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STATE OF CALIFORNIA---HEALTH AND WELFARE AGENCY PETE WILSON, Governor <br /> DEPARTMENT OF HEALTH SERVICES AUG 0 7 IM <br /> RNvIRONNENTAL LABORATORY ACCREDITATION PROGRAM ENVIRONMENTAL HEALTH 1 <br /> 2151 BERKELEY Annex 2 PERMIT/SERVICES <br /> BERKELEY, CA 947094704 <br /> (415) 540-2800 <br /> August 1, 1991 <br /> Ms. Letitia Reach <br /> Environmental Health Division <br /> San Joaquin County <br /> P.O. Box 2009 <br /> Stockton, CA 95201 <br /> Dear Ms. Reach: <br /> This letter is in reply to your concerns on the data submitted by McLaren <br /> Analytical Laboratory on sample # 40431 date 12/31/89. Based on the information <br /> in the report, it appears this sample is different from the other samples that <br /> were taken from the same site. <br /> The laboratory's comment, "1:1000 dilution required due to heavy late eluting <br /> matrix interference", was not supported by any data supplied, for our review. <br /> This comment may be true, that is one of the laboratory practices used to reduce <br /> interference in a sample. The result is then corrected for the dilution factor, <br /> which results in a higher reporting limit. <br /> The laboratory can set a reporting limit at which it can reliablj( quantitate, but <br /> that limit should meet the regulatory agency's requirements. If the laboratory <br /> cannot meet the laboratory's method detection or quantitation limits, then there <br /> should be scientifically sound reasons for not meeting those limits. Because <br /> dilution raises the method detection and quantitation limits, it should be the <br /> method of last resort in eliminating interference in a sample, except when the <br /> method detection limit is low enough that the result will still be below the <br /> regulatory limit. <br /> I hope that this clarifies the issues involved. If you have further questions, <br /> please call me at the above number. <br /> Sincerely, <br /> aa /I c6� <br /> Aida S. Dente <br /> Public Health Chemist II <br /> Environmental Laboratory <br /> Accreditation Program <br />