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. (overburden and Dakota coal) monitor wells. It was necessary to include the two multiple <br />completion monitor wells (GW-N8 and GW-N9) in the Dakota coal potentiometric contour map <br />because they are the only two wells in the northwest portion of the permit area open to the Dakota <br />coal. Generally (in the Dakota coal) static water levels are slightly deeperthan the overburden so <br />the potentiometric surface in the vicinity of the multiple completion wells may have a slightly higher <br />water surface elevation than the Dakota coal. <br />Ground water in the Dakota coal is confined in all of the areas monitored. The flow in the Dakota <br />coal aquifer is generally from the northeast to the southwest. The average water level gradient is <br />.0297 ft/ft with a range between .0228 fUft and .0343 fUft. Recharge to the Dakota coal is generally <br />from the agricultural crop areas situated to the northeast and from vertical leakage from the irrigation <br />ditches and flood irrigation via overlying units. Discharge mainly occurs along the drawswhere the <br />Dakota aquifer intersects the ground surface and by discharge to contiguous aquifers. <br />Underburden. The potentiometric surface map ofthe underburden is presented on Map 2.04,7-4. <br />The water level contours were constructed based on September,1987 water level data from eight <br />• underburden monitoring wells. <br />Ground water in the underburden is underconfrned conditions. Flow in the underburden is from the <br />northeast to the southwest. The average water level gradient is .0301 with a range between .0237 <br />and .0368. The primary recharge area is located northeast of the mine via leakage from the <br />overlying units. Discharge occurs inthedrawswheretheunderburdenaquiferintersectstheground <br />surface and to contiguous aquifers. The mining operation at the New Horizon 1 area appears to <br />have had no effect on the underburden ground water potentiometric surface. <br />Monitor Well GW-N 11 was omitted from use in the construction ofthe underburden potentiometric <br />contour map. This monitor well had enigmatic static water level readings when compared to the <br />restofthe underburden monitorwells. Because ofthe poorcompletion record and the anomalous <br />static water level readings, itwas decided to exclude this well from the potentiometric surface map. <br />Effects of the Irrigation Svstem on Potentiometric Surfaces. During the summer months <br />when flood irrigation is in full swing, each of the aquifers monitored exhibits a rise in static water <br />• (REVISED6/28/01) 2.4.7-7 <br />