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7 Oversizing In areas where the excavations for soil corrections extend below the proposed footing elevations, the excavations require oversizing. We recommend the perimeter of the excavation be extended a foot outside the proposed footprint for every foot below footing grade (1H:1V oversizing). The purpose of the oversizing is to provide lateral support of the foundation. Fill Material Additional fill required to attain design grades can consist of any mineral soil provided it is free of debris, organic soil and any soft or otherwise unsuitable materials. We recommend that fill or backfill placed in wet excavations or within 2 feet of the ground water table consist of granular soil (sand) with less than 5 percent passing the number 200 sieve and at least 50 percent retained on the number 40 sieve. Alternatively, “clear rock” can be used in wet excavations. The on-site native alluvial soils appear to be suitable for reuse as structural fill or backfill provided it is free of debris, organic soils or other unsuitable materials. Soils that will be excavated and reused as fill and backfill could require some moisture conditioning (either wetting or drying) to achieve the recommended compaction levels. Topsoil or other soils that are black in color are not suitable for reuse as structural fill or backfill. Backfilling The upper portions of the soil strata had a very loose relative density and prior to placing additional fill or foundations we recommend compacting any loose soils and any soils disturbed during excavation and grading activities. We recommend a minimum of 6 passes in each perpendicular direction with a large self-propelled vibratory compactor operating inn vibratory mode. We recommend that backfill placed to attain site grades be compacted to a minimum of 95 percent of its standard Proctor density (ASTM D 698). Granular fill classified as SP or SP-SM should be placed within 65 percent to 105 percent of its optimum moisture content as determined by the standard Proctor. Other fill soils should be placed within 3 percentage points above and 1 percentage point below its optimum moisture content as determined by the standard Proctor. All fill should be placed in thin lifts and be compacted with a large self- propelled vibratory compactor operating in vibratory mode. In areas where fill depths will exceed 10 feet, if any, we recommend that compaction levels be increased to a minimum of 100 percent of standard Proctor density. Even with the increased compaction levels a construction delay may be required to allow for post settlement of the fill mass. Fill and backfill placed on slopes, if any, must be “benched” into the underlying suitable soils to reduce the potential for slip places to develop between the fill and underlying soil. We recommend “benching” or excavating into the slope at 5 feet vertical intervals to key the fill into the slope. We recommend each bench be a minimum of 10 feet wide.