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EI"Lsc I Sample Description See the attached Sample Description Information. The samples were received under chain-of-custody. II Analysis Request The following analytical tests were requested. t. Lab ID Analysis Description 044625-1 thru 4 Chloroform LW III Quality Control LW A. Project Specific QC. No project specific QC (i .e. , spikes and/or duplicates) was requested. B. Method Blank Results. A method blank is a laboratory--generated sample which assesses the degree to which laboratory operations and procedures cause false-positive analytical results for your samples. No target parameters were detected in the method blanks associated �., with your samples at the reporting limit levels noted on the data sheets in the Analytical Results section. C. Laboratory Control Samples. An LCS is a well-characterized matrix blank water, sand or celite) which is spiked with certain target parameters and analyzed at approximately 10% of the sample load in order to establish method-specific control limits. The LCS L= results associated with your samples are on the attached Laboratory Control Sample Report. Accuracy is measured by Percent Recovery as in: % recovery = measured concentration x 100 actual concentration &. Precision is measured using duplicate tests by Relative Percent Difference ' (RPD) as in: ,.. RPD = % recovery test 1 - % recover test 2 x 100 % recovery test 1 + % recovery test 2 /2 Control limits for accuracy (percent recovery) are based on the average, historical percent recovery +/-3 standard deviation units. Control limits for precision (relative percent difference) range from 0 (identical �. duplicate LCS results) to the average, historical relative percent difference + 3 standard deviation units. These control limits are updated on a quarterly basis. In cases where there is not enough historical data, w EPA limits or advisory limits are set, with the approval of the Quality Assurance department. &.