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Home My WebLink AboutTechnical Information Report (TIR)-06-08-2020-V1 TECHNICAL INFORMATION REPORT 7-Eleven Convenience Store and Fueling Station 35620 Pacific Highway South Federal Way, WA 98003 Prepared for: Visconsi Companies, Ltd. 30050 Chargin Boulevard, Suite 360 Pepper Pike, OH 44124 May 29, 2020 Our Job No. 20948 05/29/2020 Technical Information Report 7-Eleven Convenience Store and Fueling Station Federal Way, Washington Our Job No. 20948 20948.005-TIR.doc TABLE OF CONTENTS 1.0 PROJECT OVERVIEW Figure 1 – Technical Information Report (TIR) Worksheet TDA Figure 2 – Vicinity Map Figure 3 – Assessor Map Figure 4 – FEMA Map Figure 5 – Soil Survey Map Figure 6 – Sensitive Areas Map 2.0 CONDITIONS AND REQUIREMENTS SUMMARY 2.1 Analysis of the Core Requirements 2.2 Analysis of the Special Requirements 3.0 OFF-SITE ANALYSIS 3.1 Leve 1 Off-Site Drainage Analysis 4.0 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN A. Existing Site Hydrology B. Developed Site Hydrology C. Performance Standards C.1 WWHM Calculations Figure 7 - Pre-developed Basin Map Figure 8 - Developed Basin Map D. Flow Control System E. Water Quality System F. Flow Control BMPs 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN 6.0 SPECIAL REPORTS AND STUDIES 7.0 OTHER PERMITS 8.0 EROSION SEDIMENT CONTROL ANALYSIS AND DESIGN Figure 9 – Clearing and Grading Plan 9.0 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT 10.0 OPERATIONS AND MAINTENANCE MANUAL 11.0 CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN 20948.005-TIR.doc 1.0 PROJECT OVERVIEW The project proposes to construct a 7-Eleven fueling facility and convenience store. The project site is located at 35620 Pacific Highway South, which is within a portion of Section 29, Township 21 North, Range 4 East, Willamette Meridian, City of Federal Way, King County, Washington. The site consists of 3 tax parcels, with Recording Nos. 292104-9052-06, 292104-9106-02 and 292104-9099-01. The total area of these parcels is 2.16 acres. Please see Figure 2, Site Location, for a graphical description of the exact site location. Under this proposal, the site will develop a new 7-Eleven Convenience Store, fuel canopy, underground fuel storage tanks, and a covered trash enclosure. Utility improvements will include new water, storm, and sewer services in addition to the associated dry utilities. The site is currently developed and consists of a 1-story motel and associated parking lot and hardscape. The project is subject to the 2016 King County Surface Water Design Manual and the requirements therein. Such stormwater improvements required on-site include formal flow control and water quality facilities; source and oil control requirements also apply. The project is subject to a Full Drainage Review per the 2016 KCSWMM. The project is required to adhere to Level 2 Flow Control (conservation flow control) standards, and must provide enhanced basic water quality treatment per the 2016 KCSWDM. 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 N.A.N.A. 05/29/2020 Horizontal: Scale: Vertical: For: Title: VICINITY MAP Job Number N.T.S.N/A 20948 DATE: 05/20/20 7-Eleven - S 356th St Federal Way, Washington P:\20000s\20948\exhibit\graphics\20948 vmap.cdr REFERENCE: Rand McNally (2020) SITE Horizontal: Scale: Vertical: For: Title: ASSESSOR MAP Job Number N.T.S.N/A 20948 DATE: 05/20/20 7-Eleven - S 356th St Federal Way, Washington P:\20000s\20948\exhibit\graphics\20948 amap.cdr SITE REFERENCE: King County Department of Assessments (Feb. 2019) Horizontal: Scale: Vertical: For: Title: FEMA MAP Job Number N.T.S.N/A 20948 DATE: 05/20/20 7-Eleven - S 356th St Federal Way, Washington P:\20000s\20948\exhibit\graphics\20948 fema.cdr REFERENCE: Federal Emergency Management Agency (Portion of Map 53033C1250 F, May 1995) Areas determined to be outside 500-year floodplain. ZONE X OTHER AREAS LEGEND SITE Horizontal: Scale: Vertical: For: Title: SOIL SURVEY MAP Job Number N.T.S.N/A 20948 DATE: 05/20/20 7-Eleven - S 356th St Federal Way, Washington P:\20000s\20948\exhibit\graphics\20948 soil.cdr HSG B C/D REFERENCE: USDA, Natural Resources Conservation Service LEGEND: EwC = Everett-Alderwood gravelly sandy loams, 6-15% slopes SITE Bh = Bellingham silt loam Horizontal: Scale: Vertical: For: Title: SENSITIVE AREAS MAP Job Number N.T.S.N/A 20948 DATE: 05/20/20 7-Eleven - S 356th St Federal Way, Washington P:\20000s\20948\exhibit\graphics\20948 sens.cdr SITE REFERENCE: King County iMAP (2020) 20948.005-TIR.doc 2.0 CONDITIONS AND REQUIREMENTS SUMMARY 2.1 Analysis of the Core Requirements Core Requirement No. 1: Discharge at the Natural Location. Response: On-site runoff will be treated, detained, and discharged to the natural discharge location, existing stormwater infrastructure within South Pacific Highway. Core Requirement No. 2: Off-Site Analysis. Response: The existing and proposed off-site drainage conditions are discussed in the Off-Site Analysis Report included in Section 3.0. Core Requirement No. 3: Flow Control. Response: The project site is within a Conservation Flow Control Area and shall comply with the Level 2 Flow Control Standards. The Level 2 Flow Control Standard requires matching predevelopment and post-development flow durations for all flows greater than one half of the 2-year flow up to the 50-year flow. The predevelopment condition has been modeled as forested in the provided WWHM2012 calculations demonstrating compliance with this requirement. Due to grading constraints, some portions of the development m ust bypass the flow control facility. Mitigation efforts to account for this area are further discussed in Section 4 of this report. Core Requirement No. 4: Conveyance System. Response: The conveyance system will be sized to adequately convey the 100-year storm event. Conveyance calculations will be provided with final engineering. Core Requirement No. 5: Erosion and Sediment Control. Response: Erosion and sediment controls will be provided to prevent the transport of sediment downstream and off-site. The proposed erosion and sediment control measures are further described in Section 8.0 of this report and will be designed pursuant to the 2016 King County Surface Water Design Manual (KCSWDM). Core Requirement No. 6: Maintenance and Operations. Response: Maintenance and Operations of the on-site storm system will be provided in Section 10.0 of this report for final engineering. Core Requirement No. 7: Financial Guarantees and Liability. Response: Financial guarantees will be provided upon permit approval. Core Requirement No. 8: Water Quality. Response: The project is required to provide Enhanced Basic Water Quality via the installation of a Modular Wetland Water Quality unit. Please see Section 4.0 Part E for more information. Core Requirement No. 9: Flow Control BMPs. 20948.005-TIR.doc Response: This project proposes greater than 2,000 square feet of new and replaced impervious surface, and must evaluate the feasibility of flow control BMPs for the proposed targeted surfaces. This project is located on an individual lot that is greater than 22,000 square feet inside the UGA, and must satisfy Large Lot BMP Requirements. Please see Section 4.0 Part F for Flow Control BMPs discussion. 