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Mine Tailirs¢s Ponds Evaluation <br />If seepage were to occur, it would migrate through the Creede Formation. This formation <br />• consists of sedimentary stream and lake deposits of reworked volcanic material, and travertine <br />deposits from warm water springs. Organic material, and iron and manganese oxides associated <br />with these sediments may attenuate lead, antimony, and manganese. The thickness of the Creede <br />Formation beneath both tailings sites is not known with certainty. The neazest outcrop of older <br />volcanics is approximately 2,000 feet north of the property. If the contact between the Creede <br />Formation and the older volcanics has a southerly dip similaz to that observed in neazby <br />underground mines (25 to 50 degrees), the Creede Formation could be at least 900 feet thick at <br />the northern edge of the tailings sites, and even thicker farther to the south. <br />5.4.1 Attenuation Tests Materials <br />The pore water collected for the attenuation test was obtained from the two hand augured <br />piezometers described in Section 3. The concentrations of manganese, lead, antimony, and <br />sulfates, along with the water pH, and electrical conductivity (EC) of the pore water are shown at <br />the top of Table 5.5. The manganese (4.43 mg/L) and antimony (0.066 mg/L) concentrations of <br />• the pore water sample used in the attenuation tests aze within the range or above the <br />concentrations of those constituents in previous pore water samples. The concentration of lead <br />(0.045 mg/L) in the attenuation test water sample is below the concentration of lead measured in <br />the previously analyzed pore waters, and was also below the state drinking water standazd of <br />0.05 mg/L. <br />The Creede Formation and related soil materials used in the test were collected from cut banks <br />which were excavated during the tailings impoundments construction, or by digging through the <br />soil zone in areas down-gradient of the tailings embankments until a mixture of Creede <br />Formation and soil materials were obtained. The samples containing the Creede Formation and <br />soil materials allowed the role of organics in the attenuation processes to be assessed. The <br />piezometer and soil sampling locations aze shown in Figure 3.l and Figure 3.2. The samples <br />which were selected for testing included: <br />1. Upper Pond Sediment Sample-1: very fine grained tan to brown soil and <br />. weathered Creede Formation Sediments containing approximately 30% clays and <br />25% organic material. <br />Homeslgke Mining Company Shepherd .11i(ler, /nc. <br />w--iine„u~s..~, 32 .lpril l~f, 1997 <br />