofdrain Open Drains Facility Outline Streets Points of Interest Parks Waterbodies Point #10 Point #11 Point #12 Point #13 Point #14 Point #15 Point #16 Site 1/4 Mile Downstream Sophie Jo Short Plat Page 26 February 28, 2024 Preliminary TIR 4. Flow Control & Water Quality Facility Analysis and Design 4.1 Existing Site Hydrology During the site investigation, it was found, the site is primarily covered in medium dense forest with large amounts of thorny bushes and underbrush. The water that currently flows onto the site is carried by a manmade ditch along Smithers Ave S and S 21st St. This ditch intercepts and conveys stormwater from the parcels located south of the project site and discharges it into the Zetterberg Project conveyance system at the natural discharge location at the northeast corner of the property. 4.2 Developed Site Hydrology The project proposes storm water collection and flow control prior to site discharge through the use of a detention vault and a closed conveyance network for all rooftop, driveway, and roadway runoff. The storm network will collect virtually all runoff on the project property and convey it to the detention facility. For stormwater within the existing public right-of-way, careful consideration was given to what areas are to be tributary to the detention vault upon completion of the right-of-way improvements. Each roadway adjacent to the development includes roadway widening as well as new curb, roadside planter strips, and sidewalk. A discussion of the proposed storm network along each road is described below. Smither Ave S: Smithers Ave S is tributary to a few acres of stormwater that is collected into the existing Smithers Ave roadside ditch. The project proposes to replace the existing ditch on the east side of Smithers Ave, with a closed conveyance pipe. The conveyance network proposed along Smithers Ave will bypass the proposed detention facility. This will eliminate any issue if parcels along Smithers Ave are developed in the future. To compensate for Smithers Ave improvements bypass area, the Target surfaces in Smithers Ave will be 'traded' for similar, non-target surfaces in S 21st St. S 21st St: The existing roadway is assumed to be crested along its surveyed centerline, resulting in a sheet flow runoff from half of the adjacent S 21st St onto the project site. The project proposes to collect a majority of this existing runoff, a non-target surface, in combination with any new target surfaces along S 21st St and route to the detention facility. This trade will allow for the unmitigated bypass from Smithers Ave S and a small amount of unmitigated bypass of target surfaces in S 21st S right-of-way east of the detention vault. The proposed detention vault is located within a stormwater easement between lots 2 and 3 of the project. Refer to Section 4.3 for a discussion of the flow control and treatment performance standards. Impervious and pervious areas were estimated based on a combination of zoning requirements and proposed site features. All proposed work within the existing and future rights-of-way were estimated based on the proposed surface types. The single-family lot impervious areas were estimated based on the 65% maximum allowed by zoning. Sophie Jo Short Plat Page 27 February 28, 2024 Preliminary TIR The following tables represent the pre-developed and developed runoff/discharge conditions for the project. Refer to Figures 1.3A and 13.B for maps of the existing conditions before and after the mitigation trade, and Figure 1.3C for a map of the proposed conditions. Table 4.1 – Historic Conditions Basin Total (SF) C, Forest (SF) Impervious, Flat (SF) C, Lawn, Flat (SF) Total Non - PGIS PGIS Before Mitigation Trade Site 28,837 (0.662) 28,837 - - - - After Mitigation Trade Site 29,017 (0.666) 29,017 - - - - Difference (After - Before) Site +180 (+0.004) +180 (+0.004) - - - - Table 4.2 – Developed Conditions Basin* Total (SF) C, Forest (SF) Impervious, Flat (SF) C, Lawn, Flat (SF) Total Non - PGIS PGIS** Before Mitigation Trade Vault Lots* 17,830 - 10,500 8,660 1,840 7,330 Tract A 2,861 - 1,038 - 1,038 1,823 Frontage 4,157 - 2,334 1,735 598 1,824 Frontage Bypass 3,811 - 2,736 1,355 1,381 1,075 Total 28,659 (0.658) - 16,607 (0.381) 11,750 (0.270) 4,857** (0.111) 12,052 (0.277) After Mitigation Trade Vault Lots* 17,830 - 10,500 8,660 1,840 7,330 Tract A 2,861 - 1,038 - 1,038 1,823 Frontage 7,073 - 5,249 1,735 3,514 1,824 Frontage Bypass 1,075 - - - - 1,075 Total 28,839 (0.662) - 16,787 (0.385) 10,395 (0.239) 6,392 (0.147) 12,052 (0.277) Difference (After - Before) Vault 2,916 - +2,916 - +2,916 - Bypass -2,736 - -2,736 -1,355 -1,381 - Total +180 (+0.004) - +180 (+0.004) -1,355 (-0.031) +1,535 (+0.035) - *Assumed 3,500 sf impervious per lot, includes 400 sf driveway for lot 1, and 720 sf driveways for lots 2 and 3. **Total proposed new plus replaced PGIS. Sophie Jo Short Plat Page 28 February 28, 2024 Preliminary TIR 4.3 Performance Standards Flow Control (Sec 1.2.3.2 RSWDM) Stormwater systems onsite are to be designed to mitigate runoff generated from the project per the requirements of the RSWDM. The Flow Control Applications Map provides the area- specific flow control facility standard. The project site falls within the Conservation Flow Control Area. Conservation Flow Control areas are to apply the Level 2 flow control standard. The Level 2 flow control standard is to match developed discharge durations to predeveloped durations for the range of predeveloped discharge rates from 50% of the 2- year peak flow up to the full 50-year peak flow. Also match developed peak discharge rates to predeveloped peak discharge rates for the 2- and 10- year return periods. This also assumes historic site conditions as the predeveloped condition. The project site is made up of 3 lots and 1 tract, and improvements to the existing public right-of-way. The project specific target surfaces subject to flow control are equal to all the new plus replaced impervious surfaces. The flow control basin however will consist partly of non-target areas through a mitigation trade per Section 1.2.3.2.G of the RSWDM. This section states a project’s flow control facility may be designed to mitigate an existing developed non-target surface area in trade for not mitigating part of the project target surface area, provided that all of the following conditions are met: • The non-target surface area must have runoff discharge characteristics (peak flow and volume) equivalent to those of the target surface area for which mitigation is being traded. Response: Condition is met by trading a greater than or equal amount of impervious surface and a greater than or equal amount of like impervious surface. • Runoff from both the target surface area being traded and the flow control facility must converge prior to discharge of the runoff from the target surface area being traded onto private property without an easement or through any area subject to erosion. Response: All runoff from target and non-target converge in the area of the natural discharge location. • The net effect in terms of flow control at the point of convergence downstream must be the same with or without the mitigation trade. Response: Condition is met by detaining an area equal to or greater than the target surfaces. • The undetained runoff from the target surface area being traded must not create a significant adverse impact to the downstream drainage systems, salmonid habitat, or properties prior to convergence with runoff from the flow control facility. Response: Due to the mitigation trade, the undetained runoff will have very minimal impact to the downstream system. The undetained runoff is being compensated for by detaining other contributing flows to the downstream system not currently detained. To confirm the Level 2 flow control standard have been met, the Western Washington Hydrology Model Version 2012 (WWHM), an approved model per 3.2.3 of the RSWDM, has been utilized to determine the required volume of the detention system with the proposed control structure outlet dimensions. Sophie Jo Short Plat Page 29 February 28, 2024 Preliminary TIR Bypass (Sec 1.2.3.2.E) On some sites, topography can make it difficult or costly to collect all target surface runoff for conveyance to the onsite flow control facility. Section 1.2.3.2.E of the RSWDM allows for bypass of the flow control facility. Compensatory mitigation by the flow control facility must be provided so that the net effect at the point of convergence downstream is the same with or without the bypass. After the proposed mitigation trade, there is a small portion of bypass leaving the site unmitigated. This bypassed area is the proposed planter strip along S 21st St and Smithers Ave S. The planter strip area was not traded in the mitigation trade due only trading impervious areas. Discharge There is one discharge location on the property. The discharge location will be directly connected to the existing conveyances pipes within the right-of-way. Stormwater dissipation devices will not be necessary. Water Quality (Sec 1.2.8.1) Stormwater treatment is not required for this project as the new and replaced PGIS does not propose more than 5,000 sf of new plus replaced PGIS and therefore qualifies for Surface Area Exemption #1 according to Section 1.2.8.1 of the RSWDM. 