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Pornbo Ranch Facilitya M y 2006 Site Closure Report difficult due to expansion or lofting of the material during excavation and handling. As noted in the Remedial Excavation and Source Removal Report the excavated soil was stockpiled onsite and disposed at the landfill between February 28 and April 14, 2005. The saturated and semi-saturated conditions of the material caused an increase in actual weight compared to in place estimate. Mass balance estimates of the total mass removed and the remaining residual contamination are provided below. Confirmation samples disclosed moderate levels of ethyl benzene and xylenes in the northeastern and western excavation sidewalls. Well MW4 was replaced by well MW 413 on May 4, 2005. Groundwater contamination since the remedial excavation has been limited to very low concentrations of MTBE in well MW4B and very low concentrations of gasoline range petroleum hydrocarbons in well MW5 as shown in Figure 5. As shown in Figure 6, MTBE and gasoline petroleum concentrations show a significant decline ( after the remedial excavation in February 2005. I3.0 MASS BALANCE CALCULATIONS Revised hydrogeologic cross sections were constructed using information from the 1 additional borings, samplings, and showing the extent of the excavation {Figures 7 and ! Figure S}. The trace of cross sections is shown in Figure 2. The extent of the excavation is shown on Figure 2 and on the pre-excavation and post-excavation soil contamination maps. Contamination removal efficiencies ranged from 97.4 to 100 percent were achieved. A table of estimated removal efficiencies is shown below. Mass balance f calculations for the excavated and residual soil contamination are attached in Appendix 1 B. Soil Excavation Pombo Ranch Contaminant Removed lbs Residual lbs Removal f Benzene 0.49 0.012 97.47 Toluene 1.20 0.016 98.68 Ethyl Benzene 3.13 0.021 99.33 Xylene 4.13 0.041 99.02 Gasoline 211.56 0.000 100.00 MTBE 0.90 0.000 100.00 Benzene hot spots were located in the southeast portion of the excavation in the vicinity of boring B-3 and to the northeast in the vicinity of MW4 and boring B-11 as shown in -- -- - - -- -- Figure 9. North —south and east--west cross sections showing-the extent of the benzene '— contamination enzene —contamination are shown in Figure 10 and Figure 11, Approximately 0.49 pounds of benzene was removed by the remedial excavation. Residual benzene contamination was detected in the confirmation soil sample in the eastern sidewall. An estimated 0.012 pounds of residual benzene contamination is present in the eastern side of the excavation f � 8