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Page 9 3.0 CAVITY SHAPES AND COLLAPSE MECHANISMS 3.1 Possible Solution Mining Cavern Shapes Recovery of 40% of the nahcolite resource would remove a layer of material up to 18-fr thick. This quantity of nahcolite could be recovered entirely from the UBB or could be distrib- uted vertically to include some resource from above the UBB. Figure 3-1 shows three possible cavem shape scenarios. The first scenario shows recov- ery of nahcolite from all beds in the sequence with wider spans developed in the high- bicarbonate strata (UBB and L-SE bed). This results in pillars remaining between the caverns. These pillazs could be as much as 60% of the plan azea, but locally would be more or less. This is the most credible scenario based on experience with solution mining completed to date. It has been difficult to monitor or survey the development of the cavem shape, but observations from Cavem 1 support the development of an inegulaz-shaped cavern which is primazily controlled by nahcolite content. Scenazio b shown in Figure 3-1 restricts all nahcolite recovery to the Boies Bed. This is possible and would result in caverns that would often interact and interconnect. However, rem- nant pillars between the roof and floor would be common. In other locations, wedges of unre- covered nahcolite would remain on the floor between two adjacent cavems. Some load transfer between the roof and floor would be anticipated. The third scenario somewhat unrealistically assumes that all recovery is focused in a sin- gle continuous layer, say in the highest grade section of the UBB. With this scenario, not all of the vertical column of the UBB would be recovered and no pillazs or wedges of material would ~- connect between the roof and floor. Cleazly during mining of such a large span opening, collapse of the overlying strata would occur. This last scenario is not considered credible, but is included because it results in the most adverse impacts on the overlying strata. With this scenario, maximum movement of the overly- ing strata can be anticipated. In plan view, the cavem shape is controlled by the location of injection points, duration of injection from each location, and the continuity of the resource. Some areas may be left ~ unmined because of halite intrusion. In plan view, the cavem-to-pillaz ratio will be vaziable and Agapito Associates, Inc.