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EX_06_RS_Drainage_Report_251111_v3
Windsor Court Preliminary TIR & Level 1 Downstream Analysis April 1, 2025 Revised: November 11, 2025 Prepared for Elizabeth Tat P.O. Box 829 Mercer Island, WA 98040 Submitted by ESM Consulting Engineers, LLC 32001 32nd Ave S, Ste 200 Federal Way, WA 98001 253.838.6113 tel 253.838.7104 fax www.esmcivil.com 11/11/2025 EXHIBIT 6 RECEIVED 11/13/2025 jding PLANNING DIVISION Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 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 Predeveloped Basin Map 1.3B Developed Basin Map 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 CSWPPP Appendix D Operations and Maintenance manual \\esm8\engr\esm-jobs\2328\001\022\document\rprt-001 - stormreport.docx Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 1 Preliminary TIR 1. Project Overview The proposed Windsor Court project is a 20-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), 2022 City of Kent Surface Water Design Manual (KSWDM), the King County Stormwater Pollution Prevention Manual (KCSPPM), and the latest edition of the LID Technical Guidance Manual for the Puget Sound (LID Manual), for the proposed project. 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 Windsor Court project site is located in the Northwest Quarter of Section 5, Township 23 N, Range 05 E, W.M., situated on two parcels. The site is located 19411 and 19505 108th Ave SE in the City of Renton, within the urban growth area, Zoned R-14. Parcel (662340-0232): 70,037 sf (1.61 ac) is currently developed as a single-family residence and is located at 19411 108th Ave SE. The property is rectangular in shape, approximately 252’ x 276’. Adjacent to the Parcel is 108th Ave SE (State Route 515, City of Kent jurisdiction) to the east, 19505 108th Ave SE (a single-family home) to the south, 107th Ave SE (Private Road) to the west, 19401 108th Ave SE (a single-family home) to the northeast, and 19404 107th Ave SE (a single-family home) to the northwest. Parcel (662340-0233): 41,344 sf (0.95 ac) is currently developed as a single-family residence and is located at 19505 108th Ave SE. The property is rectangular in shape, approximately 150’ x 276’. Adjacent to the Parcel is 108th Ave SE (State Route 515) to the east, 19525 108th Ave SE (a single-family home) to the southeast, 19448 107th Ave SE (a single-family home) to the southwest, 107th Ave SE (Private Road) to the west, and 19411 108th Ave SE (a single-family home) to the north. The project site is developed with two single-family homes and vegetated with trees and grass. The grades across the property slope down towards the north, west and east at grades ranging between 1% to 30%. Overall, the site is flat to moderately sloped with approximately 24 feet of vertical relief. There are no known critical areas on or adjacent to the project site. Proposed improvements: The plat infrastructure improvements include new public internal roadways, sidewalk, driveways, associated utilities, recreation area, landscaping, and an underground detention vault located within the project site. The existing buildings located on the property will be demolished as part of the project. The improvements are currently slated to be built in one phase. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 2 Preliminary TIR Stormwater will be collected and conveyed by a series of pipes and catch basins. A flow control facility, an underground detention vault located in the northeastern region of this site, is proposed to meet the flow control standards associated with this project. Access to the site will be from 108th Ave SE. Stormwater will be collected and conveyed by a series of pipes and catch basins to a proposed underground detention facility located beneath the proposed recreation area. Geotechnical: A geotechnical study has been completed by Terra Associates, Inc., dated December 30, 2024. Seven exploration pits were dug across the project site. See Figure 1.4 for the Soils Map. The underlying soils generally consisted of 18 to 30 inches of medium dense brown silty sand and fine sand with scattered fine to coarse gravel over a layer of dense gray-brown silty sand and fine sand with scattered fine to coarse gravel. Test pits ranged between 7 to 8 feet in depth with no groundwater seepage was observed in any of the test pits. Although based on observed mottling in the soils between depths of about one and one-half and four feet, the soils have been impacted by a perched groundwater table at times. Perched groundwater levels and seepage fluctuate on a seasonal basis with the highest levels developing during the wet winter months. 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 impermeable, dense to very dense, cemented till and till-like soils beneath the site. An assessment for mine hazard areas in the vicinity of the site has been completed by Terra Associates. Based on their findings, a mine hazard area does not exist on or extended below the project site. A copy of the Geotechnical Report by Terra Associates is included In Appendix B. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 3 Preliminary TIR Figure 1.1 – TIR Worksheet Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 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 __________________ __________________ __________________ x Avenue SE, Renton, WA 98055 19411 & 19505 108th x x x x x 05 05 E 23 N Windsor Court (253) 838-6113 ESM Consulting Engineers Laura Bartenhagen, PE P.O.Box 829 Mercer Island, WA 98040 Elizabeth Tat Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 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 ______________________ _____________________________________ Two natural discharge locations and two threshold discharge areas under existing condition. The project is proposing to discharge to a single discharge location under developed condition. x x 2022 City of Renton Surface Water Design Manual Black River Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 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 Detention Vault 2 TDA #1, TDA #2 x Erosion Hazard Alderwood gravelly sandy loam High >15% Alderwood gravelly sandy loam Low8 to 15% TBD Level 2 08/02/2024 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 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: Catch Basins, Storm Manholes,and Storm Piping N/A None Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 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 _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ Media Filter x x Vault x x x x x x x x x x x x x x Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 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 x Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 18,056 1,505 Figure 1.2 - Vicinity Map Legend 1,0230512 Feet Notes 1,023 WGS_1984_Web_Mercator_Auxiliary_Sphere All data, information, and maps are provided "as is" without warranty or any representation of accuracy, timeliness of completeness. The burden for determining accuracy, completeness, timeliness, merchantability and fitness for or the appropriateness for use rests solely on the user. City and County Labels City and County Boundary Renton <all other values> Project Site Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 6 Custom Soil Resource Report Soil Map 52 5 2 9 4 0 52 5 2 9 6 0 52 5 2 9 8 0 52 5 3 0 0 0 52 5 3 0 2 0 52 5 3 0 4 0 52 5 3 0 6 0 52 5 3 0 8 0 52 5 3 1 0 0 52 5 2 9 4 0 52 5 2 9 6 0 52 5 2 9 8 0 52 5 3 0 0 0 52 5 3 0 2 0 52 5 3 0 4 0 52 5 3 0 6 0 52 5 3 0 8 0 52 5 3 1 0 0 560440 560460 560480 560500 560520 560540 560560 560440 560460 560480 560500 560520 560540 560560 47° 25' 42'' N 12 2 ° 1 1 ' 5 5 ' ' W 47° 25' 42'' N 12 2 ° 1 1 ' 4 8 ' ' W 47° 25' 37'' N 12 2 ° 1 1 ' 5 5 ' ' W 47° 25' 37'' N 12 2 ° 1 1 ' 4 8 ' ' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84 0 40 80 160 240 Feet 0 10 20 40 60 Meters Map Scale: 1:834 if printed on A portrait (8.5" x 11") sheet. Soil Map may not be valid at this scale. FIGURE 1.4 - SOILS MAP (1 of 3)Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Unit Polygons Soil Map Unit Lines Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Spoil Area Stony Spot Very Stony Spot Wet Spot Other Special Line Features Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: King County Area, Washington Survey Area Data: Version 19, Aug 29, 2023 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jul 31, 2022—Aug 8, 2022 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Custom Soil Resource Report 7 FIGURE 1.4 - SOILS MAP (2 of 3) Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI AgB Alderwood gravelly sandy loam, 0 to 8 percent slopes 0.2 5.4% AgC Alderwood gravelly sandy loam, 8 to 15 percent slopes 3.1 94.6% Totals for Area of Interest 3.3 100.0% Map Unit Descriptions The map units delineated on the detailed soil maps in a soil survey represent the soils or miscellaneous areas in the survey area. The map unit descriptions, along with the maps, can be used to determine the composition and properties of a unit. A map unit delineation on a soil map represents an area dominated by one or more major kinds of soil or miscellaneous areas. A map unit is identified and named according to the taxonomic classification of the dominant soils. Within a taxonomic class there are precisely defined limits for the properties of the soils. On the landscape, however, the soils are natural phenomena, and they have the characteristic variability of all natural phenomena. Thus, the range of some observed properties may extend beyond the limits defined for a taxonomic class. Areas of soils of a single taxonomic class rarely, if ever, can be mapped without including areas of other taxonomic classes. Consequently, every map unit is made up of the soils or miscellaneous areas for which it is named and some minor components that belong to taxonomic classes other than those of the major soils. Most minor soils have properties similar to those of the dominant soil or soils in the map unit, and thus they do not affect use and management. These are called noncontrasting, or similar, components. They may or may not be mentioned in a particular map unit description. Other minor components, however, have properties and behavioral characteristics divergent enough to affect use or to require different management. These are called contrasting, or dissimilar, components. They generally are in small areas and could not be mapped separately because of the scale used. Some small areas of strongly contrasting soils or miscellaneous areas are identified by a special symbol on the maps. If included in the database for a given area, the contrasting minor components are identified in the map unit descriptions along with some characteristics of each. A few areas of minor components may not have been observed, and consequently they are not mentioned in the descriptions, especially where the pattern was so complex that it was impractical to make enough observations to identify all the soils and miscellaneous areas on the landscape. The presence of minor components in a map unit in no way diminishes the usefulness or accuracy of the data. The objective of mapping is not to delineate pure taxonomic classes but rather to separate the landscape into landforms or landform segments that have similar use and management requirements. The delineation of such segments on the map provides sufficient information for the development of resource plans. If intensive use of small areas is planned, however, Custom Soil Resource Report 8 FIGURE 1.4 - SOILS MAP (3 of 3) Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 8 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 two threshold discharge areas with two natural discharge locations. The site naturally drains toward the northeastern and southwestern corners of the property and do not converge within one-quarter mile downstream from the site’s discharge locations. A stormwater deviation application is being submitted to the City of Kent to request the allowance of stormwater discharge from the site to be made at TDA #1 to 108th Ave E because the property is not allowed to discharge to the private road 107th Ave SE. All runoff generated from the developed basin is proposed to discharge to the City of Kent’s existing public storm system located near the northeast corner of the site. See Figure 1.3A for the natural discharge locations, Figure 1.3B for proposed discharge location, and Figure 3.2 for the Downstream Study Area. 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 to release stormwater at approved rates to the proposed natural discharge location at the northeast corner of the property. 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 of the final report submitted during final engineering. Core Requirement No. 5 Erosion and Sediment Control A construction stormwater pollution prevention (CSWPP) plan will be provided to the City during the Final Engineering review process. Core Requirement No. 6 Maintenance and Operations A Maintenance and Operations manual will be provided to the City during the Final Engineering review process. Core Requirement No. 7 Financial Guarantees and Liability Financial Guarantees, including Bond Quantity Worksheets, will be provided to the City during the Final Engineering review process. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 9 Preliminary TIR Core Requirement No. 8 Water Quality The site is located within the Enhanced Basic Water Quality treatment area per the current Water Quality Applications map. A proprietary enhanced media filter system is proposed to meet requirements. 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. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 10 Preliminary TIR 3. Level 1 Off-Site Analysis This narrative is to provide a Level 1 Downstream Analysis for the proposed Windsor Court development per Core Requirement #2, Section 1.2.2 of the 2022 City of Renton Surface Water Design Manual (RSWDM) and 2022 City of Kent Surface Water Design Manual (KSWDM). 