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Home My WebLink AboutRS_Technical_Information_Report_230911_v1.pdf Western Washington Division Eastern Washington Division 165 NE Juniper St., Ste 201, Issaquah, WA 98027 108 East 2nd Street, Cle Elum, WA 98922 Phone: (425) 392-0250 Fax: (425) 391-3055 Phone: (509) 674-7433 Fax: (509) 674-7419 www.EncompassES.net CITY OF RENTON TECHNICAL INFORMATION REPORT For Index Avenue Townhouses 1709 Index Ave NE Renton, WA 98056 September 8, 2023 Prepared By: Ian Dahl Encompass Engineering Job No. 21770 Prepared For: Mike Elliott 10034 SE 218th Place Kent, WA 98031 206-947-9085 Index Avenue Townhomes Technical Information Report 09/08/2023 Page i TABLE OF CONTENTS I. PROJECT OVERVIEW ................................................................................................................ 1 II. CONDITIONS AND REQUIREMENTS SUMMARY ...................................................................... 6 III. OFFSITE ANALYSIS .................................................................................................................. 10 IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ........................... 15 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN ..................................................................... 16 VI. SPECIAL REPORTS AND STUDIES ............................................................................................ 16 VII. OTHER PERMITS ..................................................................................................................... 16 VIII. CSWPPP ANALYSIS AND DESIGN............................................................................................ 16 IX. BOND QUANTITIES AND DECLARATION OF COVENANT ....................................................... 18 X. OPERATION AND MAINTENANCE MANUAL .......................................................................... 18 LIST OF FIGURES 1. TIR Worksheet 2. Vicinity Map 3. Soils Map and Legend 4. Existing Conditions Map 5. Developed Conditions Map 6. Drainage Review Flow Chart 7. Flow Control Applications Map 8. Aquifer Protection Zone Map 9. Downstream Map 10. Flow Frequency Return Periods LIST OF APPENDICES A. Geotechnical Engineering Report by Riley Group, Inc. dated February 2, 2023 B. Operation & Maintenance Manual C. Declaration of Covenant 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 __________________ __________________ __________________ Mike Elliot 206-947-9085 10034 SE 218th Place Kent, WA 98031 Sam Salo, PE Encompass Engineering & Surveying 425-392-0250 Index Avenue Townhouses 23 N 5 E SW 4 1709 Index Ave NE Renton, WA 98056 TBD 09/08/2023 09/08/2023 t 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 ______________________  _____________________________________ Newcastle May Creek Duration (Forested) Flow Control Standard 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 Indiana Loamy Sand 5-15%Low May Creek 1 08/23/2023 1 TBD TBD TBD Duration (Forested) Flow Control 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: None Residential None 1 On-site roof drain system, conveyed to a limited infiltration trench. Two Type 1 CBs which connect to the COR storm system off-site. 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 _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ 5'x21' trench 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 09/08/2023 Index Avenue Townhomes Technical Information Report 09/08/2023 Page 1 I. PROJECT OVERVIEW Project: Index Avenue Townhouses Tax Parcel #: 722780-1935 Site Address: 1709 Index Avenue Renton, WA 98056 Site Area: 16,041 SF (0.37 AC) – As Surveyed Zoning: R-14 Figure 2: Vicinity Map Existing Site Conditions: The project is located in the City of Renton on a 16,041 SF (0.37 AC) parcel zoned R-14. The site is currently developed with a duplex residential building, with driveway access to both NE 16th St to the south and Index Avenue to the east. Slopes on-site range from 2-15% to the west over grass lawn area. The project is bordered by multi-family residences to the north and west, NE 16th St to the south and Index Ave NE to the east. Runoff leaves the site through one Natural Discharge Area (NDA) at the western limit of the site creating a single Threshold Discharge Area (TDA) for the project. See Section III of this report for a full Offsite Analysis and Figure 4 for a map of the existing site conditions. Critical Areas: Encompass has reviewed the site and the applicable resources for both listed and potential problems. There are no known critical areas or critical area buffers located on the site. Index Avenue Townhomes Technical Information Report 09/08/2023 Page 2 Soils: Per the US Department of Agriculture (USDA), Natural Resources Conservation Service (NCRS) Web Soil Survey information, the project site is generally underlain with Indianola Loamy Sand, 5 to 15% slopes. Per the Geotechnical Engineering Report prepared by Riley Group, the site contains medium dense to dense silty sand with trace gravel (Vashon till). An infiltration test was conducted, with a design rate of 2.1 in/hr determined. Limited infiltration is feasible in these soils, with a classification of loamy sand. Figure 3: Soils Map and Legend INDEX AVE NENE 16TH STEX. UNIT 1EX. UNIT 2NORTH INDEX AVENUE TOWNHOMES 1709 INDEX AVE NE RENTON, WA 98056 REVISIONS JOB NO. DATE SCALE SHEET Encompass Eastern Washington Division 407 Swiftwater Blvd. ▪ Cle Elum, WA 98922 ▪ Phone: (509) 674-7433 Western Washington Division 165 NE Juniper Street, Suite 201 ▪ Issaquah, WA 98027 ▪ Phone: (425) 392-0250 ENGINEERING & SURVEYINGEXISTING IMPERVIOUS SURFACE:1 of 1EXISTING CONDITIONS Index Avenue Townhomes Technical Information Report 09/08/2023 Page 4 Developed Site Conditions: This proposal incorporates the construction of an additional duplex residential building in the southern portion of the site. 2,409 SF of rooftop area is proposed, with 584 SF of on-site concrete driveway, as well as 163 SF of sidewalk areas. Off-site impervious areas include 945 SF of paved alley area located within an 8-foot alley dedication area along the western limit of the site, 664 SF of sidewalk area in a 1.5-foot ROW dedication along the east side of the site, and 93 SF of driveway area near the southwest corner of the site. The total new/replaced impervious area is 4,859 SF. Limited infiltration is feasible on this site, and is proposed for all new rooftop areas. The remainder of impervious surfaces have no feasible BMPs and will sheet flow or be conveyed to the City of Renton storm system in NE 16th St. See Section IV of this report for a full discussion of the proposed stormwater controls and Figure 5 for a map of the developed site conditions. INDEX AVE NENE 16TH STEX. UNIT 1EX. UNIT 2UNIT 3UNIT 4NORTH INDEX AVENUE TOWNHOMES 1709 INDEX AVE NE RENTON, WA 98056 REVISIONS JOB NO. DATE SCALE SHEET Encompass Eastern Washington Division 407 Swiftwater Blvd. ▪ Cle Elum, WA 98922 ▪ Phone: (509) 674-7433 Western Washington Division 165 NE Juniper Street, Suite 201 ▪ Issaquah, WA 98027 ▪ Phone: (425) 392-0250 ENGINEERING & SURVEYING 1 of 1PROPOSED CONDITIONS ON-SITE IMPERVIOUS SURFACE:OFF-SITE IMPERVIOUS SURFACE: Index Avenue Townhomes Technical Information Report 09/08/2023 Page 6 II. CONDITIONS AND REQUIREMENTS SUMMARY The 2022 City of Renton Surface Water Design Manual (RSWDM) has been utilized for stormwater design per the City of Renton requirements. The development will result in over 2,000 SF of new plus replaced impervious surface but does not result in over 50 acres of new impervious surface within a subbasin or multiple subbasins that are hydraulically connected. Therefore, per Figure 1.1.2.A of the RSWDM, this project must meet the Full Drainage Review requirements as detailed in Section 1.1.2.4. See Figure 6 below for more information on how the type of drainage review was determined. Figure 6: Drainage Review Flow Chart Index Avenue Townhomes Technical Information Report 09/08/2023 Page 7 Core Requirements: Core Requirement #1: Discharge at the Natural Location Currently, runoff from the site follows slopes to the west towards the downslope property to the west where it eventually enters the COR storm system on NE 16th St. Runoff from the new/replaced impervious areas will either be infiltrated on-site or collected and conveyed to the city storm system on NE 16th St. Core Requirement #2: Offsite Analysis A Level 1 Downstream analysis has been prepared and is included in Section III of this TIR. Core Requirement #3: Flow Control Facilities Per the COR Maps, this project site is located within the Flow Control Duration Standard, Forested Conditions area. The new/replaced impervious areas total 4,859 SF. Therefore, the projects meets the basic exemption from Core requirement #3, as less than 5,000 SF of new plus replaced impervious surfaces are proposed, and less than ¾ acres of new pervious surface will be added. Core Requirement #4: Conveyance System The conveyance capacity of the 12” SD pipe from the on-site catch basin to the exiting catch basin in NE 16th St has been calculated to confirm it will not be exceeded. See Section V of this TIR for further detail. Core Requirement #5: Construction Stormwater Pollution Prevention A simplified Construction Stormwater Pollution Prevention Plan (CSWPPP) is included in section VIII of this report. In addition, a corresponding Temporary Erosion and Sediment Control (TESC) Plan is included in the civil plans. Core Requirement #6: Maintenance and Operations See Section X of this report for a full discussion of the maintenance and operations. Core Requirement #7: Financial Guarantees and Liability The owner will arrange for any financial guarantees and liabilities required by the permit. Core Requirement #8: Water Quality Facilities In accordance with Section 1.2.8 of the RSWDM, Water Quality Treatment is not required for this project as new plus replaced pollution generating impervious surfaces (PGIS) do not exceed 5,000 SF, meeting exemption 1. A total of 1,622 SF of PGIS is proposed on the project. Core Requirement #9: On-Site BMPs per Section 1.2.9.1 of the 2022 Renton SWDM This project is smaller than 22,000 SF, and has therefore been designed to comply with the Small Lot BMP Requirements detailed in Section 1.2.9.2.1 of the RSWDM. On-site BMPs detailed below have been evaluated in order of preference per Section 1.2.9.2.1. The On-site BMPs for this project have been designed per the final developed impervious surface areas. See Section IV of this report for further discussion. Impervious Surface BMPs per 1.2.9.2.1 Small Lot BMP Requirements Full Dispersion: Infeasible. The site does not allow for the minimum 100-foot native vegetated flowpath lengths required per Appendix C.2.1 of the RSWDM. Index Avenue Townhomes Technical Information Report 09/08/2023 Page 8 