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Home My WebLink AboutRS_Drainage_Technical_Information_Report_250117_V1.pdfcoterra 6413 Phinney Ave N Seattle, Washington 98103 206.596.7115 TECHNICAL INFORMATION REPORT POST PERMIT REVISION Project: Homestead Willowcrest Townhomes PH II Edmonds Ave NE Renton, WA 98056 Prepared For: Homestead 412 Maynard Ave S #201 Seattle, WA 98104 Prepared By: Henry Stefan, PE Reviewed By: Peter Apostol, PE Date: December 13, 2024 ENGINEERING PLLC TABLE OF CONTENTS Section No. Subject Page No. SECTION I PROJECT OVERVIEW.....................................................................1 SECTION II CONDITIONS AND REQUIREMENTS SUMMARY.....................9 SECTION III OFFSITE ANALYSIS......................................................................12 SECTION IV FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN..........................................18 SECTION V CONVEYANCE SYSTEM ANALYSIS AND DESIGN................23 SECTION VI SPECIAL REPORTS AND STUDIES.............................................23 SECTION VII OTHER PERMITS ...........................................................................23 SECTION VIII EROSION AND SEDIMENT CONTROL ......................................23 SECTION IX BOND QUANTITIES AND DECLARATION OF COVENANTS...............................................24 SECTION X OPERATIONS AND MAINTENANCE MANUAL.......................24 LIST OF FIGURES FIGURE 1 VICINITY MAP.................................................................................4 FIGURE 2 TIR WORKSHEET ............................................................................5 FIGURE 3 EXISTING SITE SOILS.....................................................................6 FIGURE 4 EXISTING LAND COVER ...............................................................7 FIGURE 5 DEVELOPED LAND COVER ..........................................................8 FIGURE 6 OFF-SITE DRAINAGE SYSTEM...................................................16 FIGURE 7 WATER QUALITY TREATMENT AREA ....................................22 LIST OF APPENDICIES APPENDIX A CIVIL PLANS APPENDIX B FLOW CONTROL/DETENTION CALCULATIONS APPENDIX C WATER QUALITY CALCULATIONS APPENDIX D GEOTECHNICAL REPORT APPENDIX E OPERATIONS AND MAINTENANCE APPENDIX F BOND QUANTITIES WORKSHEET (INCLUDED IN FUTURE SUBMITTAL) APPENDIX G CONVEYANCE CALCULATIONS (INCLUDED IN FUTURE SUBMITTAL) APPENDIX H DRAINAGE REVIEW FLOWCHART APPENDIX I DECLARATION OF COVENANTS (INCLUDED IN FUTURE SUBMITTAL) Willowcrest Townhomes Project Phase 2 Page 1 Project No. 21011 Renton, WA Coterra Engineering PLLC SECTION I – PROJECT OVERVIEW General Description: The proposed Homestead Willowcrest Townhomes Project Phase 2 includes the construction of five townhome buildings, consisting of four townhomes each, on a proposed 0.955 acre lot located off of Edmonds Ave NE in the City of Renton (see Figure 1 for vicinity map). The site is bordered by developed parcels to the east (Willowcrest Phase 1 Townhomes), Edmonds Ave NE to the west, and developed parcels to the north and south. The site is proposed to be subdivided for this townhomes project and Edmonds Ave NE frontage improvements. The total area of the project site: the Willowcrest Townhomes Phase 2 lot; and the front improvements total 1.067 acres. The frontage improvements will include construction of new curb, gutter, bioretention planter, and sidewalk. 270 feet of right-of-way will be dedicated along the site’s frontage on Edmonds Ave NE. The proposed project has been designed to meet the requirements of the 2022 City of Renton Surface Water Design Manual (SWDM). A summary of the project data is provided in the TIR worksheet (see Figure 2). Site Soils: The NRCS map (see Figure 3) of the site shows “Ragnar-Indianola” soils located within the project area. Additional information on the site’s soils is provided in a geotechnical report prepared by GeoEngineers, Inc., and dated Nov 18, 2024. The findings of the report are based on soil samples taken from test pits that were excavated on-site. In general, the results of the test pit data uncovered about one foot of topsoil mixed with loose fill underlain by a 2-3.5 foot thick layer of silty sand that was underlain by impermeable glacial till soil. For more information, see the geotechnical report included in Appendix D. Predeveloped Conditions: The existing site consists of vegetation sloping to the west towards Edmonds Ave NE. A steep asphalt driveway accessing Edmonds Ave NE as well as an existing rockery wall ranging from 5’ to 15’. Existing grades on the project site are generally 3% - 10% with stormwater runoff draining overland from east to west towards Edmonds Ave NE. On the west margin of the site, the previously improved street, Edmonds Ave NE, slopes from north to south at approximately 7% slope along the frontage of the project site. The existing land coverage of each section of the project site is presented in the table below. The existing site is presented graphically in Figure 4 which follows this section. The downstream path of stormwater runoff is described in the offsite analysis in Section III. Willowcrest Townhomes Project Phase 2 Page 2 Project No. 21011 Renton, WA Coterra Engineering PLLC Table 1 – Existing Site Land Coverage (Acres) Rooftop (Acres) Cem. Conc. (Acres) Gravel (Acres) ACP (Acres) Pervious (Acres) Total (Acres) Basin A – Project Site - - 0.025 - 0.895 0.920 Basin B – Offsite Improvements - 0.036 0.010 - 0.078 0.124 Developed Conditions: The area of proposed improvements include five townhouse buildings – consisting of three to four connected townhomes in each building; an access drive; residential parking stalls; pedestrian walkways; and associated storm drainage, utility, and landscape improvements. The following table quantifies the areas of the proposed land coverage. The proposed site is presented graphically in Figure 5 which follows this section. Table 2 – Developed Site Land Coverage (Acres) Rooftop (Acres) Cem. Conc. (Acres) Gravel (Acres) ACP (Acres) Grass/ Landscape (Acres) Total (Acres) Basin A – Project Site 0.298 0.213 - 0.161 0.248 0.920 Basin B – Offsite Improvements - 0.0359 - 0.010 0.0781 0.124 The existing site topography will not be dramatically altered in the proposed condition. In general, the site will continue to drain from east to west towards the Edmonds Ave NE right-of-way as it currently does in the existing condition. The proposed improvements within the project site (Basin A) described above and delineated in Table 2 trigger both flow control and water quality mitigation per the City of Renton Surface Water Design Manual. Stormwater runoff will be collected by roof drains, catch basins, and area drains. Per Core Requirement #4 of the 2017 City of Renton Surface Water Design Manual, the proposed conveyance system will be designed to convey runoff resulting from the peak rates resulting from the 25-year storm event. The proposed flow control facility is a detention tank located at the west edge of the project site within a Tract, which will discharge to the existing storm drainage main in Edmonds Ave NE to the west. A bioretention planter with vertical concrete walls located at the west – and low end – of the Phase 1 project site will provide water quality treatment to meet the City of Renton’s Enhanced Basic Treatment requirement. Runoff from targeted pollution-generating impervious surfaces will sheet flow or be captured by catch basins and flow into the bioretention planter before entering the detention tank. Willowcrest Townhomes Project Phase 2 Page 3 Project No. 21011 Renton, WA Coterra Engineering PLLC See Section IV for a detailed description of the design of the flow control and water quality facilities. Willowcrest Townhomes Project Phase 2 Page 4 Project No. 21011 Renton, WA Coterra Engineering PLLC FIGURE 1 – VICINITY MAP Willowcrest Townhomes Project Phase 2 Page 5 Project No. 21011 Renton, WA Coterra Engineering PLLC FIGURE 2 CITY OF RENTON TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 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 __________________ __________________ __________________ REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 6/22/2022 2022 City of Renton Surface Water Design Manual 8-A-2 Part 6 SWDM ADJUSTMENT APPROVALS Type (circle one): Standard / Blanket Description: (include conditions in TIR Section 2) ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ Approved Adjustment No. ______________________ Date of Approval: _______________________ Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes / No Start Date: _______________________ Completion Date: _______________________ Describe: _________________________________ _________________________________________ _________________________________________ Re: SWDM Adjustment No. ________________ Part 8 SITE COMMUNITY AND DRAINAGE BASIN Community Plan: ____________________________________________________________________ Special District Overlays: ______________________________________________________________ Drainage Basin: _____________________________________________________________________ Stormwater Requirements: _____________________________________________________________ Part 9 ONSITE AND ADJACENT SENSITIVE AREAS  River/Stream ________________________  Lake ______________________________  Wetlands ____________________________  Closed Depression ____________________  Floodplain ___________________________  Other _______________________________ _______________________________  Steep Slope __________________________  Erosion Hazard _______________________  Landslide Hazard ______________________  Coal Mine Hazard ______________________  Seismic Hazard _______________________  Habitat Protection ______________________  _____________________________________ REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2022 City of Renton Surface Water Design Manual 6/22/2022 Ref 8-A-3 Part 10 SOILS Soil Type ______________________ ______________________ ______________________ ______________________ Slopes ________________________ ________________________ ________________________ ________________________ Erosion Potential _________________________ _________________________ _________________________ _________________________  High Groundwater Table (within 5 feet)  Other ________________________________  Sole Source Aquifer  Seeps/Springs  Additional Sheets Attached Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE  Core 2 – Offsite Analysis_________________  Sensitive/Critical Areas__________________  SEPA________________________________  LID Infeasibility________________________  Other________________________________  _____________________________________ LIMITATION / SITE CONSTRAINT _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________  Additional Sheets Attached Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Threshold Discharge Area: (name or description) Core Requirements (all 9 apply): Discharge at Natural Location Number of Natural Discharge Locations: Offsite Analysis Level: 1 / 2 / 3 dated:__________________ Flow Control (include facility summary sheet) Standard: _______________________________ or Exemption Number: ____________ Conveyance System Spill containment located at: _____________________________ Erosion and Sediment Control / Construction Stormwater Pollution Prevention CSWPP/CESCL/ESC Site Supervisor: _____________________ Contact Phone: _________________________ After Hours Phone: _________________________ Maintenance and Operation Responsibility (circle one): Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Liability Provided: Yes / No 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: 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 _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ Willowcrest Townhomes Project Phase 2 Page 6 Project No. 21011 Renton, WA Coterra Engineering PLLC FIGURE 3 – EXISTING SITE SOIL CONDITIONS co t e r r a 32 1 3 r d A v e n u e S o u t h , S u i t e 4 0 6 Se a t t l e , W a s h i n g t o n 9 8 1 0 4 20 6 . 5 9 6 . 7 1 1 5 c o t e r r a e n g i n e e r i n g . c o m EN G I N E E R I N G P L L C co t e r r a 32 1 3 r d A v e n u e S o u t h , S u i t e 4 0 6 Se a t t l e , W a s h i n g t o n 9 8 1 0 4 20 6 . 5 9 6 . 7 1 1 5 c o t e r r a e n g i n e e r i n g . c o m EN G I N E E R I N G P L L C Willowcrest Townhomes Project Phase 2 Page 9 Project No. 21011 Renton, WA Coterra Engineering PLLC SECTION II – CONDITIONS AND REQUIREMENTS SUMMARY The proposed project is subject to a Full Drainage Review per the 2022 City of Renton Surface Water Design Manual and is therefore subject to all nine core requirements and all six special requirements. These requirements are listed below along with a discussion of their applicability to this project. See Appendix H for drainage review type flow chart. Core Requirements: Req. #1 Discharge at Natural Location: Existing discharge locations will be maintained. Req. #2 Offsite Analysis: See Section III below. Req. #3 Flow Control: The project is required to meet the Peak Rate Flow Control Standard. The proposed improvements within Phase 1 exceed the threshold of 5,000 sf of new and replaced impervious surface, therefore triggering the requirement of a flow control facility and on-site flow control BMPs. A detention tank is proposed to meet the Peak Rate Flow Control Standard requirement. Onsite BMPs are also required as part of the project and are discussed below in Core Requirement #9. For further details see Section IV. Req. #4 Conveyance System: The new conveyance system has been designed to meet and exceed the requirement to convey the 25-year peak flow from the developed site conditions. Req. #5 Erosion and Sediment Control: Construction erosion and sediment control systems shall be implemented per the Temporary Erosion and Sediment Control plan. Willowcrest Townhomes Project Phase 2 Page 10 Project No. 21011 Renton, WA Coterra Engineering PLLC Req. #6 Maintenance and Operations: A Declaration of Covenant is required for this project and will be submitted for review by City of Renton staff before recording. The proposed facilities will be owned and maintained by Homestead. Req. #7 Financial Guarantees: A financial guarantee will be necessary for this project. Bonding will be required for the construction of improvements and will be obtained prior to construction. Req. #8 Water Quality: The proposed improvements located on the project site exceed 5,000 sf of new and replaced Pollution-Generating Impervious Surface (PGIS), therefore triggering the requirement of a water quality facility. Based on the proposed site usage, multi-family housing, Enhanced Basic Water Quality treatment is required per Core Requirement #8 of the 2022 City of Renton Surface Water Design Manual for targeted PGIS. A vertical-walled bioretention planter is proposed to meet the requirements of the Enhanced Basic Water Quality requirement within the SWDM. For further details see Section IV. Req. #9 On-Site BMPs: The proposed improvements exceed the threshold of 5,000 sf of new and replaced impervious surface, therefore triggering the requirements of Core Requirement #9 to implement on-site flow control facilities to the maximum extent feasible. Following the City of Renton SWDM required list method for implementing on- site BMPs to comply with Core Requirement #9, all listed BMPs were determined to be infeasibly for Phase 1 of the proposed project site. Despite infeasibility determinations for listed on-site BMP facilities, the proposed project plans to implement perforated pipe on all roof drain connections from the four proposed townhouse buildings per the recommendation of the City of Renton SWDM. Willowcrest Townhomes Project Phase 2 Page 11 Project No. 21011 Renton, WA Coterra Engineering PLLC Additionally, the project will implement compost-amended topsoil per SWDM requirement for all new and replaced landscape areas to aid surface water drainage. For further details see Section IV. Special Requirements: Req. #1 Area Specific Requirements: No area specific requirements are applicable to this project. Req. #2: Floodplain/Floodway Delineation This project is not adjacent to any floodplains or floodways. Therefore no delineation is necessary. Req. #3 Flood Protection Facilities: This project is not adjacent to any applicable areas and will not affect any applicable facility. Req. #4 Source Controls: This project is a multi-family project and will provide appropriate source controls. Req. #5 Oil Control: No oil control requirements are applicable to this project. Req. #6 Aquifer Protection Area The proposed project is within Zone 2 of the APA. The contractor will be required to obtain imported fill material from a Washington Department of Transportation approved source. There are no open flow control or water quality facilities which will introduce stormwater to ground water given the project soil conditions. Willowcrest Townhomes Project Phase 2 Page 12 Project No. 21011 Renton, WA Coterra Engineering PLLC SECTION III – OFFSITE ANALYSIS Task 1 – Study Area Definition and Maps Maps of the project site and surrounding area were obtained from the King County GIS website. Topographical site information is from the topographical survey for the project. Storm drainage system maps were compiled from City of Renton GIS maps and as-built plans. Aerial images were obtained from Google Earth. Task 2 – Resource Review The City of Renton Public Works Department was contacted regarding the resources listed in section 2.3.1.1 of the 2022 City of Renton Surface Water Design Manual. The following is a summary of the resource review: Adopted Basin Plans o King County Basin Name: East Lake Washington (per King County iMap) Basin Reconnaissance Summary Reports o None completed to our knowledge. Floodplain/Floodway (FEMA) Maps o The site is not within a floodplain or floodway per FEMA mapping. Other Offsite Analysis Reports o Other Offsite Analysis Reports were not available. Environmentally Sensitive Areas Map o There are no Environmentally Sensitive areas mapped within the vicinity of the site. USDA Soils Survey o A geotech report has been completed and site soils are primarily silty sand that was underlain by impermeable glacial till soil. Wetlands Inventory Maps o There are no Wetlands mapped within the vicinity of the site. Downstream Water Quality Problems Requiring Special Attention o Per Section 1.2.2.1.2 of the SWDM, possible downstream water quality issues that have been identified by the local, state, or federal jurisdiction must be reviewed as part of the Downstream Analysis. Per the EPA’s Clean Water Act, states must identify impaired waterways and identify the pollutants causing impairment. These waterways or waterbodies are listed on what is known as the 303(d) list. The eventual downstream conveyance system for the proposed project site is John’s Willowcrest Townhomes Project Phase 2 Page 13 Project No. 21011 Renton, WA Coterra Engineering PLLC Creek, which outfalls into Lake Washington. The last reaches of John’s Creek are identified by the Washington State Department of Ecology as 303(d) impacted based on the following parameters which are identified as Category 5, which lists the waterbody on the 303(d) list: -Bacteria -Temperature -Dissolved Oxygen The portions of John’s Creek which are identified as 303(d) impacted waterways at the final reaches of John’s Creek as it outfalls to Lake Washington. These sections are beyond ¼ mile from the piped- conveyance system which the proposed project site discharges to in Edmonds Ave NE. o Per Section 1.2.2.3 of the SWDM, based on the criteria listed above for the 303(d) listed waterway(s) for the downstream conveyance from the project site, the following mitigation measures must be considered as part of the proposed project: -Bacteria The proposed project does not drain to a bacteria problem located within one quarter mile/15% distance downstream from the site discharge point; therefore no further mitigation measures are required beyond Core Requirements #1 - #9 and Special Requirements #1 - #6 from the 2017 City of Renton Surface Water Design Manual. The location of the impacted 303(d) waterway was determined from Washington State DOE’s online Water Quality Atlas Mapping system. -Temperature The proposed project does not drain to a temperature problem located within one quarter mile/15% distance downstream from the site discharge point; therefore no further mitigation measures are required beyond Core Requirements #1 - #9 and Special Requirements #1 - #6 from the 2017 City of Renton Surface Water Design Manual. The location of the impacted 303(d) waterway was determined from Washington State DOE’s online Water Quality Atlas Mapping system. -Dissolved Oxygen The proposed project does not drain to a Dissolved Oxygen problem located within one quarter mile/15% distance downstream from the site discharge point; therefore no further mitigation measures are required beyond Core Willowcrest Townhomes Project Phase 2 Page 14 Project No. 21011 Renton, WA Coterra Engineering PLLC Requirements #1 - #9 and Special Requirements #1 - #6 from the 2017 City of Renton Surface Water Design Manual. The location of the impacted 303(d) waterway was determined from Washington State DOE’s online Water Quality Atlas Mapping system. Task 3 – Field Inspection A Level 1 downstream analysis was performed on 12/18/2018. Weather conditions during the downstream analysis consisted of overcast skies. Periodic rainfall occurred in the week prior to the analysis. On-site landuse and topography was confirmed, and the downstream conveyance was identified. This section is complemented by the information found in Figure 6 and the Off-site Analysis Drainage System Table which follow this section. Stormwater runoff originating from the project site sheet flows to the west across the adjacent undeveloped parcel which is primarily vacant and heavily vegetated. Grades within this parcel slope to the west at approximately 10%-15%. Sheet flow patterns persist in a westerly direction until flowing onto Edmonds Ave NE. A piped conveyance system in Edmonds Ave NE collects runoff from the project site and conveys flows to the south. Due to heavy traffic conditions, the piped conveyance system was not inspected. Based on review of City of Renton GIS Utility Mapping, the piped conveyance continues to the south in Edmonds Ave NE to NE Sunset Blvd, where larger diameter conveyance piping flows west towards Lake Washington beyond ¼ mile downstream from the site. No open drainage complaints are associated with the downstream conveyance system. Task 4 – Drainage System Description and Problem Description There are no known problems with the downstream system. Task 5 – Mitigation of Existing or Potential Problems Based on the observations made during the field inspection and the requirements for the design of the proposed drainage systems, no negative impacts to the systems downstream of the project site are anticipated. Existing Upslope Drainage Areas Portions of the adjacent property to the east – the previously developed Glennwood Townhomes drain to the west based on topography to the proposed Phase 1 project site. The areas of the adjacent off-site, upstream area that drains to the Willowcrest site are fully-established pervious landscape areas or previously undeveloped pervious areas. Based on on-site observations during the Offsite Analysis, no upstream run-on was observed. Based on current landcover, site layout, and grading, minimal offsite run-on is expected onto the Willowcrest site. Willowcrest Townhomes Project Phase 2 Page 15 Project No. 21011 Renton, WA Coterra Engineering PLLC To mitigate any upstream overland or subsurface run-on, a perforated interreceptor storm drain line is proposed at the eastern project margin of the Phase 1 property to collect any upstream flows from the Glennwood Townhomes site and route it around the proposed project improvements on the Willowcrest site. The proposed upstream drainage collection system – consisting of a French drain – and tightline routing is intended to maintain the existing drainage patterns of any upstream runoff from the adjacent property and convey it to the existing municipal storm drainage system in Edmonds Ave NE. 18" SD 18" SD 24" SD 24"SD 2 4" S D 3 0" S D 30"SD 36"SD 3 6 "S D 3 6 "S D 3 6 "S D 3 6 "S D 36"SD CB (TYP) PROJECT SITE SHALLOW CONCENTRATED SURFACE FLOW PIPED CONVEYANCE CATCH BASIN DIRECTION OF FLOW INDICATED BY ARROW SHEET FLOW co t e r r a 32 1 3 r d A v e n u e S o u t h , S u i t e 4 0 6 Se a t t l e , W a s h i n g t o n 9 8 1 0 4 20 6 . 5 9 6 . 7 1 1 5 c o t e r r a e n g i n e e r i n g . c o m EN G I N E E R I N G P L L C 1/1/05 OFF-SITE ANALYSIS DRAINAGE SYSTEM TABLE SURFACE WATER DESIGN MANUAL, CORE REQUIREMENT #2 Basin: 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 % ¼ ml = 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 Willowcrest Townhomes Project Phase 2 Page 18 Project No. 21011 Renton, WA Coterra Engineering PLLC SECTION IV – FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN Flow Control The project site is located in a Peak Flow Control Standard area per the 2022 City of Renton Surface Water Design Manual. This standard requires that the developed site discharge rates match the existing site conditions discharge rates for the 2-, 10-, and 100- year return periods. The proposed improvements will create more than 2,000 SF of new plus replaced imperious surfaces, therefore the project is required to meet the flow control standard and implement on-site flow control BMPs. Based on the engineer’s on- site visits to the proposed property and analysis of current aerial photography, the existing site conditions within the project site is assumed to be 25% forested land cover and 75% pasture land cover. MGS Flood stormwater modeling program – utilizing a continuous hydrologic model – was implemented to size a detention facility which matched the existing site discharge rates for the 2-, 10-, and 100-year return events. At this preliminary stage of design, a detention vault was sized in MGS Flood to meet the flow control requirement. As the project stormwater design is refined, the type of detention structure on the project may be revised. Based on the MGS Flood analysis, a detention tank was sized to detain Basin A of the proposed project. The proposed detention volume is 3,731 cubic feet. The MGS Flood calculations are included in Appendix B of this report. The proposed detention tank was designed per the City of Renton SWDM requirements including 0.5’ sediment storage (dead storage). Sizing details are shown on the Storm Drainage Plan, sheet 4.0 of the civil plan set, as well as the civil details. On-Site Flow Control BMPs The proposed site is classified as a Small Subdivision Project. Implementation of On- Site Flow Control BMPs is therefore required per Core Requirement #9. On-site BMPs are evaluated for targeted surfaces, per the list from section 1.2.9.3.1 for Small Subdivision Projects in the 2022 City of Renton Surface Water Design Manual. Analysis of feasibility of the on-site BMPs from the SWDM list follow in order per SWDM feasibility determination instructions. Full Dispersion: Infeasible. Per on-site BMP infeasibility criteria in section C.2.1.1, the total area of impervious surfaces plus non-native pervious surfaces on the project site exceed 35% of the total site area. Full Infiltration: Infeasible. Per criteria outlined in section 5.2 of the SWDM, in order for infiltration to be implemented on a site, “The applicant must demonstrate through infiltration testing, soil logs, and the written opinion of a geotechnical professional that sufficient permeable soil exists at the proposed facility location to allow construction of a properly functioning infiltration facility.” Per the SWDM, the Willowcrest Townhomes Project Phase 2 Page 19 Project No. 21011 Renton, WA Coterra Engineering PLLC geotechnical engineer shall obtain soil logs for possible infiltration system locations on the proposed site. Soils collected in on-site test pits per Geotechnical Engineering Services report prepared by GeoEngineers, Inc., dated 11/18/2024, are classified as “SM” or “silty sands, sand – silt mixtures” at the depth of typical on-site infiltration facilities or infiltration BMPs. The report continues, “Based on our analysis, it is our opinion that the on-site native glacial till soils have a very low infiltration capacity.” And finally they conclude, “Due to the density, high fines content, and relative impermeability of the glacial till, infiltration should be assumed to be very low when designing infiltration systems.” Based on the geotechnical engineer analysis of the existing site soils, full infiltration is not feasible. Bioretention: Infeasible For On-Site Flow Control BMPs. Bioretention is proposed to provide water quality treatment on the project site. The bioretention planter has been designed to meet the requirements of Enhanced Basic Water Quality treatment. Due