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 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 Terra Associates, Inc., dated December 30, 2024. Seven exploration pits were dug across the project site. See Figure 1.4 for the Soils Map. In summary, the underlying soils generally consisted of 18 to 30 inches of medium dense brown silty sand and fine sand with scattered fine to coarse gravel over a layer of dense gray-brown silty sand and fine sand with scattered fine to coarse gravel. Test pits ranged between 7 to 8 feet in depth with no groundwater seepage was observed in any of the test pits. Although based on observed mottling in the soils between depths of about one and one-half and four feet, the soils have been impacted by a perched groundwater table at times. Perched groundwater levels and seepage fluctuate on a seasonal basis with the highest levels developing during the wet winter months. 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 impermeable, dense to very dense, cemented till and till-like soils beneath the site. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 11 Preliminary TIR An assessment for mine hazard areas in the vicinity of the site has been completed by Terra Associates. Based on their findings, a mine hazard area does not exist on or extended below the project site. A copy of the Geotechnical Report by Terra Associates is included In Appendix B. Resource Overview According to available information at the time of writing: Drainage Basin: The site contains two threshold discharge areas (TDA #1 & TDA #2). TDA #1 drains to the 108th Ave SE Stormwater Conveyance System which discharges into Panther Creek. TDA #2 drains to the 107th Ave SE and SE 196th Street Stormwater Conveyance Systems which discharges to North Fork Springbrook Creek. Streams: There are no onsite streams. Panther Creek is located approximately 230 feet downstream from TDA #1 and North Fork Springbrook Creek is located approximately 1,360 feet downstream from TDA #2. Erosion Hazard: None mapped. According to the Geotechnical report prepared by Terra Associates, dated December 30, 2024, the vast majority of the site is categorized as having a low erosion hazard. Localized slope areas in the northeastern portion of the site has slope inclinations steeper than 15% with soils consisting of Alderwood gravelly sandy loam, 15 to 30 percent slopes (AgD), which is described as having a severe erosion hazard. Landslide Hazard Area: None mapped. According to the Geotechnical report prepared by Terra Associates, dated December 30, 2024, 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 Renton. These maps can be found on the FEMA website. Panel #53033C0987G, 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 drainage complaints from the last 10 years. A drainage complaint regarding water quality (Activity ID: WO-618) on parcel #662340070 was closed on August 12, 2020. 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 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 12 Preliminary TIR 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 TDA #1 of the project site is tributary to Panther Creek approximately 230 feet downstream of the project. Panther Creek is a tributary of Springbrook Creek which discharges to the Duwamish River. According to the assessment, pollutants of this creek are classified as Category 5. Category 5 parameters are: Bioassessment indicating degraded biological integrity. Discharge from TDA #2 of the project site is tributary to North Fork Springbrook Creek approximately 230 feet downstream of the project. North Fork Springbrook Creek is a tributary of Springbrook Creek which discharges to the Duwamish River. According to the assessment, pollutants of Springbrook Creek are classified as Category 5. Category 5 parameters are: Bioassessment indicating degraded biological integrity. Downstream Corridor The downstream corridor consists of two flow paths which do not combine within one- quarter mile downstream. Therefore, the project site contains two Threshold Discharge Areas (TDA #1 & TDA #2). TDA #1 - Stormwater discharging from the site at the northeast corner of the property drains into 108th Ave SE right-of-way and sheet flows overland for approximately 15 feet and enters the City of Kent’s public storm system, a closed conveyance system located beneath the street. This stormwater is then conveyed north along the conveyance system for approximately 215 feet before draining into Panther Creek. The stormwater continues flowing north along the creek until reaching a distance of one-quarter mile downstream from the project site. Panther Creek eventually drains into Springbrook Creek which is a tributary of Duwamish River. TDA #2 - Stormwater discharging from the site at the southwest corner of the property drains across 7th Ave SE (a private street) and enters a ditch on the west side of the street. These flows are then conveyed south by a series of ditch and pipe elements to SE 196th Street and then west along the street and eventually reach Springbrook Park. The flows are conveyed further west along conveyance pipe until reaching a distance of one-quarter mile downstream from the project site. These flows ultimately drain to North Fork Springbrook Creek which drain to Springbrook Creek, a tributary to the Duwamish River. The following is a narrative of the two natural downstream flow paths documented during the field analysis. Task 3: Field Inspection (Level 1 Inspection) A downstream analysis for the site was conducted on August 2, 2024 and June 6, 2025, by ESM Consulting Engineers for the purpose of analyzing the project site and its upstream and downstream corridors. A description of the natural drainage pathways are provided below. Refer to Figures 3.3A & 3.3B at the end of this section for maps of the downstream reaches and point locations. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 13 Preliminary TIR Upstream and onsite runoff The project site has limited potential for upstream run-on. Based on the topography conditions, the project site receives no upstream run-on from adjacent properties. The project site is developed with two single-family homes and vegetated with trees and grass. The entire area including the project property and adjacent roadways are tributary to Panther Creek. There is a channel located along the roadside edge of 107th Ave SE on the west side of the property and it is presumed that upstream stormwater is contained and conveyed along this channel. On the east side of the property is public right-of-way for 108th Ave SE which includes curb/gutter and an existing public storm system which conveys upstream flows around the property. Two upstream parcels existing along the southern limit of the project. Based on topographic mapping, these parcels appear to drain either to the east or to the west away from the project site. There are two parcels located north of the project site which are downstream of the site based on topographic mapping. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 14 Preliminary TIR Natural Discharge Location #1 Reach A-B (0’ –15’) – Upon leaving the site, stormwater enters into the 108th Ave SE right- of-way and sheet flows to a catch basin (Point B) along the roadway. From this point, stormwater heads north along underground pipe conveyance system. No signs of any conveyance nuisances or flooding problems were observed. Photo (looking west) Photo Description Point B – Natural discharge location #1. Stormwater discharged from the site enters 108th Ave SE right-of-way and sheet flows to a catch basin located on the west side of 108th Ave SE. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 15 Preliminary TIR Reach B-C (15’ –230’) – Upon entering a catch basin (Point C), site stormwater drains north under the roadway along an 18” concrete pipe system and then west into private property where it is discharged into Panther Creek. No signs of any conveyance nuisances or flooding problems were observed. Photo (looking north) Photo Description Point C – Site stormwater being conveyed along the public storm system under 108th Ave SE right-of-way drains north and then west into private property where it is discharged into Panther Creek. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 16 Preliminary TIR Reach E-F (823’ – 896’) – Stormwater from Panther Creek enters a 36” concrete culvert located under SE 192nd Street which conveys site flows north and discharges to private property located on the north side of the street. No signs of any conveyance nuisances or flooding problems were observed. Photo (looking west from SE 192nd St) Photo Description Location of a 36” concrete culvert which conveys site stormwater beneath SE 192nd Street. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 17 Preliminary TIR Natural Discharge Location #2 Reach H-L (0’ – 192’) – Upon leaving the site, stormwater sheet flows across grass and roadway pavement to a roadside ditch on the west side of 107th Ave SE. Flows then drain south to SE 196th Street through a combination of culvert and ditch conveyance elements. No signs of any conveyance nuisances or flooding problems were observed. Photo (looking southeast from 107th Ave SE) Photo Description Point I – Stormwater discharge from the site sheet flows across across107th Ave SE to a roadside ditch on the west side of the street and then flows south along an open and closed storm conveyance system. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 18 Preliminary TIR Reach L-M (’192 – 238’) – Stormwater is collected by a 12” concrete culvert and is conveyed southwest under SE 196th Street to a roadside ditch on the south side of the street. No signs of any conveyance nuisances or flooding problems were observed. Photo (looking west from SE 196th St and 107th Ave SE) Photo Description Point L – Stormwater from the site drains southwest under SE 196th Street at the intersection of 107th Ave SE and SE 196th Street. Reach M-T (238’ – 497’) – Stormwater drains along the south side of SE 196th Street through a series of culvert and ditch conveyance elements for approximately 259 feet. No signs of any conveyance nuisances or flooding problems were observed. Photo (looking west from SE 196th St) Photo Description Points M & N – Stormwater from the site drains into a roadside ditch on the south side of SE 196th Street and flows west along an open and closed storm conveyance system. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 19 Preliminary TIR Reach T-U (497’ – 550’) – Stormwater along the south side of SE 196th Street is collected by 24” CMP and conveyed northwest under the intersection of SE 196th Street and 106th Ave SE for approximately 53 feet. No signs of any conveyance nuisances or flooding problems were observed. Photo (looking west from SE 196th St) Photo Description Points T & U – Stormwater from the site drains to 24” CMP at the intersection of SE 196th Street & 106th Ave SE and flows northwest to the north side of SE 196th Street. The flows are then conveyed west along the north side of SE 196th Street via 18” CMP. Reach U-V (550’ – 1320’) – Stormwater is conveyed from the north side of SE 196th Street to the south side of the street via 18” CMP. The flows are then conveyed west via 18” CMP into Springbrook Park. No signs of any conveyance nuisances or flooding problems were observed. Photo (looking west from SE 196th St) Photo Description Point L – Stormwater from the site drains southwest under 106th Ave SE to the south side of the street and flows west. The flows are then conveyed west along the street via an underground storm conveyance system into Springbrook Park and eventually enters North Fork Springbrook Creek within the park. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 20 Preliminary TIR Task 4: Drainage Description and Problem Descriptions For TDA #1, the downstream drainage system is largely comprised of underground pipe and Panther Creek. For TDA #2, the downstream drainage system is almost entirely comprised of a series of open and closed man-made storm conveyance systems. See Task 3 for a narrative of the downstream flow paths extending 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 TDA #1 Discussed in Task 2 of the Offsite Analysis, Panther Creek is impaired with a degraded biological integrity problem. The Creek is located approximately 230 feet downstream of the project site. A detailed parameter has not been identified. This potential water quality problem is within the quarter mile threshold to warrant mitigation as suggested in the KCRSWDM Section 1.2.2.3. TDA #2 Springbrook Creek is impaired with a degraded biological integrity problem Springbrook Creek is located approximately three quarters of a mile downstream of the site. A detailed parameter has not been identified. 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 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 21 Preliminary TIR Task 5: Mitigation of Existing or Potential Problems To address the concerns discussed in Task 4, the project proposes to provide enhanced treatment for site stormwater. All site runoff is proposed to discharge to the City of Kent’s existing public storm system. