Regional Stormwater Manual
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Spokane Regional Stormwater Manual April 2008 SPOKANE REGIONAL STORMWATER MANUAL APRIL 2008 Prepared by: Spokane County 1026 W. Broadway Avenue Spokane, Washington 99260 (509) 477-3600 City of Spokane 808 W. Spokane Falls Blvd. Spokane, Washington 99201 (509) 625-6700 City of Spokane Valley 11707 E. Sprague Avenue Spokane Valley, Washington 99206 (509) 921-1000 A special thanks to the members of the committee who dedicated their time and energy in the development of the manual: Gloria Mantz, City of Spokane Valley Kris Becker, City of Spokane Gary Nelson, City of Spokane Mike Yake, City of Spokane Colleen Little, Spokane County Matt Zarecor, Spokane County Spokane County, City of Spokane, City of Spokane Valley Spokane Regional Stormwater Manual TABLE OF CONTENTS Title Page No. Table of Contents............................................................................................................................. i List of Figures..............................................................................................................................viii List of Tables ................................................................................................................................. ix Glossary .......................................................................................................................................... x References................................................................................................................................... xxv Chapter 1. Introduction ................................................................................................................1-1 1.1 Objective And Purpose ................................................................................................. 1-1 1.2 Vision Statement........................................................................................................... 1-1 1.3 Using The Stormwater Manual..................................................................................... 1-1 1.3.1 Technical Information.......................................................................................... 1-2 1.3.2 Policy Information ............................................................................................... 1-3 1.4 Relevant Programs and Concepts ................................................................................. 1-3 1.4.1 Underground Injection Control Program Compliance......................................... 1-4 1.4.2 Spokane Valley-Rathdrum Prairie Sole-Source Aquifer ..................................... 1-4 1.4.3 National Pollutant Discharge Elimination System Compliance .......................... 1-5 1.4.4 Pollutant Generating Impervious Surface............................................................ 1-6 1.5 General Requirements................................................................................................... 1-6 1.6 Standard of Care ........................................................................................................... 1-7 1.7 Severability ................................................................................................................... 1-8 Chapter 2. Basic Requirements....................................................................................................2-1 2.1 Introduction................................................................................................................... 2-1 2.1.1 Regulatory Threshold...........................................................................................2-1 2.1.2 New Development ............................................................................................... 2-1 2.1.3 Redevelopment .................................................................................................... 2-2 2.1.4 Exemptions .......................................................................................................... 2-3 2.1.5 Generally Exempt ................................................................................................ 2-4 2.1.6 Design Deviations................................................................................................ 2-5 2.2 Basic Requirements ...................................................................................................... 2-6 2.2.1 Basic Requirement No. 1 – Drainage Submittal.................................................. 2-6 2.2.2 Basic Requirement No. 2 – Geotechnical Site Characterization ......................... 2-9 2.2.3 Basic Requirement No. 3 – Water Quality Treatment....................................... 2-10 April 2008 Table of Contents i SPOKANE REGIONAL STORMWATER MANUAL 2.2.4 Basic Requirement No. 4 – Flow Control.......................................................... 2-14 2.2.5 Basic Requirement No. 5 – Natural And Constructed Conveyance Systems.... 2-16 2.2.6 Basic Requirement No. 6 – Erosion And Sediment Control ............................. 2-18 2.2.7 Basic Requirement No. 7 – Source Control....................................................... 2-19 2.2.8 Basic Requirement No. 8 – Operation And Maintenance.................................. 2-20 Chapter 3. Drainage Submittal.....................................................................................................3-1 3.1 Introduction................................................................................................................... 3-1 3.2 Applicability ................................................................................................................. 3-1 3.2.1 Required............................................................................................................... 3-1 3.2.2 Generally Required.............................................................................................. 3-1 3.2.3 Generally Exempt ................................................................................................ 3-2 3.2.4 Exempt ................................................................................................................. 3-3 3.3 Concept Drainage Report.............................................................................................. 3-4 3.3.1 Introduction.......................................................................................................... 3-4 3.3.2 Applicability ........................................................................................................ 3-4 3.3.3 Exemptions .......................................................................................................... 3-5 3.3.4 Scope.................................................................................................................... 3-5 3.4 Drainage Report............................................................................................................ 3-7 3.4.1 Introduction.......................................................................................................... 3-7 3.4.2 Narrative .............................................................................................................. 3-7 3.4.3 Figures.................................................................................................................. 3-9 3.4.4 Calculations........................................................................................................ 3-10 3.4.5 Down-Gradient Analysis................................................................................... 3-11 3.5 Road and Drainage Plans............................................................................................ 3-12 3.5.1 Introduction........................................................................................................ 3-12 3.5.2 Minimum Plan Elements.................................................................................... 3-13 3.5.3 Revisions After Plan Acceptance....................................................................... 3-14 3.6 Other Submittal Elements........................................................................................... 3-14 Appendix 3A – Example Tables for Drainage Report........................................................... 3-17 Appendix 3B – Standard Notes for Road and Drainage Plans .............................................. 3-19 Appendix 3C – Lot Plan Criteria and Example ..................................................................... 3-21 Chapter 4. Geotechnical Site Characterization ............................................................................4-1 4.1 Introduction................................................................................................................... 4-1 4.2 Applicability ................................................................................................................. 4-1 4.3 Geotechnical Site Characterization Report................................................................... 4-2 4.3.1 Field and Laboratory Testing............................................................................... 4-4 4.3.2 Sub-Level Structure Feasibility ........................................................................... 4-6 Appendix 4A – Spokane 200 Method...................................................................................... 4-9 Appendix 4B – Full-Scale Drywell Test Method .................................................................. 4-13 April 2008 Table of Contents ii SPOKANE REGIONAL STORMWATER MANUAL Appendix 4C – Test Pit Method ...........................................................................................