Laserfiche WebLink
9 <br />4.0 CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE <br />SAMPLING <br />- Cyanide concentrations were below detection in Rito Seco Creek and the <br />groundwater wells. WAD cyanide concentrations were above detection in all <br />process point samples and were the highest measured in the upper and lower <br />tailings impoundment samples thus far for the third-party monitoring trips. <br />- WAD cyanide concentrations were higher than total cyanide in both upper <br />and lower tailings impoundment samples. <br />- Core Laboratories noticed the discrepancy between total and WAD cyanide <br />concentrations after the 14-day holding time for cyanide had elapsed, but <br />conducted reanalyses of both total and WAD cyanide on the samples. The <br />recheck analyses showed appro~dmately equal concentrations of total and <br />WAD cyanide in both the upper and lower tailings impoundment samples, but <br />these results are invalid because of the exceedence of EPA holding times. <br />The results for the April sampling also showed that WAD cyanide <br />concentrations were higher than total cyanide in the tailings impoundment, <br />and the rechecks of those samples also showed lower concentrations upon <br />reanalysis. <br />- It is impossible to discern without further analytical work whether the total or <br />the WAD cyanide concentrations (or either) in the tailing impoundment <br />samples is correct. <br />- For the next third-party monitoring trip, Core labs should be requested to <br />evaluate the total and WAD cyanide analyses on the three process point '~ <br />samples before the 14-day holding time has elapsed so that meaningful <br />reanalyses can be conducted. <br />- For the next third-party monitoring trip, total and WAD cyanide spike <br />recovery analyses should be performed on unfiltered process point samples to <br />evaluate whether there are analytical interferences with the cyanide methods <br />as performed on critical samples from the site. <br />RCG/Hagler, Bailly, inc <br />