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 King County Date: 8/1/2024 Notes: The information included on this map has been compiled by King County staff from a variety of sources and issubject to change without notice. King County makes no representations or warranties, express or implied,as to accuracy, completeness, timeliness, or rights to the use of such information. This document is not intendedfor use as a survey product. King County shall not be liable for any general, special, indirect, incidental, orconsequential damages including, but not limited to, lost revenues or lost profits resulting from the use or misuseof the information contained on this map. Any sale of this map or information on this map is prohibited except bywritten permission of King County. Legend Parcels Potentiallandslide hazardareas (2016, seeexplanation--->) Erosion hazard(1990 SAO) Seismic hazard(1990 SAO) Coal mine hazard(1990 SAO) Stream (1990 SAO) class 1 class 2 perennial class 2 salmonid class 3 unclassified Wetland (1990SAO) Sensitive areanotice on title Drainagecomplaint orstudy Figure 3.2 - Downstream Study Area ± Project Site (TDA #2) Panther Creek North Fork Springbrook Creek 1/4 Mile Downstream 1/4 Mile Downstream Site Discharge Location (NDL #2) Site Discharge Location (NDL #1) Drainage complaint or study Activity type: Water quality investigation Activity ID: WO-618 Parcel: 6623400070 Activity closed on: 8/12/2020 Project Site (TDA #1) 1 Mile Downstream Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 4,544 379 Figure 3.3A - Field Study Area Legend 2570129 Feet Notes 257 WGS_1984_Web_Mercator_Auxiliary_Sphere All data, information, and maps are provided "as is" without warranty or any representation of accuracy, timeliness of completeness. The burden for determining accuracy, completeness, timeliness, merchantability and fitness for or the appropriateness for use rests solely on the user. City and County Labels Parcels Coalmines High Moderate Unclassified Erosion Hazard - High Floodway Special Flood Hazard Areas (100 year flood) Landslide Very High High Moderate Unclassified Environment Designations Natural Shoreline High Intensity Shoreline Isolated High Intensity Shoreline Residential Urban Conservancy Jurisdictions Wetlands 2' Primary 2' Intermediate Project Site (TDA #2) Culvert Panther Creek Panther Creek Point F Point E Point D Point C Point B Site Discharge Location Point A (NDL #1) Panther Creek Point G (1/4 Mile Downstream) Project Site (TDA #1) Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 4,663 389 Figure 3.3B - Field Study Area Legend 0 132 Notes 264 WGS_1984_Web_Mercator_Auxiliary_Sphere All data, information, and maps are provided "as is" without warranty or any representation of accuracy, timeliness of completeness. The burden for determining accuracy, completeness, timeliness, merchantability and fitness for or the appropriateness for use rests solely on the user. 264 Feet Parcels City and County Boundary Renton <all other values> Coalmines High Moderate Unclassified Erosion Hazard - High Floodway Special Flood Hazard Areas (100 year flood) Landslide Very High High Moderate Unclassified Environment Designations Natural Shoreline High Intensity Shoreline Isolated High Intensity Shoreline Residential Urban Conservancy Jurisdictions Point U Point T Point S Point N Point Q Point P Point O Point L Point J Point R Point M Point K Site Discharge Location Point H (NDL #2) Point I Point V (1/4 Mile Downstream) Project Site (TDA #2) Project Site (TDA #1) Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 24 Preliminary TIR 4. Flow Control & Water Quality Facility Analysis and Design 4.1 Existing Site Hydrology The project site is developed with two single-family homes and vegetated with trees and grass. The grades across the property slope down towards the north, west and east at grades ranging between 1% to 30%. Overall, the site is flat to moderately sloped with approximately 24 feet of vertical relief. No stormwater from offsite areas is expected to enter the project site. Stormwater from the site discharges at two natural discharge locations, located at the northeast and northwest corners of the site. These stormwater discharges do not combine within one-quarter mile downstream and therefore, the project site is considered to have two threshold discharge areas. 4.2 Developed Site Hydrology The project proposes storm water collection and flow control prior to site discharge with the use of a detention vault and a closed conveyance network for all rooftop, driveway, sidewalk, and roadway runoff. The storm network will collect virtually all runoff on the project property and convey it to an underground detention facility followed by a modular wetland system. Due to topography constraints, some development areas will bypass the detention vault. These areas will be compensated for by over-detaining stormwater within the flow control facility per Section 1.2.3.2 of the RSWDM and KSWDM. The following tables represent the pre-developed and developed runoff/discharge conditions for the project. Refer to Figure 1.3A for map of the existing conditions and Figure 1.3B for a map of the proposed conditions. Table 4.1 – Historic Conditions Basin Total sf (ac) C, Forest, Flat sf (ac) Impervious, Flat sf (ac) C, Lawn, Flat sf (ac) Site 107,443 (2.467) 107,443 (2.467) - - Bypass 9,280 (0.229) 9,280 (0.229) - - Total 116,723 (2.680) 116,723 (2.680) - - Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 25 Preliminary TIR Table 4.2 – Developed Conditions Basin Total sf (ac) C, Forest sf (ac) Impervious, Flat sf (ac) C, Lawn, Flat sf (ac) Areas Tributary to Flow Control and Treatment System Va u l t Impervious 71,648 (1.645) - 71,648 (1.645) - Pervious 35,796 (0.822) - - 35,796 (0.822) Total 107,443 (2.467) - 71,648 (1.645) 35,796 (0.822) Flow Control Mitigated Bypass Impervious (PGIS) 3,575 (0.082) - 3,575 (0.082) - Impervious (Non-PGIS) 1,198 (0.028) - 1,198 (0.028) - Pervious 4,507 (0.103) - - 4,507 (0.103) Total 9,280 (0.213) - 4,773 (0.110) 4,507 (0.103) Total TOTAL 116,723 (2.680) - 76,421 (1.755) 40,303 (0.925) 4.3 Performance Standards Flow Control Stormwater systems onsite are to be designed to mitigate runoff generated from the project per the requirements of the City of Renton and the City of Kent. 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 2 existing residential lots and the project proposes to subdivide the property into 20 single-family residential lots and construct new roadway, sidewalk, and driveways. The project specific target surfaces subject to flow control are equal to all the new plus replaced surface areas. To confirm the Level 2 flow control standard have been met, the Western Washington Hydrology Model Version 2012 (WWHM) has been utilized to determine the required volume of the detention system with the proposed control structure outlet dimensions. Onsite Unmitigated Flow Control Target Surface Bypass On some sites, topography can make it difficult or costly to collect all target surface runoff for discharge to the onsite flow control facility. Therefore, Section 1.2.3.2 of the RSWDM Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 26 Preliminary TIR and KSWDM allows for some project runoff subject to flow control to bypass the flow control facility provided that all of the following conditions are met: 1) The point of convergence for runoff discharged from the bypassed target surfaces and from the project’s flow control facility must be within a quarter-mile downstream of the facility’s project site discharge point. Response: Project bypass and flow control facility discharge will converge at the southeast corner of the project site, well within a quarter mile. 2) The increase in the existing site conditions 100-year peak discharge from the area of bypassed target surfaces must not exceed 0.4 cfs. Response: The increase in existing site conditions is less than 0.4 cfs. 3) Runoff from the bypass target surfaces must not create a significant adverse impact to downstream drainage systems, salmonid habitat, or properties as determined by the County. Response: A significant adverse impact to the downstream drainage system is not anticipated as the downstream conveyance system is a tightline for at least a quarter- mile downstream. 4) Water quality requirements applicable to the bypassed target surfaces must be met. Response: This site meets the water quality requirements as discussed in the Onsite Water Quality performance standards for bypass discussed further below in this Section (Part C). 5) Compensatory mitigation by a 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. This mitigation may be waived if the existing site conditions 100-year peak discharge from the area of bypassed target surfaces is increased by no more than 0.15 cfs and flow control BMPs as detailed in Appendix C of the RSWDM and KSWDM are applied to all impervious surfaces within the area of bypassed target surfaces. Response: Compensatory mitigation (mitigated bypass) has been provided for the bypass area. Discharge There is one proposed 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) Enhanced basic water quality treatment standards apply to this project. A proprietary enhanced media filter system is proposed to provide stormwater treatment for the project. Further detail will be provided with the engineering permit application. Enhanced Basic Stormwater Treatment: The required level of water quality treatment mitigation for the project site is Enhanced Basic Water Quality Treatment according to the performance standards discussed previously. The treatment system will be located downstream of the detention facility and subject to the same Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 27 Preliminary TIR land use basin as the detention vault as provided in Table 4.2 and summarized below in Table 4.3. Table 4.3 – Water Quality Basin Summary Water Quality Area Pervious sf (ac) Impervious sf (ac) Total sf (ac) 2-year release from facility cfs 100-year Flow cfs Proposed Improvements (From Table 4.2) (WWHM Time Series 1004) 35,796 (0.822) 71,648 (1.645) 107,443 (2.467) 0.0785 0.1970 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 1.3B. One riser structure with a single orifice 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. The proposed detention system will consist of an underground concrete vault. 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. The predeveloped and developed project site flow rates are provided in Table 4.4 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 4.4 – Return-Flow, Natural Discharge (POC #1) Return Period Predeveloped (cfs) Mitigated (cfs) 2-Year 0.0797 0.0785 10-Year 0.1635 0.1261 50-Year 0.2295 0.1744 100-Year 0.2547 0.1970 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 28 Preliminary TIR The analyzed and proposed storage volume is provided in Table 4.5 below. Table 4.5 – 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 discussed in section 4.3, enhanced basic water quality treatment standards apply to this project. A proprietary enhanced media filter system is proposed to provide stormwater treatment for the project. A BioClean Modular Wetlands treatment unit is proposed to achieve the minimum treatment standard. Modular Wetland units have a General Use Level Designation by the Washington State Department of Ecology’s (DOE) Emerging stormwater treatment technical program for enhanced treatment. This media filter is a flow-based system and is required to treat the 2-year release rate if located downstream of a detention facility according to Section 6.2.1 of the SWDM. The approved loading rate listed by the DOE for Modular Wetlands is 1 gpm/sf of wetland cell surface area and 2.1 gpm/sf of cartridge surface area for commercial and industrial basins. WQ Unit Sizing WQ Flow: 0.079 cfs = 35.46 gpm Wetland Loading Rate: 1 sf/gpm Min. Wetland Area: 35.46 sf Proposed Modular Wetland: Contech MWS-4-8-V-UG system Max treatment flow: 0.115 cfs Wetland Area: 50 sf 4.6 Flow Control BMPs (Core Requirement #9): On-Site BMPs were evaluated for the project site as outlined in the RSWDM and KSWDM 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 (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. Description Volume (cu-ft) Modeled, WWHM (102’L x 48’W x 7.5’D) 36,720 Proposed Vault (102’L x 48’W x7.5’D) 36,720 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 29 Preliminary TIR 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 Terra Associates, Inc. dated December 30, 2024. Based on the soil findings, the subsurface conditions observed in the test pits are not favorable for infiltration of project stormwater as described in the geotechnical study. This is due primarily to the relatively shallow presence of impermeable till soils 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. Stormwater from 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). Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 30 Preliminary TIR 5. Conveyance System Analysis and Design Onsite 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 of the final report submitted during final engineering. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 31 Preliminary TIR 6. Special Reports and Studies Geotechnical Study Geotechnical Report, Windsor Court, December 30, 2024; prepared by Terra Associates, Inc., This study has been included in Appendix B of this report. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 32 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) Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 33 Preliminary TIR 8. ESC Analysis and Design A construction stormwater pollution prevention (CSWPP) plan will be provided to the City during the Final Engineering review process. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 34 Preliminary TIR 9. Bond Quantities, Facility Summaries, and Declaration of Covenant The Bond Quantities worksheet, Facility Summaries, and Declaration of Covenant will be provided to the City upon request. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court Page 35 Preliminary TIR 10. Operations and Maintenance The Operations and Maintenance manual will be provided to the City during the Final Engineering review process. