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

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GW-N33 and GW-N34). Measurements for static water levels began at these wells immediately after they were completed and developed. All of the water level data are presented in tabular and graphic form in Appendix 7-1. Alluvial Water Levels. One alluvial monitor well (GW-N22) was installed at Nucla East to monitor the unconfined alluvial aquifer system along Calamity Draw. Static water level measurements have been taken at this site since July, 1986 (Appendix 7-1). There is approximately 23 feet of unconsolidated material (alluvium) with an average saturated thickness of 15.24 feet at this site. During the 1987 water year the maximum seasonal water level fluctuation for this monitor well was about 3.6 feet, ranging from 5.62 to 9.22 feet below ground surface. Shallowing occurs at this well from April through September when the irrigation ditches are flowing and irrigation of the local fields is occurring. Water level fluctuations in this well are controlled by the perennial flow patterns of the adjacent drainage (Calamity Draw) which returns much of the excess West Lateral irrigation water to the San Miguel River located approximately two miles downstream from this site. Water level responses to precipitation events are not discernible as the effects of recharge from the irrigation ditches mask any water level fluctuations that may result from ground water recharge by precipitation. Overburden Water Levels. Six monitor wells (GW-N15, GW-N18, GW-N18P1, GW-N21, GW-N31 and GW-N32) have been installed to monitor water levels in the overburden aquifer system at the Nucla East mining area. There are no overburden monitor wells located at the Nucla Mine. Exhibits 7-1 and 7-2 show the overburden monitor well locations and the potentiometric surface, respectively. Monthly water level data including hydrographs are contained in Appendix 7-1. Water in the overburden is unconfined or only slightly confining with a downward head pressure. Saturated thicknesses penetrated by the overburden monitor wells range from 13.5 feet at Well GW-N31 to 70.7 feet at GW-N18. The mean saturated thickness is approximately 24 feet. Perusal of overburden water level data contained in Appendix 7-1 indicates that the overburden water level fluctuations are a direct result of the operation of the ditch irrigation system. During the 1987 water year, water level fluctuations in monitor wells GW-N18, GW-N18P1 , GW-N21 and GW-N15 varied 18.4, 20.6, 23.3 and 11.4 feet, respectively. Water level shallowing generally occurs from April to September when all the irrigation 7-7 Revised 04/11/88