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Ms Vicky Mc Cartney Page 4of6 • Analytical results of soil samples collected during the investigation are summarized in Table 1 Laboratory reports and chain of custody documentation are included in Attachment 3 f At the request of EHD, Ground Zero re-calculated the residual hydrocarbon mass remaining in soil beneath the site The remaining volume of contaminated soil is estimated at a maximum of approximately 145 cubic yards, all within the saturated zone, containing an estimated 155 pounds of gasoline It is estimated that approximately 193 cubic yards of contaminated soil was removed from the UST excavations in 2001 A copy of the residual contaminant mass calculation sheet, as well as figures showing the estimated extent of residual contamination, is included in Attachment 4 4.3 Groundwater Analytical Results The grab groundwater samples collected from boring SB 1/SB l a contained elevated levels of gasoline constituents The sample collected from the top of the water table (12-15 feet bgs) contained TPHg at a concentration of 14,000 parts per billion (ppb), toluene at 45 ppb, ethylbenzene at 110 ppb, and xylenes at 160 ppb The groundwater sample collected at the base of the sand zone (21-24 feet bgs) contained TPHg at a concentration of 4,100 ppb, toluene at 23 ppb, ethylbenzene at 3 5 ppb, and xylenes at 19 ppb No benzene or gasoline additives were detected in either groundwater sample collected from boring SB 1/SB 1 a No petroleum hydrocarbon constituents were detected in the groundwater sample collected from boring SB2, which was collected from the top of the water table iThe grab groundwater samples collected from borings SB 1/SB 1 a and SB2 are considered "worst- case", because the water samples were unfiltered and contained a significant amount of sediment Groundwater samples collected from properly installed and developed monitoring wells are believed to be more representative of groundwater conditions A groundwater sample collected in 1 arch 2004 from well MW3, which was also drilled through the tank pit, contained only TPHg at 0 ppb and ethylbenzene at 1 2 ppb These levels are considerably lower than concentrations detected in the grab groundwater samples collected from boring SB 1/SB 1 a Analytical results of groundwater samples collected during the investigation are summarized in Table 1 Laboratory reports and chain of custody documentation are included in Attachment 3 Analytical results of groundwater samples collected from site wells are summarized in Table 2 Based upon the most recent analytical results from groundwater samples collected from site monitoring wells, we have estimated that less than 0 1 pound of gasoline constituents remain in the groundwater A copy of the residual contaminant mass calculation sheet, as well as figures showing the estimated extent of residual contamination, is included in Attachment 4 4.4 Groundwater Modeling To address a concern outlined in your October 10, 2003 letter, we modeled the transport of dissolved contaminants from the source area to approximately 65 feet downgradient of the former USTs This distance corresponds to the approximate location boring SB2, which was drilled in the ! median of Eleventh Street The nearest known domestic/municipal well is more that 1,000 feet upgradient from the site GIGROUNDZE1Souza\Reports\ADD_SUSSURF_SUM doe