2018-07-02_PERMIT FILE - C2010089 (16)

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Permanent sealing of holes, wells or other exposed underground openings not completed to aquifers will be sealed by replacing cuttings or other suitable media in the hole. A suitable plug will be placed ten feet below the ground surface to support a cement plug or other media to within three feet of the ground surface. Permanent sealing of holes, wells, etc. completed in aquifers will be sealed using cement or other suitable sealant. The sealant will be placed in the hole from the bottom to within ten feet of the surface. Surface plugs used to complete the permanent sealing of holes, wells, etc. will be selected and used only if DRMS gives prior approval. All associated surface sites will be reclaimed following the cessation of mining. NHN will submit to the DRMS a proof of compliance report containing pertinent information on permanent sealing of any hole, well, etc. within 60 days of completion of such activities. Ground Water Ouantity The backfilling and grading of spoil materials is accomplished by dozers and trucks (see Section 2.05.4(2)(c) Backfilling and Grading). As described in Section 2.04.7 Hydrologic Description, the NHN permit area is hydrologically isolated from adjacent areas of Dakota coal strata by stream incision. Further, the hydrologic regime at NHN is the sole product of seasonal irrigation by way of the Colorado Cooperative Company's 2nd Park Lateral irrigation ditch. This ditch was completed in about 1905 and delivers approximately 19.2 cubic feet per second (cfs) of water to the 2nd Park area. About 10.8 cfs enters the permit area in the 2nd Park Lateral (see Map 2.04.7-1) where about 2.5 cfs is used on the permit area and the remaining water goes to water shareholders located downstream. The 2nd Park Lateral was diverted into a high density polyethylene (HDPE) pipeline around the mining area. After the mine has advanced far enough north and overburden backfilling and topsoil spreading has progressed past the original ditch location, the HDPE pipeline will be rerouted to approximately the original ditch location. Infiltration and percolation of irrigation water from the banks and bed of the 2nd Park ditch will for the most part be eliminated. This will also eliminate the primary source of recharge to the overburden, coal and underburden zones. The structure of the strata (see Map 2.04.6-2) will prevent any major saturation of the backfilled overburden material as any percolating excessive irrigation water or water from intense precipitation events will drain to the south along the contact of backfill material and the relatively tight underburden. In addition to backfilling methods, topsoiling and reclamation plans outlined in Section 2.05.4(2)(d) Overburden and Topsoil Handling and Section 2.05.4(2)(e) Revegetation will enhance the potential for establishing reclaimed areas that exhibit similar infiltration rates to pre -mining conditions. Seeding and mulching of redistributed topsoil will augment moisture retention and infiltration rates of the reclaimed areas. Mechanical manipulation of the regraded spoil and topsoil (chisel plowing, disking and ripping) will further aid the percolation of soil moisture downward. Surface Water Ouality The sediment ponds are designed to prevent additional contribution of sediment to stream flow outside the permit area and incorporates detention times sufficient to ensure that all applicable effluent standards will be met. The ponds are currently planned to be removed and reclaimed following the completion of mining. Section 2.05.6(3)(b)(v) Page 2 March 2018 (TR -16)