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Appendix A – Hydrology Model Output Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 WWHM2012 PROJECT REPORT Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:16 PM Page 2 General Model Information WWHM2012 Project Name:Windsor Court 11-04-2025 Site Name:Windsor Court Site Address:19411-19505 108th Ave SE City:Renton Report Date:11/5/2025 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:0.000 (adjusted) Version Date:2024/06/28 Version:4.3.1 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year Low Flow Threshold for POC2:50 Percent of the 2 Year High Flow Threshold for POC2:50 Year Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:16 PM Page 3 Landuse Basin Data Predeveloped Land Use Pre-Developed Basin Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Mod 2.467 Pervious Total 2.467 Impervious Land Use acre Impervious Total 0 Basin Total 2.467 Element Flow Componants: Surface Interflow Groundwater Componant Flows To: POC 1 POC 1 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:16 PM Page 4 Pre-Developed Bypass Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Mod 0.213 Pervious Total 0.213 Impervious Land Use acre Impervious Total 0 Basin Total 0.213 Element Flow Componants: Surface Interflow Groundwater Componant Flows To: POC 1 POC 1 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:16 PM Page 5 Pre-Developed Bypass Flowrates Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Mod 0.213 Pervious Total 0.213 Impervious Land Use acre Impervious Total 0 Basin Total 0.213 Element Flow Componants: Surface Interflow Groundwater Componant Flows To: POC 2 POC 2 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:16 PM Page 6 Mitigated Land Use Developed Basin Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Flat 0.822 Pervious Total 0.822 Impervious Land Use acre ROADS FLAT 1.645 Impervious Total 1.645 Basin Total 2.467 Element Flow Componants: Surface Interflow Groundwater Componant Flows To: Vault 1 Vault 1 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:16 PM Page 7 Developed Bypass Bypass:Yes GroundWater:No Pervious Land Use acre C, Lawn, Flat 0.103 Pervious Total 0.103 Impervious Land Use acre ROADS FLAT 0.11 Impervious Total 0.11 Basin Total 0.213 Element Flow Componants: Surface Interflow Groundwater Componant Flows To: POC 1 POC 1 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:16 PM Page 8 Developed Bypass Flowrate Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Flat 0.103 Pervious Total 0.103 Impervious Land Use acre ROADS FLAT 0.11 Impervious Total 0.11 Basin Total 0.213 Element Flow Componants: Surface Interflow Groundwater Componant Flows To: POC 2 POC 2 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:16 PM Page 9 Routing Elements Predeveloped Routing Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:16 PM Page 10 Mitigated Routing Vault 1 Width:48 ft. Length:102 ft. Depth:8.5 ft. Discharge Structure Riser Height:7.5 ft. Riser Diameter:12 in. Orifice 1 Diameter:0.797 in.Elevation:0 ft. Orifice 2 Diameter:1.313 in.Elevation:4.8 ft. Orifice 3 Diameter:1.000 in.Elevation:6.4 ft. Element Outlets: Outlet 1 Outlet 2 Outlet Flows To: Vault Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)Infilt(cfs) 0.0000 0.112 0.000 0.000 0.000 0.0944 0.112 0.010 0.005 0.000 0.1889 0.112 0.021 0.007 0.000 0.2833 0.112 0.031 0.009 0.000 0.3778 0.112 0.042 0.010 0.000 0.4722 0.112 0.053 0.011 0.000 0.5667 0.112 0.063 0.013 0.000 0.6611 0.112 0.074 0.014 0.000 0.7556 0.112 0.084 0.015 0.000 0.8500 0.112 0.095 0.015 0.000 0.9444 0.112 0.106 0.016 0.000 1.0389 0.112 0.116 0.017 0.000 1.1333 0.112 0.127 0.018 0.000 1.2278 0.112 0.138 0.019 0.000 1.3222 0.112 0.148 0.019 0.000 1.4167 0.112 0.159 0.020 0.000 1.5111 0.112 0.169 0.021 0.000 1.6056 0.112 0.180 0.021 0.000 1.7000 0.112 0.191 0.022 0.000 1.7944 0.112 0.201 0.023 0.000 1.8889 0.112 0.212 0.023 0.000 1.9833 0.112 0.222 0.024 0.000 2.0778 0.112 0.233 0.024 0.000 2.1722 0.112 0.244 0.025 0.000 2.2667 0.112 0.254 0.025 0.000 2.3611 0.112 0.265 0.026 0.000 2.4556 0.112 0.276 0.027 0.000 2.5500 0.112 0.286 0.027 0.000 2.6444 0.112 0.297 0.028 0.000 2.7389 0.112 0.307 0.028 0.000 2.8333 0.112 0.318 0.029 0.000 2.9278 0.112 0.329 0.029 0.000 3.0222 0.112 0.339 0.030 0.000 3.1167 0.112 0.350 0.030 0.000 3.2111 0.112 0.360 0.030 0.000 3.3056 0.112 0.371 0.031 0.000 3.4000 0.112 0.382 0.031 0.000 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:16 PM Page 11 3.4944 0.112 0.392 0.032 0.000 3.5889 0.112 0.403 0.032 0.000 3.6833 0.112 0.414 0.033 0.000 3.7778 0.112 0.424 0.033 0.000 3.8722 0.112 0.435 0.033 0.000 3.9667 0.112 0.445 0.034 0.000 4.0611 0.112 0.456 0.034 0.000 4.1556 0.112 0.467 0.035 0.000 4.2500 0.112 0.477 0.035 0.000 4.3444 0.112 0.488 0.035 0.000 4.4389 0.112 0.498 0.036 0.000 4.5333 0.112 0.509 0.036 0.000 4.6278 0.112 0.520 0.037 0.000 4.7222 0.112 0.530 0.037 0.000 4.8167 0.112 0.541 0.043 0.000 4.9111 0.112 0.552 0.053 0.000 5.0056 0.112 0.562 0.059 0.000 5.1000 0.112 0.573 0.064 0.000 5.1944 0.112 0.583 0.068 0.000 5.2889 0.112 0.594 0.072 0.000 5.3833 0.112 0.605 0.075 0.000 5.4778 0.112 0.615 0.078 0.000 5.5722 0.112 0.626 0.081 0.000 5.6667 0.112 0.636 0.084 0.000 5.7611 0.112 0.647 0.087 0.000 5.8556 0.112 0.658 0.089 0.000 5.9500 0.112 0.668 0.092 0.000 6.0444 0.112 0.679 0.094 0.000 6.1389 0.112 0.690 0.096 0.000 6.2333 0.112 0.700 0.099 0.000 6.3278 0.112 0.711 0.101 0.000 6.4222 0.112 0.721 0.107 0.000 6.5167 0.112 0.732 0.114 0.000 6.6111 0.112 0.743 0.119 0.000 6.7056 0.112 0.753 0.124 0.000 6.8000 0.112 0.764 0.128 0.000 6.8944 0.112 0.774 0.132 0.000 6.9889 0.112 0.785 0.135 0.000 7.0833 0.112 0.796 0.138 0.000 7.1778 0.112 0.806 0.142 0.000 7.2722 0.112 0.817 0.145 0.000 7.3667 0.112 0.828 0.148 0.000 7.4611 0.112 0.838 0.151 0.000 7.5556 0.112 0.849 0.292 0.000 7.6500 0.112 0.859 0.761 0.000 7.7444 0.112 0.870 1.343 0.000 7.8389 0.112 0.881 1.872 0.000 7.9333 0.112 0.891 2.224 0.000 8.0278 0.112 0.902 2.455 0.000 8.1222 0.112 0.912 2.654 0.000 8.2167 0.112 0.923 2.838 0.000 8.3111 0.112 0.934 3.011 0.000 8.4056 0.112 0.944 3.174 0.000 8.5000 0.112 0.955 3.329 0.000 8.5944 0.112 0.966 3.476 0.000 8.6889 0.000 0.000 3.618 0.000 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:16 PM Page 12 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:2.68 Total Impervious Area:0 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.925 Total Impervious Area:1.755 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.079797 5 year 0.130755 10 year 0.16352 25 year 0.202495 50 year 0.229492 100 year 0.254708 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.078451 5 year 0.106222 10 year 0.126125 25 year 0.153049 50 year 0.174429 100 year 0.196969 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.092 0.090 1950 0.109 0.091 1951 0.174 0.148 1952 0.055 0.052 1953 0.044 0.058 1954 0.068 0.062 1955 0.108 0.069 1956 0.087 0.093 1957 0.071 0.079 1958 0.078 0.059 WQ treatment flowrate Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:34 PM Page 13 1959 0.067 0.057 1960 0.120 0.122 1961 0.066 0.081 1962 0.041 0.051 1963 0.057 0.065 1964 0.080 0.065 1965 0.053 0.080 1966 0.051 0.062 1967 0.123 0.091 1968 0.069 0.083 1969 0.067 0.072 1970 0.054 0.066 1971 0.061 0.078 1972 0.132 0.124 1973 0.059 0.072 1974 0.065 0.074 1975 0.091 0.081 1976 0.065 0.065 1977 0.009 0.059 1978 0.055 0.067 1979 0.033 0.072 1980 0.156 0.113 1981 0.049 0.072 1982 0.101 0.141 1983 0.086 0.071 1984 0.052 0.053 1985 0.031 0.068 1986 0.137 0.075 1987 0.121 0.113 1988 0.048 0.054 1989 0.032 0.051 1990 0.289 0.153 1991 0.153 0.125 1992 0.063 0.059 1993 0.061 0.046 1994 0.021 0.043 1995 0.088 0.066 1996 0.202 0.138 1997 0.156 0.143 1998 0.038 0.066 1999 0.171 0.118 2000 0.061 0.072 2001 0.011 0.068 2002 0.071 0.099 2003 0.105 0.076 2004 0.113 0.142 2005 0.083 0.069 2006 0.094 0.091 2007 0.218 0.193 2008 0.266 0.154 2009 0.124 0.089 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.2890 0.1927 2 0.2662 0.1539 3 0.2184 0.1526 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:34 PM Page 14 4 0.2024 0.1484 5 0.1744 0.1432 6 0.1712 0.1415 7 0.1562 0.1411 8 0.1558 0.1379 9 0.1533 0.1254 10 0.1367 0.1236 11 0.1324 0.1218 12 0.1241 0.1183 13 0.1225 0.1133 14 0.1207 0.1133 15 0.1203 0.0993 16 0.1125 0.0928 17 0.1090 0.0913 18 0.1085 0.0910 19 0.1053 0.0906 20 0.1010 0.0901 21 0.0939 0.0888 22 0.0918 0.0830 23 0.0905 0.0808 24 0.0875 0.0807 25 0.0874 0.0798 26 0.0864 0.0786 27 0.0835 0.0785 28 0.0802 0.0761 29 0.0783 0.0750 30 0.0705 0.0740 31 0.0705 0.0723 32 0.0690 0.0719 33 0.0679 0.0718 34 0.0672 0.0717 35 0.0671 0.0716 36 0.0662 0.0713 37 0.0650 0.0695 38 0.0647 0.0690 39 0.0626 0.0684 40 0.0611 0.0677 41 0.0608 0.0667 42 0.0608 0.0662 43 0.0587 0.0657 44 0.0565 0.0655 45 0.0547 0.0648 46 0.0547 0.0646 47 0.0539 0.0645 48 0.0533 0.0621 49 0.0521 0.0617 50 0.0512 0.0593 51 0.0489 0.0586 52 0.0477 0.0585 53 0.0442 0.0581 54 0.0412 0.0572 55 0.0382 0.0543 56 0.0331 0.0535 57 0.0315 0.0521 58 0.0309 0.0514 59 0.0205 0.0509 60 0.0109 0.0457 61 0.0095 0.0433 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:34 PM Page 15 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:34 PM Page 16 Duration Flows The Facility PASSED Flow(cfs)Predev Mit Percentage Pass/Fail 0.0399 17081 16046 93 Pass 0.0418 15483 12927 83 Pass 0.0437 14072 10930 77 Pass 0.0456 12797 9467 73 Pass 0.0476 11569 8393 72 Pass 0.0495 10515 7617 72 Pass 0.0514 9565 6998 73 Pass 0.0533 8750 6498 74 Pass 0.0552 8034 6044 75 Pass 0.0571 7347 5674 77 Pass 0.0590 6733 5298 78 Pass 0.0610 6190 4992 80 Pass 0.0629 5730 4686 81 Pass 0.0648 5309 4423 83 Pass 0.0667 4924 4152 84 Pass 0.0686 4569 3901 85 Pass 0.0705 4235 3675 86 Pass 0.0725 3951 3459 87 Pass 0.0744 3643 3270 89 Pass 0.0763 3388 3108 91 Pass 0.0782 3133 2956 94 Pass 0.0801 2915 2783 95 Pass 0.0820 2701 2579 95 Pass 0.0839 2490 2391 96 Pass 0.0859 2314 2220 95 Pass 0.0878 2136 2028 94 Pass 0.0897 1972 1868 94 Pass 0.0916 1824 1708 93 Pass 0.0935 1702 1564 91 Pass 0.0954 1577 1407 89 Pass 0.0974 1442 1266 87 Pass 0.0993 1325 1142 86 Pass 0.1012 1235 1032 83 Pass 0.1031 1152 910 78 Pass 0.1050 1085 788 72 Pass 0.1069 1020 675 66 Pass 0.1088 948 573 60 Pass 0.1108 887 515 58 Pass 0.1127 827 456 55 Pass 0.1146 765 425 55 Pass 0.1165 724 388 53 Pass 0.1184 674 363 53 Pass 0.1203 623 317 50 Pass 0.1222 589 289 49 Pass 0.1242 552 262 47 Pass 0.1261 506 241 47 Pass 0.1280 471 216 45 Pass 0.1299 427 192 44 Pass 0.1318 388 175 45 Pass 0.1337 356 160 44 Pass 0.1357 328 145 44 Pass 0.1376 298 136 45 Pass 0.1395 270 130 48 Pass Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:34 PM Page 17 0.1414 242 124 51 Pass 0.1433 218 111 50 Pass 0.1452 198 96 48 Pass 0.1471 174 92 52 Pass 0.1491 152 74 48 Pass 0.1510 130 67 51 Pass 0.1529 119 62 52 Pass 0.1548 104 49 47 Pass 0.1567 95 45 47 Pass 0.1586 83 42 50 Pass 0.1605 74 37 50 Pass 0.1625 69 30 43 Pass 0.1644 61 26 42 Pass 0.1663 54 21 38 Pass 0.1682 46 20 43 Pass 0.1701 39 19 48 Pass 0.1720 29 17 58 Pass 0.1740 25 13 52 Pass 0.1759 22 11 50 Pass 0.1778 20 8 40 Pass 0.1797 17 4 23 Pass 0.1816 14 1 7 Pass 0.1835 12 1 8 Pass 0.1854 8 1 12 Pass 0.1874 7 1 14 Pass 0.1893 7 1 14 Pass 0.1912 7 1 14 Pass 0.1931 6 0 0 Pass 0.1950 6 0 0 Pass 0.1969 6 0 0 Pass 0.1989 6 0 0 Pass 0.2008 6 0 0 Pass 0.2027 5 0 0 Pass 0.2046 5 0 0 Pass 0.2065 5 0 0 Pass 0.2084 5 0 0 Pass 0.2103 5 0 0 Pass 0.2123 5 0 0 Pass 0.2142 5 0 0 Pass 0.2161 4 0 0 Pass 0.2180 4 0 0 Pass 0.2199 3 0 0 Pass 0.2218 3 0 0 Pass 0.2237 3 0 0 Pass 0.2257 3 0 0 Pass 0.2276 3 0 0 Pass 0.2295 3 0 0 Pass Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:34 PM Page 18 Water Quality Water Quality BMP Flow and Volume for POC #1 On-line facility volume:0 acre-feet On-line facility target flow:0 cfs. Adjusted for 15 min:0 cfs. Off-line facility target flow:0 cfs. Adjusted for 15 min:0 cfs. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:34 PM Page 19 POC 2 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #2 Total Pervious Area:0.213 Total Impervious Area:0 Mitigated Landuse Totals for POC #2 Total Pervious Area:0.103 Total Impervious Area:0.11 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #2 Return Period Flow(cfs) 2 year 0.006342 5 year 0.010392 10 year 0.012996 25 year 0.016094 50 year 0.018239 100 year 0.020244 Flow Frequency Return Periods for Mitigated. POC #2 Return Period Flow(cfs) 2 year 0.048808 5 year 0.064739 10 year 0.075979 25 year 0.090995 50 year 0.10279 100 year 0.115119 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #2 Year Predeveloped Mitigated 1949 0.007 0.069 1950 0.009 0.064 1951 0.014 0.043 1952 0.004 0.031 1953 0.004 0.034 1954 0.005 0.040 1955 0.009 0.043 1956 0.007 0.043 1957 0.006 0.053 1958 0.006 0.038 1959 0.005 0.036 The increase in the existing site conditions 100-year peak discharge from the area of bypassed target surfaces does not exceed 0.4 cfs Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:53 PM Page 20 1960 0.010 0.045 1961 0.005 0.044 1962 0.003 0.034 1963 0.004 0.043 1964 0.006 0.039 1965 0.004 0.056 1966 0.004 0.033 1967 0.010 0.065 1968 0.005 0.067 1969 0.005 0.050 1970 0.004 0.045 1971 0.005 0.054 1972 0.011 0.065 1973 0.005 0.029 1974 0.005 0.052 1975 0.007 0.054 1976 0.005 0.040 1977 0.001 0.038 1978 0.004 0.047 1979 0.003 0.062 1980 0.012 0.074 1981 0.004 0.050 1982 0.008 0.077 1983 0.007 0.054 1984 0.004 0.037 1985 0.002 0.050 1986 0.011 0.043 1987 0.010 0.062 1988 0.004 0.035 1989 0.003 0.044 1990 0.023 0.113 1991 0.012 0.084 1992 0.005 0.036 1993 0.005 0.029 1994 0.002 0.030 1995 0.007 0.043 1996 0.016 0.054 1997 0.012 0.050 1998 0.003 0.044 1999 0.014 0.104 2000 0.005 0.049 2001 0.001 0.048 2002 0.006 0.069 2003 0.008 0.053 2004 0.009 0.096 2005 0.007 0.044 2006 0.007 0.040 2007 0.017 0.102 2008 0.021 0.082 2009 0.010 0.054 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #2 Rank Predeveloped Mitigated 1 0.0230 0.1135 2 0.0212 0.1038 3 0.0174 0.1020 4 0.0161 0.0955 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:53 PM Page 21 5 0.0139 0.0839 6 0.0136 0.0823 7 0.0124 0.0770 8 0.0124 0.0742 9 0.0122 0.0693 10 0.0109 0.0686 11 0.0105 0.0672 12 0.0099 0.0647 13 0.0097 0.0646 14 0.0096 0.0641 15 0.0096 0.0618 16 0.0089 0.0616 17 0.0087 0.0557 18 0.0086 0.0545 19 0.0084 0.0543 20 0.0080 0.0540 21 0.0075 0.0539 22 0.0073 0.0538 23 0.0072 0.0534 24 0.0070 0.0530 25 0.0069 0.0517 26 0.0069 0.0505 27 0.0066 0.0502 28 0.0064 0.0501 29 0.0062 0.0498 30 0.0056 0.0490 31 0.0056 0.0475 32 0.0055 0.0470 33 0.0054 0.0455 34 0.0053 0.0449 35 0.0053 0.0444 36 0.0053 0.0441 37 0.0052 0.0441 38 0.0051 0.0441 39 0.0050 0.0435 40 0.0049 0.0434 41 0.0048 0.0433 42 0.0048 0.0431 