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19-105850-SU-Preliminary TIR-08-6-2021-V2 Western Washington Division Eastern Washington Division 165 NE Juniper St., Ste 201, Issaquah, WA 98027 407 Swiftwater Blvd Street, Cle Elum, WA 98922 Phone: (425) 392-0250 Fax: (425) 391-3055 Phone: (509) 674-7433 Fax: (509) 674-7419 www.EncompassES.net PRELIMINARY TECHNICAL INFORMATION REPORT City of Federal Way For Kislyak Preliminary Short Plat 34402 24th Place SW Federal Way, WA 98023 December 3, 2019 Updated: July 22, 2021 Prepared By: Ian Dahl Encompass Engineering Job No. 17678 Prepared For: Petr Kislyak 6608 12th Street East Fife, WA 98424 Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page i Table of Contents I. PROJECT OVERVIEW .............................................................................................................................. 1 II. CONDITIONS AND REQUIREMENTS SUMMARY .................................................................................... 5 III. OFF-SITE ANALYSIS ................................................................................................................................ 9 IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ......................................... 18 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN .................................................................................. 23 VI. SPECIAL REPORTS AND STUDIES ......................................................................................................... 23 VII. OTHER PERMITS .................................................................................................................................. 23 VIII. CSWPPP ANALYSIS AND DESIGN ......................................................................................................... 23 IX. BOND QUANTITIES AND DECLARATION OF COVENANT ..................................................................... 23 X. OPERATION AND MAINTENANCE MANUAL ........................................................................................ 23 List of Figures Figure 1- TIR Worksheet Figure 2- Vicinity Map Figure 3- Soils Map and Legend Figure 4- Existing Conditions Map Figure 5- Developed Conditions Map Figure 6- Drainage Review Flow Chart Figure 7- Downstream Map Appendix A Geotechnical Engineering Study, by Earth Solutions NW, LLC, dated May 22, 2018 Appendix B WWHM2012 Output 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 15 EASEMENTS/TRACTS Part 16 STRUCTURAL ANALYSIS  Drainage Easement  Covenant  Native Growth Protection Covenant  Tract  Other ___________________________  Cast in Place Vault  Retaining Wall  Rockery > 4’ High  Structural on Steep Slope  Other ______________________________ Part 17 SIGNATURE OF PROFESSIONAL ENGINEER I, or a civil engineer under my supervision, have visited the site. Actual site conditions as observed were incorporated into this worksheet and the attached Technical Information Report. To the best of my knowledge the information provided here is accurate. Signed/Date 2016 Surface Water Design Manual 4/24/2016 5 Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 1 I. PROJECT OVERVIEW Project: Kislyak Preliminary Short Plat Tax Parcel #: 894720-0110 Site Address: 34402 24th Place Southwest, Federal Way, WA 98023 Site Area: The tax parcel area is 1.74 Acres Legal Description: VIRGINIA HILLS TGW UND 1/7 INT IN PVT RD PLAT LOT 11 Figure 2: Vicinity Map Pre-Developed Site Conditions The 75,869 SF (1.74 AC) project site is currently developed with a single-family residence, several out- buildings, utilities, an onsite septic system, and an existing driveway access from 24 th Place SW. The vegetation onsite consists of a lawn area on the central portion of the site, and an area that was previously cleared on the eastern portion of the site. The topography slopes to the east at approximately 8-15%. See Figure 4 for an Existing Site Conditions map. Critical Areas There are no critical areas or critical area buffers mapped on the site. Soils Per the US Department of Agriculture (USDA), Natural Resources Conservation Service (NCRS) Web Soil Survey (WSS) information, the project site is generally underlain with Alderwood gravelly sandy loam. The Geotechnical Engineering Study prepared by Earth Solutions NW, LLC, dated May 22, 2018 is included in Appendix A of this report and confirms these soil conditions. Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 2 Figure 3: Soils Map and Legend Developed Site Conditions The proposal incorporates the clearing, grading and platting of the 75,869 SF (1.74 AC) project site to accommodate the construction of 5 total lots including 4 new single-family residences, associated utilities, a public access road, and a private stormwater facility. The existing residence in the northwest corner of the project site will be retained in Lot 1. The total limits of disturbance including off-site road and frontage improvements is 63,098 SF (1.448 AC). The project site is located within the Hylebos Creek Drainage Basin which is classified as a Level 2 Flow Control Area on the City of Federal Way Flow Control Applications Map. Per the City of Federal Way’s Review Comments, the project is required to meet the Level 3 flow control criteria due to a conveyance restriction downstream of the site. For full discussion of Flow Control requirements see Section IV of this report. A combination detention and stormwater wetland will provide the required stormwater system for Level 3 flow control and Enhanced Basic water quality treatment. A “Life Estate Easement” is proposed for Lot 1 use of Lot 2. Lot 2 will remain undeveloped