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GW-N42 and GW-N45) were located at New Horizon 2 (Map 2.04.7-1). Water level data for Well GW-N4 was collected since August, 1979 and collection of water level data for Wells GW-N14, GW-N17, GW-N17P1, and GW-N20 began in July 1986. GW-N4R, GW-N29 and GW-N30 were installed in September, 1987 and collection of water level information began immediately afterthey were completed and developed. Map 2.04.7-3 shows the Dakota coal potentiometric surface. Monthly water level data including hydrographs for New Horizon 2 monitor well sites are contained in Appendix D of Attachment 2.04.7-1. An additional well, GW-N37, was drilled in May, 1993 in the north-east corner of the permit area. Ground water in the Dakota coal is under artesian conditions. Mean artesian heads in the lower Dakota coal range from 18 feet at Monitor Well GW-N14 and 42 feet at Monitor Well GW-N29. The average artesian head for the lower Dakota coal is 34 feet. Water levels in the Dakota coal display seasonal variability that coincides with the irrigation season and operation of the ditch irrigation system. The maximum seasonal water level fluctuation observed in Monitor Well GW-N4 is about 3.0 feet due to its location in the valley bottom. The New Horizon 2 wells display seasonal variability from 2.8 feet at Monitor Well GW-N17P1 to 14.6 feet at Monitor Well GW-N20. Shallowing occurs from April to September and there appears to be little lag between when the irrigation season starts and the shallowing of the static water levels occurs. There are no discernible water level responses to precipitation, nor can any affect from mining be observed at any of the Dakota coal monitor wells at the New Horizon 1 mining area. Underburden Water Levels. Fourteen monitor wells have been installed to monitor water levels in theunderburdenaquifersystem. Six of those monitor wells(GW-N1,GW-N1PI,GW-N3,GW- N5, GW-N6 and GW-N11) were located in and proximate to the New Horizon 1 mine area. The remaining six monitor wells (GW-N13, GW-N16, GW-N16P1, GW-N19, GW-N33, GW-N34, GW- N43 and GW-N46) were located proximate to the New Horizon 2 mining area. Maps 2.04.7-1 and 2.04.7-4 show the underburden monitor well site locations and the potentiometric surface, respectively. Monthly water level data including hydrographs for New Horizon 2 Mine sites maybe found in Appendix D of Attachment 2.04.7-1. In may, 1993, an additional well (GW-N36) was installed in the northeast corner of the permit area. Revised 25 Jul 2002 2.1)4.7-4