Bear Lodge Plan of Operations - page 457

Occupational Dose Evaluation in Support of the Development of the October, 2012
Rare Element Resources, Inc. Bear Lodge Project
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4.1.2 Estimated Worker Doses
Table 4.3 lists the input parameters used to estimate doses to workers. Table 4.3 also defines the
variables used in the following equations.
Equation 1 was used to estimate external doses.
ܦ௘௫௧ ൌ ൣ൫ܷ௛௚௢ ൈ ܥܦܷ௘௫௧ ൯ ൅ ሺ݄ܶ௛௚௢ ൈ ܥܦܶ௘௫௧ ሻ൧ ݐ Equation 1
Equation 2 was used to estimate internal doses from inhalation of NORM in dust. Two dust
levels were chosen to evaluate worker doses from inhalation. The first is 10 mg m-3, which
MSHA has adopted as the enforceable Threshold Limit Value (TLV) for nuisance dusts. The
second is 1 mg m-3, which is a reasonable estimate of typical dust levels at mine and processing
facilities.ܦ௜௡௛ ൌ ሾሺܷ௉௥௘ ൈ ܥܦܷ௜௡௛ሻ ൅ ሺ݄ܶ௉௥௘ ൈ ܥܦܶ௜௡௛ ሻሿܥௗ ൈ ܹ௜௡௛ ൈ ݐ Equation 2
Equation 3 was used to estimate internal doses from ingestion of NORM in dust.ܦ௜௡௚ ൌ ൣ൫ܷ௉௥௘ ൈ ܥܦ ܷ௜௡௚ ൯ ൅ ሺ݄ܶ ௉௥௘ܥܦܶ௜௡௚ ሻ൧ܹ௜௡௚ ൈ ݐௗ Equation 3
Table 4.4 lists the estimated external and internal doses. Worker exposure to radon was not
addressed in this assessment. The ambient diffusion of radon from open areas and active
ventilation of enclosed process buildings are expected to control radon and its decay products to
acceptable levels.