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

2. 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

3. OTHER DEFINITIONS
IDL RL ML

4. 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

5. 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

6. 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 MDL values impossible

7. 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!!!

8. 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

9. 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