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Home My WebLink AboutRS_Civil_Engineer_TIR_190909_V1.pdfcoterra 321 3rd Avenue South, Suite 406 Seattle, Washington 98104 206.596.7115 TECHNICAL INFORMATION REPORT Project: Renton Housing Authority Sunset Oaks Apartments Renton, WA 98056 Prepared For: Renton Housing Authority 2900 NE 10th St Renton, WA 98056 Prepared By: Max Berde, PE Reviewed By: Peter Apostol, PE Date: September 3, 2019 ENGINEERING PLLC TABLE OF CONTENTS Section No. Subject Page No. SECTION I PROJECT OVERVIEW .....................................................................1 SECTION II CONDITIONS AND REQUIREMENTS SUMMARY ...................15 SECTION III OFFSITE ANALYSIS ......................................................................19 SECTION IV FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ..........................................23 SECTION V CONVEYANCE SYSTEM ANALYSIS AND DESIGN ................27 SECTION VI SPECIAL REPORTS AND STUDIES .............................................27 SECTION VII OTHER PERMITS ...........................................................................27 SECTION VIII EROSION AND SEDIMENT CONTROL ......................................27 SECTION IX BOND QUANTITIES AND DECLARATION OF COVENANTS ...............................................28 SECTION X OPERATIONS AND MAINTENANCE MANUAL .......................28 LIST OF FIGURES FIGURE 1 VICINITY MAP .................................................................................4 FIGURE 2 TIR WORKSHEET ............................................................................5 FIGURE 3 EXISTING SITE SOILS...................................................................12 FIGURE 4 EXISTING LAND COVER .............................................................13 FIGURE 5 DEVELOPED LAND COVER ........................................................14 LIST OF APPENDICIES APPENDIX A CIVIL PLANS APPENDIX B FLOW CONTROL/DETENTION CALCULATIONS APPENDIX C WATER QUALITY CALCULATIONS APPENDIX D GEOTECHNICAL REPORT APPENDIX E CONVEYANCE CALCULATIONS APPENDIX F DRAINAGE REVIEW FLOWCHART Sunset Oaks Apartments Page 1 Project No. 19003 Renton, WA Coterra Engineering PLLC SECTION I – PROJECT OVERVIEW General Description: The proposed Sunset Oaks Apartment project includes the construction of three multi- story apartment buildings on a proposed 1.053 acre lot currently consisting of five currently-undeveloped parcels. The existing five parcels were previously developed as single-family homes and previously demolished. Proposed project includes on-site parking, landscaping, frontage improvements on Glennwood Ave NE and Harrington Ave NE, and associated utility and storm drainage improvements. The project proposes to construct a public alley between Glennwood Ave NE and Harrington Ave NE on the northern margin of the site. The alley will be dedicated to the City of Renton. The project site, located in the City of Renton, is bounded by Glennwood Ave NE to the west, Harrington Ave NE to the east, Sunset Lane NE (NE 10th Street) to the south, and residential parcels to the north (see Figure 1 for vicinity map). The proposed project has been designed to meet the requirements of the 2017 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 a majority of the site consisting of “Arents, Alderwood material “ with a small portion of the west side of the site consisting of “Ragnar-Indianola” soils. Additional information on the site’s soils is provided in a geotechnical report prepared by Zipper Geo Associates, LLC, and dated May 15, 2019. The findings of the report are based on soil samples taken from five borings that were excavated on-site. In general, the results of the borings uncovered 3’-12” of medium dense to dense sand with variable silt and gravel contents. Below that layer the borings encountered very dense sand with variable silt and gravel contents that the geotechnical engineer interprets to be glacial till. For more information, see the geotechnical report included in Appendix D. Predeveloped Conditions: The existing site is currently undeveloped with areas of impervious remaining from demolition and clearing of the former single-family residences on the 5 project parcels. The remainder of the site is considering to be pervious, former landscaping, consisting of till grass for stormwater modeling purposes. There are several significant trees spread throughout the site. The project site consists of one Threshold Discharge Area which is defined by the City of Renton Surface Water Design Manual as: “an onsite area draining to a single natural discharge location, or multiple natural discharge locations that combine within one-quarter –mile downstream.” The site is generally flat with stormwater runoff draining overland generally north to south towards Sunset Lane NE. Sunset Oaks Apartments Page 2 Project No. 19003 Renton, WA Coterra Engineering PLLC The existing land coverage 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. Table 1 – Existing Site Land Coverage (Acres) Impervious (Acres) Pervious Till Grass (Acres) Total (Acres) Project Site 0.250 0.803 1.053 Developed Conditions: The proposed developed condition includes three apartment buildings with at-grade parking stalls adjacent to and within the buildings; a public alley at the northern margin of the site; 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) Hardscape (Acres) Grass/ Landscape (Acres) Total (Acres) Project Site 0.433 0.380 0.240 1.053 The existing site topography will not be dramatically altered in the proposed condition. In general, the site will continue to drain from north to south towards Sunset Lane NE as it currently does in the existing condition. The proposed improvements within the project site 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 under the northwest parking lot and which will discharge to the existing 18” storm drainage main in Glennwood Ave NE to the west. Permeable pavements throughout the project site, including pervious asphalt and pervious concrete sidewalks, will provide water quality treatment. See Section IV for a detailed description of the design of the flow control and water quality facilities. Sunset Oaks Apartments Page 3 Project No. 19003 Renton, WA Coterra Engineering PLLC FIGURE 1 – VICINITY MAP Sunset Oaks Apartments Page 4 Project No. 19003 Renton, WA Coterra Engineering PLLC FIGURE 2 CITY OF RENTON TECHNICAL INFORMATION REPORT (TIR) WORKSHEET CITY OF RENTON SURFACE WATER DESIGN MANUAL 2017 City of Renton Surface Water Design Manual 12/12/2016 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 12/12/2016 2017 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 2017 City of Renton Surface Water Design Manual 12/12/2016 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 8 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: ____________ On-site BMPs: _______________________________ Conveyance System Spill containment located at: _____________________________ Erosion and Sediment Control / Construction Stormwater Pollution Prevention CSWPP/CESCL/ESC Site Supervisor: _____________________ Contact Phone: _________________________ After Hours Phone: _________________________ REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 12/12/2016 2017 City of Renton Surface Water Design Manual 8-A-4 Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Maintenance and Operation Responsibility (circle one): Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Liability Provided: Yes / No Water Quality (include facility summary sheet) Type (circle one): Basic / Sens. Lake / Enhanced Basic / Bog or Exemption No. _______________________ 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 2017 City of Renton Surface Water Design Manual 12/12/2016 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 Type/Description Water Quality Type/Description  Detention  Infiltration  Regional Facility  Shared Facility  On-site BMPs  Other ________________ ________________ ________________ ________________ ________________ ________________  Vegetated Flowpath  Wetpool  Filtration  Oil Control  Spill Control  On-site BMPs  Other ________________ ________________ ________________ ________________ ________________ ________________ ________________ Part 15 EASEMENTS/TRACTS Part 16 STRUCTURAL ANALYSIS  Drainage Easement  Covenant  Native Growth Protection Covenant  Tract  Other ____________________________  Cast in Place Vault  Retaining Wall  Rockery > 4′ High  Structural on Steep Slope  Other _______________________________ REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 12/12/2016 2017 City of Renton Surface Water Design Manual 8-A-6 Part 17 SIGNATURE OF PROFESSIONAL ENGINEER I, or a civil engineer under my supervision, have visited the site. Actual site conditions as observed were incorporated into this worksheet and the attached Technical Information Report. To the best of my knowledge the information provided here is accurate. ____________________________________________________________________________________ Signed/Date Sunset Oaks Apartments Page 11 Project No. 19003 Renton, WA Coterra Engineering PLLC FIGURE 3 – EXISTING SITE SOIL CONDITIONS Arents, Alderwood material Ragnar-Indianola association coterra 321 3rd Avenue South, Suite 406 Seattle, Washington 98104 206.596.7115 coterraengineering.com ENGINEERING PLLC coterra 321 3rd Avenue South, Suite 406 Seattle, Washington 98104 206.596.7115 coterraengineering.com ENGINEERING PLLC Sunset Oaks Apartments Page 14 Project No. 19003 Renton, WA Coterra Engineering PLLC SECTION II – CONDITIONS AND REQUIREMENTS SUMMARY The proposed project is subject to a Full Drainage Review per the 2017 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 F 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 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 convey the 25-year peak flow from the developed site conditions. Req. #5 Erosion and Sediment Control: Construction erosion and sediment control systems will be designed and provided for review at civil construction permit submittal. Sunset Oaks Apartments Page 15 Project No. 19003 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 Renton Housing Authority. 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 2017 City of Renton Surface Water Design Manual for targeted PGIS. Permeable pavement will be installed throughout the project site and for concrete sidewalks in any frontage improvements on Glennwood Ave NE and Harrington Ave NE. Porous asphalt, porous concrete sidewalks, and permeable parking lot pavers, underlain with a 6” sand layer, will provide water quality treatment for all proposed PGIS on the project. 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 Individual Large Lots implementing on-site BMPs to comply with Core Requirement #9, all listed BMPs were determined to be infeasible for the proposed project site. Despite infeasibility determinations for listed on-site BMP facilities, the proposed project plans to implement perforated pipe connections on all roof drains from the Sunset Oaks Apartments Page 16 Project No. 19003 Renton, WA Coterra Engineering PLLC three proposed apartment buildings per the recommendation of the City of Renton SWDM. For further details see Section IV. Special Requirements: Req. #1 Area Specific Requirements: Proposed project site is part of the Sunset Terrace Redevelopment Project within the City of Renton. Master Site Plan was reviewed and approved by City of Renton. Additionally, Sunset Terrace Redevelopment Project was reviewed by NOAA for compliance with requirements of Section 7 of the Endangered Species Act (ESA) with respect to its potential effects on species listed or proposed for listing under the ESA. Project must maintain specific impervious coverage limits for overall Sunset Terrace Redevelopment Project which were approved as part of previous reviews and agreements. To meet these approved impervious coverage thresholds, proposed Sunset Oaks Apartments project must implement permeable pavement throughout project site and for sidewalks on any frontage improvements. 