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' Report—Remedial Action Feasibility Page 23 Cutter Lumber—Western Lift Site ' GPE Protect No 102 3 August 1,2003 ' 10.0 CONCLUSIONS & RECOMMENDATIONS 10.1 Conclusions ' 1 The estimated total contaminant mass is about 14,000 pounds with the main contaminant mass currently lying 5 to 15 feet below the groundwater surface ' 2 The receptor survey documented the presence of three water production wells within the search radius None of these are likely to be affected by the release 3 The vapor extraction system alone was largely ineffective Due to the cla -nch, g Y Y impermeable character of the vadose zone soils, the vapor extraction well has a ' small radius of influence too small to be measured with the system that was used Moreover, the rate of gasoline extraction using vapor extraction alone was ' remarkable and unacceptably low 4 Air sparging was effective in introducing air (and oxygen) into the subsurface and ' bringing submerged hydrocarbons to the groundwater surface and driving them toward the vapor extraction well The combined VES/AS system was effective in removing a calculated 210 pounds of gasoline petroleum hydrocarbons The ' extraction rate was estimated to be 18 pounds initially and reached a maximum of over 40 pounds per day of gasoline When the locus of vapor extraction was switched to MW-7, the rate increased to over 150 pounds per day The bulk of the ' extracted gasoline vapor is believed to have originated in a sandy unit lying about 35 to 45 fee below the surface ' 5 The overall effectiveness of the VES / Sparge System, verifies the engineering concepts originally proposed in the Work Plan Although the initial extraction rates achieved were reasonably high, the limited available data suggest the ' extraction rate may decrease as by as much as 50 percent of the first 24 to 72 hours of system operation This rapid initial decline is likely to render the extracted vapor generally too lean for use of a thermal oxidizer as a final gasoline ' destruction method Given the assumption of a relatively lean gasoline content of the extracted vapor, a thermal oxidizer would require an extremely high percentage of propane to generate a combustible mixture This would render the use of a thermal oxidize a cost-ineffective method of hydrocarbon destruction A rough estimate was made that suggested if propane has been used to combust ' extracted gasoline vapors, the fuel cost alone would have increased the cost of the project several thousand dollars per month, and the O&M costs would also be greater with a thermal oxidizer system It is likely that a filtration or catalytic system would be most appropriate as a method to remove of destroy gasoline hydrocarbons after removal from the subsurface ' 2937 Veneman Ave, #8240 Geo-Phase Environmental Inc. Phone(209) 569-0293 Modesto, CA 95356 Fax(209)569-0295