Assessment of ground conditions regarding the light court

Hello everyone,

since this is my first post, first of all a "hello" to the community. I have really been following here for a long time and have learned a lot. However, I have not actively participated until now.
Currently, we are planning our construction project in the south of Baden-Württemberg. We will receive a plot of land from our home municipality and are currently in talks with various potential construction companies ([GÜ]) and an architect. We already have a list of our wishes and ideas for a house, but no plans exist yet. At the appropriate time, we also want to put the planning up for discussion here.

Now to the actual question. We want to build with a basement. The unanimous feedback from all companies so far is to build with a "weisse" Wanne. Although the municipality itself sees the building ground as unproblematic regarding infiltration.
However, we would also like to integrate a light well to get natural light into a basement room, up to maybe 1 - 1 1/2 meters below ground level. The feedback from one company was that this only works with drainage via a lifting station, which pumps the water away even against a full sewer if necessary. However, I absolutely do not want a lifting station. It causes ongoing costs, is complex, and prone to errors.

There is no soil investigation for the plot so far. However, investigations commissioned by the municipality were carried out as part of the development. One of these driven core soundings is directly on the border of "our" building plot, so it should have significance for the expected soil. In general, the report states that no groundwater was detected in the exposures up to 5 meters.

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0.00m - 0.20m
Topsoil, humus, slightly moist, brown, dark brown
0.20m - 1.00m
Gravel, sandy, silty, slightly moist, brown, dark brown
1.00m - 1.80m
Silt, gravelly to strongly gravelly, slightly moist, brown
1.80m - 3.00m
Gravel, sandy, slightly stony, slightly moist, gray, brown
End depth 3.00m
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(...) Considering all investigation results, the water permeability of the encountered soils in the construction area can be estimated based on the soil profile, grain size distributions (...) as well as infiltration tests (...):
Cover layer: approx. k ≈ 5 x 10^-6 - 10^-8 m/s
Terrace gravel: approx. k ≈ 10^-4 - 10^-6 m/s
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When constructing infiltration systems, care must therefore be taken to embed sufficiently deep into the terrace gravel and to replace fine-grained areas.
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Is there anyone here who can interpret the present soil for me? Is it really such poor building ground? Or is the contractor just "overcautious" regarding the lifting station?
I have the complete investigation, but understandably I do not want to post it as it is not "mine". If it helps, I can gladly copy more data.

Thanks in advance! Mini

What exactly do you mean by Lichthof? A "normal" slope where the soil is removed? Or a kind of terrace? Or even a courtyard that is enclosed by the house on all four sides?

Linking example images is unfortunately not possible here. Most hits for [Lichthof] or [Lichtgraben] in Google image search show it quite well.

More like a normal slope, maybe 4 meters, 1 - 2 meters wide and 1 - 1 1/2 meters deep. The dream would be around the corner, but I don’t want to go that far.

I actually thought this could be easily realized, with a slightly larger workspace at the cellar at that spot, then filling it with gravel/crushed stone and possibly connecting it to the infiltration system. Support it with natural or L-shaped stones in maybe two or three steps.

Thank you in advance! Mini

I am not a geologist either, but the slightly moist condition in all layers is probably the problem. With sand, water always flows to where there is a hole. But if there is a ring drainage around the basement, I don't see a problem there either. Connect a sump pit and attach the drainage there.

The problem can actually only be the surface water during heavy rain. Because the basement wall is sealed by the [weiße Wanne]. In this respect, the window is the weak point.

Thank you both for your answers. That reassures me because I had assessed it similarly.

The window is the weak point, so leave enough "space" for the floor light well, use sufficiently permeable material and connect it to the infiltration.
And honestly, either it works that way, or the pump couldn’t do anything in a hundred-year rain anyway. Then logically, only a watertight light well would be an option...

Thank you both! Mini