"Fault line" in IG Vinyl Liner Pool

[Sunny John]

All, hoping to get some suggestions on what is causing this and of course any ideas for correction.

We had these "fault lines" in our pool, one on the side, the other going from the hopper to the
bottom on the deep end (bought the house in the winter, when it was closed and covered) since
we've had it. Around 8 years ago, we replaced the liner with the work done by the original PB. They smoothed this
out, though I don't recall if they added any sand or not. The "fault" reappeared after a year or two and has gotten
progressively worse. The edges are rather sharp and and you can see in the photos, I've had to patch it (not all that
well) a couple times last year.

With the season and opening rapidly approaching I'm thinking it's time to replace the liner again...and to try to fix the underlying cause once and for all. I've thought about washouts or something like that under the pool but wouldn't have
any idea how to fix it.

Thanks for any thoughts and ideas.

 

[waste]

I'm thinking that the 'fault lines' are being caused by surface water (snow melt and heavy rains). Is the pool on or at the bottom of a hill? You might want to install a curtain drain to divert the water away from the pool.

Another obvious answer is to vermiculite the floor (sand and cement is also used but it's more abrasive to the liner and water doesn't pass through as well) - however :!: if the problem is surface water, as I suspect, without the curtain drain the cement will wash out of the vermiculite (perhaps in as few as 2 seasons) or the liner may repeatedly float.

Unfortunately, doing the fix as I suggest will cost $$$$

 

[Sunny John]

Thanks Ted. Pictures posted...

In the picture with my shadow on the pool I am looking to the deep end. There is a hill, however, the hill
really goes up from side of the pool without the problem - the side with the problem is farther away from the
bottom of the hill, if that makes sense. I'd think if it was surface water the other side of the pool would be affected.
I run downspouts through 4" flexible pipe (buried) so that it drains away from the pool, so I'm at least trying to divert
some of the water...

Somewhat adjacent to the pool is a sand mound with piping. Not sure how to determine if there are problems because of that -
I'd think I'd see the fault lines along the shallow end as well.

Assuming I get the liner replaced what should I be looking for when the old one is removed?