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Page 1 1 1.0 INTRODUCTION This report results from discussions relating to the long-range plan for solution mining of the nahcolite present in the Boies Bed at the White River Nahcolite, Inc. leases at the Wolf Ridge site. Specifically, the changed operating conditions within the cavems resulting from the use of submersible pumps to control leakage provokes reassessment of the impact of reduced cavem fluid pressures on stability of cavern and ultimate cavem size. A quick review of the controlling _ .permit requirements -impact on overlying potable water and the vulnerability of overlying oil shale -indicated that the new operating procedures allowed a significant increase in recoverable resource because collapse of a cavem would not result in leakage to the groundwater system and would have no impact on the minability of the overlying oil shale of economic interest. This report details the rock mechanics aspects and potential impacts of mining as much of the nahcolite resource in the Boies Bed and overlying strata as possible within the constraints of the mine permit using the new solution mining technique. The report is structured to first detail the proposed mine plan and available nahcolite resource. The third section details possible cav- em shapes associated with high-extraction solution mining. This takes into account the experi- 1 ence from partial mining of the first four cavems, the variability in the grade of resource, the potential for unrecoverable resource because of halite intension and the uncertainty of the solu- tion mining process and, hence, the inconsistency of cavem shape. The fourth section addresses case studies of mining impact on overlying groundwater hydrology and minability of overlying strata. Criteria established in the mining literature aze used as the basis for evaluation of high- extraction solution mining. Section 5.0 summarizes the analytical evaluation of the proposed mine plan. The analysis considers extraction of 40% of the available nahcolite in and above the Boies Bed in panels 800-ft wide. Panels would be sepazated by 200-ft barrier pillazs. The analy- sis includes the potential for mbblization of the overlying strata to fill the void created by solu- tionmining, and yield and deformation of the overlying strata. The impact of solution mining on the aquitazd between the mining horizon and the B-Groove aquifer is assessed. The impact of solution mining on the minability of the high-grade oil shale horizon know as the "Mahogany Zone" is assessed. In addition, the impact of the proposed mine plan and short- and long-term surface subsidence is assessed. In the final section, our conclusions and recommendations are presented. Agapito Associates, [nc.