4.4 Flow Control System The minimum area subject to conservation flow control standard is equal to the target surfaces of the developed conditions. An area equivalent to this minimum is proposed. This area will have similar land use characteristics and is equal to or greater than an equivalent impervious area and an equivalent pervious area. See Table 4.1 for the target areas compared to the equivalent mitigated area. See Section 4.3 for further flow control standard discussion. A basin map has been provided in Figure 1.3C. One riser structure with a single orifice and notch is proposed within the detention vault to provide flow control compliance prior to release of water downstream. The allowed release rate from the discharge point was determined based on the predeveloped natural discharge area under historic conditions. The point of compliance meets or exceeds conservation flow control standards. Table 4.2 in Section 4.2 provides the Developed flow control Basin for the Detention Analysis in WWHM. Table 4.1 in Section 4.2 provides the historic conditions for the natural discharge area with a total area equal to the developed flow control basin. See Appendix A for a copy of the WWHM output. Sophie Jo Short Plat Page 30 February 28, 2024 Preliminary TIR The proposed detention system will consist of an underground concrete vault. The proposed vault is within the Tract of the plat. The Western Washington Hydrology Model (WWHM) was used to confirm the stormwater detention system volume is adequate to comply with Level 2 flow control standards. A stage-storage table, Table 4.5, was generated based on the proposed system to check the provided volume against the flow control standards. After analysis of the proposed system, it was found to meet or exceed the Level 2 flow control standards for each natural discharge area. A discussion of how each standard criterion is met will be provided with the engineering review. WWHM output can be found in Appendix A. Table 4.5 – Stage-Storage-Discharge Stage (ft) Area (sf) Accumulative Storage (ac-ft) 0 2,108 0.000 1 2,108 0.048 2 2,108 0.094 3 2,108 0.143 4 2,108 0.191 4.75 2,108 0.228 The predeveloped and developed project site flow rates are provided in Table 4.6 to also compare the developed peak discharge rates to predeveloped peak discharge rates for the 2- and 10- year return periods as required by the standard. Table 4.6 – Return-Flow, Natural Discharge Return Period Predeveloped (cfs) Mitigated (cfs) 2 Year 0.0195 0.0114 10 Year 0.0371 0.0215 100-Year 0.0515 0.0415 The analyzed and proposed storage volume is provided in Table 4.7 below. Table 4.7 – Volumes Further control structure design, including pipe conveyance and overflow details will be provided during review of the final engineering drawings. 4.5 Water Quality System: As stated in Core Requirement #8, “the development falls under Core Requirement #8, Exemption #1, less than 5,000 sf of new plus replaced PGIS will be created and less than 3/4 acre of new PGPS will be added.” Thus, Enhanced Basic Water Quality treatment standards do not apply to this project. Description Volume (cu-ft) Modeled, WWHM 9,866 Proposed 10,198 Sophie Jo Short Plat Page 31 February 28, 2024 Preliminary TIR 4.6 Flow Control BMPs (Core Requirement #9): On-Site BMPs were evaluated for the project site as outlined in the RSWDM under Section 1.2.9.3.1 – subdivision projects on sites less than 5 acres in size OR within the Urban Growth Area. Target surfaces for application of Core Requirement #9 include new impervious surfaces, new pervious surfaces, and replaced impervious surfaces. Implementation of flow control BMPs for each lot will be deferred until a permit is obtained for building construction on each lot. The BMP’s required for the plat infrastructure per RSWDM Section 1.2.9.4 (e.g., road and sidewalk etc.) are described in order of precedence below with feasibility determined. Requirement #1 Full Dispersion (Section C.2.1) has been evaluated for the project site. There is insufficient onsite native vegetated flow path to which target impervious surfaces may be dispersed. Therefore, minimum design requirement #1 (specified in Section C.2.1.1) cannot be met; hence, this BMP is infeasible for the project site. Requirement #2 Full Infiltration (Section C.2.2 or Section 5.2, whichever is applicable) has been evaluated. A geotechnical study has been completed by Development Engineering, PLLC dated September 07, 2017. Based on the soil findings, the subsurface conditions observed in the test pits are not favorable for infiltration of significant volumes of project stormwater as stated in the geotechnical study. This is due primarily to the site soil’s relatively high fines content, and shallow groundwater observed in the test pits. Therefore, the Soils requirement (specified in Section 5.2.1 - Soils) cannot be met; hence, this BMP is infeasible for the project site. Limited Infiltration (Section C.2.3) is subject to the same minimum design requirements as Full Infiltration (per Section C.2.3.2). Since Full Infiltration has been deemed infeasible, Limited Infiltration is also infeasible for this project site. Bioretention (Section C2.6) is not a suitable BMP for this project site. In order to satisfy Core Requirement #9, bioretention facilities are not allowed to have an under-drain (per Section C.2.6.1.5). Because infiltration is infeasible onsite, the draw-down time for any bioretention facilities would likely exceed 24-hours and is estimated to enable mosquito breeding (Section C.2.6: Ponding Depth and Surface Water Draw-Down). Permeable Pavement (Section C.2.7) is not a suitable BMP for this project site due to existing shallow till layer that will restrict the percolations of water. Requirement #3 Basic Dispersion (Section C.2.4) has been evaluated for the project site. Most stormwater from the new meandering sidewalks will disperse through the adjacent vegetation. Most new plat infrastructure including new road, curb, gutter, and sidewalk will flow to the proposed conveyance system within the right-of-way without opportunity for basic dispersion. Requirement #4 All new pervious surfaces will be amended in accordance with KCC 16.82.100(F) and (G) to satisfy the requirements specified therein (notes will be included on the final landscape plans). Sophie Jo Short Plat Page 32 February 28, 2024 Preliminary TIR 5. Conveyance System Analysis and Design Onsite Conveyance System: Runoff from the developed project site will be collected from the developed lot lawns, roofs, drive aisles, and parking area by the proposed conveyance system located throughout the project. The proposed stormwater drainage system is composed of catch basin structures with varying diameter pipes. A conveyance and backwater analysis will be completed to verify the capacity of the critical pipes in the system. The proposed stormwater drainage system will be designed to convey the 25-year and 100-year peak flow rate generated by the developed tributary basin as required in the RSWDM. Conveyance