Scientific Investigations Report 2006-5056

U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006-5056

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Appendix A. Quality Assurance and Control of U.S. Geological Survey 2004 Geochemical Sampling

Quality assurance and control of geochemical sampling included collecting duplicate samples for selected redox-sensitive analytes and volatile organic compounds (VOCs) and analyzing a field blank sample for VOCs. The field blank was collected by pumping VOC-free water through previously used and cleaned tubing. Those results represent possible sampling contamination in samples collected at known contaminated wells only; new tubing was used to sample from wells that were known to be uncontaminated or slightly contaminated and from piezometers sampled for the first time. Complete laboratory quality assurance and control data from Severn Trent Laboratories is on file in the USGS office in Tacoma, Wash.

Duplicate sample results compared favorably for all constituents (table A1). The relatively high variation (30 percent) in duplicate TCE and cis-DCE analyses for site P1-9 sample may be attributed to the dilutions required to quantify such high concentrations. Chloroethenes, chloroethanes, and BTEX were not detected in the field blank sample of pumped VOC-free water (site MW1-41FB). A trace amount of methane (0.0085 mg/L) was detected in the field blank, and methane was detected in laboratory method blanks at concentrations ranging from 0.0032 to 0.027 mg/L, indicating low-level contamination at the laboratory. No ethene, ethane, or chloroethene or chloroethane compounds of interest were detected in laboratory method blanks.

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