Sewer Design Standards & Guidelines

There are specific procedures for developers and homeowners seeking drainage services from EPCOR. ​Please review the following documents for more information:

Construction requirements

Site plans for new developments must include preparations for sewer and storm water system connection and use. These procedures are different depending on the type of construction, whether a single family/duplex or commercial/multi-family development.

Sewer design standards and guidelines

These standards and guidelines are designed for 2 different types of sewers, sanitary and storm.

Sanitary drainage design criteria

• Size: Sanitary sewer mains shall be of adequate size to convey population generated (peak dry weather) flows, plus a general allowance for inflow and infiltration, plus an allowance for inflow allowance for manholes in sag locations. The inside diameter of sanitary sewer pipes must measure at least 200 mm.
• Population generated flows: Residential population generated flows are determined by the following formula:
  
  Qpdw = G x P x PF/86,400
  

  Qpdw	=	peak dry weather flow rate (litres/second)
  G	=	per capita daily sewage flow generation (300 litres/day/person)
  P	=	design contributing population
  PF	=	residential peaking factor (2.6/P0.1), where P is the population in 1,000's and has a minimum value of 1.5

• General inflow/infiltration allowance: A general allowance of 0.28 litres/second/hectare shall be used to allow for wet weather inflow to manholes not located in sag locations.
• Inflow allowance for manholes in sag locations: For manholes located in sag locations where ponding will occur or low areas subject to inundation, an inflow allowance of 0.4 litres/second shall be made for each manhole.
• Minimum slopes: All sanitary sewers should be designed with a minimum slope of 0.4% or greater. Where it is not practical to do so, the following minimum slopes will be permitted for various sewer sizes:
  

  Sewer Size (mm)	Minimum Slope (%)
  200	0.40
  250	0.28
  300	0.22
  375	0.15
  450	0.12
  ≥525	0.10

• Velocity: The velocity of flow in sanitary sewers shall be kept between 0.6 metres/second and 3.0 metres/second.
• Depth: Sanitary mains shall have depth adequate to permit sewer services to be constructed a minimum of 2.74 m deep (from the ground surface to the invert of the pipe) at the property line separating private and city land.
• Manhole: Manholes must be installed at the end of each sewer, at all changes in sewer size, grade, or alignment and at all junctions. The maximum permitted manhole spacing for all sewers less than 1200 mm in diameter is 150 metres.
• Pipe materials: Approved materials for pipe construction of sanitary sewer mains are non-reinforced concrete pipe, reinforced concrete pipe, and PVC (polyvinyl chloride) pipe.

Storm drainage design criteria

• Major/Minor system concept: An urban area will have 2 separate storm drainage systems, the minor system and the major system. The minor system consists of the pipe network, plus gutters and inlets which provide a convenience system to rapidly carry away storm runoff from road surfaces for minor rainfall events. The major system conveys runoff rates and volumes for a 1 in 100 year rainfall event which exceed the capacity of the minor system. The major drainage system consists mainly of overland drainage conveyance elements.
• Minor system level of service: Storm mains which service areas of 30 hectares or less are to be designed to convey runoff from 1 in 5 year and more frequent rainfall events. Mains servicing areas greater than 30 hectares are to be designed to convey 1.25 times the rate of runoff which would occur in a 1 in 5 year rainfall event.
• Ponding depths: The minor system should be designed such that the depth of ponding in the street does not exceed 0.15 metres in a 1 in 5 year rainfall event. The major system should be designed to limit the depth of ponding in the street to 0.35 metres in a 1 in 100 year rainfall event.
• Rational method: Design flows for storm systems may be determined by the Rational Formula for areas not exceeding 65 hectares. The Rational Formula is as follows:
  
  Q = CIA/360
  

  Q	=	flow in cubic metres per second (design flow rate)
  C	=	dimensionless runoff coefficient
  I	=	the average intensity of rainfall in millimetres per hour
  A	=	drainage area in hectares

  
  For a typical residential subdivision: C = 0.5, and I = 76.7 mm/hr (based on a time of concentration = 8 minutes)
• Minimum size: No storm sewer shall be less than 300 mm in diameter with the exception that catch basin leads may be a minimum of 250 mm in diameter.
• Velocity: All storm sewers shall be designed and constructed to give mean velocities, when flowing full, of greater than 0.6 m/sec based on Manning's Formula. Flow velocities of 0.9 to 1.0 m/sec are recommended and designs based on the lower velocities are to be justified on the basis of feasibility or unwarranted cost impacts. Where design velocities exceed 3.0 m/sec, special provisions shall be made to protect against displacement of sewers by erosions or shock. However, the designer shall ensure that supercritical flow does not occur where steep grades are utilized.
• Minimum slopes: All storm sewers should be designed with a minimum slope of 0.4% or greater. Where it is not practical to do so, the following minimum slopes will be permitted for various sewer sizes:
  

  Sewer size (mm)	Minimum slope (%)
  200	0.40 (foundation drain)
  250	0.28 (foundation drain)
  300	0.22
  375	0.15
  450	0.12
  ≥525	0.10

• Catch basin leads: Must be installed at a minimum grade of 1.0%.
• Depth: A minimum of 2.2 m of cover, measured to the invert, is to be provided for all storm sewer main lines smaller than 610 mm in diameter. A minimum of cover to crown is required for storm lines equal to or larger than 610 mm in diameter. Where storm sewer services are to be provided to properties, the storm mains must be installed at adequate depth to permit the storm sewer services to be 2.74 m deep (to invert) at the property line separating private and city land.
• Manhole: Manholes must be installed at the end of each sewer, at all changes in sewer size, grade, or alignment and at all junctions. The maximum permitted manhole spacing for all sewers less than 1200 mm in diameter is 150 metres.
• Maximum spacing of inlets: Runoff shall not be required to flow a distance greater than 120 metres along roadway gutter without reaching a catch basin. In lanes and walkways, runoff shall not be required to flow on the surface a distance greater than 180 metres to a point of interception.
• Pipe materials: Approved materials for pipe construction of storm sewer mains are non-reinforced concrete pipe, and reinforced concrete pipe. Some limited use of PVC (polyvinyl chloride) pipe is also permitted on a case-by-case basis.