calculations will be provided with the final TIR. Sophie Jo Short Plat Page 33 February 28, 2024 Preliminary TIR 6. Special Reports and Studies Geotechnical Study Geotechnical Report, Sophie Jo Short Plat, September 7, 2017; prepared by Development Engineering, Inc., This study has been included as a part of the project submittal package. Sophie Jo Short Plat Page 34 February 28, 2024 Preliminary TIR 7. Other Permits Building permits will be required for this project, together with permits for utility connections. Washington State Department of Ecology – Notice of Intent (NPDES) Sophie Jo Short Plat Page 35 February 28, 2024 Preliminary TIR 8. ESC Analysis and Design The Erosion and Sedimentation Control will be provided with the final TIR. Sophie Jo Short Plat Page 36 February 28, 2024 Preliminary TIR 9. Bond Quantities, Facility Summaries, and Declaration of Covenant The Bond Quantities worksheet will be provided with the final TIR. Sophie Jo Short Plat Page 37 February 28, 2024 Preliminary TIR 10. Operations and Maintenance The Operations and Maintenance manual will be provided with the final TIR. Appendix A – Hydrology Model Output WWHM2012 PROJECT REPORT 3500-roof-vault 12/27/2023 4:21:52 PM Page 2 General Model Information WWHM2012 Project Name:3500-roof-vault Site Name:Sophie Jo Site Address: City: Report Date:12/27/2023 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.000 Version Date:2023/01/27 Version:4.2.19 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year 3500-roof-vault 12/27/2023 4:21:52 PM Page 3 Landuse Basin Data Predeveloped Land Use Site: Historical After Mitigation Trade Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Flat 0.666 Pervious Total 0.666 Impervious Land Use acre Impervious Total 0 Basin Total 0.666 3500-roof-vault 12/27/2023 4:21:52 PM Page 4 Mitigated Land Use Vault: Tributary Area Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Flat 0.256 Pervious Total 0.256 Impervious Land Use acre ROOF TOPS FLAT 0.235 DRIVEWAYS FLAT 0.15 Impervious Total 0.385 Basin Total 0.641 3500-roof-vault 12/27/2023 4:21:52 PM Page 5 Bypassed: Frontage After Mitigation Trade Bypass:Yes GroundWater:No Pervious Land Use acre C, Lawn, Flat 0.025 Pervious Total 0.025 Impervious Land Use acre Impervious Total 0 Basin Total 0.025 3500-roof-vault 12/27/2023 4:21:52 PM Page 6 Routing Elements Predeveloped Routing 3500-roof-vault 12/27/2023 4:21:52 PM Page 7 Mitigated Routing Vault 1 Width:62 ft. Length:33.5 ft. Depth:5.75 ft. Discharge Structure Riser Height:4.75 ft. Riser Diameter:18 in. Notch Type:Rectangular Notch Width:0.005 ft. Notch Height:1.990 ft. Orifice 1 Diameter:0.476 in.Elevation:0 ft. Element Flows To: Outlet 1 Outlet 2 Vault Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)Infilt(cfs) 0.0000 0.047 0.000 0.000 0.000 0.0639 0.047 0.003 0.001 0.000 0.1278 0.047 0.006 0.002 0.000 0.1917 0.047 0.009 0.002 0.000 0.2556 0.047 0.012 0.003 0.000 0.3194 0.047 0.015 0.003 0.000 0.3833 0.047 0.018 0.003 0.000 0.4472 0.047 0.021 0.004 0.000 0.5111 0.047 0.024 0.004 0.000 0.5750 0.047 0.027 0.004 0.000 0.6389 0.047 0.030 0.004 0.000 0.7028 0.047 0.033 0.005 0.000 0.7667 0.047 0.036 0.005 0.000 0.8306 0.047 0.039 0.005 0.000 0.8944 0.047 0.042 0.005 0.000 0.9583 0.047 0.045 0.006 0.000 1.0222 0.047 0.048 0.006 0.000 1.0861 0.047 0.051 0.006 0.000 1.1500 0.047 0.054 0.006 0.000 1.2139 0.047 0.057 0.006 0.000 1.2778 0.047 0.060 0.006 0.000 1.3417 0.047 0.064 0.007 0.000 1.4056 0.047 0.067 0.007 0.000 1.4694 0.047 0.070 0.007 0.000 1.5333 0.047 0.073 0.007 0.000 1.5972 0.047 0.076 0.007 0.000 1.6611 0.047 0.079 0.007 0.000 1.7250 0.047 0.082 0.008 0.000 1.7889 0.047 0.085 0.008 0.000 1.8528 0.047 0.088 0.008 0.000 1.9167 0.047 0.091 0.008 0.000 1.9806 0.047 0.094 0.008 0.000 2.0444 0.047 0.097 0.008 0.000 2.1083 0.047 0.100 0.008 0.000 2.1722 0.047 0.103 0.009 0.000 2.2361 0.047 0.106 0.009 0.000 2.3000 0.047 0.109 0.009 0.000 3500-roof-vault 12/27/2023 4:21:52 PM Page 8 2.3639 0.047 0.112 0.009 0.000 2.4278 0.047 0.115 0.009 0.000 2.4917 0.047 0.118 0.009 0.000 2.5556 0.047 0.121 0.009 0.000 2.6194 0.047 0.124 0.009 0.000 2.6833 0.047 0.127 0.010 0.000 2.7472 0.047 0.131 0.010 0.000 2.8111 0.047 0.134 0.010 0.000 2.8750 0.047 0.137 0.011 0.000 2.9389 0.047 0.140 0.011 0.000 3.0028 0.047 0.143 0.012 0.000 3.0667 0.047 0.146 0.013 0.000 3.1306 0.047 0.149 0.014 0.000 3.1944 0.047 0.152 0.015 0.000 3.2583 0.047 0.155 0.015 0.000 3.3222 0.047 0.158 0.016 0.000 3.3861 0.047 0.161 0.017 0.000 3.4500 0.047 0.164 0.019 0.000 3.5139 0.047 0.167 0.020 0.000 3.5778 0.047 0.170 0.021 0.000 3.6417 0.047 0.173 0.022 0.000 3.7056 0.047 0.176 0.023 0.000 3.7694 0.047 0.179 0.024 0.000 3.8333 0.047 0.182 0.025 0.000 3.8972 0.047 0.185 0.027 0.000 3.9611 0.047 0.188 0.028 0.000 4.0250 0.047 0.191 0.029 0.000 4.0889 0.047 0.195 0.031 0.000 4.1528 0.047 0.198 0.032 0.000 4.2167 0.047 0.201 0.041 0.000 4.2806 0.047 0.204 0.043 0.000 4.3444 0.047 0.207 0.045 0.000 4.4083 0.047 0.210 0.047 0.000 4.4722 0.047 0.213 0.049 0.000 4.5361 0.047 0.216 0.051 0.000 4.6000 0.047 0.219 0.053 0.000 4.6639 0.047 0.222 0.055 0.000 4.7278 0.047 0.225 0.058 0.000 4.7917 0.047 0.228 0.194 0.000 4.8556 0.047 0.231 0.603 0.000 4.9194 0.047 0.234 1.159 0.000 4.9833 0.047 0.237 1.815 0.000 5.0472 0.047 0.240 2.528 0.000 5.1111 0.047 0.243 3.258 0.000 5.1750 0.047 0.246 3.960 0.000 5.2389 0.047 0.249 4.597 0.000 5.3028 0.047 0.252 5.136 0.000 5.3667 0.047 0.255 5.560 0.000 5.4306 0.047 0.258 5.874 0.000 5.4944 0.047 0.262 6.112 0.000 5.5583 0.047 0.265 6.431 0.000 5.6222 0.047 0.268 6.678 0.000 5.6861 0.047 0.271 6.916 0.000 5.7500 0.047 0.274 7.146 0.000 5.8139 0.000 0.000 7.369 0.000 3500-roof-vault 12/27/2023 4:21:52 PM Page 9 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.666 Total Impervious Area:0 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.281 Total Impervious Area:0.385 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.019581 5 year 0.030753 10 year 0.037084 25 year 0.043791 50 year 0.047942 100 year 0.051472 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.011384 5 year 0.016965 10 year 0.021548 25 year 0.028485 50 year 0.034579 100 year 0.041548 Annual Peaks 3500-roof-vault 12/27/2023 4:22:37 PM Page 10 Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.019 0.010 1950 0.024 0.012 1951 0.043 0.029 1952 0.014 0.008 1953 0.011 0.010 1954 0.017 0.010 1955 0.027 0.010 1956 0.021 0.015 1957 0.017 0.010 1958 0.019 0.010 1959 0.017 0.009 1960 0.029 0.022 1961 0.016 0.011 1962 0.010 0.008 1963 0.014 0.010 1964 0.018 0.010 1965 0.013 0.013 1966 0.013 0.009 1967 0.027 0.012 1968 0.017 0.009 1969 0.016 0.009 1970 0.013 0.010 1971 0.014 0.010 1972 0.032 0.023 1973 0.015 0.013 1974 0.016 0.010 1975 0.021 0.010 1976 0.016 0.010 1977 0.002 0.008 1978 0.014 0.010 1979 0.008 0.007 1980 0.030 0.026 1981 0.012 0.010 1982 0.023 0.015 1983 0.021 0.010 1984 0.013 0.008 1985 0.008 0.008 1986 0.034 0.011 1987 0.030 0.018 1988 0.012 0.009 1989 0.008 0.008 1990 0.063 0.022 1991 0.038 0.018 1992 0.015 0.010 1993 0.015 0.008 1994 0.005 0.007 1995 0.022 0.011 1996 0.046 0.028 1997 0.038 0.033 1998 0.009 0.009 1999 0.036 0.022 2000 0.015 0.010 2001 0.003 0.006 2002 0.017 0.012 2003 0.021 0.009 2004 0.027 0.026 3500-roof-vault 12/27/2023 4:22:37 PM Page 11 2005 0.020 0.010 2006 0.023 0.014 2007 0.047 0.044 2008 0.060 0.026 2009 0.030 0.013 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.0628 0.0443 2 0.0601 0.0327 3 0.0466 0.0291 4 0.0459 0.0283 5 0.0431 0.0264 6 0.0384 0.0262 7 0.0378 0.0256 8 0.0360 0.0233 9 0.0339 0.0225 10 0.0321 0.0220 11 0.0304 0.0219 12 0.0300 0.0182 13 0.0295 0.0176 14 0.0292 0.0150 15 0.0274 0.0147 16 0.0269 0.0141 17 0.0266 0.0133 18 0.0240 0.0130 19 0.0234 0.0125 20 0.0232 0.0119 21 0.0218 0.0116 22 0.0215 0.0116 23 0.0214 0.0115 24 0.0212 0.0114 25 0.0210 0.0110 26 0.0197 0.0104 27 0.0195 0.0104 28 0.0192 0.0104 29 0.0185 0.0103 30 0.0173 0.0103 31 0.0169 0.0103 32 0.0167 0.0099 33 0.0166 0.0099 34 0.0166 0.0098 35 0.0164 0.0098 36 0.0162 0.0098 37 0.0158 0.0097 38 0.0155 0.0097 39 0.0152 0.0097 40 0.0151 0.0097 41 0.0146 0.0096 42 0.0146 0.0096 43 0.0143 0.0096 44 0.0141 0.0095 45 0.0136 0.0095 46 0.0136 0.0092 47 0.0134 0.0091 48 