Interim Baseline Radiological Investigation Report in
Support of the Upton Rare Earth Processing Plant
November 15, 2012
20
Table 4.3. Summary Statistics for Radium-226 Concentrations in Soil Samples
Estimator/Endpoint
Ra-226
(pCi g
-1
)
Mean (arithmetic)
1.7
Mean (geometric)
1.7
Standard deviation
0.3
Median
1.6
Minimum
1.3
Maximum
2.3
1st quartile
1.5
3rd quartile
1.8
IQR
0.3
Count
16
Notes:
IQR = interquartile range
pCi g
-1
= picocuries per gram
Statistical tests (results not shown) indicate that the distribution of the radium-226 concentrations
is lognormal. The central tendency of a lognormal distribution is best described by a geometric
mean, which in this case is 1.7 pCi g
-1
. This result in central tendency is consistent with both the
arithmetic mean and median.
4.3
Other Radionuclides
Table 4.4 presents summary statistics for radium-228, natural uranium, and natural thorium.
Natural uranium and thorium results are reported in pCi g
-1
, although the laboratory reported the
results in (milligrams per kilogram) mg kg
-1
. The conversion to activity concentrations (pCi g
-
1
=0.667 x mg kg
-1
for natural uranium and 0.22 x mg kg
-1
for natural thorium) was performed to
provide a basis of directly comparing natural uranium and thorium to the other concentrations of
long-lived radionuclides in the uranium and thorium series.
Trends in the radium-228 concentrations cannot be discussed, because detections are reported by
the laboratory in 6 of 16 samples.
The distribution of natural thorium concentrations is normal, with a central tendency (mean) and
standard deviation of 2.4 and 0.6 pCi g
-1
, respectively. The range of natural thorium
concentrations is 1.4 to 3.2 pCi g
-1
.
The distribution of natural uranium concentrations is nonparametric, with a central tendency
(median) and IQR of 1.4 and 0.1 pCi g
-1
, respectively. The range of natural thorium
concentrations is 0.7 to 2.0 pCi g
-1
.
