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rC0t#g(UJ7reckMa Inc Page 19 Site Conceptual Model Report Project No 724 2 May 2,2006 Gasoline oxygenates are present within the co-nungled plume boundaries The highest detection for the Morita subject property is 17 3 ug/l MTBE (well MW-106) and the highest off site is 450 ug/l MTBE (well MW-1) on the GASCO site The levels present on the Morita site do not warrant a separate evaluation from the TPH-G plume 5.2 Conclusions Based on our interpretation of the data collected over the course of this subsurface investigation, GTI has reached several conclusions These conclusions are based on the ' premise that the data considered, although incomplete, are representative of actual site conditions We acknowledge that there may be undiscovered conditions, which would upon their consideration, change our interpretation and thus our conclusions ' Geological Technics Inc makes the following conclusions • The geology of the site consists primarily of clayey/silty or very fine sandy soils with lesser amounts of fine to coarse grained sand units Laterally continuous sand layers may be present below the water table acting as a preferential pathway for contaminant o r� ' migration off site Off site documentation suggest that these pathways may also act to of facilitate contaminant transport onto the Morita Property • As documented in the Wm J Hunter & Associates' June 1993 "Site Assessment wP { t" Report & Final Report Covering Contaminated Soil Removal", approximately 800 ee cubic yards of soil were removed from the former UST and dispenser island excavations The main source of petroleum hydrocarbons leaching to impact bi ' groundwater quality has therefore been removed In their August 12, 1993 letter correspondence (see Appendix A), the SJC PHS/EHD stated "soil at this site does not require any further removal or remediation " The residual soil contamination at the ' site does not warrant further action due to the negligible impact on groundwater quality • The historical groundwater directions indicate that an insignificant groundwater ' plume has originated from the Morita Brothers property The contaminant concentrations in monitoring wells screened across the current water table are historically low to non-detect The shallow groundwater plume was evident in well MW-4 and defined laterally to the east (down gradient) by MW-5, MW-6 and MW-7 The presence of TPH-G contamination in intermediate wells MW-106 and MW-107 SMS�w suggests that a submerged plume is being sourced by residual soil contamination o,�, ' beneath the present water table (at approximately 36 feet below surface in Februaryl a�L� 2006) It is noted that the screened intervals of these wells (55-60 feet bgs) are placed vt� near the elevation of the groundwater table in 1992— approximately 54 feet bgs ' • The TPH-G/BTEX plume has migrated to the east but attenuates to non-detectable levels in the vicinity of Aurora Street (8 3 ug/l MTBE in CPT-3 @ 70 feet bgs noted) ' • A co-mingled petroleum hydrocarbon plume is present due to an unauthorized release from the 749 E Charter Way site (GASCO) The historical groundwater directions f and increasing TPH-G concentrations in well MW-208 suggest that the off site plume