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V �t Former Beacon Station A 2474 December 22, 2003 Stockton, California„ _ _ Work Plan Addendum • Groundwater sampling adjacent to the CPT-3 boring was attempted at five intervals: 60 to 65 feet bsg; 65 to 75 feet bsg; 90 to 95 feet bsg; 119 to 129 feet bsg; and 144 to 146 feet bsg. Further advancement of the groundwater sampling tool was refused at 146 feet bsg. Groundwater samples were successfully collected from the three intervals 90 to 95 feet bsg (sample CPT3-95); 119 to 129 feet bsg (sample CPT3-129); and 144 to 146 feet bsg (sample CPT3-146). The intervals 60 to 65 feet bsg and 65 to 75 feet bsg were dry. The soil and groundwater samples were submitted to Kiff Analytical LLC and analyzed for total petroleum hydrocarbons as gasoline (TPHg), the volatile aromatic compounds benzene, toluene, ethylbenzene, total xylenes, the fuel oxygenates methyl-t-butyl ether (MTBE), diisopropyl ether (DIPS), ethyl-t-butyl ether (ETBE), tert-amyl methyl ether (TAME), tert- butanol (TBA), and the lead scavenger compounds 1,2-dichloroethane (DCA) and 1,2- dibromoethane (EDB) by Environmental Protection Agency method 8260B. Groundwater and soil analytical results are summarized in the attached Tables 1 and 2. The analytical report is attached to this letter. Groundwater analytical data indicate: • no hydrocarbon impact at the water-table depth (approximately 62 feet bsg) at the CPT-2 location; • vertical delineation of DCA not demonstrated at CPT-2 location; near reporting-limit concentration of DCA indicated at 146 feet bsg at CPT-3 location; and • vertical delineation of TPHg demonstrated at both CPT-2 and CPT-3 Iocations. Horizon proposes to install monitoring wells MW-15 and MW-16 in the southeast and southwest corners of the site, respectively, as shown on Figure 2. Monitoring well MWA 5 should be screened over the interval 143 to 148 feet bsg to confirm the results of the CPT-3 groundwater sample collected at 146 feet bsg. Monitoring well MW-16 should be screened over the interval 137 to 142 feet bsg to evaluate the vertical extent of DCA reported in the CPT-2 groundwater sample collected at 108 feet bsg and to confirm conditions at approximately 140 feet bsg. Groundwater analytical results from the proposed monitoring wells.should be evaluated for several quarters to confirm the preliminary results of the CPT groundwater analytical results. Analytical results for the soil sample collected at 80 feet bsg from the CPT boring B-11 indicate no hydrocarbon impact. This analytical result indicates that there is no secondary source of hydrocarbons in soil in the area of monitoring well MW-1 and MW-9. W PAddrn 12-03.doc Project No. 1474.14 2 HORIZON ENVIRONMENTAL INC.