to the very low infiltration capacity of the existing onsite soils, the bioretention planter has been designed utilizing an underdrain as allowed by the SWDM for water quality treatment. But, bioretention with underdrains is not allowed to meet Core Requirement #9, per the SWDM; therefore bioretention is infeasible for on-site flow control BMPs. Permeable Pavement: Infeasible. Per section C2.7, permeable pavement shall not be installed on slopes steeper than 5% for porous asphaltic concrete. Project proposes asphalt paving for access drives. Based on existing topography and proposed site layout, majority of access drive grades exceed 5%. Proposed areas of grading less than 5% in access drive would exceed maximum run-on limit ratio for PGIS of 2:1. Limited Infiltration: Per SWDM section 1.2.9.2.2, which then references section C.2.3 for feasibility of Limited Infiltration, “Where geotechnical evaluation and approval is required for limited infiltration that proposes to discharge towards or is within described setbacks of a steep slope hazard area, erosion hazard area, landslide hazard, or slopes greater than 15%, limited infiltration is considered infeasible and not required.” Existing and proposed grades down gradient from proposed project site exceed 15% grade; therefore, limited infiltration is infeasible. Basic Dispersion: o Splash blocks: Infeasible. Required 50’ vegetated flow path is infeasible based on proposed site design. o Rock pads: Infeasible. Required 50’ vegetated flow path is infeasible based on proposed site design. o Gravel-filled trenches: Infeasible. Per section C.2.4.4, setbacks of at least 10’ from buildings and 5’ from property line are required. Proposed site layout cannot accommodate 25’ flowpath with required setbacks. o Sheet flow: Infeasible. Required 10’ vegetated flow path located on the project property is infeasible based on proposed site design. Other BMPs: Per criteria set forth in section 1.2.9.2.2 of the SWDM, for projects that will result in an impervious surface coverage 45-65% on the buildable portion of the Willowcrest Townhomes Project Phase 2 Page 20 Project No. 21011 Renton, WA Coterra Engineering PLLC site/lot, on-site BMPs must be applied to 50% of target impervious surfaces reduced by 1.5% for each 1% of impervious surface coverage above 45%. The proposed project site developed condition consists of 63% impervious surfaces. Based on the above formula, 23% of the site’s targeted impervious surfaces must be mitigated by onsite BMPs (63%-45%=18%; 18*1.5=27; 50%-27%=23%). Of the 19,689 SF of new impervious surfaces, 4,528 SF are required by the SWDM to be mitigated by onsite BMPs. When the previously listed onsite stormwater BMPs are not feasible, projects shall evaluate the implementation of the following BMPs: o Reduced Impervious Surface Credit: Currently proposed townhome footprints total 20% of proposed Phase I lot. Townhomes have been designed to maximize building lot area for the benefit of providing maximum number of housing units allowed by zoning on this site. Reduced Impervious Surface Credit would decrease size of proposed townhomes and limit the project goals of providing as much low-income housing as possible with the highest site density. To meet BMP area target, proposed townhomes would need to decrease by over 50% of proposed footprint. This is infeasible for this project. o Native Growth Retention Credit: This BMP credit requires retention of existing forested portions of the site at a 3.5 to 1 ratio for credit. To meet BMP target goal, 15,850 SF of site area would need to be retained as native growth. That is over one third of proposed site area and would not make development of site possible to the desired density to meet project goal of providing maximum number of low-incoming housing units. Additionally, this BMP is infeasible due to, “The donor area must not slope more than 15%.” – existing and proposed onsite grades exceed 15%. o Tree Retention Credit: 4 Significant Trees are proposed to be retained as part of the proposed project to meet land use code requirements. These trees are shown on the Tree Retention Plan within the landscape plans. To meet the onsite BMP area target (tree retention credit can only account for up to 25% of required target mitigation area), 11,320 SF of deciduous tree canopy or 5,660 SF of evergreen tree canopy would need to be retained on the project site and within 20’ of ground-level hardscape. Based on proposed site layout to maximize housing units, it is infeasible to meet the onsite BMP target mitigation area requirement with tree retention. Soil Amendment: Feasible. New and replaced pervious surfaces within the project limits will implement soil amendment per the soil quality and depth requirements of section C2.13. Soil amendment will be implemented in all onsite disturbed areas which will be landscape area in the developed condition. See Landscape sheet 3.01 for additional details. Willowcrest Townhomes Project Phase 2 Page 21 Project No. 21011 Renton, WA Coterra Engineering PLLC Despite infeasibility for listed on-site BMPs per the SWDM criteria, perforated pipe connections from roof drain leaders from each of the three proposed buildings, upstream of detention, are proposed. These perforated pipe connections are shown on the current Utility Plan. From the initial geotechnical investigation, it was determined that the subsurface soils on the project site are composed of several feet of fill soil laying over glacial till which inhibits any practical infiltration potential for possible stormwater mitigation on the project site. Therefore, the use of large-scale infiltrative flow control facilities and on-site BMPs are not shown on the current preliminary plans. Water Quality The proposed new and replaced pollution-generating impervious surfaces (PGIS) on the project site trigger the requirement for water quality treatment of targeted surfaces. Per the City of Renton SWDM, the project site is within the Basin Water Quality Area; but the proposed site land use of multi-family housing triggers the Enhanced Basic Water Quality Menu. The proposed project will provide treatment of targeted PGIS as outlined by the Enhanced Basic Water Quality Menu. This will be provided by a single bioretention planter with vertical concrete walls located at the west side of the Phase 1 project area. Runoff from targeted PGIS will generally sheet flow towards the bioretention planter where it will be captured first by a Type 1 catch basin with an outlet pipe fitted with a downturn elbow and discharging onto cobbles to slow the velocity of the tributary flows and provide some measure of pre-treatment to the bioretention facility. The bioretention facility was sized using MGS Flood software to treat a minimum of 91% of the total runoff volume from the tributary targeted surfaces flowing to the facility. The targeted water quality surfaces for the project are shown on Figure 7 which follows. Based on the MGS Flood calculations, a 10’x12’ interior dimension bioretention planter is proposed, with a total of 120 square feet of bottom area. The bioretention cell will have vertical walls constructed from concrete due to the grading limits near the project tract line. The 144 square foot bioretention planter will treat at least 91% of all tributary flows to the facility. 6” of ponding depth is proposed and a 6” underdrain will be installed under the bioretention soil mix because of the poorly-draining soils existing on the site. Sizing calculations are provided in Appendix C. co t e r r a 32 1 3 r d A v e n u e S o u t h , S u i t e 4 0 6 Se a t t l e , W a s h i n g t o n 9 8 1 0 4 20 6 . 5 9 6 . 7 1 1 5 c o t e r r a e n g i n e e r i n g . c o m EN G I N E E R I N G P L L C Willowcrest Townhomes Project Phase 2 Page 23 Project No. 21011 Renton, WA Coterra Engineering PLLC SECTION V – CONVEYANCE SYSTEM DESIGN AND ANALYSIS The new conveyance system has been designed to convey, per SWDM requirements, at least the 25-year peak flow rate from the developed site. Conveyance capacity calculations are included in Appendix G which show that onsite conveyance can accommodate the 100-year peak flow for the full developed site in addition to upstream tributary area. SECTION VI – SPECIAL REPORTS AND STUDIES A geotechnical analysis of the project site was performed and is included in Appendix D. Additionally, specifications are provided by manufacturer to show that the proposed detention tank can accommodate at least H-20 loading per City of Renton comments. SECTION VII – OTHER PERMITS In addition to the PPUD permit, a Civil Construction Permit from the City of Renton is required. SECTION VIII – EROSION AND SEDIMENT CONTROL ESC Measures are being addressed as follows: Clearing Limits: Clearing limits are being delineated by perimeter silt fencing and chain link fencing. Cover Measures: Temporary cover shall be installed if an area is to remain unworked for more than seven days during the dry season (May 1 to September 30) or for more than two consecutive working days during the wet season (October 1 to April 30). Any area to remain unworked for more than 30 days shall be seeded or sodded, unless the City of Renton determines that winter weather makes vegetation establishment infeasible. Perimeter Protection: Perimeter protection will be implemented by silt fencing around the site perimeter where drainage paths require. Traffic Area Stabilization: A stabilized construction entrance will be built for construction traffic. Sediment Retention: Catch basin protection has been provided and is shown on the projects TESC plans. Surface Water Control: Surface water will be collected and conveyed via swales with check dams as necessary. Dust Control: Dust control, if required, will be provided through the limited use of water trucks. Willowcrest Townhomes Project Phase 2 Page 24 Project No. 21011 Renton, WA Coterra Engineering PLLC SECTION IX – BOND QUANTITIES AND DECLARATION OF COVENANTS A bond quantity worksheet for the proposed improvements is included with this submittal. There are three Declaration of Covenants which are required for the proposed project: - one for inspection and maintenance of proposed stormwater facilities - one for the inspection and maintenance of the proposed on-site BMPs. - one for the prohibition on the use of leachable metals on the property. The covenants for inspection and maintenance of stormwater facilities and on-site BMPs are provided as one document as allowed by the City of Renton. A draft version of the required covenants are provided in Appendix I. Covenants must be signed and notarized prior to recording. SECTION X – OPERATIONS AND MAINTENANCE MANUAL An Operation and Maintenance Manual is provided in this submittal in Appendix E. The maintenance of the stormwater facilities will by be performed by Homestead. Appendix A Civil Plans C1.0 NW 1/4, SEC. 9, TWP. 23N, RGE. 5E, W.M. IN COMPLIANCE WITH CITY OF RENTON STANDARDS EDMONDS AVE NE, RENTON, WA WILLOWCREST TOWNHOMES IIcoterra 6413 Phinney Ave North Seattle, Washington 98103 ph 206.596.7115 coterraengineering.com ENGINEERING PLLC WI L L O W C R E S T T O W N H O M E S I I MA S T E R S I T E P L A N R E V I E W PR : LU A : C: ’ ’ ’ C1.1 IN COMPLIANCE WITH CITY OF RENTON STANDARDS EDMONDS AVE NE, RENTON, WA WILLOWCREST TOWNHOMES IIcoterra 6413 Phinney Ave North Seattle, Washington 98103 ph 206.596.7115 coterraengineering.com ENGINEERING PLLC WI L L O W C R E S T T O W N H O M E S I I MA S T E R S I T E P L A N R E V I E W PR : LU A : C: IN COMPLIANCE WITH CITY OF RENTON STANDARDS EDMONDS AVE NE, RENTON, WA WILLOWCREST TOWNHOMES IIcoterra 6413 Phinney Ave North Seattle, Washington 98103 ph 206.596.7115 coterraengineering.com ENGINEERING PLLC WI L L O W C R E S T T O W N H O M E S I I MA S T E R S I T E P L A N R E V I E W PR : LU A : C: C2.0 IN COMPLIANCE WITH CITY OF RENTON STANDARDS EDMONDS AVE NE, RENTON, WA WILLOWCREST TOWNHOMES IIcoterra 6413 Phinney Ave North Seattle, Washington 98103 ph 206.596.7115 coterraengineering.com ENGINEERING PLLC WI L L O W C R E S T T O W N H O M E S I I MA S T E R S I T E P L A N R E V I E W PR : LU A : C: C3.0 IN COMPLIANCE WITH CITY OF RENTON STANDARDS EDMONDS AVE NE, RENTON, WA WILLOWCREST TOWNHOMES IIcoterra 6413 Phinney Ave North Seattle, Washington 98103 ph 206.596.7115 coterraengineering.com ENGINEERING PLLC WI L L O W C R E S T T O W N H O M E S I I MA S T E R S I T E P L A N R E V I E W PR : LU A : C: C3.1 IN COMPLIANCE WITH CITY OF RENTON STANDARDS EDMONDS AVE NE, RENTON, WA WILLOWCREST TOWNHOMES IIcoterra 6413 Phinney Ave North Seattle, Washington 98103 ph 206.596.7115 coterraengineering.com ENGINEERING PLLC WI L L O W C R E S T T O W N H O M E S I I MA S T E R S I T E P L A N R E V I E W PR : LU A : C: C4.0 Appendix B Flow Control/Detention Calculations Basin B - ExistingBasin B - Existing EX CP Basin A - Proposed Basin B - Proposed Basin A - Detention Pipe PR CP Detention Pipe Volume Calculator Blue Indicates Data Entry Cells, the rest are calculated. Storage Volume Provided by Horizontal Pipe of Diameter d Pipe Diameter (d)6.0 ft Pipe Length 300 ft Overflow Elevation:296.00 ft Pond Volume at Overflow (cu ft):8482 Target Volume from MGSFlood:700 Note: Volume is increased by 1 for Elevations Greater than Pipe Diameter Pond Volume Table Because Routing Routine Requires Increasing Pond Volume Circular Section Geometry Read from CircularSections Tab *** Copy Table below to MGSFlood Program Elevation Volume Input Screen elev.Wetted Area storage storage DON'T INCLUDE THE COLUMN HEADINGS! ft y/d s.f.cu.ft.(ac.ft)ELEV (FT)Top Area (Dummy)VOLUME (CU FT) 290.00 0.000 0.000 0 0 290.00 10.0 0.0. 290.20 0.030 0.248 75 0.002 290.20 10.1 74.5. 290.40 0.070 0.871 261 0.006 290.40 10.2 261.4. 290.60 0.100 1.472 442 0.010 290.60 10.3 441.7. 290.80 0.130 2.160 648 0.015 290.80 10.4 648.0. 291.00 0.170 3.186 956 0.022 291.00 10.5 955.8. 291.20 0.200 4.025 1207 0.028 291.20 10.6 1207.4. 291.40 0.230 4.914 1474 0.034 291.40 10.7 1474.2. 291.60 0.270 6.160 1848 0.042 291.60 10.8 1847.9. 291.80 0.300 7.135 2141 0.049 291.80 10.9 2140.6. 292.00 0.330 8.136 2441 0.056 292.00 11.0 2440.8. 292.20 0.370 9.511 2853 0.066 292.20 11.1 2853.4. 292.40 0.400 10.562 3169 0.073 292.40 11.2 3168.7. 292.60 0.430 11.624 3487 0.080 292.60 11.3 3487.3. 292.80 0.470 13.057 3917 0.090 292.80 11.4 3917.2. 293.00 0.500 14.137 4241 0.097 293.00 11.5 4241.2. 293.20 0.530 15.217 4565 0.105 293.20 11.6 4565.2. 293.40 0.570 16.650 4995 0.115 293.40 11.7 4995.0. 293.60 0.600 17.712 5314 0.122 293.60 11.8 5313.6. 293.80 0.630 18.763 5629 0.129 293.80 11.9 5629.0. 294.00 0.670 20.138 6042 0.139 294.00 12.0 6041.5. 294.20 0.700 21.139 6342 0.146 294.20 12.1 6341.8. 294.40 0.730 22.115 6634 0.152 294.40 12.2 6634.4. 294.60 0.770 23.360 7008 0.161 294.60 12.3 7008.1. 294.80 0.800 24.250 7275 0.167 294.80 12.4 7274.9. 295.00 0.830 25.088 7527 0.173 295.00 12.5 7526.5. 295.20 0.870 26.114 7834 0.180 295.20 12.6 7834.3. 295.40 0.900 26.802 8041 0.185 295.40 12.7 8040.6. 295.60 0.930 27.403 8221 0.189 295.60 12.8 8221.0. 295.80 0.970 28.026 8408 0.193 295.80 12.9 8407.8. 296.00 1.000 28.274 8482 0.195 296.00 13.0 8482.3. 12/18/2024 PondPipePH2.xls ————————————————————————————————— MGS FLOOD PROJECT REPORT Program Version: MGSFlood 4.63 Program License Number: 201510001 Project Simulation Performed on: 12/18/2024 11:00 AM Report Generation Date: 12/18/2024 11:00 AM ————————————————————————————————— Input File Name: Willowcrest PH 2- Prelim Sizing - Landuse.fld Project Name: Renton - Willowcrest Phase II Analysis Title: Peak Flow - Detention Comments: ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Full Period of Record Available used for Routing Climatic Region Number: 15 Precipitation Station : 96004005 Puget East 40 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961040 Puget East 40 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 3 HSPF Parameter Region Name : USGS Default ********** Default HSPF Parameters Used (Not Modified by User) *************** ********************** WATERSHED DEFINITION *********************** Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 1.044 1.044 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 1.044 1.044 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 2 ---------- Subbasin : Basin B - Existing ---------- -------Area (Acres) -------- Till Forest 0.224 Till Pasture 0.671 ROADS/FLAT 0.025 ---------------------------------------------- Subbasin Total 0.920 ---------- Subbasin : Basin B - Existing ---------- -------Area (Acres) -------- Till Forest 0.020 Till Pasture 0.059 ROADS/FLAT 0.046 ---------------------------------------------- Subbasin Total 0.124 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 2 ---------- Subbasin : Basin A - Proposed ---------- -------Area (Acres) -------- Till Grass 0.248 ROADS/FLAT 0.672 ---------------------------------------------- Subbasin Total 0.920 ---------- Subbasin : Basin B - Proposed ---------- -------Area (Acres) -------- Till Grass 0.078 ROADS/FLAT 0.046 ---------------------------------------------- Subbasin Total 0.124 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 1 ------------------------------------------ Link Name: EX CP Link Type: Copy Downstream Link: None ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 2 ------------------------------------------ Link Name: Basin A - Detention Pipe Link Type: Structure Downstream Link Name: PR CP User Specified Elevation Volume Table Used Elevation (ft) Pond Volume (cu-ft) 290.00 0. 290.20 75. 290.40 261. 290.60 442. 290.80 648. 291.00 956. 291.20 1207. 291.40 1474. 291.60 1848. 291.80 2141. 292.00 2441. 292.20 2853. 292.40 3169. 292.60 3487. 292.80 3917. 293.00 4241. 293.20 4565. 293.40 4995. 293.60 5314. 293.80 5629. 294.00 6042. 294.20 6342. 294.40 6634. 294.60 7008. 294.80 7275. 295.00 7527. 295.20 7834. 295.40 8041. 295.60 8221. 295.80 8408. 296.00 8482. Hydraulic Conductivity (in/hr) : 0.00 Massmann Regression Used to Estimate Hydralic Gradient Depth to Water Table (ft) : 100.00 Bio-Fouling Potential : Low Maintenance : Average or Better Riser Geometry Riser Structure Type : Circular Riser Diameter (in) : 8.00 Common Length (ft) : 0.000 Riser Crest Elevation : 296.00 ft Hydraulic Structure Geometry Number of Devices: 3 ---Device Number 1 --- Device Type : Circular Orifice Control Elevation (ft) : 290.50 Diameter (in) : 0.86 Orientation : Horizontal Elbow : No ---Device Number 2 --- Device Type : Circular Orifice Control Elevation (ft) : 293.00 Diameter (in) : 1.40 Orientation : Horizontal Elbow : Yes ---Device Number 3 --- Device Type : Circular Orifice Control Elevation (ft) : 294.50 Diameter (in) : 4.00 Orientation : Horizontal Elbow : Yes ------------------------------------------ Link Name: PR CP Link Type: Copy Downstream Link: None **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 2 Number of Links: 1 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 2 Number of Links: 2 ***********Groundwater Recharge Summary ************* Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures Total Predeveloped Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Basin B - Existing 156.800 Subbasin: Basin B - Existing 13.665 Link: EX CP 0.000 _____________________________________ Total: 170.465 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Basin A - Proposed 30.308 Subbasin: Basin B - Proposed 9.545 Link: Basin A - Detention Not Computed Link: PR CP 0.000 _____________________________________ Total: 39.853 Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 1.079 ac-ft/year, Post Developed: 0.252 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 1 ********** Link: EX CP ********** 2-Year Discharge Rate : 0.052 cfs 15-Minute Timestep, Water Quality Treatment Design Discharge On-line Design Discharge Rate (91% Exceedance): 0.02 cfs Off-line Design Discharge Rate (91% Exceedance): 0.01 cfs Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 160.73 Inflow Volume Including PPT-Evap (ac-ft): 160.73 Total Runoff Infiltrated (ac-ft): 0.00, 0.00% Total Runoff Filtered (ac-ft): 0.00, 0.00% Primary Outflow To Downstream System (ac-ft): 160.73 Secondary Outflow To Downstream System (ac-ft): 0.00 Volume Lost to ET (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered+ET)/Total Volume: 0.00% ----------------------SCENARIO: POSTDEVELOPED Number of Links: 2 ********** Link: PR CP ********** 2-Year Discharge Rate : 0.047 cfs 15-Minute Timestep, Water Quality Treatment Design Discharge On-line Design Discharge Rate (91% Exceedance): 0.03 cfs Off-line Design Discharge Rate (91% Exceedance): 0.02 cfs Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 387.67 Inflow Volume Including PPT-Evap (ac-ft): 387.67 Total Runoff Infiltrated (ac-ft): 0.00, 0.00% Total Runoff Filtered (ac-ft): 0.00, 0.00% Primary Outflow To Downstream System (ac-ft): 387.67 Secondary Outflow To Downstream System (ac-ft): 0.00 Volume Lost to ET (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered+ET)/Total Volume: 0.00% ***********Compliance Point Results ************* Scenario Predeveloped Compliance Link: EX CP Scenario Postdeveloped Compliance Link: PR CP *** Point of Compliance Flow Frequency Data *** Recurrence Interval Computed Using Gringorten Plotting Position Predevelopment Runoff Postdevelopment Runoff Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs) ---------------------------------------------------------------------------------------------------------------------- 2-Year 5.164E-02 2-Year 4.736E-02 5-Year 8.178E-02 5-Year 7.153E-02 10-Year 0.113 10-Year 8.836E-02 25-Year 0.188 25-Year 0.108 50-Year 0.270 50-Year 0.118 100-Year 0.331 100-Year 0.127 200-Year 0.336 200-Year 0.222 500-Year 0.340 500-Year 0.349 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals Appendix C Water Quality Calculation ————————————————————————————————— MGS FLOOD PROJECT REPORT Program Version: MGSFlood 4.63 Program License Number: 201510001 Project Simulation Performed on: 12/10/2024 3:16 PM Report Generation Date: 12/10/2024 3:22 PM ————————————————————————————————— Input File Name: Willowcrest - PH 2 WQ Bioretention.fld Project Name: Renton Homestead - Willowcrest Townhomes Analysis Title: Water Quality - Bioretention Cell - PH2 Comments: ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Full Period of Record Available used for Routing Climatic Region Number: 15 Precipitation Station : 96004005 Puget East 40 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961040 Puget East 40 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 3 HSPF Parameter Region Name : USGS Default ********** Default HSPF Parameters Used (Not Modified by User) *************** ********************** WATERSHED DEFINITION *********************** Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 0.331 0.328 Area of Links that Include Precip/Evap (acres) 0.000 0.003 Total (acres) 0.331 0.331 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : WQ BASIN ---------- -------Area (Acres) -------- ROADS/FLAT 0.331 ---------------------------------------------- Subbasin Total 0.331 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : PH 2 WQ BASIN ---------- -------Area (Acres) -------- ROADS/FLAT 0.328 ---------------------------------------------- Subbasin Total 0.328 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ------------------------------------------ Link Name: New Ecy Bio Lnk1 Link Type: Ecology Bioretention Facility Downstream Link: None Floor Elevation (ft) : 100.00 Riser Crest Elevation (ft) : 101.00 Storage Depth (ft) : 1.00 Bottom Length (ft) : 10.0 Bottom Width (ft) : 12.0 Bottom Slope (ft/ft) : 0.000 Side Slopes (ft/ft) : Z1= 0.00 Z2= 0.00 Z3= 0.00 Z4= 0.00 Bottom Area (sq-ft) : 120. Area at Riser Crest El (sq-ft) : 120. (acres) : 0.003 Volume at Riser Crest (cu-ft): 120. (ac-ft) : 0.003 Infiltration on Bottom only Selected Soil Properties Layer No Soil Name Thickness (ft) 1 ASTM 100 0.250 2 SMMWW 12 in/hr (Ecol 1.500 3 GRAVEL 1.500 KSat Safety Factor: None Native Soil Infiltration Rate (in/hr) : 0.00 Underdrain Present Underdrain Offset (in): : 6.00 Orifice Diameter (in) : 4.000 Riser Geometry Riser Structure Type : Circular Riser Diameter (in) : 6.00 Common Length (ft) : 0.000 Riser Crest Elevation : 101.00 ft Hydraulic Structure Geometry Number of Devices: 0 **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 Number of Links: 1 ********** Link: New Ecy Bio Lnk1 ********** Link WSEL Stats WSEL Frequency Data(ft) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) WSEL Peak (ft) ====================================== 1.05-Year 100.656 1.11-Year 100.820 1.25-Year 100.981 2.00-Year 101.041 3.33-Year 101.056 5-Year 101.065 10-Year 101.077 25-Year 101.100 50-Year 101.121 100-Year 101.142 ***********Groundwater Recharge Summary ************* Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures Total Predeveloped Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: WQ BASIN 0.000 _____________________________________ Total: 0.000 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: PH 2 WQ BASIN 0.000 Link: New Ecy Bio Lnk1 0.000 _____________________________________ Total: 0.000 Total Predevelopment Recharge Equals Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 0.000 ac-ft/year, Post Developed: 0.000 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ********** Link: New Ecy Bio Lnk1 ********** Basic Wet Pond Volume (91% Exceedance): 1453. cu-ft Computed Large Wet Pond Volume, 1.5*Basic Volume: 2179. cu-ft 2-Year Discharge Rate : 0.107 cfs 15-Minute Timestep, Water Quality Treatment Design Discharge On-line Design Discharge Rate (91% Exceedance): 0.05 cfs Off-line Design Discharge Rate (91% Exceedance): 0.03 cfs Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 147.06 Inflow Volume Including PPT-Evap (ac-ft): 147.53 Total Runoff Infiltrated (ac-ft): 0.00, 0.00% Total Runoff Filtered (ac-ft): 146.25, 99.13% Primary Outflow To Downstream System (ac-ft): 147.06 Secondary Outflow To Downstream System (ac-ft): 0.00 Volume Lost to ET (ac-ft): 0.47 Percent Treated (Infiltrated+Filtered+ET)/Total Volume: 99.45% ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: WQ BASIN Scenario Postdeveloped Compliance Link: New Ecy Bio Lnk1 *** Point of Compliance Flow Frequency Data *** Recurrence Interval Computed Using Gringorten Plotting Position Predevelopment Runoff Postdevelopment Runoff Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs) ---------------------------------------------------------------------------------------------------------------------- 2-Year 0.123 2-Year 0.107 5-Year 0.160 5-Year 0.150 10-Year 0.180 10-Year 0.173 25-Year 0.227 25-Year 0.223 50-Year 0.289 50-Year 0.270 100-Year 0.334 100-Year 0.310 200-Year 0.346 200-Year 0.342 500-Year 0.362 500-Year 0.384 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals Appendix D Geotechnical Report Geotechnical Engineering Services Willowcrest Townhomes Phase II Renton, Washington for Homestead Community Land Trust November 18, 2024 17425 NE Union Hill Road, Suite 250 Redmond, Washington 98052 425.861.6000 Geotechnical Engineering Services Willowcrest Townhomes Phase II Renton, Washington File No. 23656-001-01 November 18, 2024 Prepared for: Homestead Community Land Trust 412 Maynard Avenue South, Suite 201 Seattle, Washington 98104 Attention: Eric Pravitz Prepared by: GeoEngineers, Inc. 17425 NE Union Hill Road, Suite 250 Redmond, Washington 98052 425.861.6000 Colton W. McInelly, PE Senior Geotechnical Engineer Robert C. Metcalfe, PE, LEG Principal CWM:RCM:tlm:atk Disclaimer: Any electronic form, facsimile, or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record. Homestead Community Land Trust | November 18, 2024 i File No. 23656-001-01 Table of Contents 1.0 Introduction .................................................................................................................. 1 1.1 Project Description ........................................................................................................................ 1 1.2 Purpose and Scope ....................................................................................................................... 1 2.0 Field Explorations and Laboratory Testing ...................................................................... 1 2.1 Explorations ................................................................................................................................... 1 2.2 Laboratory Testing ........................................................................................................................ 1 2.3 Previous Explorations ................................................................................................................... 2 3.0 Site Description ............................................................................................................ 2 3.1 Surface Conditions........................................................................................................................ 2 3.2 Site Geology .................................................................................................................................. 