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

watertight Pipe & Joints1
FIGURE 7-21
CLOSED LOOP DISTRIBUTION NETWORK
Pretreatment
Unit
Distribution box networks are suggested only for absorption systems
located on level or gently sloping sites, where the system can be in-
stalled so that the ground surface elevation above the lowest trench is
above the box outlets (11). This is because it is difficult to prevent
the distribution box from settling (11)(17)(31). If the box were to
settle unevenly so that the lowest trench received a greater share of
the effluent, wastewater would seep onto the ground surface unless the
distribution lateral of the lowest trench were at a high enough eleva-
tion to back up the wastewater into the box, where it could flow into a
different lateral. Therefore, to utilize the full capacity of each
trench in the system, distribution box networks should be used only
where each trench can back up into the distribution box (see Figure 7-
22). On steeply sloping sites, other networks should be used, unless
great care is used to construct the distribution box on a stable
footing. If used for dividing flow between independent trenches, any
combination of trenches can be rested by plugging the appropriate
outlets.
e. Relief Line
Relief line networks may be used in place of drop box networks in
continuously ponded multi-trench systems on sites up to the maximum
permissible slopes. The network provides serial distribution as in drop
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