TM 5-814-3/AFM 88-11, Volume III
4-3. Estimating future service demand.
a. Nature of activities. The nature of the activities of the personnel at a military installation are a very
important factor in determining per capita waste loads because different activities have different water uses.
Table 4-2 illustrates this fact in terms of gallons per capita per day (gpcd); table 4-3 shows how waste loadings
vary between resident and non-resident personnel. The values shown in table 4-3, for that portion of the contri-
buting population served by garbage grinders, will be increased by 30 percent for biochemical oxygen demand
values, 100 percent for suspended solids, and 40 percent for oil and grease. Contributing compatible industrial
or commercial flows must be evaluated for waste loading on a case-by-case basis.
4-4. Volume of wastewater.
a. Variations in wastewater flow. The rates of sewage flow at military installations vary widely throughout
the day. The design of process elements in a sewage treatment plant is based on the average daily flow. Trans-
mission elements, such as conduits, siphons and distributor mechanisms, will be designed on the basis of an
expected peak flow rate of three times the average rate. Clarifiers will be designed for a peak hourly flow rate
(i.e., 1.75 times the average daily rate). Consideration of the minimum rate of flow is necessary in the design of
certain elements, such as grit chambers, measuring devices and dosing equipment; for this purpose, 40 percent
of the average flow rate will be used.
b. Average daily wastewater flow. The average daily wastewater flow to be used in the design of new treat-
ment plants will be computed by multiplying the design population by the per capita rates of flow determined
from table 4-2, and then adjusting for such factors as industrial wastewater flow, stormwater inflow and
infiltration. Where shift personnel are engaged, the flow will be computed for the shift when most of the people
are working. A useful check on sewage volumes would be to compare water consumption to the sewage
estimate (neglecting inflltration, which will be considered subsequently). About 60 to 80 percent of the
consumed water will reappear as sewage, the other 20-40 percent being lost to irrigation, fire-fighting, wash-
down, and points of use not connected to the sewer.
(1) Good practice requires exclusion of stormwater from the sanitary sewer system to the maximum
practical extent. Infiltration must also be kept to a minimum. Both must be carefully analyzed and the most
realistic practical quantity that can be used in design must be assigned to these flows, Leakage of stormwater
into sewer lines often occurs through manhole covers or collars, but this usually is no more than 20 to 70 gallons
per minute if manholes have been constructed and maintained properly. However; leakage into the sewer mains
4-2
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