Interim Baseline Radiological Investigation Report
November 14, 2012
Bear Lodge Project, for Rare Element Resources, Inc.
Rev.1
17
4.0
BASELINE RADIOLOGICAL INVESTIGATION SOIL SAMPLING
This section presents the results of the baseline soil sampling conducted in August 2011. Sample
types included random and biased samples. Section 4.1 summarizes the soil sampling field
approach, scope, and analytical methods. Section 4.2 discusses the results obtained for Ra-226,
the focus of the baseline soil sampling program. Section 4.3 addresses results for other
radiological parameters. Section 4.5 discusses the correlation between Ra-226 concentrations in
soil and gamma count rates. The laboratory analytical reports for the soil analyses are provided
in Appendix B.
4.1
Sampling Strategy and Approach
The soil sampling strategy for the Project consisted of random and biased sampling at the 32
locations shown in Figure 4.1, in accordance with the strategy in the SAP. The identifiers in
Figure 4.1 were truncated to facilitate presentation; e.g., Sample SS-05-SS-081211 was changed
to 5. Three biased samples were collected to characterize radionuclide concentrations in soils
exhibiting elevated gamma count rates. The number of and types of analytes for the surface soil
samples were based on obtaining general knowledge of the distribution of the primary long-
lived radionuclides in the uranium and thorium natural decay series. The sample locations were
determined using Equation 4 of Section 2.3.3.3 in the SAP, which is:
2
>
cv
r
t
N
Where:
N = number of samples
t = the t-statistic (1.645)
r = 0.2, the relative fraction error, or the mean minus the true mean, divided by the true mean
cv = coefficient of variation, or the standard deviation of the population divided by the mean
The coefficient of variation (standard deviation/mean= 0.67) was determined from the gamma
survey data (see Table 3.1). In this case, N=31 samples, most of which were spaced randomly at
the Project, using Visual Sampling Plan Version 6.2d. The exceptions were biased samples. One
biased sample was added (SS-35-SS-081311) to N, to evaluate a hot spot identified near Taylor
Ridge.
The soil sample results represent a baseline to compare results for soil samples collected at
similar locations and depth during the construction, operational, and closure phases of the mine.
It is recognized that topography and other features will change on the Project over time;
however, some of the sample locations are expected to remain intact.
