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Home My WebLink AboutRS_Environmental_Review_TIR_0260521_v1DEA Job No. ARDS00005035 St. Anthony’s Catholic Church Parking Lot Expansion TECHNICAL INFORMATION REPORT Environmental Review Submittal Renton, Washington Prepared For: Archdiocese of Seattle 710 9th Ave, Seattle WA 98104 Issued: April 30, 2026 Prepared By: Sarah Tiernan, EIT Reviewed By: Danielle Hori, PE April Coleman, PE Issued: April 30, 2026 St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page i April 30, 2026 TABLE OF CONTENTS 1 PROJECT OVERVIEW .......................................................................................................................... 1-1 FIGURE 1. TIR WORKSHEET ................................................................................................................... 1-1 2 CONDITIONS AND REQUIREMENTS SUMMARY ................................................................................... 2-1 CORE REQUIREMENTS ..................................................................................................................... 2-1 SPECIAL REQUIREMENTS ................................................................................................................. 2-4 3 OFFSITE ANALYSIS ............................................................................................................................. 3-1 UPSTREAM BASIN ............................................................................................................................ 3-1 DOWNSTREAM DRAINAGE PATH ..................................................................................................... 3-1 DRAINAGE COMPLAINTS ................................................................................................................. 3-1 MITIGATION MEASURES .................................................................................................................. 3-1 4 HYDRAULIC ANALYSIS AND DESIGN .................................................................................................... 4-1 EXISTING SITE HYDROLOGY ............................................................................................................. 4-1 DEVELOPED SITE HYDROLOGY ......................................................................................................... 4-2 5 CONVEYANCE SYSTEM ANALYSIS AND DESIGN ................................................................................... 5-1 CONVEYANCE DESIGN FLOWS ......................................................................................................... 5-1 6 SPECIAL REPORTS AND STUDIES ......................................................................................................... 6-1 7 OTHER PERMITS ................................................................................................................................ 7-1 8 CSWPP PLAN ANALYSIS AND DESIGN ................................................................................................. 8-1 ESC PLAN ANALYSIS AND DESIGN ............................................................................................................ 8-1 9 BOND QUANTITIES, FACILITY SUMMARIES AND DECLARATION OF COVENANT ................................... 9-1 10 OPERATIONS AND MAINTENANCE MANUAL ..................................................................................... 10-1 St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page ii April 30, 2026 LIST OF SUPPLEMENTAL INFORMATION SECTION 1 Vicinity Map TIR Worksheet SECTION 2 City of Renton Stormwater Design Manual – Fig 1.1.2.A City of Renton – Flow Control Application Map Predeveloped and Mitigated Storm Flow – WWHM REPORT SECTION 3 City of Renton COR Maps – Critical Areas City of Renton COR Maps - Downstream Overview Exhibit SECTION 4 Soils Map FEMA FIRM Panel Existing Conditions Exhibit Developed Conditions Exhibit St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 1-1 April 30, 2026 1 PROJECT OVERVIEW The St. Anthony’s Catholic Church Parking Lot Expansion (Project) proposes to increase parking count and improve vehicular and pedestrian circulation through three existing parcels (784080-0115, 784080-0110, and 784080-0105) directly north of the existing St. Anthony’s church and west of Morris Avenue South. Two existing buildings on these parcels will be demolished and an existing portion of parking lot containing 22 sub-standard parking stalls will be removed. The purpose of this report is to evaluate the proposed parking lot expansion and ensure compliance with all applicable Core Requirements and Special Requirements outlined in the 2022 City of Renton Surface Water Design Manual (2022 RSWDM) in support of the environmental review submittal. The Project improvements will occur within portions of SE ¼ of Section 18, Township 23N, Range 5 3, W.M. in King County, Washington. See the vicinity map on the next page for aid in the location of the project. The current site has several existing buildings, existing parking and limited landscaping which are included in the St. Anthony’s Catholic Church campus initially developed before 1979. There are no critical areas recorded within the Project boundary. A single 10” tree immediately adjacent to the existing building at 325 Morris Ave S is to be removed with this project. The current proposed parking layout will provide 22 standard parking stalls, 5 compact stalls and 2 accessible parking stalls, for a total of 29 parking stalls. Access to this parking lot will be available from the public alley and from within the St. Anthony’s site. Project site runoff sheet flows to an existing drainage system which flows to a vault located on the church campus on parcel 784130-0125 and ultimately connects to the City of Renton’s storm drainage system. Overland runoff combines within one-quarter mile downstream and therefore is in a single threshold discharge area (TDA). The existing drainage patterns will be maintained for the developed conditions. St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 