# digging geothermal horizontal loops in high water table



## AustinDB (Sep 11, 2006)

anyone w/ experience digging horizontal loops in areas with high water tables? With recommended tench depths of 4'-6', the water table at a particular site is 18"-24".


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## rino1494 (Jan 31, 2006)

I've dug them before, 6ft deep, but never in a high water table. Sounds like you need to dig some holes and set up some pumps. Depending on how your ground is, it would be nice to start at the lowest spot and dig a deeper hole to pump from.


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## tgeb (Feb 9, 2006)

Rino nailed it, but you might need more than one pumping station depending on the water table and how long the trenches need to be.

It's best to de-water the site than try and work through water filled trenches. I would presume the piping would float if you have a trench filled w/water.

You could be in for some serious pump work, make sure to cover it in the contract.


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## AustinDB (Sep 11, 2006)

I've noticed at times when main sewer/water lines are going in the contrators have a major manifold with many horizontal feeders drilled down and all connected to a pump running for a long period of time before the excavation for the sewar/water pipe goes in....does this process drain down the water table for a short period of time and return after days/weeks?


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## tgeb (Feb 9, 2006)

http://en.wikipedia.org/wiki/Dewatering



> Construction dewatering, unwatering, or water control are common terms used to describe removal or draining groundwater or surface water from a riverbed, construction site, caisson, or mine shaft, by pumping or evaporation. On a construction site, this dewatering may be implemented before subsurface excavation for foundations, shoring, or cellar space to lower the water table. This frequently involves the use of submersible "dewatering" pumps, centrifugal ("trash") pumps, eductors, or application of vacuum to well points.


A quick read there will give you some insight as to the theory of dewatering. But I think you may already have an idea of how it works.



72chevy said:


> ......have a major manifold with many horizontal feeders drilled down and all connected to a pump running for a long period ....*does this process drain down the water table for a short period of time and return after days/weeks?*


The short answer is yes.


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## rino1494 (Jan 31, 2006)

72chevy4x4 said:


> I've noticed at times when main sewer/water lines are going in the contrators have a major manifold with many horizontal feeders drilled down and all connected to a pump running for a long period of time before the excavation for the sewar/water pipe goes in....does this process drain down the water table for a short period of time and return after days/weeks?


$$$$$$$$$$

Wherever you start, dig a hole about 4' deeper than your ditch. Take a piece of 8" pipe, or a 55 gallon drum and drill some holes in it. Stand it vertically in the hole and backfill with gravel. Stick your suction hose down in the pipe and now you have a sump pit to pump from. Try to start digging at your lowest elevation and work up hill, that way the water will flow to your sump pit. If the ground changes elevations, and you have to dig downhill, then like Tom said, you may need a couple sump pits to pump from.


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## Kgmz (Feb 9, 2007)

You can also buy slotted PVC pipe from your pipe supplier if they carry it or a well drilling supply.

And use clean crushed gravel, no fines or binder in a larger size or drain rock. Drain rock is the round rock they use in septic drain fields, etc.


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## playsinmud (Jan 25, 2008)

We do this all the time. Why bother pumping. Dig your trenches, get your pipes ready to put in (ie obviously no joints under water. Walk out your pipes, then fill them with water to sink them. It's easy but you'd like to do it on a warm day. This high water table is going to make an awesome heat transfer. How big of a job do you need to do. House? Shop? How Many tons? And where? Curious to see what you are doing. Just want geo done right so people doesn't say it doesn't work.


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## ConstSvcs (Nov 22, 2007)

It costs a bit more but go vertical (350'/tn) +/- grouted. All of my homes are vertical bore installs because of usual space restrictions.

Here is a typical dewatering setup we use to install footings, in this case for a car elevator in a lower level garage at a home near the shoreline. The bottom of footing was located @ -1' so a sump was created with a piece of 14' SDR35 covered with stone and fabric. Dewatered during the entire install.


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## playsinmud (Jan 25, 2008)

Vertical is a nice way to go when space is an issue. If you have a nice landscape yard directional is also a good option. we have two vertical drills and one horizontal. How many feet per ton are you guys putting in? and what size pipe?


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## AustinDB (Sep 11, 2006)

wow-a car elevator? I got a good chuckle out of that one....glad people are spending money on what they want!

Thanks for the info guys-very helpful indeed. 

I was thinking the same thing about the higher heat transfer in wet soil. undecided on size, probably 3.5t down/2t up-would love to have an extra run or two for radiant slab for future additions


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## ConstSvcs (Nov 22, 2007)

playsinmud said:


> Vertical is a nice way to go when space is an issue. If you have a nice landscape yard directional is also a good option. we have two vertical drills and one horizontal. How many feet per ton are you guys putting in? and what size pipe?


360'/tn with 1.25" loop Homes are tight.........R30.5 walls (med density foam w/2" r-10 exterior foam thermal break/rain screen/siding and R-57 ceilings. ERV, etc..............WaterFurnace Evision equipment. Noritz gas fired wall hung on-demand for back-up heat and hot water flow thru from desuperheater.

This space is tighter than normal so the geo vertical bores are installed under the house foundation (3 @ 400') = $17,000 



And now.........back to the OP's original question........dewatering


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