0.0132 0.0090 49 0.0129 0.0088 3500-roof-vault 12/27/2023 4:22:37 PM Page 12 50 0.0127 0.0087 51 0.0122 0.0085 52 0.0118 0.0082 53 0.0110 0.0081 54 0.0102 0.0081 55 0.0087 0.0080 56 0.0082 0.0077 57 0.0077 0.0075 58 0.0077 0.0075 59 0.0051 0.0072 60 0.0027 0.0069 61 0.0018 0.0062 3500-roof-vault 12/27/2023 4:22:37 PM Page 13 LID Duration Flows The Development Failed :duration increase for more than 0% of the flows. Flow(cfs)Predev Mit Percentage Pass/Fail 0.0016 229502 858974 374 Fail 0.0016 220946 838869 379 Fail 0.0017 212990 819191 384 Fail 0.0018 205332 800369 389 Fail 0.0019 198060 782188 394 Fail 0.0020 191045 765077 400 Fail 0.0021 184521 749250 406 Fail 0.0021 178340 733636 411 Fail 0.0022 172372 717808 416 Fail 0.0023 166833 700055 419 Fail 0.0024 161571 682730 422 Fail 0.0025 156480 666047 425 Fail 0.0026 151711 650220 428 Fail 0.0026 147134 635247 431 Fail 0.0027 142727 620275 434 Fail 0.0028 138450 604020 436 Fail 0.0029 134279 588192 438 Fail 0.0030 130322 573006 439 Fail 0.0031 126386 558248 441 Fail 0.0031 122643 543917 443 Fail 0.0032 119007 529373 444 Fail 0.0033 115478 515042 446 Fail 0.0034 112013 500926 447 Fail 0.0035 108719 487237 448 Fail 0.0036 105447 473762 449 Fail 0.0036 102324 460073 449 Fail 0.0037 99351 447026 449 Fail 0.0038 96485 434620 450 Fail 0.0039 93683 422643 451 Fail 0.0040 91009 410451 451 Fail 0.0041 88421 398687 450 Fail 0.0041 85983 387351 450 Fail 0.0042 83609 375587 449 Fail 0.0043 81277 364251 448 Fail 0.0044 79010 353129 446 Fail 0.0045 76850 342007 445 Fail 0.0046 74732 331099 443 Fail 0.0046 72701 321046 441 Fail 0.0047 70797 311207 439 Fail 0.0048 68979 301582 437 Fail 0.0049 67075 291957 435 Fail 0.0050 65321 282760 432 Fail 0.0051 63653 273135 429 Fail 0.0051 62006 263296 424 Fail 0.0052 60488 254313 420 Fail 0.0053 59012 245971 416 Fail 0.0054 57557 237416 412 Fail 0.0055 56124 229288 408 Fail 0.0056 54713 220732 403 Fail 0.0056 53386 212947 398 Fail 0.0057 52082 205332 394 Fail 0.0058 50798 197846 389 Fail 0.0059 49579 190253 383 Fail 3500-roof-vault 12/27/2023 4:22:37 PM Page 14 0.0060 48339 183259 379 Fail 0.0061 47226 176458 373 Fail 0.0061 46071 169699 368 Fail 0.0062 44938 163346 363 Fail 0.0063 43911 157186 357 Fail 0.0064 42906 151197 352 Fail 0.0065 41922 145508 347 Fail 0.0066 40960 139861 341 Fail 0.0066 40018 134407 335 Fail 0.0067 39035 128846 330 Fail 0.0068 38179 123435 323 Fail 0.0069 37238 118130 317 Fail 0.0070 36404 113061 310 Fail 0.0070 35527 108334 304 Fail 0.0071 34735 103800 298 Fail 0.0072 33923 99073 292 Fail 0.0073 33153 94624 285 Fail 0.0074 32404 90453 279 Fail 0.0075 31677 86389 272 Fail 0.0075 30950 82497 266 Fail 0.0076 30244 78796 260 Fail 0.0077 29538 75481 255 Fail 0.0078 28896 72166 249 Fail 0.0079 28233 68744 243 Fail 0.0080 27592 65386 236 Fail 0.0080 26971 62177 230 Fail 0.0081 26372 59226 224 Fail 0.0082 25795 56402 218 Fail 0.0083 25260 53664 212 Fail 0.0084 24704 51141 207 Fail 0.0085 24191 48638 201 Fail 0.0085 23699 46093 194 Fail 0.0086 23228 43483 187 Fail 0.0087 22758 41024 180 Fail 0.0088 22309 38607 173 Fail 0.0089 21881 36211 165 Fail 0.0090 21453 34115 159 Fail 0.0090 21023 32083 152 Fail 0.0091 20621 30008 145 Fail 0.0092 20219 28062 138 Fail 0.0093 19791 26308 132 Fail 0.0094 19374 24447 126 Fail 0.0095 18989 22651 119 Fail 0.0095 18606 21126 113 Fail 0.0096 18236 19676 107 Fail 0.0097 17879 18431 103 Fail 0.0098 17550 17280 98 Pass The development has an increase in flow durations from 1/2 Predeveloped 2 year flow to the 2 year flow or more than a 10% increase from the 2 year to the 50 year flow. The development has an increase in flow durations for more than 50% of the flows for the range of the duration analysis. 3500-roof-vault 12/27/2023 4:22:49 PM Page 15 Duration Flows The Facility PASSED Flow(cfs)Predev Mit Percentage Pass/Fail 0.0098 17550 17280 98 Pass 0.0102 16183 12769 78 Pass 0.0106 14966 9447 63 Pass 0.0109 13864 8089 58 Pass 0.0113 12816 7030 54 Pass 0.0117 11824 6295 53 Pass 0.0121 10900 5728 52 Pass 0.0125 10132 5223 51 Pass 0.0129 9388 4746 50 Pass 0.0133 8748 4357 49 Pass 0.0136 8149 4021 49 Pass 0.0140 7608 3734 49 Pass 0.0144 7067 3527 49 Pass 0.0148 6588 3311 50 Pass 0.0152 6151 3189 51 Pass 0.0156 5777 3063 53 Pass 0.0160 5437 2928 53 Pass 0.0163 5097 2798 54 Pass 0.0167 4810 2669 55 Pass 0.0171 4526 2530 55 Pass 0.0175 4256 2391 56 Pass 0.0179 4017 2188 54 Pass 0.0183 3788 1994 52 Pass 0.0187 3548 1898 53 Pass 0.0190 3341 1803 53 Pass 0.0194 3138 1710 54 Pass 0.0198 2950 1625 55 Pass 0.0202 2787 1525 54 Pass 0.0206 2597 1410 54 Pass 0.0210 2449 1305 53 Pass 0.0214 2304 1202 52 Pass 0.0217 2162 1106 51 Pass 0.0221 2026 1020 50 Pass 0.0225 1901 952 50 Pass 0.0229 1790 890 49 Pass 0.0233 1689 835 49 Pass 0.0237 1586 785 49 Pass 0.0240 1483 728 49 Pass 0.0244 1381 659 47 Pass 0.0248 1293 580 44 Pass 0.0252 1221 524 42 Pass 0.0256 1154 442 38 Pass 0.0260 1098 404 36 Pass 0.0264 1048 331 31 Pass 0.0267 997 292 29 Pass 0.0271 930 266 28 Pass 0.0275 884 242 27 Pass 0.0279 837 217 25 Pass 0.0283 789 192 24 Pass 0.0287 743 177 23 Pass 0.0291 713 160 22 Pass 0.0294 668 149 22 Pass 0.0298 633 144 22 Pass 3500-roof-vault 12/27/2023 4:22:49 PM Page 16 0.0302 596 140 23 Pass 0.0306 565 134 23 Pass 0.0310 539 128 23 Pass 0.0314 496 122 24 Pass 0.0318 473 104 21 Pass 0.0321 434 91 20 Pass 0.0325 400 70 17 Pass 0.0329 366 60 16 Pass 0.0333 348 54 15 Pass 0.0337 323 49 15 Pass 0.0341 296 44 14 Pass 0.0345 272 42 15 Pass 0.0348 256 41 16 Pass 0.0352 235 41 17 Pass 0.0356 217 40 18 Pass 0.0360 195 38 19 Pass 0.0364 180 38 21 Pass 0.0368 158 38 24 Pass 0.0372 145 37 25 Pass 0.0375 129 37 28 Pass 0.0379 119 36 30 Pass 0.0383 109 36 33 Pass 0.0387 97 35 36 Pass 0.0391 91 35 38 Pass 0.0395 82 34 41 Pass 0.0398 76 33 43 Pass 0.0402 69 33 47 Pass 0.0406 61 32 52 Pass 0.0410 54 32 59 Pass 0.0414 48 31 64 Pass 0.0418 41 31 75 Pass 0.0422 38 29 76 Pass 0.0425 33 28 84 Pass 0.0429 27 22 81 Pass 0.0433 22 17 77 Pass 0.0437 21 14 66 Pass 0.0441 20 8 40 Pass 0.0445 19 0 0 Pass 0.0449 17 0 0 Pass 0.0452 14 0 0 Pass 0.0456 12 0 0 Pass 0.0460 9 0 0 Pass 0.0464 4 0 0 Pass 0.0468 3 0 0 Pass 0.0472 3 0 0 Pass 0.0476 3 0 0 Pass 0.0479 3 0 0 Pass 3500-roof-vault 12/27/2023 4:22:49 PM Page 17 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. 3500-roof-vault 12/27/2023 4:22:49 PM Page 18 LID Report 3500-roof-vault 12/27/2023 4:23:03 PM Page 19 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. 3500-roof-vault 12/27/2023 4:23:03 PM Page 20 Appendix Predeveloped Schematic 3500-roof-vault 12/27/2023 4:23:03 PM Page 21 Mitigated Schematic 3500-roof-vault 12/27/2023 4:23:04 PM Page 22 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 3500-roof-vault.wdm MESSU 25 Pre3500-roof-vault.MES 27 Pre3500-roof-vault.L61 28 Pre3500-roof-vault.L62 30 POC3500-roof-vault1.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 10 COPY 501 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<----------Title----------->***TRAN PIVL DIG1 FIL1 PYR DIG2 FIL2 YRND 1 Site: Historical After Mi 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 *** 10 C, Forest, Flat 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 *** 10 0 0 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 10 0 0 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO 3500-roof-vault 12/27/2023 4:23:04 PM Page 23 PWAT-PARM1 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** 10 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 10 0 4.5 0.08 400 0.05 0.5 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 10 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 10 0.2 0.5 0.35 6 0.5 0.7 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 10 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 *** END GEN-INFO *** Section IWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** END ACTIVITY PRINT-INFO <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* END PRINT-INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN END IWAT-PARM3 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS END IWAT-STATE1 3500-roof-vault 12/27/2023 4:23:04 PM Page 24 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** Site: Historical After Mitigation Trade*** PERLND 10 0.666 COPY 501 12 PERLND 10 0.666 COPY 501 13 ******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 *** 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 3500-roof-vault 12/27/2023 4:23:04 PM Page 25 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 END MASS-LINK END RUN 3500-roof-vault 12/27/2023 4:23:04 PM Page 26 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 3500-roof-vault.wdm MESSU 25 Mit3500-roof-vault.MES 27 Mit3500-roof-vault.L61 28 Mit3500-roof-vault.L62 30 POC3500-roof-vault1.