The Tardein wastes are several areas, or one area somewhere close to Caldeum. It's mentioned by Abd al-Hazir on his travels, and hosts Dune Thresher.
Franklin Burroughs is used to handle these threshers, and is well familiar with the wastes.
It's unknown if the 'Tardein wastes' is the full name of this (these) area(s), or if the 'wastes' are part of the Tardein region/location. More information will hopefully be made available soon.