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20-104351_Preliminary TIR_11-06-2020v1 Redondo Heights Land Use Permit Preliminary Technical Information Report November 2020 11/5/2020 KPFF Consulting Engineers ii This page intentionally left blank. Redondo Heights – City of Federal Way iii Table of Contents 1. Project Overview ........................................................................................................................................... 1 2. Conditions and Requirements Summary ................................................................................................... 2 Core Requirement No. 1 – Discharge at the Natural Location ................................................................. 2 Core Requirement No. 2 – Off-Site Analysis ............................................................................................ 2 Core Requirement No. 3 – Flow Control Facilities ................................................................................... 2 Core Requirement No. 4 – Conveyance System ..................................................................................... 2 Core Requirement No. 5 – Construction Stormwater Pollution Prevention ............................................. 2 Core Requirement No. 6 – Maintenance and Operations ........................................................................ 2 Core Requirement No. 7 – Financial Guarantees and Liability ................................................................ 3 Core Requirement No. 8 – Water Quality ................................................................................................ 3 Core Requirement No. 9 – Flow Control BMPS ....................................................................................... 3 Special Requirement No. 1 – Other Adopted Area-Specific Requirements ............................................. 3 Special Requirement No. 2 – Flood Hazard Area Delineation ................................................................. 3 Special Requirement No. 3 – Flood Protection Facilities ......................................................................... 4 Special Requirement No. 4 – Source Controls ........................................................................................ 4 Special Requirement No. 5 – Oil Control ................................................................................................. 4 3. Off-site Analysis ............................................................................................................................................ 4 Task 1: Study Area Definition and Maps ................................................................................................. 4 Task 2: Resource Review ....................................................................................................................... 4 Task 3: Field Inspection .......................................................................................................................... 4 Task 4: Drainage System Description ..................................................................................................... 5 List of Figures Figure 1: Vicinity Map ............................................................................................................................................ 2 Appendices Appendix A – TIR Worksheet Appendix B – Existing Site Conditions Exhibit Appendix C – Downstream Drainage Map Appendix D – Proposed Site Conditions Exhibit Appendix E – Flow Control Calculations Appendix F – Water Quality BioPod Detail and WADOE GULD Documentation Appendix G – Geotechnical Investigation Report KPFF Consulting Engineers iv This page intentionally left blank. Redondo Heights – City of Federal Way 1 1. Project Overview The project proposes to construct multi-family residential units on parcel numbers 720480-0172 and 720480- 0174 totaling approximately 5.025 acres located in Federal Way, Washington. The site improvements will include six multifamily residential buildings with associated drive aisles, parking, sidewalks, residential open space, drainage infrastructure and site utility services. The project site is bounded by existing multifamily residential units to the west; King County Redondo Heights Park and Ride facility to the north; a single-family residence, vacant private property, and protected open space to the east; and vacant commercial property to the south (See Figure 1 – Vicinity Map). The project site is currently undeveloped and is heavily vegetated with trees and various underbrush. Stormwater runoff generally sheet flows from the west property boundary to the east property boundary in the existing conditions, and discharges offsite overland towards an existing drainage ditch located on private property to the east. The existing multifamily residential site (Silver Shadows) to the west discharges runoff from a detention vault with flow control structure via a level spreader that sheet flows over the project site. See Appendix B for existing conditions exhibit and Appendix C for downstream drainage exhibits The proposed drainage improvements include onsite conveyance system, wat er quality treatment facilities and a detention vault with flow control structure. The project proposes to outfall to an existing City drainage manhole to the east that discharges to the existing drainage ditch described above. Additionally the project proposes to intercept the Silver Shadows outfall pipe from the detention vault and route these flows to bypass the new detention vault. No changes are anticipated for the existing Silver Shadows detention vault and control structure. See Appendix D for proposed conditions exhibit. This report is being prepared to for the City of Federal Way land use permit. The project is subject to the requirements of the 2016 King County Surface Water Design Manual (KCSWDM) and the City of Federal Way Addendum requirements. KPFF Consulting Engineers 2 Figure 1: Vicinity Map 2. Conditions and Requirements Summary The project proposes greater than 2,000 square feet of new plus replaced impervious surface; therefore, a Full Drainage Review is required, that includes complying with all nine core requirements and all five special requirements. CORE REQUIREMENT NO. 1 – DISCHARGE AT THE NATURAL LOCATION The project site currently discharges to the east via overland sheet flow and into an existing drainage ditch. The project will continue to discharge to the east in the proposed conditions, but proposes to discharge the mitigated flows through a proposed outfall pipe connection to an existing City manhole that discharges to the described drainage ditch. COR E REQUIREMENT NO. 2 – OFF -S ITE ANALYSIS A Level 1 downstream analysis is provided in Section 3. CORE REQUIREMENT NO. 3 – FLOW CONTROL FACILITIES The project is located in a Level 3 Flood Problem Flow Control area; therefore, the project is required to match historic site condition durations for 50% of the 2-year through the 50-year peak flows and match existing site condition 100-year peak flows for the post development discharge. Existing conditions are modeled as forested. The project is proposing a detention vault with flow control structure to meet the Level 3 flow control standard. See Appendix E for preliminary detention vault MGSFlood calculations demonstrating that the project meets the Level 3 Flow Control requirements. CORE REQUIREMENT NO. 4 – CONVEYANCE SYST EM The project is providing a new conveyance system to collect and route the onsite runoff to the proposed detention system. The conveyance system will be designed to convey and contain the 25-year peak flow rates and meet requirements of the KCSWDM. CORE REQUIREMENT NO. 5 – CONSTRUCTION STORMWATER POLLUTION PREVENTION Temporary erosion and sediment control (TESC) measures will be implemented during construction. A preliminary TESC plan is provided for this project submittal. It is anticipated that a construction stormwater pollution prevention plan (CSWPPP) will be required for duration of construction activities. The preliminary TESC measures include but will not be limited to silt fence, inlet protection systems, interceptor swales and silt dikes, and portable sediment treatment tanks to manage erosion during construction activities. CORE REQUIREMENT NO. 6 – MAINTENANCE AND OPER ATIONS The Owner will be responsible for the onsite drainage facility maintenance and operation. Onsite drainage facilities include catch basins, manholes, storm drain pipe, water quality facilities, and the detention vault and associated flow control structure. Coordination for maintenance responsibilities for the outfall pipe connection to the existing City drainage infrastructure will be determined prior to construction. Redondo Heights – City of Federal Way 3 CORE REQUIREMENT NO. 7 – FINANCIAL GUARANTEES AND LIABILITY All drainage facilities constructed or modified for this project will comply with the City’s financial guarantee requirements. CORE REQUIREMENT NO. 8 – WATER QUALITY The project is required to provide water quality facilities and meet the enhanced water quality treatment standard. The Oldcastle BioPod enhanced treatment system (or an approved equal) is being proposed to meet the enhanced water quality treatment requirements. This treatment facility has a general use level designation (GULD) by the Washington State Department of Ecology (WADOE) for enhanced treatment application. The treatment facilities are located upstream of the detention vault and have been preliminarily sized to meet KCSWDM requirements. See Appendix F for the BioPod general detail and WADOE GULD documentation. The final system decision will be made during construction document design and permitting CORE REQUIREMENT NO. 9 – FLOW CONTROL BM P S This project is required to evaluate flow control Best Management Practice (BMP) to the maximum extent feasible and is subject to Large Lot BMP Requirements, as the project site is greater than 22,000 square feet. The evaluation of Flow Control BMPs is based on the requirements per KCSWDM, Section 1.2.9.2.2 and Appendix C.2. The following is the evaluation of the BMP categories and summary of implementation of BMPs where feasible:  Full Dispersion: Full dispersion is not feasible, as the proposed improvements do not allow for sufficient on-site native vegetated flow paths for full dispersion.  Full infiltration of roof runoff: Full infiltration is not feasible as the project is underlain with a glacial till soils that have limited infiltration based on geotechnical analysis. See Appendix G for geotechnical report.  Full Infiltration, Partial Infiltration, Bioretention or Permeable Pavement: Infiltration is not feasible as the project is underlain with a glacial till soils that have limited infiltration based on ge otechnical analysis. See Appendix G for geotechnical report.  Basic Dispersion: Basic dispersion will be applied to roof downspouts use splash blocks and vegetated flows paths where feasible.  Native Growth Retention: Native growth retention will be evaluated and retained where possible. Proposed improvements and grading activities may limit the available native growth retention areas onsite  Post Amended Soils: Post Amended soils will be applied to landscape areas onsite.  Perforated Pipe Connection: Perforated pipe connection are not recommended due to restrictive infiltration glacial till soils onsite. SPECIAL REQUIREMENT NO. 1 – OTHER ADOPTE D AREA -SPECIFIC REQUIREMENTS This project does not fall under any area-specific requirements. SPECIAL REQUIREMENT NO. 2 – FLOOD HAZARD AREA DE LINEATION No flood hazard areas are located within the proposed site. KPFF Consulting Engineers 4 SPECIAL REQUIREMENT NO. 3 – FLOOD PROTEC TION FACILITIES The project does not contain a stream that has an existing flood protection facil ity. The project also does not propose to construct new or to modify an existing flood protection facility. SPECIAL REQUIREMENT NO. 4 – SOURCE CONTR OLS Source control BMPs are anticipated to be implemented during construction activities. The contractor shall be responsible for monitoring stormwater runoff during construction activities and implement appropriate source control BMPs to prevent illicit discharges. It is not anticipated that permanent Source Control BMPs will be required for this project. SPECIAL REQUIREMENT NO. 5 – OIL CONTROL This project does not qualify as a high-use site; therefore, no oil controls are required. 3. Off-site Analysis TASK 1: STUDY AREA DEFINITION AND MAPS A Level 1 downstream analysis has been performed for this project in accordance with the KCSWDM. The analysis consists of a project mapping investigation, a field investigation of the site, and a verification of the downstream conveyance path. The study area extends to a point approximately a quarter mile downstream of the project site. Refer to Appendix C for the downstream drainage map. TASK 2: RESOURCE RE VIEW The following resources were reviewed for this project:  City of Federal Way record drawings and inspection documents .  City of Federal Way GIS maps.  Project Site Survey TASK 3: FIELD INSPE CTION A field inspection for a quarter mile downstream of the site was conducted and consisted of inspecting the downstream drainage components visible from the surface. The downstream system consists of the proposed manhole connection point, outlet pipe, drainage ditch and downstream piped conveyance system. The adjacent subdivision has two stormwater detention ponds that also discharge to the drainage ditch . Generally, the system was observed to be consistent with available survey information and the City of Federal Way drainage information. There were no drainage concerns documented at the time of the field inspection. There was limited access to the drainage ditch and downstream piped conveyance system due to heavy vegetation and conveyance system being within private gated property. Redondo Heights – City of Federal Way 5 TASK 4: DRAINAGE SY STEM DESCRIPTION Upstream Analysis The neighboring Silver Shadows Apartments to the west is located upstream of the project site. The upstream drainage system consists of a piped conveyance system and detention vault that discharges to a level spreader and sheet flows across the project site towards the previously described drainage ditch. The outfall for this system is being routed to bypass the new detention vault and continue to discharge to the drainage ditch to the east. Downstream Analysis Runoff from the project site generally sheet flows overland to the east and drains towards an existing drainage ditch. The drainage ditch continues north and flows into a piped conveyance system that flows through an existing multifamily residential development and the out to a piped system in South Star Lake Road. The conveyance system ultimately discharges to McSorley Creek. See Appendix C for downstream drainage map. There were no existing or potential drainage, flooding, or erosion issues identified during review of available resources. Redondo Heights – City of Federal Way Appendix A Appendix A TIR Worksheet KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL 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 _________________________ DPER Permit # ________________________ Location Township ______________ Range ________________ Section ________________ Site Address __________________________ _____________________________________ Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS  Landuse (e.g.,Subdivision / Short Subd. / UPD)  Building (e.g.,M/F / Commercial / SFR)  Clearing and 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 __________________ __________________ __________________ Part 6 SWDM ADJUSTMENT APPROVALS Type (circle one): Standard / Experimental / Blanket Description: (include conditions in TIR Section 2) ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ Approved Adjustment No. ______________________ Date of Approval: ______________________ 2016 Surface Water Design Manual 4/24/2016 1 22 4 33 Redondo HeightsShelter Resources Inc 253-838-6810 PO BOX 23699 Tom Jones KPFF Consulting Engineers 206-622-5822 Federal Way, WA 98083 No Address Parcels 720480-0172 and -0174 11/4/2020 NA Lakehaven Water & Sewer 11/4/2020 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes / No Start Date: _______________________ Completion Date: _______________________ Describe: _________________________________ _________________________________________ _________________________________________ Re: KCSWDM 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 ______________________  _____________________________________ Part 10 SOILS Soil Type _________________ _________________ _________________ _________________ Slopes _________________ _________________ _________________ _________________ Erosion Potential _________________ _________________ _________________ _________________  High Groundwater Table (within 5 feet)  Other ________________________________  Sole Source Aquifer  Seeps/Springs  