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J. H. KLEINFELDER & ASSOCIATES File No. S-2568-4 November 11, 1983 Page 5 subgrade soils may swell and cause heaving of foundations and floor slabs. With this in mind, we stress the importance that the native soils beneath the floor slabs be moisture-condit)oned as described. In areas to receive asphaltic concrete, we recommend that the native soils be scarified to a minimum depth of 12 inches and recompacted at near-optimum moisture content to a minimum of 95 percent of the maximum dry density as determined by the above referenced test. In our opinion, structural or trench backfill can be mechanically compacted in the same manner as Engineered Fill, or jetted. If jetting is performed, sufficient time should be set aside to allow consolidation to occur. In addition, density tests should be taken to verify compaction. Storm Water Disposal It is currently planned to store and dispose of on-site storm water on the lots. This water is planned to be stored and percolated from shallow ponds, 18 inches deep. The results of the exploratory boring and laboratory testing indicates the soils below the site are relatively fine-grained. The field percolation test results are shown on Table 11. The average field percolation test result is 64 minutes per inch. Based on this information and experience for such disposal systems, we anticipate storm water will percolate at a rate of 1 to 4 inches per day. A percolation rate of 2 inches per day should be used for design. The variation in this rate will be a factor of moisture content of soil below ponds, surface condition at bottom of ponds, and pond depth. In order to achieve these percolation rates, we suggest depths not exceed 5 feet below the existing site grade.