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r Treadvvell&Rollo <br /> 4.1 Soil Remediation <br />' The soil and groundwater remediation work was overseen by Treadwell & Rollo, Inc between <br /> 24 April and 4 May 2004 The 2004 Workplan proposed excavation of contaminated soil and <br />' pumping out contaminated groundwater around Tank No 7 location The excavation was 30 feet <br /> long by 28 feet wide by 22 feet deep as shown on Figure 3 The excavation was extended <br />' approximately 4-feet below the groundwater table in order to remove contaminated saturated soil <br /> and groundwater The excavation dimensions were chosen to remove the majority of the <br />' identified vadose and saturated zone soil contamination, and enable removal of the most <br /> contaminated groundwater Because the excavation required shoring, the dimensions could not <br /> be modified once the shonng was in place, and the excavation work began Additionally, sheet <br /> pile shoring prevented the collection of sidewall samples <br /> The proposed excavation represented approximately 684 cubic yards (bench yards) or up to <br /> 1,100 tons of soil, and it was estimated that approximately 12,000 to 30,000 gallons of <br /> contaminated groundwater would be removed <br /> During excavation backfilling, oxygen release compound (ORCO) was to be placed into the base <br /> of excavation below the groundwater table to enhance bioremediation of groundwater <br /> downgradient of the excavation Excavation below 22 feet bgs was not proposed, because <br /> ORCObackfill would address residual groundwater contamination Treadwell & Rollo estimated <br /> that approximately 4,500 pounds of ORCO would be required to address residual contamination <br />' in the vicinity of the excavation Treadwell & Rollo based this estimate on stoichiometric <br /> equations provided by the ORC® vendor, Regenesis, and estimated post-remediation <br /> contamination concentrations The SJCEHD did not approve the use of any ORCO in their ' 11+4 <br /> { 9� <br /> 20 February 2004 letter, and subsequently requested that only up to 500 pounds of ORC®be <br /> used ed in the excavation <br />' 25971021 DJS 5 18 November 2004 <br />