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used successfully. Where 50 mm pipe is used, flow control devices connected to the interceptor tank outlet to limit peak flows and check valves installed in the service lateral to prevent backflow are used. The costs of the flow control devices and check valves generally cancel savings realized from the smaller pipe and, therefore, 100 mm pipe is most commonly used. |
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The collectors are laid out in a typical dendriform pattern similar to that of conventional sewers. Because installation is substantially less costly, mains are frequently run on both sides of a paved roadway to reduce the costs associated with pavement restoration. Alternatively, in many communities, the collectors are laid in the alleys behind the homes as the existing septic tank systems are usually located in the back of the lots. |
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Strict horizontal and vertical control during construction has not been necessary. Although utilities, large trees, rock outcroppings, etc. are usually avoided with careful planning, unforeseen obstacles often occur, but may be avoided during construction by bending or rerouting the pipe. Only elevations of major summits need to be controlled to ensure that upstream connections are not flooded. Where depressed sections occur, air venting is necessary at the summits. Between summits, the profile of the sewer should be reasonably uniform so unvented air pockets do not form to create unanticipated headlosses and excessive upstream surcharging. |
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In most systems, cleanouts are substituted for manholes except at major junctions. Cleanouts are one-fifth the cost of manholes, provide sufficient access for hydraulic flushing, and are not a source of infiltration, inflow, or grit. Manholes have also been a source of odours in SDGS systems. |
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Prefabricated, single compartment septic tanks are usually used for interceptor tanks. For residential connections, tank volumes of 3.44.0 m3 are used. For commercial connections, tank volumes are usually determined based on local septic tank system codes. |
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