2.2 Analysis of the Special Requirements Special Requirement No. 1: Other Adopted Area-Specific Requirements. Response: The project site is not located in an adopted area; therefore, this requirement does not apply. Special Requirement No. 2: Flood Hazard Area Delineation. Response: The site does not lie within any FEMA delineated Flood H azard areas; therefore, this requirement does not apply. Special Requirement No. 3: Flood Protection Facilities. Response: The site does not rely on flood protection facilities. Special Requirement No. 4: Source Control. Response: Source Control measures will be implemented for this project, as a fueling facility is part of the proposal. All necessary applicable Source Control BMPs indicated in the King County Stormwater Pollution Prevention Manual shall be implemented. Special Requirement No. 5: Oil Control. Response: The development is classified as a high-use site and is therefore required to comply with oil control requirements. An oil/water separator will be utilized to treat run-off prior to discharging off-site. 20948.005-TIR.doc 3.0 OFF-SITE ANALYSIS The following pages contain the Level 1 Off-site Analysis as required within the KCSWDM. LEVEL 1 OFF-SITE DRAINAGE ANALYSIS 7-Eleven Convenience Store and Fueling Station 35620 Pacific Hwy South Federal Way, WA 98003 Prepared for: Visconsi Companies, Ltd. 30050 Chagrin Boulevard, Suite 360 Pepper Pike, OH 44124 May 29, 2020 Our Job No. 20948 05/29/2020 20948.004-Level 1 Off-Site DRNG Analysis.doc TABLE OF CONTENTS TASK 1 STUDY AREA DEFINITION AND MAPS TASK 2 RESOURCE REVIEW Exhibit A - Reconnaissance Summary Report - Hylebos Creek Basin TASK 3 FIELD INSPECTION 3.1 Conveyance System Nuisance Problems (Type 1) 3.2 Severe Erosion Problems (Type 2) 3.3 Severe Flooding Problems (Type 3) TASK 4 DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS Exhibit B - Downstream Drainage Basin Map TASK 5 MITIGATION OF EXISTING OR POTENTIAL PROBLEMS 20948.004-Level 1 Off-Site DRNG Analysis.doc TASK 1 STUDY AREA DEFINITION AND MAPS The proposed 7-Eleven fueling facility and convenience store is located within Section 29, Township 21 North, Range 4 East, Willamette Meridian, in King County, Washington. More specifically, the site is located at 35620 Pacific Highway South, Federal Way. The vicinity map located seen as Figure 2 of the Technical Information Report and provides a graphic depiction of the site location. The site consists of 3 parcels of land containing an area of approximately 2.16 acres. The site contains a 165-foot buffer zone from the Hylebos Wetland located on the east and south borders of the site. Approximately 38 percent of the property is within the wetland buffer zone. The existing topography of the site exhibits a central high point and generally slopes down towards the adjacent streets and lots. Existing grades on the proposed area for the development range from 2 to 12 percent, and existing grades on the existing we tland buffer range from 10 to 30 percent. The majority of the site’s ground cover consists pervious pavement comprising 79 percent of the property and 21 percent existing impervious surfaces. UPSTREAM DRAINAGE ANALYSIS The site receives little to no flow from any of the adjacent sites as topography exhibits the si te higher than all of the surrounding public roadways and areas. The north and east frontage which include existing driveways are sloped away such that run-off drains off-site. Areas to the east and south are within a wetland buffer and/or the Hylebos Wetland, and run-off from this area is contained and does not flow to the proposed development. 20948.004-Level 1 Off-Site DRNG Analysis.doc TASK 2 RESOURCE REVIEW  Adopted Basin Plans: The site is located within the Hylebos Creek Basin.  Finalized Drainage Studies: This is not applicable.  Basin Reconnaissance Summary Report: This site is located in the Hylebos Creek drainage basin. A Basin Reconnaissance Summary Report is included as Exhibit A in this report.  Critical Drainage Area Maps: This project development will not discharge to any critical areas or wetlands as it will be discharging run-off to an existing storm network in Pacific Highway South.  Floodplain and Floodway FEMA Maps: This project is not located within a 100-year floodplain. See Figure 4 of the Technical Information Report for the FEMA Map.  Other Off-Site Analysis Reports: There are no other off-site reports.  Sensitive Areas Folios: Based on the King County Sensitive Areas Map Folios, the site does not contain any on-site wetlands, erosion areas, sensitive areas nor land slide areas. See Figure 6 of the Technical Information Report for the Sensitive Areas Map.  Road Drainage Problems: No road drainage problems were encountered during off -site drainage analysis.  United States Department of Agriculture King County Soils Survey: A soils map found as Figure 5 has been included in the Technical Information Report. The soils map identifies the site underlain with Everett-Alderwood gravelly sandy loam and Bellingham silt loam.  Wetland Inventory Map: As mentioned, the property is adjacent to the Hylebos Wetland. There is an area buffer 165 feet on the east portion of the site from the wetland.  Migrating River Studies: This is not applicable. 20948.004-Level 1 Off-Site DRNG Analysis.doc TASK 3 FIELD INSPECTION 3.1 Conveyance System Nuisance Problems (Type 1) Conveyance system nuisance problems, in general, are defined as any existing or predicted flooding or erosion that does not constitute a severe flooding or erosion problem. Conveyance system nuisance problems are defined as flo oding or erosion that results in the overflow of the constructed conveyance system for runoff events less than or equal to a 10-year event. Examples include inundation of a shoulder or lane of a roadway. Examples include overflows collecting in yards or pastures, shallow flows across driveways, minor flooding in crawlspaces or unheated garages/outbuildings , and minor erosion. There were no known conveyance system nuisance problems reported and observed. 3.2 Severe Erosion Problems (Type 2) Severe erosion problems are defined as downstream channels, ravines, or slopes with evidence of or potential for erosion/incision, sufficient to pose a sedimentation hazard to downstream conveyance systems or propose a landslide hazard by undercutting adjacent slopes. Severe erosion problems do not include roadway or minor ditch erosion. There were no known severe erosion problems within the downstream drainage course, nor have any such problems been observed. 