Basically, you dig the soil out. In Ottawa, we have very little top soil. It is mostly clay. That is heavy, but not insanely so. It is dense, but not rock. So, by meter 2, you have reached the rock. That gets trucked and off to plants for cleaning. That cleaning is a series of washes and then bacteria to eat away at stuff in there. Not a big deal.
Arenas need a solid 10-20 M deep holes. You are digging serious rock. But now you may be below the water line. Think what is 200 M north and is about 10 M below grade. So, you have to have pumps working 24/7 and evacuating the water, not back to the river, but to holding tanks, which then get emptied at the cleaning plants. Can you imagine a few thousand Liters a day. Now, If I am wrong and this can easily be checked. If the river is deeper down, at say 20 M.. No real issues. You evacuate the 2 M of earth/clay. And no real issue with soil remediation.
Digging out 18 M of rock and hauling that????? Wahhhhh
So, they pass it off as toxic and get the Feds to pony up as 'environmental'...
If a combo of rock and clay/soil....OOOH WAH...
Has anyone seen the geo report?