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GEOTECHNICAL STUDY SUMMARY PROPOSED CHEVRON STATION MACARTHUR DRIVE AND VALPICO ROAD TRACY, CALIFORNIA The following report was prepared for Chevron Products Company for the proposed Chevron Station to be located at the northwest corner of MacArthur Drive and Valpico Road in Tracy, California. Based on our geotechnical study, it is our opinion that the site may be developed for the proposed project. The contents of this report have been briefly summarized below for your convenience;however, the use of the summarized information without first reviewing the entire contents of the following report is not recommended. Based on our geotechnical study, we present the following summarized discussions and/or recommendations: SUBSURFACE CONDITIONS Fill was not encountered in the borings at the time of our field exploration. There may be fill in areas beyond or between our exploratory borings. In general, the native soils consisted of loose to medium dense sandy silt overlying very dense gravelly sand at a depth of about 24 feet. Testing indicates that the near surface soil have a low expansion potential. Groundwater was not encountered in the borings at the time of backfilling the borings. We expect groundwater levels to fluctuate due to variations in rainfall, groundwater recharge, and site conditions. SITE PREPARATION Results of the subsurface site investigation indicate the existing near-surface soils are loose and could be subject to adverse settlement. These near surface soils are not the best material for support of foundations, floor slabs, and exterior flatwork/sidewalks in their present state. To reduce the potential for adverse settlement, we recommend these subgrade soils be over-excavated a minimum of 2 feet below the planned footing elevation and replaced with moisture-conditioned, compacted fill in the foundation areas and at least 5 feet beyond the structure and exterior flatwork/sidewalk areas in plan view, _ if practicable. If compacted engineered fill is to be placed in these areas as part of the site grading, the depth of over-excavation may be reduced by the thickness of the fill. Deeper sub-excavation may be required depending on soil conditions encountered during grading. Figure 11, Foundation Materials Under Building, presents the details for over- excavating and replacing the soil with compacted, engineered fill within the building limits. Compaction recommendations are discussed in Section 5.1.4 Fill Placement and Compaction. • On-site soil generated by site grading may be used as structural fill provided the soil is free of deleterious and organic materials and is approved for use as fill by our representative. The on-site low to non-expansive soils should be moisture-conditioned, and compacted to a minimum of 90 percent relative compaction ata minimum of 2 percent over the optimum moisture content according to the latest ASTM test methods and procedures. All import fill to be placed must be compacted to a minimum relative compaction of 90 7 percent of the maximum dry density and moisture-conditioned to a minimum of 2 percent over the optimum moisture content according to ASTM test methods and procedures. 7 For pavement areas, the upper 12 inches of subgrade soils should be scarified, moisture- conditioned as necessary, and recompacted to a minimum of 95 percent relative compaction. 1 J 7 Mrorbmacher Engineering, Inc.