1-2 April 30, 2026 The Project exceeds thresholds for proposed and replaced hard surfaces, which requires a full drainage review per the 2022 RSWDM. As such, the Project will provide Basic Enhanced water quality treatment in accordance with the 2022 RSWDM. St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 1-1 April 30, 2026 Figure 1. TIR Worksheet CITY OF RENTON SURFACE WATER DESIGN MANUAL 2022 City of Renton Surface Water Design Manual 6/22/2022 8-A-1 REFERENCE 8-A 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 __________________________ CED Permit # ________________________ Location Township ________________ Range __________________ Section _________________ Site Address __________________________ Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS Land Use (e.g., Subdivision / Short Subd.) Building (e.g., M/F / Commercial / SFR) 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 Archdiocese of Seattle (425) 255-3132 416 S. 4th Street Renton, WA 98057 Danielle Hori David Evans and Associates (425) 415-2000 Parking Lot Expansion 23 N 5 3 18 315 Morris Ave S 325 Morris Ave S X REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 6/22/2022 2022 City of Renton Surface Water Design Manual 8-A-2 Part 6 SWDM ADJUSTMENT APPROVALS Type (circle one): Standard / Blanket Description: (include conditions in TIR Section 2) Approved Adjustment No. ______________________ Date of Approval: _______________________ Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes / No Start Date: _______________________ Completion Date: _______________________ Describe: _________________________________ Re: SWDM 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 ______________________ Black River Basin REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2022 City of Renton Surface Water Design Manual 6/22/2022 Ref 8-A-3 Part 10 SOILS Soil Type Slopes Erosion Potential High Groundwater Table (within 5 feet) Other ________________________________ Sole Source Aquifer Seeps/Springs Additional Sheets Attached 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 9 apply): Discharge at Natural Location Number of Natural Discharge Locations: Offsite Analysis Level: 1 / 2 / 3 dated:__________________ Flow Control (include facility summary sheet) Standard: _______________________________ or Exemption Number: ____________ 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 Project Area 1 Urban Land 0-5%High Exempt TBD TBD TBD TBD TBD TBD TBD REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 6/22/2022 2022 City of Renton Surface Water Design Manual 8-A-4 Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Water Quality (include facility summary sheet) Type (circle one): Basic / Sens. Lake / Enhanced Basic / Bog or Exemption No. _______________________ On-site BMPs Describe: Special Requirements (as applicable): Area Specific Drainage Requirements Type: SDO / MDP / BP / 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: Source Control commercial / 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: Modular Wetland N/A N/A N/A N/A N/A N/A N/A N/A REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2022 City of Renton Surface Water Design Manual 6/22/2022 Ref 8-A-5 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 Control Pollutants Protect Existing and Proposed BMPs/Facilities Maintain Protective 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 BMPs/Facilities, restore operation of BMPs/Facilities as necessary Flag limits of sensitive areas and open space preservation areas Other _______________________ Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch) Flow Control Description Water Quality Description On-site BMPs Description Detention Infiltration Regional Facility Shared Facility Other Vegetated Flowpath Wetpool Filtration Oil Control Spill Control Other Full Dispersion Full Infiltration Limited Infiltration Rain Gardens Bioretention Permeable Pavement Basic Dispersion Soil Amendment Perforated Pipe Connection Other X X X X X X X X X X X X X X X X X X Modular Wetland REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 6/22/2022 2022 City of Renton Surface Water Design Manual 8-A-6 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 St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 2-1 April 30, 2026 2 CONDITIONS AND REQUIREMENTS SUMMARY Full Drainage Review is required for the Project because the proposed improvements exceed the 2,000 square foot threshold of new and replaced hard surfaces. The Project is subject to Core Requirements #1 through #9 and all applicable Special Requirements # 1 through #5 of the 2022 RSWDM. See below for an outline of these requirements and how they have been addressed for the Project. CORE REQUIREMENTS 2.1.1 Core Requirement #1: Discharge at the Natural Location The site runoff flows to an existing catch basin on Parcel 784080-0110 which drains to a vault located on the church campus in Parcel 784130-0125 and is ultimately connected to the City of Renton storm drainage system. The project will maintain this connection. See Section 3 – Offsite Analysis for a description of the drainage patterns. 2.1.2 Core Requirement #2: Offsite Analysis See Section 3 of this report for an offsite analysis and Level 1 downstream analysis in accordance with RSWDM section 1.2.2. 2.1.3 Core Requirement #3: Flow Control The Project is exempt from Core Requirement #3 in accordance with Section 1.2.3.1 – A of the 2022 RSWDM. The area-specific flow control facility requirement falls within the mapped area of Renton governed by the Peak Rate Flow Control Standard. See attachment 2-2 City of Renton Flow Control Application Map. Section 1.2.3.1 – A states: The facility requirement in Peak Rate Flow Control Standard Area is waived for any threshold discharge area in which the target surfaces subject to this requirement will generation no more than a 0.15 cfs increase in the existing site conditions 100-year flow. St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 2-2 April 30, 2026 There is one threshold discharge area on-site. When analyzed compared to existing site conditions and with a 15-minute time step, the increase in stormwater flow from this site for the 100-year flow condition is 0.018 cfs. Refer to attachment 2-2 at the end of this section for the WWHM report. 