for the duration of this easement. Future Lot 2 improvements have been included in all developed conditions and site coverage calculations. See Figure 5 for a Developed Site Conditions Map. NORTH 1 OF 1 EXISTING CONDITIONS MAP KISLYAK PRELIMINARY SHORT PLATEncompass Eastern Washington Division 407 Swiftwater Blvd. ▪ Cle Elum, WA 98922 ▪ Phone: (509) 674-7433 Western Washington Division 165 NE Juniper Street, Suite 201 ▪ Issaquah, WA 98027 ▪ Phone: (425) 392-0250 ENGINEERING & SURVEYING KISLYAK PRELIMINARY SHORT PLATNW 1/4 OF SE 1/4 OF SECTION 24, T. 21 N., R. 03 E., W.M.FEDERAL WAY, STATE OF WASHINGTONKnow what'sCallbelow.before you dig.RLEGAL DESCRIPTION:VERTICAL DATUM:BENCHMARK:BASIS OF BEARINGS:INSTRUMENTATION :SURVEY LEGEND: LOT 1TRACT ALOT 4LOT 6LOT 5LOT 341.5'TRACT BTRACT CLOT 2NORTH 1 OF 1DEVELOPED CONDITIONS MAP KISLYAK PRELIMINARY SHORT PLATEncompass Eastern Washington Division 407 Swiftwater Blvd. ▪ Cle Elum, WA 98922 ▪ Phone: (509) 674-7433 Western Washington Division 165 NE Juniper Street, Suite 201 ▪ Issaquah, WA 98027 ▪ Phone: (425) 392-0250 ENGINEERING & SURVEYING KISLYAK PRELIMINARY SHORT PLATNW 1/4 OF SE 1/4 OF SECTION 24, T. 21 N., R. 03 E., W.M.FEDERAL WAY, STATE OF WASHINGTONKnow what'sCallbelow.before you dig.RNOTES: Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 5 II. CONDITIONS AND REQUIREMENTS SUMMARY The 2016 King County Surface Water Design Manual (KCSWDM) and the City of Federal Way Addendum to the King County Surface Water Design Manual (Federal Way Addendum) were utilized for stormwater design per the City of Federal Way requirements. This project is subject to a Full Drainage Review per Section 1.1.2.4 of the 2016 KCSWDM. This project proposes to create approximately 34,930 SF of new plus replaced impervious areas both on- and off-site. Figure 6: Drainage Review Flow Chart Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 6 Core Requirements Core Requirement #1: Discharge at the Natural Location Currently, the existing site drains to a storm drain system along the north side of the property which conveys flows east to the storm system in 22nd Place SW. This project proposes to convey all target impervious surface runoff through a new storm drain system in the proposed Street “A” to the proposed onsite stormwater detention facility. This facility will discharge to a newly constructed stormwater CB on the south side of Street “A”, and flow east where it will connect with the existing storm system in the intersection of 22nd Place SW and Street “A.” Refer to the Downstream Analysis in Section III for a description of the existing discharge location. Core Requirement #2: Offsite Analysis The site is contained within a single drainage basin with runoff sheet flowing to the east or being conveyed to the east by an existing storm drain system on the north side of the property. Refer to the Downstream Analysis in Section III for a complete description of the existing drainage path. Core Requirement #3: Flow Control Facilities The project site is located within the Hylebos Creek Drainage Basin which is classified as a Level 2 Flow Control Area on the City of Federal Way Flow Control Applications Map. Per the City of Federal Way’s Review Comments, the project is required to meet the Level 3 flow control criteria due to a conveyance restriction downstream of the site. This requires the project to match the developed discharge durations to the predeveloped durations for the range of predeveloped discharge rates from 50% of the 2-year peak flow up to the full 50-year peak flow, match the developed peak discharge rates to predeveloped peak discharge rates for the 2- and 10-year return periods (Level 2 Flow Control), as well as match the developed 100-year peak discharge rate to the predeveloped 100-year peak discharge rate. Historic site conditions (forested) have been assumed for the predeveloped site conditions, and the existing residence on Lot 1 has been retained in the predeveloped condition per Flood Problem Flow Control Areas Exceptions detailed in section 1.2.3.1.C of the KCSWDM. The design volume for the proposed combination detention and stormwater wetland has been determined using the WWHM software approved by the Washington Department of Ecology. See the Flow Control Facilities design in Section IV of this report for full discussion. Core Requirement #4: Conveyance System Conveyance system analysis will be provided with final engineering. Core Requirement #5: Construction Stormwater Pollution Prevention A temporary erosion and sediment control (TESC) plan to provide BMPs to be implemented during construction is included with the preliminary engineering plan set. A clearing and grading permit will be required for the project development. Core Requirement #6: Maintenance and Operations See Section X for details. Core Requirement #7: Financial Guarantees and Liability The owner will arrange for any financial guarantees and liabilities required by the permit. Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 7 Core Requirement #8: Water Quality Facilities The proposed project will create approximately 13,378 SF of pollution-generating impervious surfaces (PGIS). The project site is located within the “Enhanced Basic Water Quality Treatment Menu Required” area of the City of Federal Way Water Quality Applications Map. Enhanced Basic Water Quality treatment will be applied to the project per Section 1.2.8.1 of the KCSWDM and Section 1.2.8 of the Federal Way Addendum. Water quality requirements are proposed to be met using a combination detention and stormwater wetland. See Section IV of this report for full discussion of water quality facilities. Core Requirement #9: On-Site BMPs This project is within the UGA on a site less than 5 acres in size. Per section 3.1.2 of the Federal Way Addendum, pre-engineered BMPs in Appendix C of the KCSWDM may be used instead of modeling. Therefore, the project is subject to the Small Subdivision and Urban Subdivision Projects BMP Requirements detailed in Section 1.2.9.3.1 of the KCSWDM. The proposed lots are less than 22,000 SF; therefore, Individual Lot BMPs have been evaluated per Section 1.2.9.2.1 of the KSWDM. Plat Infrastructure BMPs Per section 1.2.9.1 of the KSWDM, Target surfaces for flow control BMP requirements include new impervious surfaces, new pervious surfaces, and replaced impervious surfaces not already mitigated with an approved FCBMP or flow control facility. This project proposes a combination detention and stormwater wetland to mitigate all target surfaces on-site. Therefore, flow control BMPs are not required for Plat Infrastructure. Individual Lot BMPs 1. Full Dispersion: Full dispersion of runoff is not feasible. The 100-foot native vegetated flowpath length requirements cannot be met. The individual lots also do not have the area available to meet Native Growth Retention Area (NGRA) requirements. 2. Full Infiltration of Roof Runoff: Full infiltration of roof runoff is not feasible based on the medium dense to dense glacial till deposits found on-site per Geotechnical Engineering Study by Earth Solutions NW, LLC dated May 22, 2018 (Appendix A). 3. Full Infiltration: Full infiltration is not feasible based on the medium dense to dense glacial till deposits found on-site per Geotechnical Engineering Study by Earth Solutions NW, LLC dated May 22, 2018 (Appendix A). 4. Limited Infiltration: Limited Infiltration is feasible, provided an overflow structure is included. Both limited infiltration drywells and gravel filled trenches have been designed to be constructed as part of the individual lot building permits. Limited infiltration drywells have been designed to accommodate 10% of the lot areas at 360 Cu-Ft / 1,000 SF of impervious surface using a sandy loam classification inside the UGA (Rainfall region Seatac 1.0 and less) per Section C.2.3.4 of the 2016 KCSWDM. Limited infiltration gravel filled trenches have been designed to accommodate 10% of the lot areas at 36 feet / 1,000 SF of impervious surface using a sandy loam classification inside the UGA (Rainfall region Seatac 1.0 and less) per Section C.2.3.3 of Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 8 the 2016 KCSWDM. See Section IV of this TIR for additional information on the drywell and gravel trench design. Feasibility of additional flow control BMPs will be evaluated during the single-family building permit process. Special Requirements Special Requirement #1: Other Adopted Area-Specific Requirements Critical Drainage Areas – N/A Master Drainage Plan – N/A Basin Plan – N/A Salmon Conservation Plan – N/A Stormwater Compliance Plans – N/A Lake Management Plan – N/A Flood Hazard Mitigation Plan – N/A Shared Facility Drainage Plan – N/A Special Requirement #2: Flood Hazard Area Delineation This project does not lie in the FEMA 100-year floodplain. Special Requirement #3: Flood Protection Facilities This project does not rely on or propose to modify or construct a new flood protection facility. Special Requirement #4: Source controls Source control is not required for this project. Special Requirement #5: Oil Control This project is not considered high-use or in need of oil control. Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 9 III. OFF-SITE ANALYSIS Level 1 Downstream Analysis A Level 1 Downstream Analysis was performed by Encompass Engineering and Surveying on Wednesday February 14, 2018. The analysis was performed at approximately 3:00 PM with a temperature of about 45°. The site is currently developed with a single-family residence on the western portion of the site. There is a lawn area on the central portion of the site, and the remaining area has been previously cleared. The residence is accessed to the east via a private driveway from 24th Place SW. The site is contained within a single drainage basin within the Hylebos Creek Drainage Basin which discharges to the Central Puget Sound Watershed per King County iMap. The USGS Web Soil Survey has mapped the soils on site as Alderwood gravelly sandy loam at slopes from 8-15%. Maps from the City of Federal Way’s Public Works Development Services Division and Community Development Planning Division have been utilized for this analysis per Section 2.3.1.1 of the CFWA. Stormwater runoff from the residence drains to a 4” CPP pipe (A) which conveys flows north to the 12” CPP storm drain (B) that runs the length of the site. This pipe connects via a 12” SD pipe (C) to the Type 1 CB (D) in 22nd Place SW. Stormwater runoff from the remainder of the site sheet flows (E) to the east off the property where it is collected by the system of 12” SD pipes with catch basins (F) in 22nd Place SW. This system also connects to the Type 1 CB (D) where the stormwater flows from both portions of the site converge. From here, runoff is conveyed east by a 12” SD pipe (G) in the SW 344th Court storm drain system. The system also collects and conveys stormwater runoff from the “Eagle Manor” development to a Type 2 CB – 72” (H). This structure directs flows through a 12” D.I. CL50 (I) to a Contech stormwater vault (J). Stormwater outlets the vault through a 12” SD pipe (K) to a Level 3 stormwater detention pond (L) located on the corner of SW 344th Street and 21st Avenue SW. This pond outlets via a 12” SD pipe (M) to the 42” SD pipe (N) in 21st Avenue SW. The 21st Avenue SW system conveys flows north for approximately 2,500 feet. This Level 1 Downstream Analysis was completed at point (O) within the 42” SD pipe at 1,320 feet downstream of the site discharge location. King County iMap shows no relevant drainage complaints for the downstream area. There are 3 drainage complaints to the east of the Fred Myer, located north of the property along 21st Avenue SW. These are call fee inquiries and are not related do drainage issues. Based on this analysis no downstream problems should occur with the proposed construction. Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 10 Figure 7: Downstream Map Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 11 Off-site Analysis Drainage System Table Surface Water Design Manual, Core Requirement #2 BASIN: Hylebos Creek SUBBASIN NAME: SUBBASIN NUMBER: SYMBOL DRAINAGE COMPONENT TYPE, NAME, AND SIZE DRAINAGE COMPONENT DESCRIPTION SLOPE DISTANCE FROM SITE DISCHARGE EXISTING PROBLEMS POTENTIAL PROBLEMS OBSERVATIONS OF FIELD INSPECTOR, RESOURCE REVIEWER, OR RESIDENT (See map) Type: sheet flow, swale, stream, channel, pipe, pond; Size: diameter, surface area Drainage basin, vegetation, cover, depth, type of sensitive area, volume % 1/4 Mile = 1,320 ft Constrictions, under capacity, ponding, overtopping, flooding, habitat or organism destruction, scouring, bank sloughing, sedimentation, incision, other erosion Tributary area, likelihood of problem, overflow pathways, potential impacts A PIPE: 4” CPP DRAINAGE FROM EXISTING RESIDENCE 2-5% ON-SITE NONE NONE TO BE REPLACED DURING SITE GRADING B PIPE: 12” CPP DRAINAGE ALONG NORTH SIDE OF EXISTING SITE 2-15% POINT OF DISCHARGE #1 - 25' NONE NONE CONVEYS STORMWATER FROM SW 344TH PLACE DEVELOPMENT C PIPE: 12” SD DRAINAGE ACROSS 22ND PLACE SW 3.25% 25-53’ NONE NONE CONVEYS STORMWATER EAST TO SW 344TH COURT D TYPE 1 CB LOCATED IN 22ND PLACE SW N/A 53’ NONE NONE CONVERGANCE OF SITE STORMWATER RUNOFF E SHEET FLOW SHEET FLOW THROUGH FORESTED AREA OFFSITE 2-15% POINT OF DISCHARGE #2: 0-10’ NONE NONE DRAINS EAST TO 22ND PLACE SW SYSTEM F PIPE: 12” SD W/ CATCH BASINS LOCATED IN 22ND PLACE SW 1-5% 10-53’ NONE NONE CONVEYS STORMWATER TO ELEMENT D G PIPE: 12” SD LOCATED IN SW 344TH COURT 1-5% 53-346’ NONE NONE DRAINGE SYSTEM FOR EAGLE MANOR DEVELOPMENT H TYPE 2 CB – 72” LOCATED IN SW 344TH COURT N/A 346’ NONE NONE DRAINAGE TO EAGLE MANOR STORMWATER DETENTION POND Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 12 I PIPE: 12” D.I. CL50 0.5% 346-358’ NONE NONE DRAINAGE TO EAGLE MANOR STORMWATER DETENTION POND J CONTECH 8’x11’ STORMWATER VAULT CONTAINS 19 LOW DROP MEDIA CARTRIDGES N/A 358-369’ NONE NONE WATER QUALITY TREATMENT FOR EAGLE MANOR STORMWATER K PIPE: 12” SD 8% 369-394’ NONE NONE DRAINAGE TO EAGLE MANOR STORMWATER DETENTION POND L LEVEL 3 STORMWATER DETENTION POND PRIVATE STORMWATER FACILITY N/A 394-450’ NONE NONE STORMWATER DETENTION POND FOR EAGLE MANOR M PIPE: 12” SD OUTFLOW FROM STORMWATER DETENTION POND 0.5% 450-487’ NONE NONE CONVEYANCE TO 21ST AVENEUE SW STORM DRAIN SYSTEM N PIPE: 42” SD LOCATED IN 21ST AVENUE SW 1-5% 487-1320’ NONE NONE CONVEYS FLOWS NORTH O PIPE: 42” SD LOCATED IN 21ST AVENUE SW 1-5% 1320’ NONE NONE END OF DOWNSTREAM ANALYSIS Downstream Table Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 13 Site Access off 24th Place SW Existing Residence Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 14 Existing Driveway to Lower Portion of the Property Yard Drain Near North Property Line Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 15 Underground Stormwater System Location Along Northern Property Line Existing Backyard Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 16 CB and Yard Drain Near East Property Line Adjacent “Eagle Manor” Development Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 17 Downstream Stormwater Detention Pond Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 18 IV. FLOW CONTROL, LOW IMPACT DEVELOPMENT (LID) AND WATER QUALITY FACILITY ANALYSIS AND DESIGN Part A: Existing Site Hydrology The 75,869 SF (1.74 AC) site is currently developed with a single-family residence, several out-buildings, utilities, an onsite septic system, and an existing driveway access from 24th Place SW. The vegetation onsite consists of a lawn area on the central portion of the site, and an area that was previously cleared on the eastern portion of the site. The topography slopes to the east at approximately 8-15%. The site is contained within a single drainage basin with runoff sheet flowing to the east or being conveyed to the east by an existing storm drain system on the north side of the property which conveys flows east to the system in 22nd Place SW. The full Downstream Analysis is included in Section III of this Technical Information Report (TIR). WWHM 2012 was used to model the existing condition within the 63,098 SF (1.448 AC) limits of disturbance using the historic forested condition. The existing residence on Lot 1 has been retained in the predeveloped condition per Flood Problem Flow Control Areas Exceptions detailed in section 1.2.3.1.C of the KCSWDM. Due to the presence of the existing residence in both predeveloped and mitigated conditions, the area of the residence has been removed from storm area calculations as it will not affect the size of the facility. See the summary of existing and developed analyses on the following pages, as well as the existing conditions map provided as Figure 4 for more details. Part B: Developed Site Hydrology The proposal incorporates the clearing, grading and platting of the project site to accommodate the construction of 5 total lots including 4 new single-family