Rainwater infiltration

Hello everyone.

The following issue arises in our construction project. According to building regulations, rainwater must be infiltrated on the property or retained. According to our soil report, however, the soil is not suitable for this.

The groundwater level is approximately at 3.50 m.

Attached is an excerpt from the report.

What options do we have for the infiltration of rainwater? I have already read a lot about soakaway shafts, infiltration trenches, and similar, but I am completely clueless.

I look forward to constructive suggestions.

Hello Anja,
just ask nicely at the building authority and the municipality how they see the chances of exempting you from this point of the development plan based on the soil survey.

Well, that's how it is. Our soil report states:

Rainwater infiltration according to the specifications of DWA-A-138 is not possible on the property. The loess and glacial till marl layers present are to be classified as only slightly permeable (kf < 1*10-8 m/s). Ideally, rainwater reuse with an overflow connection to the nearest receiving water body is recommended.

In fact, we received a cistern with an overflow into a soakaway. I'm not quite sure yet how to deal with this (purchase from the developer, I only received the report at handover, by then the cistern and soakaway were already completed).

So the proposal of a cistern with an attached soakaway was already made by some other builders from the construction area as well. I think that this will also be an option for us. The option to be exempted from the infiltration obligation is virtually zero. A connection to the sewer system is not technically planned.

In fact, we received a cistern with overflow into a soakaway.

Why should the soakaway only work when the cistern is full?!

We only have soakaway infiltration. Graf offers soakaways with a capacity of 300 liters each, which can simply be connected piece by piece. We have 11 of them. The cost per unit is 50 € from the building materials store. The infiltration area is gigantic, the volume not exactly small. If you now put a cistern in front, you get a large infiltration area + a large collection basin. That's that.

Can you say more about the overall costs?