WORK PLANS - Laserfiche WebLink

Home Browse Search

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