Roots UNDER pool liner, how?

Hi, I am new here after finding this forum in search, I have had my 24 foot above ground pool for a little over 2 years now....I recently switched from Baquacil to Chlorine after being unable to treat algae, I read through this forum and knew I needed to make the change, happy ever since. I even changed my sand and it was so green and glumped up.

I see the impression of small tree roots under my liner, early this season was the first I noticed it. I have 2 fairly large maple trees about 10 feet on either side of the pool, but there wouldn't be any place else in my yard for it. Because of that, the builder graded the land and busted the little roots with the Bobcat. Then once the area was clear, he suggested I have 25 tons of gravel delivered to place under the pool to discourage the roots from affecting the pool.....so I did, then they placed a Winter cover over that, and the sand over that. Then came the pool. I tried to trace the pattern of the root to the outside of the pool, so I dug with a shovel and was going to sever that root.....I never found one. It appears to be a small root and the liner seems ok now, but am worried.....any preventives? None of this makes sense, with that much gravel and nothing I can dig and find, right near where the impression of the root is in the liner. :( I appreciate any help.

membership updated.

Is the impression raised, or depressed?

If it's depressed, it may simply be a case of the severed root rotting away, which shouldn't be a problem.

Hello, it is raised, I am baffled how this is even possible given the precautions that we're taken before installation.