1997-04-24_REVISION - M1977493 (17)

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Mr. Bryce Romig • 3 September 9, 1996 expected to represent worst-case water quality conditions. A composite of three soil samples was collected from the area near the dam face, across from the ponds, where tailings had been removed. Summary of Sampling Results and Recommendations for Confirmation Sampling Surface Water Sampling Tables 1 and 2 summarize the analytical results of the surface water sampling. As described above, the samples were collected during poor water quality conditions that will not be present following completion of the reservoir reclamation. Conditions affect- ing water quality during the initial sampling events included direct runoff from tailings, stagnant water, and contact of tailings and water in the reservoir. Also, pore water from the buried tailings was introduced to the surface water as a result of excavation. This water will contain elevated metal levels due to equilibration with tailings over time. Another effect of excavation is to expose buried tailings to the atmosphere, resulting in acid-generating oxidation of iron and other metals. The low pH values (median field pH of 4.4) and high conductivities (ranging from 1,119 to 6,550 µmhos/cm) confirm that field conditions were poor. In comparison, the pH values in the filled reservoir following reclamation are expected to be neutral to slightly alkaline, based on pH values measured in the Chalk Mountain Reservoir which range from 7.66 to 8.62. Under these expected • pH conditions, metals will be much less mobile than under the tested conditions. As shown in Tables 1 and 2, the following analytical results were obtained for the two sampling events: • Analytes below detection: trivalent chromium, selenium, silver, fecal coliforms, and nitrite; • Analytes below detection limit or below the practical quantitation limit: arsenic, boron, mercury, free cyanide, and sulfide; • Analytes well below standards: arsenic, boron, chloride, fecal coliforms, nitrate, and nitrite; • Hexavalent chromium was below detection in all but one sample and the detected concentration was well below the water quality standard; and • Concentrations of dissolved and total recoverable iron and dissolved and total recoverable manganese in the initial samples were nearly identical, indicating that most of the iron and manganese were present in the dissolved phase. C:\PROJECTS\6102-001\1'1696102.001[9-Sep-961 _ _ _ ==Environmental