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~I <br />' 2.4 GEOCHEMISTRY <br />' Lithologic rock units associated with the geologic formations of the West Pit are primarily <br />composed of pink gneiss of the crystalline pre-Cambrian bedrock and biotite and biotite- <br />' amphibole gneiss contained within the underlying geologic formation. The pink gneiss was <br />not present in the deeper portion of the West Pit having been eroded away, but was present <br />on the higher slopes of the West Pit, in varying thicknesses. Materials contained within the <br />Rito Seco alluvium and Santa Fe Formation are comprised primarily of sands, silts and clays. <br />' Geochemical testing of the Santa Fe Formation materials, the pink-gneiss, the biotite and the <br />biotite-amphibole was conducted during the original permitting process and the TR-18 permit <br />' modification. Geochemical testing consisted of ANP/AGP, leachability and humidity cell <br />testing of the various materials to determine the material's overall composition, leaching <br />' potential and acid generation neutralization potential. <br />Analytical results of the various static and kinetic tests conducted with the overburden and <br />waste rock materials backfilled into the West Pit identified no to low acid generation potential <br />with slight to moderate neutralization potential. Of the materials evaluated the biotite gneiss <br />was the only material characterized with low acid generation potential, the other rocks <br />demonstrated no acid generation potential whatsoever. The results of sequential batch tests <br />on the pink gneiss material, conducted with the TR-18 modification, indicated the ability to <br />generate sulfate concentrations of 150 mg/1 during initial leaching. <br />2.5 HYDROCHEMISTRY <br />2.5.1 Ground Water Quality <br />As previously discussed, there are three aquifers in the area of the West Pit, each with its own <br />distinct water quality. The water quality monitoring network developed baseline data for each <br />of these aquifers, with additional data collected during the mining phase and post-mining <br />period to monitor for water quality changes. <br />Rito Seco Alluvium: Water quality data collected in the Rito Seco alluvium (well M-11) <br />' indicate a more mineralized water than that found in the Rito Seco channel. Pre-mining water <br />8 <br /> <br />