LeachField Drop Box

[rafklm]

I have a leach field design that flows from a distribution box to drop boxes located down a hill. The leach field is installed on level ground (parallel to grade), but the drop boxes are on the hill. So, our system is to enter the drop box at a higher level than the two outlet pipes (one is for the leach field lateral, one goes to the next drop box). There is different theories as to how the flow is distributied out of the drop box.

1. flow is split equaly. Meaning 1Q enters the drop box, and 1/2Q goes to the leach field lateral, and 1/2Q goes to next drop box.

2. the outlet pipe to the next drop box is set higher than the outlet pipe to the leach field lateral. This will utilized the first leach field lateral in the system more than the other approach.

Q: Does anyone have experience or preferences of these two approaches?

Thanks, rafklm

 

[bimr]

The length of the laterals is determined by the influent flow and soil percolation. I have to presume that is how the system was sized. If so, you would be overloading 1/2 of the system, if you only applied the wastewater to that 1/2. It seems logical to apply the wastewater to the entire lateral grid.

 

[LHA]

Flow will not be split equally, headloss through the pipes will be.

bimr is correct, this will give you the characteristics (length, diameter and pipe material).

Set hL equal between the leach lateral and the other drop line. Solve for velocity.

Then, apply Bernoulli's and correct for z and v, with delta p being equal (due to hL).

I think this is correct...anyone else?

Remember: The Chinese ideogram for “crisis” is comprised of the characters for “danger” and “opportunity.”
-Steve

 

[semo]

I believe you are getting two types of boxes/systems mixed up here.

One type of system (where the laterals are in a common flat area) utilizes a "Distribution Box" where the laterals are placed at an even elevation so that each lateral has water distributed equally to them.

Another type of system (where the laterals are placed horizontally along a hillside at different elevations) utilizes a "Drop Box" where the laterals at that elevation are charged and excess water then spills over to the next "Drop Box". Like you are describing your system.

I will not say which type of system is best. My feeling is that without proper management (isolation of upper laterals at various times) the Drop Box system could overload the upper laterals and provide a system that does not work properly. Isolating the upper laterals on a routine basis will give them some needed rest time. Kind of like a pressurized system with alternating absorption fields.

Even with a distributon box, the outlets will act like orifices. Provided the piping behind them is not backing up water into the box (they flow freely from the box), equal pipes at equal elevations will get equal flow.