residences, associated utilities, a public access road, and a private stormwater facility. The existing residence in the northwest corner of the project site will be retained in Lot 1 and is excluded from site area calculations. The total clearing limits including off- site road and frontage improvements is 63,098 SF (1.48 AC). This project proposes to convey all target impervious surface runoff through a new storm drain system in the proposed Street “A” to the proposed onsite combination detention and stormwater wetland. This facility will discharge to a newly constructed stormwater CB on the south side of Street “A”, and flow east where it will connect with the existing storm system in the intersection of 22 nd Place SW and Street “A.” Due to the location of the easternmost catch basin, a portion of the target impervious area near the intersection of 22nd Place SW and Street “A” will not be able to be conveyed into the proposed stormwater detention system. An area swap is proposed, which will convey an equivalent impervious area located on 24th Place SW to the west of the site to the proposed stormwater detention system. The project will be designed to comply with the Subdivision Projects BMP Requirements detailed in Section 1.2.9.3.1 of the 2017 KSWDM. Both limited infiltration drywells and limited infiltration gravel filled trenches have been designed for each lot to allow for flexibility depending on individual lot conditions. These BMPs will be constructed as part of the individual lot building permits. Drywells have been designed to accommodate 10% of the lot areas at 360 Cu-Ft / 1,000 SF of impervious surface using a sandy loam classification inside the UGA (Rainfall region Seatac 1.0 and less) per Section C.2.3.4 of the 2016 KCSWDM. Gravel filled trenches have been designed to accommodate 10% of the lot areas at 36 feet / 1,000 SF of impervious surface using a sandy loam classification inside the UGA (Rainfall region Seatac 1.0 and less) per Section C.2.3.3 of the 2016 KCSWDM. The following tables show the required drywell and infiltration trench sizing for each lot. Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 19 LOT AREA (SF) 10% OF LOT AREA (SF) DRYWELL VOLUME (CU-FT) 8’ DIAMETER DRYWELL DEPTH (FT) 2 7616 762 274 5.5 3 7200 720 259 5.2 4 7200 720 259 5.2 5 7200 720 259 5.2 Table 1: Required Drywell Sizing LOT AREA (SF) 10% OF LOT AREA (SF) 2’ WIDE TRENCH LENGTH (FT) 5’ WIDE TRENCH LENGTH (FT) 2 7616 762 28 11.2 3 7200 720 26 10.4 4 7200 720 26 10.4 5 7200 720 26 10.4 Table 2: Required Infiltration Trench Sizing Part C: Performance Standards The project site is located within the Hylebos Creek Drainage Basin which is classified as a Level 2 Flow Control Area on the City of Federal Way Flow Control Applications Map. Per the City of Federal Way’s Review Comments, the project is required to meet the Level 3 flow control criteria due to a conveyance restriction downstream of the site. The project site is therefore subject to level 3 flow control (Historic site conditions). In the Flood Problem Flow Control Areas, flow control facilities are required to match the developed discharge durations to the predeveloped durations for the range of predeveloped discharge rates from 50% of the 2-year peak flow up to the full 50-year peak flow, match the developed peak discharge rates to predeveloped peak discharge rates for the 2- and 10-year return periods (Level 2 Flow Control), as well as match the developed 100-year peak discharge rate to the predeveloped 100-year peak discharge rate. See the predeveloped and mitigated flows meeting these standards below. In addition, this site is designed to comply with the Small Subdivision Project BMP Requirements detailed in Section 1.2.9.3.1 of the 2016 KCSWDM. Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 20 This project proposes to create approximately 13,378 SF of pollution-generating impervious surfaces (PGIS). The project site is located within the “Enhanced Basic Water Quality Treatment Menu Required” area of the City of Federal Way Water Quality Applications Map. Enhanced Basic Water Quality treatment will be applied to the project per Section 1.2.8.1 of the KCSWDM and Section 1.2.8 of the Federal Way Addendum. Part D: Flow Control System This project proposes the construction of a combination detention and stormwater wetland designed per Section 5.1.1 of the KCSWDM. The proposed facility is 52-feet in width by 102-feet in length and will be located on the eastern boundary of the site. The stormwater detention and water quality volumes for the proposed development were determined using WWHM2012. The pond will outlet via a control structure and discharge to a newly constructed stormwater CB on the south side of Street “A”, where to will connect to the existing storm system in the intersection of 22nd Place SW and Street “A.” The basin area breakdown is included below in Table 3. Lot impervious surface coverage is assumed to be the maximum per zoning (60%). On-site + Off-Site Existing Proposed Condition Measured Modeled Measured Modeled Forest, Mod 31,549 SF (0.724 AC) 31,549 SF (0.724 AC) Forest, Steep 31,549 SF (0.724 AC) 31,549 SF (0.724 AC) Lawn, Flat 11,084 SF (0.254 AC) 11,084 SF (0.254 AC) Lawn, Mod: 11,084 SF (0.254 AC) 11,084 SF (0.254 AC) Road, Flat 2,000 SF (0.046 AC) 2,000 SF (0.046 AC) Road, Mod: 9,770 SF (0.224 AC) 9,770 SF (0.224 AC) Roof, Flat: 20,029 SF (0.460 AC) 20,029 SF (0.460 AC) Driveway, Flat: 1,608 SF (0.037 AC) 1,608 SF (0.037 AC) Sidewalk, Flat: 1,523 SF (0.035 AC) 1,523 SF (0.035 AC) Pond 6,000 SF (0.138 AC) 6,000 SF (0.138 AC) Total Area: 63,098 SF (1.448 AC) 63,098 SF (1.448 AC) 63,098 SF (1.448 AC) 63,098 SF (1.448 AC) Table 3: Basin Area Breakdown Based on the WWHM Model, the required water storage volume for this pond is 21,985 CF. A total water storage volume of 22,063 CF is proposed to meet this requirement. See the full WWHM output in Appendix B. Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 21 Overflow Capacity: The City of Federal Way uses the 2016 KCSWDM for the design of flow control facility overflow structures. In the event that the control structure becomes plugged, causing the pond to fill rapidly to the overflow structure, the overflow system was analyzed to verify it has adequate capacity. To verify the capacity of the system to convey the 100-year flow in the overflow condition, the inflow into the pond was used and was determined to be 0.8981 CFS by WWHM. See WWHM clip below: The overflow weir was analyzed using the Rectangular, Sharp-Crested Weir flow equation provided by Figure 5.1.4.E in the KCSWDM: Q=C(L - 0.2H)H3/2 where Q = flow (cfs) C = 3.27 + 0.40 H/P (ft) H = 0.5’ P = 3.65’ L = length (ft) of the portion of the riser circumference as necessary not to exceed 50 percent of the circumference D = inside riser diameter (ft) Inserting values, for all known quantities results in C = 3.27 + .4(.5/3.65) or 3.32 Inserting C into the flow equation results in: 1.47 = 3.32(L – 0.2*0.5)(0.53/2) Which when solved for L results in L = 1.35’ minimum length to convey the 100-year flow rate. A factor of safety of 1.5 brings the designed length to 2.03’, which is less than 50 percent of the circumference of the 54” diameter control structure. The emergency overflow capacity of the riser to convey the 100-year inflow into the pond was calculated using Figure 5.1.4.H of the 2016 KCSWDM (see below). The figure revealed that to convey 0.8981 CFS through a 12” riser, 0.12’ of head would be required. The pond has been designed with 1.0’ of freeboard above the top of the riser, therefore, the riser has the capacity to convey the flow to the outlet pipe without allowing stormwater to flow over the side of the pond. Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 22 Emergency Overflow Structure: The City of Kent uses the 2016 KCSWDM for the design of flow control facility emergency overflow structures. In addition to the overflow capacity of the control structure, an emergency overflow structure has been sized to pass the 100-year, 15-minute developed peak flow in the event of total control structure failure. A Type II manhole fitted with a birdcage has been designed per Section 5.1.1.1 of the 2016 KCSWDM to accommodate the 100-year developed peak flow, with a minimum 6 inches of freeboard. Part E: Water Quality System Developed stormwater runoff from Pollution-Generating Impervious Surfaces will be treated to meet the Enhanced Basic water quality standards detailed in Section 1.2.8.1.A of the KCSWDM. A combination detention and stormwater wetland is proposed to meet these requirements. Per the Basic Wetpond Methods of Analysis outlined in section 6.4.1.1 of the KCSWDM, the wetpond requires a volume equal to 91% of the treatment volume. A 0.1312 Ac-Ft treatment volume was provided from WWHM, therefore the required wetpond volume is 0.91(0.1312 x 43,560) = 5,201 CF. A 5,498 CF wetpond cell has been provided. 0.89 CFS 0.12 FEET CFS Kislyak Preliminary Short Plat Preliminary Technical Information Report 07/22/2021 Page 23 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN Conveyance system analysis and design will be provided with final engineering. VI. SPECIAL REPORTS AND STUDIES Geotechnical Engineering Study, by Earth Solutions NW, LLC, dated May 22, 2018 VII. OTHER PERMITS Building Permits, NPDES, and Lakehaven Utility District permits are required and will be provided with final engineering. VIII. CSWPPP ANALYSIS AND DESIGN An Erosion and Sediment Control Plan (TESC) and is included with the preliminary engineering plan set. A Construction Stormwater Pollution Prevention Plan (CSWPPP) will be prepared and provided with final engineering. IX. BOND QUANTITIES AND DECLARATION OF COVENANT Bond Quantities and Declaration of Covenant documents will be provided with final engineering. X. OPERATION AND MAINTENANCE MANUAL An Operation and Maintenance Manual will be provided with final engineering. Appendix A Geotechnical Engineering Study Proposed Residential Development 34402 – 24th Place Southwest Federal Way, Washington by Earth Solutions NW, LLC dated May 22, 2018 EarthSolutionsNWLLC EarthSolutions NW LLC Geotechnical Engineering Geology Environmental Services Construction Observation/Testing 1805 -136th Place N.E.,Suite 201 Bellevue,WA 98005 (425)449-4704 Fax (425)449-4711 www.earthsolutionsnw.com GEOTECHNICAL ENGINEERING STUDY PROPOSED RESIDENTIAL DEVELOPMENT 34402 -24 PLACE SOUTHWEST FEDERAL WAY,WASHINGTON ES-5791 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 34402 –24th Place S.W. Federal Way,Washington MRS SES 04/20/2018 April 2018 5791 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 744 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 Test Pit Location Plan 34402 –24th Place S.W. Federal Way,Washington MRS SES 04/20/2018 April 2018 5791 2 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. 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. 