We did some online research and found out that the sludge-fields of the former sewage treatment plant in the north of Amsterdam, has been a toxic waste dump!
Read here more about what 'sludge' actually is
According to the earliest records it was a dump-site from the 1930s to the 1950s. After that the sewage treatment plant for industrial- and household water was built on top. This sewage treatment plant dumped it's sludge in a 'sludge lagoon' of approximately 100 by 100 meters with (probably) no protective lawyer at the bottom. The sewage treatment plant was closed in the 1990's, because it didn't comply with new & stricter standards
(the 'sludge lagoon' in 1957)
Below is a recent screenshot from the website of the official Amsterdam municipality office ODNZKG, which records pollution. The brown square in the middle is where the sludge-fields are. According to the 'legenda': the color brown color means polluted soil :
Below is the official map of the 4 raised patches of land on the sludge-fields, created by the municipality of Amsterdam, for future ADM residents:
According to municipal workers 50 centimeters of top soil was removed, then a plastic sheet was spread out and after that a 'new' mixed layer of soil and wood mulch, of 50 centimeters was put on top.
A top layer ('leeflaag' in Dutch) should at least be 100 centimeters thick, if people are to live on it, according to this official website of the Dutch government
We took one soil sample and had it analyzed by a specialized laboratory. They said that a wide variety of (light) pollutants was detected and that it looked like that contamination of the deeper layer had been mixed with the top layer. Further research is needed, we were advised to take at least 20 samples, but we don't have the money for this (Analyzing one sample costs around 700 euros)....