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Remedial Action Plan RE: 425 W. Larch Street, Tracy, CA October 1 , 2008 W&A Project No. FTIM-08-001 Page 7 of 11 5.2 Excavation and Disposal Excavation and disposal is a conventional remedial alternative for removal of contaminated soil from a property. The excavated soil is either transported to landfills for disposal, or treated on-site. Land farming, biopiling, incineration, etc. , are some of the treatment options for remediating the excavated soil. The excavated areas are either backfilled with engineering fill (sand, pea gravel, class II aggregate base, etc.) or with the treated soil. This alternative can be very effective since physical removal of soil contamination no longer allows for continued groundwater impact from the (removed) source. Petroleum hydrocarbon impact to soil appears to be present in fine grained soil between 8 and 12 feet bgs. If the excavation alternative was to be implemented, an excavation of 200 feet wide in the east west direction and 80 feet along the north south direction would be required (area of high MTBE and GRO impact) . The excavation would be located immediately north of the station building shown in figures. Excavation of soil up to depths of 15 feet bgs would likely result in the removal of a majority of the source of petroleum hydrocarbon impact to the subsurface. Excavating at depths greater than 6 feet will require engineered shoring, and may compromise the integrity of existing structures and roadways. The movement of construction vehicles and trucks in the vicinity of the site poses a potential traffic hazard. Further, the volume of overburden soil (due to a large area of excavation) that would require excavating and disposition off-site renders this removal option cost-ineffective. The cost of implementing this alternative is estimated to be approximately $947,000. This alternative does not appear to be a viable and implementable alternative, given the large area to be excavated. 5.3 Soil Vapor Extraction and Abatement (SVE) SVE has proven to be an effective technology for remediation of petroleum hydrocarbon impacted soil. SVE involves applying vacuum in the subsurface through vapor extraction wells to induce subsurface airflow. Petroleum hydrocarbons volatilize from the soil matrix, and are drawn towards the extraction wells; hydrocarbon laden soil vapors are routed to abatement equipment through subsurface piping. The extracted air stream is subsequently treated in abatement equipment and discharged to the atmosphere. In addition, if a vapor well is screened into the groundwater, the movement of air in the subsurface can induce volatilization in the capillary fringe zone. The most common types of abatement devices used to treat extracted soil vapors are thermal oxidizers, catalytic oxidizers, internal combustion engines, and granular activated carbon (GAC) units. Given the site geology (low air permeability within vadose zone), SVE does not appear to be a technically feasible remedial alternative for this site. Since a significant residual mass continues to be present within fine grained soils at the water table interface, SVE could be useful if the water table can be lowered and air moved through this zone. Given the unexpectedly high groundwater extraction rates observed at well MW-31Z from fine grained soils, adequate soil vapor flow rates may also be achieved within the smear zone. If this remedial alternative were to be implemented (assume existing wells are used), an W Na.vEA EASSOCIATES, lN NDFCST$