SITE INFORMATION AND CORRESPONDENCE

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/4*5= GEOMATRix through MW-4, respectively. .TPHd was not detected above the laboratory reporting limit in groundwater samples from the November 1998 groundwater sampling event; during this event, TPHd analysis was performed following a silica gel preparation procedure. This indicates that the TPHd detections in July 1998 may be due to the presence of polar components resulting from intrinsic bioremediation of the residual crude oil present in the subsurface. Monitoring well MW-1 was not sampled during either event due to the presence of approximately 6 inches of separate-phase petroleum. 3.0 INVESTIGATIVE OBJECTIVES AND APPROACH In May 2002, Geomatrix implemented a soil and groundwater investigation and analytical program at the site. The field investigation was developed based on review of previous work conducted at the site and in accordance with the revised CTA. Sampling locations are shown on Figure 2. Specific objectives of the sampling program are summarized below. ■ Assess vertical extent of petroleum hydrocarbon-affected soil. Boring SB-9 was advanced within the central area of petroleum-affected soil to assess the vertical extent of affected soil in the area of MW-1. • Assess the presence ofpetroleum hydrocarbon-affected soil ill shallow soil. Borings SB-9 through SB-12 were drilled within the area of petroleum-affected soil to assess for the presence of petroleum constituents(e.g., BTEX and PAHs) in the near surface (i.e,, 1 to 2 feet bgs) and shallow soil(i.e., 2, 5, and 10 feet bgs). • Assess groundwater quality. Geomatrix collected groundwater samples from on- site monitoring Wells MW-2, MW-3, and MW-4 and a grab-groundwater sample from SB-13 to assess groundwater quality at the site and crass-downgradient(east) of affected soil. • Assess the presence of separate phase petroleum in MW-1. Geomatrix evaluated the continued presence of a thin layer of separate-phase petroleum in MW-1. 4.6 FIELD AND ANALYTICAL METHODS Prior to conducting field activities, Geomatrix obtained a boring permit from the SJC-PHS (Appendix A),notified Underground Service Alert (USA), and contacted Cruz Brothers Sub- Surface Locators,Inc.,of Milpitas, California, to perform an underground utility clearance at each boring location. Soil boring, groundwater sampling, and analytical methods are described in Sections 4.1,4.2, and 4.3,respectively. oak]dcptdstall _Safe150Ws15Gl L001%RgXWS0i1 and GW Repon.doc 4