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7 <br />difference (RPD) of 47.6%, which is not within control limits (allowable levels = <br />±20%RPD). Both values for total cyanide are therefore considered to be estimated. One <br />of these values is above and one below the WAD cyanide mean concentration of 240 µg/1. <br />The total cyanide reanalysis concentration was 190 µg/I; however, this result is considered <br />to be estimated because of the exceedence of EPA holding times. If anything, the total <br />cyanide rerun concentration may be higher than 190 µg/1 because of exceedence of holding <br />times. Resampling is not recommended, because even though the total cyanide <br />concentrations are estimated and are below concentrations measured in May, they are not <br />the lowest total cyanide concentrations measured during the third-party manitoring project. <br />The values fit within the previously measured range of total cyanide concentrations for the <br />unfiltered upper tailings impoundment samples (240 - 680 µg/I). <br />Specific conductance, sodium, copper and calcium concentrations were all lower than they <br />were in May 1993. The pH was lower and the iron concentration higher than during the <br />May 1993 sampling. <br />Lower Tailings Impoundment. Both total and WAD cyanide concentrations in the lower <br />tailings impoundment were approximately twice those in the upper tailings impoundment in <br />the October 1993 sampling. Measured total cyanide concentrations were 580 and 310 µg/1, <br />which results in a RPD of 60.7%, which is not within control levels for duplicate analysis <br />(allowable levels = ±20%RPD). As with the upper tailings impoundment samples for total <br />cyanide, Core Laboratories reran the samples but did so after the 14-day holding time had <br />been exceeded. Reanalysis of both the upper and lower tailings impoundment total cyanide <br />samples resulted in measured concentrations below those for WAD cyanide, but as discussed <br />above, the reanalysis values are estimated values because they were conducted after the 14- <br />day holding time. If anything, actual total cyanide concentrations are Nigher than the <br />reanalysis value because of exceedence of holding times. As discussed for the upper tailings <br />impoundment, resampling is not recommended because the total cyanide concentrations for <br />the lower tailings impoundment October 1993 samples fall within previously measured values <br />(180 - 580 µg/I). <br />Unlike in the upper tailings impoundment, speciSc conductance, sodium, copper and calcium <br />concentrations were all higher than they were in May 1993. As with the upper tailings <br />impoundment, however, the pH was slightly lower and the iron concentration higher than <br />during the May 1993 sampling. <br />Collection Im~undment. Laboratory duplicate analysis of the collection impoundment <br />samples for total cyanide were within control levels (1050 and 11]4 µg/1 = ±8% RPD), as <br />were lab duplicate analyses of WAD cyanide samples (620 and 720 µg/1 =_ ±15% RPD). <br />Therefore, no reanalysis of collection impoundment samples for cyanide was conducted by <br />Core Labs. Total cyanide concentrations were significantly higher than WAD cyanide <br />concentrations in collection impoundment samples, and both concentrations were slightly <br />lawer than those measured in May 1993. The collection impoundment again had the highest <br />RCG/Flagler Bailly <br />