2.1.4 Core Requirement #4: Conveyance System The proposed stormwater conveyance system for the project site has been designed to safely convey up to the 100-year peak storm flows. For more information, see Section 5 of this report. 2.1.5 Core Requirement #5: Construction Stormwater Pollution Prevention All proposed erosion and sediment control BMP’s have been designed per the requirements and design standards of the 2022 RSWDM. See Section 8 of this report for more information. 2.1.6 Core Requirement #6: Maintenance and Operations Maintenance and operations guidance from the 2022 RSWDM are provided in Section 10 of this report. 2.1.7 Core Requirement #7: Financial Guarantees and Liability Bond Quantities, Facility Summaries and the Declaration of Covenant forms will be provided after final engineering review. 2.1.8 Core Requirement #8: Water Quality All proposed projects, including redevelopment projects, must provide water quality (WQ) facilities to treat the runoff from new and replaced pollution-generating impervious surfaces and new pollution generating pervious surfaces targeted for treatment. Enhanced Basic water quality will be provided by using a Modular Wetland. See Section 4 of this report for more information St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 2-3 April 30, 2026 2.1.9 Core Requirement #9: On-Site BMPs Typically, projects proposing new impervious surfaces are required to provide onsite flow control BMPs to mitigate the impacts of stormwater runoff. The project will implement soil amendment for all new and replaced pervious surfaces to mitigate for lost moisture capacity of disturbed and compacted topsoil in accordance with KCC16.82.100 (F) and (G) which has been adopted by City of Renton into the 2022 Renton Stormwater Design Manual: “F. The duff layer and native topsoil shall be retained in an undisturbed state to the maximum extent practicable. Any duff layer or topsoil removed during grading shall be stockpiled onsite in a designated, controlled area not adjacent to public resources and critical areas. The material shall be reapplied to other portions of the site where feasible. G.1. Except as otherwise provided in subsection G.2. of this section, areas that have been cleared and graded shall have the soil moisture holding capacity restored to that of the original undisturbed soil native to the site to the maximum extent practicable. The soil in any area that has been compacted or that has had some or all of the duff layer or underlying topsoil removed shall be amended to mitigate for lost moisture-holding capacity. The amendment shall take place between May 1 and October 1. The topsoil layer shall be a minimum of eight inches thick, unless the applicant demonstrates that a different thickness will provide conditions equivalent to the soil moisture-holding capacity native to the site. The topsoil layer shall have an organic matter content of between five to ten percent dry weight and a pH suitable for the proposed landscape plants. When feasible, subsoils below the topsoil layer should be scarified at least four inches with some incorporation of the upper material to avoid stratified layers. Compost used to achieve the required soil organic matter content must meet the definition of "composted materials" in WAC 173-350-220. St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 2-4 April 30, 2026 2. This subsection does not apply to areas that: a. Are subject to a state surface mine reclamation permit; or b. At project completion are covered by an impervious surface, incorporated into a drainage facility or engineered as structural fill or slope. (Ord. 16267 § 5, 2008: Ord. 15053 § 10, 2004: Ord. 13190 § 4, 1998: Ord. 3108 § 8, 1977: Ord. 1488 § 11, 1973).” SPECIAL REQUIREMENTS 2.2.1 Special Requirement #1: Other Adopted Area-Specific Requirements Not applicable. The Project is located within the Black River Basin. This basin is not located within a designated Critical Drainage Area or in an adopted master drainage plan, basin plan, salmon conservation plan, stormwater compliance plan, flood hazard management plan, lake management plan or shared facility drainage plan. 2.2.2 Special Requirement #2: Floodplain/Floodway Delineation Special Requirement #2 does not apply, as the project is not located within a flood hazard area. 2.2.3 Special Requirement #3: Flood Protection Facilities Not applicable. The Project does not rely on an existing flood protection facility or propose to modify/construct a new flood protection facility. 2.2.4 Special Requirement #4: Source Controls Not applicable. The Project does not require a commercial building permit or commercial site development permit. St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 2-5 April 30, 2026 2.2.5 Special Requirement #5: Oil Control Special Requirement #5 does not apply. The Project is not a redevelopment project proposing $100,000 or more of improvements to an existing high-use site and is not a redevelopment project that results in new plus replaced PGUS of 5,000 sf or more or new PGPS of ¾ acres or more improvements to an existing high-use site. SECTION 1.1 DRAINAGE REVIEW 6/22/2022 2022 City of Renton Surface Water Design Manual 1-14 FIGURE 1.1.2.A FLOW CHART FOR DETERMINING TYPE OF DRAINAGE REVIEW REQUIRED Project Site WWHM2012 PROJECT REPORT 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:44:38 PM Page 2 General Model Information WWHM2012 Project Name:2026-04-21 Predev-Mitigated Flows Site Name: Site Address: City: Report Date:4/21/2026 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.000 Version Date:2024/06/28 Version:4.3.1 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:44:38 PM Page 3 Landuse Basin Data Predeveloped Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Flat 0.086 Pervious