Interim Baseline Radiological Investigation Report
November 14, 2012
Bear Lodge Project, for Rare Element Resources, Ltd.
Rev.1
31
7.0
AMBIENT RADON MONITORING
Baseline monitoring of ambient radon concentrations in air has been conducted for four periods:
November 2011 to January 2012 (Period 1), January/February/March to April 2012 (Period 2),
April to August 2012 (Period 3), and August to October 2012 (Period 4).
Radon was measured using track etch detectors that were provided and analyzed by Landauer,
Inc. of Chicago, Illinois.
Table 7.1 lists the radon concentrations in microcuries per milliliter (µCi/ml) according to
monitoring period and location. The results also are compared to a 10 CFR 20 effluent limit.
Period 1 ambient radon concentrations ranged from 6.0x10
-11
to 1.2x10
-9
, averaging 6.9x10
-10
µCi/ml. Period 2 ambient radon concentrations ranged from 4.0x10
-10
to 1.9x10
-9
, averaging
8.2x10
-10
µCi/ml. Period 3 ambient radon concentrations ranged from 1.0x10
-10
to 5.3x10
-9
,
averaging 1.7x10
-9
µCi/ml. Period 4 ambient radon concentrations ranged from 2.0x10
-10
to
1.3x10
-8
, averaging 2.7x10
-9
µCi/ml.
Although highest in Period 4, temporal trends in radon concentrations will be evaluated as more
data are collected. Figure 7.1 is provided to address spatial patterns in the ambient radon
concentrations, in that it presents the monitoring locations in relation to the exposure rates
predicted from the gamma-ray count rate data. Locations SGS-05 and SGS-06 are provided as
points of reference.
Average radon concentrations at AMS-02, SGS-02, SGS-03, and SGS-07 are an order of
magnitude higher than those at the five other locations. Each of these locations is in the vicinity
of the relatively larger source term indicated in Figure 7.1 as colors other than blue. In addition,
the SGS locations would capture radon that travels in relative topographic lows, because it is
denser than air.
In terms of effluent concentrations, the measured values exceed the 10 CFR 20 limit of 1.0 x10
-10
µCi/L for radon-222 with daughters present. However, on average the measured values are
within the range of reported worldwide ambient background radon concentrations, 2.7x10
-11
to
2.7x10
-9
µCi/ml (United Nations Scientific Committee on the Effects of Atomic Radiation
[UNSCEAR], 2000).
Duplicates were collected at AMS-02 in each of the monitoring periods. In Periods 1, 2, and 3
the RPDs between samples and duplicates were 0.1, 0.2, and 0, respectively. An RPD less than 2
indicates that the laboratory performance on duplicates is satisfactory.
Appendix D presents the laboratory analytical reports for radon concentrations in air.
