Inferring ground water flow in fractured rock from dissolved radon

Ground water radon concentrations have been measured in nested piezometers and an open borehole in fractured, metasedimentary aquifers in the Clare Va lley, South Australia. The vertical radon concentration profile within the undisturbed, open borehole appears to indicate the locations of hydraulical ly active fractures. If radon concentrations within the aquifer are uniform , then the highest radon concentration within the borehole will indicate th e location of the highest flow rate into the bare. In relatively short scre ened piezometers, radon concentrations have been measured both before and a fter purging. The ratio of radon concentration before to after purging norm alizes for variations in aquifer mineralogy, and can be used to quantify th e ground water flow rate.