0 3 0 6 0 1 2 0 Sc ale in Feet1"=6 0 ' LEGEND Approximate Location of ESNW Test Pit,Proj.No. ES-5791,April 2018 Subject Site Existing Building Proposed Lot Number TP-1 TP-2 TP-3 TP-4 TP-1 Sheds Shed House 420 410 400 390 380420 410 400 390 380 22NDPLACES.W.S.W.344TH COURT S.W. 344TH STREET 24TH PLACE S.W.1 32 4 5 6 Tract A 5 Drwn. Checked Date Date Proj.No. Plate Earth Solutions NWLLCEarthSolutionsNWLLC EarthSolutions NW LLC Geotechnical Engineer ing,C onstr uction Observation/Testing and Environmental Services 34402 –24th Place S.W. Federal Way,Washington MRS SES 04/20/2018 April 2018 5791 3 RETAINING WALL DRAINAGE DETAIL 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 34402 –24th Place S.W. Federal Way,Washington MRS SES 04/20/2018 April 2018 5791 4 FOOTING DRAIN DETAIL 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 Appendix B WWHM2012 Output WWHM2012 PROJECT REPORT 17678 - Kislyak 4-75 DEEP 2/17/2021 4:34:16 PM Page 2 General Model Information Project Name:17678 - Kislyak 4-75 DEEP Site Name: Site Address: City: Report Date:2/17/2021 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.000 Version Date:2018/10/10 Version:4.2.16 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year 17678 - Kislyak 4-75 DEEP 2/17/2021 4:34:16 PM Page 3 Landuse Basin Data Predeveloped Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Mod 0.724 C, Forest, Steep 0.724 Pervious Total 1.448 Impervious Land Use acre Impervious Total 0 Basin Total 1.448 Element Flows To: Surface Interflow Groundwater 17678 - Kislyak 4-75 DEEP 2/17/2021 4:34:16 PM Page 4 Mitigated Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Flat 0.2544 C, Lawn, Mod 0.2544 Pervious Total 0.5088 Impervious Land Use acre ROADS FLAT 0.0459 ROADS MOD 0.2243 ROOF TOPS FLAT 0.4598 DRIVEWAYS FLAT 0.0369 SIDEWALKS FLAT 0.035 POND 0.1377 Impervious Total 0.9396 Basin Total 1.4484 Element Flows To: Surface Interflow Groundwater Trapezoidal Pond 1 Trapezoidal Pond 1 17678 - Kislyak 4-75 DEEP 2/17/2021 4:34:16 PM Page 5 Routing Elements Predeveloped Routing 17678 - Kislyak 4-75 DEEP 2/17/2021 4:34:16 PM Page 6 Mitigated Routing Trapezoidal Pond 1 Bottom Length:99.00 ft. Bottom Width:50.00 ft. Depth:5.15 ft. Volume at riser head:0.5047 acre-feet. Side slope 1:0 To 1 Side slope 2:0 To 1 Side slope 3:0 To 1 Side slope 4:3 To 1 Discharge Structure Riser Height:4.15 ft. Riser Diameter:12 in. Notch Type:Rectangular Notch Width:0.021 ft. Notch Height:1.100 ft. Orifice 1 Diameter:0.8125 in.Elevation:0 ft. Orifice 2 Diameter:0.7656 in.Elevation:2.25 ft. Element Flows To: Outlet 1 Outlet 2 Pond Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)Infilt(cfs) 365.90 0.113 0.000 0.000 0.000 365.96 0.113 0.006 0.004 0.000 366.01 0.114 0.013 0.006 0.000 366.07 0.114 0.019 0.007 0.000 366.13 0.114 0.026 0.008 0.000 366.19 0.114 0.032 0.009 0.000 366.24 0.114 0.039 0.010 0.000 366.30 0.115 0.045 0.011 0.000 366.36 0.115 0.052 0.012 0.000 366.42 0.115 0.059 0.012 0.000 366.47 0.115 0.065 0.013 0.000 366.53 0.115 0.072 0.014 0.000 366.59 0.116 0.078 0.014 0.000 366.64 0.116 0.085 0.015 0.000 366.70 0.116 0.092 0.016 0.000 366.76 0.116 0.098 0.016 0.000 366.82 0.116 0.105 0.017 0.000 366.87 0.117 0.112 0.017 0.000 366.93 0.117 0.118 0.018 0.000 366.99 0.117 0.125 0.018 0.000 367.04 0.117 0.132 0.019 0.000 367.10 0.117 0.139 0.019 0.000 367.16 0.118 0.145 0.020 0.000 367.22 0.118 0.152 0.020 0.000 367.27 0.118 0.159 0.021 0.000 367.33 0.118 0.166 0.021 0.000 367.39 0.118 0.172 0.021 0.000 367.45 0.119 0.179 0.022 0.000 367.50 0.119 0.186 0.022 0.000 367.56 0.119 0.193 0.023 0.000 367.62 0.119 0.200 0.023 0.000 17678 - Kislyak 4-75 DEEP 2/17/2021 4:34:16 PM Page 7 367.67 0.119 0.207 0.023 0.000 367.73 0.119 0.213 0.024 0.000 367.79 0.120 0.220 0.024 0.000 367.85 0.120 0.227 0.025 0.000 367.90 0.120 0.234 0.025 0.000 367.96 0.120 0.241 0.025 0.000 368.02 0.120 0.248 0.026 0.000 368.07 0.121 0.255 0.026 0.000 368.13 0.121 0.262 0.026 0.000 368.19 0.121 0.269 0.030 0.000 368.25 0.121 0.276 0.032 0.000 368.30 0.121 0.283 0.034 0.000 368.36 0.122 0.290 0.035 0.000 368.42 0.122 0.297 0.036 0.000 368.48 0.122 0.304 0.037 0.000 368.53 0.122 0.311 0.038 0.000 368.59 0.122 0.318 0.039 0.000 368.65 0.123 0.325 0.040 0.000 368.70 0.123 0.332 0.041 0.000 368.76 0.123 0.339 0.042 0.000 368.82 0.123 0.346 0.043 0.000 368.88 0.123 0.353 0.044 0.000 368.93 0.124 0.360 0.045 0.000 368.99 0.124 0.367 0.046 0.000 369.05 0.124 0.374 0.048 0.000 369.10 0.124 0.381 0.051 0.000 369.16 0.124 0.389 0.054 0.000 369.22 0.125 0.396 0.058 0.000 369.28 0.125 0.403 0.061 0.000 369.33 0.125 0.410 0.065 0.000 369.39 0.125 0.417 0.069 0.000 369.45 0.125 0.424 0.073 0.000 369.51 0.126 0.432 0.078 0.000 369.56 0.126 0.439 0.082 0.000 369.62 0.126 0.446 0.086 0.000 369.68 0.126 0.453 0.091 0.000 369.73 0.126 0.461 0.095 0.000 369.79 0.127 0.468 0.100 0.000 369.85 0.127 0.475 0.104 0.000 369.91 0.127 0.482 0.109 0.000 369.96 0.127 0.490 0.114 0.000 370.02 0.127 0.497 0.119 0.000 370.08 0.128 0.504 0.170 0.000 370.13 0.128 0.512 0.382 0.000 370.19 0.128 0.519 0.680 0.000 370.25 0.128 0.526 1.025 0.000 370.31 0.128 0.534 1.379 0.000 370.36 0.129 0.541 1.707 0.000 370.42 0.129 0.548 1.976 0.000 370.48 0.129 0.556 2.171 0.000 370.54 0.129 0.563 2.302 0.000 370.59 0.129 0.571 2.446 0.000 370.65 0.130 0.578 2.566 0.000 370.71 0.130 0.586 2.681 0.000 370.76 0.130 0.593 2.790 0.000 370.82 0.130 0.600 2.895 0.000 370.88 0.130 0.608 2.996 0.000 370.94 0.131 0.615 3.094 0.000 17678 - Kislyak 4-75 DEEP 2/17/2021 4:34:16 PM Page 8 370.99 0.131 0.623 3.189 0.000 371.05 0.131 0.630 3.281 0.000 17678 - Kislyak 4-75 DEEP 2/17/2021 4:34:16 PM Page 9 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:1.448 Total Impervious Area:0 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.5088 Total Impervious Area:0.9396 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.05411 5 year 0.086967 10 year 0.107811 25 year 0.132396 50 year 0.149314 100 year 0.165046 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.031581 5 year 0.048359 10 year 0.062431 25 year 0.084111 50 