Additional Sheets Attached 2016 Surface Water Design Manual 4/24/2016 2 Fill soils over glacial till Erosion potential during construction to be addressed with ESC measures. Level 3 Flood Problem Flow Control and Enhanced WQ Treatment exist slopes are generally with 5%-15%, and slope from west PL to east PL KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 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) Level: 1 / 2 / 3 or Exemption Number ____________ Flow Control 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: _________________________ 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. ______________________ Landscape Management Plan: Yes / No Special Requirements (as applicable): Area Specific Drainage Requirements Type: CDA / SDO / MDP / BP / LMP / 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: 2016 Surface Water Design Manual 4/24/2016 3 onsite area 5.025 acres 1 Detention Vault None. Flow Control BMPs glacial till soils limiting infiltration BMPs TBD TO BE PROVIDED KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Source Control (comm ercial / 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: 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  Protection of Flow Control BMP Facilities (existing and proposed)  Maintain 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 Facilities, restore operation of Flow Control BMP Facilities as necessary  Flag limits of SAO 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  Flow Control BMPs  Other ________________ ________________ ________________ ________________ ________________ ________________  Vegetated Flowpath  Wetpool  Filtration  Oil Control  Spill Control  Flow Control BMPs  Other ________________ ________________ ________________ ________________ ________________ ________________ ________________ 2016 Surface Water Design Manual 4/24/2016 4 Detention Vault Old Castle BioPod basic dispersion downspout splash block N/A Redondo Heights – City of Federal Way Appendix B Appendix B Existing Site Conditions Map 1601 5th Avenue, Suite 1600Seattle, WA 98101206.622.5822www.kpff.com Redondo Heights – City of Federal Way Appendix C Appendix C Downstream Drainage Map PROJECT SITE CITY OF FEDERAL WAY STORMWATER GIS MAP 1/4-MILE DOWNSTREAM PATH McSorley Creek MH POC AND OUTLET PIPE DRAINAGE DITCH PUBLIC PIPED CONVEYANCE SYSTEM ON PRIVAE PROPERTY King C o unty, Ea gleVi ew Tec hno l o g ie s, Inc . King C ou n ty iM ap Date: 10/20/2020 Notes:±The i nfor ma tion inclu ded on this m ap ha s b een com pi le d by Ki ng C ounty sta ff fr om a vari e ty of so urc es an d is subject to chan ge wi tho ut notic e. King Coun tymakes n o re p re sen tati ons o r w arr antie s, expr es s or im p lied , as to accur ac y, comp l ete n ess, tim e line ss, o r r ig h ts to the use o f su ch infor m ati on . This do cum en t isnot in tended for u se as a su r ve y pr oduc t. King Coun ty shall n o t be li abl e fo r an y g ene r al , spec ia l, in dire ct, in ci den ta l, o r co nse quen tial dam ag es incl ud i ng,but n ot l im ited to, lost reve n ues or lo st p ro fits r es ul ting fr o m the us e or m is us e of the i nform a tion co ntained on this m ap. Any sale of this m ap or infor m ati on o nthis ma p is proh ib ited excep t by w ri tten perm issi on o f King County. Leg en d Pa rc els St rea m (19 90 SA O) cla ss 1 cla ss 2 pe re nnia l cla ss 2 sa lmon id cla ss 3 unclassifie d Wet lan d (1 99 0 SAO) Str eam s EX TYP 2 CB/MH EXIST DITCH CL SD OVERFLOW AND DISCHARGE PIPE EXIST 15" SD EXIST 15" SD PROP STORAGE SITE STORM OUTFALL PIPE AND DISPERSAL TRENCH EXIST DITCH CL PROP STORAGE SITE EMERGENCY OVERFLOW EXIST TYPE 2 CB/MH RIM 310.23 IE 304.49 PROP REDONDO TOD SD POC SD PROP OUTFALL PIPE CONNECTION PROP STORAGE SITE STREAM BUFFER Redondo Heights – City of Federal Way Appendix D Appendix D Proposed Site Conditions Map 1601 5th Avenue, Suite 1600Seattle, WA 98101206.622.5822www.kpff.com Redondo Heights – City of Federal Way Appendix E Appendix E Flow Control Calculations ————————————————————————————————— MGS FLOOD PROJECT REPORT Program Version: MGSFlood 4.52 Program License Number: 200410007 Project Simulation Performed on: 11/04/2020 10:01 AM Report Generation Date: 11/04/2020 11:19 AM ————————————————————————————————— Input File Name: REDONDO LAND USE VAULT SIZE.fld Project Name: Redondo Heights Analysis Title: Comments: 5.025 Acres; 3.254 acres impervious; 1.771 aces pervious ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Climatic Region Number: 15 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) 5.025 5.025 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 5.025 5.025 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 ---------- -------Area (Acres) -------- Till Forest 5.025 ---------------------------------------------- Subbasin Total 5.025 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 2 ---------- Subbasin : Subbasin 1 ---------- -------Area (Acres) -------- Till Grass 0.799 Impervious 1.464 ---------------------------------------------- Subbasin Total 2.263 ---------- Subbasin : Subbasin 2 ---------- -------Area (Acres) -------- Till Grass 0.972 Impervious 1.790 ---------------------------------------------- Subbasin Total 2.762 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 3 ------------------------------------------ Link Name: PRELIM VAULT Link Type: Structure Downstream Link: None Prismatic Pond Option Used Pond Floor Elevation (ft) : 100.00 Riser Crest Elevation (ft) : 106.00 Max Pond Elevation (ft) : 106.50 Storage Depth (ft) : 6.00 Pond Bottom Length (ft) : 271.0 Pond Bottom Width (ft) : 50.0 Pond Side Slopes (ft/ft) : L1= 0.00 L2= 0.00 W1= 0.00 W2= 0.00 Bottom Area (sq-ft) : 13550. Area at Riser Crest El (sq-ft) : 13,550. (acres) : 0.311 Volume at Riser Crest (cu-ft) : 81,300. (ac-ft) : 1.866 Area at Max Elevation (sq-ft) : 13550. (acres) : 0.311 Vol at Max Elevation (cu-ft) : 88,075. (ac-ft) : 2.022 Hydraulic Conductivity (in/hr) : 0.00 Massmann Regression Used to Estimate Hydralic Gradient Depth to Water Table (ft) : 100.00 Bio-Fouling Potential : Low Maintenance : Average or Better Riser Geometry Riser Structure Type : Circular Riser Diameter (in) : 24.00 Common Length (ft) : 0.020 Riser Crest Elevation : 106.00 ft Hydraulic Structure Geometry Number of Devices: 2 ---Device Number 1 --- Device Type : Circular Orifice Control Elevation (ft) : 100.00 Diameter (in) : 1.03 Orientation : Horizontal Elbow : No --- Device Number 2 --- Device Type : Vertical Rectangular Orifice Control Elevation (ft) : 103.60 Length (in) : 0.25 Height (in) : 28.80 Orientation : Vertical Elbow : No ------------------------------------------ Link Name: New Copy Lnk2 Link Type: Copy Downstream Link Name: PRELIM VAULT ------------------------------------------ Link Name: New Copy Lnk3 Link Type: Copy Downstream Link Name: PRELIM VAULT **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 2 Number of Links: 3 ********** Link: PRELIM VAULT ********** Link WSEL Stats WSEL Frequency Data(ft) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) WSEL Peak (ft) ====================================== 1.05-Year 101.879 1.11-Year 102.081 1.25-Year 102.373 2.00-Year 103.286 3.33-Year 103.846 5-Year 104.359 10-Year 105.000 25-Year 105.418 50-Year 105.646 100-Year 105.786 ***********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: Subbasin 1 866.456 _____________________________________ Total: 866.456 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Subbasin 1 97.646 Subbasin: Subbasin 2 118.789 Link: PRELIM VAULT 0.000 Link: New Copy Lnk2 Not Applicable Link: New Copy Lnk3 Not Applicable _____________________________________ Total: 216.435 Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 5.484 ac-ft/year, Post Developed: 1.370 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 3 ********** Link: PRELIM VAULT ********** Basic Wet Pond Volume (91% Exceedance): 16240. cu-ft Computed Large Wet Pond Volume, 1.5*Basic Volume: 24360. cu-ft Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 1815.08 Inflow Volume Including PPT-Evap (ac-ft): 1815.08 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): 1814.72 Secondary Outflow To Downstream System (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00% ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: Subbasin 1 Scenario Postdeveloped Compliance Link: PRELIM VAULT *** 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 0.107 2-Year 5.092E-02 5-Year 0.175 5-Year 9.599E-02 10-Year 0.235 10-Year 0.156 25-Year 0.298 25-Year 0.204 50-Year 0.380 50-Year 0.232 100-Year 0.412 100-Year 0.250 200-Year 0.642 200-Year 0.344 500-Year 0.950 500-Year 0.471 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals **** Flow Duration Performance **** Excursion at Predeveloped 50%Q2 (Must be Less Than or Equal to 0%): -31.6% PASS Maximum Excursion from 50%Q2 to Q2 (Must be Less Than or Equal to 0%): -26.3% PASS Maximum Excursion from Q2 to Q50 (Must be less than 10%): -8.8% PASS Percent Excursion from Q2 to Q50 (Must be less than 50%): 0.0% PASS ------------------------------------------------------------------------------------------------- MEETS ALL FLOW DURATION DESIGN CRITERIA: PASS ------------------------------------------------------------------------------------------------- Redondo Heights – City of Federal Way Appendix F Appendix F Water Quality Bio P od Detail and WADOE GULD Documentation ISOMETRIC VIEW BPU-IB C US Patents Pending THIS DOCUMENT IS THE PROPERTY OF OLDCASTLE INFRASTRUCTURE, INC. IT IS SUBMITTED FOR REFERENCE PURPOSES ONLY AND SHALL NOT BE USED IN ANY WAY INJURIOUS TO THE INTERESTS OF SAID COMPANY. COPYRIGHT © 2020 OLDCASTLE INFRASTRUCTURE, INC. ALL RIGHTS RESERVED. BioPod f Biofilter Underground Vault with Internal Bypass dOldcastle dOldcastle dOldcastle Bioretention/ Biofiltration A PLAN VIEW A SECTION A-A BPU-IB C US Patents PendingSAUDFI1325-0510USAXXXXTHIS DOCUMENT IS THE PROPERTY OF OLDCASTLE INFRASTRUCTURE, INC. IT IS SUBMITTED FOR REFERENCE PURPOSES ONLY AND SHALL NOT BE USED IN ANY WAY INJURIOUS TO THE INTERESTS OF SAID COMPANY. COPYRIGHT © 2020 OLDCASTLE INFRASTRUCTURE, INC. ALL RIGHTS RESERVED. MODEL VAULT SIZE 1 (ID) VAULT FOOTPRINT 1 (OD) TREATMENT FLOW CAPACITY (GPM/CFS) A DIM B DIM C DIM A1 DIM B1 DIM 1.6 GPM/SF (WA GULD2) 1.8 GPM/SF (NJCAT3) BPU-46IB 4'6'1.5'5'7'25.6 / 0.057 28.8 / 0.064 BPU-48IB 4'8'1.5'5'9'38.4 / 0.086 43.2 / 0.096 BPU-412IB 4'12'1.5'5'13'64.0 / 0.143 72.0 / 0.160 BPU-66IB 6'6'1.5'7'7'38.4 / 0.086 43.2 / 0.096 BPU-68IB 6'8'1.5'7'9'57.6 / 0.128 64.8 / 0.144 BPU-612IB 6'12'2'7'13'91.2 / 0.203 102.6 / 0.229 BPU-812IB 8'12'2'9'13'121.6 / 0.271 136.9 / 0.305 BPU-816IB 8'16'2'9'17'172.8 / 0.385 194.4 / 0.433 BioPod f Biofilter Underground Vault with Internal Bypass fFIDSAUXXXXUSADFI11540010FIDSAUXXXXUSADFI11540010 SITE SPECIFIC DATA Structure ID Model Size Orientation (Left or Right) Treatment Flow Rate (cfs) Peak Flow Rate (cfs) Rim Elevation Pipe Data Pipe Location (Front or Side)Pipe Size Pipe Type Invert Elevation Inlet Outlet Notes: 1 All Dimensions are nominal, ID=Inside Dimension, OD=Outside Dimension. 2 Treartment flow capacity at 1.6 gpm/sf media surface area based on an WA Ecology GULD Approval for Basic, Enhanced & Phosphorus. 3 Treatment flow capacity at 1.8 gpm/sf media surface area based on an NJCAT Verification & NJ DEP Certification. Bioretention/ Biofiltration October 2019 GENERAL USE LEVEL DESIGNATION FOR BASIC (TSS), DISSOLVED METALS (ENHANCED), AND PHOSPHORUS TREATMENT For Oldcastle Infrastructure, Inc.’s The BioPod™ Biofilter (Formerly the TreePod Biofilter) Ecology’s Decision: Based on Oldcastle Infrastructure, Inc. application submissions for the The BioPod™ Biofilter (BioPod), Ecology hereby issues the following use level designation: 1. General Use Level Designation (GULD) for Basic, Enhanced, and Phosphorus Treatment:  Sized at a hydraulic loading rate of 1.6 gallons per minute (gpm) per square foot (sq ft) of media surface area.  Constructed with a minimum media thickness of 18-inches (1.5-feet). 2. Ecology approves the BioPod at the hydraulic loading rate listed above, to achieve the maximum water quality design flow rate. The water quality design flow rates are calculated using the following procedures:  Western Washington: For treatment installed upstream of detention or retention, the water quality design flow rate is the peak 15-minute flow rate as calculated using the latest version of the Western Washington Hydrology Model or other Ecology- approved continuous runoff model.  Eastern Washington: For treatment installed upstream of detention or retention, the water quality design flow rate is the peak 15-minute flow rate as calculated using one of the three methods described in Chapter 2.2.5 of the Stormwater Management Manual for Eastern Washington (SWMMEW) or local manual.  Entire State: For treatment installed downstream of detention, the water quality design flow rate is the full 2-year release rate of the detention facility. 3. The GULD has no expiration date, but may be amended or revoked by Ecology. Ecology’s Conditions of Use: The BioPod shall comply with these conditions: 1) Applicants shall design, assemble, install, operate, and maintain the BioPod installations in accordance with Oldcastle Infrastructure, Inc.’s applicable manuals and the Ecology Decision. 2) The minimum size filter surface-area for use in Washington is determined by using the design water quality flow rate (as determined in Ecology Decision, Item 3, above) and the Infiltration Rate (as identified in Ecology Decision, Item 1, above). Calculate the required area by dividing the water quality design flow rate (cu-ft/sec) by the Infiltration Rate (converted to ft/sec) to obtain required surface area (sq ft) of the BioPod unit 3) BioPod media shall conform to the specifications submitted to and approved by Ecology 4) Maintenance: The required inspection/maintenance interval for stormwater treatment devices is often dependent on the efficiency of the device and the degree of pollutant loading from a particular drainage basin. Therefore, Ecology does not endorse or recommend a “one size fits all” maintenance cycle for a particular model/size of manufactured filter treatment device.  The BioPod is designed for a target maintenance interval of 1 year. Maintenance includes replacing the mulch, assessing plant health, removal of trash, and raking the top few inches of engineered media.  A BioPod system tested at the Lake Union Ship Canal Test Facility in Seattle, WA required maintenance after 1.5 months, or 6.3% of a water year. Monitoring personnel observed similar maintenance issues with other systems evaluated at the Test Facility. The runoff from the Test Facility may be unusual and maintenance requirements of systems installed at the Test Facility may not be indicative of maintenance requirements for all sites.  Test results provided to Ecology from a BioPod System evaluated in a lab following New Jersey Department of Environmental Protection Laboratory Protocol for Filtration MTDs have indicated the BioPod System is capable of longer maintenance intervals.  Owners/operators must inspect BioPod systems for a minimum of twelve months from the start of post-construction operation to determine site-specific inspection/maintenance schedules and requirements. Owners/operators must conduct inspections monthly during the wet season, and every other month during the dry season. (According to the SWMMWW, the wet season in western Washington is October 1 to April 30. According to the SWMMEW, the wet season in eastern Washington is October 1 to June 30.) After the first year of operation, owners/operators must conduct inspections based on the findings during the first year of inspections.  Conduct inspections by qualified personnel, follow manufacturer’s guidelines, and use methods capable of determining either a decrease in treated effluent flow rate and/or a decrease in pollutant removal ability. 5) Install the BioPod in such a manner that you bypass flows exceeding the maximum operating rate and you will not resuspend captured sediment. 6) Discharges from the BioPod shall not cause or contribute to water quality standards violations in receiving waters. Approved Alternate Configurations BioPod Internal Bypass 1) The BioPod Internal Bypass configuration may be combined with a Curb Inlet, Grated Inlet, and Piped-In Inlet. Water quality flows and peak flows are directed from the curb, overhead grate, or piped inlet to a contoured inlet rack. The inlet rack disperses water quality flows over the top surface of the biofiltration chamber. Excess flows are diverted over an curved bypass weir to the outlet area without passing through the treatment area. Both water quality flows and bypass flows are combined in the outlet area prior to being discharged out of the system. 