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06 December 1995 AGE-NC Project No. 95-0100 Page 1 I of 13 5.3. EX-SITU TREATMENT OF HYDROCARBON-IMPACTED SOIL Hydrocarbon-impacted soil can be excavated and treated on-site or transported off-site for disposal. On-site treatment alternatives (ex-situ) include aeration, bioremediation, vapor extraction, and thermal destruction. All are feasible methods of remediating sandy soil contaminated with gasoline. However, increasing clay content decreases the effectiveness of each method. Offsite disposal generally involves the transportation of the impacted soil to a licensed treatment/disposal facility. 5.3,1. EXCAVATION All of the above mentioned methods of ex-situ treatment require excavation of the impacted soil. Impacted soil in the vadose zone extends to a depth of approximately 40 feet bsg at. the site. Therefore, soil would have to excavated to depths of 40 feet bsg at the Franklyn Cole site. The impacted soil may also extend under the building on site and under Chrisinan Road on the east. Once excavated, the impacted soil would be stockpiled for on-site treatment or transportation for treatment/disposal. If soil is treated on-site and hydrocarbon concentrations can be reduced to non- detectable (ND) levels, or concentrations acceptable to the lead regulatory agency, the soil can be used to backfill the excavation; if soil is disposed of off-site, backfill must be imported for the excavation, adding to the cost of the project. 53.2. FEASIBILITY OF EXCAVATION Excavation of impacted soil, followed by ex-situ treatment and/or disposal, is a very effective method of remediation; non-detect (ND) can usually be achieved by excavation since, theoretically, all contaminated soil is removed. However, excavation is usually too costly if the volume of impacted soil is great or if the impacted soil is present at depths requiring special equipment or extensive shoring. Both special excavation equipment and shoring would be required at the Franklyn Cole site. _ Hydrocarbon-impacted soil beneath buildings or roads usually cannot be addressed by excavation, as the structural integrity of the structures may he compromised. Additionally, it is unlikely that the County of San Joaquin would allow excavation of the impacted soil under Chrisman Road if the plume extends that far. On-site treatment would also be limited at the site due to the close proximity of Jefferson School, immediately southeast of the property. Air permits and special handling of the soil would most likely be required.