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_a a• <br /> TR GLOBAL <br /> ENVIRONMENTAL <br /> February 14, 1994 <br /> Ms. Diane M. Hinson <br /> Ms. Mary Meays <br /> San Joaquin County Public Health Services <br /> P.O. Box 388 <br /> Stockton, CA 95201-0388 <br /> SUBJECT: CATELLUS DEV. PROPERTY - MOBILE LABORATORY DATA <br /> Ms. Hinson & Ms. Meays: <br /> I have just reviewed your letter to Mr. Ric Notini of Catellus Development <br /> Corporation regarding the BTEX data produced in our Sacramento mobile <br /> laboratory at the Catellus site, 1325 & 1515 West Weber St., Stockton, CA. <br /> First, before addressing some of the comments in your letter, let me state clearly <br /> that TEG will do whatever necessary to provide data to your satisfaction. We <br /> are most concerned with providing quality data that.you and our clients can have <br /> confidence in, and will do whatever it takes to achieve that level of confidence. <br /> With that said, I'd like to address the primary issue of concern: are BTEX data <br /> valid when soil samples are prepared using a liquid-solid extraction procedure <br /> with freon? The reason we use this procedure is not for time savings, but to <br /> eliminate the blanks and sample carry-over that are so common with purge & <br /> traps. Our worst fear as an analytical laboratory is to report a "false positive", <br /> and with detection levels of 5 ppb, the chances of this occurring are greatly <br /> increased. The freon extraction procedure rarely shows blanks (so long as the <br /> freon is fresh) and the potential for carry-over is eliminated because each <br /> sample has an independent, non-reusable preparation vial. You might imagine <br /> that these virtues are extremely beneficial. <br /> We conducted many tests on both soil & water samples prior to employing this <br /> method, including regular EPA performance samples. The results have <br /> convinced us that this preparation method is superior to purge & trap for both <br /> matrices. To demonstrate this to you, attached are 2 sets of EPA performance <br /> samples (January 24, 1992 & July 14, 1993). You can see that the EPA <br /> Mobile and LaboratoryAnaiyticalServices Environmental Subconsulting GeochemicalR&D Soil VaporSurveys AirMonitoring <br /> 432 N. Cedros Ave., Solana Beach, CA 92075 Ph: (619) 793-0401 Fax: (619) 793-0404 <br />