2) To select a BioPod Internal Bypass unit, the designer must determine the size of the standard unit using the sizing guidance described above. Systems that have an internal bypass, may use the off-line water quality design flow rate. 3) The internal bypass configuration has a maximum flow rate of 900 gallons per minute. Sites where the anticipated flow rate at the treatment device is larger than 900 gpm must use an external bypass, or size the treatment device for the on-line water quality design flow rate. Applicant: Oldcastle Infrastructure, Inc. Applicant’s Address: 7100 Longe St, Suite 100 Stockton, CA 95206 Application Documents: Technical Evaluation Report TreePod™ BioFilter System Performance Certification Project, Prepared for Oldcastle, Inc., Prepared by Herrera Environmental Consultants, Inc. February 2018 Technical Memorandum: Response to Board of External Reviewers’ Comments on the Technical Evaluation Report for the TreePod™ Biofilter System Performance Certification Project, Oldcastle, Inc. and Herrera Environmental Consultants, Inc., February 2018 Technical Memorandum: Response to Board of External Reviewers’ Comments on the Technical Evaluation Report for the TreePod™ Biofilter System Performance Certification Project, Oldcastle, Inc. and Herrera Environmental Consultants, Inc., January 2018 Application for Pilot Use Level Designation, TreePod™ Biofilter – Stormwater Treatment System, Oldcastle Stormwater Solutions, May 2016 Emerging Stormwater Treatment Technologies Application for Certification: The TreePod™ Biofilter, Oldcastle Stormwater Solutions, April 2016 Applicant’s Use Level Request:  General Use Level Designation as a Basic, Enhanced, and Phosphorus Treatment device in accordance with Ecology’s Stormwater Management Manual for Western Washington Applicant’s Performance Claims: Based on results from laboratory and field-testing, the applicant claims the BioPod™ Biofilter operating at a hydraulic loading rate of 153 inches per hour is able to remove:  80% of Total Suspended Solids (TSS) for influent concentrations greater than 100 mg/L and achieve a 20 mg/L effluent for influent concentrations less than 100 mg/L.  60% dissolved zinc for influent concentrations 0.02 to 0.3 mg/L.  30% dissolved copper for influent concentrations 0.005 to 0.02 mg/L.  50% or greater total phosphorus for influent concentrations 0.1 to 0.5 mg/L. Ecology’s Recommendations: Ecology finds that:  Oldcastle Infrastructure, Inc. has shown Ecology, through laboratory and field testing, that the BioPod™ Biofilter is capable of attaining Ecology’s Basic, Total Phosphorus, and Enhanced treatment goals. Findings of Fact: Field Testing 1. Herrera Environmental Consultants, Inc. conducted monitoring of the BioPod™ Biofilter at the Lake Union Ship Canal Test Facility in Seattle Washington between November 2016 and April 2018. Herrera collected flow-weight composite samples during 14 separate storm events and peak flow grab samples during 3 separate storm events. The system was sized at an infiltration rate of 153 inches per hour or a hydraulic loading rate of 1.6 gpm/ft2. 2. The D50 of the influent PSD ranged from 3 to 292 microns, with an average D50 of 28 microns. 3. Influent TSS concentrations ranged from 17 mg/L to 666 mg/L, with a mean concentration of 98 mg/L. For all samples (influent concentrations above and below 100 mg/L) the bootstrap estimate of the lower 95 percent confidence limit (LCL 95) of the mean TSS reduction was 84% and the bootstrap estimate of the upper 95 percent confidence limit (UCL95) of the mean TSS effluent concentration was 8.2 mg/L. 4. Dissolved copper influent concentrations from the 17 events ranged from 9.0 µg/L to 21.1 µg/L. The 21.1 µg/L data point was reduced to 20.0 µg/L, the upper limit to the TAPE allowed influent concentration range, prior to calculating the pollutant removal. A bootstrap estimate of the LCL95 of the mean dissolved copper reduction was 35%. 5. Dissolved zinc influent concentrations from the 17 events ranged from 26.1 µg/L to 43.3 µg/L. A bootstrap estimate of the LCL95 of the mean dissolved zinc reduction was 71%. 6. Total phosphorus influent concentrations from the 17 events ranged from 0.064 mg/L to 1.56 mg/L. All influent data greater than 0.5 mg/L were reduced to 0.5 mg/L, the upper limit to the TAPE allowed influent concentration range, prior to calculating the pollutant removal. A bootstrap estimate of the LCL95 of the mean total phosphorus reduction was 64%. 7. The system experienced rapid sediment loading and needed to be maintained after 1.5 months. Monitoring personnel observed similar sediment loading issues with other systems evaluated at the Test Facility. The runoff from the Test Facility may not be indicative of maintenance requirements for all sites. Laboratory Testing 1. Good Harbour Laboratories (GHL) conducted laboratory testing at their site in Mississauga, Ontario in October 2017 following the New Jersey Department of Environmental Protection Laboratory Protocol for Filtration MTDs. The testing evaluated a 4-foot by 6-foot standard biofiltration chamber and inlet contour rack with bypass weir. The test sediment used during the testing was custom blended by GHL using various commercially available silica sands, which had an average d50 of 69 µm. Based on the lab test results: a. GHL evaluated removal efficiency over 15 events at a Maximum Treatment Flow Rate (MTFR) of 37.6 gpm, which corresponds to a MTFR to effective filtration treatment area ratio of 1.80 gpm/ft2. The system, operating at 100% of the MTFR with an average influent concentration of 201.3 mg/L, had an average removal efficiency of 99 percent. b. GHL evaluated sediment mass loading capacity over an additional 16 events using an influent SSC concentration of 400 mg/L. The first 11 runs were evaluated at 100% of the MTFR. The BioPod began to bypass, so the remaining 5 runs were evaluated at 90% of the MTFR. The total mass of the sediment captured was 245.0 lbs and the cumulative mass removal efficiency was 96.3%. 2. Herrera Environmental Consultants Inc. conducted laboratory testing in September 2014 at the Seattle University Engineering Laboratory. The testing evaluated the flushing characteristics, hydraulic conductivity, and pollutant removal ability of twelve different media blends. Based on this testing, Oldcastle Infrastructure, Inc. selected one media blend, Mix 8, for inclusion in their TAPE evaluation of the BioPod™ Biofilter. a. Herrera evaluated Mix 8 in an 8-inch diameter by 36-inch tall polyvinyl chloride (PVC) column. The column contained 18-inches of Mix 8 on top of 6-inches of pea gravel. The BioPod will normally include a 3-inch mulch layer on top of the media layer; however, this was not included in the laboratory testing. b. Mix 8 has a hydraulic conductivity of 218 inches per hour; however, evaluation of the pollutant removal ability of the media was based on an infiltration rate of 115 inches per hour. The media was tested at 75%, 100%, and 125% of the infiltration rate. Based on the lab test results:  The system was evaluated using natural stormwater. The dissolved copper and dissolved zinc concentrations in the natural stormwater were lower than the TAPE influent standards; therefore, the stormwater was spiked with 66.4 mL of 100 mg/L Cu solution and 113.6 mL of 1,000 mg/L Zn solution.  The BioPod removed an average of 81% of TSS, with a mean influent concentration of 48.4 mg/L and a mean effluent concentration of 9.8 mg/L.  The BioPod removed an average of 94% of dissolved copper, with a mean influent concentration of 10.6 µg/L and a mean effluent concentration of 0.6 µg/L.  The BioPod removed an average of 97% of dissolved zinc, with a mean influent concentration of 117 µg/L and a mean effluent concentration of 4 µg/L.  The BioPod removed an average of 97% of total phosphorus, with a mean influent concentration of 2.52 mg/L and a mean effluent concentration of 0.066 mg/L. When total phosphorus influent concentrations were capped at the TAPE upper limit of 0.5 mg/L, calculations showed an average removal of 87%. Other BioPod Related Issues to be Addressed By the Company: 1. Conduct hydraulic testing to obtain information about maintenance requirements on a site with runoff that is more typical of the Pacific Northwest. Technology Description: Download at https://oldcastleprecast.com/stormwater/bioretention- biofiltration-applications/bioretention-biofiltration- solutions/ Contact Information: Applicant: Chris Demarest Oldcastle Infrastructure, Inc. (925) 667-7100 Chris.demarest@oldcastle.com Applicant website: https://oldcastleprecast.com/stormwater/ Ecology web link: https://ecology.wa.gov/Regulations-Permits/Guidance-technical- assistance/Stormwater-permittee-guidance-resources/Emerging-stormwater-treatment- technologies Ecology: Douglas C. Howie, P.E. Department of Ecology Water Quality Program (360) 407-6444 douglas.howie@ecy.wa.gov Revision History Date Revision March 2018 GULD granted for Basic Treatment March 2018 Provisional GULD granted for Enhanced and Phosphorus Treatment June 2016 PULD Granted April 2018 GULD for Basic and Provisional GULD for Enhanced and Phosphorus granted, changed name to BioPod from TreePod July 2018 GULD for Enhanced and Phosphorus granted September 2018 Changed Address for Oldcastle December 2018 Added minimum media thickness requirement May 2019 Changed language on who must Install and maintain the device from Oldcastle to Applicants August 2019 Added text on sizing using infiltration rate and water quality design flow rate October 2019 Added text describing ability to use off-line design water quality flow rate for sizing due to internal bypass Redondo Heights – City of Federal Way Appendix G Appendix G Geotechnical Investigation Report Earth Science + Technology Geotechnical Engineering Services Report Redondo Heights Apartments Federal Way, Washington for Shelter Resources, Inc. August 24, 2020                                         Geotechnical Engineering Services Report Redondo Heights Apartments Federal Way, Washington for Shelter Resources, Inc. August 24, 2020   1101 South Fawcett Avenue, Suite 200  Tacoma, Washington 98402 253.383.4940  Geotechnical Engineering Services Report Redondo Heights Apartments Federal Way, Washington File No. 3625-004-00 August 24, 2020 Prepared for: Shelter Resources, Inc. c/o SRI-Rochlin Construction Services 2223 112th Avenue NE, Suite 102 Bellevue, Washington 98004 Attention: James Rochlin Prepared by: GeoEngineers, Inc. 1101 South Fawcett Avenue, Suite 200 Tacoma, Washington 98402 253.383.4940 Christopher R. Newton, PE Geotechnical Engineer Lyle J. Stone, PE Associate Geotechnical Engineer 8/24/2020 CRN:LJS:tt Disclaimer: Any electronic form, facsimile or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record. August 24, 2020| Page i File No. 3625-004-00 Table of Contents 1.0 INTRODUCTION AND PROJECT UNDERSTANDING ........................................................................................ 1   2.0 SCOPE OF SERVICES ...................................................................................................................................... 1  3.0 SITE CONDITIONS ............................................................................................................................................ 1  3.1. Geologic Setting .......................................................................................................................................... 1  3.2. Surface Conditions...................................................................................................................................... 1  3.3. Subsurface Conditions ............................................................................................................................... 2  3.3.1. Subsurface Explorations and Laboratory Testing ..................................................................... 2  3.3.2. Soil and Groundwater Conditions .............................................................................................. 2  4.0 CONCLUSIONS AND RECOMMENDATIONS ................................................................................................... 2  4.1. General Geotechnical Considerations ....................................................................................................... 2  4.2. Seismic Design Considerations .................................................................................................................. 3  4.2.1. Seismic Design Parameters ....................................................................................................... 3  4.2.2. Liquefaction................................................................................................................................. 4  4.2.3. Lateral Spreading Potential ........................................................................................................ 4  4.2.4. Surface Rupture Potential .......................................................................................................... 4  4.3. Site Development and Earthwork .............................................................................................................. 4  4.3.1. General ........................................................................................................................................ 4  4.3.2. Clearing and Stripping ................................................................................................................ 5  4.3.3. Erosion and Sedimentation Control ........................................................................................... 5  4.3.4. Temporary Excavations and Cut Slopes .................................................................................... 6  4.3.5. Permanent Cut and Fill Slopes ................................................................................................... 6  4.3.6. Groundwater Handling Considerations ..................................................................................... 6  4.3.7. Surface Drainage ........................................................................................................................ 7  4.3.8. Subsurface Drainage .................................................................................................................. 7  4.3.9. Subgrade Preparation................................................................................................................. 7  4.3.10. Subgrade Protection and Wet Weather Considerations ........................................................... 7  4.4. Fill Materials ................................................................................................................................................ 8  4.4.1. On-Site Soil .................................................................................................................................. 8  4.4.2. Imported Structural Fill ............................................................................................................... 9  4.4.3. Pipe Bedding ............................................................................................................................... 9  4.4.4. Trench Backfill............................................................................................................................. 9  4.5. Fill Placement and Compaction ................................................................................................................. 9  4.5.1. General ........................................................................................................................................ 9  4.5.2. Area Fills and Pavement Bases ................................................................................................. 9   4.5.3. Backfill Behind Walls ............................................................................................................... 10  4.5.4. Trench Backfill.......................................................................................................................... 10  4.6. Foundation Support ................................................................................................................................. 10  4.6.1. General ..................................................................................................................................... 10  4.6.2. Foundation Bearing Surface Preparation ............................................................................... 10  4.6.3. Allowable Soil Bearing Pressure ............................................................................................. 11  4.6.4. Foundation Settlement ............................................................................................................ 11  4.6.5. Lateral Resistance ................................................................................................................... 11  August 24, 2020| Page ii File No. 3625-004-00 4.7. Slab-on-Grade Floors ............................................................................................................................... 12  4.8. Retaining Walls and Below-Grade Structures ........................................................................................ 