2 3.3 Geologic Hazards .......................................................................................................................... 3 3.4 Subsurface Conditions ................................................................................................................. 3 3.4.1 Soil Conditions ................................................................................................................... 3 3.4.2 Groundwater Conditions ................................................................................................... 3 4.0 Conclusions and Recommendations .............................................................................. 4 4.1 Environmentally Critical Areas ..................................................................................................... 4 4.1.1 Landslide Hazard ECA ....................................................................................................... 5 4.1.2 Regulated (Steep) Slope Hazard ECA ............................................................................... 5 4.1.3 Alterations to ECAs ............................................................................................................ 5 4.2 Earthquake Engineering ............................................................................................................... 6 4.2.1 Seismicity ........................................................................................................................... 6 4.2.2 2021 IBC Seismic Design Information ............................................................................. 7 4.2.3 Liquefaction Potential ....................................................................................................... 7 4.2.4 Ground Rupture ................................................................................................................. 7 4.2.5 Landslides .......................................................................................................................... 7 4.3 Temporary Dewatering ................................................................................................................. 8 4.4 Excavation Support ....................................................................................................................... 8 4.4.1 Excavation Considerations ................................................................................................ 9 4.4.2 Temporary Cut Slopes ....................................................................................................... 9 4.4.3 Soldier Pile and Tieback Walls ........................................................................................ 10 4.4.4 Soil Nail Walls .................................................................................................................. 12 4.4.5 Shoring Wall Performance .............................................................................................. 15 4.5 Shallow Foundations .................................................................................................................. 15 4.5.1 Allowable Bearing Pressures .......................................................................................... 16 4.5.2 Settlement ....................................................................................................................... 16 4.5.3 Lateral Resistance ........................................................................................................... 17 4.5.4 Footing Drains ................................................................................................................. 17 4.5.5 Construction Considerations .......................................................................................... 17 Homestead Community Land Trust | November 18, 2024 ii 4.6 Slab-on-Grade Floors .................................................................................................................. 18 4.6.1 Subgrade Preparation ..................................................................................................... 18 4.6.2 Design Parameters .......................................................................................................... 18 4.6.3 Underslab Drainage ......................................................................................................... 18 4.7 Below-Grade Walls and Retaining Walls .................................................................................... 19 4.7.1 Permanent Subsurface Walls Against Temporary Shoring ........................................... 19 4.7.2 Other Cast-in-Place Walls ................................................................................................ 19 4.7.3 Wall Drainage .................................................................................................................. 20 4.8 Earthwork .................................................................................................................................... 21 4.8.1 Clearing and Site Preparation ......................................................................................... 21 4.8.2 Earthwork Subgrade Preparation ................................................................................... 22 4.8.3 Structural Fill.................................................................................................................... 22 4.8.4 Fill Placement and Compaction Criteria ......................................................................... 23 4.8.5 Weather Considerations ................................................................................................. 24 4.8.6 Utility Trenches ................................................................................................................ 25 4.8.7 Pavement Subgrade Preparation ................................................................................... 25 4.8.8 Permanent Slopes ........................................................................................................... 25 4.8.9 Sedimentation and Erosion Control ............................................................................... 26 4.9 Pavement Recommendations .................................................................................................... 26 4.9.1 Subgrade Preparation ..................................................................................................... 26 4.9.2 New Hot-Mix Asphalt Pavement ..................................................................................... 26 4.9.3 Portland Cement Concrete Pavement ............................................................................ 27 4.10 Drainage Considerations ............................................................................................................ 27 4.11 Infiltration Considerations .......................................................................................................... 27 5.0 Recommended Additional Geotechnical Services ......................................................... 28 6.0 Limitations .................................................................................................................. 28 7.0 References .................................................................................................................. 29 List of Figures Figure 1. Vicinity Map Figure 2. Site Plan Figure 3. Earth Pressure Diagrams – Temporary Soldier Pile & Tieback Wall Figure 4. Recommended Surcharge Pressure Figure 5. Wall Drainage and Backfill Figure 6. Compaction Criteria for Trench Backfill File No. 23656-001-01 Homestead Community Land Trust | November 18, 2024 iii File No. 23656-001-01 Appendices Appendix A. Field Explorations Figure A-1 – Key to Exploration Logs Figures A-2 through A-7 – Logs of Test Pits Appendix B. Laboratory Testing Figure B-1 – Sieve Analysis Results Appendix C. Exploration Logs from Previous Studies Appendix D. Ground Anchor Load Tests and Shoring Monitoring Program Appendix E. Report Limitations and Guidelines for Use Homestead Community Land Trust | November 18, 2024 Page 1 File No. 23656-001-01 1.0 Introduction This geotechnical engineering report presents the results of GeoEngineers, Inc.’s (GeoEngineers’) geotechnical engineering services to support design and construction of the Willowcrest Townhomes Phase II project located in Renton, Washington. The proposed project site is shown relative to surrounding physical features in Figure 1, Vicinity Map and Figure 2, Site Plan. 1.1 PROJECT DESCRIPTION GeoEngineers previously provided geotechnical engineering services during design and construction for Phase I of the project, which is located directly east of Phase II. Our understanding of Phase II is based on conversations with, and information provided by Caitlyn Salters with Third Place Design Co-operative Inc. We understand the project consists of constructing five 3- to 4-unit wood-frame townhomes (Buildings A through E) that will be three stories in height. Buildings A through C will be constructed close to existing grades, while Buildings D and E may be cut into the hillside and may be below-grade on the east side and daylight on the west side of the buildings. A large retaining wall will replace the existing rockery on the west side of the site along Edmonds Avenue NE, and a retaining wall may be required along the north/northeast side of the site. Associated improvements include a subsurface stormwater detention facility near the southwest corner of the site, new underground utilities and access drive, sidewalks, parking area and landscaping. 1.2 PURPOSE AND SCOPE The purpose of our services is to evaluate soil and groundwater conditions as a basis for developing design criteria for the geotechnical aspects of the project. Field explorations and laboratory testing were performed to characterize subsurface conditions and to develop engineering recommendations for use in the design of the project. Our services were performed in general accordance with our proposal dated October 11, 2024. 2.0 Field Explorations and Laboratory Testing 2.1 EXPLORATIONS The subsurface soil and groundwater conditions were evaluated through a field exploration program that consisted of excavating and sampling six test pits (GEI-TP-7 through GEI-TP-12). The test pits were completed using a small track-mounted excavator at the approximate locations shown in Figure 2. The test pits were excavated to depths ranging from 7½ to 10½ feet below the ground surface (bgs). Locations of the test pits were determined in the field by measuring from physical features on site to the test pit locations. Test pits GEI-TP-1 through GEI-TP-6 were completed during Phase 1. Appendix A includes the logs of the test pits and details of the subsurface exploration program. 2.2 LABORATORY TESTING Soil samples obtained from the test pits were transported to our laboratory and evaluated to confirm or modify field classifications, as well as to evaluate engineering properties of the soil. Representative samples were selected for laboratory testing consisting of moisture content and grain size distribution (sieve analysis). The tests were performed in general accordance with test methods of the American Society for Testing and Materials (ASTM) and other applicable procedures. A description of the laboratory testing and the test results are presented in Appendix B. Homestead Community Land Trust | November 18, 2024 Page 2 File No. 23656-001-01 2.3 PREVIOUS EXPLORATIONS GeoEngineers previously provided geotechnical engineering services during Phase I of the project, which included completing six test pits (GEI-TP-1 through GEI-TP-6) in the Phase I area. Additionally, test pits and borings were completed by others in the Phase I and Phase II areas. The logs of selected explorations from these previous studies were reviewed. Logs of relevant explorations reviewed for this study are presented in Appendix C and the approximate locations of the previous explorations are shown in Figure 2. 3.0 Site Description 3.1 SURFACE CONDITIONS The subject property is approximately 0.92 acres and consists of one King County Parcel (number 943280-0130). The site is currently occupied by a gravel surfaced parking/storage area near the middle and a driveway off Edmonds Avenue NE that leads up to the gravel surfaced parking/storage area. The remainder of the site is vegetated with medium to large deciduous and coniferous trees, blackberry bushes, shrubs, ivy and other brush and grasses. Steep slopes are mapped by the City of Renton on the west side of the parcel and are associated with a cut slope used to construct Edmonds Avenue NE. A rockery was built along the cut slope. Site grades descend moderately to the west/southwest from about Elevation 330 feet on the east side to about Elevation 315 to 320 feet on the west side. Slope inclinations become steeper near the west property line as they approach the rockery along the east side of the street. The rockery is generally about 10 feet tall and borders the entire west side of the site, except near the driveway entrance. Underground utilities consisting of storm drain and sanitary sewer associated with the Phase I townhome development exist on the east side and in a 15-foot-wide sewer easement on the southern border of the site. Power, gas, water, sewer and storm utilities are located under Edmonds Avenue NE. 3.2 SITE GEOLOGY Published geologic information for the project vicinity includes a United States Geological Survey (USGS) map of Seattle and the surrounding area (Mullineaux et al. 1961). Mapped units in the immediate project vicinity consist of glacially consolidated Vashon Till deposits (glacial till). Recessional outwash is mapped west of the site. ■ Glacial till is generally a non-sorted, non-stratified mixture of sand, gravel and silt that has been overridden by over a thousand feet of ice. It typically has high shear strength, low consolidation and low permeability characteristics in the undisturbed state. It typically develops a “weathered” zone where seasonal groundwater perches on top of the relatively unweathered till and the perched groundwater occurs as seepage following the site topography. ■ Recessional outwash is predominantly composed of stratified sand and gravel that was deposited in meltwater streams that emanated from the terminus of the Vashon glacier as it receded northward. It typically has low shear strength and moderate to high permeability characteristics. Homestead Community Land Trust | November 18, 2024 Page 3 File No. 23656-001-01 Subsurface conditions encountered in the recent and existing explorations completed at the site are consistent with the mapped glacial till unit. 3.3 GEOLOGIC HAZARDS Our assessment of the geologic hazards at the site includes reviewing the environmentally critical area (ECA) geographic information system (GIS) maps defined by the City of Renton and King County. These maps identify the site for ECAs. The City of Renton identifies landslide and regulated slope hazards along the west side of the site. King County does not identify any ECAs at the site. Further discussion on these ECAs is presented in Section 4.1. 3.4 SUBSURFACE CONDITIONS 3.4.1 Soil Conditions GeoEngineers’ understanding of the subsurface soil conditions is based on review of existing geotechnical data as well as the results of our recent test pits. Figure 2 shows the approximate locations of the existing and recent explorations completed at and within the vicinity of the site. The general subsurface conditions consist of topsoil and fill overlying native glacial till. The subsurface conditions are summarized below: ■ Topsoil/Sod about ½ to 1½ feet thick was observed in most of the explorations and consists of silty sand with roots. ■ Fill was encountered below the topsoil or ground surface in test pits GEI-TP-9, -10, and -12 and extends to approximately 2 to 5 feet below the ground surface. The fill is loose to medium dense and generally consists of silty sand with gravel and variable organic content. Fill observed at the surface of test pit GEI-TP-10 consists of gravel with silt and sand and is associated with the gravel surfaced parking/storage area in that area of the site. Construction debris (concrete, fabric and plastic) as well as scattered organics were observed within the fill. ■ Weathered Glacial Till generally consisting of loose to dense silty sand with variable gravel content was observed within most of the explorations. The weathered glacial till ranges from about 1½ to 6½ feet thick and it is often difficult to distinguish the looser weathered glacial till from the overlying fill. ■ Glacial Till was observed below the fill/weathered glacial till and extends to the depths explored in the explorations. The glacial till is relatively unweathered and generally consists of dense to very dense silty sand with variable gravel content and very stiff to hard silt with variable sand content. The top of the glacial till was observed at depths ranging from 2½ to 8 feet below existing site grades. Cobbles and boulders were observed in some of the explorations and are commonly present in glacial deposits. 3.4.2 Groundwater Conditions Regional groundwater was not encountered in the explorations; however, shallow groundwater seepage interpreted as perched groundwater was observed in several of the explorations at various depths. Based on our experience in the project vicinity, the regional groundwater table is much deeper than planned excavations for the project and therefore will not be encountered. However, perched groundwater and seepage zones should be expected in the fill, weathered glacial till and relatively permeable layers of the glacial till and perched above the relatively unweathered glacial till. Homestead Community Land Trust | November 18, 2024 Page 4 File No. 23656-001-01 4.0 Conclusions and Recommendations Based on the results of our review, our recently completed explorations and our experience on similar projects, we conclude that the proposed development can be constructed satisfactorily as planned with respect to geotechnical engineering elements. A summary of the key geotechnical considerations is provided below. The summary is presented for introductory purposes only and should be used in conjunction with the complete recommendations presented in this report. ■ The west side of the site is mapped as steep slope and potential slide area ECAs based on the City of Renton GIS maps accessed online. There are development restrictions associated with these ECAs; however, an exemption should be allowed as the ECAs are associated with past legal grading activities during the construction of Edmonds Avenue NE. ■ The site is classified as Site Class C in accordance with the 2021 International Building Code (IBC). ■ Temporary excavations may employ temporary cut slopes or shoring consisting of soldier piles with wood lagging or soil nail walls. ■ Shallow foundations can be constructed on the glacial till. A maximum allowable bearing pressure of 6,000 pounds per square foot (psf) may be used for footings bearing on native undisturbed dense to very dense/very stiff to hard glacial till. An allowable bearing pressure of 3,000 psf may be used for footings bearing on native undisturbed medium dense to dense weathered glacial till or where structural fill is placed below footings, if needed, that extend to undisturbed and suitable medium dense to dense glacial till. Existing fill, highly weathered glacial till or otherwise unsuitable soils should be removed from below foundations and floor slabs prior to constructing foundations or placing structural fill. ■ Conventional slabs-on-grade are considered appropriate and should be underlain by a 4-inch-thick layer of capillary break consisting of clean crushed rock with negligible fines and sand content. ■ Below-grade walls and retaining structures should be evaluated using an equivalent fluid density of 35 pounds per cubic foot (pcf) provided there is a horizontal surface behind the top of the walls and that the walls will not be restrained against rotation when backfill is placed behind them. If the walls will be restrained from rotation, we recommend using an equivalent fluid density of 55 pcf. ■ The on-site soils generally contain a high percentage of fines (silt and clay) ranging generally from 25 to 35 percent based on laboratory tests and are highly moisture sensitive. Therefore, reuse of on-site soils should only be planned in the normal dry season (June through September). ■ We anticipate long-term design infiltration rates will be less than 0.2 inches per hour within the native glacial till. On-site pilot infiltration testing will be needed if infiltration facilities are being considered as part of the project. 4.1 ENVIRONMENTALLY CRITICAL AREAS Based on our review of the City of Renton and King County ECA GIS maps, the City of Renton identifies landslide and regulated slope hazards on the west edge of the site. No ECAs were shown on the King County maps. Homestead Community Land Trust | November 18, 2024 Page 5 File No. 23656-001-01 4.1.1 Landslide Hazard ECA The City of Renton categorizes landslide hazards into unclassified, moderate, high and very high landslide hazards. Based on the City of Renton GIS map, the west/southwest side of the site are identified as moderate and high landslide hazards. According to RMC 4-3-050G.5.b: ■ Moderate landslide hazards are “areas with slopes between fifteen percent and forty percent and underlain by soils that consist largely of sand, gravel or glacial till.” ■ High landslide hazards are “areas with slopes greater than forty percent, and areas with slopes between fifteen percent and forty percent and underlain by soils consisting largely of silt and clay.” Per RMC 4-3-050.G.2, moderate and high landslide hazards do not have a critical area buffer and there is no structure setback required beyond the buffer. However, the critical area buffer is “based upon the results of a geotechnical report and/or independent review, conditions of approval for developments may include buffers and/or setbacks from buffers” and the structure setback beyond the buffer is subject to “the adopted building code or Building Official.” 4.1.2 Regulated (Steep) Slope Hazard ECA The City of Renton categorizes regulated (steep) slope hazards into sensitive and protected slope types. Based on the City of Renton GIS map, the west edge of the site is identified as sensitive and protected slopes. According to RMC 4-3-050G.5.a: ■ Sensitive slopes are defined as “a hillside or portion thereof characterized by: (a) an average slope of twenty five percent to less than forty percent as identified by the City of Renton Steep Slope Atlas or in a method approved by the City; or (b) an average slope of forty percent or greater with vertical rise of less than fifteen feet as identified in the City of Renton Steep Slope Atlas or in a method approved by the City; (c) abutting an average slope of twenty five percent to forty percent as identified in the City of Renton Steep Slope Atlas or in a method approved by the City.” ■ Protected slopes are defined as “a hillside or portion thereof characterized by an average slope of forty percent or greater grade having a minimum vertical rise of fifteen feet as identified in the City of Renton Steep Slope Atlas or in a method approved by the City.” Per RMC 4-3-050G.2, sensitive and protected slopes do not have a critical area buffer associated with them. Sensitive slopes do not have a structure setback required beyond the buffer, while protected slopes have a 15-foot structure setback required beyond the buffer. However, the critical area buffer is “based upon the results of a geotechnical report and/or independent review, conditions of approval for developments may include buffers and/or setbacks from buffers” and the structure setback beyond the buffer is subject to “the adopted building code or Building Official.” 4.1.3 Alterations to ECAs Per RMC 4-3-050J.1.a.i, an applicant may request the administrator grant a modification to allow “regrading of any slope which was created through previous mineral and natural resource recovery activities or was created prior to adoption of applicable mineral and natural resource recover regulations or through public or private road installation or widening and related transportation improvements, railroad track installation or improvement, or public or private utility installation activities.” Homestead Community Land Trust | November 18, 2024 Page 6 File No. 23656-001-01 Based on our review of the ECA map and our understanding of the site, construction of Edmonds Avenue NE roadway created cut slope conditions along the east side of the road (west side of the site) in which rockeries were used to face the steep cut slope. Based on just mapping tools, the cut for the roadway and existing rockery can be interpreted as landslide hazard/steep slope conditions, although this was a permitted man-made cut slope. Therefore, the existing rockeries along the east side of Edmonds Avenue NE that border the west side of the project were designed and permitted through the City of Renton as part of the roadway extension. Subsurface conditions present across the site consist of shallow fill underlain by competent glacial till. The roadway extension (cut) likely removed fill soils during construction such that the rockery was excavated in competent glacial till. In our opinion, the mapped steep slope is a permitted man-made stable cut and is likely a very low landslide hazard risk. Provided that the contractor completing the construction work uses construction practices consistent with local and state regulations, and the recommendations provided in this report, GeoEngineers takes no exception to the planned work along the west edge of the site as they relate to encroaching within the mapped landslide hazard and regulated (steep) slope hazard ECAs. GeoEngineers should be on site during construction to provide construction observation services during earthwork activities. 4.2 EARTHQUAKE ENGINEERING 4.2.1 Seismicity The Puget Sound area is located near the convergent continental boundary known as the Cascadia Subduction Zone (CSZ), which extends from mid-Vancouver Island to Northern California. The CSZ is the zone where the westward advancing North American Plate is overriding the subducting Juan de Fuca Plate. The interaction of these two plates results in two potential seismic source zones: (1) the Benioff source zone and (2) the CSZ interplate source zone. A third seismic source zone, referred to as the shallow crustal source zone, is associated with the north-south compression resulting from northerly movement of the Sierra Nevada block of the North American Plate. Shallow crustal earthquakes occur within the North American Plate to depths up to 15 miles. Shallow earthquakes in the Puget Sound region are expected to have durations ranging up to 60 seconds. Four magnitude 7 or greater-known shallow crustal earthquakes have occurred in the last 1,100 years in the Cascadia region; two of these occurred on Vancouver Island and two in Western Washington. The southeast end of the east-west trending Seattle fault zone is mapped approximately 1½ miles north of the site. The Benioff zone is characterized as being capable of generating earthquakes up to magnitude (M) 7.5. The Olympia 1949 (M = 7.1), the Seattle 1965 (M = 6.5) and the Nisqually 2001 (M = 6.8) earthquakes are considered to be Benioff zone earthquakes. The recurrence interval for large earthquakes originating from the Benioff source zone is believed to be shorter than for the shallow crustal and CSZ source zones; on average, damaging Benioff zone earthquakes in Western Washington occur every 30 years or so. The CSZ is considered as being capable of generating earthquakes of magnitudes 8 to 9. No earthquakes on the CSZ have been instrumentally recorded; however, through the geologic record and historical records of tsunamis in Japan, it is believed that the most recent CSZ event occurred in the year 1700. Recurrence intervals for CSZ interplate earthquakes are thought to be on the order of 400 to 600 years. Homestead Community Land Trust | November 18, 2024 Page 7 File No. 23656-001-01 4.2.2 2021 IBC Seismic Design Information For the site, we recommend the 2021 IBC parameters for Site Class C, mapped risk-targeted maximum-considered earthquake (MCER) spectral response acceleration at short period (Ss), mapped MCER spectral response acceleration at 1-second period (S1), short period site coefficient (Fa), long period site coefficient (Fv), design spectral acceleration at 0.2-second period (SDS) and the design spectral acceleration at 1.0-second period (SD1). Table 1 summarizes recommended values for these parameters. TABLE 1. 