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Weldon Church Properties %ago, `'w Page 2 <br /> 104 West Beverly Place February 2, 2012 <br /> Tracy, California 95376 <br /> northwest corner, and one from the south-central areas beneath the residence; and three <br /> ambient air samples, one from the east, west and south areas of the backyard of the <br /> residence. Although the EHD concurs that one of the indoor air samples should be collected <br /> in the primary living area (in the center of the room, away from doors) the EHD recommends <br /> collecting the second indoor air sample in the bathroom or kitchen. The DTSC Cal EPA <br /> Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air(Vapor <br /> Intrusion Guidance), dated October 2011, suggests sampling indoor air in the kitchen or <br /> bathroom since these are likely locations for subsurface vapor entry. <br /> AGE did not provide a rational for selecting the three locations to collect crawl space samples <br /> beneath the dwelling at 104 West Beverly Place. Without this information, the EHD suggests <br /> that the proposed sampling point at the northeast corner of the crawl space be relocated near <br /> an area where utilities enter the home at 104 Beverly Place. <br /> Although there are major differences when collecting ambient air samples between the two <br /> guidance documents used to prepare the work plan (DTSC Cal EPA Guidance for the <br /> Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air (Vapor Intrusion <br /> Guidance), dated October 2011, and the Interstate Technology Regulatory Council (ITRC) <br /> Technical and Regulatory Guidance Vapor Intrusion Pathway: A Practical Guideline, dated <br /> January 2007), the EHD approves the proposals for collecting the three ambient air samples <br /> as presented by AGE in the work plan. The EHD suggests following the United States EPA <br /> (USEPA) recommendation that ambient sampling begins at least one hour and preferably two <br /> hours before indoor air monitoring begins and continue until at least 30 minutes before indoor <br /> monitoring is complete. <br /> AGE proposes to have the air samples analyzed by EPA method TO-3 for total petroleum <br /> hydrocarbons quantified as gasoline (TPH-g) and EPA method TO-15 for benzene, toluene, <br /> ethylbenzene and total xylenes (BTEX) and "volatile organic compounds including all <br /> oxygenated compounds." Please include methyl tertiary-butyl ether (MTBE), ethyl tertiary- <br /> butyl ether (ETBE), di-isopropyl ether (DIPE), tertiary-amyl methyl ether (TAME), and tertiary <br /> butyl alcohol (TBA). Since the DTSC Cal EPA Guidance for the Evaluation and Mitigation of <br /> Subsurface Vapor Intrusion to Indoor Air (Vapor Intrusion Guidance), dated October 2011, <br /> suggests a method reporting limit of at least 0.025 micrograms per cubic meter (pg/m3), <br /> please assure that the lowest possible method reporting limits be reported by the analytical <br /> laboratory. <br /> With these recommendations, the EHD approves the work plan as submitted by AGE. Please <br /> collect the air samples no later than 01 March 2012. <br /> If you have any questions concerning this letter, please contact Vicki McCartney at (209) 468- <br /> 9852, or by email at vmccartney@sjcehd.com. <br /> Sincerely, <br /> -eke,6�'� <br /> Victoria L. McCartney, REHS Nuel C., Henderson, Jr., PG <br /> Senior Registered Environmental Health pecialist Engineering Geologist <br />