2. The OP commissioned the demolition himself, then I would feel cheated in his place and would immediately call the demolition company.
Yes, that was commissioned personally. After completion of the demolition work, the pit looked very clean and neat. There was no sign of debris, etc.
The company carrying out the earthworks has the impression that instead debris was buried under normal soil, whether intentionally or negligently.
That he should provide financial reserves for the unexpected is another matter, but that has nothing to do with this case for now.
A buffer is planned. But that doesn't mean you have to throw money around recklessly, rather one should clarify this in advance if the construction manager and the earthworks service provider recommend it.
What was agreed upon during the demolition?
Disposal included regardless of actual quantity and pollutant class or according to weigh ticket and actual classification?
It was a flat-rate offer after inspection. There was an open clause that unforeseeable eventualities could possibly entail additional costs. But nothing unforeseen was found. It is not about asbestos, which nobody knew about, etc., but simply about masonry, debris, and part of a not removed foundation, which I could not see after completion of the demolition, as it was covered by other soil.
Fortunately, it remained a fairly manageable amount. It even got to the point that today the structural engineer and the soil expert came again to confirm that the house can be built on this soil, but they gave the all-clear and now everything is running according to plan again.