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V Second Semiannual 20» Groundwater Monitoring Report Former Texaco Service Station Chevron Site ID 309075 February 28, 2012 Groundwater elevations in site monitoring wells, except MW-1, have reached a historic high since monitoring began during the third quarter of 2008. A hydrograph depicting changes in groundwater elevations over time is presented as Figure 1 of Attachment E. Separate phase hydrocarbons (SPH) were not observed during the second semiannual 2011 monitoring and sampling event, nor have they historically been observed at the site. 5.1.2 Groundwater Sampling Results Analytical results from the most recent semiannual groundwater sampling event are presented in Tables 1.1 and 1.2; historical analytical results are presented in Tables 1, 2, 3, 4.1 and 4.2 of Attachment F. A site concentration map of TPH-MO with SGC, TPH-DRO with SGC, and TPH-GRO is presented as Figure 4 and a site concentration map of benzene, MTBE and 'r 1,2-DCA is presented as Figure 5. Maximum and minimum concentrations of petroleum hydrocarbon constituents detected in groundwater samples collected during the second semiannual event of 2011 are presented in the table below: Frequency Range of California Of Concentration of ,r Detected Primary Frequency of Constituent Detection Concentrations MCLS Exceedances Exceedances Above (Ng/L)2 (Ng/L) (Ng/L) by Well the MDL TPH-M04 5/7 44—420 -- -- -- TPH-DR04 1/7 120 -- -- -- TPH-G RO 1/7 180 -- -- Benzene 1/7 0.6 1 0/1 -- TBA 1/7 16 -- -- 1,2-DCA V7 200 0.5 1/1 200 (MW-1) Methanol 1/7 260 0.05 1/1 260 (MW-4) Notes: 1. MDL=method detection limit. 2. µg/L=microgram per liter, equivalent to part per billion (ppb). 3. MCL= maximum contaminant level. 4.TPH-MOITPH-DRO with silica gel cleanup(10-gram column). Although the groundwater sample collected from MW-1 contained a concentration of 1,2-DCA above the California Primary maximum contaminant level (MCL), 1,2-DCA is stable, not migrating and has not been detected in other site wells since groundwater monitoring began in 2006. The groundwater sample collected from MW-4 contained a concentration of methanol above the California Primary MCL. Methanol has not been detected in other site wells or during other events since analysis for methanol began in 2008. v V g:\aproject\env\chevron\309075\6 del iverables\periodic monitoring\2011\2sa11\temppdf\text\309075 2sa11 gmr fin 02282012.doc 5 V