2021 IBC SEISMIC PARAMETERS 2018 IBC PARAMETER1 RECOMMENDED VALUE Site Class C Mapped MCER Spectral Response Acceleration at Short Period, Ss (g) 1.432 Mapped MCER Spectral Response Acceleration at 1-second period, S1 (g) 0.49 Short Period Site Coefficient, Fa 1.2 Long Period Site Coefficient, Fv 1.5 Design Spectral Acceleration at 0.2-second period, SDS (g) 1.146 Design Spectral Acceleration at 1.0-second period, SD1 (g) 0.49 Notes: 1 Parameters developed based on latitude 47.5019 and longitude -122.1851 using the Applied Technology Council (ATC) Hazards online tool (https://hazards.atcouncil.org/). 4.2.3 Liquefaction Potential Liquefaction is a phenomenon where soils experience a rapid loss of internal strength as a consequence of strong ground shaking. Ground settlement, lateral spreading and/or sand boils may result from soil liquefaction. Structures supported on liquefied soils could suffer foundation settlement or lateral movement that could be severely damaging to the structures. Conditions favorable to liquefaction occur in loose to medium dense, clean to moderately silty sand, which is below the groundwater level. Based on our evaluation of the subsurface conditions observed in the explorations, it is our opinion that potentially liquefiable soils are not present at the project site. 4.2.4 Ground Rupture Ground rupture from lateral spreading is associated with liquefaction. Lateral spreading involves lateral displacements of large volumes of liquefied soil, and can occur on near-level ground as blocks of surface soils displace relative to adjacent blocks. In our opinion, ground rupture resulting from lateral spreading at the site is unlikely because potentially liquefiable soils are not present at the site as discussed above. Because of the thickness of the Quaternary sediments below the site, which are commonly more than 1,000 feet thick, the potential for surface fault rupture is considered low. 4.2.5 Landslides As discussed in Sections 3.3 and 4.1, steep slopes are mapped on the west edge of the site; however, they are associated with a rockery that was built during construction of Edmonds Avenue NE. We understand that the existing rockery will be replaced with an engineered retaining wall. Provided the retaining wall is designed in accordance with the recommendations of this report, it is our opinion that there will be no risk of earthquake induced landsliding as a result of strong ground shaking. Homestead Community Land Trust | November 18, 2024 Page 8 File No. 23656-001-01 4.3 TEMPORARY DEWATERING Perched seepage zones should be expected in permeable layers within the shallow fill, weathered glacial till and more permeable layers of the glacial till. We anticipate that the contractor will be able to use sumps and pumps located within excavations for required temporary dewatering to control perched groundwater seepage. Sump pumping involves removing water that has seeped into an excavation by pumping from a sump that has been excavated at one or more locations in an excavation. Drainage ditches that lead to the sump are typically excavated along the excavation sidewalls at the base of an excavation. The excavation for the sump and discharge drainage ditches should be backfilled with gravel or crushed rock to reduce the amount of erosion and associated sediment in the water pumped from the sump. In our experience, a slotted casing or perforated 55-gallon drum that is installed in the sump backfill provides suitable housing for a submersible pump. For planning purposes, perched groundwater flow rates of up to 5 gallons per minute (gpm) can be assumed for site excavations. Surface water from rainfall will contribute significantly to the volume of water that needs to be removed from the excavation during construction and will vary as a function of season and precipitation. Disposal of soil and water pumped from excavations should be in compliance with any environmental handling requirements for excavations in these areas. 4.4 EXCAVATION SUPPORT Excavations will be required to replace the existing rockery on the west side of the site, to facilitate installation of possible retaining walls on the north/northeast side of the site, to install underground utilities and to construct Buildings D and E that may be cut into the hillside and may be below-grade on the east side and daylight on the west side of the buildings. Subsurface conditions support the use of temporary cut slopes where possible. Where temporary shoring is required, soldier piles and tiebacks or soil nails with full-depth vertical elements may be used. If soil nailing is used, the soil nail wall design should consider the upper fill and looser weathered glacial soils, and utilities located in close proximity to the wall alignment. We recommend implementing full depth vertical elements on soil nail shoring walls for improved deflection control, to reduce face instability and to allow for soil nails to be located below existing utilities, as needed. Vertical elements consist of light wide flange beams placed in drilled excavations that are backfilled full depth with lean concrete. The City of Renton requires that shoring walls be designed to limit lateral deflections to 1 inch or less in order to reduce the risk of damage to existing improvements. The City of Renton requires that remedial measures be implemented when lateral deflections reach 1 inch. An existing apartment building is located north of the site. If a retaining wall (temporary and/or permanent) is utilized on the north edge of the site and that existing apartment building is located within a horizontal distance equal to the height of the retaining wall, the shoring wall design earth pressures should be increased by 1.25 to provide enhanced deformation control. This should also be considered for retaining walls along the west side of the site adjacent to Buildings A and B. Homestead Community Land Trust | November 18, 2024 Page 9 File No. 23656-001-01 The following sections provide design information for temporary cut slopes, soldier pile walls and soil nail walls. 4.4.1 Excavation Considerations The fill and glacial soils may be excavated with conventional excavation equipment, such as track hoes or dozers. It may be necessary to rip the dense to very dense glacial till soils locally to facilitate excavation. Cobbles and boulders typically exist within the glacial soils, and the contractor should be prepared to deal with them. Likewise, the surficial fill may contain foundation elements and/or utilities from previous site development, as well as debris, rubble and/or cobbles and boulders. We recommend that procedures be identified in the project specifications for measurement and payment of work associated with obstructions. 4.4.2 Temporary Cut Slopes For planning purposes, temporary unsupported cut slopes more than 4 feet high may be inclined at 1H:1V (horizontal to vertical) maximum steepness within the relatively unweathered dense to very dense glacial till soils. Temporary cuts within the fill and loose to medium dense weathered glacial till deposits may be cut at a maximum inclination of 1½H:1V. If significant seepage is present on the cut face, then the cut slopes may have to be flattened. However, temporary cuts should be discussed with the geotechnical engineer during final design development to evaluate suitable cut slope inclinations for the various portions of the excavation. The above guidelines assume that surface loads such as traffic, construction equipment, stockpiles or building supplies will be kept away from the top of the cut slopes a sufficient distance so that the stability of the excavation is not affected. We recommend that this distance be at least 5 feet from the top of the cut for temporary cuts made at 1H:1V or flatter and less than 10 feet high, and no closer than a distance equal to one half the height of the slope for cuts more than 10 feet high. Temporary cut slopes should be planned such that they do not encroach on a 1H:1V influence line projected down from the edges of nearby or planned foundation elements. New footings planned at or near existing grades and in temporary cut slope areas should extend through wall backfill and be embedded in native soils. Water that enters the excavations must be collected and routed away from prepared subgrade areas. We expect that this may be accomplished by installing a system of drainage ditches and sumps along the toe of the cut slopes. Some sloughing and raveling of the cut slopes should be expected. If excessive groundwater is observed while making cuts, then alternative groundwater control systems will be necessary, such as well points or wells. Temporary covering, such as heavy plastic sheeting with appropriate ballast, should be used to protect these slopes during periods of wet weather. Surface water runoff from above cut slopes should be prevented from flowing over the slope face by using berms, drainage ditches, swales or other appropriate methods. If temporary cut slopes experience excessive sloughing or raveling during construction, it may become necessary to modify the cut slopes to maintain safe working conditions. Slopes experiencing problems can be flattened, regraded to add intermediate slope benches or additional dewatering can be provided if the poor slope performance is related to groundwater seepage. Homestead Community Land Trust | November 18, 2024 Page 10 File No. 23656-001-01 4.4.3 Soldier Pile and Tieback Walls Soldier pile walls consist of steel beams that are concreted into drilled vertical holes located along the wall alignment, typically 8 feet on center. After excavation to specified elevations, tiebacks are installed, if necessary. Once the tiebacks are installed, the pullout capacity of each tieback is tested, and the tieback is locked-off to the soldier pile at or near the design tieback load. Tiebacks typically consist of steel strands that are installed into pre-drilled holes and then either tremie or pressure grouted. Timber lagging is typically installed behind the flanges of the steel beams to retain the soil located between the soldier piles. Geotechnical design recommendations for each of these components of the soldier pile and tieback wall system are presented in the following sections. 4.4.3.1 SOLDIER PILES We recommend that soldier pile walls be designed using the earth pressure diagrams presented in Figure 3. The earth pressures presented in Figure 3 are for full height cantilever soldier pile walls and full-height soldier pile walls with a single level or multiple levels of tiebacks and include loading from traffic surcharge. The earth pressures represent the estimated loads that will be applied to the wall system for various wall heights. No seismic pressures have been included because it is assumed that the shoring will be temporary. Additional surcharge loads (floor or foundation loads, etc.) can be evaluated using the surcharge pressures presented in Figure 4. Other surcharge loads, such as cranes, construction equipment or construction staging areas, should be considered by GeoEngineers on a case-by-case basis. We recommend that the embedded portion of the soldier piles be at least 2 feet in diameter and extend a minimum distance of 10 feet below the base of the excavation to resist “kick-out.” The axial capacity of the soldier piles must resist the downward component of the anchor loads and other vertical loads, as appropriate. We recommend using an allowable end bearing value of 40 kips per square foot (ksf) for piles supported on the glacially consolidated soils. The allowable end bearing value should be applied to the base area of the drilled hole into which the soldier pile is concreted. This value includes a factor of safety of about 2.5. The allowable end bearing value assumes that the shaft bottom is cleaned out immediately prior to concrete placement. If necessary, an allowable pile skin friction of 1.5 ksf may be used on the embedded portion of the soldier piles to resist the vertical loads. 4.4.3.2 LAGGING We recommend that the temporary timber lagging be sized using the procedures outlined in the Federal Highway Administration’s Geotechnical Engineering Circular No. 4. The site soils are best described as competent soils. Table 2 presents recommend timber lagging thicknesses (roughcut) as a function of soldier pile clear span and depth. Shotcrete lagging can be used as an alternative to timber lagging, depending upon the contractor’s preference. TABLE 2. RECOMMENDED LAGGING THICKNESS DEPTH (FEET) LAGGING THICKNESS (ROUGHCUT) FOR CLEAR SPANS OF: 5 FEET 6 FEET 7 FEET 8 FEET 9 FEET 10 FEET 0 to 25 2 inches 3 inches 3 inches 3 inches 4 inches 4 inches Homestead Community Land Trust | November 18, 2024 Page 11 File No. 23656-001-01 Lagging should be installed promptly after excavation, especially in areas where perched groundwater is present or where clean sand and gravel soils are present and caving soils conditions are likely. The workmanship associated with lagging installation is important for maintaining the integrity of the excavation. The space behind the lagging should be filled with soil as soon as practicable. The voids behind the lagging should be backfilled immediately or within a single shift, depending on the selected method of backfill. Placement of backfill will help reduce the risk of voids developing behind the wall and damage to existing improvements located behind the wall. Lean concrete or controlled density fill (CDF) is a suitable option for the use of backfill behind the walls. Lean concrete/CDF will reduce the volume of voids present behind walls. Alternatively, lean concrete may be used for backfill behind the upper 5 to 10 feet of the excavation to limit caving and sloughing of the upper soils, with on-site soils used to backfill the voids for the remainder of the excavation. Based on our experience, the voids between each lean concrete lift are sufficient for preventing the buildup of hydrostatic pressure behind the wall. 4.4.3.3 TIEBACKS Tieback anchors can be used for wall heights where cantilever soldier pile walls are not cost-effective. Tieback anchors should extend far enough behind the wall to develop anchorage beyond the “no-load” zone and within a stable soil mass. The anchors should be inclined downward at 15 to 25 degrees below the horizontal. Corrosion protection will not be required for the temporary tiebacks with a design life of less than one year. Centralizers should be used to keep the tieback in the center of the hole during grouting. Structural grout or concrete should be used to fill the bond zone of the tiebacks. A bond breaker, such as plastic sheathing, should be placed around the portion of the tieback located within the no-load zone if the shoring contractor plans to grout both the bond zone and unbonded zone of the tiebacks in a single stage. If the shoring contractor does not plan to use a bond breaker to isolate the no-load zone, GeoEngineers should be contacted to provide recommendations. Loose soil and slough should be removed from the holes drilled for tieback anchors prior to installing the tieback. The contractor should take necessary precautions to minimize loss of ground and prevent disturbance to previously installed anchors and existing improvements in the site vicinity. Holes drilled for tiebacks should be grouted/filled promptly to reduce the potential for loss of ground. Tieback anchors should develop anchorage in the glacially consolidated soils. We recommend that spacing between tiebacks be at least three times the diameter of the anchor hole to minimize group interaction. We recommend a design load transfer value between the anchor and soil of 4 kips per foot for the unweathered glacial till soils and 1.5 kips per foot for fill and weathered glacial till soils. Higher adhesion values may be developed, depending on the anchor installation technique. The contractor should be given the opportunity to use higher adhesion values by conducting performance tests prior to the start of installing the production tieback anchors. The tieback anchors should be verification- and proof-tested to confirm that the tiebacks have adequate pullout capacity. The pullout resistance of tiebacks should be designed using a factor of safety of 2. The pullout resistance should be verified by completing at least two successful verification tests in each soil type and a minimum of four total tests for the project. Each tieback should be proof tested to 133 percent of the design load. Verification and proof tests should be completed as described in Appendix D. Homestead Community Land Trust | November 18, 2024 Page 12 File No. 23656-001-01 The tieback layout and inclination should be checked to confirm that the tiebacks do not interfere with adjacent buried utilities. 4.4.3.4 DRAINAGE A suitable drainage system should be installed to prevent the buildup of hydrostatic groundwater pressures behind the soldier pile and lagging wall. It may be necessary to cut weep holes through the lagging in wet areas. Seepage flows at the base of the excavation should be contained and controlled. Drainage should be provided for permanent below-grade walls as described in Section 4.7. 4.4.3.5 CONSTRUCTION CONSIDERATIONS Shoring construction should be completed by a qualified shoring contractor having experience with similar projects in the Puget Sound area. Temporary casing or drilling fluid may be required to install the soldier piles and possibly the tiebacks where: ■ Loose fill is present; ■ The native soils do not have adequate cementation or cohesion to prevent caving or raveling; and/or ■ Groundwater is present. GeoEngineers should be allowed to observe and document the installation and testing of the shoring to verify conformance with the design assumptions and recommendations. 4.4.4 Soil Nail Walls The soil nail wall system consists of drilling and grouting rows of steel bars or “nails” behind the excavation face as it is excavated and then covering the face with reinforced shotcrete. The placement of soil nails reinforces the soils located behind the excavation face and increases the soil’s ability to inhibit a mass of soil from sliding into the excavation. Soil nails typically consist of #6 to #12 threaded steel bars (¾- to 1½-inch-diameter). The steel bars are placed in 6- to 8-inch-diameter holes drilled at angles typically ranging from 10 to 25 degrees below horizontal. Centralizers are used to center the steel bars in the holes. Once the steel bars are installed, the holes are grouted using cement grout or concrete. The soils typically are required to have an adequate standup time (to allow placement of the steel wire mesh and/or reinforcing bars to be installed and the shotcrete to be placed). Soils that have short standup times are problematic for soil nailing. Soil nail walls are typically constructed using the following sequence: 1. Install full-depth vertical elements into vertical drilled holes and grout each hole with lean concrete. 2. Excavate the soil at the wall face to between 1 and 3 feet below the row of soil nails to be installed. Depending upon the soil conditions at the wall face, the excavation may be completed with a vertical cut or with berms (native or fill). 3. Drill, install and grout soil nails. Homestead Community Land Trust | November 18, 2024 Page 13 File No. 23656-001-01 4. Excavate berm, if present, located within about 3 feet below the elevation of the soil nail. 5. Place drainage strips, steel wire mesh and/or reinforcing bars in front of the excavated soil. 6. Install shotcrete and place steel plates and nuts over the soil nails. 7. Complete nail pullout capacity testing on approximately one out of every 20 nails in an installed row. 8. Repeat steps two through seven for each row of nails located below the completed row. Full depth vertical elements should be used to improve deformation control, improve face stability of the site soils and to act as a cantilever wall to meet nail clearance requirements where buried utilities are present. Vertical elements typically consist of vertical steel beams placed in drilled holes located along the wall alignment and backfilled with lean concrete. For vertical elements that act as a cantilever wall, we recommend that the vertical elements be designed for the earth pressures presented in Section 4.7.2. Face instability where clean granular soils are present can be mitigated using vertical elements or by other means determined by the shoring contractor during shoring construction, as discussed below. 4.4.4.1 DESIGN RECOMMENDATIONS We recommend the following for design and cost estimating purposes: ■ Full depth vertical elements installed at approximately 6 feet on center with vertical element toe embedment of at least 3 feet below the base of excavation elevation; ■ A soil nail grid pattern of about 6 by 6 feet; ■ A soil nail length ranging up to the wall height (but not less than 10 feet), inclined at about 15 to 20 degrees from the horizontal; ■ An allowable load transfer of 1.5 kips per foot for fill and weathered glacial till, and 3 kips per foot for the relatively unweathered glacial till for 6- to 8-inch-diameter grouted nails; and ■ Strips of drainage material installed behind the shotcrete to relieve hydrostatic pressures. Additional drainage provisions may be necessary if significant groundwater is encountered during the excavation. Existing fill, looser weathered glacial soils and fill associated with utilities located behind the walls will affect the soil nail design. Typically, the soil nail spacing is tighter or the soil nails are longer, or both, where fill or looser native soils are present compared to where competent glacially consolidated soils are present. Difficulties associated with face stability and standup time may be experienced during construction in the site soils. Fill soils are often loose to medium dense and, as a result, may have a shorter standup time. Cleaner sand and gravel soils or soils located in areas with groundwater may also exhibit shorter standup times. Spalling and raveling of the cut face may occur at these locations during soil nail wall installation. Construction techniques used to mitigate spalling and raveling include: ■ Flash coating the cut face with 2 to 4 inches of shotcrete immediately after the cut face is excavated to final line and the drainage material is installed. This typically provides enough standup time to allow for the installation of the reinforcing steel and final shotcrete; ■ Excavating in half-height (2- to 3-foot) lifts, rather than full-height (6-foot) lifts; Homestead Community Land Trust | November 18, 2024 Page 14 File No. 23656-001-01 ■ Excavating leaving a 1H:1V earth berm in front of the wall. The soil nails are installed by drilling through the soil berm. The soil berm is then removed to allow for installation of the drainage material and reinforcing steel and shotcrete; ■ Excavating to the planned back of shotcrete facing and then placing a 1H:1V fill berm in front of the wall. The fill berm is then removed just before placement of drainage material, reinforcement and shotcrete; ■ Shortening the length of wall drilled and shotcreted using a staggered excavation approach; and ■ Installing closely spaced full-depth vertical soil nails or small steel beams (vertical elements) along the wall alignment. Contractors experienced in the soil nailing method should be able to mitigate significant spalling and raveling conditions. Contractors should also be prepared to use techniques to address problems that occur because of caving soils. The contractor should be made responsible for the safety of the shoring system. Baseline assumptions for the extent of temporary casing required for soil nail installation and the use of native/fill berms for the project are recommended to be established prior to construction. 4.4.4.2 DRAINAGE A suitable drainage system should be installed to prevent the buildup of hydrostatic groundwater pressures behind the soil nail walls. Drainage behind soil nail walls typically consists of prefabricated geocomposite drainage strips, such as Mirafi G100™, installed vertically between the soil nails. The drainage strips are typically a minimum of 16 inches wide and extend the entire height of the wall. Horizontal drainage strips may also be used in areas where perched groundwater is observed, or for other reasons. We recommend that drainage strips be connected to a prefabricated drainage grate and weep pipe installed along the base of the wall that passes through the shotcrete facing, and routed to a suitable discharge point as described below in Section 4.7. 4.4.4.3 LATERAL EARTH PRESSURES RESULTING FROM ADJACENT SURCHARGE LOADING The diagrams of recommended surcharge pressures presented in Figure 4 can be used to estimate the lateral earth pressures acting on below-grade walls as a result of other point, line and uniform surcharge loading. 4.4.4.4 SOIL NAIL WALL PERFORMANCE A soil nail wall is a passive shoring system that requires deflections for load to be applied to the soil nails. We recommend that the soil nail be designed such that average wall deflections are limited to 1 inch and ground surface settlements behind the wall are less than about 1 inch. The deflections and settlements are usually highest at the excavation face and decrease to negligible amounts beyond a distance behind the wall equal to the excavation height. Wall deflections can be reduced by pre-stressing the upper row(s) of soil nails. Localized deflections may exceed the above estimates and may reflect local variations in soil conditions (such as around abandoned side sewers) or may be the result of the workmanship used to construct the wall. Homestead Community Land Trust | November 18, 2024 Page 15 File No. 23656-001-01 4.4.4.5 CONSTRUCTION CONSIDERATIONS Temporary casing or drilling fluid will be required to install the vertical elements, and casing will be necessary for soil nails where: ■ Loose fill is present; ■ The native soils do not have adequate cementation or cohesion to prevent caving or raveling; and/or ■ Perched groundwater is present. GeoEngineers should be allowed to observe and document the installation and testing of the shoring to verify conformance with design assumptions and recommendations. Shoring construction should be completed by a qualified shoring contractor having experience with similar projects in the Puget Sound area. 4.4.5 Shoring Wall Performance Temporary shoring walls typically move up to 1 inch. The deflections and settlements are usually highest at the excavation face and decrease to negligible amounts beyond a distance behind the wall equal to the height of the excavation. Localized deflections may exceed the above estimates and may reflect local variations in soil conditions (such as around side sewers) or may be the result of the workmanship used to construct the shoring wall. Given that some movement is expected, existing improvements located adjacent to the temporary shoring system will also experience movement. The deformations discussed above are not likely to cause structural damage to structurally sound existing improvements; however, some cosmetic damage should be expected (for instance, cracks in drywall finishes; widening of existing cracks; minor cracking of slabs-on-grade/hardscapes; cracking of sidewalks, curbs/gutter and pavements/pavement panels; etc.). For this reason, it is important to complete a pre-construction survey and photo documentation of existing buildings and improvements prior to shoring construction. Refer to Appendix D for more detailed recommendations for shoring monitoring and preconstruction survey. 