Interim Baseline Radiological Investigation Report
November 14, 2012
Bear Lodge Project, for Rare Element Resources, Ltd.
Rev.1
50
10.0 SUMMARY AND CONCLUSIONS
The baseline information presented in this report, coupled with environmental data collected
once the mine is operational, will be used as a basis to evaluate its potential environmental
impacts. The results of the baseline field investigation documented herein indicate the following:
•
Readings between <15 and 35 μR/hr occur in the majority of the Project (comprising
approximately 60 percent of the site area).
•
Elevated levels of radioactivity, characterized by gamma readings greater than 50,000
cpm and estimated exposure rates greater than 35 μR/hr, appear to be limited to the
vicinity of Bull Hill and Taylor Ridge.
•
The results based on soil sampling corroborate the findings discussed above regarding
spatial trends of radioactivity at the site. The majority of the site is characterized by
surface Ra-226 concentrations < 2.5 pCi/g, with a central tendency of 1.3 pCi/g. Areas in
the known mineralized areas of the site exhibit higher levels of radioactivity indicative of
natural influences. Broad areas of elevated Ra-226 concentrations (ranging up to 20.1
pCi/g based on prediction) do occur, coinciding with near surface expressions of ore.
Thorium decay series radionuclides; e.g., Ra-228, also contribute to the gamma emissions
observed at the Project.
•
The median of the predicted concentration (1.6 pCi/g) of Ra-226 is in good agreement
with the median of the laboratory results (1.3 pCi/g). This indicates that gamma surveys
are an effective tool to predict Ra-226 concentrations in soil at the Project.
•
Because applicable soil cleanup criteria are likely to be based both on Ra-226 and Ra-
228, both radionuclides should be considered in investigations conducted during
operation and closure of the Project.
•
Areas in the known mineralized areas of the Project exhibit higher levels of radioactivity
due to near surface expressions of naturally occurring radioactive material. Based on
these findings, derivation of a single number or level that is representative of background
conditions at the Project is probably not appropriate. The background condition of the
Project would best be represented by the distribution of the observed data.
•
The measured Rn-222 flux rates range from 0.94 to 11.11 pCi/m
2
-s within the footprint of
the Project. These values are below the NESHAPS requirement of 20 pCi/m
2
-s specified
in 10 CFR 40, Appendix A, Criterion 6. Although the requirement applies to uranium
mill tailings and thus is not directly germane to this characterization, it is useful as a
context to demonstrate the magnitude of baseline radon flux levels measured at the site.
