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11 so that potential analytical interferences can be identified, and in the interim both filtered and unfiltered samples shou]d be collected for determination of total and WAD cyanide. 3.4 The Cadmium Problem ,~ SG~~ / ~~ ~~` Since the time of the first third-parry sampling, it has been brought to the attention of DMG and BMRI that there were elevated cadmium concentrations in both total and dissolved samples from several of the monitoring stations. One possible explanation for this occurrence is that the addition of cadmium nitrate to the samples that had detectable sulfide (as determined by use of lead acetate paper) could have caused the elevated cadmium concentrations. According to TR-0006, cadmium nitrate powder should be added to the sample prior to filtering if the sample tests positive for sulfide on lead acetate paper. Enough cadmium nitrate powder should be added until a negative spot-test is obtained (if sulfide is present in the sample, lead sulfide is precipitated on the lead acetate paper as a black spot). After adding cadmium nitrate to samples with sulfide, the sample is then filtered through a 0.45 micron filter and preserved with sodium hydroxide to a pH of 12 (TR-0006, pg. 31). If the barrel filter was not properly decontaminated after this procedure, it is possible that the next dissolved metals sample collected would be high in cadmium. Although it is not explicitly stated in TR-0006, one can assume (because of the preservation pH) that this precautionary measure applies to ryanide samples, where the presence of sulfides can interfere with the accurate determination of cyanide by titration or colorimetry. ASTM methods 9010 (colorimetric, manual) and 9012 (colorimetric, automated 1N) are included in TR-0006 as Appendix G. For these methods sulfides and nitrate/nitrite interfere with the analysis, and bismuth nitrate is added prior to distillation to remove the sulfide interferents. The method used for determination of total cyanide for the third-parry monitor samples was EPA method 335.2. Sulfides, fatty acids and nitrate/nitrite interfere with the procedure, and to correct for this interference lead acetate is added to the sulfide scrubber to scavenge sulfides during the distillation process. In either case, the analytical method provides for the elimination of the sulfide interference, and it is not necessary to add cadmium nitrate in the field. In addition, the cyanide samples are not supposed to be filtered according to TR-0006 (Table 5), so the addition of cadmium nitrate before filtering the sample does not match with the sample handling requirements laid out in the QA/QC protocol document for collection of samples for determination of cyanide. Because elevated cadmium_concentrations were found in both filtered and unfiltered samples, it is unlikely that the addition of cadmium nitrate is the cause, at least for the high cadmium values in unfiltered samples. Other possibilities include the release of cadmium from waste rock piles or other waste or ore materials at the site, or the leaking of solutions containing cadmium from the process point locations (or other sources) to downgradient groundwater wells. An inventory of all possible sources of cadmium at the site should be RCG/Hagler, Bailly, Inc.