4.5 SHALLOW FOUNDATIONS We recommend that the proposed buildings be supported on shallow spread footings founded on the dense to very dense/very stiff to hard glacial till encountered in the explorations. Shallow spread footings may also be supported on weathered glacial till or on properly compacted structural fill extending down to these soils. Existing fill and unsuitable highly weathered glacial till should be removed from under the planned building foundations. For shallow foundation support, we recommend widths of at least 18 and 36 inches, respectively, for continuous wall and isolated column footings supporting the proposed buildings. The design frost depth in the Puget Sound area is 12 inches; therefore, we recommend that exterior footings for the buildings be founded at least 18 inches below lowest adjacent finished grade. Interior footings should be founded at least 12 inches below bottom of slab or adjacent finished grade. The following recommendations for the building foundations are based on the subsurface conditions observed in the explorations completed at the site. Homestead Community Land Trust | November 18, 2024 Page 16 File No. 23656-001-01 4.5.1 Allowable Bearing Pressures Unsuitable soils consisting of fill, topsoil and/or highly weathered glacial till will vary across the site and must be removed from below planned footings. Based on our explorations and estimated fill depths, unsuitable soils and fill may range from approximately 2½ to 8 feet deep. Therefore, depending on the foundation locations and design elevations, overexcavation under the footings may be necessary for some building foundations. For design, we recommend the following: ■ Shallow Foundations on Dense Glacial Till: Foundations extending to and bearing on competent undisturbed dense to very dense/very stiff to hard native glacial till may be designed using a maximum allowable soil bearing pressure of 6,000 psf for isolated spread footings and continuous footings. CDF or lean concrete may be used below footings to support 6,000 psf, provided that it extends down to dense to very dense/very stiff to hard glacial till. Overexcavated areas must be backfilled with CDF having a design strength of at least 200 pounds per square inch (psi). ■ Shallow Foundations on Medium Dense Weathered Glacial Till: Foundations extending to and bearing on competent undisturbed medium dense to dense native weathered glacial till may be designed using a maximum allowable soil bearing pressure of 3,000 psf for isolated spread footings and continuous footings. ■ Shallow Foundations on Structural Fill: For foundations bearing on properly placed and compacted structural fill extending down to medium dense to very dense/ glacial till, foundations may be designed using a maximum allowable soil bearing pressure of 3,000 psf for isolated spread footings and continuous footings. Where structural fill is placed below footings, the fill should extend beyond the edges of the foundations by the depth of the overexcavation, while the CDF should extend beyond the edges of the foundations by half the depth of the overexcavation. The allowable bearing pressures presented above apply to the total dead and long-term live loads and may be increased up to one-third for short-term live loads such as wind or seismic forces. All footings near below-grade walls should be embedded to a depth that is at least below a 1H:1V line projected up from the bottom of the closest section of wall, otherwise the below-grade walls need to be designed for lateral loads from the footings. 4.5.2 Settlement Post-construction settlement of shallow footings supported on native soils or on properly compacted structural fill as recommended above should be limited to less than 1 inch, and differential settlement between comparably loaded column footings or along a 25-foot section of continuous wall footing should be less than ½ inch. We expect most of the footing settlements will occur as loads are applied. Loose or disturbed soils not removed from footing excavations prior to placing concrete will result in additional settlement. Homestead Community Land Trust | November 18, 2024 Page 17 File No. 23656-001-01 4.5.3 Lateral Resistance Lateral foundation loads may be resisted by passive resistance on the sides of the footings and by friction on the base of the footings. Frictional resistance may be computed using a coefficient of friction of 0.4 applied to vertical dead-load forces. Passive resistance may be computed using an equivalent fluid density of 350 pcf. The allowable passive resistance is for horizontal soil conditions in front of the footing and is applicable provided that the footings are surrounded by structural fill or constructed neat against native glacial soils. The structural fill should be compacted to at least 95 percent of the maximum dry density (MDD) determined in accordance with ASTM D 1557. Passive pressure resistance should be calculated from the bottom of adjacent floor slabs or below a depth of 1 foot where the adjacent area is unprotected, as appropriate. The allowable frictional resistance and passive resistance values presented above include a factor of safety of about 1.5. If soils adjacent to footings are disturbed during construction, the disturbed soils must be recompacted, otherwise the lateral passive resistance value must be reduced. 4.5.4 Footing Drains We recommend perimeter footing drains be installed around the proposed buildings. The perimeter drains should be installed at the base of the exterior footings, as shown in Figure 5. The perimeter drains should consist of at least 4-inch-diameter perforated pipe placed on a 4-inch bed of, and surrounded by, 6 inches of drainage material enclosed in a nonwoven geotextile filter fabric such as Mirafi 140N (or approved equivalent). The perimeter drains should be provided with cleanouts. The footing drainpipe should be installed at least 18 inches below the top of the adjacent floor slab. The drainage material should consist of “Gravel Backfill for Drains” per Section 9-03.12(4) of the 2024 Washington State Department of Transportation (WSDOT) Standard Specifications. We recommend the drainpipe consist of either heavy-wall solid pipe (SDR-35 polyvinyl chloride [PVC], or equal) or rigid corrugated smooth interior polyethylene pipe (ADS N-12, or equal). We recommend against using flexible tubing for footing drainpipes. The perimeter drains should be sloped to drain by gravity, if practicable, to a suitable discharge point, preferably a storm drain. We recommend the cleanouts be covered and placed in flush mounted utility boxes. Water collected in roof downspout lines must not be routed to the footing drain lines. 4.5.5 Construction Considerations We recommend that the excavations for the footings be completed with an excavator equipped with a smooth-edge bucket to minimize subgrade disturbance. Immediately prior to placing concrete, all debris and loose soils that accumulated in the footing excavations during forming and steel placement must be removed. Debris or loose soils not removed from the footing excavations will result in increased settlement. If wet weather construction is planned, we recommend that all footing subgrades be protected using a lean concrete mud mat that is about 2 inches thick. The mud mat should be placed the same day that the footing subgrade is excavated and approved for foundation support. Homestead Community Land Trust | November 18, 2024 Page 18 File No. 23656-001-01 4.6 SLAB-ON-GRADE FLOORS 4.6.1 Subgrade Preparation We recommend that concrete slabs-on-grade be constructed on a gravel layer to provide uniform support and drainage, and to act as a capillary break. We expect that slab-on-grade floors can be supported on: (1) medium dense to very dense/stiff to hard native glacial soils encountered in the explorations, (2) properly compacted structural fill extending down to these materials, or (3) on suitable on-site soils. Prior to placing the gravel layer, the subgrade should be evaluated and unsuitable soils should be removed and replaced with structural fill where needed. Then the subgrade should be proofrolled as described in Section 4.8. The exposed subgrade should be evaluated during construction and compacted to a firm and unyielding condition. 4.6.2 Design Parameters A 4-inch-thick capillary break layer of 1-inch minus clean crushed gravel with negligible sand and silt (WSDOT 9-03.1(4)C, Grading No. 67) should be placed to provide uniform support and form a capillary break beneath the slabs. For slabs designed as a beam on an elastic foundation, a modulus of subgrade reaction of 100 pounds per cubic inch (pci) may be used for subgrade soils prepared as recommended above. If water vapor migration through the slabs is objectionable, the capillary break gravel layer should be covered with heavy plastic sheeting at least 10-mil thick to act as a vapor retarder. This will be desirable where the slabs are in occupied spaces or will be surfaced with tile or will be carpeted. It may also be prudent to apply a sealer to the slab to further retard the migration of moisture through the floor. The contractor should be made responsible for maintaining the integrity of the vapor barrier during construction. Additional water proofing measures that may be needed should be evaluated during design. 4.6.3 Underslab Drainage Groundwater could accumulate below the slab-on-grade for portions of buildings that are cut into the hillside (i.e. Buildings D and E) and that have below-grade walls or utility connections that tie into the building. To mitigate this condition, we recommend that the slabs of buildings with below-grade walls be constructed with underslab drainage to collect and discharge groundwater from below the slabs. This can be accomplished by installing a 4-inch-diameter, heavy-wall perforated collector pipe in a shallow trench placed directly below the capillary break layer. The trench should measure about 18 inches wide by 12 inches deep and should be backfilled with the same drainage material as described in Section 4.5.4. The drainage material should be wrapped in a nonwoven geotextile, such as Mirafi 140N. We recommend installing a single underdrain collector pipe below the long axis of the buildings and towards the cut slope. The collector pipe should be sloped to drain and discharge into the storm water collection system to convey water off site. If connected to the footing drain pipe, the invert of the underslab drain pipe must be at a higher elevation than the footing drain pipe to prevent water from flowing under the buildings from the perimeter system. The pipe should also incorporate cleanouts, if possible. The cleanouts could be extended through the foundation walls to be accessible from the outside or could be placed in flush mounted access boxes cast into the floor slabs. Homestead Community Land Trust | November 18, 2024 Page 19 File No. 23656-001-01 4.7 BELOW-GRADE WALLS AND RETAINING WALLS We understand that below-grade retaining walls will be needed to replace the existing rockery on the west side of the site and may be necessary for construction of Buildings D and E, as well as to support grade transitions at the north/northeast side of the site and other site improvements. The following recommendations should be used in design of below-grade walls that are intended to act as retaining walls and for other retaining structures that are used to achieve grade changes. As discussed previously, an existing apartment building is located north of the site. If a retaining wall (temporary and/or permanent) is utilized on the north edge of the site and that existing apartment building is located within a horizontal distance equal to the height of the retaining wall, the shoring wall design earth pressures should be increased by 1.25 to provide enhanced deformation control. This should also be considered for retaining walls along the west side of the site adjacent to Buildings A and B. 4.7.1 Permanent Subsurface Walls Against Temporary Shoring Permanent below-grade walls cast against temporary shoring should be designed for the pressures presented in Figure 3, with the addition of seismic earth pressures, which should be determined using a rectangular distribution of 7H, where H is the wall height in feet. The rectangular distribution should be distributed the full height of the wall. The seismic pressures should be added to the earth pressures shown in Figure 3. Surcharge loads (floor slabs, construction surcharges, etc.) can be evaluated using the surcharge pressure in Figure 4. The soil pressures recommended above assume that wall drains will be installed to prevent the buildup of hydrostatic pressure behind the walls, as described in Section 4.7.3 and tied to permanent drains to remove water to suitable discharge points. 4.7.2 Other Cast-in-Place Walls Conventional cast-in-place walls may be necessary against cut slopes not supported by temporary shoring. The lateral soil pressures acting on conventional cast-in-place subsurface walls will depend on the nature, density and configuration of the soil behind the wall and the amount of lateral wall movement that can occur as backfill is placed. Lateral earth pressures for design of below-grade walls and retaining structures should be evaluated using an equivalent fluid density of 35 pcf (triangular distribution) provided that the walls will not be restrained against rotation when backfill is placed. If the walls will be restrained from rotation, we recommend using an equivalent fluid density of 55 pcf (triangular distribution). Walls are assumed to be restrained if top movement during backfilling is less than H/1000, where H is the wall height. These lateral soil pressures assume that the ground surface behind the wall is horizontal. For unrestrained walls with backfill sloping up at 2H:1V, the design lateral earth pressure should be increased to 55 pcf, while restrained walls with a 2H:1V sloping backfill should be designed using an equivalent fluid density of 75 pcf. These lateral soil pressures do not include the effects of surcharges such as floor loads, traffic loads or other surface loading. Surcharge effects should be included as appropriate. Below-grade should also include seismic earth pressures. Seismic earth pressures should be determined using a rectangular distribution of 7H in psf, where H is the wall height in feet. The seismic pressures should be added to the active/at-rest pressures. Homestead Community Land Trust | November 18, 2024 Page 20 File No. 23656-001-01 If vehicles can approach the tops of exterior walls to within half the height of the wall, a traffic surcharge should be added to the wall pressure. For car parking areas, the traffic surcharge can be approximated by the equivalent weight of an additional 1 foot of soil backfill (125 psf) behind the wall. For delivery truck parking areas and access driveway areas, the traffic surcharge can be approximated by the equivalent weight of an additional 2 feet (250 psf) of soil backfill behind the wall. Other surcharge loads, such as from foundations, construction equipment or construction staging areas, should be considered on a case-by-case basis. Positive drainage should be provided behind below-grade walls and retaining structures as discussed below. These recommendations assume that all retaining walls will be provided with adequate drainage. The values for soil bearing, frictional resistance and passive resistance presented above for foundation design are applicable to retaining wall design. Walls located in level ground areas should be founded at a depth of 18 inches below the adjacent grade. 4.7.3 Wall Drainage 4.7.3.1 PERMANENT WALLS AGAINST TEMPORARY SHORING Drainage behind the permanent below-grade walls is typically provided using prefabricated drainage board attached to the temporary shoring walls. Weep pipes that extend through the permanent below-grade wall should be installed around the perimeter of the building at the footing elevation. The weep pipes should have a minimum diameter of 2 inches. The weep pipes through the permanent below-grade wall should be spaced no more than 8 feet on center and should be hydraulically collected to the sump. The weep pipes may be designed for a hard connection to the perimeter foundation drains discussed in Section 4.5.4. The earth pressures for permanent below-grade walls assume that adequate drainage is provided behind the wall. Prefabricated geocomposite drainage material, such as Aquadrain 15X, should be installed vertically to the face of the lagging/behind the shotcrete. The vertical drainage material should extend a minimum of 2 feet below the planned weep pipe locations. The weep pipes that penetrate the basement wall should be connected to the vertical drainage material with a drain grate. For soldier pile shoring walls, the drainage material should be installed on the excavation side of the timber lagging, with the fabric adjacent to the timber lagging. For soil nail walls, the drainage material should be installed behind the shotcrete, as described in Section 4.4.4.2. 4.7.3.2 OTHER CAST-IN-PLACE WALLS To reduce the potential for hydrostatic water pressure buildup behind cast-in-place retaining walls not constructed against temporary shoring, we recommend that the walls be provided with adequate drainage, as shown in Figure 5. Wall drainage can be achieved by using free draining wall drainage material with perforated pipes to discharge the collected water. Wall drainage material may consist of Gravel Backfill for Drains per WSDOT Standard Specification Section 9-03.12(4) surrounded with a nonwoven geotextile filter fabric such as Mirafi 140N (or approved equivalent), or imported Gravel Borrow with less than 5 percent fines may be used in conjunction with a geocomposite wall drainage layer. The zone of wall drainage material should be 2 feet wide and should extend from the base of the wall to within 2 feet of the ground surface. The wall drainage material should be covered with a geotextile separator (such as Mirafi 140N) and then 2 feet of less permeable material, such as the on-site silty sand that is properly moisture conditioned and compacted. Homestead Community Land Trust | November 18, 2024 Page 21 File No. 23656-001-01 A 4-inch-diameter perforated drain pipe should be installed within the free-draining material at the base of each wall. We recommend using either heavy-wall solid pipe (SDR-35 PVC) or rigid corrugated polyethylene pipe (ADS N-12, or equal). We recommend against using flexible tubing for the wall drain pipe. The footing drain recommended above can be incorporated into the bottom of the drainage zone and used for this purpose. If gravel borrow is used against the wall in conjunction with a geocomposite wall drainage layer, then the drainage pipe at the base of the wall should be surrounded with at least 12 inches of Gravel Backfill for Drains per WSDOT Standard Specification Section 9-03.12(4) that is wrapped with a nonwoven geotextile filter fabric such as Mirafi 140N (or approved equivalent). The pipes should be laid with minimum slopes of one-quarter percent and discharge into the storm water collection system to convey the water off site. The pipe installations should include a cleanout riser with cover located at the upper end of each pipe run. The cleanouts could be placed in flush mounted access boxes. Collected downspout water should be routed to appropriate discharge points in separate pipe systems. 4.8 EARTHWORK Based on the observed subsurface soil conditions, we anticipate that the soils at the sites may be excavated using conventional heavy-duty construction equipment. Dense to very dense glacial till with variable silt and gravel content that was encountered in the explorations can be difficult to excavate. Glacial deposits in the area commonly contain cobbles and boulders that may be encountered during excavation. Accordingly, the contractor should be prepared to deal with cobbles and boulders. The fill and native soils contain significant fines (material passing the U.S. Standard No. 200 sieve) and are highly moisture-sensitive and susceptible to disturbance, especially when wet. Ideally, earthwork should be undertaken during extended periods of dry weather (June through September) when the surficial soils will be less susceptible to disturbance and provide better support for construction equipment. Dry weather construction will help reduce earthwork costs and increase the potential for using the native soils as structural fill. Trafficability on the site is not expected to be difficult during dry weather conditions. However, the fill and native soils will be susceptible to disturbance from construction equipment during wet weather conditions and pumping and rutting of the exposed soils under equipment loads may occur and could potentially generate significant quantities of mud if not protected. 4.8.1 Clearing and Site Preparation Areas to be developed or graded should be cleared of surface and subsurface deleterious matter including any debris, shrubs, trees and associated stumps and roots. Graded areas should be stripped of organic soils. We anticipate that the average stripping depth will be about 6 inches, although stripping depth around 12 inches will be needed in heavily vegetated areas. The organic soils can be stockpiled and used later for landscaping purposes or may be spread over disturbed areas following completion of grading. If spread out, the organic strippings should be in a layer less than 1-foot thick, should not be placed on slopes greater than 3H:1V (horizontal to vertical) and should be track-rolled to a uniformly compacted condition. Materials that cannot be used for landscaping or protection of disturbed areas should be removed from the project site. Homestead Community Land Trust | November 18, 2024 Page 22 File No. 23656-001-01 Undocumented fill may be present in various areas of the site and will be required to be removed under building foundations and within the upper two feet of pavement, hardscape and slab subgrade levels. Where existing fill and looser native soils are removed, they may be reused and recompacted as structural fill, if conditions allow. 4.8.2 Earthwork Subgrade Preparation Prior to placing new fills, pavement base course materials or gravel below on-grade floor slabs, subgrade areas should be proof-rolled to locate any soft or pumping soils. Prior to proof-rolling, all unsuitable soils should be removed from below building footprints and new hardscape areas. Proof-rolling can be completed using a piece of heavy tire-mounted equipment such as a loaded dump truck. During wet weather, the exposed subgrade areas should be probed to determine the extent of soft soils. If soft or pumping soils are observed, they should be removed and replaced with structural fill. After completing the proof-rolling, the subgrade areas should be recompacted to a firm and unyielding condition, if possible. The degree of compaction that can be achieved will depend on when the construction is performed. If the work is performed during dry weather conditions, we recommend that all subgrade areas be recompacted to at least 95 percent of the MDD in accordance with the ASTM D 1557 test procedure (modified Proctor). If the work is performed during wet weather conditions, it may not be possible to recompact the subgrade to 95 percent of the MDD. In this case, we recommend that the subgrade be compacted to the extent possible without causing undue weaving or pumping of the subgrade soils. Subgrade disturbance or deterioration could occur if the subgrade is wet and cannot be dried. If the subgrade deteriorates during proof-rolling or compaction, it may become necessary to modify the proof- rolling or compaction criteria or methods. 4.8.2.1 SUBGRADE PROTECTION Site soils contain significant fines content (silt/clay) and will be highly sensitive and susceptible to moisture and equipment loads. The contractor should take necessary measures to prevent site subgrade soils from becoming disturbed or unstable. 4.8.3 Structural Fill All fill, whether existing on-site soils or imported soil, that will support floor slabs, pavement areas or foundations or be placed against retaining walls or in utility trenches are classified as structural fill and should generally meet the criteria for structural fill presented below. The suitability of soil for use as structural fill depends on its gradation and moisture content. 4.8.3.1 MATERIALS Structural fill material quality varies depending upon its use as described below: ■ Structural fill placed below foundations designed for 3,000 psf or lower, floor slabs or as subbase material below pavement areas may consist of suitable on-site glacial till soils (during dry weather) or should meet the criteria for gravel borrow as described in Section 9-03.14(1) of the 2024 WSDOT Standard Specifications. Homestead Community Land Trust | November 18, 2024 Page 23 File No. 23656-001-01 ■ CDF used to support building foundations designed for bearing pressures up to 6,000 psf should be in accordance with 2024 WSDOT Standard Specification Section 2-09.3(1)E and should have a minimum compressive strength of 200 psi. The mix design should be adjusted to obtain this minimum compressive strength. Lean concrete may also be used under building foundations. ■ Structural fill placed to raise site grades below building slabs or to backfill utility trenches should meet the criteria for common borrow as described in Section 9-03.14(3) of the 2024 WSDOT Standard Specifications during dry weather conditions (typically June through September). Common borrow materials are highly moisture sensitive. For wet weather construction (October through May), structural fill placed to raise site grades or in utility trenches should meet the criteria for gravel borrow as described in Section 9-03.14(1) of the 2024 WSDOT Standard Specifications, except that the fines content (material passing the U.S. No. 200 sieve) should not exceed 5 percent. ■ Structural fill placed immediately outside below-grade walls (drainage zone) should consist of washed gravel in conformance Section 9-03.12(4) of the 2024 WSDOT Standard Specifications, as shown in Figure 5. ■ Structural fill placed as crushed surfacing base course (CSBC) below pavements should conform to Section 9 03.9(3) of the 2024 WSDOT Standard Specifications. ■ Structural fill placed as capillary break below slabs should consist of 1-inch minus clean crushed gravel with negligible sand or silt in conformance with Section 9-03.1(4)C, grading No. 67 of the 2024 WSDOT Standard Specifications. 4.8.3.2 REUSE OF ON-SITE SOILS Based on the explorations, the moisture content of the fill and the native glacial till is typically near the optimum moisture content for compaction. However, the soils are very moisture sensitive and can be difficult to compact during periods of wet weather or if impacted by groundwater seepage. Therefore, we recommend that they be used as Common Borrow only during periods of extended dry weather. Soils with high fines content, such as silt and clay will not be suitable for reuse as structural fill and should be exported from the site or used in landscape areas if encountered during construction. 4.8.4 Fill Placement and Compaction Criteria Structural fill should be mechanically compacted to a firm, non-yielding condition. Structural fill should be placed in loose lifts not exceeding 12 inches in thickness if using heavy compactors and 6 inches if using hand operated compaction equipment. The actual lift thickness will be dependent on the structural fill material used and the type and size of compaction equipment. Each lift should be moisture conditioned to within about 2 percent of the optimum moisture content and compacted to the specified density before placing subsequent lifts. Compaction of all structural fill at the site should be in accordance with the ASTM D 1557 (modified proctor) test method. Structural fill should be compacted to the following criteria: 1. Structural fill placed below floor slabs and foundations, and against foundations, should be compacted to at least 95 percent of the MDD. Homestead Community Land Trust | November 18, 2024 Page 24 File No. 23656-001-01 2. Structural fill placed behind below-grade walls should be compacted to between 90 to 92 percent of the MDD. Care should be taken when compacting fill near the face of below-grade walls to avoid over-compaction and, hence overstressing the walls. Hand-operated compactors should be used within 5 feet behind the wall. Wall backfill placed within building footprints, but under a second-floor level should be compacted to between 90 to 92 percent of the MDD within 5 feet of the walls and to at least 95 percent of the MDD beyond 5 feet of the walls. The upper 2 feet of fill below floor slab subgrade should also be compacted to at least 95 percent of the MDD. 3. Structural fill in new pavement and hardscape areas, including utility trench backfill, should be compacted to at least 90 percent of the MDD, except that the upper 2 feet of fill below final subgrade should be compacted to at least 95 percent of the MDD, see Figure 6. 