Roughly the same here but I don't know how far the blue clay goes. Mine was water from about 15 ft to 100 where I quit. I added dry sand then bentonite pellets near the top.
I think the saturated sand gives better heat transfer than dry and hope it will be better than thermal grout, maybe as much a 3/4 or 1 ton for the 100ft.
Since Scoupe in in solid rock and probably can't get anything thick down the hole, I thought water fill would be great for him
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