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Ms. Penny Fottrell GEOMATRIX Chevron Environmental Management Company February 11, 2003 Page 2 boring GMX-8, which contained 1200 milligram per kilogram (mg/kg) TPHc at 55 feet bgs and did not contain TPHc at 88 feet bgs. The lateral extent is defined by borings GMX-2, GMX-4, and GMX-9. In the eastern pod, the vertical extent of TPHc is defined by boring GMX-1B, which contained 5100 mg/kg TPHc at 30 feet bgs and did not contain TPHc at 89 feet bgs. The lateral extent is defined by borings GMX-2, GMX-5, GMX-7, and MW-3. In summary, petroleum hydrocarbon affected soil is encountered at the northwestern site bound- ary along the former OVP, between approximately 20 and 90 feet bgs. Groundwater has historically been between 30 to 35 feet bgs and groundwater flow direction varies from east to southeast. Since 1995 groundwater quality has been evaluated by collect- ing groundwater samples from on and off-site monitoring wells and from grab groundwater samples via hydropunch. Three monitoring wells, MW-3, MW-4, and WFSMW-1, do not contain TPH quantified as gasoline (TPHg) or diesel (TPHd) and thereby delineate the extent of affected groundwater to the northeast and southeast of the site (Figure 3). On-site well MW-3 is located southeast and immediately adjacent to the eastern affected area, on-site well MW-4 is located in the southeast corner of the site, and off-site monitoring well WFSMW-1 is located northeast of the western affected area. A grab groundwater sample was collected from location GMX-6 in November 1999 (off-site and east of the eastern affected area) to potentially define the eastern extent of petroleum con- stituents in groundwater. The grab groundwater sample did have detections of TPHg, TPHd, and benzene at 110 µg/l, 92 gg/1, and 1.5 gg/l, respectively. These concentrations of TPHg or TPHd were not greater than water quality objectives (WQOs), and concentrations of benzene were slightly greater than WQO of 1.0 µg/1. Based on previous site reconnaissance activities and discussions with facility personnel, GMX-6 is located adjacent to a former gasoline sta- tion. It is likely that the constituents detected in the GMX-6 sample were related to this off- site source and not from residual crude oil originating from the historical OVP(Geomatrix, 2000).1 The RWQCB has requested additional analytical information to show that detections in GMX-6 are unrelated to OVP operations. WORK PLAN TO ADDRESS DATA NEEDS At the RWQCB's request, groundwater will be investigated by advancing 2 borings along Highway 33,within the California Department of Transportation's (Caltrans) right-of-way and collecting depth-discrete grab groundwater samples. Boring GMX-10 will be located between GMX-6 and MW-2, and GMX-11 will be located between GMX-6 and MW-1 (Figure 3). Additionally, soil samples will be collected for soil logging and chemical analysis. Prior to drilling,Underground Service Alert (USA) will be notified, the soil boring locations will be cleared by a private underground utility locator, water levels will be measured in the on-site wells, and appropriate permits will be obtained for drilling and encroachment upon 1 Soil and Groundwater Investigation Report, 35275 Welty Road, by Geomatrix,February 2000.