2018-11-19_PERMIT FILE - C2010089A (6)

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sediment pond that will, at the time of pumping, have a sufficient available storage capacity, including the prescribed volume for the 10 -year, 24-hour storm. Design criteria for all ponds are addressed in Section 2.05.3(3), Mine Facilities, and include plans for storage of additional volumes pumped from pits or sumps. Maintenance of available storage capacity in the ponds involves dewatering and sediment removal. Ground Water Monitoring Since 1979, Peabody (New Horizon Mine's predecessor) and NHN have installed an extensive network of 46 hydrologic monitoring wells to monitor the shallow bed rock zones beneath both the New Horizon 1 and the New Horizon 2 mining areas. A number of these wells were located within or in close proximity to the NHN permit area (see Map 2.04.7- 1 in Section 2.04.7). This information has been supplemented by the addition of nine hydrologic monitoring wells which were installed during 2008 for baseline hydrologic data collection. These wells (numbered GW -N47 through GW -N55) are described in Section 2.04.7 and the data collected presented in Appendices 2.04.7-1. Physical data (temperature, pH, conductivity, depth) are collected monthly and samples for chemical analyses are collected quarterly. This schedule will continue for the foreseeable future. It is expected that these nine baseline monitoring wells will be employed to monitor the extent and magnitude of any mining impacts as also discussed in Sections 2.04.7 and Section 2.05.6(3)(b)(v), Hydrologic Reclamation Plan. The ground water monitoring wells will be maintained for the life of the mining operations or until such time as DRMS may agree that they are no longer necessary. All ground water monitoring installations will be removed upon completion of the post mining hydrologic monitoring phase of the Hydrologic Monitoring Program. Three (3) additional ground water monitoring wells were installed in the southwestern portion of the NHN permit area. The locations of these 3 wells are shown on Map 2.04.7-1. Ground water monitor well GW -N56 will monitor the underburden (UB), well GW -N57 will monitor the coal zone (Coal) and well GW -N58 will monitor the overburden. After review of additional data and consultation with DRMS, ground water monitoring wells GW -N56, GW -N57, and GW -N58 have been designated as points of compliance. The completion diagrams for the three monitoring wells are shown on Figure 3 of Appendix 2.04.7-1. Appendix 2.05.6(3)-4 contains State Engineer approved well permits for the New Horizon North Mine. Three (3) wells (GW -N47, -N48, -N49) located in northwestern portion of the NHN permit have been removed from the monitoring plan and will be reclaimed upon approval by DRMS. Since the wells are located outside the NHN mining area (% mile north) and are neither up nor down gradient from the NHN disturbance area, they will likely not be beneficial in monitoring the extent and magnitude of mining related impacts. The remaining wells provide monitoring both up gradient (GW -N50, -N51, -N52) and down gradient (GW -N53, -N54, -N55) of the NHN disturbance area, including three down gradient points of compliance (GW -N56, -N57, -N58). Section 2.05.6(3) Page 4 March 2018 (TR -16)