SITE INFORMATION AND CORRESPONDENCE

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Ms. Penny Fottrell GEOMATRIX Chevron Environmental Management Company February 12,2003 Page 2 cultural purposes with some limited residential use. The property to the south was historically a portion of the former Vernalis Pump Station and is currently a debris yard and a residence. EXISTING SOIL AND GROUNDWATER CONDITIONS In previous investigations, Geomatrix identified petroleum hydrocarbon-affected soil in two areas of the site: an area near boring SB-9 on the western portion of the site and in the area of boring SB-14 within the eastern portion of the site adjacent to Highway 33 (Figure 2). In the western area, the vertical extent of total petroleum hydrocarbons quantified as crude (TPHc) is defined by boring SB-9, which contained less than 100 milligrams per kilogram(mg/kg) of TPHc at 81 feet bgs. The lateral extent is defined by borings SB-3 through SB-6 and SB-9 through SB-12. The vertical extent of petroleum hydrocarbons detected in boring SB-14, which contained visually affected soil from approximately 35 feet bgs to the boring terminus at 45 feet bgs, is currently undefined. Groundwater historically has been encountered in on-site groundwater monitoring wells MW-1 through MW-4 from 31 to 37 feet bgs and groundwater flow direction varies from east to northeast. Historical well survey and groundwater elevation data, along with the screened interval for each well, is provided in Table 1. Since 1998, groundwater quality has been evaluated by on-site monitoring wells and from one grab groundwater sample collected at boring location SB-13. Samples colleted from moni- toring wells MW-2, MW-3, and MW-4 did not contain TPH quantified as gasoline(TPHg) or diesel (TPHd; with and without silica gel preparation procedure) as part of sampling activities conducted in May 2002. These wells delineate the extent of affected groundwater to the northwest(MW-3), northeast (MW-2) and southeast(MW-4) of the western affected area (Figures 2 and 3). On-site well MW-1 is located within the western affected area and is not sampled due to the presence of separate-phase petroleum in the well. The grab groundwater sample collected from boring location SB-13 in May 2002 contained TPHd at 540/77 micro- grams per liter(µg/1) (with and without silica gel,respectively), toluene at 0.8 gg/l, and polynuclear aromatic hydrocarbons (PAHs) from 0.1 to 0.5 µg/1, respectively. The focus of this scope of work will be to better evaluate the lateral and vertical extent of petroleum hydrocarbons in soil in groundwater in the vicinity of SB-14 as requested by the RWQCB staff. WORK PLAN TO ADDRESS DATA NEEDS Soil and groundwater will be investigated by advancing borings and collecting depth-discrete soil and grab groundwater samples at locations along Highway 33. As shown of Figure 3, three on-site borings (SB-15, SB-16, and SB-17)will be advanced in the area of boring SB-14 to evaluate the lateral and vertical extent of petroleum hydrocarbons in soil and groundwater