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SE C OR <br /> October 31, 2006 <br /> Ms. Lori Duncan, �ypu �UUb <br /> Senior REHS AAT 1IAL�H <br /> San Joaquin County Environmental Health Departmenty1JIRc ERVIC�S <br /> 304 E. Weber Avenue _ R�h1115 <br /> Stockton, CA 95202 <br /> Re: Revised Site Closure Report <br /> Former ARCO Station 4493 <br /> 205 North Center Street <br /> Stockton, California <br /> Dear Ms. Duncan: <br /> Secor International Inc., (SECOR), on behalf of Atlantic Richfield Company, a BP Affiliated <br /> Company, has prepared this addendum to the site closure report for the former ARCO Service <br /> Station Number 4493 (the Site) located at 205 North Center Street in Stockton, California. <br /> This revised site closure report addresses the comments in the San Joaquin County Environmental <br /> Health Department(SJCEHD)letter dated September 29,2006(Attachment A). The SJCEHD letter <br /> was prepared in response to the SECOR Site Closure Report dated July 31, 2006. The following <br /> outlines the mass of contaminant remaining,the concentration contours for contaminants,timeline <br /> projection for ground water to return to pre-release conditions, and a discussion of chlorinated <br /> hydrocarbon trends at the site. <br /> SITE BACKGROUND <br /> Former ARCO Station 4493 is located at 205 North Center Street in Stockton, California (Figure 1). <br /> Three 12,000-gallon underground storage tanks (USTs) were installed at the site in 1984. The <br /> service station was demolished, and the USTs were removed during the first quarter of 1999. The <br /> site is on property identified as Weber Point; the Stockton Channel is adjacent to the site to the <br /> south. The City of Stockton has redeveloped the Weber Point area as a city park (Figure 2). <br /> PREVIOUS INVESTIGATIONS <br /> In July 1997, SJCEHD sent a letter to Atlantic Richfield Company stating that the former Shell <br /> service station approximately 300 feet east of ARCO Station 4493 had reported increasing <br /> concentrations of methyl tertiary-butyl ether(MtBE)in the Shell upgradient wells. These wells were <br /> to the northeast of the ARCO station; northeast is a dominant historical groundwater flow direction <br /> near the ARCO site. The gasoline stored at the Shell station reportedly never contained MtBE. The <br /> Shell site was granted closure by the California Regional Water Quality Control Board (RWQCB), <br /> and the groundwater monitoring wells at the Shell site were subsequently abandoned. <br /> Excavation and removal of one waste-oil tank,three gasoline USTs,and associated dispensers and <br /> product lines were performed by Henderson Construction of Stockton, California on February 24, <br /> 1999. The excavated USTs consisted of three 12,000-gallon capacity tanks of double-walled <br /> fiberglass construction. On April 13, 1999, one 300-Ballon capacity waste-oil tank was excavated <br />