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A N A I. Y T I C A L LABORATORIES August 2, 1999 P _ San Joaquin Environmental Health Division 304 East Weber Avenue, 3`d Floor Stockton, CA 95202 Attention: Laticia Briggs Dear Ms. Briggs: BSK Analytical Laboratories uses a standardized procedure to determine Method Detection Limits(MDL) and Practical Quantitation Limits(PQL), (also known know Estimated Quantitation Limits—EQL). I have attached portions from the Handbook of Environmental Analysis, which gives an excellent explanation of detection limits and their determination. Especially note the procedure for the statistical determination of the MDL, and the need for a multiplying factor to yield the PQL. Please note also the discussion of EQL taken from EPA Method 8260B. Also included for your information is the BSK Analytical Laboratory MDL study for Oxygenates by Method 8260, and the PQL's that result for liquid and soil matrices. Also attached are mass spectra of MTBE concentrations that we would report as"Trace" hits—between the MDL and the PQL. We believe BSK Analytical Laboratories reports scientifically valid detection limits determined by techniques accepted by the environmental laboratory community. We also believe our detection limits, especially for GUMS methods, are in the realm of reasonable limits for routine, production lab operations. Of course, extraordinary techniques can be used to allow a laboratory to report lower detection limits, but at some point adherence to the analytical techniques and sample sizes allowed by SW 846 methods are exceeded. Our main concern is that all laboratories and their reporting limits be evaluated according to the same standards of data quality and reporting limit determination. Otherwise those that use the data produced by laboratories can develop unreasonable or mistaken expectations. BSK Analytical Laboratories Wabor ely elewyn atory Director 1414 Stanislaus Street • Fresno, CA 93706-1623 • Phone 559-497-2888, In CA 800-877-8310 • Fax 559-485-6935