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Mr Nuel Henderson,Jr, SJCPHS July 1,2003 Remedial Action Plan ARCO Station No 6100 Page 9 • During station remodeling activities, subgrade piping laterals were installed to wells VW-1, VW-3, VW-4, VW-6, VW-8, VW-9, VW-11 through VW-14, VW-16, and MW-2 through MW-9 No Action/Natural Attentuation Under this alternative, no remedial action, other than monitoring of perched groundwater, is undertaken This alternative was previously recommended and refected by the RWQCB due to the presence of free product and an onsite supply well Excavation and Disposal Limited remediation of soil was completed during the over-excavation around the former UST complex in November 1990, and dispenser islands in January 2002 Approximately 2,647 tons of petroleum hydrocarbon impacted soil was excavated and transported off- site for disposal during the over-excavation activities conducted during November 1990, and January 2002 Considering the current site conditions, existing structures and distribution of petroleum hydrocarbons both on-site and off-site, excavation, removal, and disposal of soil does not appear to be a technically viable and cost effective alternative Soil Vapor Extraction and Air Bubbling SVE and abatement has proven to be an effective and economical alternative for remediation of petroleum hydrocarbon impacted soil SVE involves applying a vacuum in the subsurface, through vapor extraction wells, to induce subsurface airflow Contaminants volatilize from the soil matrix and are drawn towards the extraction wells, which are then treated in abatement equipment Two mechanisms contribute to SVE mass transfer and mass transport The flux induced in the soil matrix by the applied vacuum volatilizes the adsorbed-phase and dissolved-phase petroleum hydrocarbons (mass transfer) upon contact and carnes them in the gaseous phase to the extraction wells (mass transport) 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 units Considering the extent and location of petroleum hydrocarbon impact at the subject site, SVE appears to be a viable remedial alternative to mitigate petroleum hydrocarbon impact to soil and perched groundwater In addition, results of feasibility tests and the availability of vapor extraction wells screened in the impacted zones makes SVE a feasible and cost effective technology i P 1Bp-Arco for URS161001Reports\Arco 6100 RAP doe