When Dad and I arrived mid-morning on Friday, the crew from Yoder Geothermal was already hard at work. It all started with a suggestion from an unknown source that the pond might make a great thermal resource for a geothermal heat pump for the cabin. One of many long story shorts, one year later finds yet another Yoder on our building site, drilling four holes, each four inches across, and about 160 feet deep.
A four inch shaft doesn’t represent a huge amount of material, but it took a surprising form, being much darker than expected from our experience with the golden sandstone which litters the eastern half of the Hollow.
Ours will be a closed loop system that consists of four loops of High-density polyethylene pipe, each extending 160 feet deep, that will contain a mixture of anti-freeze and water, circulating it beneath the frost line and bringing into a heat exchanger in the cabin’s utility room. The Yoder crew created each loop from two lengths of polyethylene pipe, connected together with a pair of right-angles.

A length of rebar was taped to the base of the pipe loop to provide some weight to facilitate dropping it into the well, and keeping it their during the grouting process.
After completing the shaft and moving the drilling rig out of the way, the crew carefully lowered each of the polyethylene loops into the holes.
Once the pipe loop was installed, the crew grouted the hole using two different forms of Bentonite clay. The primary form was a slurry, mixed with water and then pumped using a machine called a Well Grouter.
A large hose from the grouter was unrolled and then placed in the top of the shaft.
After a couple of minutes of pumping the Bentonite and water slurry into the first shaft, the crew started shaking their heads and discussing the situation at the bottom of the well. The lowered a plumb bob at the end of a measuring tape, which lead to more shaking of heads and muttering. The crew chief explained that there must be cracks in the rocks that kept the grout from filling up the hole. The fact that the ground leaks comes as no surprise to any of the Heisers, but apparently it leaked more than the Yoders expected.
At this point, they starting pouring a pebble-sized form of Bentonite, with the trade name ‘Hole Plug’ into the shaft. Although they expressed disappointment at the amount of Hole Plug that was required, and the level of effort it took to seal the shafts, they ultimately seemed to find their work satisfactory, because they continued drilling the rest of the wells. By the time Dad and I left, they had drilled three of the four holes, and another pair of trucks arrived with another tank of water and a lot more Hole Plug. (We also had a visit from an alarm company, which made it a 6-truck day.)
The drilling crew is only responsible for putting the pipe loops into the ground. A different crew will put a trench to the back of the foundation, and bring the four pipe loops into the utility room, where they will be plumbed into a heat exchanger. As of last week, the heat pump was still missing in action. What is normally a 1-week lead time had stretched to a cabin-delaying 6 weeks, although Bosch promised Berlin Heating and Cooling that the unit shipped from Florida on December 23.

[If you want to see all the entries for the cabin building project, they start here. The next Building the Cabin entry is Masonic Order.]