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S E C Q R <br /> Ms. Lori Duncan <br /> ARCO Station 4493 <br /> Site Closure Report <br /> October 31,2006 <br /> Page 6 <br /> visible. The ARCO site is located in Stockton's CBD and is predominantly commercial offices and <br /> retail. The Port of Stockton extends to Weber point, immediately west of the site. <br /> Eight water supply wells were located in the vicinity of the ARCO site in DWR well searches. <br /> Inquiries at CSMUD and CWS revealed that all production wells in the vicinity of the site are <br /> currently inactive due to existing water quality issues. No other sensitive receptors were identified. <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> The following information fulfills the RWQCB Central Valley Region's requirements for site closure. <br /> • All USTs and appurtenances have been removed from the site. <br /> • The extent of soil and groundwater contamination has been- ascertained from the <br /> investigations conducted at the site. <br /> f: The GRO plume will shrink both in size and concentration over time through natural <br /> attenuation. <br /> The contaminant plume is not migrating and the concentrations of benzene and MtBE will <br /> likely reach groundwater standards due to natural attenuation within the next 10 years. Z <br /> • The chlorinated hydrocarbon plume is significantly larger,more dispersed,as well asup yd <br /> cross gradient from the contaminate plume sourced at the site. Thus,the data sugge s that <br /> the source of chlorinated hydrocarbons in groundwater is offsite. <br /> • No sensitive receptors are likely to be impacted by the petroleum hydrocarbon plume. <br /> Based on the review of historical soil and groundwate I investigation, SECOR requests that ARCO <br /> Station 4493 be considered"low risk"and recommends closure and No Further Action. A checklist <br /> of data required by the RWQCB for no further action at UST sites is presented in Attachment H. <br /> References <br /> URS, 2003. Monitoring Well Installation Report. February 4, 2003. <br /> U RS, 2004a. Deep Monitoring Well Installation and Fourth Quarter 2003 Groundwater Monitoring <br /> Report. March 25, 2004. <br /> URS, 2004b. Dual-Completion Monitoring Well Installation Report. July 26, 2004. <br /> SECOR, 1999a. Soil Sampling during UST, Product Line, and Dispenser Removal Activities,July 7, <br /> 1999. - <br /> SECOR, 1999b. Monitoring Well Installation Report, July 7, 1999. <br /> SECOR, 2000. Additional Site Assessment Report. September 5, 2000. <br /> SECOR, 2002. Dual-Completion Well Installation Report. August 21, 2002. <br /> t� <br />