Soil conditions

Dear forum community,

we are planning to purchase a plot of land in a planned new development area. Before we can name 5 plots as favorites and move on to the final allocation, the municipality has issued a general information letter. Among other things, it states that exploratory drilling was carried out in advance of the development work. Of course, this was done on a random basis throughout the entire construction area.

The text says the following:

Notes on drainage:
[...]
Rainwater from unbuilt areas, such as terraces or driveways, must infiltrate through the active soil zone without technical installations or be directed to infiltration through permeable paving including the necessary substructure.
[...]
Notes on soil conditions:
[...]
Both marlstone of the Upper Cretaceous and silt, partly humous silts below the topsoil layer, have been identified. The water levels measured towards the valley represent a closed, partially pressurized groundwater table in a low-permeability aquifer. In rainy periods and after heavy rainfall events, experience shows that waterlogging can occur on the low-permeability chalk marls and silts. [...] Due to the identified low permeability of the soils, rainwater infiltration is not advisable.
[...]

It is understandable that once you have decided on a plot and it is reserved, a geotechnical report is required and a plot-specific investigation will be carried out. But based on the passages mentioned: Does it make sense at all to take a closer look? It already does not sound very good to me as a layperson. Am I correct in my assumption? As an addition: The development area slopes about 5.50m over a length of approximately 350m towards the valley (a small stream). I would appreciate some assessments.

Best regards,
Seb08

Are you planning with a basement? Just based on feeling, I would rather settle on the mountain. :)

Are you planning with a basement? Just based on feeling, I'd rather settle on the hill. :)

We are flexible. That means: Large plot = No basement, but a large garage. Small plot = Basement. :)

By "the hill" do you mean the side that is a bit higher and further away from the creek?

Our personal favorite still lies directly by the creek. An alternative, right at the beginning and thus 6m higher.

But you wouldn’t generally rule out purchasing a plot there?

But you wouldn’t generally avoid purchasing a plot of land there, would you?

"The water levels measured towards the valley represent a closed, partly pressurized groundwater level in a low-permeability aquifer. During periods of heavy rainfall and after intense rain events, experience shows that waterlogging can occur on the low-permeability chalk marl or clay layers. [...] The infiltration of rainwater is not advisable due to the observed low permeability of the soils."

For me, that means you have water standing on the property for half the year. Then you have to wait nicely for the sun so the water disappears. A basement will be an expensive undertaking there.
You write "small stream." Is that still the case, for example, when there is snowmelt or it rains for 2 weeks straight? Many a small stream then becomes a rushing river.

At least take a look at the area when the sun isn’t shining and it has rained heavily.

For me, this means you have water standing on the property for half the year. Then you just wait nicely for the sun so that the water disappears. A basement would be an expensive undertaking there. You write "small brook." Is that still the case, for example, during snowmelt or if it rains for two weeks straight? Some brooks then become raging rivers. At least take a look at the area when the sun is not shining and it has rained well.

This is exactly how I read these passages as well. Whether this also applies to the properties? After all, the previous drillings were only carried out in the area of the roads to be developed. But it will certainly be similar there. A basement would then be out of the question, which would certainly still be bearable. Further surprises regarding house construction can certainly be minimized by a property-specific survey before purchase. But I would rather not have a pond on my lawn. Here too, some structural adjustments can probably be made. But I don’t even want to imagine the additional costs to be estimated for that.

Regarding the little brook, we are in contact with the municipality to find out how often and how much more water it carries.

So I would definitely keep a basement there. Otherwise, you have to really like the property for it to make sense. Unfortunately, more and more new housing developments are being built in questionable areas. Of course you can build there, but it will definitely cause additional costs and also occasionally cause problems with water infiltration (unless you actively do something about it here as well).