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6 3 Residual Soil and Groundwater Contaminants <br /> The calculations indicate that most contaminant removed was absorbed onto soil and was <br /> TPHG relatively depleted in Benzene content. Some residual soil contaminant remains in <br /> the areas inaccessible to excavation under the two large pipelines and near the former <br /> tank pit Two soil TPHG and Benzene contaminant contour maps (Figures 3 and 4) were <br /> prepared to show the interpreted TPHG and Benzene that might remain near the <br /> excavated areas Capillary action might reach these areas and cause contaminant <br /> desorption into water Dissolved contaminants are anticipated to remain and some <br /> additional desorption that may become dissolved into groundwater might occur from <br /> disturbance of the soil excavation. Some flushing of the area occurred from excavation <br /> dewatering is anticipated to have removed some of the dissolved contaminants in the <br /> excavation vicinity Quarterly monitoring is scheduled to continue (following the re- <br /> installation of monitoring wells MW-3 and MW-9) to observe dissolved contaminant <br /> presence and plot groundwater flow direction <br /> 7.0 Conclusions and Recommendations <br /> Soil excavation was performed in the area between irrigation and sewer pipelines and <br /> wells MW-3 and MW-9, and dust down gradient of the former tank pit. Excavation <br /> removed soil containing TPHG and Benzene inferred present in and near the capillary <br /> fringe as defined from subsurface sampling and historic groundwater dissolved plume <br /> mapping The excavation was dewatered during the work and approximately 900 cubic <br /> yards of soil was shipped to the Forward Landfill in Manteca and about 239,250 gallons <br /> of water was treated on-site using carbon filtering for disposal to the City of Tracy <br /> sanitary sewer outfall under the approved permit <br /> The excavation lateral extent was constrained by two large subsurface pipelines, and <br /> Wright removed as much soil as feasible in the near proximity of the pipelines Local <br /> soil contaminant sources that were removed and these appeared to correspond to a coarse <br /> grained strata roughly parallel to the axis of the dissolved plume Wright interprets that <br /> these soil/sediment packages were a primary residual source Some of this residual <br /> contaminated soil remains under the pipelines and near the former tank pit Wright <br /> estimates that about 787 gallons of TPHG and 4 1 gallons Benzene were removed from <br /> soil and 2 3 gallons TPHG and 0 21 gallons Benzene were removed from the <br /> groundwater <br /> i <br /> Page 10 of 13 <br />