I can't dig so Husband and I had a flail around in some horse manure to get 2.5 barrow loads in the boot. Then he took it up to the plot and dug out of the contaminated dead bed; 4 barrow loads, that's 7 in total. He reckons there's another 10 to do. He thinks he's done 2/3s of the top level. He'll take out 2x spade depths. But it's claggy so it's pretty wet. When it's wet it's like grainy course poorly mixed cement but darker. It's not clay and the local survey says it's alluvial silt.
With narry a worm, beasty or anything alive in the lot. To quote him "Nothing has crawled away from me, nothing has squirmed, I'm sure there's bacteria but there's nothing I can see in that soil. it might as well be moon rock. Apart from the couch grass".