If the dirt is very hard, does it look more like hardened mud? Don't want to scare you, but read this to be sure. Please be careful! I truly hope it's not this.
Fascinating biology: Australian subterranean termites evolved more than 250 million year ago. They inhabited Australia long before flowering plants. Their survival success depends on living in a protective underground environment. In some species, their colony nest has a hardened shell, exposed above ground level. In most destructive species in NSW their nest is totally out of sight, below ground level.
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Worker termites build mud-tubes over hard objects. The tubes or "galleries" are made up of partly digested timber and mud excrete, and is moist if currently in active use. The termites keep it's colony nest and galleries at 25 to 35oC with high humidity. If they are exposed to light or open air they will dehydrate and die. Subterranean termites live in constant darkness, excepting for the annual summer swarms of the winged reproductives to set up new nests in the surrounding area.
FUMAPEST Newcastle Pest Control > Termites in Newcastle Hunter Valley Area > Termite Control methods