Regarding the article by Provost et al. (Fractured Porous Media under Influence: The Roselend Experiment, Eos, 23 March 2004; pp. 113, 119), I have some comments concerning the interpretation of radon data and the instrumentation used for this purpose. In the first instance, it is obvious that the site presents a great number of advantages for studying the fluid transport phenomena in porous media, and I encourage the authors to continue in this investigation.
My first observation is concerning the radon data shown in the article.The authors show the data obtained in one station, using a Barasol® probe to measure radon in the air. The Barasol® probe was created initially to measure radon concentrations in the soil, and its precision is not the same as a probe like an AlphaGUARD®, for example. Moreover, the authors are aware of this limitation. It will be interesting to compare this data with that obtained with the AlphaGUARD®, or in the instrumented chamber described in the article that is 55 m from the tunnel entrance, named the Inner Room by the authors.