3.3 Severe Flooding Problems (Type 3) Severe flooding problems can be caused by conveyance system overflows or the elevated water surfaces of ponds, lakes, wetlands, or closed depressions. Severe flooding problems are defined as follows:  Flooding of the finished area of a habitable building for runoff events less than or equal to the 100-year event. Examples include flooding of finished floors of homes and commercial or industrial buildings. Flooding in electrical/heating systems and components in the crawlspace or garage of a home. Such problems are referred to as "severe building flooding problems."  Flooding over all lanes of a roadway or severely impacting a sole access driveway for runoff events less than or equal to the 100-year event. Such problems are referred to as "severe roadway flooding problems." Based on a review of the FEMA Map (Figure 4 of the TIR), the proposed site is outside of the 500-year floodplain, and there is no known evidence of severe flooding problems. 20948.004-Level 1 Off-Site DRNG Analysis.doc TASK 4 DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS The existing conditions of the site exhibit runoff to sheet flow along the perimeter of the site and is drained to an existing curb and gutter and finally to catch basins located along Pacific Highway South and S.W . 356th Street. Part of the existing site's run-off (east of the proposed development area) also sheet flows towards the east and south towards the existing pervious areas. A Downstream Basin Map is shown in Exhibit B. In the developed condition, stormwater run-off will be collected by proposed catch basins and will be treated through an oil/water separator and a water quality unit following conveyance through an on-site detention facility (StormTech Facility).The point of discharge is an existing catch basin located along Pacific Highway South. No known drainage problems were encountered during the off-site analysis. Storm 20948.004-Level 1 Off-Site DRNG Analysis.doc TASK 5 MITIGATION OF EXISTING OR POTENTIAL PROBLEMS No existing or potential problems were during the off-site analysis The project proposes to provide a detention facility that will allow on-site flows to meet the Level 2 flow control standard. Additionally, the enhanced basic water quality treatment will be provided by a Modular Wetland water quality unit. This project intends to control flow rates to the extent required by the 2016 KCSWDM and is not anticipated to negatively impact the downstream conveyance systems or properties. 20948.005-TIR.doc 4.0 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN A. Existing Site Hydrology The total site is currently developed with asphalt and gravel surfacing, storm and sewer infrastructure, and associated landscaping. The site is bound by Pacific Highway South along the west, S.W . 356th Street to the north, and the Hylebos Wetlands to both the east and south. Of the 2.16 acres of the property, the site is currently covered in approximately 21 percent impervious surfaces and approximately 38 percent of the property is within the Hybelos Wetlands. The existing topography of the site exhibit slopes ranging from 2 to 12 percent with the highest elevations centralized in the property where the existing motel and 1-story building structures are situated. Currently, it appears that run-off sheet flows over the existing driveways located along Pacific Highway South and S.W . 356th Street and collects within the existing public infrastructure. B. Developed Site Hydrology The proposed project consists of the construction of a new 7-Eleven fueling facility with underground storage tanks and a conve nience store, including new sidewalks and pavement surfaces. A new driveway along South Pacific Highway is proposed to accommodate the proposed grading scheme of the site. As part of this project, the existing motel and building structure will be demolished. Along with the on-site and off-site improvements, drainage facilities will be constructed to capture runoff from the developed surfaces and conveyed to the on-site drainage facilities for detention and water quality treatment. The site will maintain the same general topographic grading characteristics and will be primarily comprised of pavement (concrete and asphalt) and structures. The onsite runoff will be detained via underground StormTech Chambers, and treated with a series of treatment facilities to meet the requirements of the Enhanced Basic Treatment per the 2016 KCSWDM. C. Performance Standards The project site is subject to Conservation (Level 2) Flow Control and Enhanced Basic Water Quality treatment. Western Washington Hydrology Model (WWHM) will be used to size the proposed detention system using the SeaTac Region Scale Factor of 1.0. Water quality and flow control facilities will be designed pursuant to the 2016 KCSWDM. See Section below for WWHM Calculations. WWHM2012 PROJECT REPORT 20948-mc4500 1.0 5/29/2020 8:09:49 AM Page 2 General Model Information Project Name:20948-mc4500 1.0 Site Name:7-Eleven Federal Way Site Address:35620 Pacific Highway S City:Federal Way Report Date:5/29/2020 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.000 Version Date:2019/09/13 Version:4.2.17 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year 20948-mc4500 1.0 5/29/2020 8:09:49 AM Page 3 Landuse Basin Data Predeveloped Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Mod 0.99 Pervious Total 0.99 Impervious Land Use acre Impervious Total 0 Basin Total 0.99 Element Flows To: Surface Interflow Groundwater 20948-mc4500 1.0 5/29/2020 8:09:49 AM Page 4 Mitigated Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Flat 0.08 Pervious Total 0.08 Impervious Land Use acre ROOF TOPS FLAT 0.09 DRIVEWAYS FLAT 0.82 Impervious Total 0.91 Basin Total 0.99 Element Flows To: Surface Interflow Groundwater SSD Table 1 SSD Table 1 20948-mc4500 1.0 5/29/2020 8:09:49 AM Page 5 Routing Elements Predeveloped Routing 20948-mc4500 1.0 5/29/2020 8:09:49 AM Page 6 Mitigated Routing SSD Table 1 Depth:5.5 ft. Discharge Structure: 1 Riser Height:5 ft. Riser Diameter:18 in. Orifice 1 Diameter:0.59 in.Elevation:0 ft. Orifice 2 Diameter:0.88 in.Elevation:2.74 ft. Orifice 3 Diameter:0.7 in.Elevation:4.15 ft. Element Flows To: Outlet 1 Outlet 2 SSD Table Hydraulic Table Stage Area Volume Outlet (feet) (ac.) (ac-ft.) Struct NotUsed NotUsed NotUsed NotUsed 0.000 0.119 0.000 0.000 0.000 0.000 0.000 0.000 0.083 0.119 0.009 0.003 0.000 0.000 0.000 0.000 0.167 0.119 0.017 0.004 0.000 0.000 0.000 0.000 0.250 0.119 0.026 0.005 0.000 0.000 0.000 0.000 0.333 0.119 0.035 0.005 0.000 0.000 0.000 0.000 0.417 0.119 0.043 0.006 0.000 0.000 0.000 0.000 0.500 0.119 0.052 0.007 0.000 0.000 0.000 0.000 0.583 0.119 0.060 0.007 0.000 0.000 0.000 0.000 0.667 0.119 0.069 0.008 0.000 0.000 0.000 0.000 0.750 0.119 