Small-Diameter Gravity Sewers (See endnote 30)
Where there are numerous problems of disposal of the effluent on-site, a small-diameter gravity sewer may be considered for collecting the effluent from several properties and allowing it to go to a central treatment location or pump station to be moved to a treatment facility. The pipes of the system are smaller in diameter than normal collection lines and are placed along the contours of the land always leading downward toward the collection station and pumping system. Most of the suspended solids have been removed by the septic tanks, thereby reducing clogging. Cleanouts and air release risers must be furnished and utilized. Odor control is a problem with the system. The advantages of this system are that: construction is rapid; unskilled people can operate and maintain the system; instead of manholes, cleanouts are used; there are reduced costs of excavation and materials (plastic pipes can be used); and final treatment is less because the organic load has been reduced. The disadvantages are that: these systems cannot handle commercial wastewater with lots of grit or settleable solids; the collected septage still has to go somewhere for treatment and disposal; and the system must be buried deep enough to keep from freezing.