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. Sunset Oaks Apartments Page 17 Project No. 19003 Renton, WA Coterra Engineering PLLC 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 groundwater given the project soil conditions. Sunset Oaks Apartments Page 18 Project No. 19003 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 2017 City of Renton Surface Water Design Manual. The following is a summary of the resource review: • Adopted Basin Plans o City of Renton Basin Name: John’s Creek Basin • 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 Sunset Terrace Regional Stormwater Facility Final TIR • 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 medium dense sand with silt that was underlain by impermeable glacial till soil. • Wetlands Inventory Maps o There are no Wetlands mapped within the vicinity of the site. Sunset Oaks Apartments Page 19 Project No. 19003 Renton, WA Coterra Engineering PLLC Task 3 – Field Inspection A full Level 1 downstream analysis will be performed for civil construction permit submittal. Based on review of City of Renton GIS Utility Mapping, due to recent construction of the Sunset Terrace Regional Stormwater Facility and associated storm drainage lines surrounding it, the downstream storm drainage system from the Sunset Oaks Apartments site has not been updated in the GIS system. It is believed that storm drainage is conveyed south and west from Glennwood Ave NE before connecting into the existing system on NE Sunset Blvd, where larger diameter conveyance piping flows west towards Lake Washington beyond ¼ mile downstream from the site. No known 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 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 There is no significant upslope unmitigated drainage areas flowing onto the proposed project site. Sunset Oaks Apartments Page 22 Project No. 19003 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 2017 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. 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 tank 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, an approximately 970 CF detention tank is required for the proposed project. 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 Utility Plan and the future civil construction permit submittal. On-Site Flow Control BMPs The proposed site is classified as a Large Lot BMP Site as the proposed site is over 22,000 SF. 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 1.2.9.2.2 for Large Lot BMP Projects in the 2017 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 Minimum Design Requirements for Full Infiltration in section C.2.2.2, existing soils must be “coarse sands or cobbles or medium sands.” Soils collected in on-site borings per the Geotechnical Engineering Report prepared by Zipper Geo Associates, LLC, dated 5/15/2019, are classified dense to dense sand with variable silt and gravel contents. Below this layer was encountered very dense sand with variable silt and gravel contents that the geotechnical engineer interpreted to be glacial till. These soils were found at a depth of typical on-site infiltration facilities or infiltration BMPs. Sunset Oaks Apartments Page 23 Project No. 19003 Renton, WA Coterra Engineering PLLC • Bioretention: Infeasible. Bioretention is considered infeasible for projects that cannot meet the minimum design requirements for bioretention. Per section C2.6 of the City of Renton SWDM, “ Many locations in the City have soils that are underlain by a compacted layer of soil (i.e., glacial till or hardpan) which severely limits soaking capacity and causes water to perch on the relatively impervious layer during the wet season. This can make bioretention impracticable, unreliable, and reduce plant survivability in the bioretention system.” Per the Geotechnical Engineering Report prepared by Zipper Geo Associates, LLC, dated 5/15/2019, “Our explorations encountered glacial till at a depth of about 3 to 5 feet below existing site grade. For purposes of stormwater infiltration, glacial till (or hardpan) is generally considered a hydraulically restrictive layer, or essentially impermeable for purposes of stormwater infiltration. As such, it is our opinion that sufficient permeable soils do not exist at the site and therefore stormwater infiltration is not feasible, in our opinion.” Based on the project geotechnical engineer guidance, bioretention is not feasible on the project site. • Permeable Pavement: Required Implementation Per Project Conditions. Per agreed upon terms between Sunset Oaks Apartments project owner/agents (Renton Housing Authority) and reviewing agencies (City of Renton, NOAA, NMFS) to maintain compliance with existing conditions of approval for the Sunset Terrace Redevelopment Project, Sunset Oaks Apartments project will implement permeable pavements for all at-grade hard surfaces throughout project site and any proposed sidewalks as part of required frontage improvements. • 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. • 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 In addition to utilization of permeable pavement throughout project site, 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. Sunset Oaks Apartments Page 24 Project No. 19003 Renton, WA Coterra Engineering PLLC 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 mitigation of on-site PGIS using permeable pavements throughout the project site. All proposed PGIS is either porous asphalt, porous concrete sidewalk, or permeable pavers. Any proposed sidewalk for frontage improvements on Glennwood Ave NE and Harrington Ave NE is porous concrete sidewalk. All permeable pavement surfaces follow City of Renton standard details and specifications. Sunset Oaks Apartments Page 25 Project No. 19003 Renton, WA Coterra Engineering PLLC SECTION V – CONVEYANCE SYSTEM DESIGN AND ANALYSIS The new conveyance system has been designed to convey at least the 25-year peak flow rate from the developed site. Conveyance capacity calculations will be included with the civil construction permit submittal. SECTION VI – SPECIAL REPORTS AND STUDIES A geotechnical analysis of the project site was performed and is included in Appendix D. SECTION VII – OTHER PERMITS In addition to the Site Plan Review, a Civil Construction Permit from the City of Renton is required, as well as an NPDES permit from the Washington State DOE for the discharge of construction stormwater from the project site. 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 will be provided on all drainage inlets on, adjacent to, and downstream of the project site. • 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. Sunset Oaks Apartments Page 26 Project No. 19003 Renton, WA Coterra Engineering PLLC SECTION IX – BOND QUANTITIES AND DECLARATION OF COVENANTS A bond quantity worksheet for the proposed improvements will be included with the civil construction permit submittal. There are two Declaration of Covenants which are required for the proposed project; one for inspection and maintenance of proposed stormwater facilities; and one for the inspection and maintenance of the proposed on-site BMPs. A draft version of these Declaration of Covenants will be provided for review and approval by City of Renton prior to recording. They will be signed and notarized prior to recording. SECTION X – OPERATIONS AND MAINTENANCE MANUAL An operation and maintenance manual which outlines required regular maintenance necessary for the proposed stormwater facilities will be provided with the civil construction permit submittal. The maintenance of the stormwater facilities will by be performed by Renton Housing Authority. Appendix A Civil Plans IN COMPLIANCE WITH CITY OF RENTON STANDARDS 5705'6.#0'0'4'06109# 5705'61#-5#2#46/'065coterra 321 3rd Ave South, Suite 406 Seattle, Washington 98104 ph 206.596.7115 coterraengineering.com ENGINEERING PLLC 5705'61#-5#2#46/'065 IN COMPLIANCE WITH CITY OF RENTON STANDARDS 5705'6.#0'0'4'06109# 5705'61#-5#2#46/'065coterra 321 3rd Ave South, Suite 406 Seattle, Washington 98104 ph 206.596.7115 coterraengineering.com ENGINEERING PLLC 5705'61#-5#2#46/'065 NO.DATEREMARKISSUE DATE:DRAWN BY:CHECKED BY:Sunset CrestTownhomesGlennwood Ave,Renton, WA.....................12.19.18MBPAPPUD SUBMITTALSHEET NO:SHEET TITLE:177 Western Avenue West Suite 266Seattle, WA 98119coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLCIN COMPLIANCE WITH CITY OF RENTON STANDARDS5705'6.#0'0'4'06109#5705'61#-5#2#46/'065coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLC5705'61#-5#2#46/'065 NO.DATEREMARKISSUE DATE:DRAWN BY:CHECKED BY:Sunset CrestTownhomesGlennwood Ave,Renton, WA.....................12.19.18MBPAPPUD SUBMITTALSHEET NO:SHEET TITLE:177 Western Avenue West Suite 266Seattle, WA 98119coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLCIN COMPLIANCE WITH CITY OF RENTON STANDARDS5705'6.#0'0'4'06109#5705'61#-5#2#46/'065coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLC5705'61#-5#2#46/'065 NO.DATEREMARKISSUE DATE:DRAWN BY:CHECKED BY:Sunset CrestTownhomesGlennwood Ave,Renton, WA.....................12.19.18MBPAPPUD SUBMITTALSHEET NO:SHEET TITLE:177 Western Avenue West Suite 266Seattle, WA 98119coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLCIN COMPLIANCE WITH CITY OF RENTON STANDARDS5705'6.#0'0'4'06109#5705'61#-5#2#46/'065coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLC5705'61#-5#2#46/'065 Appendix B Flow Control/Detention Calculations ————————————————————————————————— MGS FLOOD PROJECT REPORT Program Version: MGSFlood 4.38 Program License Number: 201510001 Project Simulation Performed on: 09/03/2019 9:15 AM Report Generation Date: 09/03/2019 9:26 AM ————————————————————————————————— Input File Name:XXXX-MGS Flood - revised areas.fld Project Name:19003 - RHA Sunset Oaks Analysis Title:Preliminary Detention Sizing Comments:60" CMP - approx 50 lf 48" CMP - approx 90 lf ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Climatic Region Number:13 Full Period of Record Available used for Routing 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:1 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)1.053 1.053 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres)1.053 1.053 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : EX ---------- -------Area(Acres) -------- Till Forest 0.000 Till Pasture 0.000 Till Grass 0.803 Outwash Forest 0.000 Outwash Pasture 0.000 Outwash Grass 0.000 Wetland 0.000 Green Roof 0.000 User 2 0.000 Impervious 0.250 ---------------------------------------------- Subbasin Total 1.053 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : PR ---------- -------Area(Acres) -------- Till Forest 0.000 Till Pasture 0.000 Till Grass 0.240 Outwash Forest 0.000 Outwash Pasture 0.000 Outwash Grass 0.000 Wetland 0.000 Green Roof 0.000 User 2 0.000 Impervious 0.813 ---------------------------------------------- Subbasin Total 1.053 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ------------------------------------------ Link Name: Prelim Det 60 in-50 lf Link Type: Structure Downstream Link: None User Specified Elevation Volume Table Used Elevation (ft) Pond Volume (cu-ft) 99.00 0. 99.20 26. 99.40 74. 99.60 134. 99.80 203. 100.00 280. 100.20 362. 100.40 450. 100.60 542. 100.80 637. 101.00 734. 101.20 832. 