0.077 0.008 0.000 0.000 0.000 0.000 0.833 0.119 0.086 0.009 0.000 0.000 0.000 0.000 0.917 0.119 0.094 0.009 0.000 0.000 0.000 0.000 1.000 0.119 0.103 0.009 0.000 0.000 0.000 0.000 1.083 0.119 0.111 0.010 0.000 0.000 0.000 0.000 1.167 0.119 0.119 0.010 0.000 0.000 0.000 0.000 1.250 0.119 0.128 0.011 0.000 0.000 0.000 0.000 1.333 0.119 0.136 0.011 0.000 0.000 0.000 0.000 1.417 0.119 0.144 0.011 0.000 0.000 0.000 0.000 1.500 0.119 0.152 0.012 0.000 0.000 0.000 0.000 1.583 0.119 0.161 0.012 0.000 0.000 0.000 0.000 1.667 0.119 0.169 0.012 0.000 0.000 0.000 0.000 1.750 0.119 0.177 0.012 0.000 0.000 0.000 0.000 1.833 0.119 0.185 0.013 0.000 0.000 0.000 0.000 1.917 0.119 0.193 0.013 0.000 0.000 0.000 0.000 2.000 0.119 0.201 0.013 0.000 0.000 0.000 0.000 2.083 0.119 0.209 0.014 0.000 0.000 0.000 0.000 2.167 0.119 0.217 0.014 0.000 0.000 0.000 0.000 2.250 0.119 0.225 0.014 0.000 0.000 0.000 0.000 2.333 0.119 0.233 0.014 0.000 0.000 0.000 0.000 2.417 0.119 0.240 0.015 0.000 0.000 0.000 0.000 2.500 0.119 0.248 0.015 0.000 0.000 0.000 0.000 2.583 0.119 0.256 0.015 0.000 0.000 0.000 0.000 2.667 0.119 0.263 0.015 0.000 0.000 0.000 0.000 2.750 0.119 0.271 0.018 0.000 0.000 0.000 0.000 2.833 0.119 0.278 0.022 0.000 0.000 0.000 0.000 2.917 0.119 0.286 0.025 0.000 0.000 0.000 0.000 3.000 0.119 0.293 0.027 0.000 0.000 0.000 0.000 3.083 0.119 0.300 0.029 0.000 0.000 0.000 0.000 3.167 0.119 0.307 0.031 0.000 0.000 0.000 0.000 20948-mc4500 1.0 5/29/2020 8:09:49 AM Page 7 3.250 0.119 0.314 0.032 0.000 0.000 0.000 0.000 3.333 0.119 0.321 0.033 0.000 0.000 0.000 0.000 3.417 0.119 0.328 0.035 0.000 0.000 0.000 0.000 3.500 0.119 0.335 0.036 0.000 0.000 0.000 0.000 3.583 0.119 0.342 0.037 0.000 0.000 0.000 0.000 3.667 0.119 0.349 0.038 0.000 0.000 0.000 0.000 3.750 0.119 0.355 0.039 0.000 0.000 0.000 0.000 3.833 0.119 0.362 0.040 0.000 0.000 0.000 0.000 3.917 0.119 0.368 0.041 0.000 0.000 0.000 0.000 4.000 0.119 0.374 0.042 0.000 0.000 0.000 0.000 4.083 0.119 0.380 0.043 0.000 0.000 0.000 0.000 4.167 0.119 0.386 0.046 0.000 0.000 0.000 0.000 4.250 0.119 0.392 0.050 0.000 0.000 0.000 0.000 4.333 0.119 0.398 0.052 0.000 0.000 0.000 0.000 4.417 0.119 0.403 0.054 0.000 0.000 0.000 0.000 4.500 0.119 0.408 0.056 0.000 0.000 0.000 0.000 4.583 0.119 0.413 0.058 0.000 0.000 0.000 0.000 4.667 0.119 0.417 0.059 0.000 0.000 0.000 0.000 4.750 0.119 0.422 0.061 0.000 0.000 0.000 0.000 4.833 0.119 0.426 0.062 0.000 0.000 0.000 0.000 4.917 0.119 0.430 0.064 0.000 0.000 0.000 0.000 5.000 0.119 0.434 0.065 0.000 0.000 0.000 0.000 5.083 0.119 0.438 0.449 0.000 0.000 0.000 0.000 5.167 0.119 0.442 1.142 0.000 0.000 0.000 0.000 5.250 0.119 0.446 2.007 0.000 0.000 0.000 0.000 5.333 0.119 0.450 2.953 0.000 0.000 0.000 0.000 5.417 0.119 0.454 3.884 0.000 0.000 0.000 0.000 5.500 0.119 0.458 4.712 0.000 0.000 0.000 0.000 20948-mc4500 1.0 5/29/2020 8:09:49 AM Page 8 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.99 Total Impervious Area:0 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.08 Total Impervious Area:0.91 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.029477 5 year 0.048301 10 year 0.060405 25 year 0.074802 50 year 0.084775 100 year 0.09409 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.018372 5 year 0.02923 10 year 0.038415 25 year 0.052656 50 year 0.065425 100 year 0.080268 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.034 0.013 1950 0.040 0.015 1951 0.064 0.048 1952 0.020 0.011 1953 0.016 0.015 1954 0.025 0.014 1955 0.040 0.013 1956 0.032 0.033 1957 0.026 0.013 1958 0.029 0.015 20948-mc4500 1.0 5/29/2020 8:10:20 AM Page 9 1959 0.025 0.013 1960 0.044 0.037 1961 0.024 0.023 1962 0.015 0.012 1963 0.021 0.015 1964 0.030 0.023 1965 0.020 0.028 1966 0.019 0.014 1967 0.045 0.017 1968 0.025 0.014 1969 0.025 0.014 1970 0.020 0.015 1971 0.022 0.015 1972 0.049 0.039 1973 0.022 0.027 1974 0.024 0.014 1975 0.033 0.013 1976 0.024 0.014 1977 0.004 0.012 1978 0.020 0.015 1979 0.012 0.011 1980 0.058 0.040 1981 0.018 0.014 1982 0.037 0.034 1983 0.032 0.014 1984 0.019 0.012 1985 0.011 0.012 1986 0.051 0.017 1987 0.045 0.036 1988 0.018 0.013 1989 0.012 0.012 1990 0.107 0.037 1991 0.057 0.039 1992 0.023 0.015 1993 0.023 0.012 1994 0.008 0.011 1995 0.032 0.024 1996 0.075 0.043 1997 0.058 0.043 1998 0.014 0.012 1999 0.063 0.039 2000 0.022 0.016 2001 0.004 0.010 2002 0.026 0.023 2003 0.039 0.014 2004 0.042 0.051 2005 0.031 0.013 2006 0.035 0.031 2007 0.081 0.086 2008 0.098 0.041 2009 0.046 0.028 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.1067 0.0865 2 0.0983 0.0507 3 0.0807 0.0475 20948-mc4500 1.0 5/29/2020 8:10:20 AM Page 10 4 0.0748 0.0428 5 0.0644 0.0425 6 0.0633 0.0406 7 0.0577 0.0396 8 0.0576 0.0394 9 0.0566 0.0394 10 0.0505 0.0388 11 0.0489 0.0373 12 0.0459 0.0372 13 0.0453 0.0358 14 0.0446 0.0343 15 0.0444 0.0330 16 0.0416 0.0314 17 0.0403 0.0283 18 0.0401 0.0276 19 0.0389 0.0269 20 0.0373 0.0242 21 0.0347 0.0232 22 0.0339 0.0230 23 0.0334 0.0229 24 0.0323 0.0171 25 0.0323 0.0165 26 0.0319 0.0159 27 0.0308 0.0154 28 0.0296 0.0153 29 0.0289 0.0152 30 0.0260 0.0151 31 0.0260 0.0148 32 0.0255 0.0147 33 0.0251 0.0146 34 0.0248 0.0146 35 0.0248 0.0142 36 0.0244 0.0141 37 0.0240 0.0141 38 0.0239 0.0140 39 0.0231 0.0140 40 0.0226 0.0139 41 0.0225 0.0137 42 0.0225 0.0137 43 0.0217 0.0136 44 0.0209 0.0135 45 0.0202 0.0135 46 0.0202 0.0135 47 0.0199 0.0134 48 0.0197 0.0132 49 0.0192 0.0131 50 0.0189 0.0128 51 0.0181 0.0124 52 0.0176 0.0123 53 0.0163 0.0122 54 0.0152 0.0119 55 0.0141 0.0119 56 0.0122 0.0117 57 0.0117 0.0116 58 0.0114 0.0115 59 0.0076 0.0107 60 0.0040 0.0105 61 0.0035 0.0100 20948-mc4500 1.0 5/29/2020 8:10:20 AM Page 11 20948-mc4500 1.0 5/29/2020 8:10:20 AM Page 12 Duration Flows The Facility PASSED Flow(cfs)Predev Mit Percentage Pass/Fail 0.0147 17096 14784 86 Pass 0.0154 15496 7948 51 Pass 0.0162 14072 7433 52 Pass 0.0169 12797 7005 54 Pass 0.0176 11576 6558 56 Pass 0.0183 10523 6284 59 Pass 0.0190 9565 6053 63 Pass 0.0197 8750 5852 66 Pass 0.0204 8044 5664 70 Pass 0.0211 7347 5446 74 Pass 0.0218 6733 5251 77 Pass 0.0225 6188 5033 81 Pass 0.0232 5730 4729 82 Pass 0.0239 5309 4492 84 Pass 0.0246 4924 4229 85 Pass 0.0254 4569 4004 87 Pass 0.0261 4239 3794 89 Pass 0.0268 3951 3555 89 Pass 0.0275 3643 3335 91 Pass 0.0282 3390 3114 91 Pass 0.0289 3133 2898 92 Pass 0.0296 2915 2733 93 Pass 0.0303 2706 2554 94 Pass 0.0310 2490 2363 94 Pass 0.0317 2314 2141 92 Pass 0.0324 2136 1936 90 Pass 0.0331 1972 1772 89 Pass 0.0338 1826 1620 88 Pass 0.0345 1702 1464 86 Pass 0.0353 1577 1313 83 Pass 0.0360 1442 1173 81 Pass 0.0367 1325 1055 79 Pass 0.0374 1232 892 72 Pass 0.0381 1147 762 66 Pass 0.0388 1083 642 59 Pass 0.0395 1020 477 46 Pass 0.0402 947 393 41 Pass 0.0409 886 344 38 Pass 0.0416 824 304 36 Pass 0.0423 760 262 34 Pass 0.0430 725 220 30 Pass 0.0437 674 204 30 Pass 0.0445 623 193 30 Pass 0.0452 589 181 30 Pass 0.0459 549 168 30 Pass 0.0466 506 158 31 Pass 0.0473 469 148 31 Pass 0.0480 427 