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Technical Information Report (TIR) LANDMARK APARTMENTS i JOB #19-019 Technical Information Report TABLE OF CONTENTS PROJECT OVERVIEW ................................................................................................ 1.1 CONDITIONS AND REQUIREMENTS SUMMARY ....................................................... 2.1 Core Requirements ......................................................................................................... 2.1 OFFSITE ANALYSIS .................................................................................................... 3.1 Study Area Definition and Maps ..................................................................................... 3.1 Resource Review ............................................................................................................. 3.1 Field Inspection and Drainage System Description ........................................................ 3.5 On-Site Basins ................................................................................................................. 3.5 Upstream Basin ............................................................................................................... 3.5 Existing Downstream Drainage Paths ............................................................................ 3.5 Mitigation of Existing or Potential Problems .................................................................. 3.6 Existing Downstream Drainage Paths ............................................................................. 3.7 FLOW CONTROL AND WATER QUALITY ANALYSIS AND DESIGN ............................. 4.1 Hydraulic Analysis ........................................................................................................... 4.1 Existing Conditions .......................................................................................................... 4.1 Developed Conditions ..................................................................................................... 4.3 Flow Control Analysis and Design ................................................................................... 4.6 Basin B Detention System ............................................................................................... 4.6 Basin C Detention System ............................................................................................... 4.6 Water Quality System ..................................................................................................... 4.7 Basin B: Detention Vault to BioPod 2-year Release Rate ................................................ 4.7 Basin C: Detention Vault to BioPod 2-year Release Rate: ............................................... 4.8 Flow Control BMPs .......................................................................................................... 4.9 CONVEYANCE SYSTEM ANALYSIS AND DESIGN ....................................................... 5.1 SPECIAL REPORTS AND STUDIES .............................................................................. 6.1 OTHER PERMITS ....................................................................................................... 7.1 SWPPP AND TESC ANALYSIS AND DESIGN ............................................................... 8.1 BOND QUANTITIES AND FACILITIES SUMMARY ...................................................... 9.1 APPENDIX · Existing Conditions Exhibit · Developed Conditions Exhibit · Downstream Drainage Exhibit · WWHM Printout: Basin A · WWHM Printout: Basin B · WWHM Printout: Basin C · BioPod GULD Letter of Approval · BioPod Detail LANDMARK APARTMENTS ii JOB #19-019 Technical Information Report · Review of Wetland Z Adjacent to Parcel 1721049036 prepared by Habitat Technologies dated July 16, 2018 · Geotechnical Engineering Study prepared by Earth Solutions NW, LLC dated June 19, 2019 LANDMARK APARTMENTS 1.1 JOB #19-019 Technical Information Report Project Overview The project is located at 33005 15th Ave S, Federal Way, WA 98003. More generally, the site is located in the SE ¼ of Section 17, Township 21N, Range 4E of the Williamette Principal Meridian in King County. Please see vicinity map below. The site contains eleven (11) parcels (Parcel Numbers 1721049034, 1721049074, 1721049051, 1721049019, 1721049046, 1721049057, 1721049028, 1721049030, 1721049035, 1721049059, 1721049060). The project proposes to develop most of the total parcel area of 7.45-ac along with frontage improvements associated with providing adequate site access from 13th Pl S and 15th Ave S. See Section 4 for detailed site areas. The site currently contains dirt roads, broken asphalt and concrete surfacing, a house, a garage, access roads, heavy brush, and trees. All hardscapes will be removed prior to construction. Refer to the Existing Conditions Exhibit included in the Appendix. In the developed condition, the project proposes to construct new multi-story apartment buildings and a daycare with parking areas, pedestrian plazas, planters, landscaping and associated utility infrastructure for the new development. Refer to the Developed Conditions Exhibit in the Appendix. Runoff from the targeted portion of the site is generated from three separate drainage basins that do not combine within 1/4-mile downstream. The project site is located within the Hylebos Creek Basin and is ultimately tributary to Brook Lake. Refer to the Level 1 Downstream Analysis included in Section 3. Per the Geotechnical Engineering Study by Earth Solutions NW, LLC, included in Section 6, “the soil conditions encountered during our fieldwork consisted primarily of loamy sand (USDA Classification), with areas of coarse sand and coarse sandy loam and are generally not favorable for infiltration.” Additionally, most test pits indicated a hard, cementitious layer below the topsoil layer, making on-site infiltration difficult. The presence of these non- infiltrative soils on-site renders several Flow Control BMP options, outlined in Section 1.2.9.2 of the King County Surface Water Design Manual (2016 KCSWDM), infeasible. See Section 4 for more information regarding Flow Control BMPs. Downstream soils are mapped as outwash soils per the USDA Web Soil Survey. Stormwater elements will be designed in accordance with the 2016 King County Surface Water Design Manual (KCSWDM) and the “Addendum to the King County Surface Water Design Manual” by the City of Federal Way. The proposed developments will create more than a 0.15 cfs increase in site runoff in two of the three existing on-site drainage basins over the historic, predeveloped condition for the 100-year storm event when modelled using a 15-minute timestep in WWHM2012. The project is therefore required to provide flow control facilities per Section 1.2.3 of the KCSWDM for Drainage Basins B & C due to the increase in runoff compared to the historic condition. The project is required to provide water quality for a new development per Section 1.1.1.A of the “Addendum to the King County Surface Water Design Manual” to meet the standards of Section 1.2.8 of the KCSWDM. Stormwater Low Impact Development (LID) features will be provided to the maximum extent feasible per Section 1.2.9.2.1 of the KCSWDM. Please see Section 4 for the LID BMP, Flow Control, and Water Quality design consideration and subsequent discussion. The project is subject to Full Drainage Review per the City of LANDMARK APARTMENTS 1.2 JOB #19-019 Technical Information Report Federal Way’s Stormwater Review Flow Chart, included on the following pages. The requirements for the Full Drainage Review are listed in Section 2. City of Federal Way Addendum to the King County, Washington Surface Water Design Manual Page 9 of 23 FIGURE 1.1.1.B Stormwater Review Flow Chart * Project or Activity Does the project meet thresholds #s 1 -5 in Section 1.1.1.B of this addendum? Stormwater Review Required See Section 1.1.2 of KCSWDM for specific requirements No Stormwater Review Required Stormwater Review Required See Section 1.1.2 of KCSWDM for specific requirements Yes Yes No No No Yes Stormwater Review (Small Project Drainage Requirements, Core Requirements 1 -7 & Special Requirements 1 -5) Does project meet definition of "redevelopment project" per KCSWDM? Does the project meet thresholds #s 6 -7 in Section 1.1.1.B of this addendum? . * The requirement to complete a stormwater review is separate from the requirements to conform to the Water Quality Review (1.1.1.A). If water quality is triggered, but a stormwater review is not, the applicant is still required to conform to the Water Quality requirements. KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Part 2 PROJECT LOCATION AND DESCRIPTION Project Owner ___________________________ Phone _________________________________ Address _______________________________ _______________________________________ Project Engineer _________________________ Company ______________________________ Phone _________________________________ Project Name _________________________ DPER Permit # ________________________ Location Township ______________ Range ________________ Section ________________ Site Address __________________________ _____________________________________ Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS  Landuse (e.g.,Subdivision / Short Subd. / UPD)  Building (e.g.,M/F / Commercial / SFR)  Clearing and Grading  Right-of-Way Use  Other _______________________  DFW HPA  COE 404  DOE Dam Safety  FEMA Floodplain  COE Wetlands  Other ________  Shoreline Management  Structural Rockery/Vault/_____  ESA Section 7 Part 5 PLAN AND REPORT INFORMATION Technical Information Report Site Improvement Plan (Engr. Plans) Type of Drainage Review (check one): Date (include revision dates): Date of Final:  Full  Targeted  Simplified  Large Project  Directed __________________ __________________ __________________ Plan Type (check one): Date (include revision dates): Date of Final:  Full  Modified  Simplified __________________ __________________ __________________ Part 6 SWDM ADJUSTMENT APPROVALS Type (circle one): Standard / Experimental / Blanket Description: (include conditions in TIR Section 2) ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ Approved Adjustment No. ______________________ Date of Approval: ______________________ 2016 Surface Water Design Manual 4/24/2016 1 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes / No Start Date: _______________________ Completion Date: _______________________ Describe: _________________________________ _________________________________________ _________________________________________ Re: KCSWDM Adjustment No. ________________ Part 8 SITE COMMUNITY AND DRAINAGE BASIN Community Plan : ____________________________________________________________________ Special District Overlays: ______________________________________________________________ Drainage Basin: _____________________________________________________________________ Stormwater Requirements: ____________________________________________________________ Part 9 ONSITE AND ADJACENT SENSITIVE AREAS  River/Stream ________________________  Lake ______________________________  Wetlands ____________________________  Closed Depression ____________________  Floodplain ___________________________  Other _______________________________ _______________________________  Steep Slope __________________________  Erosion Hazard _______________________  Landslide Hazard ______________________  Coal Mine Hazard ______________________  Seismic Hazard _______________________  Habitat Protection ______________________  _____________________________________ Part 10 SOILS Soil Type _________________ _________________ _________________ _________________ Slopes _________________ _________________ _________________ _________________ Erosion Potential _________________ _________________ _________________ _________________  High Groundwater Table (within 5 feet)  Other ________________________________  Sole Source Aquifer  Seeps/Springs  Additional Sheets Attached 2016 Surface Water Design Manual 4/24/2016 2 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE  Core 2 – Offsite Analysis_________________  Sensitive/Critical Areas__________________  SEPA________________________________  LID Infeasibility________________________  Other________________________________  _____________________________________ LIMITATION / SITE CONSTRAINT _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________  Additional Sheets Attached Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Threshold Discharge Area: (name or description) Core Requirements (all 8 apply): Discharge at Natural Location Number of Natural Discharge Locations: Offsite Analysis Level: 1 / 2 / 3 dated:__________________ Flow Control (include facility summary sheet) Level: 1 / 2 / 3 or Exemption Number ____________ Flow Control BMPs _______________________________ Conveyance System Spill containment located at: _________________________ Erosion and Sediment Control / Construction Stormwater Pollution Prevention CSWPP/CESCL/ESC Site Supervisor: _____________________ Contact Phone: _________________________ After Hours Phone: _________________________ Maintenance and Operation Responsibility (circle one): Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Liability Provided: Yes / No Water Quality (include facility summary sheet) Type (circle one): Basic / Sens. Lake / Enhanced Basic / Bog or Exemption No. ______________________ Landscape Management Plan: Yes / No Special Requirements (as applicable): Area Specific Drainage Requirements Type: CDA / SDO / MDP / BP / LMP / Shared Fac. / None Name: ________________________ Floodplain/Floodway Delineation Type (circle one): Major / Minor / Exemption / None 100-year Base Flood Elevation (or range): ______________ Datum: Flood Protection Facilities Describe: 2016 Surface Water Design Manual 4/24/2016 3 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Source Control (comm ercial / industrial land use) Describe land use: Describe any structural controls: Oil Control High-use Site: Yes / No Treatment BMP: ________________________________ Maintenance Agreement: Yes / No with whom? ____________________________________ Other Drainage Structures Describe: Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION  Clearing Limits  Cover Measures  Perimeter Protection  Traffic Area Stabilization  Sediment Retention  Surface Water Collection  Dewatering Control  Dust Control  Flow Control  Protection of Flow Control BMP Facilities (existing and proposed)  Maintain BMPs / Manage Project MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION  Stabilize exposed surfaces  Remove and restore Temporary ESC Facilities  Clean and remove all silt and debris, ensure operation of Permanent Facilities, restore operation of Flow Control BMP Facilities as necessary  Flag limits of SAO and open space preservation areas  Other ______________________ Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch) Flow Control Type/Description Water Quality Type/Description  Detention  Infiltration  Regional Facility  Shared Facility  Flow Control BMPs  Other ________________ ________________ ________________ ________________ ________________ ________________  Vegetated Flowpath  Wetpool  Filtration  Oil Control  Spill Control  Flow Control BMPs  Other ________________ ________________ ________________ ________________ ________________ ________________ ________________ 2016 Surface Water Design Manual 4/24/2016 4 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE  Core 2 – Offsite Analysis_________________  Sensitive/Critical Areas__________________  SEPA________________________________  LID Infeasibility________________________  Other________________________________  _____________________________________ LIMITATION / SITE CONSTRAINT _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________  Additional Sheets Attached Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Threshold Discharge Area: (name or description) Core Requirements (all 8 apply): Discharge at Natural Location Number of Natural Discharge Locations: Offsite Analysis Level: 1 / 2 / 3 dated:__________________ Flow Control (include facility summary sheet) Level: 1 / 2 / 3 or Exemption Number ____________ Flow Control BMPs _______________________________ Conveyance System Spill containment located at: _________________________ Erosion and Sediment Control / Construction Stormwater Pollution Prevention CSWPP/CESCL/ESC Site Supervisor: _____________________ Contact Phone: _________________________ After Hours Phone: _________________________ Maintenance and Operation Responsibility (circle one): Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Liability Provided: Yes / No Water Quality (include facility summary sheet) Type (circle one): Basic / Sens. Lake / Enhanced Basic / Bog or Exemption No. ______________________ Landscape Management Plan: Yes / No Special Requirements (as applicable): Area Specific Drainage Requirements Type: CDA / SDO / MDP / BP / LMP / Shared Fac. / None Name: ________________________ Floodplain/Floodway Delineation Type (circle one): Major / Minor / Exemption / None 100-year Base Flood Elevation (or range): ______________ Datum: Flood Protection Facilities Describe: 2016 Surface Water Design Manual 4/24/2016 3 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Source Control (comm ercial / industrial land use) Describe land use: Describe any structural controls: Oil Control High-use Site: Yes / No Treatment BMP: ________________________________ Maintenance Agreement: Yes / No with whom? ____________________________________ Other Drainage Structures Describe: Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION  Clearing Limits  Cover Measures  Perimeter Protection  Traffic Area Stabilization  Sediment Retention  Surface Water Collection  Dewatering Control  Dust Control  Flow Control  Protection of Flow Control BMP Facilities (existing and proposed)  Maintain BMPs / Manage Project MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION  Stabilize exposed surfaces  Remove and restore Temporary ESC Facilities  Clean and remove all silt and debris, ensure operation of Permanent Facilities, restore operation of Flow Control BMP Facilities as necessary  Flag limits of SAO and open space preservation areas  Other ______________________ Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch) Flow Control Type/Description Water Quality Type/Description  Detention  Infiltration  Regional Facility  Shared Facility  Flow Control BMPs  Other ________________ ________________ ________________ ________________ ________________ ________________  Vegetated Flowpath  Wetpool  Filtration  Oil Control  Spill Control  Flow Control BMPs  Other ________________ ________________ ________________ ________________ ________________ ________________ ________________ 2016 Surface Water Design Manual 4/24/2016 4 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE  Core 2 – Offsite Analysis_________________  Sensitive/Critical Areas__________________  SEPA________________________________  LID Infeasibility________________________  Other________________________________  _____________________________________ LIMITATION / SITE CONSTRAINT _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________  Additional Sheets Attached Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Threshold Discharge Area: (name or description) Core Requirements (all 8 apply): Discharge at Natural Location Number of Natural Discharge Locations: Offsite Analysis Level: 1 / 2 / 3 dated:__________________ Flow Control (include facility summary sheet) Level: 1 / 2 / 3 or Exemption Number ____________ Flow Control BMPs _______________________________ Conveyance System Spill containment located at: _________________________ Erosion and Sediment Control / Construction Stormwater Pollution Prevention CSWPP/CESCL/ESC Site Supervisor: _____________________ Contact Phone: _________________________ After Hours Phone: _________________________ Maintenance and Operation Responsibility (circle one): Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Liability Provided: Yes / No Water Quality (include facility summary sheet) Type (circle one): Basic / Sens. Lake / Enhanced Basic / Bog or Exemption No. ______________________ Landscape Management Plan: Yes / No Special Requirements (as applicable): Area Specific Drainage Requirements Type: CDA / SDO / MDP / BP / LMP / Shared Fac. / None Name: ________________________ Floodplain/Floodway Delineation Type (circle one): Major / Minor / Exemption / None 100-year Base Flood Elevation (or range): ______________ Datum: Flood Protection Facilities Describe: 2016 Surface Water Design Manual 4/24/2016 3 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Source Control (comm ercial / industrial land use) Describe land use: Describe any structural controls: Oil Control High-use Site: Yes / No Treatment BMP: ________________________________ Maintenance Agreement: Yes / No with whom? ____________________________________ Other Drainage Structures Describe: Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION  Clearing Limits  Cover Measures  Perimeter Protection  Traffic Area Stabilization  Sediment Retention  Surface Water Collection  Dewatering Control  Dust Control  Flow Control  Protection of Flow Control BMP Facilities (existing and proposed)  Maintain BMPs / Manage Project MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION  Stabilize exposed surfaces  Remove and restore Temporary ESC Facilities  Clean and remove all silt and debris, ensure operation of Permanent Facilities, restore operation of Flow Control BMP Facilities as necessary  Flag limits of SAO and open space preservation areas  Other ______________________ Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch) Flow Control Type/Description Water Quality Type/Description  Detention  Infiltration  Regional Facility  Shared Facility  Flow Control BMPs  Other ________________ ________________ ________________ ________________ ________________ ________________  Vegetated Flowpath  Wetpool  Filtration  Oil Control  Spill Control  Flow Control BMPs  Other ________________ ________________ ________________ ________________ ________________ ________________ ________________ 2016 Surface Water Design Manual 4/24/2016 4 LANDMARK APARTMENTS 2.1 JOB #19-019 Technical Information Report Conditions and Requirements Summary CORE REQUIREMENTS Core Requirement #1: Discharge at the Natural Location The proposed development will provide drainage infrastructure to manage onsite storm water and convey runoff to the existing natural discharge locations. The natural discharge locations are described further in Section 3 and Section 4 of this report. Core Requirement #2: Offsite Analysis See Section 3 of this report for a Level I Downstream Analysis completed for the project. Core Requirement #3: Flow Control Facilities See Section 4. The proposed development will capture runoff on-site prior to discharging stormwater to its natural drainage location. A detention system will be provided meeting the requirements of Section 1.2.3 of the KCSWDM, matching the historic site conditions from 50% of the 2-year peak flow up to the full 50-year peak flow and the peak discharge rates for the 2-year and 10-year return periods. Core Requirement #4: Conveyance System See Section 5. The conveyance system will be designed to convey the 100-year, 24-hour storm event without overtopping during final engineering. Core Requirement #5: Construction Stormwater Pollution Prevention See Section 8. The temporary erosion and sedimentation control (TESC) plan will consist of temporary measures (stabilized construction entrance, inlet protection, silt fence, concrete washout basin, etc.) as well as permanent measures (permanent landscaping and stabilization of the disturbed areas). The TESC plan and Stormwater Pollution Prevention Plan (SWPPP) will be provided at final engineering. Core Requirement #6: Maintenance and Operations See Section 10. A Maintenance and Operations manual will be provided at final engineering. Core Requirement #7: Financial Guarantees and Liability See Section 9. A Federal Way Bond Quantity Worksheet for the project will be provided at final engineering. Core Requirement #8: Water Quality Facilities See Section 4. The proposed improvements include construction of a mixed-use development with associated parking and road improvements. The on-site and frontage improvement basins will result in greater than 5,000 sq. ft. of new plus replaced Pollution Generating Impervious Surface (PGIS) triggering Enhanced Water Quality. Enhanced Water Quality will be achieved utilizing Oldcastle’s BioPod water quality system. The BioPod meets the General Use Level Designation for Enhanced Water Quality through the Department of Ecology’s TAPE program. Core Requirement #9: Flow Control BMPs The proposed improvements encompass greater than 22,000 sq. ft. of area but is not a Large Rural Lot. Compost amended soils will be implemented. See Section 4 for further discussion. Special Requirement #1: Other Adopted Area-Specific Requirements There are no known additional requirements for the subject project. LANDMARK APARTMENTS 2.2 JOB #19-019 Technical Information Report Special Requirement #2: Flood Hazard Area Delineation The Offsite Analysis (Section 3) identifies all sensitive areas associated with the project. The project is not located within or nearby a Flood Hazard Area. This Special Requirement, therefore, is not applicable. Special Requirement #3: Flood Protection Facilities The site does not rely on nor will the site modify an existing flood protection facility or construct a new flood protection facility. This Special Requirement, therefore, is not applicable. Special Requirement #4: Source Controls The subject project is a commercial development. Per the 2016 KCSWDM, source control measures are required per the King County Stormwater Pollution