On-Site Wastewater Treatment and Disposal Systems - Forced ...

Step 6: Determine minimum dose volume (Figure 7-30).
With: lateral diameter = l-1/4 in.
lateral length = 32 ft
number of laterals = 4
Then: pipe volume = 2 gal
Minimum dose volume = x100 gal
From Table 7-4, for a medium texture sand, 4 doses/day are
desirable. Therefore, the dose volume is:
450 gpd
4
Step 7: Determine minimum discharge rate.
= 112 gal/dose
Minimum discharge rate = (4 laterals) x (13.5 gpm/lateral)
= 54 gpm
Step 8: Select proper pump. For this example, assume the dosing tank
is located 75 ft from the network inlet, the difference in
elevation between the pump and the inverts of the distribution
laterals is 7 ft, and a 3-in. diameter delivery pipe is to be
used.
Friction loss in 3-in. pipe at 54 gpm (from Table 7-14)
Friction loss in 75 ft
= 0.58 +$ (0.81 - 0.58)
= 0.67 ft/lOO ft
= (0.67 ft/lOO ft) x (75 ft)
= 0.5 ft
Elevation head = 7.0 ft
Pressure to be maintained = 2.0 ft
Total pumping head = 9.5 ft
Therefore, a pump capable of delivering at least 54 gpm against
9.5 ft of head is required.
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