Full Infiltration: Infeasible. Per the Geotechnical Engineering Report by Riley Group, the on-site soils match the criteria for Limited Infiltration (described below). Limited Infiltration: Feasible. Per the Geotechnical Engineering Report by Riley Group, soils on-site are suitable for limited infiltration with the classification of loamy sand. For rainfall regions SeaTac 1.0 or less, a 2-foot wide gravel trench must be 21 feet in length in loamy sand soils to mitigate 1,000 SF of impervious surface. A 5’x21’ gravel filled trench has been designed to mitigate runoff from the 2,409 SF of new rooftop area. A 21-foot by 2-foot trench has a surface area of 42 SF; therefore, 42 SF of gravel infiltration trench can infiltrate up to 1,000 SF of impervious area. A 5’x21’ trench has 105 SF of surface area and therefore can infiltrate up to (105/42)x 1,000=2,500 SF of impervious area. This is larger than the 2,409 SF of tributary rooftop area. Rain Gardens/Bioretention: Infeasible. The site layout does not allow for the implementation of rain gardens or bioretention facilities on this project. Permeable Pavement: Infeasible. The current soil information in the Geotechnical Engineering Report does not meet groundwater protection requirements. Further testing would need to be done to verify organic matter content, cation exchange capacity, etc. Basic Dispersion: Infeasible. The site plan does not allow for the required dispersion flowpaths over vegetated surfaces per Appendix C.2.4 of the RSWDM. BMPs Must be implemented, at minimum, for an impervious area equal to at least 20% of the site/lot for site/lot sizes between 11,000 and 22,000 SF. The future lot created after subtracting ROW dedication areas is 14,787 SF; therefore, 14,787 x 0.2= 2,957 SF of impervious area must be mitigated by BMPs. Only 2,409 SF can be mitigated with the BMPs listed in section 1.2.9.2.1, which is 16.3% of the future lot. This is the maximum extent feasible. Pervious Surface BMPs Soil Amendment: Feasible for new pervious surfaces Retention of the existing soils and restoration of all disturbed soils shall be applied to all of the landscaped areas both on- and off-site per Appendix C.2.13 of the RSWDM. Index Avenue Townhomes Technical Information Report 09/08/2023 Page 9 Special Requirements: Special Requirement #1: Other Adopted Area-Specific Requirements Master Drainage Plan – N/A Basin Plan – N/A Salmon Conservation Plan – N/A Lake Management Plan – Lake Washington Management Plan Hazard Mitigation Plan – N/A Shared Facility Drainage Plan – N/A Special Requirement #2: Flood Hazard Area Delineation The limits of this project do not lie in the FEMA 100-year floodplain. Special Requirement #3: Flood Protection Facilities This special requirement is applicable for Class 1 or 2 streams with an existing flood protection facility. The site does not contain any streams. Therefore, Special Requirement #3 is not applicable to this project. Special Requirement #4: Source controls Source control is not required for this project. Special Requirement #5: Oil Control This project is not considered high-use in need of oil control. Special Requirement #6: Aquifer Protection Area Per COR Maps, the project is not located within an Aquifer Protection Area Zone. Index Avenue Townhomes Technical Information Report 09/08/2023 Page 10 III. OFFSITE ANALYSIS Task 1: Study Area Definition and Maps A Level 1 Offsite Analysis has been performed for the project site per Section 2.3.1.1 of the RSWDM. The site is located in the May Creek Drainage Basin, within the Cedar River Watershed. Existing structures on the site consist of a duplex residential building, with driveway access to both NE 16th St to the south and Index Avenue to the east. Slopes on-site range from 2-15% to the west over grass lawn area. The project is bordered by multi-family residences to the north and west, NE 16th St to the south and Index Ave NE to the east. The study area for this analysis extends downstream of the project site for approximately one quarter mile and includes no upstream offsite drainage area tributary to the project site. Stormwater leaves the site in one NDA, creating a single TDA for the project. A map showing the study area is included in Figure 9. Task 2: Resource Review Encompass has reviewed the site and the applicable resources for both listed and potential problems. There are no known critical areas or buffers on the site per the City of Renton maps, FEMA maps, King County Sensitive Areas Folio, CED Wetlands Inventory, or the Washington State DOE Section 303d list. Task 3: Field Inspection A Level 1 Downstream Analysis was performed by Encompass Engineering and Surveying on Wednesday, August 8, 2023. The analysis was performed at approximately 12:00 PM with a temperature of about 65°. Information collected during this study is included in the Task 4 system description. Task 4: Drainage System Description and Problem Descriptions Stormwater from the site sheet flows to the west where it enters the downslope residential properties lawn area (A) and continues over gentle slopes to the west towards the paved Harrington Ave NE roadway. Stormwater flows to the south along the east side of Harrington Ave NE along a raised asphalt edge (B) and enters a Type 1 CB (C) at the intersection of Harrington Ave NE and NE 16th St. This roadway is very flat and has the potential for ponding. From here, stormwater enters the City of Renton Storm System and flows to the southwest in an 8” concrete pipe, passing through a series of Type 1 & 2 CBs (D) along the north side of NE 16th St. At the intersection of NE 16th St and Edmonds Ave NE, stormwater passes through two Type 2 CBs and continues south along the east side of Edmonds Ave NE in a 12-inch concrete pipe. This is where the downstream analysis was concluded at approximately ¼ mile downstream of the site. Task 5: Mitigation of Existing or Potential Problems Both King County iMap and the City of Renton GIS Maps show no drainage complaints relevant to the project or the downstream drainage paths within the study limits. No existing or potential problems were observed within the site or downstream area during the field reconnaissance. Index Avenue Townhomes Technical Information Report 09/08/2023 Page 11 Figure 9: Downstream Map Index Avenue Townhomes Technical Information Report 09/08/2023 Page 12 OFFSITE ANALYSIS DRAINAGE SYSTEM TABLE BASIN: May Creek SUBBASIN NAME: SUBBASIN NUMBER: SYMBOL DRAINAGE COMPONENT TYPE, NAME, AND SIZE DRAINAGE COMPONENT DESCRIPTION SLOPE DISTANCE FROM SITE DISCHARGE EXISTING PROBLEMS POTENTIAL PROBLEMS OBSERVATIONS OF FIELD INSPECTOR, RESOURCE REVIEWER, OR RESIDENT (See map) Type: sheet flow, swale, stream, channel, pipe, pond; Size: diameter, surface area Drainage basin, vegetation, cover, depth, type of sensitive area, volume % 1/4 Mile = 1,320 ft Constrictions, under capacity, ponding, overtopping, flooding, habitat or organism destruction, scouring, bank sloughing, sedimentation, incision, other erosion Tributary area, likelihood of problem, overflow pathways, potential impacts A SHEET FLOW GRASS LAWN 5% POINT OF DISCHARGE NONE IMPACT TO DOWNSLOPE STRUCTURES B CONCENTRATED FLOW RAISED ASPHALT EDGE 0-1% 150’ PONDING PONDING C CATCH BASIN TYPE 1 N/A 550' NONE NONE 8” CONC PIPE D CATCH BASIN TYPE 2 N/A 240’ NONE NONE 12” CONC PIPE E CATCH BASIN TYPE 2 N/A 480' NONE NONE 12” CONC PIPE F CATCH BASIN TYPE 1 N/A 1200’ NONE NONE 12” CONC PIPE Table 1: Downstream Table Index Avenue Townhomes Technical Information Report 09/08/2023 Page 13 Element A: Sheet flow to the west over lawn areas Element B: Raised asphalt edge on Harrington Ave NE Index Avenue Townhomes Technical Information Report 09/08/2023 Page 14 Element C: Type 1 CB on NE 16th St Element E: Type 1 CB on Edmonds Ave NE Index Avenue Townhomes Technical Information Report 09/08/2023 Page 15 IV. FLOW CONTROL, LOW IMPACT DEVELOPMENT (LID) AND WATER QUALITY FACILITY ANALYSIS AND DESIGN Part A: Existing Site Hydrology The site is located in the May Creek Drainage Basin, within the Cedar River Watershed. Existing structures on the site consist of a duplex residential building with two separate driveways connecting to NE 16th St and Index Avenue NE. The remainder of the site is grass lawn area which slopes towards the west at slopes of 2-15%. Stormwater leaves the site via sheet flow towards the downslope properties to the west. Per the US Department of Agriculture (USDA), Natural Resources Conservation Service (NCRS) Web Soil Survey information, the project site is generally underlain with Indianola Loamy Sand, 5 to 15% slopes. Per the Geotechnical Engineering Report prepared by Riley Group, the site contains medium dense to dense silty sand with trace gravel (Vashon till). An infiltration test was conducted, with a design rate of 2.1 in/hr determined. Limited infiltration is feasible in these soils, with a classification of loamy sand. Part B: Developed Site Hydrology This proposal incorporates the construction of a new 2,409 SF duplex residential building. A 584 SF concrete driveway will connect to the existing paved driveway with access to NE 16th St. Additionally, a 6- foot paved alley will be installed along the western limit of the site within an 8-fot alley dedication. The frontage along Index Ave NE will also be improved to construct new curb/gutter, planter strip and sidewalk within a 1.5’ ROW dedication. Runoff from new rooftop areas will be conveyed to a gravel-filled limited infiltration trench located to the south of the new building. Two new catch basins will be installed in the paved alley to prevent runoff from the site impacting downstream properties. This stormwater will tie into the existing catch basin in NE 16th St near the southwest corner of the site. Part C: Performance Standards This project site is located within the “Duration Flow Control Standard (Forested Condition)” area, however meets the basic exemption from Core requirement #3, as less than 5,000 SF of new plus replaced impervious surfaces are proposed, and less than ¾ acres of new pervious surface will be added. In addition, this site has been designed to comply with the Small Lot BMP Requirements detailed in Section 1.2.9.2.1 of the RSWDM. On-site BMPs per Section 1.2.9.1 of the 2022 RSWDM have been considered in order of preference as prescribed by the Small Lot BMP Requirements and are detailed in Core Requirement #9 in Section II of this report. This project proposes the creation of less than 5,000 SF of new PGIS; therefore, this project meets Exemption 1 and water quality treatment is not required per Section 1.2.8.1 of the RSWDM. Part D: Flow Control System Flow control facilities are not required on this project as it meets the basic exemption from Core requirement #3. Instead, on-site BMPs per Section 1.2.9.1 of the 2022 RSWDM have been considered in order of preference as prescribed by the Small Lot BMP Requirements and are detailed in Core Requirement #9 in Section II of this report. Part E: Water Quality System In accordance with Section 1.2.8 of the RSWDM, Water Quality Treatment is not required for this project as new plus replaced pollution generating impervious surfaces (PGIS) do not exceed 5,000 SF, meeting exemption 1. Index Avenue Townhomes Technical Information Report 09/08/2023 Page 16 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN The conveyance capacity of the 12” SD pipe from the on-site catch basin to the exiting catch basin in NE 16th Street was calculated using a Manning’s Equation calculator. A 12” pipe at 0.5% slope can convey 3.20 CFS (See below). The 25-year storm from the proposed impervious areas generates 0.0586 CFS of runoff. This does not exceed the capacity of the proposed pipe. VI. SPECIAL REPORTS AND STUDIES Geotechnical Engineering Report by Riley Group, Inc. dated February 2, 2023 VII. OTHER PERMITS A R.O.W. Permit, and a Clearing and Grading Permit will be required. VIII. CSWPPP ANALYSIS AND DESIGN 1. Preserve Vegetation/Mark Clearing Limits a. The clearing limits are shown on the TESC plans surrounding all proposed construction activity. High visibility orange fencing is shown around the perimeter of the site. b. Retain the duff layer, native top soil and natural vegetation in an undisturbed state to the maximum degree practicable. 