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r <br /> 1 TWeadwell&Rolb <br /> i <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 shoring 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 ORC®would be required to address residual contamination <br /> ' in the vicinity ofthe_e ex_avahon. Treadwell &Rollo based this estimate on stoichiometric <br /> equations provided by the ORO® vendor,Regenesis, and estimated post-remediation <br /> ' contamination concentrations. The SJCEHD did not approve the use of any ORC® in their ' H INIoy l <br /> 20 February 2004 letter, and subsequently requested that only up to 500 pounds of ORCO be <br /> used in the excavation. <br /> D- Li <br /> t25971021.DJS 5 18 November 2004 <br />