Infiltration of rainwater, which method?

: in case I missed it, sorry. How many liters do you have to infiltrate, for how much roof area? According to Graf, over 10,000 liters accumulate for our 265 sqm (420l boxes 24 times). Is that correct? That seems really huge to me.

Just for illustration, right below the topsoil at our place there is a 6m thick layer of clay, the highest groundwater level is 1.5m below the property surface. Infiltration is impossible, therefore option a). Would have liked to infiltrate, but it’s not possible.

Hopefully this is an isolated case

Guys, this is not that hard to understand. The municipality is basically only interested in what you let infiltrate from your property into the public sewer system, or want to let infiltrate. There are initially two possibilities: a) permitted - against an annual fee depending on the sealed area drained into the sewer system b) prohibited

If b), then everything must infiltrate on your own property. Including paved surfaces and the like. Then you should have a slope away from public paths or lead it via a collection channel to infiltration on your property...

Regarding the calculation... You can send the lower water authority a manufacturer's specification related to the sealed area. It should be fine if everything is well described. They know the soil and groundwater level quite well. What is supposed to happen? You can also ask your geotechnical expert/geologist about the calculation. It costs a bit..