Drainage System Lid Came Off On Its Own

[CA2241]

Hello, I noticed recently that one of the lids in my septic tank drainage system has came loose. There is a pvc pipe coming up the tube from the ground that seems to have been pushed upwards, causing the lid to pop off. When I push down on the pvc pipe, it won't budge and I'm unable to resecure the lid. There are two other identical tubes with lids to the right and left of this one and they don't have this issue. The tube which has the issue is in the middle of the others and there are 3 total.

Does anyone know what may have caused this and if its an issue to be concerned about? Any ways that I can fix this myself and avoid the bill from having someone come out to my property to take a look at it?

Thank you!

 

[breplum]

the green cap is part of a NDS round 'valve box' .
you can dig it out/loosen it and raise it up. They are tapered, so not easy to just lift