, had a rummage around the site today, the left hand shaft (by roundabout) is probably under a 20ft earth embankment. The rest of the "field" looks very much like it has been covered with at least top soil in recent years judging from soil quality and age and types of plants. Possibly when they levelled Tesco car park. It is much more overgrown in places than I thought, the area by the roundabout is just about inaccessible, the area around the right hand shaft needs quite a bit of flattening, perhaps late Autumn I might go with a probing rod. I strongly suspect under the top soil will be a layer of waste (rubble etc) of some sorts.
It sprung to mind as to what happened to Conway Park Station debris when they dug that out?
I took a couple of photos but they don't show anything so haven't bothered putting them up.
I've put the spade away, back to map searching, it was a nice hour out in the open anyway.