139 32 Pass 0.0487 388 131 33 Pass 0.0494 356 125 35 Pass 0.0501 328 119 36 Pass 0.0508 298 108 36 Pass 0.0515 270 106 39 Pass 20948-mc4500 1.0 5/29/2020 8:10:20 AM Page 13 0.0522 241 102 42 Pass 0.0529 218 91 41 Pass 0.0536 198 85 42 Pass 0.0544 173 80 46 Pass 0.0551 152 69 45 Pass 0.0558 130 65 50 Pass 0.0565 119 61 51 Pass 0.0572 104 57 54 Pass 0.0579 95 54 56 Pass 0.0586 83 50 60 Pass 0.0593 74 46 62 Pass 0.0600 69 43 62 Pass 0.0607 61 39 63 Pass 0.0614 53 37 69 Pass 0.0621 46 34 73 Pass 0.0628 39 31 79 Pass 0.0636 29 20 68 Pass 0.0643 25 15 60 Pass 0.0650 22 7 31 Pass 0.0657 20 7 35 Pass 0.0664 17 7 41 Pass 0.0671 14 7 50 Pass 0.0678 12 6 50 Pass 0.0685 8 6 75 Pass 0.0692 7 5 71 Pass 0.0699 7 5 71 Pass 0.0706 7 4 57 Pass 0.0713 6 3 50 Pass 0.0720 6 3 50 Pass 0.0727 6 3 50 Pass 0.0735 6 3 50 Pass 0.0742 6 3 50 Pass 0.0749 5 2 40 Pass 0.0756 5 2 40 Pass 0.0763 5 2 40 Pass 0.0770 5 2 40 Pass 0.0777 5 2 40 Pass 0.0784 5 2 40 Pass 0.0791 5 2 40 Pass 0.0798 4 2 50 Pass 0.0805 4 2 50 Pass 0.0812 3 2 66 Pass 0.0819 3 2 66 Pass 0.0827 3 2 66 Pass 0.0834 3 2 66 Pass 0.0841 3 2 66 Pass 0.0848 3 1 33 Pass 20948-mc4500 1.0 5/29/2020 8:10:20 AM Page 14 Water Quality Water Quality BMP Flow and Volume for POC #1 On-line facility volume:0.0239 acre-feet On-line facility target flow:0.012 cfs. Adjusted for 15 min:0.012 cfs. Off-line facility target flow:0.0083 cfs. Adjusted for 15 min:0.0083 cfs. 20948-mc4500 1.0 5/29/2020 8:10:20 AM Page 15 LID Report 20948-mc4500 1.0 5/29/2020 8:10:30 AM Page 16 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. 20948-mc4500 1.0 5/29/2020 8:10:30 AM Page 17 Appendix Predeveloped Schematic 20948-mc4500 1.0 5/29/2020 8:10:30 AM Page 18 Mitigated Schematic 20948-mc4500 1.0 5/29/2020 8:10:31 AM Page 19 Predeveloped UCI File RUN GLOBAL WWHM4 model simulation START 1948 10 01 END 2009 09 30 RUN INTERP OUTPUT LEVEL 3 0 RESUME 0 RUN 1 UNIT SYSTEM 1 END GLOBAL FILES <File> <Un#> <-----------File Name------------------------------>*** <-ID-> *** WDM 26 20948-mc4500 1.0.wdm MESSU 25 Pre20948-mc4500 1.0.MES 27 Pre20948-mc4500 1.0.L61 28 Pre20948-mc4500 1.0.L62 30 POC20948-mc4500 1.01.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 11 COPY 501 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<----------Title----------->***TRAN PIVL DIG1 FIL1 PYR DIG2 FIL2 YRND 1 Basin 1 MAX 1 2 30 9 END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 501 1 1 END TIMESERIES END COPY GENER OPCODE # # OPCD *** END OPCODE PARM # # K *** END PARM END GENER PERLND GEN-INFO <PLS ><-------Name------->NBLKS Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 11 C, Forest, Mod 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 11 0 0 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 11 0 0 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO 20948-mc4500 1.0 5/29/2020 8:10:31 AM Page 20 PWAT-PARM1 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** 11 0 0 0 0 0 0 0 0 0 0 0 END PWAT-PARM1 PWAT-PARM2 <PLS > PWATER input info: Part 2 *** # - # ***FOREST LZSN INFILT LSUR SLSUR KVARY AGWRC 11 0 4.5 0.08 400 0.1 0.5 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 11 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 11 0.2 0.5 0.35 6 0.5 0.7 END PWAT-PARM4 PWAT-STATE1 <PLS > *** Initial conditions at start of simulation ran from 1990 to end of 1992 (pat 1-11-95) RUN 21 *** # - # *** CEPS SURS UZS IFWS LZS AGWS GWVS 11 0 0 0 0 2.5 1 0 END PWAT-STATE1 END PERLND IMPLND GEN-INFO <PLS ><-------Name-------> Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** END GEN-INFO *** Section IWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** END ACTIVITY PRINT-INFO <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* END PRINT-INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN END IWAT-PARM3 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS END IWAT-STATE1 20948-mc4500 1.0 5/29/2020 8:10:31 AM Page 21 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** Basin 1*** PERLND 11 0.99 COPY 501 12 PERLND 11 0.99 COPY 501 13 ******Routing****** END SCHEMATIC NETWORK <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** COPY 501 OUTPUT MEAN 1 1 48.4 DISPLY 1 INPUT TIMSER 1 <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** END NETWORK RCHRES GEN-INFO RCHRES Name Nexits Unit Systems Printer *** # - #<------------------><---> User T-series Engl Metr LKFG *** in out *** END GEN-INFO *** Section RCHRES*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # HYFG ADFG CNFG HTFG SDFG GQFG OXFG NUFG PKFG PHFG *** END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ******************* PIVL PYR # - # HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB PIVL PYR ********* END PRINT-INFO HYDR-PARM1 RCHRES Flags for each HYDR Section *** # - # VC A1 A2 A3 ODFVFG for each *** ODGTFG for each FUNCT for each FG FG FG FG possible exit *** possible exit possible exit * * * * * * * * * * * * * * *** END HYDR-PARM1 HYDR-PARM2 # - # FTABNO LEN DELTH STCOR KS DB50 *** <------><--------><--------><--------><--------><--------><--------> *** END HYDR-PARM2 HYDR-INIT RCHRES Initial conditions for each HYDR section *** # - # *** VOL Initial value of COLIND Initial value of OUTDGT *** ac-ft for each possible exit for each possible exit <------><--------> <---><---><---><---><---> *** <---><---><---><---><---> END HYDR-INIT END RCHRES SPEC-ACTIONS END SPEC-ACTIONS FTABLES END FTABLES EXT SOURCES <-Volume-> <Member> SsysSgap<--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # tem strg<-factor->strg <Name> # # <Name> # # *** WDM 2 PREC ENGL 1 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 1 IMPLND 1 999 EXTNL PREC 20948-mc4500 1.0 5/29/2020 8:10:31 AM Page 22 WDM 1 EVAP ENGL 0.76 PERLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 IMPLND 1 999 EXTNL PETINP END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** COPY 501 OUTPUT MEAN 1 1 48.4 WDM 501 FLOW ENGL REPL END EXT TARGETS MASS-LINK <Volume> <-Grp> <-Member-><--Mult--> <Target> <-Grp> <-Member->*** <Name> <Name> # #<-factor-> <Name> <Name> # #*** MASS-LINK 12 PERLND PWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 12 MASS-LINK 13 PERLND PWATER IFWO 0.083333 COPY INPUT MEAN END MASS-LINK 13 END MASS-LINK END RUN 20948-mc4500 1.0 5/29/2020 8:10:31 AM Page 23 Mitigated UCI File RUN GLOBAL WWHM4 model simulation START 1948 10 01 END 2009 09 30 RUN INTERP OUTPUT LEVEL 3 0 RESUME 0 RUN 1 UNIT SYSTEM 1 END GLOBAL FILES <File> <Un#> <-----------File Name------------------------------>*** <-ID-> *** WDM 26 20948-mc4500 1.0.wdm MESSU 25 Mit20948-mc4500 1.0.MES 27 Mit20948-mc4500 1.0.L61 28 Mit20948-mc4500 1.0.L62 30 POC20948-mc4500 1.01.