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Morita Brothers 16 May 6, 1992 The first option, natural in-situ biodegradation (i e , no action), is viable given the 55 ' feet of vertical separation between the deepest known impacted soil and the first occurrence of groundwater as well as the significant amount of clay in the ' intervening sedimentary section However, the concentrations of gasoline hydrocarbons present a risk of leaching to groundwater, and require that remedial ' actions be understanding to reduce the concentrations to below the RWQCB recommended guidelines ' In option 2 contaminated soil would be excavated until field hydrocarbon screening indicates that the limits of contamination have been reached Additional sampling ' from within the excavation would be performed to confirm the results of the field screening The location of suitable disposal depends on the concentration of contaminants in the soil after it is stockpiled Judging from the findings of this study, it appears likely that the soil would qualify to be recycled at the Gibson Oil Refinery's solids recycling facility in Bakersfield This disposal option would cost in { approximately of $200 per cubic yard including excavation, transportation, ' recycling, and generators fees, or approximately $100,000, and recycling alleviates the clients future liability for the soil ' Option 3 is to treat the soil in place through in-situ vapor extraction The soil remains in place, and the gasoline hydrocarbons are extracted through wells drilled ' into the impacted soil The effectiveness of this option is dependant on the ability of an air flow to be created throughout the zone of impacted soil, permitting the ' gasoline hydrocarbons to volatilize, and then being extracted through the wells The stratigraphy at this site only partially lends itself to vapor extractiondue to the lower pernicabilities in the upper sediments and very low permeabilities in the clays below 27 feet below surface grade However, the primary impacted zone from 13 to 27 feet does exhibit adequate permeability ESE has experience in vapor extraction of gasoline hydrocarbons from low permeability soils which indicates that with a well engineered system, the gasoline hydrocarbons can be successfully removed from ' these lower permeability zones However, these zones will require placement of several additional extraction wells, and the time frame for successful treatment will E13-8101-2 9204-E044 RPT