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

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underburden monitor well site locations and the potentiometric surface, respectively. Monthly water level data including hydrographs for each site may be found in Appendix 7-1 . Ground water in the underburden aquifer is under artesian conditions. Mean artesian heads in the underburden aquifer range from 9.7 feet at Monitor Well GW-Nll to 86.7 feet at Monitor Well GW-N33. The average artesian head for the underburden aquifer is 40.0 feet. A downward vertical head is generally observed in the underburden but an upward (recharging) vertical head is exhibited at Monitor Well GW-N16. All of the underburden monitor wells at Nucla and Nucla East display seasonal variability to some degree. The seasonal water level fluctuations at the Nucla and Nucla East mining area range from only a few tenths of a foot at Monitor Wells GW-N3 and GW-Nll to nearly 11.0 feet at monitor well GW-N13. All of the underburden monitor wells exhibit steady-state water levels over time with the exception of Monitor Wells GW-N1, GW-N1P1 and GW-N6. These wells have displayed a slight shallowing trend with time. There are no distinguishable effects from the mining operation at Nucla Mine or recharge from precipitation events on the underburden aquifer system. Spoil Water Levels. Four monitor wells (GW-N10, GW-N26, GW-N27 and GW-N28) have been installed to monitor water levels in the spoil aquifer at the Nucla Mine. Exhibit 7-1 shows the spoil monitor well locations. Monthly water level data including hydrographs are contained in Appendix 7-1. The spoils aquifer is dry or nearly dry except for the area in the vicinity of GW-N27. At this location the spoil aquifer has approximately 6.4 feet of saturation. This well was installed in August of 1987 and will require further monitoring to determine annual water level fluctuations and long term trends. Multiple Completion Well Water Levels. Five wells with multiple seam completions have been installed at the Nucla Mine (Exhibit 7-1). Monitor Wells GW-N8 and GW-N9 were installed in the overburden and the Dakota coal aquifers northwest of the Nucla Mine. Monitor Wells GW-N23, GW-N24 and GW-N25 are located in what has been referred to as the scraper area in the southeastern portion of the permit area Those monitor wells were completed in early June, 1986 in the overburden, Dakota coal and underburden aquifers. Water level information indicates that the scraper area monitor wells are dry. Water level information has been gathered for Monitor Wells GW-N8 and GW-N9 on a monthly basis 7-9 Revised 04/11/88