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N :VYAT1t 1117 Lone Palm Avenue, Suite B Modesto, CA 95351 www.atcassociates.co m 209-579-2, ASS OC IATE S INC . Fax 209-579--" ) Environmental, Geotechnical and Materials Engineers Figure 9 is a cross-sectional interpretation of subsurface lithology along the same line and orientation as Figures 7 and 8 . However, the subsurface lithology depicted in Figure 9 is based on well logs associated with MW12 and A-MW9, and CPT boring logs A-CPTI and A-CPTll . The lithologic descriptions associated with A-MW l l are not included in Fi re 9. The location of A-MWI1 is shown in Figure 9 for purpose of reference. Consequently igure 9 is a depiction of subsurface lithology with 1a1� emphasis on interpretation of subsurface lithology as logged electronically usingCPT technology, The tin subsurface lithology depicted in Figure 9 general }correlates we across the section line, w"ith the exception of the sandy silt layer indicated on the log of A-MW9 from approximately 67 to 100 feet I bgs . The CPT log of A-CPTI (advanced approximately ten feet east of A-MW9) suggests sand like, material is present from approximately 61 to 122 feet bgs instead of silty material as logged by the field geologist. This cross-sectional interpretation suggests MW12, A-MW9, and A-MW11 are screened in the same sandy horizon. CONCLUSIONS AND RECOMMENDATIONS To further evaluate -the lateral extent of the shallow and intermediate groundwater plume, -ATC-- — proposes to pursue access to the previously mentioned existing off-site wells associated with the former Apache Plastics facility . Cooperative efforts from ATC, the former Apache Plastics facility owner, and Stratus should result in improved understanding of subsurface conditions for both sites and reduce redundant expenses and investigation efforts . Existing groundwater monitoring wells associated -- � with the former Apache Plastics facility are screened in similar depth intervals as the wells associated `cv ' with the subject site, and are positioned to help define the extent of groundwater contamination. According to Stratus ' quarterly groundwater monitoring report for the fourth quarter 2005 , he shallow groundwater flow direction has consistently been toward the east and southeast ex t fo he first quarter of 2005, when the reported flow direction was toward the east, northeast. Apache Plastics facility well MW2 (designated as A-MW2 on Figure 3) can provide groundwater quality data southeast of the subject site. Historical groundwater sample results associated with the shallow groundwater zone wells of both sites are summarized in Table 2. The screened intervals of off-site Apache Plastics wells MW8, MW9, and AM l (designated A-MW8, - . A-MW9, and A-MWll on Figure 3) are slightly deeper than those associated with the subject site. Apache Plastics well MW9 is located in the apparent downgradient direction with respect to the subject site and is also located in close proximity to the former location of the Apache Plastics UST. According to historical groundwater flow information prepared by Stratus, this well is situated in a downgradient position with respect to the location of this former UST. It should be noted that groundwater samples collected from Apache Plastics well MW9 have historically contained high concentrations of petroleum hydrocarbons. Apache Plastics wells MW8 and MWll will serve to evaluate the intermediate groundwater plume to the southeast and southwest of the subject site, respectively and may provide information regarding potential plume commingling. Groundwater samples collected from Apache Plastics wells MW8 and M V11 ave historically contained moderate and very low concentrations of petroleum hydrocarbons, respectively. Historical groundwater sample results associated with the intermediate groundwater zone wells of both sites are summarized in Table ) . S:\Environmental\28349\comparative study.doc 6 ATC Associates Inc.