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GEOMATRIX Mr. M. Scott Mansholt Mr. James Levy June 30, 2005 Page 2 Although the southwest portion of the site does not appear to be affected by petroleum hydrocarbons, and PAHs, additional borings are recommended for spatial coverage and confirmation of the absence of petroleum hydrocarbons. Additional borings are required on the northeast portion of the site to delineate(laterally) the petroleum affected material and confirm the absence of metals near the former railroad line. Because several samples from Geomatrix's previous investigation had elevated detection limits for PAHs, samples of petroleum affected soil will be collected to obtain lower detection limits for PAHs, so that the data can be used in a future human health risk assessment (HRA). In addition,borings will be advanced around and within the known areas of impacted soil to evaluate whether groundwater has been impacted with petroleum hydrocarbons. WORK PLAN The rationale for each boring location is listed on Table 1 and boring locations are shown on Figure 2. Geomatrix will advance six soil borings to approximately 15 feet below ground surface (bgs) to assess the lateral extent of affected soil and six borings to approximately 60 feet bgs to assess whether groundwater has been impacted (Figure 2). Prior to drilling, Underground Service Alert (USA)will be notified, the soil boring locations will be cleared by a private underground utility locator, and appropriate permits and access will be obtained from the San Joaquin County Public Health Services, Environmental Health Division. The borings will be advanced using a hydraulically driven core barrel and drive sampler or equivalent. A continuous core of the soil will be collected and examined from each location and the lithology will be logged by a Geomatrix field geologist. In addition, organic vapor meter(OVM) readings will be obtained at various depths and recorded on boring logs. From each boring, three soil samples are planned to be collected in the upper 10 feet for data to be incorporated into the HRA. If affected soil is observed, samples of affected soil will be targeted. If no visually affected soil is identified, soil samples will be collected at 1, 5, and 10 feet bgs (Table 1). A sample also will be collected(soil boring GMX-27)below affected soil to define the vertical extent of affected soil (anticipated to be at 15 feet bgs). Soil sam- ples will be collected in butyrate sleeves, or equivalent, sealed with Teflon sheets, end caps, and silicon tape. Depending on the boring location, soil samples will be analyzed for TPHd and TPHmo using EPA Method 8015M, and PAHs using EPA Method 8270 with a selective ion monitoring system (SIM; Table 1). Due to matrix interference in soil samples collected during the previous Geomatrix investi- gation, PAH detection limits were raised (Figure 2). Soil borings are planned in the general area of those borings to attempt to obtain lower detection limits for PAHs. Geomatrix will communicate with the laboratory ahead of the investigation to discuss the need of low detec- tion limits and arrange to have the laboratory contact Geomatrix during analysis if a problem occurs. Additional steps may be taken at the laboratory to remove matrix interference (sam- ple cleanup using silica gel, alumina, or equivalent).