2. Establish Construction Access a. A stabilized construction entrance is shown for the project off NE 16th St on the south side of the project site. b. If sediment is tracked off site, the affected roadways are to be cleaned thoroughly at the end of each day. 3. Control Sediment a. Silt fence will also be utilized to control sediment and protect adjacent properties. 4. Install Sediment Controls a. Silt fence will be installed around the downslope perimeter of the site during the initial phase of construction. 5. Stabilize Soils a. Stabilize expose and unworked soils. Soils must not remain exposed and unworked for more than the time periods set forth below to prevent erosion: Index Avenue Townhomes Technical Information Report 09/08/2023 Page 17 • During the dry season (May 1 – September 30): 7 days • During the wet season (October 1 – April 30): 2 days • Stabilize soils at the end of the shift before a holiday or weekend if needed based on the weather forecast. b. Stockpiled soils to be covered with plastic. c. All disturbed areas shall be stabilized with landscaping or some other method prior to final construction approval. 6. Protect Slopes a. Design and construct cut-and-fill slopes in a manner to minimize erosion. 7. Protect Drain Inlets a. Drain inlets on the site and on Shattuck Ave S will equipped with inlet protection devices in the initial stages of construction. b. Clean or remove and replace inlet protection devices when sediment has filled one third of the available storage. 8. Stabilize Channels and Outlets a. No channels or outlets are proposed. 9. Control Pollutants a. Design, install, implement and maintain effective pollution prevention measures to minimize the discharge of pollutants. b. Handle and dispose all pollutants, including waste materials and demolition debris that occur on-site in a manner that does not cause contamination of stormwater. c. Provide cover, containment, and protection from vandalism for all chemicals, liquid products, petroleum products, and other materials that have the potential to pose a threat to human health or the environment. On-site fueling tanks must include secondary containment. Secondary containment means placing tanks or containers within an impervious structure capable of containing 110% of the volume contained in the largest tank within the containment structure. Double-walled tanks do not require additional secondary containment. d. Conduct maintenance, fueling and repair of heavy equipment and vehicles using spill prevention and control measures. Clean contaminated surfaces immediately following any spill incident. e. Discharge wheel wash or tire bath wastewater to a separate on-site treatment system that prevents discharge to surface water, such as closed-loop recirculation or upland application, or to the sanitary sewer, with local sewer district approval. f. Apply fertilizers and pesticides in a manner and at application rates that will not result in loss of chemical to stormwater runoff. Follow manufacturers’ label requirements for application rates and procedures. g. Use BMPs to prevent contamination of stormwater runoff by pH modifying sources. The sources for this contamination include, but are not limited to: bulk cement, cement kiln dust, fly ash, new concrete washing and curing waters, waste streams generated from concrete grinding and sawing, exposed aggregate processes, dewatering concrete vaults, concrete pumping and mixer washout waters. h. Adjust the pH of stormwater if necessary to prevent violations of water quality standards. i. Assure that washout of concrete trucks is performed off-site or in designated concrete washout areas only. Do not wash out concrete trucks onto the ground, or into storm drains, open ditches, streets, or streams. Do not dump excess concrete on-site, except in designated concrete washout areas. Concrete spillage or concrete discharge to surface waters of the State is prohibited. Index Avenue Townhomes Technical Information Report 09/08/2023 Page 18 j. Obtain written approval from Ecology before using chemical treatment other than CO2 or dry ice to adjust pH. 10. Control Dewatering a. Dewatering is not anticipated at this site. 11. Maintain BMPs a. Maintain and repair all temporary and permanent erosion and sediment control BMPs as needed to assure continued performance of their intended function in accordance with BMP specifications. b. Remove all temporary erosion and sediment control BMPs within 30 days after achieving final site stabilization or after the temporary BMPs are no longer needed. All disturbed areas shall be stabilized with landscaping or some other method prior to final construction approval. 12. Manage the Project a. Maintain an updated SWPPP 13. Protect Low Impact Development BMPs. a. Porous pavement used in walkways and driveway areas will be poured after site is stabilized. Any excess debris or sediment tracked onto the pavement will be washed and/or vacuumed. Follow operation and maintenance procedures laid out in Appendix C. b. Perforated pipe connections will be covered with filter fabric immediately after pipe is backfilled with washed rock to prevent sediment from entering the system. IX. BOND QUANTITIES AND DECLARATION OF COVENANT A Declaration of Covenant for stormwater BMPs is provided in Appendix D. A Bond Quantities Worksheet has been provided in a separate document. X. OPERATION AND MAINTENANCE MANUAL An Operation and Maintenance Manual has been prepared for the site and is included in Appendix C of this Report. Appendix A Geotechnical Engineering Report by Riley Group, Inc. dated February 2, 2023 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone 425.415.0551 ♦ Fax 425.415.0311 www.riley-group.com GEOTECHNICAL ENGINEERING REPORT PREPARED BY: THE RILEY GROUP, INC. 17522 BOTHELL WAY NORTHEAST BOTHELL, WASHINGTON 98011 PREPARED FOR: MIKE ELLIOTT 10034 SOUTHEAST 218TH PLACE KENT, WASHINGTON 98031 RGI PROJECT NO. 2022-728-1 INDEX TOWNHOMES RENTON 1711 INDEX AVENUE NORTHEAST RENTON, WASHINGTON FEBRUARY 2, 2023 Geotechnical Engineering Report i February 2, 2023 1711 Index Avenue Northeast, Renton, Washington RGI Project No. 2022-728-1 TABLE OF CONTENTS 1.0 INTRODUCTION ............................................................................................................................... 1 2.0 PROJECT DESCRIPTION ............................................................................................................... 1 3.0 FIELD EXPLORATION AND LABORATORY TESTING .......................................................... 1 3.1 FIELD EXPLORATION ................................................................................................................................... 1 3.2 LABORATORY TESTING ................................................................................................................................ 2 4.0 SITE CONDITIONS ........................................................................................................................... 2 4.1 SURFACE .................................................................................................................................................. 2 4.2 GEOLOGY ................................................................................................................................................. 2 4.3 SOILS ....................................................................................................................................................... 2 4.4 GROUNDWATER ........................................................................................................................................ 2 4.5 SEISMIC CONSIDERATIONS ........................................................................................................................... 3 4.6 GEOLOGIC HAZARD AREAS .......................................................................................................................... 4 5.0 DISCUSSION AND RECOMMENDATIONS ................................................................................. 4 5.1 GEOTECHNICAL CONSIDERATIONS ................................................................................................................. 4 5.2 EARTHWORK ............................................................................................................................................. 4 5.2.1 Erosion and Sediment Control ..................................................................................................... 4 5.2.2 Stripping and Subgrade Preparation ............................................................................................ 5 5.2.3 Excavations................................................................................................................................... 5 5.2.4 Structural Fill ................................................................................................................................ 6 5.2.5 Wet Weather Construction Considerations ................................................................................. 7 5.3 FOUNDATIONS .......................................................................................................................................... 7 5.4 RETAINING WALLS ..................................................................................................................................... 