Prevention Manual for commercial sites. On-site stormwater source controls do not apply to the project post site stabilization. Source Control Pollution created from construction of the subject project will be addressed within the SWPPP (to be provided under separate cover at final engineering). Special Requirement #5: Oil Control The proposed project is neither an industrial development nor a high-use site. This Special Requirement, therefore, is not applicable. SEPA MITIGATIONS Mitigations are not anticipated to be required to receive SEPA approval. ENVIRONMENTALLY SENSITIE AREA REQUIREMENTS No work shall be performed in the wetland buffer boundary. The buffer boundary is shown in the Developed Conditions Exhibit in the Appendix and the civil plans under separate cover. VARIANCES AND ADJUSTMENTS No variances or adjustments are proposed for the site. CONDITIONS OF PLAT APPROVAL Conditions of Plat Approval will be completed prior to final engineering. LANDMARK APARTMENTS 3.1 JOB #19-019 Technical Information Report Offsite Analysis A Level 1 offsite analysis was conducted for the project site located at 33005 15th Ave S, Federal Way, WA 98003, on September 20, 2019. Weather conditions were partly cloudy with temperatures about 60 degrees Fahrenheit. There are three existing drainage basins on-site: Basin A, Basin B, and Basin C. Each of these drainage basins provide separate downstream drainage paths that do not combine within ¼-mile. Detailed downstream drainage path descriptions are provided later in this section. STUDY AREA DEFINITION AND MAPS See Section 1 of this Report for a description of the site. Additionally, see the Existing Conditions Exhibit and the Downstream Drainage Exhibit in the Appendix. RESOURCE REVIEW The best available resource information, including King County iMap, NRCS Web Soil Survey, the Geotechnical Engineering Study prepared by Earth Solutions NW, LLC (included in Section 6), and the City of Federal Way (CFW) resource maps, were reviewed for existing or potential problems. The following is a summary of the findings from the information used in preparing this report. · The Natural Resource Conservation Service Web Soil Survey Identifies soils as, Everett-Alderwood gravelly sandy loams, 6-15% slopes. Everett-Alderwood soils are classified as outwash soils by KCSWDM 2016; however, according to the Geotechnical Report created by Earth Solutions NW, LLC, “the soil conditions encountered during our fieldwork consisted primarily of loamy sand (USDA Classification), with areas of coarse sand and coarse sandy loam and are generally not favorable for infiltration.” · The site is not located within a Flood Plain (King County iMap). · The site is not located within an Erosion Hazard Area (King County iMap and CFW Critical Areas Map). · The site is not located in a Landslide Hazard Area (King County iMap and CFW Critical Areas Map). · The site is partially located in a Seismic Hazard Area (King County iMap). LANDMARK APARTMENTS 3.2 JOB #19-019 Technical Information Report !!7Ái Hyl e b o s C r e e k W a t e r w a y Bla i r W a t e r w a y P uyallu p R i v erPuget Sound BayDumas PovertyBay Sit c u m W a t e r w a y CommencementBay HOYT RD SW MILITARY RD SWEST VALLEY HWYMILTON WAY S 288th ST DASH POINT R D DASH PT RDMILITARY RD S21st AVE SWPACIFIC HWYMARINE VIEW DRSW 336th ST NORTHSHORE PK W Y INTERSTATE 5E 11th STHWY 18H W Y 18PACIFIC HWY S28TH AVE SENC HAN T ED P KW Y 51st AVE SINTERSTATE 51st AVE SPACIFIC HWY SS 320th ST 21st AVE SWS 336th ST1st AVE SS 312th ST SW 320th ST SW 356th ST S 348th ST SR 99S 272nd ST 33rd ST NE Fife Milton Tacoma DesMoines Edgewood Pacific Auburn Algona FederalWay Kent Lower PugetSound Basin HylebosCreekBasin LowerGreenRiverBasin 126286.04851 ft MillCreekBasin City ofFederal Way Water QualityApplicationsMap This map is intended for use as a graphical representation only. The City of Federal Way makes no warranty as to its accuracy. Map Date: November 2013SWM DivisionCity of Federal Way33325 8th Ave S.Federal Way, WA. 98003(253) 835 - 2700www.cityoffederalway.com \\users\erike\swm\watqual.mxd * High density single family, multi-family, commercial, and industrial uses, as well as most roads, are subject to Enhanced Basic Water Quality Treatment Requirements. Legend Drainage Basin Boundary Streams City Limits 0 0.5 10.25 Mile´ Enhanced Basic Water QualityTreatment Menu Required* Sensitive Lake !!7Ái Identified Sphagnum Bog Wetlands Water Quality Treatment Area Types Scale: Fife Milton Tacoma DesMoines Edgewood Pacific AuburnFederalWay Kent Hyl e b o s C r e e k W a t e r w a y Bla i r W a t e r w a y P uyallu p R i v erPuget Sound BayDumas PovertyBay Sit c u m W a t e r w a y CommencementBay LakeSteel Star Lake MirrorLake GenevaLake North Lake Lorene Lake JeaneLake EasterLake Dolloff LakeTroutLake FiveMileLakeLake KillarneyHOYT RD SW MILITARY RD SWEST VALLEY HWYS 288th ST DASH POINT R D DASH PT RDMILITARY RD S21st AVE SWPACIFIC HWYMARINE VIEW DRSW 336th ST NORTHSHORE PK W Y INTERSTATE 5E 11th STHWY 18H W Y 18PACIFIC HWY S28TH AVE SENC HAN T ED P KW Y 51st AVE SINTERSTATE 51st AVE SPACIFIC HWY SS 320th ST 21st AVE SWS 336th ST1st AVE SS 312th ST SW 320th ST SW 356th ST S 348th ST SR 99S 272nd ST 33rd ST NE Lower PugetSound Basin HylebosCreekBasin MillCreekBasin LowerGreenRiverBasin 0 0.5 10.25 Mile This map is intended for use as a graphical representation only. The City of Federal Way makes no warranty as to its accuracy. Legend Drainage Basin Boundary Streams City Limits Lakes and Wetlands Scale: City of Federal Way Flow ControlApplications Map Map Date: February, 2010SWM DivisionCity of Federal Way33325 8th Ave SPO Box 9718Federal Way, WA 98063(253) 835-2700www.cityoffederalway.com R:\erike\swm\FlowControl\flowcontrol.mxd Flow Control Basic Flow Control Areas Conservation Flow Control Areas Flood Problem Flow Control Areas Major Receiving Waters1. Puget Sound LANDMARK APARTMENTS 3.5 JOB #19-019 Technical Information Report FIELD INSPECTION AND DRAINAGE SYSTEM DESCRIPTION A Level 1 Downstream Analysis was conducted on September 20, 2019, an overcast day with temperatures around 60˚F. Drainage path descriptions for the onsite basins are provided in Task 4 of this Section. Please see the Existing Conditions Exhibit, along with the Downstream Drainage Exhibit for basin delineation and downstream drainage paths included in the Appendix of this report. ON-SITE BASINS The site currently contains a single-family residence with associated access and utilities. Additionally, the site has small portions of asphalt and concrete accesses that are overgrown and in disrepair. Most of the site is currently vegetation and trees. The site has three separate drainage basins that do not combine within 1/4-mile downstream. Please see the Existing Conditions Exhibit. Stormwater from Basin A flows east prior to being collected in the public storm system located on the east side of 15th Ave S, flowing south and then east towards Pacific Hwy S. Runoff from Basin B flows south, where stormwater is then conveyed into a public storm system in 13th Place S. Stormwater from Basin C flows west into the neighboring Celebration Park parcel prior to being conveyed south towards the public drainage system located in S 332nd Street. UPSTREAM BASIN The east and southern borders of the site are bounded by roads that either slope away from the site or collect stormwater in a public conveyance system. On the west portion of the site, the existing topography is sloped away from the site towards the neighboring Celebration Park parcel. There is an upstream area to the north that slopes towards the property. In the developed condition, portions of this upstream area will be routed to the stormwater facility in Basin C, however, most of the upstream area will maintain the existing drainage patterns that are not tributary to the proposed on-site improvements. See Section 4, the Existing Conditions Exhibit, and the Developed Conditions Exhibit for itemized areas describing what upstream areas will be collected and what upstream areas will remain untouched in the developed condition. EXISTING DOWNSTREAM DRAINAGE PATHS There are three existing on-site drainage basins that do not converge within ¼-mile. All tightline systems consist of catch basins and 12-inch minimum pipes. See the below discussion describing each drainage basin. On-site Basin A sheet flows west towards 15th Avenue S. Stormwater is then collected in the public storm drainage system (Photos 1A-3A) located on the eastern side of the road flowing south. The runoff is then conveyed southeast and then east into a series of catch basins located on the north side of S 332nd Street (Photos 4A-6A). Runoff continues east until it reaches Pacific Highway S in a storm drainage manhole (Photo 7A). Stormwater is conveyed south in the southbound lanes of Pacific Highway S through a series of manholes (Photos 8A-9A) until the runoff reaches the ¼-mile downstream drainage location (Photo 10A). On-site Basin B sheet flows south and south west into the existing catch basins located in 13th Place S (Photo 1B- 2B). Stormwater then crosses S 332nd Street continuing south along the western side of 13th Place S (Photo 3B). Runoff is tightlined through a series of catch basins and pipes along the western side of 13th Place south to S LANDMARK APARTMENTS 3.6 JOB #19-019 Technical Information Report 336th Street (Photos 4B-11B). Stormwater crosses S 336th Street and daylights into a drainage swale at approximately the ¼-mile downstream drainage location. On-site Basin C sheet flows west onto the neighboring Celebration Park parcel where stormwater is then conveyed south through the Federal Way Public Schools Nutrition Services property into a manhole located in the driveway of that property on the north side of S 332nd Street (Photo 1C), beginning the tightline conveyance. Stormwater is then conveyed southeast towards the Federal Way Public Schools Support Services Center’s upper parking lot (Photo 2C). The runoff is conveyed into the lower school bus parking lot, where it is conveyed south into a manhole (Photo 3C) before being conveyed southwest into a manhole located on the northeast side of parcel 9265010030 (Photo 4C), bypassing the detention facility on the south side of the bus yard. Stormwater continues south towards the driveway of parcel 9265030055 (Photo 5C) before being conveyed east into a manhole located in the planter area (Photo 6C). Stormwater is then conveyed south across S 336th Street into another manhole at the approximate ¼-mile downstream drainage location (Photo 7C). MITIGATION OF EXISTING OR POTENTIAL PROBLEMS At the time of the site investigation, no problems were found with the existing systems beyond standard maintenance and cleaning. Existing catch basins and pipes require no immediate corrective maintenance. No significant drainage complaints within the downstream path were noted to have occurred within the preceding ten-year period per King County iMaps. There are five drainage complaints provided by Leah Myhre from the City of Federal Way. Four of the five complaints do not fall within the direct ¼-mile downstream drainage path. The fifth complaint describes gravel, debris, or automotive materials affecting the surrounding storm system along S 332nd Street due to the neighboring tow yards. The project proposes to collect, detain, and treat stormwater within the targeted basins prior to the stormwater being conveyed in a tightline system towards S 332nd Street. The proposed development will not create additional adverse impacts to this area because it is outside of the targeted on-site basin areas. The drainage complaints provided by the City are located in the Appendix. A temporary erosion and sedimentation control (TESC) plan will be designed to minimize the discharge of sediment-laden runoff from the site. The plan will be comprised of temporary measures (rock entrance, silt fence, inlet protection, etc.) as well as permanent measures (final stabilization of disturbed areas). All TESC facilities shall be periodically inspected and maintained as necessary during construction to minimize impacts to the downstream system. LANDMARK APARTMENTS 3.7 JOB #19-019 Technical Information Report EXISTING DOWNSTREAM DRAINAGE PATHS Basin A: Photo 1A – Looking South – On-site flows from Basin A are captured in the catch basin and are conveyed south along the eastern side of 15th Avenue S. Photo 2A – Looking South – Flows continue south through a series of catch basins along the eastern side of 15th Avenue S. LANDMARK APARTMENTS 3.8 JOB #19-019 Technical Information Report Photo 3A – Looking Southeast – Flows continue to the catch basin at the corner of 15th Avenue S and S 332nd Street. Runoff is then conveyed southeast to a series of catch basins located on the north side of S 332nd Street. Photo 4A – Looking East – Flows are conveyed east along the north side of S 332nd Street in a series of catch basins towards Pacific Highway S. LANDMARK APARTMENTS 3.9 JOB #19-019 Technical