Total 0.086 Impervious Land Use acre ROOF TOPS FLAT 0.063 SIDEWALKS FLAT 0.013 PARKING FLAT 0.183 Impervious Total 0.259 Basin Total 0.345 Element Flow Componants: Surface Interflow Groundwater Componant Flows To: POC 1 POC 1 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:44:38 PM Page 4 Mitigated Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Flat 0.052 Pervious Total 0.052 Impervious Land Use acre SIDEWALKS FLAT 0.009 PARKING FLAT 0.284 Impervious Total 0.293 Basin Total 0.345 Element Flow Componants: Surface Interflow Groundwater Componant Flows To: POC 1 POC 1 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:44:38 PM Page 5 Routing Elements Predeveloped Routing 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:44:38 PM Page 6 Mitigated Routing 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:44:38 PM Page 7 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.086 Total Impervious Area:0.259 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.052 Total Impervious Area:0.293 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.10424 5 year 0.133681 10 year 0.153919 25 year 0.180413 50 year 0.200854 100 year 0.221925 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.11504 5 year 0.146471 10 year 0.167958 25 year 0.195964 50 year 0.217489 100 year 0.239611 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.140 0.152 1950 0.140 0.158 1951 0.087 0.095 1952 0.072 0.081 1953 0.078 0.087 1954 0.085 0.094 1955 0.095 0.105 1956 0.094 0.104 1957 0.110 0.120 1958 0.085 0.095 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:45:02 PM Page 8 1959 0.084 0.095 1960 0.090 0.098 1961 0.093 0.102 1962 0.077 0.087 1963 0.090 0.099 1964 0.084 0.094 1965 0.114 0.124 1966 0.073 0.081 1967 0.127 0.140 1968 0.145 0.160 1969 0.104 0.113 1970 0.097 0.107 1971 0.116 0.128 1972 0.127 0.136 1973 0.069 0.078 1974 0.108 0.118 1975 0.115 0.130 1976 0.083 0.091 1977 0.084 0.095 1978 0.104 0.117 1979 0.142 0.160 1980 0.143 0.153 1981 0.108 0.120 1982 0.156 0.171 1983 0.122 0.136 1984 0.079 0.087 1985 0.108 0.120 1986 0.092 0.102 1987 0.140 0.157 1988 0.084 0.095 1989 0.104 0.118 1990 0.208 0.219 1991 0.161 0.171 1992 0.078 0.086 1993 0.066 0.074 1994 0.070 0.079 1995 0.095 0.106 1996 0.108 0.116 1997 0.103 0.112 1998 0.099 0.110 1999 0.213 0.232 2000 0.104 0.114 2001 0.109 0.122 2002 0.138 0.149 2003 0.107 0.116 2004 0.198 0.216 2005 0.091 0.099 2006 0.081 0.088 2007 0.187 0.203 2008 0.158 0.168 2009 0.128 0.145 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.2132 0.2322 2 0.2083 0.2186 3 0.1982 0.2164 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:45:02 PM Page 9 4 0.1866 0.2031 5 0.1608 0.1712 6 0.1579 0.1711 7 0.1562 0.1682 8 0.1446 0.1600 9 0.1434 0.1597 10 0.1422 0.1575 11 0.1404 0.1574 12 0.1404 0.1531 13 0.1402 0.1522 14 0.1380 0.1494 15 0.1279 0.1445 16 0.1270 0.1403 17 0.1270 0.1365 18 0.1215 0.1359 19 0.1162 0.1305 20 0.1154 0.1280 21 0.1140 0.1241 22 0.1098 0.1223 23 0.1089 0.1199 24 0.1083 0.1197 25 0.1081 0.1197 26 0.1078 0.1182 27 0.1077 0.1179 28 0.1073 0.1167 29 0.1045 0.1164 30 0.1039 0.1161 31 0.1038 0.1142 32 0.1037 0.1129 33 0.1029 0.1120 34 0.0986 0.1101 35 0.0973 0.1073 36 0.0954 0.1059 37 0.0950 0.1054 38 0.0938 0.1039 39 0.0928 0.1023 40 0.0915 0.1019 41 0.0909 0.0991 42 0.0904 0.0986 43 0.0899 0.0979 44 0.0874 0.0951 45 0.0851 0.0949 46 0.0849 0.0947 47 0.0844 0.0946 48 0.0841 0.0945 49 0.0837 0.0938 50 0.0835 0.0936 51 0.0834 0.0912 52 0.0815 0.0883 53 0.0787 0.0875 54 0.0780 0.0870 55 0.0778 0.0867 56 0.0775 0.0861 57 0.0730 0.0810 58 0.0720 0.0810 59 0.0697 0.0789 60 0.0686 0.0776 61 0.0659 0.0736 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:45:02 PM Page 10 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:45:02 PM Page 11 Duration Flows The Duration Matching Failed Flow(cfs)Predev Mit Percentage Pass/Fail 0.0521 1699 2453 144 Fail 0.0536 1545 2246 145 Fail 0.0551 1399 2048 146 Fail 0.0566 1256 1842 146 Fail 0.0581 1127 1677 148 Fail 0.0596 1031 1540 149 Fail 0.0611 951 1402 147 Fail 0.0626 871 1263 145 Fail 0.0641 783 1152 147 Fail 0.0656 717 1056 147 Fail 0.0671 666 975 146 Fail 0.0686 618 904 146 Fail 0.0701 565 831 147 Fail 0.0717 528 766 145 Fail 0.0732 491 708 144 Fail 0.0747 450 660 146 Fail 0.0762 411 608 147 Fail 0.0777 384 569 148 Fail 0.0792 362 532 146 Fail 0.0807 341 497 145 Fail 0.0822 319 453 142 Fail 0.0837 289 423 146 Fail 0.0852 271 395 145 Fail 0.0867 251 371 147 Fail 0.0882 237 351 148 Fail 0.0897 223 328 147 Fail 0.0912 204 307 150 Fail 0.0927 194 289 148 Fail 0.0942 183 270 147 Fail 0.0957 169 250 147 Fail 0.0972 157 231 147 Fail 0.0987 147 220 149 Fail 0.1002 139 210 151 Fail 0.1017 132 198 150 Fail 0.1032 123 184 149 Fail 0.1047 113 171 151 Fail 0.1062 108 161 149 Fail 0.1077 101 151 149 Fail 0.1092 93 145 155 Fail 0.1107 87 136 156 Fail 0.1122 82 126 153 Fail 0.1137 81 119 146 Fail 0.1152 79 115 145 Fail 0.1167 76 106 139 Fail 0.1182 74 102 137 Fail 0.1197 67 98 146 Fail 0.1212 66 89 134 Fail 0.1227 63 84 133 Fail 0.1242 57 80 140 Fail 0.1257 55 79 143 Fail 0.1272 51 77 150 Fail 0.1287 48 72 150 Fail 0.1302 47 69 146 Fail 0.1317 43 63 146 Fail 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:45:02 PM Page 12 0.1332 41 61 148 Fail 0.1348 40 61 152 Fail 0.1363 39 57 146 Fail 0.1378 34 52 152 Fail 0.1393 31 52 167 Fail 0.1408 27 50 185 Fail 0.1423 26 47 180 Fail 0.1438 24 45 187 Fail 0.1453 21 41 195 Fail 0.1468 20 39 195 Fail 0.1483 19 37 194 Fail 0.1498 17 35 205 Fail 0.1513 16 32 200 Fail 0.1528 15 29 193 Fail 0.1543 14 27 192 Fail 0.1558 13 26 200 Fail 0.1573 12 25 208 Fail 0.1588 9 21 233 Fail 0.1603 9 17 188 Fail 0.1618 8 16 200 Fail 0.1633 8 16 200 Fail 0.1648 8 15 187 Fail 0.1663 8 13 162 Fail 0.1678 8 12 150 Fail 0.1693 8 11 137 Fail 0.1708 8 10 125 Fail 0.1723 8 8 100 Pass 0.1738 8 8 100 Pass 0.1753 7 8 114 Fail 0.1768 7 8 114 Fail 0.1783 7 8 114 Fail 0.1798 7 8 114 Fail 0.1813 7 8 114 Fail 0.1828 7 8 114 Fail 0.1843 7 8 114 Fail 0.1858 6 8 133 Fail 0.1873 5 8 160 Fail 0.1888 5 8 160 Fail 0.1903 4 8 200 Fail 0.1918 4 8 200 Fail 0.1933 4 7 175 Fail 0.1948 4 6 150 Fail 0.1963 3 6 200 Fail 0.1978 3 6 200 Fail 0.1994 2 6 300 Fail 0.2009 2 6 300 Fail The development has an increase in flow durations from 1/2 Predeveloped 2 year flow to the 2 year flow or more than a 10% increase from the 2 year to the 50 year flow. The development has an increase in flow durations for more than 50% of the flows for the range of the duration analysis. 