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 16 IMPLND 4 IMPLND 5 RCHRES 1 COPY 1 COPY 501 COPY 601 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 1 601 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 *** 16 C, Lawn, Flat 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 *** 16 0 0 1 0 0 0 0 0 0 0 0 0 END ACTIVITY 3500-roof-vault 12/27/2023 4:23:04 PM Page 27 PRINT-INFO <PLS > ***************** Print-flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 16 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 *** 16 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 16 0 4.5 0.03 400 0.05 0.5 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 16 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 16 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 16 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 <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* 4 0 0 4 0 0 4 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 3500-roof-vault 12/27/2023 4:23:04 PM Page 28 <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# *** Vault: Tributary Area*** PERLND 16 0.256 RCHRES 1 2 PERLND 16 0.256 RCHRES 1 3 IMPLND 4 0.235 RCHRES 1 5 IMPLND 5 0.15 RCHRES 1 5 Bypassed: Frontage After Mitigation Trade*** PERLND 16 0.025 COPY 501 12 PERLND 16 0.025 COPY 601 12 PERLND 16 0.025 COPY 501 13 PERLND 16 0.025 COPY 601 13 ******Routing****** PERLND 16 0.256 COPY 1 12 IMPLND 4 0.235 COPY 1 15 IMPLND 5 0.15 COPY 1 15 PERLND 16 0.256 COPY 1 13 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 <-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 3500-roof-vault 12/27/2023 4:23:04 PM Page 29 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 0.01 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 91 4 Depth Area Volume Outflow1 Velocity Travel Time*** (ft) (acres) (acre-ft) (cfs) (ft/sec) (Minutes)*** 0.000000 0.047681 0.000000 0.000000 0.063889 0.047681 0.003046 0.001554 0.127778 0.047681 0.006093 0.002197 0.191667 0.047681 0.009139 0.002691 0.255556 0.047681 0.012185 0.003107 0.319444 0.047681 0.015232 0.003474 0.383333 0.047681 0.018278 0.003805 0.447222 0.047681 0.021324 0.004110 0.511111 0.047681 0.024370 0.004394 0.575000 0.047681 0.027417 0.004661 0.638889 0.047681 0.030463 0.004913 0.702778 0.047681 0.033509 0.005152 0.766667 0.047681 0.036556 0.005382 0.830556 0.047681 0.039602 0.005601 0.894444 0.047681 0.042648 0.005813 0.958333 0.047681 0.045695 0.006017 1.022222 0.047681 0.048741 0.006214 1.086111 0.047681 0.051787 0.006405 1.150000 0.047681 0.054834 0.006591 1.213889 0.047681 0.057880 0.006772 1.277778 0.047681 0.060926 0.006948 1.341667 0.047681 0.063972 0.007119 1.405556 0.047681 0.067019 0.007287 1.469444 0.047681 0.070065 0.007450 1.533333 0.047681 0.073111 0.007611 1.597222 0.047681 0.076158 0.007768 1.661111 0.047681 0.079204 0.007922 1.725000 0.047681 0.082250 0.008072 1.788889 0.047681 0.085297 0.008221 1.852778 0.047681 0.088343 0.008366 1.916667 0.047681 0.091389 0.008509 1.980556 0.047681 0.094436 0.008650 2.044444 0.047681 0.097482 0.008788 2.108333 0.047681 0.100528 0.008924 2.172222 0.047681 0.103575 0.009059 3500-roof-vault 12/27/2023 4:23:04 PM Page 30 2.236111 0.047681 0.106621 0.009191 2.300000 0.047681 0.109667 0.009321 2.363889 0.047681 0.112713 0.009450 2.427778 0.047681 0.115760 0.009577 2.491667 0.047681 0.118806 0.009702 2.555556 0.047681 0.121852 0.009825 2.619444 0.047681 0.124899 0.009947 2.683333 0.047681 0.127945 0.010068 2.747222 0.047681 0.130991 0.010187 2.811111 0.047681 0.134038 0.010481 2.875000 0.047681 0.137084 0.011006 2.938889 0.047681 0.140130 0.011655 3.002778 0.047681 0.143177 0.012395 3.066667 0.047681 0.146223 0.013205 3.130556 0.047681 0.149269 0.014074 3.194444 0.047681 0.152315 0.014989 3.258333 0.047681 0.155362 0.015944 3.322222 0.047681 0.158408 0.016931 3.386111 0.047681 0.161454 0.017945 3.450000 0.047681 0.164501 0.018980 3.513889 0.047681 0.167547 0.020031 3.577778 0.047681 0.170593 0.021094 3.641667 0.047681 0.173640 0.022166 3.705556 0.047681 0.176686 0.023243 3.769444 0.047681 0.179732 0.024352 3.833333 0.047681 0.182779 0.025650 3.897222 0.047681 0.185825 0.026984 3.961111 0.047681 0.188871 0.028351 4.025000 0.047681 0.191917 0.029752 4.088889 0.047681 0.194964 0.031186 4.152778 0.047681 0.198010 0.032651 4.216667 0.047681 0.201056 0.041041 4.280556 0.047681 0.204103 0.043026 4.344444 0.047681 0.207149 0.045050 4.408333 0.047681 0.210195 0.047113 4.472222 0.047681 0.213242 0.049214 4.536111 0.047681 0.216288 0.051352 4.600000 0.047681 0.219334 0.053527 4.663889 0.047681 0.222381 0.055737 4.727778 0.047681 0.225427 0.057982 4.791667 0.047681 0.228473 0.194156 4.855556 0.047681 0.231519 0.603366 4.919444 0.047681 0.234566 1.159829 4.983333 0.047681 0.237612 1.815347 5.047222 0.047681 0.240658 2.528763 5.111111 0.047681 0.243705 3.258027 5.175000 0.047681 0.246751 3.960649 5.238889 0.047681 0.249797 4.597120 5.302778 0.047681 0.252844 5.136004 5.366667 0.047681 0.255890 5.560220 5.430556 0.047681 0.258936 5.874274 5.494444 0.047681 0.261983 6.112307 5.558333 0.047681 0.265029 6.431302 5.622222 0.047681 0.268075 6.678390 5.686111 0.047681 0.271122 6.916584 5.750000 0.047681 0.274168 7.146782 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 3500-roof-vault 12/27/2023 4:23:04 PM Page 31 <-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 1000 FLOW ENGL REPL RCHRES 1 HYDR STAGE 1 1 1 WDM 1001 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 COPY 601 OUTPUT MEAN 1 1 48.4 WDM 901 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 3500-roof-vault 12/27/2023 4:23:04 PM Page 32 Predeveloped HSPF Message File 3500-roof-vault 12/27/2023 4:23:04 PM Page 33 Mitigated HSPF Message File 3500-roof-vault 12/27/2023 4:23:04 PM Page 34 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. 2005-2023; 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 Appendix B – Geotechnical Report DEVELOPMENT ENGINEERING, PLLC P.O. Box 446 Tacoma, WA 98401 Ph (253) 228-0513 www.de-civil.com September 7, 2017 Schneider Homes, Inc. 6510 Southcenter Blvd #1 Tukwila, WA 98188 Attn: Mr. Harry Schneider Geologic Assessment Report Proposed Short Plat 7XX S 21st Street Renton, Washington PN: 7222000110 Job: 17-166 Schneider.GR INTRODUCTION This letter and design report presents the results of our subsurface explorations for the proposed short plat to be located at 7XX S 21st Street in the City of Renton, Washington. The general location of the site is shown on the attached Site Vicinity Map, Figure 1. Our understanding of the project is based on our discussions with yourself, our September 4, 2017 site visit, and our experience in the area. We understand that you are proposing to subdivide the property into 3 lots in order to construct new residences on each of the sites. We anticipate that the proposed residence(s) will be a constructed with conventional wood-framing, supported on spread and continuous foundations. SCOPE We understand that the City of Renton is requesting a geotechnical report to address stormwater management and other design issues related to the site development. The purpose of our services is to evaluate the surface and subsurface conditions at the site as a basis for providing engineering recommendations for the development of the site. Specifically, our scope of services for the project included the following: 1. Reviewing the available geologic, hydrogeologic and geotechnical data for the site area. 2. Performing a geological reconnaissance of the site to assess the site’s soil, groundwater and subsurface conditions. 3. Exploring shallow subsurface conditions at the site by monitoring the excavation of two test pits across the site. 4. Evaluating the engineering characteristics of the soils encountered at the site, as appropriate. 