Information Report Photo 5A – Looking East – Flows are conveyed east along the north side of S 332nd Street in a series of catch basins towards Pacific Highway S. Photo 6A – Looking East – Flows are conveyed east from the catch basin to a manhole located in the southbound lanes of Pacific Highway South. LANDMARK APARTMENTS 3.10 JOB #19-019 Technical Information Report Photo 7A – Looking South – Flows enter the manhole from the east and are then conveyed south through a series of manholes in the southbound lanes of Pacific Highway South. Photo 8A – Looking South – Runoff continues south through a series of manholes in the southbound lane of Pacific Highway South. LANDMARK APARTMENTS 3.11 JOB #19-019 Technical Information Report Photo 9A – Looking South – Runoff continues south through a series of manholes in the southbound lane of Pacific Highway South. Photo 10A – Looking South – Runoff continues into the manhole located in Pacific Highway S at the approximate ¼-mile downstream drainage location. LANDMARK APARTMENTS 3.12 JOB #19-019 Technical Information Report Basin B: Photo 1B – Looking West – On-site flows flow south along 13th Place South and enter the public storm system through a catch basin. Runoff is then conveyed west across 13th Place South. Photo 2B – Looking South – Flows enter the catch basin on the west side of 13th Place South and is conveyed south across S 332nd Street along the west side of 13th Place South. LANDMARK APARTMENTS 3.13 JOB #19-019 Technical Information Report Photo 3B – Looking South – Flows continue south along the west side for 13th Place South in a series of pipes and catch basins. Photo 4B – Looking South – Flows continue south along the west side for 13th Place South in a series of pipes and catch basins. LANDMARK APARTMENTS 3.14 JOB #19-019 Technical Information Report Photo 5B – Looking South – Flows continue south along the west side for 13th Place South in a series of pipes and catch basins. Photo 6B – Looking South – Flows continue south along the west side for 13th Place South in a series of pipes and catch basins. LANDMARK APARTMENTS 3.15 JOB #19-019 Technical Information Report Photo 7B – Looking South – Flows continue south along the west side for 13th Place South in a series of pipes and catch basins. Photo 8B – Looking South – Flows continue south along the west side for 13th Place South in a series of pipes and catch basins. LANDMARK APARTMENTS 3.16 JOB #19-019 Technical Information Report Photo 9B – Looking South – Flows continue south along the west side for 13th Place South in a series of pipes and catch basins. Photo 10B – Looking South – Flows continue south along the west side for 13th Place South in a series of pipes and catch basins. LANDMARK APARTMENTS 3.17 JOB #19-019 Technical Information Report Photo 11B – Looking South – Flows continue south along the west side for 13th Place South in a series of pipes and catch basins. Photo 12B – Looking Southwest – Flows are conveyed southwest to a manhole located in the eastbound lanes of S 336th Street. LANDMARK APARTMENTS 3.18 JOB #19-019 Technical Information Report Photo 13B – Looking South – Flows enter a drainage course at roughly the ¼-mile downstream drainage location. Basin C: Photo 1C – Looking South – Runoff from the existing wetland west of the site enters the manhole above and continues south and southeast towards the parking lot of the Federal Way Public Schools Transportation Department. LANDMARK APARTMENTS 3.19 JOB #19-019 Technical Information Report Photo 2C – Looking South – Flows enter this manhole and are conveyed south into the bus parking lot. Photo 3C – Looking Southwest – Stormwater enters the manhole and is conveyed southwest towards the southern boundary of the Federal Way Public Schools Transportation Department. LANDMARK APARTMENTS 3.20 JOB #19-019 Technical Information Report Photo 4C – Looking Southeast – Flows enter the stormwater manhole located on the northeast corner of parcel 9265010030 and is then conveyed southeast. Photo 5C – Looking West – Flows enter the catch basin and is conveyed west into a manhole located in the planter area of parcel 9265030055. LANDMARK APARTMENTS 3.21 JOB #19-019 Technical Information Report Photo 6C – Looking South – Flows enter the manhole and are conveyed south across S 336th Street. Photo 7C – Looking South – Flows enter the manhole located in the eastbound lanes of S 336th Street at the approximate ¼-mile downstream drainage location. LANDMARK APARTMENTS 4.1 JOB #19-019 Technical Information Report Flow Control and Water Quality Analysis and Design In the existing conditions there are three existing on-site drainage basins. All on-site hardscapes will be removed prior to construction. Natural discharge locations for each on-site basin will be maintained in the developed condition. See the Existing Conditions Exhibit located in the Appendix for the locations and areas of each drainage basin that will be evaluated. In the developed condition, stormwater evaluation will occur at the discharge point for each of the three on-site drainage basins (see the Developed Conditions Exhibit). For Basins B & C, stormwater will be collected, detained, and treated in two separate on-site stormwater systems to match predeveloped flow rates while discharging to their natural locations. Basin A is flow control and water quality exempt because the flows will not create more than a 0.15-cfs increase and less than 5,000 SF of pollution generating hard surface will be created. Please see the Developed Conditions Exhibit in the Appendix of this report delineating areas tributary to the on-site stormwater systems and the areas being bypassed. The drainage analysis was modeled using the Western Washington Hydrology Model software with 15-minute time steps in accordance with the 2016 KCSWDM. According to the Geotechnical Report by Earth Solutions NW, LLC, onsite soils are predominantly till and will be modeled as such. The project was modeled with the following parameters: Rainfall Region: Seatac Scale Factor: 1.0 HYDRAULIC ANALYSIS EXISTING CONDITIONS The site generally slopes from north to south. Per the Geotechnical Report, soils are primarily till throughout the site. Ground cover in the existing condition is typically forested with small sections of impervious surfaces scattered throughout. All on-site areas were modeled as the historic forested conditions. The project study area has three (3) separate drainage basins that do not combine within ¼-mile downstream. The total targeted area of the project is approximately 7.60-acres which is mostly vegetation and trees with a total upstream area of 0.38-acre. On-site stormwater flows are not currently collected in a stormwater system on-site. Please refer to the Downstream Drainage Exhibit for information regarding each downstream drainage path for the three on-site drainage basins. In the existing condition, Basin A encompasses approximately 1.37-acres of on-site area with 0.07-acre of frontage along 15th Avenue S in the existing condition. Currently a house, garage, broken asphalt pads, trees and vegetation are located within this basin boundary. Stormwater is collected in the public storm systems located in S 330th Street and 15th Avenue S and is conveyed east towards Pacific Highway S. Basin B contains approximately 2.73-acres of on-site area and 0.25-acre of frontage along S 330th Street and 13th Place S in the existing condition. Additionally, 0.15-acre of upstream area flows through Basin B. This drainage basin is mostly trees and vegetation. Water typically sheet flows west or southwest until it is conveyed into the LANDMARK APARTMENTS 4.2 JOB #19-019 Technical Information Report existing drainage system at the corner of S 332nd Street and 13th Place S. Stormwater continues south along 13th Place S until it reaches the ¼-mile downstream drainage location. Basin C is approximately 3.17-acres of on-site area with approximately 0.01-acre of future frontage improvements near 13th Place S. The on-site basin currently contains an overgrown dirt/gravel road with a broken concrete slab surrounded by trees and vegetation. All existing hardscapes will be removed. Additionally, there is approximately 0.23-acre of upstream area which flows through this basin and into the neighboring parcel. Stormwater from Basin C flows west onto the neighboring parcel prior to being conveyed south through private parcels until it reaches the ¼-mile downstream drainage location. The site is within a Level 2 Flow Control Area which dictates that the existing condition shall be modeled in the historic (forested) condition. The areas used to compute the drainage calculations associated with the existing basin conditions, as well as the corresponding WWHM output, are summarized below. The WWHM Model Outputs are located in the Appendix. Existing Basin A On-Site Frontage 1.37-ac 0.07-ac Total (Till-Forest) 1.44-ac Flow Frequency Return Periods for Predeveloped. Basin POC #1 Return Period Flow(cfs) 2 year 0.0429 5 year 0.0703 10 year 0.0879 25 year 0.1088 50 year 0.1233 100 year 0.1369 Existing Basin B On-Site Frontage Upstream 2.73-ac 0.25-ac 0.15-ac Total (Till-Forest) 3.13-ac Existing Basin C On-Site Frontage Upstream 3.17-ac 0.01-ac 0.23-ac Total (Till-Forest) 3.41-ac LANDMARK APARTMENTS 4.3 JOB #19-019 Technical Information Report DEVELOPED CONDITIONS The proposed development will include the construction of a multi-story, mixed-use development with associated utilities and infrastructure to support the site. Site stormwater discharge locations will be maintained in the developed conditions using the proposed on-site stormwater drainage conveyance system. Infiltration and dispersion BMPs are determined to be infeasible due to the presence of till soils onsite and the lack of space for dispersion. Compost amended soils will be implemented in landscaped areas. The developed conditions will include three (3) separate drainage basins as shown on the Developed Conditions Exhibit at the end of this section. The basins have been separated by their natural drainage discharge locations, matching the discharge durations of each basin’s existing condition flow rate. Land uses in the developed conditions will consist primarily of impervious surfaces, including but not limited to roof areas, parking lots, and sidewalks. Landscaped areas are also proposed, scattered throughout the site. Pollution Generating Impervious Surfaces (PGIS) collected in each basin, will be conveyed to a water quality facility prior to being detained and then will outfall to the basin’s respective natural drainage discharge location. Basin A, the easternmost basin, encompasses a total of 0.14-acre. In the developed condition, road regrading, sidewalk and curb installation, driveway installation, and frontage landscaping will be constructed. Stormwater will not be treated for water quality because the basin produces less than 5,000 SF of PGIS. The proposed improvements do not impose more than a 0.15-cfs increase in 100-year storm event compared to the historic forested condition and is therefore exempt from flow control requirements. Basin B, the middle basin, encompasses a total of 3.77-acres. In the developed condition, a new road, apartment buildings, parking lots, pedestrian walkways, and other supporting impervious infrastructure will be constructed along with site landscaping. In the developed condition, there is a 0.15-cfs increase in 100-year peak flows when compared to the existing conditions, triggering a flow control facility. A detention vault is proposed underneath the proposed parking lot. Additionally, more than 5,000 SF of PGIS will be constructed within this basin requiring Enhanced Water Quality. All on-site runoff will be collected and conveyed into the detention facility prior to being treated in a BioPod system which provides Enhanced Water Quality treatment. After the stormwater has been treated to the enhanced water quality standard, the stormwater will be discharged to its natural discharge location in 13th Place South. All stormwater within Basin B cannot be collected for water quality treatment. For the project, there is a proposed PGIS mitigation swap to collect more PGIS area than the area that is bypassing the onsite stormwater facilities. There will be a portion of 15th Ave S that will be conveyed into the on-site stormwater system as seen on the Developed Conditions Exhibit located in the Appendix. Basin C, the westernmost basin, encompasses approximately 4.05-acres. In the developed condition parking lots, an apartment building, a daycare facility, sidewalks, and other impervious infrastructure will be constructed along with site landscaping. The proposed basin creates more than a 0.15-cfs increase in the 100-year peak flows compared to the existing conditions, triggering a detention vault that will be located on the southwestern on- site parking lot. Additionally, more than 5,000 SF of PGIS will be constructed within this basin requiring Enhanced Water Quality. On-site