8 5.5 SLAB-ON-GRADE CONSTRUCTION ................................................................................................................. 9 5.6 DRAINAGE ................................................................................................................................................ 9 5.6.1 Surface ......................................................................................................................................... 9 5.6.2 Subsurface .................................................................................................................................... 9 5.6.3 Infiltration .................................................................................................................................... 9 5.7 UTILITIES ................................................................................................................................................ 10 6.0 ADDITIONAL SERVICES .............................................................................................................. 10 7.0 LIMITATIONS ................................................................................................................................. 11 LIST OF FIGURES AND APPENDICES Figure 1 ..................................................................................................................... Site Vicinity Map Figure 2 ............................................................................................... Geotechnical Exploration Plan Figure 3 ............................................................................................... Retaining Wall Drainage Detail Figure 4 ....................................................................................................Typical Footing Drain Detail Appendix A .......................................................................... Field Exploration and Laboratory Testing Geotechnical Engineering Report ii February 2, 2023 1711 Index Avenue Northeast, Renton, Washington RGI Project No. 2022-728-1 Executive Summary This Executive Summary should be used in conjunction with the entire Geotechnical Engineering Report (GER) for design and/or construction purposes. It should be recognized that specific details were not included or fully developed in this section, and the GER must be read in its entirety for a comprehensive understanding of the items contained herein. Section 7.0 should be read for an understanding of limitations. RGI’s geotechnical scope of work included the advancement of 2 test pits to approximate depths of 7 feet below existing site grades. Based on the information obtained from our subsurface exploration, the site is suitable for development of the proposed project. The following geotechnical considerations were identified: Soil Conditions: The soils encountered during field exploration include medium dense to dense silty sand with trace gravel. Groundwater: No groundwater seepage was encountered during our subsurface exploration. Foundations: Foundations for the proposed building may be supported on conventional spread footings bearing on medium dense to dense native soil or structural fill. Slab-on-grade: Slab-on-grade floors and slabs for the proposed building can be supported on medium dense to dense native soil or structural fill. Geotechnical Engineering Report 1 February 2, 2023 1711 Index Avenue Northeast, Renton, Washington RGI Project No. 2022-728-1 1.0 Introduction This Geotechnical Engineering Report (GER) presents the results of the geotechnical engineering services provided for the Index Townhomes Renton in Renton, Washington. The purpose of this evaluation is to assess subsurface conditions and provide geotechnical recommendations for the construction of two townhomes. Our scope of services included field explorations, laboratory testing, engineering analyses, and preparation of this GER. The recommendations in the following sections of this GER are based upon our current understanding of the proposed site development as outlined below. If actual features vary or changes are made, RGI should review them in order to modify our recommendations as required. In addition, RGI requests to review the site grading plan, final design drawings and specifications when available to verify that our project understanding is correct and that our recommendations have been properly interpreted and incorporated into the project design and construction. 2.0 Project description The project site is located at 1711 Index Avenue Northeast in Renton, Washington. The approximate location of the site is shown on Figure 1. The site is currently a duplex surrounded by a yard and landscaping. RGI understands that two townhomes will be constructed on the site in the front yard area. At the time of preparing this GER, building plans were not available for our review. Based on our experience with similar construction, RGI anticipates that the proposed building will be supported on perimeter walls with bearing loads of two to six kips per linear foot. Slab- on-grade floor loading of 150 pounds per square foot (psf) are expected. 3.0 Field Exploration and Laboratory Testing 3.1 FIELD EXPLORATION On January 11, 2023, RGI observed the excavation of 2 test pits. The approximate exploration locations are shown on Figure 2. Field logs of each exploration were prepared by the geologist that continuously observed the excavation. These logs included visual classifications of the materials encountered during exploration as well as our interpretation of the subsurface conditions between samples. The test pit logs included in Appendix A represent an interpretation of the field logs and include modifications based on laboratory observation and analysis of the samples. Geotechnical Engineering Report 2 February 2, 2023 1711 Index Avenue Northeast, Renton, Washington RGI Project No. 2022-728-1 3.2 LABORATORY TESTING During the field exploration, a representative portion of each recovered sample was sealed in containers and transported to our laboratory for further visual and laboratory examination. Selected samples retrieved from the test pits were tested for moisture content and grain size analysis to aid in soil classification and provide input for the recommendations provided in this GER. The results and descriptions of the laboratory tests are enclosed in Appendix A. 4.0 Site Conditions 4.1 SURFACE The subject site is a roughly rectangular-shaped parcel of land approximately 0.37 acres in size. The site is bound to the north and west by residential lots, to the east by Index Avenue Northeast, and to the south by Northeast 16th Street. The existing site is a duplex surrounded by yards with a few trees and other vegetation. The site is relatively flat with an overall elevation difference less than 10 feet. 4.2 GEOLOGY Review of the Geologic Map of Surficial Deposits in the Seattle 30’ by 60’ Quadrangle, Washington, by James C. Yount, et al. (1993) indicates that the soil in the project vicinity is mapped as Vashon till (Qt), which is light to dark gray, nonsorted, nonstratified mixture of clay, silt, sand, and gravel. These descriptions are generally similar to the findings in our field explorations. 4.3 SOILS The soils encountered during field exploration include medium dense to dense silty sand with trace gravel (Vashon till). More detailed descriptions of the subsurface conditions encountered are presented in the test pits included in Appendix A. Sieve analysis was performed on two selected soil samples. Grain size distribution curves are included in Appendix A. 4.4 GROUNDWATER No groundwater seepage was encountered during our subsurface exploration. It should be recognized that fluctuations of the groundwater table will occur due to seasonal variations in the amount of rainfall, runoff, and other factors not evident at the time the explorations were performed. In addition, perched water can develop within seams and layers contained in fill soils or higher permeability soils overlying less permeable soils following periods of heavy or prolonged precipitation. Therefore, groundwater levels Geotechnical Engineering Report 3 February 2, 2023 1711 Index Avenue Northeast, Renton, Washington RGI Project No. 2022-728-1 during construction or at other times in the future may be higher or lower than the levels indicated on the logs. Groundwater level fluctuations should be considered when developing the design and construction plans for the project. 4.5 SEISMIC CONSIDERATIONS Based on the International Building Code (IBC), RGI recommends the follow seismic parameters for design. Table 1 IBC Parameter 2018 Value Site Soil Class1 D2 Site Latitude 47.5075499 Site Longitude -122.1824853 Short Period Spectral Response Acceleration, SS (g) 1.429 1-Second Period Spectral Response Acceleration, S1 (g) 0.49 Adjusted Short Period Spectral Response Acceleration, SMS (g) 1.429 Adjusted 1-Sec Period Spectral Response Acceleration, SM1 (g) 0.8863 Numeric seismic design value at 0.2 second; SDS(g) 0.953 Numeric seismic design value at 1.0 second; SD1(g) 0.5913 1. Note: In general accordance with Chapter 20 of ASCE 7-16. The Site Class is based on the average characteristics of the upper 100 feet of the subsurface profile. 2. Note: ASCE 7-16 require a site soil profile determination extending to a depth of 100 feet for seismic site classification. The current scope of our services does not include the required 100 foot soil profile determination. Test pits extended to a maximum depth of 7 feet, and this seismic site class definition considers that similar soil continues below the maximum depth of the subsurface exploration. Additional exploration to deeper depths would be required to confirm the conditions below the current depth of exploration. 3. Note: In accordance with ASCE 11.4.8, a ground motion hazard analysis is not required for the following cases: • Structures on Site Class E sites with SS greater than or equal to 1.0, provided the site coefficient Fa is taken as equal to that of Site Class C. • Structures on Site Class D sites with S1 greater than or equal to 0.2, provided that the value of the seismic response coefficient Cs is determined by Eq. 12.8-2 for values of T ≤ 1.5Ts and taken as equal to 1.5 times the value computed in accordance with either Eq. 12.8-3 for TL ≥ T > 1.5Ts or Eq. 12.8-4 for T > TL. • Structures on Site Class E sites with S1 greater than or equal to 0.2, provided that T is less than or equal to Ts and the equivalent static force procedure is used for design. The above exceptions do not apply to seismically isolated structures, structures with damping systems or structures designed using the response history procedures of Chapter 16. Liquefaction is a phenomenon where there is a reduction or complete loss of soil strength due to an increase in water pressure induced by vibrations from a seismic event. Liquefaction mainly affects geologically recent deposits of fine-grained sands that are below the groundwater table. Soils of this nature derive their strength from intergranular friction. The generated water pressure or pore pressure essentially separates the soil grains and eliminates this intergranular friction, thus reducing or eliminating the soil’s strength. Geotechnical Engineering Report 4 February 2, 2023 1711 Index Avenue Northeast, Renton, Washington RGI Project No. 2022-728-1 RGI reviewed the results of the field and laboratory testing and assessed the potential for liquefaction of the site’s soil during an earthquake. Since the site is underlain by glacial till, RGI considers that the possibility of liquefaction during an earthquake is minimal. 