Folks, I can guarantee the landfill site is still there. Its just closed, not disappeared. Generally speaking landfills that have had municipal waste tipped in them will be around for decades after closure. They may look nice and green but the waste is still in there decaying over time and generating gas and leachate. What stage this site is at we can only guess. Hopefully the developers already know. Development adjacent to closed landfills can provide interesting technical issues, and inevitably, cost.
It will be down to the thoroughness of the site investigation, the robustness of the engineering solutions and the exact detail of the proposals. Not impossible, perhaps, but not easy. No surprises that getting planning consent could be the key issue.
...........and just maybe the fact that there was a colliery there before may have something to add to this.
But that nice Mr Osborne's going to get rid of these obstructive namby-pamby objections, so that will be OK.