runoff will be collected and conveyed into the detention facility prior to being treated in a BioPod system which provides Enhanced Water Quality treatment. After the stormwater has been treated to the enhanced water quality standard, the stormwater will be discharged to its natural discharge location to the west. LANDMARK APARTMENTS 4.4 JOB #19-019 Technical Information Report Developed Basin A (Analysis Point # 1) Site Area [AC] Pervious – Lawn Till 0.02 PGIS Impervious 0.10 0.02 Total 0.14 ac Flow Frequency Return Periods for Developed. Basin POC #1 Return Period Flow(cfs) 2 year 0.0546 5 year 0.0699 10 year 0.0806 25 year 0.0948 50 year 0.1060 100 year 0.1176 This basin is detention exempt because less than a 0.15-cfs increase in 100-year peak flows result when comparing the existing conditions of Basin A to the developed conditions of Basin A. Change in 100-year Peak flows = Developed – Existing = 0.1176 – 0.1369 cfs = -0.0193 cfs Please see the WWHM reports in the Appendix for Basin A hydrology information. Developed Basin B (Analysis Point #2) Site Area [AC] Pervious – Till Lawn Impervious PGIS Mitigation Swap By-Pass Pervious – Till Lawn 0.48 3.08 0.05 0.15 *Bypass Impervious 0.01 Total 3.77 ac *Total impervious by-pass is 0.04-ac PGIS and 0.02-ac impervious prior to subtracting out the 0.05 PGIS Mitigation Trade. Net impervious bypass is 0.01-acres. Please see the WWHM reports in the Appendix for Basin B hydrology information. LANDMARK APARTMENTS 4.5 JOB #19-019 Technical Information Report Developed Basin C (Analysis Point #3) Site Area [AC] Pervious – Lawn Pervious Upstream – Forest PGIS Impervious Pervious Upstream Bypass - Forest Pervious Bypass – Forest Pervious Bypass – Lawn 0.33 0.08 1.26 1.05 0.30 0.68 0.35 Total 4.05 ac Please see the WWHM report in the Appendix for Basin C hydrology information. LANDMARK APARTMENTS 4.6 JOB #19-019 Technical Information Report FLOW CONTROL ANALYSIS AND DESIGN The flow control systems were designed in compliance with the 2016 KCSWDM. A detention vault and control structure will be located on the southwestern portion of the site, and a detention tank system with a control structure is proposed on the southeastern portion of the site. The outlet control structures on each of these detention systems will release runoff at rates that match the Level 2 flow control criteria of 50% of the 2-year peak flow to the 50-year peak flow. All on-site stormwater from Basins B and C (the only basins triggering flow control requirements) will be collected and conveyed to their respective detention facilities prior to offsite discharge to each basin’s respective natural discharge location. BASIN B DETENTION SYSTEM Per the WWHM printout provided in the Appendix, the live storage volume required at the maximum stage of 7.25’ is 102,080 cubic feet. The proposed detention vault will be 4 - 21’ x 176’ x 7.25’ detention cells providing 107,184 cubic feet. Therefore, the vault is adequately sized per the flow control requirements. Live Storage Volume Required = 102,080 cubic feet Provided = 107,184 cubic feet Please see the WWHM printout for Basin B in the Appendix. BASIN C DETENTION SYSTEM Per the WWHM printout provided below, the live storage volume required at the maximum stage of 8’ is 62,272 cubic feet. The proposed vault will provide 2 – 14’ x 288’ x 8’ live storage cells, totaling to 64,512 cubic feet. The proposed vault is therefore adequately sized for the required flow control. Live Storage Volume Required = 62,272 cubic feet Provided = 64,512 cubic feet Please see the WWHM printout for Basin C in the Appendix. LANDMARK APARTMENTS 4.7 JOB #19-019 Technical Information Report WATER QUALITY SYSTEM For Basins B and C, water quality is required because each basin will create more than 5,000 SF of PGIS. The Enhanced Water Quality standard will be met utilizing an Oldcastle BioPod system downstream of detention. The BioPod system is a GULD approved product through the DOE’s TAPE program for Enhanced Water Quality. Basin A, in the developed condition, contains under 5,000 SF of PGIS and is therefore exempt from water quality requirements. For Basin B and C, water quality will be provided post detention. According to the letter provided for GULD, a BioPod downstream of detention will be sized using the full 2-year release rate of the detention facility. Both the GULD Letter of Approval and the BioPod Detail are located in the Appendix of this report. BASIN B: DETENTION VAULT TO BIOPOD 2-YEAR RELEASE RATE Per the Basin B WWHM printout below, the 2-year release rate from the detention vault is 0.0488 cfs. The BioPod model that meets this 2-year flowrate is the BPU-44 (See the BioPod detail located in the Appendix). LANDMARK APARTMENTS 4.8 JOB #19-019 Technical Information Report BASIN C: DETENTION VAULT TO BIOPOD 2-YEAR RELEASE RATE: Per the Basin C WWHM printout below, the 2-year release rate from the detention vault is 0.0815 cfs. The BioPod model that meets this 2-year flowrate is the BPU-46 (See the BioPod detail located in the Appendix). LANDMARK APARTMENTS 4.9 JOB #19-019 Technical Information Report FLOW CONTROL BMPS Core Requirement #9 in Section 1.2.9 of the 2016 KCWDM requires the project to implement Flow Control BMPs for the roofs and other impervious surfaces to the maximum extent feasible. Full infiltration and Basic Dispersion were considered as preferred designs but upon analysis were found to be infeasible. Full Infiltration is infeasible due to the incompatible infiltration performance of the site, and limited infiltration is not feasible either as delineated below. Basic Dispersion is infeasible due to the lack of a viable vegetated flow path. The project will satisfy BMP requirements using post amended soils. LID BMP feasibility is summarized below. 1. Full Dispersion – The site is bounded to the north and east by S 330th Street and 15th Ave S, respectively. The south currently has a government building and 13th Place South. To the west, there is not enough of an on-site vegetated flow path to allow for full dispersion. For the above reasons, full dispersion is not feasible. 2. Full Infiltration of Roof Runoff – The Geotechnical Analysis (included in the Appendix) says that full infiltration is not feasible due to non-infiltrative soils on the site. 3. Full Infiltration, Limited Infiltration, Bioretention, or Permeable Pavement – The Geotechnical Analysis (included in the Appendix) indicates that there is a presence of till soils underlaying the site. Till soils are not conducive to infiltration making full infiltration, limited infiltration, bioretention and permeable pavement infeasible. 4. Basic Dispersion – The site’s impervious surfaces cannot be treated using basic dispersion due to a lack of vegetated flow path for the proposed project. 5. Native Growth Retention – There is no feasible native growth area onsite suitable for native growth retention. 6. Post-Amended Soils – Amended soils will be applied to landscaped areas on the site. 7. Perforated Pipe Connection – Perforated pipe connections are not recommended due to the lack of infiltrative soils onsite. LANDMARK APARTMENTS 5.1 JOB #19-019 Technical Information Report Conveyance System Analysis and Design The conveyance system will be designed at final engineering to convey the 100-year, 24-hour storm event without overtopping. LANDMARK APARTMENTS 6.1 JOB #19-019 Technical Information Report Special Reports and Studies The following reports are relevant to the project and are included in the Appendix at the end of this Report. · Geotechnical Engineering Study prepared by Earth Solutions NW, LLC dated June 19, 2019. · Review of Wetland Z Adjacent to Parcel 1721049036 prepared by Habitat Technologies dated July 16, 2018 LANDMARK APARTMENTS 7.1 JOB #19-019 Technical Information Report Other Permits At this time, there are no additional permits associated with this project. LANDMARK APARTMENTS 8.1 JOB #19-019 Technical Information Report SWPPP and TESC Analysis and Design A SWPPP will be submitted at final engineering. A TESC Plan has been provided in the planset submitted under separate cover. LANDMARK APARTMENTS 9.1 JOB #19-019 Technical Information Report Bond Quantities and Facilities Summary A bond quantity worksheet will be included at final engineering. LANDMARK APARTMENTS A JOB #19-019 Technical Information Report Appendix WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: Basin A : Analysis Point #1 Site Name: Landmark Apartments Site Address: City : Federal Way Report Date: 2/21/2020 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2019/09/13 Version : 4.2.17 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Mod 1.44 Pervious Total 1.44 Impervious Land Use acre Impervious Total 0 Basin Total 1.44 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Lawn, Mod .02 Pervious Total 0.02 Impervious Land Use acre ROADS MOD 0.12 Impervious Total 0.12 Basin Total 0.14 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:1.44 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.02 Total Impervious Area:0.12 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.042876 5 year 0.070257 10 year 0.087862 25 year 0.108803 50 year 0.123309 100 year 0.136858 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.054551 5 year 0.06985 10 year 0.080571 25 year 0.09482 50 year 0.105964 100 year 0.117576 ___________________________________________________________________ Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.049 0.071 1950 0.059 0.071 1951 0.094 0.042 1952 0.029 0.035 1953 0.024 0.042 1954 0.036 0.044 1955 0.058 0.052 1956 0.047 0.048 1957 0.038 0.052 1958 0.042 0.044 1959 0.036 0.048 1960 0.065 0.048 1961 0.036 0.046 1962 0.022 0.039 1963 0.030 0.048 1964 0.043 0.046 1965 0.029 0.054 1966 0.028 0.039 1967 0.066 0.064 1968 0.037 0.084 1969 0.036 0.050 1970 0.029 0.050 1971 0.033 0.061 1972 0.071 0.062 1973 0.032 0.039 1974 0.035 0.057 1975 0.049 0.059 1976 0.035 0.046 1977 0.005 0.045 1978 0.029 0.066 1979 0.018 0.079 1980 0.084 0.086 1981 0.026 0.052 1982 0.054 0.076 1983 0.046 0.061 1984 0.028 0.040 1985 0.017 0.051 1986 0.073 0.044 1987 0.065 0.070 1988 0.026 0.046 1989 0.017 0.072 1990 0.155 0.093 1991 0.082 0.080 1992 0.034 0.041 1993 0.033 0.050 1994 0.011 0.043 1995 0.047 0.047 1996 0.109 0.062 1997 0.084 0.049 1998 0.021 0.051 1999 0.092 0.112 2000 0.033 0.051 2001 0.006 0.062 2002 0.038 0.065 2003 0.057 0.066 2004 0.060 0.108 2005 0.045 0.041 2006 0.050 0.040 2007 0.117 0.102 2008 0.143 0.074 2009 0.067 0.076 ___________________________________________________________________ Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.1553 0.1116 2 0.1430 0.1078 3 0.1174 0.1018 4 0.1087 0.0926 5 0.0937 0.0864 6 0.0920 0.0842 7 0.0839 0.0802 8 0.0837 0.0792 9 0.0824 0.0761 10 0.0735 0.0757 11 0.0711 0.0741 12 0.0667 0.0720 13 0.0658 0.0711 14 0.0649 0.0709 15 0.0646 0.0695 16 0.0605 0.0663 17 0.0586 0.0656 18 0.0583 0.0655 19 0.0566 0.0640 20 0.0543 0.0625 21 0.0505 0.0620 22 0.0493 0.0618 23 0.0486 0.0615 24 0.0470 0.0610 25 0.0469 0.0586 26 0.0464 0.0574 27 0.0449 0.0542 28 0.0431 0.0524 29 0.0421 0.0522 30 0.0379 0.0522 31 0.0379 0.0513 32 0.0371 0.0510 33 0.0365 0.0506 34 0.0361 0.0501 35 0.0361 0.0499 36 0.0355 0.0499 37 0.0349 0.0489 38 0.0348 0.0483 39 0.0336 0.0480 40 0.0328 0.0479 41 0.0327 0.0476 42 0.0327 0.0474 43 0.0315 0.0464 44 0.0304 0.0460 45 0.0294 0.0459 46 0.0294 0.0458 47 0.0290 0.0453 48 0.0286 0.0445 49 0.0280 0.0443 50 0.0275 0.0440 51 0.0263 0.0434 52 0.0256 0.0421 53 0.0238 0.0419 54 0.0221 0.0415 55 0.0205 0.0407 56 0.0178 0.0400 57 0.0169 0.0395 58 0.0166 0.0388 59 0.0110 0.0388 60 0.0059 0.0386 61 0.0051 0.0353 ___________________________________________________________________ Stream Protection Duration POC #1 The Facility PASSED The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0214 0 0 0 Pass 0.0225 0 0 0 Pass 0.0235 0 0 0 Pass 0.0245 0 0 0 Pass 0.0256 0 0 0 Pass 0.0266 0 0 0 Pass 0.0276 0 0 0 Pass 0.0286 0 0 0 Pass 0.0297 0 0 0 Pass 0.0307 0 0 0 Pass 0.0317 0 0 0 Pass 0.0328 0 0 0 Pass 0.0338 0 0 0 Pass 0.0348 0 0 0 Pass 0.0358 0 0 0 Pass 0.0369 0 0 0 Pass 0.0379 0 0 0 Pass 0.0389 0 0 0 Pass 0.0400 0 0 0 Pass 0.0410 0 0 0 Pass 0.0420 0 0 0 Pass 0.0430 0 0 0 Pass 0.0441 0 0 0 Pass 0.0451 0 0 0 Pass 0.0461 0 0 0 Pass 0.0472 0 0 0 Pass 0.0482 0 0 0 Pass 0.0492 0 0 0 Pass 0.0503 0 0 0 Pass 0.0513 0 0 0 Pass 0.0523 0 0 0 Pass 0.0533 0 0 0 Pass 0.0544 0 0 0 Pass 0.0554 0 0 0 Pass 0.0564 0 0 0 Pass 0.0575 0 0 0 Pass 0.0585 0 0 0 Pass 0.0595 0 0 0 Pass 0.0605 0 0 0 Pass 0.0616 0 0 0 Pass 0.0626 0 0 0 Pass 0.0636 0 0 0 Pass 0.0647 0 0 0 Pass 0.0657 0 0 0 Pass 0.0667 0 0 0 Pass 0.0677 0 0 0 Pass 0.0688 0 0 0 Pass 0.0698 0 0 0 Pass 0.0708 0 0 0 Pass 0.0719 0 0 0 Pass 0.0729 0 0 0 Pass 0.0739 0 0 0 Pass 0.0749 0 0 0 Pass 0.0760 0 0 0 Pass 0.0770 0 0 0 Pass 0.0780 0 0 0 Pass 0.0791 0 0 0 Pass 0.0801 0 0 0 Pass 0.0811 0 0 0 Pass 0.0821 0 0 0 Pass 0.0832 0 0 0 Pass 0.0842 0 0 0 Pass 0.0852 0 0 0 Pass 0.0863 0 0 0 Pass 0.0873 0 0 0 Pass 0.0883 0 0 0 Pass 0.0894 0 0 0 Pass 0.0904 0 0 0 Pass 0.0914 0 0 0 Pass 0.0924 0 0 0 Pass 0.0935 0 0 0 Pass 0.0945 0 0 0 Pass 0.0955 0 0 0 Pass 0.0966 0 0 0 Pass 0.0976 0 0 0 Pass 0.0986 0 0 0 Pass 0.0996 0 0 0 Pass 0.1007 0 0 0 Pass 0.1017 0 0 0 Pass 0.1027 0 0 0 Pass 0.1038 0 0 0 Pass 0.1048 0 0 0 Pass 0.1058 0 0 0 Pass 0.1068 0 0 0 Pass 0.1079 0 0 0 Pass 0.1089 0 0 0 Pass 0.1099 0 0 0 Pass 0.1110 0 0 0 Pass 0.1120 0 0 0 Pass 0.1130 0 0 0 Pass 0.1140 0 0 0 Pass 0.1151 0 0 0 Pass 0.1161 0 0 0 Pass 0.1171 0 0 0 Pass 0.1182 0 0 0 Pass 0.1192 0 0 0 Pass 0.1202 0 0 0 Pass 0.1213 0 0 0 Pass 0.1223 0 0 0 Pass 0.1233 0 0 0 Pass _____________________________________________________ ___________________________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0 acre-feet On-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. Off-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. ___________________________________________________________________ LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft.) