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21-101125-UP-Civil Drainage-03-23-21-V1March 19, 2021    Prepared for:  City of Federal Way  1st Ave S and 348th St  Federal Way, WA 98003  Reviewed by:  Joe Taflin, P.E., LEED AP  joe@navixeng.com        PRELIMINARY  TECHNICAL INFORMATION  REPORT  FNW Federal Way Mixed‐Use  Federal Way, WASHINGTON      PRE LI MI N A R Y     TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 1  TABLE OF CONTENTS  SECTION PAGE  PROJECT OVERVIEW ........................................................................................................................... 2  1. EXISTING CONDITIONS ............................................................................................................ 2  2. SITE LOCATION ........................................................................................................................ 4  3. DRAINAGE BASIN, SUBBASINS, AND SITE CHARACTERISTICS .................................................. 5  4. SOILS ....................................................................................................................................... 5    CONDITIONS AND REQUIREMENTS SUMMARY ................................................................................. 6    OFFSITE ANALYSIS ............................................................................................................................ 10    FLOW CONTROL, LID, AND WATER QUALITY FACILITY ANALYSIS AND DESIGN .............................. 16  1. EXISTING SITE HYDROLOGY ................................................................................................... 16  2. DEVELOPED SITE HYDROLOGY .............................................................................................. 16  3. FLOW CONTROL FACILITIES ................................................................................................... 20  4. WATER QUALITY FACILITY ..................................................................................................... 39  5. 100‐YEAR FLOOD FIRM MAP/OVERFLOW CONDITION .......................................................... 39    CONVEYANCE SYSTEM ANALYSIS AND DESIGN................................................................................ 40    SPECIAL REPORTS AND STUDIES ....................................................................................................... 40    OTHER PERMITS ................................................................................................................................ 41    CSWPP ANALYSIS AND DESIGN ........................................................................................................ 42  ESC PLAN ANALYSIS AND DESIGN (PART A) ................................................................................. 42  1. EROSION RISK ASSESSMENT ........................................................................................... 42  2. CONSTRUCTION SEQUENCE AND PROCEDURE ............................................................... 42  3. TRAPPING SEDIMENT ...................................................................................................... 42  4. WET WEATHER TESC ....................................................................................................... 43  SWPPS PLAN DESIGN (PART B) .................................................................................................... 43    BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT ............................ 47    OPERATION AND MAINTENANCE GUIDELINES ................................................................................ 49      APPENDIX:  A –  EXHIBITS OF EXISTING CONDITIONS AND GRADING AND DRAINAGE PLAN    B –  WWHM2012 OUTPUT REPORTS    C –  SPECIAL REPORTS AND STUDIES    D –  CSWPPP WORKSHEETS      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 2  PROJECT OVERVIEW    DESIGN CRITERIA  The stormwater management facilities have been designed based on guidance provided by city  staff from the pre‐application conference.     STORMWATER REQUIREMENTS  Duration Analysis:Conservation Flow Control  Flow Control:The difference between Level 1  and Level 3 Flow Control Standard  is the volume the proposed project  needs to provide.  Water Quality Menu: Enhanced Basic  Downstream Analysis:¼ mile    Since the project proposes more than 2,000 SF of new impervious area, a Full Drainage Review will be  required.    EXISTING CONDITIONS  The project site is located at the SE corner of the intersection of 1st Ave S and S 348th St in Federal Way,  Washington. The site is rectangular in shape, approximately 8.32 acres in size and consists of four  parcels identified as 9129400010, 9129400020, 9129400030, 9129400040 and 91294000TR‐A. The  zoning designation is Community Business (CB). The site is bordered to the south and east by the West  Hylebos Wetlands Park.    Site topography is hilly, with a high point located at the northwest corner of the site. The site is divided  by a ridgeline running from the northwest towards the southeast corner with slopes towards the west  and east property lines ranging from 5% to 10%. The site is currently undeveloped; however, grading  and drainage improvements were constructed as a part of a previous project. See Figure 1 for a map of  the site location.    An existing wetland is located in the southeast portion of the property.  The wetland has a 100’ buffer  associated with it.      Per the Geotechnical Engineering Report, dated December 4, 2015, the subsurface soil consists of  native glacial till deposits composed of silt, sand, cobbles, and boulders. The topsoil/duff layer is  approximately 6 to 12 inches thick.        TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 3      PRE‐DEVELOPMENT STORMWATER RUNOFF  The site is currently undeveloped, with groundcover consisting primarily of brush with some mature  trees. Grading and drainage improvements including swales, ponds, and outfalls were constructed in  2002 as a part of a previous project. Rainfall primarily infiltrates site soils, any runoff generated  discharges to the West Hylebos wetland system via the constructed storm outfalls.    POST‐DEVELOPMENT STORMWATER RUNOFF  Stormwater will be managed on the project site in accordance with the standards of the 2016 King  County Surface Water Design Manual (KCSWDM). Since the project proposes more than 2,000 SF of  new impervious area, a Full Drainage Review will be required. On‐site stormwater runoff from the  paved and roof surfaces will be collected and transported via a system of curb, gutter, catch basins and  underground storm drainage pipe to a stormwater quality device prior to discharge into the existing  storm detention pond and will receive water quality treatment by means of a stormwater wetland  below the pond live storage.     The Technical Information Report (TIR) Worksheet is to be provided with the building permit  submittal.   PROJECT  SITE      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 4  SITE LOCATION        Figure 1: Vicinity Map    Location:   S 348 th St & 1st Ave S    Section, Township, Range: SW 1/4, SEC. 20, TOWNSHIP 21N, RANGE 4E, W.M.    Parcel/Tax Lot:  9129400010, 9129400020, 9129400030, 9129400040, 912940TR‐A    Size:  Approximately 8.32 acres    City, County, State:  Federal Way, King County, Washington    Governing Agency:  City of Federal Way  PROJECT SITE     TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 5  DRAINAGE BASIN, SUBBASINS, AND SITE CHARACTERISTICS    DRAINAGE BASIN  The project site is located within the West Hylebos Creek drainage basin, which is a Conservation Flow  Control Area. There are no special stormwater management requirements for this drainage basin.      Figure 2: Basin Map    SUBBASINS  The site is divided by a ridgeline running from the northwest towards the southeast corner. The  northeastern portion of the site drains towards a wetland adjacent to the southeast corner of the site.  The northwestern portion drains towards a wetland adjacent to the southwest corner of the site.     SOILS  Per the Geotechnical Engineering Report, dated December 4, 2015, the soil consists of Vashon glacial  till (Qvt) and the USGS soils map indicates Everett‐Alderwood gravelly sandy loam (EwC), both are  glacial till material. Glacial till is typically composed of silt, sand, gravel, cobbles, and boulders.  The till  is glacially consolidated and when intact is characterized by a loose to medium dense weathered  horizon on the order of about 2 to 4 feet thick underlain by denser unweathered material.  PROJECT SITE     TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 6  CONDITIONS AND REQUIREMENTS SUMMARY    As required by the 2016 King County Surface Water Design Manual, this project is subject to a Full  Drainage Review. Therefore, the storm drainage design for this project is required to comply with, or  explain exemptions for, all nine (9) Core Requirements as well as all five (5) Special Requirements. The  applicable requirements have been met as follows:    CORE REQUIREMENTS    Core Requirement #1: Discharge at Natural Location  All surface and storm water runoff from a project must be discharged at the natural location so as not  to be diverted onto or away from downstream properties. The manner in which runoff is discharged  from the project site must not create a significant adverse impact to downhill properties or drainage  systems.    Response:  Runoff will be detained to pre‐developed, fully‐forested conditions before being discharged  via level spreader to the West Hylebos Wetlands to which the site currently discharges. The existing  pond and dispersal trench will remain. No downstream impacts are anticipated.    Core Requirement #2: Offsite Analysis  All proposed projects must submit an offsite analysis report that assesses potential offsite drainage  impacts associated with development of the project site and propose appropriate mitigations of those  impacts. The initial permit submittal shall include, at a minimum, a Level 1 downstream analysis as  described in Section 1.2.2.1 of the 2016 Manual.    Response:  A Level 1 Downstream Analysis was completed for this project. Since the on‐site runoff will  be detained to match pre‐developed, fully forested conditions, and treated prior to being conveyed to  the existing municipal off‐site conveyance system, no downstream impacts are anticipated.     Core Requirement #3: Flow Control Facilities  All proposed projects, including redevelopment projects, must provide onsite flow control facilities to  mitigate the impacts of storm and surface water runoff generated by new impervious surface, new  pervious surface, and replaced impervious surface targeted for flow mitigation as specified in the  following sections.  Flow control facilities must be provided and designed to perform as specified by  the area‐specific flow control facility requirement in Section 1.2.3.1 and in accordance with the  applicable flow control facility implementation requirements in Section 1.2.3.2.    Response:  Per the City of Federal Way Flow Control Applications Map, the project site falls within the  Conservation Flow Control Area. Stormwater management facilities within the Conservation Flow  Control Area must comply with the Level 2 Flow Control standard. Since the subject property has an  existing detention pond that was sized based on an older design standard, city staff in consultation with  King County SWDM engineers, has determined the required detention volume to be the difference in  volumes between the Level 1 and Level 3 Flow Control Standards. The project has evaluated and  determined that the existing pond has capacity to comply with this noted approach. See the Flow  Control section below for detailed sizing calculations.      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 7    Core Requirement #4: Conveyance System  All engineered conveyance system elements for proposed projects must be analyzed, designed, and  constructed to provide a minimum level of protection against overtopping, flooding, erosion, and  structural failure as specified in Sections 1.2.4.1, 1.2.4.2, and 1.2.4.3 of the 2016 Manual.    Response:  The on‐site conveyance system will be sized to adequately convey the 25‐year, up to the  100‐year storm event. A detailed Conveyance System Analysis will be provided with the  construction documents submittal.    Core Requirement #5: Construction Stormwater Pollution Prevention  All proposed projects that will clear, grade, or otherwise disturb the site must provide erosion and  sediment controls to prevent, to the maximum extent practicable, the transport of sediment from the  project site to downstream drainage facilities, water resources, and adjacent properties. All proposed  projects that will conduct construction activities onsite or offsite must provide stormwater pollution  prevention and spill controls to prevent, reduce, or eliminate the discharge of pollutants to onsite or  adjacent stormwater systems or watercourses.  To prevent sediment transport and pollutant  discharges as well as other impacts related to land‐disturbing and construction activities, Erosion and  Sediment Control (ESC) measures and Stormwater Pollution Prevention and Spill Control (SWPPS)  measures that are appropriate to the project site must be applied through a comprehensive  Construction Stormwater Pollution Prevention (CSWPP) plan as described in Sections 1.2.5.1 and  1.2.5.3 and shall perform as described in Section 1.2.5.2.  In addition, these measures, both temporary  and permanent, shall be implemented consistent with the requirements in Section 1.2.5.3 that apply  to the proposed project.    Response:  Construction stormwater pollution prevention measures as outlined in the 2016 Manual are  an integral part of the project construction documents. These measures will include methods to reduce  erosion of on‐site site soils and to prevent sediment from inadvertently leaving the project site, such a  sediment trap, silt fence, straw wattles, inlet protection, and marking clearing limits. Erosion and  sediment control measures will be designed in conformance with City of Federal Way and the 2016  Manual requirements.    Core Requirement #6: Maintenance and Operations  Maintenance and operation of all drainage facilities is the responsibility of the applicant or property  owner, except those facilities for which the City of Federal Way is granted an easement, tract, or right‐ of‐way and officially assumes maintenance and operation. Drainage facilities must be maintained and  operated in compliance with King County Maintenance Standards.    Response: An Operations and Maintenance Manual is located in Appendix B of this report.    Core Requirement #7: Financial Guarantees and Liability  All drainage facilities constructed or modified for projects (except flow control facilities to be privately  maintained) must comply with the financial guarantee requirements and the liability requirements of  the City of Federal Way. There are two types of financial guarantees for projects constructing or      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 8  modifying drainage facilities; the drainage facilities restoration and site stabilization guarantee, and the  drainage defect and maintenance guarantee.    Response:  A Bond Quantity worksheet will be provided in the next submittal of the storm report.    Core Requirement #8: Water Quality   All proposed projects, including redevelopment projects, must provide water quality (WQ) facilities to  treat the runoff from new and replaced pollution‐generating impervious surfaces and pollution‐ generating pervious surfaces targeted for treatment. These facilities shall be selected from one of the  area‐specific WQ menus described in Section 1.2.8.1 and implemented according to the applicable WQ  implementation requirements in Section 1.2.8.2 of the 2016 Manual.    Response:  Per the City of Federal Way Water Quality Applications Map, the project site falls within the  Enhanced Basic WQ Treatment Area. Water quality treatment for this site will be provided by means of  OldCastle BioPod Biofilter water quality devices, which have received the Department of Ecology  General Use Level Designation for Enhanced Treatment. See the Water Quality section below for sizing  calculations and Exhibit C in the Appendix A for an illustration of the BioPod BioFilter.    Core Requirement #9: Flow Control BMPs  All proposed projects, including redevelopment projects, must provide onsite flow control BMPs to  mitigate the impacts of storm and surface water runoff generated by new impervious surface, new  pervious surface, existing impervious surfaces, and replaced impervious surface targeted for mitigation  as specified in the following sections.  Flow control BMPs must be selected and applied according to  the basic requirements, procedures, and provisions detailed in this section and the design  specifications for each BMP in Appendix C, Section C.2.    