12  4.8.1. Design Parameters .................................................................................................................. 12  4.8.2. Drainage ................................................................................................................................... 13  4.9. Stormwater Infiltration Feasibility ........................................................................................................... 13  4.10. Pavement Recommendations ................................................................................................................. 14  4.10.1. General ..................................................................................................................................... 14  4.10.2. Construction Considerations ................................................................................................... 14  4.10.3. Asphalt Concrete Pavement Design ....................................................................................... 15  5.0 LIMITATIONS ................................................................................................................................................ 15    LIST OF FIGURES Figure 1. Vicinity Map Figure 2. Site Plan APPENDICES Appendix A. Subsurface Explorations and Laboratory Testing Figure A-1 – Key to Exploration Logs Figures A-2 through A-13 – Logs of Test Pits Figure A-14 – Sieve Analysis Results Appendix B. Report Limitations and Guidelines for Use August 24, 2020| Page 1 File No. 3625-004-00 1.0 INTRODUCTION AND PROJECT UNDERSTANDING This report presents the results of our geotechnical engineering services for the proposed Redondo Heights Apartments project. The project site is located south of South 276th Street, about 600 feet east of Pacific Highway South (HWY 99) in Federal Way, Washington as shown on the Vicinity Map, Figure 1. The site is currently undeveloped and wooded. Our services have been completed in general accordance with our signed agreement dated July 31, 2020. Our understanding of the project is based on our discussions with SRI Rochlin, the project architect (Bumgardner), and the project civil engineer (KPFF) via phone and electronic mail. We understand that the development will consist of about four or five two- to three-story apartment buildings and a community center. The site will also include parking and landscaped open spaces. Some tree retention will be required at the site; therefore, some areas will remain wooded and undisturbed. Based on discussions with the KPFF, we understand that stormwater infiltration is not currently anticipated. It is our understanding that a stormwater retention vault is planned in the lower, northeast, corner of the site. 2.0 SCOPE OF SERVICES The purpose of our geotechnical engineering services is to observe subsurface explorations (test pits) and review other relevant subsurface information at the site to develop geotechnical design and construction recommendations. Our services have been provided in accordance with our signed agreement dated July 31, 2020. 3.0 SITE CONDITIONS 3.1. Geologic Setting Our understanding of the site geology is based, in part, on review of the Geologic Map of the Poverty Bay 7.5’ Quadrangle, King and Pierce Counties, Washington (Booth et al. 2004). The geologic map indicates that glacial soil deposits underlie the site and surrounding areas. These deposits are the result of glaciations that occurred during the Vashon Stade of the Fraser Glaciation, approximately 10,000 to 15,000 years ago. Surface soils at the site are primarily mapped as glacial till (Qvt). Glacial till is described as a highly compact mixture of clay, silt, sand and gravel that was deposited below and subsequently overridden by glacial ice. The upper few feet of till deposits can be weathered and in a loose to dense condition. Underlying undisturbed glacial till is typically very dense with low permeability. 3.2. Surface Conditions The property consists of two rectangular-shaped parcels totaling approximately 5 acres and is bounded by South 276th Street to the north, undeveloped properties to the east and south, and a developed property to the west. The adjacent developed property consists of an apartment complex with several multiple story buildings and driveway and parking areas. August 24, 2020| Page 2 File No. 3625-004-00 The site is currently occupied by heavy vegetation consisting of young to mature deciduous and coniferous trees and various underbrush. Site topography generally slopes down gradually to the northeast with elevation change across the property on the order of 15 to 20 feet. 3.3. Subsurface Conditions 3.3.1. Subsurface Explorations and Laboratory Testing We observed subsurface conditions at the site by observing 12 test pits (TP-1 through TP-12) at the approximate locations shown on the attached Site Plan, Figure 2. Selected samples collected from the test pits were tested in our laboratory to confirm field classifications and to evaluate pertinent engineering properties. Our laboratory testing program included grain-size analyses, percent fines determinations and moisture content determinations. A description of our subsurface exploration program, summary exploration logs, and a summary of our laboratory testing program and the test results are provided in Appendix A. 3.3.2. Soil and Groundwater Conditions At the surface of all the explorations except TP-9, we observed about 9 to 12 inches of forest duff. At TP-9 we observed approximately 12 inches of what we interpret to be fill. Fill consisted of approximately 10- to 12-inch quarry spalls overlying loose silty sand with gravel and occasional debris (plastic bags). Beneath the fill and forest duff, we observed loose to dense silty sand with variable gravel content, varying iron-oxide staining and occasional organics (¼- to 8-inch diameter tree roots). We interpret these soils as weathered glacial till. Weathered glacial till extended to depths ranging from approximately 3 to 5 feet below the ground surface (bgs). Underlying the weathered glacial till in all our explorations, we encountered what we interpret to be undisturbed glacial till soils. Undisturbed glacial till typically consisted of very dense silty sand with gravel or silty gravel and varying iron-oxide staining. All our explorations were completed in undisturbed glacial till soils at depths between approximately 8 and 10.5 feet bgs. We did not observe groundwater in the explorations. Upon completion of TP-6 and TP-12, the two excavations were left open about 5 to 6 hours. At the end of this time, no groundwater seepage was observed within the excavations. Though not encountered in our explorations, perched groundwater could be present in other areas at the site. The interface between more permeable and less permeable zones, such as the contact between weathered glacial till and undisturbed glacial till, are likely locations for accumulation of perched groundwater. Perched groundwater levels can depend on rainfall amounts, irrigation activities and other factors. We anticipate that perched groundwater, if it occurs, will be most prevalent during the wet season, typically October through May. 4.0 CONCLUSIONS AND RECOMMENDATIONS 4.1. General Geotechnical Considerations Based on our understanding of the project, the explorations performed for this study, review of subsurface information near or within the project vicinity and our experience, it is our opinion that the proposed improvements can be designed and constructed generally as envisioned with regard to geotechnical considerations. A summary of the primary geotechnical considerations for the project is provided below and is followed by our detailed recommendations. August 24, 2020| Page 3 File No. 3625-004-00 ■ The site is identified as being located within the Asarco Smelter Plume. An appropriate soil management plan will be required. ■ Soils observed at the site contain a significant quantity of fines and will likely be difficult or impossible to work with when wet or become easily disturbed if exposed to wet weather. Depending on the intended use of the material and the moisture/weather conditions, it may be difficult to use on-site soils as structural fill. ■ Clearing and stripping depths for surficial soils at the site will typically be at least 9 to 12 inches. ■ Proposed structures at the site can be supported using shallow foundations and slabs-on-grade, provided that the foundation bearing surfaces are prepared as recommended. We do not anticipate that significant overexcavation will be required unless isolated areas of loose, or otherwise unsuitable areas are encountered near foundation grade. ■ Encountered site soils are relatively impermeable and, therefore, stormwater infiltration rates at this site are likely very low. ■ Groundwater was not observed during subsurface explorations. However, the relatively impermeable glacial till can create perched groundwater conditions. This can be especially prevalent around building foundations where footing excavation can create a “bathtub” effect. Subsurface drainage including foundation or perimeter drains should be considered as a method for reducing or controlling moisture in buildings. 4.2. Seismic Design Considerations 4.2.1. Seismic Design Parameters We understand seismic design of proposed structures will be performed using procedures outlined in the 2018 International Building Code (IBC). The 2018 IBC states structures shall be designed and constructed to resist the effects of earthquake motions in accordance with American Society of Civil Engineers (ASCE) 7-16. We used map-based values as recommended by the United States Geological Survey (USGS) to determine the seismic design spectrum in accordance with ASCE 7-16. Based on conditions observed in our explorations, our review of geologic maps and our experience in the area, we anticipate soils below our explorations and extending to depth are glacially consolidated and dense to very dense. For seismic design and analysis, we recommend using a response spectrum for Site Class C. We recommend the parameters provided in Table 1 below be used for design. TABLE 1. SEISMIC DESIGN CRITERIA 2018 IBC (ASCE 7-16) Seismic Design Parameters Spectral Response Acceleration at Short Periods (SS) 1.346g Spectral Response Acceleration at 1-Second Periods (S1) 0.462g Site Class C Design Peak Ground Acceleration (PGAM) 0.684g Design Spectral Response Acceleration at Short Periods (SDS) 1.077g Design Spectral Response Acceleration at 1-Second Periods (SD1) 0.462g August 24, 2020| Page 4 File No. 3625-004-00 4.2.2. Liquefaction Liquefaction refers to a condition where vibration or shaking of the ground, usually from earthquake forces, results in development of excess pore pressures in loose, saturated soils and subsequent loss of strength in the deposit of soil so affected. In general, soils that are susceptible to liquefaction include loose to medium dense sands to silty sands that are below the water table. The Liquefaction Susceptibility Map of King County, Washington (Palmer, et al. 2004) indicates the site soils have a “very low” liquefaction potential. Based on the soil and groundwater conditions observed in our explorations and our experience, we conclude that the risk for liquefaction at the site is low. 4.2.3. Lateral Spreading Potential Lateral spreading related to seismic activity typically involves lateral displacement of large, surficial blocks of non-liquefied soil when a layer of underlying soil loses strength during seismic shaking. Lateral spreading usually develops in areas where sloping ground or large grade changes (including retaining walls) are present. Based on our understanding of the liquefaction risk at the site and the proposed improvements, it is our opinion that the risk of lateral spreading is low. 4.2.4. Surface Rupture Potential According to the Washington State Department of Natural Resources Interactive Natural Hazards Map (accessed August 14, 2020), there are no mapped faults or other seismogenic features within about 1 mile of the site. Furthermore, the bedrock in the project area is covered by several hundred feet of glacial soils. Based on the distance to the nearest mapped fault or seismogenic feature and the geologic conditions, it is our opinion the risk for surface rupture at this site is low. 4.3. Site Development and Earthwork 4.3.1. General We anticipate site development and earthwork activities will include: clearing and stripping vegetated areas; site grading; establishing subgrades for driveways, parking areas and building foundations; and placing and compacting fill and backfill materials. The site is identified as being located within the Asarco Smelter Plume. An appropriate soil management plan will be required. There might also be additional costs and testing protocols associated with removing soil or stripped materials from the site. We expect the site grading and earthwork can be accomplished with conventional earthmoving equipment. However, glacial till can be encountered in a very dense condition and may take some effort during excavation. The earthwork contractor should be prepared to encounter dense soil conditions at the site. Larger excavators with toothed buckets and bulldozers with rippers could be used for more efficient excavation. The following sections provide specific recommendations for site development and earthwork. August 24, 2020| Page 5 File No. 3625-004-00 4.3.2. Clearing and Stripping We anticipate that clearing and stripping depths at the site will typically be on the order of about 9 to 12 inches to remove forest duff, vegetation and associated root network at the surface. However, it is likely that greater stripping depths will be required in areas of heavier vegetation or relatively lower lying areas. During stripping operations excessive disturbance of surficial soils can occur, especially if left exposed to wet conditions. Glacial till soils expected to be exposed after clearing and stripping have a relatively high fines content and can be easily disturbed during wet weather. Clearing and stripping at the site should be performed during dry weather and/or exposed soils should be promptly covered and protected to avoid excessive disturbance. Disturbed soils may require additional compaction or remediation during construction and grading. Cobbles and boulders can be present in glacial till soils in the project area. Although no boulders were observed, the contractor should be prepared to remove cobbles and boulders if encountered during grading or excavation. Boulders may be removed from the site or used in landscape areas. Voids caused by boulder removal should be backfilled with structural fill. 4.3.3. Erosion and Sedimentation Control Erosion and sedimentation rates and quantities can be influenced by construction methods, slope length and gradient, amount of soil exposed and/or disturbed, soil type, construction sequencing and weather. Implementing an Erosion and Sedimentation Control Plan will reduce impacts to the project where erosion- prone areas are present. The plan should be designed in accordance with applicable county and/or state standards. The plan should incorporate basic planning principles, including: ■ Scheduling grading and construction to reduce soil exposure; ■ Re-vegetating or mulching denuded areas; ■ Directing runoff away from exposed soils; ■ Reducing the length and steepness of slopes with exposed soils; ■ Decreasing runoff velocities; ■ Preparing drainage ways and outlets to handle concentrated or increased runoff; ■ Confining sediment to the project site; and ■ Inspecting and maintaining control measures frequently. Temporary erosion protection should be used and maintained in areas with exposed or disturbed soils to help reduce erosion and reduce transport of sediment to adjacent areas and receiving waters. Permanent erosion protection should be provided by paving, structure construction or landscape planting. Until permanent erosion protection is established and the site is stabilized, site monitoring may be required by qualified personnel to evaluate the effectiveness of the erosion control measures and to repair and/or modify them as appropriate. Provisions for modifications to the erosion control system based on monitoring observations should be included in the erosion and sedimentation control plan. Where sloped areas are present, some sloughing and raveling of exposed or disturbed soil on slopes should be expected. We recommend that disturbed soil be restored promptly so that surface runoff does not become channeled. August 24, 2020| Page 6 File No. 3625-004-00 4.3.4. Temporary Excavations and Cut Slopes Based on observations made during excavation of our test pits and our experience with other projects in similar soil conditions, we anticipate that shallow or even moderately deep (about 10-foot) excavations could maintain vertical slopes for extended periods of time with only minor caving. However, excavations deeper than 4 feet should be shored or laid back at a stable slope if workers are required to enter. Shoring and temporary slope inclinations must conform to the provisions of Title 296 Washington Administrative Code (WAC), Part N, “Excavation, Trenching and Shoring.” Regardless of the soil type encountered in the excavation shoring, trench boxes or sloped sidewalls will be required under Washington Industrial Safety and Health Act (WISHA). We recommend contract documents specify that the contractor is responsible for selecting excavation and dewatering methods, monitoring the excavations for safety and providing shoring, as required, to protect personnel and structures. In general, we recommend that for planning purposes all temporary cut slopes be inclined no steeper than about 1½H to 1V (horizontal to vertical) if workers are required to enter the excavation. This guideline assumes all surface loads are kept at a minimum distance of at least one-half the depth of the cut away from the top of the slope and that seepage is not present on the slope face. Flatter cut slopes will be necessary where seepage occurs or if surface surcharge loads are anticipated. Temporary covering with heavy plastic sheeting should be used to protect these slopes during periods of wet weather. 