DETECTION LIMITS, PQLs AND NJQLs Presented by Stu Nagourney NJDEP, OQA

MDL DEFINITION Defined at 40 CFR 136 Appendix D The minimum concentration of a substance that can be measured and reported with 99-percent confidence that the analyte concentration is greater than zero and is determined from the analysis of a sample in a given matrix containing the sample

OTHER DEFINITIONS IDL RL ML

MDL CALCULATION Seven (7) replicates at ~ [5 times] the background noise: should be at or near the low calibration standard Multiply by (z) distribution factor 3.14 time the S.D. = MDL The MDL is more dependent upon precision than accuracy Labs. must demonstrate that they can see a signal at the MDL

MDL ISSUES TO CONSIDER Many regulatory standards near detection limit Lab credibility often associated with detection limits Maze of tests and matrices make it difficult to find a universally applicable technique Calculating detection limits can be expensive

WHY YOU CAN’T SET PERMIT LEVELS @ THE MDL MDLs vary by day, lab., analyst & method Precision at low levels are usually poor Good for false-positives; false negatives may be reported 50% of the time Inherent uncertainties make enforcing permit levels @ MDL values impossible

MDLs to PQLs PQL: Practical Quantitation Limit PQL = Average (Median) MDL x 5 Sources of MDL data Interlaboratory low-level studies Applying statistics to low-level cal. data Method data where available Most data is now 5-12 years old!!!

PQLs to NJQLs The Department recognizes that the current PQL data is based upon out-dated technology OQA already requires certified labs. to collect MDL data by method and media What we need is current, representative data and a way to manage it

NJQLs & NJDEP OQA is contracting for the development of a database to collect MDL data from NJ certified labs. and then generate NJQLs (avg. MDL x 5) NJQLs to be generated by analyte, matrix, method DW WP SHW DEP programs will have a choice in selecting an NJQL for their individual needs