Flow control BMPs are methods and designs for dispersing, infiltrating, or otherwise reducing or  preventing development‐related increases in runoff at or near the sources of those increases.  Flow  control BMPs include, but are not limited to, preservation and use of native vegetated surfaces to fully  disperse runoff; use of other pervious surfaces to disperse runoff; roof downspout infiltration;  permeable pavements; bioretention; limited infiltration systems; and reduction of development  footprint.    Response:  This project is subject to Large Lot BMP requirements.  The feasibility and applicability of full  dispersion, full infiltration, and other Flow Control BMPs were evaluated.  Per the Geotechnical report  provided by Zipper Geo Associates, LLC, the site contains low permeable native soils, little infiltration of  water passing through permeable surfaces should be expected. To prevent erosion and geodetic  hazards, infiltration based flow control BMPs will not be utilized on‐site.    SPECIAL REQUIREMENTS    Special Requirement #1: Other Adopted Area‐Specific Requirements  The drainage requirements of adopted CDAs, MDPs, BPs, SCPs, SFDPs, LMPs, FHMPs, and SFDPs shall  be applied in addition to the drainage requirements of the 2016 Manual unless otherwise specified in      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 9  the adopted regulation. Where conflicts occur between the two, the drainage requirements of the  adopted area‐specific regulation shall supersede those in the 2016 Manual.    Response: There are no area‐specific requirements applicable to this project site.    Special Requirement #2: Flood Hazard Area Delineation  Floodplains and floodways are subject to inundation during extreme events. The 100‐year floodplains  are delineated in order to minimize flooding impacts to new development and to prevent aggravation  of existing flooding problems by new development. Regulations and restrictions concerning  development within a 100‐year floodplain are found in the Sensitive Areas Ordinance.    Response:  Per the most current FIRM Map, shown on Figure 5 of this report, the project site does not  lie within the 100‐year floodplain.    Special Requirement #3: Flood Protection Facilities  Developing sites protected by levees and revetments require a high level of confidence in their  structural integrity and performance. Proper analysis, design, and construction are necessary to  protect against the potentially catastrophic consequences if such facilities should fail.    Response:  The project site does not contain any levees or revetments.    Special Requirement #4: Source Controls  Water quality source controls prevent rainfall and runoff water from coming into contact with  pollutants, thereby reducing the likelihood that pollutants will enter public waterways and violate  water quality standards and County stormwater discharge permit limits. The County may require  mandatory source controls at any time through formal code enforcement if complaints or studies  reveal water quality violations or problems.    Response:  Since the project proposes multiple buildings and various pollution generating impervious  surfaces, water quality source control is proposed as part of the redevelopment.      Special Requirement #5: Oil Control  Projects proposing to develop or redevelop a high‐use site must provide oil controls in addition to any  other water quality controls required by the 2016 Manual. Such sites typically generate high  concentrations of oil due to high traffic turnover or the frequent transfer of oil.    Response:  Per the 2016 Manual, commercial developments with an expected average daily traffic  (ADT) count of 100 or more vehicles per 1,000 square feet of gross building area are considered high  use sites.  This project is not considered a high‐use site.      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 10  OFFSITE ANALYSIS    TASK 1: STUDY AREA DEFINITION AND MAPS  Available resources such as the survey and topographic maps were utilized to prepare the downstream  analysis.  The study area extended 1/4‐mile downstream of the project site.      Figure 2: Study Areas Map       PROJECT SITE A B C     TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 11  TASK 2: RESOURCE REVIEW  The following resources were reviewed for existing/potential problems within the study area:     Basin Plan or Basin Reconnaissance Summary Reports   FEMA Maps (See Figure 5 of this report.)   Sensitive Areas Folio   Reported Drainage Complaints   Reported Road Drainage Problems   USDA Soils Survey (See Figure 2 of this report.)   Wetland Inventory Maps   Migrating River Studies   WSDOE Section 303d   King County Designated Water Quality Problems   Stormwater Compliance Plans    A review of drainage complaints from the last 10 years within one‐quarter mile around the project site,  as supplied by King County, indicates that there have been no relevant complaints related to drainage  or water quality concerns that would impact or be impacted by the development of this site.  The only  complaints are records of stormwater audits.         Complaint A                                     Complaint B                                  Complaint C UPSTREAM ANALYSIS  A portion of the frontage improvements along South 348th ST is tributary to the site via a catch basin  located along the curb line.  The catch basin has a tee with 1.25” orifice conveying 0.32 acres of  impervious surface via a 12” CPEP pipe to the property. This runoff will be intercepted in a piped  system and conveyed to the water quality treatment system for treatment prior to release to the  existing detention pond.       No other additional upstream runoff is received by as noted below.    DOWNSTREAM ANALYSIS   A formal downstream analysis has been completed in accordance with the 2016 Manual.  The  downstream analysis was completed on September 15, 2015.  The temperature was approximately 60      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 12  degrees, and it was cloudy.  A map of the downstream path and an analysis of this system for nearly ¼  mile from the site are provided below.        Figure 3 shows the downstream analysis path from the project site to ¼ mile downstream.      Figure 3: Downstream Path       PROJECT  SITE  DOWNSTREAM  PATH  PROJECT SITE  DISCHARGE  LOCATION 1  2  3  4  5      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 13    #  Photo  Description  1  Looking south over  the combined  detention & water  quality ponds towards  the control structure.     2  Two risers within the  outfall. First riser  discharges to dispersal  trench/level spreader,  second riser (capped)  splits ¼ of flow to  wetland downstream.   Refer to Appendix D  for existing pond  control structure  design information.  Control   Structure      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 14  3  Stormwater  discharges through a  level spreader near  the southern property  line.  4  Downstream of the  level spreader,  discharge sheet flows  or is infiltrated.  Downstream area is  heavily vegetated with  brush and small trees.       TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 15  5  Runoff from the site  sheet flows through  brush and small trees  for approximately 300  feet before entering  West Hylebos creek.  TASK 4: DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS There are no known problems with the drainage paths around the site. No downstream impacts from  the proposed project are anticipated.  Complaint  Location  Complaint  Number  Complaint  Type  Problem Date  Closed  Address Parcel  comments A  1987‐0727  C  TILE 6/18/1987,  5:00 PM  120 S  356TH ST  2921049029  ILLEGAL  INSTALLATION?  A  1987‐0727  E  VIOLATE 8/25/1987,  5:00 PM  120 S  356TH ST  2921049029  PIPE WAS OLD  COVERED WITH  DIRT  B  1990‐0339  C  CULVERT 2/21/1990,  4:00 PM  629 S  356TH ST  2921049019  CONST OF  CHURCH  C  1980‐0111  C  DUMPING 2/19/1980,  4:00 PM  35929   PACIFIC  HWY S  2921049098  NEXT TO  HYLEBOS CRK  TASK 5: MITIGATION OF EXISTING OR POTENTIAL PROBLEMS No current problems or signs of damaging erosion were observed.  In the event that a downstream  conveyance issue does exist, the King County Stormwater Manual contains area‐specific flow control  requirements for problems identified downstream of a project. The project site is located within a  Conservation Flow Control Area, which requires Level 2 flow control (as discussed above). For a Type I  drainage problem (conveyance system nuisance problem) identified downstream, there are no  additional flow control or other mitigation needed.          TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 16  FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN    EXISTING SITE HYDROLOGY  The project site is located at the SE corner of S 348th St and 1st Ave S in Federal Way, Washington. The  subject property is approximately 8.32 acres in size and is primarily undeveloped forested land, a  manmade stormwater pond is located in the southeast portion of the site.     Site topography is hilly, with a high point located at the northwest corner of the site. The site is divided  by a ridgeline running from the northwest towards the southeast corner with slopes towards the west  and east property lines ranging from 5% to 10%. The site is currently undeveloped; however, grading  and drainage improvements were constructed as a part of a previous project. See Figure 1 for a map of  the site location and Figure 4 for an exhibit of the existing conditions.    The project site is located in a Conservation Flow Control Area and per the requirements of the 2016  KCSWDM, the existing conditions have been modeled assuming historic site conditions as forested. A  portion of the site is located in wetland and associated buffer and will not be cleared as part of this  project.    The pre‐developed conditions are shown in Table 1:    Table 1  Existing Conditions  Area (AC)  Description  7.68  Forest  0.64  Wetland   0.32  S. 348 th Street (Upstream ‐ offsite)  8.64  Total Basin Area      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 17      Figure 4: Existing Conditions Map    DEVELOPED SITE HYDROLOGY  The proposed development consists of eight apartment buildings (Buildings 1 to 8), two retail  buildings, and associated utilities, landscaping, parking, and stormwater improvements.      To the maximum extent practicable, on‐site stormwater runoff from the developed surfaces will be  collected and transported via a system of asphalt, catch basins and underground storm drainage pipe  to an underground stormwater water quality facility for treatment prior to discharge to the existing  detention pond.  The existing pond and associated outlet control structure are not proposed to be  modified.  Due to site grading and existing pond outfall constraints, a portion of the site is not tributary  to the pond and is considered bypass. However, the evaluation of the existing pond detention capacity      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 18  will include the entire 8‐acre drainage basin summarized in Table 2 below. Water quality treatment  evaluation considers all project areas with the exception of the detention pond and wetlands area,  which are downstream of the treatment devices.    See Figure 5 and Exhibit B in the Appendix A for the Developed Conditions Map.    The post‐developed and bypass conditions are shown in Table 2 to 4 below:      Table 2: Pond Basin Developed Conditions  Proposed Conditions  Area (AC)  Description  1.60  Buildings (Roof)  3.78  Asphalt Pavement /Sidewalk/Gravel  0.57  Pond Surface  1.73  Landscape (Lawn)  0.32  From 348 th St (Upstream)  8.0  Total Pond Basin Area    Table 3: Bypass (Pond oversized to account for Bypass)  Proposed Conditions  Area (AC)  Description  0.33  Asphalt Pavement   0.56  Landscape (Lawn)  0.89  Total Bypass Area    Table 4: Wetland Developed Condition  Proposed Conditions  Area (AC)  Description  0.64  Wetland  0.64  Total Wetland Area          TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 19  Figure 5: Developed Conditions Map           TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 20  FLOW CONTROL FACILITIES    The site currently has an existing detention pond that was sized under old standards that are no longer  applicable. The proposed project is subject to the current Conservation Level 2 Flow Control  requirement.  Since there is no direct correlation between the current and old standards, based on  direction provided by city staff, the project is required to provide a pond volume that is equivalent to  the differences in volume between the Level 1 and Level 3 Flow Control Standards.  Based on the  results of the noted volume analysis, the existing detention pond can either be modified to provide the  required volume or remain unaltered in the analysis determined that the constructed existing pond  has the required capacity.    Level 1 Flow Control Standards require matching the predevelopment peak flow rates for the 2‐year  and 10‐year runoff events. Maintaining the durations of high flows at their predevelopment is not  required for compliance with Level 1 Level 1 Flow Control Standards.    Level 3 Flow Control Standards require maintaining the durations of high flows at their  predevelopment levels for all flows greater than one‐half of the 2‐year flow up to the 50‐year flow and  holding the 100‐year peak flow rate at its predevelopment level. The predevelopment peak flow rates  for the 2‐year and 10‐year runoff events are also intended to be maintained when applying Level 3  flow control.     Table 5 below summarizes the peak flows associated with a Level 1 analysis, with the resulting  required pond volume needed for the project of approximately 79,243 cf.      Table 5: LEVEL 1 FLOW CONTROL STANDARDS ‐ PEAK RATES SUMMARY  STORM  EVENT  PRE‐DEV Q  PEAK (CFS)  POST‐DEV Q  MITIGATED  RELEASE Q STAGE (FT)  VOLUME(CF)  2‐YEAR  0.2382  2.7492 0.2341 1.8846  45,259 10‐YEAR  0.4881  4.0936 0.3235 3.1291  78,277   Table 6 below summarizes the peak flows associated with a Level 3 analysis, with the resulting  required pond volume needed for the project of approximately 219,366 cf.      Table 6: LEVEL 3 FLOW CONTROL STANDARDS ‐ PEAK RATES SUMMARY  STORM  EVENT  PRE‐DEV Q  PEAK (CFS)  POST‐DEV Q  MITIGATED  RELEASE Q STAGE (FT)  VOLUME(CF)  2‐YEAR  0.2382  2.7492 0.1391 2.95  73,626 10‐YEAR  0.4881  4.0936 0.2683 4.26  111,339 100‐YR  0.7603  6.0209 0.5272 5.62  155,424   The difference in volumes between the Level 1 and Level 3 Flow Control Standards is 77,147 cf.  Required storm detention volume    = Level 3 volume – Level 1 Volume   = 155,424 cf – 78,277 cf   = 77,147 cf      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 21    Based on field survey and as shown on the Existing Conditions Exhibit A in Appendix A, the existing  pond has an available dead storage capacity of 20,960 cf and a live storage volume of approximately  79,740 cf, which exceeds the required detention volume calculated above. The project proposes to  maintain the existing pond in place with minor grading improvements along the north and west side of  the pond to accommodate a pedestrian walkway. The existing pond capacity will be impacted by the  proposed improvements.     The WWHM model inputs (Predeveloped Conditions and Developed Conditions) and model output for  the Level 1 and Level 3 Flow Control standards analysis are included in the Appendix B.    WATER QUALITY FACILITY    The proposed development is a commercial and multifamily development and lies within an Enhanced  Basic Water Quality area. Stormwater runoff from the developed site will be routed to BioPod Biofilter  storm quality devices for treatment prior to discharge to the existing detention pond.  The BioPod  Biofilters units are approved for Enhanced Treatment by the Department of Ecology. They will be sized  per WWHM2012 during the permitting phase. The anticipated overall treatment rate for the  developed drainage basin located upstream of the detention pond is as follows:    Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0.7519 acre-feet On-line facility target flow: 0.9831 cfs. Adjusted for 15 min: 0.9831 cfs. Off-line facility target flow: 0.5509 cfs. Adjusted for 15 min: 0.5509 cfs.   An illustration of a BioPod Biofilter water quality device is shown in Exhibit C in the Appendix A.    100‐YEAR FLOOD/OVERFLOW CONDITION    Review of the most recent FIRM maps indicates that the development area on the project site does not  lie within the 100‐year flood plain. The portion of FIRM containing the subject property is included  below.  The site lies within the unshaded Zone X, as shown.  This zone represents areas determined to  be outside of the 500‐year flood plain.        TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 22   Figure 5: FEMA Flood Insurance Rate Map (FIRM)     CONVEYANCE SYSTEM ANALYSIS AND DESIGN    Primary conveyance of stormwater on site is via 12” diameter storm drainage pipe at a minimum  slope of 0.5%. Preliminary calculations using the Manning equation show that a pipe of this  diameter, at the minimum slope is capable of conveying approximately 2.94 cfs.   