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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.
Residential population generated flows are determined by the following formula:
Qpdw = G x P x PF/86,400
where:
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
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.
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 recommended for various sewer sizes:
Sewer Size (mm) | 200 | 250 | 300 | 375 | 450 | >500 |
Minimun Slope (%) | 0.40 | 0.28 | 0.22 | 0.15 | 0.12 | 0.10 |
The velocity of flow in sanitary sewers shall be kept between 0.6 metres/second and 3.0 metres/second.
In general, sewers should be sufficiently deep to receive wastewater from basements and to prevent freezing. Insulation shall be provided for sewers that cannot be placed at a depth sufficient to prevent freezing.
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 100 metres.
Approved materials for pipe construction of sanitary sewer mains are non-reinforced concrete pipe, reinforced concrete pipe,PVC (polyvinyl chloride) and Corrugated HDPE pipe.