How Level is Level

I am building an above-ground pool kit and have read endless posts and watched YouTube videos about levelling. Here is my question. I am at the dirt-digging stage, I know sand comes later but I am not there yet.

OK, I understand why it is supremely important that the pool walls be as level as possible.

But if I have a dip of, say, an inch or two x a couple of square feet in the middle of the pool ... what does it really matter? Especially given some pools actually have "deep ends" with tons of water in what is really just a very large "dip in the middle of the pool".

These dips will of course disappear when I put sand down but I know the sand may compress over time and eventually the pool bottom may be a bit bumpy. I am OK with that as long as it's all safe.

I am a bit of a perfectionist, but levelling within more than an inch or two x 300 square feet of dirt that is full of rocks is VERY difficult! Any advice greatly appreciated!

It may be difficult, but level means level. Having an area 'dish' in the center a few inches won't matter. But the sides are altogether different: level means level!

You have to keep in mind that your pool is a 'water level' -- that is the pool surface when still will be completely level to within a 1/16" (or 2 mm if you prefer). If your sides are out of level 2", the pool *might* work, but if your skimmer is on that side, keeping the water up into the skimmer throat is likely to mean it will slosh out on the low side!

Commercial gutter pools are supposed to be level within 1/16", regardless of size. I currently service a 200,000 gallon pool that is 4" out of level across a 90' distance, and it causes no end of problems that I have to dance around. Unfortunately, the original project engineers ignored the soil tests that indicated the pool need to be built on piers that extended 20' down to non-plastic soil. The customer had to spend $30,000+ in temporary repairs 4 years ago; they are planning to replace the pool in 2015 at a cost of $1,000,000+

You might consider using imported material to level before bringing in your sand. In most places you can get recycled crushed concrete that is pretty easy to spread and level. A little compactation and it will be smooth and hard. If you cant get that, Lowes or Home Depot sells paver base that will work as well.

1. It's a week later and a couple of days ago I came across an enormous boulder that I had to dig out, leaving a 2 FOOT deep crater near one edge of my pool site. "Digging down" is really not practical, even if I did, I would surely just keep finding more of them. So I am thinking I should fill this with sand and tamp the **** out of it. Any other advice? Would paver base or crushed limestone be worth the trouble?

2. Suppose I finish this off eventually (maybe in 2016 at the rate I'm going) and after filling it and letting it sit for a while, it becomes 1" - 2" out of level. Is it practical to take out all the water and liner and re-level? Of course this would be a solid weekend worth of work, but I'm wondering if these pools are designed to be taken apart and put back together again.

Thanks all and always!

Sand has a nasty habit of moving - I wouldn't recommend it. What I'd use -- if you can get it -- is what the limestone quarries here (limestone areas of N. Georgia and middle Tennessee) call "crusher run". It's mix of particles from fines up to sharp 1/2" stones, and compacts well.

Out of level (depressed) in the MIDDLE of the pool by 1 - 2" is not an issue. The issue is side to side.

Doc's right about the type of material you need or recycled crushed concrete is cheap if you can get it. One ton will cover 100 sq.ft. 2 inches deep. Moisten the ground a couple inches deep and tamp it first, then add about 3 inches of material, moisten and tamp. Repeat till level. If you could get a vibrating plate compacter (usually can rent them) that would be better. Work in layers and your base will be as hard as concrete. You could compact all around the perimeter as above (moisten then compact). It sounds like it's worth a little extra effort to prep under the sides. Not sure about taking it apart - I'd try to get it right the first time. Vancouver, BC? Should be highly compactable soils.