1988-04-11_PERMIT FILE - C1981008A (9)

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since September, 1979. Monitor Well GW-N8 is located upgradient and adjacent to the mine pit. As a result, a 13 foot drawdown in static water level occurred prior to 1983. Since mining ceased in late 1983, the static water level has begun to recover. Both Monitor Wells GW-N8 and GW-N9 show seasonal fluctuations in water levels as a result of recharge from the ditch irrigation system. There is no evidence of any discernible responses to precipitation events at these wells. There are no single aquifer (overburden or Dakota coal) monitor wells completed in the northwest portion of the Nucla Mine permit area. Consequently, Monitor Wells GW-N8 and GW-N9 have been incorporated and used in both the overburden and Dakota coal potentiometric surface maps (Exhibit 7-2 and 7-3). Potentiometric Surfaces. Potentiometric surface maps for the overburden, Dakota coal and underburden aquifers are presented in Exhibits 7-2 and 7-3, respectively. Overburden. The potentiometric surface map of the overburden is presented on Exhibit 7-2. The water level contours were constructed based on the static water level measurements made in September, 1987 from five overburden monitor wells and two multiple completion (overburden and Dakota coal) monitor wells. It was necessary to include the two multiple completion monitor wells (GW-N8 and GW-N9) in the overburden potentiometric map because they are the only monitor wells located in the northwest portion of the permit area. The overburden generally has the shallowest static water level of the bedrock aquifers that are monitored within the study area, so the multiple completion monitor wells should be representative of the overburden aquifer water levels. Ground water in the overburden aquifer is generally unconfined to only slightly confining. The flow in the overburden is generally from the northeast to the southwest and is topographically controlled. Potentiometric contours indicate that there is discharge of ground water along Tuttle and Calamity Draws. The ridge that separates the two draws is a ground water divide, causing the ground water to flow from the ridge top toward both Tuttle and Calamity Draws. The primary recharge area is from the northeast and from vertical leakage from the irrigation ditches and flood irrigation. The average water level gradient in the overburden is .0342 ft/ft with a range between .0333 ft/ft and .0375 ft/ft. Dakota Coal . The potentiometric surface map of the Dakota coal is presented on Exhibit 7-3. The water level contours were constructed based on the static water level measurements collected in September, 1987 from seven Dakota coal monitor wells and two 7-10 Revised 04/11/88