4. Structural fill placed as crushed rock base course below pavements should be compacted to 95 percent of the MDD. 5. Non-structural fill, such as fill placed in landscape and planting areas, should be compacted to at least 90 percent of the MDD. 4.8.5 Weather Considerations The on-site soils and common borrow contain a sufficient percentage of fines (silt and clay) to be highly moisture sensitive. When the moisture content of these soils is more than a few percent above the optimum moisture content, these soils become muddy and unstable, operation of equipment on these soils will be difficult and it will be difficult or impossible to meet the required compaction criteria. Additionally, disturbance of near-surface soils should be expected if earthwork is completed during periods of wet weather. It will be preferable to schedule site preparation and earthwork activities during periods of dry weather when the soils will: (1) be less susceptible to disturbance and (2) provide better support for construction equipment. The wet weather season in the Puget Sound region generally begins in October and continues through May; however, periods of wet weather may occur during any month of the year. The optimum earthwork period for these types of soils is typically June through September. If wet weather earthwork is unavoidable, we recommend the following: ■ Structural fill placed during the wet season or during periods of wet weather should consist of imported gravel borrow with less than 5 percent fines (material passing the U.S. No. 200 sieve). ■ The ground surface in and around the work area should be sloped so that surface water is directed away from the work area. ■ The ground surface should be graded such that areas of ponded water do not develop. ■ The contractor should take measures to prevent surface water from collecting in excavations and trenches. ■ Earthwork activities should not take place during periods of heavy precipitation. ■ Slopes with exposed soils should be covered with plastic sheeting or similar means. Homestead Community Land Trust | November 18, 2024 Page 25 File No. 23656-001-01 ■ Measures should be taken to prevent on-site soils and soils to be used as fill from becoming wet or unstable. These measures may include the use of plastic sheeting, sumps with pumps and grading. The site soils should not be left uncompacted and exposed to moisture. Sealing the surficial soils by rolling with a smooth-drum roller prior to periods of precipitation will reduce the extent to which these soils become wet or unstable. ■ The contractor should cover all soil stockpiles that will be used as structural fill with plastic sheeting. ■ Construction and foot traffic should be restricted to specific areas of the site, preferably areas that are surfaced with materials not susceptible to wet weather disturbance. ■ Construction activities should be scheduled so that the length of time that soils are left exposed to moisture is reduced to the extent practicable. 4.8.6 Utility Trenches Trench excavation, pipe bedding and trench backfilling should be completed using the general procedures described in the 2024 WSDOT Standard Specifications or other suitable procedures specified by the project civil engineer. The glacial deposits and fill soils encountered at the site are generally of low corrosivity based on our experience in the Puget Sound area. Utility trench backfill should consist of structural fill and should be placed in lifts of 12 inches or less (loose thickness) when using heavy compaction equipment or 6 inches or less when using hand-operated equipment such that adequate compaction can be achieved throughout the lift. Each lift must be compacted as described in Section 4.8.4 and shown in Figure 6, prior to placing the subsequent lift. Prior to compaction, the backfill should be moisture conditioned to within about 2 percent of the optimum moisture content, if necessary. 4.8.7 Pavement Subgrade Preparation We recommend that the subgrade soils in new pavement areas be prepared and evaluated as described in Sections 4.8.2 and 4.9. For cuts in medium dense to very dense glacial till, we recommend that the exposed subgrade be proof-rolled. Where existing fill or loose to medium dense/soft to stiff native soils exist, we recommend that the upper 12 inches of the existing site soils be compacted to at least 95 percent of the MDD per ASTM D1557 and then proof-rolled prior to placing pavement section materials. If the subgrade soils are loose or soft, it may be necessary to excavate the soils and replace them with structural fill, gravel borrow or gravel base material. Based on the explorations, the majority of the subgrade soils are expected to consist of fill, weathered native soils and relatively unweathered glacial till. Pavement subgrade conditions should be observed and proof-rolled during construction to evaluate the presence of unsuitable subgrade soils and the need for over excavation. 4.8.8 Permanent Slopes We recommend that permanent cut or fill slopes be constructed at inclinations of 2H:1V or flatter. To achieve uniform compaction, we recommend that fill slopes be overbuilt at least 2 feet and subsequently cut back to expose properly compacted fill. Permanent slopes constructed at 3H:1V or flatter provide better conditions for future maintenance. Homestead Community Land Trust | November 18, 2024 Page 26 File No. 23656-001-01 To reduce erosion, newly constructed slopes should be planted or hydroseeded shortly after completion of grading. Until the vegetation is established, some sloughing and raveling of the slopes should be expected. This may require localized repairs and reseeding. Temporary covering, such as clear heavy plastic sheeting, jute fabric or erosion control blankets (such as American Excelsior Curlex 1 or North American Green SC150) could be used to protect the slopes during periods of rainfall. 4.8.9 Sedimentation and Erosion Control In our opinion, the erosion potential of the on-site soils is low to moderate. Construction activities including stripping and grading will expose soils to the erosion effects of wind and water. The amount and potential impacts of erosion are partly related to the time of year that construction actually occurs. Wet weather construction will increase the amount and extent of erosion and potential sedimentation. Erosion and sedimentation control measures may be implemented by using a combination of interceptor swales, straw bale barriers, silt fences and straw mulch for temporary erosion protection of exposed soils. All disturbed areas should be finish graded and seeded as soon as practicable to reduce the risk of erosion. Erosion and sedimentation control measures should be installed and maintained in accordance with the requirements of the City of Renton. 4.9 PAVEMENT RECOMMENDATIONS 4.9.1 Subgrade Preparation We recommend the subgrade soils in new pavement areas be prepared and evaluated as described in sections 4.8.2 and 4.8.7. All new pavement and hardscape areas should be supported on subgrade soils that have been proof rolled or probed, and approved by the geotechnical engineer. If the exposed subgrade soils are loose or soft, it may be necessary to excavate localized areas and replace them with structural fill or gravel base course. Pavement subgrade conditions should be observed during construction and prior to placing the base course materials in order to evaluate the presence of zones of unsuitable subgrade soils and the need for over-excavation and replacement of these zones. 4.9.2 New Hot-Mix Asphalt Pavement In light-duty pavement areas (e.g., automobile parking), we recommend a pavement section consisting of at least a 2.5-inch thickness of ½-inch hot-mix asphalt (HMA) (PG 58-22) per WSDOT Sections 5-04 and 9-03, over a 4-inch thickness of densely compacted crushed rock base course per WSDOT Section 9-03.9(3). In heavy-duty pavement areas (e.g., truck traffic areas, materials delivery), we recommend a pavement section consisting of at least a 4-inch thickness of ½-inch HMA (PG 58-22) over a 6-inch thickness of densely compacted crushed rock base course. The base course should be compacted to at least 95 percent of the MDD (ASTM D 1557). We recommend that a proof-roll of the compacted base course be observed by the geotechnical engineer of record prior to paving. Soft or yielding areas observed during proof-rolling may require over-excavation and replacement with compacted structural fill. The pavement sections recommended above are based on our experience. Thicker asphalt sections may be needed based on the actual subgrade conditions, traffic data and intended use, or City of Renton requirements. Homestead Community Land Trust | November 18, 2024 Page 27 File No. 23656-001-01 4.9.3 Portland Cement Concrete Pavement PCC sections should be considered for loading dock aprons, trash dumpster areas and where other concentrated heavy loads may occur. We recommend that these pavements consist of at least 6 inches of PCC over 6 inches of crushed rock base course. A thicker concrete section may be needed based on the actual traffic data. If the concrete pavement will have doweled joints, we recommend that the concrete thickness be increased by an amount equal to the diameter of the dowels. The base course should be compacted to at least 95 percent MDD. We recommend PCC pavements incorporate construction joints and/or crack control joints spaced maximum distances of 12 feet apart, center-to-center, in both the longitudinal and transverse directions. Crack control joints may be created by placing an insert or groove into the fresh concrete surface during finishing, or by sawcutting the concrete after it has initially set-up. We recommend the depth of the crack control joints be approximately one-fourth the thickness of the concrete; or about 1.5 inches deep for the recommended concrete thickness of 6 inches. We also recommend the crack control joints be sealed with an appropriate sealant to help restrict water infiltration into the joints. 4.10 DRAINAGE CONSIDERATIONS The contractor should anticipate shallow perched groundwater conditions may exist, and seepage may enter excavations depending on the time of year construction takes place, especially in the spring and winter months. However, we expect this seepage water can be handled by digging interceptor trenches in the excavations and pumping from sumps. The seepage water, if not intercepted and removed from the excavations, will make it difficult to place and compact structural fill and may destabilize cut slopes. All paved and landscaped areas should be graded so surface drainage is directed away from the buildings to appropriate catch basins. Water collected in roof downspout lines must not discharge into or be routed to the perforated pipes intended for footing, underslab or wall drainage. 4.11 INFILTRATION CONSIDERATIONS Sieve analyses were performed on selected soil samples collected from the test pits that were completed as part of this study, as well as from previous explorations complete at and within the site vicinity. The soil samples typically consisted of native weathered or relatively unweathered glacial till. The design infiltration value described below is based on the results of the grain size analyses, the United States Department of Agriculture (USDA) Textural Triangle, and the Washington State Department of Ecology Storm Water Management Manual (2024). The grain size analyses are presented in Appendix B. Based on our analysis, it is our opinion that the on-site native glacial till soils have a very low infiltration capacity. The majority of the soils across the site contain significant fines, which limits the infiltration capacity. The results of the sieve analyses indicated that the fines content (material passing the U.S. No. 200 sieve) typically ranges from 25 to 35 percent. Due to the density, high fines content and relative impermeability of the glacial till, infiltration should be assumed to be very low when designing infiltration systems. We recommend a preliminary infiltration rate of not more than 0.2 inches per hour be used for design of the infiltration facilities. Depending on the depth of proposed infiltration facilities, the infiltration rate will vary; however, we recommend site specific pilot infiltration testing be performed to determine the design infiltration rate if specific infiltration facilities are being considered. Homestead Community Land Trust | November 18, 2024 Page 28 File No. 23656-001-01 5.0 Recommended Additional Geotechnical Services Throughout this report, recommendations are provided where we consider additional geotechnical services to be appropriate. These additional services are summarized below: ■ GeoEngineers should be retained to review the project plans and specifications when complete to confirm that our design recommendations have been implemented as intended. ■ GeoEngineers should be retained to provide additional recommendations for design of stormwater infiltration facilities, including performing pilot infiltration testing, if infiltration is being considered at the site. ■ During construction, GeoEngineers should observe the installation and evaluate the performance of temporary shoring (if used) and cut slopes, observe and evaluate the suitability of the wall and foundation subgrades, observe removal of unsuitable soils, evaluate the suitability of floor slab and pavement subgrades, observe installation of subsurface drainage measures including footing drains and underslab drains, observe and test structural backfill including wall and trench backfill and provide a summary letter of our construction observation services. The purposes of GeoEngineers construction phase services are to confirm that the subsurface conditions are consistent with those observed in the explorations and other reasons described in Appendix E. 6.0 Limitations We have prepared this report for the exclusive use of Homestead Community Land Trust and their authorized agents for design and construction of the proposed project. Our report, conclusions and interpretations should not be construed as a warranty of the subsurface soil conditions. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in the field of geotechnical engineering in this area at the time this report was prepared. No warranty or other conditions, express or implied, should be understood. Any electronic form, facsimile or hard copy of the original document (email, text, table and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record. Please refer to Appendix E for additional information pertaining to use of this report. Homestead Community Land Trust | November 18, 2024 Page 29 File No. 23656-001-01 7.0 References ASCE 7-16, 2016, “Minimum design loads for buildings and other structures.” Applied Technology Council, “Hazards by Location” accessed via: https://hazards.atcouncil.org/#/. GeoEngineers, Inc., “Geotechnical Engineering Services, Sunset Crest Townhomes, Renton, Washington,” dated November 15, 2018. International Code Council, “International Building Code,” 2021. Mullineaux, D.R. et al., 1961, “Preliminary Geologic Map of Seattle and Vicinity, Washington.” Soil & Environmental Engineers, Inc., “Report of Geotechnical Investigation, Proposed Residential Development, Edmonds and Glennwood Ave NE, Renton, Washington,” dated January 10, 2011. U.S. Department of Transportation, Federal Highways Administration, 1999, “Geotechnical Engineering Circular No. 4, Ground Anchors and Anchored Systems,” FHWA Report No. FHWA-IF-99-015. Washington Administration Code, “Title 296, Chapter 296-155, Part N, “Excavation, Trenching and Shoring,” November 2024. Washington State Department of Transportation, Geotechnical Design Manual, 2022. Washington State Department of Transportation. 2024. “Standard Specifications for Road, Bridge and Municipal Construction.” Figures Lake Washington Renton Municipal Airport M a y C r e e k Pa rk A v e N N 32nd S t N 30th St N 3 1st S t N 29th St SE 9 1 s t S t May Creek Park - County May Creek Park 900 H o u s e r Wa y N NE 20th S t J o n e s A v e N E Ga r d e n A v e N NE 1 2 t h S t NE 1 6th St NE 7th S t N 8th S t NE 9 th St M o n r o e A v e N E NE 4t h St M o n t e r e y A v e NE R e d m o n d A v e NE NE 27th St NE 2 4 t h S t NE S u n s e t Blv d Logan A v e N S uns e t B lvd N E S u n s et B l vd N E P a r k A v e N NE 4t h S tN 4 t h S t The Landing Honey Creek Open Space Gene Coulon Memorial Beach Park N 1 s t S t N E 3 r d S t N 3rd St Greenwood Memorial Park Cedar River Park - Renton May Creek NE 6 th St U n i o n A v e N E NE 1 0 t h St NE 7 t h P l NE 2 4 t h S t NE 17th St D u v a ll A v e NE NE S uns et B lv d May Creek Open Space Maplewood Heights Elementary School 1 SITE Vicinity Map Figure 1 Willowcrest Townhomes Phase II Renton, Washington 101 Alpine Lakes Wilderness Kent Everett Seattle 0 2,000 Feet P: \ 2 3 \ 2 3 6 5 6 0 0 1 \ G I S \ 2 3 6 5 6 0 0 1 _ P r o j e c t \ 2 3 6 5 6 0 0 1 _ P r o j e c t . a p r x \ 2 3 6 5 6 00 1 0 1 _ F 0 1 _ V i c i n i t y M a p D a t e E x p o r t e d : 1 1 / 0 1 / 2 4 b y J f e l l o w s Source(s): • ESRI Coordinate System: NAD 1983 StatePlane Washington North FIPS 4601 Feet Disclaimer: This figure was created for a specific purpose and project. Any use of this figure for any other project or purpose shall be at the user's sole risk and without liability to GeoEngineers. The locations of features shown may be approximate. GeoEngineers makes no warranty or representation as to the accuracy, completeness, or suitability of the figure, or data contained therein. The file containing this figure is a copy of a master document, the original of which is retained by GeoEngineers and is the official document of record. 3 1 0 3 1 5 3 2 0 325 3 3 0 3 1 1 3 1 2 3 1 3 3 1 4 3 1 6 3 1 7 3 1 8 3 1 9 32 1 32 2 32 3 32 4 326 3 2 7 3 2 8 3 2 9 31 0 31 5 32 0 3 2 5 33 0 3 0 9 31 1 31 2 31 3 314 31 6 31 7 31 8 31 9 32 2 3 2 3 3 2 4 3 2 6 3 2 7 32 8 32 9 33 1 3 3 2 290 295 300 305 310 291 292 293 294 296 297 298 299 301 302 303 304 306 307 308 309 311 312 313 33 1 3 3 2 33 3 33333 3 33 533 1 33 2 33 3 33 4 33 6 3 3 5 3 3 6 3 3 7 33 8 34 0 341342343 3 3 5 333 3 3 3 33 4 33 4 3 3 6 3 3 7 3 3 8 33 3 335 334 330 329 331 33 2 333 30 5 3 1 0 3 1 5 3 2 0 32 5 330 30 1 30 1 30 2 30 3 30 4 30 6 30 7 30 8 30 9 3 1 1 3 1 2 3 1 3 3 1 4 3 1 6 3 1 7 3 1 8 3 1 9 3 2 1 3 2 2 32 3 32 4 3 2 6 3 2 7 3 2 8 3 2 9 29 2 29 3 294 3 0 5 31 0 3 1 5 32 0 3 2 5 33 0 3 0 3 3 0 4 3 0 6 30 7 30 8 30 9 31 1 31 2 31 3 31 4 31 6 31 7 31 8 31 9 32 1 32 2 32 3 32 4 326 32 7 32 8 32 9 3 1 0 3 1 5 32 0 3 2 5 3 0 8 3 0 9 3 1 1 3 1 2 3 1 3 3 1 4 3 1 6 31 7 31 7 3 1 7 31 8 31 9 32 1 32 2 32 3 32 4 32 6 32 7 3 3 0 3 2 9 3 3 1 3 3 2 3 3 3 Ed m o n d s A v e N E Gl e n w o o d A v e N E GEI-TP-1 GEI-TP-2 GEI-TP-3 GEI-TP-4 GEI-TP-5 GEI-TP-6 B-1 B-2 TP-1 TP-2 TP-3 TP-4 TP-5 TP-6 GEI-TP-11 GEI-TP-10 GEI-TP-12 GEI-TP-8 GEI-TP-7 GEI-TP-9 Re t a i n i n g W a l l Re t a i n i n g W a l l Figure 2 Site Plan P: \ 2 3 \ 2 3 6 5 6 0 0 1 \ C A D \ 0 1 \ G e o t e c h \ 2 3 6 5 6 0 0 1 0 1 _ F 0 2 _ S i t e P l a n . d w g T A B : F 0 2 D a t e E x p o r t e d : 1 1 / 1 2 / 2 4 - 8 : 0 7 b y J f e l l o w s Legend Test Pit by GeoEngineers, 2018GEI-TP-1 Boring by Soil & Environmental Engineers, 2011B-1 Test Pit by Soil & Environmental Engineers, 2011TP-1 Site Boundary Source(s): ·Survey from Lank Tree Land Surveying, dated 11/6/24 ·Proposed site features from Third Place Design Co-op, dated 9/13/24 Coordinate System: WA State Plane, North Zone, NAD83, US Foot Disclaimer: This figure was created for a specific purpose and project. Any use of this figure for any other project or purpose shall be at the user's sole risk and without liability to GeoEngineers. The locations of features shown may be approximate. GeoEngineers makes no warranty or representation as to the accuracy, completeness, or suitability of the figure, or data contained therein. The file containing this figure is a copy of a master document, the original of which is retained by GeoEngineers and is the official document of record.Feet 0 40 N Willowcrest Townhomes Phase II Renton, Washington GEI-TP-7 Test Pit by GeoEngineers, 2024 (Current Study) Building C FFE Varies from 325' - 332.5' Building B FFE = 323' Building A FFE = 320.5' Building E FFE Varies from 320' - 321' Building D FFE Varies from 322.5' - 324' h1 Earth Pressure Diagrams - Temporary Soldier Pile & Tieback Wall Notes: 1. Active/apparent earth pressure and traffic surcharge pressure act over the pile spacing above the base of the excavation. 2. Passive earth pressure acts over 3 times the concreted diameter of the soldier pile, or the pile spacing, whichever is less. 3. Passive pressure includes a factor of safety of 1.5 and includes the net pressure (difference between active and passive) below the base of excavation. 4. Additional surcharge from footings of adjacent buildings should be included in accordance with recommendations provided on Figure 4. 5. This pressure diagram is appropriate for temporary soldier pile and tieback walls. If additional surcharge loading (such as from soil stockpiles, excavators, dumptrucks, cranes, or concrete trucks) is anticipated, GeoEngineers should be consulted to provide revised surcharge pressures. H/5 60° P P= 27.H psf 2' H D 15' 55 psf 400.D psf Ground Surface Net Allowable Passive Pressure Apparent Earth Pressure Traffic Surcharge Pressure Conventional Soldier Pile Wall with One Level of Tiebacks Conventional Soldier Pile Wall with Multiple Levels of Tiebacks H 3 2(H-H1) 3 2.H1 3 H/5 60° P P= 22.H psf 2' H D 15' 55 psf 400.D psf Ground Surface Net Allowable Passive Pressure Apparent Earth Pressure Traffic Surcharge Pressure 0.2H Not To Scale H = D = Height of Excavation, Feet Soldier Pile Embedment Depth, Feet Maximum Apparent Earth Pressure, Pounds per Square Foot Design Groundwater Elevation for Drained Walls/ Passive Resistance Design P = T = Horizontal Load in Uppermost Ground Anchor Distance From Ground Surface to Uppermost Tieback, FeetH =1 Legend No Load Zone H1 Th1 0.2H 1 1 400 Willowcrest Townhomes Phase II Renton, Washington Figure 3 P: \ 2 3 \ 2 3 6 5 6 0 0 1 \ C A D \ 0 1 \ G e o t e c h \ 2 3 6 5 6 0 0 1 0 1 _ F 0 3 _ E P D . d w g T A B : 3 D a t e E x p o r t e d : 1 1 / 1 1 / 2 4 - 1 1 : 5 8 b y J f e l l o w s H/2 H/2 400 400.D psf H D 27.H psf 55 psf 2' Base of Excavation 27 1 Ground Surface Cantilever Soldier Pile Active Earth Pressure Traffic Surcharge Pressure Net Allowable Passive Pressure 15' 1 400 Base of Excavation Base of Excavation Figure 4 P: \ 2 3 \ 2 3 6 5 6 0 0 1 \ C A D \ 0 1 \ G e o t e c h \ 2 3 6 5 6 0 0 1 0 1 _ F 0 4 _ R S P . d w g T A B : 4 D a t e E x p o r t e d : 1 1 / 1 2 / 2 4 - 8 : 0 8 b y J f e l l o w s H X= m H X= m H Z=nH R H X= m H Z=nH R σH m R 0.1 0.60H 0.3 0.60H 0.5 0.56H 0.7 0.48H Q P For m ≤ 0.4 H2(0.16+n2 )3 For m > 0.4 q (psf) 0.2 · q (psf) Section A-A' H Point load in pounds Line load in pounds/foot Excavation height below footing, feet Lateral earth pressure from surcharge, psf Surcharge pressure in psf Radians Distribution of σH in plan view Resultant lateral force acting on wall, pounds Distance from base of excavation to resultant lateral force, feet H ' m P R 0.2 0.78 0.59H 0.4 0.78 0.59H 0.6 0.45 0.48H Recommended Surcharge Pressure Fa c e o f W a l l σH σ QP = QL = H = σH = q = σ'H = PH = R = σ Notes: 1. Procedures for estimating surcharge pressures shown above are based on Manual 7.02 Naval Facilities Engineering Command, September 1986 (NAVFAC DM 7.02). 2. Lateral earth pressures from surcharge should be added to earth pressures presented on Figure 3. 3. See report text for where surcharge pressures are appropriate. 4. Determination of surcharge factor (k). Flexible is for a system that allows small movements (temporary shoring, retaining walls, etc.) and rigid is for a system that does not allow small movements (permanent basement walls, below grade utility structures, etc.). If permanent basement walls are cast/poured directly against temporary shoring, then the lateral surcharge factor should be assumed as flexible when analyzing lateral surcharges. θ θ = PH H Q( ) Pressures from Point Load QP QP PH Lateral Earth Pressure from Point Load, QP (Spread Footing) QL PH Lateral Earth Pressure from Line Load, QL (Continuous Wall Footing) Uniform Surcharges, q (Floor Loads, Large Foundation Elements or Traffic Loads) σH = Lateral Surcharge Pressure from Uniform SurchargeσH= K · 0.28QPn2 H2(m2+n2 )3 σH = K · 1.77QPm2n2 σ'H = σ COS2 (1.1θ ) Resultant PH = K · 0.64QL (m2 +1) For m ≤ 0.4 H(0.16+n2 )2 For m > 0.4 σH = K · 0.2n · QL H(m2+n2 )2 σH = K · 1.28m2nQL Definitions: Base of Excavation Base of Excavation Base of Excavation A A' σH Resultant lateral force acting on wall, poundsX = Depth of σH to be evaluated below the bottom of QP or QLZ = Ratio of X to Hm = Ratio of Z to Hn = Not To Scale Wall Type Surcharge Factor, k Rigid 1.0 Flexible 0.5 Willowcrest Townhomes Phase II Renton, Washington Figure 5 P: \ 2 3 \ 2 3 6 5 6 0 0 1 \ C A D \ 0 1 \ G e o t e c h \ 2 3 6 5 6 0 0 1 0 1 _ F 0 5 _ W a l l D r a i n a g e . d w g T A B : 5 D a t e E x p o r t e d : 1 1 / 1 1 / 2 4 - 1 2 : 0 0 b y J f e l l o w s Floor Slab 4" 2' Min. 12" Min. Cover Of Drainage Material (6" Min. On Sides Of Pipe) MATERIALS: Not To Scale May consist of "Gravel Backfill for Drains" per WSDOT Standard Specification 9-03.12(4), surrounded with a non-woven geotextile such as Mirafi 140N (or approved equivalent). Alternatively, the wall drainage material may consist of Gravel Borrow Per WSDOT Standard Specification 9-03.14(1) when used in combination with geocomposite drainage board. Geotextile Filter Fabric Temporary Excavation Slope Pavement Or 24" Low Permeability Soil Retained Soil Sloped To Drain Away From Structure 4" Diameter Perforated Drain Pipe Capillary Break Vapor Retarder Damp Proofing/Water Proofing Geocomposite Drainage Board Per Others Wall Drainage Material Exterior Wall Should consist of structural fill, either on-site soil or imported. The backfill should be compacted in loose lifts not exceeding 6 inches. Wall backfill supporting building floor slabs should consist of imported sand and gravel per WSDOT Standard Specification 9-03.14 compacted to at least 95 percent ASTM D1557. Backfill not supporting building floor slabs, sidewalks, or pavement should be compacted to 90 to 92 percent of the maximum dry density, per ASTM D1557. Backfill supporting sidewalks or pavement areas should be compacted to at least 95 percent in the upper two feet. Only hand-operated equipment should be used for compaction within 5 feet of the walls and no heavy equipment should be allowed within 5 feet of the wall. Should consist of a 4-inch diameter perforated heavy-wall solid pipe (SDR-35 PVC) or rigid corrugated polyethylene pipe (ADS N-12) or equivalent. Drain pipes should be placed with 0.25 percent minimum slopes and discharge to the storm water collection system. Should consist of at least 4 inches of clean crushed gravel with a maximum size of 1-inch and negligible sand or fines, per WSDOT 9-03.1(4)c Grading No. 67. A. WALL DRAINAGE MATERIAL B. RETAINED SOIL C. CAPILLARY BREAK D. PERFORATED DRAIN PIPE Wall Drainage and Backfill Willowcrest Townhomes Phase II Renton, Washington Compaction Criteria for Trench Backfill 95 90 90 95 90 Pipe Varies Varies (See Note 1) 2 Feet Varies (Modified Proctor) Pipe Bedding Trench Backfill Base Course Concrete or Asphalt Pavement Maximum Dry Density, by Test Method ASTM D1557 Recommended Compaction as a Percentage of Legend 95 Not To Scale Notes: 1. All backfill under building areas should be compacted to at least 95 percent per ASTM D1557. Non-structural Areas Hardscape Or Pavement Areas Ground Surface P: \ 2 3 \ 2 3 6 5 6 0 0 1 \ C A D \ 0 1 \ G e o t e c h \ 2 3 6 5 6 0 0 1 0 1 _ F 0 7 _ C o m p a c t i o n C r i t e r i a f o r T r e n c h B a c k f i l l . d w g T A B : 7 D a t e E x p o r t e d : 1 1 / 1 1 / 2 4 - 1 2 : 0 0 b y J f e l l o w s Figure 6 Willowcrest Townhomes Phase II Renton, Washington Appendices Appendix A Field Explorations Homestead Community Land Trust | November 18, 2024 Page A-1 File No. 23656-001-01 Appendix A FIELD EXPLORATIONS Subsurface soil and groundwater conditions were evaluated through a field exploration program that consisted of excavating six test pits (GEI-TP-7 through GEI-TP-12) at the approximate locations shown on Figure 2. Locations of the test pits were determined in the field by pacing and tape measuring distances from the test pit locations to existing site features. Ground surface elevations were interpolated from the site survey. Exploration locations and elevations should be considered accurate to the degree implied by the method used. The test pits were completed on October 24, 2024 to depths ranging from approximately 7½ to 10½ feet below the ground surface. The test pits were completed using a track-mounted excavator owned and operated by Kelly’s Excavating under subcontract to GeoEngineers. The test pits were continuously monitored by staff from our firm who reviewed and classified the soils encountered, obtained representative soil samples, observed groundwater conditions and prepared a detailed log of each test pit. Disturbed samples of representative soil types were obtained from the excavator bucket at representative depths. Soils encountered in the test pits were classified in the field in general accordance with ASTM D 2488, the Standard Practice for Classification of Soils, Visual-Manual Procedure, which is summarized in Figure A-1. Logs of the test pits are provided in Figures A-2 through A-7. The test pit logs are based on our interpretation of the field and laboratory data and indicate the various types of soil and groundwater conditions encountered. The logs also indicate the depths at which these soils or their characteristics change, although the change may be gradual. Observations of groundwater conditions were made during the excavations. The groundwater conditions encountered during excavation of the test pits are presented on the test pit logs. Groundwater conditions observed during the excavation of the test pits represent short-term condition and may or may not be representative of the long-term groundwater conditions at the site. Groundwater conditions observed during test pit excavations should be considered approximate. Measured groundwater level in exploration, well, or piezometer Measured free product in well or piezometer Distinct contact between soil strata