4.3.5. Permanent Cut and Fill Slopes We recommend permanent slopes be constructed at a maximum inclination of 2H to 1V to manage erosion. Where 2H to 1V permanent slopes are not feasible, protective facings and/or retaining structures should be considered. To achieve uniform compaction of fill slopes, we recommend fill slopes be overbuilt and subsequently cut back to expose well-compacted fill. Fill placement on existing slopes steeper than 5H to 1V should be benched into the slope face. The configuration of benches depends on the equipment being used and the inclination of the existing slope. Bench excavations should be level and extend into the slope face at least half the width of the compaction equipment used. Exposed areas should be re-vegetated as soon as practical to reduce surface erosion and sloughing. Temporary protection should be used until permanent protection is established. 4.3.6. Groundwater Handling Considerations Based on our understanding of the proposed site improvements and our explorations we do not anticipate that the regional groundwater table will be encountered during excavations at the site. Although not encountered in our explorations, areas of perched groundwater could be encountered at the site. The interface between more permeable and less permeable zones, such as the contact between weathered glacial till and undisturbed glacial till, are likely locations for accumulation of perched groundwater. Perched groundwater could also develop in site excavations as relatively permeable fill and backfill soils are placed over undisturbed glacial till. Groundwater handling needs will typically be lower during the summer and early fall months. We anticipate that shallow perched groundwater can be handled adequately with sumps, pumps, and/or diversion ditches, August 24, 2020| Page 7 File No. 3625-004-00 as necessary. Ultimately, we recommend that the contractor performing the work be made responsible for controlling and collecting groundwater encountered. 4.3.7. Surface Drainage Surface water from roof downspouts, driveways and landscape areas should be collected and controlled. Curbs or other appropriate measures such as sloping pavements, sidewalks and landscape areas should be used to direct surface flow away from buildings, erosion sensitive areas and from behind retaining structures. Roof and catchment drains should not be connected to wall or foundation drains. 4.3.8. Subsurface Drainage Based on our subsurface explorations, the site generally consists of low permeable, undisturbed glacial till soils at relatively shallow depths (on the order of 3 to 5 feet bgs). Excavations that extend into undisturbed glacial till, such as foundation excavations, will likely create a perched groundwater condition. Utility trenches that extend into undisturbed glacial till and are backfilled with structural fill could also create perched groundwater due to difference in permeability between trench backfill and undisturbed glacial till. To manage perched groundwater within site excavations, we recommend that subsurface drainage, including foundation drains, be considered where groundwater or high moisture would be detrimental to structures or other site improvements. Special drainage details could be required to clear groundwater accumulation in utility trenches and other excavations near structures. 4.3.9. Subgrade Preparation Subgrades that will support structures and roadways should be thoroughly compacted to a uniformly firm and unyielding condition on completion of stripping and before placing structural fill. We recommend that subgrades for structures and roadways be evaluated, as appropriate, to identify areas of yielding or soft soil. Probing with a steel probe rod or proof-rolling with a heavy piece of wheeled construction equipment are appropriate methods of evaluation. If soft or otherwise unsuitable subgrade areas are revealed during evaluation that cannot be compacted to a stable and uniformly firm condition, we recommend that: (1) the unsuitable soils be scarified (e.g., with a ripper or farmer’s disc), aerated and recompacted, if practical; or (2) the unsuitable soils be removed and replaced with compacted structural fill, as needed. 4.3.10. Subgrade Protection and Wet Weather Considerations Near-surface soils observed at the site contain a significant quantity of fines and will be susceptible to disturbance during periods of wet weather. The wet weather season generally begins in October and continues through May in western Washington; however, periods of wet weather can occur during any month of the year. It may be possible to conduct earthwork at the site during wet weather months provided appropriate measures are implemented to protect exposed soil. If earthwork is scheduled during the wet weather months, we offer the following recommendations: ■ Measures should be implemented to remove or eliminate the accumulation of surface water from work areas. The ground surface in and around the work area should be sloped so that surface water is directed away and graded so that areas of ponded water do not develop. Measures should be taken by the contractor to prevent surface water from collecting in excavations and trenches. August 24, 2020| Page 8 File No. 3625-004-00 ■ Earthwork activities should not take place during periods of heavy precipitation. ■ Slopes with exposed soils should be covered with plastic sheeting. ■ The contractor should take necessary measures to prevent on-site soils and other soils to be used as fill from becoming wet or unstable. These measures may include the use of plastic sheeting, sumps with pumps and grading. The site soils should not be left uncompacted and exposed to moisture. Sealing exposed soils by rolling with a smooth-drum roller prior to periods of precipitation will help reduce the extent to which these soils become wet or unstable. ■ Construction traffic should be restricted to specific areas of the site, preferably areas that are surfaced with working pad materials not susceptible to wet weather disturbance. ■ Construction activities should be scheduled so that the length of time that soils are left exposed to moisture is reduced to the extent practical. ■ Protective surfacing such as placing asphalt-treated base (ATB) or haul roads made of quarry spalls or a layer of free-draining material such as well-graded pit-run sand and gravel may be considered to limit disturbance to completed areas. Minimum quarry spall thicknesses should be on the order of 12 to 18 inches. Typically, minimum gravel thicknesses on the order of 24 inches are necessary to provide adequate subgrade protection. 4.4. Fill Materials 4.4.1. On-Site Soil Based on our subsurface explorations and experience, it is our opinion that existing site soils, excluding the forest duff, may be considered for use as structural fill, provided the soils can be adequately moisture conditioned, placed and compacted as recommended and do not contain organics or other deleterious material. The glacial till soils present at the site contain a significant quantity of fines and are extremely moisture sensitive and will be very difficult or impossible to properly compact when wet. Based on our laboratory testing, glacial till samples collected during the explorations were typically at or slightly above optimum moisture content for compaction. Once disturbed, these soils can quickly absorb moisture and become unstable. In addition, fill or weathered soils located just above undisturbed glacial till in the perched groundwater zone are more likely to have moisture contents above optimum. If the on-site soils will be used as fill we recommend that: (1) earthwork be scheduled for spring or summer months where extended periods of dry weather are more likely; (2) earthwork is staged such that material is placed and compacted shortly after it is excavated, even covered stockpiles should be avoided if practical, as loose soil more readily absorbs moisture from precipitation; and (3) cut and fill quantities should assume that some material will become wet, unworkable, and must be removed from the site. Alternatively, a non-structural area could be designated on site for disposal of wet and unworkable material. If earthwork occurs during the wet season, or if the soils are persistently wet and cannot be dried back to near optimum due to prevailing wet weather conditions, we recommend the use of imported structural fill or select granular fill as described below. August 24, 2020| Page 9 File No. 3625-004-00 4.4.2. Imported Structural Fill Imported structural fill should consist of well-graded sand and gravel or crushed rock with a maximum particle size of 6 inches and less than 5 percent fines by weight based on the minus ¾-inch fraction. Organic matter, debris or other deleterious material should not be present. In our opinion, material with gradation characteristics similar to Washington State Department of Transportation (WSDOT) Specifications 9-03.9 (Aggregates for Ballast and Crushed Surfacing), 9-03.14(1) (Gravel Borrow), or 9-03.14(2) (Select Borrow) is suitable for use as imported structural fill, with the exception that the fines content is less than 5 percent (based on the minus ¾-inch fraction) and the maximum particle size is 6 inches. If prolonged dry weather prevails during the earthwork phase of construction, materials with a somewhat higher fines content may be acceptable. 4.4.3. Pipe Bedding Trench backfill for the bedding and pipe zone should consist of well-graded granular material similar to “Gravel Backfill for Pipe Zone Bedding” described in Section 9-03.12(3) of the WSDOT Standard Specifications. The material must be free of roots, debris, organic matter and other deleterious material. Other materials may be appropriate depending on manufacturer specifications and/or local jurisdiction requirements. 4.4.4. Trench Backfill We recommend that trench backfill within structural areas such as roadways and within building footprints consist of Imported Structural Fill, as described above. In non-structural areas the excavated glacial till can be reused as backfill provided it is free of debris, organic material, and rock fragments larger than 6 inches. 4.5. Fill Placement and Compaction 4.5.1. General To obtain proper compaction, fill and backfill material should be placed in uniform horizontal lifts and compacted near the optimum moisture content. Lift thickness and compaction procedures will depend on the moisture content and gradation characteristics of the soil and the type of compaction equipment used. The maximum allowable moisture content varies with the soil gradation and should be evaluated during construction. Generally, 8- to 12-inch loose lifts are appropriate for steel-drum vibratory roller compaction equipment. Compaction should be achieved by mechanical means. During fill and backfill placement, sufficient testing of in-place density should be conducted to check that adequate compaction is being achieved. 4.5.2. Area Fills and Pavement Bases Fill placed to raise site grades and materials under pavements and structural areas should be placed on subgrades prepared as previously recommended. All fill material placed below structures and footings and extending beyond the edge of the structures a distance equal to the depth of the fill should be compacted to at least 95 percent of the theoretical maximum dry density (MDD) per ASTM International (ASTM) D 1557. Fill material placed shallower than 2 feet below pavement sections should be compacted to at least 95 percent of the MDD. Fill placed deeper than 2 feet below pavement sections should be compacted to at least 92 percent of the MDD. Fill material placed in landscaping areas should be compacted to a firm August 24, 2020| Page 10 File No. 3625-004-00 condition that will support construction equipment, as necessary, typically around 85 to 90 percent of the MDD. 4.5.3. Backfill Behind Walls Backfill behind retaining walls or below-grade structure walls should be compacted to between 90 and 92 percent of the MDD. Over compaction of fill placed directly behind walls should be avoided. We recommend use of hand-operated compaction equipment and maximum 6-inch loose lift thickness when compacting fill within about 5 feet behind walls. 4.5.4. Trench Backfill For utility excavations, we recommend that the initial lift of fill over the pipe be thick enough to reduce the potential for damage during compaction, but generally should not be greater than about 18 inches above the pipe. In addition, rock fragments greater than about 1 inch in maximum dimension should be excluded from this lift. Trench backfill material placed below structures and footings should be compacted to at least 95 percent of the MDD. In paved areas, trench backfill should be uniformly compacted in horizontal lifts to at least 95 percent of the MDD in the upper 2 feet below subgrade. Fill placed below a depth of 2 feet from subgrade in paved areas must be compacted to at least 92 percent of the MDD. In non-structural areas, trench backfill should be compacted to a firm condition that will support construction equipment as necessary. 4.6. Foundation Support 4.6.1. General Based on our understanding of the proposed development it is our opinion the proposed structures can be adequately supported on shallow foundations, reinforced mat foundations, and slabs-on-grade. Exterior footings should be established at least 18 inches below the lowest adjacent grade. Interior footings can be founded a minimum of 12 inches below the bottom of the floor slab. Isolated column and continuous wall footings should have minimum widths of 24 and 18 inches, respectively. Based on the groundwater conditions in our explorations and our understanding of the proposed footing elevations (bottom of footings established within a few feet of existing site grade), it is our opinion footing drains are not necessary to maintain bearing support as provided in this report. However, it is possible and even likely that perched groundwater zones will develop within fill placed over native glacial till soils at the site. Footing drains or perimeter drains should be considered to reduce the potential for perched groundwater accumulation in the fill around building foundations. The sections below provide our recommendations for foundation bearing surface preparation and foundation design parameters. 4.6.2. Foundation Bearing Surface Preparation Foundations should bear on existing glacial till soils or on structural fill extending to these soils. If existing fill material is present at the base of foundation excavations, we recommend it be overexcavated and replaced with structural fill. We recommend that glacial till soils exposed at the base of foundation excavations be proof compacted to a firm and unyielding condition. Loose or disturbed materials present August 24, 2020| Page 11 File No. 3625-004-00 at the base of foundation excavations should be removed or compacted prior to placement of formwork and reinforcing steel. If structural fill is placed below foundations as either replacement of overexcavated soils or to establish a bearing pad, we recommend the structural fill extend laterally beyond the foundation perimeter a distance equal to the depth of fill (measured from the base of the footing where necessary), or 3 feet, whichever is less. Foundation bearing surfaces should not be exposed to standing water. If water is present in the excavation, it must be removed before placing formwork and reinforcing steel. A 6-inch-thick layer of crushed rock or a 3- to 4-inch layer of lean-mix concrete, could be used to protect the base of excavations and limit disturbance to bearing surfaces during construction. Prepared foundation bearing surfaces should be evaluated by a member of our firm prior to placement of formwork or reinforcing steel to verify that bearing surface has been prepared in accordance with our recommendations or to provide recommendations for remediating unsuitable bearing soils. 