Interim Baseline Radiological Investigation Report in
Support of the Upton Rare Earth Processing Plant
November 15, 2012
38
9.0
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
at the Upton Project:
•
The central tendency and variability of measured gamma count rates can be described
non-parametrically by the median and the interquartile range (IQR), respectively. The
median of the population is 16,091 cpm. The IQR encompasses the range between the 1
st
quartile (the first 25 percent of ascending, ranked values) and 3
rd
quartile (the first 75
percent of ascending, ranked values). The IQR is 2,405 cpm (or 17,092 less 14,687 cpm).
•
The relationship between gamma count and exposure rates is highly predictable. The
range of predicted exposure rates is 10.1 and 19.3 µR hr
-1
, with a central tendency of 13.8
µR hr
-1
.
•
The medians of the predicted concentrations (1.6 pCi g
-1
) of radium-226 and natural
thorium (2.7 pCi g
-1
) are in good agreement with the median of the laboratory results (1.6
and 2.4 pCi g
-1
, respectively). This indicates that gamma surveys can effectively predict
radium-226 and natural thorium concentrations in soil.
•
The largely homogeneous distribution of radium-226 and natural thorium concentrations
is indicated by the low variability in gamma count rates at the Upton Project.
•
Because applicable soil cleanup criteria are likely to be based both on radium-226 and
radium-228, both radionuclides should be considered in investigations conducted during
operation and closure.
•
The measured radon flux rates range from 0.20 to 1.22 pCi m
-2
s
-1
. For comparison
purposes, these values are below the NESHAPS requirement of 20 pCi m
-2
s
-1
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.
•
Particulate radionuclide concentrations in air across the site are consistently low and at
levels at least 99 % below their respective 10 CFR 20 effluent levels. More data are
needed to compare site measurements to applicable standards.
•
Site-wide cerium and lanthanum particulate concentrations in air are 2.0x10
-3
and 9.8x10
-
4
µg m
-3
, respectively. In the current set of data, lanthanum concentrations are an order of
magnitude lower than those of cerium. The range of cerium concentrations is 9.2x10
-4
to
4.0x10
-3
µg m
-3
. The range of lanthanum concentrations is 4.4x10
-4
to 2.0x10
-3
µg m
-3
.
