Planning a DIY IG - Looking for High Water Table Solutions

[cavediver]

Hi Group,

Our family is in the planning stages of a DIY IG 18x36 with an 8' deep end for the end of this summer. I'm targeting the end of the summer because I think I will end up dealing with a water table issue and I'm hoping that the dry summer will work in my favor. I have been monitoring the water table, and find that it's at about the 6-7' mark from finished grade. I "water drilled" a 12' piece of 1.5" ABS pipe vertically into the ground using a garden hose and fittings, then I can check the level with a fishing float and some string. For what it's worth I'm going to be working in soil that appears to have a high sand content.

I've been searching this site (awesome), Google, and YouTube for information of dealing with this issue during the installation of the pool and haven't really found any information that puts my mind at rest... I think I have a couple of viable options, and am asking for suggestions from those with some experience. Here's my list of ideas at the moment:

1.) Overdig the hopper and add a sump - This appears to be the most common solution. Basically overdigging the sump, adding a bucket with lots of holes (basic strainer), gravel to relevel to working height, and a suction line 12" or so below finished grade of the hopper bottom.
Q1.1) What type of pump would be attached to the suction side of this pipe? A self priming trash pump would make sense, but how would you maintain the prime and prevent the pump from running dry once the water is lowered? Any suggestions on a pump? I'm guessing the pump would need to run almost continuously during the build of the pool which might take a month of evenings and weekends (still gotta work)!?


2.) Same Idea as with #1, but installing a sacrificial sump pump. This is possibly a cheap temporarily solution - but I see lots of pitfalls that I'd like to stay away from (premature failure, future service requirements perhaps after a couple of years of inactivity, etc...)

3.) Large Sump - I was thinking of finding a 12-14" piece of pipe (culvert perhaps), and burying it vertically beside the pool, then somehow digging a drainage trench from the gravel in the bottom of the hopper, to the "sump". Then I could add a servicable sumppump which could be pulled and plugged in as needed. I envision a 18" patio stone as a cap, and then interlocking pavers around the pool covering it over until needed.
Q3.1) I can see the installation of this concept being a PITA to excavate, but really effective once installed.

4.) Dewatering - I know I can use the "well boring" idea that I used to sink the 1.5" ABS pipe (for my DIY ground-water meter) into the area around the planned dig site. I think I could use this technique to do say 4-6 of them around the overdig, then add some type of foot valve, or screen, or something to the bottoms. Then I could connect them together, and use some type of self priming pump to temporarily lower the water level. Once this was in place it would be easy to add idea#1 to the hopper for future requirements.
Q4.1) Same as Q1.1 really - What type of pump, and what prevents it from burning out once the water level is lowered to the point where the suction starts to possibly pull air break the prime?

5.) - I'd love to hear more ideas!

If you've made it this far, thanks for taking the time to read my ramblings
Many thanks to those who have previously posted information about their installations - the information has been invaluable!
John

 

[Bama Rambler]

Re: Planning a DIY IG - Looking for High Water Table Solutio

If it's sandy soil I'd consider #3. I don't even think you'd need to dig a trench under the hopper. Set a sump pump in it and start it pumping and it'll drain the water from the surrounding soil.

 

[cavediver]

Re: Planning a DIY IG - Looking for High Water Table Solutio

Thanks Dave,
I agree that #3 would probably be the easiest solution after it is installed, and yes, being sandy soil it's likely not going to require drainage between the hopper bottom and "the sump" (good point). But I am concerned with the difficulty of installing a 12-14" pipe 10' below grade in wet conditions - I know the hyrdo truck truck has a huge auger - but that's a little more than I might be able to get my hands on Mostly I'm concerned about destabilizing the existing soil near the wall of the hopper that I would now be excavating both sides of...

I'm kinda leaning towards the #4 idea, I drilled my water gauge using this idea http://www.drillyourownwell.com and think it would be easy to install 4 1" pipes in four corners of the overdig area directly outside of the hopper... they could be joined together and permanently left in position with one line running to the pad for evacuation of the ground water. These would basically lie beside my return plumbing - Thoughts?

If I do go this route, the question remains about selecting a pump for this application (Q1.1). I'm assuming that any self priming well pump would work until the point when the highest well point starts to suck air, the the prime would be lost. Are there pool pumps (or well pumps?) that are designed to be run dry for any length of time? I'm assuming it would "reprime" for a few minutes once the level re-established itself, but is this enough to cool an impeller? What about sand/dirt - Does this have to be a trash pump too??
Any comments would be appreciated!

 

[schirico]

Re: Planning a DIY IG - Looking for High Water Table Solutio

I'm not an expert here, but I had a inground put in last year at the bottom of a hill and we have a very high water table. How high you ask? well here is a comment from a neighbor we met a few months after we moved in 2 years ago

"oh you bought THAT house? Wet property! I remember one year water coming in the back door, running through the house, and out the front...that poor family!!!"

it was true! Our basement was wet (2 sump pumps) every time it rained.

The grown up children of the family that used to live in our house told us stories of how they used to ice skate when it ponded and froze in the back.

Stubborn me went ahead and had the pool built anway!!!

1. the builder put in a sump under the hopper as in #1 in your description and used a sacrificial pump (it was a pool pump!!!) all during construction to keep water out and maintain the form.....this was covered in gravel and eventually a concrete flooring (and sides) put on top of that, then the vermiculte base and (padding on the sides) then the vinyl liner...this sump has a pipe coming out the ground near the filter which I can then hook up any pump that can take a 2" connection if I ever get water under the pool in the future (and the liner rises). My builder did most of this at no extra charge, to protect their warranty.

2. my patio construction company - concerned about their warranty and the newly laid material to backfill the pool built a curtain drain the length of the pool (little longer actually) that feeds into a drainage pipe and eventually a dry well about 75 feet away, the drywell then empty's to a lower area another 200 feet away with a separate pipe - anyway if I remember correctly this is a 4 foot deep, 1 foot wide trench filled with stones and the drainage pipe which connects to an already established drainage system (to the drywell) - intent is to keep the deluge of water that comes down the hilll in winter and spring away from patio and pool and divert it.

so far so good, we've had tons (I mean TONS) of rain and the basement is bone dry, patio hasn't sunk yet, and the liner hasn't risen - again it was built late last year, and we just opened up pool for business, but patio has been used since March.

good luck to you (and to me too for that matter!).