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6 7' 4.0 CONCLUSIONS ANDRECOMNII:NDQTIONS The soil boring data and analytical results indicate the following: o The silt layers beneath the site have adsorbed greater quantities of TPHg contaminants than the sandy layers. These results are consistent with the fact that fine particles, such as silt, have more surface area for adsorption of contaminants. a The soil clean-up rate would be relatively slow and be controlled by the diffusion of the TPHg vapor from the silt to the sand layers. These site conditions make prediction of cleanup time very uncertain. o TPHg contaminants were present in the groundwater. Based on the analytical results of soil boring samples taken at 66 feet,it appears that the decline of the groundwater table, from a depth of approximately 60 feet in past years, to below 66 feet, has resulted in contamination of the lower vadose zone. No soil data was obtained below 66 feet. o The vertical and lateral extent of contamination has not been completely defined from the three soil borings. used on the concentrations shown on Figure 3 and on the assumption that the contaminants have dispersed in the north-south directions similarly to the dispersion indicated in the east-west direction (Cross-section A-A'), the estimated total quantity of TPHg in the vadose soil beneath the tank emplacement is approximately 13,000 pounds. Calculations are included in Appendix C. The pilot test field data and analytical results indicate the following.- 0 ollowing:o The radius of influence of VEW-1 is adequate to extract soil vapor from a 25-30 foot radius around the well. The location of the extraction well is in the apparent source area and therefore would facilitate removal of the contaminants. o The size of the pilot blower, piping and carbon beds is adequate for full scale operation of a one extraction well system. o The calculated quantity of TPHg adsorbed by the carbon beds during the pilot test is inconsistent with the average adsorption rate, (approximately 15 pounds hydrocarbon/100 pounds carbon)specified by the manufacturer. Calculations base on va or sarn le laborato anal ses estima 40 ounds of T?Hg were removed durin the ..lot test. However, monitoring of the outlet of the first stage carbon beds wit t e PID did not, however,indicate breakthrough of VOC's. At a maximum of 10-20%rate of TPHg adsorption on activated carbon for two 220 pound carbon beds,88 pounds of TPHg contaminants would have been removed from the soil, Calculations are included in Appendix C. The reason for this discrepancy is being evaluating. 4 REMEDIATION SERVICES, INC.