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"i <br /> ombo Ranch Facility April 24,2005 <br /> Remedial Excavation&Source Removal <br /> 3.0 CONCLUSIONS & RECOMMENDATIONS <br /> ' Petroleum contaminated soil approximately 12 feet in depth with a lateral area of 3640 <br /> square feet was excavated from the Pombo Ranch Facility area of investigation. The <br /> ' contamination was apparent at an average depth of 8 feet to groundwater and below. The <br /> excavation depth was limited to the soil above the depth to groundwater on February 28th <br /> and March 1" 2005. Confirmation samples disclosed moderate levels of ethyl benzene <br /> and xylenes in the northeastern and western excavation sidewalls. <br /> Minor concentrations of petroleum contamination may remain at levels below 12 feet and <br /> ' in the soils in the northeastern and westerly directions. Groundwater contamination <br /> slightly above established water quality goals was detected in the well MW4 (destroyed <br /> as part of remedial excavation) and in the down gradient well, MW5, during the January <br /> 2005 monitoring event. Well MW4 is scheduled for replacement on May 4, 2005. <br /> Quarterly monitoring should continue for at least one year to evaluate the effect of the <br /> removal of the source area material on the residual groundwater contamination. If the <br /> ' residual groundwater contamination does not degrade below water quality goals, <br /> enhanced aerobic biodegradation should be evaluated as discussed in the Corrective <br /> Action Plan. <br /> • <br /> 8 <br />