43 0.0047 0.0430 44 0.0045 0.0427 45 0.0043 0.0403 46 0.0043 0.0399 47 0.0043 0.0397 48 0.0042 0.0392 49 0.0041 0.0385 50 0.0041 0.0378 51 0.0039 0.0366 52 0.0038 0.0363 53 0.0035 0.0356 54 0.0033 0.0355 55 0.0030 0.0343 56 0.0026 0.0339 57 0.0025 0.0334 58 0.0025 0.0313 59 0.0016 0.0296 60 0.0009 0.0295 61 0.0008 0.0293 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:53 PM Page 22 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:53 PM Page 23 Duration Flows The Duration Matching Failed Flow(cfs)Predev Mit Percentage Pass/Fail 0.0032 17075 103008 603 Fail 0.0033 15483 98303 634 Fail 0.0035 14070 93811 666 Fail 0.0036 12799 89747 701 Fail 0.0038 11569 85812 741 Fail 0.0039 10515 82090 780 Fail 0.0041 9563 78732 823 Fail 0.0042 8750 75481 862 Fail 0.0044 8034 72358 900 Fail 0.0045 7347 69492 945 Fail 0.0047 6733 66776 991 Fail 0.0048 6190 64145 1036 Fail 0.0050 5728 61643 1076 Fail 0.0051 5309 59204 1115 Fail 0.0053 4924 56980 1157 Fail 0.0055 4569 54755 1198 Fail 0.0056 4235 52766 1245 Fail 0.0058 3951 50777 1285 Fail 0.0059 3645 48938 1342 Fail 0.0061 3388 47077 1389 Fail 0.0062 3133 45323 1446 Fail 0.0064 2915 43655 1497 Fail 0.0065 2706 42093 1555 Fail 0.0067 2490 40575 1629 Fail 0.0068 2314 39099 1689 Fail 0.0070 2136 37751 1767 Fail 0.0071 1972 36425 1847 Fail 0.0073 1824 35099 1924 Fail 0.0074 1702 33880 1990 Fail 0.0076 1577 32789 2079 Fail 0.0077 1442 31591 2190 Fail 0.0079 1325 30500 2301 Fail 0.0080 1232 29495 2394 Fail 0.0082 1147 28533 2487 Fail 0.0083 1085 27549 2539 Fail 0.0085 1020 26608 2608 Fail 0.0087 947 25688 2712 Fail 0.0088 886 24854 2805 Fail 0.0090 824 24020 2915 Fail 0.0091 760 23164 3047 Fail 0.0093 725 22458 3097 Fail 0.0094 674 21731 3224 Fail 0.0096 623 21004 3371 Fail 0.0097 589 20287 3444 Fail 0.0099 549 19629 3575 Fail 0.0100 506 19004 3755 Fail 0.0102 469 18444 3932 Fail 0.0103 428 17881 4177 Fail 0.0105 389 17267 4438 Fail 0.0106 357 16752 4692 Fail 0.0108 328 16198 4938 Fail 0.0109 298 15693 5266 Fail 0.0111 270 15267 5654 Fail 0.0112 242 14799 6115 Fail Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:53 PM Page 24 0.0114 219 14369 6561 Fail 0.0115 198 13886 7013 Fail 0.0117 175 13522 7726 Fail 0.0118 152 13088 8610 Fail 0.0120 131 12720 9709 Fail 0.0122 119 12305 10340 Fail 0.0123 104 11931 11472 Fail 0.0125 95 11552 12160 Fail 0.0126 84 11229 13367 Fail 0.0128 75 10908 14544 Fail 0.0129 69 10602 15365 Fail 0.0131 61 10307 16896 Fail 0.0132 54 10006 18529 Fail 0.0134 46 9736 21165 Fail 0.0135 39 9456 24246 Fail 0.0137 29 9154 31565 Fail 0.0138 25 8915 35660 Fail 0.0140 22 8682 39463 Fail 0.0141 20 8474 42370 Fail 0.0143 17 8230 48411 Fail 0.0144 14 8025 57321 Fail 0.0146 12 7805 65041 Fail 0.0147 9 7593 84366 Fail 0.0149 7 7371 105300 Fail 0.0150 7 7197 102814 Fail 0.0152 7 7003 100042 Fail 0.0153 6 6814 113566 Fail 0.0155 6 6601 110016 Fail 0.0157 6 6400 106666 Fail 0.0158 6 6216 103600 Fail 0.0160 6 6055 100916 Fail 0.0161 5 5884 117680 Fail 0.0163 5 5719 114380 Fail 0.0164 5 5550 111000 Fail 0.0166 5 5384 107680 Fail 0.0167 5 5247 104940 Fail 0.0169 5 5110 102200 Fail 0.0170 5 4986 99720 Fail 0.0172 4 4877 121925 Fail 0.0173 4 4744 118600 Fail 0.0175 3 4614 153800 Fail 0.0176 3 4485 149500 Fail 0.0178 3 4374 145800 Fail 0.0179 3 4269 142300 Fail 0.0181 3 4158 138600 Fail 0.0182 3 4036 134533 Fail 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. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:53 PM Page 25 Water Quality Water Quality BMP Flow and Volume for POC #2 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. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:53 PM Page 26 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. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:53 PM Page 27 Appendix Predeveloped Schematic Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:53 PM Page 28 Mitigated Schematic Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:54 PM Page 29 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 Windsor Court 11-04-2025.wdm MESSU 25 PreWindsor Court 11-04-2025.MES 27 PreWindsor Court 11-04-2025.L61 28 PreWindsor Court 11-04-2025.L62 30 POCWindsor Court 11-04-20251.dat 31 POCWindsor Court 11-04-20252.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 11 COPY 501 COPY 502 DISPLY 1 DISPLY 2 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<----------Title----------->***TRAN PIVL DIG1 FIL1 PYR DIG2 FIL2 YRND 1 Pre-Developed Basin MAX 1 2 30 9 2 Pre-Developed Bypass Flow MAX 1 2 31 9 END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 501 1 1 502 1 1 END TIMESERIES END COPY GENER OPCODE # # OPCD *** END OPCODE PARM # # K *** END PARM END GENER PERLND GEN-INFO <PLS ><-------Name------->NBLKS Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 11 C, Forest, Mod 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 11 0 0 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:54 PM Page 30 <PLS > ***************** Print-flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 11 0 0 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO PWAT-PARM1 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** 11 0 0 0 0 0 0 0 0 0 0 0 END PWAT-PARM1 PWAT-PARM2 <PLS > PWATER input info: Part 2 *** # - # ***FOREST LZSN INFILT LSUR SLSUR KVARY AGWRC 11 0 4.5 0.08 400 0.1 0.5 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 11 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 11 0.2 0.5 0.35 6 0.5 0.7 END PWAT-PARM4 PWAT-STATE1 <PLS > *** Initial conditions at start of simulation ran from 1990 to end of 1992 (pat 1-11-95) RUN 21 *** # - # *** CEPS SURS UZS IFWS LZS AGWS GWVS 11 0 0 0 0 2.5 1 0 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 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:54 PM Page 31 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS END IWAT-STATE1 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** Pre-Developed Basin*** PERLND 11 2.467 COPY 501 12 PERLND 11 2.467 COPY 501 13 Pre-Developed Bypass*** PERLND 11 0.213 COPY 501 12 PERLND 11 0.213 COPY 501 13 Pre-Developed Bypass Flowrates*** PERLND 11 0.213 COPY 502 12 PERLND 11 0.213 COPY 502 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 COPY 502 OUTPUT MEAN 1 1 48.4 DISPLY 2 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 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:54 PM Page 32 END RCHRES SPEC-ACTIONS END SPEC-ACTIONS FTABLES END FTABLES EXT SOURCES <-Volume-> <Member> SsysSgap<--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # tem strg<-factor->strg <Name> # # <Name> # # *** WDM 2 PREC ENGL 1 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 1 IMPLND 1 999 EXTNL PREC WDM 1 EVAP ENGL 0.76 PERLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 IMPLND 1 999 EXTNL PETINP END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** COPY 501 OUTPUT MEAN 1 1 48.4 WDM 501 FLOW ENGL REPL COPY 502 OUTPUT MEAN 1 1 48.4 WDM 502 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 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:54 PM Page 33 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 Windsor Court 11-04-2025.wdm MESSU 25 MitWindsor Court 11-04-2025.MES 27 MitWindsor Court 11-04-2025.L61 28 MitWindsor Court 11-04-2025.L62 31 POCWindsor Court 11-04-20252.dat 30 POCWindsor Court 11-04-20251.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 16 IMPLND 1 RCHRES 1 COPY 502 COPY 1 COPY 501 COPY 601 DISPLY 2 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<----------Title----------->***TRAN PIVL DIG1 FIL1 PYR DIG2 FIL2 YRND 2 Developed Bypass Flowrate MAX 1 2 31 9 1 Vault 1 MAX 1 2 30 9 END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 502 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 ***************************** Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:54 PM Page 34 # - # 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 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 *** 1 ROADS/FLAT 1 1 1 27 0 END GEN-INFO *** Section IWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** 1 0 0 1 0 0 0 END ACTIVITY PRINT-INFO <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* 1 0 0 4 0 0 4 1 9 END PRINT-INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** 1 0 0 0 0 0 END IWAT-PARM1 IWAT-PARM2 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:54 PM Page 35 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC 1 400 0.01 0.1 0.1 END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN 1 0 0 END IWAT-PARM3 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS 1 0 0 END IWAT-STATE1 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** Developed Basin*** PERLND 16 0.822 RCHRES 1 2 PERLND 16 0.822 RCHRES 1 3 IMPLND 1 1.645 RCHRES 1 5 Developed Bypass*** PERLND 16 0.103 COPY 501 12 PERLND 16 0.103 COPY 601 12 PERLND 16 0.103 COPY 501 13 PERLND 16 0.103 COPY 601 13 IMPLND 1 0.11 COPY 501 15 IMPLND 1 0.11 COPY 601 15 Developed Bypass Flowrate*** PERLND 16 0.103 COPY 502 12 PERLND 16 0.103 COPY 502 13 IMPLND 1 0.11 COPY 502 15 ******Routing****** PERLND 16 0.822 COPY 1 12 IMPLND 1 1.645 COPY 1 15 PERLND 16 0.822 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 502 OUTPUT MEAN 1 1 48.4 DISPLY 2 INPUT TIMSER 1 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 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:54 PM Page 36 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ******************* PIVL PYR # - # HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB PIVL PYR ********* 1 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO HYDR-PARM1 RCHRES Flags for each HYDR Section *** # - # VC A1 A2 A3 ODFVFG for each *** ODGTFG for each FUNCT for each FG FG FG FG possible exit *** possible exit possible exit * * * * * * * * * * * * * * *** 1 0 1 0 0 4 0 0 0 0 0 0 0 0 0 2 2 2 2 2 END HYDR-PARM1 HYDR-PARM2 # - # FTABNO LEN DELTH STCOR KS DB50 *** <------><--------><--------><--------><--------><--------><--------> *** 1 1 0.02 0.0 0.0 0.5 0.0 END HYDR-PARM2 HYDR-INIT RCHRES Initial conditions for each HYDR section *** # - # *** VOL Initial value of COLIND Initial value of OUTDGT *** ac-ft for each possible exit for each possible exit <------><--------> <---><---><---><---><---> *** <---><---><---><---><---> 1 0 4.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 END HYDR-INIT END RCHRES SPEC-ACTIONS END SPEC-ACTIONS FTABLES FTABLE 1 92 4 Depth Area Volume Outflow1 Velocity Travel Time*** (ft) (acres) (acre-ft) (cfs) (ft/sec) (Minutes)*** 0.000000 0.112397 0.000000 0.000000 0.094444 0.112397 0.010615 0.005296 0.188889 0.112397 0.021230 0.007489 0.283333 0.112397 0.031846 0.009173 0.377778 0.112397 0.042461 0.010591 0.472222 0.112397 0.053076 0.011842 0.566667 0.112397 0.063691 0.012972 0.661111 0.112397 0.074307 0.014011 0.755556 0.112397 0.084922 0.014979 0.850000 0.112397 0.095537 0.015887 0.944444 0.112397 0.106152 0.016747 1.038889 0.112397 0.116768 0.017564 1.133333 0.112397 0.127383 0.018345 1.227778 0.112397 0.137998 0.019094 1.322222 0.112397 0.148613 0.019815 1.416667 0.112397 0.159229 0.020510 1.511111 0.112397 0.169844 0.021183 1.605556 0.112397 0.180459 0.021835 1.700000 0.112397 0.191074 0.022468 1.794444 0.112397 0.201690 0.023084 1.888889 0.112397 0.212305 0.023683 1.983333 0.112397 0.222920 0.024268 2.077778 0.112397 0.233535 0.024839 2.172222 0.112397 0.244151 0.025398 2.266667 0.112397 0.254766 0.025944 2.361111 0.112397 0.265381 0.026479 2.455556 0.112397 0.275996 0.027003 2.550000 0.112397 0.286612 0.027518 2.644444 0.112397 0.297227 0.028022 2.738889 0.112397 0.307842 0.028518 2.833333 0.112397 0.318457 0.029006 2.927778 0.112397 0.329073 0.029485 3.022222 0.112397 0.339688 0.029957 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:54 PM Page 37 3.116667 0.112397 0.350303 0.030422 3.211111 0.112397 0.360918 0.030879 3.305556 0.112397 0.371534 0.031330 3.400000 0.112397 0.382149 0.031774 3.494444 0.112397 0.392764 0.032213 3.588889 0.112397 0.403379 0.032645 3.683333 0.112397 0.413994 0.033072 3.777778 0.112397 0.424610 0.033493 3.872222 0.112397 0.435225 0.033909 3.966667 0.112397 0.445840 0.034320 4.061111 0.112397 0.456455 0.034727 4.155556 0.112397 0.467071 0.035128 4.250000 0.112397 0.477686 0.035525 4.344444 0.112397 0.488301 0.035918 4.438889 0.112397 0.498916 0.036306 4.533333 0.112397 0.509532 0.036690 4.627778 0.112397 0.520147 0.037070 4.722222 0.112397 0.530762 0.037447 4.816667 0.112397 0.541377 0.043854 4.911111 0.112397 0.551993 0.053771 5.005556 0.112397 0.562608 0.059748 5.100000 0.112397 0.573223 0.064520 5.194444 0.112397 0.583838 0.068634 5.288889 0.112397 0.594454 0.072316 5.383333 0.112397 0.605069 0.075686 5.477778 0.112397 0.615684 0.078817 5.572222 0.112397 0.626299 0.081757 5.666667 0.112397 0.636915 0.084540 5.761111 0.112397 0.647530 0.087191 5.855556 0.112397 0.658145 0.089727 5.950000 0.112397 0.668760 0.092165 6.044444 0.112397 0.679376 0.094515 6.138889 0.112397 0.689991 0.096787 6.233333 0.112397 0.700606 0.098990 6.327778 0.112397 0.711221 0.101129 6.422222 0.112397 0.721837 0.107256 6.516667 0.112397 0.732452 0.114508 6.611111 0.112397 0.743067 0.119687 6.705556 0.112397 0.753682 0.124154 6.800000 0.112397 0.764298 0.128210 6.894444 0.112397 0.774913 0.131982 6.988889 0.112397 0.785528 0.135543 7.083333 0.112397 0.796143 0.138933 7.177778 0.112397 0.806758 0.142184 7.272222 0.112397 0.817374 0.145316 7.366667 0.112397 0.827989 0.148345 7.461111 0.112397 0.838604 0.151282 7.555556 0.112397 0.849219 0.292867 7.650000 0.112397 0.859835 0.761706 7.744444 0.112397 0.870450 1.343195 7.838889 0.112397 0.881065 1.872620 7.933333 0.112397 0.891680 2.224924 8.027778 0.112397 0.902296 2.455586 8.122222 0.112397 0.912911 2.654391 8.216667 0.112397 0.923526 2.838736 8.311111 0.112397 0.934141 3.011399 8.405556 0.112397 0.944757 3.174365 8.500000 0.112397 0.955372 3.329115 8.594444 0.112397 0.965987 3.476786 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 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:54 PM Page 38 END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** RCHRES 1 HYDR RO 1 1 1 WDM 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 COPY 2 OUTPUT MEAN 1 1 48.4 WDM 702 FLOW ENGL REPL COPY 502 OUTPUT MEAN 1 1 48.4 WDM 802 FLOW ENGL REPL COPY 602 OUTPUT MEAN 1 1 48.4 WDM 902 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 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:54 PM Page 39 Predeveloped HSPF Message File Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:54 PM Page 40 Mitigated HSPF Message File Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Windsor Court 11-04-2025 11/5/2025 3:26:54 PM Page 41 Disclaimer Legal Notice This program and accompanying documentation are provided 'as-is' without warranty of any kind. 