After serious thinking James Wilkinson Sword wrote :
On Thu, 05 Jan 2017 21:20:58 -0000, wrote:

On Thu, 05 Jan 2017 21:02:28 -0000, "James Wilkinson Sword"
wrote:

20 feet deep. How deep is the concrete in your floor? 6 inches?

The 20 feet is horizontal.

If it's not below the water table, no conduction.

All materials conduct, some better than others.