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ditches mask any water level fluctuations that may result from ground water recharge by precipitation. Monitoring of this well was discontinued after New Horizon 2 Mine became operational. In May 1993, it was replaced by two wells (GW-N39 and GW-N40) along the Calamity draw. The upstream well {GW-N39) is located in the flood plain near Lincoln Street in the south- eastcorner of the mine while the downstream well (GW-N40) is located down gradient of the mine but up gradient of the Nucla waste lagoons in Calamity Draw. Overburden Water Levels. Eight monitorwells (GW-N15, GW-N18, GW-N18P1, GW-N21, GW- N31, GW-N32, GW-N41 and GW-N44) were installed to monitor water levels in the overburden aquifer system at the New Horizon 2 mining area. Maps 2.04.7-1 and 2.04.7-2 show the overburden monitorwell locations and the potentiometric surface, respectively. Monthlywater level data including hydrographs for New Horizon 2 Mine are contained in Appendix D of Attachment 2.04.7-1 Hydrological Monitoring Plan. In May 1993, an additional well, GW-N36, was drilled in the north-east corner of the permit area. Water in the overburden is unconfined or only slightly confining with a downward head pressure Saturated thicknesses penetrated by the overburden monitor wells range from 13.5 feet at WeII GW-N31 to 70.7 feet at GW-N18. The mean saturated thickness is approximately 24 feet Perusal of overburden water level data contained in Appendix D of Attachment 2.04.7-1 indicates that the overburden water level fluctuations are a direct result of the operation of the ditch irrigation system. During the 1987 water year, water level fluctuations in monitor wells GW-N18, GW- N18P1, GW-N21 and GW-N15 varied 18.4, 20.6, 23.3 and 11.4 feet, respectively. Water level shallowing generally occurs from April to Septemberwhen all the irrigation ditches are flowing and flood irrigation is occurring. Water level responses to precipitation events are indistinguishable, as the effects of recharge from the ditch irrigation system have masked any evidence of recharge that could be attributable to precipitation. Mining at the New Horizon 1 area has had no discernible affects on the water levels of the overburden monitor wells. Dakota Coal Water Levels. Ten monitor wells were installed to monitorwater levels in the Dakota coal aquifer. Two of the monitor wells (GW-N4 and GW-N4R) were located at New Horizon 1 and the remaining eight monitorwells (GW-N14, GW-N17, GW-N17P1, GW-N20, GW-N29, GW-N30, Revised 25 Jul 2002 2.04.7-3