CITY OF MODESTO STORMWATER MANAGEMENT PROGRAM 2011 Guidance Manual for Development Stormwater Quality Control Measures Prepared for NPDES Permit No. CAS083526; Order R5-2008-0092 This page intentionally left blank. Table of Contents Section 1. Introduction ........................................................................................... 1-1 1.1. Purpose and Goals ......................................................................................... 1-1 1.2. Background ..................................................................................................... 1-1 1.3. 2008 Municipal Stormwater Permit Requirements .......................................... 1-2 1.4. Low Impact Development Strategies ............................................................... 1-2 1.5. Updates to the Guidance Manual: Key Concepts ........................................... 1-4 1.6. Stormwater Quality Requirements vs. Flood Control Requirements ............... 1-5 1.7. Organization of the 2011 Guidance Manual .................................................... 1-6 Section 2. Guidance Manual Overview and Use .................................................... 2-1 2.1. Implementation Schedule ................................................................................ 2-1 2.2. Process to Comply with City Standards .......................................................... 2-1 Step 1: Determine if the Project is Subject to the 2011 Guidance Manual ........... 2-2 Step 2. Conduct Site Assessment ........................................................................ 2-5 Step 3: Apply Site Design Control Measures ....................................................... 2-6 Step 4: Apply Source Control Measures .............................................................. 2-6 Step 5: Calculate Volume Retention Requirement ............................................... 2-7 Step 6: Apply Low Impact Development Control Measures ................................. 2-7 Step 7: Apply Treatment Control Measures ......................................................... 2-9 Step 8: Determine Additional Retention Volume, if necessary ............................. 2-9 Step 9: Submit Project Stormwater Quality Control Measures Plan and Maintenance Plan ................................................................................................. 2-9 Section 3. Site Assessment .................................................................................... 3-1 3.1. Assessing Site Conditions and Other Constraints ........................................... 3-1 Project Location .................................................................................................... 3-1 Site Conditions ...................................................................................................... 3-2 3.2. Pollutants of Concern ...................................................................................... 3-4 Section 4. Site Design Control Measures ............................................................... 4-1 4.1. Introduction ..................................................................................................... 4-1 4.2. Description ...................................................................................................... 4-1 G-1: Site Planning ................................................................................................ 4-2 G-2: Protect and Restore Natural Areas .............................................................. 4-3 G-3: Minimize Land Disturbance .......................................................................... 4-4 G-4: Minimize Impervious Area ............................................................................ 4-6 City of Modesto i May 2011 Stormwater Management Program Section 5. Source Control Measures ...................................................................... 5-1 5.1. Introduction ..................................................................................................... 5-1 5.2. Description ...................................................................................................... 5-1 S-1: Storm Drain Message and Signage .............................................................. 5-3 S-2: Outdoor Material Storage Area ..................................................................... 5-5 S-3: Outdoor Trash Storage and Waste Handling Area ....................................... 5-8 S-4: Outdoor Loading/Unloading Dock Area ...................................................... 5-10 S-5: Outdoor Vehicle/Equipment Repair/Maintenance Area .............................. 5-12 S-6: Outdoor Vehicle/Equipment/Accessory Washing Area ............................... 5-14 S-7: Fuel and Maintenance Area........................................................................ 5-16 S-8: Building Materials ....................................................................................... 5-19 Section 6. Volume Retention Requirement and Water Quality Volume/Water Quality Flow .............................................................................................................. 6-1 6.1. Introduction ..................................................................................................... 6-1 6.2. Volume Retention Requirement ...................................................................... 6-1 C-1: Volume Retention Requirement Calculation ................................................. 6-2 Example Calculation ............................................................................................. 6-2 C-2: Water Quality Flow /Water Quality Volume Calculation ................................ 6-4 Section 7. Low Impact Development Control Measures ......................................... 7-1 7.1. Introduction ..................................................................................................... 7-1 7.2. Description of Low Impact Development Control Measures ............................ 7-2 L-1: Rain Garden .................................................................................................. 7-3 L-2: Rain Barrel/Cistern ........................................................................................ 7-8 L-3: Vegetated Roof ........................................................................................... 7-12 L-4: Interception Trees ....................................................................................... 7-17 L-5: Grassy Channel .......................................................................................... 7-20 L-6: Vegetated Buffer Strips ............................................................................... 7-28 Section 8. Treatment Control Measures ................................................................. 8-1 8.1. Introduction ..................................................................................................... 8-1 8.2. Selection of Treatment Controls ...................................................................... 8-4 Volume Retention Requirement ............................................................................ 8-4 Volume Retention Requirement Waiver ................................................................ 8-4 8.3. Description of Treatment Control Measures .................................................... 8-5 R-1: Infiltration Well .............................................................................................. 8-8 City of Modesto ii May 2011 Stormwater Management Program R-2: Water Quality Infiltration Basin ................................................................... 8-13 R-3: Water Quality Infiltration Trench ................................................................. 8-20 R-4: Bioretention without an Underdrain ............................................................ 8-26 R-5: Dry Well ...................................................................................................... 8-31 R-6: French Drain ............................................................................................... 8-36 R-7: Permeable Pavement without an Underdrain ............................................. 8-37 R-8: Bioretention with an Underdrain ................................................................. 8-43 R-9: Permeable Pavement with an Underdrain .................................................. 8-49 R-10: Stormwater Planter ................................................................................... 8-55 R-11: Tree-Well Filter ......................................................................................... 8-63 R-12: Vegetated Swales .................................................................................... 8-71 R-13: Grassy Swale ........................................................................................... 8-79 R-14: Vegetated Filter Strip ................................................................................ 8-86 C-1: Media Filter ................................................................................................. 8-92 C-2: Constructed Wetland ................................................................................ 8-116 C-3: Extended Detention Basin ........................................................................ 8-126 C-4: Wet Pond.................................................................................................. 8-137 P-1: Proprietary Treatment Control Measures.................................................