2010-12-17_REVISION - C1981019 (108)

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RULE 2 PERMITS revisions were submitted to the Division and approved on January 24, 1984, August 17, 1983, April 24, 1990, and PR -02 respectively. The following summarizes the requirements of the current regraded overburden (backfill) sampling program and supersedes all previous commitments. It is based on the following limitations of the earlier program. 1. Placing weathered overburden material onto reclamation areas prior to final regarding, and 2. Sampling regraded overburden at a density of one composite surface sample per 5 acres of regraded spoil. The regrading of overburden is an event that takes place sporadically during the year. Once backfill areas are regraded, but prior to topsoil replacement, the new locations are identified and sampled. A life -of- mine sampling grid has been established on 500 -foot centers, and each sample location on the grid corresponds to a letter /number combination as established on the sampling map. Using this grid interval, each sample location represents an area of about 5.7 acres in size. A hand shovel is used to take small, representative surface samples of spoil across the sample area. Regraded Overburden Suspect Levels: Parameter Suspect Level H Less than 5 or greater than 9 standard units Electrical Conductivity Greater than 12 millimhos /cm Sodium Absorption Ratio Greater than 15 The laboratory results are kept at the mine site. Results of the sampling program are provided in the appropriate Annual Reclamation Report and are periodically checked during CDRMS quarterly complete inspections. The mining sequence for the planned operation is shown on the Mine Plan Map (Map 2313). Cross sections showing the post mining pit backfill are presented on the Pre - Mining and Post - Mining Cross Sections (Map 20C). The temporary overburden stockpile location is presented on Map 23B. The map depicting spoil grading is presented as Map 29B. The temporary overburden stockpile that is to be built will be placed in a stable location that will not exceed a 33 percent slope to ensure stability. The spoil suitability and special handling procedures are described in detail in section 2.05.3(1) of the Collom permit revision. The initial development of the stockpile is anticipated to begin during the year 2012 with the excavation of the initial box cuts and continue over the next five years of operation. Following this period mine pit advancement will allow for placement of mined spoil into the original box cut area. The temporary spoil pile will be used to fill and recontour the final pit sequence in the final two years of mining activities (See Map 29C — Temporary Spoil Pile Design). Out of pit stored spoils will be used in the construction of the post mine topography. Approximately 250 million cubic yards of storage capacity for the temporary spoil stockpile will be needed. The toe of the fill will be placed near the floor of the X4 coal seam and the stockpile will eventually extend upward about 775 feet in thickness to an elevation of 7675. The stockpile will remain in place until the last few years of mining and will have a life of about 15 -20 years depending on production rates. Construction of the stockpile is expected to take about 7 to 10 years. As such, the lower portions of the stockpile will be completed and stabilized before the top is completed. To ensure that a phreatic water surface does not develop during the life of the stockpile, a rock drain will be installed at the base of the Collom — Rule 2, Page 98 Revision Date: 1/23/09 Revision No.: PR -03