White tub - Water exposure class W2.2-E

Hello everyone,
our soil report arrived last week and the soil apparently has good quality and can be used for backfilling.
Unfortunately, a water exposure class W2.2-E was determined and the developer therefore recommends a white tank due to the pressing water. Now, the construction site is a vineyard with a slight slope and the winemaker who has been "cultivating" the area for more than 30 years told me in a conversation that he would be very surprised and does not understand where the pressing water would come from.
Of course, we are both laypeople and therefore my question: I have heard that soil experts nowadays always cover themselves and assume a worst-case scenario. Would you install a white tank with this exposure class? What information would you need to be able to say something about this?

Thank you!

Are you the first ones building there?

I’d say you don’t need to. :p

It is a new building area with about 30 building plots and unfortunately it has not yet been released by the developing company, but that is supposed to happen next Thursday. Therefore, no one is building there yet. The area located at the same level next door is definitely about 50-60 years old.

The winemaker usually only tills the topsoil; the statement is worth as much as the meteorologists' forecast for summer 2023.

Was groundwater or stratified water encountered in the report or during the drilling? If so, at what depth?
Were nearby groundwater monitoring stations mentioned?
What is the exact soil structure (soil layers, composition, and thickness)?

If applicable, rainwater temporarily accumulates as stratified water.

I would not claim that the geologist "dressed up" especially much in my soil report.

The report states: Groundwater was not encountered. The sandy gravels are highly permeable. Possible are layer water inflows (suspended groundwater) from GOK.
And further below:
4.8 Infiltration of Rainwater
Infiltration of rainwater is possible in the sandy-gravelly stones. A kf-value of max. 1·10-4 m/sec can be assumed for a preliminary design. This must be verified by an infiltration test.

As mentioned, as a layperson this does not tell me much.

The kf-value is the permeability coefficient of the soil which is approximately determined in the report based on the grain size distribution. The exact value can only be obtained through the mentioned infiltration tests.
At a value of 1x10-4, water infiltrates purely by gravity, i.e. at 0.0001 m/s, meaning 36 cm per hour. That is low, even though it is described as "well permeable" in the report. Probably due to this value, there is stagnant layer water. I have a value of 5x10-3, which corresponds to a theoretical infiltration velocity of 18 m/h. That is a well permeable soil.

Here are some food for thought:
- No construction company will be liable if the building method does not follow the recommendations in the report.
- Weather phenomena tend to increase in intensity.
- A [WU-Keller] is an investment in the quality and value stability of the property.
- After a sufficiently large damage event, the insurance might send an expert. If, based on investigations, the expert identifies various inconsistencies in the construction method, it could become unpleasant, as you might then be accused of breaching pre-contractual disclosure obligations, which could lead to exclusion from the natural hazard insurance or its ineffectiveness.
- If you sell the house one day and have only built with a [schwarzer Wanne], you have a duty to disclose the unfulfilled water exposure class of the basement. (My expert even confirmed this to me emphatically)
- You want to sleep well in the new house even during storms and rain, right?

At least you do not have permanently standing groundwater, which means you do not need groundwater lowering for the basement construction. That saves a lot of money.