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I _,ample Description EnseCC <br />. See the attached Sample Description Information. <br /> The samples were received under chain-of-custody. <br /> II <br /> Analysis Request <br /> The following analytical tests were requested. <br /> Lab ID Analysis Description <br /> 045870-1,2 Total Petroleum Hydrocarbons <br /> Benzene, Toluene, Ethyl Benzene, Xylenes <br /> III Ouality Control <br /> A. Project Specific QC. No project specific QC (i .e. , spikes and/or <br /> duplicates) was requested. <br /> B. Method Blank Results. A method blank is a laboratory-generated <br /> sample which assesses the degree to which laboratory operations <br /> and procedures cause false-positive analytical results for your <br /> samples. <br />. No target parameters were detected in the method blanks associated <br /> with your samples at the reporting limit levels noted on the data <br /> sheets in the Analytical Results section. <br /> C. Laboratory Control Sam les. An LCS is a well -characterized matrix <br /> (blank water, sand or celite) which is spiked with certain target <br /> parameters and analyzed at approximately 10% of the sample load in <br /> order to establish method-specific control limits. The LCS <br /> results associated with your samples are on the attached <br /> Laboratory Control Sample Report. <br /> Accuracy is measured by Percent Recovery as in: <br /> recovery = measured concentration x 100 <br /> (actual concentration) <br /> Precision is measured using duplicate tests by Relative Percent Difference <br /> (RPD) as in: <br /> RPD = (% recovery test I - % recovery test 21 x 100 <br /> (% recovery test 1 _+ % recovery test 2)/2 <br /> Control limits for accuracy (percent recovery) are based on the average, <br /> historical percent recovery +/-3 standard deviation units. Control limits <br /> for precision (relative percent difference) range from 0 (identical <br /> duplicate LCS results) to the average, historical relative percent <br /> difference + 3 standard deviation units. These control limits are updated <br /> on a quarterly basis. In cases where there is not enough historical data, <br /> EPA limits or advisory limits are set, with the approval of the Quality <br /> Assurance department. <br /> i <br />