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Mftodward-Clyde <br /> Consultants <br /> 3.3 QUALITY ASSURANCE/QUALITY CONTROL <br /> Travel/equipment blanks and blind duplicates were used to provide quality assurance and <br /> control The analytical results for the blanks were below the detection limits of the TFH and <br /> BTEX analyses The analytical results for the December 31, 1991 blind duplicate sample <br /> (MW-23) were within twenty percent for each of the analytical parameters €(TFH (1$%), <br /> benzene (15%) and ethylbenzene (0%)] of the original sample (MW-3) The field duplicate <br /> precision, expressed as relative percent difference (RPD), exceeded thirty percent for two <br /> compounds (toluene and total xylenes) Since these compounds were not found in one <br /> sample in the duplicate pair, the detection limit can be considered a maximum concentration <br /> which could be present in the samples Toluene was found at 1.7 ppb, which is over five <br /> times the detection limit Total xylenes were found at 1 8 ppb, which is twice the detection <br /> limit. Although the BPDs for toluene and total xylenes are relatively high, the validity of <br /> RPD as a quality control measurements decreases as concentrations approach the detection <br /> limit, thus increasing the margin of error The data is therefore not considered invalidated <br /> by low readings of these compounds in one sample of the sample pair A lack of detection <br /> of these compounds in either the equipment blank or the method blank further suggests that <br /> laboratory or field contamination did not cause the difference reported results for the <br /> duplicate pair The detection limit for each analysis is shown on the analytical report <br /> (Appendix B). The chemical data assessed by the above review are considered adequate and <br /> valid for their intended use <br /> 91CO238$/MAJORMAR7 Qkff 02-20.92 3-4 <br />