Cistern overflow into a soakaway shaft

Hello,

I am currently thinking about the sizing of the cistern and the connected soakaway shaft. According to calculations, a cistern with a little more than 3000 liters should be sufficient (rainwater from the roof). I would still prefer a bit more buffer and am thinking around 4-5000 liters. Now the question arises as to how the following soakaway shaft should be planned? There are plastic shafts with 140 liters for around €160, the next step is 500 liters for about €350, and then 900 liters for approximately €430. Does anyone have any ideas or use such a combination themselves? Discharge into the RW sewer should preferably not take place.

Thank you!

Depends on the conditions. Is infiltration on your own property required, or are you allowed to discharge? What was specified in the building permit? The extreme case would be infiltration on your own land and proof obligation to the water authority. Then you need a calculated proof that during a heavy rain event and with a full cistern the water still dissipates through the infiltration capacity proven by a geotechnical investigation. If nobody cares about that, you can simply dig a hole and pour water in, then measure how long it takes to infiltrate, repeating several times before measuring. Then you can calculate how much water falls on your roof in an hour at most and then size the infiltration shaft accordingly.

Soil survey says: that infiltration from the overflow of a cistern is possible and can be realized with a vertical structure (infiltration shaft).

Development plan says: RW is collected and drained within the building area (this probably refers to the RW channel?), or infiltrated on the property. This is only addressed with this one sentence.

Building permit is still pending. The application mentioned cistern and infiltration shaft.

On our property, we installed a soakaway corresponding to the calculated sealed surface area. On the way there, the cistern is simply used as an "intermediate storage." It is simply approved. Overflow is therefore not a problem; it goes into the soakaway.

Hello,

I have to ask a question here again:

If the overflow of a cistern goes into the RW sewer, is that possible as a direct connection, or does there have to be an inspection chamber in between, or is that not required for RW (but only for RW)? Is such a chamber "law," or what does it depend on?

Thanks!

I do not know the legal requirements. But even if a connection with a free slope were possible, I would optionally consider a downstream inspection shaft (possibly only plastic DN 400 if no accessibility is required) with a check valve.

In the event of backflow, the question still arises as to where to put the excess [RW]. So possibly plan an emergency overflow, for example into the existing infiltration.