EI 11C201
CEMP-E
1 March 1997
Commercial Buildings
10 offices with 700 nonresidents, or employees from off-post, working 8-hour shifts
(30 gpcd --Table 3-1)
Elementary School
500 students for 8 hours per day, 200 of the students live in the area and
300 are nonresidents (30 gpcd--Table 3-1)
Laundromat
50 machines--open 12 hours per day (500 gpd/machine is a typical allowance)
Domestic Flows
Resident 1800 x 100
= 180,000 gpd on a 24-hour basis
Nonresident (700 + 300) x 30
= 30,000 gpd on an 8-hour basis
Note that the nonresident population includes office workers and students who do not live in the
area.
total average daily flow
= 210,000 gpd
Use a 24-hour basis since wastes are from a large area on the installation and 85 percent is
generated by residents.
Extreme peak flowrate
= 38.2/(210,000)0.167 = 4.93
R
4.93 x 210,000
= 1,035,300 = 1.04 mgd
Peak diurnal flowrate
= 1/2 x 1.04 = 0.52 mgd
Industrial Flow
Laundromat
50 x 500
= 25,000 gpd over 12 hours
Peak flowrate
= 50,000 gpd = 0.05 mgd
Infiltration Allowance
Assume a 12-inch sewer
1000 x 12 x (2000/5280)
= 4545 gpd = 0.005 mgd
Design Flows
Extreme peak
= 1.04 + 0.005 + 0.05 = 1.095 mgd
Diurnal peak
= 0.52 + 0.005 + 0.05 = 0.575 mgd
Average daily
= 0.21 + 0.005 + 0.05 = 0.265 mgd
Typical Sewer Design
Try a 12-inch sewer on a 0.35 percent slope (n = 0.013).
Flow depths and velocities
Q = 1.095 mgd
d/D = 0.68 < 0.80 (para. 3-2)
V = 2.9 fps
Q = 0.575 mgd
d/D = 0.46
V = 2.5 fps = minimum
Q = 0.265 mgd
d/D = 0.30
V = 2.5 fps = minimum
Critical depths
Q = 1.095 mgd dc/D = 0.55 < 0.68
Q = 0.575 mgd dc/D = 0.40 < 0.46 Flows are subcritical
B-2
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