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Antonia K.J. Vorster _3_ <br /> Camilla Williams 16 April 1992 <br /> 1) I concur with the conclusions of ESE. Soil flushing has been attempted at <br /> other sites with TCE contaminated soils (eg. , Aerojet-General , Sacramento) <br /> and proved unsuccessful . This remedial technology is especially <br /> inefficient if neat liquid is found in the soils as I suspect is the case <br /> at some of these areas at this site. With neat liquid present, soil <br /> flushing is limited by phase transfer and many of these solvents, such as <br /> TCE, are relatively insoluble. Moreover, neat liquid in the soil column <br /> may be trapped in interstitial pores and the micro-mechanics of soil <br /> flushing do not prove effective. <br /> 2) ESE references a soil leaching model developed by Baes and Sharp (1983) and <br /> estimates that 99 percent of the TCE would be leached within the firsty ear <br /> of operation. I believe this is very optimistic and the model used may <br /> oversimplify the situation at Sharpe. If this study were to be conducted <br /> again, I would recommend the use of a more sophisticated model for <br /> contaminant transport in the vadose zone. A sensitivity analysis should <br /> then be performed on the results of the model and these results should be <br /> combined with other site information (including regulatory constraints) <br /> before a final decision is made. If there is neat liquid in the soil <br /> column at these sites, it will take much longer than one year to remediate <br /> with soil flushing. Whether or not there is neat liquid present, I believe <br /> that soil vapor extraction technology will prove much more effective than <br /> soil flushing at Sharpe. Therefore, I concur with ESE's recommendation to <br /> use soil vapor extraction as a remedial measure at this site rather than <br /> soil flushing. <br /> RJY:mm <br />