Consequences of legacy contamination on property

The plot is listed as a contaminated site "..." in the soil protection and contaminated sites register and is rated with action requirement "B" (leave as is - re-evaluation in case of change of use).

There is no contaminated site within the meaning of the Federal Soil Protection Act. Based on the current use and state of knowledge, there is no further action required.

In case of structural changes on the plot, disposal-relevant soil contamination must be expected. Unsealing measures (dismantling of buildings or other sealed surfaces) or changes to more sensitive uses (e.g., from commercial area to residential area or children's playground) require approval by the district office. The respective threshold values of the Federal Soil Protection Ordinance must be complied with. Construction projects and investigation measures must be coordinated with the district office at an early stage.

The property is developed with a house from around 1950 which would be demolished and replaced by a new single-family house.

There is no contamination within the meaning of the Federal Soil Protection Act. Based on the current use, there is no further need for action according to current knowledge. In case of structural changes on the property, contamination of the subsoil relevant for disposal must be expected. Unsealing measures (dismantling of buildings or other paved areas) or changes of use towards more sensitive uses (e.g. commercial area to residential area or children’s play area) require approval from the district office. The respective threshold values of the Federal Soil Protection Ordinance must be observed. Construction projects and investigative measures must be coordinated with the district office at an early stage. [...] In the attached excerpt, the cause is given as a "waste disposal site" from 1935 to 1949.

Is a soil survey before purchase advisable, unnecessary, or even insufficient?

Even the youngest of the three (with the gable roof, seen from the garden side on the right) is probably quite a bit older.

I would take that statement relatively calmly. You are planning "only" a new single-family house. Just include a €10-20k buffer. That's how I would do it. Otherwise, follow up on old reports and/or have a soil / groundwater analysis carried out.

Would it still be possible to differentiate which part of the information and assessment contributes to the "take it easy" and which to the "T€ 10-20 as a buffer"?