A number of studies have been performed in earth media ranging from slightly fractured granite to a highly-fractured tuff. General objectives of these studies were to: measure quantitatively tracer-gas flow through a region of interest to evaluate flow communication; determine the permeability and its distribution within this region; determine the accessible porosity and its distribution within the region of interest; assess qualitatively the uniformity of localized fracturing within the region of interest; evaluate the pressurization, leak and recovery characteristics of the region under study.