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:45:02 PM Page 13 Water Quality Water Quality BMP Flow and Volume for POC #1 On-line facility volume:0 acre-feet On-line facility target flow:0 cfs. Adjusted for 15 min:0 cfs. Off-line facility target flow:0 cfs. Adjusted for 15 min:0 cfs. 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:45:03 PM Page 14 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. 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:45:03 PM Page 15 Appendix Predeveloped Schematic 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:45:03 PM Page 16 Mitigated Schematic 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:45:03 PM Page 17 Predeveloped UCI File 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:45:03 PM Page 18 Mitigated UCI File 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:45:03 PM Page 19 Predeveloped HSPF Message File 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:45:03 PM Page 20 Mitigated HSPF Message File 2026-04-21 Predev-Mitigated Flows 4/21/2026 12:45:03 PM Page 21 Disclaimer Legal Notice This program and accompanying documentation is provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by the user. Clear Creek Solutions, Inc. disclaims 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. has been advised of the possibility of such damages. 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 St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 3-1 April 30, 2026 3 OFFSITE ANALYSIS UPSTREAM BASIN The site is surrounded by existing stormwater infrastructure that routes water around the site, so no upstream basin exists. See the Existing Conditions Exhibit located at the end of this section which presents the site’s existing conditions for reference. DOWNSTREAM DRAINAGE PATH Site runoff currently sheet flows to a catch basin located on Parcel 784080-0110 which conveys stormwater to the stormwater vault on the Church Campus. The stormwater vault discharges to the City of Renton surface water network located along Shattuck Ave S. ¼ mile downstream, the stormwater joins the City of Renton surface water network and ultimately is discharged to the Black River Southeast of the site. See the Downstream Overview Exhibit located at the end of this section which presents the site’s downstream flow path for reference. DRAINAGE COMPLAINTS Based on a review of site conditions and available information, the upstream and downstream drainage systems in the vicinity of the project site appear to be functioning adequately at the time of this assessment. No evidence of surcharging, ponding, or capacity-related deficiencies was observed during site reconnaissance. In addition, to the best of our knowledge, there are no known or documented drainage-related complaints within the immediate vicinity of the project site. The project is located within the City of Renton, Washington, and the existing drainage infrastructure appears to be operating as intended under current conditions. MITIGATION MEASURES No mitigation measure proposed for this project due to above stated lack of drainage complaints and upstream run-on. 9,028 752 WGS_1984_Web_Mercator_Auxiliary_Sphere City of Renton Critical Areas Notes Legend 512 0 256 512 Feet All data, information, and maps are provided "as is" without warranty or any representation of accuracy, timeliness of completeness. The burden for determining accuracy, completeness, timeliness, merchantability and fitness for or the appropriateness for use rests solely on the user. None City and County Labels Parcels City and County Boundary Renton <all other values> Coalmines High Moderate Unclassified Erosion Hazard - High Floodway Special Flood Hazard Areas (100 year flood) Landslide Very High High Moderate Unclassified Slope City of Renton >15% & <=25% >25% & <=40% (Sensitive) >40% & <=90% (Protected) >90% (Protected) Wetlands Seismic Hazard Areas Faults 2023.sid Red: Band_1 Green: Band_2 Blue: Band_3 PROJECT SITE 2,257 188 WGS_1984_Web_Mercator_Auxiliary_Sphere Downstream Overview Notes Legend 128 0 64 128 Feet All data, information, and maps are provided "as is" without warranty or any representation of accuracy, timeliness of completeness. The burden for determining accuracy, completeness, timeliness, merchantability and fitness for or the appropriateness for use rests solely on the user. None City and County Labels Addresses Parcels City and County Boundary Renton <all other values> Discharge Point Discharge Point (Municipal - Surface Water Utility) Discharge Point (Municipal - Other) Discharge Point (Private) Detention Facility Detention Facility (Municipal - Surface Water Utility) Detention Facility (Municipal - Other) Detention Facility (Private) Pipe Flow Direction Pipe Pipe (Municipal - Surface Water Utility) Pipe (Municipal - Other) Pipe (Private) Drainage Complaints Known Drainage Issues Renton King County 2023.sid Red: Band_1 Green: Band_2 Blue: Band_3 PROJECT SITE0.08 MILES DOWNSTREAM 1/4 MILE DOWNSTREAM CATCHBASIN St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 4-1 April 30, 2026 4 HYDRAULIC ANALYSIS AND DESIGN EXISTING SITE HYDROLOGY 4.1.1 Resource Review Available existing resources were researched for the site and relevant information has been summarized below. 4.1.2 FEMA Maps The project site is not within a floodplain as shown on the attached Firmette Panel 0977G. 4.1.3 Sensitive Areas The Project location has been identified on copies of the following City of Renton Hazard Maps: Coal Mine: Site not mapped as lying within a hazard area. Erosion: Site not mapped as lying within a hazard area. Flooding: Site not mapped as lying within a hazard area. Liquefaction: Site not mapped as lying within a hazard area. Seismic: Site mapped as lying within a hazard area. Landslide: Site not mapped as lying within a hazard area. Critical Aquifer Recharge: Site not mapped as lying within a hazard area. Steep Slope: Site not mapped as lying within a hazard area. Refer to the City or Renton Critical Areas Map, attached to this section, for mapping of off- site sensitive areas. 