I don't want to comment about the water table and its affect on thermal properties. I just want to further comment on the nature of mechanical engineering. And, I'm not a mechanical engineer.
In typical HVAC design, the heat transfer occurs with air, which is considered an infinite, "Sink." The heat transfer does not affect the overall air temperature.
Below the ground it's different. The heat transfer makes a heated bulb, which is determined by various thermal properties. These thermal properties are influenced by all of the typical geo-variables, like soil type, soil density (void ratio), moisture content and expectations of temporal changes during the year.
I'm not a source for quantifying these variables. I just wanted to echo the thoughts about water AND all the other stuff.
I know it's frustrating that the geotechnical engineers have not really developed some generally accepted practice for geothermal studies.
f-d
ípapß gordo ainÆt no madre flaca!