REP20861 - Laserfiche WebLink

Home Browse Search

10 4.0 CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE SAMPLING Cyanide concentrations were below detection in Rito Seco C;reek and the groundwater wells. WAD cyanide concentrations were above detection in all process point samples, but were less than 1 mg/I and were lower than those measured during the May, 1993 sampling. Total cyanide concentrations were once again highest in the collection impoundment sample. The dissolved oxygen meter was not operating properly during this sampling trip. Measured dissolved oxygen readings were above 100% saturation for the relevant elevations, and all dissolved oxygen measurements (for RS-5, Upper Tailings Impoundment, Lower Tailings Impoundment, and the Collection Impoundment) are not considered reliable. Aback-up meter and probe would have obviated this problem with dissolved oxygen field measurements. Acceptance criteria for laboratory duplicate analyses were not met for total cyanide measurements made on both the upper and the lower tailings impoundment samples. The fact that control criteria were not met makes it difficult to assess whether total cyanide concentrations were higher than WAD cyanide concentrations in the same sample, although total cyanide was clearly higher than WAD cyanide in the collection impoundment sample. Core Laboratories noticed that acceptance criteria for tailings impoundment lab duplicates were not met after the 14-day holding time for cyanide had elapsed, but conducted reanalyses for total cyanide on these samples. High spike recovery percentages (above control limits) were reported for both total and WAD cyanide analyses for the collection impoundment sample. Core Laboratories ascribes this to the dilution required for sample color. Dilution of another aliquot of the sample prior to spike additia~n would have circumvented this problem. Core Labs was requested to perform spike recovery analyses on unfiltered process point samples and to evaluate all total and WAD cyanide analyses on the three process point samples before the 14-day holding time has elapsed so that meaningful reanalyses can be conducted. However, rechecks were conducted after the 14-day holding time had elapsed. RCG/Hagler, Bailly, Inc.