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C� VAT 1117 Lone Palm Avenue, Suite 8 � Modesto, 57 -2221 www.atcassociates.com 209-579-2221 A S S O C I A T E S I N C . Fax 209-579-2225 tnvtronmental, Geotechnical and Materials Engineers from approximately 85 to 90 feet bgs. A-MW8, A-MW9, and A-MWI I are screened at slightly deeper intervals ranging from approximately 94 to 109 . 5 feet bgs. Review of the intermediate (MW4, MW5 , MW6, and MW12) and deeper (MW7 and MW15) groundwater zone monitoring well logs associated with the subject site, and intermediate zone (A- MW8, A-MW9, and A-MWI11 ) well logs and CPT logs associated with the former Apache Plastics facility do not provide confirmatory information as to whether or not the intermediate zone wells associated with the subject site are screened in the same distinct hydrogeologic zone as those of the former Apache Plastics facility. Cross-section B-B ' (Figure 6) depicts subsurface lithology looking toward the northeast and is based on well logs associated with MW6, MW7, MW9, MW12, MW15, and A-MW8. This cross-section suggests that intermediate zone wells MW6 and MW12 of the subject site are screened in the same sandy/hydrogeologic unit as is A-MW8 . The bottom portion of the screened interval of A-MW8 extends into the sandy unit while most of the screen is in a silty layer that pinches out toward the weed does appeati�o be present at a similar depth-helow t eh�jecf site. This interme td`a e - zone sandy unit appears to be separated from the shallower sandy zone by a laterally extensive silt and clay layer. Three cross-sections (Figures 7, 8, and 9) were generated to illustrate potential subsurface conditions (! along the same line of cross-section (B-C) . Cross-section B-C (Figure 7) depicts subsurface lithology looking toward the east and is based on well logs associated with MW12, A-MW9, and A-MW11 ; and CPT boring logs A-CPTI and A-CPTI 1 . A-CPTI was advanced within approximately ten feet of A- MW9 and A-CPTll was advanced within approximately ten feet of A-MWll . This cross-section shows lithological interpretive consistencies and inconsistencies with respect to CPT logged data versus data logged by field geologists, and provides a basis for two additional cross-sections (Figures 8 and 9). Figure 8 is a cross-sectional interpretation of subsurface lithology along the same line and orientation as cross-section B-C (Figure 7). However, the subsurface lithology depicted in Figure 8 is based on well logs associated with MW12, A-MW9, and A-MW 11 . The lithologic data associated with A-CPTI and A-CPTI l from 0 to approximately 110 feet bgs are not included in Figure 8. The locations of A- CPTI and A-CPTI l are shown in Figure 8 for purpose of reference. Consequently, Figure 8 is a depiction of subsurface lithology based on subjective observations of field geologists _ This cross- section suggests that A-MW9 and A-MWll may be screened in a different sandy horizon than is MW12 . It is not known if the silty/clayey zone indicated at approximately 100 feet bgs on the well logs of A-MW9 and A-MW l 1 extends northward beneath the terminal depth of MW 121 wayt ' A well log for A-MW I 1 was not observed ling ATC' s review of San Joaquin County Environmental Health Department's file for the former Apache Plastics facility. Consequently, lithology associated with A-MW I 1 is based on Geologic Cross Section B-B' TPHg/Benzene1TBA1l, 2-DCA Concentrations in Soil & Groundwater, Figure 4 prepared by Stratus. S,\Environmental\28349\comparative study.doc 5 ATC Associates Inc.