White tub - Water exposure class W2.2-E

What I just thought of:
If necessary, one could call the geologist again and ask if he sees an alternative to the white watertight structure. I don't know the local conditions, but maybe there is the possibility to fill the excavation pit with really well-draining soil after the cellar is built and eliminate the risk of occasionally stagnant groundwater through a sufficiently sized drainage system. The question is whether it's financially worthwhile at the end of the day.

Thank you. That already helps me a lot. According to the developer, the basement will be constructed from precast concrete parts made of WU concrete. The [weiße Wanne] is then basically the additional waterproofing on top, right? We will probably do that as a precaution. We still have three basement windows that are about 150 cm below the [GOK], all on the downhill side of the house. The developer wanted to install special concrete light wells for [2.2 Klasse] that would each cost an additional 10,000 euros. Is that really necessary?

There is no such thing as a "white tank" as sealing - it is simply a principle/system made up of several components. There is WU concrete, crack width limitations through additional steel reinforcement, certain dimensioning requirements regarding wall thicknesses, some restrictions concerning installations and sealing systems for construction and expansion joints (e.g. Pentaflex, etc.) as well as for all penetrations ([Mehrsparen], drain pipes, etc.). Basically, only steel reinforcement as well as joint tapes/joint sheets are really relevant as cost drivers.

The ACO plastic light wells can all be installed to be watertight against pressure water - I don’t see why you would need concrete wells...

We still have three basement windows that are about 150 cm below the GOK, all facing downhill on the house. The developer wanted to install special concrete light shafts due to class 2.2, which would each cost another 10,000 euros. Is that really necessary?

Who builds basement windows 1.5 m deep?

In my opinion, the tip about the drainage is a good idea. Then you also don't need special concrete light shafts.

Show the plan of the house on the plot with elevations.

What does the expert gain by compromising and saying "Yeah, sure, that could work..."? He changes the report accordingly and three years later the builder drags him to court because when the first heavy rain came, it didn’t work after all and the basement was flooded.

The builder has to make the decision anyway and find a construction company that doesn’t care.

They exist. Neighbors a few houses down got rammed pile foundations recommended by the geologist as ground improvement... and then built on a sand cushion with another general contractor, without strip foundations... it all works. The question is whether you’ll be happy with it in the end.

And what the winemaker says... well, he knows about wine. I don’t ask a bricklayer which wine over 25 EUR/bottle he can recommend.

A section of the house and the layer directories would be helpful.

As I said, give me some information, then I'll write you what I would have recommended. You can then ask the expert again with that.