THE legacy of Kirklees' chemical and dye industries could be 4,000 dangerously polluted sites around the region.
Council figures show there are thousands of potentially contaminated areas which need cleaning up.
The council Cabinet has approved new policies for treating polluted land.
This means the council has a greater responsibility to check suspect areas and make them safe.
The issues were discussed at the latest meeting of the Overview and Scrutiny panel for the Environment
Huddersfield's wealth is founded on the textile, engineering, chemical and dyeing industries.
In the past - when safeguards were more lax - pollution was rife.
Now, there is a push to redress the balance, based on the principle `the polluter pays'.
If that person or company no longer exists, the bill could be passed to the current owner.
But ultimate responsibility falls to the council.
The Government wants 60% of all new housing to be built on brownfield sites - that is, those previously used by industry.
About a third of Kirklees brownfield sites are potentially contaminated areas or next to such sites.
Robert Crossland, the council's control manager, said there had been a doubling of applications from developers wanting to move on to brownfield sites over the past year, up from 70 in 2002/03 to a projected 145 by the end of this month.
He said that a lot of the current improvement of land was driven by commercial pressures.
"The test will come when we start looking at some sites where there isn't commercial pressure to redevelop them."
Mr Crossland said just a handful of the 4,000 potentially contaminated sites could be harmful.
But he added: "We have got to check and double-check all the sites, to make sure there is no risk of harm."