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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 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Appendix B – Geotechnical Report Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 GEOTECHNICAL REPORT Windsor Court 19411 and 19505 108th Avenue Southeast Renton, Washington Project No. T-8955 Prepared for: DeDonato Group, LLC Kirkland, Washington July 23, 2024 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 7-23-2024 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 TABLE OF CONTENTS Page No. 1.0 Project Description .......................................................................................................... 1 2.0 Scope of Work ................................................................................................................. 1 3.0 Site Conditions ................................................................................................................ 2 3.1 Surface ................................................................................................................ 2 3.2 Soils .................................................................................................................... 2 3.3 Groundwater ....................................................................................................... 3 3.4 Geologic Hazards ............................................................................................... 3 3.4.1 Erosion Hazard Areas ............................................................................... 3 3.4.2 Steep Slope Hazard Areas ........................................................................ 4 3.4.3 Landslide Hazard Areas ............................................................................ 4 3.4.3 Seismic Hazard Areas ............................................................................... 5 3.4.4 Coal Mine Hazard Areas .......................................................................... 5 3.5 Seismic Site Class ............................................................................................... 6 4.0 Discussion and Recommendations .................................................................................. 6 4.1 General ......................................................................................................... 6 4.2 Site Preparation and Grading ....................................................................... 6 4.3 Excavations .................................................................................................. 7 4.4 Foundations ................................................................................................. 8 4.5 Slab-on-Grade Floors................................................................................... 8 4.6 Lateral Earth Pressure for Retaining Walls ................................................. 9 4.7 Infiltration Feasibility .................................................................................. 9 4.8 Drainage ..................................................................................................... 10 4.9 Utilities ...................................................................................................... 10 4.10 Pavements ................................................................................................ 10 5.0 Additional Services ........................................................................................................ 11 6.0 Limitations ..................................................................................................................... 11 Figures Vicinity Map ......................................................................................................................... Figure 1 Exploration Location Plan .................................................................................................... Figure 2 Typical Wall Drainage Detail ............................................................................................... Figure 3 Appendix Field Exploration and Laboratory Testing ....................................................................... Appendix A Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Geotechnical Report Windsor Court 19411 and 19505 108th Avenue Southeast Renton, Washington 1.0 PROJECT DESCRIPTION The proposed project is a residential development with associated infrastructure improvements. Site development and building plans are currently not available. We were provided with an undated concept plan by ESM Consulting Engineers, LLC, that shows the project consisting of 12 duplex buildings and 2 triplex buildings, with a total of 30 units, that are accessed by a road off 108th Avenue Southeast. Based on existing topography grading is expected to be minimal with cuts and fills from one to six feet. We expect that the residences would be two- to three- story, wood-frame structures, with their main floors constructed at grade or framed over a crawl space. Foundation loads should be relatively light, in the range of 2 to 4 kips per foot for bearing walls and 25 to 75 kips for isolated columns. The recommendations contained in the following sections of this report are preliminary and based on our understanding of the above design features. We should review design drawings as they become available to verify that our recommendations have been properly interpreted and incorporated into project design and to amend or supplement our recommendations, if required. 2.0 SCOPE OF WORK We explored subsurface conditions at the site in seven test pits excavated to maximum depths of about seven to eight feet below existing surface grades using a track-mounted excavator. Using the results of our field study and laboratory testing, analyses were undertaken to develop geotechnical recommendations for project design and construction. Specifically, this report addresses the following: Soil and groundwater conditions. Geologic hazards per the City of Renton Municipal Code. Seismic site class per the current International Building Code (IBC). Site preparation and grading. Excavations. Foundations. Slab-on-grade floors. Lateral earth pressures for retaining walls. Infiltration Feasibility. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 July 23, 2024 Project No. T-8955 Page No. 2 Drainage. Utilities. Pavements. It should be noted that recommendations outlined in this report regarding drainage are associated with soil strength, design earth pressures, erosion, and stability. Design and performance issues with respect to moisture as it relates to the structure environment are beyond Terra Associates’ purview. A building envelope specialist or contactor should be consulted to address these issues, as needed. 3.0 SITE CONDITIONS 3.1 Surface The project site is a 2.52-acre assemblage of two residential parcels located west of and adjacent to 108th Avenue Southeast, approximately 180 to 580 feet north of the intersection with Southeast 196th Street in Renton, Washington. The site location is shown on Figure 1. Two residences and a detached garage/shop building currently occupy the northern parcel. The southern parcel is occupied by a residence and detached garage/shop. Site vegetation generally consists of grass lawn, landscape trees and shrubs, and mature coniferous trees. Site topography is relatively flat except for the northeastern site corner, which slopes gently to moderately down to the northeast. Elevation contours shown on the City of Renton COR Maps interactive map website (COR Maps) (https://maps.rentonwa.gov/Html5viewer/Index.html?viewer=cormaps) shows slope gradients in this area are generally between about 14 and 16 percent, with localized 4- to 6-foot high slope areas between 20 and 40 percent. The southern approximately 320 feet of the eastern site margin is adjacent to the top of a 5- to 6-foot high rockery constructed along the western side of the 108th Avenue Southeast right-of-way (ROW). We did not observe any indications of instability, groundwater seepage, or erosion on the site slopes. The ROW rockery appeared sound with no indications of soil loss or seepage through the rocks. 3.2 Soils The native soils observed in the test pits are till-like glacial deposits consisting of silty sand with gravel. The upper approximately 1.5 to 2.5 feet of soil are generally in a medium dense and moist condition. We observed exceptions to this in Test Pit TP-2, where the upper approximately 5 feet of soil was medium dense and dry, and in Test Pit TP-3, where the upper 2.5 feet of soil was moist to wet. The soils observed below these depths are generally dense to very dense, weakly to strongly cemented, and moist. We observed approximately 1.5 feet of medium dense, moist, silty sand with gravel fill overlying the native deposits in Test Pit TP-1. The fill at this location appears to be related to grading of the yard area on the eastern side of the residence. The site soils are typically mantled by about two to six inches of sod and topsoil. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 July 23, 2024 Project No. T-8955 Page No. 3 The Geologic map of the Renton quadrangle, King County, Washington by D.R. Mullineaux (1965) shows the site mapped as Vashon ground moraine deposits (Qgt). The dense to very dense, cemented, silty sand with gravel that we observed in the test pits is generally consistent with this geologic map unit. Detailed descriptions of the subsurface conditions we observed in the test pits are presented on the Test Pit Logs in Appendix A. The approximate locations of the test pits are shown on Figure 2. 3.3 Groundwater We did not observe groundwater seepage in the test pits. However, we observed mottling in the soils between depths of about one and one-half and four feet, indicating that they have been impacted by perched groundwater at times. The occurrence of shallow perched groundwater is typical for sites underlain by relatively impermeable till and till-like soils. Perched groundwater levels and seepage flow rates will typically fluctuate on a seasonal basis with the highest levels developing during the wet winter months. 3.4 Geologic Hazards We evaluated potential geologic-related hazards at the subject site as defined in Title IV, Chapter 3, Section 4-3- 050G (Geologically Hazardous Areas Defined) of the Renton Municipal Code (RMC). Geologic hazards are defined by the RMC as “Areas which may be prone to one or more of the following conditions: erosion, flooding, landslides, coal mine hazards, or seismic activity.” 3.4.1 Erosion Hazard Areas RMC Title IV, Chapter 3, Section 4-3-050G5c defines erosion hazards as follows: i. Low Erosion Hazard (EL): Areas with soils characterized by the Natural Resource Conservation Service (formerly U.S. Soil Conservation Service) as having slight or moderate erosion potential, and a slope less than 15 percent. ii. High Erosion Hazard (EH): Areas with soils characterized by the Natural Resource Conservation Service (formerly U.S. Soil Conservation Service) as having severe or very severe erosion potential, and a slope more than 15 percent. The NRCS has mapped the site soils as Alderwood gravelly sandy loam, 8 to 15 percent slopes (AgC), which are described as having a moderate erosion hazard. Based on this erosion hazard rating, per the above criteria, the vast majority of the site is categorized as having a low erosion hazard (EL). However, as discussed, localized slope areas exist in the northeastern portion of the site with slope inclinations steeper than 15 percent that would be better classified as Alderwood gravelly sandy loam, 15 to 30 percent slopes (AgD), which is described as having a severe erosion hazard. Accordingly, the slope areas in the northeastern portion of the site that are steeper than 15 percent meet the criteria defining a high erosion hazard area (EH). Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 July 23, 2024 Project No. T-8955 Page No. 4 As discussed, we did not observe any indications of erosion on the site slopes. Additionally, COR Maps shows no erosion hazard areas mapped onsite. In our opinion, the erosion potential of the site soils would be adequately mitigated with proper implementation and maintenance of Best Management Practices (BMPs) for erosion prevention and sedimentation control. All BMPs for erosion prevention and sedimentation control will need to be in place prior to and during site grading activities, and should conform to City of Renton requirements. 3.4.2 Steep Slope Hazard Areas RMC Title IV, Chapter 3, Section 4-3-050G5a defines steep slopes as follows: i. Sensitive Slopes: A hillside, or portion thereof, characterized by: (a) an average slope of 25 percent to less than 40 percent as identified in the City of Renton Steep Slope Atlas or in a method approved by the City; or (b) an average slope of 40 percent or greater with a vertical rise of less than 15 feet as identified in the City of Renton Steep Slope Atlas or in a method approved by the City; (c) abutting an average slope of 25 percent to 40 percent as identified in the City of Renton Steep Slope Atlas or in a method approved by the City. This definition excludes engineered retaining walls. ii. Protected Slopes: A hillside, or portion thereof, characterized by an average slope of 40 percent or greater grade and having a minimum vertical rise of 15 feet as identified in the City of Renton Steep Slope Atlas or in a method approved by the City. Based on our field observations, and site slope gradients shown on COR Maps, portions of the northeast-facing slope in the northeastern portion of the site, and the ROW rockery adjacent to the eastern site margin meet the above geometric criteria defining a sensitive steep slope hazard area. However, COR Maps does not show any sensitive slopes (<15’ height, >25 percent to <40 percent inclination) onsite. Based on our observation of stable slope conditions, and considering that the slope areas are underlain by inherently- stable, dense to very dense, cemented, till-like soils at relatively shallow depths, it is our opinion that any potential hazard associated with the site slopes would be adequately mitigated by the geotechnical recommendations presented herein. 