Basic questions about heat pump variants in new construction

We are planning to build a house in Carinthia/Austria with a gross floor area of approximately 180m² (evenly divided over two floors) and a heating energy demand of about 25 kWh/m²a. The plot has 890m² and is fairly flat. As a heat source, we plan to use a heat pump with underfloor heating and a central ventilation system (manufacturer of the ventilation system Zewotherm, it is actually an Austrian product and I work for the manufacturer in Austria). Heat pump hmm, Ochsner or Neura for a start. Possible variants would be surface collector (brine or direct evaporator) or deep drilling. Surface collector would be cheaper and also possible because the plot is large enough. But where I am stuck: There is seepage water about 1m below the surface, roughly at the frost line. The soil is otherwise rather sandy. Now the question is: Is the seepage water more of an advantage or disadvantage regarding surface collectors?? For groundwater heat pumps, it is unfortunately unusable. We inherited the plot from my mother-in-law and the existing house is a case for the bulldozer (built in 1947 with very basic means).