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Appendix A Site Closure Request July 2,2010 Speedy Foods-Stockton Page 9 of 13 • Free Product removal o Free product/water mixture was bailed from MW1 for over two years. o Approximately 180 gallons(approximately 1,200 lbs)was removed by bailing. • Soil Vapor Extraction and Treatment o Soil vapor extraction and treatment was conducted over a 3'/2-year period. o Conditions became asymptotic and the system was shutdown. o Approximately 2,500 lbs of TPHg was removed by the vapor extraction and treatment system. o Confirmation soil borings in the core of the plume indicate the vadose zone contamination has been treated. • Groundwater Extraction and Treatment o Groundwater extraction and treatment was conducted for more than five years. o 4,457,049 gallons of petroleum impacted groundwater was treated during that period. o Approximately 125 lbs of TPHg, 14 lbs of benzene, and 44 lbs of MTBE were removed by groundwater extraction and treatment o Groundwater modeling suggests that the remaining groundwater contamination will degrade prior to migrating off-site. 15.0 Discussion of Contaminant Mass Remaining Ground Zero installed vapor extraction well VW2 in January 2005. Soil samples collected during the installation of VW2 indicated the presence of petroleum hydrocarbon contaminants. Vapor extraction and treatment was conducted over a 3Y2-year period. In November 2007, two confirmation borings (CB1 and CB2) were advanced in the location of the former USTs next to borings that previously contained the highest TPHg and MTBE concentrations. The confirmation borings indicated that. there was no detectable concentrations of TPHg, BTEX, Fuel Oxygenates (except TBA), or lead scavengers. Details are discussed in Ground Zero's Monitoring Well Installation and Soil Investigation Report—Fall 2007, November 28, 2007. Although the results of soil samples collected from CB 1 and CB2 indicate that there is,no soil contamination remaining in the area of the former UST pit Ground Zero approached the calculation o1 mass estimates conservatively. The average concentrations of the contaminants found from samples collected from VW2 were used to estimate the maximum mass remaining in soil. Currentf groundwater monitoring data were used to determine the mass remaining in groundwater. To remain conservative Ground Zero overestimated the volume of the groundwater plume and used the highest concentrations within a contour line to represent the entire isoconcentration contour. Estimates indicate approximately 155 lbs of TPHg and 1 lb of MTBE remains in soil. Estimates indicate approximately 9.24 lbs of TPHg, 0.21 lbs of benzene, and 1.38 lbs of MTBE are dissolved in groundwater. Soil and groundwater mass estimate calculations are summarized in Table 8. TPHg and MTBE groundwater contamination isoconcentration maps included as Figure 8 and 9, respectively and were used to determine the area of contamination.