SECTION 9 SEWER COLLECTION SYSTEMS TABLE OF CONTENTS 9.1 PURPOSE AND DEFINITIONS .......................................................................................... 1 9.1.1 Purpose ........................................................................................................................ 1 9.1.2 DOU Sewer System ...................................................................................................... 1 9.1.3 Definitions ..................................................................................................................... 2 9.2 GENERAL REQUIREMENTS ........................................................................................... 11 9.2.1 Authority and Responsibility ....................................................................................... 11 9.2.2 Disclaimer ................................................................................................................... 11 9.2.3 Acceptance ................................................................................................................. 12 9.2.4 Variances .................................................................................................................... 12 9.2.5 Gravity vs. Pumped Systems ...................................................................................... 12 9.2.6 New Sewer Systems ................................................................................................... 13 9.2.7 Diversion of Flows ...................................................................................................... 13 9.2.8 Phasing of Sewer Facilities ......................................................................................... 13 9.2.9 Geotechnical Investigation .......................................................................................... 13 9.2.10 Groundwater Discharges .......................................................................................... 16 9.3 SEPARATED SEWER SYSTEM ....................................................................................... 17 9.3.1 Feasibility Study .......................................................................................................... 17 9.3.2 Plan Study .................................................................................................................. 17 9.3.3 Study Software ........................................................................................................... 17 9.3.4 ESD Flow Factor ......................................................................................................... 17 9.3.5 Average Dry Weather Flow (ADWF) ........................................................................... 18 9.3.6 Rainfall Dependent Infiltration and Inflow ................................................................... 19 9.3.7 Peak Wet Weather Flow (PWWF) .............................................................................. 19 9.4 COMBINED SEWER SYSTEM (CSS) .............................................................................. 20 9.4.1 General ....................................................................................................................... 20 9.4.2 Separated Systems .................................................................................................... 20 9.4.3 Combined Sewer Development Policy ....................................................................... 20 9.4.4 Mitigation of Sewer Impacts ........................................................................................ 20 9-i 7/24/18 9.4.5 Mitigation of Drainage Impacts ................................................................................... 21 9.4.6 Combined Sewer Studies ........................................................................................... 21 9.4.7 Combined Sewer Flows .............................................................................................. 22 9.4.8 Combined Sewer Pipe Sizing ..................................................................................... 22 9.4.9 Stormwater Detention Ponds ...................................................................................... 22 9.4.10 Underground Storage ............................................................................................... 23 9.4.11 On-site Storage ......................................................................................................... 23 9.4.12 Hydromodification Plan (HMP) ................................................................................. 23 9.4.13 Combined Sewer Credits .......................................................................................... 23 9.5 DESIGN OF PIPELINES ................................................................................................... 24 9.5.1 Pipe Sizing .................................................................................................................. 24 9.5.2 Slope and Velocity ...................................................................................................... 24 9.5.3 Surcharge of Pipelines ................................................................................................ 24 9.5.4 Horizontal Alignment ................................................................................................... 25 9.5.5 Vertical Alignment ....................................................................................................... 25 9.5.6 Pipe Cover .................................................................................................................. 25 9.5.7 Buoyancy .................................................................................................................... 26 9.5.8 Trench Dams .............................................................................................................. 26 9.5.9 Levee Crossings ......................................................................................................... 26 9.5.10 Track, Freeway, and Waterway Crossings ............................................................... 27 9.5.11 Inverted Siphons ....................................................................................................... 27 9.5.12 Trenching, Bedding, and Backfill .............................................................................. 27 9.5.13 Pipe Materials ........................................................................................................... 27 9.5.14 Removal or Replacement ......................................................................................... 27 9.6 MANHOLES ...................................................................................................................... 28 9.6.1 Location ...................................................................................................................... 28 9.6.2 Manhole Spacing ........................................................................................................ 28 9.6.3 Manhole Types ........................................................................................................... 28 9.6.4 Venting ........................................................................................................................ 29 9.6.5 Manhole Connections ................................................................................................. 29 9.6.6 Drop Connections ....................................................................................................... 30 9.6.7 Buoyancy .................................................................................................................... 30 9-ii 7/24/18 9.6.8 Flusher Branch ........................................................................................................... 30 9.6.9 Pipe Stubs .................................................................................................................. 30 9.6.10 Cross Connections ................................................................................................... 31 9.6.11 Separation and Summit Manholes ............................................................................ 31 9.7 SEWER SERVICES .......................................................................................................... 32 9.7.1 Service Requirements ................................................................................................ 32 9.7.2 Service Size ................................................................................................................ 32 9.7.3 Depth and Material ..................................................................................................... 32 9.7.4 Location ...................................................................................................................... 32 9.7.5 Slope ........................................................................................................................... 32 9.7.6 Cleanouts .................................................................................................................... 33 9.7.7 Backflow Preventers ................................................................................................... 33 9.7.8 Main Connections ....................................................................................................... 33 9.7.9 Easement Services ..................................................................................................... 33 9.7.10