City of Richmond, Virginia Department of Public Utilities CSO Interim Plan Report July 1, 2021 Prepared by Brown and Caldwell Interim Plan Report Legend for Cover Photos: 1. Patrick Griffin: Founder and Instructor for RVA Paddlesports 2. Mark Lewis: Senior Construction Inspector for Richmond DPU Stormwater Utility 3. Susan Mitchell: Senior Account Director for West Cary Group Richmond DPU | RVAH2O Interim Plan Report Table of Contents Table of Contents List of Tables ................................................................................................................................................ ii List of Figures .............................................................................................................................................. iii List of Abbreviations ................................................................................................................................... iv 1. Executive Summary ...........................................................................................................................1-1 1.1 Background .............................................................................................................................1-1 1.2 Interim Plan Purpose ..............................................................................................................1-1 1.3 Project Identification...............................................................................................................1-2 1.4 Initial Screening ......................................................................................................................1-2 1.5 Project Evaluation ...................................................................................................................1-3 1.6 Final Screening .......................................................................................................................1-4 1.7 Project Selection .....................................................................................................................1-4 2. Introduction .......................................................................................................................................2-1 2.1 Combined Sewer System History ...........................................................................................2-1 2.2 Amendment to the 2005 Special Order by Consent ............................................................2-2 2.3 Interim Plan Purpose ..............................................................................................................2-3 3. System Characterization ...................................................................................................................3-1 3.1 Combined Sewer System Description ...................................................................................3-1 3.2 System Monitoring Data .........................................................................................................3-9 3.2.1 Rainfall Data .......................................................................................................... 3-10 3.2.2 Flow and Level Data .............................................................................................. 3-11 3.3 CSS Hydrologic and Hydraulic Modeling ............................................................................ 3-12 3.3.1 Model Updates ...................................................................................................... 3-12 3.3.2 Existing Conditions ................................................................................................ 3-12 3.3.3 Baseline Scenario .................................................................................................. 3-12 3.4 Receiving Water Data .......................................................................................................... 3-13 3.5 Water Quality Modeling ....................................................................................................... 3-15 3.5.1 Model Updates ...................................................................................................... 3-15 3.5.2 Existing Conditions ................................................................................................ 3-15 3.5.3 Baseline Scenario .................................................................................................. 3-15 4. Project Identification .........................................................................................................................4-1 4.1 RT-DSS Controls ......................................................................................................................4-1 4.2 Project Types ...........................................................................................................................4-1 4.2.1 In-Line Storage ..........................................................................................................4-2 4.2.2 Diversion ...................................................................................................................4-3 4.2.3 Dynamic Underflow Control .....................................................................................4-4 4.2.4 Controls Update ........................................................................................................4-5 Richmond DPU | RVAH2O i Interim Plan Report Table of Contents 4.3 Initial Project Screening .........................................................................................................4-5 5. Project Evaluation .............................................................................................................................5-1 5.1 Performance Evaluation .........................................................................................................5-1 5.1.1 CSS H&H Model Results ..........................................................................................5-1 5.1.2 Receiving Water Quality Model Results ..................................................................5-4 5.2 Qualitative Evaluation .............................................................................................................5-5 5.3 Cost Estimates ........................................................................................................................5-8 5.4 Cost Effectiveness Evaluation ............................................................................................. 5-11 5.5 Project Evaluation Summary ............................................................................................... 5-13 6. Project Selection ...............................................................................................................................6-1 6.1 Selected Interim Plan Projects ...............................................................................................6-1 6.2 Implementation Schedule ......................................................................................................6-3 6.3 Proposed Funding Strategies .................................................................................................6-5 6.4 Remaining Special Order Project Comparison ......................................................................6-6 7. Stakeholder Engagement .................................................................................................................7-1 Appendix A: Amendment to the 2005 Special Order by Consent .......................................................... A-1 Appendix B: CSS H&H Model Documentation ........................................................................................ B-1 Appendix C: Water Quality Model Documentation ..................................................................................C-1 Appendix D: Interim Plan Project Details ................................................................................................ D-1 Appendix E: DEQ Substitution Approval Letter ........................................................................................ E-1 Appendix F: Stakeholder Engagement Materials .................................................................................... F-1 List of Tables Table 1-1. Summary of Selected Interim Plan Projects .........................................................................1-5 Table 3-1. Baseline Scenario Water Quality Improvement.................................................................. 3-15 Table 4-1. Summary of Identified Projects .............................................................................................4-6 Table 5-1. Project Performance Evaluation Summary ...........................................................................5-2 Table 5-2. Water Quality Modeling Evaluation Summary ......................................................................5-4 Table 5-3. Qualitative Evaluation Criteria ...............................................................................................5-5 Table 5-4. Project Qualitative Assessment Summary ............................................................................5-6 Table 5-5. Project Cost Estimate Summary ............................................................................................5-9 Table 5-6. Project Cost Effectiveness Summary ................................................................................. 5-11 Table 5-7. Project Evaluation Summary .............................................................................................