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C.5 Special Notes <br />To reduce the potential for cross-contamination, samples should be collected so that the least <br />contaminated stations areas are sampled first. Subsequent sampling should be completed in <br />the order of increasing contamination. Areas that typically have lower levels of contamination <br />include those upgradient of source, background areas, and the periphery of the contaminated <br />area. <br />Prepare rinsate blanks. To ensure proper decontamination, submit a rinsate blank for analysis. <br />It is best to do this just before sampling. The blank should be analyzed for the same chemicals <br />the samples are being checked for and for the chemical used to decontaminate equipment, if <br />appropriate. <br />To prepare a rinsate blank, pour analyte-free water through or into the sampler. Pour the <br />collected rinsate water into the appropriate sample container(s). It is advisable to prepare one <br />rinsate blank every day in the field. Use water specifically for blank preparation. <br />Monitoring instruments that come into contact with sampled materials must be decontaminated, <br />along with sampling devices. They should be washed, or at least rinsed before monitoring other <br />sampling sites. <br />As determined from analysis of rinsate blanks, decontamination using soap and water is <br />adequate in removing detectable quantities of contaminants. This type of decontamination has <br />been compared to laboratory procedures for decontaminating sampling bottles. Using methanol <br />as a rinse does help in cases of contamination with organic compounds. <br />C.6 References <br />U.S. Environmental Protection Agency. 1987. Handbook: Groundwater. U.S. Environmental <br />Protection Agency, Office of Research and Development, Cincinnati, Ohio. <br />Additional Soil and Groundwater Sample Work Plan, 3 <br />BNSF Mormon Yard, Stockton, CA <br />rk_platudlappc sogegtapclecon acpt Gang wp doc