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• In May 1993, it was replaced by two wells (GW-N39 and GW-N40) along the Calamity draw. The <br />upstream well (GW-N39) is located in the flood plain near Lincoln Street in the south-east corner <br />of the mine while the downstream well (GW-N40) is located down gradient of the mine but up <br />gradient of the Nucla waste lagoons in Calamity Draw. <br />Overburden Water Levels. Eight monitorwells(GW-N15,GW-N18,GW-N18P1,GW-N21,GW- <br />N31, GW-N32, GW-N41 and GW-N44) were installed to monitor water levels in the overburden <br />aquifer system atthe New Horizon 2 mining area. Maps 2.04.7-1 and 2.04.7-2 show the overburden <br />monitor well locations and the potentiometric surface, respectively. Monthiy water level data <br />including hydrographs for New Horizon 2 Mine are contained in Appendix D ofAttachment 2.04.7-1 <br />Hydrological Monitoring Plan. In May 1993, an additional well, GW-N36, was drilled in the north-east <br />corner of the permit area. <br />Water in the overburden is unconfined or only slightly confining with a downward head pressure. <br />Saturated thicknesses penetrated by the overburden monitorwells range from 13.5 feet at Well GW- <br />• N31 to 70.7 feet at GW-N18. The mean saturated thickness is approximately 24 feet. <br />Perusal of overburden water level data contained in Appendix D ofAttachment 2.04.7-1 indicates <br />that the overburden water level fluctuations are a direct result of the operation of the ditch irrigation <br />system. During the 1987wateryear,waterlevelfluctuationsinmonitorwellsGW-N18,GW-N18P1, <br />GW-N21 and GW-N15 varied 18.4, 20.6, 23.3 and 11.4 feet, respectively. Water level shallowing <br />generally occurs from April to September when all the irrigation ditches are flowing and flood <br />irrigation is occurring. Water level responses to precipitation events are indistinguishable, as the <br />effects of recharge from the ditch irrigation system have masked any evidence of recharge that <br />could be attributable to precipitation. Mining at the New Horizon 1 area has had no discernible <br />affects on the water levels of the overburden monitor wells. <br />Dakota Coal WaterLevels. Ten monitorwellswere installed to monitorwaterlevels in the Dakota <br />coal aquifer. Two ofthe monitorwells (GW-N4 and GW-N4R) were located at New Horizon 1 and <br />the remaining eight monitorwells (GW-N14, GW-N17, GW-N17P1, GW-N20, GW-N29, GW-N30, <br />GW-N42 and GW-N45) were located at New Horizon 2 (Map 2.04.7-1). Water level data for Well <br />(REVISED 6/28/01) 2.04.7-3 <br />