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11 <br />Project Plan <br />Revision 6 <br />1/8/1988 <br />Page 17 of 37 <br />Percentage of analyte recovered and % R.S.D. are the main parameters <br />for building the Laboratory Control Chart. The control chart is updated <br />monthly. The mean and S.D. are calculated monthly based on the raw data <br />which falls inside the control limits. The 95% (mean 2 S.D.) confidence <br />interval of each parameter is used as warning limits, while the 99% <br />interval (mean 3 S.D.) is used as rejecting limits. <br />A result outside the warning limits will be verified by a repeat <br />measurment. A verified result outside the Critical Limits will be <br />investigated as to cause and corrective action will be taken. <br />5.3 IntralaboratorY Check Samples <br />Intralaboratory check samples are submitted on a regular basis, the <br />frequency of which is governed by the frequency and importance of the <br />analyses results of the last check sample and actual samples in the same <br />way, with no special treatment. Some Intralaboratory check samples will be <br />disguised as actual sample to further insure no special treatment. The <br />intralaboratory check sample is used to check in house QA procedures. <br />5.4 Sources for Standards <br />To ensure the quality of working standards, several sources are <br />available. <br />5.4.1 EPA Reference Samples <br />samples is the EPA. A wide variety of <br />The best source for reference <br />pollutant samples is available and the list is increasing. Most of the <br />supplied true values are now complete with SD the results of previous <br />analyses by many different laboratories. These precision data are the best <br />available for judging the overall performance of a method. <br />23 <br />