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TreadweII&Rollo <br /> bgs. Soil and groundwater collected at 23 feet in the base of the excavation contained TPH- <br /> g <br /> i concentrations of 11 mg/kg and 16,000 micrograms per liter(ug/1) respectively. <br /> 4.2 Proposed.Remediation <br /> The site development planned for this coming spring will limit future site access around sample <br /> location CPT-EXC-BT-19 for future monitoring or in-situ remediation efforts. Consequently, <br /> we propose to excavate the contaminated soil in the area as shown on Figure 3. The proposed <br /> excavation is 25 feet long by 10 feet wide by 25 feet,deep. The scope of the work is similar to <br /> the work performed at the adjacent shored excavation. The proposed excavation would be <br /> I <br /> extended to approximately 6.5 feet below the groundwater table (18.5 feet bgs) in order to <br /> remove contaminated groundwater, and contaminated saturated soil. During excavation <br /> backfilling, approximately 800 pounds of oxygen release compound (ORC) would be placed into <br /> I <br /> the excavation to assist with enhanced bioremediation of groundwater downgradient of the <br /> excavation, and to address deeper soil contamination that may be present. <br /> i <br /> i <br /> The excavation dimensions were determined after considering the previous and current soil and <br /> groundwater analytical data and the geologic and hydrogeologic data gathered during our recent <br /> fiinvestigations and excavation work, as described below. The western portion of the excavation <br /> is bounded by Boring CSB-5, which did not have significant TPH-g concentrations, and by the <br /> previous excavation to the north. The excavation extends to the edge of the previous excavation <br /> to the east. We anticipate that contaminant concentrations in soil and groundwater will decrease <br /> i <br /> in the westerly, upgradient location(no TPH-g was detected in groundwater in CSB-4, located <br /> 30 feet west of the excavation), and are proposing to extend the excavation 10 feet west of the <br /> edge of the former excavation. Shoring will be required due to the presence of Fremont Street, <br /> and because of the proposed excavation depth below the water table. <br /> Residual soil impacts identified deeper than 25 feet bgs will be addressed by backfilling with <br /> ORC. Excavation below 25 feet bgs will not be attempted because the shored excavation will be <br /> 5 <br /> ' 25970122.DGD 14 February 2005 <br /> ' I <br />