2019-07-11_PERMIT FILE - M2019027

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C-12 r1 (d) THICKNESS OF DEPOSIT TO BE MINED Exploratory drilling completed to date indicates that the target sand horizon is on the order of 35 to 40 ft. thick, on average. It is CSC's intent to mine a depth horizon sufficient to justify the proposed Keenesburg Project economic objectives while leaving a pit-floor sub-horizon comprised of sand, as well, in order to accommodate infiltration and dispersal of both precipitation moisture and process-related residual moisture content in the fines slurry,both during and subsequent to the operational life-of-mine. Accordingly, the anticipated mining depth will be limited to approximately 25-ft. below the existing ground surface for both the main pit area and the fines recovery pit, respectively,such that the invert elevation of each pit will be established at an elevation of 4,880 ft. amsl. CSC will maintain this invert elevation, within an estimated +/- 2 ft. variance, in order to accommodate the unavoidable undulations that result from the types of mining equipment being employed (i.e., front-end loaders and hydraulic excavators), the nature of the material(i.e., sand), and pit water management requirements(if warranted). CSC notes that the fines recovery pit will be excavated(mined)to its full completion depth prior to the initiation of sand processing, and thereafter will be incrementally filled with process fines. Thus, it is not anticipated that the fines recovery pit would ever be "deepened". In the event incremental storage capacity is required in the fines recovery pit, CSC would (through submittal and Division approval of a Technical Revision, in advance of doing so)likely accomplish such via an increase in,or raising of,the perimeter containment. Therefore,the fines recovery pit invert elevation would remain at the initially established 4,880 ft. amsl (+/- 2 ft.). Based on the fines recovery pit location and localized surface topography(average elevation across the fines recovery pit is approximately 4,905 ft. (m/1), excavation depth is anticipated to be on the order of 25 ft., on average. The main mine pit footprint area, however, is overlain (in its pre-mining condition) by surface topography that ranges from a"high"of approximately 4,910 ft. (in the south central zone)to a"low"of approximately 4,905 ft. in its northeast corner. Therefore, employing/establishing a 4,880 ft. amsl (+/-2 ft.) invert elevation for the pit floor will require that the true mining depth horizon(s)vary from 25 ft. ("low"zone)to as much as 30 ft. ("high"zone), in order to accommodate all areas of the main mine pit. In the event CSC were to consider a deepening of the main mine pit (to potentially accommodate incremental production in the latter stages of mine life), such would be addressed through the submittal(and Division approval) of a Technical Revision, in advance of doing so.