I assume you mean the road that loops round the back of Hope Valley Cement works? I drive that road regularly on my way to Castleton for caving, and they have 'peeled' back the top soil to within 20m+ of the road. As you drive round it is obviously terraced where they blast and remove the stone, as far as I can work out the face is about 100m from the road.
However, that is close to the 390m AOD mark, and the factory is at about 200m AOD, so they have a working face of 500 to 700m long x 150 to 200m deep x 100m to road, so a conservative estimate is 7.5million cubic meters of stone, plus whatever is terraced down towards the factory.
Good for a few years yet methinks.
As for within 400m of Peak - dunno. I know there has been problems with paper waste seeping in via Dirtlow Rake, just to the W of the quarry, and I think it ends up somewhere around Ink Sump, which I suppose is the closest bit of Peak to Dirtlow and the quarry.