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Mr Nuel Henderson,Jr, SJCPHS July 1, 2003 Remedial Action Plan ARCO Station No 6100 Page 8 wells MW-1 and VW-4, respectively A table documenting historical free product removal is included in Appendix D EVALUATION OF REMEDIAL ALTERNATIVES The petroleum hydrocarbon impact in the subsurface appears to be primarily in the lower portion of the silt unit and in Sand 1 (approximately 10 to 45 feet bgs) Petroleum hydrocarbons adsorbed to soil appear to be further impacting the perched groundwater in Sand 1 Therefore, the primary objective of the selected remedial action is to mitigate petroleum hydrocarbon impact to the soil in the vicinity of the pump islands and the former UST complex The secondary objective of the selected remedial alternative is to mitigate the petroleum hydrocarbon impact to the perched groundwater in Sand 1, and therefore, reduce the potential for further migration and impact to soil and groundwater in Sand The occurrence, source, and movement of the perched groundwater are not completely characterized Groundwater at this site appears to be an isolated occurrence of perched water The rate of recharge of groundwater was evaluated through limited pump tests on various vapor extraction wells that contain groundwater (1St quarter 2001 Status Report, April 6, 2001) Results of these tests did not indicate adequate yield, and therefore, remediation of perched groundwater through technologies that involve extraction have not been considered in this document Instead, viable in-situ remedial alternatives for mitigation of petroleum hydrocarbon impact to groundwater are evaluated In this section This section reviews and evaluates commercially available remedial alternatives, commonly used to remediate petroleum hydrocarbon impact to the subsurface, based on site-specific conditions for technical feasibility, implementability, regulatory acceptance, and cost effectiveness Certain site specific conditions listed below were taken into consideration in evaluating the remedial alternatives • Floating product or sheen has been observed in wells VW-1, VW-4, and MW-1 • A water supply well is located in the southwest corner of the site that has a gravel pack from approximately 35 feet to 540 feet bgs and is screened from 396 to 416 and from 496 to 536 feet bgs • TPHG and benzene represent the primary chemicals of concern (COC) for remediation • The results of SVE pilot tests conducted during October 1991, indicate that SVE is a viable remedial alternative • Extraction of groundwater is not practical P 113p-Arco for URS161001Reports\Arco 6100 RAP doe