4.6 GEOLOGIC HAZARD AREAS Regulated geologically hazardous areas include erosion, landslide, earthquake, or other geological hazards. Based on the King County iMap and the City of Renton sensitive areas map, the site does not contain geologically hazardous areas. 5.0 Discussion and Recommendations 5.1 GEOTECHNICAL CONSIDERATIONS Based on our study, the site is suitable for the proposed construction from a geotechnical standpoint. Foundations for the proposed building can be supported on conventional spread footings bearing on competent native soil or structural fill. Slab-on-grade floors can be similarly supported. Detailed recommendations regarding the above issues and other geotechnical design considerations are provided in the following sections. These recommendations should be incorporated into the final design drawings and construction specifications. 5.2 EARTHWORK The earthwork is expected to include excavating and backfilling the building foundations and preparing slab subgrades. 5.2.1 EROSION AND SEDIMENT CONTROL Potential sources or causes of erosion and sedimentation depend on construction methods, slope length and gradient, amount of soil exposed and/or disturbed, soil type, construction sequencing and weather. The impacts on erosion-prone areas can be reduced by implementing an erosion and sedimentation control plan. The plan should be designed in accordance with applicable city and/or county standards. RGI recommends the following erosion control Best Management Practices (BMPs):  Scheduling site preparation and grading for the drier summer and early fall months and undertaking activities that expose soil during periods of little or no rainfall  Retaining existing vegetation whenever feasible  Establishing a quarry spall construction entrance  Installing siltation control fencing or anchored straw or coir wattles on the downhill side of work areas  Covering soil stockpiles with anchored plastic sheeting Geotechnical Engineering Report 5 February 2, 2023 1711 Index Avenue Northeast, Renton, Washington RGI Project No. 2022-728-1  Revegetating or mulching exposed soils with a minimum 3-inch thickness of straw if surfaces will be left undisturbed for more than one day during wet weather or one week in dry weather  Directing runoff away from exposed soils and slopes  Minimizing the length and steepness of slopes with exposed soils and cover excavation surfaces with anchored plastic sheeting  Decreasing runoff velocities with check dams, straw bales or coir wattles  Confining sediment to the project site  Inspecting and maintaining erosion and sediment control measures frequently (The contractor should be aware that inspection and maintenance of erosion control BMPs is critical toward their satisfactory performance. Repair and/or replacement of dysfunctional erosion control elements should be anticipated.) Permanent erosion protection should be provided by reestablishing vegetation using hydroseeding and/or landscape planting. Until the permanent erosion protection is established, site monitoring should be performed by qualified personnel to evaluate the effectiveness of the erosion control measures. Provisions for modifications to the erosion control system based on monitoring observations should be included in the erosion and sedimentation control plan. 5.2.2 STRIPPING AND SUBGRADE PREPARATION Stripping efforts should include removal of pavements, vegetation, organic materials, and deleterious debris from areas slated for building, pavement, and utility construction. The test pits encountered 6 inches of topsoil and rootmass during exploration. However, deeper areas of stripping may be required in heavily vegetated areas of the site. Subgrade soils that become disturbed due to elevated moisture conditions should be overexcavated to reveal firm, non-yielding, non-organic soils and backfilled with compacted structural fill. In order to maximize utilization of site soils as structural fill, RGI recommends that the earthwork portion of this project be completed during extended periods of warm and dry weather if possible. If earthwork is completed during the wet season (typically November through May) it will be necessary to take extra precautionary measures to protect subgrade soils. Wet season earthwork will require additional mitigative measures beyond that which would be expected during the drier summer and fall months. 5.2.3 EXCAVATIONS All temporary cut slopes associated with the site and utility excavations should be adequately inclined to prevent sloughing and collapse. The site soils consist of medium dense to dense silty sand with trace gravel. Geotechnical Engineering Report 6 February 2, 2023 1711 Index Avenue Northeast, Renton, Washington RGI Project No. 2022-728-1 Accordingly, for excavations more than 4 feet but less than 20 feet in depth, the temporary side slopes should be laid back with a minimum slope inclination of 1H:1V (Horizontal:Vertical). If there is insufficient room to complete the excavations in this manner, or excavations greater than 20 feet in depth are planned, using temporary shoring to support the excavations should be considered. For open cuts at the site, RGI recommends:  No traffic, construction equipment, stockpiles or building supplies are allowed at the top of cut slopes within a distance of at least five feet from the top of the cut  Exposed soil along the slope is protected from surface erosion using waterproof tarps and/or plastic sheeting  Construction activities are scheduled so that the length of time the temporary cut is left open is minimized  Surface water is diverted away from the excavation  The general condition of slopes should be observed periodically by a geotechnical engineer to confirm adequate stability and erosion control measures In all cases, however, appropriate inclinations will depend on the actual soil and groundwater conditions encountered during earthwork. Ultimately, the site contractor must be responsible for maintaining safe excavation slopes that comply with applicable OSHA or WISHA guidelines. 5.2.4 STRUCTURAL FILL RGI recommends fill below the foundation and floor slab, behind retaining walls, and below pavement and hardscape surfaces be placed in accordance with the following recommendations for structural fill. The structural fill should be placed after completion of site preparation procedures as described above. The suitability of excavated site soils and import soils for compacted structural fill use will depend on the gradation and moisture content of the soil when it is placed. As the amount of fines (that portion passing the U.S. No. 200 sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and adequate compaction becomes more difficult or impossible to achieve. Soils containing more than about 5 percent fines cannot be consistently compacted to a dense, non-yielding condition when the moisture content is more than 2 percent above or below optimum. Optimum moisture content is that moisture that results in the greatest compacted dry density with a specified compactive effort. Non-organic site soils are only considered suitable for structural fill provided that their moisture content is within about two percent of the optimum moisture level as determined by American Society of Testing and Materials D1557-09 Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (ASTM D1557). Excavated site soils may not be suitable for re-use as structural fill depending on the Geotechnical Engineering Report 7 February 2, 2023 1711 Index Avenue Northeast, Renton, Washington RGI Project No. 2022-728-1 moisture content and weather conditions at the time of construction. If soils are stockpiled for future reuse and wet weather is anticipated, the stockpile should be protected with plastic sheeting that is securely anchored. Even during dry weather, moisture conditioning (such as, windrowing and drying) of site soils to be reused as structural fill may be required. The site soils are moisture sensitive and may require moisture conditioning prior to use as structural fill. If on-site soils are or become unusable, it may become necessary to import suitable soils for structural fill. Prior to use, an RGI representative should observe and test all materials imported to the site for use as structural fill. Structural fill materials should be placed in uniform loose layers not exceeding 12 inches and compacted to 95 percent of the maximum dry density. The soil’s maximum density and optimum moisture should be determined by ASTM D1557. Placement and compaction of structural fill should be observed by RGI. 5.2.5 WET WEATHER CONSTRUCTION CONSIDERATIONS RGI recommends that preparation for site grading and construction include procedures intended to drain ponded water, control surface water runoff, and to collect shallow subsurface seepage zones in excavations where encountered. It will not be possible to successfully compact the subgrade or utilize on-site soils as structural fill if accumulated water is not drained prior to grading or if drainage is not controlled during construction. Attempting to grade the site without adequate drainage control measures will reduce the amount of on-site soil effectively available for use, increase the amount of select import fill materials required, and ultimately increase the cost of the earthwork phases of the project. Free water should not be allowed to pond on the subgrade soils. RGI anticipates that the use of berms and shallow drainage ditches, with sumps and pumps in utility trenches, will be required for surface water control during wet weather and/or wet site conditions. 