year 0.103458 100 year 0.125873 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.061 0.022 1950 0.069 0.033 1951 0.110 0.083 1952 0.038 0.020 1953 0.030 0.025 1954 0.043 0.026 1955 0.076 0.025 1956 0.059 0.040 1957 0.052 0.026 1958 0.052 0.029 17678 - Kislyak 4-75 DEEP 2/17/2021 4:34:49 PM Page 10 1959 0.044 0.023 1960 0.079 0.064 1961 0.043 0.035 1962 0.029 0.020 1963 0.039 0.026 1964 0.051 0.027 1965 0.036 0.040 1966 0.034 0.024 1967 0.081 0.030 1968 0.045 0.025 1969 0.046 0.024 1970 0.039 0.025 1971 0.042 0.027 1972 0.086 0.050 1973 0.041 0.037 1974 0.042 0.027 1975 0.064 0.025 1976 0.044 0.026 1977 0.007 0.022 1978 0.040 0.032 1979 0.022 0.019 1980 0.102 0.067 1981 0.033 0.025 1982 0.076 0.045 1983 0.057 0.026 1984 0.037 0.022 1985 0.021 0.023 1986 0.094 0.039 1987 0.082 0.052 1988 0.034 0.023 1989 0.021 0.022 1990 0.185 0.066 1991 0.103 0.055 1992 0.044 0.033 1993 0.042 0.022 1994 0.014 0.019 1995 0.054 0.034 1996 0.126 0.084 1997 0.106 0.088 1998 0.030 0.022 1999 0.102 0.056 2000 0.043 0.034 2001 0.009 0.018 2002 0.049 0.042 2003 0.068 0.024 2004 0.089 0.085 2005 0.060 0.026 2006 0.063 0.039 2007 0.140 0.138 2008 0.179 0.084 2009 0.083 0.041 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.1850 0.1382 2 0.1790 0.0884 3 0.1399 0.0848 17678 - Kislyak 4-75 DEEP 2/17/2021 4:34:49 PM Page 11 4 0.1258 0.0843 5 0.1104 0.0837 6 0.1055 0.0835 7 0.1031 0.0665 8 0.1023 0.0660 9 0.1016 0.0639 10 0.0939 0.0561 11 0.0889 0.0549 12 0.0864 0.0517 13 0.0829 0.0497 14 0.0825 0.0452 15 0.0808 0.0417 16 0.0793 0.0412 17 0.0758 0.0397 18 0.0757 0.0395 19 0.0690 0.0392 20 0.0683 0.0385 21 0.0636 0.0373 22 0.0628 0.0351 23 0.0612 0.0342 24 0.0601 0.0339 25 0.0587 0.0333 26 0.0568 0.0328 27 0.0544 0.0319 28 0.0523 0.0296 29 0.0521 0.0289 30 0.0511 0.0268 31 0.0487 0.0267 32 0.0460 0.0266 33 0.0452 0.0263 34 0.0441 0.0261 35 0.0438 0.0260 36 0.0436 0.0258 37 0.0432 0.0256 38 0.0430 0.0255 39 0.0427 0.0254 40 0.0419 0.0251 41 0.0417 0.0251 42 0.0416 0.0250 43 0.0410 0.0248 44 0.0402 0.0245 45 0.0395 0.0245 46 0.0388 0.0243 47 0.0384 0.0236 48 0.0373 0.0230 49 0.0364 0.0228 50 0.0342 0.0226 51 0.0342 0.0224 52 0.0326 0.0224 53 0.0304 0.0221 54 0.0299 0.0217 55 0.0292 0.0216 56 0.0219 0.0216 57 0.0211 0.0202 58 0.0205 0.0199 59 0.0141 0.0194 60 0.0086 0.0190 61 0.0069 0.0185 17678 - Kislyak 4-75 DEEP 2/17/2021 4:34:49 PM Page 12 17678 - Kislyak 4-75 DEEP 2/17/2021 4:34:49 PM Page 13 Duration Flows The Facility PASSED Flow(cfs)Predev Mit Percentage Pass/Fail 0.0271 13107 10596 80 Pass 0.0283 11914 10125 84 Pass 0.0295 10868 9648 88 Pass 0.0308 9935 9133 91 Pass 0.0320 9037 8532 94 Pass 0.0332 8243 7841 95 Pass 0.0345 7574 7065 93 Pass 0.0357 6977 6314 90 Pass 0.0369 6412 5557 86 Pass 0.0382 5910 4919 83 Pass 0.0394 5454 4229 77 Pass 0.0406 5026 3717 73 Pass 0.0419 4614 3292 71 Pass 0.0431 4263 2926 68 Pass 0.0443 3998 2522 63 Pass 0.0456 3713 2095 56 Pass 0.0468 3465 1876 54 Pass 0.0480 3236 1705 52 Pass 0.0493 3031 1564 51 Pass 0.0505 2834 1431 50 Pass 0.0518 2644 1320 49 Pass 0.0530 2470 1205 48 Pass 0.0542 2286 1114 48 Pass 0.0555 2102 1043 49 Pass 0.0567 1935 986 50 Pass 0.0579 1779 927 52 Pass 0.0592 1641 878 53 Pass 0.0604 1528 830 54 Pass 0.0616 1413 776 54 Pass 0.0629 1311 725 55 Pass 0.0641 1214 655 53 Pass 0.0653 1123 601 53 Pass 0.0666 1036 525 50 Pass 0.0678 983 489 49 Pass 0.0690 934 457 48 Pass 0.0703 888 431 48 Pass 0.0715 842 408 48 Pass 0.0727 798 389 48 Pass 0.0740 748 359 47 Pass 0.0752 703 325 46 Pass 0.0765 666 298 44 Pass 0.0777 628 269 42 Pass 0.0789 594 239 40 Pass 0.0802 559 213 38 Pass 0.0814 520 190 36 Pass 0.0826 468 165 35 Pass 0.0839 434 137 31 Pass 0.0851 392 117 29 Pass 0.0863 364 104 28 Pass 0.0876 325 93 28 Pass 0.0888 295 85 28 Pass 0.0900 271 81 29 Pass 0.0913 243 74 30 Pass 17678 - Kislyak 4-75 DEEP 2/17/2021 4:34:49 PM Page 14 0.0925 217 69 31 Pass 0.0937 192 66 34 Pass 0.0950 175 64 36 Pass 0.0962 153 61 39 Pass 0.0974 134 58 43 Pass 0.0987 124 55 44 Pass 0.0999 112 53 47 Pass 0.1012 97 51 52 Pass 0.1024 88 48 54 Pass 0.1036 76 46 60 Pass 0.1049 67 44 65 Pass 0.1061 55 42 76 Pass 0.1073 52 40 76 Pass 0.1086 47 38 80 Pass 0.1098 44 36 81 Pass 0.1110 42 34 80 Pass 0.1123 41 30 73 Pass 0.1135 38 24 63 Pass 0.1147 35 21 60 Pass 0.1160 33 20 60 Pass 0.1172 30 17 56 Pass 0.1184 29 15 51 Pass 0.1197 27 12 44 Pass 0.1209 24 11 45 Pass 0.1221 21 11 52 Pass 0.1234 19 10 52 Pass 0.1246 16 10 62 Pass 0.1259 14 9 64 Pass 0.1271 12 8 66 Pass 0.1283 11 8 72 Pass 0.1296 11 8 72 Pass 0.1308 7 5 71 Pass 0.1320 6 4 66 Pass 0.1333 6 4 66 Pass 0.1345 5 3 60 Pass 0.1357 4 2 50 Pass 0.1370 4 2 50 Pass 0.1382 4 1 25 Pass 0.1394 4 0 0 Pass 0.1407 3 0 0 Pass 0.1419 3 0 0 Pass 0.1431 3 0 0 Pass 0.1444 3 0 0 Pass 0.1456 3 0 0 Pass 0.1468 3 0 0 Pass 0.1481 3 0 0 Pass 0.1493 3 0 0 Pass 17678 - Kislyak 4-75 DEEP 2/17/2021 4:34:49 PM Page 15 Water Quality Water Quality BMP Flow and Volume for POC #1 On-line facility volume:0.1312 acre-feet On-line facility target flow:0.1534 cfs. Adjusted for 15 min:0.1534 cfs. Off-line facility target flow:0.0857 cfs. Adjusted for 15 min:0.0857 cfs. 17678 - Kislyak 4-75 DEEP 2/17/2021 4:34:49 PM Page 16 LID Report 17678 - Kislyak 4-75 DEEP 2/17/2021 4:35:13 PM Page 17 POC 2 POC #2 was not reported because POC must exist in both scenarios and both scenarios must have been run. 17678 - Kislyak 4-75 DEEP 2/17/2021 4:35:13 PM Page 18 Model Default Modifications Total of 0 changes have been made. PERLND Changes No PERLND changes have been made. IMPLND Changes No IMPLND changes have been made. 17678 - Kislyak 4-75 DEEP 2/17/2021 4:35:13 PM Page 19 Appendix Predeveloped Schematic 17678 - Kislyak 4-75 DEEP 2/17/2021 4:35:14 PM Page 20 Mitigated Schematic