Welcome to the Forum, Beth!

Ben's got the right idea. You've got a ground or surface water problem (the 2 have similar results - i.e. pockets of water 'bubbling' the liner- but have different causes and fixes)

I'm gonna guess that you either live at the bottom of a hill and/ or have clay soil/ hardpan. Pics would help (a Google Earth shot of your property would be nice).

To fix the problem you may need to install curtain drains or a well point(s). Give us some more info and we'll help decide the best way to keep this from happening again. Do you know if they hit water when they installed the pool? (if so, the PB may already have a well point in place, but I imagine he would have mentioned that) I would really like to get a 'picture' of the topography of your yard.

Please help me help you by answering my questions