2020-06-04_PERMIT FILE - C1981008A (2)

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During November 1998, six (6) new ground water monitoring holes were installed to collect baseline data. Three of these (GW -N41, GW -N42, and GW -N43) were located in an up dip area while the other three (GW -N44, GW -N45 and GW -N46) were located in a down dip area of the permit area. The three holes at each site will monitor overburden, coal zone, and underburden respectively. Baseline data collected between October 1988 and September 1999 are given in Attachment 2.04.7-2. During March 1999, two underburden monitoring holes, GW -N 13 and GW -N 19 were plugged and abandoned. Alluvial Water Levels One alluvial monitor well (GW -N22) was installed to monitor the unconfined alluvial aquifer system along Calamity Draw. Static water level measurements were taken at this site since July, 1986. 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. Monitoring of this well was discontinued after New Horizon 2 Mine became operational. In May 1993, it was replaced by two wells (GW -N39 and GW -N40) along the Calamity draw. The upstream well (GW -N39) is located in the flood plain near Lincoln Street in the south-east corner of the mine while the downstream well (GW -N40) is located down gradient of the mine but up gradient of the Nucla waste lagoons in Calamity Draw. Overburden Water Levels Eight monitor wells (GW -N15, GW -N18, GW-N18P1, GW -N21, GW -N31, GW -N32, GW -N41 and GW -N44) were installed to monitor water levels in the overburden aquifer system at the New Horizon 2 mining area. Maps 2.04.7-1A and 2.04.7-2 show the overburden monitor well locations and the potentiometric surface, respectively. Monthly water level data including hydrographs for New Horizon 2 Mine are contained in Appendix D of Attachment 2.04.7-5 Hydrological Monitoring Plan. In May 1993, an additional well, GW -N36, was drilled in the north-east corner of the permit area. 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 D of Attachment 2.04.7-5 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 ditches are flowing and flood irrigation is occurring. Water level responses to precipitation events are indistinguishable, as the effects of recharge from the ditch irrigation system have masked any evidence of recharge that could be attributable to precipitation. Mining Page 2.04.7-4 March 2017 (TR -77)