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 16 IMPLND 4 IMPLND 5 RCHRES 1 COPY 1 COPY 501 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<----------Title----------->***TRAN PIVL DIG1 FIL1 PYR DIG2 FIL2 YRND 1 SSD Table 1 MAX 1 2 30 9 END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 501 1 1 END TIMESERIES END COPY GENER OPCODE # # OPCD *** END OPCODE PARM # # K *** END PARM END GENER PERLND GEN-INFO <PLS ><-------Name------->NBLKS Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 16 C, Lawn, Flat 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 16 0 0 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ***************************** PIVL PYR 20948-mc4500 1.0 5/29/2020 8:10:31 AM Page 24 # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 16 0 0 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO PWAT-PARM1 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** 16 0 0 0 0 0 0 0 0 0 0 0 END PWAT-PARM1 PWAT-PARM2 <PLS > PWATER input info: Part 2 *** # - # ***FOREST LZSN INFILT LSUR SLSUR KVARY AGWRC 16 0 4.5 0.03 400 0.05 0.5 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 16 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 16 0.1 0.25 0.25 6 0.5 0.25 END PWAT-PARM4 PWAT-STATE1 <PLS > *** Initial conditions at start of simulation ran from 1990 to end of 1992 (pat 1-11-95) RUN 21 *** # - # *** CEPS SURS UZS IFWS LZS AGWS GWVS 16 0 0 0 0 2.5 1 0 END PWAT-STATE1 END PERLND IMPLND GEN-INFO <PLS ><-------Name-------> Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 4 ROOF TOPS/FLAT 1 1 1 27 0 5 DRIVEWAYS/FLAT 1 1 1 27 0 END GEN-INFO *** Section IWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** 4 0 0 1 0 0 0 5 0 0 1 0 0 0 END ACTIVITY PRINT-INFO <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* 4 0 0 4 0 0 0 1 9 5 0 0 4 0 0 0 1 9 END PRINT-INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** 4 0 0 0 0 0 5 0 0 0 0 0 END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC 20948-mc4500 1.0 5/29/2020 8:10:31 AM Page 25 4 400 0.01 0.1 0.1 5 400 0.01 0.1 0.1 END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN 4 0 0 5 0 0 END IWAT-PARM3 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS 4 0 0 5 0 0 END IWAT-STATE1 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** Basin 1*** PERLND 16 0.08 RCHRES 1 2 PERLND 16 0.08 RCHRES 1 3 IMPLND 4 0.09 RCHRES 1 5 IMPLND 5 0.82 RCHRES 1 5 ******Routing****** PERLND 16 0.08 COPY 1 12 IMPLND 4 0.09 COPY 1 15 IMPLND 5 0.82 COPY 1 15 PERLND 16 0.08 COPY 1 13 RCHRES 1 1 COPY 501 16 END SCHEMATIC NETWORK <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** COPY 501 OUTPUT MEAN 1 1 48.4 DISPLY 1 INPUT TIMSER 1 <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** END NETWORK RCHRES GEN-INFO RCHRES Name Nexits Unit Systems Printer *** # - #<------------------><---> User T-series Engl Metr LKFG *** in out *** 1 SSD Table 1 1 1 1 1 28 0 1 END GEN-INFO *** Section RCHRES*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # HYFG ADFG CNFG HTFG SDFG GQFG OXFG NUFG PKFG PHFG *** 1 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ******************* PIVL PYR # - # HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB PIVL PYR ********* 1 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO HYDR-PARM1 20948-mc4500 1.0 5/29/2020 8:10:31 AM Page 26 RCHRES Flags for each HYDR Section *** # - # VC A1 A2 A3 ODFVFG for each *** ODGTFG for each FUNCT for each FG FG FG FG possible exit *** possible exit possible exit * * * * * * * * * * * * * * *** 1 0 1 0 0 4 0 0 0 0 0 0 0 0 0 2 2 2 2 2 END HYDR-PARM1 HYDR-PARM2 # - # FTABNO LEN DELTH STCOR KS DB50 *** <------><--------><--------><--------><--------><--------><--------> *** 1 1 0.01 0.0 0.0 0.5 0.0 END HYDR-PARM2 HYDR-INIT RCHRES Initial conditions for each HYDR section *** # - # *** VOL Initial value of COLIND Initial value of OUTDGT *** ac-ft for each possible exit for each possible exit <------><--------> <---><---><---><---><---> *** <---><---><---><---><---> 1 0 4.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 END HYDR-INIT END RCHRES SPEC-ACTIONS END SPEC-ACTIONS FTABLES FTABLE 1 67 4 Depth Area Volume Outflow1 Velocity Travel Time*** (ft) (acres) (acre-ft) (cfs) (ft/sec) (Minutes)*** 0.000000 0.119303 0.000000 0.000000 0.083333 0.119303 0.008659 0.002727 0.166666 0.119303 0.017295 0.003856 0.250000 0.119303 0.025915 0.004723 0.333333 0.119303 0.034518 0.005454 0.416666 0.119303 0.043101 0.006098 0.500000 0.119303 0.051665 0.006680 0.583333 0.119303 0.060208 0.007215 0.666666 0.119303 0.068730 0.007713 0.750000 0.119303 0.077228 0.008181 0.833333 0.119303 0.085701 0.008623 0.916666 0.119303 0.094149 0.009044 1.000000 0.119303 0.102571 0.009446 1.083333 0.119303 0.110963 0.009832 1.166666 0.119303 0.119327 0.010203 1.250000 0.119303 0.127659 0.010561 1.333333 0.119303 0.135960 0.010908 1.416666 0.119303 0.144227 0.011243 1.500000 0.119303 0.152459 0.011569 1.583333 0.119303 0.160657 0.011886 1.666666 0.119303 0.168815 0.012195 1.750000 0.119303 0.176934 0.012496 1.833333 0.119303 0.185012 0.012790 1.916666 0.119303 0.193047 0.013078 2.000000 0.119303 0.201038 0.013359 2.083333 0.119303 0.208984 0.013635 2.166666 0.119303 0.216883 0.013905 2.250000 0.119303 0.224732 0.014169 2.333333 0.119303 0.232531 0.014429 2.416666 0.119303 0.240277 0.014685 2.500000 0.119303 0.247969 0.014936 2.583333 0.119303 0.255604 0.015183 2.666666 0.119303 0.263180 0.015426 2.750000 0.119303 0.270695 0.017766 2.833333 0.119303 0.278148 0.022321 2.916666 0.119303 0.285534 0.024966 3.000000 0.119303 0.292853 0.027077 3.083333 0.119303 0.300100 0.028901 3.166666 0.119303 0.307273 0.030537 3.250000 0.119303 0.314370 0.032037 3.333333 0.119303 0.321387 0.033434 3.416666 0.119303 0.328319 0.034747 20948-mc4500 1.0 5/29/2020 8:10:31 AM Page 27 3.500000 0.119303 0.335164 0.035993 3.583333 0.119303 0.341916 0.037180 3.666666 0.119303 0.348573 0.038318 3.750000 0.119303 0.355127 0.039412 3.833333 0.119303 0.361575 0.040468 3.916666 0.119303 0.367909 0.041490 4.000000 0.119303 0.374121 0.042482 4.083333 0.119303 0.380202 0.043445 4.166666 0.119303 0.386144 0.046099 4.250000 0.119303 0.391931 0.049502 4.333333 0.119303 0.397546 0.051884 4.416666 0.119303 0.402962 0.053930 4.500000 0.119303 0.408137 0.055785 4.583333 0.119303 0.412931 0.057508 4.666666 0.119303 0.417396 0.059134 4.750000 0.119303 0.421751 0.060681 4.833333 0.119303 0.426024 0.062164 4.916666 0.119303 0.430208 0.063593 5.000000 0.119303 0.434257 0.064974 5.083333 0.119303 0.438234 0.448603 5.166666 0.119303 0.442211 1.141879 5.250000 0.119303 0.446188 2.007314 5.333333 0.119303 0.450164 2.952637 5.416666 0.119303 0.454141 3.883944 5.500000 0.119303 0.458118 4.711608 END FTABLE 1 END FTABLES EXT SOURCES <-Volume-> <Member> SsysSgap<--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # tem strg<-factor->strg <Name> # # <Name> # # *** WDM 2 PREC ENGL 1 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 1 IMPLND 1 999 EXTNL PREC WDM 1 EVAP ENGL 0.76 PERLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 IMPLND 1 999 EXTNL PETINP END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** RCHRES 1 HYDR RO 1 1 1 WDM 1002 FLOW ENGL