101.40 932. 101.60 1032. 101.80 1132. 102.00 1230. 102.20 1327. 102.40 1422. 102.60 1514. 102.80 1601. 103.00 1684. 103.20 1761. 103.40 1830. 103.60 1890. 103.80 1937. 104.00 1964. 104.20 1965. 104.40 1966. 104.60 1967. 104.80 1968. 105.00 1969. Massmann Infiltration Option Used Hydraulic Conductivity (in/hr) : 0.00 Depth to Water Table (ft): 100.00 Bio-Fouling Potential : Low Maintenance : Average or Better Riser Geometry Riser Structure Type : Circular Riser Diameter (in): 24.00 Common Length (ft): 0.280 Riser Crest Elevation : 104.00 ft Hydraulic Structure Geometry Number of Devices: 3 ---Device Number 1 --- Device Type : Circular Orifice Control Elevation (ft) : 100.50 Diameter (in): 2.21 Orientation : Horizontal Elbow : No ---Device Number 2 --- Device Type : Circular Orifice Control Elevation (ft) : 102.50 Diameter (in): 2.90 Orientation : Horizontal Elbow : Yes --- Device Number 3 --- Device Type : Rectangular Weir that Intersects the Riser Top Invert Elevation (ft): 103.50 Length (ft): 0.280 **********************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: Prelim Det 60 in-50 lf ********** Link WSEL Stats WSEL Frequency Data(ft) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) WSEL Peak (ft) ====================================== 1.05-Year 101.341 1.11-Year 101.496 1.25-Year 101.589 2.00-Year 102.049 3.33-Year 102.443 5-Year 102.563 10-Year 102.755 25-Year 103.199 50-Year 103.335 100-Year 103.834 ***********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: EX 98.135 _____________________________________ Total:98.135 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: PR 29.331 Link: Prelim Det 60 in-50 0.000 _____________________________________ Total: 29.331 Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 0.621 ac-ft/year, Post Developed: 0.186 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ********** Link: Prelim Det 60 in-50 lf ********** Basic Wet Pond Volume (91% Exceedance): 3843. cu-ft Computed Large Wet Pond Volume, 1.5*Basic Volume: 5765. cu-ft Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 412.77 Inflow Volume Including PPT-Evap (ac-ft): 412.77 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): 414.39 Secondary Outflow To Downstream System (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00% ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: EX Scenario Postdeveloped Compliance Link: Prelim Det 60 in-50 lf *** 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 0.166 2-Year 0.162 5-Year 0.234 5-Year 0.241 10-Year 0.320 10-Year 0.303 25-Year 0.442 25-Year 0.392 50-Year 0.573 50-Year 0.414 100-Year 0.659 100-Year 0.633 200-Year 0.702 200-Year 0.654 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals 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)5.0 ft Pipe Length 100 ft Overflow Elevation:104.00 ft Pond Volume at Overflow (cu ft):1937 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) 99.00 0.000 0.000 0 0 99.00 10.0 0.0. 99.20 0.040 0.263 26 0.001 99.20 10.1 26.3. 99.40 0.080 0.735 74 0.002 99.40 10.2 73.5. 99.60 0.120 1.335 134 0.003 99.60 10.3 133.5. 99.80 0.160 2.028 203 0.005 99.80 10.4 202.8. 100.00 0.200 2.795 280 0.006 100.00 10.5 279.5. 100.20 0.240 3.623 362 0.008 100.20 10.6 362.3. 100.40 0.280 4.500 450 0.010 100.40 10.7 450.0. 100.60 0.320 5.418 542 0.012 100.60 10.8 541.8. 100.80 0.360 6.365 637 0.015 100.80 10.9 636.5. 101.00 0.400 7.335 734 0.017 101.00 11.0 733.5. 101.20 0.440 8.320 832 0.019 101.20 11.1 832.0. 101.40 0.480 9.318 932 0.021 101.40 11.2 931.8. 101.60 0.520 10.318 1032 0.024 101.60 11.3 1031.8. 101.80 0.560 11.315 1132 0.026 101.80 11.4 1131.5. 102.00 0.600 12.300 1230 0.028 102.00 11.5 1230.0. 102.20 0.640 13.270 1327 0.030 102.20 11.6 1327.0. 102.40 0.680 14.218 1422 0.033 102.40 11.7 1421.8. 102.60 0.720 15.135 1514 0.035 102.60 11.8 1513.5. 102.80 0.760 16.010 1601 0.037 102.80 11.9 1601.0. 103.00 0.800 16.840 1684 0.039 103.00 12.0 1684.0. 103.20 0.840 17.608 1761 0.040 103.20 12.1 1760.8. 103.40 0.880 18.300 1830 0.042 103.40 12.2 1830.0. 103.60 0.920 18.900 1890 0.043 103.60 12.3 1890.0. 103.80 0.960 19.373 1937 0.044 103.80 12.4 1937.3. 104.00 1.000 19.635 1964 0.045 104.00 12.5 1963.5. 104.20 1.040 19.635 1964 0.045 104.20 12.6 1964.5. 104.40 1.080 19.635 1964 0.045 104.40 12.7 1965.5. 104.60 1.120 19.635 1964 0.045 104.60 12.8 1966.5. 104.80 1.160 19.635 1964 0.045 104.80 12.9 1967.5. 105.00 1.200 19.635 1964 0.045 105.00 13.0 1968.5. 9/3/2019 PondPipe.xls Appendix C Water Quality Calculation Appendix D Geotechnical Report GEOTECHNICAL ENGINEERING REPORT HARRINGTON AVE APARTMENTS NE 10TH STREET AND HARRINGTON AVENUE NE RENTON, WASHINGTON PROJECT NO. 2072.01 May 15, 2019May 15, 2019 Prepared for: Renton Housing Authority Prepared by: 19019 36th Avenue W., Suite E Lynnwood, WA 98036 19019 36th Avenue West, Suite E Lynnwood, WA 98036 (425) 582-9928 Project No. 2072.01 May 15, 2019 Renton Housing Authority P.O. Box 2316 Renton, Washington 98056-0316 Attn: Mr. Mark Gropper Subject: Geotechnical Engineering Report Harrington Ave Apartments NE 10th Street and Harrington Avenue NE Renton, Washington Dear Mr. Gropper, In accordance with your request and written authorization, Zipper Geo Associates, LLC (ZGA) has completed the subsurface exploration and geotechnical engineering evaluation for the Harrington Ave Apartments project. This report presents the results of the subsurface exploration, as well as our geotechnical engineering recommendations for the project. Our services were completed in general accordance with our Proposal for Geotechnical Engineering Services (Proposal No. P18283) dated August 23, 2018. Written authorization to proceed on our proposed scope of services was provided by Renton Housing Authority on August 27, 2018. We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report, or if we may be of further service, please contact us. Sincerely, Zipper Geo Associates, LLC Robert A. Ross, P.E. Principal 5/15/19 TABLE OF CONTENTS Page INTRODUCTION ........................................................................................................................................... 1 PROJECT UNDERSTANDING..................................................................................................................... 1 SITE CONDITIONS ....................................................................................................................................... 1 Surface Conditions .......................................................................................................................................... 1 Subsurface Conditions ..................................................................................................................................... 2 Groundwater Conditions ................................................................................................................................. 2 LABORATORY TESTING ............................................................................................................................ 3 CONCLUSIONS AND RECOMMENDATIONS ............................................................................................ 3 General Considerations ................................................................................................................................... 3 Geologically Hazardous Areas ......................................................................................................................... 3 Seismic Design Considerations ........................................................................................................................ 4 Site Preparation ............................................................................................................................................... 5 Structural Fill Materials, Placement, and Compaction .................................................................................... 7 Utility Trenching and Backfilling ...................................................................................................................... 8 Construction Dewatering ................................................................................................................................ 9 Shallow Foundation Recommendations .......................................................................................................... 9 On-Grade Concrete Slabs .............................................................................................................................. 10 Permanent Drainage Considerations ............................................................................................................ 11 Retaining Wall ............................................................................................................................................... 11 Stormwater Infiltration Feasibility ................................................................................................................ 12 Pavements ..................................................................................................................................................... 12 CLOSURE ................................................................................................................................................... 14 FIGURES Figure 1 – Site and Exploration Plan APPENDICES Appendix A – Subsurface Exploration Procedures and Logs Appendix B – Laboratory Testing Procedures and Results Cover Page Photo Credit: Google Earth Pro, 2018 Aerial Photo Page 1 GEOTECHNICAL ENGINEERING REPORT HARRINGTON AVE APARTMENTS RENTON, WASHINGTON Project No. 2072.01 May 15, 2019 INTRODUCTION This report documents the surface and subsurface conditions encountered at the project site and our geotechnical engineering recommendations for the current proposed Harrington Ave Apartments in Renton, Washington. Our geotechnical engineering scope of services for the project included subsurface explorations, laboratory testing, geotechnical engineering analysis, and preparation of this report. The observations and conclusions summarized herein are based in part upon conditions observed in our subsurface explorations and site observations. In the event that site conditions change, it may be necessary to modify the conclusions and recommendations presented in this report. This report is an instrument of service and has been prepared in general accordance with locally accepted geotechnical engineering practice. This report has been prepared for the exclusive use of the Renton Housing Authority, and its agents, for specific application to the subject property and stated purpose. PROJECT UNDERSTANDING The project site consists of five undeveloped parcels zoned as R-14 and located at the northwest corner of the intersection of NE 10th Street and Harrington Ave NE in Renton, Washington. The project site was previously developed with single-family homes that were demolished. We understand the project will consists of developing the site with a 62 unit, 3-story, wood-framed apartment building and related site improvements including underground utilities, pavements, and stormwater management facilities. We expect that the finished floor elevation of the building will be near existing site grades. Grading for the project is expected to consist of cuts and fills with a maximum anticipated depth/thickness of about 5 feet. However, deeper cuts may be required for underground utilities and stormwater management facilities. Design drawings for the proposed apartment building and associated site improvements were not available at the time this report was prepared. Once details regarding the proposed apartment building and additional site