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Page 2 <br /> Weldon Church Property April 1, 2011 <br /> 104 West Beverly Place <br /> Tracy, California 95376 <br /> monitoring, and not indoor air monitoring, is being completed, the Guidance states that the <br /> United States Environmental Protection Agency (EPA) "recommends that ambient sampling <br /> begin at least one hour and preferably two hours before indoor air monitoring begins and <br /> continue until at least 30 minutes before indoor monitoring is complete. This practice is <br /> recommended since most buildings have an hourly air exchange rate in the range of 0.25- <br /> 1.0, and thus air entering the building in the period before the indoor sampling remains in <br /> the building for a long time." The EHD suggests this procedure be followed for the crawl <br /> space air monitoring. <br /> AGE proposes to collect air samples over an approximate 24-hour period based on a <br /> calibrated flow rate of 3.8 milliliters per minute (ml/min.), and analyze the samples for total <br /> petroleum hydrocarbons quantified as gasoline (TPH-g) by EPA method TO-3; and <br /> benzene, toluene, ethylbenzene, and total xylenes (BTEX); and other volatile organic <br /> compounds including methyl tertiary-butyl ether (MTBE), ethyl tertiary-butyl ether (ETBE), <br /> tertiary-amyl methyl ether (TAME), di-isopropyl ether (DIPE), and tertiary butyl alcohol (TBA) <br /> by EPA method TO-15. AGE states that"The lowest possible method detection limits will be <br /> achieved, which will allow comparison with established guidelines." The EHD directs that <br /> the laboratory not report sample concentrations at the method detection limit but at the <br /> laboratory reporting limit. AGE also states that "Air sample analytical results will be <br /> compared and evaluated with threshold concentrations established by the San Francisco <br /> Bay Regional Water Quality Control Board Environmental Screening Levels (ESLs) and <br /> California Human Health Screening Levels (CHHSLs). Since it was not specified what ESLs <br /> will be used to evaluate the analytical results, the EHD directs that ESLs listed in Table E-3. <br /> Ambient and Indoor Air Screening Levels be used to evaluate the air sample concentrations. <br /> The EHD approves the work plan with these modifications. Please notify the EHD when the <br /> air samples will be collected and complete the fieldwork by 25 May 2011. <br /> If you have any questions concerning this letter, please contact Vicki McCartney at (209) <br /> 468-9852, or by email at vmccartney@sjcehd.com. <br /> Sincerely, <br /> �--6��Cv, <br /> Victoria L. McCartney, REHS Nuel C., Henderson, Jr., PG <br /> Senior Registered Environmental HeaTItSpecialist Engineering Geologist <br /> c: Mr. Brian Millman, Advanced GeoEnvironmental, Inc. 837 Shaw Road, Stockton, <br /> California 95215 <br /> Mr. James L.L. Barton, PG, California Regional Water Quality Control Board Central <br /> Valley Region, 11020 Sun Center Drive, Suite 200, Rancho Cordova, California 95670 <br /> Frank and Bette A. Grande Family LP, Post Office Box 1076, Tracy, California 95378 <br />