REPL RCHRES 1 HYDR STAGE 1 1 1 WDM 1003 STAG ENGL REPL COPY 1 OUTPUT MEAN 1 1 48.4 WDM 701 FLOW ENGL REPL COPY 501 OUTPUT MEAN 1 1 48.4 WDM 801 FLOW ENGL REPL END EXT TARGETS MASS-LINK <Volume> <-Grp> <-Member-><--Mult--> <Target> <-Grp> <-Member->*** <Name> <Name> # #<-factor-> <Name> <Name> # #*** MASS-LINK 2 PERLND PWATER SURO 0.083333 RCHRES INFLOW IVOL END MASS-LINK 2 MASS-LINK 3 PERLND PWATER IFWO 0.083333 RCHRES INFLOW IVOL END MASS-LINK 3 MASS-LINK 5 IMPLND IWATER SURO 0.083333 RCHRES INFLOW IVOL END MASS-LINK 5 MASS-LINK 12 PERLND PWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 12 MASS-LINK 13 PERLND PWATER IFWO 0.083333 COPY INPUT MEAN END MASS-LINK 13 20948-mc4500 1.0 5/29/2020 8:10:31 AM Page 28 MASS-LINK 15 IMPLND IWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 15 MASS-LINK 16 RCHRES ROFLOW COPY INPUT MEAN END MASS-LINK 16 END MASS-LINK END RUN 20948-mc4500 1.0 5/29/2020 8:10:31 AM Page 29 Predeveloped HSPF Message File 20948-mc4500 1.0 5/29/2020 8:10:31 AM Page 30 Mitigated HSPF Message File ERROR/WARNING ID: 238 1 The continuity error reported below is greater than 1 part in 1000 and is therefore considered high. Did you specify any "special actions"? If so, they could account for it. Relevant data are: DATE/TIME: 2002/ 8/31 24: 0 RCHRES : 1 RELERR STORS STOR MATIN MATDIF -0.00576 0.00000 0.0000E+00 0.00000 -1.526E-08 Where: RELERR is the relative error (ERROR/REFVAL). ERROR is (STOR-STORS) - MATDIF. REFVAL is the reference value (STORS+MATIN). STOR is the storage of material in the processing unit (land-segment or reach/reservior) at the end of the present interval. STORS is the storage of material in the pu at the start of the present printout reporting period. MATIN is the total inflow of material to the pu during the present printout reporting period. MATDIF is the net inflow (inflow-outflow) of material to the pu during the present printout reporting period. ERROR/WARNING ID: 238 1 The continuity error reported below is greater than 1 part in 1000 and is therefore considered high. Did you specify any "special actions"? If so, they could account for it. Relevant data are: DATE/TIME: 2004/ 7/31 24: 0 RCHRES : 1 RELERR STORS STOR MATIN MATDIF -1.097E-03 0.00000 0.0000E+00 0.00000 -7.979E-08 Where: RELERR is the relative error (ERROR/REFVAL). ERROR is (STOR-STORS) - MATDIF. REFVAL is the reference value (STORS+MATIN). STOR is the storage of material in the processing unit (land-segment or reach/reservior) at the end of the present interval. STORS is the storage of material in the pu at the start of the present printout reporting period. MATIN is the total inflow of material to the pu during the present printout reporting period. MATDIF is the net inflow (inflow-outflow) of material to the pu during the present printout reporting period. ERROR/WARNING ID: 238 1 The continuity error reported below is greater than 1 part in 1000 and is therefore considered high. Did you specify any "special actions"? If so, they could account for it. Relevant data are: 20948-mc4500 1.0 5/29/2020 8:10:31 AM Page 31 DATE/TIME: 2006/ 7/31 24: 0 RCHRES : 1 RELERR STORS STOR MATIN MATDIF -7.669E-03 0.00000 0.0000E+00 0.00000 -1.142E-08 Where: RELERR is the relative error (ERROR/REFVAL). ERROR is (STOR-STORS) - MATDIF. REFVAL is the reference value (STORS+MATIN). STOR is the storage of material in the processing unit (land-segment or reach/reservior) at the end of the present interval. STORS is the storage of material in the pu at the start of the present printout reporting period. MATIN is the total inflow of material to the pu during the present printout reporting period. MATDIF is the net inflow (inflow-outflow) of material to the pu during the present printout reporting period. 20948-mc4500 1.0 5/29/2020 8:10:31 AM Page 32 Disclaimer Legal Notice 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. Clear Creek Solutions, Inc. 6200 Capitol Blvd. Ste F Olympia, WA. 98501 Toll Free 1(866)943-0304 Local (360)943-0304 www.clearcreeksolutions.com Dial 811Callbefore you dig.below.Know what's Dial 811Callbefore you dig.below.Know what's 20948.005-TIR.doc D. Flow Control System The site is contained within a Conservation Flow Control Area and shall comply with the Level 2 Flow Control Standards. Based on initial geotechnical evaluation, infiltration is not suitable and as such full infiltration is infeasible for this project. The Western Washington Hydrology Model program was used to size the proposed detention facility in the form of Stormtech chambers. The Stormtech detention arch chambers sizing calculations are included within this Section. This project will propose to route runoff from proposed impervious surfaces to the proposed detention facility. On-site runoff will be collected to the maximum extent feasible; however, a portion of the runoff from proposed impervious surfaces will bypass the detention facility due to grading constraints. In accordance with Section 1.2.3.2.E of the 2016 KCSWDM, the stormwater design provides mitigation of the target surfaces that bypass the detention facility. Per Section 1.2.3.2.E the following conditions must be met. 1. The point of convergence for runoff discharged from the bypassed target surfaces and from the project's flow control facility must be within a quarter-mile downstream of the facility's project site discharge point, AND Response: The point of convergence between the bypass area, and the project's flow control facility appear to be within a quarter mile downstream of the facility's project site discharge point. The point of convergence can be identified as an existing catch basin shown to the south west of the site. This catch basin is connected to the conveyance system that this project intends to discharge into. 2. The increase in the existing site conditions 100-year peak discharge from the area of bypassed target surfaces must not exceed 0.4 cfs, AND Response: The 100-year peak discharge from the area of bypassed target surfaces does not exceed 0.4 cfs. 3. Runoff from the bypassed target surfaces must not create a signifi cant adverse impact to downstream drainage systems, salmonid habitat, or properties as determined by DPER, AND Response: The bypassed target surfaces appear to be developed in their present state, and are not anticipated to create a significant adverse imp act to the downstream drainage systems, salmonid habitat, or properties. 4. Water quality requirements applicable to the bypassed target surfaces must be met, AND Response: Per Section 1.2.8.2.D of the 2016 KCSWMM, the bypassed target surfaces are allowed to be untreated as conditions under this section and are to be complied with. Such conditions include site constraints, which makes a filter strip, bioswale, or a linear sand filter infeasible, and the pollution generating hard surfaces of the bypassed area that do not exceed 5,000 square feet and do not contain any pollution generating pervious surfaces. 