Approximate contact between soil strata Contact between geologic units SYMBOLS TYPICAL DESCRIPTIONS GW GP SW SP SM FINE GRAINED SOILS SILTS AND CLAYS NOTE: Multiple symbols are used to indicate borderline or dual soil classifications MORE THAN 50% RETAINED ON NO. 200 SIEVE MORE THAN 50% PASSING NO. 200 SIEVE GRAVEL AND GRAVELLY SOILS SC LIQUID LIMIT LESS THAN 50 (APPRECIABLE AMOUNT OF FINES) (APPRECIABLE AMOUNT OF FINES) COARSE GRAINED SOILS MAJOR DIVISIONS GRAPH LETTER GM GC ML CL OL SILTS AND CLAYS SANDS WITH FINES SAND AND SANDY SOILS MH CH OH PT (LITTLE OR NO FINES) CLEAN SANDS GRAVELS WITH FINES CLEAN GRAVELS (LITTLE OR NO FINES) WELL-GRADED GRAVELS, GRAVEL -SAND MIXTURES CLAYEY GRAVELS, GRAVEL - SAND -CLAY MIXTURES WELL-GRADED SANDS, GRAVELLYSANDS POORLY-GRADED SANDS, GRAVELLYSAND SILTY SANDS, SAND - SILT MIXTURES CLAYEY SANDS, SAND - CLAYMIXTURES INORGANIC SILTS, ROCK FLOUR,CLAYEY SILTS WITH SLIGHTPLASTICITY INORGANIC CLAYS OF LOW TOMEDIUM PLASTICITY, GRAVELLYCLAYS, SANDY CLAYS, SILTY CLAYS,LEAN CLAYS ORGANIC SILTS AND ORGANIC SILTYCLAYS OF LOW PLASTICITY INORGANIC SILTS, MICACEOUS ORDIATOMACEOUS SILTY SOILS INORGANIC CLAYS OF HIGHPLASTICITY ORGANIC CLAYS AND SILTS OFMEDIUM TO HIGH PLASTICITY PEAT, HUMUS, SWAMP SOILS WITHHIGH ORGANIC CONTENTSHIGHLY ORGANIC SOILS SOIL CLASSIFICATION CHART MORE THAN 50% OF COARSE FRACTION RETAINED ON NO. 4 SIEVE MORE THAN 50% OF COARSE FRACTION PASSING ON NO. 4 SIEVE SILTY GRAVELS, GRAVEL - SAND -SILT MIXTURES POORLY-GRADED GRAVELS,GRAVEL - SAND MIXTURES LIQUID LIMIT GREATER THAN 50 Contact between soil of the same geologic unit Material Description Contact Graphic Log Contact NOTE: The reader must refer to the discussion in the report text and the logs of explorations for a proper understanding of subsurface conditions. Descriptions on the logs apply only at the specific exploration locations and at the time the explorations were made; they are not warranted to be representative of subsurface conditions at other locations or times. Groundwater Contact Blowcount is recorded for driven samplers as the number of blows required to advance sampler 12 inches (or distance noted). See exploration log for hammer weight and drop. "P" indicates sampler pushed using the weight of the drill rig. "WOH" indicates sampler pushed using the weight of the hammer. Key to Exploration Logs Figure A-1 ADDITIONAL MATERIAL SYMBOLS SYMBOLS Asphalt Concrete Cement Concrete Crushed Rock/ Quarry Spalls Topsoil GRAPH LETTER AC CC SOD Sod/Forest Duff CR DESCRIPTIONS TYPICAL TS No Visible Sheen Slight Sheen Moderate Sheen Heavy Sheen Laboratory / Field Tests %F %G AL CA CP CS DD DS HA MC MD Mohs OC PM PI PL PP SA TX UC UU VS Sheen Classification NS SS MS HS Percent fines Percent gravel Atterberg limits Chemical analysis Laboratory compaction test Consolidation test Dry density Direct shear Hydrometer analysis Moisture content Moisture content and dry density Mohs hardness scale Organic content Permeability or hydraulic conductivity Plasticity index Point load test Pocket penetrometer Sieve analysis Triaxial compression Unconfined compression Unconsolidated undrained triaxial compression Vane shear Continuous Coring Bulk or grab Direct-Push Piston Shelby tube Standard Penetration Test (SPT) Sampler Symbol Descriptions Modified California Sampler (6-inch sleeve) or Dames & Moore Rev. 03/2024 Dark brown silty sand (topsoil) Brown sandy silt with gravel (stiff to very stiff, moist) (weathered glacial till) Light grayish brown silt with sand and gravel (hard, moist) (glacial till) Light grayish brown silty fine to medium sand with occasional gravel (very dense, moist) TS ML ML SM 1 MC 2 MC 3SA 4 5 8 9 10 Probed 0 inches Probed 0 inches Probed 0 inches29 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Aerial Imagery. Da t e : 1 1 / 1 4 / 2 4 P a t h : P : \ 2 3 \ 2 3 6 5 6 0 0 1 \ G I N T \ 2 3 6 5 6 0 0 1 0 1 . G P J D B L i b r a r y / L i b r a r y : G E O E N G I N E E R S _ D F _ S T D _ U S _ J U N E _ 2 0 1 7 . G L B / G E I 8 _ T E S T P I T _ 1 P _ G E O T E C _ % F Sheet 1 of 1Project Number: Project Location: Project: 23656-001-01 Log of Test Pit GEI-TP-7 Figure A-2 Willowcrest Townhomes Phase II Renton, Washington El e v a t i o n ( f e e t ) 32 0 31 9 31 8 31 7 31 6 31 5 31 4 31 3 31 2 De p t h ( f e e t ) 1 2 3 4 5 6 7 8 9 Te s t i n g S a m p l e Gr a p h i c L o g SAMPLE MATERIAL DESCRIPTION Gr o u p Cl a s s i f i c a t i o n Sa m p l e N a m e Te s t i n g Mo i s t u r e Co n t e n t ( % ) REMARKS Fi n e s Co n t e n t ( % ) Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)10/24/2024 9.5 321 NAVD88 1306249 186101 WA State Plane North NAD83 (feet) JSP Checked By SK Groundwater not observed Caving not observedEquipment Takeuchi TB 138 Excavator Logged By Excavator Dark brown silty sand with organic matter (topsoil) Brown silty fine to medium sand with gravel (medium dense, moist) (weathered glacial till) Light gray silty fine to medium sand with gravel (very dense, moist) (glacial till) TS SM SM 1 MC 2MC 3 SA 4 6 7 7 29 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Aerial Imagery. Da t e : 1 1 / 1 4 / 2 4 P a t h : P : \ 2 3 \ 2 3 6 5 6 0 0 1 \ G I N T \ 2 3 6 5 6 0 0 1 0 1 . G P J D B L i b r a r y / L i b r a r y : G E O E N G I N E E R S _ D F _ S T D _ U S _ J U N E _ 2 0 1 7 . G L B / G E I 8 _ T E S T P I T _ 1 P _ G E O T E C _ % F Sheet 1 of 1Project Number: Project Location: Project: 23656-001-01 Log of Test Pit GEI-TP-8 Figure A-3 Willowcrest Townhomes Phase II Renton, Washington El e v a t i o n ( f e e t ) 32 7 32 6 32 5 32 4 32 3 32 2 32 1 De p t h ( f e e t ) 1 2 3 4 5 6 7 Te s t i n g S a m p l e Gr a p h i c L o g SAMPLE MATERIAL DESCRIPTION Gr o u p Cl a s s i f i c a t i o n Sa m p l e N a m e Te s t i n g Mo i s t u r e Co n t e n t ( % ) REMARKS Fi n e s Co n t e n t ( % ) Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)10/24/2024 7.5 328 NAVD88 1306326 186093 WA State Plane North NAD83 (feet) JSP Checked By SK Groundwater not observed Caving not observedEquipment Takeuchi TB 138 Excavator Logged By Excavator Dark brown silty sand with organic matter (topsoil) Light brown silty fine to medium sand with gravel; organic matter (loose, moist) (fill) Light gray silty fine to medium sand with gravel (dense to very dense, moist) (glacial till) Gray silty fine to coarse gravel with cobbles (dense to very dense, moist) Grayish brown silty fine to medium sand with occasional gravel (dense to very dense, moist) TS SM SM GM SM 1 MC 2MC 3 4 5 5 5 Probed 10 inches Probed 8 inches Probed 4 inches Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Aerial Imagery. Da t e : 1 1 / 1 4 / 2 4 P a t h : P : \ 2 3 \ 2 3 6 5 6 0 0 1 \ G I N T \ 2 3 6 5 6 0 0 1 0 1 . G P J D B L i b r a r y / L i b r a r y : G E O E N G I N E E R S _ D F _ S T D _ U S _ J U N E _ 2 0 1 7 . G L B / G E I 8 _ T E S T P I T _ 1 P _ G E O T E C _ % F Sheet 1 of 1Project Number: Project Location: Project: 23656-001-01 Log of Test Pit GEI-TP-9 Figure A-4 Willowcrest Townhomes Phase II Renton, Washington El e v a t i o n ( f e e t ) 31 5 31 4 31 3 31 2 31 1 31 0 30 9 30 8 De p t h ( f e e t ) 1 2 3 4 5 6 7 8 Te s t i n g S a m p l e Gr a p h i c L o g SAMPLE MATERIAL DESCRIPTION Gr o u p Cl a s s i f i c a t i o n Sa m p l e N a m e Te s t i n g Mo i s t u r e Co n t e n t ( % ) REMARKS Fi n e s Co n t e n t ( % ) Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)10/24/2024 8.5 316 NAVD88 1306242 185969 WA State Plane North NAD83 (feet) JSP Checked By SK Groundwater not observed Caving not observedEquipment Takeuchi TB 138 Excavator Logged By Excavator Dark gray fine to coarse gravel with silt and sand; construction debris (concrete, fabric and plastic) (loose, moist) (fill) Brown silty fine to medium sand with gravel (dense to very dense, moist) (weathered glacial till) Gray silty fine sand (very dense, moist) (glacial till) GP-GM SM SM 1 2 MC 3SA 4 MC 5 11 9 8 Probed 2 inches Probed 0 inches Probed 0 inches16 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Aerial Imagery. Da t e : 1 1 / 1 4 / 2 4 P a t h : P : \ 2 3 \ 2 3 6 5 6 0 0 1 \ G I N T \ 2 3 6 5 6 0 0 1 0 1 . G P J D B L i b r a r y / L i b r a r y : G E O E N G I N E E R S _ D F _ S T D _ U S _ J U N E _ 2 0 1 7 . G L B / G E I 8 _ T E S T P I T _ 1 P _ G E O T E C _ % F Sheet 1 of 1Project Number: Project Location: Project: 23656-001-01 Log of Test Pit GEI-TP-10 Figure A-5 Willowcrest Townhomes Phase II Renton, Washington El e v a t i o n ( f e e t ) 32 5 32 4 32 3 32 2 32 1 32 0 31 9 31 8 31 7 31 6 De p t h ( f e e t ) 1 2 3 4 5 6 7 8 9 10 Te s t i n g S a m p l e Gr a p h i c L o g SAMPLE MATERIAL DESCRIPTION Gr o u p Cl a s s i f i c a t i o n Sa m p l e N a m e Te s t i n g Mo i s t u r e Co n t e n t ( % ) REMARKS Fi n e s Co n t e n t ( % ) Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)10/24/2024 10.5 326 NAVD88 1306342 185988 WA State Plane North NAD83 (feet) JSP Checked By SK Groundwater not observed Caving not observedEquipment Takeuchi TB 138 Excavator Logged By Excavator Brown silty sand with organic matter (topsoil) Brown silty fine to medium sand; organic matter (loose, moist) (weathered glacial till) Boulder Light grayish brown silty fine to medium sand with occasional gravel (dense to very dense, moist) (glacial till) TS SM SM 1 MC 2MC 3MC 4 6 7 8 Probed 10 inches Probed 10 inches Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Aerial Imagery. Da t e : 1 1 / 1 4 / 2 4 P a t h : P : \ 2 3 \ 2 3 6 5 6 0 0 1 \ G I N T \ 2 3 6 5 6 0 0 1 0 1 . G P J D B L i b r a r y / L i b r a r y : G E O E N G I N E E R S _ D F _ S T D _ U S _ J U N E _ 2 0 1 7 . G L B / G E I 8 _ T E S T P I T _ 1 P _ G E O T E C _ % F Sheet 1 of 1Project Number: Project Location: Project: 23656-001-01 Log of Test Pit GEI-TP-11 Figure A-6 Willowcrest Townhomes Phase II Renton, Washington El e v a t i o n ( f e e t ) 31 6 31 5 31 4 31 3 31 2 31 1 31 0 30 9 De p t h ( f e e t ) 1 2 3 4 5 6 7 8 Te s t i n g S a m p l e Gr a p h i c L o g SAMPLE MATERIAL DESCRIPTION Gr o u p Cl a s s i f i c a t i o n Sa m p l e N a m e Te s t i n g Mo i s t u r e Co n t e n t ( % ) REMARKS Fi n e s Co n t e n t ( % ) Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)10/24/2024 8.5 317 NAVD88 1306253 185909 WA State Plane North NAD83 (feet) JSP Checked By SK Groundwater not observed Caving not observedEquipment Takeuchi TB 138 Excavator Logged By Excavator Dark brown silty sand with organic matter (topsoil) Brown silty fine to medium sand with gravel; organic matter (loose, moist) (fill) Orange Fabric Tan silty fine to medium sand with gravel (very dense, moist) (glacial till) TS SM SM 1 MC 2MC 3 SA 4 5 6 4 Probed 6 inches Probed 0 inches 28 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Aerial Imagery. Da t e : 1 1 / 1 4 / 2 4 P a t h : P : \ 2 3 \ 2 3 6 5 6 0 0 1 \ G I N T \ 2 3 6 5 6 0 0 1 0 1 . G P J D B L i b r a r y / L i b r a r y : G E O E N G I N E E R S _ D F _ S T D _ U S _ J U N E _ 2 0 1 7 . G L B / G E I 8 _ T E S T P I T _ 1 P _ G E O T E C _ % F Sheet 1 of 1Project Number: Project Location: Project: 23656-001-01 Log of Test Pit GEI-TP-12 Figure A-7 Willowcrest Townhomes Phase II Renton, Washington El e v a t i o n ( f e e t ) 32 7 32 6 32 5 32 4 32 3 32 2 32 1 32 0 De p t h ( f e e t ) 1 2 3 4 5 6 7 8 Te s t i n g S a m p l e Gr a p h i c L o g SAMPLE MATERIAL DESCRIPTION Gr o u p Cl a s s i f i c a t i o n Sa m p l e N a m e Te s t i n g Mo i s t u r e Co n t e n t ( % ) REMARKS Fi n e s Co n t e n t ( % ) Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)10/24/2024 8.5 328 NAVD88 1306363 185909 WA State Plane North NAD83 (feet) JSP Checked By SK Groundwater not observed Caving not observedEquipment Takeuchi TB 138 Excavator Logged By Excavator Appendix B Laboratory Testing Homestead Community Land Trust | November 18, 2024 Page B-1 File No. 23656-001-01 Appendix B LABORATORY TESTING Soil samples obtained from the test pits were visually classified in the field before being transported to our laboratory and evaluated to confirm or modify field classifications, as well as to evaluate index properties of the soil samples. Representative samples were selected for laboratory testing consisting of moisture content and grain size distribution (sieve analysis). The tests were performed in general accordance with test methods of the ASTM International (ASTM) or other applicable procedures. Visual Classifications Soil samples obtained from the test pits were visually classified in the field and/or in our laboratory using a system based on the Unified Soil Classification System (USCS) and ASTM classification methods. ASTM test method D 2488 was used to visually classify the soil samples, while ASTM D 2487 was used to classify the soils based on laboratory tests results. These classification procedures are incorporated in the test pit logs shown in Appendix A. Moisture Content Moisture content tests were completed in general accordance with ASTM D 2216 for representative samples obtained from the test pits. The results of these tests are presented on the test pit logs in Appendix A at the depths at which the samples were obtained. Grain Size Distribution Sieve analyses were performed on selected samples in general accordance with ASTM D 6913. The wet sieve analysis method was used to estimate the percentage of soil greater than the U.S. No. 200 mesh sieve. The results of the sieve analyses were plotted, classified in general accordance with the USCS, and presented in Figure B-1. 0 10 20 30 40 50 60 70 80 90 100 0.0010.010.11101001000 PE R C E N T P A S S I N G B Y W E I G H T GRAIN SIZE IN MILLIMETERS U.S. STANDARD SIEVE SIZE 2” SAND SILT OR CLAYCOBBLES GRAVEL COARSE MEDIUM FINECOARSEFINE Boring Number Depth (feet)Soil Description GEI-TP-7 GEI-TP-8 GEI-TP-10 GEI-TP-12 4 6 4 6 Silty fine to medium sand with occasional gravel(SM) Silty fine to medium sand with gravel (SM) Silty fine sand (SM) Silty fine to medium sand with gravel (SM) Symbol Moisture (%) 10 7 9 4 3/8”3” 1.5”#4 #10 #20 #40 #60 #1003/4” Fi g u r e B - 1 Si e v e A n a l y s i s R e s u l t s Wi l l o w c r e s t T o w n h o m e s P h a s e I I Re n t o n , W a s h i n g t o n 23656-001-00 Date Exported: 11/14/2024 Note: This report may not be reproduced, except in full, without written approval of GeoEngineers, Inc. Test results are applicable only to the specific sample on which they were performed, and should not be interpreted as representative of any other samples obtained at other times, depths or locations, or generated by separate operations or processes. The grain size analysis results were obtained in general accordance with ASTM D6913. GeoEngineers 17425 NE Union Hill Road Ste 250, Redmond, WA 98052 #2001”#140 Appendix C Exploration Logs from Previous Studies Homestead Community Land Trust | November 18, 2024 Page C1 File No. 23656-001-01 Appendix C EXPLORATION LOGS FROM PREVIOUS STUDIES Included in Appendix C are relevant logs from available previous studies completed in the immediate vicinity of the project site. ■ The logs of six test pits (GEI-TP-1 through GEI-TP-6) completed by GeoEngineers, Inc., in 2018 for Phase I of the Willowcrest Townhomes project. ■ The logs of two borings (B-1 and B-2) and six test pits (TP-1 through TP-6) completed by Soil and Environmental Engineers, Inc., in 2010 for the Proposed Development at Edmonds Avenue NE and Glennwood Avenue NE project. Blackberry brambles Dark brown fine to medium sand with silt, occasional gravel, roots (loose, moist) (fill) Light brown silty fine to medium sand with gravel, occasional cobbles, trace roots (medium dense, moist) (weathered glacial till) Gray silty fine to medium sand with gravel (very dense, moist) (glacial till) WD SP-SM SM SM 1 SA 2 %F 3 4 4 3 Pocket Pen / Probe Penetration 0.0 kg/cm2 / 6 inches 0.5 kg/cm2 / 4 inches >4.5 kg/cm2 / ½ inch >4.5 kg/cm2 / <½ inch 21 30 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Google Earth. Da t e : 1 1 / 5 / 1 8 P a t h : W : \ P R O J E C T S \ 2 3 \ 2 3 6 5 6 0 0 1 \ G I N T \ 2 3 6 5 6 0 0 1 0 0 . G P J D B L i b r a r y / L i b r a r y : G E O E N G I N E E R S _ D F _ S T D _ U S _ J U N E _ 2 0 1 7 . G L B / G E I 8 _ T E S T P I T _ 1 P _ G E O T E C _ % F Sheet 1 of 1Project Number: Project Location: Project: Renton, Washington 23656-001-00 Log of Test Pit GEI-TP-1 Sunset Crest Townhomes Figure A-2 El e v a t i o n ( f e e t ) 33 9 33 8 33 7 33 6 33 5 33 4 33 3 33 2 De p t h ( f e e t ) 1 2 3 4 5 6 7 8 Te s t i n g S a m p l e Gr a p h i c L o g SAMPLE MATERIAL DESCRIPTION Gr o u p Cl a s s i f i c a t i o n Sa m p l e N a m e Te s t i n g Mo i s t u r e Co n t e n t ( % ) REMARKS Fi n e s Co n t e n t ( % ) Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)10/22/2018 8 340 NAVD88 1306462 186084 WA State Plane North NAD83 (feet) AJF Checked By MAG Groundwater not observed Caving not observedEquipment Takeuchi TB138FR Logged By Excavator Kelly's Excavating, Inc. Blackberry brambles Dark brown fine to medium sand with silt, roots (loose, moist) (fill) Brown silty coarse gravel with sand and occasional cobbles, roots (medium dense to dense, moist) (weathered glacial till) No roots below 2 feet Gray silty fine sand with occasional gravel and cobbles (very dense, moist) (glacial till) WD SP-SM GM SM 1 SA 2 3 4 3 Pocket Pen / Probe Penetration 0.0 kg/cm2 / 8 inches 1.0 kg/cm2 / 3 inches >4.5 kg/cm2 / 1 inch >4.5 kg/cm2 / ¼ inch 17 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Google Earth. Da t e : 1 1 / 5 / 1 8 P a t h : W : \ P R O J E C T S \ 2 3 \ 2 3 6 5 6 0 0 1 \ G I N T \ 2 3 6 5 6 0 0 1 0 0 . G P J D B L i b r a r y / L i b r a r y : G E O E N G I N E E R S _ D F _ S T D _ U S _ J U N E _ 2 0 1 7 . G L B / G E I 8 _ T E S T P I T _ 1 P _ G E O T E C _ % F Sheet 1 of 1Project Number: Project Location: Project: Renton, Washington 23656-001-00 Log of Test Pit TEI-TP-2 Sunset Crest Townhomes Figure A-3 El e v a t i o n ( f e e t ) 33 9 33 8 33 7 33 6 33 5 33 4 33 3 33 2 De p t h ( f e e t ) 1 2 3 4 5 6 7 8 Te s t i n g S a m p l e Gr a p h i c L o g SAMPLE MATERIAL DESCRIPTION Gr o u p Cl a s s i f i c a t i o n Sa m p l e N a m e Te s t i n g Mo i s t u r e Co n t e n t ( % ) REMARKS Fi n e s Co n t e n t ( % ) Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)10/22/2018 8 340 NAVD88 1306453 186046 WA State Plane North NAD83 (feet) AJF Checked By MAG Groundwater not observed Caving not observedEquipment Takeuchi TB138FR Logged By Excavator Kelly's Excavating, Inc. Blackberry brambles Dark brown fine to medium sand with silt and occasional gravel, roots (loose, moist) (fill) Light brown silty fine sand with gravel and occasional cobbles, roots (loose to medium dense, moist) (weathered glacial till) No roots below 2 feet Light gray silty fine to medium sand with occasional gravel and cobbles (very dense, moist) (glacial till) Gray fine to medium sand with silt, gravel and occasional cobbles (very dense, moist) WD SP-SM SM SM SP-SM 1 SA 2 3 4 5 Pocket Pen / Probe Penetration 0.0 kg/cm2 / 12 inches 2.0 kg/cm2 / 3 inches >4.5 kg/cm2 / ½ inch >4.5 kg/cm2 / ¼ inch 32 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Google Earth. Da t e : 1 1 / 5 / 1 8 P a t h : W : \ P R O J E C T S \ 2 3 \ 2 3 6 5 6 0 0 1 \ G I N T \ 2 3 6 5 6 0 0 1 0 0 . G P J D B L i b r a r y / L i b r a r y : G E O E N G I N E E R S _ D F _ S T D _ U S _ J U N E _ 2 0 1 7 . G L B / G E I 8 _ T E S T P I T _ 1 P _ G E O T E C _ % F Sheet 1 of 1Project Number: Project Location: Project: Renton, Washington 23656-001-00 Log of Test Pit GEI-TP-3 Sunset Crest Townhomes Figure A-4 El e v a t i o n ( f e e t ) 33 9 33 8 33 7 33 6 33 5 33 4 33 3 33 2 De p t h ( f e e t ) 1 2 3 4 5 6 7 8 Te s t i n g S a m p l e Gr a p h i c L o g SAMPLE MATERIAL DESCRIPTION Gr o u p Cl a s s i f i c a t i o n Sa m p l e N a m e Te s t i n g Mo i s t u r e Co n t e n t ( % ) REMARKS Fi n e s Co n t e n t ( % ) Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)10/22/2018 8 340 NAVD88 1306422 185979 WA State Plane North NAD83 (feet) AJF Checked By MAG Groundwater not observed Caving not observedEquipment Takeuchi TB138FR Logged By Excavator Kelly's Excavating, Inc. Blackberry brambles Dark brown fine to medium sand with silt and occasional gravel, roots (loose, moist) (fill) Light brown silty fine sand with gravel and occasional cobbles (loose to medium dense, moist) (weathered glacial till) Light gray silty fine to medium sand with gravel and occasional cobbles; partially cemented (very dense, moist) (glacial till) Boulder encountered at 3½ feet WD SP-SM SM SM 1 2 SA 3 4 6 Pocket Pen / Probe Penetration 0.0 kg/cm2 / 12 inches 2.25 kg/cm2 / 4 inches >4.5 kg/cm2 / 1 inch >4.5 kg/cm2 / ¼ inch 35 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Google Earth. Da t e : 1 1 / 5 / 1 8 P a t h : W : \ P R O J E C T S \ 2 3 \ 2 3 6 5 6 0 0 1 \ G I N T \ 2 3 6 5 6 0 0 1 0 0 . G P J D B L i b r a r y / L i b r a r y : G E O E N G I N E E R S _ D F _ S T D _ U S _ J U N E _ 2 0 1 7 . G L B / G E I 8 _ T E S T P I T _ 1 P _ G E O T E C _ % F Sheet 1 of 1Project Number: Project Location: Project: Renton, Washington 23656-001-00 Log of Test Pit GEI-TP-4 Sunset Crest Townhomes Figure A-5 El e v a t i o n ( f e e t ) 33 9 33 8 33 7 33 6 33 5 33 4 33 3 33 2 De p t h ( f e e t ) 1 2 3 4 5 6 7 8 Te s t i n g S a m p l e Gr a p h i c L o g SAMPLE MATERIAL DESCRIPTION Gr o u p Cl a s s i f i c a t i o n Sa m p l e N a m e Te s t i n g Mo i s t u r e Co n t e n t ( % ) REMARKS Fi n e s Co n t e n t ( % ) Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)10/22/2018 8 340 NAVD88 1306466 185974 WA State Plane North NAD83 (feet) AJF Checked By MAG Groundwater not observed Caving not observedEquipment Takeuchi TB138FR Logged By Excavator Kelly's Excavating, Inc. Blackberry brambles Brown fine to medium sand with silt and occasional gravel (loose, moist) (fill) Light brown silty fine sand with gravel and cobbles, roots (loose to medium dense, moist) (weathered glacial till) Gray silty fine sand with gravel and occasional cobbles; partially cemented (dense to very dense, moist) (glacial till) WD SP-SM SM SM 1 %F 2 3 4 8 Pocket Pen / Probe Penetration 0.0 kg/cm2 / 12 inches 1.5 kg/cm2 / 5 inches 2.5 kg/cm2 / 2 inches >4.5 kg/cm2 / ¼ inch 26 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Google Earth. Da t e : 1 1 / 5 / 1 8 P a t h : W : \ P R O J E C T S \ 2 3 \ 2 3 6 5 6 0 0 1 \ G I N T \ 2 3 6 5 6 0 0 1 0 0 . G P J D B L i b r a r y / L i b r a r y : G E O E N G I N E E R S _ D F _ S T D _ U S _ J U N E _ 2 0 1 7 . G L B / G E I 8 _ T E S T P I T _ 1 P _ G E O T E C _ % F Sheet 1 of 1Project Number: Project Location: Project: Renton, Washington 23656-001-00 Log of Test Pit GEI-TP-5 Sunset Crest Townhomes Figure A-6 El e v a t i o n ( f e e t ) 33 9 33 8 33 7 33 6 33 5 33 4 33 3 33 2 De p t h ( f e e t ) 1 2 3 4 5 6 7 8 Te s t i n g S a m p l e Gr a p h i c L o g SAMPLE MATERIAL DESCRIPTION Gr o u p Cl a s s i f i c a t i o n Sa m p l e N a m e Te s t i n g Mo i s t u r e Co n t e n t ( % ) REMARKS Fi n e s Co n t e n t ( % ) Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)10/22/2018 8 340 NAVD88 1306422 185911 WA State Plane North NAD83 (feet) AJF Checked By MAG Groundwater not observed Caving not observedEquipment Takeuchi TB138FR Logged By Excavator Kelly's Excavating, Inc. Blackberry brambles Brown fine to medium sand with silt and occasional gravel (loose, moist) (fill) Light brown silty fine to medium sand with gravel and cobbles, roots (loose to medium dense, moist) (weathered till) Gray silty fine to medium sand with gravel and occasional cobbles (dense to very dense, moist) (glacial till) WD SP-SM SM SM 1 2 SA 3 4 5 Pocket Pen / Probe Penetration 0.0 kg/cm2 / 12 inches 1.5 kg/cm2 / 5 inches 4.0 kg/cm2 / 1½ inches >4.5 kg/cm2 / ¼ inch 33 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Google Earth. Da t e : 1 1 / 5 / 1 8 P a t h : W : \ P R O J E C T S \ 2 3 \ 2 3 6 5 6 0 0 1 \ G I N T \ 2 3 6 5 6 0 0 1 0 0 . G P J D B L i b r a r y / L i b r a r y : G E O E N G I N E E R S _ D F _ S T D _ U S _ J U N E _ 2 0 1 7 . G L B / G E I 8 _ T E S T P I T _ 1 P _ G E O T E C _ % F Sheet 1 of 1Project Number: Project Location: Project: Renton, Washington 23656-001-00 Log of Test Pit GEI-TP-6 Sunset Crest Townhomes Figure A-7 El e v a t i o n ( f e e t ) 33 9 33 8 33 7 33 6 33 5 33 4 33 3 33 2 De p t h ( f e e t ) 1 2 3 4 5 6 7 8 Te s t i n g S a m p l e Gr a p h i c L o g SAMPLE MATERIAL DESCRIPTION Gr o u p Cl a s s i f i c a t i o n Sa m p l e N a m e Te s t i n g Mo i s t u r e Co n t e n t ( % ) REMARKS Fi n e s Co n t e n t ( % ) Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)10/22/2018 8 340 NAVD88 1306474 185878 WA State Plane North NAD83 (feet) AJF Checked By MAG Groundwater not observed Caving not observedEquipment Takeuchi TB138FR Logged By Excavator Kelly's Excavating, Inc. Appendix D Ground Anchor Load Tests and Shoring Monitoring Program Homestead Community Land Trust | November 18, 2024 Page D1 File No. 23656-001-01 Appendix D GROUND ANCHOR LOAD TESTS AND SHORING MONITORING PROGRAM Ground Anchor Load Testing The locations of the load tests shall be approved by the Engineer and shall be representative of the field conditions. Load tests shall not be performed until the ground anchor grout and shotcrete wall facing, where present, have attained at least 50 percent of the specified 28-day compressive strengths. Where temporary casing of the unbonded length of test ground anchors is provided, the casing shall be installed to prevent interaction between the bonded length of the ground anchor and the casing/testing apparatus. The testing equipment shall include two dial gauges accurate to 0.001 inch, a dial gauge support, a calibrated jack and pressure gauge, a pump and the load test reaction frame. The dial gauge should be aligned within 5 degrees of the longitudinal ground anchor axis and shall be independently supported from the load frame/jack and the shoring wall. The hydraulic jack, pressure gauge and pump shall be used to apply and measure the test loads. The jack and pressure gauge shall be calibrated by an independent testing laboratory as a unit. The pressure gauge shall be graduated in 100 pounds per square inch (psi) increments or less and shall have a range not exceeding twice the anticipated maximum pressure during testing unless approved by the Engineer. The ram travel of the jack shall be sufficient to enable the test to be performed without repositioning the jack. The jack shall be independently supported and centered over the ground anchor so that the ground anchor does not carry the weight of the jack. The jack, bearing plates and stressing anchorage shall be aligned with the ground anchor. The initial position of the jack shall be such that repositioning of the jack is not necessary during the load test. The reaction frame should be designed/sized such that excessive deflection of the test apparatus does not occur and that the testing apparatus does not need to be repositioned during the load test. If the reaction frame bears directly on the shoring wall facing, the reaction frame should be designed to not damage the facing. VERIFICATION TESTS Prior to production soil nail/tieback installation, at least two soil nails/tiebacks for each soil type shall be tested to validate the design pullout value. All test nails/tiebacks shall be installed by the same methods, personnel, material and equipment as the production anchors. Changes in methods, personnel, material or equipment may require additional verification testing as determined by the Engineer. At least two successful verification tests shall be performed for each installation method and each soil type. The nails/tiebacks used for the verification tests may be used as production nails/tiebacks if approved by the Engineer. Homestead Community Land Trust | November 18, 2024 Page D2 File No. 23656-001-01 For soil nails, the unbonded length of the test nails shall be at least 3 feet unless approved otherwise by the Engineer. The bond length of the test nails shall not be less than 10 feet and shall not be longer than the bond length that would prevent testing to 200 percent of the design load while not exceeding the allowable bar load. The allowable bar load during testing shall not exceed 80 percent of the steel ultimate strength for Grade 150 bars or 90 percent of the steel ultimate strength for Grade 60 and 75 bars. The allowable tieback load should not exceed 80 percent of the steel ultimate strength. For soil nails, the design test load shall be determined by multiplying the bond length of the nail times the design load pullout resistance (load transfer). Tieback design test loads should be the design load specified on the shoring drawings. Verification test nails/tiebacks shall be incrementally loaded and unloaded in accordance with the following schedule: LOAD HOLD TIME Alignment Load 1 minute 0.25 Design Load (DL) 1 minute 0.5DL 1 minute 0.75DL 1 minute 1.0DL 1 minute 1.25DL 1 minute 1.5DL 60 minutes 1.75DL 1 minute 2.0DL 10 minutes The alignment load shall be the minimum load required to align the testing apparatus and should not exceed 5 percent of the design