4.6.3. Allowable Soil Bearing Pressure Shallow foundations bearing on subgrades prepared as recommended may be designed using an allowable soil bearing pressure of 3,500 pounds per square foot (psf) when bearing on proof-compacted glacial till (weathered or undisturbed) or structural fill extending to proof compacted glacial till. This bearing pressure applies to the total of dead and long-term live loads and may be increased by one-third when considering total loads, including earthquake or wind loads. These are net bearing pressures. The weight of the footing and overlying backfill can be ignored in calculating footing sizes. Significantly higher bearing pressures can be achieved for foundations bearing directly on undisturbed glacial till, but these higher bearing pressures must be considered on a case-by-case basis and might require special or more detailed bearing surface preparation recommendation to limit settlement. If higher bearing pressures would be beneficial to the design, please contact us for further recommendations. 4.6.4. Foundation Settlement Disturbed soil must be removed from the base of footing excavations and the bearing surface should be prepared as recommended. Provided these measures are taken, we estimate the total static settlement of shallow foundations will be on the order of 1 inch or less for the bearing pressures presented above. Differential settlements could be on the order of ¼ to ½ inch between similarly loaded foundations or over a distance of 50 feet of continuous footings. The settlements should occur rapidly, essentially as loads are applied. Settlements could be greater than estimated if disturbed or saturated soil conditions are present below footings. 4.6.5. Lateral Resistance The ability of the soil to resist lateral loads is a function of the base friction, which develops on the base of foundations and slabs, and the passive resistance, which develops on the face of below-grade elements of the structure as these elements move into the soil. For cast-in-place foundations supported in accordance with the recommendations presented above, the allowable frictional resistance on the base of the foundation may be computed using a coefficient of friction of 0.40 applied to the vertical dead-load forces. If precast foundations are included as part of project plans, we can provide specific recommendations for August 24, 2020| Page 12 File No. 3625-004-00 base friction resistance for precast foundations. The allowable passive resistance on the face of the foundation or other embedded foundation elements may be computed using an equivalent fluid density of 290 pounds per cubic foot (pcf). These values include a factor of safety of about 1.5. The passive earth pressure and friction components may be combined provided that the passive component does not exceed two-thirds of the total. The top foot of soil should be neglected when calculating passive lateral earth pressure unless the area adjacent to the foundation is covered with pavement or a slab-on-grade. 4.7. Slab-on-Grade Floors Slab-on-grade floors should bear on glacial till soils or on structural fill extending to these soils and should be prepared as recommended in the “Subgrade Preparation” section of this report. We recommend the slab subgrades be observed by a member of our firm during construction. Disturbed areas should be compacted, if possible, or removed and replaced with compacted structural fill. In all cases, the exposed soil should be compacted to a firm and unyielding condition. We recommend the slab-on-grade floors be underlain by a minimum 6-inch-thick capillary break layer consisting of clean sand and gravel, crushed rock, or washed rock. The capillary break material should contain less than 3 percent fine material based on the percent passing the ¾-inch sieve size. Provided that loose soil is removed, and the subgrade is prepared as recommended, we recommend slabs-on-grade be designed using a modulus of subgrade reaction of 200 pounds per cubic inch (pci). We estimate that settlement for slabs-on-grade constructed as recommended will be less than ¾ inch for a floor load of up to 300 psf. Based on our understanding of subsurface conditions at the site, it is our opinion that an underslab drain system is not necessary provided that footing or perimeter drains are provided. If dry slabs are required (e.g., where adhesives are used to anchor carpet or tile to slab), a waterproof liner may be placed as a vapor barrier below the slab. 4.8. Retaining Walls and Below-Grade Structures 4.8.1. Design Parameters We recommend the following lateral earth pressures be used for design of conventional retaining walls and below-grade structures. Our design pressures assume that the ground surface around the retaining structures will be level or near level. If drained design parameters are used, drainage systems must be included in the design in accordance with the recommendations presented in the “Drainage” section below. The active soil pressure condition assumes the wall is free to move laterally 0.001 H, where H is the wall height. The at-rest condition is applicable where walls are restrained from movement. The above recommended lateral soil pressures do not include the effects of sloping backfill surfaces or surcharge loads, except as described. Overcompaction of fill placed directly behind retaining walls or below-grade structures must be avoided to limit lateral pressures placed on the wall. We recommend use of hand- operated compaction equipment and maximum 6-inch loose lift thickness when compacting fill within about 5 feet of retaining walls and below-grade structures. ■ Active soil pressure may be estimated using an equivalent fluid density of 35 pcf for the drained condition. August 24, 2020| Page 13 File No. 3625-004-00 ■ Active total soil and hydrostatic pressure may be estimated using an equivalent fluid density of 80 pcf for the undrained condition; this value includes hydrostatic pressures. ■ At-rest soil pressure may be estimated using an equivalent fluid density of 55 pcf for the drained condition. ■ At-rest total soil and hydrostatic pressure may be estimated using an equivalent fluid density of 90 pcf for the undrained condition; this value includes hydrostatic pressures. ■ For seismic considerations, a uniform lateral pressure of 16*H psf (where H is the height of the retaining structure or the depth of a structure below ground surface) should be added to the lateral earth pressure. ■ A traffic surcharge can be estimated should be included if vehicles are allowed to operate within a zone equal to the height of the retaining walls. This can be estimated with a uniform horizontal load of 70 psf, or by assuming an additional 2 feet of fill. This is based on a uniform surface load of 250 psf, other surface loads should be considered on a case-by-case basis. Retaining wall foundations may be designed using the recommendations presented above for building foundation design. We estimate settlement of retaining structures will be similar to the values previously presented for structure foundations. 4.8.2. Drainage If retaining walls or below-grade structures are designed using drained parameters, a drainage system behind the structure must be included to collect water and prevent the buildup of hydrostatic pressure against the structure. We recommend the drainage system include a zone of free-draining backfill against the back of the wall. This drainage layer can consist of either a 24-inch thick layer of a graded drainage material such as WSDOT Specification 9-03.12(2) (Gravel Backfill for Walls) or a 12-inch thick layer of pea- gravel with a non-woven geotextile designed for soil separation placed between the pea-gravel and backfill. Drain boards or other prefabricated drainage systems can be used provided they can be adequately connected to an appropriate collection and discharge pipe system. A perforated, rigid, smooth-walled drain pipe with a minimum diameter of 4 inches should be placed along the base of the structure within the free-draining backfill and extend for the entire wall length. The drain pipe should be metal or rigid PVC pipe and be sloped to drain by gravity. Discharge should be routed to appropriate discharge areas and to reduce erosion potential. Cleanouts should be provided to allow routine maintenance. Roof downspouts or other types of drainage systems must not be connected to retaining wall drain systems. 4.9. Stormwater Infiltration Feasibility We anticipate that stormwater facilities on site, if planned, will be designed in accordance with the 2016 King County Surface Water Design Manual (SWDM), which has been adopted by the City of Federal Way. According to the SWDM, measured infiltration rates shall be determined using a Pilot Infiltration Test (PIT) or single-ring percolation test. The manual does not allow the use of soil grain-size analysis to determine design infiltration rates and grain-size analysis is very inaccurate in glacially consolidated soils like those observed on site. Additionally, detailed infiltration analyses including performance testing and groundwater mounding analysis are noted in the SWDM and may also be required for final design. August 24, 2020| Page 14 File No. 3625-004-00 The site is generally underlain by undisturbed glacial till at relatively shallow depths (on the order of 3 to 5 feet bgs). In our experience with similar soil and density conditions (undisturbed glacial till), PITs typically measure very slow infiltration rates, on the order of 0.05 to 0.25 inches per hour without correction factors and in some cases, no infiltration can be measured. If infiltration of on-site stormwater is pursued, alternative testing methods such as a PIT, will likely be required to establish the final design infiltration rates. However, as discussed above we anticipate that design infiltration rates will be very low. 4.10. Pavement Recommendations 4.10.1. General We anticipate that pavements for the proposed improvements will include new parking areas and driveways. Our recommended pavement sections provided below are based on our explorations and experience in the area. We understand asphalt concrete (AC) may be used for the proposed improvements. The recommended pavement sections below may not be adequate for heavy construction traffic loads such as those imposed by concrete transit mixers, dump trucks or cranes. Additional pavement thickness may be necessary to prevent pavement damage during construction. An asphalt-treated base (ATB) section can also be used during construction to protect partially constructed pavement sections and pavement subgrades. The recommended sections assume final improvements surrounding the pavement areas will be designed and constructed such that stormwater or excess irrigation water from landscape areas does not accumulate below the pavement section or pond on pavement surfaces. If pavements in parking areas slope inward (toward the center of the parking area) full depth curbs or other measures should be used to prevent water from entering and ponding on the subgrade and within the base section. 4.10.2. Construction Considerations Existing pavements, hardscaping or other structural elements should be removed prior to placement of new pavement sections. Pavement subgrade should be prepared to a uniformly firm, dense and unyielding condition as previously described. Crushed surfacing base course and subbase should be moisture conditioned to near optimum moisture content and compacted to at least 95 percent of the MDD (ASTM D 1577). Crushed surfacing base course (CSBC) should conform to applicable sections of 4-04 and 9-03.9(3) of the WSDOT Standard Specifications. Subbase should conform to applicable sections of 4-02 “Gravel Base” and 9-03.10 “Aggregate Gravel for Base” of the WSDOT Standard Specifications. Hot mix asphalt should conform to applicable sections of 5-04, 9-02 and 9-03 of the WSDOT Standard Specifications. Portland cement concrete (PCC) mix design should conform with Section 5-05.3(1) of the WSDOT Standard Specifications. Aggregates for PCC should conform to applicable sections of 9-03.1 of the WSDOT Standard Specifications. Some areas of pavement may exhibit settlement and subsequent cracking over time. Cracks in the pavement will allow water to infiltrate to the underlying base course, which could increase the amount of pavement damage caused by traffic loads. To prolong the effective life of the pavement, cracks should be sealed as soon as possible. August 24, 2020| Page 15 File No. 3625-004-00 4.10.3. Asphalt Concrete Pavement Design 4.10.3.1. Standard-Duty ACP – Automobile Driveways and Parking Areas ■ 2 inches of hot mix asphalt, class ½-inch, PG 58-22 ■ 4 inches of CSBC ■ 6 inches of subbase consisting of select granular fill, previously described, to provide a uniform grading surface, to provide pavement support, to maintain drainage, and to provide separation from fine- grained subgrade soil (this layer can be omitted for select granular fill subgrades or glacial till subgrades if dry weather persists through construction and final paving of the section) ■ Subgrade consisting of proof-compacted firm and unyielding conditions or structural fill prepared in accordance with the “Subgrade Preparation" and “Area Fills and Pavement Bases" sections of this report. 4.10.3.2. Areas Subject to Occasional Heavy Truck Traffic (Garbage or Delivery Truck Routes) ■ 3 inches of hot mix asphalt, class ½ inch, PG 58-22 ■ 6 inches of CSBC ■ 6 inches of subbase consisting of select granular fill, previously described, to provide a uniform grading surface, to provide pavement support, to maintain drainage, and to provide separation from fine- grained subgrade soil (this layer can be omitted for select granular fill subgrades or glacial till subgrades if dry weather persists through construction and final paving of the section) ■ Subgrade consisting of proof-compacted firm and unyielding conditions or structural fill prepared in accordance with the “Subgrade Preparation" and “Area Fills and Pavement Bases" sections of this report 4.10.3.3. Temporary Construction Surfacing A temporary surfacing of ATB can be used to protect partially constructed pavement sections and pavement subgrades during construction. This can provide a relatively clean working surface, prevent construction traffic from damaging final paving surfaces and reduce subgrade repairs required for final paving. A 2-inch- thick section of ATB can be substituted for the upper 2 inches of CSBC in either the light-duty or heavy-duty pavement sections. Prior to placement of the final pavement surface sections, we recommend that any areas of ATB pavement failure be removed and the subgrade repaired. If ATB is used and is serviceable when final pavements are constructed, the design asphalt concrete pavement thickness can be placed directly over the ATB. Cement treatment of subgrades is sometimes used to create construction surfacing or to control soil moisture during wet weather construction. In our opinion cement treatment would not likely be cost effective for creating a construction surface due to the high fines content in the soil. Cement treatment or cement stabilization would likely only be cost effective as an emergency or contingency action for reducing soil moisture in the subgrade so that a traditional asphalt pavement could be constructed. It would take a significant amount of cement (likely on the order of 8 to 12 percent by weight) to create a firm and stable working surface that could handle wet weather construction. August 24, 2020| Page 16 File No. 3625-004-00 5.0 LIMITATIONS We have prepared this report for Shelter Resources, Inc. for the Redondo Heights Apartments project located in Federal Way, Washington. Shelter Resources, Inc. may distribute copies of this report to owner’s authorized agents and regulatory agencies as may be required for the Project. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices for geotechnical engineering in this area at the time this report was prepared. The conclusions, recommendations, and opinions presented in this report are based on our professional knowledge, judgment and experience. No warranty, express or implied, applies to the services or this report. Please refer to Appendix B titled “Report Limitations and Guidelines for Use” for additional information pertaining to use of this report. µ SITE Vicinity Map Figure 1 Redondo Heights ApartmentsFederal Way, Washington 2,000 2,0000 Feet Data Source: Mapbox Open Street Map, 2016 Notes:1. The locations of all features shown are approximate.2. This drawing is for information purposes. It is intended to assist in showing features discussed in an attached document. GeoEngineers, Inc. cannot guarantee the accuracy and content of electronic files. The master file is stored by GeoEngineers, Inc. and will serve as the official record of this communication. Projection: NAD 1983 HARN StatePlane Washington South FIPS 4602 Feet P:\3\3625004\GIS\MXD\362500400_F01_VicinityMap.mxd Date Exported: 08/14/20 by ccabrera X X X XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXOH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SDW W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W XXX22.5'15'15'10'10'30'XXXXP P P P P P P P P P P P S S SS S XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX X X X X X X X X X X XXXXXXXXXX X P P PPBPBPBPBPBPBPBPBP T T T TLTV TV TV CB CBCB CB S S Y Y Y Y Y Y YXX X XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXS S S S S SS Y T T T T T TV TV TV TV TV TV P P P P P P PBPBPBS 320321322321 322 323324325326327328329330331328329330331332333328329330331 31932032132232332432532632731531631731831531631 7 31831932032 1 3 2 2 323323324325326327328329330331320 321 322 323 324 325 326 327 328 329 319320 321 322 323 324325326327 320321322323324 31231331431531631731 8319 31831932033 4 330 3143 1 5316317318319320321322323324 311312313TP-10 TP-11 TP-12 TP-9 TP-7 TP-8 TP-6 TP-4 TP-3 TP-1 TP-2 TP-5Pacific Highway S276th Street Figure 2 Redondo Heights Apartments Federal Way, Washington Site Plan W E N S \\geoengineers.com\WAN\Projects\3\3625004\CAD\00\Geotech\362500400_F02_Site Plan.dwg TAB:F02 Date Exported: 08/18/20 - 14:21 by tbyrdNotes: 1.The locations of all features shown are approximate. 2.This drawing is for information purposes. It is intended to assist in showing features discussed in an attached document. GeoEngineers, Inc. cannot guarantee the accuracy and content of electronic files. The master file is stored by GeoEngineers, Inc. and will serve as the official record of this communication. Data Source: Background data from kpff dated 07/22/20. Projection: Washington State Plane, North Zone, NAD83, US Foot Feet 0 Legend 100 100 TP-1 Site Boundary Test Pit by GeoEngineers, Inc., 2020 APPENDIX A Subsurface Explorations and Laboratory Testing August 24, 2020| Page A-1 File No. 3625-004-00 APPENDIX A SUBSURFACE EXPLORATIONS AND LABORATORY TESTING Subsurface Explorations Subsurface conditions for the proposed Redondo Heights Apartments project were explored by excavating 12 test pits between August 6, 2020 at the approximate locations shown on Figure 2. The test pits were excavated to depths between about 8 and 10½ feet below ground surface (bgs) using a backhoe and operator provided by SRI-Rochlin Construction Services. After each test pit was completed, the excavation was backfilled using the generated material and compacted using the bucket of the excavator. During the exploration program our field representative obtained samples, classified the soils encountered and maintained a detailed log of each exploration. The relative densities noted on the test pit logs are based on the difficulty of excavation and our experience and judgment. The samples were collected and retained in sealed plastic bags and then transported back to our office. The soils were classified visually in general accordance with the system described in Figure A-1, which includes a key to the exploration logs. Summary logs of the explorations are included as Figures A-2 through A-13. The locations of the test pits were determined using an electronic tablet with global positioning system (GPS) software. The locations of the explorations should be considered approximate. Elevations were estimated from supplemental survey information provided by SRI-Rochlin Construction Services. Laboratory Testing Soil samples obtained from the borings were transported to GeoEngineers laboratory. Representative soil samples were selected for laboratory tests to evaluate the pertinent geotechnical engineering characteristics of the site soils and to confirm our field classification. Our testing program consisted of the following: ■ Four grain-size distribution analyses (sieve analyses [SA]) ■ Four percent fines determinations (%F) ■ Seven moisture content determinations (MC) Tests were performed in general accordance with test methods of ASTM International (ASTM) or other applicable procedures. The following sections provide a general description of the tests performed. Sieve Analysis (SA) Grain-size distribution analyses were completed on selected samples in general accordance with ASTM Test Method D 6913. This test method covers the quantitative determination of the distribution of particle sizes in soils. Typically, the distribution of particle sizes larger than 75 micrometers (μm) is determined by sieving. The results of the tests were used to verify field soil classifications and determine pertinent engineering characteristics. Figure A-14 presents the results of our sieve analyses. August 24, 2020| Page A-2 File No. 3625-004-00 Percent Fines (%F) Selected samples were “washed” through the U.S. No. 200 sieve to estimate the relative percentages of coarse- and fine-grained particles in the soil. The percent passing value represents the percentage by weight of the sample finer than the U.S. No. 200 sieve (75 m). Tests were conducted in general accordance with ASTM D 1140. Test results are used to aid in soil classification and correlation with other pertinent engineering soil properties and are presented on the exploration logs at the respective sample depths. Moisture Content (MC) The moisture content of selected samples was determined in general accordance with ASTM Test Method D 2216. The test results are used to aid in soil classification and correlation with other pertinent engineering soil properties. The results are presented on the test pit logs at the depth tested. Measured groundwater level in exploration, well, or piezometer Measured free product in well or piezometer Distinct contact between soil strata Approximate contact between soil strata Contact between geologic units SYMBOLS TYPICAL DESCRIPTIONS GW GP SW SP SM FINE GRAINED SOILS SILTS AND CLAYS NOTE: Multiple symbols are used to indicate borderline or dual soil classifications MORE THAN 50% RETAINED ON NO. 200 SIEVE MORE THAN 50% PASSING NO. 200 SIEVE GRAVEL AND GRAVELLY SOILS SC LIQUID LIMIT LESS THAN 50 (APPRECIABLE AMOUNT OF FINES) (APPRECIABLE AMOUNT OF FINES) COARSE GRAINED SOILS MAJOR DIVISIONS GRAPH LETTER GM GC ML CL OL SILTS AND CLAYS SANDS WITH FINES SAND AND SANDY SOILS MH CH OH PT (LITTLE OR NO FINES) CLEAN SANDS GRAVELS WITH FINES CLEAN GRAVELS (LITTLE OR NO FINES) WELL-GRADED GRAVELS, GRAVEL -SAND MIXTURES CLAYEY GRAVELS, GRAVEL - SAND -CLAY MIXTURES WELL-GRADED SANDS, GRAVELLYSANDS POORLY-GRADED SANDS, GRAVELLYSAND SILTY SANDS, SAND - SILT MIXTURES CLAYEY SANDS, SAND - CLAYMIXTURES INORGANIC SILTS, ROCK FLOUR,CLAYEY SILTS WITH SLIGHTPLASTICITY INORGANIC CLAYS OF LOW TOMEDIUM PLASTICITY, GRAVELLYCLAYS, SANDY CLAYS, SILTY CLAYS,LEAN CLAYS ORGANIC SILTS AND ORGANIC SILTYCLAYS OF LOW PLASTICITY INORGANIC SILTS, MICACEOUS ORDIATOMACEOUS SILTY SOILS INORGANIC CLAYS OF HIGHPLASTICITY ORGANIC CLAYS AND SILTS OFMEDIUM TO HIGH PLASTICITY PEAT, HUMUS, SWAMP SOILS WITHHIGH ORGANIC CONTENTSHIGHLY ORGANIC SOILS SOIL CLASSIFICATION CHART MORE THAN 50% OF COARSE FRACTION RETAINED ON NO. 4 SIEVE MORE THAN 50% OF COARSE FRACTION PASSING ON NO. 4 SIEVE SILTY GRAVELS, GRAVEL - SAND -SILT MIXTURES POORLY-GRADED GRAVELS,GRAVEL - SAND MIXTURES LIQUID LIMIT GREATER THAN 50 Continuous Coring Bulk or grab Direct-Push Piston Shelby tube Standard Penetration Test (SPT) 2.4-inch I.D. split barrel Contact between soil of the same geologic unit Material Description Contact Graphic Log Contact NOTE: The reader must refer to the discussion in the report text and the logs of explorations for a proper understanding of subsurface conditions. Descriptions on the logs apply only at the specific exploration locations and at the time the explorations were made; they are not warranted to be representative of subsurface conditions at other locations or times. Groundwater Contact Blowcount is recorded for driven samplers as the number of blows required to advance sampler 12 inches (or distance noted). See exploration log for hammer weight and drop. "P" indicates sampler pushed using the weight of the drill rig. "WOH" indicates sampler pushed using the weight of the hammer. Key to Exploration Logs Figure A-1 Sampler Symbol Descriptions ADDITIONAL MATERIAL SYMBOLS NS SS MS HS No Visible Sheen Slight Sheen Moderate Sheen Heavy Sheen Sheen Classification SYMBOLS Asphalt Concrete Cement Concrete Crushed Rock/ Quarry Spalls Topsoil GRAPH LETTER AC CC SOD Sod/Forest Duff CR DESCRIPTIONS TYPICAL TS Percent fines Percent gravel Atterberg limits Chemical analysis Laboratory compaction test Consolidation test Dry density Direct shear Hydrometer analysis Moisture content Moisture content and dry density Mohs hardness scale Organic content Permeability or hydraulic conductivity Plasticity index Point lead test Pocket penetrometer Sieve analysis Triaxial compression Unconfined compression Vane shear %F %G AL CA CP CS DD DS HA MC MD Mohs OC PM PI PL PP SA TX UC VS Laboratory / Field Tests Rev 07/2019 12 inches forest duff Tan with iron-oxide staining silty fine to medium sand with gravel and occasional organic matter (roots) (dense, moist) (weathered glacial till) Grades to without roots Gray with iron-oxide staining silty fine to medium sand with gravel (very dense, moist) (glacial till) Grades to without iron-oxide staining DUFF SM SM 1%F 2MC 3 7 8 46 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Locational Survey.Date:8/21/20 Path:P:\3\3625004\GINT\362500400.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number: Project Location: Project: Federal Way, Washington 3625-004-00 Log of Test Pit TP-1 Figure A-2 SRI-Redondo Heights ApartmentsElevation (feet)331330329328327326325324323Depth (feet)1 2 3 4 5 6 7 8 9 Testing SampleGraphic LogSAMPLE MATERIAL DESCRIPTION GroupClassificationSample NameTestingMoistureContent (%)REMARKS FinesContent (%)Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)8/6/2020 9 331.3 NGVD29 1274713 132113 WA State Plane North NAD83 (feet) CJL Checked By CRN Groundwater not observed Caving not observedEquipment Komatsu PC128 Logged By Excavator SRI-Rochlin 12 inches forest duff Brown silty fine to medium sand with gravel and occasional organic matter (roots) (loose, moist) (weathered glacial till) Brown-gray with iron-oxide staining silty fine to medium sand with gravel and occasional organic matter (roots) (medium dense, moist) Gray silty fine to medium sand with gravel (very dense, moist) (glacial till) DUFF SM SM SM 1MC 2 10 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Locational Survey.Date:8/21/20 Path:P:\3\3625004\GINT\362500400.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number: Project Location: Project: Federal Way, Washington 3625-004-00 Log of Test Pit TP-2 Figure A-3 SRI-Redondo Heights ApartmentsElevation (feet)322321320319318317316315314313Depth (feet)1 2 3 4 5 6 7 8 9 Testing SampleGraphic LogSAMPLE MATERIAL DESCRIPTION GroupClassificationSample NameTestingMoistureContent (%)REMARKS FinesContent (%)Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)8/6/2020 9.5 322.3 NGVD29 1274820 132111 WA State Plane North NAD83 (feet) CJL Checked By CRN Groundwater not observed Caving not observedEquipment Komatsu PC128 Logged By Excavator SRI-Rochlin 12 inches forest duff Brown-gray silty fine to medium sand with occasional gravel and organic matter (roots) (medium dense, moist) (weathered glacial till) Gray with occasional iron-oxide staining silty fine to medium sand with gravel (very dense, moist) (glacial till) Grades to without iron-oxide staining DUFF SM SM 1 %F 2MC 9 7 33 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Locational Survey.Date:8/21/20 Path:P:\3\3625004\GINT\362500400.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number: Project Location: Project: Federal Way, Washington 3625-004-00 Log of Test Pit TP-3 Figure A-4 SRI-Redondo Heights ApartmentsElevation (feet)330329328327326325324323Depth (feet)1 2 3 4 5 6 7 8 Testing SampleGraphic LogSAMPLE MATERIAL DESCRIPTION GroupClassificationSample NameTestingMoistureContent (%)REMARKS FinesContent (%)Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)8/6/2020 8 330.3 NGVD29 1274647 132222 WA State Plane North NAD83 (feet) CJL Checked By CRN Groundwater not observed Caving not observedEquipment Komatsu PC128 Logged By Excavator SRI-Rochlin 9 inches forest duff Brown-gray silty fine to medium sand with occasional gravel and organic matter (roots) (loose, moist) (weathered glacial till) Grades to medium dense Gray silty fine to medium sand with gravel (very dense, moist) (glacial till) DUFF SM SM 1%F 2 7 ¼- to 8-inch diameter roots in upper approximately 2feet32 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Locational Survey.Date:8/21/20 Path:P:\3\3625004\GINT\362500400.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number: Project Location: Project: Federal Way, Washington 3625-004-00 Log of Test Pit TP-4 Figure A-5 SRI-Redondo Heights ApartmentsElevation (feet)329328327326325324323322321Depth (feet)1 2 3 4 5 6 7 8 Testing SampleGraphic LogSAMPLE MATERIAL DESCRIPTION GroupClassificationSample NameTestingMoistureContent (%)REMARKS FinesContent (%)Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)8/6/2020 8.5 329.3 NGVD29 1274672 132341 WA State Plane North NAD83 (feet) CJL Checked By CRN Groundwater not observed Caving not observedEquipment Komatsu PC128 Logged By Excavator SRI-Rochlin 12 inches forest duff Brown-gray silty fine to medium sand with gravel and occasional organic matter (roots) (loose, moist) (weathered glacial till) Grades to trace roots, dense Gray with iron-oxide staining silty fine to medium sand with gravel (very dense, moist) (glacial till) Grades to without iron-oxide staining DUFF SM SM 1 MC 2 12 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Locational Survey.Date:8/21/20 Path:P:\3\3625004\GINT\362500400.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number: Project Location: Project: Federal Way, Washington 3625-004-00 Log of Test Pit TP-5 Figure A-6 SRI-Redondo Heights ApartmentsElevation (feet)324323322321320319318317316Depth (feet)1 2 3 4 5 6 7 8 Testing SampleGraphic LogSAMPLE MATERIAL DESCRIPTION GroupClassificationSample NameTestingMoistureContent (%)REMARKS FinesContent (%)Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)8/6/2020 8.5 324.3 NGVD29 1274785 132320 WA State Plane North NAD83 (feet) CJL Checked By CRN Groundwater not observed Caving not observedEquipment Komatsu PC128 Logged By Excavator SRI-Rochlin 12 inches forest duff Brown silty fine to medium sand with gravel and occasional organic matter (roots) (loose, moist) (weathered glacial till) Grades to brown-gray with iron-oxide staining, medium dense Grades to dense Gray silty fine to medium sand with gravel (very dense, moist) (glacial till) Gray silty fine to coarse gravel with sand (very dense, moist) DUFF SM SM GM 1MC 2SA 6 6 Left hole open for approximately 5 hours; nogroundwater seepage observed.30 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Locational Survey.Date:8/21/20 Path:P:\3\3625004\GINT\362500400.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number: Project Location: Project: Federal Way, Washington 3625-004-00 Log of Test Pit TP-6 Figure A-7 SRI-Redondo Heights ApartmentsElevation (feet)324323322321320319318317316315Depth (feet)1 2 3 4 5 6 7 8 9 10 Testing SampleGraphic LogSAMPLE MATERIAL DESCRIPTION GroupClassificationSample NameTestingMoistureContent (%)REMARKS FinesContent (%)Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)8/6/2020 10 324.3 NGVD29 1274884 132369 WA State Plane North NAD83 (feet) CJL Checked By CRN Groundwater not observed Caving not observedEquipment Komatsu PC128 Logged By Excavator SRI-Rochlin 12 inches forest duff Brown-gray silty fine to medium sand with gravel and occasional organic matter (roots) (loose, moist) (weathered glacial till) Tan with iron-oxide staining silty fine to medium sand with occasional gravel (medium dense, moist) Grades to dense Gray silty fine to medium sand with gravel (very dense, moist) (glacial till) DUFF SM SM SM 1 %F 2 7 39 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Locational Survey.Date:8/21/20 Path:P:\3\3625004\GINT\362500400.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number: Project Location: Project: Federal Way, Washington 3625-004-00 Log of Test Pit TP-7 Figure A-8 SRI-Redondo Heights ApartmentsElevation (feet)328327326325324323322321320319318Depth (feet)1 2 3 4 5 6 7 8 9 10 Testing SampleGraphic LogSAMPLE MATERIAL DESCRIPTION GroupClassificationSample NameTestingMoistureContent (%)REMARKS FinesContent (%)Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)8/6/2020 10.5 328.3 NGVD29 1274683 132441 WA State Plane North NAD83 (feet) CJL Checked By CRN Groundwater not observed Caving not observedEquipment Komatsu PC128 Logged By Excavator SRI-Rochlin 12 inches forest duff Brown-gray silty fine to medium sand with gravel and occasional organic matter (roots) (loose, moist) (weathered glacial till) Grades to dense Gray silty fine to medium sand with gravel (very dense, moist) (glacial till) DUFF SM SM 1SA 2 8 32 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Locational Survey.Date:8/21/20 Path:P:\3\3625004\GINT\362500400.