|
|
|
|
|
|
|
gravity sewers, with an average savings of 30 per cent (Otis, 1986). The average cost per connection was US$5,353 (1991). Although the costs per connection were higher than is typical for urban areas, the installation cost per meter of pipe was significantly less than that for conventional sewers. Of the projects reviewed, the in-place pipe costs averaged US$49.51 with a range of US$8.7556.72. The average total project cost per metre of collection main installed was US$189.80 (EPA, 1991). The installation of the collectors and interceptor tanks accounted for over 50 percent of the total costs of construction. In projects where the collectors could have shallow burial, and cleanouts rather than manholes were used, the construction costs per meter of pipe installed were the lowest of the projects reviewed. |
|
|
|
|
|
|
|
|
SDGS have potential for wide application. They are a viable alternative to conventional sewers in many situations, but are particularly well suited for low-density residential and commercial developments such as small communities and residential fringe developments of larger urban areas. Because of their smaller size, reduced gradients and fewer manholes, they have a distinct cost advantage over conventional gravity sewers where adverse soil or rock conditions create mainline excavation problems or where restoration costs in developed areas can be excessive. In new developments, construction of the sewers can be deferred until the number of homes built warrant their installation. In the interim, septic tank systems or holding tanks can be used. When the sewers are constructed, the tanks can be converted for use as interceptor tanks. However, SDGS usually are not well suited in high-density developments because of the cost of installing and maintaining the interceptor tanks. |
|
|
|
 |
|
|
|
|
EPA (1991). Alternative Wastewater Systems. Report No. EPA/625/1-91/024. Washington, DC: Office of Research and Development, Office of Water, Environmental Protection Agency. |
|
|
|
|
|
|
|
|
Gutteridge, Haskins and Davey Ltd. (1977). Planning for the Use Of |
|
|
|
|
|