This is wood blocking that really shows no signs of compression after 3 years holding 45,000 gallons of diesel fuel.
The weather has curled the edges up a bit, but it's fine.
They are sitting on top of swamp mats, which are sitting on muskeg. Even the mats have hardly any deflection in them.
Each of the 4 corners of all these tanks look like the above photo. They are all 100 barrel tanks.
I know this thread is beat to death. But just for future reference.