5. Compensatory mitigation by a flow control facility must be provided so that the net effect at the point of convergence downstream is the same with or without the bypass. This mitigation may be waived if the existing site conditions 100-year peak discharge from the area of bypassed target surfaces is increased by no more than 20948.005-TIR.doc 0.1 cfs (modeled using 1 hour time steps) or no more than 0.15 cfs (modeled using 15 minute time steps) and flow control BMPs as detailed in Appendix C are applied to all impervious surfaces within the area of bypassed target surfaces. One or combination of the following methods may be used to provide compensatory mitigation by a flow control facility subject to permission/approvals from other parties as deemed necessary by DPER: Response: Compensatory mitigation by the proposed flow control facility is provided as a part of this project’s flow control design. Additionally, the existing site conditions 100-year peak discharge from the area of bypassed target surfaces is increased by no more than 0.15 cfs. a) Design the project's flow control facility or retrofit an existing offsite flow control facility as needed to achieve the desired effect at the point of convergence, OR b) Design the project's flow control facility or provide/retrofit an offsite flow control facility to mitigate an existing developed area (either onsite or offsite) that has runoff characteristics (i.e., peak flow and volume) equivalent to those of the bypassed target surfaces but is currently not mitigated or required to be mitigated to the same flow control performance requirement as the bypassed target surfaces. Response: The project’s flow control facility has been sized to accept runoff from an area equivalent to the bypassed target surfaces. Please see the following figures and calculations, which demonstrate the project's compliance with flow control requirements. E. Water Quality System The project proposes a Modular Wetland unit to provide Enhanced Basic Water Quality, which will be placed downstream of the proposed detention system. Water quality facilities will be sized in accordance with the 2016 KCSWDM and the Department of Ecology General Use Level Designation. Modular Wetland unit sizing calculations and GULD Approval will be provided in this Section within a subsequent submittal. F. Flow Control BMPs This project proposes greater than 2,000 square feet of new and replaced impervious surface and therefore must demonstrate compliance with "Individual Lot BMP Requirements," per Section 1.2.9.2. This project is defined as a Large Lot and will evaluate the feasibility of Large Lot BMP Requirements. See below for a discussion of the feasibility of each Stormwater Management BMP. 1. Full dispersion is not feasible for this project as the site layout contains a critical buffer area on the east portion of the site and exhibits slopes of more than 20 percent, 165 feet from the Hybelos Wetland. Dispersion devices are are not allowed in critical area buffers and on slopes steeper than 20 percent. Furthermore, the project cannot provide the required vegetated flowpath as required per the KCSWDM. 2. Full infiltration of roof runoff is not feasible as existing soils are glacial till (Everett- Alderwood gravelly sandy loam) and not conducive to infiltration. A Geotechnical Report prepared by Cobalt Geosciences will be submitted on subsequent submittal. 20948.005-TIR.doc 3. Full infiltration per Section C.2.2, or per Section 5.2; Limited Infiltration per Appendix C, Section C.2.3; Bioretention per Appendix C, Section C.2.6; and Permeable Pavement per Appendix C, Section C.2.7 are infeasible as existing soils (Everett- Alderwood gravelly sandy loam) exhibit poor infiltration per the initial geotechnical evaluation. A Geotechnical Report prepared by Cobalt Geosciences will be submitted upon subsequent submittal. 4. Basic Dispersion per Appendix C, Section C.2.4 is not feasible due to the project being contained within a wetland buffer area, and the potential area for dispersion devices are to be located on slopes steeper than 20 percent. In addition, the required vegetated flowpath cannot be provided due to site constraints and proposed hardscape. 5. This project will result in greater than 65 percent impervious surface coverage within the site’s buildable area. Flow control BMPs must be applied to 20 percent of the target impervious surface, or to an impervious area equal to at least 10 percent of the site/lot, whichever is less. Target Impervious Surface = 38,620 square feet (Within parcel boundary) Site/Lot area = 94,279 square feet 20 percent of Target Surface = 7,724 square feet 10 percent of Site Area = 9,430 square feet This project must provide flow control BMPs for at least 7,724 square feet of new and replaced impervious surface. Both Reduced Impervious Surface Credit per Appendix C, Section C.2.9, and Native Growth Retention Credit per Appendix C, Section C.2.10 are infeasible due to the site layout. 6. Bioretention per Appendix C, Section C.2.6 is not feasible as determined by the Bioinflitration Infeasibility Criteria List. The potential area for a bioretention facility is within 100 feet of an underground storage tank and connecting underground pipes of a system than holds more than 1,100 gallons; therefore, bioretention is infeasible. 7. Permeable Pavement per Appendix C, Section C.2.7 as existing soils are not conducive to infiltration per an initial geotechnical evaluation. A Geotechnical Report prepared by Cobalt Geosciences and will be submitted on subsequent submittal. In addition, permeable pavement is generally not recommended on high -use sites nor fueling stations. 20948.005-TIR.doc 5.0 CONVEYANCE SYSTEM AN ALYSIS AND DESIGN Conveyance calculations for the project will be provided in this section in s ubsequent submittal. 20948.005-TIR.doc 6.0 SPECIAL REPORTS AND STUDIES A Geotechnical Engineering Report prepared by Cobalt Geosciences will be submitted as part of a subsequent submittal. 20948.005-TIR.doc 7.0 OTHER PERMITS  City of Federal Way Building Permit 20948.005-TIR.doc 8.0 EROSION AND SEDIMENT CONTROL ANALYSIS AND DESIGN A. Erosion and Sediment Control (ESC) Plan Analysis and Design A copy of the preliminary plan showing the Erosion and Sediment Control measures has been provided in this section. Dial 811Callbefore you dig.below.Know what'sPreliminary Not For Construction 20948.005-TIR.doc 9.0 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT A Bond Quantity Worksheet will be provided with subsequent submittal. 20948.005-TIR.doc 10.0 OPERATIONS AND MAINTENANCE MANUAL An Operation and Maintenance Manual will be provided upon a subsequent submittal. 20948.005-TIR.doc 11.0 STORMWATER POLLUTION PREVENTION PLAN (SWPPP) A SWPPP will be included with subsequent submittal.