Best way to repair a drilled well that leaks? Line it with PVC pipe and bentonite?

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NorthAtlantic

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How can I repair our water well? The steel casing has developed a leak, even though the well was drilled just 14 years ago. Repairing it will be expensive, but I need to fix it, because it is the source of drinking water for our home.

Recently we noticed grit, and sometimes mud, accumulating in our whole-house water-filter canister. To diagnose the cause, I bought an endoscopic camera on Amazon. Using that, I discovered a quarter-inch leak in the steel casing, at about 40 feet underground. See the attached photo. Through that leak, water is pouring into the well continually, even in dry weather.

Three solutions have been suggested to me:

1. Drill a new well. This would be expensive. Moreover, I would need to use a steel casing again, which would be just as vulnerable to corrosion and leaks. That’s because the local drillers don’t use PVC casings. I guess they don’t think PVC would stand up to the cold winters here. Alternatively, I could install a stainless-steel casing, but that would be prohibitively expensive.

OR

2. Replace the leaky casing with a new one, within the existing drilled hole. I'd like to do this, but it might be difficult to remove the existing casing. The steel casing goes down to 103 feet. In addition, there is some PVC casing that starts at 90 feet below ground, and goes down to 220 feet. Pulling all this out of the ground would be risky, because it might fall apart in the process. Then I would have to decommission the well, and drill an entirely new one. Even if the operation is successful, I would still end up with a steel casing again, which would be vulnerable to corrosion, and might eventually leak.

OR

3. Line the existing well. To do this, the drop pipe and pump would be removed first. Then, a PVC pipe and packer would be lowered into the well, inside the existing steel casing. The PVC pipe’s diameter would be narrow enough to get past the existing pitless adapter. Next, bentonite would be injected into the annular space between the PVC pipe and the steel casing. That would hopefully seal off any existing leaks. Finally, the existing submersible pump and the drop pipe would be lowered into the pvc pipe. I believe this procedure is known as “lining” the well. Please correct me if I am wrong.

Number three would likely be the cheapest solution. And I guess it would be effective, assuming that the Bentonite would make a water-tight seal with the existing steel casing. But I have two questions:

Question 1: The existing steel casing will inevitably continue to corrode. Eventually, a gap could form between the corroding steel casing and the bentonite. If so, then muddy water could travel down the inside of the steel pipe, and contaminate the water at the bottom of the well. Is this likely? Is there a solution?

Question 2: If the well ever needs to be decommissioned, how could that be done? Would the driller simply remove the pump, the drop pipe, and the pitless adapter, and then fill the pvc pipe with bentonite?

Are there any other drawbacks that I should be aware of?

Is there any other solution that I should consider?

Thanks.

For reference, here is more info about the well:

Pump type: Submersible
Steel Casing diameter: 6 inches.
Thickness of the steel casing: About 1/8 inch.
Steel Casing above ground: 2 ft
Steel Casing below ground: 103 ft
PVC pipe, 5 inch diameter, from 90 ft. to 220 ft
Drive Shoe Used? Yes
Overall Well Depth: 220 ft
Bedrock Level: 78 ft
Final Water Level (BTC) 51 ft


Driller's Log:
0ft 12ft Brown Overburden
12ft 40ft Brown Broken Sandstone
40ft 50ft Grey Clay and Gravel
50ft 60ft Grey Broken Sandstone
60ft 75ft Grey Clay and Sand
75ft 78ft Brown Clay and Shale
78ft 81ft Grey Sandstone
81ft 99ft Brown Clay and Stone
99ft 156ft Grey Sandstone
156ft 175ft Grey Clay and Shale
175ft 181ft Brown Clay and Shale
181ft 220ft Grey Sandstone
 

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Valveman

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The 5" PVC casing from 90' to 220' is what I would call a liner. Too bad they didn't just line it all the way to surface and seal between the 5" and 6" to 103'. Not much room between 5" and 6" casing to make seal though.

The local well driller may know how to do this. I think you would need to pull the liner, add 90' to the top. and set it back down. There maybe some kind of seal they could wrap around the 5" at 102' to keep cement and/or bentonite from passing, which could be used to make the seal needed.
 

NorthAtlantic

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Not much room between 5" and 6" casing to make seal though.
Could I use a 4-inch PVC pipe instead of a 5" PVC pipe? Would that leave enough space to inject the bentonite between the PVC pipe and the steel casing? Also, would a 4" PVC pipe be large enough in diameter to accommodate the submersible pump? Is there any risk that the pump might get stuck in the PVC pipe?

I think you would need to pull the liner, add 90' to the top. and set it back down. There maybe some kind of seal they could wrap around the 5" at 102' to keep cement and/or bentonite from passing, which could be used to make the seal needed.
Could I also replace the existing 5" PVC liner in the lower section with a 4-inch PVC pipe? In that case, all the PVC pipe would be 4-inches, starting near grade, and going all the way down to 220 feet below ground level. Would that help prevent the pump from getting stuck on the 4" pipe at 103 feet, next time it needs to be pulled out of the well?

Anyway, I guess the existing borehole would be too large for a 4" pipe in the lower section, below 103 feet. I mean, it is already wide enough for a 5" PVC pipe. Since it is too wide for a 4" pipe, I suppose higher water might move down the bore hole in the lower section, beside the PVC pipe, and potentially contaminate the water at the bottom of the well. Would there be any way to prevent that?
 
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Valveman

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While a normal 4" pump will fit in 4" casing, it is a tight fit. This can cause problems down the road. But at that depth you can use a 3" pump like the SQ, which should work fairly well. You should have enough room to install 4" casing to the bottom if the well doesn't cave it when pulling the 5", which is a real possibility. If it caves, it could probably be drilled back out. If there is enough annular space between the 4" casing and bore hole and/or 6" surface casing, you could gravel pack the lower section to well up into the 6" steel casing, which would keep the cement needed to seal off the hole in the steel casing from going any deeper. But you will need a good driller to go along with a plan like that. :)
 

NorthAtlantic

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Here’s what we ended up doing: The driller lined the well with a 4-inch PVC pipe down to 90 feet. That’s where the existing 5-inch liner starts. At the bottom of the new liner, he installed two shale traps. One would probably have been sufficient, but I requested two, to decrease the odds that any bentonite would leak past and get into our well water. Finally, the driller used bentonite to fill the annular space between the new PVC liner and the existing steel casing.

The top of the new 4-inch PVC liner is positioned just below the pitless adapter. That allows the drop pipe to go down inside the new PVC liner to the pump. The pump is hanging about 160 feet below ground level, inside the existing 5-inch PVC liner.

Before the repair work started, I raised one concern with the driller: The new 4-inch PVC liner would be only slightly wider in diameter than the pump. So next time the pump needed to be pulled out, it could get caught on the bottom edge of the new PVC liner.

To avoid this problem, the driller used a grinder to bevel the bottom inside of the new 4-inch PVC liner. I requested that to make it easier to pull up the pump in the future. In other words, the slight flaring effect of the bevel might help to funnel the pump into the 4-inch pipe, as the pump is being pulled up. Whether that actually helps, we'll find out next time we need to pull up the pump for replacement or repair.

Anyway, several days have passed since the work was completed, and our water has become clear again. So apparently, the repair was successful.

Thanks for your advice Valveman.
 
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