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Comparison Criteria for Environmental Chemical Analyses of Split Samples Sent to Different Laboratories: Corps of Engineers Archived Data

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Data comparison criteria were developed for quality control QC and quality assurance QA chemical analyses obtained during environmental studies directed by the U.S. Army Corps of Engineers USACE. Archived results for 124 sets of eight metals in soils, 69 sets of fourteen volatile organic compounds VOCs in soils, 163 sets of total petroleum hydrocarbons TPH in soils, 79 sets of six explosives in soils, and 153 sets of fourteen VOCs in groundwater were analyzed statistically. Concentration ratios QC1QC2 and QCQA were log normally distributed and this was the model used for comparisons. For both metals in soils and VOCs in groundwater, duplicate QC results should yield ratios between 0.50-2.00 less than 4 of the archived results were outside these limits. For QCQA ratios, the limits suggested are 0.40-2.50 only 10.2 of metals ratios in soils and 5.6 of the VOCs in groundwater exceeded these limits. Considering that both methods are multi-analyte, we find only 4.0 of the metals samples and 2.0 of the VOC samples had more than one offending ratio per sample. Application of these limits to recent analyses produced very similar results. For V0Cs, TPH, and explosives in soils, temporary limits of 0.25-4.00 are suggested with the understanding that improvements leading to tightening should be energetically pursued. Even with these wide limits, approximately 42 of V0Cs, 14 of TPH, and 11 of explosives QCQA ratios must be considered outliers. Here, too, recent analyses yielded very comparable percentages. The situation for VOCs in soils requires immediate attention to improve sampling and preparation procedures, but all methods can and should be capable of producing improved agreement between laboratories. Numerous recommendations are offered with this goal in mind.

Subject Categories:

  • Physical Chemistry
  • Inorganic Chemistry
  • Organic Chemistry
  • Logistics, Military Facilities and Supplies
  • Solid Wastes and Pollution and Control
  • Water Pollution and Control

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