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(T ATC Associates Inc 1117 Lone Palm Avenue, Suite B Modesto, California 95351 209-579-2221 • Fax 209-579-2225 A S S O C I A T E S I N C concentrations of 41 pg/L, 38 µg/L, 21 µg/L, 29 µg/L, and 44 pg/L, respectively 1,2-DCA was detected in the groundwater samples collected from MWl through MW7 at concentrations ranging from 4 0 pg/L to 68 gg/L The Maximum Contaminant Level (MCL) for benzene, 10 pg/L, was exceeded in the groundwater sample collected from MW2 The MCL for MTBE, 13 µg/L, was exceeded In the groundwater samples collected from MW 1, MW2, MW3, MW4, and MW7 The MCL for 1,2-DCA, 0 5 µg/L, was exceeded in the groundwater samples collected from all of the monitoring wells The California Drinking Water Notification Level for TBA, 12 gg/L, was exceeded to the groundwater samples collected from MW1, MW2, MW3,MW6, and MW7 A summary of the laboratory analytical data is presented in Table 2 A copy of the laboratory analytical report is included in Attachment 2 An isoconcentratlon map depicting MTBE concentrations in the groundwater samples collected during the fourth quarter 2005 is shown on Figure 4 ADDITIONAL ACTIVITIES On November 17 and 18, and December 5 and 28, 2005, an ATC geologist supervised the advancement of five soil bonngs, S139 through SB 13 The bonngs were advanced for the purposes of evaluating the horizontal extent of petroleum impacted soil and groundwater surrounding the site Details of these activities are summarized in ATC's Summary Report of Additional Subsurface Investigation, dated July 12, 2006 GEOTRACKER DATA UPLOAD The depth to water and the laboratory data were submitted electronically to the State Water Resources Control Board (SWRCB) Geotracker database (confirmation numbers 6329806268 and 3993945002, respectively) Documentation of the data submittal is contained in Attachment 3 CONCLUSIONS Groundwater flow direction and gradient are generally consistent with previous sampling events Water table elevations have decreased since the July 2005 monitoring event The laboratory analytical results of the groundwater samples collected from MW1 through MW7 are generally similar to the results of the groundwater samples collected from these wells in July 2005 TPHg decreased In groundwater samples collected from MWl through MW7 while BTEX concentrations remained fairly consistent with respect to recent sampling events TPHg and BTEX remain undetected In groundwater samples collected from MW4 RECOMMENDATIONS Based on the results of the fourth quarter 2005 monitoring event, we recommend continued quarterly groundwater monitoring and evaluating remedial action alternatives for the site s lenvironmenta1122493aeponsl4QR-05 doe 4