SITE INFORMATION AND CORRESPONDENCE

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New West Petroleum • - 2 - • 26 November 2012 6437 Banner Street Lodi, San Joaquin County USTs, and screened from 25' to 45' bgs in the B zone, while MtBE was not detected in adjacent A zone MW-4A, indicative of a MtBE plume that was diving while migrating towards the southeast (groundwater flow direction). On 12 September 2005, Regional Board staff collected split groundwater samples from MW-4A and MW-4B. The split sample results were MtBE, 400 pg/L at MW-413, which correlated to the previous 360 pg/L result. Split sample results from two San Joaquin County municipal water supply wells for Flag City, County Supply Area 31 Well 1 (CSA-31-1), located approximately 1,600' southeast of the Site; and CSA-31-2, located approximately 700' south-southeast of the Site, were non-detect in September 2005. In November 2005, off-site monitoring wells MW-5A, MW-5B, MW-61B, and MW-6C and Site groundwater extraction wells EW-1 through EW-5 were installed, and batch groundwater extraction began onsite. On 5 December 2005, MtBE at 210,000 pg/L and Tert Butyl Alcohol at 260,000 pg/L were detected in EW-4. Benzene (1.1 pg/L) and Toluene (1 pg/L) were also detected on that date in MW-6C. Approximately 103,105 gallons of water and 38.73 lbs. of MtBE were extracted and transported offsite for disposal through June 2006. An Enhanced Leak Detection (ELD) tracer gas test was conducted 18 January 2006. The ELD report showed no tracer gas vapor leaks, however, a vapor recovery bucket for the 87 octane tank failed containment in a separate watertight test, indicating that vapors and/or vapor condensate could be the source of the MTBE release. In March 2006, MtBE was detected at 160 pg/L in groundwater at MW-6B, screened in the B zone at 25' to 45' bgs, 400' downgradient from the USTs, and approximately 300' upgradient from CSA-31-2. MtBE was not detected in the adjacent deeper well MW-6C (54' to 74' bgs). At that time supply well CSA-31-2 was being used as a backup to CSA-31-1 during periods of high demand, in order to slow MTBE plume migration. When CSA-31-1 went offline due to mechanical problems in June 2006, CSA-31-2 became the primary source of drinking water for Flag City. Subsequently SJCEHD requested installation of an interim groundwater extraction and treatment system (GWETS) as soon as possible. On 23 June 2006, the SJCEHD transferred regulatory oversight of the USTs case to the Regional Board due to threats to a nearby municipal supply well. Monitoring wells 7B, 7C, 813, 8C, 9B, 9C, and 9D were installed in August 2006. In September 2006, the GWETS (extraction and treatment) system went online under Regional Board General Permit R5-2008-0085 for an NPDES discharge to the CSA-31 storm sewer. A Cleanup and Abatement Order (CAO) No. R5-2007-0709 was issued by the Regional Board Executive Officer on 30 April 2007. CAO No. R5-2007-0709 required a Corrective Action Plan and a Human Health Risk Assessment for the Site and adjacent properties impacted by the groundwater plume. Four soil vapor samples were collected and eight monitoring wells (MW-10A through MW-10D, MW-11 B,