3.4.3 Landslide Hazard Areas RMC Title IV, Chapter 3, Section 4-3-050G5b defines landslide hazards as follows: i. Low Landslide Hazard (LL): Areas with slopes less than 15 percent. ii. Medium Landslide Hazard (LM): Areas with slopes between 15 percent and 40 percent and underlain by soils that consist largely of sand, gravel, or glacial till. iii. High Landslide Hazards (LH): Areas with slopes greater than 40 percent, and areas with slopes between 15 percent and 40 percent and underlain by soils consisting largely of silt and clay. iv. Very High Landslide Hazards (LV): Areas of known mapped or identified landslide deposits. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 July 23, 2024 Project No. T-8955 Page No. 5 Based on the above criteria, the site slopes would generally be categorized as having a low landslide hazard (LL) or medium landslide hazard (LM). In our opinion, there is no landslide hazard associated with the site slopes. The slopes are underlain by dense to very dense, inherently stable till or till-like glacial deposits with no evidence of groundwater seepage or significant erosion. 3.4.4 Seismic Hazard Areas RMC Title IV, Chapter 3, Section 4-3-050G5d defines seismic hazards as follows: i. Low Seismic Hazard (SL): Areas underlain by dense soils or bedrock. These soils generally have site classifications of A through D, as defined in the International Building Code, 2012. ii. High Seismic Hazard (SH): Areas underlain by soft or loose, saturated soils. These soils generally have site classifications E or F, as defined in the International Building Code, 2012. The site is underlain by dense to very dense till and till-like soils. As discussed in Section 3.5, the site soil classification “C” would apply to the subject site. This site classification meets the above criteria defining a low seismic hazard (SL). In our opinion, unusual seismic hazards requiring mitigation do not exist at the site, and design in accordance with local building codes for determining seismic forces would adequately mitigate potential impacts associated with ground shaking. 3.4.5 Coal Mine Hazard Areas RMC Title IV, Chapter 3, Section 4-3-050G5e defines coal mine hazards as follows: i. Low Coal Mine Hazards (CL): Areas with no known mine workings and no predicted subsidence. While no mines are known in these areas, undocumented mining is known to have occurred. ii. Medium Coal Mine Hazards (CM): Areas where mine workings are deeper than 200 feet for steeply dipping seams, or deeper than 15 times the thickness of the seam or workings for gently dipping seams. These areas may be affected by subsidence. iii. High Coal Mine Hazard (CH): Areas with abandoned and improperly sealed mine openings and areas underlain by mine workings shallower than 200 feet in depth for steeply dipping seams, or shallower than 15 times the thickness of the seam or workings for gently dipping seams. These areas may be affected by collapse or other subsidence. Coal mining activities have not occurred on or extended below the subject site. In our opinion, no coal mine hazard exists at the site. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 July 23, 2024 Project No. T-8955 Page No. 6 3.5 Seismic Site Class Based on the site soil conditions and our knowledge of the area geology, per the current International Building Code (IBC), site class “C” should be used in structural design. 4.0 DISCUSSION AND RECOMMENDATIONS 4.1 General Based on our study, there are no geotechnical conditions that would preclude development of the site as currently planned. Residences can be supported on conventional spread footings bearing on competent native soils underlying organic topsoil and existing fill materials or on structural fill placed on a competent native soil subgrade. Floor slabs and pavements can be similarly supported. The site soils contain a sufficient amount of fines (silt- and clay-sized particles) such that they will be difficult to compact as structural fill when too wet or too dry. Accordingly, the ability to use the soils from site excavations as structural fill will depend upon their moisture content and the prevailing weather conditions at the time of construction. If grading activities take place during the winter season, the owner should be prepared to import free- draining granular material for use as structural fill and backfill. Detailed recommendations regarding these issues and other geotechnical design considerations are provided in the following sections of this report. These recommendations should be incorporated into the final design drawings and construction specifications. 4.2 Site Preparation and Grading To prepare the site for construction, all vegetation, organic surface soils, and other deleterious materials should be stripped and removed from the site. We expect surface stripping depths of about four to six inches will generally be required to remove the organic surficial soils in the planned development areas. Stripped vegetation debris should be removed from the site. Organic soils will not be suitable for use as structural fill but may be used for limited depths in nonstructural areas or for landscaping purposes. In the developed portions of the site, demolition of existing structures should include removal of existing foundations, slabs, and pavements, and abandonment of drainfields and buried utilities. Abandoned utility pipes that fall outside of new building areas can be left in place provided they are sealed to prevent intrusion of groundwater seepage and soil. Once clearing and grubbing operations are complete, cut and fill operations to establish desired building pad and roadway elevations can be initiated. A representative of Terra Associates, Inc. should examine all bearing surfaces to verify that conditions encountered are as anticipated and are suitable for placement of structural fill or direct support of building and pavement elements. Our representative may request proofrolling exposed surfaces with a heavy rubber-tired vehicle to determine if any isolated soft and yielding areas are present. If unstable yielding areas are observed, they should be cut to firm bearing soil and filled to grade with structural fill. If the depth of excavation to remove unstable soils is excessive, use of geotextile fabric such as Mirafi 500X or equivalent in conjunction with structural fill can be considered in order to limit the depth of removal. In general, our experience has shown that a minimum of 18 inches of clean, granular structural fill over the geotextile fabric should establish a stable bearing surface. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 July 23, 2024 Project No. T-8955 Page No. 7 Our study indicates that the site soils typically contain a significant percentage of fines (silt and clay sized particles) that will make the soils difficult to compact as structural fill when too wet or too dry. Provided these soils are near optimum moisture when excavated, and are placed during dry weather conditions, we anticipate they will be suitable for direct use as structural fill. Soils that are wet of optimum when excavated or become wet prior to use as structural fill will require drying by aeration during dry weather conditions or using soil amendments such as lime or Portland cement to reduce and stabilize the soil’s moisture content. If soil amendment products are used, additional Temporary Erosion and Sedimentation Control (TESC) BMPs will need to be implemented to mitigate potential impacts to stormwater runoff associated with possible elevated pH levels. If grading activities are planned during the wet winter months, or if they extend into fall and winter, the owner should be prepared to import wet weather structural fill. For this purpose, we recommend importing a granular soil that meets the following grading requirements: U.S. Sieve Size Percent Passing 6 inches 100 No. 4 75 maximum No. 200 5 maximum* *Based on the 3/4-inch fraction. Prior to use, Terra Associates, Inc. should examine and test all materials planned to be imported to the site for use as structural fill. Structural fill should be placed in uniform loose layers not exceeding 12 inches and compacted to a minimum of 95 percent of the soil’s maximum dry density, as determined by American Society for Testing and Materials (ASTM) Test Designation D-698 (Standard Proctor). The moisture content of the soil at the time of compaction should be within two percent of its optimum, as determined by this ASTM standard. In nonstructural areas, the degree of compaction may be reduced to 90 percent. 4.3 Excavations All excavations at the site associated with confined spaces must be completed in accordance with local, state, and federal requirements. Based on the Washington State Safety and Health Administration (WSHA) regulations, the medium dense to dense, weathered soils would typically be classified as Type C soils. The dense to very dense, cemented, till and till-like soils would typically be classified as Type A soil. Accordingly, for temporary excavations of more than 4 feet and less than 20 feet in depth, the side slopes in Type C soils should be laid back at a slope inclination of 1.5:1 (Horizontal: Vertical) or flatter. Temporary excavations in Type A soils can be laid back at inclinations of 0.75:1 or flatter. For temporary excavation slopes less than 8 feet in height in Type A soils, the lower 3.5 feet can be cut to a vertical condition with a 0.75:1 slope graded above. For temporary excavation slopes greater than 8 feet in height up to a maximum height of 12 feet, the slope above the 3.5-foot high vertical portion should be laid back to an inclination of 1:1 or flatter. No vertical cut with a backslope immediately above is allowed for excavation depths that exceed 12 feet. In this case, a 4-foot high vertical cut with an equivalent horizontal bench to the cut slope toe is required. If there is insufficient room to complete the excavations in the manners discussed above, or if excavations greater than 20 feet deep are planned, you may need to use temporary shoring to support the excavations. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 July 23, 2024 Project No. T-8955 Page No. 8 Seepage of perched groundwater should be anticipated within excavations extending to the surface of the dense to very dense till and till-like soils, particularly during the wet winter months. In our opinion, the volume of water and rate of seepage flow into the excavation should be relatively minor and would not be expected to impact the stability of the excavations that are sloped as described above. Conventional sump pumping procedures along with a system of collection trenches, if necessary, should be capable of maintaining a relatively dry excavation for construction purposes in these soils. The above information is provided solely for the benefit of the owner and other design consultants, and should not be construed to imply that Terra Associates, Inc. assumes responsibility for job site safety. It is understood that job site safety is the sole responsibility of the project contractor. 4.4 Foundations Residential structures may be supported on conventional spread footing foundations bearing on competent native soils or on structural fill placed above these native soils. Foundation subgrades should be prepared as recommended in Section 4.2 of this report. Perimeter foundations exposed to the weather should bear at a minimum depth of one and one-half feet below final exterior grades for frost protection. Interior foundations can be constructed at any convenient depth. We recommend designing foundations for a net allowable bearing capacity of 2,500 pounds per square foot (psf). For short-term loads, such as wind and seismic, a one-third increase in this allowable capacity can be used in design. With the anticipated loads and this bearing stress applied, building settlements should be less than one-half inch total and one-fourth inch differential. For designing foundations to resist lateral loads, a base friction coefficient of 0.35 can be used. Passive earth pressure acting on the sides of the footings may also be considered. We recommend calculating this lateral resistance using an equivalent fluid weight of 300 pounds per cubic foot (pcf). We recommend not including the upper 12 inches of soil in this computation because they can be affected by weather or disturbed by future grading activity. This value assumes the foundations will be constructed neat against competent native soil or the excavations are backfilled with structural fill, as described in Section 4.2 of this report. The recommended passive and friction values include a safety factor of 1.5. 4.5 Slab-on-Grade Floors Slab-on-grade floors may be supported on a subgrade prepared as recommended in Section 4.2 of this report. Immediately below the floor slab, we recommend placing a four-inch thick capillary break layer composed of clean, coarse sand or fine gravel that has less than five percent passing the No. 200 sieve. This material will reduce the potential for upward capillary movement of water through the underlying soil and subsequent wetting of the floor slab. