Demolition site - Filling with compacted concrete "gravel"

Hello,

this is my first post in this forum and I have only recently started considering building a house.

We have set our eyes on a plot that is to be designated on the grounds of a former demolished indoor swimming pool. In the area where the future house will be built, there used to be an outdoor pool. According to the real estate agent, this pool will be filled and compacted with recycling material resulting from the demolition (i.e., crushed concrete), and then covered by a layer of soil (the thickness of which he will still inform me about). We plan to build our house with a basement. Now, as a "layman," I naturally have some concerns regarding the backfilling. The real estate agent, on the other hand, said that for the drainage of the base slab, gravel is normally used, and here the backfill presumably has a similar effect. I, however, could imagine that excavation and disposal costs on this plot might increase. Does anyone perhaps have experience with similar conditions?

Thank you and best regards Achim