5.3 FOUNDATIONS Following site preparation and grading, the proposed building foundation can be supported on conventional spread footings bearing on competent native soil or structural fill. Loose, organic, or other unsuitable soils may be encountered in the proposed building footprint. If unsuitable soils are encountered, they should be overexcavated and backfilled with structural fill. If loose soils are encountered, the soils should be moisture conditioned and compacted to a firm and unyielding condition. Perimeter foundations exposed to weather should be at a minimum depth of 18 inches below final exterior grades. Interior foundations can be constructed at any convenient depth below the floor slab. Finished grade is defined as the lowest adjacent grade within 5 feet of the foundation for perimeter (or exterior) footings and finished floor level for interior footings. Geotechnical Engineering Report 8 February 2, 2023 1711 Index Avenue Northeast, Renton, Washington RGI Project No. 2022-728-1 Table 2 Foundation Design Design Parameter Value Allowable Bearing Capacity 2,000 psf1 Friction Coefficient 0.30 Passive pressure (equivalent fluid pressure) 250 pcf2 1. psf = pounds per square foot 2. pcf = pounds per cubic foot The allowable foundation bearing pressures apply to dead loads plus design live load conditions. For short-term loads, such as wind and seismic, a 1/3 increase in this allowable capacity may be used. At perimeter locations, RGI recommends not including the upper 12 inches of soil in the computation of passive pressures because they can be affected by weather or disturbed by future grading activity. The passive pressure value assumes the foundation will be constructed neat against competent soil or backfilled with structural fill as described in Section 5.2.4. The recommended base friction and passive resistance value includes a safety factor of about 1.5. With spread footing foundations designed in accordance with the recommendations in this section, maximum total and differential post-construction settlements of 1 inch and 1/2 inch, respectively, should be expected. 5.4 RETAINING WALLS If retaining walls are needed for the buildings, RGI recommends cast-in-place concrete walls be used. Modular block walls may be used for grade changes in other areas. The magnitude of earth pressure development on cast-in-place retaining walls will partly depend on the quality of the wall backfill. RGI recommends placing and compacting wall backfill as structural fill. Wall drainage will be needed behind the wall face. A typical retaining wall drainage detail is shown in Figure 3. With wall backfill placed and compacted as recommended, level backfill and drainage properly installed, RGI recommends using the values in the following table for design. Table 3 Retaining Wall Design Design Parameter Value Active Earth Pressure (unrestrained walls) 35 pcf At-rest Earth Pressure (restrained walls) 50 pcf Geotechnical Engineering Report 9 February 2, 2023 1711 Index Avenue Northeast, Renton, Washington RGI Project No. 2022-728-1 For seismic design, an additional uniform load of 7 times the wall height (H) for unrestrained walls and 14H in psf for restrained walls should be applied to the wall surface. 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 5.3. 5.5 SLAB-ON-GRADE CONSTRUCTION RGI recommends that the concrete slab be placed on top of medium dense native soil or structural fill. Immediately below the floor slab, RGI recommends placing a four-inch thick capillary break layer of clean, free-draining sand or gravel that has less than five percent passing the U.S. 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. Where moisture by vapor transmission is undesirable, an 8- to 10-millimeter thick plastic membrane should be placed on a 4-inch thick layer of clean gravel. For the anticipated floor slab loading, we estimate post-construction floor settlements of 1/4- to 1/2-inch. 5.6 DRAINAGE 5.6.1 SURFACE Final exterior grades should promote free and positive drainage away from the building area. Water must not be allowed to pond or collect adjacent to foundations or within the immediate building area. For non-pavement locations, RGI recommends providing a minimum drainage gradient of 3 percent for a minimum distance of 10 feet from the building perimeter. In paved locations, a minimum gradient of 1 percent should be provided unless provisions are included for collection and disposal of surface water adjacent to the structure. 5.6.2 SUBSURFACE RGI recommends installing perimeter foundation drains. A typical footing drain detail is shown on Figure 4. The foundation drains and roof downspouts should be tightlined separately to an approved discharge facility. Subsurface drains must be laid with a gradient sufficient to promote positive flow to a controlled point of approved discharge. 5.6.3 INFILTRATION RGI understands that an infiltration system is being considered for the on-site disposal of storm water run-off. Field infiltration test INF-1, was placed in the southwest portion of the site. The small-scale Pilot Infiltration Test (PIT) was completed at a depth of approximately 3.5 feet below grade and measured 2 feet by 6 feet. The infiltration test was conducted in accordance with the 2017 City of Renton Surface Water Design Manual. Geotechnical Engineering Report 10 February 2, 2023 1711 Index Avenue Northeast, Renton, Washington RGI Project No. 2022-728-1 Table 4 Measured Infiltration Rates Test Location Test Depth Measured Rate Design Rate INF-1 3.5 feet 5.3 inches/hour 2.1 inches/hour A Total Correction Factor was applied to the field measured infiltration rate. Idesign = Imeasured X Ftesting X Fgeometry X Fplugging Ftesting = 0.5 (Small-scale PIT) Fgeometry = assumed 1 (may be adjusted based on actual infiltration facility dimensions) Fplugging = 0.8 (fine sands and loamy sands) Idesign = 5.3 inches/hour X 0.5 X 1 X 0.8 = 0.24 inches/hour Site soils fall under the criteria for Limited Infiltration in Appendix C.2.3. Based on the loamy sand soil classification gravel filled trenches should be 21 feet in length for every 1,000 aquare feet of tributary impervious area. Drywells should have 315 cubic feet of gravel for every 1,000 square feet of tributary impervious area. 5.7 UTILITIES Utility pipes should be bedded and backfilled in accordance with American Public Works Association (APWA) specifications. For site utilities located within the right-of-ways, bedding and backfill should be completed in accordance with City of Renton specifications. At a minimum, trench backfill should be placed and compacted as structural fill, as described in Section 5.2.4. Where utilities occur below unimproved areas, the degree of compaction can be reduced to a minimum of 90 percent of the soil’s maximum density as determined by the referenced ASTM D1557. 6.0 Additional Services RGI is available to provide further geotechnical consultation throughout the design phase of the project. RGI should review the final design and specifications in order to verify that earthwork and foundation recommendations have been properly interpreted and incorporated into project design and construction. RGI is also available to provide geotechnical engineering and construction monitoring services during construction. The integrity of the earthwork and construction depends on proper site preparation and procedures. In addition, engineering decisions may arise in the field in the event that variations in subsurface conditions become apparent. Construction monitoring services are not part of this scope of work. Geotechnical Engineering Report 11 February 2, 2023 1711 Index Avenue Northeast, Renton, Washington RGI Project No. 2022-728-1 7.0 Limitations This GER is the property of RGI, Mike Elliott, and its designated agents. Within the limits of the scope and budget, this GER was prepared in accordance with generally accepted geotechnical engineering practices in the area at the time this GER was issued. This GER is intended for specific application to the Index Townhomes Renton project in Renton, Washington, and for the exclusive use of Mike Elliott and its authorized representatives. No other warranty, expressed or implied, is made. Site safety, excavation support, and dewatering requirements are the responsibility of others. The scope of services for this project does not include either specifically or by implication any environmental or biological (for example, mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, we can provide a proposal for these services. The analyses and recommendations presented in this GER are based upon data obtained from the explorations performed on site. Variations in soil conditions can occur, the nature and extent of which may not become evident until construction. If variations appear evident, RGI should be requested to reevaluate the recommendations in this GER prior to proceeding with construction. It is the client’s responsibility to see that all parties to the project, including the designers, contractors, subcontractors, are made aware of this GER in its entirety. The use of information contained in this GER for bidding purposes should be done at the contractor’s option and risk. USGS, 2020, Mercer Island, Washington USGS, 2020, Renton, Washington 7.5-Minute Quadrangle Approximate Scale: 1"=1000' 0 500 1000 2000 N Site Vicinity Map Figure 1 02/2023 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone: 425.415.0551 Fax: 425.415.0311 Index Townhomes Renton RGI Project Number: 2022-728-1 Date Drawn: Address: 1711 Index Avenue Northeast, Renton, Washington 98056 SITE TP1 TP2 INF1 N Geotechnical Exploration Plan Figure 2 Approximate Scale: 1"=20' 0 15 30 60 = Infiltration pit by RGI, 01/11/23 = Test pit by RGI, 01/11/23 = Site boundary 02/2023 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone: 425.415.0551 Fax: 425.415.0311 Index Townhomes Renton RGI Project Number: 2022-728-1 Date Drawn: Address: 1711 Index Avenue Northeast, Renton, Washington 98056 Incliniations) 12" Over the Pipe 3" Below the Pipe Perforated Pipe 4" Diameter PVC Compacted Structural Backfill (Native or Import) 12" min. Filter Fabric Material 12" Minimum Wide Free-Draining Gravel Slope to Drain (See Report for Appropriate Excavated Slope 02/2023 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone: 425.415.0551 Fax: 425.415.0311 Index Townhomes Renton RGI Project Number: 2022-728-1 Date Drawn: Address: 1711 Index Avenue Northeast, Renton, Washington 98056 Retaining Wall Drainage Detail Figure 3 Not to Scale 3/4" Washed Rock or Pea Gravel 4" Perforated Pipe Building Slab Structural Backfill Compacted Filter Fabric 02/2023 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone: 425.415.0551 Fax: 425.415.0311 Index Townhomes Renton RGI Project Number: 2022-728-1 Date Drawn: Address: 1711 Index Avenue Northeast, Renton, Washington 98056 Typical Footing Drain Detail Figure 4 Not to Scale Geotechnical Engineering Report February 2, 2023 1711 Index Avenue Northeast, Renton, Washington RGI Project No. 2022-728-1 APPENDIX A FIELD EXPLORATION AND LABORATORY TESTING On January 11, 2023, RGI performed field explorations using a mini excavator. We explored subsurface soil conditions at the site by observing the excavation of two test pits to a maximum depth of 7 feet below existing grade. The test pit locations are shown on Figure 2. The