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Total Volume Infiltrated 0.00 0.00 0.00 0.00 0.00 0% No Treat. Credit Compliance with LID Standard 8 Duration Analysis Result = Passed ___________________________________________________________________ Perlnd and Implnd Changes No changes have been made. ___________________________________________________________________ This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2020; All Rights Reserved. WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: BASIN B VAULT: Analysis Point #2 Site Name: Landmark Apartments Site Address: City : Federal Way Report Date: 2/21/2020 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2019/09/13 Version : 4.2.17 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Mod 3.13 Pervious Total 3.13 Impervious Land Use acre Impervious Total 0 Basin Total 3.13 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Lawn, Flat .48 Pervious Total 0.48 Impervious Land Use acre ROADS FLAT 3.13 Impervious Total 3.13 Basin Total 3.61 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Vault 1 Vault 1 ___________________________________________________________________ Name : Vault Width : 176 ft. Length : 80 ft. Depth: 10 ft. Discharge Structure Riser Height: 7.25 ft. Riser Diameter: 12 in. Orifice 1 Diameter: 0.8125 in. Elevation: 0 ft. Orifice 2 Diameter: 1.625 in. Elevation: 5.75 ft. Orifice 3 Diameter: 1.5 in. Elevation: 6.25 ft. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Vault Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.323 0.000 0.000 0.000 0.1111 0.323 0.035 0.006 0.000 0.2222 0.323 0.071 0.008 0.000 0.3333 0.323 0.107 0.010 0.000 0.4444 0.323 0.143 0.011 0.000 0.5556 0.323 0.179 0.013 0.000 0.6667 0.323 0.215 0.014 0.000 0.7778 0.323 0.251 0.015 0.000 0.8889 0.323 0.287 0.016 0.000 1.0000 0.323 0.323 0.017 0.000 1.1111 0.323 0.359 0.018 0.000 1.2222 0.323 0.395 0.019 0.000 1.3333 0.323 0.431 0.020 0.000 1.4444 0.323 0.466 0.021 0.000 1.5556 0.323 0.502 0.022 0.000 1.6667 0.323 0.538 0.023 0.000 1.7778 0.323 0.574 0.023 0.000 1.8889 0.323 0.610 0.024 0.000 2.0000 0.323 0.646 0.025 0.000 2.1111 0.323 0.682 0.026 0.000 2.2222 0.323 0.718 0.026 0.000 2.3333 0.323 0.754 0.027 0.000 2.4444 0.323 0.790 0.028 0.000 2.5556 0.323 0.826 0.028 0.000 2.6667 0.323 0.862 0.029 0.000 2.7778 0.323 0.897 0.029 0.000 2.8889 0.323 0.933 0.030 0.000 3.0000 0.323 0.969 0.031 0.000 3.1111 0.323 1.005 0.031 0.000 3.2222 0.323 1.041 0.032 0.000 3.3333 0.323 1.077 0.032 0.000 3.4444 0.323 1.113 0.033 0.000 3.5556 0.323 1.149 0.033 0.000 3.6667 0.323 1.185 0.034 0.000 3.7778 0.323 1.221 0.034 0.000 3.8889 0.323 1.257 0.035 0.000 4.0000 0.323 1.292 0.035 0.000 4.1111 0.323 1.328 0.036 0.000 4.2222 0.323 1.364 0.036 0.000 4.3333 0.323 1.400 0.037 0.000 4.4444 0.323 1.436 0.037 0.000 4.5556 0.323 1.472 0.038 0.000 4.6667 0.323 1.508 0.038 0.000 4.7778 0.323 1.544 0.039 0.000 4.8889 0.323 1.580 0.039 0.000 5.0000 0.323 1.616 0.040 0.000 5.1111 0.323 1.652 0.040 0.000 5.2222 0.323 1.688 0.040 0.000 5.3333 0.323 1.723 0.041 0.000 5.4444 0.323 1.759 0.041 0.000 5.5556 0.323 1.795 0.042 0.000 5.6667 0.323 1.831 0.042 0.000 5.7778 0.323 1.867 0.055 0.000 5.8889 0.323 1.903 0.070 0.000 6.0000 0.323 1.939 0.079 0.000 6.1111 0.323 1.975 0.087 0.000 6.2222 0.323 2.011 0.093 0.000 6.3333 0.323 2.047 0.117 0.000 6.4444 0.323 2.083 0.132 0.000 6.5556 0.323 2.119 0.143 0.000 6.6667 0.323 2.154 0.154 0.000 6.7778 0.323 2.190 0.163 0.000 6.8889 0.323 2.226 0.172 0.000 7.0000 0.323 2.262 0.180 0.000 7.1111 0.323 2.298 0.188 0.000 7.2222 0.323 2.334 0.195 0.000 7.3333 0.323 2.370 0.456 0.000 7.4444 0.323 2.406 1.082 0.000 7.5556 0.323 2.442 1.755 0.000 7.6667 0.323 2.478 2.234 0.000 7.7778 0.323 2.514 2.515 0.000 7.8889 0.323 2.549 2.750 0.000 8.0000 0.323 2.585 2.966 0.000 8.1111 0.323 2.621 3.167 0.000 8.2222 0.323 2.657 3.355 0.000 8.3333 0.323 2.693 3.533 0.000 8.4444 0.323 2.729 3.702 0.000 8.5556 0.323 2.765 3.863 0.000 8.6667 0.323 2.801 4.018 0.000 8.7778 0.323 2.837 4.167 0.000 8.8889 0.323 2.873 4.311 0.000 9.0000 0.323 2.909 4.450 0.000 9.1111 0.323 2.945 4.585 0.000 9.2222 0.323 2.980 4.716 0.000 9.3333 0.323 3.016 4.843 0.000 9.4444 0.323 3.052 4.967 0.000 9.5556 0.323 3.088 5.088 0.000 9.6667 0.323 3.124 5.206 0.000 9.7778 0.323 3.160 5.322 0.000 9.8889 0.323 3.196 5.435 0.000 10.000 0.323 3.232 5.545 0.000 10.111 0.323 3.268 5.654 0.000 10.222 0.000 0.000 5.760 0.000 ___________________________________________________________________ Name : Bypass Bypass: Yes GroundWater: No Pervious Land Use acre C, Lawn, Flat .15 Pervious Total 0.15 Impervious Land Use acre ROADS FLAT 0.01 Impervious Total 0.01 Basin Total 0.16 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:3.13 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.63 Total Impervious Area:3.14 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.093196 5 year 0.152711 10 year 0.190977 25 year 0.236497 50 year 0.268026 100 year 0.297477 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.048847 5 year 0.07236 10 year 0.091186 25 year 0.119076 50 year 0.143096 100 year 0.170128 ___________________________________________________________________ Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.107 0.051 1950 0.127 0.066 1951 0.204 0.166 1952 0.064 0.031 1953 0.052 0.057 1954 0.079 0.043 1955 0.127 0.040 1956 0.102 0.143 1957 0.082 0.042 1958 0.091 0.041 1959 0.078 0.042 1960 0.140 0.053 1961 0.077 0.050 1962 0.048 0.032 1963 0.066 0.045 1964 0.094 0.045 1965 0.062 0.048 1966 0.060 0.040 1967 0.143 0.067 1968 0.081 0.046 1969 0.078 0.041 1970 0.063 0.040 1971 0.071 0.049 1972 0.155 0.104 1973 0.069 0.043 1974 0.076 0.047 1975 0.106 0.048 1976 0.076 0.042 1977 0.011 0.029 1978 0.064 0.042 1979 0.039 0.028 1980 0.182 0.084 1981 0.057 0.038 1982 0.118 0.068 1983 0.101 0.044 1984 0.061 0.037 1985 0.036 0.032 1986 0.160 0.045 1987 0.141 0.052 1988 0.056 0.036 1989 0.037 0.034 1990 0.337 0.097 1991 0.179 0.079 1992 0.073 0.038 1993 0.071 0.030 1994 0.024 0.028 1995 0.102 0.047 1996 0.236 0.153 1997 0.182 0.131 1998 0.045 0.037 1999 0.200 0.088 2000 0.071 0.048 2001 0.013 0.025 2002 0.082 0.055 2003 0.123 0.048 2004 0.131 0.063 2005 0.098 0.037 2006 0.110 0.076 2007 0.255 0.126 2008 0.311 0.071 2009 0.145 0.056 ___________________________________________________________________ Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.3375 0.1661 2 0.3109 0.1532 3 0.2551 0.1433 4 0.2363 0.1310 5 0.2036 0.1256 6 0.2000 0.1045 7 0.1824 0.0965 8 0.1820 0.0880 9 0.1790 0.0838 10 0.1597 0.0792 11 0.1546 0.0755 12 0.1450 0.0706 13 0.1431 0.0682 14 0.1410 0.0674 15 0.1405 0.0657 16 0.1314 0.0628 17 0.1273 0.0570 18 0.1267 0.0561 19 0.1230 0.0553 20 0.1180 0.0528 21 0.1097 0.0524 22 0.1073 0.0508 23 0.1057 0.0504 24 0.1022 0.0486 25 0.1020 0.0483 26 0.1010 0.0482 27 0.0975 0.0479 28 0.0936 0.0479 29 0.0915 0.0475 30 0.0824 0.0472 31 0.0823 0.0461 32 0.0806 0.0452 33 0.0793 0.0452 34 0.0784 0.0450 35 0.0784 0.0438 36 0.0773 0.0429 37 0.0759 0.0426 38 0.0755 0.0424 39 0.0731 0.0422 40 0.0713 0.0420 41 0.0710 0.0418 42 0.0710 0.0414 43 0.0685 0.0405 44 0.0660 0.0404 45 0.0639 0.0403 46 0.0638 0.0400 47 0.0629 0.0383 48 0.0622 0.0378 49 0.0608 0.0374 50 0.0598 0.0374 51 0.0571 0.0373 52 0.0557 0.0363 53 0.0516 0.0342 54 0.0481 0.0319 55 0.0446 0.0316 56 0.0386 0.0313 57 0.0368 0.0302 58 0.0361 0.0288 59 0.0240 0.0276 60 0.0128 0.0276 61 0.0111 0.0249 ___________________________________________________________________ Stream Protection Duration POC #1 The Facility PASSED The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0466 17079 5854 34 Pass 0.0488 15483 4800 31 Pass 0.0511 14067 4241 30 Pass 0.0533 12799 3835 29 Pass 0.0555 11567 3559 30 Pass 0.0578 10515 3332 31 Pass 0.0600 9563 3123 32 Pass 0.0623 8750 2883 32 Pass 0.0645 8031 2693 33 Pass 0.0667 7347 2492 33 Pass 0.0690 6733 2291 34 Pass 0.0712 6188 2137 34 Pass 0.0734 5728 1968 34 Pass 0.0757 5309 1766 33 Pass 0.0779 4924 1608 32 Pass 0.0801 4569 1443 31 Pass 0.0824 4235 1282 30 Pass 0.0846 3951 1106 27 Pass 0.0869 3643 971 26 Pass 0.0891 3388 872 25 Pass 0.0913 3133 788 25 Pass 0.0936 2915 704 24 Pass 0.0958 2706 638 23 Pass 0.0980 2488 551 22 Pass 0.1003 2325 502 21 Pass 0.1025 2136 456 21 Pass 0.1048 1974 419 21 Pass 0.1070 1830 396 21 Pass 0.1092 1702 377 22 Pass 0.1115 1579 356 22 Pass 0.1137 1445 339 23 Pass 0.1159 1326 302 22 Pass 0.1182 1235 282 22 Pass 0.1204 1147 265 23 Pass 0.1226 1086 245 22 Pass 0.1249 1022 231 22 Pass 0.1271 947 212 22 Pass 0.1294 887 198 22 Pass 0.1316 827 176 21 Pass 0.1338 760 161 21 Pass 0.1361 725 148 20 Pass 0.1383 674 134 19 Pass 0.1405 623 114 18 Pass 0.1428 590 88 14 Pass 0.1450 549 69 12 Pass 0.1472 506 61 12 Pass 0.1495 470 53 11 Pass 0.1517 427 42 9 Pass 0.1540 388 30 7 Pass 0.1562 356 27 7 Pass 0.1584 328 23 7 Pass 0.1607 298 19 6 Pass 0.1629 270 13 4 Pass 0.1651 241 7 2 Pass 0.1674 219 0 0 Pass 0.1696 198 0 0 Pass 0.1719 174 0 0 Pass 0.1741 152 0 0 Pass 0.1763 130 0 0 Pass 0.1786 119 0 0 Pass 0.1808 105 0 0 Pass 0.1830 95 0 0 Pass 0.1853 84 0 0 Pass 0.1875 74 0 0 Pass 0.1897 69 0 0 Pass 0.1920 61 0 0 Pass 0.1942 53 0 0 Pass 0.1965 46 0 0 Pass 0.1987 39 0 0 Pass 0.2009 29 0 0 Pass 0.2032 25 0 0 Pass 0.2054 22 0 0 Pass 0.2076 20 0 0 Pass 0.2099 17 0 0 Pass 0.2121 14 0 0 Pass 0.2143 12 0 0 Pass 0.2166 8 0 0 Pass 0.2188 7 0 0 Pass 0.2211 7 0 0 Pass 0.2233 7 0 0 Pass 0.2255 6 0 0 Pass 0.2278 6 0 0 Pass 0.2300 6 0 0 Pass 0.2322 6 0 0 Pass 0.2345 6 0 0 Pass 0.2367 5 0 0 Pass 0.2389 5 0 0 Pass 0.2412 5 0 0 Pass 0.2434 5 0 0 Pass 0.2457 5 0 0 Pass 0.2479 5 0 0 Pass 0.2501 5 0 0 Pass 0.2524 4 0 0 Pass 0.2546 4 0 0 Pass 0.2568 3 0 0 Pass 0.2591 3 0 0 Pass 0.2613 3 0 0 Pass 0.2636 3 0 0 Pass 0.2658 3 0 0 Pass 0.2680 3 0 0 Pass _____________________________________________________ ___________________________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0 acre-feet On-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. Off-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. ___________________________________________________________________ LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft.) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Vault 1 POC N 482.26 N 0.00 Total Volume Infiltrated 482.26 0.00 0.00 0.00 0.00 0% No Treat. Credit Compliance with LID Standard 8 Duration Analysis Result = Passed ___________________________________________________________________ Perlnd and Implnd Changes No changes have been made. ___________________________________________________________________ This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2020; All Rights Reserved. WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: Basin C : Analysis Point #1 Site Name: Landmark Apartments Site Address: City : Federal Way Report Date: 2/21/2020 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2019/09/13 Version : 4.2.17 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Mod 3.41 Pervious Total 3.41 Impervious Land Use acre Impervious Total 0 Basin Total 3.41 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Lawn, Flat .33 C, Forest, Mod .08 Pervious Total 0.41 Impervious Land Use acre ROADS FLAT 2.31 Impervious Total 2.31 Basin Total 2.72 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Vault 1 Vault 1 ___________________________________________________________________ Name : Bypass Bypass: Yes GroundWater: No Pervious Land Use acre C, Lawn, Flat .35 C, Forest, Mod .98 Pervious Total 1.33 Impervious Land Use acre Impervious Total 0 Basin Total 1.33 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ Name : Vault Width : 28 ft. Length : 278 ft. Depth: 10 ft. Discharge Structure Riser Height: 8 ft. Riser Diameter: 12 in. Orifice 1 Diameter: 0.6875 in. Elevation: 0 ft. Orifice 2 Diameter: 1.4375 in. Elevation: 5.9 ft. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Vault Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.178 0.000 0.000 0.000 0.1111 0.178 0.019 0.004 0.000 0.2222 0.178 0.039 0.006 0.000 0.3333 0.178 0.059 0.007 0.000 0.4444 0.178 0.079 0.008 0.000 0.5556 0.178 0.099 0.009 0.000 0.6667 0.178 0.119 0.010 0.000 0.7778 0.178 0.139 0.011 0.000 0.8889 0.178 0.158 0.012 0.000 1.0000 0.178 0.178 0.012 0.000 1.1111 0.178 0.198 0.013 0.000 1.2222 0.178 0.218 0.014 0.000 1.3333 0.178 0.238 0.014 0.000 1.4444 0.178 0.258 0.015 0.000 1.5556 0.178 0.278 0.016 0.000 1.6667 0.178 0.297 0.016 0.000 1.7778 0.178 0.317 0.017 0.000 1.8889 0.178 0.337 0.017 0.000 2.0000 0.178 0.357 0.018 0.000 2.1111 0.178 0.377 0.018 0.000 2.2222 0.178 0.397 0.019 0.000 2.3333 0.178 0.417 0.019 0.000 2.4444 0.178 0.436 0.020 0.000 2.5556 0.178 0.456 0.020 0.000 2.6667 0.178 0.476 0.020 0.000 2.7778 0.178 0.496 0.021 0.000 2.8889 0.178 0.516 0.021 0.000 3.0000 0.178 0.536 0.022 0.000 3.1111 0.178 0.555 0.022 0.000 3.2222 0.178 0.575 0.023 0.000 3.3333 0.178 0.595 0.023 0.000 3.4444 0.178 0.615 0.023 0.000 3.5556 0.178 0.635 0.024 0.000 3.6667 0.178 0.655 0.024 0.000 3.7778 0.178 0.675 0.024 0.000 3.8889 0.178 0.694 0.025 0.000 4.0000 0.178 0.714 0.025 0.000 4.1111 0.178 0.734 0.026 0.000 4.2222 0.178 0.754 0.026 0.000 4.3333 0.178 0.774 0.026 0.000 4.4444 0.178 0.794 0.027 0.000 4.5556 0.178 0.814 0.027 0.000 4.6667 0.178 0.833 0.027 0.000 4.7778 0.178 0.853 0.028 0.000 4.8889 0.178 0.873 0.028 0.000 5.0000 0.178 0.893 0.028 0.000 5.1111 0.178 0.913 0.029 0.000 5.2222 0.178 0.933 0.029 0.000 5.3333 0.178 0.953 0.029 0.000 5.4444 0.178 0.972 0.029 0.000 5.5556 0.178 0.992 0.030 0.000 5.6667 0.178 1.012 0.030 0.000 5.7778 0.178 1.032 0.030 0.000 5.8889 0.178 1.052 0.031 0.000 6.0000 0.178 1.072 0.049 0.000 6.1111 0.178 1.092 0.057 0.000 6.2222 0.178 1.111 0.063 0.000 6.3333 0.178 1.131 0.069 0.000 6.4444 0.178 1.151 0.073 0.000 6.5556 0.178 1.171 0.078 0.000 6.6667 0.178 1.191 0.082 0.000 6.7778 0.178 1.211 0.085 0.000 6.8889 0.178 1.231 0.089 0.000 7.0000 0.178 1.250 0.092 0.000 7.1111 0.178 1.270 0.095 0.000 7.2222 0.178 1.290 0.099 0.000 7.3333 0.178 1.310 0.101 0.000 7.4444 0.178 1.330 0.104 0.000 7.5556 0.178 1.350 0.107 0.000 7.6667 0.178 1.370 0.110 0.000 7.7778 0.178 1.389 0.112 0.000 7.8889 0.178 1.409 0.115 0.000 8.0000 0.178 1.429 0.117 0.000 8.1111 0.178 1.449 0.509 0.000 8.2222 0.178 1.469 1.168 0.000 8.3333 0.178 1.489 1.808 0.000 8.4444 0.178 1.509 2.215 0.000 8.5556 0.178 1.528 2.476 0.000 8.6667 0.178 1.548 2.702 0.000 8.7778 0.178 1.568 2.910 0.000 8.8889 0.178 1.588 3.104 0.000 9.0000 0.178 1.608 3.286 0.000 9.1111 0.178 1.628 3.459 0.000 9.2222 0.178 1.648 3.623 0.000 9.3333 0.178 1.667 3.780 0.000 9.4444 0.178 1.687 3.930 0.000 9.5556 0.178 1.707 4.075 0.000 9.6667 0.178 1.727 4.214 0.000 9.7778 0.178 1.747 4.350 0.000 9.8889 0.178 1.767 4.481 0.000 10.000 0.178 1.787 4.608 0.000 10.111 0.178 1.806 4.732 0.000 10.222 0.000 0.000 4.852 0.000 ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:3.41 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:1.74 Total Impervious Area:2.31 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.101533 5 year 0.166371 10 year 0.208061 25 year 0.257653 50 year 0.292003 100 year 0.324088 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.081534 5 year 0.129413 10 year 0.165612 25 year 0.216279 50 year 0.257535 100 year 0.301766 ___________________________________________________________________ Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.117 0.101 1950 0.139 0.127 1951 0.222 0.204 1952 0.070 0.049 1953 0.056 0.083 1954 0.086 0.064 1955 0.138 0.080 1956 0.111 0.134 1957 0.090 0.078 1958 0.100 0.069 1959 0.085 0.064 1960 0.153 0.107 1961 0.084 0.072 1962 0.052 0.045 1963 0.072 0.065 1964 0.102 0.079 1965 0.068 0.075 1966 0.065 0.055 1967 0.156 0.130 1968 0.088 0.078 1969 0.085 0.068 1970 0.069 0.055 1971 0.077 0.081 1972 0.168 0.173 1973 0.075 0.065 1974 0.083 0.075 1975 0.115 0.092 1976 0.082 0.070 1977 0.012 0.032 1978 0.070 0.059 1979 0.042 0.038 1980 0.198 0.147 1981 0.062 0.054 1982 0.129 0.128 1983 0.110 0.077 1984 0.066 0.049 1985 0.039 0.036 1986 0.174 0.100 1987 0.154 0.102 1988 0.061 0.046 1989 0.040 0.038 1990 0.368 0.264 1991 0.195 0.174 1992 0.080 0.062 1993 0.078 0.053 1994 0.026 0.033 1995 0.111 0.076 1996 0.257 0.219 1997 0.199 0.158 1998 0.049 0.058 1999 0.218 0.195 2000 0.077 0.067 2001 0.014 0.022 2002 0.090 0.084 2003 0.134 0.100 2004 0.143 0.137 2005 0.106 0.076 2006 0.119 0.111 2007 0.278 0.275 2008 0.339 0.196 2009 0.158 0.114 ___________________________________________________________________ Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.3677 0.2752 2 0.3387 0.2638 3 0.2779 0.2195 4 0.2575 0.2042 5 0.2218 0.1962 6 0.2179 0.1951 7 0.1987 0.1743 8 0.1983 0.1730 9 0.1950 0.1580 10 0.1740 0.1465 11 0.1684 0.1371 12 0.1579 0.1336 13 0.1559 0.1303 14 0.1536 0.1283 15 0.1531 0.1266 16 0.1432 0.1144 17 0.1387 0.1107 18 0.1380 0.1066 19 0.1340 0.1023 20 0.1286 0.1014 21 0.1195 0.1002 22 0.1169 0.1001 23 0.1152 0.0917 24 0.1114 0.0845 25 0.1112 0.0830 26 0.1100 0.0815 27 0.1062 0.0797 28 0.1020 0.0787 29 0.0996 0.0782 30 0.0897 0.0777 31 0.0897 0.0769 32 0.0878 0.0759 33 0.0864 0.0758 34 0.0855 0.0749 35 0.0854 0.0748 36 0.0842 0.0719 37 0.0827 0.0698 38 0.0823 0.0690 39 0.0796 0.0681 40 0.0777 0.0674 41 0.0774 0.0647 42 0.0774 0.0646 43 0.0746 0.0641 44 0.0719 0.0639 45 0.0696 0.0621 46 0.0695 0.0594 47 0.0686 0.0578 48 0.0678 0.0553 49 0.0662 0.0550 50 0.0651 0.0536 51 0.0622 0.0535 52 0.0606 0.0487 53 0.0563 0.0485 54 0.0524 0.0463 55 0.0486 0.0446 56 0.0421 0.0378 57 0.0401 0.0377 58 0.0393 0.0356 59 0.0261 0.0332 60 0.0139 0.0316 61 0.0121 0.0221 ___________________________________________________________________ Stream Protection Duration POC #1 The Facility PASSED The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0508 17079 16993 99 Pass 0.0532 15481 14604 94 Pass 0.0556 14070 12769 90 Pass 0.0581 12799 11355 88 Pass 0.0605 11567 10031 86 Pass 0.0630 10515 8953 85 Pass 0.0654 9563 8083 84 Pass 0.0678 8750 7373 84 Pass 0.0703 8031 6690 83 Pass 0.0727 7347 6166 83 Pass 0.0751 6733 5640 83 Pass 0.0776 6188 5183 83 Pass 0.0800 5726 4840 84 Pass 0.0824 5309 4496 84 Pass 0.0849 4924 4196 85 Pass 0.0873 4569 3933 86 Pass 0.0898 4235 3670 86 Pass 0.0922 3951 3373 85 Pass 0.0946 3643 3110 85 Pass 0.0971 3388 2883 85 Pass 0.0995 3133 2676 85 Pass 0.1019 2917 2475 84 Pass 0.1044 2712 2280 84 Pass 0.1068 2490 2090 83 Pass 0.1092 2319 1955 84 Pass 0.1117 2141 1818 84 Pass 0.1141 1973 1716 86 Pass 0.1166 1828 1598 87 Pass 0.1190 1706 1507 88 Pass 0.1214 1578 1406 89 Pass 0.1239 1443 1305 90 Pass 0.1263 1325 1192 89 Pass 0.1287 1233 1107 89 Pass 0.1312 1150 999 86 Pass 0.1336 1085 881 81 Pass 0.1361 1021 798 78 Pass 0.1385 950 709 74 Pass 0.1409 886 635 71 Pass 0.1434 826 572 69 Pass 0.1458 764 512 67 Pass 0.1482 725 462 63 Pass 0.1507 675 425 62 Pass 0.1531 623 388 62 Pass 0.1555 589 347 58 Pass 0.1580 552 306 55 Pass 0.1604 506 257 50 Pass 0.1629 469 222 47 Pass 0.1653 428 194 45 Pass 0.1677 388 158 40 Pass 0.1702 356 144 40 Pass 0.1726 328 127 38 Pass 0.1750 298 112 37 Pass 0.1775 270 103 38 Pass 0.1799 241 95 39 Pass 0.1824 218 88 40 Pass 0.1848 198 75 37 Pass 0.1872 173 62 35 Pass 0.1897 152 56 36 Pass 0.1921 130 39 30 Pass 0.1945 119 32 26 Pass 0.1970 104 24 23 Pass 0.1994 95 17 17 Pass 0.2018 83 12 14 Pass 0.2043 74 4 5 Pass 0.2067 69 4 5 Pass 0.2092 61 4 6 Pass 0.2116 54 4 7 Pass 0.2140 46 4 8 Pass 0.2165 39 4 10 Pass 0.2189 29 4 13 Pass 0.2213 25 3 12 Pass 0.2238 22 3 13 Pass 0.2262 20 3 15 Pass 0.2286 17 3 17 Pass 0.2311 14 3 21 Pass 0.2335 12 3 25 Pass 0.2360 8 3 37 Pass 0.2384 7 2 28 Pass 0.2408 7 2 28 Pass 0.2433 7 2 28 Pass 0.2457 6 2 33 Pass 0.2481 6 2 33 Pass 0.2506 6 2 33 Pass 0.2530 6 2 33 Pass 0.2555 6 2 33 Pass 0.2579 5 2 40 Pass 0.2603 5 2 40 Pass 0.2628 5 2 40 Pass 0.2652 5 1 20 Pass 0.2676 5 1 20 Pass 0.2701 5 1 20 Pass 0.2725 5 1 20 Pass 0.2749 4 1 25 Pass 0.2774 4 0 0 Pass 0.2798 3 0 0 Pass 0.2823 3 0 0 Pass 0.2847 3 0 0 Pass 0.2871 3 0 0 Pass 0.2896 3 0 0 Pass 0.2920 3 0 0 Pass _____________________________________________________ ___________________________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0 acre-feet On-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. Off-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. ___________________________________________________________________ LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft.) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Vault 1 POC N 357.10 N 0.00 Total Volume Infiltrated 357.10 0.00 0.00 0.00 0.00 0% No Treat. Credit Compliance with LID Standard 8 Duration Analysis Result = Passed ___________________________________________________________________ Perlnd and Implnd Changes No changes have been made. ___________________________________________________________________ This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2020; All Rights Reserved. August 2019 GENERAL USE LEVEL DESIGNATION FOR BASIC (TSS), DISSOLVED METALS (ENHANCED), AND PHOSPHORUS TREATMENT For Oldcastle Infrastructure, Inc.’s The BioPod™ Biofilter (Formerly the TreePod Biofilter) Ecology’s Decision: Based on Oldcastle Infrastructure, Inc. application submissions for the The BioPod™ Biofilter (BioPod), Ecology hereby issues the following use level designation: 1. General Use Level Designation (GULD) for Basic, Enhanced, and Phosphorus Treatment:  Sized at a hydraulic loading rate of 1.6 gallons per minute (gpm) per square foot (sq ft) of media surface area.  Constructed with a minimum media thickness of 18-inches (1.5-feet). 2. Ecology approves the BioPod at the hydraulic loading rate listed above, to achieve the maximum water quality design flow rate. The water quality design flow rates are calculated using the following procedures:  Western Washington: For treatment installed upstream of detention or retention, the water quality design flow rate is the peak 15-minute flow rate as calculated using the latest version of the Western Washington Hydrology Model or other Ecology- approved continuous runoff model.  Eastern Washington: For treatment installed upstream of detention or retention, the water quality design flow rate is the peak 15-minute flow rate as calculated using one of the three methods described in Chapter 2.2.5 of the Stormwater Management Manual for Eastern Washington (SWMMEW) or local manual.  Entire State: For treatment installed downstream of detention, the water quality design flow rate is the full 2-year release rate of the detention facility. 3. The GULD has no expiration date, but may be amended or revoked by Ecology. Ecology’s Conditions of Use: The BioPod shall comply with these conditions: 1) Applicants shall design, assemble, install, operate, and maintain the BioPod installations in accordance with Oldcastle Infrastructure, Inc.’s applicable manuals and the Ecology Decision. 2) The minimum size filter surface-area for use in Washington is determined by using the design water quality flow rate (as determined in Ecology Decision, Item 3, above) and the Infiltration Rate (as identified in Ecology Decision, Item 1, above). Calculate the required area by dividing the water quality design flow rate (cu-ft/sec) by the Infiltration Rate (converted to ft/sec) to obtain required surface area (sq ft) of the BioPod unit 3) BioPod media shall conform to the specifications submitted to and approved by Ecology 4) Maintenance: The required inspection/maintenance interval for stormwater treatment devices is often dependent on the efficiency of the device and the degree of pollutant loading from a particular drainage basin. Therefore, Ecology does not endorse or recommend a “one size fits all” maintenance cycle for a particular model/size of manufactured filter treatment device.  The BioPod is designed for a target maintenance interval of 1 year. Maintenance includes replacing the mulch, assessing plant health, removal of trash, and raking the top few inches of engineered media.  A BioPod system tested at the Lake Union Ship Canal Test Facility in Seattle, WA required maintenance after 1.5 months, or 6.3% of a water year. Monitoring personnel observed similar maintenance issues with other systems evaluated at the Test Facility. The runoff from the Test Facility may be unusual and maintenance requirements of systems installed at the Test Facility may not be indicative of maintenance requirements for all sites.  Test results provided to Ecology from a BioPod System evaluated in a lab following New Jersey Department of Environmental Protection Laboratory Protocol for Filtration MTDs have indicated the BioPod System is capable of longer maintenance intervals.  Owners/operators must inspect BioPod systems for a minimum of twelve months from the start of post-construction operation to determine site-specific inspection/maintenance schedules and requirements. Owners/operators must conduct inspections monthly during the wet season, and every other month during the dry season. (According to the SWMMWW, the wet season in western Washington is October 1 to April 30. According to the SWMMEW, the wet season in eastern Washington is October 1 to June 30.) After the first year of operation, owners/operators must conduct inspections based on the findings during the first year of inspections.  