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<br />AGAPITO ASSOCIATES, INC. <br />CONSULTING ENGINEERS <br />Caann Jt'~cno~' Orru:r: <br />,Tune 17. 2003 <br />Max Ramey <br />American Soda, LLP <br />3717 County Road 21 S <br />Parachute, CO 81635 <br />254-33 <br />I2G: Mechanical Stability of Solution Caverns During Cavern Characterization <br />Testing <br />Dear Max: <br />At the request of American Soda LLP, Agapito Associates. Inc (AAI) has assessed the <br />impact of cavern depressurization on cavern stability for a typical cavern at the Yankee Gulch <br />Project Figure 1 shows the location of Che Yankee Gulch Project with the Upper plant and <br />Yankee Gulch lease area near the Piceance G'eeh in Rio Blanco County, Colorado. Cavern <br />depressurization and pressure cycling is a possibility during the cavern characterization tests <br />planned for this fall. Concern was raised during discussions with various regulatory agencies as <br />[o the effect of cavern depressurization and pressure cycling on cavern stability. <br />Currently, caverns are approaching their permitted maximum size of 200 ft in effective <br />diameter. At the time of application for mining and in the development of the mine plan, <br />American Soda had no experience in developing large caverns in nahcolite-rich oil shale, so the <br />limit of 200 ft on the allowable caveat radius was not based on cavern stability concerns but <br />more on cavern layout considerations such as resource recovery, subsidence, and protection of <br />overlying aquifers. The mine plan included an initial well spacing of 600 ft to allow for later <br />intilling with wells on a spacing of 300 ft. If caverns did not develop to near 200 ft, the initial <br />spacing of 600 ft allowed secondary infilling of wells to a spacing of 200 ft if necessary. Recent <br />experience has demonstrated that caverns of 190 tt are practical, and there are no operational <br />constraints from allowing the caverns to grow to diameters greater than 200 ft. This stud}' <br />evaluates the stability of caverns of diameters greater than 200 ft and the stability impacts of <br />reduced pressure in the caverns. The issue of cavern spacing and future cavern layouts if caverns <br />of greater than 200 ft were acceptable is not addressed. This study focuses on the stability of <br />single caverns. <br />The following document describes a numerical model of a solution cavity and the <br />implications of modeling results on cavern stability. The purpose of the study is to provide <br />information on the struchual integrity of solution cavities under conditions of reduced cavern <br />pressure at varied temperatures and diameters. The evaluation is based on athermal-mechanical <br />cl;olcn~crurealxc • ~mrvc rxclxt:[:a[n'c , cn u, r~'c!~'t:r:alxc <br />%lJ t/ori=ax Drive, Suile 310, Grmxd Junc[iax, C031~~6 Plc (970) 7a ~_:l»p l:,aX' ?4~-9~3J F_-omit :i dkii'avnpi(o enrrr <br />?East 22nd S[ree[, Sui(e 30%, Lombard, /L 601JS-6106 Ph: (630/ 797-1.i?!1 !?Lt': %97-/SSO E-moil: 6~<mkamenuimkinuLcnm <br />