4.1.4 Existing Conditions The Project site is currently part of the St Anthony’s Catholic Church campus. Two onsite buildings are located on Parcels 784080-0115 and 784080-105 respectively. St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 4-2 April 30, 2026 The site has relatively flat slopes (0 - 5% slopes) over the proposed footprint of the parking lot with existing grades sloping generally to the center of parcel 784080-110. There is a hedge along the site boundary bordering Morris Ave S. According to available data from USGS Web Soil Survey, site soils are classified as Urban land over the footprint of the Project. Site runoff currently flows to a catch basin located on Parcel 784080-0110 which conveys stormwater to the stormwater vault on the church campus. The stormwater vault discharges to the City of Renton surface water network located along Shattuck Ave S. See the Existing Conditions Exhibit and USGS Soil Map Exhibits located at the end of this section which presents the site’s existing conditions for reference. DEVELOPED SITE HYDROLOGY 4.2.1 Performance Standards As mentioned in Section 2 – Conditions and Requirements Summary, the Project is required to comply with Core Requirements #1-9 and applicable Special Requirements of the 2022 RSWDM. Per the manual, the following Flow Control and Water Quality Treatment standards are required for the Project. 4.2.2 Flow Control Systems The Project is exempt from Core Requirement #3 in accordance with Section 1.2.3.1 – A of the 2022 RSWDM. The area-specific flow control facility requirement falls within the mapped area of Renton governed by Peak Rate Flow Control Standard. See Attachment 2-2 City of Renton Flow Control Application Map. Section 1.2.3.1 – A states: The facility requirement in Peak Rate Flow Control Standard Area is waived for any threshold discharge area in which the target surfaces subject to this requirement will generation no more than a 0.15 cfs increase in the existing site conditions 100-year flow. St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 4-3 April 30, 2026 There is one threshold discharge area on-site. When analyzed compared to existing site conditions and with a 15-minute time step, the increase in stormwater flow from this site for the 100-year flow condition is 0.018 cfs. Refer to Attachment 2-2 at the end of this section for the WWHM report. 4.2.3 Water Quality System The project proposes the use of a Modular Wetland vault to provide basic and enhanced treatment for stormwater. Modular Wetland stormwater biofiltration system received the General Use Level Designation (GULD) as a stand-alone facility for Basic (TSS), Enhanced and Phosphorus Treatment by the Washington State Department of Ecology (DOE). WWHM will be utilized to calculate the water quality design flow rate for the proposed Modular Wetland facilities. Per the GULD certification, the hydraulic loading rate of the Modular Wetland prefilter media can be no greater than 3.0 gallons per minute (gpm) per square foot (sq. ft.) of media surface. Final design of the Modular Wetland vault will be provided with final construction plans. 4.2.4 TDA Area Swap Site topography requires that an approximately 485 sq ft area on the southeast portion of the site does not flow to the existing catch basin located in the center of the site. To maintain site hydrology, this area has been added to the northwest portion of the lot from the adjacent alley which is also paved area. See the Developed Conditions Exhibit at the end of this section for details. Soil Map—King County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 4/21/2026 Page 1 of 3 52 5 8 6 4 0 52 5 8 6 5 0 52 5 8 6 6 0 52 5 8 6 7 0 52 5 8 6 8 0 52 5 8 6 9 0 52 5 8 7 0 0 52 5 8 7 1 0 52 5 8 7 2 0 52 5 8 7 3 0 52 5 8 6 4 0 52 5 8 6 5 0 52 5 8 6 6 0 52 5 8 6 7 0 52 5 8 6 8 0 52 5 8 6 9 0 52 5 8 7 0 0 52 5 8 7 1 0 52 5 8 7 2 0 52 5 8 7 3 0 559410 559420 559430 559440 559450 559460 559470 559410 559420 559430 559440 559450 559460 559470 559480 47° 28' 45'' N 12 2 ° 1 2 ' 4 1 ' ' W 47° 28' 45'' N 12 2 ° 1 2 ' 3 7 ' ' W 47° 28' 42'' N 12 2 ° 1 2 ' 4 1 ' ' W 47° 28' 42'' N 12 2 ° 1 2 ' 3 7 ' ' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84 0 20 40 80 120 Feet 0 5 10 20 30 Meters Map Scale: 1:478 if printed on A portrait (8.5" x 11") sheet. Soil Map may not be valid at this scale. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Unit Polygons Soil Map Unit Lines Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Spoil Area Stony Spot Very Stony Spot Wet Spot Other Special Line Features Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: King County Area, Washington Survey Area Data: Version 21, Aug 28, 2025 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jul 31, 2022—Aug 8, 2022 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Soil Map—King County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 4/21/2026 Page 2 of 3 Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI Ur Urban land 1.2 100.0% Totals for Area of Interest 1.2 100.0% Soil Map—King County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 4/21/2026 Page 3 of 3 PROJECT LOCATION MO R R I S A V E S 784080-0100 784080-0105 784080-0110 784080-0050 784080-0055 784080-0060 784080-0065 6 5 4 3 2 1 7 24 8 23 9 22 10 21 11 20 12 19 SS SS SS SS SS SS SS SS SS SS SS SS SS FOUND TACK IN LEAD S 0.2' x E 3.1' FOUND TACK IN LEAD S 0.2' x E 3.1' xxxx OP OP OP OP OP OP OP OP OP OP OP OP OP W W W W W W W W W W W W W W W W W W W W W COCO x x x x x x x x x x x x x 784080-0115 784080-0120 O P OP OP OP OP OP OP OP OP SS SS SS SS SS S S SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD 33 33 33 32 32 32 33 33 33 33 33 SSMH #10212 RIM EL=33.15 8"PVC(W)IE=28.11 SSMH #10211 RIM EL=33.38 8"PVC(W,E,S) CNTR CHANNEL=26.93 CB #10382, TYPE I RIM EL=33.05 8"CONC(NE,S)IE=28.96 CB #10350, TYPE I RIM EL=32.76 6"CONC(E)IE=29.51 8"CONC(SW)IE=29.36 CB #10624, TYPE I RIM EL=31.34 12"ADS(E,S)IE=26.9 12"ADS(W)IE=26.6 CB #10625, TYPE I RIM EL=32.18 6"CONC(E)IE=28.50 8"CONC(N)IE=28.26 8"CONC(S)IE=28.16 BLOCK 1 SMITHERS F O U R T H A D D I T I O N VOL. 11, PG. 1 9 RECORDS O F K I N G C O . , W A . CB #10443, TYPE I RIM EL=31.85 12"ADS(W)IE=27.61 784080-0045 784080-0040 784080-0005784080-0010784080-0020 PUBLIC ALLEY PU B L I C A L L E Y 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 34 34 0.34 AC PROJECT SITE 0123456789 CO S GRAVEL PATH CONCRETE PAVING ASPHALT PAVING BOUNDARY LINE PROPERTY LINE PLATTED LOT LINE EXISTING RIGHT-OF-WAY LINE EXISTING RIGHT-OF-WAY CENTER LINE TRAFFIC STRIPING BUILDING LINE BUILDING OVERHANG EDGE OF GRAVEL FENCE LINE (TYPE AS NOTED) HEDGE FLOWLINE WATER PIPE SANITARY SEWER PIPE STORM DRAIN PIPE POWER OVERHEAD LINE x x x W W SS SS SD SD OP OP ASPH ASPHALT CC CONCRETE CURB CLF CHAIN LINK FENCE CONC CONCRETE CW CONCRETE SIDEWALK DW DRIVEWAY ECC EXTRUDED CONCRETE CURB FFE FINISH FLOOR ELEVATION GVL GRAVEL PA PLANTED AREA WDF WOOD FENCE LEGEND MONUMENT, FOUND AS NOTED TACK IN LEAD, FOUND AS NOTED SEWER MANHOLE SEWER CLEANOUT STORM CATCH BASIN WV WATER VALVE WM WATER METER FIRE HYDRANT ICV IRRIGATION CONTROL VALVE EM POWER METER POWER POLE POWER POLE WITH LIGHT LIGHT POLE GUY ANCHOR TJR TELEPHONE RISER GV GAS VALVE GM GAS METER SIGN POST OR BOLLARD DECIDUOUS TREE CONIFEROUS TREE TAX LOT / PARCEL NUMBER PROJECT NO. DRAWN BY: DESIGNED BY: DA T E : RE V I E W E D B Y : DA T E NO . RE V I S I O N CK BY FIRST SUBMITTAL DATE: SHEET NO. Sa v e D a t e : Pl o t D a t e : 4/ 3 0 / 2 0 2 6 1 0 : 2 4 A M 4/ 3 0 / 2 0 2 6 1 0 : 2 5 A M By : Sj d P: \ A \ A R D S 0 0 0 0 5 0 3 5 \ 0 4 0 0 C A D \ E X H I B I T S \ D r a i n a g e R e p o r t \ 2 0 2 6 - 0 4 - 2 9 - E x i s t i n g C o n d i t i o n s . d w g Sa r a h T i e r n a n By : Fi l e : CHECKED BY: ® 20300 Woodinville Snohomish Road NE Suite A Woodinville, WA 98072 425-415-2000 EN V I R O N M E N T A L R E V I E W AR C H D I O C E S E O F S E A T T L E EX I S T I N G C O N D I T I O N S APDC GAON DMPI ENVIRONMENTAL REVIEW ST A N T H O N Y ' S P A R K I N G L O T CI T Y O F R E N T O N WA 05/07/2026 ARDS00005035 1 SE 1/4 OF SECTION 18, T 23 N, R 5 3, W.M. ( FEET ) SCALE 1 INCH = 20 FT. 20 20 40100 EXISTING BASIN SITE DISCHARGE TO DETENTION VAULT N0 1 ° 2 0 ' 5 0 " E 5 6 0 . 1 2 ' N0 1 ° 2 0 ' 5 0 " E 1 6 0 . 0 4 ' N88°38'58"W 128.05' N01°21'07"E 80.01' N0 1 ° 2 1 ' 0 7 " E 8 0 . 0 1 ' 8.00' N88°39'07"W SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS xxxxxxxxx W W W W W W W W W W W W W W W W W W W W W W x x x x x x x x x x x x x x x x x x x x x x x x x OP SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD 33 32 3 3 33 -4 . 8 % -1. 0 % -1.3% -1.7 % -1.9% -0.9 % -0.9%-1.7 % -1.0% -2 . 9 % -0.9% -1 . 6 % 1. 6 % -2 . 5 % -2 . 6 % -1.5% -1.3% -1.0% -1 . 0 % GRADE BREAK 33 3 3 33 3 2 32 32 33 33 33 33 33 33 33 33 33 32 MO R R I S A V E S PU B L I C A L L E Y DISCHARGE TO EXISTING CB AREA TO BE REMOVED FROM DRAINAGE BASIN (0.01 AC) AREA TO BE ADDED TO DRAINAGE BASIN (0.01 AC) DEVELOPED DRAINAGE BASIN PROPOSED WATER QUALITY FACILITY EN V I R O N M E N T A L R E V I E W AR C H D I O C E S E O F S E A T T L E DE V E L O P E D C O N D I T I O N S E X H I B I T ST A N T H O N Y ' S P A R K I N G L O T CI T Y O F R E N T O N WA 05/07/2026 ARDS00005035 1 SE 1/4 OF SECTION 18, T 23 N, R 5 3, W.M. PROJECT NO. DRAWN BY: DESIGNED BY: DA T E : RE V I E W E D B Y : DA T E NO . RE V I S I O N CK BY FIRST SUBMITTAL DATE: SHEET NO. Sa v e D a t e : Pl o t D a t e : 4/ 3 0 / 2 0 2 6 1 0 : 2 6 A M 4/ 3 0 / 2 0 2 6 1 0 : 2 7 A M By : Sj d P: \ A \ A R D S 0 0 0 0 5 0 3 5 \ 0 4 0 0 C A D \ E X H I B I T S \ D r a i n a g e R e p o r t \ 2 0 2 6 - 0 4 - 2 9 - D e v e l o p e d C o n d i t i o n s . d w g Sa r a h T i e r n a n By : Fi l e : CHECKED BY: ® 20300 Woodinville Snohomish Road NE Suite A Woodinville, WA 98072 425-415-2000 ( FEET ) SCALE 1 INCH = 10 FT. 10 10 2050 SAWCUT SAWCUT ENVIRONMENTAL REVIEW St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 5-1 April 30, 2026 5 CONVEYANCE SYSTEM ANALYSIS AND DESIGN Calculations for conveyance system design for the Project will be provided with final construction plans. The Project plans to design according to City of Renton 2022 code for 100-year storm conditions. CONVEYANCE DESIGN FLOWS Per Sections 1.2.4.3 and 3.2.2 of the 2022 RSWDM, WWHM is an acceptable continuous model for analyzing and determining design flow rates and will be used to calculate all conveyance flows. The conveyance systems for this project will be designed to safely convey the modeled 100-year flow from the areas tributary to the system. St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 6-1 April 30, 2026 6 SPECIAL REPORTS AND STUDIES At this time, no special reports and/or studies have been prepared for the Project. St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 7-1 April 30, 2026 7 OTHER PERMITS The following approvals/permits will likely be needed for the project (this list may not include all necessary permits Permit Agency Civil Construction Permit City of Renton Demolition Permit City of Renton St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 8-1 April 30, 2026 8 CSWPP PLAN ANALYSIS AND DESIGN A Construction Stormwater Pollution Prevention (CSWPP) plan will be prepared and submitted as a separate document with final construction plans. ESC Plan Analysis and Design A Construction Stormwater Pollution Prevention (CSWPP), a.k.a. the Temporary Erosion and Sediment Control (TESC) Plan/Details of the site development plan set have been designed per the 2022 RSWDM and will be provided with final construction plans. The CSWPP measures are intended to prevent the transport of sediment from the site to significant drainage features and adjacent properties. All new and redevelopments shall comply with the 13 