CEMP-E
EI 11C201
1 March 1997
APPENDIX B
EXAMPLE PROBLEMS
B-1. Design 1 mile of interceptor sewer serving a military installation with the following
populations and industrial discharges.
20,000 residents living on the installation (100 gpcd--Table 3-1)
6,000 nonresidents or employees coming from off-post and working 8-hour shifts
(30 gpcd --Table 3-1)
Peak industrial flowrate = 1.0 mgd
Allow for an infiltration rate of 1000 gpd/in/mi.
Domestic Flows
20,000 x 100
= 2,000,000 gpd = 2.0 mgd
6,000 x 30
= 180,000 gpd = 0.18 mgd
total average daily flow
= 2.18 mgd
Use a 24-hour basis since waste load is from the entire installation, and 92 percent of total is
generated by residents.
Extreme peak flowrate
R = 3.8/(2.18)0.167
= 3.34
3.34 x 2.18
= 7.28 mgd
Peak diurnal flowrate
= 1/2 x 7.28 = 3.64 mgd
Infiltration Allowance
Assume a 30-inch sewer 1000 X 30 x 1 = 30,000 gpd = 0.03 mgd
Design Flows
Extreme peak
= 7.28 + 0.03 + 1.0 = 8.31 mgd
Peak diurnal
= 3.64 + 0.03 + 1.0 = 4.67 mgd
Average daily
= 2.18 + 0.03 + 1.0 = 3.21 mgd
Typical Sewer Design
Try a 30-inch sewer on a 0.10 percent slope (n = 0.013)
Flow depths and velocities
Q = 8.31 mgd d/D = 0.80 < 0.90 (Para. 3-2) V = 3.0 fps
Q = 4.67 mgd d/D = 0.53
V = 2.7 fps > 2.5 fps
Q = 3.21 mgd d/D = 0.43
V = 2.5 fps > 2.0 fps
Critical depths
Q = 8.31 mgd
dc/D = 0.48 < 0.80
Q = 4.67 mgd
dc/D = 0.36 < 0.53 Flows are subcritical
Q = 3.21 mgd
dc/D = 0.30 < 0.43
B-2. Design 2000 feet of main or trunk sewer serving a large portion of the above installation
with the following facilities.
Family Housing
500 units with 1800 residents (500 x 3.6 at 100 gpcd--Table 3-1)
B-1
Previous Page
