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' Cola leaf recknics lac. Page 3 <br /> G g � <br /> Sinclair Trucking <br /> SCM&CAP Addendum <br /> Project No. 1030.3 <br /> July 12,2004 <br /> ' issues brought up by contractors and further site review, which resulted in a higher <br /> estimated contaminated soil volume. These additional factors are discussed below: <br /> ' D a. Our original estimate of soil removal made the assumption that the excavation could <br /> be performed with surgical precision. See section 4.0 and review Figures 5 and 6 of <br /> Fw LJ,e.- the Additional Site Characterization & 4`h Quarter Groundwater Monitoring Report <br /> ' /1tt° 01 dated February 20, 2004. However, after further discussion with contractors it was <br /> C( determined that the assumption may not be practical or reasonable to achieve unless <br /> " 5 field conditions were perfectly suited to that. Therefore, we squared off the <br /> excavation to the area contaminated by the deeper horizon (9 to 12 feet bgs) rather <br /> than trying to follow contaminant contour during soil removal excavation. So the <br /> area of the excavation was changed to 60 X 60 as discussed in section 2.3 of the <br /> Feasibility Study Addendum. <br /> b. Surgical removal of multiple layers above groundwater raised issues of sidewall <br /> t f sloughing and thus commingling of contaminated and non-contaminated soils, <br /> ' resulting in added volume of contaminated soil to remove. <br /> c. Removal of soil below the water table raised the problem of sidewall sloughing into <br /> ' the excavation pit that contains groundwater, thus adding contaminant mass to <br /> ' groundwater. These factors will make distinguishing clean soil from contaminated <br /> impractical and will increase the volume of soil to be removed and the increase of <br /> contaminant levels found in groundwater. <br /> d. The original plan was to excavate the heavy contamination from the leach field, not <br /> disturbing the septic tank or influent lines, and replace the leach lines when the 2 t <br /> excavation was backfilled. However, Ms. Duncan informed Eric Price of GTI that if� <br /> ' any portion of the septic system were altered the entire system would have to be <br /> replaced. So the new calculation includes the additional volume of soil under and <br /> directly around the septic system that was originally not included. <br /> ' e. No GeoProbe samples were analyzed above 7.5 feet bgs and we originally assumed <br /> there was 7 feet of overburden that could be used. However, MW-I and MW-101 <br /> ' indicate contamination at approximately 6 feet bgs, and 7 out of 10 GeoProbe <br /> borehole logs indicate low to elevated OVM readings between 2 and 8 feet bgs. It <br /> may be possible that the excavation would reveal shallow contamination or areas of <br /> ' contamination not detected during soil investigation. <br /> £ The original estimate did not include a fluff factor, which for the soil at this site <br /> could be up to 30% greater. <br /> ' Conclusion <br /> The Feasibility Study Addendum is a cost comparison of remedial alternatives. In <br /> ' comparing estimated costs we feel that the worst-case scenario:should be presented. If <br /> = subsurface site conditions allow us to remove a smaller volume of contaminated soil and =_ <br /> preserve additional clean overburden the estimated costs would be less than anticipated. <br /> ' The new estimate is an adjustment based on the assumptions listed above, which we <br /> believe more accurately reflects "real-world" conditions. The 2003 SCR is a <br /> scientifically sound estimate of the amount of contaminated soil the laboratory data <br />