Page 355 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

SITE UTILITY SYSTEMS

SITE UTILITY SYSTEMS 6.77

3. Allowance for future
4. Infiltration for long runs of piping
Peak Sanitary Discharge. Peak sanitary discharge is calculated using fixture units in
accordance with local plumbing codes. A method of converting sanitary fixture units into
gpm is presented in Fig. 6.36. Private sewers serving multiple buildings are also sized in
the same manner until the fixture unit count becomes too large. After the code fixture unit
value is exceeded, the drainage flow rate figure is then calculated by using the facility water
fixture unit flow rate demand.

Peak Nonsanitary Discharge. The process, utility, and manufacturing discharge can only
be calculated by a study of the entire facility and a determination of the total gpm expected
to be discharged from all sources. It is doubtful that all discharges will occur at the same
time, therefore some diversity might be used to reduce the peak flow. If there is any doubt,
use the highest figure.
It is often necessary to prepare a preliminary estimate for pipe size before the exact
information is available. Table 6.25 provides the gallons per day for various types of facili-
ties based on population or other easily found criteria. These same values should be used to
estimate the quantities of sewage required for a private sewage disposal system system.
To estimate a size, find the total gallons per day for the facility. Divide that figure by
the number of hours the facility is in operation to give the average hourly flow. Double the
hourly flow rate and divide by 60 to find the average peak flow rate in gpm. This is only
an average figure. To determine pipe size, allow an additional 10-percent safety factor for
peak flow rate.
Allowance for the Future. Allowance for the future should be obtained and added to the
peak discharge.
Infiltration. Infiltration is the amount of groundwater or storm water entering the sewer
piping network from faulty joints in underground piping, leakage around manholes and
manhole covers, or cracked pipe. Another major contributor to infiltration is poorly installed
laterals. Infiltration should be considered only for a very long run from the building to the

FIGURE 6.36 Fixture unit conversion to gpm.

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