improvements are known, we should be consulted to review the details and revise this report if necessary. SITE CONDITIONS Surface Conditions The project site consists of five parcels with a total area of slightly above one acre. The site is bordered to the north by single-family residences, to the east by Harrington Ave NE, to the south by the new extension of NE 10th Street, and to the west by Glennwood Ave NE. Parcel number 7227801305 overlaps with the new construction of the NE 10th Street extension with a portion remaining to the north of the road construction. We anticipate that this portion will be included in the project area. Harrington Ave Apartments ZGA Project No. 2072.01 May 15, 2019 Page 2 Topographically, the site is relatively flat. Ground cover consists primarily of grass with a few scattered large deciduous and coniferous trees. The northwest corner of the project site was used as a staging area for construction equipment associated with the extension of NE 10th Street and is covered with medium gravel. A plan view of the project site is shown on the attached Figure 1, Site and Exploration Plan. Subsurface Conditions Mapped Geology: We reviewed published geologic mapping of the site vicinity through the Washington State Department of Natural Resource’s web-based mapping application Washington Geologic Information Portal (https://geologyportal.dnr.wa.gov/). The published mapping indicates the site is underlain by Vashon glacial till (Qgt). The mapping describes this soil as mostly thin ablation till over lodgment till, deposited by the Puget glacial lobe consisting of a generally compact, coherent unsorted mixture of sand, silt clay and gravel. The mapping notes that north of the Cedar River, where the project site is located, the till is mostly sand. Subsurface Exploration: The subsurface evaluation for this project included advancement of five borings (B-1 through B-5) completed throughout the area of the project site. The borings were extended to depths of about 16 to 26½ feet below the existing ground surface (bgs) and their approximate locations are shown on Figure 1, Site and Exploration Plan. Soils were visually classified in general accordance with the Unified Soil Classification System. Descriptive logs of the subsurface explorations and the procedures utilized in the subsurface exploration program are presented in Appendix A. A generalized description of soil conditions encountered in the explorations is presented below. Please refer to the exploration logs in Appendix A for a more detailed description of the conditions encountered at each exploration location. Soil conditions observed in the borings generally consisted of three to twelve feet of medium dense to dense sand with variable silt and gravel contents. Below this layer we encountered very dense sand with variable silt and gravel contents that we interpret to be glacial till. All the explorations terminated within the glacial till. The upper 4 to 5 feet of soils observed in our explorations was interpreted to be possibly undocumented fill associated with previous development of the site and possibly demolition of the previously existing homes. Groundwater Conditions Groundwater was not encountered within our explorations. Fluctuations in groundwater levels will likely occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time the exploration was performed. Therefore, groundwater levels during construction or at other times in the life of the structure may be higher than indicated on the logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project. Harrington Ave Apartments ZGA Project No. 2072.01 May 15, 2019 Page 3 LABORATORY TESTING Laboratory testing included soil moisture content, grain size distribution, and modified proctor tests on selected samples obtained from our explorations. The results of the moisture content tests are presented on the boring logs in Appendix A and the grain size distribution and modified proctor test results are presented in Appendix B. In general, moisture content testing indicates the sands within the upper 10 feet of existing site grade had moisture contents ranging from about 4 to 12 percent with an average of about 9 percent. Grain size distribution testing indicates the sands within the upper 7 feet of existing site grade had fines contents ranging from about 19 to 30 percent. We collected cuttings from the auger and performed a modified proctor test on the material. The modified proctor test yielded a maximum dry density of 136.2 pcf and an optimum moisture content of 8.3 percent. CONCLUSIONS AND RECOMMENDATIONS General Considerations Based on the results of our subsurface investigation as described in previous sections, it is our opinion the proposed building can be supported on conventional shallow foundations bearing on medium dense to very dense native soil or structural fill placed on properly prepared native soils, contingent on proper design and construction practices and implementation of the recommendations presented in this report. Geotechnical engineering recommendations for conventional shallow foundations and other earthwork related phases of the project are presented below. The recommendations contained in this report are based upon the results of field and laboratory testing (which are presented in Appendices A and B), engineering analyses, and our current understanding of the proposed project. ASTM and Washington State Department of Transportation (WSDOT) specification codes cited herein respectively refer to the current manual published by the American Society for Testing & Materials and the 2016 edition of the Standard Specifications for Road, Bridge, and Municipal Construction (M41-10). Geologically Hazardous Areas As part of our services, we evaluated the presence of regulated geologically hazardous areas (GHAs) at the site. Chapter 4-3-050 of the Renton Municipal Code (the Code) designates GHAs as Erosion, Landslide, Seismic, and Coal Mine Hazard Areas. Steep Slope Hazard Areas: The code defines steep slope hazard areas as areas with an average slope of 25 percent or greater with a total relief of 15 feet or greater, or having an average slope of 40 percent or greater. The project site does not meet the definition of a steep slope area. Landslide Hazard Areas: The code defines a low landslide hazard area as an area with slopes less than fifteen percent. Based on the relative flat topography, the site classifies as having a “low landslide hazard”, based on the code definition. Harrington Ave Apartments ZGA Project No. 2072.01 May 15, 2019 Page 4 Erosion Hazard Areas: The code characterizes sites as having a low or high erosion hazard based on information available through the Natural Resource Conservation Service (NRCS). The NRCS maps the site as being 70% Arents, Alderwood material (AmC) and 30% Ragnar-Indianola association both with a slope less than 15 percent. Therefore, the site classifies as having a “low erosion hazard”, based on the code definition. Seismic Hazard Areas: The code characterizes sites as having either “low seismic hazard” or “high seismic hazard” based on the subsurface conditions. A low seismic hazard area is defined as an area underlain by dense soils or bedrock, generally having site classifications of A through D, as defined in the International Building Code, 2012. It is our opinion that the project site classifies as having a “low seismic hazard”, based on the code definition. More detailed information regarding seismic hazards is provided in the seismic design considerations section of this report. Coal Mine Hazard Areas: The code defines areas with low coal mine hazards as areas with no known mine workings and no predicted subsidence. We reviewed the King County iMap for coal mine hazard mapping as well as the Coal Mine Map Database located within the Washington State Department of Natural Resources online Washington Geologic Information Portal. Based on a review of the readily available information provided by these sources, no coal mine workings are documented within close vicinity of the project site. Therefore, in our opinion the project site classifies as having a “low coal mine hazard”, based on the code definition. Seismic Design Considerations The tectonic setting of western Washington is dominated by the Cascadia Subduction Zone formed by the Juan de Fuca plate subducting beneath the North American Plate. This setting leads to intraplate, crustal, and interplate earthquake sources. Seismic hazards relate to risks of injury to people and damage to property resulting from these three principle earthquake sources. Ground Surface Rupture: Based on our review of the USGS Quaternary age fault database for Washington State, an inferred fault trace of the Seattle Fault Zone is located approximately 1 ½-miles to the north and northwest of the project site. As the fault does not appear to cross the site, it is our opinion that the risk of ground surface rupture at the site is low. Landsliding: Based on the relatively flat topography of the site and surrounding vicinity, it is our opinion that the risk of earthquake-induced landsliding is low. Soil Liquefaction: Liquefaction is a phenomenon wherein cohesionless soils below the groundwater table build up excess pore water pressures during earthquake loading. Liquefaction typically occurs in loose, cohesionless soils, but may occur in denser soils if the ground shaking is sufficiently strong. The potential hazardous impacts of liquefaction include liquefaction-induced settlement and lateral spreading. Soil conditions observed in our explorations consisted of dense to very dense sands with variable silt/gravel Harrington Ave Apartments ZGA Project No. 2072.01 May 15, 2019 Page 5 contents. We did not encounter groundwater within our explorations. Based on the subsurface conditions we encountered on the site, it is our opinion that the risk of liquefaction is low. IBC Seismic Design Parameters: Based on site location and soil conditions, the values provided below are recommended for seismic design. The values provided below are based on the 2015 IBC as the building code reference document. Site Preparation Erosion Control Measures: Stripped surfaces and soil stockpiles are typically a source of runoff sediments. We recommend that silt fences, berms, and/or swales be installed around the downslope side of stripped areas and stockpiles in order to capture runoff water and sediment. If earthwork occurs during wet weather, we recommend that all stripped surfaces be covered with straw to reduce runoff erosion, whereas soil stockpiles should be protected with anchored plastic sheeting. Temporary Drainage: Stripping, excavation, grading, and subgrade preparation should be performed in a manner and sequence that will provide drainage at all times and provide proper control of erosion. The site should be graded to prevent water from ponding in construction areas and/or flowing into and/or over excavations. Exposed grades should be crowned, sloped, and smooth-drum rolled at the end of each day to facilitate drainage if inclement weather is forecasted. Accumulated water must be removed from subgrades and work areas immediately and prior to performing further work in the area. Equipment access may be limited and the amount of soil rendered unfit for use as structural fill may be greatly increased if drainage efforts are not accomplished in a timely manner. Description Value 2015 IBC Site Classification 1 C Ss Spectral Acceleration for a Short Period 1.430 g (Site Class B) S1 Spectral Acceleration for a 1-Second Period 0.537 g (site Class B) SMS Maximum considered spectral response acceleration for a Short Period 