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<br />' through where the West Pit would be located, and separated the ore body from the Santa Fe <br />Formation and Rito Seco alluvium. <br />During mining, the Rito Seco alluvial was removed and much of the overlying Santa Fe <br />' ' Formation and green clay overburden was removed. Concurrent backfilling operations during <br />mining and continuing through the reclamation placed this removed waste rock and overburden <br />' back into the pit to establish a final free draining reclamation surface. The backfill material <br />was composed primarily of Pre-Cambrian pink gneiss waste rock and the sands, silts, and <br />clays of the Santa Fe Formation. <br />2.3 HYDROLOGY <br />2.3.1 Ground Water Hydrology <br />' There are three principle aquifers in the vicinity of the West Pit, (1) the Rito Seco alluvial <br />' aquifer, (2) the Santa Fe Formation, and (3) the pre-Cambrian bedrock. Pre-mining, water <br />in both the pre-Cambrian and Santa Fe Formations flowed from the ridge lines to the north <br />and northeast to towards the Rito Seco Valley to the south and southwest as shown in Figure <br />5. Water from these formations ultimately co-mingled and discharged to either the Rito Seco <br />alluvium aquifer or to Rito Seco at some point along its course from the mine area to the San <br />Luis Valley floor. <br />Prior to mining, the site-specific hydraulic connection between the Santa Fe Formation and <br />the pre-Cambrian bedrock was believed to be minimal due to a confining green clay fault <br />' zone, which acted as an aquitard separating the two aquifers. This hydraulic separation was <br />demonstrated by the distinctly different potentiometric surface elevations in the pre-Cambrian <br />' rock from the Santa Fe, as discussed in permit application documents for Permit M-88-112. <br />' With excavation of the West Pit, the green clay fault zone separating the Santa Fe from the <br />pre-Cambrian rock was removed. Dewatering operations conducted during mining interrupted <br />the localized West Pit ground water flow, reversing hydraulic gradients from pre-mining <br />' towards the Rito Seco to during mining towards the West Pit. These changes in the hydraulic <br />gradients are illustrated in Figure 2. <br />5 <br />1 <br />