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. f REMEDIAL ACTION PLAN ALTERNATIVES Based upon data acquired to date, it appears that several options may be considered for remediation of gasoline contaminated soils (and perhaps groundwater) which appears to exist at the site. An overview of the three options believed to be the most cost effective are presented below: Vapor Extraction The vapor extraction process employs the principle that many of the organic hydrocarbons contained within gasoline will volatilize at ambient soil temperatures; with the volatilized contaminants then entering the void spaces between soil particles until an equilibrium is achieved. This partitioning is described by Raoult' s Law. A relatively strong vacuum is applied to the soil to remove the vapor phase contamination from the soil pore spaces. This is an effective method of removing contamination, however, it is limited in that soil capillary forces may eventually exceed the vacuum extraction forces. This, coupled with the fact that not all of the constituents in gasoline have sufficient volatility, suggests that soil vapor extraction may not be effective for complete removal of gasoline contamination; however, remediation to the low parts per million (ppm) range is likely. Contaminants with vapor pressures greater than 25 mm/Hg are generally accepted as good candidates for vacuum extraction with vapor pressures as low as 1 mm/Hg acceptable. The vapor pressure of gasoline is between 37 and 260 mm/Hg depending upon the degree of environmental degradation. t t The vacuum extraction process works best with compounds which S have a low water solubility as the compound is not }wound to soil moisture. Management of the extracted vapors would be necessary to comply with San Joaquin County Air Pollution Control District regulations requiring a 90% reduction in, hydrocarbon concentrations for remediation projects. This could be accomplished using a catalytic/thermal oxidizer during the initial start up when concentrations are expected to be quite high. After vapor concentrations have diminished, granular activated carbon (GAC) could be using to capture the contaminant vapors. It would, however, be as efficient, and more cost effective to condense extracted vapors upon extraction. This would permit introduction of an estimated 80% of the vapors into a biological treatment system. Based upon available data, it is estimated that the cost for soil remediation using vapor extraction would be approximately $50, 000. 00 t.