Page 352 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

SITE UTILITY SYSTEMS

6.74 CHAPTER SIX

SANITARY GRAVITY SEWERS

This section will discuss gravity sewers collecting domestic sanitary waste and acceptable
industrial discharge. These sewers carry this combined waste from small areas or build-
ings from the property line or building wall to a connection with a public sanitary sewer.
Sanitary sewers are called house sewers for private residences and service laterals for larger
facilities. On large sites, long runs of private sewers receiving discharge from various build-
ings route the sewage into the public sewer for disposal.
If a public sewer is available, it is the least expensive method of disposing sanitary
waste. In urban areas, a sewer could be considered available if it is within 500 ft of a prop-
erty line. This distance varies based on local requirements. It may be necessary for a house
sewer to travel a considerable distance, often in a public street.
If a public sewer is not available, the sanitary effluent must be treated by a septic tank or
a sewage treatment system to the extent required by local authorities. The treated effluent
can then be discharged to the environment.
Plumbing codes govern the size and installation of house sewers and building sewers,
or building laterals. Any discharge into the public sewer other than sanitary effluent must
be treated so that the quality of the effluent is within guidelines established by the local
authorities. These guidelines vary based on the municipal sewage measurements. It could
combine with the sanitary house sewer prior to discharge into the public sewer to save
installation costs.
The following information should be obtained before designing a sewer:
1. The size, location, and depth of the existing public sewer, and whether the public sewer
is a sanitary or combined sewer
2. The location and size of spurs and manholes in the public sewer
3. The allowable method of connection to the public sewer
• Do the local authorities require a manhole? Will the local authority build the man-
hole? If so, who will bear the cost?
• If a pipe is installed in a public street, are there special installation or other
requirements?
4. Topographical map along the proposed route of the sewer
5. Minimum depth of bury if mandated by the local authorities

SEWER COMPONENTS

The components of the sewer system consist of appurtenances, or structures, such as man-
holes, cleanouts to grade for smaller lines, and the piping network.

MANHOLES

A manhole is an underground structure that facilitates pipe connections, access into the
sewer for observation and maintenance, and keeps hydraulic interference from connections
and changes in direction to a minimum. A typical manhole is illustrated in Fig. 6.10.
There are several different types of manholes, each used for a different purpose. A shal-
low manhole (Fig. 6.35) is used when the depth from the invert of the sewer to grade is less
than approximately 3 ft (1 m). A drop manhole (Fig. 6.11) should be used when the invert
of the incoming pipe is more than 2 ft (60 cm) higher than the discharge pipe. This is to

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