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STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY / <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br />Denver, Colorado 80203 <br />Phone: (303) 866-3567 <br />FAX: (303) 832-8106 <br />March 26, 2004 '~ <br />Mr. Ed Cooley <br />American Soda, LLP <br />2717 County Road 215 <br />Parachute, CO 81635 <br />RE: American Soda, LLP, Yankee Gulch Minerals Project, Permit No. M-1999-002 <br />Cavity Characterization and Stability of Laze Diameter Cavities <br />Dear Mr. Cooley, <br />COLORADO <br />DIVISION OF <br />MINEBRALS <br />GEOLOGY <br />0.ECLANATION•NINING <br />SAf ETY.SCIENCE <br />Bill Owens <br />Governor <br />Russell George <br />Executive Director <br />Ronald W. Cottony <br />Division Director <br />Natural Resource Trustee <br />The Division received American Soda's letter dated Mazch 5, 2004 regazding the proposal to <br />mine we1129-24 to 225 feet and to characterize the we1128-21 cavity. <br />Previous discussions of cavity characterization had centered on production we1129-24 having <br />the first cavity to undergo characterization. This is because we1129-24 has been on a growth <br />track to be the first well to reach an estimated 200 feet diameter. However, 29-24 continues to <br />be American Soda's best producing well even as it approaches 200 feet diameter and American <br />Soda believes that the 29-24 cavity can continue to be mined successfully to at least 225 feet in <br />diameter. Accordingly, American Soda is proposing to characterize the we1128-21 cavity. Well <br />28-21 is currently on standby and has an estimated cavity diameter of 159 feet. <br />Review of the DMG American Soda permit file indicates that there is no permit restriction on <br />the maximum diameter for solution-mined cavities. This is because during original permitting it <br />was assumed, based on results at the test mine facility and thermal-economic modeling, that <br />even reaching 200 feet diameters in the cavities was unlikely. Now that American Soda has <br />determined that for at least some of the cavities, mining to beyond 200 feet diameter is <br />desirable, the potential for adverse environmental results must be evaluated. American Soda <br />has provided a report prepared by Agapito Associates dated June 17, 2003. This report <br />concludes that the cavities can be mined to diameters significantly beyond 200 feet without <br />causing caving of the cavern roof (crown pillar) to anywhere neaz the elevation of the <br />dissolution surface water bearing strata. Hence there should be no adverse impacts to ground <br />water. <br />One of the criteria that are regulated in the mined land reclamation permit is spacing between <br />adjacent cavities. A minimum intact pillar width of 50 feet must be maintained between <br />adjacent cavities to prevent cross communication of the mining fluids and the potential for <br />unacceptable amounts of cavity collapse in the direction of the dissolution surface. The extent <br />of cavity width variation that maybe caused, for example, by more rapid dissolution of rich <br />nahcolite beds, is the chief reason for the requirement to conduct cavity characterization. Once <br />the shape of the cavities is better understood, a stable spacing for adjacent solution mining wells <br />Office of Office of Colorado <br />Mined Land Reclamation Active and Inactive Mines Geological Survey <br />