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April 15, 1999 Pagc 1 1.0 INTRODUCTION The subsidence monitoring plan includes both surface and subsurface monitoring of vertical Bound movement resulting from solution mining at the Yankee Gulch Lease. Subsidence monitoringwill be performed throughoutthe commercial operating life ofthe Yankee Gulch Project. Results of the subsidence monitoring (both surface and subsurface) will be checked periodically, as needed, to verify and calibrate numerical models used in the design of the well field layout. Surface monitoring will be conducted by surveying monument locations. Subsurface monitoring will be conducted by downhole instrumentation over cavities and borehole geophysical logging of the overlying strata. 2.0 SURFACE SUBSIDENCE MONTTORWG The purpose of the surface monitoring is to determine surface movement as a response to solution mining. The surface monitoring plan has been designed to ascertain the shape and extent of a subsidence basin should one develop over the well field. 2.1 Monument Locations for the Initial Mining Area Figure 1 shows the approximate locations of surface subsidence monuments over the initial mining area. Twenty-seven monuments will be included th the database for the initial mining area shown in Figure 1. Cun ent plans are for construction of the well field during 1999 and 2000. Some monument locations are existing section and quarter-section comer mazkers. New monuments will be established prior to the start of commercial mine operations. The subsidence monument arrangement in Figure 1 is designed to characterize the shape and extent of a subsidence basin should one develop. The geometry of the monument locations is consistent with cuaent practice over longwall coal mining panels where significant subsidence often occurs. 2.2 Monument Locations for Future Mining Areas Surface monitoring locations will be established for future mining areas similazly to the plan for the initial mining area shown in Figure 1. American Soda's intent is to have sufficient monitoring points for characterisation of the shape and extent of a subsidence basin will be continued throughout the project. Other section and quarter-section comer mazkers will be added • Agapito Associates, Inc.