Sacramento River Basin NAWQA Program
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Water-Quality Assessment of the Sacramento River Basin, California: Water-Quality, Sediment and Tissue Chemistry, and Biological Data, 1995-1998 (Open-File Report 2000-391)Quality Control Data
Quality-control samples were collected in the Sacramento River Basin NAWQA to estimate the bias and variability in sample collection. Bias is the systematic error that is manifested as a positive or negative deviation from the known or true value (Mueller and others, 1997). Variability, sometimes referred to as precision, is defined as the degree of random error in repeated measurements of the same quantity (Mueller and others, 1997). The objectives for the NAWQA program to evaluate sampling bias and variability for surface water and ground water chemical analyses are to the determine the extent to which:
Equipment blanks are used to determine if any contaminants or interferences are introduced as part of the sampling equipment or the processes of cleaning that equipment prior to sampling. All equipment used for sampling are cleaned according to established NAWQA protocols. Water, which has been analyzed or is known to be free of the constituents of concern or is otherwise certified with known concentrations for specific constituents or constituent groups, is then passed through the sampling equipment and collected in sampling bottles. These samples are sent to the laboratory for analyses. Corrective action is taken if any contamination is found in these blank samples. Field blanks are quality-control samples that measure bias. Field blanks were used to make sure the sampling and processing equipment were not introducing contamination to the sample. Field blanks were also used to assure that there was no cross-contamination occurring after sequential sampling. Field blanks were taken at most sites to ensure that contamination of samples did not occur at specific locations. The same types of water used for equipment blanks, and free of the analytes to be measured, was passed through the sampling and processing equipment as if it was an environmental sample. The sample was shipped with the environmental samples and analyzed at the same laboratory. Replicates are quality-control samples used to measure the variability in water samples during sample processing and analysis. A composite water sample is collected in the field and split into subsamples. Each of the subsamples is considered to be identical in composition. The subsamples are individually processed sequentially using the same processing equipment and then shipped to the laboratory for analysis. Spiked samples are environmental field samples fortified with a known concentration of selected analytes to measure bias in analyte degradation during shipping, in analyte recovery, or in testing the effects of various waters on the analyses of specific constituent groups. Spikes were completed in the Sacramento River Basin NAWQA for pesticides and for volatile organic chemicals. In the field, a set of two water samples was processed. One set was designated as the environmental sample. The other water sample was spiked with a known concentration of selected analytes and then processed and shipped to the laboratory. Stream Water Frequency Tables Field blank samples (not including mercury and
volatile organic chemicals) Mercury and methylmercury blank samples Replicate, spike, and associated environmental samples
(not including mercury and volatile organic chemicals) Replicate frequency for mercury and methylmercury
samples Blank, replicate, and spike frequency for volatile
organic chemicals samples Stream Water Blank Data Major inorganic constituents:
view data | download data Stream Water Replicate Data Major inorganic constituents:
view data | download data Stream Water Spiked Sample Data Pesticides analyzed by gas chromatography/mass
spectrometry:
view data | download data Ground Water Frequency Tables Field blank samples:
view frequency table Ground Water Blank Data Major inorganic constituents:
view data | download data Ground Water Replicate Data Major inorganic constituents:
view data | download data Ground Water Spiked Sample Data Pesticides analyzed by gas chromatography/mass
spectrometry: view data |
download data |
U.S. Department of the Interior | U.S.
Geological Survey
URL: http://
ca.water.usgs.gov
/sac_nawqa/Publications/ofr_2000-391/data_qc.html
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Page Last Modified:
Wednesday, 02-May-2007 18:19:50 EDT
