Experts are carrying out tests at a site where rubble from Second World War bombing raids was dumped, to see if it is safe to build homes on the land.
Investigations are under way to establish the scale of contamination on a 10.5 acre site, off Mile Cross Road, where City Hall leaders want to build 200 council houses.
Norwich City Council agreed two years ago that it wanted to redevelop the site, which used to be the Mile Cross Business Centre.
Before that, it was the council's City Works depot, where City Hall's fleet of vehicles were based.
The buildings on the site were demolished in 2019, but the land needs to be checked to establish the scale of contamination.
The council says that is important work as the site was used to dispose of rubble after buildings in the city were bombed during the Baedeker Raids of 1942.
A council spokeswoman said: "Examination of the land has included recent work to dig trial pits which will help determine the scale and type of contamination in the ground.
"It also provides information about the ground conditions to help develop the next stages of engineering tasks."
The work was carried out by Attleborough-based Anglian Demolition.
The company excavated four trial pits, removing the materials inside and leaving the excavated ground materials beside each pit.
A trommel - a perforated, cylindrical, drum which sorts material - was used to separate what was dug up.
The next stage will see contaminated groundwater treated by removing the pollutants or converting them into harmless products.
Plans would then be lodged for up to 200 homes, which would be available to rent for people on City Hall's council housing waiting list.
Previous investigations found chemical contaminants such as asbestos, along with low levels of ground gas.
The council received almost £1m from the government to help pay for decontamination works.
In November 2018, the council revealed it was considering whether a new swimming pool could form part of the proposals for the site.
The council wanted to explore whether money generated by the new homes could allow the construction of the leisure facility.
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