For some reason,
this area caught my attention. Is anyone more knowledgeable about that general are? East and South of PMK Recycling and Cemex Baston Fen Quarry and Concrete plant, there is a lot of wetland, for lack of a better word. There might be places where water is easy to access via the small roads. Some of it is probably a recreational area, like the farthest East end, but I suspect there might be plenty of murkier and more hidden or industrial parts.
No idea how likely a drive there would be, but this area stands out in the map and is in the "zone" one previous poster pointed out (though I understand that many people seem to think it more likely he deposited of the body East from Peterborough, not North, as the last trip all the way up to Spalding might have had different aims than disposal.
So zero basis for that suggestion, was just interested in the area, as it stood out on the map.