Conduct inspections by qualified personnel, follow manufacturer’s guidelines, and use methods capable of determining either a decrease in treated effluent flow rate and/or a decrease in pollutant removal ability. 5) Install the BioPod in such a manner that you bypass flows exceeding the maximum operating rate and you will not resuspend captured sediment. 6) Discharges from the BioPod shall not cause or contribute to water quality standards violations in receiving waters. Applicant: Oldcastle Infrastructure, Inc. Applicant’s Address: 7100 Longe St, Suite 100 Stockton, CA 95206 Application Documents: Technical Evaluation Report TreePod™ BioFilter System Performance Certification Project, Prepared for Oldcastle, Inc., Prepared by Herrera Environmental Consultants, Inc. February 2018 Technical Memorandum: Response to Board of External Reviewers’ Comments on the Technical Evaluation Report for the TreePod™ Biofilter System Performance Certification Project, Oldcastle, Inc. and Herrera Environmental Consultants, Inc., February 2018 Technical Memorandum: Response to Board of External Reviewers’ Comments on the Technical Evaluation Report for the TreePod™ Biofilter System Performance Certification Project, Oldcastle, Inc. and Herrera Environmental Consultants, Inc., January 2018 Application for Pilot Use Level Designation, TreePod™ Biofilter – Stormwater Treatment System, Oldcastle Stormwater Solutions, May 2016 Emerging Stormwater Treatment Technologies Application for Certification: The TreePod™ Biofilter, Oldcastle Stormwater Solutions, April 2016 Applicant’s Use Level Request:  General Use Level Designation as a Basic, Enhanced, and Phosphorus Treatment device in accordance with Ecology’s Stormwater Management Manual for Western Washington Applicant’s Performance Claims: Based on results from laboratory and field-testing, the applicant claims the BioPod™ Biofilter operating at a hydraulic loading rate of 153 inches per hour is able to remove:  80% of Total Suspended Solids (TSS) for influent concentrations greater than 100 mg/L and achieve a 20 mg/L effluent for influent concentrations less than 100 mg/L.  60% dissolved zinc for influent concentrations 0.02 to 0.3 mg/L.  30% dissolved copper for influent concentrations 0.005 to 0.02 mg/L.  50% or greater total phosphorus for influent concentrations 0.1 to 0.5 mg/L. Ecology’s Recommendations: Ecology finds that:  Oldcastle Infrastructure, Inc. has shown Ecology, through laboratory and field testing, that the BioPod™ Biofilter is capable of attaining Ecology’s Basic, Total Phosphorus, and Enhanced treatment goals. Findings of Fact: Field Testing 1. Herrera Environmental Consultants, Inc. conducted monitoring of the BioPod™ Biofilter at the Lake Union Ship Canal Test Facility in Seattle Washington between November 2016 and April 2018. Herrera collected flow-weight composite samples during 14 separate storm events and peak flow grab samples during 3 separate storm events. The system was sized at an infiltration rate of 153 inches per hour or a hydraulic loading rate of 1.6 gpm/ft2. 2. The D50 of the influent PSD ranged from 3 to 292 microns, with an average D50 of 28 microns. 3. Influent TSS concentrations ranged from 17 mg/L to 666 mg/L, with a mean concentration of 98 mg/L. For all samples (influent concentrations above and below 100 mg/L) the bootstrap estimate of the lower 95 percent confidence limit (LCL 95) of the mean TSS reduction was 84% and the bootstrap estimate of the upper 95 percent confidence limit (UCL95) of the mean TSS effluent concentration was 8.2 mg/L. 4. Dissolved copper influent concentrations from the 17 events ranged from 9.0 µg/L to 21.1 µg/L. The 21.1 µg/L data point was reduced to 20.0 µg/L, the upper limit to the TAPE allowed influent concentration range, prior to calculating the pollutant removal. A bootstrap estimate of the LCL95 of the mean dissolved copper reduction was 35%. 5. Dissolved zinc influent concentrations from the 17 events ranged from 26.1 µg/L to 43.3 µg/L. A bootstrap estimate of the LCL95 of the mean dissolved zinc reduction was 71%. 6. Total phosphorus influent concentrations from the 17 events ranged from 0.064 mg/L to 1.56 mg/L. All influent data greater than 0.5 mg/L were reduced to 0.5 mg/L, the upper limit to the TAPE allowed influent concentration range, prior to calculating the pollutant removal. A bootstrap estimate of the LCL95 of the mean total phosphorus reduction was 64%. 7. The system experienced rapid sediment loading and needed to be maintained after 1.5 months. Monitoring personnel observed similar sediment loading issues with other systems evaluated at the Test Facility. The runoff from the Test Facility may not be indicative of maintenance requirements for all sites. Laboratory Testing 1. Good Harbour Laboratories (GHL) conducted laboratory testing at their site in Mississauga, Ontario in October 2017 following the New Jersey Department of Environmental Protection Laboratory Protocol for Filtration MTDs. The testing evaluated a 4-foot by 6-foot standard biofiltration chamber and inlet contour rack with bypass weir. The test sediment used during the testing was custom blended by GHL using various commercially available silica sands, which had an average d50 of 69 µm. Based on the lab test results: a. GHL evaluated removal efficiency over 15 events at a Maximum Treatment Flow Rate (MTFR) of 37.6 gpm, which corresponds to a MTFR to effective filtration treatment area ratio of 1.80 gpm/ft2. The system, operating at 100% of the MTFR with an average influent concentration of 201.3 mg/L, had an average removal efficiency of 99 percent. b. GHL evaluated sediment mass loading capacity over an additional 16 events using an influent SSC concentration of 400 mg/L. The first 11 runs were evaluated at 100% of the MTFR. The BioPod began to bypass, so the remaining 5 runs were evaluated at 90% of the MTFR. The total mass of the sediment captured was 245.0 lbs and the cumulative mass removal efficiency was 96.3%. 2. Herrera Environmental Consultants Inc. conducted laboratory testing in September 2014 at the Seattle University Engineering Laboratory. The testing evaluated the flushing characteristics, hydraulic conductivity, and pollutant removal ability of twelve different media blends. Based on this testing, Oldcastle Infrastructure, Inc. selected one media blend, Mix 8, for inclusion in their TAPE evaluation of the BioPod™ Biofilter. a. Herrera evaluated Mix 8 in an 8-inch diameter by 36-inch tall polyvinyl chloride (PVC) column. The column contained 18-inches of Mix 8 on top of 6-inches of pea gravel. The BioPod will normally include a 3-inch mulch layer on top of the media layer; however, this was not included in the laboratory testing. b. Mix 8 has a hydraulic conductivity of 218 inches per hour; however, evaluation of the pollutant removal ability of the media was based on an infiltration rate of 115 inches per hour. The media was tested at 75%, 100%, and 125% of the infiltration rate. Based on the lab test results:  The system was evaluated using natural stormwater. The dissolved copper and dissolved zinc concentrations in the natural stormwater were lower than the TAPE influent standards; therefore, the stormwater was spiked with 66.4 mL of 100 mg/L Cu solution and 113.6 mL of 1,000 mg/L Zn solution.  The BioPod removed an average of 81% of TSS, with a mean influent concentration of 48.4 mg/L and a mean effluent concentration of 9.8 mg/L.  The BioPod removed an average of 94% of dissolved copper, with a mean influent concentration of 10.6 µg/L and a mean effluent concentration of 0.6 µg/L.  The BioPod removed an average of 97% of dissolved zinc, with a mean influent concentration of 117 µg/L and a mean effluent concentration of 4 µg/L.  The BioPod removed an average of 97% of total phosphorus, with a mean influent concentration of 2.52 mg/L and a mean effluent concentration of 0.066 mg/L. When total phosphorus influent concentrations were capped at the TAPE upper limit of 0.5 mg/L, calculations showed an average removal of 87%. Other BioPod Related Issues to be Addressed By the Company: 1. Conduct hydraulic testing to obtain information about maintenance requirements on a site with runoff that is more typical of the Pacific Northwest. Technology Description: Download at https://oldcastleprecast.com/stormwater/bioretention- biofiltration-applications/bioretention-biofiltration- solutions/ Contact Information: Applicant: Chris Demarest Oldcastle Infrastructure, Inc. (925) 667-7100 Chris.demarest@oldcastle.com Applicant website: https://oldcastleprecast.com/stormwater/ Ecology web link: https://ecology.wa.gov/Regulations-Permits/Guidance-technical- assistance/Stormwater-permittee-guidance-resources/Emerging-stormwater-treatment- technologies Ecology: Douglas C. Howie, P.E. Department of Ecology Water Quality Program (360) 407-6444 douglas.howie@ecy.wa.gov Revision History Date Revision March 2018 GULD granted for Basic Treatment March 2018 Provisional GULD granted for Enhanced and Phosphorus Treatment June 2016 PULD Granted April 2018 GULD for Basic and Provisional GULD for Enhanced and Phosphorus granted, changed name to BioPod from TreePod July 2018 GULD for Enhanced and Phosphorus granted September 2018 Changed Address for Oldcastle December 2018 Added minimum media thickness requirement May 2019 Changed language on who must Install and maintain the device from Oldcastle to Applicants August 2019 Added text on sizing using infiltration rate and water quality design flow rate EarthSolutionsNWLLC EarthSolutions NW LLC 1805 -136th Place N.E.,Suite 201 Bellevue,WA 98005 (425)449-4704 Fax (425)449-4711 www.earthsolutionsnw.com Geotechnical Engineering Construction Observation/Testing Environmental Services GEOTECHNICAL ENGINEERING STUDY CELEBRATION PARK ASSEMBLAGE 33040-33090 -14 AVENUE SOUTH & 33002,33061 &33101 -15 AVENUE SOUTH FEDERAL WAY,WASHINGTON ES-1026.04 TH TH Drwn. Checked Date Date Proj.No. Plate Earth Solutions NWLLC Geotechnical Engineering,Construction EarthSolutionsNWLLC EarthSolutions NW LLC Observation/Testing and Environmental Services Vicinity Map Celebration Park Assemblage Federal Way,Washington MRS AZS 05/22/2019 May 2019 1026.04 1 NORTH NOTE:This plate may contain areas of color.ESNW cannot be responsible for any subsequent misinterpretation of the information resulting from black &white reproductions of this plate. Reference: King County,Washington Map 745 By The Thomas Guide Rand McNally 32nd Edition SITE Drwn. Checked Date Date Proj.No. Plate Earth Solutions NWLLC Geotechnical Engineering,Construction EarthSolutionsNWLLC EarthSolutions NW LLC Observation/Testing and Environmental Services Boring Location Plan Celebration Park Assemblage Federal Way,Washington MRS AZS 05/22/2019 May 2019 1026.04 2 NORTH NOT -TO -SCALE NOTE:This plate may contain areas of color.ESNW cannot be responsible for any subsequent misinterpretation of the information resulting from black &white reproductions of this plate. NOTE:The graphics shown on this plate are not intended for design purposes or precise scale measurements,but only to illustrate the approximate test locations relative to the approximate locations of existing and /or proposed site features.The information illustrated is largely based on data provided by the client at the time of our study.ESNW cannot be responsible for subsequent design changes or interpretation of the data by others. LEGEND Approximate Location of ESNW Boring,Proj.No. ES-1026.04,May 2019 Subject Site B-1 B-2 B-3 B-4 UST-1 B-1 370 380 390 400 370 380 390 400 S. 330TH STREET 15TH AVENUE S.S. 332ND STREET Drwn. Checked Date Date Proj.No. Plate Earth Solutions NWLLCEarthSolutionsNWLLC EarthSolutions NW LLC Geotechnical Engineer ing,C onstr uction Observation/Testing and Environmental Services Retaining Wall Drainage Detail Celebration Park Assemblage Federal Way,Washington MRS AZS 05/22/2019 May 2019 1026.04 3 NOTES: Free-draining Backfill should consist of soil having less than 5 percent fines. Percent passing No.4 sieve should be 25 to 75 percent. Sheet Drain may be feasible in lieu of Free-draining Backfill,per ESNW recommendations. Drain Pipe should consist of perforated, rigid PVC Pipe surrounded with 1-inch Drain Rock. LEGEND: Free-draining Structural Backfill 1-inch Drain Rock 18"Min. Structural Fill Perforated Rigid Drain Pipe (Surround in Drain Rock) SCHEMATIC ONLY -NOT TO SCALE NOT A CONSTRUCTION DRAWING Drwn. Checked Date Date Proj.No. Plate Earth Solutions NWLLC Geotechnical Engineering,Construction Observation/Testing and Environmental Services EarthSolutionsNWLLC EarthSolutions NW LLC Footing Drain Detail Celebration Park Assemblage Federal Way,Washington MRS AZS 05/22/2019 May 2019 1026.04 4 Slope Perforated Rigid Drain Pipe (Surround in Drain Rock) 18"Min. NOTES: Do NOT tie roof downspouts to Footing Drain. Surface Seal to consist of 12"of less permeable,suitable soil.Slope away from building. LEGEND: Surface Seal:native soil or other low-permeability material. 1-inch Drain Rock SCHEMATIC ONLY -NOT TO SCALE NOT A CONSTRUCTION DRAW ING