load. The dial gauge should be zeroed after the alignment load is applied. Nail/tieback deflections during the 1.5DL test load shall be recorded at 1, 2, 3, 5, 6, 10, 20, 30, 50 and 60 minutes. PROOF TESTS Proof tests shall be completed on approximately 5 percent of the production nails at locations selected by the owner’s representative. Additional testing may be required where nail installation methods are substandard. Proof tests shall be completed on each production tieback. For soil nails, the unbonded length of the test nails shall be at least 3 feet unless approved otherwise by the Engineer. The bond length of the test nails shall not be less than 10 feet and shall not be longer than the bond length that would prevent testing to 200 percent of the design load while not exceeding the allowable bar load. The allowable bar load during testing shall not exceed 80 percent of the steel ultimate strength for Grade 150 bars or 90 percent of the steel ultimate strength for Grade 60 and 75 bars. The allowable tieback load should not exceed 80 percent of the steel ultimate strength. For soil nails, the design test load shall be determined by multiplying the bond length of the nail times the design load pullout resistance (load transfer). Tieback design test loads should be the design load specified on the shoring drawings. Proof test nails/tiebacks shall be incrementally loaded and unloaded in accordance with the following schedule: Homestead Community Land Trust | November 18, 2024 Page D3 File No. 23656-001-01 LOAD HOLD TIME Alignment Load 1 minute 0.25 Design Load (DL) 1 minute 0.5DL 1 minute 0.75DL 1 minute 1.0DL 1 minute 1.25DL (soil nails) 1 minute 1.33DL (tiebacks) 10 minutes 1.5DL (soil nails) The alignment load shall be the minimum load required to align the testing apparatus and should not exceed 5 percent of the design load. The dial gauge should be zeroed after the alignment load is applied. Nail/tieback deflections during the 1.33DL and 1.5DL test loads shall be recorded at 1, 2, 3, 5, 6 and 10 minutes. Depending upon the nail/tieback deflection performance, the load hold period at 1.33DL (tiebacks) or 1.5DL (soil nails) may be increased to 60 minutes. Nail/tieback movement shall be recorded at 1, 2, 3, 5, 6 and 10 minutes. If the nail/tieback deflection between 1 minute and 10 minutes is greater than 0.04 inches, the 1.33DL/1.5DL load shall be continued to be held for a total of 60 minutes and deflections recorded at 20, 30, 50, and 60 minutes. TEST GROUND ANCHOR ACCEPTANCE A test ground anchor shall be considered acceptable when: 1. For verification tests, a nail/tieback is considered acceptable if the creep rate is less than 0.04 inches per log cycle of time between 1 and 10 minutes, and the creep rate is linear or decreasing throughout the creep test load hold period; 2. For proof tests, a ground anchor is considered acceptable if the creep rate is less than 0.04 inches per log cycle of time between 1 and 10 minutes or less than 0.08 inches per log cycle of time between 6 and 60 minutes, and the creep rate is linear or decreasing throughout the creep test load hold period; 3. The total movement at the maximum test load exceeds 80 percent of the theoretical elastic elongation of the unbonded length; and 4. Pullout failure does not occur. Pullout failure is defined as the load at which continued attempts to increase the test load result in continued pullout of the test ground anchor. Acceptable proof-test ground anchors may be incorporated as production ground anchors provided that the unbonded test length of the ground anchor hole has not collapsed and the test ground anchor length and bar size/number of strands are equal to or greater than the scheduled production ground anchor at the test location. Test ground anchors meeting these criteria shall be completed by grouting the unbonded length, as necessary. Maintenance of the temporary unbonded length for subsequent grouting is the contractor’s responsibility. Homestead Community Land Trust | November 18, 2024 Page D4 File No. 23656-001-01 The Engineer shall evaluate the verification test results. Ground anchor installation techniques that do not satisfy the ground anchor testing requirements shall be considered inadequate. In this case, the contractor shall propose alternative methods and install replacement verification test ground anchors. The Engineer may require that the contractor replace or install additional production ground anchors in areas represented by inadequate proof tests. Shoring Monitoring PRECONSTRUCTION SURVEY A shoring monitoring program should be established to monitor the performance of the temporary shoring walls and to provide early detection of deflections that could potentially damage nearby improvements. We recommend that a preconstruction survey of adjacent improvements, such as streets, utilities and buildings, be performed prior to commencing construction. The preconstruction survey should include a video or photographic survey of the condition of existing improvements to establish the preconstruction condition, with special attention to existing cracks in streets or buildings. OPTICAL SURVEY The shoring monitoring program should include an optical survey monitoring program. The recommended frequency of monitoring should vary as a function of the stage of construction as presented in the following table. CONSTRUCTION STAGE MONITORING FREQUENCY During excavation and until wall movements have stabilized Twice weekly During excavation if lateral wall movements exceed 1 inch and until wall movements have stabilized Three times per week After excavation is complete and wall movements have stabilized, and before the floors of the building reach the top of the excavation Twice monthly Monitoring should include vertical and horizontal survey measurements accurate to at least 0.01 feet. A baseline reading of the monitoring points should be completed prior to beginning excavation. The survey data should be provided to GeoEngineers for review within 24 hours. For shoring walls, we recommend that optical survey points be established: (1) along the top of the shoring walls; (2) at the curb line behind the shoring walls; and (3) on existing buildings/structures located within 100 feet of the site. The survey points should be spaced every other soldier pile for soldier pile walls, every 20 feet for soil nail walls and the points along the curb line/existing buildings should be located at an approximate spacing of 25 feet. GeoEngineers recommends that a survey monitoring plan be developed for GeoEngineers’ review prior to establishing the survey points in the field. If lateral wall movements are observed to be in excess of ½ inch between successive readings or if total wall movements exceed 1 inch, construction of the shoring walls should be stopped to determine the cause of the movement and to establish the type and extent of remedial measures required. Appendix E Report Limitations and Guidelines for Use Homestead Community Land Trust | November 18, 2024 Page E-1 File No. 23656-001-01 Appendix E Report Limitations and Guidelines for Use1 This appendix provides information to help you manage your risks with respect to the use of this report. Read These Provisions Closely It is important to recognize that the geoscience practices (geotechnical engineering, geology, and environmental science) rely on professional judgment and opinion to a greater extent than other engineering and natural science disciplines, where more precise and/or readily observable data may exist. To help clients better understand how this difference pertains to our services, GeoEngineers includes the following explanatory “limitations” provisions in its reports. Please confer with GeoEngineers if you need to know more how these “Report Limitations and Guidelines for Use” apply to your project or site. Geotechnical Services Are Performed for Specific Purposes, Persons, and Projects This report has been prepared for Homestead Community Land Trust and for the Project(s) specifically identified in the report. The information contained herein is not applicable to other sites or projects. GeoEngineers structures its services to meet the specific needs of its clients. No party other than the party to whom this report is addressed may rely on the product of our services unless we agree to such reliance in advance and in writing. Within the limitations of the agreed scope of services for the Project, and its schedule and budget, our services have been executed in accordance with our Agreement with Homestead Community Land Trust dated October 15, 2024 and generally accepted geotechnical practices in this area at the time this report was prepared. We do not authorize, and will not be responsible for, the use of this report for any purposes or projects other than those identified in the report. A Geotechnical Engineering or Geologic Report is Based on a Unique Set of Project- Specific Factors This report has been prepared for the proposed Willowcrest Townhomes Phase II project in Renton, Washington. GeoEngineers considered a number of unique, project-specific factors when establishing the scope of services for this project and report. Unless GeoEngineers specifically indicates otherwise, it is important not to rely on this report if it was: ■ Not prepared for you, ■ Not prepared for your project, ■ Not prepared for the specific site explored, or ■ Completed before important project changes were made. For example, changes that can affect the applicability of this report include those that affect: 1 Developed based on material provided by GBA, GeoProfessional Business Association, www.geoprofessional.org. Homestead Community Land Trust | November 18, 2024 Page E-2 File No. 23656-001-01 ■ The function of the proposed structure, ■ Elevation, configuration, location, orientation or weight of the proposed structure, ■ Composition of the design team; or ■ Project ownership. If important changes are made after the date of this report, GeoEngineers should be given the opportunity to review our interpretations and recommendations and provide written modifications or confirmation, as appropriate. Subsurface Conditions Can Change This geotechnical or geologic report is based on conditions that existed at the time the study was performed. The findings and conclusions of this report may be affected by the passage of time, by man-made events such as construction on or adjacent to the site, new information or technology that becomes available subsequent to the report date, or by natural events such as floods, earthquakes, slope instability or groundwater fluctuations. If more than a few months have passed since issuance of our report or work product, or if any of the described events may have occurred, please contact GeoEngineers before applying this report for its intended purpose so that we may evaluate whether changed conditions affect the continued reliability or applicability of our conclusions and recommendations. Geotechnical and Geologic Findings are Professional Opinions Our interpretations of subsurface conditions are based on field observations from widely spaced sampling locations at the site. Site exploration identifies the specific subsurface conditions only at those points where subsurface tests are conducted or samples are taken. GeoEngineers reviewed field and laboratory data and then applied its professional judgment to render an informed opinion about subsurface conditions at other locations. Actual subsurface conditions may differ, sometimes significantly, from the opinions presented in this report. Our report, conclusions and interpretations are not a warranty of the actual subsurface conditions. Geotechnical Engineering Report Recommendations are Not Final We have developed the following recommendations based on data gathered from subsurface investigation(s). These investigations sample just a small percentage of a site to create a snapshot of the subsurface conditions elsewhere on the site. Such sampling on its own cannot provide a complete and accurate view of subsurface conditions for the entire site. Therefore, the recommendations included in this report are preliminary and should not be considered final. GeoEngineers’ recommendations can be finalized only by observing actual subsurface conditions revealed during construction. GeoEngineers cannot assume responsibility or liability for the recommendations in this report if we do not perform construction observation. Homestead Community Land Trust | November 18, 2024 Page E-3 File No. 23656-001-01 We recommend that you allow sufficient monitoring, testing and consultation during construction by GeoEngineers to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes if the conditions revealed during the work differ from those anticipated, and to evaluate whether earthwork activities are completed in accordance with our recommendations. Retaining GeoEngineers for construction observation for this project is the most effective means of managing the risks associated with unanticipated conditions. If another party performs field observation and confirms our expectations, the other party must take full responsibility for both the observations and recommendations. Please note, however, that another party would lack our project- specific knowledge and resources. A Geotechnical Engineering or Geologic Report Could Be Subject to Misinterpretation Misinterpretation of this report by other design team members can result in costly problems. You could lower that risk by having GeoEngineers confer with appropriate members of the design team after submitting the report. Also retain GeoEngineers to review pertinent elements of the design team's plans and specifications. Contractors can also misinterpret a geotechnical engineering or geologic report. Reduce that risk by having GeoEngineers participate in pre-bid and preconstruction conferences, and by providing construction observation. Do Not Redraw the Exploration Logs Geotechnical engineers and geologists prepare final boring and testing logs based upon their interpretation of field logs and laboratory data. The logs included in a geotechnical engineering or geologic report should never be redrawn for inclusion in architectural or other design drawings. Photographic or electronic reproduction is acceptable, but separating logs from the report can create a risk of misinterpretation. Give Contractors a Complete Report and Guidance To help reduce the risk of problems associated with unanticipated subsurface conditions, GeoEngineers recommends giving contractors the complete geotechnical engineering or geologic report, including these “Report Limitations and Guidelines for Use.” When providing the report, you should preface it with a clearly written letter of transmittal that: ■ Advises contractors that the report was not prepared for purposes of bid development and that its accuracy is limited; and ■ Encourages contractors to conduct additional study to obtain the specific types of information they need or prefer. Contractors Are Responsible for Site Safety on Their Own Construction Projects Our geotechnical recommendations are not intended to direct the contractor’s procedures, methods, schedule or management of the work site. The contractor is solely responsible for job site safety and for managing construction operations to minimize risks to on-site personnel and to adjacent properties. Homestead Community Land Trust | November 18, 2024 Page E-4 File No. 23656-001-01 Geotechnical, Geologic and Environmental Reports Should Not Be Interchanged The equipment, techniques and personnel used to perform an environmental study differ significantly from those used to perform a geotechnical or geologic study and vice versa. For that reason, a geotechnical engineering or geologic report does not usually relate any environmental findings, conclusions or recommendations, e.g., about the likelihood of encountering underground storage tanks or regulated contaminants. Similarly, environmental reports are not used to address geotechnical or geologic concerns regarding a specific project. Biological Pollutants GeoEngineers’ Scope of Work specifically excludes the investigation, detection, prevention, or assessment of the presence of Biological Pollutants. Accordingly, this report does not include any interpretations, recommendations, findings, or conclusions regarding the detecting, assessing, preventing or abating of Biological Pollutants, and no conclusions or inferences should be drawn regarding Biological Pollutants as they may relate to this project. The term “Biological Pollutants” includes, but is not limited to, molds, fungi, spores, bacteria, and viruses, and/or any of their byproducts. A Client that desires these specialized services is advised to obtain them from a consultant who offers services in this specialized field. Appendix E Operations and Maintenance Manual APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 12/12/2016 2017 City of Renton Surface Water Design Manual A-6 NO. 3 – DETENTION TANKS AND VAULTS 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. Tank or Vault Storage Area Trash and debris Any trash and debris accumulated in vault or tank (includes floatables and non- floatables). No trash or debris in vault. Sediment accumulation Accumulated sediment depth exceeds 10% of the diameter of the storage area for ½ length of storage vault or any point depth exceeds 15% of diameter. Example: 72-inch storage tank would require cleaning when sediment reaches depth of 7 inches for more than ½ length of tank. All sediment removed from storage area. 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. 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. 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 pipes 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. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 2017 City of Renton Surface Water Design Manual 12/12/2016 A-7 NO. 3 – DETENTION TANKS AND VAULTS MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Access Manhole (cont.) 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 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. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 12/12/2016 2017 City of Renton Surface Water Design Manual A-8 NO. 4 – CONTROL STRUCTURE/FLOW RESTRICTOR MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITION WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Structure Trash and debris Trash or debris of more than ½ cubic foot which is located immediately in front of the structure opening or is blocking capacity of the structure by more than 10%. No Trash or debris blocking or potentially blocking entrance to structure. Trash or debris in the structure 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 structure. Deposits of garbage exceeding 1 cubic foot in volume. No condition present which would attract or support the breeding of insects or rodents. Sediment accumulation Sediment exceeds 60% of the depth from the bottom of the structure to the invert of the lowest pipe into or out of the structure or the bottom of the FROP-T section or is within 6 inches of the invert of the lowest pipe into or out of the structure or the bottom of the FROP-T section. Sump of structure contains no sediment. 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 structure through cracks, or maintenance person judges that structure is unsound. Structure is sealed and 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 structure through cracks. No cracks more than 1/4 inch wide at the joint of inlet/outlet pipe. Settlement/ misalignment Structure 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 structure 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. Ladder rungs missing or unsafe Ladder is unsafe due to missing rungs, misalignment, rust, cracks, or sharp edges. Ladder meets design standards and allows maintenance person safe access. FROP-T Section Damaged FROP-T T section is not securely attached to structure wall and outlet pipe structure should support at least 1,000 lbs of up or down pressure. T section securely attached to wall and outlet pipe. Structure is not in upright position (allow up to 10% from plumb). Structure in correct position. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 2017 City of Renton Surface Water Design Manual 12/12/2016 A-9 NO. 4 – CONTROL STRUCTURE/FLOW RESTRICTOR MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITION WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED FROP-T Section (cont.) Damaged FROP-T (cont.) Connections to outlet pipe are not watertight or show signs of deteriorated grout. Connections to outlet pipe are water tight; structure repaired or replaced and works as designed. Any holes—other than designed holes—in the structure. Structure has no holes other than designed holes. Cleanout Gate Damaged or missing cleanout gate Cleanout gate is missing. Replace cleanout gate. Cleanout gate is not watertight. Gate is watertight and works as designed. Gate cannot be moved up and down by one maintenance person. Gate moves up and down easily and is watertight. Chain/rod leading to gate is missing or damaged. Chain is in place and works as designed. Orifice Plate Damaged or missing orifice plate Control device is not working properly due to missing, out of place, or bent orifice plate. Plate is in place and works as designed. Obstructions to orifice plate Any trash, debris, sediment, or vegetation blocking the plate. Plate is free of all obstructions and works as designed. Overflow Pipe Obstructions to overflow pipe Any trash or debris blocking (or having the potential of blocking) the overflow pipe. Pipe is free of all obstructions and works as designed. Deformed or damaged lip of overflow pipe Lip of overflow pipe is bent or deformed. Overflow pipe does not allow overflow at an elevation lower than design 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. 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 (If applicable) 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. footnote to guidelines for disposal Damaged or missing grate Grate missing or broken member(s) of the grate. 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 12/12/2016 2017 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 2017 City of Renton Surface Water Design Manual 12/12/2016 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. footnote to guidelines for disposal 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 12/12/2016 2017 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. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 12/12/2016 2017 City of Renton Surface Water Design Manual A-40 NO. 28 – NATIVE VEGETATED SURFACE/NATIVE VEGETATED LANDSCAPE BMP MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITION WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Site Trash and debris Trash and debris accumulated on the native vegetated surface/native vegetated landscape site. Native vegetated surface site free of any trash or debris. Vegetation Insufficient vegetation Less than two species each of native trees, shrubs, and groundcover occur in the design area. A minimum of two species each of native trees, shrubs, and groundcover is established and healthy. Poor vegetation coverage Less than 90% if the required vegetated area has healthy growth. A minimum of 90% of the required vegetated area has healthy growth. Undesirable vegetation present Weeds, blackberry, and other undesirable plants are invading more than 10% of vegetated area. Less than 10% undesirable vegetation occurs in the required native vegetated surface area. Vegetated Area Soil compaction Soil in the native vegetation area compacted. Less than 8% of native vegetation area is compacted. Insufficient vegetation Less than 3.5 square feet of native vegetation area for every 1 square foot of impervious surface. A minimum of 3.5 square feet of native vegetation area for every 1 square foot of impervious surface. Excess slope Slope of native vegetation area greater than 15%. Slope of native growth area does not exceed 15%. NO. 29 – PERFORATED PIPE CONNECTIONS BMP MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Preventive Blocking, obstructions Debris or trash limiting flow into perforated pipe system or outfall of BMP is plugged or otherwise nonfunctioning. Outfall of BMP is receiving designed flows from perforated pipe connection. Inflow Inflow impeded Inflow into the perforated pipe is partially or fully blocked or altered to prevent flow from getting into the pipe. Inflow to the perforated pipe is unimpeded. Pipe Trench Area Surface compacted Ground surface over the perforated pipe trench is compacted or covered with impermeable material. Ground surface over the perforated pipe is not compacted and free of any impervious cover. Outflow Outflow impeded Outflow from the perforated pipe into the public drainage system is blocked. Outflow to the public drainage system is unimpeded. Outfall Area Erosion or landslides Existence of the perforated pipe is causing or exasperating erosion or landslides. Perforated pipe system is sealed off and an alternative BMP is implemented. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 12/12/2016 2017 City of Renton Surface Water Design Manual A-42 NO. 31 – BIORETENTION BMP MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Preventive Vegetation Vegetation to be watered and pruned as needed and mulch applied to a minimum of 2 inches to maintain healthy growth. Healthy vegetation growth with full coverage as designed. Bioretention Area Trash and debris Trash and debris in the bioretention area; leaf drop in the fall season. No trash or debris In the bioretention area. Sediment accumulation Sediment accumulation in the bioretention area interfering with infiltration. Water in the bioretention infiltrates as designed. Excessive ponding Standing water in the bioretention area for more than two days. Standing water infiltrates at the desired rate. Inflow restricted Inflow not getting into bioretention; debris/sediment blockage at inlet features; native soil is exposed or other signs of erosion damage is present. Unobstructed and properly routed inflow into bioretention area; inlet is stabilized and appropriately armored. Overflow not controlling excess water Overflow water not controlled by outlet features; native soil is exposed or other signs of erosion damage is present. Outlet features control overflow; overflow is stabilized and appropriately armored. Underdrain not freely flowing Underdrain is not flowing when bioretention area has been infiltrating water. Underdrain flows freely when water is present. Vegetation Poor vegetation coverage Plants not thriving across at least 80% of the entire design vegetated area within the BMP; overly dense vegetation requiring pruning. Healthy water tolerant plants in bioretention area, plants thriving across at least 80% of the entire design vegetated area within the facility. Insufficient vegetation Plants not water tolerant species. Plants are water tolerant. Weeds present Weeds growing in bioretention area. No weeds in bioretention area. Watering not occurring Planting schedule requires frequent watering (approx. weekly Year 1, bimonthly Years 2 and 3) for new facilities, and as needed for established plantings or dry periods Plants are established and thriving Pest control Signs of pests, such as wilting or chewed leaves or bark, spotting or other indicators; extended ponding period encouraging mosquitoes Plant community is pest-free when following an approved Integrated Pest Management plan; bioretention functioning normally and ponding controlled as needed for pest control Containment Berm and Earthen Slopes Erosion Erosion occurring at earthen slopes or containment berm side slope. Erosion on the containment berm and side slopes has been repaired and the cause of the erosion corrected. Voids created by nuisance animals (e.g., rodents) or tree roots Voids affecting berm integrity or creating leaky pond condition Voids have been repaired; facility is free of nuisance animals following an approved Integrated Pest Management plan. Settlement Any part of the containment berm top has less than 6 inches of freeboard from the maximum pond level to the top of the berm. A minimum of 6 inches freeboard from the maximum pond level to the top of the berm. Amended Soil Poor soil nutrients Soil not providing plant nutrients. Soil providing plant nutrients. Bare spots Bare spots on soil in bioretention area. No bare spots, bioretention area covered with vegetation or mulch mixed into the underlying soil. Compaction Poor infiltration due to soil compaction in the bioretention area. No soil compaction in the bioretention area. Appendix F Bond Quantities Worksheet Appendix G Conveyance Calculations Appendix H Drainage Review Flow Chart SECTION 1.1 DRAINAGE REVIEW 6/22/2022 2022 City of Renton Surface Water Design Manual 1-14 FIGURE 1.1.2.A FLOW CHART FOR DETERMINING TYPE OF DRAINAGE REVIEW REQUIRED Appendix I Declarations of Covenant