Detailed Conveyance system analysis, using Storm and Sanitary Sewer Analysis will be provided  with subsequent submittal.         PROJECT SITE     TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 23  SPECIAL REPORTS AND STUDIES    Special reports and studies for this property include the following (See Appendix C):    “Geotechnical Engineering Report ‐ Draft, Proposed Mixed‐use Development, South 348th Street  & 1st Avenue South, Federal Way, WA” by Zipper Geo Associates, dated December 4, 2015.           TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 24  OTHER PERMITS    Other permits required for this project include the following:   An NPDES Construction Stormwater General Permit will be provided prior to construction.          TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 25  CSWPP ANALYSIS AND DESIGN    ESC Plan Analysis and Design (Part A)  All erosion and sediment control measures shall be governed by the requirements of the King County.   A temporary erosion and sedimentation control plan has been prepared to assist the contractor in  complying with these requirements.  The Erosion and Sediment Control (ESC) plan is included with the  construction plans.    1. Erosion Risk Assessment  The degree of erosion risk on the proposed project site is minimal.  The following factors contribute to  a low degree of erosion risk:   Slope across the site is slight to moderate.  Runoff will not travel at high velocities across the  site and, therefore, will not cause noticeable erosion impacts.   The site is already stabilized with hard surfaces and the portions that will be removed will  generally create temporary closed depression areas that will trap stormwater runoff.       2. Construction Sequence and Procedure  The proposed development will include an erosion/sedimentation control plan designed to prevent  sediment‐laden run‐off from leaving the site during construction.  The erosion potential of the site is  influenced by four major factors: soil characteristics, vegetative cover, topography and climate.   Erosion/sedimentation control is achieved by a combination of structural measures, cover measures,  and construction practices that are tailored to fit the specific site.    Prior to the start of any grading activity upon the site, all erosion control measures, including stabilized  construction entrances, shall be installed in accordance with the construction documents.    The best construction practice will be employed to properly clear and grade the site and to schedule  construction activities.  The planned construction sequence for the construction of the site will be  provided with a subsequent submittal.    3. Trapping Sediment  Structural control measures will be used to reduce erosion and retain sediment on the construction  site.  The control measures will be selected to fit specific site and seasonal conditions.    The following structural items will be used to control erosion and sedimentation processes:     Compost Socks   Filter fabric fences   Catch Basin Inlet Sediment Protection   Proper Cover measures   Sediment Trap    The proposed sediment trap was designed in accordance with the 2016 Manual.  The required surface  area is:  Required Surface Area = 2 * (2 year peak developed flow) / 0.00096 = 2 * (0.3241 cfs)/0.00096 = 675 SF        TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 26  Weekly inspection of the erosion control measures will be required during construction.  Any sediment  buildup shall be removed and disposed of off‐site.    Vehicle tracking of mud off‐site shall be avoided.  Installation of a stabilized construction entrance will  be installed at a location to enter the site.  The entrances are a minimum requirement and may be  supplemented if tracking of mud onto public streets becomes excessive.  In the event that mud is  tracked off site, it shall be swept up and disposed of off‐site on a daily basis.  Depending on the  amount of tracked mud, a vehicle road sweeper may be required.     Because vegetative cover is the most important form of erosion control, construction practices must  adhere to stringent cover requirements.  More specifically, the contractor will not be allowed to leave  soils open for more than 14 days and, in some cases, immediate seeding will be required.      4.  Wet Weather TESC Operating Plan  Work between October 1st and April 30th must adhere to the Wet Season Special Provisions noted in  Section D.5.2 in Appendix D of the 2016 KCSWDM.    SWPPS Plan Design (Part B)  A variety of storm water pollutant controls are recommended for this project.  Some controls are  intended to function temporarily and will be used as needed for pollutant control during the  construction period.  These include temporary sediment barriers such as silt fences.  For most  disturbed areas, permanent stabilization will be accomplished by covering the soil with pavement,  building, or vegetation.    The CSWPPP Worksheet Forms are located in Appendix D.  A. Erosion and Sediment Controls   1. Soil Stabilization ‐ The purpose of soil stabilization is to prevent soil from leaving  the site.  In the natural condition, soil is stabilized by native vegetation.  The  primary technique to be used at this project for stabilizing site soil will be to  provide a protective cover of grass, pavement, or building.    a) See  2016  KCSWDM  Section  D.3.2.6  for  Temporary  and  Permanent  Seeding requirements.    b) Structural Controls – See construction plans for the T.E.S.C. Plan, D‐2.0.   Inlet  protection  and  silt  fence  are  proposed  to  minimize  siltation  of  construction activities.   c) Silt Fence – Silt fence is a synthetic permeable mesh fabric typically  incorporating wooden support stakes at intervals sufficient to support  the fence and water and sediment retained by the fence.  Silt fence is also  available with a wire mesh backing.  The fence is designed to retain  sediment‐laden  water  to  allow  settlement  of  suspended  soils  before  filtering through the mesh fabric for discharge downstream.  Silt fence  shall be located to capture overland, low‐velocity sheet flows as follows:      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 27  provide silt fence along the perimeter of the disturbed area, this site does  not contain sloped area that would warrant additional silt fencing.   Install  silt fence at a fairly level grade (along the contour) to provide sufficient  upstream storage volume for the anticipated runoff.  d) Construction Entrance – All access points from the public street into the  construction  site  shall  include  a  construction  entrance  composed  of  course stone to the dimensions shown on the T.E.S.C. Plan, D‐2.0.  The  rough texture of the stone helps to remove clumps of soil adhering to  construction vehicle tires through the action of vibration and jarring over  the  rough  surface  and  the  friction  of  the  stone  matrix  against soils  attached to vehicle tires.  e) Clearing Limits – Clearing limits are defined by the placement of silt fence  or construction fence.  f) Storm Drain Inlet Protection – Curb and grated inlets are protected from  the intrusion of silt and sediment through a variety of measures as shown  on the Construction Drawings.  The primary mechanism is to place  controls in the path of flow sufficient to slow sediment‐laden water to  allow settlement of suspended soils before discharging into the storm  sewer.  Controls typically provide a secondary benefit by means of  filtration.  Grated inlets typically include a sturdy frame wrapped in silt  fence or crushed stone‐lined perimeter to slow the flow of water.  Curb  inlets typically include crushed stone barriers held in place with silt fence  material or geotextile fabric.  Where inlets are located in paved areas the  contractor shall install filter fabric in the catch basin.  See 2016 KCSWDM Section D.5.5 for Final Stabilization requirements.    B.  Other Pollutant Controls    Control of sediments has been described previously.  Other aspects of this SWPPP are  listed below:  1. Dust Control ‐ Construction traffic must enter and exit the site at the stabilized  construction entrance.  The purpose is to trap dust and mud that would otherwise  be carried off‐site by construction traffic.  Water trucks will be used as needed during construction to reduce dust generated  on the site.  Dust control must be provided by the General Contractor to a degree  that is acceptable to the owner, and in compliance with applicable local and state  dust control regulations.  After construction, the site will be stabilized (as described  elsewhere), which will reduce the potential for dust generation.      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 28  Chemical treatments have not been approved for this site.  The Civil Engineer of  Record must be contacted if these are requested to be utilized.  2. Solid Waste Disposal ‐ No solid materials, including building materials, are allowed  to  be  discharged  from  the  site  with  stormwater.    All  solid  waste,  including  disposable  materials  incidental  to  the  major  construction  activities,  must  be  collected and placed in containers. The containers will be emptied as necessary by  a contract trash disposal service and hauled away from the site. The location of solid  waste receptacles shall be shown on the T.E.S.C. Plan, D‐2.0.   Substances that have the potential for polluting surface and/or groundwater must  be controlled by whatever means necessary in order to ensure that they do not  discharge from the site.  As an example, special care must be exercised during  equipment fueling and servicing operations.  If a spill occurs, it must be contained  and disposed so that it will not flow from the site or enter groundwater, even if this  requires  removal,  treatment,  and  disposal  of  soil.    In  this  regard,  potentially  polluting substances should be handled in a manner consistent with the impact they  represent.  3. Sanitary Facilities ‐ All personnel involved with construction activities must comply  with state and local sanitary or septic system regulations.  Temporary sanitary  facilities will be provided at the site throughout the construction phase.  They must  be utilized by all construction personnel and will be serviced by a commercial  operator.  The location of sanitary facilities shall be shown on T.E.S.C. Plan, D‐2.0.  4. Water Source ‐ Non‐storm water components of site discharge must be clean water.   Water used for construction which discharges from the site must originate from a  public water supply or private well approved by the State Health Department.   Water used for construction that does not originate from an approved public supply  must not discharge from the site.  5. Concrete Waste from Concrete Ready‐Mix Trucks – Discharge of excess or waste  concrete  and/or  wash  water  from  concrete  trucks  will  be  allowed on the  construction site, but only in specifically designated diked areas that have been  prepared to prevent contact between the concrete and/or wash water and storm  water that will be discharged from the site. Waste concrete can be placed into forms  to make riprap or other useful concrete products. The cured residue from the  concrete washout diked areas shall be disposed in accordance with applicable state  and federal regulations.  The jobsite superintendent is responsible for assuring that  these procedures are followed.  The location of concrete washout areas shall be  shown on the T.E.S.C. Plan, D‐2.0.  6. Fuel Tanks – Temporary on‐site fuel tanks for construction vehicles shall meet all  state and federal regulations.  Tanks shall have approved spill containment with the  capacity required by the applicable regulations.  The tank shall be in sound condition  free of rust or other damage which might compromise containment.  Hoses, valves,      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 29  fittings, caps, filler nozzles, and associated hardware shall be maintained in proper  working condition at all times.   Temporary on‐site fuel tanks are not proposed for this project at this time.    7. Hazardous Waste Management and Spill Reporting Plan – Any hazardous or  potentially hazardous waste that is brought onto the construction site will be  handled properly in order to reduce the potential for storm water pollution.  All  materials used on this construction site will be properly stored, handled and  dispensed following any applicable label directions.  Material Safety Data Sheets  (MSDS) information will be kept on site for any and all applicable materials.    Should an accidental spill occur, immediate action will be undertaken by the  General Contractor to contain and remove the spilled material.  All hazardous  materials will be disposed of by the Contractor in the manner specified by local,  state, and federal regulations and by the manufacturer of such products.  As soon  as possible, the spill will be reported to the appropriate state and local agencies.   As required under the provisions of the Clean Water Act, any spill or discharge  entering the waters of the United States will be properly reported.  The General  Contractor will prepare a written record of any such spill and will provide notice to  the Owner within 24‐hours of the occurrence of the spill.    Any spills of petroleum products or hazardous materials in excess of Reportable  Quantities as defined by EPA or the state or local agency regulations, shall be  immediately reported to the EPA National Response Center (1‐800‐424‐8802) and  the Washington State Department of Ecology at (360) 407‐6300 or 1‐800‐258‐ 5990.  The reportable quantity for petroleum products is per the State of  Washington is any amount that contacts public waterways or public storm systems  OR equal to or greater than 1 gallon on a commercial project that does not contact  public water systems such as creeks, rivers, lakes, or storm systems and must be  reported within 24 hours.  The EPA guidelines define spills within the public water systems as those that:  violate applicable water quality standards; cause a film or “sheen” upon, or  discoloration of the surface of the water or adjoining shorelines; or cause a sludge  or emulsion to be deposited beneath the surface of the water or upon adjoining  shorelines.  The reportable quantity for hazardous materials is per the  Comprehensive Environmental Response, Compensation and Liability Act  (CERCLA), and is any hazardous substance with reportable quantity that appears in  Table 302.4of 40 CFR parts 302, for other substance not found on this list, the  reportable quantity is one pound.   In order to minimize the potential for a spill of hazardous materials to come in  contact with stormwater, the following steps will be implemented:  a) All materials with hazardous properties (such as pesticides, petroleum      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 30  products, fertilizers, detergents, construction chemicals, acids, paints,  paint solvents, cleaning solvents, additives for soil stabilization,  concrete, curing compounds and additives, etc.) will be stored in a  secure location, under cover, when not in use.  b) The minimum practical quantity of all such materials will be kept on the  job site and scheduled for delivery as close to time of use as practical.  c) A spill control and containment kit (containing for example, absorbent  such as kitty litter or sawdust, acid neutralizing agent, brooms, dust  pans, mops, rags, gloves, goggles, plastic and metal trash containers,  etc.) will be provided at the storage site.  d) All of the product in a container will be used before the container is  disposed of.  All such containers will be triple rinsed, with water prior to  disposal.  The rinse water used in these containers will be disposed of in  a manner in compliance with state and federal regulations and will not  be allowed to mix with storm water discharges.  e) All products will be stored in and used from the original container with  the original product label.  f) All products will be used in strict compliance with instructions on the  product label.  g) The disposal of excess or used products will be in strict compliance with  instructions on the product label.  8. Long‐Term Pollutant Controls ‐ Storm water pollutant control measures installed  during construction, that will also provide benefits after construction, will not be  applicable to this project since most of the pollution control measures are already  in place.  Those sediment barriers that do not interfere with normal operations and  appear  to  provide  long‐term  benefits  can  be  left  in  place  after  construction  is  completed.  9. Source Controls – Per Section 1.3.4 of the 2016 KCSWDM, structural source control  measures, such as car was pads or dumpster area roofing, shall be applied to the  entire site containing the proposed project, not just the project site.  