Approximately 150 Rn-222 analyses from groundwater wells in fractured lithologies of eastern Connecticut were made to evaluate the intralithologic and interlithologic variability. Although there is a control of Rn-222 activity in porefluids by uranium (radium) concentration in the host rock, the variability of local Rn-222 is dominated by site-specific rock properties. These are (with their contribution to the variability); (i) the specific fracture surface area (>103x), which is functionally dependent on crack width, (ii) the emission efficiency (<102x) which is functionally related to the fracture spacing and (iii) the enrichment of uranium (Ra-226) on the fracture surface (<102x). Thus, the activity of radon in fractured lithologies is difficult to predict and the measurement of radon activity does not uniquely constrain the geometry of the rock or the chemical inhomogeneity.