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• Mr Nuel Henderson, Jr, SJCPHS July 1, 2003 Remedial Action Plan ARCO Station No 6100 Page 7 SCM, small quantities of groundwater are flowing along the lithologic contact, within Sand 1, and when the water encounters the well, enters and slowly fills the casing Floating product (up to 0 02 feet thick) or a product sheen have historically have been observed in wells VW-1 and VW-4, installed near the product dispensers Free product has been observed in well MW-1 since the third quarter 2000 (up to 1 47 feet thick) Review of historical quarterly analytical data indicates that the highest TPHG, benzene, and MTBE concentrations were observed in groundwater samples collected from VW-4 at 605,000 micrograms per liter (pg/L), 33,900 pg/L, and 1,890 µg/L, respectively Historical quarterly monitoring data of groundwater elevations and analytical results are presented in Appendix D REMEDIAL ACTIONS & FEASIBILITY STUDY Based on visual inspection of staining in the soil during UST removal in November 1990, limited over-excavation was conducted in the former UST cavity extending towards the new UST complex The depth of this over-excavation was reported to be approximately 25 feet bgs (Underground Storage Tank Removal and Soil Sampling, May 29, 1991) Excavated soil impacted with petroleum hydrocarbons was transported to BFI's landfill in Livermore, California, for disposal Based on review of reports prepared by previous consultants and regulatory correspondence, approximately 2,332 tons of soil was excavated and disposed of during the over-excavation Approximately 2,300 pounds of TPHG and 602 pounds of BTEX were estimated to have been removed during over- excavation (Underground Storage Tank Removal and Soil Sampling, May 29, 1991) Resna conducted a soil vapor extraction (SVE) pilot test in October 1991, extracting from wells VW-1 through VW-4, with an applied vacuum range of 10 to 43 inches of water column and an extraction rate of up to 98 cubic feet per minute During the test, influent TPHG concentrations ranged from 130,000 milligrams per cubic meter (mg/m) to 160,000 mg/m3 The radius of influence was estimated to be 35 feet During the line upgrade activity, Delta excavated and disposed offsite approximately 315 tons of petroleum hydrocarbon impacted soil from beneath the former product dispensers and piping on January 23, 2002 The perimeter of the excavated areas are included on a figure presented in Appendix A The soil was transported to Forward Landfill in Manteca, California, for disposal Free product was first bailed from well MW-1 on September 28, 2000 A passive skimmer was installed in the well on October 3, 2000 The passive skimmer was removed and active bailing of the product once each week was initiated on January 3, 2001 Based on quarterly monitoring data collected to date, a cumulative free product and water mixture of approximately 102 gallons and 7 5 gallons has been removed from P 13P-Arco for URS161001Rcports\Arco 6100 RAP doe