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laboratory prepares a formal written response to each DQR explaining the <br /> discrepancy. The DQR is the first line of investigation following any <br /> anomalous result. <br /> 6.3 Practical Quantitation Limits (PQLs) <br /> JHC proposes to utilize laboratory-specific PQLs as the reporting limits of <br /> applicable low-detection analytes (especially organics). The U.S. EPA <br /> developed the concept of the PQL to address the issue of analytical <br /> variability. The PQL concept was developed for compliance with the Safe <br /> Drinking Water Act(50 FR 46906, Nov. 13, 1985)where it is defined: "The <br /> PQL thus represents the lowest level achievable by good laboratories <br /> within specified limits during routine laboratory operating conditions." <br /> The U.S. EPA's defined method detection limit(MDL), as published in 40 <br /> CFR 136,has limited application. The Agency acknowledges that"MDLs <br /> are not necessarily reproducible over time in a given laboratory, even <br /> when the same analytical procedures,instrumentation and sample matrix <br /> are used" (50 FR 46906, Nov. 13, 1985). Use of MDLs may result in false <br /> positives since U.S. EPA admits it is an ideal limit that cannot be reliably <br /> measured by even the best laboratories. Therefore, in its regulatory <br /> programs, U.S.EPA has determined that the PQL is a more appropriate <br /> measure for compliance purposes. <br /> In contrast to the PQL, which is a measure of analytical precision, the <br /> method detection limit(MDL)is a hypothesis test that leads to the binary <br /> decision of whether or not an analyte is present or absent in a sample. The <br /> MDL is defined by the U.S. EPA as the "minimum concentration of a <br /> substance that can be measured and reported with 99 percent confidence <br /> that the true value is greater than zero" (50 FR 46906, Nov. 13, 1985). <br /> California Concentrates Monitoring Well Work Plan Issued: June 8,2001 <br /> JHC Project No.493-01 11 Revision 1 <br />