locations were approximately determined by measurements from existing property lines and paved roads. A geologist from our office conducted the field exploration and classified the soil conditions encountered, maintained a log of each test exploration, obtained representative soil samples, and observed pertinent site features. All soil samples were visually classified in accordance with the Unified Soil Classification System (USCS). Representative soil samples obtained from the explorations were placed in closed containers and taken to our laboratory for further examination and testing. As a part of the laboratory testing program, the soil samples were classified in our in house laboratory based on visual observation, texture, plasticity, and the limited laboratory testing described below. Moisture Content Determinations Moisture content determinations were performed in accordance with ASTM D2216-10 Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass (ASTM D2216) on representative samples obtained from the exploration in order to aid in identification and correlation of soil types. The moisture content of typical sample was measured and is reported on the test pit logs. Grain Size Analysis A grain size analysis indicates the range in diameter of soil particles included in a particular sample. Grain size analyses was determined using D6913-04(2009) Standard Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis (ASTM D6913) on two of the samples. Project Name:Index Townhomes Renton Project Number:2022-728-1 Client:Mike Elliott Test Pit No.:TP-1 Date(s) Drilled:January 11, 2023 Excavation Method(s):Excavator Excavator Type:Mini Excavator Groundwater Level:Not Encountered Test Pit Backfill:Cuttings Logged By:LW Bucket Size:2' Excavation Contractor:Kelly's Excavating Sampling Method(s):Grab Location:1711 Index Avenue Northeast, Renton, Washington Surface Conditions:Grass Total Depth of Excavation:7 feet bgs Approximate Surface Elevation:370 Compaction Method:Bucket Tamp USCS SymbolTpsl SM SM SM REMARKS Graphic LogMATERIAL DESCRIPTION 6" of topsoil and rootmass Brown silty SAND with some gravel, moist, loose Tan silty SAND with some gravel, moist, medium dense, (Weathered Vashon Till) 12% moisture Gray silty SAND with some gravel and occasional cobbles, moist, dense 14% moisture, 13.9% fines Becomes very dense 13% moisture Test pit terminated at 7'Depth (feet)0 5 Sample IDTP1-2 TP1-4 TP1-6.5 Sample TypeElevation (feet)370 365 Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Index Townhomes Renton Project Number:2022-728-1 Client:Mike Elliott Test Pit No.:TP-2 Date(s) Drilled:January 11, 2023 Excavation Method(s):Excavator Excavator Type:Mini Excavator Groundwater Level:Not Encountered Test Pit Backfill:Cuttings Logged By:LW Bucket Size:2' Excavation Contractor:Kelly's Excavating Sampling Method(s):Grab Location:1711 Index Avenue Northeast, Renton, Washington Surface Conditions:Grass Total Depth of Excavation:5 feet bgs Approximate Surface Elevation:373 Compaction Method:Bucket Tamp USCS SymbolTpsl SM SW-SM SM REMARKS Graphic LogMATERIAL DESCRIPTION 6" of topsoil and rootmass Brown silty SAND with trace gravel, moist, loose Tan SAND with some silt and trace gravel, moist, medium dense, (Weathered Vashon Till) 12% moisture, 10.1% fines Gray silty SAND with trace gravel, moist, dense, (Vashon Till) Becomes very dense 14% moisture Test pit terminated at 5'Depth (feet)0 5 Sample IDTP2-2 TP2-4 Sample TypeElevation (feet)373 368 Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Index Townhomes Renton Project Number:2022-728-1 Client:Mike Elliott Key to Log of Boring USCS SymbolREMARKS Graphic LogMATERIAL DESCRIPTIONDepth (feet)Sample IDSample TypeElevation (feet)1 2 3 4 5 6 7 8 COLUMN DESCRIPTIONS 1 Elevation (feet): Elevation (MSL, feet). 2 Depth (feet): Depth in feet below the ground surface. 3 Sample ID: Sample identification number. 4 Sample Type: Type of soil sample collected at the depth interval shown. 5 USCS Symbol: USCS symbol of the subsurface material. 6 Graphic Log: Graphic depiction of the subsurface material encountered. 7 MATERIAL DESCRIPTION: Description of material encountered. May include consistency, moisture, color, and other descriptive text. 8 REMARKS : Comments and observations regarding drilling or sampling made by driller or field personnel. FIELD AND LABORATORY TEST ABBREVIATIONS CHEM: Chemical tests to assess corrosivity COMP: Compaction test CONS: One-dimensional consolidation test LL: Liquid Limit, percent PI: Plasticity Index, percent SA: Sieve analysis (percent passing No. 200 Sieve) UC: Unconfined compressive strength test, Qu, in ksf WA: Wash sieve (percent passing No. 200 Sieve) MATERIAL GRAPHIC SYMBOLS Silty SAND (SM)Well graded SAND with Silt (SW-SM) Topsoil TYPICAL SAMPLER GRAPHIC SYMBOLS Auger sampler Bulk Sample 3-inch-OD California w/ brass rings CME Sampler Grab Sample 2.5-inch-OD Modified California w/ brass liners Pitcher Sample 2-inch-OD unlined split spoon (SPT) Shelby Tube (Thin-walled, fixed head) OTHER GRAPHIC SYMBOLS Water level (at time of drilling, ATD) Water level (after waiting, AW) Minor change in material properties within a stratum Inferred/gradational contact between strata ?Queried contact between strata GENERAL NOTES 1: Soil classifications are based on the Unified Soil Classification System. Descriptions and stratum lines are interpretive, and actual lithologic changes may be gradual. Field descriptions may have been modified to reflect results of lab tests. 2: Descriptions on these logs apply only at the specific boring locations and at the time the borings were advanced. They are not warranted to be representative of subsurface conditions at other locations or times. Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 THE RILEY GROUP, INC. 17522 Bothell Way NE Bothell, WA 98011 PHONE: (425) 415-0551 FAX: (425) 415-0311 GRAIN SIZE ANALYSIS ASTM D421, D422, D1140, D2487, D6913 PROJECT TITLE Exploration Type TP1 Test Pit PROJECT NO.Depth TECH/TEST DATE RT/CC Date Received WATER CONTENT (Delivered Moisture) Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture Wt Wet Soil & Tare (gm) (w1)1249.4 Weight Of Sample (gm)1109.4 Wt Dry Soil & Tare (gm) (w2)1109.4 Tare Weight (gm) 133.6 Weight of Tare (gm) (w3)133.6 (W6) Total Dry Weight (gm) 975.8 Weight of Water (gm) (w4=w1-w2) 140.0 SIEVE ANALYSIS Weight of Dry Soil (gm) (w5=w2-w3) 975.8 Cumulative Moisture Content (%) (w4/w5)*100 14 Wt Ret (Wt-Tare) (%Retained)% PASS +Tare {(wt ret/w6)*100}(100-%ret) % COBBLES 0.0 12.0"133.6 0.00 0.00 100.00 cobbles % C GRAVEL 9.2 3.0"133.6 0.00 0.00 100.00 coarse gravel % F GRAVEL 6.1 2.5" coarse gravel % C SAND 3.8 2.0" coarse gravel % M SAND 33.6 1.5"133.6 0.00 0.00 100.00 coarse gravel % F SAND 33.4 1.0" coarse gravel % FINES 13.9 0.75"223.8 90.20 9.24 90.76 fine gravel % TOTAL 100.0 0.50" fine gravel 0.375"259.4 125.80 12.89 87.11 fine gravel D10 (mm)0.05 #4 283.8 150.20 15.39 84.61 coarse sand D30 (mm)0.22 #10 320.8 187.20 19.18 80.82 medium sand D60 (mm)0.78 #20 medium sand Cu 15.6 #40 648.7 515.10 52.79 47.21 fine sand Cc 1.2 #60 fine sand #100 912.9 779.30 79.86 20.14 fine sand #200 974.2 840.60 86.14 13.86 fines PAN 1109.4 975.80 100.00 0.00 silt/clay 556.6 423 43.349047 56.6509531 DESCRIPTION USCS SM Prepared For: Reviewed By: Mike Elliott LW Index Townhomes Renton 2022-728 4' 1/11/2023 Silty SAND with some gravel 0 10 20 30 40 50 60 70 80 90 100 0.0010.010.11101001000 % P A S S I N G Grain size in millimeters 12"3" 2" 1" .75" .375" #4 #10 #20 #40 #60 #100 #200 THE RILEY GROUP, INC. 17522 Bothell Way NE Bothell, WA 98011 PHONE: (425) 415-0551 FAX: (425) 415-0311 GRAIN SIZE ANALYSIS ASTM D421, D422, D1140, D2487, D6913 PROJECT TITLE Exploration Type TP2 Test Pit PROJECT NO.Depth TECH/TEST DATE RT/LW/CC Date Received WATER CONTENT (Delivered Moisture) Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture Wt Wet Soil & Tare (gm) (w1)998.8 Weight Of Sample (gm)905.1 Wt Dry Soil & Tare (gm) (w2)905.1 Tare Weight (gm) 124.6 Weight of Tare (gm) (w3)124.6 (W6) Total Dry Weight (gm) 780.5 Weight of Water (gm) (w4=w1-w2) 93.7 SIEVE ANALYSIS Weight of Dry Soil (gm) (w5=w2-w3) 780.5 Cumulative Moisture Content (%) (w4/w5)*100 12 Wt Ret (Wt-Tare) (%Retained)% PASS +Tare {(wt ret/w6)*100}(100-%ret) % COBBLES 0.0 12.0"124.6 0.00 0.00 100.00 cobbles % C GRAVEL 1.2 3.0"124.6 0.00 0.00 100.00 coarse gravel % F GRAVEL 8.1 2.5" coarse gravel % C SAND 7.9 2.0" coarse gravel % M SAND 39.7 1.5"124.6 0.00 0.00 100.00 coarse gravel % F SAND 33.0 1.0" coarse gravel % FINES 10.1 0.75"133.8 9.20 1.18 98.82 fine gravel % TOTAL 100.0 0.50" fine gravel 0.375"161.7 37.10 4.75 95.25 fine gravel D10 (mm)0.075 #4 196.9 72.30 9.26 90.74 coarse sand D30 (mm)0.25 #10 258.4 133.80 17.14 82.86 medium sand D60 (mm)0.8 #20 medium sand Cu 10.7 #40 568.6 444.00 56.89 43.11 fine sand Cc 1.0 #60 fine sand #100 783.7 659.10 84.45 15.55 fine sand #200 826.3 701.70 89.90 10.10 fines PAN 905.1 780.50 100.00 0.00 silt/clay 556.6 432 55.349135 44.6508648 DESCRIPTION USCS SW-SM Prepared For: Reviewed By: Mike Elliott LW Index Townhomes Renton 2022-728 2' 1/11/2023 Well graded SAND with some silt and trace gravel 0 10 20 30 40 50 60 70 80 90 100 0.0010.010.11101001000 % P A S S I N G Grain size in millimeters 12"3" 2" 1" .75" .375" #4 #10 #20 #40 #60 #100 #200 Appendix B Operation & Maintenance Manual APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 6/22/2022 2022 City of Renton Surface Water Design Manual A-4 NO. 2 – INFILTRATION FACILITIES MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Site Trash and debris Any trash and debris which exceed 1 cubic foot per 1,000 square feet (this is about equal to the amount of trash it would take to fill up one standard size office garbage can). In general, there should be no visual evidence of dumping. Trash and debris cleared from site. Noxious weeds Any noxious or nuisance vegetation which may constitute a hazard to City personnel or the public. Noxious and nuisance vegetation removed according to applicable regulations. No danger of noxious vegetation where City personnel or the public might normally be. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Excessive growth of grass/groundcover Grass or groundcover exceeds 18 inches in height. Grass or groundcover mowed to a height no greater than 6 inches. Infiltration Pond, Top or Side Slopes of Dam, Berm or Embankment Rodent holes Any evidence of rodent holes if facility is acting as a dam or berm, or any evidence of water piping through dam or berm via rodent holes. Rodents removed or destroyed and dam or berm repaired. Tree growth Tree growth threatens integrity of dams, berms or slopes, does not allow maintenance access, or interferes with maintenance activity. If trees are not a threat to dam, berm, or embankment integrity or not interfering with access or maintenance, they do not need to be removed. Trees do not hinder facility performance or maintenance activities. Erosion Eroded damage over 2 inches deep where cause of damage is still present or where there is potential for continued erosion. Any erosion observed on a compacted slope. Slopes stabilized using appropriate erosion control measures. If erosion is occurring on compacted slope, a licensed civil engineer should be consulted to resolve source of erosion. Settlement Any part of a dam, berm or embankment that has settled 4 inches lower than the design elevation. Top or side slope restored to design dimensions. If settlement is significant, a licensed civil engineer should be consulted to determine the cause of the settlement. Infiltration Pond, Tank, Vault, Trench, or Small Basin Storage Area Sediment accumulation If two inches or more sediment is present or a percolation test indicates facility is working at or less than 90% of design. Facility infiltrates as designed. Liner damaged (If applicable) Liner is visible or pond does not hold water as designed. Liner repaired or replaced. Infiltration Tank Structure Plugged air vent Any blockage of the vent. Tank or vault freely vents. Tank bent out of shape Any part of tank/pipe is bent out of shape more than 10% of its design shape. Tank repaired or replaced to design. Gaps between sections, damaged joints or cracks or tears in wall A gap wider than ½-inch at the joint of any tank sections or any evidence of soil particles entering the tank at a joint or through a wall. No water or soil entering tank through joints or walls. Infiltration Vault Structure Damage to wall, frame, bottom, and/or top slab Cracks wider than ½-inch, any evidence of soil entering the structure through cracks or qualified inspection personnel determines that the vault is not structurally sound. Vault is sealed and structurally sound. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 2022 City of Renton Surface Water Design Manual 6/22/2022 A-5 NO. 2 – INFILTRATION FACILITIES MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Inlet/Outlet Pipes Sediment accumulation Sediment filling 20% or more of the pipe. Inlet/outlet pipes clear of sediment. Trash and debris Trash and debris accumulated in inlet/outlet pipes (includes floatables and non-floatables). No trash or debris in pipes. Damaged inlet/outlet pipe Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering at the joints of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of the inlet/outlet pipe. Access Manhole Cover/lid not in place Cover/lid is missing or only partially in place. Any open manhole requires immediate maintenance. Manhole access covered. Locking mechanism not working Mechanism cannot be opened by one maintenance person with proper tools. Bolts cannot be seated. Self-locking cover/lid does not work. Mechanism opens with proper tools. Cover/lid difficult to remove One maintenance person cannot remove cover/lid after applying 80 lbs of lift. Cover/lid can be removed and reinstalled by one maintenance person. Ladder rungs unsafe Missing rungs, misalignment, rust, or cracks. Ladder meets design standards. Allows maintenance person safe access. Large access doors/plate Damaged or difficult to open Large access doors or plates cannot be opened/removed using normal equipment. Replace or repair access door so it can be opened as designed. Gaps, doesn't cover completely Large access doors not flat and/or access opening not completely covered. Doors close flat; covers access opening completely. Lifting rings missing, rusted Lifting rings not capable of lifting weight of door or plate. Lifting rings sufficient to lift or remove door or plate. Infiltration Pond, Tank, Vault, Trench, or Small Basin Filter Bags Plugged filter bag (if applicable) Filter bag more than 1/2 full. Replace filter bag or redesign system. Infiltration Pond, Tank, Vault, Trench, or Small Basin Pre- settling Ponds and Vaults Sediment accumulation 6" or more of sediment has accumulated. Pre-settling occurs as designed Infiltration Pond, Rock Filter Plugged rock filter High water level on upstream side of filter remains for extended period of time or little or no water flows through filter during heavy rain storms. Rock filter replaced evaluate need for filter and remove if not necessary. Infiltration Pond Emergency Overflow Spillway Rock missing Only one layer of rock exists above native soil in area five square feet or larger, or any exposure of native soil at the top of out flow path of spillway. Rip-rap on inside slopes need not be replaced. Spillway restored to design standards. Tree growth Tree growth impedes flow or threatens stability of spillway. Trees removed. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 6/22/2022 2022 City of Renton Surface Water Design Manual A-10 NO. 5 – CATCH BASINS AND MANHOLES MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITION WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Structure Sediment accumulation Sediment exceeds 60% of the depth from the bottom of the catch basin to the invert of the lowest pipe into or out of the catch basin or is within 6 inches of the invert of the lowest pipe into or out of the catch basin. Sump of catch basin contains no sediment. Trash and debris Trash or debris of more than ½ cubic foot which is located immediately in front of the catch basin opening or is blocking capacity of the catch basin by more than 10%. No Trash or debris blocking or potentially blocking entrance to catch basin. Trash or debris in the catch basin that exceeds 1/3 the depth from the bottom of basin to invert the lowest pipe into or out of the basin. No trash or debris in the catch basin. Dead animals or vegetation that could generate odors that could cause complaints or dangerous gases (e.g., methane). No dead animals or vegetation present within catch basin. Deposits of garbage exceeding 1 cubic foot in volume. No condition present which would attract or support the breeding of insects or rodents. Damage to frame and/or top slab Corner of frame extends more than ¾ inch past curb face into the street (If applicable). Frame is even with curb. Top slab has holes larger than 2 square inches or cracks wider than ¼ inch. Top slab is free of holes and cracks. Frame not sitting flush on top slab, i.e., separation of more than ¾ inch of the frame from the top slab. Frame is sitting flush on top slab. Cracks in walls or bottom Cracks wider than ½ inch and longer than 3 feet, any evidence of soil particles entering catch basin through cracks, or maintenance person judges that catch basin is unsound. Catch basin is sealed and is structurally sound. Cracks wider than ½ inch and longer than 1 foot at the joint of any inlet/outlet pipe or any evidence of soil particles entering catch basin through cracks. No cracks more than 1/4 inch wide at the joint of inlet/outlet pipe. Settlement/ misalignment Catch basin has settled more than 1 inch or has rotated more than 2 inches out of alignment. Basin replaced or repaired to design standards. Damaged pipe joints Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering the catch basin at the joint of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of inlet/outlet pipes. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Inlet/Outlet Pipe Sediment accumulation Sediment filling 20% or more of the pipe. Inlet/outlet pipes clear of sediment. Trash and debris Trash and debris accumulated in inlet/outlet pipes (includes floatables and non-floatables). No trash or debris in pipes. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 2022 City of Renton Surface Water Design Manual 6/22/2022 A-11 NO. 5 – CATCH BASINS AND MANHOLES MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITION WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Inlet/Outlet Pipe (cont.) Damaged inlet/outlet pipe Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering at the joints of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of the inlet/outlet pipe. Metal Grates (Catch Basins) Unsafe grate opening Grate with opening wider than 7/8 inch. Grate opening meets design standards. Trash and debris Trash and debris that is blocking more than 20% of grate surface. Grate free of trash and debris. Damaged or missing grate Grate missing or broken member(s) of the grate. Any open structure requires urgent maintenance. Grate is in place and meets design standards. Manhole Cover/Lid Cover/lid not in place Cover/lid is missing or only partially in place. Any open structure requires urgent maintenance. Cover/lid protects opening to structure. Locking mechanism not working Mechanism cannot be opened by one maintenance person with proper tools. Bolts cannot be seated. Self-locking cover/lid does not work. Mechanism opens with proper tools. Cover/lid difficult to remove One maintenance person cannot remove cover/lid after applying 80 lbs. of lift. Cover/lid can be removed and reinstalled by one maintenance person. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 6/22/2022 2022 City of Renton Surface Water Design Manual A-12 NO. 6 – CONVEYANCE PIPES AND DITCHES MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Pipes Sediment & debris accumulation Accumulated sediment or debris that exceeds 20% of the diameter of the pipe. Water flows freely through pipes. Vegetation/root growth in pipe Vegetation/roots that reduce free movement of water through pipes. Water flows freely through pipes. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Damage to protective coating or corrosion Protective coating is damaged; rust or corrosion is weakening the structural integrity of any part of pipe. Pipe repaired or replaced. Damaged pipes Any dent that decreases the cross section area of pipe by more than 20% or is determined to have weakened structural integrity of the pipe. Pipe repaired or replaced. Ditches Trash and debris Trash and debris exceeds 1 cubic foot per 1,000 square feet of ditch and slopes. Trash and debris cleared from ditches. Sediment accumulation Accumulated sediment that exceeds 20% of the design depth. Ditch cleaned/flushed of all sediment and debris so that it matches design. Noxious weeds Any noxious or nuisance vegetation which may constitute a hazard to City personnel or the public. Noxious and nuisance vegetation removed according to applicable regulations. No danger of noxious vegetation where City personnel or the public might normally be. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Excessive vegetation growth Vegetation that reduces free movement of water through ditches. Water flows freely through ditches. Erosion damage to slopes Any erosion observed on a ditch slope. Slopes are not eroding. Rock lining out of place or missing (If applicable) One layer or less of rock exists above native soil area 5 square feet or more, any exposed native soil. Replace rocks to design standards.