Dumpster area  roofing is proposed as a structural source control for this project.    B. Construction Phase "Best Management Practices"  During the construction phase, the General Contractor shall implement the following  measures:  1. Materials resulting from the clearing and grubbing or excavation operations shall be  stockpiled up slope from adequate sedimentation controls.  Materials removed to      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 31  an off‐site location shall be protected with appropriate controls  and  properly  permitted.  2. The  General  Contractor  shall  designate  areas  on  the  T.E.S.C.  Plan,  D‐2.0  for  equipment  cleaning,  maintenance,  and  repair.    The  General  Contractor  and  subcontractors shall utilize such designated areas.  Cleaning, maintenance, and  repair areas shall be protected by a temporary perimeter berm, shall not occur  within 150 feet away of any waterway, and in areas located as far as practical from  storm drains.  3. Use of detergents for large scale washing is prohibited (i.e., vehicles, buildings,  pavement surfaces, etc.)  4. Chemicals, paints, solvents, fertilizers, and other toxic materials must be stored in  weatherproof containers.  Except during application, the contents must be kept in  trucks or within storage facilities.  Runoff containing such material must be collected,  removed from the site, treated, and disposed at an approved solid waste or chemical  disposal facility.  C. Off‐Site Facilities  Whenever dirt, rock, or other materials are imported to the construction site or exported  for placement in areas off of the primary construction site, the General Contractor is  responsible for determining that all stormwater permitting and pollution control  requirements are met for each and every site which receives such materials or from which  such materials are taken.  Prior to the disturbance of any such site, the General Contractor  will furnish the Owner with a copy of the storm water permit issued for each such site, as  well as a copy of the off‐site Owners certification statement agreeing to implement  necessary storm water pollution prevention measures.  The General Contractor will also  furnish a copy of the SWPPP for each such site, including a description of the erosion  control measures, which will be applied.  At a minimum, each off‐site area that provides or receives materials or is disturbed by  project activities must implement erosion control measures consisting of perimeter  controls on all down slope and side slope boundaries and must also provide for both  temporary stabilization measures and for permanent re‐vegetation after all disturbance is  ended.    BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT    The following information will be provided in the next submittal of the storm report:     Stormwater Facility Summary Sheet   Site Improvement Bond Quantity Worksheet   Declaration of Covenant for Maintenance and Inspection of Flow Control BMPs         TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 32  OPERATIONS AND MAINTENANCE GUIDELINES    The following operations and maintenance guidelines are provided for the on‐site stormwater  management system:       TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 33        TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 34        TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 35         TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 36      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 37      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 38      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 39      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 40      TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use  Page 41        TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use               APPENDIX A      EXHIBITS        EXHIBIT A – EXISTING CONDITIONS EXHIBIT    EXHIBIT B – POST DEVELOPMENT CONDITIONS EXHIBIT    EXHIBIT C – OLDCASTLE BIOPOD BIOFILTER         WATER QUALITY VAULT                                S 348TH STREET1ST AVENUE SOUTH OFFSITE RUNON= 13,847 SF = 0.32 ACRESEXISTING WATERQUALITY/DETENTION PONDAVAILABLEDEAD STORAGE =20,960 CF ±LIVE STORAGEVOLUME = 79,740 CF ±PROPERY BOUNDARYEXISTING PONDOUTLET /FLOWCONTROL SYSTEM12" PIPE OUTLET TOPROPERTYWETLAND ANDBUFFER AREA TOREMAINUNDISTURBED= 27,864 SF= 0.64 ACRESSITE (FORESTED MOD HSG C)334,726 SF= 7.68 ACRES (EXCLUDESWETLAND/BUFFER AREA)EXHIBIT AEXISTING CONDITIONS TRASH/RECYCLECCCCCCCCCCBLDG #4BLDG #1BLDG #5BLDG #6BLDG #7BLDG #8C C C C C C C C C C CCCCCCCCCCCBLDG #2BLDG #3S 348TH STREET1ST AVENUE SOUTH OFFSITE RUNON= 13,847 SF= 0.32 ACRESEXISTING PONDOUTLET /FLOWCONTROL SYSTEMEX 12" PIPE OUTLETDISCHARGES ONTOPROPERTYWETLAND AND BUFFER AREATO REMAIN UNDISTURBED= 27,864 SF= 0.64 ACRESPOST-DEVELOPMENTCONDITIONS1.60 AC - BLDG3.78 AC - PAVEMENT/GRAVEL0.57 AC POND1.73 LANDSCAPE = 7.68 ACLEVEL 3 VOLUME REQUIRED = 155, 424 CFLEVEL 1 VOLUME REQUIRED = 78,277 CFVOLUME NEEDED:155,424 CF - 78,277 CF = 77,147 CFLIVE STORAGE VOLUME AVAILABLE INEXISTING POND = 79,740 CF ±WETPOOL STORAGE VOLUME AVAILABLEIN EXISTING POND = 20,960 CF ±WQ UNIT #1WQ UNIT #2EXISTING DETENTION PONDTO REMAIN IN PLACEEXHIBIT BPOST-DEVELPED CONDITIONS A PLAN VIEW 1'-0" TOP 25'-6" WALL OD 26'-6" SLAB OD 13'-6" WALL OD 14'-6" FOOTING RIM ELEV 24'-0" WALL ID 12'-0" WALL ID 9" TYPICAL WALL THICKNESS 7'-10" 10" BASE SECTION A-ASECTION D-D 10'-0"8" INLET IE D RIM ELEV SECTION B-B A D SAU DFI1325-05 10 USAXXXXSAU DFI1325-05 10 USAXXXXINLET, Ø30" MAXIMUM 2X 6"x24" INLET WINDOW COBBLES FOR ENERGY DISSIPATION. 6X Ø4.00" SLOTTED PVC UNDERDRAIN PIPE. INTERIOR/EXTERIOR JOINT SEALANT REQUIRED, (CONSEAL CS-231 OR EQUIVALENT), BY OTHERS. 2X Ø36.00" BOLTED & GASKETED ACCESS COVERS, FIELD POURED CONCRETE COLLAR REQUIRED, BY OTHERS. GRADE RINGS AS REQUIRED. 6X Ø4.00" SLOTTED PVC UNDERDRAIN PIPE. UNDERDRAIN OUTLET ORIFICE INTO OUTLET CHAMBERINTERIOR/EXTERIOR JOINT SEALANT REQUIRED, (CONSEAL CS-231 OR EQUIVALENT), BY OTHERS. BYPASS WEIR EL INTERIOR/EXTERIOR JOINT SEALANT REQUIRED, (CONSEAL CS-231 OR EQUIVALENT), BY OTHERS. 2X 6"x24" INLET WINDOW 3X Ø4.00" SLOTTED PVC UNDERDRAIN PIPE. 6.00" DRAIN ROCK. 18.00" StormMixf MEDIA 2.00" MULCH. UNDERDRAIN OUTLET ORIFICE INTO OUTLET CHAMBER FIDSAUXXXX USADFI1154 0010 FIDSAU XXXX USADFI11540010 B DRAIN DOWN DEVICE 2'-8"10'-0"8" B OUTLET, Ø30" MAXIMUM DRAIN DOWN DEVICE 2X 6"x24" INLET WINDOW COBBLES FOR ENERGY DISSIPATION. 2X Ø24.00" BOLTED & GASKETED ACCESS COVERS, FIELD POURED CONCRETE COLLAR REQUIRED, BY OTHERS. INLET, Ø30" MAXIMUM OUTLET, Ø30" MAXIMUM BAFFLE WALL BAFFLE WALL DRAIN DOWN DEVICE SAUDFI132 5- 051 0USAXXXX 6'-0" (STANDARD) 2'-10" (STANDARD) BYPASS WEIR EL OUTLET IE SAUDFI 132 5- 051 0 USAXXXX2.2' [26"] DROP RECOMMENDED, 6" MIN. 7'-4" MINIMUM RIM TO INVERT OUT (STANDARD) Bioretention/ Biofiltration INTERNAL DRAWING ID REVISION OF SHEET MFG DRAWN ENGINEER CHECKEDDATE SALES ORDER REV DATE BioPod™ Biofilter Underground 12' x 24' Panel Vault with Internal Bypass THIS DOCUMENT IS THE PROPERTY OF OLDCASTLE INFRASTRUCTURE, INC. IT IS CONFIDENTIAL, SUBMITTED FOR REFERENCE PURPOSES ONLY AND SHALL NOT BE USED IN ANY WAY INJURIOUS TO THE INTERESTS OF, OR WITHOUT THE WRITTEN PERMISSION OF OLDCASTLE INFRASTRUCTURE, INC. COPYRIGHT © 2019 OLDCASTLE INFRASTRUCTURE, INC. ALL RIGHTS RESERVED. CUSTOMER JOB NAME 09/06/19 PPS ARG ARG 1BPU1224-IB-PV 1 Ph: 800.579.8819 | www.oldcastleinfrastructure.com/stormwater BPU1224-IB-PV.dwg, 2019-09-06 2:28 PM Generes, Ayn 6.691NOTES: 1.DESIGN LOADINGS: A.AASHTO HS-20-44 W/ IMPACT. B.DESIGN FILL: X' MAXIMUM. C.ASSUMED WATER TABLE = 5' BELOW GRADE. D.DRY LATERAL EARTH PRESSURE (EFP) = 40 PCF. E.LATERAL LIVE LOAD SURCHARGE = 80 PSF (APPLIED TO 8' BELOW GRADE). F.NO LATERAL SURCHARGE FROM ADJACENT BUILDINGS, WALLS, PIERS, OR FOUNDATIONS. 2.CONCRETE 28 DAY COMPRESSIVE STRENGTH SHALL BE 5,000 PSI MINIMUM. 3.STEEL REINFORCEMENT: REBAR, ASTM A-615 OR A-706, GRADE 60. 4.MESH REINFORCEMENT: ASTM A-1064, S1.2, GRADE 80. 5.CEMENT: ASTM C-150 SPECIFICATION. 6.REFERENCE STANDARD: A.ASTM C 890 B.ASTM C 913 7.THIS STRUCTURE IS DESIGNED TO THE PARAMETERS NOTED HEREIN. PLEASE VERIFY THAT THESE PARAMETERS MEET PROJECT REQUIREMENTS (I.E. LIVE LOAD, FILL RANGE, WATER TABLE). IF DESIGN PARAMETERS ARE INCORRECT, REVIEWING ENGINEER/AUTHORITY SHALL NOTIFY OLDCASTLE INFRASTRUCTURE UPON REVIEW OF THIS SUBMITTAL. 8.OVERSIZED HOLES TO ACCOMMODATE SPECIFIC PIPE TYPE MUST BE CONCENTRIC TO PIPE ID. AFTER PIPES ARE INSTALLED, ALL ANNULAR SPACES SHALL BE FILLED WITH A MINIMUM OF 3000 PSI CONCRETE FOR FULL THICKNESS OF PRECAST WALLS. 9.CONTRACTOR RESPONSIBLE TO VERIFY ALL SIZES, LOCATIONS AND ELEVATIONS OF OPENINGS. 10.CONTRACTOR RESPONSIBLE TO ENSURE ADEQUATE BEARING SURFACE IS PROVIDED (I.E. COMPACTED AND LEVEL PER PROJECT SPECIFICATIONS). 11.ADAPTORS/ANGLES AND EXTERNAL PIPING BY OTHERS. 12.SYSTEM SHIPPED EMPTY. INTERNAL PIPE, FILTER MEDIA & DRAIN ROCK PROVIDED IN BULK & INSTALLED BY OTHERS. 13.MAXIMUM PICK WEIGHT: = 50,740 LBS. (MEDIA SHIPPED SEPARATELY AND INSTALLED BY CONTRACTOR). 14.OLDCASTLE REPRESENTATIVE TO BE ON SITE TO OVERSEE THE INSTALLATION OF ALL INTERNAL COMPONENTS BY INSTALLING CONTRACTOR. BPU1224-IB-PV *WADOE GULD APPROVED* Max Treatment Flow = 0.86 cfs Max Peak Flow = 20 cfs 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 (IE) Inlet Outlet Notes: EXHIBIT C     TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use           APPENDIX B      WWHM2012 OUTPUT REPORTS           WWHM2012 PROJECT REPORT WATER QUALITY ANAYLSIS FNW WATER QUALITY 3/19/2021 2:05:03 PM Page 2 General Model Information Project Name:FNW WATER QUALITY Site Name: Site Address: City: Report Date:3/19/2021 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.000 Version Date:2019/09/13 Version:4.2.17 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year FNW WATER QUALITY 3/19/2021 2:05:03 PM Page 3 Landuse Basin Data Predeveloped Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Mod 7.43 Pervious Total 7.43 Impervious Land Use acre Impervious Total 0 Basin Total 7.43 Element Flows To: Surface Interflow Groundwater FNW WATER QUALITY 3/19/2021 2:05:03 PM Page 4 Mitigated Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Mod 1.73 Pervious Total 1.73 Impervious Land Use acre ROADS MOD 0.32 ROOF TOPS FLAT 1.6 PARKING MOD 3.78 Impervious Total 5.7 Basin Total 7.43 Element Flows To: Surface Interflow Groundwater WATER QUALITY TREATMENT RATE ANALYSIS DOES NOT INCLUDE AREAS OF THE EXISTING DETENTION POND AND WETLANDS. THE WATER QUALITY RATE DOES INCLUDE / ACCOUNT FOR AREAS CONSIDERED TO BYPASS THE POND DUE TO TOPOGRAPHY. FNW WATER QUALITY 3/19/2021 2:05:03 PM Page 7 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:7.43 Total Impervious Area:0 Mitigated Landuse Totals for POC #1 Total Pervious Area:1.73 Total Impervious Area:5.7 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.22123 5 year 0.362504 10 year 0.453341 25 year 0.561396 50 year 0.636241 100 year 0.706151 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 2.535363 5 year 3.268036 10 year 3.7841 25 year 4.472857 50 year 5.013463 100 year 5.578365 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.255 3.413 1950 0.302 3.310 1951 0.483 2.039 1952 0.152 1.584 1953 0.123 1.922 1954 0.188 2.045 1955 0.301 2.411 1956 0.242 2.134 1957 0.195 2.534 1958 0.217 2.065 FNW WATER QUALITY 3/19/2021 2:05:29 PM Page 13 Water Quality Water Quality BMP Flow and Volume for POC #1 On-line facility volume:0.7519 acre-feet On-line facility target flow:0.9831 cfs. Adjusted for 15 min:0.9831 cfs. Off-line facility target flow:0.5509 cfs. Adjusted for 15 min:0.5509 cfs.     TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use       APPENDIX C      SPECIAL REPORTS AND STUDIES     GEOTECHNICAL ENGINEERING REPORT - DRAFT Proposed Mixed-use Development South 348th Street & 1st Avenue South Federal Way, Washington Project No. 1536.01 4 December 2015 Prepared for: FNW, Inc. Prepared by: Zipper Geo Associates, LLC Geotechnical and Environmental Consultants 19023 36th Avenue W., Suite D Lynnwood, WA 9803 ZGA Zipper Geo Associates, LLC Geotechnical and Environmental Consulting 19023 36th Avenue West, Suite D Lynnwood, WA 98036 (425) 582-9928 Project No. 1536.01 4 December 2015 FNW, Inc. 2711 West Valley Highway North, Suite 200 Auburn, Washington 98001 Attention: Mr. Brett Jacobsen Subject: Geotechnical Engineering Report - DRAFT Proposed Mixed-use Development South 348th Street & 1st Avenue South Federal Way, Washington Dear Brett: In accordance with your request and written authorization, Zipper Geo Associates, LLC (ZGA) has completed the geotechnical engineering evaluation for the proposed multi-use development in Federal Way, Washington. This report presents the findings of the subsurface exploration and laboratory testing and presents our geotechnical recommendations for the project. Our services have been completed in general accordance with our Scope of Services and Fee Estimate (Proposal No. P15250) dated 16 September 2015. Written authorization to proceed was provided by FNW, Inc. on 4 November 2015. We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report, or if we may be of further service, please contact us. Sincerely, Zipper Geo Associates, LLC David C. Williams, LG, LEG Thomas A. Jones, PE Principal Engineering Geologist Managing Principal Copies: Addressee (1 electronic) TABLE OF CONTENTS Page INTRODUCTION ........................................................................................................................................... 1 SITE DESCRIPTION ..................................................................................................................................... 1 PROJECT UNDERSTANDING..................................................................................................................... 1 SURFACE CONDITIONS ............................................................................................................................. 1 SUBSURFACE CONDITIONS...................................................................................................................... 2 Regional Geology ............................................................................................................................................. 2 Soil Conditions ................................................................................................................................................. 2 Groundwater Conditions ................................................................................................................................. 4 CONCLUSIONS AND RECOMMENDATIONS ............................................................................................ 4 General .......................................................................................................................................................... 4 Regulated Geologic Hazard Environmentally Critical Areas ............................................................................ 4 Seismic Design Considerations ........................................................................................................................ 6 Site Preparation ............................................................................................................................................... 6 Structural Fill ................................................................................................................................................... 9 Utility Trenches ............................................................................................................................................. 11 Temporary and Permanent Slopes ................................................................................................................ 12 Shallow Foundations ..................................................................................................................................... 13 Backfilled Permanent Retaining Walls .......................................................................................................... 14 On-Grade Concrete Slabs .............................................................................................................................. 15 Drainage Considerations ............................................................................................................................... 15 Asphalt Pavements ........................................................................................................................................ 16 Stormwater Management Considerations .................................................................................................... 17 CLOSURE ................................................................................................................................................... 