5. Providing geotechnical recommendations for site infiltration site grading including site preparation, subgrade reparation, fill placement criteria, suitability of on-site soils for use as structural fill, temporary and permanent cut and fill slopes, drainage and erosion control measures. 6. Providing site-specific seismic criteria based on the subsurface conditions encountered at the site. 7. Preparing a written report summarizing our observations, conclusions and recommendations along with the supporting data. Subsurface explorations or laboratory testing were completed as part of this assessment. 17-166 Schneider.GR September 7, 2017 Page 2 SITE CONDITIONS Surface Conditions The subject parcel is located at 7XX S 21st Street in the City of Renton, Washington. The site consists of a single parcel that is rectangular in shape, approximately 290 feet in length (west to east) by 70 feet in width (north to South) and encompasses an area of approximately 0.46 acres. The site is an existing lot of record that is currently undeveloped and is well vegetated with trees, grasses and brush. Access to the site will be from a private driveway from S 21st Street, see Figure 2 Site Plan. The parcel is nearly level with a slight slope to the north, site grades are generally less than 5 percent with less than 5 feet of elevation change across the lot. No surface water or seepage was observed on the site at the time of our first site visit, however we did observe signs of a potentially high groundwater in the upper soils of the site, see below for more information. No evidence of erosion, soil movement, landslide activity or deep-seated slope instability was observed at the site or within 300 feet of the site at the time of our site visit. Site Soils The USDA Natural Resource Conservation Service Web Soil Survey for King County mapped the soils in the area of the site as Beausite gravelly sandy loam (BeC). The Beausite soils are a gravelly sandy loam, formed from glacial deposits overlying sandstone bedrock on slopes of 6 to 15 percent slope and are listed as having a “moderate” erosion potential, see Figure 3 USDA Soil Map. Site Geology The Geological Map of the Renton Quadrangle, King County, Washington by D. R. Mullineaux, 1965 indicates the site is underlain by glacial till (Qvt). These glacial soils were deposited during the latest stage of the most recent Vashon Stade of the Fraser Glaciation, approximately 12,000 to 15,000 years ago. These soils are characterized as mix of silt, sand with gravel which were overridden by the glacial ice. As such, these soils are generally very dense exhibiting high strength and low compressibility characteristics. An excerpt of the above referenced map is included as Figure 4. Based on our site observations the near surface soils at the site are most consistent with the USDA mapped soils. Subsurface Explorations On September 4, 2017 we visited the site and observed the excavation of three test pits to a maximum depth of 6 feet for the purpose of determining infiltration feasibility for the project, soil samples were collected for later analysis in our lab. The test pits were excavated by a track mounted excavator operated by a licensed earthwork contractor. The test pits were located in the field by our representative by pacing from existing site features such as property corners and adjacent roadways and fences. The approximate location of the test pits are indicated on the attached Site Plan as Figure 2. A geotechnical engineer from our office logged the subsurface conditions encountered in each test pit, obtained representative soil samples, and observed pertinent site features. Representative soil samples obtained from the test pits were placed in sealed plastic bags and taken to our laboratory for further examination and testing, as deemed appropriate. Based on our experience in the area and extent of our explorations in the area it is our opinion that the soils encountered in the test pits are generally representative of the soils at the site. 17-166 Schneider.GR September 7, 2017 Page 3 Because the soils encountered were consistent between the test sites and other exposed site soils and the soil mapping, it is our opinion that no additional soils tests required to evaluate the subsurface conditions at the site. The explorations performed as part of this evaluation indicate conditions only at the specific locations and that the actual condition in other locations could vary. Furthermore, the nature and extent of any such variations would not become evident until additional explorations are performed or until construction activities have begun. Subsurface Conditions Our test pits encountered uniform subsurface conditions that confirmed the general geological mapping stratigraphy. The site soils generally consisted of a minimum of 24 to 36 inches of weathered silty sand and gravel over a dense sandstone layer. Test pit #2 showed signs of a shallow fill layer (approximately 12 to 18 inches). Based on our review of our test pits, the upper weathered site soils in the area of development are consistent with the Beausite soils. The soils encountered were visually classified in accordance with the Unified Soil Classification System (USCS) described on Figure 5. The test pit logs are included as Figures 6. Groundwater Conditions No groundwater seepage was observed in any of the test pits. Although based on our observations we anticipate that during periods of heavy rainfall the upper soils would become saturated. Perched groundwater typically develops when the vertical infiltration of precipitation through a more permeable soil is slowed at depth by a deeper, less permeable soil type. We expect that perched groundwater will develop seasonally atop the shallow sandstone layer. Based on the observed mottling and nature of the near surface soils, we anticipate fluctuations in the local groundwater levels will occur in response to precipitation patterns, off-site construction activities, and site utilization. CONCLUSIONS Based on our site observations, subsurface explorations and engineering analysis, it is our opinion that the proposed development is feasible from a geotechnical standpoint. The residences may be supported on new conventional spread footings or floor slabs bearing on competent native soils or on structural fill placed above these native soils. We understand that grading at the site will be minimal, and will consist primarily of excavating the footings for the proposed residence(s), site utilities, and the stormwater facilities. If grading activities will take place during the winter season, the owner should be prepared to import free-draining granular material for use as structural fill and backfill. Proper surface drainage and erosion control measures will reduce the risk for future erosion at the site. Site Preparation Areas to be graded should be cleared of deleterious matter including any existing structures, foundations, abandoned utility lines, debris and vegetation. The portions of the site covered with vegetation should be stripped of any forest duff and organic-laden soils. Based on our test pits we anticipate stripping depths to be on the order of 6 to 18 inches. These materials can be stockpiled and later used for erosion control. Material that cannot be utilized on the site should be removed from the site. Where placement of fill material is required, the stripped/exposed subgrade areas should be compacted to a firm and unyielding surface prior to placement of any fill. Excavations for debris 17-166 Schneider.GR September 7, 2017 Page 4 removal should be backfilled with structural fill compacted to the densities described in the “Structural Fill” section of this report. We recommend that a member of our staff evaluate the exposed subgrade conditions after removal of vegetation and topsoil stripping is completed and prior to placement of structural fill. The exposed subgrade soil should be proof-rolled with heavy rubber-tired equipment during dry weather or probed with a 1/2-inch-diameter steel rod during wet weather conditions. Any soft, loose or otherwise unsuitable areas