Clearing waste from plot

Hello,

I have an area at the top of my garden, around 40mx10m, which I want to use to grow vegetable and fruit.

When I moved in to the house a few years ago, the area had a large mound of garden waste, which we cleared away to reveal a mound of earth. The area became quite overgrown with mostly nettles and so I cleared and covered with landscape fabric a couple years ago.

Yesterday, I was looking forward to digging into my rich mound of earth, but I've been disappointed. In amongst the good stuff, I've found what looks like ash and/or building waste. Without going too deep I've also found bricks, rocks, an old bath tap, some metal rails for a machine, and a small slab of reenforced concrete!

My neighbour, who lived here for years says that all he's ever seen put there is garden waste, so he believes the junk is many years old.

My question is, do I remove the bricks and rubbish and then mix the ash-like stuff in to the soil, or do I remove the possibly contaminated soil and dispose of it?

Thanks.