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I <br /> GEOMATRIX <br /> J TPH quantified as gasoline(TPHg)has not been detected in the groundwater samples collected <br /> 1 from monitoring wells MW-2, MW-3,.and MW-4 (Table 4). TPHd concentrations exceeding <br /> 100 micrograms per liter(ttg/L)have not been detected in the groundwater samples collected <br /> l from MW-2, MW-3, and MW-4 since November 1998. The estimated lateral extent of TPHd <br /> concentrations in groundwater exceeding 100 gg/L is shown on Figure 4. <br /> 2.2 INVESTIGATION OBJECTIVES AND APPROACH <br /> After a review of the results of the 2002 investigation (Geomatrix, 2002a),the RWQCB <br /> requested additional assessment of the vertical and lateral extent of affected soil and <br /> l groundwater, specifically at depths greater than 45 feet bgs in the vicinity of SB-14 and at <br /> 1 off-site locations hydraulically downgradient of the Bellini property. In response to the <br /> RWQCB request, ChevronTexaco submitted a work plan(Geomatrix, 2003a), which was <br /> `] subsequently approved by the RWQCB (2003a). <br /> -� In August 2003, Geomatrix conducted a soil and grab groundwater investigation at the site. <br /> Sampling locations are shown on Figure 3. Specific objectives and approach of the sampling <br /> -1 program are summarized as follows: <br /> JAssess the lateral and verKcal extent of petroleum hydrocarbons in soil <br /> ' (Section 2.3.1). Four borings (SB-15 through SB-17 and SB-21), including one <br /> contingency step-out boring, were advanced at on-site(Former Vernalis Pump <br /> Station) locations. Three borings (SB-18 through SB-20)were advanced at <br /> downgradient, off-site locations. <br /> �. Characterize the petroleum hydrocarbons in shallow soil(Section 2.3.1). Shallow <br /> soil samples were collected from on-site borings SB-15, SB-16, SB-17, and SB-21 <br /> to characterize the type and concentrations of petroleum constituents in soil at <br /> -� depths of less than or equal to 10 feet bgs at the site. <br /> • Assess the lateral and vertical extent of petroleum hydrocarbons in groundwater <br /> (Section 2.3.2). Grab groundwater samples were collected from borings SB-15, <br /> SB-17, SB-18, and SB-21 to assess the presence of petroleum constituents in <br /> 1 groundwater at and downgradient of the site. <br /> `J 2.3 FIELD AND ANALYTICAL METHODS <br /> Prior to conducting field activities, Geomatrix obtained boring permits from the San Joaquin <br /> County Public Health Service(SJC-PHS) and Stanislaus County and an encroachment permit <br /> from the California Department of Transportation (Appendix A). Underground Service Alert <br /> (USA) and Cruz Brothers Sub-Surface Locators, Inc., of Milpitas, California, were notified to <br /> 4 perform an underground utility clearance at each boring location. Soil boring, grab <br /> CNROJECIl5000SM 1.000\5011-03.d.c 5 <br /> 1 <br />