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Vapor Intrusion Mitigation System Work Plan WELDON CHURCH PROPERTY 104 West Beverly Place, Tracy, California 1.0. INTRODUCTION At the request of Mr. Weldon Church, Advanced GeoEnvironmental, Inc. (AGE) has prepared the enclosed work plan for 104 West Beverly Place, Tracy, California. The scope of work includes the installation of a vapor intrusion mitigation system in the crawl space at 104 West Beverly Place, Tracy, CA. The work plan was prepared as directed by San Joaquin County Environmental Health Department(EHD) letter dated 22 November 2011 . The location of the site is illustrated in Figure 1. A plan of the site is illustrated in Figure 2. In May and September 2011, air samples were collected from the crawl space of the residence at 104 West Beverly Place, Tracy, CA. Total petroleum hydrocarbons quantified as gasoline (TPH-g), benzene, toluene, ethylbenzene, and xylenes (BTEX)were detected in crawl space air samples collected during both events. Concentrations of TPH-g and BTEX detected in crawl space air samples in May and September 2011 were above the San Francisco Bay Regional Water Quality Control Board Environmental Screening Levels (ESLs) and California Human Health Screening Levels (CHHSLs)for indoor air. However, TPH-g and BTEX concentrations detected during the September 2011 were significantly higher than the May 2011 concentrations. A Human Health Risk Assessment(HH RA) was performed using the maximum benzene concentration (930 pg/m3; Crawl Space-2) detected in crawl space samples collected in September 2011. The assessment calculated the cancer risk at 0.00068 and the hazard index at 23. Procedures and results of previous crawl space air and soil-vapor investigations are summarized in the site background presented in Appendix A.Analytical results of air samples and soil-vapor samples collected at the site are presented in Tables 1 and 2, respectively. Based on the results of the September 2011 crawl space air investigation and the HHRA, the EHD directed that a vapor intrusion mitigation system be designed to abate the petroleum-impacted soil vapor intrusion within the crawl space of the residence at 104 West Beverly Place, Tracy, CA. This work plan has been prepared in accordance with Central Valley Regional Water Quality Control Board (CVRWQCB)guidelines for the investigation of underground storage tanks (UST) sites. Additionally, the work plan was prepared utilizing guidance provided in the Interstate Technology Regulatory Council (ITRC)-prepared, Vaporintrusion Pathway: A Practical Guideline dated January 2007 and the Department of Toxic Substance Control (DTSC)-prepared, Guidance For The Evaluation And Mitigation Of Subsurface Vapor Intrusion To Indoor Air-Final(Vapor Intrusion Guidance), dated October 2011 and Vapor Intrusion Mitigation Advisory - Final (VIMA), dated October 2011. Advanced GeoEnvironmental,Inc.