The U.S. Environmental Protection Agency has proposed regulating 222Rn in public drinking water. When implemented, the regulation will require periodic sampling to demonstrate compliance. The work reported in this paper was conducted to evaluate how reliably grab samples can be used to characterize the average 222Rn concentration in a groundwater source. Periodic samples were collected from 14 wells over sampling periods ranging from 2 to 26 mo. Samples were collected using a "slow-flow" collection method, and samples were analyzed using liquid scintillation techniques. The results reveal variation in 222Rn concentration over the study period; however, for the 1,468 samples collected from the 14 wells, approximately 97% of the measurement results were within 30% of the mean value for the well.
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