19 FIGURES Figure 1 – Site and Exploration Plan Figure 2 – Building Location Plan APPENDICES Appendix A – Subsurface Exploration Procedures and Logs Appendix B – Laboratory Testing Procedures and Results Page 1 GEOTECHNICAL ENGINEERING REPORT - DRAFT PROPOSED MIXED-USE DEVELOPMENT SOUTH 348TH STREET & 1ST AVENUE SOUTH FEDERAL WAY, WASHINGTON Project No. 1536.01 4 December 2015 INTRODUCTION This report documents the surface and subsurface conditions encountered at the site and our geotechnical engineering recommendations for the proposed Federal Way mixed-use development. The project description, site conditions, and our geotechnical conclusions and design recommendations are presented in the text of this report. Supporting data including detailed exploration logs and field exploration procedures, and results of laboratory testing are presented as appendices. SITE DESCRIPTION The project site is a largely undeveloped parcel located in the southeast quadrant of the 1st Avenue South and South 348th Street intersection and occupies approximately 8.3 acres. Undeveloped properties border the site to the east and south. The adjacent undeveloped properties have been mapped as wetlands on the City of Federal Way Critical Areas Map (September 2012). The site is illustrated on the Site and Exploration Plan, Figure 1. PROJECT UNDERSTANDING We understand that the proposed site improvements will include constructing one single-story wood- framed retail building (Building A) in the northwest portion of the site and two four-story wood-framed apartment buildings to the east and south (Buildings B and C) as illustrated on the Building Location Plan, Figure 2. The buildings will be serviced by asphalt paved parking and access drives, and Buildings B and C will include partial below-grade parking. Stormwater management is expected to include use of the existing detention ponds and likely some form of LID management elements, although these have yet to be selected. Moderate cuts and fills will be required to achieve site grades. SURFACE CONDITIONS The property is partially developed in that three detention ponds occupying approximately the southeastern 1.5 acres were constructed a few years ago. The detention pond area is bordered by chain- link fence and is accessed by about a 275-foot long gravel access road extending east from 1st Avenue South. The site gradually slopes downward from the northwest corner to the south and west at an approximate overall 10H:1V gradient. However, the western border of the site and approximately the Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 2 northwestern 275 feet of the site slopes down to 1st Avenue South and 348th Street with approximately 8 to 12-foot tall slopes inclined as steeply as approximately 45 to 50 percent. The slopes appear to be cut slopes, probably graded in association with construction of South 348th Street and 1st Avenue South. Total relief on the site is about 50 feet from north to south. Vegetation is varied and includes stands of mature trees, blackberry bushes, brush, and grass. Scattered debris (pieces of pipe, ecology blocks, and small piles of gravel), the obvious cut made for the existing access road, and slightly irregular topography indicate that some limited grading occurred in portions of the site other than the detention ponds. SUBSURFACE CONDITIONS Regional Geology We assessed the geologic setting of site and the surrounding vicinity by reviewing the following publication:  Booth, DB, Waldron, HH, and Troost, KG, Geologic map of the Poverty Bay 7.5’ Quadrangle, King and Pierce Counties, Washington, US Geological Survey Scientific Investigations Map 2854, 1:24,000, 2004. The published geologic mapping indicates the site and vicinity are underlain by Vashon glacial till (Qvt). Glacial till is typically composed of silt, sand, gravel, cobbles, and boulders. The till is glacially consolidated and when intact is characterized by a loose to medium dense weathered horizon on the order of about 2 to 4 feet thick underlain by denser unweathered material. Unweathered till typically has a relatively high density, relatively low permeability, and is generally well-suited for support of shallow foundations. The partially developed nature of the site suggests that fill material may be present as well. Both native till and some fill material were encountered in our test pits. Soil Conditions The subsurface evaluation for this project included excavating twelve test pits located approximately as shown on the Site and Exploration Plan, Figure 1. Descriptive logs of the subsurface explorations and the procedures utilized in the subsurface exploration program are presented in Appendix A. A generalized description of soil conditions encountered at the exploration locations is presented below. Detailed descriptions of soils encountered are provided on the descriptive logs in Appendix A. The soil descriptions presented below have been generalized for ease of report interpretation. Please refer to the test pit logs for more detailed soil descriptions. Variations in subsurface conditions may exist in proximity to exploration locations and the nature and extent of such variation may not become evident Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 3 until construction. If variations then appear, it may be necessary to reevaluate the recommendations of this report. The test pits disclosed subsurface conditions that were generally consistent with the published mapping. Subsurface conditions at the exploration locations are summarized below. Undocumented Fill Probable fill material was observed at six of the exploration locations (test pits 3, 4, 6, 7, 8, and 12). The fill depth in five of the test pits generally ranged from approximately 1 to 2 feet and was located either near the detention ponds or the adjacent roadways. The fill composition varied, but generally consisted of sandy silt with gravel with a varied organic content. The fill was underlain by a relic topsoil horizon at the locations of test pits TP-3 and TP-12. It should be noted that the character and depth of undocumented fill may vary over relatively short distances. In addition to the fill observed at and below grade as described above, a 6 to 10-foot tall stockpile is present to the northwest of the detention pond and at the location of TP-7. The material in the stockpile consisted of brown silty sand with some gravel. Based upon the observed composition and location it is likely that the stockpile was generated by stripping topsoil during construction of the detention pond area, in our opinion. The fill observed at the test pit locations and in the stockpile is considered undocumented in that it appears to have been placed in a non-engineered condition and due to its composition and density is considered inadequate for support of structures, pavements, and utilities without mitigation. Topsoil / Forest Duff All of the explorations disclosed a surficial horizon of organic topsoil that ranged in thickness from approximately 6 inches to 1 foot. In general the topsoil horizon consisted of brown silty sand with gravel, and contained fine to medium roots throughout. In some locations roots were observed to extend below the organic-rich topsoil horizon. Glacial Till The topsoil was underlain by glacial till that typically consisted of medium dense to very dense silty gravelly sand with occasional cobbles up to approximately 12 inches in diameter. Although not observed at the test pit locations, boulders are commonly present within the till. The upper 1 to 3 feet of the glacial till consisted of a medium dense to dense, light orange to brown weathered zone. Below the weathered till we generally observed dense to very dense, gray, silty gravelly sand with some sandy silt horizons with scattered cobbles. Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 4 Groundwater Conditions Groundwater was not observed in any of the twelve test pits at the time of excavation. It should be noted that groundwater conditions may fluctuate seasonally due to variations in precipitation, land use, irrigation, or other factors. CONCLUSIONS AND RECOMMENDATIONS General The proposed mixed-use development will include the construction of single-story retail building (Building A) in the northwest portion of the site as well as two multi-story retail/apartment buildings (Buildings B and C) to the east and south. Building A will be at grade, while Buildings B and C will include partial below- grade parking. A grading plan had not been provided for our review at the time this report was written, but from preliminary building grades it appears that overall grading will primarily involve cutting the higher northern and western portions of the site to better match the grades of the adjacent streets to the north and west. Tiered retaining walls will be constructed along the southern portions of Buildings B and C. The proposed building layout is illustrated on Figure 2, the Building Location Plan. Based on the results of the subsurface exploration program and our analysis, we have concluded that the proposed development is feasible from the geotechnical perspective, contingent on proper design and construction practices and implementation of the recommendations presented in this report. Geotechnical engineering recommendations for foundation systems and other earthwork related phases of the project are outlined below. The recommendations contained in this report are based upon the results of the field exploration and laboratory testing, engineering analyses, and our current understanding of the proposed project. ASTM and Washington State Department of Transportation (WSDOT) specification codes cited herein respectively refer to the current manual published by the American Society for Testing & Materials and the current edition of the Standard Specifications for Road, Bridge, and Municipal Construction, (Publication M41-10). Regulated Geologic Hazard Environmentally Critical Areas The City of Federal Way regulates certain geologic hazards including areas susceptible to erosion, landsliding, seismic, or other geological events, as well as defined steep slopes. These areas are defined Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 5 in Section 15.05.030 of the Federal Way Revised Code (FWRC). A summary of the regulated geologically hazardous critical areas is presented below. Erosion Hazard The FWRC defines erosion hazard areas as having a severe to very severe erosion hazard due to natural agents such as wind, rain, splash, frost action, or stream flow. Mapping obtained from the USDA Natural Resources Conservation Service (NRCS) indicates that the site has been characterized by the Everett- Alderwood gravelly sand loam soils, 6 to 15 percent (EwC). These soils are formed in glacial till parent material and are described as presenting a slight to moderate erosion hazard. Consequently, the site does not meet the SMP criteria as an erosion hazard. Provided that site grading and construction occur in accordance with a Temporary Erosion and Sedimentation Control (TESC) plan approved by the City of Federal Way, and provided that TESC BMPs are adequately maintained during construction, it is our opinion that the risk of significant sediment generation and off-site sediment transport is low. The site is not designated as an erosion hazard area on the City’s September 2012 Critical Areas Map. Steep Slope Hazard A regulated steep slope is one with 10 or more feet of relief and an inclination of 40 percent or steeper. Based upon review of the topographic survey of the site provide to us, and our site observations, a slope segment meeting this definition is limited to a small section of the graded slope along the west side of the site bordering 1st Avenue South. The cut slopes along the west and north sides of the site are inclined at about 45 to 50 percent, and a segment of the west slope with approximately 10 to 12 feet of relief meets the criteria for a regulated steep slope. The southern end of this slope segment, which is approximately 120 feet long, is approximately 80 feet north of the site access drive. The approximate location of the steep slope is highlighted on Figure 1. Regrading of this slope is feasible from the geotechnical perspective. Landslide Hazard The FWRC defines landslide hazard areas as those areas potentially subject to episodic downslope movement of a mass of soil or rock with including a combination of slopes greater than 15 percent, permeable sediment, or with springs or groundwater seepage. The site is characterized by dense to very dense glacial till, and within the depths of the test pits or along the existing graded slopes along South 348th Street and 1st Avenue South and the detention ponds in the southeastern portion of the site, we did not observe permeable granular soils and groundwater seepage. The site does not meet the Code definition of a landslide hazard. Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 6 Seismic Hazard The FWRC defines a seismic hazard as an area subject to severe risk of earthquake damage as a result of soil liquefaction in areas underlain by cohesionless soils of low density and usually in association with a shallow groundwater table or of other seismically-induced settlement. The site is underlain by glacial till, a glacially consolidated soil characterized by a high density, and shallow groundwater is not present. As such, the risk of damage due to a seismic event is low, in our opinion. The site does not meet the Code definition of a seismic hazard. The site is not designated as a seismic hazard area on the City’s September 2012 Critical Areas Map. Seismic Design Considerations IBC Seismic Design Parameters: IBC Seismic Design parameters are summarized in the table below. Description Value 2012 IBC Site Classification C 1,2 SS Spectral Acceleration for a Short Period 1.286g (Site Class B) S! Spectral Acceleration for a 1-Second Period 0.495g (Site Class B) SMS Spectral Acceleration for a Short Period 1.286g (Site Class C) SM! Spectral Acceleration for a 1-Second Period 0.646g (Site Class C) 1. In general accordance with the 2012 International Building Code, Table 1613.5.2. 2. The 2012 International Building Code (IBC) requires a site soil profile determination extending a depth of 100 feet for seismic site classification. The approved scope did not include the complete 100 foot soil profile determination. The test pits performed for this evaluation extended to a maximum depth of approximately 15 feet, and this seismic Site Class C assignment considers that at least dense soils continue below the maximum depth of the subsurface exploration based upon published geologic mapping. Site Preparation Erosion Control Measures: The site has variable topography and significant grading is proposed. Consequently, the potential for construction phase erosion may be considered relatively high unless City- approved TESC BMPs are adequately designed, installed, and maintained. We recommend that silt fences, berms, and/or swales be installed around stripped areas and stockpiles in order to capture runoff water and sediment. If earthwork occurs during wet weather, we recommend covering stripped surfaces with straw and protecting soil stockpiles with anchored plastic sheeting when areas are not being worked for long periods. Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 7 Temporary Drainage: Stripping, excavation, grading, and subgrade preparation should be performed in a manner and sequence that will provide drainage at all times and provide proper control of erosion. The site should be graded to prevent water from ponding in construction areas and/or flowing into excavations. Exposed grades should be crowned, sloped, and smooth-drum rolled at the end of each day to facilitate drainage if inclement weather is forecasted. Accumulated water must be removed from subgrades and work areas immediately and prior to performing further work in the area. The site soils have a relatively high fines content and should be considered highly moisture-sensitive. As such, equipment access may be limited and the amount of soil rendered unfit for use as structural fill may be greatly increased if drainage efforts are not accomplished in a timely manner. Stripping: In preparation for grading we recommend removal of all existing vegetation, root grubbing, and removal of existing fill material containing organic or deleterious material. This would include the stockpile located northwest of the detention ponds. Organic-rich topsoil (soils containing more than 4 percent organic material by weight) will need to be stripped from structure and pavement locations, as well as those areas to receive structural fill. The thickness of organic duff and topsoil observed at the test pit locations ranged from about 6 to 12 inches, and roots extended to depths of about 18 inches. However, variation in the organic material thickness should be expected; deeper accumulations of organics may be encountered in depressions and around root masses. Duff and topsoil should be removed and should not be reused as structural fill. Organic materials may be used in landscaping. Stripping is recommended to include removal of undocumented fill material and any relic organic topsoil below the fill due to the risk of future settlement if these materials are left in place. The undocumented fill we observed at the test pit locations was typically in a loose condition and in some locations contained organic material as well as debris. The depth of the fill ranged from approximately 1.5 to 2 feet (not including the stockpile of strippings at the test pit TP-7 location) and relic topsoil was observed to about a foot below the fill at the locations of test pits TP-3 and TP-12. Variation in the fill depth and composition, and the depth of organics below the fill, should be expected. These materials should be removed under the observation of a ZGA representative. Our representative will identify unsuitable materials that should be removed and those that may be re-used as structural fill. The resultant excavations should be backfilled in accordance with the subsequent recommendations for structural fill placement and compaction. We recommend that site preparation activities take place in the drier summer months. Operating wheeled and tracked equipment when the weathered glacial till soils are wet will result in significant disturbance of the non-organic weathered glacial till soils and likely requiring its removal. This will increase construction costs. Completion of logging and stripping under dry site and weather conditions will reduce the potential for disturbance of the weathered till soils and reduce the likelihood of subgrade disturbance and the need to replace disturbed soils with imported granular fill. Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 8 Subgrade Preparation: Once stripping has been completed, all areas that are at design subgrade elevation or areas that will receive new structural fill should be compacted to a firm and unyielding condition and to a compaction level of at least 95 percent of the maximum laboratory density (per ASTM D 1557) within the upper 12 inches. Some moisture conditioning of site soils may be required to achieve an appropriate moisture content for compaction within ±2 percent of the soils laboratory optimum moisture content, particularly during the warmer summer months when the soils will tend to dry relatively quickly when exposed to sun and wind. Subgrades should be evaluated through density testing and proof rolling with a loaded dump truck or heavy rubber-tired construction equipment in order to detect soft and/or yielding soils. In the event that soft or yielding areas are detected during proof rolling, the upper 12 inches of subgrade should be scarified, moisture conditioned and re-compacted as necessary to obtain at least 95 percent of the maximum laboratory density (per ASTM D 1557) and to a firm, non-yielding condition. Those soils which are soft/loose, yielding, or unable to be compacted to the specified criteria should be over-excavated and replaced with suitable material as recommended in the Structural Fill section of this report. If subgrade compaction during wet site conditions or wet weather cannot be achieved, a minimum of 12 inches of subgrade should be over-excavated and backfilled with compacted imported structural fill consisting of free-draining Gravel Borrow or crushed rock. A stabilization geotextile could be used in unstable areas to reduce the depth of over-excavation. We recommend completing earthwork during drier periods of the year when the soil moisture content can be controlled by aeration and drying, if necessary. If earthwork or construction activities take place during extended periods of wet weather, the site-characteristic glacial till may become unstable or not be compactable. In the event the exposed subgrade becomes unstable, yielding, or unable to be compacted due to high moisture conditions, we recommend that the affected material be removed to a sufficient depth in order to develop a stable subgrade that can be compacted to the minimum recommended levels. The severity of construction problems will be dependent, in part, on the precautions that are taken by the contractor to protect the subgrade soils. Once subgrades are compacted, it may be desirable to protect prepared subgrades such as building pads or haul roads. To protect stable subgrades, we recommend using crushed rock. The thickness of the protective layer should be determined at the time of construction and be based on the moisture condition of the soil and the amount of anticipated traffic. Freezing Conditions: If earthwork takes place during freezing conditions, all exposed subgrades should be allowed to thaw and then be compacted prior to placing subsequent lifts of structural fill. Alternatively, the frozen material could be stripped from the subgrade to expose unfrozen soil prior to placing subsequent lifts of fill or foundation components. The frozen soil should not be reused as structural fill Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 9 until allowed to thaw and adjusted to the proper moisture content, which may not be possible during winter months. Structural Fill Structural fill includes any material placed below foundations and pavement sections, within utility trenches, and behind retaining walls. Prior to the placement of structural fill, all surfaces to receive fill should be prepared as previously recommended in the Site Preparation section of this report. Laboratory Testing: Representative samples of imported soil to be used as structural fill should be submitted for laboratory testing at least four days in advance of its intended use in order to complete the necessary Proctor tests. Re-use of Site Soils as Structural Fill: The non-organic native soil encountered on the site is adequate for use as general structural fill from a compositional standpoint provided the soil is placed and compacted in accordance with the compaction recommendations presented in this report. Soil will need to be near the optimum moisture content in order to compact it to the recommended density. Drying of over- optimum moisture soils may be achieved by scarifying or windrowing surficial materials during extended periods of dry weather. If encountered, soils which are dry of optimum may be moistened through the application of water and thorough blending to facilitate a uniform moisture distribution in the soil prior to compaction. Simply moistening the upper surface of a loose lift of the site soils will not allow adequate distribution of the water in the lift; blending will be necessary to achieve an adequate moisture distribution in the lift. We recommend that site soils used as structural fill have less than 4 percent organics by weight as determined by the ASTM D 2974 and have no woody debris greater than ½ inch in diameter. We recommend that all pieces of organic material greater than ½ inch in diameter be picked out of the fill before it is compacted. Any organic-rich soil derived from earthwork activities should be utilized in landscape areas or wasted from the site. Imported Structural Fill: In the event that imported structural fill is required, the appropriate type of imported structural fill will depend on weather conditions. During extended periods of dry weather, we recommend that imported fill, at a minimum, meet the requirements of Common Borrow as specified in Section 9-03.14(3) of the 2014 Washington State Department of Transportation, Standard Specifications for Road, Bridge, and Municipal Construction (Publication M41-10). During wet weather, higher-quality structural fill might be required, as Common Borrow may contain sufficient fines to be moisture-sensitive. During wet weather we recommend that imported structural fill meet the requirements of Gravel Borrow as specified in Section 9-03.14(1) of the WSDOT Standard Specifications. Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 10 Retaining Wall Backfill: Retaining walls should include a drainage fill zone extending at least 2 feet back from the back face of wall for the entire wall height. The drainage fill should meet the requirements of Gravel Backfill for Walls as specified in Section 9-03.12(2) of the WSDOT Standard Specifications. Pavement Subgrades: Any structural fill used within the upper one foot of pavement subgrades should have a minimum California Bearing Ratio (CBR) of at least 15 when compacted to 95 percent of the modified Proctor maximum dry density. Based on our experience and correlations between soil type and CBR values, we have considered that a CBR value of 15 is representative of the native soil and has been used to develop our pavement section recommendations. Our design recommendations assume that imported fill types as recommended above (Common Borrow or Gravel Borrow) will meet the minimum CBR requirement. However, samples of proposed imported fill should be submitted for laboratory testing and approval prior to use. Moisture Content: The suitability of soil for use as structural fill will depend on the time of year, the moisture content of the soil, and the fines content (that portion passing the US No. 200 sieve) of the soil. As the amount of fines increases, the soil becomes increasingly sensitive to small changes in moisture content. Soils containing more than about 5 percent fines cannot be consistently compacted to the appropriate levels when the moisture content is more than approximately 2 percent above or below the optimum moisture content (per ASTM D1557). The optimum moisture content is that moisture content which results in the greatest compacted dry density with a specified compactive effort. The fines content of the samples tested in our laboratory ranged from approximately 18 to 24 percent. Consequently, the soils should be considered highly moisture-sensitive. The moisture content of the samples of native soil that we tested indicated that the soils were generally in a moist to wet condition relative to an anticipated modified Proctor maximum dry density. However, soil moisture contents at the time of construction should be expected to vary from our test results. Fill Placement: Structural fill should be placed in horizontal lifts not exceeding 12 inches in loose thickness. Thinner lifts may be required depending up the soil conditions and the type of compaction equipment in use. Each lift of fill should be compacted using compaction equipment suitable for the soil type and lift thickness. Each lift of fill should be compacted to the minimum levels recommended below based on the maximum laboratory dry density as determined by the ASTM D 1557 testing procedure (modified Proctor). The moisture content of fill at the time of placement should be within plus or minus 2 percent of optimum moisture content for compaction as determined by the ASTM D 1557 test method. Compaction Criteria: Our recommendations for soil compaction are summarized in the following table. Structural fill for roadways and utility trenches in municipal rights-of-way should be placed and compacted in accordance with the City of Federal Way standards. We recommend that a ZGA representative be Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 11 present during grading so that an adequate number of density tests may be conducted as structural fill placement occurs. In this way, the adequacy of the earthwork may be evaluated as it proceeds. RECOMMENDED SOIL COMPACTION LEVELS Location Minimum Percent Compaction* Stripped native subgrade soils, prior to fill placement (upper 12 inches) 95 All fill below building floor slabs and foundations 95 Upper 2 feet of fill below pavements 95 Conventional pavement fill below two feet 90 Retaining wall backfill less than 3 feet from wall 90 Retaining wall backfill more than 3 feet from wall 95 Utility trench backfill 95 Landscape Areas 88 - 90 * ASTM D 1557 Modified Proctor Maximum Dry Density Utility Trenches We recommend that utility trenching conform to all applicable regulations, such as OSHA, for open excavations. Trench excavation safety guidelines are presented in 29 CFR 1926.650, 1926.651, and 1926.652. Trench Dewatering: Groundwater was not observed at the test pit locations, and the observed soil conditions did not suggest the presence of groundwater within the anticipated excavation depths. We do not anticipate that trench dewatering will be required. Utility Subgrade Preparation: We recommend that all utility subgrades be firm and unyielding and free of all soils that are loose, disturbed, or pumping. Such soils should be removed and replaced, if necessary. All structural fill used to replace over-excavated soils should be compacted as recommended in the Structural Fill section of this report. If utility foundation soils are soft, we recommend that they be over- excavated 12 inches and replaced with compacted crushed rock. Bedding: We recommend that a minimum of 4 inches of bedding material be placed above and below all utilities or in general accordance with the utility manufacturer’s recommendations and local requirements. We recommend that pipe bedding consist of Gravel Backfill for Pipe Zone Bedding as described in Section 9-03.12(3) of the WSDOT Standard Specifications. All trenches should be wide enough to allow for compaction around the haunches of the pipe, or material such as pea gravel should Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 12 be used below the spring line of the pipes to eliminate the need for mechanical compaction in this portion of the trenches. If water is encountered in the excavations, it should be removed prior to fill placement. Trench Backfill: Materials, placement and compaction of utility trench backfill should be in accordance with the recommendations presented in the Structural Fill section of this report. We recommend that the initial lift thickness not exceed one foot unless recommended by the manufacturer to protect utilities from damage by compacting equipment. Light hand operated compaction equipment may be utilized directly above utilities if damage resulting from heavier compaction equipment is of concern. Temporary and Permanent Slopes Temporary excavation slope stability is a function of many factors, including:  The presence and abundance of groundwater;  The type and density of the various soil strata;  The depth of cut;  Surcharge loadings adjacent to the excavation; and  The length of time the excavation remains open. As a cut is deepened, or as the length of time an excavation is open, the likelihood of bank failure increases; therefore, maintenance of safe slopes and worker safety should remain the responsibility of the contractor, who is present at the site, able to observe changes in the soil conditions, and monitor the performance of the excavation. It is exceedingly difficult under the variable circumstances to pre-establish a safe and “maintenance-free” temporary cut slope angle. Therefore, it should be the responsibility of the contractor to maintain safe temporary slope configurations since the contractor is continuously at the job site, able to observe the nature and condition of the cut slopes, and able to monitor the subsurface materials and groundwater conditions encountered. Unsupported vertical slopes or cuts deeper than 4 feet are not recommended if worker access is necessary. The cuts should be adequately sloped, shored, or supported to prevent injury to personnel from local sloughing and spalling. The excavation should conform to applicable Federal, State, and Local regulations. According to OSHA regulations, the contractor should make a determination of excavation side slopes based on classification of soils encountered at the time of excavation. Temporary cuts may need to be constructed at flatter angles based upon the soil moisture and groundwater conditions at the time of construction. Adjustments to the slope angles should be determined by the contractor at that time. It should be noted that much of the native soil encountered in excavations is expected to consist of relatively clean sand and gravel and may be susceptible to rapid collapse in unsupported conditions. Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 13 We recommend that all permanent cut or fill slopes constructed in native soils or with imported structural fill be designed at a 2H:1V inclination or flatter. All permanent cut and fill slopes should be adequately protected from erosion both temporarily and permanently. If the slopes are exposed to prolonged rainfall before vegetation becomes established, the surficial soils will be prone to erosion and possible shallow sloughing. We recommend covering permanent slopes with a rolled erosion protection product, such as coir matting or Curlex II, if vegetation has not been established by the wet season (typically November through May). Shallow Foundations Based on our analyses, conventional spread footings will provide adequate support for the proposed buildings provided that the foundation subgrades are properly prepared. We anticipate that foundation subgrade soils will generally consist of native glacial till or compacted structural fill. Allowable Bearing Pressure: Continuous and isolated column footings bearing on undisturbed, dense to very dense native glacial till may be designed for a maximum allowable net bearing capacity of 5,000 psf. Foundations bearing on structural fill placed and compacted in accordance with the recommendations presented herein may be designed for a maximum allowable net bearing capacity of 2,500 psf. A one- third increase of these bearing pressures may be used for short-term transient loads such as wind and seismic forces. The above-recommended allowable bearing pressures include a factor of safety of 3. Shallow Foundation Depth and Width: For frost protection, the bottom of all exterior footings should bear at least 18 inches below the lowest adjacent outside grade, whereas the bottoms of interior footings should bear at least 12 inches below the surrounding slab surface level. We recommend that all continuous wall and isolated column footings be at least 12 and 24 inches wide, respectively. Lateral Resistance: Resistance to lateral loads can be calculated assuming an ultimate passive resistance of 540 pcf equivalent fluid pressure (triangular distribution) and an ultimate base friction coefficient of 0.5. An appropriate safety factor (or load/resistance factors) should be included for calculating resistance to lateral loads. For allowable stress design, we recommend a minimum 1.5 safety factor. We recommend neglecting passive resistance in the upper 18 inches of embedment. Estimated Static Settlement: Assuming the foundation subgrade soils are prepared in accordance with recommendations presented herein, we estimate that total static settlement may approach 0.75 inches and differential static settlement may approach half the total settlement over a distance of about 40 feet. Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 14 Backfilled Permanent Retaining Walls The project is expected to include backfilled cast-in-place (cip) concrete retaining walls, primarily along the southern portions of Buildings B and C. For recommended bearing capacities and lateral resistance parameters, refer to the Shallow Foundations section above. Additional recommendations for these structures are provided below. Lateral Earth Pressures: The lateral soil pressures acting on backfilled retaining walls will depend on the nature and density of the soil behind the wall, and the ability of the wall to yield in response to the earth loads. Yielding walls (i.e. walls that are free to translate or rotate) that are able to displace laterally at least 0.001H, where H is the height of the wall, may be designed for active earth pressures. Non-yielding walls (i.e. walls that are not free to translate or rotate) should be designed for at-rest earth pressures. Non-yielding walls include walls that are braced to another wall or structure, and wall corners. Assuming that walls are backfilled and drained as described in the following paragraphs, we recommend that yielding walls supporting horizontal backfill be designed using an equivalent fluid density of 35 pcf (active earth pressure). Non-yielding walls should be designed using an equivalent fluid density of 50 pcf (at-rest earth pressure). Design of permanent retaining walls should consider additional earth pressure resulting from the design seismic event. For the seismic case, yielding walls should be designed for a uniform (rectangular), total earth pressure distribution of 10H and non-yielding walls should be designed for a uniform, total earth pressure distribution of 18H. The recommended total earth pressure distributions for the seismic case include both the seismic and static components of earth pressures (i.e. the active or at-rest static components of 35 pcf or 50 pcf should not be added to the total uniform pressure distribution). For cantilever cast-in-place walls, the total earth pressure distributions for the seismic case should be applied from finished grade at the bottom of the wall to the top of wall. The above-recommended lateral earth pressures do not include the effects of sloping backfill surfaces, surcharges such as traffic loads, other surface loading, or hydrostatic pressures. If such conditions exist, we should be consulted to provide revised earth pressure recommendations. Tiered Wall Considerations: Preliminary architectural drawings provided for our review indicated that some of the retaining walls will be constructed in a tiered configuration. We recommend configuring the walls such that the foundations of walls above a lower wall not intrude past a 1H:1V slope extended upward from the base of the lower wall. Otherwise, it will be necessary to design successive lower walls to accommodate the additional lateral earth pressures resultant from the loading of the upper wall(s). Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 15 Wall Drainage: Adequate drainage measures must be installed to collect and direct subsurface water away from retaining walls. All backfilled walls should include a drainage aggregate zone extending at least 2 feet from the back of wall for the full height of the wall. The drainage aggregate should consist of material meeting the requirements of WSDOT 9-03.12(2) Gravel Backfill for Walls. We did not observe at the test pit locations any soils that would meet the gradational requirements for wall backfill, so it will be necessary to import the wall drainage aggregate. A minimum 4-inch diameter perforated rigid thermoplastic drain pipe should be provided at the base of backfilled walls to collect and direct subsurface water to an appropriate discharge point. Drain pipe perforations should be protected using a non-woven geotextile fabric such as Mirafi 140N in order to prevent soil particles from entering the pipe. Wall drainage systems should be independent of other drainage systems such as roof drains. We recommend incorporating cleanouts in wall drainage systems. On-Grade Concrete Slabs The following sections provide recommendations for on-grade floor slabs. Subgrade Preparation: Subgrades for on-grade slabs should be prepared in accordance with the Site Preparation and Structural Fill sections of this report. Capillary Break: We recommend the on-grade slabs be underlain by a minimum 4-inch thick layer of compacted granular fill consisting of coarse sand and fine gravel containing less than 5 percent fines, based on that soil fraction passing the US No. 4 sieve. Alternatively, a clean angular gravel such as No. 7 Aggregate per WSDOT 9-03.1(4) C could be used for this purpose. Alternative capillary break materials should be submitted to ZGA for review and approval before use. Vapor Retarder: The use of a vapor retarder should be considered beneath concrete slabs on grade that will be covered with wood, tile, carpet or other moisture sensitive or impervious coverings, or when the slab will support equipment sensitive to moisture or is otherwise considered moisture-sensitive. When conditions warrant the use of a vapor retarder, the slab designer and contractor should refer to ACI 302 and/or ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder. We generally recommend a minimum 10 mil vapor retarder. Drainage Considerations Surface Drainage: Final site grades should be sloped to carry surface water away from the buildings and other drainage-sensitive areas. Additionally, site grades should be designed such that concentrated runoff toward softscape surfaces is avoided. Any surface runoff directed towards softscape slopes should be Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 16 collected at the top of the slope and routed to the bottom of the slope and discharged in a manner that prevents erosion. Building Foundation Drains: Similar to the retaining wall drains, building foundation drains are recommended to consist of a minimum 4-inch diameter, Schedule 40, rigid, perforated thermoplastic pipe placed at the base of the heel of the footing with the perforations facing down. The pipe should be surrounded by a minimum of 6 inches of clean free-draining granular material conforming to WSDOT Standard Specification 9-03.12(4), Gravel Backfill for Drains or similar gradation material. A non-woven geotextile fabric such as Mirafi 140N, or equivalent, should envelope the free-draining granular material. At appropriate intervals such that water backup does not occur, the drainpipe should be connected to a tightline system leading to a suitable discharge. Cleanouts should be provided for future maintenance. The foundation drains should be separate from the roof drain system. Asphalt Pavements Pavement Life and Maintenance: It should be realized that asphaltic pavements are not maintenance- free. The following pavement sections represent our minimum recommendations for an average level of performance during a 20-year design life; therefore, an average level of maintenance will likely be required. A 20-year pavement life typically assumes that an overlay will be placed after about 12 years. Thicker asphalt, base, and subbase courses would offer better long-term performance, but would cost more initially. Conversely, thinner courses would be more susceptible to “alligator” cracking and other failure modes. As such, pavement design can be considered a compromise between a high initial cost and low maintenance costs versus a low initial cost and higher maintenance costs. Please note that we made assumptions regarding traffic type and frequency in the absence of specific traffic count data. Soil Design Values: Pavement subgrade soils are anticipated to consist of the site-characteristic native glacial till (silty gravelly sand). Our analysis assumes the pavement section subgrade will have a CBR value of 15. This value is based upon published correlations between soil type and CBR values and our experience. Recommended Pavement Sections: For light duty pavements (parking stalls), we recommend 2.5 inches of asphalt concrete over either 4 inches of crushed surfacing base course or 3 inches of Asphalt Treated Base (ATB). For heavy duty pavements (main access routes, truck delivery routes), we recommend 3 inches of asphalt concrete over either 6 inches of crushed rock surfacing course or 4 inches of ATB. Areas subject to heavy surface loading, such as dumpster approach slabs that experience short-term high wheel loading, would benefit from either a thicker asphalt pavement section or the use of concrete pavement. Please note that using ATB instead of crushed surfacing base course below the pavement will provide limited opportunity for sub-pavement drainage and may shorten the pavement lifespan as the site soils Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 17 have a relatively low permeability. Placing some clean crushed surfacing base course below the ATB (such as 3 inches, for example) will improvement pavement section drainage. In the event that this is considered favorably, we can provide a revised pavement section that considers the value (other than drainage) contributed by free draining granular material below the ATB. Materials and Construction: We recommend the following regarding asphalt pavement materials and pavement construction.  Subgrade Preparation and Compaction: The upper 12 inches of native stripped subgrade should be prepared in accordance with the recommendations presented in the Subgrade Preparation section of this report, and all fill should be compacted in accordance with the recommendations presented in the Structural Fill section of this report.  Asphalt Concrete: We recommend that the asphalt concrete conform to Section 9-02.1(4) for PG 58-22 or PG 64-22 Performance Graded Asphalt Binder as presented in the 2014 WSDOT Standard Specifications. We also recommend that the gradation of the asphalt aggregate conform to the aggregate gradation control points for ½-inch mixes as presented in Section 9-03.8(6) HMA Proportions of Materials.  Base Course: We recommend that the crushed aggregate base course conform to Section 9-03.9(3) of the WSDOT Standard Specifications.  Compaction and Paving: All base material should be compacted to at least 95 percent of the maximum dry density determined in accordance with ASTM D 1557. We recommend that asphalt be compacted to a minimum of 92 percent of the Rice (theoretical maximum) density or 96 percent of Marshall (Maximum laboratory) density. Placement and compaction of asphalt should conform to requirements of Section 5-04 of the 2012 WSDOT Standard Specifications. Stormwater Management Considerations The site contains stormwater detention ponds constructed as part of a previous abandoned development effort. We understand that the City of Federal way will require some additional stormwater management features and that stormwater management improvements will need to comply with the King County 2009 Surface Water Design Manual (2009 Manual). Based on the findings of the field exploration, laboratory testing, and our analysis, conventional stormwater infiltration does not appear feasible from the geotechnical perspective given the relatively high fines content and the density of the unweathered glacial till that characterizes the site. The relatively Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 18 low permeability of the soils is illustrated by the fact that the on-site ponds retain water all year long, based upon our review of historic aerial photographs. We have concluded that limited stormwater infiltration as defined by the 2009 Manual may be feasible, but that the long-term infiltration rate that should be applied to the site soils will be relatively low. Preliminary Infiltration Rate Determination Our scope of services did not include field infiltration testing as required by the 2009 Manual as part of designing an infiltration system. However, conclusions regarding stormwater infiltration can be drawn from subsurface conditions disclosed by the subsurface explorations and laboratory testing completed to date. For reference, per the USDA textural classification method allowed under earlier versions of some stormwater manuals, the glacial till soils at the site are considered sandy loam and would under other circumstances be assigned a short-term infiltration rate on the order of 1 inch per hour and a long-term rate of 0.25 inches per hour using a previously recommended reduction factor of 4. A similar rate is obtained when correlating ASTM grain size distribution test data to observed infiltration system performance. However, these rates would be applicable to normally consolidated soils and do not consider the influence of soil density. The unweathered soils observed at the test pit locations are glacially consolidated, dense, and would be less permeable than the overlying weathered soils. Based upon our experience with other projects of a similar nature, we would recommend applying a reduction factor of at least 10 to the 1 inch per hour short-term rate to achieve a long-term infiltration rate of no greater than 0.1 inches per hour. Additional reductions of this rate applicable to the type of infiltration system that reflect the potential for lack of future maintenance and soil clogging used should be applied as well. Groundwater Considerations Groundwater was not observed at the test pit locations. However, the possibility exists that a seasonal perched groundwater condition may develop above the unweathered glacial till due to the relatively high density and high fines content of the soils. This condition may adversely affect the performance of systems that rely on infiltration, if on a limited basis. General Stormwater Infiltration Considerations One LID stormwater management technique that may be applicable to the site is the use of permeable pavements/hardscape surfaces. Given the low permeability of the native site soils, little infiltration of water passing through permeable surfaces should be expected. Consequently, it would likely be necessary to include a section of permeable crushed reservoir rock below the pavement, and this would increase the overall pavement section costs. The disposition of water in the reservoir rock section should be Zipper Geo Associates, LLC Proposed Mixed-use Development – DRAFT Federal Way, Washington Project No. 1536.01 4 December 2015 Page 19 considered and measures taken to present water flowing out from the rock section at pavement edges into areas where the water could be detrimental, such as immediately next to the buildings or along property boundaries. Installing perforated collection pipes in the reservoir rock section may be required as well. On sloping sites it may be necessary to include dams in the rock section in order to achieve the necessary storage capacity. It should be recognized that a conventional permeable pavement section on the site may not provide the necessary treatment for water originating form pollution generating surfaces and that other means of treatment will be necessary. The use of rain gardens in low permeability soils is increasingly common. Rain gardens typically include a zone of amended soil to provide for treatment of water originating from pollution generating surfaces, as well as a collection zone below consisting of clean washed rock that