2016-01-07_PERMIT FILE - C2010089A (16)

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Overburden Spoil Compactibility and Erodibility Determining the compaction potential of the overburden backfill material is important to assess post -mine conditions including: hydraulic conductivity, revegetation success, landscape stability, and equipment traffic. Unsuitable clay textures are identified in two thin clay beds located in the uppermost overburden in the N14N permit area (see Section 2.04.6, Stratigraphy, Cross Sections A -A', Map 2.04.6-4). These clay beds occur about 60 to 65 feet above the top of the LDX Seam and only exist in the southern part of the mineable area where the overburden (above LDX) is at least 60 to 90 ft. thick. Map 2.04.6-3, the LDX Overburden Thickness Map, shows the area that has sufficient overburden to contain the clay beds. These clay beds will be mined in the area where the overburden is the thickest. When these two clay lenses are being excavated during mining, they will be thoroughly mixed with coarser textured overburden materials. The mixing and dilution process will be accomplished in the backfill by: 1) the overburden shovel will be digging a full face through the clay beds, and 2) the haul trucks with the diluted clay beds which were mixed and diluted during mining will dump their load along a dump face which will result in significant additional mixing and diluting of the clayey materials. After this process, the concentration of the high clay material will be minimal and compactability of the regraded overburden will be negligible. Where the clay beds may be below the overburden zone they will be handled as less suitable material along with the rest of the overburden and be buried in the backfill prior to placement of Bench 1. Bench 1 Monitoring Program To document the suitability of the Bench 1 as potential rooting material, a Bench 1 sampling and analysis program will be implemented. A life of mine sampling grid has been established on 500 - foot centers, and each sampling location on the grid corresponds to a letter/number combination. Using this grid interval, each sampling location represents an area of about 5.7 acres in size. A minimum of four feet of Bench 1 will be sampled prior to topsoil replacement with a hydraulic soil sampler, a bucket auger, or other suitable equipment. Two representative samples, each representing a two -foot depth increment will be collected. The vertical sampling increments will be 0.0 to 2.0 feet and 2.0 to 4.0 feet. Bench 1 suitability parameters are presented on Table 2.05.4(2)(d)-1 and the results will be presented annually in the Annual Reclamation Report. Section 2.05.4(2)(d) Page 2 Sept. 2015 (TR -11)