CONTROLS ON GROUNDWATER RN-222 CONCENTRATIONS IN FRACTURED ROCK

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. Copyright 1990 by the American Geophysical Union.