A typical ground freezing system for a shaft or tunnel consists of a series of freeze pipes installed along the perimeter of the proposed excavation, extending into the subsurface strata. To freeze an area, freeze pipes are installed in a grid pattern and extend into the subsurface strata.
Typically, calcium chloride (brine) is used as the cooling medium and is chilled by one or more electrically-powered mobile refrigeration units. The cold brine (at -30 to -25°C) is pumped from the refrigeration unit though a distribution manifold to each freeze pipe. The manifold has supply and return lines. Larger ground freeze systems often require a reverse return manifold line. Chilled brine flows down a pipe inserted within each freeze pipe and then flows back to the surface in the annulus created by the downpipe and the freeze pipe. As the warmer brine returns from the freeze pipes, it flows into the return manifold which permits flow back to the refrigeration plant. As the refrigerated brine is circulated through individual freeze pipes, frozen cylinders begin to form. After approximately six to eight weeks, the cylinders merge together, forming a massive frozen earth wall.
Seems like a lot of trouble to explore an old garbage pit. When you bury treasure, you do so with the idea of retrieving it later, not making it impossible to get to again. It is a "money pit", but not in the good way.