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ameO-' investigations indicated that most of the petroleum impacts in soil are present in the northern and northeastern portions of the Site. However, the highest concentrations of PAHs were found near the southwestern boundary of the Site in a sample collected at 5.5 feet bgs from ' boring GMX-09. Petroleum hydrocarbons encountered at this boring had a different color and consistency than those found elsewhere at the Site. This difference is further indicated by the ' chemical data. Generally, the stained soil in this area was described as a hard, black material (with occasional trace of soft, sticky material) with an odor, mixed within a fine-grained soil matrix at depths ranging from near the surface to approximately 5 feet bgs. Samples of petroleum-affected soil from several borings on-site near the southwest property boundary contained higher concentrations of PAHs than samples of affected soil from the northern and northeastern portions of the Site. Grab groundwater samples were collected from 4 of the 14 borings during the May 2001 ' investigation. Samples were analyzed for TPH quantified as gasoline (TPHg), TPH quantified as diesel (TPHd), BTEX, and PAHs. Analytical results indicated that groundwater within petroleum hydrocarbon-affected soil in the northern portion of the Site (GMX-01) is marginally ' impacted by petroleum constituents (Table 2). Petroleum constituents were not detected above the laboratory reporting limits from groundwater samples collected in the central and southern portions of the Site (GMX-04, GMX-07, and GMX-12; Figure 4). The area surrounding GMX-09 was further investigated by Geomatrix in October 2003 to delineate the lateral and vertical extent of PAHs in soil. Twenty-one borings were advanced to depths ranging from 6 and 7 feet; fourteen of these borings were advanced in the greenbelt area that borders the west and southwest portions of the Site. Fifteen soil samples were collected from the greenbelt and analyzed for PAHs. As indicated above, the greenbelt area southwest of the Site is part of the Alden Park Property. ' The analytical results for chemicals detected in soil at the Site are presented in Table 1; the soil boring locations are depicted on Figure 4. The results of the investigations indicate that ' PAHs and TPH in soil at the Site are the primary chemicals of potential concern. 1 3.0 SUMMARY OF SCREENING-LEVEL RISK ASSESSMENT Geomatrix completed a SLRA for the Site and submitted it to the Regional Water Quality 1 Control Board—Central Valley Region (Water Board) in a report dated March 18, 2008. The SLRA was prepared to provide an analysis of the potential for adverse human health effects to hypothetical future commercial/industrial and residential receptors as a result of exposure to chemicals detected in the subsurface at the Site if no remedial actions were to take place. AMEC Geomatrix Inc I:\Doc_Safe\6000s\6628.001\3000 REPORTS\Excavation Work Plan_8.12.0811 Text,cover and slips\Text.doc 3