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29 November 2005 <br /> Flag City Chevron Fact Sheet <br /> Page 4 of 5 <br /> an estimated 0.28 gallons of MTBE remaining in ground water at the site. <br /> 6.0. RISK ASSESSMENT ANALYSIS <br /> RISC Workbench 4(RISC), a commercial risk assessment and fate and transport software initially <br /> developed by British Petroleum Company in 1994,was utilized to demonstrate potential impact to <br /> down-gradient municipal water well CSA No. 2,and to assess the potential human health risk; in <br /> addition,clean-up levels for all identified exposure routes were evaluated for the more conservative <br /> residential exposure at the site.The RISC analyses followed standard procedures outlined in the U.S. <br /> EPA's Risk Assessment Guidance for Superfund, dated 2001, to calculate exposure assessment, <br /> toxicity assessment, and risk characterization, and ASTM E-1739 for risk-based corrective action <br /> (RSCA). The following is a brief summary of risk assessment findings: <br /> • The fate and transport study of the contaminated ground water plume and the contaminated <br /> soil plume predicted that CSA Well No. 2 was unlikely to be impacted by MTBE from a soil <br /> or ground water source. <br /> • AGE analyzed the risks to a residential adult and child inside the mini-mart building on the <br /> site. MTBE was the only constituent considered to be a carcinogenic risk; the maximum <br /> (worst case scenario) carcinogenic risk from MTBE was approximately I case per million <br /> inhabitants for all fate and transport models analysed. The hazard index from MTBE was <br /> 0.01 or less. <br /> • The RISC analysis determined that no MTBE clean-up was necessary for the typical site <br /> models because the site MTBE concentrations did not exceed the site-specific target cleanup <br /> levels (SSTL). <br /> • AGE concludes that MTBE-impacted soil and ground water remaining beneath the site <br /> appear to pose minimal risk to human health and beneficial use of ground water down- <br /> gradient from the subject site. <br /> 7.0. REQUEST FOR SITE CLOSURE <br /> Based on the findings from the Flag City Chevron leaking UST investigation,a Site Closure Report <br /> (dated 31 August 2005) was prepared for the RWQCB with the following requests: <br /> • That no further subsurface investigation be performed at this site. Flag City Chevron has <br /> adequately assessed MTBE-impacted soil and ground water associated with the Flag City <br /> Chevron UAR. <br /> • That the RWQCB rescind Cleanup and Abatment Order (C&A) 5-00-700. AGE is of the <br />