Tim,
Where are you located?
I am building a house with geothermal in Arkansas. Initially I approached contractors about a horizontal loop system. No one wanted to install a horizontal loop. There is too much rock here. To dig my basement to 9' we used a 80,000 pound Komatsu PC300 which was able to dig as deep as 6' to 7' then we jack hammered out the rest. In open farm land it would be possible to use such an excavator to create horizontal loops.
Perhaps the ground is much softer where you are located?