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`} Mr Jeff Wong Page 6 of 10 (� Although no odors were noted in any of the soil samples collected from boring VW1 (the vapor extraction test well), each of the samples collected between the depths of 45 and 74 feet bgs contained MTBE MTBE in the soil in boring V W 1 ranged from 0 043 to 2 7 ppm Relatively minor concentrations of TPHg and/or BTEX constituents were also detected in the samples collected from depths of 60, 70, and 74 feet bgs in boring VW1 Due to the nature of the mud rotary drilling method, no soil or groundwater samples could be collected from borings MW13C and MW14B during drilling Soil analytical data are summarized in Table 2 Laboratory reports and chain of custody documentation are included in Attachment D Groundwater Elevation and Gradient The depth to groundwater in the shallow groundwater zone (A Zone) beneath the site, excluding well MW1, which has been used as a groundwater extraction well since November 5, 2003, averaged approximately 67 9 feet btoc on October 17, 2003, 66 6 feet btoc on December 12, 2003 and 65 6 feet btoc in March 2004 Groundwater in the A Zone aquifer generally flows to the northeast Figures 5, 6, and 7 present groundwater gradient maps for the A Zone aquifer during October 2003, December 2003, and March 2004, respectively The groundwater elevations in B Zone wells MW9B and MW14B were generally lower than in the nearest A zone wells, which suggests a downward vertical gradient exists at the site between the A Zone and B Zone groundwater elevations The groundwater elevation in C Zone well MW13C, by comparison, has not exhibited a consistent relationship to the B Zone wells Historical groundwater elevations in site wells are summarized in Table 3 Groundwater Analytical Results No gasoline constituents, including gasoline additives, were detected in the groundwater samples collected from wells MW10 and MW11 in October 2003 The groundwater sample collected from well MW14B contained only 11 parts per billion (ppb) toluene No other gasoline constituents were detected in well MW14B The groundwater sample collected from well MW12 contained MTBE at 2,500 ppb The groundwater sample collected from well MW13C contained toluene at 50 ppb and MTBE at 36 ppb Laboratory reports and chain of custody documentation for groundwater samples collected from the newly installed wells in October 2003 are included in Attachment D Groundwater samples were also collected from wells MW10 through MW14B, along with other site monitoring wells, in December 2003 and March 2004 The samples collected during these months essentially confirmed the results of the initial sampling round MTBE has been detected in samples collected in October 2003, December 2003, and March 2004 from wells MW12 and MW13C, while no MTBE has been detected in wells MW10, MW11, and MW14B MTBE in well MW12 has ranged from a high of 2,500 ppb in October 2003 to a low of 1,500 ppb in March 2004 MTBE in well MW13C has ranged from a low of 36 ppb in October 2003 to a high of 110 ppb in March 2004 Analytical results of groundwater samples collected from site wells are summarized in Table 4 The estimated extent of dissolved benzene in groundwater beneath the site in December 2003 and March 2004 are presented on Figures 8 and 9, respectively The estimated extent of dissolved G%GROUNI)ZE\TULESURGIReportsVHSA_Mud wells Report 2 doe