delineated during proof-rolling or probing should be recompacted, if practical, or over-excavated and replaced with structural fill, based on the recommendations of our site representative. The areas of old fill material should be evaluated during grading operations to determine if they need mitigation; recompaction or removal. Structural Fill All material placed as fill associated with mass grading, as utility trench backfill, under building areas, or under asphalt pavement should be placed as structural fill. The structural fill should be placed in horizontal lifts of appropriate thickness to allow adequate and uniform compaction of each lift. Fill should be compacted to at least 95 percent of MDD (maximum dry density as determined in accordance with ASTM D-1557). The appropriate lift thickness will depend on the fill characteristics and compaction equipment used. We recommend that the appropriate lift thickness be evaluated by our field representative during construction. We recommend that our representative be present during site grading activities to observe the work and perform field density tests. The suitability of material for use as structural fill will depend on the gradation and moisture content of the soil. As the amount of fines (material passing US No. 200 sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and adequate compaction becomes more difficult to achieve. During wet weather, we recommend use of well-graded sand and gravel with less than 5 percent (by weight) passing the US No. 200 sieve based on that fraction passing the 3/4-inch sieve, such as Gravel Backfill for Walls (9-03.12(2)). If prolonged dry weather prevails during the earthwork and foundation installation phase of construction, higher fines content (up to 10 to 12 percent) will be acceptable. Material placed for structural fill should be free of debris, organic matter, trash and cobbles greater than 6-inches in diameter. The moisture content of the fill material should be adjusted as necessary for proper compaction. Suitability of On-Site Materials as Fill During dry weather construction, any non-organic on-site soil may be considered for use as structural fill; provided it meets the criteria described above in the structural fill section and can be compacted as recommended. If the soil material is over-optimum in moisture content when excavated, it will be necessary to aerate or dry the soil prior to placement as structural fill. We generally did not observe the site soils to be excessively moist at the time of our subsurface exploration program. The native weathered and glacial till soils in the site generally consisted of silty gravel with fine sand. These soils are generally comparable to “common borrow” material and will be suitable for use as structural fill provided the moisture content is maintained within 3 percent of the optimum moisture level. However, because of the high fines content, the till soils encountered across the site will likely be unsuitable during extended periods of wet weather. We recommend that completed graded-areas be restricted from traffic or protected prior to wet weather conditions. The graded areas may be protected by paving, placing asphalt-treated base, a 17-166 Schneider.GR September 7, 2017 Page 5 layer of free-draining material such as pit run sand and gravel or clean crushed rock material containing less than 5 percent fines, or some combination of the above. Temporary Excavations All job site safety issues and precautions are the responsibility of the contractor providing services/work. The following cut/fill slope guidelines are provided for planning purposes only. Temporary cut slopes will likely be necessary during grading operations or utility installation. All excavations at the site associated with confined spaces, such as utility trenches and retaining walls, must be completed in accordance with local, state, or federal requirements. Based on current Washington Industrial Safety and Health Act (WISHA, WAC 296-155-66401) regulations, the shallow upper soils on the site would be classified as Type C soils, whereas the very dense sandstone soils would be classified as Type A soils. According to WISHA, for temporary excavations of less than 20 feet in depth, the side slopes in Type A soils should be laid back at a slope inclination of ¾H:1V (Horizontal: Vertical) and Type C soils should be laid back at a slope inclination of 1½H:1V or flatter from the toe to the crest of the slope. It should be recognized that slopes of this nature do ravel and require occasional maintenance. All exposed slope faces should be covered with a durable reinforced plastic membrane, jute matting, or other erosion control mats during construction to prevent slope raveling and rutting during periods of precipitation. These guidelines assume that all surface loads are kept at a minimum distance of at least one half the depth of the cut away from the top of the slope and that significant seepage is not present on the slope face. Flatter cut slopes will be necessary where significant raveling or seepage occurs, or if construction materials will be stockpiled along the slope crest. Where it is not feasible to slope the site soils back at these inclinations, a retaining structure should be considered. Where retaining structures are greater than 4-feet in height (bottom of footing to top of structure) or have slopes of greater than 15 percent above them, they should be engineered. This information is provided solely for the benefit of the owner and other design consultants, and should not be construed to imply that Development Engineering, PLLC assumes responsibility for job site safety. It is understood that job site safety is the sole responsibility of the project contractor. Foundation Support Based on the subsurface soil conditions encountered across the site, we recommend that spread footings for the new residences be founded on dense to very dense native soils or on structural fill that extends to suitable native soils. Given the presence of fill material on the site it is anticipated that some footings may be located in areas where existing fill material is present. Provided the exposed soils area evaluated and verified by a representative from our office at time of construction to be suitable to support the design loads we do not anticipate that the presence of the fill material on site will be a detrimental factor to the site development. We do not recommend that footings be supported on a mix of sandstone and weathered material. If areas of sandstone are exposed we recommend that those areas are over excavated a minimum of 12 inches and brought back to grade with structural fill. The soil at the base of the footing excavations should be disturbed as little as possible. All loose, soft or unsuitable material should be removed or recompacted, as appropriate. A representative from our firm should observe the foundation excavations to determine if suitable bearing surfaces have been prepared, particularly in the areas where the foundation will be situated on fill material. 