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Geotechnical Engineering and Geological Hazard Study Lincoln Elementary School Modernization Project Manteca, California Page 16 • All concrete curbs separating pavement and landscaped areas should extend at least 2 inches into the subgrade and below the bottom of the adjacent aggregate base to provide a barrier against lateral migration of landscape water or runoff into the pavement section. For better performance, we recommend that subdrains be considered along edges of roads where there are slopes and especially swales that descend towards pavement • Periodic maintenance should be performed to repair degraded areas and seal cracks with appropriate filler. The pavement sections provided above are based on the subsurface conditions encountered during our field investigation, our assumptions regarding final site grades, and limited laboratory testing. Due to grading operations, the actual pavement subgrade materials may vary significantly from those tested for this study. If this is the case, representative subgrade samples should be obtained and additional R -value tests performed. If the results of these tests vary significantly, the pavement sections presented above will need to be revised. Portland cement concrete pavements may be constructed directly over recompacted native soils. Concrete pavements that support truck and bus traffic should be a minimum of 8 inches in thickness and should be designed to accommodate temperature expansion/contraction using reinforcement or appropriate joint control. All Portland cement concrete used for driveways and exterior traffic uses should have a minimum compressive strength of 3,000 psi and should contain entrained air to help prevent freeze damage. 10.1 PAVED HARDCOURT AREAS AND MISCELLANEAOUS RECREATION FEATURES For the proposed AC paved hardcourt areas, we recommend that a minimum pavement section of 2 inches of asphaltic concrete over 4 inches of Class 2 Aggregate Base over 12 inches of native soil compacted to the requirements of engineered fill. All other recreation features that require a base of non -expansive subgrade materials should be constructed over a minimum of 24 inches of non -expansive engineered fill. The specific foundation and subgrade design for such recreation features should be reviewed by the Geotechnical Engineer prior to bidding. 11.0 CORROSION POTENTIAL Chemical tests performed on one discrete sample of the near -surface soils. Test results yielded a pH of 8.06, water soluble sulfate content of less than 15 parts per million (ppm), chloride concentration of less than 15 ppm, and soil redox potential of 280 mv. Resistivity tests performed on the same discrete soil sample indicated that the soils are mildly corrosive to buried metal objects as indicated by result of 8,300 ohm -centimeters. A commonly accepted correlation between soil resistivity and corrosivity towards ferrous metals is provided in the following table developed by the National Association of Corrosion Engineers (MACE): to ka