CSWPP elements taken from the 2022 RSWDM. The project will be managed by a Certified Erosion and Sedimentation Control Lead (CESCL) that will be selected for the project prior to the start of construction. The CESCL is responsible for the operation and maintenance of the site BMP’s. The following 13 CSWPP elements per the 2022 RSWDM have been addressed below. Element 1 – Clearing Limits To protect adjacent properties and to reduce the area of soil exposed to construction, the clearing limits shall be clearly marked, as shown on the TESC plan, in the field prior to any land disturbing activity. Natural vegetation and native topsoil shall be retained in an undisturbed state to the maximum extent possible. Element 2 – Cover Measures Exposed and unworked soils will be stabilized with some combination of mulching or temporary seeding. The time-period of soil exposure allowed depends upon the season. No soils shall remain exposed and unworked for more than seven days during the dry season, May 1 through September 30, or two days during the wet season, October 1 through April 30. Permit conditions shall require that soils be stabilized at the end of the St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 8-2 April 30, 2026 work week, if needed, when weather conditions or forecasts indicate that precipitation is likely. Element 3 – Perimeter Protection All stormwater runoff from disturbed areas shall pass through an appropriate sediment removal BMP before leaving the construction site. Element 4 – Traffic Area Stabilization The unnamed Alley West and North of the Project will be utilized as the stabilized construction entrance to serve the site. Construction vehicle ingress and egress shall be limited to one route, when possible. Construction access or activities occurring on unpaved areas shall be minimized, yet where necessary, access points shall be stabilized to minimize the tracking of sediment onto public roads. Street cleaning shall be required if sediment is tracked offsite. Element 5 – Sediment Retention Inlet protection will be provided at the existing catch basin. Element 6 - Surface Water Collection Surface water runoff shall pass through erosion control BMP’s prior to continuing along the downstream path to the existing stormwater vault. Element 7 - Dewatering Control If needed, all dewatering water shall be discharged into a controlled conveyance system. Highly turbid dewatering water from soils known or suspected to be contaminated, or from use of construction equipment, will require additional monitoring and treatment as required for the specific pollutants based on the receiving waters into which the discharge is occurring. Such monitoring is the responsibility of the contractor. The dewatering of soils St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 8-3 April 30, 2026 known to be free of contamination will trigger BMPs to trap sediment and reduce turbidity. Ata a minimum, geotextile fabric socks/bags/cells will be used to filter this material. Element 8 - Dust Control Preventative measures to minimize wind transport of soil shall be implemented when a traffic hazard may be created or when sediment transported by wind is likely to be deposited in water resources. Dust control, if required, will be provided by a water truck. Determination of watering frequency of the site and any additional erosion and sediment control requirements as needed during the process of site work is the responsibility of the contractor. Element 9- Flow Control Surface water runoff shall pass through erosion control BMP’s (i.e. silt fence, catch basin protection, etc.) prior to continuing along the downstream path. Element 10 - Control Pollutants All pollutants, including waste materials and demolition debris, that occur onsite shall be handled and disposed of in a manner that does not cause contamination of stormwater. Good housekeeping and preventative measures will be taken to ensure that the site will be kept clean, well-organized and free of debris. Protect Existing and Proposed Stormwater facilities and On-sit BMPs Element 11 - Protect Existing and Proposed Stormwater Facilities and On-site BMPs Protection measures shall be applied/installed and maintained so as to prevent adverse impacts to existing flow control BMPs and areas of proposed flow control BMPs for the project. Element 12 – Maintain Protective BMPs St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 8-4 April 30, 2026 All temporary and permanent erosion and sediment control BMP’s shall be maintained and repaired as needed to assure continued performance of their intended function. Maintenance and repair shall be conducted in accordance with each particular BMP’s specifications. Visual monitoring of the BMP’s will be conducted at least once every calendar week and within 24 hours of any rainfall event that causes a discharge from the site. If the site becomes inactive, and is temporarily stabilized, the inspection frequency will be reduced to once every month. All temporary erosion and sediment control BMP’s shall be removed within 30 days after the final site stabilization is achieved or after the temporary BMP’s are no longer needed. Trapped sediment shall be removed or stabilized on site. Disturbed soil resulting from removal of BMP’s or vegetation shall be permanently stabilized. Element 13 – Manage the Project The project will be managed by the contractor and will be responsible for the operation and maintenance of site BMP’s St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 9-1 April 30, 2026 9 BOND QUANTITIES, FACILITY SUMMARIES AND DECLARATION OF COVENANT Bond Quantities will be addressed at the end of the engineering review process as required by King County and the City of Renton. St Anthony’s Catholic Church Parking Lot Expansion DEA Job No. ARDS00005035 Page 10-1 April 30, 2026 10 OPERATIONS AND MAINTENANCE MANUAL Maintenance and operation excerpts from the 2022 RSWDM for the elements of the proposed drainage system that will be maintained will be included with the final drainage report.