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<br />Review: "Ironclad Mill Tailings; Results of Cyanide Detox" <br />Memo to B. Keffelew, June 27, 1994 <br />Page 4 <br /> <br />8. In Section 6 is a calculation showing that under worst case conditions the concentration <br />of cyanide leaving the liner through the underdrain will be about 0.002 mg/L WAD <br />cyanide. The assumptions inherent in the calculation appear conservative except for the <br />assumption stating that cyanide concentration will be 51 mg/L. The 51 mg/L value was <br />apparently taken from the cyanide concentration measurement of 51 mg/kg; however, the <br />two values do not equate directly. (Previous reviews of Amendment rY6 and the <br />Division's responses explained how to convert from mg/kg to mg/L by knowing or <br />assuming the fluid volume in the tailings. Obviously, the Division's explanation was not <br />adopted for the present report as the present report presents a previously presented <br />section of the Amendment application ver batim to justify the calculations. <br />Our previous calculations showed that cyanide is present in the Ironclad tailings in <br />concentrations indicating the presence of process solutions. Provided the concentration <br />of WAD cyanide is 300 ppm, and all of the assumptions of the Section 6 calculation hold <br />true, the concentration of WAD cyanide in the effluent would be about 0.34 mg/L. If <br />the concentration is 500 ppm, the effluent concentration would be about 0.57 mg/L. As <br />stated previously, the percent of fluid in the tailings has not been adequately established. <br />Although these very conservative calculations indicate exceedences of the water quality <br />limitations, they do present a problem under a worst case situation. It would be <br />appropriate to model the system using more realistic concentrations and accounting for <br />the lower cyanide concentrations that will result from treatment with calcium <br />hypochlorite. <br />The assumption that water could only reach the clay liner from above is not necessarily <br />true. If the pipes plug, and that is a very real possibility, and the underdrain plugs as <br />well, the compacted liner can be expected to saturate from beneath. <br />9. There are several problems with the data given in Table 2, "Summary of MWMP testing <br />performed on samples of Ironclad Tailings." <br />Several elements and parameters show exceedences for surface water quality. <br />a. Most of the samples exceed the restrictions for WAD and Total cyanide. <br />b. Values for pH exceed the upper limit (9.0) for surface water in all cases. <br />c. Chloride was exceeded in two cases. Because the majority of chloride will be <br />derived from the Calcium hypochlorite itself, the wide range of values reported <br />for treated samples (157 to 407) should be re-evaluated. It is not reasonable to <br />believe that the rocks in question (either granite or granodiorite) can yield the <br />differences that must be explained by the broad range of concentrations. <br />