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Weldon Church Site Background Information <br /> Page 12 of 12 <br /> • MTBE was not detected above laboratory reporting limits in the air samples <br /> collected. Laboratory reporting limits were below the established SFBRWQCB <br /> Residential ESL of 9.4 pg/m3 for MTBE in indoor air. <br /> • DIPE, ETBE, TAME, and TBA were not detected above laboratory reporting limits <br /> in the air samples collected. <br /> • TPH-g and BTEX concentrations detected in crawl space samples collected in <br /> September 2011 increased by a factor of 1,000 compared to the May 2011 <br /> investigation. <br /> HUMAN HEALTH RISK ASSESSMENT <br /> Using RISC5 software(human health and ecological risk assessment tool for contaminated <br /> sites), a Human Health Risk Assessment (HHRA) was performed for inhalation of indoor <br /> air by an average adult at 104 West Beverly Place, Tracy, CA. The HHRA was performed <br /> to assess the cancer risk and hazard index of inhalation of indoor air from benzene <br /> concentrations detected in crawl space samples at the site. The maximum benzene <br /> concentration (930 pg/m3; Crawl Space-2) detected in crawl space samples collected on <br /> 27 September 2011 was used for the assessment. The assessment calculated the cancer <br /> risk at 0.00068 and the hazard index at 23. <br /> The HHRA indicated a risk for exposure (inhalation of indoor air) to benzene greater than <br /> the acceptable cancer risk and hazard index determined by the Department of Toxic <br /> Substance Control. <br /> Advanced CeoEnvironnrental,Inc. <br />