1.430 g (Site Class C) SM1 Maximum considered spectral response acceleration for a 1-Second Period 0.699 g (Site Class C) SDS Five-percent damped design spectral response acceleration for a Short Period 0.953 g (Site Class C) SD1 Five-percent damped design spectral response acceleration for a 1-Second Period 0.466 g (Site Class C) 1. In general accordance with the 2015 International Building Code, Table 1613.5.2. IBC Site Class is based on the average characteristics of the upper 100 feet of the subsurface profile. The borings completed for this study extended to a maximum depth of 26½ feet below grade. ZGA therefore determined the Site Class assuming that similar density soils extend to 100 feet as suggested by published geologic maps for the project area. Harrington Ave Apartments ZGA Project No. 2072.01 May 15, 2019 Page 6 Clearing and Stripping: Once TESC measures are installed, we expect site preparation to continue with clearing and grubbing brush and trees, and stripping of organic rich topsoil. We recommend all tree stumps and roots larger than ½ inch in diameter be cleared and grubbed from the areas planned for improvement. Based on our explorations, stripping depths to remove topsoil is estimated to be about 6 inches. Stripping depths may be greater near trees and brush to fully remove root systems. All clearing and stripping debris should be wasted off site or, if approved, used for topsoil in landscape areas. Subgrade Preparation: Once site preparation is complete, all areas that are at design subgrade elevation or areas that will receive new structural fill should be moisture conditioned to a moisture content within plus or minus two percent of optimum moisture content for compaction. The subgrade should then be compacted to a firm and unyielding condition. The existing near-surface site soils consist of loose to dense silty sand or sand with silt at or generally somewhat above optimum moisture content for compaction. During wet weather, achieving a moisture content adequate for compaction will be impossible. Therefore, we recommend subgrade preparation and earthwork, in general, be completed during drier periods of the year when the soil moisture content can be controlled by aeration and drying. If earthwork or construction activities take place during extended periods of wet weather, or if the in situ moisture conditions are elevated above the optimum moisture content, the soils will become unstable and not compactable. In the event the exposed subgrade becomes unstable, yielding, or unable to be compacted due to high moisture conditions, we recommend that the materials be removed to a sufficient depth in order to develop stable subgrade soils that can be compacted to the minimum recommended levels. The severity of construction problems will be dependent, in part, on the precautions that are taken by the contractor to protect the subgrade soils. Once compacted, subgrades should be evaluated through density testing and proof rolling with a loaded dump truck or heavy rubber-tired construction equipment weighing at least 20 tons to assess the subgrade adequacy and to detect soft and/or yielding soils. In the event that compaction fails to meet the specified criteria, the upper 12 inches of subgrade should be scarified and moisture conditioned as necessary to obtain at least 95 percent of the maximum laboratory density (per ASTM D1557). Those soils which are soft, yielding, or unable to be compacted to the specified criteria should be over-excavated and replaced with suitable material as recommended in the Structural Fill section of this report. As an alternate to subgrade compaction during wet site conditions or wet weather, the upper 12 inches of subgrade should be overexcavated to a firm, non-yielding and undisturbed condition and backfilled with compacted imported structural fill consisting of free-draining Gravel Borrow or crushed rock. Freezing Conditions: If earthwork takes place during freezing conditions, exposed subgrades should be allowed to thaw and then be compacted prior to placing subsequent lifts of structural fill. Alternatively, the frozen material could be stripped from the subgrade to expose unfrozen soil prior to placing subsequent lifts of fill or foundation components. The frozen soil should not be reused as structural fill until allowed to thaw and adjusted to the proper moisture content, which may not be possible during winter months. Harrington Ave Apartments ZGA Project No. 2072.01 May 15, 2019 Page 7 Structural Fill Materials, Placement, and Compaction Structural fill includes any material placed below or adjacent to foundations, below concrete slabs, within utility trenches, or other areas to support settlement-sensitive site improvements. Prior to the placement of structural fill, all surfaces to receive fill should be prepared as previously recommended in the Site Preparation section of this report. Laboratory Testing: Representative samples of on-site and imported soils to be used as structural fill should be submitted for laboratory testing at least 4 days in advance of its intended use in order to complete the necessary Proctor tests. Reuse of Site Soils as Structural Fill: We expect that the finished grade will stay very close to the existing grade and therefore no substantial fill placement will be required. However, we expect the reuse of site soils as structural fill will be desirable for underground utilities. The suitability for reuse of site soils as structural fill depends on the composition and moisture content of the soil. Soils encountered in excavations at the site are expected to consist of silty sand or sand with silt. As the amount of fines increases, the soil becomes increasingly sensitive to small changes in moisture content. Soils containing more than about 5 percent fines cannot be consistently compacted to the appropriate levels when the moisture content is more than approximately 2 percent above or below the optimum moisture content (per ASTM D1557). Optimum moisture content is the moisture content which results in the greatest compacted dry density with a specified compactive effort. Laboratory testing of select soil samples indicates the in-place moisture content of site soils ranges from about 4 to 12 percent. Based on the results of the modified proctor test, the optimum moisture content of site soils is 8.3 percent. Therefore, site soils appear near the optimum moisture content for compaction. Site soils should be suitable for structural fill during periods of dry weather with some slight moisture conditioning. However, during wet weather, site soils will quickly become too wet for reuse as structural fill. Therefore, we recommend earth work for the project be scheduled for the drier summer months. Imported Structural Fill: The appropriate type of imported structural fill will depend on weather conditions. During extended periods of dry weather, we recommend imported fill, at a minimum, meet the requirements of Common Borrow as specified in Section 9-03.14(3) of the 2016 Washington State Department of Transportation, Standard Specifications for Road, Bridge, and Municipal Construction (WSDOT Standard Specifications). During wet weather and/or wet site conditions, higher-quality structural fill might be required, as Common Borrow may contain sufficient fines to be moisture-sensitive. During wet conditions, we recommend that imported structural fill consist of a “clean”, free-draining pit- run sand and gravel. Such material should generally contain less than 5 percent fines, based on that soil fraction passing the U.S. No. 4 sieve, and not contain discrete particles greater than 3 inches in maximum dimension. Alternatively, Crushed Surfacing Base Course or Gravel Borrow conforming to Sections 9- 03.9(3) and 9-03.14(1), respectively, of the WSDOT Standard Specifications could be used during wet Harrington Ave Apartments ZGA Project No. 2072.01 May 15, 2019 Page 8 weather. It should be noted that the placement of structural fill is, in many cases, is weather-dependent. Delays due to inclement weather are common, even when using select granular fill. We recommend that site grading and earthwork be scheduled for the drier months, if possible. Fill Placement and Compaction: Structural fill should be placed in horizontal lifts of a thickness adequate for adequate compaction throughout the entire lift thickness with the compaction equipment used. Typically, the maximum loose lift thickness that can be adequately compacted with typical compaction equipment is 12 inches. However, in cases where large vibratory rollers and imported fill with less than 5% fines are used, the lift thickness can be increased. Increasing the loose lift thickness beyond 12 inches should be based on field performance testing during construction prior to placement of production fills. Thinner lifts may be necessary, depending on the size and weight of the compaction equipment. Each lift of fill should be compacted to the minimum levels recommended in the table below based on the maximum laboratory dry density as determined by the ASTM D 1557 Modified Proctor Compaction Test. Structural fill placed in municipal rights-of-way should be placed and compacted in accordance with the jurisdiction codes and standards. We recommend that a geotechnical engineer be present during grading so that an adequate number of density tests may be conducted as structural fill placement occurs. In this way, the adequacy of the earthwork may be evaluated as it proceeds. Recommended Soil Compaction Levels Location Minimum Percent Compaction* Stripped native subgrade soils, prior to fill placement (upper 12 inches) 95 All fill below building floor slabs and foundations 95 Upper two feet of fill below pavement finished grade 95 Pavement fill below two feet from finished grade 92 Utility trench backfill greater than two feet from finished grade 92 Upper two feet of trench backfill from finished grade 95 Landscape Areas 90 * ASTM D 1557 Modified Proctor Maximum Dry Density Utility Trenching and Backfilling We recommend that utility trenching conform to all applicable federal, state, and local regulations, such as OSHA and WISHA, for open excavations. Trench excavation safety guidelines are presented in WAC Chapter 296-155 and WISHA RCW Chapter 49.17. Utility Subgrade Preparation: We recommend that all utility subgrades be firm and unyielding and free of soils that are loose, disturbed, or pumping. Soils that pump or yield should be removed and replaced. All structural fill used to replace over-excavated soils should be compacted as recommended in the Structural Fill section of this report. Bedding and Initial Backfill: We recommend that a minimum of 4 inches of bedding material be placed below and at least 12 inches above all utilities or in general accordance with the utility manufacturer’s Harrington Ave Apartments ZGA Project No. 2072.01 May 15, 2019 Page 9 recommendations and local ordinances. We recommend the bedding consist of granular material free from particles greater than 3 inches. All trenches should be wide enough to allow for compaction around the haunches of the pipe, or material such as pea gravel should be used below the spring line of the pipes to eliminate the need for mechanical compaction in this portion of the trenches. If water is encountered in the excavations, it should be removed prior to fill placement. Trench Backfill: Materials, placement and compaction of utility trench backfill should be in accordance with the recommendations presented in the Structural Fill section of this report. In our opinion, the initial lift thickness should not exceed 1 foot unless recommended by the manufacturer