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aC • Ms Devra Lewis Page 2 Regional Water Quality Control Board Clayton Project No. 70-03759.00 September 3, 2004 Streets, Marina Boulevard to the west(recently renamed Altamont Parkway), Main Street to the North, Central Parkway to the east, and Mascot Boulevard to the south. The parcel is bisected by Mountain House Creek, which runs to the northeast across the parcel (Figure 2). The former Shell pipeline crosses the southwest portion of Neighborhood E, crossing the future Mascot Boulevard and leaving the parcel just north of Mountain House Creek. As noted above this summary report discusses only an approximately 1,500 foot section of the pipeline alignment between the Creek area and Mascot Boulevard. 2.0 SITE INVESTIGATION AND REMEDIAL SUMMARY As described in Clayton's "Summary Report of Activities", dated March 17, 2004, soil impacted by petroleum hydrocarbons were initially noted during June 2003. Subsequent to this, Shell collected soil samples along the alignment and performed a subsurface investigation along the alignment within Neighborhood E. Figure 3 presents a summary of the investigation results. As seen on the Figure 3, in addition to the location of the initially noted impact (referred to as Area 1, or main excavation area), three smaller areas of impact were noted north of Area 1. These were referred to as Area 2, Area 3, and Area 4. Areas 2, 3 and 4 were excavated to depths of 11 to 14 feet, at which point evidence of impact was no longer observed. Confirmation samples collected from the base and sidewalls of these excavations showed either non-detectable results or low concentrations of petroleum hydrocarbons (Figure 4). Figure 4 also presents confirmation sampling results from the main excavation area(Area 1). This excavation was performed between October 10, 2003 and October 23, 2003. The excavation removed at total of 34,000 cubic yards of material, of which approximately 15,400 cubic yards were hauled to a landfill for disposal. Approximately 18,600 cubic yards of material were stockpiled for use as backfill with the approval of the Regional Water Quality Control Board. Excavation proceeded until hydrocarbons were not noted along the sidewalls of the excavation,with the exception of two small areas on the east side of the excavation, at a depth corresponding to the water table. A thin lens (approximately 1 to 2 feet thick) of impacted material was noted at a depth of 29 feet below the ground surface. Two exploratory cuts were excavated into the eastern sidewall of the excavation to evaluate the extent of the impacted material in the lens, and soil samples were collected from the base of the sidecut and the back wall of the excavation to evaluate soil conditions.. Two samples were collected from each sidecut, labeled NE-ST-28 (Northeast side trench at 28 feet), NE-ST-B (Northeast side trench back wall), SE-ST-29, and SE-ST-B. The results indicated non-detectable results for all but one of the samples, which showed only very low concentrations The excavation was extended into the groundwater where indications of impact were • noted,primarily in the northern part of the excavation. The excavation was generally extended two feet below the water table,though in some areas it extended as much as five or six feet into groundwater. Soil samples were collected along the centerline of the