17-166 Schneider.GR September 7, 2017 Page 6 We recommend a minimum width of 2 feet for isolated footings and at least 16 inches for continuous wall footings. All footing elements should be embedded at least 18 inches below grade for frost protection. Footings founded as described above can be designed using an allowable soil bearing capacity of 2,000psf (pounds per square foot) for combined dead and long-term live loads. For deeper footings supported entirely on the sandstone a bearing capacity of 5,000psf may be used. The weight of the footing and any overlying backfill may be neglected. The allowable bearing value may be increased by one-third for transient loads such as those induced by seismic events or wind loads. Lateral loads may be resisted by friction on the base of footings and floor slabs and as passive pressure on the sides of footings. We recommend that an allowable coefficient of friction of 0.40 be used to calculate friction between the concrete and the underlying soil. Passive pressure may be determined using an allowable equivalent fluid density of 300 pcf (pounds per cubic foot). Factors of safety have been applied to these values. We estimate that settlements of footings designed and constructed as recommended will be less than 1 inch, for the anticipated load conditions, with differential settlements between comparably loaded footings of 1/2 inch or less. Most of the settlements should occur essentially as loads are being applied. However, disturbance of the foundation subgrade during construction could result in larger settlements than predicted. Floor Slab Support Slabs-on-grade, if constructed, should be supported on the medium dense native soils or on structural fill prepared as described above. Any areas of old fill material should be evaluated during grading activity for suitability of structural support. Areas of significant organic debris should be removed. We recommend that floor slabs be directly underlain by a capillary break material with minimum 6- inch thickness of coarse sand, pea gravel, or gravel containing less than 3 percent fines. The drainage material should be placed in one lift and compacted to an unyielding condition. A synthetic vapor barrier is recommended to control moisture migration through the slabs. This is of particular importance where the foundation elements are underlain by the silty till, or where moisture migration through the slab is an issue, such as where adhesives are used to anchor carpet or tile to the slab. A subgrade modulus of 400 kcf (kips per cubic foot) may be used for floor slab design. We estimate that settlement of the floor slabs designed and constructed as recommended, will be 1/2 inch or less over a span of 50 feet. Site Drainage All ground surfaces, pavements and sidewalks at the site should be sloped away from structures. The lot should also be carefully graded to ensure positive drainage away from all structures and property lines. Surface water runoff from the roof area, driveways, perimeter footing drains, and wall drains, should be collected, tightlined, and conveyed to an appropriate discharge point. Based on our site evaluation, it is our opinion that the infiltration of stormwater at the site not feasible on the site. Further, based on our understanding of the current City of Renton Stormwater Management Manual, it will likely be necessary to visit the site and perform additional explorations and possibly at least one full scale “Pilot Infiltration Test” (PIT) between December 1 and April 30 (winter months) in order to determine seasonal groundwater levels and infiltration feasibility. Since our field final work was done in early Suptember we recommend that we revisit our Site Drainage 17-166 Schneider.GR September 7, 2017 Page 7 recommendations once this additional field work is complete. For preliminary design purposes we are not recommending that infiltration be pursued. LID Feasibility The following table presents our recommendations for various Best Management Practices (BMP’s) for various Low Impact Development (LID) BMP’s. BMP Viable Limitations or Infeasibility Criteria Lawn and Landscape Areas T5.13: Post Construction Soil Quality and Depth Yes None. Roofs T5.30: Full Dispersion No The site does not have sufficient dispersion area. T5.10A: Downspout full infiltration systems. No Infiltration appears to be infeasible due to a high groundwater table. Bio Retention No This BMP also has limited feasibility for the same general reasons as for full infiltration. T5.10B Downspout Dispersion systems Limited This BMP may be feasible depending on final lot configurations. T5.10C Perforate stub connections Limited Similar to the infiltration systems there will be limited depths of soil for the connection to ensure that it is at least 1 foot above the till layers. Other Hard Surfaces T5.30 Full Dispersion No The site does not have sufficient dispersion area. T5.15 Permeable Surfacing No The soils in the areas of the proposed pavement included a very shallow groundwater depth which does not allow for the required 12 inches of separation between the bottom of the pavement section and the groundwater. Further, given the silty nature of the site soils, permeable surfacing would not be sufficiently supported and would likely fail in a short period of time. Bio Retention No This BMP also has limited feasibility for the same general reasons as for full infiltration. T5.12: Sheet Flow Dispersion T5.11 Concentrated flow dispersion Limited No flooding or erosion impacts are anticipated. However, this BMP may be feasible dependent on the final lot configurations and the available areas for dispersion of runoff. LIMITATIONS We have prepared this report for Schneider Homes, Inc, and other members of the design team for use in evaluating a portion of this project. Subsurface conditions described herein are based on our observations of exposed soils on the parcel. This report may be made available to regulatory agencies or others, but this report and conclusions should not be construed as a warranty of subsurface conditions. Subsurface conditions can vary over short distances and can change with time. 17-166 Schneider.GR September 7, 2017 Page 8 Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in this area at the time this report was prepared. No warranty, express or implied, should be understood. We trust this is sufficient for your current needs. Should you have any questions, or require additional information, please contact us at your earliest convenience. Respectfully submitted, Development Engineering, PLLC Glen Coad, PE Owner WGC DocID:17-166 Schneider.GR Attachments: Figure 1: Vicinity Map Figure 2: Site Plan Figure 3: SCS Soil Survey Figure 4: USGS Geology Map Figure 5: Soils Classification Chart Figure 6: Test Pit Logs Approximate Site Location Not to Scale DE-CIVIL, PLLC P.O. Box 446 Tacoma, WA 98401 Ph (253) 228-0513 www.de-civil.com Site Vicinity Map Schneider SP 7XX S 21st Street Renton County, Washington Job No: 17-166 September 2017 Figure 1 DEVELOPMENT ENGINEERING, PLLC P.O. Box 446 Tacoma, WA 98401 Ph (253) 228-0513 www.de-civil.com Approximate Test Pit Location Site Plan Schneider SP 7XX S 21st Street Renton County, Washington Job No: 17-166 September 2017 Figure 2 TP-1 TP-2 TP-3 TP-1 Approximate Site Location Not to Scale DE-CIVIL, PLLC P.O. Box 446 Tacoma, WA 98401 Ph (253) 228-0513 www.de-civil.com USDA Web Soil Survey Schneider SP 7XX S 21st Street Renton County, Washington Job No: 17-166 September 2017 Figure 3 Approximate Site Location Not to Scale DE-CIVIL, PLLC P.O. Box 446 Tacoma, WA 98401 Ph (253) 228-0513 www.de-civil.com USGS Geologic Map Schneider SP 7XX S 21st Street Renton County, Washington Job No: 17-166 September 2017 Figure 4 DEVELOPMENT ENGINEERING, PLLC P.O. Box 446 Tacoma, WA 98401 Ph (253) 228-0513 www.de-civil.com Soil Classification Chart Schneider SP 7XX S 21st Street Renton County, Washington Job No: 17-166 September 2017 Figure 5 ` Test Pit TP-1 Location: (See Figure 2) Depth (ft.) Soil Type Description 0 – 0.5 Topsoil 0.5 – 5.0 SM Brown silty sand and gravel (cemented, dense) 5.0 – 6.0 Tan Sandstone (fractured) Terminated at 6.0 feet below ground surface. No caving observed. Evidence of seasonal groundwater at 6 inches. Test Pit TP-2 Location: (See Figure 2) Depth (ft.) Soil Type Description 0 – 1.0 Brown silty SAND with gravel Fill (asphalt and concrete debris) 1.0 – 2.5 SM Brown silty SAND w/ gravel, (weakly cemented, dense) 2.5 – 7.0 ML grey SILT w/sand & gravel, (stiff) 7.0 – 8.0 tan Sandstone (fractured) Terminated at 8.0 feet below ground surface. No caving observed. Evidence of seasonal groundwater at 12 inches. Test Pit TP-3 Location: (See Figure 2) Depth (ft.) Soil Type Description 0 – 0.5 Top soil 0.5 – 2.0 SM Brown silty SAND w/ gravel, (weakly cemented, dense) 2.0 – 4.5 ML grey SILT w/sand & gravel, (stiff) 4.5 – 6.0 tan Sandstone (fractured) Terminated at 6.0 feet below ground surface. No caving observed. Evidence of seasonal groundwater at 12 inches. Logged by WGC, 9/4/17 DE-CIVIL, PLLC P.O. Box 446 Tacoma, WA 98401 Ph (253) 228-0513 www.de-civil.com Test Pit Logs Schneider SP 7XX S 21st Street Renton County, Washington Job No: 17-166 September 2017 Figure 6 Appendix C – Additional Documents (None at this time)