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Small Cabin Forum / Off-Grid Living / How deep to bury cistern tank?
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Missourihunter
Member
# Posted: 19 Nov 2020 22:29
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I will be building an off grid cabin this summer. I am planning on using approximately a 500 gallon underground poly tank. How deep do these need to be burried? This will be in mid Missouri. Does the top of the water storage area of the tank need to be below the frost line or can these be burried shallower and still not be damaged from freezing? The average maximum frost depth for here is 20 inches but I believe the reccomended depth for footings and foundations is 36 inches. Would I be okay burying this tank with the top at only 20 inches below grade? The shallower it is the better it will be for the pump setup I hope to use. What are your opinions on the depth it should be burried? Thank you for any help.

frankpaige
Member
# Posted: 20 Nov 2020 22:36
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36 inches, good luck.

ICC
Member
# Posted: 20 Nov 2020 22:52
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If it gets cold enough to freeze a layer of ice on the top of the water, that can be enough to stop being able to pump water from the tank even if the pump is submersed in the unfrozen bottom of the tank. The ice layer may prevent the entry of air needed to replace the pumped out water. I had that happen owith my first buried cistern.

I solved that by digging away the surface dirt and laying a double layer of foam insulation sheets horizontally over the tank and extending out three feet past the sides of the cistern. Then I replaced the earth over the foam. The heat from the earth was then sufficient to keep the water from freezing.

Aklogcabin
Member
# Posted: 21 Nov 2020 11:01
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Having rigid insulation panels helps with the freezing ground but also acts to shed water away. I you don’t use insulation or such. At a minimum use a layer or two of tar paper over the tank.
Slope it so water sheds out . Keeping moisture out of the frozen ground surrounding your tank will reduce frost jacking. If you are running your water line underground use insulation and or felt paper over the line. Good luck man

NorthRick
Member
# Posted: 21 Nov 2020 20:02
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Your tank will be fine at 20". However, the pipe supplying water out of the tank may freeze. I think if you had a some sort of drain-back feature to the system you would be ok. In other words, make it so the supply pipe is empty except when supplying water.

gcrank1
Member
# Posted: 23 Nov 2020 16:19
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500 gal., seems like a lot. The two of use get by on a 30gal. filtered rainbarrel for utility and rotate fresh potable into our inside 2gal. ss jug each trip. The biggest use is utility water but this whole last summer and now fall when I dumped it before freeze we never even used 5 gal. out of it any one trip.
I very much like the idea of not having a lot of stagnant water on hand to depend upon.

halfmarathondon
Member
# Posted: 24 Nov 2020 16:09 - Edited by: halfmarathondon
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Hey MOHunter, I'm in Dent Co. I used two 275 gal IBC totes (food grade) for my cistern. I buried them at 4' deep. Lined the sides with foundation plywood. I have an un-insulated plywood top covering it. I ran the water lines at 18" into the cabin. I use gravity to drain the lines back into the cistern when we are not out there. Going on our 3rd winter and never had an issue with freezing.
cistern6.jpg
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Missourihunter
Member
# Posted: 24 Nov 2020 22:40
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Halfmarathondon, that is very similar to what I am wanting to do. Where do you have your water pump? I was wanting to put mine inside the cabin for easy access and ease of draining. Also Also do you have any issues with the water going stagnant? I wanted to do a tank around 500 gallons so I only had to fill it up once or twice a year. I have a portable 500 gallon tank I would use to haul city water there with or haul water from our house and bleach it.

Missourihunter
Member
# Posted: 24 Nov 2020 22:50
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NorthRick
How long would it take for the water to go stagnant? I didn't think about that issue. I just assumed if the tank was sealed up and only used city water or water from my house treated with bleach that it would stay clean for a long period. The reason for the 500 gal tank is for hoping to only fill it up once or twice a year. We would be using it for washing deer out, shower, toilet, and sink and would have several people staying there for a few weeks during deer season. Would the water get nasty sitting other times of the year when not being used for long periods?

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