allows for conveyance of treated water to an appropriate discharge point. We recommend including overflow pipes in raingardens as well. CLOSURE The analysis and recommendations presented in this report are based, in part, on the explorations completed for this study, review of referenced documents, and laboratory testing results. We recommend ZGA be provided an opportunity to review the plans and specifications as the project progresses in order to assess that the recommendations and design considerations presented in this report have been properly interpreted and implemented into the project design. The performance of earthwork, structural fill, foundations, and pavements depend greatly on proper site preparation and construction procedures. We recommend that ZGA be retained to provide geotechnical engineering services during the earthwork-related construction phases of the project. If variations in subsurface conditions are observed at that time, a qualified geotechnical engineer could provide additional geotechnical recommendations to the contractor and design team in a timely manner as the project construction progresses. This report has been prepared for the exclusive use of FNW, Inc., and its agents, for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranties, express or implied, are intended or made. Site safety, excavation support, and dewatering requirements are the responsibility of others. In the event that changes in the nature, design, or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless ZGA reviews the changes and either verifies or modifies the conclusions of this report in writing. APPENDIX A FIELD EXPLORATION PROCEDURES & LOGS APPENDIX A FIELD EXPLORATION PROCEDURES AND LOGS Field Exploration Description The field exploration included excavating 12 test pits (TP-1 through TP-12) at the approximate locations shown on the Site and Exploration Plan, Figure 1. The locations of the test pits were determined by pacing and taping from site features shown on a topographic site map, dated 21 September, prepared by Prizm Surveying, Inc. Ground surface elevations at the test pit locations were interpolated from contours and spot elevations on the referenced site plan. The locations and elevations of the explorations should be considered as accurate as the methods used to determine them. Test Pit Procedures The test pits were excavated with a tracked excavator operated by an FNW, Inc. employee. A ZGA engineering geologist observed the test pit excavations, logged the subsurface conditions, and obtained representative soil samples. The samples were stored in moisture tight containers and transported to our laboratory for further visual classification and testing. The enclosed boring and test pit logs describe the vertical sequence of soils and materials encountered in each exploration, based primarily upon our field classifications. Where a soil contact was observed to be gradational, the logs indicate the average contact depth. Where a soil type changed between sample intervals, the contact depth has been inferred. The logs also graphically indicate the blow count, sample type, sample number, and approximate depth of each soil sample obtained from the boring. If groundwater was encountered in a borehole, the approximate groundwater depth, and date of observation, are depicted on the log. Test Pit TP-1 Location: See Site and Exploration Plan, Figure 1 Approx. Ground Surface Elevation: 243 feet Project: Federal Way Mixed-use Project No: 1536.01 Date Excavated: 11/12/15 Depth (ft) Material Description Sample NC %M Testing Grass over loose, moist to wet, dark brown, silty SAND, with gravel, fine to medium roots throughout (Topsoil) Medium dense to dense, moist, light orange to brown, silty SAND, with gravel (Weathered Glacial Till) Very dense, moist, gray, silty gravelly SAND (Glacial Till) Grades with scattered cobbles to 10-inch diameter TP-1 completed at approximately 15 feet. No groundwater seepage observed at time of excavation. 1 S-1 @ 0.5 ft. 17 2 S-2 @ 2 ft. 17 3 4 S-3 @ 4 ft. 14 5 6 7 8 9 S-4 @ 9 ft. 10 10 11 12 13 14 ` 15 S-5 @ 14.5 ft. 7 Test Pit TP-2 Location: See Site and Exploration Plan, Figure 1 Approx. Ground Surface Elevation: 244 feet Project: Federal Way Mixed-use Project No: 1536.01 Date Excavated: 11/12/15 Depth (ft) Material Description Sample NC %M Testing Grass over loose, moist to wet, brown, sandy SILT, with gravel, fine to medium roots throughout (Topsoil) Medium dense to dense, moist, light orange to brown, fine sandy SILT, with gravel (Weathered Glacial Till) Dense to very dense, moist, gray, silty gravelly SAND, trace cobbles to 10-inch diameter (Glacial Till) TP-2 completed at approximately 15 feet. No groundwater seepage observed at time of excavation. 1 S-1 @ 0.5 ft. 9 2 S-2 @ 2 ft. 9 3 4 S-3 @ 4 ft. 10 5 6 7 S-4 @ 7 ft. 10 8 9 10 11 12 13 14 ` 15 S-5 @ 14.5 ft. 6 Test Pit TP-3 Location: See Site and Exploration Plan, Figure 1 Approx. Ground Surface Elevation: 239 feet Project: Federal Way Mixed-use Project No: 1536.01 Date Excavated: 11/12/15 Depth (ft) Material Description Sample NC %M Testing Grass over loose, moist, brown, silty SAND, with gravel, fine roots throughout (Topsoil) Medium dense, moist, gray, sandy SILT, with gravel, some 10-inch diameter quarry spalls (Fill) Medium dense, moist, black, SILT, with sand, some gravel (Probable Relic Topsoil) Medium dense to dense, moist, light orange to brown, fine sandy SILT, with gravel (Weathered Glacial Till) Very dense, moist, gray, silty gravelly SAND, trace cobbles and boulders (Glacial Till) TP-3 completed at approximately 10 feet. No groundwater seepage observed at time of excavation. 1 S-1 @ 0.5 ft. S-2 @ 1 ft. 2 3 S-3 @ 2.5 ft. 4 S-4 @ 4 ft. 6 GSA 5 6 7 8 9 10 S-5 @ 9.5 ft. 11 12 Test Pit TP-4 Location: See Site and Exploration Plan, Figure 1 Approx. Ground Surface Elevation: 254 feet Project: Federal Way Mixed-use Project No: 1536.01 Date Excavated: 11/12/15 Depth (ft) Material Description Sample NC %M Testing Grass over loose, moist, brown, silty SAND, with gravel, fine roots in upper 10 inches (Possible fill) Medium dense, moist, light orange to brown, sandy SILT, with gravel, trace cobbles (Weathered Glacial Till) Very dense, moist, gray, silty gravelly SAND, trace cobbles and boulders to 1-foot diameter (Glacial Till) TP-4 completed at approximately 8 feet. No groundwater seepage observed at time of excavation. 1 S-1 @ 1 ft. 2 3 S-2 @ 2 ft. 4 S-3 @ 4 ft. 5 6 7 8 S-4 @ 8 ft. 9 10 11 12 Test Pit TP-5 Location: See Site and Exploration Plan, Figure 1 Approx. Ground Surface Elevation: 251 feet Project: Federal Way Mixed-use Project No: 1536.01 Date Excavated: 11/12/15 Depth (ft) Material Description Sample NC %M Testing Grass over loose, moist, brown, sandy SILT, with gravel, fine roots throughout (Topsoil) Medium dense, moist, light orange to brown, silty gravelly SAND (Weathered Glacial Till) Very dense, moist, gray, silty gravelly SAND, trace cobbles and boulders (Glacial Till) TP-5 completed at approximately 6 feet. No groundwater seepage observed at time of excavation. 1 S-1 @ 0.5 ft. S-2 @ 1 ft. 17 GSA 2 3 4 S-3 @ 3.5 ft. 5 6 S-4 @ 6 ft. 7 8 9 10 11 12 13 Test Pit TP-6 Location: See Site and Exploration Plan, Figure 1 Approx. Ground Surface Elevation: 244 feet Project: Federal Way Mixed-use Project No: 1536.01 Date Excavated: 11/12/15 Depth (ft) Material Description Sample NC %M Testing Grass over loose, moist, brown, sandy SILT, with gravel, fine roots throughout (Topsoil) Medium dense, moist, brown, sandy SILT, with gravel, trace fine roots (Possible Fill) Medium dense, moist, light orange to brown, silty SAND, with gravel (Weathered Glacial Till) Very dense, moist, gray, silty gravelly SAND, trace cobbles and boulders (Glacial Till) TP-6 completed at approximately 15 feet. No groundwater seepage observed at time of excavation. 1 S-1 @ 1 ft. 7 2 3 S-2 @ 3 ft. 6 4 S-3 @ 4 ft. 6 5 6 7 8 S-4 @ 8 ft. 5 9 10 11 12 13 14 ` 15 S-5 @ 15 ft. 8 Test Pit TP-7 Location: See Site and Exploration Plan, Figure 1 Approx. Ground Surface Elevation: 257 Project: Federal Way Mixed-use Project No: 1536.01 Date Excavated: 11/12/15 Depth (ft) Material Description Sample NC %M Testing Grass over loose to medium dense, moist, brown, sandy SILT to silty SAND, with to some gravel (Strippings fill) TP-7 completed at approximately 5.5 feet. No groundwater seepage observed at time of excavation. 1 2 3 4 S-1 @ 4 ft. 5 6 7 8 9 10 11 12 Test Pit TP-8 Location: See Site and Exploration Plan, Figure 1 Approx. Ground Surface Elevation: 253 feet Project: Federal Way Mixed-use Project No: 1536.01 Date Excavated: 11/12/15 Depth (ft) Material Description Sample NC %M Testing Grass over loose, moist, brown, sandy SILT, with gravel, fine roots throughout (Topsoil) Medium dense, moist, brown, sandy SILT, with gravel (Possible Fill) Medium dense, moist, light orange to brown, silty gravelly SAND, trace cobbles (Weathered Glacial Till) (3-inch diameter tree root at 3 feet) Dense to very dense, moist, gray, silty gravelly SAND, trace cobbles and boulders (Glacial Till) TP-8 completed at approximately 6 feet. No groundwater seepage observed at time of excavation. 1 S-1 @ 1 ft. 2 S-2 @ 2 ft. 11 GSA 3 4 S-3 @ 3.5 ft. 5 6 S-4 @ 6 ft. 7 8 9 10 11 12 13 Test Pit TP-9 Location: See Site and Exploration Plan, Figure 1 Approx. Ground Surface Elevation: 260 feet Project: Federal Way Mixed-use Project No: 1536.01 Date Excavated: 11/12/15 Depth (ft) Material Description Sample NC %M Testing Ferns and grass over loose, moist, brown, sandy SILT, with gravel, fine roots throughout (Topsoil) Medium dense, moist, light orange to brown, silty gravelly SAND, trace decaying tree roots (Weathered Glacial Till) Dense to very dense, moist, gray, silty gravelly SAND, trace cobbles (Glacial Till) TP-9 completed at approximately 6 feet. No groundwater seepage observed at time of excavation. 1 S-1 @ 0.5 ft. S-2 @ 1 ft. 2 3 S-3 @ 2.5 ft. 4 5 6 S-4 @ 6 ft. 7 8 9 10 11 12 Test Pit TP-10 Location: See Site and Exploration Plan, Figure 1 Approx. Ground Surface Elevation: 232 feet Project: Federal Way Mixed-use Project No: 1536.01 Date Excavated: 11/12/15 Depth (ft) Material Description Sample NC %M Testing Grass and brush over loose, moist, brown, sandy SILT, with gravel, fine roots throughout (Topsoil) Medium dense, moist, light orange to brown, gravelly sandy SILT, trace decaying tree limb (Possible Weathered Glacial Till) Very dense, moist, gray, silty gravelly SAND (Glacial Till) Very dense, moist, gray, silty SAND, with gravel, trace cobbles and boulders (Glacial Till) TP-10 completed at approximately 15 feet. No groundwater seepage observed at time of excavation. 1 S-1 @ 0.5 ft. 12 S-2 @ 1 ft. 15 2 3 S-3 @ 3 ft. 7 GSA 4 5 6 S-4 @ 6 ft. 6 7 8 9 10 11 12 13 14 ` 15 S-5 @ 15 ft. 6 Test Pit TP-11 Location: See Site and Exploration Plan, Figure 1 Approx. Ground Surface Elevation: 227 feet Project: Federal Way Mixed-use Project No: 1536.01 Date Excavated: 11/12/15 Depth (ft) Material Description Sample NC %M Testing Grass and brush over loose, moist, brown, sandy SILT, with gravel, fine roots throughout (Topsoil) Medium dense, moist, light gray, silty gravelly SAND (Weathered Glacial Till) Very dense, moist, dark gray, silty gravelly SAND, trace cobbles and boulders (Glacial Till) Very dense, moist, gray, silty SAND to sandy SILT, with gravel, trace cobbles and boulders (Glacial Till) TP-11 completed at approximately 15 feet. No groundwater seepage observed at time of excavation. S-1 @ 0.3 ft. 9 1 S-2 @ 1 ft. 7 2 3 4 S-3 @ 3.5 ft. 5 5 6 7 8 9 10 S-4 @ 10 ft. 6 11 12 13 14 ` 15 S-5 @ 15 ft. 7 Test Pit TP-12 Location: See Site and Exploration Plan, Figure 1 Approx. Ground Surface Elevation: 235 feet Project: Federal Way Mixed-use Project No: 1536.01 Date Excavated: 11/12/15 Depth (ft) Material Description Sample NC %M Testing Grass and brush over loose, moist, brown, sandy SILT, with gravel, fine roots throughout (Topsoil) Loose to medium dense, moist, gray, silty SAND, with gravel, trace roots (Fill) Medium dense, to soft, moist, dark brown to black, SILT, with sand (Probably Relic Topsoil) Medium dense to dense, moist, light orange to brown, sandy SILT, with gravel (Weathered Glacial Till) Very dense, moist, gray, silty gravelly SAND, trace cobbles and boulders (Glacial Till) TP-12 completed at approximately 15 feet. No groundwater seepage observed at time of excavation. S-1 @ 0.3 ft. 1 S-2 @ 1 ft. 2 S-3 @ 1.5 ft. S-4 @ 2 ft. 3 S-5 @ 3 ft. 4 5 6 7 8 9 10 11 12 13 14 ` 15 S-6 @ 15 ft. APPENDIX B LABORATORY TESTING PROCEDURES & RESULTS APPENDIX B LABORATORY TESTING PROCEDURES AND RESULTS Descriptions of the types of tests performed on selected soil samples by TCI are given below. Visual Classification Samples recovered from the exploration locations were visually classified in the field during the exploration program. Representative portions of the samples were carefully packaged in moisture tight containers and transported to our laboratory where the field classifications were verified or modified as required. Visual classification was generally done in accordance with ASTM D 2488. Visual soil classification includes evaluation of color, relative moisture content, soil type based upon grain size, and accessory soil types included in the sample. Soil classifications are presented on the exploration logs in Appendix A. Moisture Content Determinations Moisture content determinations were performed on representative samples obtained from the explorations in order to aid in identification and correlation of soil types. The determinations were made in general accordance with the test procedures described in ASTM D 2216. The results are shown on the exploration logs in Appendix A. Grain Size Analysis A grain size analysis indicates the range in diameter of soil particles included in a particular sample. Grain size analyses were performed on representative samples in general accordance with ASTM D 422. The results of the grain size determinations for the samples were used in classification of the soils, and are presented in this appendix. 0 10 20 30 40 50 60 70 80 90 100 0.0010.0100.1001.00010.000100.0001000.000PERCENT FINER BY WEIGHTPARTICLE SIZE IN MILLIMETERS GRAIN SIZE ANALYSIS Comments: 36"12"6"3"1 1/2"3/4"3/8"4 10 20 40 60 140 200 Coarse Medium Fine Silt ClayFineCoarse COBBLESBOULDERS GRAVEL SAND FINE GRAINED SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER Project No.:PROJECT NAME: Federal Way Mixed-UseDATE OF TESTING: Exploration Sample Depth (feet)Moisture (%)Fines (%)Description TP-3 5.0 6.4 Silty gravelly SANDS-4 23.7 1536.01 11/25/2015 ASTM D 422Test Results Summary Zipper Geo Associates, LLC Geotechnical and Environmental Consultants 0 10 20 30 40 50 60 70 80 90 100 0.0010.0100.1001.00010.000100.0001000.000PERCENT FINER BY WEIGHTPARTICLE SIZE IN MILLIMETERS GRAIN SIZE ANALYSIS Comments: 36"12"6"3"1 1/2"3/4"3/8"4 10 20 40 60 140 200 Coarse Medium Fine Silt ClayFineCoarse COBBLESBOULDERS GRAVEL SAND FINE GRAINED SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER Project No.:PROJECT NAME: Federal Way Mixed-UseDATE OF TESTING: Exploration Sample Depth (feet)Moisture (%)Fines (%)Description TP-5 1.0 16.9 Silty gravelly SANDS-2 22.8 1536.01 11/25/2015 ASTM D 422Test Results Summary Zipper Geo Associates, LLC Geotechnical and Environmental Consultants 0 10 20 30 40 50 60 70 80 90 100 0.0010.0100.1001.00010.000100.0001000.000PERCENT FINER BY WEIGHTPARTICLE SIZE IN MILLIMETERS GRAIN SIZE ANALYSIS Comments: 36"12"6"3"1 1/2"3/4"3/8"4 10 20 40 60 140 200 Coarse Medium Fine Silt ClayFineCoarse COBBLESBOULDERS GRAVEL SAND FINE GRAINED SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER Project No.:PROJECT NAME: Federal Way Mixed-UseDATE OF TESTING: Exploration Sample Depth (feet)Moisture (%)Fines (%)Description TP-8 2.0 10.6 Silty gravelly SAND S-2 18.3 1536.01 11/25/2015 ASTM D 422Test Results Summary Zipper Geo Associates, LLC Geotechnical and Environmental Consultants 0 10 20 30 40 50 60 70 80 90 100 0.0010.0100.1001.00010.000100.0001000.000PERCENT FINER BY WEIGHTPARTICLE SIZE IN MILLIMETERS GRAIN SIZE ANALYSIS Comments: 36"12"6"3"1 1/2"3/4"3/8"4 10 20 40 60 140 200 Coarse Medium Fine Silt ClayFineCoarse COBBLESBOULDERS GRAVEL SAND FINE GRAINED SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER Project No.:PROJECT NAME: Federal Way Mixed-UseDATE OF TESTING: Exploration Sample Depth (feet)Moisture (%)Fines (%)Description TP-10 3.0 7.4 Silty gravelly SAND S-3 20.6 1536.01 11/25/2015 ASTM D 422Test Results Summary Zipper Geo Associates, LLC Geotechnical and Environmental Consultants     TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use               APPENDIX D      CSWPP WORKSHEETS         TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use         TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use         TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use         TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use         TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use         TECHNICAL INFORMATION REPORT        NAVIX  FNW Federal Way Mixed‐Use