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1*1 (S4-S1 -\> F'. -Z - <br />IM, 110 <br />ASHWORTH <br />LEININGER <br />G R O U P <br />RECEIV-60 <br />MAR L 8 2011 <br />RECEDED <br />March 22, 2011 Division of Rc.31amation, MAR 2 3 2011 <br />Alining and Safety <br />GRAND JUNCA i:.? -i-o OFFICE <br />Mr. Mark Del Pico DIVISION OF <br />Oil Shale Regulatory Coordinator / REC AmATION MINING & SAFETY <br />ExxonMobil Upstream Research Companyv / <br />P.O. Box 2189 f qc? G? <br />Houston, TX 77252-2189 r 6 U?- ® l <br />Re: Air Quality Requirements -SF6 Testing - Colony Mine <br />Dear Mark: <br />We understand that ExxonMobil proposes to conduct a tracer test at the Colony <br />Mine using Sulfur Hexafluoride (SF6). SF6 has been selected as the tracer gas for <br />the test because it can be detected at extremely low concentrations. We understand <br />that ExxonMobil proposes to conduct several days of testing where approximately <br />230 lbs. of S176 will be released to the atmosphere. You have requested our <br />assistance in determining whether or not this testing activity would be regulated <br />under the Colorado Department of Public Health and Environment (CDPHE). <br />Conclusion <br />The proposed testing program does not trigger any regulatory requirements of the <br />CDPHE based on the evaluation provided below. ALG recommends that the <br />amount of SF6 be tracked during the test in order to confirm the conclusions of this <br />analysis. <br />Regulatory Evaluation <br />EPA has promulgated regulations under the Clean Air Act (CAA) to control <br />emissions and, as a result, trigger permitting under Prevention of Significant <br />Deterioration (PSD) and Title V. GHG emissions are regulated under the federal <br />regulations under what is called the "Tailoring Rule." (See 75 FR31514, June 3, <br />2010). The State of Colorado has promulgated its own regulations that parallel the <br />Tailoring Rule requirements. These regulations are implemented in two steps. <br />Between January and June 2011, no sources would be subject to any Clean Air Act <br />permitting requirement due solely to GHG emissions. After July 1, 2011, any <br />source that has the potential to emit 100,000 tons/year of carbon dioxide equivalent <br />(C02e) and 100 tons/year (for listed sources) and 250 tons/year (for all other <br />sources) total GHG mass emissions would be regulated by the state. A memo <br />providing additional guidance on the Colorado GHG program is attached for your <br />reference.