to protect utilities from damage by compacting equipment. Light, hand operated compaction equipment may be utilized directly above utilities if damage resulting from heavier compaction equipment is of concern. Construction Dewatering Groundwater was not encountered in our explorations. If groundwater is encountered during construction, some form of temporary dewatering may be required. Conventional dewatering methods, such as pumping from sump pits, should likely be adequate for temporary removal of groundwater encountered during shallow excavation at the site. Construction dewatering systems should be designed, maintained, and permitted by the contractor. Shallow Foundation Recommendations We recommend the building foundations be supported on the medium dense to very dense soils encountered in our explorations at a depth of 2.5 to 4 feet below existing site grades. Based on the results of our explorations, some loose, undocumented fill may be encountered at footing subgrade elevations. As such, some over-excavation and replacement of loose, undocumented fill with structural fill may be required. The need for over-excavation and replacement of loose, undocumented fill should be evaluated by a representative from Zipper Geo Associates during construction. Where over-excavation is required, the width of the over-excavation beyond footing edges should be equal to the required over-excavation depth. For example, if the footing width is 12 inches and an over-excavation depth of two feet is required, the total width of the over-excavation should be five feet. As an alternative, the width of over-excavations can be limited to the footing width provided the over-excavation is backfilled with controlled density fill or lean mix concrete having a minimum 28 day compressive strength of 100 psi. Over-excavation and replacement with structural fill shall be in accordance with the recommendations provided in the Structural Fill Materials, Placement and Compaction section of this report. Recommendations for shallow spread footings are provided below. Subgrade Preparation: Where loose, undocumented fill is not encountered at footing subgrade elevation, we recommend that the subgrade exposed at the bottom of foundation excavations be compacted to a firm and non-yielding condition and to at least 95 percent of the modified Proctor maximum dry density determined in accordance with ASTM D 1557. If the exposed subgrade cannot be compacted to the required density, we recommend that it be removed to an adequate depth as recommended by a representative from ZGA and replaced with compacted structural fill placed in accordance with this report. Harrington Ave Apartments ZGA Project No. 2072.01 May 15, 2019 Page 10 Allowable Bearing Pressure: Continuous and isolated column footings bearing on subgrades prepared as recommended above may be designed for a maximum allowable, net, bearing pressure of 3,000 psf if supported as recommended in this report. A one-third increase of the bearing pressure may be used for short-term transient loads such as wind and seismic forces. Shallow Foundation Depth and Width: For frost protection, the bottom of all exterior footings should bear at least 18 inches below the lowest adjacent outside grade, whereas the bottoms of interior footings should bear at least 12 inches below the surrounding slab surface level. We recommend that all continuous wall and isolated column footings be at least 12 and 24 inches wide, respectively. Lateral Resistance: Resistance to lateral loads can be calculated assuming a ultimate passive resistance of 405 pcf equivalent fluid pressure (triangular distribution) for footings backfilled with structural fill as recommended in this report. We recommend an ultimate base friction coefficient of 0.50. If allowable stress design is used, we recommend a minimum safety factor of 1.5 be used for lateral resistance calculations. We recommend that passive resistance be neglected in the upper 18 inches of embedment. Estimated Settlement: Assuming the foundation subgrade soils and structural fill compaction are completed in accordance with recommendations presented herein, we estimate that total static footing settlements will be 1 inch or less. We estimate that differential footing settlement will be ½ inch or less in 40 feet. Subsurface Drainage: Although no groundwater was encountered in our explorations, as a precautionary measure, we recommend a perimeter footing drain be installed around the building to collect surface water infiltration if impermeable hard surfacing, such as asphalt pavement, is not extended to the foundation walls of the building. The perimeter footing drain should consist of a 4-inch-diameter perforated pipe within an envelope of pea gravel or washed rock, extending at least 6 inches on all sides of the pipe. The gravel envelope should be wrapped with filter fabric (such as Mirafi 140N) to reduce the migration of fines from the surrounding soil. The invert of the footing drain should be placed no higher than the bottom of the footing. The perforations should be placed down. The perimeter foundation drain with cleanouts should not be connected to roof downspout drains and should be constructed to discharge into the site storm water system or other appropriate outlet. On-Grade Concrete Slabs Subgrade Preparation: Subgrades for on-grade slabs should be prepared in accordance with the Site Preparation and Structural Fill sections of this report. Slab Base: To provide a uniform slab bearing surface, capillary break, and even working surface, we recommend that on-grade slabs be underlain by a 6-inch thick layer of clean, compacted crushed rock meeting the requirements of Crushed Surfacing Top Course as specified in Section 9-03.9(3) of the WSDOT Standard Specifications with the modification that a maximum of 7.5 percent of the material passes the U.S. No 200 sieve. Harrington Ave Apartments ZGA Project No. 2072.01 May 15, 2019 Page 11 Vapor Barrier: From a geotechnical perspective, a vapor barrier is not considered necessary beneath the slab on grade floor unless moisture sensitive floor coverings and/or adhesives are used. If a vapor barrier is used, we recommend using a 10-mil (minimum), puncture-resistant proprietary product such as Stego Wrap, or an approved equivalent that is classified as a Class A vapor retarder in accordance with ASTM E 1745. Overlap lengths and the appropriate tape used to seal the laps should be in accordance the vapor retarder manufacturer’s recommendations. When conditions warrant the use of a vapor retarder, the slab designer and slab contractor should refer to ACI 302 and ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder/barrier. Permanent Drainage Considerations Surface Drainage: Final site grades should be sloped to carry surface water away from buildings and other drainage-sensitive areas. Additionally, site grades should be designed such that concentrated runoff on softscape surfaces is avoided. Any surface runoff directed towards softscaped slopes should be collected at the top of the slope and routed to the bottom of the slope and discharged in a manner that prevents erosion. Retaining Wall Lateral Earth Pressures: The lateral soil pressures acting on backfilled retaining walls will depend on the nature and density of the soil behind the wall, and the ability of the wall to yield in response to the earth loads. Yielding walls (i.e. walls that are free to translate or rotate) that are able to displace laterally at least 0.001H, where H is the height of the wall, may be designed for active earth pressures. Non-yielding walls (i.e. walls that are not free to translate or rotate) should be designed for at-rest earth pressures. Non-yielding walls include walls that are braced to another wall or structure, and wall corners. Assuming that walls are backfilled and drained as described in the following paragraphs, we recommend that yielding walls supporting horizontal backfill be designed using an equivalent fluid density of 35 pcf (active earth pressure). Non-yielding walls should be designed using an equivalent fluid density of 50 pcf (at-rest earth pressure). Surcharge pressures due to sloping backfill, adjacent footings, vehicles, construction equipment, etc. must be added to these lateral earth pressure values. For traffic loads, we recommend using an equivalent two-foot soil surcharge of about 250 psf. For yielding and non-yielding walls with level backfill conditions, we recommend that a uniformly distributed seismic pressure of 7H psf for the active case and 12H psf for the at-rest case, where H is the height of the wall, be applied to the walls. The above equivalent fluid pressures are based on the assumption of no buildup of hydrostatic pressure behind the wall. If groundwater is allowed to saturate the backfill soils, hydrostatic pressures will act against a retaining wall; however, if the recommended drainage system is included with each retaining wall, we do not expect that hydrostatic pressures will develop. Harrington Ave Apartments ZGA Project No. 2072.01 May 15, 2019 Page 12 Adequate drainage measures must be installed to collect and direct subsurface water away from subgrade walls. All backfilled walls should include a drainage aggregate zone extending a minimum of two feet from the back of wall for the full height of the wall and wide enough at the base of the wall to allow seepage to flow to the footing drain. The drainage aggregate should consist of material meeting the requirements of WSDOT 9-03.12(2), Gravel Backfill for Walls. A minimum 4-inch diameter, perforated PVC drain pipe should be provided at the base of backfilled walls to collect and direct subsurface water to an appropriate discharge point. We recommend placing a non-woven geotextile, such as Mirafi 140N, or equivalent, around the free draining backfill material. Stormwater Infiltration Feasibility With respect to stormwater infiltration, the City of Renton adopts the 2016 King County Surface Water Design Manual (KCSWDM) with amendments. Based on our review of the 2016 KCSWDM, the applicant must demonstrate, through the opinion of a geotechnical professional, that sufficient permeable soil exists to allow construction of a properly functioning infiltration facility. Our explorations encountered glacial till at a depth of about 3 to 5 feet below existing site grade. For purposes of stormwater infiltration, glacial till (or hardpan) is generally considered a hydraulically restrictive layer, or essentially impermeable for purposes of stormwater infiltration. As such, it is our opinion that sufficient permeable soils do not exist at the site and therefore stormwater infiltration is not feasible, in our opinion. Pavements Pavement Life and Maintenance: It should be realized that asphaltic pavements are not maintenance- free. The following pavement sections represent our minimum recommendations for an average level of performance during a 20-year design life; therefore, an average level of maintenance will likely be required. A 20-year pavement life typically assumes that an overlay will be placed after about 12 years. Thicker asphalt, base, and subbase courses would offer better ling-term performance, but would cost more initially. Conversely, thinner courses would be more susceptible to “alligator” cracking and other failure modes. As such, pavement design can be considered a compromise between a high initial cost and low maintenance costs versus a low initial cost and higher maintenance costs. The recommendations presented below are based on AASHTO Low-Volume Road Design methodologies as presented in the 1993 AASHTO Guide for Design of Pavement Structures. Traffic