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Mr Nuel Henderson, Jr, SJCPHS July 1,2003 Remedial Action Plan ARCO Station No 6100 Page 5 for physical analysis These samples were reported to have relatively low permeability values of 6 5 x 10-centimeters per second (cm/s) and 2 4 x 10-6 cm/s, respectively Hydrogeologic Conditions Wells VW-1 through VW-20, MW-2, MW-4, MW-6, and MW-8 are screened into, or across, Sand 1 Wells MW-1, MW-3, MW-5, MW-7, and MW-9 are screened into Sand 2 Well construction details are presented in Table 1. Histoncal groundwater monitoring data (Appendix D) indicate that wells VW-1 through VW-6, VW-14, MW-1, and MW-2 either contain, or have contained in the past, rechargeable quantities of groundwater The groundwater in these wells appears to be perched The source of the groundwater encountered in Sand 1 appears to be due to meteoric water, likely due to percolation of rainwater on the undeveloped lands surrounding the ARCO facility Standing water levels in the water supply well have previously been measured at approximately 45 feet bgs The supply well located onsite, was constructed with a gravel pack from approximately 35 feet to 540 feet bgs, and is screened from 396 to 416 and 496 to 536 feet bgs Previous site assessment studies have indicated that the water present in wells MW-1 and MW-2 may be originating from the gravel pack of water supply well EXTENT OF PETROLEUM HYDROCARBON IMPACT Soil Analytical data for soil samples collected during construction and drilling activities are presented in Appendix B A reap summarizing all soil analytical data collected during site assessment studies is presented in Figure 5 Petroleum hydrocarbons appear to have been released to the subsurface beneath the product dispensers, product piping, and the former UST complex Based on the analytical data collected during UST and product line replacement activities, the highest concentrations of petroleum hydrocarbons were found in the vicinity of the dispensers, and in samples collected from the southeastern and southwestern walls of the UST pit These data suggest that the former USTs, dispensers, and product piping were likely the primary source of the release The SCM presented iso-concentration contours for BTEX (prepared by others), the depths chosen did not necessarily correlate with the description of geology discussed above To better illustrate the extent of impact and correlate the distribution of petroleum hydrocarbons within the upper silt unit and sand unit (containing Sand 1 and Sand 2), Stratus has prepared iso-concentrations contours for TPHG and benzene at various depths (see Figures 6 through 22) P IBp-Arco for URS161001Reports\Arco 6100 RAP doc