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<br />A 5 C I <br />'ate,.. ~,~1'l. I'1~61t^'f!f!T.f~._ ~.~ <br />' 4.2 TOTAL CYANIDE <br />' The total cyanide (TCN) analyses of the samples were determined by two different, <br />but USEPA certified, analytical methods. Laboratory "A" used an autoanalyzer <br />procedure, while Laboratory "C" used the chemical, manual method. While the <br />' autoanalyzer gives excellent results for samples with a relatively simple matrix <br />chemistry, (e.g., water samples) it tends to overestimate total cyanide values with <br />complex solution matrixes, such as mining related solutions. (Examples of these <br />' potential problems are addressed in Smith and Mudder, 1991). The manual method <br />performed by a skilled technician will give a more reliable estimation of the total <br />cyanide level in a sample, based on other studies and prior experience. Accordingly, <br />the total cyanide analyses from Laboratory "C" are considered to be representative <br />of the four samples from the tailings system. <br />4.3 WEAK ACID DISSOCIABLE CYANIDE (WAD CN1 <br />' Laboratory "A" determined WAD Cyanide values on three samples, (r»s 2, 3 and 4). <br />In each case, the WAD value determined exceeded the Laboratory "AP' total cyanide <br />' value, itself considered to be an overestimate of the actual total cyanide present, <br />(see above. <br />' Clearly, WAD cyanide cannot exceed total cyanide by definition. The metal analyses <br />for the samples show the presence of both iron and cobalt which will report as <br />strong cyanide complexes to the total cyanide analysis, but not to a WAD cyanide <br />' determination. This is because the WAD cyanide method is not capable of liberating <br />the cyanide from iron or cobalt complexes. Therefore the WAD cyanide cannot be <br />' the same as the total cyanide, but must be some value less than th@ total cyanide <br />concentration. <br />' The WAD cyanide determinations by Laboratory "A" are clearly incorrect because <br />the WAD cyanide was reported at levels which exceed cyanide levels. <br />' Laboratory "C" determined WAD cyanide on all four samples. However, they were <br />not able to obtain reproducible results for WAD cyanide on sample u2. Sample rY2 <br />_ gave 153 mg/L and 277 mg/L WAD cyanide on successive determinations. <br />The other three WAD cyanide analyses from Laboratory "C" are considered to be <br />' credible determinations for the following reasons: <br /> <br />5 <br />