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4.0 RADON-222 EMISSION AND DOSE ESTIMATES <br />Future radon-222 emissions from the Whirlwind Mine and associated doses that could be <br />received by proximate residents are estimated in this section based on the data collected <br />to date, future mining plans, and modeling using EPA's COMPLY-R Program. The <br />modeling results indicate that the potential radon dose that could be received by the <br />nearest member of the public would be less than the 10 mrem/yr regulatory limit in all <br />phases of mine development and production. <br />4.1 Baseline Emission Calculation <br />Energy Fuels conducted radon-222 and air flow measurements at the Whirlwind Mine <br />from September 2008 through December 2009. During the time from September through <br />November 2008, the mine workings were being rehabilitated. In late November 2008, the <br />mine went on standby; however, it continued to be ventilated on a periodic basis for <br />inspections and dewatering operations. The collected measurements were used to <br />calculate radon-222 emissions from the Whirlwind portal and estimate, using the <br />i <br />COMPLY-R program, the effective radon-222 dose received at the nearest public <br />receptor. These findings were provided to the EPA in Energy Fuels' letters of April 1, <br />2009 and February 22, 2010 (see Appendix A). A summary of the collected radon-222 <br />concentration data, ventilation rate and calculated radon-222 emissions is provided in <br />Table 1 on the following page. <br />The average of the monthly radon-222 emissions from September to November 2008 <br />(0.225 Curies per month [Ci/mo]) was used to calculate an annual radon-222 emission <br />rate of 2.70 Ci/yr for current mining conditions when mine operations resume. These <br />three months of data were used because they had similar ventilation rates (41,000 cubic <br />feet per minute [cfm]) to those proposed for Phase I mine production operations and the <br />hours of ventilation (171 to 207 hours per month) were sufficient to establish steady-state <br />conditions. The remaining months had significantly lower ventilation rates (5,700 cfm to <br />11,400 cfm) and hours of operation (17 to 77 hours per month), and correspondingly <br />lower radon-222 emissions (0.003 to 0.081 Ci per month). <br />The annual radon-222 emission rate for current conditions was used to develop a baseline <br />emission rate per unit area of exposed ore of 0.18 Ci per 1,000 square feet (SF). This <br />emission rate per unit area of exposed ore is based on the calculated annual emission rate <br />of 2.70 Ci/yr discussed above and the current area of exposed ore zone within the <br />Whirlwind Mine production drifts and stopes (15,000 SF). The remainder of the currently <br />11