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 July 23, 2024 Project No. T-8955 Page No. 9 The capillary break layer will not prevent moisture intrusion through the slab caused by water vapor transmission. Where moisture by vapor transmission is undesirable, such as covered floor areas, a common practice is to place a durable plastic membrane on the capillary break layer and then cover the membrane with a layer of clean sand or fine gravel to protect it from damage during construction, and aid in uniform curing of the concrete slab. It should be noted that if the sand or gravel layer overlying the membrane is saturated prior to pouring the slab, it will be ineffective in assisting uniform curing of the slab and can actually serve as a water supply for moisture seeping through the slab and affecting floor coverings. Therefore, in our opinion, covering the membrane with a layer of sand or gravel should be avoided if floor slab construction occurs during the wet winter months and the layer cannot be effectively drained. 4.6 Lateral Earth Pressures for Retaining Walls The magnitude of earth pressures developing on below-grade walls will depend upon the quality and compaction of the wall backfill. We recommend placing and compacting wall backfill as structural fill as described in Section 4.2 of this report. To prevent overstressing the walls during backfilling, heavy construction machinery should not be operated within five feet of the wall. Wall backfill in this zone should be compacted with hand-operated equipment. To prevent hydrostatic pressure development, wall drainage must also be installed. A typical wall drainage detail is shown on Figure 3. With wall backfill placed and compacted as recommended, and drainage properly installed, we recommend designing unrestrained walls for an active earth pressure equivalent to a fluid weighing 35 pounds per cubic foot (pcf). For restrained walls, an additional uniform load of 100 psf should be added to the 35 pcf. To account for typical traffic surcharge loading, the walls can be designed for an additional imaginary height of two feet (two-foot soil surcharge). For evaluation of wall performance under seismic loading, a uniform pressure equivalent to 8H psf, where H is the height of the below-grade portion of the wall should be applied in addition to the static lateral earth pressure. These values assume a horizontal backfill condition and that no other surcharge loading, sloping embankments, or adjacent buildings will act on the wall. If such conditions exist, then the imposed loading must be included in the wall design. Friction at the base of foundations and passive earth pressure will provide resistance to these lateral loads. Values for these parameters are provided in Section 4.4 of this report. 4.7 Infiltration Feasibility In our opinion, onsite infiltration of site stormwater will not be feasible due to the shallow presence of relatively impermeable, dense to very dense, cemented, till and till-like soils beneath the site. It is also our opinion that soil conditions are not favorable for the use of low impact development (LID) natural drainage practices (NDPs) due the potential for the development of shallow, seasonal perched groundwater, as indicated by soil mottling within one and one-half to two and one-half feet of the ground surface, and the fine-grained nature of the site soils, which have a USDA textural classification of silt loam. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 July 23, 2024 Project No. T-8955 Page No. 10 4.8 Drainage Surface Final exterior grades should promote free and positive drainage away from the building areas. We recommend providing a positive drainage gradient away from the building perimeter. If a positive gradient cannot be provided, provisions for collection and disposal of surface water adjacent to the structure should be provided. Surface water from developed areas must not be allowed to flow in an uncontrolled and concentrated manner toward or onto site slopes. Surface water should be directed away from the slopes to a point of collection and controlled discharge. If site grades do not allow for directing surface water away from the slope, then the water should be collected and tightlined to an approved point of controlled discharge. Subsurface We recommend installing a continuous drain along the outside lower edge of the perimeter building foundations. The drains can be laid to grade at an invert elevation equivalent to the bottom of footing grade. The drains can consist of four-inch diameter perforated PVC pipe that is enveloped in washed 1/2- to 3/4-inch gravel-sized drainage aggregate. The aggregate should extend six inches above and to the sides of the pipe. The foundation drains and roof downspouts should be tightlined separately to an approved point of controlled discharge. All drains should be provided with cleanouts at easily accessible locations. These cleanouts should be serviced at least once each year. 4.9 Utilities Utility pipes should be bedded and backfilled in accordance with American Public Works Association (APWA) or local jurisdictional requirements. At minimum, trench backfill should be placed and compacted as structural fill as described in Section 4.2 of this report. As noted, soils excavated onsite should generally be suitable for use as backfill material provided, they are near optimum moisture when excavated, and are placed during dry weather conditions. However, the site soils are fine grained and moisture sensitive; therefore, moisture conditioning may be necessary to facilitate proper compaction. If utility construction takes place during the winter, it may be necessary to import suitable wet weather fill for utility trench backfilling. 4.10 Pavements Pavements should be constructed on subgrades prepared as recommended in Section 4.2 of this report. Regardless of the degree of relative compaction achieved, the subgrade must be firm and relatively unyielding before paving. Proofrolling the subgrade with heavy construction equipment should be completed to verify this condition. The pavement design section is dependent upon the supporting capability of the subgrade soils and the traffic conditions to which it will be subjected. For traffic consisting mainly of light passenger vehicles with only occasional heavy traffic, and with a stable subgrade prepared as recommended, we recommend the following pavement sections: Two inches of hot mix asphalt (HMA) over four inches of crushed rock base (CRB). Three and one-half inches full depth HMA over prepared subgrade. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 July 23, 2024 Project No. T-8955 Page No. 11 The paving materials used should conform to the Washington State Department of Transportation (WSDOT) specifications for ½-inch class HMA and CRB. Long-term pavement performance will depend upon surface drainage. A poorly-drained pavement section will be subject to premature failure as a result of surface water infiltrating into the subgrade soils and reducing their supporting capability. For optimum pavement performance, we recommend surface drainage gradients of at least two percent. Some degree of longitudinal and transverse cracking of the pavement surface should be expected over time. Regular maintenance should be planned to seal cracks when they occur. 5.0 ADDITIONAL SERVICES Terra Associates, Inc. should review the final designs and specifications in order to verify that earthwork and foundation recommendations have been properly interpreted and implemented in project design. We should also provide geotechnical services during construction in order to observe compliance with our design concepts, specifications, and recommendations. This will allow for design changes if subsurface conditions differ from those anticipated prior to the start of construction. 6.0 LIMITATIONS We prepared this report in accordance with generally accepted geotechnical engineering practices. No other warranty, expressed or implied, is made. This report is the copyrighted property of Terra Associates, Inc. and is intended for specific application to the Windsor Court project in Renton, Washington. This report is for the exclusive use of DeDonato Group, LLC, and their authorized representatives. No other warranty, expressed or implied, is made. The analyses and recommendations presented in this report are based on data obtained from our on-site test pits. Variations in soil conditions can occur, the nature and extent of which may not become evident until construction. If variations appear evident, Terra Associates, Inc. should be requested to reevaluate the recommendations in this report prior to proceeding with construction. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 REFERENCE: KING COUNTY IMAP Environmental Earth Sciences Terra Associates, Inc. Consultants in Geotechnical Engineering Geology and NOT TO SCALE Figure 1Date JULY 2024 VICINITY MAP WINDSOR COURT RENTON, WASHINGTON Proj. No.T-8955 SITE Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 10 8 T H A V E S E 10 7 T H A V E S E TP-1 TP-2 TP-3 TP-4 TP-5 TP-6 TP-7 Environmental Earth Sciences Terra Associates, Inc. Consultants in Geotechnical Engineering Geology and Proj. No.T-8955 EXPLORATION LOCATION PLAN WINDSOR COURT RENTON, WASHINGTON Date JULY 2024 Figure 2 REFERENCE ONLY AND SHOULD NOT BE USED FOR DESIGN OR CONSTRUCTION PURPOSES. DIMENSIONS ARE APPROXIMATE. IT IS INTENDED FOR NOTE: THIS SITE PLAN IS SCHEMATIC. ALL LOCATIONS AND REFERENCE: SITE PLAN PROVIDED BY ESM. LEGEND: APPROXIMATE TEST PIT LOCATION 0 80 160 APPROXIMATE SCALE IN FEET Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 12" COMPACTED STRUCTURAL FILL EXCAVATED SLOPE (SEE REPORT TEXT FOR APPROPRIATE INCLINATIONS) SLOPE TO DRAIN 12" MINIMUM 3/4" MINUS WASHED GRAVEL 3" BELOW PIPE 12" OVER PIPE 4" DIAMETER PERFORATED PVC PIPE SEE NOTE 6"(MIN.) NOT TO SCALE NOTE: MIRADRAIN G100N PREFABRICATED DRAINAGE PANELS OR SIMILAR PRODUCT CAN BE SUBSTITUTED FOR THE 12-INCH WIDE GRAVEL DRAIN BEHIND WALL. DRAINAGE PANELS SHOULD EXTEND A MINIMUM OF SIX INCHES INTO 12-INCH THICK DRAINAGE GRAVEL LAYER OVER PERFORATED DRAIN PIPE. Environmental Earth Sciences Terra Associates, Inc. Consultants in Geotechnical Engineering Geology and Proj. No.T-8955 TYPICAL WALL DRAINAGE DETAIL WINDSOR COURT RENTON, WASHINGTON Date JULY 2024 Figure 3 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Project No. T-8955 APPENDIX A FIELD EXPLORATION AND LABORATORY TESTING Windsor Court 19411 and 19505 108th Avenue Southeast Renton, Washington On October 9, 2023, we explored subsurface conditions at the site in seven test pits excavated to maximum depths of about seven to eight feet below existing surface grades using a track-mounted excavator. The test pit locations were approximately determined in the field by sighting relative to existing surface features. The approximate test pit locations are shown on Figure 2. The Test Pit Logs are presented on Figures A-2 through A-8. An engineering geologist from our office maintained a log of each test pit as it was excavated, classified the soil conditions encountered, and obtained representative soil samples. All soil samples were visually classified in the field in accordance with the Unified Soil Classification System. A copy of this classification is presented as Figure A-1. Representative soil samples obtained from the test pits were placed in sealed plastic bags and taken to our laboratory for further examination and testing. The moisture content of each sample was measured and is reported on the Test Pit Logs. Grain size analyses were performed on five select soil samples. The results are shown on Figures A-9 and A-10. Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Environmental Earth Sciences Terra Associates, Inc. Consultants in Geotechnical Engineering Geology and MAJOR DIVISIONS LETTER SYMBOL TYPICAL DESCRIPTION GRAVELS More than 50% of coarse fraction is larger than No. 4 sieve Clean Gravels (less than 5% fines) GW Well-graded gravels, gravel-sand mixtures, little or no fines. GP Poorly-graded gravels, gravel-sand mixtures, little or no fines. Gravels with fines GM Silty gravels, gravel-sand-silt mixtures, non-plastic fines. GC Clayey gravels, gravel-sand-clay mixtures, plastic fines. SANDS More than 50% of coarse fraction is smaller than No. 4 sieve Clean Sands (less than 5% fines) SW Well-graded sands, sands with gravel, little or no fines. SP Poorly-graded sands, sands with gravel, little or no fines. Sands with fines SM Silty sands, sand-silt mixtures, non-plastic fines. SC Clayey sands, sand-clay mixtures, plastic fines. SILTS AND CLAYS Liquid Limit is less than 50% ML Inorganic silts, rock flour, clayey silts with slight plasticity. CL Inorganic clays of low to medium plasticity. (Lean clay) OL Organic silts and organic clays of low plasticity. SILTS AND CLAYS Liquid Limit is greater than 50% MH Inorganic silts, elastic. CH Inorganic clays of high plasticity. (Fat clay) OH Organic clays of high plasticity. HIGHLY ORGANIC SOILS PT Peat. CO A R S E G R A I N E D S O I L S Mo r e t h a n 5 0 % m a t e r i a l l a r g e r th a n N o . 2 0 0 s i e v e s i z e FI N E G R A I N E D S O I L S Mo r e t h a n 5 0 % m a t e r i a l s m a l l e r th a n N o . 2 0 0 s i e v e s i z e DEFINITION OF TERMS AND SYMBOLS CO H E S I O N L E S S CO H E S I V E Standard Penetration Density Resistance in Blows/Foot Very Loose 0-4 Loose 4-10 Medium Dense 10-30 Dense 30-50 Very Dense >50 Standard Penetration Consistancy Resistance in Blows/Foot Very Soft 0-2 Soft 2-4 Medium Stiff 4-8 Stiff 8-16 Very Stiff 16-32 Hard >32 2" OUTSIDE DIAMETER SPILT SPOON SAMPLER 2.4" INSIDE DIAMETER RING SAMPLER OR SHELBY TUBE SAMPLER WATER LEVEL (Date) Tr TORVANE READINGS, tsf Pp PENETROMETER READING, tsf DD DRY DENSITY, pounds per cubic foot LL LIQUID LIMIT, percent PI PLASTIC INDEX N STANDARD PENETRATION, blows per foot Proj. No.T-8955 UNIFIED SOIL CLASSIFICATION SYSTEM WINDSOR COURT RENTON, WASHINGTON Date JULY 2024 Figure A-1 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2 Docusign Envelope ID: DF429B06-CA80-4493-87D6-C67576B95CF2