SITE INFORMATION AND CORRESPONDENCE

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• .A°'� California Regional Water Quality Control Board OWCentral Valley Region � Linda S.Adams Arnold Secreian.for 11020 Sun Center Drive 8200.Rancho Cordova,Cal itornia 956706114 Schwarzene er bnwomnenial Phone(916)464-3291 •FAX(916)464-4645 BB Prwecrimr help:/hvw%v.waterboards.ca gov/central alley Goremor To: Jim Munch�/ FROM: Jim Barton Senior Waterrll. Resources ontro Engineering Geologist Engineer OCT 14 2009 Underground Storage Tanks ENVIRON6IENT HEALTH Enforcement Unit II� PERMIT/SERVICES DATE: 30 September 2009 SIGNATURE: A� SUBJECT: CLOSURE MEMO, SHELL NO. 204-7524-4404, 3011 W. BENJAMIN HOLT DRIVE, STOCKTON, (CASE #390557) Background The Site was an operating Shell-owned station located north of West Benjamin Holt Drive and east of Interstate 5 (1-5) in Stockton. On 4 April 1990, the San Joaquin County Environmental Health Department (SJCEHD) issued an Unauthorized Release Form (URF) for total petroleum hydrocarbons as diesel (TPHd, 1.2 milligrams per kilogram or mg/kg) release to soil reported in January 1990. The SJCEHD notified Shell on 23 March 1992 that the Site had been placed in the Local Oversight Program. Shell reported low levels of petroleum hydrocarbons in soil in 1990, and also in groundwater in 1994. There have been USTs releases at two separate locations at the Site (enclosed Figure 2): Release #1, from a first generation (Gen 1) of underground storage tanks (USTs) removed in 1987 and 1996; and Release #2, from a second generation (Gen 2) of USTs installed in 1996 approximately 120 feet southeast of the Gen 1 tanks. After installation of the Gen 2 tanks, Shell reported high levels of MTBE in groundwater that increased three orders of magnitude from 1996 to 1997. The Gen 2 tanks were removed in 2004. Release #1: One 550-gallon waste oil UST was removed in June 1987. Two 8,000-gallon gasoline and a second 550—gallon waste oil USTs were removed in October 1996. Maximum soil confirmation sample results from the Gen 1 USTs excavation in 1996 were: total petroleum hydrocarbons as gasoline (TPHg), 41 mg/kg; benzene, 0.064 mg/kg; and methyl tert-butyl ether (MTBE), 1 .1 mg/kg. After the 1996 Gen 1 USTs were removed, two 15,000-gallon gasoline and one 550-gallon waste oil Gen 2 LISTS were installed and the Shell station continued operations. Release #2: The MTBE impacts to groundwater increased several orders of magnitude from November 1996 to February 1997. In 1999, during Site remodeling for street construction, a piping leak was observed near a product dispenser and confirmed by one soil sampling result (MTBE, 0.0404 mg/kg). Subsequently, Shell terminated their ownership of the Site, and in November 2004 the two 15,000-gallon gasoline and one 550-gallon waste oil Gen 2 USTs, and dispensers and piping were removed (Figure 2). Confirmation soil samples obtained from the 2004 Gen 2 USTs excavation pit did not contain detectable soil contamination, however, California Environmental Protection Agency Qd Re,I,led raper