and Reliability: Our design assumes 100,000, 18-kip equivalent single axle loads over the life of the pavement along the main access roads and a 75% reliability. Soil Design Values: Pavement subgrade soils are anticipated to consist of the medium stiff silt deposit we encountered in our explorations. Our analysis assumes a minimum California Bearing Ration (CBR) value of 10 is appropriate for this material. Recommended Pavement Sections: For light duty pavements (parking stalls), we recommend 2 inches of asphalt concrete over 4 inches of crushed rock base course. For heavy duty pavements (main access roads, truck delivery routes, etc.), we recommend 3 inches of asphalt concrete over 6 inches of crushed Harrington Ave Apartments ZGA Project No. 2072.01 May 15, 2019 Page 13 rock base course. A thicker asphalt section or concrete pavements should be considered in front of dumpster enclosures. Materials and Construction: We recommend the following regarding asphalt pavement materials and pavement construction. • Subgrade Preparation: Upper 24 inches of pavement subgrade should be prepared in accordance with the recommendations presented in the Subgrade Preparation section of this report. • Asphalt Concrete: We recommend that the asphalt concrete conform to Section 9-02.1(4) for PG 58-22 or PG 64-22 Performance Graded Asphalt Binder as presented in the WSDOT Standard Specifications. We also recommend that the gradation of the asphalt aggregate conform to the aggregate gradation control points for ½-inch mixes as presented in Section 9-03.8(6), HMA Proportions of Materials. • Base Course: We recommend that the crushed aggregate base course conform to Section 9-03.9(3) of the WSDOT Standard Specifications. • Compaction: All base material should be compacted to at least 95 percent of the maximum dry density determined in accordance with ASTM D1557. We recommend that asphalt be compacted to a minimum of 92 percent of the Rice (theoretical maximum) density or 96 percent of Marshall (Maximum laboratory) density. We recommend that a Portland cement concrete pavement (CCP) be utilized in entrance and exit sections, dumpster pads, loading dock areas, drive-thru areas or other areas where extensive wheel maneuvering or repeated loading are expected. The dumpster pad should be large enough to support the wheels of the truck which will bear the load of the dumpster. We recommend a minimum of 6 inches of CCP underlain by 4 inches of crushed aggregate base. Although not required for structural support, the base course layer is recommended to help reduce potentials for slab curl, shrinkage cracking, and subgrade “pumping” through joints. Proper joint spacing will also be required to prevent excessive slab curling and shrinkage cracking. All joints should be sealed to prevent entry of foreign material and dowelled where necessary for load transfer. Portland cement concrete should be designed with proper air-entrainment and have a minimum compressive strength of 4,000 psi after 28 days of laboratory curing. Adequate reinforcement and number of longitudinal and transverse control joints should be placed in the rigid pavement in accordance with ACI requirements. The joints should be sealed as soon as possible (in accordance with sealant manufacturer’s instructions) to minimize water infiltration into the soil. Harrington Ave Apartments ZGA Project No. 2072.01 May 15, 2019 Page 14 CLOSURE The analysis and recommendations presented in this report are based, in part, on the explorations completed for this study. The number, location, and depth of the explorations for the current phase of the project were completed within the constraints of budget and site access so as to yield the information to formulate our recommendations. Project plans were not available at the time this report was prepared. We therefore recommend Zipper Geo Associates, LLC be provided an opportunity to review the final plans and specifications when they become available in order to assess that the recommendations and design considerations presented in this report have been properly interpreted and implemented into the project design. The performance of shallow foundations and slabs on grade depend greatly on proper site preparation and construction procedures. We recommend that Zipper Geo Associates, LLC be retained to provide geotechnical engineering services during the site preparation and foundation construction phases of the project. If variations in subsurface conditions are observed at that time, a qualified geotechnical engineer could provide additional geotechnical recommendations to the contractor and design team in a timely manner as the project construction progresses. This report has been prepared for the exclusive use of Renton Housing Authority, and its agents, for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranties, express or implied, are intended or made. Site safety, excavation support, and dewatering requirements are the responsibility of others. In the event that changes in the nature, design, or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless Zipper Geo Associates, LLC reviews the changes and either verifies or modifies the conclusions of this report in writing. B-4GLENNWOOD AVE NE HARRINGTON AVE NENE 10TH STB-1B-2B-3B-5FIGUREJob No.Zipper Geo Associates, LLC19019 36th Ave. W.,Suite ELynnwood, WASHT. of11SITE AND EXPLORATION PLAN2072.01SEPTEMBER 20181HARRINTON APARTMENTSNE 10TH ST AND HARRINGTON AVE NERENTON, WASHINGTONAPPROXIMATE SCALE IN FEET0808040LEGENDB-1BORING NUMBER ANDAPPROXIMATE LOCATIONAPPROXIMATE PROPERTY LINEREFERENCE: GOOGLE MAPS 2018. APPENDIX A SUBSURFACE EXPLORATION PROCEDURES AND LOGS APPENDIX A SUBSURFACE EXPLORATION PROCEDURES AND LOGS Field Exploration Description Our field exploration for this project included advancing five borings across the proposed site of the project on September 12, 2018. The approximate locations of the explorations are presented on Figure 1, the Site and Exploration Plan. Exploration locations were determined in the field based on hand measurements from existing site features. As such, the exploration locations should be considered accurate only to the degree implied by the measurement method. Descriptive logs of the borings are enclosed in this appendix. A current topographic survey of the site was not available at the time of this report. Therefore, ground surface elevations of the explorations were not determined. The borings were advanced using a truck-mounted drill rig operated by an independent drilling company (Holocene Drilling Inc.) working under subcontract to ZGA. The borings were advanced using the hollow- stem auger drilling method. An engineer from our firm continuously observed the borings, logged the subsurface conditions encountered, and obtained representative soil samples. All samples were stored in moisture-tight containers and transported to our laboratory for further evaluation and testing. Samples were obtained by means of the Standard Penetration Test at 2.5- to 5-foot intervals throughout the drilling operation. The Standard Penetration Test (ASTM D 1586) procedure consists of driving a standard 2-inch outside diameter steel split spoon sampler 18 inches into the soil with a 140-pound hammer free falling 30 inches. The number of blows required to drive the sampler through each 6-inch interval is recorded, and the total number of blows struck during the final 12 inches is recorded as the Standard Penetration Resistance, or “blow count” (N value). If a total of 50 blows is struck within any 6-inch interval, the driving is stopped and the blow count is recorded as 50 blows for the actual penetration distance. The resulting Standard Penetration Resistance values indicate the relative density of granular soils and the relative consistency of cohesive soils. The enclosed boring logs describe the vertical sequence of soils and materials encountered in the borings, based primarily upon our field classifications. Where a soil contact was observed to be gradational, our log indicates the average contact depth. Where a soil type changed between sample intervals, we inferred the contact depth. Our logs also graphically indicate the blow count, sample type, sample number, and approximate depth of each soil sample obtained from the borings. If groundwater was encountered, the approximate groundwater depth, and date of observation, are depicted on the logs. Drilling Company:Bore Hole Dia.: Top Elevation:Drilling Method:Hammer Type: Drill Rig:Logged by: Standard Penetration Test Hammer Weight and Drop: 0 5 10 15 20 25 SAMPLE LEGEND % Fines (<0.075 mm) 2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content 3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit Grout/Concrete Natural Water Content Screened Casing Blank Casing GSA = Grain Size Analysis Date:Project No.: 200W = 200 Wash Analysis Cons. = Consolidation Test Att. = Atterberg Limits NE 10th St & Harrington Ave NE TESTING KEY Groundwater level at time of drilling (ATD) or on date of measurement. Renton, WA Sep-18 2072.01 19019 36th Ave. W, Suite E Lynnwood, WA BORING LOG:B-1 Page 1 of 2 GROUNDWATER LEGEND Harrington Ave Apartments The stratification lines represent the approximate boundaries between soil types. The transition may be gradual. Refer to report text and appendices for additional information. Boring Location: B-1 Date Drilled:Depth (ft)SOIL DESCRIPTION Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan N/A September 12, 2018 Holocene H.S.A. D90 Truck Rig 8 in. Auto SNM 11/2/120 602040 S-1 18 S-2 18 S-3 0 S-4 8 S-5 18 S-6 18 47 30 20 20 76 72 GSA MC MC 5 inches of organics Dense, damp, light brown, Silty SAND, with gravel (Possible fill) Medium dense, moist, brown, SAND, with silt, trace gravel No Recovery Medium dense, moist, brown-gray, SAND, with silt, some gravel, slight mottling (Weathered Glacial Till) Grades to very dense Very dense, moist, tan, SAND, some silt (Glacial till) Drilling Company:Bore Hole Dia.: Top Elevation:Drilling Method:Hammer Type: Drill Rig:Logged by: Standard Penetration Test Hammer Weight and Drop: 25 30 35 40 45 50 SAMPLE LEGEND % Fines (<0.075 mm) 2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content 3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit Grout/Concrete Natural Water Content Screened Casing Blank Casing GSA = Grain Size Analysis Date:Project No.: 200W = 200 Wash Analysis Cons. = Consolidation Test Att. = Atterberg Limits NE 10th St & Harrington Ave NE TESTING KEY Groundwater level at time of drilling (ATD) or on date of measurement. Renton, WA Sep-18 2072.01 19019 36th Ave. W, Suite E Lynnwood, WA BORING LOG:B-1 Page 2 of 2 GROUNDWATER LEGEND Harrington Ave Apartments The stratification lines represent the approximate boundaries between soil types. The transition may be gradual. Refer to report text and appendices for additional information. Boring Location: B-1 Date Drilled:Depth (ft)SOIL DESCRIPTION Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan N/A September 12, 2018 Holocene H.S.A. D90 Truck Rig 8 in. Auto SNM 11/2/120 602040 S-7 18 65 GSA Very dense, moist, gray, SAND, with silt, some gravel (Glacial till) Boring terminated at approximately 26 1/2 feet. No groundwater observed during exploration. Drilling Company:Bore Hole Dia.: Top Elevation:Drilling Method:Hammer Type: Drill Rig:Logged by: Standard Penetration Test Hammer Weight and Drop: 0 5 10 15 20 25 SAMPLE LEGEND % Fines (<0.075 mm) 2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content 3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit Grout/Concrete Natural Water Content Screened Casing Blank Casing GSA = Grain Size Analysis Date:Project No.: 200W = 200 Wash Analysis