The Technical Team concluded that FLDOH 226Ra results were slightly lower than the NAREL results due to the use of too low an intensity (3.28% vs. 3.59%) for the 186.2 keV photopeak, and that the NAREL 234Th results were slightly higher due to the use of too high an intensity (5.6% vs. 4.25%) for the 63.3 keV photopeak. Although these differences proportionally change the reported results, both approaches support the Technical Team conclusions.
As discussed in the EPA report, the Technical Team noted that for 8 samples there was interlaboratory variability. Those were for 226Ra (#44), 40K (#42 and
, 232Th/228Ra (38, 41, 48, and 52), and 238U/234Th (#45). After considering the standard errors and differences in intensity values used, the Technical Team conclusion was that the differences were likely due to non-homogeneous samples (either as non-uniform distribution of sample material in the container or non- uniform distribution of radioactivity within the sample) and secondarily to differences between sample geometries. Homogenizing the samples and spacing the samples farther from the detector, or at equal distances, may reduce interlaboratory variability.
The Technical Team conducted a comparison of the 7 imported, 13 domestic, and 1 of unknown origin samples. The Technical Team noted that four samples contained levels of radioactive material that were at the upper end of the range of
226 40 the other samples. One was of imported origin (#53 for domestic origin (#42 for 226Ra and 238U/234Th, #46 for Ra). Three were of K and 228Ra, and #48 for
The Technical Team concurs with the conclusions of the EPA NAREL, July 31, 2009 report: Specifically,
Within the limited sample of drywall assayed, there were no elevated levels of
The 226Ra content measured in these samples were generally more than a factor of 10 lower than those found in phosphogypsum (10 to 35 pCi/g)(see Appendix 2, Table 3), and comparable to levels found in other commonly used building materials including brick and concrete (see Appendix 2, Tables 1 and 2).
The EPA assessment confirms FLDOH measurements which demonstrate that these drywall samples contain only background concentrations of naturally- occurring radionuclides (see Appendix 2, Table 1).
2. Based on the above, the Technical Team concludes that: the reported concentrations were typical of background soil but not of phosphogypsum as reported by Rajkovic