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number: Project Location: Project: Federal Way, Washington 3625-004-00 Log of Test Pit TP-8 Figure A-9 SRI-Redondo Heights ApartmentsElevation (feet)316315314313312311310309Depth (feet)1 2 3 4 5 6 7 8 Testing SampleGraphic LogSAMPLE MATERIAL DESCRIPTION GroupClassificationSample NameTestingMoistureContent (%)REMARKS FinesContent (%)Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)8/6/2020 8 316.3 NGVD29 1274757 132427 WA State Plane North NAD83 (feet) CJL Checked By CRN Groundwater not observed Caving not observedEquipment Komatsu PC128 Logged By Excavator SRI-Rochlin 6 inches quarry spalls (dense, moist) (fill) Brown silty fine to medium sand with gravel and occasional organic matter (roots) and deleterious debris (plastic bags) (loose, moist) Tan with iron-oxide staining silty fine to medium sand with gravel (medium dense, moist) (weathered glacial till) Grades to dense Brown-gray with iron-oxide staining silty fine to medium sand with gravel (very dense, moist) (glacial till) Grades to gray with iron-oxide staining Grades to without iron-oxide staining CR SM SM SM 1MC 2 3 4 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Locational Survey.Date:8/21/20 Path:P:\3\3625004\GINT\362500400.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number: Project Location: Project: Federal Way, Washington 3625-004-00 Log of Test Pit TP-9 Figure A-10 SRI-Redondo Heights ApartmentsElevation (feet)320319318317316315314313Depth (feet)1 2 3 4 5 6 7 8 Testing SampleGraphic LogSAMPLE MATERIAL DESCRIPTION GroupClassificationSample NameTestingMoistureContent (%)REMARKS FinesContent (%)Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)8/6/2020 8 320.3 NGVD29 1274639 132562 WA State Plane North NAD83 (feet) CJL Checked By CRN Groundwater not observed Caving not observedEquipment Komatsu PC128 Logged By Excavator SRI-Rochlin 12 inches forest duff Brown silty fine to medium sand with gravel and occasional organic matter (roots) (medium dense, moist) (weathered glacial till) Grades to brown-gray with iron-oxide staining, dense Brown-gray with iron-oxide staining silty fine to medium sand with gravel (very dense, moist) (glacial till) Grades to gray and without iron-oxide staining DUFF SM SM 1 2 3 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Locational Survey.Date:8/21/20 Path:P:\3\3625004\GINT\362500400.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number: Project Location: Project: Federal Way, Washington 3625-004-00 Log of Test Pit TP-10 Figure A-11 SRI-Redondo Heights ApartmentsElevation (feet)320319318317316315314313312311Depth (feet)1 2 3 4 5 6 7 8 9 Testing SampleGraphic LogSAMPLE MATERIAL DESCRIPTION GroupClassificationSample NameTestingMoistureContent (%)REMARKS FinesContent (%)Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)8/6/2020 9.5 320.3 NGVD29 1274666 132632 WA State Plane North NAD83 (feet) CJL Checked By CRN Groundwater not observed Caving not observedEquipment Komatsu PC128 Logged By Excavator SRI-Rochlin 12 inches forest duff Brown silty fine sand with occasional gravel and organic matter (roots) (loose, moist) (weathered glacial till) Brown-gray silty fine to medium sand with gravel (medium dense, moist) Gray silty fine sand with gravel (very dense, moist) (glacial till) DUFF SM SM SM 1MC 2 SA 3 10 6 32 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Locational Survey.Date:8/21/20 Path:P:\3\3625004\GINT\362500400.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number: Project Location: Project: Federal Way, Washington 3625-004-00 Log of Test Pit TP-11 Figure A-12 SRI-Redondo Heights ApartmentsElevation (feet)321320319318317316315314313Depth (feet)1 2 3 4 5 6 7 8 9 Testing SampleGraphic LogSAMPLE MATERIAL DESCRIPTION GroupClassificationSample NameTestingMoistureContent (%)REMARKS FinesContent (%)Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)8/6/2020 9 321.3 NGVD29 1274754 132602 WA State Plane North NAD83 (feet) CJL Checked By CRN Groundwater not observed Caving not observedEquipment Komatsu PC128 Logged By Excavator SRI-Rochlin 9 inches forest duff Brown silty fine to medium sand with gravel and occasional organic matter (roots) (loose, moist) (weathered glacial till) Tan silty fine to medium sand with occasional gravel (dense, moist) Gray with occasional iron-oxide staining silty fine to medium sand with gravel (very dense, moist) (glacial till) DUFF SM SM SM 1 2 SA 3 8 1- to 3-inch diameter roots Left hole open for approximately 6 hours; nogroundwater seepage observed 27 Notes: See Figure A-1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot. Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Locational Survey.Date:8/21/20 Path:P:\3\3625004\GINT\362500400.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number: Project Location: Project: Federal Way, Washington 3625-004-00 Log of Test Pit TP-12 Figure A-13 SRI-Redondo Heights ApartmentsElevation (feet)316315314313312311310309308307Depth (feet)1 2 3 4 5 6 7 8 9 10 Testing SampleGraphic LogSAMPLE MATERIAL DESCRIPTION GroupClassificationSample NameTestingMoistureContent (%)REMARKS FinesContent (%)Date Excavated Surface Elevation (ft) Vertical Datum Coordinate System Horizontal Datum Easting (X) Northing (Y) Total Depth (ft)8/6/2020 10 316.3 NGVD29 1274863 132637 WA State Plane North NAD83 (feet) CJL Checked By CRN Groundwater not observed Caving not observedEquipment Komatsu PC128 Logged By Excavator SRI-Rochlin 0 10 20 30 40 50 60 70 80 90 100 0.0010.010.11101001000PERCENT PASSING BY WEIGHT GRAIN SIZE IN MILLIMETERS U.S. STANDARD SIEVE SIZE 2” SAND SILT OR CLAYCOBBLESGRAVEL COARSE MEDIUM FINECOARSEFINE Test Pit Number Depth(feet)Soil Description TP-6 TP-8 TP-11 TP-12 9.5 2 4.5 6 Silty fine to coarse gravel with sand (GM) Silty fine to medium sand with gravel (SM) Silty fine sand with gravel (SM) Silty fine to medium sand with gravel (SM) Symbol Moisture(%) 6 8 6 8 3/8”3”1.5”#4 #10 #20 #40 #60 #1003/4”Figure A-14Sieve Analysis ResultsSRI-Redondo Heights ApartmentsFederal Way, Washington3625-004-00 Date Exported: 8/18/20 Note:This report may not be reproduced,except in full,without written approval of GeoEngineers,Inc.Test results are applicable only to the specific sample on which they were performed,and should not be interpreted as representative of any other samples obtained at other times,depths or locations,or generated by separate operations or processes. The grain size analysis results were obtained in general accordance with ASTM C 136.GeoEngineers 17425 NE Union Hill Road Ste 250,Redmond,WA 98052 #2001”#140 APPENDIX B Report Limitations and Guidelines for Use August 24, 2020| Page B-1 File No. 3625-004-00 APPENDIX B REPORT LIMITATIONS AND GUIDELINES FOR USE1 This appendix provides information to help you manage your risks with respect to the use of this report. Read These Provisions Closely It is important to recognize that the geoscience practices (geotechnical engineering, geology and environmental science) rely on professional judgment and opinion to a greater extent than other engineering and natural science disciplines, where more precise and/or readily observable data may exist. To help clients better understand how this difference pertains to our services, GeoEngineers includes the following explanatory “limitations” provisions in its reports. Please confer with GeoEngineers if you need to know more how these “Report Limitations and Guidelines for Use” apply to your project or site. Geotechnical Services are Performed for Specific Purposes, Persons and Projects This report has been prepared for Shelter Resources, Inc. and for the Project(s) specifically identified in the report. The information contained herein is not applicable to other sites or projects. GeoEngineers structures its services to meet the specific needs of its clients. No party other than the party to whom this report is addressed may rely on the product of our services unless we agree to such reliance in advance and in writing. Within the limitations of the agreed scope of services for the Project, and its schedule and budget, our services have been executed in accordance with our signed Agreement with Shelter Resources, Inc. dated July 31, 2020 and generally accepted geotechnical practices in this area at the time this report was prepared. We do not authorize, and will not be responsible for, the use of this report for any purposes or projects other than those identified in the report. A Geotechnical Engineering or Geologic Report is based on a Unique Set of Project-Specific Factors This report has been prepared for the proposed Redondo Heights Apartments project in Federal Way, Washington. GeoEngineers considered a number of unique, project-specific factors when establishing the scope of services for this project and report. Unless GeoEngineers specifically indicates otherwise, it is important not to rely on this report if it was: ■ not prepared for you, ■ not prepared for your project, ■ not prepared for the specific site explored, or ■ completed before important project changes were made. For example, changes that can affect the applicability of this report include those that affect:   1 Developed based on material provided by ASFE, Professional Firms Practicing in the Geosciences; www.asfe.org.  August 24, 2020| Page B-2 File No. 3625-004-00 ■ the function of the proposed structure; ■ elevation, configuration, location, orientation or weight of the proposed structure; ■ composition of the design team; or ■ project ownership. If changes occur after the date of this report, GeoEngineers cannot be responsible for any consequences of such changes in relation to this report unless we have been given the opportunity to review our interpretations and recommendations. Based on that review, we can provide written modifications or confirmation, as appropriate. Environmental Concerns are Not Covered Unless environmental services were specifically included in our scope of services, this report does not provide any environmental findings, conclusions, or recommendations, including but not limited to, the likelihood of encountering underground storage tanks or regulated contaminants. Information Provided by Others GeoEngineers has relied upon certain data or information provided or compiled by others in the performance of our services. Although we use sources that we reasonably believe to be trustworthy, GeoEngineers cannot warrant or guarantee the accuracy or completeness of information provided or compiled by others. Subsurface Conditions Can Change This geotechnical or geologic report is based on conditions that existed at the time the study was performed. The findings and conclusions of this report may be affected by the passage of time, by man-made events such as construction on or adjacent to the site, new information or technology that becomes available subsequent to the report date, or by natural events such as floods, earthquakes, slope instability or groundwater fluctuations. If more than a few months have passed since issuance of our report or work product, or if any of the described events may have occurred, please contact GeoEngineers before applying this report for its intended purpose so that we may evaluate whether changed conditions affect the continued reliability or applicability of our conclusions and recommendations. Information Provided by Others GeoEngineers has relied upon certain data or information provided or compiled by others in the performance of our services. Although we use sources that we reasonably believe to be trustworthy, GeoEngineers cannot warrant or guarantee the accuracy or completeness of information provided or compiled by others. Geotechnical and Geologic Findings are Professional Opinions Our interpretations of subsurface conditions are based on field observations from widely spaced sampling locations at the site. Site exploration identifies the specific subsurface conditions only at those points where subsurface tests are conducted or samples are taken. GeoEngineers reviewed field and laboratory data and then applied its professional judgment to render an informed opinion about subsurface conditions at other locations. Actual subsurface conditions may differ, sometimes significantly, from the opinions August 24, 2020| Page B-3 File No. 3625-004-00 presented in this report. Our report, conclusions and interpretations are not a warranty of the actual subsurface conditions. Geotechnical Engineering Report Recommendations are Not Final We have developed the following recommendations based on data gathered from subsurface investigation(s). These investigations sample just a small percentage of a site to create a snapshot of the subsurface conditions elsewhere on the site. Such sampling on its own cannot provide a complete and accurate view of subsurface conditions for the entire site. Therefore, the recommendations included in this report are preliminary and should not be considered final. GeoEngineers’ recommendations can be finalized only by observing actual subsurface conditions revealed during construction. GeoEngineers cannot assume responsibility or liability for the recommendations in this report if we do not perform construction observation. We recommend that you allow sufficient monitoring, testing and consultation during construction by GeoEngineers to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes if the conditions revealed during the work differ from those anticipated, and to evaluate whether earthwork activities are completed in accordance with our recommendations. Retaining GeoEngineers for construction observation for this project is the most effective means of managing the risks associated with unanticipated conditions. If another party performs field observation and confirms our expectations, the other party must take full responsibility for both the observations and recommendations. Please note, however, that another party would lack our project- specific knowledge and resources. A Geotechnical Engineering or Geologic Report Could Be Subject to Misinterpretation Misinterpretation of this report by members of the design team or by contractors can result in costly problems. GeoEngineers can help reduce the risks of misinterpretation by conferring with appropriate members of the design team after submitting the report, reviewing pertinent elements of the design team’s plans and specifications, participating in pre-bid and preconstruction conferences, and providing construction observation. Do Not Redraw the Exploration Logs Geotechnical engineers and geologists prepare final boring and testing logs based upon their interpretation of field logs and laboratory data. The logs included in a geotechnical engineering or geologic report should never be redrawn for inclusion in architectural or other design drawings. Photographic or electronic reproduction is acceptable, but separating logs from the report can create a risk of misinterpretation. Give Contractors a Complete Report and Guidance To help reduce the risk of problems associated with unanticipated subsurface conditions, GeoEngineers recommends giving contractors the complete geotechnical engineering or geologic report, including these “Report Limitations and Guidelines for Use.” When providing the report, you should preface it with a clearly written letter of transmittal that: ■ advises contractors that the report was not prepared for purposes of bid development and that its accuracy is limited; and August 24, 2020| Page B-4 File No. 3625-004-00 ■ encourages contractors to confer with GeoEngineers and/or to conduct additional study to obtain the specific types of information they need or prefer. Contractors are Responsible for Site Safety on Their Own Construction Projects Our geotechnical recommendations are not intended to direct the contractor’s procedures, methods, schedule or management of the work site. The contractor is solely responsible for job site safety and for managing construction operations to minimize risks to on-site personnel and adjacent properties. Biological Pollutants GeoEngineers’ Scope of Work specifically excludes the investigation, detection, prevention or assessment of the presence of Biological Pollutants. Accordingly, this report does not include any interpretations, recommendations, findings or conclusions regarding the detecting, assessing, preventing or abating of Biological Pollutants, and no conclusions or inferences should be drawn regarding Biological Pollutants as they may relate to this project. The term “Biological Pollutants” includes, but is not limited to, molds, fungi, spores, bacteria and viruses, and/or any of their byproducts. A Client that desires these specialized services is advised to obtain them from a consultant who offers services in this specialized field.