SITE INFORMATION AND CORRESPONDENCE

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r Shell Service Station 2320 N.EI Dorardo Street Page 2 of 2 During November 2006, MW-5 and MW-6 were installed down-gradient to a depth of 40 feet below surface grade (bsg) to define the lateral extent of impacted groundwater. The soil samples from these well borings contained 1,2-dichloroethane (1,2-DCA) and ethylene dibromide (EDB) at low concentrations.During December 2006, MW-5 groundwater sample contained 150 µg/1 methyl-t-butyl ether (MTBE) and 250 µg/i TPH-g, and MW-6 contained 77 µg/1 TPH-g. During first quarter 2007, ground water samples from MW-1, MW-2, MW-4, MW-5, and MW-6 (MW-3 was not sampled)contained various COCs. Based on these data, it appears that the vertical and lateral extent of the plume has not been defined. Further site assessment is needed to define the vertical and lateral extent of impacted groundwater. Submit a workplan in the content of the SCM to further investigate the vertical and lateral extent of your groundwater plume to the EHD by December 3, 2007. • Source of Tetrachloroethene (PCE) and Trichloroethene (TCE). Historical groundwater data shows that PCE and TCE are present on-site. During fourth quarter 2004, the MW-1 groundwater sample contained 300 µg/1 PCE and 350 µg/1 TCE, and MW-2 contained 300 µg/1 PCE and 390 µg/1 TCE. During fourth quarter 2005, MW-3 contained 1.4 µg/l PCE and 1.1 pg/L TCE, and MW-4 contained 3.6 µg/1 PCE and 0.82 µg/l TCE. During first quarter 2007, MW-5 contained 7.2 µg/1 PCE and 3.0 µg/1 TCE, and MW-6 contained 14 µg/1 PCE and 11 µg/1 TCE. No other analysis for PCE and TCE has been conducted on MW-1 through MW-4 groundwater samples. PCE and TCE were detected in soil samples collected during the UST system removal at shallow depths which is unlikely to have originated from the Castle Motors site. Castle Motors is being directed to identify all compounds detected by EPA Method 8260B for the next two groundwater monitoring events. The EHD directs that all peaks be reported for your groundwater samples for the next two groundwater quarterly monitoring events. The EHD has not yet received information on the location of the former waste oil tank that was removed prior to 1984 from this site. A file review was conducted by CET during March 2006, but no information has been provided to the EHD regarding this waste oil tank. EHD requests you to provide the information by December 3, 2007. • 1,2-dichloroethane and ethylene dibromide. Groundwater samples from MW-1 through MW- 4 are currently not being tested for 1,2-DCA and EDB. During first quarter 2007, Castle Motors MW-8 contained 2.1 µg/l 1,2-DCA, and Shell MW-6 contained 2.0 µg/1 1,2-DCA. Soil borings for MW-6 contained 0.041 mg/kg 1,2-DCA and 0.016 mg/kg EDB. EHD directs that 1,2-DCA and EDB be added to the suite of constituents for future quarterly monitoring events for MW-1 through MW-4, in addition to MW-5 and MW-6. Please include analytical results, including historical results, for 1,2 DCA, EDB, PCE, and TCE in the "Well Concentrations"table. Please contact Frank Girardi at(209) 953-7868 if you have any questions. Donna Heran,REHS, Director Environmental Health Department A.JU 1�%�VL/%-- - '!,! Frank Girardi, Senior REHS Nuel C. Henderson,Jr.,PG LOP/Site Mitigation Unit fV LOP/Site Mitigation Unit IV c: RWQCB, Central Valley Region—James L.L. Barton c: Cambria— Mike Murphy