When I had my home built 8 years ago, I installed a geothermal heating/
cooling system. It is a vertical system with 3 wells although I am
unsure which are supply and which are return wells. I have had no
problem with the system itself but several years ago, I noticed a
sinkhole about a yard wide in the middle of my lawn. At first, I
didn't associate it with the geothermal system, but later I noticed
two other sinkholes at about where I believe the other two wells were.
In addition, the ground has sunk between the 3 wells and leading up to
the house. I have little doubt this is related to the geothermal
system but have no idea what is causing this. Is this a common problem
with geothermal systems and what can I do about it?
That Phenomenon is called the *China Syndrome*! Quite common in cracked
Nuclear reactors and piss poor installed Geothermal Units. There is a
bright side though. Many survived Chernobyl with only slightly massive
Sounds like your house is about 2-3000sf, if sized for cooling...if your
in Northern climes & it was sized for full heating then your 1500-1800sf.
The 3 vertical boreholes are probably vertical closed loops & I'd bet the
bores drove through an open cave, or a soft stone or peat layer.
I'd also bet your contractor didn't use a decent bentonite grout or even a
reasonable sludge pumped down the hole (via trembe tube) after the loops
were inserted. This grout/sludge insures the holes are sealed from surface
water drainage down & water swaps between the water tables a typical
vertical loops typically penetrate.
Here in MN we're not allowed to use vertical bore wells w/o bentonite
grout sealing the loops. I've got a 268' well for domestic & pump & dump
geothermal. when installed, I was told we shot through 5 or 6 different
water tables. The Grout keeps the rusty iron laden 35' water table from
contaminating the various lower water tables. We're also not allowed to
return the pumped water into a return well.
ECOLAB was fined a big chunk a while back for reinjection wells in it's
downtown St.Paul office building. We take fresh water pretty serious here in
the land of 10,000 lakes.
I'd bet your sinkholes are from the collapse of soft soil or cave layers
down below, or surface drainage washing down the tubes & dragging the slurry
to the bottom. In either case the install is suspect, but a few yards of
surface soil & grass seed should cure the problem. Although it may take a
generation or two to fully seal, when it finally stops, be assured your
loops will has a good a thermal transfer as is possible.
If your system is keeping your house comfortable, I'd have a couple
truckloads of soil spread about & live w/it.
If it's not working, call your installer...
Of course I might be mistaken.
Thanks for the intelligent reply. The house is about 1760 sq. ft. with
a 1200 sq ft basement. The system itself is working fine. The supply
and return pipes enter the house about 4-5 feet below grade. Since
this home was built about an hour from my previous home, I was not
present when the wells were drilled, but having seen the ground after
they were covered over, it appeared to me that they dug a trench
diagonally from the front of the house to connect to the row of wells
about 25 feet from the house. Another trench connected the 3 wells. It
is along these two trenches that ground is sinking. I can understand
why the ground might be sinking around the head of the wells, but why
would it be sinking along these horizontal trenches. At the wells the
sink holes are about 2 feet wide and 1 to 2 feet deep. Along the
trenches ground has sunk about 6 to 12 inches. Grass already covers
the are of the sinking. If it is just a matter of bringing in some
dirt to level the ground, I'm OK with that but if this problem is
going to persist, I need to find a more permanent sollution. One idea
I had is to dig out the trenches again and put a layer of concrete
several feet below the turf but if the soil is going to continue to
sink beneath it, is that really going to fix the problem.
I'd buy a few loads of dirt before I started laying concrete.
You can get a lot of topsoil & spread it around for the cost of the
excavating & concrete work.
Concrete may cure the problem, but it may also get in the way of a future
fix... though I doubt it.
If the system is operating properly & the space is comfortable, it's a "wait
& see" thing.
I'd monitor the water levels & make sure there aren't any leaks, call the
local dirt digger & spread some grass seed.
If I have to do it again is 5-6 years, sobeit...
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