Cons. = Consolidation Test Att. = Atterberg Limits NE 10th St & Harrington Ave NE TESTING KEY Groundwater level at time of drilling (ATD) or on date of measurement. Renton, WA Sep-18 2072.01 19019 36th Ave. W, Suite E Lynnwood, WA BORING LOG:B-2 Page 1 of 1 GROUNDWATER LEGEND Harrington Ave Apartments The stratification lines represent the approximate boundaries between soil types. The transition may be gradual. Refer to report text and appendices for additional information. Boring Location: B-2 Date Drilled:Depth (ft)SOIL DESCRIPTION Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan N/A September 12, 2018 Holocene H.S.A. D90 Truck Rig 8 inches Auto SNM 11/2/120 602040 S-1 12 S-2 12 S-3 16 S-4 18 S-5 11 49 60 63 73 50/5 MC MC MC MC 6 inches of organics Dense, damp, brown, Silty SAND, with gravel slight mottling (Possible fill) Dense, damp, gray, SAND, with silt and gravel (Weathered Glacial Till) Very dense, moist, gray, SAND, with silt, trace gravel (Glacial Till) Very dense, moist, gray, SAND, with silt, some gravel, slight mottling (Glacial till) Boring terminated at approximately 16 ft. No groundwater observed during time of drilling. Drilling Company:Bore Hole Dia.: Top Elevation:Drilling Method:Hammer Type: Drill Rig:Logged by: Standard Penetration Test Hammer Weight and Drop: 0 5 10 15 20 25 SAMPLE LEGEND % Fines (<0.075 mm) 2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content 3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit Grout/Concrete Natural Water Content Screened Casing Blank Casing GSA = Grain Size Analysis Date:Project No.: 200W = 200 Wash Analysis Cons. = Consolidation Test Att. = Atterberg Limits NE 10th St & Harrington Ave NE TESTING KEY Groundwater level at time of drilling (ATD) or on date of measurement. Renton, WA Sep-18 2072.01 19019 36th Ave. W, Suite E Lynnwood, WA BORING LOG:B-3 Page 1 of 1 GROUNDWATER LEGEND Harrington Apartments The stratification lines represent the approximate boundaries between soil types. The transition may be gradual. Refer to report text and appendices for additional information. Boring Location: B-3 Date Drilled:Depth (ft)SOIL DESCRIPTION Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan N/A September 12, 2018 Holocene H.S.A. D90 Truck Rig 8 in. Auto SNM 11/2/120 602040 S-1 0 S-2 6 S-3 18 S-4 9 S-5 11 S-6 10 50/2 23 74 50/3 50/5 50/4 GSA MC MC 4 inches of organics Light brown, silty SAND, some gravel (Possible fill) No recovery (Blow counts overstated) Medium dense, moist, gray-tan, SAND, with silt, some gravel (Weathered glacial till) Very dense, moist, gray, silty SAND, some gravel (Glacial till) Grades to with silt and gravel Grades to trace gravel Grades to some silt and gravel Boring terminated at approximately 21 ft. No groundwater observed at the time of drilling. Drilling Company:Bore Hole Dia.: Top Elevation:Drilling Method:Hammer Type: Drill Rig:Logged by: Standard Penetration Test Hammer Weight and Drop: 0 5 10 15 20 25 SAMPLE LEGEND % Fines (<0.075 mm) 2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content 3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit Grout/Concrete Natural Water Content Screened Casing Blank Casing GSA = Grain Size Analysis Date:Project No.: 200W = 200 Wash Analysis Cons. = Consolidation Test Att. = Atterberg Limits NE 10th St & Harrington Ave NE TESTING KEY Groundwater level at time of drilling (ATD) or on date of measurement. Renton, WA Sep-18 2072.01 19019 36th Ave. W, Suite E Lynnwood, WA BORING LOG:B-4 Page 1 of 1 GROUNDWATER LEGEND Harrington Ave Apartments The stratification lines represent the approximate boundaries between soil types. The transition may be gradual. Refer to report text and appendices for additional information. Boring Location: B-4 Date Drilled:Depth (ft)SOIL DESCRIPTION Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan N/A September 12, 2018 Holocene H.S.A. D90 Truck Rig 8 inches Auto SNM 11/2/120 602040 S-1 6 S-2 18 S-3 12 S-4 0 S-5 8 S-6 4 7 26 50/6 50/3 50/2 50/3 GSA MC MC 2 inches of organics Loose, damp, orange-brown, Gravelly SAND, with silt, trace organics (Possible fill) Medium dense, moist, gray, SAND, with silt, some gravel (Weathered glacial till Very dense, moist, gray-brown, SAND, with silt and gravel (Glacial till) No recovery (Blow counts overstated) Grades to gray, some gravel Grades to with gravel, some silt Boring terminated at approximately 20 1/2 feet. No groundwater observed at the time of drilling. Drilling Company:Bore Hole Dia.: Top Elevation:Drilling Method:Hammer Type: Drill Rig:Logged by: Standard Penetration Test Hammer Weight and Drop: 0 5 10 15 20 25 SAMPLE LEGEND % Fines (<0.075 mm) 2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content 3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit Grout/Concrete Natural Water Content Screened Casing Blank Casing GSA = Grain Size Analysis Date:Project No.: 200W = 200 Wash Analysis Cons. = Consolidation Test Att. = Atterberg Limits NE 10th St & Harrington Ave NE TESTING KEY Groundwater level at time of drilling (ATD) or on date of measurement. Renton, WA Sep-18 2072.01 19019 36th Ave. W, Suite E Lynnwood, WA BORING LOG:B-5 Page 1 of 1 GROUNDWATER LEGEND Harrington Ave Apartments The stratification lines represent the approximate boundaries between soil types. The transition may be gradual. Refer to report text and appendices for additional information. Boring Location: B-5 Date Drilled:Depth (ft)SOIL DESCRIPTION Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan N/A September 12, 2018 Holocene H.S.A. D90 Truck Rig 8 in. Auto SNM 11/2/120 602040 S-1 9 S-2 10 S-3 9 S-4 6 S-5 14 S-6 6 32 25 50/3 50/6 50/6 50/6 MC MC MC MC 6 inches of organics Dense, moist, tan, SAND, with silt, some gravel (Possible fill) Medium dense, moist, gray, SAND, with silt, some gravel (Weathered glacial till) Very dense, moist, gray, SAND, with silt, trace gravel (Glacial till) Grades to some gravel Grades to some silt Boring terminated at approximately 20 1/2 feet. No groundwater observed at the time of drilling. APPENDIX B LABORATORY TESTING PROCEDURES AND RESULTS APPENDIX B LABORATORY TESTING PROCEDURES AND RESULTS A series of laboratory tests were performed by ZGA during the course of this study to evaluate the index and geotechnical engineering properties of the subsurface soils. Descriptions of the types of tests performed are given below. Visual Classification Samples recovered from the exploration locations were visually classified in the field during the exploration program. Representative portions of the samples were carefully packaged in moisture tight containers and transported to our laboratory where the field classifications were verified or modified as required. Visual classification was generally done in accordance with ASTM D 2488. Visual soil classification includes evaluation of color, relative moisture content, soil type based upon grain size, and accessory soil types included in the sample. Soil classifications are presented on the exploration logs in Appendix A. Moisture Content Determinations Moisture content determinations were performed on representative samples obtained from the explorations to aid in identification and correlation of soil types. The determinations were made in general accordance with the test procedures described in ASTM D 2216. Moisture contents are presented on the exploration logs in Appendix A. Grain Size Distributions A grain size analysis determines the range in diameter of soil particles included in a particular sample. Grain size analyses were performed on representative samples in general accordance with ASTM D 422. The results of the grain size determinations for the samples were used in classification of the soils, and are presented in this appendix. Modified Proctor A modified proctor test determines the maximum dry density and optimum moisture to obtain a maximum density under a certain compaction effort. The modified proctor test was performed on representative samples in general accordance with ASTM D1557. The results of the modified proctor test are presented in Appendix B. 0 10 20 30 40 50 60 70 80 90 100 0.0010.0100.1001.00010.000100.0001000.000PERCENT FINER BY WEIGHTPARTICLE SIZE IN MILLIMETERS GRAIN SIZE ANALYSIS Comments: 36"12"6"3"1 1/2"3/4"3/8"4 10 20 40 60 140 200 Coarse Medium Fine Silt ClayFineCoarse COBBLESBOULDERS GRAVEL SAND FINE GRAINED SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER Project No.:PROJECT NAME: Harrington Ave Apartment DATE OF TESTING: Exploration Sample Depth (feet) Moisture (%)Fines (%) Description B-1 2 1/2-4 9.3 Silty SAND, with gravelS-1 30.5 2072.01 9/13/2018 ASTM D 422Test Results Summary Zipper Geo Associates, LLC Geotechnical and Environmental Consultants 0 10 20 30 40 50 60 70 80 90 100 0.0010.0100.1001.00010.000100.0001000.000PERCENT FINER BY WEIGHTPARTICLE SIZE IN MILLIMETERS GRAIN SIZE ANALYSIS Comments: 36"12"6"3"1 1/2"3/4"3/8"4 10 20 40 60 140 200 Coarse Medium Fine Silt ClayFineCoarse COBBLESBOULDERS GRAVEL SAND FINE GRAINED SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER Project No.:PROJECT NAME: Harrington Ave Apartments DATE OF TESTING: Exploration Sample Depth (feet) Moisture (%)Fines (%) Description B-1 25-26 1/2 8.3 SAND, with silt, some gravelS-7 12.7 2072.01 9/13/2018 ASTM D 422Test Results Summary Zipper Geo Associates, LLC Geotechnical and Environmental Consultants 0 10 20 30 40 50 60 70 80 90 100 0.0010.0100.1001.00010.000100.0001000.000PERCENT FINER BY WEIGHTPARTICLE SIZE IN MILLIMETERS GRAIN SIZE ANALYSIS Comments: 36"12"6"3"1 1/2"3/4"3/8"4 10 20 40 60 140 200 Coarse Medium Fine Silt ClayFineCoarse COBBLESBOULDERS GRAVEL SAND FINE GRAINED SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER Project No.:PROJECT NAME: Harrington Ave Apartments DATE OF TESTING: Exploration Sample Depth (feet) Moisture (%)Fines (%) Description B-3 5-6 1/2 7.3 SAND, with silt, some gravelS-2 27.6 2072.01 9/13/2018 ASTM D 422Test Results Summary Zipper Geo Associates, LLC Geotechnical and Environmental Consultants 0 10 20 30 40 50 60 70 80 90 100 0.0010.0100.1001.00010.000100.0001000.000PERCENT FINER BY WEIGHTPARTICLE SIZE IN MILLIMETERS GRAIN SIZE ANALYSIS Comments: 36"12"6"3"1 1/2"3/4"3/8"4 10 20 40 60 140 200 Coarse Medium Fine Silt ClayFineCoarse COBBLESBOULDERS GRAVEL SAND FINE GRAINED SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER Project No.:PROJECT NAME: Harrington Ave Apartments DATE OF TESTING: Exploration Sample Depth (feet) Moisture (%)Fines (%) Description B-4 2 1/2-4 9.1 Gravelly SAND, with siltS-1 19.3 2072.01 9/13/2018 ASTM D 422Test Results Summary Zipper Geo Associates, LLC Geotechnical and Environmental Consultants 90 95 100 105 110 115 120 125 130 135 140 145 150 0 5 10 15 20 25 30 35 40 45Dry Unit Weight (pcf)Moisture Content (%) LABORATORY COMPACTION CURVE Compaction Size Test Standard Mold Harrington Ave Apartments Job No. Job Name Date Tested Sample No. Location Test Results Zipper Geo Associates, LLC 19023 36th Avenue West, Suite D Lynnwood, Washington 98036 (425) 582-9928 Test No.Field Moist.2 3 4 Dry Density (lbs/cu.ft.)132.9 129.4 130.4 #DIV/0! Moisture Content (%)9.3 10.1 6.5 #DIV/0! 1557-B 4-inch 2.80 2.70 2.60 2.50 2.40 Zero Air Voids Curves For Various Specific Gravities 2072.01 Depth / Elevation9/14/2018 09122018 Cuttings 5-7 1/2 ft 134.0 136.2 8.38.3 Maximum Dry Density / Oversize Corrected (pcf) Opt. Moisture Content / Oversize Corrected (%) Sample Description: Comments: Oversize Fraction (%) / Sieve Used 3/49 Appendix E Conveyance Calculations Appendix F Drainage Review Flow Chart SECTION 1.1 DRAINAGE REVIEW 12/12/2016 2017 City of Renton Surface Water Design Manual 1-14 FIGURE 1.1.2.A FLOW CHART FOR DETERMINING TYPE OF DRAINAGE REVIEW REQUIRED