Energy Resources Program
A QUALITY CONTROL ISSUE WAS IDENTIFIED WITH SOME GEOCHEMICAL DATA PRODUCED BY THE DENVER ENERGY GEOCHEMICAL LABORATORY FROM 1996-2008.
Quality Assurance Update
The USGS Energy Resources Program Geochemistry Laboratory initiated a review of its quality assurance practices in 2008, covering quality control and methodology used in inorganic chemical analyses of coal, coal power plant ash, water and sediment samples.
This quality control review found that inorganic chemical analyses by the USGS ERP Geochemistry Laboratory from 1996 through 2008 incorporated quality practices that did not meet standards commonly in use at the time. The most serious shortcoming was the adjustment of raw data to a standard when the instrument reading for the standard was beyond acceptable limits, or when the frequency of repeat analyses of standards was insufficient. In general, adjustment of raw data to account for instrument drift is acceptable practice within strictly defined limits. During the period in question, the maximum adjustment of instrument readings, guided by calibration standards, was not allowed to exceed 10%. However, in some cases the adjustment exceeded 10% and/or was not constrained by an adequate number of control standards. Original instrument readings no longer exist for about 80% of the analyses in question and we are unable to determine the acceptability of drift corrections for most of the samples analyzed during this period. For these reasons, 1996-2008 data from the USGS ERP Inorganic Geochemistry Laboratory should be described as "semi-quantitative" and should be used with care.
DATA REVIEW SUMMARY RELATED TO DATA PRODUCED BY THE DENVER ENERGY GEOCHEMICAL LABORATORY FROM 1996-2008
The review showed that in 25-30 percent of the samples, some analysis had standard deviations greater than 20 percent due to normalization including ICP, ICPMS, Cl, Hg, Se, and S analysis.
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