Prepare a firefighting pond for the construction site

Hello,
I am in the process of acquiring a firefighting water pond to build a house on a slab there.
The plot has an area of 670 sqm and the pond is approximately 10m x 23m in size and 4.5m deep at its deepest point.
Roughly calculated, 800m3 need to be filled.
A soil expert said it would be possible to fill it with excavated soil from another plot, which we would get delivered for free. He would come by layer by layer and perform pressure tests to check whether it is properly compacted.

Has anyone done something similar in terms of type and scale?
The question is whether a pile foundation might be necessary? Or completely fill with gravel?
Who is responsible if the house would sink in 10 years?

I would be very grateful for tips and advice.

I am in the process of acquiring an extinguishing water pond in order to build a house on a slab foundation there. The property has an area of 670 sqm and the pond is approximately 10m x 23m in size and 4.5m deep at the deepest point.

First of all, I see a structure requiring approval in the filling and secondly, regarding the height of the filling, the question arises what can actually be built there considering heights possibly related to the original terrain. Someone will first have to reclassify the pond before it can even become residential building land. Even if the pond has been dry for a while, at least the district administration should be responsible for assessing the impact on the groundwater level. This is not just any property where you can casually slide a suitcase of money across the table with a notary's seal – it affects more than just private concerns.

Currently, all kinds of plots are being bought from us. Even plots with a slope like the Zugspitze. There, layers of soil, clay, and who knows what are compacted, and subsequently concrete pillars approximately 1x0.5m are poured onto the natural ground. This usually results in multi-family houses. So if you saved money on the plot, you can gladly offset a pile foundation against it.

The local municipality is selling me the property, the district administration is on board. For me, it’s more about the proper filling here.

If you don't trust your [Bodengutachter], what kind of help do you expect from this forum?

Well, I thought I’d see if someone here had accomplished something similar. That would just give me a bit of confidence with my project. Last week I watched a documentary on ZDF where a house sank sideways by 15 cm.