Radon emanation from NORM-contaminated pipe scale and soil at petroleum industry sites

Radon-222 emanation fractions were determined for barite scale deposits associated with petroleum production tubing and soil contaminated with naturally occurring radioactive material (NORM). Samples were analyzed for Ra-226 concentration, the results of which were used to calculate the Rn-222 emanation fraction for the sample. An important parameter determining the overall Rn activity Bur from a solid medium, Rn-222 emanation fraction represents the fraction of Rn-222 produced that enters the interconnected pore space within a medium contaminated with Ra-226 before the Rn-222 undergoes radioactive decay. The primary objective of the study was to determine whether Rn-222 emanation fractions from pipe scale and soil from petroleum production sites are similar to those of uranium mill tailings. Pipe scale samples were collected at four sites representing a wide geographical area, and consisted primarily of barite scale where Ra atoms have replaced a fraction of the Pa within the crystal lattice of the scale. Soil samples were collected at five sites, from areas exhibiting elevated surface gamma exposure rates indicating the presence of NORM. For comparison, Ra-226 concentrations and Rn-222 emanation fraction were also determined for uranium mill tailings samples provided from a site in Utah. Although Ra-226 concentrations from pipe scale samples were similar to those found in uranium mill tailings, Rn-222 emanation fractions from scale were generally lower. Emanation fractions from each data set were statistically different from those of mill tailings (p less than or equal to 0.01). The differences are probably due to physical differences between the two media and to the method by which the Ra is deposited in the material. Radon emanation from soils was extremely variable owing not only to differences in physical and chemical soil properties, but also to the means by which NORM has entered the soil. Although additional emanation measurements from other sites are needed, the data collected at these sites indicate that regulations intended to protect human health from Rn-222 inhalation should consider the type and properties of the medium in which the NORM is contained, rather than relying strictly on concentrations of the parent Ra-226. (C) 2001 Elsevier Science Ltd. All rights reserved.